New Isoindoline Electron Acceptors
Analogous To Benzo-TCNQ
A thesis presented for the degree of Doctor of Philosophy
by
Shane P. Conway Dip(AppSci), BSc(AppSci)
at
DUBLIN CITY UNIVERSITY
School of Chemical Sciences
JUNE 1996
To my parents, Betty and Joe.
ii
Declaration
I, th e u n d ersigne d, h e re b y d e cla re th a t th is th e sis, w h ich I now s u b m it fo r
a s s e s s m e n t on th e p ro g ra m m e
o f stu d y
le a d in g to th e
aw ard
o f Ph.D.
re p re se n ts th e so le w o rk o f th e a u th o r and has n o t bee n ta ke n fro m th e w o rk o f
o th e rs save and to th e e x te n t th a t such w o rk has bee n cited and a ckn o w le d g e d
w ith in th e te x t o f w ork.
S h a n e P. C o n w a y
Acknowledgements
I
w o u ld
like
to
th a n k
my
s u p e rviso r
Prof.
A lb e rt
P ratt
fo r
his
help,
e n c o u ra g e m e n t and g u id a n c e during the co urse o f th is w ork.
I am d e e p ly in d e b te d to both th e a ca d e m ic s ta ff and in p a rtic u la r th e te ch n ica l
s ta ff o f th e S ch o o l o f C h e m ica l S cience s fo r th e ir a s s is ta n c e durin g m y stay.
I
p a rtic u la rly w ish to th a n k M ick B urke m ost sin c e re ly fo r all his help, w ith th e aid
o f M a urice, D a m ien and V e ro n ica .
I w ould also like to th a n k D r R o b e rt F orster
and J o e O ’ K elly fo r th e ir help, a d vice and use o f th e ir e q u ip m e n t fo r the C yclic
V o lta m m e try e xp e rim e n ts, Dr C o n o r Long fo r th e X -ra y cry s ta llo g ra p h ic data
a nd stru ctu re s, and D r Jo sh H ow arth and Dr P a dra ig Ja m e s fo r th e ir advice.
I a lso w ish to e xp re s s m y d e e p e st th a n ks to m y fe llo w p o stg ra d u a te s fo r th e ir
frie n d s h ip o v e r th e years, in p a rticu la r the m e m b e rs o f th e A lb e rt P ratt research
g ro u p , Fang, C o rm a c F.F. O 'D onnell, M ark, Ja m e s (Jim m y) D elaney, Farm er, Li
Jin g, O llie E gan, R o ry (aka RO D), Orla, Joe, C o llette, Ben, and M auro and all
th e p re vio u s in m a te s o f A G 07. I w ould also like to a c k n o w le d g e th e m e m b e rs
o f th e D C U s ta ff s o c c e r te a m e sp e cia lly Jarlath, Liam , S te vie N. and, last and
v e ry m uch least, S to rm in ' N orm an the sparks.
I w o u ld also like to th a n k John
D e n n is ju s t fo r ta lkin g to me.
I w ish to th a n k all th e
m em b ers o f m y fa m ily w h o have su p p o rte d and
e n c o u ra g e d m e th ro u g h o u t th is w o rk and in p a rtic u la r to P a tricia fo r h e r help in
ty p in g th is th e sis.
I w o u ld also like to e x p re s s m y a pp re ciation to A n a fo r h e r e n co u ra g e m e n t and
p a tie n ce .
F in a lly I w ish to e x p re s s m y m ost sin cere th a n ks to m y pa re n ts fo r putting up
w ith and su p p o rtin g m e all th e se years and to w h o m I o w e everythin g.
Abstract
In te re s t in novel h e te ro c y c lic d e riv a tiv e s a n a lo g o u s to T C N Q in w h ich the ne le c tro n s o f a c a rb o n -c a rb o n d o u b le bond are replaced by a lone pair o f
e le c tro n s on a h e te ro a to m has led to in ve stig a tio n o f the syn th e sis o f A/-alkyl
d e riv a tiv e s o f 2 ,2 '-(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile .
K n o e ve n a g e l c o n d e n s a tio n o f A /-m ethylphthalim ide w ith m alon onitrile
u n d e r a n u m b e r o f c o n d itio n s yie ld e d co m p le x p ro d u ct m ixture s fro m w h ich the
so d iu m
and
m é th y la m m o n iu m
salts
of
o -( 2 ,2 -d ic y a n o e th e n y l- 1 -olate-)/V-
m e th y lb e n z a m id e and 3 -(d ic y a n o m e th y lid e n e )p h th a lid e w e re isolated as m inor
p ro d u cts.
R e action o f m a lo n o n itrile w ith d iim in o iso in d o lin e and 1 -p h e n ylim in o -3 im in o is o in d o lin e
in d im e th y lfo rm a m id e yie lde d th e a m m o n iu m
sa lt o f
2 ,2 '-
(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile .
In m eth a n o l the highly in solu ble
m o n o -c o n d e n s a tio n
and this w a s also th e
p ro d u c t w a s
o b tained
pro d u ct
o b ta in e d by reaction o f s o d io -m a lo n o n itrile w ith p h th a lo n itrile in m eth anol.
2 ,2 '-
(ls o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile w a s o b tained fro m its a m m o n iu m
s a lt by a cid ifica tio n .
R e action
of
2 ,2 '-(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile
or
its
a m m o n iu m sa lt w ith a v a rie ty o f acyla tin g and alkyla tin g a ge nts did n o t yield the
d e s ire d
co m p o u n d s.
A
ve ry
low
yield
of
2 ,2 '-(2 -m e th y l-is o in d o lin -1 ,3 -
d iy lid e n e )b is p ro p a n e d in itrile w a s o b ta in e d on reaction w ith d im e th ylsu lp h a te .
R e a c tio n o f th e a m m o n iu m s a lt w ith a va rie ty o f a m ine s yie ld e d p ro d u cts w h ich
X -ra y cry s ta llo g ra p h y sh o w e d to a rise from a m ine add ition a cro ss a cyano
g ro u p .
2 ,2 '-(2 -M e th y l-is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile
s u c c e s s fu lly s yn th e sise d b y he a tin g th e té tra m é th yla m m o n iu m sa lt o f
was
2 ,2 '-
(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile in 1,2 -d ich lo ro b e n ze n e .
C yclic v o lta m m e try m e a s u re m e n ts o f th e 2 ,2 '-(iso in d o lin -1 ,3 -d iylid e n e )
b is p ro p a n e d in itrile s sh o w th e y are e le c tro c h e m ic a lly irre v e rs ib le . U V stu d ie s o f
th e
ch a rg e -tra n s fe r
c o m p le xin g
d iy lid e n e )b is p ro p a n e d in itrile
and
its
abilities
A/-methyl
of
d e riva tive
2 ,2 '-(is o in d o lin -1 ,3 w ith
a
va rie ty
of
e le c tro n d o n o rs w e re ca rrie d o u t and a n u m b e r o f ch a rg e -tra n s fe r co m p le xe s
h a v e bee n syn th e sise d .
X -ra y cry s ta llo g ra p h y
2 ,2 '-(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile
o f th e 1:1 co m p le x betw e en
and
N,N,N',N'-teiramethy\-p-
p h e n y le n e d ia m in e sh o w s th a t it crysta llise s in a m ixed sta ckin g arra n g e m e n t.
Table of Contents
T itle P age
D e dica tion
ii
D e cla ra tio n
iii
A c k n o w le d g e m e n ts
iv
A b s tra c t
V
T a b le o f co n te n ts
vi
List o f a b b re via tio n s
xiii
Chapter 1
1 .A .1
In tro d u ctio n , 2
1.A.2
B a ckg ro u n d , 2
1.A.3
T h e Band T h e o ry, 5
1.A.4
G eneral P ro p e rtie s o f C h a rg e -T ra n s fe r C o m p le xe s, 7
1 .A .4.1
S ta cking F o rm a tio n in C -T C o m p le xe s, 9
1.A .4.2
S to ich io m e trie s in C -T C o m p le xe s, 10
1.A .4.3
T h e U n id im e n s io n a lity o f C -T C o m p le xe s, 11
1.A .4.4
L attice in sta b ilitie s in q u a si o n e -d im e n s io n a l co n d u cto rs, 11
1.A.5
S u p e rco n d u ctivity, 14
1.A.5.1
BC S T h e o ry o f S u p e rco n d u ctivity, 14
1.A .6
D esign o f O rg a n ic M etals, 15
Section 1.B Donor Molecules
1.B.1
In tro d u ctio n , 17
1.B.2
G e n e ra l S y n th e s is o f T TF and its D e riva tive s, 18
1.B .3
P e rip h e ra lly su b stitu te d T T F a n a lo g u e s, 20
1.B.3.1
T M T T F and H M T T F , 21
1.B .3.2
B is(e th y le n e d ith io lo )te tra th io fu lv a le n e (B E D T -T T F ) or ET, 21
1 .B .3.3
B is (e th y le n e d io x y )-te tra th io fu lv a le n e (B E D O -T T F )
1.B .3.4
O th e r su b s titu te d T TF s, 24
1.B.4.1
S e le n iu m D e riva tive s o f TTF, 27
1.B.4.1.1
S y n th e s is o f S a lts o f T M T S F , 28
1 .B .4.1.2
D e riva tive s o f T S F , 30
1.B .4.2
T e llu riu m D e riva tive s, 30
1.B .5
E x te n d e d - 7i-D o n o rs , 32
Section
1.C Acceptors
1.C.1
Introdu ction, 35
1.C .2
S yn th e sis o f TC N Q , 36
1.C.2.1
S yn the sis o f T C N Q D e rivatives, 36
1 .C .2 .2
A lte rn a tiv e routes to T C N Q D e rivatives, 39
1.C .3
T C N Q C -T C o m plexes, 40
1.C .3.1
C -T C o m p le xe s o f N on-ring fu se d T C N Q D e riva tive s, 41
1 .C .3 .2
C -T C o m p le xe s o f rc-extended T C N Q D e riva tive s, 43
1.C .4
H e te ro q u in o id E lectron A c c e p to rs , 48
1.C.4.1
A c c e p to r P rope rtie s o f H e te ro -T C N Q s, 50
1.C .5
/^ /V -D ic y a n o -p -q u in o d iim in e (D C N Q I) A cce p to rs, 53
1.C.5.1
S yn th e sis o f D C N Q I and its D erivatives, 53
1 .C .5.2
C -T C o m p le xe s o f D C N Q I, 57
1 .C .5 .3
D C N Q I R adical A n io n S alts, 58
1 .C .6
M e ta l(d m it )2 A cce p to rs, 60
1 .C .7
F u lle re n e s as A cce p to rs, 63
RESULTS AND DISCUSSION
Chapter 2
Section 2.A
66
2.A.1
In trodu ction,
2 .A .2
K n o e ve n a g e l C o n d e n s a tio n s o f A /-M ethylphthalim ide,
2.A .2.1
T h e K n o e ve n a g e l R eaction,
2 .A .2 .2
K n o e ve n a g e l C o n d e n s a tio n s using T ita n iu m T e tra c h lo rid e , 76
2 .A .3
C o n clu sio n , 77
68
68
Section 2.B
2.B.1
C o n d e n sa tio n R e a ctio n s w ith Im idines, 78
2 .B .2
S yn th e sis o f 2 -(3 -lm in o is o in d o lin -1 -d iy lid e n e )b is p ro p a n e d in itrile , 82
2 .B .4
C o n clu sio n s,
86
Section 2.C
2.C .1
/^-S u b stitu te d
b isp ro p a n e d in itrile , 87
d e riv a tiv e s
of
2 ,2 '-(ls o in d o lin -1 ,3 -d iy lid e n e )
2C .1.1
G a b rie l T yp e A /-Substitution re action s o f 2 ,2 '-(ls o in d o lin -1 ,3 -d iy lid e n e )
b isp ro p a n e d in itrile ,
2.C . 1.2
88
A lte rn a tiv e M e th ods fo r A/-S ubstitution o f 2 ,2 '-(ls o in d o lin -1 ,3 -d iy lid e n e )
b isp ro p a n e d in itrile , 90
2 .C. 1.2.1
M é th yla tio n using the té tra m é th y la m m o n iu m s a lt (155), 90
2 .C .1.2.2 A tte m p te d
B e nzyla tion
of
2 ,2 '-(ls o in d o lin -1 ,3 -d iy lid e n e )
b isp ro p a n e d in itrile , 93
2 .C .2
D iscussion, 96
2 .C .3
C o n clu sio n , 98
Section 2.D
2.D .1
R e a ctio n s
of
2 ,2 '-(ls o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile
w ith
A m in e s , 101
2 .D .2
R e a ctio n s o f A m in e s w ith th e A m m o n iu m S a lt o f 2 ,2 '-(ls o in d o lin -1 ,3 -
d iy lid e n e )b is p ro p a n e d in itrile , 105
2.D .2.1
R e a ctio n o f B e n zyla m in e w ith th e A m m o n iu m salt, 105
2 .D .2 .2
R e a ctio n o f n -P ro p yla m in e w ith th e A m m o n iu m salt, 113
2 .D .2 .3
R e a ctio n o f Iso p ro p yla m in e w ith th e A m m o n iu m salt, 115
2 .D .2 .4
R e a ctio n o f n -B u tyla m in e w ith th e A m m o n iu m salt, 117
2 .D .2 .5
R e a ctio n o f C yclo h e xyla m in e w ith th e A m m o n iu m salt, 118
2 .D .2 .6
R e a ctio n o f n -O ctyla m in e and n -D e cyla m in e w ith th e A m m o n iu m salt,
121
2 .D .2 .7
R e a ctio n o f A/,A/-D ibutylam ine w ith th e A m m o n iu m salt, 124
2 .D .3
D iscu ssio n , 125
2 .D .4
C o n clu sio n s, 133
Chapter 3
3.0
Cyclic Voltammetric Analysis, 136-145
3.1
In tro d u ctio n , 136
3.2
E le ctro ch e m ica l
S tudies
of
2 ,2 '-(ls o in d o lin -1 ,3 -d iy lid e n e )
b is p ro p a n e d in itrile and 2 ,2 '-(2 -M e th y lis o in d o lin -1 ,3 -d iy lid e n e ) b isp ro p a n e d in itrile
3.3
C o n clu sio n s, 144
Chapter 4
4.0
Charge-Transfer
bispropanedinitrile
(110)
Studies
and
bispropanedinitrile (151), 147-172
4.1
In tro d u ctio n , 147
of
2,2'-(lsoindolin-1,3-diylidene)
2,2'-(2-Methylisoindolin-1,3-diylidene)
4 .2
C h a rg e -T ra n s fe r
b is p ro p a n e d in itrile
C o m p le x
(110)
w ith
of
2 ,2 '-(ls o in d o lin -1 ,3 -d iy lid e n e )
A/, A/, A/' A /'-T e tra m e th yl-p -p h e n yle n e d ia m in e
(T M D A ), 148
4.2.1
X -ra y C rystal S tru ctu re
o f th e 1:1C -T C o m p le x o f (1 10)-T M D A ,
4 .3
A tte m p te d C -T C o m p le x fo rm a tio n o f (110) w ith o th e r do n o rs, 159
4 .4
C -T
C o m p le xe s
of
148
2 ,2 '-(iso in d o lin -2 -m e th yl-1 ,3 -d iylid e n e )
b is p ro p a n e d in itrile (151) w ith va riou s don ors, 164
4 .5
D iscussion, 170
4 .6
C o n clu sio n s, 172
Chapter 5
Experimental
In tro d u c to ry R em arks, 174
Attempted
Knoevenagel
Reactions
of
Malononitrile
with
N-
Methylphthalimide;
U sing S o d iu m as th e ba se and T o lu e n e as solvent, 175
U sing S o d iu m hyd rid e as th e base and d ry T e tra h yd ro fu ra n as so lve n t, 175
U sing S o d iu m hyd rid e as th e base, d ry T e tra h yd ro fu ra n as s o lv e n t and heating
u n d e r reflux, 177
U sing
P yrid in e
as
base,
D ic h lo ro m e th a n e
as
so lv e n t
and
Titan ium
T e tra c h lo rid e , 178
U sing P yrid in e as b a se and so lve n t and T ita n iu m T e tra ch lo rid e , 178
S y n th e s is o f 1,3 -D iim in o iso in d o lin e , 178
S y n th e s is o f 3 -P h e n y lim in o is o in d o lin e , 179
S y n th e s is
of
th e A m m o n iu m
sa lt
of
2 ,2 '-(ls o in d o lin -1 ,3 -d iy lid e n e )
b is p ro p a n e d in itrile
M e th o d (a): U sing 1 ,3 -D iim in o iso in d o lin e , 180
M e th o d (b): U sing 3 -P h e n ylim in o -1 -im in o iso in d o lin e , 180
S y n th e s is o f 2 ,2 '-(ls o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile
M e th o d (a): P yro lysis o f th e A m m o n iu m salt o f 2 ,2 '-(ls o in d o lin -1 ,3d iy lid e n e )b is p ro p a n e d in itrile (119), 181
M e th o d (b): A c id ific a tio n o f (119), 181
S y n th e s is o f 2 -(3 -im in o is o in d o lin -1 -d iy lid e n e )b is p ro p a n e d in itrile , 181
S y n th e s is
of
th e
b is p ro p a n e d in itrile , 182
S o d iu m
s a lt
of
2 ,2 '-(ls o in d o lin -1 ,3 -d iy lid e n e )
Attempted
Benzoylation
of
2,2'-(lsoindolin-1,3-diylidene)
bispropanedinitrile;
M e th o d (a): U sing B enzoyl C h lo rid e and a q u e o u s S o diu m H ydroxide,
183
M eth od (b): U sing B enzoyl C h lo rid e and P yridine, 183
M e th o d (c): R e action o f th e S o d iu m S a lt o f 2 ,2 '-(ls o in d o lin -1 ,3d iy lid e n e )b is p ro p a n e d in itrile w ith B e n zo yl C hloride, 183
A tte m p te d
re a ctio n
o f th e A m m o n iu m
sa lt o f 2 ,2 ’-(lso in d o lin -1 ,3 -d iylid e n e )
b isp ro p a n e d in itrile w ith Form alin, 184
Méthylation of 2,2'-(lsoindolin-1,3-diylidene)bispropanedinitrile
A tte m p te d m é th yla tio n using M e th ylio d id e , 184
M é th yla tio n using D im ethyl S u lp h a te , 185
M é th yla tio n using th e T é tra m é th y la m m o n iu m sa lt o f 2 ,2 '-(ls o in d o lin 1,3 -d iylid e n e )b isp ro p a n e d in itrile ;
P re p a ra tio n o f th e T é tra m é th y la m m o n iu m s a lt (155), 185
H e ating th e d ry T é tra m é th y la m m o n iu m salt u n d e r vacuu m , 186
H e ating th e T é tra m é th y la m m o n iu m s a lt in 1,2 -D ich lo ro b e n ze n e , 186
Attempted Benzylation of 2,2'-(lsoindolin-1,3-diylidene)bispropanedinitrile
S y n th e s is o f th e B e n zylp yrid in iu m s a lt o f 2 ,2 '-(lso in d o lin -1 ,3 -d iylid e n e )
b is p ro p a n e d in itrile , 187
A tte m p te d fo rm a tio n o f 2 ,2 '-(2 -b e n z y lis o in d o lin -1 ,3 -d iy lid e n e )
b is p ro p a n e d in itrile , 188
Synthesis of the amidino derivatives of 2,2'-(lsoindolin-1,3-diylidene)
bispropanedinitrile
S y n th e s is o f 2-C yano-A / 2-b e n z y l-2 -(3 -d ic y a n o m e th y le n e is o in d o l-1 d iy lid e n e )a c e ta m id in e , 189
S y n th e s is o f 2-C yano-A / 2-p ro p y l-2 -(3 -d ic y a n o m e th y le n e is o in d o l-1 d iy lid e n e )a c e ta m id in e , 190
A lte rn a tiv e s y n th e s is o f 2-C yano-A / 2-p ro p y l-2 -(3 -d ic y a n o m e th y le n e
is o in d o l- 1 -d iy lid e n e )a c e ta m id in e , 191
S y n th e s is o f 2-C yano-A / 2-is o p ro p y l-2 -(3 -d ic y a n o m e th y le n e is o in d o l-1 d iylid e n e )a c e ta m id in e , 192
S yn th e sis o f 2-C yano-A / 2-b u ty l-2 -(3 -d ic y a n o m e th y le n e is o in d o l-1 d iylid e n e )a ce ta m id in e , 193
S yn th e sis o f 2-C yano-A / 2-c y c lo h e x y l-2 -(3 -d ic y a n o m e th y le n e is o in d o l-1 d iy!id e n e )a ce ta m id in e , 194
S yn th e sis o f A /-lso p ro p ylid e n e cyclo h e xyla m m o n iu m sa lt o f 2 ,2 '(ls o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile , 194
S yn th e sis o f 2-C yano-A / 2-o c ty l-2 -(3 -d ic y a n o m e th y le n e is o in d o l-1 d iylid e n e )a ce ta m id in e , 195
S yn th e sis o f 2-C yano-/V 2-d e c y l-2 -(3 -d ic y a n o m e th y le n e is o in d o l-1 d iylid e n e )a ce ta m id in e , 196
S yn the sis o f 2-C yano-A/^,A/i -d ib u ty l-2 -(3 -d ic y a n o m e th y le n e is o in d o l-1 d iylid e n e )a ce ta m id in e , 197
Crystal Structure Determination
S tru ctu re a na lysis and refinem ent, 197
C rysta l
da ta
fo r
B e n zyla m m o n iu m
sa lt
of
2 ,2 '-(ls o in d o lin -1 ,3 -d iy lid e n e )
b is p ro p a n e d in itrile , 198
C rysta l da ta fo r A /-lso p ro p ylid e n e cyclo h e xyla m m o n iu m sa lt o f 2 ,2 '-(ls o in d o lin 1 ,3 -d iylid e n e )b isp ro p a n e d in itrile , 198
C rysta l
data
fo r
2-C yano-A/'/ ,/N/i -d ib u ty l-2 -(3 -d ic y a n o m e th y le n e is o in d o l-1 -
d iy lid e n e )a c e ta m id in e , 198
C rysta l da ta fo r C -T co m p le x ( 1 1 0 )-A /,A /,A /'A /'-T e tram eth yl-p-p henylene diam in e
(TMDA), 198
Cyclic Voltammetry, 199
Ultra-Violet Studies of C-T Complexes in Solution, 199
Synthesis of C-T Complexes
2 ,2 '-(ls o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile -T M D A C o m p le x, 200
2 ,2 '-(ls o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile -T T F C o m p le x, 200
2 ,2 '-(ls o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile -A n th ra c e n e C om plex,
200
2 ,2 '-(ls o in d o lin -2 -m e th y l-1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile -T M D A
C o m plex, 200
2 ,2 '-(ls o in d o lin -2 -m e th y l-1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile -T T F
C o m p le x, 201
Chapter 6
R e fe re n c e S e ctio n 2 0 2 -2 1 3
List of abbreviations
AN
a n th ra ce n e
B E D T -T T F (or ET)
b is (e th y le n e d ith io lo )te tra th io fu lv a le n e
B E D O -T T F
b is (e th y le n e d io x a )te tra th io fu lv a le n e
BTC
b is(trim e th ylsilyl)ca rb o d iim id e
CDW
ch a rg e d e n sity w a ve
C -T
ch a rg e -tra n s fe r
CV
cyclic vo lta m m e try
DBTSF
d ib e n z o te tra s e le n a fu lv a le n e
DBTTF
d ib e n z o te tra th ia fu lv a le n e
DBTeTF
d ib e n z o te tra te llu ra fu lv a le n e
DCNQI
A /,A/'-dicyano-quinone d iim ine
DDQ
2 ,3 -d ich lo ro -5 ,6 -d ic y a n o -1 ,4 -b e n z o q u in o n e
DMA
A/, A /,-dim ethylaniline
DMF
N, /V -dim ethylform a m ide
DM SO
D im e th ylsu lp h o xid e
ET
b is (e th y le n e d ith io lo )te tra th io fu lv a le n e
HM TTF
h e x a m e th y le n e te tra th ia fu lv a le n e
HM TTeF
h e x a m e th y le n e te tra te llu ra fu lv a le n e
HOMO
h ig h e st occu p ie d m o le c u la r orbital
LD A
lith ium d iiso p ro p yla m id e
LUM O
lo w e st un o ccu p ie d m o le cu la r orbital
M (d m it)
m eta l co m p le x o f 4 ,5 -d im e rc a p to -1 ,3 -d ith io le -2 th io n e
TCAQ
te tra cy a n o a n th ra q u in o n e
TCNDQ
1 3 ,1 3 ,1 4 ,1 4 -te tra c y a n o d ip h e n o q u in o d im e th a n e
TCNE
te tra c y a n o e th y le n e
TCNEO
te tra c y a n o e th y le n e oxide
TCNP
1 1 , 1 1 , 1 2 , 1 2 -te tra c y a n o p y re n e
TCNQ
7 ,7 ,8 ,8 -te tra c y a n o -p -q u in o d im e th a n e
THF
te tra h y d ro fu ra n
TM A
té tra m é th y la m m o n iu m
TM DA
A /,A /,A /'/V '-tetram ethly-p-phenylenediam ine
TM TTF
te tra m e th y le n e te tra th ia fu lv a le n e
TM TSF
te tra m e th y le n e te tra s e le n a fu lv a le n e
TNAP
1 1 , 1 1 , 1 2 , 1 2 -te tra c y a n o n a p h th o - 2 ,6-q u in o d im e th a n e
TSF
te tra se le n a fu lv a le n e
TTF
te tra th ia fu lv a le n e
TTeF
te tra te llu ra fu lv a le n e
SDW
spin d e n sity w a ve
xiv
Chapter 1
l
1.A.1 Introduction
T h e a v a ila b ility of lig h tw e ig h t m a te ria ls w ith high e le c tric a l c o n d u c tiv ity
a n d h igh p ro ce ssib ility, o r liq u id n itro g e n te m p e ra tu re s u p e rc o n d u c tiv ity , w ould,
if a tta in a b le , have p h e n o m e n a l c o n s e q u e n c e s fo r th e e le c tro n ic s in d u stry.
E le c tric a l p o w e r tra n s m is s io n w ith o u t re s is ta n c e w o u ld in c re a s e th e e ffic ie n c y
o f th e natio nal grid and e le c tric a l m otors.
P o w e rfu l s u p e rc o m p u te rs using
s u p e rc o n d u c tin g ga te s w ith e x tre m e ly fa st re s p o n s e tim e s, w ith o u t th e nee d fo r
a c o m p le x cooling system , are se e n as th e next g e n e ra tio n of co m p u te r.
d e v e lo p m e n t of p o w e rfu l s u p e rc o n d u c tin g
e le c tro m a g n e ts
c o u ld
The
a llo w th e
re a lis a tio n of high s p e e d tra in s tra v e llin g a lo n g fric tio n le s s s u p e rc o n d u c tin g
tra c k s by e xp e llin g an e x te rn a l m a g n e tic fie ld .
E le c tric cars, p o w e re d by
e x tre m e ly lig h t-w e ig h t b a tte rie s , a n d w ith o u t th e to x ic e m is s io n s o f th e ir fo s s il
fu e l-b u rn in g c o u n te rp a rts , w o u ld
h e lp the p o llu tio n
p ro b le m s in c itie s and
p o s s ib ly reduce the d a m a g e being do n e to the e n v iro n m e n t.
O ne area of re se a rch w h ich is a tte m p tin g to m ake such m a te ria ls a
re a lity is th a t of O rg a n ic M e ta ls. O rg a n ic M eta ls, w h ile e n c o m p a s s in g the fie ld s
o f c o n d u c tin g po lym e rs a nd c o n d u c tin g c h a rg e -tra n s fe r (C -T) co m p le xe s, have
b u t o n e com m on p ro p e rty w ith th a t of m etals, i.e. p a rtia lly -fille d d e lo c a lis e d
bands.
It has been th e h ig h ly brittle , c ry s ta llin e C -T c o m p le xe s w h ich have
y ie ld e d m ost in fo rm a tio n on th e s e s o lid sta te p ro p e rtie s .
W h ile it is u n lik e ly
th a t th e s e c rysta llin e s o lid s w ill re p la ce c o p p e r as a m eans to m a kin g a sim p le
e le c tric a l
contact,
m e c h a n is m
of
u n d e rs ta n d in g
in te re s t
c h a rg e
d oe s
p h o to c o n d u c to rs
and
in
th e s e
tra n s p o rt
ha ve
m a te ria ls
a nd
p ra c tic a l
m a te ria ls
to
te s tin g
use
m o d ify
in
th e
lies
in
u n d e rs ta n d in g
th e o re tic a l
the
m odels.
d e sig n
s u rfa c e
th e
of
of
T h is
o rg a n ic
s e m ic o n d u c to r
e le c tro d e s . It may even g ive an in s ig h t in to the co m p le x ra p id e le c tro n tra n s fe r
p ro c e s s e s in b io lo g ica l s y ste m s. F igure 1.01 g iv e s so m e e x a m p le s o f the ty p e s
o f c o n d u c tiv itie s a c h ie v e d in th e fie ld of O rg a n ic M e ta ls.
1.A.2 B a c k g ro u n d
In te re st in
h ig h ly
c o n d u c tin g
C -T
c o m p le x e s
cam e
a b o u t w ith
d is c o v e ry in 1954 of th e firs t e le c tric a lly c o n d u c tin g m o le c u la r c o m p o u n d
th e
1 w ith
a c o n d u c tiv ity of - 1 x 1 0-3 S c rrr1. H o w e v e r the tru e im p e tu s w as in itia te d by the
d is c o v e ry of the h ig h ly c o n d u c tin g ( -5 0 0 S c n r 1) C -T sa lt
2 of th e a cce p to r,
7 ,7 ,8 ,8 -te tra c y a n o -p -q u in o d im e th a n e 3 (T C N Q ; 1) and th e donor,
2
Temperature (K)
Figure 1.01. Temperature dependence o f conductivity for various
electrical conductors
te tra th ia fu lv a le n e
m a g n e tic
4 (T T F ; 2a).
W h ile C -T co m p le x e s a lso e x h ib it in te re stin g
5 and n o n -lin e a r o p tica l p ro p e rtie s 6, m ost re se a rch has centred
a ro u n d a ch ie vin g e v e r h ig h e r c o n d u c tiv itie s .
th o u s a n d s
of
C -T
s a lts
have
bee n
In try in g to reach th is goal m any
sy n th e s is e d ,
w ith
th e
ultim ate,
su p e rc o n d u c tiv ity , b e in g firs t a c h ie v e d in 1980 by B e c h g a a rd a n d Jerom e 7.
To date the h ig h e st T c fo r an o rg a n ic s u p e rc o n d u c to r is 11.6 K at a m b ie n t
pressure,
8 o r 1 2.5 K at 0.3 K b a r of p re s s u re ,9 fo r th e (E T )2X (3) cla ss of salts.
A h ig h e r T c of 40 K has be e n re p o rte d 10 fo r th e n e w e st c la s s of o rg a n ic
s u p e rco n d u cto rs, th e fü lle n d e s , Ceo.
H o w e v e r th e se o rg a n ic co m p o u n d s still
have a long w ay to go to co m p a re w ith the m ost h ig h ly s u p e rc o n d u c tin g
in o rg a n ic cu p ra te s, w h ich at p re s e n t have th e h ig h e s t T c= 133 K fo r a m ercury-
3
b a riu m -c a lc iu m -o x id e .1 1
It is th ro u g h c o n tin u e d re se a rch and c o -o p e ra tio n
b etw e en ch e m ists a nd p h ysicists th a t so m uch has bee n a ch ie ve d in recent
years.
T h e o n g o in g syn th e sis o f n o ve l d o n o r and a c c e p to r m olecu les should
fu rth e r these g o a ls o r at least yie ld a d d itio n a l in s ig h ts into how they m ay be
realised.
NC
CN
■ V S
C >=0
x*^
^X
(a) X = S ,
NC
TTF
(b) X = S e ,
CN
(c) X = T e ,
TSeF
T T eF
(ET)2x
TCNQ
(2)
( 1)
Atom ic orbitals
(3)
M o le c u la r o rb ita ls
(«I Lij
(Cl Li 4
-onnr
2s
2s
2s
2s
A to m A to m A to m A to m
1
2
A to m
1
3
M any
a to m s
4
M a n y c lo s e ly s p a c e d
M O le v e ls c o n s titu tin g
a b a n d . ( N o te th a t
th e re a re n e n e rg y
le v e ls , a n d n e le c tro n s .
S o the b a n d is o n ly
h a lf fille d )
A to m
n
Figure 1.02 Development o f m olecular orbitals into bands in lithium metal
4
1.A.3 Conductivity in a solid: The Band Theory
In th e fo rm a tio n o f c rysta llin e m ate rials, th e e le c tro n ic o rb ita ls o f the
c o m p o n e n t atom s o r m o le cu le s o ve rla p and m ix to fo rm bands, each band
c o n ta in in g a range o f e n e rg y sta te s o r levels. T h e se b a n d s are filled according
to P a uli's exclu sio n p rinciple, w ith th e lo w e st e n e rg y s ta te s being filled first and
th e n th e n ext h ig h e st state s right up to the h ig h e st o ccu p ie d state, w h ich is
kn o w n as th e Ferm i Level, E F. A n e xa m p le o f th is is se e n in F ig u re 1.02 fo r the
o ve rla p o f th e
2 s-o rb ita ls o f lithium .
T h e se ban ds m ay o ve rla p o r a gap m ay exist.
T h e lo w e r band (or
va le n c e band) is fo rm e d fro m th e h ig h e st occu p ie d m o le c u la r o rbitals (H O M O s)
and th e u p p e r (or c o n d u c tio n ) ban d fro m th e lo w e st u n o ccu p ie d m olecu lar
o rb ita ls (LU M O s) o f th e in te ra ctin g species.
A sim ple th e o re tic a l basis fo r o n e -d im e n sio n a l co n d u c tio n is illustrated
by th e tig h t-b in d in g
band
a p p ro xim a tio n ,
in w h ich
one
co n sid e rs
a o ne­
d im e n s io n a l arra y o r ch ain o f N e q u a lly sp ace d m o le c u le s a d is ta n c e c apart,
F ig u re 1.03.
< c >
—O
-
O
O
O
O
O—
normal
0 - 0 — 0 - 0 ------ 0 - 0 — 0 - 0 —
<
2c
d istorted
>
Figure 1.03Showing the normal separations between an
array o f atoms or
molecules which form a one dimensional metallic conductor and
the distorted
separations which can occur at low er temperatures which result in the loss of
electrical conductivity and the opening o f a band gap.
In th e isolated s ta te ea ch a to m o r m o le cu le has an o rb ita l w ith e ne rg y E 0
th a t o ve rla p s w ith th e e q u iv a le n t o rbitals o f its tw o n e a re s t neighb ours. This is
e q u iv a le n t to th e e n e rg y o f an o rb ita l be fo re its lin e a r co m b in a tio n w ith an o th e r
o rb ita l to give th e co rre s p o n d in g bo n d in g and a n ti-b o n d in g m o le c u la r orbitals.
T h e e n e rg ie s o f th e s e o rb ita ls w h ich c o n stitu te this a rra y o r band are derived
fro m a H u ckel-like tig h t-b in d in g band d e scrip tion.
T h e s e e n e rg y levels are
s u ffic ie n tly clo se in e n e rg y th a t an a p p a re n t co n tin u u m o f a llo w e d e n e rg y levels
e x is t a b o ve and b e lo w th e e n e rg y level o f th e iso lated m o le cu le E 0, Figure
1.04.
T his co n tin u u m is b o u n d e d w ith in a band o f w id th 2 W and is com posed
5
of N o rb ita ls c a p a b le of a c c o m m o d a tin g 2N e le c tro n s . T he b a n d w id th is related
to th e tra n s fe r in te g ra l t (the re s o n a n c e in te g ra l p in the H u cke l m e th o d ) by
2 W = 4 t, Figure 1.04.
Number oI m onom er u nits
Infinite
Figure 1.04 Schematic illustration o f the formation of a band from the
overlap of the molecular subunits in a stack
In m ost n o n -m e ta llic so lids th e v a le n c e b a n d is c o m p le te ly fille d and the
u p p e r c o n d u ctio n ba n d is co m p le te ly em pty.
T h e s e m a te ria ls are in s u la to rs or
at best se m ic o n d u c to rs as th e re are no e m p ty ¿tates n ea r th e F erm i level to
a c co m m o d a te e le c tro n s as th e y g a in e n e rg y d u rin g co n d u c tio n .
If th e band
g a p is not too la rg e (<2eV ), Figure 1 .05(b), th e e le c tro n s at the F erm i le ve l m ay
be th e rm a lly o r p h o to e xcite d into the c o n d u c tio n band.
B oth th e s e e le c tro n s
a nd th e p o sitive ho le s th e y leave b e h in d can m ove and c o n trib u te to the
c o n d u c tiv ity .
S uch a m ate rial is a s e m ic o n d u c to r and c o n d u c tiv ity in cre a se s
w ith in cre a se d te m p e ra tu re .
If the ba n d gap is to o la rg e ( > 2 e V ) fo r the
e x c ita tio n of e le c tro n s a cross the gap th e n th e m a te ria l is an in s u la to r, Figure
1.05(a). W h e n th e re is o ve rla p of the v a le n c e a nd c o n d u c tio n b a n d s o r th e re is
an in co m p le te ban d, then little o r no e n e rg y is re q u ire d fo r th e m o ve m e n t of
e le c tro n s from the h ig h e st o c c u p ie d s ta te s of the Ferm i le vel in to the va ca n t
s ta te s
of
the
co n d u c tio n
band,
F igure
1 .05(c).
T h is
d e fin e s
m e ta llic
c o n d u c tiv ity .
Thu s th e 'e x te n t of o c cu p a tio n of the e n e rg y le ve ls and th e m a g n itu d e of
th e ban d gap d e te rm in e the e le ctrica l p ro p e rtie s of a m a te ria l.
In o rd e r to
d e s ig n and s y n th e s is e a m ate rial w ith the p a rtia lly fille d d e lo c a lis e d ba n d of a
m etal a c o lle c tio n of atom s o r m o le cu le s m ust be fo u n d w h ich , w h e n a rra n g e d
in clo se p ro xim ity and in sim ila r c ry s ta llo g ra p h ic a nd e le c tro n ic e n v iro n m e n ts ,
fo rm an e n e rg e tic a lly flat e xte n d e d p a th w a y e n a b lin g th e fre e m o ve m e n t of
6
e le c tro n s .
S uch a s itu a tio n is fre q u e n tly re a lis e d w h e n p la n a r, co n ju g a te d
m o le cu le s c ry s ta llis e in a stack, as in th e ca se fo r c h a rg e -tra n s fe r com ple xes,
in w h ich e le ctro n tra n s fe r from th e d o n o r to the a c c e p to r p ro v id e s th e m eans
fo r th e fo rm a tio n of a p a rtia lly fille d ban d.
Empty Band
Band
gap
♦
Filled Band
(a)
(b)
(c)
Figure 1.05 Schematic illustration o f the electron occupancy o f allow ed energy
bands in (a) an insulator, (b) a semiconductor, and (c) a metal.
1.A.4 General Properties of Charge-Transfer Complexes
C h a rg e -tra n s fe r
(C -T)
co m p le xe s,
or
a lte rn a tiv e ly
e le c tro n
donor-
a c c e p to r (E D A ) co m p le xe s, are a s s o c ia tio n s of d e fin ite s to ic h io m e try betw een
tw o d iffe re n t m o le cu le s, each of clo se d shell e le c tro n ic s tru c tu re s .
T h e y are
fre q u e n tly fo rm e d w h e n a m o le cu le of low io n is a tio n p o te n tia l, an electron
d o n o r (D), in te ra c ts w ith a m o le cu le of re la tiv e ly high e le c tro n a ffin ity, an
e le c tro n a c c e p to r (A), (e q u a tio n 1).
T h e s e C -T co m p le x e s are ca p a b le of
d is c re te a b s o rp tio n of lig h t givin g rise to b a n d s in th e n e a r UV o r visible
s p e ctru m w h ich are d is tin c t from th o s e of e ith e r co m p o n e n t o f the co m p le x.
D + A
^
O ne th e o ry as to th e
[A ,D ] — ►
nature
[A ",D + ]
of th e b in d in g
e q u a tio n 1
a nd th e
c h a ra c te ris tic
e le c tro n ic a b s o rp tio n w a s put fo rw a rd by M u ilik e n .12 His th e o ry s ta te d th a t the
g ro u n d sta te fo r a co m p le x, O n (D A ), w a s a c o m b in a tio n
stru c tu re ,
d>(D,A),
in
w h ich
A and
D are
of a "n o-bo nd"
held to g e th e r by
d ip o le -d ip o le
in te ra c tio n s a nd o th e r in te rm o le c u la r fo rce s, and a "d a tiv e b o n d " structure,
<i>(D+-A'), in w h ich one e le ctro n has bee n tra n s fe rre d from th e D to A. Thus,
7
O n (D A) = aO (D ,A ) + b O (D + -A _)
e q u a tio n 2
w h e re a and b are co e ffic ie n ts and a>b.
T h e e xcited sta te o f th e com plex, ® E(D A ), co rre sp o n d s to the co m b in a tio n :
<E>e (D A) = a * 0 (D + -A _) + b * 0 (D ,A)
e q u a tio n 3
w ith a "d a tive b o n d " stru ctu re as th e m ain co n trib u to r.
Thus
th e
o p tica l
a b so rp tio n
c h a ra c te ris tic
id e n tifie d w ith th e tra n sitio n ® E(D A ) < - O n (DA).
of
th e se
c o m p le xe s
is
T h e se spectral ban ds result
fro m th e p ro m o tio n o f an e le ctro n fro m th e H O M O o f D to th e LU M O o f A,
F ig u re 1.06.
■LUMO
■LUMO
hv
■LUMO
■LUMO
■HOMO
■HOMO
-
4
■HOMO
HOMO
-
D+ '
D
A'
Figure 1.06 Transfer o f an electron from the HOMO o fD to the LUMO o f A
It is im p o rta n t to note th a t fo r m a n y E D A co m p le xe s the "no b o n d " stru ctu re is
th e m a jo r c o n trib u to r to th e gro u n d state , i.e. a » b in e q u a tio n 2.
T h e re fo re
th e re is little C -T in th e g ro u n d state.
T h e m a g n itu d e o f C-T, and w ith it th e in te n sity o f th e C -T bands, is
d e p e n d e n t on th e d e g re e o f d o n o r-a c c e p to r o verla p and on the ionisation
p o te n tia l o f th e d o n o r and th e e le ctro n a ffin ity o f th e acceptor.
T h e d e g re e of
C -T m ay be p artial o r com ple te , w ith co m p le te C -T resulting in th e fo rm a tio n of
a radica l ion salt.
8
1.A.4.1 Stacking formation in C-T Complexes
T h e re are tw o c la s s e s of a g g re g a tio n is o m e rs in to w h ich C -T com ple xes
m ay form .
T h e firs t ty p e
is th a t in w h ich th e d o n o rs and th e a cce p to rs
a g g re g a te into m ixed s ta c k s co m p risin g a lte rn a te D and A m o le cu le s, Figure
1.07(a).
The se c o n d c la s s in v o lv e s th e fo rm a tio n of s e g re g a te d sta cks of
d o n o rs and a cc e p to rs , F ig u re 1.07.
D A D A
A D A D
A D A D
A D A D
D A D A
A D A D
A D A D
A D A D
D A D A
A D A D
(a)
(b)
Figure 1.07 Illustration o f the types o f stacking motifs found in C -T complexes;
(a) Mixed Stacks and (b) Segregated Stacks.
T he po te n tia l a b ility of th e s e tw o s ta c k in g syste m s to co n d u ct e le ctricity
is ve ry d ifferent.
In o rd e r to co n d u ct dow n a m ixed s ta c k an u n p a ire d electron
on an a c ce p to r m o le cu le w o u ld have to s ta rt h o p p in g to th e a d ja ce n t m olecule,
a don or.
S ince th e m o le c u la r p o te n tia l of th is a c c e p to r is ve ry d iffe re n t from
th a t o f the don or, th is w ill act as a la rg e a c tiv a tio n e n e rg y to co n d u ctio n .
B rin g in g an e le ctro n a lo n g a se g re g a te d s ta ck of a c c e p to rs a g a in in vo lve s the
h o p p in g of an e le c tro n o n to a d ja ce n t m o le c u le s but w ith o u t th e la rg e p otentia l
d iffe re n c e e x p e rie n c e d in th e m ixed stack.
S u ch a situ a tio n e xists w ith the
m e ta llic com plex, T T F -T C N Q , w h ich is h ig h ly c o n d u c tin g and form s se g re g a te d
s ta c k s
2 in its c ry s ta llin e state . H o w e ve r th e re m ay be som e ba rrie rs, like the
C o u lo m b ic re p u lsio n
U, w h ich , if U » 4 t ,
th e
b a n d w id th ,
m ay lead to the
fo rm a tio n of a M o tt-H u b b a rd ty p e in su la to r. T h is o c c u rs in co m p le xe s w ith half
fille d bands.
A ba n d b e c o m e s half fille d w h e n th e re is co m p le te tra n s fe r of an
e le c tro n b etw e en th e d o n o rs and th e a c c e p to rs and as a re su lt th e re are no
n e u tra l sites in th e s ta c k fo r the e le c tro n s to h op to, due to an electron
be co m in g a sso cia te d w ith ea ch site. T h e re s u lt of m oving an e le c tro n from one
s ite to a n o th e r in v o lv e s in c re a s e d re p u ls io n b e tw e e n th e like cha rg e s.
T his
u s u a lly o ccu rs w h en th e re are e ith e r s tro n g d o n o rs o r stro n g a c c e p to rs in the
co m p le x.
By c o m b in in g d o n o rs and a c c e p to rs in w h ich th e ch a rg e tra n s fe r is
in co m p le te , th e o ve ra ll v a le n c e of th e s ta c k is e ffe c tiv e ly m ixed w ith the result
9
th a t th e re are ne u tra l s ite s in the s ta c k c a p a b le o f a cco m m o d a tin g an e le c tro n .
T h e d e g re e of C -T fo r th e T C N Q C -T c o m p le x e s of T T F , T S F and T T e F have
b e e n fo u n d to be 0.59, 0 .6 3 and 0.71 of an e le c tro n re s p e c tiv e ly .13
In g e n e ra l m ost se g re g a te d s ta c k in g
C -T co m p le xe s are c o n d u c tin g
w h ile th e m ixed s ta c k in g co m ple xes are in s u la tin g .
s u g g e s te d
th a t th e
m ixe d -sta ck form
is
as,
or
H o w eve r, w h ile it has been
m ore,
th e rm o d y n a m ic a lly
s ta b le ,14 it a p p e a rs th a t both iso m e rs m ay in a n y e v e n t co e xist a nd th e o n ly
way
to
e n su re
s e g re g a te d
sta ckin g
is
to
d e s ig n
m o le cu le s
w h e re
the
s e g re g a tio n is b u ilt-in .15
1.A.4.2 Stoichiometries in C-T Complexes
In a d d itio n to th e d iffe re n c e s in th e s ta c k in g ty p e s o rg a n ic C -T s a lts are
fo u n d w ith d iffe rin g s to ic h io m e tric ra tio s of d o n o r to a cce p to r. T C N Q (1) alone
fo rm s a m u ltitu d e of v a ria b le s to ic h io m e tric co m p le x e s w ith
m a n y d o n o rs
in c lu d in g 1:1 s a lts w ith T T F (2a), a 1:1 a nd 2:1 s a lt w ith /V,A/,A/',A/'-tetramethyl-
17 a n d e ve n a 4:1 com p le x w ith an
a n th ra q u in o n e d e riv a tiv e of T T F (5 ).18 T h e v a ria b le s to ic h io m e try of th e se
p -p h e n y le n e d ia m in e
co m p le xe s, even
(T M D A ;
4 ) 16-
be tw e e n the sam e d o n o rs a n d acce p to rs, is m ost like ly
d e te rm in e d by p a ckin g co n s id e ra tio n s .
c o m p le x
fo rm a tio n
s to ic h io m e try .19
m e th a th e sis
W heland and Gillson have sh o w n th a t
o c c a s io n a lly
a ffo rd s
c o n tro l
o ve r
In th e case of th e h a lid e s a lts of T T F it is a rg u e d th a t the
s to ic h io m e try is d e te rm in e d by c o m p e titio n b e tw e e n th e cost of io n is in g a D-A
p a ir (I - A), io n is a tio n p o te n tia l m inus th e e le c tro n affin ity, and th e e le c tro s ta tic
(o r M a d e lu n g ) e n e rg y, E M,of the so lid th a t is g a in e d by fo rm in g io n s .20
Me
Me
N
Me
)==(
Me
S
I
S
n V
&
Me
-N,
Me
s
1
Me
(5)
(4)
10
s
Me
1.A.4.3 The Unidimensionality of C-T Complexes
As m e n tio n e d p re v io u s ly , the p a rtia lly fille d d e lo c a lis e d ba n d of a m etal
can
be
re a lis e d
in
C -T
co m p le xe s
cry s ta llis e in s e g re g a te d sta cks.
when
p la n a r,
c o n ju g a te d
m o le cu le s
B e ca u se th e g re a te s t o v e rla p of o rb ita ls
o ccu rs along th e sta ck, e le c tric a l c o n d u c tiv ity is g re a te r in th is d ire c tio n th a n in
a n y o th e r d ire c tio n . A s a re su lt of th is a n is o tro p ic b e h a v io u r th e s e co m p o u n d s
have also bee n re fe rre d to as q u a si- o r p s e u d o -o n e -d im e n s io n a l m eta ls. S ince
C -T is u su a lly co m p le te o r p artial, the b a n d s are u s u a lly at m ost h a lf fu ll o r in
a n y case in c o m p le te .
U n like m etals, in w h ic h e le c tro n s can a v o id ea ch o th e r
by m oving in th re e d im e n s io n s , the q ua si o n e -d im e n s io n a l C -T s a lts a re su b je ct
to va rio u s p h a se tra n s itio n s due to in c re a s e d
e le c tro n
in te ra c tio n s .
T he
problem of th e h a lf fille d sta te giving rise to a M o tt-H u b b a rd in s u la to r has been
m e n tio n e d a lre a d y .
T h e p a rtia lly fille d q u a si o n e -d im e n s io n a l s a lts are also
su b je c t to m etal to in s u la to r (M -l) tra n s itio n s at lo w te m p e ra tu re s .
T h e s e are a
re su lt of la ttice d is to rtio n s and the fo rm a tio n of an a n tife rro m a g n e tic sta te and
are the p rin cip a l b a rrie r to h ig h e r c o n d u c tiv itie s .
1.A.4.4 Lattice instabilities in quasi one-dimensional conductors
T h e na tu re of q u a si o n e -d im e n s io n a l C -T co m p le xe s re su lts in ce rta in
p h ysica l re s tric tio n s on co n d u c tiv ity as th e te m p e ra tu re is lo w e re d .
T he se
la ttice in s ta b ilitie s are c h a ra c te ris tic of th is cla ss of c o n d u c to rs d u e to the
in cre a se d e le c tro n in te ra c tio n and are m ade up of :
(i)
P e ie rls d is to rtio n s (or C h a rg e D e n sity W a v e s (C D W ))
(ii)
S pin D e n sity W a v e s (S D W )
(i) P eierls d is to rtio n s :
By a n a lo g y w ith J a h n -T e lle r's th e o ry , p a rtia lly -fille d e n e rg y b a n d s, w hich
are a n a lo g o u s to m eta ls, are subject to g e o m e tric a l d is to rtio n s a s s o c ia te d w ith
a lo w e rin g of th e to ta l en e rg y.
An e xa m p le of th is is give n fo r co m p a ris o n of
th e J a h n -T e lle r e ffe c t in cyclo b u ta d ie n e , F ig u re 1.08(a), and P e ie rls d is to rtio n
in an e xte n d e d ch a in m ade up of prc-orbitals, F ig u re 1.08(b). T h e lo w e r e n e rg y
stru c tu re in both s y s te m s is the one w h e re th e bo n d le n g th s a lte rn a te .
If the
e le c tro n s w e re d e lo c a lis e d o ve r th e e n tire system , th e n th e n -e x te n d e d o n e ­
d im e n s io n a l ch a in of p o ly a c e ty le n e w o u ld have a h a lf-fille d ba n d and w o u ld be
e xp e cte d to be m e ta llic.
11
71*
/
t
PTC
\
71
- t f
t
pK
It
f f l
o
(b)
(a )
Figure 1.08 Showing the comparison in the geometric distortions o f (a)
Jahn-Teller effect in cyclobutadiene and (b) Peierl's distortion in an
extended chain o f pn-orbitals.
T h e s e g e o m e tric d is to rtio n s are v a rio u s ly know n as P e ie rls 21 d is to rtio n s or
C h a rg e D e n sity W a v e s (C D W ).22
At the F erm i le ve l th e re is a d e g e n e ra c y a n d ju s t above o r b e lo w it, n e a r­
d e g e n e ra c y , fo r any p a rtia lly -fille d band. T h e re is a d rivin g force fo r th e system
to lo w e r its energy.
In o rd e r to do th is th e s tru c tu re m ust disto rt and th u s the
e le c tro n s in th e se d e g e n e ra te sta te s b e co m e p a ire d , op e n in g up a g a p at the
F erm i level.
T h is is re fe rre d to as E le c tro n -P h o n o n coup ling.
T h e size o f the
g a p w ill d e te rm in e w h e th e r the s o lid is in s u la tin g o r se m i-co n d u ctin g .
T his
p a irin g of e le c tro n s re s u lts in re g io n s of th e la ttice h aving a lte rn a tin g high and
lo w cha rg e d e n s ity a n d h e n ce g e n e ra tin g a C D W .
C D W s can also be th o u g h t of as e le c tro n -h o le p a irs as w e ll as e le ctro n e le c tro n pairs, F igure 1.09(a).
W e can th in k of an e lectron as be in g paired
e ith e r w ith a hole to its rig h t o r le ft o r w ith th e e le c tro n o p p osite.
As a s o lid is
c o o le d to w a rd s a b s o lu te ze ro (0 K) th e re is a te n d e n c y fo r e le ctro n s to pair. A
C D W fo rm s w h e n b e lo w th e p h a s e -tra n s itio n te m p e ra tu re and the e le c tro n s are
tra p p e d in pairs.
T h e fo rm a tio n of th is
CDW
is a cco m p a n ie d by la ttice
d is to rtio n s and th e s e can be se e n by x -ra y d iffra c tio n .
T h e co u p lin g of C D W s w ith la ttice v ib ra tio n s also show s v a ria b le effects
on co n d u ctivity. T h e w a v e le n g th of a C D W v a rie s w ith th e num ber of e le ctro n s
in th e solid, i.e. th e g re a te r th e n u m b e r of e le c tro n s th e sh o rte r the w a ve le n g th .
H e n c e the w a v e le n g th of th e C D W m ay not m atch th a t of the o rig in a l lattice.
T h e C D W is sa id to be in c o m m e n s u ra te w ith the o rig in a l lattice sp a cin g s and is
fre e to tra ve l th ro u g h o u t th e la ttice until p in n e d by a lattice defect.
12
CDW s
w h ic h are c o m m e n su ra te w ith th e la ttice s p a c in g s are tra p p e d and do not
co n trib u te to the c o n d u c tiv ity .
I
1•
•
I
•t
•
•
•
I
t
•
r
•
i
.
(a) C D W
•
i
•
i
• i
•
;
•
i
.
i
.
i
t
.
i
.
(b) S D W
Figure 1.09 (a) Pairing o f electrons and holes in a stack giving a CDW.
(b)
Pairing of electron spins on adjacent molecules in a stack giving a SDW.
(ii)
S p in D e n sity W a v e s (S D W )
E le ctro n s w ith th e sam e spin te n d to o p p o s e o n e a n o th e r and so p re fe r
to p a ir-u p w ith e le c tro n s o f o p p o s ite spin, i.e. a n tife rro m a g n e tic a lly .
So a S D W
can be like n e d to tw o C D W s su p e rim p o s e d but s h ifte d one space to the left or
rig h t, Figure 1.09(b), so th a t th e to ta l ch a rg e d e n s ity is c o n sta n t but the spin
d e n s ity a lte rn a te s a lo n g th e la ttice .
T h is a n tife rro m a g n e tic phase is in su la tin g
d u e to the p e rio d ic ity of th e S D W w h ich d e s tro y s th e Ferm i surface. T his type
o f d is to rtio n
is e x h ib ite d
by th e
B e ch g a a rd
s a lts
fo rm e d from
octa h e d ra l
a n io n s 23 and th e se M -l tra n s itio n s give w a y to a s u p e rc o n d u c tin g state u n d e r
th e a p p lic a tio n of high p re s s u re s .
A n o th e r ca u se of M -l tra n s itio n s o b s e rv e d in th e B e ch g a a rd salts is due
to th e o rd e rin g of th e a n io n s at lo w e r te m p e ra tu re s .23
T h e lo w e r sym m etry
a n io n s u n d e rg o th e s e tra n s itio n s at h ig h e r te m p e ra tu re s , w ith th e e xcep tion of
th e p e rch lo ra te salt, th a n th o s e of th e o c ta h e d ra l a n io n s . T h e se tra n s itio n s can
be s u p p re sse d by th e a p p lic a tio n of p re ssu re , a g a in w ith th e o b se rva tio n of a
s u p e rc o n d u c tin g state.
13
1.A.5 Superconductivity
S u p e rco n d u ctivity is the a b ility to co n d u ct e le c tric ity w ith zero resistance.
A c u rre n t s e t up in a s u p e rc o n d u c to r is not d issip a te d as heat, as in an ord in a ry
co n d u c to r, b u t instead co n tin u e s to flo w fore ver. A th e o ry fo r su p e rc o n d u c tiv ity
in m e ta ls w a s put forw ard by B ardeen, C o o p e r and S c h rie ffe r in 1957 called the
B C S th e o ry .24
1.A.5.1 BCS Theory of Superconductivity
T h e BCS th e o ry pro p o se d that, unlike c o n v e n tio n a l c o n d u c tiv ity w hich
in vo lve s
th e
m o ve m e n t
s u p e rc o n d u c tiv ity
in volve s
in te re le c tro n attraction
of
th e
fre e
e le ctro n s
pairing
of
in
a
c o n d u ctio n
c o n d u ctio n
e le ctro n s
by
band,
som e
and a c o n d e n sa tio n o f th e s e pairs, know n as C o o p e r
pairs, a t so m e critical te m p e ra tu re , T c , to fo rm a m a c ro s c o p ic q u a n tu m state.
T h is sta te has m any u n iq u e p ro p e rtie s in clu d in g ze ro re sista n ce and p e rfe ct
d ia m a g n e tis m , w h ich e xclu d e s an e xte rn a l m a g n e tic field fro m
its interior,
kn o w n as th e M e issn e r effect, up to a lim iting critica l field stren gth .
m e c h a n is m
fo r th e fo rm a tio n
v ib ra tio n s called phonons.
o f th e C o o p e r pairs is m ed ia te d
T he
by lattice
T h e pro ce ss b eg ins w h e n o n e e le ctro n a ttra cts the
s u rro u n d in g p ositive ions o f th e crystal la ttice and cre a te s a region o f low ered
p o te n tia l e n e rg y fo r itse lf and o th e r ele ctro n s.
B e ca u se th e s e ions are m uch
h e a v ie r th a n th e e le ctro n th e y m ove m ore slo w ly and as a result th is region of
lo w e re d e n e rg y persists and a se con d e le ctro n is a ttra cte d , F igure 1.10.
*
e-
e
w
O -*O - O
* -C
* U
*0
-#0 - *•0 - *0 i
o - o -o - o ^ J o -o -o -o '
I I I I
O I I I I.°
o - o - o - o , I ^ o - o -o - o
O
o - o - o - o e —► 0 -0
oLo Lo'-o:' (j)^ o - o - o :-o JL
.
I
I I I
n
I I I I.
0 —0 —0 —0 "
0 —0 —0 —0
Figure 1.10 Mechanism for the formation o f Cooper pairs
In te ra ctio n s be tw e e n th e c o n d u ctio n e le ctro n s and th e p h o n o n s take
p la c e in a region w h o s e e n e rg y range s fro m th e F erm i level, E F, to th e Ferm i
le vel plus the a ve ra g e e xcita tio n e n e rg y o f the p h o n o n (E F + Ev ). B e ca u se the
P a u li e xclu sio n prin cip le fo rb id s th e s e in te ra ctio n s fro m sca tte rin g e le ctro n s into
th e fu lly o ccup ied sta te s b e lo w th e F erm i level, th e lo w e r sta te s p ro vid e a
14
p a s s iv e s u p p o rt base fo r th e in te ra ctio n region.
A t T c , th e te m p e ra tu re is
s u ffic ie n tly low th a t th e rm a l a gita tion at th e F erm i s u rfa c e is in su fficie n tly large
to
b re a k up th e
pairing
process.
A s a re su lt m a n y C o o p e r pairs form
s im u lta n e o u s ly to cre a te th e su p e rco n d u ctin g state.
In th e s im p le s t fo rm o f the BCS theory, T c d e p e n d s lin e a rly on the
e x c ita tio n e n e rg y o f th e system th a t m edia te s th e e le ctro n pairing, th e lattice
v ib ra tio n E v . C o n s e q u e n tly a d e cre a se in the la ttice v ib ra tio n w ill d e cre a se T c ,
sin ce th e h e a v ie r lattice w ill vib ra te at lo w er fre q u e n c ie s . Isoto pe su b stitu tio n is
o n e m e th o d w h ich has been used to ascertain w h e th e r s u p e rc o n d u c tiv e pairing
is m e d ia te d by la ttice vib ratio ns.
H o w eve r, w h ile th e ge n e ra l p rinciples o f th e B C S th e o ry p ro b a b ly can
a c c o u n t fo r th e new su p e rco n d u cto rs like the cu p ra te s and the new o rgan ic
s u p e rc o n d u c to rs , th e m e ch a n ism fo r th e fo rm a tio n o f th e s u p e rco n d u ctin g state
is still un kn o w n .
M o d ifica tio n s o f th e cla ssic B C S th e o ry are still required. T h e
m o s t like ly m o d ifica tio n is an a lte rn a tive e le ctro n -p a irin g m e ch a n ism m ediated
n o t by p h o n o n s b u t by in teractio n o f th e c o n d u ctio n e le c tro n s w ith charge or
e le c tro n spin flu c tu a tio n s in the e le ctro n ic s u b s y s te m .25
1.A.6 Design of Organic Metals
In th e la st tw e n ty years th e re has been in te n s e in te re st in trying to
d e te rm in e and u n d e rsta n d th e p rope rties n e ce ssa ry to e n a b le an o rg a n ic solid
c o n d u c t e le ctricity.
O n g o in g
research fo cu se d
on th e syn th e sis
o f new
d e riv a tiv e s o f both T C N Q and TTF, along w ith th e s o p h is tic a te d m e a su re m e n ts
a nd in te rp re ta tio n s o f th e so lid -sta te physicist, has c o n trib u te d g re a tly to the
w e a lth o f k n o w le d g e n o w available.
From th is in fo rm a tio n ce rta in com m o n
c h a ra c te ris tic p ro p e rtie s have been found
in all th e
o rg a n ic solids w hich
c o n d u c t e le c tric ity .26
In o rd e r to a tta in th e m eta llic state, an o rg a n ic solid has to fu lfil the
fo llo w in g b a sic re q u ire m e n ts ;
(i)
th e m o le c u la r co m p o n e n ts m ust be p la n a r w ith e xte n sive nd e lo c a lis a tio n in o rd e r to fa cilita te e x te n s iv e ove rla p
(ii)
th e c o m p o n e n ts should be o f sim ila r size and h ighly sym m e tric
(iii)
th e c o m p o n e n ts shou ld crystallise into a u n ifo rm stru ctu re w ith
s e g re g a te d sta ckin g o f the don ors and a cce p to rs
(iv)
th e d e g re e o f c h a rg e -tra n sfe r shou ld be p a rtia l to e n su re m ixed
va le n ce sta cks
15
(v)
th e o rg a n ic s o lid sh o u ld be ca p a b le of m in im isin g e le ctro n e le ctro n in te ra c tio n s
In a d d itio n to th e a b o v e b a s ic re q u ire m e n ts, in c re a s e d d im e n s io n a lity ,
n e c e s s a ry fo r e n h a n ce d c o n d u c tiv ity and th e re d u ctio n o r e lim in a tio n of M -l
tra n s itio n s
a ss o c ia te d
te m p e ra tu re s ,
is
w ith
a c h ie v e d
th e
by
th e
q u a s i-o n e -d im e n s io n a l
in c o rp o ra tio n
of
s a lts
h ig h ly
at
low
p o la riz a b le
h e te ro a to m s su ch as S, Se o r T e on th e p e rip h e ra l s ite s o f th e d o n o r and
a cce p to rs.
S in ce th e a b ility of c h e m is ts to in d u c e m o le cu le s to p a c k w ith in a crysta l
la ttic e in a p re s c rib e d m a n n e r is v e ry lim ite d , one is re stricte d to c o n tro llin g the
key p ro p e rtie s of the in d iv id u a l m o le c u le s in a d va nce.
O ne of th e m a jo r g o a ls
fo r c h e m is ts in recent ye a rs has be e n to d is c o v e r new fa m ilie s of d o n o rs and
a c c e p to rs ,
using
th e
a b o ve
g u id e lin e s ,
s u p e rc o n d u c tiv ity .
16
w h ich
w o u ld
e x h ib it
m e ta llic
or
1.B Donor Molecules
1.B.1 Introduction
S in ce the d isco ve ry of th e e le ctro n d o n a tin g a b ility
c o n d u c tin g p ro p e rtie s of T T F (2a)
4 and e le ctrica l
2 in the e a rly 1970s m uch e ffo rt has been
d e v o te d to s yn th e sisin g a n a lo g u e s of T T F w ith th e aim of d e te rm in in g the
e ffe c t of s tru ctu ra l v a ria tio n on c o n d u c tiv ity and s u p e rc o n d u c tiv ity .
T he m ost
re m a rk a b le a n a lo g u e s are b is (e th y le n e d ith io lo )te tra th io fu lv a le n e (B E D T -T T F ),
or
ET
(6 a)
fo r
short,
te tra m e th y lte tra s e le n a fu lv a le n e
b is (e th y le n e d io x a )-te tra th io fu lv a le n e
su p e rc o n d u c tin g
salts.
O f th e
(B E D O -T T F ;
p ro p e rtie s
e le c tric a lly co n d u ctin g o rg a n ic m eta ls
6b),
(T M T S F ;
all
of
7a)
w h ich
and
form
n e c e s s a ry fo r th e fo rm a tio n
of
26 T T F p o sse sse s the re q u ire d p lanarity,
sym m e try and low o xid a tio n p o te n tia l to form both a sta b le ca tio n a nd dica tio n ,
w h o se s ta b ility arises from th e fo rm a tio n of a 4 n + 2 rc-electron H u cke l-typ e
a ro m a tic ring system . A s a re su lt m ost of the re se a rch to d e v e lo p new don ors
has c e n tre d on e xp lo itin g th e s e p ro p e rtie s by m o d ifyin g th e b a sic T T F unit.
(2 )a :X = S, TTF
b: X = Se, TSF
c: X = Te, TTeF
(6)a: X = S, BEDT-TTF
b: X = O, BEDO-TTF
(7)a:X = Se, Y = Me, TM TSF
b:X = S, Y = Me, TM TTF
c:X = S, Y -Y = (CH2)3 HMTTF
T h e m ain d ire ctio n of th e se e ffo rts in vo lve s:
(i)
e xte n d in g the ^ -c o n ju g a te d system in o rd e r to m in im ise th e C o u lo m b
re p u lsio n in th e d o u b ly io n ise d sta te of the d o n o r; th is is a ch ie v e d by
in co rp o ra tio n of cyclic or v in y lo g o u s sp a ce rs b e tw e e n th e tw o
1 ,3 -d ith io le rings;
(ii)
th e re p la ce m e n t of the s u lp h u r ato m s w ith s e le n iu m and te llu riu m in
o rd e r to in crea se th e b a n d w id th and in cre a se both th e in te r and
in tra s ta c k S e-S e and T e -T e in te ra c tio n s w h ich re su lt in in cre a se d
d im e n s io n a lity ; th e in c re a s e d p o la ris a b ility of Se and T e s h o u ld also
red u ce the o n -site C o u lo m b re p u lsio n ;
(iii)
s y n th e s is in g T T F d e riv a tiv e s w ith s u b s titu e n ts on the p e rip h e ra l 2,3 and
6,7 p o sitio n s to m o d ify th e e le c tro n ic p ro p e rtie s of th e p a re n t 7i-syste m
and to in cre a se the in te rm o le c u la r in te ra ctio n .
S in ce th e num bers of d o n o rs sy n th e s is e d in the last 20 ye a rs is e n o rm o u s only
th e m ore im p o rta n t o ne s w ill be d iscu sse d here.
17
1.B.2 General synthesis of TTF and its derivatives
T h e m ost w id e ly used routes to T T F d e riv a tiv e s p ro ce e d v ia co u p lin g of
1,3 -d ith io liu m sa lts (8 ) o r 1,3 -d ith io le -2 -th io n e s (9a) o r -2 -o n e s (9b).
R
R
RX * -
H
X-
X !h
or
(9) a: X= S
b: X= O
(8)
T h e 1 ,3 -d ith io liu m s a lts are c o u p le d v ia the g e n e ra tio n of a s ta b ilis e d ca rben e,
by d e p ro to n a tio n of th e ca tio n w ith a base, w h ich can th e n a tta ck the p o sitive
C 2 c e n tre of a n o th e r cation .
T T F (2a)
T his m ethod has been used fo r the s y n th e s is of
4 a nd its d e riv a tiv e s T M T T F (7 b )27 and H M T T F (7 c ),28 S ch em e 1.01.
Et^N
R
2
HCS
+
(2) a R’ = R2 = H, TTF
(8 )a: R 1 = R2 = H, X = H S 0 4‘
b: R1 = R2 = Me, X = C I0 4
(7)b R1 = R2 = Me, TMTTF
c: R 1 - R2 = (CH2)3, X- = C I0 4'
(7)c R1 ' R2 = (CH2)3, HMTTF
S ch e m e 1.01
T h e 1,3 -d ith io liu m and 1 ,3 -d ise le n iu m s a lts p o sse ssin g a hyd ro g e n in the 2
p o sitio n are o b ta in e d by th e a lk y la tio n of th e co rre s p o n d in g 1 ,3 -d ith io lo -2 th io n e o r -2 -s e le n o n e w ith an a lk y la tin g a g e n t, u su a lly m e th ylio d ld e , Schem e
1.0 2 .
t> :
Mel
NaBH,
Me
Cx
H
XMe
(11) a: X = S
b: X = Se
(10) a: X = S
b: X = Se
C: X = O
S ch e m e 1 .02
T h is is fo llo w e d by re d u ctio n of th e s e s a lts w ith sodium b o ro h yd rid e , NaBFU,
w h ich g e n e ra te s the
2 -a lk y lth io - ( 1 1 a) o r 2 -a lk y ls e le n o - 1 ,3 -d ith io ls ( 1 1 b), and
18
fin a lly tre a tm e n t of th e s e w ith a s tro n g acid like flu o ro b o ric acid, o r p e rc h lo ric
acid.
The
re a ctio n
of
1,3 -d ith io liu m
c a tio n s
w ith
tria lk y lp h o s p h in e s
or
p h o s p h ite s g ive W ittig a nd W ittig -H o rn e r p h o s p h o n iu m s a lts (12), w h ich are
the key in te rm e d ia te s in the s y n th e s is o f th e v a st a rra y of v in y lo g u e s of T T F ,29
o b ta in e d b y th e ir re a ctio n w ith a ld e h y d e s in th e p re se n ce of base, S chem e
1.03.30
PFg
S
+ OHC -
H
ON -
CHO
NEt,
" V
OHC
N
Me
Me
( 12 )
N
Me
S ch e m e 1.03
T h e p h o s p h o ra n e s fo rm e d
by th e
rem o val of a pro to n
by base, u su a lly
trie th y la m in e o r b u tyllith iu m , can a lso co u p le w ith o th e r 1,3 -d ith io liu m sa lts to
yie ld h yb rid o r u n s y m m e tric a l T T F s.
T h e 1 ,3 -d ith io lo -, and 1,3 -d is e le n o -, -2 -th io n e s , -2 -s e le n o n e s and -2one s (1 3 a -c) are also c o u p le d u sing tria lk y l o r tria ry l p h o s p h in e s o r tria lkyl
p h o s p h ite s via d e s u lfu ris a tio n , d e s e le n a tio n and d e o x y g e n a tio n .
route
has
p ro ve n
to
be
d e s u lp h u ris a tio n -c o u p lin g
useful fo r se le n o n e s,
w h ich
was
w h en
o n ly
s u cce ssfu l
are
W h ile this
m ore
reactive,
e le c tro n -w ith d ra w in g
s u b s titu e n ts w e re p re se n t in th e 4- and 5- p o s itio n s of th e 1,3 -d ith io le -2 th io n e s ,31 S ch e m e 1.04.
R1 - ^ X
P(OAIk)3 or P(Aryl)g
JC~ > = Y
r2 ^
(13)
—
x
*■
r 1^
r
X
2^ x
x - ï - r1
^
x
(6a) BEDT-TTF
a: R 1 - R2 = S (C H 2)2S, X = S, Y = O
b: R 1 = R2 = H, X = Se, Y = Se
(2b) TSeF
c : R 1 = R2 = M e , X = S e , Y = S
(7a) TM TSF
S ch e m e 1.04
19
^
r
2
It has been s u g g e s te d 32 th a t in th e
m a jo rity
of cases th e se T T F
d e riv a tiv e s are m ost like ly form ed by re a c tio n s of the ca rb e n e w ith th e ir
p re cu rso r, o r o c c a s io n a lly by re a ctio n s not in v o lv in g c a rb e n e s at all, ra th e r
th a n by b im o le c u la r ca rb e n e co u p lin g , S ch em e 1.05.
T his m ethod of co u p lin g
is th e m ost w id e s p re a d but it does have its lim ita tio n s in th a t the s y n th e sis of
u n s y m m e tric a l d e riva tive s w ill yield m ixtu re s of iso m e rs.
An a lte rn a tiv e to th e p h o sp h in e o r p h o s p h ite c o u p lin g has been th e use
of d ic o b a lto c ta c a rb o n y l, C o 2 (C O )g.
T his c o u p lin g re a g e n t m ay be p re fe ra b le
in th a t it a llo w s fo r a w id e r range of s u b s titu e n ts .33
1.B.3 Peripherally substituted TTF analogues
O f th e m any m o d ific a tio n s w h ich have bee n c a rrie d out to im prove the
e le c tro n ic p ro p e rtie s of th e p aren t T T F rc-system, in tro d u c tio n of he te ro a to m s
on its p e rip h e ra l 2,3- and 6,7- p o sitio n s have been the m ost e xciting.
T he se
s u b s titu e n ts w e re e xp e cte d to in cre a se in te rc h a in in te ra c tio n s , th u s in cre a sin g
th e
d im e n s io n a lity
and
s u p p re ssin g
th e
M -l
tra n s itio n s
to
se m ic o n d u c tin g sta te s a ss o c ia te d with o n e -d im e n s io n a l system s.
+ isomers
pr
3
I .+
Scheme 1.05
20
in su la tin g
or
1.B.3.1 TMTTF (7b) and HMTTF (7c)
T e tra m e th y lte tra th ia fu lv a le n e ,
TM TTF
(7b),
a nd
h e xa m e th yle n e -
te tra th ia fu lv a le n e , H M T T F (7c), w e re th e firs t co m p o u n d s to s u g g e s t th a t
p e rip h e ra l
s u b stitu tio n
m ay
a c tu a lly
im p ro ve
th e
co n d u c tiv ity .
W h ile
co m p a ris o n of the room te m p e ra tu re c o n d u c tiv itie s of th e ir T C N Q s a lts d id not
s h o w a n y im p ro ve m e n t (500, 350, 5 00 S cm *1 fo r T T F -T C N Q , T M T T F -T C N Q
and H M T T F -T C N Q re sp e ctive ly), th e ir c m ax d id s h o w im p ro v e m e n t (2 x 10 4,
5 x 103, a nd 2 x 103 S c m '1 at T max= 59, 60 a nd 7 5 K re s p e c tiv e ly b e fo re the
o n se t o f a M -l tra n sitio n ).
1.B.3.2 Bis(ethylenedithiolo)tetrathiofulvalene (BEDT-TTF) or ET (6a).
O f the la rge n u m b e r of o rg a n ic s u p e rc o n d u c to rs know n to date the
m a jo rity are d e rive d from ET.
ET w a s the firs t s u lp h u r-b a s e d d o n o r to e xh ib it
s u p e rc o n d u c tiv ity and, c o n tra ry to p re v io u s c o n d itio n s fo u n d n e c e s s a ry fo r
good
c o n d u c tio n ,
p re v e n tin g
go o d
it w a s
p -o ve rla p
n o n -p la n a r w ith
be tw e e n
the
th e
p e rip h e ra l
e th y le n e
d o n o r m o le cu le s.
g ro u p s
ET w a s first
s y n th e s is e d 34 using ca rb o n d isu lp h id e , C S 2 (14), as th e sta rtin g
m aterial
a cc o rd in g to S ch em e 1.06. T h is p ro c e d u re has sin ce bee n im p ro v e d u p o n .35
electrochemical
(14)
►
cs2
(14)
ET (6a)
Na
S ch em e 1.06
The
ET fa m ily
of s u p e rc o n d u c to rs
can
be
d iv id e d
in to
tw o
m ain
s tru c tu ra l ty p e s a cco rd in g to the m ode of th e in te rn a l a rra n g e m e n t of th e d o n o r
m o le cu le s.
T h e y are the |3-phase a n d the ic-phase.
e x is t but are less com m on.
An a and 0 p h a se also
In the [3-phase s u p e rc o n d u c to rs the ET la y e rs are
c o m p o s e d of loose s ta c k s w h ich are p a ra lle l to each other, g iv in g rise to a
“c o rru g a te d sh e e t" type 2-D n e tw o rk (F ig u re 1.11), in w h ich the S -S in te rs ta c k
c o n ta c t d is ta n c e s are le ss th a n th e in tra s ta c k d ista n ce s. In (3-(ET ) 2A u l 2 ,
in te rs ta c k d s-s ^ 3.60A , th e van d e r W a a ls ra d iu s sum fo r S, w h e re a s the
in tra s ta c k ds-s ^
3-60 A ).36 T h is 2 -d im e n s io n a lity is re fle cte d in the a n is o tro p y
21
of the electrical cond uctivity, w h ich for (E T ) 2 CI 0 4 (C 2 H 3 C l 3 )o .5 37 |S a hun dred
to a th o u sa n d tim es h ig h e r in the shee t dire ctio n th a n in the stack direction.
The "corru gated shee t" of d o n o r m o le c u le s
sheets of anions.
is sa n d w ic h e d
betw een
T h e first ET salt s y n th e s is e d , (E T )2 C I0 4 (C 2 H3Cl3)o.5 ,37 and
the first ET based su p e rc o n d u c to r, (E T ) 2 ReC>4,37 (Tc~2 K at p re s s u re s >4
kbar), exhibit a sim ilar co rru g a te d s h e e t netw ork.
On replacing the te tra h e d ra l
and o c ta h e d ra l
Be chgaa rd
a
salts
(15),
with
lin e a r
anion,
a n io n s so s u cce ssfu l
the
first
am b ie n t
in the
pressure
su p e rc o n d u c to r P(ET )2 I3 (Tc = 1.4 - 1 .6 K) 37 w a s obtained.
Figure 1.11 Corrugated sheet network of ET. cations found in fi-phase salts.
—,
Se
X nX
X2'
(15)
By replacing the I3
anion with o th e r lin e a r a n io n s of sho rte r length, it was
belie ved that the S-S in te rsta ck d ista n ce s w o u ld sho rte n and d e c re a s e the H
atom cavity volum e su rro u n d in g the anion.
T he IB r 2 * anion, - 7 % s h o rte r than
I3 , gave P(ET )2 IBr 2 , with
s h o rte n in g
an a ve ra g e
of the
in te rsta ck
distances of - 0.02 A and resulting in a rise in T c by a facto r of 2-3.
37
S-S
W ith the
d iscovery that anion d is o rd e r inhibits the o nse t of s u p e rco n d u ctivity, even on
applying pressure up to 5 k b a r ,38 it was p ro p o s e d 36 that new a m b ie n t-p re s s u re
o rg a n ic su p e rc o n d u c to rs in the |3(E T ) 2 X cla ss w o u ld contain c e n tro s y m m e tric
anio n s of specific length, clo se to that of IBr 2 ~ but less than I3 ".
vin dica ted by the syn th e s is of fi( E T )2 ( l- A u - l )36 with T q = - 5
This was
K at am b ie n t
pressure, and the length of the anion, l-Au-l, being in term ediate b e tw e e n that
of IBr2~ and 13*.
Following this line of in vestigatio n into the effects of anion le ngth led to
the synthesis of the first o rg a n ic com p o u n d , (E T ) 2 C u (N C S ) 2 , to have T c > 10 K
22
at a m b ie n t p re s s u re .39 H o w e ve r this salt w as fo u n d to have a d iffe re n t la y e r
packing, called K-phase type. K-Phase type superconductors are comprised of
ET dim ers, w ith each d im e r o rien ta ted o rth o g o n a lly to its n e ig h b o u r, g ivin g rise
to a zig -za g type p attern , Figure 1.12.
Figure
1.12
Zig-zag
packing
mode
of ET
cations
in
K-phase
type
superconductors.
T h is re su lts in the fo rm a tio n of a 2-D S-S ne tw o rk w ith th e in te rc e llu la r ds-s <
3.6 A.
F or the K(ET) 2 H g (S C N ) 3-nXn, [X=CI (n = 1 ,
2 ), F, Br, I (n = 1 )] salts, the
in tra -d im e r S -S co n ta ct dista n ce s varied from 3.5 5 to 3 .5 7
d im e r S-S co n ta cts w e re in the range 3.40 - 3.53
A .40
A
and th e in te r­
T h e co n d u ctin g la ye r of
“z ig -z a g g e d ” ET d im ers in K-phase salts is sa n d w ich e d by the in su ltin g layers
of V -sh a p e d a n io n s w h ich arrange th em selve s in to a 1-D fla t polym e r.
T h e se arch fo r o th e r metal com plex a n io n s w h ich w e re iso stru ctu ra l to
(E T ) 2C u (N C S )2 led to the synthesis of K-(ET) 2 C u [N (C N ) 2]B r
8 w h ich has the
h ig h e st a m b ie n t p re ssu re su p e rco n d u ctivity (T c = 1 1 .6 K) to date fo r an org a n ic
ca tio n sa lt and k -(E T ) 2C u [N (C N ) 2]C I ,9 a s e m i-c o n d u c to r at a m b ie n t pressure
but w ith a T c = 1 2.5 K at the slight pressure of 0.3 kbar.
At p re se n t no w e ll-d e fin e d stru ctu re -p ro p e rty co rre la tio n s exist fo r the
d e te rm in a tio n
of im p ro ve d
su p e rco n d u ctivity
in
th e
K-phase
salts.
The
s y n th e s is of new ET sa lts w ith polym er m etal co m p le x a n io n s seem s to be the
m ost p ro m isin g directio n.
23
1.B.3.3 Bis(ethylenedioxy)-tetrathiofulvalene (BEDO-TTF; 6b)
T h e d is c o v e ry of s u p e rc o n d u c tiv ity in ET s a lts p ro m p te d the se a rch fo r
T h is re su lte d in the s y n th e s is 41
new d o n o rs s tru c tu ra lly s im ila r to B E D T -T T F .
o f th e o xyg e n e q u iv a le n t of ET, B E D O -T T F (6 b), w ith o xyg e n atom s re p la cin g
s u lp h u r atom s on the p e rip h e ry, g ivin g rise to a c y c lic e th e r a n a lo g u e of T T F .
T h is w a s in s p ire d by th e p o s s ib ility that, if th e o rg a n ic s u p e rc o n d u c to rs w ere
B C S s u p e rc o n d u c to rs , th e n th e T c w o u ld in c re a s e w ith in a se rie s of id e n tica l
d o n o rs if th e re w a s a d e c re a s e in th e o ve ra ll m o le c u la r m ass of th e c o n stitu e n t
m o le c u le s
(B C S
is o to p e
effe ct)
and,
sin ce
o xyg e n
is
s m a lle r a nd
less
p o la ris a b le th a n s u lp h u r, th e m e ta llic b a n d w id th w o u ld d e cre a se , th e d e n s ity of
s ta te s n e a r th e Ferm i le vel w o u ld in cre a se and T q w o u ld be ra is e d .42
(6b)
C y c lic v o lta m m e try s tu d ie s sh o w e d th a t th e first o xid a tio n p o te n tia l fo r
B E D O -T T F is h ig h e r th a n th a t of T T F but its se c o n d is lo w e r show in g it to be
b e tte r a ble to s ta b ilis e th e d ic a tio n ic state.
O f th e m a n y m e ta llic sa lts w h ich
B E D O -T T F fo rm s w ith in o rg a n ic anions, o n ly tw o have been fo u n d to be
su p e rc o n d u c tin g , (3-(B E D O -T T F ) 3 C u 2 (N C S )3 a r|d (B E D O -T T F )2 R e 04 (H 2O),
at a m b ie n t p re ssu re and b e lo w 1 K and 2.5 K re s p e c tiv e ly .39 C ry s ta llo g ra p h ic
a n a ly s is 42 sh o w s th a t w h ile B E D O -T T F salts give c rysta ls of p o o r q ua lity, th o se
th a t have bee n c h a ra c te ris e d show th a t the s a lts co n ta in sh e e ts of d o n o r
s ta c k s in w h ich the
in te rs ta c k
S-S
re s p e c tiv e va n d e r W a a ls radii of 3.6
A
and
S -0
and 3.33
co n ta c ts
are
less th a n the
A.
W h ile o th e r o rg a n ic s u p e rc o n d u c to rs e x is t 39 non e have so fa r have
b ee n as p ro m isin g as th e ET base d salts.
F u rth e r in v e s tig a tio n s into w h y ET
s h o u ld e x h ib it s u p e rc o n d u c tiv ity w h ile re la te d co m p o u n d s w ith s im ila r crystals tru c tu re s do not are n e c e s s a ry and m ay e v e n tu a lly le ad to even h ig h e r
tra n s itio n te m p e ra tu re s .
1.B.3.4 Other substituted TTFs
d e riv a tiv e s
e x is t ,43 th e ir
s y n th e s is in v o lv e s se v e ra l ste p s to give th e p re -s u b s titu te d
1 ,2 -d ith io lo - 2 -
W h ile
a
huge
v a rie ty
o f s u b s titu te d
TTF
th io n e , -2 -k e to n e o r -2 -s e le n o n e , w h ich m ust th e n be co u p le d . H o w e v e r recent
w o rk in th e s y n th e s is of fu rth e r d e riv a tiv e s of T T F s has in v o lv e d m odifyin g the
p re fo rm e d
TTF.
T h is
has
been
a ch ie v e d
24
by
th e
m o n o -lith ia tio n
and
te tra lith ia tio n of T T F , w h ich se rve s as the b u ild in g b lo c k to a huge v a rie ty of
new don ors, w ith the a b ility to attach v a ry in g fu n c tio n a litie s and to s yn th e sise
d o n o rs w ith m u ltip le T T F units.
M o n o lith ia tio n of T T F w as first re p o rte d by G ree n
44 u sing n -b u tyllith iu m
(n -B u L i) and also w ith lithium d iis o p ro p y la m id e (LD A ) in e th e r at -70°C .
The
re su ltin g m o n o -lith ia te d d e riva tive T T F L i (16) c o u ld th e n be tra p p e d w ith a
v a rie ty of e le c tro p h ile s (S chem e 1.07), e.g. C IC 0 2 Et, C O 2 , C H 3 CO CI, d im e th yl
s u lp h a te , H C H O .
H o w e ve r one c o m p lic a tio n to th is re a ctio n in v o lv e s th e fact
th a t T T F L i re a d ily d is p ro p o rtio n a te s at te m p e ra tu re s a b o ve -7 0 °C to give diand m u lti-s u b s titu te d produ cts. T h is m e th o d has be e n used in th e s y n th e s is of
a huge v a rie ty of m o n o -su b stitu te d d e riv a tiv e s , lin k e d to v a ry in g sid e ch a in s
th ro u g h c a rb o n ,45- 46 silico n, sulphur, s e le n iu m a n d te llu riu m .46- 47
rV<sl
rsHsr R
(16)
R= Et, C 0 2H, CH 3
R= C O C 15H31, C 0 2C 16H33, SiM e3 ,
C 0 2H, S C 18H 37, T e C 18H37
R= SC H 20 (C H 2)2SiM e3 , SeCH20 (C H 2)2SiM e3
S chem e 1.07
R e a ctio n of th e m o n o -lith ia te d T T F (16) w ith e le m e n ta l s u lp h u r o r se le n iu m at
-7 8 °C yie ld s th e co rre s p o n d in g c h a lc o g e n a te a n io n , (17) o r (18), w h ich is
tra p p e d by tre a tin g in situ w ith v a ry in g e le c tro p h ile s and a lk y lh a lid e s .
T h e se
c h a lc o g e n a te a n io n s are re p o rte d to be c o n s id e ra b ly m ore re a ctive to w a rd s
e le c tro p h ile s th a n the lith ia te d T T F p re c u rs o r .47
s
i+
3 ^
or
s
y
j 86'
s
s
(16)
[
(17)
(18)
T ra p p in g of th e m o n o se le n o la te a n io n (18) w ith trim e th y ls ily l eth o xym e th yl
(S E M ) c h lo rid e a ffo rd e d a s h e lf-s ta b le e q u iv a le n t fo r the s e le n o la te anion, (19).
T h is
co u ld
be
re co ve re d
using
te tra b u ty la m m o n iu m
flu o rid e
and
the
a p p ro p ria te e le c tro p h ile . W h ile th is m e th o d did yie ld th e SE M d e riv a tiv e of the
m o n o th io la te sa lt, it w as not re co ve ra b le as th e th io la te an io n .
25
H o w e ve r the
b e n zo yl d e riv a tiv e of the th io la te an io n , ( 20 ), is a s h e lf s ta b le e q u iv a le n t and is
re g e n e ra te d w ith b a s e .48
Css
s—
w-.SeCH20 (C H 2)2SiM e3
S
SCOC6H5
J
( 20 )
(19)
T h e T T F -th io la te a n io n has also bee n used to s y n th e s is e a range of new -b is
and tris -T T F d e riv a tiv e s in clu d in g (21) a n d (2 2 ).48
S -T T F
O
(22 )
( 21 )
O th e r re a c tio n s in v o lv in g the m o n o -lith ia te d T T F have led to th e o n e -p o t
s y n th e s is of th e know n u n sym m e trica l d on or, E D T -T T F (23a) a nd E D S -T T F
(23b), in lo w y ie ld s (1 0 -2 0 % ) .47 O n v a ry in g th e m olar ra tio s B E D T -T T F w as
o b ta in e d in stea d.
(23) a: X = S,
EDT-TTF
(6a) BEDT-TTF
b: X = Se, EDS-TTF
The
te tra th io la te
(T T F S 44';
24)
49 has also bee n e xp lo ite d as a
p re c u rs o r to m any te tra s u b s titu te d T T F d e riv a tiv e s and like th e m o n o lith ia te d
co m p o u n d has bee n re a cte d w ith s e le n iu m .50
B E D T -T T F (6 a) has re ce n tly
been s y n th e s is e d from th e te tra th io la te (24) by H a nsen et al
51 from th e te tra
e s te r (25) by d e p ro te c tio n o f the e s te r g ro u p s w ith so d iu m te rt-b u ty lth io la te ,
S ch e m e 1.08.
PhCOS
S -^ S C O P h
PhCOS
SCOPh
s-
Bul S N
Br(CH2)2 Br
BEDT-TTF
(25)
(24)
Scheme 1.08
26
(6a)
The
a b ility
of both
th e
te tra lith ia te d
and
the
m o n o lith ia te d
te tra th ia fu lv a le n e s to u n d e rg o re a ctio n w ith su c h a v a rie ty of e le c tro p h ile s
w h ic h in tu rn can th e m s e lv e s u n d e rg o a v a rie ty o f fu rth e r re a ctio n s, o p e n s up a
m u ltitu d e of syn th e tic p a th w a ys to new d o n o r co m p o u n d s w h o se s y n th e s is
s h o u ld fu rth e r in cre a se both the u n d e rs ta n d in g o f th e stru ctu ra l c h a ra c te ris tic s
w h ic h
can
lead
to im p ro ve d
c o n d u c tiv ity
a nd
h ig h e r
te m p e ra tu re
s u p e rc o n d u c tiv ity .
1.B.4 Selenium and Tellurium Derivatives of TTF
1.B.4.1 Selenium Derivatives of TTF
T h e exte n d e d d -o rb ita l of both se le n iu m and te llu riu m m ade th e m ideal
re p la c e m e n ts fo r s u lp h u r in the s e a rch fo r in c re a s e d in te rs ta c k in te ra ctio n s,
re s u ltin g in la rg e r b a n d w id th s and in c re a s e d d im e n s io n a lity .
T h e s y n th e s is of
s e le n iu m d e riv a tiv e s has be e n fa r m ore s u c c e s s fu l th a n th o se of te llu riu m due
to th e d iffic u lty in
th e s y n th e s is
of the
la tte r. T h e
va rie ty
of se le n iu m
d e riv a tiv e s is vast and m any have been re p o rte d by K rie f .43 Initial in d ic a tio n s
th a t the
re p la ce m e n t of s u lp h u r w ith
s e le n iu m
w o u ld
result in in cre a se d
c o n d u c tiv ity w ere p ro ve d c o rre c t w h en the 1 :1 s a lt of T S F -T C N Q w a s fo u n d to
ha ve a c o n d u c tiv ity of a rt= 800 S c m “1, (T T F -T C N Q has C7rt= 500 S c m '1), and a
M -l tra n s itio n ~ 40 K, 18 K b e lo w th a t of T T F -T C N Q .
It also has a c o n d u c tiv ity
of 10 4 S cm ’1 at 40 K .52
T h e te tra m e th y lte tra s e le n a fu lv a le n e s a lts (T M T S F ^ X (15), w h e re X is a
m o n o v a le n t in o rg a n ic a n io n such as PFe", C IO 4’ , R e C V , B F O 3", know n as the
B e c h g a a rd s a lts ,7 ca u se d a g re a t s e n sa tio n at th e tim e of th e ir syn th e sis, by
b e co m in g the first o rg a n ic s u p e rc o n d u c to rs .
O f th e s e , the (T M T S F ) 2C I 04 salt
w a s the first a m b ie n t p re s s u re s u p e rc o n d u c to r (T c = 1 .3 K), w hich w as a ch ie ve d
by s lo w co o lin g of the s a lt .53
2+
(7a)
(15) x = PF6-, C I0 4-, R e 0 4-, B F 0 3',
(26)
TaF6' and S bF6
27
T h e o rig in a l s y n th e s e s 26 of T M T S F (7a) and H M T S F (26) in vo lve d the
use of th e extre m e ly m a lo d o ro u s ca rb o n d is e le n id e a nd th e hig h ly to x ic H 2 Se
(15 tim e s m ore to xic th a n H 2 S). An a lte rn a tive ro u tin e 54 has been fo u n d using
e le m e n ta l se le n iu m
and d im e th y lp h o s g e n e
im in iu m
ch lo rid e
(27), S chem e
1.09.
x +
' Cl
/ N _C ' C|
\
+
2[NaHSe, Et3N]
^,e
►
DMF
+
f
►
(27)
y
Se
N
. sy
H2S 0 4
^
<
Se
—
CHgCOOH
^ c s > -se
^ 'S e
P(OCH3)3
►
TMTSF
S ch e m e 1.09
1.B.4.1.1 Synthesis of salts of TMTSF
S in g le crysta ls of (T M T S F ) 2X are o b ta in e d by e le ctro ch e m ica l o xid a tio n
a cc o rd in g to e q u ation 4.
2n (T M T S F ) + n X
-n e '
►
[(TM TSF)2X ]n
eq u a tio n 4
U sing a low co n sta n t cu rre n t, th e so lve n t (re d istille d , d rie d and de o xyg e n a te d ,
u s u a lly T H F o r C H 2C I 2) and th e te tra b u ty la m m o n iu m sa lt of the a p p ro p ria te
a n io n are p la ce d in the ca th o d e co m p a rtm e n t of a H -s h a p e d cell, w h ile at the
a n o d e th e solvent, the a n io n ic sa lt and th e T M T S F are in tro d u ce d .
P latinum
e le c tro d e s are p laced in the cell and it is th ro u g h o x id a tio n of the d o n o r at the
a n o d e th a t the crysta ls b e g in to grow .
T h e se 2:1 s a lts are all iso stru ctu ra l,
in d e p e n d e n t of w h e th e r te tra h e d ra l o r o c ta h e d ra l s a lts are used.
The TM TSF
m o le c u le s are fo u n d to s ta c k in a zig -zig pattern, w ith th e h ighest c o n d u c tiv ity
a lo n g th e sta ckin g d ire c tio n , Figure 1.13(a).
In a d d itio n to this, th e re are short
in te rs ta c k S e-S e in te ra c tio n s , d< 4.0A (van d e r W a a ls ra d iu s fo r Se) betw e en
th e T M T S F m olecu les, w h ich results in a s h e e t-lik e 2-D ne tw o rk w ith sh e e ts of
a n io n s se p a ra tin g th e d o n o r shee ts, Figure 1.13(b).
T h e a n io n s th e m s e lv e s play no role in the e le c tric a l co n d u ctivity, w h ich
o cc u rs th ro u g h th e n e tw o rk of Se-S e in te ra c tio n s but th e ir sym m etry and
o rd e rin g do.
B e ch g a a rd 53(b) found th a t th e o c ta h e d ra l (ce n tro sym m e tric)
28
salts, (X = P F 6 , T a F 6 , SbFg ) all e x h ib it high m e ta llic c o n d u c tiv ity w ith M-l
tra n s itio n s o ccu rrin g b etw e en 12 and 18 K.
U nlike th e o n e -d im e n s io n a l salts
fo u n d before, the M -l tra n s itio n fo u n d in these sa lts w as the e ffe c t of a spind e n s ity wave (S D W ) d is to rtio n ra th e r th a n a ch a rg e -d e n s ity w a ve (C D W ). The
s a lts of T M T S F co n ta in in g the n o n -ce n tro sym m e tric, te tra h e d ra l a n io n s (with
th e e xcep tion of a p e rc h lo ra te salt) sh ow ed am bie nt p re ssu re p h a se tra n s itio n s
at m uch
h ig h e r te m p e ra tu re s
(-4 0
K and -1 3 0
K fo r
BF4
and
ReC >4
re s p e c tiv e ly ).23
s=s=8*~—■0»=*
HjC
S»
Se
CH3
TMTSF
(a)
Figure 1.13
(b)
View of the crystal structure of (TMTSF)2Br 04 (a) perpendicular to
the stacking direction showing the zig-zag pattern o f the salt and (b) looking
down the stacking direction showing the short interstack interactions.
T he se tra n s itio n s are a ss o c ia te d with the o rd e rin g of th e a n io n s.
The
te tra h e d ra l a n io n s o ccu p y tw o s ta tis tic a lly e q u iv a le n t p o sitio n s a nd so are
d iso rd e re d .
A s lh e te m p e ra tu re is low ered the a n io n s becom e o rd e re d givin g
rise to a P eierls type in sta b ility. T h e a p p lica tio n of p re ssu re re su lte d in all but
one, (the N b F 6
salt), of the o cta h e d ra l a nions sa lt of T M T S F b e co m in g
su p e rco n d u ctin g at a critica l pressure, Pc (6 .5 —>1 2 kbar) at low te m p e ra tu re s
(T c - 0 .4 -1.4 K).
T his is not s u rp risin g in light of the fin d in g s of W illia m s
et a l 37 that the d e cre a se in the ratio of in te rsta ck to in tra s ta c k S e -S e d is ta n c e s
29
I
is n e a rly
2 :1 , as the te m p e ra tu re is lo w e re d , as co m p a re d to th e room
te m p e ra tu re
S e -S e
d is ta n c e s
(-3 .9
-
4.0
Â)
w h ich
re su lts
in
g re a te r
d e lo c a lis a tio n th ro u g h g re a te r in te rc h a in in te ra c tio n s .
T he p e rc h lo ra te salt, (T M T S F ) 2C I 0 4 , is u n iq u e am ong th e T M T S F salts
in th a t not o n ly is the a n io n te tra h e d ra l but it is s u p e rc o n d u c tin g at a m b ie n t
p re s s u re .53(a)
O ne re a so n s u g g e ste d fo r this, by W illia m s et al,37 is aga in
re la te d to a n io n o rd e rin g .
It w as n o te d th a t in th e (T M T S F )2 X syste m s the
a n io n s reside in a “m ethyl g roup H -atom c a v ity ” . T h u s th e p e rc h lo ra te anion
re sid e s in an a s y m m e tric H -atom e n viro n m e n t, w ith h yd ro g e n -ty p e bon din g
be tw e e n H 2C — H — O C IO 3", w h ich “fre e z e s ” th e a n io n in a d is o rd e re d p o sition
even on co o lin g . H o w eve r, th e p e rc h lo ra te sa lt has to be co o le d s lo w ly fo r th is
“fre e z in g ” to be a ch ie ve d .
T h is a b ility to m a in ta in its o rd e r w ith in th e lattice
alo n g w ith its s m a lle r cell vo lu m e (as co m p a re d w ith th e la rg e r o cta h e d ra l
a n io n ) m ay a c c o u n t fo r its s u p e rc o n d u c tiv ity at a m b ie n t pre ssu re .
1.B.4.1.2 Derivatives of TSF
The
re a d y
co u p lin g
of
1 ,3 -d is e le n o le -2 -s e le n o n e s
by th e
com m on
p h o s p h ite co u p lin g m eth od had led to the s y n th e s is of u n sym m e trica l d ith ia d is e le n a fu lv a le n e s ,55 co m p o u n d s (28 a-d).
O f th e s e th e D M E T d o n o r (28a)
w h ich is a h yb rid be tw e e n T M T S F and B E D T -T T F , has been fo u n d to form
se ve n s u p e rc o n d u c tin g s a lts .39
F or th e p re p a ra tio n of (28a), it w as fo u n d th a t u sing 1,3 -d ith io lo -2 -o n e
gave a b e tte r yie ld and a c le a n e r re a ctio n th a n th e co rre s p o n d in g - 2 -th io n e and
-2 -s e le n o n e .
T h e d e s ire d cro s s -c o u p lin g p ro d u c ts w e re fo rm e d a lo n g w ith the
sym m e trica l p ro d u cts B E D T -T T F and T M T S F , in a s u rp ris in g ly h ig h e r ratio
th a n e x p e c te d 55 and th e co m p o n e n ts w e re s e p a ra te d by c h ro m a to g ra p h y.
(28) a: R 1 = R2 = Me, n = 2
b: R 1-R2 = (CH2)3 , n = 2
c: R 1 = R2 = Me, n = 3
d: R 1-R2 = (CH2)3 , n = 3
1.B.4.2 Tellurium Derivatives
In o rd e r to see w h e th e r th e a n tic ip a te d e ffe c ts of in c re a s e d b a n d w id th s
a nd m ore p o la riz a b le d o n o rs w e re p o ssib le by re p la c e m e n t of the s u lp h u r atom
in T T F w ith te llu riu m , to give te tra te llu ra fu lv a le n e T T e F (2c), ch e m ists had to
30
w a it
until
1982
fo r
th e
syn th e sis
of
th e
firs t
te tra te llu ra fu lva le n e ,
h e x a m e th y le n e te tra te llu ra fu lv a le n e H M T T e (29).56
(2c)
(29) H M TTeF
(30) a: X = S, D BTTF
b: X = Se, D BTSeF
c: X = Te, D BTTeF
T h e syn th e sis o f d ib e n z o te tra te llu ra fu lv a le n e ,57 D B T T eF (30c), soon
fo llo w e d .
C yclic v o lta m m e try sh ow ed th a t
D B T T eF had a lo w e r oxidation
p o te n tia l th a n D B T S F (30b) but th e sam e as its s u lp h u r a n a lo g u e (30a).
w a s e xp la in e d
by tw o fa cto rs w h ich
have o p p o site e ffe cts
This
in the series
S, Se, Te. T h e se are that, w h ile the ionisation po te n tia l d e cre a se s in th e series
S> Se> Te, th e d iffe re n c e s in th e orbital in te ra ctio n s b etw e en carbon and the
se rie s m e m b e rs b e co m e sm a lle r due to lo n g e r bond lengths.
T his has a
sta b ilisin g e ffe ct on th e H O M O m aking it m ore d iffic u lt to rem o ve an electron.
The
se p a ra tio n
be tw e e n
th e
first
and
se con d
oxid a tio n
p o tentia ls
(A E = E Y z- E y22) d e c re a s e s in th e series D B TTF> D B T S F > D B TTeF .
T his is
c o n s is te n t w ith the p redicte d e ffe ct o f the h e te ro a to m c h a n g e on th e on-site
C o u lo m b repulsion.
The
h ighly
e lusive ,
te tra te llu ra fu lva le n e ,
TTeF
s y n th e s is e d in 1987, by C o w an and c o w o rk e rs .58
(2c)
was
e ve n tu a lly
T T e F w a s p repa red by
tre a tin g 1,2 -b is (trim e th y ls ta n n y l)-1 ,3 -b u ta d ie n e (31) w ith n-b u tyllith iu m a t -78 °C
and th e n w ith m icro crysta llin e te llu riu m at the sa m e te m p e ra tu re .
A fte r all the
te llu riu m had reacted, th e firs t tw o ste p s w e re repea ted and 0.5 e q u iva le n ts of
te tra c h lo ro e th y le n e w a s add ed at -78 °C to re a ct w ith 1 ,2 -dilithio ditelluride .
A fte r
c h ro m a to g ra p h y,
TTeF
w as
isolated
pure,
S ch e m e
1.10.
C yclic
v o lta m m e try sh ow ed th a t T T e F had a first oxid a tio n po te n tia l in te rm e d ia te
b e tw e e n th a t o f T S F
and TTF,
sim ila r to th e
case w ith
th e
a n a lo g u e s
d ib e n z o fu lv a le n e s .
T h e a n ticip a te d e n h a n ce d co n d u ctivity w a s ob ta in e d w h e n th e T C N Q
c o m p le x o f T T e F w a s syn th e sise d by re crysta llisa tio n fro m a carbon d isu lp h id e
s o lu tio n 59 in a g lo ve box, due to e asy air o xid a tio n o f TT eF . T T e F -T C N Q w as
fo u n d to have a room te m p e ra tu re co n d u ctivity g r t ~ 1 ,800 S cm
.
Like T T F -
T C N Q , T T e F -T C N Q co n siste d o f se greg ate d sta cks o f T T e F m o lecu les and
T C N Q m o le cu le s and had a c h a rg e -tra n sfe r o f 0.71 o f an electron.
31
U nlike its
s u lp h u r and se le n iu m c o u n te rp a rts, it did not u n d e rg o a p ha se tra n s itio n at low
te m p e ra tu re s , n o r did it u n d e rg o a tra n s itio n to a s u p e rc o n d u c tin g state .
W h ile
th e
te tra m e th y lte tra te llu ra fu lv a le n e
still
rem a ins
to
be
s y n th e s is e d , o th e r e x te n d e d alkyl s u b s titu te d T T e F s have been re p o rte d
13 in
an atte m pt to im p ro ve th e ir p o o r s o lu b ility and to p e rm it in v e s tig a tio n into th e ir
a b ility to fo rm s a lts w ith in o rg a n ic anions.
SnM e3
(
—
SnM e3
01)
M
n-BuLi
■
T e /-7 8 ° C
(
T H F /-7 8 ° C
—
*
TeLi
^ TeLi
(
SnM e3
(
SnM e3
TeLi
'
CI2C = CCI2
Te.
■Te
►
(
H
Te
-78°C to 25°C
)
Te
(2c)
S chem e 1.10
1.B.5 Extended-7i-Donors
R e cent a tte n tio n in the fie ld of e le c tro n d o n o r m o le cu le s has been
d ire c te d at th e s y n th e s is of ^ -e x te n d e d d o n o rs.
T h e key to th e s yn th e sis of
th e s e co m p o u n d s in v o lv e s the reaction of the 1,3 -d ith io l-2 y l- o r 1 ,3 -d ise le n o l2 y l-p h o s p h o n iu m s a lts ( 3 2a and 32b) o r th e p h o s p h o n a te s ( 33a and 33b) with
an a ld e h y d e in th e p re s e n c e of BuLi in a W ittig o r W ittig -H o rn e r co n d e n sa tio n
reaction .
R -^ -X
H
R
R^ X
P R 3
R ^ X
X x +1
X H
Xx
(32) a: X = S
1
PO (O R1)2
(33) a: X = S
b: X = Se
b: X = Se
T h is m ethod w as u se d by Y o sh id a et al to p re p a re the firs t v in y lo g o u s T T F s 60
using the d ia ld e h y d e , g lyo xa l (34), S ch e m e 1.11.
T h is s y n th e tic a p p ro a c h w as also used to s y n th e s is e both sym m e trica l and
u n s y m m e tric a l v in y lo g u e s of B E D T -T T F .61
V in y lo g o u s T T F w as o b ta in e d from
(36; R i= R 2= C 0 2 M e) by d é c a rb o m é th o x y la tio n using lith iu m b ro m id e /H 20 in
H e x a m e th y lp h o s p h o ric tria m id e H M PA .
32
Scheme 1.11
A third d o u b le bon d w a s also introdu ced by th e re d u ctive coup ling o f the
a ld e h y d e
a lu m in iu m
(35)
in
hydrid e
S ch e m e
and
1.11
abo ve
trib u ty la m in e
using
tita n iu m
in TH F.
On
trich lo rid e ,
co m p a rin g
th e
lithium
cyclic
v o lta m m e try data o f th e tw o vin ylo g o u s T TF c o m p o u n d s w ith th a t o f T T F itself,
it w a s fo u n d th a t in th e d e riva tive w ith tw o d o u b le bonds, th e d iffe re n ce in the
1
2
firs t and secon d o xid a tio n potentia ls, AE = E yz - E y2 , w e re less th a n th a t fo r
TTF.
In th e ca se o f th e d ith io le units se pa ra ted by th re e d o u b le bonds, th e AE
va lu e d e cre a se d to zero, w ith only one o xidation w a ve being discern ible.
In co rp o ra tio n o f va rio u s h e te ro cyclic ring system s, including pyrrole,
th io p h e n e and furan, b e tw e e n th e 1,3-dithiole rings has also been carried out.
T h e s e re a ctio n s also ta k e a d va n ta g e o f the reaction be tw e e n the p re vio u sly
m e n tio n e d
p h o sp h o ra n e s
or
ph o sp h o n a te s
w ith
th e
d ia ld e h yd e
of
the
co rre s p o n d in g h e te ro c y c le .31 S o m e exa m p le s in clu d e th e e xtende d E T (40a-c)
and T T F (39a-c) syste m s, S ch e m e 1.12.
If th e in co rp o ra tio n o f a h e terocycle can be vie w e d as tw o d ith io le rings
s e p a ra te d by fo u r c a rb o n -ca rb o n dou ble b on ds th e n , by a n a lo g y w ith the
b e h a v io u r o f th e tw o d ith io le rings sepa ra ted by th re e e th yle n e bonds, there
sh o u ld be little o r no d iffe re n c e in the first and se con d o xidation p o tentia ls
(A E = E yz - E yz ). T h is w a s fo u n d to be th e case w ith th e fura n d e riva tive (39a),
w h ic h had AE= 0.00 V .31
T his sm all AE va lu e is a s c rib a b le to th e d e cre a se d
in te rm o le c u la r C o u lo m b re p ulsion in th e d ic a tio n ic state.
T h e role o f the
h e te ro a ro m a tic ring a nd th e h eteroatom also in flu e n ce s tro n g ly the AE values.
T h e s e are d e te rm in e d by th e sta b ility o f the a ro m a tic syste m w h en con sid e rin g
th e va rio u s radical ca tio n
re sona nce stru ctu re s and
by the a bility o f the
he te ro a to m to b e a r a p o sitive c h a rg e in th e d ic a tio n ic state , th e o rd e r of
im p o rta n ce being p y rro le > fura n> th io p h e n e .
R--y-S^po(O M e)2
R -^ S
h
THF/ Bu Li
+ OHC -
O
-
CHO
- 78 °C
(37) a: R = H
(39) a: R = H, X = O
(38) a: X = O
b: X = NMe
b: R = H, X = NMe
c: X = S
c: R = H, X = S
(40) a: R-R = S(C H 2) 2 S, X = O
b: R-R = S(C H 2)2S
b: R-R = S(C H 2) 2 S, X = NMe
c: R-R = S(C H 2)2S, X = S
S ch e m e 1.12
M any
o th e r
e xte n d e d
a n a lo g u e s
of
TTF
exist
w ith
so m e
being
s y n th e s is e d not o n ly w ith a vie w to re ducing o n -s ite C o u lo m b re p u lsio n but
also to e n h a n ce d im e n s io n a lity th ro u g h th e g re a te r n u m b e r of in tra a nd in te r SS co n ta cts by in c re a s in g th e n u m b e r of s u lp h u r h e te ro c y c lic m o ie tie s.
Som e
e xa m p le s of th e s e in c lu d e (41 ),62 (4 2 ),63 (43), 64 w h ich w e re a g a in s yn th e sise d
by W ittig and W ittig -H o rn e r re a ctio n s.
T h e y all form C -T co m p le x e s with
T C N Q and (41) has fo rm e d m ic ro c ry s ta llin e in o rg a n ic s a lts w ith
(X = C I0 4’ , B F4‘ and l3").
R
R
H
R
H
R
(41)
(42)
34
R
(43)
B u 4 N+X '
1.C Acceptors
1.C.1 Introduction
The
a b ility
of
p la n a r
o rg a n ic
a c c e p to r
com pounds
co m p le x e s d e riv e s fro m th e p re se n ce o f lo w -lying em p ty
to
fo rm
C -T
71-m o le c u la r o rb ita ls
(L U M O s) a n d a lso from th e ir a b ility to s ta b ilis e th e ra d ic a l fo rm e d on re d u ctio n
by d is trib u tin g th e odd e le ctro n o v e r se ve ra l atom s.
F o r th is re a so n p -
b e n z o q u in o n e (44a), a n d its te tra -h a lo d e riv a tiv e s (44 b,c,d), th e a nils, are
s tro n g e le c tro n a c c e p to rs and ha ve be e n fo u n d to fo rm h ig h ly co n d u c tin g 1:1
C -T co m p le x e s w ith T T F a nd T M T T F . 65 T h e re p la c e m e n t o f tw o h a lid e s w ith
cya n o
g ro u p s
g ive s
a
s tro n g e r
b e n z o q u in o n e , (D D Q ; 4 4 e ).
accep tor,
2 ,3 -d ic h lo ro -5 ,6 -d ic y a n o -1 ,4 -
T h e fu lly cya n o -s u b s titu te d anil, te tra c y a n o -1 ,4-
b e n z o q u in o n e , c ya n il (44f), is th e stro n g e s t a c c e p to r th a t has bee n iso la te d in
th e n e u tra l fo rm .66
It has a re d u ctio n p o te n tia l m ore th a n 0.3 V g re a te r than
D D Q a nd te tra flu o ro -T C N Q (46b).
■S
NC
CN
>=<
NC
(44) a: R’ = R2= R3= R<= H
s=<
CN
ox
s ^ -s
•C*sx^Q' xs ^ sQ> = s
(48) M(DMIT)
(45) TONE
b: R1= R2= R3= R4= F
b: RM = F
c: R1= R2= R3= R4= Br
d: R 1= R2= R3= R4= Cl
N^CN
NC^N
■ S ^ -S
T>
=
s
e: R1= R2= Cl, R3= R4= CN
f: R1= R2= R3= R4= CN
(49) DCNQI
- S '^ - 'S
(47)
O le fin s c o n ta in in g
a c c e p to r m ole cu le s.
s tro n g ly e le c tro n -w ith d ra w in g g ro u p s a lso act as
T e tra c y a n o e th y le n e (TC N E ; 47) is a h ig h ly e le c tro n -
d e fic ie n t a n d s tro n g ly e le c tro p h ilic re a g e n t and fo rm s C -T co m p le xe s w ith
c y c lo a lk a n e s 67, a lke n e s, a lkyn e s and th e ir aryl d e riv a tiv e s .68
By co m b in in g
th e a c c e p to r a b ilitie s o f both T C N E and th e p -b e n z o q u in o n e s , a p o w e rfu l
e le c tro n
a c c e p to r
was
co n ce ive d ,
7 ,7 ,8 ,8 -te tra c y a n o -p -q u in o d im e th a n e
(T C N Q ; 46a ), w h o se e le c tro n a c c e p to r a b ility w as soon re c o g n is e d .3
S in ce th e d is c o v e ry o f o n e -d im e n sio n a l e le c tric a l co n d u c tiv ity in the
T C N Q -T T F com ple x, m u ch e ffo rt has bee n d e vo te d to th e syn th e sis o f novel
d o n o r a nd a c c e p to r system s.
T h e d isco ve ry th a t d e riv a tiv e s o f T TF , T M T S F
a n d ET, fo rm e d s u p e rc o n d u c tin g sa lts in the a b se n ce o f an o rg a n ic accep tor,
35
d ire c te d th e a tte n tio n a w a y fro m a c c e p to r m o lecu les.
C o n se q u e n tly, w h ile
th e re has bee n a c o n s id e ra b le a m o u n t o f re se a rch c a rrie d o u t o n a cce p to rs
d u rin g the la st tw e n ty years, m ost o f th e re ce n t w o rk has b e e n c a rrie d o u t by
o n ly a fe w g ro u p s a ro u n d th e w o rld. T h is re search has fo c u s e d m a in ly on the
p re p a ra tio n o f d e riv a tiv e s o f T C N Q b u t a lso on tw o n o ve l fa m ilie s o f a c c e p to r
m o le cu le s; th o s e o f th e m eta l co m p le xe s o f the 4 ,5 -d im e rc a p to -1 ,3 -d ith io le -2 th io n e lig a n d (47), M (d m it )2 (48) and /V ,/V '-dicyano-quinone d iim in e (D C N Q I;
49). B oth o f th e s e fo rm h ig h ly c o n d u c tin g com plexes, w ith th e fo rm e r e xh ib itin g
su p e rc o n d u c tiv ity .
1.C.2 Synthesis of TCNQ
The
s y n th e sis
of TCNQ
was
firs t
d e s c rib e d
in
1 9 6 2 .69
It w as
s y n th e s is e d by th e c o n d e n s a tio n o f m a lo n o n itrile w ith c y c lo h e x a n e -1 ,4 -d io n e ,
fo llo w e d
by
b ro m in a tio n
and
d e h y d ro b ro m in a tio n
of
1,4-
b is (d ic y a n o m e th y le n e )c y c lo h e x a n e in th e p re se n ce o f p y rid in e , S ch e m e 1.13.
T h e re a ctio n can be c a rrie d out in b e n ze n e in the p re s e n c e o f a sm all am oun t
o f a c e tic a cid and a m m o n iu m a ce ta te (this g ives a m ixtu re o f iso m e rs be fo re
b ro m in a tio n ) o r in w a te r in th e p re s e n c e o f p -ala nin e, w h ic h g iv e s o n e o f the
iso m e rs (b) in h ig h e r yie ld.
o
0
CH2(CN)2
o
S chem e 1.13
1.C.2.1 Synthesis of TCNQ Derivatives
B e ca u se o f th e u n u su a l s ta b ility and e le c tric a l p ro p e rtie s o f T C N Q , it
h a s be e n d e s ira b le to in v e s tig a te th e ste ric a nd e le c tro n ic e ffe cts o f ring
s u b stitu tio n . T h e m ain d ire c tio n o f effo rts has involved:
(i) s u b s titu tin g v a rio u s e le c tro n -w ith d ra w in g and e le c tro n -d o n a tin g
g ro u p s onto th e 2-, 3-, 4 - and 5 - p o sitio n s o f th e T C N Q ring; th is a llow s
36
"fin e -tu n in g " o f th e e le c tro n -a ffin ity and can also a ffe c t th e crystal
packing and sto ic h io m e try o f th e C -T com plex;
(ii) e xte n d in g ^ -c o n ju g a tio n o f th e TC N Q unit both a n n u la rly and
linearly; th is can re d u ce th e o n site C o ulo m b re p u lsio n and th e be tte r
o ve rla p in cre a se s th e ban dw idth;
(iii) in trodu cing larger, m ore h ig h ly po la risa b le hete ro a to m s, such as
oxyge n, nitroge n and sulphur, into the accep tor, e ith e r into the T C N Q
ring its e lf o r into a d ja ce n t fu se d -rin g system s; th is also reduce s the
o n site C o u lo m b re p ulsion and also increa ses both th e in ter- and in tra ­
m o le cu la r in te ra ctio n and th u s w id e n s th e ban d w id th .
T h e alkyl d e riva tive s, 2 -m e thyl-, 2-propyl-, and 2 ,5 -d im e th yl-T C N Q , w e re
s y n th e s is e d by a s im ila r p ro ce d u re to th a t o f T C N Q .70 T h e syn th e sis o f ab o u t
20 d e riv a tiv e s w ith d iffe re n t s u b stitu e n ts on the 3- and
6- p o s itio n s 71 has been
ca rrie d o u t according to S ch e m e 1.14. T he se su b s titu e n ts in clud e alkyl, alkoxy,
h a lo g e n o , th io a lkyl and cya n o groups.
C 0 2Me
NC-
c h 2x
c h 2c n
(1) NaOMe
NaCN
■CN
(1) KOH
(2) HCI
Y
(MeO)2CO
►
►
(2) CICN
CH2X
NC.
•CN
(3)Br,
C 0 2Me
S ch e m e 1.14
The
1 ,4 -d i(cya n o m e th yl)b e n ze n e
c o rre s p o n d in g p -x y ly le n e d ih a lid e s .
d e riva tive s
w e re
syn th e sise d
fro m
the
T he syn thesis o f th e te tra flu o ro - and 2,5-
d lc y a n o -T C N Q d e riva tive s, (46b) and (50) respective ly, w a s carried o u t by the
c o n d e n s a tio n o f f-b u tyl-m a lo n o n itrile w ith h e xa flu o ro b e n ze n e and 3 ,6 -dich loro1 ,4 -d ic y a n o b e n z e n e re sp e ctive ly in th e presen ce o f so d iu m hydride, fo llow e d
by th e rm o ly s is and o x id a tio n as before, S ch em e 1.15.
A c o n v e n ie n t a lte rn a tiv e to cya n o g e n ch lo rid e , CNCI, used in S ch em e
1.15, is 2 -ch lo ro b e n z y lth io c y a n a te .
toxic.
T his co m p o u n d is sh e lf-sta b le and non­
It has been used to syn th e sise a range o f T C N Q d e riv a tiv e s 72 and has
th e a d v a n ta g e that, u n like CNCI, it is a selective cya n a tin g a g e n t and does not
re a ct w ith highly sta b ilise d anions. T h e re fo re tricy a n o m e th a n e produ cts are not
37
fo rm e d and th e re is no need to in se rt th e p rotecting e s te r groups.
It is also
v e rs a tile in th a t it has been used in a o n e -p o t p ro ce d u re fo r th e syn th e sis of
T C N Q d e riva tive s bearing e le ctro n -w ith d ra w in g , e le c tro n -d o n a tin g o r fu se d ring
g ro u p s .72
H
C(CH3)3
NCNaH
F
-CN
NC-
CN
F
Br-►
c; n
F
H
F
NC
-CN
NC-
c; n
(46b)
base
CN
H
C(CH3)3
C(CH3)3
ci
NCCN
NaH
c: n
NC
Cl
NC
-CN
NC-
CN
CN
NC &
NC &
NC-4
c: n
- cCN
n
~y—
NC
CN
-CN
Br0
base
NC
-CN
C(CH3)3
S ch e m e 1.15
T e re p h th a lo yl
c h lo rid e
trim e th y ls ila n e c a rb o n itrile
(51)
w hen
p ro d u ce s
a
tre a te d
w ith
an
1,4 -b is[d icya n o
e xce ss
of
(trim ethylsiloxy)
m e th yl]b e n ze n e . T re a tm e n t o f th is w ith pho sp h o ro u s o x ych lo rid e rem oved the
s ilo x y g roup , S ch e m e 1.16.
NC
OSiMe'
CN
COCI
O /s
^
O
OAc
OAc
(51)
Scheme 1.16
38
OAc
1.C.2.2 Alternative routes to TCNQ derivatives
(i)
K n o e ve n a g e l co n d e n sa tio n
o f m a lo n o n itrile w ith
th e
co rre s p o n d in g
q u in o n e s in th e p re se n ce o f L e h n e rt's re a g e n t ( T iC ^ a nd p y rid in e ),73 S chem e
1.17.
NC
CN
NC
CN
S chem e 1.17
T h is m eth od has been u se fu l in its sim plicity, in th a t it a ffo rd s ready
re p la c e m e n t
of
the
ca rb o n yl
m o ie ty
of
the
q u in o n e /a ry lk e to n e
w ith
a
d icy a n o m e th y le n e .
M a n y T C N Q d e riv a tiv e s 74 have be e n s y n th e s is e d in th is
w ay, in c lu d in g m any
71-e xte n d e d T C N Q de riva tive s.
H o w e v e r th is m ethod is n o t alw a ys a p p lica b le .
A
1 ,4 -a d d itio n
of
m a lo n o n itrile to the q u in o n e ring o f 2 ,5 - and 2 ,6 -d ip h e n y lth io b e n z o q u in o n e s 75
(52a and b) (S chem e 1.18) and a 1 ,6 -a d d itio n o f m a lo n o n itrile to th e in itia lly
fo rm e d m o n o -d icya n o m e th yl q u in o n e (5 3 ), g ivin g a tric y a n o d e riv a tiv e (54)
(S ch e m e 1.19), have bee n reported.
(ii) P alladium (O ) ca ta lyse d reactions.
P h e n y le n e d im a lo n o n itrile and som e alkyl and a lk o x y d e riv a tiv e s w e re
a lso
s y n th e s is e d
by
th e
palladium (O )
ca ta lyse d
re a ctio n
betw een
d ic y a n o m e th a n id e a nd the c o rre s p o n d in g 1 ,4 -d iio d o - o r d ib ro m o -b e n z e n e s .77
M a n y h e te ro -T C N Q a n a lo g u e s ha ve a lso been s yn th e sise d b y th is m ethod,
S ch e m e 1.20.
PhS
OH
(52) a: 2,5 isom er
b: 2,6 isom er
Scheme 1.18
39
OH
1
NC
CN
NC
CN
TiCI^/pyridine
CH2(CN)2
OH
CH2(CN)2
o j c o
NC
CN
(54)
(53)
S ch em e 1.19
,R 1
OI
Pd catalyst
+ 2 "C H (C N )2
------------- ►
a: X= I, R 1= R2= H
b: X= Br, R 1= R2= H
c: X= I, R 1= R2= Me, Et or OMe
S ch em e 1.20
1.C.3 TCNQ C-T Complexes
In itia l e v id e n c e o f the e le ctrica l c o n d u ctin g a b ility o f T C N Q w a s fo u n d as
fa r b a ck as 196 3 w h e n it w a s re p o rte d th a t the 1:2 sa lts o f q u in o lin iu m (T C N Q )2 (5 5 a ) a nd A /-m e th ylq u in o lin iu m -(T C N Q )2 (55b) w e re fo u n d to have a
room te m p e ra tu re co n d u ctivity, a rt, o f ~ 1 0 0 S c rrr 1 .78 T h e d is c o v e ry o f T T F T C N Q w a s to be th e m ile sto n e by w h ich th e syn thesis o f fu tu re C -T s a lts w o u ld
be m e a su re d a nd it has a lso been the m ost e x te n s iv e ly studie d.
T h e crystal
s tru c tu re o f T T F -T C N Q w a s fo u n d to be m ade up o f se g re g a te d c o lu m n a r
40
sta cks
o f p la n a r d o n o r and
a c c e p to r m o le cu le s w ith
th e
in te r-m o le c u la r
sta ckin g d is ta n c e s le ss th a n th e v a n d e r W a a ls sta ckin g d is ta n c e s fo r the
n e u tra l sp ecies.
2 It w a s also fo u n d to e x h ib it m e ta llic b e h a v io u r b e tw e e n 2 9 3 K
(crrt= 500 S cnrr1) and 59 K (a max= ~ 1 0 4 S c rrr1) and u n d e rg o a M -l tra n s itio n at
53 K .79
(55) a: X = H
b: X= Me
T h e d e g re e o f C-T, p, h a s be e n fo u n d to be incom p lete, w ith 0.5 9 e le c tro n s
b e in g tra n s fe rre d to th e T C N Q stack.
80
T T F -T C N Q has a lso be e n fo u n d to be
h ig h ly a n is o tro p ic in its co n d u ctivity, w ith h ig h e r c o n d u c tiv ity in th e sta ckin g
d ire c tio n th a n in a n y o th e r directio n.
T h e key fe a tu re s o f T T F -T C N Q w h ich m ake it so h ig h ly co n d u c tin g is
th e s im ila rity in size and sym m etry o f th e d o n o r and a c c e p to r m ole cu le s.
Both
are p la n a r m o le c u le s w ith e xte n sive Tc-delocalisation th ro u g h o u t th e m o le cu le
a nd both th e io n is a tio n p o te n tia l o f T T F and th e e le c tro n -a ffin ity o f T C N Q
fa v o u r p a rtia l e le c tro n tra n sfe r.
T C N Q a lso fo rm s C -T com ple xes w ith a va rie ty o f T T F d e riv a tiv e s .81
T T e F -T C N Q
82 w a s fo u n d to ha ve a rt= 1 8 0 0 + /-3 0 0 Scnrr 1 a nd is m e ta llic in
b e h a v io u r dow n to 9 0 -1 0 0 K.
T h is in cre a se in room te m p e ra tu re c o n d u c tiv ity
can be a cco u n te d fo r by th e e xp e cte d in cre a se in th e d o n o r overla p.
1.C.3.1 C-T Complexes of Non-ring fused TCNQ Derivatives
In th e s e a rc h to id e n tify th e re q u ire m e n ts fo r e n h a n ce d c o n d u c tiv ity in
c o m p o u n d s s im ila r to T C N Q and TT F , W h e la n d and G illso n s y n th e s is e d abo ut
80 c o n d u c tiv e C -T co m p le xe s
19 w ith the m a jo rity o f the a c c e p to rs being
d e riv a tiv e s o f T C N Q a nd w e re able to c o rre la te e le ctrica l c o n d u c tiv ity w ith
re d o x p o te n tia ls, s te ric e ffe cts and h e a vy atom s u b s titu tio n 83.
In lo o kin g fo r
tre n d s in a se rie s o f co m p le xe s o f T C N Q d e riv a tiv e s w ith T TF , it w a s fo u n d that
41
th e s tro n g e r a cce p to rs fo r w h ich c o m p le te e le c tro n tra n s fe r w a s m ost likely,
T C N Q (C N )2 (56a) a nd T C N Q F 4 (46b), g a ve p o o rly c o n d u c tiv e c o m p le x e s w ith
co m p a ctio n re s is tiv itie s o f 10 6 and 5 0 0 0 H em re sp e ctive ly, w h e re a s th e w e a k e r
e le c tro n
a ccep tors,
c o n d u c tiv e
TCNQ
co m p le xe s w ith
re sp e ctive ly.
(46a)
T C N Q C IC H 3
a nd
c o m p a ctio n
re s is tiv itie s
(56b),
gave
h ig h ly
0.1 a n d 0.2 H em
of
It a p p e a rs th a t c o n d u c tiv ity is a s s o c ia te d w ith m o d e ra te ly stron g
a cce p to rs, i.e. th o s e w ith a re d o x p o te n tia l b e tw e e n -0 .0 2 V a n d + 0 .3 5 V, in
co m b in a tio n w ith m o d e ra te ly stron g d o n o rs w ith a firs t re d o x p o te n tia l be tw e e n
0.1 V and 0 .4 V, such th a t th e re d o x p o te n tia ls are c lo s e ly m a tch e d , i.e. (E 1AE 1D < 0.25 V). H o w e ve r th e se co rre la tio n s are su b je ct to s trict c ry s ta l structure.
S u b s titu tio n o f th e T C N Q ring w ith in c re a s in g ly b u lk y g ro u p s a p p e a rs to have
o n ly m in o r e ffe cts
u n til five
to
six sid e
c h a in
ca rb o n s
or oxygens
are
T h e re s is tiv ity o f T T F c o m p le xe s o f T C N Q E t 2 (5 6 c) a n d T C N Q
in trodu ced.
Pr 2 (56d) in cre a se s fro m 0.0 5 to 2 .1 0 Q cm .
T M T C N Q (57) has b e e n re p o rte d
to be n o n -p la n a r,72c w ith stron g d e fo rm a tio n o f th e T C N Q s k e le to n in to a b o a tc o n fo rm a tio n ow ing to th e s te ric fa c to r and in a d d itio n to its w e a k 7t-acidity fa ils
to fo rm C -T co m p le xe s w ith T T F o r T M T T F .74 S im ila r ste ric e ffe c ts h a v e also
be e n o b se rve d fo r T C N Q B r 2 (56e) and T C N Q C I 2 (56f). T h e X -ra y s tru c tu re o f
n e u tra l (56e) 72b sho w s th a t w h ile th e m o le c u le is e s s e n tia lly p la nar, the
e x o c y c lic c a rb o n -c a rb o n d o u b le bon d b e n d s in th e p la n e o f th e rin g a w a y from
th e a d ja ce n t b ro m in e atom s and th a t th e cy a n id e g roup
NC
CN
NC
Rv
r
Y
CN
r-
V
Û
S t r%
V
Et Et
Y
NC
I
CN
(56) a: X= Y= CN
b: X= Cl, Y= Me
c: X= Y= Et
d: X= Y= i'P r
e: X= Y= Br
f: X= Y= Cl
NC
CN
(57) R<1-4>= Me
(58)
a d ja ce n t to th e b ro m in e is s lig h tly n o n -lin e a r u n lik e th e cy a n id e g ro u p rem oved
fro m th e b ro m in e w h ich is alm o st linear. T h is is pre su m e d to be a s te ric effect.
C o m p o u n d (56e) a lso fo rm s fo u r co m p le xe s w ith 4 ,4 -d ie th y lm o rp h o lin iu m (58)
o f s to ic h io m e trie s 1:1, 1:2, 2 :3 and 3: 4 w ith all fo u r com p le xe s b e in g in su la to rs
at 2 9 3 K .84 T h e X -ra y crysta l stru ctu re o f th e 1:2 co m p le x
42
85 s h o w s th a t the
(56e) d im e ris e s in co lu m n s s im ila r to th e 1 :1 com p le x but w ith a p e c u lia r
in te rd im e r tw iste d rin g -rin g overla p.
T his in tra -s ta c k "m irro r im age flip " and
tw istin g of th e T C N Q B r 2 m o le cu le s has been e x p la in e d as a w a y o f e ffic ie n tly
m inim ising
ste ric
re p u lsio n
betw een
b u lky
b rom ine
atom s.
The
p oo r
c o n d u c tiv ity of th e se co m p le xe s has been a s s o c ia te d w ith in c re a s e d ele ctro n
a ffin ity of (56e) (0.41 V co m pared w ith 0.1 7 V fo r T C N Q )19 w h ich se e m s to
result in co m p le te e le ctro n tra n s fe r .84
1.C.3.2 C-T Complexes of rc-extended TCNQ Derivatives
In an e ffo rt to a c h ie v e the m e ta llic state , th e C o u lo m b in te ra c tio n m ust
be m in im is e d .86
T h is is a ch ie ve d by d e s ig n in g a c c e p to r c o m p o u n d s with
e le c tro n -w ith d ra w in g g ro u p s at d ia m e tric a lly d is ta n t points on th e m o le cu le and
is m a n ife ste d by a lo w e rin g of the d iffe re n ce , A E 1/2, of the first and se co n d h a lf­
w ave re d u ctio n p o te n tia ls of the a c c e p to r (
T h e first ^ -e x te n d e d
T C N Q d e riv a tiv e to be s yn th e sise d w as T N A P (59), s yn th e sise d
70 from 2,6-
d im e th y ln a p h th a le n e (60a) by a m ethod s im ila r to th a t used fo r th e s y n th e s is of
TCNQ .
T h is m ethod has sin ce been im p ro ve d by in cre a sin g the y ie ld of the
in te rm e d ia te
2 ,6 -n a p h th a le n e d ia c e to n itrile (6 0 b )87 and also by th e a d o p tio n of
a novel s y n th e s is o f
2 ,6 -n a p h th a le n e d im a lo n o n itrile (60c).
(59)
(60) a: R= Me
b: R= CH 2CN
c: R= C H (C N)2
d: R= CH 2Br
T N A P w a s also sy n th e s is e d by B ryce et at 72b in th re e ste p s from
b is (b ro m o m e th y l)n a p h th a le n e (60d) in a p o o re r yield.
2,6-
TN A P is a s tro n g e r n-
acid th a n T C N Q and the s m a lle r A E 1/2 va lu e show s th a t th e re is a re d u ctio n of
th e o n -s ite C o u lo m b ic re p u lsio n .
be
a
p o o re r
c o n d u c to r
H o w e ve r w h ile T T F -T N A P has bee n fo u n d to
(a rt=40
S c rrr 1
)
th a n
its
TCNQ
c o u n te rp a rt
(a rt= 500 S c n r 1 ), H M T S F -T N A P has bee n fo u n d to be highly c o n d u ctin g with
43
tf3ooK=2400+/-600 S c rrr 1 risin g to 15,000 S c n r 1 at T = 5 0 K and its e xtra p o la te d
zero te m p e ra tu re c o n d u c tiv ity is at le ast 250 S c n r 1 .88
In the se a rch
fo r new
a cce p to rs w ith
the
d e s ira b le
fe a tu re s
of a
7t-e x te n d e d system co m b in e d w ith the high s ym m e try of TC N Q , a n u m b e r of
g ro u p s 89
atte m p te d
to
syn th e sise
1 3 ,1 3 ,1 4 ,1 4 -te tra c y a n o d ip h e n o -
q u in o d im e th a n e (T C N D Q ; 61a ) but th is re su lte d in th e re co ve ry of p o lym e ric
m a te ria ls a ttrib u te d to th e high in s ta b ility o f T C N D Q due to the re p u lsive
in te ra c tio n of the "b ip h e n y lic h ydrog ens".
a lo n g
w ith
its
m ore
d id e p ro to n a tio n
sta b le
of
b rid g e d
T C N D Q w as fin a lly syn th e sise d ,
a n a lo g u e
TCNTHPQ
4 ,4 '-b is (d ic y a n o m e th y l)b ip h e n y l
(61b),
(62a)
by
and
2 ,7 -b is (d ic y a n o m e th y l)-4 ,5 ,9 ,1 0 -te tra h y d ro p y re n e (62b) re s p e c tiv e ly to give the
c o rre sp o n d in g
d ia n io n
w h ich
In
tu rn
was
o x id is e d .90
e le c tro c h e m ic a lly
T C N T H P Q and its p yre n e a n a lo g u e (T C N P ; 63) have also been s y n th e s is e d by
a s im ila r m ethod w ith fin a l oxid a tio n , o r d e h y d ro g e n a tio n step, be in g ca rrie d
out using D D Q .91 T h e se all sh o w tw o re ve rsib le re d u ctio n p o te n tia ls but
R R
(62) a: R= H
b: R= CH 2-CH2
(61) a: R= H, TCNDQ
b: R= C H 2 CH2, TCNTHPQ
(64) TCQQ
(63) TCNP
w ith the A E 1/2 va lu e s (0.16, 0.23 and 0.30 V fo r T C N D Q , T C N T H P Q and TC N P
re sp e ctive ly) less th a n th o s e fo r T C N Q (0.56 V), and show in g re d u ctio n of the
o n -site
C o u lo m b
re p u lsio n .
C-T
co m p le xe s
of
TCNDQ
w ith
TTF
and
T C N T H P Q w ith T T F and T M T T F (o rt= 0.2 S c n r 1) have also been o b tained.
The nitrogen a n a lo g u e of T C N P , T C Q Q (64) has also been re p o rte d
presen ce
of the
m ore
e le c tro n e g a tiv e
n itro g e n s
resulted
potentia l being o b s e rv e d in the range from - 0.88 to + 1 .8 V.
44
in
no
92 and the
o xid a tio n
O u tlin e d in T a b le 1.0 are m ost o f th e ^ -e x te n d e d T C N Q d e riv a tiv e s that
ha ve bee n s y n th e s is e d in re ce n t ye a rs a nd a c o m p a riso n o f th e ir re d u ctio n
re d o x p o te n tia ls. A g e n e ra l tre n d w h ich is a p p a re n t is th a t the s tre n g th o f the
a c ce p to rs a p p e a rs to be re d u ce d as in c re a s in g num b e rs o f fu s e d b e n ze n o id
rin g s are added. T h is m arke d d e cre a se has be e n a ttrib u te d to th e d e v ia tio n of
th e d icy a n o m e th y le n e g ro u p s fro m p la n a rity as a re s u lt o f th e c lo s e p ro x im ity o f
per/'-hydrogens.
T h is has bee n v e rifie d by th e X -ra y cry s ta l s tu d ie s o f 10-
d ic y a n o m e th y le n e a n th ro n e (6 5 ),97 b e n zo -T C N Q ( 66),98 T C A Q (67)
s u lfu r c o n ta in in g co m p o u n d s (68 ) and (6 9 ).96
99 a n d the
A ll o f th e s e e x h ib it th e sam e
b u tte rfly s h a p e d is to rtio n s , w ith th e ce n tra l rin g b en t into b o a t form , and th a t
th is m ay be d u e to s te ric h in d ra n ce s, is fu rth e r su p p o rte d b y th e fa c t th a t the
d ic y a n o m e th y le n e g ro u p n e a re s t the s u lp h u r atom in (68 ) is m ore c o p la n a r w ith
th e rin g s th a n th e o th e r d ue to th e a b se n ce o f th e p e / 7-h yd ro g e n . F u rtherm ore,
(69) w ith its a d d itio n a l fu s e d ring, as w ith th e o th e r e xte n d e d a cce p to rs, sh o u ld
be m ore s e v e re ly d is to rte d fro m p la n a rity a nd th is has be e n c o n firm e d fro m the
U V sp ectrum a n d th e sh iftin g o f th e c o n ju g a te d cya n o g ro u p s in th e FT-IR .
T h e se e x te n d e d T C N Q d e riv a tiv e s all fa il to fo rm C -T c o m p le xe s w ith T T F and
th is can be a ttrib u te d to th e ir re d u ce d p la n a rity.
In a d d itio n som e o f th e se
co m p o u n d s sh o w a th ird a d d itio n a l e le c tro n re d u c tio n to th e tria n io n .
It has
bee n s u g g e ste d th a t th is a d d itio n a l e le c tro n is ta ke n up by th e le ss ch a rg e d
re sid u a l a re n e d iy l fra g m e n t w h ich is the n e xt LU M O .
T h e s e N L U M O s are
s im ila r in sh a p e a n d e n e rg y to th e co m p a ra b le LU M O s o f d ia lk y l-s u b s titu te d
h y d ro c a rb o n s .100
(65)
(66)
(67)
45
T a b le 1.0 C y c lic V o lta m m e tric data fo r ^ -e x te n d e d T C N Q d e riv a tiv e s ( in vo lts)
47
1.C.4 Heteroquinoid Electron Acceptors
In
c o n tra st
to
th e
e x te n s iv e ly
stu d ie d
te tra c y a n o q u in o d im e th a n e
(T C N Q ), it is o n ly re c e n tly th a t h e te ro q u in o id a n a lo g u e s o f T C N Q h a ve bee n
s y n th e s is e d
a n a lo g u e s
and
are
e xa m in e d
d e riv e d
as
fro m
im p o rta n tly, th io p h e n e (70a).
p o te n tia l acce p to rs.
s e le n o p h e n e
(70b),
These
fu ra n
h e te ro q u in o id
(70c),
and
m ost
It w a s b e lie ve d th a t th e in cre a se d in tra - a nd
in te r-m o le c u la r in te ra c tio n s o f th e cha lco g e n s, w h ic h w e re so s u cce ssfu l fo r th e
d o n o rs, w o u ld be as e ffe c tiv e fo r the a ccep tors.
In a d d itio n , the h e te ro c y c lic
syste m s w o u ld a lso a v o id th e s te ric in te ra ctio n s in lin e a rly c o n ju g a te d syste m s
by a ssu m in g th e trans co n fig u ra tio n , and co u ld a lso re d u ce th e a m o u n t o f
in te ra c tio n be tw e e n d ic y a n o m e th y le n e g roup s and peri- hydrog ens.
Q
x
(70) a:X= S
b:X= Se
c:X= O
NC> = Q = < CN
NC
X
NCK
CN
H
NC
(71) a:X= S
b:X=Se
c:X=O
X
V
'= /
<
CN
CN
(72) a:X= S
b:X= Se
c:X= O
(73)a:X= S, R1=R2= H
b:X= O, R1=R2= H
c:X= O, R1= H, R2= Br
(74)
„
T h e firs t h e te ro q u in o id TC N Q , o r h e te ro -T C N Q , to be s y n th e s is e d w a s
2 ,5 -b is (d ic y a n o m e th y le n e )-2 ,5 -d ih y d ro th io p h e n e (71a), w h ich w as d is c o v e re d
s e re n d ip ito u s ly by G ro n o w itz and U ppstrom w h ile in v e s tig a tin g cyc lo a d d itio n
re a c tio n s o f te tra c y a n o e th y le n e oxid e (T C N E O ) w ith d ih a lo th io p h e n e s .101
On
re a c tin g T C N E O w ith 2 ,5 -d ib ro m o th io p h e n e a red liq u id and a y e llo w solid
w e re o b ta in e d w h ic h w e re fo u n d to be ca rb o n yl cya n id e and (71a) re sp e ctive ly ,
S ch e m e 1.21.
n
B r—1v
^
NC p . CN
/~ B r + 2
S
NC
CN
nc
CN
\
NC
Scheme 1.21
48
^
S
+
CN
2CO(CN)2
+
Br2
T h e m e ch a n ism fo r th is re a c tio n w a s th o u g h t to be ra th e r com plex, the
m ost lik e ly b e in g th e 2 ,3 - and 4 ,5 -c y c lo a d d itio n o f th e ca rb e n e , d ic y a n o m e th yle n e , to th e 2 ,5 -d ib ro m o th io p h e n e fo llo w e d b y th e re a rra n g e m e n t show n
below .
T h e c a rb e n e and c a rb o n yl cya n id e a re g e n e ra te d by th e th e rm a l
d is s o c ia tio n o f T C N E O . A w e a k su p p o rt fo r th is m e ch a n ism is th e p re s e n c e of
te tra c y a n o e th y le n e a s a m in o r by-p ro d u ct.
NCy 5 ^ CN
NC
A
„
¡£ c :
+
CO(CN)2
CN
CN
BrX
>
Br^ S
Br
+ 2 n c ;C:
^ Br
NC
* -\C N
--------► C^ x 3 ^ " ° N --------- ► N° > = 0 = < CN
Br
S
Br
NC
S
CN
T h e s e le n o q u in o id and fu ra n o q u in o id a n a lo g u e s, (7 1 b )101 and (7 1 c ),102 w e re
a lso s y n th e s is e d b y a s im ila r m ethod, as w a s th e ir e xte n d e d a n a lo g u e s,
c o m p o u n d s (7 2 a ),103 (72 b a nd c ),102 (7 3 a )103 a n d (7 4 a a nd b ).104
Som e
h e te ro -T C N Q s
w e re
a lso
s y n th e s is e d
by
P d (0)
ca ta lyse d
s u b s titu tio n o f th e c o rre s p o n d in g h a lid e s o f th e h e te ro a ro m a tic s w ith sodium
d icya n o m e th a n id e , fo llo w e d by a p p ro p ria te o xid a tio n u sin g brom ine , D D Q , or
le ad te tra a ce ta te , S ch e m e 1.22. T h is m eth od has bee n used to s y n th e s is e the
a c c e p to rs (73a and b ),102 (7 5 ),104 (76) to (7 8 )105 a n d (7 9 )106
CN
W
' SV t>
B r ^ O -O -B ,
S
3
O N aC H (C N )2. Pd(PPh3)4
Nc
\ = ( S' j = J
CN
-----------------(2) Br2
NC
S
R
(75)
S ch e m e 1.22
A re a c tio n path fo r th is m eth od has p o s tu la te d th e in itia l fo rm a tio n o f an
a ry lp a lla d iu m in te rm e d ia te ,107 S ch e m e 1.23, w h ich m ay be a b le to u n d e rg o
in s e rtio n o f th e s ta b ilis e d a n io n w ith lo ss o f halid e, g iv in g in te rm e d ia te (80)
w h ic h th e n re a rra n g e s to g ive the su b s titu te d produ ct.
49
(76)
(77)
NC
NC
CN
S
CN
(78)
(79)a:R1=R2=R3= H
b:R1= H, R2=R3= Br
c:R1=R2= Br, R3= H
ArCH(CN)2 -
P d °— ^
ArX
V
Y
A r-Pd-CH(CN)2
A r-P d -X
(80)
-X
-CH(CN)2
S ch e m e 1.23
1.C.4.1 Acceptor Properties of Hetero-TCNQs
C o m p o u n d (7 1 a ) w a s fo u n d to ha ve p o o r a c c e p to r a b ility, E 1/21= +0.07,
E 1/22= -0 .5 0 V, w ith th e s e le n o q u in o id and fu ra n o q u in o id a n a lo g u e s b e in g
p o o re r a ga in, E 1/21= + 0.03, E 1/22= -0.51 V, a nd E 1/21= +0.03, E1/22= -0 .5 5 V,
re s p e c tiv e ly .102
The
fu ra n o q u in o id
a c c e p to r (7 1 c)
is a p o o re r a c c e p to r
b e ca u se , a lth o u g h o x y g e n is m o re e le c tro n e g a tiv e and w o u ld be e xp e cte d to
b e a b e tte r a cce p to r, th is sam e p ro p e rty re d u c e s th e a ro m a tic ity o f th e
re s u lta n t fu ra n ring o f th e d ia n io n .
h e te ro q u in o id s w e re a lso
a c c e p to rs
but sh o w e d
T h e c o n ju g a te d h o m o lo g u e s o f th e s e
in ve stig a te d .
enhanced
a b ility
T h e s e w e re fo u n d to be p o o re r
to
re d u c e
th e
o n -site
C o u lo m b
re p u lsio n , w ith te rh e te ro q u in o id co n ju g a tio n le a d in g to a c o a le s c e n c e o f th e
firs t a n d se co n d re d o x p o te n tia ls.
H ow ever, in s p ite o f th e ir p o o r e le ctro n
50
a c c e p to r a b ility, th e y w e re still c a p a b le o f fo rm in g som e C -T co m p le xe s w ith
TTF.
It w a s fo u n d that, fo r th e T T F co m p le xe s w ith (7 1 a ) and its e xtende d
hom o lo g u e s, (72a) a n d (73a), the c o n d u c tiv ity o f th e c o m p le x e s in cre a se d in
lin e w ith the e xte n d e d c o n ju g a tio n fro m 6 .7 x 1 0 -9, 2 .2 x 10 '4 to 3 .3 x 10 -3 S c rrr 1
re s p e c tiv e ly .103
A c c e p to r a b ility w a s e n h a n ce d b y in tro d u c tio n o f a d d itio n a l
e le c tro n -w ith d ra w in g su b stitu e n ts.
co n d e n s e d
h o m o lo g u e ,
T h e 3 ,6 -d ib ro m o d e riv a tiv e (74b) o f the
2 ,5 -b is (d ic y a n o m e th y le n e )-2 ,5 -d ih y d ro th ie n o [3 ,2 -
b jth io p h e n e (74a), has b e e n fo u n d to be a b e tte r a c c e p to r th a n TC N Q , i.e.
E 1/21= +0.25,
E 1/22=
-0 .1 3
V,
AE =
0.38
fo r th e d ib ro m o
d e riv a tiv e
E 1/21= +0.25, E 1/22= -0 .4 7 V, AE= 0.7 2 fo r T C N Q . C o m p o u n d s
and
(74a) and (74b)
fo rm h ig h ly c o n d u c tin g C -T co m p le xe s w ith m any do n o rs, e s p e c ia lly H M TTeF,
w hose
1:1
co m p le x w ith
te m p e ra tu re
p re s s e d
(74a)
p e lle t
a nd
2:1
c o m p le x w ith
c o n d u c tiv itie s o f
140
(74b)
and
ha ve
room
S c rrr 1
170
re s p e c tiv e ly .104
A crysta l s tru c tu re o f (74a) a nd B E D T -T T F 108 h a s sh o w n th a t (7 4 a ) is
p la n a r and fo rm s a
se g re g a te d
s ta ck s tru c tu re
p e rp e n d ic u la r to th e m o le c u la r plane.
a lo n g
th e
a-axis,
n e a rly
In te rm o le c u la r S -S co n ta c t d ista n ce s
be tw e e n a lte rn a te ly s ta cke d co m p o n e n ts are s lig h tly lo n g e r th a n the van d e r
W a a ls ra d iu s (3 .7 0
plane.
A).
T h e re are, how ever, s e v e ra l s h o rt co n ta cts w ith in the
T h e re a re in te ra c tio n s be tw e e n the S atom s o f a d ja ce n t B E D T -T T F
m o le c u le s (3 .6 4 a n d 3 .5 9
A)
and th e n itro g e n a tom s o f th e a c c e p to r (3.3 3
T h e re are a lso in te ra c tio n s b etw e en the S atom s o f th e a c c e p to r (3.48
A)
A).
w h ich
sh o w s th e ir p o te n tia l as m u lti-d im e n s io n a l o rg a n ic m etals.
R e cently,
condensed
b e n z o th io p h e n e s
(7 6 )-(7 8 )
ha ve
been
s y n th e s is e d .105 T h e s e w e re in ve stig a te d b e ca u se th e w e a k e le c tro n a ffin ity of
th e o th e r h e te ro -T C N Q s w a s m a in ly a ttrib u te d to th e le s s e r a ro m a tic ity o f the
a ro m a tic
sextets
b e n z o th io p h e n e s
a ris in g
have
th e
fro m
th e
a b ility
to
h e te ro q u in o id
fo rm
s tro n g ly
reductio n.
a ro m a tic
The
b e n ze n o id
in te rm e d ia te s on re d u c tio n and sh o u ld th e re fo re fo rm s tro n g e le ctro n a cce p to rs
w ith o u t th e ne e d fo r th e in tro d u c tio n o f m ore e le c tro n e g a tiv e g ro u p s w h ich can
in te rfe re w ith th e c ry s ta l p a ckin g and
in te rm o le c u la r in te ra ctio n s.
T h e se
a c c e p to rs sh o w im p ro ve d e le ctro n a c c e p to r a b ility c o m p a re d to T C N Q and the
re d u c e d
AE
v a lu e s
show
e n h a n ce d
re d u c tio n s
o f th e
o n -s ite
C o ulo m b
re p u lsio n s.
In an a tte m p t to e lim in a te th e d is to rtin g e ffe ct on th e p la n a rity d u e to the
s te ric
in te ra c tio n
b e tw e e n
th e
d icy a n o m e th y le n e
g ro u p s
and
th e
peri-
h yd ro g e n s o f b e n z a n n u la te d d e riva tive s o f T C N Q , like T C A Q , a n u m b e r o f new
a c c e p to rs ha ve b e e n s y n th e s is e d w h ich are h e te ro c y c lic rin g s fu s e d to TC N Q .
It w a s a lso hop ed th a t th e p re s e n c e o f th e h e te ro a to m s w o u ld a lso lead to
in c re a s e d
in tra -
a nd
in te rm o le c u la r
in te ra ctio n s.
The
fo u r
iso m e ric
b e n z o th io p h e n e a n a lo g u e s (8 1 )-(8 4 ) o f T C A Q all sh ow ed tw o re v e rs ib le o n e e le c tro n re d u ctio n p o te n tia ls, w ith (81) and (82) show in g p o te n tia ls clo se to
th a t o f TC N Q ,
E 1/21= +0.13, E 1/22= -0 .1 9 V, AE= 0.32, and E 1/21= +0.13,
E 1/22= -0.21 V, AE = 0.34, re s p e c tiv e ly and (83) and (84) sh o w in g w e a k e r
a c c e p to r a b ility .109
(81)
(82)
(83)
(84)
CN
(86) a:X= S
(85) a:R= H
b:R= Cl
b:X= Se
T h is has bee n a ttrib u te d to th e fo rm a tio n o f a sta b le a ro m a tic b e n z o th io p h e n e
on re d u c tio n o f (81) and (82). T h is im p ro ve d a c c e p to r a b ility su g g e s ts th a t the
a c c e p to rs are p la n a r a nd th is is e n h a n ce d by th e ir a b ility to fo rm h ig h ly
c o n d u c tin g
C -T co m p le x e s w ith T TF ;
(8 1 ):T T F
and (8 2 ):T T F
ha ve
p e lle t
c o n d u c tiv ity s o f 0 .8 9 and 4 .7 8 S c rrr 1 re sp e ctive ly. T h e m o n o -th io p h e n e fu se d
d e riv a tiv e s o f TC A Q , (8 5 a and b), w h ich co n ta in e d an a n n u la te d b e n z e n e ring,
still e xh ib ite d a b u tte rfly sh a p e w ith th e c e n tra l b e n ze n e ring ta k in g on a boat
c o n fo rm a tio n d ue to th e s te ric in te ra c tio n s o f th e p e /i-h y d ro g e n s w ith th e cyano
g ro u p s .110
X -ra y stru ctu ra l a n a ly s is o f T C N Q s fu s e d w ith 1 ,2 ,5 -th ia d ia z o le ( 86a)
a n d 1 ,2 ,5 -s e le n a d ia z o le ( 86b) rin g s sh o w th a t th e y are p la n a r and c ry s ta llis e in
s h e e tlik e
n e tw o rks
c o n ta c ts .111
w ith
sh o rt s u lp h u r to
cya n o
and
se le n iu m
to
cyano
T h e m o n o -fu se d 1 ,2 ,5 -d ith ia z o le d e riv a tiv e (87) w as fo u n d to
h a v e im p ro ve d a c c e p to r a b ility o v e r th e b is -fu s e d h o m o lo g u e w ith a first
re d u c tio n p o te n tia l o f E 1/21= + 0 .1 2 V, co m p a re d w ith E 1/21= -0 .0 2 V fo r ( 86a).
C o m p o u n d (87) a lso fo rm e d m ore h ig h ly c o n d u ctin g C -T c o m p le xe s w ith T T F
a n d its d e riv a tiv e s
in d ica tin g th a t the in c lu s io n b e h a v io u r show n
by C -T
co m p le xe s o f ( 86a), w h o s e extra h e te ro c y c lic ring gave rise to th e fo rm a tio n of
in clu sio n ca vitie s, w e re d im in is h e d .112 T h e X -ra y stru ctu re o f (87) sh o w e d th a t
th e p la n a r m o le cu le fo rm s a c o p la n a r d ya d by h y d ro g e n b o n d in g w ith the
cyano
g ro u p s
a nd th e
h y d ro g e n s
on th e
a d ja ce n t q u in o d im e th a n e
ring.
A lth o u g h th e re is no S -S o r S-N h e te ro a to m in te ra ctio n in th e c r y s ta l, the dyad
fo rm a tio n o f (87) sh o w s the p o s s ib ility th a t th e n e g a tiv e c h a rg e can be
d e lo c a lis e d o v e r tw o m o le cu le s in the a n io n ra d ic a l salts, w h ich is a n o th e r
a p p ro a ch to re d u cin g th e o n -s ite C o u lo m b repulsion .
1.C.5 /V,A/'-Dicyano-p-quinodiimine (DCNQI) Acceptors
A n a lte rn a tiv e fa m ily o f a c c e p to r m o le cu le s w ith th e sam e W u rs te r type
re d o x system as T C N Q is th e /V ,A /'-d icyano -p-qu inod iim ine (D C N Q I;
w h ich w a s d is c o v e re d b y H u nig and c o w o rk e rs .113
88) fa m ily
T h is fa m ily o f a cce p to rs
has se v e ra l d is tin c t fe a tu re s w h ich m ake it a ttra ctive a s a n ove l g ro u p o f
a cce p to rs.
O ne o f th e m ain a d v a n ta g e s is th a t o f its fa c ile o n e -ste p syn th e sis
fro m th e c o rre s p o n d in g qu in o n e . S e condly, o w in g to th e sm all a n g le fo rm e d by
th e = N -C N group , th e p la n a rity o f th e a c c e p to r m o le c u le re m a in s v irtu a lly
u n a lte re d eve n upo n te tra s u b s titu tio n . F in a lly D C N Q I has e s s e n tia lly th e sam e
re d o x p o te n tia ls 114 ( E ^ W o . 3 9 and E21/2= -0 .2 5 V) as T C N Q ( E " 2= + 0 .3 9 and
E21/2= -0 .2 8 V ) and th is can be v a rie d e a s ily by a p p ro p ria te s u b s titu tio n w ith
m ore e le c tro n e g a tiv e gro u p s. F u rtherm ore, the sym m e trie s a nd e n e rg ie s o f the
LU M O s o f D C N Q I a nd T C N Q ha ve be e n fo u n d to be alm o st id e n tic a l .115
(88)
1.C.5.1 Synthesis of DCNQI and its derivatives
T h e s y n th e sis o f D C N Q I can be c a rrie d o u t in a o n e -p o t re a c tio n by a
m e th o d w h ic h can be a p p lie d to n o n -e n o liz in g ke to n e s a n d a w h o le v a rie ty o f
s u b s titu te d benzo-, n a p h th o - and a n th ra q u in o n e s, S ch em e 1.24 .
53
o
TiCI3
TiCI4
BTC
-
+
A
Me3SLMe3SL-N = C = N -S iM e 3
▼
CN
9 l>
f> c
N
l2
or
r
- TiOCI2
A
-
- Me3SiCI
S ch e m e 1.24
T h e cru cia l re a g e n ts in th is re a ctio n are b is (trim e th y ls ily l)c a rb o d iim id e
(B T C ) a n d tita n iu m te tra c h lo rid e (T iC I4). T h is re a ctio n co u n ts am ong th e fe w
re a c tio n s in vo lvin g c o n d e n s a tio n at th e ca rb o n yl g ro u p o f a q uinon e. W h ile an
a lte rn a tiv e
syn th e sis
u sin g
1 ,4 -su b stitu te d
p -p h e n y le n e d ia m in e s
(89a-c)
e x is ts ,116 th is has its lim ita tio n s in th a t it in vo lve s m ore th a n o n e step, g ives
in te rm e d ia te s w h ich a re d iffic u lt to handle, and a le sse r v a rie ty o f d e riva tive s
c o m p a re d to the qu in o n e s, sin ce o n ly a fe w s u b stitu te d p h e n y le n e d ia m in e s are
e a s ily a cce ssib le . T h e use o f c y a n id e as w e ll as flu o rid e ca ta ly s ts did w o rk fo r
som e d iffic u lt to e n o lis e ke to n e s but not fo r som e q u in o n e s w h ic h te n d to
u n d e rg o 1 ,4 -a d d itio n and a re m ore re a d ily re d u c e d .113
T h is w a s o vercom e
w ith th e use o f a Lew is acid.
A v a rie ty o f Lew is a cid s w e re in ve stig a te d
in c lu d in g
tin (IV )
alu m in iu m
ch lo rid e ,
chloride,
e th e r-b o ro n triflu o rid e ,
and
triis o p ro p o x y tita n iu m c h lo rid e all o f w h ich w e re fo u n d to be in a ctive o r cause d
d e c o m p o s itio n o f the p -b e n z o q u in o n e . F in a lly th e h ig h e s t yie ld s w e re o b ta in e d
u s in g tita n iu m te tra c h lo rid e e s p e c ia lly w h e n a dd ed firs t to th e quinon e.
T h is m e th o d has p ro ve d v e ry v e rs a tile g ivin g re a s o n a b le y ie ld s fo r a broad
ra n g e o f s u b s titu te d p -b e n z o q u in o n e s (9 0 a -e ),113- 116’
b u lk y
s u b s titu e n ts
n a p h th o q u in o n e s ,113’
and
d iffe rin g
116-
117
redox
117 in c lu d in g th o se w ith
p o te n tia ls
as
w e ll
9 ,1 0 -a n th ra q u in o n e s ,113'
as
116’
a n th ra q u in o n e s 118 and th e h ig h ly exte n d e d q u in o n e s (91) and (9 2 ).119
54
1,41,4-
0
o
nh2
(89) a: r i = r 2= h
b: R1=R2= Me
c:
(90) a:R 1= R 2=R 3= R 4= H
b:R1= Me, R2=R 3= R 4= H
ci
R i= R 2 =
c:R1= R 3= Me, R2= R 4= H
d:R 1= R 2=R 3=R 4= Me
e:R 1= R 3= M e, R 2= R 4= Me
O
O
(92)
(91)
T h e N -C N g ro u p o f th e b ifu n c tio n a l d icya n im in e s m ay o c c u p y syn and
anti p o s itio n s w ith re s p e c t to the n e ig h b o u rin g ring atom s, so th a t a m axim um
o f fo u r is o m e rs is p o ssib le .
In all the D C N Q I d e riv a tiv e s th e c o n fig u ra tio n o f
th e c y a n o g ro u p is d e te rm in e d b y th e s u b s titu e n t pattern.
In g e n e ra l the
2 ,5 -s u b s titu te d and 2 ,3 -s u b s titu te d d ic y a n im in e s exist o n ly in th a t c o n fig u ra tio n
in w h ic h th e CN m o ie ty p refers th e anti p o sitio n to th e ring su b stituen ts.
A c c o rd in g ly th e anti c o n fig u ra tio n is o b s e rv e d in s u b stitu e n t ty p e s (93) and (94)
115and th e syn c o n fig u ra tio n in ty p e s (95) and (96). T h is has bee n v e rifie d by
13C and 1H N M R d a ta o f th e se c o m p o u n d s .113- 116
T h e n o n -s u b s titu te d
D C N Q I co m p o u n d (88) can be fo u n d as a syn lanti m ixture a c c o rd in g to 13C
NM R
s p e c tro s c o p y .
The
te tra s u b s titu te d
d icya n im in e s
u n d e rg o
rapid
is o m é ris a tio n w h ic h is e v id e n t fro m th e NM R, w ith th e n u m b e r o f N M R s ig n a ls
NC.
'N
(93)
NC.
N
.C N
NC.
Cl
(95)
(94)
R 1 and R 2 can be M e , Et, /Pr, fl3u, Ph, Cl, F, Br, I, O M e, SM e etc.
55
(96)
b e in g s tro n g ly d im in ish e d .
T h e m o n o s u b s titu te d d e riv a tiv e s a lso e xist as a
m ixtu re o f syn lanti iso m e rs w ith o ne cya n o g ro u p fix e d in th e anti position.
M o le c u la r
m e c h a n ic a l
stu d ie s
on
th e
DCNQI
d e riv a tiv e
of
2 -m e th y la n th ra q u in o n e p re d icte d th is and w a s in a g re e m e n t w ith th e N M R
re s u lts .118
It also in d ic a te d th a t th e a n th ra q u in o n e D G N Q I d e riv a tiv e s w ere
n e a rly planar. T h is h a s be e n fo u n d to be th e ca se e ve n fo r th e te tra s u b s titu te d
D C N Q I d e riv a tiv e o f th e 2 -m e th y l-9 ,1 0 -a n th ra q u in o n e as d e m o n s tra te d by
X -ra y a n a lysis. X -ra y s tru c tu ra l a n a lysis o f th e tri- a n d te tra m e th y l-s u b s titu te d
h y b rid d e riv a tiv e s o f D C N Q I a nd TC N Q , (97) and (9 8 ),120 sh o w e d th a t (98) is
s tro n g ly d isto rte d in to a b o a t c o n fo rm a tio n w ith g re a te r d e fo rm a tio n a b o u t the
b u lk ie r = C (C N )2 th a n a b o u t th e = N C N group.
In c o n tra s t (9 7 ) is e s s e n tia lly
p la n a r sin ce th e N -C N g ro u p can e a s ily a d o p t an e n la rg e d d ih e d ra l angle.
A
s im ila r s itu a tio n w a s a ls o fo u n d fo r a n o th e r T C N Q -D C N Q I h y b rid acceptor,
(99), w h ich sh o w e d a s lig h t d e v ia tio n from p la n a rity, a g a in w ith th e g re a te r
d e v ia tio n o c c u rin g a b o u t th e = C (C N )2 g ro u p .119
A s sta te d a lre a d y D C N Q I its e lf has s im ila r re d o x re d u ctio n p o te n tia ls to
TCNQ.
T h e a c c e p to r a b ility can th e n be im p ro ve d by in tro d u c in g m ore
e le c tro n e g a tiv e
s u b s titu e n ts
E 21/2= + 0 .1 6 V ).113
(te tra c h lo ro -D C N Q I
has
+ 0 .7 6
and
N e a rly all th e D C N Q I d e riv a tiv e s sh o w tw o o n e -e le c tro n
re v e rs ib le re d u c tio n w a v e s to th e co rre s p o n d in g a n io n a nd dia n io n . H o w e ve r a
c o n tin u o u s tre n d has be e n fo u n d w h ich show s th a t in cre a se d b e n z a n n u la tio n
re s u lts in a sh ift o f th e firs t re d u ctio n p o te n tia ls to w a rd m ore n e g a tiv e v a lu e s 121
a n d th is le ads to a re d u c tio n o f th e o n -site C o u lo m b re p u lsio n .
re d u c tio n
p o te n tia ls
can
e le c tro n e g a tiv e su b s titu e n ts .
be
im p ro ve d
as
b e fo re
by
T h e lo w e r
in tro d u c in g
m ore
1.C.5.2 C-T Com plexes of DCNQI
C h a rg e -T ra n s fe r co m ple xes h a v e b e e n su c c e s s fu lly o b ta in e d fro m a
n u m b e r o f d e riv a tiv e s
of DCNQI
and
v a rio u s
donors.
O ne o f th e firs t
s y n th e s is e d , a nd th e firs t to y ie ld c ry s ta ls o f s u ffic ie n t q u a lity to g ive an X -ra y
cry s ta l stru ctu re , w a s th a t o f A /,A /'-d icya n o -1 ,4 -n a p h th o q u in o n e d iim in e (96) and
T T F .122 T h is c o m p le x has a 1:1 s to ic h io m e try o f d o n o r to a c c e p to r and a 300K =
2 5 S c rrr1. T h e fa c t th a t th is a c c e p to r fo rm s a C -T co m p le x w ith T T F w h ile its
T C N Q a n a lo g u e d o e s not, due to n o n -p la n a rity e n fo rce d on it b y th e = C (C N )2
group , d e m o n s tra te s th e a d v a n ta g e o f th e = N C N g roup o v e r th e = C (C N )2. T h e
c o m p le x c o n s is ts o f s e p a ra te d s ta cks o f d o n o rs and a c ce p to rs w h ic h o c c u r in
pairs, a n d w h ic h a re e q u id is ta n t at ro o m te m p e ra tu re .
It is s u g g e s te d th a t an
e le c tro s ta tic in te ra c tio n be tw e e n th e n e g a tiv e ly ch a rg e d N -atom s on the syn
c o n fig u re d = N -C N g ro u p s and th e s u lp h u r a to m s o f th e T T F w a s re s p o n s ib le
fo r this.
T h is in te ra c tio n ca u se s tw o s ta c k s o f th e a c c e p to r to c ry s ta llis e in
p a irs in su ch a w a y th a t th e u n s u b s titu te d p a rt o f th e n a p h th a le n e ske le to n are
fa c in g e a ch other.
T h e co m p le x e x h ib its m e ta llic b e h a v io u r and u n d e rg o e s a
p h a s e -tra n s itio n to a s e m ic o n d u c tin g s ta te at 140 K.
In th e X -ra y s tru c tu re o f th e D C N Q I-T T F . 2 H20 , 123 th e d o n o rs and
a c c e p to rs c ry s ta llis e o u t in s e g re g a te d s ta cks in c h e s s -b o a rd -lik e a rra ngem ent.
B o th d o n o rs a n d a c c e p to rs are s k e w e d in th e sam e d ire c tio n w h ich is in
c o n tra s t to T C N Q -T T F , in w h ich th e d o n o rs a n d a cce p to rs w e re ske w e d in
o p p o s ite d ire c tio n s .
group , P 2 1/c.
H o w e ve r bo th c o m p le x e s c ry s ta llis e in th e sam e space
T h e d e g re e o f c h a rg e tra n s fe r has bee n fo u n d to be 0.48
e le c tro n s w h ic h is o n e o f th e p re re q u is ite s fo r m e ta llic c o n d u c tiv ity in th a t there
is in c o m p le te c h a rg e tra n sfe r.
D C N Q I-T T F . 2 H20
show s a s in g le crystal
c o n d u c tiv ity o f o rt = 1-10 S c rrr1 and e x h ib its s e m ic o n d u c to r b e h a v io u r in that
its c o n d u c tiv ity d e c re a s e s as th e te m p e ra tu re d e crea ses.
O ne
DCNQI
d e riv a tiv e
w ith
has
show n
ve ry
h ig h
co n d u ctivity,
S cnrr1), and w h ic h is o n e o f th e b e st co n d u c tin g C -T
( CT (single crystal) = 2 ° 0
c o m p le x e s
w h ic h
TM TSeF
as
d o n o r,
is
th e
h e te ro q u in o id
a c c e p to r
2 ,5 -
b is (c y a n o im in o )-3 ,6 -d ib ro m o -2 ,5 -d ih y d ro th ie n o -[3 ,2 -b ]th io p h e n e (1 0 0 ).124 This
n o ve l g ro u p o f S -h e te ro q u in o id a c c e p to rs w e re in v e s tig a te d to see if the
p ro p e rtie s
of
h e te ro q u in o id
th e
DCNQI
system .
system
w e re
re ta in e d
if
in c o rp o ra te d
into
a
T h e s e n e w a c c e p to rs w e re s y n th e s is e d fro m the
c o rre s p o n d in g q u in o n e s as before, b u t u s in g h ig h e r te m p e ra tu re s.
C om po und
(1 0 0 ) a lso fo rm e d C -T c o m p le xe s w ith T T F , T M T T F , TT T , and B E D T -T T F . T he
c ry s ta l
s tru c tu re
of
(1 0 0 )-T T F
sho w s
s e g re g a te d
stacks
o f d o n o rs
and
a c c e p to rs w h ic h are a lm o s t e q u id is ta n t a t room te m p e ra tu re .
(1 0 0 )-T T F also
e xh ib its m e ta llic b e h a v io u r and u n d e rg o e s a tra n s itio n to a se m i-c o n d u c tin g
sta te at 160 K.
Br
Br
(100)
1.C.5.3 DCNQI Radical Anion Salts
In a d d itio n to fo rm in g C -T co m p le x e s w ith o rg a n ic d o n o r m o le cu le s, the
D C N Q I fa m ily o f a c c e p to rs also fo rm
ra d ic a l ion salts.
By fa r th e m ost
im p o rta n t D C N Q I d e riv a tiv e s to fo rm ra d ic a l ion s a lts are th e 2 ,5 -d is u b s titu te d
D C N Q Is w h ic h fo rm 2:1 salts w ith m e ta ls ,123 in c lu d in g th e a lka lis, th a lliu m ,
ru b id iu m , s ilv e r and, m ost im p o rta n tly co p p e r.
U n u su a lly, all th e s e m e ta l salts
c ry s ta llis e in th e sam e space g ro u p o r at le a st in s u b g ro u p s .123’ 125
A ll the
n o n -c o p p e r m e ta ls a re ve ry s im ila r in th a t th e m e ta l-to -N in te ra c tio n s o f the
cya n o g ro u p are c lo s e to the van d e r W a a ls ra d iu s o f n itro g e n a n d th e io n ic
ra d iu s o f th e m etal ions, w h ich su g g e s ts th a t C o u lo m b in te ra c tio n s a re present.
T h is h a s be e n fo u n d to be th e ca se w ith th e n o n -c o p p e r ra d ica l ion salts. T h e y
b e h a ve
as
m e ta l-lik e
se m ico n d u cto rs,
sh o w in g
a
g ra d u a l
in c re a s e
in
c o n d u c tiv ity on lo w e rin g th e te m p e ra tu re a nd th e n at a p a rtic u la r te m p e ra tu re ,
- 1 0 0 K, th e y u n d e rg o a sud d e n p h a s e tra n s itio n to a se m ic o n d u c tin g state.
T h is is c h a ra c te ris tic o f o n e -d im e n s io n a l c o n d u c to rs w h ich are p ro n e to phase
tra n s itio n s at lo w te m p e ra tu re s.
O f th e m etal ra d ica l ion sa lts to be m e n tio n e d th u s far, th e c o p p e r salts
d e s e rv e sp e c ia l m ention. T h e (2 ,5 -d im e th y l-D C N Q I)2 Cu sa lt in p a rticu la r, w as
fo u n d to be h ig h ly c o n d u c tiv e w ith a s in g le -c ry s ta l c o n d u c tiv ity o f 8 0 0 S c rrr1
w h ic h
in c re a s e s
c o n tin u a lly
as
th e
te m p e ra tu re
c o n d u c tiv ity , a, o f 5 0 0 0 00 S c rrr1 at 3.5 K .126
is
low ered,
g iv in g
a
R a d ica l a n io n s w ith such
e x tre m e ly h ig h e le c tric a l c o n d u c tiv itie s w e re p re v io u s ly u n h e a rd of. T h e crystal
s tru c tu re o f (2 ,5 -d im e th y l-D C N Q I)2Cu c o n s is ts o f sta cks o f c o p p e r ions, w ith
e a ch c o p p e r ion b e in g co o rd in a te d in a d is to rte d te tra h e d ra l m a n n e r to th e Natom s o f fo u r cya n o gro u p s. T h u s e a ch c o p p e r ion s ta ck is s u rro u n d e d by fo u r
D C N Q I stacks.
Group M
Group M-l
j:R 1 = Cl, R2= Cl
a:R1 = Me, R2= Me
b:R1 = Me, R2= I
c:R1 = Cl, R2= I
d:R1 = Br, R2= I
e:R1 = Me, R2= OMe
f:R1 = Br, R2= OMe
g:R1 = I, R2= OMe
k:R1 = Cl, R2= Me
l:R1 = Cl, R2= Br
m:R1 = Br, R2= Me
n:R1 = Br, R2= Br
o:R1 = Cl, R2= OMe
h:R1 = OMe, R2= OMe
i:R1 = I, R2= I
E le ctro n tra n s p o rt in th e se salts ta k e s p la c e alo n g th e a c c e p to r stacks,
w ith c o n d u c tiv ity a lo n g th e ca tio n sta cks b e in g ru le d o u t due to th e in tra -c a tio n
s ta c k se p a ra tio n b e in g to o large .( C u-C u 3 .8 8
2 .5 6
A
fo r
Cu
m etal).
The
A
fo r (2 ,5 -M e 2-D C N Q I)2C u and
2 ,5 -d is u b s titu te d -D C N Q I
m eta l
salts,
(R 1,R2-D C N Q I)2 C u (101), can be c la s s ifie d in to tw o g ro u p s a c c o rd in g to the
te m p e ra tu re d e p e n d e n c e o f th e ir c o n d u c tiv itie s at a m b ie n t pre ssu re :
G ro u p M
salts, (101 a-i), w h ic h s h o w m e ta llic b e h a v io u r d ow n to low te m p e ra tu re s .123127
G rou p M -l salts, (101 j- o ) ,123- 127 w h ic h u n d e rg o a M -l tra n s itio n in the
te m p e ra tu re ra n g e T M_,= 160- 230 K.
A n a ly s is o f th e s e s a lts 127- 128 su g g e sts
th a t th e s o lid -s ta te b e h a v io u r o f th e C u s a lts is d e p e n d e n t on th e s iz e o f the
s u b stitu e n ts, w ith la rg e su b stitu e n ts, O M e a nd I, g iv in g rise to s ta b le m e ta llic
sta te s and c o m b in a tio n s o f sm all s u b s titu e n ts g iv in g rise to p h a se tra n s itio n s ,
(2 ,5 -M e 2-D C N Q I)2C u b e in g an e xce p tio n a l case.
T h e e le c tro n ic b e h a v io u r is
a lso d e p e n d e n t on th e d iffe re n t e le c tro n ic p ro p e rtie s o f the s u b stitu e n ts.
In a d d itio n to th e s e s u b stitu e n t e ffe cts,
crysta l stru ctu re s tu d ie s at
v a rio u s te m p e ra tu re s s h o w th e im p o rta n ce o f th e te tra h e d ra l c o o rd in a tio n of
th e a c c e p to r g ro u p s to th e m e ta l.127- 129 T h is stru ctu ra l fe a tu re in tro d u c e s a
n e w p a ckin g m o tif o f th e m o le cu la r c o n d u cto r, in w h ich th e o n e -d im e n s io n a l
colum n s, as a re s u lt o f b e in g te tra h e d ra lly c o o rd in a te d to th e c o p p e r cation,
b e co m e s th re e -d im e n s io n a l due to the in te ra c tio n b etw e en th e prc o rb ita l o f the
o rg a n ic m o le c u le s a nd th e 3d o rb ita ls o f th e ca tio n . T h is g ive s rise to a "m u ltiF erm i s u rfa c e " w h ic h is n o t s u sce p tib le to p h a s e tra n sitio n s. A n y "fla tte n in g " or
d e fo rm a tio n o f the c o o rd in a tio n te tra h e d ro n (o r N -C u -N a n g le ) re su lts in a
d e c re a s e in th e n u m b e r o f d o rb ita ls p a rtic ip a tin g in th e p7t-3d m ixing a n d so
w e a k e n s th e m u lti-F e rm i s u rfa ce nature, w h ich le ads to th e fo rm a tio n o f a gap
by a CDW .
1.C.6 Metal(dmit)2 Acceptors
T h e ge n e ra l e m p h a s is o f m uch o f th e re ce n t s y n th e tic w o rk in th e area
o f C -T co m p le xe s has be e n on the d e v e lo p m e n t o f syste m s w ith e n h a n ce d
in te rs ta c k in te ra ctio n s, le a d in g to in cre a se d d im e n s io n a lity .
T h e s e e ffo rts are
m o tiva te d b y th e d e s ire to a vo id th e m e ta l-to -in s u la to r tra n s itio n s w h ic h are
a s s o c ia te d w ith 1-D m e ta ls on co o lin g to lo w te m p e ra tu re s. T h is a p p ro a c h has
a lso be e n a p p lie d to ^ -a c c e p to r m olecu les.
These
a cce p to rs a re m etal
co m p le xe s o f th e s u lp h u r ligand, 4 ,5 -d im e rc a p to -1 ,3 -d ith io le -2 -th io n e (102),
and are know n as M (d m it)2 a cce p to rs (103) fo r short.
T h e m ost im p o rta n t
co m p le x e s to d a te h a ve be e n o b ta in e d fro m nickel, p la tin u m a nd p a lla d iu m as
th e m eta l and th e s e m eta l co m p le xe s ha ve be e n s y n th e s is e d 130 fro m the
d ith io la te (102) and th e m e ta l-d ich lo rid e , S ch em e 1.25.
T h e s e a re p la n a r
m o le c u le s and th e s u lp h u r lig a n d m o ie tie s a llo w fo r b oth in tra - and in te r-s ta c k
in te ra ctio n s.
The
n a tu re
o f the m etal atom
p la ys
an
im p o rta n t ro le
in
d e te rm in in g th e stru c tu ra l and p h ysica l p ro p e rtie s o f th e co m p le xe s w h ic h are
form ed.
2
”
(103)
(102)
S ch em e 1.25
M (d m it)2 a c c e p to rs fo rm com p le xe s w ith a v a rie ty o f ca tio n s /d o n o rs , the
m ost im p o rta n t b e in g T T F and te tra m e th yl am m o niu m ca tion s, w h ic h give
s u p e rc o n d u c tin g co m p le xe s.
T h e se co m p le xe s are u s u a lly s y n th e s is e d by a
m e ta th e s is re a ctio n b y s lo w in te rd iffu sio n , in a th re e c o m p a rtm e n t "H -tu b e "
u n d e r an in e rt a tm o sp h e re , o f sa tu ra te d a c e to n itrile s o lu tio n s o f th e co u n te r
cation ,
e.g.
(T T F )3(B F 4)2,
and
th e
a p p ro p ria te
m etal
sa lt
(n -B u 4N + )2
[M (d m it)2]2_. O r a lte rn a tiv e ly by e le c tro c ry s ta llis a tio n in a U -tu b e in a m ethod
s im ila r to th a t d e s c rib e d b e fo re fo r th e ra d ica l ca tio n salts o f B E D T -T T F in the
d o n o rs s e c tio n .131
60
The
firs t
M (d m it)2
T T F [N i(d m it)2] 2 - on th e
a c c e p to r
a p p lic a tio n
to
of 7
e x h ib it
s u p e rc o n d u c tiv ity
k b a r o f p re s s u re .132
w as
At
room
te m p e ra tu re and a m b ie n t pressure, it had a co n d u c tiv ity o f a rt= 3 0 0 S c rrr1
a lo n g th e sta ckin g axis and d isp la ye d m e ta llic b e h a v io u r rig h t do w n to 4 K,
w h e re a max= 1.5 x 1 0 5 S c rrr1, w ith o u t u n d e rg o in g a p ha se tra n s itio n .133 T h e
cry s ta l stru ctu re o f T T F [N i(d m it) 2]2 in d ica te s th a t the e s s e n tia lly p la n a r T T F
a nd N i(d m it)2 m o le c u le s s ta ck in d is tin c t co lu m n s p a ra lle l to th e b axis, w h ic h is
th e d ire c tio n o f h ig h e s t co n d u ctivity.
T h e s e co lu m n s give a lte rn a te s h e e ts of
d o n o r and a c c e p to r m o le cu le s p a ra lle l to th e b ,c plane.
T h e in te ra to m ic
s e p a ra tio n s be tw e e n a d ja ce n t m o le cu le s in e ith e r th e T T F and N i(d m it)2 sta cks
a re not s h o rte r th a n th e sum o f th e van d e r W a a ls ra d ii.133 H o w e ve r th e in te rs ta c k S-S d ista n ce s a re s h o rte r (3 .4 5 - 3 .5 4 A ) th a n the van d e r W a a ls radii
s e p a ra tio n (3 .7 0 A). E ven s h o rte r S-S d is ta n c e s ha ve been fo u n d b e tw e e n the
te rm in a l S atom s o f N i(d m it)2 m o le cu le s and th e S atom s o f th e T T F m o le cu le s
(3 .3 9 A). D e sp ite th is e n h a n ce d in te ra ctio n th e e le c tro n ic stru c tu re o f this, and
o th e r salts, are q u a si o n e -d im e n s io n a l.39
R e p la ce m e n t
T T F [P d (d m it)2] 2 -131
of
Ni
w ith
Pd
to 2 2 0
K,
a t w h ich
se m ic o n d u c tin g state.
th e
TTF
co m p le x
g ives
T h is co m p le x has a room te m p e ra tu re c o n d u c tiv ity of
crrt = 7 5 0 S c rrr1 a lo n g th e sta ckin g axis.
d ow n
in
It e xh ib its a m e ta llike c o n d u c tiv ity
p o in t it u n d e rg o e s
a gra d u a l tra n s itio n
to
a
T h e m e ta llike b e h a v io u r o f th is co m p le x is m a in ta in e d
o n c e it is n o t co o le d b e lo w 2 2 0 K.
C rysta ls w h ich w e re co o le d b e lo w the
tra n s itio n te m p e ra tu re w e re fo u n d to rem a in s e m ico n d u ctin g even a fte r sto ra g e
at room te m p e ra tu re fo r p e rio d s o f up to 12 days.
Such b e h a v io u r is in d ica tive
o f a stru ctu ra l p h a s e tra n s itio n at 2 2 0 K a n d th is w a s co n firm e d by the
o b s e rv a tio n o f 3 d iffe re n t p h a se s by X -ra y d iffra c tio n studie s.
T h e firs t pha se
re fe rs to the m e ta llic pha se, w h ich is th e s tru ctu ra l phase be fo re th e cry s ta l is
co o led.
T h is p ha se is iso m o rp h o u s w ith th e a n a lo g o u s n ickel d e riva tive .
The
se co n d p h a se c o rre s p o n d s to the se m ic o n d u c tin g phase on c o o lin g th e crystal
d o w n to th e
p h a se tra n s itio n
te m p e ra tu re .
A n d fin a lly th e
th ird
pha se
c o rre s p o n d s to w a rm in g th e se con d p h a se b a c k to room te m p e ra tu re , w h ich
g ive s a crystal stru c tu re d is tin c t fro m th a t o f th e firs t phase.
T h e p la tin u m co m p le x, T T F [P t(d m it)2] 3, u n like its n icke l and p a lla d iu m
c o u n te rp a rts, is se m ic o n d u c tin g th ro u g h o u t th e te m p e ra tu re ra n g e 3 0 0 to
100 K and has a room te m p e ra tu re c o n d u c tiv ity o f ju s t a rt = 2 0 S c rrr1.131 T he
s tru c tu re of T T F [P t(d m it)2] 3, like th e sto ich io m e try, is d istin ct fro m th a t o f both
its n icke l and p a lla d iu m d e riva tive s.
It c o n s is ts o f a lte rn a te layers, p a ra lle l to
61
th e ab plane, o f T T F a n d P t(d m it)2 m olecules, th e a c c e p to r la ye r c o n s is tin g of
b o th P t(d m it)2 m o n o m e rs a n d dim ers.
In the a c c e p to r la yers th e m onom ers
a n d d im e rs are sta cke d a lte rn a te ly in colum ns.
T h e tw o P t(d m it)2 u nits o f the
d im e r a re d isto rte d fro m p la n a rity and re su lts in in cre a se d in te rm o le c u la rin te ra to m ic d ista n ce s w ith in a dim er. S-S co n ta cts le ss th a n the van d e r W a a ls
ra d ii a re o b se rve d b e tw e e n m onom ers and d im e rs w ith in a sta ck and w ith in
d im e rs w ith in a s ta ck a n d b e tw e e n e ith e r m o n o m e rs o r dim e rs b e lo n g in g to
a d ja c e n t stacks.
U n u s u a lly the c o n d u c tiv ity is m uch lo w e r th a n a n ticip a te d .
It
h a s b e e n su g g e ste d th a t th is m ay be due to th e o p e n in g o f a band gap at th e
F erm i s u rfa c e as a re s u lt o f th e a lte rn a te sta ckin g o f th e m onom ers a nd dim ers.
It is c le a r th a t the n a tu re o f th e m eta l atom has an im p o rta n t role in d e te rm in in g
th e s tru c tu ra l and p h ysica l p ro p e rtie s o f th e M (d m it)2 accep tors.
S u p e rc o n d u c to rs
b a se d
on
7t-acceptor m o le c u le s
a nd
c lo s e d -s h e ll
c a tio n s h a v e also bee n fo u n d . T h e firs t o f th e se w a s (M e )4N [N i(d m it)2]2, w ith a
s u p e rc o n d u c tin g tra n s itio n u n d e r 3.2 kb a r at T c = 3 .0 K a nd at T c= 5 .0 K u n d e r
7 k b a r o f p re s s u re .39
T h e crysta l stru ctu re c o n s is ts o f shee ts o f N i(d m it)2
m o le c u le s and (M e )4N c a tio n s a lte rn a tiv e ly p ile d up p a ra lle l to each other, w ith
th e c a tio n sh e e ts s e p a ra tin g th e co n d u c tiv e a c c e p to r sheets.
In th e a c c e p to r
shee t, th e m o le cu le s a re sta cke d in 1-D colu m n s w ith th e d ire ctio n o f ad ja ce n t
c o lu m n s at an a n g le o f 52.2 ° to each other.
T h is re s u lts in tw o 1-D Ferm i
s u rfa c e s w ith d iffe re n t o rie n ta tio n s being su p e rp o se d and g ivin g rise to a m u ltiF erm i s u rfa c e w h ich is s ta b le a g a in s t la ttic e -m o d u la tio n w aves.
T h e p a lla d iu m d e riv a tiv e , l3-(M e)4N [P d (d m it)2]2, w a s also fo u n d to be a
s u p e rc o n d u c to r a b o ve 6 kbar.
T=
6 .2
K at 6.5
k b a r.134
The
T h e m id -p o in t tra n s itio n te m p e ra tu re w a s
crysta l s tru c tu re 135 is
(M e )4N [N i(d m it)2]2 e x c e p t fo r th e ca tio n sites.
iso stru ctu ra l w ith
T h e P d (d m it)2 m o le cu le s form
d im e ric 1-D stacks, w ith th e tw o a n io n s fo rm in g a e c lip s e d c o n fig u ra tio n w ith in
th e d im e rs and b e tw e e n th e d im ers the a n io n s are d is p la c e d sid e w a ys w ith
re s p e c t to each other.
T h e Pd atom s w ith in th e d im e rs are also d is p la c e d out
o f th e p la n e o f the m o le c u le by 0 .07 A to w a rd s e a ch other.
T h e re are m any
S -S c o n ta c ts w h ich a re s h o rte r th a n the van d e r W a a ls d ista n ce (3.7 0 A ) along
th e a a n d b d ire c tio n s b u t in te rm o le c u la r tra n s v e rs e in te ra ctio n s are sm all. As
a re s u lt th e com p le x is e s s e n tia lly 1-D. B e cause o f th e stron g d im e ric n a tu re o f
th is co m p le x, in te rm o le c u la r in te ra ctio n w ith in th e d im ers is m uch s tro n g e r than
th e in te r-d im e r, it is s u g g e s te d th a t the c o n d u c tio n ba n d is c o n sid e re d to be
fo rm e d fro m th e H O M O o f M (d m it)2 in stea d o f th e L U M O .134 A t h igh pressure,
th e d im e ric na tu re is d im in is h e d and the LU M O m ay fo rm the c o n d u ctio n band.
62
1.C.7 Fullerenes as Acceptors
The
new est and m ore
u n u s u a l a c c e p to r m olecu les to be
re c e n tly
d is c o v e re d are the sp h e ro id a l fu lle re n e s , C 6o (103), o r B u ckm in ste rfu lle re n e , in
p a rticu la r.
T he se a cce p to rs a re p a rtic u la rly in te re stin g in that, a lth o u g h they
a re not p la n a r like c o n v e n tio n a l o rg a n ic a cce p to rs, th e y do ha ve ra d ia tin g
71-o rb ita ls w h ich fo rm a 3-D e le c tro n ic p a th w a y w h ic h can form bo th c o n d u c tin g
a n d su p e rc o n d u c tin g c o m p le xe s w ith b oth a lk a li a nd a lka lin e e a rth m e ta ls .136
T h e h ig h e s t tra n s itio n te m p e ra tu re T c to d a te is fo r the cesium d o p e d C 6o,
C s 3C 6o, w h ic h has a T c = 4 0 K u n d e r a p re ssu re o f 15 k b a r.10 T h e a b ility o f
fu lle re n e s to fu n ctio n as a c c e p to rs h a s be e n a ttrib u te d to th e ir in te rm e d ia te
h y b rid is a tio n and surfa ce to p o lo g y . B e ca u se o f the cu rva tu re o f the surfa ce, a b o n d s at th e co n ju g a te d c a rb o n d e v ia te fro m p la n a rity so th a t a 7t-bond is no
lo n g e r o f pu re ly
p -o rb ita l
c h a ra c te r and
c o m p le te ly s -o rb ita l character.
o f th e fu lle re n e s b e in g
d ia m o n d (s p 3) i.e. sp 2-28.
th e
a -b o n d s
no
lo n g e r co n ta in
T h is re h y b rid is a tio n re su lts in th e h y b rid is a tio n
in te rm e d ia te
b e tw e e n th a t o f g ra p h ite
(s p 2) and
T h is m e a n s th a t as a c o n se q u e n ce o f th e lo w er
e n e rg y 2 s -o rb ita l m ixing w ith th e 7i-orbital, th e m o le cu la r o rb ita ls w h ic h form
fro m th e se re h yb rid ise d rc-orbitals w ill ha ve e n h a n ce d e le ctro n affin ity.
In
a d d itio n to this, the fu lle re n e s , in o rd e r to fo rm th e ir sp h e rica l stru ctu re , are
m a d e up o f b e n z e n e -lik e 6 -m e m b e re d rin g s and co n ju g a te d 5 -m e m b e re d rings.
It is th e p re se n ce o f th e s e 5 -m e m b e re d rin g s a nd th e ir a s s o c ia te d s ta b ility
w h ic h re s u lts in th e fu lle re n e s h a v in g six lo w -lyin g trip ly -d e g e n e ra te m o le c u la r
o rb ita ls .
(103)
T h e a c c e p to r a b ility o f C 60, d e te rm in e d by so lu tio n e le c tro c h e m is try and
re fe re n c e d to the s ta n d a rd c a lo m e l e le ctro d e , g a ve a firs t re d u c tio n p o te n tia l,
E 11/2= -0 .3 9 9 V in d ic h lo ro e th a n e .
on
c o n v e rs io n u s in g
T h is ga ve a E 11/2= -0 .4 2 2 V in a c e to n itrile ,
an e m p iric a l
re la tio n be tw e e n the
63
E recj0x v a lu e s
in
a c e to n itrile and d ic h lo ro e th a n e fo r a nu m b e r o f a c c e p to rs and don ors.
T h is
re d u c tio n p o te n tia l su g g e s ts th a t C 60 is a m uch p o o re r a c c e p to r than T C N Q
(E 11/2= 0 .2 2 2 V in a c e to n itrile ).137 T h is po o r a c c e p to r a b ility w a s a lso re fle cte d
in its in a b ility to fo rm C -T co m p le x e s w ith a w id e v a rie ty o f o rg a n ic d o n o rs
in c lu d in g som e d e riv a tiv e s o f T T F .137 W h ile som e do n o rs, e.g. o c ta m e th y le n e T T F a n d B E D T -T T F , d id g ive b la c k crystals, w ith w h a t se e m s to b e C -T ban ds
a ro u n d 12 x 103 cm -1, th e ir IR sp e c tra su g g e st th e y h a v e n e u tra l io n ic ity and
a re in s u la tin g (O M T T F c o m p le x h a s a rt= 10-8 Scnrr1). T h is su g g e s ts th a t m uch
s tro n g e r o rg a n ic d o n o rs a re n e c e s s a ry to form c o n d u c tin g C -T com ple xes.
Chapter 2
Results and Discussion
65
2.A.1
In tr o d u c tio n
It can be seen in C h a p te r 1 th a t m ost of th e a c c e p to rs sy n th e s is e d in
re ce n t ye a rs have been d e riv a tiv e s of T C N Q , the m ajority of th e s e having jre x te n d e d system s.
T he re m a in d e r are th e h e te ro c y c lic -T C N Q
u su a lly d e riv a tiv e s of co m p o u n d s (1 0 5 -1 0 7 ).
a n a lo g u e s,
T h e s e co m p o u n d s , in clu d in g
(109), are sa id to be iso-rc-e lectronic w ith T C N Q by virtu e of th e p re s e n c e of a
h e te ro a to m w ith in the ring system .
T h e lo ne p a ir of p-rc e le c tro n s on the
h e te ro a to m is capa ble of co n trib u tin g to the m e s o m e ric bo n d syste m .
NC.
N C . ^C N
>
XN
NC
s
>=<
NC
NC
°N
^NR
>=<
S
on
NC
'C N
(105) X = S
(109)
''C N
(110) R= H
(111) R= Me, Et, acyl, etc.
(106) X= Se
(107) X = 0
(108) X= NR
T o date th e re have been no re p o rts of th e n itro g e n a n a lo g u e of (105),
system (108).
O ne- a nd tw o -e le c tro n re d u ctio n of (1 0 5 -1 0 8 ) sh o u ld re su lt in
the fo rm a tio n
of a 4 n+ 2
ji-e le c tro n
c y c lic
p la n a r system
w h o se
po te n tia l
a ro m a tic ity sh o u ld re su lt in a lo w e r re d u ctio n p o te n tia l and a s ta b ilis in g e ffe ct
on th e a n io n radical.
S ince the d e g re e of a ro m a tic ity d e c re a s e s in the o rd e r
th io p h e n e > p yrro le > fura n, the a c c e p to r a b ility of (108) s h o u ld be e xp e cte d to
be at le a st in te rm e d ia te b etw e en th a t of (105) and (107).
a d v a n ta g e
of the p yrro le
system
w o u ld
be th e
a b ility to
A n a d d itio n a l
“fin e
tu n e ” the
p ro p e rtie s of the p y rro lid in e ring by va ry in g th e s u b s titu e n ts at th e nitroge n.
T his w o u ld also allow fo r the p o s s ib ility of a tta ch in g a v a rie ty of fu n c tio n a litie s ,
w h ich can in cre a se th e s o lu b ility o f th e s e co m p o u n d s, in a d d itio n to the
in tro d u c tio n of p o ly m e ris a b le g roup s w h ich m ay in cre a se th e ir a p p lic a tio n s .
W ith th e s e p o s s ib ilitie s
in m ind it w as in te n d e d to
in v e s tig a te the
s y n th e s is of the is o in d o lin e a n a lo g u e of (108), (110), a nd its A /-substituted
d e riv a tiv e s (111), w h ich are iso-7t-ele ctronic w ith the T C N Q d e riv a tiv e , ben zoT C N Q (112).
T h e se co m p o u n d s w e re of in te re s t in o rd e r to d e te rm in e the
e ffe c ts of W -substitution on e le ctro n a c c e p to r a b ility and on th e fo rm a tio n of C -T
tra n s fe r c o m p le xe s w ith va rio u s do n o rs, w h o se e le ctrica l p ro p e rtie s w o u ld be of
in te re st.
C o m po und
(110)
sh o u ld
form
66
a
10
n -e le c tro n
is o in d o le ,
or
b e n zo [c]p yrro le , in te rm e d ia te on o ne - and tw o - e le ctro n re d uctio n.
se rie s b e n zo [c]fu ra n
(113a), b e n z o [c ]p y rro le
O f the
(1 1 3 b ) and b e n zo [c]th io p h e n e
(1 13c), (1 13b) has bee n ca lcu la te d to be th e m o st a ro m a tic .138
fr o
(113a)
The
s u lp h u r
CO
NH
(113b)
a n a lo g u e
of
(110),
(113c)
com pound
(114)
has
been
p re vio u sly
re p o rte d 139 a n d c y c lic v o lta m m e try stu d ie s s h o w e d tw o reversible redox w aves.
C o m p o u n d (114) w a s s y n th e s is e d fro m (115) in 5% y ie ld by w a rm in g (115) w ith
1 ,8 -d ia z a b ic y c lo [5 .4 .0 ]u n d e c -7 -e n e , (D B U ), in D M F o r a lte rn a tiv e ly , in 25%
yie ld,
from
(115)
v ia
the
d ic h lo rid e
(116)
w h ich
w as
tre a te d
with
te tra c y a n o e th y le n e o xid e (T C N E O ), S ch e m e 2.01.
(116)
S ch e m e 2.01
We
d e riv a tiv e s
in v e s tig a te d tw o p o ssib le ro utes to
(111).
The
first
in vo lve d
th e
(110) and its /V-substituted
K noevenagel
c o n d e n sa tio n
of
m a lo n o n itrile w ith a p h th a lim id e , e.g. /V -m e th ylp h th a lim id e (117), S chem e 2.02.
T h is route w a s in itia lly c o n s id e re d a ttra c tiv e as a re a d ily a c c e ssib le su p p ly of
sta rtin g m a te ria ls, th e A /-substituted p h th a lim id e s , w a s a va ila b le .
T he se co n d route in v e s tig a te d in v o lv e d th e co n d e n s a tio n reaction of
m a lo n o n itrile w ith th e im id in e s (118a) and (1 1 8 b ) to give (110), S chem e 2.03.
/V -S ubstitution re a c tio n s of (110) w e re th e n in ve stig a te d .
67
NCL .CN
o
NMe
+
2C H 2(CN)2
NMe
O
NC
CN
NC.
.CN
(117)
S ch em e 2 ,0 2
NR
NH
+
*■
2 C H 2(CN)2
NH
NH
NC
CN
(118) a: R= H
b: R= Ph
S ch e m e 2.03
In th is C h a p te r th e re su lts of th e s e in v e s tig a tio n s are d is c u s s e d as w ell
as th e re a c tiv ity of th e s a lt (119) w ith v a rio u s am ines. T h e fo llo w in g C hapters,
th re e and fo u r re s p e c tiv e ly , w ill d e a l w ith the d e te rm in a tio n of th e e le ctro n a c c e p tin g
a b ility
of
th e
a c c e p to rs
(110),
a nd
(111,
R=
M e),
by
cyclic
v o lta m m e try and a s tu d y o f th e ir c h a rg e -tra n s fe r p rope rties.
NC^ XN
NC
CN
(119)
2.A.2 Knoevenagel Condensations of A^Methylphthalimide
2.A.2.1 The Knoevenagel Reaction
T h e K n o e v e n a g e l c o n d e n s a tio n is e ffe cte d by tre a tin g a ca rb o n y l with
an a ctive m eth yle n e c o m p o u n d , u s u a lly in th e p resen ce of at le a st a c a ta lytic
a m o u n t of base o r s o m e tim e s a cid .
T he active m e th yle n e g ro u p u su a lly
c o n ta in s tw o e le c tro n -w ith d ra w in g gro u p s, a lth o u g h the c o n d e n s a tio n can be
e ffe cte d using a s tro n g base w h e n o n ly one s tro n g ly e le ctro n -w ith d ra w in g
g ro u p is presen t.
T h e a ctive m e th yle n e co m p o u n d s can in c lu d e m alonates,
68
a c e to a ce ta te s, a ce to n itrile s, m a lo n o n itrile , 1 ,3 -d io n e s and b a rb itu ric acid.
A
v a rie ty of a ld e h yd e s can be used fo r th e s e re a c tio n s but the use of k e to n e s is
lim ite d due to th e ir lo w e r reactivity.
T h e ca ta lysts used are of g re a t im p o rta n c e .
in c lu d e
prim ary,
s e co n d a ry
and
te rtia ry
a m in e s
T h e m ore co m m o n ones
or
th e ir
c o rre s p o n d in g
a m m o n iu m salts. By fa r the m ost w id e ly used c a ta ly s ts are p yrid in e , a lo n e o r in
th e p re se n ce of a sm all am o u n t of p ip e rid in e , and a m m o niu m s a lts such as
a m m o n iu m or p ip e rid in iu m acetate.
T h e use of the Lew is a cid tita n iu m te tra c h lo rid e in th e p re s e n c e of
p y rid in e , know n as L e h n e rt's re age nt, in te tra h y d ro fu ra n o r 1 ,4 -d io xa n as
s o lv e n t, has pro ve d to give e ffe ctive y ie ld s of th e o le fin d e riv a tiv e s fo r re a ctio n s
w ith le ss re a ctive ke to n e s .73
Tw o d iffe re n t m echanism s, d e p e n d in g m a in ly on th e ba se used , have
b e e n p ro p o s e d 140 fo r the re a ctio n of an a ctive m e th yle n e g ro u p w ith a ca rb o n yl
g ro u p .
O ne
m echanism ,
the
H a h n -L a p w o rth
m echan ism ,
p o s tu la te s
the
fo rm a tio n of an in te rm e d ia te fi-h y d ro x y a d d u c t (120), S chem e 2.04.
T his
m e ch a n ism is su g g e ste d fo r bases such as te rtia ry a m in e s and p y rid in e .
The
p -h y d ro x y a d d u ct (120) is also fo rm e d as the in te rm e d ia te w h en th e s o d iu m salt
of th e active m eth ylen e c o m p o u n d is used.
K n o e ve n a g e l su g g e ste d th a t w h en p rim a ry a nd s e c o n d a ry a m in e s are
u se d as ca ta lysts, the co n d e n s a tio n of th e a ld e h yd e a nd the a m in e ta k e s place
firs t to give an im inium sa lt (121) w h ich th e n re a cts w ith th e a c tiv e m eth yle n e
co m p o u n d , S chem e 2.04. T h is is th e n fo llo w e d by e lim in a tio n of th e a m ine .
O
II
CH2
R C 'R
Y
Y
Y
OH
y - b w
X
R
►
Hahn-Lapworth
X
R
FT
( 120 )
O
II
R .
,C .
R
+
R'
H N R "2
^
+
CH2X'
R M
)= K
R
Y
N R "2
y - t i ir>
X
R"
(121)
Scheme 2 .0 4
69
R
Knoevenagel
It has been sh o w n th a t w e a k base s pro d u cin g so lu tio n s o f pH 7 .5-8.0
are th e m o st e fficie n t.
H ow ever, w h en m a lo n o n itrile is used w ith stro n g e r
base s to e ffe c t m ore rapid con d e n sa tio n , th e yie ld is fo u n d to be lo w er b eca use
o f te lo m e risa tio n o f th e m alon onitrile.
a m ine s
In g e n eral, th e p re se n ce o f te rtia ry
in K n o e ve n a g e l co n d e n sa tio n s, w ith
o r w ith o u t acid,
ca u se s the
reaction to p rocee d via th e p-hydroxy in term ediate . For prim a ry and se co n d a ry
a m in e s
th e
tw o
m e ch a n ism s
com pete,
th e
fo rm a tio n
of
the
¡m inium
in te rm e d ia te being d e p e n d e n t on the bulkin e ss o f th e a m ine and the carbon yl
co m pou nd.
W h ile
reports
o f th e
K n o e ve n a g e l
reaction
o f activa te d
m e th yle n e
c o m p o u n d s w ith an e xte n sive range o f a ld e h yd e s and keto n e s are num erous,
such re a ctio n s w ith p h th a lim id e s have not been reported.
A se arch o f the
ch e m ica l lite rature to d a te has yie lde d reports o f tw o a tte m pted K n o e ve n a g e l
re a ctio n s w ith the related co m pou nd p h th a lic a n h y d rid e .141’ 142
T h e firs t o f th e s e reported th e reaction o f e th y lc y a n o a c e ta te w ith p h thalic
a n h y d rid e
in
b e n ze n e
using
sodium
as
th e
cy a n o (p h th a lid y lid e n e )a c e ta te (122) in 9% y ie ld .141
p re v io u s ly
re p o rte d
by
S orm
ca ta lyst
to
g ive
ethyl
This m ethod had been
et a /.143 w ith o u t a n y m ention
o f yie ld
or
s te re o ch e m istry. In an a tte m p t to in crea se th e yield, trie th yla m in e w a s used as
th e ba se in to lu e n e . T h is ga ve the b e n zo fu lva le n e d e riva tive (123).
NCx .C 0 2Et
O
O
(122)
I
i) - C O N H 2
NC
CH2CN
NCM
NH2
OH
(123)
(124)
In an e ffo rt to syn th e sis e (111, R= Me), th e K n o e ve n a g e l reaction of
m a lo n o n itrile w ith A /-m ethylphthalim ide w a s a tte m p te d using a va rie ty o f bases,
se e S ch e m e 2.02. T h e s e w e re sodium , trie th y la m in e and sodium hydride. T he
initial re a ctio n c o n d itio n s used w e re based on th o se reported by R e n fre w and
B o sto ck fo r th e re a ctio n o f e th ylcya n o a ce ta te w ith p h th a lic a n h y d rid e .141
W h e n so d iu m w a s used as th e base a co m p le x m ixture o f p ro d u cts w as
o b ta in e d and from th is a sm all q u a n tity o f th e m a lo n o n itrile dim er, 2 -a m in o -1 p ro p e n e -1 ,1 ,3 -tric a rb o n itrile (124) w as iso lated and its id e n tity co n firm e d by
co m p a riso n w ith d a ta .144 T h e d im e r (124) had p re vio u sly been syn th e sise d by
C a rb o n i
et a /.144(a) in a very sim ila r m a n n e r by tre a tin g
70
a
so lu tio n
of
m a lo n o n itrile in e th e r o r te tra h yd ro fu ra n w ith so d iu m
and
h ydrolysing the
re su ltin g solid w ith a stron g m ineral acid.
T h e a lte rn a tive m eth od re p o rte d ,141 using trie th y la m in e as base fo r the
re a ctio n o f e th y lc y a n o a c e ta te w ith p h th a lic an h yd rid e , w a s also a tte m p te d for
th e
reaction
of
m a lo n o n itrile
c o m p le x ity o f th e reaction
a tte m p te d .
w ith
/V -m ethylphthalim ide,
m ixture form ed,
iso latio n
but
d ue
to
the
o f p rodu cts w a s not
R e n fre w a nd B o sto ck also reporte d th a t th e K n o e ve n a g e l reaction
o f p h th a lic a n h yd rid e w a s a tte m pted w ith o th e r a ctive m e th yle n e co m p o u n d s
in clu d in g
m a lo n o n itrile ,
e th ylcya n o a ce ta te ,
but
under
o n ly
th e
stated
sam e
th a t
co n d itio n s
no
p ro d u cts
as
th o se
related
to
fo r
the
b e n z o fu lv a le n e (123) w e re isolated.
W h e n th e K n o e ve n a g e l reaction w a s a tte m p te d using sodium h ydrid e as
th e base an o ff-w h ite solid w a s recovered w hich, on the basis o f its spectra,
w a s p ro b a b ly th e so d iu m s a lt in te rm e d ia te (125).
T h is solid w a s o b ta in e d by
tritu ra tio n w ith e thyl a c e ta te o f the oil o b tained on e va p o ra tio n o f th e reaction
so lvent.
A tte m p ts to re crysta llise the solid fa ile d due to its in so lu b ility in m ost
o rg a n ic solvents.
It could be dissolve d in boiling e th a n o l o r m eth a n o l but this
resulted in the o b se rva tio n o f fu rth e r p rodu cts by TLC .
T he sa lt w as fo u n d to
be re a d ily so lu b le in w a te r giving an ora n g e /re d solution.
T h e 1H NM R
s p e ctru m o f (125) sh o w e d a broad one proton NH m u ltip le t
o
o
(125)
(126)
at 8.0 8 ppm , a fo u r pro to n a ro m a tic m u ltip le t be tw e e n 7 .60 and 7.2 7 ppm and a
th re e proton do u b le t, J= 4 .9 Hz, at 2.6 9 ppm . T he 13C N M R sp e ctru m show ed
a m eth yl carbon a b so rp tio n at 26 .2 ppm , the C2 carb o n a b so rp tio n o f th e 2,2d ic y a n o v in y lid e n e g ro u p at 48 .8 ppm , tw o cya n o a b so rp tio n s at 120.9 and
122.07, and six a ro m a tic a b so rp tio n s betw e en 127.0 and 140.0 ppm . T h e 2,2d ic y a n o v in y lid e n e C-] carbon and carb o xa m id e carb o n a b so rp tio n s w e re found
a t 168.41
and 189 .4 7 ppm respectively.
T h e IR sp ectrum co n firm e d the
p re se n ce o f a m id e NH, cyano, and a m ide ca rb o n yl a b so rp tions.
O n d isso lvin g th e so dium salt (125) in w ater, and acidifyin g w ith 10%
h y d ro c h lo ric acid, a sm all q u a n tity o f an o ff-w h ite solid p re cip itated.
71
T h is w as
filte re d o ff and re crystallised from ethanol, giving th e m e th yla m m o n iu m salt
(126), w h o se stru ctu re w a s co n firm e d by spectral and e le m e n ta l analysis.
T h e 1H N M R sp e ctru m o f th is co m pou nd, in D M S O -d 6, w a s identical to
th a t o f th e sodium sa lt (125) but w ith an a d d itio n a l th re e proton m ethyl sin g le t at
2 .3 4 ppm and a broad th re e proton singlet, in fring ing on th e fo u r proton
a ro m a tic m ultiplet, at 7.5 0 ppm , arising from the m e th yla m m o n iu m group . A s in
th e 1H N M R sp ectrum fo r th e so d iu m salt, a broad one proton m u ltip le t a t 8.10
ppm , and a th re e proton do u b le t, J= 4.9 Hz, at 2 .6 8 ppm w e re obse rve d. W hen
th e 1H N M R sp e ctru m w a s m e a su re d in m e th a n o l-d 4 th e broad p ea k ce n tre d at
7 .5 5 ppm and th e a m id o NH at 8.06 ppm d isa p p e a re d and the d o u b le t
o b se rve d at 2.6 8 ppm a p p e a re d as a singlet.
T h e red filtrate re m a in in g on rem oval o f th e m e th yla m m o n iu m sa lt (126),
fro m th e a cidifie d so lu tio n , w a s e xtra cte d w ith e thyl acetate. T h is yie ld e d a red
oil w h ich w as fo u n d to be a co m p le x m ixture o f p ro d u cts w h o se co m p o n e n ts
could not be iso lated in a pure sta te by colum n ch ro m a to g ra p h y.
T h e e thyl a c e ta te filtra te rem a ining from th e tritu ra tio n o f th e so dium salt
yie ld e d u n rea cted A /-m ethylphthalim ide.
S ince a cid ifica tio n o f th e sodium salt (125) fa iled to yield the desired
co m p o u n d , rin g -clo su re w a s atte m p te d by hea ting th e so lu tio n u n d e r reflux.
T h e re a ctio n w a s ca rrie d o u t as before, fo llo w e d by heating u n d e r reflux w hen
all th e m a lo n o n itrile had been added.
T h e w h ite solid w h ich pre cip ita te d on
co o lin g w a s filte re d o ff and w a s fo u n d to be un ch a n g e d sodium salt (125).
C o n ce n tra tio n o f th e filtra te gave a red oil fro m w h ich tw o p ro d u cts w e re
o b ta in e d .
T h e first, a g re y crysta llin e solid, w a s ob ta in e d from a w h ite solid
w h ich pre cip ita te d fro m an e thyl acetate so lution o f the red oil on acidifica tion.
O n a tte m p tin g to re crysta llise th e w h ite solid fro m boiling e thyl a ce ta te an
in so lu b le g rey solid re m a in e d .
T his w a s rem o ved fro m th e hot so lu tio n by
filtra tio n and id entified as th e m e th yla m m o n iu m sa lt (126). A sm all q u a n tity o f
a n o th e r w h ite p ro d u ct w a s ob ta in e d from the filtrate . T his w as id entified as the
p s e u d o a n h yd rid e 3 -(d ic y a n o m e th y lid e n e )p h th a lid e (127) by co m p a riso n o f its
N M R and IR sp e ctra w ith th o se in the lite ra tu re .142
T h e pse u d o a n h yd rid e
(127) has bee n reporte d b e fo re by M oore and J i-H e u n g .142
T h e y fo u n d th a t
th e related K n o e ve n a g e l reaction o f m a lo n o n itrile w ith p h th a lic a n h yd rid e using
d iis o p ro p y la m in e (D IP A ) as the base gave the sa lt (128) w h ich on reaction with
p h o s p h o ro u s o xy c h lo rid e ga ve th e pseu do a n h yd rid e (127), S ch e m e 2.05.
72
NC
CN
0
2 DIPA
o r
°
+
° ’ 2 DIPAH+
c h 2(cn)2
o-
THF
o
o
(128)
rir
POCI3
ON
M r.
O
(127)
S ch e m e 2.05
T h e 1H N M R s p e ctru m of (127) sh o w e d a fo u r pro to n a ro m a tic m u ltip le t
b e tw e e n 8.11 and 8.44 ppm . T h e 13C N M R sp e ctru m sh o w e d the p re se n ce of
th e d icy a n o m e th y le n e ca rb o n a b s o rp tio n at 6 5 .1 5 ppm , tw o cyano a b so rp tio n s
at 110.4 and 111.9 ppm , six a ro m a tic a b s o rp tio n s b etw e en 125.9 a nd 137.4
ppm , th e 2 ,2 -d ic y a n o v in y lid e n e
ca rb o n a b so rp tio n at 162.4 ppm and the
c a rb o n y l a b so rp tio n of th e la cto n e at 170.4 ppm .
It w a s hoped th a t a c id ific a tio n of th e so d iu m salt (125) w o u ld yie ld th e Ns u b s titu te d pseu do p h th a lim id e (129), S chem e 2.06.
H o w e ve r it is a p p a re n t
fro m th e results th a t in s te a d of rem o val of a m o le cu le of w ater, a m o le cu le of
th e a m in e is lost on rin g -c lo s u re to give the p se u d o a n h yd rid e (127). T h is m ost
p ro b a b ly o ccurs via a tta c k by th e e n o lic OH at the a d ja ce n t am ido g ro u p of
(130) o r a lte rn a tiv e ly , u n d e r the a cid ic co n d itio n s, at the e le ctro n d iffid e n t
im in iu m
carbon
of
(131),
S ch e m e
2.07,
re su ltin g
in
the
e lim in a tio n
of
m e th yla m in e and the fo rm a tio n of (127). T h e m e th yla m in e re le a se d d u rin g the
fo rm a tio n of (127) is re s p o n s ib le fo r the fo rm a tio n of th e m éth ylam m o niu m salt
(126). S uch a m e ch a n ism w o u ld exp la in the p ro d u cts o b ta in e d in th is reaction.
O
O
(125)
(129)
Scheme 2.06
73
NC^ XN
O' +Na
NHMe
(130)
I
NC.
I
XN
N+HMe
LA
* NH2Me
S ch em e 2.07
S tu d ie s on the n u c le o p h ilic a tta ck by a m in e s on the pse u d o a n h y d rid e
(127) at room te m p e ra tu re have bee n re p o rte d .142
It w a s fo und, on fo llo w in g
th e re a ctio n by N M R sp e ctro s c o p y , th a t n u c le o p h ilic a tta ck o ccu rre d at the
ca rb o n y l, ra th e r th a n th e 2 ,2 -d ic y a n o v in y lid e n e C-i ca rb o n , re su ltin g in ringo p e n in g to give an a c id -a m in e salt. T h is s lo w ly d is s o c ia te d to th e in te rm e d ia te
(132) w h ich th e n u n d e rw e n t s u b s e q u e n t im id is a tio n , S chem e 2.08.
It w a s
p o s tu la te d th a t e lim in a tio n of m a lo n o n itrile a n io n ra th e r th a n h yd ro xid e w as
fa v o u re d by the e n h a n c e d s ta b ility g ra n te d to th e le a vin g g ro u p by th e tw o
e le c tro n -w ith d ra w in g n itriles.
74
NC.
NC .
XN
O
NC^ X N
XN
OH
O
NHR
NHR
O
O
(132)
(127)
I
O
+
CH2(CN)2
O
S ch em e 2.08
T h is w a s fu rth e r s u p p o rte d by th e d is c o v e ry th a t th e re a ctio n of a n ilin e w ith
(h y d ro x y p h e n y lm e th y le n e )p ro p a n e d in itrile
(133)
g a ve
b e n z a n ilid e
(134)
on
hea ting the salt in itia lly fo rm e d at e le v a te d te m p e ra tu re s ,145 S ch em e 2.09.
NCL
XN
(133)
(134)
S ch e m e 2.09
O u r fin d in g s show th a t an a lte rn a tiv e rin g -c lo s u re to th a t re p o rte d fo r
in te rm e d ia te (132) can a lso occur, y ie ld in g th e p se u d o a n h yd rid e (127).
e x p la n a tio n fo r th is m ay be a ttrib u te d to the a c id ic co n d itio n s.
c o n d itio n s
it is p o s s ib le
th a t th e
O ne
U n d e r such
enol ta u to m e r of in te rm e d ia te
(130) is
p ro m o te d , and the p o s s ib ility of the fo rm a tio n of the ¡m inium in te rm e d ia te (131 ),
h aving a m ore e le ctro n d e fic ie n t ca rb o n than th a t of th e u n p ro to n a te d am ide,
m ay fa v o u r n u c le o p h ilic a tta c k by the enol O H at th e ca rb o xa m id e g ro u p to
y ie ld (127).
T he c o n d itio n s used by M oore w e re in esse n ce b a sic and so
in te rm e d ia te (132) m ay have fa vo u re d the keto form , due to the e n h a n ce d
d e lo c a lis a tio n g ra n te d by th e tw o nitrile s, m aking th e a m ide nitroge n th e b e tte r
n u c le o p h ile
re su ltin g
in th e
fo rm a tio n
p h th a lim id e .
75
of th e
co rre s p o n d in g
A/-substituted
2.A.2.2 Knoevenagel Condensations using Titanium Tetrachloride
T he
m ost o b vio u s p ro b le m
in try in g to c a rry o u t the
K n o e ve n a g e l
c o n d e n s a tio n w ith p h th a lim id e s w a s to e n co u ra g e th e e lim in a tio n of w a te r and
th u s p re ve n t ring o p e n in g .
A /-m ethylphthalim ide
(117)
In an e ffo rt to p o ssib ly a ch ie ve th is, th e reaction of
w ith
te tra c h lo rid e w as in v e s tig a te d .
m a lo n o n itrile
in
the
p re se n ce
of titaniu m
T ita n iu m te tra c h lo rid e , in th e p resen ce of
p y rid in e , know n as L e h n e rt's re a g e n t, has been use d to e ffe ct d e h yd ra tio n of
a m id e s to n itrile s .146 T h e re are a lso several re p o rts of tita n iu m te tra c h lo rid e
be in g used to e ffe ct K n o e ve n a g e l co n d e n s a tio n s at s te ric a lly h in d e re d ketones,
by a id in g the e lim in a tio n of w a ter, to syn th e sise e le ctro n a c c e p to rs .147
te tra s u b s titu te d
b e n z o q u in o n e s
d ic y a n o m e th y lid e n e
d e riv a tiv e s
(135)
have bee n
(136)
using
re p o rte d 120 to
L e h n e rt's
re a g e n t
The
yie ld the
in
dry
d ich lo ro m e th a n e , S ch em e 2.10, a nd (138) has been s y n th e s is e d from (1 3 7 )95
by refluxin g in p yridine, S ch e m e 2.11.
NC
R1
CN
TiCI4/ Pyridine
►
R2
A
'
0
CH2(CN)2
R T R2
o
(136)
(135)
r 1 = r 2 = r 3 = r 4 = Me
R1 = H , R 2 = R3 = R4 = Me
R1 = r 2 = h , R3 = R4 = -S-(CH2)2-S-
S ch e m e 2.10
CH2(CN)2
TiCI4/ Pyridine
(138)
R= H ,C H 30.(-C H =C H -)2
S ch e m e 2.11
The
K n o e ve n a g e l
c o n d e n s a tio n
L e h n e rt's re a g e n t w as in v e s tig a te d .
of
m a lo n o n itrile
w ith
(117)
using
T re a tm e n t of (117) w ith m a lo n o n itrile and
76
L e h n e rt's re a g e n t in dry d ic h lo ro m e th a n e at room te m p e ra tu re did not give any
p ro d u c ts
and
o n ly
u n re a cte d
/V -m e th ylp h th a llm id e
was
a lte rn a tiv e , a nd m ore vig o ro u s p ro c e d u re atte m p te d ,
re a ctio n u n d e r reflux fo r 14 h ou rs in d ry p y rid in e .
reco ve re d .
in v o lv e d
An
hea ting the
A sm all a m o u n t of a w hite
s o lid w a s filte re d from the hot s o lu tio n and p y rid in e w a s d is tille d fro m th e filtra te
to c o n c e n tra te it to one fifth of its vo lu m e . T h is y ie ld e d a c ry s ta llin e s o lid w hich
was
h ig h ly
hyg ro sco p ic,
im m e d ia te ly.
and
w h ic h
fo rm e d
an
o ily
red
liq u id
O n a cid ific a tio n th is y ie ld e d A /-m e th ylp h th a lim id e .
alm ost
T h is w hite
s o lid w a s tita n iu m d io xid e and m ay have fo rm e d d ue to th e p y rid in e not being
to ta lly a n h yd ro u s.
It did not d is s o lv e in w a te r o r a n y o rg a n ic s o lv e n ts and did
not s h o w a n y c h a ra c te ris tic pea ks in its IR sp e ctru m .
O
(139a)
(139b)
T h e fa ilu re of tita n iu m te tra c h lo rid e to e ffe c t c o n d e n s a tio n in th e reaction of
m a lo n o n itrile w ith (117) m ay p o s s ib ly be re la te d to the s ta b ility of th e ch lo rid e
sa lt in te rm e d ia te (139) fo rm e d by c o m p le x a tio n of tita n iu m te tra c h lo rid e at the
ca rb o n y l oxyge n.
T h is m ight be s u ffic ie n tly s ta b ilis e d by d e lo c a lis a tio n of
e le c tro n d e n s ity from th e n itro g e n to re d u ce its re a ctivity to w a rd s a tta ck by a
m a lo n o n itrile anion.
T h e h y g ro s c o p ic s o lid re co ve re d from th e reaction in
p yrid in e m ay p o ssib ly have been th e sa lt (139).
2 .A .3 C o n c lu s io n
T he p ro p e n sity of (117) to u n d e rg o ring o p e n in g on n u c le o p h ilic atta ck
by s o d io -m a lo n o n itrile to give sa lt (125), and th e fa ilu re of th is sa lt to und ergo
ring c lo s u re to the d e sire d A /-substituted pse u d o p h th a lim id e , m akes th is route
n o n -v ia b le fo r the s y n th e s is of /V -substituted d e riv a tiv e s of (110).
are
in te re s tin g
in th a t th e y
sh o w
th a t th e
ring
c lo s u re
O u r results
of th e
p roba ble
in te rm e d ia te (132), p ro p o se d by M o o re fo r the re a ctio n of a m in e s w ith the
p s e u d o a n h yd rid e (127) to give p h th a lim id e s , can a lte rn a tiv e ly , u n d e r th e a cidic
c o n d itio n s of o u r rea ctio n , give th e p se u d o a n h y d rid e (127). A ttem p ts to avoid
rin g -o p e n in g ,
by
e ffe c tin g
c o n d e n s a tio n
te tra c h lo rid e w e re not su cce ssfu l.
77
in
th e
p re se n ce
of
tita n iu m
Section 2.B
2.B.1 Condensation Reactions with Imidines
S ince th e re a ctio n of m a lo n o n itrile w ith A /-m ethylphthalim ide (117) did
not yie ld th e d e s ire d co m p o u n d an a lte rn a tiv e a p p ro a ch to syn th e sise (111)
w a s in ve stig a te d .
T h e p ro p e n s ity of th e e x o c y c lic im in o g ro u p of th e im id ine s
(1 1 8 a and b), the o x o -is o in d o lin e (140) a nd th e s u c c in im id in e (141), to u n d ergo
b a se
co n d e n s a tio n
w ith
p rim a ry
a m in e s
a nd
v a rio u s
a ctive
m eth ylen e
co m p o u n d s w as e x te n s iv e ly in v e s tig a te d d u rin g the 1950s by E lvld g e and c o ­
w o rk e rs .148' 149
NR
NC
NH
CN
(111) R= alkyl etc.
(118) a: R= H
b: R= Ph
(142)
It w a s fo u n d 148 th a t w h ile the im in o g ro u p s w e re re a d ily rea ctive , th e ca rb o n yl
g ro u p s of (140) sh o w e d no te n d e n c y at all to react w ith ba se s w ith the
e lim in a tio n o f w ater.
th e
S im ila r fin d in g s w e re re p o rte d in tw o p a te n ts 150 in w h ich
m o n o c o n d e n s a tio n
p ro d u c ts
fro m
re a c tio n s
w ith
an
a rra y
of
active
m e th yle n e re a g e n ts w e re re c o g n is e d as u se fu l dye in te rm e d ia te s e.g. (142).
S im ila r
m o n o c o n d e n s a tio n
e q u iv a le n ts
had
been
com pounds
p re v io u s ly
as
w e ll
re p o rte d .149'
as
th e ir
151
b is c o n d e n sa tio n
Som e
of
th e se
b is c o n d e n s a tio n co m p o u n d s have o u ts ta n d in g p ig m e n t p ro p e rtie s and have
fo u n d
a p p lic a tio n s
a p p lic a tio n s .150(b)- 153
in
p a in t
m a n u fa c tu re 152
and
e le c tro p h o to g ra p h ic
As a re s u lt q u ite a n u m b e r of p a te n ts 154 have been
p u b lis h e d on th is ra th e r novel c la s s of p ig m e n ts know n as the iso in d o lin e
pig m e n ts.
T h e se is o in d o lin e co m p o u n d s are s yn th e sise d , in high yie ld s and
78
under
m ild
co n d itio n s,
from
the
c o n d e n s a tio n
m e th yle n e co m p o u n d , S chem e 2.12.
of
(118a)
and
an
active
T h e m o n o c o n d e n s a tio n p ro d u ct can be
is o la te d o r re a cte d fu rth e r with m ore a ctive m e th yle n e co m p o u n d .
F or the
sy n th e s is of u n sym m e trica l p igm e nts the m o n o c o n d e n s a tio n p ro d u c t is iso la te d
and th e n re a cte d w ith an a lte rn a tiv e a ctive m e th yle n e c o m p o u n d o r am ino
co m p o u n d .
CONHR
NH
n c c h 2c o n h r
►
NH
n c c h 2c o n h r
NCCH2CONHR
yellow
CONHR
c h 3o 2c
Cl
INU
CONHR
reddishyellow
Cl
(c) R= — /
\-C I
scarlet
S chem e 2.12
T h e is o in d o lin e p ig m e n ts have p ro d u ce d c o n s id e ra b le in te re s t not just
b e ca u se of th e ir fa c ile s yn th e sis from e a sily a v a ila b le raw m a te ria ls but also
b e ca u se of th e b road va rie ty of sh a d e s w h ich are o b ta in a b le .
T h is va rie ty is
not s o le ly due to th e d iffe rin g s u b s titu e n ts but is also due to the va ryin g
m o rp h o lo g ie s of th e co m p o u n d s in th e s o lid s ta te .152
Such crysta l stru ctu re
v a ria tio n s can also a ffe c t the fa s tn e s s p ro p e rtie s of th e p ig m e n ts 152 and the
in te rm o le c u la r fo rce s of a ttra ctio n , such as h yd ro g e n b o n d in g , w h ich in flu e n ce
the im p o rta n t p ro p e rty of in s o lu b ility in th e s e co m p o u n d s.
T h e is o in d o lin e p ig m e n ts have now beco m e a new a re a fo r e xp lo ita tio n
as d ye s tu ffs w ith v a rie d a p p lic a b ility .
T h e se co m p o u n d s sh o w o u tsta n d in g
c o lo u r fa s tn e s s and w h e n m ixed w ith d iffe re n t o rg a n ic and in o rg a n ic pigm ents
give rise to a b road sp e ctru m of sh a d e s and m e ta llic fin is h e s w ith o u tsta n d in g
w e a th e rin g
re sista n ce .
They
have
79
also
fo u n d
a p p lic a tio n s
as
charge
g e n e ra tin g a g e n ts in e le c tro p h o to g ra p h ic tw o -la y e r recording m ate rials. 15°(b).
153
T h e syn th e sis o f (110), by reaction o f (118a) w ith m a lo n o n itrile , w as
p re v io u s ly reported in a French p a te n t151 acco rd in g to S ch e m e 2.13.
It w as
reporte d th a t one m ole e q u iva le n t o f a ce tic acid w as added to ca ta lyse the
re a ctio n d u rin g w h ich th e m o n o co n d e n sa tio n pro d u ct (143) p re cip ita te d from
th e m e th a n o lic so lu tio n and the b is-co n d e n sa tio n pro d u ct (110) re m a in e d in
NC-
XN
2 CH2(CN)2
►
H /methanol
(143)
S ch e m e 2.13
so lu tio n
and
was
p re cip itated
by
a cidifica tion.
We
fo u n d
th a t a
m ore
c o n v e n ie n t and im proved m eth od w a s a ch ie ve d b y using e ith e r (118a), or
( 1 18b), w ith d im e th ylfo rm a m id e as th e solvent.
CN
H2NR
(a) R= H or (b) R= Ph
'CN
NaOMe
(144)
S ch e m e 2.14
C o m p o u n d (118a ) w a s s y n th e s is e d 155 by bub bling a m m o n ia th ro u g h a
m e th a n o lic so lu tio n o f (144), S ch e m e 2.14(a), and its stru ctu re co n firm e d by 1H
and 13C N M R , and IR sp e ctro sco p y.
T h e syn th e sis o f (118b ) w a s carried out
a c co rd in g to a p re vio u sly reported p ro c e d u re 156 w h ich in volve d reacting aniline
w ith p h th a lo n itrile in th e p re se n ce o f a base, sodium m e th o xid e , S ch em e
2.14(b).
Its stru ctu re w a s su p p o rte d by its 1H and 13C N M R sp e ctra and its IR
sp e ctru m .
O n a d d itio n o f th e m a lo n o n itrile to (118a), o r (118b), in D M F at room
te m p e ra tu re ,
an
im m e d ia te
e lim in a tio n o f am m o n ia .
co n d e n sa tio n
reaction
to o k
pla ce
w ith
the
T his g a ve th e a m m o niu m salt o f (110), (119), w hich
w a s iso la te d by p re cip ita tio n w ith chloro fo rm , S ch e m e 2.15.
80
(l) A
2CH2(CN)2
►
or
(2)H*(118) a: R= H
b: R= Ph
S chem e 2.15
T h e 1H N M R sp e ctru m of (119) in p y rid in e -d s d is p la y e d a b ro a d fo u r
pro to n NH s in g le t at 9 .29 ppm a n d tw o sym m e trica l tw o p ro to n a ro m a tic
m u ltip le ts at 7 .3 0 and 8.3 5 ppm . O n th e b a sis o f th e s ym m e trica l n a tu re o f the
p e a ks in the 1H N M R sp e ctru m and th e 13C N M R spectrum , w h ich sh o w e d the
C 2 c a rb o n a b so rp tio n of th e 2 ,2 -d ic y a n o v in y lid e n e g ro u p at 5 4 .6 3 ppm , two
cya n o a b s o rp tio n s at 1 1 6 .2 7 and 11 7 .1 4 ppm , th re e a ro m a tic a b s o rp tio n s at
123.25, 131.04, and 138 .0 ppm , a nd th e 2 ,2 -d ic y a n o v in y lid e n e C i carbon
a b so rp tio n at 172.0 ppm , it w as also p o ssib le th a t th e iso m e ric co m p o u n d (145)
had bee n form ed.
s tru ctu re s .
T he e le m e n ta l a n a ly s is o b ta in e d w as c o n s is te n t w ith both
H o w e ve r in d im e th yl s u lp h o x id e -d ^ , as w ell as th e fo u r proton
s ym m e trica l a ro m a tic m u ltip le t b etw e en 7.58 a nd 8.05 ppm , a fo u r pro to n 1 :1:1
trip le t, (J= 50 Hz), w as o b se rve d at 7.0 7 ppm a risin g from 14N /1H sp in -sp in
co u p lin g , th e 14N n u cle u s having sp in 1 ra th e r th a n a half.
N u cle i w ith spins
g re a te r th a n a half are q u a d ru p o la r a n d g e n e ra lly relax so ra p id ly in a nonc u b ic e n v iro n m e n t th a t all re so lve d c o u p lin g s to them are lost.
H o w e v e r the
a m m o n iu m ca tio n is u n u su a l in that the n itro g e n is in a c u b ic e n v iro n m e n t and
so re la xe s s lo w ly th u s a llo w in g the 14N /1H c o u p lin g s to be re so lve d .
T h e 1H
N M R sp e ctru m of the a m m o n iu m ca tio n in a c id ifie d H20 / D 20 g ive s a J (14N -1H)
~ 52 H z ,157 ve ry s im ila r to th a t d is p la y e d fo r (119) and p ro v id in g co n clu sive
e v id e n c e th a t th e p ro d u c t w a s the
a m m o niu m
iso m e ric c o m p o u n d (145).
(145)
81
sa lt (119) ra th e r th a n the
O f th e tw o m e th o d s ava ila b le fo r th e syn th e sis o f th e a m m o n iu m salt
(145), th e m eth od using (118b) as startin g m ate rial w a s th e preferred , beca use
o f its m ore c o n v e n ie n t syn thesis w h ich did not require th e use o f gase o u s
a m m o nia .
T h e p ro to n a tio n o f (119) to give (110) w a s a chieved by tw o m ethods.
T h e firs t involve d th e p yrolysis o f (119) u n d e r an a tm o sp h e re o f nitroge n, w hich
yie ld e d (110) a s an o ra n g e /b ro w n pow der.
T h e secon d, and m ore c o n ve n ie n t
m eth od, in volve d a cid ifica tio n o f a m e th a n o lic so lu tio n o f (119), by a d d itio n o f
d ilu te h yd ro ch lo ric acid, w h ich g a ve (110) as a fin e y e llo w pow der.
Both th e
o ra n g e /b ro w n solid and th e ye llo w p o w d e r sh ow ed identical IR, 1H and 13C
N M R spectra.
T h e stru ctu ra l a s s ig n m e n t o f (110) w as su p p o rte d by the
re le v a n t IR, 1H and 13C N M R spectra and by e le m e n ta l a n a lysis and m ass
sp e ctro sco p y.
T h e IR sp e ctru m show ed th e p re se n ce o f tw o NH ban ds at 32 4 3 and
318 9 c m '1 and tw o co n ju g a te d nitrile pe a ks a t 22 4 0 and 222 7 c m '1. A large
h yp s o c h ro m ic s h ift in th e m axim um a b so rp tio n o f the sa lt (119) (496 nm)
re la tive to th a t o f th e neutral com p o u n d (110) (408 nm ) in th e U V /visible
sp e ctru m w a s o b se rve d and th is w a s a ttrib u te d to th e lo w er co n ju g a tio n o f
(110).
T h e 1H N M R sp e ctru m show ed tw o m u ltip le ts at 7.79 and 8.1 9 ppm ,
ea ch in te g ra tin g fo r tw o protons, and co rre sp o n d in g to th e a ro m a tic pro to n s o f
th e sym m e trica l product. A broad sin g le t at 4 .8 5 ppm w h ich in te g ra te d fo r one
proton co rre s p o n d e d to th e NH o f th e p yrro lid in e ring. T h e 13C N M R spectrum
w a s c o n s is te n t w ith th e assigned stru ctu re and show ed a to ta l o f seven
d iffe re n t carbon s.
T h e C 2 carbon a b so rp tio n o f the 2 ,2 -d icya n o vin ylid e n e
g ro u p w a s o b se rve d at 5 6 .5 4 ppm , th e tw o cya n o carbon a b so rp tio n s at 114.65
and 115 .66 ppm and th e th re e a ro m a tic ca rb o n a b so rp tio n s at 123.84, 132.83
and
134.90
ppm .
The
o b se rve d at 166.27 ppm .
2 ,2 -d icya n o vin ylid e n e
Ci
carbon
a b so rp tio n
w as
C o m po und (110) w a s hig h ly in so lu b le in m ost
so lve n ts and could o n ly be recrystallised fro m a m ixture o f d im e th ylfo rm a m id e
and m e th a n o l to g ive b rig h t orang e needles.
2.B.2 Synthesis of 2-(3-lminoisoindolin-1-diylidene)propanedinitrile (143)
An
a lte rn a tiv e
sy n th e tic
route
to
(110)
involved
th e
reaction
of
p h th a lo n itrile (144) w ith m a lo n o n itrile in the p re se n ce o f so d iu m m ethoxide.
T his g a ve co m p o u n d (143) in a o n e -p o t synthesis, S ch em e 2.15.
T h e IR, 1H
and 13C N M R sp e ctra and e le m e n ta l a n a lysis w e re co n siste n t w ith th e assigned
stru ctu re .
T h e IR sp e ctru m show ed th e p re se n ce o f a broad NH p ea k at
82
2 ,9 9 0 cm "1 as w e ll as a ca rb o n -n itro g e n d o u b le bond stretch at 1610 c m '1. A
c o n ju g a te d nitrile stretch w a s also a p p a re n t at 222 2 c m '1.
T h e 1H NM R
s p e ctru m sh o w e d th e p resen ce o f tw o broad, o ne proton, NH sin g le ts at 9.95
a nd 3.37 ppm , w ith th e fo rm e r being d ue to the h ighly d e sh ie ld e d im ino proton.
A ls o
p re s e n t w e re
fo u r a ro m a tic
proton
a b so rp tio n s
as
tw o
tw o
proton
m u ltip le ts at 7.7 and 9.95 ppm . T h e 13C N M R sp e ctru m sh ow ed th e presence
o f th e h ig h ly shie ld e d C 2 carbon a b so rp tio n o f th e 2 ,2 -d ic y a n o v in y lid e n e group
a t 59.14 ppm , tw o cya n o carbon a b so rp tio n s at 114.83 and 115.63 ppm , and
fo u r a ro m a tic a b so rp tio n s betw e en 122.91 and 132.0 ppm and tw o m ore at 137
and 171.9 ppm . A n im ino carbon a b so rp tio n w a s o bse rve d at 134.18 ppm and
th e 2 ,2 -d ic y a n o v in y lid e n e C ^ ca rb o n ab so rp tio n at 175.81 ppm .
T h e high
in s o lu b ility o f co m p o u n d (143) in m ost so lve n ts m ade it d iffic u lt to react further.
H o w e ve r reaction o f (143) w ith s o d io -m a lo n o n itrile in boiling m e th a n o l gave the
so d iu m sa lt o f (110), (146), S ch e m e 2.16.
CN
CH2(CN)2
►
CN
NaOMe
NH
(144)
(143)
S ch e m e 2.15
CH2(CN)2
►
NaOMe
(146)
(143)
S ch e m e 2.16
S tru ctu ra l e lu cid a tio n o f (146) w a s m ade on the basis o f IR, 'H and '''C N M R
sp e ctra .
T h e a b s e n c e o f a NH stre tching fre q u e n cy in th e IR sp e ctru m and a
NH a b so rp tio n in th e 1H N M R sp e ctru m w e re th e m ost re m a rka b le diffe re n ce s
b e tw e e n (146) and (110). T h e 1H N M R sp e ctru m o f th e so d iu m sa lt w a s very
sim p le and o n ly sh o w e d tw o s ym m e tric a ro m a tic m u ltip le ts at 7.61 and 8.21
ppm , e a ch in te g ra tin g fo r tw o protons. T he solid w a s heated to 360 °C w ith o u t
m elting , fu rth e r su g g e s tin g th e fo rm a tio n o f a salt.
C o m p a riso n o f th e IR and
1H and 13C N M R sp e ctra o f (146) w ith th a t o f co m p o u n d (146) recovered form
83
th e
a tte m p te d
b e n zo yla tio n
o f (110)
using
ben zoyl ch lo rid e
and
sodium
h yd ro xid e as th e base, see page 88 S e ctio n 2.C, co n firm e d th e structure.
2.B.3 Discussion
T h e fo rm a tio n o f (110) is th o u g h t to o c c u r via th e m e ch a n ism show n in
S ch e m e 2.17. W h e n ( 1 18b) w a s used as th e starting m ate rial th e e lim in a tio n of
a n ilin e w a s o b se rve d
by TLC .
The
isolation o f co m p o u n d
(110) as its
a m m o n iu m sa lt (119) is not su rp rising w h en th e p o te n tia l a cid ity o f (110) is
c o n sid e re d . T h e ca rb o n yl a n a lo g u e o f (110), phthalim id e, is re la tive ly a cidic
NH
NH
NH
▼
S ch em e 2.17
w ith a pK a o f ~ 9.
S tu d ie s o f th e a n a lo g y betw e en o xyge n and C (C N )2 have
been ca rrie d o u t158 and the pK a va lu e s o f C (C N ) 2-H acids are up to 4.5 units
s m a lle r th a n th o s e o f th e co rre sp o n d in g O H acids. S im ila rly co m p o u n d (147) is
fo u n d to be m ore acidic, (pK a= ~ 1 ),159 than its ca rb o n yl e q u iv a le n t b e n zo ic
acid (1 4 8 ),(p K a = 4 .2 ).160
o
(148)
(147)
84
A s a result of the g re a te r e le c tro n e g a tiv ity of the cya n o g ro u p s, c o u p le d with
th e ta c t th a t re so n a n ce s th a t s ta b ilis e th e c o n ju g a te base of an a cid result in
the a cid having a h ig h e r s ta b ility th a n o th e rw is e e xpe cted , It co u ld be expected
th a t (110) w o u ld be even m ore a c id ic th a n p h th a lim id e .
T h e s ta b ility of the
a n io n of (110) is fu rth e r e n h a n ce d by th e p re se n ce of fo u r s tro n g ly electron
w ith d ra w in g g ro u p s in c o n ju g a tio n w ith th e
n itro g e n
of th e
is o in d o lin -1 ,3-
d iy lid e n e system w h ich can give rise to a n u m b e r of d iffe re n t m e som ers, fo u r of
w h ich are show n below in S chem e 2 .1 8 .
T h is a d d itio n a l re s o n a n c e a llo w s fo r
eve n g re a te r d e lo c a lis a tio n of the ch a rg e .
NC^CN
NC
CN
S ch e m e 2.18
S uch e n h a n ce d d e lo c a lis a tio n has g ive n rise to the u n u s u a lly high a c id ity of 2d ic y a n o m e th y le n e -1 ,1 ,3 ,3 -te tra c y a n o p ro p e n e
b e lo w -8.5 and a se co n d pK a at - 2 .5 .161
v e rifie d
by the
a d d itio n
of sodium
(149),
w h ich
has
a firs t pK a
T h e a c id ity of (110) w as sim ply
c a rb o n a te
to
a so lu tio n
of
(110)
in
d im e th y lfo rm a m id e w ith th e im m e d ia te e v o lu tio n of carb o n d io xid e gas.
(a): X+ = Na +
NC+ NEt 2
C = C[CH(CN)2]2
NEt2
NC
(b): X+ =
N, * T
NEt2
1 T /N
NEt2
+
(149)
S alts of co m p o u n d s s tru c tu ra lly s im ila r to (110) have also bee n reported.
G o m p p e r et al. re p o rte d th e s y n th e s is of th e bis a n a lo g u e of (110) as tw o salts
(1 5 0 a ) and (150b).
T h e se w e re s y n th e s is e d from th e te tra flu o ro b o ra te salt of
ca tio n (b) by reaction w ith s o d io -m a lo n o n itrile .162 T h e v a st d iffe re n c e s in the
s h a d e s of the
(110) is o la te d
by th e tw o
m ethods,
b ro w n /o ra n g e fo r the
p y ro ly s is m eth od, brigh t y e llo w by a c id ific a tio n w ith d ilu te h y d ro c h lo ric acid and
85
th e n th e b rig h t o ra n g e n e e d le s o b ta in e d on re c ry s ta llis a tio n , can be e xp la in e d
by th e d iffe re n t m o rp h o lo g ie s in w h ich (110) w a s iso la te d using th e s e m ethods.
2 .B .4 C o n c lu s io n s
S e vera l a d v a n ta g e s are g a in e d in u sin g th e im p ro ve d s y n th e s is o f (110)
from th e a m m o niu m s a lt (119). T h e s y n th e s is a n d is o la tio n of (119) m akes fo r
a m ore e a s ily p u rifie d c o m p o u n d a n d it can be u se d as a h ig h ly so lu b le
e q u iv a le n t o f (110), w h o se in s o lu b ility m a ke s it an e x c e lle n t p ig m e n t151 but
re s tric ts its use fo r fu rth e r reaction .
A lth o u g h th e
m ore d ire c t route to
c o m p o u n d (143), and u ltim a te ly th e so d iu m s a lt (146), from p h th a lo n itrile (144),
S ch em e 2.16, g ive s a v ia b le route fo r th e s y n th e s is of (110), th e p o o r s o lu b ility
o f (143) in m o st o rg a n ic s o lv e n ts m a ke s th is route less a ttra ctive .
86
Section 2.C
2.C.1
W-Substituted
derivatives
of
2,2'-(lsoindorm-1,3-diylidene)
bispropanedinitrile (110)
In v e s tig a tio n s in to th e syn th e sis of nove l /V -substituted co m p o u n d s of
(110) w e re ca rrie d out, p rim a rily to d e te rm in e th e e ffe c ts of v a ry in g s u b s titu e n ts
on th e e le ctro n a c c e p to r a b ility of th e s e is o in d o lin e d e riv a tiv e s .
th e s e
A /-substituted
in v e s tig a te d .
co m p o u n d s
to
form
C -T
co m p le x e s
T h e a b ility of
w o u ld
th e n
be
In a d d itio n , it w as hop ed th a t su c h s u b s titu tio n s w o u ld re su lt in
im p ro ve d s o lu b ility p ro p e rtie s and a llo w fo r th e a tta c h m e n t of a b ro a d ra nge of
fu n c tio n a l g ro u p s in clu d in g p o lym e risa b le s u b s titu e n ts .
Cl
CN
Ph
CN
O
(110) R= H
(153)
(154)
(151) R= Me
(152) R= Ph
On se a rc h in g th e lite ra tu re it w a s fo u n d th a t th e m eth yl- a n d p h e n yld e riv a tiv e s of (110), (151) and (152), had been re p o rte d as ch a rg e c a rrie rs in an
e le c tro -c o n d u c tiv e
s u p p o rt
by
the
BASF
A .-G .
com pany
in
a
p a te n t.153
H o w e v e r th e p a te n t ga ve no in d ica tio n o r re fe re n c e as to how th e s e co m p o u n d s
w e re s y n th e s is e d . T h e y only d e scrib e d the s y n th e s is of (110).
W e w e re in te re s te d in fin d in g v ia b le m e th o d s fo r th e /^-su b stitu tio n of
(110) in high y ie ld s .
T h e a n a lo g y b etw e en th e C (C N )2 g ro u p a nd o xyg e n has
p re v io u s ly bee n m ade and m any s im ila ritie s in th e re a ctivity and p ro p e rtie s of
ca rb o n y l co m p o u n d s a nd th e ir a lk y lid e n e m a lo n o n itrile a n a lo g u e s have been
fo u n d .163 S om e e xa m p le s include, th e a d d itio n re a c tio n s of a G rig n a rd and the
a d d itio n -é lim in a tio n
K n o e ve n a g e l re a ctio n
sh o w n
in
S chem e 2 .19
and the
re a ctio n of an a m in e w ith th e acyl c h lo rid e a n a lo g u e (1 5 3 )159 in S ch e m e 2.20.
W ith th is in m ind w e sp e cu la te d th a t (110) m ight also u n d e rg o th e sam e
/^/-substitution
re a c tio n s
as
its
o xyge n
a n a lo g u e ,
p h th a lim id e
(154).
/V -S ubstituted p h th a lim id e s are s yn th e sise d b y firs t g e n e ra tin g th e so d iu m o r
po ta ssiu m
s a lt of p h th a lim id e and th e n
re a ctin g th e sa lt w ith a su b stra te
c o n ta in in g a d is p la c e a b le g roup such as an a lkyl o r acyl halid e, o r an alkyl
87
to s y la te or s u lp h o n a te . T h e s e
A /-substituted p h th a lim id e s are e xte n sive ly used
in the G a b rie l s y n th e s is of p rim a ry a m in e s .164 T h e G a b rie l typ e A /-substitution
re a ctio n of (110) w ith a v a rie ty of su b s tra te s w a s in v e s tig a te d and th e se shall
now be discu sse d .
1. R-Mg-Hal
2. H20
:c=x
x
(a): X= O
(b): X=C(CN)2
-C-XH
i
R
CH2(CN)2
-C-OR
X
— C -C H (C N )2
----------- ►
+
(a): X= O
(b): X=C(CN)2
HOR
S ch e m e 2.19
Cl
CN
Ph
CN
H<
ArHN
+
CN
ArNH2
Ph
CN
(153)
S ch e m e 2.20
2.C.1.1 Gabriel Type ^/-substitution reactions of (110)
B e n zo yla tio n of (110) by a nu m b e r of m e th o d s w a s atte m p te d , S chem e
2.21.
T h e se
in c lu d e d
th e
S c h o tte n -B a u m a n n
m ethod,
w h ich
in vo lve d
g e n e ra tin g th e sodium s a lt of (110), (146), u s in g so d iu m h ydroxide, a nd stirring
th e resultin g s u s p e n s io n w ith ben zoyl c h lo rid e at room te m p e ra tu re .
N C ^ .C N
f
{
.
N + Na
Benzoyl chloride
►
(
NC^
CN
(146)
S ch e m e 2.21
T h is yie ld e d a y e llo w p o w d e r w h ich w as id e n tifie d , from its s p e ctra l data, as
th e sodium s a lt of (110) on c o m p a riso n w ith a p re v io u s ly c h a ra c te ris e d sam ple.
T h e m ore v ig o ro u s c o n d itio n s of hea ting th e so d iu m sa lt of (110), g e n e ra te d
from the a m m o niu m s a lt (119) by re a ctio n w ith so d iu m hydrid e, w ith benzoyl
c h lo rid e u n d e r reflux in te tra h y d ro fu ra n , o r a lte rn a tiv e ly he a tin g (110) u nd er
88
re flu x w ith ben zoyl c h lo rid e in p y rid in e , w ere a lso a tte m p te d .
w e re o b se rve d on fo llo w in g th e s e re a c tio n s by T L C .
No new p rodu cts
W o rk -u p of th e reaction
m ixture in pyrid in e gave (1 10), id e n tifie d by co m p a ris o n of its s p e c tra w ith th a t
of th e know n c o m p o u n d .
S im ila r re su lts w e re also o b ta in e d on atte m p te d
a c y la tio n w ith a ce tic a n h y d rid e and a tte m p te d to s y la tio n w ith to s y lc h lo rid e .
T h e M annich ty p e re a ctio n of the a m m o n iu m s a lt (119) w ith fo rm a lin
(3 6 %
fo rm a ld e h yd e
s o lu tio n
in w a te r) w a s
in v e s tig a te d ,
S ch e m e
2.22, to
e s ta b lis h w h e th e r a h y d ro x y m e th y l g ro u p co u ld be a p p e n d e d to (110). T h e aim
of th is re a ctio n w a s to in tro d u c e a fu n c tio n a l g ro u p on to (110) w h ich co u ld then
u n d e rg o a m u ltitude of re a c tio n s o ffe rin g a w id e r ra nge o f s u b s titu e n ts .
A
s im ila r re a ctio n be tw e e n p h th a lim id e (154) and fo rm a lin w a s re p o rte d to give
/V -(h y d ro x y m e th y l)p h th a lim id e .165 T h e a m m o niu m sa lt of (110) w a s tre a te d w ith
fo rm a lin and he a te d u n d e r reflux.
(119)
S ch e m e 2.22
T L C sh o w e d no new p ro d u c ts w e re form ed.
T h e s p e ctra l d a ta fo r th e ye llow
s o lid o b ta in e d on te rm in a tin g th e e xp e rim e n t w e re c o n s is te n t w ith th o s e for
( 110 ).
/V -M ethylation of (110) w as in itia lly a tte m p te d using m ethyl io d id e but the
y e llo w so lid reco ve re d , on te rm in a tin g the rea ctio n , w as id e n tifie d as th e sodium
s a lt of (110) by c o m p a ris o n of its IR and m elting p o in t w ith th o s e of an a u th e n tic
sa m p le .
/V -S ubstitution of (110) w a s fin a lly a ch ie v e d w h en m e th yla tio n w as
a cc o m p lis h e d in a v e ry p o o r yie ld using d im e th y ls u lp h a te as th e
S ch e m e 2.23.
reagent,
R e a ctio n of th e so d iu m salt of (110) w ith d im e th y ls u lp h a te
s h o w e d th e fo rm a tio n o f a m uch fa s te r e lu tin g p rin c ip a l co m p o u n d , and a
n u m b e r of m in o r p ro d u c ts n e a re r the ba se lin e , on fo llo w in g th e re a ctio n by TLC .
T h is fa s te r m oving p ro d u c t w a s e v e n tu a lly is o la te d by colum n c h ro m a to g ra p h y
u s in g te tra h y d ro fu ra n as th e m obile phase.
com pound
in c h lo ro fo rm -d }
sh o w e d th re e
T h e 1H N M R sp e ctru m of th is
pea ks
in to ta l, tw o
sym m e trica l
a ro m a tic m u ltip le ts at 7 .1 9 and 8 .6 7 ppm , in te g ra tin g fo r tw o p ro to n s each , and
a th ird peak, a th re e p ro to n s in g le t at 4.1 7 ppm , a s s ig n e d to the A/-methyl group.
89
A fu rth e r in dica tion th a t m é th yla tio n had taken p lace w a s a p p a re n t from the IR
s p e ctru m w h ich show ed th e a b se n ce o f NH b an ds a b o ve 3150 c m '1.
NaH, Mel
►
NC.
XN
NaH, Dimethylsulphate
NMe
►
NC
CN
(151)
S ch e m e 2.23
O n ca rryin g o u t a 13C N M R e xp e rim e n t in d im e th y ls u lp h o x id e -d 6, so m e heating
w a s n e ce s s a ry in o rd e r to d isso lve th e co m pou nd.
T h e 13C N M R sp ectrum
o b ta in e d sh o w e d an u n e xp e cte d ly large n u m b e r o f carb o n abso rp tions.
T LC o f
th e 13C N M R sa m p le no lo n g e r show ed ju s t o ne p ro d u ct b u t several p rodu cts
in d ica tin g th a t th e co m p o u n d w as u nstable w hen hea ted in d im e th ylsu lp h o xid e .
O n th e basis o f th e 1H N M R and IR spectra th is co m p o u n d w a s belie ved to be
th e
N -m e th yla te d
d e riv a tiv e
(151).
T his
a s s ig n m e n t w a s
co n firm e d
by
co m p a riso n o f th e 1H N M R , IR sp e ctra and m elting p o in t o f (151) s y n th e sise d by
th is
m e th o d
w ith
th o s e
of
th e
sam e
co m p o u n d
syn th e sise d
té tra m é th y la m m o n iu m s a lt discu sse d in th e next se ction .
fro m
th e
T h e p oo r yield o f this
re a ctio n and th e need to use h ighly to xic d im e th ylsu lp h a te m e a n t an a lte rn a tive
and s a fe r s y n th e sis w a s needed.
2 .C .1 .2 Alternative Methods for /V-Substitution of (110)
2 .C .1.2.1 Méthylation using the tétraméthylammonium (TMA) salt (155)
T h e use o f q u a te rn a ry a m m o niu m salts in n u cle o p h ilic d isp la ce m e n t
re a ctio n s have been rare and su ffe r from p oo r yie ld s and lack o f gen erality.
90
S om e e xa m p le s in clu d e th e n u c le o p h ilic d is p la c e m e n ts on gram m e q u a te rn a ry
s a lts ,166 S ch e m e 2.24.
+
CH2NMe3
CN
i
i
H
H
S ch em e 2.2 4
In th e H o fm ann d e g ra d a tio n of a m in e s, c le a v a g e of q u a te rn a ry am m onium
h y d ro x id e s is th e fin a l step.
N M e 4+O H \ u n d e r va cu u m
T he p y ro ly s is of té tra m é th yla m m o n iu m hydroxide,
has bee n fo u n d to y ie ld trim e th yla m in e , dim ethyl
e th e r and m e th a n o l.167 O ne m e ch a n ism p ro p o s e d s u g g e s te d th a t the fo rm a tio n
o f th e
e th e r m ay be
e x p la in e d
by th e
a b s tra c tio n
of a proton
from
té tra m é th y la m m o n iu m g ro u p by th e O H ' g ro u p to give a n itro g e n ylid e .
the
T his
ylid e , w h ich can b e h a v e like a c a rb e n e , can th e n react w ith the m ethanol
p re se n t, w h ich m ay be fo rm e d in itia lly by n u c le o p h ilic d isp la ce m e n t of a m ethyl
g ro u p from
th e té tra m é th y la m m o n iu m
ca tio n
by a h yd roxide
anion, o r by
re a c tio n of th e y lid e w ith a sm all a m o u n t of w a ter, to form an ether.
re s u lts
w e re
also
o b ta in e d
from
té tra m é th y la m m o n iu m
S im ila r
a lk o x id e s .168
D é m é th y la tio n of trie th y lm e th y la m m o n iu m ca tio n in th e dry state and also in
n o n -p ro tic s o lv e n ts by th io p h e n o x id e has also be e n re p o rte d .169
It w a s d e c id e d th a t th is a p p ro a c h m ay p ro vid e a v ia b le w a y of o b ta in in g
(151).
W e fo u n d on h e a ting th e té tra m é th y la m m o n iu m (TM A ) sa lt (155) in
1 .2 -d ic h lo ro b e n z e n e th a t (151) w a s o b ta in e d , S ch e m e 2.25.
T h e T M A s a lt (155) w as is o la te d in 6 0 % yie ld by m ixing an a q u e o u s
s o lu tio n of té tra m é th y la m m o n iu m c h lo rid e w ith a s o lu tio n of (119) in m ethanol.
T h e IR, 1H N M R and 13C NM R sp e ctra , and e le m e n ta l a n a lysis of (155) w e re all
c o n s is te n t w ith the a s s ig n e d stru c tu re .
T h e 1H N M R spectrum sh ow ed fo u r
a ro m a tic p ro to n s as tw o sy m m e tric m u ltip le ts at 7.56 and 8.1 4 ppm and tw e lve
m eth yl p ro to n s as a s in g le t at 3.41 ppm . T h e 13C N M R spectrum sh o w e d th e C 2
c a rb o n a b s o rp tio n of th e 2 ,2 -d ic y a n o v in y lid e n e g ro u p at 54.06 ppm , a trip le t at
5 4 .4 3 ppm , J = 15 Hz, w h ich c o rre s p o n d e d to th e m ethyl ca rb o n s of the
té tra m é th y la m m o n iu m
ca tio n , tw o
n itrile
c a rb o n a b s o rp tio n s at 116 .32 and
117 .2 0 ppm , th re e a ro m a tic a b s o rp tio n s at 122.9, 131.4 and 137.33 ppm and a
2 .2 -d ic y a n o v in y lid e n e
ca rb o n a b s o rp tio n at 171 .8 7 ppm . T h e m ethyl carbon
a b s o rp tio n at 54.43 ppm o ccu rs as a trip le t d ue to co u p lin g of the 14N nucleus
91
w ith th a t of 13C.
C o u p lin g s b etw e en 13C and th e a b u n d a n t iso to p e 14N, w hich
has a na tu ra l a b u n d a n c e of 99.6 % and I =1, are u s u a lly not m e a su ra b le . T his
is b e c a u s e 14N has a n u c le a r q u a d ru p o le m o m e n t w h ich re s u lts in a more
e ffe c tiv e m ode of re la xa tio n w h ich is u su a lly so fa s t th a t th e c o u p lin g e ffe cts are
not o b se rve d . 13C -14N s p littin g s h o w e v e r are o b s e rv e d in sp e c ia l ca se s such as
te tra a lk y la m m o n iu m ions, is o n itrile s a nd d ia z o m e th a n e s , w h e re th e nitroge n
n u cle u s is in a re la tiv e ly sym m e trica l e n v iro n m e n t and so th e e le c tric field
g ra d ie n t at th e 14N n u cle u s is zero o r s u ffic ie n tly sm a ll.
A ty p ic a l J (13C, 14N)
va lu e is of th e o rd e r of 10 H z .170
(151)
(155)
S ch em e 2.25
H e a tin g th e T M A s a lt (155) u n d e r reflux in 1 ,2 -d ic h lo ro b e n z e n e fo r 150
ho u rs ga ve (151) as b la c k /p u rp le nee dle s, S ch em e 2.25.
th e s e
n e e d le s,
and
th e
so lid
re m a in in g
from
R e c ry s ta llis a tio n of
e v a p o ra tin g
o ff
the
1,2-
d ic h lo ro b e n z e n e from th e filtra te , gave (151) as an o ra n g e /y e llo w crysta llin e
so lid in 5 4 % yie ld . T h e 1H N M R sp e ctru m of (151) sh o w e d o n ly th re e d iffe re n t
ty p e s of pro to n .
F o u r a ro m a tic p ro to n s w e re o b s e rv e d as tw o sym m e tric
m u ltip le ts at 7.9 8 a nd 8.65 ppm , in the ratio 2:2, and a th re e pro to n sin g le t at
4 .10 ppm c o rre s p o n d in g to th e m ethyl pro to n s at th e 2 p o sitio n of th e is o in d o lin 1,3 -d iy lid e n e ring system .
T h e sym m e trica l na tu re of the m o le cu le w as fu rth e r
s u p p o rte d by th e 13C N M R sp e ctru m w h ich sh o w e d a m ethyl ca rb o n a b so rp tio n
at 3 7 .4 9 ppm , the C 2 a b s o rp tio n of 2 ,2 -d ic y a n o v in y lid e n e g ro u p at 6 1 .9 0 ppm,
o n ly tw o cya n o c a rb o n a b s o rp tio n s at 113.76 a nd
a ro m a tic ca rb o n
a b s o rp tio n s b etw e en
125.70 and
11 4 .5 2 ppm and th re e
135 .30
ppm .
T h e 2,2-
d ic y a n o v in y lid e n e Ci ca rb o n a b so rp tio n w as fo u n d at 160 .92 ppm .
A le ss c o n v e n ie n t m ethod fo r th e s y n th e s is o f (151) in v o lv e d hea ting the
sa lt (155) u n d e r a vacu u m of 0.5 m m H g at 180 °C fo r tw e lve hours.
D uring the
c o u rs e of th e re a ctio n a y e llo w s o lid s u b lim e d on to the s id e s of th e reaction
v e sse l.
T h is w as re m o ve d by w a sh in g the s id e s of th e re a ctio n ve sse l w ith
92
a ce to n e .
T LC show ed th a t th is y e llo w p ro d u c t w a s m ade up of tw o main
co m p o u n d s w ith ve ry s im ila r Rf v a lu e s .
co m p o n e n ts w ere
u n su cce ssfu l.
A tte m p ts to s e p a ra te th e in d ivid u a l
The
1H N M R
sp e c tru m
sh o w e d th a t there w e re tw o p a irs of a ro m a tic pro to n s.
in
c h lo ro fo rm -d i
T h e m a jo r com pon ent
sh o w e d a p a ir of s y m m e tric a ro m a tic m u ltip le ts, w h ich o c c u rre d at 7.8 6 and 8.67
ppm and w h ich in te g ra te d fo r a to ta l of fo u r p ro to n s.
w h ich
in te g ra te d
fo r
th re e
p ro to n s
was
a lso
A s in g le t at 4.18 ppm
o b s e rv e d .
These
va lu e s
co rre s p o n d e d w ith th e ch e m ic a l s h ifts o b se rve d fo r th e p u re co m p o u n d , (151),
o b ta in e d using d im e th y ls u lp h a te as th e m e th yla tin g a g e n t a n d of th a t ob ta in e d
b y hea ting (155) in 1 ,2 -d ic h lo ro b e n z e n e . T h is v e rifie d th a t o ne of th e produ cts
o f th is m ethod w as (151).
m ore
co m p lica te d
T h e 13C N M R sp e ctru m , a lso In c h lo ro fo rm -d ], was
and
sh o w e d
m any
carb o n
a b s o rp tio n s
w ith
5
cyano
a b s o rp tio n s o b se rve d b e tw e e n 116.0 and 111.0 ppm a lo n g w ith a to ta l of 9
a ro m a tic a b so rp tions.
2.C.1.2.2
Attempted
Benzylation
of
2,2'-(lsoindolin-1,3-diylidene)
bispropanedinitrile (110)
A p a rt from the te tra a lk y la m m o n iu m
h ig h ly s p e c ific m eth ods of A /-alkylation exist.
g ro u p s
u n d e rg o
a lk y la tio n
by a m id e
s a lts p re v io u s ly m e ntion ed, other
C o m p o u n d s c o n ta in in g a c id ic NH
a ce ta ls
at the
n itro g e n
atom .
This
e x c e p tio n a lly s e le c tiv e re a ctio n w a s used until re c e n tly w ith n u c le o s id e s ,171
S ch e m e 2.26
OR
H C -O R
NMe2
S ch e m e 2.26
T h e d is c o v e ry th a t (110) c o u ld be m e th yla te d u sing d im e th y ls u lp h a te , o r its
té tra m é th y la m m o n iu m
salt, s u g g e s te d th a t o th e r s u b s titu e n ts co u ld also be
a p p e n d e d by s y n th e s is in g s u b s tra te s a lts w ith a p p ro p ria te le a vin g group s. O ne
such g ro u p is the p y rid in iu m salts, (1 5 6 )-(1 60), e x te n s iv e ly in v e s tig a te d and
d e v e lo p e d by K a tritz k y 172 fo r th e co n v e rs io n of a lip h a tic a m in o g ro u p s into
le a v in g groups.
ra nge
of
T h e s e p y rid in iu m s a lts can tra n s fe r A /-substituents to a wide
n u cle o p h ile s
such
as
h a lid e s
93
and
oxyg e n -,
s u lp h u r-,
nitrogen-,
p h o s p h o ru s - and c a rb o n -n u c le o p h ile s .
A v a rie ty of /V-substituted p h th a lim id e s
(161) has bee n p re p a re d in high y ie ld s from th e p o tassium s a lt of p h thalim id e
w ith th e a p p ro p ria te ly A /-substituted 2 ,4 ,6 -trip h e n y lp y rid in iu m te tra flu o ro b o ra te s
(157) by p yro lysis o r by h e a tin g u n d e r reflux in d im e th y lfo rm a m id e .173
Û
Y
R
(156)
(157)
R= Me, Et, i-Pr, etc.
R= Me, t-Bu, Ph, N 0 2C6H4
(158) a: Y= Ph, X= Me, t-Bu, 2-thienyl
b: Y= X= Me
c: Y= X= Mesityl
Ph
Ph
/ ^ N |, T
R
Ph
r i r
k
(160)
(159)
R= Me, n-Bu, Benzyl, Ph
= Me, n-Bu, Benzyl, Ph
A /-S ubstituted
R
o -b e n z e n e s u lp h o n im id e s
(162)
have
also
been
in v e s tig a te d as p o te n tia l a lk y la tin g a g e n ts b e ca u se of the e xp e cte d high charge
s ta b ilis a tio n of the a n io n .174
H o w e v e r th e se co m p o u n d s w e re fo u n d to be
re la tiv e ly in e rt on h e a tin g w ith n u c le o p h ile s u n d e r reflux in d im e th ylfo rm a m id e
w ith low re co ve ry of th e im ide.
so2
NR
SO ,
R= Alkyl (C1-C6), i-Pr, benzyl,
R= CH2Ph and CH2CH2Ph
CIC6H4CH2(o), etc
(162)
(161)
94
W e a tte m p te d to b e n z y la te co m p o u n d (110), b a se d on K a tritz k y 's m eth od, by
first fo rm in g the b e n zylp yrid in iu m s a lt of (110), (163), and th e n h e a tin g th is salt
in
1,2 -d ic h lo ro b e n z e n e as done p re v io u s ly w ith th e T M A s a lt (155), S chem e
2.27.
The
u n s u b s titu te d
p yrid in iu m
sa lt w a s
in v e s tig a te d
because
th e se
s u b s tra te s a lts had been s u c c e s s fu lly use d to c o n v e rt the ve ry p o o r n u cle o p h ile
triflu o ro a c e tic acid to its co rre s p o n d in g e s te r by s o lv o ly s is of triflu o ro a c e tic acid
w ith a v a rie ty of /V-substituted p y rid in iu m s a lts and a lso b e ca u se it w a s m ore
e a s ily s y n th e s is e d th a n th e a lte rn a tiv e p y rid in iu m sa lts.
th a t s te ric
h in d ra n ce
d is p la c e m e n t
o f th e
re a c tio n 172^
a tta c k in g
and
n u c le o p h ile
w h ile
th e
In a d d itio n it is know n
a ffe cts th e
d is p la c e m e n t
rate
ra te s
o f the
are
also
d e p e n d e n t on th e s u b s titu e n ts on th e p y rid in iu m ring, w ith th e s a lts (159) and
(160) be in g show n to be b e tte r s u b s tra te s fo r re a c tio n w ith so d iu m a ce ta te than
th e 2 ,4 ,6 -trip h e n y lp y rid in iu m s a lt,175 it w a s c o n s id e re d th a t su ch s te ric e ffe cts
m ay not o c c u r if the u n su b titu te d p y rid in iu m s a lt w e re u tilised .
(164)
(163)
S chem e 2.27
T h e N-b e n zyl d e riv a tiv e w a s chose n as th is /V -substituent has bee n fo u n d to be
m ore
e a sily
tra n s fe rre d
A /-su b stitu e n ts172(b)
a nd
to
the
has
n u c le o p h ile
bee n
than
d is p la c e d
in
the
o th e r
re a c tio n s
a lip h a tic
w ith
som e
n u c le o p h ile s w h e re o th e r a lip h a tic /V -substituents have n o t.175
M ixin g
a
m e th a n o l
so lu tio n
of
th e
so d iu m
s a lt
of
(110)
w ith
b e n z y lp y rid in iu m ch lo rid e , s y n th e s is e d by h e a tin g ben zyl ch lo rid e a n d pyrid in e
to g e th e r,
g a ve the
b e n z y lp y rid in iu m
s a lt
(163),
S ch em e
2.28.
T h is
was
s u p p o rte d by th e IR, 1H and 13C N M R s p e c tra and by e le m e n ta l a n a ly s is .
The
1H and 13C N M R s p e c tra of the b e n z y lp y rid in iu m ca tio n co m p a re ve ry w e ll with
th o s e of th e b e n z y lp y rid in iu m p e rc h lo ra te s a lt re p o rte d by K a tritz k y .176
T he
a ro m a tic p ro to n s fo r th e anion of (110) w e re fo u n d at 7.62 a n d 8.08 ppm , w ith
bo th m u ltip le ts in te g ra tin g fo r tw o p ro to n s each. T h e carb o n a b s o rp tio n s fo r the
a n io n
of
(110) w e re
fo u n d
at 5 4 .4
ppm
95
fo r th e
C 2 ca rb o n
of th e
2,2-
d ic y a n o v in y lid e n e
g roup , at 116.3 and
117.3
ppm fo r th e cya n o carbons,
a ro m a tic ca rb o n s at 122.9, 131.4 and 1 37 .4 ppm and the 2 ,2 -d ic y a n o v in y lid e n e
C! carbon at 171.9 ppm .
(163)
S ch e m e 2.28
H e ating sa lt (163) u n d e r reflux in 1 ,2 -d ic h lo ro b e n z e n e fo r sixteen hours
re su lte d in th e fo rm a tio n of a b lack s o lu tio n as fo u n d fo r the c o rre s p o n d in g TM A
sa lt (155).
A lth o u g h a ve ry sm all q u a n tity of a fa st e lu tin g co m p o u n d w as
o b se rve d by TLC , th e a m o u n t g e n e ra te d w as in s u ffic ie n t to be iso la te d . A black
n o n -e lu tin g d e c o m p o s itio n pro d u ct w a s o b ta in e d on filte rin g th e s o lu tio n and
th is w as in s o lu b le in all the so lve n ts trie d .
S ta rtin g m ate rial w as also re covered
fro m the filtra te , on e v a p o ra tio n to d ryn e ss.
2.C.2 Discussion
T he sam e in flu e n c e s w hich d e te rm in e th e a c id ity of (110) also contribu te
to its p oo r n u c le o p h ilic ity .
The lone p a ir of e le c tro n s in th e 2 -p o sitio n of the
a n io n of (110) are h ig h ly d e lo ca lise d . A s a re s u lt it is not to o su rp ris in g th a t the
sta n d a rd m eth ods of s u b s titu tio n , in v o lv in g n u c le o p h ilic reaction w ith an alkyl or
acyl halide, w e re not su cce ssfu l.
A lth o u g h m é th yla tio n w ith d im e th ylsu lp h a te
w a s e ffe ctive , the p o o r yie ld s o b ta in e d and ne e d to use such a h ighly toxic
m e th yla tin g ag e n t m ade th is m ethod ve ry u n a ttra c tiv e .
T he
re p o rts of hig h ly s p e c ific
n u c le o p h ilic
a lk y la tio n
su b s tra te s
w h en
show the
s ta n d a rd
m e th o d s 166- 171 fo r a lk y la tin g
need
m e th o d s
fo r fin d in g
are
a lte rn a tiv e
not
w e akly
m ethods
s u c ce ssfu l.
of
The
té tra m é th y la m m o n iu m sa lt m ethod re p o rte d here w as s u cce ssfu l and provided
re a so n a b le yie lds. T h e fo rm a tio n of (151) is th o u g h t to o c c u r via a d isp la ce m e n t
re a ctio n
be tw e e n
th e
w e a kly
té tra m é th y la m m o n iu m group .
w ho
re p o rte d
th a t
té tra m é th y la m m o n iu m
fo r
anion
of
(110)
and
the
T his is c o n s is te n t w ith the fin d in g s of M u s h e r167
the
s a lts
n u c le o p h ilic
of
re la te d
H o fm a n n
v a rio u s
a n io n s,
d e g ra d a tio n
hyd ro g e n
of
va riou s
a b s tra ctio n
was
fa vo u re d fo r stron g base s, w h ile w e a k e r base s, like the halid es, w e re th o u g h t to
96
u n d e rg o a d is p la c e m e n t reaction.
T h e a tte m p te d A /-benzylation of (110) using
the b e n z y lp y rid in iu m s a lt (163) fa ile d to yie ld s u ffic ie n t q u a n titie s o f the new
p ro d u c t o b s e rv e d by T LC .
A s im ila r typ e d is p la c e m e n t re a ctio n w o u ld be
e x p e cte d to ta k e p la ce fo r th is reaction , w ith g e n e ra tio n of p y rid in e as the
le a vin g group .
u n s u b s titu te d
W h ile th e re are fe w e r re p o rts by K a tritzky of th e use of the
A /-a lkylp yrid in iu m s a lts (156), th e y have bee n sh o w n to a lkylate
eve n th e m ost p o o rly n u c le o p h ilic co m p o u n d s su ch as triflu o ro a c e tic a cid w hich
ga ve th e c o rre s p o n d in g e s te r as th e s o lv o ly s is p ro d u c t.177
C o n s id e rin g these
re p o rts, it is e v id e n t th a t th e a n io n of (110) is e x tre m e ly n o n -n u c le o p h llic . It was
a lso re p o rte d th a t th e A /-substituted p y rid in iu m s a lts u n d e rw e n t h yd ro lysis to
g ive th e c o rre s p o n d in g a lc o h o ls at te m p e ra tu re s be tw e e n 60 a nd 100 ° C .177
T h e p o s s ib ility th a t th e A /-b e n zyl-d e riva tive (164) is u n sta b le at th e te m p e ra tu re
at w h ich th e re a ctio n w a s ca rrie d out seem s p la u s ib le b u t a tte m p ts to effect
re a ctio n at lo w e r te m p e ra tu re s w e re not su c c e s s fu l.
In te re stin g ly, th e m ethods
fo r A/-alkylation re p o rte d here, th e te tra a lk y la m m o n iu m sa lt m ethod and th e Nb e n z y lp y rid in iu m s a lt m e th o d , have sin ce bee n a p p lie d to th e p yra zin e ana log ue
of (110), (1 6 5 a ),178 a n d have s u c c e s s fu lly y ie ld e d th e /V-methyl, -e th yl and b e n zyl d e riv a tiv e s (1 6 5 b ) u n d e r s im ila r c o n d itio n s .
W h y th e s e m e th o d s shou ld
w o rk e ffe c tiv e ly fo r th e p yra zin e a n a lo g u e and not (110) is not u n d e rsto o d .
a:R= H
b:R= Me, Et and Benzyl
C o m p a ris o n of th e U V /visib le s p e c tra of (110), its a m m o niu m s a lt (119)
a nd its /V-methyl d e riv a tiv e (151) in a c e to n itrile sh o w v a ryin g A.m ax, see Figure
2.1.
The
A.max
of
(110)
co m p a re d
w ith
(119)
occur
at
m uch
s h o rte r
w a v e le n g th s , 386 and 4 08 nm co m p a re d w ith 466 and 496 nm. T h is diffe re n ce
can be a ttrib u te d to th e g re a te r a u xo ch ro m ic e ffe c t of the anion, w h ich results in
g re a te r c o n ju g a tio n , c o m p a re d w ith th e p ro to n a te d NH co m pou nd.
C o m pa rison
of th e U V /visib le s p e c tra of (110) and (151) sho w s th a t A/-alkyl s u b stitu tio n
s lig h tly
enhances
th e
a u x o c h ro m ic
e ffe ct
of th e
ring
n itroge n
w ith
A.max
a s s o c ia te d w ith th e /V-m ethyl d e riv a tiv e o ccu rin g at s lig h tly lo n g e r w a ve le n g th s,
(394 and 416 nm ).
T h e use of a m ore p o la r so lve n t, A/,A/-dim ethylform am ide,
sh o w s a s ig n ific a n t e ffe c t on the U V /visib le sp e ctru m of (110).
97
C o m p a riso n of
th e
U V /visible
sp e ctru m
of
(110)
and
its
a m m o n iu m
d im e th ylfo rm a m id e , F igure. 2.2, sho w s th a t bo th are id e n tic a l.
sa lt
in
N,N-
T h is sh o w s that
in so lu tio n the b e tte r so lva tin g a b ility of th e A /,A /-dim ethylform am ide e n h a n ce s
d e p ro to n a tio n of (110) re su ltin g in th e fo rm a tio n of th e m ore h ig h ly co n ju g a te d
a n io n ic system .
The
/V-methyl
d e riv a tiv e
(151)
h o w e v e r c a n n o t u n d ergo
d e p ro to n a tio n and th u s s h o w s little c h a n g e in its V n a x v a lu e s - se e F ig u re 2.2.
2.C.3 Conclusion
In lig h t of th e s e fin d in g s it is a p p a re n t th a t th e s u b s ta n tia l a n io n ic charge
s ta b ilis a tio n , g ra n te d by th e d ic y a n o m e th y le n e g ro u p s , m akes (110) a p oo r
n u cle o p h ile thus m a kin g it e x tre m e ly d iffic u lt to c a rry o u t s ta n d a rd a lk y la tio n and
a cyla tio n re a ctio n s.
In sp ite of th is it se e m s w o rth w h ile th a t a lk y la tio n of (110)
w ith o th e r s u b s titu te d p y rid in iu m s a lts s h o u ld be in v e s tig a te d to d e te rm in e if
th e s e m ethods are m ore effe ctive.
98
Figure 2.1 UV/visible spectra of (110), (119) and (151) in acetonitrile.
99
Figure 2.2 UV/visible spectra of (110), (119) and (151) in dimethylformamide.
100
Section 2.D
2.D.1
Reactions of 2,2'-(lsoindolin-1,3-diylidene)bispropanedinitriie (110)
with Amines
A p art from re p o rts of the p ig m e n t p ro p e rtie s and u se s of (110) in the
p a te n t lite ra tu re th e re has been no re p o rt of th e c h e m is try of th is co m pou nd.
As
sta te d
p re v io u s ly ,
th e
re a c tio n s
of
ca rb o n y l
com pounds
and
th e ir
a n a lo g u e s , the a lk y lid e n e m a lo n o n itrile s , have sh o w n m any s im ila ritie s .159- 163
S o m e of th e se have b e e n m e n tio n e d a lre a d y , (see S ch em e 2.19 and 2.20,
S e ctio n 2.C ).- W e ha ve fo u n d (S e ctio n 2.C ) th a t it w as e xtre m e ly d iffic u lt to
a c h ie v e
A /-substitutlon
p h th a lim id e ,
and
th a t
of
(110),
m e th o d s
th e
use d
a lk y lid e n e m a lo n o n itrile
a n a lo g u e
fo r
/V-substituted
p h th a lim ld e s w e re not e ffe c tiv e fo r (110).
th e
s y n th e s is
of
of
T h is w a s a ttrib u te d to th e p o o re r
n u c le o p h ilic ity of th e n itro g e n in th e 2 -p o s itio n of th e ring, due to th e g re a te r
d e lo c a lis a tio n of th e a n io n ic ch a rg e , re s u ltin g from th e p re se n ce of h ig h ly
e le c tro n -w ith d ra w in g d ic y a n o m e th y le n e g ro u p s.
On th e b a sis of a po ssib le
s im ila rity in th e c h e m is try of p h th a lim id e a nd (110), w e w e re in te re s te d in
in v e s tig a tin g the re a c tiv ity of (110) to w a rd s a m in e s.
N u c le o p h ilic a tta ck on an
/V -substituted p h th a lim id e by h yd ra zin e , the fin a l ste p in th e G a b rie l s yn th e s is
o f a m in e s ,164 o cc u rs at th e c a rb o n yl c a rb o n re su ltin g in rin g -o p e n in g and
s u b s e q u e n t e lim in a tio n of an a m ine b e a rin g th e /V -substituent.
o f an a n a lo g o u s
re a c tio n
o c c u rrin g
b e tw e e n
(110) a nd an
T h e p o s s ib ility
am ine ,
o r of
n u c le o p h ilic a tta ck by th e a m ine o c c u rrin g at a n o th e r po sitio n , w a s of in te re s t
In v ie w of th e p o s s ib le p ro d u c ts w h ich co u ld be form ed.
T h e se shall now be
d iscu sse d .
T h e re are fo u r p rin c ip a l s ite s on (110) at w h ich an am ine co u ld a tta ck
a nd th e se are sh o w n b e lo w as A, B, C and D, S ch e m e 2.29.
c
B
(110)
Scheme 2.29
101
N u c le o p h ilic a tta ck at site A, by a n a lo g y w ith p h th a lim id e , co u ld re su lt in ringo p e n in g , g ivin g in te rm e d ia te (166), S ch e m e 2.30.
CN
N C ^ ,CN
NC .
. CN
+
NH
NC
NH2R
CN
NC
n h 2r
NHR
NH '
NH2
CN
NC
CN
( 166 )
Schem e 2.30
In te rm e d ia te (166) co u ld then u n d ergo rin g -c lo s u re , fo llo w e d by e lim in a tio n of
a m m o n ia , to give an /V-substituted d e riva tive o f (110), (167), S chem e 2.31.
E q u a lly p o ssib le is th e a lte rn a tive rin g -clo su re to (110), w ith lo ss of th e am ine .
(166)
(167)
S chem e 2.31
A lte rn a tiv e ly e ith e r m oiety in the 1- and 2- p o s itio n s of the b e n ze n e ring
o f (166) co u ld rotate fre e ly aro u n d the c a rb o n -to -c a rb o n s in g le bon d g ivin g rise
to th e fo rm a tio n of a se v e n -m e m b e re d ring system (1 6 8 -1 7 0 ). T h is co u ld o c c u r
via a d d itio n of e ith e r n u c le o p h ilic am ino g ro u p to a cya n o on the a d ja ce n t
d ic y a n o e th e n y la m in o group , S chem e 2.32.
N u c le o p h ilic a tta c k at postio n A co u ld a lso give an a d d itio n reaction
a c ro s s th e c a rb o n -to -c a rb o n dou ble bond of th e d ic y a n o v in y lid e n e g ro u p g ivin g
a d d u c t (171), S ch e m e 2.33.
A tta ck by an a m in e at site B of (110) c o u ld re su lt in a 1,6 -a d d itio n e lim in a tio n reaction g iv in g (172), Schem e 2.34.
re a c tio n s
of
a m ine s
w ith
T C N Q 179
a nd
S im ila r a d d itio n -é lim in a tio n
o th e r
c o m p o u n d s have been re p o rte d ,180 e.g. S ch em e 2.35.
a lk y lid e n e m a lo n o n itrile
RHN
(169)
NHR
(170)
S ch e m e 2.32
NC^
v.
y> CN
V-/I
i *
,NHR
NH
NC
NH2R
cx"
CN
NC
CN
(171)
S ch e m e 2.33
NHR
H<
N C_,N H R
-CN'
NC - CN
NC
CN
( 172)
Scheme 2.34
103
Scheme 2.35
R e a ctio n at site C, o r at a n y of the cya n o g ro u p s, co u ld re s u lt in 1,2a d d itio n of th e am ine to a cya n o g ro u p re su ltin g in th e fo rm a tio n o f an a m idine,
(173), w h ich can e xist in ta u to m e ric fo rm s (a) and (b), S ch e m e 2.36.
NH
II
C=NR
n h 2r
(173)
S ch e m e 2.36
In lig h t of the a c id ic n a tu re of (110) re a ctio n at site D w o u ld re su lt in the
fo rm a tio n of th e c o rre s p o n d in g a lkyla m m o n iu m s a lt of (110) by a b s tra c tio n of
th e a c id ic p ro to n by th e a m in e . It w o u ld seem lik e ly th a t th is re a ctio n w o u ld be
th e firs t step in any re a c tio n s b e tw e e n (110) and an a m ine .
T h is is v e rifie d by
th e iso la tio n of th e a m m o n iu m s a lt (119) from the K n o e v e n a g e l c o n d e n s a tio n of
m a lo n o n itrile w ith th e
g e n e ra te d
by th e
d e p ro to n a tio n
im id in e s
c o n d e n s a tio n
of the
re la te d
(118a) and (118b), in w h ich th e
re a ctio n
co m p o u n d ,
d e p ro to n a te d
(174), w ith
(110).
a lka li
am m o nia
Im m ediate
has also
been
re p o rte d .149
B e ca u se
of th e
p o o r s o lu b ility
of
(110)
in
com m o n
s o lve n ts,
the
a m m o n iu m s a lt (119) w a s use d in its place fo r th e re a c tio n s w ith va rio u s
a m in e s in a v a rie ty of s o lv e n ts .
d is c u s s e d in th e next s e c tio n .
T h e re su lts of th e s e e xp e rim e n ts w ill be
E t0 2C
(118a)
(118b)
CN
NC'
CN
(119)
(174)
2.D.2 Reactions of Amines with the Ammonium Salt (119)
2.D.2.1 Reaction of Benzylamine with (119)
A solution of the ammonium salt (119) in 1,4-dioxan was treated with
benzylamine and heated under reflux for four hours. During the course of the
reaction the formation of a new product, which precipitated from solution as an
orange solid, was observed by TLC and was isolated by filtration. It was found
to be insoluble in most organic solvents and was recrystallised from a
DMF/ethanol mixture.
The TH NMR spectrum showed four unsymmmetrical aromatic multiplets
at 8.29, 8.11, 7.62 and 7.36 ppm whose integrations were in the ratio 1:1:2:5
respectively. The five proton aromatic multiplet at 7.36 ppm was assigned to
the benzyl aromatic protons.
Also present were two broad singlets at 10.29
and 9.25 ppm whose integrations were in the ratio 1:2 respectively which were
assigned as NH and NH 2 protons and a two proton singlet at 4.67 ppm was
assigned to the methylene protons of the benzyl group.
The unsymmetrical
nature of the aromatic multiplets, and the presence of two NH absorptions in
the ratio 1 :2 , suggested that, of the products postulated in the introduction, the
product was probably the amidine (175) or either of the two benzoazepines
(176) or (177). The absence of a dicyanomethyl signal in the proton NMR
1 *
NC.
.C = NR
(175)
where R=CH2Ph
RHN
(176)
NC .
,CN
(177)
spectrum
eliminated the
possibility
of an
addition
dicyanovinylidene C] carbon as in Scheme 2.33.
reaction
at the
2 ,2 -
The 13C NMR spectrum
further supported the hypothesis that the structure was unsymmetrical and
showed the correct number of different carbon absorptions for the structures
postulated. A total of 19 different carbon absorptions were observed of which
10 were aromatic.
Four of these were attributed to the benzyl group, three of
which were assigned conclusively with the aid of a C-H correlation spectrum,
and the remaining six aromatic absorptions to the isoindolin-1,3-diylidene ring.
Only three cyano carbon absorptions were observed, at 114.66, 115.35 and
116.80 ppm.
Since a 1,6-addition elimination reaction would have given a
product having a total of 18 different carbons, see Scheme 2.34, this possibility
was disregarded.
The carbon absorption at 44.9 ppm was assigned to the
methylene carbon of the benzyl group and the carbon at 57.25 ppm, by
comparison with the carbon NMR spectrum of (110) and various derivatives of
bis[ 2 ,2 -dicyano- 1-(phenylam ino)vinyl]benzene (178),159 was assigned as the
(178)
C 2 carbon of the 2 ,2 -dicyanovinylidene group, which is common to all three
possible structures. The IR spectrum showed two NH stretching bands at 3382
and 3321
cm*1.
Since the
NH stretching bands were sharp, and the
characteristically very broad band of an imino NH stretch was absent, this
suggested that either isomer (175) or (176) was the most probable structure.
However on the basis of this information alone it was not possible to determine
which structure was correct and further evidence was needed, either an X-ray
crystal structure of the product, which was not possible due to the inability to
grow adequate crystals, or a crystal structure of a compound which was
structurally very sim ilar and whose spectral data would also be very similar,
and which by comparison would allow the true structure to be assigned.
Recrystallisation of the solid obtained on evaporating the filtrate, gave
the benzylammonium salt (179).
The structure of (179) was assigned on the
106
basis of 1H, 13C NMR and IR spectral data and was confirmed by X-ray
structural analysis.
The lH NMR spectrum of (179) showed a broad singlet overlapping a
symmetrical aromatic multiplet at 8.52 ppm, giving a total integration of five
protons, and a symmetrical two proton aromatic multiplet at 7.65 ppm.
The
addition of deuterium oxide D2O to the lH NMR spectrum sample resulted in
the disappearance of the broad singlet, leaving a two proton aromatic multiplet
at 8.52 ppm, and verifying the presence of the three exchangeable protons of
the benzylammonium cation. The symmetrical aromatic peaks at 8.52 and 7.65
corresponded to the aromatic protons of the anion of ( 110 ). The five aromatic
protons of the benzylammonium cation were observed as a multiplet at 7.45
ppm and the two methylene protons occurred as a singlet at 4.5 ppm.
(179)
The symmetrical nature of the molecule was also apparent from the ]3C NMR
spectrum which showed a total of seven different aromatic peaks between 123
and 138 ppm and two cyano peaks at 116.24 and 117.19 ppm. The C i and C2
absorptions of the 2,2-dicyanovinylidene group were observed at 171.97 and
53.89 ppm respectively and the methylene carbon absorption at 42.28 ppm.
The
C-H
correlation
spectrum
showed
that the
three
aromatic carbon
absorptions at ~ 128 ppm corresponded to the benzylammonium group and the
absorptions at 122.8 and 131.3 corresponded to the anion of (110), as did the
quaternary aromatic absorption at 137.38 by comparison with the carbon NMR
spectra of the ammonium salt (119) and the tétraméthylammonium salt (155).
Comparison of the UV/visible spectrum of (179) with that of (119), and (155),
showed that they had identical ^ max values, see Figure 2.3.
The strong
similarities in the lH , ]3C NMR and UV/visible spectra suggested that the
orange solid was the benzylammonium salt.
In order to confirm the structure of (179) an X-ray crystal structure
analysis was carried out.
Compound (179) gave orange cubic crystals on
107
recrystallisation from acetonitrile. The crystal structure data showed that (179)
was monoclinic with space group P48 symmetry.
The crystal structure is
shown in Figure 2.4(a) and (b) and the corresponding bond lengths and bond
angles are given in Tables 2.1 and 2.2 respectively.
Figure 2.3 UV/Visible spectra o f (a) (179) and (b) (119)
108
T a b le 2 1
B o n d te m th s rA l
N(1 )-C( 8 )
1.347(10)
N(1)-C(1)
1.388(10)
N(2)-C(10)
1.113(12)
N (3)-C (1 1)
1.150(11)
N(4)-C(13)
1.169(12)
N(5)-C(14)
1.132(11)
N(6)-C(21 )
1.487(5)
C(1 )-C(9)
1.374(10)
C(1)-C(2)
1.519(11)
C(2)-C(3)
1.350(12)
C(2)-C(7)
1.395(5)
C(3)-C(4)
1.363(13)
C(4)-C(5)
1.381(6)
C(5)-C(6)
1.423(14)
C(6)-C(7)
1.413(12)
C(7)-C(8)
1.440(12)
C( 8 )-C ( 12 )
1.384(11)
C (9)-C (1 1 )
1.369(11)
C(9)-C(1 0 )
1.418(12)
C(12)-C(13)
1.428(12)
C (12)-C(14)
1.475(10)
C(15)-C(16)
1.35(2)
C(15)-C(20)
1.39(2)
C(15)-C(21 )
1.494(6)
C (16)-C(17)
1.49(2)
C (17)-C(18)
1.55(2)
C (18)-C (19)
1.16(2)
C(19)-C(20)
1.25(2)
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-S
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C(9)-C(1)-C(2)
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121.2(10)
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z
N3
Figure 2.4(a) SCHAKAL drawing of the crystal structure o f (179)
111
a * al
reP ras e n /
m in*
The crystal structure confirmed conclusively that the compound isolated
from the filtrate was in fact the corresponding benzylam monium salt (179).
2.D.2.2 Reaction of n-Propylamine with (119)
Treatment of (119) with n-propylamine under the same conditions as
used for the benzylamine reaction, with heating under reflux being maintained
for 22 hours, gave a sim ilar result. The new product which was observed by
TLC precipitated from solution. The lH NMR spectrum was consistent with that
of the benzylamino derivative, in that the same unsymmetrical character was
observed in the aromatic peaks.
Three aromatic multiplets integrated in the
ratio 1:1:2 as before and two different NH proton peaks, with an integration
ratio of 1 :2 , were also present.
The main difference, on comparing the two
proton NMR spectra, was the expected difference in the /V-substituent of the
amine used. The /V-propyl group gave the expected splitting pattern, a triplet,
multipiet and triplet with J= 7.4 Hz, and an integration ratio of 2:2:3.
By the
same reasoning arrived at for the benzylamino adduct discussed previously,
three possible structures were postulated for the product, (180), (181) and
(182).
The 13C NMR spectrum was also consistent with these findings and
showed the correct number of different peaks for the postulated structures.
NH2
C = NR
Nü
CN
( 180 )
where R= Propyl
The unsymmetrical structure of the product was verified by the observation of
six different aromatic absorptions between 123 and 138 ppm and three cyano
absorptions at 115.15, 115.95, and 117.18 ppm.
The three propyl carbons
were observed at 11.65, 21.09 and 44.2 ppm. The carbon observed at 56.96
ppm was assigned as the C 2 carbon of the 2 ,2 -dicyanovinylidene group by
comparison with the findings for the benzylamine derivative.
All the carbon
absorptions observed occurred at chemical shifts very sim ilar to those found for
the corresponding carbons of the benzylamino derivative, (see Table 2.7 in
Discussion Section, pg 129).
This showed that the propyl and benzyl
derivatives had essentially the same basic structure. The IR spectrum showed
113
the presence of three sharp NH stretching bands at 3350, 3278 and 3205 cm-1.
The absence of a broad imino NH stretch again suggested (179) and (180)
were the most probable structures. The UV/visible spectra of both derivatives
were also found to be essentially the same, Figure 2.5, and this further
confirmed the same type of structure for both derivatives.
Figure 2.5 UV/Visible spectra of (a) Propylamino derivative (180) and
(b) Benzylamino derivative (175)
The ] H, and 13C NMR spectra of the solid isolated from the filtrate of the
propylamine reaction with (119) were consistent with the assigned structure
(183).
The !h NMR spectrum showed a symmetrical two proton multiplet at
8.07 ppm and another symmetrical aromatic multiplet overlapping with a broad
singlet at 7.59-7.62 ppm integrating for a total of five protons.
These
corresponded to the aromatic protons of the anion of ( 110 ) and the NH 3
protons of the propylammonium cation.
114
The propyl protons gave a splitting
pattern consistent with that expected and integrated for a total of seven
protons. The 13C NMR spectrum, (see Table 2.8, discussion section pg 131),
showed three aromatic carbon absorptions, two cyano absorptions, and two
absorptions
corresponding
to
the
and
C2
carbons
of
the
2,2-
dicyanovinylidene group as expected for the symmetrical structure of the anion
of (110).
The remaining three carbon absorptions corresponded to the N-
propyl group.
Since the 1H, and 13C NMR, and UV/visible spectra were
essentially identical to those of the benzylammonium salt, except for the
differences due to the different N-alkyl substituents, it was concluded that
assigned structure (183) was correct.
NC^ XN
NC
CN
(183)
2.D.2.3 Reaction of Isopropylamine with (119)
The reaction of isopropylamine with (119) gave results very similar to
those for the propylamine and benzylamine reactions.
The new product
observed by TLC was again found to have unsymmetrical aromatic proton NMR
absorptions in the ratio 1:1:2 and two types of NH protons integrating in the
ratio 1:2. The other protons observed corresponded to the isopropyl group and
were found as a multiplet at 3.94 ppm and a doublet at 1.26 ppm in a ratio of
1:6. Three possible structures were postulated as before, (184)-(186). The 13C
NMR spectrum showed the correct number of carbons for the structures
postulated,
with
six
different aromatic
carbon
absorptions,
three
cyano
absorptions and the C 2 carbon absorption of the 2,2-dicyanovinylidene group,
as well as the remaining carbon absorptions, being observed at very similar
1 c
NC.
X = NR
(184)
RHN
NC.
(185)
.C N
(186)
where R= Isopropyl
115
chemical shifts to
those found for the corresponding benzylamino and
propylamino derivatives, (see Table 2.7). The main difference, on comparing
the carbon NMR spectra, was the observation of the different number of carbon
absorptions corresponding to the different N-alkyl groups.
The equivalent
methyl carbon absorptions for the isopropyl group were found at 21.6 ppm and
the remaining CH carbon absorption was found at 43.6 ppm. The IR spectrum
showed the presence of three sharp NH stretching bands at 3424, 3341 and
3233 cm-1 as before.
propylamino
The UV/visible spectrum was identical to that of the
derivative
and
it
was
concluded
that
the
reaction
of
isopropylamine with (119) gave a product with a correspondingly analogous
structure.
Once again the product isolated from the filtrate was identified as the
corresponding salt, the isopropylammonium salt (187), on comparison of the ] H
and
13c NMR spectra,
and the
UV/visible
spectra,
with those of the
benzylammonium salt. Two symmetrical aromatic multiplets were observed as
before with a broad three proton singlet, corresponding to the NH protons of
the isopropylammonium cation, infringing on the multiplet at 7.62 ppm. The
(187)
isopropyl protons were observed as a one proton multiplet at 3.26 ppm and a
six proton doublet, J= 6.4 Hz, at 1.13 ppm.
Also present was a broad one
proton OH singlet at 4.36 ppm, a two proton quartet at 3.41 ppm, J= 6.8 Hz,
and a three proton triplet, J= 6.8 Hz, at 1.03 ppm which corresponded to
ethanol, present as a solvent of crystallisation.
The disappearance of the
broad five proton multiplet at 7.62 ppm, giving instead a two proton multiplet,
and the broad singlet at 4.36 ppm on addition of deuterium oxide to the NMR
sample confirmed the presence of exchangeable NH and OH protons. The l 3C
NMR spectrum was also very sim ilar to those of the previous alkylammonium
salts, (see Table 2.8). The symmetrical structure of the salt was apparent from
the presence of three aromatic absorptions, two cyano absorptions, and the C^
and C 2 carbon absorptions of the 2,2-dicyanovinylidene group, all occuring at
chemical shifts similar to those of the other salts and the anion of (110). The
main difference was the observation of carbons corresponding to the isopropyl
116
group and the ethanol, which gave a total of four carbons between 19 and 54
ppm.
The UV/visible spectrum was also identical to those of the previous
alkylammonium salts and thus on the basis of the strong similarities of all the
spectral properties it was concluded that the assigned structure (187) was
correct.
2.D.2.4 Reaction of n-Butylam ine with (119)
Treatment of (119) with n-butylamine under reflux for six hours in
ethanol gave an orange precipitate in high yield. The precipitate was assigned
as one of the three possible structures (188)-(190) on the basis of the strong
sim ilarities in the 1H, 13C NMR and IR spectra, and by comparison of its
UV/visible spectrum, with those of the previous alkylamino derivatives.
The
unsymmetrical aromatic multiplets were observed as before in the ratio 1:1:2 as
were the two NH absorptions, in the ratio 1:2, at 10.8 and 8.7 ppm respectively.
The remaining absorptions in the proton NMR spectrum corresponded to the nbutyl group, observed as a series of multiplets between 3.3 and 0.9 ppm and
which gave a total integration for nine protons.
NH2
C = NR
nu
CN
R= n-butyl
(188)
(189)
The 13c NMR spectrum was very similar to those of the previous N-alkyl
derivatives (see Table 2.7 ) the main difference being the number of carbon
absorptions observed for the different N-alkyl group. The butyl group appeared
as four peaks between 13.4 and 42.3 ppm. The IR spectrum showed two NH
stretches at 3326 and 3270 cm_i and comparison of the UV/visible spectrum of
the n-butylamino derivative with that of the isopropylamino derivative showed
they had identical Xmax values again demonstrating that the n-butylamino
derivative of (110) had essentially a structure analogous to those of the other
amino derivatives.
Comparison of the 1H, 13C NMR and UV/visible spectra with those of the
other alkylammonium salts showed that the product obtained from the filtrate
was the butylammonium salt (191). Two symmetrical aromatic multiplets, in the
117
ratio 2:2, were observed at 8.07 and 7.62 ppm with a broad three proton singlet
at 7.58 ppm, corresponding to the NH protons of the butylammonium cation,
infringing on the multiplet at 7.62 ppm. The butyl group gave the anticipated
splitting pattern and integrated for a total of nine protons.
The carbon NMR
spectrum showed three aromatic absorptions, two cyano absorptions, the
and C 2 carbon absorptions of the 2,2-dicyanovinylidene group all occurlng at
chemical shifts similar to those of the other salts, (see Table 2.8). Also present
were four carbons between 13.5 and 38.6 ppm corresponding to the butyl
group.
NC.
,C N
NC
CN
(191)
2.D.2.5 Reaction of Cyclohexyiamine with (119)
Treatment of cyclohexyiamine with (119) in pyridine under reflux for 11
hours gave a new product which was isolated by precipitation from water. This
product exhibited similar unsymmetrical character in its ÏH NMR spectrum and
showed the presence of two NH absorptions in the ratio of 1:2 as before with
the main difference being the observation of a total of eleven protons as six
multiplets corresponding to the cyclohexyl group. The 13C NMR spectrum was
essentially the same (see Table 2.7 ), as the other alkylamino derivatives the
only difference being the observation of four carbon absorptions between 24
and 51 ppm corresponding to the cyclohexyl group. The UV/visible spectrum
was identical to the previous alkylamino derivatives and on the basis of the
previous findings it was concluded that the cyclohexylamino derivative also had
the same structure, either (192), (193) or (194), as the other derivatives.
1 *
NC.
X = NR
NC.
RHN
XN
R= Cyclohexyl
(192)
(194)
(193)
118
W hile no salts were obtained from this reaction, as had been obtained with the
other amines, one unusual product which was recovered while investigating
this reaction was the /V-isopropylldenecyclohexylamnnonium salt (195).
Salt (195) was obtained as an orange cubic crystalline solid by
recrystallisation, from acetone, of a red oil obtained when cyclohexylamine and
the ammonium salt (119) were stirred together at room temperature in acetone
and the acetone evaporated off.
The IR, 1H and 13C NMR spectra and
elemental analysis were in agreement with the assigned structure.
(195)
The 1H NMR spectrum showed the characteristic symmetrical peaks for
the four aromatic protons of the anion of (110) at 8.0 and 7.6 ppm, and a broad
NH proton absorption at 12.2 ppm corresponding to the protonated imino
nitrogen. Apart from the cyclohexylamino proton absorptions which integrated
for a total of 11 protons, two additional three proton absorptions corresponding
to the isopropylidene methyl protons were observed at 2.34 and 2.32 ppm.
The 13C NMR spectrum showed a total of fourteen different absorptions, three
aromatics at 122.9, 131.4 and 137.4 ppm, two cyano at 116.3 and 117.3 ppm,
the 2,2-dicyanovinylidene C] carbon absorption at 178.9 ppm and a carbon
absorption at 53.9 ppm corresponding to the 2,2-dicyanovinylidene C2 carbon,
all of which corresponded to the anion of (110) (see Table 2.8).
carbon absorptions were observed between 20.9 and 56.4 ppm.
Six alkyl
These
corresponded to four cyclohexyl carbons and two methyl carbons of the
isopropylidene group.
the
imino carbon.
The carbon absorption at 172.0 ppm corresponded to
The structure was conclusively confirmed by X-ray
crystallography.
The single crystals required for the X-ray analysis were obtained by
recrystallisation from acetone. The crystal structure analysis data showed that
the salt was triclinic with space group P-1 symmetry. The crystal structure is
shown in Figure 2.6 and the relevant bond lengths and bond angles are given
in Tables 2.3 and 2.4.
119
Figure 2.6 SCHAKAL drawing o f the crystal structure o f salt (195)
120
The formation of (195) may be explained by the condensation reaction
of the cyclohexylamine with acetone, giving /V-isopropylidenecyclohexylamine
(196),
Scheme
2.37,
which
is
subsequently
protonated
to
give
the
corresponding iminium salt (195).
(196)
Scheme 2.37
Table 2.3 showing bondlengths for (195)
C(1)-C(6)
1.384(5)
C(13)-N(14)
1.141(4)
C(1)-C(2)
1.400(4)
C (15)-C (16)
1.421(5)
C(1)-C(7)
1.473(4)
C(15)-C(18)
1.424(5)
C(2)-C(3)
1.383(4)
C(16)-N(17)
1.147(4)
C(2)-C(9)
1.474(4)
C (18)-N (19)
1.146(4)
I
C(3)-C(4)
1.381(5)
C(20)-N(26)
1.478(4)
j
C(5)-C(4)
1.378(5)
C(20)-C(21)
1.514(4)
C(5)-C(6)
1.386(5)
C(20)-C(25)
1.515(4)
!
C(7)-N(8)
1.370(4)
C(21 )-C(22)
1.513(5)
|
C(7)-C(15)
1.374(4)
C(22)-C(23)
1.510(5)
j
N(8)-C(9)
1.361(4)
C(23)-C(24)
1.517(5)
I
C(9)-C(10)
1.383(4)
C(24)-C(25)
1.528(5)
I
C(10)-C(11)
1.421(5)
N(26)-C(27)
1.278(4)
C(10)-C(13)
1.426(5)
C(27)-C(29)
1.476(5)
C(11)-N(12)
1.150(4)
C(27)-C(28)
1.477(5)
|
I
j
;
2.D.2.6 Reaction of n-Octylam ine and n-Decylamine with (119)
Results similar to those for the other amines were observed on treating
(119) with n-octylamine or with n-decylamine.
these reactions precipitated from solution.
The new product in each of
The 1H and 13C NMR spectra of
each indicated unsymmetrical structures consistent with previous findings. The
n-octylamino product showed two broad NH singlets at 10.7 and 8.5 ppm in the
ratio 1:2 as before as well as unsymmetrical aromatic multiplets integrating in
Table 2.4 showing bondangles for (195)
C(6)-C(1)-C(2)
120.5(3)
C(6)-C(1)-C(7)
i
N(12)-C(11)-C(10)
177.1(3)
133.9(3)
N(14)-C(13)-C(10)
178.6(3)
C(2)-C(1)-C(7)
105.6(3)
C(7)-C(15)-C(16)
122.5(3)
C(3)-C(2)-C(1 )
120.8(3)
C(7)-C(15)-C(18)
120.4(3)
C(3)-C(2)-C(9)
133.4(3)
C(16)-C(15)-C(18)
117.0(3)
C(1)-C(2)-C(9)
105.8(3)
N(17)-C(16)-C(15)
179.6(4)
C(4)-C(3)-C(2)
118.0(3)
N(19)-C(18)-C(15)
179.7(3)
C(5)-C(4)-C(3)
121.5(3)
N(26)-C(20)-C(21)
109.1(3)
C(4)-C(5)-C(6)
120.9(3)
N(26)-C(20)-C(21)
110.5(2)
C(1)-C(6)-C(5)
118.3(3)
C(21 )-C(20)-C(25)
111.4(3)
N(8)-C(7)-C(1)
110.6(3)
C(22)-C(21)-C(20)
110.4(3)
N(8)-C(7)-C(15)
122.2(3)
C(23)-C(22)-C(21)
111.2(3)
C(15)-C(7)-C(1 )
127.2(3)
C(22)-C(23)-C(24)
112.3(3)
C(9)-N(8)-C(7)
107.2(2)
C(23)-C(24)-C(25)
111.8(3)
N(8)-C(9)-C(10)
122.3(3)
C(20)-C(25)-C(24)
109.8(3)
N(8)-C(9)-C(2)
110.7(2)
C(27)-N(26)-C(20)
127.4(3)
C(10)-C(9)-C(2)
126.9(3)
N(26)-C(27)-C(29)
119.7(3) |
C(9)-C(10)-C(11)
123.3(3)
N(26)-C(27)-C(28)
122.0(3) I
C(9)-C(10)-C(13)
121.4(3)
C(29)-C(27)-C(28)
118.3(3)
C(11)-C( 10)-C( 13)
115.3(3)
!
i
the ratio 1:1:2. The remaining protons corresponded to the n-octyl protons and
these integrated for total of seventeen protons.
The 13C NMR spectrum was
very similar to those of the previous A/-alkyl derivatives (see Table 2.7) with the
main difference being for the carbons of the A/-alkyl group.
Eight carbons
corresponding to the n-octyl group were observed between 14 and 42 ppm.
The aromatic proton absorptions of the n-decylamino derivative were
unsymmetrical as before, with two broad NH peaks, in the ratio 1:2, being
observed at 10.8 and 8.6 ppm.
The other protons present occurred between
3.29 and 0.79 ppm and these integrated in total for 21 protons, corresponding
122
to the n-decyl protons. The 13C NMR spectrum was very similar to those of the
previous A/-alkyl derivatives (see Table 2.7) with the expected difference of ten
carbon absorptions being observed between 14 and 42 ppm, corresponding to
the n-decyl carbons.
Both the n-octyl and n-decyl derivatives had essentially
identical UV/visible spectra.
Unfortunately a crystal structure of neither of
these products could be obtained.
Once again on the basis of the strong
sim ilarities in the spectral data between all the A/-alkyl derivatives it was
concluded that the products obtained from the reaction of n-octyl and n-decyl
amine
with
(119)
were
either
the
amidines
(197)
and
(198)
or the
benzoazepines (199) and (200) or (201) and (202).
:= N R
NC
RHN
CN
(197) R= n-octyl
(199) R= n-octyl
(201) R= n-octyl
(198) R= n-decyl
(200) R= n-decyl
(202) R= n-decyl
W hile both the filtrates from the n-octylamine reaction and the ndecylamine reaction gave black oils on evaporating off the solvents, only the ndecylammonium salt was obtained, by precipitation of a chloroform solution of
the oil with light petroleum. Attempts to isolate the n-octylammonium salt in a
sim ilar manner were unsuccessful.
The
ïH
NMR spectrum
of the
n-
decylammonium salt again showed two symmetrical aromatic multiplets at 8.08
ppm, integrating for two protons, and another at 7.6 ppm which overlapped with
a broad singlet which together gave a total integration for five protons.
The
remaining protons were observed as four multiplets at 2.7, 1.48, 1.18 and 0.8
ppm, in the ratio 2:2:14:3, corresponding to the n-decyl protons. The 13C NMR
spectrum showed the same symmetrical character of the salt as before, with
three
aromatic
carbon
absorptions,
two
cyano
absorptions,
and
two
absorptions corresponding to the 2,2-dicyanovinylidene C i and C 2 carbons
being observed which corresponded to the anion of (110), (see Table 2.8).
The remaining ten carbons between 14 and 48 ppm corresponded to the decyl
group.
On the basis of the strong sim ilarities in the spectral data with the
conclusively identified benzylammonium salt it was concluded that the solid
isolated was the n-decylammonium salt.
123
Since it had not been possible to obtain crystals of adequate quality for
X-ray crystal structure determination of the possible amidine/benzoazepine
products obtained from
reaction
of (119)
with
described, it was decided to investigate the
secondary amine with (119).
the
primary amines just
reaction the reaction of a
The use of a secondary amine might also be
expected to yield products with fewer possible tautom ers.
2.D.2.7 Reaction of /V,/'£Dibutylamine with (119)
Treatment of the ammonium salt (119) with the secondary amine N,Ndibutylamine under reflux in ethanol for six hours gave almost complete
conversion to a new product. This new product was isolated as a red solid by
evaporation of the ethanol and recrystallisation from acetonitrile gave red
needles. The identity of this new product was determ ined by 1H, 13C NMR and
IR spectral data and its structure was confirmed conclusively by X-ray crystal
structure analysis.
The
NMR spectrum showed many sim ilarities to those of the primary
amine products mentioned already.
Three unsymmetrical aromatic multiplets
were observed at 8.3, 8.2 and 7.7 ppm respectively in the ratio 1:1:2 as before.
Two broad NH peaks were also observed at 9.6 and 9.0 ppm and integrated in
the ratio 1:1. The remaining protons integrated for a total of eighteen protons
and these occurred
as four multiplets
between
3.6 and 0.9
ppm and
corresponded to the A/,A/-dibutyl group. The 13C NMR spectrum also showed
many similarities to those of the primary amine products (see Table 2.7), with
the
main
difference
being
the
number
of
different
carbon
absorptions
corresponding to the A/-alkyl substituents. Thus four carbon absorptions were
observed between 13 and 29 ppm, corresponding to the butyl carbons.
Six
aromatic carbon absorptions were observed as before between 123 and 138
ppm as were three cyano absorptions at 116.8, 118.2 and 118.5 ppm. The C2
carbon absorption of the 2,2-dicyanovinylidene group was also found at 50.8
ppm. The IR spectrum showed a NH stretch at 3340 cm-1 and the UV/visible
spectrum showed Vnax at 482, 460 and 336 nm, slightly shorter wavelengths
than those of the previous addition products.
information
two
possible
structures,
(203)
On the basis of the spectral
and
(204),
were
postulated.
Fortunately this compound yielded crystals of sufficient quality for X-ray
structural analysis to allow the exact structural assignment be made.
Crystals of good quality for X-ray structural determination of the
A/,A/-dibutylamine adduct of (110) were
obtained
recrystallisation from dimethylformamide.
The single crystal X-ray structure
124
as scarlet needles by
conclusively
identified
the
product
to
be
2-cyano-/V?,/V?-dibutyl-2-(3-
dicyanom ethyleneisoindolin-1-diylidene)acetam idine (203).
The structure is
triclinic, with P-1 symmetry and is shown in Figure 2.7.
N(butyl)2
NCV
X = NH
(204)
(203)
The relevant bond lengths and bond angles are shown in Tables 2.5 and 2.6.
The crystal structure shows that the molecule is essentially planar except for
the 2-cyano-A/,,/Vi-dibutylacetamidino group which is twisted out of the plane
due to the steric bulk of the /V,/V-dibutylamino group.
2.D.3 Discussion
At the outset of these reactions we were interested in seeing how and
where an amine would react with compound (110). On the basis of the strong
similarities found in the proton and carbon NMR data of the products from the
reaction of (119) with primary amines and those for (203), it was concluded that
the products of the addition reactions of the primary amines were also
amidines, Scheme 2.38.
The unsymmetrical
character of the aromatic
multiplets, in the ratio 1:1:2, was common to all the amidines. Two NH proton
peaks in the ratio 1:2 in the 1H NMR spectrum, showing the presence of an NH
and an NH2 group, were found in the primary amine derivatives, confirming that
these amidines exist in the tautomeric form (173b) (Scheme 2.36).
The
A/,A/-dibutyl derivative (203) exhibited two one proton NH absorptions and can
only exist in one form as expected.
The common carbon absorptions of the
13C NMR spectra of all the amidines, with the A/-alkyl peaks omitted, are shown
in Table 2.7. It is clear from the table that essentially the same carbon skeleton
is common to all structures.
The slight variations in the chemical shifts for
some of the absorptions for (203) can be attributed to reduced conjugation in
the system due to the greater steric bulk of the A/,/V-dibutylacetamidino group
compared with the other amidines, as also evident from the UV/visible spectra.
125
c
2<t
Figure 2.7 SCHAKAL drawing of the crystal structure of (203)
126
Table 2.5 showing the bondlengths for (203)
Table 2,5 Band lengths
fA j
N(1)-C(8)
1.347(10)
N(1)-C(1)
N(2)-C(10)
1.388(10)
I
1.113(12)
N(3)-C(11)
1.150(11)
N(4)-C(13)
1 .169(12)
N(5)-C(14)
1.132(11)
N(6)-C(21)
1.487(5)
C(1)-C(9)
1.374(10)
C(1 )-C(2)
1.519(11)
C(2)-C(3)
1.350(12)
C(2)-C(7)
1.395(5)
C(3)-C(4)
1.363(13)
C(4)-C(5)
1.381(6)
C(5)-C(6)
1.423(14)
C(6)-C(7)
1.413(12)
C(7)-C(8)
1.440(12)
C(8)-C(12)
1.384(11)
C (9)-C (11)
1.369(11)
C(9)-C(10)
1.418(12)
NH2
NR2
C = NR
N C ^ J,C = N H
RNH,
R2NH
NC
(175): R= benzyl
(119)
(180): R= propyl
(184): R= isopropyl
(188): R= butyl
(192): R= cyclohexyl
(197): R= octyl
(198): R= decyl
Scheme 2.38
107
CN
(203): R= butyl
Table 2.6 showing the bondangles for (203)
c
c
c
c
c
c
c
c
c
c
c
c
c
c
N
N
c
N
N
C
c
c
c
N
N
C
C
C
N
N
N
N
N
C
C
N
C
C
9 )**N(8 )~C (7 )
18)-N(20)-C(21)
18)-N(20)-C(25)
21)”N (20)-C(25)
6)-C(l)-C(2)
6)-C(l)-C(7)
2)-C(l)-C(7)
3)“C (2)-C(1)
3)“C (2)-C(9)
1)~C(2)-C(9)
2)“C(3)-C(4)
5)-C(4)-C(3)
4)“C (5)-C(6)
1)“C (6)-C(5)
8)-C(7)-C(15)
8)-C(7)-C(l)
15)“C (7)-C(1)
8)-C(9)-C(10)
8)-C(9)-C(2)
10)-C(9)-C(2)
9)-C(10)-C(13)
9)-C(10)-C(11)
13)-C(10)-C(11)
12)-C(11)_C(10)
14)-C(13)- C ( 10)
7)-C(15)-C(16)
7)-C(15)-C(18)
16)-C(15)-C(18)
17)-C(16)-C(15)
19)-C(18)-N(20)
19)—C (18)-C(15)
20)-C(18)-C(15)
20)-C(21)“C(22)
23)-C(22)-C(21)
22)-C ( 23 ) -C ( 24 )
20)-C ( 25 ) -C ( 26 )
25)- C(26) —C ( 27 )
28 ) -C(27)-C(26)
107. 9
125.1
120.3
113.7
119.8
134.4
105.5
121. 1
133.4
105.5
118.2
121.1
121. 1
118.7
123.0
109.9
127. 1
120.8
111.0
128. 1
120.4
122.5
117.0
179.5
178.3
116.7
123.8
119.0
177.0
119.4
117.7
122.8
113.6
111.7
113.7
113.2
113.0
115.2
128
2)
2)
2)
2)
2)
2)
2)
2)
2)
2)
3)
3)
2)
2)
2)
2)
2)
2)
2)
2)
2)
2)
2)
3)
3)
2)
2)
2)
3)
2)
2)
2)
2)
2)
3)
2)
2)
3)
y u i u y a i n.
inm n opecira ui
able ¿ J
ComDOund
(175)
(180)
(184)
(188)
(192)
(197)
(198)
(203)
N-Substituent
Benzyl
Propyl
Isopropyl
But yl
Cvclohexyl
Octyl
Decyl
Dibutyl
C2
57.25
56.96
56.36
56.9
56.8
56.9
57.0
50.8
114.66,
115.15
114.8
115.1
115.2
114.9
115.1
116.8
115.35,
115.95
115.3
115.9
115.8
115.7
115.9
118.2
116.8
117.18
116.7
117.1
117.2
116.9
117.1
118.5
123.12
123.25
122.6
123.2
123.2
122.9
123.2
122.7
123.44
123.61
123.0
123.5
123.5
123.3
123.5
122.9
131.03
131.21
130.6
131.1
131.2
130.8
131.1
131.0
131.46
131.66
131.1
131.5
131.6
131.2
131.5
131.1
135.0
134.97
134.3
134.9
134.9
134.7
134.9
137.7
137.97
137.98
137.4
137.9
137.9
137.7
137.9
137.8
71.37
71.95
71.5
71.9
71.9
71.59
71.8
73.2
Other
159.56
159.1
157.4
158.9
157.7
158.7
158.9
159.2
non-alkyl C
167.26
166.79
166.1
166.7
166.7
166.5
166.7
165.4
170.1
170.25
169.8
170.1
170.3
169.9
170.2
171.5
of
2,2-
dicyanovinylidene qroup
Cyano C
Aromatic C
127.05
Benzyl
127.19
Aromatic Cs
128.01
135.54
*: in DMSO-dg and referenced to 39.49 ppm.
Comparison of the UV/visible spectrum of (203) with the spectra of the
other acetamidines synthesised from primary amines, showed that there was a
10 nm hypsochromic shift for the UV/visible spectrum of (203), whose A,max in
DMF occurs at 482 and 460 nm compared with 492 and 460 nm for the adducts
of the primary amines. This suggests that there is less deviation from planarity
for the acetamidines derived from the primary amines due to their lesser steric
bulk.
The recovery of the alkylammonium salts, Scheme 2.39, and the
/V-isopropylidenecyclohexylammonium salt (195) from the reaction of the
alkylamines with (119) is not surprising in light of the acidic nature of (110).
(195)
(179): R= benzyl
(183): R= propyl
(187): R= isopropyl
(191): R= butyl
Scheme 2.39
These salts were also identified by comparison of their spectral data with
those of the conclusively identified benzylammonium salt (179).
They all
showed the same symmetrical character in the aromatic multiplets of their
proton NMR spectra, with a three proton NH singlet, corresponding to the alkyl
ammonium group, infringing on one of the aromatic multiplets. Comparison of
the carbon NMR spectra, Table 2.8, with the absorptions corresponding to the
different alkyl groups omitted, showed the same symmetrical character for all
the salts and that the absorptions all occurred at very similar chemical shift
values.
The reactions of the amines with (119) are summarised in Table 2.9 and
are thought to involve an initial proton exchange between the ammonium cation
and the alkylamine releasing ammonia and forming the alkylammonium salt. It
is the alkylammonium salt which then reacts to give the amidine p ro d u c t. This
was verified by taking the n-propylammonium salt (183) and heating it under
reflux in 1,4-dioxan to give the corresponding amidine (180).
130
Table 2.8
13C NMR spectra* of the anion of the alkylammonium salts of 2,2'-
(isoindolin-1,3-diylidene)bispropanedinitrile (110).
S alt
A rom atic C
Benzyl
122.83, 131.27,
Ammonium
137.38
C-i
of
2,2-
C2
of
2,2-
d ic y a n o v in y l-
d ic y a n o v in y l-
idene g ro u p
idene g ro u p
171.97
53.89
C yano C
116.24,
117.19
(179)
Propyl
122.9,
ammonium
137.5
131.3,
172.1
54.0
116.4,
117.3
(183)
Isopropyl
122.93, 131.37,
ammonium
137.48
172.07
56.08
116.35,
117.3
(187)
Butyl
122.9,
ammonium
137.5
131.4,
172.1
54.1
116.3,
117.3
(191)
Isopropylid
122.9,
ene-
137.4
131.4,
172.0
53.9
116.3,
117.3
cyclohexyl
ammonium
(195)
Decyl
123.5,
ammonium
138.3
131.3,
172.5
116.7,
54.8
117.4
*: all spectra were measured in DMSO-d6 except for the n-decylammonium salt
which was determined in acetone-d6.
W hy
nucleophilic attack does not occur at the
1-position of the
isoindolin-1,3-diylidene ring may somehow be resonance related.
By analogy
with the nitrogen in an amide group, the lone pair on the nitrogen in the
2-position of the isoindolin-1,3-diylidene ring can delocalise into the adjacent
2,2-dicyanovinylidene groups, thus making the adjacent carbons in the 1- and
3-positions less prone to nucleophilic attack due to the greater stability granted
by the resonance structures.
Table 2.9 Summary of the reactions of various amines with (119)
benzylamine
1,4-dioxan
46
I 28
n-propylamine
1,4-dioxan
65
|8
isopropylamine
1,4-dioxan
47
] 25
n-butylamine
ethanol
77
] 17
A/,/V-dibutylamine
ethanol
94
|-
cyclohexylamine
pyridine
64
!-
n-octylamine
1,4-dioxan
27
!-
ethanol
30
I-
\ n-decylamine
Formation of the amidines from the corresponding alkylammonium salts
probably involves an equilibrium between the alkylammonium salt of (110) and
the neutral components (Scheme 2.40), maintaining a small concentration of
the free amine.
1,2-Addition of the amine across a cyano group of (110) can
then occur.
NHRR'
NC
CN
Scheme 2.40
The
X-ray crystal
structure
of (203)
shows that addition
of the
A/,/V-dibutylamine occurs at the cyano group farthest from the aromatic ring,
giving the Z-isomer,
and that there
is significant twisting
of the
N,N-
dibutylacetamidino group out of the plane of the molecule due to the steric bulk
of A/,A/-dibutyl group.
W ere addition to occur at the cyano group adjacent to
the benzene ring, this would result in greater steric strain in the system due to
unfavourable interaction between the A/,A/-dibutylacetamidino group and the
peri hydrogen of the aromatic ring.
132
As
mentioned
previously
the
greater
steric
bulk
of
the
/V,A/-dibutylacetamidino group of (203) is apparent from comparison of its
UV/visible spectrum with those of the primary amine derivatives in that its Vnax
occurs at a shorter wavelength due to reduced conjugation.
Interestingly the
primary amine derivatives all exhibit essentially the same solution-phase
UV/visible spectrum yet show various shades of orange and even a yellow in
their solid state. It has been reported152 that some pigments can crystallise in
different phases and these can have different colour properties. For example,
pigment (205) exists in two phases, a and (3, which give a yellow and scarlet
pigment respectively and the phase obtained is dependent on the solvent used
in their synthesis. Standard solvents give the yellow pigment and solvents like
DMF give the scarlet pigment.
Thus these morphological effects on pigment
shade and colour may explain why (203) occurs as a scarlet red crystalline
solid with A.max values at shorter wavelengths, 482 and 460 nm, compared to
the varying orange powders found for the primary amine derivatives, all with
Vnax values at 492 and 460 nm.
(206)
(205)
The UV/visible spectra of (206), with various substituents, have ^ max values at
495 and 498 nm in DMF and these occur at values similar to those for the
primary amine derivatives and this further supports the assigned amidine
structures.
2.D.4 C o n c lu s io n s
It is apparent from the reactions carried out on (110), via its ammonium
salt (119), that it is not prone to nucleophilic attack at the sp2-hybridised
carbon adjacent to the nitrogen as is the carbonyl carbon of phthalimide. Thus
it seems that sim ilarities in the reactivity of carbonyl compounds and their
alkylidenem alononitrile analogues does not hold for phthalimide and (110) and
unfortunately did not provide a route to the /V-alkyl derivatives of (110). The
amidines in Scheme 2.38, which have not been reported before, show poor
133
solubility in nearly all organic solvents and may be of use as pigments. Further
studies with a greater range of nucleophiles
may yield
further related
isoindoline pigments with a greater variety of shades and good pigment
properties.
134
C hapter
3.0 Cyclic Voltammetric Analysis
3.1 In tro d u c tio n
Cyclic Linear Sweep Voltammetry (CV) is a popular technique for
characterising the electrochemical properties of new species and has proven
useful for determining the electron affinity and electron donating ability of
compounds.
This method is well reported181 and has allowed the electron
acceptor ability of novel acceptor groups to be compared with those already
known and gives a good indication as to the potential C-T forming abilities of
new acceptor groups. In this chapter, the results of the electrochemical studies
on the acceptor molecules (110) and (151) shall be reported.
(1 10)
(151)
In a typical CV experiment,182 the applied potential at the working
electrode, measured with respect to a reference electrode, is varied linearly
with time at a controlled sweep rate and the resulting current is measured.
Typical sweep rates range from 0.04 to about 1,000 V/sec.
It is customary to
record the current as a function of potential, which is equivalent to recording
the current versus time. A typical CV is shown in Figure 3.1.
0
E
p.o
Figure 3.1 Typical Cyclic Voltammogram for a freely diffusing species.
136
During the forward sweep of a species O for reduction to a species R,
the scan is begun well positive of the formal potential E0' for the process,
position (A), and no current flows at this initial potential.
As the electrode
potential approaches E0', a current begins to flow, (B), and as the potential
becomes more negative the current continues to grow, (C), as the surface
concentration of the neutral species at the working electrode drops.
As the
potential moves past E0' the surface concentration drops to near zero, mass
transfer of the neutral species to the surface reaches a maximum, (D), and then
declines as the depletion effect sets in and the current decays, (E).
By
reversing the potential at (F) and sweeping in a positive direction, the large
concentration of oxidisable anion radical R, in the vicinity of the electrode,
generates a reversal current which gives a curve having a shape much like that
of the forward sweep.
In a cyclic voltammogram the parameters of most importance are: the
peak potentials Ep C and Ep a (c = cathodic and a = anodic), their difference
AEp_ and the peak currents ip C and ip a. These parameters give important
information as to the
reversibility of the electrochem ical system.
electrochemical system follows the Nernst equation
If an
(equation 5), or an
equation derived from it, the system is said to be reversible or Nernstian.
E = E ° + RT/nF lnC0/C R
equation 5
where E is the applied potential, E0' is the formal potential, R is the Gas
Constant, T is the absolute Temperature, F is the Faraday Constant, n is the
number of electrons per molecule of oxidised or reduced species, C0 is the
concentration of oxidised species in mol/cm3, and C r is the concentration of
reduced species in mol/cm3.
For an electrochemically reversible system the difference in the peak
potentials, AEp, at 25°C is 0.059/n V.
For a chemically reversible system the
ratio of the peak currents ip ^ / ip ^ 's ur,ity since both the oxidised and reduced
species are chemically stable. A cause of non-reversibility, which can occur for
organic species, is if a chemical reaction occurs at the electrode resulting in the
generation of a new organic entity leading to the initial product of electron
transfer being lost.
137
3.2 Electrochemical Stud ie s of (110) and (151)
Figures 3.2 and 3.3 show the cyclic voltammograms of (110) and (151)
respectively, measured in dimethylformamide at room temperature, where the
supporting electrolyte was lithium perchlorate.
A hanging
mercury drop
electrode was used as the working electrode and a Ag/AgCI electrode as the
reference electrode.
Dimethylformamide was used as the solvent as this was
the only solvent in which (110) was sufficiently soluble. It is apparent from both
CVs that neither species was reversible, under the chemical conditions used
and at the timescale employed, suggesting that the reduction products formed
were chemically unstable.
In the CV of (110) (Figure 3.2), the potential was scanned between -0.2
and -2.0 V at a sweep rate of 0.1 V/s. The resulting voltammogram showed the
formation of a reduction peak at Ep = -1.09 V and there was evidence of a
subsequent reduction product past -2.0 V as observed by the continued
increase in the current. In an effort to see if the reduction wave at -1.09 V was
reversible, the potential range between -0.4 to -1.3 V was scanned with varying
sweep rates.
Figures 3.4 to 3.6 show the CVs for (110) measured at
decreasing sweep rates, from 0.5 V/s to 0.01 V/s, and it is evident from these
that the species in solution was irreversible.
We have found, by UV/visible studies, that (110), due to its acidity,
exists as its anionic form in DMF (see Chapter 2 Section 2.C). This suggests
that the species which is being reduced in solution is the anion of (110) and not
the neutral acceptor.
It has been reported that the electrochemical studies of
phthalimide have been complicated due to the acidic NH proton but in spite of
its acidity the anion
radical of phthalimide was observable183 by cyclic
voltammetry in DMF and the first reduction peak (Ep= -1.49 V ys SCE) was
reversible at a sweep rate of 20 V/s.
At slow er sweep rates self-protonation
occured giving products which gave anomalous currents. See Scheme 4.01.
O
w
O
o
n-
o
Scheme 4.01
W e have found that the anion of (110) shows irreversible electrochemical
behaviour, even at millisecond timescales.
The irreversibility of (110) most
likely results from the formation of an unstable reduction product, the identity of
-• •»«
( (V)
Figure 3.2
Cyclic Voltammogram of (110) in 0.1 M lithium perchlorate in
Dimethylformamide at a hanging mercury-drop electrode, scan rate 0.1 V/s.
sa. ••
«. •• --7M
Figure 3.3
- I. 3M
E (V)
- I .7M
*i .**•
Cyclic Voltammogram of (151) in 0.1 M lithium perchlorate in
Dimethylformamide at a hanging mercury-drop electrode, scan rate 0.1 V/s.
139
29. •
--------------------- 1
-2M.I
-4M.«
i
-IM.I
I------------------------ »------------------------ ------- —
-129«.«
— ---------
-14H.I
C <*U>
Figure 3.4
Cyclic Voltammogram of (110) in 0.1 M lithium perchlorate in
Dimethylformamide at a hanging mercury-drop electrode, scan rate 0.5 V/s.
C <aV>
Figure 3.5
Cyclic Voltammogram of (110) in 0.1 M lithium perchlorate in
Dimethylformamide at a hanging mercury-drop electrode, scan rate 0.1 V/s.
140
c <»v>
Figure 3.6
Cyclic Voltammogram of (110) in 0.1 M lithium perchlorate in
Dimethylformamide at a hanging mercury-drop electrode, scan rate 0.01 V/s.
34«. •
)•••
2ft«. •
229.9
c
a
w
I II !
14«.■
IM.I
11.«
2 «. •
-2ft. •
HI
-1.21«
-1.4ft«
-l.ftftft
-I.«««
-*.«••
C <V)
Figure 3.7
Cyclic Voltammogram o f (151) in 0.1 M lithium perchlorate in
Dimethylformamide at a hanging mercury-drop electrode, scan rate 5.0 V/s.
141
which is unknown.
Such a product may possibly result from an analogous
reaction to that for phthalimide in Scheme 4.01, giving the 1,3-disubstituted
isoindole
(207)
which
in turn
could
lose
hydrogen
cyanide
giving the
isoindolenine (208). Scheme 4.02. Since the half wave potential E1/2 for (110),
or its anion, cannot be determined, because of the non-reversibility of the
reduction wave, it is not possible to compare its acceptor ability accurately with
that of TCNQ (1), which has E1/2(1) = -0.12, E1/2(2) = -0.72 V in DMF, or its
isoelectronic equivalent benzo-TCNQ (112), E1/2(1) = -0.30, E1/2(2) = -0.73 V in
DMF.
NC,
H
,CN
2e
c s >•p NCiJ/CN
(207)
|
-HCN
NC, J , C N
X
N
H'^ C N
(208)
Scheme 4.02
W hile the deprotonation associated with the formation of the anion of
(110) is not possible for (151), its CV also showed non-reversibilty on reduction
(Figure 3.3). Two reduction waves were observed at -1.35 and -1.62 V. In an
effort to determine whether the second reduction wave was associated with
(151) itself or with the formation of a new species on reduction of (151), the
sweep rate was increased from 0.1 V/s to 5.0 V/s. Increasing the sweep rate in
cyclic voltammetry decreases the amount of time taken for each scan, thus
reducing the likelihood that the product of electron transfer will undergo a
following chemical reaction.
Figure 3.7 shows that on increasing the sweep
rate only a single redox couple is observed at approximately -1.400 V,
corresponding to reduction of (151).
That a single redox couple is observed
suggests that the kinetics of the chemical reaction that follows electron transfer
are relatively slow, and that by employing a relatively fast sweep rate, 5 V/s,
this chemical reaction can be out run.
can
be
injected
into
(151)
and
Under the circumstances, an electron
removed
before
significant
chemical
decomposition has occurred. W hen Figures 3.3 and 3.7 are compared, there
are two significant differences in the voltam m etric responses observed for the
reduction of (151).
First, in the higher sweep rate experiment (Figure 3.7) a
significant oxidation response is observed corresponding to the re-oxidation of
electrochemically
reduced
(151).
Second,
there
is
a
difference
of
approximately 50 mV in the half-wave potential for the irreversible redox
reaction of Figure 3.3 compared to the formal potential of the quasi-reversible
response illustrated in Figure 3.7.
This difference is expected since the
position of the irreversible wave is controlled in part by the rate constant of the
following chemical reaction. Moreover, because of the higher currents that are
observed in Figure 3.7, there will be a larger iR drop, where i is the total current
flow and R is the resistance of the electrolytic solution, which tend to shift the
formal potential of the voltammetric response shown in Figure 3.3 in a negative
potential direction.
As a result of the non-reversibility of (151) it was not possible to
compare the reduction peak potential at Ep = -1.35 V with the half wave
potentials of (1) and (112).
However, the reduction peak potential does give
some indication of the electron acceptor ability of (151) and the stability of the
anion radical formed.
The reduction peak potential observed suggests that
(151) is not a strong acceptor and its irreversibility shows that the anion radical
is unstable.
One explanation for the instability of the anion radical of (151),
initially considered, was the formation of an isoindole intermediate (209) which
might form on one electron reduction of (151).
143
Although
/V-substituted
isoindoles are stabilised when strongly electron withdrawing groups are present
in the C-| and C3 postions,184 the excess negative charge may reduce this
stability.
NC
‘
CN
NMe
NC
CN
NC
CN
(209)
However (114), the sulphur analogue of (110), shows two reversible reduction
waves in dichlorom ethane139 at E1/2(1) = -0.31, and E1/2(2) = -0.78 V, and this
compound would be expected to form similar benzo[c]thiophene radical anion
intermediates. This suggests that either the isoindole derivative is less stable
than its sulphur analogue or that some other chemical reaction is taking place
at the electrode.
NC.
XN
NC
CN
(114)
Conclusions
Due to the limitations in the use of dimethylformamide as the solvent for
the electrochemical studies of (110), it cannot be conclusively stated how the
acceptor ability of (110) compares to that of (1) or the iso-electronic (112). The
electrochemical studies of (151), however, show that the
radical anion
intermediates are not stable and are not electrochemically reversible. Although
the half-wave potentials cannot be calculated, comparison of the first reduction
potential Ep with the half-wave reduction potentials of (112) shows that (151) is
not as good an acceptor as (112). This suggests that in order for (151), and
possibly (110), to form C-T complexes, more strongly donating donor groups
may be necessary. Since the reduction potential obtained for (110) is less than
that of (151), and is most likely due to the reduction of the anion of (110), it is
144
possible that the electron affinity of the neutral acceptor may be greater than
that of (151).
145
Chapter 4
146
4.0
C ha rg e -T ra n sfe r
b is p ro p a n e d in itrile
S tud ie s
(110)
and
of
2,2’-(ls o in d o lin -1 ,3 -d iy lid e n e )
2,2’-(2 -M e th y lis o in d o lin -1 ,3 -d iy lid e n e )
b is p ro p a n e d in itrile (151)
4.1 In tro d u c tio n
As stated previously in Chapter 1, (Section 1.A ), when an electron
donor D and an electron acceptor A interact, their physical properties are
perturbed and new properties arise which can be attributed to the formation of
a charge-transfer complex.
These new properties are responsible for the
observation of new bands in the UV/visible spectrum which are not attributable
to either the donor D or the acceptor A. UV/visible spectroscopy provides one
of the most widely used methods for the study of both strong and weak C-T
complexes
and
it
also
provides
a
reliable
means
thermodynamic properties of these com plexes.185
of
determining
the
However weak electron-
donor-acceptor interactions give complexes which last sufficiently long for
intermolecular C-T to occur but are sometimes unstable and cannot be isolated
as a solid complex.
As a result their concentrations are less than the donor
and acceptor concentrations and thus it may be difficult to observe their C-T
bands in solution by UV/visible spectroscopy.
In an effort to see which donors might potentially form stable C-T
complexes with the acceptors (110) and (151), UV/visible studies were carried
out with a range of donors, (2a) and (210)-(212), and the spectrum of the
solution of the complex recorded to determine whether C-T was taking place.
The method employed involved adding a sufficient quantity of the acceptor to a
Me
Me
N
Me
.N.
Me. .Me
N
Me
(210) TM D A
(211) DMA
(2a) TTF
(212) AN
fixed volume of a suitable solvent in a quartz cell and then recording the
spectrum. The donor was then added to this solution in known quantities and
the spectrum recorded again. A spectrum of the donor in the same solvent was
also recorded and the formation of the new C-T band could then be seen on
comparison of the spectra.
dichloromethane
Fortunately (110) was sufficiently soluble in
and tetrahydrofuran
to
147
permit the
measurement of its
UV/visible spectrum, which allowed for the determ ination of the C-T complexing
ability of the neutral compound. The C-T complex was subsequently isolated
by mixing together concentrated solutions of the donor and the acceptor in an
appropriate solvent, filtering it off if it formed on standing, or else by
evaporating off the solvent and recrystallising the complex from an alternative
solvent.
In this chapter the UV/visible studies for the acceptors (110) and (151)
with a variety of donors are reported along with the C-T complexes isolated,
and the X-ray crystal structure of the C-T complex of (110) with N,N,N',N'tetram ethyl-/>phenylenediam ine (TMDA).
4.2
Charge-Transfer
Complex
of
(110)
with
A/,A/,/V',/V-Tetramethyl-p-
phenylenediam ine (TMDA)
Because of the acidity of the NH group in (110) it was of interest to see
whether (110) would form a C-T complex or a salt with the strong donor
/V,A/,A/',/V-tetramethyl-p-phenylenediamine (TMDA; 210).
On adding TMDA to
(110) in dichloromethane, and measuring the UV/visible spectrum, a new broad
intense band was observed at 500-680 nm with ^ max = 642 nm, attributed to
the formation of a C-T band, (Figure 4.01).
On combining a concentrated solution of (110) in tetrahydrofuran with a
two molar equivalent solution of TMDA in acetonitrile a black/dark green
solution formed immediately and green/black needles precipitated.
Elemental
analysis showed that a 1:1 C-T complex had been formed. The X-ray crystal
structure permitted determination of the stacking pattern found in the complex.
4.2.1 X-ray Crystal Structure of the 1 :1 C-T complex of (110)-TMDA
Crystals of the 1:1 complex of (110)-TMDA (Figure 4.02), suitable for
X-ray crystallography, were obtained from acetonitrile as black/dark green
needles.
The 1:1 complex crystallised in a m onoclinic crystal system in the
P121/n space group. The relevant bond lengths and bond angles are given in
Table 4.01.
The crystal packing diagram (Figure 4.03) shows the infinite one­
dimensional alternate or mixed stacking of the donor (TMDA) and the acceptor
(110) in the complex.
The highly planar nature of (110), an important
prerequisite for the synthesis of electrically conducting C-T complexes, can be
seen in Figure 4.04.
To calculate the distance between the two components
within a stack of the C-T complex the mean plane of the nitrile component of
(110) was calculated and the orthogonal distance of any atom on the adjacent
148
Figure 4.01 UV/visible spectra of TMDA (210), (110) and the Charge-Transfer
com plex (110)-TMDA.
149
N3
Figure 4.02 SCHAKAL drawing of the crystal structure o f the 1:1 complex o f
(110)-TMDA.
150
Figure 4.03 SCHAKAL illustration o f the alternate or mixed stacking
the crystal structure of the 1:1 complex o f (1 10)-TMDA.
151
Figure 4.04
A lte rn a tiv e p e rp e c tiv e o f th e
m o tif fo u n d in th e c ry s ta l s tru c tu re o f th e
SCHAKAL illu s tra tio n o f th e
1: 1 c o m p le x o f (110)-TMDA.
Table 4.01 showing the bond lengths and bond angles for (110)-TMDA
Bond angles (deg)
121.2(4)
C(1A)-N(1A)-C(7A)
122.1(4)
C(1A)-N(1A)-C(8A)
116.7(4)
C(7A)-N(1 A)-C(8A)
122.2(4)
C(4A)-N(2A)-C(9A)
121.7(4)
C(4A)-N(2A)-C(10A)
C(9A)-N(2A)-C(10A)
116.2(4)
N(1A)-C(1 A)-C(2A)
121.3(4)
121.2(3)
N(1 A)-C( 1A)-C (6A)
117.5(4)
C(2A)-C(1 A)-C(6A)
120.8(4)
C(3A)-C(2A)-C(1 A)
C(2A)-C(3A)-C(4A)
122.0(4)
N(2A)-C(4A)-C (5A)
121.2(4)
N(2A)-C(4A)-C(3A)
122.4(4)
C(5A)-C(4A)-C(3A)
116.4(4)
C(6A)-C(5A)-C(4A)
121.8(4)
C(5A)-C(6A)-C(1A)
121.5(4)
108.1(3)
C(7)-N(1)-C(8)
119.4(5)
C(6)-C(1)-C(2)
120.7(5)
C(1)-C(2)-C(3)
120.8(5)
C(4)-C(3)-C(2)
118.4(5)
C(3)-C(4)-C(5)
120.7(4)
C(4)-C(5)-C(6)
133.6(4)
C(4)-C(5)-C(8)
105.8(4)
C(6)-C(5)-C(8)
120.0(4)
C(1)-C(6)-C(5)
135.0(4)
C(1)-C(6)-C(7)
105.0(3)
C(5)-C(6)-C(7)
121.6(4)
N(1)-C(7)-C(12)
110.8(3)
N(1)-C(7)-C(6)
127.6(4)
C(12)-C(7)-C(6)
121.0(4)
N(1)-C(8)-C(9)
110.2(3)
N(1)-C(8)-C(5)
128.7(4)
C(9)-C(8)-C(5)
119.8(4)
C(8)-C(9)-C(10)
123.6(4)
C(8)-C(9)-C(11)
116.5(4)
C(10)-C(9)-C(11)
179.3(5)
N(2)-C(10)-C(9)
179.4(5)
N(3)-C(11)-C(9)
C(7)-C(12)-C(14)
125.0(4)
120.3(4)
C(7)-C(12)-C(13)
114.7(4)
C(14)-C(12)-C(13)
178.0(5)
N(4)-C(13)-C(12)
178.2(6)
N(5)-C(14)-C(12)
Bond lengths (A)
1.355(5)
N(1A)-C(1A)
1.455(6)
N(1A)-C(7A)
1.454(6)
N(1A)-C(8A)
1.337(5)
N(2A)-C(4A)
1.444(6)
N(2A)-C(9A)
1.472(6)
N(2A)-C(10A)
1.411(5)
C(1A)-C(2A)
1.411(5)
C(1A)-C(6A)
1.362(6)
C(2A)-C(3A)
1.418(6)
C(3A)-C(4A)
1.416(5)
C(4A)-C(5A)
1.351(6)
C(5A)-C(6A)
1.344(5)
N(1)-C(7)
1.346(5)
N(1)-C(8)
N(2)-C(10)
1.150(6)
1.142(6)
N(3)-C(11)
1.143(6)
N(4)-C(13)
1.132(5)
N(5)-C(14)
1.374(6)
C(1)-C(6)
1.375(7)
C(1)-C(2)
1.383(7)
C(2)-C(3)
1.381(7)
C(3)-C(4)
1.385(6)
C(4)-C(5)
1.399(5)
C(5)-C(6)
C(5)-C(8)
1.467(5)
C(6)-C(7)
1.467(5)
1.375(5)
C(7)-C(12)
1.378(5)
C(8)-C(9)
1.417(7)
C(9)-C(10)
1.428(6)
C(9)-C(11)
1.425(6)
C(12)-C(14)
C(12)-C(13)
1.434(6)
donor molecule was then determined.
These distances are shown in Table
4.02. It can be seen that the nearest mean plane contact distance between the
donor and acceptor is 3.41
interplanar distances (-3.5
A)
A
and the farthest is 3.60
A,
similar to the
found in other mixed stack complexes186 and are
153
Table 4.02 Mean plane contact distances between the (110) and TMDA
Donor Atoms
Mean
orthogonal
plane
distance
(A)
C1a
3.5400
C2a
3.4335
C3a
3.4128
C4a
3.5012
C5a
3.5770
C6a
3.5988
N1 a
3.6027
N2a
3.5168
greater than those for segregated stack complexes (-3 .2 Â).
Figure 4.04 also
shows the two-dimensional alternating stacking structure of the complex and in
addition it can be seen that the donor and acceptor components of the stacks
are tilted out of the plane normal to the stacking direction.
The sheet-like
nature of the donors and acceptors in the alternate stacks is also seen in
Figure 4.03.
This mixed stacking motif of the complex is the most common
arrangement 187 and is consistent with complexes composed of strong donors,
such as TMDA and TTF, and weak electron acceptors, such as (110) and the
extended furanoquinoid TCNQ analogue (213).102
The other structural feature of interest from the X-ray crystal analysis is
the relative orientations of the component molecules to each other. This can
be seen in Figure 4.05, which gives a side view of the D-A pair, and Figure
4.06, which shows the relative overlap of the two component molecules by
projection of the mean plane of the donor onto that of the acceptor. Both these
figures show that there is half a ring displacement of the aromatic rings of each
component. Such a half ring displacement was postulated by Mulliken 12(a) to
yield maximised C-T interactions in k - k complexes, by allowing maximum
overlap of the filled donor orbital and the empty acceptor orbital. While similar
154
Figure 4.05 Side view of the relative orientation of the donor molecule
acceptor molecule in (110)-TMDA.
Figure 4.06
Orthogonal view, showing how the donor m olecule and the
acceptor overlap in (110)-TMDA.
156
half ring displacements can be seen in the 1:1 complexes of pyromellitic
dianhydride-benz[a]anthracene (214) and naphthalene-dg-tetrachlorophthalic
anhydride (215),188 it has been suggested187(a) that Mulliken did not take into
account dispersion forces, which tend to be largest in orientations bringing
maximum
polarisabilities into play and which are associated with short
interplanar spacings. Mulliken later conceded that electrostatic forces may be
responsible, and sometimes predominantly, for the stability of weak n-n
complexes, but he stated that dispersion-force contribution to the stability was
only important in the vapour state since their effects were approximately
cancelled in the formation of complexes in solution.12(b)
Similar findings to
Mullikens were also reported by W allw ork189 who, on investigating the structure
and relative disposition of components in C-T complexes, claimed that where
C-T forces might be expected to be more significant in determining the structure
(e.g. from low ionisation potential of the donor) the relative orientation and
positions of the component donor and acceptor are found to be such as to allow
the maximum overlap between their Ti-molecular orbitals.
However it seems
that since short interplanar separations are not in evidence in the (110)-TMDA
complex, as compared with the interplanar spacing of 3.27 and 3.24
A
for the
1:1 and 2:1 complexes of TCNQ with TMDA, and since there seems to be no
particular overlap of the polarisable groups, (the carbon to carbon double bond
of the acceptor and the nitrogens of the donor), this may suggest that C-T
interaction contributes to the relative orientation of TMDA and (110) which may
result from maximum donor-acceptor orbital overlap.
We also compared (110)-TMDA with the 2:1 and a 1:1 complexes of
TCNQ with TMDA. The X-ray crystal structures of both the 1:1 complex 16 and
the 2:1 com plex17 show segregated stacking of the TMDA and the TCNQ
molecules with interplanar spacing of 3.27 and 3.24 A respectively, suggesting
a stronger C-T interaction than that found in (110)-TMDA. Comparison of the
bond lengths of the aromatic ring system for the TMDA molecule in the complex
157
with (110), with those for the 1:1 and 2:1 complexes for TMDA with TCNQ,
(Table 4.03), shows similar values and on examining the bond lengths it is
evident that the TM DA molecule has pseudo-quinonoidal character, structure
(216), confirming that C-T has taken place between TMDA and (110).
1.416
1-411
1.418
1.411
(216)
Table 4.03 Comparison of the bondlengths found in TMDA in the neutral form
and in C-T com plexes with TCNQ and (110)
Bond lengths (Â)
Bond
C1A-C2A
2:1
1:1
1:1
TCNQ-TMDA
TCNQ-TMDA
(110)-TMDA
1.418
1.416
1.411
1.402
1.411
1.400
1.362
1.398
1.357
1.382
1.418
1.392
1.416
1.394
1.337
1.420
1.355
1.407
1.454
1.412
1.472
1.445
C1A-C6A
C2A-C3A
1.367
1.374
C5A-C6A
C3A-C4A
-
-
C4A-C5A
C4A-N2A
1.373
1.365
C1A-N1A
N1A-C8A
1.458
1.474
N2A-N10A
TM D A190
Further evidence for the occurrence of C-T is also apparent from the marked
low wavenum ber shift of the nitrile stretching vibration, 2198 cm '1 for the
complex, compared with 2227 cm '1 for neutral (110). Such shifts are indicative
of C-T in which the coupling of conduction electrons and intramolecular
phonons affect the vibrational modes of the complex components and result in
a shifting of f r e q u e n c ie s .191
158
4.3 Attempted C-T Complex form ation of (110) with other donors
It seemed likely that the structurally similar, yet slightly poorer donor
relative to TMDA,
/V,/V-dimethylaniline (DMA; 211) would give analogous
results with (110). However, when DMA was added to a solution of (110) it did
not show the formation of a new C-T band but instead showed the formation of
the anion of (110), corresponding to the dim ethylanilinium salt of (110), (Figure
4.07).
This was confirmed by comparing its spectrum with that of the
ammonium salt (119) (Figure 4.08) which was shown to be identical to the UV
spectra of the alkylammonium salts reported in Chapter 2, Section D.
Mixing
solutions of the DMA and (110) in THF did not show any darkening of the
resulting solution, usually an indication that C-T has taken place.
The use of a strong donor which would not deprotonate (110) was then
investigated.
The addition of increasing amounts of the strongly electron-
donating compound TTF to a fixed concentration of (110) in acetonitrile
resulted in the formation of a C-T band with X.max = 460 nm (Figure 4.09). On
adding a solution of (110) in tetrahydrofuran to a concentrated one molar
equivalent solution of TTF in acetonitrile, an immediate colour change in the
solutions, from light yellow to green, was observed.
Attempts to isolate
sufficient quantities of the dark green flake crystals, observed on evaporating
off the solvent mixture, failed on attempting to recrystallise the complex from a
variety of solvents and thus it was not possible to determine the ratio of donor
to acceptor in the complex formed.
In order to determine whether complex formation with weaker donor
systems was possible, spectroscopic studies on the addition of anthracene
(AN) to a solution of (110) in tetrahydrofuran were carried out.
Figure 4.10
shows the effect of adding increasing amounts of AN to the acceptor.
The
formation of a new C-T band at 450-520 nm, as two broad peaks, was
observed. Although these bands are sim ilar to those observed at 466 and 496
nm on the dropwise addition of water to a solution of (110) in THF (Figure
4.11), the considerably broadened nature of the bands due to the addition of
AN and the different A.max values suggest that C-T occurs. The bands due to
the addition of water were identical to those of anion of (110) (see Figure 4.08)
and these disappeared on addition of a drop of concentrated hydrochloric acid
to the aqueous THF solution, confirming their assignment as being due to the
anion of (110).
It seems likely that due to the acidic nature of (110) and the
amphoteric nature of water that the anion is formed on addition of water. The
possibility of the formation of the anion of (110) on addition of AN is unlikely.
159
I m i r u r i t n t
0*t»,
Figure 4.07 UV/visible spectra of DMA (211), (110) and the (110)-DMA salt.
160
Figure 4.08
UV/visible spectra o f Dimethylammonium salt o f (110) and the
am monium salt (119)
161
Figure 4.09
UV/visible spectra o f TTF (2a), (110) and the Charge-Transfer
com plex (110)-TTF.
162
Figure 4.10
UV/visible spectra of AN (212), (110) and the Charge-Transfer
complex (110)-AN.
163
Figure 4.11
UV/visible spectrum o f (110) showing the formation o f bands due
to the anion on drop-wise addition of water to (110)
Mixing equimolar THF solutions of (110) and AN gave a resulting dark
orange/red coloured solution which was in strong contrast with the pale yellow
solution of (110) and the colourless solution of AN.
On concentration of the
solution and storing under argon, the resulting claret coloured solution yielded
large black/metallic purple needles of the C-T complex.
It was found that on
filtering in air these needles were unstable, readily changing from purple to
yellow.
On filtering under argon the complex remained stable and this
suggested that the C-T complex formed was susceptible to gradual oxidation
from atmospheric oxygen.
Charge-Transfer Complexes of (151) with various donors.
The C-T complex forming ability of (151) was also investigated in a
sim ilar manner. Figure 4.12 shows the effects of adding increasing amounts of
TM D A to a solution of (151) in acetonitrile. The UV/visible absorption spectrum
show s the formation of a C-T band which tails out to 700 nm. This band can be
attributed to the formation of a C-T complex between (151) and TMDA.
By
combining two concentrated solutions of (151) and TMDA in tetrahydrofuran a
da rk green solution was obtained. The tetrahydrofuran was removed and the
green solid obtained was recrystallised from acetonitrile giving a 2:1 complex of
164
(151)-TMDA based on its elemental analysis.
A shift in the cyano peak in the
IR spectrum was also observed for the complex, with the cyano stretching band
occurring at 2221 cm-1 compared with 2224 cm '1 for the neutral acceptor.
W hile these results showed that (151) was capable of forming a C-T complex,
the small bathochromic shift to longer wavelengths suggested that the degree
of transfer was not as great as for the corresponding complex of (110), in which
there was a shift of 29 cm '1.
This suggests that (151) is not as strong an
acceptor as (110). Unfortunately attempts to obtain crystals of sufficient quality
for X-ray crystallography were not successful.
It was hoped that a C-T complex with DMA might be obtained for (151)
as it did not have the same complication of an acidic NH as (110).
However
the addition of increasing quantities of DMA to a solution of (151) in acetonitrile
showed no formation of a C-T band (Figure 4.13).
The combination of (151)
and DMA in equimolar quantities in THF showed no colour change for the
resulting solution and it was concluded that no C-T had taken place.
When the more strongly electron-donating compound, TTF, was added
to a solution of (151) in acetonitrile the formation of a C-T band was observed
with Xmax = 452 nm and this was attributed to the formation of a C-T complex
between (151) and TTF (Figure 4.14).
Dark green plates of the complex of
(151)-TTF were obtained from the dark green solution which formed when two
concentrated solutions of (151) and TTF were mixed.
The ratio of the
components in the complex was determined by elemental analysis as 1:1.
A
shift in the cyano stretching frequency peak in the IR spectrum was also
observed, with the cyano
peak occurring
at 2213 cm '1 compared with
2224 cm“1 observed for the neutral acceptor, suggesting that the degree of C-T
from TTF to (151) is slightly greater than for TMDA.
The ability of (151) to form a C-T complex with the weak donor,
anthracene, was also investigated. The UV/visible spectrum recorded after the
addition of AN to a solution of (151) (Figure 4.15) showed that the weaker
donor was not capable of forming a C-T complex with (151) and no complex
was formed on mixing equimolar solutions of the donor and acceptor together.
165
Figure 4.12
UV/visible spectra of TMDA, (151) and the Charge-Transfer
com plex (151)-TMDA.
166
InstruDint
0* t *
)
Figure 4.13 UV/visible spectra o f DMA, (151) and the DMA/(151) mixture.
167
Figure 4.14 UV/visible spectra o f TTF, (151) and the Charge-Transfer complex
(151)-TTF.
168
Figure 4.15 UV/visible spectra of AN, (151) and the AN/(151) mixture.
169
4.5 D is c u s s io n
It is c le a r from th e U V /visib le s p e c tra l d a ta , and from th e com ple xes
iso la te d , th a t both (110) and (151) are c a p a b le o f fo rm in g C -T co m p le xe s w ith a
v a rie ty of do n o rs.
T h e se re su lts are s u m m a ris e d in T a b le 4.1.
It is a p p a re n t
fro m th is d a ta th a t w h ile it w as d iffic u lt to d e te rm in e the e lectron accep ting
a b ility of (110) and (151) by e le c tro c h e m ic a l m e th o d s, it a p p e a rs th a t (110) is a
b e tte r a c c e p to r th a n its N -m e th yl a n a lo g u e . T h is is s u g g e ste d from th e g re a te r
s h ift in th e n itrile s tre tc h in g fre q u e n c ie s fo r th e cy a n o g roup s in (1 1 0 )-T M D A
co m p a re d w ith th o s e fo r (1 5 1 )-T M D A and (1 5 1 )-T T F and from th e a b ility of
(110) to fo rm a C -T co m p le x w ith a w e a k d o n o r s u c h as a nthracen e. T h is is not
to o s u rp ris in g in th a t th e m ethyl g ro u p m ay re d u c e th e e le ctro n a ffin ity of (151),
a nd in a d d itio n it m ay also reduce th e d e g re e of in te rm o le c u la r in te ra ctio n
w h ic h
in tu rn
in te ra c tio n .
in flu e n c e s
th e
d e g re e
of o v e rla p
re q u ire d
fo r stron g
C -T
H o w eve r, sin ce no X -ray c ry s ta l s tru c tu re w a s ob ta in e d fo r any of
th e c o m p le x e s of (151) and sin ce the c y c lic v o lta m m e try stu d ie s of the p revio us
c h a p te r w e re in c o n c lu s iv e , th is re m a in s to be v e rifie d .
T h e p a ra lle l, fa c e -to -fa c e clo se c ry s ta l p a c k in g of the e s s e n tia lly p la n a r
T M D A a nd (110) m o le c u le s in m ixed s ta c k s c o n firm e d th a t (110) w as capa ble
of fo rm in g a C -T co m p le x.
Such m ixed s ta c k in g syste m s have been fo u n d to
be p o o r e le c tric a l c o n d u c to rs .192
The
m ix e d -s ta c k in g a rra n g e m e n t of the
d o n o rs and the a c c e p to rs a nd th e g re a te r in te rp la n a r sp a cin g s also show , by
co m p a ris o n of ( 1 1 0 )-T M D A w ith th e 1:1 a n d 2:1
com p le xe s of T C N Q w ith
T M D A , th a t (110) is not as stron g an a c c e p to r as T C N Q .
NC
CN
N(Me)2
(217)
W h y D M A s h o u ld form a s a lt w ith (110) and T M D A sh o u ld form a
co m p le x is d iffic u lt to e x p la in , e s p e c ia lly w h e n T M D A is a stro n g e r base than
DM A.
It is know n
th a t som e
e le c tro n
d o n o r-a c c e p to r system s
not only
im m e d ia te ly form C -T c o m p le x e s but th e s e can m ore slo w ly form new species
b y irre v e rs ib le c h e m ic a l re a c tio n .188
/V ,A /-d im e th yl-4 -tricya n o a n ilm e
(217),
O n e su ch e xa m p le is the fo rm a tio n of
fo rm e d
by
the
reaction
d im e th y la n ilin e w ith te tra c y a n o e th y le n e . T h is re a c tio n 193 w as studie d
170
of
N,N-
Table 4.1 Charge-Transfer complexes of (110) and (151) with various donors
A c c e p to r
(110 )
(110 )
(1 1 0 )
Donor
Me2N - ^ Q ^ —NMe2
<JO)-NMe2
c ^ g
C -T C o m p le x
m p , °C
C -T A.m a x
( s o lv e n t) /n m
b la c k /d a rk
g re e n nee dle s
1 5 4 -1 5 5
6 2 4 (d ic h lo ro m e th ane)
none- form s a
sa lt
4 50 (C H 3 CN)
g reen p o w d e r
(110 )
(151)
M92N—
—NMe2
v io le t needles
u n s ta b le
4 5 0 -5 2 0 (TH F)
gre e n nee dle s
198
465 (C H 3 C N )
190 (d)
452 (C H 3 CN)
(151)
<^0
)-N M e 2
none
(151)
Q -ç >
g reen plates
(151)
none
s p e c tro p h o to m e tric a lly by U V /visib le s p e c tro s c o p y and w a s fo u n d to o c c u r via
a 1 :1 Tt-complex b e tw e e n th e reactants.
T h e U V /v is ib le s p e ctra l s tu d ie s of
(110) and D M A do not sh o w any C -T ban d a n d th u s it a p p e a rs th a t the
d im e th y la n ilin iu m
s a lt
of
(110)
is
form ed
im m e d ia te ly .
O ne
p o te n tia l
e x p la n a tio n fo r th e s a lt fo rm a tio n is that, if D M A d id fo rm a C -T co m p le x it m ay
not be as sta b le as th a t fo rm e d by T M D A s in c e th e ca tio n ra d ica l fo rm e d by
D M A w o u ld have a le ss d e lo c a lis e d charge.
A s s ta te d in th e in tro d u c tio n , the
a b s o rp tio n b a n d s of w e a k C -T co m ple xes are d iffic u lt to o b se rve sin ce th e ir
c o n c e n tra tio n s are le ss th a n th o s e of the d o n o r a n d th e a c c e p to r a nd th u s th is
171
m ay e xplain w h y no C -T is o b s e rv e d .185 A s a re su lt th e re m ay be a g re a te r
g ain in sta b ility if D M A reacts w ith (110) and fo rm s th e io n ic salt.
4 .6 C o n c lu s io n s
A t th e o u ts e t o f th is w o rk o u r goal w a s to s y n th e s is e (110) and som e Nsu b stitu te d d e riva tive s and to in ve stig a te th e ir a b ility to form C -T com ple xes.
W h ile
we
have fo u n d
d ifficu lty
in s yn th e sisin g
a
range
o f A/-substituted
d e riv a tiv e s o f (110) w e ha ve been able to d e te rm in e th a t (110) and its A/-methyl
d e riv a tiv e (151) can fo rm C -T com ple xes. W h ile th e e le ctro ch e m ica l stu d ie s did
n o t g ive co n clu sive re su lts and c o n s e q u e n tly did n o t allow fo r an accurate
co m p a riso n o f th e e le ctro n a ffin ity o f (110) a nd (151) w ith b e n zo -T C N Q and
T C N Q it did s u g g e s t th a t th e se new a c c e p to rs w o u ld form c o m p le xe s with
stron g don ors. T his in d e e d has been fo u n d to be th e case. H ow ever, w h ile we
ha ve co n clu d e d th a t u n d e r th e co n d itio n s o f th e e le c tro c h e m ic a l stu d ie s it w as
m o st likely th e anion o f ( 1 1 0 ) w h ich w a s b e in g re d u ce d , th e a b ility o f th e neutral
co m p o u n d to fo rm C -T c o m p le xe s w a s unsu re .
It can be seen fro m th e C -T
stu d ie s th a t (110) is c a p a b le o f fo rm in g C -T co m p le xe s, even w ith th e w eak
d o n o r a n th ra ce n e and in a d d itio n can fo rm a s tro n g e r co m p le x th a n (151) with
T M D A . S ingle crysta l c o n d u c tiv ity m e a su re m e n ts ha ve ye t to be ca rrie d o u t on
th e 1:1 co m p le x o f (1 1 0 )-T M D A b u t sin ce th e c o m p le x is m ade up o f m ixed
s ta cks and such sta ckin g a rra n g e m e n ts are p o o rly co n d u ctin g , it w o u ld be
pre d icte d th a t at b e st th is co m p le x w o u ld be s e m ico n d u ctin g .
172
C h a p te r 5
E X P E R IM E N T A L
173
Introductory Remarks
N u c le a r M a g n e tic R e so n a n ce (N M R ) s p e c tra w e re re co rd e d on a B ruker
A C 400 in stru m e n t o p e ra tin g at 400 M H z fo r 1H N M R and 100 M H z fo r 13C NM R.
A ll s p e c tra w ere re co rd e d using d e u te ra te d d im e th y ls u lp h o x id e (D M S O -de) as
s o lv e n t u n le ss o th e rw is e sta te d (s = sin g le t, d = d o u b le t, t = trip le t, q = quartet,
q n = q u in te t, m =
m u ltip le t, brm = b ro a d m u ltip le t, and brs = b ro a d s in g le t ).
C h e m ic a l s h ifts are g ive n in p a rts p e r m illio n (ppm ) a nd co u p lin g co n s ta n ts (J) are
g iv e n in H e rtz (Hz).
In fra -re d
(IR)
s p e c tra
w e re
re co rd e d
on
a
P e rk in -E lm e r
983G
IR
s p e c tro p h o to m e te r o r a N icolet 205 F T -IR fo r K B r p e lle ts unless o th e rw is e stated.
U ltra vio le t (U V) s p e c tra w e re re co rd e d on a H e w le tt-P a c k a rd 8 4 5 2 A diode
a rra y U V -V is s p e c tro p h o to m e te r. T h e u n its fo r e a re d m 3 m o l' 1 c n r 1. S p e ctro g ra d e
d im e th y lfo rm a m id e (D M F) w a s use d as the s o lv e n t u n le ss o th e rw ise stated.
M e ltin g p o in t d e te rm in a tio n s w ere re c o rd e d u s in g a G riffin m elting point
a p p a ra tu s and are u n c o rre c te d .
E lem ental a n a ly s e s w e re c a rrie d out by the
M ic ro a n a ly tic a l L a b o ra to ry at U n ive rsity C o lle g e D u blin.
T h in la yer c h ro m o to g ra p h y (TLC ) w a s c a rrie d out using s ilic a gel TLC
p la te s co n ta in in g a flu o re s c e n t in d ic a to r (R ie d e l de H aen, 5q c a rd s SiF, la yer
th ic k n e s s
0 .2 mm).
M ass S p e ctra w e re re co rd e d on a V G 1 2 2 5 0 M ass s p e c tro m e te r
174
A tte m p te d
K noevenagel
R e a c tio n s
of
M a lo n o n itr ile
w ith
A /-M ethyl-
p h th a lim id e
U s in g s o d iu m a s th e b a s e a n d to lu e n e a s s o lv e n t
M a lo n o n itrile (0.3 3 g, 0 .0 0 4 9 m oles) w a s a d d e d to sodium (0.11 g, 0.0049
m o le s) in d ry to lu e n e and left stirring on a boiling w a te r-b a th fo r 1.5 hours and then
s tirre d o v e rn ig h t at room te m p e ra tu re giving a cre a m y -w h ite suspension.
M e th y lp h th a lim id e (117) (0.50 g, 0.0031
N-
m oles) w a s added and th e reaction
m ix tu re he a te d u n d e r reflux. A fte r th re e h ou rs a y e llo w "gum " form ed on the sides
o f th e re a ctio n flask.
H eating at reflux w a s c o n tin u e d fo r a fu rth e r 4 hours.
T he
re a ctio n m ixtu re w a s a dd ed to w a ter, a cidifie d and e x tra cte d w ith ethyl acetate and
th e co m b in e d e xtra cts dried o v e r m a g n e siu m su lp h a te .
T his ga ve a gre e n /b ro w n
solid (0.6 g) on e va p o ra tin g th e e thyl acetate. T L C o f th is solid show ed it to be a
c o m p le x m ixtu re o f p ro d u cts and A /-m ethylphthalim ide.
O ne p ro d u ct w a s iso lated by disso lvin g th e im p u re solid in te trahyd rofuran.
O n a dd ing light p e tro le u m a solid pre cip ita te d w h ich form ed a brow n oil on
sta n d in g . T h e oil and th e y e llo w su p e rn a ta n t w e re se p a ra te d . TLC show ed th e oil
to be a co m p le x m ixtu re o f p ro d u cts and th e s u p e rn a ta n t show ed one m ajor and
tw o m in o r produ cts.
solid.
T h e s o lv e n t w as rem o ved fro m th e s u p e rn a ta n t to give a
T h is solid w a s purifie d b y a dd ing it to hot to lu e n e , in w h ich it w as m ainly
in s o lu b le and filte rin g hot.
T L C sh ow ed th is re m o ve d th e m inor im purities.
The
in so lu b le solid w a s th e n re crysta llise d fro m w a te r to g ive 2 -a m in o -1 -p ro p e n e -1 ,1 ,3 tric a rb o n itrile (0 .0 4 3 g); m p 170-171 °C (lit .,194 171 -1 73 °C); v max: 3345, 3233,
320 5,
2920,
2265,
2223,
2205,
1657,
1554,
1447,
1383
and
909
cm -1;
8h (acetone-dg): 7.1 2 (brs, 2H , NH) and 3.70 ppm (s, 2H, CH); 5q (acetone-dg):
2 3 .2 5 (C H 2 ), 54.13 (= C (C N ) 2 ), 114.17, 114.61, 115 .23 (CN) and 118.38 ppm
(= C N H 2 ).
IR and N M R sp e ctra w e re in goo d a g re e m e n t w ith th o se found in the
lite ra tu re .144
U s in g s o d iu m h y d r id e a s th e b a s e a n d d r y te tr a h y d r o fu r a n a s s o lv e n t
D ry lig h t p e tro le u m (4 0 -6 0 )(1 0 c m 3) w a s a d d e d to sodium hydrid e (60%
s u s p e n s io n in oil; 0.9 9 g, 0 .0 2 5 m oles), th e su sp e n sio n sw irled and th e so lvent/oil
so lu tio n rem o ve d w ith a P a s te u r p ip e tte on ce th e m ixtu re had settled. A solution
o f A /-m e th ylp h th a lim id e (2.0 0 g, 0.012 m oles) in d ry te tra h yd ro fu ra n (60 cm 3) w a s
added.
M a lo n o n itrile (1 .6 4 g, 0.025 m oles) in d ry te tra h yd ro fu ra n (50 c m 3) w a s
175
a d d e d d ro p w ise to the /V -m e th ylp h th a lim id e /so d iu m
re a c tio n
m ixture w as s tirre d fo r 15 hours.
e v a p o ra tin g off the te tra h y d ro fu ra n .
h y d rid e su sp e n sio n .
An o ra n g e
T he
oil w a s o b ta in e d on
T ritu ra tio n of th e oil w ith ethyl acetate,
fo llo w e d by filtra tio n , gave th e sodium salt of o -( 2 , 2 -d ic y a n o e th e n y l- 1 -olate-)-/Vm e th y lb e n z a m id e (125) as an o ff-w h ite solid (3.1 0 g); m p 2 3 0 -2 3 4 °C .; v max:
3 3 9 9 , 307 5, 2989, 2947, 2 2 2 1 , 2199, 2189, 2164, 2 1 5 8 , 1656, 1628, 1596, 1441,
141 2, 1369, 1312, 1162, 984, 951, 919, 841, 773, 7 4 3 , 6 96 a nd 621 c m '1; 5H: 8.08
(brm , 1H, N H ), 7 .6 0 -7 .2 7 (m, 4H, a ro m a tic H), 2.69 pp m (d, J 4 .9 , 3H, N H C H 3 ); 5q:
122.0 (C N ), 127.4, 127.8,
128 .2, 129.0, 135.1 and 1 4 1 .4 (a ro m a tic C), 1 6 8 .4 (C = C (C N ) 2 ) a nd 189.4 ppm
2 6 .2 (m ethyl am ino C), 4 8 .8 (= C (C N )2), 120.9 a n d
(c a rb o x a m id e C).
The s a lt co u ld not be re c ry s ta llis e d due to its in s o lu b ility in
n e a rly all o rg a n ic s o lve n ts trie d and its ready s o lu b ility in w a te r. It w a s fo u n d to be
s o lu b le
in
b o ilin g
eth a n o l
and
m eth anol
but th e
re s u ltin g
s o lu tio n
sh ow ed
a d d itio n a l p ro d u cts by TLC .
O n d is s o lv in g th e s a lt in w a te r (150 cm ) a nd a c id ify in g w ith 10% v/v
h y d ro c h lo ric acid an o ff-w h ite s o lid p re cip ita te d fro m s o lu tio n .
T h is w as filte re d
g iv in g a g re y solid ( 0.22 g) and th is w as re c ry s ta llis e d from e th a n o l to give the
m e th yla m m o n iu m
salt
of
o -(2 ,2 -d ic y a n o e th e n y l-1 -o la te -)-A /-m e th y lb e n z a m id e
(1 2 6 ) as gre y crystals (0.09 g), m p 163-164
°C ; v max: 330 9, 3129, 2991, 2871,
2 7 5 7 , 2207, 2193, 2165, 1709, 1632, 1596, 1492, 1406, 1360, 1331, 1266, 1169,
1 H, N H ), 7 .5 5 -7 .2 7 (m
w ith b ro a d sh o u ld e r, 7H, N H 3 and aro m a tic H), 2 .6 8 (d, J 4.9, 3H, N H C H 3) and
9 63 , 919, 842, 782, 751, 7 2 8 and 702 c m '1; 5H: 8 .0 6 (m,
2 .3 4 ppm (s, 3H, M e);
(m e th a n o l-d 4): 7 .5 6 -7 .4 5 (m, 4H , a ro m a tic H), 2.88 (s,
3H , N H C H 3) and 2.52 ppm (s, 3H, m eth yla m m o n iu m H );
(m e th yl am m o niu m
8C (m e th a n o l-d ^ : 25.4
C), 26.9 (m ethyl am ino C), 5 2 .6 (= C (C N ) 2), 120.6 and 122.2
(C N ), 128.8, 129.1, 130.2, 131.0, 135.9 and 141.0 (a ro m a tic
and
193.7
ppm
C).
(ca rb o xa m id e
(F ound:
C), 171.7 (C = C (C N )2)
C, 6 0 .3 1 ; H, 4 .9 5 ; N, 2 1.75%
C 13 H 14N 4O 2 re quire s: C, 6 0 .4 5 ; H, 5.46; N, 2 1 .6 9 % ).
T h e a q u e o u s filtra te re m a in in g on filte rin g o ff th e m e th yla m m o n iu m s a lt w as
e x tra c te d w ith ethyl a c e ta te and the extra ct d rie d o v e r m agne sium su lp h a te .
E v a p o ra tio n of the ethyl a c e ta te gave a red oil.
c o m p le x m ixture of p ro d u cts.
T L C of th e oil sh ow ed it to be a
A tte m p ts w ere m ade to iso la te th e se p ro d u cts by
co lu m n ch ro m a to g ra p h y b u t w ith o u t success.
T h e ethyl a ce ta te filtra te rem a ining from th e tritu ra tio n of the sodium sa lt
w a s e va p o ra te d o ff g ivin g an oil.
A sm all q u a n tity of a w h ite c ry s ta llin e so lid w as
176
is o la te d on hea ting the oil in e th a n o l.
T h is w as id e n tifie d as /V-m ethylphthalim ide
(TLC , IR and mp).
U s in g s o d iu m h y d r id e a s b a s e , t e tr a h y d r o fu r a n a s s o lv e n t a n d h e a tin g u n d e r
r e flu x
Dry lig h t p e tro le u m (4 0 -6 0 ) (10 cm 3) w a s a d d e d to sodium hydrid e (60%
s u s p e n s io n in oil; 0.99 g, 0 .0 2 5 m o les), the s u s p e n s io n sw irle d and the so lve n t/o il
s o lu tio n rem o ved w ith a P a ste u r p ip e tte on ce th e m ixtu re had settled.
A so lu tio n
o f A /-m e th ylp h th a lim id e (2.0 0 g, 0 .0 1 2 m oles) in d ry te tra h y d ro fu ra n (70 cm 3) w as
added.
M a lo n o n itrile (1 .6 4 g, 0 .0 2 5 m oles) in d ry te tra h y d ro fu ra n (50 cm 3) w as
a d d e d d ro p w ise to th e A /-m e th y lp h th a lim id e /s o d iu m
h yd rid e su sp e n sio n .
re a c tio n m ixture w as h e a te d u n d e r reflux fo r th re e h o u rs.
p re c ip ita te d on co o lin g a nd w as filte re d off.
s o d iu m
salt
(125)
(TLC ,
IR,
1H
A w hite so lid (1.07 g)
T h is w a s fo u n d to be id e n tica l to the
N M R ).
h y d ro c h lo ric acid an o ff-w h ite s o lid
The
On
a c id ific a tio n
p re c ip ita te d .
w ith
10%
d ilu te
T h is w as id e n tifie d as the
m e th y la m m o n iu m salt (126) (IR, m e ltin g p o in t and N M R ).
A red oil w as o b ta in e d from the te tra h y d ro fu ra n filtra te rem aining a fte r
filte rin g off th e w h ite so lid , by e v a p o ra tin g o ff th e te tra h y d ro fu ra n .
T his oil w as
d is s o lv e d in ethyl a ce ta te a nd on a c id ific a tio n w ith 10 % d ilu te h yd ro ch lo ric acid
o
(40 cm ), a w h ite s o lid p re c ip ita te d . O n try in g to re c ry s ta llis e th is so lid (0.92 g)
fro m ethyl a c e ta te an in s o lu b le s o lid w a s is o la te d on filte rin g hot. This w as found
to
be
th e
m e th yla m m o n iu m
s a lt
of
o -( 2 , 2 -d ic y a n o e th e n y l- 1 -olate-)-/V-
m e th y lb e n z a m id e (126) as g re y c ry s ta ls (0.29 g) (TLC , IR, 1H and 13C NM R, mp).
O n e v a p o ra tin g th e ethyl a c e ta te filtra te w h ich w a s rem a ining a fte r filte rin g
o ff th e m e th yla m m o n iu m o -(2 ,2 -d ic y a n o e th e n y l-1 -o la te -)-A /-m e th y lb e n z a m id e salt
(126)
hot,
an
ora n g e
c ry s ta llin e
s o lid
(0 .1 2 4
g)
was
o b tained.
T his
w as
re c ry s ta llis e d tw ice from to lu e n e to give 3 -(d ic y a n o m e th y lid e n e )p h th a lid e (127) as
a w h ite s o lid (0.0 43 g); m p 155 ° C (lit .,142 157.5 °C ); v max: 2238, 1835, 1617,
1590, 1472, 1380, 1308, 1279, 1215, 1181, 1145, 1099, 1022, 972, 877, 792, 781,
7 8 8 a nd 701 c m '1; 5h (a ce to n e -d g ): 8 .4 4 (d, 1H, a ro m a tic ), 8.24 (d, 1H, arom atic),
8 .1 8 (m, 1H, a ro m a tic) a n d 8.11 ppm (m ,1H , a ro m a tic );
8q (a cetone- d 6): 65.15
(= C (C N )2), 110.4 and 1 1 1 .9 (C N ), 125.9. 126.3, 127.8, 134.9, 136.5 and 137.4
(a ro m a tic C), 162.4 (C = C (C N ) 2) and 170 4 ppm (C = 0 ). T h is stru ctu ra l assig n m e n t
177
was made on comparing these IR, 1H and 13C NMR spectra and mp values with
those of the known com pound.142
U s in g
p y r id in e
as
base,
d ic h lo r o m e th a n e
as
s o lv e n t
and
tita n iu m
t e tr a c h lo r id e
T ita n iu m te tra c h lo rid e (2 .9 4 g; 50% so lu tio n , 0 .0 0 7 8 m oles) w as add ed to a
s o lu tio n of A /-m e th ylp h th a lim id e (0.5 0 g, 0.0031
m oles) in d ry d ic h lo ro m e th a n e
(40 cm 3) and stirre d at 20 °C fo r 30 m inutes u n d e r a rg o n .
0 .0 1 5 5
m oles) and
m a lo n o n itrile
(10 cm ) w a s a d d e d d ro p w ise .
hou rs.
(1.52 g, 0 .0 0 7 8
D ry p yrid in e (1.23 g,
m oles)
in d ic h lo ro m e th a n e
T h e pale y e llo w s o lu tio n w a s le ft s tirrin g fo r 11
T h e s o lu tio n w a s a d d e d to w a te r (100 cm 3), e xtra cte d w ith ethyl acetate
a nd d rie d o v e r m a g n e siu m
e v a p o ra tin g
o ff th e
so lve n t.
su lp h a te , givin g a pale
T h is
was
ye llo w so lid
re c ry s ta llis e d
from
(0.5 7 g) on
eth a n o l
to
give
A /-m e th ylp h th a lim id e as a w h ite so lid (IR and m e ltin g p o int).
U s in g p y r id in e a s b a s e a n d s o lv e n t a n d tita n iu m te tr a c h lo r id e
T ita n iu m te tra c h lo rid e (5.8 0 g; 50% so lu tio n , 0 .0 1 5 5 m oles) w as a dd ed to a
3
s o lu tio n of A /-m e th ylp h th a lim id e ( 1.00 g, 0 .0 0 6 2 m o le s) in dry p yrid in e (30 cm )
u n d e r n itro g e n .
M a lo n o n itrile (1.1 6 g, 0.176 m oles) in p yrid in e (20 cm ) w as
a d d e d to th e w a rm e d s u s p e n s io n and he a te d u n d e r re flu x fo r 14 hours. The d a rk
red so lu tio n w as filte re d hot to rem ove a sm all q u a n tity of w h ite so lid and the
filtra te c o n c e n tra te d to a fifth of its volum e , y ie ld in g a c ry s ta llin e so lid on coolin g.
T h is c ry s ta llin e s o lid w as fo u n d to be highly h y g ro s c o p ic on filte rin g and passed
th ro u g h the filte r p a p e r into th e filtra te . O n a dd ing w a te r to the filtra te , an o ff-w h ite
s o lid p re c ip ita te d w h ich w a s filte re d off and w a s h e d w ith d ilu te h y d ro c h lo ric acid
(10% ) a nd w a ter.
O n re c ry s ta llis in g from e th a n o l, th e o ff-w h ite c ry s ta llin e so lid
(0.62 g) w a s fo u n d to be /V -m e th ylp h th a lim id e (IR, m e ltin g point and T LC ).
S y n th e s is o f 1 , 3 - D iim in o is o in d o lin e (118a)
D ry lig h t p e tro le u m (4 0 -6 0 )(1 0 c m 3) w a s add ed to so d iu m h ydrid e (80% d isp e rsio n
in oil ; 0 .5 4 g, 0 .0 2 5 m oles), th e su sp e n sio n s w irle d a nd th e s o lv e n t/o il so lu tio n
^
3
re m o ve d w ith a P a ste u r p ip e tte once the m ixture had se ttle d . M e th a n o l (10 cm )
w a s a d d e d g ra d u a lly w ith ca re and the re su ltin g so d iu m m eth o xid e su sp e n sio n
178
a d d e d to a so lu tio n of p h th a io n itrile (5.00 g, 0.03 m o le s) in m e th a n o l (110 cm 3).
A m m o n ia w a s then bu b b le d th ro u g h th e s tirre d so lu tio n fo r o n e hou r. T h e reaction
m ixtu re w a s heated u n d e r reflux fo r 3 h o u rs w ith c o n tin u e d b u b b lin g of am m o nia
th ro u g h th e so lu tio n . T h e hot s o lu tio n w a s filte re d to re m o ve a v e ry sm all am ount
o f g re y s o lid .
v is c o u s
oil
T he s o lv e n t w a s re m o ve d by ro ta ry e v a p o ra tio n g ivin g a green
w h ich
yie ld e d
a
y e llo w
s o lid
on
s c ra tc h in g
w ith
a
g lass
rod.
R e c ry s ta llis a tio n from m e th a n o l/ d ie th y l e th e r (7 0 :3 0 ) u s in g d e c o lo u ris in g charcoa l
y ie ld e d b rig h t y e llo w c ry s ta ls of 1,3 -d iim in o is o in d o lin e
(1 1 8 a )
(2 .1 7 g, 49% ),
m .p .(m e th a n o l) 195 -1 96 °C (lit .,148 196 °C ); v max: 3 2 8 1 , 32 5 5 , 2 9 8 4 (broad,
C = N H ), 1693, 1530, 1468, 1312, 1276, 1177, 1158, 1136, 1081, 1015, 950, 891,
7 7 6 , 745, 7 08 and 695 c m '1; X.max (C H 3 O H ): 3 44
(e =
1 8 93 , b r sh), 316 (3 595),
8.8 (brs, 2H, N H ), 7 .8 5 (m, 2H , a ro m a tic), 7.55
(m, 2H , a ro m a tic), and 3.85 ppm (brs, 1H, N H ); 8c (m e th a n o l-d 4): 119.98 and
26 0 (16 113) and 232 (16 7 9 6 ); 5H:
1 2 9 .9 4 (a ro m a tic C), 134.36 (q u a te rn a ry a ro m a tic C) a n d 1 6 9 .7 5 pp m (C =N H ).
S y n th e s is o f 3 - P h e n y lim in o - 1 - im in o is o in d o lin e (1 1 8 b )
D ry lig h t p e tro le u m (4 0 -6 0 )(1 0 c m 3) w a s a dd ed to so d iu m h y d rid e (80% d isp e rsio n
in oil ; 1.68 g, 0.031 m oles), th e s u s p e n s io n s w irle d a n d th e s o lv e n t/o il so lution
re m o v e d w ith a P a ste u r p ip e tte o n ce th e m ixture had s e ttle d .
M e th a n o l (40 cm 3)
w a s a d d e d g ra d u a lly w ith ca re a n d th e re su ltin g so d iu m m e th o xid e susp e n sio n
a d d e d to a so lu tio n of p h th a lo n itrile (2 0 .0 2 g, 0 .1 5 6 m o le s) in m e th a n o l (350 cm 3).
A n ilin e (1 4 .5 7 g, 0.156 m oles) w a s a d d e d and th e m ix tu re w a s h e a te d u n d e r reflux
fo r tw o a nd a half h o u rs and th e n filte re d hot to re m o ve a ve ry sm a ll am oun t of
n a v y -b lu e s o lid (p h th a lo c y a n in e s ).
R em oval of th e s o lv e n t y ie ld e d a crude ye llo w
s o lid (2 0 .5 0 g). T his w a s re c ry s ta llis e d tw ice from e th a n o l to g ive
1 -im in o is o in d o lin e
(118b)
as
a
m ic ro c ry s ta llin e
s o lid
(18.5
3 -p h e n ylim in o g,
54
%),
m .p. 203 °C (d), (lit .,156 203 °C ); v max: 3031, 1692, 1604, 1594, 1530, 1432, 1332,
129 0, 1215, 1128, 1100, 999, 908, 780, 743, 7 20 , 6 9 7 and 6 4 4 cm -1; Xmax
(C H 3 O H ): 372
(e =
4 585), o v e rla p p in g w ith 348 (4 7 1 3 ), 3 1 4 (4 538) and 2 32 (12
866 ); SH: 8.7 2 (brs, 1 H, N H ), 8.51 (brs, 1 H, NH) a n d 6 .9 9 - 7 .9 4 ppm (m, 9H,
a ro m a tic ); Sc : 119.78, 120 .78 , 121 .47 , 123.19, 12 3 .7 1 , 128 .15 , 129.12, 130.11,
1 3 0 .9 3 , 135.21, 140.56, and 1 5 0 .3 9 (a ro m a tic C), 1 6 5 .1 0 a n d 171 .58 ppm (C =N );
m /z
221 (M +. 100 % ), 205 (15), 194 ( 2 1 ), 129 (2 2 ), 102 (23), 93 (33), 77 (67) and
6 5 (20).
179
Ammonium salt of 2,2'-(isoindolin-1,3-diylidene)bispropanedinitrile (119)
M e th o d (a ): U s in g 1 , 3 - D iim in o is o in d o lin e (1 1 8 a )
20 % e xcess) w a s a d d e d d ro p w ise to a stirring
M a lo n o n itrile (9.53 g, 0 .1 4 4 m oles,
s o lu tio n
of
1 ,3 -d iim in o is o in d o lin e
(118a )
(1 0 .0 9
d im e th y lfo rm a m id e (100 cm ) at room te m p e ra tu re .
g,
0.06
m oles)
in
T h e c o lo u r of the so lution
c h a n g e d im m e d ia te ly fro m a lig h t g re e n /y e llo w c o lo u r to d a rk red, a cco m p a n ie d by
th e d is tin c t sm e ll of a m m o n ia .
A d d itio n of c h lo ro fo rm
p re c ip ita te .
by
F iltra tio n
a m m o n iu m s a lt of
fo llo w e d
re c ry s ta llis a tio n
ca u se d a red solid to
from
m eth anol
gave the
2 ,2 '-(is o in d o lin - 1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile (119), as d a rk
red crysta ls ( 12.22 g, 7 8% ). T h e s a lt u n d e rw e n t a g ra d u a l c o lo u r cha n g e from red
to lig h t b row n at 1 8 0 -2 00 °C, a nd d e c o m p o s e d at 3 4 8 -3 4 9 °C ; v max: 3181, 3091,
221 1, 1612, 1577, 1501, 1450, 1432, 1307, 1259, 1195, 1164, 1096, 920, 770,
749 and 7 0 4 c n v 1 ; Xmax (C H 3C N ): 496 (e=
25 9 0 5 ), 466 (27 120), 360 (9 612),
3 4 4 (12 259) and 240 nm (9 331) ; 5h (p y rid in e -d 5) : 9.2 9 (brs, 4H, NH), 8.35 (m,
2H , a ro m a tic), and 7.3 ppm (m, 2H , a ro m a tic ); 5|_|; 8.05 (m, 2H, arom atic), 7.58 (m,
2 H, a ro m a tic) a nd 7.0 7 ppm ( 1 : 1:1 t, J 5 0 , 4H , N H ); 5C : 5 4 .6 3 (C = C (C N )2), 116.27
a n d 117 .14 (C N ),
C), 172 .02
123 .25 and 1 3 1 .0 4 (a ro m a tic C),
ppm (C = C (C N )2 ).
(F o u n d :
138.0 (q u a te rn a ry arom atic
C, 6 4 .5 3 ; H, 3 .0 4 ; N, 32.4% .
C-|4H 8N 6
re q u ire s: C, 6 4 .6 1 ; H, 3 .0 7 ; N, 32 .3 % ).
M e th o d (b ): U s in g 3 - P h e n y lim in o - 1 - im in o is o in d o lin e (1 1 8 b )
M a lo n o n itrile (9.42 g, 0 .1 4 3 m oles,
10 % e xce ss) w as a d d e d d ro p w ise to a stirrin g
so lu tio n of 3 -p h e n ylim in o -1 -im in o is o in d o lin e
(1 1 8 b )
(15.00 g, 0.068 m oles) in
d im e th y lfo rm a m id e (130 cm ) at room te m p e ra tu re .
T h e c o lo u r of th e so lution
ch a n g e d im m e d ia te ly from a y e llo w c o lo u r to d a rk red, a c c o m p a n ie d by the d istin ct
sm e ll of am m o nia .
A d d itio n of c h lo ro fo rm
c a u s e d a red so lid to p recip itate.
F iltra tio n fo llo w e d by re c ry s ta llis a tio n from m e th a n o l ga ve the am m onium salt of
2 ,2 '-(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile
(119)
as
da rk
red
crysta ls
(1 5 .6 3 g, 89% ). T h is gave id e n tic a l m p, IR, and N M R s p e c tra as m ethod (a).
180
2 , 2 '- ( ls o in d o lin - 1 ,3 - d iy lid e n e ) b is p r o p a n e d in itr ile (110)
M e th o d (a): P y r o ly s is o f (119)
T h e a m m o n iu m salt (119) ( 1.00 g, 0 .0 3 8 5 m oles) w a s p la c e d in a 250 cm 3 round b o tto m e d fla s k and hea te d at ca 1 8 0 -2 0 0 °C on a sa n d b a th u n d e r a n itroge n
a tm o s p h e re fo r 5 hours.
to
a
dull
D uring th is tim e the c o m p o u n d c h a n g e d from a d a rk red
o ra n g e /b ro w n
so lid
(0.70
g,
7 5 % ).
R e c ry s ta llis a tio n
from
2 ,2 ’-(is o in d o lin 1.3 -d iy lid e n e )b is p ro p a n e d in itrile (1 10), m .p. 3 4 9 -3 5 0 °C (d.) (lit .,151 350 °C ) ;
d im e th y lfo rm a m id e /e th a n o l 2 0 :8 0 g a ve sh in y o ra n g e n e e d le s of
v max: 324 3, 31 8 9 , 281 8, 3004, 224 0, 222 7, 1865, 1701, 1685, 1664, 1612, 1470,
144 9, 1414, 1398, 1321, 1244, 1207, 1170, 1158, 1102, 1014, 916, 7 93 , 752, 691
and 6 5 2 c m '1; Xmax (C H 3C N ): 408 (e=
65 884), 3 8 6 (71 823), 366 sh (56 400),
2 8 2 (42 838 ), 2 74 (41 846), 242 (35 2 23 ) and 194 nm (53 261) ; 5H: 8 .1 9 a n d 7.79
(m, 4H , a ro m a tic) ,and 4.8 5 ppm (brs,
1 H, NH) ; 5q: 5 6 .5 4 (= C (C N )2), 114 .65 and
11 5 .6 6 (C N ), 132 .83 a nd 1 2 3 .8 4 (a ro m a tic c a rb o n s ), 134.9 (a ro m a tic C) and
1 6 6 .2 7 ppm (C = C (C N )2 ); m /z 243 (M +,
100 % ), 216 (9), 189 (18), 153 (9), 129 (8 ),
99 (13), 73 (18), 55 (19), 39 (39) and 28 (94).
(F o u n d :
C, 6 9 .2 4 ; H, 2 .1 6 ; N,
29 .1 % . C 14H 5N 5 re q u ire s: C, 6 9 .1 3 ; H, 2.08; N, 2 9 .1 % ).
M e th o d (b ): A c id if ic a tio n o f (119)
T o a s o lu tio n of (119) (3 .2 7 g, 0 .0 1 2 5 m oles) in m e th a n o l (70 cm 3) w a s add ed
o
1% v /v HCI (100 cm ) ca u s in g a fin e y e llo w s o lid to p re c ip ita te .
T h is w a s filte re d
and th e s o lid w a sh e d s e v e ra l tim e s w ith w a te r a nd d rie d to g ive
2 ,2 '-(is o in d o lin -
1.3 -d iy lid e n e )b is p ro p a n e d in itrile (110) (2.27 g, 7 6 % ). T h is ga ve th e sam e IR, UV,
N M R s p e c tra l d a ta as b e fo re and th e sam e m e ltin g p o int.
It co u ld be use d in th is
s ta te o r re c ry s ta llis e d fro m d im e th y lfo rm a m id e /m e th a n o l 20:80.
2 - ( 3 - lm in o is o in d o lin - 1 - d iy lid e n e ) b is p r o p a n e d in itr ile (143)
Dry lig h t p e tro le u m (4 0 -6 0 )(1 0 c m 3) w a s a dd ed to s o d iu m h yd rid e (80% d isp e rsio n
in oil ; 1.96 g, 0.06 m oles), th e s u s p e n s io n s w irle d a n d th e s o lv e n t/o il so lu tio n
re m o ve d w ith a P a ste u r p ip e tte on ce th e m ixture h ad se ttle d .
M e th a n o l (15 cm )
w a s a d d e d g ra d u a lly w ith ca re and th e re s u ltin g s o d iu m m e th o xid e s u sp e n sio n
a d d e d to a s o lu tio n of p h th a lo n itrile
(60 cm 3).
(144) (3.0 5 g, 0 .0 2 m oles) in m ethanol
M a lo n o n itrile (1.98 g, 0 .0 3 m oles) w a s th e n a d d e d , th e p ale ye llo w
181
co lo u re d so lution ch an ged to a ruby red colour.
T h e reaction m ixtu re w a s stirred
a t 30 °C fo r th re e hours during w h ich a p o w d e ry y e llo w solid p re cip ita te d .
The
solid w a s filte re d o ff u n d e r vacuu m and re crysta llise d th re e tim e s fro m ace tic acid
to yie ld 2 -(3 -im in o -is o in d o lin -1 -d iy lid e n e )b is p ro p a n e d in itrile (143) (2.7 0 g, 58% ),
m p 2 10 °C (d) ; v max: 3401, 2990 (broad, C = N H ). 2222, 1688, 1610, 1591, 1519,
1469, 1309, 1262, 1205, 774, and 704 c m '1; SH: 9.95 (brs, 1H, C = N H )), 8.05 (m,
2H , a ro m a tic), 7.7 (m, 2H, arom atic), and 3 .37 ppm (brs, 1H, N -H );
8q: 59.14
(= C (C N )2), 114.84 and 115.63 (CN), 122.91, 123.22, 131.90, 132, 137 and 171.9
pp m (a ro m a tic C), 134.18 (C =N H ), 175.81 ppm (C = C (C N ) 2 ). (F ound : C, 67.84; H,
3.11; N, 2 8 .87% .
requires: C, 6 8 .03; H, 3.11; N, 28.85% ).
S o d iu m s a lt o f 2 ,2 ,- (ls o in d o lin - 1 ,3 - d iy lid e n e ) p r o p a n e d in itr ile (146)
D ry lig h t p e tro le u m (40 -6 0 )(1 0 c m 3) w a s a dd ed to sodium h yd rid e (80% dispersion
in oil ; 0.026 g, 0.0009 m oles), the s u sp e n sio n sw irled and th e s o lv e n t/o il solution
re m o ve d w ith a P a ste u r pip e tte on ce th e m ixtu re had settled.
M e th a n o l (4 cm )
w a s a dd ed g ra d u a lly w ith care and th e re su ltin g sodium m e th o xid e suspe nsio n
w a s a dd ed to a su sp e n sio n o f 2 -(3 -im in o -is o in d o lin -1 -d iy lid e n e )b is p ro p a n e d in itrile
(143) (0.0 15 g, 0.0 0 0 7 m oles) in m e th a n o l (20 cm 3).
M a lo n o n itrile (0.081 g,
0 .0 0 1 2 m oles, 58% e xcess) w a s a dd ed and th e su sp e n sio n hea te d u n d e r reflux
fo r o n e and a h a lf hours. T h e o ra n g e so lu tio n w a s th e n e va p o ra te d to d ryn e ss to
give an o ra n g e solid.
O n re crysta llisin g fro m e th yl a ce ta te 2 -(3 -im in o -is o in d o lin -1 -
d iylid e n e )b is p ro p a n e d in itrile (143) (0.04 g) w a s iso lated (verified by IR and m elting
po in t) by filte rin g the e thyl a ce ta te su s p e n s io n hot.
T h e so d iu m sa lt o f 2,2'-
(lso in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile (146) w a s iso lated fro m th e filtra te as
an o ra n g e p o w d e r (0.091 g, 44% ), m p > 360 °C; v max: 2218, 1676, 1598, 1583,
1493, 1461, 1386, 1309, 1264, 1196, 1164, 1155, 1096, 920, 771, 751, and 706
c m '1;
8h (acetone-dg): 8.21 (m, 2H , a ro m a tic) and 7.61 ppm (m, 2H , arom atic);
8C (a c e to n e -d 6): 55.1 (C = C (C N )2), 116.99 and 118.29 (C N ), 122.89, 131.34 and
13 9 .2 6 (a ro m a tic C), and 173.12 ppm (C = C (C N ) 2).
182
Attempted Benzoylation of 2,2'-(isoindolm-1,3-diylidene)bispropanedinitrile
(110)
M e th o d (a ): U s in g b e n z o y l c h lo r id e a n d a q u e o u s s o d iu m h y d r o x id e
(2 cm 3, 0 .0 1 7 m oles, 8 e q u iv a le n ts ) w as a d d e d in 0.5 cm 3
p o rtio n s w ith c o n tin u o u s sh a k in g to a s u s p e n s io n of ( 1 1 0 ) ( 1.00 g, 0.0021 m oles)
B e n z o y l c h lo rid e
in a 5% a q u e o u s so d iu m h y d ro x id e s o lu tio n .
S h a kin g w as co n tin u e d until th e
b e n zo yl c h lo rid e o d o u r d is a p p e a re d .
A d d itio n a l so d iu m h yd ro xid e so lu tio n
Q
(~3 cm ) w a s a d d e d to m ake th e s u s p e n s io n a lk a lin e . It w as th e n filte re d and the
s o lid w a s h e d w ith co ld w a te r. R e c ry s ta llis a tio n fro m e th a n o l gave a y e llo w po w d e r
(0 .3 6 g,
66% ), th e s o d iu m s a lt of (110), m p > 350 °C ; v max: 2227, 2217, 1677,
1598, 1583, 1497, 1463, 1387, 1310, 1265, 1198, 1096, 920, 771, 751 and 706
cm '1 ; 5h : 7 .9 4 (m, 2H , a ro m a tic) and 7 .4 9 ppm (m, 2H, a ro m a tic ); 5q: 53.79
(= C (C N )2), 116 .13 a nd 117 .09 (C N ), 122.72, 131.18 and 137.28 (a ro m a tic C) and
171 .8 8 ppm (C = C (C N )2).
M e th o d (b ): U s in g b e n z o y l c h lo r id e a n d p y r id in e
B e n zo yl c h lo rid e (0.5 9 g, 0 .0 0 4 2 m oles) w as a d d e d d ro p w ise from a d ropp ing
fu n n e l
to
a
s o lu tio n
of
2 ,2 '-(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile
(110)
(1.0 g, 0.0041 m oles) in p y rid in e on an ice bath and th e re a ctio n m ixture w as left
s tirrin g fo r 2.5 h ou rs. A fu rth e r 3 c m 3 of b e n zo yl c h lo rid e w as a d d e d at 0-5 °C and
th e m ixture w a s s tirre d o v e rn ig h t in th e ic e -b a th .
No new p ro d u cts w e re obse rve d
on fo llo w in g th e re a c tio n by T L C u sing e thyl a c e ta te /lig h t p e tro le u m (80:20) as the
m o b ile p h a se. T h e re a ctio n m ixtu re w as th e n h e a te d at 70 °C fo r
2 hou rs w ith o u t
a n y o b s e rv a b le c h a n g e on T LC . O n p o u rin g into co ld w a te r (100 cm 3) and adding
d ilu te HCI (1 0 % v/v) a y e llo w p re c ip ita te w a s o b ta in e d a nd filte re d off. T his did not
d is s o lv e in e th a n o l and th e IR and m e ltin g p o in t of th e d rie d so lid w a s fo u n d to be
id e n tic a l to th a t of 2 ,2 '-(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile (110).
M e th o d
(c ):
R e a c tio n
of
th e
s o d iu m
s a lt
of
2 ,2 '- (is o in d o lin - 1 ,3 -
d iy lid e n e ) b is p r o p a n e d in it r ile (110) w ith b e n z o y l c h lo r id e
D ry
lig h t
s u s p e n s io n
p e tro le u m
in
oil;
(4 0 -6 0 )(1 0
0 .0 7
g,
cm 3) w a s
0 .0 0 2 3
m oles),
added
th e
to
sodium
s u s p e n s io n
hyd rid e
sw irle d
(80%
and the
s o lv e n t/o il s o lu tio n re m o ve d w ith a P a ste u r p ip e tte on ce the m ixture had settled.
183
A
s o lu tio n
of
2 ,2 '-(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile
(1.0
g,
0.0021
m oles) in dry te tra h y d ro fu ra n (50 cm 3) w as a d d e d g ra d u a lly to give the sodium
s a lt of 2 ,2 '-(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile
(1 46).
B e nzoyl c h lo rid e
(0.2 9 g, 0.0021 m oles) w a s a d d e d d ro p w is e to th e s tirrin g s o d iu m s a lt so lu tio n and
w a s a llo w e d to stir fo r
6 h ou rs.
No new p ro d u c ts w e re o b s e rv e d on T LC using
b o th e thyl a c e ta te /lig h t p e tro le u m (80:20) a nd e th a n o l/e th y l a c e ta te (50:50) as the
m o b ile p h a se .
T h is re a c tio n w a s re p e a te d usin g a 25% e x c e s s of b e n zo yl c h lo rid e fo llo w e d by
h e a tin g u n d e r reflux fo r 5.5 hours.
A g ain no c h a n g e w a s o b s e rv e d on T LC using
th e sa m e s o lv e n t syste m s.
A tte m p te d
re a c tio n
of
th e
A m m o n iu m
s a lt
of
2 ,2 '- (ls o in d o lin - 1 ,3 -
d iy lid e n e ) b is p r o p a n e d in it r ile (119) w ith F o r m a lin
The
a m m o n iu m
s a lt
of
2 ,2 '-(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile
(119)
(0.4 0 g, 0 .0 0 1 5 m oles) and fo rm a lin (36% s o lu tio n in w a te r, 0.5 cm 3, 0.05 m oles)
3
in w a te r (50 cm ) w ere h e a te d u n d e r reflux fo r se v e n h ou rs.
T h e w a te r w as
e v a p o ra te d o ff a nd th e y e llo w so lid o b ta in e d w a s d rie d (0 .2 7 g ).
IR and m elting
p o in t
d a ta
w e re
id e n tic a l
w ith
th o s e
of
2 ,2 '-(is o in d o lin - 1 ,3-
d iy lid e n e )b is p ro p a n e d in itrile ( 1 1 0 ).
M e th y la tio n o f 2 , 2 '- ( is o in d o lin - 1 ,3 - d iy lid e n e ) b is p r o p a n e d in itr ile (110)
A tte m p te d m e th y la tio n u s in g m e th y lio d id e
D ry
lig h t
p e tro le u m
(4 0 -6 0 )(1 0
cm 3) w a s
s u s p e n s io n in oil; 0 .0 5 8 g, 0 .0 0 1 9 3
added
to
so d iu m
hyd rid e
(80%
m oles), th e s u s p e n s io n s w irle d and the
s o lv e n t/o il s o lu tio n re m o ve d w ith a P a ste u r p ip e tte o n ce th e m ixture had settled.
A
s o lu tio n
of
2 ,2 '-(is o in d o lin - 1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile
o
(110)
(0.51
g,
0 .0 0 1 9 6 m o le s) in dry te tra h y d ro fu ra n (100 cm ) w a s a d d e d g ra d u a lly to control
th e e v o lu tio n of h yd ro g e n .
d ry te tra h y d ro fu ra n
re a ctio n m ixture .
M e th y lio d id e (1.11 g, 0 .0 0 7 8 m oles, 3 0 0 % excess) in
(30 cm 3) w a s in tro d u c e d from
a d ro p p in g fu n n e l into the
T h e re a ctio n m ixture w a s s tirre d fo r 4 h o u rs and p ro gress
fo llo w e d by T L C usin g 8 0 :2 0 ethyl a c e ta te /lig h t p e tro le u m as m o b ile phase.
new p ro d u c ts w e re a p p a re n t.
No
T he re a ctio n m ixtu re w a s p o u re d in to iced w a te r
a nd a y e llo w s o lid p re c ip ita te d .
T h is w a s id e n tifie d as th e so d iu m s a lt of 2,2'-
184
(is o in d o lin - 1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile (146) on th e b a sis of IR and m elting
point.
M é th y la tio n u s in g D im e th y l S u lp h a te
D ry light p e tro le u m (4 0 -6 0 )(1 0 c m 3) w a s a d d e d to s o d iu m h yd rid e (80% d isp e rsio n
in oil, 0.118 g, 0.0 0 3 9
m oles), th e s u s p e n s io n s w irle d a n d th e s o lv e n t/o il so lu tio n
re m o ve d w ith a P a ste u r p ip e tte o n ce th e m ixture had s e ttle d .
A so lu tio n of the
a m m o n iu m sa lt of 2 ,2 '-(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile (119) (1.02 g,
0 .0 0 3 9 m oles) in dry te tra h y d ro fu ra n (100 cm 3) w a s th e n a d d ed, fo llo w e d by
d im e th y l su lp h a te (0.51 g, 0 .0 0 4 m o le s) and th e re a c tio n m ixture he a te d to reflux
fo r 7 hours.
T h e re a ctio n w a s fo llo w e d by T L C u s in g 8 0 :2 0 ethyl a c e ta te /lig h t
p e tro le u m as th e m obile p h a se .
T h e fo rm a tio n of o n e p rin cip a l fa st eluting
co m p o u n d , and a n u m b e r of m ore slo w ly e lu tin g m in o r p ro d u c ts n e a r th e base
line,
was
o b se rve d .
c h ro m a to g ra p h y
using
ye llo w /b ro w n
The
p rin c ip a l
te tra h y d ro fu ra n
c ry s ta llin e
p ro d u c t
as
m o b ile
so lid ,
d iy lid e n e )b is p ro p a n e d in itrile (1 5 1 ) (0 .0 8 5 g,
was
is o la te d
p h a se .
T his
by
colum n
yie ld e d
a
2 ,2 '-(2 -m e th y lis o in d o lin -1 ,3-
8% ) from a c e to n itrile , mp 2 6 3 -2 6 4 °C;
v max: 3122, 2225, 1599, 1560, 1 470, 1445, 1320, 1225, 1109, 1073, 778 and 690
c m '1; S|_| (ch loroform -d-|): 8 .6 7 a nd 7.1 9 (m, 4H, a ro m a tic ) and 4.17 ppm (s, 3H,
M e).
A
13
C N M R c a rrie d o u t in d e u te ra te d d im e th y l su lp h o x id e , w h ich required
h e a tin g to get the so lid in to s o lu tio n , sh o w e d a v e ry la rg e n u m b e r of peaks.
A
T L C of th is sa m p le sh o w e d th e fo rm a tio n of a d d itio n a l p ro d u cts, s u g g e stin g the
c o m p o u n d had u n d e rg o n e fu rth e r re a ctio n w ith th e s o lv e n t.
M é th y la tio n
u s in g
th e
té tr a m é th y la m m o n iu m
(T M A )
s a lt
of
2 ,2 '-(2 -
m e th y lis o in d o lin - 1 ,3 - d iy lid e n e ) b is p r o p a n e d in it r ile (1 5 5 )
P re p a ra tio n o f th e T M A s a lt (155)
T h e am m o niu m sa lt (2.01 g, 0 .0 0 7 7 m oles) w a s d is s o lv e d in m eth anol (150 cm 3)
w ith heating.
w a te r
T é tra m é th y la m m o n iu m ch lo rid e (0.9 6 g, 0 .0 0 8 8 m oles) d isso lve d in
(20 cm ) w as a d d e d and th e re a ctio n m ixtu re le ft s tirrin g o v e rn ig h t and
o ra n g e n e e d le s w ere filte re d (0 .6 2 g).
by p re c ip ita tio n
using w a te r.
F u rth e r s o lid w a s o b ta in e d from the filtrate
T h is w a s va cu u m
filte re d and d rie d
(1.21
g).
R e c ry s ta llis a tio n tw ice fro m e th a n o l ga ve red n e e d le s of th e T M A sa lt (155) (1.8 g,
6 0% ), m p 2 5 1 -2 5 2 °C ; v max: 30 2 9 , 2205. 1653, 1598, 1577, 1496, 1309, 1256,
185
109 8, 947, 917, 778, 767, 745, 711 and 703 c n r 1 ; ^ max (C H 3 C N ): 496 (e= 83
3 4 0 ), 466 (87 132), 342 (40 692) and 238 nm (84 840) ; 5H (a c e to n e -d 6): 8 .1 4 a n d
7 .5 6 (m, 4H , a ro m a tic) and 3.41 ppm (s, 12H, M e) ; 5C: 5 4 .0 5 9 (= C (C N )2), 5 4 .4 3
(t, J 15, M e), 116.32 and 117.2 (CN), 122.9 and 131.4 (a ro m a tic C), 137 .33
(q u a te rn a ry C) a nd 171 .87 ppm (C = C (C N )2). (F o u n d :
C, 6 8 .3 9 ; H, 4 .8 9 ; N,
2 6 .5 2 % . C 18 H 16N 6 re q u ire s: C, 6 8 .3 4 ; H .5.10; N, 2 6 .5 6 % ).
(a) H e a tin g th e d r y T M A s a lt u n d e r v a c u u m
T h e T M A s a lt (155) (0.2 g, 0 .0 0 0 3
m m H g.
m oles) w a s h e a te d u n d e r a vacu u m of 0.5
A s th e s a lt sta rte d to m elt a b rig h t y e llo w s o lid b eg an to su b lim e on th e
e d g e s of th e fla s k and th e cold fin g e r.
H e a tin g w a s m a in ta in e d at 180 °C fo r 12
h o u rs d u rin g w h ich the sta rtin g m a te ria l ch a n g e d fro m being d a rk red crysta ls to a
b la c k solid. A sm a ll q u a n tity (~2-3 cm 3) of c le a r liq u id w h ic h sm e lle d of am ine w a s
c o lle c te d in th e liq u id n itro g e n trap . The y e llo w so lid w a s re trie ve d from th e co ld fin g e r by d is s o lv in g it in a c e to n e and e v a p o ra tin g to g ive a y e llo w so lid m ixture
(0 .0 1 7 g) w h ich m a n ife ste d its e lf as two co m p o u n d s w ith alm o st id e n tica l Rf
v a lu e s on T L C in a v a rie ty of s o lv e n t system s.
A T L C of th e b la ck so lid using
8 0 :2 0 ethyl a c e ta te /lig h t p e tro le u m as m obile p h a se sh o w e d it w a s com p o se d of
b la c k b a s e lin e m a te ria l a n d som e sta rtin g m a te ria l.
A
1 H, 13C N M R and an IR
s p e c tru m of th e y e llo w m ixture w e re re co rd e d . v max: 312 0, 3075, 2915, 2849,
2 2 1 5 , 1618, 1558, 1470, 1446, 1318, 1227, 1098, 1158, 785, 6 9 7 and 675 cm -1;
5h (c h lo ro fo rm -d -i): 8 .6 7 (m, 2H, a ro m a tic), 8 .60 (m, 2H , a ro m a tic), 7.86 (m, 2H,
a ro m a tic ), 7.7 8 (m, 2H, a ro m a tic), 5.25 (s,
4 H );
3 6 .7 7
1 H), 4.18 (s, 3H, M e), and 3.81 ppm (s,
(c h lo ro fo rm -d -|): m any pea ks o b s e rv e d , p rin c ip a l pea ks at ; 3 1.89 a nd
(M e),
7 4 .4 8
(C = C (C N )2),
1 1 1 .0 -1 1 6 .0
(5
CN
pe a ks),
123.76-134.31
(9 a ro m a tic C) and 1 5 3 .0 -1 5 9 .0 (3 peaks).
(b ) H e a tin g th e T M A s a lt (1 5 5 ) in 1 ,2 -D ic h lo ro b e n z e n e
T h e T M A s a lt (155) (0 .9 0 g, 0 .0 0 2 8
m oles) in
1 ,2 -d ic h lo ro b e n z e n e (20 cm 3) w as
h e a te d to re flu x fo r 150 h o u rs d u rin g w h ich the re a ctio n m ixture c h a n g e d c o lo u r
fro m a red to a b la ck s o lu tio n .
T h e re a ctio n w a s fo llo w e d by T LC using 30:70
e th yl a c e ta te /lig h t p e tro le u m as m obile pha se a nd th is sh o w e d the p ro d u ctio n of
o n e new p ro d u ct.
T h e b la c k c ry s ta llin e so lid (0.71 g) w h ich c ry s ta llis e d out on
c o o lin g w as filte re d w a s h e d th re e tim es w ith d ie th yl e th e r a nd dried.
186
T h is w as
th e n re c ry s ta llis e d th re e tim es from a c e to n itrile to g ive
1,3 -d iy lid e n e )b is p ro p a n e d in itrile (151) (0 .3 6 4 g).
2 ,2 '-( 2 -m e th y lis o in d o lin -
T h e 1,2 -d ic h lo ro b e n z e n e w as
re m o ve d from th e filtra te by va cu u m d is tilla tio n to g ive a g o ld e n s o lid w ith the
sam e Rf va lu e and IR as 2 ,2 '-(2 -m e th y lis o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile .
T h is
was
re c ry s ta llis e d
th re e
tim e s
to
d iy lid e n e )b is p ro p a n e d in itrile (151) (0 .0 3 4 g).
g iv e
2 ,2 '-(2 -m e th y lis o in d o lin -1 ,3-
T h e to ta l y ie ld w as 0.3 9 8 g (54% ),
m p 2 6 4 °C ; v max: 3121, 2224, 1598, 1557, 147 1, 1446, 1318, 1225, 1109, 785
and 6 9 0 cm -1 ; Xmax (C H 3C N ): 416 (e= 25 2 4 7 ), 3 9 4 (25 017 ), 294, 280 and 244
868 ) ; 5h (a c e to n e -d 6): 8.65 (m, 2H , a ro m a tic ), 7 .9 8 (m, 2H, arom atic) and
4.1 0 ppm (s, 3H , M e); 5q (a ce to n e d 6): 3 7 .4 9 (M e), 6 1 .9 (C = C (C N ) 2 ), 113.76 and
1 1 4 .5 2 (C N ), 125.7, 132.1 and 135.3 (a ro m a tic C) a n d 160 .92 ppm (C = C (C N ) 2).
(F o u n d : C, 6 9 .9 1 ; H, 2.87; N, 2 7 .1 0 % . C 15 H 7 N 5 re q u ire s : C, 7 0 .0 3 ; H, 2.74; N,
nm (10
2 7 .2 2 % ).
A tte m p te d
B e n z y la tio n
of
2 ,2 '- ( is o in d o lin - 1 ,3 - d iy lid e n e ) b is p r o p a n e d in itr ile
of
2 ,2 '- ( is o in d o lin - 1 ,3 - d iy lid e n e ) b is p r o p a n e d in itr ile
(110)
B e n z y lp y r id in iu m
s a lt
(1 6 3 )
D ry lig h t p e tro le u m (4 0 -6 0 )(1 0 c m 3) w a s a d d e d to so d iu m h yd rid e (60% dispersion
in o il; 0 .3 0 7 g, 0 .0 0 7 6 m oles), the s u s p e n s io n s w irle d a n d th e s o lv e n t/o il so lution
re m o ve d w ith a P a ste u r p ip e tte on ce th e m ixtu re had se ttle d . A s o lu tio n of 2,2'(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile
(110)
(2 .2 g, 0.0 0 7 6
m oles) in dry
te tra h y d ro fu ra n (80 c m 3) w as a d d e d g ra d u a lly to g ive th e so d iu m sa lt of
(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile (1 46).
e v a p o ra te d
o ff and th e so d iu m
salt w a s
2 ,2 '-
T h e te tra h y d ro fu ra n w as then
re d is s o lv e d
in
m e th a n o l (50 cm ).
B e n z y lp y rid in iu m c h lo rid e w a s th e n p re p a re d by h e a tin g p y rid in e (0.61 g, 0.0 0 7 7
m o le s) w ith b e n z y lc h lo rid e (0 .9 7 g, 0 .0 0 7 6 m o le s) on a he a tin g m antle for 20
m in u te s.
th e
T h e re s u ltin g c le a r p in k s o lu tio n s o lid ifie d on co o lin g .
so d iu m
s a lt of
T h e solution of
2 ,2 '-(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile
(110)
w as
a d d e d to th e ben zyl p y rid in iu m ch lo rid e and h e a te d u n d e r reflux fo r 30 m inutes.
T h e b e n z y lp y rid in iu m s a lt of 2 ,2 '-(is o in d o lin -1 , 3 -d iy lid e n e )b is p ro p a n e d in itrile (163)
w a s o b ta in e d as b rig h t o ra n g e n e e d le s (1.95 g) on le a v in g to cool.
T he filtra te
w a s e v a p o ra te d to d ryn e ss, re d is s o lv e d in b o ilin g e thyl a ce ta te and in so lu b le
s o d iu m c h lo rid e filte re d off.
T h e ethyl a c e ta te w a s re m o ve d , both b a tch e s of the
s a lt w e re c o m b in e d and re c ry s ta llis e d fro m e th a n o l to g ive th e b e n zylp yrid in iu m
187
s a lt
of
2 ,2 '-(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile
(163)
as
fine
o ra n g e
n e e d le s (1.52 g, 48% ); m p 1 7 4 -1 7 5 °C ; v max: 3 1 3 0 , 3086, 3062, 2199, 1633,
1613, 1598, 1578, 1488, 1378, 1364, 1313, 1268, 1254, 1158, 1094, 1027, 947,
917, 817, 775, 703, 6 84 and 6 1 7 c m '1; §H ; 9.2 (d, J 5 .9 1 , 2H, p yrid in iu m CH),
8.6
(t, J 7.88, 1H, p y rid in iu m C H ), 8 .2 (t, J 7 . 1 4 , 2H , p y rid in iu m CH), 8.08 (m, 2H,
a ro m a tic), 7 .6 2 (m, 2H , a ro m a tic ), 7.51 (m, 2H , a ro m a tic ), 7.4 2 (m, 3H, a ro m a tic)
a nd 5 .84 ppm (s,
2 H, b e n zyl C H 2 ); 8C: 5 4 .0 4 (= C (C N ) 2 ), 6 3 .4 (benzyl C H 2), 116.3
a n d 117.3 (C N ), 122.9 (a ro m a tic C), 128.5, 128.8, 1 2 9 .2 and 129.4 (a ro m a tic C),
1 3 1 .4 (a ro m a tic C), 1 34 .2 and 137 .4 (q u a te rn a ry a ro m a tic C), 144.8 and 146.0
(p y rid in iu m C H ) a nd 171.9 ppm (C = C (C N ) 2). T h e s e a s s ig n m e n ts w e re m ade w ith
th e aid of C -H
c o rre la tio n
s p e c tra a nd by c o m p a ris o n w ith b e n zylp yrid in iu m
p e rc h lo ra te .176
(F o u n d : C, 7 4 .2 ; H, 3 .8 5 ; N, 2 0 .6 1 % C 2 6 H i6 N 6 .1/2 H 2 0 re quire s
C, 7 4 .1 8 ; H, 3.95;N , 19.96% ).
A tte m p te d
f o r m a t io n
of
2 ,2 '- (2 -b e n z y lis o in d o lin - 1 ,3 -
d iy lid e n e ) b is p r o p a n e d in it r ile (164)
T h e b e n z y lp y rid in iu m sa lt of
(0.5 g,
2 ,2 '-(is o in d o lin - 1 ,3 -d iy tid e n e )b is p ro p a n e d in itrile (163)
0.0012 m oles) in 1,2 -d ic h lo ro b e n z e n e (12 cm 3) w a s he a te d u n d e r reflux fo r
sixte e n hou rs, d u rin g w h ic h th e s o lu tio n ch a n g e d from a b rig h t orang e c o lo u r to a
b la c k so lu tio n .
T h e re a c tio n w a s m o n ito re d b y T L C
p e tro le u m (40 -6 0 °C ) 8 0 :2 0 as th e m obile p h a se .
e lu tin g p ro d u ct w a s o b s e rv e d .
c o n c e n tra tio n s
in v o lv e d .
A
using ethyl a c e ta te /lig h t
A v e ry sm all am oun t of a fa ste r
T h is co u ld not be is o la te d due to the sm all
n o n -e lu tin g
b la c k
c a rb o n ife ro u s
co m pou nd
o b ta in e d on filte rin g . T h is w a s in s o lu b le in a ra n g e of s o lv e n ts tried.
o ff the 1 ,2 -d ic h lo ro b e n z e n e y ie ld e d sta rtin g m a te ria l (0.031 g).
188
w as
E va porating
S y n th e s is
of
th e
a m id in o
d e r iv a tiv e s
of
2 ,2 '- (is o in d o lin - 1 ,3 -
d iy iid e n e ) b is p r o p a n e d in it r ile (110)
T h e sam e g e n e ra l p ro c e d u re w as c a rrie d out fo r th e s y n th e s e s of all the a m id in e s
b u t w ith v a ry in g reaction s o lv e n ts and re a ctio n tim e s.
T h e s y n th e s is of 2 -cya n o -
/V2-b e n z y l- 2 - ( 3 -d ic y a n o m e th y le n e is o in d o l- 1 -d iy lid e n e )a c e ta m id in e is g iven as a
ty p ic a l e x p e rim e n ta l p ro ce d u re w ith any d e v ia tio n s o r d iffe re n c e s sta te d in th e
s u b s e q u e n t p ro ce d u re s.
2 -C y a n o -W 2- b e n z y l- 2 - ( 3 - d ic y a n o m e th y le n e is o in d o l- 1 - d iy lid e n e ) a c e ta m id in e
(1 7 5 )
The
a m m o n iu m
salt
of
2 ,2 '-(is o in d o rm -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile
(110)
(0 .5 0 g, 0 .0 0 1 9 m oles) a nd b e n zyl am ine (0.21 g, 0 .0 0 1 9 m oles) in 1,4 -d io xa n
(30 cm 3) w e re hea ted to reflux for fo u r hours d u rin g w h ich an o ra n g e so lid
p re c ip ita te d .
T h is w as th e n filte re d off from the s o lu tio n and a se co n d batch of
s o lid p re c ip ita te d , w h ich w a s a lso filte re d off.
T h e s e b a tch e s w ere co m b in e d ,
d rie d u n d e r vacu u m and re c ry s ta llis e d from d im e th y lfo rm a m id e /e th a n o l (10:90) to
y ie ld
2-cyano -A / 2-b e n z y l-2 -(3 -d ic y a n o m e th y le n e is o in d o l-1 -d iy lid e n e
)a ce ta m id in e
(1 7 5 ) (0.31 g, 46 % ), m p 300-301 °C (d); v max: 33 8 2 , 3321, 2927, 2216, 2204,
163 6, 1611, 1568, 1519, 1464, 1312, 1260, 1090, 879, 799, 734, 695 and 605
c m -1 ; A.max: 492 nm (e= 34 0 7 0 ), 464 (31 756) a n d 3 4 4 nm
(10 5 5 2 ); SH: 10.29
1 H, N H ), 9.25 (brs, 2 H, N H 2), 8.29 (m, 1 H, is o in d o lin - 1 ,3 -d iy lid e n e a rom atic
H), 8.11 (m, 1 H, is o in d o lin -1 ,3 -d iy lid e n e a ro m a tic H), 7 .6 2 (m, 2H, is o in d o lin -1 ,3 (brs,
d iy lid e n e a ro m a tic H), 7 .36 (m, 5H , ben zyl a ro m a tic H) and 4.67 ppm (s,
2 H, C H 2);
5C : 44.9 (benzyl C H 2), 5 7 .2 5 (= C (C N )2), 71.37, [1 1 4 .6 6 , 115.35 and 116.8 (CN)],
[1 2 3 .1 2 , 123.44, 127.05, 127.19, 128.01, 131.03, 131 .46 , 135.00, 135 .54 and
13 7 .9 7 (a ro m a tic C)], 159.56, 167 .26 and 170.10 ppm , (C = N ) and (C = C (C N )-).
T a ble 5.1
sh o w in g th e c o rre la tin g p e a ks from the C -H C o rre la tio n s pe ctru m
1H N M R p e a k s (p p m )
13C NM R p e a k s (p p m )
4.66
44.9
7.3 6
127.05. 127.19, 128.01
7.6 2
131.03, 131.46
8.11
123.12
8.29
123.44
189
(F o u n d :
C, 7 1 .5 7 ; H, 4.14; N, 2 3 .5 8 % .
C 21 H 14 N 6 re q u ire s : C, 7 1 .9 9 ; H, 4.02; N,
2 3 .9 9 % ).
T h e filtra te w as e va p o ra te d to d ry n e s s and re c ry s ta llis e d from a ce to n itrile
to g ive an o ra n g e crysta llin e so lid , th e b e n z y la m m o n iu m s a lt of
2 ,2 '-(is o in d o lin -
1,3 -d iy iid e n e )b is p ro p a n e d in itrile (179) (0.1 9 g, 28% ), m p 2 9 8 -2 9 9 °C ; v max: 3134,
309 4, 261 2, 2209, 1596, 1586, 1504, 1381, 1310, 1248, 1129, 1098, 952, 848,
7 5 4 a n d 708 c m '1; \ max (C H 3 C N ): 4 9 6 ( e =
32 597 ), 4 64 (32 393), 342 (13 124)
a n d 2 4 0 nm (28 786 ); 5H: 8 .52 (brm , 5H , is o in d o lin -1 ,3 -d iy iid e n e a ro m a tic H and
N H 3 ), 7 .6 5 (m, 2H, is o in d o lin -1 ,3 -d iy lid e n e a ro m a tic H), 7.4 5 (m, 5H, benzyl
a ro m a tic H) and 4.5 ppm (s,
2 H, C H 2); on a d d itio n o f D 2 O to th e N M R sam ple the
m u ltip le t at 8.5 2 ppm w a s no lo n g e r b ro a d a n d in te g ra te d fo r 2 p ro to n s ; 5q: 42.28
(b e n zyl C H 2), 53.89 (= C (C N )2), 1 1 6 .2 4 and 1 1 7 .1 9 (C N ), 122.83, 128.45, 128.57,
128.76, 131.27, 133.83 and 137.38 (a ro m a tic C) and 1 7 1 .9 7 (C = C (C N )2).
T a ble 5.2 sh o w in g the co rre la tin g p e a ks fro m th e C -H C o rre la tio n s pectrum
1H N M R p e a k s (p p m )
13C N M R p e a k s (p p m )
4 .5 0
42 .2 8
7.45
12 8 .4 5 , 128 .57 , 128 .76
7.6 5
1 3 1 .2 7
8.52
122.83
(F o u n d : C, 7 2 .1 5 ; H, 4.12; N, 2 4 .5 2 % .
C 21 H 14N 6 re q u ire s : C, 7 1 .9 9 ; H, 4.02; N,
2 3 .9 9 % ).
2 -C y a n o -A /2- p r o p y l- 2 - ( 3 - d ic y a n o m e th y le n e is o in d o lin - 1 - d iy lid e n e ) a c e ta m id in e
( 180 )
n -P ro p y la m in e (0.35 g, 0.0 0 5 9 m oles) w a s a d d e d to a s o lu tio n of th e am m onium
s a lt
of
2 ,2 '-(is o in d o lin -1,3 -d iy lid e n e )b is p ro p a n e d in itrite
m o le s) in
(119)
(1.5 0
g,
0.0058
1 ,4-d ioxa n and he a te d u n d e r re flu x fo r 22 h ou rs. T h is ga ve 2 -cya n o -N2-
p ro p y l-2 (3 -d ic y a n o m e th y le n e is o in d o lin -1 -d iy iid e n e )a c e ta m id in e
(180)
o ra n g e s o lid (1.13 g, 65% ), m p 2 9 8 -2 9 9 °C, g ra d u a lly d a rk e n s above
as
an
200 °C;
v max: 335 0, 3278, 3205, 2965, 28 7 5 , 2215, 1672, 1621, 1535, 1481, 1380, 1312,
1259, 1092, 914, 773, 734, 6 97 a n d 6 32 c n r 1: ^ max: 4 92 (e=
37 159), 460 (33
4 67 ) a n d 346 nm (13 664 ); SH: 10.69 (brs, 1H, N H ), 8.61 (brs, 2H, N H 2), 8.03 (m,
190
1H, a ro m a tic), 7.90 (m,
C H 2), 1.65 (m,
1 H, a ro m a tic), 7.51 (m, 2H, a ro m a tic), 3.21 (t, J 7 .4 , 2H , N-
2 H, C H 2) and 0.9 2 ppm (t, J 7.4, 3H , M e); 5C: 11.65 (M e), 21.09
(C H 2), 4 4 .2 0 (N -C H 2 ), 5 6.96 (= C (C N ) 2), 7 1.95, [1 1 5 .1 5 , 115.95 and 117.18] (C N ),
[1 2 3 .2 5 , 123 .61 , 131.21, 131.66, 1 3 4 .9 7 and 137 .98 ] (a ro m a tic C), 159.10, 166.79
and 1 7 0 .2 5 ppm (C =N ) and (C = C (C N )-).
(F o u n d :
C, 6 7 .0 0 ; H, 4.7; N, 27.91% .
C i 7 H 14 N 6 re q u ire s : C, 6 7 .5 4 ; H, 4 .6 7 ; N, 2 7 .7 9 % ).
The
n -p ro p y la m m o n iu m
s a lt of 2 ,2 '-(is o in d o lin -1 ,3 -d iy iid e n e )b is p ro p a n e d in itrile ,
(183) w a s o b ta in e d from th e filtra te in
8% yie ld ; m p 298 °C (d), g ra d u a lly d a rke n s
from 180 °C ; v max: 3210, 316 9, 29 6 8 , 2208, 1584, 1478, 1309, 1251, 1092, 950,
917, 7 6 6 a n d 701 c m '1; Xmax (C H 3C N ): 496 (e=
32 458 ), 4 64 (32 200), 342 (13
536 ) a nd 240 nm (28 7 4 7 ); 5|_|: 8 .0 7 (m, 2H, a ro m a tic), 7 .6 2 -7 .5 9 [m, (a ro m a tic H)
o v e rla p p in g brs (N H 3), 5H ], 2.7 2 (t, J 7 .6 ,
2 H, N -C H 2), 1.53 (m, 2H, C H 2) and 0.93
ppm (t, J 7.4, 3H , M e); 5C: 10.8, 20 .5 and 40.5 (C H ), 54 .0 (=C (C N ) 2), 116.4 and
117.3 (C N ), 122.9, 131.3 and 137.5 (a ro m a tic C) a nd 172.1 ppm (C = C (C N )2).
(F o u n d :
C, 6 7 .4 ; H, 4.63; N, 2 7 .8 6 % .
C 17 H 14N 6 re q u ire s :
C, 6 7 .5 4 ; H, 4.67; N,
2 7 .7 9 % ).
A lte r n a tiv e s y n th e s is o f 2 -C y a n o -A /2- p r o p y l- 2 - ( 3 - d ic y a n o m e th y le n e is o in d o lin 1 - d iy lid e n e ) a c e ta m id in e (180)
The
n -p ro p y la m m o n iu m
sa lt
of
2 , 2 '-(is o in d o lin - 1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile
(183) (0.3 5 g, 0 .0 0 1 2 m oles) in 1 ,4 -d io xa n w a s h e a te d u n d e r reflux fo r tw e lve
h ou rs. A n o ra n g e so lid p re c ip ita te d and w a s filte re d o ff to give 2-cyano-A / 2-p ro p yl2 -(3 -d ic y a n o m e th y le n e is o in d o lin -1 -d iy lid e n e )a c e ta m id in e
(180)
(0.13
g,
36% ).
T h is g a v e th e s a m e IR and m e ltin g p o in t as before.
T h e filtra te
re c ry s ta llis e d
was
e v a p o ra te d to
from
d ry n e s s
and th e
ethyl a c e ta te to give th e
o ra n g e
so lid
n -p ro p yla m m o n iu m
(is o in d o lin - 1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile (183) (0.2 2 g, 62% ).
th e s a m e m e ltin g p o in t and IR s p e c tru m as before.
191
o b ta in e d w as
salt of
2 ,2 '-
T h is also gave
2-Cyano-/V2-isopropyl-2-(3-dicyanomethyleneisoindol-1-diylidene)
acetamidine (184)
Iso p ro p y la m in e (0.2 7 g, 0 .0 0 4 6 m oles) w as a d d e d to a s o lu tio n of th e am m onium
s a lt
of
2 ,2 '-(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile
(119)
(1.00
g,
0.0038
m oles) in 1 ,4 -d io xa n (40 cm ) and h e a te d to re flu x fo r 24 hours. T h e s o lv e n t w as
e v a p o ra te d to d ry n e s s and the o ra n g e s o lid o b ta in e d w a s re c ry s ta llis e d from
a c e to n itrile
to
y ie ld
2-cyano -A /2-is o p ro p y l-2 -(3 -d ic y a n o m e th y le n e is o in d o l-1 -
d iy lid e n e )a c e ta m id in e (184) (0.55 g, 4 7 % ); m p 2 7 2 °C ; v max: 342 4, 3341, 3233,
29 7 5 , 293 1, 220 5, 1659, 1619, 1530, 1482, 1449, 1398, 1309, 1263, 1127, 1092,
910, 769, 7 3 2 and 679 c m '1; Xmax\ 4 92 ( e = 35 3 8 4 ), 4 6 0 (31 852) and 348 nm
(11 8 0 6 ); 5h : 11.26 (brs, 1H, NH), 8.4 2 (brs, 2H , N H 2), 8.0 4 and 7.91 (m, 2H,
a ro m a tic H), 7.5 3 (m, 2H, a ro m a tic H), 3 .94 (brm , 1H, N -C H ) a nd 1.26 ppm (d, J
4.9, 6H, C H 3); 5c : 21.6 (C H 3), 43.6 (N -C ), 5 6 .3 6 (= C (C N )2), 7 1 .50, [1 14.8, 115.3
and 116.7] (C N ), [1 2 2.6, 123.0, 130.6, 131.1, 134 .3 and 137.4] (a ro m a tic C),
157.4, 166.1 and 169.8 ppm (C =N ) and (C = C (C N )-).
(F o u n d ;
C, 6 7 .4 4 ; H, 4.69;
N, 2 7 .8 3 % . C 17H 14N 6 re q u ire s: C, 6 7 .5 4 ; H, 4 .6 7 ; N, 2 7 .7 9 % ).
T h e a c e to n itrile filtra te from the re c ry s ta llis a tio n w a s e v a p o ra te d to d ryn e ss and
th e s o lid o b ta in e d w a s a d d e d to b o ilin g c h lo ro fo rm and an in s o lu b le so lid w as
filte re d
off
hot.
T h is
so lid
was
th e n
re c ry s ta llis e d
from
e th a n o l
to
give
is o p ro p y la m m o n iu m sa lt of 2 ,2 '-(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile (187)
(0.29 g, 2 5 % ); m p 180 °C ; v max: 3167, 297 9, 22 0 9 , 1637, 1578, 1504, 1379, 1311,
1244, 1244, 1097, 1047, 917, 773 and 703 c m '1; Xmax (C H 3C N ): 496 (e= 11 433),
466 (11 373), 342 (4 985 ) a nd 240 nm (10 6 9 2 ); 5H: 8 .0 7 (m, 2H, a ro m a tic), 7.62
(brm , 5H , a ro m a tic H and N H 3), 4.36 (brs, 1H, O H ) 3.41 (q, J 6.8, 2H, C H 2 of
e th a n o l), 3.2 6 (m, 1H, N -C H ), 1.13 (d, J 6 . 4 , 6H , M e of is o p ro p y l g ro u p ) and 1.03
ppm (t, J 6 .8 , 3H, M e of e th a n o l); on a d d itio n of D20 to th e N M R s a m p le th e broad
m u ltip le t at 7.6 2 ppm be ca m e a tw o pro to n m u ltip le t a n d th e b ro a d p e a k at 4.36
ppm w a s no lo n g e r o b s e rv e d ; 8C: 18.56 and 20.39 (M e), 43.1 (N -C ), 54.00 (C H 2 of
e th a n o l), 5 6 .0 8 (= C (C N )2), 116.35 and 117.3 (C N ), 122.93, 131 .37 and 137.48
(a ro m a tic C) and 172 .0 7 ppm (C = C (C N )2). (F o u n d : C, 6 5 .5 3 ; H, 5 .5 9 ; N, 24.27% .
c
17 h 14n 6-c 2 h 5o h re q u ire s: C, 6 5 .5 ; H, 5 .7 8 ; N, 2 4 .1 2 % ).
192
2-Cyano-N2-butyl-2-(3-dicyanomethyleneisoindolin-1-diylidene)acetamidine
(188)
The
a m m o niu m
sa lt
of
2 ,2 '-(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile
(119)
(2.0 0 g, 0 .0 0 7 7 m oles) and n -b u ty la m in e (0 .5 7 g, 0 .0 0 7 7 m oles) w e re heated
u n d e r reflux in ethano l
(100 cm ) fo r six hours. O n le a v in g to cool o v e rn ig h t an
o ra n g e solid p re cip ita te d . T h is w a s filte re d o ff and d rie d to yie ld 2 -cya n o -/\/ 2-butyl2 -(3 -d ic y a n o m e th y le n e is o in d o lin -1 -d iy lid e n e )a c e ta m id in e
(188)
(1 .8 6
g,
77% );
m p 290 °C (d); v max: 33 2 6 , 327 0, 2 9 5 9 , 28 7 2 , 22 1 1 , 1654, 1611, 1587, 1568,
1516, 1463, 1 3 1 3 ,1 2 5 2 , 1149, 1091, 910, 781, 733, 775, 765 a nd 6 3 0 c m '1; >.max:
492
(e =
37 516 ), 460 (33 598) a nd 3 4 8 nm
(12 6 4 2 ); 5H: 10.83 (brs, 1H, NH), 8.70
(brs, 2H, NH), 8.17 (m, 1H, a ro m a tic ), 8.0 3 (m, 1H, a ro m a tic ), 7.6 2 (m, 2H,
a ro m a tic), 3.3 (m,
2 H, N -C H 2), 1.63 (m, 2 H, C H 2), 1.38 (m, 2H , C H 2) and 0.91
ppm (t, J 7 .4 , 3H , M e); 5C : 13.4 (M e), 19.8, 29.5 a nd 4 2.3 (C H 2), 5 6 .9 (= C (C N )2),
71.9, [115.1, 115.9 and 117 .1] (C N ), [1 2 3 .2 , 123.5, 131.1, 131.5, 134.9 and 137.9]
(a ro m a tic C), 1 5 8 .9 ,1 6 6 .7 and 170.1 ppm (C =N ) a n d (C = C (C N )-).
(F ound ;
C,
6 8 .0 6 ; H, 5 .0 7 ; N, 2 6 .7 2 % . C 18 H 16N 6 re q u ire s : C, 6 8 .3 4 ; H, 5 .0 9 ; N, 26.56% ).
T h e filtra te w a s e va p o ra te d to d ry n e s s and re c ry s ta llis e d from ch lo ro fo rm to yield
th e n -b u tyla m m o n iu m sa lt of 2 ,2 '-(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile (190)
(0.4 2 g, 17% ) as o ra n g e p la te s ; m p 2 8 9 -2 9 0 °C (d); v max: 32 2 0 , 3176, 2963,
293 6, 2207, 1597, 1478, 1309, 1244, 1225, 1244, 1096, 9 10 a nd 7 78 cm -1; \ max
(C H 3 C N ): 496
(e =
40 556), 4 6 4 (40 354 ), 342 (17 4 38 ) a n d 240 nm (36 670); 5H:
8 .0 7 (m, 2H, a rom atic), 7.62 (m, 2H , a ro m a tic) o v e rla p p in g w ith 7.5 8 (brs, 3H,
N H 3), 2.75 (t, J 7.4, 2H, N C H 2), 1.45 (m, 2H, C H 2), 1.28 (m, 2H , C H 2) and 0.86
ppm (t, J 7.4, 3H, M e); Sc : 13.5 (M e), 19.1, 29.1 a nd 3 8 .6 (C H 2), 54.1 (= C (C N )2),
116.3 and 117.3 (C N ), 122.9,
(C = C (C N )2).
(F ound :
131 .4 and 137.5 (a ro m a tic C) and 172.1
C, 6 8 .2 5 ;
H, 5 .0 8 ; N, 2 6 .8 2 % .
C, 6 8 .3 3 ; H, 5 .0 9 ; N, 2 6 .5 6 % ).
193
ppm
C 18H 16N 6 requires:
2-Cyano-A/2-cyclohexyl-2-(3-dicyanomethyleneisoindolin-1-diylidene)
acetamidine (192)
C y c lo h e x y la m in e (0.39 g, 0 .0 0 4 m oles) w a s a d d e d to a so lu tio n of th e am m o niu m
s a lt of 2 ,2 '-(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile (119) (0.51 g, 0 .0 0 2 m oles)
in p y rid in e (4 cm 3) a nd th e so lu tio n h e a te d u n d e r re flu x fo r e le ve n hou rs.
It w as
(200 cm ) and a y e llo w s o lid p re c ip ita te d . D ilu te HCI (10% ,
th e n p o u re d into w a te r
30 cm ) w a s a d d e d a n d th e so lid w as filte re d u n d e r vacuu m a nd w a s h e d w ith
w a te r.
T h e s o lid w a s re c ry s ta llis e d tw ice from a c e to n itrile to g ive 2-cyano -A /2-
c y c lo h e x y l-2 -(3 -d ic y a n o m e th y le n e is o in d o lin -1 -d iy lid e n e )a c e ta m id in e (192) as fin e
n e e d le s (0.4 3 g, 6 4 % ); m p 2 7 7 -2 7 8 °C ; v max: 342 4, 3338, 32 7 1 , 3236, 2935,
2 2 1 9 , 220 3, 1659, 1619, 1527, 1484, 1308, 1259, 1093, 910, 7 9 5 a nd 7 25 cm "1;
X.max : 492
(e =
34 364 ), 460 (29 988) and 348 nm
(12 3 6 3 ); 5H: 11.25 (brd, 1 H,
2 H, N H 2 ), 8.09 (m, 1 H, a ro m a tic), 7 .95 (m, 1H, a ro m a tic), 7.5 (m,
2H , a ro m a tic H), 3.6 (m, 1 H, N C H ), 1.95 (m, 2 H, C H 2), 1.7 (m, 2 H, C H 2), 1.55 (m,
1 H, C H ), 1.3 (m, 4H, C H 2) and 1.1 ppm (m, 1 H, C H ); 5C : 24.2 (C H 2), 2 4 .7 (C H 2),
3 1 .7 (C H 2 ), 50 .9 (C H ), 56.8 (= C (C N )2), 71.9, [1 1 5 .2 , 115.8 a nd 117.2] (CN),
N H ), 8.4 (brs,
[1 2 3 .2 , 123.5, 131.2, 131.6, 134.9 and 137.9] (a ro m a tic C), 157.7, 1 66 .7 and
1 7 0 .3 ppm (C =N ) a nd
(C = C (C N )-).
(F o u n d :
C, 7 0 .0 5 ; H, 5 .3 4 ; N, 24.71% .
C 20H 18N 6 re q u ire s : C, 7 0 .1 6 ; H, 5 .2 9 ; N, 2 4.5% )
A i- ls o p r o p y lid e n e c y c lo h e x y la m m o n iu m
s a lt
of
2 ,2 '- (is o in d o lin - 1 ,3 -
d iy lid e n e ) b is p r o p a n e d in it r ile (195)
The
(0 .5 2
a m m o n iu m
g,
0 .0 0 2
sa lt
of
m o le s)
2 ,2 '-(is o in d o lin - 1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile
in
a c e to n e
(40
cm 3) w a s
a dd ed
c y c lo h e x y la m in e (0.20 g, 0 .0 0 2 m oles) in a c e to n e (20 cm 3).
to
a
(119)
s o lu tio n
of
T h e so lu tio n w as
s tirre d at room te m p e ra tu re fo r one and a h a lf days, a nd th e n e v a p o ra te d to give a
red oil w h ich s o lid ifie d on c o o lin g .
y ie ld e d
th e
R e c ry s ta llis a tio n from a ce to n e in tw o b a tch e s
/V -is o p ro p y lid e n e c y c lo h e x y la m m o n iu m
d iy lid e n e )b is p ro p a n e d in itrile
(195)
as
o ra n g e
sa lt
of
pla te s
2 ,2 '-(is o in d o lin - 1 ,3(0.4 7
g,
62% );
m p 1 8 9 -1 9 0 °C (d); v max: 3086, 2941, 2863, 2207, 2218, 1689, 1498, 1453, 1313,
125 0, 1098, 920, 902, 766, 7 49 and 705 cm -1; Xmax (C H 3 C N ): 496 (e= 34 566),
4 6 4 (34 306 ), 342 (14 7 05 ) and 240 nm (30 9 8 2 ); 5H: 12.2 (brs, 1H, N H ), 8.0 (m,
2H , a ro m a tic), 7.6 (m, 2H, a ro m a tic), 3.8 (brs, 1H, N -C H ), 2.3 4 (s, 3H, M e), 2.32
(s, 3H , M e), 1.8 (brm ,
2 H, C H 2), 1.67 (brm , 2 H, C H 2), 1.53 (brm , 1 H, CH), 1.28 (m,
194
4H, C H 2) and 1.05 ppm (m,
1 H, C H ); 5C : 20.9, 2 3 .7 , 2 4 .3 , and 26.3 (C H 2), 30.5
(M e), 5 6 .4 (= N + H C ), 53.9 (= C (C N )2), 116.3 a n d 1 1 7 .3 (C N ), 122.9, 131.4 and
137.4 (a ro m a tic C), 172.0 (C =N ) and 188.9 ppm (C = C (C N )2).
(F ound :
C, 71.92;
H, 5 .7 7 ; N, 2 2 .0 2 % . C 20H 22 N 6 re q u ire s: C, 7 2 .2 3 ; H, 5 .7 9 ; N, 21.97% ).
2 -C y a n o -/V 2- o c ty l- 2 - ( 3 - d ic y a n o m e th y le n e is o m d o lin - 1 - d iy lid e n e ) a c e ta m id in e
(197)
n -O c ty la m in e (0.51 g, 0 .0 0 3 9 m oles) w a s a d d e d to a s u s p e n s io n of th e am m onium
s a lt of 2 ,2 '-(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile (1 1 9 ) (1.0 g, 0.0 0 3 8 m oles)
in 1 ,4 -d io xa n (30 cm 3) T h is w a s hea ted u n d e r re flu x fo r fo u r and a h a lf hours and
a b rig h t o ra n g e s o lid fell out of so lu tio n on c o o lin g .
w ashed
w ith
d ie th yl
e th e r
to
g ive
T h is w a s filte re d off and
2-cyano-/V 2-o ctyl-2 -(3 -
d ic y a n o m e th y le n e is o in d o lin -1 -d iy lid e n e )a c e ta m id in e (197) (0.48 g).
w as e v a p o ra te d to give a d a rk re d /b la c k oil.
T h e filtra te
O n d is s o lv in g in hot a cetone , som e
d ie th yl e th e r w a s a d d e d and a fin e ora n g e p o w d e r (0 .0 8 g) w a s filte re d off.
T he
co m b in e d o ra n g e s o lid s w e re re c ry s ta llis e d fro m m e th a n o l to give 2-cyano-A /2o c ty l-2 -(3 -d ic y a n o m e th y le n e is o in d o lin -1 -d iy lid e n e )a c e ta m id in e
(197)
as
sm all
o ra n g e n e e d le s (0.39 g, 27% ) ; mp 2 3 2 -2 3 3 "C ; v max: 3438, 3345, 3238, 2940,
2868, 2 2 0 1 ,1 6 5 9 , 1623, 1528, 1489, 1310, 1268, 1093, 768, 730 and 694 cm -1 ;
X.max: 4 92 (£= 38 656 ), 460 (34 2 5 8 )a n d 348 nm (13 0 9 4 ); 5H: 10.7 (b rs , 1 H, NH),
8.5 (brs, 2H, N H ), 7.95 (m ,1H , a ro m a tic), 7 .8 5 (m ,1 H , a rom atic), 7.4 (m, 2H,
a ro m a tic), 3.2 (m, 2H , N C H 2), 1.6 (m, 2H, C H ), 1.2 (brm , 10H, CH) and 0.8 ppm
(m, 3H, M e): 5C: 13.7, 21.9, 26.4, 27.4, 28.3, 2 8 .5 , 3 1 .2 a nd 42 .4 (octyl CH s), 56.9
(= C (C N )2), 7 1 .5 9 , [1 1 4.9, 115.7 and 116.9] (C N ), [1 2 2 .9 , 123.3, 130.8, 131.2,
134.7 and
(C = C (C N )-).
137 .7]
(a ro m a tic
C),
158.7,
166 .5
(F o u n d : C, 7 1 .0 6 ; H, 6.18, N, 2 2 .9 8 % .
and
169.9
ppm
(C=N)
and
C 22 H 24N 6 re q u ire s: C, 70.96;
H, 6 .4 5 ; N, 2 2 .9 8 % ).
O n e v a p o ra tin g th e filtra te again, a b la c k oil w a s reco ve re d .
A ttem p ts to
p re c ip ita te fu rth e r so lid by th e a d d itio n of lig h t p e tro le u m w e re not s u c ce ssfu ll as a
ta cky oil w a s o b ta in e d .
195
2-Cyano-/V2-decyl-2-(3-dicyanomethyleneisoindolin-1-diylidene)acetamidine
(198)
n -D e c y la m in e
am m o niu m
s a lt
(1.2 5 g, 0 .0 0 7 9
of
m oles) w a s a d d e d to a so lu tio n
2 ,2 '-(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile
(1.03 g, 0 .0 0 3 9 m oles) in e th a n o l (30 cm 3).
hea te d
under
reflux
of the
fo r
nine
and
a
(119)
T h is w a s s tirre d o v e rn ig h t and then
h a lf
h o u rs.
d ic y a n o m e th y le n e is o in d o lin -1 -d iy lid e n e )a c e ta m id in e
2-C yan o-/V 2-d e c y l-2 -(3 (198)
(0.4 7
g,
30% )
p re c ip ita te d as a fin e g o ld e n p o w d e r on c o o lin g a n d w a s re c ry s ta llis e d from
to lu e n e , m p 2 0 4 °C ; v max: 330 6, 292 5, 28 5 4 , 2 2 2 2 , 219 9, 1648, 1612, 1573,
1524, 1478, 1314, 1272, 1093, 770, 733 and 6 9 4 c m '1; Xmax: 4 92 (e= 3 7 776), 460
(34 085) and 346 nm (12 5 1 6 ); 5H: 10.8 (brs, 1H, N H ), 8.6 (brs, 2H, NH), 8.04 (m,
1H, a ro m a tic), 7 .9 2 (m, 1H, a ro m a tic), 7.5 (m, 2H , a ro m a tic ), 3.23 (m, 2H, N C H 2),
1.6 (m, 2H, C H ), 1.17 (brm , 14H, C H ) and 0.7 9 ppm (m 3H, M e); 5C: 13.9, 22.2,
26.5,
27.5,
28.5,
2 8 .8 ,
28.9,
29.0,
3 1 .4
and
42 .5
(d e c y la m in o
C H s),
57.0
(= C (C N )2), 71.8, [1 1 5 .1 , 115.9 and 117.1] (C N ), [1 2 3 .2 , 123.5, 131.1, 131.5, 134.9
a nd 137.9] (a ro m a tic C), 158.9, 166.7 and 1 7 0 .2 ppm (C =N ) a nd (C = C (C N )-).
(F o u n d : C, 7 1 .9 5 ; H, 7 .0 8 ; N, 2 1 .13% .
C 24H 2aN 6 re q u ire s C, 7 1 .9 7 ; H, 7.05; N,
2 0 .9 8 % )
T h e filtra te g a v e a d a rk red oil on e v a p o ra tin g th e s o lv e n t. On d is s o lv in g the oil in
hot
c h lo ro fo rm
and
a d d in g
light
p e tro le u m ,
a
sm all
am ount
of
the
n -d e cyla m m o n iu m s a lt of 2 ,2 '-(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile (0 .0 4 3 g)
w a s o b ta in e d as a y e llo w po w d e r.
R e p e a tin g th is p ro c e d u re ga ve a tacky, o ily
s o lid w h ich co u ld not be p u rifie d fu rth e r. A tte m p ts to o b ta in th e pure s a lt w ere not
su c c e s s fu l; v max: 31 6 5 , 30 2 5 , 2928, 2851, 22 1 2 , 1641, 1578, 1481, 1377, 1309,
1258, 1193, 1188, 1098, 917, 7 78 and 715 c m '1; 5H : 8 .0 8 (m, 2H, a rom atic), 7.67 .4 [m, (a ro m a tic H) o v e rla p p in g brs (N H 3), 5H ], 2.7 (m, 2H, N C H 2), 1.48 (m, 2H,
C H 2), 1.18 (m, 14H , C H ) and 0.8 ppm (m, 3H , M e); 5q (a ce to n e d 6): 13.8, 22.7,
26.4,
26.6,
27.4,
2 7 .6 ,
28.8,
32.0,
40 .7
a nd
48 .2
(d e cyla m in o
C H s),
54.8
(= C (C N )2), 116 .7 and 1 17 .4 (C N ), 123.5, 131.3 a n d 1 38 .3 (a ro m a tic C) and 172 .5
ppm (C = C (C N )2).
196
2-Cyano-/Vi ,/Vi-dibutyl-2-(3-dicyanomethyleneisoindol-1-diylidene)
acetamidine (203)
The
am m o niu m
sa lt
of
2 ,2 '-(is o in d o lin -1 ,3 -d iy lid e n e )b is p ro p a n e d in itrile
(119)
(1.6 g, 0 .006 m oles) and /V./V-dibutylam ine (0.81 g, 0 .0 0 6 m o le s) w e re heated
u n d e r reflux in eth a n o l (50 cm ) fo r six hours.
T h e s o lu tio n w a s e va p o ra te d to
d ry n e s s and re c ry s ta llis e d from a c e to n itrile to g ive 2 -c y a n o -A /i ,/S/i -d ib u ty l-2 -(3 d ic y a n o m e th y le n e is o in d o l-1 -d iy lid e n e )a c e ta m id in e (203) a s red n e e d le s (2.20 g,
9 4 % ); mp 2 1 2 -2 1 3 °C ; v max: 33 4 0 , 2950, 2867, 221 8, 2 1 9 5 , 1648, 1604, 1584,
156 1, 1478, 1370, 1314, 1258, 1234, 1116, 1087, 752, 7 3 4 a n d 6 50 c m '1; Xmax:
4 8 2 (£= 28 580 ), 460 (28 150) a nd 336 nm (9 0 7 0 ); 8H: 9.6 (brs, 1H, N H ), 9.0 (brs,
1H, N H ), 8.3 (m, 1H, a ro m a tic), 8.2 (m, 1H, a ro m a tic), 7 .7 (m, 2H , a rom atic), 3.6
(m, 4H, N C H 2), 1.7 (m, 4H, C H 2), 1.4 (m, 4H, C H 2) a nd 0.9 ppm (m, 6H, M e);
5C : 13.4 (M e), 13.6, 19.2 and 28.5 (C H 2), 50.8 (= C (C N )2), 7 3 .2 , [1 1 6 .8 , 118.2 and
1 1 8 .5 ] (CN), [122.7, 122.9, 131.0, 131.1, 137.7 and 137 .8] (a ro m a tic C), 159.2,
1 6 5 .4 and 171.5 ppm . (F o u n d ; C, 7 1 .2 ; H, 6.5; N, 23.0% . C 22 H 24N 6 re q u ire s: C,
7 0 .9 ; H, 6 .4 9 ; N, 22.56% ).
C r y s ta l S tr u c tu re D e te r m in a tio n
S tr u c tu r e a n a ly s is a n d r e fin e m e n t
A ll c o lle c tio n s of c ry s ta llo g ra p h ic d ata w e re c a rrie d out at T rin ity C ollege
D u b lin exce p t fo r th a t of th e b e n zyla m m o n iu m s a lt of (110), (179), w h ich w as
c a rrie d out at th e U n ive rsity of A b e rd e e n , S co tland.
X -R a y d iffra c tio n d a ta w e re co lle cte d using M o -K a ra d ia tio n (A. = 0.71609
A ) m o n o c h ro m a tis e d w ith a g ra p h ite plate g ivin g N in d e p e n d e n t re fle ctio n s, A/oof
th e s e being used in th e s tru c tu re a n a lysis.
cry s ta l.
T h e in d e x range is g ive n fo r each
All s tru c tu re s w e re so lv e d using the P a tte rso n h e a vy atom m ethod w ith
p a rtia l stru ctu re e x p a n s io n to fin d all n o n -h y d ro g e n s u sin g S H E L X S -8 6 .195 T he
a to m ic co o rd in a te s w e re re fin e d w ith full m atrix le a st s q u a re s re fin e m e n t using
S H E L X L -9 3 .196
H yd ro g e n ato m s w e re lo ca te d in th e ir c a lc u la te d p o sitio n s and
re fin e d w ith re sp e ct to th e c a rb o n and nitroge n a to m s to w h ic h th e y w e re attached.
197
Crystal data for Benzylammonium salt (179)
C ry s ta llis e d from a c e to n itrile to g ive o ra n g e c u b ic c rysta ls.
0 .3 6
X
0 .4 2
X
a = 11 .4 6 3 (1 0 ),
0.30
m m 3.
¿1 = 1 3 .0 9 4 (9 ),
M = 3 5 0 .3 8 ,
C rysta l d im en sion s
m o n o c lin ic ,
c = 1 3 .5 6 3 (9 ) A,
sp a ce
g roup
P48,
V = 1 8 5 7(2) A 3, Z = 4,
Dx =
1 .2 5 4 g /cm 3 . N = 2731, No = 25 3 3 , in dex range = 0 < h < 12, 0 < k < 15, -16 < I <
14; R = 0.0 4 5 6 , wR = 0.1 0 9 1 .
C r y s ta l d a ta f o r A /- ls o p r o p y lid e n e c y c lo h e x y la m m o n iu m s a lt (195)
C ry s ta llis e d from a c e to n e to g ive a lm o s t c u b ic lig h t o ra n g e crysta ls.
C rystal
d im e n s io n s 0.4 5 X 0.4 0 X 0.3 5 m m 3. M = 3 8 2 .4 7 , tric lin ic , sp a ce g ro u p P -1 , a =
9 .3 5 3 (1 5 ),
b = 1 0 .4 9 2 (1 9 ),
c = 1 1 .2 5 7 (1 6 )
A,
V = 1 0 2 1 .1 (2 9 )
A3,
Dx =
Z = 2,
1 .2 4 4 g /cm 3. N = 2484, No = 1957, in d e x range = 0 < h < 9 , - 1 0 < k < 1 1 , - 1 1 < l <
11;
R = 0.0 7 2 3 , w R = 0 .1 2 7 2 .
C r y s ta l
d a ta
fo r
2 -C y a n o -/V r ,A/i - d ib u ty l- 2 - ( 3 - d ic y a n o m e th y le n e is o in d o l- 1 -
d iy lid e n e ) a c e ta m id in e (203)
C ry s ta llis e d from d im e th y lfo rm a m id e to g ive red c o lu m n s.
C rysta l dim en sion s
0 .4 0 X 0.30 X 0.25 m m 3. M = 3 7 2 .4 7 , tric lin ic , s p a c e g ro u p P-1,
¿3= 1 1 .3 8 2 (2 ), c = 1 1 .7 4 8 (3 ) A,
V = 1 0 3 6 .0 (3 ) A 3 , Z = 2 ,
a = 8.889(10),
Dx = 1.194 g/cm 3
2 7 3 1 , N0 = 2533, in dex ra nge = 0 < h < 9 , -11 < k < 11, -12 < I < 11;
N=
R = 0.0479,
wR = 0.1240 .
C r y s ta l d a ta f o r C -T c o m p le x (1 1 0 )-T M D A (210)
C ry s ta llis e d
from
a c e to n itrile
to
g ive
d im e n s io n s 0.40 X 0.5 0 X 0 .6 0 m m 3.
P 1 21 /n,
a = 7 .3 1 3 3 (1 1 9 ),
d a rk
g re e n /b la c k
M = 4 0 7 .4 8 ,
b = 2 9 .8 1 3 (2 ),
co lu m n s.
m o n o clin ic,
c = 1 0 .2 2 6 (2 )
A,
C rystal
space group
V = 2123.1 (6)
A3,
Z = 4, Dx = 1.275 g /c m 3. N = 39 4 7 , N0 = 3731, in d e x ra nge = -8 < h < 8 < k < 35,
0 < I < 12; R = 0 .0 6 0 7 , w f l = 0 .1 7 5 0 .
198
Cyclic Voltammetry
C y c lic
v o lta m m e try
p o te n tio s ta t/g a lv a n o s ta t
w as
p e rfo rm e d
in te rfa c e d
to
u sin g
an
EG&G
m odel
an
E G &G
174A
273
m odel
p o la ro g ra p h ic
a n a ly s e r and an E G & G m odel 3 0 3 A S ca n n in g M e rc u ry D rop E le ctro d e (S M D E ), all
o f w h ich w e re re la ye d to a p e rs o n a l co m p u te r.
All s o lu tio n s w e re m ade up in
0.1 M lith iu m p e rc h lo ra te as th e e le c tro ly te
H P LC g ra d e d im e th y lfo rm a m id e u sin g
a n d d e g a s s e d fo r tw e n ty m in u te s using n itro g e n .
All p o te n tia ls are qu o te d w ith
re s p e c t to B A S A g /A g C I g e l-fille d re fe re n ce e le c tro d e , th e p o te n tia l of w h ich w a s
35
mV m ore p o s itiv e th a n th a t o f th e s a tu ra te d ca lo m e l e le c tro d e (SC E), w ith
p la tin u m w ire as th e c o u n te r e le ctro d e .
U ltr a - V io le t S tu d ie s o f C -T C o m p le x e s in S o lu tio n
C -T in te ra c tio n s w e re in itia lly in v e s tig a te d u sin g UV s p e ctro sco p y.
The
s p e c tra w e re m e a su re d on a H e w le tt P a cka rd 8 4 5 2 UV D iode A rra y S p e ctro m e te r
u sin g s ta n d a rd te c h n iq u e s .
C -T a b so rp tio n b a n d s w e re d e te rm in e d , e ith e r by
a d d itio n of o n e e q u iv a le n t of the d o n o r to a s o lu tio n of the a cce p to r, o r by adding
in c re a s in g a m o u n ts of th e d o n o r to a fix e d c o n c e n tra tio n of th e accep tor, and
co m p a rin g th e s e s p e c tra w ith th o s e of th e in d iv id u a l d o n o r and a cce p to r.
All s p e c tra w e re d e te rm in e d fo r fre s h ly p re p a re d s o lu tio n s .
s o lv e n ts
w e re
te tra h y d ro fu ra n
d ic h lo ro m e th a n e
used
as
re c e iv e d :
(L a b s c a n -H P L C
(L a b s c a n -
g rade
H P LC
T h e fo llo w in g
a c e to n itrile
(L a b sca n -H P L C
d rie d
s ta n d a rd
g ra d e ).
under
In v e s tig a tio n s
w ith
grade );
c o n d itio n s )197;
co m m e rcia lly
a v a ila b le d o n o r c o m p o u n d s in c lu d e d a n th ra c e n e ( 2 1 2 ), te tra th ia fu lv a le n e ( 2 a),
/V ,A /-dim ethylaniline (211), and A /,/V ,/\/',A /'-tetram ethyl-p-phe nyle nediam ine (210),
a nd all u se d w ith o u t fu rth e r p u rific a tio n .
S o lu tio n s
of
/V ,A /-dim ethylaniline
(211)
and
A/,A/,A/’,A /-te tra m e th y l-p -
p h e n y le n e d ia m in e (210) w e re d e g a s s e d w ith n itro g e n b e fo re th e UV s p e ctra w ere
m e a su re d .
199
Synthesis of C-T Complexes
(1 1 0 )-T M D A c o m p le x
C o m p o u n d ( 1 1 0 ) (0.278 g, 0 .0 0 1 4 m oles) in te tra h y d ro fu ra n (10 cm 3) w as
a d d e d to a hot s o lu tio n of T M D A (0 .3 7 6 g, 0 .0 0 2 8 m oles, tw o e q u iva le n ts) in
a c e to n itrile (10 c m 3) g ivin g a d a rk red s o lu tio n .
T h e s o lv e n t w as e va p o ra te d off
and th e b la c k s o lid re m a in in g w as re c ry s ta llis e d from a c e to n itrile .
d a rk g reen s o lu tio n w a s le ft fo r 36 h ou rs at room te m p e ra tu re .
T h e resultin g
(1 1 0 )-T M D A w as
o b ta in e d as b la c k /g re e n co lu m n s (0 .1 9 6 g); m p 1 5 4 -1 5 5 °C ; v max: 2925, 2199
(C N ), 1653, 1611, 1544, 1475, 1312, 1260, 1182, 1151, 1093, 978, 943, 824, 778,
a nd 708 cm -1.
(F o u n d : C, 7 0 .6 9 ; H, 4 .9 7 ; N, 2 4 .0 8 % .
C 24H 21 N 7 . re quire s
C,
7 0 .7 4 ; H, 5 .1 9;N , 2 4 .0 6 % ).
(1 1 0 )-T T F C o m p le x
A so lu tio n of (110) (0.1 OOg, 0 .0 0 0 4 m oles) in T H F w a s a d d e d to a boiling
so lu tio n of T T F (0.0 88 g, 0 .0 0 0 4 m oles) in a c e to n itrile g iv in g a g re e n so lu tio n . On
h a lvin g the v o lu m e of so lu tio n by e v a p o ra tio n no s o lid w a s o b ta in e d .
at 0 °C fo r tw o d ays o n ly a very sm all a m o u n t
p re c ip ita te d .
On storing
of a d a rk g re e n s o lid had
O n e v a p o ra tin g off all th e s o lv e n t a d a rk g re e n so lid w a s obtained.
A tte m p ts to re c ry s ta llis e th is green s o lid from a n u m b e r of s o lv e n ts w ere not
s u c ce ssfu l.
(1 1 0 )-A n th ra c e n e C o m p le x
C o m p o u n d (110) (0 .2 6 7 g, 0.0011 m oles) d is s o lv e d in T H F (70 cm 3) in a
s o n ic a to r bath, and d e g a s s e d w ith a rgon , w a s a d d e d to a so lu tio n of anthracen e
(0 .1 9 7 g, 0.0011 m oles) in T H F (20 cm 3), also d e g a s s e d , g ivin g a da rk orange
/re d so lu tio n .
T h is w as fu rth e r d e g a sse d , s to p p e re d a n d le ft fo r 48 hours.
Large
p u rp le c ry s ta ls w e re fo rm e d w h ich w e re fo u n d to be u n s ta b le w h en filte re d in air.
T h e s e c ry s ta ls w e re is o la te d u n d e r argon in an g lo ve bag but w e re not stable fo r a
s u ffic ie n t p erio d of tim e to obtain e le m e n ta l a n a lysis.
(1 5 1 )-T M D A C o m p le x
C o m p o u n d (151) (0 .1 0 0 g, 0 .0 0 3 9 m oles) d is s o lv e d in T H F (25 cm 3) w as
a d d e d to a so lu tio n of T M D A (0 .0 6 4 g, 0 .0 0 3 9 m o le s) in T H F (10 cm 3) giving a
d a rk g reen so lu tio n .
u n d e r a rgon .
T h e vo lu m e w a s re d u ce d to 10 cm 3 a n d th e fla s k sto p p e re d
W h e n no s o lid w as fo rm e d a fte r tw o d a ys all th e so lve n t w as
200
e va p o ra te d
off
and
the
re s u ltin g
d a rk
green
s o lid
was
re c ry s ta llis e d
from
a c e to n itrile givin g the 2:1 co m p le x of (1 5 1 )-T M D A as g re e n p la te s (0.041 g); on
h e a tin g from 100 -1 80 °C the p la te s d a rk e n s to a red s o lid w h ich m elts at 198 °C;
v max: 3125, 2918, 2868, 2812,
2221 (C N ), 1561, 1519, 1472, 1445, 1386, 1319,
1279, 1212, 1110, 1075, 951, 816, 775, and
686 c m '1. (F o u n d : C, 7 0 .1 9 ; H, 4.32;
N, 24.04% . C 4oH 3o N i 2 - re q u ire s : C, 7 0 .7 8 ; H, 4 .4 5 ; N, 2 4 .7 6 % ).
(1 5 1 )-T T F C o m p le x
A b o ilin g so lu tio n of (151) (0 .1 0 0 g, 0 .0 0 3 9 m oles) in a c e to n itrile (15 cm 3)
w a s a d d e d to a b o ilin g s o lu tio n of T T F (0 .0 7 9 g, 0 .0 0 3 9 m oles) in acetonitrile
(10 cm 3) g ivin g a d a rk g re e n /b ro w n so lu tio n .
O n c o o lin g th e 1:1 com plex of
(1 5 1 )-T T F w a s o b ta in e d as b rig h t g re e n p la te s (0 .0 2 3 g); m p 160 °C (darkens),
190 °C (d); v max: 3075, 297 5, 2 9 3 3 , 286 8, 221 3 (CNI), 1561, 1444, 1384, 1069,
699, 766 and 6 70 cnrr1.
(F o u n d : C, 5 4 .3 4 ; H, 2 .3 7 ; N, 1 4 .95% .
re q u ire s : C, 5 4 .6 4 ; H, 2 .4 0 : N, 1 5 .1 7 % ),
201
C 21 H 11 N 5
Chapter 6
202
Reference Section
1
H. A ka m a tu , H. Inokuchi, and Y. M a tsu n a g a , Nature, 1954, 173, 168.
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T. E. P hillips, T. J. K iste nm a cher, J. P. F erraris, and D. O. C ow an, Chem.
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3
L. R. M elby, R. J. H arder, W . R. H ertler, W . M ahler, R. E. B e nson, and W.
E. M ochel, J. Am. Chem. Soc., 1962, 84, 3374.
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F. W udl, G. M. S m ith, and E. J. H ufna gel, J. Chem. Soc., Chem.
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5
J. S. M ille r and A. J. E pstein, Angew. Chem. Int. Ed. Engl., 1994, 33, 385.
6
P.
N.
P rasad, D. J. W illiam s, Introduction to Nonlinear Optical Effects in
Molecules and Polymers, W ile y & S ons, N ew York, 1991.
7
(a) D. Jerom e, A. M azand, M. R ibault, and K. B echgaa rd, J. Phys. Lett.,
1980, 41, L95; (b) K. B e chgaa rd, C. S. Ja co b se n , K. M o rte n se n , H. J.
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