Reactions of aminophosphines and aminobis(phosphines)
with aldehydes and ketones: Coordination complexes of the resultant
aminobis(alkylphosphineoxides) with cobalt, uranium, thorium
and gadolinium salts
Crystal and molecular structures of Ph2P(O)CH(C6H4OH-o)N(H)Ph,
Ph2P(O)CH(OH)C6H4OH-o and Ph2P(O)N(H)Ph
Srinivasan Priya, Maravanji S. Balakrishna *, Shaikh M. Mobin
Department of Chemistry, Indian Institute of Technology, Bombay, Mumbai 400 076, India
Abstract
The reaction of aminophosphines and aminobis(phosphines) with aldehydes leads to either insertion of carbon fragments into the
P(III)–N bonds or formation of a-hydroxyphosphine oxides through P(III)–N bond cleavage. Reaction of 1,2-C6H4{N(H)PPh2}2
with paraformaldehyde gives the P(III)–N bond inserted product 1,2-C6H4{N(H)CH2P(O)Ph2}2, whereas 1,3-C6H4{N(H)PPh2}2
forms an analogous product but with an additional methylene group inserted between the two nitrogen centers through nucleophilic
addition to form a bicyclic derivative, 1,3-C6H4{Ph2P(O)CH2N(l-CH2)NCH2P(O)Ph2}. Reactions of Ph2PN(H)Ph with aromatic
aldehydes, RCHO (R = C6H4OH-o, 5-BrC6H3OH-o, (g5-C5H5)Fe(g5-C5H4–)) lead to the insertion of RCH into the P(III)–N bond
to give Ph2P(O)CH(R)N(H)Ph. The reactions of aminobis(phosphine), Ph2PN(nBu)PPh2 with both aromatic and aliphatic aldehydes lead to the formation of a-hydroxy phosphine oxide derivatives of the type Ph2P(O)CH(R)OH, through P(III)–N bond cleavage. The N-bridged bis(phosphine oxide) nPrN(CH2P(O)Ph2)2 readily forms chelate complexes with U(VI), Th(IV) and Gd(III)
derivatives.
Keywords: Aminophosphines; Insertion; a-Hydroxy phosphine oxides; Coordination; P–N bond cleavage; Crystal structure
1. Introduction
The stability of P(III)–N bonds in cyclic and acyclic
phosphazanes depends to a large extent on the phosphorus and nitrogen substituents [1]. P(III)–N bonds are
stable to lithium and Grignard reagents [2] and can survive a variety of nucleophilic substitution reactions at
the phosphorus centers both in cyclic and acyclic sys-
tems [1]. However, P(III)–N bonds can undergo hydrolytic cleavage in the presence of trace amounts of acid/
base impurities [3]. Even during complexation reactions
with transition metals, P(III)–N bonds can undergo
cleavage as demonstrated by King [4], Burrows [5] and
also our research group [6]. Previously we have reported
the insertion of carbon fragments into the P(III)–N
bonds and the coordination chemistry of the resulting
phosphine oxides [7]. As a part of our interest on multifunctional phosphines and aminophosphines and their
catalytic applications [8,6b], herein we report the reactions of aminophosphines and aminobis(phosphines)
1642
with aldehydes and ketones. The molecular structures
and the complexing ability of some of the bisphosphine
oxides thus obtained are also described.
H
N
O
H
N
PPh2
2 (HCHO)n
PPh2
O
H
2. Results and discussion
The aminophosphines, Ph2PN(H)Ph, Ph2PN(nBu)PPh2 and 1,2-C6H4(N(H)PPh2)2 were prepared as
described in the literature (see Section 4). The 1,3-phenylenediamine derivative 1,3-C6H4(N(H)PPh2)2 (1) was
prepared in 46% yield by reacting chlorodiphenylphosphine with 1,3-phenylenediamine in THF in the presence
of a catalytic amount of 4-dimethylaminopyridine. The
IR spectrum of 1 shows mNH at 3218 cm1 and the 31P
NMR spectrum of 1 exhibits a single resonance at
35.2 ppm. The structural composition was further confirmed by mass spectral and micro analytical data.
The reaction of 1 with two equivalents of paraformaldehyde affords the P–N bond inserted product,
1,3-C6H4(N(H)CH2P(O)Ph2)2 (2) similar to the analogous reaction of Ph2PNC2H4NPPh2 with paraformaldehyde, reported earlier [7b]. The reaction of 1 with
one equivalent of paraformaldehyde did not give a
monofunctionalized product of the type Ph2PN(H)C6H4N(H)CH2P(O)Ph2, instead compound 2 was obtained in 35% yield with half of the reactant 1 left
unreacted in the solution. The 31P NMR spectrum
of 2 shows a single resonance at 28.7 ppm and the
methylene protons appear at 2.39 ppm in its 1H
NMR spectrum. Interestingly, the reaction of 1,2C6H4(N(H)PPh2)2 with two equivalents of paraformaldehyde afforded a similar product but containing three
methylene groups as indicated by its 1H NMR spectrum (Scheme 1). When the reaction was carried out
using three equivalents of paraformaldehyde the yield
was almost quantitative indicating the insertion of
two methylene groups into two P(III)–N bonds and
another one between two nitrogen centers through nucleophilic addition to give a product of the type, 1,2C6H4{N(CH2P(O)Ph2)(l-CH2)N(CH2P(O)Ph2)} (3) in
quantitative yield. The 31P NMR spectrum of 3 shows
a single resonance at 26.6 ppm. In the 1H NMR spectrum of 3, the protons due to the methylene groups
inserted into the P–N bonds appear at 3.82 ppm as
broad singlets, whereas the bridging methylene protons resonate at 4.96 ppm. When the aminophosphines
are treated with aromatic aldehydes, the CH(R)
groups insert into the P–N bonds followed by oxidation of the phosphorus from P(III) to P(V), whereas
aliphatic aldehydes, such as butylaldehyde, afford an
a-hydroxy phosphine oxide through P–N bond cleavage [7b]. The reactions of Ph2PN(H)Ph with RCHO
afford P–N inserted products Ph2P(O)CH(R)N(H)Ph
(R = C6H4OH-o, 4; 5-BrC6H3OH-p, 5; (g5-C5H5)Fe(g5-C5H4), 6) in 65–85% yield as shown in Eq. (1).
N
1
PPh2
H
N
N
H
PPh2
H
2 (HCHO)n
2 (HCHO)n
N
Ph2P
PPh2
Ph2P
O
O
3
O
PPh2
O
3 (HCHO)n
N
2
N
H
N
H
Ph2P
O
PPh2
PPh2
N
N
H
HO
N
PPh2
O
Scheme 1.
The 31P NMR spectra of compounds 5 and 6 show
single resonances at 37.8 and 29.2 ppm, respectively.
The 1H NMR spectrum of 5 shows a doublet at
5.5 ppm for the CH protons with a 2JPH coupling of
5.9 Hz whereas for 6 the analogous signal appears as
a broad singlet at 5.1 ppm. The spectroscopic data
of 4 is given in our previous report [7b].
H
Ph
N
PPh2 + RCHO
Ph
H
N
H
O
PPh2
ð1Þ
R
R = C6H4OH-o, 4
5-Br-C6H3OH-o, 5
(C5H5)Fe(C5H4), 6
The structure of Ph2P(O)CH(C6H4OH-o)N(H)Ph (4)
was confirmed by single crystal X-ray diffraction studies
and is shown in Fig. 1. Crystal data and the details of
the structure determination are given in Table 1 while
selected bond lengths and inter bond angles are listed
in Table 2. The asymmetric unit of compound 4 contains
two identical independent molecules but the corresponding bond lengths and bond angles are not significantly
different. The P–O bond distances are P(1)–O(1) =
1.522(9), P(2)–O(3) = 1.458(9) Å and the P–C bond distances are in the range 1.720(14)–1.872(11) Å. The geometry around the nitrogen is strictly planar and the sum
of the angles is 360. Although in the lattice the molecules exhibit intra and inter molecular O–H- - -O type
interactions, they are not significantly prominent.
1643
Table 2
Selected bond distances (Å) and bond angles () of 4
Bond distances
P(1)–O(1)
P(1)–C(1)
P(1)–C(7)
P(1)–C(13)
C(13)–N(1)
N(1)–C(20)
Fig. 1. Molecular structure of Ph2P(O)CH(C6H4OH-o)N(H)Ph (4)
with the atom numbering scheme. The ellipsoids are drawn at the 50%
probability level.
The reactions of nBuN(PPh2)2 with RCHO (R = nPr,
Ph, C6H4OH-o, OC4H3) gave a-hydroxy phosphine oxides, Ph2P(O)CH(OH)R (R = nPr, 7; Ph, 8; C6H4OH-o,
9; OC4H3, 10) in 40–45% yields (Scheme 2). The formation of these products may be due to the prior cleavage
of the P–N bond through the elimination of primary
amine to form Ph2P(O)H, which then reacts with the
aldehyde to give Ph2P(O)CH(OH)R. Compounds 7–10
show mOH around 3200–3250 cm1 in their IR spectra.
The 31P NMR spectra of 7–10 show a single resonance
in the range of 30–37 ppm and the 1H NMR spectra
show doublets around 4.4–5.5 ppm for the CH proton,
with 2JPH couplings in the range of 5–10 Hz.
The structure of Ph2P(O)CH(OH)C6H4OH-o (9) is
established by single crystal X-ray diffraction studies
and the perspective view of the molecule is shown in
Fig. 2. The crystallographic data, selected bond distances and inter bond angles are listed in Tables 1 and
3, respectively. The asymmetric unit contains two identical independent molecules but the corresponding bond
1.522(9)
1.721(14)
1.770(13)
1.871(11)
1.449(15)
1.382(16)
Bond angles
O(1)–P(1)–C(1)
O(1)–P(1)–C(7)
O(1)–P(1)–C(13)
C(1)–P(1)–C(13)
C(1)–P(1)–C(7)
C(7)–P(1)–C(13)
C(20)–N(1)–C(13)
111.0(6)
115.4(5)
108.8(5)
109.1(6)
106.7(6)
105.4(6)
120.0(10)
P(2)–O(3)
P(2)–C(26)
P(2)–C(20)
P(2)–C(32)
C(45)–N(2)
N(2)–C(38)
1.458(9)
1.845(12)
1.762(13)
1.819(9)
1.383(17)
1.470(15)
O(3)–P(2)–C(38)
O(3)–P(2)–C(32)
O(3)–P(2)–C(26)
C(32)–P(2)–C(38)
C(38)–P(2)–C(26)
C(26)–P(2)–C(32)
C(45)–N(2)–C(38)
111.7(5)
113.7(6)
109.4(6)
105.5(6)
108.9(6)
107.4(6)
121.3(10)
distances and bond angles are very similar. The structure of 9 shows a distorted tetrahedral geometry around
the phosphorus centers. The P@O bond distance varies
PPh2
R'
O
N
PPh2
O
R
N
O
O
O
RCHO
PPh2
R' = nPr
PPh2
R' = nPr
n Bu
O
O
CHO
CHO
R' = nBu
O
PPh2
PPh2
O
H
HO
n
R = Pr,
7
8
C6H5,
C6H4OH-o, 9
HO
H
10
Scheme 2.
Table 1
Crystallographic data for 4, 9 and 11
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
a ()
b ()
c ()
V (Å3)
Z
Dcalc (g cm1)
l (Mo Ka) (mm1)
Theta range ()
Temperature (K)
R
Rw
Compound 4
Compound 9
Compound 11
C25H22NO2P
399.41
orthorhombic
Pbc21 (No. 29)
12.567(2)
16.452(1)
20.968(1)
90
90
90
4335.2(8)
8
1.224
0.2
1.62–24.92
293(2)
0.0757
0.1194
C19H17O3P
324.30
monoclinic
P21/c (No. 14)
5.678(1)
24.500(2)
25.552(4)
90
92.06(1)
90
3552.3(7)
8
1.213
0.2
1.1–24.9
293
0.084
0.281
C18H16NOP
293.29
orthorhombic
Pca21 (No. 29)
9.590(3)
9.698(1)
16.985(3)
90
90
90
1579.7(6)
4
1.233
0.2
2.12–24.92
293(2)
0.0395
0.0886
1644
Fig. 2. Molecular structure of Ph2P(O)CH(OH)C6H4OH-o (9) with
the atom-numbering scheme.
from 1.486(2) to 1.495(4) Å and the P–C bond distances
are in the range of 1.785(5)–1.829(3) Å.
The reactions of the corresponding aminobis(phosphines), nPrN(PPh2)2 with aldehydes in a 1:2 ratio proceeds in a similar way as described earlier [7b] to give
the corresponding a-hydroxy phosphine oxides through
P(III)–N bond cleavage, except furfural. The reaction of
furfural with the n-butyl derivative, nBuN(PPh2)2, leads
to the P(III)–N bond cleavage product, Ph2P(O)CH(C4H3O)OH, whereas the n-propyl derivative gives the
P–N insertion product, nPrN{CH(C4H3O)P(O)Ph2}2.
Ph2P(O)N(H)Ph (11). The 31P NMR spectrum of 11
shows a single resonance at 18.5 ppm. The structure of
11 was confirmed by a single crystal X-ray structure
determination. A perspective view of the molecule 11
is shown in Fig. 3(a) and the selected bond distances
and bond angles are given in Table 4. The P–O and
P–C distances are comparable with the literature for
compounds of a similar type [9–12]. The phosphorus is
in a tetrahedral environment as in other phosphine oxides. Compound 11 shows intermolecular P@O. . .H–N
type hydrogen bonding interaction [dH(IN)–O(1) =
2.06(5) Å; dN(1N)–O(1) = 2.807(6) Å; N(1)–H(1N)–O(1) =
169(5)], thus resulting in a zig-zag arrangement in the
lattice as shown in Fig. 3(b).
The reaction of Ph2PN(H)Ph with benzophenone
afforded tetraphenyl diphosphine monoxide Ph2PP(O)Ph2 (12) through P–N bond cleavage as shown in
Scheme 3. The formation of product 12 was confirmed
2.1. Reactions of aminophosphines with ketones
The reactions of aminophosphines and aminobis(phosphines) with aldehydes led to the isolation of
either P(III)–N bond inserted products or a-hydroxyphosphine oxides via P(III)–N bond cleavage. In order
to get more insight into the reactivity of P(III)–N bonds,
similar reactions with ketones were carried out with
N-phenyldiphenylphosphinous amide, Ph2PN(H)Ph as
a representative example.
The reactions of Ph2PN(H)Ph with aliphatic ketones
such as 2-butanone, 4-methyl-2-pentanone and 4-hydroxy acetophenone yielded only the phosphine oxide,
Table 3
Selected bond distances (Å) and bond angles () of 9
Bond distances
P(1)–O(1)
P(1)–C(7)
P(2)–O(4)
P(2)–C(26)
Bond angles
O(1)–P(1)–C(1)
O(1)–P(1)–C(13)
C(1)–P(1)–C(13)
P(1)–C(13)–O(2)
O(2)–C(13)–C(14)
O(4)–P(2)–C(32)
C(20)–P(2)–C(32)
C(20)–P(2)–C(26)
P(2)–C(32)–O(5)
1.498(4)
1.785(5)
1.495(4)
1.790(5)
112.1(3)
110.4(3)
106.6(3)
102.3(5)
112.3(5)
111.3(3)
106.8(3)
107.0(3)
103.0(4)
P(1)–C(1)
P(1)–C(13)
P(2)–C(20)
P(2)–C(32)
O(1)–P(1)–C(7)
C(1)–P(1)–C(7)
C(7)–P(1)–C(13)
P(1)–C(13)–C(14)
O(4)–P(2)–C(26)
O(4)–P(2)–C(20)
C(26)–P(2)–C(32)
P(2)–C(32)–O(33)
O(5)–C(32)–C(33)
1.818(5)
1.827(7)
1.794(8)
1.829(6)
112.7(3)
106.7(2)
108.0(3)
113.4(4)
113.7(3)
110.7(3)
106.9(3)
112.6(4)
112.5(2)
Fig. 3. (a) Molecular structure of Ph2P(O)N(H)Ph (11) with the atomnumbering scheme. (b) Intermolecular hydrogen bonding interaction
of P@O of one molecule with N–H of an adjacent molecule in a zig-zag
arrangement (view down crystallographic axis a).
Table 4
Selected bond distances (Å) and bond angles () for 11
Bond distances
P(1)–O(1)
P(1)–C(7)
P(1)–N(1)
Bond angles
O(1)–P(1)–N(1)
O(1)–P(1)–C(7)
N(1)–P(1)–C(7)
P(1)–N(1)–C(13)
P(1)–N(1)–H(1N)
1.481(4)
1.798(5)
1.642(5)
114.5(2)
109.4(2)
108.6(2)
127.0(4)
114(3)
P(1)–C(1)
N(1)–C(13)
O(1)–P(1)–C(1)
N(1)–P(1)–C(1)
P(1)–N(1)–C(13)
C(13)–N(1)–H(1N)
1.794(5)
1.406(6)
113.6(2)
102.6(2)
127.0(4)
119(3)
1645
Ph
H
O
N
PPh2 11
O
R
R = C2H5
CH2CH(CH3)2
C6H4-OH-p
O
H
Ph N
Me
O
O
H
Ph
PPh2
Ph
N
PPh2
O
Ph
Ph
O
Ph
Ph2P
O
PPh2
12
14
O
P
Ph Ph OH
13
Scheme 3.
by 31P NMR spectral data, which shows two doublets at
36.7 and 21.7 ppm for the P(III) and P(V) centers,
respectively with a 1JPP coupling of 228 Hz. The reaction
of Ph2PN(H)Ph with acetyl acetone lead to the formation of Ph2P(O)OH (13) through P–N bond cleavage.
Compound 13 exhibits a single resonance in its 31P
NMR spectrum at 29.6 ppm. When Ph2PN(H)Ph was
treated with acetophenone, insertion of C(Me)Ph into
the P–N bond takes place, to afford Ph2P(O)C(Me)(Ph)N(H)Ph (14) in good yield (Scheme 3). The
31
P NMR spectrum of 14 shows a single resonance at
29.9 ppm. The structural composition of 14 was further
supported by 1H NMR and mass spectral data and by
elemental analysis (Scheme 4).
2.2. Coordination chemistry
The phosphine oxides readily react with oxophilic
metals to give coordination complexes [13]. The
reactions of Ph2P(O)CH2N(H)Ph and (Ph2P(O)CH2)2-
NEt with uranyl acetate in dichloromethane yielded
eight-coordinate complexes, trans-[UO2(OAc)2{(Ph2P(O)CH2N(H)Ph)2-jO,jO}] (15) and trans-[UO2(OAc)2{(Ph2P(O)CH2)2NEt-jO,jO}] (16), respectively in good
yields. The IR spectra of complexes 15 and 16 show
a low frequency shift for P@O (15 cm1) compared
to the free ligands indicating the coordination to the
metal centre. The 31P NMR spectra of complexes 15
and 16 show single resonances at 46.8 and 46.6 ppm,
which are considerably deshielded compared to the
free ligand values, with coordination shifts of 17.3
and 16.4 ppm, respectively.
The reactions of (Ph2P(O)CH2)2NnPr with Th(NO3)4 Æ
5H2O affords a 10-coordinate complex, [Th(NO3)3{(Ph2P(O)CH2)2NnPr}2](NO3) (17). The 31P NMR spectrum
of 17 shows a single resonance at 40.1 ppm with a coordination shift of 11 ppm. The IR and 1H NMR spectral
data and the micro-analytical data support the proposed
structure. The mass spectrum of 17 shows m/z at 1392
corresponding to the cation. Similarly the reaction of
Ph2P(O)CH((g5-C5H4)Fe(g5-C5H5))N(H)Ph (6) with
Th(NO3)4 Æ 5H2O in a 4:1 ratio affords a 10-coordinate
complex, [Th(NO3)3{Ph2P(O)CH((g5-C5H4)Fe(g5-C5H5))N(H)Ph}4](NO3) (18). The 31P NMR spectrum of 18
shows two resonances at 23.9 and 28.2 ppm (broad)
whereas the free ligand resonates at 29.2 ppm. The
IR and 1H NMR spectral data and the micro-analytical
data support the proposed structure. The mass spectrum
of 18 shows m/z at 1394 corresponding to the cation.
The reaction of (Ph2P(O)CH2)2NnPr with Gd(NO3)3 Æ
5H2O affords an 8-coordinate complex, [Gd(NO3)2{(Ph2P(O)CH2)2NnPr}2](NO3) (19). The 31P NMR spectrum
of 19 shows a single resonance at 28.1 ppm. The mass
spectrum of 19 shows m/z at 1256 corresponding to
the cation.
O
N
Pr N
O NO
3
Ph2 O O O N
P O
Th(NO3)4.5H2O
Th O
P O
O Ph2
Pr N
Ph2 O
P
OO
P
N
Ph2
N
Pr
O
17
Ph2
P O UO2(OAc)2.5H2O
P O
Ph2
Gd(NO3)3.5H2O
O
N
Pr N
Ph2 O O
O
P O
Gd
P O
O
Ph2
O O
N
O
Scheme 4.
Ph2
P
N Pr
P
Ph2
19
NO3
OO O
O
O
Ph2
P
N Et
U
O
O O
16
P
Ph2
1646
The reaction of two equivalents of Ph2P(O)CH((g5C5H4)Fe(g5-C5H4))N(H)Ph (6) with Co(NO3)2 Æ 6H2O
gave a purple coloured octahedral complex, [Co(NO3)2{Ph2P(O)CH((g5-C5H4)Fe(g5-C5H5))NHPh}2] (20) in
good yield. The 31P NMR spectra of 20 shows a broad
peak around 39 ppm due to the paramagnetic nature
of the complex. IR and micro analytical data are consistent with the proposed structure.
olet Impact 400 FT IR instrument in KBr disks.
Microanalyses were performed on a Carlo Erba model
1112 elemental analyser. The FAB mass spectra were recorded on a JEOL SX 102/DA-6000 mass spectrometer/
Data system using Argon/Xenon (6 kV, 10 mA) as the
FAB gas. Melting points were recorded in capillary
tubes and are uncorrected.
4.1. 1,3-C6H4{N(H)PPh2}2 (1)
3. Conclusions
The reactions of aminophosphines with aldehydes
give either P–N inserted products or P–N cleavage
products. P–N insertion reactions provide a new route
to phosphorus–carbon bond formation whereas P–N
cleavage reactions provide a-hydroxy phosphine oxides which can serve as valuable synthons [14] in asymmetric synthesis. Further, P–N inserted products can
be used as ligands with oxophilic metal centers. The
reactions of both aliphatic and aromatic aldehydes
with nBuN(PPh2)2 lead to a-hydroxy phosphine oxides
via P–N bond cleavage whereas the n-propyl derivative gives a P–N inserted product with furfural and
a-hydroxy derivatives with other aldehydes. It is observed that these reactions mainly depend on the oxidation state of the phosphorus center and not on the
acidic proton present on the nitrogen center. The reactivity also depends on the nature of nitrogen substituents in the aminophosphines. Further investigations to
understand the influence of phosphorus substituents
on product formation are in progress in our laboratory. Also, this methodology can be adopted to obtain
mixed donor ligands which have potential applications
in homogeneous catalysis and also in asymmetric synthesis [15].
4. Experimental
All the solvents were purified by conventional procedures and distilled prior to use. PhN(H)PPh2 [16],
RN(PPh2)2 (nPr, nBu [17]) and 1,2-Ph2PN(H)C6H4N(H)PPh2 [18] were prepared according to the literature
procedures. Ph2P(O)CH2N(H)Ph and [Ph2P(O)CH2]2NnPr were prepared as described in our previous report
[7b]. 5-Bromo salicylaldehyde was prepared following
the reported procedure [19], and all other aldehydes
were used after purification except ferrocene carboxaldehyde (Strem). Metal salts were purchased from Loba
Chemicals, India and used with out further purification.
The 1H and 31P NMR spectra were recorded using VXR
300 S and Bruker spectrometers; Me4Si was used as an
internal standard for the 1H NMR and 85% H3PO4 as
external standard for the 31P NMR. Positive values indicate downfield shifts. IR spectra were recorded on a Nic-
To a solution of m-phenylene diamine (1.0 g,
9.24 mmol), Et3N (1.87 g, 18.4 mmol) and 4-dimethylaminopyridine (0.038 g, 0.31 mmol) in THF (30 mL) at
0 C, was added dropwise a solution of Ph2PCl (4.08 g,
18.4 mmol) in THF (20 mL). The reaction mixture was
stirred at room temperature for 4 h, the solution was
then filtered through celite and the filtrate was concentrated and cooled to give an analytically pure sample
of 1. Yield: 46% (2.02 g, 4.23 mmol), m.p.: 88–92 C.
Anal. Calc. for C30H26N2P2: C, 75.61; H, 5.50; N,
5.88. Found: C, 75.91; H, 5.39; N, 5.83%. FTIR (KBr
disk) cm1: mNH 3218 s. 1H NMR (CDCl3): d 7.21–
7.55 (m, phenyl). 31P{1H} NMR (CDCl3): d 35.2 (s).
MS (HRMS): 476.16 (M+).
4.2. 1,3-C6H4{N(H)CH2P(O)Ph2}2 (2)
A mixture of 1,3-N,N 0 -bis(diphenylphosphino)diaminobenzene (0.20 g, 0.419 mmol) and paraformaldehyde (0.025 g, 0.839 mmol) in 7 mL of toluene was
heated under reflux conditions for 10 h and cooled to
room temperature. The solvent was removed under reduced pressure and the residue obtained was washed
with hexane (4 · 3 mL) and re-dissolved in a mixture
of CH2Cl2-hexane (2:1) to give the crystalline product
2. Yield: 72% (0.160 g, 0.298 mmol), m.p.: 133–136 C.
Anal. Calc. for C32H30N2O2P2: C, 71.62; H, 5.64; N,
5.22. Found: C, 71.92; H, 5.31; N, 5.25%. FTIR (KBr
disk) cm1: mPO 1174 s. 1H NMR (CD2Cl2): d 2.39 (s,
CH2, 4H), 7.15–7.99 (m, phenyl, 24H). 31P{1H} NMR
(CD2Cl2): d 28.7 (s). MS (HRMS): 536.18 (M+).
4.3. 1,2-C6H4NCH2N(CH2P(O)Ph2)2 (3)
A mixture of 1,2-N,N 0 -bis(diphenylphosphino)diaminobenzene S(0.20 g, 0.419 mmol) and paraformaldehyde (0.037 g, 1.257 mmol) in toluene (7 mL) was
refluxed for 10 h. From the cooled reaction mixture,
solvent was removed under reduced pressure and the
residue obtained was washed with hexane (4 · 3 mL)
and redissolved in a mixture of CH2Cl2-n-hexane (2:1)
to give the crystalline product 3. Yield: 52% (0.120 g,
0.219 mmol), m.p.: 169–172 C. Anal. Calc. for C33H30N2O2P2: C, 72.25; H, 5.51; N, 5.11. Found: C,
72.19; H, 5.31; N, 5.17%. FTIR (KBr disk) cm1: mPO
1180 s. 1H NMR (CDCl3): d 3.82 (br s, P–CH2–N,
1647
4H), 4.96 (s, N–CH2–N, 2H), 6.34–8.65 (m, phenyl,
24H). 31P{1H} NMR (CDCl3): d 26.6 (s). MS (FAB):
547.21 (M+ 1).
4.41 (d, CH, 2JPH = 10.32 Hz, 2H), 7.43–7.89 (m, phenyl, 10H). 31P{1H} NMR (CDCl3): d 31.3 (s).
4.9. Ph2P(O)CH(OH)Ph (8)
4.4. General procedure for the preparation of Ph2P(O)CH(R)NHPh (R = 5-Br-C6H3OH-o, ferrocenyl)
A mixture of Ph2PN(H)Ph (0.40 g, 1.44 mmol) and
one equivalent of aldehyde, RCHO was stirred at
room temperature for 12 h. The resultant slurry was
subjected to a vacuum to remove any volatiles and
the residue obtained was washed with n-hexane
(3 · 5 mL) and crystallized in a mixture of CH2Cl2-nhexane (2:1) at 0 C to give analytically pure products.
4.5. Ph2P(O)CH(5-Br-C6H4OH-o)N(H)Ph (5)
Yield: 61% (0.215 g, 0.450 mmol), m.p.: 183–188 C.
Anal. Calc. for C25H21NO2BrP: C, 62.78; H, 4.43; N,
2.93. Found: C, 62.79; H, 4.55; N, 2.83%. FTIR (KBr
disk) cm1: mOH 3382 br s, mNH 3053 s, mPO 1150 vs.
1
H NMR (CDCl3): d 4.68 (br s, NH, D2O exchangeable), 5.49 (dd, CH, 2JPH = 5.9 Hz, 1H), 6.60–7.79 (m,
phenyl, 18H). 31P{1H} NMR (CDCl3): d 37.8 (s).
4.6. Ph2P(O)CH{(g5-C5H5)Fe(g5-C5H4)}N(H)Ph (6)
Yield: 66% (0.230 g, 0.500 mmol), m.p.: 175–178 C.
Anal. Calc. for C29H26NOPFe: C, 70.89; H, 5.33; N,
2.85. Found: C, 70.82; H, 5.36; N, 2.80%. FTIR (KBr
disk) cm1: mNH 3426 s, mPO 1173 vs. 1H NMR (CDCl3):
d 3.90–4.98 (m, ferrocenyl, 9H), 5.01 (br s, CH, 1H),
6.68–7.72 (m, phenyl, 15H). 31P{1H} NMR (CDCl3): d
29.2 (s).
4.7. General procedure for the reaction of nBuN(PPh2)
(R = nPr,) with R 0 CHO (R 0 = nPr, Ph, OC4H3,
C6H4OH-o)
A mixture of Ph2PN(nBu)PPh2 (0.400 g, 0.94 mmol)
and two equivalents of aldehyde, RCHO (R = nPr, Ph,
OC4H3 and C6H4OH-o) was stirred at room temperature for 24 h. The resultant slurry was subjected to a
vacuum to remove any volatiles and the residue obtained was washed with n-hexane (3 · 5 mL) and crystallized in a mixture of CH2Cl2-n-hexane (2:1) at 0 C to
give analytically pure products.
4.8. Ph2P(O)CH(OH)CH2CH2CH3 (7)
Yield: 42% (0.215 g, 0.784 mmol), m.p.: 116–118 C.
Anal. Calc. for C16H19O2P: C, 70.06; H, 6.98. Found:
C, 70.67; H, 6.87%. FTIR (KBr disk) cm1: mOH 3207
s, mPO 1179 vs. 1H NMR (CDCl3): d 0.85 (t, CH3,
3
JHH = 6.32 Hz, 3H), 1.38 (m, CH2, 2H), 1.65 (m,
CH2, 2H), 1.73 (br s, OH, D2O exchangeable, 1H),
Yield: 51% (0.291 g, 0.944 mmol), m.p.: 164–166 C
(dec.). Anal. Calc. for C19H17O2P: C, 74.01; H, 5.56.
Found: C, 73.86; H, 5.49%. FTIR (KBr disk) cm1:
mOH 3388 s, mPO 1163 vs. 1H NMR (CDCl3): d 1.83 (br
s, OH, D2O exchangeable), 5.48 (d, CH, 2JHH =
5.24 Hz, 1H), 7.13–7.90 (m, phenyl, 15H). 31P{1H}
NMR (CDCl3): d 30.6 (s).
4.10. Ph2P(O)CH(OH)C6H4OH-o (9)
Yield: 51% (0.311 g, 0.959 mmol), m.p.: 90–92 C.
Anal. Calc. for C19H17O3P: C, 70.37; H, 5.28. Found:
C, 70.25; H, 5.33%. FTIR (KBr disk) cm1: mOH
3229 br s, mPO 1139 vs. 1H NMR (CDCl3): d 4.01
(br s, OH, D2O exchangeable), 5.45 (d, CH, 2JPH =
5.86 Hz, 1H), 6.67–7.82 (m, phenyl, 14H), 9.65 (br s,
OH, D2O exchangeable). 31P{1H} NMR (CDCl3): d
37.4 (s).
4.11. Ph2P(O)CH(OH)(OC4H3) (10)
Yield: 77% (0.313 g, 1.050 mmol), m.p.: 148–151 C.
Anal. Calc. for C17H15O3P: C, 68.45; H, 5.06. Found:
C, 68.32; H, 4.93%. FTIR (KBr disk) cm1: mOH 3380
br s, mPO 1154 vs. 1H NMR (CDCl3): d 4.77 (br s, OH,
D2O exchangeable), 5.59 (d, CH, 2JPH = 5.5 Hz, 1H),
6.23–6.29 (m, furfuryl, 2H), 7.18–7.88 (m, phenyl & furfuryl, 11H). 31P{1H} NMR (CDCl3): d 31.5 (s).
5. Reaction of aminophosphines with ketones
5.1. Reaction of Ph2PN(H)Ph with CH3C(O)R
(R = C2H5, CH2CH(CH3)2, C6H4OH-p)
A mixture of Ph2PN(H)Ph (0.400 g, 1.44 mmol) and
CH3C(O)R (1.44 mmol) in toluene (10 mL) was stirred
at room temperature for 10 h. The solution was evaporated under reduced pressure and the residue obtained
was crystallized from a 1:1 mixture of CH2Cl2–petroleum ether at 0 C to give analytically pure
Ph2P(O)N(H)Ph (11). Yield: 47% (0.20 g, 0.682 mmol)
(for R = C2H5); 55% (0.23 g, 0.784 mmol) (for
R = CH2CH(CH3)2); 50% (0.21 g, 0.716 mmol) (for
R = C6H4OH-p), m.p.: 230 C (dec.). Anal. Calc.
for C18H16NOP: C, 73.70; H, 5.49; N, 4.78. Found: C,
73.63; H, 5.55; N, 4.59%. FTIR (KBr disk) cm1: mNH
3121 s, mPO 1183 vs. 1H NMR (CDCl3): d 4.39 (d, NH,
D2O exchangeable, 1H), 6.70–7.13 (m, NPh, 5H),
7.15–7.77 (m, PPh2, 10H). 31P{1H} NMR (CDCl3): d
18.5 (s).
1648
5.2. Reaction of Ph2PN(H)Ph with benzophenone
A mixture of Ph2PN(H)Ph (0.200 g, 0.7 mmol) and
benzophenone (0.131 g, 0.7 mmol) was heated to 75–
80 C with stirring. The melt was cooled to room temperature after 4 h and the volatiles were removed under
reduced pressure to give a white residue. The residue obtained was crystallized from CH2Cl2–petroleum ether
(2:1) mixture at 0 C to get analytically pure
Ph2PP(O)Ph2 (12). Yield: 94% (0.131 g, 0.34 mmol),
m.p.: 152–154 C. Anal. Calc. for C24H20OP2: C,
74.62; H, 5.22. Found: C, 74.69; H, 5.33%. 31P{1H}
NMR (CDCl3): d 21.7 (d), 36.7(d); 1JPP = 228.3 Hz.
5.3. Reaction of Ph2PN(H)Ph with acetylacetone
To a solution of Ph2PN(H)Ph (1.00 g, 3.60 mmol) in
toluene (10 mL) was added acetylacetone (0.360 g,
3.60 mmol) also in toluene (5 mL) and the reaction mixture was stirred at room temperature for 12 h. The solution was then concentrated to 3 mL, diluted with diethyl
ether (7 mL) and on storing the solution at room temperature yielded an analytically pure sample identified
as Ph2P(O)OH (13). Yield: 77% (0.590 g, 2.70 mmol),
m.p.: 170–172 C (dec.). FTIR (KBr disk) cm1: mPO
1181 s. 1H NMR (CDCl3): d 7.45–7.88 (m, phenyl).
31
P{1H} NMR (CDCl3): d 29.6 (s). MS (FAB): 218.67
(M+).
5.4. Reaction of Ph2PN(H)Ph with acetophenone
To a solution of Ph2PN(H)Ph (0.400 g, 1.44 mmol) in
toluene (10 mL), was added acetophenone (0.173 g,
1.44 mmol) and the reaction mixture was allowed to stir
at room temperature for 12 h. The solution was then
concentrated to 3 mL, diluted with diethyl ether
(10 mL) and cooled to 0 C to give analytically pure
Ph2P(O)C(CH3)PhN(H)Ph (14). Yield: 46% (0.320 g,
0.660 mmol), m.p.: 156–158 C (dec.). Anal. Calc. for
C26H24NOP Æ CH2Cl2: C, 67.23; H, 5.43; N, 2.90.
Found: C, 67.49; H, 5.24; N, 2.79%. 1H NMR (CDCl3):
d 1.25 (s, CH3, 3H), 6.91–6.97 (m, phenyl, 5H), 7.10–7.92
(m, phenyl, 15H). 31P{1H} NMR (CDCl3): d 29.9 (s).
MS (FAB): 395 (M+ 2).
Found: C, 50.32; H, 4.16; N, 2.67%. FTIR (KBr disk)
cm1: mNH 3291 s, mCO 1612 s, mPO 1138 s. 1H NMR
(CDCl3): d 0.73 (br s, CH3, 6H), 4.51 (br s, CH2, 4H),
6.70–7.60 (m, phenyl, 30H). 31P{1H} NMR (CDCl3): d
46.9 (s).
5.6. [UO2(CH3COO)2{(Ph2P(O)CH2)2NEt}] (16)
A solution of EtN(CH2P(O)Ph2)2 (0.056 g, 0.10
mmol) in CH2Cl2 (10 mL) was added to UO2(OAc)2
(0.050 g, 0.10 mmol) also in CH2Cl2 (10 mL) and the
reaction mixture was stirred at room temperature for
6 h. The solvent was evaporated from the reaction mixture under reduced pressure and the residue obtained
was re-crystallized from EtOH–diethyl ether (1:1) at
0 C to give an analytically pure sample of 16. Yield:
88% (0.091 g, 0.110 mmol), m.p.: 118–121 C (dec.).
Anal. Calc. for C32H35NO8P2U: C, 44.61; H, 4.09; N
1.63. Found: C, 43.92; H, 3.99; N, 1.51%. FTIR (KBr
disk) cm1: mPO 1148 s, mCO 1611 m. 1H NMR (CDCl3):
d 0.89 (m, CH3, 6H), 1.25 (s, CH3, 3H), 2.46 (m, CH2,
2H), 4.07 (br s, P–CH2–N, 4H), 7.26–9.92 (m, phenyl,
20H). 31P{1H} NMR (CDCl3): d 42.4 (s).
5.7. [Th(NO3)3{(Ph2P(O)CH2)2NnPr}2]NO3 (17)
A solution of, nPrN(CH2P(O)Ph2)2 (0.170 g,
0.350 mmol) in ethanol (5 mL) was added to a solution
of Th(NO3)4 Æ 5H2O (0.1 g, 0.175 mmol) also in ethanol
(10 mL). The clear solution was allowed to stir at room
temperature for 4 h, during which time, the product precipitated out, was filtered and dried. The product was
re-crystallized from CH2Cl2–diethylether (1:1) mixture.
Yield: 76% (0.195 g, 0.121 mmol), m.p.: 109–111 C
(dec.). Anal. Calc. for C58H62N6O16P4Th: C, 47.87; H,
4.29; N, 5.78%. Found: C, 48.11; H, 4.19; N, 5.94%.
FTIR (KBr disk) cm1: mNO3 1529 vs, mPO 1138 vs. 1H
NMR (CDCl3): d 0.26 (t, CH3, 3JHH = 7.00 Hz, 3H),
0.81(m, CH2, 2H), 3.15 (m, CH2, 2H), 3.97 (s, P–CH2–
N, 4H), 6.87–7.73 (m, phenyl, 20H). 31P{1H} NMR
(CDCl3): d 40.1 (s). MS (FAB): 1392.4 (M+ NO3).
5.8. [Th(NO3)3{Ph2P(O)CH(C5H4FeC5 H5)N(H)Ph}4]NO3 (18)
5.5. [UO2(CH3COO)2(Ph2P(O)CH2N(H)Ph)2] (15)
Uranyl acetate (0.10 g, 0.23 mmol) in methanol
(5 mL) was added to Ph2P(O)CH2N(H)Ph (0.146 g,
0.47 mmol) also in methanol (5 mL) and the yellow solution obtained was stirred at room temperature for 2 h.
The solvent was evaporated under reduced pressure
and the residue was washed with n-hexane (2 · 5 mL)
and dried to give the crystalline product 15. Yield:
77% (0.184 g, 0.180 mmol), m.p.: 72–74 C (dec.). Anal.
Calc. for C42H42N2O8P2U: C, 50.31; H, 4.22; N, 2.79.
A solution of Ph2P(O)CH2N(H)C5H4FeC5H5 (0.103 g,
0.021 mmol) in CH2Cl2 (5 mL) was added to a solution
of Th(NO3)4 Æ 5H2O (0.03 g, 0.05 mmol) in ethanol
(10 mL). The clear solution was allowed to stir at room
temperature for 4 h, during which time, the product precipitated out, was filtered and dried. The product was recrystallized from CH2Cl2–diethylether (1:1) mixture.
Yield: 64% (0.082 g, 0.034 mmol), m.p.: 152–154 C.
Anal. Calc. for C116H104N8O16P4Fe4Th Æ 3CH2Cl2: C,
52.93; H, 4.11; N, 4.15. Found: C, 52.74; H, 4.07; N,
1649
4.13%. FTIR (KBr disk) cm1: mNO3 1515 s, mPO 1138 vs.
1
H NMR (CDCl3): signals are broad, so not incorporated and the 31P signal is also slightly broad in this case.
31
P{1H} NMR (CDCl3): d 23.9 (s). MS (FAB): 2382
(M+ 1 NO3).
parameters. All the hydrogen atoms were geometrically
fixed and allowed to refine using a riding model.
5.9. [Gd(NO3)2{(Ph2P(O)CH2)2NnPr}2]NO3 (19)
Full details of data collection and structure refinement
have been deposited with Cambridge Crystallographic
Data Center, CCDC reference numbers 245668, 245669
and 245670 for compounds 4, 9 and 11, respectively.
Copies of this information can be obtained free of charge
from the Director, CCDC, 12 Union Road, Cambridge,
CB2 1EZ, UK (fax: +44-1223-336033; e-mail: deposit
@ccdc.cam.ac.uk or www:http://www.ccdc.cam.ac.uk).
A solution of the dioxide, nPrN(CH2P(O)Ph2)2
(0.225 g, 0.460 mmol) in CH2Cl2 (5 mL) was added to
a solution of Gd(NO3)3 Æ 5H2O (0.1 g, 0.230 mmol) also
in ethanol (10 mL). The clear solution was allowed to
stir at room temperature for 4 h, during which time,
the product precipitated out, was filtered and dried.
The product was washed with diethylether and re-crystallized from MeOH–CH2Cl2 (1:1) mixture. Yield: 84%
(0.256 g, 0.194 mmol), m.p.: 110–114 C (dec.). Anal.
Calc. for C58H62N5O13P4Gd Æ CH2Cl2: C, 50.50; H,
4.60; N, 4.99. Found: C, 50.37; H, 4.65; N, 4.86%. FTIR
(KBr disk) cm1: mNO3 1490 vs, mPO 1159 s. 1H NMR
(DMSO-d6): d 0.29 (br s, CH3, 3H), 1.78 (br s, CH2,
2H), 2.51 (br s, CH2, 2H), 3.57 (br s, DMSO & P–
CH2–N), 7.48–7.79 (br m, phenyl, 20H). 31P{1H}
NMR (DMSO-d6): d 28.1 (br s). MS (FAB): 1256
(M+ NO3).
5.10. [Co(O2NO)2(Ph2P(O)CH((g5-C5H4)Fe(g5-C5H5))N(H)Ph)2] (20)
To an ethanolic solution (5 mL) of Co(NO3)2 Æ 6H2O
(0.030 g, 0.10 mmol), Ph2P(O)CH((g5-C5H4)Fe(g5-C5H5))N(H)Ph (0.101 g, 0.20 mmol) also in ethanol (10 mL)
was added and the mixture was stirred for 2 h at
room temperature. The resultant brown solution was
evaporated to dryness and the residue was washed
with n-hexane (3 · 5 mL) to give the analytically pure
product 20. Yield: 92% (0.110 g, 0.094 mmol), m.p.:
116–120 C (dec.). Anal. Calc. for C58H52N4O8P2CoFe2:
C, 59.76; H, 4.49; N, 4.81. Found: C, 59.69; H, 4.56; N,
4.86%. FTIR (KBr disk) cm1: mNH 3384 br m, mNO3
1388 s, mPO 1143 vs. 31P{1H} NMR (CDCl3 &DMSOd6): d 38.7 (br s).
5.11. X-ray Crystallography
Crystals of compounds 4, 9 and 11 obtained as above
were mounted on pyrex resin. A Nonius MACH3 diffractometer was used for the unit cell determination and the
intensity data collection. The initially obtained unit cell
parameters were refined by accurately centering randomly selected reflections. Periodic monitoring of check
reflections showed the stability of the intensity data. Details of crystal and data collection are given in Table 1.
The structures were solved by direct methods (SHELXS
97) and refined using SHELXL 97 software [20]. The nonhydrogen atoms were refined with anisotropic thermal
6. Supplementary material
Acknowledgements
We are grateful to the Department of Science and
Technology (DST) and CSIR, New Delhi, India for generous support. SP thanks CSIR, New Delhi, India for
JRF and SRF fellowships. The X-ray structural studies
were carried out at the National Single Crystal X-ray
Diffraction Facility, Indian Institute of Technology,
Bombay. We also thank RSIC, Mumbai, Sophisticated
Instrumentation Facility (SIF), Bangalore, for the spectral facility. The referees suggestions at the revision
stage were very helpful.
References
[1] M.S. Balakrishna, V.S. Reddy, S.S. Krishnamurthy, J.F. Nixon,
J.C.T.R. Burckett, St. Laurent, Coord. Chem. Rev. 129 (1994) 1.
[2] M.T. Ashby, Z. Li, Inorg. Chem. 31 (1992) 1321.
[3] M.S. Balakrishna, B.D. Santarsiero, R.G. Cavell, Inorg. Chem.
33 (1994) 3079.
[4] M.G. Newton, R.B. King, M. Chang, J. Gimeno, J. Am. Chem.
Soc. 100 (1978) 1632.
[5] A.D. Burrows, M.F. Mahon, M.T. Palmer, M. Varrone, Inorg.
Chem. 41 (2002) 1695;
(a) M.S. Balakrishna, S.S. Krishnamurthy, Indian J. Chem. 30A
(1991) 356;
(b) S. Priya, M.S. Balakrishna, J.T. Mague, J. Organomet. Chem.
679 (2003) 116;
(c) M.S. Balakrishna, P.P. George, J.T. Mague, J. Organomet.
Chem. 689 (2004) 3388.
[6] (a) S. Priya, M.S. Balakrishna, J.T. Mague, Inorg. Chem.
Commun. 4 (2001) 437;
(b) S. Priya, M.S. Balakrishna, J.T. Mague, S.M. Mobin, Inorg.
Chem. 42 (2003) 1272.
[7] (a) M.S. Balakrishna, K. Ramaswamy, R.M. Abhyankar, J.
Organomet. Chem. 560 (1998) 131;
(b) M.S. Balakrishna, R.M. Abhyankar, J.T. Mague, J. Chem.
Soc., Dalton Trans. (1999) 1407;
(c) M.S. Balakrishna, R. Panda, J.T. Mague, Inorg. Chem. 40
(2001) 5620;
(d) M.S. Balakrishna, R.M. Abhyankar, M.G. Walawalker,
Tetrahedron Lett. 42 (2001) 2733;
(e) M.S. Balakrishna, M.G. Walawalker, J. Organomet. Chem.
628 (2001) 76;
1650
[8]
[9]
[10]
[11]
[12]
(f) S. Priya, M.S. Balakrishna, S.M. Mobin, R. McDonald, J.
Organomet. Chem. 688 (2003) 227;
(g) M.S. Balakrishna, P. Chandrasekaran, P.P. George, Coord.
Chem. Rev. 241 (2003) 87;
(h) M.S. Balakrishna, S. Priya, R. Panda, Phosphorus, sulfur,
silicon and Rel. Elem. 179 (2004) 911;
(i) S. Priya, M.S. Balakrishna, J.T. Mague, Chem. Lett. 33 (2004)
308;
(j) S. Priya, M.S. Balakrishna, J.T. Mague, J. Organomet. Chem.
689 (2004) 3335.
R.G. Cavell, K.I. The, L. van de Griend, Inorg. Chem. 20 (1981)
3813.
P. Kafarski, P. Mastalerz, Aminophosphonates, Beitrage zur
Wirkstofforschung (1984) 1.
J.M. Barendt, R.C. Haltiwanger, C.A. Squier, A.D. Norman,
Inorg. Chem. 30 (1991) 2342.
C. Panattoni, G. Bandoli, G. Bortolozzo, D.A. Clemente, U.
Croatto, J. Chem. Soc. A (1970) 2778.
K. Aparna, S.S. Krishnamurthy, M. Nethaji, J. Chem. Soc.,
Dalton Trans. (1995) 2991.
[13] V.V. Grushin, Chem. Rev. 104 (2004) 1629.
[14] (a) D.R. Armstrong, M.G. Davidson, R.P. Davies, H.J. Mitchell,
R.M. Oakley, P.R. Raithby, R. Snaith, S. Warren, Angew Chem.,
Int. Ed. Engl. 35 (1996) 1942;
(b) K.K. Praveen Kumar, S. Kumaraswamy, K.C. Kumaraswamy, Tetrahedron Lett. 42 (2001) 3219;
(c) J. Claydon, E.W. Collington, S. Warren, Tetrahedron Lett. 34
(1993) 1327.
[15] (a) J. Claydon, E.W. Collington, S. Warren, Tetrahedron Lett. 33
(1992) 7043;
(b) D.R. Armstrong, D. Barr, M.G. Davidson, G. Hutton, P.
OBrien, R. Snaith, S. Warren, J. Organomet. Chem. 529 (1997)
29.
[16] W. Wiegraebe, H. Bock, Chem. Ber. 101 (1968) 1414.
[17] H. Noeth, L. Meinel, Z. Anorg. Allg. Chem. 349 (1967) 225.
[18] T.Q. Ly, A.M.Z. Slawin, J.D. Woollins, J. Chem. Soc., Dalton
Trans. (1997) 1611.
[19] C.M. Brewster, L.H. Millam, J. Am. Chem. Soc. 55 (1933) 763.
[20] G.M. Sheldrick, SHELXL97. Program for Crystal Structure Refinement, University of Göttingen, Göttingen, Germany, 1997.