Indian Journal of Chemistry
Vol. 39A April 2000, pp. 453 -456
Synthesis and characterization of Ru(II)
arene complexes, [Ru(11 6 -arene )( dppm )Ht
(11 6-arene=benzene, p-cymene or hexamethyl2
benzene ), [Ru(11 6-arene)(py ) 3] + and
[Ru(11 6 -arene )(py)2Cit
0 S Sisodiya, AN Sahay & D S Pandey*
Department of Chemistry, A P S University,
Rewa (MP) 486 003, India
Received 26 May 1999; revisPd 22 November 1999
6
6
Reaction s of [{Ru(11 -arene)Cl 2 }z] (11 -arene = benzene. pcymene, hexamethylbenzene) in methanol, in presence of
AgBF 4/ AgPF 6 with I ,2-bis( diphenylphosphino )methane ( dppm)
6
give cationic hydrido complexes [Ru(11 -arene)(dppm)Ht.
However, under similar and some changed conditions, reaction
6
wi th pyridine result in the formati on of [Ru(11 -arene)(pyhf+ and
6
[Ru(11 -arene)(py)zCit. The reaction products have been
1
31
characterized by elemental analyses, IR, H, P NMR and FAB
mass spectra.
Synthesis and characterization of arene-ruthenium
complexes have drawn special attention owing to their
catalytic potential and their use as precursors for the
17
synthesis of Ru(O) and Ru(ll) complexes - . The
6
6
dimeric complexes, [ {Ru(l1 -arene)CI2}2] ('11 -arene =
benzene and its derivatives) undergo bridge cleavage
reaction, upon treatment with ligands L [L= PR3,
P(OR)3, AsRy, pyridine, etc.] to give monomeric
complexes. However, upon treatment with AgBF4 in
CH3CN , it yields [Ru(l1 6-arene)(CHJCN)Jf + (ref. 8).
6
Recently, we have shown that treatment of [ {Ru(l1 arene)CI 2}2](l16-arene = benzene,
p-cymene
or
hexamethylbenzene) with AgBF4 or AgPF6 in
methanoL in presence of triphenylphosphine,
triphenylarsine
and
triphenylstibine
yield
mononuclear, cationic, arene hydrido complexes with
6
the formulations [Ru(l1 -arene)H(Lht (L = PPh3,
AsPh 3 or SbPh 3) and have confirmed the structure of
one representative complex by single crystal X-ray
analysis 9 . In an extension of our earlier studies, we
found that under similar reaction conditions, the
complexes [ {Ru(l1 6 -arene)C I2}2], upon treatment with
dppm yield hydrido complexes [RuH{l1 6 -arene)(LL)t. However, in presence of pyridine we could
isolate [Ru('11 6 -arene)(py)3f + and [Ru(l1 6-arene )(py)2Cif
instead of a hydrido complex. In this note we report the
synthesis and characterization of the products like
6
2
[RuH( '11 6-arene( dppm)f,
[Ru('11 -arene)(py)3) + and
6
[Ru('11 -arene)(py)2Cif.
Experimental
All the chemicals used were either chemically pure
or AR grade. Solvents were distilled and dried before
use. All the synthetic manipulations were performed
under oxygen free dry nitrogen atmosphere.
Silvertetrafluoroborate, silverhexafluorophosphate, 1,2bis(diphenyl-phosphino )methane, and pyridine (all
Aldrich) were used as received. Starting complexes
6
[ {Ru(l1 6-arene)CI 2}2] ('11 -arene =benzene, p-cymene
or hexamethylbenzene) were prepared following the
literature procedure 10' 11 . C,H and N analyses were
performed by microanalysis division , RSIC, CDRI,
Lucknow. Infrared spectra were recorded in KBr discs
1
31
on a Shimadzu-8201 PC, FTIR; H and P NMR on a
Bruker DRX-300 and FAB mass on a Jeol SXI02
spectrometers, respectively.
Preparation of complexes
The following general method ~as used for the
preparation of all the complexes:
To a suspension of[ {Ru(l1 6-arene)Cb}2] (0.5 mmol)
in methanol (25 mL) AgBF 4/AgPF 6 (2.0 mmol) was
added and it was stirred at room temperature . After 30
min, white precipitate of AgCI was filtered off and the
orange yellow filtrate was treated with dppm/pyridine.
Immediately upon addition, colour of the solution
turned from organge yellow to pale yellow. It was
stirred at room temperature for 3 h, filtered to remove
any solid residue and then left for slow crystallizati on
in refrigerator. Yellow to greenish yellow crystals
separated out. These were filtered, washed several
times with methanol, diethylether and dried in vacuo
(Yield 60-75%) . For the preparation of [Ru(l1 66
areneXpy)2Cif complexes, [ {Ru(l1 -arene)Ch h J and
AgPF 6 were taken in I: l molar ratio.
Results and discussion
Dimeric ruthenium complexes [ {Ru(l1 6-arene)C bh]
('11 -arene =benzene, p-cymene or hexamethylbenzene)
upon reaction with dppm in presence of AgPF6/BF4 in
methanol gives pale yellow, air-stable, non-hygroscopic,
6
454
INDIAN J CHEM, SEC. A, APRIL 2000
Table 1-Analytical data of the complexes
S. no. Complexes
Found/{Calcd.}, %
Colour
c
H
N
52.25
3.92
[Ru(11 6-C6H6)( dppm)H]PF6
Pale yellow
(52.46) (4.09)
4.68
2
[Ru(11 6-C 10H 14)( dppm)H]PF6 54.76
Pale yellow
(54 .90) (4.83)
5.26
3
[Ru(11 6-C 6 Me6)( dppm)H]PF 6 55 .71
Yellow
(55 .98.) (5 .17)
43.11
3.62
4
7.28
[Ru( 11 6-C6H6)(py)J](BF4)2
(42 .71 ) (3.77)
(7 .11)
Greenish yellow
6
36.52
3.02
6.02
5
[Ru(11 -C6H6)(py)3](PF6h
(35 .69) (2.97)
(5.94)
Greenish yellow
46.48
4.56
6.52
6
[Ru(11 6-C10H 14)(pyh(BF4)2
(46.43) (4.48)
(6.50)
Bright yellow
40.06
3.82
6.64
7
[Ru(11 6-C 10H 14)(py)3](PF6h
(39.37) (3.80)
(5.51)
Greenish yellow
48.12
4.96
6.42
8
[Ru(11 6-C6Me 6((py) 3](BF4h
(48 .07) (4.89)
Yellow
(6.23)
41.06
4.28
5.26
9
[Ru( 11 6-C6Me6)(py)3](PF6)2
(41.01) (4.17)
(5.31)
Greenish yellow
37.14
3.40
5.36
10
[Ru(11 6-C6H6)(pyhCI]PF6
Pale yellow
(37.06) (3.09)
(5.40)
41.96
4.20
4.86
II
[Ru( 11 6-C 10 H14)(pyhCI]PF6
(41.81) (4.18)
(4.87)
Yellow
43 .92
4.86
4.68
12
[Ru(11 6-C6Me 6)(pyhCI]PF6
(43.85) (4.65)
(4 .65)
Yellow
cationic hydrido complexes of the general formula
[Ru(11 6-arene) (dppm)Hf (Table 1). However,
reactions of Ru(II) arene complexes with pyridine
under varying reaction conditions led to tl-ie formation
of cationic complexes with the formulations
6
6
[Ru(11 -areneXpy)3
and [Ru(T] -arene) (py)2Ctf
(Table I). These complexes are readily .soluble in
dichloromethane, chloroform, methanol, and acetone,
less solub le in benzene and insoluble in diethyl ether
and pet. ether. The spectral studies have been found to
be very useful to elucidate the bonding modes in these
complexes .
6
Infrared spectra of the complexes [Ru(11 -C6 H6)
6
6
(L-L)Hf
[Ru(11 -C1 oH14)(L-L)Hf and
[Ru(11 C6Me6)(L-L)Hf (L-L = dppm) exhibited sharp bands
1
at 1995, 1976 and 1965 cm- respectively assignable
to v(Ru-H) alongwith the characteristic bands due to
arenes and bis phosphine. It is observed that the
position of v(Ru-H) in these complexes is sensitive to
the methyl substitution in the arene ring. This band
shifted towards higher wave number as one move
from the benzene complex to hexamethylbenzene
complex (Table I). It suggests, that more electron
donating arenes induce greater electron density on the
hydride ligand 12. In the IR spectra of the complexes
6
6
[Ru(11 -arene) (py) 3
or [Ru(11 -arene(py)2Ctf, the
t
f+
presence of pyridine has been confirmed by presence of
its characteristic IR absorption frequency . In these
complexes, the pyridine ring vibrations in the high
frequency region are not shifted appreciably whereas
those at 604 cm- 1 in-plane deformation shifted to higher
frequencies. Such observations have been made by pther
13
workers also . Characteristic bands due to counter
anions BFJPF6 were observed at 1071 and 840 cm- 1 in
theIR spectra of the respective complexes.
1
The H NMR spectra of the complex [Ru(11 6 arene)(dppm)Hf consisted of triplets in the region
-6.9 to -11.26 ppm alongwith the signals due to 11 6arene and dppm. The resonances observed in high
field side, have been assigned to metal bound hydride
(Ru-H). The presence of a triplet in the 1H NMR
spectra of these complexes suggested that the hydride
ligand be coupled with two equivalent phosphorus
14
nuclei . However, in the 1HNMR spectra of pcymene complex [Ru(n 6-C 10 H 14 )(dpprn)H]PF6 , a
doublet of triplet centred at 8-9.45 ppm with
JH-r= 48 Hz is observed. The presence of a doublet of
triplet indicates that the hydride proton interacts with
methylene protons of the dppm. ligand. It has also
been observed that the chemical shifts of Ru-H
resonance, in these complexes are depdent upon the
nature of the arene ring. This observation is consistent
with the conclusions drawn from IR spectral studies.
The integrated intensity of different bands conforms
well to the stoichiometry of the complexeds. Cationic
pyridine complexes [Ru(11 6 -arene)(py)3] 2+ and [Ru(11 6arene)(py)2Cif in their respective 1H NMR displayed
resonances in the region 8 7.2, 8.07 and 8.94 ppm,
assignable to the protons of ~he pyridine ligand
alongwith the resonances due to 11 6 -arene protons
(Table 2). In these complexes, pyridine resonances
exhibited downfield shift as compared to that in the
free ligand, indicating the complexation of pyridine N
atom with the meta l centre.
31
The P NMR spectra of the comp lex [Ru(11 6-
o
C10H14)(dppm)Hf displayed a sharp singlet at 8 8. J 4
31
ppm, assignable to P nuclei. The presence of a
single sharp resonance suggested that both the 31P
nuclei of the dppm ligand in the complex are
chemically equivalent. Further, the deshielding of 31P
nuclei in the complex 8 8.142 ppm as compared to
that in the free ligand 8 -22.48 ppm, suggested that
both the phosphorus atoms are coordinated with the
metal centre. The 31P nuclei of the PF6 anion resonated
in its cHaracteristic septet pattern at 8 - 143.75 ppm.
NOTES
455
Table 2- 1H NMR Spectral data of the complexes
S. no.
Complexes
Arene protons (8 ppm)
Other protons (8 ppm)
2
[Ru(T] 6-~H 6 )( dppm)H]PF 6
[Ru(T] 6-C 10H 14 ((dppm)H)PF 6
5.60
1.07 (doublet, CHMe 2 protons)
1.90 (singlet, CH 3 protons)
2.56 (septet, CHMe 2 protons)
6.26-6.30 (doublet, C6H4 protons)
3.40-3 .44 (doublet of doublet)
4.2, 5.2 (multiplet)
2.06 (singlet, methyl protons ofC6Me 6)
4.4, 5.6 (multiplet)
4
5.65 (sharp singlet, aromatic protons of
C6H6)
7.2, 8.07 and 8.94 a , p andy
protons of pyridine
5
1.21 (doublet, CHtv,fe 2 protons)
7.51, 8.07, 8.93 a, p andy
2.04 (singlet, CH 3 protons)
protons of pyridine
2.83 (septet, CHMe 2 protons)
5.81-6.16 (doublet of doublet, protons of
C6H4)
6
2.16 (singlet, methyl protons of C6Me 6)
7.65, 8. 17, 8.97 a , 13 andy
protons of pyridine
7
6. 16 (singlet, aromatic protons of C6H6)
7.42, 8.00, 8.88 a, p andy
protons of pyridine
8
I. 19 (doublet, CHMe 2 protons)
7.45, 8.00, 8.92 a, p and
1.98 (singlet, CH 3 protons) 2.83, (septet, y protons of pyridine
CHMe 2) 6.20-6.35 (doublet of doublet,
C6H 4 protons)
2. 12 (singlet, CH 3 protons of C6Me 6)
7.38, 8.26, 8.94 a, P andy
protons of pyridine
9
6
FAB mass spectra of the complex [Ru(TJ C10H14)(py)2CI)]PF6 displayed a peak at m/z 429,
6
[Ru(TJ corresponding
to
molecular
ion
C 10H14)(py) 2CJt. The molecular ion loses one
6
pyridine ligand to form [Ru(TJ -CJOHJ4)(py)Ctt. It is
reflected in the mass spectra of the complex in the
form of basal peak at m/z 350. In the next step, the
other metal bound pyridine ligand is also given out to
form , [Ru(TJ 6 -C 10 H 14 )CJt which is evident from the
presence of a peak at m/z 271. The overall
fragmentation patterns for this molecule may be given
as:
[Ru( 11 6-c 10H14)(py)2Cl))PF 6~[Ru( 11 6-C 10H 14)(pyhCt)r
[(m/z) calcd. 429; obs. 429]
6
- Py ~[Ru( T] -C 10 H 14)(py)CI)]
[(m/z) calcd. 350; obs. 350]
basal peak
-CI~ [Ru(T] 6-CIOHI 4))++
[(m/z) calcd. 271 ; obs. 271] [(m/z) calcd. 235 ; obs. 233]
-Py~ [Ru(T] 6-C10H14)CI)r
The F AB mass spectral data of the complex
supported well for the formulation of our complex.
Ru-H (8 ppm)
-6.62
-9.45
-11.24
The analytical and spectr~l data of the complexes
6
suggested that reactions of [{Ru(TJ -arene)Chh] (TJ 6arene =benzene, p-cymene, or hexamethylbenzene)
with dppm in presence of excess {)f AgBF 4/AgPF 6 in
methanol results in the formation of cationic hydrido
6
complex [Ru(TJ -arene)(dppm)Ht. The products from
6
the reactions of [ {Ru(TJ -arene)CI 2}2] with pyridine in
presence of AgBF 4/AgPF 6 are dependent upon the
reaction conditions. Reaction of [Ru(TJ 6-arene)Ch h ]
with an excess of AgBF 4/AgPF 6 are dependent upon
the . reaction conditions. Reaction of [Ru(TJ 6 arene)CI2}2] with an excess of AgBF 4 /AgPF 6 in
methanol and followed by treatment with pyridine led
to the formation of [Ru(TJ 6-arene)(Py)3] 2+. However,
reaction involving I: 1 molar ratio of the dimeric
ruthenium arene complex in methanol followed by
treatment with pyri~ine led to [Ru(TJ 6 -arene)(Py) 2CJt
complexes.
Acknowledgement
Thanks are due to the CSIR, New Delhi for providing
financial assistance [HRDG 0 I ( 13 75)/95/EMR-II].
456
INDIAN J CHEM, SEC. A, APRIL 2000
We also thank the Head, Department of Chemistry, A
P S University, Rewa for cooperation and
encouragement and RSfC, CDRJ, Lucknow, for
providing facilities for the analytical and spectral
data.
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