Platinum bis(tricyclohexylphosphine) silyl hydride complexes

Article abstract of DOI:10.1021/om049549n

A series of platinum metal silyl hydride complexes were prepared in solution by reaction of Pt(PC_y3)₂ with the appropriate silane, HSiR₂R′. The complex was characterized using x ray crystallography at -100°C. The platinum center was found to exhibit a distorted-square-planar geometry with angles P(1)-Pt-P(2)=113.55(3)°, P(1)-Pt-Si=146.83(3)°, and P(2)-Pt-Si=99.37(3)°. The reaction of Pt(PC_y3)₂ with chlorinated hydrosilanes at -78°C was also found to yield analogues complexes which isomerized to their trans isomers on warming at room temperatures.

Full text of DOI:10.1021/om049549n

5744
Organometallics 2004, 23, 5744-5756
Platinum Bis(tricyclohexylphosphine) Silyl Hydride
Complexes
Danny Chan,† Simon B. Duckett,*,† Sarah L. Heath,† Iman G. Khazal,†
Robin N. Perutz,*,† Sylviane Sabo-Etienne,‡ and Philippa L. Timmins†
Department of Chemistry, University of York, York YO10 5DD, U.K., and
Laboratoire de Chimie de Coordination du CNRS, 205 Route de Narbonne,
31077 Toulouse Cedex 04, France
Received June 20, 2004
A series of platinum metal silyl hydride complexes, cis-Pt(PCy3)2(H)(SiR2R′) (SiR2R′ )
SiPh2H, SiEt2H, SiPh3, SiEt3, SiMe2(OSiHMe2), Si(OSiMe3)2Me, SiMe2(CH2CHdCH2), SiMe2-
Et, SiMe2[OCH2C(Me)dCH2], Si(OMe)2(CH2CHdCH2), SiPh2(OSiPh2H)), have been prepared
in solution by reaction of Pt(PCy3)2 with the appropriate silane, HSiR2R′. The complex cis-
Pt(PCy3)2(H)(HSiPh2) (1-cis) has been characterized by X-ray crystallography at -100 °C.
The platinum center exhibits a distorted-square-planar geometry with angles P(1)-Pt-
P(2) ) 113.55(3)°, P(1)-Pt-Si ) 146.83(3)°, and P(2)-Pt-Si ) 99.37(3)°. The reaction of
Pt(PCy3)2 with chlorinated hydrosilanes at -78 °C yields the analogous complexes cis-Pt-
(PCy3)2(H)(SiR2R′) (SiR2R′ ) SiMe2Cl, SiMeCl2, SiCl3), which isomerize to their trans isomers
on warming to room temperature. The complex 1-cis and several analogues convert to the
trans isomers photochemically at room temperature. Ready silane exchange is demonstrated
by the reaction of HSiPh3 with cis-Pt(PCy3)2(D)(SiPh3) and by the reaction of H2SiPh2 with
cis-Pt(PCy3)2(H)(SiPh3). These experiments also revealed the relative thermodynamic stability
of some of the platinum silyl complexes, of which the most stable was cis-Pt(PCy3)2(H)-
(SiPh2H). NMR spectroscopy demonstrates that the inequivalent phosphine ligands of the
cis isomers undergo intramolecular mutual exchange on the NMR time scale. In competition
with this process, the complexes undergo reversible reductive elimination of silane. Analysis
of the NMR spectra yields the thermodynamic data for dissociation of silanes for SiR2R′ )
SiPh3, SiMe2Et. Rate constants for phosphine exchange were calculated via line-shape
1
analysis of H NMR spectra. Rate constants for reductive elimination of silane in cis-Pt-
(PCy3)2(H)(SiR2R′) (SiR2R′ ) SiPh2H, SiMe2Et, SiPh3) were calculated via 1H EXSY
measurements. The three distinct reaction pathways, photochemical cis-trans isomerization,
intramolecular thermal phosphine site exchange, and reductive elimination, are shown to
involve three distinct transition states. The transition states for the independent processes
of phosphine site exchange and for reductive elimination must retain substantial Pt-H and
Pt-Si interactions, while there is also significant Si-H bond formation. This situation can
therefore be described as involving Pt(η2-H-SiR3) interactions.
Introduction
containing this grouping are becoming increasingly
important. Metal η2-Si-H complexes are also thought
to be involved in the oxidative addition and reductive
elimination of Si-H bonds.2,5 Recent investigations of
the dynamics of metal η2-silane hydride complexes have
shown the importance of metal silyl dihydrogen isomers
in fluxional behavior.6 In this paper, we are concerned
with the oxidative addition of Si-H bonds at platinum
and the dynamics of the resulting complexes.
Silylmetal complexes are known for nearly all of the
transition metals1,2 and have been shown to play a key
role in many metal-catalyzed silylation reactions.3 The
oxidative addition of a Si-H bond to a coordinatively
unsaturated metal complex has proved to be a very
versatile method for their synthesis. Indeed, the activa-
tion of Si-H bonds is featured in the industrial pro-
cesses hydrosilylation, dehydrogenative silylation, and
polysilane production.4 The silyl ligand exerts a high
trans influence, which is manifested in NMR spectra
as well as in metal-ligand bond lengths. Silyl hydrides
may also bind in the η2-Si-H mode, and complexes
(4) (a) Reichl, J. A.; Berry, D. H. Adv. Organomet. Chem. 1999, 43,
197. (b) Gauvin, F.; Harrod, J. F.; Woo, H. G. Adv. Organomet. Chem.
1998, 42, 363. (c) Wright, M. E.; Cochran, B. B. Organometallics 1996,
15, 317. (d) Matsuda, I.; Fukuta, Y.; Tsuchihashi, T.; Nagashima, H.;
Itoh, K. Organometallics 1997, 16, 4327.
(5) (a) Delpech, F.; Sabo-Etienne, S.; Daran, J.-C.; Chaudret, B.;
Hussein, K.; Marsden, C. J.; Barthelat, J.-C. J. Am. Chem. Soc. 1999,
121, 6668. (b) Delpech, F.; Mansas, J.; Leuser, H.; Sabo-Etienne, S.;
Chaudret, B. Organometallics 2000, 19, 5750. (c) Lachaize, S.; Sabo-
Etienne, S.; Donnadieu, B.; Chaudret, B. Chem. Commun. 2003, 214.
(6) Atheaux, I.; Delpech, F.; Donnadieu, B.; Sabo-Etienne, S.;
Chaudret, B.; Hussein, K.; Barthelat, J.-C.; Braun, T.; Duckett, S. B.;
Perutz, R. N. Organometallics 2002, 21, 5347.
* To whom correspondence should be addressed. E-mail: rnp1@
york.ac.uk (R.N.P.).
† University of York.
‡ Laboratoire de Chimie de Coordination du CNRS.
(1) Corey, J. Y.; Braddock-Wilking, J. Chem. Rev. 1999, 99, 175.
(2) Schubert, U. Adv. Organomet. Chem. 1990, 30, 151.
(3) Speier, J. L. Adv. Organomet. Chem. 1979, 17, 407.
10.1021/om049549n CCC: $27.50 © 2004 American Chemical Society
Publication on Web 10/28/2004

Pt Bis(tricyclohexylphosphine) Silyl Hydrides
Organometallics, Vol. 23, No. 24, 2004 5745
Scheme 1. Preparation and Numbering of
In the late 70s Ebsworth et al. reacted trans-Pt-
(PCy3)2(H)2 with the series of silanes SiH4, SiH3Cl, and
Si2H6 to form the corresponding complexes trans-Pt-
(PCy3)2(H)(SiH2R) (R ) H, Cl, SiH3).7 Their studies
revealed a six-coordinate trihydride platinum(IV) spe-
cies of the type trans-Pt(PCy3)2(H)3(SiH2R) formed by
the oxidative addition of the silane to the trans-dihy-
dride platinum complex at -80 °C. When it was warmed
to room temperature, the trihydride platinum species
lost H2 to form trans-Pt(PCy3)2(H)(SiH2R).
cis-Pt(PCy3)2(H)(SiR2R′)
Trogler and co-workers examined the photochemical
reactions of complexes of Pt(C2O4)L2 and Pd(C2O4)L2
(L ) tertiary phosphine).8 Their observations point to
formation of highly reactive 14-electron ML2 species that
undergo oxidative addition reactions with organosilanes
to yield platinum(II) or palladium(II) derivatives. They
derived a photocatalyst for hydrosilation from this
system by supporting it on silica via the functional
ligand L ) (OMe)3Si(CH2)2PEt2.9 Complexes of the type
cis-Pt(PEt3)2(H)(SiR3) have also been made by silane
transfer from a rhodium complex.10
Ozawa and co-workers have proposed that Si-C bond
formation during hydrosilation can occur via both
reductive elimination and silyl migration in the same
system.11 They reported that cis-PtL2(Me)(SiPh3) com-
plexes (L ) PMePh2, PMe2Ph) readily afford MeSiPh3
in solution12,13 and studied the kinetics of MeSiPh3
formation in the presence of diphenylacetylene. They
also examined the thermolysis reaction of cis-Pt(PMe2-
Ph)2(R)(SiPh3) complexes in solution.14 The thermolysis
reactions were found to involve two additional pro-
cesses: reversible â-hydrogen elimination from the alkyl
ligand and isomerization of cis-Pt(PMe2Ph)2(R)(SiPh3)
to cis-Pt(PMe2Ph)2(Ph)(SiRPh2).
An early example of the observation of a mutual
phosphine exchange process was noted by Pidcock et al.
for cis-Pt(PPh3)2(H)(SiPh3).15 Their 1H NMR spectra
revealed behavior indicative of phosphine dissociation
rather than reversible addition-elimination of the
silane ligand. Clark and Hampden-Smith later found
that the analogous compound cis-Pt(PCy3)2(H)(SiPh3)16,17
undergoes both intramolecular phosphine interchange
and reversible addition-elimination of silane. They
proposed that a complex containing an η2-silane ligand
enabled mutual phosphine exchange to occur via rota-
tion about the Si-H bond.
yielding Pd(Cy2PCH2CH2PCy2)(SiR3)H, and have shown
that equilibria are established between the resulting
complexes in the presence of different silanes.18 They
have also shown that the phosphorus nuclei undergo
dynamic exchange and use a temperature-dependent
kinetic isotope effect as evidence to support a Pd(η2-
silane) intermediate in the fluxional process.
Our studies expand the earlier work of Clark and
Hampden-Smith into new silyl hydride complexes of the
form cis-Pt(PCy3)2(H)(SiR2R′). We examine the reactiv-
ity of Pt(PCy3)2 toward a variety of silanes and charac-
terize the products by extensive NMR studies. Compe-
tition experiments and deuterium labeling have been
employed to follow silane exchange at cis-Pt(PCy3)2(H)-
(SiPh3). These experiments also serve to demonstrate
the relative stability of different species of this class.
Several complexes of the type cis-Pt(PCy3)2(H)(SiR2R′)
undergo photochemical cis-trans isomerization, but
those with R or R′ ) Cl isomerize thermally. The
dynamic behavior of the complexes where SiR2R′ )
SiPh2H, SiPh3, SiMe2Et has been studied by line-shape
analysis and EXSY spectroscopy.19 Intramolecular phos-
phine site exchange competes with a second process
involving reductive elimination-oxidative addition of
silane that renders the phosphorus centers equivalent.
Results and Discussion
Preparation of cis-Pt(PCy3)2(H)(SiR2R′) Com-
plexes. The 14-electron complex20 Pt(PCy3)2 reacts with
a variety of silanes, HSiR2R′, to form Si-H bond
activation products, Pt(PCy3)2(H)(SiR2R′) (Scheme 1),
which can be isolated as white solids in moderate yields
(40-50%) in favorable cases. The characterization of the
most stable product in this series, cis-Pt(PCy3)2(H)-
(SiPh2H) (1-cis), is now discussed as the example that
includes crystallographic data. Tables 1 and 2 contain
essential NMR features for cis and trans products,
respectively.
Characterization of cis-Pt(PCy3)2(H)(SiPh2H) (1-
cis). Reaction of Pt(PCy3)2 with H2SiPh2 in hexane in
the absence of light yields a single white product that
was recrystallized from hexane/toluene at -30 °C. The
1H NMR spectrum of this product in [2H8]toluene
contains a hydride resonance at δ -3.1 (1H) that
Recently, Boyle et al. have described the oxidative
addition of tertiary silanes to [Pd(Cy2PCH2CH2PCy2)]2,
(7) Ebsworth, E. A. V.; Marganian, V. M.; Reed, F. J. S.; Gould, R.
O. J. Chem. Soc., Dalton Trans. 1978, 1167.
(8) Paonessa, R. S.; Prignano, A. L.; Trogler, W. C. Organometallics
1985, 4, 647.
(9) Prignano, A. L.; Trogler, W. C. J. Am. Chem. Soc. 1987, 109,
3586.
(10) Koizumi, T.; Osakada, K.; Yamamoto, T. Organometallics 1997,
16, 6014.
(11) Maruyama, Y.; Yamamura, K.; Nakayama, I.; Yoshiuchi, K.;
Ozawa, F. J. Am. Chem. Soc. 1998, 120, 1421.
(12) (a) Ozawa, F.; Hikida, T.; Hayashi, T. J. Am. Chem. Soc. 1994,
116, 2844. (b) Ozawa, F. J. Organomet. Chem. 2000, 611, 332.
(13) Ozawa, F.; Hikida, T.; Hasebe, K.; Mori, T. Organometallics
1998, 17, 1018.
(14) Hasebe, K.; Kamite, J.; Mori, T.; Katayama, H.; Ozawa, F.
Organometallics 2000, 19, 2022.
(15) Azizian, H.; Dixon, K. R.; Eaborn, C.; Pidcock, A.; Shuaib, N.
M.; Vinaixa, J. J. Chem. Soc., Chem. Commun. 1982, 1020.
(16) Clark, H. C.; Hampden-Smith, M. J. Coord. Chem. Rev. 1987,
79, 229.
(17) Clark, H. C.; Ferguson, G.; Hampden-Smith, M. J.; Ruegger,
H.; Ruhl, B. L. Can. J. Chem. 1988, 66, 3120.
(18) Boyle, R. C.; Mague, J. T.; Fink, M. J. J. Am. Chem. Soc. 2003,
125, 3228.
(19) Heise, J. D.; Raftery, D.; Breedlove, B. K.; Washington, J.;
Kubiak, C. P. Organometallics 1998, 17, 4461.
(20) Mann, B. E.; Musco, A. J. Chem. Soc., Dalton Trans. 1980, 776.

5746 Organometallics, Vol. 23, No. 24, 2004
Chan et al.
Table 1. 1H and 31P NMR Data (295 K) for the Complexes cis-Pt(PCy3)2(H)(SiR2R′) (1-cis-14-cis)
complex, T (K)
1H NMR hydride,c δ (J, Hz)
31P NMR,d δ (J, Hz)
Pt(PCy3)2(H)(SiPh2H) (1-cis),a 293
-3.1 (J(PH)cis ) 24.5, J(PH)trans ) 138.4,
J(PtH) ) 838)
38.5 (Pb), 46.2 (Pa) (J(PP) ) 11.6,
J(PtPb) ) 2632, J(PtPa) ) 1675)
42.8 (Pb), 50.8 (Pa) (J(PP) ) 11.6,
J(PtPb) ) 2687, J(PtPa) ) 1540)
42.9 (Pb), 43.1 (Pa) (J(PP) ) 12,
J(PtPb) ) 2721, J(PtPa) ) 1368)
42.2(Pb), 43.1 (Pa) (J(PP) ) 12,
J(PtPb) ) 2704, J(PtPa) ) 1387)
37.3(Pb), 41.1 (Pa) (J(PP) ) 13,
J(PtPb) ) 2642, J(PtPa) ) 1560)
41.6 (Pb), 42.8 (Pa) (J(PP) ) 12,
JH(PtP) ) 2677, J(PtPa) ) 1420)
43.4 (Pb), 43.1 (Pa) (J(PP) ) 15,
J(PtPb) ) 2612, J(PtPa) ) 1428)
43.0 (Pb), 43.2 (Pa) (J(PP) ) 13,
J(PtPb) ) 2656, J(PtPa) ) 1320)
46.9(Pb), 45.5 (Pa) (J(PP) ) 13,
J(PtPb) ) 2594, J(PtPa) ) 1280)
41.9 (Pb), 42.0 (Pa) (J(PP) ) 13,
J(PtPb) ) 2658, J(PtPa) ) 1369)
41.9 (Pb), 42.4 (Pa) (J(PP) ) 14,
J(PtPb) ) 2638, J(PtPa) ) 1408)
38.2 (Pb), 36.5 (Pa) (J(PP) ) 18,
J(PtPb) ) 2716, J(PtPa) ) 1520)
34.0 (Pb), 36.0 (Pa), (J(PP) ) 14,
J(PtPb) ) 2628, J(PtPa) ) 1800)
35.6 (Pb), 33.3 (Pa) (J(PP) ) 14,
J(PtPb) ) 2594, J(PtPa) ) 2055)
Pt(PCy3)2(H)(SiEt2H) (2-cis),a 293
-3.4 (J(PH)cis ) 25, J(PH)trans ) 142,
J(PtH) ) 873)
Pt(PCy3)2(H)(SiEt3) (3-cis),a 243
-3.6 (J(PH)cis ) 26, J(PH)trans ) 146,
J(PtH) ) 823)
Pt(PCy3)2(H)(SiMe2Et) (4-cis),a 250
Pt(PCy3)2(H)(SiPh3) (5-cis),a 250
-3.5 (J(PH)cis ) 26, J(PH)trans ) 141,
J(PtH) ) 858)
-4.0 (J(PH)cis ) 23, J(PH)trans ) 142,
J(PtH) ) 784)
Pt(PCy3)2(H){SiMe2CH2(CHdCH2)} (6-cis),a 250
Pt(PCy3)2(H)(SiPh2OSiPh2H) (7-cis),b 295
Pt(PCy3)(H)(SiMe2OSiHMe2) (8-cis),a 268
Pt(PCy3)2(H){SiMe(OSiMe3)2} (9-cis),a 225
-3.5 (J(PH)cis ) 26, J(PH)trans ) 141,
J(PtH) ) 853)
-4.0 (J(PH)cis ) 27, J(PH)trans ) 141,
J(PtH) ) 851)
-4.2 (J(PH)cis ) 27, J(PH)trans ) 141,
J(PtH) ) 912)
-3.8 (J(PH)cis ) 28, J(PH)trans ) 138,
J(PtH) ) 912)
Pt(PCy3)2(H)(SiMe2OCH2C(Me)dCH2) (10-cis),a
-4.2 (J(PH)cis ) 28, J(PH)trans ) 141,
J(PtH) ) 889)
240
Pt(PCy3)2(H)(SiOMe2CH2CHdCH2) (11-cis),b
295
-4.0 (J(PH)cis ) 28, J(PH)trans ) 142,
J(PtH) ) 883)
Pt(PCy3)2(H)(SiMe2Cl) (12-cis),b 295
-4.8 (J(PH)cis ) 24, J(PH)trans ) 136,
J(PtH) ) 957)
Pt(PCy3)2(H)(SiCl2Me) (13-cis),a 260
Pt(PCy3)2(H)(SiCl3) (14-cis),a 260
-4.5 (J(PH)cis ) 22, J(PH)trans ) 135,
J(PtH) ) 895)
-4.4 (J(PH)cis ) 19, J(PH)trans ) 133,
J(PtH) ) 826)
a In [2H8]toluene. b In C6D6. c All hydride signals appears as doublets of doublets, except those for 1-cis and 2-cis, which show additional
3.4 Hz couplings to the SiH proton. d See Schemes 1 and 2 for labels.
Table 2. 1H and 31P NMR Data for the Complexes trans-Pt(PCy3)2H(SiR2R′) (1-trans-14-trans)
complex
1H NMR hydride,c δ (J, Hz)
31P NMR, δ (J, Hz)
Pt(PCy3)2(H)(SiPh2H) (1-trans)a
Pt(PCy3)2(H)(SiEt2H) (2-trans)a
Pt(PCy3)2(H)(SiMe2Et) (4-trans)a
Pt(PCy3)2(H)(SiPh3) (5-trans)a
-1.3 (J(PH) ) 16, J(PtH) ) 666)
-1.3 (J(PH) ) 18, J(PtH) ) 616)
-2.9 (J(PH) ) 19, J(PtH) ) 552)
-3.0 (J(PH) ) 17, J(PtH) ) 584)
-2.6 (J(PH) ) 18, J(PtH) ) 561)
-3.9 (J(PH) ) 17, J(PtH) ) 646)
-4.5 (J(PH) ) 15, J(PtH) ) 628)
-5.5 (J(PH) ) 14, J(PtH) ) 695)
39.9 (J(PtP) ) 2657)
42.8 (J(PtP) ) 2714)
43.4 (J(PtP) ) 2772)
37.5 (J(PtP) ) 2656)
43.5 (J(PtP) ) 2747)
40.0 (J(PtP) ) 2677)
35.5 (J(PtP) ) 2627)
34.0 (J(PtP) ) 2560)
Pt(PCy3)2(H){SiMe2CH2(CHdCH2)} (6-trans)a
Pt(PCy3)2(H)(SiMe2Cl) (12-trans)b
Pt(PCy3)2(H)(SiCl2Me) (13-trans)a
Pt(PCy3)2(H)(SiCl3) (14-trans)a
a In [2H8]toluene. b In C6D6. c No hydride coupling to the SiH proton is visible in 1-trans and 2-trans; all hydride resonances, therefore,
appear as simple triplets.
appears as a doublet of doublets of doublets (ddd) with
195Pt satellites and another ddd feature at δ 5.4 (1H)
due to a new silyl hydride group. These two proton
resonances are linked by a 3.4 Hz coupling. The associ-
ated 31P{1H} NMR spectrum contains two mutually
coupled resonances, each with 195Pt satellites, at δ 38
and 46. It has been shown previously that the magni-
tude of a Pt-P coupling decreases as the trans influence
of the ligand trans to phosphine increases.21,22 In the
complex 1-cis, the values of J(PtP) are substantially
different, with the lower value being indicative of the
phosphorus center that is trans to silicon rather than
hydride, as is confirmed by 1H-31P HMQC experiments.
These data are consistent with a higher trans influence
Figure 1. 1H-29Si 2D-HMQC correlation spectrum of cis-
for the silyl group than for hydride.
The characterization of this complex was further
Pt(PCy3)2(H)(SiPh2H) (1-cis) with projections of the 2D
1
spectrum in the 29Si and H dimensions plotted along the
facilitated by a series of heteronuclear multiple quan-
horizontal (δ(1H)) and vertical (δ(29Si)) axes. The 1H
tum 1H-29Si (Figure 1) and 1H-195Pt correlation experi-
spectrum shows a triplet at δ -1.33 for trans-Pt(PCy3)2-
(H)(SiPh2H) and a triplet at δ -3.2 for trans-Pt(PCy3)2(H)2.
1
ments. In the H-29Si-HMQC experiment, active cou-
plings to 29Si enable us to produce a map that contains
passive H-31P and H-195Pt couplings. In this way, the
1H-29Si correlation locates a 29Si signal at δ 3.4 with
(21) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev.
1973, 10, 335.
195Pt satellites, which connects to both the Si-H and
(22) Hartley, F. R. Chemistry of Platinum and Palladium; Applied
Science: London, 1973.
Pt-H signals with additional couplings to phosphorus.

Pt Bis(tricyclohexylphosphine) Silyl Hydrides
Organometallics, Vol. 23, No. 24, 2004 5747
Table 3. NMR Data for 1-cis (δ; J, Hz)a
in the Cambridge Structural Database.23 The P(1)-Pt-
P(2) angle is 113.55(3)°, while the P(1)-Pt-Si and P(2)-
Pt-Si angles are 146.83(3) and 99.37(3)°. Thus, the
angles at platinum are far from the ideal 90° of a
square-planar arrangement. The platinum atom lies
0.0619 Å from the P(1)P(2)Si plane. The length of the
Pt-P bond approximately trans to silicon (Pt-P(1) )
2.3493(8) Å) is greater than the Pt-P bond approxi-
mately cis to silicon (Pt-P(2) ) 2.3127(8) Å). There are
two published structures of complexes with the same
coordination set at platinum: cis-Pt(PEt3)2(H)(SiPh3)
and cis-Pt(PPh3)2(H)(SiPh3). In both cases, the P(1)-
Pt-P(2) angles (107.2(1) and 108.05(9)°, respectively)
and the P-Pt-Si angles are smaller than ours.10,24 The
P(1)-Pt-P(2) angle is slightly larger in our complex
than in the ruthenium(II) complexes containing cis PCy3
groups, Ru(PCy3)2(H)2{[η2-HSiMe2]2X}, where it is typi-
cally 108-109°.5
X
Pt
Si
Ha
Hb
Pa
Pb
δ
-5370
3.43
1206
-3.09
838
10
5.37
15
164
3.4
46.2
1675
154
24.5
17.6
38.5
2632
12.4
138
7.3
11.6
JX-Pt
JX-Si
JX-H
JX-H
JX-P
a
b
a
a See Scheme 1 for labels. Ha is the hydride bound to Pt, and
Hb is bound to Si.
ReactionofPt(PCy3)2 withOtherSilanesHSiR2R′.
The reactions of Pt(PCy3)2 with the silanes H2SiEt2,
HSiEt3, HSiMe2Et, HSiPh3, HSiMe2(CH2CHdCH2),
HMe2SiOSiMe2H, HSiPh2OSiPh2H, HSiMe(OSiMe3)2,
HSiMe2OCH2C(Me)dCH2, and HSi(OMe)2CH2CHdCH2
were followed by NMR spectroscopy in a similar way.
Samples were prepared at -78 °C as described in the
Experimental Section. The corresponding low-temper-
Figure 2. Crystal structure (ORTEP digram) of cis-Pt-
(PCy3)2(H)(SiPh2H) (1). Hydrogen atoms bonded to carbon
are not shown. Ellipsoids are at the 50% level.
1
ature H NMR spectra of the products formed in these
Table 4. Selected Bond Lengths (Å) and Angles
reactions (2-cis-11-cis, Scheme 1) contain hydride
resonances that appear as undistorted doublets of
doublets, indicative of a cis ligand arrangement with
195Pt satellites at -25 °C (Table 1). The products of these
reactions, cis-Pt(PCy3)2(H)(SiR2R′), are highly fluxional,
as described later, and many contain relatively labile
silanes. Consequently, only the complexes formed from
H2SiPh2 and HSiPh3 have been isolated in analytically
pure form.
(deg) for cis-Pt(PCy3)2H(SiPh2H) (1-cis)
Bond Lengths
Pt-P(1)
Pt-P(2)
Pt-Si
2.3493(8)
2.3127(8)
2.3311(9)
Pt-H(1)
1.44(3)
1.42(3)
Si-H(1SI)
Bond Angles
146.83(3)
99.37(3)
Si-Pt-P(1)
Si-Pt-P(2)
P(1)-Pt-P(2)
113.55(3)
Reactions with Hydrochlorosilanes. We have also
explored the reactivity of Pt(PCy3)2 toward the hydro-
chlorosilanes HSiMe2Cl, HSiMeCl2, and HSiCl3. When
these reactions are carried out at -78 °C, the cis
complexes 12-cis, 13-cis, and 14-cis were formed
together with minor amounts of trans-Pt(PCy3)2(H)(Cl).
Comparison of the platinum-phosphorus coupling con-
A
1H-195Pt NMR spectrum revealed the platinum
chemical shift and passive hydride-29Si coupling. The
NMR data are fully consistent with the structure cis-
Pt(PCy3)2(H)(SiPh2H) (1-cis). A complete set of chemical
shifts and couplings for Pt, Si, P, and the two hydridic
protons is given in Table 3.
1
The value J(SiH) ) 164 Hz for the directly bonded
SiH group contrasts with the value 2J(SiH) ) 10 Hz for
the HPtSi linkage, providing a very clear distinction
between the bonding interactions of silicon to these two
hydridic protons. Furthermore, we tested for magneti-
zation transfer between these two protons in an EXSY
experiment and found no evidence of exchange at room
temperature. These data allow us to exclude an η2-silane
moiety in the ground state, since we would expect to
find intermediate values of J(SiH).1,5 The complex 1-cis
is fluxional above room temperature: its dynamic
behavior is described below.
X-ray Structure Determination of cis-Pt(PCy3)2-
(H)(SiPh2H) (1-cis). Crystals of cis-Pt(PCy3)2(H)-
(SiPh2H)‚1.5(toluene) suitable for X-ray analysis were
grown from a hexane/toluene solution at -20 °C. The
structure determined at -100 °C (see Table 4 and
Figure 2) reveals that the PtSiP2 unit is close to planar
with cis phosphine ligands. The platinum hydride and
the silicon hydride were located via a difference map.
The Pt-H distance of 1.44(3) Å is somewhat short,
corresponding to the 14th percentile of Pt-H distances
stants for the series of complexes cis-Pt(PCy3)2(SiMe3-x
-
Clx)H (x ) 1-3) reveals that J(PtPa), where Pa lies trans
to silicon, grows linearly with x.25 When they were
warmed to 20 °C, the complexes rearranged to their
trans counterparts 12-trans, 13-trans, and 14-trans
(Scheme 2). NMR data for cis and trans complexes are
presented in Tables 1 and 2, respectively.
Photochemical Reactions of cis-Pt(PCy3)2(H)-
(SiR2R′). Clark et al. found that the complex cis-Pt-
(PCy3)2(H)(SiPh3) (5-cis) undergoes quantitative cis-
trans isomerization when irradiated by a weak UV
source to yield trans-Pt(PCy3)2(H)(SiPh3).17 In our stud-
ies, we have found that the complexes cis-Pt(PCy3)2(H)-
(23) Cambridge Structural Database; Allen, F. H. Acta Crystallogr.
2002, B58, 380.
(24) Latif, L. A.; Eaborn, C.; Pidcock, A. P.; Weng, N. S. J.
Organomet. Chem. 1994, 474, 217.
(25) (a) Lemke, F. R.; Chaitheerapapkul, C. Polyhedron 1996, 15,
2559. (b) Lemke, F. R.; Galat, K. J.; Wiley, J. Y. Organometallics 1999,
18, 1419. (c) Freeman, S. T. N.; Lofton, L. L.; Lemke, F. R. Organo-
metallics 2002, 21, 4776. (d) Freeman, S. T. N.; Petersen, J. L.; Lemke,
F. R. Organometallics 2004, 23, 1153.

5748 Organometallics, Vol. 23, No. 24, 2004
Chan et al.
Scheme 2. Reaction of Pt(Cy3)2 with
Hydrochlorosilanes
Scheme 3. Photochemical Isomerization of
Pt(PCy3)2(SiR2R′)H
Figure 3. 1H NMR spectra (300.13 MHz) in [2H8]toluene:
(a) cis-Pt(PCy3)2(H)(SiPh3) (5-cis) at 273 K; (b) 5-cis and
H2SiPh2 at 273 K (×× denotes Pt satellites); (c) 5-cis and
H2SiPh2 at 293 K.
spectroscopy. Addition of 1 equiv of either H2SiPh2 or
H2SiEt2 to 5-cis-D resulted in the immediate formation
of undeuterated 1-cis or 2-cis, respectively. Further
evidence of exchange was obtained by addition of
HSiPh3 to a sample of cis-Pt(PCy3)2(D)(SiPh3) (5-cis-
D). These exchange experiments may be compared with
the exchange of hydrosilanes with trans-Pt(PEt3)2-
(SiMe3)X (X ) Br, I).26
Thermal Decomposition of 1-cis. An NMR tube
containing 1-cis and its trans isomer 1-trans in [2H8]-
toluene was prepared in order to follow their thermal
decomposition. The complexes are stable at 295 K, but
20% of both are converted to trans-Pt(PCy3)2H2 after 1
h at 343 K. At higher temperatures, the dihydride
complex rapidly became the major product (δH ) -3.2,
J(PH) ) 17.6, J(PtH) ) 793 Hz; δP 53.5, J(PtP) ) 2872
Hz; δPt ) -5481). The silicon products were not identi-
fied. The same dihydride was observed on decomposition
of other silyl hydride complexes, as is illustrated for the
complex 2-cis (Figure 4). Thermal decomposition of
5-cis-D yielded trans-Pt(PCy3)2D2 (31P δ 51.5 with
J(PtP) ) 2872 Hz).
Dynamic Behavior of cis-Pt(PCy3)2(H)(SiR2R′).
We have already alluded to the observation that the
shapes of the hydride resonances for complexes 1-cis-
11-cis are temperature dependent. This effect is ob-
served for 1-cis, 7-cis, 8-cis, 9-cis, and 11-cis above
room temperature but is readily discernible for the
others at lower temperatures. It manifests itself in the
gradual decrease in intensity of the outer lines of the
hydride pattern as the temperature increases, while the
inner lines remain sharp with constant separation, as
shown for 5-cis in Figure 5. The observation that only
the outer lines collapse indicates that the phosphine
ligands undergo mutual exchange while retaining P-H
spin correlation; i.e., the mechanism of the underlying
phosphorus exchange is intramolecular (eq 2).27 More-
over, the appearance of such spectra depends on the
(SiR2R′) (1-cis, 2-cis, 4-cis, 5-cis, and 6-cis) also
undergo quantitative cis-trans isomerization when
photolyzed with UV light at room temperature to form
trans-Pt(PCy3)2(H)(SiR2R′) (1-trans-6-trans) (Scheme
3). For example, the hydride of trans-Pt(PCy3)2(H)-
(SiPh2H) is characterized by a triplet with Pt satellites
in the 1H NMR spectrum (δ -1.33, J(PH) ) 16, J(PtH)
) 666 Hz). The 31P NMR spectrum shows a singlet at
δ 39.9 (J(PtP) ) 2657 Hz). The 29Si spectrum exhibits
a triplet at δ 0.26 (J(SiP) ) 9.7 Hz), while the 195Pt
chemical shift is δ -5359 (see the Experimental Sec-
tion). When the complex 1-cis was prepared in the
absence of light, only the cis isomer was observed, but
without such precautions some trans isomer was de-
tected. No attempt was made to isolate the trans
complexes. Table 2 summarizes NMR data for trans-
Pt(PCy3)2(H)(SiR2R′).
Competition Reaction between cis-Pt(PCy3)2(H)-
(SiPh2H) (1-cis) and cis-Pt(PCy3)2(H)(SiPh3) (5-cis).
To explore the relative stabilities of 1-cis and 5-cis, a
sample of 5-cis was prepared in [2H8]toluene and 1
equiv of H2SiPh2 added at low temperature. The corre-
1
sponding H and 31P{1H} NMR spectra, recorded im-
mediately at 273 K, revealed that complete silane
exchange had occurred (Figure 3a,b). There was no
further change on warming to room temperature (Figure
3c). We can therefore conclude that {1-cis + HSiPh3}
is far more stable than {5-cis + H2SiPh2} (eq 1). Similar
results were obtained when H2SiEt2 was added to
5-cis: thus, {2-cis + HSiPh3} proved more stable than
{5-cis + H2SiEt2}.
Deuterium labeling has also been used to learn about
the reactivity of these systems.5 When DSiPh3 was
added to Pt(PCy3)2, cis-Pt(PCy3)2(D)(SiPh3) (5-cis-D)
was formed in quantitative yield, as shown by NMR

Pt Bis(tricyclohexylphosphine) Silyl Hydrides
Organometallics, Vol. 23, No. 24, 2004 5749
Figure 4. 1H NMR spectra (300.13 MHz) showing effect
of heating cis-Pt(PCy3)2(H)(SiEt2H) (2-cis) in [2H6]benzene
(t denotes trans-Pt(PCy3)2H2).
Figure 5. 1H NMR spectra (500.13 MHz) of the hydride
region of the spectrum of cis-Pt(PCy3)2(H)(SiPh3) (5-cis) in
[2H8]toluene.
relative signs of the phosphorus hydride couplings, with
the broadening of the outer lines indicating that
2
2J(PH)trans and J(PH)cis have opposite signs. When it
tween cis-Pt(PCy3)2(H)(SiR3) and free silane (eq 4), or
a combination of the two.
is the inner lines that broaden selectively, the signs are
the same. The separation of the inner lines is given by
Variable-temperature 31P NMR spectra are consistent
with 1H NMR data for phosphine exchange; for instance,
the spectrum of 6-cis is at the low-temperature limit
at 250 K but each of the resonances and their satellites
broadens up to ca. 290 K. At higher temperature the
two 31P resonances coalesce, so that the room-temper-
ature spectrum is very broad indeed. In the correspond-
ing 31P EXSY measurements, cross-peaks connected
phosphorus centers within specific platinum isoto-
pomers, confirming the intramolecularity of phosphorus
site exchange.
2
2
{| J(PH)trans| - | J(PH)cis|}.28
At higher temperatures, more general broadening
occurs but no central resonance develops. This behavior
can be readily understood if a second dynamic process
competes with the intramolecular phosphine exchange.
This second process must be intermolecular and re-
quires the loss of P-H coupling. It is consistent with
dissociative exchange between cis-Pt(PCy3)2(H)(SiR3)
and free phosphine (eq 3), dissociative exchange be-
The processes in eqs 3 and 4 involve the disruption
of the spin-spin coupling between the phosphorus
(26) Yamashita, H.; Tanaka, M.; Goto, M. Organometallics 1997,
16, 4696.
(27) Jesson, J. P.; Muetterties, E. L. In Dynamic Nuclear Magnetic
Resonance Spectroscopy; Jackman, L. M., Cotton, F. A., Eds.; Academic
Press: New York, 1975; p 279.
(28) Stahl, S. S.; Labinger, J. A.; Bercaw, J. E. Inorg. Chem. 1998,
37, 2422.

5750 Organometallics, Vol. 23, No. 24, 2004
Chan et al.
Table 5. Thermodynamic Parameters for the
Reductive Elimination of HSiR2R′ from
cis-Pt(PCy3)2(H)(SiR2R′) in [2H8]Toluenea
∆H°, kJ
∆S°, J
∆G°300,
complex
mol-1
K-1 mol-1
kJ mol-1
cis-Pt(PCy3)2(H)(SiMe2Et) (4-cis) 32 ( 2
cis-Pt(PCy3)2(H)(SiPh3) (5-cis) 64 ( 9
117 ( 8
207 ( 30
-2.9 ( 0.4
1.9 ( 0.2
a Error bars as 95% probability on least-squares fit.
atoms and the hydride. Clark and Hampden-Smith have
suggested that silane reductive elimination occurs as
in eq 4.16 We report several pieces of evidence to support
this conclusion. When 6-cis is dissolved in C6D6, at 295
K, detectable amounts of free silane and Pt(PCy3)2 are
observed by 1H and 31P{1H} NMR spectroscopy, al-
though no free phosphine is detected. When an NMR
sample of 6-cis was prepared at low temperature in
[2H8]toluene and 31P{1H} NMR spectra were subse-
quently measured at 250 K, only signals due to 6-cis
were observed. However, when the sample was warmed
to 290 K a signal corresponding to Pt(PCy3)2 was
detected. The establishment of a similar equilibrium
process was demonstrated for the complex 5-cis: free
silane is detected at 315 K but is absent at 280 K. In
none of these experiments was free phosphine evident,
nor was trans-Pt(PCy3)2(SiR2R′)H formed. Furthermore,
the competition and H/D exchange experiments can be
explained by rapid reductive elimination of HSiPh3 or
H2SiEt2. Evidence for silane exchange was also revealed
by spin saturation transfer methods.29 When the hy-
dride resonance was irradiated selectively, the intensity
of the 1H Si-H resonance of free silane decreased
markedly. These effects appeared to be independent of
the concentration of silane, thus excluding a mechanism
involving a Pt(IV) complex.
Figure 6. van’t Hoff plots for (a) cis-Pt(PCy3)2(H)(SiMe2-
Et) (4-cis) and (b) cis-Pt(PCy3)2(H)(SiPh3) (5-cis).
Scheme 4. Dynamic Exchange Processes of
Thermodynamic Parameters for the Free Silane
Exchange Process in 1-cis, 5-cis, and 4-cis. Three
complexes were chosen for detailed examination of
kinetics and dissociation behavior: 1-cis, 5-cis, and
4-cis. Of these, 5-cis and 4-cis exhibited equilibrium
dissociation of silane (eq 4), while 1-cis was too inert
to attain equilibrium at temperatures below the decom-
position point. The relative concentrations of cis-Pt-
(PCy3)2(H)(SiR2R′), HSiR2R′, and Pt(PCy3)2 for 5-cis and
cis-Pt(PCy3)2(H)(SiR2R′)
1
4-cis were measured by quantitative H and 31P{1H}
NMR spectroscopy, and the equilibrium constant Kd was
obtained (eq 5). The temperature dependence of the
[Pt(PCy3)2][HSiR2R′]
simulated with DNMR-SIM30 or g-NMR31 up to those
temperatures where the intermolecular exchange rate
was significant compared to the intramolecular ex-
change; i.e., the inner lines remained sharp but the
outer lines broadened. The programs were inappropriate
at higher temperatures, since they could not simulate
simultaneous intra- and intermolecular processes quan-
titatively. These simulations yielded k3 for complexes
1-cis, 4-cis, and 5-cis.
Kd )
(5)
[cis-Pt(PCy3)2(H)(SiR2R′)]
values of Kd (see the Supporting Information) was used
to determine ∆H° and ∆S° for the dissociation (Table
5, Figure 6). The values of ∆H° and ∆S° for 5-cis are
both much larger than for complex 4-cis, but the
difference in ∆G°300 is slight.
Kinetics and Activation Parameters for the
Dynamic Processes of cis-Pt(PCy3)2(H)(SiR2R′).
Scheme 4 illustrates the exchange processes that occur
in 1-cis-7-cis. The temperature-dependent line shape
of the 1H NMR spectra of cis-Pt(PCy3)2(H)(SiR2R′) were
1
In addition to line-shape analysis, we employed H
and 31P EXSY spectroscopy to measure rate constants.32
(30) Ha¨gele, G.; Fuhler, R. DNMR-SIM, Simulation for Dynamic
NMR Spectra V1.00; Heinrich-Heine University of Du¨sseldorf, Du¨s-
seldorf, Germany, 1994.
(31) Budzelaar, P. H. M. g-NMR, version 4; Cherwell Scientific
Publishing Limited, Oxford, U.K., 1995-1997.
(32) Meier, B. H.; Ernst, R. R. J. Am. Chem. Soc. 1979, 101, 6441.
(29) Faller, J. W. In The Determination of Organic Structures by
Physical Methods; Nachod, F. C., Zuckerman, J. J., Eds.; Academic
Press: New York, 1973; Vol. 5, Chapter 2.

Pt Bis(tricyclohexylphosphine) Silyl Hydrides
Organometallics, Vol. 23, No. 24, 2004 5751
Table 6. Activation Parameters for the Complexes 1-cis, 5-cis, and 4-cis in [2H8]Toluenea
complex
rate processb
∆Hq, kJ mol-1
∆Sq, J K-1 mol-1
∆Gq300, kJ mol-1
cis-Pt(PCy3)2(SiPh2H)H (1-cis)
k1, s-1
87 ( 5
c
24 ( 15
c
80.1 ( 0.4
c
k2, dm3 mol-1 s-1
k3, s-1 EXSY
k3, s-1 (line shape)
k1, s-1
87 ( 3
90 ( 8
62 ( 4
31 ( 4
52 ( 3
77 ( 5
13 ( 5
60 ( 5
50 ( 10
53 ( 26
12 ( 15
-104 ( 15
-19 ( 11
34.7 ( 19
-173 ( 19
-16 ( 16
72.3 ( 0.1
74.1 ( 0.7
58.6 ( 0.7
61.3 ( 0.8
57.4 ( 0.6
66.4 ( 0.4
64.5 ( 0.3
64.5 ( 0.2
cis-Pt(PCy3)2(SiMe2Et)H (4-cis)
cis-Pt(PCy3)2(SiPh3)H (5-cis)
k2, dm3 mol-1 s-1
k3, s-1
k1, s-1
k2, dm3 mol-1 s-1
k3, s-1
a Error bars quoted as 95% probability on least-squares fit. b k1 from EXSY, k2 from combination of k1 and Kd, k3 from line-shape
analysis and from EXSY for 1-cis. c Not determined.
Figure 7. Eyring plots of k1 (b) and k3 ([, line-shape
analysis; 9, EXSY) for cis-Pt(PCy3)2(H)(SiPh2H) 1-cis.
Figure 8. Eyring plots of k1 (b), k2 (2), and k3 (9) for cis-
Pt(PCy3)2(H)(SiMe2Et) (4-cis).
For EXSY measurements, samples were made up con-
taining a 12-14-fold excess of silane, so that the rate
of oxidative addition was high compared to the rate of
reductive elimination. This concentration also ensures
that any silane released has a low probability of
recombining with the same molecule it came from. The
transfer of magnetization was examined from hydride
to free silane by 1H EXSY spectroscopy over the follow-
ing temperature ranges: 310-340 K for 1-cis, 270-312
K for 5-cis, and 242-265 K for 4-cis. The results were
analyzed to yield k1 by numerical solution of the
differential equations with the aid of a version of
EXCEL adapted for kinetic simulation. The values of
the rate constant for oxidative addition, k2, were calcu-
lated by employing the values of k1 and Kd, and k2 )
k1/Kd. Eyring plots of ln(k/T) vs T-1 yielded activation
parameters ∆Hq, ∆Sq, and ∆Gq (Figures 7-9, Table
300
6).
We also used the EXSY experiments to examine the
possibility of exchange between the SiH and PtH
protons of 1-cis. No such exchange was detected in the
presence of a large excess of silane, but some magneti-
zation transfer was observed when the silane concentra-
tion was reduced to ca. 5-10 times the concentration
of 1-cis. The rate of this exchange is so low that it can
be explained entirely by reductive elimination and
recombination of the same molecule of silane.
Figure 9. Eyring plots of k1 (b), k2 (2), and k3 (9) for cis-
Pt(PCy3)2(H)(SiPh3) (5-cis).
an uncoupled system of spins A and B with equal
populations and equal spin-lattice relaxation times,
T1A ) T1B ) T1, the rate of phosphorus exchange, kobsd
/
s-1, may be determined for a mixing time τm using eq
6, where I ) (IAA + IBB)/(IAB + IBA) compares the
1
I + 1
k )
ln
τm I - 1
(6)
Rate constants for mutual phosphine exchange (k3)
for 1-cis were also calculated by 31P EXSY methods. The
2D-EXSY spectra were recorded as a function of mixing
time in order to determine the rate for the exchange
process in d8-toluene for 1-cis from 297 to 313 K. For
volumes of the diagonal peaks and cross-peaks.30,31,33,34
In this analysis, the forward and reverse rate constants
are averaged.

5752 Organometallics, Vol. 23, No. 24, 2004
Chan et al.
These experiments yielded the rate constant, kobsd, for
magnetization leaving a phosphorus site. Since magne-
tization can be transferred both directly by mutual
phosphine exchange and indirectly by silane reductive
elimination-oxidative addition, both k3 and k1 contrib-
ute to the value of kobsd. When a silane undergoes
reductive elimination, it may recombine with the same
nuclear configuration of the phosphines (Pa and Pb
retain their identity) or the opposite (Pa and Pb re-
versed). The contribution to kobsd from silane elimination
does not require the same molecule of silane to add as
eliminate. Because we use excess silane, addition of
silane is fast compared to reductive elimination and
there is no contribution from k2 to the rate expression.
As a result of the equal probability of addition in the
two configurations, kobsd is related to k3 and k1 by kobsd
) k3 + 1/2k1. The value of k3 is derived accordingly, and
the activation parameters were obtained from the
Eyring plot (Table 6). The values of the activation
parameters obtained by EXSY spectroscopy are better
determined than those obtained by line-shape analysis.
The activation parameters determined by the two
methods overlap when 95% confidence limits are in-
cluded, although there are differences in the absolute
rate constants.
The effect of steric strain is apparent in the lower
stability of {R2SiH2 + cis-Pt(PCy3)2(SiPh3)H} as com-
pared to the {Ph3SiH + cis-Pt(PCy3)2(SiR2H)H} (R )
Ph, Et) complex.
The more sterically strained complexes are at equi-
librium with Pt(PCy3)2 and free silane. We can use the
experimental value of ∆H° and the bond enthalpy of the
Si-H bond to estimate the sum of the Pt-Si and Pt-H
bond enthalpies (assuming that the reorganization
energy of Pt(PCy3)2 is negligible). Taking the Si-H bond
enthalpy of Me2EtSi-H as 396 kJ mol-1 (the published
value for Me3Si-H) and that of Ph3Si-H as 371 kJ
mol-1 36
the sums of the Pt-Si and Pt-H bond enthal-
,
pies are 428 and 435 kJ mol-1 for 4-cis and 5-cis,
respectively. If the Pt-H bond enthalpy is constant, it
follows that the Pt-SiPh3 bond is stronger than the Pt-
SiMe2Et bond.
Mechanisms of Reductive Elimination and Phos-
phine Site Exchange. The evidence for the reductive
elimination of silane is compelling: line broadening,
EXSY experiments, silane exchange, and isotope label-
ing all point in the same direction. The values obtained
for ∆Hq show that the barrier to reductive elimination
increases in the order SiMe2Et < SiPh3< SiPh2H. These
values may be compared to those for ∆H° for the first
two substituents of 32 and 64 kJ mol-1. The values of
∆Gq follow the same pattern as the values of ∆Hq. The
enthalpy barrier, ∆Hq, to silane reductive elimination
is higher than the standard enthalpy of reductive
elimination, ∆H°. The values of ∆Sq are very small for
a dissociative reaction, implying that dissociation is far
from complete. Thus, the transition states for the
reductive elimination process appear to be early and the
Si-H bond formation must be incomplete in the transi-
tion state to account for the values of ∆Hq.
Discussion
Energetics and the Structure of cis-Pt(PCy3)2-
(SiR2R′)H. The products of reaction of Pt(PCy3)2 with
hydrosilanes are cis platinum silyl hydride complexes
for all silanes reported in this paper. Only with a
chlorinated silyl group have we observed thermal cis to
trans isomerization. For these complexes, we can be sure
that the trans complex is thermodynamically more
stable than the cis complex for SiMe2Cl, SiMeCl2, and
SiCl3 substituents. For the remaining complexes, we
observe the cis isomer as the kinetic product and
heating leads to silane exchange and decomposition but
not isomerization. The cis isomer can be converted to
the trans isomer photochemically in each case that we
have attempted. Thus, the trans isomers are also
kinetically stable, but we cannot be sure that they are
thermodynamically more stable than the cis isomers.
For comparison, it is worth noting that cis-Pt(PEt3)2-
(H)(SiPh3) appears to be more stable than its trans
analogue.35
An examination of the crystal structure of cis-Pt-
(PCy3)2(H)(SiPh2H) shows that the angles at platinum
are far from ideal. The angles between the cis ligands
are 99.4 and 113.5°, while the nominally “trans” ligands
lie at 146.9° to one another. This arrangement must
relieve the majority of the steric strain, and it is likely
that the trans isomer is only favored strongly with a
sterically undemanding silyl group. A cis arrangement
of PCy3 groups has also proved stable for Ru(PCy3)2-
(H)2{[η2-HSiMe2]2X}.5
The phosphine site exchange process, k3, is demon-
strated to be intramolecular by the selectivity of the line
broadening. The barriers to phosphine site exchange
follow the same order as for k1: SiMe2Et < SiPh3<
SiPh2H.
When we include the photoisomerization, our experi-
ments point to the existence of two distinct transition
states for isomerization and one for reductive elimina-
tion. (A) The transition state for photoisomerization
leads to the trans isomer. It is likely that this TS is
pseudo-tetrahedral, as has been postulated for other
photoisomerization reactions at platinum(II).37 (B) The
transition state for phosphine site exchange does not
lead to the trans complex, although the latter is kineti-
cally stable. It must therefore have an alternative
geometry, and it is most reasonable to postulate that
this is an η2-silane complex. Our magnetization transfer
experiments indicate that exchange between Si-H and
Pt-H in 1-cis proceeds more slowly than phosphine site
exchange. Thus, there cannot be any positional ex-
change of SiH groups in a putative Pt(PCy3)2(η2-H-
SiHPh2) transition state. (C) The third transition state
is distinct from the other two and leads to silane
Our experiments also give information about the
relative stability of complexes with different silyl groups.
(36) (a) Kalinowski, I. J.; Gutman, D.; Krasnoperov, L. N.; Goumri,
A.; Yuan, W.-J.; Marshall, P. J. Phys. Chem. 1994, 98, 9551. (b)
Becerra, R.; Walsh, R. In The Chemistry of Organic Silicon Compounds;
Rappoport, Z., Apeloig, Y., Eds.; Wiley: New York, 1998; Vol. 2,
Chapter 4, p 153.
(37) Ford, P. C.; Hintze, R. E.; Petersen, J. D. In Concepts of
Inorganic Photochemistry; Adamson, A. W., Fleischauer, P. D., Eds.;
Wiley: New York, 1975; Chapter 5, p 203.
(33) Perrin, C. L.; Dwyer, J. Chem. Rev. 1990, 90, 935.
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(35) Koizumi, T.; Osakada, K.; Yamamoto, T. Organometallics 1997,
16, 6014.

Pt Bis(tricyclohexylphosphine) Silyl Hydrides
Organometallics, Vol. 23, No. 24, 2004 5753
reductive elimination. If this is also described as an η2-
silane complex, its geometry must be distinct from the
transition state for phosphine site exchange.
isomerization. The standard enthalpy of reductive elimi-
nation has been determined as 32 ( 2 and 64 ( 9 kJ
mol-1 for SiMe2Et and SiPh3 substituents, respectively.
Furthermore, the SiPh2H and SiEt2H complexes have
been shown to be energetically more stable than the
SiPh3 complex. Reversible thermal reductive elimination
of hydrosilane and intramolecular phosphine site ex-
change result in complex NMR dynamics. The barriers
to reaction have been determined independently for
these two processes: 1H EXSY methods were employed
for the former, while 1H line-shape analysis and 31P
EXSY spectroscopy allowed determination of the latter.
The barriers show substantial variation with substitu-
ents at silicon increasing in the order SiMe2Et < SiPh3<
SiPh2H. The transition states for phosphine site ex-
change and reductive elimination of silane may both
involve η2-silane coordination but must be distinct. A
third transition state, probably of tetrahedral geometry,
is implicated in the photoisomerization.
The transition state for mutual phosphine exchange
could, in principle, involve a tetrahedral twist rather
than an η2-SiHR2R′ complex. A twisted structure has
been observed in the bis(silyl) complex Pt(PMe2Ph)2-
(SiPh2Me)2; consequently, this complex exhibits a low
barrier to ligand exchange via a twisting mechanism.38
However, we exclude this mechanism for 1-cis and
related complexes, since 1-cis exhibits almost planar
coordination of platinum in the crystal structure. More-
over, a twisting motion may also be expected to yield a
trans product for such a hindered complex.
Sakaki et al. have shown by theoretical treatments
of oxidative addition of Si-H bonds to Pt(PH3)2 that
these reactions proceed via an η2-SiHR3 (R ) H, Cl, Me)
transition state with a minimal activation energy (<13
kJ mol-1). It is also significant that the precursor
complex Pt(PH3)2(η2-SiHR3) was bound by only 9 kJ
mol-1 with respect to the reactants.39 These calculations
might be regarded as models for transition state C, and
they would suggest that ∆H° and ∆Hq should be close
to one another, which is not in accord with the experi-
mental data.
Experimental Section
General Methods. All syntheses and manipulations were
carried out under argon using standard Schlenk (vacuum 10-2
mbar) and high-vacuum techniques (10-4 mbar) or in an argon-
filled glovebox. Toluene, benzene, hexane, and tetrahydrofuran
(Fison AR or HPLC grade) were dried over sodium/benzophe-
none and distilled under argon. Ethanol (Fison AR grade) was
dried over magnesium metal turnings and iodine and distilled
under argon. The dried solvents were stored under argon in
ampules fitted with a Young ptfe tap. All deuterated solvents,
[2H6]benzene, and [2H8]toluene (Goss Scientific), were dried
over potassium and vacuum-distilled prior to use. All NMR
tubes (Wilmad 528-PP) were either fitted with a Young tap to
allow sealing under argon atmosphere or were flame-sealed
under vacuum. Mass spectra were measured in a VG Autospec
mass spectrometer and are quoted for 196Pt, and infrared
spectra were recorded on a Mattson RS FTIR spectrometer.
Chemicals were obtained from the following sources. Tri-
cyclohexylphosphine, triisopropylphosphine, 1-hexene, molec-
ular sieves, potassium, styrene, and the following silanes were
obtained from Aldrich: HSiEt3, H2SiPh2, H2SiEt2, and HSiMe2-
Et. The following silanes came from Gelest: Me3SiOSiHCH3-
OSiMe3, Me2SiHOSiHMe2, Me2HSiCl, MeHSiCl2, (CH2d
CHSiMe2)2O, HSiMe2CH2CHdCH2, and HSi(OMe)CH2CHd
CH2. Me3SiO(SiMeH)OSiMe3 was a gift from Dow Corning.
Sodium dispersion was obtained from Strem. Potassium tet-
rachloroplatinate was recovered from platinum residues by a
standard procedure.
Considering the stability of many metal-η2-silane
complexes, the pathway for reductive elimination may
involve both an intermediate and a transition state of
the type Pt(PCy3)2(η2-SiHR3). The same applies to the
pathway for mutual phosphine exchange. However, we
consider that the kinetic data are not sufficiently precise
to warrant splitting either reaction pathway without
independent evidence for a two-step process. We have
recently shown that such evidence can be obtained if
the molecular design introduces asymmetry between the
rotamers of the M(η2-H-SiR3) complex. Thus, (η5-C5H5)-
Rh{Si(OMe)3}(H)(η2-C2H3CO2 Bu) exists as two inter-
t
converting rotamers in solution. However, the hydride
resonances of the two rotamers broaden at different
rates, because the barriers to the Rh{η2-H-Si(OMe)3}
intermediate are different for the two rotamers.40 These
experiments raise the possibility of designing a plati-
num silyl hydride with the necessary asymmetry to
detect the presence of an Pt(η2-H-SiR3) intermediate
and hence obtain direct evidence for a two-step process.
Photolysis (λ > 290 nm) of samples was carried out in Pyrex
NMR tubes using a Philips HPK 125 W medium-pressure
mercury lamp at room temperature equipped with a water
filter.
Summary
Reaction of Pt(PCy3)2 with hydrosilanes yields cis-Pt-
(PCy3)2(SiR2R′)H for all silanes that we have examined,
even with silanes capable of forming bidentate ligands.
The X-ray structure determined for the SiPh2H complex
shows considerable distortion from the ideal square-
planar geometry with a P-Pt-P angle of 113.54(3)°. For
alkyl- and arylsilanes, the trans isomer is formed
photochemically, but thermal reaction yields trans-Pt-
(PCy3)2(H)2. The silanes with chlorinated substituents
yield both cis and trans products on low-temperature
reaction. In these cases, heating results in cis-trans
NMR Measurements. NMR spectra were recorded on
Bruker AC200 (1H recorded at 200.13 MHz, 31P at 81.015
MHz), Bruker MSL300 (1H at 300.13 MHz, 31P at 121.49 MHz),
Bruker AMX500 (1H at 500.13 MHz, 31P at 202.46 MHz), and
Bruker DRX400 spectrometers (1H at 400.13 MHz, 31P at 161.9
MHz, 29Si at 79.46 MHz, 195Pt at 86.024 MHz). All 31P{1H}
spectra were referenced to external 85% H3PO4. The 195Pt
spectra were referenced relative to the absolute frequency of
86.024 MHz at δ 0. Temperature calibration was determined
using an ethylene glycol chemical shift thermometer above
room temperature and a methanol thermometer at low tem-
perature.41
(38) Tsuji, Y.; Nishiyama, K.; Hori, S.; Ebihara, M.; Kawamura, T.
Organometallics 1993, 12, 507.
The spin-lattice relaxation values (T1) were measured by
the standard inversion recovery method with a variable delay
(39) (a) Sakaki, S.; Ieki, M. J. Am. Chem. Soc. 1993, 115, 2873. (b)
Sakaki, S.; Mizoe, N.; Musashi, Y.; Biswas, B.; Sugimoto, M. J. Phys.
Chem. A 1998, 102, 8027.
(41) (a) Ammann, C.; Meier, P.; Merbach, A. E. J. Magn. Reson.
1982, 46, 319. (b) Van Geet, A. L. Anal. Chem. 1970, 42, 679.
(40) Ampt, K. A. M.; Duckett, S. B.; Perutz, R. N. Dalton 2004, 3331.

5754 Organometallics, Vol. 23, No. 24, 2004
Chan et al.
d1.42 The results were analyzed using the 2D Bruker package,
which fits the 1D peak integrals, I, to the expression I(t) ) I0
+ P* exp(-t/T1), where P* is a constant.43 Quantitative 31P-
{1H} NMR spectra were recorded using an inverse gated pulse
sequence, with a delay period of at least 10 times the
acquisition time.44 The 1H NMR resonance of the Si-H group
on the free silane was found to have a relaxation time of up to
8 s at room temperature. A 60 s delay between acquisitions
was therefore used to allow for reliable integration analysis
of the proton spectrum.
Table 7. Crystal Data and Structure Refinement
Details for cis-Pt(PCy3)2H(SiPh2H)‚1.5C7H8 (1-cis)
empirical formula
fw
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C58.5H90P2PtSi
1078.43
triclinic
P1h
10.335(2)
12.915(3)
22.289(5)
77.357(4)
80.503(4)
67.598(3)
2672.8(9)
2
2D EXSY spectra were recorded on a Bruker DRX400
spectrometer with the noesygp pulse program, which uses
TPPI phase cycling to generate phase-sensitive spectra.45 The
EXSY spectra were recorded as a function of mixing time in
order to determine the rate for the exchange process. EXSY
experiments were recorded in [2H8]toluene at several values
of τm (0.75, 0.5, 0.4, 0.3, 0.2, 0.1 s) for complexes 1-cis and
5-cis at different temperatures. Recycle times for EXSY pulse
sequence were set to 5 times the measured T1 values. The total
acquisition time was approximately 15 to 20 h/experiment. The
2D spectra were phased in both dimensions. Exchange during
the mixing period is detected in off-diagonal cross-peaks. The
volume element was determined by integration under the
peaks in both dimensions. The 31P spin-lattice relaxation time
(T1) was determined by the inversion recovery pulse sequence,
yielding values for the resonances of 1.5 s for one phosphorus
ligand and 1.6 s for the other, for both 1-cis and 5-cis.
Exchange Process Monitoring. For processes involving
the exchange of nuclei between sites, exact rate constants can
then be determined via analysis of the intensity versus mixing
time profile.33 Integration of the excited peak and exchange
peak areas was first completed to obtain the data necessary.
A series of values were then calculated on the basis of a
differential model for a given set of exchange rate constants
as a function of reaction time using Microsoft Excel 97. The
calculated peak intensities were then compared to the experi-
mental values, noting the squares of the differences.46 The rate
constants were varied until the sum of the squares of the
differences between measured and simulated points was
minimized. Rate constants obtained in this way were multi-
plied by a factor of 2 to take into account the analysis method.47
X-rayStructureDeterminationofPt(PCy3)2(H)(SiPh2H)‚
1.5(toluene). Single crystals of 1 were obtained by slow
cooling of a hexane/toluene solution. Details of the data
collection are given in Table 7. Data were collected on a Bruker
SMART 1000 CCD diffractometer (Mo KR radiation, λ )
0.710 73 Å). The data were integrated and corrected for
Lorentz and polarization effects using SAINT.48 Corrections
for incident and diffracted beam absorption effects were
applied using SADABS.48 No significant crystal decay was
observed during data collection. The structure was solved by
direct methods and refined by full-matrix least squares against
F2 using all data, with the SHELXTL software package.48 All
non-hydrogen atoms were refined with anisotropic displace-
ment parameters. The hydrogen atoms on Pt and Si were
located from difference maps and were refined as riding atoms.
Z
F
calcd (g/cm3)
1.340
F(000)
1126
µ(Mo KR) (mm-1
temp (K)
)
2.743
150(2)
no. of measd rflns
no. of unique rflns
no. of unique rflns (I > 2σ(I))
Rint
32 707
13 077
10 881
0.0524
no. of data/params
R1a (I > 2σ(I))
wR2a (all data)a
GOFb
13 077/584
0.0325
0.0551
0.993
235452
CCDC ref no.
2 2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo ) ]}1/2
.
2
2
b GOF ) {∑[w(Fo - Fc )2]/(n - p)}1/2, where n is the number of
data and p is the number of parameters refined.
All other hydrogen atoms were placed geometrically and
refined as riding atoms. The structure contains 1.5 toluene
molecules of solvation. One toluene molecule is ordered; the
half-molecule of toluene is disordered over a crystallographic
special position. No hydrogen atoms have been fixed to the
disordered toluene molecule.
Syntheses. The complexes Pt(PCy3)2 and Pt(PiPr3)2 were
synthesized according to the literature procedures.49 NMR data
are given in the tables except where shown.
cis-Pt(PCy3)2(H)(SiPh2H) (1-cis). Pt(PCy3)2 (0.10 g, 0.15
mmol) was dissolved in hexane (15 mL). To this was added a
solution of diphenylsilane (0.024 g, 0.13 mmol) in hexane (10
mL) dropwise with stirring. The reaction mixture was then
stirred in an ice bath for 30 min. The resulting white
precipitate of cis-(Pt(PCy3)2(H)(SiPh2H) was collected and
washed with 3 × 10 mL of cold hexane (yield 55%). The product
was recrystallized by dissolving in toluene and layering with
hexane. Anal. Found: C, 62.1; H, 8.8. Calcd for C48H78PtP2Si:
C, 61.32; H, 8.36. IR: KBr, 2051, 2039 cm-1; THF, 2042, 2020
(sh) cm-1; ν(PtH) and ν(SiH). MS (FAB): m/z 940 (M+, 22%),
756 (M+ - H2SiPh2, 100%). 1H NMR (400.13 MHz, [2H8]-
toluene, 293 K): δ 1.2-2.8 (66H, m, C6H11), 7.21 (2H, m, p-Ph),
7.33 (4H, m, m-Ph), 8.08 (4H, m, o-Ph), 5.37 (1H, s with
satellites, SiH, J(SiH) ) 164 Hz).
cis-Pt(PCy3)2(H)(SiEt2H) (2-cis). The complex 2-cis was
prepared using the same procedure as for 1-cis. Pt(PCy3)2 (0.10
g. 0.15 mmol) was dissolved in hexane (15 mL), the silane H2-
SiEt2 solution (0.07 g, 0.193 mmol) was added, and the
resulting solution was stirred in an ice bath for 2 h. The solvent
was removed, the residue was dried under vacuum, and a
white solid was obtained (yield, 40%). 1H NMR spectrum
(300.13 MHz, [2H8]toluene, 293 K): δ 1.12-2.65 (m, PC6H11
and C2H5), 4.34 (1H, s with satellites, SiH, J(SiH) ) 131 Hz).
trans-Pt(PCy3)2(H)(SiPh2H) (1-trans) and trans-Pt-
(PCy3)2(H)(SiEt2H) (2-trans). trans-Pt(PCy3)2(H)(SiPh2H) (1-
trans) and trans-Pt(PCy3)2(H)(SiEt2H) (2-trans) were formed
by the photolysis of the corresponding cis complexes with UV
light at room temperature. Samples were made up in C6D6 in
an NMR tube. The reaction was followed by measurement of
1H NMR spectra at 10 min intervals for the first 30 min of
(42) Ernst, R. R.; Bodenhausen, G.; Wokaun, A. Principles of Nuclear
Magnetic Resonance in One and Two Dimensions; Oxford University
Press: Oxford, U.K., 1987.
(43) Bruker Analytische Messtechnik GmbH, 1989, 1990, 1991.
(44) Braun, S.; Kalinowski, H.-O.; Berger, S. 100 and More Basic
NMR Experiments-A Practical Course; VCH: Cambridge, U.K., 1996;
p 99.
(45) Freeman, R. A Handbook of Nuclear Magnetic Resonance;
Longmans: Harlow, U.K., 1988.
(46) Jones, W. D.; Rosini, G. P.; Maguire, J. A. Organometallics
1999, 18, 1754.
(47) Green, M. L. H.; Wong, L.-L.; Sella, A. Organometallics 1992,
11, 2660.
(48) (a) SMART Version 5.624, SAINT Version 6.02a, and SADABS;
Bruker Analytical X-ray Systems, Inc., Madison, WI, 1998. (b) Sheld-
rick, G. M. SHELXTL Version 5.1; Bruker Analytical X-ray Systems,
Inc., Madison, WI, 1997.
(49) Yoshida, T.; Otsuka, S. Inorg. Synth. 1989, 28, 113.

Pt Bis(tricyclohexylphosphine) Silyl Hydrides
Organometallics, Vol. 23, No. 24, 2004 5755
1
photolysis and then after 2 h photolysis. H NMR of 1-trans
cis-Pt(PCy3)2(H)[Si(OMe)2CH2CHdCH2] (11-cis). 11-cis
was prepared by reacting Pt(PCy3)2 and excess HSi(OMe)2CH2-
CHdCH2 in C6D6 in an NMR tube at room temperature.
Attempts to isolate this product only produced an oily residue.
1H NMR (200.13 MHz, C6D6, 295 K): δ 0.80-2.77 (66H, m,
PC6H11), 2.40 (2H, d, SiCH2CHdCH2, J(HH) ) 8.9 Hz), 3.84
(6H, s, Si(OCH3)), 5.13-5.30 (2H, m, SiCH2CHdCH2), 6.50
(1H, m, SiCH2CHdCH2).
(300.13 MHz, [2H8]-toluene, 300 K): δ 0.9-2.5 (m, PC6H11),
5.68 (1H, s with satellites, SiH, J(SiH) ) 124 Hz). 1H NMR of
2-trans (300.13 MHz, [2H8]toluene, 300 K): δ 0.5-2.4 (m,
PC6H11 and C2H5), 4.98 (1H, s with satellites, SiH, J(SiH) )
198 Hz).
cis-Pt(PCy3)2(H)(SiEt3) (3-cis). The complex was prepared
in situ in an NMR tube by reacting Pt(PCy3)2 (0.023 g) with
an excess of HSiEt3, in [2H8]toluene at -78 °C, and following
the reaction by low-temperature NMR spectroscopy. 1H NMR
spectrum (300.13 MHz, [2H8]toluene, 243 K): δ 0.9-1.9 (m,
PC6H11 and C2H5).
cis-Pt(PCy3)2(H)(SiR2R′) (12-cis-14-cis). The cis plati-
num silyl hydride complexes 12-cis-14-cis were prepared by
the reaction of Pt(PCy3)2 with chlorosilanes in [2H8]toluene.
In a typical reaction, excesses of HSiMe2Cl, HSiMeCl2, and
HSiCl3 were added by vacuum transfer to cold (195 Κ)
solutions of Pt(PCy3)2 in NMR sample tubes. When these
samples were warmed, white precipitates formed of the trans-
Pt(PCy3)2(H)(SiR2R′) complexes 12-trans-14-trans. 1H NMR
(300.13 MHz, [2H8]toluene, 295 K) for 12-cis: δ 0.7-2.1 (m,
PC6H11 and CH3). 1H NMR (300.13 MHz, [2H8]toluene, 235 K)
cis-Pt(PCy3)2(H)(SiMe2Et) (4-cis) and cis-Pt(PCy3)2(H)-
[SiMe2OCH2C(Me)dCH2] (10-cis). The complexes 4-cis and
10-cis were prepared in situ in an NMR tube by reacting Pt-
(PCy3)2 with an excess of silane in [2H8]toluene at -78 °C.
Attempts to obtain a solid product only yielded an oily residue.
1H NMR (500.13 MHz, [2H8]toluene, 240 K) of 4-cis: δ 0.85
(6H, d, SiCH3, 4J(PH) ) 1.6 Hz, 3J(PtH) ) 26.7 Hz), 1.10-
1
for 13-cis: δ 1.1-2.5 (m, PC6H11 and CH3). H NMR (300.13
MHz, [2H8]toluene, 270 K) for 14-cis: δ 0.6-2.5 (m, PC6H11).
1H NMR (300.13 MHz, [2H8]toluene, 295 K) for 12-trans:
δ 0.7-2.6 (m, PC6H11 and CH3). 1H NMR (300.13 MHz, [2H8]-
toluene, 295 K) for 13-trans: δ 1.2-3.0 (m, PC6H11 and CH3).
1H NMR (300.13 MHz, [2H8]toluene, 295 K) for 14-trans:
δ 1.2-3.1 (m, PC6H11).
1
2.40 (m, PC6H11 and C2H5). H NMR of 10-cis (500.13 MHz,
[2H8]toluene, 250 K): δ 1.16 (6H, s, SiCH3, 3J(PtH) ) 29.9 Hz),
1.20-2.40 (69H, m, PC6H11, CH2C(CH3)dCH2), 4.52 (2H, br,
SiOCH2), 5.24 (1H, br, C(CH3)dCH2), 5.51 (1H, br, C(CH3)d
CH2).
cis-Pt(PCy3)2(H)(SiPh3) (5-cis). Pt(PCy3)2 (0.10 g, 0.15
mmol) was dissolved in pentane (15 mL). Triphenylsilane (0.07
g, 0.26 mmol) in pentane (10 mL) was added dropwise with
stirring. The reaction mixture was stirred in an ice bath for 2
h, and a white precipitate was formed. The white solid 5-cis
was collected and washed with 3 × 10 mL of cold pentane
(yield 0.70 g, 47%) Anal. Found: C, 63.8; H, 8.1. Calcd for
C54H82P2SiPt: C, 63.1; H, 8.1. MS (FAB): m/z 1016 {M+, 79%}.
1H NMR (500.13 MHz, [2H8]toluene, 250 K): δ 1.12-2. 50
(66H, m, PC6H11), 7.20-8.40 (15H, m, C6H5). 195Pt NMR
Deuterated Triphenylsilane. The compound was pre-
pared with a slight variation from the literature procedure.50
Triphenylchlorosilane (0.5 g) was dissolved in 50 mL of dry
ether in a three-necked flask equipped with a reflux condenser,
mechanical stirrer, and argon inlet, and a suspension of LiAlD4
(0.15 g) in dry ether was added dropwise over a period of 30
min. When the addition was complete, the mixture was stirred
and heated to reflux. Dry benzene was added dropwise to the
reaction flask, and simultaneously ether was distilled off until
the distillation temperature reached 351 K. The mixture was
allowed to settle, and benzene was siphoned off under argon
pressure. The solvent was pumped off from the benzene
solution, and the residue was dried under vacuum to give
DSiPh3. Full deuteration was indicated by the total dis-
appearance of the Si-H septet at δ 5.5 and the shift of the
a
spectrum (86.024 MHz, 295 K): δ -5205 (dd, JPtP ) 1555,
JPtP ) 2650 Hz (see Scheme 1)). IR (KBr): ν(PtH) 2078 cm
-1
b
.
cis-Pt(PCy3)2(H)(SiMe2CH2CHdCH2) (6-cis). 6-cis was
prepared using the same procedure as for cis-Pt(PCy3)2(H)-
(SiPh3). Pt(PCy3)2 (0.43 g, 0.57 mmol) and HSiMe2CH2CHd
CH2 (0.33 µL, 2.27 mmol) were dissolved in hexane and stirred
in an ice bath for 5 h. The white solid that formed was collected
and washed with 3 × 10 mL of cold hexane (yield 0.20 g, 41%).
MS (FAB): m/z 855 {M+, 79%}. 1H NMR (500.13 MHz, [2H8]-
toluene, 240 K): δ 1.05 (6H, d, SiCH3, 4J(PH) ) 1.6 Hz, 3J(PtH)
) 26.5 Hz), 1.10-2.30 (66H, m, PC6H11), 2.41 (2H, d, SiCH2-
ν(Si-H) band from 2124 to 1546 cm-1
.
Measurement of Equilibrium Parameters for Silane
Dissociation: 5-cis, 6-cis, and 4-cis. NMR samples of 5-cis,
6-cis, and 4-cis were prepared in [2H8]toluene and kept in ice
prior to recording the NMR spectra. This precaution was
required to prevent excessive decomposition to trans-Pt(PCy3)2-
(H)2, which occurs at room temperature. Quantitative 1H and
31P{1H} NMR spectra were recorded initially at 290 K and
subsequently at 5 K intervals to 310 K. The relative concen-
trations of 5-cis, [HSiPh3], and [Pt(PCy3)2] were obtained from
the integrals of the hydride resonance of 5-cis, the Si-H
resonance of HSiPh3 in the 1H NMR spectra, and the integrals
of the phosphorus resonance of 5-cis and Pt(PCy3)2. The
equilibrium constants for the dissociation of 5-cis and 6-cis
were calculated, and the thermodynamic parameters were
determined. An NMR sample of cis-Pt(PCy3)2(H)(SiMe2Et) (4-
cis) was prepared by adding a slight excess of the silane
HSiMe2Et to a [2H8]toluene solution of Pt(PCy3)2, where the
SiH:Pt ratio was 1.06:1.00. Equilibrium constants for dissocia-
tion were obtained for 4-cis, as for 5-cis and 6-cis.
3
CHdCH2, J(HH) ) 8.3 Hz, J(PtH) ) 30.8 Hz), 5.16 (1H, m,
SiCH2CHdCH2), 5.25 (1H, m, SiCH2CHdCH2), 6.52 (1H, m,
SiCH2CHdCH2). IR (KBr): ν(PtH) 2085 cm-1
.
trans-Pt(PCy3)2(H)(SiPh3) and trans-Pt(PCy3)2(H)-
(SiMe2CH2CHdCH2) (5-trans and 6-trans). The photolysis
reactions were carried out as for 1-trans, but the photolysis
was carried out at 195 K and the spectra were recorded at
250 K after 4 h of irradiation.
cis-Pt(PCy3)2(H)(SiPh2OSiPh2H) (7-cis). 7-cis was pre-
pared by reacting Pt(PCy3)2 and HSiPh2OSiPh2H in a 1:1 ratio
in C6D6 in an NMR tube at room temperature. 1H NMR (200.13
MHz, C6D6, 295 K): δ 0.71-2.79 (66H, m, PC6H11), 6.06 (1H,
s, with satellites, SiH, J(SiH) ) 213 Hz), 7.04-7.15 (20H, m,
SiC6H5). When a 2:1 ratio of Pt(PCy3)2 and HSiPh2OSiPh2H
was used in the reaction, 7-cis was again the only product.
Chelated disilyl complexes or dimeric species were not de-
tected.
Acknowledgment. We thank the EPSRC, Dow
Corning, the French Ministry of Foreign Affairs, CNRS,
and The British Council for support through the “Alli-
ance” program. We thank Professor W. D. Jones (Roch-
ester) for the copy of the modified EXCEL program and
Dr. A. Roy and Dr. P. Hupfield (Dow Corning) for helpful
advice.
cis-Pt(PCy3)2(H)(Me2SiOSiHMe2) (8-cis) and cis-Pt-
(PCy3)2(H){SiMe(OSiMe3)2} (9-cis). 8-cis and 9-cis were
prepared by reacting Pt(PCy3)2 (0.026 g) and 1 equiv of Me2-
HSiOSiHMe2 and HSiMe(OSiMe3)2 in [2H8]toluene in an NMR
tube at -15 °C. H NMR of 8-cis (300.13 MHz, [2H8]toluene,
1
268 K): δ 0.43 (6H, d, 6 Hz, SiHMe2), 0.8-2.5 (m, PC6H11 and
1
CH3), 5.29 (1H, m with satellites, SiH, J(SiH) ) 198 Hz). H
NMR of 9-cis (300.13 MHz, [2H8]toluene, 225 K): δ 0.48 (s,
9H, Si(CH3)3), 0.8-2.1 (m, PC6H11 and CH3).
(50) Hart-Davis, A. J.; Graham, W. A. G. J. Am. Chem. Soc. 1971,
93, 4388.

5756 Organometallics, Vol. 23, No. 24, 2004
Chan et al.
Supporting Information Available: Tables of atomic
coordinates and equivalent isotropic displacement coefficients,
anisotropic thermal parameters, experimental details of the
X-ray study, and bond distances and angles for 1-cis; crystal-
lographic data are also available as CIF files. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM049549N