Reaction of a symmetrical diplatinum complex containing bridging μ-η2-H-SiH(IMP) ligands (IMP = 2-isopropyl-6-methylphenyl) with PMe2Ph. Formation and characterization of {(PhMe2P)2Pt[μ-SiH(IMP)]}2

Article abstract of DOI:10.1021/om990080j

A dinuclear Pt-Si complex containing bridging η²-H-SiH(IMP) (IMP = 2-isopropyl-6-methylphenyl) ligands, {(Ph₃P)Pt[μ-η²-H-SiH(IMP)]}₂ (1) has been synthesized and characterized by NMR and X-ray crystallography. A

Full text of DOI:10.1021/om990080j

Organometallics 1999, 18, 2583-2586
2583
Rea ction of a Sym m etr ica l Dip la tin u m Com p lex
Con ta in in g Br id gin g µ-η2-H-SiH(IMP ) Liga n d s (IMP )
2-Isop r op yl-6-m eth ylp h en yl) w ith P Me2P h . F or m a tion
a n d Ch a r a cter iza tion of {(P h Me2P )2P t[µ-SiH(IMP )]}2
Yanina Levchinsky, Nigam P. Rath, and J anet Braddock-Wilking*,‡
Department of Chemistry, University of MissourisSt. Louis, 8001 Natural Bridge Road,
St. Louis, Missouri 63121
Received February 8, 1999
Summary: A dinuclear Pt-Si complex containing bridg-
ing η2-H-SiH(IMP) (IMP ) 2-isopropyl-6-methylphenyl)
ligands, {(Ph3P)Pt[µ-η2-H-SiH(IMP)]}2 (1) has been
synthesized and characterized by NMR and X-ray
crystallography. A 3c-2e nonclassical interaction between
Pt‚‚‚H‚‚‚Si is supported by spectroscopic and crystal-
lographic data. Complex 1 reacts with the more basic
and less hindered phosphine PMe2Ph to afford a differ-
ent dinuclear Pt-Si complex with loss of H2, {(PhMe2P)2-
Pt[µ-SiH(IMP)]}2 (2). Complex 2 was characterized by
multinuclear NMR spectroscopy.
The oxidative addition of a Si-H bond in a hydrosi-
lane to a low-valent transition metal center is a versatile
method for the formation of complexes containing a
M-Si bond.1 Reaction of a hydrosilane with a transition
metal complex can provide different products, some of
which depend on the number of available Si-H bonds
in the starting silane. Primary as well as secondary
silanes can provide both mono- and bimetallic species
(where the silicon center bridges two metal centers).
1
F igu r e 1. (a) H NMR spectrum (25 °C) of 1 (300 MHz,
Bimetallic bis(µ-silylene) complexes have also been
generated by dimerization of metal-silylenes or by
reaction of bis(silyl) metal complexes with another metal
precursor.2
C6D6). The inset shows an expanded view of the terminal
Si-H region with 195Pt satellites. (b) H{31P} NMR spec-
1
trum (25 °C) of 2 (300 MHz, C6D6). The inset shows an
expanded view of the terminal Si-H region with 195Pt
satellites.
A number of metal systems are known to catalyze
transformations of hydrosilanes including hydrosilyla-
tion of alkenes and dehydrocoupling to oligo- and
polysilanes. The mechanism for dehydrocoupling with
early transition metals is believed to proceed through
a σ-bond metathesis reaction,3 but with the late transi-
tion metal catalysts, no mechanism has been clearly
established.4 Mechanistic studies with late transition
metal catalysts have not excluded the involvement of
dinuclear species in the dehydrocoupling reactions.
Diplatinum bis(µ-silylene) complexes have been shown
to catalyze the oligomerization (stepwise) of primary
silanes to small-chain oligosilanes.5 Recently, a series
of dinuclear rhodium (µ-silylene) and (µ-η2-silyl) com-
plexes have been prepared, and involvement of the
latter in the catalytic dehydrocoupling of diphenylsilane
to 1,1,2,2-tetraphenyldisilane was proposed.6 Despite
the growing number of µ-silylene complexes reported,
little is known about their reactivity, most of which
involve small molecules or catalytic reactions.2
We report here the preparation and characterization
of the dinuclear Pt complex {(Ph3P)Pt[µ-η2-H-SiH-
(IMP)]}2 (IMP ) 2-isopropyl-6-methylphenyl), which
contains two nonclassical Pt‚‚‚H‚‚‚Si interactions, and
its novel reaction with PMe2Ph to form a different four-
membered ring with loss of H2.7 To the best of our
‡ Corresponding author. Tel.: (314) 516-6436. Fax: (314) 516-5342.
E-mail: wilking@jinx.umsl.edu.
(1) Corey, J . Y.; Braddock-Wilking, J . Chem. Rev. 1999, 99, 175.
(2) Ogino, H.; Tobita, H. Adv. Organomet. Chem. 1998, 42, 223.
(3) (a) Tilley, T. D. Acc. Chem. Res. 1993, 26, 22. (b) Corey, J . Y. In
Advances in Silicon Chemistry; Larson, G. L., Ed.; J AI Press: Green-
wich, CT, 1991; Vol. 1, p 327. (c) For a recent review on catalytic
dehydrocoupling see: Gauvin, F.; Harrod, J . F.; Woo, H. G. Adv.
Organomet. Chem. 1998, 42, 363.
(4) Two pathways have been proposed for the later metals: a series
of oxidative addition/reductive elimination steps (Curtis, M. D.; Ep-
stein, P. S. Adv. Organomet. Chem. 1981, 19, 213) and a route involving
metal-silylenes (LnMdSiRR′) via a 1,2-hydrogen shift from silicon to
the metal center (Ojima, I.; Inaba, S. I.; Kogure, T.; Nagai, Y. J .
Organomet. Chem. 1973, 55, C7). See also ref 3c.
(5) Tessier, C. A.; Kennedy, V. O.; Zarate, E. A. In Inorganic and
Organometallic Oligomers and Polymers; Harrod, J . F., Laine, R. M.,
Eds.; Kluwer Academic Publishers: The Netherlands, 1991; p 13.
(6) Rosenberg, L.; Fryzuk, M. D.; Rettig, S. J . Organometallics 1999,
18, 958.
(7) Braddock-Wilking, J .; Levchinsky, Y.; Rath, N. P. Thirty-First
Organosilicon Symposium, May 1998, New Orleans, LA, abstract B9.
10.1021/om990080j CCC: $18.00 © 1999 American Chemical Society
Publication on Web 06/15/1999

2584 Organometallics, Vol. 18, No. 14, 1999
Communications
knowledge, this is the first example of the conversion
of a dinuclear bis(µ-η2-H-SiR2) complex to a bis(µ-
silylene) species. In fact, the reverse reaction of a
bridging silylene complex containing no metal-metal
bond to a system with a metal-metal bond is fairly
common.2
More recently, Kim and co-workers reported two di-
nuclear Pd complexes containing Ph2Si groups bridging
the Pd centers, (Me3P)Pd(µ-η2-H-SiPh2)2Pd(PMe3)n (n
) 1, 2).12
Although stable in the solid state, a benzene solution
of 1 is stable only for several days at room temperature
or for months at -35 °C. The solid appears to be
moderately air stable. When 1 is treated with the more
basic, less sterically demanding phosphine, PhMe2P, a
new dinuclear Pt-Si complex, trans-213 (with elimina-
tion of H2), was formed which no longer contains a
Pt‚‚‚H‚‚‚Si interaction or a Pt-Pt bond (eq 2).14 Complex
Reaction of (Ph3P)2Pt(η2-C2H4) with 1 equiv (or a
4-fold excess) of (IMP)SiH3 in benzene or toluene at
room temperature afforded 1 (as a mixture of cis and
trans isomers in a ratio of approximately 1:3)8 in 83%
yield (eq 1).9 The reaction occurs instantly with vigorous
gas evolution (H2 and C2H4) followed by precipitation
of the product. This is the first example of a dinuclear
Pt-Si system containing both a nonclassical Pt‚‚‚H‚‚‚
Si interaction and a terminal Si-H unit. Complex 1 was
2 was characterized by multinuclear NMR, X-ray crys-
tallography,15 and elemental analysis. Several Pt2Si2
ring systems analogous to 2 have been prepared by
Tessier,14b,c Fink,14d Tilley,14e and Tanaka.14f
Compounds 1 and 2 display quite different NMR
chemical shifts despite their similar basic structures.
For example, the terminal Si-H proton resonances
appear at very low field for the cis and trans isomers of
1 (Figure 1a) and are located at 8.42 and 8.92 ppm
(flanked by two sets of Pt satellites, which confirms
inequivalent coupling of the terminal Si-H to each Pt
center). In contrast, the terminal Si-H resonance for 2
1
characterized by H, 31P{1H}, and 29Si{1H} NMR spec-
troscopy as well as X-ray crystallography (trans-1 only).
There are only a few complexes of the group 10 metals
that contain a nonclassical M‚‚‚H‚‚‚Si interaction and
include several diplatinum complexes {(R′3P)Pt(µ-η2-H-
SiR2)}2 (R′ ) alkyl or aryl; R ) Me, Ph) prepared by
Stone et al.10 Tessier and co-workers synthesized the
novel dinuclear platinum complex {(Pr3P)Pt[µ-η2-H-Si-
(Hex)PtH(PPr3)2]}2 (Pr ) n-propyl, Hex ) n-hexyl).11
(8) The trans isomer is believed to be the major component due to
steric hindrance within the molecule. The ratio of isomers was
determined from the relative intensities of the Si-H resonances in
the 1H NMR spectrum.
(10) Auburn, M.; Ciriano, M.; Howard, J . A. K.; Murray, M.; Pugh,
N. J .; Spencer, J . L.; Stone, F. G. A.; Woodward, P. J . Chem. Soc.,
Dalton Trans. 1980, 659.
(11) Sanow, L.; Chai, M.; Galat, P.; Rinaldi, P.; Youngs, W.; Tessier,
C. Thirtieth Organosilicon Symposium, May 1997, London, Ontario,
Canada, abstract P69.
(9) A benzene solution (2 mL) of (IMP)SiH3 (22 mg, 0.13 mmol) was
added slowly to (Ph3P)2Pt(η2-C2H4) (97 mg, 0.13 mmol). Vigorous
bubbling was seen, and the solution turned golden-yellow. An off-white
microcrystalline solid formed and was washed with 3 aliquots of C6H6
(1 mL each) and then dried in vacuo to give 67 mg (83%) of 1 as a
mixture of cis and trans isomers. An alternative preparation of 1 from
(Ph3P)4Pt and (IMP)SiH3 gave 70% yield and much lower yield from
(Ph3P)2PtMe2. Spectroscopic and physical data for 1: 1H NMR (300
(12) Kim, Y.-J .; Lee, S.-C.; Park, J .-I.; Osakada, K.; Choi, J .-C.;
Yamamoto, T. Organometallics 1998, 17, 4929.
(13) A solution of PMe2Ph (8 mg, 5.8 × 10-5 mol) in 0.5 mL of C6D6
was added to 1 (16 mg, 1.3 × 10-5 mol) in 0.5 mL of C6D6. Vigorous
gas evolution was observed, and the color changed from colorless to
intense yellow. The reaction was quantitative by NMR, and trans-2
was obtained in 87% (14 mg) isolated yield from slow evaporation of a
pentane/C6D6 solution (data are consistent with an authentic sample
prepared independently by reaction of (PhMe2P)2PtMe2 with IMPSiH3,
results to be published). (PhMe2P)2PtMe2 was prepared from a modified
procedure described in: Ruddick, J . D.; Shaw, B. L. J . Chem. Soc. A
1969, 2801. Spectroscopic and physical data for 2: 1H{31P} NMR (300
3
MHz, δ) 0.89 (br d, 12H, J H-H ) 5.7 Hz, CH(CH3)2, cis and trans
3
resonances overlapping), 1.16 (br d, 12H, J H-H ) 6.3 Hz, CH(CH3)2,
cis and trans resonances overlapping), 2.22 (s, 6H, o-CH3 for trans-1;
overlapping with Pt‚‚‚H‚‚‚Si), 2.31 (s, 6H, o-CH3 for cis-1; overlapping
with Pt‚‚‚H‚‚‚Si), 3.75 (br s, 2H, CH for cis-1), 4.08 (br s, 2H, CH for
trans-1), 6.78 (br s, Ar-H), 6.90 (br s, Ph3P), 7.10 (br m, Ph3P), 7.61
2
(br s, Ph3P), 8.42 (br s, 2H, J Pt-H ) 137, 78 Hz, Si-H for cis-1), 8.92
2
(br s, 2H, J Pt-H ) 137, 72 Hz, Si-H for trans-1); 31P{1H} NMR (202
1
2
3
3
MHz, THF, and C6D6, δ) 37.5 (s, J Pt-P ) 4276 Hz, J Pt-P ) 261 Hz,
3J P-P ) 60 Hz, trans-1), 37.2 (s, coupling constants not well resolved
for cis-1); 29Si NMR (500 MHz, CD2Cl2, 1H-29Si HMQC, δ) 131 (trans-
1), 126 (cis-1); IR (KBr) ν (Si-H) 2111.2 cm-1, ν(Pt‚‚‚H‚‚‚Si) 1680.0
cm-1. Anal. Calcd For C56H60P2Pt2Si2: C, 54.18; H, 4.87. Found: C,
56.17; H, 5.10 (these values are consistent with benzene solvate, calcd
C, 56.39; H, 5.00; however the exact amount could not be determined
by 1H NMR spectroscopy due to overlapping resonances in the aromatic
region). HR-MAS (FAB) calcd for M-H2: 1238.2848. Found: 1238.2842.
MHz, δ) 1.12 (s, 12H, J Pt-Me ) 20 Hz, PMe3), 1.35 (s, 12H, J Pt-Me )
3
22 Hz, PMe3), 1.70 (d, 12H, J H-H ) 6.6 Hz, CH(CH3)2), 2.62 (s, 6H,
Ar-CH3), 4.81 (sept, 2H, 3J H-H ) 6.6 Hz, CH(CH3)2), 5.79 (s, 2H, 1J Si-H
) 169 Hz,2J Pt-H ) 30 Hz, Si-H), 6.89-6.94 (m, Ar-H), 7.16-7.20 (m,
Ar-H), 7.32 (d, J ) 8.1 Hz, Ar-H); 31P{1H} NMR (121 MHz, δ) -2.06
1
3
4
(s, J Pt-P ) 1725 Hz, J Pt-P ) 271 Hz, J P-P ) 20 Hz); 29Si{1H} (99
MHz, DEPT, δ) -134.2 (m, 1J Pt-Si ) 699 Hz, 2J P-Si ) 66 Hz (cis), 2J P-Si
) 107 Hz (trans)). Anal. Calcd For C52H72P4Pt2Si2: C, 49.24; H, 5.73.
Found: C, 49.38; H, 5.79.

Communications
Organometallics, Vol. 18, No. 14, 1999 2585
F igu r e 3. Molecular structure of trans-{(Ph3P)Pt[µ-η2-H-
SiH(IMP)]}2, 1 (50% probability). Selected bond distances
(Å) and angles (deg): Pt-Pt#1 ) 2.7021(2), Pt-Si )
2.3248(9), Pt-Si#1 ) 2.4280(9), Pt-P ) 2.2485(8), Si-H
) 1.593, Si‚‚‚H ) 1.669, Pt‚‚‚H ) 1.799; P-Pt-Si ) 105.08-
(3), P-Pt-Si#1 ) 143.89(3), Si-Pt-Si#1 ) 110.74(3),
P-Pt-Pt#1 ) 161.78(2), Si-Pt-Pt#1 ) 57.17(2), Si#1-
Pt-Pt#1 ) 53.57(2), Pt‚‚‚H‚‚‚Si ) 88.8, Pt-Si-C1 )
119.23(11), Pt#1-Si-C1 ) 121.79(12), Pt-Si-Pt#1 )
69.26(3).
F igu r e 2. (a) 31P{1H} NMR spectrum (25 °C) of 1 (202
MHz, THF, and C6D6). (b) 31P{1H} NMR spectrum (25 °C)
of 2 (121 MHz, C6D6).
1
(Figure 1b) appears at 5.79 ppm in the H{31P} NMR
spectrum, in the typical region (3.0-6.0 ppm) for Si-H
chemical shifts in free silanes or M-SiH moieties.1
The nonclassical Pt‚‚‚H‚‚‚Si resonance could not be
and high-field signals of -75 and -94 ppm (cis and
trans isomers) were found for the related ring systems
{(Pr3P)2Pt[µ-SiH(Hex)]}2. The Si-H stretching vibra-
tions for 1 found in the IR spectrum clearly indicate a
terminal Si-H unit (2111 cm-1) and a weaker stretching
frequency for the bridging Pt‚‚‚H‚‚‚Si moiety (1618
cm-1). Complex 2 exhibits a stretching vibration at 2021
cm-1 for the terminal Si-H unit.
1
resolved from the H NMR experiment in C6D6 (better
1
resolved in CD2Cl2), but a 2D H-1H EXSY experiment
confirmed that the bridging hydride resonance over-
lapped with the aryl-CH3 resonance (δ 2.17 ppm). The
Pt‚‚‚H‚‚‚Si chemical shift value is in close agreement
1
with the values reported by Stone et al.10 The H-1H
The 31P{1H} NMR spectra for 1 and 2 (Figure 2, parts
a and b, respectively) display a characteristic pattern
for a dinuclear platinum complex but differ in the
splitting of the satellite peaks due to the number of
phosphines bound to Pt. A central line is seen for both
the cis and trans (major) isomers of 1 at ∼37 ppm. The
resonance for 2 is shifted significantly upfield (-2 ppm).
An X-ray crystal structure for the trans isomer of 1
was obtained (Figure 3),16 and both the terminal and
bridging hydrides were located and refined. The central
core containing the Pt2Si2(µ-H)2 unit is planar with two
different Pt-Si distances, 2.3248(9) and 2.4280(9) Å.
The former value is in good agreement with other
reported Pt-Si single-bond distances.1 The longer Pt-
Si distance suggests a 3c-2e interaction between Pt‚‚‚
H‚‚‚Si. In addition, the Pt‚‚‚H and Si‚‚‚H distances are
elongated relative to typical 2c-2e bonds between these
elements. The terminal Si-H distance is 1.593 Å, and
EXSY experiment also revealed that the molecule is
fluxional on the NMR time scale at room temperature.
Exchange of the terminal and bridging hydrides results
in concomitant cis-trans isomerization. No fluxionality
was observed in the Pt dimers reported by Stone and
co-workers: however, the unsymmetrical Pd complex
(Me3P)Pd(µ-SiHPh2)2Pd(PMe3)2 was found to be flux-
ional by NMR (involving dissociation of PMe3).12 Com-
pound 2 does not show fluxional behavior.
The 29Si NMR chemical shifts for 1 and 2 are vastly
1
different. The 2D H-29Si HMQC (CD2Cl2) experiment
showed two distinct resonances for trans-1 (131 ppm)
and cis-1 (126 ppm). Compound 2 exhibits a high-field
resonance in the solution 29Si{1H} NMR spectrum at
-134 ppm, clearly indicating a dissimilar environment
at silicon. These data are in agreement with related Pt-
Si four-membered ring structures prepared by Tessier
and co-workers.11 A low-field resonance of 195 ppm
was observed for {(Pr3P)Pt[µ-η2-H-Si(Hex)PtH(PPr3)2]}2,
(16) Crystal Data for 1 (223 K): C56H60P2Pt2‚2CH3CN, triclinic, P1h,
a ) 9.2722(1) Å, b ) 13.118 Å, c ) 13.1805(1) Å, R ) 65.309 (1)°, â )
69.848 (1)°, γ ) 89.902 (1)°, V ) 1348.26 (2) Å3, Z ) 2, Dcalc ) 1.630
Mg/m3, F(000) ) 654, µ(Mo KR) ) 5.326 mm-1, R(F) ) 2.51% for I >
(14) A preliminary X-ray structure indicates a Pt‚‚‚Pt distance in 2
of 3.962 Å, outside the range of a Pt-Pt interaction. A detailed
structure will be published elsewhere. Such distances are observed in
other four-membered Pt-Si ring systems such as reported in: (a) See
ref 5. (b) Zarate, E. A.; Tessier-Youngs, C. A.; Youngs, W. J . J . Am.
Chem. Soc. 1988, 110, 4068. (c) Zarate, E. A.; Tessier-Youngs, C. A.;
Youngs, W. J . J . Chem. Soc., Chem. Commun. 1989, 577. (d) Michal-
czyk, M. J .; Recatto, C. A.; Calabrese, J . C.; Fink, M. J . J . Am. Chem.
Soc. 1992, 114, 7955. (e) Heyn, R. H.; Tilley, T. D. J . Am. Chem. Soc.
1992, 114, 1917. (f) Shimada, S.; Tanaka, M.; Honda, K. J . Am. Chem.
Soc. 1995, 117, 8289.
2σI reflections, wR2(F2) ) 6.26% for 6136 unique reflections (Rint
)
2.83%), 312 parameters, GOOF ) 1.070. Data collected using Bruker
CCD area detector system. The H atoms attached to silicon were
located and refined freely. The crystal contains disordered solvent (CH3-
CN). A second X-ray structure determination was performed on a
sample of 1 recrystallized from benzene, and the preliminary structure
revealed three molecules of benzene per molecule of 1. The cell
parameters for the second structure are as follows: P1h, a ) 9.3543(3)
Å, b ) 13.2467(5) Å, c ) 14.2850(5) Å, R ) 81.564(2)°, â ) 80.1846(2)°,
γ ) 69.974(2)°, V ) 1631.121(1) Å3.
(15) Unpublished results.

2586 Organometallics, Vol. 18, No. 14, 1999
Communications
a significant lengthening is observed for the nonclassical
Si‚‚‚H (1.669 Å).1 Typically, Pt-H distances are about
1.7 Å,17 and in compound 1, the Pt‚‚‚H distance was
notably longer, 1.799 Å. Similar structural features were
seen in the complex prepared by Stone et al., [(Cy3P)-
Pt(µ-η2-H-SiMe2)]2 (Cy ) cyclohexyl): Pt-Si, 2.324(2)
Å; Pt-Si, 2.420(2) Å; Si‚‚‚H, 1.72 Å; Pt‚‚‚H, 1.78 Å.10
The related Pd dimer, (Me3P)Pd(µ-η2-H-SiPh2)2Pd-
(PMe3), also revealed two inequivalent Pd-Si distances,
2.328(2) and 2.386(2) Å, with the longer distance as-
sociated with the “agostic” Pd‚‚‚Si distance.12 The Pd‚‚
‚H and Si‚‚‚H distances were 1.91 and 1.75 Å, respec-
tively.12 The Pt-Pt#1 [2.7021 (2) Å] and the Pt-P
[2.2485 (8) Å] distances are similar to other complexes
containing two Pt(I) centers bound to each other with
phosphine ligands (covalent radii for Pt, 2.62 Å).18 Each
Pt center resides in a distorted square planar environ-
ment. The P-Pt-Pt#1 angle is nonlinear, 161.78 (2)°,
and the phosphines bend away from the Pt‚‚‚H‚‚‚Si unit.
The Pt-Si-Pt#1 angle is more acute, [69.26(3)°] than
anticipated as a result of the formation of the Pt-Pt
bond. The spectroscopic and solid-state data support the
presence of a 3c-2e interaction both in solution and in
the solid state.
Further studies are under way with other mono- and
diarylsilanes to determine the electronic and steric
factors that influence the formation of 1. Additional
variable-temperature NMR experiments and reactivity
studies are planned.
Ack n ow led gm en t. This work is supported by the
University of MissourisSt. Louis Research Award. The
support of the NSF (CHE-9318696) and the University
of Missouri-Research Board are gratefully acknowl-
edged for the purchase of a Varian Unity Plus 300 and
Bruker ARX-500 NMR spectrometers. The UM-St. Louis
X-ray Crystallography Facility was funded in part by
an NSF Instrumentation Grant (CHE-9309690) and the
UM-St. Louis Research Award. J .B-W. is also grateful
to Professors J oyce Y. Corey, Peter P. Gaspar, and Mr.
Brian Grimmond for interesting discussions and com-
ments.
Su p p or tin g In for m a tion Ava ila ble: Experimental, NMR
spectra, and crystallographic information (trans-1). This
material is available free of charge via the Internet at
http://pubs.acs.org.
(17) See for example: Koizumi, T.-a.; Osakada, K.; Yamamoto, T.
Organometallics 1997, 16, 6014.
(18) See for example: (a) Green, M.; Howard, J . A. K.; Proud, J .;
Spencer, J . L.; Stone, F. G. A.; Tsipis, C. A. J . Chem. Soc., Chem.
Commun. 1976, 671. (b) Taylor, N. J .; Chieh, P. C.; Carty, A. J . J .
Chem. Soc., Chem. Commun. 1975, 448.
OM990080J