Spectroscopic and reactivity studies of platinum-silicon monomers and dimers

Article abstract of DOI:10.1021/om060009v

Mononuclear Pt-Si-containing complexes with the general formulas (Ph ₃P)₂Pt(H)(SiAr₂H) and (Ph₃P) ₂-Pt(SiAr₂H)₂ were produced at low temperature from the reaction of the secondary arylhydrosilanes Ph₂-SiH ₂, C₁₂H₈SiH₂ (silafluorene), and C₂₀H₂₄SiH₂ (3,7-di-tert-butylsilafluorene) with (Ph₃P)₂Pt(η²-C₂H₄). When solutions of the mononuclear complexes were run at low temperature and then warmed to room temperature, or when the reactions were run at room temperature or above, dinuclear Pt-Si-containing complexes were produced, [(Ph ₃P)Pt(μ-η²-HSiAr₂)]₂ (Ar = Ph (4)) and [(Ph₃P)₂Pt(H)(μ-SiAr₂)(μ- η²-HSiAr₂)Pt(PPh₃)] (Ar₂ = C₁₂H₈ (8), C₂₀H₂₄ (15); both fluxional). A mechanism is proposed for the formation of the unsymmetrical dinuclear complexes (8 and 15) that involves a bimolecular reaction between two mononuclear species, (Ph₃P)₂Pt(H)(SiAr₂H) and (Ph₃P)Pt(H)(SiAr₂H). VT-NMR studies of complexes 8 and 15 illustrate that a fluxional process occurs which can be explained by elimination and recoordination of a PPh₃ ligand. Complex 15 reacted with added P(p-Tol)₃ to produce a mixture of dinuclear products consistent with the presence of both types of phosphines in the dinuclear complexes. Reaction of the dinuclear complex 8 with the mononuclear complex 16 as well as the elevated-temperature reaction between 8 and 15 will be described.

Full text of DOI:10.1021/om060009v

Organometallics 2006, 25, 2859-2871
2859
Spectroscopic and Reactivity Studies of Platinum-Silicon Monomers
and Dimers
Janet Braddock-Wilking,* Joyce Y. Corey, Kevin A. Trankler, Huan Xu, Lisa M. French,
Ngamjit Praingam, Colin White, and Nigam P. Rath
Department of Chemistry and Biochemistry, UniVersity of MissourisSt. Louis, St. Louis, Missouri 63121
ReceiVed January 4, 2006
Mononuclear Pt-Si-containing complexes with the general formulas (Ph3P)2Pt(H)(SiAr2H) and (Ph3P)2-
Pt(SiAr2H)2 were produced at low temperature from the reaction of the secondary arylhydrosilanes Ph2-
SiH2, C12H8SiH2 (silafluorene), and C20H24SiH2 (3,7-di-tert-butylsilafluorene) with (Ph3P)2Pt(η2-C2H4).
When solutions of the mononuclear complexes were run at low temperature and then warmed to room
temperature, or when the reactions were run at room temperature or above, dinuclear Pt-Si-containing
complexes were produced, [(Ph3P)Pt(µ-η2-HSiAr2)]2 (Ar ) Ph (4)) and [(Ph3P)2Pt(H)(µ-SiAr2)(µ-η2-
HSiAr2)Pt(PPh3)] (Ar2 ) C12H8 (8), C20H24 (15); both fluxional). A mechanism is proposed for the
formation of the unsymmetrical dinuclear complexes (8 and 15) that involves a bimolecular reaction
between two mononuclear species, (Ph3P)2Pt(H)(SiAr2H) and (Ph3P)Pt(H)(SiAr2H). VT-NMR studies of
complexes 8 and 15 illustrate that a fluxional process occurs which can be explained by elimination and
recoordination of a PPh3 ligand. Complex 15 reacted with added P(p-Tol)3 to produce a mixture of dinuclear
products consistent with the presence of both types of phosphines in the dinuclear complexes. Reaction
of the dinuclear complex 8 with the mononuclear complex 16 as well as the elevated-temperature reaction
between 8 and 15 will be described.
product observed with Si-H bond activation of secondary
hydrosilanes has been a dinuclear complex containing either a
bridging µ-SiR2 unit or a µ-η2-HSiR2 group.3-6 Activation of
Si-H bonds by late-transition-metal centers such as Pt and Pd
are of considerable interest, due to the involvement of these
metals in catalytic processes such as hydrosilylation.2e
Recently, we reported the room-temperature reactions of 9,9-
dihydrosilafluorene (abbreviated silafluorene) and the related
substituted system 3,7-di-tert-butylsilafluorene with the Pt(0)
complex (Ph3P)2Pt(η2-C2H4).6 The formation of mono-, di-, and
trinuclear Pt-Si complexes was described, and the formation
of the last type can be attributed to activation of both Si-H
bonds in the silafluorene precursors.6 An intriguing question
arose from these studies: “How are these complexes formed,
and what intermediate species are involved in the reaction
pathway?” To address this question, several variable-temperature
experiments were performed to try to observe potential inter-
mediates in the reaction and to gain insight into the mechanistic
Introduction
The field of transition-metal silicon chemistry continues to
attract substantial interest. Complexes containing transition-
metal-silicon bonds are readily prepared by formal insertion
of a transition-metal center into a Si-H bond.1,2 Hydrosilanes
containing varying numbers of Si-H bonds, from SiH4 to
HSiR3, are known to react with a range of transition-metal
precursors, but by far, the majority of examples reported involve
tertiary hydrosilanes (HSiR3).1 Secondary (R2SiH2) and primary
(RSiH3) systems are interesting precursors, due to the presence
of additional potential sites of reactivity at the silicon center.
The expected initial product from Si-H activation of a tertiary
hydrosilane at a metal center is a complex with the general
formula LnM(H)(SiR3). The formation of a σ-complex, LnM-
(η2-HSiR3), resulting from an arrested addition of the Si-H
bond at the metal center could also be produced. A common
* To whom correspondence should be addressed. E-mail: wilkingj@
umsl.edu. Fax: (314) 516-5342. Tel: (314) 516-6436.
(1) Corey, J. Y.; Braddock-Wilking, J. Chem. ReV. 1999, 99, 175.
(2) (a) Tilley, T. D. Transition-Metal Silyl Derivatives. In The Chemistry
of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: New
York, 1989; p 1416. (b) Tilley, T. D. Transition-Metal Silyl Derivatives.
In The Silicon Heteroatom Bond; Patai, S., Rappoport, Z., Eds.; Wiley:
New York, 1991; p 245. (c) Eisen, M. Transition-Metal Silyl Complexes.
In The Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z.,
Eds.; Wiley: New York, 1998; 2 (Pt. 3), p 2037. (d) Ojima, I.; Li, Z.; Zhu,
J. Recent Advances in Hydrosilylation and Related Reactions. In The
Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.;
Wiley: New York, 1998; Vol. 2 (pt. 2), p 1687. (e). Lewis, L. N.; Stein,
J.; Gao, Y.; Colborn, R. E.; Hutchins, G. Platinum Met. ReV. 1997, 41, 66.
(f) Corey, J. Y. Dehydrogenative Coupling Reactions of Hydrosilanes. AdV.
Silicon Chem. 1991, 1, 327. (g) Corey, J. Y. Dehydrocoupling of
Hydrosilanes to Polysilanes and Silicon Oligomers: A 30 Year Overview.
AdV. Organomet. Chem. 2004, 51, 1. (h) Gauvin, F.; Harrod, J. F.; Woo,
H. G. Catalytic Dehydrocoupling: A General Strategy for the Formation
of Element-Element Bonds. AdV. Organomet. Chem. 1998, 42, 363-405.
(i) Schubert, U. Transition Met. Chem. 1991, 16, 126. (j) Aylett, B. J. AdV.
Inorg. Chem. Radiochem. 1982, 25, 1.
(3) (a) Osakada, K.; Tanabe, M. Bull. Chem. Soc. Jpn. 2005, 78, 1887.
(b) Yamada, T.; Tanabe, M.; Osakada, K.; Kim, Y.-J. Organometallics 2004,
23, 4771. (c) Tanabe, M.; Yamada, T.; Osakada, K. Organometallics 2003,
22, 2190. (d) Braunstein, P.: Boag, N. M. Angew. Chem., Int. Ed. 2001,
40, 2427. (e) Braddock-Wilking, J.; Levchinsky, Y.; Rath, N. P. Organo-
metallics 2000, 19, 5500. (f) Sanow, L. M.; Chai, M.; McConnville, D. B.;
Galat, K. J.; Simons, R. S.; Rinaldi, P. L.; Youngs, W. J.; Tessier, C. A.
Organometallics 2000, 19, 192. (g) Levchinsky, Y.; Rath, N. P.; Braddock-
Wilking, J. Organometallics 1999, 18, 2583. (h) Kim, Y.-J.; Lee, S.-C.;
Park, J -I.; Osakada, K.; Choi, J.-C.; Yamamoto, T. Dalton Trans. 2000,
417. (i) Kim, Y.-J.; Lee, S.-C.; Park, J -I.; Osakada, K.; Choi, J.-C.;
Yamamoto, T. Organometallics 1998, 17, 4929.
(4) For a recent review on bridged silylene and germylene complexes
see: Ogino, H.; Tobita, H. AdV. Organomet. Chem. 1998, 42, 223.
(5) For recent theoretical calculations see: (a) Lin, Z. Chem. Soc. ReV.
2002, 239. (b) Choi, S.-H.; Lin, Z. J. Organomet. Chem. 2000, 608, 42.
(6) (a) Braddock-Wilking, J.; Corey, J. Y.; Trankler, K. A.; Dill, K. M.;
French, L. M.; Rath, N. P. Organometallics 2004, 23, 4576. (b) Braddock-
Wilking, J.; Corey, J. Y.; Dill, K. M.; Rath, N. P. Organometallics 2002,
21, 5467.
10.1021/om060009v CCC: $33.50 © 2006 American Chemical Society
Publication on Web 04/26/2006

2860 Organometallics, Vol. 25, No. 11, 2006
Braddock-Wilking et al.
aspects of this and related reactions. Herein, we report these
variable-temperature reaction studies of (Ph3P)2Pt(η2-C2H4) with
Ph2SiH2, silafluorene, and 3,7-di-tert-butylsilafluorene as well
as the reactions of silafluorene-d2. In addition, several reactions
were performed to probe the reactivity of the fluxional unsym-
metrical dinuclear complexes, including their variable-temper-
ature dynamic NMR behavior.
2). Complex 4 was reported by Stone et al. but limited
spectroscopic data were provided.8 Stone suggested that 4 was
unstable in benzene-d6 solution, but the observation may likely
be due to fluxional behavior on the NMR time scale.8 The low-
temperature 1H NMR spectrum for 4 exhibited a slightly
broadened resonance for the two nonclassical Pt‚‚‚H‚‚‚Si
hydrides, and the 31P{1H} NMR spectrum exhibited a broadened
resonance with the expected Pt satellite pattern for a symmetrical
diplatinum complex with a phosphine group at each metal
center.8
Results
Reactions with Ph2SiH2. The reaction of (Ph3P)2Pt(η2-C2H4)
(1) with diphenylsilane, Ph2SiH2 (2), and a number of tertiary
hydrosilanes was reported by Eaborn et al. in the early 1970s.7
The reaction produced the expected Si-H oxidative-addition
product, cis-(Ph3P)2Pt(H)(SiPh2H) (3; eq 1). However, NMR
Reactions with H2SiC12H8 and D2SiC12H8. We recently
found that modifying the spatial requirements of secondary
arylhydrosilanes by tying the aryl rings together can greatly
enhance the reactivity of the silane.6 For example, the simplest
constrained secondary arylhydrosilane, silafluorene (H2SiC12H8,
5), exhibited pronounced reactivity compared to diphenylsilane
2. When the reaction between 1 and 5 was carried out at low
temperature (195 K) and monitored by NMR spectroscopy at
223 K, broadened signals indicating the formation of the
mononuclear complex9 (Ph3P)2Pt(H)[Si(C12H8)H] (6), analogous
to those of complex 3, were observed immediately after mixing.
In addition, sharp signals consistent with the formation of the
bis(silyl) complex10 cis-(Ph3P)2Pt[Si(C12H8)H]2 (7) as well as
H2 and C2H4 were observed (eq 3). Also identified was the
minor byproduct from hydrosilylation, HSi(C12H8)(CH2CH3).11
spectroscopic characterization data for 3 were not reported.
Complex 3 was described as an air-stable solid, but other related
complexes were reported to undergo slow decomposition in
benzene solution.7
With our interest in Si-H bond activation reactions of
primary and secondary hydrosilanes by Pt(0), we reexamined
the reaction of 1 with 2 by multinuclear NMR spectroscopy to
obtain spectroscopic data for 3 and to determine if the remaining
Si-H bond in 2 could be activated by Pt to form a dinuclear
product. Selected spectroscopic data for the major products
observed and isolated from the reactions with Ph2SiH2 and other
substrates described in this study are given in Table 1 (data are
presented in the sequence of mononuclear, dinuclear, and
trinuclear products).
When the reaction of 1 with 2 was performed at low
temperature in C7D8 and monitored by NMR spectroscopy (223
K), well-resolved signals for 3 were observed immediately after
addition. The expected doublet of doublets pattern for the
terminal Pt-H resonance was observed in the 1H NMR
spectrum, as was a signal for the remaining hydride at silicon.
The inequivalent phosphorus sites in 3 gave rise to two expected
signals in the 31P{1H} spectrum. The low-temperature 29Si{1H}
spectrum exhibited a signal for the silicon center consistent with
coupling to two different phosphorus nuclei as well as platinum.
The proton and phosphorus spectra remained unchanged for
several hours at 223 K. When the temperature was increased
slowly over several hours, the resonances began to broaden
significantly as the temperature was raised. At room temperature,
the 1H and 31P{1H} spectra showed very broad signals and after
5 days broad resonances for 3 were still present, even at low
temperature. Free PPh3 was also observed in the reaction mixture
at low temperature as a broad resonance, suggesting that
fluxional exchange may be occurring with complex 3.
If the reaction of 1 and 2 was conducted at room temperature,
the NMR data collected shortly after mixing exhibited substan-
tially broadened resonances assigned to 3, but after several hours
only a broad baseline was observed in the 31P{1H} NMR
spectrum in the region characteristic of 3.
After the temperature was raised slowly from 223 K to room
temperature, the NMR signals broadened significantly. At 283
K, the 31P{1H} spectrum exhibited essentially two broad
absorbances centered at 37 and 15 ppm, but at room temperature,
the major component was only one broad peak centered at 12
ppm. In addition, the 1H NMR spectrum exhibited a new broad
Pt-H signal at -1.3 ppm. After 1 day these signals remained
(8) 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.
(9) For some recent examples of cis- and trans-P2Pt(H)SiR3 complexes
see: (a) Chan, D.; Duckett, S. B.; Heath, S. L.; Khazal, I. G.; Perutz, R.
N.; Sabo-Etienne, S.; Timmins, P. L. Organometallics 2004, 23, 5744. (b)
Ebsworth, E. A.; Marganian, V. M.; Reed, F. J. S.; Gould, R. O. J. Chem.
Soc. Dalton Trans. 1978, 1167. (c) Mullica, D. F.; Sappenfield, E. L.;
Hampden-Smith, M. Polyhedron 1991, 10, 867. (d) Simons, R. S.; Sanow,
L. M.; Galat, K. J.; Tessier, C. A.; Youngs, W. J. Organometallics 2000,
19, 3994. (e) Kang, Y.; Kang, S. O.; Ko, J. Organometallics 2000, 19,
1216. (f) Feldman, J. D.; Mitchell, G. P.; Nolte, J.-O.; Tilley, T. D. Can. J.
Chem. 2003, 81, 1127. (g) Paonessa, R. S.; Prignano, A. L.; Trogler, W. C.
Organometallics 1985, 4, 647. (h) Abdol Latif, L.; Eaborn, C.; Pidcock, A.
P.; Ng, S. W. J. Organomet. Chem. 1994, 414, 217. (i) Mitchell, G. P.;
Tilley, T. D. J. Am. Chem. Soc. 1998, 120, 7635. (j) Packett, D. L.; Syed,
A.; Trogler, W. C. Organometallics 1988, 7, 159. (k) Koizumi, T.; Osakada,
K.; Yamamoto, T. Organometallics 1997, 16, 6014.
Heating a C7D8 solution containing the mononuclear complex
3 for 30 min at 323 K resulted in the formation of the
symmetrical dinuclear complex [(Ph3P)Pt(µ-η2-HSiPh2)]2 (4; eq
(10) For a related bis(silyl)platinum phosphine complex see: Kim, Y.-
J.; Park, J.-I.; Lee, S.-C. Organometallics 1999, 18, 1349.
(7) (a) Eaborn, C.; Ratcliff, B.; Pidcock, A. J. Organomet. Chem. 1974,
65, 181. (b) Eaborn, C.; Pidcock, A.; Ratcliff, B. J. Organomet. Chem.
1972, 43, C5.
(11) The minor product H(CH3CH2)SiC12H8) was not isolated and was
characterized in solution only: Braddock-Wilking, J.; French, L. A.; Corey,
J. Y. Unpublished results.

Platinum-Silicon Monomers and Dimers
Organometallics, Vol. 25, No. 11, 2006 2861
Table 1. Comparison of Selected NMR Spectroscopic Data for Complexes in This Reporta
a In C7D8 solution unless otherwise noted. Chemical shifts are given in ppm and coupling constants in Hz. Si-H coupling was not resolved. b Pt satellites
1
d
not resolved. c Resonance located by 2D H-29Si HMQC experiment. No hydrides were observed. 2JPtP not resolved.

2862 Organometallics, Vol. 25, No. 11, 2006
Braddock-Wilking et al.
and after the sample was recooled to 223 K the spectral data
indicated essentially quantitative formation of the unsymmetrical
dinuclear complex 8 and PPh3 as the major components in the
reaction mixture. However, no signals were observed for the
trinuclear complex [(Ph3P)Pt(µ-SiC12H8)]3 (9) (eq 3).6 When
solutions containing 8 were kept for several weeks at room
temperature and analyzed by 31P NMR spectroscopy, a small
resonance was observed for complex 9 as well as resonances
for OPPh3 and (Ph3P)4Pt.12
observed, suggesting that the formation of 11 occurred by
addition of two molecules of 5 to 1.
After the solution from the reaction between 1 and 2 equiv
of 5 was warmed and pentane was added, complex 7 was
isolated in 52% yield as a golden yellow, air-sensitive solid
(eq 4). Bis(silyl)platinum phosphine complexes have been
reported previously.14,15
The 1H NMR spectrum (300 K) collected immediately after
the room-temperature addition of 5 to 1 showed sharp signals
for the Pt-H resonance of the mononuclear product 6 and H2.
The resonances for the second mononuclear complex, 7, were
absent in both the 1H and 31P spectra (possibly due to fluxional
behavior on the NMR time scale). In addition to the signals for
6 and unreacted 1, the other major features in the 31P{1H} NMR
spectrum were several broad, ill-defined signals between 10 and
55 ppm and a small signal for 9. Cooling the solution to 223 K
When a solution prepared from the isolated complex 7 in
C7D8 was warmed from 223 to 300 K, the dinuclear complex 8
was observed as the major product by 31P{1H} NMR spectros-
copy (eq 5). After 1 day at room temperature the spectrum
1
after 30 min showed broad H and 31P signals for 6, sharp
resonances for 7, and peaks for the major species 8. Small
signals for the siloxane product (Ph3P)2Pt[Si(C12H8)OSi(C12H8)]
(10) (see below) and the hydrosilylation byproduct HSi-
(C12H8)(CH2CH3) were also observed. Signals for the latter
compound as well as for 6 and 7 were observed in the low-
temperature 29Si{1H} NMR spectrum. From our previous
studies, we found that the trinuclear complex 9 was gradually
formed over a 2-3 h period in the room-temperature reaction
of 1 with 5, and the result above suggests that the formation of
9 is inhibited at lower temperature.
remained unchanged, except for the formation of a small
resonance for the trinuclear complex 9. However, heating a
sample of 7 in C7D8 at 323 K resulted in nearly complete
consumption of 7 and formation of 8 as the major product, along
with a minor amount of the trinuclear complex 9. Heating a
solution of 7 for 1 h at 373 K produced only complex 8, but no
signals for 9 were observed at this higher temperature.
In contrast, with 1 in excess (1:5 ) 2:1) the low-temperature
addition reaction resulted in the formation of only the mono-
nuclear complex 6 and unreacted 1. However, when the mixture
was warmed to room temperature complete consumption of 6
was accompanied by the formation of 8 as the major product
and a trace of the trinuclear complex 9.
When the reaction of silafluorene 5 with 1 was performed at
low temperature and then the mixture was warmed to room
temperature and exposed to air for approximately 1 h, the
dinuclear complex 8 was the major product, along with a minor
amount of the trinuclear complex 9. This result suggests that
the products are possibly moderately air stable in solution for
a short time.
Attempts to isolate 6 have been unsuccessful. However,
isolation of 7 was achieved from the reaction of 1 and 5 in a
1:2 ratio. After addition at 195 K, the major Pt-Si-containing
product observed by 31P{1H} NMR spectroscopy was 7. In
addition, resonances for a species tentatively assigned to a six-
coordinate complex, (Ph3P)2Pt(H)2[Si(C12H8)H]2 (11), were
observed. Six-coordinate Pt(IV) phosphine complexes containing
silyl ligands are uncommon. Only a few examples have been
reported, and in some cases the complexes are thermally
unstable.13,14 One distinguishing feature of complexes of this
Reaction of the deuterated silafluorene 5-d2 with 1 was also
monitored by 2H NMR spectroscopy. NMR data were collected
at 223 K, and then the temperature was raised to room
temperature over a period of several hours. The variable-
2
temperature H NMR data are shown in Figure 1.
The 2H NMR spectrum collected at 223 K immediately after
addition of 5-d2 to 1 in C7H8/C6D6 showed several new
resonances. The major and prominent resonances were assigned
to the terminal Pt-D and the remaining deuteride at silicon in
6-d2, and those resonances became better resolved after 1.5 h.
Additional resonances were assigned to the minor products
(C12H8)Si(D)[C(H/D)2C(H/D)3] (from hydrosilylation),11 D2, and
11-d4. Approximately 1-1.5 h after addition, the region near 5
ppm became broad, consistent with the formation of the bis-
(silyl)platinum complex 7-d2. As the temperature was raised to
273 K, some signals became sharper, along with the gradual
disappearance of the Pt-D resonance for 6-d2 and the appear-
ance of a new broad signal at -1 ppm assigned to the averaged
signal for the two deuterides in the unsymmetrical dinuclear
1
type is a significantly smaller JPtP coupling value. Complex
11 exhibited an upfield shift of the 31P{1H} NMR resonance
compared to the signals for the mononuclear complexes 6 and
1
7 as well as a reduced JPtP coupling value compared to the
values obtained for 6 and 7. Complexes such as 11 (or 18; see
eq 7) could be generated by a stepwise addition of two Si-H
bonds in two molecules of 5 at one Pt center or by addition of
H2 to 7. The NMR spectroscopic data from the low-temperature
reaction of 1 with 5 exhibited signals assigned to 11 only in
the earliest stage of the reaction. Complex 11 appeared to be
unstable, and at later stages signals for both H2 and 7 were
(15) For some recent examples of bis(silyl)platinum complexes, see for
example: (a) Kim, Y.-J.; Park, J.-I.; Lee, S.-C.; Osakada, K.; Tanabe, M.;
Choi, J.-C.; Koizumi, T.; Yamamoto, T. Organometallics 1999, 18, 1349.
(b) Ozawa, F. J. Organomet. Chem. 2000, 611, 332. (c) Lee, Y.-J.; Bae,
J.-Y.; Kim, S.-J.: Ko, J.; Choi, M.-G.; Kang, S. O. Organometallics 2000,
19, 5546. (d) Tsuji, Y.; Nishiyama, K.; Hori, S.; Ebihara, M.; Kawamura,
T. Organometallics 1998, 17, 507. (e) Yamashita, H.; Tanaka, M.; Goto,
G. Organometallics 1992, 11, 3227.
(12) Sen, A.; Halpern, J. Inorg. Chem. 1980, 19, 1073.
(13) See for example: (a) Shimada, S.; Tanaka, M.; Honda, K. J. Am.
Chem. Soc. 1995, 117, 8289. (b) Michalczyk, M. J.; Calabrese, J. C.; Recatto,
C. A.; Fink, M. J. J. Am. Chem. Soc. 1992, 114, 7955. (c) Grundy, S. L.;
Holmes-Smith, R. D.; Stobart, S. R.; Williams, M. A. Inorg. Chem. 1991,
30, 3333.
(14) Heyn, R. R.; Tilley, T. D. J. Am. Chem. Soc. 1992, 114, 1917.

Platinum-Silicon Monomers and Dimers
Organometallics, Vol. 25, No. 11, 2006 2863
conditions, unlike the previously discussed 8-d2 system (see VT
NMR discussion below). However, when a solution containing
8 in C7D8 was treated with an excess (>2 equiv) of PPh3, a
broad signal near -1.3 ppm appeared, suggesting that the
presence of free phosphine influences the ability to observe the
resonance.
The low-temperature addition of silafluorene 5 to the Pt(0)
phosphine complex (Ph3P)4Pt (12) produced products similar
to those observed in the reaction of 5 with 1. For example, just
after addition at 223 K, signals for both of the mononuclear
complexes 6 and 7 (major product) were observed along with
H2. Additional minor resonances were also observed for the
tentatively assigned six-coordinate13 Pt complex 11. When the
solution was warmed to room temperature, the unsymmetrical
dinuclear complex 8 became the major product, in addition to
free PPh3. No trinuclear complex 9 was detected in the reaction
mixture.
One of the byproducts observed in the reaction of 1 with 5
was the complex (Ph3P)2Pt[Si(C12H8)OSi(C12H8)] (10). The
formation of 10 is probably due to the reaction of 7 with
adventitious oxygen or water in the reaction vessel and is likely
a consequence of the experimental procedure involved in the
low-temperature reaction studies. Related platinum-disiloxy
complexes have been described previously.16,17 Complex 10 was
prepared by an independent route from reaction of 1 with the
1,3-dihydrosiloxane HSi(C12H8)OSi(C12H8)H18 (13; eq 6). In-
evitably, minor 31P resonances for 10 are observed in reaction
mixtures after several hours following a variable-temperature
experiment.
2
Figure 1. Variable-temperature H NMR data for reaction of 1
with 5-d2: (a) just after mixing (223 K); (b) after 20 min (223 K);
(c) after 1.5 h (223 K); (d) after 2.5 h (243 K); (e) after 3 h (263
K); (f) after 4 h (273 K); (g) after 4.5 h (283 K); (h) after 5 h (300
K); (i) after ca. 24 h (300 K).
2
Figure 2. Selected H NMR data (76 MHz, C7D8): (a) reaction
solution containing 8-d2 after 24 h at 300 K; (b) solution containing
dissolved pure 8-d2 at 300 K; (c) reaction solution containing 8-d2
after 24 h at 223 K; (d) solution containing pure 8-d2 at 223 K.
complex 8-d2 present in the reaction mixture. When the sample
was recooled to 223 K, the spectrum showed the presence of
the terminal Pt-D in 8-d2 and a broad unresolved region near
2 ppm for the bridging hydride (Pt‚‚‚D‚‚‚Si) in 8-d2.
2
The room-temperature H NMR spectrum taken after 24 h
was comparable to the room-temperature spectrum obtained
earlier but with a significantly enhanced averaged Pt-D signal
for 8-d2. The 31P{1H} NMR spectrum for the reaction solution
exhibited a broad resonance due to the averaged signal from
the exchange between the phosphines in 8-d2 with free PPh3.
No signals were observed for the trinuclear complex 9. The
solution was recooled to 223 K, and the 31P{1H} NMR spectrum
exhibited resonances primarily for the unsymmetrical dinuclear
complex 8-d2 as well as for PPh3 and OPPh3. A minor resonance
was present for the byproduct (Ph3P)2Pt[Si(C12H8)OSi(C12H8)]
(10).
Reactions with H2SiC20H24. We previously reported that the
room-temperature reaction of the substituted silafluorene 3,7-
di-tert-butylsilafluorene18 (14) with complex 1 gave the unsym-
metrical dinuclear complex (Ph3P)2(H)Pt(µ-SiC20H24)(µ-η2-
HSiC20H24)Pt(PPh3) (15) in 86% yield, whose structure was
confirmed by X-ray crystallography.6a The direct Si-H addition
product (Ph3P)2Pt(H)(Si(C20H24)H) (16) was not observed at
room temperature. However, when the reaction was performed
at 193-195 K and monitored by 1H and 31P{1H} NMR
spectroscopy, resonances for 16 were observed just after
addition, as the major product from the reaction (eq 7). In
An interesting comparison was noted for the 2H NMR
resonances for 8-d2 found in solution compared to the spectrum
for the isolated and redissolved pure sample of 8-d2. The room-
temperature 2H NMR spectrum for 8-d2 in the reaction mixture
showed an averaged Pt-D signal at -1.1 ppm (1JPtD ) 102
Hz), but the isolated sample is shifted downfield to -0.17 ppm
(1JPtD ) 99 Hz) (Figure 2a,b). The low-temperature spectrum
for 8-d2 in the reaction mixture compared to the spectrum of
the pure sample contained essentially identical resonances for
the bridging and terminal deuterides (Figure 2c,d). The shifting
of resonances observed at room temperature may be influenced
by the presence (or absence) of free PPh3 or other species in
the reaction mixture.
(16) (a) Goikhman, R.; Karakuz, T.; Shimon, L. J. W.; Leitus, G.;
Milstein, D. Can. J. Chem. 2005, 83, 786. (b) Pham, E. K.; West, R. J.
Am. Chem. Soc. 1989, 11, 7667. (c) Pham, E. K.; West, R. Organometallics
1990, 9, 1517. (d) Bell, L. G.; Gustavson, W. A.; Thanedar, S.; Curtis, M.
D. Organometallics 1983, 2, 740. (e) Curtis, M. S.; Greene, J. J. Am. Chem.
Soc. 1978, 100, 6362.
(17) Osakada, K.; Tanabe, M.; Tanase, T. Angew. Chem., Int. Ed. 2000,
39, 4053.
(18) Chang, L. S.; Corey, J. Y. Organometallics 1989, 8, 1885.
The room-temperature 1H NMR spectrum for 8 in the reaction
solution resulting from the mixing of 1 and 5 (or 5 and 12; see
below) exhibited a broad Pt-H resonance for the averaged
hydride signals in 8. However, a pure sample of 8 does not
exhibit a well-defined signal for the hydrides under similar

2864 Organometallics, Vol. 25, No. 11, 2006
Braddock-Wilking et al.
Figure 3. 1H VT NMR data for 8 (500 MHz, C7D8): (a) 300 K;
(b) 290 K; (c) 280 K; (d) 270 K; (e) 260 K; (f) 250 K; (g) 240 K;
(h) 230 K.
Figure 4. 31P{1H} VT NMR data for 15 (202 MHz, C7D8): (a)
183 K; (b) 203 K; (c) 213 K; (d) 243 K; (e) 263 K; (f) 273 K; (g)
284 K; (h) 292 K.
addition, trace amounts of three other components were identi-
fied: the bis(silyl) complex cis-(Ph3P)2Pt(Si(C20H24)H)2 (17),
a product tentatively assigned to a six-coordinate species similar
to 10, the complex (Ph3P)2Pt(H)2[Si(C20H24)H]2 (18), and a third
species 19, which was unassigned.
heated in 10 K increments to 370 K, and this resulted in a shift
slightly downfield for the hydride resonance. These data are in
good agreement with NMR data collected on a pure sample of
21 in CD2Cl2 (see below). Recooling the solution to 223 K
showed 31P resonances for 8, 9, PPh3, and a minor amount of
OPPh3. In fact, heating a sample of 8 for 20 h at 358 K resulted
in complete consumption of 8 and formation of the trimer 9 as
the major Pt-Si-containing product. When the reaction of 1
and 5 was performed at room temperature followed by immedi-
ate heating to 323 K, the trinuclear complex 9 was formed (28%
isolated yield) in a yield essentially identical with that obtained
from the room-temperature reaction.6a
After the mixture was warmed to room temperature, the major
resonance in the 31P{1H} spectrum was a significantly broad
region centered at 18 ppm due to the averaged signals for the
unsymmetrical dinuclear complex 15. A minor signal was
assigned to the disiloxyplatinum complex (Ph3P)2Pt[Si(C20H24)-
OSi(C20H24)] (20), analogous to complex 10. When the reaction
1
was monitored by variable-temperature H and 31P{1H} NMR
spectroscopy, the signals for 16 began to broaden at 263 K,
while those for 17 remained sharp. When the solution was then
recooled to 223 K, signals for the dinuclear complex 15 were
observed along with those for 16 and 17. If the sample was
warmed to room temperature for just a few minutes and then
recooled to 223 K, signals for 16 disappeared and resonances
for 15 and 17 remained.
Approximately 15 h after a pure sample of 8 was dissolved
in C7D8, a small amount of a peach-colored solid was often
observed in the NMR tube. The solid was determined to be the
symmetrical dinuclear complex 21. Complex 21 is soluble in
CD2Cl2, but no resonance was observed in the room-temperature
31P NMR spectrum, indicating fluxional behavior on the NMR
Dynamic NMR Behavior of 8 and 15. Both of the dinuclear
complexes 8 and 15 showed fluxional behavior on the NMR
1
1
time scale. The H NMR spectrum of pure 8 in C7D8 at room
time scale. Examination of the H NMR spectrum at 223 K
temperature showed a substantially broadened signal near 0 ppm
for the two hydrides (Figure 3). When the temperature was
lowered, the hydride resonance initially became more broadened
and disappeared into the baseline by 270 K. At 250 K, a broad
signal became visible near -5 ppm that sharpened considerably
below 240 K due to the terminal hydride in 8. The low-
temperature resonance for the bridging hydride in 8 appears as
a partially obscured doublet overlapping with the resonance for
the solvent at 2 ppm (C7D8).
The coalescence temperature obtained from the variable-
temperature 31P{1H} NMR spectra for complex 8 was Tc ) 260
K, giving an approximate free energy of activation for ∆Gq of
11 kcal/mol. The coalescence temperature determined from
variable-temperature 31P{1H} experiments for complex 15 was
Tc ) 288 K, providing an approximate value for ∆Gq of 12
kcal/mol. The variable-temperature 31P NMR data for 15 are
shown in Figure 4. The exchange of phosphorus sites was
confirmed by a low-temperature 2D 31P-31P EXSY experiment.
The low-temperature 31P{1H} NMR data for 15 at 183 K
exhibited three broadened signals at 30, 22, and 20 ppm, each
with Pt satellites for the three different phosphorus sites in the
complex.
revealed a resonance for the equivalent bridging hydrides with
two sets of platinum satellites. The 31P{1H} spectrum displayed
a resonance with a satellite pattern characteristic of a dinuclear
Pt complex containing one phosphine at each platinum center.19
Heating a pure sample of 15 in C7D8 to 360 K did not show
1
any significant decomposition, as determined by H and 31P-
{1H} NMR spectroscopy. At 320 K, a broad signal was observed
that was assigned to the equivalent bridging hydrides in the
symmetrical dinuclear complex [(Ph3P)Pt(µ-η2-HSiC20H24)]2
(22). At 360 K, the signal was shifted downfield and appeared
as a sharp singlet with two sets of Pt satellites. The 31P{1H}
NMR spectrum obtained at 223 K after heating the solution to
360 K exhibited the characteristic signals for 15 as the major
species in solution. These results suggest that phosphine
coordination is reversible and that, if decomposition occurs, it
is to a minor extent. The molecular structure of 22 was
determined by X-ray crystallography (see the Supporting
Information); however, the structure was of low quality but
confirmed the connectivity of the complex. The structural
environment in 22 was similar to those of related symmetrical
dinuclear complexes previously reported.3e,g
When a sample of 15 was heated to higher temperatures
(368-373 K) in C7D8, the formation of several products was
Upon heating a sample of 8 in C7D8 to 320 K, a new broad
signal was observed in the 1H NMR spectrum that was assigned
to two equivalent bridging hydrides in the symmetrical dinuclear
complex [(Ph3P)Pt(µ-η2-HSiC12H8)]2 (21). The sample was
(19) Bender, R.; Braunstein, P.; Jud, J. M.; Dusausoy, Y. Inorg. Chem.
1984, 23, 4489.

Platinum-Silicon Monomers and Dimers
Organometallics, Vol. 25, No. 11, 2006 2865
observed. A new signal appeared at 71 ppm in the 31P{1H} NMR
spectrum and was assigned to the symmetrical trinuclear
complex [(Ph3P)Pt(µ-SiC20H24)]3 (23) (eq 8).6 A resonance was
Scheme 1
Scheme 2
also observed at 198 ppm (with Pt satellites) and was assigned
to the bridging phosphido group in the complex [(Ph3P)Pt(µ-
PPh2)]2. The phosphido complex was isolated from the mixture,
and the structure was confirmed crystallographically to be
identical with that in the published structure report.20 The
formation of the phosphido-bridged dinuclear complex resulted
from a formal extrusion of the silicon moiety and loss of a
phenyl group from the phosphorus center, but the fate of the
silicon unit was not determined. Several other resonances were
observed that are unassigned. Thus, the trinuclear complex 23
can be formed from the thermolysis of 15 but the more rigorous
reaction conditions produced a mixture where several other
minor products were formed in addition to the trimer 23.
However, the trimer 23 was isolated in 27% yield.
taining silicon ligands are known and were prepared from a
preexisting Pt3 cluster by Si-H bond activation.21
A proposed mechanism for the fluxional process responsible
for the variable-temperature behavior of 8 and 15 is shown in
Scheme 1. This mechanism involves loss of one of the two
equivalent phosphines at the (Ph3P)2(H)Pt site followed by
coordination of phosphine at the other Pt(PPh3) site with
concomitant transformation of the terminal Pt-H to a bridging
hydride and bridging Pt‚‚‚H‚‚‚Si to a terminal Pt-H unit. This
type of process would equilibrate the two different phosphorus
and hydride sites in the complex. Exchange of the two different
phosphorus and hydride sites was confirmed by low-temperature
proton and phosphorus EXSY experiments. A similar mecha-
nism has been proposed by Osakada et al. for related dipalladium
and mixed platinum-palladium dinuclear complexes.3a,h
A possible mechanism for the formation of the dinuclear
complex 8 (or 15) from the mononuclear complex 6 (or 16) is
shown in Scheme 2. The initial step in the process would involve
loss of the phosphine trans to the silicon center, producing a
reactive three-coordinate (T- or Y-shaped) intermediate. Oxida-
tive addition of the Si-H bond in 6 (or 16) with the three-
coordinate intermediate, followed by reductive elimination of
H2 and ring closure, would provide 8 (or 15). Loss of PPh3
from 8 would generate the symmetrical dinuclear complex 21
(or 22).
The formation of complex 8 from the bis(silyl)platinum
phosphine complex 7 may involve a similar process, where the
first step involves loss of PPh3 to give a three-coordinate species,
(Ph3P)Pt(SiR2H)2. A bimolecular reaction of this three-
coordinate species with 7 followed by reductive elimination of
a disilane (HSiR2-SiR2H, not observed by NMR spectroscopy)
and cyclization would give 8. An alternative mechanism could
involve reductive elimination of silafluorene and formation of
a platinum-silylene complex, (Ph3P)2PtdSiC12H8. Formation
of 8 from a PtdSi species of this type would then require
dimerization, loss of PPh3, and incorporation of H2 to give the
unsymmetrical dinuclear complex. A signal at 4.9 ppm was
observed in the early stages of the thermal decomposition of 7
to give 8, which may be due to the formation of silafluorene 5.
No signals were observed in the 31P NMR data that could be
attributed to the formation of a PtdSi species. The major
pathway for the formation of the trinuclear complex 9 is
probably due to a bimolecular reaction between 6 and 8. Further
studies are required to provide evidence in support of any
mechanism.
Discussion
Addition of the Si-H bond of Ph2SiH2 (2) to (Ph3P)2Pt(η2-
C2H4) (1) produced the previously described mononuclear
complex (Ph3P)2Pt(H)(SiPh2H) (3) as the major product.8 In our
examination of this reaction we found that the mononuclear
complex 3 appeared to exhibit fluxional behavior on the NMR
1
time scale, as evidenced by broad signals in both the H and
31P spectra at room temperature. Our studies also showed that
3 could be converted to the symmetrical dinuclear complex 4
upon heating. More recently, our studies have shown that
reducing the spatial requirements of the diarylhydrosilane
enhanced the reactivity of the Si-H-containing precursors. The
reaction of silafluorene 5 with 1 also produced the expected
Si-H bond activation product 6 as well as the bis(silyl) complex
7, resulting from addition of two Si-H units to the Pt center.
A minor amount of the unstable six-coordinate species 11 was
observed by low-temperature NMR spectroscopy. None of the
corresponding bis(silyl) or six-coordinate complexes were
observed in the reaction of 1 with 2. Complexes 6 and 7 were
stable at low temperature only for several hours. Warming a
C7D8 solution containing 6 and/or 7 resulted in the formation
of the unsymmetrical dinuclear complex 8 as the major product,
suggesting that the mononuclear compounds 6 and 7 are
precursors to 8. The room-temperature reaction of 1 with 5,
however, showed that the dinuclear product 8 was formed
immediately, followed by the formation of the trinuclear
complex 9 over a period of a few hours.6a
Compound 9 is a rare example of a trinuclear complex
containing either a bridging µ-SiR2 or terminal SiR3 ligand.
Osakada et al. reported that the thermolysis of cis-(Me3P)2Pt-
(SiPh2H)2 at 100 °C produced the trinuclear system [(Me3P)-
Pt(µ-SiPh2)]3.17 Two other related triplatinum complexes con-
(20) The complex [(Ph3P)Pt(µ-PPh2)]2 was previously characterized by
X-ray crystallography: Taylor, N. J.; Chieh, P. C.; Carty, A. J. J. Chem.
Soc., Chem. Commun. 1975, 448.
(21) (a) Itazaki, M.; Nishihara, Y.; Osakada, K. Organometallics 2004,
23, 1610. (b) Bender, R.; Braunstein, P.; Bouaoud, S.-E.; Merabet, N.;
Rouag, D.; Zanello, P.; Fontani, M. New J. Chem. 1999, 23, 1045.

2866 Organometallics, Vol. 25, No. 11, 2006
Braddock-Wilking et al.
Figure 6. Partial 31P{1H} NMR spectrum (C7D8, 223 K) of the
mixture obtained from the reaction between 8 and 15 after 24 h.
Figure 5. Partial 31P{1H} NMR spectrum of the mixture obtained
from the reaction of 15 with (p-Tol)3P (202 MHz, C7D8, 223 K).
exchange of silafluorenyl ligands could occur. The addition was
performed at 223 K (due to the thermal instability of 16 at room
temperature) followed by slow warming of the solution to room
temperature. A mixture of three unsymmetrical dinuclear
complexes, including unreacted 8, 15, and a new complex (eq
10) tentatively assigned to the mixed silafluorene system (Ph3P)2-
The low-temperature experiments described above confirmed
that the initial major products involved in the reactions shown
in eqs 1, 3, 4, and 7 were mononuclear Pt-Si complexes of the
types P2Pt(H)(SiAr2H) and P2Pt(SiAr2H)2. These complexes are
thermally unstable, and when they are warmed to room
temperature (or above), dinuclear complexes are produced. The
formation of the dinuclear products can be rationalized by the
mechanism shown in Scheme 2. No other intermediate species
were observed by low-temperature NMR spectroscopy. Both
mononuclear complexes appear to be precursors to the unsym-
metrical Pt2 complexes. Deuterium labeling studies between 5-d2
and 1 support these observations. In contrast to the low-
temperature reaction between 1 and 5, the room-temperature
reaction also produced the unsymmetrical dinuclear complex 8
as well as the trimer 9.6 These results suggest that 9 is probably
formed from a bimolecular reaction involving mononuclear and
dinuclear species. The observed fluxional behavior of the
unsymmetrical dinuclear complexes prompted us to investigate
their reactivity.
Reactivity Studies of Isolated Complexes. To evaluate the
mechanism shown in Scheme 1, complex 15 was reacted with
an external phosphine. Complex 15 was found to undergo
exchange with added (p-Tol)3P. In theory, the reaction of 15
with 2 equiv of (p-Tol)3P could produce a mixture of complexes
incorporating one, two, or three (p-Tol)3P ligands, as illustrated
in eq 9.
(H)Pt(µ-SiC20H24)(µ-η2-H-SiC12H8)Pt(PPh3) (24) were ob-
served, as determined by 31P{1H} NMR spectroscopy (Figure
6). No trinuclear complexes were observed, as determined by
the absence of any resonances in the region near 70 ppm, where
signals are typically observed for a species of the type [(Ph3P)-
Pt(µ-SiR2)]3.6
When the reaction was monitored by NMR spectroscopy at
223 K immediately after addition, signals for both 8 and 24
(but not 15) were observed by 1H and 31P{1H} NMR spectros-
copy, indicating that exchange takes place even at low temper-
ature. Further warming of the reaction mixture to room
temperature resulted in complete consumption of 16 and
formation of the mixture of dinuclear complexes 8, 15, and 24.
A minor amount of an unassigned product was also observed
(δ 15). In contrast, the room-temperature reaction between 5
and 15 gave a complex mixture of products, as shown by the
31P{1H} NMR spectrum.
The reaction between the two unsymmetrical dinuclear
complexes 8 and 15 was performed, and upon mixing of the
two complexes, no reaction was observed at room temperature
or after heating to 330 K for 45 min. However, heating the
mixture at 348 K for ca. 16 h resulted in the formation of several
new resonances near 70 ppm (with Pt satellites) in the 31P NMR
spectrum (eq 11). In addition, several smaller resonances were
observed near 30 and 65 ppm that have not been assigned. The
low-temperature (223 K) 31P NMR spectrum showed similar
resonances in addition to unreacted 15 and PPh3. The presence
of several resonances near 70 ppm suggests that the thermal
reaction between 8 and 15 produced not only the trinuclear
complex 9 but possibly also mixed trinuclear complexes
containing both bridging silafluorenyl and 3,7-di-tert-butylsi-
When a sample of 15 was reacted with 2 equiv of (p-Tol)3P,
the 31P NMR spectrum consisted of overlapping signals (with
Pt satellites), indicating replacement of PPh3 in the complex
with added P(p-Tol)3 (Figure 5). Signals for complex 15 were
observed, but due to the complexity of the spectrum, it is
probable that a number of products are formed. The spectrum
remained unchanged after 24 h, and phosphine exchange was
confirmed by a 2D 31P-31P EXSY experiment.
The low-temperature addition of the dinuclear complex 8 to
the mononuclear complex 16 was performed to determine if

Platinum-Silicon Monomers and Dimers
Organometallics, Vol. 25, No. 11, 2006 2867
ylphosphine)platinum(0) were obtained from Strem Chemical Co.
and used as received. Ethylenebis(triphenylphosphine)platinum(0)
was purchased from Aldrich Chemical Co. and was used as
received. Toluene-d8, benzene-d6, and methylene chloride-d2 were
purchased from Cambridge Isotopes, Inc., degassed by freeze-
thaw vacuum cycles, and stored over activated molecular sieves.
NMR spectroscopic data were recorded on a Bruker ARX-500
1
spectrometer at 500 MHz for H, 99 MHz for 29Si, and 202 MHz
for 31P. Proton chemical shifts (δ) are reported relative to the
residual protonated solvents C7D8 (2.09 ppm), C6D6 (7.15 ppm),
and CD2Cl2 (5.32 ppm). Silicon chemical shifts (δ) are reported
relative to external TMS (0 ppm). Phosphorus chemical shifts (δ)
are reported relative to external H3PO4 (0 ppm). Chemical shifts
are given in ppm and coupling constants in Hz. The majority of
the NMR data listed in this section for reaction mixtures include
selected key resonances that are characteristic for the particular
product; resonances for aromatic protons, for example, are not
included, since there are often many overlapping resonances.
Compounds 3,7 4,8 and 6, 8, 9, 15, and 166 have been reported
and/or characterized previously. Key NMR spectroscopic data for
compounds 3, 4, 6-11, 15-18, and 20-23 are summarized in
Table 1. Infrared spectra were recorded on a Thermo-Nicolet Avatar
360 E. S. P. FT-IR spectrometer. Elemental analysis determinations
were performed by Atlantic Microlabs, Inc., Norcross, GA.
General Procedure for Low-Temperature Addition Reac-
tions. The reactions are typically run on a 1:1 ratio between the
platinum and hydrosilane precursors. A solution of the platinum
precursor (Ph3P)2Pt(η2-C2H4) (1) (or Pt(PPh3)4 (12)) was made in
approximately 0.5 mL of C7D8 and transferred to a NMR tube
capped with a rubber septum. In a separate shortened NMR tube
capped with a septum was placed the hydrosilane precursor in 0.25-
0.5 mL of C7D8.. The solutions were then cooled in a dry ice/acetone
bath (-78 °C unless otherwise noted), and the hydrosilane solution
was added by syringe to the NMR tube containing the platinum
precursor. After sitting for a few minutes at low temperature, the
tube was removed, shaken vigorously for a few seconds, and then
returned to the cold bath. The sample was then placed in the
precooled NMR magnet at the desired temperature and NMR data
then collected at various reaction times after addition.
lafluorenyl ligands. No signal was observed for the trinuclear
complex [(Ph3P)Pt(µ-SiC20H24)]3 (23).
Conclusions
Part of the current study involved the examination of the low-
temperature reactions of diphenylsilane (2), silafluorene (5),
silafluorene-d2 (5-d2), and 3,7-di-tert-butylsilafluorene (14) with
(Ph3P)2Pt(η2-C2H4) (1). The major initial products obtained from
these reactions were mononuclear complexes with the general
formula (Ph3P)2Pt(H)(SiAr2H) and (Ph3P)2Pt(SiAr2H)2 (but not
with Ar ) Ph). Dinuclear complexes were obtained from these
reactions by warming solutions to room temperature or above.
Labeling studies involving 5-d2 with 1 at low temperature
provided additional evidence for the formation of mono- and
dinuclear products. The proposed mechanism of formation of
the unsymmetrical dinuclear complexes likely involves a
bimolecular reaction involving the mononuclear complex (Ph3P)2-
Pt(H)(SiAr2H) with the related three-coordinate reactive inter-
mediate. An important observation was that the formation of
the trinuclear complex 9 appears to be inhibited when the
reaction is performed at low temperature and probably involves
a bimolecular reaction between mononuclear and dinuclear
species.
VT-NMR studies of the unsymmetrical dinuclear complexes
8 and 15 suggested a fluxional process involving loss/recoor-
dination of a PPh3 ligand. This was confirmed by reaction of
complex 15 with added P(p-Tol)3 to produce a mixture of
dinuclear products resulting from phosphine exchange. Exchange
of silafluorenyl ligands was also observed from reactions
between mononuclear and dinuclear complexes as well as
between two different dinuclear complexes. Additional reactivity
studies are in progress and will be reported in the future.
Reaction of Diphenylsilane (2) with (Ph3P)2Pt(η2-C2H4) (1):
Isolation of 4. (a) Low-Temperature Addition. The NMR tube
containing 1 (40 mg, 0.054 mmol, 0.5 mL of C7D8) was cooled in
a Dewar of liquid N2. A solution of 2 (10 mg, 0.054 mmol, 0.25
mL of C7D8) was added slowly by syringe to the tube containing
1, and then after approximately 5 min the tube was transferred to
a cold bath (-78 °C) and then placed in the precooled magnet of
the spectrometer. NMR data collection was started at 223 K
approximately 5 min after mixing. After approximately 4.5 h the
temperature was raised to 243 K and then gradually up to room
temperature over ∼7 h. NMR signals for (Ph3P)2(H)PtSiHPh2 (3)
were observed within minutes after addition at 223 K, and no new
resonances were observed in the NMR spectra as the temperature
was raised, but the resonances broadened significantly above 243
K. After reaching room temperature, the NMR sample was then
heated at 323 K for 0.5 h, after which no mononuclear complex
was observed and white crystals of complex 4 (12 mg, 70%)8 had
formed in the NMR tube. The resulting solution was examined by
31P{1H} NMR spectroscopy at 193 K, and signals for PPh3 (δ -7.7),
1
OPPh3 (25.8), and Pt(PPh3)4 (δ 10.3, JPtP ) 3828, major compo-
nent)12 were observed as well as an unidentified resonance at 14.6
Experimental Section
ppm (1JPtP ) 3612).
General Considerations. All glassware was oven- or flame-
dried prior to use. Reactions were performed (or samples prepared)
under an argon or nitrogen atmosphere, either on a double-manifold
Schlenk line or in an inert-atmosphere drybox. Silafluorene,22 3,7-
di-tert-butylsilafluorene,18 and diphenylsilane23 were prepared as
described previously. Tri-p-tolylphosphine and tetrakis(triphen-
(22) (a) Chang, L. S.; Corey, J. Y., J. Organomet. Chem. 1986, 307, 7.
(b) For a recent report on the synthesis of dichlorosilafluorene see: Liu,
Y.; Stringfellow, T. C.; Ballweg, T.; Guzei, I. A.; West, R., J. Am. Chem.
Soc. 2002, 124, 49.
(23) Benkeser, R. A.; Landesman, H.; Foster, D. J. J. Am. Chem. Soc.
1952, 74, 648.

2868 Organometallics, Vol. 25, No. 11, 2006
Braddock-Wilking et al.
1
Selected NMR spectroscopic data for 3 are as follows. 1H NMR
(500 MHz, C7D8, 223 K, 5 min after mixing): δ 4.82 (br m, SiH),
7), 35.3 (br s with Pt satellites, JPtP ) 1885, P trans to Si for 6),
32.5 (br s with Pt satellites, 1JPtP ) 2500, P cis to Si for 6), 25.7 (s,
OPPh3).
1
2
2
-1.0 (dd, JPtH ) 1008, JPH(trans) ) 155, JPH(cis) ) 21, PtH).
1
31P{1H} NMR (202 MHz, C7D8, 223 K, 10 min): δ 35.5 (d, JPtP
After 2.5 h, the temperature was raised slowly by 20 K
increments and broadening of the 1H and 31P resonances listed above
was observed. Selected 31P{1H} NMR (C7D8, 202 MHz, 283 K, 4
2
1
) 2506, JPP ) 10, cis-P-Pt-Si), 35.2 (d, JPtP ) 1785, trans-
P-Pt-Si). 29Si{1H} NMR (99 MHz, C7D8, 223 K, 2.5 h after
1
2
1
mixing, DEPT): δ 9.6 (dd, JPtSi ) 1113, JPSi ) 136 (trans), 15
h after mixing): δ 37.5 (br, JPtP ) 1928, 7), 29.2 (s, minor
(cis)).7 Selected 1H NMR (500 MHz, C7D8, 303 K, 7 h after
component, 10), 24.9 (s, OPPh3), 23.2 (unsassigned minor com-
ponent), 15.0 (br, 8). Selected 1H NMR data (C7D8, 500 MHz, 300
K, 5 h after mixing): δ 4.88 (br, HR2SiCH2CH3), 0.97 (t, HR2-
1
addition): δ 4.74 (br s, SiH), -1.35 (br s, JPtH ) 1018, PtH).
Selected 31P{1H} NMR (202 MHz, C7D8, 303 K, 7 h after
addition): δ 35.7 (br s, 1JPtP ) 2494). Selected 1H NMR (500 MHz,
C7D8, 223 K, 5 days after addition): δ 4.83 (br s, SiH), -0.94 (br
1
SiCH2CH3), 0.81 (m, HR2SiCH2CH3), -1.17 (br s, JPtH ) 658,
Pt‚‚‚H‚‚‚Si for 8). 31P{1H} NMR data (C7D8, 202 MHz, 300 K, 5
h after mixing): δ 46.4 (s, unassigned minor product), 45.2 (m,
s, JPtH ) 1016, PtH). Selected 31P{1H} NMR (202 MHz, C7D8,
1
223 K, 5 days after addition): δ 35.5 (br s, 1JPtP ) 2466), 25.4, s,
OPPh3), -6.0 (br s, PPh3); several minor unassigned resonances
were observed between 10 and 44 ppm.
1
unassigned minor product), 29.3 (s, JPtP ) 1710, 10), 24.8 (s,
OPPh3), 11 (br covering 4-18 ppm, major component, 8). 31P-
{1H} NMR data (C7D8, 202 MHz, 300 K, 19.5 h after mixing): δ
1
(b). Room-Temperature Addition. In a separate experiment at
room temperature, a solution of 2 (12 mg, 0.065 mmol, 0.5 mL of
C6D6) was added to 1 (47 mg, 0.063 mmol, 0.5 mL of C6D6).
Vigorous bubbling was observed. 1H NMR (500 MHz, C6D6, 300
K, 10 min after addition at room temperature): δ 4.8 (br, SiH),
24.8 (s with Pt satellites, JPtP ) 2039, minor product), 24.3 (s,
OPPh3), 12.8 (br covering 4-18 ppm, major component, 8).
Selected 1H NMR data (C7D8, 500 MHz, 223 K, 24 h after
2
1
mixing): δ 2.0 (d, JPH ) 12, Pt‚‚‚H‚‚‚Si for 8), -4.9 (t, JPtH
)
577, JPtH ) 80, JPH ) 10, Pt-H for 8). 31P{1H} NMR (C7D8,
2
2
1
-1.2 (br with Pt satellites, JPtH ) 1000 Hz). 31P{1H} NMR (202
202 MHz, 223 K, 24 h after mixing): δ 31.1 (t, 1JPtP ) 4260, 2JPtP
3
1
2
MHz, C6D6, 300 K, 10 min after addition): δ 35.6 (br with Pt
) 265, JPP ) 25, 8), 25.1 (s, OPPh3), 17.3 (d, JPtP ) 3438, JPtP
) 135, 8), -6.8 (s, PPh3).
After 48 h the 223 K H and 31P spectra remained essentially
unchanged. Lowering the temperature to 183 K gave severely
broadened resonances, and no new peaks were observed. Selected
NMR data 3 weeks after addition for the soluble fraction of the
reaction mixture are as follows. 31P{1H} NMR (C7D8, 202 MHz,
183 K): δ 69.7 (s, minor component, 9), 30.9 (br, minor component,
8), 25.5 (s, major component, OPPh3), 17.4 (br, minor component,
1
satellites, JPtP ) 2495 Hz). 29Si{1H} NMR (99 MHz, C6D6, 300
K, 1 h after mixing, DEPT): δ 8.0 (1JPtSi ) 1133 Hz). 31P{1H}
NMR (202 MHz, C6D6, 300 K, 5 h after addition): δ 10-50 (br,
maximum peak height at 35 ppm), 25.1 (s, OPPh3).
1
In a separate experiment at low temperature, a solution of 2 (5
mg, 0.027 mmol, ca. 0.5 mL of C7D8) was added to 1 (20 mg,
0.027 mmol, ca. 0.5 mL of C7D8). Formation of the mononuclear
complex 3 was observed by 1H and 31P{1H} NMR spectroscopy at
223 K, and then the solution was heated to 323 K for 30 min. A
white crystalline solid of 4 formed in the NMR tube and was
isolated in 70% yield (12 mg). NMR spectroscopic data for isolated
1
8), 10.3 (s, major component, Pt(PPh3)4, JPtP ) 3832), -7.7 (s,
major component, PPh3). After 48 h, the sample was returned to
the drybox, where several drops of pentane were added to the
solution. Three weeks later, a small amount of a dark red-purple
crystalline solid was present in the NMR tube (probably trinuclear
complex 9, yield not determined). The dark red soluble fraction
was decanted and examined by low-temperature 31P{1H} NMR
spectroscopy.
1
4 are as follows. H NMR (500 MHz, CD2Cl2, 223 K): δ 6.94-
1
7.80 (m, aromatic region), 2.84 (s with Pt satellites, JPtH ) 624,
2JPtH ) 111, Pt‚‚‚H‚‚‚Si). 31P{1H} NMR (202 MHz, CD2Cl2, 223
1
2
K): δ 34.6 (s with Pt satellites, JPtP ) 4242, JPtP ) 282,3JPP
)
52). IR (neat, cm-1): ν 1685 (Pt‚‚‚H‚‚‚Si).
(b) Addition of Silafluorene to (Ph3P)2Pt(η2-C2H4) at Room
Temperature followed by Cooling to -50 °C: Observation of
6-8. A solution of silafluorene (12 mg, 0.066 mmol, 0.25 mL of
C7D8) was added to a solution of (PPh3)2Pt(η2-C2H4) (41 mg, 0.055
mmol, 0.75 mL of C7D8) at room temperature (significant bubbling
was observed); the mixture was shaken vigorously and then
immediately placed in the NMR magnet at 300 K. Selected 1H NMR
data (500 MHz, C7D8, 300 K, just after mixing): δ 5.25 (br, C2H4
and overlapping SiH resonance), 4.50 (s, H2), 2.52 (br, coordinated
Low-Temperature Reaction Studies of Silafluorene with
(Ph3P)2Pt(η2-C2H4). (a) Addition of Silafluorene to (Ph3P)2Pt-
(C2H4) at -50 °C: Observation of 6-8. A solution containing 5
(12 mg, 0.066 mmol, 0.25 mL of C7D8) was added to a cooled
solution of 1 (50 mg, 0.067 mmol, 0.75 mL of C7D8). A small
amount of bubbling was observed. The tube was then transferred
to a precooled NMR magnet at 223 K. Experiments were begun
within 5 min and were run continuously for 24 h at varying
temperatures. After 24 h, the temperature was returned to 223 K
and then to 183 K, and further measurements were obtained. The
sample was checked again after approximately 48 h, and measure-
ments were taken again at 300, 223, and 183 K, showing no change
in comparison to data collected after 24 h.
1
C2H4 for 1), -0.9 (br, Pt‚‚‚H‚‚‚Si for 8), -1.73 (dd, JPtH ) 956,
2JPH ) 156 (trans), 21 (cis), PtH for 6). 31P{1H} NMR data (202
MHz, C7D8, 300 K, just after mixing): δ 70.6 (s, minor component,
1
1
9), 34.7 (br s, JPtP ) 3746, unreacted 1), 32.8 (d, JPtP ) 1879,
2JPP ) 8, P trans to Si for 6), 32.6 (prob d, JPtP ) 2539, P cis to
1
1H NMR data (C7D8, 500 MHz, 223 K, 5 min after mixing): δ
2
Si for 6), 29.7 (s, minor component, 10), 24.8 (s, OPPh3), 10-55
(br multiple resonances). Selected 1H NMR data (500 MHz, C7D8,
223 K, 30 min after mixing): δ 5.29 (s, C2H4), 5.0 (m, overlapping
Si-H resonance for 7 and H(C12H8)SiCH2CH3), 4.55 (s, H2), 0.97
(t, HR2Si-CH2CH3), 0.75 (m, HR2Si-CH2CH3), -1.38 (br d, 1JPtH
7.8-6.7 (aromatic resonances), 6.6 (s with Pt satellites, JPtH
)
57, SiH for 6), 5.2 (s, C2H4), 5.0 (m, overlapping SiH resonances
3
for 7 and H(C12H8)SiCH2CH3), 4.5 (s, H2), 0.98 (t, JHH ) 7.5,
1
HR2SiCH2CH3), 0.76 (m, HR2SiCH2CH3), -1.61 (br d, JPtH
)
944,2JPH ) 139, PtH for 6). 31P{1H} NMR (C7D8, 202 MHz, 223
2
1
1
) 975, JPH ) 149, unassigned Pt-H), -1.66 (br s, JPtH ) 940,
Pt-H for 6), -4.95 (t, 1JPtH ) 569, 2JPtH ≈ 90, 2JPH ) 9, Pt-H for
8). 29Si{1H} NMR data (99 MHz, 223K, DEPT, 30 min after
mixing): δ -15.1 (s, HR2SiCH2CH3), -17.2 (dd, Pt satellites not
K, 10 min after mixing): δ 37.5 (s, JPtP ) 1953 Hz, 7); small
broad resonances observed at 38, 35, and 33 ppm (unassigned, but
1
the last two resonances are probably due to 6). Selected H{31P}
NMR data (C7D8, 500 MHz, 223 K, 1.5 h after mixing): δ 6.56 (s,
1
2
2JPtH ) 56, SiH for 6), 4.98 (s, JSiH ) 176 Hz,2JPtH ) 29, Si-H
resolved, JPSi ) 144 (trans), 20 (cis), 7), -20.7 (br, Pt satellites
1
for 7), -1.4 (s, JPtH ) 973, PtH for unassigned minor product),
not resolved, 6). Selected 31P{1H} NMR data (202 MHz, C7D8,
1
1
-1.61 (s, JPtH ) 944 Hz, PtH for 6). 31P{1H} NMR (C7D8, 202
223 K, 2.5 h after mixing): δ 37.7 (s, JPtP ) 1952, 7), 31.1 (t,
1
2
3
1
MHz, 183 K, 1.75 h after mixing): δ 37.5 (br, JPtP ) 1948 Hz,
1JPtP ) 4257, JPtP ) 247, JPP ) 26, 8) 17.2 (d, JPtP ) 3427,

Platinum-Silicon Monomers and Dimers
Organometallics, Vol. 25, No. 11, 2006 2869
Pt(PPh3)2, 8); several minor resonances were also observed between
20 and 42 ppm but were not assigned, -7 (br, PPh3).
component), a small amount of the trinuclear complex 9 (δ 69.7),
and some remaining unreacted complex 1.
Reaction of Silafluorene-d2 with (Ph3P)2Pt(η2-C2H4). Silafluo-
rene-d2 (10 mg, 0.054 mmol, 0.5 mL of C7H8) was added to a cooled
NMR tube containing 1 (40 mg, 0.054 mmol, 0.5 mL of C7H8 and
1 drop of C6D6). NMR spectroscopic data were collected at 223 K
immediately after addition and at multiple time intervals for several
hours thereafter with warming to room temperature.
Reaction of (Ph3P)2Pt(η2-C2H4) with Silafluorene in a 1:2
Ratio of Pt to Si. Isolation of (Ph3P)2Pt(SiHC12H8)2 (7). A cooled
solution of 5 (11 mg, 0.054 mmol, 90% purity, 0.3 mL of C7D8)
was added to a cooled solution of 1 (20 mg, 0.027 mmol, 0.5 mL
1
of C7D8). The 31P{1H} and H NMR spectra were recorded just
after addition at 223 K, and resonances for 6 (broadened),6a 7 (major
product, data for isolated 7 are given below), and a complex that
has been tentatively assigned to the six-coordinate species (Ph3P)2-
Pt(H)2[Si(C12H8)H]2 (11) were observed. Selected NMR data for
11 obtained just after addition are as follows. 1H NMR (C7D8, 500
MHz, 223 K): δ 5.58 (m, Si-H), -7.52 (t, 1JPtH ) 672, 2JPH (cis)
) 11, Pt-H). 31P{1H} NMR (C7D8, 202 MHz, 223 K) δ 10.1 (s,
2H NMR (76 MHz, C7D8, 223 K, immediately after mixing): δ
6.6 (br shoulder overlapping C6D6 resonance, SiD for 6-d2), 5.5-
5.0 (br), 4.9 (br s, unreacted 5-d2), 4.5 (s, D2), 2.0 (t, J ) 2, probably
due to toluene with deuterium incorporation),24 1.3 (br s, assigned
to D(C12H8)Si[C(H/D)2C(H/D)3]), 0.9 (br s, assigned to D(C12H8)-
Si[C(H/D)2C(H/D)3]), -1.6 (br, PtD for 6-d2), -7.3 (br, PtD for
11-d4).
1
with Pt satellites, JPtP ) 1330 Hz).
At T ) 223 K for the time interval from t ) 20 min to 1.5 h the
region near 4.9 ppm (for 5-d2) broadened and increased in intensity
and a new small peak (s) appeared at 0.8 ppm (possibly due to
deuterioethane). In addition, the broad resonance centered at -7
ppm for 11-d4 disappeared.
At T ) 243 K (t ) 2.5 h) the 2H NMR spectrum showed a peak
at 6.5 ppm for 6-d2 and a more defined broad peak centered at
approximately 5.1 ppm (probably due to 7-d2) overlapping with a
decreased amount of 5-d2 at 4.9 ppm. Essentially the same spectral
features were observed at T ) 263 K (t ) 3 h).
The temperature was kept at 223 K for 30 min, and then the
solution was warmed to 273 K and maintained at that temperature
for 30 min. The solution was then transferred to a Schlenk tube,
and 10 mL of cold pentane was added, resulting in precipitation of
a pale yellow solid. The sample was placed in a freezer (-50 °C)
overnight. The solvent was removed by syringe and the solid dried
under vacuum to give 7 (15 mg, 52%). NMR spectroscopic data
1
for 7 are as follows. H NMR (C7D8, 500 MHz, 223 K): δ 8.0-
6.6 (aromatic resonances); 5.02 (m, Si-H). 31P{1H} NMR (C7D8,
1
202 MHz, 223 K): δ 37.7 (s, with Pt satellites, JPtP ) 1952 Hz).
At T ) 273-283 K (t ) 4-4.5 h) the following changes were
Selected 1H{31P} NMR (500 MHz, C7D8, 223 K): δ 5.04 (s, 1JSiH
2
observed in the H NMR spectrum. Resonances at 6.5, 5.1, and
2
) 176, JPtH ) 29). Anal. Calcd for C60H48P2PtSi2: C, 66.59; H,
4.9 ppm were less broad (latter peak also lower intensity) and the
peak at 0.8 ppm became more intense. In addition, a new broad
resonance was now prominent at -1.3 ppm (assigned to Pt-D in
8-d2) overlapping with the now less intense (but slightly sharper)
peak at -1.9 ppm for 6-d2.
When the temperature had reached 300 K (t ) 5 h), the signals
for the products 6-d2 and 7-d2 were absent. The resonance at -1.2
remained but had shifted to -1.0 ppm with partially defined Pt
satellites.
4.47. Found: C, 66.83; H, 4.91. Selected IR data for 7 (cm-1): ν
2054 (Si-H).
A pure sample of 7 was dissolved in C7D8 at 223 K, kept at that
temperature for 1 h, and then warmed to 300 K. The 31P{1H} NMR
spectrum showed signals for the dinuclear complex 8 at 31.1 and
17.2 ppm.6a After 2 h the 31P NMR resonance for 7 had nearly
disappeared and signals for 8 (major Pt-Si containing product),
as well as PPh3, OPPh3, and (Ph3P)2Pt[Si(C12H8)OSi(C12H8)] (10,
see below) were all present in addition to an unidentified resonance
at 32.9 ppm (1JPtP ) 1753). After 1 day at room temperature the
spectrum was essentially the same, except that a new resonance
was observed for the trinuclear complex [(Ph3P)Pt(µ-SiC12H8)]3 (9)
at 70 ppm.6 The relative ratio of the dinuclear (8) to the trinuclear
complex (9) after 1 day was approximately 6:1.
The reaction solution was then cooled to 223 K (t ) 5.25 h) to
confirm the presence of the unsymmetrical dinuclear complex 8-d2.
Two new broad resonances were now present near 2.1 ppm
overlapping with the triplet peak at 2.08 ppm (assigned to the
partially deuterated toluene) and -4.9 ppm (with broad Pt satellite
shoulder) assigned to 8-d2. The 2H spectrum collected after 24 h at
223 K was essentially identical. 31P{1H} NMR (202 MHz, C7H8/
C6D6, 223 K, 24 h): δ 31.2 (t, Pt-PPh3, 1JPtP ) 4267, 2JPtP ) 264,
3JPP ) 28, for 8-d2), 17.4 (d, Pt(PPh3)2, 1JPtP ) 3441, 2JPtP ) 135,
for 8-d2). Minor resonances were observed for OPPh3 (25 ppm),
PPh3 (-6 ppm), and a trace amount of 10 (29 ppm).
Heating a pure sample of 7 in C7D8 at 323 K for ca. 1.5 h resulted
in nearly complete consumption of 7 and the formation of 8 (major
product), 10 (see below), PPh3, OPPh3, an unidentified peak at 32
ppm (minor), and a small amount of the trinuclear complex 9 (ratio
of 8:9 ) 20:1) as determined by 31P{1H} NMR spectroscopy. When
a sample of 7 in C7D8 was heated to 373 K for 1 h, all of 7 had
been consumed and the major product observed by 31P{1H} NMR
spectroscopy was the dinuclear complex 8, along with PPh3 and
OPPh3. No signals for the trinuclear complex 9 were observed. A
minor unidentified product appeared at 21.2 ppm.
Reaction of (Ph3P)2Pt(η2-C2H4) with Silafluorene in a 2:1
Ratio of Pt to Si. A cooled solution of 5 (2 mg, 0.01 mmol, 0.4
mL of C7D8) was added to a cooled solution of 1 (16 mg, 0.021
mmol, 0.5 mL of C7D8). The sample was then transferred to a
precooled NMR magnet at 223 K, and then the temperature
immediately decreased to 193 K. Only the mononuclear complex
6 (δ 35.3 and 32.7), unreacted 1 (δ 33.7),12 and a small amount of
OPPh3 (δ 25.9) were observed by 31P{1H} NMR spectroscopy.
However, complex 6 was thermally unstable, and when the
temperature was maintained at 253 K for 1 h, signals for the
dinuclear complex 8 were then observed (δ 30.1, 17.2) along with
a trace amount of complex 7 (δ 37.4). The intensity of the signals
for 8 increased with time, and the resonances for complex 6
disappeared. Warming the sample to 300 K for 40 min followed
by examination of the mixture by 31P{1H} NMR spectroscopy at
223 K showed signals for the dinuclear complex 8 (major
2
The H NMR spectrum was also collected after 24 h at 300 K.
The spectrum obtained was essentially the same as that collected
at t ) 5 h at 300 K, but the resonance at - 1 ppm (for 8-d2) was
now better resolved, with clearly defined Pt satellites (1JPtD ) 101).
The NMR sample containing the reaction mixture was treated
with approximately 5 mL of pentane and the solution placed in a
low-temperature freezer (-35 °C). After several hours a red-brown
solid (8-d2) was obtained. The solid was washed with additional
pentane, dried in vacuo, and then redissolved in fresh C7H8 with 1
drop of C6D6 and analyzed by 2H NMR at 223 and 300 K. 2H NMR
(76 MHz, C7H8/C6D6, 300 K): δ -0.8 (s with Pt satellites, 1JPtD
)
100, for 8-d2); a small amount of the toluene with D incorporation
was observed at 2.1 ppm. 2H NMR (76 MHz, C7H8/C6D6, 223 K):
δ 2.07 (br s, Pt‚‚‚D‚‚‚Si, for 8-d2), -4.8 (br, Pt-D, for 8-d2) observed
in approximately 1:1 ratio by NMR integration.
Low-Temperature Reaction of Silafluorene with (Ph3P)4Pt.
Silafluorene (5; 8 mg, 0.04 mmol, 0.25 mL of C7D8) was added to
a cooled solution of (Ph3P)4Pt (12; 48 mg, 0.039 mmol, 0.75 mL
(24) The signal could be due to C7D8 vapors present in the drybox
atmosphere that were introduced during sample preparation.

2870 Organometallics, Vol. 25, No. 11, 2006
Braddock-Wilking et al.
of C7D8). NMR data collection was performed immediately after
addition at 223 K and at multiple time intervals and temperatures
during an approximately 24 h time period.
C7D8, 263 K): δ 7.04 (s, SiH for 16, tentative assignment), 5.27
(s, C2H4), 5.03 (m, SiH for 17), 4.53 (s, H2), 2.58 (br, C2H4 for 1),
2
-1.44 (br d, 1JPtH ) 950, JPH ) 149, PtH for 16). 31P{1H} NMR
1
1
data (202 MHz, C7D8, 263 K): δ 38.8 (s, JPtP ) 1965, 17), 36-
Selected H NMR data (500 MHz, C7D8, 223 K, immediately
33 (br, overlapping 16 and unreacted 1), 25.0 (s, OPPh3). The
after mixing): δ 6.60 (s, SiH overlapping with aromatic region,
6), 5.59 (m, SiH, minor product, tentative assignment 11), 5.05
solution was kept at 263 K for 30 min and then recooled to 223 K.
1
1
Selected H NMR data after warming to 263 K for 30 min (500
(m, SiH for 7), 4.46 (s, H2), -1.75 (br, JPtH ) 938, Pt-H, 6),
-7.51 (t, 1JPtH ) 673, 2JPH ) 11, PtH for 11). 31P{1H} NMR (202
MHz, C7D8, 223 K, 1-2 h after mixing): δ 40-10 (br), 37.7 (s,
MHz, C7D8, 223 K): δ 7.07 (s, SiH for 16), 5.29 (s, C2H4), 5.09
(m, SiH for 17), 4.55 (s, H2), 2.70 (br, C2H4 for 1), 1.92 (d, Pt‚‚‚
1
2
1
1JPtP ) 1953, 7), 10.1 (s, JPtP ) 1330, assigned to 11), -5.9 (br,
H‚‚‚Si for 15), -1.21 (br d, 16), -5.22 (t, JPtH ) 561, JPH ) 8,
PtH for 15). 31P{1H} NMR data after warming to 263 K for 30
min (202 MHz, C7D8, 223 K): δ 38.6 (s, 17), 35.1 (br s, 16), 34.0
(s, 1), 33. 5 (br s, 16), 30.3 (t, 15), 25.4 (s, OPPh3), 21.5 (br, 15).
NMR data were collected after the solution was warmed to room
temperature for a few minutes and then recooled to 223 K. Selected
1H NMR data (500 MHz, C7D8, 223 K, after warming to room
temperature): δ 5.29 (s, C2H4), 5.10 (m, SiH for 17), 4.55 (s, H2),
2.70 (s, C2H4 for 1), 1.93 (d, Pt‚‚‚H‚‚‚Si, 2JPH ) 12, 15), -5.20 (t,
15). 31P{1H} NMR (202 MHz, C7D8, 223 K, after warming to room
temperature): δ 38.1 (17), 30.3 (t, 15), 29.5 (20), 25.4 (OPPh3),
21.5 (br, 15), -6.8 (PPh3).
PPh3); distinct signals were not observed for 6, possibly due to
exchange. 29Si{1H} NMR (99 MHz, C7D8, 223 K, 3.5 h after
1
2
mixing): δ - 17.2 (dd, JPtSi ) 1095, JPSi ) 144, 20, 7), -20.8
(br s, JPtSi ) 1128, 6). After 7 h at 223 K, H and 31P NMR data
were essentially identical with the data collected just after mixing.
After 7 h the solution was slowly warmed to room temperature
over a period of several hours. When the temperature had reached
1
1
283 K, the H and 31P resonances for 6 and 7 were substantially
1
reduced in intensity and disappeared as the sample reached room
temperature.
Selected 1H NMR (500 MHz, 303 K, 13 h after mixing): δ -1.3
ppm (JPtH ≈ 650, averaged PtH for 8). Selected 31P{1H} NMR data
(202 MHz, C7D8, 303 K, 13 h after mixing): δ 46.4 (s unassigned
minor product), 45.1 (d, unassigned minor product), 24.4 (s, OPPh3),
NMR data were collected from a similar low-temperature
experiment 45 min after addition at low temperature. 1H-31P-COSY
(500 MHz, C7D8, 223 K): correlations observed between (1H, 31P)
resonances at (5.1, 38.4) for 17, (-1.26, 33.7) for 16, (-5.96, -8.4)
for 18, and (-9.35, 5.4) for 19. 1H-29Si HMQC (500 MHz, C7D8,
223 K): correlation observed between (1H, 29Si) resonances at (7.07,
-18.5) for 16, (5.1, -17.2) for 17, and (4.9, -42.7) for 14. Selected
29Si{1H} NMR (99 MHz, 223 K, 2.5 h after addition): δ -17.2
(dd, for 17, 1JPtSi not resolved, 2JPSi ) 141 (trans), 19 (cis)), -18.5
1
-1 ppm (covering region from +5 to -10 ppm, 8). Selected H
NMR data (500 MHz, 223 K, 24 h after mixing): δ 2.04 (d,
1
2
2JPH ) 13, Pt‚‚‚H‚‚‚Si for 8), - 4.94 ppm (t, JPtH ) 574, JPH
≈
10, Pt-H for 8). Selected 31P{1H} NMR data (202 MHz, C7D8,
223 K, 24 h after mixing): δ 31.0 (t, JPtP ) 4260, JPtP ) 257,
3JPP ) 28, Pt-PPh3 for 8), 25.2 (s, OPPh3), 17.3 (d, 1JPtP ) 3434,
Pt(PPh3)2 for 8), -6.8 (s, PPh3).
1
2
1
2
(dd, for 16, JPtSi ) 1105, JPSi ) 154 (trans), 11 (cis)).6a
Variable-Temperature NMR Study of (Ph3P)2(H)Pt(µ-SiC12H8)-
(µ-η2-HSiC12H8)Pt(PPh3) (8). A sample of 8 (10 mg) in 0.75 mL
of C7D8 was monitored by VT-31P{1H} NMR spectroscopy over
the temperature range between 300 and 223 K. The coalescence
temperature was determined to be Tc ) 260 K. A separate sample
Synthesis of (Ph3P)2Pt[Si(C12H8)OSi(C12H8)] (10). A low-
temperature solution of [H(C12H8Si)]2O (13; 8 mg, 0.02 mmol, 0.3
mL of C7D8) was added to a low-temperature solution of 1 (16
mg, 0.021 mmol, 0.5 mL of C7D8). The reaction tube was shaken
several times to mix the contents, and after approximately 10 min,
1
1
the31P{1H} and H NMR data showed the presence of 10 as the
of 8 (6 mg) in ca. 0.75 mL of C7D8 was examined by H NMR
1
spectroscopy from 310 to 370 K. Selected H NMR data for Pt‚‚‚
major species. Pentane (5 mL) was added, and a yellow precipitate
formed. The yellow solid was dried under vacuum to give 10 (13
mg, 56%). 1H NMR (C7D8, 500 MHz, 300 K): δ 8.4-6.5 (aromatic
resonances). 31P{1H} NMR (C7D8, 202 MHz, 300 K): δ 29.5 (s,
1JPtP ) 1708 Hz). Anal. Calcd for C60H46P2PtSi2O: C, 65.74; H,
4.23. Found: C, 61.68; H, 4.12.
H‚‚‚Si for 21 (500 MHz, C7D8): T ) 320 K, δ 2.53 (br with broad
flanking Pt satellites (J not resolved); T ) 330 K, δ 2.85 (br with
broad flanking Pt satellites (J not resolved)); T ) 340 K, δ 3.03
(br); T ) 350 K, δ 3.17 (br); T ) 360 K, δ 3.22 (br); T ) 370 K,
δ 3.24 (br). 31P{1H} NMR data after heating to 370 K (202 MHz,
C7D8, 223 K): δ 69.7 (s, 9), 31.2 (t, 8), 28.9 (minor component,
20), 25.3 (minor component, OPPh3), 17.2 (d, 8), -6.8 (s, PPh3).
Low-Temperature Reaction of 3,7-Di-tert-butylsilafluorene
(14) with (Ph3P)2Pt(η2-C2H4) (1). At low temperature, a solution
of 14 (20 mg, 0.068 mmol, 0.3 mL of C7D8) was added to 1 (50
mg, 0.068 mmol, 0.5 mL of C7D8). 31P{1H} NMR (202 MHz, C7D8,
193 K, immediately after addition): δ 38.5 (s, trace amount of 17),
The 1H-1H EXSY (500 MHz, C7D8, 223 K, mixing time 0.025
s) experiment showed a correlation between the two distinct hydride
sites in 8 at 2.0 and -4.9 ppm, indicating exchange between the
two sites. The 31P-31P EXSY experiment (202 MHz, C7D8, 223
K, mixing time 0.80 s) showed a correlation between the two
phosphorus sites in complex 8 at 31 and 17 ppm, indicating
exchange between the two different sites.
1
1
35.4 (br d, JPtP ) 1890, P trans to Si in 16), 33.7 (br d, JPtP
)
2543, P trans to H in 16), 33.6 (small amount of unreacted 1, 1JPtP
) 3702), 24.5 (s, OPPh3), 5.5 (br s, 1JPtP ) 1846, 19), -8.4 (br s,
1JPtP ) 1109, 18). Three hours after addition the solution was
warmed to 300 K. 31P{1H} NMR (202 MHz, C7D8, 300 K, 3 h
after addition, major resonances): δ 29.8 (s, JPtP ) 1705, 20),
24.8 (s, OPPh3), 18 (br, 15).
After ca. 20 h, the C7D8 solution containing 8 showed the
formation of a peach-colored solid identified as the symmetrical
dinuclear complex [(Ph3P)Pt(µ-η2-HSiC12H8)]2 (21; 1 mg, 12%).
Selected 1H NMR data for 21 (500 MHz, CD2Cl2, 223 K): δ 2.83
1
In a separate experiment at low temperature, a solution of 14
(10 mg, 0.034 mmol, ca. 0.5 mL of C7D8) was added to 1 (25 mg,
0.034 mmol, ca. 0.5 mL of C7D8). 1H NMR (500 MHz, C7D8, 195
K, immediately after addition): δ 7.22 (br, SiH for 16, tentative
assignment), 6.31 (br, SiH in 18, tentative assignment), 6.12 (br,
SiH in 19, tentative assignment), 5.29 (s, C2H4), 5.18 (br, overlap-
ping with C2H4, SiH for 17), 5.00 (br, SiH for 14), 4.5 (s, H2),
1
2
(br s, JPtH ) 696, JPtH ) 123). 31P{1H} NMR (202 MHz, CD2-
1
2
3
Cl2, 223 K): δ 35.7 (s, JPtP ) 4302, JPtP ) 303, JPP ) 56).
Elevated-Temperature Reaction of Silafluorene (5) with
(Ph3P)2Pt(η2-C2H4) (1). A solution of 5 (6 mg, 0.03 mmol, 0.2
mL of C7D8) was added to a solution of 1 (23 mg, 0.031 mmol,
0.3 mL of C7D8) at room temperature. The reaction mixture was
transferred immediately to a preheated NMR magnet at 323 K.
Selected 31P{1H} NMR data (202 MHz, 323 K, 10 min after
mixing): δ 70.8 (s, 9), 29.5 (s, 10), 24.1 (s, OPPh3), 14.4 (br s,
major component, 8). After 6 h the 31P NMR spectrum was
identical, except the signal for 9 had increased and 8 had decreased.
1
2.81 (br s, with Pt satellites, C2H4 for 1), -1.02 (dd, JPtH ) 942,
1
2JPH ) 150 (trans), 17 (cis), Pt-H for 16), -5.92 (br s, JPtH
)
628, PtH for 19, tentative assignment), - 9.35 (br dd, 1JPtH ) 799,
2JPH ) 188, PtH for 18, tentative assignment). After 2.5-3 h, the
temperature was raised to 263 K. Selected 1H NMR data (500 MHz,

Platinum-Silicon Monomers and Dimers
Organometallics, Vol. 25, No. 11, 2006 2871
1
The reaction mixture was heated for a total of 6 h, and after cooling
to room temperature, red crystalline 9 was isolated in 27% yield
(6 mg).
spectroscopy just after mixing and after 24 h. Selected H NMR
data for the reaction mixture (500 MHz, 223 K, just after mixing):
δ 1.9 (m, overlapping resonances, Pt‚‚‚H‚‚‚Si), -5.0 (m, overlap-
ping resonances, JPtH ) 530 (combined), Pt-H). 31P{1H} NMR
1
Variable-Temperature NMR Study of (Ph3P)2(H)Pt(µ-
SiC20H24)(µ-η2-HSiC20H24)Pt(PPh3) (15). A sample of 15 (ap-
proximately 10 mg) in 0.75 mL of C7D8 was monitored by VT-
31P{1H} NMR spectroscopy over the temperature range between
300 and 223 K, and the coalescence temperature Tc ) 288 K was
observed. 31P{1H} NMR data for 15 (202 MHz, C7D8, 183 K): δ
30, 22, 20 (with overlapping Pt satellites). The VT-1H NMR data
(246-300 K) for 15 are provided in the Supporting Information.
(202 MHz, 223 K, just after mixing): δ 30.3 (t, 15), 27.7 (m,
overlapping resonances), 21.3 (m, overlapping resonances for 15
and other mixed dinuclear species), 18.6 (m, overlapping reso-
nances), -6.8 (s, PPh3), -15.9 (s, P(p-Tol)3). The 31P{1H} NMR
spectrum after 24 h (223 K) was identical with the 31P NMR
spectrum collected just after addition. The 31P-31P EXSY experi-
ment collected after 24 h (202 MHz, 223 K, mixing time 0.80 s)
exhibited correlation peaks between all resonances at 30.3, 27.7,
21.3, and 18.6 ppm and with free PPh3 and P(p-Tol)3.
Addition of (Ph3P)2Pt(H)[Si(C20H24)H] (16) to (Ph3P)2(H)Pt-
(µ-SiC12H8)(µ-η2-HSiC12H8)Pt(PPh3) (8). To a cooled solution of
1 (4 mg, 0.006 mmol, ca. 0.5 mL of C7D8) was added a solution of
14 (2 mg, 0.007 mmol, ca. 0.25 mL of C7D8), and the resulting
mixture was then analyzed by 31P{1H} NMR (223 K) spectroscopy,
which indicated the formation of 16.6a A solution of 8 (8 mg, 0.005
mmol, ca. 0.25 mL of C7D8) was added to the above reaction
1
A separate sample of 15 in C7D8 was examined by H NMR
spectroscopy from 320 to 360 K. Selected NMR data for 22 are as
follows. T ) 320 K: 1H NMR data (500 MHz, C7D8) δ 2.21 (br
with broad flanking Pt satellites (J not resolved); 31P{1H} NMR
data (202 MHz, C7D8) δ 24 (br). T ) 340 K: 1H NMR data (500
MHz, C7D8) δ 3.22 (br s with flanking Pt satellites); 31P{1H} NMR
data (202 MHz, C7D8) δ 24 (br). T ) 360 K: 1H NMR data (500
1
2
MHz, C7D8) δ 3.27 (s, JPtH ) 684, JPtH ) 117); 31P{1H} NMR
data (202 MHz, C7D8) δ 24 (br). 31P{1H} NMR data after heating
to 360 K (202 MHz, C7D8, 223 K): δ 30.2 (t, 15), 21.4 (br, 15).
An X-ray crystal structure was determined for 22 on an aged sample
from a room-temperature reaction of 1 with 14 (see the Supporting
Information). The X-ray crystallographic structure for 22 was of
poor quality but was used to confirm the connectivity of the
complex.
1
mixture at 195 K. The reaction mixture was analyzed by H and
31P{1H} NMR spectroscopy just after addition (223 K). After 1 h
the temperature was raised to room temperature for several minutes
and then returned to 223 K for NMR data collection. After 24 h at
room temperature, the 1H and 31P{1H} NMR spectra (223 K) were
1
essentially identical. Selected H NMR (500 MHz, 223 K, im-
mediately after addition): δ 5.29 (s, C2H4), 4.94 (br s, small amount
of unreacted 14), 4.5 (s, H2), -1.21 (br d, Pt-H for 16), -1.59 (br
d, Pt-H, unassigned), -4.96 (br m, Pt-H for 8), -5.19 (br t, Pt-H
for 24). Selected 31P{1H} NMR (202 MHz, 223 K, immediately
after addition): δ 35.1 (d, 16), 33.6 (d, 16), 31.1 (t, Pt(PPh3) for
1H-1H EXSY (500 MHz, C7D8, 223 K, mixing time 0.90 s)
experiment showed a correlation between the two distinct hydride
sites in 15 at 1.9 and -5.2 ppm, indicating exchange between the
two sites. The 31P-31P EXSY experiment (202 MHz, C7D8, 223
K, mixing time 0.80 s) showed a correlation between the two
phosphorus sites for 15 at 30.3 and 21.5 ppm, indicating exchange
between the two different sites.
1
3
8), 30.9 (t, JPtP ) 4200, JPP ) 25, Pt(PPh3) for 24), 25.4 (s,
OPPh3), 19.4 (d, 1JPtP ) 3454, Pt(PPh3)2 for 24), 17.2 (d, Pt(PPh3)2
1
for 8). Selected H NMR (500 MHz, 223 K, after 24 h at room
Elevated-Temperature Study of (Ph3P)2(H)Pt(µ-SiC20H24)(µ-
η2-H-SiC20H24)Pt(PPh3) (15). In a NMR tube were placed 15
(8 mg, 0.004 mmol) and OPPh3 (1 mg, 0.004 mmol, as internal
standard) in C7D8 (1 mL). The sample was heated for 12 h at 363
K, followed by additional heating at 368 (30 h) and 373 K (17 h).
NMR spectroscopic data were recorded at room temperature and
at 223 K to monitor the disappearance of 15 and formation of new
signals with intensities relative to OPPh3. A minor amount of the
trinuclear complex 23 was observed after 3 h at 368 K. The highest
amount of 23 was observed after heating to 373 K for 17 h, where
the ratio OPPh3:23:16 was ca. 12.5:1:1.5. Selected 31P{1H} NMR
spectroscopic data for the reaction mixture after heating to 373 K
for 17 h (202 MHz, C7D8, 300 K): δ 198.3 (s, 1JPtP ) 2787, [(Ph3P)-
temperature): δ 2.0 (m, overlapping with C7D8 resonance, Pt‚‚‚
H‚‚‚Si for 8, 15, 24), -4.9 (m, Pt-H for 8), -5.15 (m, overlapping
Pt-H for 15 and 24). Selected 31P{1H} NMR (202 MHz, 223 K,
after 24 h at room temperature): δ 31.1 (t, for 8), 30.9 (t, for 24),
30.3 (t, for 15), 21.4 (br d, for 15), 19.4 (d, for 24), 17.2 (d, for 8).
Signals were also observed for PPh3 (-6.8 ppm) and OPPh3 (25.5
ppm); a minor amount of 10 (28.9 ppm) and an unidentified
resonance at 14.8 ppm (d) were also observed. The approximate
ratio of the three dinuclear complexes 8, 15, and 24 after 24 h was
1:1.6:1.4 by integration of the 31P{1H} NMR spectrum using the
Pt(PPh3) resonances for each complex.
Reaction between (Ph3P)2(H)Pt(µ-SiC12H8)(µ-η2-HSiC12H8)-
Pt(PPh3) (8) and (Ph3P)2Pt(H)(µ-SiC20H24)(µ-η2-HSiC20H24)Pt-
(PPh3) (15). In a NMR tube were placed 8 (5 mg, 0.003 mmol)
and 15 (6 mg, 0.003 mmol) in ca. 0.75 mL of C7D8. The orange
solution was heated in an oil bath at 348 K for approximately 16
h to give a red solution that was analyzed by 1H and 31P{1H} NMR
spectroscopy. Selected 31P{1H} NMR spectroscopy (202 MHz, 300
K, 16 h after heating to 348 K): δ 71.2, 70.8, 70.5 (9), 70.1, 65.2,
64.8, 64.4, 30.6-28.9, 24.8, 24.5 (OPPh3). Selected 31P{1H} NMR
spectroscopy (202 MHz, 223 K, 16 h after heating to 348 K): δ
71.2, 70.5, 70.0, 69.4, 69.2, 69.0, 63.2, 62.8, 62.4, 59.0, 30.1 (t,
16), 21.4 (br d, 16), -6.6 (PPh3).
1
2
3
Pt(µ-PPh2)]2), 71.6 (s, JPtP ) 3320, JPtP ) 445, JPP ) 81, 23),
1
61.6 (s, JPtP ) 2268, unassigned), 99 (m), 54.1, 52.7, 21.0, 19.5
(unassigned resonances). In a separate experiment, a C7D8 solution
of 15 was heated at 348 K for approximately 1 week. Analysis by
31P{1H} NMR spectroscopy at 223 K showed a resonance at 24.6
ppm for OPPh3 and a resonance assigned to 22 at 36.6 ppm (s,
1JPtP ) 4290, 2JPtP ) 252, 3JPP ) 60), as well as a number of minor
unassigned resonances.
In a separate experiment, complex 15 (40 mg, 0.023 mmol) was
dissolved in 1.0 mL of C7D8 and placed in a NMR tube. The sample
was heated for a total of 19 h at 373 K, after which a bright orange-
red crystalline solid had formed in the tube. The solid was washed
with pentane and dried to give 9 mg of complex 23 (27% based on
Pt). NMR spectroscopic data for isolated 23 are as follows. 1H NMR
data (500 MHz, CD2Cl2, 300 K): δ 7.0-6.2 (aromatic CH), 1.3
(s, t-Bu), 1.2, (s, t-Bu). 31P{1H} NMR data (202 MHz, CD2Cl2,
Acknowledgment. We are grateful for a grant from the
National Science Foundation (Grant NO. CHE-0316023) for
support of this work.
Supporting Information Available: Figures giving selected
VT and 2D NMR spectroscopic data for 8 and 15 and 31P{1H}
NMR data for the elevated-temperature reaction between 8 and 15
and a CIF file containing X-ray crystallographic data for complex
22. This material is available free of charge via the Internet at
http://pubs.acs.org.
1
2
3
300 K): δ 70.0 (s, JPtP ) 3327, JPtP ) 448, JPP ) 82).
Phosphine Exchange with (Ph3P)2(H)Pt(µ-SiC20H24)(µ-η2-
HSiC20H24)Pt(PPh3) (15). In a J. Young NMR tube were placed
15 (11 mg, 0.0062 mmol) and P(p-Tol)3 (4 mg, 0.01 mmol) in 0.75
mL of C7D8. The solution was monitored by 1H and 31P{1H} NMR
OM060009V