Reaction of silafluorenes with (Ph3P) 2Pt(η2-C2H4): Generation and characterization of Pt-Si monomers, dimers and trimers

Article abstract of DOI:10.1021/om0400447

The reaction of silafluorene (1; H₂SiC₁₂H ₈) with (Ph₃P)₂Pt(η²-C ₂H₄) (2) at room temperature in C₇D₈ initially provided the mononuclear complex (Ph₃P) ₂Pt(H)[Si(H)C₁₂H₈] (3), followed by the appearance of the unsymmetrical dinuclear complex (Ph₃P) ₂(H)Pt(μ-SiC₁₂H₈)(μ-η²- HSiC₁₂H₈)Pt(PPh₃) (4) and finally the novel trinuclear complex [(Ph₃P)Pt(μ-SiC₁₂H ₈)]₃ (5). The three complexes were characterized by multinuclear NMR spectroscopy and by X-ray crystallography (5). The molecular structure of 5 exhibits a nonplanar Pt₃Si₃ core. When the reaction was conducted at low temperature until the silafluorene was consumed and the mixture then warmed to room temperature, the dinuclear complex 4 could be isolated. The related substituted silafluorene system 3,7-di-tert- butylsilafluorene (6; H₂SiC₂₀H₂₄) also reacted with 2 to provide both mono- and dinuclear complexes (7 and 8) analogous to 3 and 4. The dinuclear complex 8 was isolated and crystallographically characterized. Each of the two Pt centers in complex 8 exhibits a unique environment. In solution at low temperature 8 is best described as having one platinum center with a terminal hydride, [Pt(H)(PPh₃)₂], and the second platinum with a nonclassical [Si...H...Pt(PPh ₃)] unit. However, in the solid state, the two hydrides may both adopt a bridging environment. Heating a sample of the unsymmetrical dimer 8 led to the formation of several products, one of which was the trimer 9, analogous to 5.

Full text of DOI:10.1021/om0400447

4576
Organometallics 2004, 23, 4576-4584
Rea ction of Sila flu or en es w ith (P h 3P )2P t(η2-C2H4):
Gen er a tion a n d Ch a r a cter iza tion of P t-Si Mon om er s,
Dim er s, a n d Tr im er s
J anet Braddock-Wilking,* J oyce Y. Corey, Kevin A. Trankler, Kimberly M. Dill,
Lisa M. French, and Nigam P. Rath
Department of Chemistry and Biochemistry, University of MissourisSt. Louis,
St. Louis, Missouri 63121
Received March 23, 2004
The reaction of silafluorene (1; H2SiC12H8) with (Ph3P)2Pt(η2-C2H4) (2) at room temperature
in C7D8 initially provided the mononuclear complex (Ph3P)2Pt(H)[Si(H)C12H8] (3), followed
by the appearance of the unsymmetrical dinuclear complex (Ph3P)2(H)Pt(µ-SiC12H8)(µ-η2-
HSiC12H8)Pt(PPh3) (4) and finally the novel trinuclear complex [(Ph3P)Pt(µ-SiC12H8)]3 (5).
The three complexes were characterized by multinuclear NMR spectroscopy and by X-ray
crystallography (5). The molecular structure of 5 exhibits a nonplanar Pt3Si3 core. When
the reaction was conducted at low temperature until the silafluorene was consumed and
the mixture then warmed to room temperature, the dinuclear complex 4 could be isolated.
The related substituted silafluorene system 3,7-di-tert-butylsilafluorene (6; H2SiC20H24) also
reacted with 2 to provide both mono- and dinuclear complexes (7 and 8) analogous to 3 and
4. The dinuclear complex 8 was isolated and crystallographically characterized. Each of the
two Pt centers in complex 8 exhibits a unique environment. In solution at low temperature
8 is best described as having one platinum center with a terminal hydride, [Pt(H)(PPh3)2],
and the second platinum with a nonclassical [Si‚‚‚H‚‚‚Pt(PPh3)] unit. However, in the solid
state, the two hydrides may both adopt a bridging environment. Heating a sample of the
unsymmetrical dimer 8 led to the formation of several products, one of which was the trimer
9, analogous to 5.
In tr od u ction
Reactions of primary and secondary hydrosilanes with
Pt(0) or Pt(II) precursors have provided a variety of
structural motifs (see Figure 1).1 Formal insertion of the
metal center into the Si-H bond initially provides a
complex with the general formula LnM(H)SiR3 (such as
A in Figure 1).3 If the groups at silicon and the metal
center are not too hindered, then addition of a second
hydrosilane is possible and leads (at least formally) to
a bis(silyl) complex (LnM(SiR3)2; B in Figure 1).3b,d,e,4
Of significance is the observation that, for primary and
secondary hydrosilanes, the additional sites of reactivity
from residual hydrides at the bound silicon center can
give rise to dinuclear or higher order metal clusters.
Dinuclear complexes containing bridging silylene units
(C)3e,4a,5,6,7b as well as dinuclear species having nonclas-
sical Pt‚‚‚H‚‚‚Si interactions8 (D3b,5g,7 and E (including
this work and a related dipalladium system9)) have now
been prepared. These will be referred to as symmetrical
(D) and unsymmetrical (E) dimers, respectively, through-
The study of Si-H bond activation by transition-metal
complexes has grown significantly over the last two
decades.1,2 Insertion of a metal center into a Si-H bond
is by far the most common and versatile approach for
the preparation of compounds containing an M-Si
bond.1 A multitude of ligands both at the metal center
and at silicon have been utilized, and all varieties of
silanes from SiH4 to R3SiH have been found to react
with an appropriate transition-metal precursor for
nearly all the metals from groups 3 through 11. The
most common type of hydrosilane employed in these
reactions is a tertiary hydrosilane (R3SiH).1 However,
due to the presence of additional Si-H bonds in primary
and secondary silanes further reactions with additional
transition-metal centers are possible and such hydrosi-
lanes could be interesting and desirable precursors for
Si-H bond activation studies.
(1) Corey, J . Y.; Braddock-Wilking, J . Chem. Rev. 1999, 99, 175.
(2) For selected general reviews on transition-metal silyl complexes
see: (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. Appendix to
Transition-Metal Silyl Derivatives. In The Silicon-Heteroatom Bond;
Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1991; p 309. (c)
Schubert, U. Transition Met. Chem. 1991, 16, 136. (d) Schubert, U.
Activation of Si-X Bonds by Electron-Deficient Transition Metals. In
Progress in Organosilicon Chemistry; Marciniec, B., Chojnowski, J .,
Eds.; Gordon and Breach: Lausanne, Switzerland, 1995; p 287. (e)
Eisen, M. S. Transition-Metal Silyl Complexes. In The Chemistry of
Organic Silicon Compounds; Wiley: New York, 1998; Vol. 2, Part 3, p
2037. (f) Aylett, B. J . Adv. Inorg. Chem. Radiochem. 1982, 25, 1.
(3) For selected recent examples involving primary and secondary
hydrosilanes see: (a) Simons, R. S.; Sanow, L. M.; Galat, K. J .; Tessier,
C. A.; Youngs, W. J . Organometallics 2000, 19, 3994. (b) Braddock-
Wilking, J .; Levchinsky, Y.; Rath, N. P. Organometallics 2000, 19,
5500. (c) Feldman, J . D.; Mitchell, G. P.; Nolte, J .-O.; Tilley, T. D. J .
Am. Chem. Soc. 1998, 120, 11184. (d) Kim, Y.-J .; Park, J .-I.; Lee, S.-
C.; Osakada, K.; Tanabe, M.; Choi, J .-C.; Koizumi, T.; Yamamoto, T.
Organometallics 1999, 18, 1349. (e) Heyn, R. H.; Tilley, T. D. J . Am.
Chem. Soc. 1992, 114, 1917.
(4) (a) Shimada, S.; Tanaka, M.; Honda, K. J . Am. Chem. Soc. 1995,
117, 8289. (b) Michalczyk, M. J .; Recatto, C. A.; Calabrese, J . C.; Fink,
M. J . J . Am. Chem. Soc. 1992, 114, 7955. (c) Schubert, U.; Kalt, D.;
Gilges, H. Monatsh. Chem. 1999, 130, 207.
10.1021/om0400447 CCC: $27.50 © 2004 American Chemical Society
Publication on Web 08/26/2004

Reaction of Silafluorenes with (Ph3P)2Pt(η2-C2H4)
Organometallics, Vol. 23, No. 20, 2004 4577
Sch em e 1
out the remainder of this report. More recently, two
trinuclear platinum clusters containing bridging silylene
groups have been isolated (F ).10,11 Dinuclear and espe-
cially trinuclear complexes containing Pt and Si are
quite rare.6
We recently reported the synthesis of a triplatinum
cluster that contained a bridging silafluorenyl unit
(SiC12H8) starting from silafluorene (H2SiC12H8, 1; a
secondary hydrosilane)12 and the Pt(0) precursor (Ph3P)2-
Pt(η2-C2H4) (2).11 This was the first example of a
trinuclear platinum complex containing bridging si-
lylene units formed from mononuclear precursors of
both silicon and platinum. We now report the synthesis
and characterization of an unsymmetrical dinuclear
complex also formed in this reaction as well as a related
dinuclear system from reaction of the substituted ring
system 3,7-di-tert-butylsilafluorene13 with (Ph3P)2Pt(η2-
C2H4).
Resu lts a n d Discu ssion
Reaction of (H2SiC12H8) (1) with (Ph3P)2Pt(η2-C2H4)
(2) (ca. 1:1 ratio) at room temperature initially provided
the oxidative-addition product (Ph3P)2Pt(H)[Si(H)C12H8]
1
(3), as determined by H and 31P{1H} NMR spectros-
(5) (a) Zarate, E. A.; Tessier-Youngs, C. A.; Youngs, W. J . J . Chem.
Soc., Chem. Commun. 1989, 577. (b) Tessier, C. A.; Kennedy, V. O.;
Zarate, E. A. In Inorganic and Organometallic Oligomers and Poly-
mers; Harrod, J . F., Laine, R. M., Eds.; Kluwer Academic: Dordrecht,
The Netherlands, 1991; p 13. (c) Anderson, A. B.; Shiller, P.; Zarate,
E. A.; Tessier-Youngs, C. A.; Youngs, W. J . Organometallics 1989, 8,
2320. (d) Zarate, E. A.; Tessier-Youngs, C. A.; Youngs, W. J . J . Am.
Chem. Soc. 1988, 110, 4068. (e) Levchinksy, Y.; Rath, N. P.; Braddock-
Wilking, J . Organometallics 1999, 18, 2583. (f) Braddock-Wilking, J .;
Levchinsky, Y.; Rath, N. P. Organometallics 2001, 20, 474. (g) 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. (h)
Braddock-Wilking, J .; Levchinksy, Y.; Rath, N. P. Inorg. Chim. Acta
2002, 330, 82. (i) Tanabe, M.; Osakada, K. Inorg. Chim. Acta 2003,
350, 201.
(6) Ogino, H.; Tobita, H. Adv. Organomet. Chem. 1998, 42, 223.
(7) (a) 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. (b) Tanabe, M.; Yamada, T.; Osakada, K.
Organometallics 2003, 22, 2190.
(8) Schubert, U. Adv. Organomet. Chem. 1990, 30, 151.
(9) (a) Kim, Y.-J .; Lee, S.-C.; Park, J .-I.; Osakada, K.; Choi, J .-C.;
Yamamoto, T. Organometallics 1998, 17, 4929. (b) Kim, Y.-J .; Lee, S.-
C.; Park, J .-I.; Osakada, K.; Choi, J .-C.; Yamamoto, T. Dalton 2000,
417.
F igu r e 1. Various structural motifs formed from Si-H
bond activation at Pt(0).
copy. The composition of the reaction mixture changed
over time, and the products that evolved are sum-
marized in Scheme 1. Characterization of each of the
complexes is described in the following paragraphs.
Table 1 lists the various products formed in this study
along with selected NMR spectroscopic data for each
complex.
Complex 3 was characterized in solution only (C7D8).
Two different 31P resonances were observed as doublets
at 33.9 and 34.2 ppm, both with platinum satellites. In
addition, a sharp doublet of doublets with platinum
satellites was observed at -1.72 ppm in the 1H spec-
trum. The remaining silicon-bound hydride in 3 was
tentatively assigned to a resonance at 5.1 ppm that
overlapped the resonance due to free C2H4.14 After
approximately 30 min the NMR signals for 3 disap-
peared and a new broad resonance (ca. 20 ppm) intensi-
(10) Osakada, K.; Tanabe, M.; Tanase, T. Angew. Chem., Int. Ed.
2000, 39, 4053.
(11) Braddock-Wilking, J .; Corey, J . Y.; Dill, K.; Rath, N. P.
Organometallics 2002, 21, 5467.
(12) (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.
(14) Attempts to confirm the position of this resonance by 2D NMR
(13) Chang, L. S.; Corey, J . Y. Organometallics 1989, 8, 1885.
spectroscopy failed, due to the limited lifetime of 3.

4578 Organometallics, Vol. 23, No. 20, 2004
Braddock-Wilking et al.
Ta ble 1. Com p a r ison of Selected NMR Sp ectr oscop ic Da ta for Com p lexes 3-5 a n d 7-9
a
b
C7D8 solution. Chemical shifts are given in ppm and coupling constants in Hz. Si-H coupling not resolved. Pt satellites not resolved.
c Resonance located by 2D 1H-29Si HMQC experiment. No hydrides observed.
J
not resolved.
PtP
d
e 2
fied in the 31P{1H} spectrum and was accompanied by
1
a broad resonance in the H spectrum at -1 ppm with
platinum satellites. A low-temperature 31P{1H} NMR
experiment provided resolved signals which were as-
signed to the unusual dinuclear complex 4. An isolated
sample of 4, when redissolved, showed peaks identical
with those observed in the 31P{1H} spectra (223 K)
obtained from the original reaction mixture containing
4 (see Experimental Section and Table 1). However, no
hydride resonances associated with 4 were observed in
the 1H spectrum of the isolated sample at room tem-
perature.
Two distinct resonances were observed at 17.3 and
31.1 ppm for 4 in the 31P{1H} NMR spectrum (223 K in
C7D8) as a doublet and triplet, respectively, in a 2:1
ratio, and each exhibited two sets of Pt satellites (Figure
2a). The doublet resonance is assigned to the two
equivalent phosphines (Pa) which couple to the unique
phosphine (Pb). Coupling between these two phosphine
sites was confirmed by a 2D 31P-31P{1H} COSY experi-
ment.
The 1H NMR spectrum (223 K in C7D8) for 4 exhibited
two distinct hydride signals centered at -4.9 (t, with
F igu r e 2. 31P{1H} NMR data (202 MHz, 223 K, C7D8) for
(a) 4 and (b) 8.
two sets of Pt satellites) and 2.0 ppm (d, Pt satellites
not resolved) (Figure 3a shows the upfield hydride
region for 4). The triplet pattern at -4.9 ppm indicates
that the hydride couples equivalently to two phosphines,

Reaction of Silafluorenes with (Ph3P)2Pt(η2-C2H4)
Organometallics, Vol. 23, No. 20, 2004 4579
significantly low field (269 ppm) and is close to the value
reported for the related complex [(Me3P)Pt(µ-SiPh2)]3
(279 ppm).10 Thus, all spectroscopic data for 5 are in
agreement with a trimer species in solution.
The reactivity of the aryl-substituted silafluorene
system 3,7-di-tert-butylsilafluorene (6)13 with (Ph3P)2-
Pt(η2-C2H4) (2) was also examined. Our goals for study-
ing this hydrosilane were 3-fold. Increased solubility in
hydrocarbon solvents should be observed, due to the
presence of tert-butyl groups on the aromatic rings meta
to the silicon. Second, the t-Bu groups could potentially
1
provide an additional NMR probe for H NMR analyses.
Another advantage of using the tert-butyl groups may
be the additional steric bulk slightly away from the
silicon center that would still allow reaction with the
Pt complex. The presence of the t-Bu substituents could
kinetically stabilize any reactive intermediate that may
be generated and that may otherwise not be observed
in the parent silafluorene system.
1
F igu r e 3. Selected H NMR data (500 MHz, 223 K, C7D8)
for (a) 4 and (b) 8, showing terminal hydride regions.
The room-temperature reaction between (Ph3P)2Pt-
(η2-C2H4) (2) and 3,7-di-tert-butylsilafluorene (6) was
1
monitored by H and 31P{1H} NMR spectroscopy. Ad-
dition of 6 to 2 (both in C7D8 solution) resulted in
vigorous bubbling, followed by darkening of the solution
to an amber red. The NMR spectroscopic analysis of the
reaction mixture indicated the formation of the di-
nuclear species 8 as the major product (Scheme 2), as
confirmed by low-temperature 1H and 31P{1H} NMR
spectroscopy. No resonances for a mononuclear species
analogous to 3 were observed at room temperature.
However, when the addition was performed at lower
temperature (223 K), signals for the monomer 7 could
F igu r e 4. 31P{1H} NMR data (202 MHz, 223 K, C7D8) for
5.
1
be observed in both the H and 31P{1H} NMR spectra
and the higher field resonance suggests that thishydride
is terminal in nature. The downfield resonance for the
other hydride appears in the typical range for bridging
nonclassical Pt‚‚‚H‚‚‚Si interactions.3b,5g,7 Furthermore,
the 29Si{1H} NMR spectrum (223 K) showed two peaks
at 151 (probable t) and 160 (d) ppm, indicating two
different silicon centers. The room-temperature 29Si{1H}
spectrum showed an averaged signal with Pt satellites
for the two silicon centers at 156 ppm. Attempts to
obtain 4 in crystalline form suitable for X-ray analysis
have been unsuccessful.
(see Table 1).17
Approximately 10 min after the mixing of the com-
ponents, the 31P{1H} spectrum showed a broad reso-
nance centered at 24 ppm (range 10-30 ppm). No
resolved hydride resonances for 8 were observed at room
1
temperature. However, upon cooling to 223 K, the H
NMR spectrum displayed two distinct hydride reso-
nances. An upfield signal at -5.2 ppm was observed as
a triplet with two sets of Pt satellites and was assigned
to a hydride bound to the Pt(PPh3)2 (Pa) center. Another
hydride was observed at 1.93 ppm as a doublet, which
was assigned to the bridging hydride associated with
the monophosphine platinum center (PtPb), but Pt
satellites could not be resolved due to overlapping
resonances. Figure 3b shows the upfield hydride region
in the 1H NMR spectrum for 8. On the basis of the
chemical shifts and the observed coupling constants, we
assign the upfield hydride resonance to a terminal
hydride unit and the downfield hydride as bridging the
Pt and silicon centers (a Pt‚‚‚H‚‚‚Si nonclassical interac-
tion).
The reaction mixture was continuously monitored by
NMR spectroscopy over a period of several hours. Over
the course of 2-3 h an additional new resonance
intensified in the 31P{1H} NMR spectrum (room tem-
perature) at 70.5 ppm as a singlet with a complex Pt
satellite pattern (Figure 4).15 This resonance was as-
signed to the trinuclear Pt complex 5, which was
1
isolated as a deep red solid. The H NMR spectrum for
3 exhibited only aromatic resonances in the range from
7.4 to 6.07 ppm. No signals were observed that could
be attributed to a terminal or bridging hydride in 5. To
verify this, the reaction of d2-silafluorene with (Ph3P)2-
Pt(η2-C2H4) was monitored by 2H NMR spectroscopy and
no resonances for either bridging or terminal metal
deuterides that could be attributed to 5 were detected.16
In addition, a 29Si{1H} resonance was observed at
The 31P{1H} NMR spectrum for 8 at 223 K showed
two unique resonances: one at 21.5 ppm as a broadened
singlet with satellites and a second at 30.3 ppm as a
triplet with Pt satellites. These resonances were ob-
served in a 2:1 ratio and were assigned to the equivalent
phosphines (Pa, (Ph3Pa)2Pt) and unique phosphine (Pb,
(Ph3Pb)Pt) centers, respectively. Figure 2b shows the
low-temperature 31P{1H} NMR spectrum of 8.
(15) The satellite pattern observed in the 31P{1H} NMR spectrum
for 5 is in good agreement with a calculated spectrum for the related
triplatinum complex Pt3(µ-CO)3(PCy3)3. See: Moor, A.; Pregosin, P. S.;
Venanzi, L. M. Inorg. Chim. Acta 1981, 48, 153.
(16) Braddock-Wilking, J .; Corey, J . Y.; Dill, K. M. Unpublished
results.
(17) Variable-temperature reaction conditions are currently being
examined with both the unsubstituted and substituted silafluorene
systems 1 and 6 to monitor the sequence of steps.

4580 Organometallics, Vol. 23, No. 20, 2004
Braddock-Wilking et al.
Sch em e 2
complex 9, analogous to 5.19,20 A new resonance was
observed in the 31P{1H} NMR spectrum at 71.6 ppm
with a Pt satellite pattern similar to that exhibited by
5.11 The mechanism of formation of the trimer 5 as well
as the dimers 4 and 8 is not certain.
A related unsymmetrical dipalladium system, (Me3P)2-
Pd(µ-η2-HSiPh2)2Pd(PMe3), has recently been reported
from reaction of Ph2SiH2 with Pd(Et)2(PMe3)2.9 In
addition to the unsymmetrical complex analogous to 4
and 8, a minor amount of a symmetrical dimer, [(Me3P)-
Pd(µ-η2-HSiPh2)2Pd(PMe3), was formed and both struc-
tures were confirmed by X-ray crystallography.9 The
solid-state structure of the unsymmetrical dipalladium
complex suggested that both hydrides were bridging and
were involved in 3c-2e Pd‚‚‚H‚‚‚Si interactions. The
low-temperature 31P NMR spectrum for (Me3P)Pd(µ-η2-
HSiPh2)2Pd(PMe3) exhibited a doublet and a triplet in
a 2:1 ratio, indicating two distinct PMe3 sites. In
addition, the low-temperature 1H NMR spectrum showed
a doublet at 1.24 ppm and a triplet at -2.34 ppm with
1J SiH couplings of 84 and 86 Hz, respectively. The high-
field signal was assigned to the (Me3P)Pd‚‚‚H‚‚‚SiPh2
hydride on the basis of the coupling pattern, which
F igu r e 5. 1H-31P COSY NMR data (500 MHz, 223 K,
C7D8) for 8.
2
A two-dimensional 31P-31P{1H} COSY NMR experi-
suggested that J PH coupling through Pd was probably
much smaller due to the elongated Pd-H distance.9a
The unsymmetrical palladium dimer was found to have
temperature-dependent NMR spectra, and a fluxional
process involving either an intra- or intermolecular
exchange of the coordinated PMe3 ligands was pro-
posed.9 A similar process may be responsible for the
fluxional behavior found in 4 and 8.
ment confirmed coupling between the two phosphorus
1
sites. In addition, a H-31P COSY experiment showed
correlation only between the triplet phosphorus signal
at 30 ppm (for the unique phosphine) and the bridging
hydride at 1.93 ppm in the 1H spectrum (Figure 5).
Likewise, the doublet resonance in the 31P spectrum
assigned to the two equivalent PPh3 groups (Pa) showed
a correlation only to the terminal hydride found at -5.2
X-r a y Cr ysta llogr a p h ic An a lyses of 5 a n d 8.
X-ray-quality crystals of 5 were obtained by slow
evaporation from a toluene solution. The deep red
crystals of 5, however, provided reduced quality struc-
tural data and only allowed for evaluation of the basic
features of the molecule.11 Figure 6 shows the core
structure for the complex 5. Figure 7 shows selected
bond distances for 5 as well as the related trimer
[(Me3P)Pt(µ-SiPh2)]3.10 Also given in Figure 7 are se-
lected bond distances for the unsymmetrical dimer (8;
see discussion below) and the related dipalladium
complex (Me3P)2Pd(µ-η2-HSiPh2)2Pd(PMe3).9a
1
ppm in the H spectrum. The IR spectrum of 8 showed
no absorbances between 2000 and 2300 cm-1, suggesting
that in the solid state no terminal Pt-H or Si-H units
exist.18
The 29Si{1H} NMR spectrum (223 K) also supported
the unsymmetrical nature of 8. Two resonances were
observed at 164 (d) and 154 (m) ppm, indicating two
different silicon centers in 8. The Pt-Si couplings could
not be resolved in the low-temperature spectrum.
An interesting observation from the reaction of 6 and
2 conducted at room temperature was the fact that no
trimer analogous to 5 formed. The m-tert-butyl groups
on the aromatic ring system in 8 may provide sufficient
steric bulk to prevent formation of a trinuclear system
(at room temperature). However, heating a toluene-d8
sample of 8 at 100 °C overnight provided NMR spec-
troscopic evidence for the formation of the trinuclear
(19) Trankler, K.; Braddock-Wilking, J .; Corey, J . Y. Unpublished
results. A 31P{1H} NMR spectrum showed a major component with a
signal at 71.6 ppm, which has been assigned to the trinuclear complex
9. The coupling constant values for 9 are similar to those of the trimer
5. In addition, several other unassigned resonances were observed to
those for 9. Experiments are in progress to identify and characterize
9 and other products formed in the reaction. One product that has
been assigned is the previously characterized phosphido-bridged dimer
[(Ph3P)Pt(µ-PPh2)]2.20
(20) (a) Taylor, N. J .; Chieh, P. C.; Carty, A. J . J . Chem. Soc., Chem.
Commun. 1975, 448. (b) Bender, R.; Bouaoud, S.-E.; Braunstein, P.;
Dusausoy, Y.; Merabet, N.; Raya, J .; Rouag, D. J . Chem. Soc., Dalton
Trans. 1999, 735.
(18) (a) Nakamoto, K. Infrared and Raman Spectra of Inorganic and
Coordination Compounds; 4th ed.; Wiley: New York, 1986; pp 323,
384, 399. (b) Collman, J . P.; Hegedus, L. S., Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987; p 83.

Reaction of Silafluorenes with (Ph3P)2Pt(η2-C2H4)
Organometallics, Vol. 23, No. 20, 2004 4581
Ta ble 2. Selected Bon d Dista n ces (Å) a n d
An gles (d eg) for 8
Pt1-Pt2
Pt1-Si1
Pt1-Si2
Pt2-Si1
2.74415(19)
2.3035(10)
2.3626(9)
2.4875(9)
Pt2-Si2
Pt1-P1
Pt2-P2
Pt2-P3
2.3365(9)
2.2443(9)
2.2963(9)
2.3797(9)
Pt1-Si1-Pt2
Pt2-Si2-Pt1
Si1-Pt1-Si2
Si2-Pt2-Si1
P2-Pt2-P3
P1-Pt1-Pt2
Pt1-Pt2-P3
Pt1-Pt2-P2
69.77(3)
71.46(3)
P1-Pt1-Si2
P2-Pt2-Si1
P3-Pt2-Si1
P2-Pt2-Si2
P3-Pt2-Si2
C1-Si1-C7
C21-Si2-C27
144.35(3)
131.13(3)
105.76(3)
95.21(3)
108.36(3)
90.17(15)
90.42(15)
111.23(3)
105.89(3)
108.50(3)
160.92(2)
111.35(2)
135.99(2)
F igu r e 6. Molecular structure of 5 showing the core
atoms.
Ta ble 3. Cr ysta l Da ta a n d Str u ctu r e
Refin em en t for 8
empirical formula
C101H103P3Pt2Si2
fw
1856.10
temp
wavelength
cryst syst
space group
150(2) K
0.710 73 Å
monoclinic
P21/n
unit cell dimens
a
13.6578(2) Å
b
26.7070(3) Å
c
23.6581(3) Å
R
90°
91.5540(10)°
â
γ
V, Z
density (calcd)
abs coeff
cryst size
no. of rflns collected
no. of indep rflns
completeness to θ ) 30.00°
abs cor
90°
8626.33(19) Å3, 4
1.429 Mg/m3
3.370 mm-1
0.22 × 0.16 × 0.10 mm3
167 487
F igu r e 7. Selected bond distances (Å) for 5 and 8 and
related complexes. Bond distance data for 8 with esd’s are
included in Table 2.
24 186 (R(int) ) 0.0574)
96.1%
semiempirical from
equivalents (sadabs)
0.7293 and 0.5243
full-matrix least squares on F2
24 186/1/1032
1.151
max and min transmission
refinement method
The three Pt-Pt bonds in the triangular core of 5 are
each bridged by a silafluorenylidene moiety, and one
PPh3 ligand is bound to each Pt center. The Pt3Si3 core
is nonplanar. The Pt-Si distances in 5 (2.344-2.388 Å)
fall in the range for other known Pt-Si complexes
(2.34-2.38 Å),1 and the overall structure is similar to
that published for the related complex [(Me3P)Pt(µ-
SiPh2)]3.10 The Pt-Pt distances in 5 are in the range
for Pt-Pt single bonds in triangular platinum systems
(2.70-2.71 Å).20-22 The Pt-Pt distances in 5 are also
similar to those observed in the related cluster [(Me3P)-
Pt(µ-SiPh2)]3.10
Trinuclear complexes of Pt containing bridging car-
bonyl,21 nitrile, or phosphido22 ligands are known, but
those that incorporate silyl substituents are rare. Re-
cently, Osakada et al. prepared the triplatinum complex
[(Me3P)Pt(µ-SiPh2)]3 from thermolysis of the preformed
mononuclear complex (Me3P)2Pt(SiPh2H)2 at 100 °C.10
In contrast to the Pt3Si3 system reported by Osakada,
the triplatinum-µ-silylene complex 5 was generated at
room temperature. There are three additional known
Pt3 systems incorporating a terminal silyl group at a
single Pt center. These complexes were synthesized by
reaction of a preexisting triplatinum cluster with a
hydrosilane, and their structures were confirmed by
no. of data/restraints/params
goodness of fit on F2
final R indices
largest diff peak and hole
R1 ) 0.044, wR2 ) 0.065
1.409 and -1.912 e Å-3
X-ray crystallography.23 Trinuclear complexes of other
transition metals with bridging silylene units are also
rare.6
X-ray-quality crystals of 8 were obtained from slow
evaporation of a solution in toluene-d8. The molecular
structure of 8 is shown in Figure 8. Selected bond angles
and distances for 8 are listed in Table 2. Table 3 lists
the crystal data and structure refinement details for 8.
A molecule of C7D8 was found in the unit cell lattice
and was disordered. The X-ray crystal structure of 8
revealed that the Pt2Si2 core has one long and three
shorter Pt-Si bonds (see Figures 7 and 8). For com-
parison, the symmetrical dimer [(Ph3P)Pt(µ-η2-HSi-
HAr)]2 showed alternating long-short Pt-Si bonds,
where the long Pt-Si bonds are associated with the
Pt‚‚‚H‚‚‚Si interactions.3b,5e For example, when Ar )
IMP, Pt-Si distances of 2.3248(9) and 2.4280(9) Å were
observed and the longer distance corresponded to the
Pt-Si bond involved in the nonclassical Pt‚‚‚H‚‚‚Si
interaction.5e
The Pt-Pt distance in 8 was 2.74415(19) Å, which is
slightly longer than the distance found in the sym-
(21) For a recent review see: Imhof, D.; Venanzi, L. M. Chem. Soc.
Rev. 1994, 23, 185.
(22) See for example: (a) Bender, R.; Braunstein, P.; Dedieu, A.;
Ellis, P. D.; Huggins, B.; Harvey, P. D.; Sappa, E.; Tiripicchio, A. Inorg.
Chem. 1996, 35, 1223. (b) Bennett, M. A.; Berry, D. E.; Dirnberger,
T.; Hockless, D. C. R.; Wenger, E. J . Chem. Soc., Dalton Trans. 1998,
2367.
(23) (a) Bender, R.; Braunstein, P.; Bouaoud, S.-E.; Merabet, N.;
Rouag, D.; Zanello, P.; Fontani, M. New. J . Chem. 1999, 23, 1045. (b)
Itazaki, N.; Nishihara, Y.; Osakada, K. Organometallics 2004, 23, 1610.

4582 Organometallics, Vol. 23, No. 20, 2004
Braddock-Wilking et al.
F igu r e 8. (a) Molecular structure of 8. (b) View of the molecular structure of 8 showing core Pt, P, Si, and H atoms.
metrical dimer [(Ph3P)Pt(µ-η2-HSiHAr)]2 (Ar ) IMP,
2.7021(2) Å).5e This distance is larger than the sum of
the covalent platinum radii (2.62 Å)24 but is within the
range for other reported Pt-Pt single bonds.20,21,22,25
The hydrides at platinum and silicon were located in
8 from the difference Fourier map and were refined
freely. The distances ranged from 1.5 to 1.9 Å. The Pt-H
and Si-H distances at the Pt2 center were similar:
Pt2-H12b ) 1.626 and Si1-H12b ) 1.710 Å. These
distances suggest a Pt‚‚‚H‚‚‚Si bridging environment in
the solid state. The Pt2-Si1 distance associated with
this hydride is the longest of the four Pt-Si distances.
However, in solution this hydride (H12b) appears to
adopt a terminal Pt-H site, as indicated by an upfield
the Pd2 unsymmetrical dimer reported by Osakada (see
above).9a One would expect the longest Pt-Si bonds to
be associated with nonclassical Pt‚‚‚H‚‚‚Si interactions,
and on the basis of the Pt‚‚‚Si bond lengths, it appears
that a bridging hydride could be associated with Pt2-
Si1 (and Pt1-Si2) for 8 in the solid. However, the
shorter Pt1-H12a distance coupled with the elongated
Si2-H12a distance indicates that in the solid the
hydride could be assigned to a terminal position.
Overall, the molecular structure of 8 shows an unusual
unsymmetrical environment about the two Pt centers.
The hydrides in the Pd dimer9a were described by
Osakada as bridging hydrides, where H1 was assigned
to the triplet and H2 to the doublet signal in the 1H
NMR spectrum, in contrast to our assignments for the
hydrides in 8, where H12b is assigned to the triplet
signal.
1
resonance at -5.2 ppm in the H NMR spectrum (see
previous discussion). The remaining hydride, H12a,
shows two very different distances to platinum and
silicon, Pt1-H12a ) 1.503 and Si2-H12a ) 1.959 Å,
with a Pt1-Si2 distance of 2.36 Å. These distances
suggest that this hydride is more closely associated with
the Pt1 center than the Si2 center. However, in solution,
this hydride appears near 2 ppm, which is in the
chemical shift range for reported bridging Pt‚‚‚H‚‚‚Si
environments.3b,5g,7
The related Pd dimer (Me3P)2Pd(µ-η2-HSiPh2)2Pd-
(PMe3) showed a similar pattern for the Pd-Si bond
lengths, one long and three shorter bonds with similar
distances, and the longest distance is analogous to the
Pt2-Si1 bond in the current study (see Figure 7).9a Both
hydrides were described with bridging environments.
The palladium-hydride distance associated with the
Pd(PMe3)2 unit was the longest distance, Pd2‚‚‚H2 )
1.89 Å, and the Si-H distance was similar to a typical
Si-H bond at Si2‚‚‚H2 ) 1.56 Å,1 whereas the distances
for the Pd(PMe3) unit were Pd1‚‚‚H1 ) 1.75 Å and
Si1‚‚‚H1 ) 1.68 Å. An interesting difference is observed
between the Pt dimer 8 and (Me3P)2Pd(µ-η2-HSiPh2)2-
Pd(PMe3).9 In the former case, the Pt-H distances are
shorter than the Si-H distances but the Pd-H dis-
tances are longer than the Si-H distances.
Con clu sion
Both unsubstituted and substituted silafluorenes (1
and 6) reacted with the Pt(0) complex 2 at room
temperature to provide initially the mononuclear prod-
ucts [(R3P)2Pt(H)(SiR2H)] (3 and 7), which were identi-
fied in solution only and showed similar NMR spectro-
scopic data. The major species formed in the reaction
involving both silafluorenes was an unsymmetrical
dimer, (Ph3P)2(H)Pt(µ-SiR2)(µ-η2-HSiR2)Pt(PPh3) (4 and
8), both of which were isolated. Attempts to obtain
X-ray-quality crystals of complex 4 were unsuccessful;
however, the solution NMR data are similar to those of
the dimer 8, whose structure was confirmed by X-ray
crystallography. In the case of the unsubstituted si-
lafluorene, a trinuclear complex, [(Ph3P)Pt(µ-SiR2)]3 (5),
was formed at room temperature, and its structure was
also confirmed by X-ray crystallography. The analogous
trimer 9 was observed from a thermal reaction involving
the tert-butyl-substituted dimer 8, but to date it has only
been observed in solution. The solution 31P{1H} NMR
data for 9 are consistent with the data observed for
trimer 5, which supports the assignment of 9 as a
trimer. The presence of the tert-butyl groups on the
silafluorene unit appear to impart added solubility to
the trimer 9 relative to the unsubstituted system 5.
Attempts to grow X-ray-quality crystals of 9 are in
progress.
In solution at low temperature, the NMR spectro-
scopic data for 8 support the presence of a terminal and
a bridging hydride. However, the solid-state structure
of 8 could contain two bridging hydrides, analogous to
(24) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornell
University Press: Ithaca, NY, 1960; p 224.
(25) 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.
Further studies with other constrained secondary
hydrosilanes are planned, to determine if such silicon

Reaction of Silafluorenes with (Ph3P)2Pt(η2-C2H4)
Organometallics, Vol. 23, No. 20, 2004 4583
then transferred to a vial in the drybox, where ∼5 mL of
pentane was added, and the sample was stored several days
at -40 °C, whereupon a dark orange solid formed. The solution
was filtered and the solid dried in vacuo to give 4 (19 mg, 45%
yield based on Pt, mp 214 °C dec). NMR spectroscopic data
for 4: 1H NMR (C7D8, 500 MHz, 223 K) δ 8.0-6.6 (overlapping
aromatic resonances); 31P-31P{1H} COSY (223 K, 500 MHz)
cross-peak correlation observed between peak at 31.1 ppm with
peak at 17.3 ppm; 1H-31P COSY (223 K, 500 MHz) correlation
between hydride peak at -4.9 ppm with phosphorus resonance
at 17.3, correlation between hydride peak at 2.0 with phos-
phorus resonance at 31.1 ppm. Anal. Calcd for C78H63P3Pt2-
Si2: C, 60.85; H, 4.12. Found: C, 61.18; H, 4.34.
Obser va tion of (P h 3P )2P t(H)[Si(C12H8)H] (3). In a typi-
cal run, 1 and 2 were mixed in C7D8 (1:1 ratio). NMR
spectroscopic data were collected at room temperature im-
mediately after addition. Complex 3 was characterized in
solution only, since its lifetime was approximately 30 min.
Attempts to confirm the Si-H assignment (room temperature)
at 5.1 ppm by 2D NMR experiments failed, due to the limited
lifetime of 3. A sample containing 3 was cooled to -50 °C, and
1H NMR data were obtained.
R ea ct ion of 3,7-Di-ter t-b u t ylsila flu or en e (6) w it h
(P h 3P )2P t(η2-C2H4) (2). In a drybox, 3,7-di-tert-butylsilafluo-
rene (6; 20.0 mg, 0.068 mmol) in C7D8 (0.5 mL) was added to
(Ph3P)2Pt(η2-C2H4) (2; 50.0 mg, 0.067 mmol) in C7D8 (0.5 mL),
resulting in gas evolution and formation of a dark amber
solution. Slow evaporation of the solvent (over several days)
resulted in precipitation of bright orange crystals of 8 as a
toluene solvate (54 mg, yield 86% based on Pt), mp 186-192
°C dec. Crystals of 8 were washed with toluene-d8 and were
suitable for X-ray crystallographic analysis. 1H NMR (C7D8,
500 MHz, 223 K): δ 8.4-6.3 (overlapping multiplets, ArH
region), 1.34 (s, C(CH3)3), 1.03 (broad s, C(CH3)3). 31P-31P{1H}
COSY (223 K, 500 MHz): cross-peak correlation observed
between peak at 30.3 ppm with peak at 21.5 ppm. 1H-31P
COSY (223 K, 500 MHz): correlation between hydride peak
at -5.2 ppm with phosphorus resonance at 21.5 ppm; correla-
tion between hydride peak at 1.93 ppm with phosphorus
resonance at 30.3 ppm. Anal. Calcd for C94H95P3Si2Pt2‚C7D8:
C, 65.36; H, 5.59. Found: C, 65.40; H, 5.60.
systems will generate trinuclear or higher order poly-
nuclear clusters (as well as their mechanism of forma-
tion). It is expected that other silicon ring systems will
exhibit monomer/dimer/trimer species, and we expect
to probe the sequence of molecular events that occur
from monomer to dimer and/or trimer. It is probable
that there is more than one pathway by which the
trimer or higher aggregates are formed.
Exp er im en ta l Section
All glassware was oven- or flame-dried prior to use. Reac-
tions were performed under an argon or nitrogen atmosphere.
Melting point determinations were obtained on a Thomas-
Hoover capillary melting point apparatus and are uncorrected.
Infrared spectra were recorded on a Thermo-Nicolet Avatar
1
360 ESP FT-IR spectrometer. H, 29Si, and 31P NMR spectra
were recorded on a Bruker ARX-500 spectrometer at 500 MHz
1
for H, 99 MHz for 29Si, and 202 MHz for 31P. Proton chemical
shifts (δ) are reported relative to residual protonated solvent,
C7D8 (2.09 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. Both 29Si{1H} and 31P{1H} NMR spectroscopic
data for compounds 3-5 and 7-9 are listed in Table 1. The
Pt-H and/or Si-H resonances in the 1H NMR spectra for
compounds 3, 4, 7, and 8 are also given in Table 1. X-ray
crystal structural determinations were performed on a Bruker
SMART diffractometer equipped with a CCD area detector.
Silafluorene12 and 3,7-di-tert-butylsilafluorene13 were pre-
pared as described previously. (Ethylene)bis(triphenylphos-
phine)platinum(0) was purchased from Aldrich Chemical Co.
and used as received. Toluene-d8 was purchased in 1 g ampules
from Cambridge Isotopes, Inc., and used as received.
Rea ction of Sila flu or en e (1) w ith (P h 3P )2P t(η2-C2H4)
(2). Isola tion of [(P h 3P )P t(µ-SiC12H8)]3 (5). Silafluorene (1;
73 mg, 0.34 mmol) was added to (Ph3P)2Pt(η2-C2H4) (2; 250
mg, 0.34 mmol) in a 20 mL vial, and then C6D6 (1.5 mL) and
C6H6 (3.5 mL) were added, resulting in a clear, amber red
solution. After several hours, red crystals of 5 had precipitated,
which were separated. Addition of hexane (8 mL) to the mother
liquor resulted in precipitation of an additional crop of 5. The
solid sample of 5 (as the bis solvate) was dried under vacuum
for 2 h to give a total of 64 mg (27% yield based on Pt). 1H
NMR (500 MHz, CD2Cl2, room temperature): δ 7.40 (d,
A sample of 8 was heated in C7D8 in the probe of the NMR
spectrometer in 20 K increments from ambient temperature
to 360 K and held at that temperature for approximately 1 h
with no observable decomposition, as determined by cooling
1
the sample to 223 K and monitoring by H and 31P NMR for
resonances associated with 8. Additional heating at 373 K
overnight provided a new resonance with platinum satellites,
in the 31P spectrum. This new resonance has tentatively been
assigned to the trinuclear system 9, analogous to 5.11 Loss of
the broad room-temperature resonance for 8 also occurred.
X-r a y Cr ysta llogr a p h ic An a lysis of 8. A crystal (obtained
from slow evaporation of C7D8) with approximate dimensions
0.22 × 0.16 × 0.10 mm was mounted on glass fibers in a
random orientation. Preliminary examination and data col-
lection were performed using a Bruker SMART charge coupled
device (CCD) detector system single-crystal X-ray diffracto-
meter. SMART and SAINT software packages (Bruker Ana-
lytical X-ray, Madison, WI, 2002) were used for data collection
(ω and 2θ scans) and data integration. Collected data were
corrected for systematic errors using SADABS.27
3J HH ) 7.6), 7.06 (t, 3J HH ) 7.3), 6.95-6.87 (m), 6.07 (t, 3J HH
)
7.6) ArH. Anal. Calcd for C90H69P3Pt3Si3‚2C6H6: C, 59.21; H,
3.95. Found: C, 59.32; H, 4.11. The remaining solution was
evaporated to give a chocolate brown solid (199 mg) as a
mixture of components. Low-temperature 31P{1H} NMR in
toluene-d8 indicated that the mixture contained mainly (Ph3P)3-
Pt, (Ph3P)4Pt, and Ph3PO with chemical shifts at δ 52.3 (s, Pt
satellites, J PtP ) 4440), 11.7 (s, Pt satellites, J PtP ) 3840), and
27.1 (s).26
Isola tion of (P h 3P )2(H)P t(µ-SiC12H8)(µ-η2-HSiC12H8)P t-
(P P h 3) (4). In a drybox, silafluorene (1; 11 mg, 0.060 mmol)
was dissolved in ∼0.25 mL of C7D8. In an NMR tube, (PPh3)2-
Pt(η2-C2H4) (2; 41 mg, 0.055 mmol) was dissolved in ∼0.75 mL
of C7D8 and placed in liquid N2. The silafluorene solution was
then added to the frozen (Ph3P)2Pt(η2-C2H4) solution. After the
additional sample had frozen, the tube was removed to a dry
ice/acetone bath, and when the matrix melted, the reaction
tube was shaken several times to mix the contents and then
placed into a precooled NMR magnet (193 K). The temperature
was slowly raised to 300 K over a period of several hours. After
approximately 7 h, 31P{1H} NMR and 1H NMR data showed
the presence of dimer 4 as the major species. The solution was
Collection parameters for crystal data collection are listed
in Table 3 and in the Supporting Information. Structure
solution and refinement were carried out using the SHELXTL-
PLUS software package.28 The structure was solved by Patter-
son methods and refined successfully in the space group P21/
n. The non-hydrogen atoms were refined anisotropically to
(27) Blessing, R. H. Acta Crystallogr. 1995, A51, 33.
(28) Sheldrick, G. M. Bruker Analytical X-ray Division, Madison,
WI, 2002.
(26) Sen, A.; Halpern, J . Inorg. Chem. 1980, 19, 1073.

4584 Organometallics, Vol. 23, No. 20, 2004
Braddock-Wilking et al.
convergence. The two bridging H atoms were located from the
difference Fourier and were refined freely. The rest of the
hydrogen atoms were treated using an appropriate riding
model (AFIX m3). A molecule of toluene was found in the
crystal lattice. The toluene solvate exhibits rotational disorder.
The disorder was resolved by locating two partial molecules,
which were refined as rigid bodies.
NSF (Grant No. CHE-9974801) and an UM-Research
Board grant for the purchase of a Bruker Avance 300
NMR spectrometer are gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Selected NMR spec-
troscopic data and crystallographic data for 8, including tables
of crystal data and structure refinement details, atomic
coordinates, and bond distances and angles. This material is
available free of charge via the Internet at http://pubs.acs.org.
Ack n ow led gm en t. We are grateful for a grant from
the National Science Foundation (Grant No. CHE-
0316023) for support of this work. The support of the
OM0400447