Synthesis, characterization, and X-ray structural analysis of diplatinum complexes containing bridging μ-SiHAr ligands, {(PhnMe3-nP)2Pt[μ-SiHAr]}2 [n = 0-2; Ar = 2-isopropyl-6-methyl(phenyl)]

Article abstract of DOI:10.1021/om000638j

Reaction of (IMP)SiH₃ with (Ph_nMe_3-nP)₂PtMe₂ at 50°C provided the dinuclear complexes trans-[(Ph_nMe_3-nP)₂Pt(μ-SiHAr)]₂ [Ar = 2-isopropyl-6-methylphenyl (IMP

Full text of DOI:10.1021/om000638j

474
Organometallics 2001, 20, 474-480
Syn th esis, Ch a r a cter iza tion , a n d X-r a y Str u ctu r a l
An a lysis of Dip la tin u m Com p lexes Con ta in in g Br id gin g
µ-SiHAr Liga n d s, {(P h n Me3-n P )2P t[µ-SiHAr ]}2 [n ) 0-2;
Ar ) 2-isop r op yl-6-m eth yl(p h en yl)]
J . Braddock-Wilking,*,‡ Y. Levchinsky, and N. P. Rath
Department of Chemistry, University of MissourisSt. Louis, St. Louis, Missouri 63121
Received J uly 24, 2000
Reaction of (IMP)SiH3 with (PhnMe3-nP)2PtMe2 at 50 °C provided the dinuclear complexes
trans-[(PhnMe3-nP)2Pt(µ-SiHAr)]2 [Ar ) 2-isopropyl-6-methylphenyl (IMP)]. These complexes
were characterized by multinuclear NMR and IR spectroscopy and X-ray crystallography.
The 29Si NMR chemical shift for {(PhMe2P)2Pt[µ-SiH(IMP)]}2 appears at unusually high
field (-134 ppm) for complexes containing bridging silylene moieties. The X-ray structures
of these complexes reveal acute Si-Pt-Si and obtuse Pt-Si-Pt angles. In solution,
{(Ph2MeP)2Pt[µ-SiH(IMP)]}2 undergoes dissociation of PMePh2 down to -90 °C.
Ch a r t 1
In tr od u ction
The stoichiometric interaction of hydrosilanes with
transition metal complexes can provide a diverse range
of products depending upon the metal precursor used
(Chart 1).1 For example, sterically unhindered primary
silanes (RSiH3) react with Pt(0) precursors to produce
dinuclear Pt2Si2 complexes with µ-SiHR groups bridging
the platinum centers (C, Chart 1) or mononuclear bis-
(silyl) complexes (B, Chart 1).2-6 However, sterically
demanding groups at silicon can provide mononuclear,
P2Pt(H)SiH2R complexes (A, Chart 1). Secondary silanes
(R2SiH2) provide either dinuclear complexes with bridg-
ing µ-SiR2 groups or mononuclear species containing a
M-SiHR2 unit depending upon the steric bulk of the
groups at silicon.1
workers prepared a number of ring systems of type C
(Chart 1) from reaction of RSiH3 with (Et3P)2PtCl2 in
the presence of 2 equiv of Na metal (R ) phenyl, p-tolyl,
cyclohexyl).2 Recently, they have examined the reaction
of (R3P)3Pt (R ) Et, Pr) with (Hex)SiH3 and observed
the formation of two different types of disilaplatina-
cycles, {[(R3P)2Pt[µ-SiH(Hex)]}2 and {(R3P)Pt[µ-η2-
HSi[Pt(PR3)2H](Hex)]}2 depending upon the reaction
conditions.3 Tilley’s group has also generated several
Pt2Si2 metallacycles from reaction of RSiH3 (R ) Ph,
p-Tol, and Mes) with (Et3P)3Pt when a 2:1 ratio of Pt:Si
precursors are used or from a 1:1 ratio of (Et3P)2Pt-
(SiH2Ar)2 with Pt(PEt3)3.4 In addition, they observed the
formation of an unusual dinuclear Pt-Si complex.4 Fink
and Michalczyk reacted disilane (H3Si-SiH3) and 1,2-
dimethyldisilane (MeH2Si-SiH2Me) with (dcpe)PtH2
[dcpe ) 1,2-bis(dicyclohexylphosphino)ethane] and ob-
served the formation of some novel platinum silyl
complexes including the disiladiplatinacycle [(dcpe)Pt-
(µ-SiHR)]2 (R ) H, Me).5 Tanaka et al. examined the
reactivity of 1,2-disilylbenzene with (Et3P)3Pt.6 Different
products were formed depending upon the reaction
conditions. When a 1:1 ratio of 1,2-bis(SiH3)2C6H4 and
(Et3P)3Pt was used, quantitative formation of a novel
mixed valence PtIIPtIVSi4P4 disiladiplatinacycle was
observed. A recent review has summarized the chem-
A number of dinuclear Pt2Si2 complexes containing
bridging silylene groups are known (C, Chart 1), and
several of these compounds have been structurally
characterized by X-ray crystallography. Tessier and co-
‡ Corresponding author. Tel: (314) 516-6436. Fax: (314) 516-5342.
E-mail: jwilking@umsl.edu.
(1) (a) Corey, J . Y.; Braddock-Wilking, J . Chem. Rev. 1999, 99, 175.
(b) Tilley, T. D. In The Silicon Heteroatom Bond; Patai, S., Rappoport,
Z., Eds.; J ohn Wiley and Sons: New York, 1991; p 245. (c) Tilley, T.
D. In The Chemistry of Organic Silicon Compounds; Patai, S.,
Rappoport, Z., Eds.; J ohn Wiley and Sons: New York, 1989; p 1416.
(d) Aylett, B. J . Adv. Inorg. Chem. Radiochem. 1982, 25, 1.
(2) (a) They also found that reaction of Ph2SiHLi and (PEt3)2PtCl2
afforded dinuclear Pt2Si2 ring systems as cocrystallized mixtures:
Zarate, E. A.; Tessier-Youngs, C. A.; Youngs, W. J . J . Am. Chem. Soc.
1988, 110, 4068. (b) Tessier, C. A.; Kennedy, V. O.; Zarate, E. A. In
Inorganic and Organometallic Oligomers and Polymers: Proceedings
of the 33rd IUPAC Symposium on Macromolecules; Harrod, J . F.,
Laine, L. M., Eds.; Kluwer Academic: Boston, MA, 1991; p 13. (c)
Zarate, E. A.; Tessier-Youngs, C. A.; Youngs, W. J . J . Chem. Soc.,
Chem. Commun. 1989, 577. (d) Anderson, A. B.; Shiller, P.; Zarate, E.
A.; Tessier-Youngs, C. A.; Youngs, W. J . Organometallics 1989, 8, 2320.
(3) 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.
(4) Heyn, R. H.; Tilley, T. D. J . Am. Chem. Soc., 1992, 114, 1917.
(5) Michalczyk, M. J .; Calabrese, J . C.; Recatto, C. A.; Fink, M. J .
J . Am. Chem. Soc. 1992, 114, 7955.
(6) Shimada, S.; Tanaka, M.; Honda, K. J . Am. Chem. Soc. 1995,
117, 8289.
10.1021/om000638j CCC: $20.00 © 2001 American Chemical Society
Publication on Web 01/06/2001

Diplatinum Complexes Containing µ-SiHArLigands
Organometallics, Vol. 20, No. 3, 2001 475
Ta ble 1. Selected NMR Da ta for Com p lexes 2-4
istry of complexes containing bridging SiR2 and GeR2
ligands.7 These types of complexes are of importance
since platinum complexes containing both mono- and
bis(silyl) groups are believed to play a role in dehydro-
coupling8 and hydrosilylation9 reactions.
1H (SiH)a
31P{1H}a
[(Me3P)2Pt(µ-SiH(IMP)]2, 2
[(PhMe2P)2Pt(µ-SiH(IMP)]2, 3
[(Ph2MeP)2Pt(µ-SiH(IMP)]2, 4
5.35
-13.8
J ) 27b
J ) 1693c
J ) 266d
J ) 21e
-2.1
Dinuclear platinum complexes containing bridging
silylene groups and bridging hydrides (Pt‚‚‚H‚‚‚Si) are
also known (D, Chart 1).3,10,11,12 Recently, we prepared
complexes of the formula [(Ph3P)Pt(µ-η2-H-SiHAr)]2
from reaction of bulky arylsilanes (ArSiH3) with (Ph3P)2-
Pt(η2-C2H4).11,12 In our quest to understand the mecha-
nistic details involved in the formation of these com-
plexes, we examined how steric and/or electronic factors
associated with the metal precursor influence their
formation. Herein, we report the study of reactions of
platinum complexes of the type (PhnMe3-nP)2PtMe2 (n
) 0-2) with the sterically demanding arylsilane
(IMP)SiH3 (1, IMP ) 2-isopropyl-6-methylphenyl),12
which provided complexes {(PhnMe3-nP)2Pt[µ-SiH(IMP)]}2
[n ) 0 (2), 1 (3), 2 (4)]. The platinum precursors utilized
in the current study contain a series of phosphines
which differ in both steric requirements (cone angles
range from 118° to 136°) and basicity (pKa’s range from
8.65 to 4.57).
5.79
J ) 169f
J ) 30b
J ) 1725c
J ) 271d
J ) 20e
13.5
5.80
J ) 36b
J ) 1793c
J ) 287d
J ) 39e
a
Chemical shift given in ppm, coupling constants in Hz, data
collected in C6D6 solvent. 2J PtH
.
J
.
3J PtP
.
J
.
J
.
b
c 1
d
e 4
f 1
PtP
PP
SiH
collapses to a single line flanked by Pt satellites. Due
to the low solubility of 2-4, it was only possible to
observe the Si satellites in compound 3. The Si-H
1
coupling in 3 was J SiH ) 160 Hz, lower than that
observed in the starting silane 1 [1J SiH ) 200 Hz]. This
observation is consistent with an expected decrease in
the magnitude of the Si-H coupling in a metal-
coordinated silyl complex relative to the free silane.1 The
1H NMR data for 2-4 are in good agreement with those
reported by Tessier et al. for {(Pr3P)2Pt[µ-SiH(Hex)]}2,
which exhibited a 1H NMR resonance at 3.89 ppm for
the trans isomer (1J SiH ) 159 Hz) and 3.54 ppm for the
cis isomer.3
Resu lts a n d Discu ssion
Reaction of (PhnMe3-nP)2PtMe2 (n ) 0-2) in a 1:1
ratio with the sterically hindered silane (IMP)SiH3, 1,
afforded the dinuclear complexes 2-4 (eq 1) exclusively
as the trans isomers in yields of 20-30%. Complex 4
The P-CH3 resonances appeared in the expected
1
region in the H NMR spectrum near 1.1 ppm, and a
single resonance was found for compounds 2 and 4.
However, two P-CH3 resonances were found for com-
3
plex 3, with two slightly different J PtH coupling con-
stants (20 and 23 Hz). These resonances couple equally
to the 31P nuclei, as observed from a 1H-31P COSY
experiment. No change was observed in the 1H{31P}
NMR spectrum for 3 upon heating to 105 °C. The
presence of two PMe2Ph resonances in 3 might be
explained on the basis of a hindered rotation of the Me
groups around the P center. Since the presence of
π-stacking between the phenyl groups on adjacent
phosphorus atoms is strongly suggested in 3 in the solid
state (see below), it is plausible that the interaction is
also favorable in solution.
was generated in 70% yield using the platinum precur-
sor Pt(PMePh2)4, but the reaction was slow.13 Com-
pounds 2-4 appear to be air stable both in solution and
in the solid and were characterized by 1H, 1H{31P},
31P{1H}, and 29Si{1H} (3 only) NMR spectroscopy, IR,
X-ray crystallography, and elemental analyses. Selected
spectroscopic data are shown in Table 1.
The 31P{1H} NMR spectra for 2-4 exhibit part of an
AA′A′′A′′′XX′ spin system. Complexes 2 and 3 show the
expected resonances associated with a symmetrical
dinuclear species containing one 195Pt nucleus, i.e., four
sets of pseudotriplets centered around a main central
peak (Figure 1 shows spectrum for 2). Compound 4
exhibits some unusual features and is discussed in
detail below. It was possible to resolve only two peaks
for the case where both 195Pt nuclei are present (11.4%)
due to low solubility. The chemical shifts for the
phosphorus resonance in 2-4 appear successively down-
field from -13 to +13 ppm with increasing Ph substitu-
The 1H NMR spectra for complexes 2-4 exhibit a
complex multiplet for the Si-H resonance due to
coupling to 31P and 195Pt nuclei in the region 5.35-5.80
ppm. Upon decoupling of the 31P nuclei, the multiplet
(7) Ogino, H.; Tobita, H. Adv. Organomet. Chem. 1998, 42, 223.
(8) (a) Gauvin, F.; Harrod, J . F.; Woo, H. G. Adv. Organomet. Chem.
1998, 42, 363. (b) Yamashita, H.; Tanaka, M. Bull. Chem. Soc. J pn.
1995, 68, 403. (c) Tilley, T. D. Acc. Chem. Res. 1993, 26, 22. (d) Corey,
J . Y. Adv. Silicon Chem. 1991, 1, 327. (e) Tilley, T. D. Comm. Inorg.
Chem. 1990, 10, 37.
(9) Comprehensive Handbook on Hydrosilylation; Marciniec, B., Ed.;
Pergamon Press: Oxford, U.K., 1992.
(10) Auburn, M.; Ciriano, M.; Howard, J . A. K.; Murray, M.; Pugh,
N. J .; Spencer, J . L.; Stone, F. G. A.; Woodward, P. J . Chem. Soc.,
Dalton Trans. 1980, 659.
(11) Braddock-Wilking, J .; Levchinsky, Y.; Rath, N. P. Organo-
metallics 2000, 19, 5500.
(12) Levchinsky, Y.; Rath, N. P.; Braddock-Wilking, J . Organo-
metallics 1999, 18, 2583.
(13) Slow dissociation of PMePh2 from the platinum precursor which
probably accounts for a slow reaction with the silane. Clark, H. C.;
Itoh, K. Inorg. Chem. 1971, 10, 17.
1
tion on the phosphine. The values of J PtP coupling
constants for 2-4 (1684, 1720, and 1793 Hz, respec-
tively) are consistent with a species that has phosphorus
atoms in a cis arrangement and one that contains a
ligand that has a strong trans influence (silicon) at the
Pt center. These values fall in the range observed for
other P2Pt(µ-SiR2)2 ring structures (i.e., 1J PtP for {(R3P)2-
Pt[µ-SiH(Hex)]}2 was 1744 Hz).3 Additionally, the values

476 Organometallics, Vol. 20, No. 3, 2001
Braddock-Wilking et al.
F igu r e 3. 29Si{1H} DEPT NMR spectrum of 3 (99 MHz,
C6D6).
F igu r e 1. 31P{1H} NMR spectrum of 2 (121 MHz, C6D6).
the phosphine ligands on the Pt center could be an
important factor, as PPh3 is also less basic (e.g., pKa
for PPh3 ) 2.73, pKa for PMePh2 ) 4.57).
The 29Si NMR spectrum17 of 3 showed two sets of
overlapping triplets centered at -134 ppm flanked by
Pt satellites (1J SiPt ) 699 Hz) (Figure 3). This is a
significant shift compared to the value of the silane
precursor 1, which appears at -77 ppm.12 In general,
the chemical shift for a metal-bound silyl group moves
to low field compared to the parent hydrosilane.17 The
multiplicity pattern is due to inequivalent coupling of
cis and trans phosphines to the Si center [2J PSi ) 66 Hz
2
(cis), J PSi ) 107 Hz (trans)]. The platinum satellites
appear as an overlapping pseudo triplet of triplets and
are due to the inequivalency between four phosphorus
nuclei when one of the Pt nuclei is NMR active. Thus,
four sets of overlapping satellite doublets would be
expected.
F igu r e 2. 31P{1H} NMR spectrum of 4 (121 MHz, C6D6).
1
of J PtP decrease as the basicity of the phosphine
increases and the cone angle decreases. This was a
surprising observation considering the fact that, in
The high-field value for the 29Si resonance for 3 (and
a related system prepared by Tessier et al., see below)
is unusual since the recent review by Ogino and Tobita
summarized the 29Si chemical shift range for most
bridging silylene moieties in transition metal complexes
(including those with M‚‚‚H‚‚‚Si interactions) as +60 to
+290 ppm.7 Dinuclear complexes containing a bridging
silylene group without a metal-metal bond generally
exhibit 29Si resonances in the region 60-160 ppm, and
those that contain a hydrogen bridging the metal-
silylene bond (M‚‚‚H‚‚‚Si interaction) appear between
85 and 165 ppm.7 A low-field shift of >200 ppm is often
observed for bridging silylene complexes containing a
metal-metal bond with the general formula Cp2Fe2-
(CO)2(µ-CO)(µ-SiR2).7
1
general, the values of J PtP decrease as the steric
requirements of the phosphine ligands increase.14 On
1
the other hand, Grim and associates found that J WP
couplings decrease as the basicity of the phosphine
ligands increases.15
While the solid-state structure of 4 (see below) showed
two phosphine ligands at each platinum center, the
satellite pattern in the 31P{1H} NMR spectrum (Figure
2) of 4 was consistent with the presence of only one
phosphine and can be described as a part of an AA′XX′
spin system. The 31P{1H} NMR and 1H{31P} NMR
spectra for an analytically pure sample of 4 indicated
the presence of free phosphine, which appeared as a
broad resonance. Cooling the sample to - 90 °C had no
effect on the spectrum, even though it was not possible
to see the free phosphine at lower temperatures. The
most likely reason for phosphine dissociation is due to
steric effects associated with a small P-Pt-P angle.
The observation of phosphine dissociation from each
Pt center in 4 strongly suggests that the PMePh2 ligand
(θ ) 136°) defines the upper limit of steric capacity at
platinum in complexes of the type {[(R3P)2Pt][µ-
SiHAr]}2 (Ar ) IMP, or any other bulky aryl group).11
In fact, reaction of (Ph3P)2PtMe2 (cone angle for Ph3P
) 145°)14 with (IMP)SiH3 did not generate {(Ph3P)2Pt-
[µ-SiH(IMP)]}2 analogous to 2-4 but instead gave a
dinuclear complex containing bridging silylene groups
and bridging hydrides, {(Ph3P)Pt[µ-η2-H-SiH(IMP)]}2.16
However, a possibility still exists that the basicity of
In contrast, the 29Si signal for {(Ph3P)Pt[µ-η2-H-
SiH(IMP)]}2 was found ca. +130 ppm with a substan-
tially larger coupling to Pt (1J PtSi ) 1527 Hz).11,12
Therefore, two platinum silyl dimers containing the
same Si substituents and slightly different phosphine
ligands were found to have 29Si chemical shifts that
span a range of ∼260 ppm! This trend was also observed
in the related systems {(Et3P)2Pt[µ-SiH(Hex)]}2 and
{(R3P)Pt[µ-η2-H-Si[Pt(PR3)2H](Hex)]},2 which exhibited
1
29Si resonances at -66 ppm (cis, J PtSi ) 676 Hz), -93
1
(trans, J PtSi ) 667 Hz), and +194 ppm (1J PtSi ) 707
Hz), respectively.3
(16) Braddock-Wilking, J .; Levchinsky, Y. Unpublished results. See
ref 11 for synthesis and characterization of {(R3P)Pt[µ-η2-H-SiH(Ar)]}2.
(17) For a recent review on NMR spectroscopy of organosilicon
compounds see for example: Williams, E. A. In The Chemistry of
Organic Silicon Compounds, Part 1; Patai, S., Rappoport, Z., Eds.; J ohn
Wiley & Sons: New York, 1989; Chapter 8.
(14) Tolman, C. A. Chem. Rev. 1977, 77, 313.
(15) Grim, S. O.; Wheatland, D. A.; McFarlane, W. J . Am. Chem.
Soc. 1967, 89, 5573.

Diplatinum Complexes Containing µ-SiHArLigands
Organometallics, Vol. 20, No. 3, 2001 477
F igu r e 5. Molecular structure of {(PhMe2P)2Pt[µ-SiH-
(IMP)]}2, 3, with thermal ellipsoids drawn at 50% prob-
ability. Hydrogen atoms (except Si-H) have been omitted
for clarity.
F igu r e 4. Molecular structure of {(Me3P)2Pt[µ-SiH-
(IMP)]}2, 2, with thermal ellipsoids drawn at 50% prob-
ability. Hydrogen atoms (except Si-H) have been omitted
for clarity.
The Si-H stretching frequency of 2-4 appeared in
the infrared region between 2021 and 2054 cm-1. These
values are in good agreement with those reported by
Tessier et al. for {(R3P)2Pt[µ-SiH(Hex)]}2 (R ) Et, ν(Si-
H) ) 1985 cm-1; R ) Pr, ν(Si-H) ) 1984 cm-1).3
The reaction of 1 with (PhMe2P)2PtMe2 was moni-
1
tored by H, 29Si{1H}, and 31P{1H} NMR spectroscopy.
Both the 1H and 31P NMR spectra of the reaction
mixture indicated the presence of two new platinum-
containing products (one of them corresponding to 3).
The second platinum-containing complex was assigned
to the bis(silyl) species (PhMe2P)2Pt[SiH2(IMP)]2, 6.
Complex 6 was not isolated and could not be separated
from unreacted (PhMe2P)2PtMe2. These results are
consistent with those reported by Tilley et al., who
observed the formation of Pt2Si2 dimers from bis(silyl)
platinum intermediates with Pt(PEt3)3.4
F igu r e 6. Molecular structure of {(Ph2MeP)2Pt[µ-SiH-
(IMP)]}2, 4, with thermal ellipsoids drawn at 50% prob-
ability. Hydrogen atoms (except Si-H) have been omitted
for clarity.
1
In addition, H and 29Si NMR spectroscopy (as well
as GC-MS analysis) of the reaction mixture showed the
presence of an organosilane which was assigned to
(IMP)SiH2Me.18 The formation of this compound sug-
gests that oxidative addition of a Si-H bond in (IMP)SiH3
to the Pt center could occur to give a Pt(IV) complex19
with the composition (PhnMe3-nP)2Pt(H)(Me)2[SiH2(IMP)].
This species could reductively eliminate MeSiH2(IMP)
(or CH4) followed by reaction with a second equivalent
of (IMP)SiH3 to give the bis(silyl) complex. The genera-
tion of a Pt(IV) species is consistent with the report by
Fink and Michalczyk, who observed the formation of fac-
(dcpe)Pt(SiMeHSiMeH2)H3 by low-temperature NMR
spectroscopy from the reaction of (dcpe)PtH2 with
H2MeSiSiMeH2.5 An alternative mechanism would in-
volve a metathesis reaction between (R3P)2PtMe2 and
(IMP)SiH3, which could also generate (IMP)SiH2Me.
X-r a y Cr ysta llogr a p h ic Stu d y of 2-4. Compounds
2-4 were structurally characterized by X-ray crystal-
lography, and the molecular structures are shown in
Figures 4-6, respectively. Crystallographic data and
structural refinement data for 2-4 are given in Table
2, and selected bond distances and angles for 2-4 and
related derivatives are in Table 3. As a general trend,
complexes 2-4 were found to exhibit a planar diamond
shaped Pt2Si2 core with the IMP groups lying directly
above and below the central ring. The hydrogen atoms
on Si were located and refined in complexes 2 and 3.
One notable feature found in 2-4 as well as related
Pt2Si2 ring systems is the Si‚‚‚Si separation.2,3 These
distances fall in the upper range of known Si-Si single-
bond distances (2.33-2.70 Å).20 Theoretical studies have
suggested a µ2-η2-disilene type geometry for the model
(18) GC-MS, 1H NMR, and 29Si{1H} NMR spectroscopic data are
analogous to an authentic sample prepared from (IMP)MgBr
MeSiHCl2 followed by LiAlH4 reduction. Braddock-Wilking, J . Unpub-
lished results.
+
(20) For a comparison of reported bond distances of Si-X see for
example: (a) Klebe, G. J . Organomet. Chem. 1985, 293, 147. (b) Corey,
J . Y. In The Chemistry of Organic Silicon Compounds, Part 1; Patai,
S., Rappoport, Z., Eds.; J ohn Wiley & Sons: New York, 1989; Chapter
1. (c) Sheldrick, W. S. In The Chemistry of Organic Silicon Compounds,
Part 1; Patai, S., Rappoport, Z., Eds.; J ohn Wiley & Sons: New York,
1989; Chapter 3.
(19) Eaborn et al. suggested the formation of Pt(IV) species from
reaction of P2PtMe2 with some secondary and tertiary hydrosilanes.
Eaborn, C.; Pidcock, A.; Ratcliff, B. J . Organomet. Chem. 1974, 66,
23.

478 Organometallics, Vol. 20, No. 3, 2001
Ta ble 2. Cr ysta l Da ta a n d Str u ctu r e Refin em en t for 2-4
Braddock-Wilking et al.
2
3
4
formula
fw
C
16H32P2PtSi
C52H72P2Pt2Si2
1267.34
223(2)
0.28 × 0.22 × 0.14
triclinic
P1h
9.2786(1)
12.0407(1)
12.922(1)
84.338(1)
72.68(1)
71.10(1)
1303.94(2)
1
C42H46P2PtSi
835.91
223(2)
0.34 × 0.30 × 0.22
triclinic
P1h
12.5935(1)
12.7862(1)
14.1237(1)
94.051(1)
116.342(1)
109.575(1)
1854.39(2)
2
509.54
293(2)
0.22 × 0.20 × 0.20
triclinic
P1h
9.7269(1)
10.9682(1)
11.0411(1)
111.026(1)
109.503(1)
93.665(1)
1013.58(2)
2
temperature (K)
cryst dimens (mm)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
d
calc (mg/m3)
1.670
7.130
1.118
1.614
5.560
1.016
1.497
3.930
1.022
µ (mm-1
)
GOF
R1 (obsd data)
0.0298
0.0282
0.0292
wR2 (all data)
0.0684
1.215
0.0538
1.517
0.0641
1.756
largest diff peak (e Å3)
Ta ble 3. Selected Bon d Len gth s [Å] a n d An gles
crease), Pt-Si-Pt (increase), Si-Pt-Si (decrease) and
an increase in the Pt-P bond length, as the phosphine
becomes more sterically demanding. The steric bulk of
the phosphines increases on going from 2 f 4 [cone
angle for the PMe2Ph ligand (122°) lies between PMe3
(118°) and PMePh2 (136°)]. The Si-Pt-Si angles in 3
are significantly higher than the corresponding angles
in 2 and 4, while the value of the Pt-Si-Pt angle in 3
is smaller. Furthermore, the Si‚‚‚Si distance in 3 was
found to be the longest (2.718 Å).22 These unusual
observations might be explained by the presence of
π-stacking interactions between the phenyl groups on
the adjacent phosphine atoms. The plane-to-plane dis-
tance between the phenyl groups in 3 was calculated to
be 3.97 Å. Although this distance is long, π-stacking may
account for the greater solubility of 3 in aromatic
solvents (as opposed to 2 and 4).
[d eg] for 2-4 a n d Rela ted Com p ou n d s
(R3P)2Pt-
2,3
2
3
4
(µ-SiR’R’’)2
Bond Distances
Pt-P1
Pt-P2
Pt-Si
Pt-Si#1
Pt‚‚‚Pt
Si‚‚‚Si#1
2.3215(13) 2.3124(9) 2.3306(8)
2.3164(13) 2.3163(10) 2.3397(8)
2.4054(12) 2.4039(8) 2.4089(9) 2.355-2.408
2.4087(12) 2.4006(10) 2.4070(8)
4.004
3.962
4.030
3.973-4.046
2.673(2)
2.718(2)
2.637(2) 2.554-2.612
Bond Angles
68.89(4)
112.54(5) 111.11(4) 113.60(3) 112.6-115.5
94.67(4) 164.10(3) 95.83(3)
Si-Pt-Si#1
Pt-Si-Pt#1
P1-Pt-Si
67.46(5)
66.40(3) 64.4-66.6
P1-Pt-Si#1 160.59(5) 95.80(3)
161.77(3)
162.35(3)
P2-Pt-Si
160.44(4) 94.59(3)
P2-Pt-Si#1 94.34(4)
162.81(3) 98.92(3)
104.24(5) 100.99(3) 99.28(3)
P2-Pt-P1
Pt-Si-Si#1
56.33(4)
55.50(3)
55.61(3)
56.76(3)
56.83(3)
Pt#1-Si-Si#1 56.21(4)
Con clu sion
compound trans-Pt2(PH3)4(SiPhCl)2, where the Si-Si
Mulliken overlap was 0.27.2d The Pt‚‚‚Pt nonbonding
distances in 2-4 and these related Pt2Si2 ring systems2,3
are 3.9-4.0 Å (van der Waals radius of Pt21 1.7-1.8 Å).
The Pt-Si bond lengths in 2-4 (∼2.4 Å) are found at
the higher end of the range for Pt-Si distances (2.25-
2.44 Å)1 and are similar to those reported by Tessier
for related complexes.2,3
A prominent feature found in 2-4 and related Pt2Si2
ring systems are acute Si-Pt-Si and obtuse Pt-Si-Pt
angles. The Si-Pt-Si angles for 2-4 range from 66° to
69°, but the related complexes prepared by Tessier show
slightly smaller angles.2,3 The Pt-Si-Pt angles for 2-4
and Tessier’s complexes2,3 (trans isomers) fall in the
range 111-116°. These Pt2Si2 systems display ring
structures opposite the complexes [(R3P)Pt(µ-η2-H-
SiHR′)]2, which possess bridging hydrides (Pt‚‚‚H‚‚‚Si).
The latter systems exhibit acute Pt-Si-Pt angles,
obtuse Si-Pt-Si angles, Pt-Pt bonds, and long Si‚‚‚Si
separations.3,10,11,12
Dimeric (µ-silylene)platinum species of the type
{[(R3P)2Pt][µ-SiH(IMP)]}2 (C, Chart 1) were obtained
from reaction of (IMP)SiH3, 1, with a series of Pt(II)
phosphine complexes. Despite the difference in the
basicity and the steric requirements of the phosphine
ligands on the starting platinum material, complexes
2-4 exhibit similar structural features, as determined
by NMR spectroscopy and X-ray crystallography. In
addition, complex 4 (containing the most sterically
hindered phosphine, PMePh2) was found to undergo
dissociation of one of the phosphine ligands at each Pt
center in solution. This suggests that reaction of 1 with
other platinum precursors containing phosphine ligands
with a cone angle of greater than 136° should give a
Pt-Si product of the type {(Ph3P)Pt[µ-η2-H-SiH(Ar)]}2
(D, Chart 1).11,12 Thus, it appears that steric constraints
with respect to the substituents at Pt have a significant
impact on the nature of the product formed.
In a previous paper we reported that bulky groups at
silicon (RSiH3) provided compounds of type A or D
(Chart 1). However, less sterically demanding primary
silanes generally produced bis(silyl) complexes analo-
gous to B. The current study has demonstrated that the
Examination of the ring environment in 2-4 reveals
some unusual features. It is reasonable to expect the
following changes in the key angles P2-Pt-Si (in-
(21) Huheey, J . E. Inorganic Chemistry, 3rd ed.; Harper & Row:
New York, 1983.
(22) The Si‚‚‚Si distance in 3 represents the longest separation
among structurally characterized dimers of this type.

Diplatinum Complexes Containing µ-SiHArLigands
Organometallics, Vol. 20, No. 3, 2001 479
for 24 h. Yellow crystals of {[(PhMe2P)2Pt][µ-SiH(IMP)]}2, 3
(suitable for X-ray analysis), were obtained in 26% yield (49
mg).
nature of the phosphine in the platinum precursor
influences the nature of the product formed (using the
same silane precursor). In addition, the stronger coor-
dinating ability of basic phosphines to a metal center
could be important in the dissociation of the phosphine,
which is required for the formation of complexes of the
type [(Ph3P)Pt(µ-η2-H-SiHAr)]2. A study of the influ-
ence of electronic effects associated with groups at
silicon and platinum on the formation of dinuclear Pt2Si2
complexes is in progress.
3
1H{31P} NMR (C6D6, 300 MHz): δ 1.12 (s, 24H, J PtH ) 20
Hz, 23 Hz, P(CH3)2), 2.62 (s, 6H, ArCH3), 3.40 (d, 12H, 3J HH
)
6 Hz, ArCH(CH3)2), 4.81 (bm, 2H, ArCH(CH3)2), ArH region
6.87-7.33 (26H). 29Si{1H} NMR (C6D6, DEPT, 99 MHz): δ
1
2
2
-134.2 [m, J PtSi ) 699 Hz, J PSi ) 66 Hz (cis), J PSi ) 107 Hz
(trans)]. 1H-31P COSY NMR (500 MHz, C7D8): δ -2.1 (31P
resonance) showed cross-peak coupling to protons δ 1.11
(PCH3), 1.35 (PCH3), 5.73 (Si-H), 7.16 [o-PMe2(C6H5)]. IR
(KBr, cm-1): ν 2021.4 (Si-H). Anal. Calcd for C52H72P4Pt2Si2:
C, 49.28; H, 5.73. Found: C, 49.38; H, 5.79.
Exp er im en ta l Section
Va r ia ble-Tem p er a tu r e NMR Sp ectr oscop y of 3. A
sample of 3 (5 mg, 0.004 mmol) was dissolved in 1 mL of
toluene-d8 and analyzed by VT-NMR. The sample was ana-
lyzed by 1H{31P} NMR from room temperature (23 °C) to 90
°C in 10 deg increments to determine if a fluxional process
was occurring between the two P(CH3)2Ph resonances (1-2
ppm). No change was observed in the spectra over this
temperature range, and no decomposition was found to take
place after heating.
Gen er a l Ma ter ia ls a n d P r oced u r es. All reactions and
manipulations were performed in dry glassware under an
argon atmosphere in an inert atmosphere drybox or on a
double manifold Schlenk line. 1H and 31P NMR data were
obtained on a Varian Unity Plus 300 MHz WB spectrometer
or a Bruker ARX-500 MHz spectrometer (ambient and variable
temperatures) using a 5 mm tunable broadband probe. 29Si
NMR data were collected on a Bruker ARX-500 MHz spec-
trometer. NMR experiments were performed in C6D6, CD2Cl2,
or toluene-d8, and chemical shifts are reported relative to
residual protonated solvent. Phosphorus chemical shifts are
reported relative to external H3PO4 (0 ppm). 29Si{1H} NMR
data were collected using the DEPT sequence23 at room
temperature and are reported relative to external TMS (0
ppm). Infrared spectra were recorded on a Perkin-Elmer 1600
Series FT-IR (as KBr pellets). X-ray crystal structure deter-
minations were performed on a Bruker SMART diffractometer
equipped with a CCD area detector at 223 K. Elemental
analyses were obtained from Atlantic Microlab, Inc., Norcross,
GA.
Pentane and benzene were distilled over CaH2. Diethyl
ether and 1,2-dimethoxyethane were distilled from sodium/
benzophenone ketyl. Solvents were degassed by standard
methods before they were taken into the drybox. Toluene-d8,
CD2Cl2, and C6D6 were dried over activated alumina (neutral)
or Lindle catalyst before use. The platinum (phosphine)
complexes Me2PtL2 (L ) PMe3, PMe2Ph, PMePh2) were
prepared according to the literature procedures.24 Pt(PMePh2)4
was prepared in a manner similar to Pt(PPh3)4.25 The synthesis
of (IMP)SiH3, 1, was previously reported.12
Syn th esis of {[(P h 2MeP )2P t][µ-SiH(IMP )]}2 (4). A solu-
tion of (IMP)SiH3, 1 (24 mg, 0.15 mmol), in 1 mL of C6D6 was
added to (Ph2MeP)2PtMe2 (83 mg, 0.13 mmol). The resulting
pale yellow-brown solution was heated to 65 °C for 39 h. The
reaction mixture was cooled to 0 °C, and Et2O and pentane
(20 mL, 50:50 mixture) were added. The solution was filtered,
and the solid was dried in vacuo to afford {[(Ph2MeP)2Pt][µ-
SiH(IMP)]}2, 4, as a bright yellow solid (30 mg, 30% yield).
Crystals suitable for an X-ray analysis were obtained by slow
1
evaporation of a C6D6 solution at room temperature. H{31P}
NMR (C6D6, 300 MHz): δ 1.51 (s, 6H, ArCH3), 1.72 (s, 12H,
3
3J PtH ) 24 Hz, P(CH3)), 1.89 (d, 12H, J HH ) 6 Hz, ArCH-
(CH3)2), 4.83 (bm, 2H, ArCH(CH3)2), ArH region 6.54-7.41
(46H). IR (KBr, cm-1): ν 2054.0 (Si-H). Anal. Calcd for
C
72H80P4Pt2Si2‚Et2O: C, 57.37; H, 5.66. Found: C, 57.34; H,
5.62.
Alter n a tive P r ep a r a tion of 4 fr om P t(P MeP h 2)4 a n d
(IMP )SiH3 (1). A sample of Pt(PMePh2)4 (125 mg, 0.082 mmol)
was dissolved in 3 mL of C6H6, and a solution of (IMP)SiH3, 1
(19 mg, 0.12 mmol, 1 mL of C6H6), was added to give a pale
yellow mixture with mild gas evolution. After 24 h, additional
C6H6 (3 mL) was added, and the reaction was heated to 50 °C
for 24 h, during which the color changed from yellow to orange.
After addition of pentane (7 mL) the reaction mixture was
stored at -35 °C for 2 days, which resulted in the formation
of large yellow crystals of 4. The crystalline material was
washed with DME (3 × 1 mL) and dried in vacuo, giving 67
mg (71%) of 4. Spectroscopic data for 4 obtained from this route
were identical to the data obtained from the (PMePh2)2PtMe2/
(IMP)SiH3 route.
Va r ia ble-Tem p er a tu r e NMR Sp ectr oscop y of 4. A
sample of 4 (7 mg, 0.005 mmol) was dissolved in 1 mL of
CD2Cl2 and analyzed by VT-NMR. The sample was analyzed
by 31P{1H} NMR from room temperature (23 °C) to -90 °C in
10 deg increments to determine if a fluxional process was
occurring. No change was observed in the 31P{1H} spectra over
the temperature range studied. In addition, no free PMePh2
was observed.
Syn th esis of {[(Me3P )2P t][µ-SiH(IMP )]}2 (2). A solution
of (IMP)SiH3, 1 (57 mg, 0.35 mmol), in 1 mL C6H6 was added
to a solution of (Me3P)2PtMe2 (130 mg, 0.35 mmol, 1.5 mL
C6H6), resulting in a pale yellow mixture. The pale yellow
solution was heated to 50 °C for 21 h, and the color changed
from pale yellow to bright orange. Addition of Et2O (2 mL) to
the reaction mixture followed by cooling at -35 °C resulted
in the formation of orange microcrystals of {[(Me3P)2Pt][µ-
SiH(IMP)]}2, 2 (38 mg, 22%). Crystals of 2 suitable for an X-ray
analysis were obtained by slow evaporation of a C6D6 solution
at room temperature.
3
1H{31P} NMR (C6D6, 300 MHz): δ 1.09 (s, 36H, J PtH ) 20
Hz, P(CH3)3), 1.43 (d, 12H, 3J HH ) 7 Hz, ArCH(CH3)2), 3.07 (s,
6H, ArCH3), 4.46 (bm, 2H, ArCH(CH3)2), ArH region 6.88-
7.43 (6H). IR (KBr, cm-1): ν 2024.0 (Si-H). Anal. Calcd for
C
32H64P4Pt2Si2: C, 37.72; H, 6.33. Found: C, 37.72; H, 6.53.
Syn th esis of {[(P h Me2P )2P t][µ-SiH(IMP )]}2 (3). A solu-
NMR Stu d y of Rea ction of 1 w ith (P h Me2P )2P tMe2. The
formation of the bis(silyl)platinum complex 6 was monitored
by multinuclear NMR spectroscopy. Complex 6 was not
isolated and thus was characterized in solution only. A
description of the experiment is given for reaction of (PhMe2P)2-
PtMe2 with 1. The analogous systems 5 and 7 are proposed
on the basis of 31P{1H} NMR data.
tion of (IMP)SiH3, 1 (49 mg, 0.30 mmol), in 1 mL C6D6 was
added to (PhMe2P)2PtMe2 (150 mg, 0.30 mmol) to give a pale
yellow solution. The reaction mixture was heated to 60 °C for
24 h, and rapid bubbling was observed for the first 3 h, along
with a gradual color change from yellow to orange. The
solution was layered with 15 mL of pentane and set aside
(PhMe2P)2PtMe2 (66 mg, 0.13 mmol) and (IMP)SiH3, 1 (21
mg, 0.13 mmol), were placed in an NMR tube (sample prepared
inside an inert atmosphere drybox). Benzene-d6 (0.75 mL) was
added, which gave a pale yellow solution. The sample was
(23) Blinka, T. A.; Helmer, B. J .; West, R. Adv. Organomet. Chem.
1984, 23, 193.
(24) Ruddick, J . D.; Shaw, B. L. J . Chem. Soc. A 1969, 2801.
(25) Clark, H. C.; Itoh, K. Inorg. Chem. 1971, 10, 17.

480 Organometallics, Vol. 20, No. 3, 2001
Braddock-Wilking et al.
heated at 60 °C for approximately 20 h. Analysis of the reaction
mixture by 1H, 29Si{1H}, and 31P{1H} NMR spectroscopy
revealed the formation of cis-(PhMe2P)2Pt[SiH2(IMP)]2, 6, and
{(PhMe2P)2Pt[µ-SiH(IMP)]}2, 3 (as well as unreacted (PhMe2P)2-
PtMe2).
systematic errors using SADABS27 based upon the Laue
symmetry using equivalent reflections.
Crystal data and intensity data collection parameters are
listed in Table 2.
Structure solution and refinement were carried out using
the SHELXTL-PLUS software package.26 The structures were
solved by direct methods and refined successfully in the space
group P1h for all three crystals. Full-matrix least-squares
Selected NMR d a ta for 6: 1H{31P} NMR (C6D6, 500
1
2
MHz): δ 5.0 (s, 4H, J SiH ) 172 Hz, J PtH ) 33 Hz, SiH).
31P{1H} NMR (C6D6, 202 MHz): δ -7.3 (1J PtP ) 1773 Hz).
29Si{1H} NMR (C6D6, 99 MHz): δ -51.8 (dd, 1J PtSi ) 1075 Hz,
refinements were carried out by minimizing ∑w(Fo - Fc2)2.
2
3
3J PSi ) 157 Hz, J PSi ) 21 Hz).
The non-hydrogen atoms were refined anisotropically to
convergence. The terminal Si-H hydrogen atoms were located
and refined freely. All other H atoms were treated using an
appropriate riding model (AFIX m3). The final residual values
and relevant structure refinement parameters are provided
in the Supporting Information. Projection view of the molecules
with non-hydrogen atoms represented by 50% probability
ellipsoids and showing the atom labeling is presented in
Figures 4-6.
Selected NMR d a ta for 5: 31P{1H} NMR (C6D6, 121
MHz): δ -18.6 (1J PtP ) 1786 Hz).
Selected NMR d a ta for 7: 31P{1H} NMR (C6D6, 121
MHz): δ 10.1 (1J PtP ) 1801 Hz).
In addition, an organosilane product was observed and was
assigned the composition (IMP)MeSiH2.18 Selected NMR data
for (IMP)MeSiH2: 1H NMR (C6D6, 300 MHz): δ 4.65 (q, 2 H,
1
2
SiH, J SiH ) 192 Hz, J SiH ) 4.4 Hz). 29Si{1H} NMR (C6D6, 99
MHz): δ -51.5 (s). GC-MS (EI, 70 eV): m/z 178 (30), 163
(11), 161 (24), 159 (22), 145 (10), 135 (28), 133 (100), 119 (14),
105 (25), 91 (10).
Ack n ow led gm en t. This work was supported by the
University of Missouri-St. Louis Research Award. The
support of the NSF (CHE-9318696) and the University
of Missouri Research Board are gratefully acknowledged
for the purchase of a Varian Unity Plus 300 and Bruker
ARX-500 NMR spectrometers. The UM-St. Louis X-ray
Crystallography Facility was funded in part by a NSF
Instrumentation Grant (CHE-9309690) and the UM-St.
Louis Research Award. J .B.-W. is also grateful to
Professors Claire Tessier, J oyce Y. Corey, and Peter P.
Gaspar for stimulating discussions.
X-r a y Cr ysta llogr a p h y for 2, 3, a n d 4. Crystals of
appropriate dimensions were mounted on glass fibers in
random orientations. Preliminary examination and data col-
lection were performed using a Bruker SMART charge coupled
device (CCD) detector system single-crystal X-ray diffrac-
tometer using graphite-monochromated Mo KR radiation (λ
) 0.71073 Å) equipped with a sealed tube X-ray source.
Preliminary unit cell constants were determined with a set of
45 narrow frames (0.3° in $ scans). A typical data set consists
of 4028 frames of intensity data collected with a frame width
of 0.3° in $ and counting time of 15 s/frame at a crystal-to-
detector distance of 4.930 cm. The double pass method of
scanning was used to exclude any noise. The collected frames
were integrated using an orientation matrix determined from
the narrow frame scans. SMART and SAINT software pack-
ages26 were used for data collection and data integration.
Analysis of the integrated data did not show any decay. Final
cell constants were determined by a global refinement of xyz
centroids of 8192 reflections. Collected data were corrected for
Su p p or tin g In for m a tion Ava ila ble: Complete listings
of the atomic coordinates, geometrical parameters and aniso-
tropic displacement coefficients for the non-hydrogen atoms,
and positional and isotropic displacement coefficients for
hydrogen atoms are submitted as Supporting Information for
2-4. Selected NMR data for 3 are included. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM000638J
(26) Sheldrick, G. M. Bruker Analytical X-ray: Madison, WI, 1999.
(27) Blessing, R. H. Acta Crystallogr. 1995, A51, 33-38.