Thermolysis reactions of cis-PtR(SiPh3)(PMe2Ph)2 in solution

Article abstract of DOI:10.1021/om000012t

A series of trans- and cis-PtR(SiPh₃)(PMe₂Ph)₂ complexes have been prepared and their thermolysis reactions in solution examined. The trans isomers (R = Me, Et) are robust, and only the methyl complex affords MeSiPh₃ as the reductive elimination product in 72-82% yields. In contrast, the cis isomers (R = Me, Et, Pr, Bu) form the corresponding alkylsilanes in almost quantitative yields (>97%). Despite the selective formation of the reductive elimination products, the cis-alkyl-silyl complexes bearing β-hydrogens undergo a rapid repetition of the β-hydrogen elimination and insertion processes, as confirmed by a deuterium-labeling experiment using cis-Pt(CH₂CD₃)(SiPh₃)(PMe₂Ph) ₂. The alkylsilane formation from the cis isomers proceeds via two reaction paths. One is the direct C-Si reductive elimination. On the other path, the cis-PtR(SiPh₃)(PMe₂Ph)₂ complexes are initially isomerized to the corresponding cis-PtPh(SiRPh₂)(PMe₂Ph)₂ complexes by the exchange of the Pt-R group with the Si-Ph group, and the resulting phenyl-silyl complexes reductively eliminate alkylsilanes. The methyl-silyl complex decomposes exclusively by the former path, while the other alkyl-silyl complexes (R = Et, Pr, Bu) follow mainly the latter path. Preparation and thermolysis reaction of the related cis-PtEt(GePh₃)(PMe₂Ph)₂ are also reported.

Full text of DOI:10.1021/om000012t

2022
Organometallics 2000, 19, 2022-2030
Th er m olysis Rea ction s of cis-P tR(SiP h 3)(P Me2P h )2 in
Solu tion
Koh Hasebe, J un Kamite, Takuya Mori, Hiroyuki Katayama, and
Fumiyuki Ozawa*
Department of Applied Chemistry, Faculty of Engineering, Osaka City University,
Sumiyoshi-ku, Osaka 558-8585, J apan
Received J anuary 7, 2000
A series of trans- and cis-PtR(SiPh3)(PMe2Ph)2 complexes have been prepared and their
thermolysis reactions in solution examined. The trans isomers (R ) Me, Et) are robust, and
only the methyl complex affords MeSiPh3 as the reductive elimination product in 72-82%
yields. In contrast, the cis isomers (R ) Me, Et, Pr, Bu) form the corresponding alkylsilanes
in almost quantitative yields (>97%). Despite the selective formation of the reductive
elimination products, the cis-alkyl-silyl complexes bearing â-hydrogens undergo a rapid
repetition of the â-hydrogen elimination and insertion processes, as confirmed by a deuterium-
labeling experiment using cis-Pt(CH2CD3)(SiPh3)(PMe2Ph)2. The alkylsilane formation from
the cis isomers proceeds via two reaction paths. One is the direct C-Si reductive elimination.
On the other path, the cis-PtR(SiPh3)(PMe2Ph)2 complexes are initially isomerized to the
corresponding cis-PtPh(SiRPh2)(PMe2Ph)2 complexes by the exchange of the Pt-R group
with the Si-Ph group, and the resulting phenyl-silyl complexes reductively eliminate
alkylsilanes. The methyl-silyl complex decomposes exclusively by the former path, while
the other alkyl-silyl complexes (R ) Et, Pr, Bu) follow mainly the latter path. Preparation
and thermolysis reaction of the related cis-PtEt(GePh3)(PMe2Ph)2 are also reported.
In tr od u ction
reaction is effectively accelerated by alkynes and alk-
enes added to the systems, particularly by those with
electron-withdrawing substituents. Kinetic studies in-
dicated that the MeSiPh3 formation in the presence of
diphenylacetylene proceeds via the mechanism involv-
ing prior replacement of one of the phosphine ligands
(L) with diphenylacetylene, followed by reductive elimi-
nation of MeSiPh3 from the resulting [PtMe(SiPh3)-
(PhCtCPh)(L)] intermediate.
While the C-Si bond formation from alkyl(silyl)-
platinum complexes is the most widely accepted product-
forming step for platinum-catalyzed hydrosilylation of
alkenes,1,2 little is known about this elementary
process.3-5 We recently reported that cis-PtMe(SiPh3)-
L2 complexes (L ) PMePh2, PMe2Ph) readily afford
MeSiPh3 in quantitative yields in solution.6,7 This
To gain further insights into the C-Si bond formation
from a platinum(II) center, we prepared in this study a
series of cis-PtR(SiPh3)(PMe2Ph)2 complexes bearing R
groups with â-hydrogens (i.e., Et, Pr, Bu) and examined
their thermolysis reactions in solution. While the reac-
tivity was much lower than that of cis-PtMe(SiPh3)(PMe2-
Ph)2, the alkyl-silyl complexes exclusively afforded
alkylsilanes as the C-Si reductive elimination products.
In addition, the alkylsilane formation was found to take
place mainly from cis-PtPh(SiRPh2)(PMe2Ph)2 interme-
diates, which are formed by the exchange of the Pt-R
group with the Si-Ph group. Related studies on the
thermolysis of trans-PtR(SiPh3)(PMe2Ph)2 (R ) Me, Et)
and cis-PtEt(GePh3)(PMe2Ph)2 are also reported.
(1) (a) Hiyama, T.; Kusumoto, T. In Comprehensive Organic Syn-
thesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991;
Vol. 8, p 763. (b) Ojima, I. In The Chemistry of Organic Silicon
Compounds; Patai, S., Rappoport, Z., Eds.; J ohn Wiley: Chichester,
1989; p 1479. (c) Braunstein, P.; Knorr, M. J . Organomet. Chem. 1995,
500, 21. (d) Recatto, C. A. Aldrichim. Acta 1995, 28, 85. (e) Tilley, T.
D. In The Chemistry of Organic Silicon Compounds; Patai, S.,
Rappoport, Z., Eds.; J ohn Wiley: Chichester, 1989; p 1415.
(2) (a) Chalk, A. J .; Harrod, J . F. J . Am. Chem. Soc. 1965, 87, 16.
(b) Harrod, J . F.; Chalk, A. J . J . Am. Chem. Soc. 1965, 87, 1133. (c)
Stein, J .; Lewis, L. N.; Gao, Y.; Scott, R. A. J . Am. Chem. Soc. 1999,
121, 3693, and references therein.
(3) van der Boom, M. E.; Ott, J .; Milstein, D. Organometallics 1998,
17, 4263.
(4) Sakaki, S.; Mizoe, N.; Sugimoto, M. Organometallics 1998, 17,
2510.
(5) For related studies other than platinum systems, see: (a)
Maruyama, Y.; Yamamura, K.; Ozawa, F. Chem. Lett. 1998, 905. (b)
Tanaka, Y.; Yamashita, H.; Shimada, S.; Tanaka, M. Organometallics
1997, 16, 3246. (c) Akita, M.; Hua, R.; Oku, T.; Tanaka, M.; Moro-oka,
Y. Organometallics 1996, 15, 4162. (d) Okazaki, M.; Tobita, H.; Ogino,
H. Organometallics 1996, 15, 2790. (e) Mitchell, G. P.; Tilley, T. D.
Organometallics 1996, 15, 3477. (f) Aizenberg, M.; Milstein, D. J . Am.
Chem. Soc. 1995, 117, 6456. (g) Schubert, U. Angew. Chem., Int. Ed.
Engl. 1994, 33, 419. (h) Lin, W.; Wilson, S. R.; Girolami, G. S.
Organometallics 1994, 13, 2309. (i) Schubert, U.; Mu¨ller, C. J .
Organomet. Chem. 1989, 373, 165. (j) Brinkman, K. C.; Blakeney, A.
J .; Krone-Schmidt, W.; Gladysz, J . A. Organometallics 1984, 3, 1325.
(6) Ozawa, F.; Hikida, T.; Hayashi, T. J . Am. Chem. Soc. 1994, 116,
2844.
Resu lts a n d Discu ssion
P r ep a r a tion of tr a n s- a n d cis-P tR(SiP h 3)(P Me2-
P h )2. The alkyl-silyl complexes (1 and 2) employed in
this study are listed in Chart 1. Complexes 1a , 1b, 2a ,
and 2b were prepared previously.7,8 The propyl and
butyl complexes (2c and 2d ) were synthesized similarly
(7) Ozawa, F.; Hikida, T.; Hasebe, K.; Mori, T. Organometallics 1998,
17, 1018.
(8) Ozawa, F.; Hikida, T. Organometallics 1996, 15, 4501.
10.1021/om000012t CCC: $19.00 © 2000 American Chemical Society
Publication on Web 04/21/2000

Thermolysis Reactions of cis-PtR(SiPh3)(PMe2Ph)2
Organometallics, Vol. 19, No. 10, 2000 2023
F igu r e 1. Molecular structure of cis-Pt(n-Pr)(SiPh3)(PMe2-
Ph)2 (2c). Thermal ellipsoids are drawn at the 50% prob-
ability level. Selected bond distances (Å) and angles (deg):
Pt-P(1) ) 2.358(2), Pt-P(2) ) 2.304(2), Pt-Si ) 2.367(2),
Pt-C(1) ) 2.128(8), P(1)-Pt-P(2) ) 94.75(8), P(1)-Pt-
Si ) 169.5(1), P(1)-Pt-C(1) ) 85.5(2), P(2)-Pt-Si )
93.6(1), P(2)-Pt-C(1) ) 172.9(2), Si-Pt-C(1) ) 87.0(2).
F igu r e 2. Molecular structure of cis-PtEt(GePh3)(PMe2-
Ph)2 (3b). Thermal ellipsoids are drawn at the 50% prob-
ability level. Selected bond distances (Å) and angles (deg):
Pt-Ge
) 2.437(1), Pt-P(1) ) 2.307(2), Pt-P(2) )
2.311(2), Pt-C(1) ) 2.134(9), Ge-Pt-P(1) ) 166.50(6),
Ge-Pt-P(2) ) 94.35(5), Ge-Pt-C(1) ) 85.6(2), P(1)-
Pt-P(2) ) 96.76(8), P(1)-Pt-C(1) ) 84.1(2), P(2)-Pt-C(1)
) 174.8(2).
Ch a r t 1
ness of the SiPh3 ligand. The Pt-P(1) bond (2.358(2) Å)
is longer than the Pt-P(2) bond (2.304(2) Å), owing to
the higher trans influence of the SiPh3 ligand than the
Pr ligand. However, the difference between the two
Pt-P distances in 2c (0.054 Å) was much smaller than
that observed for cis-PtMe(SiPh3)(PMePh2)2 (0.268 Å).6
This is mainly due to the higher trans influence of the
1
Pr ligand than the Me ligand. Actually, the J Pt-P(2)
value of 2c (1783 Hz) was significantly smaller than
that of 2a (2048 Hz)8 and cis-PtMe(SiPh3)(PMePh2)2
(2136 Hz).6
P r ep a r a tion of cis-P tEt(GeP h 3)(P Me2P h )2. The
title compound (3b) was synthesized by the reaction of
trans-PtCl(GePh3)(PMe2Ph)2 with EtLi in THF at 0 °C,
followed by methanolysis of the reaction mixture at -30
°C. The X-ray structure is given in Figure 2. The
geometry around the platinum is very similar to that
of cis-PtMe(GePh3)(PMe2Ph)2 (3a ).7 Thus, the platinum
atom is in a slightly distorted square planar environ-
ment, and the Ge-Pt-P(2) angle is much wider than
the P(1)-Pt-C(1) angle. The Pt-Ge bond (2.437(1) Å)
is somewhat shorter than that of 3a (2.4495(7) Å), while
the Pt-C(1) bond (2.134(9) Å) is longer than that of 3a
(2.127(5) Å). The Pt-P(1) and Pt-P(2) bond distances
in 3b are almost identical with each other (2.31 Å). This
fact differs from 3a , in which the Pt-P bond trans to
the GePh3 ligand (2.330(1) Å) is somewhat longer than
the Pt-P bond trans to the Me ligand (2.308(2) Å).
Th er m olysis P r od u cts. The alkyl-silyl and alkyl-
germyl complexes thus prepared were subjected to
thermolysis in benzene-d6 or toluene-d8 in the presence
of an excess amount of diphenylacetylene, which was
added to facilitate the reductive elimination and to trap
platinum(0) species generated in the systems as Pt-
(PhCtCPh)(PMe2Ph)2 (6).6,7 The reaction progress was
to 2a and 2b. Thus, the treatment of trans-PtCl-
(SiPh3)(PMe2Ph)2 with an excess amount of RLi (R )
Pr or Bu) in THF at 0 °C gave a platinate complex
Li[PtR2(SiPh3)(PMe2Ph)] with liberation of 1 equiv of
PMe2Ph. Methanolysis of the reaction mixture at -30
°C formed the alkyl-silyl complex.
Complexes 2c and 2d were isolated as white crystal-
line solids and identified by NMR spectroscopy and
elemental analysis. Complex 2c was also examined by
single-crystal X-ray diffraction analysis. Figure 1 shows
an ORTEP diagram. The platinum atom has a slightly
distorted square planar geometry; the sum of four
angles about platinum is 360.85°. The propyl group is
extruded linearly from the platinum center. The P(2)-
Pt-Si angle (93.6(1)°) is much wider than the P(1)-
Pt-C(1) angle (85.5(2)°), probably reflecting the bulki-

2024 Organometallics, Vol. 19, No. 10, 2000
Hasebe et al.
Sch em e 1
EtSiPh3 (δ 1.08 and 1.28, respectively) in a 3.1:1.9 ratio,
the value of which was close to the ratio expected for
the random H-D scrambling in these two groups
(3.0:2.0).
The EtSiPh3 formation involving a reversible â-hy-
drogen elimination process can be rationalized by as-
suming a rapid equilibrium between 2b and a hydri-
dosilylethylene complex 7 (R′ ) H) under thermolysis
conditions (Scheme 1). As previously demonstrated for
cis-PtEt2(PPh3)2,9 the â-hydrogen elimination very prob-
ably involves prior dissociation of the phosphine ligand
cis to the ethyl ligand, giving 7, having the hydrido and
SiPh3 ligands in mutually trans positions. Owing to this
geometry, 7 is unable to undergo H-Si reductive
elimination. Therefore, the thermolysis of 2b exclusively
forms the C-Si reductive elimination product, despite
the occurrence of rapid â-hydrogen elimination.
On the other hand, the participation of process C in
the thermolysis reaction was indicated by NMR spec-
troscopy. Figure 3 shows a typical 31P{1H} NMR spec-
trum of the thermolysis solution of 2c in benzene-d6 at
55 °C in the presence of diphenylacetylene (10 equiv).
Besides the signals due to 2c (δ -5.2 and -12.5) and
the reductive elimination product Pt(PhCtCPh)(PMe2-
Ph)2 (6) (δ -13.0), two sets of doublets are observed at
δ -6.2 and -14.1 in a 1:1 ratio. As described in the
following section, these signals are assigned to cis-PtPh-
(SiPrPh2)(PMe2Ph)2 (5c), formed by the exchange of the
Pt-Pr group with the Si-Ph group in 2c. Similarly, the
formation of cis-PtPh(SiEtPh2)(PMe2Ph)2 (5b) [δ -6.4
followed by 31P{1H} NMR spectroscopy, and the organic
products were analyzed by GLC and GC-mass spec-
trometry.
The trans-methyl-silyl complex (1a ) decomposed
mainly by a reductive elimination process. The reaction
examined in toluene-d8 in the presence of diphenyl-
acetylene (40 equiv) was completed for 45 h at 70 °C,
yielding MeSiPh3 in 72%. In the presence of MeO2C-
CtCCO2Me (40 equiv) in place of diphenylacetylene, the
C-Si reductive elimination took place under much
milder conditions (35 °C, 2.5 h) to give MeSiPh3 in 82%
yield. The trans-ethyl-silyl complex (1b) also decom-
posed under heated conditions (>60 °C), but only small
amounts of EtSiPh3 (<2%) and HSiPh3 (<4%) were
observed in the reaction solution; no other product was
detected by GC-mass spectrometry.
Unlike the trans complexes, cis-alkyl-silyl complexes
(2a -2d ) afforded the reductive elimination products
(RSiPh3) in almost quantitative yields (>97%) irrespec-
tive of the alkyl ligands. The reaction of 2a proceeded
even at room temperature, while 2b-2d were more
stable and decomposed under heated conditions (>35
°C).
The cis-ethyl-germyl complex (3b) was extremely
stable toward reductive elimination, and no trace of
EtGePh3 was formed by the thermolysis in toluene-d8
at 90 °C. The high stability of the alkyl-germyl com-
plex, as compared with alkyl-silyl analogues, has
already been observed for cis-PtMe(GePh3)(PMe2Ph)2
(3b).7
Th er m olysis P r ocesses of cis-P t R (SiP h 3)(P Me-
P h 2)2. While 2b-2d gave the corresponding alkylsilanes
as the reductive elimination products in almost quan-
titative yields, the thermolysis reactions were found to
involve two additional processes (Scheme 1). One is
reversible â-hydrogen elimination from the alkyl ligand
(process B), and the other is isomerization of cis-PtR-
(SiPh3)(PMe2Ph)2 to cis-PtPh(SiRPh2)(PMe2Ph)2 (pro-
cess C).
2
1
2
(d, J P-P ) 19 Hz, J Pt-P ) 1133 Hz), -14.4 (d, J P-P
)
19 Hz, 1J Pt-P ) 1953 Hz)] and cis-PtPh(SiBuPh2)(PMe2-
2
1
Ph)2 (5d ) [δ -6.7 (d, J P-P ) 18 Hz, J Pt-P ) 1130 Hz),
2
1
-14.6 (d, J P-P ) 18 Hz, J Pt-P ) 1950 Hz)] was found
in the thermolysis solutions of 2b and 2d , respectively.
Figure 4 shows the change of platinum complexes
with time in the thermolysis solution of 2b. On heating
the sample solution at 50 °C, 5b and 6 simultaneously
appeared at the expense of 2b. The amount of 5b
reached a maximum (17%) after ca. 60 min and then
gradually decreased, while the amount of diphenyl-
acetylene complex 6 increased further. Finally, 2b and
5b disappeared, and only the signal of 6 was observed
in the 31P{1H} NMR spectrum.
The time-course in Figure 4 corresponds to the
consecutive reaction path (2b f 5b f 6) in Scheme 1
(R ) Et). However, detailed analysis of the reaction
curves indicated the concurrent operation of a direct
path from 2b to 6 (process A) as well. Thus, the dot lines
in this figure show ideal reaction curves for the stepwise
conversion of 2b to 6 via 5b with the rate constants k2
) 1.4 × 10-4 s-1 and k3 ) 2.6 × 10-4 s-1 (k1 ) 0.0 s-1).
It is seen that the calculated curve for 6 is clearly
S-shaped, showing a slow formation of 6 at the initial
stage, while the amount of 6 increases linearly from the
beginning in reality. This fact strongly indicates the
concomitance of the direct path from 2b to 6. Actually,
the experimental data are in good agreement with the
solid lines, which are calculated for the parallel forma-
tion of 6 via processes A and C: k1 ) 6.0 × 10-5 s-1, k2
The occurrence of process B was confirmed by ther-
molysis experiments using a deuterium-labeled complex
cis-Pt(CH2CD3)(SiPh3)(PMe2Ph)2 (2b-d3). Heating a mix-
ture of 2b-d3 and diphenylacetylene (10 equiv) in
benzene-d6 at 40 °C overnight led to the formation of
EtSiPh3 in 98% yield, as confirmed by GLC using
) 8.0 × 10-5 s-1, k3 ) 2.1 × 10-4 s-1 10
.
2
MeSiPh3 as an internal standard. The D NMR spec-
(9) (a) McCarthy, T. J .; Nuzzo, R. G.; Whitesides, G. M. J . Am. Chem.
Soc. 1981, 103, 1676 and 3396. (b) Komiya, S.; Morimoto, Y.; Yama-
moto, A.; Yamamoto, T. Organometallics 1982, 1, 1528.
trum of the resulting solution exhibited two signals
assignable to the methyl and methylene groups of

Thermolysis Reactions of cis-PtR(SiPh3)(PMe2Ph)2
Organometallics, Vol. 19, No. 10, 2000 2025
F igu r e 3. 31P{1H} NMR spectrum (121.48 MHz) of the thermolysis solution of 2c in benzene-d6 in the presence of
diphenylacetylene (10 equiv) at 55 °C.
Ta ble 1. Ra te Con sta n ts for th e Th er m olysis of
2b-2d (Sch em e 1) a t 55 °C in Ben zen e-d 6 in th e
a
P r esen ce of Dip h en yla cetylen e
complex
2b (R ) Et)
rate constant (104 k, s-1
)
k1 ) 1.0
k2 ) 1.5
(k1 + k2 ) 2.5)
k3 ) 3.5
2c (R ) Pr)
2d (R ) Bu)
k1 ) 0.61
k2 ) 1.0
(k1 + k2 ) 1.6)
k3 ) 1.8
k1 ) 0.58
k2 ) 0.81
(k1 + k2 ) 1.4)
k3 ) 1.4
2a (R ) Me) (toluene-d8)
k1 ) 33b
a
Initial concentration: [complex]0 ) 20 mM, [PhCtCPh] ) 0.20
b
M. The value was extrapolated from an Eyring plot at 20-45 °C
(see ref 7).
from 2a (k1). The k2 value is about 1.5 times larger than
the k1 value for all systems, showing the predominant
operation of the consecutive reaction path (2 f 5 f 6)
in Scheme 1. The rate constants for the direct formation
of 6 (k1), which decrease in the order 2b > 2c g 2d , are
much smaller than that of 2a .
Iden tification of cis-P tP h (SiRP h 2)(P MeP h 2)2. The
conversion of 2b-2d into 5b-5d , respectively (process
C in Scheme 1), could be observed in over 80% selectivi-
ties, when the reactions were performed in CD2Cl2 at
room temperature in the absence of diphenylacetylene
as a promoter of the C-Si reductive elimination. The
isomerization was a significantly slow process, taking
a few days for completion. Although 5b-5d could not
be isolated from the reaction solutions due to contami-
F igu r e 4. Time-course of the thermolysis of 2b in benzene-
d6 at 50 °C in the presence of diphenylacetylene: [2b]0 )
20 mM, [PhCtCPh]0 ) 0.20 M. The solid and dotted lines
exhibit calculated reaction curves (see text).
Table 1 summarizes the rate constants for the ther-
molysis of 2b, 2c, and 2d in benzene-d6 at 55 °C in the
presence of diphenylacetylene (0.20 M, 10 equiv). Also
listed is the rate constant for the reductive elimination
(10) The calculation was performed with the following rate expres-
sions: -d[2]/dt ) (k1 + k2)[2]; d[5]/dt ) k2[2] - k3[5]; d[6]/dt ) k1[2] +
k3[5]. The rate constants k2 and k3 include terms of [PhCtCPh], as
confirmed for the formation of MeSiPh3 from 2a .7 The amount of each
component at time t is given as follows. [2] ) [2]0 exp(-(k1 + k2)t). [5]
) [2]0{k2/(k3 - k1 - k2)}{exp(-(k1 + k2)t) - exp(-k3t)}. [6] ) [2]0 - [2]
- [5].

2026 Organometallics, Vol. 19, No. 10, 2000
Hasebe et al.
a
Ta ble 2. Ch a r a cter istic NMR Da ta of cis-P tP h (SiRP h 2)(P Me2P h )2
1H NMR 31P{1H} NMR
3J Pt-H
complex
(R)
δ
2J P-H
assignment
δ
2J P-P
1J Pt-P
2J Si-P
5b
(Et)
0.90 (d)
1.00 (d)
6.72 (brt)
6.88 (brt)
0.91 (d)
7.2
8.4
15.6
19.2
PMe
PMe
p-Ph
m-Ph
PMe
PMe
p-Ph
m-Ph
PMe
PMe
p-Ph
m-Ph
PMe
PMe
p-Ph
m-Ph
PMe
PMe
p-Ph
m-Ph
-14.6 (d)
-6.1 (d)
19
19
1948
1160
174
5c
(Pr)
7.6
8.0
16.0
22.4
-14.8 (d)
-6.1 (d)
19
19
1949
1188
1.04 (d)
182
182
178
183
6.68 (brt)
6.84 (brt)
0.91 (d)
5d
(Bu)
7.6
8.4
17.6
21.6
-14.8 (d)
-6.2 (d)
18
18
1949
1184
1.03 (d)
6.67 (brt)
6.82 (brt)
0.94 (d)
5a
(Me)
7.6
8.4
16.8
22.4
-14.8 (d)
-5.6 (d)
19
19
1936
1240
1.03 (d)
6.67 (brt)
6.85 (brt)
0.91 (d)
1.03 (d)
6.36 (brt)
6.47 (brt)
5e
(Ph)
7.8
8.3
16.6
22.0
-13.4 (d)
-4.2 (d)
19
19
1808
1156
a
Solvent: CD2Cl2 (5a , 5c, 5d , 5e), CDCl3 (5b). Temp (°C): 23 (5b, 5c, 5d , 5e), -20 (5a ).
nation with the starting complexes and some unidenti-
fied platinum species, their structures could be un-
equivocally confirmed by NMR spectroscopy.
methyl-silyl complex 2a undergoes direct reductive
elimination, exclusively.7 Although we reexamined the
thermolysis solution of 2a by 31P{1H} NMR spectros-
copy, no sign of the formation of cis-PtPh(SiMePh2)(PMe2-
Ph)2 (5a ) was detected. It was further confirmed that
the C-Si reductive elimination from 2a (k1 ) 1.2 × 10-3
s-1 at 45 °C in toluene-d8 in the presence of diphenyl-
acetylene (0.20 M)) is about 8 times faster than the
MeSiPh3 formation from 5a (k3 ) 1.5 × 10-4 s-1 at 45
°C in benzene-d6 in the presence of diphenylacetylene
(0.20 M)).
The difference of thermolysis paths between 2a and
the other alkyl-silyl complexes 2b-2d will be at-
tributed to differences in the reactivity of these com-
plexes toward direct reductive elimination. Thus, the
k1 value of 2a was 33-57 times larger than that of 2b-
2d (Table 1). The observed reactivity order for C-Si
reductive elimination (R ) Me . Et > Pr g Bu) is
significant because this order is just the reverse of
conventional C-C reductive elimination.12 This fact
implies a unique mechanistic feature of the C-Si
reductive elimination and deserves a discussion.
As we already confirmed for the thermolysis of 2a ,
the rate of reductive elimination of alkylsilane is
controlled at two stages.6,7 One is the reversible ex-
change of the PMe2Ph ligand trans to the SiPh3 ligand
with diphenylacetylene, and the other is the reductive
elimination of alkylsilane from the [PtR(SiPh3)-
(PhCtCPh)(PMe2Ph)] intermediate. Since the former
stage may be affected mainly by the trans effect of the
silyl ligand, the equilibrium constants for 2a -2d bear-
ing the same SiPh3 ligand will be very similar to each
other. Accordingly, one may consider that the reactivity
order observed for the SiPh3 complex series (2a . 2b >
2c g 2d ) should be determined at the second stage as
the rate-determining step.
Table 2 lists the characteristic NMR data of 5b-5d .
Also included for comparison are data of the related
phenyl-silyl complexes 5a and 5e, which were isolated
and fully characterized by NMR spectroscopy and
1
elemental analysis (see Experimental Section). The H
NMR spectra exhibited two broad triplets assignable to
the para and meta protons of the Pt-Ph group at
around δ 6.7 and 6.8, which were not observed for cis-
alkyl-silyl complexes 2a -2d and characteristic of the
phenyl-silyl complexes. The distinct upfield shifts
observed for the phenyl protons are attributable to ring-
current of the P-Ph and Si-Ph groups, which may be
situated near the Pt-Ph group. The 31P{1H} NMR
signals were observed as two sets of doublets at around
δ -14.8 and -6.1 with relatively large and small 1J Pt-P
values (ca. 1950 and 1180 Hz), respectively. These
coupling constants were comparable to those of 5a and
5e, but clearly different from those of 2b-2d (1792-
1783 and 1437-1367 Hz).
On th e Differ en ce of Th er m olysis P r ocesses
betw een Meth yl a n d th e Oth er Alk yl Com p lexes.
We found in this study that the alkylsilane formation
from 2b-2d proceeds mainly via the isomerization of
these complexes to cis-PtPh(SiRPh2)(PMe2Ph)2 (5b-5d )
(process C).11 Thus, the isomerization of 2 (k2) and the
successive C-Si reductive elimination from 5 (k3) took
place about 1.5 and 3 times faster than the direct
reductive elimination from 2 (k1), respectively (Table 1).
On the other hand, we previously reported that the
(11) (a) Process C is thought to proceed via a silylene intermediate,
which is formed by dissociation of a phosphine ligand, followed by R-Ph
group elimination from the SiPh3 ligand. Such a process has been
proposed for an iridium system: Burger, P.; Bergman, R. G. J . Am.
Chem. Soc. 1993, 115, 10462. (b) For precedents of platinum silylene
complexes, see: Mitchell, G. P.; Tilley, T. D. Angew. Chem., Int. Ed.
1998, 37, 2524; J . Am. Chem. Soc. 1998, 120, 7635. (c) The C-Si bond
formation via R-migration of an alkyl ligand to a silylene ligand has
been proposed: Okazaki, M.; Tobita, H.; Ogino, H. J . Chem. Soc.,
Dalton Trans. 1997, 3531. Ozawa, F.; Kitaguchi, M.; Katayama, H.
Chem. Lett. 1999, 1289. (d) For further information on the related
chemistry, see: Peters, J . C.; Feldman, J . D.; Tilley, T. D. J . Am. Chem.
Soc. 1999, 121, 9871, and references therein.
(12) The reactivity toward C-C reductive elimination generally
increases as the σ-donating ability of the alkyl ligand increases. (a)
Tatsumi, K.; Hoffmann, R.; Yamamoto, A.; Stille, J . K. Bull. Chem.
Soc. 1981, 54, 1857. (b) Yamamoto, A. Organotransition Metal Chem-
istry, Fundamental Concepts and Applications; Wiley-Interscience:
New York, 1986; p 286. (c) Brown, J . M.; Cooley, N. A. Chem. Rev.
1988, 88, 1031.

Thermolysis Reactions of cis-PtR(SiPh3)(PMe2Ph)2
Organometallics, Vol. 19, No. 10, 2000 2027
pounds employed in this study were obtained from commercial
sources and used without further purification.
The activation energy of reductive elimination at the
second stage corresponds to the energy difference be-
tween the ground state and the transition state. Since,
in the reactions of 2a -2d , all of the [PtR(SiPh3)-
(PhCtCPh)(PMe2Ph)] intermediates possess the same
ligands except for the alkyl ligands, the stability of
ground states may be dependent predominantly upon
the Pt-R bond energies, which decrease in the order
Pt-Me > Pt-Et > Pt-Pr g Pt-Bu.12,13 On the other
hand, the relative stability of the transition states will
be dependent mainly upon the bond energies of partially
formed R-Si bonds. Since Si-Me bond is known to be
7.9 kcal/mol stronger than Si-Et bond,14 the bond
strengths decrease very probably in the order Si-Me
. Si-Et > Si-Pr g Si-Bu. Consequently, the observed
reactivity order (2a . 2b > 2c g 2d ) toward reductive
elimination does not coincide with the expected stability
order of the ground states, but agrees with the stability
order of the transition states, which is governed mainly
by the R-Si bond strengths.
Recent theoretical and thermochemical data have
indicated that the Pt-Si bond is much stronger than
the Pt-C bond,15 and this will be one of the reasons for
the relatively insensitive nature of ground states, as
compared with transition states, to the sorts of alkyl
ligands. Furthermore, the marked dependence of reduc-
tive elimination rates upon the R-Si bond strengths
strongly suggests the reaction mechanism involving a
late transition state. This assumption is well in accord
with the recent ab initio MO calculation for the C-Si
reductive elimination from Pt(CH3)(SiMe3)(η2-ethylene)-
(PH3).4 Thus, the calculated C-Si bond distance in the
transition state (2.042 Å) is closer to that in the product
methylsilane (1.923 Å) than that in the ground state
(2.889 Å), showing a product-like transition state.
P r ep a r a tion of cis-P tR(SiP h 3)(P Me2P h )2 (R ) P r (2c),
Bu (2d )). Complex 2c was synthesized as follows. To a solution
of trans-PtCl(SiPh3)(PMe2Ph)216 (342 mg, 0.449 mmol) in THF
(4 mL) was added a hexane solution of PrLi (2.59 M, 0.69 mL,
1.79 mmol). The solution was stirred for 30 min at room
temperature and then cooled to -30 °C. Methanol (0.3 mL)
was slowly added, and the mixture was concentrated to
dryness by pumping. The resultant white solid was extracted
with CH2Cl2 and filtered through a short Celite column. The
filtrate was concentrated to ca. 1 mL, and Et2O (3 mL) was
carefully layered on the CH2Cl2 solution. The solvent layers
were allowed to stand at -70 °C overnight, giving colorless
crystals of 2c (241 mg, 69%). Complex 2d was similarly
prepared by using BuLi in place of PrLi (55%).
1
3
2c: H NMR (CDCl3) δ 0.28 (t, J H-H ) 6.5 Hz, 3H, PtCH2-
CH2CH3), 1.01 (d, 2J P-H ) 7.8 Hz, 3J Pt-H ) 20.4 Hz, 6H, PCH3),
ca. 1.1 (m, 4H, PtCH2CH2CH3, the coupling pattern and exact
chemical shift were obscured due to overlap with the PCH3
signals), 1.26 (d, 2J P-H ) 7.2 Hz, 3J Pt-H ) 15.0 Hz, 6H, PCH3),
7.17 (m, 9H, Ph), 7.30 (m, 6H, Ph), 7.48 (m, 4H, Ph), 7.67 (m,
6H, Ph). 13C{1H} NMR (CDCl3): δ 13.6 (d, 1J P-C ) 21 Hz, 2J Pt-C
1
3
2
) 8 Hz, PCH3), 17.1 (dd, J P-C ) 28 Hz, J P-C ) 5 Hz, J Pt-C
3
2
) 30 Hz, PCH3), 19.6 (d, J P-C ) 12 Hz, J Pt-C ) 107 Hz,
2
1
PtCH2CH2CH3), 21.1 (dd, J P-C ) 78 and 7 Hz, J Pt-C ) 532
Hz, PtCH2CH2CH3), 25.5 (s, PtCH2CH2CH3), 126.6 (s, SiPh),
126.8 (s, SiPh), 128.1 (d, 3J P-C ) 9 Hz, PPh), 129.3 (d, 4J P-C
)
4
1 Hz, PPh), 129.4 (d, J P-C ) 1 Hz, PPh), 130.8-131.3 (m,
3
3
PPh), 137.2 (s, J Pt-C ) 23 Hz, SiPh), 137.9 (d, J P-C ) 33 Hz,
1
3
PPh), 140.5 (dd, J P-C ) 40 Hz, J P-C ) 5 Hz, PPh), 145.6 (d,
3J P-C ) 8 Hz, J Pt-C ) 51 Hz, SiPh); 31P{1H} NMR (CDCl3) δ
2
2
1
2
-12.6 (d, J P-P ) 18 Hz, J Pt-P ) 1783 Hz), -3.9 (d, J P-P
)
1
2
18 Hz, J Pt-P ) 1369 Hz, J Si-P ) 196 Hz,). Anal. Calcd for
C
37H44P2PtSi: C, 57.43; H, 5.73. Found: C, 57.13; H, 5.71.
2d : 1H NMR (CDCl3) δ 0.44 (t, J H-H ) 7.8 Hz, 3H, PtCH2-
3
3
CH2CH2CH3), 0.55 (qui, J H-H ) 7.2 Hz, 2H, PtCH2CH2CH2-
2
CH3), 0.95 (m, 2H, PtCH2CH2CH2CH3), 1.07 (d, J P-H ) 8.0
3
Hz, J Pt-H ) 20.0 Hz, 6H, PCH3), ca. 1.1 (m, 2H, PtCH2CH2-
CH2CH3, the coupling pattern and the exact chemical shift
were obscure due to overlap with the PCH3 signals), 1.33 (d,
2J P-H ) 6.8 Hz, 3J Pt-H ) 15.2 Hz, 6H, PCH3), 7.21 (m, 9H, Ph),
7.36 (m, 6H, Ph), 7.53 (m, 4H, Ph), 7.72 (m, 6H, Ph); 13C{1H}
Exp er im en ta l Section
Gen er a l P r oced u r e a n d Ma ter ia ls. All manipulations
were carried out under a nitrogen atmosphere using conven-
tional Schlenk techniques. Nitrogen gas was dried by passing
through P2O5 (Merck, SICAPENT). NMR spectra were re-
1
3
2
NMR (CDCl3) δ 13.6 (d, J P-C ) 22 Hz, J P-C ) 3 Hz, J Pt-C
)
)
)
1
16 Hz, PCH3), 13.8 (s, PtCH2CH2CH2CH3), 17.1 (dd, J P-C
3
2
2
28 Hz, J P-C ) 3 Hz, J Pt-C ) 28 Hz, PCH3), 18.1 (dd, J P-C
corded on
a J EOL J NM-A400 and Varian Mercury 300
1
79 and 7 Hz, J Pt-C ) 530 Hz, PtCH2CH2CH2CH3), 28.3 (d,
spectrometers. Chemical shifts are reported in δ ppm referred
to an internal SiMe4 standard for 1H and 13C NMR and to an
external 85% H3PO4 standard for 31P NMR. Mass spectra were
measured using a Shimadzu QP-5000 GC-mass spectrometer
(EI, 70 eV, capillary column). GLC analysis was performed
with a GL Sciences GC-353 instrument equipped with a FID
detector and a capillary column (TC-1, 30 m). THF, Et2O, and
hexane were dried over sodium benzophenone ketyl and
distilled prior to use. CH2Cl2 and CD2Cl2 were dried over CaH2
and distilled prior to use. Benzene-d6 and toluene-d8 were dried
over LiAlH4, vacuum transferred, and stored under a nitrogen
atmosphere. CDCl3 was purified by passing through a short
Al2O3 column and stored under a nitrogen atmosphere. PMe2-
Ph was prepared by the reaction of MeMgBr with PCl2Ph.
trans- and cis-PtR(SiPh3)(PMe2Ph)2 (R ) Me (1a , 2a ), Et (1b,
2b)) were prepared as previously reported.7,8 All other com-
3J P-C ) 11 Hz, J Pt-C ) 98 Hz, PtCH2CH2CH2CH3), 34.3 (s,
2
PtCH2CH2CH2CH3), 126.6 (s, SiPh), 126.8 (s, SiPh), 128.1 (d,
3J P-C ) 9 Hz, PPh), 129.3 (s, PPh), 129.4 (s, PPh), 130.8-131.2
3
3
(m, PPh), 137.2 (s, J Pt-C ) 23 Hz, SiPh), 137.9 (d, J P-C ) 35
1
3
Hz, PPh), 140.5 (dd, J P-C ) 40 Hz, J P-C ) 4 Hz, PPh), 145.6
(d, 3J P-C ) 7 Hz, 2J Pt-C ) 51 Hz, SiPh); 31P{1H} NMR (CDCl3)
2
1
2
δ -12.8 (d, J P-P ) 18 Hz, J Pt-P ) 1784 Hz), -4.9 (d, J P-P
)
1
2
18 Hz, J Pt-P ) 1367 Hz, J Si-P ) 196 Hz). Anal. Calcd for
C38H46P2PtSi: C, 57.93; H, 5.88. Found: C, 57.63; H, 5.88.
P r ep a r a tion of cis-P tEt(GeP h 3)(P Me2P h )2 (3b). trans-
PtCl(GePh3)(PMe2Ph)27 (249 mg, 0.307 mmol) and EtLi (60 mg,
1.67 mmol) were placed in a Schlenk tube, and THF (4 mL)
was added at 0 °C. The mixture was stirred for 30 min at room
temperature and then cooled to -30 °C. MeOH (3 mL) was
slowly added, and the mixture was concentrated to dryness
by pumping. The resulting white solid was extracted with CH2-
Cl2 (3 mL × 2) and filtered through a short Celite column.
The filtrate was concentrated to ca. 1 mL. Et2O (3 mL) was
layered on the CH2Cl2 solution, and the solvent layers were
allowed to stand at -70 °C overnight to give colorless crystals
of 3b (123 mg, 50%).
(13) Simo˜es, J . A. M.; Beauchamp, J . L. Chem. Rev. 1990, 90, 629.
(14) Pilcher, G.; Skinner, H. A. In The Chemistry of the Metal-
Carbon Bond, Vol. 1; Hartley, F. R., Patai, S., Eds.; J ohn Wiley:
Chichester, 1982; p 43.
(15) (a) Sakaki, S.; Ieki, M. J . Am. Chem. Soc. 1991, 113, 5063. (b)
Sakaki, S.; Ieki, M. J . Am. Chem. Soc. 1993, 115, 2373. (c) Sakaki, S.;
Kai, S.; Sugimoto, M. Organometallics 1999, 18, 4825. (d) Levy, C. J .;
Puddephatt, R. J . J . Am. Chem. Soc. 1997, 119, 10127. (e) Levy, C. J .;
Puddephatt, R. J . Organometallics 1997, 16, 4115.
(16) Chatt, J .; Eaborn, C.; Ibekwe, S. D.; Kapoor, P. N. J . Chem.
Soc. (A) 1970, 1343.

2028 Organometallics, Vol. 19, No. 10, 2000
Hasebe et al.
3
2
3b: 1H NMR (CDCl3) δ 0.77 (q, J H-H ) 7.5 Hz, J Pt-H
)
Ta ble 3. Cr ysta l Da ta a n d Deta ils of th e Str u ctu r e
Deter m in a tion of 2c a n d 3b
55.2 Hz, 2H, PtCH2CH3), 1.16 (d, 2J P-H ) 7.8 Hz, 3J Pt-H ) 19.5
2
Hz, 6H, PCH3), 1.28 (m, 2H, PtCH2CH3), 1.40 (d, J P-H ) 7.5
2c
3b
3
Hz, J Pt-H ) 21.0 Hz, 6H, PCH3), 7.20 (m, 9H, Ph), 7.31 (m,
formula
fw
C
37H44P2SiPt
C36H42P2GePt
804.36
3H, Ph), 7.36 (m, 3H, Ph), 7.54 (m, 4H, Ph), 7.20 (m, 6H, Ph);
773.88
13C{1H} NMR (CDCl3) δ 8.7 (dd, 2J P-C ) 82 and 7 Hz, 1J Pt-C
)
cryst size, mm
color/shape
cryst syst
space group
a, Å
0.32 × 0.20 × 0.16 0.25 × 0.20 × 0.18
1
3
503 Hz, PtCH2CH3), 13.8 (dd, J P-C ) 26 Hz, J P-C ) 3 Hz,
colorless/prism
monoclinic
P21 (No. 4)
11.130(2)
9.315(3)
17.426(2)
89.44(2)
106.17(1)
97.85(2)
1735.1(6)
2
colorless/prism
triclinic
2J Pt-C ) 24 Hz, PCH3), 16.8 (dd, J P-C ) 5 and 2 Hz, J Pt-C
)
3
2
22 Hz, PtCH2CH3), 17.4 (dd, 1J P-C ) 28 Hz, 3J P-C ) 4 Hz, 2J Pt-C
) 25 Hz, PCH3), 126.4 (s, GePh), 126.9 (s, GePh), 128.2 (d,
P1h (No. 2)
10.549(3)
19.195(4)
8.920(2)
3J P-C ) 9 Hz, PPh), 129.5 (d, J P-C ) 2 Hz, PPh), 129.6 (d,
4
b, Å
c, Å
4J P-C ) 2 Hz, PPh), 131.0 (d, J P-C ) 12 Hz, J Pt-C ) 17 Hz,
2
3
2
3
R, deg
PPh), 131.2 (d, J P-C ) 11 Hz, J Pt-C ) 19 Hz, PPh), 136.6 (d,
â, deg
108.93(2)
4J P-C ) 1 Hz, 3J Pt-C ) 15 Hz, GePh), 137.4 (dd, 1J P-C ) 41 Hz,
γ, deg
1
3
3J P-C ) 1 Hz, PPh), 140.0 (dd, J P-C ) 40 Hz, J P-C ) 3 Hz,
V, Å3
1691.4(8)
2
3
2
PPh), 148.5 (dd, J P-C ) 10 and 2 Hz, J Pt-C ) 71 Hz, GePh);
31P{1H} NMR (CDCl3) δ -14.5 (d, 2J P-P ) 17 Hz, 1J Pt-P ) 1699
Hz), -5.1 (d, 2J P-P ) 17 Hz, 1J Pt-P ) 2048 Hz). Anal. Calcd for
Z
d
calcd, g cm-3
1.481
1.579
µ(Mo KR), cm-1
F(000)
41.78
51.20
C
36H42P2PtGe: C, 53.76; H, 5.26. Found: C, 53.14; H, 5.09.
776
796
radiation
Mo KR
Mo KR
X-r a y Diffr a ction Stu d ies. All measurements were per-
(λ ) 0.71069 Å)
graphite
+h, +k, (l
55.0
(λ ) 0.71069 Å)
graphite
+h, (k, (l
55.1
formed on a Rigaku AFC7R four-circle diffractometer with
graphite-monochromated Mo KR radiation (λ ) 0.71069 Å).
Unit cell dimensions were obtained from least-squares treat-
ments of the setting angles of 25 reflections in the range 29.8°
< θ < 30.0° for 2c and of 23 reflections in the range 29.5° < θ
< 30.0° for 3b, respectively. Diffraction data were collected at
23 °C using ω-2θ scan technique at a scan rate of 16° min-1
in omega.
monochromator
data collected
2θ max, deg
scan type
ω-2θ
1.26 + 0.30 tan θ
ω-2θ
∆ω, deg
1.89 + 0.35 tan θ
16, fixed
293
scan speed, deg min-1 16, fixed
temp, K
linear decay, %
abs corr
min and max
transmn factors
no. of reflns collected
no. of unique reflns
no. of obsd reflns
(I g 3σ(I))
293
3.93
empirical
0.473, 0.999
10.97
empirical
0.485, 0.999
All calculations were performed with the Texsan Crystal
Structure Analysis Package provided by Rigaku Corp., Tokyo.
The scattering factors were taken from ref 17. The structures
were solved by heavy atom Patterson methods (PATTY) and
expanded using Fourier techniques (DIRDIF94). Each struc-
ture was refined by full-matrix least-squares with anisotropic
thermal parameters for all non-hydrogen atoms. In the final
cycles of refinement, hydrogen atoms were located at idealized
positions (d(C-H) ) 0.95 Å) with isotropic temperature factors
(Biso ) 1.20Bbonded atom) and were included in calculation without
refinement of their parameters. The function minimized in
4431
8138
4220 (Rint ) 0.067) 7725 (Rint ) 0.020)
3992
7028
no. of variables
R indices
370
362
R1 ) 0.035
R ) 0.067
Rw ) 0.102
GOF ) 1.03
R1 ) 0.035
Rw ) 0.104
R1 ) 0.056
R ) 0.090
Rw ) 0.201
GOF ) 1.40
R1 ) 0.059
Rw ) 0.245
0.001
(I g 3σ(I))a
R indices (all data)a
least-squares was ∑w(Fo2 - Fc )2 (w ) 1/[σ2(Fo2)]). Crystal data
2
and details of data collection and refinement are summarized
in Table 3. Additional data are available as Supporting
Information.
max ∆/σ in final cycle 0.001
max and min
2.50, -2.79
(near Pt)
4.16, -3.59
(near Pt)
peak, e Å-3
Function minimized ) ∑w(Fo - Fc2)2; w ) 1/[σ2(Fo2)]. R1 )
a
2
Th er m olysis Rea ction s. A typical procedure for the ther-
molysis of 2b is as follows. cis-PtEt(SiPh3)(PMe2Ph)2 (2b) (9.35
mg, 12.3 µmol), diphenylacetylene (21.4 mg, 0.120 mmol), and
MeSiPh3 (3.02 mg, 11.0 µmol) as an internal standard for GLC
analysis were placed in an NMR sample tube equipped with
a rubber septum cap. The system was replaced with nitrogen
gas at room temperature, and benzene (0.6 mL) was added.
The resulting colorless solution was heated at 40 °C using an
oil bath, and the reaction progress was monitored at intervals
by 31P{1H} NMR spectroscopy at room temperature. After the
reaction was completed, the solution was analyzed by GLC and
GC-mass spectrometry, showing the formation of EtSiPh3 in
98% yield.
∑||Fo| - |Fc||/∑|Fo|. R ) ∑(Fo - Fc2)/∑(Fo2). Rw ) [∑w(Fo - Fc2)2/
∑w(Fo2)2]1/2. GOF ) [∑w(|Fo| - |Fc|)2/(No - Nv)]1/2, where No is the
number of observations and Nv the number of variables.
2
2
The filtrate was concentrated to ca. 1 mL, and Et2O (4 mL)
was layered on the CH2Cl2 solution. The solvent layers were
allowed to stand at -70 °C overnight to give colorless crystals
of 2b-d3 (138 mg, 69%). The 1H NMR spectrum measured in
CD2Cl2 at -20 °C was identical with 2b except for the absence
of the PtCH2CH3 signal at δ 0.65.8,19
Complex 2b-d3 (10.0 mg, 13.1 µmol) and diphenylacetylene
(23.0 mg, 0.129 mmol) were placed in an NMR sample tube
and dissolved in benzene-d6 (0.60 mL) at room temperature.
P r epar ation an d Th er m olysis of cis-P t(CH2CD3)(SiP h 3)-
(P Me2P h )2 (2b-d 3). To a Schlenk tube were added trans-PtCl-
2
The mixture was heated at 40 °C overnight. D NMR spectra
16
of the resulting solution exhibited the signals arising from
methyl and methylene protons of EtSiPh3 (δ 1.09 and 1.28,
respectively) in a 3.1:1.9 ratio.
Kin etic Stu d ies on th e Th er m olysis of 2b-2d . cis-PtEt-
(SiPh3)(PMe2Ph)2 (2b) (10.64 mg, 14.0 µmol), diphenylacetylene
(24.95 mg, 0.140 mmol), and 4,4′-dimethylbiphenyl (1.28 mg,
7.0 µmol) were placed in an NMR sample tube equipped with
(SiPh3)(PMe2Ph)2 (200 mg, 0.263 mmol) and CD3CH2Li (46
mg, 1.18 mmol), which was prepared by the reaction of Li
metal and CD3CH2Br (99% isotopic purity)18 in pentane under
reflux. THF (3.5 mL) was added at 0 °C, and the mixture was
stirred at room temperature for 30 min. MeOH (3 mL) was
slowly added, and the mixture was concentrated to dryness
by pumping. The resulting white solid was extracted with CH2-
Cl2 (3 mL × 2) and filtered through a short Celite column.
(19) In the previous report,8 we assigned the signal at δ 0.65 to the
methylene protons of the PtEt group. However, the 1H NMR spectrum
of 2b-d3 revealed that the signal was arising from the methyl protons,
not from the methylene protons. The methylene proton signal was
overlapped with the PMe signal at δ 1.05 in CD2Cl2, but clearly
observed at δ 1.72, separating from the PMe signal, in benzene-d6.
(17) Cromer, D. T.; Waber, J . T. International Tables for X-ray
Crystallography; The Kynoch Press: Birmingham, U.K., 1974; Vol. IV.
(18) Yamamoto, T.; Saruyama, T.; Nakamura, Y.; Yamamoto, A.
Bull. Chem. Soc. J pn. 1976, 49, 589.

Thermolysis Reactions of cis-PtR(SiPh3)(PMe2Ph)2
Organometallics, Vol. 19, No. 10, 2000 2029
a rubber septum cap, and the system was replaced with
nitrogen gas at room temperature. Benzene-d6 was added to
adjust total volume of the solution to 0.70 mL. The sample
tube was placed in an NMR sample probe controlled to 50.0 (
0.1 °C, and the thermolysis reaction was followed by 1H NMR
spectroscopy. The amounts of 2b, cis-PtPh(SiEtPh2)(PMe2Ph)2
(5b), and Pt(PhCtCPh)(PMe2Ph)2 (6) at intervals were deter-
mined by measuring relative peak integration of the methyl
signal of 4,4′-dimethylbiphenyl (δ 2.15), the methylene signal
of 2b (δ 1.72 (m)), the PMe signal of 5b (δ 0.72 (d)), and the
PMe signal of 6 (δ 1.48 (d)). The relative amounts of the
platinum complexes were confirmed also by 31P{1H} NMR
spectroscopy: 2b [δ -5.3 (d, 2J P-P ) 18 Hz, 1J Pt-P ) 1369 Hz),
Calcd for C40H42SiP2Pt: C, 59.47; H, 5.24. Found: C, 59.20;
H, 5.09.
(b) P r ep a r a tion of 5a a n d 5e. Complex 4a (250 mg, 0.34
mL) was placed in a Schlenk tube and dissolved in CH2Cl2 (3
mL) at room temperature. The solution was cooled to -30 °C,
and CO gas was bubbled for 1 h with stirring. The 31P{1H}
NMR spectrum showed complete conversion of 4a to cis-PtPh-
(SiMePh2)(PMe2Ph)2 (5a ). The solution was concentrated to
dryness, and the resulting white solid was washed with hexane
(3 mL × 2) and dried under vacuum (208 mg, 83%). The
conversion of 4e to 5e was similarly conducted. The isomer-
ization was complete after 4 h at -20 °C, and 5e was isolated
as a white solid in 97% yield.
2
1
3
5a : 1H NMR (CD2Cl2, -20 °C) δ -0.24 (s, J Pt-H ) 25.8 Hz,
-12.8 (d, J P-P ) 18 Hz, J Pt-P ) 1773 Hz)], 5b [δ -6.4 (d,
1
2
2J P-P ) 19 Hz, J Pt-P ) 1133 Hz), -14.4 (d, J P-P ) 19 Hz,
2
3
3H, SiCH3), 0.94 (d, J P-H ) 7.6 Hz, J Pt-H ) 16.8 Hz, 6H,
1J Pt-P ) 1953 Hz)], 6 [δ -13.2 (s, J Pt-P ) 3305 Hz)].
1
2
3
PCH3), 1.03 (d, J P-H ) 8.4 Hz, J Pt-H ) 22.4 Hz, 6H, PCH3),
6.67 (brt, 1H, Ph), 6.85 (brt, 2H, Ph), 7.14-7.44 (m, 18H, Ph),
7.70 (d, 4H, Ph); 13C{1H} NMR (CD2Cl2, -20 °C) δ 4.8 (s, 2J Pt-C
) 66 Hz, SiCH3), 13.3 (d, 1J P-C ) 26 Hz, 2J Pt-C ) 23 Hz, PCH3),
16.4 (d, J P-C ) 31 Hz, J P-C ) 5 Hz, J Pt-C ) 30 Hz, PCH3),
120.9 (s, PtPh), 127.0 (s, SiPh), 127.0 (s, PtPh), 127.3 (s, SiPh),
The thermolysis reactions of 2c and 2d were followed by
31P{1H} NMR spectroscopy. A typical spectrum for 2c is given
in Figure 3, together with the NMR data of 2c, 5c, and 6. The
data of 2d and 5d in the thermolysis solution (benzene-d6, 55
°C) are as follows: 2d [δ -5.5 (d, 2J P-P ) 19 Hz, 1J Pt-P ) 1324
1
3
2
3
3
2
1
128.2 (d, J P-C ) 8 Hz, PPh), 128.3 (d, J P-C ) 8 Hz, PPh),
Hz), -12.8 (d, J P-P ) 19 Hz, J Pt-P ) 1778 Hz)], 5d [δ -6.7
2
2
1
2
129.3 (s, PPh), 129.6 (s, PPh), 130.7 (d, J P-C ) 12 Hz, PPh),
(d, J P-P ) 18 Hz, J Pt-P ) 1130 Hz), -14.6 (d, J P-P ) 18 Hz,
2
1
1J Pt-P ) 1950 Hz)].
130.9 (d, J P-C ) 12 Hz, PPh), 137.6 (d, J P-C ) 33 Hz, PPh),
138.6 (s, 3J Pt-C ) 40 Hz, PtPh), 139.0 (dd, 1J P-C ) 42 Hz, 3J P-C
P r ep a r a tion a n d Id en tifica tion of cis-P tP h (SiRP h 2)-
(P Me2P h )2. The cis-phenyl-silyl complexes bearing SiMePh2
and SiPh3 ligands (5a and 5e, respectively) were prepared by
isomerization of the corresponding trans isomers (4a and 4e,
respectively) promoted by carbon monoxide in solution.
2
3
) 3 Hz, J Pt-C ) 46 Hz, PPh), 147.8 (dd, J P-C ) 8 and 3 Hz,
2J Pt-C ) 49 Hz, SiPh), 161.3 (dd, J P-C ) 97 and 13 Hz, J Pt-C
2
1
) 720 Hz, PtPh); 31P{1H} NMR (CD2Cl2, -20 °C) δ -5.6 (d,
2J P-P ) 19 Hz, J Pt-P ) 1240 Hz, J Si-P ) 178 Hz), -14.8 (d,
1
2
2J P-P ) 19 Hz, J Pt-P ) 1936 Hz). Anal. Calcd for C35H40SiP2-
1
(a ) P r ep a r a tion of 4a a n d 4e. The complex trans-PtCl-
Pt: C, 56.37; H, 5.41. Found: C, 56.17; H, 5.45.
16
(SiMePh2)(PMe2Ph)2 (504 mg, 0.72 mmol) was placed in a
5e: 1H NMR (CD2Cl2) δ 0.91 (d, J P-H ) 7.8 Hz, J Pt-H
)
2
3
Schlenk tube and dissolved in THF (7 mL) at room tempera-
ture. The solution was cooled to -30 °C, and an Et2O solution
of PhLi (1.8 M, 0.44 mL, 0.79 mmol) was added. After stirring
for 30 min at the same temperature, MeOH (0.1 mL) was
added, and the mixture was concentrated to dryness to give a
white solid, which was extracted with CH2Cl2 (3 mL × 3) at
room temperature, filtered through a filter-paper-tipped can-
nula, and then concentrated to dryness. The resulting solid of
trans-PtPh(SiMePh2)(PMe2Ph)2 (4a ) was washed with a 2:5
mixture of Et2O and hexane (7 mL × 2) and dried under
vacuum (350 mg, 66%). Similarly, trans-PtPh(SiPh3)(PMe2Ph)2
(4e) was obtained in 55% yield from trans-PtCl(SiPh3)(PMe2-
Ph)2.16
16.6 Hz, 6H, PCH3), 1.03 (d, 2J P-H ) 8.3 Hz, 3J Pt-H ) 22.0 Hz,
6H, PCH3), 6.36 (brt, 1H, Ph), 6.47 (brt, 2H, Ph), 6.96 (brt,
2H, Ph), 7.05-7.40 (m, 19H, Ph), 7.53 (m, 6H, Ph); 13C{1H}
NMR (CD2Cl2) δ 13.4 (d, 1J P-C ) 25 Hz, 2J Pt-C ) 23 Hz, PCH3),
1
2
3
16.6 (d, J P-C ) 30 Hz, J Pt-C ) 30 Hz, J P-C ) 5 Hz, PCH3),
120.7 (d, 5J P-C ) 3 Hz, PtPh), 126.9 (s, SiPh), 127.1 (dd, 3J P-C
2
3
) 4 and 2 Hz, J Pt-C ) 59 Hz, PtPh), 128.4 (d, J P-C ) 10 Hz,
3
PPh), 128.7 (d, J P-C ) 9 Hz, PPh), 129.4 (s, PPh), 120.0 (s,
2
3
PPh), 131.0 (d, J P-C ) 10 Hz, J Pt-C ) 9 Hz, PPh), 131.4 (d,
2J P-C ) 12 Hz, J Pt-C ) 17 Hz, PPh), 137.2 (s, J Pt-C ) 22 Hz,
3
3
2
4
SiPh), 137.6 (dd, J P-C ) 38 Hz, J P-C ) 3 Hz, PPh), 138.9 (d,
4J P-C ) 2 Hz, 3J Pt-C ) 36 Hz, PtPh), 139.6 (dd, 2J P-C ) 41 Hz,
4J P-C ) 2 Hz, PPh), 145.8 (dd, J Pt-C ) 52 Hz, J P-C ) 6 and
2
3
4a : 1H NMR (CD2Cl2) δ 0.29 (s, 3J Pt-H ) 14.8 Hz, 3H, SiCH3),
1.18 (virtual triplet, J ) 3.6 Hz, 3J Pt-H ) 32.0 Hz, 12H, PCH3),
6.71 (t, 1H, Ph), 6.86 (t, 2H, Ph), 7.09 (d, 2H, Ph), 7.10 (d, 4H,
2 Hz, SiPh), 159.0 (dd, 2J P-C ) 101 and 14 Hz, PtPh); 31P{1H}
2
1
NMR (CD2Cl2) δ -4.2 (d, J P-P ) 19 Hz, J Pt-P ) 1156 Hz,
2J Si-P ) 183 Hz), -13.4 (d, J P-P ) 19 Hz, J Pt-P ) 1808 Hz).
Anal. Calcd for C40H42SiP2Pt: C, 59.47; H, 5.24. Found: C,
59.41; H, 5.04.
2
1
3
Ph), 7.17 (d, J Pt-H ) 31.2 Hz, 2H, Ph), 7.26-7.50 (m, 14H,
2
Ph). 13C{1H} NMR (CD2Cl2): δ 4.5 (s, J Pt-C ) 36 Hz, SiCH3),
2
15.9 (virtual triplet, J ) 20 Hz, J Pt-C ) 40 Hz, PCH3), 122.0
(c) Id en tifica tion of 5b-5d . A typical example is as
follows. Complex 2d (15.0 mg, 19.0 mmol) was placed in an
NMR sample tube and dissolved in CD2Cl2 (0.6 mL) under a
nitrogen atmosphere. The sample was allowed to stand at room
temperature and examined by 31P{1H} NMR spectroscopy at
intervals. After 2 days, about 84% of 2d was converted into
5d . In addition, two singlets arising from unidentified species
were observed at δ -4.8 and -21.2. The NMR data of 5b-5d
are as follows.
2
(s, PtPh), 126.7 (s, SiPh), 127.1 (s, SiPh), 127.3 (s, J Pt-C ) 40
Hz, PtPh), 128.3 (virtual triplet, J ) 5 Hz, PPh), 129.8 (s, PPh),
131.6 (virtual triplet, J ) 6 Hz, 3J Pt-C ) 25 Hz, PPh), 135.9 (s,
2
3J Pt-C ) 12 Hz, SiPh), 137.0 (virtual triplet, J ) 28 Hz, J Pt-C
) 33 Hz, PPh), 139.8 (s, 3J Pt-C ) 20 Hz, PtPh), 150.3 (s, 2J Pt-C
) 26 Hz, SiPh), 172.5 (t, 2J P-C ) 13 Hz, 1J Pt-C ) 527 Hz, PtPh);
1
31P{1H} NMR (CD2Cl2) δ -7.5 (s, J Pt-P ) 2793 Hz). Anal.
Calcd for C35H40SiP2Pt: C, 56.37; H, 5.41. Found: C, 56.44;
H, 5.47.
3
5b: 1H NMR (CDCl3) δ 0.42 (q, J H-H ) 7.6 Hz, 2H, SiCH2-
4e: 1H NMR (CD2Cl2) δ 1.08 (virtual triplet, J ) 3.4 Hz,
3J Pt-H ) 32.2 Hz, 12H, PCH3), 6.69 (t, J ) 7.3 Hz, 1H, Ph),
6.80 (t, J ) 7.3 Hz, 2H, Ph), 7.04-7.30 (m, 21H, Ph), 7.52 (m,
6H, Ph); 13C{1H} NMR (CD2Cl2) δ 15.3 (virtual triplet, J ) 20
CH3), 0.55 (t, 3J H-H ) 8.0 Hz, 3H, SiCH2CH3), 0.90 (d, 2J P-H
)
3 2
7.2 Hz, J Pt-H ) 15.6 Hz, 6H, PCH3), 1.00 (d, J P-H ) 8.4 Hz,
3J Pt-H ) 19.2 Hz, 6H, PCH3), 6.72 (brt, 1H, Ph), 6.88 (brt, 2H,
Ph), 7.15-7.60 (m, 18H, Ph), 7.81 (m, 4H, Ph); 31P{1H} NMR
2
1
2
2
(CDCl3) δ -6.1 (d, J P-P ) 19 Hz, J Pt-P ) 1160 Hz, J Si-P
)
Hz, J Pt-C ) 40 Hz, PCH3), 122.1 (s, PtPh), 127.0 (s, SiPh),
2
1
2
174 Hz), -14.6 (d, J P-P ) 19 Hz, J Pt-P ) 1948 Hz).
127.1 (s, SiPh), 127.3 (s, J Pt-C ) 40 Hz, PtPh), 128.1 (virtual
1
triplet, J ) 5 Hz, PPh), 129.5 (s, PPh), 131.4 (virtual triplet,
J ) 7 Hz, 3J Pt-C ) 26 Hz, PPh), 136.6 (t, 2J P-C ) 29 Hz, PtPh),
137.4 (s, 2J Pt-C ) 15 Hz, SiPh), 140.0 (s, 3J Pt-C ) 15 Hz, PtPh),
5c: H NMR (CD2Cl2) δ 0.42 (m, 2H, SiCH2CH2CH3), 0.58
3
2
(t, J H-H ) 7.2 Hz, 3H, SiCH2CH2CH3), 0.91 (d, J P-H ) 7.6
Hz, 3J Pt-H ) 16.0 Hz, 6H, PCH3), 1.04 (d, 2J P-H ) 8.0 Hz, 3J Pt-H
) 22.4 Hz, 6H, PCH3), 1.42 (m, 2H, SiCH2CH2CH3), 6.68 (brt,
1H, Ph), 6.84 (brt, 2H, Ph), 7.16-7.65 (m, 18H, Ph), 7.75 (m,
2
147.9 (s, J Pt-C ) 28 Hz, SiPh), 170.9 (t, J ) 13 Hz, PtPh);
1
31P{1H} NMR (CD2Cl2) δ -9.2 (s, J Pt-P ) 2756 Hz). Anal.

2030 Organometallics, Vol. 19, No. 10, 2000
Hasebe et al.
4H, Ph); 31P{1H} NMR (CD2Cl2) δ -6.1 (d, 2J P-P ) 19 Hz, 1J Pt-P
“The Chemistry of Inter-element Linkage” (No. 09239105)
from the Ministry of Education, Science, Sports and
Culture, J apan.
) 1188 Hz, 2J Si-P ) 182 Hz), -14.8 (d, 2J P-P ) 19 Hz, 1J Pt-P
)
1949 Hz).
5d : 1H NMR (CD2Cl2) δ 0.45 (m, 2H, SiCH2CH2CH2CH3),
2
0.63 (brt, 3H, SiCH2CH2CH2CH3), 0.91 (d, J P-H ) 7.6 Hz,
2
3
3J Pt-H ) 17.6 Hz, 6H, PCH3), 1.03 (d, J P-H ) 8.4 Hz, J Pt-H
)
Su p p or tin g In for m a tion Ava ila ble: Details of the struc-
ture determination of 2c and 3b including figures giving
atomic numbering schemes and tables of atomic coordinates,
thermal parameters, and full bond distances and angles. This
material is available free of charge via the Internet at
http://pubs.acs.org.
21.6 Hz, 6H, PCH3), 1.41 (m, 4H, SiCH2CH2CH2CH3), 6.67 (brt,
1H, Ph), 6.82 (brt, 2H, Ph), 7.10-7.55 (m, 18H, Ph), 7.75 (d,
4H, Ph); 31P{1H} NMR (CD2Cl2) δ -6.2 (d, 2J P-P ) 18 Hz, 1J Pt-P
) 1184 Hz, 2J Si-P ) 182 Hz), -14.8 (d, 2J P-P ) 18 Hz, 1J Pt-P
)
1949 Hz).
Ack n ow led gm en t. This work was supported by a
Grant-in-Aid for Scientific Research on Priority Area
OM000012T