Diplatinum complexes with bridging silyl ligands. Si-H bond activation of μ-silyl ligand leading to a new platinum complex with bridging silylene and silane ligands

Article abstract of DOI:10.1021/om060930c

A diplatinum complex with bridging diethylsilyl ligands, [{Pt(PCy ₃)}₂(μ-η²-HSiEt₂) ₂] (1), reacted with an excess of H₂SiPH₂ to yield [{Pt(PCy₃)}₂(ν-η

Full text of DOI:10.1021/om060930c

©
Copyright 2007
Volume 26, Number 3, January 29, 2007
American Chemical Society
Communications
Diplatinum Complexes with Bridging Silyl Ligands. Si-H Bond
Activation of µ-Silyl Ligand Leading to a New Platinum Complex
with Bridging Silylene and Silane Ligands
Makoto Tanabe, Daisuke Ito, and Kohtaro Osakada*
Chemical Resources Laboratory (R1-3), Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku,
Yokohama 226-8503, Japan
ReceiVed October 10, 2006
Summary: A diplatinum complex with bridging diethylsilyl
M-Si and M-H-Si bonds as well as a bond between the two
2
9
ligands, [{Pt(PCy3)}2(µ-η -HSiEt2)2] (1), reacted with an excess
d metal centers. A theoretical study of the complexes revealed
2
of H2SiPh2 to yield [{Pt(PCy3)}2(µ-η -HSiPh2)2] (2) Via ex-
a partial character of µ-silane and hydride ligands bonded to
change of the bridging SiHEt2 ligands with SiHPh2 groups. An
7
two metal centers caused by Si-H bond activation. Dinuclear
equimolar reaction of H2SiPh2 with 1 afforded a mixture of the
Rh complexes with µ-silylene and hydride ligands were reported
to undergo intramolecular hydrogen exchange via an intermedi-
ate complex with a silyl ligand bonded to two Rh atoms via
2
2
dinuclear complexes [{Pt(PCy3)}2(µ-η -HSiEt2)(µ-η -HSiPh2)]
2
2
(
3) and [{Pt(PCy3)}2(µ-η :η -H2SiEt2)(µ-SiPh2)] (4). X-ray
crystallographic structure determination of 4 showed bridging
coordination of the H2SiEt2 ligand to two Pt centers Via two
Pt-H-Si three-center two-electron bonds (Pt-Si ) 2.375(8)
and 2.39(1) Å).
8,9
Rh-Si and Rh-H-Si bonds. Dinuclear transition metal
complexes with bridging silane ligands are much less common
(4) (a) Levchinsky, Y.; Rath, N. P.; Braddock-Wilking, J. Organome-
Bridging primary (RSiH2) or secondary (R2SiH) organosilyl
ligands in dinuclear transition metal complexes are bonded to
one metal via an M-Si σ-bond and to the other via an M-H-
tallics 1999, 18, 2583-2586. (b) Braddock-Wilking, J.; Levchinsky, Y.;
Rath, N. P. Organometallics 2000, 19, 5500-5510. (c) Braddock-Wilking,
J.; Corey, J. Y.; Dill, K.; Rath, N. P. Organometallics 2002, 21, 5467-
5469. (d) Braddock-Wilking, J.; Corey, J. Y.; Trankler, K. A.; Dill, K. M.;
1
2-4
5
Si three-center two-electron bond. Diplatinum, dipalladium,
French, L. M.; Rath. N. P. Organometallics 2004, 23, 4576-4584. (e)
Braddock-Wilking, J.; Corey, J. Y.; Trankler, K. A.; Xu, H.; French, L.
M.; Praingam, N.; White, C.; Rath, N. P. Organometallics 2006, 25, 2859-
6
and Pd-Pt heterobimetallic complexes with two bridging silyl
2
ligands, formulated as [{M(PR3)}2(µ-η -HSiR2)2] (M ) Pd and/
2871. (f) Braddock-Wilking, J.; Corey, J. Y.; French, L. M.; Choi, E.;
or Pt), have a four-membered M2Si2 core, which contains the
Speedie, V. J.; Rutherford, M. F.; Yao, S.; Xu, H.; Rath, N. P. Organo-
metallics 2006, 25, 3974-3988.
(5) (a) Kim, Y.-J.; Lee, S.-C.; Park, J.-I.; Osakada, K.; Choi, J.-C.;
Yamamoto, T. Organometallics 1998, 17, 4929-4931. (b) Kim, Y.-J.; Lee,
S.-C.; Park, J.-I.; Osakada, K.; Choi, J.-C.; Yamamoto, T. J. Chem. Soc.,
Dalton Trans. 2000, 417-421.
(6) (a) Tanabe, M.; Yamada, T.; Osakada, K. Organometallics 2003,
22, 2190-2192. (b) Yamada, T.; Tanabe, M.; Osakada, K.; Kim, Y.-J.
Organometallics 2004, 23, 4771-4777.
(7) Nakajima, S.; Sumimoto, M.; Nakao, Y.; Sato, H.; Sakaki, S.;
Osakada, K. Organometallics 2005, 24, 4029-4038.
(8) (a) Wang, W.-D.; Hommeltoft, S. I.; Eisenberg, R. Organometallics
1988, 7, 2417-2419. (b) Wang, W.-D.; Eisenberg, R. J. Am. Chem. Soc.
1990, 112, 1833-1841. (c) Wang, W.-D.; Eisenberg, R. Organometallics
1992, 11, 908-912.
*
Corresponding author. E-mail: kosakada@res.titech.ac.jp.
(1) For reviews: (a) Schubert, U. AdV. Organomet. Chem. 1990, 30,
1
2
2
2
1
51-187. (b) Ogino, H.; Tobita, H. AdV. Organomet. Chem. 1998, 42, 223-
90. (c) Corey, J. Y.; Braddock-Wilking, J. Chem. ReV. 1999, 99, 175-
92. (d) Braunstein, P.; Boag, N. M. Angew. Chem., Int. Ed. 2001, 40,
427-2433. (e) Osakada, K.; Tanabe, M. Bull. Chem. Soc. Jpn. 2005, 78,
887-1898. (f) Nikonov, G. AdV. Organomet. Chem. 2005, 53, 217-309.
(2) 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, 659-666.
(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,
9, 192-205.
1
1
0.1021/om060930c CCC: $37.00 © 2007 American Chemical Society
Publication on Web 01/03/2007

4
60 Organometallics, Vol. 26, No. 3, 2007
Communications
than those with bridging silyl or silylene ligands. Graham,
Carre nˇ o, Suzuki, Kira, and their respective co-workers reported
dinuclear Re, Mn, and Ru complexes in which the secondary
silane coordinated to the metal centers via two M-H-Si
1
0-12
bonds.
C6H4Me)2 ligand in the Ru complexes suggest partial activation
of the Si-H bond involved in the three-center two-electron
Small JH-Si values (36 Hz) of the bridging HSi-
(
1
2
bonds. Herein, we report the reactions of H2SiPh2 with a
diplatinum complex that contains two dialkylsilyl ligands, which
results in formation of a new diplatinum complex with bridging
silane and silylene ligands via migration of a hydrogen atom
of the bridging diphenylsilyl ligands.
Repeated recrystallization of the products of reaction 2 from
toluene-hexane (1:7) at -20 °C yielded a solid composed of
3 and 4 in 6:94 molar ratio. Single crystals of 3 and 4 suitable
for X-ray crystallography were obtained by carefully choosing
the crystals from the mixtures. Isolation of pure samples of 3
or 4 was not feasible partly due to mutual isomerization of the
complexes in solution (vide infra). Figure 1 shows molecular
A diplatinum complex with bridging diethylsilyl ligands, [{Pt-
PCy3)}2(µ-η -HSiEt2)2] (1), reacted with an excess of H2SiPh2
2
(
(
(
Pt:Si ) 1:3.7) at room temperature to produce [{Pt(PCy3)}2-
2
µ-η -HSiPh2)2] (2) in 96% yield, as shown in eq 1. Complex
1
6
structures of 3 and 4. Distances between the two Pt centers
of 3 (2.6591(7) Å) and 4 (2.708(1) Å) are within the range of
2
,3,4a,d,f
Pt-Pt bonds in diplatinum(I) complexes.
The Pt1-Si1
(
2.402(4) Å) and Pt2-Si2 (2.388(3) Å) bonds of 3 are
significantly longer than two other bonds (Pt1-Si2 ) 2.318(3)
Å, Pt2-Si1 ) 2.306(4) Å). The longer Pt-Si bonds are assigned
to those involved in the Pt-H-Si interaction, although positions
of the Pt-H-Si hydogens were not determined by difference
2
was characterized by comparison of its NMR data with those
2
2
in the previous report. Recently, Braddock-Wilking reported
Fourier synthesis. The complex, [{Pt(PCy3)}2(µ-η -HSiMe2)2],
that a diplatinum complex with bridging silafluorenyl groups,
was also reported to have the Pt2Si2 core with a distorted
rectangular structure (Pt-Si ) 2.324(2), 2.420(2) Å). The Pt-
2
2
[{Pt(PPh3)2(H)}{Pt(PPh3)}(µ-SiC20H24)(µ-η -HSiC20H24)], un-
dergoes exchange of the Si ligands with bridging HGePh2 groups
H-Si bonds of 3 are assigned at opposite positions of the Pt2-
Si2 core, which is formed by two Pt centers and the bridging
diphenylsilyl and diethylsilyl ligands. The Pt2Si2 core of 4
contains two longer Pt-Si bonds on the same side of the Pt-
Pt bond (Pt1-Si1 ) 2.375(8) Å, Pt2-Si1 ) 2.39(1) Å) and
two other Pt-Si bonds that are shorter (Pt1-Si2 ) 2.314(8)
Å, Pt2-Si2 ) 2.304(7) Å). The two former bonds are assigned
to those involved in the Pt-H-Si interactions, while the latter
bonds are due to Pt-Si bonds, indicating a structure with
bridging H2SiEt2 and SiPh2 ligands. The torsion angle for the
P2-Pt2-Pt1-P1 unit of 4 (160.9(3)°) indicates an syn-
orientation of the Pt-P bonds with respect to the Pt-Pt bond,
while the corresponding angle of 3 is smaller (113.9(6)°).
2
to produce [{Pt(PPh3)}2(µ-η -HGePh2)2] caused by addition of
1
3
H2GePh2. Mononuclear Pt complexes containing a Pt-Ge
bond were reported to be thermodynamically more stable than
that of the silyl ligand of the Pt complexes.14 Fink reported
higher stability of M-Si (M ) Pd, Pt) bonds of the complexes
with aryl-substituted silyl ligands than those with alkylsilyl
ligands.15
An equimolar reaction of H2SiPh2 with 1 formed a mixture
of a diplatinum complex with two different bridging secondary
2
2
silyl ligands, [{Pt(PCy3)}2(µ-η -HSiPh2)(µ-η -HSiEt2)] (3; 50%),
and the complex with bridging diethylsilane and diphenylsilylene
2
2
ligands, [{Pt(PCy3)}2(µ-η :η -H2SiEt2)(µ-SiPh2)] (4; 45%), to-
gether with a small amount of 2 (5%) (eq 2). Recrystallization
of the products formed a mixture of 3 and 4 in 55:45 molar
ratio, which was determined by integration of C6H5-ortho
1
13
1
29
1
31
1
The multinuclear NMR ( H, C{ H}, Si{ H}, and P{ H}
NMR) spectra were obtained from a mixture of 3 and 4 in 6:94
molar ratio, while NMR data of 3 were obtained from the
1
31
1
hydrogen signals in the H NMR spectrum. Addition of H2-
mixture in 55:45 molar ratio. The P{ H} NMR spectrum of 4
displays a single signal at δ 51.8 as part of an AA′XX′ spin
SiPh2 to the mixture of 3 and 4 (Pt:Si ) 1:3) at room
temperature formed complex 2 in 67% yield as the sole product.
This result indicates that the displacement of bridging silyl
ligands proceeds via formation of intermediates 3 and 4, and
then further reaction with H2SiPh2 produces 2.
3
system (JPt-P ) 3849, 362 Hz, JP-P ) 55 Hz). Complex 3
3
1
1
3
exhibits two P{ H} NMR signals at δ 53.2 and 53.5 ( JP-P )
59 Hz), which is consistent with the unsymmetrical structure
29
shown in eq 2. Two Si resonances of 4 are observed at δ 230.1
(
9) (a) Fryzuk, M. D.; Rosenberg, L.; Rettig, S. J. Organometallics 1991,
(16) Crystallographic data for 3: C52H88P2Si2Pt2, fw ) 1221.57, triclinic,
space group P 1h , a ) 13.792(3) Å, b ) 14.357(2) Å, c ) 14.581(3) Å, R )
1
0, 2537-2539. (b) Fryzuk, M. D.; Rosenberg, L.; Rettig, S. J. Inorg. Chim.
3
Acta 1994, 222, 345-364. (c) Fryzuk, M. D.; Rosenberg, L.; Rettig, S. J.
Organometallics 1996, 15, 2871-2880.
63.636(5)°, â ) 88.025(8)°, γ ) 84.744(8)°, V ) 2575.8(8) Å , Z ) 2, T
-3
-1
) 133 K, Fcalcd ) 1.575 g cm , µ ) 5.5449 mm , F(000) ) 1228, Rigaku
Saturn-CCD diffractometer using graphite-monochromated Mo KR radiation
(λ ) 0.71073 Å), yellow crystal (0.20 × 0.32 × 0.45 mm). Of 19314
reflections collected, 10 980 were independent (Rint ) 0.024); 609 variables
refined with 8459 reflections to final R indices R1(I > 2σ(I)) ) 0.0644,
wR2(I > 2σ(I)) ) 0.1383, GOF ) 1.088. Crystallographic data for 4:
C52H88P2Si2Pt2, fw ) 1221.57, triclinic, space group P 1h , a ) 13.897(3) Å,
b ) 13.971(4) Å, c ) 14.889(3) Å, R ) 86.84(2)°, â ) 69.18(1)°, γ )
(10) (a) Hoyano, J. K.; Elder, M.; Graham, W. A. G. J. Am. Chem. Soc.
1
3
969, 91, 4568-4569. (b) Graham, W. A. G. J. Organomet. Chem. 1986,
00, 81-91. (c) Carre nˇ o, R.; Riera, V.; Ruiz, M. A.; Jeannin, Y.; Philoche-
Levisalles, M. J. Chem. Soc., Chem. Commun. 1990, 15-17.
(
11) Takao, T.; Yoshida, S.; Suzuki, H.; Tanaka, M. Organometallics
995, 14, 3855-3868. Fe2 complex: Ohki, Y.; Kojima, T.; Oshima, M.;
Suzuki, H. Organometallics 2001, 20, 2654-2656.
12) Hashimoto, H.; Hayashi, Y.; Aratani, I.; Kabuto, C.; Kira, M.
Organometallics 2002, 21, 1534-1536.
13) Braddock-Wilking, J.; Corey, J. Y.; White, C.; Xu, H.; Rath, N. P.
Organometallics 2005, 24, 4113-4115.
14) (a) Clemmit, A. F.; Glockling, F. Chem. Commun. 1970, 705-706.
b) Clemmit, A. F.; Glockling, F. J. Chem. Soc. (A) 1971, 1164-1169.
15) Jacobsen, H.; Fink, M. J. Organometallics 2006, 25, 1945-1952.
1
3
-3
(
79.58(1)°, V ) 2657(1) Å , Z ) 2, T ) 133 K, Fcalcd ) 1.527 g cm , µ )
-1
5.3752 mm , F(000) ) 1228, Rigaku Saturn-CCD diffractometer using
graphite-monochromated Mo KR radiation (λ ) 0.71073 Å), yellow crystal
(0.30 × 0.20 × 0.20 mm). Of 19 998 reflections collected, 11296 were
independent (Rint ) 0.061); 604 variables refined with 5788 reflections to
final R indices R1(I > 2σ(I)) ) 0.1149, wR2(I > 2σ(I)) ) 0.3341, GOF )
1.118.
(
(
(
(

Communications
Organometallics, Vol. 26, No. 3, 2007 461
2
1
Figure 2. H{ H} NMR spectra (toluene, 40 °C) of the products
obtained from an equimolar reaction of D SiPh with 1 (a) after
purification and (b) before purification. Peaks with [, b, and *
are due to 3-DSiPh , 3-DSiEt , and 4-d, respectively.
2
2
2
2
Figure 1. ORTEP drawings of (a) 3 and (b) 4 at 30% ellipsoidal
level. Hydrogens except for bridging hydrogen atoms are omitted
for clarity. Selected bond distances (Å) and angles (deg) for 3: Pt1-
Pt2 2.6951(7), Pt1-P1 2.270(2), Pt1-Si1 2.402(4), Pt1-Si2 2.318-
(
3), Pt2-P2 2.266(2), Pt2-Si1 2.306(4), Pt2-Si2 2.388(3), Pt2-
Pt1-P1 163.74(5), P1-Pt1-Si1 142.7(1), P1-Pt1-Si2 107.7(1),
Si1-Pt1-Si2 109.5(2), Pt1-Pt2-P2 174.08(6), P2-Pt2-Si1
1
21.2(1), P2-Pt2-Si2 127.2(1), Si1-Pt2-Si2 110.4(2), Pt1-Si1-
Pt2 69.8(1), Pt1-Si2-Pt2 69.86(9). Selected bond distances (Å)
and angles (deg) for 4: Pt1-Pt2 2.708(1), Pt1-P1 2.264(5), Pt1-
Si1 2.375(8), Pt1-Si2 2.314(8), Pt2-P2 2.262(5), Pt2-Si1 2.39-
(
(
1
1), Pt2-Si2 2.304(7), Pt2-Pt1-P1 162.4(2), P1-Pt1-Si1 141.8-
3), P1-Pt1-Si2 108.6(2), Si1-Pt1-Si2 109.6(2), Pt1-Pt2-P2
61.4(2), P2-Pt2-Si1 142.8(2), P2-Pt2-Si2 107.5(2), Si1-Pt2-
Figure 3. Change in amounts of H
equimolar reaction of H SiPh with 1 at 25 °C. [1] ) 18 mM in
toluene-d . Dibenzyl was used as an internal standard (18 mM).
2 2
SiPh , 3, and 4 during the
Si2 109.4(2), Pt1-Si1-Pt2 69.3(2), Pt1-Si2-Pt2 71.8(2).
2
2
8
and 141.3. The signals are assigned to the Si nuclei of the SiPh2
ligand and of H2SiEt2, respectively, based on their peak
positions. The difference of the 29Si NMR peak positions
between the µ-HSiEt2 and µ-HSiPh2 ligands of 3 (δ 195.5 and
2
2
(PCy3)}2(µ-η -DSiPh2)(µ-η -HSiEt2)] (3-DSiPh2) and [{Pt-
2
2
(PCy3)}2(µ-η -HSiPh2)(µ-η -DSiEt2)] (3-DSiEt2). The assigned
1
1
63.7) is much smaller than that of the two Si signals of 4. The
Si{ H} NMR spectrum of [Ru2(CO)6{µ-Si(C6H4Me)2}(µ-PPh2-
signal for 3-DSiPh2 is at a similar position (δ 2.43) to the H
2
9
1
NMR peak position for the Pt-H-SiPh2 hydrogen of 2 (δ
6
a
CH2PPh2)] exhibited a signal due to the µ-silylene ligand at δ
72.6, which was at lower magnetic field position than the signal
2.45). Formation of 3-DSiEt2 indicates intramolecular ex-
change of Si-H hydrogen atoms between the diethylsilyl and
diphenylsilyl ligands.
1
2
2
of [Ru2(CO)4{SiH(C6H4Me)2}2{µ-η :η -H2Si(C6H4Me)2}(µ-
PPh2CH2PPh2)] (δ 154.8).12 The Si NMR signal of the H2-
29
Figure 3 plots the change in the amount of the complexes
2
1
SiEt2 ligand of 4 shows a larger coupling constant ( JP-Si ) 72
during the reaction of H2SiPh2 with 1, as determined by H
2
Hz) than the signal of the SiPh2 ligand ( JP-Si ) 3.5 Hz). Two
NMR spectroscopy. The increase in the formation of 3 is much
faster than that of 4 at the initial stage of the reaction, while
gradual isomerization of 3 and 4 is observed after about 2 h.
After 10 h a mixture of the complexes 3 and 4 is observed in
a 55:45 molar ratio. The isomerization of the complexes starting
from a mixture of 3 and 4 in a 6:94 ratio in the presence of
added PCy3 (Pt:PCy3 ) 1:0.6) eventually gives a new ratio of
3 to 4 of close to 55:45 after 25 h, but it occurs more slowly in
the absence of PCy3 and requires 2 weeks to attain equilibrium.
Scheme 1 illustrates a possible mechanistic pathway that
accounts for hydrogen migration between the Si ligands.
Transformation of an Si-H bond (Ha) in the bis(µ-silyl)platinum
complex 3 and formation of a new bond between the resulting
hydride ligand in the intermediate species and the Si atom of
the other silyl ligand (SiEt2) yield the bridging silane ligand in
4. Intramolecular transfer of a hydrogen from the silane ligand
in 4 to the silylene ligand regenerates the complex with two
bridging silyl ligands in 3. Repetition of the transformation
2
JP-Si values observed with the Si signal of 3 (60 and 11 Hz)
are assigned to an interaction through the Pt-H-Si bond and
to that through the Pt-Si bond, respectively, on the basis of
comparison of the values with 4.
1
The H NMR signals due to Pt-H-Si hydrogens of 3 and 4
are overlapped severely by the signals of the PCy3 hydrogens.
Preparation of a partially deuterated complex by the reaction
2
1
of D2SiPh2 with 1 and H{ H} NMR measurement of the
products enabled determination of the peak positions. Figure
2
1
2
a displays the H{ H} NMR spectrum of [{Pt(PCy3)}2(µ-
2
2
SiPh2)(µ-η :η -DHSiEt2)] (4-d) obtained by repeated recrystal-
lization of the products. A single signal at δ 1.01 flanked by
Pt satellites (JPt-D ) 99 Hz) is assigned to the deuterium
1
95
coordinated to the diethylsilane ligand. Figure 2b shows the
spectrum of the products before recrystallization. Two signals
with equal intensity are observed at δ 2.43 and 1.44, which are
assigned to deuterium nuclei of two isotopomers of 3, [{Pt-

4
62 Organometallics, Vol. 26, No. 3, 2007
Communications
Scheme 1
to be formed by addition of the phosphine ligand to the dinuclear
complexes with two bridging silyl ligands.
4
c,f,6b
In summary, we observed stepwise displacement of the two
bridging diethylsilyl ligands caused by addition of diphenyl-
silane. One of the two intermediates has a new structure
composed of two Pt centers bridged by H2SiEt2 and SiPh2
ligands.
Acknowledgment. This work was financially supported by
a Grant-in-Aid for Scientific Research for Young Chemists No.
1
7750049 and for Scientific Research on Priority Areas, from
the Ministry of Education, Culture, Sport, Science, and Technol-
ogy Japan, and by The 21st Century COE Program “Creation
of Molecular Diversity and Development of Functionalities”.
process in Scheme 1 results in hydrogen exchange between the
two silyl ligands of 3.
Supporting Information Available: Experimental procedures
for the synthesis of complexes 1-4 and crystallographic data of 3
and 4. This material is available free of charge via the Internet at
http://pubs.acs.org.
Activation of the Si-H bond to form an intermediate complex
with hydride and µ-silylene ligands may be facilitated by the
coordination of an additional phosphine ligand, because Pd-
Pt and Pt-Pt complexes with hydride and µ-silylene ligands,
2
[
{M(H)(PR3)2}{M(PR3)}(µ-SiR2)(µ-η -HSiR2)], were reported
OM060930C