Substitution reactions at a bridging silicon ligand. Formation of a bis(μ-silylene) complex containing a trifluoroacetoxy group. Mechanistic studies of the site-exchange process of the hydride ligands

Article abstract of DOI:10.1021/om049328h

Treatment of a bis(μ-diphenylsilyl) complex, {Cp*Ru(μ- η²-HSiPh₂)}₂(μ-H)(H) (2a, Cp* = η⁵-C₅Me₅), with trifluoroacetic acid in toluene resulted in introduction of a trifluoroacetoxy group on a bridging silicon atom with concomitant loss of one phenyl group as benzene, affording a mixed-bridging bis(μ-silylene) complex, {Cp*Ru(μ-H)} ₂{μ-SiPh(OCOCF₃)}(μ-SiPh₂) (3b), in moderate yield. Nucleophilic addition of the acetoxy group took place in the intermediate μ-silyl,μ-silylene complex (Cp*Ru)₂(μ- η²-HSiPh₂)(μ-SiPh₂)(μ-CFs ₃CO₂)(μ-H)(H) (7), containing a bridging carboxylate group. The trifluoroacetoxy group of 3b underwent nucleopbilic displacement at the bridging silicon atom, which afforded the mixed-bridging bis(μ-silylene) complexes {Cp*Ru(μ-H)}₂(μ-SiPhX)(μ-SiPh₂) (3c, X = OMe; 3d, X = OH) upon treatment with methanol and aqueous KOH, respectively. VT NMR studies of 3b, 3c, 3d, {Cp*Ru(μ-H)} ₂(μ-SiPhMe)(μ-SiMe₂) (3e), and {Cp*Ru(μ-H) (μ-SiPhMe)}₂ (3f-syn) revealed a linear correlation between the electronic nature of the substituants on the bridging silicon atom and the activation parameters of the hydride site-exchange process occurring in the bis(μ-silylene) complex.

Full text of DOI:10.1021/om049328h

Organometallics 2005, 24, 521-532
521
Substitution Reactions at a Bridging Silicon Ligand.
Formation of a Bis(µ-silylene) Complex Containing a
Trifluoroacetoxy Group. Mechanistic Studies of the
Site-Exchange Process of the Hydride Ligands
Toshiro Takao, Shigeru Yoshida, and Hiroharu Suzuki*
Department of Applied Chemistry, Graduate School of Science and Engineering,
Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-Ku, Tokyo 152-8552, Japan
Received August 30, 2004
Treatment of a bis(µ-diphenylsilyl) complex, {Cp*Ru(µ-η2-HSiPh2)}2(µ-H)(H) (2a, Cp* )
η5-C5Me5), with trifluoroacetic acid in toluene resulted in introduction of a trifluoroacetoxy
group on a bridging silicon atom with concomitant loss of one phenyl group as benzene,
affording a mixed-bridging bis(µ-silylene) complex, {Cp*Ru(µ-H)}2{µ-SiPh(OCOCF3)}(µ-SiPh2)
(3b), in moderate yield. Nucleophilic addition of the acetoxy group took place in the
intermediate µ-silyl,µ-silylene complex (Cp*Ru)2(µ-η2-HSiPh2)(µ-SiPh2)(µ-CF3CO2)(µ-H)(H)
(7), containing a bridging carboxylate group. The trifluoroacetoxy group of 3b underwent
nucleophilic displacement at the bridging silicon atom, which afforded the mixed-bridging
bis(µ-silylene) complexes {Cp*Ru(µ-H)}2(µ-SiPhX)(µ-SiPh2) (3c, X ) OMe; 3d, X ) OH) upon
treatment with methanol and aqueous KOH, respectively. VT NMR studies of 3b, 3c, 3d,
{Cp*Ru(µ-H)}2(µ-SiPhMe)(µ-SiMe2) (3e), and {Cp*Ru(µ-H)(µ-SiPhMe)}2 (3f-syn) revealed a
linear correlation between the electronic nature of the substituents on the bridging silicon
atom and the activation parameters of the hydride site-exchange process occurring in the
bis(µ-silylene) complex.
Introduction
We have studied the reactivity of the diruthenium
tetrahydride complex Cp*Ru(µ-H)4RuCp* (1, Cp* ) η5-
C5Me5) with hydrosilanes in relation to bimetallic
activation on the Ru2 system.1 We have shown that the
reaction of 1 with diphenylsilane afforded the bis(µ-
diphenylsilyl) complex {Cp*Ru(µ-η2-HSiPh2)}2(µ-H)(H)
(2a), whose 3c-2e Ru-H-Si bonds were readily cleaved
upon thermolysis to yield the bis(µ-diphenylsilylene)
complex {Cp*Ru(µ-SiPh2)(µ-H)}2 (3a) (eq 1).1a This
successive bond cleavage performed on the bimetallic
system showed that the agostic Si-H interaction was
(1) (a) Suzuki, H.; Takao, T.; Tanaka, M.; Moro-oka, Y. J. Chem.
Soc., Chem. Commun. 1992, 476-478. (b) Takao, T.; Yoshida, S.;
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3422. (d) Takao, T.; Amako, M.; Suzuki, H. Organometallics 2003, 22,
3855-3876.
(2) Takao, T.; Yoshida, S.; Suzuki, H. Chem. Lett. 2001, 1100-1101.
(3) See for example: (a) Davies, D. L.; Gracey, B. P.; Guerchais, V.;
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Organometallics 1995, 14, 5686-5694.
really an intermediary state for the oxidative addition,
and two metal nuclei played an important role during
the bimetallic activation as a coordination site and an
activation site.
Recently, we have demonstrated that protonation of
the bis(µ-silyl) complexes in dichloromethane affords the
cationic bis(µ-silane) complexes [{Cp*Ru(µ-η2:η2-H2-
SiR2)}2(µ-H)][X-] (4a, R ) Ph; 4b, R ) Et, X ) CF3SO3,
BPh4) (eq 2).2 The positive charge on the metal center
caused reductive coupling between the bridging silyl
ligand and the hydride, thereby resulting in transfor-
(5) (a) Suzuki, H.; Kakigano, T.; Igarashi, M.; Tanaka, M.; Moro-
oka, Y. J. Chem. Soc., Chem. Commun. 1991, 283-285. (b) Suzuki,
H.; Kakigano, K.; Tada, K.; Igarashi, M.; Matsubara, K.; Inagaki, A.;
Ohshima, M.; Takao, T. Bull. Chem. Soc., Jpn. 2005, 78, 1-21.
10.1021/om049328h CCC: $30.25 © 2005 American Chemical Society
Publication on Web 01/13/2005

522 Organometallics, Vol. 24, No. 4, 2005
Takao et al.
ture.4 For example, Et3SiF was obtained in the reaction
of (C5H5)Fe(CO)(PEt3)SiEt3 with HBF4 as a result of
nucleophilic attack of the BF4 anion at the Fe-SiEt3
group.4c Instability of 4 toward nucleophiles prompted
us to investigate the reactivity of 4 with nucleophiles
in a substitution reaction at the bridging silicon ligand.
Substitution reaction at an Si-H or Si-X bond on a
bridging silylene ligand has been well investigated.6
However, there are few example of the Si-C bond
cleavage of an organic substituent on a bridging silyl
group to introduce a functional group on silicon. Re-
cently, bromodemethylation of the trimethylsilyl group
attached to an iron center using BBr3 was reported by
Tobita and co-workers.7 Herein, we report displacement
of a phenyl group from a bridging silicon atom of the
cationic bis(µ-silane) complex 4a by trifluoroacetate ion
to afford the neutral bis(µ-silylene) complex {Cp*Ru(µ-
H)}2{µ-SiPh(OCOCF3)}(µ-SiPh2) (3b), having a trifluo-
roacetoxy group on the bridging silylene ligand. The
trifluoroacetoxy group on the bridging silicon atom
readily underwent nucleophilic displacement. Thus,
complex 3b could be a good precursor affording various
mixed-bridging bis(µ-silylene) complexes.
In our preceding paper,1d we showed that the site-
exchange process of the hydride ligands occurs in the
bis(µ-silylene) complex 3. This process occurs via the
formation of an intermediate silyl complex containing
an Si-H bond. Therefore, the energy level of the σ*-
(Si-H) would affect the activation parameters of the
fluxional process. The electronic nature of the substit-
uents on the silicon atom has been shown to highly
affect the energy level of the σ*(Si-H) orbital.8 Thus,
kinetic studies of the bis(µ-silylene) complexes contain-
ing various substituents afford a deeper understanding
of the fluxional process of the bis(µ-silylene) complex as
well as the nature of the bridging silylene ligand.
mation of the µ-silyl ligand to the µ-silane ligand.
Although formation of an agostic M-H-C bond by
protonation has been well documented for µ-alkylidene
and µ3-alkylidyne complexes,3 formation of a cationic
µ-silane complex by protonation is still rare. Only
limited examples of the protonation of a monometallic
silyl complex to yield a cationic silane complex have
been reported.4
We employed dichloromethane as solvent for the
protonation. However, when other solvents, such as
THF, Et2O, and MeOH, were used, elimination of the
silicon ligands resulted due to rapid nucleophilic attack
at the electrophilic silicon center of the cationic µ-silane
complex. Protonation of 2a and 2b in Et2O led to the
formation of the cationic η6-benzene complex [Cp*Ru-
(η6-C6H6)]+ (5) and the cationic triruthenium hexahy-
dride complex [Cp*Ru(µ-H)2]3+ (6),5 respectively. Treat-
ment of 4 with these solvents also gave the same result
(eq 3). These facts implied formation of a monometallic
Results and Discussion
While the reaction of bis(µ-diphenylsilyl) complex 2a
with CF3SO3H in CH2Cl2 quantitatively affords the
cationic bis(µ-diphenylsilane) complex 4a as shown eq
2,2 the mixed-bridging bis(µ-silylene) complex {Cp*Ru-
(µ-H)}2{µ-SiPh(OCOCF3)}(µ-SiPh2) (3b) was obtained by
the reaction of 2a with trifluoroacetic acid in toluene
(eq 4). Formation of 3b was confirmed on the basis of
1H, 13C, and 29Si NMR and IR spectra, respectively, as
well as elemental analysis.
Introduction of the trifluoroacetoxy group at the
bridging silicon atom was clearly shown in the 29Si NMR
spectra. While one signal appeared at δ 109.8 in the 29Si
NMR spectrum of the bis(µ-diphenylsilylene) complex
3a, two signals were observed for 3b at δ 109.2 and
137.5, respectively. The signal observed at δ 109.2 was
straightforwardly assigned to the µ-SiPh2 bridge from
its similarity of the chemical shift in 3a. The signal
observed at δ 137.5 is thus attributed to the µ-SiPh-
(OCOCF3) bridge.
[Cp*RuH2]+ fragment via in situ elimination of the
bridging silicon ligands. Especially, formation of 5
indicated generation of benzene as a result of Si-C(aryl)
bond cleavage by protonation. Such instability toward
nucleophiles has been well documented in the litera-
(6) (a) Kawano, Y.; Tobita, H.; Shimoi, M.; Ogino, H. J. Am. Chem.
Soc. 1994, 116, 8575-8581. (b) Kawano, Y.; Tobita, H.; Ogino, H.
Angew. Chem., Int. Ed. Engl. 1991, 30, 843-844. (c) Tobita, H.;
Kawano, Y.; Ogino. H. Chem. Lett. 1989, 2155-2158. (d) Malisch, W.;
Ries, W. Angew. Chem., Int. Ed. Engl. 1978, 17, 120-121. (e) Malish,
W.; Ries, W. Chem. Ber. 1979, 112, 1304-1315. (f) Malisch, W.; Vo¨gler,
M.; Schumacher, D.; Nieger, M. Organometallics 2002, 21, 2891-2897.
(g) Aylett, B. J.; Colquhoun, H. M. J. Chem. Res., Synop. 1977, 148.
(7) Watanabe, T.; Hashimoto, H.; Tobita, H. Organometallics 2004,
23, 4150-4153.
(8) (a) Lichtenberger, D. L.; Rai-Chaudhuri, A. J. Am. Chem. Soc.
1989, 111, 3583-3591. (b) Lichtenberger, D. L.; Rai-Chaudhuri, A.
Inorg. Chem. 1990, 29, 975-981. (c) Lichtenberger, D. L.; Rai-
Chaudhuri, A. Organometallics 1990, 9, 1686-1690. (d) Lichtenberger,
D. L.; Rai-Chaudhuri, A. J. Am. Chem. Soc. 1990, 112, 2492-2497.

Substitution Reactions at a Bridging Silicon Ligand
Organometallics, Vol. 24, No. 4, 2005 523
The magnetic environments of the hydride ligands of
3b should be inequivalent because of the trifluoro-
acetoxy group on the bridging silicon atom. Neverthe-
less, only one signal was observed in the hydride region
of the 1H NMR spectra measured at 21 °C. This means
that site-exchange of the hydride ligands is occurring.
Such motion of the hydride ligands of the bis(µ-silylene)
complexes has been reported earlier in our previous
paper.1d At -65 °C, the signal split into two sharp
doublets at δ -20.17 and -18.50. These coalesced at
10 °C, and activation parameters were estimated as ∆Hq
) 12.8 ( 0.4 kcal mol-1 and ∆Sq ) 1.9 ( 1.5 cal mol-1
K-1 by means of line shape analysis. Mechanistic
studies of the fluxional processes are discussed in detail
later.
Figure 1. Molecular structure of (Cp*Ru)2(µ-η2-HSiPh2)-
{µ-η2-HSiPh(OCOCF3)}(µ-H)(H) (2c) with thermal ellip-
soids at the 30% probability level. Hydrogen atoms except
for those attached to the ruthenium atoms were omitted
for clarity.
Table 1. Selected Bond Distances (Å) and Angles
(deg) for 2c
Ru(1)-Ru(2)
Ru(1)-Si(2)
Ru(2)- Si(2)
Si(1)-C(15)
Si(2)-C(3)
O(2)-C(1)
2.9878(7)
2.3395(10)
2.4120(10)
1.888(4)
Ru(1)-Si(1)
Ru(2)- Si(1)
Si(1)-C(9)
Si(2)-O(1)
O(1)-C(1)
C(1)-C(2)
2.4223(11)
2.4942(10)
1.899(4)
1.760(3)
1.291(5)
1.512(6)
In the IR spectra of 3b, ν(CdO) and ν(C-F) of the
trifluoroacetoxy group was observed at 1754 and 1164
cm-1, respectively. In the 13C NMR spectra, two quartets
coupled with the 19F nucleus were observed at δ 155.8
1.891(4)
1.203(5)
2
(q, JC-F ) 40.2 Hz) and 115.9 (q, JC-F ) 288.0 Hz),
Ru(2)-Ru(1)-Si(1) 53.68(3) Ru(2)-Ru(1)-Si(2) 52.13(2)
Si(1)-Ru(1)-Si(2) 82.31(4) Ru(1)-Ru(2)-Si(1) 51.49(2)
Ru(1)-Ru(2)-Si(2) 49.97(2) Si(1)-Ru(2)-Si(2)
which were assignable to the carbonyl and CF3 carbon
atoms, respectively.
79.39(3)
99.57(15)
128.9(4)
118.8(4)
C(9)-Si(1)-C(15)
Si(2)-O(1)-C(1)
O(1)-C(1)-C(2)
107.76(16) O(1)-Si(2)-C(3)
Although a single-crystal of 3b suitable for the X-ray
diffraction studies was not obtained, the trifluoroacetoxy
group on the bridging silicon atom was confirmed by
the X-ray diffraction studies of a bis(µ-silyl) complex,
(Cp*Ru)2(µ-η2-HSiPh2){µ-η2-HSiPh(OCOCF3)}(µ-H)(H)
(2c), which was obtained by the reaction of 3b with
hydrogen (eq 5). Quantitative formation of a bis(µ-silyl)
complex by hydrogenation is characteristic of the bis-
(µ-silylene) complexes.1d
122.2(3)
112.3(4)
O(1)-C(1)-O(2)
O(2)-C(1)-C(2)
on the edges opposite of each other and formed a C2
structure. Two of the four hydride ligands, H(1) and
H(2), are located between Ru(2) and the silicon atoms
and form 3c-2e Ru-H-Si bonds. H(3) bridges Ru(1) and
Ru(2), and the H(4) is coordinated to Ru(1) as a terminal
hydride. Bond distances between Ru(2) and the silicon
atoms were considerably longer than those between the
Ru(1) and silicon atoms due to 3c-2e interaction (Ru-
(2)-Si(1), 2.4942(10) Å; Ru(1)-Si(1), 2.4223(11) Å; Ru-
(2)-Si(2), 2.4120(10) Å; Ru(1)-Si(2), 2.3395(10) Å). This
structural difference between two ruthenium atoms was
also confirmed by the 1H NMR spectra recorded at -80
°C, in which two Cp* signals and four hydride signals
were observed. This fact indicates that the folded
structure was also adopted in solution.
(9) (a) Fryzuk, M. D.; Rosenberg, L.; Rettig, S. J. Inorg. Chim. Acta
1994, 222, 345-364. (b) Fryzuk, M. D.; Rosenberg, L.; Rettig, S. J.
Organometallics 1999, 18, 958-969.
(10) (a) Auburn, M.; Ciriano, M.; Howard, J. A. K.; Murray, M.;
Pugh, N. J.; Spencer, J. L.; Stone, F. G. A.; Woodward, P. J. Chem.
Soc., Dalton Trans. 1980, 659-666. (b) Levchinsky, Y.; Rath, N. P.;
Braddock-Wilking, J. Organometallics 1999, 18, 2583-2586. (c) Brad-
dock-Wilking, J.; Levchinsky, Y.; Rath, N. P. Organometallics 2000,
19, 5500-5510.
(11) (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. Dalton
2000, 417-421.
(12) (a) Butts, M. D.; Bryan, J. C.; Luo, X.-L.; Kubas, G. J. Inorg.
Chem. 1997, 36, 3341. (b) Simons, R. S.; Tessier, C. A. Organometallics
1996, 15, 2604-2610. (c) Aitken, T. C.; Harrod, J. F.; Samuel, E. J.
Am. Chem. Soc. 1986, 108, 4059-4066.
The structure of 2c is shown in Figure 1, and selected
bond distances and angles are summarized in Table 1.
The Ru2Si2 core of 2c forms a folded quadrangle. The
3c-2e Ru-H-Si interactions were held on the adjacent
two edges (Ru(2)-Si(1) and Ru(2)-Si(2)) as well as other
bis(µ-silyl) complexes of the type {Cp*Ru(µ-η2-HSiR2)}2-
(µ-H)(H) (2) synthesized by ourselves.1a,b It is in sharp
contrast to other bimetallic bis(µ-silyl) complexes of
rhodium,9 platinum,10 palladium,11 and other transition
metals,12 in which two 3c-2e M-H-Si bonds were held

524 Organometallics, Vol. 24, No. 4, 2005
Takao et al.
Although IR spectroscopy is a good method for ob-
serving the η2-Si-H interaction,1b the ν(Ru-H-Si) of
2c was obscured by the strong absorption of the carbonyl
group (ν(CO) ) 1756 cm-1). The ν(Ru-H) of the termi-
nal Ru-H bond was, however, clearly seen at 2060
cm-1, which lay in the range of the ν(Ru-H) of bis(µ-
silyl) complex 2 (2054-2092 cm-1).1
The trifluoroacetoxy group was shown to be σ-bonded
to the bridging silicon atom. While the Si(2)-O(1) bond
length (1.760(3) Å) is slightly longer than those of other
compounds that have a trifluoroacetoxy group on the
silicon atom (Si(OCOCF3)(OH)2{C(SiMe3)3}, 1.713 Å;13a
Zn[C(SiMe3)2{SiMe2(OCOCF3)}]2, 1.726 Å13b), it is still
shorter than the sum of the covalent radii (1.83 Å).
The trifluoroacetoxy group on Si(2) occupied the
equatorial site with respect to the four-membered Ru-
(1)-Si(1)-Ru(2)-Si(2) ring. This was most likely due
to steric repulsion between the Cp* groups and the
phenyl groups. The bulkier phenyl group tends to occupy
the axial position, which was far away from the two Cp*
groups. The same trend was seen in the bis(µ-silyl)
complex (Cp*Ru)2(µ-η2-HSitBu2)(µ-η2-HSiPhH)(µ-H)(H)
(2d).1b
δ 121.7 to be a doublet (JSi-H ) 60 Hz), while the 29Si
signal observed at δ 75.2 was a singlet. Thus, the former
was assignable to the silicon atom comprising the 3c-
2e bond, and the latter was that of the µ-silylene ligand.
Upon selective irradiation at each hydride signal, the
intensities of the other hydride signals did not change.
This implies that site-exchange of the hydride ligands
was negligible within the NMR time scale at least at
-20 °C.
While the reaction of 2a with trifluoroacetic acid in
toluene afforded the neutral bis(µ-silylene) complex 3b,
the cationic bis(µ-silane) complex 4a-CF3CO2 was formed
in the reaction carried out in CH2Cl2. In the reaction
conducted in CH2Cl2, nucleophilic substitution of the
phenyl group with a trifluoroacetoxy group at the
bridging silicon atom did not occur. Although 4a-CF3-
CO2 was not isolated, formation of 4a was confirmed
by the subsequent anion-exchange to BPh4-.2 On the
other hand, reaction of 4a-BPh4 with trifluoroacetic acid
in toluene resulted in formation of the neutral bis(µ-
silylene) complex 3b. Benzene was detected by GC
during the reaction. This implies that anion exchange
from BPh4 to CF3COO causes Si-C(aryl) bond cleavage.
Thus, it is concluded that complex 3b was formed via
initial protonation to form 4a and that subsequent
coordination of the trifluoroacetoxy anion to the ruthe-
nium center in toluene promotes the addition of the
trifluoroacetoxy group to the bridging silylene moiety.
Treatment of 2a with trifluoroacetic acid in toluene
at -20 °C resulted in the exclusive formation of a
µ-carboxy intermediate, (Cp*Ru)2(µ-η2-HSiPh2)(µ-SiPh2)-
(µ-CF3CO2)(µ-H)(H) (7), which has µ-carboxy, µ-silyl, and
µ-silylene groups between the ruthenium atoms (eq 6).
Complex 7 was characterized by means of 1H, 13C, and
29Si NMR and IR spectra and analytical data. Although
the relative positions of the bridging ligands could not
be determined on the basis of the spectral data, we
tentatively assigned complex 7 as shown in eq 6.
The IR spectra of 7 showed a sharp absorption at 2058
cm-1, which was likely assignable to the ν(Ru-H) for a
terminal hydride ligand. Since only one strong absorp-
tion for the ν(Ru-H) was observed, the rest of the
hydride ligands were considered to be bridging ones.
The integration of the phenyl groups (20H) showed
that all of the phenyl groups were still bonded to the
bridging silicon atoms in 7. This indicates that Si-
C(aryl) bond cleavage did not occur at this stage. Four
signals of the ipso-carbon of the phenyl groups were
observed at δ 148.8, 147.9, 147.4, and 146.6 in the 13C
NMR spectra, respectively. The 13C signals coupled with
the 19F nucleus were observed at δ 114.9 (1JC-F ) 285.6
Hz) and 164.3 (2JC-F ) 41.2 Hz) as quartets. These were
assigned to the CF3 group and the carbonyl carbon
atoms, respectively. These results strongly indicated the
coordination of the trifluoroacetoxy group in 7.
A hypsochromic shift for the ν(CO) of the trifluoro-
acetoxy group in 7 was observed in comparison to those
for 2c and 3b. While ν(CO) for 2c and 3b were 1756
and 1754 cm-1, respectively, that for 7 was 1702 cm-1
.
This indicates the bridging coordination of the trifluo-
roacetoxy group in 7. This value is comparable to the
ν(CO) of 1656 cm-1 for {Cp*Ru(µ-CF3COO)(µ-H)}2, of
which the structure has been established by the X-ray
diffraction study.5
In the 1H NMR spectra of 7 measured at -30 °C,
three signals due to the hydride ligands were observed
at δ -13.35, -11.16, and -4.78, respectively. Among
them, a set of satellite signals due to spin-spin coupling
1
between 29Si and H was observed around the signal
observed at δ -4.78 (JSi-H ) 60 Hz). The JSi-H value
strongly indicates the existence of a 3c-2e Ru-H-Si
bond in 7.14 One of the two 29Si signals was observed at
(13) (a) Al-Juaid, S. S.; Eaborn, C.; Hitchcock, P. B. J. Organomet.
Chem. 1992, 423, 5-12. (b) Al-Juaid, S. S.; Eaborn, C.; Habtemariam,
A.; Hitchcock, P. B. J. Organomet. Chem. 1992, 437, 41-55.
(14) Shubert, U. Adv. Organomet. Chem. 1990, 30, 151-187.
Upon warming from -20 °C to room temperature, 7
was quantitatively converted into 3b (eq 7). The reaction
rate in toluene was almost similar to that performed in

Substitution Reactions at a Bridging Silicon Ligand
Organometallics, Vol. 24, No. 4, 2005 525
THF, which implied that 3b was formed by way of a
nonionic pathway; that is, the carboxy group was not
eliminated as a carboxylate anion during the reaction.
When the reaction was carried out in THF/H2O with
excess amount of sodium acetate, a bis(µ-silylene)
complex having an acetoxy group on the bridging silicon
atom was not observed. Instead, complex 3b was formed
in the reaction. This result also implied the intra-
molecular mechanism for the substitution reaction.
Instead, a bis(µ-silylene) complex having a hydroxyl
group on the bridging silicon atom, {Cp*Ru(µ-H)}2{µ-
SiPh(OH)}(µ-SiPh2) (3d), was obtained in this reaction
(ca. 10% by NMR). Complex 3d was likely formed by
the reaction of 3b with H2O (vide infra).
its thermal instability, the structure could not be
determined. However, the broad hydride signal observed
at δ -20.99 in the crude mixture implied that a bis(µ-
silylene) complex was also formed, and ν(CO), which
appeared at 1749 cm-1, also implied that the ethyl group
on the bridging silicon was substituted with the tri-
fluoroacetoxy group.
Nucleophilic Displacement at the Bridging Sili-
con Atom of 3b. The trifluoroacetoxy group of 3b was
readily converted to other functional groups by nucleo-
philic displacement. Treatment of 3b with MeOH re-
sulted in the formation of the bis(µ-silylene) complex
{Cp*Ru(µ-H)}2{µ-SiPh(OMe)}(µ-SiPh2) (3c), containing
a methoxy group on the bridging silicon (eq 8). Complex
A plausible reaction mechanism for the formation of
3b by the reaction of 2a with trifluoroacetic acid is
shown in Scheme 1. Protonation of 2a should take place
first to yield 4a, then the trifluoroacetoxy anion was
coordinated to the metal center. The µ-carboxy inter-
medaite 7 was formed by way of elimination of dihy-
drogen. Oxidative addition of the η2-Si-H bond and
subsequent nucleophilic attack of the coordinated car-
boxy group at the bridging silicon atom took place to
form an intermediate silylene-silyl complex I-2 probably
due to the strong affinity between Si and O. Then, the
Si-C(aryl) bond should be cleaved to yield I-3. The
conversion from I-1 to I-3 would proceed stepwise via
I-2 probably due to the poor leaving ability of the phenyl
group on the silicon. This type of Si-C(aryl) bond
cleavage has been already observed in the reaction of
Cp*Ru(µ-H)4RuCp* (1) with Ph3SiH to yield bis(µ-
diphenylsilylene) complexes {Cp*Ru(µ-SiPh2)(µ-H)}2 (3a)
and {Cp*Ru(µ-H)}2(µ-SiPh2).1d Although substitution
reaction of the Si-C(aryl) group by way of orthometa-
lation of the arylsilyl group has been known for the
monometallic platinum silyl complex,15 the orthometa-
lation path requires a much higher formal oxidation
state for the metal center.
3c was characterized by its 1H, 13C, and 29Si NMR and
IR spectra. Although the structure of 3c was not
determined by X-ray diffraction because of difficulty in
obtaining a single crystal, complex 3c was concluded to
be a trans-bis(µ-silylene) structure like 3a and 3b on
the basis of its spectral data and fluxional behavior.
Complex 3c underwent further addition of methanol,
and a prolonged reaction afforded the zwitterionic η6-
arene complex Cp*Ru+(η6-C6H5[SiPh(OMe){Cp*Ru-(H)2-
Si(OMe)2Ph}]) (8) (eq 9). During the formation of 8, two
Ru-Si bonds were cleaved, and one of the phenyl groups
on the silicon atom coordinated to one of the Ru centers
in an η6-fashion. Thus, complex 8 may be regarded as
an intermediate in the formation of the η6-benzene
complex [Cp*Ru(η6-C6H6)]+ (5) by treatment of 4a with
The diethyl analogue of the cationic bis(µ-silane)
complex 4b also reacted with trifluoroacetic acid in
toluene. Since the product could not be isolated due to
Scheme 1

526 Organometallics, Vol. 24, No. 4, 2005
Takao et al.
methanol, which was apparently formed as a result of
Ru-Si and Si-C(aryl) bond cleavage. Complex 8 was
isolated as a colorless crystalline solid, and the structure
was determined by means of X-ray diffraction studies.
Nucleophilic attack of methoxides at the bridging
silicon atoms leads to cleavage of the Ru-Si bonds and
the Ru-Ru bond, and the Cp*Ru fragment was bound
to one of the phenyl groups on the silicon atom in an
η6-fashion.
Figure 2. Molecular structure of Cp*Ru+(η6-C6H5[SiPh-
(OMe){Cp*Ru-(H)2Si(OMe)2Ph}]) (8) with thermal ellip-
soids at the 30% probability level. The solvent molecules
were omitted for clarity.
The structure of complex 8 is illustrated in Figure 2,
and the relevant bond distances and angles are listed
in Table 2. The two ruthenium atoms are apart from
each other by 5.86 Å, and there is no bonding interaction
between them. Since complex 8 is diamagnetic, the
formal oxidation states of Ru(1) and Ru(2) should be +4
and +2, respectively. Coordination geometry around Ru-
(2) is very similar to that of [Cp*Ru(η6-arene)]+,16 and
the angle among the centroids of the Cp*, Ru(2), and
the centorid of the phenyl group is almost linear
(179.0°). This shows that Ru(2) is charged monocationic
and the Ru(1) center is, therefore, monoanionic.
The coordination geometry around Ru(1) is that of a
four-legged piano stool. Both silicon atoms, Si(1) and Si-
(2), and two hydrogen atoms, H(1) and H(2), are mutu-
ally trans with respect to the Ru(1) center. The partial
structure of 8 around Ru(1) is isoelectronic with trans-
bis(silyl) complexes, Cp*M(SiR3)2(H)2 (M ) Co,17 Rh,18
Ir19) and (η6-C6R6)M(SiR3)2(H)2 (M ) Fe,20 Ru21), on
account of the formal minus charge on Ru(1). A char-
acteristic feature of the structure of 8 is the relatively
short Ru-Si distances, 2.3107(17) Å for Ru(1)-Si(1) and
2.3116(17) Å for Ru(1)-Si(2). Although the Ru-Si bond
lengths lie within the reported range for the Ru-Si
σ-bonds (2.28-2.50 Å),22 they are considerably shorter
than those of (η6-C6Me6)Ru(SiMe3)2(H)2 (2.396(1) and
2.391(1) Å).21 The shortening of the Ru-Si bonds in 8
is most likely due to enhanced dπ-dπ interaction
between Ru(1) and the silicon atoms as a result of an
anionic charge on Ru(1).
Table 2. Selected Bond Distances (Å) and Angles
(deg) for 8
Ru(1)-Si(1)
Ru(2)- C(7)
Ru(2)- C(9)
Ru(2)- C(11)
Si(1)-C(1)
Si(1)-O(1)
Si(2)-O(2)
2.3107(17)
2.293(6)
2.197(7)
2.208(6)
1.886(6)
1.676(4)
1.658(5)
Ru(1)-Si(2)
Ru(2)- C(8)
Ru(2)- C(10)
Ru(2)- C(12)
Si(1)-C(7)
Si(2)-C(14)
Si(2)-O(3)
2.3116(17)
2.225(6)
2.216(6)
2.233(6)
1.924(6)
1.896(7)
1.691(5)
Si(1)-Ru(1)-Si(2) 106.07(6)
Ru(1)-Si(1)-O(1) 118.21(17)
Ru(1)-Si(1)-C(1) 114.82(19) Ru(1)-Si(1)-C(7)
114.84(17)
101.8(2)
O(1)-Si(1)-C(1)
C(1)-Si(1)-C(7)
99.2(3)
105.9(3)
O(1)-Si(1)-C(7)
Ru(1)-Si(2)-O(2) 114.16(16)
Ru(1)-Si(2)-O(3) 117.84(18) Ru(1)-Si(2)-C(14) 117.2(2)
O(2)-Si(2)-O(3)
O(3)-Si(2)-C(14)
104.9(3)
97.8(3)
O(2)-Si(2)-C(14)
102.6(3)
A µ-hydroxysilylene complex, {Cp*Ru(µ-H)}2{µ-SiPh-
(OH)}(µ-SiPh2) (3d), was obtained in 20% yield by the
treatment of 3b with aqueous KOH at ambient tem-
perature for 12 h (eq 10). The reaction is much slower
than that of 3b with MeOH shown in eq 8. While the
reaction of 3b with MeOH was homogeneous and
terminated within 1 h, that of 3b with aqueous KOH
was biphasic and only 36% of 3b was consumed after
12 h. The yield of 3d was estimated at 20% on the basis
of the 1H NMR spectra, and a small amount of uniden-
tified byproducts was formed during the reaction to-
gether with the dinuclear tetrahydride complex 1 (9%
yield). Complex 3d was alternatively synthesized by the
reaction of 4a-OTf, which was prepared in situ by
reaction of 2a with trifluoromethanesulfonic acid, with
adventitious water absorbed on alumina in 56% yield
(15) Chang, L. S.; Johnson, M. P.; Fink, M. J. Organometallics 1991,
10, 1219-1221.
(16) (a) Fagan, P. J.; Ward, M. D.; Calabrese, J. C. J. Am. Chem.
Soc. 1989, 111, 1698-1719. (b) Ward, M. D.; Fagan, P. J.; Calabrese,
J. C.; Johnson, D. C. J. Am. Chem. Soc. 1989, 111, 1719-1732.
(17) Brookhart, M.; Grant, B. E.; Lenges, C. P.; Prosenc, M. H.;
White, P. S. Angew. Chem., Int. Ed. 2000, 39, 1676-1679.
(18) Fernandez, M.-J.; Bailey, P. M.; Bentz, P. O.; Ricci, J. S.;
Koetzle, T. F.; Maitlis, P. M. J. Am. Chem. Soc. 1984, 106, 5458-5463.
(19) Ricci, J. S.; Koetzle, T. F.; Fernandez, M.-F.; Maitlis, P. M.;
Green, J. C. J. Organomet. Chem. 1986, 299, 383-389.
(20) (a) Klabunde, K. J.; Yao, Z.; Hupton, A. C. Inorg. Chim. Acta
1997, 259, 119-124. (b) Yao, Z.; Klabunde, K. J.; Asirvatham, A. S.
Inorg. Chem. 1995, 34, 5289-5294. (c) Yao, Z.; Klabunde, K. J.
Organometallics 1995, 14, 5013-5014. (d) Asirvatham, V. S.; Yao, Z.;
Klabunde, K. J. J. Am. Chem. Soc. 1994, 116, 5493-5494.
(21) Djurovich, P. I.; Carroll, P. J.; Berry, D. H. Organometallics
1994, 13, 2551-2533.
1
(eq 11), and characterized on the basis of the H, 13C,
and 29Si NMR and IR spectra. Although a single crystal
of 3d suitable for the diffraction studies was not
(22) Corey, J. Y.; Braddock-Wilking, J. Chem. Rev. 1999, 99, 175-
292.

Substitution Reactions at a Bridging Silicon Ligand
Organometallics, Vol. 24, No. 4, 2005 527
Scheme 2
obtained, complex 3d was concluded to have the same
structure as 3a and 3b on the basis of the spectral data.
separation is very large (4.12 Å). Thus, to the best of
our knowledge, complex 3d is the first example of a
dimetallosilanol containing a direct metal-metal bond-
ing interaction.
1
In the H NMR spectra of 3d measured in C6D6, the
hydroxy proton was observed at δ 1.30 as a broad peak.
The resonances of the hydride ligands were observed
at δ -20.50 and -20.04 as doublets with JH-H ) 5.8
1
Hz at -50 °C in THF-d8. The H NMR spectra of 3d
showed temperature dependence quite similar to those
1
of 3b and 3c. In the H NMR spectra, the two hydride
ligands in 3b, 3c, and 3d were observed to be inequiva-
lent at low temperature, but these signals coalesced into
one signal at elevated temperature due to rapid ex-
change of the coordination site.
Substitution of a phenyl group on the bridging silyl
group with a hydroxy group would be accelerated by the
cationic charge on the ruthenium center. A similar
reaction has been reported for a platinum silyl com-
plex.15
Site-Exchange of the Hydride Ligands of Bis(µ-
silylene) Complexes. The hydride ligands of the bis-
(µ-silylene) complex 3 mutually exchange coordination
sites via a cis-bis(µ-silylene) intermediate D, as shown
in Scheme 2. We previously reported the hydride site-
exchange reaction in bis(µ-silylene) complexes {Cp*Ru-
(µ-H)}2(µ-SiMe2)(µ-SiPhMe) (3e) and {Cp*Ru(µ-H)(µ-
SiPhMe)}2 (3f-syn), and the activation parameters were
estimated as ∆Hq ) 16.4 ( 0.7 kcal mol-1 and ∆Sq )
15.5 ( 2.7 cal mol-1 K-1 for 3e and ∆Hq ) 16.7 ( 0.4
kcal mol-1 and ∆Sq ) 12.5 ( 1.5 cal mol-1 K-1 for 3f-
syn, respectively (Table 3).1d While 3e and 3f-syn
contain a µ-SiPhMe bridge, the substituents on the
second silylene bridge are different; complex 3e pos-
sesses a µ-SiMe2 bridge in place of the additional
µ-SiPhMe bridge in 3f-syn. Irrespective of the different
combination of substituents on the bridging silicon
atoms in 3e and 3f-syn, activation parameters for the
hydride site-exchange reaction are the same within
experimental error. These facts imply that the electronic
nature of substituents on the bridging silicon does not
influence the activation parameters of the hydride site-
exchange reaction.
Complex 3d is a dimetallosilanol, in which the Si-
OH group is directly bound to the metal atom. Reac-
tivities of metallosilanols, M-Si-OH, have been well
documented by Malisch et al.6f,23 It has been shown that
the metallosilanols are less acidic than organosilanols
due to the strong electron-releasing nature of the metal
fragment, and as a result, the tendency toward self-
condensation is noticeably diminished. Complex 3d is
stable and did not undergo self-condensation similar to
{CpFe(CO)2}2(µ-SiROH) (R ) Me, p-Tol, H, Cl, and OH).
The interatomic distance between the two ruthenium
atoms in {Cp*Ru(µ-H)(µ-SiPh2)}2 (3a) is 2.665 Å.1a,d
Complex 3d would adopt a similar structure to 3a on
the basis of spectral data; therefore, a direct metal-
metal bond seems to exist in 3d. In contrast, bis(ferrio)-
silanol {CpFe(CO)2}}2{µ-Si(H)OH} has no bonding in-
teraction between the two iron atoms, and the Fe-Fe
(23) (a) Malisch, W.; Jehle, H.; Mo¨ller, S.; Saha-Mo¨ller, C.; Adam,
W. Eur. J. Inorg. Chem. 1998, 1585-1587. (b) Malisch, W.; Hofmann,
M.; Kaupp, G.; Ka¨b, H.; Reising, J. Eur. J. Inorg. Chem. 2000, 3235-
3241.

528 Organometallics, Vol. 24, No. 4, 2005
Takao et al.
Table 3. Activation Parameters of the Hydride Site-Exchange Process of Bis(µ-silylene) Complexes
a 29Si{1H} NMR spectra for 3b, 3c, and 3d were recorded at ambient temperature in benzene-d6.
We examined the influence of the substituents on the
fluxional process using the new bis(µ-silylene) complexes
3b-d containing an O-functionalized group on the
bridging silicon atom as the probes. At -65 °C, hydride
signals of 3b appeared at δ -18.50 and -20.17 as two
doublet peaks with JH-H ) 5.6 Hz. They coalesced into
one peak at 10 °C. Activation parameters of this process
were estimated at ∆Hq ) 12.8 ( 0.4 kcal mol-1 and ∆Sq
) 1.9 ( 1.5 cal mol-1 K-1 on the basis of the line shape
analysis. Introduction of the trifluoroacetoxy group
resulted in a decrease of ∆Hq and ∆Sq by ca. 4 kcal/mol
and ca. 10 eu, respectively, in comparison to those of
3e and 3f-syn (Table 3).
The difference in the activation parameters between
3b and 3e most likely stems from the difference in the
electronic nature of the substituents on the silicon atom.
The electron-withdrawing trifluoroacetoxy group re-
duces the electron density at the silicon atom. The effect
of the electronic nature of the substituents was also
reflected in the 29Si NMR spectra. While the 29Si signal
of 3b was observed at δ 137.5, those of the phenylm-
ethylsilylene group of 3e and 3f-syn were observed at
δ 107.9 and 108.2, respectively. The downfield shift of
the 29Si signal of 3b is probably attributable to the
reduction of electron density at the silicon atom due to
introduction of the electron-withdrawing substituent.
Thus, on the basis of the 29Si NMR data, the electron-
withdrawing nature of the substituent on the bridging
silicon atom would lie in the order CF3CO2 > OMe >
OH > Me.
the Si-H bond cleavage due to enhanced back-donation
from the metal center. In contrast, the electron-donating
methyl group on the bridging silicon atom reduces the
back-donation, and as a result, the η2-Si-H coordination
would be favored.
As shown in Table 3, a linear correlation between the
electronic nature of the substituents on the bridging
silicon atom and activation parameters of the hydride
site-exchange process was clearly seen; the electron-
withdrawing substituent OR (R ) CF3CO2, OMe, OH)
on the bridging silicon atom decreases both ∆Hq and ∆Sq
in comparison with the methyl group in 3e and 3f-syn.
Thus, the activation parameters of the fluxional process
would have a close relationship with the strength of the
Si-H bond in the transition state for the site-exchange.
These results indicate that the rate-determining step
of the site-exchange process involves formation and
cleavage of an Si-H bond, and the resonance hybrid of
the transition state is likely influenced by the electronic
nature of the substituents. The reason the parameters
of 3e and 3f-syn were the same was thus attributed to
the µ-SiPhMe bridge common in the structures.
The activation parameters were highly affected by the
electronic nature of the substituents, which strongly
indicates the participation of the transient µ-silyl com-
plex during the site-exchange process of the hydride
ligands of the bis(µ-silylene) complex 3. This also
suggests that the rate-determining step of the site-
exchange process most likely includes the formation and
cleavage of the η2-coordinated Si-H bond (A, C, E, or
F in Scheme 2). Similar transformation of the µ-silylene
ligand to a transient µ-silyl group also has been pro-
posed for the dirhodium complex Rh2(µ-SiRH)H2(CO)2-
(dppm)2 by Eisenberg and co-workers, in which rapid
exchange between the Si-H and Rh-H took place.24
Lichtenberger et al. elucidated that the electronic
nature of the substituents on a silicon atom significantly
influenced the energy level of the σ*(Si-H) as studied
by photoelectron spectroscopy.8 An electron-withdraw-
ing group on the silicon atom has been shown to lower
the energy level of the σ*(Si-H). This would facilitate

Substitution Reactions at a Bridging Silicon Ligand
Organometallics, Vol. 24, No. 4, 2005 529
Conclusion
the bridging silicon atom on the reactivity of the
µ-silylene ligand.
Treatment of the bis(µ-diphenylsilyl) complex 2a with
trifluoroacetic acid in toluene resulted in the exclusive
formation of the mixed-bridging bis(µ-silylene) complex
3b, which contained a trifluoroacetoxy group on the
bridging silicon atom. This is in sharp contrast to
protonation carried out in CH2Cl2, which afforded
cationic bis(µ-silane) complexes. These results mean
that protonation of the bis(µ-silylene) complex was
highly affected by the solvent and nucleophilicity of the
counteranion. Nucleophilic addition of the trifluoro-
acetoxy group to the ruthenium centers was confirmed
by the observation of the intermediate µ-silyl,µ-silylene
complex 7, containing a µ-carboxy group. The carboxy
group would move to the bridging silicon atom, forming
an intermediary µ-silyl group. Subsequent Si-C(aryl)
bond cleavage then resulted in formation of 3b.
Complex 3b is a good precursor for functionalized
µ-silylene complexes. Treatment of 3b with MeOH and
H2O afforded 3c and 3d, which contained a methoxy
and a hydroxy group at the bridging silicon atom,
respectively. There have been quite limited examples
of nucleophilic displacement reaction performed on the
bridging silicon atom, and introduction of the hydroxy
group on the bridging silicon atom by way of protonation
was a novel synthetic method for the dimetallosilanols.
Since the stereochemistry at the bridging silicon of the
bis(µ-silylene) complex 3 was not maintained due to 1,2-
shift of the intermediary µ-silyl group,1d at present the
substitution reaction cannot be precisely clarified as to
whether it proceeds by an SN1 or SN2 mechanism.
Isolation of the various bis(µ-silylene) complexes 3a-
f, which contain various substituents on the bridging
silicon atom, allowed us to understand the fluxional
process of 3 in detail. VT-NMR studies revealed that
the activation parameters were significantly influenced
by the electronegativity of the substituents on the
bridging silicon. An electron-withdrawing substituent
on the bridging silicon atom decreases both ∆Hq and
∆Sq, and an electron-donating one increases them. This
phenomenon can be explained by the mechanism in
which the hydride site-exchange proceeds by the forma-
tion of an intermediate silyl complex as a result of
reductive coupling between the µ-silylene ligand and
hydride. Rotation of the silyl group and oxidative
addition of the Si-H bond should result in formation
of the cis-bis(µ-silylene) intermediate. Subsequent for-
mation of the silyl group by reductive coupling between
the other µ-silylene and hydride ligands would complete
the site-exchange of the hydride ligands.
Formation of the intermediate Si-H bond is relevant
to the formation of a vacant site on the dinuclear
system. If there were substrates that can react with a
bis(µ-silylene) complex, reactivities of the bis(µ-silylene)
complexes should show linear correlation with the
activation parameters obtained by the NMR studies. We
are continuing research on the reactivity of the bis(µ-
silylene) complexes. In particular, we will focus on the
influence of the electronic nature of the substituents on
Experimental Section
General Procedures. All experiments were carried out
under an argon atmosphere. All compounds were handled
using Schlenk techniques. Reagent grade toluene, Et2O, and
THF were dried over sodium-benzophenone ketyl and stored
under an argon atmosphere. Pentane and dichloromethane
were dried over phosphorus pentoxide and stored under an
argon atmosphere. Benzene-d6, toluene-d8, and THF-d8 were
dried over sodium-benzophenone ketyl and stored under an
argon atmosphere. Trifluoroacetic acid and other substrates
were used as received. IR spectra were recorded on a JASCO
FT/IR-5000 spectrophotometer. 1H and 13C NMR spectra were
recorded on JEOL GX-500, Varian Gemini-3000, and Varian
INOVA-400 Fourier transform spectrometers with tetrameth-
ylsilane as an internal standard. Variable-temperature 1H
NMR spectra were recorded on a Varian INOVA-400. 29Si
NMR spectra were recorded on JEOL EX-270 and Varian
INOVA-400 instruments with tetramethylsilane as an external
standard. Elemental analyses were performed by the Analyti-
cal Facility at the Research Laboratory of Resources Utiliza-
tion, Tokyo Institute of Technology. The dinuclear ruthenium
tetrahydride complex Cp*Ru(µ-H)4RuCp* (1),25 the bis(µ-
diphenylsilyl) complex {Cp*Ru(µ-η2-HSiPh2)}2(µ-H)(H) (2a),1a
the bis(µ-diphenylsilylene) complex {Cp*Ru(µ-SiPh2)(µ-H)}2
(3a),1a and the cationic bis(µ-silane) complex [{Cp*Ru(µ-η2:η2-
H2SiR2)}2(µ-H)][X-] (4a, R ) Ph; 4b, R ) Et, X ) CF3SO3,
BPh4)2 were prepared according to previously published meth-
ods. Formation of the cationic η6-benzene complex [Cp*Ru(η6-
C6H6)]+ (5) shown in eq 3 was confirmed on the basis of the
1H NMR data by comparing with the authentic complex
prepared according to previously published methods.5,25a For-
mation of the cationic triruthenium hexahydride complex
[Cp*Ru(µ-H)2]3+ (6) shown in eq 3 was confirmed on the basis
of the 1H NMR data by comparing with the authentic complex
prepared according to the reported method.5
X-ray Structure Determination. X-ray-quality crystals
of 2c and 8 were obtained directly from the preparations
described below and mounted on glass fibers. Diffraction
experiments were performed on a Rigaku RAXIS-RAPID
imaging plate at -20 °C for 2c and on a Rigaku AFC-5R four-
circle diffractometer at 23 °C for 8 with graphite-monochro-
mated Mo KR radiation (λ ) 0.71069 Å), respectively. The
structures of 2c and 8 were solved by a direct method and
subsequent Fourier difference techniques and refined aniso-
tropically for all non-hydrogen atoms by full-matrix least-
squares calculation on F2 using the SHELXL-97 program
package.26 The positions of hydrogen atoms bonded to the
ruthenium atoms of 2c and 8 were located by the sequential
difference Fourier synthesis. Neutral atom scattering factors
were obtained from the standard sources.27 Crystal data and
results of the analyses are listed in Table 4.
Variable-Temperature NMR Spectra and Dynamic
NMR Simulations. Variable-temperature NMR studies were
performed in flame-sealed NMR tubes in toluene-d8 for 3b-d
using a Varian INOVA-400 Fourier transform spectrometer.
NMR simulations for the hydride ligands of 3b-d were
performed using gNMR v4.1.0. (©1995-1999 Ivory Soft). The
1H-1H coupling constants between hydride ligands were
(25) (a) Suzuki, H.; Omori, H.; Lee, D.-H.; Yoshida, Y.; Moro-oka,
Y. Organometallics 1988, 7, 2243-2245. (b) Suzuki, H.; Omori, H.; Lee,
D.-H.; Yoshida, Y.; Fukushima, M.; Tanaka, M.; Moro-oka, Y. Orga-
nometallics 1984, 13, 1129-1146.
(26) (a) Sheldrick, G. M. SHELXS-97, Program for Crystal Structure
Solution; University of Gottingen: Germany, 1997. (b) Sheldrick, G.
M. SHELXL-97, Program for Crystal Structure Solution; University
of Gottingen, Germany, 1997.
(27) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, U.K., 1975; Vol. 4.
(24) (a) Wang, W.-D.; Eisenberg, R. J. Am. Chem. Soc. 1990, 112,
1833-1841. (b) Wang, W.-D.; Eisenberg, R. Organometallics 1992, 11,
908-912. (c) Wang, W.-D.; Hommeltoft, S. I.; Eisenberg, R. Organo-
metallics 1988, 7, 2417-2419.

530 Organometallics, Vol. 24, No. 4, 2005
Takao et al.
30H, Cp*), 8.5-7.0 (m, 15H, Ph). 13C NMR (125 MHz, 23 °C,
THF-d8): δ 10.9 (q, JC-H ) 126.9 Hz, C5Me5), 92.1 (s, C5Me5),
116.2 (q, JC-F ) 289.2 Hz, CF3), 135.9 (d, JC-H ) 159.2 Hz,
Ph), 137.8 (d, JC-H ) 156.7 Hz, Ph), 138.3 (d, JC-H ) 158.4
Hz, Ph), 143.1 (s, Ph-ipso), 145.0 (s, Ph-ipso), 145.1 (s, Ph-
Table 4. Crystallographic Data for 2c and 8
2c
8
(a) Crystal Parameters
formula
fw
cryst syst
space group
a, Å
C40H49F3O2Ru2Si2
C
56H71O3Ru2Si2
877.11
monoclinic
P21/a
14.922(3)
15.2334(18)
17.2535(3)
1050.45
triclinic
P1h
2
ipso), 155.7 (q, JC-F ) 40.4 Hz, COCF3). Whereas 12 signals
were expected to be observed for the three phenyl groups, only
six signals can be identified because of the overlap of the
signals. IR (KBr, cm-1): 3068, 2984, 2902, 1754 (ν(CO)), 1678,
1483, 1429, 1377, 1212, 1164 (ν(CF)), 1096, 1033, 733, 698,
675. Anal. Calcd for C40H47O2F3Ru2Si2: C, 54.90; H, 5.42.
Found: C, 54.96; H, 5.14.
13.3038(19)
17.652(3)
12.608(3)
104.194(17)
110.127(13)
78.481(14)
2673.5(9)
2
b, Å
c, Å
R, deg
â, deg
95.452(8)
γ, deg
Preparation of (Cp*Ru)2(µ-η2-HSiPh2){µ-η2-HSiPh(O-
COCF3)}(µ-H)(H) (2c). A 50 mL flask was charged with
toluene (15 mL) and {Cp*Ru(µ-H)}2{µ-SiPh(OCOCF3)}(µ-
SiPh2) (3b) (0.175 g, 0.20 mmol) under 1 atm of H2. The
solution was stirred for 2 h at 23 °C, and the color of the
solution changed from red to pale orange. After removal of the
solvent in vacuo, a residual solid was extracted three times
with 5 mL of pentane. The combined extracts were then dried
under reduced pressure. Complex 2c was obtained as an
orange crystalline solid (0.153 g, 87% yield). 1H NMR (500
MHz, -90 °C, THF-d8): δ -14.32 (s, 1H, RuHRu or RuH),
-12.86 (s, 1H, RuHSi), -12.46 (s, 1H, RuHSi), -11.40 (s, 1H,
RuHRu or RuH), 1.84 (s, 15H, Cp*), 2.07 (s, 15H, Cp*), 6.7-
7.4 (m, 15H, SiPh). 1H NMR (500 MHz, 50 °C, THF-d8): δ
-12.74 (br, 4H, RuH), 1.96 (s, 30H, Cp*), 2.07 (s, 15H, Cp*),
7.0-7.4 (m, 15H, SiPh). 13C{1H} NMR (100 MHz, 23 °C,
V, Å3
3904.1(12)
Z
4
Dcalcd, g cm-1
temp, °C
µ(Mo KR), cm-1
cryst dimens, mm
1.492
1.305
-20
23
8.82
6.50
0.50 × 0.30 × 0.20
0.20 × 0.10 × 0.10
(b) Data Collection
Rigaku AFC-5R
Mo KR
diffractometer
radiation
Rigaku AFC-5R
Mo KR
(λ ) 0.71069 Å)
graphite
(λ ) 0.71069 Å)
graphite
ω/2θ
monochromator
scan type
2θmax, deg
absorp corr type
no. of reflns measd
no. of reflns obsd
ω/2θ
60.0
empirical
11 077
7197 (I > 2σ)
50.0
æ scan
9389
6611 (I > 2σ)
(c) Refinement
0.0493
benzene-d6): δ 11.8 (C5Me5), 95.8 (C5Me5), 115.9 (q, JC-F
)
R1 [I > 2σ]
0.0651
0.1017
0.1586
0.1774
622
288.0 Hz, CF3), 127.0 (Ph), 127.3 (Ph), 128.8 (Ph), 133.4 (Ph),
134.7 (Ph), 137.0 (Ph), 142.1 (Ph-ipso), 144.7 (Ph-ipso), 146.1
R1 (all data)
wR2 [I > 2σ]
wR2 (all data)
no. of params
GOF on F2
0.0850
0.1034
2
(Ph-ipso), 155.8 (q, JC-F ) 40.2 Hz, COCF3). Whereas 12
0.1145
signals were expected to be observed for the three phenyl
groups, only 9 signals can be identified because of the overlap
of the signals with those of the solvent. 29Si{1H} NMR (54
MHz, 23 °C, benzene-d6): δ 80.5 (µ-SiPh2), 129.4 (µ-SiPhOC-
OCF3). IR (KBr, cm-1): 3064, 2966, 2906, 2060 (ν(RuH)), 1756
(ν(CO)), 1479, 1429, 1381, 1212, 1164 (ν(CF)), 1102, 1027, 737,
698. Anal. Calcd for C40H49O2F3Ru2Si2: C, 54.76; H, 5.64.
Found: C, 54.32; H, 5.71.
552
0.942
1.032
estimated at JH-H ) 5.60 Hz for 3b, 5.67 Hz for 3c, and 5.25
Hz for 3d, respectively. The coupling constants between
hydrides and the bridging silicon atoms were estimated at
2JSi-H ) 4.00-9.00 Hz from the line shapes of satellite signals
around the resonance of the hydride ligands. In the case of
3b, small spin-spin coupling with 19F of the trifluoroacetoxy
group was observed for the hydride signals (JH-F ) 1.10, 0.95
Hz). Final simulated line shapes were obtained via an iterative
parameter search upon the exchange constant k. Full details
of the fitting procedure may be found in the Supporting
Information. The rate constants k that accurately modeled the
experimental spectra at each temperature are also given in
the Supporting Information. The activation parameters ∆Hq
and ∆Sq were determined from the plot of ln(k/T) versus 1/T.
Estimated standard deviations (σ) in the slope and y-intercept
of the Eyring plot determined the error in ∆Hq and ∆Sq,
respectively. The standard deviation in ∆Gq was determined
from the formula σ(∆Gq)2 ) σ(∆Hq)2 + [Tσ(∆Sq)]2 -2Tσ(∆Hq)
σ(∆Sq).
Treatment of {Cp*Ru(µ-η2-HSiPh2)}2(µ-H)(H) (2a) with
Trifluoroacetic Acid in Dichloromethane. A 50 mL flask
was charged with dichloromethane (10 mL) and {Cp*Ru(µ-η2-
HSiPh2)}2(µ-H)(H) (2a) (0.050 g, 0.059 mmol). After the reac-
tion flask was cooled at -78 °C with a dry ice/methanol bath,
trifluoroacetic acid (5 µL, 0.065 mmol) was added with vigorous
stirring. The solution was then slowly warmed to room
temperature. After stirring for 5 min at room temperature, a
large excess amount of NaBPh4 was added. The product was
extracted three times with 10 mL of CH2Cl2, and the combined
extract was passed through Celite on a glass filter. After the
solvent was removed in vacuo, the residual solid was rinsed
five times with 5 mL of pentane. Removal of pentane in vacuo
afforded 54 mg of 4a-BPh4 as a yellow solid (yield 79%).
Identification to 4a-BPh4 was carried out by comparing its
spectral data with that prepared according to the reported
method.2
Preparation of {Cp*Ru(µ-H)}2{µ-SiPh(OCOCF3)}(µ-
SiPh2) (3b). A 100 mL flask was charged with toluene (35
mL) and {Cp*Ru(µ-η2-HSiPh2)}2(µ-H)(H) (2a) (0.999 g, 1.19
mmol). After the reaction flask was cooled at -20 °C, trifluo-
roacetic acid (0.10 mL, 1.30 mmol) was added with vigorous
stirring. The solution was allowed to react for 2 h at -20 °C,
and the color of the solution turned from orange to dark red.
The flask was then warmed to room temperature with bub-
bling argon gas into the solution to remove dihydrogen, and
the solution was stirred for 2 h at 23 °C. The solvent was then
removed under reduced pressure. The red residual solid was
rinsed three times with 5 mL of pentane. The solid was dried
under reduced pressure, and 0.827 g of 3b was obtained as a
Preparation of (Cp*Ru)2(µ-η2-HSiPh2)(µ-SiPh2)(µ-CF3-
CO2)(µ-H)(H) (7). A 50 mL flask was charged with toluene
(5 mL) and {Cp*Ru(µ-η2-HSiPh2)}2(µ-H)(H) (2a) (0.118 g, 0.14
mmol). After the reaction flask was cooled to -20 °C, trifluo-
roacetic acid (11 µL, 0.15 mmol) was added with vigorous
stirring. The solution was allowed to react for 2 h at -20 °C,
and the color of the solution turned from orange to red. The
solvent was removed under reduced pressure at -20 °C. The
brownish-red residual solid was rinsed three times with 2 mL
of methanol. The solid was dried under reduced pressure, and
1
1
red solid (80% yield). H NMR (400 MHz, 21 °C, toluene-d8):
0.115 g of 7 was obtained as a red solid (86% yield). H NMR
δ -19.43 (br, 2H, RuH), 1.40 (s, 30H, Cp*), 7.9-7.0 (m, 15H,
Ph). 1H NMR (400 MHz, -65 °C, toluene-d8): δ -20.17 (d, JH-H
) 5.60 Hz, RuH), -18.50 (d, JH-H ) 5.60 Hz, RuH), 1.39 (s,
(300 MHz, -30 °C, THF-d8): δ -13.35 (s, 1H, RuH), -11.16
(s, 1H, RuH), -4.78 (s, JSi-H ) 60 Hz, 1H, RuHSi), 1.57 (s,
15H, Cp*), 1.63 (s, 15H, Cp*), 7.1-8.3 (m, 20H, Ph). Selective

Substitution Reactions at a Bridging Silicon Ligand
Organometallics, Vol. 24, No. 4, 2005 531
irradiation at each hydride signal at -20 °C did not change
the intensities of the other hydride signals. 13C NMR (125
MHz, -30 °C, THF-d8): δ 12.3 (q, JC-H ) 126.8 Hz, C5Me5),
12.6 (q, JC-H ) 126.8 Hz, C5Me5), 86.5 (s, C5Me5), 96.6 (s, C5-
Me5), 114.9 (q, JC-F ) 285.6 Hz, CF3), 127.1 (d, JC-H ) 160.9
Hz, Ph), 128.0 (d, JC-H ) 157.7 Hz, Ph), 128.5 (d, JC-H ) 158.8
Hz, Ph), 129.0 (d, JC-H ) 157.7 Hz, Ph), 130.0 (d, JC-H ) 158.7
Hz, Ph), 130.7 (d, JC-H ) 156.7 Hz, Ph), 136.0 (d, JC-H ) 157.8
Hz, Ph), 138.2 (d, JC-H ) 157.7 Hz, Ph), 146.6 (s, Ph-ipso),
147.4 (s, Ph-ipso), 147.9 (s, Ph-ipso), 148.8 (s, Ph-ipso), 164.3
(q, 2JC-F ) 41.2 Hz, COCF3). Whereas 16 signals were expected
to be observed for the three phenyl groups, only 12 signals
can be identified because of the overlap of the signals. 29Si
NMR (54 MHz, -30 °C, toluene-d8): δ 75.2 (s, µ-SiPh2), 121.7
(d, JSi-H ) 60 Hz, µ-η2-HSiPh2). IR (KBr, cm-1): 3062, 2996,
2906, 2058 (ν(RuH)), 1702 (ν(CO)), 1482, 1457, 1430, 1380,
1202 (ν(CF)), 1157, 1096, 1029, 859, 733, 700. Anal. Calcd for
C46H53O2F3Ru2Si2: C, 57.95; H, 5.62. Found: C, 57.91; H, 5.47.
Preparation of (Cp*Ru)2(µ-η2-HSiPh2)(µ-SiPh2)(µ-CF3-
CO2)(µ-H)(H) (7) from Cationic Bis(µ-silane) Complex 4a-
BPh4. A 50 mL flask was charged with toluene (20 mL) and
[{Cp*Ru(µ-η2:η2-H2SiPh2)}2(µ-H)][BPh4] (4a-BPh4) (0.104 g,
0.089 mmol). After the reaction flask was cooled to -20 °C,
trifluoroacetic acid (7 µL, 0.093 mmol) was added with vigorous
stirring. The solution was allowed to react for 2 h at -20 °C,
and the color of the solution turned from yellow to red. The
solvent was removed under reduced pressure at -20 °C. The
brownish-red residual solid was rinsed three times with 2 mL
of methanol. The solid was dried under reduced pressure, and
0.111 g of 7 was obtained as a red solid (86% yield).
Preparation of Cp*Ru+[η6-C6H5[SiPh(OMe){Cp*Ru--
(H)2Si(OMe)2Ph}]] (8). A 50 mL flask was charged with
toluene (3 mL) and {Cp*Ru(µ-H)}2{µ-SiPh(OMe)}(µ-SiPh2) (3c)
(0.021 g, 0.026 mmol). Methanol (1 mL) was added with
vigorous stirring at 25 °C and allowed to react for 18 h. The
solvent was removed under reduced pressure. The product was
dissolved in 1 mL of toluene and purified by the use of column
chromatography on neutral alumina (Merck Art. 1097) with
toluene. Removal of the solvent in vacuo afforded 8 as a white
1
crystalline solid (0.021 g, 95% yield). H NMR (300 MHz, 25
°C, benzene-d6): δ -13.90 (s, 1H, RuH), -13.30 (s, 1H, RuH),
1.23 (s, 15H, Cp*), 1.87 (s, 15H, Cp*), 3.40 (s, 3H, OMe), 3.47
(s, 3H, OMe), 4.06 (t, JH-H ) 5.7 Hz, 1H, η6-C6H5Si), 4.12 (s,
3H, OMe), 4.21 (t, JH-H ) 5.7 Hz, 1H, η6-C6H5Si), 4.32 (t, JH-H
) 5.7 Hz, 1H, η6-C6H5Si), 5.54 (d, JH-H ) 5.8 Hz, 1H, η6-C6H5-
Si), 5.66 (d, JH-H ) 5.8 Hz, 1H, η6-C6H5Si), 7.2-8.4 (m, 10H,
Ph). 13C NMR (75 MHz, 25 °C, benzene-d6): δ 10.3 (q, JC-H
)
128.3 Hz, C5Me5), 11.4 (q, JC-H ) 125.6 Hz, C5Me5), 49.5 (q,
JC-H ) 138.3 Hz, OMe), 49.6 (q, JC-H ) 138.3 Hz, OMe), 53.8
(q, JC-H ) 140.2 Hz, OMe), 84.0 (d, JC-H ) 176.4 Hz, η6-C6H5-
Si), 84.1 (d, JC-H ) 173.6 Hz, η6-C6H5Si), 85.1 (d, JC-H ) 170.7
Hz, η6-C6H5Si), 88.9 (d, JC-H ) 170.7 Hz, η6-C6H5Si), 91.6 (d,
JC-H ) 176.4 Hz, η6-C6H5Si), 92.7 (s, C5Me5), 93.3 (s, C5Me5),
117.2 (s, η6-C6H5Si-ipso), 135.4 (d, JC-H ) 150.7 Hz, Ph), 135.7
(d, JC-H ) 159.3 Hz, Ph), 148.3 (s, Ph-ipso), 148.8 (s, Ph-ipso).
Whereas 8 signals were expected to be observed for the two
phenyl groups, only 4 signals can be identified because of the
overlap of the signals and solvent. IR (KBr, cm-1): 3058, 2906,
2812, 1945 (ν(RuH)), 1479, 1381, 1178, 1089, 1029, 698.
Preparation of {Cp*Ru(µ-H)}2{µ-SiPh(OH)}(µ-SiPh2)
(3d). A 50 mL flask was charged with dichloromethane (10
mL) and {Cp*Ru(µ-η2-HSiPh2)}2(µ-H)(H) (2a) (0.105 g, 0.13
mmol). The reaction flask was cooled to -78 °C with a dry
ice/methanol bath. Trifluoromethanesulfonic acid (13 µL, 0.14
mmol) was then added to the solution with vigorous stirring.
The color of the solution quickly turned from orange to bright
yellow. The solution was gently warmed to room temperature
and was allowed to react for 10 min at 25 °C, which resulted
in exclusive formation of the cationic bis(µ-diphenylsilane)
complex 4a-OTf.2 Alumina (Merck Art. 1097) was then added
to the solution, and the color of the solution changed to dark
red. The product was extracted three times with 10 mL of
dichloromethane, and the combined extract was passed through
alumina on a glass filter (Merck Art. 1097). Removal of the
solvent in vacuo afforded 0.044 g of 3d as a brownish-red solid
(56% yield). Although the origin of the hydroxy group found
in 3d was not identified, adventitious water on alumina is most
likely the source of the hydroxy group. 1H NMR (500 MHz, 23
°C, THF-d8): δ -20.29 (br, 2H, RuH), 1.43 (s, 30H, Cp*), 6.7-
8.2 (m, 15H, Ph). 1H NMR (500 MHz, -50 °C, THF-d8): δ
Reaction of (Cp*Ru)2(µ-η2-HSiPh2)(µ-SiPh2)(µ-CF3CO2)-
(µ-H)(H) (7) to 3b in the Presence of Sodium Acetate. A
50 mL flask was charged with (Cp*Ru)2(µ-η2-HSiPh2)(µ-SiPh2)(µ-
CF3CO2)(µ-H)(H) (7, 0.030 mg, 0.032 mmol) and THF (3 mL).
After the reaction flask was cooled at -78 °C with a dry ice/
methanol bath, the solution of sodium acetate (0.026 mg, 0.317
mmol) in H2O/acetone (1:2, 3 mL) was added dropwise to the
flask. The solution was then slowly warmed to room temper-
ature. The solution became homogeneous at -15 °C. After the
solution was allowed to react for 3 h at room temperature, the
solvent was removed under reduced pressure. The product was
extracted three times with 5 mL of toluene, and the combined
extract was passed through Celite on a glass filter. Removal
of the solvent in vacuo afforded 28 mg of brownish solid.
Formation of 3b and 3d was confirmed by the 1H NMR spectra
of the residual solid, and the yield of 3b and 3d was estimated
at 87% and 10%, respectively, on the basis of the 1H NMR
spectra.
Preparation of {Cp*Ru(µ-H)}2{µ-SiPh(OMe)}(µ-SiPh2)
(3c). A 50 mL flask was charged with toluene (3 mL) and
{Cp*Ru(µ-H)}2{µ-SiPh(OCOCF3)}(µ-SiPh2) (3b) (0.056 g, 0.063
mmol). Methanol (1 mL) was added with vigorous stirring at
25 °C and allowed to react for 1 h. The solvent was removed
under reduced pressure. The brownish-red residual solid was
rinsed three times with 2 mL of pentane. The solid was dried
under reduced pressure, and 0.029 g of 3c was obtained as a
-20.50 (d, 1H, JH-H ) 5.8 Hz, RuH), -20.04 (d, 1H, JH-H
)
5.8 Hz, RuH), 1.42 (s, 30H, Cp*), 6.9-8.2 (m, 15H, Ph). The
resonance for OH was not observed when using THF-d8 as
solvent. 1H NMR (300 MHz, 23 °C, benzene-d6): δ -20.03 (br,
2H, RuH), 1.30 (br, 1H, OH), 1.47 (s, 30H, Cp*), 7.1-7.9 (m,
15H, Ph). 13C{1H} NMR (125 MHz, -50 °C, THF-d8): δ 11.2
(C5Me5), 90.8 (C5Me5), 127.3 (Ph), 127.5 (Ph), 127.8 (Ph), 128.5
(Ph), 129.2 (Ph), 136.9 (Ph), 137.1 (Ph), 137.7 (Ph), 137.9 (Ph),
146.6 (Ph-ipso), 147.2 (Ph-ipso), 147.6 (Ph-ipso). IR (KBr,
cm-1): 3400 br (ν(OH)), 3048, 2988, 2906, 1479, 1429, 1378,
1121, 1094, 1029, 926, 908, 740, 702.
1
red solid (58% yield). H NMR (300 MHz, 25 °C, benzene-d6):
δ -20.08 (br, 2H, RuH), 1.47 (s, 30H, Cp*), 3.35 (s, 3H, OMe),
1
7.1-7.9 (m, 15H, Ph). H NMR (400 MHz, -60 °C, toluene-
d8): δ -20.35 (d, JH-H ) 5.7 Hz, 1H, RuH), -19.68 (d, JH-H
)
5.7 Hz, 1H, RuH), 1.49 (s, 30H, Cp*), 3.33 (s, 3H, OMe), 7.1-
8.4 (m, 15H, Ph). 13C NMR (75 MHz, 25 °C, benzene-d6): δ
10.9 (q, JC-H ) 127.2 Hz, C5Me5), 51.6 (q, JC-H ) 141.1 Hz,
OMe), 90.8 (s, C5Me5), 136.7 (d, JC-H ) 159.2 Hz, Ph), 137.6
(d, JC-H ) 157.6 Hz, Ph), 137.7 (d, JC-H ) 158.2 Hz, Ph), 145.8
(s, Ph-ipso), 145.9 (s, Ph-ipso), 146.3 (s, Ph-ipso). Whereas 12
signals were expected to be observed for the three phenyl
groups, only 6 signals can be identified because of the overlap
of the signals and solvent. IR (KBr, cm-1): 3058, 2982, 2906,
1582, 1480, 1429, 1383, 1177, 1127, 1091 (ν(SiO)), 1077, 1031,
822, 735, 700.
Reaction of {Cp*Ru(µ-H)}2{µ-SiPh(OCOCF3)}(µ-SiPh2)
(3b) with Aqueous KOH. A 50 mL flask was charged with
toluene (4 mL) and {Cp*Ru(µ-H)}2{µ-SiPh(OCOCF3)}(µ-SiPh2)-
(3b) (0.036 g, 0.041 mmol). Then 1.0 M aqueous KOH (2 mL,
2.0 mmol) was added to the flask with vigorous stirring. The
solution was allowed to react for 12 h at 25 °C. After the
solvent was removed under reduced pressure, the residual
solid was extracted three times with 10 mL of pentane. The
combined extracts were then dried under reduced pressure,
and 0.025 mg of residual solid including {Cp*Ru(µ-H)}2{µ-

532 Organometallics, Vol. 24, No. 4, 2005
Takao et al.
SiPh(OH)}(µ-SiPh2) (3d), Cp*Ru(µ-H)4RuCp* (1), and unre-
acted 3b was obtained. The yields of 3d and 1 were estimated
at 20 and 9%, respectively, on the basis of the 1H NMR spectra
of the residual solid.
Promotion of Science for Japanese Junior Scientists. We
acknowledge Kanto Chemical Co., Inc., for generous
gifts of pentamethylcyclopentadiene and several kinds
of silanes.
Supporting Information Available: Tables of atomic
coordinates and thermal parameters, bond lengths and angles,
torsion angles, and structure refinement details and ORTEP
drawings of 2c and 8 with full numbering schemes. Param-
eters for the dynamic NMR simulations of 3b-d. This material
is available free of charge via the Internet at http://pubs.acs.org.
Acknowledgment. This work was partially sup-
ported by a Grant-in-Aid for Scientific Research on
Priority Areas (No. 14078101, “Reaction Control of
Dynamic Complexes”) and the 21st Century COE pro-
gram from the Ministry of Education, Culture, Sports,
Science and Technology, Japan. This research was also
supported by fellowships of the Japan Society for the
OM049328H