Synthesis, structure, and reactivity of hydridobis(silylene)ruthenium(IV)- xantsil complexes (xantsil = (9,9-dimethylxanthene-4,5-diyl)bis(dimethylsilyl)) - A stabilized form of key intermediates in the catalytic oligomerization- deoligomerization of hydrosilanes

Article abstract of DOI:10.1139/v03-151

Ru {K²(Si,Si)-xantsil}(CO)(η⁶-C₆H ₅CH₃) (1) was found to be a catalyst for oligomerization-deoligomerization of HSiMe₂SiMe₃ to give H(SiMe₂)_nMe (n = 1-8 at 90°C for 2 days). Treatment of 1 with HSiMe₂SiMe₂OR (R = Me, f-Bu) led to quantitative formation of Ru{κ³(O,Si,Si)-xantsil}(CO)(H) {(SiMe₂...O(R)...SiMe₂)} (R = Me (2a), t-Bu (2b)), which also worked as a catalyst for oligomerization-deoligomerization of HSiMe₂SiMe₃. Based on these experimental results, a mechanism involving silyl(silylene) intermediates was proposed for the oligomerization-deoligomerization of HSiMe₂SiMe₃. Complex 2a reacted with MeOH in toluene-d₈ to give Ru{κ ²(Si,Si)-xantsil}(CO)(η⁶-toluene-d₈) and Me₂Si(OMe)₂ with evolution of H₂. Under a CO atmosphere, 2a was smoothly converted to its CO adduct Ru{κ ²(Si-Si)-xantsil}(CO)₂(H){(SiMe₂...O(Me) ...SiMe₂)} (3).

Full text of DOI:10.1139/v03-151

1350
Synthesis, structure, and reactivity of
hydridobis(silylene)ruthenium(IV)–xantsil
complexes (xantsil = (9,9-dimethylxanthene-4,5-
diyl)bis(dimethylsilyl)) — A stabilized form of key
intermediates in the catalytic oligomerization–
deoligomerization of hydrosilanes1
Masaaki Okazaki, Jim Josephus Gabrillo Minglana, Nobukazu Yamahira,
Hiromi Tobita, and Hiroshi Ogino
Abstract: Ru{κ2(Si,Si)-xantsil}(CO)(η6-C6H5CH3) (1) was found to be a catalyst for oligomerization–deoligomerization
of HSiMe2SiMe3 to give H(SiMe2)nMe (n = 1–8 at 90 °C for 2 days). Treatment of 1 with HSiMe2SiMe2OR (R = Me,
t-Bu) led to quantitative formation of Ru{κ3(O,Si,Si)-xantsil}(CO)(H){(SiMe2•••O(R)•••SiMe2)} (R = Me (2a), t-Bu
(2b)), which also worked as a catalyst for oligomerization–deoligomerization of HSiMe2SiMe3. Based on these experi-
mental results, a mechanism involving silyl(silylene) intermediates was proposed for the oligomerization–
deoligomerization of HSiMe2SiMe3. Complex 2a reacted with MeOH in toluene-d8 to give Ru{κ2(Si,Si)-
xantsil}(CO)(η6-toluene-d8) and Me2Si(OMe)2 with evolution of H2. Under a CO atmosphere, 2a was smoothly con-
verted to its CO adduct Ru{κ2(Si,Si)-xantsil}(CO)2(H){(SiMe2•••O(Me)•••SiMe2)} (3).
Key words: silylene complex, ruthenium, polysilane, dehydrogenative coupling, oligomerization.
Résumé : On a observé que le Ru{κ2(Si,Si)-xantsil}(CO)(η6-C6H5CH3) (1) est un catalyseur pour l’oligomérisation–
désoligomérisation du HSiMe2SiMe3 conduisant à la formation de H(SiMe2)nMe (n = 1–8, à 90 °C pour deux jours).
Le traitement du composé 1 avec du HSiMe2SiMe2OR (R = Me, t-Bu) conduit à la formation quantitative du
Ru{κ3(O,Si,Si)-xantsil}(CO)(H){(SiMe2•••O(R)•••SiMe2)} (R = Me (2a), t-Bu (2b)) qui peut aussi être utilisé comme
catalyseur pour l’oligomérisation–désoligomérisation du HSiMe2SiMe3. Sur la base de ces résultats expérimentaux, on
propose un mécanisme impliquant des intermédiaires silyl(silylènes) pour l’oligomérisation–désoligomérisation du
HSiMe2SiMe3. Le complexe 2a réagit avec le MeOH dans le toluène-d8 pour donner du Ru{κ2(Si,Si)-xantsil}(CO)(η6-
toluène-d8) et du Me2Si(OMe)2 avec évolution de H2. Sous atmosphère de CO, le composé 2a est facilement trans-
formé en un adduit avec du CO, Ru{κ2(Si,Si)-xantsil}(CO)2(H){(SiMe2•••O(R)•••SiMe2)} (3).
Mots clés : complexe de silylène, ruthénium, polysilane, couplage déshydrogénant, oligomérisation.
[Traduit par la Rédaction] Okazaki et al. 1358
Introduction
of the metal–silicon bonds which participate in the catalytic
pathways (3) and only little attention has been paid to the
possibility of silyl groups as ancillary ligands. Taking ac-
count of its strongly electron-releasing ability and exception-
ally high trans influence (4), the silyl groups could work as
an excellent ancillary ligand that generates an electron-rich
and coordinatively unsaturated metal center (5, 6). Usual
metal–silicon bonds are, however, highly reactive, and the
The chemistry of transition-metal silyl complexes is a
continuously growing field and an area of active research
over the past few decades (1). They have been found as key
intermediates in the metal-mediated catalytic transformation
reactions of organosilicon compounds (1, 2). However, stud-
ies on silyl complexes have mostly focused on the reactivity
Received 26 May 2003. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on 27 October 2003.
M. Okazaki, J.J.G. Minglana,2 N. Yamahira, H. Tobita,3 and H. Ogino.4,5 Department of Chemistry, Graduate School of
Science, Tohoku University, Sendai 980-8578, Japan.
1This article is part of a Special Issue dedicated to Professor John Harrod.
2Present address: Institute of Chemistry, University of the Philippines, Diliman, Quezon City 1101, Philippines.
3Corresponding author (e-mail: tobita@mail.tains.tohuku.ac.jp).
4Corresponding author (e-mail: ogino@agnus.chem.tohoku.ac.jp).
5Present address: Miyagi Study Center, The University of the Air, Sendai 980-8577, Japan.
Can. J. Chem. 81: 1350–1358 (2003)
doi: 10.1139/V03-151
© 2003 NRC Canada

Okazaki et al.
1351
Scheme 1.
rich chemistry of transition-metal silyl complexes is derived
from this reactivity (1). In most cases, the silyl ligands are
lost from the metals as a result of reductive elimination, mi-
gratory insertion, nucleophilic substitution, and so on. To
avoid this drawback of silyl ligands, we designed a new type
of bis(silyl) bidentate ligand “xantsil” (7). Thermolysis of
Ru3(CO)12 and 4,5-bis(dimethylsilyl)-9,9-dimethylxanthene
(xantsil-H2) at 120 °C afforded Ru{κ2(Si,Si)-xantsil}(CO)4
in which three carbonyl ligands can be further replaced with
a η6-toluene ligand on reflux in toluene to give Ru{κ2(Si,Si)-
xantsil}(CO)(η6-C6H5CH3) (1) (Scheme 1). Complex 1 un-
dergoes an extremely facile exchange of the toluene ligand
for a free arene, indicating that 1 can formally become a
source of either 12- or 14-electron, coordinatively unsatu-
rated species (I or II), depending on the coordination mode
of the xantsil ligand (Scheme 2). We report here the
Scheme 2.
1
was flame-sealed and the reaction was monitored by H
NMR spectroscopy. The sample was heated at 60 °C for 3 h
and a red solution was obtained. The H NMR spectral data
showed that 1 was completely consumed and free toluene
and xantsil-H2 were formed as the major products. Unidenti-
fied signals can also be observed but their signals are of low
intensities.
1
catalytic performance of
1
toward oligomerization–
deoligomerization of HSiMe2SiMe3 to give H(SiMe2)nMe
(n = 1–8). We also describe the isolation and reactivity of
the stabilized form of a silyl(silylene) complex, which can
be considered as a key intermediate in the catalytic reaction.
A part of this work has been communicated previously (7b).
Oligomerization–deoligomerization of HSiMe2SiMe3 in
the presence of 1
(a) NMR scale monitoring of the reaction
A Pyrex NMR tube (5 mm o.d.) was charged with 1
(13.4 mg, 0.0246 mmol) and was then attached to a vacuum
line. HSiMe2SiMe3 (65.0 mg, 0.492 mmol) and dichloro-
methane-d2 (800 µL) were trap-to-trap transferred into it.
The NMR tube was flame-sealed and the reaction was moni-
Experimental section
General methods
Infrared spectra were obtained on a Horiba FT-730 spec-
trometer. NMR spectra were recorded on Bruker ARX-300
and AVANCE-300 instruments. Mass spectra were obtained
on JEOL-HX110 and Hitachi M-2500S instruments operat-
ing in the EI mode. All reactions were performed under a
dry nitrogen atmosphere using deoxygenated solvents dried
with appropriate reagents. The organosilicon compounds p-
Tol2SiH2 (8), HSiMe2SiMe3 (9), and HSiMe2SiMe2OR (R =
Me (10), t-Bu (11)) were synthesized according to published
procedures. The complex 1 was synthesized by a procedure
we previously reported (7a).
1
tored by H NMR spectroscopy. At room temperature, the
solution turned yellow in color and several signals corre-
sponding to oligomerization–deoligomerization products
H(SiMe2)nMe appeared. No further changes were observed
after 40 h at room temperature.
(b) GC and GC–MS monitoring of the reaction with a
catalytic amount of 1
HSiMe2SiMe3 (65.0 mg, 0.49 mmol), n-decane (10.0 µL
as an internal standard), and 1 (270 µg, 0.1 mol%) were
placed in a 5 mL flask and the solution was stirred at room
temperature for 2 days. The reaction was monitored by gas
chromatography. Formation of H(SiMe2)nMe in the molar
ratio of 81 (n = 1) : 56 (n = 2) : 11 (n = 3) : 3 (n = 4) : 1
(n = 5) was observed based on the peak areas of the gas
chromatogram. The products were confirmed by GC–MS.
Reaction of 1 with p-Tol2SiH2
A Pyrex NMR tube (5 mm o.d.) was charged with 1
(5.0 mg, 0.00916 mmol) and was then attached to a vacuum
line. p-Tol2SiH2 (19.5 mg, 0.00916 mmol) and chloroform-d
(0.4 mL) were trap-to-trap transferred into it. The NMR tube
© 2003 NRC Canada

1352
Can. J. Chem. Vol. 81, 2003
When the same reaction was performed at 90 °C for 2 days,
formation of products with n of up to 8 were observed in the
molar ratio of 346 (n = 1) : 96 (n = 2) : 83 (n = 3) : 64 (n = 4) :
35 (n = 5) : 13 (n = 6) : 4 (n = 7) : 1 (n = 8). These silicon-
containing products were not isolated.
served at δ 4.51. In this experiment, the products were not
isolated.
Reaction of 2a with CO
A Schlenk tube was charged with 2a (75 mg, 0.13 mmol)
and toluene (12 mL). The solution was degassed by freeze–
pump–thaw cycles and filled with CO introduced from a bal-
loon. The procedure was repeated five times. After stirring
the solution at room temperature for 16 h, volatiles were re-
moved in vacuo. The yellow residue was washed with hex-
ane to afford Ru{κ2(Si,Si)-xantsil}(CO)2{(SiMe2•••O(Me)•••
SiMe2)} (3) as a white solid. Yield: 67 mg, 85%. IR (KBr
pellet, cm–1): 1954 (ν (COasym)). MS (FAB) m/z: 630 (M+,
17), 602 (M+ – CO, 24), 512 (M+ – CO – SiMe2OMe, 64).
1H NMR (300 MHz, C6D6) δ: –3.81 (s, 1H, RuH), 0.40 (s,
12H, SiMe), 1.05 (s, 12H, SiMe), 1.51 (s, 6H, CMe2), 2.33
Synthesis of Ru{κ3(O,Si,Si)-
xantsil}(CO)(H){(SiMe2•••O(Me)•••SiMe2)} (2a)
HSiMe2SiMe2OMe (81.0 mg, 0.546 mmol) was added to
a solution of 1 (150 mg, 0.275 mmol) in CH2Cl2 (2.0 mL).
After 90 min of stirring at room temperature, volatiles were
removed under reduced pressure to give a pale yellow solid.
Washing the solid with hexane three times afforded a color-
less solid that was characterized as Ru{κ3(O,Si,Si)-
xantsil}(CO)(H){(SiMe2•••O(Me)•••SiMe2)} (2a). Yield:
160 mg, 98%. MS (EI, 70 eV) m/z: 602 (M+, 72), 512 (M+ –
HMe2SiOMe, 79), 480 (100). Anal. calcd. for
C25H40RuO3Si4: C 49.88, H 6.70; found: C 49.79, H 6.67.
3
3
(s, 3H, OMe), 7.16 (t, J = 7.4 Hz, 2H, Ar), 7.29 (dd, J =
4
3
4
7.4 Hz, J = 1.6 Hz, 2H, Ar), 7.56 (dd, J = 7.4 Hz, J =
1.6 Hz, 2H, Ar). 13C NMR (75.5 MHz, C6D6) δ: 6.3, 9.8
(SiMe), 27.3 (CMe2), 36.3 (CMe2), 51.4 (OMe), 123.4,
124.9, 131.0, 133.2, 134.6, 160.1 (Ar), 202.2 (CO). 29Si
NMR (C6D6) δ: –8.7 (xantsil), 97.3 (silylene). Anal. calcd.
for C26H40RuO4Si4: C 49.57, H 6.40; found: C 49.04, H
5.98.
Synthesis of Ru{κ3(O,Si,Si)-
xantsil}(CO)(H){(SiMe2•••O(t-Bu)•••SiMe2)} (2b)
HSiMe2SiMe2O-t-Bu (35.0 mg, 0.184 mmol) was added
to a solution of 1 (50.0 mg, 0.0916 mmol) in CH2Cl2
(1.0 mL). After 90 min of stirring at room temperature, the
reaction mixture was treated similarly as described for the
synthesis of 2a to afford 2b as a colorless solid. Yield:
50.0 mg, 84%. MS (EI, 70 eV) m/z: 587 (M+ – t-Bu, 26),
513 (M+ – t-Bu-SiMe2O, 41), 325 (100). Anal. calcd. for
C28H46RuO3Si4: C 52.21, H 7.20; found: C 51.71, H 7.16.
X-ray crystal structure determination of 2b and 3
Intensity data for X-ray crystal structure analysis were
collected at 150 K on a Rigaku RAXIS-RAPID Imaging
Plate diffractometer with graphite-monochromated Mo Kα
radiation. A total of 44 images, corresponding to 220.0° os-
cillation angles, were collected with two different
goniometer settings. Exposure time was 0.30 min for 2b and
2.00 min for 3 per degree. Readout was performed in the
0.100 mm pixel mode. Numerical absorption corrections
were applied on each crystal shape. The structures were
solved by Patterson methods (PATTY) and refined by the
least-squares technique. All non-hydrogen atoms were lo-
cated and refined anisotropically. An atomic coordinate of a
hydrogen atom connected to Ru in 3 was determined by the
difference Fourier synthesis and refined isotropically. Other
hydrogen atoms were placed at their geometrically calcu-
lated positions. Data reduction and refinement were per-
formed using teXsan software packages. Crystallographic
data of 2b and 3 are listed in Table 1.6
Oligomerization–deoligomerization of HSiMe2SiMe3 in
the presence of 2a
A Pyrex tube (7 mm o.d.) was charged with 2a (10 mg,
0.017 mmol), HSiMe2SiMe3 (44 mg, 0.33 mmol), and dec-
ane (10 µL) and was connected to the vacuum line. The tube
was flame-sealed under vacuum and placed in the oil bath at
90 °C. After heating for 2 days, the tube was unsealed in the
glovebox. Formation of H(SiMe2)nMe with the molar ratio
of 12 (n = 1) : 6 (n = 2) : 5 (n = 3) : 5 (n = 4) : 4 (n = 5) : 2
(n = 6) : 3 (n = 7) : 1 (n = 8) was observed based on the
peak areas of the gas chromatogram. These organosilicon
compounds were not isolated.
Reaction of 2a with MeOH in toluene-d8
A Pyrex NMR tube (5 mm o.d.) was charged with 2a
(5.0 mg, 0.0083 mmol) and was then attached to a vacuum
line. Toluene-d8 (0.4 mL) and MeOH (6.7 mL, 0.17 mmol)
were trap-to-trap transferred into it. The NMR tube was
Results and discussion
Reaction of 1 with dihydrosilane
1
flame-sealed and the reaction was monitored by H and 29Si
It has been reported that transition-metal complexes medi-
ate the dehydrogenative coupling of polyhydrosilanes and
(or) redistribution of substituents on silicon atoms (2). The
activity of Ru{κ2(Si,Si)-xantsil}(CO)(η6-toluene) (1) toward
this reaction was first investigated. When a solution of 1 and
excess p-Tol2SiH2 in CDCl3 was heated at 60 °C for 3 h, a
red solution containing xantsil-H2 and toluene as the major
NMR spectroscopy. Within 1 h at room temperature, the sig-
nals of 2a were cleanly replaced by those of Ru{κ2(Si,Si)-
xantsil}(CO)(η6-toluene-d8) (1-d8) and Me2Si(OMe)2. NMR
spectroscopic data of 1 were used to identify 1-d8 while an
authentic sample matched the NMR and GC data for
Me2Si(OMe)2. A singlet signal corresponding to H2 was ob-
6 Supplementary data may be purchased from the Directory of Unpublished Data, Document Delivery, CISTI, National Research Council
Canada, Ottawa, ON K1A 0S2, Canada (http://www.nrc.ca/cisti/irm/unpub_e.shtml for information on ordering electronically). CCDC
210554 (2b) and 210555 (3) contain the crystallographic data for this manuscript. These data can be obtained, free of charge, via
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
U.K.; fax +44 1223 336033; or deposit@ccdc.cam.ac.uk).
© 2003 NRC Canada

Okazaki et al.
Table 1. Crystallographic data of 2b and 3.
1353
Compound
Formula
2b
3
C28H46O3RuSi4
C26H40O4RuSi4
Formula weight
Crystal system
Space group
644.08
Monoclinic
P21 (No. 4)
630.01
Monoclinic
P21/n (No. 14)
a (Å)
b (Å)
c (Å)
18.216(3)
9.634(1)
19.327(2)
109.647(6)
3194.2(7)
4
10.1538(5)
17.1435(8)
18.0994(8)
93.999(3)
3142.9(2)
4
β (°)
V (Å3)
Z
Dcalcd. (g cm–3)
1.339
1.331
Dobserved (g cm–3)
Not measured
Not measured
µ (Mo Kα) (cm–1)
Crystal size (mm)
Radiation
Monochromator
T (°C)
6.67
6.79
0.10 × 0.10 × 0.10
Mo Kα (λ = 0.71069 Å)
Graphite
0.20 × 0.20 × 0.10
Mo Kα (λ = 0.71069 Å)
Graphite
–123
–123
2θ Range (°)
2.2–55.0
3.3–55.0
No. of reflections measured
No. of unique data
23 418
7668 (Rint = 0.066)
25 522
7157 (Rint = 0.052)
No. of parameters refined
650
320
Ra
0.114
0.216
0.075
6219
1.40
0.091
0.93 / –1.01
0.061
0.117
0.034
6061
1.01
0.003
0.47 / –0.55
b
Rw
R1c
No. of reflections to calc R1
Goodness-of-fit indicatord
Largest shift (esd, final cycle)
Max / min resid electron dens (eÅ–3)
aR = Σ (Fo – Fc2) / Σ Fo
2
2
bRw = [Σ w(Fo – Fc2)2 / Σ w(Fo )2]1/2, w = [σc2(Fo ) + (p(Max(Fo , 0) + 2Fc2)/3)2]–1, where p = 0.1130 (2b) and 0.0920 (3).
cR1 = Σ ||Fo| – |Fc|| / Σ |Fo| for I > 2.0σ(I).
2
2
2
2
d[Σ w(|Fo| – |Fc|)2 / (Nobservns – Nvariables)]1/2
.
1
products was obtained (eq. [1]). The H NMR spectrum
showed the signals for xantsil-H2, toluene, and other less-
intense signals of the unidentified by-products, which did
not provide any sign of dehydrogenative coupling or redis-
tribution reaction of the dihydrosilane.
room temperature, and after 2 days, H(SiMe2)nMe (n = 1–5)
was formed in the molar ratio of 81 (n = 1) : 56 (n = 2) : 11
(n = 3) : 3 (n = 4) : 1 (n = 5) (eq. [2]). A similar reaction
performed at 90 °C provided H(SiMe2)nMe (n = 1–8) in the
molar ratio of 346 (n = 1) : 96 (n = 2) : 83 (n = 3) : 64 (n =
4) : 35 (n = 5) : 13 (n = 6) : 4 (n = 7) : 1 (n = 8). The prod-
1
[1]
ucts were also confirmed by H NMR spectral data.
[2]
Reaction of 1 with hydrodisilane
A CD2Cl2 solution of HSiMe2SiMe3 was treated with a
catalytic amount of 1 (5.0 mol%) and the reaction was moni-
tored by 1H NMR spectroscopy. Oligomerization and
deoligomerization occurred to give H(SiMe2)nMe (n = 1–5).
Identification of the oligosilanes was carried out by compari-
son of spectroscopic data with authentic samples (9, 12).7
The reaction was performed using 0.1 mol% of 1 and was
monitored by GC and GC–MS spectroscopy. The
oligomerization–deoligomerization reactions proceeded at
A plausible mechanism for the ruthenium-mediated
oligomerization–deoligomerization of HSiMe2(SiMe2)nMe is
given in Scheme 3. The catalytic reaction proceeds via re-
peated oxidative addition of Si-H, 1,2-silyl migration, and
reductive elimination processes. Initial oxidative addition of
7 1H NMR data for H(SiMe2)nMe (300 MHz, CDCl3) δ n = 3: 0.06 (s, 9H, SiMe3), 0.09 (s, 6H, SiMe2), 0.12 (d, J = 4.5 Hz, 6H, SiMe2H),
3.69 (septet, J = 4.5 Hz, 1H, SiH); n = 4: 0.07 (s, 9H, SiMe3), 0.09 (s, 6H, SiMe2), 0.12 (s, 6H, SiMe2), 0.13 (d, J = 4.5 Hz, 3H, SiMe2H),
3.72 (septet, J = 4.5 Hz, 1H, HSi); n = 5 (C6D6): 0.15 (s, 9H, SiMe3), 0.20 (d, J = 4.5 Hz, 6H, SiMe2H), 0.22 (s, 6H, SiMe2), 0.23 (s, 6H,
SiMe2), 0.26 (s, 6H, SiMe2), 4.11 (septet, J = 4.5 Hz, 1H, SiH); n = 6 (C6D6): 0.16 (s, 9H, SiMe3), 0.20 (d, J = 4.5 Hz, 6H, SiMe2H), 0.23
(s, 6H, SiMe2), 0.25 (s, 6H, SiMe2), 0.30 (s, 6H × 2, SiMe2), 4.11 (septet, J= 4.5 Hz, 1H, SiH).
© 2003 NRC Canada

1354
Can. J. Chem. Vol. 81, 2003
Table 2. NMR and IR spectroscopic data of 2a and 2b.
2a
2b
1H NMR (300 MHz, C6D6) δ
1H NMR (300 MHz, CD2Cl2) δ
Ru-H
SiMe
CMe2
OR
–1.75
–2.23
–0.07(1), 0.67(2), 0.89(3), 1.01(4)
1.21(5), 1.43(6)
2.52 (Me)
0.13(1), 0.59(3), 0.62(4), 0.88(2)
1.24(5), 1.75(6)
1.38 (t-Bu)
ArH
6.97–7.03 (m, 7,8),
7.48 (dd, J = 2.6, 6.1 Hz, 9)
7,12 (t, J = 7.4 Hz, 8),
7.23 (dd, J = 1.6, 7.4 Hz, 7),
7.48 (dd, J = 1.6, 7.4 Hz, 9)
13C{1H} NMR (75.5 MHz, THF-d8) δ
13C{1H} NMR (75.5 MHz, THF-d8) δ
SiMe
CMe2
OR
3.4(1), 4.8(2), 7.7(3), 14.6(4)
23.2(5), 31.9(6), 36.4(13)
52.0 (Me)
6.2(1), 7.2(3), 10.0(4), 14.0(2)
30.7(5), 30.9(6), 35.8(13)
22.6 (CMe3), 92.3 (CMe3)
Ar
124.4, 125.8, 131.4(7, 8, 9), 135.0,
136.4(10, 12), 162.5(11)
204.3
29Si{1H} NMR (59.6 MHz, C6D6) δ
123.5, 124.9, 130.7 (7, 8, 9), 134.4,
136.0(10, 12), 161.9(11)
204.2
29Si{1H} NMR (59.6 MHz, CD2Cl2) δ
CO
Xantsil
Silyene
14.6
15.4
107.4
IR (KBr), v/cm–1
107.6
IR (KBr), v/cm–1
~
~
ν (CO)
1929
1923
urated silylene complex C, which in turn undergoes oxidative
addition of H(SiMe2)mMe to generate hydrido(silyl)(silylene)
intermediate D. 1,2-Migration of the silyl ligand followed by
Si-H reductive elimination regenerates the coordinatively
unsaturated [Ru(xantsil)(CO)] species together with
H(SiMe2)m+1Me. The 1,2-migration steps of the silyl groups
are responsible not only for the cleavage of silicon–silicon
bonds which leads to deoligomerization, but also for the for-
mation of silicon–silicon bonds, which leads to oligomeri-
zation.
Scheme 3.
Transition-metal-mediated redistribution of hydropoly-
silanes have been reported for titanium (13), zirconium (13),
and platinum (14). Complex 1 is the first ruthenium catalyst
that is effective in the redistribution of hydropolysilanes.
Reaction of 1 with HSiMe2SiMe2OMe
The mechanism in Scheme 3 involves the silyl(silylene)
complexes as key intermediates. This kind of complex hav-
ing a metal–silicon double bond is highly reactive and diffi-
cult to isolate but can be internally stabilized by an alkoxy
group (15). Thus, treatment of 1 with HSiMe2SiMe2OR (R =
Me, t-Bu) in CH2Cl2 resulted in the clean formation of
Ru{κ3(O,Si,Si)-xantsil}(CO)(H){SiMe2•••O(R)•••SiMe2} (2a (R =
Me), 2b (R = t-Bu)), which were isolated in 98% and 84%
yields, respectively (eq. [3]). Spectroscopic data of 2a and
2b are summarized in Table 2. Spectroscopic features of 2a
HSiMe2(SiMe2)nMe to
a
coordinatively unsaturated
[Ru(xantsil)(CO)] species gives a hydrido(silyl)ruthenium(IV)
intermediate A, which undergoes 1,2-silyl migration to form
a hydrido(silyl)(silylene) intermediate B. Reductive elimina-
tion of Si-H gives H(SiMe2)nMe and a coordinatively unsat-
© 2003 NRC Canada

Okazaki et al.
1355
Scheme 4.
Table 3. Selected bond lengths (Å) and angles (°) for 2b.
Molecule A
Molecule B
Bond lengths (Å)
Ru—Si(1)
Ru—Si(2)
Ru—Si(3)
Ru—Si(4)
2.395(4)
2.402(4)
2.443(3)
2.424(4)
2.289(8)
1.79(1)
2.407(4)
2.394(4)
2.439(3)
2.425(3)
2.277(8)
1.80(1)
Ru—O(2)
Ru—C(5)
Si(1)—O(1)
Si(2)—O(1)
O(1)—C(1)
O(3)—C(5)
1.813(9)
1.827(9)
1.52(1)
1.810(9)
1.844(9)
1.51(1)
[3]
1.17(2)
1.18(2)
Bond angles (°)
Si(1)-Ru-Si(2)
Si(1)-Ru-Si(3)
Si(1)-Ru-Si(4)
Si(1)-Ru-O(2)
Si(1)-Ru-C(5)
Si(2)-Ru-Si(3)
Si(2)-Ru-Si(4)
Si(2)-Ru-O(2)
Si(2)-Ru-C(5)
Si(3)-Ru-Si(4)
Si(3)-Ru-O(2)
Si(3)-Ru-C(5)
Si(4)-Ru-O(2)
Si(4)-Ru-C(5)
O(2)-Ru-C(5)
Ru-Si(1)-O(1)
Ru-Si(2)-O(1)
Si(1)-O(1)-Si(2)
Si(1)-O(1)-C(1)
Si(2)-O(1)-C(1)
Ru-C(5)-O(3)
67.9(1)
151.1(1)
87.1(1)
93.8(2)
89.0(5)
84.2(1)
154.3(1)
95.0(2)
89.6(5)
119.4(1)
80.6(2)
98.8(5)
80.2(2)
96.0(5)
175.2(6)
98.9(3)
98.2(3)
94.8(4)
132.5(7)
131.6(7)
178(1)
68.0(1)
152.6(1)
83.4(1)
92.7(2)
90.4(5)
85.5(1)
150.3(1)
92.4(2)
88.8(4)
121.3(1)
81.1(2)
96.1(4)
80.6(2)
99.8(4)
176.9(5)
98.9(3)
98.3(3)
94.6(4)
132.9(8)
131.8(8)
177(1)
and 2b are almost the same and, thus, all further discussions
of spectroscopic data refer to 2a. The 29Si{1H} NMR spec-
trum shows two singlet signals at δ 14.6 and 107.4, which
are assigned to the xantsil silicon and silylene silicon atoms,
respectively. The chemical shift of silylene moieties is char-
1
acteristic of base-stabilized silylene complexes (1c). The H
NMR spectrum of 2a shows a singlet at –1.75 ppm that can
be assigned to Ru-H. Four singlet signals for the methyl
groups on silicon atoms appear at –0.07 (6H), 0.67 (6H),
0.89 (6H), and 1.01 (6H), which are assigned to SiMe(1),
SiMe(2), SiMe(3), and SiMe(4), respectively (see Table 2).
The signals of the CMe2 part on xantsil appear
inequivalently at 1.21 (Me(5)) and 1.43 (Me(6)). These as-
signments are established by the combination of 29Si–1H
1
1
COLOC and H NOESY spectra. In the H NOESY spec-
trum, a positive correlation peak is clearly observed between
Ru-H and SiMe(4) resonances, indicating that the Ru-H hy-
drogen atom is located within the SiA-Ru-SiB angle.
data. The IR spectrum shows a strong band at 1929 cm–1 at-
tributable to the CO-stretching vibration mode. Elemental
analysis and mass spectral data are in good agreement with
the formula of 2a.
1
The H NOESY spectrum also shows a negative correla-
tion peak between the signals of methyl groups on the
silylene silicon atoms (Me(1) and Me(2)), implying the
intramolecular exchange process of the methyl groups on the
bis(silylene) ligand. The dynamic process probably involves
the cleavage of a silicon–oxygen bond, followed by rotation
of the resulting donor-free silylene moiety around the ruthe-
nium–silicon double bond to exchange the methyl group en-
vironments (Scheme 4). This mechanism is essentially the
same as those of the exchange of SiMe groups in
Cp(CO)2W{SiMe2•••Do•••SiMe2} (Do = OMe, NEt2) (16)
and Cp*(Me3P)Ru{SiMe2•••OR•••SiMe2} (R = Me, t-Bu)
(11). The strongly electron-releasing xantsil ligand is ex-
pected to make the ruthenium center electron rich. Enhanced
back donation from the metal dπ orbital toward the Si-O σ*
orbital weakens the Si—O bond and accelerates its cleavage
to generate the base-free silyl(silylene) complex E. This in-
termediate E is also stabilized by the electron-rich ruthe-
nium center through back donation from the metal dπ orbital
toward the empty p orbital of the silylene silicon atom.
The 13C{1H} NMR spectrum displays the expected reso-
X-ray structure analysis of 2b
The structure of 2b was unequivocally determined by the
X-ray diffraction study. The crystal contains two independ-
ent molecules A and B, but there is no essential difference
between them. The selected bond lengths and angles for 2b
are listed in Table 3. All further discussions of structural de-
tails refer to molecule A. The ORTEP view of A is shown in
Fig. 1. The Ru-H hydrogen atom could not be located crys-
1
tallographically, but the H NOESY spectrum clearly shows
that it must be found inside the unusually widened Si(3A)-
Ru(A)-Si(4A) angle (119.4(1)°). Thus, the molecule takes a
distorted seven-coordinate pentagonal bipyramid geometry
with the nearly planar arrangement of all four silicon atoms
(mean deviation from the least square Si4 plane: 0.0161 Å).
The xanthene moiety is strongly bent (dihedral angle be-
tween the arene rings C(14A)-C(19A) and C(20A)-C(25A):
136.5°). The bond lengths of Ru-Si (bis(silylene)) (avg.
2.399 Å) are shorter than those of Ru-Si (xantsil) (avg.
1
nances for 2a that are consistent with the H NMR spectral
© 2003 NRC Canada

1356
Can. J. Chem. Vol. 81, 2003
Scheme 5.
Fig 1. An ORTEP drawing of 2b.
2.434 Å), but significantly longer than those of the previ-
ously reported bis(silylene) ruthenium complexes (2.31–
2.33 Å) (17). This lengthening could be due to the trans in-
fluence of silyl groups (4) and (or) to the weaker back dona-
tion from the highly oxidized Ru(IV) center to silicon. The
distance of Ru-O(2A) is 2.289(8) Å, which clearly indicates
that the oxygen atom of the xanthene moiety is coordinated
to the ruthenium center to satisfy the 18-electron rule. Thus,
xantsil in 2b is working as a terdentate ligand.
Catalytic oligomerization–deoligomerization of
HSiMe2SiMe3 in the presence of 2a
To get further convincing evidence in support of the exis-
tence of silyl(silylene) complexes in the catalytic reaction of
eq. [2], we carried out the thermal reaction of HSiMe2SiMe3
in the presence of a catalytic amount of 2a. Indeed,
HSiMe2SiMe3 was converted to H(SiMe2)nMe (n = 1–8) af-
ter 2 days at 90 °C with the molar ratios of 12 (n = 1) : 6
(n = 2) : 5 (n = 3) : 5 (n = 4) : 4 (n = 5) : 2 (n = 6) : 3 (n =
7) : 1 (n = 8). This result clearly showed that the
bis(silylene) complex 2a can be incorporated into the cata-
lytic cycle in Scheme 3.
molecules of Me2Si(OMe)2 via intermediate formation of H.
An intramolecular nucleophilic attack of the methoxy group
in G must also be considered, which leads to the formation
of the silylene complex intermediate I (path b). Nucleophilic
attack of MeOH on a silylene silicon atom in I gives H,
which is finally converted to 1-d8 through an intermolecular
nucleophilic attack by MeOH.
Reaction of 2a with CO
When the reaction of 2a with 1 atm (1 atm =
101.325 kPa) of CO was monitored by means of H NMR
spectroscopy at room temperature, quantitative formation of
3 was observed (eq. [5]). An analytically pure sample was
obtained in 85% yield by washing the residue with hexane.
Reaction of 2a with MeOH
It has been reported that silylene complexes show high re-
activity toward various nucleophiles such as alcohols (18).
The reaction of 2a with MeOH in toluene-d8 was carried out
and monitored by NMR spectroscopy. It proceeded cleanly
to give Ru{κ2(Si,Si)-xantsil}(CO)(η6-toluene-d8) (1-d8) and
Me2Si(OMe)2 with evolution of H2 gas (eq. [4]). Spectro-
scopic data of 1 was used to identify 1-d8, while that of the
authentic sample was used to identify Me2Si(OMe)2.
1
[5]
[4]
In a proposed mechanism for this reaction (Scheme 5), the
highly polarized ruthenium–silylene bond is attacked by
MeOH to give a hydrido(methoxysilyl)ruthenium intermedi-
ate F. Reductive elimination of dihydrogen gives bis(me-
thoxysilyl) complex G. In path a, successive nucleophilic
attacks of excess MeOH toward the silyl silicon atom, fol-
lowed by reductive elimination of H2, gives 1-d8 and two
The X-ray diffraction study of 3 was performed using a
colorless crystal obtained by cooling a toluene–hexane solu-
tion at –30 °C. The structure of 3 is depicted in Fig. 2. The
selected interatomic distances and bond angles for 3 are
listed in Table 4. The distance of Ru-O(4) is 3.581(2) Å, in-
dicating the cleavage of the Ru—O bond in 2a. One CO
molecule is coordinated to the resulting vacant site of the ru-
© 2003 NRC Canada

Okazaki et al.
1357
Fig 2. An ORTEP drawing of 3.
Table 4. Selected interatomic distances (Å)
and bond angles (°) for 3.
Interatomic distances (Å)
Ru—Si(1)
Ru—Si(2)
Ru—Si(3)
Ru—Si(4)
Ru—C(1)
Ru—C(2)
Ru-H(1)
2.4108(6)
2.4191(7)
2.4970(6)
2.4970(7)
1.917(2)
1.918(3)
1.59(4)
Si(1)—O(3)
Si(2)—O(3)
O(1)—C(1)
O(2)—C(2)
Ru•••O(4)
1.802(2)
1.800(2)
1.141(3)
1.142(3)
3.581(2)
Bond angles (°)
Si(1)-Ru-Si(2)
Si(1)-Ru-Si(3)
Si(1)-Ru-C(1)
Si(1)-Ru-C(2)
Si(2)-Ru-Si(3)
Si(2)-Ru-Si(4)
Si(2)-Ru-C(1)
Si(3)-Ru-Si(4)
Si(3)-Ru-C(1)
Si(3)-Ru-C(2)
Si(4)-Ru-C(1)
Si(4)-Ru-C(2)
C(1)-Ru-C(2)
Si(1)-Ru-H(1)
Si(2)-Ru-H(1)
Si(3)-Ru-H(1)
Si(4)-Ru-H(1)
C(1)-Ru-H(1)
C(2)-Ru-H(1)
Ru-Si(1)-O(3)
Ru-Si(2)-O(3)
Si(1)-O(3)-Si(2)
69.73(2)
160.34(2)
87.81(7)
91.13(8)
90.74(2)
159.89(3)
90.01(7)
109.37(2)
90.05(7)
91.07(8)
89.66(7)
89.99(9)
178.9(1)
145(1)
145(1)
54(1)
55(1)
88(1)
thenium center. The hydrogen atom of the Ru—H bond was
located inside the widened Si(3)-Ru-Si(4) angle (109.37(2)°)
by the difference Fourier synthesis and refined isotropically.
Thus, complex 3 also takes a distorted seven-coordinate pen-
tagonal bipyramid geometry with the nearly planar arrange-
ment of all four silicon atoms and one hydrogen atom. The
bond lengths of Ru—Si (silylene) (avg. 2.41 Å) and Ru—Si
(xantsil) (avg. 2.50 Å) are similar to the values of 2b.
92(1)
94.71(6)
94.50(6)
100.09(9)
1
In the H NMR spectrum, the CMe2 portion and the Si-
Me groups on xantsil, as well as the Si-Me groups on the
bis(silylene) ligand each appear as one singlet signal at
δ 1.51 (CMe2, 6H)), 0.40 (SiMe, 12H), and 1.05 ppm (SiMe,
12H), although the assignment of Si-Me groups is not clear.
If complex 3 maintains the crystal structure illustrated in
Fig. 2 in solution without any dynamic behavior, six singlet
signals should appear. However, this is not the case even at
210 K. A likely process is the rapid inversion of the puck-
ered chelate ring of xantsil. This dynamic behavior of 3 is in
sharp contrast with Ru{κ2(Si,Si)-xantsil}(CO)4. In this com-
plex, each of the CMe2 and SiMe2 groups on xantsil shows
two signals at 210 K. On warming, each of them coalesces
and finally becomes a sharp singlet at room temperature
(7a). Other spectroscopic features of 3 resemble those of 2.
vide further evidence for the participation of silyl(silylene)
complexes in the catalytic cycles of the metal-mediated
oligomerization–deoligomerization of hydrodisilanes.
Reactivity of 2a toward CO indicates that complex 2a is
labile and generates a coordinatively unsaturated silylene
complex via dissociation of the xantsil oxygen atom under
mild conditions. A number of metal-mediated stoichiometric
and catalytic transformations of organosilicon compounds
appear to involve coordinatively unsaturated silylene com-
plexes (1, 2, 3, 19). Although synthesis and reactivity of
silylene complexes have been reported, only scattered re-
ports on coordinatively unsaturated ones are available (19).
Complex 3 would be an ideal candidate for examining the
reactivity of coordinatively unsaturated silylene complexes.
Conclusions
Acknowledgments
Over the past few decades, silyl(silylene) complexes have
been proposed as intermediates in the stoichiometric and
catalytic metal-mediated transformation reactions of organo-
silicon compounds (2, 3b). The results described here pro-
This work was supported by Grants-in-Aid for Scientific
Research (Nos. 13440193 and 14204065), Grants-in Aid for
Scientific Research on Priority Area (Nos. 14078202 Reac-
© 2003 NRC Canada

1358
Can. J. Chem. Vol. 81, 2003
S. Ohshitanai, H. Tobita, and H. Ogino. Chem. Lett. 952
(2001); (f) M. Okazaki, S. Ohshitanai, M. Iwata, H. Tobita,
and H. Ogino. Coord. Chem. Rev. 226, 167 (2002); (g) M.
Okazaki, S. Ohshitanai, H. Tobita, and H. Ogino. J. Chem.
Soc. Dalton Trans. 2061 (2002).
tion Control of Dynamic Complexes and 14044010 Exploita-
tion of Multi-Element Cyclic Molecules), and a Grant-in-Aid
for the COE project (Giant Molecules and Complex Sys-
tems, 2002) from the Ministry of Education, Culture, Sports,
Science, and Technology, Japan.
7. (a) H. Tobita, K. Hasegawa, J.J.G. Minglana, L.-S. Luh, M.
Okazaki, and H. Ogino. Organometallics, 18, 2058 (1999);
(b) J.J.G. Minglana, M. Okazaki, H. Tobita, and H. Ogino.
Chem. Lett. 406 (2002).
8. R.A. Benkeser, H. Landesman, and D.J. Foster. J. Am. Chem.
Soc. 74, 648 (1952).
9. (a) M. Kumada, M. Ishikawa, and S. Maeda. J. Organomet.
Chem. 2, 478 (1964); (b) J.V. Urenonvitch and R. West. J.
Organomet. Chem. 3, 138 (1965).
10. K. Ueno, A. Masuko, and H. Ogino. Organometallics, 16,
5023 (1997).
References
1. (a) T.D. Tilley. In The chemistry of organic silicon com-
pounds. Edited by S. Patai and Z. Rappoport. John Wiley and
Sons, New York. 1989. p. 1415; (b) T.D. Tilley. In The silicon-
heteroatom bond. Edited by S. Patai and Z. Rappoport. John
Wiley and Sons, New York. 1991. p. 245 and p. 309; (c) M.S.
Eisen. In The chemistry of organic silicon compounds. Vol. 2.
Edited by Z. Rappoport and Y. Apeloig. John Wiley and Sons,
New York. 1998. p. 2037; (d) J.Y. Corey and J. Braddock-
Wilking. Chem. Rev. 99, 175 (1999).
2. (a) M.D. Curtis and P.S. Epstein. Adv. Organomet. Chem. 19,
213 (1981); (b) J.Y. Corey. Adv. Silicon Chem. 1, 327 (1991);
(c) H. Yamashita and M. Tanaka. Bull. Chem. Soc. Jpn. 68,
403 (1995).
3. (a) P. Braunstein and M. Knorr. J. Organomet. Chem. 500, 21
(1995); (b) K.H. Pannell and H.K. Sharma. Chem. Rev. 95,
1351 (1995).
4. (a) J. Chatt, C. Eabon, and S. Ibekwe. J. Chem. Soc. Chem.
Commun. 700 (1966); (b) R.N. Haszeldine, R.V. Parish, and
J.H. Setchfield. J. Organomet. Chem. 55, 279 (1973); (c) L.A.
Latif, C. Eabon, and A.P. Pidcock. J. Organomet. Chem. 474,
217 (1994).
11. H. Wada, H. Tobita, and H. Ogino. Chem. Lett. 993 (1998).
12. Y. Moteki. MSc. Thesis, Tohoku University, Sendai, Japan,
1996.
13. (a) E. Hengge, M. Weinberger, and Ch. Jammegg. J. Organo-
met. Chem. 410, C1 (1991); (b) E. Hengge and M. Weinberger.
J. Organomet. Chem. 433, 21 (1992); (c) E. Hengge and M.
Weinberger. J. Organomet. Chem. 443, 167 (1991).
14. (a) K. Yamamoto, H. Okinoshima, and M. Kumada. J. Organo-
met. Chem. 23, C7 (1970); (b) K. Yamamoto, H. Okinoshima,
and M. Kumada. J. Organomet. Chem. 27, C31 (1971); (c) H.
Yamashita, M. Tanaka, and M. Goto. Organometallics, 11,
3227 (1992).
15. H. Ogino. Chem. Rec. 2, 291 (2002).
5. (a) M.J. Auburn, R.D. Holmes-Smith, and S.R. Stobart. J. Am.
Chem. Soc. 106, 1314 (1984); (b) M.J. Auburn and S.R.
Stobart. Inorg. Chem. 24, 318 (1985); (c) M.J. Auburn, S.L.
Grundy, S.R. Stobart, and M.J. Zaworotko. J. Am. Chem. Soc.
107, 266 (1985); (d) F.L. Joslin and S.R. Stobart. J. Chem.
Soc. Chem. Commun. 504 (1989); (e) G.W. Bushnell, M.A.
Casado, and S.R. Stobart. Organometallics, 20, 601 (2001);
(f) X. Zhou and S.R. Stobart. Organometallics, 20, 1898
(2001); (g) S.R. Stobart, X. Zhou, R. Cea-Olivares, and A.
Toscano. Organometallics, 20, 4766 (2001).
6. (a) M. Okazaki, H. Tobita, and H. Ogino. Organometallics, 15,
2790 (1996); (b) M. Okazaki, H. Tobita, and H. Ogino. Chem.
Lett. 437 (1997); (c) M. Okazaki, H. Tobita, and H. Ogino. J.
Chem. Soc. Dalton Trans. 3531 (1997); (d) M. Okazaki, H.
Tobita, and H. Ogino. Chem. Lett. 69 (1998); (e) M. Okazaki,
16. K. Ueno, A. Masuko, and H. Ogino. Organometallics, 18,
2694 (1999).
17. (a) H. Tobita, H. Wada, K. Ueno, and H. Ogino. Organo-
metallics, 13, 2545 (1994); (b) H. Tobita, H. Kurita, and H.
Ogino. Organometallics, 17, 2844 (1998).
18. M. Okazaki, H. Tobita, and H. Ogino. Dalton Trans. 493 (2003).
19. For group 10 transition metal triads, silylene complexes with
16e have been reported: (a) B. Gehrhus, P.B. Hitchcock, M.F.
Lappert, and H. Maciejewski. Organometallics, 17, 5599
(1998); (b) J.D. Feldman, G.P. Mitchell, J.-O. Nolte, and T.D.
Tilley. J. Am. Chem. Soc. 120, 11 184 (1998); (c) W.A.
Herrmann, P. Härter, C.W.K. Gstöttmayr, F. Bielert, N. See
both, and P. Sirsch. J. Organomet. Chem. 649, 141 (2002).
© 2003 NRC Canada