Interconversion among μ-silylene, μ-silyl, and μ-silane diruthenium complexes in the presence of dihydrosilane

Article abstract of DOI:10.1021/om0109814

Irradiation of a toluene solution of[Ru₂(CO)₆-(μ-dppm)(μ-SiTol₂)] (1) in the presence of an excess of Tol₂SiH₂ produced a μ-silyl complex, [Ru₂(CO)₅(SiTol₂H)-(μ-dppm)(μ-n² -HSiTol₂)] (2), which was further converted to a μ-silane complex, [{Ru(CO)₂(SiTol₂H)}₂(μ-dppm)(μ-n² :n²-H₂SiTol₂)] (3), quantitatively. Complex 3 released Tol₂SiH₂ in the presence of CO to regenerate 2, which finally reverted to 1 under thermal conditions. The X-ray crystal structures of 1 and 3 were determined.

Full text of DOI:10.1021/om0109814

1534
Organometallics 2002, 21, 1534-1536
In ter con ver sion a m on g µ-Silylen e, µ-Silyl, a n d µ-Sila n e
Dir u th en iu m Com p lexes in th e P r esen ce of
Dih yd r osila n e
Hisako Hashimoto, Yuichiro Hayashi, Ichihiro Aratani, Chizuko Kabuto, and
Mitsuo Kira*
Department of Chemistry, Graduate School of Science, Tohoku University,
Aoba-ku, Sendai 980-8578, J apan
Received November 13, 2001
Ch a r t 1
Summary: Irradiation of a toluene solution of [Ru2(CO)6-
(µ-dppm)(µ-SiTol2)] (1) in the presence of an excess of
Tol2SiH2 produced a µ-silyl complex, [Ru2(CO)5(SiTol2H)-
(µ-dppm)(µ-η2-HSiTol2)] (2), which was further converted
to a µ-silane complex, [{Ru(CO)2(SiTol2H)}2(µ-dppm)(µ-
η2:η2-H2SiTol2)] (3), quantitatively. Complex 3 released
Tol2SiH2 in the presence of CO to regenerate 2, which
finally reverted to 1 under thermal conditions. The X-ray
crystal structures of 1 and 3 were determined.
Complexes containing an agostic M-H-Si interaction
(three-center-two-electron bond) have been of great
interest in synthetic, structural, and theoretical organo-
metallic chemistry.1 These complexes have attracted
much attention because of their importance not only as
possible key intermediates in catalytic reactions such
as hydrosilylation2 and dehydrogenative polymerization
of silanes3 but also as models for intermediate complexes
in C-H bond activation.4 Although a large number of
such complexes have been reported, dinuclear µ-silane
complexes with two M-H-Si interactions are quite
rare.5-7 Graham and co-workers first suggested the
existence of a µ-silane ligand in the dirhenium complex
Re2(CO)8(µ-η2:η2-H2SiPh2) 30 years ago.5a Among the
known µ-silane complexes, only two dinuclear com-
plexes, [Cp*MX]2(µ-η2:η2-H2SitBu2) (M ) Ru and X )
CO,7a M ) Fe and X ) µ-H;7b Cp* ) η5-C5Me5) were
fully characterized by X-ray crystallography and spec-
troscopic techniques. We report here the synthesis of
new µ-silyl (2, Ru2(CO)5(SiTol2H)(µ-dppm)(µ-η2-HSiTol2);
Chart 1) and µ-silane complexes (3, {Ru(CO)2(SiTol2H)}2-
(µ-dppm)(µ-η2:η2-H2SiTol2)) by the reaction of [Ru2(CO)6-
(µ-dppm)(µ-SiTol2)] (1) with Tol2SiH2 under UV irra-
diation. The present results constitute the first convincing
transformation of a µ-silylene complex to the corre-
sponding µ-silyl and µ-silane complexes without appar-
ent destruction of the µ-silylene-diruthenium ring
skeleton. In the presence of an excess of carbon mon-
oxide, the µ-silane complex 3 reverted thermally to 2
and then to 1.
Complexes 1 and 2 were prepared by the reaction of
Ru3(CO)10(µ-dppm)8 with Tol2SiH2 (5 equiv) at 40 °C
(Scheme 1). These complexes were isolated after their
separation by flash chromatography (on silica gel, eluant
2/1 toluene/hexane) in 46% and 24% yields, respectively,
and characterized by spectroscopy9,10 and X-ray crystal-
lography.11,12 Although 1 and 2 structurally resemble
each other except for a ligand on the Ru-Ru axis, 1 did
not react with Tol2SiH2 up to ca. 60 °C, indicating that
2 was formed without the intermediacy of 1 during the
reaction; at higher temperatures, a complex mixture
containing 2 and unidentified products was obtained.
* To whom correspondence should be addressed. E-mail: mkira@
si.chem.tohoku.ac.jp.
(1) For reviews, see: (a) Schubert, U. Adv. Organomet. Chem. 1990,
30, 151. (b) Corey, J . Y.; Braddock-Wilking, J . Chem. Rev. 1999, 99,
175. For theoretical studies, see for example: (c) Rabaaˆ, H.; Baillard,
Y.-Y.; Schubert, U. J . Organomet. Chem. 1987, 330, 397. (d) Fan, M.-
F.; J ia, G.; Lin, Z. J . Am. Chem. Soc. 1996, 118, 9915. (e) Lin, Z.; Fan,
M.-F. Organometallics 1998, 17, 1092. (f) Delpech, F.; Sabo-Etienne,
S.; Daran, J . C.; Chaudret, B.; Hussein, K.; Marsden, C. J .; Barthelat,
J .-C. J . Am. Chem. Soc. 1999, 121, 6668.
(2) (a) Ojima, I.; Li. Z.; Zhu, J . In The Chemistry of Organic Silicon
Compounds; Rappoport, Z., Apeloig, Y., Eds.; Wiley: New York, 1998;
Chapter 29. (b) Lewis, L. N. J . Am. Chem. Soc. 1990, 112, 5998. (c)
Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis: the Application
and Chemistry of Catalysis by Soluble Transition Metal Complexes;
Wiley: New York, 1992. (d) Lapointe, A. M.; Rix, F. C.; Brookhart, M.
J . Am. Chem. Soc. 1997, 119, 906.
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1992, 114, 5698. (b) Gauvin, F.; Harrod, J . F.; Woo, H.-G. Adv.
Organomet. Chem. 1998, 42, 363. (c) Procopio, L. J .; Carroll, P. J .;
Berry, D. H. J . Am. Chem. Soc. 1994, 116, 177.
(4) (a) Brookhart, M.; Green, M. L. H. J . Organomet. Chem. 1983,
250, 395. (b) Graham, W. A. G. J . Organomet. Chem. 1986, 300, 81.
(c) Luo, X.-L.; Crabtree, R. H. J . Am. Chem. Soc. 1989, 111, 2527. (d)
Crabtree, R. H. Angew. Chem., Int. Ed. Engl. 1993, 32, 789. (e) Cook,
G. K.; Mayer, J . M. J . Am. Chem. Soc. 1994, 116, 1855. (f) Musaev, D.
G.; Morokuma, K. J . Am. Chem, Soc. 1995, 117, 799.
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Soc. 1969, 91, 4568. (b) Graham, W. A. G. J . Organomet. Chem. 1986,
300, 81.
(6) Carreno, R.; Riera, V.; Ruiz, M. A.; J eannin, Y.; Philoche-
Levisalles, M. J . Chem. Soc., Chem. Commun. 1990, 15.
(7) (a) Takao, T.; Yoshida, S.; Suzuki, H.; Tanaka, M. Organo-
metallics 1995, 14, 3855. (b) Ohki, Y.; Kojima, T.; Oshima, M.; Suzuki,
H. Organometallics 2001, 20, 2654.
(8) Bruce, M. I.; Nicholson, B. K.; Williams, M. L. W. Inorg. Synth.
1989, 26, 271.
10.1021/om0109814 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 03/14/2002

Communications
Organometallics, Vol. 21, No. 8, 2002 1535
Sch em e 1
Sch em e 3
Sch em e 2
Interestingly, irradiation of a toluene solution of 1 in
the presence of an excess of Tol2SiH2 using a 450 W
high-pressure mercury arc lamp (λ > 300 nm) in a
sealed Pyrex tube at ca. 5 °C afforded a 1:1 mixture of
two products, 2 and the µ-silane complex 3. Removal of
gaseous CO from the reaction mixture and then ad-
ditional irradiation led to quantitative formation of 3,
which was isolated in 67% yield by recrystallization
(Scheme 2). Complex 3 was characterized by spectros-
copy13 and by X-ray crystallography.14,15
Monitoring the photoreaction of 1 with Tol2SiH2 by
1H NMR spectroscopy showed clearly the stepwise
transformation of 1 to 2 and then to 3 without formation
of any other stable intermediates. As shown in Scheme
3, the reaction is reasonably well understood in terms
of the photochemical dissociation of a CO ligand from 1
followed by the oxidative addition of Tol2SiH2 to form
intermediate A, which rearranges to 2 to balance the
formal oxidation states of the two Ru atoms. Repeating
a similar process from 2 leads to the formation of
µ-silane complex 3.16 It is interesting to note that the
Ru-H hydrides in 2 and 3 have an agostic Si- - -H
interaction with a µ-silylene silicon but not with a side-
bound silyl silicon. The present results provide a novel
process to form agostic Si- - -H(M) bonds, in which the
agostic hydrides are provided by external hydrosilanes.
In this relation, Tessier et al. have suggested the µ-silyl
complex Fe2(CO)5(SiPh2H)(µ-η2-HSiPh2) might be formed
by the thermal reaction of Ph2SiH2 with the postulated
Sch em e 4
complex Fe2(CO)8(µ-SiPh2).17 Suzuki et al. have dem-
onstrated that H2 reacts with [Cp*Ru(µ-SiPh2)(µ-H)]2
under high pressure to produce [Cp*Ru(µ-η2-HSiPh2)]2-
(µ-H)(H), which regenerates the µ-SiPh2 complex when
it is heated.18
When a benzene solution of 3 was allowed to stand
at room temperature in the presence of an excess of CO,
complex 2 was regenerated cleanly with loss of Tol2SiH2.
Upon further heating at 40 °C for 2 days, complete
reversion of 2 to 1 resulted (Scheme 4). Easier release
of Tol2SiH2 from 3 rather than from 2 may suggest that
the terminal silyl group instead of the bridging silylene
is eliminated during the conversion of 3 to 2 and that
of 2 to 1; the reactivity difference between 3 and 2 is in
accord with the trans effect of a silyl group being
stronger than that of the CO group.16
The crystal structures of 1 and 3 determined by X-ray
crystallography are shown in Figures 1 and 2 with
selected bond lengths and angles. In 3, ditolylsilane
bridges two ruthenium atoms almost symmetrically.
The bridging hydrides are observed at 1.58(9) and
1.61(9) Å from Ru1 and Ru2, respectively, and at 1.86(9)
and 1.88(12) Å from Si2 and Si3, respectively. These
Si-H distances are much longer than the covalent Si-H
bond distances of 1.56(9) and 1.57(10) Å in the terminal
silyl groups in 3 but within the corresponding distances
for other reported compounds with apparent M-H-Si
interactions.1 There is no interaction between the
agostic hydrogens and the silyl silicon atoms in 3, as
evidenced by the long distances between these atoms
(9) 1 (yellow crystals): Anal. Calcd for C45H36O6P2Ru2Si: C, 56.01;
H, 3.76. Found: C, 56.35; H, 4.01. For spectral data, see the supporting
information.
(10) 2 (yellow crystals): Anal. Calcd for C58H52O5P2Ru2Si2: C, 60.61;
H, 4.56. Found: C, 60.21; H, 4.95. For spectral data, see the supporting
information.
(11) X-ray analysis of 1: C45H36O6P2Ru2Si; fw 964.95; yellow prism;
monoclinic; space group P21/n (No. 14); a ) 10.842(3) Å, b ) 18.947(5)
Å, c ) 20.201(2) Å, b ) 90.59(3)°, V ) 6468.6(3) Å3; Z ) 4; Fcalcd
)
1.545 g/cm3; µ(Mo KR) ) 8.82 cm-1. The reflection intensities were
collected on a Rigaku/AFC-5R four-circle diffractometer with graphite-
monochromated Mo KR radiation (λ ) 0.710 69 Å) at 150 K. The
structure was solved by direct methods, using SIR 92,12 and refined
by full-matrix least squares on F2. A total of 10 018 reflections were
measured, and of these, 7087 reflections (I > 3.0σ(I)) were used in the
refinement: R ) 0.034, Rw ) 0.072.
(15) Debaerdemaeker, T.; Germain, G.; Main, P.; Refaat, L. S.; Tate,
C.; Woolfson, M. M. MULTAN88: Computer Programs for the Auto-
matic Solution of Crystal Structures from X-ray Diffraction Data;
University of York, York, U.K., 1988.
(12) SIR 92: Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano,
M.; Giacovazzo, C.; Guagliardi, A.; Polidori, G., J . Appl. Crystallogr.
1994, 27, 435.
(13) 3 (yellow crystals): Anal. Calcd for C71H68O4P2Ru2Si3: C, 63.94;
H, 5.14. Found: C, 63.51; H, 5.24. For spectral data, see the supporting
information.
(16) When a mixture of 1 and an excess of (p-t-BuC6H4)2SiH2 in
benzene-d6 was irradiated at 5 °C, the stepwise formation of Ru2(CO)5-
[Si(p-t-BuC6H4)2H](µ-dppm)(µ-η2-HSiTol2) (2a ) and {Ru(CO)2[Si(p-t-
BuC6H4)2H]}2(µ-dppm)(µ-η2:η2-H2SiTol2) (3a ) was observed by NMR
spectroscopy. However, thermal reaction of 3a in the presence of CO
gave several products. These results suggest that the bridging silylene
is intact during these transformations at low temperatures, while at
high temperatures, scrambling occurs between the bridging silylene
and side-bound silyl groups. For experimental details, see the Sup-
porting Information.
(14) X-ray analysis of 3:
C71H68O4P2Ru2Si3; fw 1333.66; yellow
prism; monoclinic; space group P21/ c (No. 14); a ) 12.4237(2) Å, b )
27.4560(9) Å, c ) 21.6781(6) Å, â ) 118.9812(2)°, V ) 6468.6(3) Å3; Z
) 4; Fcalcd ) 1.369 g/cm3; µ(Mo KR) ) 6.20 cm-1. The reflection
intensities were collected on a Rigaku/MSC CCD diffractometer with
graphite-monochromated Mo KR radiation (λ ) 0.710 69 Å) at 150 K.
The structure was solved by direct methods, using MULTAN 88,15 and
refined by full-matrix least squares on F2. A total of 26 327 reflections
were measured, and of these, 10 248 reflections (I > 4.0σ(I)) were used
in the refinement: R ) 0.037, Rw ) 0.076.
(17) Simons, R. S.; Tessier, C. A. Organometallics 1996, 15, 2604.
(18) Takao, T.; Suzuki, H.; Tanaka, M. Organometallics 1994, 13,
2554.

1536 Organometallics, Vol. 21, No. 8, 2002
Communications
F igu r e 2. ORTEP drawing of 3. Thermal ellipsoids are
drawn at 30% probability. Selected bond lengths (Å) and
angles (deg): Ru1-Ru2, 3.0248(7); Ru1-Si1, 2.422(2);
Ru2-Si2, 2.427(2); Ru1-Si3, 2.432(2); Ru2-Si3, 2.408(2);
Ru1-H2, 1.58(9); Ru2-H3, 1.61(9); Si3-H2, 1.86(9); Si3-
H3, 1.88(12); Ru2-Ru1-Si3, 50.97(5); Ru1-Ru2-Si3,
51.67(4); Ru1-Si3-Ru2, 77.36(6).
F igu r e 1. ORTEP drawing of 1. Thermal ellipsoids are
drawn at 30% probability. Selected bond lengths (Å) and
angles (deg): Ru-Ru, 2.9072(8); Ru1-Si1, 2.425(2); Ru2-
Si2, 2.427(2); Ru1-P1, 2.390(2); Ru2-P2, 2.394(2); Ru2-
Ru1-Si3, 53.21(5); Ru1-Si-Ru2, 73.64(6).
24.4 Hz, respectively). The J SiH values are in the range
of those for known complexes having agostic M-H-Si
interactions (20-136 Hz)1,4d,21 but close to the lower end
of the range; the interaction may be comparable to that
in a µ-silyl complex, Fe2(CO)5(SiPh2H)(µ-η2-HSiPh2)
(J SiH ) 48.3 Hz).17 Remarkably, the J SiP value between
the bridging 29Si and 31P nuclei for 3 (13.1 Hz) is less
than half of that for 1 (35.5 Hz); two J SiP values (9.3
and 48.3 Hz) were observed for 2. The smaller J SiP
values would also be a good indication of the Ru-H-Si
bonding. Furthermore, the 29Si resonances for the
bridging silicon nuclei for 2 and 3 (2; 150.4 ppm, 3; 154.8
ppm) are shifted to the higher field compared to that of
µ-silylene complex 1 (172.6 ppm). The high-field shift
of the bridging 29Si resonances can be taken as another
indication of the significant agostic Ru-H-Si interac-
tion in 2 and 3.7
(>2.5 Å). The Ru-Ru distance of 3.0248(7) Å in 3 is near
the longer limit of the reported Ru-Ru single-bond
distances19 and longer than those in µ-silylene complex
1 (2.9072(8) Å) and the known µ-silane diruthenium
complex [Cp*Ru(CO)]2(µ-η2:η2-H2SitBu2) (2.9637(8) Å).7a
The lengthening of the Ru-Ru bond is ascribed to the
strong trans influence of the terminal silyl groups which
occupy positions trans to the Ru-Ru bond. No signifi-
cant differences are found among Ru-Si distances in 1
and 3, despite the difference of the bonding nature; all
the Ru-Si distances were between 2.408 and 2.432 Å.
The IR spectrum (KBr) of 3 showed broad peaks at
1863 cm-1 and 1817 cm-1 assigned to Ru-H-Si stretch-
ing bands, which was confirmed by comparison of the
spectra of 3 and the deuterated complex {Ru(CO)2-
(SiTol2D)}2(µ-dppm)(µ-η2:η2-D2SiTol2) (3-d4).20 For 2, a
broad peak at 1790 cm-1 is assignable to the Ru-H-Si
stretching bands.7
Although significant agostic interaction in 2 and 3 is
evidenced both in the solid state and in solution, the
interaction may be rather weak, as suggested by the
rather small J SiH values of ca. 30 Hz. To elucidate the
whole bonding nature in 1-3, DFT calculations of their
model complexes are now in progress.
The existence of the agostic Ru-H-Si interaction in
2 and 3 in solution was clearly demonstrated by NMR
spectroscopy. The 1H resonances due to the Ru-H
hydrogens in 2 and 3 appeared at -8.87 (d, 2J HP ) 34.2
Hz) and -8.84 ppm (m,2J HP ) 31.0 Hz),13 respectively,
with satellites due to a 29Si nucleus (J SiH ) 36.0 and
Ack n ow led gm en t. This work was supported by the
Ministry of Education, Culture, Sports, Science and
Technology of J apan (Grant-in-Aids for Scientific Re-
search (B) No. 11440185 (M. K.)).
(19) For examples of diruthenium complexes with a silyl or a silylene
ligand, see: (a) Crozat, M. M.; Watkins, S. F. J . Chem. Soc., Dalton
Trans. 1972, 2512. (b) Auburn, M. J .; Holmes-Smith, R. D.; Stobart,
S. R.; Zaworotko, M. J .; Cameron, T. S.; Kumari, A. J . Chem. Soc.,
Chem. Commun. 1983, 1523. (c) Suzuki, H.; Takao, T.; Tanaka, M.;
Moro-oka, Y. J . Chem. Soc., Chem. Commun. 1992, 476. (d) Campion,
B. K.; Heyn, R. H.; Tilley, D. T. Organometallics 1989, 111, 2527. For
the complexes having dppm bridging ligands, see: (e) Colombie, A.;
Lavigne, G.; Bonnet, J .-J . J . Chem. Soc., Dalton Trans. 1986, 899. (f)
Clucas, J . A.; Harding, M. M.; Nicholls, B. S.; Smith, A. K. J . Chem.
Soc., Dalton Trans. 1985, 1835. (g) Coleman, A. W.; J ones, D. F.;
Dixneuf, P. H.; Brisson, C.; Bonnet, J .-J .; Lavigne, G. Inorg, Chem.
1984, 23, 952. (h) Bruce, M. I.; Hinchliffe, J . R.; Humphrey, P. A.;
Surynt, R.; Skelton, B. W.; White, A. H. J . Organomet. Chem. 1998,
552, 109.
Su p p or tin g In for m a tion Ava ila ble: Tables giving de-
tails of the X-ray structure determination, atomic coordinates,
and bond lengths and angles, figures giving thermal ellipsoid
1
plots for 1 and 3, IR spectra of 3 and 3-d4, H NMR spectra of
2, 3, and 3-d4, and text giving experimental details for the
preparation of 1-3 and 3-d4. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM0109814
(20) For spectral data of 3-d4 (yellow crystals), see the supporting
information.
(21) Driess, M.; Reigys, M.; Pritzkow, H. Angew. Chem., Int. Ed.
Engl. 1992, 31, 1510.