J. Am. Chem. Soc. 2000, 122, 11511-11512
11511
Scheme 1
Synthesis, Structure, and Silylene Exchange Reaction
of Base-Stabilized Hydrido(silylene)tungsten
Complexes and Rearrangement of
Hydrosilyl(pyridine)tungsten Complexes to the
Base-Stabilized Hydrido(silylene) Complexes via
1,2-Hydrogen Migration
Hiroyuki Sakaba,* Masanori Tsukamoto, Takeshi Hirata,
Chizuko Kabuto, and Hiroshi Horino*
Department of Chemistry, Graduate School of Science
Tohoku UniVersity, Sendai 980-8578, Japan
to rearrange to the hydrido(silylene) complexes via 1,2-hydrogen
migration, and a novel silylene exchange reaction for the hydrido-
(silylene) complexes.
ReceiVed September 9, 1999
There has been considerable recent interest in migration
reactions of transition-metal silyl and silylene complexes. 1,2-
Silyl migration in coordinatively unsaturated disilanyl complexes
has been shown to generate intermediate silyl(silylene) com-
plexes,1-5 and in some cases they are isolated as base-stabilized
silyl(silylene) or bis(silylene) complexes in the presence of
external or intramolecular bases.2b-d,5 1,3-Substituent migration
in the silyl(silylene) intermediates has been proposed in a variety
of reactions.1,2,4-6 Compared to the recent extensive studies on
these migrations, however, investigations focused on 1,2-hydrogen
migration converting a hydrosilyl complex to a hydrido(silylene)
complex are relatively limited,7-9 despite the facts that this
migration process has been postulated as a key step in several
reactions of transition-metal complexes with organosilicon com-
pounds,10 and that the corresponding migration has been estab-
lished in the chemistry of carbene complexes.11 Quite recently
reversible 1,2-hydrogen migration has been shown to occur in a
hydrosilylplatinum complex via an intermediate hydrido(silylene)
complex by low-temperature NMR studies.8a,12 Here we report
the synthesis and structure of base-stabilized hydrido(silylene)-
tungsten complexes via Si-H bond activation of secondary
silanes, the reactivity of hydrosilyl(pyridine)tungsten complexes
We have recently reported the synthesis of cis-Cp*(CO)2-
(MeCN)WMe (2) by the photolysis of Cp*(CO)3WMe (1) in
MeCN and its reactivity to substitution and oxidative addition
reactions.13 The corresponding pyridine complex cis-Cp*(CO)2-
(py)WMe (3), which was conveniently obtained by dissolving 2
in pyridine, reacted immediately with Ph2SiH2 (3 equiv) in C6D6
at room temperature to give exclusively the base-stabilized
hydrido(silylene) complex cis-Cp*(CO)2(H)WdSiPh2‚py (4a)
accompanied by generation of methane (0.16 ppm) (Scheme 1).
In a preparative scale reaction in toluene, 4a was isolated as air-
sensitive orange crystals in 78% yield based on 1, and similar
reactions using Et2SiH2 and MePhSiH2 gave cis-Cp*(CO)2(H)Wd
SiEt2‚py (4b) and cis-Cp*(CO)2(H)WdSiMePh‚py (4c) in 72 and
85% yields, respectively. A possible mechanism for the formation
of 4a-c is shown in Scheme 1. (i) Oxidative addition of the
secondary silane to the coordinatively unsaturated intermediate
generated by dissociation of the pyridine ligand from 3 produces
the hydrido(methyl)silyl intermediate A. (ii) Reductive elimination
of methane forms the unsaturated intermediate B. (iii) 1,2-
Hydrogen migration from the silicon to the tungsten gives the
hydrido(silylene) complex C, which is subsequently coordinated
by pyridine to give the stabilized product 4a-c.
(1) (a) Pannell, K. H.; Cervantes, J.; Hernandez, C.; Cassias, J.; Vincenti,
S. Organometallics 1986, 5, 1056. (b) Jones, K. L.; Pannell, K. H. J. Am.
Chem. Soc. 1993, 115, 11336. (c) Pannell, K. H.; Sharma, H. K.; Kapoor, R.
N.; Cervantes-Lee, F. J. Am. Chem. Soc. 1997, 119, 9315 and references
therein.
(2) (a) Tobita, H.; Ueno, K.; Ogino, H. Chem. Lett. 1986, 1777. (b) Tobita,
H.; Ueno, K.; Shimoi, M.; Ogino, H. J. Am. Chem. Soc. 1990, 112, 3415. (c)
Ueno, K.; Sakai, M.; Ogino, H. Organometallics 1998, 17, 2138. (d) Tobita,
H.; Kurita, H.; Ogino, H. Organometallics 1998, 17, 2844 and references
therein.
(3) Haynes, A.; George, M. W.; Haward, M. T.; Poliakoff, M.; Turner, J.
J.; Boag, N. M.; Green, M. J. Am. Chem. Soc. 1991, 113, 2011.
(4) (a) Mitchell, G. P.; Tilley, T. D.; Yap, G. P. A.; Rheingold, A. L.
Organometallics 1995, 14, 5472. (b) Mitchell, G. P.; Tilley, T. D. Organo-
metallics 1996, 15, 3477.
(5) Nlate, S.; Herdtweck, E.; Fischer, R. A. Angew. Chem., Int. Ed. Engl.
1996, 35, 1861.
(6) Pestana, D. C.; Koloski, T. S.; Berry, D. H. Organometallics 1994, 13,
4173.
(7) (a) Okazaki, M.; Tobita, H.; Ogino, H. Chem. Lett. 1996, 477. (b)
Okazaki, M.; Tobita, H.; Kawano, Y.; Inomata, S.; Ogino, H. J. Organomet.
Chem. 1998, 553, 1.
(8) (a) Mitchell, G. P.; Tilley, T. D. J. Am. Chem. Soc. 1998, 120, 7635.
(b) Mitchell, G. P.; Tilley, T. D. Angew. Chem., Int. Ed. 1998, 37, 2524.
(9) Fickert, C.; Nagel, V.; Kiefer, W.; Mo¨ller, S.; Jehle, H.; Malisch, W.;
Stowasser, R.; Bringmann, G. J. Organomet. Chem. 1998, 566, 225.
(10) (a) Burger, P.; Bergman, R. G. J. Am. Chem. Soc. 1993, 115, 10462.
(b) Esteruelas, M. A.; Nu¨rnberg, O.; Oliva´n, M.; Oro, L. A.; Werner, H.
Organometallics 1993, 12, 3264. (c) Chen, W.; Edwards, A. J.; Esteruelas,
M. A.; Lahoz, F. J.; Oliva´n, M.; Oro, L. A. Organometallics 1996, 15, 2185.
(d) Yamashita, H.; Tanaka, M. Bull. Chem. Soc. Jpn. 1995, 68, 403 and
references therein.
(11) For reversible 1,2-hydrogen migration in carbene complexes, see:
Winter, M. J. Polyhedron, 1989, 8, 1583 and references therein.
(12) After this paper was submitted for publication, the following reports
concerning Si-H activation and 1,2-hydrogen migration to form iridium
silylene complexes have appeared: (a) Peters, J. C.; Feldman, J. D.; Tilley,
T. D. J. Am. Chem. Soc. 1999, 121, 9871. (b) Klei, S. R.; Tilley, T. D.;
Bergman, R. G. J. Am. Chem. Soc. 2000, 122, 1816.
Complexes 4a-c exhibit the characteristic high-field 1H
resonances due to the tungsten hydrides and low-field 29Si
resonances with large coupling constants between Si and 183W.
For instance, 4a gives the hydride signal at -7.70 ppm (1JWH
)
65 Hz) and the 29Si resonance at 94.0 ppm (1JWSi ) 111 Hz). A
similar observation for the 29Si resonance has been reported for
the base-stabilized silyl(silylene)tungsten complex trans-Cp(CO)2-
(Me3Si)WdSiMe2‚HMPA, which shows the 29Si resonances of
the silylene and silyl ligands at 92.5 ppm (1JWSi ) 121 Hz) and
18.6 ppm (1JWSi ) 59 Hz), respectively, and the significant low-
field shift and largely increased coupling constants observed for
the silylene ligand have been recognized as consequences of the
partial double-bond character of the tungsten-silylene bond.2c
In contrast with the reaction of 3 with of Ph2SiH2 in C6D6, the
reaction of cis-Cp*(CO)2(py-d5)WMe (3-d5) with a large excess
of Ph2SiH2 (51 equiv) in pyridine-d5 proceeded slowly to give
two new products 5-d5 and 6-d5 in addition to the expected product
4a-d5 (4a-d5:5-d5:6-d5 ) 15:52:33 at ∼96% conversion after 2
h) (Scheme 2). Complex 6-d5 was gradually converted to 5-d5
with a slight increment of 4a-d5 (4a-d5:5-d5:6-d5 ) 17:79:4 at
complete conversion after 8.5 h). The undeuterated complex 5
was isolated in 34% from the reaction of 3 with the silane in
pyridine and fully characterized as trans-Cp*(CO)2(py)WSiHPh2,
which showed a SiH signal (5.96 ppm, 1JSiH ) 176 Hz), a single
1
CO signal (241.3 ppm), and a 29Si signal (22.4 ppm, JWSi ) 38
Hz) in the NMR spectra in C6D6. Complex 6 was unable to be
isolated, but characterized as cis-Cp*(CO)2(py)WSiHPh2 on the
(13) (a) Sakaba, H.; Ishida, K.; Horino H. Chem. Lett. 1995, 1145. (b)
Sakaba, H.; Ishida, K.; Horino H. Chem. Lett. 1998, 149.
10.1021/ja993279w CCC: $19.00 © 2000 American Chemical Society
Published on Web 11/01/2000