9702
J. Am. Chem. Soc. 2001, 123, 9702-9703
High Oxidation-State (Formally d0) Tungsten Silylene
Complexes via Double Si-H Bond Activation
Scheme 1. Syntheses of Tucked Cp* Complex 1 and Doubly
Tucked Cation 2
Benjamin V. Mork and T. Don Tilley*
Department of Chemistry
UniVersity of California, Berkeley
Berkeley, California 94720-1460
ReceiVed July 3, 2001
Transition metal silylene complexes are of interest as silicon
analogues of metal carbenes, and as possible intermediates in a
number of metal-catalyzed transformations involving organosili-
con compounds.1 In metal carbene chemistry, it is well established
that the reactivity and electronic structure of the CR2 ligand (R
) H, alkyl, or aryl) are highly dependent on the nature of the
metal fragment to which it is bound.2 Late transition metal carbene
complexes are typically electrophilic at carbon, while early metal
centers often give rise to nucleophilic carbene ligands. To date,
a number of base-free transition metal dialkyl and diaryl silylene
complexes have been synthesized, and these feature ruthenium,3
osmium,4 iridium,5,6 and platinum7,8 in relatively high dn con-
figurations (n g 6). In general, these late metal silylene complexes
have been shown to be very electrophilic at silicon. Thus, it is of
interest to investigate silylene complexes involving strongly
π-donating early transition metal centers with low dn configura-
tions. Such species may exhibit novel chemical properties for the
metal silylene fragment, opening pathways to new transformations
for organosilicon compounds. Our efforts to synthesize base-free
silylene complexes of the more electropositive early transition
metals initially focused on the group 6 metals, and herein we
report base-free tungsten silylene complexes of the type [Cp*-
(dmpe)(H)2WdSiR2][B(C6F5)4], (Cp* ) η5-C5Me5, dmpe ) Me2-
PCH2CH2PMe2). These compounds were prepared with use of a
new, reactive tungsten-based synthon featuring a doubly metalated
Cp* ligand. Previously, base-stabilized silylene complexes of the
Cp′W(CO)2 fragment (Cp′ ) C5H5, C5Me5) have been reported.9,10
We have established routes to platinum and iridium silylene
complexes involving activation of two silicon-hydrogen bonds
of a hydrosilane, via oxidative addition and subsequent R-elimina-
tion.5,8 Significantly, this route requires access to coordinatively
unsaturated metal centers (eq 1).
Given the promise of this silylene-extrusion reaction as a general
route to metal silylene complexes, we sought to synthesize d0
examples via reactions of hydrosilanes with coordinatively
unsaturated but inherently electron-rich fragments of the type
[Cp*L2W]+.11 A possible precursor to such a fragment is Cp*-
(Me3P)(η2-Me2PCH2)W(H)Cl, which appears to be in equilibrium
with Cp*(Me3P)2WCl.12 In an attempt to develop a route to the
[Cp*(dmpe)W]+ fragment, Cp*WCl413 was reduced with 3.0 equiv
of Na/Hg (0.8% w/w) in the presence of dmpe. This procedure
afforded crystalline orange-red (η6-C5Me4CH2)(dmpe)W(H)Cl (1)-
in 75% yield after recrystallization from pentane (Scheme 1).
Thus, unlike Cp*(Me3P)2WCl, which undergoes intramolecular
C-H activation of a phosphine ligand, 16-electron Cp*(dmpe)-
WCl degrades via metalation of the Cp* ligand.14,16 The NMR
spectra of 1 reflect the absence of mirror or rotational symmetry.
For example, the four methyl groups of the dmpe ligand give
rise to individual doublet resonances at δ 0.98, 1.23, 1.29, and
1.53 in the 1H NMR spectrum. Compound 1 was also character-
ized by X-ray crystallography.15
Reaction of 1 with [Li(OEt2)2.5][B(C6F5)4] in fluorobenzene
under argon gives [(η7-C5Me3(CH2)2)(dmpe)W(H)2][B(C6F5)4], 2,
(Scheme 1), a rare example of a “doubly tucked” Cp* metal
LnM + R2SiH2 f Ln(H)2MdSiR2
(1)
(1) (a) Tilley, T. D. In The Silicon-Heteroatom Bond; Patai, S., Rappoport,
Z., Eds.; Wiley: New York, 1991, pp 245. (b) Tilley, T. D. In The Chemistry
of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: New
York, 1989, p 1415. (c) Tilley, T. D. Comments Inorg. Chem. 1990, 10, 37.
(d) Zhang, Z. Y.; Sanchez, R.; Pannell, K. H. Organometallics 1995, 14, 2605.
(e) Sharma, H. K.; Pannell, K. H. Chem. ReV. 1995, 95, 1351. (f) Pannell, K.
H.; Cervantes, J.; Hernandez, C.; Cassias, J.; Vincenti, S. Organometallics
1986, 5, 1056. (g) Pannell, K. H.; Rozell, J. M.; Hernandez, C. J. Am. Chem.
Soc. 1989, 111, 4482. (h) Pannell, K. H.; Wang, L. J.; Rozell, J. M.
Organometallics 1989, 8, 550. (i) Tobita, H.; Ueno, K.; Ogino, H. Bull. Chem.
Soc. Jpn. 1988, 61, 2797. (j) Ueno, K.; Tobita, H.; Ogino, H. Chem. Lett.
1990, 369. (k) 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. (l)
Tanaka, Y.; Yamashita, H.; Tanaka, M. Organometallics 1995, 14, 530. (m)
Mitchell, G. P.; Tilley, T. D.; Yap, G. P. A.; Rheingold, A. L. Organometallics
1995, 14, 5472. (n) Mitchell, G. P.; Tilley, T. D. Organometallics 1996, 15,
3477. (o) Tamao, K.; Sun, G. R.; Kawachi, A. J. Am. Chem. Soc. 1995, 117,
8043.
(2) (a) Crabtree, R. H. The Organometallic Chemistry of the Transition
Metals, 2nd ed.; Wiley Interscience: New York, 1994. (b) Collman, J. P.;
Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and Applications of
Organotransition Metal Chemistry, 2nd ed.; University Science Books: Mill
Valley, California, 1987. (c) Nugent, W. A.; Mayer, J. M. Metal-Ligand
Multiple Bonds; Wiley Interscience: New York, 1988.
(3) Grumbine, S. K.; Mitchell, G. P.; Straus, D. A.; Tilley, T. D.; Rheingold,
A. L. Organometallics 1998, 17, 5607.
(4) Wanandi, P. W.; Glaser, P. B.; Tilley, T. D. J. Am. Chem. Soc. 2000,
122, 972.
(5) Peters, J. C.; Feldman, J. D.; Tilley, T. D. J. Am. Chem. Soc. 1999,
121, 9871.
(6) Klei, S. R.; Tilley, T. D.; Bergman, R. G. J. Am. Chem. Soc. 2000,
122, 1816.
(7) Feldman, J. D.; Mitchell, G. P.; Nolte, J. O.; Tilley, T. D. J. Am. Chem.
Soc. 1998, 120, 11184.
(8) Mitchell, G. P.; Tilley, T. D. Angew. Chem. Int. Ed. 1998, 37, 2524.
(9) Ueno, K.; Sakai, M.; Ogino, H. Organometallics 1998, 17, 2138.
(10) Sakaba, H.; Tsukamoto, M.; Hirata, T.; Kabuto, C.; Horino, H. J. Am.
Chem. Soc. 2000, 122, 11511.
(11) In this discussion, a d0 silylene complex is one in which invocation
of two metal-based electrons in bonding to the silylene ligand results in a d0
electron configuration. Of course, it should also be possible to obtain silylene
complexes in which the metal atom uses all of its valence electrons in bonding
to other ligands (as with the novel silylenes that are stable as free species and
act as primarily σ-donors).
(12) Baker, R. T.; Calabrese, J. C.; Harlow, R. L.; Williams, I. D.
Organometallics 1993, 12, 830.
(13) Murray, R. C.; Blum, L.; Liu, A. H.; Schrock, R. R. Organometallics
1985, 4, 953.
(14) Examples of metallated Cp* complexes: (a) Bercaw, J. E. J. Am.
Chem. Soc. 1974, 96, 5087. (b) Bulls, A. R.; Schaefer, W. P.; Serfas, M.;
Bercaw, J. E. Organometallics 1987, 6, 1219. (c) Schock, L. E.; Brock, C.
P.; Marks, T. J. Organometallics 1987, 6, 232.
(15) See Supporting Information for details of X-ray crystallographic
characterization.
(16) Cloke, F. G. N.; Green, J. C.; Green, M. L. H.; Morley, C. P. J. Chem.
Soc., Chem. Commun. 1985, 14, 945.
10.1021/ja0165436 CCC: $20.00 © 2001 American Chemical Society
Published on Web 09/01/2001