Paramagnetic vanadium silyl complexes: Synthesis, structure, and reactivity

Article abstract of DOI:10.1021/om800712k

Vanadium silyl complexes of the type Cp(dmpe)VSiHRR′ are formed by reaction of Cp(dmpe)VMe (1) with RR′SiH₂ (2, R, R′ = Ph; 3, R = Mes, R′ = H) in benzene at room temperature with concomitant release of CH₄ gas. These complexes are paramagnetic, with high-spin d³ configurations, and exhibit broad ¹H NMR resonances. They possess three-legged piano-stool geometries, and each silicon atom adopts a tetrahedral structure with no agostic V ... HSi interaction. The V-Si bond length of 2 is 2.5629(8) A, and the V-P bond lengths are 2.4613(8) and 2.4621(8) A. A KIE value of 2.1 ± 0.1 was observed for the reaction of Cp(dmpe)VCH₂Ph (4) with Ph₂SiH₂/Ph ₂SiD₂ at room temperature. The reaction of 2 with Ph ₂SiHCl in benzene resulted in silyl group exchange to give Cp(dmpe)VSiClPh₂ (5) in 82% yield. A vanadium(III) silyl complex was obtained by oxidation of 5 with Ph₃CCl to give Cp(dmpe)V(Cl) SiClPh₂ (6). The V-Si and V-Cl bond lengths of 6 are 2.573(1) and 2.388(1) A, respectively. The Si-Cl bond length of 2.160(1) A is longer than those typically observed (ca. 2.023 A). Reaction of 2 with CO afforded Cp(dmpe)V(CO)₂ (7) via homoleptic cleavage of the V-Si bond. The reaction of 5 with Li(Et₂O)₃B(C₆F ₅)₄ generated what appears to be the silylene complex [Cp(dmpe)VSiPh₂]B(C₆F₅)₄, on the basis of elemental analysis.

Full text of DOI:10.1021/om800712k

Organometallics 2008, 27, 5717–5722
5717
Paramagnetic Vanadium Silyl Complexes: Synthesis, Structure, and
Reactivity
Akihiro Shinohara, Jennifer McBee, Rory Waterman, and T. Don Tilley*
Department of Chemistry, UniVersity of California, Berkeley, California 94720
ReceiVed July 27, 2008
Vanadium silyl complexes of the type Cp(dmpe)VSiHRR′ are formed by reaction of Cp(dmpe)VMe
(1) with RR′SiH2 (2, R, R′ ) Ph; 3, R ) Mes, R′ ) H) in benzene at room temperature with concomitant
release of CH4 gas. These complexes are paramagnetic, with high-spin d3 configurations, and exhibit
1
broad H NMR resonances. They possess three-legged piano-stool geometries, and each silicon atom
adopts a tetrahedral structure with no agostic V · · · HSi interaction. The V-Si bond length of 2 is 2.5629(8)
Å, and the V-P bond lengths are 2.4613(8) and 2.4621(8) Å. A KIE value of 2.1 ( 0.1 was observed
for the reaction of Cp(dmpe)VCH2Ph (4) with Ph2SiH2/Ph2SiD2 at room temperature. The reaction of 2
with Ph2SiHCl in benzene resulted in silyl group exchange to give Cp(dmpe)VSiClPh2 (5) in 82% yield.
A vanadium(III) silyl complex was obtained by oxidation of 5 with Ph3CCl to give Cp(dmpe)V(Cl)SiClPh2
(6). The V-Si and V-Cl bond lengths of 6 are 2.573(1) and 2.388(1) Å, respectively. The Si-Cl bond
length of 2.160(1) Å is longer than those typically observed (ca. 2.023 Å). Reaction of 2 with CO afforded
Cp(dmpe)V(CO)2 (7) via homoleptic cleavage of the V-Si bond. The reaction of 5 with Li(Et2O)3B(C6F5)4
generated what appears to be the silylene complex [Cp(dmpe)VSiPh2]B(C6F5)4, on the basis of elemental
analysis.
Common synthetic pathways to stable complexes containing
a transition-metal-silicon bond involve oxidative addition or
σ-bond metathesis of the Si-H bond of a hydrosilane.2,4 For
the application of such methods in the synthesis of vanadium
silyl complexes, the vanadium hydrocarbyl derivatives Cp-
(dmpe)VR, Cp(PMe3)2VR2, and Cp(dmpe)V(CHCMe3) (dmpe
) 1,2-bis(dimethylphosphino)ethane; R ) Me, nBu, Ph),
reported by Teuben and co-workers,5 were targeted. As reported
here,thesecompoundswereusedtopreparenewvanadium-silicon-
bonded complexes, which have been characterized by structural
and reactivity studies.
Introduction
Since the synthesis of the first transition-metal silyl complex,
CpFe(CO)2SiMe3, by Wilkinson and co-workers in 1956,1 this
area has undergone extensive development.2 It is now widely
appreciated that silyl complexes are important intermediates in
a variety of transformations involving organosilanes. However,
despite the importance of compounds with metal-silicon bonds
in catalysis, only a few vanadium silyl complexes, such as
(CO)5VSiH3, Cp2V(SiCl3)2, and CpV(dN-t-Bu)(NH-t-Bu)Si-
(SiMe3)3, have been reported, and very little is known about
the chemistry of such compounds.2,3 For example, compounds
with vanadium-silicon bonds have not been structurally
characterized by single-crystal X-ray crystallography.2d Un-
doubtedly, the paramagnetism associated with much of orga-
nometallic vanadium chemistry has contributed to the lack of
progress in this area.
Results and Discussion
Synthesis and Characterization of Vanadium Silyl
Complexes. Treatment of a solution of Cp(dmpe)VMe (1) with
1 equiv of Ph2SiH2 in benzene at room temperature resulted in
a dark red solution and the rapid release of CH4 gas. Workup
of this solution allowed for isolation of the vanadium silyl
complex Cp(dmpe)VSiHPh2 (2) in 74% yield as red-brown
crystals (eq 1). In a similar manner, addition of 1 equiv of
* To whom correspondence should be addressed. E-mail: tdtilley@
berkeley.edu.
(1) Piper, T. S.; Lemal, D.; Wilkinson, G. Naturwissenschaften 1956,
43, 129.
(2) For reviews on transition-metal silyl complexes, see: (a) Tilley, T. D.
In The Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z.,
Eds.; Wiley: New York, 1989; Chapter 24. (b) Tilley, T. D. In The Silicon-
Heteroatom Bond; Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1991;
Chapter 10. (c) Eisen, M. S. In The Chemistry of Organic Silicon
Compounds; Rappoport, Z., Apeloig, Y., Eds.; Wiley: New York, 1998;
Chapter 35. (d) Corey, J. Y.; Braddock-Wilking, J. Chem. ReV. 1999, 99,
175. (e) Pannell, K. H.; Sharma, H. K. Chem. ReV. 1995, 95, 1351. (f)
Reichl, J. A.; Berry, D. H. AdV. Organomet. Chem. 1999, 43, 197.
(3) (a) Cardoso, A. M.; Clark, R. J. H.; Moorhouse, S. J. Organomet.
Chem. 1980, 186, 241. (b) Snee, P. T.; Yang, H.; Kotz, K. T.; Payne, C. K.;
Harris, C. B. J. Phys. Chem. A 1999, 103, 10426. (c) Allinson, J. S.; Aylett,
B. J.; Colquhoun, H. M. J. Organomet. Chem. 1976, 112, C7. (d) Kreisel,
V. G.; Seidel, W. Z. Anorg. Allg. Chem. 1981, 478, 106. (e) Preuss, F.;
Wieland, T.; Perner, J.; Heckmann, G. Z. Naturforsch., B 1992, 47b, 1355.
(f) Ignatov, S. K.; Rees, N. H.; Merkoulov, A. A.; Dubberley, S. R.;
Razuvaev, A. G.; Mountford, P.; Nikonov, G. I. Chem. Eur. J. 2008, 14,
296.
(4) (a) Peters, J. C.; Feldman, J. D.; Tilley, T. D. J. Am. Chem. Soc.
1999, 121, 9871. (b) Mork, B. V.; Tilley, T. D. J. Am. Chem. Soc. 2001,
123, 9702. (c) Mork, B. V.; Tilley, T. D. Angew. Chem., Int. Ed. 2003, 42,
357. (d) Mork, B. V.; Tilley, T. D.; Schultz, A. J.; Cowan, J. A. J. Am.
Chem. Soc. 2004, 126, 10428. (e) Woo, H.-G.; Walzer, J. F.; Tilley, T. D.
J. Am. Chem. Soc. 1992, 114, 7047. (f) Sadow, A. D.; Tilley, T. D. Angew.
Chem., Int. Ed. 2003, 42, 803. (g) Spaltenstein, E.; Palma, P.; Kreutzer,
K. A.; Willoughby, C. A.; Davis, W. M.; Buchwald, S. L. J. Am. Chem.
Soc. 1994, 116, 10308. (h) Jiang, Q.; Carroll, P. J.; Berry, D. H.
Organometallics 1991, 10, 3648.
(5) (a) Hessen, B.; Teuben, J. H.; Lemmen, T. H.; Huffman, J. C.;
Caulton, K. G. Organometallics 1985, 4, 946. (b) Hessen, B.; Lemmen,
T. H.; Luttikhedde, H. J. G.; Teuben, J. H.; Petersen, J. L.; Huffman, J. C.;
Jagner, S.; Caulton, K. G. Organometallics 1987, 6, 2354. (c) Hessen, B.;
Meetsma, A.; Teuben, J. H. J. Am. Chem. Soc. 1989, 111, 5977. (d) Hessen,
B.; Buijink, J.-K. F.; Meetsma, A.; Teuben, J. H.; Helgesson, G.; Hakansson,
M.; Jagner, S. Organometallics 1993, 12, 2268.
10.1021/om800712k CCC: $40.75
2008 American Chemical Society
Publication on Web 10/01/2008

5718 Organometallics, Vol. 27, No. 21, 2008
Shinohara et al.
Scheme 1
MesSiH3 (Mes ) 2,4,6-Me3C6H3) to a benzene solution of 1
afforded Cp(dmpe)VSiH2Mes (3) in 64% yield. Although these
primary and secondary silanes readily gave vanadium silyl
complexes, tertiary silanes, such as triphenylsilane and trieth-
ylsilane, did not react with 1 at room temperature in benzene
over 1 day. Heating compound 1 with these tertiary silanes at
60 °C for 1 h resulted in decomposition. The V(II) silyl
complexes 2 and 3 are soluble in aromatic solvents, and 3 is
moderately soluble in pentane. These compounds are stable
under an inert atomosphere at room temperature, both in the
solid state and in solution. Heating a solution of 2 in benzene-
d6 at 100 °C for 13 h resulted in partial decomposition to
intractable vanadium-containing products, including Ph2SiH2 and
free dmpe.
Two possible reaction pathways for the formation of 2 and 3
from the interaction of 1 with silanes are σ-bond metathesis
(path a, Scheme 1) and oxidative addition followed by reductive
elimination (path b). To further characterize the reaction
mechanism of this process, a kinetic isotope effect (KIE) was
obtained by measuring the relative rates of the reaction of
Cp(dmpe)VCH2Ph (4) with excess Ph2SiH2 and Ph2SiD2 in a
1:1 ratio. The benzyl complex 4 was found to undergo reactions
analogous to those of 1, but at a slower rate. With compound
4, the release of toluene may be monitored by NMR spectros-
copy, and this allows for the determination of a KIE. It was
independently determined that toluene does not react with the
product 2 under the reaction conditions. After a benzene-d6
solution of 4 and Ph2SiH2/Ph2SiD2 was stirred for 24 h at 23
°C, the volatile components were vacuum-transferred to a J.
Young NMR tube and the ratio of toluene/toluene-d was
measured by 1H NMR spectroscopy. The KIE observed for this
reaction was 2.1 ( 0.1 (average of three runs). Whereas this
value indicates that the Si-H bond is broken in a rate-
determining step, it does not allow differentiation between the
two mechanisms of Scheme 1.
Reactions of the V(III) compounds Cp(PMe3)2VMe2,
Cp(PMe3)V(CH2CMe3)2, and Cp(dmpe)V(dCHCMe3) with
Ph2SiH2 did not proceed at room temperature, and heating the
reaction mixtures at 60 °C resulted in decomposition of the
starting materials. These results suggest that V(III) alkyl and
alkylidene complexes may be less suitable as precursors to
vanadium silyl complexes.
1
Complexes 2 and 3 exhibit broad H NMR resonances, as
expected for paramagnetic V(II) complexes.5 For complex 2,
the chemical shifts for the P-Me groups of the dmpe ligand
were observed at -3.32 (∆ν1/2 ) 3800 Hz) and 24.36 ppm
(∆ν1/2 ) 3800 Hz), and overlapping resonances for the ethylene
group appeared at 29.30 and 31.74 ppm. In addition, resonances
for the silicon-bound Ph groups were observed at 5.08 (∆ν1/2
) 2000 Hz) and 11.11 ppm (∆ν1/2 ) 870 Hz), while the
hydrogen on the silicon atom was not observed. The 1H NMR
spectrum of 3 contained mesityl group resonances at 6.39 ppm
(∆ν1/2 ) 480 Hz, aromatic H), -6.25 ppm (∆ν1/2 ) 500 Hz,
p-Me), and -1.84 ppm (overlapping with peaks for the Me
groups of dmpe, o-Me). The 1H NMR signals for the Cp ligands
were not observed; such resonances for similar CpV complexes
are typically observed at very low field.5,6 The infrared ν(SiH)
stretching frequencies for 2 and 3 are observed at 1984 and
1991 cm-1, respectively. These values are relatively low with
respect to those of many other metal silyl derivatives2d but are
in the range expected for metal complexes involving the more
electropositive early transition metals. For example,
Cp2Ti(H)(SiHPh2)(PMe3)4g exhibits a ν(SiH) stretching fre-
quency of 1924 cm-1, and corresponding values for the tantalum
silyls Cp2Ta(H)(SiHMe2)2 and Cp2Ta(SiH2Me)(PMe3) are 1985
and 1976 cm-1, respectively.4h
The addition of 1 equiv of MesSiH3 to a benzene-d6 solution
of 2 at room temperature resulted in an equilibrium mixture of
2, 3, Ph2SiH2, and MesSiH3 (Keq ≈ 0.6, by 1H NMR spectros-
copy).8 Cooling the reaction mixture in toluene-d8 to -80 °C
provided no evidence for reaction intermediates (such as
oxidative addition products).
Vanadium complexes with a halogen-substituted silyl group
are of interest as precursors to vanadium silylene complexes,
via exchange of the halide for a noncoordinating ion, because
this route has previously been used to obtain cationic silylene
complexes of various transition metals.9 Thus, an attempt was
made to prepare Cp(dmpe)VSiClPh2, by addition of 1 equiv of
Ph2SiHCl to a benzene solution of 1. This resulted in a rapid
color change of the solution to dark green; however, the product
isolated from solution was Cp(dmpe)VCl, as determined by
comparison of spectra with those previously reported by
Teuben.5 The silicon-containing product of this reaction is
Ph2SiHMe (ca. 90% from 1H NMR spectroscopy). Reaction of
1 with Ph2SiMeCl also gave Cp(dmpe)VCl, as well as Ph2SiMe2
(ca. 90% yield from 1H NMR spectroscopy). The mechanisms
The solution magnetic moments of compounds 2 (µeff ) 3.3
µB) and 3 (µeff ) 3.5 µB), determined by the Evans method,7
are slightly lower than the calculated spin-only value for d3
complexes (µeff ) 3.8 µB). Nonetheless, these values strongly
support the characterization of 2 and 3 as high-spin d3
complexes.
(6) Ko¨hler, F. H. J. Organomet. Chem. 1976, 110, 235.
(7) (a) Evans, D. F. J. Chem. Soc. 1959, 2003. (b) Baker, M. V.; Field,
L. D.; Hambley, T. W. Inorg. Chem. 1988, 27, 2872.
(8) The equilibrium constant Keq was difficult to accurately determine
from 1H NMR data, due to the broadness of the resonances and overlapping
of Si-H peaks; Keq
VSiH2Mes][Ph2SiH2].
) [Cp(dmpe)VSiHPh2][MesSiH3]/[Cp(dmpe)-

Paramagnetic Vanadium Silyl Complexes
Organometallics, Vol. 27, No. 21, 2008 5719
of these reactions are currently unknown, but possibilities
include oxidative addition of the Si-Cl bond, followed by
Si-Me reductive elimination, and a more concerted exchange
of Me and Cl groups between the V and Si centers.
Fortunately, it proved possible to prepare Cp(dmpe)VSiClPh2
(5) by an alternate procedure involving reaction of Ph2SiHCl
with 2 at room temperature (eq 3). This reaction afforded
Ph2SiH2 and 5 in 82% yield as a dark brown solid. The structure
of 5 is further supported by its reaction with LiAlH4 in Et2O/
benzene, which gave the expected product 2, albeit in low yield
1
(ca. 5% by H NMR). Complex 5 was also obtained by the
silyl-exchange reaction of 3 with Ph2SiHCl, which gave
1
MesSiH3 and 5 in 83% yield. Monitoring this reaction by H
NMR spectroscopy provided no evidence for an equilibrium
process, as observed in the related interconversion of 2 and 3
(vide supra).
A vanadium(III) silyl complex was obtained by a one-electron
oxidative addition to complex 5. Addition of Ph3CCl to a
benzene solution of 5 gave complex 6, Cp(dmpe)V(Cl)SiClPh2,
as a purple solid in 77% yield (eq 4). An additional product,
observed by 1H NMR spectroscopy, was trityl dimer.10 The 16-
electron complex 6 is paramagnetic and sparingly soluble in
common organic solvents. However, pure samples were obtained
by crystallization from benzene.
Figure 1. ORTEP drawings of Cp(dmpe)VSiHPh2 (2), with thermal
ellipsoids drawn at the 50% probability level: (a) general view with
hydrogen atoms, except for those on the silicon atom, omitted for
clarity; (b) view along the V-Cp(centroid) axis with groups on
the Si and P atoms removed for clarity. Selected bond distances
(Å) and angles (deg): V-Si ) 2.5629(8), V-P2 ) 2.4621(8),
V-P1 ) 2.4613(8), Si-H ) 1.45(3), Si-C1 ) 1.915(2), Si-C2
) 1.913(2), V-Cp(centroid) ) 1.946; P1-V-P2 ) 81.68(3),
P2-V-Si ) 87.67(3), P1-V-Si ) 92.82(3), V-Si-H ) 115(1),
V-Si-C1 ) 116.93(8), V-Si-C2 ) 117.55(8).
Molecular Structures of Vanadium Silyl Complexes. The
structures of 2, 3, and 6 were determined by X-ray crystal-
lography (Figures 1-3). To our knowledge, these are first
examples of crystallographically determined structures for
vanadium-silicon-bonded complexes.
Complex 2 possesses a three-legged piano-stool geometry
with a V-Si bond length of 2.5629(8) Å, a value which falls
between typical Ti-Si (ca. 2.69 Å) and Cr-Si (ca. 2.38 Å)
bond lengths.2d The conformation about the Si atom is ap-
proximately tetrahedral, as defined by V-Si-H, V-Si-C1, and
V-Si-C2 bond angles of 115(1), 116.93(8), and 117.55(8)°,
respectively. The silicon-bound hydrogen atom was located from
the Fourier difference map, and this allowed determination of
a Si-H bond length of 1.46(3) Å. There is no evidence for an
agostic interaction involving the Si-H bond, as indicated by
the position of the silicon-bound hydrogen atom and by the
presence of roughly similar V-Si–R angles (vide supra). The
V-P distances of 2.4613(8) and 2.4621(8) Å are quite similar
to those of Cp(dmpe)VMe (2.462(1) and 2.470(1) Å).5 The
average V-C(Cp) bond distance in 2 is slightly shorter than
that of Cp(dmpe)VMe (2.279(3) vs 2.300(4) Å) but rather
similar to the corresponding distance in vanadocene (average
2.260 Å).11
The structure of 3 is very similar to that of 2. However, as
shown by Newman projections, 2 is staggered about the V-Si
bond, while 3 adopts a more eclipsed structure (Chart 1). The
staggered nature of the bonding about the V-Si bond of 2 is
described by a Cp(centroid)-V-Si-H torsion angle of 178(1)°.
Note that there are two independent molecules (rotamers) in
the unit cell of 3, one of which is shown in Figure 2. The
Cp(centroid)-V-Si-C torsion angles associated with these
molecules are 2(1) and 134(1)°. The V-Si bond lengths
observed for the two independent molecules in the unit cell are
2.576(2) and 2.577(2) Å. The Si-H bond lengths observed for
3 (average 1.42(3) Å) are similar to that found in 2, and there
is no interaction between this bond and the vanadium center.
(9) (a) Straus, D. A.; Tilley, T. D.; Rheingold, A. L.; Geib, S. J. J. Am.
Chem. Soc. 1987, 109, 5872. (b) Grumbine, S. D.; Tilley, T. D.; Arnold,
F.; Rheingold, A. L. J. Am. Chem. Soc. 1993, 115, 7884. (c) Straus, D.;
Zhang, C.; Quimbita, G. E.; Grumbine, S. D.; Heyn, R. H.; Tilley, T. D.;
Rheingold, A. L.; Geib, S. J. J. Am. Chem. Soc. 1990, 112, 2673. (d) Straus,
D. A.; Grumbine, S. D.; Tilley, T. D. J. Am. Chem. Soc. 1990, 112, 7801.
(e) Grumbine, S. D.; Chadha, R. K.; Tilley, T. D. J. Am. Chem. Soc. 1992,
114, 1518. (f) Grumbine, S. D.; Tilley, T. D.; Rheingold, A. L.; Arnold,
F. P. J. Am. Chem. Soc. 1993, 115, 7884. (g) Grumbine, S. K.; Tilley, T. D.
J. Am. Chem. Soc. 1994, 116, 5495. (h) Klei, S. R.; Tilley, T. D.; Bergman,
R. G. Organometallics 2002, 21, 4648. (i) Glaser, P. B.; Wanandi, P. W.;
Tilley, T. D. Organometallics 2004, 23, 693. (j) Glaser, P. B.; Tilley, T. D.
Organometallics 2004, 23, 5799.
Compound 6 exhibits a four-legged piano-stool structure, as
determined by X-ray crystallographic analysis. The bond length
(10) Lankamp, H.; Nauta, W. Th.; MacLean, C. Tetrahedron Lett. 1968,
9, 249.
(11) Rogers, R. D.; Atwood, J. L.; Foust, D.; Rausch, M. D. J. Cryst.
Mol. Struct. 1981, 11, 183.

5720 Organometallics, Vol. 27, No. 21, 2008
Shinohara et al.
Chart 1
(2.160(1) Å) is considerably longer than comparable values
found in chlorosilanes (ca. 2.02 Å).2d This suggests that
d-electron density at vanadium may be interacting, in a VfSi
donor sense, with the Si-Cl σ* orbital.12
Reactions of Vanadium Silyl Complexes. Compounds 2 and
3 were examined as catalysts for the hydrosilation of 1-hexene,
using Ph2SiH2 or MesSiH3 as the silane in benzene-d6 solution.
In both cases, after 24 h at room temperature, no conversion
1
was observed by H NMR spectroscopy.
When CO gas (1 atm) was added to a benzene solution of 2
at room temperature, the solution color changed to dark green
and eventually to dark orange. The resulting product, isolated
in 94% yield by crystallization from a toluene-diethyl ether
solvent mixture, was identified as the 18-electron dicarbonyl
compound Cp(dmpe)V(CO)2 (7). The byproducts of this reaction
included Ph2SiH2 (60% by 1H NMR spectroscopy), which would
imply that the reaction proceeds by homolytic cleavage of the
V-Si bond, to generate a V(I) species that is then trapped by
carbon monoxide to form 7. The resulting silyl radical presum-
ably abstracts hydrogen from species present in the reaction
mixture. Teuben has described a similar process, by which
Figure 2. ORTEP drawing of one of the two independent molecules
in the unit cell of Cp(dmpe)VSiH2Mes (3), with thermal ellipsoids
drawn at the 50% probability level. Hydrogen atoms, except for
those bonded to the silicon atom, are omitted for clarity. Selected
bond distances (Å) and angles (deg): V-Si ) 2.576(2), 2.577(2),
V-P1 ) 2.441(2), 2.439(2), V-P2 ) 2.465(2), 2.455(2), Si-H
) 1.41(4), 1.38(4), 1.50(5), 1.43(5), Si-C ) 1.909(5), 1.909(5),
V-Cp(centroid) ) 1.947, 1.941; P1-V-P2 ) 80.95(5), 80.17(6),
P2-V-Si ) 92.95(6), 89.02(5), P1-V-Si ) 99.76(6), 93.15(5),
V-Si-H ) 120(2), 117(2), 108(2), 118(2), V-Si-C1 ) 126.0(2),
109.6(2).
Cp(PMe3)2VMe2 reacts with
1 atm of CO to afford
CpV(CO)2(PMe3)2 and acetone, presumably via an acyl
intermediate.5a For comparison, we examined the reaction of
Cp(dmpe)VMe (1) with CO (1 atm), which gave 7 in 90% yield
1
but no acetone by H NMR spectroscopy. Characteristic 51V
and 31P NMR chemical shifts for 7 were observed at -1229
ppm (t, JVP ) 30 Hz) and 78.81 ppm (∆ν1/2 ) 2000 Hz),
respectively.13 The infrared spectrum of 7 exihibts CO stretching
vibrations at 1830 and 1747 cm-1. The structure of 7 was
determined by X-ray crystallography (Figure 4).
Preliminary reactivity studies were designed to exploit the
halide leaving groups in 5 and 6 in the synthesis of vanadium-
silicon double bonds. In related work, Egorov and co-workers
have reported the generation of Cp*2VdSiMe2, identified on
Figure 3. ORTEP drawing of Cp(dmpe)V(Cl)SiClPh2 (6), with
thermal ellipsoids drawn at the 50% probability level. Hydrogen
atoms and the benzene molecule of crystallization are omitted for
clarity. Selected bond distances (Å) and angles (deg): V-Si )
2.574(2), V-P2 ) 2.518(1), V-P1 ) 2.480(1), Si-Cl ) 2.160(1),
V-Cl ) 2.388(1), V-Cp(centroid) ) 1.962; P1-V-P2 )
74.63(4), P1-V-Cl ) 125.30(4), P2-V-Cl ) 81.73(4), P1-V-Si
) 83.67(4), P2-V-Si ) 135.86(4), V-Si-Cl ) 114.95(5),
V-Si-C1 ) 120.6(1), V-Si-C2 ) 114.4(1).
of V-Si (2.573(1) Å) is within the range observed for the
corresponding bond lengths in 2 and 3. The Si-Cl bond length
Figure 4. ORTEP drawing of Cp(dmpe)V(CO)2 (7), with thermal
ellipsoids drawn at the 50% probability level. Hydrogen atoms are
omitted for clarity. Selected bond distances (Å) and angles (deg):
V-C1 ) 1.861(4), C1-O1 ) 1.173(4), V-P1 ) 2.393(1),
V-Cp(centroid) ) 1.922; Cl-V-C1* ) 72.9(2), P1-V-P1* )
74.84(5), P1-V-C1 ) 77.7(1), P1-V-C1* ) 120.6(1), V-C1-O1
) 177.4(3). Asterisks indicate symmetry-generated atoms.
(12) (a) Freeman, W. P.; Tilley, T. D.; Rheingold, A. L.; Ostrander,
R. L. Angew. Chem., Int. Ed. Engl. 1993, 32, 1744. (b) Koloski, T. S.;
Pestana, D. C.; Carroll, P. J.; Berry, D. H. Organometallics 1994, 13, 489.
(c) Lemke, F. R.; Galat, K. J.; Youngs, W. J. Organometallics 1999, 18,
1419. (d) Freeman, S. T. N.; Petersen, J. L.; Lemke, F. R. Organometallics
2004, 23, 1153.

Paramagnetic Vanadium Silyl Complexes
Organometallics, Vol. 27, No. 21, 2008 5721
Table 1. Crystallographic Data for Compounds 2, 3, 6, and 7
2
3
6
7
formula
formula wt
cryst size (mm)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
C23H32P2SiV
449.46
0.30 × 0.25 × 0.25
monoclinic
P21/c
10.1297(11)
8.8751(10)
26.927(3)
90
100.262(2)
90
C20H34P2SiV
415.44
0.20 × 0.20 × 0.10
orthorhombic
P212121
15.365(6)
17.074(6)
17.199(7)
90
90
90
4512(3)
8
1.223
C23H31Cl2P2SiV · C6H6
C13H21O2P2V
322.18
0.15 × 0.18 × 0.09
monoclinic
P21/m
7.024(2)
13.185(4)
8.438(2)
90
101.602(4)
90
765.5(4)
2
597.46
0.30 × 0.22 × 0.15
orthorhombic
Pna21
17.424(1)
9.4930(7)
17.848(1)
90
90
90
2952.2(4)
4
1.344
2382.0(5)
4
1.253
Z
Dcalcd (g cm-3
)
1.398
no. of indep rflns
no. of params
R1 (I > 2σ(I))
wR2 (all data)
goodness of fit
13 628
248
0.043
0.078
23 691
449
0.061
0.108
0.992
16 012
316
0.034
0.054
0.632
3920
85
0.039
0.079
0.931
0.86
400 spectrometer operating at 105.2 MHz (51V). Chemical shifts
are reported in ppm relative to an internal standard of C6D5H (7.15
ppm) (1H), an external standard of 85% H3PO4 (31P), or an external
standard of VOCl3 (51V). Elemental analyses were perfomed by
the Microanalytical Facility in the College of Chemistry at the
University of California, Berkeley (C and H), and Desert Analytics,
Inc. (V). Infrared spectra were recorded as KBr pellets on a Mattson
FTIR 3000 instrument.
X-ray Data Collection. All single-crystal X-ray analyses were
carried out at the UC Berkeley CHEXRAY crystallographic facility.
Measurements were made with a Bruker SMART OCD area
detector with graphite-monochromated Mo KR radiation (λ )
0.710 69). Data were integrated by the program SAINT and
analyzed for agreement using XPREP. Empirical absorption cor-
rections were made using SADABS. The structures were solved
by direct methods (SHELXS-97) and refined by full-matrix least-
squares procedures on F2 for all reflections (SHELX-97).17 All non-
hydrogen atoms and hydrogen atoms on the silicon atoms of 2 and
3 were refined anisotropically. All other hydrogen atoms were
placed using AFIX instructions. Details of data collections and
refinments are given in Table 1 and in the CIF files given in the
Supporting Information.
the basis of an ESR spectrum.14 The reaction of KC8 with 6 in
C6H6 for 1 day at room temperature afforded a complex mixture.
The reaction of 5 with Li(Et2O)3B(C6F5)4 in fluorobenzene
led to a color change of the reaction mixture from dark red to
dark green. Workup of the reaction mixture produced a dark
green solid, which is insoluble in common organic solvents
except PhF, and this compound exhibited no observable peaks
by 1H NMR spectroscopy (PhF/toluene-d8 (1/5) cosolvent).
Although little structural information could be obtained from
spectroscopic methods, the combustion analysis is consistent
with the formula [Cp(dmpe)VSiPh2][B(C6F5)4] (8). Thus, we
tentatively conclude that 8 is a paramagnetic, cationic silylene
complex of vanadium.
Conclusion
This report describes the synthesis and characterization of
new types of vanadium silyl complexes. These complexes are
readily derived from the vanadium alkyl complexes Cp-
(dmpe)VR (R ) Me, CH2Ph) in high yields. Given the ligand
sets involved in these complexes, they are expected to be
relatively electron-rich, and this is supported by the oxidation
of 5 under mild conditions, to give the vanadium(III) silyl
complex 6. In general, spectroscopic features for these com-
plexes suggest that they are similar to the related alkyl
derivatives from which they are derived. Significantly, these
studies have produced the first structural information for
vanadium silyl complexes.
The new compounds reported here represent relatively rare
examples of fully characterized paramagnetic silyl complexes2,15
and, therefore, provide an opportunity to explore the chemistry
of metal-silicon bonds in odd-electron systems. Future work
in this laboratory will address this issue, and further attempts
will be made to explore the synthesis and study of paramagnetic
silylene complexes of vanadium.
Synthesis of Cp(dmpe)VSiHPh2 (2). Ph2SiH2 (0.078 g, 0.42
mmol) was added to a benzene solution of 1 (0.119 g, 0.423 mmol)
at room temperature. After it was stirred for 1 h, the solution was
filtered and then evaporated to dryness. The resulting solid was
washed with pentane several times and then recrystallized from a
mixed toluene (1 mL)-pentane (2 mL) solvent system at -30 °C
in 74% yield as red-brown crystals. 1H NMR (benzene-d6): δ -3.32
(br, ∆ν1/2 ) 3800 Hz, 6H, PMe), 5.08 (br, ∆ν1/2 ) 2000 Hz, 4H,
SiPh2), 11.11 (br, ∆ν1/2 ) 870 Hz, 6H, SiPh2), 24.36 (br, ∆ν1/2
)
3800 Hz, 6H, PMe), 29.30 (br, 2H, PCH2), 31.74 (br, 2H, PCH2).
IR (KBr pellet): ν(SiH) 1984 cm-1. Anal. Calcd for C23H32P2SiV:
C, 61.46; H, 7.18. Found: C, 61.25; H, 7.32.
(13) (a) Borowski, R.; Rehder, D.; von Deuten, K. J. Organomet. Chem.
1981, 220, 45. (b) Herberhold, M.; Schrepfermann, M. J. Organomet. Chem.
1993, 458, 19.
Experimental Section
(14) Lalov, A. V.; Egorov, M. P.; Nefedov, O. M.; Cherkasov, V. K.;
Ermolaev, N. L.; Piskunov, A. V. Russ. Chem. Bull. Int. Ed. 2005, 54,
807.
All manipulations were conducted under an N2 atmosphere using
standard Schlenk or glovebox techniques. In general, solvents were
distilled from appropriate drying agents and were stored in PTFE-
valved flasks. Deuterated solvents (Cambridge Isotope) were dried
with appropriate drying agents and vacuum-transferred prior to use.
The reagents Cp(dmpe)VCl, Cp(dmpe)VMe,5 and dmpe16 were
prepared according to literature procedures. 1H, 31P, and 51V NMR
spectra were recorded on a Bruker DRX-500 spectrometer operating
at 500.1 MHz (1H) and 202.5 MHz (31P) and on a Bruker AMX-
(15) (a) Arnold, J.; Tilley, T. D. Organometallics 1987, 6, 473. (b)
Samuel, E.; Mu, Y.; Harrod, J. F.; Dromzee, Y.; Jeannin, Y. J. Am. Chem.
Soc. 1990, 112, 3435. (c) Britten, J.; Mu, Y.; Harrod, J. F.; Polowin, J.;
Baird, M. C.; Samuel, E. Organometallics 1993, 12, 2672. (d) Woo, H. G.;
Harrod, J. F.; He´nique, J.; Samuel, E. Organometallics 1993, 12, 2883.
(16) Burt, J. R.; Chatt, J.; Hussain, W.; Leigh, J. J. Organomet. Chem.
1979, 182, 203.
(17) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.

5722 Organometallics, Vol. 27, No. 21, 2008
Shinohara et al.
Syntheisis of Cp(dmpe)VSiH2Mes (3). MesSiH3 (0.052 g, 0.35
mmol) was added to a solution of 1 (0.099 g, 0.35 mmol) in 5 mL
of benzene, and the resulting solution was stirred for 2 h at room
temperature. After filtration and removal of the solvent in vacuo,
the resulting solid was washed several times with pentane.
Recrystallization of the solution from a mixture of toluene (1 mL)
and pentane (2 mL) at -30 °C gave pure 3 in 64% yield. 1H NMR
(benzene-d6): δ -6.25 (br, ∆ν1/2 ) 500 Hz, 3H, p-Me), -2.50 (br,
6H, PMe), -1.84 (br, 6H, o-Mes), 6.39 (s, 2H, aromatic H on Mes
purple. The solution was then stirred for 2 h at room temperature
and filtered, and the solvent was removed in vacuo. The resulting
solid was washed with pentane (3 mL) several times and dried under
reduced pressure to give 6 in 77% yield as purple crystals. Anal.
Calcd for C23H31Cl2P2SiV: C, 53.19; H, 6.02. Found: C, 52.84; H,
6.20.
Cp(dmpe)V(CO)2 (7). CO gas (1 atm) was admitted into a
Schlenk tube containing a solution of 2 (0.113 g, 0.251 mmol) in
benzene (5 mL). After the reaction mixture was stirred for 24 h, a
precipitate was filtered followed by drying under vacuo. After the
resulting solid was washed several times by pentane (3 × 2 mL),
it was dried under reduced pressure and then crystallized from a
mixture of toluene (1 mL) and Et2O (3 mL). The product (7; 0.076
group), 18.29 (br, ∆ν1/2 ) 3000 Hz, 6H, PMe), 25.19 (br, ∆ν1/2
)
2700 Hz, 2H, PCH2) 40.33 (br, ∆ν1/2 ) 2700 Hz, 2H, PCH2). IR
(KBr pellet): ν(SiH) 1991 cm-1. Anal. Calcd for C20H34P2SiV: C,
57.82; H, 8.25. Found: C, 57.99; H, 8.58.
1
Synthesis of Cp(dmpe)VCH2Ph (4). A suspension of Cp(d-
mpe)VCl (0.808 g, 2.68 mmol) in 30 mL of diethyl ether was cooled
to -30 °C, and 1.4 mL of a 2.0 M PhCH2MgBr solution in THF
was added dropwise. The reaction solution was warmed to 0 °C
and stirred for 2 h. The solution was filtered and concentrated to
ca. 5 mL, and then 5 mL of pentane was added. Concentration and
cooling (-30 °C) of the resulting solution gave 4 in 38% yield. 1H
NMR (benzene-d6): δ -12.57 (br, 6H, PMe), 3.77 (br, 3H, Ph),
11.25 (br, 6H, PMe), 14.23 (br, 2H, Ph), 15.83 (br, 2H, PCH2),
31.45 (br, 2H, PCH2). Anal. Calcd for C18H28P2V: C, 60.51; H,
7.90. Found: C, 60.23; H, 8.16.
Reaction of Cp(dmpe)VCH2Ph with Silanes. A 1:1 solution
of Ph2SiH2/Ph2SiD2 (0.085 mL, 2.0 M solution) was added to a
solution of 4 (0.020 g, 0.056 mmol) in benzene-d6 (1 mL). After
24 h, the volatile components were transferred into a J. Young NMR
tube by trap-to-trap distillation. The ratio of toluene to toluene-d
was determined by the integration of resonances in 1H NMR spectra.
Synthesis of Cp(dmpe)VSiPh2Cl (5). Ph2SiHCl (0.110 g, 0.504
mmol) was added to a benzene solution (3 mL) of 2 (0.200 g, 0.445
mmol). After the mixture was stirred for 20 h at room temperature,
the resulting solution was filtered and then the solvent was removed
in vacuo. The resulting solid was washed several times with pentane
(3 × 2 mL). Recrystallization from a toluene (1 mL)-pentane(2
mL) solvent mixture at -30 °C gave Cp(dmpe)VSiPh2Cl in 82%
as a red-purple solid. 1H NMR (benzene-d6): δ -5.72 (br, 6H, PMe),
2.36 (br, 4H, SiPh2), 8.01 (br, 2H, SiPh2), 9.70 (br, 4H, SiPh2),
26.19 (br, 6H, PMe), 30.00 (br, 4H, PCH2). Anal. Calcd for
C23H31ClP2SiV: C, 57.09; H, 6.46. Found: C, 56.75; H, 6.43.
Synthesis of Cp(dmpe)V(Cl)SiPh2Cl (6). Ph3CCl (0.054 g, 0.19
mmol) was added to a benzene solution (4 mL) of 4 (0.093 g, 0.19
mol), and color of the resulting solution immediately changed to
g, 0.24 mmol) was obtained in 94% yield as yellow crystals. H
NMR (benzene-d6): δ 0.87 (br, 10H, overlapping PMe and PCH2
resonances), 1.14 (br, 6H, PMe), 4.49 (br, 5H, Cp). 13C{1H} NMR
(benzene-d6): δ 19.03, 19.96, 29.78, 87.86; 31P{1H} NMR (benzene-
d6): δ 78.8. 51V NMR (benzene-d6): δ -1229.2 (t, 1JVP ) 208 Hz).
IR (KBr pellet): ν(CO) 1830, 1747 cm-1. Anal. Calcd for
C13H21O2P2V: C, 48.46; H, 6.57. Found: C, 48.80; H, 6.30.
Reaction of 5 with Li(Et2O)3B(C6F5)4. To a solution of 5 (0.104
g, 0.215 mmol) in fluorobenzene (5 mL) was added
Li(Et2O)3B(C6F5)4 (0.188 g, 0.207 mmol). The reaction mixture
was stirred for 3 h at room temperature, and then the solution was
filtered. The volatile components were removed under reduced
pressure to leave an oily foam. This solid was washed with pentane
(3 × 2 mL) and toluene (3 × 2 mL), and drying under vacuum
resulted in a dark green solid in 62% yield. Anal. Calcd for
C47H31BF20P2SiV: C, 50.07; H, 2.77; V, 4.52. Found: C, 49.73; H,
3.15; V, 4.54.
Acknowledgment. This work was supported by the
National Science Foundation under Grant No. CHE-0649583.
Prof. Renaldo Poli is thanked for helpful discussions.
Additional support was provided by the JSPS through a
Postdoctoral Fellowship for Research Abroad (A.S.) and the
Miller Institute for Basic Research in Science through a
Research Fellowship (R.W.).
Supporting Information Available: CIF files giving crystal-
lographic data for 2, 3, 6, and 7. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM800712K