Silylene hydride complexes of molybdenum with silicon-hydrogen interactions: Neutron structure of (η5-C5Me 5)(Me2PCH2CH2PMe2) Mo(SiEt2)

Article abstract of DOI:10.1021/ja040026g

Reduction of Cp*MoCl₄ with 3.1 equiv of Na/Hg amalgam (1.0% w/w) in the presence of 1 equiv of dmpe and 1 equiv of trimethylphosphine afforded the molybdenum(II) chloride complex Cp*(dmpe)(PMe ₃)MoCl (1) (Cp= 1,2,3,4,5-pentamethylcyclopentadienyl, dmpe = 1,2-bis(dimethylphosphino)ethane). Alkylation of 1 with PhCH₂MgCl proceeded in high yield to liberate PMe₃ and give the 18-electron π-benzyl complex Cp*(dmpe)Mo(η³-CH₂Ph) (2). Variable temperature NMR experiments provided evidence that 2 is in equilibrium with its 16-electron η¹-benzyl isomer [Cp*(dmpe) Mo(η¹-CH₂Ph)]. This was further supported by reaction of 2 with CO to yield the carbonyl benzyl complex Cp*(dmpe)(CO) Mo(η¹-CH₂Ph) (3). Complex 2 was found to react with disubstituted silanes H₂SiRR' (RR' = Me₂, Et₂, MePh, and Ph₂) to form toluene and the silylene complex Cp*(dmpe)Mo(H)(SiRR') (4a: RR' = Me₂; 4b: RR' = Et₂; 4c: RR' = MePh; 4d: RR' = Ph₂). Reactions of 2 with monosubstituted silanes H₃SiR (R = Ph, Mes, Mes = 2,4,6-trimethylphenyl) produced rare examples of hydrosilylene complexes Cp*(dmpe)Mo(H)Si(H)R (5a: R = Ph; 5b: R = Mes; 5c: R = CH₂Ph). Reactivity of complexes 4a-c and 5a-d is dominated by 1,2-hydride migration from metal to silicon, and these complexes possess H...Si bonding interactions, as supported by spectroscopic and structural data. For example, the J_HSi coupling constants in these species range in value from 30 to 48 Hz and are larger than would be expected in the absence of H...Si bonding. A neutron diffraction study on a single crystal of diethylsilylene complex 4b unequivocally determined the hydride ligand to be in a bridging position across the molybdenum-silicon bond (Mo-H 1.85(1) A, Si-H 1.68(1) A). The synthesis and reactivity properties of these complexes are described in detail.

Full text of DOI:10.1021/ja040026g

Published on Web 07/31/2004
Silylene Hydride Complexes of Molybdenum with
Silicon-Hydrogen Interactions: Neutron Structure of
(η5-C5Me5)(Me2PCH2CH2PMe2)Mo(H)(SiEt2)
Benjamin V. Mork,† T. Don Tilley,*,† Arthur J. Schultz,‡ and John A. Cowan‡
Contribution from the Department of Chemistry, UniVersity of California,
Berkeley, California 94720-1460, and Intense Pulsed Neutron Source,
Argonne National Laboratory, Argonne, Illinois 60439-4814
Received January 22, 2004; E-mail: tdtilley@socrates.berkeley.edu
Abstract: Reduction of Cp*MoCl4 with 3.1 equiv of Na/Hg amalgam (1.0% w/w) in the presence of 1 equiv
of dmpe and 1 equiv of trimethylphosphine afforded the molybdenum(II) chloride complex Cp*(dmpe)-
(PMe3)MoCl (1) (Cp* ) 1,2,3,4,5-pentamethylcyclopentadienyl, dmpe ) 1,2-bis(dimethylphosphino)ethane).
Alkylation of 1 with PhCH2MgCl proceeded in high yield to liberate PMe3 and give the 18-electron π-benzyl
complex Cp*(dmpe)Mo(η3-CH2Ph) (2). Variable temperature NMR experiments provided evidence that 2
is in equilibrium with its 16-electron η1-benzyl isomer [Cp*(dmpe)Mo(η1-CH2Ph)]. This was further supported
by reaction of 2 with CO to yield the carbonyl benzyl complex Cp*(dmpe)(CO)Mo(η1-CH2Ph) (3). Complex
2 was found to react with disubstituted silanes H2SiRR’ (RR’ ) Me2, Et2, MePh, and Ph2) to form toluene
and the silylene complexes Cp*(dmpe)Mo(H)(SiRR’) (4a: RR’ ) Me2; 4b: RR’ ) Et2; 4c: RR’ ) MePh;
4d: RR’ ) Ph2). Reactions of 2 with monosubstituted silanes H3SiR (R ) Ph, Mes, Mes ) 2,4,6-
trimethylphenyl) produced rare examples of hydrosilylene complexes Cp*(dmpe)Mo(H)Si(H)R (5a: R )
Ph; 5b: R ) Mes; 5c: R ) CH2Ph). Reactivity of complexes 4a-c and 5a-d is dominated by 1,2-hydride
migration from metal to silicon, and these complexes possess H‚‚‚Si bonding interactions, as supported
by spectroscopic and structural data. For example, the JHSi coupling constants in these species range in
value from 30 to 48 Hz and are larger than would be expected in the absence of H‚‚‚Si bonding. A neutron
diffraction study on a single crystal of diethylsilylene complex 4b unequivocally determined the hydride
ligand to be in a bridging position across the molybdenum-silicon bond (Mo-H 1.85(1) Å, Si-H 1.68(1)
Å). The synthesis and reactivity properties of these complexes are described in detail.
silicon.4 The chemistry of metal carbene complexes is much
more extensively developed,5 and these complexes exhibit great
utility in organic and organometallic chemistry (e.g., in olefin
metathesis reactions).6 Thus, silylene complexes are expected
to be of use in stoichiometric and catalytic reactions involving
Introduction
Metal silylene complexes have attracted much attention as
silicon analogues of metal carbenes and as potential intermedi-
ates in metal-catalyzed syntheses and transformations of orga-
nosilanes.1 To date, more than 20 examples of base-free metal
silylene complexes are known,2,3 and these include a variety of
transition metals, ancillary ligand sets, and substituents at
(4) (a) Grumbine, S. K.; Mitchell, G. P.; Straus, D. A.; Tilley, T. D.; Rheingold,
A. L. Organometallics 1998, 17, 5607. (b) Wanandi, P. W.; Glaser, P. B.;
Tilley, T. D. J. Am. Chem. Soc. 2000, 122, 972. (c) Gusev, D. G.; Fontaine,
F.-G.; Lough, A. J.; Zargarian, D. Angew. Chem., Int. Ed. 2003, 42, 216.
(d) Peters, J. C.; Feldman, J. D.; Tilley, T. D. J. Am. Chem. Soc. 1999,
121, 9871. (e) Mork, B. V.; Tilley, T. D. J. Am. Chem. Soc. 2001, 123,
9702. (f) Mitchell, G. P.; Tilley, T. D. Angew. Chem., Int. Ed. 1998, 37,
2524. (g) Ueno, K.; Asami, S.; Watanabe, N.; Ogino, H. Organometallics
2002, 21, 1326. (h) Feldman, J. D.; Mitchell, G. P.; Nolte, J. O.; Tilley, T.
D. J. Am. Chem. Soc. 1998, 120, 11184. (i) Klei, S. R.; Tilley, T. D.;
Bergman, R. G. J. Am. Chem. Soc. 2000, 122, 1816. (j) Simons, R. S.;
Gallucci, J. C.; Tessier, C. A.; Yougs, W. J. J. Organomet. Chem. 2002,
654, 224.
† University of California, Berkeley.
‡ Argonne National Laboratory.
(1) (a) Tilley, T. D. In The Silicon Heteroatom Bond; Patai, S., Rappoport, Z.,
Eds.; Wiley: New York, 1991; p 245. (b) Okazaki, M.; Tobita, H.; Ogino,
H. J. Chem. Soc., Dalton Trans. 2003, 493. (c) Klei, S. R.; Tilley, T. D.;
Bergman, R. G. Organometallics 2002, 21, 4648. (d) Eisen, M. S. In The
Chemistry of Organosilicon Compounds; Rappoport, Z., Apeloig, Y., Eds.,
Wiley: New York, 1998; Vol. 2, Chapter 35. (e) Sharma, H. K.; Pannell,
K. H. Chem. ReV. 1995, 95, 1351. (f) Tamao, K.; Sun, G. R.; Kawachi, A.
J. Am. Chem. Soc. 1995, 117, 8043. (g) Tilley, T. D. Comments Inorg.
Chem. 1990, 10, 37. (h) Brook, M. A. Silicon in Organic, Organometallic,
and Polymer Chemistry; Wiley-Interscience: New York, 2000.
(2) For the purposes of this discussion, the term “base-free silylene complexes”
refers to those complexes that feature three-coordinate silicon centers and
no stabilization by Lewis bases. This excludes those complexes that have
coordinated Lewis bases and those that have π-donating substituents at
silicon.
(5) (a) Do¨tz, K. H.; Fischer, H.; Hoffman, P.; Kreissel, R.; Schubert, U.; Weiss,
K. Transition Metal Carbene Complexes; Verlag Chemie: Deerfield Beach,
FL, 1983. (b) Schrock, R. R. J. Chem. Soc., Dalton Trans. 2001, 2451. (c)
Crabtree, R. H. The Organometallic Chemistry of the Transition Metals,
2nd ed.; Wiley-Interscience: New York, 1994. (d) 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, CA, 1987. (e) Nugent, W. A.; Mayer, J. M. Metal-Ligand Multiple
Bonds; Wiley-Interscience: New York, 1988. (f) Elschenbroich, Ch.; Salzer,
A. Organometallics, A Concise Introduction, 2nd ed.; VCH: New York,
1992.
(3) For some examples of base-stabilized molybdenum silylene complexes,
see: (a) Ueno, K.; Masuko, A.; Ogino, H. Organometallics 1999, 18, 2694.
(b) Clendenning, S. B.; Gehrhus, B.; Hitchcock, P. B.; Moser, D. F.; Nixon,
J. F.; West, R. J. Chem. Soc., Dalton Trans. 2002, 2002, 484. (c) Petri, S.
H. A.; Eikenberg, D.; Neumann, B.; Stammler, H.-G.; Jutzi, P. Organo-
metallics 1999, 18, 2615.
(6) (a) Schrock, R. R. Acc. Chem. Res. 1990, 23, 158. (b) Trnka, T. M.; Grubbs,
R. H. Acc. Chem. Res. 2001, 34, 18.
9
10428
J. AM. CHEM. SOC. 2004, 126, 10428-10440
10.1021/ja040026g CCC: $27.50 © 2004 American Chemical Society

Silylene Hydride Complexes of Molybdenum
A R T I C L E S
Scheme 1
silicon, but such applications may require the availability of a
larger and more diverse family of compounds of the type LnMd
SiR2 (R ) H, alkyl, or aryl). Toward this end, a number of
research efforts have been directed toward the synthesis and
study of new silylene complexes.1-4,7
Many of the known base-free silylene complexes are cationic,
since their preparations involve anion abstraction steps.4
A
significant challenge is therefore the synthesis of neutral silylene
complexes, as these species should be compatible with a wide
range of solvents and should exhibit reactivity that is not
influenced by the participation of counteranions. Few examples
of neutral silylene complexes have been published, and these
include (Cy3P)2PtdSiMes2,4h Cp(CO)2(SiMe3)WdSiMes2,4g
OsH3(SiClPh){2,6-(CH2PtBu2)2C6H3},4c and the zwitterionic
complexes [κ3-PhB(CH2PPh2)3](H)2IrdSiR2 (R2 ) Mes2, Me2,
Et2, and Ph2).4d Neutral silylene complexes have also been
synthesized from cyclic diamido silylenes, which are stable as
free species and act as primarily σ-donors.7 The chemical and
spectroscopic properties of these silylene complexes appear to
be distinctly different from the former type,4 which involves
silylene groups that are not stable as free species and feature
alkyl, aryl, silyl, or hydride substituents at silicon.
the type Cp*(dmpe)MoSiHRR’. The molybdenum benzyl
complex and the silylene complex Cp*(dmpe)Mo(H)SiClMes
were communicated previously as precursors to the first complex
with silylyne character, [Cp*(dmpe)Mo(H)(SiMes)][B(C6F5)4].8
Results and Discussion
Recently, we have developed routes to silylene complexes
that employ reactive transition-metal fragments and double
Si-H bond activations of a hydrosilane.4d,e,8 This typically
involves an oxidative addition of one Si-H bond, followed by
R-elimination of the second Si-H in an electronically unsatur-
ated hydrosilyl intermediate. If the starting metal complex
features a σ-bonded organic ligand, then liberation of a
hydrocarbon via C-H bond reductive elimination may provide
a driving force for the formation of a silylene complex (eq 1).
Coordinatively and electronically unsaturated metal alkyl com-
plexes therefore represent promising precursors to silylene
complexes.
Synthesis and Characterization of a Molybdenum Benzyl
Complex. The initial goal of this work was the synthesis of a
16-electron alkyl complex that could be used in the synthesis
of a silylene complex (eq 1). Baker and co-workers have
reported the 16-electron chloride complex Cp*(PMe3)2MoCl,
which undergoes oxidative addition of H2 to give the 18-electron
complex Cp*(PMe3)2MoH2Cl.9 Unfortunately, analogous 16-
electron alkyl complexes are not known. The allyl complex Cp*-
(PMe3)2Mo(η3-C3H5)10 may be envisioned as a source of the
16-electron species Cp*(PMe3)2Mo(η1-C3H5), via η1/η3 inter-
conversion of the allyl ligand. However, elimination of propene
in reactions of an allyl complex with silanes may result in
secondary processes such as hydrosilylation.
For application of the synthetic procedure outlined in eq 1,
benzyl derivatives were targeted as starting compounds. Benzyl
ligands are known to participate in η1/η3 interconversions, and
toluene should be a generally unreactive elimination product.
The synthesis of an appropriate η3-benzyl complex required
access to the corresponding Cp*LnMoCl (n ) 2 or 3) precursor.
The chelating diphosphine dmpe was employed to impart
stability to the complexes and provide a relatively metalation-
For these reasons, we have synthesized the molybdenum
benzyl complex Cp*(dmpe)Mo(η3-CH2Ph) (Cp* ) η5-C5Me5,
dmpe ) 1,2-bis(dimethylphosphino)ethane), which reacts with
hydrosilanes H2SiRR’ (RR’ ) Me2, Et2, MePh, Ph2, (H)Ph,
(H)Mes, and (H)CH2Ph) to eliminate toluene and form the
molybdenum(II) silylene complexes Cp*(dmpe)Mo(H)(SiRR’).
These are neutral, early transition-metal silylene complexes, and
three of these compounds feature rare incorporation of hydrogen
as a substituent at a silylene center. Structural and spectroscopic
data support the presence of H‚‚‚Si bonding interactions in this
series of compounds, and their reactivities indicate that they
are in equilibria with reactive 16-electron silyl complexes of
11
resistant ancillary ligand framework. Reduction of Cp*MoCl4
in the presence of 1 equiv of dmpe and 1 equiv of PMe3
proceeded at 60 °C in benzene over 16 h to give Cp*(dmpe)-
(PMe3)MoCl (1) in 89% yield as a red-purple microcrystalline
solid (Scheme 1). Compound 1 is analogous to Poli’s Cp*-
(PMe3)3MoCl, and its preparation was derived from the
published procedure for the latter compound.10
The spectroscopic properties of 1 are consistent with the
structure shown in Scheme 1. For example, the 1H NMR
spectrum of 1 exhibits four separate doublet resonances for the
symmetry-inequivalent dmpe methyl groups at δ 1.47, 1.35,
1.15, and 0.94 (JHP ) 8, 8, 7, and 7 Hz, respectively). The
(7) For some examples of metal complexes of stable silylenes, see: (a) Haaf,
M.; Schmedake, T. A.; West. R. Acc. Chem. Res. 2000, 33, 704. (b) Gehrus,
B.; Hitchcock, P. B.; Lappert, M. F.; Maciejewski, H. Organometallics
1998, 17, 5599. (c) Evans, W. T.; Perotti, J. M.; Moser, D. F.; West, R.
Organometallics 2003, 22, 1160. (d) Dysard, J. M.; Tilley, T. D.
Organometallics 2000, 19, 4726. (e) Amoroso, D.; Haaf, M.; Yap, G. P.;
West, R.; Fogg, D. E. Organometallics 2002, 21, 534.
(9) Baker, R. T.; Calabrese, J. C.; Harlow, R. L.; Williams, I. D. Organome-
tallics 1993, 12, 830.
(10) Abugideiri, F.; Kelland, M. A.; Poli, R.; Rheingold, A. L. Organometallics
1992, 11, 1303.
(11) Murray, R. C.; Blum, L.; Liu, A. H.; Schrock, R. R. Organometallics 1985,
4, 954.
(8) Mork, B. V.; Tilley, T. D. Angew Chem., Int. Ed. 2003, 42, 357.
9
J. AM. CHEM. SOC. VOL. 126, NO. 33, 2004 10429

A R T I C L E S
Mork et al.
Scheme 2
recrystallization from pentane gave the dimethylsilylene complex
Cp*(dmpe)Mo(H)(SiMe2) (4a, eq 2) as dark red crystals in 83%
yield.
resonance due to the PMe3 methyl groups is observed at δ 1.29
(JHP ) 7 Hz). The 31P{1H} NMR spectrum of 1 also agrees
with the low-symmetry structure, and it exhibits three separate
resonances at δ 66.0 (dd, JPP ) 30 Hz, JPP′ ) 22 Hz), 61.2 (dd,
JPP′ ) 59 Hz, JPP′′ ) 30 Hz), and 13.3 (dd, JPP′ ) 59 Hz, JPP′′
) 22 Hz).
Alkylation of 1 with PhCH2MgCl in benzene at room
temperature occurred immediately upon mixing the reagents.
The color of the solution changed from red-purple to orange-
red, and a precipitate was observed. The new product, Cp*-
(dmpe)Mo(η3-CH2Ph) (2, Scheme 1), was isolated in 85% yield
as an orange-brown solid by recrystallization from toluene.
The spectroscopic characterization of 4a is in agreement with
its description as a silylene hydride complex. The H NMR
1
spectrum of 4a in benzene-d6 exhibits a Cs symmetric structure
at room temperature. Two doublet resonances are observed at
δ 1.35 and 1.06 for the two pairs of dmpe methyl groups, and
the molybdenum hydride is observed as a triplet with 29Si
satellites at δ -14.06 (JHP ) 17 Hz, JHSi ) 30 Hz). The silicon-
methyl groups are observed as a singlet resonance at δ 0.67.
Symmetry equivalent phosphorus nuclei are observed by 31P-
{1H} NMR spectroscopy as a singlet resonance at δ 70.2. A
common indication of sp2 hybridization at silicon is a signifi-
cantly downfield-shifted 29Si{1H} NMR resonance.1h The 29Si-
{1H} NMR spectrum of 4a implies silylene character for the
silicon-based ligand in this compound, which exhibits a
resonance at δ 263.
Spectroscopic data support the description of 2 as an
1
η3-benzyl complex. For example, the H NMR spectrum of 2
in benzene-d6 exhibits four inequivalent resonances for the dmpe
methyl groups at δ 1.48, 1.10, 0.98, and 0.62. The methylene
protons of the benzyl group are inequivalent and are observed
at δ 2.76 and -0.50. The ligand peaks in this spectrum, with
the exception of a sharp singlet for the Cp* ligand, are slightly
broadened, and this is likely due to a dynamic η1/η3 equilibrium
involving the benzyl ligand (Scheme 1). The 1H NMR spectrum
of 2 at 50 °C displays a sharp Cp* resonance, while the dmpe
and benzyl ligand resonances are nearly broadened into the
baseline at this temperature. Attempts to obtain spectra at
temperatures above 80 °C were unsuccessful because of
decomposition of the benzyl complex to a mixture of unidenti-
fied products. At -20 °C in toluene-d8, the 1H NMR spectrum
of 2 displays sharp resonances for all of the ligand protons,
indicating the slow exchange limit for this dynamic process.
For example, inequivalent resonances are observed for the aryl
hydrogens at δ 7.09, 6.98, 6.56, 6.24, and 2.60. The latter
resonance is shifted upfield because of binding of the aryl carbon
to the molybdenum center.
Reactions of 2 with secondary silanes provide a general route
to silylene hydride complexes via the liberation of toluene.
Reactions of the silanes H2SiEt2, H2SiMePh, and H2SiPh2 were
complete after 15 min at 50 °C, and the color of the product
silylene complexes depends somewhat on the substituents at
silicon. Table 1 provides 29Si NMR chemical shifts as well as
the JHSi values and colors of these silylene hydride complexes.
Generally, the 29Si NMR chemical shifts of the resonances for
Cp*(dmpe)Mo(H)Si(RR’) complexes (4a-d: RR’ ) Me2, Et2,
MePh, and Ph2, respectively; eq 2) are downfield-shifted and
support their identification as silylene complexes. However, it
is noteworthy that the observed JHSi values are in the range of
30-48 Hz. These hydrogen-silicon coupling constants are
larger than those observed in the cationic tungsten silylene
complexes [Cp*(dmpe)(H)2WdSiRR’][B(C6F5)4] (RR’ ) Me2,
PhMe, Ph2), which are in the range of 7-17 Hz.4e It is often
accepted that JHSi values of e20 Hz indicate little or no bonding
interaction between H and Si centers in the coordination sphere
of a metal center.12 The JHSi values observed in complexes 4a-d
are therefore indicative of the presence of weak H‚‚‚Si bonding
interactions in these compounds. No absorbances assigned to
molybdenum hydride stretching frequencies were observed by
IR spectroscopy of complexes 4a-d. Comparison of the IR
spectra for Cp*(dmpe)Mo(H)(SiPh2) (4d) and Cp*(dmpe)Mo-
(D)(SiPh2) (4d-d1, synthesized by reaction of 2 with Ph2SiD2)
resulted in no detectable differences, indicating that any
absorbances due to vibrational modes involving the metal
hydride or deuteride in these compounds are very weak.
Structural Studies of Dialkylsilylene Complexes. Further
characterization of the molecular structures of these silylene
complexes involved analysis by single-crystal X-ray diffraction.
Details of the data collection are listed in Table 2, and an
ORTEP diagram of 4a is shown in Figure 1. Selected bond
The reaction of complex 2 with carbon monoxide provided
evidence for the equilibrium in Scheme 1, as it results in trapping
of the putative 16-electron benzyl complex as a CO adduct. A
dark orange-red solution of 2 was placed under 1 atm of CO at
room temperature, and the flask was sealed. Heating the mixture
at 60 °C for 1 h resulted in a light orange solution of Cp*-
(dmpe)(CO)Mo(CH2Ph) (3, Scheme 2). The carbonyl complex
3 was recrystallized from diethyl ether, but because of its high
solubility in hydrocarbon solvents it was isolated in only 21%
yield. The infrared spectrum of 3 indicates that the molybdenum
center of the [Cp*(dmpe)Mo(CH2Ph)] fragment is quite electron-
rich and strongly π-back-donating; 3 exhibits an absorbance for
the CO stretch at νCO ) 1779 cm-1
.
Silylene Complexes via Double Si-H Bond Activation
Reactions. The apparent η1/η3 equilibrium of 2 was exploited
in the synthesis of silylene complexes. For example, the reaction
of 2 with an excess (approximately 5 equiv) of H2SiMe2 at 50
°C for 15 min resulted in a color change of the solution from
orange-red to dark red. Isolation of the new product by
(12) Corey, J. Y.; Braddock-Wilking, J. Chem. ReV. 1999, 99, 175.
9
10430 J. AM. CHEM. SOC. VOL. 126, NO. 33, 2004

Silylene Hydride Complexes of Molybdenum
A R T I C L E S
Table 1. Selected NMR Data and Colors of Silylene Complexes 4a-d and 5a-c
silylene complex
δ, 29Si{1H} NMR
JHSi (1H NMR)
color
Cp*(dmpe)Mo(H)(SiMe2), 4a
Cp*(dmpe)Mo(H)(SiEt2), 4b
Cp*(dmpe)Mo(H)(SiMePh), 4c
Cp*(dmpe)Mo(H)(SiPh2), 4d
Cp*(dmpe)Mo(H)(SiHPh), 5a
Cp*(dmpe)Mo(H)(SiHMes), 5b
Cp*(dmpe)Mo(H)(SiHCH2Ph), 5c
263
273
214
242
250
214
239
30 Hz
44 Hz
46 Hz
37 Hz
30 Hz
48 Hz
42 Hz
red
red
purple
red-purple
yellow-black
purple
purple
Table 2. Details of Crystallographic Data Collection
compound
4a
4b (X-ray)
4b (neutron)
5a
7
8
empirical formula
fw
C18H38MoP2Si
440.47
C20H42MoP2Si
468.53
C20H42MoP2Si
468.53
2 × 1 × 1
red
monoclinic
P21/n (No. 14)
8.615(3)
17.087(5)
16.187(6)
90
C22H38MoP2Si
488.52
C28H46MoP2Si2
596.73
C23H48MoP2Si2
538.69
cryst size (mm3)
color
0.20 × 0.17 × 0.11
0.28 × 0.25 × 0.18
0.22 × 0.16 × 0.15
yellow-black
orthorhombic
Pnma (No. 62)
14.111(1)
12.242(1)
14.001(1)
90
0.14 × 0.10 × 0.02
0.20 × 0.18 × 0.10
red
red
yellow
orange
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
monoclinic
P21/m (No. 11)
8.7648(9)
13.714(1)
9.811(1)
90
109.383(1)
90
1112.5(2)
2
monoclinic
P21/n (No. 14)
8.700(1)
17.233(1)
16.333(1)
90
102.332(1)
90
2392.2(3)
4
monoclinic
P21/c (No. 14)
15.894(1)
10.642(1)
17.582(1)
90
95.083(3)
90
2962.2(2)
4
monoclinic
P21/n (No. 14)
9.0505(5)
14.5815(8)
21.9795(12)
90
96.229(1)
90
2883.5(3)
4
102.49(3)
90
2326.6(14)
4
90
90
2418.54(7)
4
temp (K)
radiation
R
171(1)
X-ray
0.048
144(1)
X-ray
0.032
20(1)
neutron
0.085
143(1)
X-ray
0.030
116(1)
X-ray
0.072
128(1)
X-ray
0.043
wR2
0.124
0.088
0.135
0.076
0.168
0.100
Rall
GOF
0.130
1.12
0.037
1.15
-
1.44
0.041
0.91
0.151
0.99
0.112
1.05
Chart 1
Figure 1. ORTEP diagram of dimethylsilylene complex 4a.
Table 3. Selected Bond Distances (Angstroms) and Angles (deg)
for 4a
The crystallographic mirror plane for crystals of 4a results
in a disorder of the dmpe ligand, which cannot adopt a
conformation that is consistent with this mirror symmetry. Thus,
the zigzag conformation of the dmpe ligand backbone is
disordered over two possible orientations. This disorder was
modeled by refining the dmpe backbone carbon at 50%
occupancy over two positions. In addition, one of the phosphorus
methyl groups is disordered. It was refined over two positions
at 50% occupancy. For clarity, only one conformation of the
dmpe ligand is shown in Figure 1.
Bond Distances
Mo-Si
Mo-P1
Mo-Cl
Mo-C2
2.315(2)
2.377(1)
2.326(5)
2.321(4)
Mo-C3
Si-C10
Si-C11
2.362(4)
1.896(7)
1.892(7)
Bond Angles
P1-Mo-P1A
P1-Mo-Si
C10-Si-C11
76.87(6)
93.98(5)
99.5(3)
Mo-Si-C10
Mo-Si-C11
127.3(2)
133.2(3)
Crucial ambiguities that arise in the analysis of the structure
of 4a are the location of the hydride ligand and its proximity to
the silicon center. The hydride ligand was not located in the
Fourier difference electron density map, and therefore its
absolute location is unknown. Five possible representations of
the structure for this complex are shown in Chart 1. Structure
type I features a hydride ligand positioned approximately trans
to the centroid of the Cp* ligand. This structure would conform
distances and angles from the structure are given in Table 3. A
crystallographic mirror plane bisects the molecule, and two Cp*
carbon atoms, the molybdenum, silicon, and silicon-methyl
carbon atoms reside on the mirror plane. The molybdenum-
silicon bond distance of 2.315(2) Å is considerably shorter than
other reported Mo-Si distances, which fall into the range of
2.412(1)-2.670(2) Å (Cambridge Structural Database).
9
J. AM. CHEM. SOC. VOL. 126, NO. 33, 2004 10431

A R T I C L E S
Mork et al.
to the observed mirror symmetry in the solid state, but is
inconsistent with a hydrogen-silicon bonding interaction, as
implied by the JHSi coupling constant. The silylene ligand is
oriented such that its p orbital is directed away from the vicinity
of the metal hydride in structure I, and this geometry would
not likely produce a JHSi value as high as 30 Hz. In structure
II, the hydride ligand is one of the four “legs” of a four-legged
piano stool-type structure. Structure type II would also appear
to be a poor description of 4a, since it does not feature an Si-H
bonding interaction. Structure III describes an R-agostic hy-
drosilyl complex, which features a formal Si-H bond. However,
the planarity at the silicon center in the solid-state structure and
the low-field shift of its 29Si NMR resonance in solution imply
more silylene character and therefore argue against this depiction
of the structure. Another relevant structure may be described
as a silylene hydride complex in which the hydride ligand
donates electron density to the electrophilic silicon center
(structure IV). Related interactions have been proposed to
describe short hydrogen-silicon contacts in silyl hydride
complexes.13 The planarity at silicon in the solid state, the short
molybdenum-silicon bond distance, the significantly downfield-
shifted 29Si NMR resonance, and a relatively weak H‚‚‚Si
bonding interaction for 4a favor the latter two descriptions, with
structure type IV being perhaps most important. This view may
be simply described by structure V, which represents a hybrid
of the two structures possessing a silicon-hydrogen interaction
(III and IV). However, the proposed structure V would not have
mirror symmetry. A reasonable hypothesis is that the hydride
ligand is disordered over bridging positions on both sides of
the Mo-Si bond, and that the heavier atoms (carbon, phospho-
rus, molybdenum, and silicon) conform to the crystallographi-
cally imposed mirror symmetry.
Figure 2. ORTEP diagram of diethylsilylene complex 4b.
Figure 3. ORTEP diagram from the neutron structure of diethylsilylene
complex 4b.
Table 4. Selected Bond Distances (Angstroms) and Angles (deg)
for 4b from Neutron Diffraction Data at 20 K
Bond Distances
Mo-Si
Mo-H
Si-H1
Si-C17
2.343(10)
1.847(12)
1.683(13)
1.873(10)
Si-C19
Mo-P1
Mo-P2
1.899(11)
2.399(9)
2.395(9)
It is, of course, possible that two or more of these structures
are quite close in energy and in fast exchange with one another
in solution. Variable temperature NMR spectroscopy reveals a
low-symmetry structure for 4a at -50 °C in toluene-d8. For
example, two separate resonances are observed by 31P{1H}
NMR spectroscopy at δ 76.2 and 74.1 (JPP ) 28 Hz). Although
the dmpe methyl groups are nonequivalent by 1H NMR
spectroscopy at this temperature, the silicon-methyl groups
remain symmetry-equivalent. The JHSi value does not change
over the temperature range of -75 to 50 °C, and it is difficult
to ascertain the nature of this exchange process. This behavior
could be simply explained by a “freezing out” of the confor-
mational exchange of the dmpe molybdenum ring. The same
behavior is observed for diethylsilylene complex 4b. Even at
-80 °C, the 13C {1H} NMR spectrum of 4b exhibits a
symmetry-equivalent set of ethyl groups.
Bond Angles
Mo-H-Si
83.0(6)
45.5(4)
51.5(4)
125.3(5)
131.5(5)
102.1(5)
C17-Si-H1
C19-Si-H1
Si-Mo-P1
Si-Mo-P2
P1-Mo-P2
102.0(6)
114.5(6)
87.1(3)
101.9(4)
77.4(3)
H-Mo-Si
Mo-Si-H1
Mo-Si-C17
Mo-Si-C19
C17-Si-C19
Mo-Si bond distance in 4b (2.348(7) Å) is similar to the short
Mo-Si separation observed in the structure of 4a.
Single-crystal neutron diffraction is a useful tool for accurately
determining locations of hydrogen atoms in molecular structures.
Therefore, neutron data were collected for a large (2 mm3) dark
red crystal of 4b. The sample was later determined to contain
a second crystallite. The two components were indexed sepa-
rately with their respective orientation matrixes. In general,
observed peaks were indexed for one or the other crystallite,
but not for both. Attempts to refine the 42 hydrogen atoms with
anisotropic thermal ellipsoids led to nonpositive definite el-
lipsoids for two of the hydrogen atoms. Therefore, in the final
refinement all the atoms were refined isotropically. An ORTEP
diagram of the structure of 4b, as determined by neutron
diffraction, is shown in Figure 3, and bond distances and angles
are given in Table 4.
X-ray diffraction data were also collected for a dark red
crystal of the diethylsilylene complex 4b. An ORTEP diagram
of 4b (Figure 2) reveals a structural model that is distinctly
different from that of 4a. The hydride ligand of 4b was located
as the largest peak in the residual electron density map, and its
coordinates were refined. The hydride was located in a bridging
position across the molybdenum-silicon bond and resides in
the wedge between Si and P2. The P-Mo-Si angles of 101.44-
(3)° and 86.88(3)° reveal that this complex is far from mirror-
symmetric and that it has a structure of type V in Chart 1. The
The structure derived from the neutron data unequivocally
determines the location of the hydride ligand of 4b to be in a
bridging position associated with the molybdenum-silicon
(13) Nikonov, G. I. Organometallics 2003, 22, 1597 and references therein.
9
10432 J. AM. CHEM. SOC. VOL. 126, NO. 33, 2004

Silylene Hydride Complexes of Molybdenum
A R T I C L E S
bond. The molybdenum-hydrogen separation of 1.85(1) Å is
approximately 15 pm longer than those observed in the
structures of Cp2MoH2 (Mo-H ) 1.685(3) Å)14 and (2,6-
Me2C6H3(iPr)N)2(η2-2,6-Me2C6H3NdCMe2)MoH15 (Mo-H )
1.69(5) Å). The silicon-hydrogen separation of 1.68(1) Å is
approximately 20 pm longer than 1.48 Å, the average value
observed in hydrosilanes.12
For comparison, the only other complex characterized by
neutron diffraction that features a metal-hydrogen-silicon
three-center bonding interaction is the compound (η5-C5H4Me)-
(CO)2(H)Mn(SiFPh2), which was reported by Schubert and co-
workers.16 This complex features a long silicon-hydrogen
distance of 1.802(5) Å and a manganese-hydrogen bond length
of 1.569(4) Å. The structure of this species has been described
as representing an “arrested” stage of oxidative addition of the
silicon-hydrogen bond to the Mn center.
Figure 4. ORTEP diagram of phenylsilylene complex 5a.
Reactions of Complex 2 with Monosubstituted Silanes.
Silylene complexes featuring hydride substituents at silicon are
rare, and very little is known about the chemistry of the Si-H
bonds at sp2 hybridized silicon centers. Hydrosilylene complexes
have been generated and studied in situ, but none have been
isolated and structurally characterized.4d,j It is therefore note-
worthy that reactions of 2 with the monosubstituted silanes
PhSiH3, MesSiH3, and PhCH2SiH3 resulted in formation of the
hydrosilylene complexes Cp*(dmpe)Mo(H)Si(H)R (5a: R )
Ph, 5b: R ) Mes, 5c: R ) CH2Ph), as shown in eq 3.
Table 1. Infrared spectroscopy of complexes 5a and 5b revealed
Si-H stretching absorbances at 1896 and 1948 cm-1, respec-
tively. The metal hydride stretching absorbances were not
detected for complexes 5a and 5b. Compounds 5a and 5b were
isolated by recrystallization from pentane in 69 and 60% yields,
respectively. Benzylsilylene complex 5c was isolated as a purple
sticky solid and could not be obtained as an analytically pure
material. Reactions of 2 with the hydrosilanes C6F5SiH3 and
SiH4 resulted in decomposition to mixtures of unidentified
products.
Phenylsilylene complex 5a was isolated as black-yellow
crystals by recrystallization from pentane, and its structure was
determined by an X-ray diffraction study. An ORTEP diagram
of the structure is shown in Figure 4. A crystallographically
imposed mirror plane bisects the molecule, as in the structure
of 4a. This results in the same disorder in the dmpe ligand
conformation, and this disorder was modeled accordingly. For
clarity, only one orientation of the dmpe ligand is shown in
Figure 4. The molybdenum hydride ligand was not located in
the final Fourier difference electron density map, although it
probably interacts with the silicon center in a three-center two-
electron fashion, as is clearly the case in the structure of 4b. A
peak for the terminal silicon hydride was located in the electron
density map, and its position was refined to a location on the
mirror plane 1.43(4) Å from the silicon center. This is in the
expected range of Si-H bond distances for organosilanes and
metal-hydrosilyl complexes (the average Si-H distance in
hydrosilanes is approximately 1.48 Å).12 The Mo-Si distance
of 2.317(1) Å is quite short and is in keeping with the
descriptions of these species as having significant silylene
character.
Spectroscopic data for complexes 5a-c are consistent with
their descriptions as silylene hydride complexes with significant
hydrogen-silicon bonding interactions. For example, the phe-
nylsilylene complex 5a exhibits a downfield-shifted triplet
resonance in its 29Si{1H} NMR spectrum at δ 250 (JSiP ) 26
Hz). Silylene character at the silicon centers of 5b and 5c is
also implied by downfield-shifted 29Si NMR resonances at δ
214 and 239, respectively. Significant features of the 1H NMR
spectrum of 5a are the Si-H and bridging Mo-H resonances
at δ 9.45 and -9.96, respectively. The Si-H resonance is a
multiplet coupled to the molybdenum-bound hydride ligand (JHH
) 3 Hz) and the phosphorus nuclei (JHP ) 3 Hz). This resonance
exhibits 29Si satellites with a JHSi value of 130 Hz. The
molybdenum hydride resonance is observed as a doublet of
Reactions of Molybdenum Silylene Complexes with CO.
As further characterization of these new silylene complexes,
their reactions with carbon monoxide were examined. An excess
(approximately 5 equiv at 1 atm) of carbon monoxide was
introduced to a red benzene solution of Cp*(dmpe)Mo(H)-
(SiMe2). After 5 min, the solution changed color to yellow-
orange, and a new product had formed by 31P{1H} NMR
spectroscopy (δ 60.5, 54.4; JPP ) 20 Hz). The new compound,
isolated by recrystallization from toluene, was characterized as
the silyl carbonyl complex Cp*(dmpe)(CO)MoSiHMe2 (6a,
Scheme 3). This species is a CO adduct of the putative 16-
electron silyl intermediate [Cp*(dmpe)MoSiHMe2], and its
triplets with silicon satellites (JHP ) 19 Hz, JHH ) 3 Hz, JHSi
)
30 Hz). Selected data for these complexes are also included in
(14) Schultz, A. J.; Stearley, K. L.; Williams, J. M.; Mink, R.; Stucky, G. D.
Inorg. Chem. 1977, 12, 3303.
(15) Tsai, Y.-C.; Johnson, M. J. A.; Mindiola, D. J.; Cummins, C. C. J. Am.
Chem. Soc. 1999, 121, 10426.
(16) (a) Schubert, U.; Ackermann, K.; Wo¨rle, B. J. Am. Chem. Soc. 1982, 104,
7378. (b) Schubert, U.; Scholz, G.; Mu¨ller, J.; Ackermann, K.; Wo¨rle, B.;
Stansfield, R. F. D. J. Organomet. Chem. 1986, 306, 303.
9
J. AM. CHEM. SOC. VOL. 126, NO. 33, 2004 10433

A R T I C L E S
Mork et al.
Scheme 3
formation suggests the possibility of reversible hydride migration
from silicon to molybdenum, as shown in Scheme 3. The same
result was observed in the reaction of phenylsilylene complex
5a with CO to give the phenylsilyl compound 6b (Scheme 3).
Characteristic data for complexes 6a and 6b include their 29Si-
{1H} NMR shifts at δ 21 and 16, respectively. In addition, the
complexes exhibit CO stretching frequencies at 1781 and 1788
cm-1, respectively. Carbon-oxygen stretching frequencies of
such low energy indicate that the molybdenum centers are quite
electron-rich and strongly π-back-donating.
Reaction of 5a with PhSiH3. Phenylsilylene complex 5a was
found to react with 1 equiv of PhSiH3 at 60 °C over 14 h in
benzene solution. As the reaction progressed, the solution
changed from the black-yellow color of 5a to the light yellow
color of the new product. Isolation and spectroscopic charac-
terization of this product identified it as the bis(silyl) hydride
complex Cp*(dmpe)(H)Mo(SiH2Ph)2 (7, eq 4). Compound 7
possesses Cs symmetry by 31P{1H} NMR spectroscopy, and its
proton NMR spectrum features resonances for a single Mo-H
and four Si-H hydrogens. The hydride ligand resonance (δ
-7.27, JHP ) 40 Hz) does not feature observable silicon
satellites, and therefore JHSi e 10 Hz. This suggests that there
is little or no bonding interaction between the hydride and the
two silicon centers in 7. A single resonance at δ 10.1 is observed
for the symmetry-equivalent silicon centers in the 29Si{1H}
NMR spectrum of 7, implying silyl character for the silicon-
based ligands.
Figure 5. ORTEP diagram of bis(silyl) complex 7.
Table 5. Selected Bond Distances (Angstroms) and Angles (deg)
for 7a
Bond Distances
Mo-Si1
Mo-P1
2.504(3)
2.447(3)
Mo-Si2
Mo-P2
2.531(3)
2.480(3)
Bond Angles
P1-Mo-P2
75.7(1)
89.5(1)
131.4(1)
116.5(3)
109.7(3)
Si1-Mo1-Si2
P1-Mo-Si2
P2-Mo-Si2
CNT-Mo-P2
CNT-Mo-Si2
78.1(1)
134.6(1)
80.5(1)
118.4(3)
108.8(3)
P1-Mo-Si1
P2-Mo-Si1
CNT-Mo-P1
CNT-Mo-Si1
a
The abbreviation CNT represents the centroid of the C5Me5 ligand.
triplet resonance for the molybdenum deuteride at δ -7.30 (JDP
) 6 Hz), as well as a broad resonance for the -SiD2Ph group
at δ 4.97. The isotopomer that is formed in this reaction appears
to result from Si-D bond activation of PhSiD3 by an intermedi-
ate 16-electron molybdenum silyl complex. Thus, this reaction
also proceeds via the initial migration of hydrogen from
molybdenum to silicon.
Yellow, X-ray quality crystals of the bis(silyl) hydride
complex 7 were obtained by recrystallization from toluene, and
the structure of 7 was determined by X-ray diffraction tech-
niques. An ORTEP diagram of complex 7 is shown in Figure
5, and selected bond distances and angles are listed in Table 5.
Although the molybdenum hydride ligand was not located in
the electron density map, it might be located in the open
coordination site trans to the Cp* ligand. This five-legged piano
17
stool geometry has precedent in complexes such as Cp*WMe5
and [WCl4(PMe3)]2(η5,η5-C5Et4CH2CH2C5Et4).18 Unfortunately,
determination of the silicon-hydrogen bond distances of interest
was not possible by neutron diffraction, since crystals of
complex 7 were too small and thin. The X-ray diffraction data
collected for this complex were somewhat weak, and this
resulted in a low data-to-parameter ratio for the model refine-
ment. The final model included anisotropically refined Mo, Si,
and P atoms, while the carbon atoms were refined isotropically.
Although accurate metric parameters could not be obtained for
the structure of 7, the data unambiguously determine the
connectivity of the complex and its identity as a bis(silyl)
species.
A deuterium-labeling study was performed by reaction of 5a
with PhSiD3 over 14 h at 60 °C in benzene. The product of this
reaction was the deuterated species Cp*(dmpe)(D)Mo(SiD2Ph)-
(SiH2Ph) (7-d3). The 2H{1H} NMR spectrum of 7-d3 exhibits a
(17) Liu, A. H.; Murray, R. C.; Dewan, J. C.; Santarsiero, B. D.; Schrock, R.
R. J. Am. Chem. Soc. 1987, 109, 4282.
(18) MacLaughlin, S. A.; Murray, R. C.; Dewan, J. C.; Schrock, R. R.
Organometallics 1985, 4, 796.
9
10434 J. AM. CHEM. SOC. VOL. 126, NO. 33, 2004

Silylene Hydride Complexes of Molybdenum
A R T I C L E S
Scheme 4
Reactions of Silylene Complexes with Unsaturated Or-
ganic Compounds. It was of interest to define the reactivity of
these new silylene complexes toward unsaturated organic
substrates. In reactions of complexes 4a and 5a with benzal-
dehyde and benzophenone, decomposition to unidentified
mixtures of products was observed. No clean compounds could
be isolated from these mixtures by crystallization from pentane
or toluene at -30 °C over 12 h. Complexes 4a and 5a were
found to be unreactive toward stoichiometric or excess amounts
of bis(trimethylsilyl)acetylene, diphenylacetylene, ethylene, and
1-hexene at room temperature. In each reaction, heating the
mixture to 100 °C resulted in decomposition to a complex
mixture of products. However, a clean transformation was
observed in the reaction of complex 4a with the terminal alkyne
Me3SiCtCH in benzene solution. Recrystallization of the new
product from diethyl ether resulted in orange crystals of the
vinylidene complex Cp*(dmpe)(H)ModCdC(SiMe3)(SiMe2H)
(8, eq 5). Interestingly, this is the first observation of a reaction
that transforms a silylene complex into a carbene-like complex.
determine whether the vinylidene complex 8 possesses a
hydrogen-R-carbon interaction. This issue was addressed by
acquiring a proton-coupled 13C NMR spectrum and observing
the resonance for CR. The 13C NMR spectrum of complex 8
displays a multiplet resonance for CR (JCP ) 13 Hz, JCH ) 13
Hz). A JCH coupling constant of 13 Hz is much lower than would
be expected for a significant bonding interaction between CR
and the hydride ligand.19
The mechanism of the reaction that forms 8 would seem to
involve multiple steps, though no intermediates were observed
1
when the reaction was monitored by H and 31P{1H} NMR
spectroscopy at room temperature. A plausible mechanism for
this transformation is shown in Scheme 4 and involves
coordination of the alkyne to the intermediate 16-electron silyl
complex as a first step. Insertion of the alkyne into the metal-
silicon bond and subsequent R-elimination of the vinyl hydrogen
would result in the observed product 8. The closely related
vinylidene complex Cp[P(OMe3)]2BrModCdC(H)Ph was re-
ported by Green et al. and was formed by a mechanism
involving nucleophilic attack of a hydride on coordinated
1-bromo-2-phenylacetylene in the cation {Cp[P(OMe)3]2Mo-
(η2-PhCtCBr)}+.20
The structure of vinylidene complex 8 was verified by an
X-ray diffraction study, and an ORTEP diagram of the complex
is shown in Figure 6. Table 6 lists selected bond distances and
angles for the structure. The short Mo-C17 bond distance (C17
) CR) of 1.920(4) Å and the Mo-C17-C18 angle of 171.5-
(3)° support the formulation of 8 as a vinylidene complex. The
hydride ligand was located as a peak in the Fourier difference
electron density map, and its coordinates were refined to a
location 1.52(8) Å from the molybdenum center. The H-C17
distance of 1.723 Å is much longer than that of a typical C-H
bond (approximately 1.0 Å), and this also indicates the absence
of an Mo-H‚‚‚CR interaction.
Spectroscopic data for 8 are in agreement with its description
as a vinylidene hydride complex. The H NMR spectrum of 8
1
features a triplet resonance for the molybdenum hydride ligand
at δ -7.34 (JHP ) 34 Hz). Compound 8, like the silylene
complexes reported here, exhibits Cs symmetry by NMR
spectroscopy at room temperature. The 13C{1H} NMR spectrum
of 8 exhibits characteristic resonances for the CR and Câ carbons
of the vinylidene ligand at δ 317.9 (triplet, JCP ) 12 Hz) and
92.5 (singlet), respectively.
Reactions of Complex 4a with Lewis Bases. Most of the
reported base-free silylene complexes are electrophilic at silicon
and bind Lewis bases at their silicon centers.4 In fact, many
silylene complexes have only been isolated in their base-
(19) Brookhart, M.; Green, M. L. H.; Wong, L.-L. Prog. Inorg. Chem. 1988,
36, 1.
(20) (a) Beevor, R. G.; Greem, M.; Orpen, A. G.; Williams, I. D. J. Chem.
Soc., Chem. Commun. 1983, 673. (b) Beevor, R. G.; Green, M.; Orpen, A.
G.; Williams, I. D. J. Chem. Soc., Dalton Trans. 1987, 1319.
Given the observed structures for the molybdenum silylene
hydride complexes described above, it was of interest to
9
J. AM. CHEM. SOC. VOL. 126, NO. 33, 2004 10435

A R T I C L E S
Mork et al.
Scheme 5
Figure 6. ORTEP diagram of vinylidene complex 8.
Table 6. Selected Bond Distances (Angstroms) and Angles (deg)
for 8
as two inequivalent silicon-methyl groups. The NMR data
therefore suggest that the new product resulted from a reaction
involving one of the dmpe methyl groups. The chemical shift
of the 29Si{1H} NMR resonance (δ 9.0) is consistent with a
molybdenum silyl complex. Taken together, the spectroscopic
data are in keeping with the structure Cp*(κ3-Me2PCH2-
CH2P(Me)CH2SiMe2)MoH2 (10a, Scheme 5), in which the
silylene and dmpe fragments have been coupled to form a
tridentate bis(phosphine)silyl ligand. A plausible mechanism for
this rearrangement involves initial C-H activation of a dmpe
methyl group. Subsequent C-Si bond reductive elimination
followed by Si-H bond oxidative addition would give the
observed product (Scheme 5).
The structure of complex 10a was confirmed by an X-ray
diffraction study. Although the solution verifies the connectivity
proposed for 10a, the structure contains a significant amount
of positional disorder in the Cp* and Me2PCH2CH2P(Me)CH2-
SiMe2 ligands. The data are not of sufficient quality to obtain
a good model for this disorder, and therefore accurate metric
parameters for 10a could not be derived from the analysis.
Stobart and co-workers have published related examples of
transition-metal complexes containing bis(phosphine)silyl
ligands.22
Bond Distances
Mo-C17
Mo-P1
Mo-P2
Mo-H
1.920(4)
2.408(1)
2.407(1)
1.52(8)
C17-C18
C18-Si1
C18-Si2
1.345(5)
1.840(4)
1.865(4)
Bond Angles
76.23(4)
86.2(1)
P1-Mo-P12
P1-Mo-C17
P2-Mo-C17
P1-Mo-H
P2-Mo-H
C17-Mo-H
121(3)
71(3)
59(3)
105.0(1)
stabilized forms.1,21 To explore the electronic properties of the
silylene complexes reported here, the interactions of silylene
complex 4a with the Lewis bases THF and DMAP were
examined (DMAP ) 4-(dimethylamino)pyridine). When 1 equiv
of THF was added to a solution of dimethylsilylene complex
4a in benzene-d6, there was no apparent change in color of the
red solution. Analysis of NMR spectra of this mixture revealed
that the THF does not bind to 4a under these conditions. The
chemical shift of the 29Si NMR resonance for the mixture is
exactly the same as for 4a in the absence of THF (δ 263).
Addition of 1 equiv of DMAP to a benzene-d6 solution of
4a resulted in an immediate color change to a darker red. The
spectral data of this solution are consistent with the formation
of the base-stabilized silylene complex Cp*(dmpe)Mo(H)-
A thermal rearrangement was also observed for diphenylsi-
lylene complex 4d at 100 °C in benzene, and the new complex
exhibits a 29Si NMR resonance at δ -3.4. The product exhibited
1H, 13C{1H}, 31P{1H}, and NMR spectra very similar to those
of 10a and was therefore characterized as the diphenyl analogue
of 10a, Cp*(κ3-Me2PCH2CH2P(Me)CH2SiPh2)MoH2 (10b). For
comparison, the hydrosilylene complexes 5a and 5b do not
decompose cleanly at 110 °C over a few hours.
1
(SiMe2‚DMAP) (9). The H NMR spectrum of compound 9
features a resonance for its hydride ligand at -12.92 (triplet,
JHP ) 20 Hz). The 1H, 29Si HMBC NMR spectrum of 9 exhibits
a cross-peak for the hydride ligand resonance at δ 179 (JSiH
)
17 Hz). In comparison with the attempted reaction of 4a with
THF, it seems that the stronger donor DMAP coordinates to
the dimethylsilylene silicon center. However, the 29Si NMR
resonance is significantly downfield-shifted, indicating signifi-
cant silylene character for complex 9. It seems that the DMAP
ligand is only weakly bound to the silicon center, and 9 appears
to be in rapid equilibrium with 4a and free DMAP.
Thermal Rearrangements of 4a and 4d. Thermal decom-
positions proceeded cleanly for 4a and 4d. Heating a benzene
solution of 4a at 100 °C for 4 h quantitatively produced a new
product. This species exhibits two doublet resonances in the
31P{1H} NMR spectrum, at δ 59.5 and 39.6 (JPP′ ) 18 Hz).
Concluding Remarks
These investigations highlight the utility of a coordinatively
unsaturated transition-metal alkyl complex as a starting point
for the synthesis of molybdenum silylene complexes. Benzyl
complex 2 reacts with a series of hydrosilanes to give a new
class of neutral, base-free silylene complexes. These species
are remarkably stable, and their thermal decompositions are
observed only at temperatures above 100 °C.
1
Careful analysis of the H NMR spectrum of the new product
revealed resonances for three inequivalent PMe groups, as well
The compounds 4a-d and 5a-c are best described as silylene
hydride complexes that feature weak H‚‚‚Si bonding interactions
(21) See, for example: (a) Leis, C.; Wilkinson, D. L.; Handwerker, H. Zybill,
C. Organometallics 1992, 11, 514. (b) Sakaba, H.; Tsukamoto, M.; Hirata,
T.; Kabuto, C.; Horino, H. J. Am. Chem. Soc. 2000, 122, 11511. (c) Ueno,
K.; Sakai, M.; Ogino, H. Organometallics 1998, 17, 2138.
(22) See, for example: (a) Zhou, X.; Stobart, S. R. Organometallics 2001, 20,
1898. (b) Bushnell, G. W.; Casado, M. A.; Stobart, S. R. Organometallics
2001, 20, 601.
9
10436 J. AM. CHEM. SOC. VOL. 126, NO. 33, 2004

Silylene Hydride Complexes of Molybdenum
A R T I C L E S
in their ground-state structures. The 29Si NMR resonances for
these complexes fall in the range of δ 213-273. These chemical
shifts, taken with the planar geometries observed for the MoSiR2
fragments in their solid-state structures, provide support for their
formulation as silylene complexes. However, the combination
of high JHSi coupling constants (in the range of 30-48 Hz) and
the bridging hydride ligand in the solid-state neutron structure
of 4b provides good evidence for the presence of weak
hydrogen-silicon bonding interactions in this class of com-
pounds. Therefore, it is suitable to describe these silylene
compounds with the structural model depicted by structure V
in Chart 1. This structure is intermediate between a silylene
hydride complex with a hydride silicon donor interaction and
one with entirely R-agostic hydrosilyl character (structures IV
and III in Chart 1, respectively). These compounds are the first
examples of base-free molybdenum silylene complexes and
represent an important step in expanding silylene chemistry to
the early transition elements. These complexes may be consid-
ered as possessing molybdenum(II), d4 metal centers. Alterna-
tively, in the extreme case of complete scission of the Si-H
bond and very strong π-back-bonding to the silylene ligand they
could be classified as having molybdenum(IV), d2 metal centers.
As most of the known examples of silylene complexes feature
late transition elements with six or more d-electrons, these
molybdenum silylenes are rare in that they have a relatively
low dn electron configuration.
Chemistry at the University of California, Berkeley. FT-infrared spectra
were recorded as KBr pellets on a Mattson FTIR 3000 instrument.
NMR Measurements. Routine 1H, 13C{1H}, 31P{1H}, and 29Si{1H}
NMR spectra were recorded at 298 K on either a Bruker DRX-500
instrument equipped with a 5 mm broad band probe and operating at
500.1 MHz (1H), 125.8 MHz (13C), 202.5 MHz (31P), and 99.4 MHz
(29Si), or a Bruker AMX-400 instrument operating at 400.1 MHz (1H)
or 100.6 MHz (13C). Chemical shifts are reported in ppm downfield
from internal SiMe4 (1H, 13C, 29Si), and external 85% H3PO4 (31P);
coupling constants are given in Hz. Bruker XWINNMR software (ver.
2.1) was used for all data processing.
X-ray Crystallography. All single-crystal X-ray analyses were
carried out at the UC Berkeley CHEXRAY crystallographic facility.
Measurements were made on a Bruker SMART CCD area detector
with graphite monochromated Mo KR radiation (λ ) 0.71069 Å). Data
were integrated by the program SAINT and analyzed for agreement
using XPREP. Empirical absorption corrections were made using
SADABS. Structures were solved by direct methods and expanded using
Fourier techniques. Calculations for all structures were performed using
the SHELX-TL software package. Details of data collections and
refinements are given in Table 2 and in the supporting CIF files.
Neutron Crystallography. Neutron diffraction data were obtained
at the Intense Pulsed Neutron Source (IPNS) at Argonne National
Laboratory using the time-of-flight Laue single-crystal diffractometer
(SCD).26 A crystal of compound 4b with approximate dimensions of 2
× 1 × 1 mm3 was covered in a fluorocarbon grease in a glovebag,
wrapped in aluminum foil, and glued to an aluminum pin, which was
mounted on the cold stage of a closed-cycle helium refrigerator
operating at 20 ( 0.1 K for data collection. The GSAS software package
was used for structural analysis.27 Data collection and refinement
parameters are summarized in Table 2, with details provided in the
supporting CIF files.
The observed reactions of silylene complexes of the type Cp*-
(dmpe)Mo(H)(SiRR’) are dominated by initial R-hydrogen
migrations to form 16-electron silyl species, Cp*(dmpe)-
MoSiHRR’. This suggests that the silylene hydride and 16-
electron silyl complexes are in rapid equilibrium, with the latter
species being more reactive. This reactivity mode is also
consistent with the observation of significant hydrogen-silicon
interactions in the ground-state structures of the silylene
complexes. Thus, these complexes act as resting states for
reactive, coordinatively unsaturated silyl compounds. Future
studies will involve use of the synthetic methodology described
here in the synthesis of early metal silylene complexes without
hydride ligands. Such complexes should allow further charac-
terization of the chemistry of silylene complexes with low dn
configurations.
Cp*(dmpe)(PMe3)MoCl (1). A slurry of Cp*MoCl4 (5.00 g, 13.4
mmol) in 100 mL of benzene was added to a rapidly stirring mixture
of PMe3 (1.39 mL, 13.4 mmol), dmpe (2.24 mL, 13.4 mmol), and 94
g Na/Hg (1.0% w/w) in 100 mL of benzene. Stirring was continued
for 16 h at 60 °C, and then the mixture was allowed to cool to room
temperature. The purple-red solution was filtered to remove salts, and
the benzene was removed under reduced pressure to give 5.85 g of 1
1
as a purple solid in 89% yield. The crude product was pure by H
NMR spectroscopy and was of sufficient purity for further use.
Analytically pure 1 can be obtained by recrystallization from pentane.
1H NMR (benzene-d6): δ 1.64 (s, 15 H, C5Me5), 1.47 (d, 3 H, PMe,
JHP ) 8 Hz), 1.35 (d, 3 H, PMe, JHP ) 8 Hz), 1.29 (d, 9 H, PMe3, JHP
) 7 Hz), 1.15 (d, 3 H, PMe, JHP ) 7 Hz), 0.94 (d, 3 H, PMe, JHP ) 7
Hz). 13C{1H} NMR (benzene-d6): δ 98.7 (s, C5Me5), 36.9 (m, PMe),
27.2 (dd, PCH2, JCP )23 Hz, JCP′ ) 7 Hz), 25.1 (dd, PCH2, JCP ) 23
Hz, JCP′ ) 17 Hz), 24.5 (m, PMe), 21.4 (m, PMe), 21.2 (d, PMe3, JCP
) 20 Hz), 19.4 (m, PMe), 12.7 (s, C5Me5). 31P{1H} NMR (benzene-
d6): δ 66.0 (dd, JPP′ ) 30 Hz, JPP′′ ) 22 Hz), 61.2 (dd, JPP′ ) 59 Hz,
Experimental Section
General. All experiments were performed under an atmosphere of
dry nitrogen using standard Schlenk techniques or in a drybox. Pentane
and ether were distilled from sodium/benzophenone, and benzene was
distilled from potassium. Toluene was pretreated with H2SO4, NaHCO3,
and MgSO4 to remove trace thiophene impurities and then distilled
from sodium. To remove olefin impurities, pentane was pretreated with
concentrated H2SO4, 0.5 N KMnO4 in 3M H2SO4, NaHCO3, and then
anhydrous MgSO4. Benzene-d6 and toluene-d8 were distilled from Na/K
alloy. The reagents Cp*MoCl4,11 1,2-bis(dimethylphosphino)ethane,23
JPP′′ ) 30 Hz), 13.3 (dd, JPP′ ) 59 Hz, JPP′′ ) 22 Hz). IR (KBr, cm-1
)
2972 m, 2946 w, 2902 s, 1462 w, 1415 m, 1371 m, 1296 w, 1263 m,
1076 w, 1024 m, 933 s, 912, s, 897 s, 833 m, 802 w, 690 m, 659 w,
631 m, 453 w. Anal. Calcd for C19H40ClMoP3: C, 46.31; H, 8.18.
Found: C, 46.14; H, 8.37.
Cp*(dmpe)Mo(η3-CH2Ph) (2). A solution of 9.74 mmol of PhCH2-
MgCl (1.0 M in Et2O) was added dropwise over 10 min to a stirred
solution of 4.80 g (9.74 mmol) of 1 in 200 mL of benzene. Upon
addition, the mixture changed color from red-purple to red-orange.
Stirring was continued for 1 h, and a precipitate was observed. The
mixture was then allowed to settle, and the supernatant was filtered
into another flask. The remaining salts were washed with benzene (2
MesSiH3,24 PhSiH3,25 and Ph2CH2SiH3 were synthesized according
25
to published procedures. Other chemicals were obtained from com-
mercial suppliers and used as received. Elemental analyses were
performed by the Microanalytical Laboratory in the College of
(23) Burt, R. J.; Chatt, J.; Hussain, W.; Leigh, G. J. J. Organomet. Chem. 1979,
182, 203.
(24) (a) Malisch, W.; Hindahl, K.; Ka¨b, H.; Reising, J.; Adam, W.; Prechtl, F.
Chem. Ber. 1995, 128, 9632. (b) So¨ldner, M.; Sandor, M.; Schier, A.;
Schmidbaur, H. Chem. Ber. 1997, 130, 1671.
(26) Schultz, A. J.; Srinivasan, K.; Teller, R. G.; Williams, J. M.; Lukehart, C.
M. J. Am. Chem. Soc. 1984, 106, 999-1003.
(27) Larson, A. C.; Von Dreele, R. B. General Structure Analysis System--
GSAS. Los Alamos National Laboratory: Report LAUR 86-748, 2000.
(25) Sakurai, H.; Shoji, M.; Yajima, M.; Hosomi, A. Synthesis 1984, 7, 598.
9
J. AM. CHEM. SOC. VOL. 126, NO. 33, 2004 10437

A R T I C L E S
Mork et al.
× 10 mL), and the filtrates were combined. Removal of the solvent
under reduced pressure gave crude 2 as an orange-brown solid.
Recrystallization from 40 mL of toluene at -80 °C over 14 h gave
JHSi ) 30 Hz). 13C {1H} NMR (benzene-d6): δ 98.3 (s, C5Me5), 34.8
(m br, 2 PMe), 33.9 (m br, 2 PMe), 23.2 (m, br 2 PCH2), 19.8 (s, SiMe2),
14.1 (s, C5Me5). 31P {1H} NMR (benzene-d6): δ 70.2 (s). 31P {1H}
NMR (toluene-d8, 223 K): δ 76.2 (d, JPP ) 28 Hz), 74.1 (d, JPP ) 28
Hz). 29Si {1H} NMR (benzene-d6): δ 263 (m). IR (KBr, cm-1): 2955
s, 2898 s br, 2803 m, 1548 m br, 1480 w, 1453 w, 1416 m, 1370 m,
1268 m, 1219 m, 1063 w, 1025 m, 924 s br, 826 s, 731 m, 686 m, 654
s, 624 m, 457 w. Anal. Calcd for C18H38MoP2Si: C, 49.08; H, 8.70.
Found: C, 49.09; H, 8.56.
1
3.91 g of 2 (85% yield). H NMR (benzene-d6, 23 °C): δ 7.13 (s br,
1 H, Ar-H), 7.03 (s br, 1 H, Ar-H), 6.58 (t, 1 H, Ar-H, JHH ) 7 Hz),
6.25 (s br, 1 H, Ar-H), 2.80 (m br, 1 H, PhCH2), 2.70 (s br, 1 H, Ar-
H), 1.70 (s, 15 H, C5Me5), 1.48 (s br, 3 H, PMe), 1.3 (br, 2 H, PCH2),
1.10 (s br, 3 H, PMe), 0.98 (s br, 3 H, PMe), 0.8 (br, 2 H, PCH2), 0.62
(s br, 3 H, PMe), -0.54 (s br, 1 H, PhCH2). 1H NMR (toluene-d8, -20
°C): 7.09 (m, 1 H, Ar-H), 6.98 (m, 1 H, Ar-H), 6.56 (m, 1 H, Ar-H),
6.24 (m, 1 H, Ar-H), 2.76 (dd, 1 H, PhCH2, JHP ) 13 Hz, JHH ) 3 Hz),
2.60 (d, 1 H, Ar-H, JHH ) 6 Hz), 1.69 (s, 15 H, C5Me5), 1.47 (d, 3 H,
Cp*(dmpe)Mo(H)(SiEt2) (4b). Diethylsilane (0.045 g, 0.508 mmol)
and 0.200 g (0.423 mmol) of 2 were dissolved in 5 mL of benzene.
The mixture was heated at 50 °C for 15 min, and the solution changed
color to red. The product was isolated by the same method as for 4a,
which gave 0.133 g of red crystals of 4b in 67% yield. 1H NMR
(benzene-d6): δ 2.02 (s, 15 H, C5Me5), 1.5 (m br, 4 H, 2 PCH2), 1.38
(m, 6 H, 2 PMe), 1.11 (s, 6 H, 2 SiCH2CH3), 1.1 (br, 4 H, 2 SiCH2-
CH3), 1.06 (m, 6 H, 2 PMe), -13.91 (t, 1 H, Mo-H, JHP ) 17 Hz, JHSi
PMe, JHP ) 6 Hz), 1.3 (m br, 1 H, PCH2), 1.09 (d, 3 H, PMe, JHP
)
5 Hz), 1.0 (m br, 1 H, PCH2), 0.99 (d, 3 H, PMe, JHP ) 7 Hz), 0.82
(m, 1 H, PCH2), 0.75 (m, 1 H, PCH2), 0.58 (d, 3 H, PMe, JHP ) 6 Hz),
-0.62 (m, 1 H, PhCH2). 13C{1H} NMR (benzene-d6, 23 °C): δ 139.1,
135.5, 122.4, 120.6, 98.2 (s, Ar), 95.9 (s, C5Me5), 66.2 (s, Ar, Mo-
bound), 36.9 (s, ArCH2), 29.8 (s br, PCH2), 28.0 (s br, PCH2), 25.2,
23.2, 21.0, 14.4 (s, PMe), 12.7 (s, C5Me5). 31P {1H} NMR (benzene-
d6, 23 ° C): δ 63.8 (s), 61.2 (s). IR (KBr, cm-1): 3027 w, 2979 m,
2964 m, 2905 s, 2854 m, 1587 w, 1508 w, 1463 w, 1410 m, 1371 m,
1354 w, 1286 m, 1269 m, 1082 m, 1022 m, 926 s, 897 m, 825 w, 764
w, 727 s, 701 m, 683 m, 623 w, 604 w. Anal. Calcd for C23H38MoP2:
C, 58.47; H, 8.11. Found: C, 58.39; H, 8.22.
1
) 44 Hz). H NMR (toluene-d8, -80 °C): δ 2.00 (s, 15 H, C5Me5),
1.8 (m, 1 H, PCH2), 1.5 (m, 1 H, PCH2), 1.45 (d, 3 H, PMe, JHP ) 7
Hz), 1.31 (m, 1 H, PCH2), 1.2 (m br, 4 H, 2 SiCH2), 1.18 (d, 3 H,
PMe, JHP ) 6 Hz), 1.17 (m, 6 H, 2 SiCH2CH3), 1.09 (d, 3 H, PMe, JHP
) 6 Hz), 0.9 (m, 1 H, PCH2), 0.84 (d, 3 H, PMe, JHP ) 5 Hz), -13.9
(dd, Mo-H, JHP ) 25 Hz, JHP′ ) 5 Hz). 13C{1H} NMR (benzene-d6, 23
°C): δ 98.5 (s, C5Me5), 35.1 (m, 2 PMe), 35 (br, 2 PCH2), 23.6 (s, 2
SiCH2), 23.4 (m, 2 PMe), 14.1 (s, C5Me5), 8.5 (s, 2 SiCH2CH3). 13C-
{1H} NMR (toluene-d8, -80 °C): δ 97.9 (s, C5Me5), 35.5 (m, PCH2),
35.3 (m, PMe), 32.9 (m, PCH2), 32.6 (PMe), 23.3 (m, PMe), 23.2 (br,
2 SiCH2), 21.8 (m, PMe), 14.1 (s, C5Me5), 8.7 (s, 2 SiCH2CH3). 31P-
{1H} NMR (benzene-d6, 23 °C): δ 71.3 (s). 31P{1H} NMR (toluene-
d8, -80 °C): δ 72.0 (d, JPP ) 28 Hz), 69.9 (d, JPP ) 28 Hz). 29Si{1H}
NMR (benzene-d6, 23 °C): δ 273 (m). IR (KBr, cm-1): 2944 s, 2897
s, 2865 s, 1482 w, 1454 w, 1415 m, 1370 m, 1284 w, 1268 m, 1220
w, 1025 m, 927 s, 882 m, 826 m, 703 m, 675 m, 621 m, 590 w, 454
w. Anal. Calcd for C20H42MoP2Si: C, 51.27; H, 9.04. Found: C, 51.41;
H, 9.04.
Cp*(dmpe)(CO)MoCH2Ph (3). A solution of 0.170 g (0.360 mmol)
of 2 in 5 mL of benzene was placed under an excess (approximately 5
equiv) of CO at 1 atm. The mixture was heated at 60 °C for 1 h, and
this resulted in a light orange solution. The volatile materials were
removed under reduced pressure, and the product was redissolved in 5
mL of diethyl ether. The ether solution was concentrated to ap-
proximately 1 mL and placed in the freezer at -30 °C for 3 d. Orange
crystals of 3 were isolated in 21% yield (0.038 g) by decanting the
supernatant and drying the product under vacuum. The yield of 3 is
1
low because of its high solubility. H NMR (benzene-d6): δ 7.13 (m,
2 H, Ar-H), 7.06 (m, 2 H, Ar-H), 6.94 (m, 1 H, Ar-H), 2.37 (s, 2 H,
PhCH2), 1.68 (s, 15 H, C5Me5), 1.54 (d, 3 H, PMe, JHP ) 10 Hz), 1.4
Cp*(dmpe)Mo(H)(SiMePh) (4c). Phenylmethylsilane (0.052 g,
0.423 mmol) and 0.200 g (0.423 mmol) of 2 were dissolved in 5 mL
of benzene. The mixture was heated at 50 °C for 15 min, and the
solution changed color to burgundy. The product was isolated by the
same method as for 4a, which gave 0.132 g of purple microcrystalline
(m br, 1 H, PCH2), 1.3 (m br, 1 H, PCH2), 1.15 (d, 3 H, PMe, JHP
)
8 Hz), 1.0 (m, 1 H, PCH2), 0.89 (d, 3 H, PMe, JHP ) 8 Hz), 0.8 (m, 1
H, PCH2), 0.38 (d, 3 H, PMe, JHP ) 9 Hz). 13C{1H} NMR (benzene-
d6): δ 253.2 (m, CO), 165.8, 147.4, 146.2, 143.3 (Ar), 100.4 (s, C5-
Me5), 34.4 (dd, PCH2, JCP ) 31 Hz, JCP′ ) 19 Hz), 30.4 (m, PCH2),
21.5 m, PhCH2), 21.2 (m, PMe), 19.8 (m, PMe), 17.0 (m, PMe), 15.3
(m, PMe), 12.2 (s, C5Me5). 31P{1H} NMR (benzene-d6): δ 54.1 (d, JPP
) 26 Hz), 42.9 (d, JPP ) 26 Hz). IR (KBr, cm-1): 3046 w, 2963 w,
2901 m, 2861 w, 1779 s (νCO), 1572 w, 1553 w, 1478 m, 1421 m,
1374 m, 1278 m, 1024 w, 932 m, 893 m, 835 w, 798 m, 766 w, 712
w, 689 m, 653 m, 577 w, 516 w. Anal. Calcd for C24H38MoOP2: C,
57.60; H, 7.65. Found: C, 57.65; H, 7.73.
1
4c in 62% yield. H NMR (benzene-d6): δ 7.44 (m, 2H, o-Ph), 7.25
(t, 2 H, m-Ph, JHH ) 7 Hz), 7.12 (m, 1 H, p-Ph), 1.91 (s, 15 H, C5Me5),
1.49 (m, 4 H, 2 PCH2), 1.45 (m, 6 H, 2 PMe), 1.04 (m, 6 H, 2 PMe),
0.78 (d, SiMe, JHH ) 2 Hz), -13.10 (t, 1 H, Mo-H, JHP ) 17 Hz, JHSi
) 46 Hz). 13C{1H} NMR (benzene-d6): δ 156.5, 130.5, 127.5, 127.0
(s, Ph), 98.6 (s, C5Me5), 34.5 (m, 2 PCH2), 33.8 (m, 2 PMe), 23.3 (m,
2 PMe), 21.2 (s, SiMe), 13.9 (s, C5Me5). 31P{1H} NMR (benzene-d6):
δ 69.9 (s). 29Si{1H} NMR (benzene-d6): δ 214 (t, JSiP ) 25 Hz). IR
(cm-1): 3059 w, 3043 w, 2959 m, 2898 s, 1480 w, 1422 m, 1372 m,
1284 w, 1270 m, 1225 w, 1092 m, 1062 w, 1025 m, 932 s, 901 m, 830
w, 781 m, 728 w, 701 s, 666 m, 479 m, 434 m. Anal. Calcd for C23H40-
MoP2Si: C, 54.79; H, 8.03. Found: C, 54.98; H, 8.18.
Cp*(dmpe)Mo(H)(SiMe2) (4a). A 50-mL Schlenk flask was charged
with 0.350 g (0.741 mmol) of 2 and 10 mL of benzene. The headspace
above the solution was evacuated briefly and then backfilled with 1
atm of Me2SiH2. The reaction mixture was agitated for a few seconds
to draw Me2SiH2 into solution. The flask was then sealed and heated
to 50 °C for 15 min. The benzene was removed in vacuo, and the
resulting solid was extracted into 20 mL of pentane. The red solution
was filtered into another Schlenk flask and concentrated to 3 mL under
reduced pressure. Cooling the concentrated solution at -30 °C for 20
h gave 0.165 g (51% yield) of 4a as dark red crystals. A second crop
of crystals raised the total yield to 0.271 g (83% yield). 1H NMR
(benzene-d6): δ 2.02 (s, 15 H, C5Me5), 1.5 (m, 4 H, 2 PCH2), 1.35 (m,
6 H, 2 PMe), 1.06 (m, 6 H, 2 PMe), 0.67 (d, 6 H, SiMe2, JHH ) 2 Hz),
-14.06 (t, 1 H, Mo-H, JHP ) 17 Hz, JHSi ) 30 Hz). 1H NMR (toluene-
d8, 223 K): δ 2.06 (s, 15 H, C5Me5), 1.65 (m, 1 H, PCH2), 1.55 (m, 1
H, PCH2), 1.48 (d, 3 H, PMe, JHP ) 7 Hz), 1.38 (m, 1 H, PCH2), 1.22
(m, 3 H, PMe, JHP ) 6 Hz), 1.19 (d, 3 H, PMe, JHP ) 5 Hz), 1.08 (m,
1 H, PCH2), 0.93 (d, 3 H, PMe, JHP ) 5 Hz), -14.04 (m, 1 H, MoH,
Cp*(dmpe)Mo(H)(SiPh
2) (4d). Diphenylsilane (0.078 g, 0.423
mmol) and 0.200 g (0.423 mmol) of 2 were dissolved in 5 mL of
benzene. The mixture was heated at 50 °C for 15 min, and the solution
changed color to burgundy. The product was isolated by the same
method as for 4a, which gave 0.138 g of purple microcrystalline 4d in
1
58% yield. H NMR (benzene-d6): δ 7.54 (m, 4 H, o-Ph), 7.18 (m, 4
H, m-Ph), 7.07 (m, 2 H, p-Ph), 1.88 (s, 15 H, C5Me5), 1.52 (m, 6 H,
2 PMe), 1.49 (m, 2 H, 2 PCH2), 1.35 (m, 2 H, 2 PCH2), 1.00 (m, 6 H,
2 PMe), -11.36 (t, 1 H, MoH, JHP ) 18 Hz, JHSi ) 37 Hz). 13C{1H}
NMR (benzene-d6): δ 154.7, 131.9, 127.5, 127.2 (s, Ph), 98.6 (s, C5-
Me5), 34.3 (m, 2 PMe), 33.3 (m, 2 PCH2), 23.3 (m, 2 PMe), 13.8 (s,
C5Me5). 31P{1H} NMR (benzene-d6): δ 70.0 (s). 29Si{1H} NMR
(benzene-d6): δ 242 (t, JSiP ) 24 Hz). IR (cm-1): 3056 w, 3041 w,
2980 m, 2961 m, 2945 m, 2899 s, 1476 w, 1421 m, 1372 w, 1269 m,
9
10438 J. AM. CHEM. SOC. VOL. 126, NO. 33, 2004

Silylene Hydride Complexes of Molybdenum
A R T I C L E S
1091 m, 1026 w, 927 s, 896 w, 740 w, 726 w, 701 s, 681 m, 628 w,
513 s, 464 m. Anal. Calcd for C28H42MoP2Si: C, 59.56; H, 7.50.
Found: C, 59.81; H, 7.70.
31P{1H} NMR (benzene-d6): δ 66.3 (s). 29Si{1H} NMR (benzene-d6):
δ 239 (m). IR (KBr, cm-1): 2961 m, 2898 s, 2857 m, 1979 m (νSiH),
1597 w, 1490 m, 1418 m, 1373 w, 1271 w, 1202 w, 1113 m, 1027 m,
932 s, 859 s, 801 m, 754 m, 697 s, 630 w, 479 w.
Cp*(dmpe)Mo(D)(SiPh2) (4d-d1). Complex 2 (0.020 g, 0.042 mmol)
and Ph2SiD2 (0.0078 g, 0.042 mmol) were combined in 0.4 mL of
benzene-d6, and the tube was heated at 50 °C for 20 min. The 1H NMR
spectrum of 4-d1 is identical to that of 4 except for the absence of a
Cp*(dmpe)(CO)MoSiHMe2 (6a). The dimethylsilylene complex 4a
(0.100 g, 0.227 mmol) was dissolved in 4 mL of benzene in a 25 mL
sealable flask, and the headspace was evacuated briefly. The flask was
then backfilled with CO, and the mixture was agitated to dissolve the
gas. The reaction vessel was sealed under 1 atm of CO, and the mixture
was stirred at room temperature. After 5 min, the solution had changed
color from dark red to orange-yellow. The volatiles were removed in
vacuo, and the yellow product was extracted into 3 mL of toluene.
Recrystallization from 1 mL of a concentrated toluene solution at -30
°C gave the silyl complex 6a in 58% yield (0.062 g). 1H NMR (benzene-
d6): 4.87 (m, 1 H, SiH, JHSi ) 162 Hz), 1.79 (s, 15 H, C5Me5), 1.51
(d, 3 H, PMe, JHP ) 8 Hz), 1.25 (d, 3 H, PMe, JHP ) 7 Hz), 1.2 (m, 2
H, 2 PCH2), 1.0 (m, 2 H, 2 PCH2), 0.98 (d, 3 H, PMe, JHP ) 7 Hz),
0.92 (d, 3 H, SiMe, JHH ) 3 Hz), 0.89 (d, 3 H, PMe, JHP ) 6 Hz), 0.65
(d, 3 H, SiMe, JHH ) 3 Hz). 13C{1H} NMR (benzene-d6): δ 243.0 (m,
CO), 98.5 (s, C5Me5), 31.9 (dd, PCH2, JCP ) 24 Hz, JCP′ ) 17 Hz),
31.4 (dd, PCH2, JCP ) 27 Hz, JCP′ ) 20 Hz), 23.5 (d, PMe, JCP ) 20
1
resonance for the hydride ligand. The reaction is quantitative by H
and 31P NMR spectroscopy. 2H{1H} NMR (benzene-d6): δ -11.45 (t,
JDP ) 3 Hz). 31P{1H} NMR (benzene-d6): δ 69.5 (s). The JPD coupling
is not resolved in the 31P{1H} NMR spectrum of 4d-d1.
Cp*(dmpe)Mo(H)Si(H)Ph (5a). Phenylsilane (0.058 g, 0.54 mmol)
and 2 (0.250 g, 0.529 mmol) were dissolved in 6 mL of benzene, and
the solution was heated at 50 °C for 15 min, resulting in a brown
solution. The benzene was removed under reduced pressure, and the
resulting solid was extracted into 10 mL of pentane. Filtration of the
pentane solution removed a small amount of insoluble impurities. The
solution was then concentrated in vacuo to 2 mL and placed in the
freezer at -30 °C for 14 h, and this resulted in crystallization of 0.179
g of dark green crystals of complex 5a (69% yield). 1H NMR (benzene-
d6): δ 9.45 (m, 1 H, SiH, JHsi ) 130 Hz, JHH ) 3 Hz, JHP ) 3 Hz),
8.09 (d, 2 H, o-Ph, JHH ) 7 Hz), 7.32 (t, 2 H, m-Ph, JHH ) 7 Hz), 7.19
(m, 1 H, p-Ph), 2.01 (s, 15 H, C5Me5), 1.47 (m, 4 H, 2 PCH2), 1.44
Hz), 20.1 (d, PMe, JCP ) 12 Hz), 19.3 (dd, PMe, JCP ) 35 Hz, JCP′
)
4 Hz), 17.3 (dd, PMe, JCP ) 24 Hz, JCP′ ) 7 Hz), 12.0 (s, C5Me5), 5.4
(d, SiMe, JCP ) 5 Hz), 3.6 (d, SiMe, JCP ) 3 Hz). 31P{1H} NMR
(benzene-d6): δ 60.5 (d, JPP ) 20 Hz), 54.4 (d, JPP ) 20 Hz). 29Si{1H}
NMR (benzene-d6): δ 21 (dd, JSiP ) 39 Hz, JSiP′ ) 8 Hz). IR (cm-1):
2962 w, 2947 w, 2904 m, 1987 m (νSiH), 1781 s (νCO), 1478 w, 1421
w, 1374 w, 1228 w, 1089 w, 1025 w, 936 m, 904 m, 864 m, 823 w,
695 w, 627 w. Anal. Calcd for C19H38MoOP2Si: C, 48.71, H, 8.18.
Found: C, 48.90; H, 8.16.
(m, 6 H, 2 PMe), 1.02 (m, 6 H, 2 PMe), -9.96 (td, 1 H, Mo-H, JHP
)
19 Hz, JHH ) 3 Hz, JHSi ) 30 Hz). 13C{1H} NMR (benzene-d6): δ
151.8, 135.2, 128.6, 127.9 (s, Ph), 98.0 (s, C5Me5), 34.8 (m, 2 PCH2),
30.8 (m, 2 PMe), 22.1 (m, 2 PMe), 13.8 (s, C5Me5). 31P{1H} NMR
(benzene-d6): δ 63.5 (s). 29Si{1H} NMR (benzene-d6): δ 250 (t, JSiP
) 26 Hz). IR (cm-1): 3056 w, 2960 m, 2891 s, 1896 s (νSiH), 1475 w,
1413 m, 1375 m, 1286 w, 1273 m, 1088 m, 1062 w, 1026 w, 931 s,
885 s, 831 w, 735 m, 700 m, 683 m, 636 m, 474 w. Anal. Calcd for
C22H38MoP2Si: C, 54.10; H, 7.84. Found: C, 54.11; H, 7.87.
Cp*(dmpe)(CO)MoSiH2Ph (6b). This complex was prepared in the
same manner as that used for 6a. Recrystallization of the product from
1 mL of toluene at -30 °C gave 0.069 g of the molybdenum silyl 6b
Cp*(dmpe)Mo(H)Si(H)Mes (5b). Mesitylsilane (0.064 g, 0.426
mmol) and 0.200 g (0.423 mmol) of 2 were dissolved in 5 mL of
benzene. The mixture was heated at 50 °C for 15 min, and the solution
changed color to purple. The product was isolated by the same method
as for 5a, which gave 0.134 g of purple crystals of 5b in 60% yield.
1H NMR (benzene-d6): δ 9.36 (s, 1 H, SiH, JHSi ) 139 Hz), 6.82 (s,
2 H, Ar-H), 2.54 (s, 6 H, o-Me), 2.21 (s, 3 H, p-Me), 1.84 (s, 15 H,
C5Me5), 1.65 (m, 4 H, 2 PCH2), 1.45 (m, 6 H, 2 PMe), 1.04 (m, 6 H,
2 PMe), -13.08 (t, 1 H, MoH, JHP ) 17 Hz, JHSi ) 48 Hz). 13C{1H}
NMR (benzene-d6): δ 146.3, 139.1, 137.0, 128.1 (s, Ar), 98.7 (s, C5-
Me5), 33.9 (m, 2 PCH2), 32.5 (m, 2 PMe), 22.8 (m, 2 PMe), 22.6 (s,
o-Me), 21.3 (s, p-Me), 13.3 (s, C5Me5). 31P{1H} NMR (benzene-d6): δ
66.5 (s). 29Si{1H} NMR (benzene-d6): δ 214 (t, JSiP ) 26 Hz). IR
(cm-1): 2964 s, 2892 s, 2848 m, 1948 s (νSiH), 1601 m, 1460 m, 1411
s, 1373 m, 1284 w, 1269 m, 1116 w, 1065 m, 1024 m, 929 s, 852 m,
838 s, 705 m, 682 m, 605 m, 457 m. Anal. Calcd for C25H45MoP2Si:
C, 56.49; H, 8.53. Found: C, 56.14; H, 8.36.
1
(65% yield). H NMR (benzene-d6): δ 8.16 (d, 2 H, o-Ph, JHH ) 7
Hz), 7.26 (t, 2 H, m-Ph, JHH ) 7 Hz), 7.16 (m, 1 H, p-Ph), 5.04 (m, 1
H, SiH, JHSi ) 167 Hz), 5.00 (m, 1 H, SiH, JHSi ) 159 Hz), 1.75 (s, 15
H, C5Me5), 1.55 (d, 3 H, JHP ) 8 Hz), 1.18 (m, 1 H, PCH2), 1.13 (m,
1 H, PCH2), 1.06 (d, 3 H, PMe, JHP ) 7 Hz), 1.04 (m, 1 H, PCH2),
1.01 (d, 3 H, PMe, JHP ) 8 Hz), 0.89 (d, 3 H, PMe, JHP ) 7 Hz), 0.85
(m, 1 H, PCH2). 13C{1H} NMR (benzene-d6): δ 244.7 (m, CO), 145.3
(m, i-Ph), 137.1 s, o-Ph), 127.5 (s, m-Ph), 127.4 (s, p-Ph), 97.8 (s,
C5Me5), 32.2 (dd, PCH2, JCP ) 25 Hz, JCP′ ) 19 Hz), 29.8 (dd, PCH2,
JCP ) 25 Hz, JCP′ ) 19 Hz), 21.3 (dd, PMe, JCP ) 11 Hz, JCP′ ) 3 Hz),
21.0 (dd, PMe, JCP ) 34 Hz, JCP′ ) 3 Hz), 20.2 (dd, PMe, JCP ) 14
Hz, JCP′ ) 1 Hz), 17.4 (dd, PMe, JCP ) 26 Hz, JCP′ ) 5 Hz), 11.3 (s,
C5Me5). 31P{1H} NMR (benzene-d6): δ 60.0 (d, JPP ) 24 Hz), 50.9 (d,
JPP ) 24 Hz). 29Si{1H} NMR (benzene-d6): δ 16. IR (cm-1): 2971 w,
2951 w, 2907 m, 2855 w, 2023 m (νSiH), 1997 m (νSiH), 1788 s (νCO),
1478 w, 1424 w, 1374 w, 1294 w, 1281 w, 1094 w, 1027 w, 936 m,
830 s, 729 w, 703 w, 630 w, 544 w. Anal. Calcd for C23H38MoOP2Si:
C, 53.48, H, 7.42. Found: C, 53.86; H, 7.77.
Cp*(dmpe)Mo(H)Si(H)CH2Ph (5c). Benzylsilane (0.020 g, 0.164
mmol) and 0.075 g (0.159 mmol) of 2 were dissolved in 2 mL of
benzene. The mixture was heated at 50 °C for 15 min, and the solution
changed color to purple. The volatile materials were removed in vacuo,
and the residue was redissolved in 3 mL of pentane. The resulting
solution was filtered and then concentrated to approximately 0.3 mL
under reduced pressure. The solution was cooled to -30 °C for 12 h,
and complex 5c was isolated as 0.41 g of a sticky solid (51% yield).
The high solubility of the product made it difficult to separate from
Cp*(dmpe)(H)Mo(SiH2Ph)2 (7). A sealable flask was charged with
0.100 g (0.205 mmol) of 5a, 0.024 g (0.225 mmol) of PhSiH3, and 0.4
mL of benzene. The flask was heated in an oil bath at 60 °C for 14 h,
and this produced a yellow-brown solution. The volatile materials were
removed under reduced pressure, and the orange-red solid residue was
washed twice with 3 mL of pentane to remove dark-colored impurities.
The off-white solid was then dissolved in 10 mL of toluene. Concentra-
tion of this solution to 3 mL under vacuum and storage in the freezer
at -30 °C for 18 h gave yellow crystals of 7. Decanting the supernatant
and drying the sample under vacuum gave 0.075 g of the product (61%
1
trace impurities. H NMR (benzene-d6): δ 8.51 (t, 1 H, SiH, JHH ) 3
Hz, JHSi ) 138 Hz), 7.22 (m, 2 H, Ar-H), 7.11 (m, 2 H, Ar-H), 7.00
(m, 1 H, Ar-H), 2.59 (br, 2 H, CH2Ph), 1.97 (s, 15 H, C5Me5), 1.5 (m
br, 4 H, 2 PCH2), 1.32 (m, 6 H, 2 PMe), 0.97 (m, 6 H, 2 PMe), -13.29
(t, 1 H, MoH, JHP ) 17 Hz, JHSi ) 42 Hz). 13C{1H} NMR (benzene-
d6): δ 141.6, 128.7, 128.4, 123.9 (s, Ar), 98.9 (s, C5Me5), 42.9 (s, CH2-
Ph), 34.5 (t, 2 PCH2, JCP ) 23 Hz), 33.8 (dd, 2 PMe, JCP ) 16 Hz, JCP′
) 12 Hz), 22.4 (dd, 2 PMe, JCP ) 8 Hz, JCP′ ) 5 Hz), 13.8 (s, C5Me5).
1
yield). H NMR (benzene-d6): δ 8.10 (d, 4 H, o-Ph, JHH ) 8 Hz),
7.27 (t, 4 H, m-Ph, JHH ) 8 Hz), 7.10 (m, 2 H, p-Ph), 5.00 (d, 2 H,
SiH, JHP ) 7 Hz, JHSi ) 165 Hz), 4.97 (d, 2 H, SiH, JHP ) 9 Hz, JHSi
) 158 Hz), 1.59 (s, 15 H, C5Me5), 1.05 (m, 12 H, 4 PMe), 0.97 (m, 2
H, 2 PCH2), 0.74 (m, 2 H, 2 PCH2), -7.27 (t, 1 H, MoH, JHP ) 40
9
J. AM. CHEM. SOC. VOL. 126, NO. 33, 2004 10439

A R T I C L E S
Mork et al.
Hz). 13C{1H} NMR (benzene-d6): δ 150.0 (s, i-Ph), 137.4 (s, o-Ph),
127.3 (s, m-Ph), 127.1 (s, p-Ph), 93.5 (s, C5Me5), 31.1 (m, 2 PCH2),
23.1 (m, 2 PMe), 16.8 (m, 2 PMe), 10.6 (s, C5Me5). 31P{1H} NMR
1273 w, 1224 s, 1065 w, 1014 m, 988 m, 919 s, 810 s, 778 m, 637 m,
623 m, 534 w, 504 w. Anal. Calcd for C25H48N2P2MoSi: C, 53.36; H,
8.60; N, 4.98. Found: C, 53.43; H, 8.47; N, 4.59.
1
(benzene-d6): δ 47.5 (s). H, 29Si HMQC NMR (benzene-d6): δ (1H,
Cp*(K3-Me2PCH2CH2P(Me)CH2SiMe2)MoH2 (10a). Heating 0.100
g of dimethylsilylene complex 4a at 100 °C in 3 mL of benzene resulted
in a green-yellow solution. Removal of the solvent under reduced
pressure and scraping the product from the flask gave 0.069 g of 10a
as a sticky green solid (69% yield). The yield is less than quantitative
because of difficulty removing the product from the reaction flask. 1H
NMR (benzene-d6): 2.22 (m, 1 H, PCH2Si), 1.99 (m, 1 H, PCH2Si)
1.98 (s, 15 H, C5Me5), 1.6 (m br, 1 H, PCH2), 1.50 (m br, 1H, PCH2),
1.41 (d, 3 H, PMe, JHP ) 8 Hz), 1.4 (m br, 1 H, PCH2), 1.37 (d, 3 H,
PMe, JHP ) 8 Hz), 1.03 (d, 3 H, PMe, JHP ) 6 Hz), 0.87 (m br, 1 H,
PCH2), 0.85 (s, 3 H, SiMe), 0.53 (s, 3 H, SiMe), -8.57 (m, 2 H, MoH2).
13C{1H} NMR (benzene-d6): δ 96.2 (s, C5Me5), 45.4 (br, PCH2Si),
33.6 (dd, PCH2 JCP ) 22 Hz, JCP′ ) 17 Hz), 31.9 (dd, PCH2, JCP ) 28
Hz, JCP′ ) 15 Hz), 24.7 (dd, PMe, JCP ) 20 Hz, JCP′ ) 5 Hz), 21.9 (d,
PMe, JCP ) 16 Hz), 20.7 (s, PMe), 15.8 (s, SiMe), 13.8 (s, C5Me5),
12.9 (s, SiMe). 31P{1H} NMR (benzene-d6): 59.5 (d, JPP ) 18 Hz),
39.6 (d, JPP ) 18 Hz). 29Si{1H} NMR (benzene-d6): δ -9.0 (m). IR
(KBr, cm-1): 3044 w, 2985 m, 2936 w, 2829 m, 1829 w (νMoH), 1735
m (νMoH), 1474 w, 1457 w, 1416 s, 1374 s, 1273 m, 1228 m, 1091 m,
1067 m, 933 m, 875 m, 830 w, 795 w, 752 w, 687 w, 667 w. Anal.
Calcd for C18H38MoP2Si: C, 49.08; H, 8.70. Found: C, 50.21; H, 8.60.
Compound 10a is very soluble in hydrocarbon solvents, and this
prevented isolation of analytically pure material. Small amounts (<5%
yield) of crystalline 10a were obtained by storing a 0.5-mL toluene
solution containing 0.100 g of 10a in the freezer at -30 °C for 14 h.
Cp*(K3-Me2PCH2CH2P(Me)CH2SiPh2)MoH2 (10b). Heating 0.100
g of diphenylsilylene complex 4d at 100 °C in 3 mL of benzene resulted
in an orange solution. Removal of the solvent in vacuo and recrystal-
lization from 2 mL of diethyl ether at -30 °C over 12 h gave 0.073 g
of 10b as orange crystals (73% yield). 1H NMR (benzene-d6): δ 7.89
(m, 4 H, o-Ph), 7.82 (m, 4 H, m-Ph), 7.27 (m, 1 H, p-Ph), 7.21 (m, 1
H, p-Ph), 2.76 (m, 1 H, PCH2Si), 2.52 (m, 1 H, PCH2Si), 1.94 (s,
C5Me5), 1.75 (m br, 1 H, PCH2), 1.39 (m, br, 1 H, PCH2), 1.37 (d, 3
H, PMe, JHP ) 8 Hz), 1.10 (m br, PCH2), 0.94 (d, 3 H, PMe, JHP ) 8
Hz), 0.90 (m br, 1 H, PCH2), 0.89 (d, 3 H, PMe, JHP ) 7 Hz), -8.06
(m, 2 H, MoH2). 13C{1H} NMR (benzene-d6): δ 152.0 (s, i-Ph), 148.8
(s, i-Ph), 135.1 (s, o-Ph), 135.0 (s, o-Ph), 134.1 (s, m-Ph), 134.0 (s,
m-Ph), 127.2 (s, p-Ph), 127.0 (s, p-Ph), 96.2 (s, C5Me5), 43.5 (d, PCH2-
Si, JCP ) 13 Hz), 32.8 (dd, PCH2, JCP ) 23 Hz, JCP′ ) 16 Hz), 31.3
(dd, PCH2, JCP ) 29 Hz, JCP′ ) 14 Hz), 22.2 (d, PMe, JCP ) 16 Hz),
20.7 (dd, PMe, JCP ) 20 Hz, JCP′ ) 5 Hz), 20.0 (m, PMe), 13.7 (s,
C5Me5). 31P{1H} NMR (benzene-d6): δ 56.1 (d, JPP ) 18 Hz), 39.9 (d,
JPP ) 18 Hz). 1H,29Si HMQC NMR (benzene-d6): δ -3.4. IR (cm-1):
3058 w, 2973 m, 2950 w, 2897 s, 2855 w, 1819 w (νMoH), 1763 w
(νMoH), 1479 w, 1423 m, 1372 w, 1092 m, 1066 w, 1017 m, 934 m,
917 w, 878 m, 842 w, 743 m, 703 s, 685 w, 497 m, 434 w. Anal.
Calcd for C28H42MoP2Si: C, 59.56; H, 7.50. Found: C, 59.53; H, 7.72.
29Si) 5.0 (m), 10.1. IR (cm-1): 3054 w, 2997 w, 2955 w, 2095 m,
2043 m (νSiH), 2020 s (νSiH), 1989 m (νSiH), 1478 w, 1424 w, 1375 w,
1088 w, 1025 w, 954 m, 939 m, 856 s, 832 s, 722 m, 699 m, 632 m,
531 w. Anal. Calcd for C28H46MoP2Si2: C, 56.36; H, 7.77. Found: C,
56.12; H, 7.88.
Cp*(dmpe)(D)Mo(SiH2Ph)(SiD2Ph) (7-d3). A sealable flask was
charged with 0.100 g (0.205 mmol) of 5a, 0.025 g (0.225 mmol) of
PhSiD3, and 0.4 mL of benzene. The flask was heated in an oil bath at
60 °C for 14 h, and this gave a yellow-brown solution. The volatile
materials were removed under reduced pressure, and the orange-red
solid residue was washed twice with 3 mL of pentane to remove dark-
colored impurities. The off-white solid was then dissolved in 10 mL
of toluene. Concentration of this solution to 4 mL under vacuum and
storage in the freezer at -30 °C for 12 h gave yellow crystals of 7-d3.
Decanting the supernatant and drying the sample under vacuum gave
0.68 g of the product (55% yield). This complex’s NMR spectra were
analogous to those of the 7 with the predicted exceptions. For example,
1
the H NMR spectrum exhibited the two doublets for the SiH2 group
integrating to just one hydrogen atom each, and no Mo-H resonance
was observed. In addition, the 31P{1H} NMR spectrum exhibits coupling
to the deuterium nuclei. 31P{1H} NMR (benzene-d6): δ 47.5 (m). IR
(cm-1): 2043 w (νSiH), 2018 m (νSiH), 1992 w (νSiH), 1486 w (νSiD),
1466 m (νSiD), 1450 w (νSiD). 2H{1H} NMR (benzene-d6): δ 4.97 (br,
SiD2Ph), -7.30 (t br, MoD, JDP ) 6 Hz).
Cp*(dmpe)(H)ModCdC(SiHMe2)(SiMe3) (8). Dimethylsilylene
complex 4a (0.085 g, 0.193 mmol) was dissolved in 3 mL of benzene,
and 0.095 g (0.97 mmol) of trimethylsilylacetylene was added to the
solution. The red solution was stirred for 16 h, and the color changed
to orange. The volatile material was removed under reduced pressure,
and the product was dissolved in diethyl ether (2 mL). Crystallization
from this concentrated solution at -30 °C for 14 h gave 0.060 g of 8
as orange crystals (58% yield). 1H NMR (benzene-d6): δ 4.69 (septet,
1 H, SiH, JHH ) 3 Hz), 1.93 (s, 15 H, C5Me5), 1.39 (m, 6 H, 2 PMe),
1.22 (m, 2 H, 2 PCH2), 1.09 (m, 2 H, 2 PCH2), 1.08 (m, 6 H, 2 PMe),
6.27 (d, 6 H, SiMe2H, JHH ) 3 Hz), 0.37 (s, 9 H, SiMe3), -7.34 (t, 1
H, MoH, JHP ) 34 Hz). 13C{1H} NMR (benzene-d6): δ 317.9 (t,
Mo)C)C, JCP ) 12 Hz), 100.4 (s, C5Me5), 92.5 (s, ModC)C), 32.2
(t, 2 PCH2, JCP ) 23 Hz), 23.9 (m, 2 PMe), 20.4 (m, 2 PMe), 12.8 (s,
C5Me5), 2.2 (s, SiMe2H, JCSi ) 51 Hz), 0.4 (s, JCSi ) 49 Hz). 31P{1H}
NMR (benzene-d6): δ 57.2. 29Si{1H} NMR (benzene-d6): δ -9.9 (s,
SiMe2H), -18.2 (s, SiMe3). IR (cm-1): 2948 m, 2900 s, 2085 m (νSiH),
1815 w (νMoH), 1476 s, 1422 s, 1376 m, 1286 w, 1274 w, 1239 m,
1064 w, 1024 m, 929 s, 879 s, 828 s, 759 w, 718 w, 688 m, 642 m,
605 w. Anal. Calcd for C23H47MoP2Si2: C, 51.28; H, 8.98. Found: C,
51.35; H, 8.92.
Cp*(dmpe)Mo(H)(SiMe2‚DMAP) (9). To 0.015 g (0.0341 mmol)
of complex 4a in 0.5 mL of benzene-d6 was added 0.0042 g (0.341
mmol) of DMAP. The mixture immediately became darker red in color,
and the reaction was complete by 1H NMR spectroscopy. The product
was lyophilized from the benzene-d6 under reduced pressure to give 9
as 0.018 g of an orange powder in 94% yield. 1H NMR (benzene-d6):
δ 8.69 (m, 2 H, o-DMAP), 5.98 (m, 2 H, m-DMAP), 2.15 (s, 15 H,
C5Me5), 2.10 (s, 6 H, NMe2), 1.55 (m, 4 H, 2 PCH2), 1.40 (d, 6 H, 2
PMe), 1.28 (d, 6 H, 2 PMe), 0.72 (s, 6 H, SiMe2), -12.93 (t, 1 H,
MoH, JHP ) 20 Hz, JHSi ) 17 Hz). 13C {1H} NMR (benzene-d6): δ
154.5 (s, p-DMAP), 149.1 (s, o-DMAP), 106.0 (s, m-DMAP), 96.3 (s,
C5Me5), 38.2 (s, NMe2), 35.1 (m br, 2 PCH2), 32.0 (m br, 2 PMe),
24.5 (m br, 2 PMe), 18.5 (s, SiMe2), 14.3 (s, C5Me5). 31P{1H} NMR
(benzene-d6): δ 70.3 (s br). 1H, 29Si HMQC (benzene-d6): δ (1H, 29Si)
-12.93, 179 (JHSi ) 17 Hz). IR (KBr, cm-1): 2955 m, 2896 s, 1836
w (νMoH), 1621 m, 1603 s, 1537 m, 1524 m, 1445 w, 1418 w, 1376 m,
Acknowledgment. We acknowledge the National Science
Foundation for their generous support of this work. We thank
Dr. Frederick J. Hollander and Dr. Allen G. Oliver for assistance
with the X-ray structure determinations. Work at Argonne was
supported by the U.S. Department of Energy, Basic Energy
Sciences, under Contract W-31-109-Eng-38.
Supporting Information Available: Structures of 4a, 4b, 5a,
7, and 8 (CIF). Neutron data collection, refinement, and
description of structure I (PDF). This material is available free
of charge via the Internet at http://pubs.acs.org.
JA040026G
9
10440 J. AM. CHEM. SOC. VOL. 126, NO. 33, 2004