Synthesis and reactivity of d0 Bis(imido) silyl and germyl complexes of molybdenum and tungsten

Article abstract of DOI:10.1021/om970527t

The syntheses and reactivities of d⁰ bis(imido) molybdenum/tungsten silyl chloride complexes (2,6-ⁱPr₂C₆H₃N) ₂M[Si(SiMe₃)₃]Cl (1, M = Mo; 2, M = W) and the corresponding germyl complexes (2,6-ⁱPr₂C₆H₃N) ₂M[Ge(SiMe₃)₃]Cl (3, M = Mo; 4, M = W) are described. The complex (2,6-ⁱPr₂C₆H₃N) ₂Mo[Si(SiMe₃)₃]Cl (1), prepared by the reaction of (2,6-1Pr₂C₆H₃N)₂MoCl ₂(dme) with (THF)₃LiSi(SiMe₃)₃, has been structurally characterized. In general, these complexes are rather stable and do not react with CO, H₂, or CH₃CN. Complex 1 reacts with 2,6-Me₂C₆H₃NC to provide the insertion product (2,6^-iPr₂C₆H₃N) ₂Mo[η²-C(N-2,6-Me₂C₆H ₃)Si(SiMe₃)₃](Cl) (5) and with AgOTf to give the silyl triflate complex (2,6-ⁱPr₂C₆H₃N) ₂Mo[Si(SiMe₃)₃]OSO₂CF₃ (6) in high yield. Complexes 1-6 react with neopentylmagnesium chloride to produce the silyl neopentyl complexes (2,6-ⁱPr₂C₆H₃N) ₂M[E(SiMe₃)₃](CH₂CMe₃) (7, M = Mo, E = Si; 8, M = W, E = Si; 9, M = Mo, E = Ge; 10, M = W, E = Ge). Complex 7, which was characterized by X-ray crystallography, contains an agostic interaction involving the α hydrogen of the neopentyl ligand (d(Mo-H) 2.55(4)A?). The neopentyl complexes 7-10 readily react with hydrogen (1 atm) to generate free neopentane and HSiMe₃, probably via hydrogenation of the Mo-C bond to generate a highly unstable silyl hydride intermediate. The mechanism of HSiMe₃ formation is unknown but may involve decomposition of the silyl hydride species via a four-membered transition state to generate a highly reactive silylene species. The corresponding tungsten analog 8 undergoes a similar reaction, but at a much slower rate. Attempts to trap the possible silylene intermediates (2,6^-iPr₂C₆H₃N) ₂M=Si(SiMe₃)₂ (M = Mo, W) were unsuccessful.

Full text of DOI:10.1021/om970527t

4746
Organometallics 1997, 16, 4746-4754
Syn th esis a n d Rea ctivity of d 0 Bis(im id o) Silyl a n d
Ger m yl Com p lexes of Molybd en u m a n d Tu n gsten
Gary L. Casty and T. Don Tilley*
Department of Chemistry, University of California at Berkeley,
Berkeley, California 94720-1460
Glenn P. A. Yap and Arnold L. Rheingold*
Department of Chemistry, University of Delaware, Newark, Delaware 19716
Received J une 23, 1997X
The syntheses and reactivities of d0 bis(imido) molybdenum/tungsten silyl chloride
complexes (2,6-iPr2C6H3N)2M[Si(SiMe3)3]Cl (1, M ) Mo; 2, M ) W) and the corresponding
germyl complexes (2,6-iPr2C6H3N)2M[Ge(SiMe3)3]Cl (3, M ) Mo; 4, M ) W) are described.
The complex (2,6-iPr2C6H3N)2Mo[Si(SiMe3)3]Cl (1), prepared by the reaction of (2,6-
iPr2C6H3N)2MoCl2(dme) with (THF)3LiSi(SiMe3)3, has been structurally characterized. In
general, these complexes are rather stable and do not react with CO, H2, or CH3CN. Complex
1 reacts with 2,6-Me2C6H3NC to provide the insertion product (2,6-iPr2C6H3N)2Mo[η2-C(N-
2,6-Me2C6H3)Si(SiMe3)3](Cl) (5) and with AgOTf to give the silyl triflate complex (2,6-
iPr2C6H3N)2Mo[Si(SiMe3)3]OSO2CF3 (6) in high yield. Complexes 1-6 react with neopen-
tylmagnesium
chloride
to produce
the
silyl neopentyl complexes
(2,6-
iPr2C6H3N)2M[E(SiMe3)3](CH2CMe3) (7, M ) Mo, E ) Si; 8, M ) W, E ) Si; 9, M ) Mo, E )
Ge; 10, M ) W, E ) Ge). Complex 7, which was characterized by X-ray crystallography,
contains an agostic interaction involving the R hydrogen of the neopentyl ligand (d(Mo-H)
2.55(4)Å). The neopentyl complexes 7-10 readily react with hydrogen (1 atm) to generate
free neopentane and HSiMe3, probably via hydrogenation of the Mo-C bond to generate a
highly unstable silyl hydride intermediate. The mechanism of HSiMe3 formation is unknown
but may involve decomposition of the silyl hydride species via a four-membered transition
state to generate a highly reactive silylene species. The corresponding tungsten analog 8
undergoes a similar reaction, but at a much slower rate. Attempts to trap the possible
silylene intermediates (2,6-iPr2C6H3N)2MdSi(SiMe3)2 (M ) Mo, W) were unsuccessful.
In tr od u ction
focused on use of group 4 d0 metallocene complexes as
catalysts for silane dehydropolymerizations.16 Mecha-
nistic studies have suggested that this dehydropolym-
erization occurs by a purely σ-bond metathesis mecha-
nism mediated by a metal hydride catalyst and involving
Early transition-metal silicon chemistry is an emerg-
ing field of increasing importance in organometallic
chemistry.1-15 Our interest in this area has recently
X Abstract published in Advance ACS Abstracts, October 1, 1997.
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S0276-7333(97)00527-X CCC: $14.00 © 1997 American Chemical Society

Bis(imido) Silyl and Germyl Complexes of Mo and W
Organometallics, Vol. 16, No. 21, 1997 4747
only two steps. Studies directed toward optimization
of catalyst structures for production of high molecular
weight polysilanes have indicated that the activities are
dramatically influenced by subtle changes in the struc-
tures of zirconocene-type catalyst precursors. On the
basis of these studies, however, we predicted that the
next generation of catalysts with substantially superior
properties “will be monomer-stabilized d0 hydride de-
rivatives (or direct precursors thereof) featuring ancil-
lary ligands other than cyclopentadienyl groups”.16b In
this paper, we describe attempts to develop the silyl
chemistry of d0 metal centers with ancillary imido
ligands. On the basis of the “isolobal” relationship
between bent metallocenes of the group 4 elements and
bis(imido) complexes of group 6,17 it seemed that
complexes of the latter type might represent interesting
candidates for investigation.
istry have concentrated on reactions with hydrosilanes
and attempts to generate coordinatively unsaturated,
d0 silyl hydride complexes. Complexes of the latter type
are of interest as potential intermediates in the dehy-
dropolymerization of silanes, and they appear to be
highly reactive based on the fact that they have proven
difficult to isolate. We have recently reported the first
16-electron d0 silyl hydride complexes CpCp*Hf[Si-
(SiMe3)3]H and CpCp*Hf[SiH(SiMe3)2]H, which are
reactive toward hydrosilanes and unsaturated mol-
ecules.18 As described herein, attempts to produce silyl
hydride complexes of molybdenum and tungsten appear
to generate highly reactive intermediates which degrade
via a novel σ-bond metathesis process.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations were per-
formed under an inert atmosphere of nitrogen or argon using
either standard Schlenk techniques or a Vacuum Atmospheres
glovebox. Dry, oxygen-free solvents were employed through-
out. To remove olefin impurities, pentane and benzene were
pretreated with concentrated H2SO4, then 0.5 N KMnO4 in 3
M H2SO4, followed by NaHCO3, and finally MgSO4. Benzene-
d6 and toluene-d8 were purified by vacuum distillation from
Na/K alloy. Yields determined by 1H NMR spectroscopy were
measured by relative integration against ferrocene as an
internal standard, using a long delay time and a short pulse
width. The compounds (2,6-iPr2C6H3N)2MoCl2(dme),19 (2,6-
iPr2C6H3N)2WCl2(dme),20 (THF)3LiSi(SiMe3)3,21 and (THF)3-
In this report, we describe synthetic routes to silyl
and germyl derivatives of the (2,6-iPr2C6H3N)2M (M )
Mo, W) fragment. Initial investigations into this chem-
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22
LiGe(SiMe3)3 were prepared according to literature proce-
dures. Elemental analyses were performed by the Micro-
analytical Laboratory in the College of Chemistry at the
University of California, Berkeley. NMR spectra were re-
corded on AMX-300 and VBAMX-400 spectrometers, and
infrared spectra were recorded on a Mattson FTIR 3000
instrument.
(2,6-iP r 2C6H3N)2Mo[Si(SiMe3)3]Cl (1). (2,6-iPr2C6H3N)2-
MoCl2(dme) (4.80 g, 7.91 mmol) and (THF)3LiSi(SiMe3)3 (3.71
g, 7.90 mmol) were combined in a round bottom Schlenk flask
equipped with a stir bar, and this mixture was then cooled to
-80 °C. Cold (-80 °C) diethyl ether (50 mL) was added, the
resulting solution was allowed to warm to room temperature,
and stirring was continued for 10 h. The volatile material was
removed by vacuum transfer, and the resulting residue was
extracted with hexanes (50 mL). The hexane extract was
filtered, and then the solvent was removed by vacuum transfer.
The resulting deep red foam was dissolved in hexamethyldi-
siloxane (2 × 20 mL). This solution was filtered, concentrated,
and cooled to 0 °C to afford deep red crystals of complex 1 (1.55
g, 1.97 mmol, 27%). Efforts to isolate more of complex 1 via
crystallization afforded only a red oil. IR (Nujol, NaCl, cm-1):
3052 (w), 2951 (s), 2922 (s), 2854 (s), 2358 (m), 2341 (m), 1460
(s), 1379 (m), 1321 (m), 1257 (m), 1242 (m), 1176 (m), 1105
(m), 1043 (m), 1018 (m), 813 (s), 750 (m). 1H NMR (dichlo-
romethane-d2, 300 MHz, 24 °C): δ 7.15-6.95 (m, 6 H,
i
NC6H3 Pr2), 3.54 (sept, J ) 6.8 Hz, 4 H, NC6H3CHMe2), 1.05
(d, J ) 6.8 Hz, 12 H, NC6H3CHMe2), 0.99 (d, J ) 6.8 Hz, 12
H, NC6H3CHMe2), 0.41 (s, Si(SiMe3)3, 27 H). 13C{1H} NMR
(dichloromethane-d2, 75 MHz, 24 °C): δ 153.8, 143.1, 127.6,
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4748 Organometallics, Vol. 16, No. 21, 1997
Casty et al.
i
i
123.4 (NC6H3 Pr2), 28.8 (NC6H3CHMe2), 24.2, 24.1 (NC6H3-
(NC6H3 Pr2), 28.6 (NC6H3CHMe2), 24.3, 24.1 (NC6H3CHMe2),
4.23 (Si(SiMe3)3). 29Si{1H} NMR (benzene-d6, 59.6 MHz, 24
°C): δ 4.43 (Ge(SiMe3)3).
CHMe2), 3.25 (Si(SiMe3)3). 29Si{1H} NMR (benzene-d6, 59.6
MHz, 24 °C): δ -4.5 (Si(SiMe3)3), -9.3 (Si(SiMe3)3). Anal.
C33H61ClN2MoSi4: C, 54.33; H, 8.43; N, 3.84.
Found: C, 53.70; H, 8.54; N, 3.73.
2
Calcd for
i
(2,6- P r 2C6H 3N)2Mo[η -C(N-2,6-Me 2C6H 3)Si(SiMe 3)3]-
(Cl) (5). In a Schlenk tube, (2,6-iPr2C6H3N)2Mo[Si(SiMe3)3]Cl
(0.400 g, 0.549 mmol) and 2,6-dimethylphenyl isocyanide
(0.075 g, 0.58 mmol) were combined. Benzene (15 mL) was
added at room temperature, and the solution was stirred for
6 h. The volatile material was removed, and the resulting
residue was extracted into pentane (2 × 10 mL). The combined
extracts were filtered, concentrated, and cooled to -80 °C to
afford complex 5 (0.388 g, 0.451 mmol, 82%) as light orange
crystals. IR (neat, NaCl, cm-1): 3874 (w), 3709 (w), 3425 (w),
3055 (w), 3026 (w), 2960 (m), 2916 (m), 2906 (m), 2864 (m),
1608 (br, υCdN), 1460 (m), 1423 (m), 1381 (m), 1360 (m), 1323
(m), 1286 (m), 1263 (m), 1248 (m), 1223 (m), 1113 (m), 1093
(m), 1059 (m), 1045 (m), 976 (m), 835 (s), 795 (m), 773 (m),
750 (m), 690 (m). 1H NMR (benzene-d6, 300 MHz, 24 °C): δ
(2,6-iP r 2C6H3N)2W[Si(SiMe3)3]Cl (2). To a cold (-80 °C)
diethyl ether (30 mL) solution of (2,6-iPr2C6H3N)2WCl2(dme)
(5.00 g, 7.20 mmol) was added a diethyl ether (30 mL) solution
of (THF)3LiSi(SiMe3)3 (3.38 g, 7.20 mmol). The reaction
mixture was allowed to slowly warm to room temperature with
stirring over a 12 h period. The volatile material was removed
under vacuum, and the resulting residue was extracted with
hexanes (50 mL). Filtration and concentration of the hexanes
solution followed by cooling to -80 °C afforded an orange
powder that was impure by 1H NMR spectroscopy and con-
tained numerous organosilicon species, as indicated by the
presence of peaks near δ 0.00. In an effort to obtain an
analytically pure sample, this material was extracted into
hexamethyldisiloxane (2 × 20 mL) to afford a dark orange
solution, which was filtered, concentrated, and cooled to 0 °C.
Unfortunately, crystallization attempts at both 0 and -35 °C
were unsuccessful. Structural assignment for 2 follows from
analysis of spectroscopic data for the crude material and by
its conversion to the completely characterized neopentyl
derivative 8. 1H NMR (benzene-d6, 300 MHz, 24 °C): δ 7.10-
i
7.10-6.85 (m, 9 H, NC6H3 Pr2, C6H3Me2), 4.02 (sept, J ) 6.7
Hz, 4 H, NC6H3CHMe2), 2.13 (s, 6 H, CNC6H3Me2), 1.27 (d, J
) 6.7 Hz, 12 H, NC6H3CHMe2), 1.26 (d, J ) 6.7 Hz, 12 H,
NC6H3CHMe2), 0.13 (s, 27 H, Si(SiMe3)3). 13C{1H} NMR
(dichloromethane-d2, 100 MHz, 24 °C): δ 232.8 (C(NAr)Si-
i
(SiMe3)3), 153.7, 143.4, 128.8, 122.7 (NC6H3 Pr2), 142.3, 130.0,
127.8, 125.7 (NC6H3Me2), 28.5 (NC6H3CHMe2), 24.5, 24.3
(NC6H3CHMe2), 19.3 (NC6H3Me2), 2.21 (Si(SiMe3)3). 29Si{1H}
NMR (benzene-d6, 59.6 MHz, 24 °C): δ -9.7 (Si(SiMe3)3),
-75.2 (Si(SiMe3)3). Anal. Calcd for C42H70ClMoN3Si4: C,
58.61; H, 8.20; N, 4.88. Found: C, 58.91; H, 8.34; N, 4.74.
i
6.85 (m, 6 H, NC6H3 Pr2), 3.68 (sept, J ) 6.8 Hz, 4 H,
NC6H3CHMe2), 1.11 (d, J ) 6.8 Hz, 12 H, NC6H3CHMe2), 1.07
(d, J ) 6.8 Hz, 12 H, NC6H3CHMe2), 0.44 (s, Si(SiMe3)3, 27
H). 13C{1H} NMR (benzene-d6, 75 MHz, 24 °C): δ 151.9, 143.2,
i
(2,6-iP r 2C6H 3N)2Mo[Si(SiMe3)3](OSO2CF 3) (6). In
a
127.1, 122.9 (NC6H3 Pr2), 28.6 (NC6H3CHMe2), 24.3, 24.2
(NC6H3CHMe2), 3.60 (Si(SiMe3)3). 29Si{1H} NMR (benzene-d6,
59.6 MHz, 24 °C): δ -2.0 (Si(SiMe3)3), -22.9 (Si(SiMe3)3).
Schlenk tube, (2,6-iPr2C6H3N)2Mo[Si(SiMe3)3]Cl (0.200 g, 0.274
mmol) and silver trifluoromethanesulfonate (0.074 g, 0.288
mmol) were combined. Benzene (20 mL) was added, and the
solution was allowed to stir overnight at room temperature.
The volatile material was removed, leaving a foamy residue
to which hexanes (∼40 mL) was added. The resulting slurry
was filtered to remove the solids, and the filtrate was
concentrated and cooled to -35 °C to afford complex 6 (0.207
g, 0.245 mmol, 89%) as purple crystals. IR (neat, NaCl, cm-1):
2960 (m), 2929 (m), 2914 (m), 2883 (m), 1527 (w), 1458 (m),
1259 (m), 1244 (m), 1093 (m), 1030 (m), 837 (s), 795 (m), 752
(m), 634 (m). 1H NMR (benzene-d6, 300 MHz, 24 °C): δ 6.90
(2,6-iP r 2C6H3N)2Mo[Ge(SiMe3)3]Cl (3). The method for
1 was followed, utilizing (2,6-iPr2C6H3N)2MoCl2(dme) (5.00 g,
8.24 mmol) and (THF)3LiGe(SiMe3)3 (4.24 g, 8.23 mmol).
Complex 3 was isolated as red crystals in 29% yield (1.81 g,
2.34 mmol) after four successive crops from hexamethyldisi-
loxane at -35 °C. Efforts to crystallize more material afforded
a dark red oil containing the desired material. IR (toluene,
NaCl, cm-1): 3058 (m), 2969 (m), 2889 (m), 2279 (s), 1328 (m),
1244 (s), 854 (s), 827 (s), 619 (m). 1H NMR (benzene-d6, 400
i
MHz, 24 °C): δ 6.93 (s, 6 H, NC6H3 Pr2), 3.76 (sept, J ) 7.0
i
Hz, 4 H, NC6H3CHMe2), 1.12 (d, J ) 6.9 Hz, 12 H, NC6H3-
CHMe2), 1.08 (d, J ) 6.9 Hz, 12 H, NC6H3CHMe2), 0.51 (s, 27
H, Ge(SiMe3)3). 13C{1H} NMR (benzene-d6, 100 MHz, 24 °C):
(s, 6 H, NC6H3 Pr2), 3.61 (sept, J ) 6.9 Hz, 4 H, NC6H3CHMe2),
1.11 (d, J ) 6.9 Hz, 12 H, NC6H3CHMe2), 1.08 (d, J ) 6.9 Hz,
12 H, NC6H3CHMe2), 0.43 (s, 27 H, Si(SiMe3)3). 13C{1H} NMR
(benzene-d6, 75 MHz, 24 °C): δ 153.7, 143.9, 128.9, 123.6
i
δ 153.8, 143.0, 127.7, 123.2 (NC6H3 Pr2), 28.7 (NC6H3CHMe2),
i
24.1 (NC6H3CHMe2), 3.90 (Ge(SiMe3)3). 29Si{1H} NMR (benzene-
d6, 59.6 MHz, 24 °C): δ 2.23 (Ge(SiMe3)3). Anal. Calcd for
(NC6H3 Pr2), 29.1 (NC6H3CHMe2), 24.6, 24.2 (NC6H3CHMe2),
3.48 (Si(SiMe3)3). 29Si{1H} NMR (benzene-d6, 59.6 MHz, 24
°C): δ 4.7 (Si(SiMe3)3), -2.9 (Si(SiMe3)3). Anal. Calcd for
C
33H61ClGeMoN2Si3: C, 51.20; H, 7.94; N, 3.62. Found: C,
51.42; H, 8.30; N, 3.46.
C34H61F3MoN2O3SSi4: C, 48.43; H, 7.29; N, 3.32. Found: C,
(2,6-iP r 2C6H3N)2W[Ge(SiMe3)3]Cl (4). The method for
complex 2 was followed, utilizing (2,6-iPr2C6H3N)2WCl2(dme)
(5.00 g, 7.20 mmol) and (THF)3LiGe(SiMe3)3 (3.71 g, 7.20
mmol). The volatile materials were removed by vacuum
transfer, and the resulting orange foam was extracted with
hexanes (50 mL). The hexanes solution was filtered, concen-
trated, and cooled to -80 °C to afford an orange solid which
was contaminated by organogermanium compounds, as de-
termined by the presence of several singlets near δ 0.00 in
48.39; H, 7.43; N, 3.30.
(2,6-iP r 2C6H3N)2Mo[Si(SiMe3)3](CH2CMe3) (7). P r oce-
d u r e A: Compound 6 (0.200 g, 0.237 mmol) and (Me3CCH2)2-
Mg (0.021 g, 0.125 mmol) were combined in a Schlenk tube.
Toluene (∼25 mL) was added, and the solution was stirred
overnight at room temperature. The volatile material was
removed under reduced pressure, and the resulting residue
was extracted into pentane (2 × 10 mL). The combined
pentane extracts were filtered, concentrated (∼5 mL), and
cooled to -35 °C to afford complex 7 (0.136 g, 0.178 mmol,
75%) as deep red crystals. IR (neat, NaCl, cm-1): 2960 (m),
2883 (w), 2353 (w), 1261 (m), 1242 (m), 1093 (m), 1016 (m),
978 (m), 814 (s), 750 (m), 679 (m), 619 (m). 1H NMR (benzene-
1
the H NMR spectrum. In an effort to obtain an analytically
pure sample, this material was extracted into hexamethyldi-
siloxane (2 × 20 mL) to afford a dark orange solution, which
was filtered, concentrated, and cooled to 0 °C. Unfortunately,
crystallization attempts at both 0 and -35 °C were unsuc-
cessful. Structural assignment for 4 follows from analysis of
spectroscopic data for the crude material and by its conversion
to the completely characterized neopentyl derivative 10. 1H
NMR (benzene-d6, 400 MHz, 24 °C): δ 7.10-6.85 (m, 6 H,
i
d6, 400 MHz, 24 °C): δ 7.05-6.90 (m, 6 H, NC6H3 Pr2), 3.85
(sept, J ) 6.8 Hz, 4 H, NC6H3CHMe2), 2.08 (br s, 2 H, CH2-
CMe3), 1.21 (s, 9 H, CH2CMe3), 1.15 (d, J ) 6.8 Hz, 12 H,
NC6H3CHMe2), 1.12 (d, J ) 6.8 Hz, 12 H, NC6H3CHMe2), 0.44
(s, 27 H, Si(SiMe3)3). 13C{1H} NMR (benzene-d6, 100 MHz, 24
i
i
NC6H3 Pr2), 3.78 (sept, J ) 7.0 Hz, 4 H, NC6H3CHMe2), 1.18
°C): δ 153.3, 143.0, 126.6, 123.3 (NC6H3 Pr2), 124.7 (CH2CMe3),
(d, J ) 7.0 Hz, 12 H, NC6H3CHMe2), 1.14 (d, J ) 7.0 Hz, 12
H, NC6H3CHMe2), 0.52 (s, Ge(SiMe3)3, 27 H). 13C{1H} NMR
(benzene-d6, 75 MHz, 24 °C): δ 151.9, 143.2, 127.0, 122.9
40.1 (CH2CMe3), 33.1 (CH2CMe3), 28.3 (NC6H3CHMe2), 24.7,
24.1 (NC6H3CHMe2), 3.80 (Si(SiMe3)3). 29Si{1H} NMR (benzene-
d6, 59.6 MHz, 24 °C): δ -5.3 (Si(SiMe3)3), -65.0 (Si(SiMe3)3).

Bis(imido) Silyl and Germyl Complexes of Mo and W
Organometallics, Vol. 16, No. 21, 1997 4749
Anal. Calcd for C38H72MoN2Si4: C, 59.64; H, 9.48; N, 3.66.
Found: C, 59.69; H, 9.72; N, 3.65.
CH2CMe3), 1.17 (d, J ) 8.7 Hz, 12 H, NC6H3CHMe2), 1.15 (d,
J ) 8.7 Hz, 12 H, NC6H3CHMe2), 0.47 (s, 27 H, Si(SiMe3)3).
13C{1H} NMR (benzene-d6, 100 MHz, 24 °C): δ 152.4, 142.9,
P r oced u r e B: To a diethyl ether (20 mL) solution of (2,6-
iPr2C6H3N)2Mo[Si(SiMe3)3]Cl (1.00 g, 1.37 mmol) was added
an ether solution of ClMgCH2CMe3 (0.78 M, 1.80 mL, 1.40
mmol) at room temperature. Immediately the color of the
solution changed from dark red to light red, and the solution
was stirred overnight at room temperature. The volatile
material was evacuated, and the resulting residue was ex-
tracted into pentane (3 × 5 mL). The combined extracts were
filtered, concentrated, and cooled to -35 °C to afford complex
7 (0.590 g, 0.771 mmol, 55%) as deep red crystals.
i
125.9, 122.9 (NC6H3 Pr2), 132.1 (CH2CMe3), 40.6 (CH2CMe3),
33.6 (CH2CMe3), 28.3 (NC6H3CHMe2), 24.7, 24.1 (NC6H3-
CHMe2), 4.60 (Si(SiMe3)3). 29Si{1H} NMR (benzene-d6, 59.6
MHz, 24 °C): δ 3.41 (Ge(SiMe3)3). Anal. Calcd for C38H72
-
MoN2Si4: C, 50.84; H, 8.08; N, 3.12. Found: C, 50.52; H, 8.18;
N, 3.02.
2
i
(2,6- P r 2C6H 3N)2Mo[η -C(N-2,6-Me 2C6H 3)Si(SiMe 3)3]-
(CH2CMe3) (11). The compounds 7 (0.200 g, 0.261 mmol) and
2,6-dimethylphenyl isocyanide (0.035 g, 0.267 mmol) were
combined in a Schlenk flask. Benzene (∼10 mL) was added
at room temperature, and the solution was stirred for an
additional 3 h. The volatile materials were removed, and the
residue was extracted with pentane (10 mL). The combined
extracts were filtered, concentrated, and cooled to -35 °C to
afford complex 11 as small yellow crystals (0.092 g, 39%).
NMR-tube experiments indicate that the reaction proceeds in
greater than 80% yield. IR (neat, NaCl, cm-1): 3058 (w), 3048
(m), 2925 (m), 2897 (m), 2865 (m), 2781 (w), 1594 (br, υCdN),
1460 (m), 1423 (m), 1319 (m), 1250 (m), 1246 (m), 1101 (m),
1020 (m), 830 (s), 827 (s), 750 (m). 1H NMR (benzene-d6, 300
(2,6-iP r 2C6H3N)2Mo[Ge(SiMe3)3](CH2CMe3) (8). This com-
plex was prepared as described for 7 (procedure B), from 3
(0.280 g, 0.362 mmol) and a dilute ether solution (5 mL) of
ClMgCH2CMe3 (0.78 M, 1.80 mL, 1.40 mmol). Complex 8 was
isolated as dark red crystals in 30% yield (0.072 g). IR
(toluene, NaCl, cm-1): 3068 (m), 3039 (m), 2989 (m), 2870 (m),
2698 (w), 1361 (w), 1323 (m), 1263 (m), 1242 (s), 860 (s), 823
(s), 619 (s). 1H NMR (benzene-d6, 300 MHz, 24 °C): δ 7.10-
i
6.90 (m, 6 H, NC6H3 Pr2), 3.85 (sept, J ) 6.8 Hz, 4 H,
NC6H3CHMe2), 2.03 (br s, 2 H, CH2CMe3), 1.21 (s, 9H,
CH2CMe3), 1.15 (d, J ) 7.2 Hz, 12 H, NC6H3CHMe2), 1.13 (d,
J ) 7.2 Hz, 12 H, NC6H3CHMe2), 0.47 (s, 27 H, Ge(SiMe3)3).
13C{1H} NMR (benzene-d6, 100 MHz, 24 °C): δ 153.3, 142.9,
i
MHz, 24 °C): δ 7.15-6.80 (m, 9 H, NC6H3 Pr2, CNC6H3Me2),
3.94 (sept, J ) 7.0 Hz, 4 H, NC6H3CHMe2), 2.68 (s, 2 H, CH2-
CMe3), 2.04 (s, 6 H, CNC6H3Me2), 1.28 (d, J ) 7.0 Hz, 12 H,
NC6H3CHMe2), 1.26 (d, J ) 7.0 Hz, 12 H, NC6H3CHMe2), 1.00
(s, 9H, CH2CMe3), 0.18 (s, 27 H, Si(SiMe3)3). 13C{1H} NMR
(benzene-d6, 100 MHz, 24 °C): δ 244.8 (C(NAr)Si(SiMe3)3),
i
126.5, 123.2 (NC6H3 Pr2), 121.6 (CH2CMe3), 39.7 (CH2CMe3),
33.1 (CH2CMe3), 28.3 (NC6H3CHMe2), 24.7 (NC6H3CHMe2),
24.0 (NC6H3CHMe2), 4.38 (Ge(SiMe3)3). 29Si{1H} NMR (benzene-
d6, 59.6 MHz, 24 °C): δ 0.20 (Ge(SiMe3)3). Anal. Calcd for
C38H72GeMoN2Si3: C, 56.36; H, 8.96; N, 3.46. Found: C, 56.63;
H, 9.16; N, 3.36.
i
153.7, 143.1, 129.2, 123.2 (NC6H3 Pr2), 142.3, 129.2, 127.0,
124.5 (NC6H3Me2), 53.6 (CH2CMe3), 35.6 (CH2CMe3), 34.7
(CH2CMe3), 27.9 (NC6H3CHMe2), 25.1, 24.8 (NC6H3CHMe2),
19.1 (NC6H3Me2), 2.70 (Si(SiMe3)3). 29Si{1H} NMR (benzene-
d6, 59.6 MHz, 24 °C): δ -10.2 (Si(SiMe3)3), -78.5 (Si(SiMe3)3).
Anal. Calcd for C47H81MoN3Si4: C, 62.97; H, 9.11; N, 4.69.
Found: C, 62.68; H, 9.09; N, 4.64.
X-r a y Cr ysta llogr a p h y. Crystallographic data for com-
plexes 1 and 7 are collected in Table 1. For 1 the space group
was uniquely determined by systematic absences, and for 7
the centrosymmetric alternative was initially assumed and
was found to be computationally stable. Empirical corrections
for absorption were applied to the data. Solutions were by
direct methods, and all non-hydrogen atoms were anisotropi-
cally refined. Hydrogen atoms were idealized, except for H(1)
in 7 which was located and refined with a fixed thermal
parameter. In 7, the SiMe3 groups are disordered over two
sites in an 80/20 ratio. For the minority site, only the Si atom
positions were resolved as Si(2′), Si(3′), and Si(4′). SHELXTL-
(5.1) software was used for all computations (G. Sheldrick,
Siemens XRD, Madison, WI).
(2,6-iP r 2C6H3N)2W[Si(SiMe3)3](CH2CMe3) (9). In a round
bottom flask, a diethyl ether solution (20 mL) of crude (2,6-
iPr2C6H3N)2W[Si(SiMe3)3]Cl (0.500 g) was stirred at room
temperature. To this mixture was added a diethyl ether
solution (diluted to ∼5 mL) of ClMgCH2CMe3 (0.78 M; 1.5
equiv). The color of the solution immediately changed from
dark orange to light orange, and the solution was stirred
overnight. The volatile materials were removed under vacuum,
and the resulting residue was extracted with pentane (2 × 5
mL). The combined extracts were filtered, concentrated, and
cooled to -35 °C to afford complex 9 (0.11 g, ca. 20%;
unoptimized) as orange crystals. IR (neat, NaCl, cm-1): 2960
(m), 2931 (m), 2902 (m), 2862 (m), 2353 (w), 2337 (w), 1454
(m), 1425 (m), 1327 (m), 1279 (m), 1259 (m), 1242 (m), 1109
(m), 1088 (m), 1024 (m), 804 (s), 750 (m), 680 (m). 1H NMR
i
(benzene-d6, 400 MHz, 24 °C): δ 7.10-6.85 (m, 6 H, NC6H3 Pr2),
3.80 (sept, J ) 6.8 Hz, 4 H, NC6H3CHMe2), 1.62 (br s, 2 H,
CH2CMe3), 1.19 (s, 12 H, CH2CMe3), 1.17 (d, J ) 6.8 Hz, 12
H, NC6H3CHMe2), 1.14 (d, J ) 6.8 Hz, 12 H, NC6H3CHMe2),
0.43 (s, 27 H, Si(SiMe3)3). 13C{1H} NMR (benzene-d6, 100 MHz,
i
Resu lts a n d Discu ssion
24 °C): δ 152.4, 143.0, 135.3, 123.0 (NC6H3 Pr2), 126.0 (CH2-
CMe3), 41.0 (CH2CMe3), 33.5 (CH2CMe3), 28.3 (NC6H3CHMe2),
24.7, 24.1 (NC6H3CHMe2), 4.00 (Si(SiMe3)3). 29Si{1H} NMR
(benzene-d6, 59.6 MHz, 24 °C): δ -2.1 (Si(SiMe3)3), -59.4
(Si(SiMe3)3). Anal. Calcd for C38H72MoN2Si4: C, 53.50; H,
8.51; N, 3.28. Found: C, 52.95; H, 8.57; N, 3.29.
Bis(im id o) Silyl a n d Ger m yl Com p lexes. The
silyl chloride complexes (2,6-iPr2C6H3N)2M[Si(SiMe3)3]-
Cl (1, M ) Mo; 2, M ) W) were prepared by reaction of
(THF)3LiSi(SiMe3)3 with the corresponding dichlorides
(2,6-iPr2C6H3N)2MCl2(dme) (M ) Mo,19 W20) in diethyl
ether (eq 1). To our knowledge, compound 1 represents
(2,6-iP r 2C6H 3N)2W[Ge(SiMe3)3](CH 2CMe3) (10). To a
stirred diethyl ether solution (∼15 mL) of crude (2,6-
iPr2C6H3N)2W[Ge(SiMe3)3]Cl (2.00 g, 2.32 mmol) was added an
excess of ClMgCH2CMe3 (∼3 equiv) as a diethyl ether solution
at room temperature. The solution was stirred for an ad-
ditional 8 h. The volatile materials were removed, and the
residue was extracted with pentane (2 × 10 mL). The
combined extracts were filtered, concentrated, and cooled to
-35 °C to afford 10 (1.50 g, 72%) as orange crystals. IR
(toluene, NaCl, cm-1): 3068 (m), 3026 (m), 3001 (m), 2960 (m),
2916 (m), 2887 (m), 2873 (w), 2802 (w), 1604 (w), 1468 (w),
1346 (m), 1327 (m), 1284 (m), 1242 (m), 849 (s), 831 (s), 748
(m), 619 (m). 1H NMR (benzene-d6, 400 MHz, 24 °C): δ 7.08-
i
6.90 (m, 6 H, NC6H3 Pr2), 3.80 (sept, J ) 6.8 Hz, 4 H,
NC6H3CHMe2), 1.57 (br s, 2 H, CH2CMe3), 1.19 (s, 9H,

4750 Organometallics, Vol. 16, No. 21, 1997
Casty et al.
Ta ble 1. Cr ysta llogr a p h ic Da ta for Com p ou n d s 1
a n d 7
1
7
(a) Crystal Parameters
C33H61ClMoN2Si4
729.59
formula
fw
C38H72MoN2Si4
764.27
cryst color, habit
cryst size, mm
cryst syst
space group
a, Å
red block
red plate
0.14 × 0.10 × 0.08 0.40 × 0.40 × 0.20
monoclinic
P21/n
triclinic
P1h
9.3039(3)
20.5308(5)
21.7343(5)
11.2900(9)
12.895(1)
16.756(5)
96.378(9)
94.183(9)
109.141(7)
2274.6(4)
2
b, Å
c, Å
R, deg
â, deg
97.360(10)
γ, deg
volume, Å3
Z
4117.4(2)
4
1.177
5.22
F (calcd), g cm-3
µ (Mo KR), cm-1
temp, K
1.116
4.19
233(2)
193(2)
(b) Data Collection
Siemens SMART
Mo KR
(λ ) 0.710 73 Å)
1.37-26.38
diffractometer
radiation
Siemens SMART
Mo KR
(λ ) 0.710 73 Å)
2.09-30.00
F igu r e 1. ORTEP view of the molecular structure of (2,6-
iPr2C6H3N)2MoCl[Si(SiMe3)3] (1).
θ range for data
collection, deg
no. of rflns collected
no. of unique rflns
Ta ble 2. Selected In ter a tom ic Dista n ces (Å) a n d
16 610
8012
(Rint ) 0.0546)
14 801
13 082
(Rint ) 0.0344)
An gles (d eg) for (2,6-iP r 2C6H3N)2Mo[Si(SiMe3)3](Cl)
(1)
(c) Refinement
21.6
7.43
17.11
1.481
(a) Bond Distances
rfln/param ratio
R(F), %
30.0
5.88
11.01
1.203
Mo(1)-N(1)
Mo(1)-Si(1)
Si(1)-Si(2)
Si(1)-Si(4)
N(1)-C(1)
1.748(4)
2.562(2)
2.355(2)
2.365(2)
1.394(6)
Mo(1)-N(2)
Mo(1)-Cl(1)
Si(1)-Si(3)
Si(2)-C(25)
N(2)-C(13)
1.753(4)
2.3093(14)
2.363(2)
1.857(8)
1.408(7)
R(wF2), %
GOF
max/min peak in final 0.643, -0.574
0.674, -0.478
diff map, e Å-3
(b) Bond Angles
N(1)-Mo(1)-N(2) 109.3(2) Cl(1)-Mo(1)-Si(1) 109.24(5)
N(1)-Mo(1)-Cl(1) 112.83(14) C(13)-N(2)-Mo(1) 151.3(4)
N(1)-Mo(1)-Si(1) 103.19(14) C(1)-N(1)-Mo(1) 155.5(4)
the first example of a d0 silyl complex of molybdenum,
however, the d0 tungsten complex (Me3CCH2)2WtCMe3-
[Si(SiMe3)3] is known.7a An analytically pure sample
of 1 was obtained from hexamethyldisiloxane at 0 °C
as dark red, platelike crystals in 27% yield. Complex
2, however, was obtained as a bright orange powder that
was contaminated by a number of organosilicon byprod-
The structure of complex 1 is shown in Figure 1, and
selected bond distances and angles are summarized in
Table 2. The Mo-N bond distances of 1.748(4) and
1.753(4) Å are consistent with related values in other
molybdenum imido complexes.25 The Mo-Si bond
distance of 2.562(2) Å is similar to the corresponding
distance in the d2 molybdocene silyl complex Cp2Mo-
(SiMe2Cl)H, 2.513(1) Å26 but is slightly shorter than the
Mo-Si bond length of 2.670(2) Å in Mo2[Si(SiMe3)3]2-
(NMe2)4.27 The M-N-C angles of 155.5(4)° (Mo-N(1)-
C(1)) and 151.3(4)° (Mo-N(2)-C(13)) are consistent
with the corresponding angles in [(2,6-iPr2C6H3N)(tBuN)-
Mo(CH2CMe3)2] (156.2(1)° and 157.9(1)°).25
The analogous germyl complexes (2,6-iPr2C6H3N)2M-
[Ge(SiMe3)3]Cl (3, M ) Mo; 4, M ) W) have been
prepared by reaction of (THF)3LiGe(SiMe3)3 with the
corresponding dichlorides (2,6-iPr2C6H3N)2MCl2(DME)
(M ) Mo, W; eq 1). As for the silyl derivatives, only
the molybdenum analog was obtained in analytically
pure form. Complex 3 was isolated from hexamethyl-
disiloxane at 0 °C as dark red crystals in 29% yield.
Spectroscopic data for the germyl complexes are, as
expected, very similar to those for the corresponding
silyl derivatives.
1
ucts, as determined by H NMR spectroscopy. Spectro-
scopic data for 1 and 2 are consistent with the proposed
structures. The 1H NMR spectra contain singlets for
the silyl ligands, at 0.41 ppm for 1 and 0.44 ppm for 2,
and two doublets (δ 0.99 and 1.05 for 1; δ 1.07 and 1.11
for 2) for the inequivalent methyl groups of the imido
ligands reflecting an unsymmetrical substitution pat-
tern at the metal. As expected, only one septet for the
methine protons of the isopropyl groups is observed (1,
δ 3.54; 2, δ 3.68). The 29Si NMR spectra for complexes
1 and 2 are quite unusual in that the metal-bound
silicon atoms are remarkably downfield-shifted (1, δ
-9.3; 2, δ -22.9) relative to similar silicon atoms in
other early metal -Si(SiMe3)3 derivatives. For com-
parison, the 29Si shifts for the metal-bound silicon atoms
in CpCp*Zr[Si(SiMe3)3]Cl,3k CpCp*Hf[Si(SiMe3)3]Cl,23
and Cp*(2,6-iPr2C6H3N)Ta[Si(SiMe3)3]Cl24 are -87.3,
-77.9, and -48.3 ppm, respectively. Further support
for the structural assignments for complexes 1 and 2 is
based on their conversions to silyl-neopentyl deriva-
tives (vide infra). Finally, the molecular structure of
complex 1 was confirmed by X-ray crystallography.
(25) Bell, A.; Clegg, W.; Dyer, P. W.; Elsegood, M. R. J .; Gibson, V.
C.; Marshall, E. L. J . Chem. Soc., Chem. Commun. 1994, 2547.
(26) Koloski, T. S.; Pestana, D. C.; Carroll, P. J .; Berry, D. H.
Organometallics 1994, 13, 489.
(27) Chisholm, M. H.; Chiu, H. T.; Folting, K.; Huffman, J . C. Inorg.
Chem. 1984, 23, 4097.
(23) Woo, H.-G.; Heyn, R. H.; Tilley, T. D. J . Am. Chem. Soc. 1992,
114, 5698.
(24) Casty, G. L.; Tilley, T. D. Unpublished results.

Bis(imido) Silyl and Germyl Complexes of Mo and W
Organometallics, Vol. 16, No. 21, 1997 4751
Rea ction s of Bis(im id o) Silyl a n d Ger m yl Com -
p lexes. Complex 1 does not react with H2, CO, or C2H4
(benzene-d6, 1 atm, 24 h) or with CH3CN (1.5 equiv,
benzene-d6, 24 h). Also, there is no reaction between 1
and PhSiH3 (1.0 equiv) in benzene-d6 at room temper-
ature over 12 h. After the latter mixture was heated
to 62 °C for 1 day, mostly starting material remained
(94%) but trace amounts of the products HSi(SiMe3)3
(7%), Ph2SiH2 (5%), and HSiMe3 (3%) were also de-
tected. Heating to 80 °C for a second day produced a
mixture containing 65% of the starting material 1 as
well as HSi(SiMe3)3 (18%), HSiMe3 (4%), and the
redistribution product Ph2SiH2 (8%). Similarly, a ben-
zene-d6 solution of complex 1 did not react with Ph2-
SiH2 (1.0 equiv) at room temperature, but heating for 4
days at 62 °C produced trace amounts of HSi(SiMe3)3
(8%), HSiMe3 (2%), and Ph3SiH (2%). The generation
of HSi(SiMe3)3 in these reactions suggests a σ-bond
metathesis mechanism,16,23 but the molybdenum-con-
taining product(s) could not be characterized. Particu-
larly interesting is the production of HSiMe3, which
results from Si-Si bond cleavage. As discussed below,
this product may result from decomposition of (2,6-
iPr2C6H3N)2Mo[Si(SiMe3)3](H), which could form in the
above reactions of the silanes via an Si-H/Mo-Cl
exchange.
triflate complex.29 Complex 6 did not react with PhSiH3
(1 equiv) in benzene-d6 at room temperature after 6 h,
but when this reaction mixture was heated to 62 °C for
12 h, complete consumption of PhSiH3 occurred and 35%
of 6 remained unreacted. Also produced in this reaction
was HSi(SiMe3)3 (0.19 equiv), HSiMe3 (0.11 equiv), Ph2-
SiH2 (0.12 equiv), and Me3SiOTf (0.19 equiv).
Silyl-Neop en tyl a n d Ger m yl-Neop en tyl Com -
p lexes of Mo(VI) a n d W(VI). Complexes 1-4 and 6
react with neopentylmagnesium chloride or bis(neopen-
tyl)magnesium to afford the corresponding neopentyl
complexes 7-10 (eq 3). Analytically pure samples of
7-10 were obtained from pentane at -35 °C as red (7
and 9) or orange (8 and 10) crystals, typically in greater
than 70% yield. These complexes contain R-agostic
M-C-H interactions, as determined by NMR spectros-
copy and X-ray crystallography. Complexes containing
R-agostic interactions are often highly fluxional and
undergo rapid exchange of the agostic hydrogen with
other hydrogens bound to the same carbon atom.30 In
Complex 1 reacted rapidly with 2,6-dimethylphenyl-
isocyanide in benzene at room temperature to afford the
corresponding insertion product 5 (eq 2). An analyti-
1
the H NMR spectrum of 7, the methylene hydrogens
of the neopentyl ligand appear at δ 2.08 as a broad
singlet, suggesting a dynamic process involving ex-
change of the two methylene hydrogen atoms. This
resonance only broadened further as a dichloromethane-
d2 solution of 7 was cooled to -80 °C, suggesting a
barrier to interconversion of <7-8 kcal mol-1. This
situation, therefore, differs somewhat from the recently
characterized complexes [Cp(2,6-iPr2C6H3N)Nb(CH2-
CMe3)Cl],31 (2,6-iPr2C6H3N)(tBuN)Mo(CH2CMe3)2],25 and
[Cp(2,6-iPr2C6H3N)Nb(CH2CMe3)Cl],31 which exhibit
sharp doublet resonances for the methylene protons
(2J HH ≈ 12 Hz).
cally pure sample of 5 was obtained in 82% yield from
pentane as light orange needles. The 1H NMR spectrum
of complex 5 contains two doublets (δ 1.26 and 1.27) for
the inequivalent methyl groups of the imido ligands and
a singlet at δ 2.13 for the methyl groups of the
isocyanide group. The 13C NMR spectrum contains a
resonance for the deshielded isonitrile carbon at δ 232.8,
and the infrared stretch for the iminosilaacyl ligand at
1608 cm-1 is characteristic for complexes of this
type.3d,k,n,28
To examine potential electronic effects on reactions
of Mo-Si bonds in this system, we prepared the silyl
triflate complex (2,6-iPr2C6H3N)2Mo[Si(SiMe3)3](OTf) (6)
from 1 and silver triflate in benzene solution. The
complex was obtained in 89% yield as purple needles
from hexanes. The 1H NMR spectrum of complex 6
contains two doublets (δ 1.08 and 1.11) for the inequiva-
lent methyl groups of the imido ligand and a new singlet
at δ 0.43 for the silyl ligand. Also, the 29Si NMR
spectrum reveals that the chemical shift for the coor-
dinated silicon atom, at δ 4.73, is dramatically down-
field-shifted relative to silicon atoms in similar early-
metal complexes (vide supra). The infrared spectrum
contains a band at 1458 cm-1 which may be assigned
as the ν(SO3) stretching frequency for an inner-sphere
The 13C NMR spectrum of 7 contains a resonance at
δ 124.7 attributed to the highly deshielded R carbon of
the neopentyl ligand. For comparison, the 13C shifts for
the R-carbon atoms of the neopentyl ligands in [(2,6-
iPr2C6H3N)(tBuN)Mo(CH2CMe3)2],25 [Cp(2,6-iPr2C6H3N)-
Nb(CH2CMe3)Cl],31 and [Cp(2,6-iPr2C6H3N)Nb(CH2-
CMe3)2]31 are 77.9, 86.3, and 85.7 ppm, respectively. The
IR spectra for complexes containing an R-agostic inter-
action typically contain a C-H stretch in the range
2700-2300 cm-1 30,31
but no such assignment for an
,
R-agostic C-H stretch could be made for complexes
7-10.
The structure of 7 is shown in Figure 2, and selected
bond distances and angles are summarized in Table 3.
(29) Lawrance, G. A. Chem. Rev. 1986, 86, 17.
(30) (a) Brookhart, M.; Green, M. L. H. J . Organomet. Chem. 1983,
250, 395. (b) Brookhart, M.; Green, M. L. H.; Wong, L. Prog. Inorg.
Chem. 1988, 36, 1 and references therein.
(31) Poole, A. D.; Williams, D. N.; Kenwright, A. M.; Gibson, V. C.;
Clegg, W.; Hockless, D. C. R.; O’Neil, P. A. Organometallics 1993, 12,
2549.
(28) Heyn, R. H.; Tilley, T. D. Inorg. Chem. 1989, 28, 1768.

4752 Organometallics, Vol. 16, No. 21, 1997
Casty et al.
The reaction of complex 7 with excess PhSiH3 (3
equiv) resulted in complete consumption of both starting
materials after 12 h and production of neopentane (1
equiv), trimethylsilane (1.08 equiv), and minor amounts
of tris(trimethylsilyl)silane (0.12 equiv) and Ph2SiH2
(0.05 equiv). The remaining molybdenum-containing
material could not be identified, and the 1H NMR
spectrum of the crude reaction mixture reveals a
plethora of broad, featureless peaks in the imido, aryl,
and silyl regions. In the absence of a precipitate, this
suggests that at least some of the molybdenum-contain-
ing product(s) are paramagnetic. The formation of 1
equiv of neopentane suggests that the initial product
of reaction is the bis(silyl) complex (2,6-iPr2C6H3N)2Mo-
[Si(SiMe3)3](SiH2Ph). However, this species could not
be observed in solution, and based on the chemistry
described below, it is tempting to speculate that the
trimethylsilane results from decomposition of the silyl
hydride (2,6-iPr2C6H3N)2Mo[Si(SiMe3)3](H) (A), which
could arise from reaction of the bis(silyl) complex with
a second equivalent of PhSiH3. Interestingly, however,
PhH2SiSiH2Ph is not observed as a product in the
reaction mixture. Of course, PhH2SiSiH2Ph may be
consumed as it is formed and converted to other,
unidentified organosilicon compounds. If 1 equiv of
PhSiH3 is employed in the reaction, only ca. 40% of 7 is
consumed and the observed products (by 1H NMR
spectroscopy) are neopentane (0.42 equiv), HSiMe3 (0.60
equiv), HSi(SiMe3)3 (0.08 equiv), and Ph2SiH2 (0.01
equiv).
F igu r e 2. ORTEP view of the molecular structure of (2,6-
iPr2C6H3N)2Mo[Si(SiMe3)3](CH2CMe3) (7).
Ta ble 3. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) for
(2,6-iP r 2C6H3N)2Mo(CH2CMe3)[Si(SiMe3)3] (7)
(a) Bond Distances
Mo(1)-N(1)
Mo(1)-Si(1)
N(1)-C(20)
Mo(1)-H(1)
Si(1)-Si(4)
C(2)-C(3)
1.754(2)
2.6048(9)
1.404(3)
2.55(4)
2.321(2)
1.503(5)
Mo(1)-N(2)
Mo(1)-C(1)
N(2)-C(32)
Si(1)-Si(3)
Si(1)-Si(2)
C(1)-C(2)
1.752(2)
2.083(3)
1.399(4)
2.416(2)
2.3431(14)
1.502(4)
To further probe the possibility of silyl hydride
intermediates in the above reaction involving phenyl-
silane, we investigated the reactions of 7-10 with
hydrogen. When a benzene-d6 solution of 7 was placed
under an atmosphere of H2 at room temperature, the
color of the solution changed from red to brown and free
neopentane (0.94 equiv) and HSiMe3 (1.8 equiv) were
produced within 3 h. When the reaction was complete
(b) Bond Angles
N(1)-Mo(1)-N(2) 112.68(11) C(1)-Mo(1)-Si(1) 106.39(10)
N(1)-Mo(1)-C(1) 110.66(10) C(20)-N(1)-Mo
161.6(2)
157.4(2)
118.13(5)
N(1)-Mo(1)-Si(1) 104.87(7)
C(2)-C(1)-Mo 136.6(2)
C(32)-N(2)-Mo
Si(2)-Si(1)-Mo
The interesting feature of this structure is the presence
of an R-agostic interaction involving a hydrogen of the
neopentyl ligand. The hydrogen atom involved in this
interaction was located and refined with a fixed thermal
parameter. The Mo-H(agostic) distance of 2.55(4) Å is
comparable to related distances in molybdenum neo-
pentyl complexes. For example, R-agostic interactions
1
(6 h), the only observable products (by H NMR spec-
troscopy) were neopentane and trimethylsilane. The
absence of any well-defined 1H NMR resonances at-
tributable to 2,6-iPr2C6H3N ligands and the lack of a
precipitate suggest that the Mo-containing products are
paramagnetic. In addition, the silanes HSi(SiMe3)3 and
H2Si(SiMe3)2 were not detected as products. The initial
step in this reaction appears to involve hydrogenolysis
of the Mo-C bond of 7 to produce neopentane, and
further evidence for this was found in the reaction of 7
with deuterium, which gave neopentane-d1 and DSiMe3
(by 2H NMR spectroscopy). Thus, the initial Mo-
containing product is probably the silyl hydride species
(2,6-iPr2C6H3N)2Mo[Si(SiMe3)3](H) (A), which is appar-
ently too reactive to be detected as an intermediate
during the course of the reaction. It therefore appears
that the HSiMe3 product in this reaction results from
an interesting elimination from A. Further support for
this was observed in the reaction of 1 (in benzene-d6)
with a THF solution of LiBEt3H (1.5 equiv), which
for the two neopentyl ligands in (2,6-Pri C6H3N)(tBuN)-
2
Mo(CH2CMe3)2 result in Mo-H distances of 2.35 and
2.44 Å.25 The Mo-Si bond distance of 2.608(9) Å in 7
is close to the related distance in 1 of 2.562(2) Å.
Furthermore, the Mo-N bond distances of 1.754(2) and
1.752(2) Å are consistent with alkyl and aryl imido
ligands bonded to molybdenum. The M-N-C angles
of 157.4(2)° (Mo-N(2)-C(32)) and 161.6(2)° (Mo-N(1)-
C(20)) are consistent with the corresponding angles of
156.2(1)° and 157.9(1)° in [(2,6-Pri2C6H3N)(ButN)Mo(CH2-
CMe3)2].25
Rea ction s of th e Silyl-Neop en tyl a n d Ger m yl-
Neop en tyl Com p lexes. Complex 7 reacted rapidly
with 2,6-dimethylphenyl isocyanide to afford the inser-
tion product (2,6-iPr2C6H3N)2Mo[CH2CMe3][η2-C(N-2,6-
Me2C6H3)Si(SiMe3)3] (11), isolated from pentane in 39%
yield. Exclusive insertion of the isocyanide into the
Mo-Si bond is revealed by characteristic 13C NMR and
infrared data.3d,k,n,28 The iminosilaacyl carbon resonates
at δ 244.8 in the 13C NMR spectrum, and the ν(CdN)
1
produced trimethylsilane as the major product (by H
NMR spectroscopy). On the basis of our very limited
knowledge of d0 silyl hydride complexes, it is difficult
at this time to speculate on the mechanism of such an
elimination. However, an intriguing possibility involves
decomposition of A via a 4-centered transition state to
generate a silylene complex (Scheme 1). The observed
stretch was observed at 1594 cm-1
.

Bis(imido) Silyl and Germyl Complexes of Mo and W
Organometallics, Vol. 16, No. 21, 1997 4753
Sch em e 1
formation of ca. 2 equiv of HSiMe3 requires that such a
process be repeated, and this could occur via hydrogena-
tion of the proposed silylene complex with a second
equivalent of hydrogen, as shown in Scheme 1. Hengge
and co-workers have suggested a similar elimination
involving Si-Si bond cleavage for a polymerization
catalyzed by titanocene derivatives.8b
We also considered the possibility that the HSiMe3
product arises via a metal-catalyzed redistribution
reaction of HSi(SiMe3)3, which is the typical silicon-
containing decomposition product of M-Si(SiMe)3 de-
rivatives. To test this, complex 7 was allowed to react
with hydrogen in the presence of 10 equiv of HSi-
(SiMe3)3. In this reaction, the conversion of 7 occurred
without enhanced production of HSiMe3. It therefore
seems that free HSi(SiMe3)3 is not an intermediate in
the decomposition of A to HSiMe3.
Numerous attempts to trap a potential silylene in-
termediate with excess amounts of various silylene
trapping reagents failed. Interestingly, when a benzene-
d6 solution of complex 7 was allowed to react with excess
PMe3, 2-butyne, or 1,3-butadiene under 1 atm of hy-
drogen for 24 h, the major products were free neopen-
tane and HSi(SiMe3)3 and only a minor amount of
HSiMe3 was detected (by NMR spectroscopy). However,
hydrogenations in the presence of diphenylacetylene,
methyl iodide, or trimethylsilyl bromide produced neo-
pentane and HSiMe3 as the major products, and only a
minor amount of HSi(SiMe3)3 was observed. In all but
one case, the remaining molybdenum-containing mate-
rial could not be isolated. In the presence of excess
PMe3, the hydrogenation of 7 produced (2,6-iPr2C6H3N)2-
Mo(PMe3)2.17d These observations seem to indicate that
better ligands for molybdenum (L ) PMe3, 2-butyne, or
1,3-butadiene) transiently trap the proposed silyl hy-
dride intermediate to give species of the type (2,6-
iPr2C6H3N)2Mo[Si(SiMe3)3](H)(L), which then decom-
pose via reductive elimination of silane. Alternatively,
with less coordinating reagents (MeI, diphenylacetylene,
Me3SiBr), the silyl hydride intermediate is not inter-
cepted and decomposition via Si-Si bond cleavage
occurs.
With the hope of stabilizing intermediates such as B,
we examined the reactions of 8-10 with hydrogen. The
tungsten complex 8 undergoes the same reaction with
hydrogen (1 atm, room temperature) but at a much
slower rate (complete conversion after ca. 7 days). No
intermediates were observed in this reaction, and only
broad, featureless peaks were observed for the imido
1
ligands (by H NMR spectroscopy). The reactions of 9
and 10 with hydrogen were also examined, which
according to Scheme 1 would generate the potentially
more stable germylene complexes (2,6-iPr2C6H3N)2MdGe-
(SiMe3)2 (M ) Mo, W). However, attempts to trap these
possible germylene intermediates with 2-butyne and
diphenyl acetylene were unsuccessful.
Con clu sion s
In summary, we have prepared and investigated the
reactivity of several d0, bis(imido) silyl complexes. In
some respects, these silyl complexes are less reactive
than the corresponding group 4 metallocene complexes.
The bis(imido) silyl complexes do not polymerize hy-
drosilanes, but instead mediate interesting reactions
involving Si-Si bond cleavage. Complexes 1-4 are
readily alkylated to the corresponding neopentyl com-
plexes 7-10 in good to high yield. Complexes 7-10
react with hydrogen or hydrosilanes to generate the
probable hydride intermediates (2,6-iPr2C6H3N)2M-
[E(SiMe3)3](H) (A), which rapidly decompose via elimi-
nation of trimethylsilane. In contrast, the group 4
hydrido silyl complex CpCp*Hf[Si(SiMe3)3]H decomposes
by elimination of HSi(SiMe3)3, and no HSiMe3 is ob-

4754 Organometallics, Vol. 16, No. 21, 1997
Casty et al.
served.18 This chemistry raises some interesting ques-
tions concerning possible reactivity patterns for early
transition-metal silyl complexes. It suggests operation
of a σ-bond metathesis mechanism for Si-Si bond
cleavage, but this remains quite speculative at the
moment given the lack of direct experimental evidence.
The observed elimination chemistry also suggests the
possible formation of heretofore unknown early transi-
tion-metal silylene complexes and the possible inter-
mediacy of such complexes in catalytic chemistry.
Efforts in this area continue to focus on isolating or
trapping such silylene species.
Ack n ow led gm en t is made to the National Science
Foundation for their generous support of this work. Dr.
Charles Campana is acknowledged for his assistance
with the structure determinations.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, collection, and refinement parameters, positional and
anisotropic displacement parameters, bond distances and
angles, and hydrogen coordinates for 1 and 7 (13 pages).
Ordering information is given on any current masthead page.
OM970527T