5604 Organometallics, Vol. 20, No. 26, 2001
Castillo and Tilley
Ca u tion : Extreme care must be taken in conducting
reactions that produce SiH4, which is a flammable and
potentially explosive gas.
but only trace amounts of PhMeSiH2 were observed.
Therefore, the Lu-Me bond of 3 seems to react with
PhSiH3 via two major pathways: exchange of hydro-
carbyl groups to produce 2 and MeSiH3, and formal
protonation of the methyl group to yield Cp*2LuSiH2-
Ph and methane. The direct σ-bond metathesis reaction
of 2 with Si-H bonds probably accounts for the observed
benzene product. Another postulated intermediate,
Cp*2LuSiH2Ph, and other lutetium species could play
a significant role in mediating dehydrocoupling reac-
tions of PhSiH3 and MeSiH3 to polysilanes.
Despite the high reactivity of lutetium hydride 1
toward organosilanes, it displays good selectivity for
Si-C over Si-H activation. Use of dihydrogen in the
lutetium hydride-catalyzed Si-C activations provides
a source of hydrogen atoms, which allow complete
conversion of Si-C to Si-H and C-H bonds. Thus,
under hydrogenolysis conditions, selective and catalytic
Si-C bond cleavage can be achieved. Moreover, such
activation reactions have been demonstrated for both
Si-C(sp2) and Si-C(sp3) bonds, as well as for disubsti-
tuted silanes. The hydrogenolysis of n-hexylsilane, in
particular, appears to represent the first example of
catalytic cleavage of an unactivated (no adjacent π-sys-
tem) and unstrained Si-C bond. This type of reactivity
had not been observed in other organolanthanide sys-
tems, and it can be attributed to the high charge density
of lutetium relative to the rest of the lanthanide metals.
The hydrosilane products of the hydrogenolysis reac-
tions seem to react further with Lu species in solution
by dehydrogenative coupling, which does not allow the
isolation of well-characterized Si-H compounds. Despite
this limitation, these reactions are potentially useful in
future developments of new catalytic reactions of orga-
nosilicon compounds.
Cp *2Lu P h (2). To a solution of [Cp*2LuMe]2 (3) (5.0 mg,
0.01 mmol) and [Cp*2Lu(µ-H)]2 (1) (0.1 mg, 2 × 10-4 mmol) in
ca. 0.7 mL of cyclohexane-d12 was added benzene (1.4 µL, 4 ×
10-4 mmol) via microsyringe. The colorless mixture was placed
in a J -Young equipped NMR tube and heated to 80 °C.
Monitoring the reaction by 1H NMR spectroscopy revealed the
progressive liberation of methane with concomitant formation
of 2 (>90%). After approximately 5 days, complexes 3 and 1
had been completely consumed and the only two lutetium-
containing species detected were 2 and small amounts (<5%)
of Cp*2Lu(µ-1,4-C6H4)LuCp*2.11a Both 2 and Cp*2Lu(µ-1,4-
C6H4)LuCp*2 were identified by 1H NMR spectroscopy, as
attempts to isolate 2 from large-scale syntheses resulted in
samples that were contaminated with considerable amounts
of Cp*2Lu(µ-1,4-C6H4)LuCp*2. 1H NMR (300 MHz, cyclohex-
ane-d12): δ 1.79 (s, 30 H, Cp*), 6.79 (d, 2 H, o-Ph), 6.93 (t, 1
H, p-Ph), 7.10 (t, 2 H, m-Ph).
Cp *2Lu C6F 5 (4). A solution of [Cp*2Lu(µ-H)]2 (1) (0.08 g,
0.09 mmol) in ca. 5 mL of pentane was stirred vigorously in a
Schlenk tube. In another Schlenk tube, C6F5SiH3 (0.04 g, 0.17
mmol) was dissolved in ca. 3 mL of pentane. The latter solution
was added via cannula to the colorless solution of 1, which
underwent an immediate color change to bright yellow.
Formation of the yellow solution was accompanied by vigorous
bubbling that continued for about 1 min. After approximately
15 min, the mixture slowly turned colorless again. At this
point, the solution was cannula filtered into another Schlenk
tube and concentrated to a volume of about 3 mL. Cooling to
-35 °C afforded off-white crystalline 4 in 67% yield (0.07 g,
0.11 mmol). Mp: 147-149 °C. IR: 2968 (s), 2903 (s), 2912 (s),
2864 (s), 1749 (w, br), 1633 (w), 1602 (w), 1535 (m), 1495 (s),
1432 (s), 1382 (m), 1358 (w), 1307 (w), 1245 (m, sh), 1181 (w),
1079 (m), 1026 (s), 955 (w), 910 (s), 801 (w), 745 (w), 710 (w),
587 (w, sh), 532 (w, br). 1H NMR (300 MHz, benzene-d6): δ
1.72 (s, 60 H, Cp*). 13C{1H} NMR (126 MHz): δ 27.35 (C5Me5),
119.63 (C5Me5). 19F NMR (376 MHz): δ -158.67 (m, 2 F,
o-C6F5), -154.79 (t, 1 F, p-C6F5), -129.57 (m, 2 F, m-C6F5).
Anal. Calcd for C26H30F5Lu: C, 50.99; H, 4.94. Found: C, 51.22;
H, 5.01.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. Unless otherwise specified, all
manipulations were performed under a nitrogen or argon
atmosphere using standard Schlenk techniques or an inert
atmosphere drybox. Dry, oxygen-free solvents were employed
throughout. Olefin-free pentane was obtained by treatment
with concentrated H2SO4, then 0.5 N KMnO4 in 3 M H2SO4,
followed by NaHCO3, and finally MgSO4. Thiophene-free
benzene and toluene were obtained by pretreating the solvents
with concentrated H2SO4, followed by Na2CO3 and CaCl2.
Pentane, benzene, toluene, and diethyl ether were distilled
from sodium/benzophenone and stored under nitrogen prior
to use, whereas benzene-d6 was vacuum distilled from Na/K
alloy. Cyclohexane-d12 was vacuum distilled from Na and
stored under nitrogen. Reagents were purchased from com-
mercial suppliers and used without further purification unless
otherwise specified. [Cp*2Lu(µ-H)]2,4 [Cp*2LuMe]2,11b C6F5-
Cp *2Lu SiH2(o-MeOC6H4) (5). A solution of [Cp*2Lu(µ-H)]2
(1) (0.08 g, 0.09 mmol) in ca. 5 mL of pentane was stirred
vigorously in
a Schlenk tube. In another Schlenk tube,
o-MeOC6H4SiH3 (0.03 g, 0.18 mmol) was dissolved in ca. 3 mL
of pentane. As in the synthesis of 4, the latter solution was
added via cannula to the colorless solution of 1. In this case,
the reaction mixture remained colorless upon addition of the
silane, and gentle bubbling was observed for about 1 min. After
further stirring for 5 min, colorless crystals of 5 began to form.
The mixture was allowed to settle, and the supernatant
solution was cannula filtered and concentrated to a volume of
approximately 3 mL. A second crop of crystals was obtained
upon cooling to -35 °C for a combined yield of 75% (0.08 g,
0.14 mmol). Mp: 189-192 °C (dec). IR: 3058 (w), 3036 (w),
2969 (s), 2903 (s), 2858 (s), 2725 (w), 2034 (s, br, νSiH), 2013 (s,
br, νSiH), 1685 (w), 1584 (w), 1565 (m), 1458 (s), 1428 (s), 1378
(m), 1260 (m), 1240 (m), 1206 (m, sh), 1150 (s), 1128 (m), 1085
(w), 1059 (m, sh), 1022 (m), 1001 (s, sh), 953 (s), 920 (m), 852
(w, br), 779 (m), 756 (s), 730 (s), 673 (w, sh), 588 (w), 467 (w,
br). 1H NMR (500 MHz, benzene-d6) δ 1.95 (s, 30 H, Cp*), 2.67
(s, 3 H, OMe), 4.71 (s, 2 H, SiH), 6.32 (d, 1 H, Ar), 6.94 (m, 1
H, Ar), 7.01 (m, 1 H, Ar), 8.09 (d, 1 H, Ar). 13C{1H} NMR (126
MHz): δ 12.29 (C5Me5), 54.08 (OMe), 110.34 (Ar), 117.98 (C5-
Me5), 124.00 (Ar), 133.42 (Ar), 143.49 (Ar), 163.54 (Ar). 29Si
NMR (99 MHz): δ -39.57. Anal. Calcd for C27H39LuOSi: C,
55.66; H, 6.75. Found: C, 55.29; H, 6.92.
SiH3,21 and o-MeOC6H4SiH3 were prepared by literature
13
methods. NMR spectra were recorded on Bruker AMX-300,
AMX-400, or DRX-500 spectrometers at ambient temperature
unless otherwise noted. Elemental analyses were performed
by the Microanalytical Laboratory in the College of Chemistry
at the University of California, Berkeley. Infrared spectra were
recorded on a Mattson Infinity 60 FT IR instrument. Samples
were prepared as KBr pellets unless otherwise noted, and data
are reported in units of cm-1
.
(20) (a) Nolan, S. P.; Porchia, M.; Marks, T. J . Organometallics 1991,
10, 1450. (b) Forsyth, C. M.; Nolan, S. P.; Marks, T. J . Organometallics
1991, 10, 2543. (c) King, W. A.; Marks, T. J . Inorg. Chim. Acta 1995,
229, 343.
P r ep a r a tion of Sa m p les for GC-Ma ss Sp ectr om etr y.
The benzene-d6 and cyclohexane-d12 solutions of silanes ob-
(21) Molander, G. A.; Corrette, C. P. Organometallics 1998, 17, 5504.