Synthesis of Sm-SiH3 complexes via σ-bond metathesis of the Si-C bond of phenylsilane

Article abstract of DOI:10.1021/om000516r

Reaction of PhSiH₃ with the samarium complexes Cp*₂SmCH(SiMe₃)₂ (1) and [Cp*₂Sm-(μ;-H)]₂ (8) (Cp* = C₅Me₅) leads to redistribution at silicon, yielding benzene, silane, Ph₂-SiH₂, Ph₃SiH, and dehydrocoupling products. Cleavage of the Si-C bond of PhSiH₃ is accompanied by formation of the lanthanide hydrosilyl complex [Cp*₂SmSiH₃]₃ (2). Complex 2 activates the S-O bond of dimethyl sulfoxide (DMSO) to form the bridged species Cp*₂-Sm(DMSO)OSiH₂OSm(DMSO)Cp*₂ (3). The hard Lewis bases Ph₃PO and HMPA (HMPA = (Me₂N)₃PO) react with 2 to produce the base adducts Cp*₂SmSiH₃(OPPh₃) (4) and Cp*₂-SmSiH₃(HMPA) (5), respectively. Complex 5 thermally decomposes, although not cleanly, to produce Cp*₂Sm[OP(NMe₂)₂](HMPA) (6) in low yield. Compound 4 thermally decomposes via liberation of silane to produce Cp*₂SmC₆H₄P(O)Ph₂ (7). In toluene solution, 4 acts as a source of SiH₃^- in reactions with MeI and benzophenone, producing Cp*₂SmI(OPPh₃) (9) and Cp*₂SmOCPh₂(SiH₃) (10), respectively. The high reactivity of 8 toward a stable Si-C bond is discussed in terms of possible mechanisms for this σ-bond metathesis.

Full text of DOI:10.1021/om000516r

Organometallics 2000, 19, 4733-4739
4733
Syn th esis of Sm -SiH3 Com p lexes via σ-Bon d Meta th esis
of th e Si-C Bon d of P h en ylsila n e
Ivan Castillo and T. Don Tilley*
Department of Chemistry, University of California at Berkeley,
Berkeley, California 94720-1460
Received J une 19, 2000
Reaction of PhSiH3 with the samarium complexes Cp*2SmCH(SiMe3)2 (1) and [Cp*2Sm-
(µ-H)]2 (8) (Cp* ) C5Me5) leads to redistribution at silicon, yielding benzene, silane, Ph2-
SiH2, Ph3SiH, and dehydrocoupling products. Cleavage of the Si-C bond of PhSiH3 is
accompanied by formation of the lanthanide hydrosilyl complex [Cp*2SmSiH3]3 (2). Complex
2 activates the S-O bond of dimethyl sulfoxide (DMSO) to form the bridged species Cp*2-
Sm(DMSO)OSiH2OSm(DMSO)Cp*2 (3). The hard Lewis bases Ph3PO and HMPA (HMPA )
(Me2N)3PO) react with 2 to produce the base adducts Cp*2SmSiH3(OPPh3) (4) and Cp*2-
SmSiH3(HMPA) (5), respectively. Complex 5 thermally decomposes, although not cleanly,
to produce Cp*2Sm[OP(NMe2)2](HMPA) (6) in low yield. Compound 4 thermally decomposes
via liberation of silane to produce Cp*2SmC6H4P(O)Ph2 (7). In toluene solution, 4 acts as a
-
source of SiH3 in reactions with MeI and benzophenone, producing Cp*2SmI(OPPh3) (9)
and Cp*2SmOCPh2(SiH3) (10), respectively. The high reactivity of 8 toward a stable Si-C
bond is discussed in terms of possible mechanisms for this σ-bond metathesis.
In tr od u ction
Despite being ineffective at catalyzing dehydropolym-
erization, 1 appears to be remarkably active in σ-bond
metathesis reactions, since it mediates the formation
and cleavage of relatively strong Si-C bonds in the
redistribution process. To learn more about the latter
reactivity, we have examined the interaction of 1 with
PhSiH3 in more detail. Here we report the isolation of
a well-defined samarium-containing product from this
reaction, [Cp*2SmSiH3]3 (2). This compound is a rare
example of a lanthanide silyl complex and represents
the first example of an f-element-SiH3 derivative. For
comparison, the known early metal-SiH3 complexes
consist of the spectroscopically characterized CpCp*Hf-
(SiH3)Cl4 (d0) and the structurally characterized [Cp2-
Organometallic f-element chemistry is associated with
reactive metal-carbon and metal-hydrogen bonds,
which are particularly active in σ-bond metathesis.1,2
Given our interest in reactive d0 metal-silicon bonds,
we have been examining the chemistry of lanthanide-
silicon bonds in (for example) the dehydrocoupling of
hydrosilanes to polysilanes.3 In a previous report, we
described the reaction of Cp*2SmCH(SiMe3)2 (1) (Cp*
) C5Me5) with PhSiH3 in benzene, which resulted in
both dehydrocoupling of the silane and redistribution
at silicon to produce Ph2SiH2, Ph3SiH, and a mixture
of trisamarium clusters [Cp*2SmSiHx]3.3a These results
are consistent with our previous suggestion that the low
activity of Cp*2LnR lanthanide complexes as catalysts
for phenylsilane dehydropolymerization may be at-
tributed to competing redistribution at silicon.3a,b,e
Ti(µ-HSiH2)]2 (d1).
5
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, and toluene were distilled from sodium/
benzophenone and stored under nitrogen prior to use, whereas
benzene-d6 and toluene-d8 were vacuum distilled from Na/K
alloy. Pyridine was distilled from Na and stored under
nitrogen. Ph3PO was purchased from Aldrich Chemical Co. and
recrystallized from toluene. (Me2N)3PO (HMPA) and dimethyl
(1) For recent examples see: (a) Douglass, M. R.; Marks, T. J . J .
Am. Chem. Soc. 2000, 122, 1824. (b) Gountchev, T. I.; Tilley, T. D.
Organometallics 1999, 18, 5661. (c) Dash, A. K.; Wang, J . Q.; Eisen,
M. S. Organometallics 1999, 18, 4724. (d) Gountchev, T. I.; Tilley, T.
D. Organometallics 1999, 18, 2896. (e) Arredondo, V. M.; Tian, S.;
McDonald, F. E.; Marks, T. J . J . Am. Chem. Soc. 1999, 121, 3633. (f)
Tian, S.; Arredondo, V. M.; Stern, C. L.; Marks, T. J . Organometallics
1999, 18, 2568. (g) Arredondo, V. M.; McDonald, F. E.; Marks, T. J .
Organometallics 1999, 18, 1949. (h) Molander, G. A.; Corrette, C. P.
J . Org. Chem. 1999, 64, 9697. (i) Schumann, H.; Keitsch, M. R.;
Demtschuk, J .; Molander, G. A. J . Organomet. Chem. 1999, 582, 70.
(2) For reviews see: (a) Marks, T. J . Acc. Chem. Res. 1992, 25, 57.
(b) Bercaw, J . E. Pure Appl. Chem. 1990, 62, 1151. (c) Selective
Hydrocarbon Activation; Davis, J . A., Watson, P. L., Liebman, J . F.,
Greenberg, A., Eds.; VCH Publishers: New York, 1990. (d) Watson, P.
L.; Parshall, G. W. Acc. Chem. Res. 1985, 18, 51.
(3) (a) Radu, N. S.; Hollander, F. J .; Tilley, T. D.; Rheingold, A. L.
Chem. Commun. 1996, 2459. (b) Radu, N. S.; Tilley, T. D. J . Am. Chem.
Soc. 1995, 117, 5863. (c) Radu, N. S. Ph.D. Thesis, University of
California, San Diego, 1995. (d) Tilley, T. D.; Radu, N. S.; Walzer, J .
F.; Woo, H.-G. Polym. Prepr. (Am. Chem. Soc. Div. Polym. Chem.) 1992,
33 (1), 1237. (e) Radu, N. S.; Tilley, T. D. J . Am. Chem. Soc. 1992,
114, 8293.
(4) Woo, H.-G.; Heyn, R. H.; Tilley, T. D. J . Am. Chem. Soc. 1992,
114, 5698.
(5) Hao, L.; Lebuis, A.-M.; Harrod, F. J .; Samuel, E. Chem. Commun.
1997, 2459.
10.1021/om000516r CCC: $19.00 © 2000 American Chemical Society
Publication on Web 10/10/2000

4734 Organometallics, Vol. 19, No. 23, 2000
Castillo and Tilley
sulfoxide (DMSO) were distilled from CaH2. Cp*2SmCH-
(SiMe3)2 and [Cp*2Sm(µ-H)]2 were prepared by literature
methods.6 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, and data are reported in units
69% of yellow, microcrystalline 5 (0.13 g, 0.21 mmol). Mp >
260 °C (171-174 °C dec). IR: 2902 (s), 2858 (s), 2819 (m), 2723
(w), 2003 (m, sh, νSiH), 1986 (m, sh, νSiH), 1487 (m), 1450 (m),
1376 (w), 1304 (s), 1193 (s), 1134 (s), 1114 (s), 1071 (w, sh),
993 (s), 955 (m), 873 (m), 798 (w), 760 (m, sh), 740 (m), 466
1
(m, sh). H NMR (500 MHz): δ 1.41 (d, J PH ) 13.5 Hz, 18 H,
NMe2), 1.68 (s, 30 H, Cp*). 13C{1H} NMR (126 MHz): δ 17.12
(C5Me5), 36.84 (NMe2), 114.77 (C5Me5). 31P{1H} NMR (162
MHz): δ 13.18. Anal. Calcd for C26H51N3OPSiSm: C, 49.48;
H, 8.14; N, 6.66; P, 4.91. Found: C, 49.33; H, 8.34; N, 7.32; P,
4.75.
of cm-1
[Cp *2Sm SiH 3]3 (2). A Schlenk tube equipped with
.
a
magnetic stirbar was charged with Cp*2SmCH(SiMe3)2 (1)
(0.30 g, 0.52 mmol) and 10 mL of pentane. Another Schlenk
tube was charged with PhSiH3 (0.56 g, 5.20 mmol). The orange-
red solution of 1 was stirred while PhSiH3 was added via
cannula. After a variable induction period of 5-30 min, an
orange solid started to deposit. Evolution of H2 (confirmed by
1H NMR spectroscopy for reaction in benzene-d6) was evident,
and the color of the solution changed from orange-red to deep
red. The deep red solution was removed by filtration, and the
orange solid 2 was washed with ca. 5 mL of pentane and dried
under vacuum. Yields varied between 35 and 56% (0.08-0.14
g, 0.18-0.29 mmol). Mp > 260 °C (210 °C dec). IR: 2964 (s),
2908 (s), 2855 (s), 2144 (w, br), 1992 (m, br, νSiH), 1884 (m, br,
Cp *2Sm [OP (NMe2)2](HMP A) (6). A toluene solution of 5
(0.12 g, 0.19 mmol) and HMPA (33 µL, 0.19 mmol) was stirred
at ambient temperature for a period of 2 weeks. Removal of
volatile materials under vacuum was followed by extraction
with ca. 15 mL of pentane. The yellow pentane solution was
cannula filtered, concentrated to 5 mL, and cooled to -35 °C.
Low yields of isolated yellow microcrystals were always
obtained, ranging from 7 to 16% (10-23 mg, 0.01-0.03 mmol).
1H NMR (300 MHz): δ 0.76 (s, 18 H, HMPA), 1.57 (s, 30 H,
Cp*), 3.10 (d, J PH ) 7.92 Hz, 12 H, NMe2).
Cp *2Sm C6H4(O)P h 2 (7). A Schlenk tube was charged with
[Cp*2Sm(µ-H)]2 (8) (0.15 g, 0.35 mmol), Ph3PO (0.10 g, 0.35
mmol), and 10 mL of toluene. A burgundy solution was
obtained after stirring overnight at room temperature. The
solution was cannula filtered and concentrated. Compound 7
was isolated by crystallization from ca. 5 mL of toluene at -35
°C, but the burgundy crystals contained toluene and other
unidentified impurities. Analytically pure compound was
obtained by washing the crystals with ca. 5 mL of pentane. In
this manner, yellow, microcrystalline 7 was obtained in 58%
yield (0.14 g, 0.20 mmol). Mp: 204-208 °C. IR: 3055 (w), 2960
(m), 2906 (s), 2854 (s), 2721 (w), 1591 (w, sh), 1485 (w, sh),
1437(s), 1378 (w), 1189 (m), 1154 (m), 1119 (s), 1081 (m), 1058
(m), 1026 (w, sh), 999 (w, sh), 749 (m), 721 (s), 695 (s), 540 (s),
445 (w, sh). For the following NMR data, the positions of the
protons in the metalated phenyl ring are labeled a though d
starting from samarium. 1H NMR (300 MHz): δ -4.41 (s, 1
H, a-C6H4), 1.25 (s, 30 H, Cp*), 5.67 (m, 1 H, b-C6H4), 7.21 (m,
4 H, m-Ph), 7.30 (m, 2 H, p-Ph), 7.56 (m, 1 H, c-C6H4), 7.95
(m, 4 H, o-Ph), 9.01 (t, 1 H, d-C6H4). 13C{1H} NMR (126
MHz): δ 16.96 (C5Me5), 116.49 (C5Me5), 122.36 (C6H4), 126.76
(d, J PC ) 13.9 Hz, ipso-Ph), 129.21 (d, J PC ) 11.3 Hz, o-Ph),
132.77 (p-Ph), 133.47 (d, J PC ) 8.8 Hz, m-Ph), 135.55 (C6H4),
136.33 (C6H4), 139.01 (d, J PC ) 22.7 Hz, ipso-C6H4), 151.06
(C6H4), 152.01 (C6H4). 31P{1H} NMR (162 MHz): δ 52.08. Anal.
Calcd for C38H44OPSm: C, 65.38; H, 6.35. Found: C, 65.36;
H, 6.10.
ν
SiH), 1437 (s), 1377 (m, sh), 985 (s), 895 (s). 1H NMR (300
MHz): δ 1.01 (s, 30 H, Cp*). Anal. Calcd for C20H33SiSm: C,
53.15; H, 7.36. Found: C, 53.30; H, 7.35.
Cp *2Sm (DMSO)OSiH2OSm (DMSO)Cp *2 (3). To a stirred
toluene suspension of 2 (0.13 g, 0.30 mmol) in a Schlenk tube
was added DMSO (43 µL, 0.60 mmol) via syringe at room
temperature. Solid 2 immediately dissolved and afforded a
yellow solution, which after further stirring for 2 h was filtered,
concentrated to ca. 5 mL, and cooled to -35 °C. Crystalline 3
was obtained in this manner in 53% yield (0.08 g, 0.08 mmol).
Mp > 260 °C (224 °C dec). IR: 2963 (s), 2909 (s), 2855 (s),
2080 (m, br, νSiH), 1658 (w), 1435 (s), 1314 (m, sh), 1261 (m),
1115 (m), 1018 (m), 960 (s), 905 (s), 869 (m, sh), 803 (w), 738
1
(w). H NMR (300 MHz): δ 0.93 (s, 12 H, DMSO), 1.48 (s, 60
H, Cp*), 2.47 (s, 2 H, SiH). 13C{1H} NMR (126 MHz): δ 17.22
(C5Me5), 39.30 (DMSO), 125.87 (C5Me5). 29Si{1H} NMR (99
MHz): δ -45.83. Anal. Calcd for C44H74O2S2SiSm2: C, 49.85;
H, 7.04. Found: C, 49.52; H, 7.02.
Cp *2Sm SiH3(OP P h 3) (4). A Schlenk tube equipped with
magnetic stirbar was charged with 2 (0.08 g, 0.14 mmol) and
5 mL of toluene. Another Schlenk tube was charged with Ph3-
PO (0.04 g, 0.15 mmol) and 5 mL of toluene, and both solutions
were cooled to -80 °C. The solution of Ph3PO was then added
with a cannula to the stirred suspension of 2 to produce a
yellow solution upon warming to room temperature. After
further stirring for 2 h the solution was filtered and concen-
trated to a volume of 5 mL. Yellow microcrystals of 4 were
isolated in 81% yield (0.10 g, 0.11 mmol) after cooling to -35
°C. Mp > 260 °C (185 °C dec). IR: 3056 (w, sh), 2965 (m), 2899
(s), 2853 (s), 2072 (m, sh, νSiH) 1994 (m, sh, νSiH), 1977 (s, sh,
Cp *2Sm I(OP P h 3) (9). A Schlenk tube was charged with 4
(0.15 g, 0.14 mmol), 5 mL of toluene, and a magnetic stirbar.
To the stirred yellow solution was added MeI (14 µL, 0.14
mmol) via syringe at room temperature. After further stirring
for 2 h, the volatile materials were evaporated under vacuum.
The resulting yellow-orange oil was triturated with 10 mL of
pentane. The yellow-orange microcrystals were then washed
further with 5 mL of pentane and dried in vacuo. The isolated
yield of 9 was 71% (0.13 g, 0.10 mmol). Mp > 260 °C. IR: 3058
(w), 2963 (m), 2900 (s), 2854 (s), 2722 (w), 2107 (w, br), 1438
(s), 1262 (w, sh), 1143 (s), 1120 (s), 1085 (s), 1025 (m), 998
(m), 803 (m), 751 (m, sh), 725 (s, sh), 694 (s, sh), 540 (s). 1H
NMR (500 MHz): δ 1.35 (s, 30 H, Cp*), 6.91 (m, 12 H, o,m-
Ph), 7.04 (t, 3 H, p-Ph). 13C{1H} NMR (126 MHz): δ 19.08
(C5Me5), 116.27 (C5Me5), 128.90 (broad, ipso-Ph), 129.08 (d, J PC
) 11.3 Hz, o-Ph), 133.46 (d, J PC ) 8.8 Hz, m-Ph), 133.60 (p-
νSiH), 1438 (s, sh), 1150 (s), 1120 (s), 1087 (s), 992 (s, br), 956
(m), 868 (m), 725 (s), 693 (m, sh), 539 (s). 1H NMR (300 MHz):
δ 1.57 (s, 30 H, Cp*), 6.37 (m, 6 H, o-Ph), 6.82 (t, 6 H, m-Ph),
6.96 (t, 3 H, p-Ph). 13C{1H} NMR (126 MHz): δ 16.49 (C5Me5),
114.42 (C5Me5), 128.24 (d, J PC ) 11.3 Hz, -Ph) 131.79 (d, J PC
) 10.8 Hz, -Ph), 132.73 (s, -Ph). 31P{1H} NMR (162 MHz):
δ 26.96. Anal. Calcd for C38H48OPSiSm: C, 62.50; H, 6.62.
Found: C, 63.01; H, 6.94.
Cp *2Sm SiH3(HMP A) (5). To a vigorously stirred and cold
(-80 °C) suspension of 2 (0.13 g, 0.30 mmol) in 5 mL of toluene
was added HMPA (0.05 mL, 0.30 mmol) via syringe. The
mixture was stirred for 2 h while warming to room tempera-
ture. The resulting yellow solution was then filtered and
concentrated to approximately 5 mL. Cooling to -35 °C yielded
Ph). 31P{1H} NMR (162 MHz): δ 25.85. Anal. Calcd for C38H45
-
IOPSm: C, 55.25; H, 5.49. Found: C, 55.07; H, 5.75.
Cp *2Sm OCP h 2(SiH3) (10). A Schlenk tube equipped with
stirbar was charged with 2 (0.10 g, 0.24 mmol) and ca. 5 mL
of toluene. In another Schlenk tube, benzophenone (0.04 g, 0.24
mmol) was dissolved in ca. 5 mL of toluene, and both solutions
(6) J eske, G.; Lauke, H.; Mauermann, H.; Swepston, P. N.; Schu-
mann, H.; Marks, T. J . J . Am. Chem. Soc. 1985, 107, 8091.

Synthesis of Sm-SiH3 Complexes
Organometallics, Vol. 19, No. 23, 2000 4735
Ta ble 1. Su m m a r y of Cr ysta llogr a p h ic Da ta
X-r a y Cr ysta l Str u ctu r e Deter m in a tion of 10. A yellow-
orange, rhomboidal crystal with approximate dimensions 0.21
× 0.18 × 0.16 mm was mounted on a glass capillary using
Paratone N hydrocarbon oil and placed under a stream of cold
nitrogen on the same SMART diffractometer. Preliminary
orientation matrix and unit cell parameters were determined
as described above. A hemisphere of data was collected at a
temperature of -161 ( 1 °C using ω scans of 0.30° and a
collection time of 20 s per frame. Frame data were integrated
using SAINT. An absorption correction was applied using
SADABS (Tmax ) 0.977, Tmin ) 0.787). The 14 144 reflections
that were integrated were averaged in point group P1h to yield
9865 unique reflections (Rint ) 0.037). No correction for decay
was necessary. The structure was solved using direct methods
(SIR92) and refined by full-matrix least-squares methods using
teXsan. The two independent molecules in the unit cell are
virtually identical. All non-hydrogen atoms were refined
anisotropically. The six hydrogen atoms on the two silicon
centers were found in the difference Fourier map, and all other
hydrogen atoms were included at calculated positions, but
neither were refined. The number of variable parameters was
649, giving a data/parameter ratio of 19.20. The maximum and
minimum peaks on the final difference Fourier map correspond
to 1.48 and -2.17 e-/Å3: R ) 0.041, Rw ) 0.065, GOF ) 2.48.
The crystallographic data are summarized in Table 1.
6
10
formula
C
30H60SmO2P2N5
C33H43SmSiO
643.19
MW
735.18
cryst color, habit
cryst dimens, mm
cryst syst
yellow, plate
yellow, rhomboidal
0.26 × 0.09 × 0.08 0.21 × 0.18 × 0.16
monoclinic
triclinic
cell determination
(2θ range)
6636 (4.0-45.0°)
8192 (4.0-45.0°)
lattice params
a ) 10.0228(1) Å
b ) 17.9055(3) Å
c ) 10.7947(2) Å
a ) 12.4727(2) Å
b ) 14.4791(2) Å
c ) 17.2790(2) Å
R ) 80.291(1)°
â ) 73.983(1)°
γ ) 79.002(1)°
â ) 111.413(1)°
V ) 1803.54(8) Å3 V ) 2985.17(8) Å3
P21 (#4)
space group
Z value
Dcalc
µ(Mo KR)
diffractometer
radiation
temperature
scan type
no. of reflns measd
no. of reflns obsd
solution
P1h (#2)
4
4
2.707 g/cm3
35.04 cm-1
Siemens SMART
Mo KR
1.411 g/cm3
15.50 cm-1
Siemens SMART
Mo KR
-119.0 °C
-161.0 °C
ω (0.3° per frame) ω (0.3° per frame)
8735
14 144
2969 (I > 3.00σ(I)) 12460 (I > 3.00σ(I))
direct methods
(SIR92)
direct methods
(SIR92)
refinement
full-matrix
least-squares
0.025; 0.029
full-matrix
least-squares
0.041; 0.065
1.48 e-/Å3
Resu lts a n d Discu ssion
R; Rw
The reaction of 1 with 10 equiv of PhSiH3 in pentane
results in rapid formation of the insoluble orange
powder 2 after a variable induction period (5-30 min).
This product was spectroscopically identified as the
intermediate previously observed in the transformation
of 1 to the mixture of trisamarium clusters [Cp*2-
max. peak in diff map 0.45 e-/Å3
min. peak in diff map -0.47 e-/Å3
-2.17 e-/Å3
were cooled to -80 °C. The benzophenone solution was then
added to the stirred suspension of 2 via cannula. The reaction
mixture was allowed to reach room temperature, and after
approximately 2 h, the volatile materials were removed under
vacuum. The solid products were extracted into ca. 20 mL of
pentane and filtered with a cannula. Concentrating to a
volume of 5 mL and cooling to -35 °C yielded 79% of yellow-
orange, crystalline 10 (0.12 g, 0.19 mmol). Mp > 260 °C (225-
229 °C dec). IR: 3029 (w), 2963 (m), 2910 (s), 2856 (m), 2177
(m, νSiH), 2146 (s, νSiH), 1596 (w), 1491 (m, sh), 1443 (s), 1380
(w), 1184 (w), 1158 (w), 1045 (s), 1025 (s), 942 (s), 904 (s), 765
SmSiHx]3.3a It exhibits only one peak in the H NMR
1
spectrum (at δ 1.01 in benzene-d6), and ν(SiH) stretch-
ing frequencies at 1992 and 1884 cm-1 indicate the
presence of the hydrosilyl ligand. Apparently, the Si-H
1
hydrogens are not observed in the H NMR spectrum
due to their close proximity to the paramagnetic Sm
center. In addition, the relatively low value for the
stretching frequencies is consistent with binding of the
-SiH3 group to an electropositive element.3a,e,7 The
combustion analysis of 2 is consistent with the formula
Cp*2SmSiH3. On the basis of this formulation, the
isolated yield of 2 was 35-56%. Further characteriza-
tion of 2 has been precluded by its low solubility in
solvents that do not promote decomposition.
1
(m), 747 (m), 700 (s), 661 (w, sh). H NMR (500 MHz): δ 0.25
(s, 30 H, Cp*), 4.44 (d, 4 H, o-Ph), 6.05 (t, 4 H, m-Ph), 6.68 (s,
3 H, SiH), 6.76 (t, 3 H, p-Ph). 13C{1H} NMR (126 MHz): δ 22.29
(C5Me5), 93.59 (CPh2), 120.21 (C5Me5), 126.73 (-Ph), 127.98
(-Ph), 130.42 (ipso-Ph), 148.23 (-Ph). 29Si{1H} NMR (99
MHz): δ -59.88 (q, J SiH ) 196.0 Hz). Anal. Calcd for C33H43
OSiSm: C, 62.50; H, 6.83. Found: C, 62.20; H, 7.18.
-
Slow diffusion of PhSiH3 into a pentane solution of 1
produced microcrystalline 2, and further attempts to
obtain X-ray quality crystals have proven unsuccessful.
We have also been unable to observe a parent ion by EI
mass spectroscopy due to the negligible volatility of 2.
In addition, the FAB method has been unavailable due
to the low solubility of 2 in suitable solvents, and this
property has also precluded the determination of a
solution molecular weight. However, on the basis of the
fact that a trimeric form of 2 has been characterized in
the solid state as a part of a solid solution with other
samarium-silicon clusters,3a we assume that 2 exists
predominantly as the trimer.
X-r a y Cr ysta l Str u ctu r e Deter m in a tion of 6. A yellow,
platelike crystal of approximate dimensions 0.26 × 0.09 × 0.08
mm was mounted on a glass capillary using Paratone N
hydrocarbon oil and placed under a stream of cold nitrogen
on a Siemens SMART diffractometer with a CCD area detector.
Preliminary orientation matrix and unit cell parameters were
determined by collecting 60 10-s frames. A hemisphere of data
was collected at a temperature of -119 ( 1 °C using ω scans
of 0.30° and a collection time of 20 s per frame. Frame data
were integrated using SAINT. An absorption correction was
applied using SADABS (Tmax ) 0.976, Tmin ) 0.886). The 8735
reflections that were integrated were averaged in the point
group P21 to yield 3311 unique reflections (Rint ) 0.031). No
correction for decay was necessary. The structure was solved
using direct methods (SIR92) and refined by full-matrix least-
squares methods using teXsan. The number of variable
parameters was 360, giving a data/parameter ratio of 8.25.
The maximum and minimum peaks on the final difference
Fourier map correspond to 0.45 and -0.48 e-/Å3: R ) 0.025,
Rw ) 0.029, GOF ) 1.19. The crystallographic data are
summarized in Table 1.
Compound 2 is unstable in benzene-d6 and decom-
poses within 1 h to the above-mentioned trinuclear
1
samarium clusters (by H NMR spectroscopy). In ethe-
real and chlorinated solvents, decomposition to intrac-
(7) Huheey, J . E.; Keiter, E. A.; Keiter, R. L. Inorganic Chemistry:
Principles of Structure and Reactivity; Harper Collins: New York, 1993.

4736 Organometallics, Vol. 19, No. 23, 2000
Castillo and Tilley
Sch em e 1
table samarium-containing products occurs within min-
utes. In contrast, 2 does not undergo significant
decomposition over one week in aliphatic solvents such
as pentane and cyclohexane.
d6 or toluene solution, 5 slowly decomposes to several
samarium-containing products over a period of 7 days.
We were able to identify one of these decomposition
products as Cp*2Sm[OP(NMe2)2](HMPA) (6), on the
basis of its 1H NMR spectrum. A low yield of yellow
single crystals of 6 suitable for X-ray diffraction was
obtained by crystallization from pentane. The solid state
structure determination revealed a pseudo-tetrahedral
environment about the Sm atom, with two distinct
Sm-O distances of 2.22 and 2.32 Å associated with the
-OP(NMe2)2 and HMPA ligands, respectively. The Sm-
Cp* centroid distances of 2.49 and 2.51 Å and the
centroid-Sm-centroid angle of 131.2° are characteristic
for Sm(III) metallocenes.8 The molecular structure of 6
is shown in Figure 1, and selected bond distances and
angles are listed in Table 2. The -OP(NMe2)2 ligand is
likely formed via activation of a P-N bond in HMPA
by the reactive Sm-SiH3 group. To support this hy-
pothesis, the decomposition of 5 was carried out in a
sealed NMR tube in the presence of 1 equiv of HMPA.
The 1H NMR spectrum contained two singlets (at δ 2.51
and δ 4.70) in an approximately 3:1 ratio, assigned to
Me2NSiH3.
In the absence of structural data for pure 2, we sought
to prepare soluble base adducts which might be more
amenable to structural and chemical investigations.
Addition of PMe3 or pyridine to suspensions of 2 in
pentane or toluene resulted in production of complex
reaction mixtures. An attempt to prepare a dimethyl
sulfoxide (DMSO) adduct instead led to reaction of the
Sm-Si bond. Addition of 2 equiv of DMSO to a toluene
suspension of 2 gave sparingly soluble, yellow Cp*2Sm-
(DMSO)OSiH2OSm(DMSO)Cp*2 (3, eq 1). Monitoring
the reaction by 1H NMR spectroscopy (benzene-d6
solution) revealed the production of Me2S (1 equiv) and
1
SiH4 as the only byproducts. The H NMR spectrum of
Complex 4 is considerably more stable in solution, but
attempts to obtain X-ray quality crystals have so far
3 consists of a singlet at δ 1.48 (for the Cp* ligands)
and a broad resonance centered at δ 0.93 (for the DMSO
ligands). In the IR spectrum the ν(SiH) stretch was
observed at 2080 cm-1. X-ray quality crystals of 3 were
obtained by cooling a concentrated toluene solution to
-35 °C. Although the structure and connectivity of 3
were confirmed by X-ray crystallography, including the
bridging nature of the -OSiH2O- unit, the refinement
of accurate metric parameters was not possible due to
severe disorder of two toluene molecules of crystalliza-
tion present in the unit cell.
Isolable base adducts were obtained by use of the hard
Lewis bases Ph3PO and (Me2N)3PO (HMPA), which
react with 2 in toluene at -78 °C to produce Cp*2-
SmSiH3(OPPh3) (4) and Cp*2SmSiH3(HMPA) (5, Scheme
1), respectively. Both compounds were isolated as yel-
low, air- and moisture-sensitive microcrystals by cooling
concentrated toluene solutions to -35 °C. In benzene-
(8) (a) Schumann, H.; Meese-Marktscheffel, J . A.; Esser, L. Chem.
Rev. 1995, 95, 865. (b) Evans, W. J .; Foster, S. E. J . Organomet. Chem.
1992, 433, 79, and references therein.
Figu r e 1. ORTEP diagram of Cp*2Sm[OP(NMe2)2](HMPA)
(6).

Synthesis of Sm-SiH3 Complexes
Organometallics, Vol. 19, No. 23, 2000 4737
Ta ble 2. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) for 6
(a) Bond Distances
Sm(1)
Sm(1)
P(1)
P(1)
P(1)
O(1)
2.222(3)
2.5089(1)
1.572(3)
1.722(5)
1.703(4)
Sm(1)
Sm(1)
P(2)
P(2)
P(2)
O(2)
Cp*(2)
O(2)
N(3)
N(4)
N(5)
2.324(3)
2.4858(1)
1.498(3)
1.623(4)
1.640(4)
1.639(4)
Cp*(1)a
O(1)
N(1)
N(2)
P(2)
(b) Bond Angles
O(1) Sm(1) O(2) 89.0(1) Cp*(1) Sm(1) Cp*(2) 131.166(6)
Sm(1) O(1) P(1) 137.4(2) Sm(1) O(2) P(2)
173.2(2)
110.3(2)
114.0(2)
108.6(2)
111.2(2)
107.8(2)
O(1) P(1)
O(1) P(1)
N(1) P(1)
N(3) P(2)
N(1) 99.6(2) O(2)
N(2) 104.2(2) O(2)
N(2) 106.2(2) O(2)
N(4) 104.9(2) N(3)
N(4)
P(2)
P(2)
P(2)
P(2)
P(2)
N(3)
N(4)
N(5)
N(5)
N(5)
a
Cp* denotes the centroids of the rings.
F igu r e 2. ORTEP view of Cp*2SmOCPh2(SiH3) (10).
proven unsuccessful. In benzene-d6 solution, 4 decom-
Ta ble 3. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) for 10
poses quantitatively at 65 °C over 18 h via the clean
1
elimination of SiH4 (by H NMR spectroscopy; Scheme
(a) Bond Distances
1). The resulting cyclometalated phosphineoxide com-
Sm(1)
Sm(1)
Sm(1)
O(1)
O(1)
2.125(5)
2.4358(4)
2.5572(4)
1.415(8)
1.922(8)
Sm(2)
Sm(2)
Sm(2)
O(2)
O(2)
2.120(5)
2.4319(4)
2.4262(4)
1.410(9)
1.913(8)
Cp*(1)a
Cp*(2)
C(21)
C(21)
Cp*(3)
Cp*(4)
C(54)
C(54)
plex Cp*2SmC6H4P(O)Ph2 (7) was independently syn-
thesized by the reaction of [Cp*2Sm(µ-H)]2 (8) with
Ph3PO. The thermal decomposition of 4 in benzene-d6
is inhibited by an atmosphere of hydrogen, such that it
requires 48 h at 65 °C, and in this case the generation
of 7 is accompanied by SiH4, Si2H6, and unidentified
samarium-containing compounds as byproducts.
Si(1)
Si(2)
(b) Bond Angles
Sm(1) O(1) C(21) 162.9(4) Cp*(1) Sm(1) Cp*(2) 131.01(1)
Sm(2) O(2) C(54) 162.9(5) Cp*(3) Sm(2) Cp*(4) 134.73(2)
Si(1) C(21) O(1) 105.5(5) Si(2)
C(54) O(2)
107.1(5)
a
Cp* denotes the centroids of the rings.
Other reactions of 4 characterize this complex as a
source of the SiH3- silyl anion. For example, the reaction
with MeI in benzene-d6 produces quantitative yields of
MeSiH3 and Cp*2SmI(OPPh3) (9; Scheme 1). Both 2 and
4 react quantitatively (by 1H NMR spectroscopy in
benzene-d6) with benzophenone to produce the insertion
product Cp*2SmOCPh2(SiH3) (10). The 29Si NMR spec-
trum of 10 consists of a quartet centered at δ -59.88
associated with a coupling constant of J SiH ) 196 Hz.
The -SiH3 group of 10 also gives rise to an infrared
stretching band at 2146 cm-1. The X-ray crystal struc-
ture of 10 revealed the presence of a simple insertion
product, with the alkoxide ligand bound to the sa-
marium center only through the oxygen atom. All three
hydrogen atoms bound to silicon were found in the
difference Fourier map, but their positions were not
refined. Two molecules with virtually identical bond
lengths are present in the asymmetric unit. An ORTEP
view of one of the molecules is shown in Figure 2, and
a list of selected bond distances and angles is shown in
Table 3. The Sm-O distance of 2.12 Å is within the
range of known samarium-oxygen single bond dis-
tances (2.09-2.25 Å), as are the Sm-ring centroid
average distance of 2.46 Å and the centroid-Sm-
centroid angle of 132.9°.8 The large Sm-O-C angle of
162.9° probably reflects the high steric demand of the
-OCPh2(SiH3) ligand and perhaps donation of a lone
pair on oxygen to the samarium center.
SiH (trace), PhSiH2SiH2Ph (0.18 equiv), benzene (1.53
equiv), silane oligomers, and a mixture of the previously
reported trisamarium clusters.3a The identities and
quantities of the silane products were confirmed by GC-
mass spectrometry.
Addition of catalytic amounts of hydrogen (<1 atm)
to the above reaction mixture results in elimination of
the induction period. On this basis and our earlier study
of the mechanism of the metathesis reaction of 1 with
(Me3Si)2SiH2,3b we propose that the observed induction
period is associated with conversion of 1 to a samarium
hydride species, which is much more active toward
σ-bond metathesis. To further investigate this possibil-
ity, we examined the reaction of [Cp*2Sm(µ-H)]2 (8) with
PhSiH3 (8 equiv), which after 10 min (no induction
period observed) gave a mixture of products similar to
that observed in the reaction with 1: PhSiH3 (5.80
equiv), H2 (0.16 equiv in solution), Ph2SiH2 (0.39 equiv),
PhSiH2SiH2Ph (0.12 equiv), benzene (1.15 equiv), and
uncharacterized silane oligomers. Trace amounts of
SiH4 were detected when less than 1 equiv of PhSiH3
was added to solutions of either 1 or 8 (presumably more
SiH4 existed in the headspace of the NMR tube). Thus,
although less PhSiH3 is consumed in this reaction, it
appears that 8 may be the active species which mediates
redistribution via Si-C bond cleavage. The stoichiom-
etry of this redistribution chemistry corresponds ap-
proximately to that shown in eq 2.
To gain more insight into the Si-C bond cleavage
chemistry responsible for the formation of 2, we estab-
lished the stoichiometry of the reaction of PhSiH3 (8
equiv) with 1 in cyclohexane-d12. The reaction mixture
turns deep red after an induction period of 5-30 min,
at which point quantitative formation of CH2(SiMe3)2
was observed, along with unreacted PhSiH3 (2.11 equiv),
H2 (0.19 equiv in solution), Ph2SiH2 (0.63 equiv), Ph3-
Cp*2SmH + 2PhSiH3 f
Cp*2SmSiH3 + 0.5SiH4 + 0.5Ph2SiH2 + C6H6 (2)
In the chemistry described above, we have not yet
directly observed the elementary processes responsible

4738 Organometallics, Vol. 19, No. 23, 2000
Castillo and Tilley
Sch em e 2
for Si-C bond cleavage. However, it is interesting to
speculate on the mechanisms of these unusual σ-bond
metathesis reactions. Particularly since oxidative ad-
dition/reductive elimination processes for Sm are highly
unlikely, the observations suggest the presence of a
highly active samarium species which can mediate
σ-bond metathesis reactions through four-centered tran-
sition states for bonds (Si-C) that normally do not
participate in such processes. It is important to note that
when the reaction between 1 or 8 and PhSiH3 is carried
out in aliphatic solvents (pentane or cyclohexane-d12),
the only source of phenyl groups is PhSiH3, thus ruling
out the possible involvement of benzene as a co-reagent
in the redistribution at silicon. We propose that the
dehydrocoupling chemistry occurs via Cp*2SmSiH2Ph,
which reacts with PhSiH3 to produce 8 and PhSiH2SiH2-
Ph. Although one can also imagine interaction of the
Sm-Si bond of Cp*2SmSiH2Ph with the Si-C bond of
PhSiH3 to produce Ph2SiH2 and Cp*2SmSiH3, we believe
that this is unlikely for two reasons. First, the four-
centered transition state required for this transforma-
tion (A, Scheme 2) would be very crowded.3b Second,
four-centered transition states with a carbon atom in
the â-position seem to be disfavored.2b,9,10 In an attempt
to observe the proposed intermediate Sm-silyl species
in this system, we examined the reaction of 8 with 1
equiv of PhSiH3 at -80 °C in toluene-d8. However, even
at this temperature, dehydrocoupling and redistribution
products appear rapidly, and no intermediates could be
detected. Kinetic studies have so far been prevented by
the speed of the reaction, even at low temperatures, and
by the formation of insoluble species.
A more likely scenario that could account for the
redistribution chemistry is outlined in Scheme 2. An
interaction between 8 and the Si-C bond of PhSiH3
proceeds through transition state B, which corresponds
to nucleophilic attack at an unhindered silicon center.
The resulting samarium phenyl species could arylate
PhSiH3 (transition state C) in a hydrocarbyl/hydrogen
exchange process that is well known in σ-bond meta-
thesis chemistry.1b,c,i,11 Alternatively, the samarium
phenyl species could undergo reactions with Si-H or
H-H bonds present in the reaction mixture to produce
benzene (via transition state D).
Con clu sion s
The samarium complex [Cp*2SmSiH3]3 (2), which
represents the first f-element complex of the simplest
silyl ligand (SiH3), has been prepared. Although 2 is
rather insoluble, it forms soluble adducts with Ph3PO
and HMPA, which are in some ways more amenable to
reactivity studies. As might be expected for a complex
featuring a bond between two rather electropositive
elements, 2 has a high affinity for oxygen, as demon-
strated by its deoxygenation of DMSO. Also, the -SiH3
ligand in 2 and 4 is nucleophilically transferred to
electrophiles such as MeI and benzophenone. The
formation of 2 involves cleavage of a very stable Si-C
(11) (a) Fu, P.-F.; Brard, L.; Li, Y.; Marks, T. J . J . Am. Chem. Soc.
1995, 117, 7157. (b) Molander, G. A.; J ulius, M. J . Org. Chem. 1992,
57, 6347. (c) Molander, G. A.; Dowdy, E. D.; Noll, B. C. Organometallics
1998, 17, 3754. (d) Koo, K.; Fu, P.-F.; Marks, T. J . Macromolecules
1999, 32, 981. (e) Molander, G. A.; Nichols, P. J . J . Am. Chem. Soc.
1995, 117, 4415. (f) Kesti, M. R.; Waymouth, R. M. Organometallics
1992, 11, 1095. (g) Carter, M. B.; Schiott, B.; Gutierrez, A.; Buchwald,
S. L. J . Am. Chem. Soc. 1994, 116, 11667.
(12) Curtis, M. D.; Epstein, P. S. Adv. Organomet. Chem. 1981, 19,
213.
(13) (a) Horton, A. D.; Orpen, A. G. Organometallics 1992, 11, 1193.
(b) Nakano, T.; Nakamura, H.; Nagai, Y. Chem. Lett. 1989, 83.
(9) (a) Rappe´, A. K. Organometallics 1990, 9, 466. (b) Steigerwald,
M. L.; Goddard, W. A., III. J . Am. Chem. Soc. 1984, 106, 308.
(10) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J .;
Nolan, M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J . E. J . Am.
Chem. Soc. 1987, 109, 203.

Synthesis of Sm-SiH3 Complexes
Organometallics, Vol. 19, No. 23, 2000 4739
bond and represents a redistribution of phenyl groups
at silicon.12 Such redistributions are known to be
catalyzed by late transition metals, but have only been
rarely observed for d0 transition metal systems.3a,13 For
the samarium system under study, this process is
proposed to occur via σ-bond metathesis steps that pass
through four-center transition states in a σ-bond me-
tathesis process. The exact mechanism of the Si-C bond
activation and cleavage is open to speculation, but the
proposed pathways outlined in Scheme 2 seem reason-
able based on the known reactivity of organolanthanide
complexes.2,10
Ack n ow led gm en t is made to the National Science
Foundation for their generous support of this work.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal,
data collection and refinement parameters, atomic coordinates,
bond distances, bond angles, and anisotropic displacement
parameters for 6 and 10. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM000516R