Unusual reactivities of linear disilanes with o-carboranyl unit

Article abstract of DOI:10.1021/om0341146

The linear disilanes l,2-bis(1′-R-o-carboranyl)-1,1,2,2-tetramethyl-1,2-disilane (R = H (2a), Me (2b), Ph (2c)) were prepared by reacting the lithium salt of 1-R-o-carborane (1) with 1,2-dichlorotetramethyldisilane. These linear disilanes (2) were found to be useful precursors for the synthesis of a variety of cyclic compounds. For instance, reaction of the linear dilithiodisilane 2a with 1,2-dichlorotetramethyldisilane afforded the four-membered cyclic compound 3,4-o-carboranylene-1,1,2,2-tetramethyl-1,2-disilacyclobutane (3). Further, whereas the reaction of linear disilane (2a) with Pt(PEt₃)₃ was found to yield the cyclic bis(silyl)platinum complex 4, the reaction of the methyl-o-carboranyl-substituted disilane 2b with Pt(PEt₃)₃ under the same conditions yielded the decomposed bis(silyl)platinum complex 5, formed via oxidative addition of a Si-Si bond at the platinum atom. The reaction of the cyclic disilane 3 using a catalytic amount of lithium metal afforded a five-membered cyclic trisilyl compound (6). The reaction of 6 with phenylacetylene in the presence of a catalytic amount of Pd(CNBu^t)₂ was found to yield the seven-membered trisilyl ring compound 6,7-o-carboranylene-1,1,4,4,5,5-hexamethyl-2-phenyl-l,4,5-trisilacyclohept-2-ene (7). The structures of compounds 2a,b, 4-6, and 7 were determined using single-crystal X-ray crystallography.

Full text of DOI:10.1021/om0341146

490
Organometallics 2004, 23, 490-497
Un u su a l Rea ctivities of Lin ea r Disila n es w ith
o-Ca r bor a n yl Un it
Young-J oo Lee,† J ong-Dae Lee,† Sung-J oon Kim,† Byung Woo Yoo,†
J aejung Ko,*,† Il-Hwan Suh,† Minserk Cheong,‡ and Sang Ook Kang*,†,§
Department of Chemistry, Korea University, 208 Seochang, Chochiwon, Chung-nam 339-700,
Korea, Department of Chemistry and Research Institute for Basic Sciences,
Kyung Hee University, Seoul 130-701, Korea
Received August 16, 2003
The linear disilanes 1,2-bis(1′-R-o-carboranyl)-1,1,2,2-tetramethyl-1,2-disilane (R ) H (2a ),
Me (2b), Ph (2c)) were prepared by reacting the lithium salt of 1-R-o-carborane (1) with
1,2-dichlorotetramethyldisilane. These linear disilanes (2) were found to be useful precursors
for the synthesis of a variety of cyclic compounds. For instance, reaction of the linear
dilithiodisilane 2a with 1,2-dichlorotetramethyldisilane afforded the four-membered cyclic
compound 3,4-o-carboranylene-1,1,2,2-tetramethyl-1,2-disilacyclobutane (3). Further, whereas
the reaction of linear disilane (2a ) with Pt(PEt3)3 was found to yield the cyclic bis(silyl)-
platinum complex 4, the reaction of the methyl-o-carboranyl-substituted disilane 2b with
Pt(PEt3)3 under the same conditions yielded the decomposed bis(silyl)platinum complex 5,
formed via oxidative addition of a Si-Si bond at the platinum atom. The reaction of the
cyclic disilane 3 using a catalytic amount of lithium metal afforded a five-membered cyclic
trisilyl compound (6). The reaction of 6 with phenylacetylene in the presence of a catalytic
amount of Pd(CNBut)2 was found to yield the seven-membered trisilyl ring compound 6,7-
o-carboranylene-1,1,4,4,5,5-hexamethyl-2-phenyl-1,4,5-trisilacyclohept-2-ene (7). The struc-
tures of compounds 2a ,b, 4-6, and 7 were determined using single-crystal X-ray crystal-
lography.
Sch em e 1. Sequ en tia l Tr a n sfor m a tion of Lin ea r
Disila n e 2a to th e Cyclic Di- a n d Tr isila n es 3 a n d 6
In tr od u ction
The synthesis and study of organometallic complexes
possessing an ancillary silyl-o-carboranyl ligand have
continued to receive attention.1 In particular, our inter-
est in the reactivity of silyl-o-carborane has led us to
explore the use of silyl-o-carboranyl ligands in the
formation of unusual ring complexes. In this respect,
we have started investigating the reactivity of linear
disilanes bearing a bulky o-carboranyl unit, which might
confer some additional reactivity on the silicon-silicon
bond. Using suitable linear disilanes (2), it has been
possible for us to show that the bulkiness of the
o-carboranyl group in these disilyl compounds plays an
important role in Si-Si activation, producing di- and
trisilane (3, 6) (Scheme 1).
Resu lts a n d Discu ssion
of n-BuLi with 1-R-C2B10H12
, were reacted with
P r ep a r a tion of th e Lin ea r Disila n es 1,2-Bis(1′-
R -o-ca r b or a n yl)-1,1,2,2-t et r a m et h yl-1,2-d isila n e
(R ) H (2a ), Me (2b), P h (2c)). The bis(o-carboran-
yl)disilanes 2 were readily prepared from dichlorodi-
silane with 2 equiv of the monolithiated o-carboranes
1. The monolithiated o-carboranes 2-Li-1-R-C2B10H11 (R
) H (1a ), Me (1b), Ph (1c)), generated by the reaction
(SiMe2Cl)2 to give 2 in 91-96% yield (Scheme 2).
The colorless products 2 were crystalline solids that
were relatively stable in air and during brief heating
to 110-120 °C. Compounds 2 were readily soluble in
hexane, toluene, and THF. The structures of 2a ,b were
unambiguously established using single-crystal X-ray
analysis and are shown in Figures 1 and 2. The four
C(1), C(1)*, Si(1), and Si(1)* atoms comprising the
central skeleton of the molecule are nearly coplanar.
The C(1)-Si(1) bond lengths (1.933(2)-1.943(3) Å) are
slightly longer than the typical values for carbon-silicon
bonds (1.88-1.91 Å) and are comparable to those of the
cyclic 1,2-bis(o-carboranyl)-1,1,2,2-tetramethyl-1,2-disi-
† Korea University.
‡ Kyung Hee University.
§ Tel: +82-41-860-1334. Fax: +82-41-867-5396. E-mail: sangok@
korea.ac.kr.
(1) Review: (a) Kang, S. O.; Ko, J . Adv. Organomet. Chem. 2001,
47, 66. (b) Kang, S. O.; Lee, J .; Ko, J . Coord. Chem. Rev. 2002, 231,
47.
10.1021/om0341146 CCC: $27.50 © 2004 American Chemical Society
Publication on Web 01/03/2004

Unusual Reactivities of Linear Disilanes
Organometallics, Vol. 23, No. 3, 2004 491
Sch em e 2. Syn th esis of Lin ea r Disila n es 2a
Sch em e 3. F or m a tion of Cyclic Disila n es 3a
a
1
Conditions: (i) /2 (SiMe2Cl)2, THF, -78 °C.
a
Conditions: (i) 2 n-BuLi, THF, -78 °C; (ii) (SiMe2Cl)2,
THF, -78 °C.
be consistent with the structures determined using
X-ray crystallography.
Rea ction of 2a w ith 1,2-Dich lor otetr a m eth yl-
d isila n e. When the dilithium salt of 2a was reacted
with dichlorodisilane, the cyclic disilane 3 was produced
in 78% yield (Scheme 3).
Initially, we attempted to promote the substitution
reaction of dichlorodisilane with linear dilithiodisilane
2a in order to generate the eight-membered tetrasilane,
but no such reaction occurred, probably due to the steric
bulkiness of the o-carboranyl substituent. After many
attempts, we found that the linear disilane 2a can be
used in a reaction with an Si-Cl bond of dichlorodisi-
lane to form the cyclic disilane 3, without any cleavage
of the Si-C(o-carborane) bond. Compound 3 was puri-
fied by low-temperature recrystallization from toluene
F igu r e 1. Molecular structure of 2a with thermal ellip-
soids drawn at the 30% level.
1
as colorless crystals. The H, 13C, and 29Si NMR spectra
of 3 were found to be identical with those of an authentic
sample.2
Rea ction of th e Lin ea r Bis(o-ca r bor a n yl)d isi-
la n e 2a w ith P t(P Et3)3. Linear disilanes with bulky
ancillary o-carboranyl units have also been used in
chemical transformations, such as Si-Si bond activa-
tions with transition metals. Initially, we attempted the
double-silylation reaction of linear bis(o-carboranyl)-
disilane 2a and acetylenes in the presence of a catalytic
amount of Pt(PEt3)3 at 60-80 °C. However, after careful
workup, the product was found to be a cyclic bis(silyl)-
platinum complex rather than a double-silylated prod-
uct; when a mixture of Pt(PEt3)3 (0.05 mmol) and bis(o-
carboranyl)disilane 2a (0.07 mmol) was heated in a
sealed NMR tube (80 °C, 6 h), the solution changed
slowly from orange to yellow (eq 1).
F igu r e 2. Molecular structure of 2b with thermal ellip-
soids drawn at the 30% level.
lanes.2 The Si(1)-Si(1)* bond lengths (2.365(1)-2.386-
(1) Å) are within the range of values of Si-Si bond
lengths found in analogous complexes.3 The 1H, 13C, and
29Si NMR spectra and mass spectra of 2 were found to
(3) (a) So¨ldner, M.; Sˇandor, M.; Schier, A.; Schmidbaur, H. Chem.
Ber. 1997, 130, 1671. (b) So¨ldner, M.; Schier, A.; Schmidbaur, H. J .
Organomet. Chem. 1996, 521, 259.
(2) De Rege, F. M.; Kassebaum, J . D.; Scott, B. L.; Abney, K. D.;
Balaich, G. J . Inorg. Chem. 1999, 38, 486.

492 Organometallics, Vol. 23, No. 3, 2004
Lee et al.
F igu r e 4. Molecular structure of 5 with thermal ellipsoids
drawn at the 30% level.
F igu r e 3. Molecular structure of 4 with thermal ellipsoids
drawn at the 30% level.
involving the ethyl moiety of the phosphine group and
the o-carboranyl unit of the dimethylsilyl group.
Syn th esis of 4,5-o-Car bor an ylen e-1,1,2,2,3,3-h exa-
m eth yl-1,2,3-tr isila cyclop en ta n e (6). Of particular
interest is the reaction of disilacyclobutane with lithium
reagents in a polar solvent (eq 3), since a reactive
silyllithium species might be involved in the transfor-
mation of trisilacyclopentane. Indeed, when lithium was
An initial indication of the formulation of 4 was
obtained from the observation of a parent ion in the
mass spectrum at m/z 691. The 31P NMR signal was
shifted from -42.0 ppm for Pt(PEt3)3 to 18.4 ppm. The
structure of 4 was unambiguously established using
single-crystal X-ray analysis and is shown in Figure 3.
Complex 4 has a slightly distorted square-planar geom-
etry. The five Si, P, and Pt atoms comprising the central
skeleton of the molecule are all nearly coplanar, with a
dihedral angle of 18.02(7)° between the two planes
defined by Si(1), Pt(1), Si(2) and P(1), Pt(1), P(2). The
observed Pt-Si bond lengths (2.354(2), 2.362(2) Å) are
within the range of values of Pt-Si bond lengths found
in analogous complexes.4
The formation of the cyclic bis(silyl)platinum complex
(4) is unexpected and may involve the initial formation
of 3 followed by the oxidative addition of a strained
Si-Si bond. In an attempt to extend our understanding
of this oxidative addition process, we attempted to carry
out the analogous reactions of Pt(PEt3)3 with linear
disilanes such as methyl- (2b) and phenyl-o-carboranyl
(2c) derivatives, but these disilanes did not react under
the same experimental conditions. However, a trace
amount of decomposed product 5 was observed in the
case of 2b (eq 2) on extended heating in a refluxing
used as the reagent, treatment of the reaction mixture
with 3 produced the trisilane 6 (46%). The reaction of
lithium with the disilacyclobutane did not stop after the
Si-Si cleavage; an intermolecular addition of the silyl-
lithium species to the o-carboranylsilyl group followed.
The addition of metal silyl reagents to disilane systems
is a known reaction;5 therefore, this closure to a five-
membered ring is not surprising.
The colorless product 6 is a crystalline solid that is
relatively stable in air and during brief heating to 110-
120 °C. The structure of 6 was unambiguously estab-
(4) Recent articles on silylplatinum complexes: (a) Ozawa, F.;
Hikida, T. Organometallics 1996, 15, 4501. (b) Goikhman, R.; Aizen-
berg, M.; Shimon, L. J . W.; Milstein, D. J . Am. Chem. Soc. 1996, 118,
10894. (c) Levy, C. J .; Vittal, J . J .; Puddephatt, R. J . Organometallics
1996, 15, 2108. (d) Levy, C. J .; Puddephatt, R. J .; Vittal, J . J .
Organometallics 1994, 13, 1559. (e) Ozawa, F.; Hikida, T.; Hayashi,
T. J . Am. Chem. Soc. 1994, 116, 2844. (f) Yamashita, H.; Tanaka, M.;
Goto, M. Organometallics 1993, 12, 988. (g) Sakaki, S.; Ieki, M. J . Am.
Chem. Soc. 1993, 115, 2373. (h) Braunstein, P.; Knorr, M.; Hirle, B.;
Reinhard, G.; Schubert, U. Angew. Chem., Int. Ed. Engl. 1992, 31,
1583. (i) Tanaka, M.; Uchimaru, Y.; Lautenschlager, H.-J . J . Orga-
nomet. Chem. 1992, 428, 1. (j) Yamashita, H.; Tanaka, M.; Goto, M.
Organometallics 1992, 11, 3227. (k) Heyn, R. H.; Tilley, T. D. J . Am.
Chem. Soc. 1992, 114, 1917. (l) Grundy, S. L.; Holmes-Smith, R. D.;
Stobart, S. R.; Williams, M. A. Inorg. Chem. 1991, 30, 3333. (m) Pham,
E. K.; West, R. Organometallics 1990, 9, 1517.
toluene solution (Figure 4). The formation of 5 is
probably due to traces of oxygen in the reacting system.
However, another experiment showed that 5 is probably
not formed from the disilane 2b. A possible explanation
for the formation of 5 is the oxidation of the phosphorus
and silicon atoms, followed by an elimination reaction
(5) (a) Komoriya, H.; Kako, M.; Nakadaira, Y.; Mochida, K. J .
Organomet. Chem. 2000, 611, 420. (b) Naka, A.; Hayashi, M.; Okazaki,
S.; Ishikawa, M. Organometallics 1994, 13, 4994.

Unusual Reactivities of Linear Disilanes
Organometallics, Vol. 23, No. 3, 2004 493
(disilacyclobutane) (3′) and benzo(trisilacyclopentane)
(6′) and their o-carboranyl analogoues (3 and 6) were
carried out using the DFT method.13,14 These di- and
trisilacycloalkanes are nearly planar molecules (Figure
6). In these structures, the observed Si-Si distances of
2.381-2.405 Å and Si-C distances of 1.951 Å are as
expected, because the atomic radii (rcov) of Si and C are
1.18 and 0.77 Å, respectively.15 Our computational
results are consistent with the results from X-ray
structural studies of 3 and 6. As shown in Figure 6, the
trisilacyclopentanes 6′ and 6 are lower in energy than
their disilacyclobutane counterparts 3′ and 3. In addi-
tion, the o-carboranyl trisilacyclopentane 6 appears to
have the lower energy state; thus, the o-carboranyl
disilacyclobutane 3 is expected to be easily converted
into the corresponding cyclic trisilane 6. This compu-
tational result is qualitatively consistent with the
experimental observation that the o-carboranyl trisila-
cyclopentane 6 is readily prepared.
F igu r e 5. Molecular structure of 6 with thermal ellipsoids
drawn at the 30% level.
Rea ction of 6 w ith P h en yla cetylen e. Because of
the stability of the 1,2,3-trisilacyclopentane ring, the
structure of 6 might have a damping effect on the usual
reactivity of the Si3C2 ring. Nevertheless, we hoped that,
as in the cases of 1,2-disilacyclobutanes 3′ and 3, the
cyclic trisilane 6 would be a very reactive system.
Accordingly, we embarked upon a study of the reactivity
of 6. One of the interesting reactions of the Si-Si bond
of the more reactive disilanes is the transition-metal-
catalyzed insertion of unsaturated hydrocarbons. Equa-
tion 4 suggests that such a reaction occurs for 6 with
lished using single-crystal X-ray analysis and is shown
in Figure 5. The five C(1), C(2), Si(1), Si(2), and Si(3)
atoms comprising the central skeleton of the molecule
are nearly coplanar. The C(1)-Si(1) and C(2)-Si(3) bond
lengths (1.917(4)-1.930(4) Å) are slightly longer than
the typical values for the carbon-silicon bonds (1.88-
1.91 Å)6 and are comparable to those in 3 (R ) Me (a ),2
Et (b)7). The Si(1)-Si(2) and Si(2)-Si(3) bond lengths
(2.336(2)-2.341(2) Å) are within the range of values of
Si-Si bond lengths found in analogous compounds.8 The
1H, 13C, and 29Si NMR spectra and the elemental
analysis of 6 were found to be consistent with the
structure determined using X-ray crystallography. Simi-
lar results were observed in the thermolysis of the four-
membered phenylene disilacycle,5b digermacycle,9 and
distannacycle.10
Although the cyclic disilane analogue 3′ has been used
extensively in double-silylation reactions,11 many vari-
ants of this compound remain virtually unexplored.
Variants from the series of cyclic trisilanes 4,5-benzo-
1,1,2,2,3,3-hexaalkyl-1,2,3-trisilacyclopent-4-ene (6′) have
only been identified by Ishikawa (alkyl ) Et)5b and
Tanaka (alkyl ) Me).12 However, the yields obtained
in their thermolysis reactions are too low. To advance
the understanding of such compounds, a methodology
is needed for synthesizing cyclic trisilane precursors
with high efficiency and under mild conditions. We feel
that the o-carboranyl substituent is very useful for the
promotion of the formation of cyclic five-membered
trisilyl species.
phenylacetylene in the presence of a catalytic amount
of Pd(CNBut)2. The palladium-catalyzed reaction of 6
with phenylacetylene afforded 6,7-o-carboranylene-
1,1,4,4,5,5-hexamethyl-2-phenyl-1,4,5-trisilacyclohept-
2-ene (7) in 80% yield as the sole product.
To obtain structural information for the newly pre-
pared compound, a single-crystal X-ray diffraction study
of the phenylacetylene insertion product 7 was under-
taken (Figure 7). The X-ray crystal structure of 7
confirmed the presence of a seven-membered ring
comprised of o-carborane, three silicon atoms, and an
unsaturated hydrocarbon fragment containing a CdC
bond. The CdC bond length (1.342(3) Å) is slightly
longer than the typical value for the carbon-carbon
double bond (1.317 Å)16 and is comparable to that of the
six-membered-ring product formed in the reaction be-
tween phenylacetylene and 3 (1.355(4) Å).6
To obtain a better understanding of the results of the
present experiments, computational analyses of benzo-
(6) Song, K. H.; J ung, I.; Lee, S. S.; Park, K.-M.; Ishikawa, M.; Kang,
S. O.; Ko, J . Organometallics 2001, 20, 5537.
(7) Beagley, B.; Monaghan, J . J .; Hewitt, T. G. J . Mol. Struct. 1971,
8, 401.
(8) (a) Sita, L. R.; Lyon, S. R. J . Am. Chem. Soc. 1993, 115, 10374.
(b) Carrell, H. L.; Donohue, J . Acta Crystallogr., Sect. B 1972, 28, 1566.
(9) Komoriya, H.; Kako, M.; Nakadaira, Y. Organometallics 1996,
15, 2014.
(10) Lee, C.; Lee, J .; Lee, S. W.; Kang, S. O.; Ko, J . Inorg. Chem.
2002, 41, 3084.
In summary, we have prepared a series of linear
disilanes (2). These linear disilanes readily undergo a
Si-Si activation reaction with suitable metals to afford
(11) (a) Naka, A.; Hayashi, M.; Okazaki, S.; Kunai, A.; Ishikawa,
M. Organometallics 1996, 15, 1101. (b) Naka, A.; Okazaki, S.; Hayashi,
M.; Ishikawa, M. J . Organomet. Chem. 1995, 499, 35. (c) Ishikawa,
M.; Okazaki, S.; Naka, A.; Tachibana, A.; Kawauchi, S.; Yamabe, T.
Organometallics 1995, 14, 114.
(13) Becke, A. D. J . Chem. Phys. 1993, 98, 5648.
(14) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. 1988, B37, 785.
(15) Huheey, J . E.; Keiter, E. A.; Keiter, R. L. Inorganic Chemistry,
4th ed.; HarperCollins College: New York, 1993.
(16) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen,
A. G.; Taylor, R. J . Chem. Soc., Perkin Trans. 1 1987, 51.
(12) Uchimara, Y.; Tanaka, M. J . Organomet. Chem. 1996, 521, 335.

494 Organometallics, Vol. 23, No. 3, 2004
Lee et al.
F igu r e 6. Energy profiles of 3′, 3, 6′, and 6.
special precautions. We have further exploited this
potential in a series of novel chemical transformations.
We now describe (i) the synthesis of the series of linear
disilanes 2, (ii) the facile conversion of the linear disilane
2a to the cyclic disilane 3, (iii) the isolation of the bis-
(disilyl)platinum complex 4 by the oxidative addition
reaction of linear disilane 2a , (iv) the efficient synthesis
of the cyclic trisilane 6 from cyclic disilane 3, and (v)
the double-silylation reaction of 6 with phenylacetylene
in the presence of palladium catalyst.
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were performed
under a dry, oxygen-free nitrogen or argon atmosphere using
standard Schlenk techniques or in a Vacuum Atmospheres
HE-493 drybox. Diethyl ether, toluene, hexane, and pentane
were distilled under nitrogen from sodium/benzophenone.
Dichloromethane was dried with CaH2. Benzene-d6 was dis-
tilled under nitrogen from sodium and stored in a Schlenk
storage flask until needed. CDCl3 was predried under CaH2
and vacuum-transferred. n-BuLi (1.6 M in hexanes) and 1,2-
dichlorotetramethyldisilane were used as received from Ald-
rich. o-Carborane was purchased from KATCHEM Ltd. and
used without purification. Pt(PEt3)3 17 and Pt(CNBut)2 18 were
prepared according to the literature procedures. All 1H (300.1
F igu r e 7. Molecular structure of 7 with thermal ellipsoids
drawn at the 30% level.
new classes of cyclic di- and trisilanes (3-7). We have
shown that the o-carboranyl unit is an excellent sub-
stituent, because this unit stabilizes reactive intermedi-
ates and is stable enough to be handled without any

Unusual Reactivities of Linear Disilanes
Organometallics, Vol. 23, No. 3, 2004 495
Ta ble 1. NMR Sp ectr oscop ic Da ta for Com p ou n d s 2, 4, 6, a n d 7
NMR (δ)
compd
1H
13C
29Si
2a a
0.46 (s. 12H, SiMe2)
3.38 (s. 1H, CcabH)
-1.35 (SiMe2)
-3.29
-9.63
60.16, 65.11 (C(cab))
2ba
2ca
0.61(s, 12H, SiMe2)
2.01 (s, 6H, C(cab)CH3)
0.76 (SiMe2)
26.14 (C(cab)CH3)
71.40 (C(cab))
-0.06 (s, 12H, SiMe2)
7.30-7.62 (10H, C(cab)Ph)
-1.79 (SiMe2)
86.42 (C(cab))
128.56, 129.26, 131.24,
132.84 (C(cab)Ph)
-6.84
3
2
4a
0.33 (s, 12H, SiMe2, J Pt-H ) 18 Hz)
-0.01 (SiMe2)
38.40 (dd, J Pt-Si ) 1285 Hz,
2J P-Si(trans)) 132 Hz,
2J P-Si(cis) ) 10 Hz)
1.04 (q, 18H, PCH2Me)
8.62 (d, PCH2Me,
2J Pt-C ) 105 Hz)
19.46 (PCH2Me)
1.90 (q, 12H, PCH2Me)
6b
7a
-0.11 (s, 6H, Si(cent)Me2)
0.05 (s, 12H, Si(cab)Me2)
-7.52 (Si(cent)Me2)
-2.65 (Si(cab)Me2)
-42.22 (Si(cent)Me2)
-0.70 (Si(cab)Me2)
0.28, 0.34, 0.43 (s, 18H, SiMe2,)
6.72 (s, 1H, CdCH)
-0.86, 1.66, 2.89 (SiMe2)
126.53, 126.75, 128.32,
151.35 (CdCPh)
-25.88, -4.75, 0.36 (SiMe2)
7.05-7.33 (5H, CdCPh)
147.73, 159.85 (CdC)
a
b
CDCl3 was used as the solvent, and the chemical shifts are reported relative to the residual H of the solvent. C6D6 was used as the
solvent, and the chemical shifts are reported relative to the residual H of the solvent.
Ta ble 2. X-r a y Cr ysta llogr a p h ic Da ta a n d P r ocessin g P a r a m eter s for Com p ou n d s 2a ,b a n d 4-7
2a
2b
4
5
6
7
formula
fw
cryst class
space group
Z
B
10C4H17Si
B10C5H19Si
215.39
monoclinic
P21/c
B10C18H52Si2P2Pt
B10C17H50OSi2P2Pt B20C16H56Si6
B10C16H34Si3
418.80
monoclinic
P21/c
201.37
monoclinic
P21/n
689.91
monoclinic
P21/c
691.88
monoclinic
P21/c
633.35
triclinic
P1h
4
4
4
4
2
4
cell constants
a, Å
b, Å
7.0029(6)
15.1842(9)
11.5040(8)
8.1440(6)
12.5958(6)
13.4148(9)
16.052(2)
12.059(9)
16.648 (1)
8.7323(2)
19.005(4)
19.217(4)
9.452(2)
10.5643(6)
12.8852(7)
19.510(1)
13.841(8)
16.754(1)
100.523(5)
105.372(9)
106.040(8)
1952.1(4)
0.227
c, Å
R, deg
â, deg
91.296(6)
106.940(6)
90.512(8)
94.23(3)
105.056(1)
γ, deg
V, Å3
1223.0(2)
0.094
1316.4(2)
0.135
3222.5(5)
4.536
3180.6(1)
4.599
2564.6(2)
0.187
µ, mm-1
cryst size, mm
0.3 × 0.35 × 0.4 0.4 × 0.4 × 0.4 0.35 × 0.35 × 0.40 0.3 × 0.3 × 0.4
0.4 × 0.4 × 0.5 0.2 × 0.2 × 0.25
d
calcd, g/cm3
1.094
420
1.087
452
1.422
1384
1.445
1384
1.077
672
1.085
888
F(000)
radiation
Mo KR (λ) 0.7107)
θ range, deg
h, k, l collected
no. of rflns measd
no. of unique rflns
no. of rflns used in 1570
refinement
2.22-24.97
+8, +18, (13
2328
2.27-25.97
1.27-25.97
1.51-25.97
+10, +23, (23
6701
1.31-25.97
1.91-28.32
+10, +15, (16 +19, +14, (20
+11, +17, (20 (14, (17, (25
2768
2583
1618
6586
6318
4306
8178
7649
5002
18 488
6349
3615
2145
6240
3770
(I > 2σ(I))
no. of params
149
158
318
318
411
278
a
R1 (I > 2σ(I))
0.0453
0.1300
1.032
0.0518
0.1447
1.006
0.0358
0.0777
1.037
0.0464
0.1129
0.889
0.0746
0.2000
1.177
0.0491
0.1539
1.000
a
wR2 (all data)
GOF
a
2
b
2
R1 ) ∑||Fo| - |Fc|| (based on reflections with Fo > 2σF2). wR2 ) [∑[w(Fo - Fc2)2]/∑[w(Fo2)2]]1/2; w ) 1/[σ2(Fo2) + (0.095P)2], P )
[max(Fo2, 0) + 2Fc2]/3 (also with Fo > 2σF2).
2
MHz), 13C (75.4 MHz), 31P (121.4 MHz), and 29Si (59.60 MHz)
NMR spectra were recorded on a Varian Mercury-300BB
spectrometer unless otherwise stated. High-resolution mass
spectra were measured at the Korea Basic Science Institute.
The NMR data for complexes 2, 4, 6, and 7 are given in Table
1. Elemental analyses were performed with a Carlo Erba
Instruments CHNS-O EA1108 analyzer.
Syn th esis of th e Lin ea r Disila n e 1,2-Bis(1′-R-o-ca r bo-
r a n yl)-1,1,2,2-tetr a m eth yl-1,2-d isila n e (R ) H (2a ), Me
(2b), P h (2c)). A representative procedure is as follows: to a
solution of 1.44 g (10.0 mmol) of o-carborane in 40 mL of THF,
precooled to -78 °C, was added 6.30 mL of n-butyllithium (1.6
M in hexanes). The reaction mixture was warmed to room
temperature and stirred for 2 h, whereupon it was transferred,
via cannula, to a suspension of 1.0 mL (0.5 equiv) of 1,2-
dichlorotetramethyldisilane in 20 mL of Et2O that was cooled
to -78 °C. The resultant yellow mixture was warmed to room
temperature and stirred for 2 h. The volatiles were then
removed under reduced pressure; the crude mixture was taken
up in a minimal amount of Et2O and filtered through a 1 × 5
(17) Yoshida, T.; Matsuda, T.; Otsuka, S. Inorg. Synth. 1979, 19,
107.
(18) Suginome, M.; Oike, H.; Shuff, P. H.; Ito, Y. Organometallics
1996, 15, 2170.

496 Organometallics, Vol. 23, No. 3, 2004
Ta ble 3. Selected In ter a tom ic Dista n ces (Å) for Com p ou n d s 2a ,b a n d 4-7
Compound 2a
Lee et al.
Si(1)-Si(1)#1
2.365(1)
Si(1)-C(1)
1.933(2)
Si(1)-C(3) 1.857(3)
Si(1)-C(4)
1.865(3)
C(1)-C(2)
1.670(3)
1.692(4)
Compound 2b
Si(1)-C(4) 1.860(3)
Si(1)-Si(1)#1
C(2)-C(3)
2.386(1)
1.512(4)
Si(1)-C(1)
1.943(3)
Si(1)-C(5)
1.859(3)
C(1)-C(2)
Compound 4
Pt(1)-P(1)
Si(2)-C(2)
P(2)-C(13)
P(1)-C(11)
C(15)-C(16)
2.378(2)
1.938(6)
1.842(7)
1.844(6)
1.51(1)
Pt(1)-P(2)
Si(2)-C(5)
P(2)-C(15)
C(7)-C(8)
C(17)-C(18)
2.370(2)
1.890(8)
1.820(7)
1.52(1)
Pt(1)-Si(1)
2.354(2)
1.887(7)
1.840(7)
1.51(1)
Pt(1)-Si(2)
Si(1)-C(3)
P(1)-C(7)
2.362(2)
1.893(7)
1.821(7)
1.520(8)
Si(1)-C(1)
Si(1)-C(4)
P(1)-C(9)
C(13)-C(14)
1.950(6)
1.889(7)
1.855(7)
1.49(1)
Si(2)-C(6)
P(2)-C(17)
C(9)-C(10)
C(11)-C(12)
1.528(9)
Compound 5
Pt(1)-P(1)
P(1)-C(10)
Si(1)-C(2)
C(16)-C(17)
C(12)-C(13)
2.363(2)
1.82(1)
2.00(1)
1.52(2)
1.508(2)
Pt(1)-P(2)
P(1)-C(12)
Si(1)-C(4)
Si(2)-C(7)
C(14)-C(15)
2.324(3)
1.83(1)
1.88(1)
1.88(1)
1.51(2)
Pt(1)-Si(1)
P(2)-O(1)
Si(1)-C(5)
C(1)-C(3)
2.380(3)
1.605(7)
1.87(1)
1.51(2)
Pt(1)-Si(2)
P(2)-C(14)
Si(2)-O(1)
C(8)-C(9)
2.351(3)
1.80(1)
1.738(7)
1.51(2)
P(1)-C(8)
1.82(1)
1.81(1)
1.86(1)
1.51(2)
P(2)-C(16)
Si(2)-C(6)
C(10)-C(11)
Compound 6
Si(1)-Si(2)
Si(1)-C(4)
C(1)-C(2)
Si(1′)-C(3′)
Si(3′)-C(8′)
2.341(2)
1.871(4)
1.727(5)
1.868(4)
1.861(4)
Si(2)-Si(3)
Si(2)-C(5)
Si(1′)-Si(2′)
Si(1′)-C(4′)
C(1′)-C(2′)
2.336(2)
1.877(4)
2.335(2)
1.859(5)
1.714(5)
Si(1)-C(1)
Si(2)-C(6)
Si(2′)-Si(3′)
Si(2′)-C(5′)
1.930(4)
1.882(4)
2.344(2)
1.883(4)
Si(3)-C(2)
Si(3)-C(7)
Si(1′)-C(1′)
Si(2′)-C(6′)
1.917(4)
1.856(5)
1.922(4)
1.877(4)
Si(1)-C(3)
Si(3)-C(8)
Si(3′)-C(2′)
Si(3′)-C(7′)
1.859(4)
1.868(5)
1.936(4)
1.860(4)
Compound 7
Si(1)-Si(2)
C(9)-C(10)
Si(2)-C(6)
C(12)-C(13)
2.361(1)
1.342(3)
1.867(3)
1.378(4)
Si(1)-C(1)
C(10)-Si(2)
Si(3)-C(7)
C(13)-C(14)
1.933(2)
1.862(3)
1.859(3)
1.333(6)
C(1)-C(2)
Si(1)-C(3)
Si(3)-C(8)
C(14)-C(15)
1.685(3)
1.868(3)
1.854(3)
1.360(7)
C(2)-Si(3)
Si(1)-C(4)
C(9)-C(11)
C(15)-C(16)
1.928(2)
1.871(3)
1.488(3)
1.383(6)
Si(3)-C(9)
Si(2)-C(5)
C(11)-C(12)
C(16)-C(11)
1.885(2)
1.872(3)
1.377(4)
1.379(4)
Ta ble 4. Selected In ter a tom ic An gles (d eg) for Com p ou n d s 2a ,b a n d 4-7
Compound 2a
C(1)-Si(1)-Si(1)#1 107.53(8) C(3)-Si(1)-Si(1)#1 111.0(1)
C(4)-Si(1)-C(1) 107.1(1) C(2)-C(1)-Si(1) 118.0(2)
C(4)-Si(1)-Si(1)#1 112.1(1)
C(3)-Si(1)-C(4) 111.7(2)
C(3)-Si(1)-C(1)
107.2(1)
Compound 2b
C(5)-Si(1)-Si(1)#1 111.9(1)
C(5)-Si(1)-C(4) 108.7(2)
C(1)-Si(1)-Si(1)#1 110.35(8) C(4)-Si(1)-Si(1)#1 111.7(1)
C(4)-Si(1)-C(1)
C(3)-C(2)-C(1)
109.8(1)
119.6(2)
C(5)-Si(1)-C(1)
104.1(1)
C(2)-C(1)-Si(1)
123.9(2)
Compound 4
P(2)-Pt(1)-P(1)
Si(1)-Pt(1)-P(2)
C(17)-P(2)-Pt(1)
Pt(1)-Si(1)-C(3)
C(13)-P(2)-C(15)
C(7)-P(1)-C(11)
Si(1)-C(1)-C(2)
97.05(6) Si(1)-Pt(1)-P(1)
167.35(6) Si(1)-Pt(1)-Si(2)
91.52(6) Si(2)-Pt(1)-P(1)
83.92(6) C(13)-P(2)-Pt(1)
164.13(7) Si(2)-Pt(1)-P(2)
90.15(7)
116.4(3)
122.7(2)
125.7(3)
105.9(4)
107.1(4)
111.2(2)
117.2(2)
108.3(3)
102.0(4)
104.2(5)
C(15)-P(2)-Pt(1)
C(11)-P(1)-Pt(1)
Pt(1)-Si(2)-C(6)
C(7)-P(1)-C(9)
C(3)-Si(1)-C(4)
121.0(2)
119.0(3)
103.9(4)
101.9(3)
112.5(4)
C(7)-P(1)-Pt(1)
Pt(1)-Si(1)-C(4)
C(13)-P(2)-C(17)
C(9)-P(1)-C(11)
108.1(3)
112.6(3)
100.0(3)
99.1(3)
C(9)-P(1)-Pt(1)
Pt(1)-Si(2)-C(5)
C(15)-P(2)-C(17)
C(5)-Si(2)-C(6)
Compound 5
P(1)-Pt(1)-P(2)
P(2)-Pt(1)-Si(2)
Pt(1)-P(1)-C(12)
Pt(1)-Si(1)-C(2)
98.55(9) P(1)-Pt(1)-Si(1)
101.97(9) P(1)-Pt(1)-Si(2)
163.02(9) P(2)-Pt(1)-Si(1)
159.34(9)
108.4(4)
123.8(6)
121.2(9)
67.2(1)
124.8(4)
114.8(3)
P(2)-O(1)-Si(2)
Pt(1)-P(2)-O(1)
O(1)-P(2)-C(14)
101.4(3)
98.1(3)
Pt(1)-P(1)-C(8)
Pt(1)-Si(2)-O(1)
O(1)-P(2)-C(16)
113.7(4)
93.3(2)
Pt(1)-P(1)-C(10)
Si(1)-C(2)-C(1)
C(3)-C(1)-C(2)
104.2(5)
104.3(5)
Compound 6
Si(1)-Si(2)-Si(3)
C(2)-Si(3)-Si(2)
C(1′)-Si(1′)-Si(2′)
C(3′)-Si(1′)-C(4′)
98.12(5) C(1)-Si(1)-Si(2)
102.4(1)
111.3(2)
118.5(2)
111.9(2)
Si(1)-C(1)-C(2)
C(7)-Si(3)-C(8)
C(1′)-C(2′)-Si(3′)
C(7′)-Si(3′)-C(8′)
117.8(2)
111.5(3)
118.0(2)
111.1(2)
C(1)-C(2)-Si(3)
Si(1′)-Si(2′)-Si(3′)
C(2′)-Si(3′)-Si(2′)
118.1(2)
98.33(5)
102.3(1)
102.8(1)
102.7(1)
111.4(2)
C(5)-Si(2)-C(6)
Si(1′)-C(1′)-C(2′)
C(5′)-Si(2′)-C(6′)
Compound 7
Si(1)-C(1)-C(2)
C(9)-C(10)-Si(2)
C(1)-Si(1)-C(3)
Si(3)-C(9)-C(11)
123.4(2)
134.6(2)
108.9(1)
118.6(2)
C(1)-C(2)-Si(3)
Si(2)-Si(1)-C(1)
C(1)-Si(1)-C(4)
C(10)-C(9)-C(11)
123.5(2)
C(2)-Si(3)-C(9)
111.2(1)
106.6(1)
106.9(1)
122.6(2)
Si(3)-C(9)-C(10)
Si(1)-Si(2)-C(6)
C(2)-Si(3)-C(8)
C(9)-C(11)-C(16)
122.7(2)
110.1(1)
110.9(1)
120.3(3)
114.83(8) Si(1)-Si(2)-C(5)
106.0(1)
118.5(2)
C(2)-Si(3)-C(7)
C(9)-C(11)-C(!2)
cm pad of silica gel on a glass frit. Removal of the volatiles
provided the final crude product, which was further crystal-
lized from toluene at -5 °C to provide the pure bis(o-car-
boranyl)disilane 2a as a colorless solid. Yield: 90% (1.81 g,
4.5 mmol). Anal. Calcd for B20C8H34Si2: C, 23.62; H, 8.43.
Found: C, 23.70; H, 8.40. Mp: 183-185 °C. IR (cm-1): 3069
m, 2959 m (νCH), 2654 s, 2629 s, 2567 s (νBH).
For 2b, a procedure analogous to the preparation of 2a was
used, but starting from 1b (1.58 g, 10.0 mmol) in benzene.
Thus, 2b was crystallized from toluene at -5 °C. Yield: 96%
(2.07 g, 4.8 mmol). Anal. Calcd for B20C10H38Si2: C, 27.62; H,
8.82. Found: C, 27.70; H, 8.79. Mp: 197-199 °C. IR (cm-1):
2953 m (νCH), 2648 w, 2577 vs (νBH).
For 2c, a procedure analogous to the preparation of 2a was
used, but starting from 1c (2.20 g, 10.0 mmol) in benzene.
Thus, 2c was crystallized from toluene at -5 °C. Yield: 94%
(2.56 g, 4.7 mmol). Anal. Calcd for B20C20H42Si2: C, 42.97; H,
7.58. Found: C, 42.84; H, 7.55. Mp: 232-234 °C. IR (cm-1):
3065 w, 2961 w (νCH), 2631 w, 2567 s (νBH).
Rea ction of th e Dilith iu m Sa lt of 2a w ith 1,2-Dich lo-
r otetr a m eth yld isila n e. THF (20 mL) and 1.0 mmol of 2a
were added to the reaction flask. The solution was cooled to

Unusual Reactivities of Linear Disilanes
Organometallics, Vol. 23, No. 3, 2004 497
-78 °C, and n-butyllithium (1.25 mL, 2.0 mmol, 1.6 M in
hexanes) was added. The solution was warmed to room
temperature, whereupon a thick suspension of white precipi-
tate formed. After the reaction mixture had stirred for 1 h at
room temperature, it was again cooled to -78 °C and 1,2-
dichlorotetramethyldisilane (1.1 equiv) was added as a neat
liquid. The solution was warmed to -5 °C very slowly (for over
1 h) and stirred at -5 °C for a total of 3 h. The volatiles were
then removed under reduced pressure; the crude mixture was
taken up in a minimal amount of Et2O and filtered through a
1 × 5 cm pad of silica gel on a glass frit. Removal of the
volatiles provided the final crude product, which was further
crystallized from toluene at -5 °C to provide pure 3,4-o-
carboranylene-1,1,2,2-tetramethyl-1,2-disilacyclobutane (3) as
a colorless solid. Yield: 78% (0.762 g, 1.56 mmol).
while the remaining H atoms were calculated in idealized
positions and included in the refinement with fixed atomic
contributions. Further detailed information is given in Table
1, and selected interatomic distances and angles are given in
Tables 3 and 4, respectively.
Com p u ta tion a l Deta ils. Stationary points on the potential
energy surface were calculated using the Amsterdam Density
Functional (ADF) program, developed by Baerends et al.20,21
and vectorized by Ravenek.22 The numerical integration
scheme applied for the calculations was developed by te Velde
et al.23,24 The geometry optimization procedure was based on
the method due to Versluis and Ziegler.25 The electronic
configurations of the molecular systems were described by
double-ú STO basis sets with polarization functions for the H,
B, and C atoms, while triple-ú Slater type basis sets were
employed for the Si, P, and Pt atoms.26,27 The 1s electrons of
B and C, the 1s-2p electrons of Si and P, and the 1s-4d
electrons of Pt were treated as frozen cores. A set of auxiliary28
s, p, d, f, and g STO functions, centered on all nuclei, was used
in order to fit the molecular density and the Coulomb and
exchange potentials in each SCF cycle. Energy differences were
calculated by augmenting the local exchange-correlation po-
tential by Vosko et al.29 with Becke’s30 nonlocal exchange
corrections and Perdew’s31 nonlocal correlation corrections
(BP86). Geometries were optimized by including nonlocal
corrections at this level of theory. First-order Pauli scalar
relativistic corrections32,33 were added variationally to the total
energy for all systems. In view of the fact that all systems
investigated in this work show a large HOMO-LUMO gap, a
spin-restricted formalism was used for all calculations. No
symmetry constraints were used.
R ea ct ion of Lin ea r Bis(o-ca r b or a n yl)d isila n e 2a
w ith P t(P Et3)3. Benzene (15 mL) was added to a mixture of
Pt(PEt3)3 (0.110 g, 0.2 mmol) and 2a (0.080 g, 0.2 mmol). The
mixture was stirred for 3 h, and then the volatile compounds
were removed under reduced pressure. Extraction of the
residue with toluene (20 mL), followed by concentration of the
extract to approximately half its volume and cooling to -5 °C,
resulted in crystallization of the cyclic bis(silyl)platinum
complex 4. Yield: 75% (0.103 g, 0.15 mmol). The supernatant
was decanted and further reduced, and the residue was
chromatographed. Elution with hexane removed a UV-active
band, from which o-carborane (0.020 g, 69%) was obtained as
a white crystalline solid after evaporation in vacuo. 31P{1H}
NMR: δ 18.40 (d, 1J Pt-P ) 1695 Hz). Anal. Calcd for B10C18H52
-
Si2P2Pt: C, 31.24; H, 7.58. Found: C, 31.35; H, 7.61. Mp )
173-175 °C dec. IR (cm-1): 3120 s, 2913 w (νCH), 2647 w, 2597
s (νBH).
For 5, a procedure analogous to the preparation of 4 was
used, but starting from 2b (0.086 g, 0.2 mmol) in benzene.
Thus, 5 was crystallized from toluene at -5 °C. Yield: 2.5%
(0.004 g, 0.005 mmol). IR (cm-1): 2963 s, 2930 m, 2876 w (νCH),
2581 (νBH).
Syn th esis of 4,5-o-Ca r bor a n ylen e-1,1,2,2,3,3-h exa m eth -
yl-1,2,3-tr isilacyclopen tan e (6). A catalytic amount of lithium
metal (0.014 g, 0.02 mmol) was added to a solution of 3 (0.488
g, 1.0 mmol) in THF (20 mL), and the mixture was stirred for
1 h at 25 °C; conversion into 6, as monitored by 1H NMR
spectroscopy, was quantitative. The solvent was removed in
vacuo and the resulting solid crystallized from toluene to give
0.146 g (0.46 mmol) of colorless microcrystals (46% yield). Anal.
Calcd for B10C8H28Si3: C, 30.17; H, 8.87. Found: C, 30.06; H,
8.84. Mp: 142-144 °C. IR (cm-1): 2963 w, 2897 w (νCH), 2588
vs, 2559 s (νBH).
Rea ction of 6 w ith P h en yla cetylen e. Phenylacetylene
(0.12 mL, 1.1 mmol) and Pt(CNBut)2 (0.0055 g, 20 µmol) were
added to a solution of 6 (0.316 g, 1.0 mmol) in toluene (20 mL),
and the mixture was heated for 1 h at 110 °C; conversion into
7, as monitored by 1H NMR spectroscopy, was quantitative.
The solvent was removed in vacuo and the resulting solid crys-
tallized from toluene to give 0.335 g (0.80 mmol) of colorless
microcrystals (80% yield). Anal. Calcd for B10C16H34Si3: C,
45.68; H, 8.15. Found: C, 45.84; H, 8.18. Mp: 150-154 °C. IR
(cm-1): 3074 w, 3053 w, 3018 w, 2961 m, 2901 w (νCH), 2633
w, 2598 s, 2584 s, 2572 s, 2557 s (νBH), 1487 m (νCdC).
Cr ysta l Str u ctu r e Deter m in a tion . Crystals of 2a ,b and
4-7 were obtained from toluene, sealed in glass capillaries
under argon, and mounted on the diffractometer. Data were
collected and corrected for Lorentz and polarization effects.
Each structure was solved by the application of direct methods
using the SHELXS-96 program19a and least-squares refine-
ment using SHELXL-97.19b After anisotropic refinement of all
non-H atoms several H atom positions could be located in
difference Fourier maps. These were refined isotropically,
Ack n ow led gm en t. We are grateful to the Korea
Research Foundation (Grant No. KRF-2002-015-CP0200)
for their financial support.
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data (excluding structure factors) for the structures of 2a ,b
and 4-7 reported in this paper and listings giving optimized
geometries of the crucial structures (3, 3′, 6, and 6′) reported
(Cartesian coordinates, in Å); crystallographic data are also
available in electronic form as CIF files. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM0341146
(19) (a) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, A46, 467.
(b) Sheldrick, G. M. SHELXL, Program for Crystal Structure Refine-
ment; University of Go¨ttingen, Go¨ttingen, Germany, 1997.
(20) Baerends, E. J .; Ellis, D. E.; Ros, P. Chem. Phys. 1973, 2, 41.
(21) Baerends, E. J .; Ros, P. Chem. Phys. 1973, 2, 52.
(22) Ravenek, W. In Algorithms and Applications on Vector and
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