Palladium-catalyzed double-silylation reactions of 3,4-carboranylene-1,1,2,2-tetraethyl-1,2-disilacyclobut-3-ene

Article abstract of DOI:10.1021/om010535g

The reaction of the 1,2-dilithiated o-carborane with 1,2-dichlorotetraethyldisilane yielded the strained 3,4-carboranylene-1,1,2,2-tetraethyl-1,2-disilacyclobut-3-ene (2), which was found to be a good reactant for the double-silylation reaction. Thus, the reaction of 2 with RC≡CR′ in the presence of a catalytic amount of Pd(PPh₃)₄ yielded the six-membered disilyl ring compounds B₁₀H₁₀C₂(SiEt₂)₂ (RC=CR′) R = Ph, R′ = H (6); R = Ph, R′ = CH₃ (7); R = R′ = COOCH₃ (8); R = C₄H₉, R′ = H (9). The palladium-catalyzed reaction of 2 with 4-nitrobenzaldehyde afforded 5,6-carboranylene-2-oxa-1,4-disilacyclohex-5-ene (10). In contrast, the reaction of 2 with trans-cinnamaldehyde under the same reaction conditions yielded the insertion compound 11 formed via insertion of a carbonyl group into each of the C-Si bonds of 2. The structures of compounds 2, 6, and 11 were determined by single-crystal X-ray crystallography.

Full text of DOI:10.1021/om010535g

Organometallics 2001, 20, 5537-5541
5537
P a lla d iu m -Ca ta lyzed Dou ble-Silyla tion Rea ction s of
3,4-Ca r bor a n ylen e-1,1,2,2-tetr a eth yl-1,2-d isila cyclobu t-3-en e
Kyu Ho Song,† Il J ung,† Shim Sung Lee,‡ Ki-Min Park,‡ Mitsuo Ishikawa,§
Sang Ook Kang,*,† and J aejung Ko*,†
Department of Chemistry, Korea University, Chochiwon, Chungnam 339-700, Korea,
Department of Chemistry, and Institute of Natural Sciences, Gyeongsang National University,
Chinju 660-701, Korea, and Department of Chemical Technology, Kurashiki University of
Science and the Arts, 2640 Nishinoura, Tsurajima-cho, Kurashiki, Okayama 712-8505, J apan
Received J une 20, 2001
The reaction of the 1,2-dilithiated o-carborane with 1,2-dichlorotetraethyldisilane yielded
the strained 3,4-carboranylene-1,1,2,2-tetraethyl-1,2-disilacyclobut-3-ene (2), which was found
to be a good reactant for the double-silylation reaction. Thus, the reaction of 2 with RCt
CR′ in the presence of a catalytic amount of Pd(PPh3)4 yielded the six-membered disilyl ring
compounds B10H10C2(SiEt2)2(RCdCR′) (R ) Ph, R′ ) H (6); R ) Ph, R′ ) CH3 (7); R ) R′ )
COOCH3 (8); R ) C4H9, R′ ) H (9)). The palladium-catalyzed reaction of 2 with 4-nitroben-
zaldehyde afforded 5,6-carboranylene-2-oxa-1,4-disilacyclohex-5-ene (10). In contrast, the
reaction of 2 with trans-cinnamaldehyde under the same reaction conditions yielded the
insertion compound 11 formed via insertion of a carbonyl group into each of the C-Si bonds
of 2. The structures of compounds 2, 6, and 11 were determined by single-crystal X-ray
crystallography.
In tr od u ction
unit toward unsaturated organic substrates in the
presence of a transition metal catalyst because o-
carborane has been described as “superaromatic” due
to the delocalized nature of the bonding in the frame-
work.3 We now report the synthesis and reactivity of
3,4-carboranylene-1,1,2,2-tetraethyl-1,2-disilacyclobut-
3-ene (2).
Recently, we found that 3,4-benzo-1,1,2,2-tetraethyl-
1,2-disilacyclobut-3-ene (1) displayed interesting chemi-
cal behavior with organic substrates such as aromatic
compounds, carbonyl compounds, alkenes, and alkynes
in the presence of a metal catalyst.1 We have also
Resu lts a n d Discu ssion
P r ep a r a tion of 2. The 3,4-carboranylene-1,1,2,2-
tetraethyl-1,2-disilacyclobut-3-ene (2) was readily pre-
pared by a method similar to that reported by de Rege.4
Thus, the 1,2-dilithiated carborane5 generated by the
reaction of n-BuLi with o-carborane reacted with 1,2-
dichlorotetraethyldisilane to give 2 in 53% yield (eq 1).
The colorless product 2 was a crystalline solid that was
described the double-silylation reaction of a variety of
unsaturated organic substrates with cyclic bis(silyl)-
metal complexes containing an o-carboranylene.2 Ac-
cordingly, it seemed interesting to investigate the
chemical behavior of the 3,4-carboranylene-1,1,2,2-tet-
raethyl-1,2-disilacyclo-but-3-ene (2) with a carboranyl
† Korea University.
‡ Gyeongsang National University.
§ Kurashiki University of Science and the Arts.
(1) (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. (d) Naka, A.; Hayashi, M.; Okazaki,
S.; Ishikawa, M. Organometallics 1994, 13, 4994. (e) Ishikawa, M.;
Naka, A.; Oshita, J . Organometallics 1993, 12, 4987. (f) Ishikawa, M.;
Naka, A.; Okazaki, S.; Sakamoto, H. Organometallics 1993, 12, 87.
(g) Ishikawa, M.; Okazaki, S.; Naka, A.; Sakamoto, H. Organometallics
1992, 11, 4135. (h) Ishikawa, M.; Naka, A. Synlett. 1995, 794.
(2) (a) Kang, Y.; Lee, J .; Kong Y. K.; Kang, S. O.; Ko, J . Chem.
Commun. 1998, 2343. (b) Kang, Y.; Kang, S. O.; Ko, J . Organometallics
1999, 18, 1818. (c) Kang, Y.; Kang, S. O.; Ko, J . Organometallics 2000,
19, 1216. (d) Kang, Y.; Lee, J .; Kong, Y. K.; Kang, S. O.; Ko, J .
Organometallics 2000, 19, 1722. (e) Kang, Y.; Kim, J .; Kong Y. K.; Lee,
J .; Lee, S. W.; Kang, S. O.; Ko, J . Organometallics 2000, 19, 5026. (f)
Kim, J .; Kang, Y.; Lee, J .; Kong Y. K.; Gong, M. S.; Kang, S. O.; Ko, J .
Organometallics 2001, 20, 937.
relatively stable in air and to brief heating to 110-120
°C. Compound 2 is readily soluble in hexane, toluene,
and THF. The structure of 2, unambiguously estab-
lished by single-crystal X-ray analysis, is shown in
Figure 1. The four C(1), C(2), Si(1), and Si(2) atoms
(3) (a) J emmis, E. D.; Kiran, B. J . Am. Chem. Soc. 1997, 119, 4076.
(b) Ho, D. M.; Cunningham, R. J .; Brewer, J . A.; Bian, N.; J ones, M.
Inorg. Chem. 1995, 34, 5274.
(4) de Rege, F. M.; Kassebaum, J . D.; Scott, B. L.; Abney, K. D.;
Balaich, G. J . Inorg. Chem. 1999, 38, 486.
(5) Grimes, R. N. Carboranes; Academic Press: New York, 1975.
10.1021/om010535g CCC: $20.00 © 2001 American Chemical Society
Publication on Web 11/20/2001

5538 Organometallics, Vol. 20, No. 26, 2001
Song et al.
by reacting H2O with 1,2-bis(chlorodimethylsilyl)carbo-
rane9 or by reacting O2 with the strained disilane.8
Since the C-H bond activation of benzene in the
nickel-1g and platinum-catalyzed1e reaction of 1 took
place at higher temperature, we carried out a similar
reaction of 2 under the same reaction conditions.
However, no products arising from C-H bond activation
were formed. The starting compound 2 was recovered
unchanged. In contrast to the above reactions, the
palladium-catalyzed reaction of 2 in refluxing benzene
for 72 h afforded 1-(diethylphenylsilyl)-2-(diethylsilyl)-
carborane (5) in 38% yield (eq 3). The structure of 5 was
F igu r e 1. X-ray crystal structure of 2 with 50% probability
thermal ellipsoids depicted. Selected bond lengths (Å) and
angles (deg): C(1)-C(2) ) 1.691(7), Si(1)-Si(2) ) 2.344(2),
Si(1)-C(1) ) 1.931(6), Si(2)-C(2) ) 1.934(6), Si(1)-C(3)
) 1.847(7), Si(2)-C(7) ) 1.857(7), Si(1)-C(5) ) 1.889(6),
Si(2)-C(9) ) 1.924(13), C(1)-Si(1)-Si(2) ) 80.3(2), C(2)-
Si(2)-Si(1) ) 99.7(3).
confirmed by spectroscopic analysis as well as elemental
analysis. The 13C NMR spectrum of 5 reveals resonances
at δ 7.62, 7.24, 5.76, and 4.85 ppm, assigned to the two
kinds of ethyl carbons and six resonances in the aryl
region. The 29Si NMR spectrum shows two resonances
at δ -2.74 and -6.46 ppm, arising from the two
nonequivalent silicon atoms. The IR spectrum of 5
shows a strong absorption band at 2096 cm-1, due to
the Si-H stretching frequency.
Rea ction s of 2 w ith Alk yn es. Previously, we re-
ported the nickel-1e, palladium-,1d and platinum-
catalyzed1b reaction of 1 with alkynes to give 5,6-benzo-
1,4-disilacyclohexa-2,5-dienes arising from insertion of
a carbon-carbon triple bond into a silicon-silicon bond
of the starting compound 1. While a Pd complex readily
catalyzed this type of double silylation with 2, Pt and
Ni complexes proved to be much less effective. For
example, the Ni-catalyzed double silylation of 2 led
predominantly to decomposition, and the Pt complex is
not active in the double silylation of alkynes. Thus, the
palladium-catalyzed reaction of 2 with phenylacetylene
afforded 5,6-carboranylene-1,1,4,4-tetraethyl-2-phenyl-
1,4-disilacyclohex-2-ene (6) as colorless crystals in 62%
yield (eq 4). In a similar fashion, the reaction of 2 with
comprising the central skeleton of the molecule are
nearly coplanar. The C(1)-Si(1) bond distance (1.931-
(6) Å) is slightly longer than the typical value for the
carbon-silicon bond (1.88-1.91 Å)6 and is comparable
to that of the 1,2-(1′,1′,2′,2′-tetramethyldisilane-1′,2′)-
carborane.4 The Si(1)-Si(2) bond distance (2.344(2) Å)
is within known values of the Si-Si bond lengths in
analogous complexes.7
The 1H, 13C, and 29Si NMR spectra and the mass
spectrum of 2 were consistent with the structure
determined by X-ray crystallography. The 29Si NMR
chemical shift of 21.68 ppm was downfield shifted from
8.05 ppm for 1.
Oxid a tion , Su lfu r iza tion , a n d C-H Activa tion of
2. From consideration of the reaction conditions, 2 seems
to be less reactive than the strained disilanes.8 However,
2 in toluene is rapidly oxidized in oxygen gas to give
4,5-carboranylene-1,3-disila-2-oxacyclopent-4-ene (3) in
92% yield (eq 2). It is well known that the 1,2-disilacy-
clobutenes are readily oxidized in air, giving 1,3-disila-
2-oxacyclopentenes.1h Under similar conditions, sulfur
is also inserted into the Si-Si bond of 2 to give
4,5-carboranylene-1,3-disila-2-thiacyclopent-4-ene (4) in
82% yield. A similar 4,5-carboranylene-1,1,3,3-tetram-
ethyl-1,3-disila-2-oxacyclopent-4-ene has been prepared
other alkynes such as 1-phenylpropyne, dimethyl acety-
lenedicarboxylate, and 1-hexyne yielded the six-mem-
bered cyclic insertion products. However, compound 2
did not react with the disubstituted acetylenes such as
diphenylacetylene and 3-hexyne under the same condi-
tions. The formation of 6-9 can best be explained by
(6) Beagley, B.; Monaghan, J . J .; Hewitt, T. G. J . Mol. Struct. 1971,
8, 401.
(7) (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.
(8) (a) Barton, T. J .; Kilgour, J . A. J . Am. Chem. Soc. 1976, 98, 7746.
(b) Sakurai, H.; Kobayashi, T.; Nakadaira, Y. J . Organomet. Chem.
1978, 162, C43. (c) Atwell, W. H.; Uhlmann, J . G. J . Organomet. Chem.
1973, 521. (d) Seyferth, D.; Annarelli, D. C.; Vick, S. C. J . Organomet.
Chem. 1984, 272, 123.
(9) Papetti, S.; Heying, T. L. Inorg. Chem. 1963, 2, 1105.

Pd-Catalyzed Double Silylation Reactions
Organometallics, Vol. 20, No. 26, 2001 5539
with the upfield shift for 5,6-benzo-1,4-disilacyclohex-
5-enes which appears in the region from -3 to -18
ppm.1e
Rea ction of 2 w ith 4-Nitr oben za ld eh yd e. As the
metal complex-catalyzed 1,2-double silylation of the
carbonyl groups with cyclic disilanes has been well-
established,1f we attempted the double silylation of
carbonyl compounds such as benzaldehyde, acetone, and
acetophenone with 2. No reactions were observed in all
reactions in the presence of a palladium catalyst.
However, reactive 4-nitrobenzaldehyde readily reacted
with 2 to give the [4+2] cycloadduct (10) in 37% yield
(eq 5).
F igu r e 2. X-ray crystal structure of 6 with 50% probability
thermal ellipsoids depicted. Selected bond lengths (Å) and
angles (deg): Si(1)-C(11) ) 1.859(3), Si(1)-C(1) ) 1.905-
(3), Si(2)-C(12) ) 1.873(3), Si(2)-C(2) ) 1.920(3), C(1)-
C(2) ) 1.691(4), C(11)-C(12) ) 1.355(4), C(12)-C(13) )
1.500(4), C(11)-Si(1)-C(1) ) 108.0(1), C(12)-Si(2)-C(2)
) 108.6(1), C(12)-C(11)-Si(1) ) 130.4(2), C(11)-C(12)-
C(13) ) 119.5(3), C(11)-C(12)-Si(2) ) 124.6(2), C(13)-
C(12)-Si(2) ) 115.9(2).
1
The H NMR spectrum of 10 contained a distinguish-
ing low-field methine resonance (δ 4.95), which was used
to monitor its formation. The 13C NMR spectrum of
product 10 revealed four resonances at δ 7.15, 6.60, 5.56,
and 4.42, attributed to the two nonequivalent ethyl
carbons. The 29Si NMR spectrum of 10 exhibited two
resonances at 9.96 and 0.23 ppm arising from the
nonequivalent silicon atoms. Such a 1,2-double-silyla-
tion reaction of the carbonyl unit has been reported
using a platinum complex as the catalyst with o-bis-
(dimethylsilyl)benzene14 and with a nickel complex as
the catalyst with 1,2-bis(dimethylsilyl)carborane.2e The
insertion of an aldehyde carbonyl group into the Si-Si
bond promoted by a fluoride ion was also noted.15
Rea ction of 2 w ith tr a n s-Cin n a m a ld eh yd e. The
treatment of 2 with 4 equiv of trans-cinnamaldehyde
in the presence of a catalytic amount of Pd(PPh3)4 gave
6,7-carboranylene-1,5-bis(styrenyl)-2,4-dioxa-3,3-diethyl-
3-silacyclohept-6-ene (11) (eq 6). The 1H NMR spectrum
the reaction of the intermediate 4,5-carboranylene-
1,1,3,3-tetraethyl-1-pallada-2,3-disilacyclopent-4-ene with
alkynes.10 Such alkyne insertion reactions have been
effected using palladium and platinum complexes as
catalysts with o-(dimethylsilyl)benzene11 and 1,2-bis-
(dimethylsilyl)carborane.2b-d
To provide the structural information for one of the
newly prepared compounds, a single-crystal X-ray dif-
faction study of the phenylacetylene insertion product
6 was undertaken. The molecular structure of 6 is
shown in Figure 2. The X-ray crystal structure of 6
confirmed the presence of a six-memberd ring comprised
of an o-carboranylene, two silicon atoms, and an unsat-
urated hydrocarbon fragment containing a CdC bond.
The CdC bond length (1.355(4) Å) is slightly longer than
the typical value for the carbon-carbon double bond
(1.317 Å)12 and is comparable to that of the tricyclic
product formed in the reaction between diphenylacety-
lene and tetrakis(dimethylsilyl)benzene13 and 5,6-car-
boranylene-1,1,4,4-tetramethyl-2,3-diphenyl-1,4-disila-
cyclohex-2-ene1c (1.33(2) Å).
1
The H, 13C, and 29Si NMR spectra, the mass spec-
trum, and elemental analyses of compounds 6-9 were
1
consistent with the structure determined for 6. The H
NMR spectrum of 6 showed a low-field resonance at 6.61
ppm due to the olefinic proton. In the olefinic region of
the 13C NMR spectrum of 6, two resonances at 160.42
and 146.69 ppm were present. The 29Si NMR spectrum
of 6 showed two resonances at -4.95 and -6.60 ppm
arising from the nonequivalent silicon atoms, in accord
of 11 exhibits the characteristic methine resonance (δ
5.19) in addition to two resonances at 6.62 and 6.23 ppm
as a doublet of doublets due to the olefinic protons. The
29Si NMR spectrum of our product exhibited a single
resonance at -1.79 ppm. The mass spectrum of the
product showed a molecular ion at m/z 492. As the
(10) Ishikawa, M.; Sakamoto, H.; Okazaki, S.; Naka, A. J . Orga-
nomet. Chem. 1992, 439, 19.
(11) (a) Uchimaru, Y.; Lautenschlager, H.-J .; Wynd, A. J .; Tanaka,
M.; Goto, M. Organometallics 1992, 11, 2639. (b) Tanaka, M.; Uchi-
maru, Y.; Lautenschlager, H.-J . J . Organomet. Chem. 1992, 482, 1. (c)
Tanaka, M.; Uchimaru, Y. Bull. Soc. Chim. Fr. 1992, 129, 667.
(12) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen,
A. G.; Taylor, R. J . Chem. Soc., Perkin Trans. 1987, 1, 51
(13) Uchimaru, Y.; Brandl, P.; Tanaka, M. J . Chem. Soc., Chem.
Commun. 1993, 744.
(14) Uchimaru, Y.; Lautenschlager, H.-J .; Wynd, A. J .; Tanaka, M.;
Goto, M. Organometallics 1992, 11, 2639.
(15) Hiyama, T.; Obayashi, M. Tetrahedron Lett. 1983, 24, 4109.

5540 Organometallics, Vol. 20, No. 26, 2001
Song et al.
perature. The solution of 1,2-dichlorotetraethyldisilane (2.43
g, 10 mmol) in diethyl ether (15 mL) was slowly added to the
reaction mixture at 0 °C. The reaction mixture was warmed
to room temperature and stirred for 3 h. All volatiles were
removed under reduced pressure, followed by extraction of the
residues with n-hexane (30 mL). The extracts were concen-
trated to 15 mL and cooled to -10 °C to furnish 1.68 g (53%)
of colorless crystals of 2. Mp: 100 °C. 1H NMR (CDCl3): δ
1.12-0.96 (m, Et). 13C{1H} NMR (CDCl3): δ 7.69 (CH2), 4.63
(CH3). 29Si NMR (CDCl3): δ 21.68. MS: m/z 314 [M+]. Anal.
Calcd for C10H30B10Si2: C, 38.17; H, 9.60. Found: C, 38.64; H,
9.86.
4,5-Ca bor a n ylen e-1,1,3,3-tetr a eth yl-1,3-d isila -2-oxa cy-
clop en t-4-en e (3). Oxygen gas was bubbled into a solution of
2 (0.1 g, 0.32 mmol) in toluene (20 mL) for 20 min. The solvent
was removed under reduced pressure, yielding a white solid.
The pure product 3 was obtained by crystallization from a
saturated solution of ether at -20 °C in 92% yield. Mp: 43
°C. 1H NMR (CDCl3): δ 1.08-0.82 (m, Et). 13C{1H} NMR
(CDCl3): δ 6.41 (CH2), 5.53 (CH3). MS: m/z 331 [M+]. Anal.
Calcd for C10H30B10OSi2: C, 36.33; H, 9.13. Found: C, 36.88;
H, 9.01.
4,5-Ca bor a n ylen e-1,1,3,3-tetr a eth yl-1,3-d isila -2-th ia cy-
clop en t-4-en e (4). A mixture of 0.1 g (0.32 mmol) of 2 and
0.19 g (3.2 mmol) of ethylene sulfide in toluene (20 mL) was
refluxed for 8 h. The solvent was removed in vacuo, and the
residue was sublimed to give 4 in 82% yield. 1H NMR
(CDCl3): δ 1.01-0.81 (m, Et). 13C{1H} NMR (CDCl3): δ 10.64,
7.22 (Et). MS: m/z 346 [M+]. Anal. Calcd for C10H30B10SSi2:
C, 34.64; H, 8.71. Found: C, 34.48; H, 8.54.
F igu r e 3. X-ray crystal structure of 11 with 50% prob-
ability thermal ellipsoids depicted. Selected bond lengths
(Å) and angle (deg): Si-O(2) ) 1.6552(16), O(1)-C(3) )
1.425(2), O(2)-C(16) ) 1.416(2), C(1)-C(16) ) 1.562(3),
C(1)-C(2) ) 1.701(3), C(2)-C(3) ) 1.555(3), C(3)-C(4) )
1.497(3), C(4)-C(5) ) 1.319(3), C(5)-C(6) ) 1.470(3), O(2)-
Si-O(1) ) 103.52(7), C(3)-O(1)-Si ) 117.35(12), C(16)-
C(1)-C(2) ) 121.17(16), C(3)-C(2)-C(1) ) 122.03(15),
O(1)-C(3)-C(2) ) 111.80(15), C(5)-C(4)-C(3) ) 123.3(2),
C(4)-C(5)-C(6) ) 127.2(6), O(2)-C(16)-C(1) ) 111.21(15),
C(18)-C(17)-C(16) ) 125.3(2), C(17)-C(18)-C(19) ) 125.3-
(2).
structure of the product was not deduced on the basis
of the spectroscopic data, a single-crystal X-ray diffrac-
tion study was undertaken. The molecular structure of
11 is shown in Figure 3. The X-ray study of 11 showed
it to be the insertion product of two carbonyl ligands
into the C-Si bond of 2. The molecule contains a C4-
SiO2 seven-membered ring. Such an insertion of the
carbonyl unit into o-carborane has been observed in the
reaction of the cyclic bis(silyl)platinum complex and
trans-cinnamaldehyde2c in Yamamoto’s work on the
chemoselective addition of o-carborane to aldehyde
groups,14 and in the fluoride-promoted reaction of o-
carborane with aldehydes.15
In conclusion, we have prepared a strained 3,4-
carboranylene-1,1,2,2-tetraethyl-1,2-disilacyclobut-3-
ene (2). In marked contrast to the o-bis(dimethylsilyl)-
carborane, which reacted with a variety of unsaturated
organic substrates in the presence of the Ni and Pt
complexes, compound 2 reacted with a few activated
alkynes and aldehydes only in the presence of the Pd
catalyst to afford the double-silylated products. The
present reaction provides a new route to a novel class
of heterocyclic compounds.
1-(Dieth ylp h en ylsilyl)-2-(d ieth ylsilyl)ca r bor a n e (5). A
mixture of 2 (0.15 g, 0.48 mmol) and Pd(PPh3) (0.027 g) in
4
benzene (15 mL) was heated to reflux for 72 h. The solvent
was removed in vacuo, and the residue was chromatographed
using benzene/hexane (1:2) as the eluent (Rf ) 0.46) to give 5
1
in 38% yield. Mp: 108 °C. H NMR (CDCl3): δ 7.44-7.04 (m,
5H, Ph), 4.30 (quint, 1H, J ) 3.38 Hz, SiH), 1.16-0.82 (m,
20H, Et). 13C{1H} NMR (CDCl3): δ 143.26, 138.64, 134.02,
128.84, 127.74, 127.29, 7.62, 7.24, 5.76, 4.85. 29Si NMR
(CDCl3): δ -2.74, -6.46. IR (KBr pellet; cm-1): 2096. Anal.
Calcd for C16H36B10Si2: C, 47.96; H, 9.04. Found: C, 47.58; H,
8.82.
Rea ction of 2 w ith P h en yla cetylen e (6). A mixture of
0.1 g (0.32 mmol) of 2 and 0.13 g (1.28 mmol, 4 equiv) of
phenylacetylene in the presence of a catalytic amount of Pd-
(PPh3)4 (0.018 g, 5 mol %) in toluene (30 mL) was refluxed for
24 h. The solvent was removed in vacuo, and the residue was
chromatographed using benzene/hexane (1:2) as the eluent (Rf
) 0.8). The first band was crystallized from hexane at -10 °C
to give 5,6-carboranylene-1,1,4,4-tetraethyl-2-phenyl-1,4-disi-
lacyclohex-2-ene (6) as colorless crystals in 62% yield. Mp: 90
°C. 1H NMR (CDCl3): δ 7.36-7.07 (m, 5H, Ph), 6.61(s, 1H,
CH), 1.12-0.85 (m, 20H, Et). 13C{1H} NMR (CDCl3): δ 160.42,
146.69, 142.70, 128.64, 127.45, 127.05, 126.36, 126.02, 68.95,
67.43, 7.66, 7.48, 6.56, 5.90. 29Si NMR (CDCl3): δ -4.95, -6.60.
MS: m/z 416 [M+]. Anal. Calcd for C18H36B10Si2: C, 51.87; H,
8.69. Found: C, 51.62; H, 8.52.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. For the general experimental
procedure see ref 2c. o-Carborane was purchased from the
Katchem, Ltd., and used without purification. All the alkynes,
aldehydes, and ethylenesulfide were purchased from Aldrich.
Pd(PPh3)416 and 1,2-dichlorotetraethyldisilane17 were prepared
according to the literature.
3,4-Car bor an ylen e-1,1,2,2-tetr aeth yl-1,2-disilacyclobu t-
3-en e (2). To a stirred diethyl ether (200 mL) solution of
o-carborane (1.44 g, 10 mmol) at 0 °C was added n-BuLi (20
mmol), and the reaction solution was warmed to room tem-
Rea ction of 2 w ith 1-P h en ylp r op yn e (7). The same
procedure was used as described for 6, except 1-phenylpropyne
was used instead of phenylacetylene. Pure 7 was isolated by
chromatographic workup (eluent: benzene/hexane (1:6), Rf )
1
0.4) in 53% yield. Mp: 98 °C. H NMR (CDCl3): δ 7.37-6.86
(m, 5H, Ph), 1.61 (s, 3H, CH3), 1.11-0.73 (m, 20H, Et). 13C-
{1H} NMR (CDCl3): δ 154.66, 148.40, 142.61, 132.26, 130.76,
128.83, 127.36, 126.51, 67.72, 67.42, 21.12, 7.74, 7.55, 5.62,
5.52. 29Si NMR (CDCl3): δ -5.13, -8.41. MS: m/z 430 [M+].
Anal. Calcd for C19H38B10Si2: C, 52.97; H, 8.88. Found: C,
53.25; H, 9.02.
Rea ction of 2 w ith Dim eth yl Acetylen ed ica r boxyla te
(8). The same procedure was used as described for 6, except
dimethyl acetylenedicarboxylate was used instead of pheny-
(16) Brauer, G. Handbuch der Pra¨parativen Anorganischen Chemie;
Ferdinand Enke Verlag: Stuttgart, 1981; p 2013.
(17) Matsumoto, H.; Motegi, T.; Hasegawa, M.; Nagai, Y. J . Orga-
nomet. Chem. 1977, 142, 149.

Pd-Catalyzed Double Silylation Reactions
Organometallics, Vol. 20, No. 26, 2001 5541
Ta ble 1. Cr ysta l Da ta of 2, 6, a n d 11
lacetylene. Pure 8 was isolated by chromatographic workup
(eluent: ethyl acetate/hexane (1:2), Rf ) 0.9) as a yellow oil in
2
6
11
1
61% yield. H NMR (CDCl3): δ 3.75 (s, 6H, CH3), 1.05-0.98
empirical formula
mol wt
cryst syst
space group
a (Å)
C10H30B10Si2 C18H36B10Si2 C24H36B10O2Si
(m, 20H, Et). 13C{1H} NMR (CDCl3): δ 169.14, 151.91, 66.18,
52.53, 7.25, 6.15. 29Si NMR (CDCl3): δ -3.73. MS: m/z 457
[M+]. Anal. Calcd for C16H36B10O4Si2: C, 42.07; H, 7.93.
Found: C, 41.88; H, 7.74.
314.62
monoclinic
P21/n
416.75
monoclinic
P21/c
492.72
triclinic
P1h
7.5845(9)
16.346(2)
16.3645(16)
9.663(1)
24.421(2)
9.979(1)
10.6814(9)
11.6686(11)
12.4992(12)
75.755(2)
74.570(2)
73.167(2)
1413.0(2)
2
Rea ction of 2 w ith 1-Hexyn e (9). The same procedure
was used as described for 6, except 1-hexyne was used instead
of phenylacetylene. Pure 9 was isolated by chromatographic
workup (eluent: benzene/hexane (1:9), Rf ) 0.4) as a colorless
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V, Å3
90.629(8)
96.281(9)
1
oil in 65% yield. H NMR (CDCl3): δ 6.41 (t, 1H, J HH ) 1.52
2028.6(4)
4
2532.5(5)
4
Hz, dCH), 2.16 (t, 2H, J HH ) 1.52 Hz, dCCH2), 1.46-1.25 (m,
7H, CH2CH2 CH3), 1.06-0.75 (m, 20H, Et). 13C{1H} NMR
(CDCl3): δ 160.19, 156.50, 68.74, 67.81, 39.40, 38.81, 22.62,
14.16, 7.72, 7.51, 6.00, 5.60. 29Si NMR (CDCl3): δ -5.77, -6.95.
MS: m/z 396 [M+]. Anal. Calcd for C16H40B10Si2: C, 48.43; H,
10.15. Found: C, 48.08; H, 10.02.
Z
D(calcd) (g cm-3
F(000)
)
1.030
672
1.093
888
1.158
520
µ (mm-1
)
0.162
0.7107
graphite
ω
0.145
0.7107
graphite
ω
0.105
λ(Mo KR) (Å)
monochromator
scan type
no. of reflns
measd
0.7107
graphite
ω-2θ
Rea ction of 2 w ith 4-Nitr oben za ld eh yd e (10). The same
procedure was used as described for 6, except 4-nitrobenzal-
dehyde was used instead of phenylacetylene. Pure 5,6-carbo-
ranylene-1,1,4,4-tetraethyl-2-oxa-3-(4-nitrobenz-yl)-1,4-disila-
cyclohex-5-ene (10) was isolated by chromatographic workup
(eluent: ethyl acetate/hexane (1:9), Rf ) 0.3) as a colorless
3794
4722
9323
no. of reflns with
1248
3108
6541
I > 2σ(I)
R
Rw
0.0836
0.1947
1.007
0.0574
0.1419
1.042
0.0542
0.1338
1.022
1
crystal in 37% yield. Mp: 181 °C. H NMR (CDCl3): δ 8.21-
goodness of fit
7.34 (m, 5H, Ph), 4.95 (s, 1H, CH), 1.05-0.79 (m, 20H, Et).
13C{1H} NMR (CDCl3): δ 148.41, 129.18, 129.02, 128.37,
127.22, 126.64, 124.84, 124.01, 70.62, 7.15, 6.60, 5.56, 4.42.
29Si NMR (CDCl3): δ 9.96, 0.23. MS: m/z 465 [M+]. Anal. Calcd
for C17H35B10 NO3Si2: C, 43.84; H, 7.56. Found: C, 43.62; H,
7.72.
R ea ct ion of 2 w it h tr a n s-Cin n a m a ld eh yd e (11). The
same procedure was used as described for 6, except trans-
cinnamaldehyde was used instead of phenylacetylene. Pure
6,7-carboranylene-1,5-bis(styrenyl)-2,4-dioxa-3,3-diethyl-3-si-
lacyclohept-6-ene (11) was isolated by chromatographic work-
up (eluent: benzene/hexane (1:4), Rf ) 0.1) as a colorless
crystal in 26% yield. Mp: 68 °C. 1H NMR (CDCl3): δ 7.44-
7.29 (m, 10H, Ph), 6.62 (d, 2H, J HH ) 15.90 Hz, dCH), 6.23
(dd, 2H, J HH ) 15.90 Hz, J HH ) 6.60 Hz, dCH), 5.19 (d, 2H,
J HH ) 6.60 Hz, CH), 1.06-0.78 (m, 10H, Et), 13C{1H} NMR
(CDCl3): δ 139.03, 135.89, 132.03, 128.86, 128.53, 128.00,
127.05, 75.02, 6.39, 2.79. 29Si NMR (CDCl3): δ -1.79. MS: m/z
492 [M+]. Anal. Calcd for C24H36B10O2Si: C, 58.50; H, 7.35.
Found: C, 58.28; H, 7.16.
X-r a y Cr ysta llogr a p h y. Details of the crystal data and a
summary of intensity data collection parameters for 2, 6, and
11 are gave in Table 1. Crystals of 2 and 6 were grown from
hexane at -10 °C, and a crystal of 11 was grown from CH2-
Cl2/hexane. Crystals of 2, 6, and 11 were mounted in thin-
walled glass capillaries and sealed under argon. The data sets
of 2 and 6 were collected on an Enraf CAD 4 automated
diffractometer, and those of 11 on a Siemens P4 diffractometer.
Mo KR radiation (λ ) 0.7107 Å) was used for all structures.
Each structure was solved by the application of direct methods
using the SHELX-96 program and least-squares refinement
using SHELXL-97. All non-hydrogen atoms in compound 2,
6, and 11 were refined anisotropically. All other hydrogen
atoms were included in the calculated positions.
Su p p or tin g In for m a tion Ava ila ble: This material is
available free of charge via the Internet at http://pubs.acs.org.
OM010535G