Stable bis(silyl)nickel complexes with o-carboranyl unit: A facile double silylation of alkynes and alkenes

Article abstract of DOI:10.1039/a806457a

The reaction of o-bis(dimethylsilyl)carborane with Ni(PEt₃)₄ in pentane affords the reactive intermediate, [o-(SiMe₂)₂C₂B₁₀H ₁₀]Ni(PEt₃)₂ 2; the facile double silylation of alkynes catalyzed by 2 is reported.

Full text of DOI:10.1039/a806457a

Stable bis(silyl)nickel complexes with o-carboranyl unit: a facile double
silylation of alkynes and alkenes
Youngjin Kang,a Junghyun Lee,b Young Kun Kong,b Sang Ook Kang,*a and Jaejung Ko*a
a Department of Chemistry, Korea University, Chochiwon, Chungnam 339-700, Korea. E-mail: jko@tiger.korea.ac.kr
b Department of Chemistry, Kyunggi University, Suwon, Kyunggido 440-760, Korea
Received (in Cambridge, UK) 17th August 1998, Accepted 15th September 1998
The reaction of o-bis(dimethylsilyl)carborane with Ni(PEt3)4
was quite sensitive to the reaction conditions. When the same
reaction was carried out at higher temperature (70–75 °C), the
major component was identified as the acetylene cyclotrimer-
ization product 4 (Scheme 1), which has been characterized by
spectroscopic techniques.
in
pentane
affords
the
reactive
intermediate,
[o-(SiMe2)2C2B10H10]Ni(PEt3)2 2; the facile double silylation
of alkynes catalyzed by 2 is reported.
The double silylation of unsaturated organic substrates cata-
lyzed by group 10 metals has been well documented for two
decades.1 Nickel complexes, in particular, provide excellent
catalysts for the transformation of silicon-containing linear
compounds. Cyclic bis(silyl)nickel complexes have been impli-
cated as important intermediates in the nickel-catalyzed double
silylation of arenes,3 alkynes,4 alkenes5 and aldehydes.6
However, the intermediates have not been isolated due to their
instability. We now describe (i) the isolation of the reactive
intermediate cyclic bis(silyl)nickel compound with a bulky
o-carborane unit; (ii) the facile double silylation of alkynes
catalyzed by the intermediate under mild conditions; and (iii)
the double silylation of alkenes by the stoichiometric reaction
with the intermediate.
Addition of 1.2 equiv. of o-bis(dimethylsilyl)carborane,
prepared from 1,2-Li2C2B10H10 and 2 equiv. of SiMe2ClH, to
Ni(PEt3)4 in pentane at 25 °C gave a dark red solution,
concomitant with the evolution of gas. Standard workup and
crystallization from toluene–pentane gave [o-(SiMe2)2C2
B10H10]Ni(PEt3)2 2 as a spectroscopically pure, dark red
crystalline solid sensitive to air and stable during brief heating
to 100–110 °C in 86% yield [eqn. (1)].† The unusual thermal
When hex-1-yne is employed as a terminal alkyne in the
reaction with 1 under the same conditions, the five-membered
disilyl ring compound 5 is isolated as a colorless liquid in 71%
yield. All the spectral data of 5 was consistent with the proposed
formulation.
The reaction of 2 with 1 equiv. of styrene takes place at a
higher temperature (80 °C) and affords a moderate yield of the
five-membered disilyl ring compound 6 (Scheme 2). A key
feature in the 1H NMR spectrum of 6 includes a singlet at d 7.71
assigned to the vinyl proton. A characteristic low frequency 13
C
NMR resonance at d 139.75 provides evidence for a tethered
carbon atom of the two silicon moieties. The structure of 6 has
been determined by X-ray crystallography.‡ Such formation of
the disilyl ring compound has been observed during the nickel-
catalyzed reaction of benzo-disilacyclobutene with styrene.5
Treatment of 2 with 1 equiv. of 1,1-diphenyl-ethylene in toluene
at 80 °C resulted in a brown solution from which the five-
membered disilyl ring compound 7 was isolated in a yield of
Me2
Me2
Si
Si H
PEt3
PEt3
Ni(PEt3)4
Ni
(1)
Si
Me2
Si H
Me2
1
2
stability of the nickel bis(silyl) compound is attributed to the
advantageous properties of the carboranyl unit, including
electronic and steric effect.
1
The H, 13C, 31P and 29Si NMR spectra for 2 support the
proposed structure. In particular, the 29Si NMR chemical shift
of d 43.19 as a triplet (JSi–P(cis) 40.11 Hz) resembles the
literature value reported for the cis-NiSi2PC complex.7 The
structure of 2 was unambiguously established by a single-
crystal X-ray analysis (Fig. 1).‡ Complex 2 has a distorted
tetrahedral geometry with the dihedral angle between P(1)–Ni–
P(2) and Si(1)–Ni–Si(2) being 86.03°. Such bis(silyl)nickel
complexes are rare as indicated by a search of the Cambridge
Data Base which revealed only a few previous examples.8 As
expected, the average Ni–Si bond length [2.2424(9) Å] is
slightly longer than that of 2.171(3) Å in [(m-Cl)2Ni2(SiCl3)4]
[(CMe3)2C5H3NH]2.8 The Ni–P bond distance [2.2305(8) Å] is
consistent with those observed in other phosphine nickel
compounds.9
Fig. 1 Molecular structure of 2 showing the atom numbering scheme.
Selected distances (Å) and angles (°): Ni(1)–P(1) 2.2265(8), Ni(1)–P(2)
2.2346(8), Ni(1)–Si(1) 2.2371(9), Ni(1)–Si(2) 2.2477(9), Si(1)–C(1B)
1.941(3), Si(2)–C(2B) 1.940(3), C(1B)–C(2B) 1.669(4); P(1)–Ni(1)–P(2)
101.95(3), Si(1)–Ni(1)–Si(2) 83.69(3), P(1)–Ni(1)–Si(1) 96.06(3), P(2)–
Ni(1)–Si(1) 140.35(4).
Compound 2 was found to be a good reactive intermediate for
the double silylation reaction. The reaction of o-bis(dimethyl-
silyl)carborane 1 with 1-phenylprop-1-yne (1 equiv.) in the
presence of a catalytic amount of 2 (0.03 equiv.) for 6 h afforded
the double-silylated product 3 in 94% (GC) yield. The reaction
Chem. Commun., 1998, 2343–2344
2343

Me2
Si
resonance at d 49.87 provides evidence for the tethered carbon
atom of the two silicon moieties.
PEt3
+ RC CR′
PEt3
Ni
In summary, we have isolated the reactive intermediate, the
cyclic bis(silyl) nickel complex, which reacts with unsaturated
organic substrates such as an alkyne and alkene, generating a
new class of heterocyclic compounds. The intermediate 2 is
quite reactive and readily attacked by a variety of organic
substrates. This potential has been further exploited in a series
of novel chemical transformations with this system.
We are grateful to KOSEF for the generous financial
support.
Si
Me2
i
R = Ph, R′ = Me
R = C4H9, R′ = H
ii
Me2
Si
Me2
Si
Me
Ph
H
Notes and references
C
C
† Experimental procedure for 2: compound 1 (0.48 g, 1.85 mmol) in 20 ml
of pentane was added to a stirred solution of Ni(PEt3)4 (0.98 g, 1.85 mmol)
in 20 ml of pentane pentane at 220 °C. The solution was warmed to room
temperature for 2 h. The solution was filtered. The residue was dissolved in
toluene (20 ml) and this solution was covered with a layer of a pentane (20
ml) at 215 °C. Dark red crystals of 2 formed over a period of several days
(0.88 g, 86% yield). 1H NMR (C6D6): d 1.13 (dq, JHH 5.6, JHP 6.4 Hz, CH2),
0.63 (dt, JHH 5.6 Hz, JHP 14.2 Hz, CH3), 0.42(s, SiCH3). 13C{1H} NMR
(C6D6): d 71.08, 17.05 (d, JCP 16.64 Hz, CH2), 6.737 (s, CH3), 4.105 (s,
SiCH3). 31P{1H} NMR (C6D6) : d 5.58. 29Si NMR(C6D6) : d 43.19 (t, JSiP
40.11 Hz).
C4H9
Si
Si
Me2
Me2
5
3
+
Ph
Me
Ph
Me
Ph
Me
‡ Crystal data: 2: C18H52B10NiP2Si2, M = 553.53, monoclinic, space group
P21/n, a = 9.4833(6), b = 19.2061(13), c = 16.8724(10) Å, b = 93.029(2),
4
V = 3068.8(3) Å3, Z = 4, Dc = 1.198 g cm23, m(Mo-Ka) = 0.823 mm21
,
Scheme 1 Reagents and conditions: i, PhCCMe (1 equiv.), 1 (1 equiv.), 2
(0.03 equiv.), toluene, 25 °C, 94%; ii, HCCC4H9 (1 equiv.), 1 (1 equiv.), 2
(0.03 equiv.), toluene, 25 °C, 71%.
6498 reflections observed [I > 2s(I) ], 298 parameters, largest difference
peak 0.401 e Å23. final R, Rw on [I > 2s(I)] data were 0.0545, 0.1072,
goodness of fit on F2 = 1.083.
7: C14H28B10Si2, M = 360.64, monoclinic, space group P21/n, a =
9.6874(4), b = 18.2763(15), c = 12.7310(7) Å, b = 106.587(4)°, V =
2160.2(2) Å3, Z = 4, Dc = 1.109 g cm23, m(Mo-Ka) = 0.160 mm21, 4239
reflections observed [I > 2s(I)], 255 parameters, largest difference peak
0.243 e Å3, final R, Rw on [I > 2s(I)] data were 0.0506, 0.1316, goodness
of fit on F2 = 0.967. CCDC 182/1017.
Me2
Si
PEt3
PEt3
Ni
Si
Me2
1 H. K. Sharma and K. H. Pannell, Chem. Rev., 1995, 95, 1351; H.
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ii
i
Me2
Si
Me2
Si
H
CHCHPh2
C
C
Ph
Si
Me2
Si
Me2
5 M. Ishikawa, S. Okazaki, A. Naka, A. Tachibana, S. Kawauchi and T.
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6
7
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Scheme 2 Reagents and conditions: i, PhCHCH2 (1 equiv.), 2 (1 equiv.),
toluene, 80 °C, 84%; ii, Ph2CCH2 (1 equiv.), 2 (1 equiv.), toluene, 80 °C,
74%.
8 M. M. Brezinski, J. Schneider, L. J. Radonovich and K. J. Klabunde,
Inorg. Chem., 1989, 28, 2414.
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74%. The formulation of 7 was confirmed by a spectrometric
analysis. The mass spectrum of the product showed a molecular
ion at m/z 440.
Two doublets (d 3.93, 1.81) in the 1H NMR spectrum of 7 are
assigned to the methine protons. A low-frequency 13C NMR
Communication 8/06457A
2344
Chem Commun., 1998