Angewandte
Chemie
DOI: 10.1002/anie.201300988
Heterogeneous Catalysis
Heterogeneously Catalyzed Aerobic Cross-Dehydrogenative Coupling
of Terminal Alkynes and Monohydrosilanes by Gold Supported on
OMS-2**
Kazuya Yamaguchi, Ye Wang, Takamichi Oishi, Yoshiyuki Kuroda, and Noritaka Mizuno*
Alkynylsilane derivatives are an important class of com-
pounds and have been used not only as versatile alkynyl
nucleophiles for common organic synthesis but also as silicon-
protected intermediates for olygo-yne polymers, silylene–
acetylene copolymers, and acetylene-bridged organometallic
complexes.[1] Up to the present, the vast majority have
commonly used metal–acetylides and halosilanes (or pseudo-
halosilanes) for synthesis of alkynylsilanes; that is, silylation
has been performed by pre-functionalization of terminal
alkynes with alkyl lithium or Grignard reagents to form
metal–acetylide species, followed by coupling with halosi-
lanes.[2] However, this antiquated silylation has shortcomings
of 1) multi-step procedures with stoichiometric reagents,
2) inevitable formation of large amounts of byproducts
during the pre-functionalization step as well as the coupling,
and 3) use of toxic halosilanes and moisture-sensitive
reagents. Thus, the development of efficient catalytic proce-
dures instead of the above-mentioned stoichiometric ones,
that is, the direct use of terminal alkynes without pre-
activation and the replacement of halosilanes with hydro-
silanes, is an important subject. If the coupling could be
performed with recoverable and reusable heterogeneous
catalysts, it would be more desirable from the standpoint of
green chemistry.[3]
(TMEDA = N,N,N’,N’-tetraethylenediamine),[5b]
M(h2-
Ph2CNPh)(hmpa)3 (M = Yb[5c] or Ca,[5d] hmpa = hexamethyl-
phosphoramide), LiAlH4,[5e] and Zn(OTf)2/pyridine (Tf =
SO2CF3).[5f] These procedures typically require additives to
attain high yields of desired alkynylsilanes, and the recovery
and reuse of the catalysts are very difficult.[5] Although
[6b]
MgO[6a] and KNH2/Al2O3 can catalyze the cross-dehydro-
genative coupling, the scope of both terminal alkynes and
hydrosilanes is quite limited; for example, the reaction of
ethynylbenzene hardly proceeds with KNH2/Al2O3.[6b] There-
fore, efficient catalytic systems with widely usable and
reusable heterogeneous catalysts have never been reported
to date, to the best of our knowledge.
Herein, we demonstrate for the first time that gold
supported on a cryptomelane-type manganese oxide-based
octahedral molecular sieve OMS-2[7] (Au/OMS-2, average
particle size of gold: 4.5 nm, Figure S1, see the Supporting
Information for the preparation) can act as an efficient
reusable heterogeneous catalyst for cross-dehydrogenative
coupling of terminal alkynes and monohydrosilanes using O2
as a terminal oxidant [Eq. (1)]. Various kinds of structurally
Metal-catalyzed cross-dehydrogenative coupling repre-
sents the next generation of cross-coupling and is now
emerging as an important reaction in organic synthesis.[4]
diverse terminal alkynes (including acetylene) and monohy-
drosilanes can be applied to the present coupling, affording
the corresponding alkynylsilanes in moderate to high yields.
Initially, the cross-dehydrogenative coupling of ethynyl-
benzene (1a) and triethylsilane (2a, 1.1 equivalents with
respect to 1a) was carried out in the presence of catalytic
amounts of various kinds of supported metal catalysts (e.g.,
gold, palladium, platinum, ruthenium, rhodium, and copper,
approximately 2 mol% with respect to 1a; Table S1). The
reaction was performed at 808C under 1 atm of O2 with slow
addition of 2a (see the Experimental Section in the Support-
ing Information). Under the present conditions, the reaction
did not proceed at all in the absence of the catalysts or the
presence of OMS-2 alone. Only the gold catalyst gave the
desired alkynylsilane, triethyl(phenylethynyl)silane (3aa). No
reaction proceeded in the presence of platinum, ruthenium,
and rhodium catalysts. When using the copper catalyst, only
the alkyne–alkyne homocoupling product of 1,4-diphenylbu-
tadiyne was obtained.[8] Among catalyst supports examined,
OMS-2 showed the highest selectivity to 3aa (Table S2, see
the latter part). Thus, gold supported on OMS-2 (Au/OMS-2)
was the best catalyst; for example, when the cross-dehydro-
genative coupling was carried out under the conditions
ꢀ
ꢀ
Cross-dehydrogenative coupling can construct C C, C X,
ꢀ
and X X bonds (X = heteroatoms) through direct activation
ꢀ
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of C H and/or X H bonds, which can avoid pre-functional-
ization of substrates and formation of vast amounts of
byproducts.[4] With regard to cross-dehydrogenative coupling
of terminal alkynes and hydrosilanes, to date there have been
several homogeneously catalyzed procedures using metal
salts and complexes such as H2PtCl6/I2,[5a] CuCl/TMEDA
[*] Dr. K. Yamaguchi, Dr. Y. Wang, T. Oishi, Dr. Y. Kuroda,
Prof. Dr. N. Mizuno
Department of Applied Chemistry, School of Engineering
The University of Tokyo
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)
E-mail: tmizuno@mail.ecc.u-tokyo.ac.jp
[**] We thank S. Itagaki and X. Jin (The University of Tokyo) for their help
with preliminary experiments and discussion. This work was
supported in part by the Grants-in-Aid for Scientific Researches
from the Ministry of Education, Culture, Sports, Science and
Technology.
Supporting information for this article is available on the WWW
Angew. Chem. Int. Ed. 2013, 52, 5627 –5630
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5627