Tetrahedron Letters
Selective catalytic monoreduction of dichlorooligosilanes
with Grignard reagents
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Ken-ichiro Kanno , Yuka Niwayama, Soichiro Kyushin
Division of Molecular Science, Faculty of Science and Technology, Gunma University, Kiryu, Gunma 376-8515, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Transition metal-catalyzed monoreduction of dichlorooligosilanes with Grignard reagents is reported.
Among the examined catalysts, group 4 metal chlorides such as TiCl4 and Cp2TiCl2 gave the highest reac-
tivity and good selectivity. The reducing power is effectively controlled by changing the catalysts and
Grignard reagents to achieve sufficient selectivity depending on the oligosilane substrates.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 14 August 2013
Revised 5 October 2013
Accepted 10 October 2013
Available online 17 October 2013
Keywords:
Oligosilane
Monoreduction
Grignard reagent
Transition metal catalyst
Studies on oligosilanes with unique properties and structures
are one of the most rapidly developing research areas in organosil-
icon chemistry. For example, linear oligosilanes with fixed confor-
mations,1 push–pull oligosilanes,2 polysilane dendrimers,3 and
organosilicon clusters4–15 have recently been reported. To con-
struct these oligosilanes, the design of appropriate organosilicon
building blocks is very important.
R
R(')
Cl Si Si
R(')
R
R
+ R'2HS iCl path a
or
R'2HSiLi + R2SiCl2
XR2SiLi
path b
H
Cl Si Si Cl
R
R
R
Scheme 1. Methodologies for the synthesis of 1-chloro-2-hydrodisilanes.
1-Chloro-2-hydrodisilanes are simple but versatile organosil-
icon building blocks because two different groups can be intro-
duced to the chlorosilane and hydrosilane moieties. In some
special cases, 1-chloro-2-hydrodisilanes have been reported to be
formed by silylene insertion to chlorohydrosilanes16 and by addi-
tion of hydrogen chloride to disilenes.17,18 More commonly, 1-
chloro-2-hydrodisilanes can be synthesized by the reaction of
(diethylamino)silyllithium with chlorohydrosilane followed by
deaminochlorination19 and the reaction of hydrosilyllithium with
dichlorosilane16a,20 (Scheme 1, path a). This method has usefully
been used in the synthesis of 1-chloro-2-hydrodisilanes with differ-
ent R and R0 groups at the 1,1- and 2,2-positions, respectively.19,20
For the synthesis of more simple 1-chloro-2-hydrodisilanes such
as 1-chloro-2-hydro-1,1,2,2-tetramethyldisilane, selective monore-
duction of readily available 1,2-dichlorodisilanes is a more desirable
way (Scheme 1, path b). However, the desymmetrization of sym-
metrically substituted disilanes is not easy. For example, the reduc-
tion of 1,2-dichloro-1,1,2,2-tetramethyldisilane (1) with lithium
aluminum hydride does not give 1-chloro-2-hydro-1,1,2,2-tetra-
methyldisilane (2) selectively.21 Important progress in solving this
problem was made by Roewer and co-workers.22 They reduced
1,3-dichloro-1,1,2,2,3,3-hexamethyltrisilane
with
tributyltin
hydride in the presence of a catalytic amount of tetrabutylphospho-
nium iodide and obtained 1-chloro-3-hydro-1,1,2,2,3,3-hexameth-
yltrisilane in 67% yield together with the starting compound and
1,3-dihydro-1,1,2,2,3,3-hexamethyltrisilane.22 Improvement of this
method would lead to a practical synthetic way to 1-chloro-2-
hydrodisilanes and their homologs. Another desymmetrization is
the monochlorination of 1,2-dihydrodisilanes. Ishikawa, Kunai,
Ohshita, and co-workers have reported selective monochlorination
of 1,2-dihydrodisilanes with copper salts to give the corresponding
1-chloro-2-hydrodisilanes.23
We report herein the transition metal-catalyzed reduction of
1,2-dichlorodisilanes with Grignard reagents. Although this reduc-
tion method has been reported for several decades,24 the applica-
tion was limited only to monosilanes. We found that the
monoreduction of dichlorodisilanes by this method gives 1-
chloro-2-hydrodisilanes selectively without SiꢀSi bond breaking.
We also applied this method to longer dichlorooligosilanes.
A typical experimental procedure is as follows (Scheme 2). A
solution of BuMgCl (3.2 equiv to disilane 3) in diethyl ether was
added dropwise to a solution of 1,2-dichloro-1,1,2,2-tetraisopropyl-
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Corresponding authors. Tel.: +81 277 30 1292; fax: +81 277 30 1291 (K. Kanno);
tel.: +81 277 30 1290; fax: +81 277 30 1291 (S. Kyushin).
(S. Kyushin).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.