Angewandte
Communications
Chemie
Hydrosilylation
An Easily Accessed Nickel Nanoparticle Catalyst for Alkene
Hydrosilylation with Tertiary Silanes
Ivan Buslov, Fang Song, and Xile Hu*
Abstract: The first efficient and non-precious nanoparticle
catalyst for alkene hydrosilylation with commercially relevant
tertiary silanes has been developed. The nickel nanoparticle
catalyst was prepared in situ from a simple nickel alkoxide
precatalyst Ni(OtBu)2·xKCl. The catalyst exhibits high activity
for anti-Markovnikov hydrosilylation of unactivated terminal
alkenes and isomerizing hydrosilylation of internal alkenes.
The catalyst can be applied to synthesize a single terminal alkyl
silane from a mixture of internal and terminal alkene isomers,
and to remotely functionalize an internal alkene derived from
a fatty acid.
Compared to the significant progress of base metal-
catalyzed homogeneous alkene hydrosilylation, the develop-
ment of their heterogeneous counterparts falls much behind.
Heterogeneous catalysts are potentially less costly and more
amenable to immobilization and separation. Several hetero-
geneous Pt catalysts have been successfully used for alkene
hydrosilylations.[11] Moreover, a recent study[11d] reopened the
debates[12] on the nature of the active species, homogeneous
or heterogeneous, formed upon activation of Karstedtꢀs
catalysts. However, to our knowledge, there is no prior
report of non-precious metal nanoparticle catalysts capable of
alkene hydrosilylation using tertiary silanes.[13] Herein we
show that nickel nanoparticles catalyze hydrosilylation of
unactivated alkenes with tertiary silanes. The nanoparticles
can be easily accessed from in situ activation of a Ni-
(OtBu)2·xKCl precatalyst by the silane substrate. The pre-
catalyst can be made in one step from stable and readily
available reagents. Not only terminal alkenes are hydro-
silylated with high anti-Markovnikov selectivity, but also
internal alkenes are hydrosilylated through a tandem isomer-
ization–hydrosilylation process to give terminal alkyl silanes.
The catalytic system can be applied to synthesize a single
terminal alkyl silane from a mixture of internal and terminal
alkene isomers, and to remotely functionalize an internal
alkene derived from a fatty acid.
H
ydrosilylation of alkenes is a main method to synthesize
organosilicon compounds, which have broad applications in
synthetic and material chemistry.[1] Platinum-based catalysts
such as Karstedtꢀs[2] and Speierꢀs[3] catalysts are the most
widely used in the industry owing to their stability, high
activity, and broad scope. The high cost and low abundance of
Pt have motivated the development of alternative catalysts
based on Earth-abundant transition metals. While a number
of systems based on Fe,[4] Co,[5] and Ni[6] complexes were
shown to be efficient catalysts for hydrosilylation of alkenes,
many of them are active only when using PhSiH3 and Ph2SiH2
as hydrosilanes. The products of these reactions contain
À
residual Si H bonds, which leads to lower stability and utility
of final products. Tertiary silanes are much more commer-
cially relevant and are widely used to make silicones and
silane coupling reagents. However, they are sterically
demanding and less reactive. Chirik and co-workers showed
that reducing the steric bulk of pyridine diimine (PDI) ligands
enabled the first efficient iron-catalyzed alkene hydrosilyla-
tion using tertiary silanes.[7] This strategy proved successful in
the development of several other Fe- and Co-based catalysts
that hydrosilylated alkenes using tertiary silanes.[4c,8] Never-
theless, these catalysts employ designer ligands which can be
expensive or difficult to make. Although Ni-based catalysts
for alkene hydrosilylation are known,[6,9] only one system was
shown to catalyze hydrosilylation of an unactivated alkene
using a tertiary silane, and its scope was not reported.[10]
We previously reported nickel pincer complexes as active
alkene hydrosilylation catalysts.[6e] However, they were not
efficient when using tertiary silanes. To develop catalysts for
alkene hydrosilylation using tertiary silanes, we screened
a large number of nickel alkoxide complexes with reduced
steric bulk for the reaction of 1-decene with trimethoxysilane
(MeO)3SiH. Certain nickel complexes appeared to lose the
ligands and decompose into black residues during the
reaction; nevertheless, the desired hydrosilylation product
was formed using these complexes. We hypothesized that
these complexes were converted into nickel nanoparticles
upon reaction with silane, which were responsible for the
hydrosilylation activity. We then searched for simpler pre-
cursors of the presumed nickel nanoparticles which contained
no designer ligands. A number of nickel salts including
Ni(OAc)2 (OAc = acetate), Ni(OTf)2 (OTf = trifluorometha-
nesulfonate), Ni(acac)2 (acac = acetylacetonate), and Ni-
(OH)2 were tested, but the best yield, obtained using Ni-
(acac)2, was only 23% (Supporting Information, Table S1). A
Ni0 source, Ni(COD)2, was also ineffective, giving a yield of
5%. The use of Ni alkoxides, however, led to much higher
yields. While a method employing anhydrous NiCl2 was
reported for the synthesis of Ni(OtBu)2,[14] we chose to
prepare it by reaction of a soluble nickel source, Ni-
[*] I. Buslov, Dr. F. Song, Prof. Dr. X. L. Hu
Laboratory of Inorganic Synthesis and Catalysis
Institute of Chemical Sciences and Engineering
Ecole Polytechnique Fꢀdꢀrale de Lausanne (EPFL)
ISCI-LSCI, BCH 3305, 1015 Lausanne (Switzerland)
E-mail: xile.hu@epfl.ch
Supporting information for this article can be found under:
(TMEDA)Cl2
(TMEDA = tetramethylethylenediamine)
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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