Synthesis of dialkoxydiphenylsilanes via the rhodium-catalyzed hydrosilylation of aldehydes

Article abstract of DOI:10.1016/j.tetlet.2019.151101

The commercially available rhodium(I) complex [RhCl(CO)₂]₂ (1) was shown to be an effective catalyst for the reduction of carbonyls with organosilanes under mild conditions. This study focusses on the hydrosilylation of aldehydes with diphenylsilane leading to the isolation of a series of dialkoxydiphenylsilanes with low catalytic loading of complex 1.

Full text of DOI:10.1016/j.tetlet.2019.151101

Tetrahedron Letters 60 (2019) 151101
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Tetrahedron Letters
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Synthesis of dialkoxydiphenylsilanes via the rhodium-catalyzed
hydrosilylation of aldehydes
⇑
Christophe Nogues, Gilles Argouarch
ISCR – UMR 6226, Univ Rennes, CNRS, F-35000 Rennes, France
a r t i c l e i n f o
a b s t r a c t
Article history:
The commercially available rhodium(I) complex [RhCl(CO)2]2 (1) was shown to be an effective catalyst for
the reduction of carbonyls with organosilanes under mild conditions. This study focusses on the hydrosi-
lylation of aldehydes with diphenylsilane leading to the isolation of a series of dialkoxydiphenylsilanes
with low catalytic loading of complex 1.
Received 14 June 2019
Revised 23 August 2019
Accepted 30 August 2019
Available online 31 August 2019
Ó 2019 Elsevier Ltd. All rights reserved.
Keywords:
Hydrosilylation
Rhodium
Silanes
Silyl acetals
Introduction
poor regioselectivity [8], whereas the carbonylation of enamines
via their reaction with silanes under a pressure of CO (50 atm) pro-
The chlorodicarbonylrhodium(I) dimer [Rh(
l
Cl)(CO)2]2 (1) has
vided an efficient route to various a-(siloxymethylene)amines [9].
been extensively used in catalysis, and aside from its role as a pre-
cursor of a plethora of other catalytic species, this commercially
available compound has served directly in many important
catalytic processes. Foremost, complex 1 is a well-known active
catalyst in carbocyclization reactions of polyunsaturated hydrocar-
bons; a topic that has recently led to significant achievements [1].
Indeed these cascade cycloadditions (or cycloisomerizations) cat-
alyzed by 1 can give access to complex polycyclic systems which
are key intermediates in the total synthesis of important fused-ring
natural products [1a,g,m,n]. Other cycloaddition reactions pro-
moted by 1 involving the participation of a functional group were
also described, and have allowed the construction of diverse O- and
N-heterocycles [2]. In addition, the ready-to-use catalyst 1 has
been utilized in miscellaneous synthetic transformations, includ-
ing cross-coupling reactions such as the direct arylation of N-
heteroaromatic substrates [3], Claisen rearrangements of propargyl
vinyl ethers [4], allylic alkylations of allylic carbonates [5], and the
Narasaka desilylation-acylation coupling [6]. Several studies have
also reported the ring opening of strained rings such as epoxides
or cyclopropanes mediated by 1 [7].
In 2018, the synthesis of b-silylated (Z)-enamides was achieved via
the hydrosilylation of internal ynamides with bulky silanes as reac-
tants [10]. Very recently, we have disclosed that complex 1 is also
an efficient catalyst for the deoxygenation of ketones to alkanes in
the presence of hydrosilanes [11]. Finally, [RhCl(CO)2]2 was used
for the catalytic hydrolysis of silanes to generate silanols and dihy-
drogen [12].
Over the years, the rhodium-catalyzed hydrosilylation of car-
bonyl compounds has been extensively studied and has emerged
as a classical method for the synthesis of alcohols [13]. Inspired
by these studies and in line with our interest in utilising metal car-
bonyls in catalysis [14], we present herein the catalytic properties
of 1 in the hydrosilylation of aldehydes which has resulted in the
development of a new method for the synthesis of dialkoxy-
diphenylsilane derivatives.
Results and discussion
Initial experiments exploring the catalytic performance of 1 in
the reduction of carbonyls were carried out with 4-bromoben-
zaldehyde (2a) as the model substrate (Table 1). In the presence
of HSiEt3 as the hydride source and with a catalytic loading of
1 mol%, several solvents were screened (Table 1, entries 1–5). Chlo-
rinated solvents were clearly the best suited since full conversions
of 2a were only reached in CHCl3 and CH2Cl2 over 12 h at room
temperature. Other common hydrosilanes were then tested in
On the other hand, very little has been reported regarding the
catalytic ability of 1 in the presence of hydrosilanes. In 1992, the
hydrosilylation of vinyl acetate was briefly described and showed
⇑
Corresponding author.
E-mail address: gilles.argouarch@univ-rennes1.fr (G. Argouarch).
https://doi.org/10.1016/j.tetlet.2019.151101
0040-4039/Ó 2019 Elsevier Ltd. All rights reserved.

2
C. Nogues, G. Argouarch / Tetrahedron Letters 60 (2019) 151101
Table 1
Hydrosilylation of 4-bromobenzaldehyde (2a) catalyzed by 1.
Entry
Solvent
Silane
Conversiona (%)
1
THF
HSiEt3
12
2
3
4
5
6
7
8
9
CH3NO2
CH3CN
CHCl3
HSiEt3
HSiEt3
HSiEt3
HSiEt3
(EtO)2MeSiH
(MeO)2MeSiH
PMHS
PhSiH3
Ph3SiH
3
traces
>99
>99
50
54
95
>99
>99
>99
>99
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
10
11
12b
Ph2SiH2
Ph2SiH2
a
Conversions were determined by 1H NMR spectroscopy after evaporation of the crude products.
With 0.1 mol% of 1.
b
Table 2
Synthesis of dialkoxydiphenylsilanes 3 via the hydrosilylation of aldehydes with Ph2SiH2 catalyzed by 1.a,b
a
Reagents and conditions: aldehyde (1.18 mmol), diphenylsilane (0.54 mmol), complex 1 (0.1 mol%, based on the aldehyde), CH2Cl2 (3 mL), room
temperature, 12 h, under argon.
b
Isolated yield.

C. Nogues, G. Argouarch / Tetrahedron Letters 60 (2019) 151101
3
CH2Cl2. Conversions were around 50% with dialkoxymethylsilanes,
whereas polymethylhydrosiloxane (PMHS) gave a good conversion
of 95% (Table 1, entries 6–8).
course to further enhance complex 1 as a reliable commercial tool
for catalysis.
The phenylated silanes PhSiH3, Ph3SiH, and Ph2SiH2 were all
highly effective in the hydrosilylation of 2a despite their rather dif-
ferent reactivities (Table 1, entries 9–11). Interestingly, decreasing
the catalytic amount of 1 to 0.1 mol% with Ph2SiH2 had no effect on
the reaction (Table 1, entry 12).
Acknowledgement
We thank Université de Rennes 1 and CNRS for financial
support.
As previously noted, in most studies on the hydrosilylation of
aldehydes or ketones, the hydrosilylated adducts are generally
converted into the corresponding alcohols, either by in situ hydrol-
ysis in protic media or during aqueous work-up of the silyl ether
intermediates. In an alternative approach motivated by atom econ-
omy concerns, the hydrosilylation of aldehydes catalyzed by 1 was
further investigated with the aim of isolating the alkoxysilanes,
which can be valuable commodity reagents [15], rather than their
alcohol derivatives. The dihydrosilane Ph2SiH2 was used as the lim-
iting reagent with various aldehydes in a slight excess (2.2 equiv.)
according to the reaction conditions depicted in entry 12 of Table 1.
Following this procedure, a series of dialkoxydiphenylsilanes 3
were obtained successfully (Table 2).
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tetlet.2019.151101.
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