Communications
DOI: 10.1002/anie.201105639
Hydrosilylation
Synthesis of a Phosphine-Stabilized Silicon(II) Hydride and Its
Addition to Olefins: A Catalyst-Free Hydrosilylation Reaction**
Ricardo Rodriguez, David Gau, Yohan Contie, Tsuyoshi Kato,* Nathalie Saffon-Merceron, and
Antoine Baceiredo*
À
Hydrosilanes (R3Si H) are powerful chemical tools and are
often used as hydride donors or as reducing agents owing to
the labile silicon–hydrogen bond, which has a significant
À
base-stabilized three-coordinate silicon(II) hydride remains
elusive,[19] although the corresponding heavier germanium
and tin analogues have already been synthesized.[20] Herein,
we present the synthesis and reactivity of the first stable and
negative polarization toward the hydrogen atom (Sid+
H
dÀ).[1]
Particularly, transition-metal-catalyzed addition of silicon
hydrides to unsaturated substrates such as olefins or
ketones—the hydrosilylation reaction—is one of the most
important reactions in synthetic chemistry.[2] Furthermore,
the versatile reactivity of hydrosilanes also allows for their use
as precursors of various highly reactive intermediates, such as
silylium cations,[3–5] silyl radicals,[6] and silylenes.[7]
isolable phosphine-stabilized silicon(II) hydrides
(Scheme 1).
2
Although a broad range of tetravalent hydrosilanes are
known, divalent species (silylenes) with a terminal hydride
are highly reactive, and their chemistry is very poorly
developed. Indeed, only a few stable and isolable silicon(II)
hydride species are known, and most of them are stabilized
transition-metal complexes.[8] Very recently stable bis-adducts
(Lewis acid)(Lewis base)SiIIH I, have also been reported.[9]
Scheme 1. The synthesis of phosphine-stabilized silicon(II) hydride 2.
The phosphine-stabilized silicon(II) hydrides 2 were
readily prepared by reduction of the corresponding dichloro-
silane derivatives 1 using magnesium metal and were isolated
as pale yellow crystals (70% (2a), 79% (2b)). The silicon(II)
hydride 2a appeared to be highly reactive, but it is thermally
robust. Indeed, no degradation of 2a was observed after
heating a toluene solution under argon at 1108C for several
hours. In the 31P NMR spectrum, derivative 2a displays two
singlet signals (d = 91.2 and 90.4 ppm), in agreement with the
presence of two diastereomers (60:40), as expected for this
type of phosphonium silaylide.[17] In the 29Si NMR spectrum
two doublets were observed in the same ratio, both having a
typically large phosphorus–silicon coupling constant (d =
Base-stabilized silylenes II have attracted much attention
because they are thermally stable and they keep their
reactivity as SiII species.[10–15] The efficiency of this method-
ology has been well demonstrated by the isolation of
silicon(II) halides (DSiX2, X = Cl, Br) as N-heterocyclic
carbene complexes and their use in molecular silicon(II)
chemistry.[15a,16] We also recently reported the synthesis of a
stable phosphine-stabilized silylene III (Dipp = 2,6-
iPr2C6H3),[17] which displays a unique ability to reversibly
react with ethylene gas.[18] However, the synthesis of isolable
À44.8 ppm (1JSiP = 143.2 Hz) and À38.0 ppm (1JSiP
=
140.1 Hz)), thus indicating a direct silicon–phosphorus inter-
action. The signals corresponding to the terminal hydride
1
appear as doublets in the H NMR spectrum at a somewhat
lower field (d = 5.99 ppm (2JPH = 3.3 Hz) and 5.76 ppm (2JPH
=
2.9 Hz)). The 29Si satellites (ca. 4.7%) for the terminal
hydrogen atoms appear as a doublet of doublets with a
large silicon–hydrogen coupling constant (1JH–Si = 85.1 and
85.7 Hz), which indicates a direct silicon–hydrogen bond in
2a. However, this value is much smaller than those observed
for tetravalent silicon hydrides (150–380 Hz)[21] or for silicon-
(II) species stabilized by the push–pull complexation system I
(235 Hz).[9]
[*] Dr. R. Rodriguez, Dr. D. Gau, Y. Contie, T. Kato, A. Baceiredo
Universitꢀ de Toulouse, UPS, and CNRS
LHFA UMR 5069, F-31062 Toulouse (France)
E-mail: baceired@chimie.ups-tlse.fr
Dr. N. Saffon-Merceron
The molecular structure of 2b was unambiguously deter-
mined by X-ray crystallography,[22] which reveals that the
molecule is monomeric in the solid state (Figure 1). Although
the geometric features of 2b are quite similar to those of the
reported phosphine-stabilized silylene III, which bears a
phenyl group on the silicon atom, the tricoordinate SiII center
(ꢀ8Sia = 2758) is much more pyramidalized and has a more
Universitꢀ de Toulouse, UPS, and CNRS
ICT FR2599, F-31062 Toulouse (France)
[**] We are grateful to the CNRS and the ANR (NOPROBLEM) for
support of this work. R.R. acknowledges the Ministerio de
Educaciꢁn (MEC, Spain) for a postdoctoral fellowship.
Supporting information for this article is available on the WWW
11492
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2011, 50, 11492 –11495