Redistribution at silicon by ruthenium complexes. Bonding mode of
the bridging silanes in Ru
2
H
4
(-
2
:
2
:
2
:
2
-SiH
4
)(PCy
3
)
4
and
Ru
2
H
2
(-
2
:
2
-H
2
Si(OMe)
2
)
3
(PCy
3
)
2
†
Ridha Ben Said,‡
a
Khansaa Hussein,§
a
Jean-Claude Barthelat,
a
Isabelle Atheaux,
b
Sylviane Sabo-Etienne,*
b
Mary Grellier,
b
Bruno Donnadieu
b
and Bruno Chaudret
b
a
Laboratoire de Physique Quantique, IRSAMC (UMR 5626), Université Paul Sabatier,
118 route de Narbonne, 31062 Toulouse Cedex 4, France
b
Laboratoire de Chimie de Coordination du CNRS, 205 route de Narbonne,
31077 Toulouse Cedex 04, France. E-mail: sabo@lcc-toulouse.fr; Fax: +33 5 61 55 30 03;
Tel: +33 5 61 33 31 77
Received 14th April 2003, Accepted 15th July 2003
First published as an Advance Article on the web 22nd September 2003
The bis(dihydrogen) complex RuH
2
(η
2
-H
2
)
2
(PCy
3
)
2
(1) reacts with 2 equiv. of H
2
SiMePh to produce a mixture of
Ru
2
H
4
(μ-η
2
:η
2
:η
2
:η
2
-SiH
4
)(PCy
3
)
4
(2) and RuH
2
(η
2
-H
2
)(η
2
-HSiPh
3
)(PCy
3
)
2
(4) together with HSiMePh
2
, HSiMe
2
Ph
and traces of HMe
2
SiSiMe
2
H as a result of redistribution at silicon. The bridging SiH
4
ligand in 2 is coordinated to
the two ruthenium via four σ-Si–H bonds in agreement with NMR, X-ray data (on 2, and 2' the analogous P
i
Pr
3
complex) and DFT calculations. Each interaction involves σ-donation to a ruthenium and back-bonding from the
other ruthenium. Elimination of SiH
4
and formation of RuH
2
(CO)
2
(PCy
3
)
2
(5), RuH
2
(
t
BuNC)
2
(PCy
3
)
2
(6) or
RuH(η
2
-H
2
)Cl(PCy
3
)
2
(7) were observed upon the reaction of 2 with CO,
t
BuNC, CH
2
Cl
2
, respectively. No reaction
occurred in the presence of H
2
, but H/D exchange was observed under D
2
atmosphere. Another redistribution
reaction at silicon can be obtained by adding 4 equiv. of HSi(OMe)
3
to 2 to produce Si(OMe)
4
and Ru
2
H
2
(μ-η
2
:η
2
-
H
2
Si(OMe)
2
)
3
(PCy
3
)
2
(3) displaying three bridging (μ-η
2
:η
2
alkoxysilane) ligands. Complex 3 is characterized by
multinuclear NMR spectroscopies and by a crystal structure. DFT calculations show that the model complex
Ru
2
H
2
(μ-η
2
:η
2
-H
2
Si(OR)
2
)
3
(PR
3
)
2
(R = H, Me) is a minimum on the potential energy surface, and support the
dihydride formulation with three bridging H
2
Si(OMe)
2
ligands coordinated to the two ruthenium through σ-Si–H
bonds.
Introduction
Redistribution represents an important reaction in silane chem-
istry. This process is normally catalyzed by strong bases and
strong acids, whereas catalysis by transition metal complexes
has not been very much developed.
1
However, in this latter case,
the reactions could be more specific leading to useful appli-
cations. In this context, the possibility to generate the simplest
silane SiH
4
can be an interesting alternative to avoid hazardous
procedures associated to a direct use of gas. The only transition
metal η
2
-SiH
4
complex Mo(η
2
-SiH
4
)(CO)(R
2
PC
2
H
4
PR
2
)
2
was
reported in 1995 by Luo, Kubas et al. This compound was
obtained by direct reaction of SiH
4
on the molybdenum
complex Mo(CO)(R
2
PC
2
H
4
PR
2
)
2
.
2
SiH
4
in situ generation by
catalytic redistribution of HSi(OEt)
3
by Cp
2
TiMe
2
was
exploited by Harrod et al.
3
Such alkoxyhydrosilane redistri-
butions were also catalyzed by zirconium and hafnium
complexes as shown by Tilley et al.
4
We have recently discovered that redistribution reaction of
dihydrogenosilanes can be performed from the bis(dihydrogen)
complex RuH
2
(η
2
-H
2
)
2
(PCy
3
)
2
(1). This reaction results in the
isolation of the dinuclear complex Ru
2
H
4
(μ-η
2
:η
2
:η
2
:η
2
-SiH
4
)-
(PCy
3
)
4
(2) characterized by a novel coordination mode of
SiH
4
.
5
Numerous examples of σ-silane complexes have been
reported. They are all characterized by the same bonding
picture used to classify the well-known class of σ-dihydrogen
complexes.
2b
Coordination of the H–H (or H–Si) bond results
† Based on the presentation given at Dalton Discussion No. 6, 9–11th
September 2003, University of York, UK.
‡ Permanent address: Unité de Recherche de Physico Chimie Molécu-
laire, Institut Préparatoire des Etudes Scientifiques et Techniques
(IPEST), boite postale 51, 2070 La Marsa, Tunisia.
§ Permanent address: Department of Chemistry, Faculty of Sciences,
University Al-Baath, Homs, Syria.
from a subtle balance between the σ-donation from the H–H
(or H–Si) bond to an empty d
σ
orbital and the back donation
from the M(d) filled orbital of appropriate symmetry to the
H–H (or H–Si) σ* orbital. We have reported in a preliminary
communication the characterization of 2 by multinuclear
spectroscopies and an X-ray determination of the analogous
complex with triisopropylphosphine in place of PCy
3
.
5
Theor-
etical DFT/B3LYP calculations have allowed us to understand
the bonding nature between SiH
4
and the two ruthenium atoms.
Coordination is achieved through four σ-Si–H bonds that differ
from the classical Chatt, Dewar and Duncanson model.
Each interaction involves σ-donation to a ruthenium and
back-bonding from the other ruthenium.
In this paper, we will summarize the key properties of 2 and
describe its reactivity toward a few substrates, CO, CH
2
Cl
2
,
t
BuNC and D
2
. We then present a new redistribution reaction
leading to the dinuclear complex (PCy
3
)HRu(μ-η
2
:η
2
-H
2
Si-
(OMe)
2
)
3
RuH(PCy
3
) (3). The bonding mode of the bridging
alkoxysilanes in 3 is ascertained by NMR and structural char-
acterizations, and more particularly by theoretical calculations.
Results and discussion
Synthesis and characterization of Ru
2
H
4
(-
2
:
2
:
2
:
2
-SiH
4
)-
(PCy
3
)
4
(2)
The SiH
4
dinuclear complex (PCy
3
)
2
H
2
Ru(μ-η
2
:η
2
:η
2
:η
2
-SiH
4
)-
RuH
2
(PCy
3
)
2
(2) is isolated as a white solid in 32% yield by
addition at room temperature of 2 equiv. of H
2
SiMePh to
a suspension of the bis(dihydrogen) complex RuH
2
(η
2
-H
2
)
2
-
(PCy
3
)
2
(1) in pentane. Complex 2 results from the coordination
of a SiH
4
ligand on two dihydridobis(phosphine)ruthenium
moieties, SiH
4
being generated in situ by redistribution at sili-
con. Complex 2 can be obtained from other dihydrogenosilanes
such as H
2
SiEt
2
or H
2
SiPh
2
, but the more hindered H
2
Si
t
Bu
2
DOI: 10.1039/ b304122k
4139
This journal is © The Royal Society of Chemistry 2003 Dalton Trans. , 2003, 4139–4146