Mechanistic studies on ethylene silylation with chlorosilanes catalysed by ruthenium complexes

Article abstract of DOI:10.1039/b210552g

Silylation of ethylene by chlorosilanes is catalysed by ruthenium complexes. Mechanistic investigations reveal the presence of a complicated network of reactions leading to new σ-silane, ethylene and silyl complexes.

Full text of DOI:10.1039/b210552g

Mechanistic studies on ethylene silylation with chlorosilanes catalysed by
ruthenium complexes†
Sébastien Lachaize, Sylviane Sabo-Etienne,* Bruno Donnadieu and Bruno Chaudret
Laboratoire de Chimie de Coordination du CNRS, 205 route de Narbonne, 31077 Toulouse Cedex 04,
France. E-mail: sabo@lcc-toulouse.fr
Received (in Cambridge, UK) 29th October 2002, Accepted 29th November 2002
First published as an Advance Article on the web 11th December 2002
Silylation of ethylene by chlorosilanes is catalysed by
ruthenium complexes. Mechanistic investigations reveal the
presence of a complicated network of reactions leading to
new s-silane, ethylene and silyl complexes.
that the vinyl product was favoured with a low pressure of
ethylene. This is in contrast to our previous results on
triethylsilane activation and prompted us to carry out mecha-
nistic investigation. In a first stage, we have examined the
results of the addition of HSiMe2Cl to 1 and then the behaviour
of the new mixture under ethylene. In a second set of
experiments, we have changed the order of addition of the
reactants, adding ethylene to 1 and then the silane.
Vinylsilanes are useful reagents in organic chemistry and
chlorovinylsilanes are important monomers for polyorganosi-
loxane and ceramic production.1 Dehydrogenative silylation of
olefins catalysed by transition metal complexes can be an
interesting alternative to the various methods available for their
preparation. In some cases, it can compete favourably with
hydrosilylation to produce vinylsilanes in rather good yields.
We have previously reported an efficient synthesis of triethylvi-
Reaction of 1 with an excess of HSiMe2Cl (2 or 10 equiv.)
gives a mixture of three silicon-containing complexes 4–6
2
characterised by NMR studies (see Scheme 1). RuH2(h -
2
2
H2)(h -H–SiMe2Cl)(PCy3)2
(4)
and
RuH2(h -H–Si-
Me2Cl)2(PCy3)2 (5) are formulated as s-silane complexes5 by
comparison with analogous mono and bis(silane) complexes,6
previously characterised by NMR and X-ray structures. Com-
plexes 4 and 5 adopt a cis configuration for the two bulky PCy3
ligands as a result of stabilising Secondary Interactions between
Silicon and Hydrogen Atoms (SISHA interactions).ठThe third
complex 6 results from Si–Cl bond breaking and is formulated
2
nylsilane by using the bis(dihydrogen) complex RuH2(h -
H2)2(PCy3)2 (1)2 as catalyst precursor and shown that the best
results were obtained when using the ethylene complex
3
RuH(C2H4){(h -C6H8)PCy2}(PCy3) (2) deriving from 1, and a
high pressure of ethylene.3a We have recently extended the
scope of our system to disilane activation. In that case, a more
complicated system is obtained and the selectivity and activity
are highly dependent on the chain length n of the disilane
HSiR2(CH2)nSiR2H.3b We now report an unexpected tolerance
of our system for chlorosilane activation by ethylene. Mecha-
nistic studies allow the identification of new s-chlorosilane and
chlorosilyl complexes which generate different catalytic cycles.
Our findings evidence the competition between Si–H and Si–Cl
bond activation.
2
as a 16-electron dihydrogen(silyl) complex RuCl(h -H2)(Si-
Me2Cl)(PCy3)2 on the basis of multinuclear NMR data and
deuteration experiment.¶ 6 can be directly generated by addition
of 1 equiv. HSiMe2Cl to 3. It is noteworthy that traces of 3 were
detected in the reaction mixture of 1 with one equiv. of
HSiMe2Cl.
The C7D8 solution containing 4–6, obtained by addition of 2
equiv. of HSiMe2Cl to 1, was then saturated with C2H4 and the
reaction was monitored by multinuclear NMR spectroscopies
(1H, 31P, 13C and 29Si). The starting silane was totally consumed
and chlorodimethylvinylsilane was detected as a result of
dehydrogenative silylation. Two new ethylene complexes,
RuH(C2H4)(SiMe2Cl)(PCy3)2 (7) and RuHCl(C2H4)(PCy3)2
(8), were characterised. It is likely that 8 arises from the reaction
The catalytic experiments were performed at room tem-
perature with ethylene pressure in the range 1.5–20 bar and 1, 2
2
or the chloro complex RuHCl(h -H2)(PCy3)2 (3)4 were tested as
catalyst precursors (eqn. 1).
(1)
Analysis of the results concerning chlorodimethylsilane
activation are described in Table 1. We were surprised to find
Table 1 Reactiona of ethylene with HSiMe2Cl catalysed by the compounds
1, 2 and 3
C2H3SiMe2Cl/
Entry no.
Catalyst
PC H /bar
C2H5SiMe2Clb
2
4
1
2
3
4c
5c
6c
7
1
1
1
2
2
2
3
3
3
1.5
3
54+46
27+73
10+90
45+55
24+76
15+85
41+59
31+69
8+92
20
1.5
3
20
1.5
3
8
9
20
a In toluene, with 100 equiv. of HSiMe2Cl. b Determined by GC; in all
cases, HSiMe2Cl was totally consumed. c C2H4 atmosphere before
HSiMe2Cl addition.
† Electronic supplementary information (ESI) available: full character-
isation data. See http://www.rsc.org/suppdata/cc/b2/b210552g/
Scheme 1
214
CHEM. COMMUN., 2003, 214–215
This journal is © The Royal Society of Chemistry 2003

of 6 with C2H4. This was confirmed by adding HSiMe2Cl to 3,
thus generating 6 in situ, and then bubbling C2H4. This resulted
in quantitative formation of 8.∑ Complex 7 should play a major
role in catalysis as the three key ligands , i.e. a hydride, a silyl
and an ethylene, are linked to the ruthenium.
phere: formation of vinylsilane was observed, 9 remaining the
only detected organometallic species. The reaction occurs at a
much lower rate compared to the system with 10. We note that
9 and 10 present the same overall structure, but the main
difference is a more electropositive Si atom on 9. This might be
one of the factors responsible for the difference of activity and
selectivity between HSiMe2Cl and HSiEt3.
In a second set of experiments, we have inverted the addition
order of the reactants to our precursor 1, and first produced the
ethylene complex (2). We then added 2 equiv. of HSiMe2Cl to
2 and detected vinylsilane, ethane and the formation of a new
In summary, activation of chlorosilane by ethylene is
2
achieved by using RuH2(h -H2)2(PCy3)2 as catalyst precursor.
2
3
complex RuH(h -H–SiMe2Cl){(h -C6H8)PCy2}(PCy3) (9) that
was fully characterised by multinuclear NMR and X-ray data
(see Scheme 2).†
However, chloro substituents induce a dramatic influence on
selectivity and activity. A better selectivity in chlorovinylsilane
might be reached by a control of the factors favouring Si–H
versus Si–Cl bond breaking. It is remarkable that s-Si–H and
SISHA interactions play a major role in the process, as
highlighted by the characterisation of 9. This complex can be
considered as an intermediate between arrested Ru(II) and
Ru(IV) structures which are normally invoked in the elementary
step of oxidative addition of a silane in catalysis. Further
investigation including a full theoretical analysis and compar-
ative experiments with HSiMeCl2 are in progress.
Notes and references
‡ Their geometry is supported by DFT calculations that will be published
elsewhere. The role of SISHA interactions has been recently demonstrated
in s-silane ruthenium complexes. They represent the key factor for the
stabilisation of several complexes and play a major role in the exchange
processes.7
Scheme 2
We have already reported analogous complexes in the case of
HSiEt3 and HSiMe2(CH2)2SiMe2H activation.3 The corre-
§ The complex RuH3(SiMeCl2)(PPh3)3 analogous to 4, has been reported
from the reaction of HSiMeCl2 with RuCl2(PPh3)3.8 The authors describe
this complex as a trihydride stabilised by Ru–H…Si–E (E = Cl or C)
interactions, closely related to the IHI theory developed by Nikonov.9
¶ The dihydrogen ligand in 6 is characterized by a triplet at 213.8 ppm with
a very short JH–P constant of 10 Hz and a T1min value of 29 ms at 253 K (300
MHz). The HD isotopomer was generated from the addition of HSiMe2Cl
2
3
sponding complexes, RuH(h -H–SiEt3){(h -C6H8)PCy2}
2
3
(PCy3) (10) and RuH(h -H–SiMe2(CH2)2SiMe2H){(h -
C6H8)PCy2}(PCy3) (11), were formulated as dihydride(silyl)
ruthenium (IV) complexes as a result of oxidative addition of the
silane. In view of the X-ray and Si NMR data obtained for 9, we
now propose a ruthenium (II) formulation as we have evidenced
the presence of a s-Si–H bond. The X-ray structure of 9 is
shown in Fig. 1.** The phosphines are in a cis position,
favouring the formation of a s-Si–H bond and a SISHA
interaction.7 The distance H1–Si is 1.91(2) Å, at the higher limit
for s-Si–H bonds.5 The SISHA interaction H2…Si is charac-
terised by a distance of 1.99(2) Å. These data are in agreement
with the results obtained from a 1D HMQC 29Si–1H–{31P}
NMR experiment allowing the determination of two JSi–H
constants of 37 Hz for H1 and 24 Hz for H2.
2
to 3d3. The measurement of a coupling constant JHD of 12 Hz in RuCl(h -
HD)(SiMe2Cl)(PCy3)2, leads to a calculated distance rHD of 1.24 Å, in favor
of a stretched dihydrogen ligand.
∑ The analogous PiPr3 complex was previously reported.10
** Crystal data for 9: C38H71ClP2SiRu, M = 754.50, triclinic, space group
¯
P1, T = 180(2) K, a = 10.702(5), b = 10.739(5), c = 18.617(5) Å, a =
90.882(5), b = 91.127(5), g = 112.928(5)°, V = 1969.6(14) Å3, Z = 2, m
= 0.602 mm21, reflections collected/unique = 19343/7182, R1 = 0.0300,
wR2 = 0.0645, GOF = 1.027. In the silyl group, one methyl and the
chlorine were disordered. CCDC 196457. See http://www.rsc.org/suppdata/
cc/b2/b210552g/ for crystallographic files in CIF format.
Remarkably, 9 is stable under C2H4 whereas the analogous
complex 10 regenerates 2 and eliminates ethyl and vinylsilane.
Thus 9 generates another catalytic cycle as seen by NMR
monitoring after mixing 9 and HSiMe2Cl under C2H4 atmos-
1
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and B. Chaudret, Organometallics, 2000, 19, 5750.
4 M. L. Christ, S. Sabo-Etienne and B. Chaudret, Organometallics, 1994,
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5 (a) For recent reviews on s-silane complexes, see: G. J. Kubas, Metal
Dihydrogen and s-Bond complexes, Kluwer Academic/Plenum Pub-
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Fig. 1 ORTEP drawing of compound 9. Selected bond lengths (Å): Ru–Si,
2.3534 (11); Ru–H(1), 1.57 (2); Ru–H(2), 1.62 (3); Si–Cl, 2.110 (5); Si–
C(1), 1.924 (17); Si–C(11), 1.919 (2); Si–H(1), 1.91 (2); Si–H(2), 1.99 (2);
H(1)–H(2), 2.33 (3). Selected bond angles (deg): P(1)–Ru–P(2), 107.80 (3);
P(2)–Ru–H(2), 175.2 (9); P(2)–Ru–H(1), 83.2 (9); H(1)–Ru–H(2), 94.0
(13); Si–Ru–P(1), 110.67 (3); Si–Ru–P(2), 118.71 (2); Si–H(1)–Ru, 84.5
(10); Si–H(2)–Ru, 80.7 (10).
CHEM. COMMUN., 2003, 214–215
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