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Fig. 2 Yield of 1-octyltrichlorosilane from oct-l-ene and trichlorosilane
catalysed by C1–C5 with the heterogeneous catalyst removed after 1 h.
Fig. 1 Yield of 1-octyltrichlorosilane as a function of time in oct-1-ene
hydrosilylations using trichlorosilane catalysed by: (5) Speier’s catalyst;
(/), C1; (-), C2; (:), C3; (3) C4; (8), C5.
Some assessment of the level of Pt leaching with C1–C5 was
obtained from a sixth cycle of use of these samples in which
hydrosilylations were run as before for 1 h, and then the reaction
mixtures decanted from the resin beads, and the mixtures
monitored for a further 24 h. The results are shown in Fig. 2. The
left-hand bar in each case shows the percentage of 1-octyltri-
chlorosilane formed after 1 h in the presence of polymer
catalysts, and the right-hand bar the conversion after a further
and compared to the performance of soluble Speier’s catalyst (5
2
3
wt% H
The appearance of l-octyltrichlorosilane and octene isomers
oct-2-, -3- and -4-enes as a non-resolved group) was monitored
2 6 2
PtCl ·6H O in isopropyl alcohol using 10 mmol Pt).
(
by GC analysis using nonane as an internal standard. The mole
ratio of oct-l-ene: trichlorosilane of 2+1 was chosen to highlight
any isomerisation induced by the catalyst while minimising
competition from the hydrosilylation reaction, i.e. isomerisation
was deliberately given a competitive advantage. In addition, to
demonstrate the high activity and stability of the polymer
catalysts (identified in preliminary ligand screening experi-
ments) each sample reported here was utilised in four previous
reactions, i.e. the data here refer to the fifth cycle of use in each
case. Data for Speier’s catalyst refer to its first use. No attempt
was made to recover and re-use this homogeneous species.
The results of the catalytic studies are summarised in Fig. 1.
The behaviour of the homogeneous catalyst is as expected from
the literature. The conversion of trichlorosilane to l-octyltri-
chlorosilane reached ca. 75% in ca. 1 h. However, simultane-
ously the isomerisation of oct-l-ene to internal alkenes was ca.
2
4 h in the absence of polymer catalysts. Though some increase
in l-octyltrichlorosilane is seen, particularly with C2 and C3
presumably reflecting the presence of some soluble catalytic
(
species), the effect is not large. With C4 the small additional
conversion seen after 24 h is within the analytical experimental
error. In addition no measurable increase in the amount of
isomerised alkene is observed, which remains very low. Thus it
seems that the level of Pt leached is itself very low, or any
species in solution is inactive as a catalyst either in hydro-
silylation or in isomerisation.
Thus we have succeeded in producing a polymer-supported
Pt alkene hydrosilylation catalyst (C4) with activity compara-
ble to that of Speier’s catalyst, with greatly enhanced selectivity
in terms of minimising concurrent alkene isomerisation, and
with considerable long term recycling stability along with
minimal Pt leaching characteristics. The catalyst performs well
with trichlorosilane as the silylating agent and displays
considerable potential for both small- and large-scale applica-
tion. We are currently undertaking a more detailed investigation
to improve our understanding of this catalyst system.
6
0%. (Note initial mole ratio oct-l-ene+trichlorosilane is 2+1.)
The performance of the polymer catalysts varies considerably.
Catalyst C1 shows very low activity. Since this is a polar gel-
type methacrylate-based resin, it would not be expected to swell
in the non-polar reaction mixture and presumably therefore
catalytic Pt sites are accessed only very inefficiently as a result
of poor mass transport. Likewise though catalyst C5 is a non-
polar styrene-based resin, and is nominally macroporous, in fact
2
21
R. D. and S. J. T. acknowledge the receipt of studentships
from Dow Corning. The gift of vinylbenzyl chloride from the
Dow Chemical Company is appreciated. The useful discussions
with Z. M. Michalska are warmly acknowledged.
the surface area of this species is very low (ca. 30 m g ), and
we believe the morphology is substantially collapsed. Catalysts
8
C2 and C3 perform well yielding ca. 70% l-octyltrichlorosilane
after ca. 6 h. Though these are polar methacrylate-based resins,
they have permanent macroporous morphologies with good
2
21
surface area (ca. 110–120 m g ). Catalyst C4 is significantly
the most active yielding ca. 70% l-octyltrichlorosilane after 2 h,
and ultimately delivering ca. 90%. In this respect it performs
better than Speier’s catalyst. C4 is a non-polar styrene-based
resin and is macroporous with a good surface area (ca. 100
Notes and references
1
B. Marciniec, J. Gulinski, W. Urbaniak and Z. W. Kornetka in
Comprehensive Handbook on Hydrosilylation, ed. B. Marciniec, Perga-
mon Press, Oxford, UK, 1992, ch. 2, p. 8.
2
3
J. L. Speier, J. A. Webster and C. H. Barnes, J. Am. Chem. Soc., 1957, 79,
2
21
m
g
). It clearly offers no significant mass transfer
9
74.
limitations. Furthermore with C4 the level of oct-l-ene iso-
merisation is only ca. 9%, and indeed less than ca. 4% with the
other polymer catalysts. C4 therefore is also significantly more
selective in favour of hydrosilylation than Speier’s catalyst.
These results are even more remarkable when it is borne in mind
that these data refer to the fifth cycle of use of this sample of
C4.
Overall it is tempting to conclude that the heterogenised Pt
complexes are highly selective in favour of the hydrosilylation
reaction, and the low level of alkene isomerisation observed
may be due to very low levels of leached Pt species acting as a
less selective homogeneous catalyst.
For a summary of work prior to 1985, see F. R. Hartley, Supported Metal
Complexes—A New Generation of Catalysts, D. Reidel Pub. Co.,
Dordrecht, Germany, 1985, ch. 7, p. 204.
4 For a further summary of work to 1992 see ref 1. p. 84.
5
Z. M. Michalska, K. Strzelec and J. W. Sobczak, J. Mol. Catal. A, 2000,
56, 91; Z. M. Michalska, B. Ostaszewski and K. Strzelec, J. Organomet.
1
Chem., 1995, 496, 19; Z. M. Michalska, B. Ostaszewski, K. Strzelec, R.
Kwiatkowski and A. Wlochowicz, React. Polym., 1994, 23, 85.
H. S. Hilal, M. A. Suleiman, W. J. Jondi, S. Khalaf and M. M. Masoud,
J. Mol. Catal. A, 1999, 144, 47.
6
7
P. M. van Berkel and D. C. Sherrington, Polymer, 1996, 37, 1431.
8 S. M. Howdle, K. Jerabeck, V. Leocorbo, P. C. Marr and D. C.
Sherrington, Polym. Commun., 2000, 41, 7273.
1932
Chem. Commun., 2000, 1931–1932
Drake
