Regiospesific addition of methyldichlorosilane to styrene

Article abstract of DOI:10.1134/S1070363214020200

Influence of various Pt-containing catalytic systems and additives to them on regioselectivity of styrene hydrosilylation by methyldichlorosilane was studied. The regiospesific approach to methyl(2-phenylethyl)dichlorosilane in the presence of tetrakis(triphenylphosphine)platinum Pt(0) is developed.

Full text of DOI:10.1134/S1070363214020200

ISSN 1070-3632, Russian Journal of General Chemistry, 2014, Vol. 84, No. 2, pp. 277–279. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © Yu.V. Frantsuzova, Yu.V. Khoroshavina, G.A. Nikolaev, 2014, published in Zhurnal Obshchei Khimii, 2014, Vol. 84, No. 2, pp. 285–
287.
Regiospesific Addition of Methyldichlorosilane to Styrene
Yu. V. Frantsuzova, Yu. V. Khoroshavina, and G. A. Nikolaev
Lebedev Research Institute of Synthetic Rubber, ul. Gapsal’skaya 1, St. Petersburg, 198035 Russia
e-mail: julfran@yandex.ru
Received April 25, 2013
Abstract―Influence of various Pt-containing catalytic systems and additives to them on regioselectivity of
styrene hydrosilylation by methyldichlorosilane was studied. The regiospesific approach to methyl(2-
phenylethyl)dichlorosilane in the presence of tetrakis(triphenylphosphine)platinum Pt(0) is developed.
DOI : 10.1134/S1070363214020200
Polymethyl(phenyl) siloxane rubbers are the bais of
compounds, insolating and thermoprotecting (ablating)
coatings characterized by high stability to radiation.
These rubber coatings possess also outstanding
dielectric properties and can be used in the temperature
range from –70 to 300°С.
We report here on the study of the addition reaction
of methyldichlorosilane to styrene with the goal to
optimize the conditions leading to compound II and to
minimize the styrene polymerization.
Various additives to the platinum catalysts shift the
ratio of products towards methyl(phenethyl)dichloro-
silane II but do not exclude the formation of methyl(1-
phenylethyl)dichlorosilane (I) [8].
Domestic industry does not produce methylphenyl-
dichlorosilane therefore new rubbers that would
substitute imported polymethyl(phenyl)siloxane rubbers
are welcome.
We have carried out a number of experiments in
order to elucidate the influence of additives upon the
yield and selectivity of the reaction. The following
catalysts were used: siloxane complex of Pt(0) [9] and
the Speier catalyst [4]. Platinum concentration in
the catalysts was 5×10–5 g-atom Pt/mL and concentra-
tion of platinum with respect to styrene was 5×
10–5 g-atom Pt/mol. The reaction progress and the ratio
of isomers formed was monitored by GLC.
Methyl(2-phenylethyl)dichlorosilane (II) [hereinafter
“methyl(phenethyl)dichlorosilane”] is the product of
styrene hydrosilylation by methyldichlorosilane.
Compound II acts as a monomer and/or comonomer
for production of polymethyl(phenyl)siloxane rubbers
[1, 2]. The starting materials, namely, styrene and
methyldichlorosilane, are inexpensive products of
Russian multi-ton technology.
Experimental data are presented in the table.
The reaction results in formation of methyl(1-
phenylethyl)dichlorosilane (I) (α-isomer), methyl-
(phenethyl)dichlorosilane (II) (β-isomer), and styrene
polymerization products in accordance with the
equation below.
The data show that the additives under study do not
affect the regiospecific character of the reaction.
The next step of the study was the selection of a
catalyst that would lead to high yield in the
regiospecific hydrosilylation.
(CH3)HSiCl2 + C6H5CH=CH2
→ C6H5CH(CH3)Si(CH3)Cl2 + C6H5CH2CH2(CH3)SiCl2
I
II
Phosphine complexes of Pt(0) and Pt(II) are known
to act as efficient catalysts of silicon hydrides addition
to olefins. The reactions in their presence proceed with
an induction period and a high rate [10–13]. Kinetic
data and mechanism of the process of arylalkenes
hydrosilylation including that of styrene with Pt(II)
+ styrene polymerization products.
In the presence of the conventional platinum catalysts
the addition of methyldichlorosilane to styrene results in
predominant formation of compound II [3, 4]. Nickel
catalysts direct this reaction towards α-isomer I [5–7].
277

278
FRANTSUZOVA et al.
Influence of additives to the platinum catalyst on the total yield and the ratio of adducts
Amount of additive
(×103 mol/g-atom Pt)
Additive : catalyst
I : II
(wt %)
Catalyst
Catalyst additive
No additive
Total yiels of I, II, %
(vol %)
Speier
PSCа
PSC
83
1 : 1
1 : 1
1 : 5
1 : 99
1 : 49
1 : 1
1 : 2
1 : 2
–
No additive
85
Acetic acid
3.5
2.1
0.3
0.3
0.2
0.3
0.1
0.2
10 : 1
6 : 1
1 : 1
2 : 1
1 : 1
1 : 1
1 : 1
1 : 1
89
PSC
Acetic acid
93
PSC
Acetic acid
91
PSC
Triethylamine
86
Speier
Speier
Speier
Speier
Trifluoromethane sulfonic acid
Trifluoromethane sulfonic acid
Triphenylphosphine
Ethyltrifluoroacetate
92
81
No reaction
88
1 : 2
a Platinum complex with siloxane.
bistriphenylphosphine complexes are reported in [12]
and with Pt(0) tetrakis triphenylphosphine complexes,
in [11, 13]. Hydrosilylation of styrene by various
silane hydrides under the action of tetrakis(triphenyl-
phosphine)platinum(0) proceeded regiospecifically
without α-isomer formation and resulted in a high yield
of compound II [10].
showed that the increased catalyst concentration does
not result in a higher yield and a shorter reaction time,
but at the lower catalyst concentration leads to higher
content of polystyrene. Longer boiling of the reaction
mixture did not provide a higher yield.
It was shown recently [15] exposed that along with
adducts I and II in sometimes side product formed in a
pronounced yield (up to 25%) resulting from dehyd-
rogenation, methyl(2-phenylvinyl)dichlorosilane with.
GLC data show that in the process carried out
according the developed procedure no side products
are formed. Polystyrene is accumulated in insignificant
quantity (8%).
Our data on the styrene hydrosilylation in the
presence of platinum phosphine complexes are
presented below.
Catalyst
I : II, wt %
(PPh3)2PtCl2
(PPh3)4Pt
99 : 1
88
0 : 100
1
According to Н NMR spectra the addition of
Yield of compound II, %
93
7
methyldichlorosilane to styrene proceeded entirely in
accordance with the Farmer rule.
Polystyrene fraction, %
10
The obtained data show that the styrene hydro-
silylation in the presence of all tested catalysts results
in a high yield of two isomers mixture with the
prevalence of compound II. The only catalyst that
promoted regiospecific pathway of the reaction was
tetrakis(triphenylphosphine)platinum.
EXPERIMENTAL
Chromatographic analysis of reaction products was
carried out on a chromatograph LKhM-8MD, equipped
with a column 2 m long of inner diameter 3 mm,
stationary phase 20% SKTFT-50 on Cilite 545 (0.2–
0.4 mm), carrier gas helium.
1H and 29Si NMR spectra were registered in
standard 5 and 10 mm test tubes on a spectrometer
Bruker Spectrospin AM-500, operating frequency
470.6 MHz with up to 1000 scans accumulation,
internal reference TMS, solvent C6D6.
We developed the conditions of hydrosilylation
into compound II avoiding the induc-tion period [14].
Temperature threshold of the reaction was 90°С.
Methyldichlorosilane was added slowly to the mixture
of styrene and the catalyst preheated to 90°С and the
reaction started upon addition of the first fraction of
chlorosilane.
The catalyst tetrakis(triphenylphosphine)platinum(0)
was prepared by procedure [16].
The study of the dependence of the product yield
and the reaction time on the catalyst concentration
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279
REGIOSPESIFIC ADDITION OF METHYLDICHLOROSILANE TO STYRENE
5. Bennet, E.W. and Orenski, P.J., J. Organomet. Chem.,
Methyl(2-phenylethyl)dichlorosilane. A four neck
flask equipped with a mechanical stirrer, condenser,
dropping funnel, and thermometer was charged with
920 mL (8 mol) of styrene and 0.8 g (6×10–4 mol) of
tetrakis(triphenylphosphine)platinum(0). The mixture
was heated to 90°С followed by addition of 850 mL
(8 mol) of methyldichlorosilane at a rate so as to
maintain the reaction mixture temperature no higher
than 120–130°С. Upon the end of addition of
methyldichlorosilane the mixture was heated at 130°С
for 2 h. The subsequent distillation in a vacuum gave
1634 g (93% yield) of methyl(phenethyl)dichloro-
1971, vol. 28, p. 137.
6. Reikhsfeld, V.O., Khvatova, T.P., Astrakhanov, M.I.,
and Saenko, G.I., Zh. Org. Khim., 1977, vol. 47, no. 3,
p. 726.
7. Moldavskaya, N.A., Khvatova, T.P., Skvortsov, N.K.,
and Reikhsfeld, V.O., Zh. Org. Khim., 1980, vol. 50,
no. 4, p. 851.
8. Mamoru Tachikawa, USA Patent no. 6054602, 2000;
С. А., 2000, vol. 132, 64399p.
9. Nikolaev, G.A., Egorov, A.G., Plashkin, V.S.,
Khoroshavina, Yu.V., Kolokoltseva, I.G., Lobkov, V.D.,
and Kormer, V.A., Russian Patent no. 2220769, 2001;
С. А., 2004, vol. 141. 123755n.
1
silane. Н NMR spectrum, δ, ppm: 0.9–0.95 m (3H),
1.68–1.72 m (2H), 3.05–3.09 m (2H), 7.43–7.54 m
(5H). 29Si NMR spectrum: 31.56 ppm.
10. Fink, W., Helv. Chim. Acta, 1971, vol. 54, no. 133,
p. 1304.
ACKNOWLEDGMENTS
11. Reikhsfeld, V.O., Khvatova, T.P., and Astrakhanov, M.I.,
Zh. Org. Khim., 1977, vol. 47, no. 11, p. 2625.
The study is carried out under the financial support
of Ministry of Education and Science (Federal targeted
program no. 16.523.12.3007).
12. Reikhsfeld, V.O., Gel’fman, M.I., Khvatova, T.P.,
Astrakhanova, M.I., and Gavrilova, I.V., Zh. Org.
Khim., 1977, vol. 47, no. 9, p. 2093.
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