Direct synthesis of organodichlorosilanes by the reaction of metallic silicon, hydrogen chloride and alkene/alkyne and by the reaction of metallic silicon and alkyl chloride

Article abstract of DOI:10.1039/b007068h

Dichloroethylsilane was synthesized by the reaction of metallic silicon, hydrogen chloride and ethylene using copper(I) chloride as the catalyst, the silicon conversion and the selectivity for dichloroethylsilane being 36 and 47%, respectively. At a lower reaction temperature or at a higher ratio of ethylene: hydrogen chloride a higher selectivity was obtained, however the silicon conversion was lower. The silicon-carbon bond formation is caused by the reaction of a surface silylene intermediate with ethylene. The reaction with propylene in place of ethylene gave dichloroisopropylsilane (22% selectivity) and dichloro-n-propyl-silane (8% selectivity) together with chlorosilanes. A part of the dichloroisopropylsilane is formed by the reaction of silicon, hydrogen chloride and isopropyl chloride formed by hydrochlorination of propylene. Use of acetylene instead of alkenes resulted in dichlorovinylsilane formation with a 34% selectivity. Alkyldichlorosilanes were also produced directly from silicon with alkyl chlorides, propyl and butyl chlorides. During the reaction the alkyl chloride is dehydrochlorinated over the surface of copper originating from the catalyst to afford hydrogen chloride and alkene. The hydrogen chloride formed participates in the formation of the silicon-hydrogen bond in alkyldichlorosilane, and the reaction of silicon, hydrogen chloride and alkene also causes alkyldichlorosilane formation. The reaction with isopropyl chloride gave a very high selectivity (85%) for dichloroisopropylsilane, the silicon conversion being 86%. The Royal Society of Chemistry 2001.

Full text of DOI:10.1039/b007068h

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Direct synthesis of organodichlorosilanes by the reaction of
metallic silicon, hydrogen chloride and alkene/alkyne and by the
reaction of metallic silicon and alkyl chloride
Masaki Okamoto, Satoshi Onodera, Yuji Yamamoto, Eiichi Suzuki and Yoshio Ono
Department of Chemistry and Materials Science, Tokyo Institute of Technology, Ookayama,
Meguro-ku, Tokyo 152-8550, Japan. Fax: ϩ81-3-5734-2878; E-mail: esuzuki@o.cc.titech.ac.jp
Received 31st August 2000, Accepted 9th November 2000
First published as an Advance Article on the web 13th December 2000
Dichloroethylsilane was synthesized by the reaction of metallic silicon, hydrogen chloride and ethylene using
copper() chloride as the catalyst, the silicon conversion and the selectivity for dichloroethylsilane being 36 and
47%, respectively. At a lower reaction temperature or at a higher ratio of ethylene:hydrogen chloride a higher
selectivity was obtained, however the silicon conversion was lower. The silicon–carbon bond formation is caused
by the reaction of a surface silylene intermediate with ethylene. The reaction with propylene in place of ethylene gave
dichloroisopropylsilane (22% selectivity) and dichloro-n-propyl-silane (8% selectivity) together with chlorosilanes. A
part of the dichloroisopropylsilane is formed by the reaction of silicon, hydrogen chloride and isopropyl chloride
formed by hydrochlorination of propylene. Use of acetylene instead of alkenes resulted in dichlorovinylsilane
formation with a 34% selectivity. Alkyldichlorosilanes were also produced directly from silicon with alkyl chlorides,
propyl and butyl chlorides. During the reaction the alkyl chloride is dehydrochlorinated over the surface of copper
originating from the catalyst to afford hydrogen chloride and alkene. The hydrogen chloride formed participates in
the formation of the silicon–hydrogen bond in alkyldichlorosilane, and the reaction of silicon, hydrogen chloride and
alkene also causes alkyldichlorosilane formation. The reaction with isopropyl chloride gave a very high selectivity
(85%) for dichloroisopropylsilane, the silicon conversion being 86%.
1 to afford chlorosilicon species 2. The addition of hydrogen
Introduction
chloride to dichlorosilylene to give trichlorosilane has been
Dichlorodimethylsilane is industrially produced in the largest
reported.5 Attack of hydrogen chloride on species 2 leads to
scale in the silicon industry as a raw material for synthesizing
formation of dichlorosilicon species 3, which is subsequently
silicone polymers.1,2 Methylchlorosilanes, mainly dichloro-
attacked by hydrogen chloride and two Si–Cu bonds are simul-
dimethylsilane, are obtained by reaction of metallic silicon
taneously cleaved to give trichlorosilane. In the presence of
with methyl chloride using a copper catalyst.1,2 To yield organo-
halogenosilanes directly from metallic silicon commercially,
only organic halides, such as methyl chloride and chloro-
benzene, have been used as a reactant.
ethylene (eqn. 2) the silylene intermediate 1 reacts to form
silacyclopropane species 4. It is well known that a silylene
intermediate adds to an alkene to give a vinylsilane via a sila-
cyclopropane intermediate.6,7 Then, species 4 is ring-cleaved
Hydrogen chloride also reacts with metallic silicon to afford
by attack of hydrogen chloride, and hydrogen chloride attacks
surface species 5 consequently to form dichloroethylsilane. We
trichlorosilane as a main product together with dichlorosilane
and tetrachlorosilane.3 We have found that the reaction
have also reported the intermediacy of surface silylene 1 in the
of metallic silicon and hydrogen chloride in the presence of
reaction of silicon with methanol.8 Thus, adding ethylene to the
ethylene affords ethylchlorosilanes, mainly dichloroethylsilane,
methanol feed resulted in the formation of ethyldimethoxy-
together with chlorosilanes.4 Furthermore, when acetylene was
silane via 1.8,9
used instead of ethylene dichlorovinylsilane was obtained.4
In this work the reaction of metallic silicon, hydrogen
This is a new reaction for a direct synthesis of organochloro-
silanes.
To explain trichlorosilane formation as a main product in
the Si–HCl reaction and dichloroethylsilane formation in the
chloride and an unsaturated hydrocarbon, ethylene, propylene
or acetylene, was carried out for synthesis of alkyl- or vinyl-
dichlorosilane, and the effects of variables and the reaction
pathway were examined. Propylchlorosilanes and butylchloro-
Si–HCl–C2H4 reaction, we have proposed a mechanism involv-
silanes can be prepared from metallic silicon and propyl and
ing surface silylene intermediate4 as shown in eqns. (1) and (2),
butyl chlorides, respectively, the main products being alkyl-
dichlorosilanes, not dialkyldichlorosilane.10 This is different
(1)
from the product distribution of methylchlorosilane formation
in the Si–CH3Cl reaction, which gives dichlorodimethylsilane as
a main product. The alkyldichlorosilane formed in the reaction
of silicon with propyl or butyl chloride is the same as the main
product4 in the Si–HCl–alkene reaction. This suggests that
alkyldichlorosilanes are formed by the reaction of silicon,
hydrogen chloride and propylene/butene formed by dehydro-
chlorination of propyl or butyl chloride. In this work the
reactions of silicon with propyl and butyl chlorides were carried
out, and the mechanism of alkyldichlorosilane formation was
examined.
(2)
respectively. In the Si–HCl reaction (eqn. 1) a silylene 1 is
formed on the silicon surface. Hydrogen chloride reacts with
DOI: 10.1039/b007068h
J. Chem. Soc., Dalton Trans., 2001, 71–78
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71

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Fig. 2 Effect of reaction temperature on the silicon conversion (a), the
selectivity (b) and the yield of dichloroethylsilane (c) in the reaction of
silicon, hydrogen chloride and ethylene. The pretreatment and reaction
conditions are the same as those in Fig. 1. The reaction time was 5 h.
Fig. 1 Time courses of the formation rates of dichloroethylsilane
(filled triangle), dichlorosilane (open circle), trichlorosilane (open
triangle) and tetrachlorosilane (open square) in the reaction of silicon,
hydrogen chloride and ethylene at 533 (a), 513 (b) and 493 K (c).
Catalyst amount was 10 wt%, amount of silicon charged in the reactor
8.9 mmol, pretreatment at 723 K for 10 min, flow rates of hydrogen
chloride and ethylene 5 and 10 mmol hϪ1, respectively.
Experimental
Silicon grains (45–63 µm, purity 99.9%, impurities Fe 0.008
wt%, Sb 0.003 wt%) were washed by a 46% hydrogen fluoride
aqueous solution for 1 h at room temperature to remove SiO2
overlayers. The grains (7.1 or 8.9 mmol) and copper() chloride
grains (45–63 µm, purity 99.9%, Cu/(CuCl ϩ Si) = 2.5–40 wt%)
as a catalyst were physically mixed, placed in a quartz tube (i.d.
10 mm) in a fixed-bed flow reactor system and preheated at 723
K for 10 min in a helium stream. A mixture of hydrogen chlor-
ide (3–15 mmol hϪ1) and alkene/alkyne (5–12 mmol hϪ1) gases
was fed to the reactor at 553–723 K. The reactor effluents were
analysed by a gas chromatograph every 10 min. The products
Fig. 3 Effect of the ratio of ethylene to hydrogen chloride on the
silicon conversion (a), the selectivity (b) and the yield of dichloroethyl-
silane (c) in the reaction of silicon, hydrogen chloride and ethylene.
Catalyst amount 10 wt%, amount of silicon charged 8.9 mmol, pre-
treatment carried out at 723 K for 10 min, total flow rate 15 mmol hϪ1
,
reaction temperature 513 K, reaction time 5 h.
increased after starting to feed the mixture of hydrogen chloride
and ethylene to the reactor, and were almost constant after
20 min. An induction time was observed below 513 K and
lengthened with decreasing reaction temperature. The rate of
trichlorosilane formation at the steady period decreased with
decrease of reaction temperature, while the rate of formation
of dichloroethylsilane did not change. The effect of reaction
temperature on the overall selectivity for ethyldimethoxysilane
and the silicon conversion for 5 h is shown in Fig. 2. The select-
ivity for dichloroethylsilane was higher at a lower temperature,
while the silicon conversion was lower.
1
were identified by H NMR and GC–MS. In the reaction of
silicon with alkyl chloride the flow rates of alkyl chloride and
helium were 5 and 10 mmol hϪ1, respectively. Selectivity
(%) = 100 × amount of product (mmol)/sum of amounts of
silicon-containing products (mmol); yield (%) = 100 × amount
of product (mmol)/amount of silicon charged in the reactor
(7.1 or 8.9 mmol); silicon conversion (%) = 100 × sum of
amounts of silicon-containing products (mmol)/amount of
silicon charged in the reactor (7.1 or 89 mmol).
The ratio of ethylene to hydrogen chloride was varied. The
results for 5 h are shown in Fig. 3. The selectivity for dichloro-
ethylsilane increased with the ratio and reached 39% at 4:1.
With decreasing ratio the silicon conversion increased to 80%
at 0.5:1. The reaction rate had fallen to zero at 4 h with an
ethylene to hydrogen chloride ratio of 0.5:1, whereas with a
ratio of 2 or 5:1, the reaction was still observed after 5 h. At
a ratio of 4:1 and a reaction time of 12 h, 36% of the silicon
charged in the reactor had been converted and the selectivity for
dichloroethylsilane was 47%. The silicon conversion must be
larger when the reaction time is prolonged.
Results and discussion
Dichloroethylsilane synthesis from metallic silicon, hydrogen
chloride and ethylene
The reaction of silicon, hydrogen chloride and ethylene was
carried out at various temperatures, after preheating a mixture
of silicon and copper() chloride grains in a helium stream at
723 K for 10 min. Fig. 1 shows the changes of the formation
rates with time at 493, 513 and 533 K. Dichloroethylsilane
was formed together with trichlorosilane, dichlorosilane and
tetrachlorosilane. At 533 K all the formation rates immediately
72
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Table 1 Effect of reaction temperature on the silicon conversion, product distribution and mole ratio of iso- to n-propyldichlorosilane in the
reaction of silicon, hydrogen chloride and propylene
Selectivity (%)
Reaction
temperature/K
Silicon conversion
(%)
Mole ratio
iso:n
(iso-C3H7)HSiCl2
(n-C3H7)HSiCl2
H2SiCl2
HSiCl3
SiCl4
573
553
533
513
493
94
87
90
64
19
9
13
7
5
2
3
3
1
1
1
13
10
6
3
1
74
73
84
87
86
1
1
2
4
10
3.2:1
5.0:1
7.3:1
5.8:1
4.0:1
Catalyst amount 5 wt%, amount of silicon charged in the reactor 7.1 mmol, pretreatment carried out at 723 K for 10 min, flow rates of hydrogen
chloride and propylene 10 and 5 mmol hϪ1, respectively.
Table 2 Effect of the ratio of propylene to hydrogen chloride on the silicon conversion, product distribution and mole ratio of iso- to n-
propyldichlorosilane in the reaction of silicon, hydrogen chloride and propylene
Selectivity (%)
Mole ratio
C3H6 :HCl
Silicon conversion
(%)
Mole ratio
iso:n
(iso-C3H7)HSiCl2
(n-C3H7)HSiCl2
H2SiCl2
HSiCl3
SiCl4
4:1
2:1
0.5:1
60
75
87
19
17
13
8
5
3
9
9
10
64
68
73
0
1
1
2.4:1
3.4:1
5.0:1
Catalyst amount 5 wt%, the amount of silicon charged 7.1 mmol, pretreatment at 723 K for 10 min, reaction temperature 553 K, total flow rate 15
mmol hϪ1
.
the reaction rates were almost zero at 3, 3 and 5 h, respec-
tively. Above 533 K the silicon conversion reached around
90%. At 553 K the highest selectivity for dichloroisoprop-
ylsilane was obtained. The ratio of the iso to the n
product changed with temperature, and 7.3:1 at 533 K was the
highest.
The ratio of propylene to hydrogen chloride was changed,
while the total flow rate was maintained at 15 mmol hϪ1, the
results being shown in Table 2. The conversion was higher at
a lower ratio and was 87% at 0.5:1. Both the selectivities for
iso- and n-propyldichlorosilanes increased with increase of
the ratio. The ratio of iso:n product also changed. Under
HCl-rich conditions the product ratio was high.
The optimum conditions for a high selectivity for dichloro-
isopropylsilane were determined. A 22% selectivity for di-
chloroisopropylsilane and an 8% selectivity for dichloro-
n-propylsilane were obtained at 553 K at 12 mmol hϪ1 of
propylene and 3 mmol hϪ1 of hydrogen chloride using 3 wt%
copper catalyst after pretreatment at 773 K for 10 min, the
silicon conversion being 61%.
A plausible mechanism for propyldichlorosilanes formation
is shown in eqn. (3). The reaction of surface silylene 1 with
propylene gives a methylsilacyclopropane species 6, which
is attacked by hydrogen chloride. When bond a in 6 is cleaved a
n-propylchlorosilicon species is formed and finally dichloro-
n-propylsilane is obtained. On the other hand, cleavage of bond
b gives dichloroisopropylsilane.
Fig. 4 Time courses of the formation rates of dichloroisopropylsilane
(filled circle), dichloro-n-propylsilane (filled triangle), dichlorosilane
(open circle), trichlorosilane (open triangle) and tetrachlorosilane (open
square) in the reaction of silicon, hydrogen chloride and propylene.
Catalyst amount 3 wt%, amount of silicon charged 7.1 mmol, pre-
treatment carried out at 823 K for 10 min, flow rates of hydrogen chlor-
ide and propylene 3 and 12 mmol hϪ1, reaction temperature 553 K.
Dichloropropylsilane synthesis from silicon, hydrogen chloride
and propylene
In the reaction of silicon, hydrogen chloride and propylene,
ca. 0.3 mmol hϪ1 of isopropyl chloride was formed as a by-
product by hydrochlorination of propylene. It has been
reported that isopropyl chloride reacts with metallic silicon10
and that, in the presence of hydrogen chloride, dichloromethyl-
silane is formed in the reaction of silicon with methyl chloride
for the synthesis of dichlorodimethylsilane.11 It is highly
possible that the isopropyl chloride formed during the Si–HCl–
C3H6 reaction also contributes to the dichloroisopropylsilane
formation.
Instead of ethylene, propylene was fed with hydrogen chloride.
The time courses of the formation rates are shown in Fig. 4.
Dichloroisopropylsilane and dichloro-n-propylsilane were
formed as organosilanes together with dichlorosilane, trichloro-
silane and tetrachlorosilane. The formation rate of dichloro-
isopropylsilane was almost twice as high as that of the n-propyl
product. The reaction stopped at 9.5 h and the silicon con-
version reached 61%. The overall selectivities for dichloro-
isopropylsilane and dichloro-n-propylsilane were 22 and 8%,
respectively.
Between 1 and 2 h, 2 mmol hϪ1 of isopropyl chloride was
added to the feed of the HCl–C3H6 mixture. Fig. 5 shows the
changes of formation rates with time. Just after adding iso-
propyl chloride, only the rate of formation of dichloroiso-
propylsilane increased. This strongly indicates that isopropyl
The effect of reaction temperature was examined. In Table 1
the results for 5 h reaction are summarized. At 513 and 493 K
the reaction still proceeded at 5 h, while at 573, 553 and 533 K
J. Chem. Soc., Dalton Trans., 2001, 71–78
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(3)
Fig. 5 Effect of isopropyl chloride addition on the formation rates of
the products in the reaction of silicon, hydrogen chloride and prop-
ylene. Dichloroisopropylsilane (filled circle), dichloro-n-propylsilane
(filled triangle), dichlorosilane (open circle), trichlorosilane (open tri-
angle) and tetrachlorosilane (open square). Catalyst amount 5 wt%,
amount of silicon charged in 7.1 mmol, pretreatment at 723 K for 10
Fig. 6 Time courses of the formation rates of dichlorovinylsilane
(filled circle), dichloroethylsilane (filled triangle), dichlorosilane (open
circle), trichlorosilane (open triangle) and tetrachlorosilane (open
square) in the reaction of silicon, hydrogen chloride and acetylene.
Catalyst amount 1 wt%, amount of silicon charged 8.9 mmol, pre-
treatment at 723 K for 10 min, silicon–catalyst mixture activated by
15 mmol hϪ1 of hydrogen chloride at 513 K for 10 min, flow rates
of hydrogen chloride and acetylene 15 and 4 mmol hϪ1, respectively,
reaction temperature 513 K.
min, flow rates of hydrogen chloride and propylene 10 and 5 mmol hϪ1
flow rate of isopropyl chloride added between 1 and 2 h 2 mmol hϪ1
reaction temperature 553 K.
,
,
was 13% for 5 h, the overall selectivities of dichlorovinylsilane,
dichloroethylsilane and trichlorosilane being 39, 23 and 38%,
respectively. Trace amounts of dichlorosilane and tetrachloro-
silane were formed.
chloride participates in the formation of dichloroisopropyl-
silane. As shown in eqn. (4), isopropyl chloride reacts with
(4)
The ratio of acetylene to hydrogen chloride was varied. The
silicon conversion and the product distribution greatly
depended on the ratio, as described in our previous commun-
ication.4 Without acetylene, trichlorosilane was mainly formed,
and the silicon conversion was very high, 85%. On increasing
the ratio the conversion decreased, while the selectivity for
dichlorovinylsilane increased and reached 34% at 0.26:1.
The effect of reaction temperature is summarized in Table 3.
The silicon conversion increased with reaction temperature
till 523 K. Both the selectivities for dichlorovinylsilane
and dichloroethylsilane were higher at a lower temperature and
reached 36 and 26% at 493 K, respectively.
surface silylene 1 to afford the surface species 7, which is
converted into dichloroisopropylsilane by attack of hydrogen
chloride.
Dichlorovinylsilane synthesis from silicon, hydrogen chloride and
acetylene
A mixture of silicon and copper() chloride was preheated in
a helium stream at 723 K for 10 min. First, only hydrogen
chloride was fed to the reactor at 513 K for 10 min to activate
the silicon–catalyst mixture before feeding a mixture of
hydrogen chloride and acetylene, because the reaction did not
proceed without activation by hydrogen chloride. During the
activation period 1% of the silicon charged was consumed
to form chlorosilanes, mainly trichlorosilane. After the feed
was changed to the mixture of hydrogen chloride and acetylene,
dichlorovinylsilane and dichloroethylsilane were formed
together with chlorosilanes.3 Fig. 6 shows the time courses of
the formation rates. The rate curves of dichlorovinylsilane and
trichlorosilane were very similar. Before 2 and 4 h, the rate of
formation of dichloroethylsilane was almost same as those of
dichlorovinylsilane and trichlorosilane, while around 2.5 h it
was half that of dichlorovinylsilane. The silicon conversion
Eqn. (5) shows the mechanism of formation of dichloro-
vinylsilane and dichloroethylsilane. The reaction of surface
silylene 1 with acetylene gives a silacyclopropene species 8,
which is ring-cleaved by attack of hydrogen chloride. The
formed vinylchlorosilicon species 9 is finally converted into
dichlorovinylsilane. Normally a gas-phase silylene reacts with
acetylene to afford 1,4-disilacyclohexa-2,5-diene, which is a
double-added product.7,12 No formation of 1,4-disilacyclohexa-
2,5-diene in the Si–HCl–C2H2 reaction indicates that the
silylene species is not present in the gas phase, but on the
surface. During the Si–HCl–C2H2 reaction vinyl chloride was
not formed by hydrochlorination of acetylene. This shows that
vinyl chloride does not participate in the dichlorovinylsilane
formation. Additionally, under the reaction conditions, the
hydrogenation of acetylene or dichlorovinylsilane by hydrogen
formed as a by-product did not proceed. This strongly suggests
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Table 3 Effect of reaction temperature on the silicon conversion and the product distribution in the reaction of silicon, hydrogen chloride and
acetylene
Selectivity (%)
(C2H3)HSiCl2
Reaction
temperature/K
Silicon conversion
(%)
(C2H5)HSiCl2
H2SiCl2
HSiCl3
SiCl4
533
523
513
503
493
24
29
16
13
8
18
29
34
31
36
10
16
21
18
26
8
4
0
1
0
63
50
45
49
38
1
1
0
1
0
Catalyst amount 5 wt%, amount of silicon charged 8.9 mmol, pretreatment at 723 K for 10 min, flow rates of hydrogen chloride and acetylene 15 and
4 mmol hϪ1, respectively.
(5)
Fig. 7 Time courses of the formation rates of dichloroisopropylsilane
(filled circle), trichloroisopropylsilane (filled square), dichlorosilane
(open circle) and trichlorosilane (open triangle) in the reaction of
silicon and isopropyl chloride. Catalyst amount 5 wt%, amount of
silicon charged 7.1 mmol, pretreatment at 723 K for 10 min, flow
rates of isopropyl chloride and helium 5 and 10 mmol hϪ1, reaction
temperature was 573 K.
that dichloroethylsilane is formed neither by the reaction
of surface silylene with ethylene nor by hydrogenation of
dichlorovinylsilane and that the vinyl group in species 9 is
not converted into an ethyl group. Thus, it was concluded
that hydrogenation of the surface intermediate 8 occurs to form
dichloroethylsilane.
7, which is attacked by hydrogen chloride formed, as shown
in eqn. (4). Additionally, the formation of large amounts of
propylene and hydrogen chloride strongly indicate that the
Si–HCl–C3H6 reaction occurs.
On the other hand, the reaction with n-propyl chloride gave a
very low silicon conversion at 5 h, 2%. Dichloro-n-propylsilane
was selectively formed with a 98% selectivity. n-Propyl chloride
hardly decomposed to form propylene and hydrogen chloride,
the amount of propylene formed being below 0.2 mmol hϪ1.
This probably accounts for the low silicon conversion, because
hydrogen chloride is necessary for dichloropropylsilane form-
ation in the last step, which is rate-determining.
Alkyldichlorosilane synthesis from silicon and alkyl chloride
Petrov et al. have reported that propylchlorosilanes and butyl-
chlorosilanes were directly synthesized by the reaction of
silicon with propyl and butyl chlorides, respectively, and that
the corresponding alkyldichlorosilanes were mainly formed
among organosilanes.10 In the reaction of silicon with alkyl
chloride it is possible that the reaction of silicon with hydrogen
chloride and alkene coming from alkyl chloride also causes the
formation of alkyldichlorosilane since the main product is the
same as that in the Si–HCl–alkene reaction. The synthesis
of alkyldichlorosilanes was performed by the reaction of
silicon with various alkyl chlorides, and the mechanism of
alkyldichlorosilane formation was examined.
(b) Butyldichlorosilane synthesis. The reactions with n-, sec-,
iso- and tert-butyl chlorides were carried out at 573 K at 5
mmol hϪ1 of butyl chloride and 10 mmol hϪ1 of helium. The
changes of formation rates are shown in Figs. 8–11, and the
silicon conversion and the product distribution are summarized
in Table 4. In all the reactions, alkyldichlorosilanes were main
products among alkylchlorosilanes. This is consistent with the
results from the reactions of propyl chlorides.
Ishikawa et al. have reported the reaction of phenyl(tri-
methylsilyl)silylene with alkyl chlorides.13 The reaction with
n-octyl chloride resulted in carbon–chlorine insertion of the
silylene to form 1-chloro-1-octyl-1-phenyltrimethyldisilane
with 9% yield. sec-Butyl chloride also gave the carbon–chlorine
insertion product (7% yield) together with 1-chloro-2,2,2-
trimethyl-1-phenyldisilane (10% yield), 1-butene (7% yield) and
trans-2-butene (5% yield). They proposed a mechanism for
(a) Dichloropropylsilane synthesis. Fig. 7 shows the results of
the reaction of silicon and isopropyl chloride. The silicon
conversion at 5 h and the overall selectivity for dichloroiso-
propylsilane were 86 and 85%, respectively. Trichloroisoprop-
ylsilane, dichlorosilane and trichlorosilane were formed as
by-products with 4, 1 and 10% selectivities, respectively. During
the reaction ca. 2.5 mmol hϪ1 of propylene was constantly
detected, suggesting that hydrogen chloride is also formed from
isopropyl chloride. Thus, it is most likely that hydrogen chloride
participates in the silicon–hydrogen bond formation: surface
silylene 1 reacts with isopropyl chloride to give a surface species
J. Chem. Soc., Dalton Trans., 2001, 71–78
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Fig. 8 Time courses of the formation rates of n-butyldichlorosilane
(filled circle), n-butyltrichlorosilane (filled square), sec-butyldichloro-
silane (filled triangle) and trichlorosilane (open triangle) in the reaction
of silicon and n-butyl chloride. Catalyst amount 5 wt%, amount
of silicon charged 7.1 mmol, pretreatment at 723 K for 10 min, flow
rates of n-butyl chloride and helium 5 and 10 mmol hϪ1, reaction
temperature 573 K.
Fig. 10 Time courses of the formation rates of sec-butyldichlorosilane
(filled circle), sec-butyltrichlorosilane (filled triangle), dichlorosilane
(open circle) and trichlorosilane (open triangle) in the reaction of sil-
icon and sec-butyl chloride. Flow rates of sec-butyl chloride and helium
5 and 10 mmol hϪ1. Other details as in Fig. 8.
Fig. 11 Time courses of the formation rates of tert-butyldichloro-
silane (filled circle), dichlorosilane (open circle) and trichlorosilane
(open triangle) in the reaction of silicon and tert-butyl chloride. Flow
rates of tert-butyl chloride and helium 5 and 10 mmol hϪ1. Other details
as in Fig. 8.
Fig. 9 Time courses of the formation rates of tert-butyldichlorosilane
(filled circle), tert-butyltrichlorosilane (filled square), isobutyldichloro-
silane (filled triangle), dichlorosilane (open circle) and trichlorosilane
(open triangle) in the reaction of silicon and isobutyl chloride. Flow
rates of isobutyl chloride and helium 5 and 10 mmol hϪ1, respectively.
Other details as in Fig. 8.
ination of alkene decreases for the zwitterion intermediate
formed from tert- > sec- > n-alkyl chloride. The reactivity of
alkyl chloride to a silylene intermediate can be determined by
comparing the total yield of the insertion and elimination
products. Thus, the order of the reactivity of alkyl chloride is
tert > sec > n.
butene formation that involves a zwitterion intermediate 10
shown in eqn. (6). When reaction a proceeds the insertion
product is formed. Reaction b leads to formation of butene and
hydrodisilane.
In the case of tert-butyl chloride, no silylene insertion
product was detected, and 1-chloro-2,2,2-trimethyl-1-phenyl-
disilane and isobutene were formed with 27 and 28% yields,
respectively. These results show that the tendency to the elim-
The study of β-hydride elimination of various alkyl groups
formed on a copper crystal by corresponding alkyl chlorides
has been reported.14 sec- and tert-Butyl groups more easily
decompose to form butenes than n-butyl. This strongly
suggests that decomposition of sec- and tert-butyl chloride
occurs easily over a copper surface to give butene and hydrogen
chloride.
(6)
Taking account of these literature results,13,14 in the reactions
of silicon with butyl chlorides it is highly plausible that form-
ation of butenes is caused both by the butyl chloride decom-
position over the copper surface and by decomposition of a
zwitterion intermediate formed by the reaction of surface
silylene and butyl chloride. In the reactions of silicon with butyl
chlorides sec- and tert-butyl chlorides resulted in 100% con-
versions of butyl chloride, and the formation rates of butenes
were 4.5 and 3.5 mmol hϪ1, respectively, while iso- and n-butyl
76
J. Chem. Soc., Dalton Trans., 2001, 71–78

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(7)
Table 4 The silicon conversion and the product distribution in the
tert-butyldichlorosilane. Since the isobutyl group is primary a
reactions of silicon with butyl chlorides
smaller amount of hydrogen chloride is probably formed than
that using sec- or tert-butyl chloride. This causes a lower silicon
conversion. The formation rate of tert-butyl chloride was below
0.02 mmol hϪ1, indicating no reaction of silicon, hydrogen
chloride and tert-butyl chloride to afford tert-butyldichloro-
silane. Thus, isobutene and hydrogen chloride formed from
isobutyl chloride take part in the formation of tert-butyl-
dichlorosilane.
Taken in total, it is concluded that alkyldichlorosilane is
formed both by the reaction of silicon, hydrogen chloride and
alkyl chloride and by the reaction of silicon, hydrogen chloride
and alkene.
Selectivity (%)
Butyl
chloride
Silicon
(%)
(C4H9)HSiCl2 (C4H9)SiCl3 HSiCl3 SiCl4
n
29
66
68 (n)
3 (n)
18
40
0
2
11 (sec)
39 (tert)
18 (iso)
16 (sec)
3 (tert)
iso
1 (tert)
sec
tert
82
79
0
0
79
81
5
16
The parentheses represent the kinds of butyl group in butyldichloro-
silanes or butyltrichlorosilanes. Catalyst amount 5 wt%, amount of
silicon charged 7.1 mmol, pretreatment at 723 K for 10 min, flow rates
of helium and butyl chloride 10 and 5 mmol hϪ1, respectively.
Conclusion
Alkyl- or vinyl-dichlorosilane was synthesized by the reaction
of silicon, hydrogen chloride and alkene/alkyne. A silicon–
carbon bond is formed mainly by the reaction of a surface
silylene intermediate with alkene or alkyne. During the reaction
a small part of the alkene undergoes hydrochlorination to yield
alkyl chloride, which subsequently reacts with the surface
silylene to form the silicon–carbon bond. The reaction of
silicon with propyl or butyl chloride also gave alkyldichloro-
silane as a main organosilicon product. Alkyl chloride is
dehydrochlorinated over the copper surface, and hydrogen
chloride formed participates in the formation of the silicon–
hydrogen bond. Alkyldichlorosilane is formed not only by the
reaction of silicon, hydrogen chloride and alkyl chloride but by
the reaction of silicon, hydrogen chloride and alkene.
chloride were not completely converted. The amounts of
butenes formed from iso- and n-butyl chloride were 2.5 and 1.0
mmol hϪ1, respectively. These results are compatible with both
the zwitterion stability and the butyl chloride stability over
copper metal.
The reaction mechanism is shown in eqn. (7). Butyl chloride
reacts with surface silylene 1 to form surface species 11. If the
reaction a proceeds butyldichlorosilane is formed via inter-
mediate 12. Reaction b leads to the formation of butene and
species 2, the latter reacting with hydrogen chloride originating
from butyl chloride to give trichlorosilane finally. Among
various butyl chlorides, tert-butyl chloride gave the highest
selectivity for trichlorosilane. This result is in agreement with
the highest yield of hydrodisilane in the reaction of phenyl-
(trimethylsilyl)silylene with tert-butyl chloride and with easy
formation of hydrogen chloride from tert-butyl chloride over
the copper surface. Comparing the silicon conversion for 5 h in
the reactions of silicon with various butyl chlorides, use of
n-butyl chloride resulted in the lowest silicon conversion,
because it is not easy to form hydrogen chloride by decom-
position of butyl chloride over copper.
The reaction with n-butyl chloride resulted in the formation
of sec-butyldichlorosilane together with n-butylchlorosilanes.
The sec-butyldichlorosilane formation may be caused by the
reaction of silicon, hydrogen chloride and 1-/2-butene formed
from n-butyl chloride and/or by the reaction of silicon, hydro-
gen chloride and sec-butyl chloride formed by isomerization
of n-butyl chloride. Actually, the formation of ca. 0.2 mmol hϪ1
of sec-butyl chloride was observed during the reaction.
References
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78
J. Chem. Soc., Dalton Trans., 2001, 71–78