Reaction of chloro(ethyl)silanes with chloro(phenyl)silanes in the presence of aluminum chloride. Synthesis of chloro(ethyl)(phenyl)silanes

Article abstract of DOI:10.1134/S1070363215030111

Abstract Substituent exchange at the silicon atom between chloro(phenyl)silanes (PhSiCl₃, MePhSiCl₂, Ph₂SiCl₂) and chloro(ethyl)silanes (EtSiCl₃, Et₂SiCl₂, Et₃SiCl, Et₄Si) in the presence of aluminum chloride has been studied. The examined compounds, except for PhSiCl₃ and Et₄Si, react fairly readily to give chloro(ethyl)-(phenyl)silanes in up to 48-52% yield. A probable mechanism has been proposed.

Full text of DOI:10.1134/S1070363215030111

ISSN 1070-3632, Russian Journal of General Chemistry, 2015, Vol. 85, No. 3, pp. 595–599. © Pleiades Publishing, Ltd., 2015.
Original Russian Text © V.G. Lakhtin, M.I. Eremeeva, E.G. Gordeev, N.V. Ushakov, V.G. Bykovchenko, A.D. Kirilin, E.A. Chernyshev, 2015, published in
Zhurnal Obshchei Khimii, 2015, Vol. 85, No. 3, pp. 431–435.
Reaction of Chloro(ethyl)silanes with Chloro(phenyl)silanes
in the Presence of Aluminum Chloride.
Synthesis of Chloro(ethyl)(phenyl)silanes
V. G. Lakhtina, M. I. Eremeevaa, E. G. Gordeevb, N. V. Ushakovc, V. G. Bykovchenkoa,
A. D. Kirilinb, and E. A. Chernysheva
a State Research Institute of Chemistry and Technology of Organoelement Compounds,
shosse Entuziastov 38, Moscow, 105118 Russia
e-mail: vlachtin@rambler.ru
b Lomonosov Moscow State University of Fine Chemical Technologies, pr. Vernadskogo 86, Moscow, 119571 Russia
c Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Leninskii pr. 29, Moscow, 119991 Russia
Received January 9, 2014
Abstract—Substituent exchange at the silicon atom between chloro(phenyl)silanes (PhSiCl3, MePhSiCl2,
Ph2SiCl2) and chloro(ethyl)silanes (EtSiCl3, Et2SiCl2, Et3SiCl, Et4Si) in the presence of aluminum chloride has
been studied. The examined compounds, except for PhSiCl3 and Et4Si, react fairly readily to give chloro(ethyl)-
(phenyl)silanes in up to 48–52% yield. A probable mechanism has been proposed.
Keywords: organosilanes, aluminum chloride, disproportionation
DOI: 10.1134/S1070363215030111
In recent years, substituent exchange reactions at
the silicon or germanium atom have been used to
obtain chloro(organyl)silanes and -germanes. These
reactions are usually carried out in the presence of
aluminum chloride [1, 2]. However, the exchange
process has been poorly studied. In particular, it
remains unclear why in some cases substituent
exchange occurs while in other cases does not or is
difficult.
Dichloro(methyl(phenyl)silane reacted with EtSiCl3,
Et2SiCl2, and Et3SiCl, but the results depended on the
number of ethyl groups on the silicon atom. Substituent
exchange in the reaction of MePhSiCl2 (I) with EtSiCl3
(II) followed two paths: (1) Ph/Cl and (2) Ph/Et.
MePhSiCl2 + EtSiCl3
I
II
AlCl3 (30 mol %)
EtPhSiCl2 + MeSiCl3,
(1)
(2)
III (15%) IV (9%)
In the present work we studied substituent
exchange reactions between chloro(ethyl)silanes and
chloro(phenyl)silanes with a view to obtaining chloro
(ethyl)(phenyl)silanes which attract interest as
monomers. As substrates we used EtSiCl3, Et2SiCl2,
Et3SiCl, Et4Si, PhSiCl3, MePhSiCl2, and Ph2SiCl2.
3 h
I + II
MeEtSiCl2 + PhSiCl3.
8%
9%
Exchange of methyl and ethyl groups between
compounds I and II is hardly probable. By special
experiments we showed that reactions of chloro(ethyl)-
silanes (EtSiCl3, Et2SiCl2) with chloro(methyl)silanes
(MeSiCl3, Me2SiCl2) do not afford substituent ex-
change products under the given conditions, but small
amounts of Me2SiCl2 (6%) and Ph2SiCl2 (6%) are
formed as a result of disproportionation [3] of
MePhSiCl2 in the presence of AlCl3 [reaction (3)].
The reactions of chloro(ethyl)silanes EtnSiCl4–n
(n = 1–3) with trichloro(phenyl)silane were carried out
at 110–130°C in the presence of 10–30 mol % of
AlCl3. No exchange of ethyl and phenyl groups was
observed at 110°C in the presence of 10 mol % of
AlCl3. Raising the amount of the catalyst to 30 mol %
and temperature to 130°C resulted in the formation of
a small amount of EtPhSiCl2 (2 wt %).
595

596
LAKHTIN et al.
EtPhSiCl2 and MeEtSiCl2 as the major products
[reaction (4)].
ω, wt %
MePhSiCl2 + Et2SiCl2
AlCl3 (30 mol %)
EtPhSiCl2 + MeEtSiCl2.
26% 20%
(4)
3 h, 120°C
In addition, traces of MeSiCl3, EtSiCl3, PhSiCl3,
Me2SiCl2 (6%), and Ph2SiCl2 (8%) were detected.
Figure 1 shows kinetic curves for the consumption
of initial reactants and accumulation of major products
I and V (AlCl3, 110°C). As the reaction started, rapid
increase in the concentration of three major products,
EtPhSiCl2 (curve 1), MeEtSiCl2 (curve 3), and
Ph2SiCl2 (curve 6) was observed due to predominance
of reactions (3) and (4). However, the concentrations
of EtPhSiCl2 and MeEtSiCl2 continuously increase
until the reaction completion, whereas the
concentration of dichloro(diphenyl)silane turns to
decrease after 30–40 min due to reaction (5).
τ, h
Fig. 1. Kinetic curves for the consumption of the initial
reactants and accumulation of products in the reaction of
MePhSiCl2 with Et2SiCl2 in the presence of AlCl3 (reactant
ratio 1 : 1, 110°C, AlCl3 30 mol %): (1) EtPhSiCl2,
(2) Et2SiCl2, (3) MeEtSiCl2, (4) MePhSiCl2, (5) Me2SiCl2,
(6) Ph2SiCl2.
Ph2SiCl2 + Et2SiCl2 → EtPhSiCl2.
(5)
The concentration of dichloro(dimethyl)silane (Fig. 1,
curve 5) formed via reaction (3) also rapidly increases
only in the initial period, and its growth considerably
slows down as the concentration of dichloro(methyl)-
(phenyl)silane (Fig. 1, curve 4) decreases.
AlCl3
2MePhSiCl2
Me2SiCl2 + Ph2SiCl2.
(3)
In the reactions of dichloro(methyl)(phenyl)silane
with dichloro(diethyl)silane and chloro(triethyl)silane,
the main pathway was phenyl/ethyl group exchange.
Thus, MePhSiCl2 reacted with Et2SiCl2 yielding
The reactions conditions and yields of the major
products are given in Table 1. The optimum conditions
for the formation of MeEtSiCl2 and PhEtSiCl2 are
Et2SiCl2-to-MePhSiCl2 ratio 1–1.5, amount of AlCl3
30 mol %, reaction time ~3 h, and temperature 110–
130°C.
Table 1. Conditions and yields of the reaction of dichloro-
(methyl)(phenyl)silane (I) with dichloro(diethyl)silane (V)
at 120°C
Amount of
AlCl3,
mol %
Yield,a %
Molar ratio
Reaction
time, h
The reactivity of Ph2SiCl2 toward chloro(ethyl)-
silanes EtnSiCl4–n (n = 1–3) was also studied. In the
reaction of Ph2SiCl2 with EtSiCl3 (II) the following
four products were detected: dichloro(ethyl)(phenyl)-
silane (III), chloro(ethyl)(diphenyl)silane (VII), tri-
chloro(phenyl)silane (VIII), and chloro(triphenyl)-
silane (IX).
V : I
EtPhSiCl2 MeEtSiCl2
1
10
20
30
30
40
30
30
30
30
3
3
3
5
3
3
6
3
6
7
33
43
48
39
52
33
25
15
6
28
40
45
36
44
30
23
16
1
1
1
AlCl3 (30 mol %)
EtPhSiCl2
Ph2SiCl2 + EtSiCl3
VI II
1
3 h, 120°C
III
1.5
1.5
2
+ Ph2EtSiCl + PhSiCl3 + Ph3SiCl.
VII VIII IX
(6)
2
The major products were compounds III and VIII
(19 and 45 wt %, respectively; Table 2). It should be
a
Calculated on the initial MePhSiCl2.
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REACTION OF CHLORO(ETHYL)SILANES WITH CHLORO(PHENYL)SILANES
597
Table 2. Product composition in the reaction of dichloro(diphenyl)silane with chloro(ethyl)silanes in the presence of
aluminum chloridea
Product fraction in the distillate, wt %
Chloro(ethyl)silane
PhEtSiCl2
Ph2EtSiCl
PhSiCl3
Ph3SiCl
PhEt2SiCl
total
73
64
60
0
EtSiCl3
Et2SiCl2
Et3SiClb
Et4Si
19
25
29
5
4
45
4
7
–
–
–
28
3
14
14
No reaction (8)
a
Equimolar amounts of the reactants, 30 mol % of AlCl3, 120°C, reaction time 3 h.
The distillate also contained 22 wt % of Et2SiCl2.
b
noted that these compounds can be formed as a result
of both Ph/Cl and Ph/Et exchange.
The mechanism of the reaction under study and its
thermodynamic parameters were analyzed by
PBE1PBE/6-31+G(d) quantum chemical calculations
[4]. The results obtained for reactions (8)–(13) are
collected in Table 3. It is seen that reactions (8)–(10)
are more probable than (11)–(13). Chloride ion transfer
from chloro(organyl)silane molecule to aluminum
chloride is characterized by ΔH and ΔG values of 87–
105 kcal/mol [reactions (8–10); Table 3]. The ΔH and
ΔG values for the transfer of organic phenyl anion Ph–
[reactions (11)–(13); Table 3] are considerably higher
(128–157 kcal/mol).
Dichloro(diphenyl)silane reacted with Et2SiCl2 (V)
to give the same products as in reaction (6) (Table 2).
In the reaction with Et3SiCl (X), apart from products
III, VII, and VIII, the formation of chloro(diethyl)-
(phenyl)silane (XI) and dichloro(diethyl)silane (V)
was observed (Table 2).
Compounds III and XI are formed via inter-
molecular exchange of phenyl and ethyl groups between
the initial reactants [reaction (7)].
PhSiCl3 + AlCl3 → PhSiCl+2 + AlCl–4,
Ph2SiCl2 + AlCl3 → Ph2SiCl+ + AlCl–4,
MePhSiCl2 + AlCl3 → MePhSiCl+ + AlCl–4,
PhSiCl3 + AlCl3 → SiCl+3 + PhAlCl–3,
Ph2SiCl2 + AlCl3 → PhSiCl+2 + PhAlCl–3,
(8)
(9)
Ph2SiCl2 + Et3SiCl → EtPhSiCl2 + Et2PhSiCl.
VI III XI
(7)
X
The product mixture also contained a considerable
amount of dichloro(diethyl)silane (22 wt %) resulting
from the reaction of initial Et3SiCl with AlCl3. As
shown by special experiments, up to 20% of Et2SiCl2
is formed in the presence of 30 mol % of AlCl3 in 10 h
at 130–140°C. The conversion of the other chloro-
(ethyl)silanes (EtSiCl3, Et2SiCl2) under analogous
conditions was insignificant. Tetraethylsilane Et4Si
failed to react with Ph2SiCl2, and no substituent
exchange was detected.
(10)
(11)
(12)
MePhSiCl2 + AlCl3 → MeSiCl+2 + PhAlCl–3. (13)
It should be noted that the chloride ion transfer
from PhSiCl3 to AlCl3 [reaction (8)] is less energe-
tically favorable (ΔH = 105.1, ΔG = 105.5 kcal/mol)
Table 3. Total energies and thermodynamic parameters of
reactions (8)–(13) according to PBE1PBE/6-31+G(d)
calculations
The composition of products of the AlCl3-catalyzed
reactions of Ph2SiCl2 with chloro(ethyl)silanes is
presented in Table 2. Chloro(ethyl)silanes EtSiCl3,
Et2SiCl2, and Et3SiCl react with dichloro(diphenyl)-
silane to give up to 60–70 wt % of substituent
exchange products. We can conclude that the presence
of at least one chlorine atom is necessary for
substituent exchange, i.e., the role of Si–Cl bond is
crucial in the examined transformations. As shown
subsequently, MePhSiCl2 also failed to react with
Et4Si.
Reaction
ΔE, kcal/mol ΔH, kcal/mol ΔG, kcal/mol
no.
8
9
105.2
88.4
105.1
89.1
105.5
87.2
10
11
12
13
95.8
95.5
94.8
157.4
127.9
141.0
156.7
127.8
140.2
156.5
124.7
138.2
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 85 No. 3 2015

598
LAKHTIN et al.
Scheme 1.
+
+
Ph
Si
Cl
Et
Ph
Cl
Et
Cl
Cl
Cl
Cl
Et
Si
Si
Si
Si
Cl
Si
+
Me
Me
Cl
Me
Et
Cl
Et
Et
А
TS-1
B
+
−
Ph
Cl
Ph
Ph
Cl
Et
AlCl3
AlCl4
Cl
Me
Cl
Cl
Me
Cl
+
Si
Si
Si
Si
C
C
C
C
MeEtSiCl2 + PhEtSiCl2
C
TS-2
than the transfer of Cl– from Ph2SiCl2 and MePhSiCl2
[reactions (9) and (10); ΔH and ΔG do not exceed
95 kcal/mol]. This is consistent with the experimental
data according to which PhSiCl3 is weakly reactive in
substituent exchange reactions with chloro(ethyl)silanes.
possess chlorine atoms, elimination of chloride ion by
the action of AlCl3 is possible from both of them.
Et2SiCl2 + AlCl3 → Et2SiCl+ + AlCl–4.
(14)
However, on the basis of the calculated energies of
reactions (10) and (14) we presumed the formation of
MePhSiCl+ cation to be more favorable: the ΔG value
for reaction (10) 94.8 kcal/mol against ΔG =
103.2 kcal/mol for reaction (14) [PBE1PBE/6-31+G(d)
calculations].
The role of aluminum chloride consists of initial
generation of chloro(diorganyl)silyl cations which
exchange organic substituents more readily than do
neutral molecules. Insofar as both reactants in (4)
A probable scheme of the examined substituent
exchange reactions is shown in Scheme 1 for the
reaction of MePhSiCl+ with dichloro(diethyl)silane as
example.
According to the proposed scheme, attack by
MePhSiCl+ cation on neutral Et2SiCl2 molecule gives
intermediate complex A where the silicon atom of the
cation is coordinated to one chlorine atom of the
neutral molecule. Complex A is then converted into
intermediate B through transition state TS-1 whose
structure is shown in Fig. 2. In the next step, transfer of
the ethyl group is mediated by transition state TS-2 in
which both silicon atoms are linked to the methylene
carbon atom of the migrating ethyl group. Further
movement along the reaction coordinate leads to
intermediate C whose reaction with AlCl4– anion yields
final disproportionation products.
This scheme rationalizes the fact that no substituent
exchange reaction occurs with SiEt4. First, SiEt4 mole-
cule lacks chlorine atoms and is therefore incapable of
forming cationic species in reaction with AlCl3.
Second, tetraethylsilane is less prone to coordination
with already generated cations with formation of
88i
Fig. 2. Structure of transition state TS-1 in the reaction of
MePhSiCl+ with Et2SiCl2 according to PBE1PBE/6-31+G(d)
calculations. Interatomic distances (Å) are given; imaginary
frequency 88i.
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REACTION OF CHLORO(ETHYL)SILANES WITH CHLORO(PHENYL)SILANES
599
complex A since this coordination also involves
chlorine atom.
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Reaction of dichloro(methyl)(phenyl)silane with
dichloro(diethyl)silane in the presence of aluminum
chloride. A round-bottom flask equipped with a stirrer,
thermometer, and reflux condenser was charged with
47.8 g (0.25 mol) of dichloro(methyl)(phenyl)silane,
39.2 g (0.25 mol) of dichloro(diethyl)silane, and 28.0 g
(0.21 molya) of AlCl3. The mixture was stirred for 3 h
at 120°C and cooled, 32.5 g (0.21 molya) of POCl3
was added, and the precipitate was filtered off. The
filtrate was distilled first under atmospheric pressure at
70–130°C and then under reduced pressure (10–
12 mmHg) at 90–170°C. The distillate, 75.5 g,
contained 4.7 g of Me2SiCl2, 14.3 g of MeEtSiCl2,
19.5 g of Et2SiCl2, 11.0 g of MePhSiCl2, 22.1 g of
EtPhSiCl2, and 3.9 g of Ph2SiCl2. The yields of
EtPhSiCl2 and MeEtSiCl2, calculated on the initial
MePhSiCl2, were 43 and 40%, respectively.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 85 No. 3 2015