Allylsilylation of alkenes catalyzed by H+-exchanged montmorillonite with water

Article abstract of DOI:10.1016/j.cattod.2013.09.058

Proton-exchanged montmorillonite (H⁺-montmorillonite) was found to be a heterogeneous catalyst for allylsilylation of alkenes with allylsilanes. A wide variety of aromatic and aliphatic alkenes were effectively converted to the corresponding allylsilylated products in 15-120 min at 60-100 °C using H⁺-montmorillonite with ca. 1-2 wt% of water. The increasing of the amount of water drastically accelerated the allylsilylation of alkenes. For example, the reaction of p-chlorostyrene with allyltrimethysilane afforded 90% yield of the product for 15 min at 40 °C using H⁺-montmorillonite with 8.8 wt% of water, whereas only 2% yield of the product was obtained with 1.3 wt% of water. However, the final product yields with H⁺- montmorillonite with 1-2 wt% of water were higher than that with the 8.8 wt% of water. A reaction mechanism including the formation of a disilylpropyl cation was proposed. One possible explanation for the role of water is stabilization of the active disilylcation on the montmorillonite surface and/or edges via electron donation from water molecules.

Full text of DOI:10.1016/j.cattod.2013.09.058

Catalysis Today 226 (2014) 141–149
Contents lists available at ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Allylsilylation of alkenes catalyzed by H+-exchanged montmorillonite
with water
Ken Motokura, Shigekazu Matsunaga, Hiroto Noda, Akimitsu Miyaji, Toshihide Baba∗
Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8502, Japan
a r t i c l e i n f o
a b s t r a c t
Proton-exchanged montmorillonite (H+-montmorillonite) was found to be a heterogeneous catalyst
for allylsilylation of alkenes with allylsilanes. A wide variety of aromatic and aliphatic alkenes were
effectively converted to the corresponding allylsilylated products in 15–120 min at 60–100 ◦C using
H+-montmorillonite with ca. 1-2 wt% of water. The increasing of the amount of water drastically acceler-
ated the allylsilylation of alkenes. For example, the reaction of p-chlorostyrene with allyltrimethysilane
afforded 90% yield of the product for 15 min at 40 ◦C using H+-montmorillonite with 8.8 wt% of water,
whereas only 2% yield of the product was obtained with 1.3 wt% of water. However, the final product
yields with H+-montmorillonite with 1–2 wt% of water were higher than that with the 8.8 wt% of water.
A reaction mechanism including the formation of a disilylpropyl cation was proposed. One possible
explanation for the role of water is stabilization of the active disilylcation on the montmorillonite surface
and/or edges via electron donation from water molecules.
Article history:
Received 18 July 2013
Received in revised form
24 September 2013
Accepted 26 September 2013
Available online 28 October 2013
Keywords:
Allylsilylation
Alkene
Montmorillonite
Water
Heterogeneous catalysis
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
the addition of the allyl group, immediate elimination of the silyl
group and exchange between the silyl group and an electrophilic
Carbosilylation is a green synthetic protocol because of the
stability and low toxicity of organosilicon compounds compared
with other organometallic compounds such as organolithium and
organozinc [1]. Allylsilylation is one of the carbosilylation reactions
that allows the installation of both the allyl and silyl groups onto
an organic molecule. In the case of allylsilylation of alkenes with
allylsilane, the reaction affords 5-silyl-1-pentene derivatives (Eq.
(1)). The allylsilylation products have high potential as intermedi-
ates for organic synthesis, because the allyl and silyl groups can
be transferred by various organic reactions, such as oxidation and
coupling reactions [2].
activator (acid catalyst) affords the allylsilylation product. This
reaction pathway suggests that acidic materials would be effective
catalysts for the allylsilylation.
Cation-exchanged montmorillonites have been found to be
highly active heterogeneous Lewis and Brønsted acid catalysts for
various organic reactions [5–10]. Allylsilylation of alkenes with
allylsilanes was examined by our group using various heteroge-
neous and homogeneous acids. As a result, among the protonic
acids evaluated, H+-montmorillonite was found to be an excellent
catalyst for allylsilylation of both aromatic and aliphatic alkenes
[11,12].
(1)
Allylsilylation of alkenes using allylsilanes with aluminum
trichloride as a Lewis acid catalyst was first reported in 1995 by
JungandYoo’sgroup [3,4]. Generally, allylsilanes act asnucleophilic
reagents in organic reactions. Thus, electrophilic activation of an
alkene molecule is first effective to introduce the allyl group. After
Montmorillonite naturally possesses water molecules on its
outer surface and in its interlayer space [13,14]. It can be expected
that the water molecule affects montmorillonite-catalyzed reac-
tions. For example, in the clay-catalyzed Diels–Alder reaction, the
stereoselectivity of the product depends on the amount of resid-
ual water in the clay [15]. During the course of our investigation
on the effect of water on the catalysis of allylsilylation by H+-
montmorillonite, we found that the reaction was significantly
accelerated by the presence of a small amount of water [16].
∗
Corresponding author. Tel.: +81 45 924 5480; fax: +81 45 924 5441.
E-mail address: tbaba@chemenv.titech.ac.jp (T. Baba).
0920-5861/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.cattod.2013.09.058

142
K. Motokura et al. / Catalysis Today 226 (2014) 141–149
Table 1
Allylsilylation of p-chlorostyrene with allyltrimethylsilane using Brønsted acids.a
Entry
Catalyst
Conversion of
alkene (%)b
Conversion of
allylsilane (%)b
Yield (%)b
1
2
3
4
5
6
7
8
H+-montmorillonite
MontK10
99
55
7
4
85
7
<1
2
<1
<1
<1
<1
<1
<1
<1
16
20
33
24
7
6
3
20
15
5
Na+-montmorillonite
H+-USY
24
24
8
<1
<1
25
11
9
H+-L
H+-mordenite
H+-beta
FSM-16
9
10
11
Amberlyst
p-TsOH·H2Oc
c
H2SO4
a
Reaction conditions: p-chlorostyrene (1a: 1.0 mmol), allyltrimethylsilane (2a: 3.0 mmol), catalyst (0.10 g), n-heptane (1.0 mL), 100 ◦C and 30 min.
Determined by GC using internal standards. Yield was based on p-chlorostyrene used.
0.1 mmol of acid was used.
b
c
In this paper, we summarize the results for the H+-
week. H+-montmorillonites with different amounts of adsorbed
water were prepared as follows: the parent H+-montmorillonite
was dried under vacuum (ca. 1 mmHg) at the required temperature
for 1 h before the catalytic reaction.
montmorillonite-catalyzed allylsilylation of alkenes. The rela-
tionship between the amount of adsorbed water and catalytic
performance in the allylsilylation of alkenes is discussed. We also
report the role of water molecules in the catalytic allylsilylation.
MontK10
was
purchased
from
Aldrich.
H+-Beta
H+-USY
(SiO2/Al2O3 = 25),
H+-L
(SiO2/Al2O3 = 6.3),
(SiO2/Al2O3 = 5.9), and H+-Mordenite (SiO2/Al2O3 = 18.0) were
purchased from Nikki Chemical Co. These zeolites were heated
at 500 ◦C under air before use. FSM-16 was purchased from
FUJI SYLYSIA Co. Amberlyst was purchased from Organo Co. as
Amberlyst® 15DRY. Unless otherwise noted, all other materials
were purchased from Wako Pure Chemicals, Tokyo Kasei Co., Kanto
Kagaku Co., and Aldrich Inc.
2. Experimental
2.1. Characterization procedures
Proton nuclear magnetic resonance (1H NMR) and carbon
nuclear magnetic resonance (13C NMR) spectra were recorded
in CDCl3 with Jeol JNM-AL300 and Bruker AVANCE III 400 spec-
trometers operating at 300 and 75 MHz, or 400 and 100 MHz,
respectively. Thermal gravimetric differential thermal analysis(TG-
DTA) was performed using a Shimadzu DTG-60 with a heating rate
of 5 K min−1 under a N2 flow of 100 mL min−1, from room tempera-
ture. Powder X-ray diffraction (XRD) patterns were measured using
a RigakuDenki Multi Flex diffractometer with Cu K␣ radiation, at
40 kV and 40 mA at a rate of 0.5◦ (2Â) per minute.
2.3. Procedure for allylsilylation
Procedure for allylsilylation of p-chlorostyrene (1a) with
allyltrimethylsilane (2a) is as follows. H+-montmorillonite (0.10 g),
toluene (1.0 mL), 1a (1.0 mmol), and 2a (3.0 mmol) were placed
into a glass reactor under a dry Ar atmosphere using Schlenk tech-
niques. The resulting mixture was vigorously stirred at 100 ◦C.
After 180 min, the catalyst was separated by filtration. GC analysis
of the filtrate showed a 95% yield of [2-(4-chlorophenyl)pent-4-
enyl]trimethylsilane (3a). The filtrate was evaporated and the crude
product was purified by column chromatography using silica (n-
hexane elute) to afford the pure product. The product was identified
by 1H and 13C NMR and mass spectral data. Detailed reaction con-
ditions are shown in Table footnote.
Analytical GLC was measured using a Shimadzu GC-7A equipped
with a Silicon SE-30 column and a flame ionization detector. Shi-
madzu QP5000 was used as GC–MS equipped with DB-1 column.
2.2. Materials
Na+-montmorillonite [Na0.66(OH)4Si8(Al3.34Mg0.66Fe0.19)O20
;
Kunipia F] was obtained from Kunimine Industry. Proton-
exchanged montmorillonite (H+-montmorillonite) was prepared
from Na+-montmorillonite using
a
previously reported
3. Results and discussion
ion exchange procedure with aqueous hydrogen chloride
[17,18]. Physicochemical properties, such as acid amount
(0.86 mmol g−1), strength (ꢀH = 111 kJ mol−1), and concentration
(6.3 × 10−3 mmol m−2), of the H+-montmorillonite were reported
in the literature [17,18]. After the drying of H+-montmorillonite
at 110 ◦C, the amount of adsorbed water was ca. 1–2 wt%. Unless
otherwise noted, H+-montmorillonite was used without further
treatment.
3.1. Catalytic performances of H+-montmorillonite
Allylsilylation of p-chlorostyrene (1a) with three equivalents
of allyltrimethylsilane (2a) was carried out at 100 ◦C using
various heterogeneous and homogeneous protonic acids. The
results are shown in Table 1. H+-montmorillonite showed the
highest catalytic performance to give [2-(4-chlorophenyl)pent-
4-enyl]trimethylsilane (3a) in 85% yield based on 1a (entry 1).
The product yield using commercially available montK10 was
much lower than that for the H+-montmorillonite (entry 2). The
The procedure to produce the H+-montmorillonite with dif-
ferent amount of adsorbed water is as follows. The parent
H+-montmorillonite was stored under 30% humidity for at least one

K. Motokura et al. / Catalysis Today 226 (2014) 141–149
143
Table 2
Allylsilylation of p-chlorostyrene with allyltrimethylsilane using H+-montmorillonite in various solvents.a
Solvent
Conversion of alkene (%)b
Yield (%)b
Toluene
Toluene
n-Heptane
1,4-Dioxane
Isopropanol
DMF
99
95
99
12
15
6
95c
90
85
2
<1
<1
<1
DMSO
<1
a
Reaction conditions: H+-montmorillonite (0.10 g), 1a (1.0 mmol), 2a (3.0 mmol) solvent (1.0 mL), 100 ◦C and 30 min.
Determined by GC using internal standard technique. Yield was based on p-chlorostyrene.
120 min.
b
c
product did not form when using sodium-exchanged montmoril-
electron-donating groups, such as p-methoxystyrene and
p-methylstyrene, did not work well as substrates. H+-
montmorillonite also promoted the allylsilylation of aliphatic
alkenes, such as 1-hexene, with 2a. In addition to 2a, allyltriethyl-
silane and methallyltrimethylsilane were also found to be good
allylsilylating reagents.
lonite (entry 3). Zeolites, such as USY and mordenite, were less
active (entries 4–7). The reaction also did not proceed with p-
toluenesulfonic acid and H2SO4 (entries 10 and 11).
The conditions for the H+-montmorillonite-catalyzed reaction
of 1a with 2a were optimized with respect to the solvent, as shown
in Table 2. Toluene was found to be a better solvent than n-heptane,
affording a 95% yield of 3a. 4-[(Trimethylsilyl)methyl]-6-silahept-
1-ene, a dimerized product of 2a, was also detected in 16% yield
based on the amount of 2a used. An 86% yield of 3a was obtained
with toluene, even in the presence of two equivalents of 2a. Allylsi-
lylation did not proceed in polar solvents, such as dioxane and
DMF. The substrate ratio was also investigated as shown in Table 3.
The best yield of the product was obtained with alkene/allylsilane
ratio of 1.0/3.0. The yield decreased upon decreasing the amount of
allylsilane.
Next, the effect of adsorbed water on the montmorillonite
surface on the catalytic performance of the allylsilylation was
investigated. The amount of adsorbed water was determined
by thermal gravimetric analysis (TGA) [16]. Aliouane and co-
workers have reported that the two periods of weight loss below
100 ◦C and between 100 and 150 ◦C during TGA are assignable to
weakly linked water and H+-coordinated water (H3O+), respec-
tively [14]. Based on the TGA results, the amounts of water on
the H+-montmorillonites treated at different temperatures were
determined as 5.6, 2.1, and 1.3 wt%, respectively (Table 6). These
H+-montmorillonites are denoted as H+-montmorillonite-(5.6), -
(2.1), and -(1.3), respectively. Differential thermal analysis (DTA)
curves of the H+-montmorillonites showed an endothermic peak
below 150 ◦C. This result confirms that the weight loss below 150 ◦C
corresponds to adsorbed water [16]. Maintenance of the layered
structure of H+-montmorillonite after the heat treatment was con-
firmed by X-ray diffraction (XRD) measurements [16].
After the reaction, the H+-montmorillonite could be easily
recovered from the reaction mixture by filtration. In the reuse
experiment, the catalytic activity decreased slightly; however, up
to 70% yield of the product was obtained by prolonged reaction
time at least 3rd use (Table 4).
The scope of substrates is shown in Table 5. The allylsilylation
occurred with simple styrene to give the corresponding product
in 72% yield. The H+-montmorillonite-catalyzed reactions of other
p-substituted styrenes, such as p-bromo, and p-fluorostyrenes,
with 2a afforded the corresponding allylsilylated products in 87
and 91% yields, respectively. This is the first report of the allylsi-
lylation of styrene derivatives with allylsilane. Styrenes with
To clarify the effect of water on the catalytic activity of
H+-montmorillonite in the allylsilylation reaction, allylsilyla-
tion of p-chlorostyrene with allyltrimethylsilane was carried
out. Fig. 1 shows the time course of the product yield. Cat-
alytic activity increased with the amount of adsorbed water
Table 3
Allylsilylation of p-chlorostyrene with allyltrimethylsilane using H+-montmorillonite with various alkene/allylsilane ratios.a
Alkene/allylsilane (mmol/mmol)
Conversion of alkene (%)b
Yield (%)b
1.0/3.0
1.0/2.0
1.0/1.0
95
96
89
90
89
53
a
Reaction conditions: H+-montmorillonite (0.10 g), toluene (1.0 mL), 100 ◦C and 30 min.
Determined by GC using internal standard technique. Yield was based on p-chlorostyrene.
b

144
K. Motokura et al. / Catalysis Today 226 (2014) 141–149
Table 4
Reuse of H+-montmorillonite for allylsilylation of p-chlorostyrene with allyltrimethylsilane.a
Reuse
Reaction time (min)
Conversion of alkene (%)b
Yield (%)b
Fresh
30
60
120
120
95
92
87
81
90
88
77
73
1st use
2nd use
3rd use
a
Reaction conditions: H+-montmorillonite (0.10 g), 1a (1.0 mmol), 2a (3.0 mmol), toluene (1.0 mL), 100 ◦C and 30 min.
Determined by GC using internal standard technique. Yield was based on p-chlorostyrene.
b
Table 5
Allylsilylation of alkenes (1) with allylsilanes (2) using H+-montmorillonite catalyst.a
Alkene
Allylsilane
1/2 (mmol/mmol)
Time (min)
Conversion of 1 (%)b
Yield (%)b
2a
2a
1.0/3.0
1.0/3.0
120
15
99
93
95
72c
2a
1.0/3.0
30
96
87d
2a
2a
1.0/3.0
3.0/1.0
60
60
98
91
97e
88f
2a
3.0/1.0
1.0/3.0
60
30
99e
55f
1a
99
61
1a
1.0/3.0
30
99
86
a
Reaction conditions: H+-montmorillonite (0.10 g), toluene (1 mL) and 100 ◦C.
Determined by GC using internal standard technique. Yield was based on alkene 1.
5.0 × 10−2 g of H+-montmorillonite was used.
b
c
d
80 ◦C.
e
f
Conversion of allylsilane 2a was shown.
Reaction carried out at 60 ◦C. Yield was based on allylsilane 2a.
[H+-montmorillonite-(1.3) < -(2.1) < -(5.6)]. Next, allylsilylation
using H+-montmorillonite-(1.3) was carried out in the presence
of additional water. The reaction rate in the initial period was
increased by a factor of 60 by the addition of 7.5 mg of water to
the reaction mixture including 0.10 g of H+-montmorillonite-(1.3)
(ꢀ) compared with no additional water (ꢁ). When the amount
of water was increased to 50 mg (2.8 mmol), an induction period
was observed in the allylsilylation, as shown in Fig. 2. During the
Table 6
Amount of adsorbed water and interlayer distance of H+-montmorillonites treated at different temperatures.
b
Treatment temp. (◦C)
Adsorbed water (wt%)a
Interlayer distance (A)
˚
Catalyst
H+-montmorillonite-(5.6)
H+-montmorillonite-(2.1)
H+-montmorillonite-(1.3)
25
100
120
5.6
2.1
1.3
3.4
2.6
2.4
a
Determined by TG analysis.
b
˚
Determined by subtracting the c dimension of the silicate sheet (9.6 A) from the observed d001 values in the XRD spectrum.

K. Motokura et al. / Catalysis Today 226 (2014) 141–149
145
80
60
40
20
0
0
50
100
150
200
Reaction time / min
Fig. 1. Time course for allylsilylation of p-chlorostyrene with allyltrimethyl-
silane using (ꢁ) H+-montmorillonite-(1.3), (ꢀ) H+-montmorillonite-(2.1), (ꢁ)
H+-montmorillonite-(5.6), and (ꢀ) H+-montmorillonite-(1.3) with 7.5 mg of H2O
(total: 8.8 wt%). Reaction conditions: p-chlorostyrene (1.0 mmol), allyltrimethylsi-
lane (3.0 mmol), H+-montmorillonite (0.10 g), toluene (1.0 mL), 50 ◦C.
Fig. 2. Time course for the amount of allylsilylationproduct (ꢂ) and hexamethyldis-
iloxane (ꢁ). Reaction conditions: H+-montmorillonite-(1.3) (0.10 g), p-chlorostyrene
(1.0 mmol), allyltrimethylsilane (3.0 mmol), toluene (1.0 mL), H2O (50 mg) and 50 ◦C.
contrast, the allylsilyaltion completed in 15–60 min at 40 ◦C using
H+-montmorillonite with 8.8 wt% of water due to the much faster
reaction rate (Table 7). However, the final product yields were
slightly lower than in the case of no additional water (Table 5).
For example, the final yields from 1-hexene (1e) with and without
the additional water were 88 (Table 5) and 64% (Table 7), respec-
tively. The presence of water induced decomposition of allylsilane,
resulting in the low final yield of the allylsilylation product.
induction period, the formation of ca. 1.0 mmol of hexamethyl-
disioxane (Me3SiOSiMe3) was observed. In other words, ca.
0.5 mmol of water was consumed during the induction period
by the reaction with allyltrimethylsilane to give Me3SiOSiMe3.
Results shown in Figs. 1 and 2 indicated that the presence of an
appropriate amount of water for the allylsilylation.
The allylsilylation of various alkenes was examined using
H+-montmorillonite-(1.3) with additional H2O, and the results
are summarized in Table 7. H+-montmorillonite contains 8.8 wt%
of water after the addition of 7.5 mg of water to the 0.10 g
of H+-montmorillonite-(1.3). The reactions of styrenes having
electron-withdrawing groups proceeded at 40 ◦C. For example, the
reaction of p-chlorostyrene was completed within 15 min, giving
a 90% yield of the product, while a yield of only 2% was obtained
without the additional H2O under the same reaction conditions.
The reaction of styrene with allyltrimethylsilane was also accel-
erated by the addition of H2O. In the case of H+-montmorillonite
with 1–2 wt% of water, as shown in Table 5, high reaction tem-
peratures (60–100 ◦C) and long reaction times (15–120 min) were
necessary to complete the allylsilylation of various alkenes. In
3.2. Investigation of reaction mechanism
In order to elucidate the H+-montmorillonite-catalyzed reac-
tion pathway, we examined the reaction of cyclohexene with
allyltrimethylsilane (2a). 1H NMR study revealed the formation
of the allylsilylated product with exclusively trans allyl and silyl
groups (Scheme 1). There were no other major products converted
from cyclohexene. This result suggests stepwise addition of the silyl
and allyl groups of the allylsilane to the alkenes [3,4].
Jung and co-workers proposed a reaction mechanism for the
AlCl3-catalyzed allylsilylation of alkenes, which involves a cationic
silane intermediate, a 1,3-disilylpropyl cation (SiCH2C+HCH2Si)
Table 7
Allylsilylation of alkenes with allyltrimethylsilane using H+-montmorillonite-(1.3) at 40 ◦C.a
Alkene (R
)
Time (min)
Additional H2O (mg)
Conversion of alkene (%)b
Yield (%)b
p-Cl-Ph-(1a)
p-Cl-Ph-(1a)
p-F-Ph (1d)
p-Br-Ph-(1c)
Ph-(1b)
15
15
15
60
15
15
15
7.5
0
7.5
7.5
7.5
0
93
2
91
99
95
4
90
2
81
74
55
2
Ph-(1b)
n-C4H9-(1e)
7.5
96
64
a
Reaction conditions: alkene (1.0 mmol), allyltrimethylsilane (3.0 mmol), H+-montmorillonite (0.10 g), toluene (1.0 mL) and 40 ◦C. H+-montmorillonite was treated at
120 ◦C under vacuum before the reaction (H+-montmorillonite-(1.3)). After 10 min, 1.0 mmol of additional allylsilane was added.
b
Determined by GC and 1H NMR using internal standard technique.

146
K. Motokura et al. / Catalysis Today 226 (2014) 141–149
Scheme 1. Allylsilylation of cyclohexene with allyltrimethylsilane using H+-montmorillonite.
Scheme 2. Possible pathway for 1,3-disilylpropyl cation formation from allyltrimethylsilane and H+-montmorillonite.
Scheme 3. Estimated pathway for dimerization of allyltrimethylsilane on montmorillonite surface.
[3]. A possible pathway of formation of the 1,3-disilylpropyl
cation from 2a and H+-montmorillonite is shown in Scheme 2.
Formation of propylene by reaction of allylsilane with H+-
montmorillonite also supports this pathway. During the treatment
of H+-montmorillonite with allyltrimethylsilane, the dimerization
of allyltrimethylsilane took place. The dimerized product is thought
to be obtained from the reaction of the 1,3-disilylpropyl cation
with allyltrimethylsilane (Scheme 3). To confirm the participa-
tion of the 1,3-disilylpropyl cation in the catalytic allylsilylation
of alkenes, reaction of 1a with allyltriethylsilane was examined
in the presence of 1,3-di(trimethylsilyl)propan-2-ol, a precursor
to the 1,3-disilylpropyl cation. After the reaction, the formation
of an allylsilylated product with a SiMe3 group was observed
(Scheme 4). These results suggest that the 1,3-disilylpropyl cation
forms from allylsilane on the montmorillonite surface, and acts as
a reaction intermediate. Thus, a catalytic cycle for the allylsilyla-
tion of alkenes using H+-montmorillonite is proposed, as shown
in Scheme 5: (i) nucleophilic attack of an alkene to a disilylca-
tion to form allylsilane and a secondary carbocation intermediate
stabilized by the silyl group at the ␤-position, (ii) nucleophilic
attack of an allylsilane to the intermediate to form a new C
C
bond, and (iii) formation of allylsilylated product and disilylca-
tion by nucleophilic addition of another allylsilane. To determine
the rate-determining step, the allylsilylation was conducted at
50 ◦C with various p-chlorostyrene concentrations. Reaction condi-
tions are as follows: H+-montmorillonite (0.10 g), toluene (1.0 mL),
p-chlorostyrene (1.0, 2.0, and 3.0 mmol), and allyltrimethylsi-
lane (3.0 mmol). In all cases, the product yields were ca. 10% at
Scheme 4. Allylsilylation of p-chlorostyrene with allyltriethylsilane in the presence of 1,3-disilylpropan-2-ol.

K. Motokura et al. / Catalysis Today 226 (2014) 141–149
147
Scheme 5. Proposed catalytic cycle for the allylsilylation of alkenes with allylsilane using H+-montmorillonite.
1.5 h. The rate of allylsilylation at low conversion (<10%) was
almost independent of the p-chlorostyrene concentration. The
electron-withdrawing substitution of para-position of styrene
enhanced the allylsilylation rate. These results indicate that nucle-
ophilic addition of allylsilane (step (ii) or (iii)) is included in the
rate-determining step.
If the carbocation center is more electrophilic than the
silyl group of the disilylcation, 1,3-bis(trimethylsilyl)-2-propanol
should form in the presence of H2O. Upon careful analysis of the
reaction mixture by GC–MS, however, 1,3-bis(trimethylsilyl)-2-
propanol was not detected. This indicates that the Si center is more
electrophilic in the disilylcation. Because Si atom shows high affin-
ity for oxygen atom, the H2O molecule might interact with the Si
atom of the cationic species. The formation of silanol and disiloxane
as byproducts (Fig. 2) also supports this hypothesis.
3.3. Role of adsorbed water
As shown in Scheme 5, all cationic intermediates include SiMe3
group. Since the interaction between H2O and SiMe3 group is an
election donation from H2O to Si atom, the rate-determining step
(Scheme 5, (ii) or (iii)) cannot be accelerated by such interaction.
One possible explanation for the role of water is stabilization of the
active disilylcation on the montmorillonite surface and/or edges via
electron donation from the water molecules to increase the con-
centration or life time of active species, as shown Scheme 6. We
have previously reported the formation of inactive SiMe3 species
on the montmorillonite surface after the catalytic reaction [11,16].
This is a reason for the gradually decreasing of the catalytic activity
during reuse experiment (Table 4). The water may suppress such
deactivation pathway.
As shown in Scheme 6, at least two H2O molecules could interact
with the possible cationic silyl species. Table 9 summarizes amount
of H2O, H2O/H+ site ratio, and reaction rate for the allylsilylation of
p-chlorostyrene with allyltrimethylsilane in each catalytic system.
At least five times more water than acid sites are necessary to pro-
mote the catalytic allylsilylation significantly. This is a reasonable
value because two types of H2O molecules can be observed on the
montmorillonite surface: (i) H2O close to the H+ site and (ii) weakly
linked water on the montmorillonite surface [14].
The interlayer space of montmorillonite expands slightly in non-
polar solvents. However, this expanded interlayer space is not
sufficient to allow the entrance and reaction of organic molecules.
The allylsilylation reaction proceeded in nonpolar solvents, such
as toluene and n-heptane. As shown in Table 6, the interlayer
+
˚
distances of the H -montmorillonites (2.4–3.4 A), which corre-
spond to the sizes of H2O and H3O+, are too narrow to allow the
entrance of p-chlorostyrene and allyltrimethylsilane molecules.
These facts indicate that differences in the interlayer distances of
the H+-montmorillonites (Table 6) do not affect their catalytic per-
formances in the allylsilylation reaction.
To investigate the interaction between the Si group and the
water molecule, the reaction using allyltriethylsilane was examined
using H+-montmorillonite-(1.3) with and without the addition of
H2O at 40 ◦C, as shown in Table 8. The reaction of p-chlorostyrene
with allyltriethylsilane was accelerated by the addition of H2O,
however, the accelerating effect was much smaller than in the
reaction of allyltrimethylsilane. Due to the bulky ethyl group on
the Si atom, the interaction between the SiEt3 group and the H2O
molecule is much weaker compared with that of the SiMe3 group.
This suggests that the interaction between the Si atom and H2O
(Scheme 6) plays a key role in the acceleration of the allylsilyla-
tion.
The possibility of abstraction of SiMe3 group from cationic inter-
mediate (iii) (Scheme 5) by H2O molecule cannot be completely

148
K. Motokura et al. / Catalysis Today 226 (2014) 141–149
Table 8
Allylsilylation of p-chlorostyrene with allyltrimethylsilane or allyltriethylsilane with and without additional H2O.a
Allylsilane (SiRꢂ3
)
Product yield (%)b
With additional H2Oc
Without additional H2O
SiMe3
SiEt3
73
8
<1
<1
a
Reaction conditions: alkene (1.0 mmol), allyltrimethylsilane (3.0 mmol), H+-montmorillonite (0.10 g), toluene (1.0 mL), 40 ◦C and 10 min. H+-montmorillonite was treated
at 120 ◦C under vacuum before the reaction (H+-montmorillonite-(1.3)).
b
Determined by 1H NMR using internal standard technique.
H2O (7.5 mg).
c
Table 9
Effect of H2O/acid site molecular ratios on the rate of the allylsilylation catalyzed by H+-montmorillonite.
Catalyst and additive
Amount of H2O (mmol)
H2O/acid sitea
Rate (mmol/min)b
H+-montmorillonite-(1.3)
0.072
0.12
0.31
0.49
0.83
1.4
3.6
1.0 × 10−3
1.8 × 10−3
1.3 × 10−2
6.6 × 10−2
H+-montmorillonite-(2.1)
H+-montmorillonite-(5.6)
H+-montmorillonite-(1.3) + 7.5 mg of H2O (total: 8.8 wt%)
5.7
a
Amount of acid site in 0.10 g of H+-montmorillonite is calculated to be 0.086 mmol.
b
Reaction conditions: p-chlorostyrene (1.0 mmol), allyltrimethylsilane (3.0 mmol), H+-montmorillonite (0.10 g), toluene (1.0 mL) and 50 ◦C.
Scheme 6. Proposed roles of water: stabilization of the catalytically active species.
ruled out. In this case, silanol and/or disiloxane formation occurs,
and a stoichiometric amount of H2O is consumed. In fact, the for-
mation of both silanol and disiloxane was detected. However, the
abstraction of SiMe3 group by H2O is not the primal reason for the
acceleration effect by water due to following reasons.
In Scheme 4, the ratio of SiMe3 and SiEt3 group in substrates
(allylsilane and alcohol) and products are very close. This result
indicates that the rapid exchange of silyl groups between a cationic
intermediate and an allylsilane occurs during the catalytic cycle.
This fact indicates that step (iii) in Scheme 5, the Si exchange reac-
tion, proceeds more rapidly than the C C bond formation step
(ii). This fact indicates that step (ii) is the rate-determining step
in the allylsilylation. This conclusion supports that the abstraction
of SiMe3 by H2O, which can accelerate step (iii), should not be the
primal reason for the acceleration of allylsilylation.
4. Conclusion
H+-montmorillonite was found to be an active catalyst for the
allylsilylation of alkenes with allylsilanes at 60–100 ◦C without
additional water. Styrene derivatives having electron-withdrawing
groups and aliphatic alkenes can be used as alkene substrates. The
catalyst can be reused at least three times with maintenance of
the high product yields. Addition of 7.5 wt% of water to the 0.10 g
of H+-montmorillonite improved the catalytic activity: the allylsi-
lylation of almost all alkenes completed within 15 min at 40 ◦C.

K. Motokura et al. / Catalysis Today 226 (2014) 141–149
149
However, the final product yields were slightly lower than in the
case of no additional water. Experimental results suggest that an
interaction between the water molecule and SiMe3 stabilizes the
active intermediate.
[4] I.N. Jung, B.R. Yoo, Synlett (1999) 519.
[5] K. Kaneda, Synlett (2007) 999.
[6] K. Kaneda, K. Ebitani, T. Mizugaki, K. Mori, Bull. Chem. Soc. Jpn. 79 (2006)
981.
[7] Y. Izumi, K. Urabe, M. Onaka, Microporous Mesoporous Mater. 21 (1998) 227.
[8] J.H. Clark, D.J. Macquarrie, Chem. Soc. Rev. 25 (1996) 303.
[9] Y. Izumi, M. Onaka, Adv. Catal. 38 (1992) 245.
[10] P. Laszlo, Acc. Chem. Res. 19 (1986) 121.
Acknowledgement
[11] K. Motokura, S. Matsunaga, A. Miyaji, Y. Sakamoto, T. Baba, Org. Lett. 12 (2010)
1508.
[12] K. Motokura, T. Baba, Green Chem. 14 (2012) 565.
[13] F. Bergaya, B.K.G. Theng, G. Lagaly (Eds.), Handbook of Clay Science, Elsevier
Science, Amsterdam, 2006.
This work was supported by Grant-in-Aid for Young Scientists
(A) (24686092).
[14] N. Aliouane, A. Hammouche, R.W. De Doncker, L. Telli, M. Boutahala, B. Brahimi,
Solid State Ionics 148 (2002) 103.
References
[15] C. Collet, P. Laszlo, Tetrahedron Lett. 32 (1991) 2905.
[16] K. Motokura, S. Matsunaga, H. Noda, A. Miyaji, T. Baba, ACS Catal. 2 (2012)
1942.
[17] K. Motokura, N. Fujita, K. Mori, T. Mizugaki, K. Ebitani, K. Kaneda, Angew. Chem.
Int. Ed. 45 (2006) 2605.
[1] N. Asao, Y. Yamamoto, Bull. Chem. Soc. Jpn. 73 (2000) 1071.
[2] For reviews, see:
(a) Y. Ishii, S. Sakaguchi, T. Iwahama, Adv. Synth. Catal. 343 (2001) 393;
(b) T. Punniyamurthy, S. Velusamy, J. Iqbal, Chem. Rev. 105 (2005) 2329;
(c) S. Bracegirdle, E.A. Anderson, Chem. Soc. Rev. 39 (2010) 4114.
[3] S.H. Yeon, B.W. Lee, B.R. Yoo, M.-Y. Suk, I.N. Jung, Organometallics 14 (1995)
2361.
[18] K. Motokura, N. Nakagiri, T. Mizugaki, K. Ebitani, K. Kaneda, J. Org. Chem. 72
(2007) 6006.