MCM-41-supported mercapto platinum complex as a highly efficient catalyst for the hydrosilylation of olefins with triethoxysilane

Article abstract of DOI:10.1016/j.catcom.2009.12.020

A novel MCM-41-supported mercapto platinum complex was conveniently synthesized from commercially available and cheap γ-mercaptopropyltriethoxysilane via immobilization on MCM-41, followed by reacting with potassium chloroplatinite. The powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were employed to characterize the title platinum complex. It was found that the title complex is an efficient catalyst for hydrosilylation of olefins with triethoxysilane and can be reused several times without noticeable loss of activity.

Full text of DOI:10.1016/j.catcom.2009.12.020

Catalysis Communications 11 (2010) 563–566
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
MCM-41-supported mercapto platinum complex as a highly efficient catalyst
for the hydrosilylation of olefins with triethoxysilane
Ronghua Hu a,b, Lingfang Zha a, Mingzhong Cai a,
*
a Department of Chemistry, Jiangxi Normal University, Nanchang 330022, PR China
b Department of Chemistry, Jinggangshan University, Jian 343009, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel MCM-41-supported mercapto platinum complex was conveniently synthesized from commer-
Received 10 November 2009
Received in revised form 13 December 2009
Accepted 16 December 2009
Available online 23 December 2009
cially available and cheap
c-mercaptopropyltriethoxysilane via immobilization on MCM-41, followed
by reacting with potassium chloroplatinite. The powder X-ray diffraction (XRD) and X-ray photoelectron
spectroscopy (XPS) were employed to characterize the title platinum complex. It was found that the title
complex is an efficient catalyst for hydrosilylation of olefins with triethoxysilane and can be reused sev-
eral times without noticeable loss of activity.
Keywords:
Supported catalyst
MCM-41
Ó 2009 Elsevier B.V. All rights reserved.
Hydrosilylation
Mercapto platinum complex
Heterogeneous catalysis
1. Introduction
loxane grafted on fumed silica-supported phosphine platinum
complex has been proved to be efficient catalyst for hydrosilylation
The hydrosilylation of alkenes is an important industrial pro-
cess, but is also extremely valuable in laboratory scale synthesis
as well and a variety of silicon monomers containing functional
groups have been synthesized via this reaction [1]. Many metal
complexes are known to be catalysts for the reaction [2], but the
discovery by Speier et al. that hexachloroplatinic acid is a highly
efficient catalyst, even under ambient conditions [3], has led to
Pt complexes becoming the catalysts of choice for these reactions.
Generally, hydrosilylation is performed in the liquid phase using a
homogeneous catalyst. However, separation of the catalyst from
the reaction mixture may be troublesome. Over the past few dec-
ades major research efforts have been devoted to the development
of a new generation of heterogenized transition metal complex cat-
alysts. This type of catalyst can combine the advantages of easy
catalyst recovery, characteristic for a heterogeneous catalyst, with
the high activity and selectivity of soluble complexes [4,5]. These
‘third generation’ catalysts [4,6] have received much attention
[7–14]. In the preparation of supported catalysts a wide variety
of support materials have been used including cross-linked poly-
mers [12,14–16], silica [13,17–20], high surface area glasses [21]
and dendrimers [22–25]. Functionalized polysiloxane grafted on
fumed silica is a better support because they have large surface
area, high mechanical strength, heat and chemical stability. Polysi-
of olefins with triethoxysilane [26]. It is known that catalysts con-
taining phosphine ligands are unstable at high temperatures [27–
29]. Furthermore, the procedure for preparing the polymer-bound
phosphine platinum complex is rather complicated since the syn-
thesis of the phosphine ligands requires multi-step sequences.
Therefore, the development of phosphine-free heterogeneous plat-
inum catalysts having a high activity and stability is a topic of
enormous importance.
Study of new types of supported platinum complexes catalysts
which might be suitable for hydrosilylation of olefins with trieth-
oxysilane has practical significance. Our approach was guided by
three imperatives: the polymeric ligand should be easily accessible
(1), starting from readily available and cheap reagents (2), the
polymeric platinum catalyst should be air stable at room tempera-
ture, which should allow its storage in normal bottles with unlim-
ited shelf life (3). Developments on the mesoporous material
MCM-41 provided a new possible candidate for a solid support
for immobilization of homogeneous catalysts [30]. MCM-41 has a
regular pore diameter of ca. 5 nm and a specific surface area
>700 m2/g. Its large pore size allows passage of large molecules
such as organic reactants and metal complexes through the pores
to reach to the surface of the channel [31,32]. Shyu et al. reported
phosphinated MCM-41-supported rhodium complex for catalytic
hydrogenation of olefins and found that the turnover frequency
(TOF) of this MCM-41-supported phosphine rhodium complex is
three times higher than that of [RhCl(PPh3)3] in the hydrogenation
* Corresponding author. Tel./fax: +86 791 8120388.
E-mail address: caimzhong@163.com (M. Cai).
1566-7367/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2009.12.020

564
R. Hu et al. / Catalysis Communications 11 (2010) 563–566
OEt
OH
OH
OH
O
O
o
SiCH2CH2CH2SH
1.Toluene, 100
C, 24 h
MCM-41
+ (EtO)3SiCH2CH2CH2SH
MCM-41
2. Me SiCl, rt, 24 h
3
OSiMe3
MCM-41-SH
OEt
O
K PtCl , CH COCH
] PtCl
SiCH2CH2CH2SH
2
2
4
3
3
2
O
MCM-41
reflux, 72 h
OSiMe3
MCM-41-SH-Pt
Scheme 1. Preparation of the MCM-41-SH-Pt complex.
of cyclohexene [33]. However, to the best of our knowledge, no
hydrosilylation reaction of olefins with triethoxysilane catalyzed
by MCM-41-supported transition metal complexes has been re-
ported until now. In this paper, we wish to report the synthesis
of MCM-41-supported mercapto platinum complex (abbreviation:
MCM-41-SH-Pt) and its catalytic properties in the hydrosilylation
of olefins with triethoxysilane.
2.3. Hydrosilylation of olefins with triethoxysilane
Hydrosilylation was carried out in a 5 ml plane-bottomed flask
equipped with a magnetic stirrer and a reflux condenser to the
upper of which a drying system was attached. Olefin and platinum
complex were stirred at the reaction temperature for 30 min be-
fore triethoxysilane was added. The structure and yield of hydrosi-
lylation products were determined based on a standard sample
and a standard curve by GLC at regular intervals. Typical reaction
conditions are as follows: olefin 5.0 mmol, triethoxysilane
5.0 mmol, platinum complex 5.0 Â 10À3 mmol Pt. The catalyst
can be recovered by simple filtration and reused in the next run
without any treatment.
All hydrosilylation products were characterized by comparison
of their spectra and physical data with authentic samples. IR spec-
tra were obtained using a Perkin–Elmer 683 instrument. 1H NMR
spectra were recorded on a Bruker AC-P400 (400 MHz) spectrom-
eter with TMS as an internal standard in CDCl3 as solvent.
2. Experimental
The mesoporous material MCM-41 was prepared according to
literature procedure [34]. Acetone, triethoxysilane and olefins were
distilled before use, other reagents were used as received without
further purification.
2.1. Preparation of the catalyst
2.1.1. Preparation of MCM-41-SH
A
solution of
c-mercaptopropyltriethoxysilane (1.70 g,
7.1 mmol) in dry CHCl3 (12 ml) was added to a suspension of the
mesoporous support MCM-41 (2.20 g) in dry toluene (120 ml).
The mixture was stirred for 24 h at 100 °C. Then the solid was fil-
tered and washed by CHCl3 (2 Â 20 ml), and dried in vacuum at
160 °C for 5 h. The dried white solid was then soaked in a solution
of Me3SiCl (3.05 g, 28 mmol) in dry toluene (100 ml) at room tem-
perature under stirring for 24 h. Then the solid was filtered,
washed with acetone (3 Â 20 ml) and diethyl ether (3 Â 20 ml),
and dried in vacuum at 160 °C for 5 h to obtain 2.82 g of hybrid
material MCM-41-SH. The sulfur content was found to be
0.95 mmol/g by elemental analysis.
3. Results and discussion
The novel MCM-41-supported mercapto platinum complex
[MCM-41-SH-Pt] was conveniently synthesized from commercially
available and cheap c-mercaptopropyltriethoxysilane via immobi-
lization on MCM-41, followed by reacting with potassium chloro-
platinite (Scheme 1). The XRD analysis of the MCM-41-SH-Pt
indicated that, in addition to an intense diffraction peak (1 0 0),
two higher order peaks with lower intensities were also detected,
and therefore the chemical bonding procedure did not diminish
the structural ordering of the MCM-41. The nitrogen adsorption
studies demonstrated that significant decreases in surface area
and pore size by virtue of modification of the MCM-41 were ob-
served. The MCM-41 had surface area of 904.6 m2/g and diameter
of 2.7 nm, however, MCM-41-SH-Pt had surface area of 653.5 m2/g
and diameter of 2.2 nm. Elemental analyses and X-ray photoelec-
tron spectroscopy (XPS) were used to characterize this polymeric
platinum complex. The S:Pt mole ratio of the MCM-41-SH-Pt was
determined to be 3.54. The XPS data for MCM-41-SH-Pt, MCM-
2.1.2. Preparation of MCM-41-SH-Pt
To a solution of K2PtCl4 (0.205 g) in acetone (50 ml) was added
MCM-41-SH (1.51 g). The mixture was heated at reflux under
nitrogen for 72 h. The solid product was filtered by suction, washed
with acetone, distilled water and acetone successively and dried at
70 °C/26.7 Pa under nitrogen for 3 h to give 1.438 g of the light yel-
low platinum complex (MCM-41-SH-Pt). The sulfur and platinum
content was 0.78 mmol/g and 0.22 mmol/g, respectively.
Table 1
2.2. Characterization techniques of the catalyst
XPS data for MCM-41-SH-Pt, MCM-41-SH, K2PtCl4 and Pt foil (in eV).a
Sample
Pt4f7/2
72.2
S2p
Si2p
O1s
Cl2p
Microanalyses were obtained using a Perkin–Elmer 240 ele-
mental analyzer. X-ray photoelectron spectroscopy (XPS) spectra
were obtained using a KRATOS XSAM 800 electron energy spec-
trometer. X-ray powder diffraction patterns were obtained on
Damx-rA (Rigaku). The BET surface area and pore analysis were
performed on ASAP2010 (micromeritics) by N2 physical adsorp-
tion–desorption at 77.4 K.
MCM-41-SH-Pt
MCM-41-SH
K2PtCl4
163.9
163.4
103.4
103.4
532.9
532.8
198.8
73.1
71.2
198.9
Pt foil
a
The binding energies are referenced to C1s (284.6 eV), and the energy differ-
ences were determined with an accuracy of 0.2 eV.

R. Hu et al. / Catalysis Communications 11 (2010) 563–566
565
100
80
60
40
20
41-SH, K2PtCl4 and Pt foil are listed in Table 1. It can be seen that
the binding energies of Si2p and O1s of MCM-41-SH-Pt are similar
to those of MCM-41-SH, and the binding energy of Cl2p of MCM-
41-SH-Pt is similar to that of K2PtCl4. However the difference of
S2p binding energies between MCM-41-SH-Pt and MCM-41-SH is
0.5 eV. The binding energy of Pt4f7/2 in MCM-41-SH-Pt is 0.9 eV less
than that in K2PtCl4, but 1.0 eV larger than that in Pt foil. These re-
sults show that a coordination bond between S and Pt is formed.
Considering the fact that the S:Pt mole ratio of the MCM-41-SH-
Pt is 3.54 and platinum usually forms four coordinate complexes,
we supposed that two SH groups are coordinated to one platinum
center in MCM-41-SH-Pt.
In order to evaluate the catalytic activity of the novel MCM-41-
supported mercapto platinum complex catalyst, the hydrosilyla-
tion reaction of olefins with triethoxysilane was studied. At first,
the catalytic activity of this supported platinum complex at differ-
ent temperatures was investigated using the hydrosilylation of 1-
decene with triethoxysilane as the model reaction. The results
are presented in Fig. 1. The experimental results show that there
was an induction period of about 15 min at 90 °C, however, no
remarkable induction period was observed at 100 °C and the reac-
tion rate increased with increase in the reaction temperature.
When the hydrosilylation reaction was carried out at 110 °C, dec-
yltriethoxysilane was obtained in 94% yield after 80 min. So, for
the temperatures evaluated [90, 100, 110, 120 °C], 110 °C gave
the best result, which has good reproducibility of the experiments.
The effect of the amount of the MCM-41-SH-Pt complex on the
hydrosilylation reaction was also investigated using 5.0 mmol of 1-
decene as substrate at 110 °C and the results are shown in Fig. 2. It
was found that the reaction rate increased with increase of the
B
C
D
0
20
40
60
80
100
Time (min)
Fig. 2. Effect of the amount of the catalyst on the yield of decyltriethoxysilane.
Conditions: 1-decene 5.0 mmol, HSi(OEt)3 5.0 mmol, reaction temperature 110 °C.
B: 1.0 Â 10À3 mmol Pt, C: 5.0 Â 10À3 mmol Pt, D: 2.0 Â 10À2 mmol Pt.
ier’s catalyst was not so effective when HSi(OEt)3 was used. It was
reported that the yield of decyltriethoxysilane was only 40% in the
case of using H2PtCl6 as catalyst [35]. Under the same conditions,
hydrosilylation reactions of allyl phenyl ether, allylbenzene and al-
lyl glycidyl ether with HSi(OEt)3 could also proceed smoothly to
give the corresponding addition products in good yields. Hydrosi-
amount of the catalyst, for the amount evaluated [1.0 Â 10À3
,
lylation of styrene with HSi(OEt)3 afforded a-adduct in 18% yield
5.0 Â 10À3, 2.0 Â 10À2 mmol Pt], 5.0 Â 10À3 mmol Pt gave the best
result, decyltriethoxysilane was obtained in 94% yield. When
2.0 Â 10À2 mmol of MCM-41-SH-Pt was used, the reaction rate
was the fastest, but the final yield of decyltriethoxysilane was only
89% and tetraethoxysilane was formed in 4% yield.
in addition to the b-adduct as a major product. In order to show
the effect of mesoporous structure on activity of MCM-41-SH-Pt,
we prepared the silica-supported mercapto platinum complex
(‘‘Si”-SH-Pt) from
c-mercaptopropyltriethoxysilane via immobili-
zation on silica, followed by reacting with potassium chloroplati-
nite. It was found that hydrosilylation reaction of 1-decene with
HSi(OEt)3 at 110 °C using 1 mol‰ of ‘‘Si”-SH-Pt as catalyst afforded
decyltriethoxysilane in only 82% yield, which showed that the
mesoporous structure of MCM-41 plays an important role in
hydrosilylation reaction catalyzed by MCM-41-SH-Pt. We also
measured the activity of MCM-41-SH (without Pt) in hydrosilyla-
tion of olefins with HSi(OEt)3 and it was found that no reaction
was observed.
Hydrosilylation reactions of a variety of olefins with triethoxysi-
lane were studied at 110 °C using 1 mol‰ of MCM-41-SH-Pt as cat-
alyst, the typical results are listed in Table 2. As shown in Table 2,
in the presence of catalytic amount of MCM-41-SH-Pt catalyst,
hydrosilylation reactions of 1-decene, 1-dodecene and
x-chloro-
1-undecene with HSi(OEt)3 proceeded smoothly, the correspond-
ing hydrosilylation products were obtained in 90–94% yields. Spe-
A further objective of our studies was to determine whether the
catalysis was due to the MCM-41-SH-Pt complex or to a homoge-
neous platinum complex that comes off the support during the
reaction and then returns to the support at the end. To test this,
we focused on the hydrosilylation reaction of 1-decene with trieth-
oxysilane. We filtered off the MCM-41-SH-Pt complex after 20 min
of reaction time and allowed the filtrate to react further. The cata-
lyst filtration was performed at the reaction temperature (110 °C)
in order to avoid possible recoordination or precipitation of soluble
platinum upon cooling. We found that, after this hot filtration, no
further reaction was observed. This suggests that the platinum cat-
alyst remains on the support at elevated temperatures during the
reaction. The hydrosilylation of 1-decene with triethoxysilane
was examined to evaluate the reusable property of MCM-41-SH-
Pt. It was demonstrated that the novel supported mercapto plati-
num complex could be recovered by simple filtration and reused
several times. The hydrosilylation of 1-decene with triethoxysilane
was repeated five times using the same batch of supported cata-
lyst, the yields of decyltriethoxysilane from the first to the 5th
run were 94%, 92%, 91%, 90% and 87% clearly illustrating good reus-
ability of the catalyst. The high stability and good reusable prop-
erty of MCM-41-SH-Pt should result from the strong coordination
100
80
60
B
C
D
E
40
20
0
20
40
60
80
100
Time (min)
Fig. 1. Effect of reaction temperature on the yield of decyltriethoxysilane. Condi-
tions: 1-decene 5.0 mmol, HSi(OEt)3 5.0 mmol, catalyst 5.0 Â 10À3 mmol Pt. B:
90 °C, C: 100 °C, D: 110 °C, E: 120 °C.

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R. Hu et al. / Catalysis Communications 11 (2010) 563–566
Table 2
Catalytic activity of MCM-41-SH-Pt for the hydrosilylation reaction of olefins with triethoxysilane.
Olefin
Producta
Time (min)
Yieldb (%)
CH3(CH2)7CH@CH2
CH3(CH2)9CH@CH2
C6H5OCH2CH@CH2
C6H5CH2CH@CH2
Cl(CH2)9CH@CH2
C6H5CH@CH2
CH3(CH2)9Si(OEt)3
CH3(CH2)11Si(OEt)3
C6H5O(CH2)3Si(OEt)3
C6H5(CH2)3Si(OEt)3
Cl(CH2)11Si(OEt)3
C6H5(CH2)2Si(OEt)3
80
90
70
110
80
94
90
86
74
92
63
85
130
100
CH2 CHCH2OCH2CH=CH2
O
CH2 CHCH2O(CH2)3Si(OEt)3
O
Conditions: olefin, 5.0 mmol; triethoxysilane, 5.0 mmol; MCM-41-SH-Pt, 5.0 Â 10À3 mmol; temperature, 110 °C.
a
The structure of product was further identified by 1H NMR.
No increase in yield with increasing the reaction time.
b
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We have described a novel MCM-41-supported mercapto plati-
num complex whose preparation is very simple and convenient.
This complex has not only high activity for hydrosilylation of ole-
fins with triethoxysilane, but offers practical advantages such as
easy handling, separation from the product and reuse.
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This work was supported by the Natural Science Foundation of
Jiangxi Province of China (Project No. 2007GZW0172).
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