MCM-41-immobilised bidentate nitrogen platinum complex: A highly efficient and recyclable phosphine-free catalytic system for the hydrosilylation of olefins

Article abstract of DOI:10.3184/174751912X13324196074823

An MCM-41-immobilised bidentate nitrogen platinum complex (MCM-41-2N-Pt) was very conveniently synthesised from commercially available and cheap 3-(2-aminoethylamino)propyltrimethoxysilane by immobilisation on the mesoporous silica nanoparticles, MCM-41, followed by reaction with potassium chloroplatinite. It was found that the MCM-41-2N-Pt complex is a highly efficient catalyst for the hydrosilylation of olefins with triethoxysilane and can be easily recovered and reused several times without significant loss of activity.

Full text of DOI:10.3184/174751912X13324196074823

JOURNAL OF CHEMICAL RESEARCH 2012
APRIL, 241–243
RESEARCH PAPER 241
MCM-41-immobilised bidentate nitrogen platinum complex: a highly
efficient and recyclable phosphine-free catalytic system for the
hydrosilylation of olefins
a
b
b
b
Hean Zhang *, Jiaqin Liu , Shaojuan Cheng and Mingzhong Cai
a
Department of Chemistry, College of Science, Nanchang University, Nanchang 330047, P. R. China
bDepartment of Chemistry, Jiangxi Normal University, Nanchang 330022, P. R. China
An MCM-41-immobilised bidentate nitrogen platinum complex (MCM-41-2N-Pt) was very conveniently synthesised
from commercially available and cheap 3-(2-aminoethylamino)propyltrimethoxysilane by immobilisation on the
mesoporous silica nanoparticles, MCM-41, followed by reaction with potassium chloroplatinite. It was found that the
MCM-41-2N-Pt complex is a highly efficient catalyst for the hydrosilylation of olefins with triethoxysilane and can be
easily recovered and reused several times without significant loss of activity.
Keywords: supported catalyst, hydrosilylation, platinum, functionalised MCM-41, heterogeneous catalysis
2
–1
The hydrosilylation of alkenes is one of the most important
Si-C bond formation reactions in organosilicon chemistry and
a variety of silicon monomers containing functional groups
diameter of ca 5 nm and a specific surface area > 700 m g .
Its large pore size allows passage of large molecules such
as organic reactants and metal complexes through the pores
1
21,22
have been synthesised by this reaction. It is a homogeneous
to reach the surface of the channel.
Shyu et al. reported
reaction, generally using soluble platinum or rhodium com-
a phosphinated MCM-41-supported rhodium complex for
catalytic hydrogenation of olefins and found that the turnover
frequency (TOF) of this MCM-41-supported phosphine rho-
2
,3
plexes such as Pt(PPh ) , H PtCl , RhCl(PPh ) as catalysts.
3
4
2
6
3 3
However, industrial applications of these homogeneous platinum
or rhodium complexes remain a challenge because the com-
plexes are expensive and cannot be recycled. They are also
difficult to separate from the product mixture, which is a
particularly significant drawback for their applications in the
pharmaceutical industry. From the standpoint of environmen-
tally benign organic synthesis, development of immobilised
transition-metal catalysts is challenging and important. In an
ideal system, they can be recovered from the reaction mixture
by simple filtration, re-used indefinitely and contamination of
products by metals is prevented. Polymer-supported transition
metal complexes catalysts are currently attracting great inter-
est since they have the advantages of both homogeneous
dium complex is three times higher than that of [RhCl(PPh ) ]
3 3
2
3
in the hydrogenation of cyclohexene. Recently, we have
reported the synthesis of MCM-41-immobilised bidentate
nitrogen palladium complex and found that it was a highly
24
efficient and recyclable catalyst for the Suzuki reaction and
2
5
the carbonylative Suzuki coupling reaction. In continuing
our efforts to develop greener synthetic pathways for organic
transformation, our new approach, described in this paper,
was to design and synthesise a novel MCM-41-supported
bidentate nitrogen platinum complex (MCM-41-2N-Pt), which
was used as an effective catalyst for the hydrosilylation of
olefins with triethoxysilane.
4
–6
and heterogeneous catalysed processes. So far, a number of
Although phosphine ligands stabilise platinum and influ-
ence its reactivity, the simplest and cheapest platinum catalysts
are of course phosphine-free systems, specifically when
used in low loading. A novel MCM-41-immobilised bidentate
nitrogen platinum complex (MCM-41-2N-Pt) was very conve-
niently synthesised from commercially available and cheap
3-(2-aminoethylamino)propyltrimethoxysilane by immobili-
sation on MCM-41, followed by reaction with potassium
chloroplatinite (Scheme 1). The X-ray powder diffraction
7
–12
13–16
supported platinum or rhodium
complexes have proved
to be efficient catalysts for the hydrosilylation of olefins.
However, these catalysts have generally suffered from limited
mass transfer and the leaching of the catalytic species from
the surface of the support. Most of them are polystyrene or
silica-supported phosphine platinum or rhodium complexes.
It is known that catalysts containing phosphine ligands are
1
7–19
unstable at high temperatures.
Furthermore, the procedure
(
XRD) analysis of the MCM-41-2N-Pt indicated that, in addi-
for preparing the polymer-bound phosphine platinum or rho-
dium complexes is rather complicated; the non-crosslinked
poly(chloromethylstyrene) is not commercially available,
and the chloromethylation requires the use of carcinogenic
chloromethyl methyl ether. Therefore, the development of
phosphine-free heterogeneous platinum or rhodium catalysts
having a high activity and excellent recyclability is a topic of
enormous importance.
tion to an intense diffraction peak (100), two higher order
peaks (110) and (200) with lower intensities were also present,
and therefore the chemical bonding procedure did not diminish
the structural ordering of the MCM-41.
Elemental analyses and X-ray photoelectron spectroscopy
XPS) were used to characterise this heterogeneous platinum
(
complex. The N:Pt mole ratio of the MCM-41-2N-Pt was
determined to be 5.15. The XPS data for MCM-41-2N-Pt,
Study of new types of supported platinum complexes cata-
lysts which might be suitable for hydrosilylation of olefins
with triethoxysilane 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 temperature, which should allow its
storage in normal bottles with unlimited shelf life (3). Devel-
opments on the mesoporous material MCM-41 provided a
new possible candidate for a solid support for immobilisation
MCM-41-2N, K PtCl and Pt foil are listed in Table 1. It can
2
4
be seen that the binding energies of Si and O of MCM-41-
2p
1s
2
N-Pt are similar to those of MCM-41-2N and the binding
energy of Cl of MCM-41-2N-Pt is similar to that of K PtCl .
2p
2
4
However, the difference of N1s binding energies between
MCM-41-2N-Pt and MCM-41-2N is 0.9 eV. The binding
energy of Pt4f7/2 in MCM-41-2N-Pt is 1.1 eV less than that in
K PtCl , but 0.8 eV larger than that in Pt foil. These results
2
4
show that a coordination bond between N and Pt is formed.
In order to evaluate the catalytic activity of the MCM-41-
immobilised bidentate nitrogen platinum complex (MCM-41-
2
0
of homogeneous catalysts. MCM-41 has a regular pore
2
N-Pt), the hydrosilylation reactions of olefins with triethoxysilane
*
Correspondent. E-mail: zhanghean96@sina.com
were studied. At first, the catalytic activity of the platinum

2
42 JOURNAL OF CHEMICAL RESEARCH 2012
Scheme 1
and
Table 1 XPS data for MCM-41-2N-Pt, MCM-41-2N, K
2
PtCl
4
Table3 CatalyticactivityofMCM-41-2N-Ptforthehydrosilylation
reaction of olefins with triethoxysilane
a
Pt foil (in eV)
Sample
Pt4f7/2
N
1s
Si2p
O
1s
Cl2p
Entry Olefin
Producta
Time GC
b
/h
yield
MCM-41-2N-Pt
MCM-41-2N
72.1
400.6
399.7
103.4
103.4
532.9
532.8
198.8
/%
K
2
PtCl
4
73.2
71.3
198.9
1
2
3
4
5
6
7
CH
CH
3
(CH
(CH
2
)
)
7
9
CH=CH
CH=CH
2
CH
CH
3
(CH
(CH
2
)
)
9
Si(OEt)
11Si(OEt)
Si(OEt)
3
3
1.5
1.6
1.4
1.6
1.7
1.3
1.3
92
91
95
86
91
73
82
Pt foil
3
2
2
3
2
3
C
C
6
H
H
5
OCH
CH CH=CH
CH=CH
CH=CH
2
CH=CH
2
C
C
6
H
H
5
O(CH
2
)
3
a
The binding energies are referenced to C1s(284.6 eV), and the
energy differences were determined with an accuracy of ± 0.2 eV.
6
5
2
2
6
5
(CH
2
)
3
Si(OEt)
3
3
Cl(CH
2
)
9
2
Cl(CH
2
)
11Si(OEt)
Si(OEt)
3
C
6
H
5
2
6
C H
5
(CH )
2 2
complex at different temperatures was investigated by using
hydrosilylation of 1-dec-1-ene with triethoxysilane as the
model reaction. The results are summarised in Table 2. The
experimental results show that no remarkable induction period
was observed and the reaction rate increased with the increase
in the reaction temperature. When hydrosilylation reaction was
carried out at 120 °C, decyltriethoxysilane was obtained in
a
1
The structure of product was further identified by H NMR.
No increase in yield with increasing the reaction time.
b
Reaction conditions: olefin (5.0 mmol); triethoxysilane (5.5 mmol);
MCM-41-2N-Pt (0.1 mol%); temperature (120 °C).
9
2% yield after 1.5 h (entry 3). So, for the temperatures evalu-
(entries 1–3 and 5). Speier’s catalyst (H PtCl ) was not as
2
6
ated [100, 110, 120, 130 °C], 120 °C gave the best result. The
effect of the amount of the MCM-41-2N-Pt complex on the
hydrosilylation reaction was also investigated using 5.0 mmol
of dec-1-cene as substrate at 120 °C. The experimental results
are shown in Table 2. The reaction rate became larger with the
increase in the amount of the catalyst, for the amounts evaluated
effective when HSi(OEt) was reacted; it was reported that the
3
26
yield of decyltriethoxysilane was only 40%. Under the new
conditions, hydrosilylation reactions of allylbenzene and allyl
glycidyl ether with HSi(OEt) could also proceed smoothly to
3
give the corresponding addition products in good yields
(
entries 4 and 7). Hydrosilylation of styrene with HSi(OEt)3
–3
–3
–2
–3
afforded the α-adduct in 15% yield in addition to the β-adduct
as a major product (entry 6).
[2.5 × 10 , 5.0 × 10 , 1.0 × 10 mmol Pt], 5.0 × 10 mmol Pt
gave the best result when decyltriethoxysilane was obtained in
–
2
A further objective of our studies was to determine whether
the catalysis was due to the MCM-41-2N-Pt complex or to a
homogeneous platinum complex that leaves the support during
the reaction and then returns to the support at the end. To test
this, we focused on the hydrosilylation reaction of dec-1-
ene with triethoxysilane. We filtered off the MCM-41-2N-Pt
complex after 30 min of reaction time and allowed the filtrate
to react further. The catalyst filtration was performed at the
reaction temperature (120 °C) in order to avoid possible reco-
ordination or precipitation of soluble platinum upon cooling.
We found that, after this hot filtration, no further reaction was
observed. This suggests that the platinum catalyst remains
on the support at elevated temperatures during the reaction.
The hydrosilylation of dec-1-ene with triethoxysilane was
examined to evaluate the reusable property of MCM-41-2N-
Pt. It was demonstrated that the novel supported bidentate
nitrogen platinum complex could be recovered by simple
filtration and reused several times. The hydrosilylation of
dec-1-ene with triethoxysilane was repeated five times using
the same batch of supported catalyst, the yields of decyl-
triethoxysilane from the first to the fifth run were 92%, 92%,
91%, 90% and 90% clearly illustrating good reusability of
the catalyst. The high stability and good reusable property of
MCM-41-2N-Pt should result from the strong coordination
of bidentate nitrogen ligand on platinum and the mesoporous
9
2% yield (entry 3). When 1.0 × 10 mmol of MCM-41-2N-
Pt was used, the reaction rate was the largest, but the final yield
of decyltriethoxysilane was only 84% and tetraethoxysilane
was formed in 7% yield (entry 6).
Hydrosilylation reactions of a variety of olefins with
triethoxysilane were studied at 120 °C using 0.1 mol% of the
MCM-41-2N-Pt as catalyst, the typical results are summarised
in Table 3. As shown in Table 3, in the presence of 0.1 mol%
of MCM-41-2N-Pt complex, hydrosilylation reactions of
dec-1-ene, dodec-1-ene, allyl phenyl ether, and ω-chloroundec-
1
-ene with HSi(OEt) proceeded smoothly and the correspond-
3
ing hydrosilylation products were obtained in 91–95% yields
Table 2 The effects of reaction temperature and amount of
the catalyst on the catalytic activity of MCM-41-2N-Pt
a
Entry Temp. /°C
Amount of
Time/h GC yield/%
catalyst/mol%
8
8
9
8
8
8
1
7
2
8
9
4
1
2
3
4
5
6
100
110
120
130
120
120
0.1
0.1
0.1
0.1
0.05
0.2
2.0
1.7
1.5
1.2
2.2
1.1
a
3
Reaction conditions: dec-1-ene (5.0 mmol); HSi(OEt) (5.5 mmol).

JOURNAL OF CHEMICAL RESEARCH 2012 243
2
9
structure of the MCM-41 support. The result is important from
a practical point of view.
3-Phenoxypropyltriethoxysilane: Oil, b.p. 154–155 °C/6 mmHg.
–1
IR (film): ν (cm ) 3056, 2943, 2841, 1595, 1471, 1389, 1245, 1086,
53, 690; H NMR (400 MHz, CDCl ): δ 7.19–7.13 (m, 2H), 6.91–
.78 (m, 3H), 3.94 (t, J = 7.6 Hz, 2H), 3.83 (q, J = 7.2 Hz, 6H),
.83–1.78 (m, 2H), 1.23 (t, J = 7.2 Hz, 9H), 0.59–0.57 (m, 2H).
-Phenylpropyltriethoxysilane: Oil, b.p. 139–141 °C/6 mmHg. IR
film): ν (cm ) 3058, 2980, 1594, 1576, 1494, 1465, 1390, 1107,
067, 750, 692; H NMR (400 MHz, CDCl ): δ 7.35–7.18 (m, 5H),
.76 (q, J = 7.2 Hz, 6H), 2.64–2.61 (m, 2H), 1.75–1.72 (m, 2H), 1.19
1
7
6
1
In conclusion, we have developed a novel, phosphine-free,
practical and economic catalyst system for the hydrosilylation
of olefins with triethoxysilane by using MCM-41-immobilised
bidentate nitrogen platinum complex [MCM-41-2N-Pt] as
catalyst. This novel heterogeneous platinum catalyst can be
conveniently prepared by a simple two-step procedure from
commercially available and cheap reagents and can be reused
at least five times without significant loss of activity. This
novel platinum complex has not only high activity for the
heterogeneous hydrosilylation of olefins with triethoxysilane,
but offers practical advantages such as easy handling, easy
separation from the product and reuse.
3
30
3
–1
(
1
3
1
3
(t, J = 7.2 Hz, 9H), 0.57–0.54 (m, 2H).
3
0
11-Chloroundecyltriethoxysilane: Oil, b.p. 147–149 °C/2 mmHg.
IR (film): ν (cm ) 2977, 2927, 2856, 1441, 1391, 1297, 1167, 1104,
081, 957, 791; H NMR (400 MHz, CDCl ): δ 3.83 (q, J = 7.2 Hz,
H), 3.42 (t, J = 6.8 Hz, 2H), 1.83–1.76 (m, 2H), 1.42–1.39 (m, 2H),
.35–1.21 (m, 23H), 0.68–0.64 (m, 2H).
Phenylethyltriethoxysilane: Oil, b.p. 129–131 °C/6 mmHg. IR
film): ν (cm ) 3057, 2974, 1598, 1575, 1497, 1461, 1392, 1104,
1076, 752, 690; H NMR (400 MHz, CDCl ): δ 7.27–7.18 (m, 5H),
–1
1
1
6
1
3
31
–1
(
1
Experimental
3
All hydrosilylation products were characterised by comparison of
their spectra and physical data with authentic samples. IR spectra
were obtained using a Perkin-Elmer 683 instrument. H NMR spectra
3.82 (q, J = 7.2 Hz, 6H), 2.75–2.73 (m, 2H), 1.22 (t, J = 7.2 Hz, 9H),
1.01–0.97 (m, 2H).
3-(2,3-Epoxypropoxy)propyltriethoxysilane: Oil, b.p. 134–135 °C/
1
30
–1
were recorded on a Bruker Avance (400 MHz) spectrometer with
2 mmHg. IR (film): ν (cm ) 2944, 2841, 1468, 1264, 1194, 1160,
1
TMS as an internal standard in CDCl as solvent. Microanalyses were
1088, 910, 821; H NMR (400 MHz, CDCl ): δ 3.82 (q, J = 7.2 Hz,
3
3
obtained using a Perkin-Elmer 240 elemental analyser. X-ray photo-
electron spectroscopy (XPS) spectra were obtained using a KRATOS
XSAM 800 electron energy spectrometer. X-ray powder diffraction
patterns were obtained on Damx-rA (Rigaka). Platinum content
was determined with inductively coupled plasma atom emission
Atomscan16 (ICP-AES, TJA Corporation). The mesoporous material
MCM-41 was prepared according to a literature procedure. Acetone,
triethoxysilane and olefins were distilled before use, other reagents
were used as received without further purification.
6H), 3.52–3.49 (m, 2H), 3.42–3.33 (m, 2H), 2.91–2.80 (m, 1H), 2.61–
2.49 (m, 2H), 1.55–1.46 (m, 2H), 1.23 (t, J = 7.2 Hz, 9H), 0.58–0.56
(m, 2H).
This work was supported by the National Natural Science
Foundation of China (Project No. 20862008) and the Natural
Science Foundation of Jiangxi Province of China (Project No.
27
2
008GQH0034).
Preparation of MCM-41-2N
A solution of 3-(2-aminoethylamino)propyltrimethoxysilane (1.54 g)
in dry chloroform (18 mL) was added to a suspension of the MCM-41
Received 17 January 2012; accepted 18 February 2012
Paper 1201112 doi: 10.3184/174751912X13324196074823
Published online: 17 April 2012
(
2.2 g) in dry toluene (180 mL). The mixture was stirred for 24 h
at 100 °C. Then the solid was filtered off and washed by CHCl (2 ×
3
References
2
0 mL), and dried under vacuum at 160 °C for 5 h. The dried white
solid was then soaked in a solution of Me SiCl (3.1 g) in dry toluene
1
I. Ojima, S. Patai and Z. Rappaport, The chemistry of organic silicon
compounds, Wiley-Interscience, New York, 1989, Chap. 25, p.1479.
B. Marciniec, Coord. Chem. Rev., 2005, 249, 2374.
3
(
100 mL) at room temperature under stirring for 24 h. Then the solid
was filtered off, washed with acetone (3 × 20 mL) and diethyl ether
3 × 20 mL), and dried under vacuum at 120 °C for 5 h to obtain
.49 g of hybrid material MCM-41-2N. The nitrogen content was
2
3
4
5
6
7
8
M. Tanabe, D. Ito and K. Osakada, Organometallics, 2007, 26, 459.
A. Corma and H. Garcia, Chem. Rev., 2002, 102, 3837.
A. Corma, H. Garcia and A. Leyva, J. Catal., 2006, 240, 87.
T. Onoe, S. Iwamoto and M. Inoue, Catal. Commun., 2007, 8, 701.
W.R. Cullen and N. F. Han, J. Organomet. Chem., 1987, 333, 269.
R. Drake, D.C. Sherrington and S.J. Thomson, React. Funct. Polym., 2004,
60, 65.
(
3
–1
found to be 1.84 mmol g by elemental analysis.
Preparation of MCM-41-2N-Pt
In a small Schlenk tube, the above-functionalised MCM-41 (MCM-
4
1-2N) (1.52 g) was mixed with K PtCl4 (0.249 g, 0.6 mmol) in
9
M. Czakova and M. Capka, J. Mol. Catal., 1981, 11, 313.
2
dry acetone (50 mL). The mixture was refluxed for 72 h under an
argon atmosphere. The solid product was filtered by suction, washed
with acetone, distilled water and acetone successively and dried at
10 J.P. Collman, J.A. Belmont and J.I. Brauman, J. Am. Chem. Soc., 1983,
05, 7288.
Z.M. Michalska, L. Rogalski and K.R. Wijas, J. Mol. Catal. A: Chem.,
004, 208, 187.
1
1
1
2
7
0 °C/26.7 Pa under Ar for 5 h to give 1.61 g of a yellow platinum
12
13
14
M. Okamoto, H. Kiya and H. Yamashita, Chem. Commun., 2002, 1634.
R. Sayah, E. Framery and V. Dufaud, Green Chem., 2009, 11, 1694.
B. Marciniec, K. Szubert, R. Fiedorow, I. Kownacki, M.J. Potrzebowski,
M. Dutkiewicz and A. Franczyk, J. Mol. Catal. A: Chem., 2009, 310, 9.
Z. M. Michalska, J. Mol. Catal., 1983, 19, 345.
complex [MCM-41-2N-Pt]. The nitrogen and platinum content was
–1
–1
found to be 1.65 mmol g and 0.32 mmol g , respectively.
Hydrosilylation of olefins with triethoxysilane
1
5
Hydrosilylation was carried out in a 5 mL flat-bottomed flask equipped
with a magnetic stirrer and a reflux condenser to the upper of which a
drying system was attached. The olefin and the platinum complex
were stirred at the reaction temperature for 30 min before triethoxysi-
lane was added. The structure and yield of hydrosilylation products
were determined based on a standard sample and a standard curve
by GLC at regular intervals. Typical reaction conditions are as fol-
lows: olefin 5.0 mmol, triethoxysilane 5.5 mmol, platinum complex
0
.1 mol%. The products were isolated by distillation under reduced
1
pressure and characterised by IR and H NMR.
28
Decyltriethoxysilane: Oil, b.p. 149–150 °C/8 mmHg. IR (film): ν
–1
1
(
cm ) 2974, 2927, 2855, 1469, 1391, 1295, 1158, 1106, 1083; H
NMR (400 MHz, CDCl ): δ 3.81 (q, J = 7.2 Hz, 6H), 1.41–1.38 (m,
3
2
H), 1.31–1.22 (m, 23H), 0.88 (t, J = 7.2 Hz, 3H), 0.66–0.64 (m, 2H).
28
Dodecyltriethoxysilane: Oil, b.p. 151–152 °C/3 mmHg. IR (film):
–1
1
ν (cm ) 2973, 2926, 2853, 1468, 1390, 1294, 1157, 1105, 1084; H
NMR (400 MHz, CDCl ): δ 3.82 (q, J = 7.2 Hz, 6H), 1.40–1.38 (m,
3
2
2
H), 1.32–1.21 (m, 27H), 0.89 (t, J = 7.2 Hz, 3H), 0.67–0.64 (m,
H).

Copyright of Journal of Chemical Research is the property of Science Reviews 2000 Ltd. and its content may
not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written
permission. However, users may print, download, or email articles for individual use.