N-heterocyclic carbene platinum complexes functionalized with a polyether chain and silyl group: Synthesis and application as a catalyst for hydrosilylation

Full text of DOI:10.1080/10426507.2017.1321647

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: http://www.tandfonline.com/loi/gpss20
N-heterocyclic carbene platinum complexes
functionalized with a polyether chain and silyl
group: Synthesis and application as a catalyst for
hydrosilylation
Fengxiang Zhang, Ying Bai, Xiaoling Yang, Jiayun Li & Jianjian Peng
To cite this article: Fengxiang Zhang, Ying Bai, Xiaoling Yang, Jiayun Li & Jianjian Peng (2017):
N-heterocyclic carbene platinum complexes functionalized with a polyether chain and silyl group:
Synthesis and application as a catalyst for hydrosilylation, Phosphorus, Sulfur, and Silicon and the
Related Elements, DOI: 10.1080/10426507.2017.1321647
To link to this article: http://dx.doi.org/10.1080/10426507.2017.1321647
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Date: 27 April 2017, At: 01:07

N-heterocyclic carbene platinum complexes functionalized with a polyether
chain and silyl group: Synthesis and application as a catalyst for hydrosilylation
Fengxiang Zhang, Ying Bai*, Xiaoling Yang, Jiayun Li, Jianjian Peng*
Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of
Education, Hangzhou Normal University, Yuhangtang Road 2318, Hangzhou 311121,
China
*Corresponding author: Ying Bai, Hangzhou Normal University, Yuhangtang Road
2318, Hangzhou, 311121, China. Fax: +86-571-28865135. E-mail address:
baiying0912@163.com; Jiajian Peng, Hangzhou Normal University, Yuhangtang
Road 2318, Hangzhou, 311121, China. Fax: +86-571-28865135. E-mail address:
jjpeng@hznu.edu.cn.
Abstract
The synthesis and characterization of new N-heterocyclic carbene platinum(II)
complexes functionalized with a polyether chain and silyl group are described. In
addition, their application towards the catalytic hydrosilylation of unsaturated carbon–
carbon bonds, including alkenes, alkynes, vinyl ether and unsaturated esters, is
reported. These new complexes exhibit both excellent catalytic activity and selectivity
for hydrosilylation. The catalytic system can be recycled >27 times.

Keywords
N-heterocyclic carbene; platinum; hydrosilylation

INTRODUCTION
The catalytic hydrosilylation of unsaturated compounds, such as alkynes, alkenes,
imines and ketones, is one of the most efficient methods used for the synthesis of
organosilicon compounds including silane coupling agents, silicone rubber, silicone
oil and silicone [1,2]. A number of catalysts have been explored in hydrosilylation
processes with most research and industrial syntheses carried out using platinum or
rhodium complexes due to the fact that these complexes often exhibit high catalytic
activity. Although recent efforts have been directed towards the development of new
low-cost metal catalyst systems for hydrosilylation [3,4], the platinum catalyst-based
systems are still the most commonly used [5]. The two common catalysts used for
industrial applications are Speier’s catalyst [6,7] and Karstedt’s catalyst [8,9]. One of
the disadvantages of these catalysts is the ease of generation of colloidal platinum,
which is responsible for other undesired reactions, such as hydrogenation [3]. To
improve the activity, selectivity and stability of the catalysts, numerous efforts are still
being made to search for new catalysts [5].
N-Heterocyclic carbene (NHC) ligands and supported transition-metal
complexes have widespread applications in catalysis [10-12]. In 2002, the Marko
group reported that platinum(0)-complexes with monodentate NHC-ligands can be
successfully
applied
in
the
hydrosilylation
of
octene
using
bis(trimethylsiloxy)methysilane [13]. In addition, a series of NHC-Pt complexes have
been prepared and used as the catalyst in hydrosilylation [14-19]. When compared
with NHC-Pt(0) complexes, the synthesis and application of NHC-Pt(II)complexes in

hydrosilylation are rarely reported [20-22] due to their lower activity than NHC-Pt(0).
However, the NHC-Pt(II) complexes show greater stability than the NHC-Pt(0)
complexes. On the other hand, polyethylene glycol functionalized ionic liquids have
been prepared and applied in hydrosilylation reactions catalyzed by rhodium [23-25]
and the polyethylene glycol chain also shows special properties in hydrosilylation
reactions catalyzed by platinum [26,27]. Furthermore, trimethylsilylmethyl(TMSCH2-)
is chosen as an alkyl substituent to increase the solubility [28], which is envisaged to
promote the selectivity of the reaction and the activity of the catalyst in the
hydrosilylation reaction.
In this work, we present the synthesis and characterization of novel NHC-Pt(II)
complexes functionalized with a polyether chain and silyl group and their application
in the hydrosilylation of alkenes, alkynes, vinyl ether and unsaturated esters.
RESULTS AND DISCUSSION
Synthesis and characterization
XPS data were collected to further confirm the formation of the mPEG-NHC-Pt
complexes. Figure 1 shows the XPS spectrum of mPEG-NHC-Pt complex and the
NHC precursor (mPEGImin). The Pt (4f7/2) and Pt (4f5/2) peaks of K2PtCl4 were
present at 73.5 and 76.8 eV, respectively [29, 30]. After platinum atom bonds to the
NHC, the Pt (4f7/2) and Pt (4f5/2) peaks are shifted to 74.4 and 77.8 eV, respectively,
which indicates that the mPEG-NHC-Pt complex was successfully obtained. On the
other hand, the Cl(2p3/2) peak of K2PtCl4 is at 198.4 eV, while the Cl(2p3/2) peak of
the mPEG-NHC-Pt complex 3d was observed at 200.6 eV. Furthermore, the Si peak

of the imidazolium salt is at 102.4 eV and the peak of the mPEG-NHC-Pt complex is
at 104.5 eV, which indicates that the silyl groups have an influence on the Pt atom.
Unfortunately, due to the presence of a long polyether chain in the complex, no data
for the single crystal structure of mPEG-NHC-Pt was obtained.
Figure 2 shows the thermogravimetric analysis (TGA) curves obtained for
mPEG-NHC-Pt 3d and mPEGImin 2d. It can be seen that mPEGImin only shows one
big weight loss at 387 C, which corresponds to the loss of the polyether chain in
mPEGImin. On the other hand, it can be seen that mPEG-NHC-Pt shows two weight
losses. The first one, in the range 183-273 C, corresponds to the dissociation of the
covalently bonded metal. The second weight loss, in the range 350-409 C,
corresponds to the decomposition of the mPEGImin polymer chain. The residue of
mPEGImin was 4.0% and the residue of mPEG-NHC-Pt was 9.3%. The difference
between them is the mass of platinum in mPEG-NHC-Pt (4.6%), which is consistent
with the results obtained from the elemental analysis.
Infrared spectroscopy is a useful tool to confirm the chemical modifications
proposed. The result of infrared spectroscopy was shown in Figure 3. The peaks in the
range 1200-1300 cm−1 contain the C-N stretching vibration and C-H vibration
deformation of the imidazole ring. Two bands present in the diffuse reflection infrared
Fourier-transform spectra of mPEGImin at 1240.3 cm−1 and 1278.9 cm−1 are assigned
to the presence of the imidazolium cation cycle coupling. On the other hand, in the
spectrum of mPEG-NHC-Pt these peaks occur at 1241.9 cm−1 and 1280.8 cm−1,
respectively. The wavenumber shifts can be attributed due to Pt being coordinated to

the carbon atom of the carbene.
From the results obtained from the elementary analysis of mPEG-NHC-Pt, the
content of N and Pt was 1.25% and 4.6%, respectively, the molar ratio was ~4:1. This
illustrates that the platinum atom was coordinated to the carbene according to a 1:2
ratio.
Hydrosilylation of styrene catalyzed by the various Pt catalysts
The various NHC-Pt complexes prepared were used as catalysts for the
hydrosilylation of styrene using triethoxysilane. As a comparison, mPEGImin 2a-d
were used in the K2PtCl4 catalyzed hydrosilylation. All of the results are listed in
Table 1. Styrene conversions of 61.1% with a β-adduct selectivity of 77.7% were
achieved in the hydrosilylation catalyzed by K2PtCl4 (entry 1, Table 1). Under the
same conditions, the catalytic activity of the mPEGImin 2a-d/K2PtCl4 system was
somewhat higher than that of K2PtCl4 only (entry 2-5, Table 1), but the selectivity was
lower. mPEG-NHC-Pt 3a-d were shown to have an improved excellent catalytic
performance in the hydrosilylation of styrene, giving almost complete conversion and
better selectivity for the β-adduct. The presence of the polyether chain and silyl-group
suppressed the side reactions, including hydrogenation and dehydrogenative silylation.
When 3a was used as the catalyst, the selectivity for the β-adduct was improved to
92.2% with a 99.0% conversion of styrene (entry 8, Table 1). As a comparison, the
mPEG-NHC-Pt complex with butyl instead of silyl was prepared and used in this
reaction. A reaction conversion of 95.1% and 87.3% selectivity for the β-adduct were
attained under the same reaction conditions. However, when the amount of catalyst

was decreased to 0.02 mol%, catalyst 3d showed the highest activity and selectivity,
at 97.0% and 90.5%, respectively (entry 9, Table 1). Furthermore, when the amount
of 3d was 0.01%, a 99.2% conversion of styrene was obtained with 86.1% selectivity
for the β-adduct (entry 14, Table 1). It is interesting that a higher conversion of
styrene was attained using less catalyst; too much catalyst may result in the H-Si bond
of the silane to cleave and decrease number of moles of silane available to react with
styrene. On the other hand, the selectivity was reduced upon decreasing the dose of
catalyst 3d. The optimum amount of catalyst was found to be 0.02 mol% based on
styrene and was subsequently used in the next experiments. In short, the results
demonstrate that the mPEG-NHC-Pt complexes are an effective catalytic system for
hydrosilylation. The silyl groups and polyether chain contribute to the increased
activity and selectivity in the hydrosilylation reaction of styrene using triethoxysilane.
Hydrosilylation of different alkenes using triethoxysilane
To investigate the scope and limitations of the mPEG-NHC-Pt complexes in the
hydrosilylation process, the reactions of various alkenes with triethoxysilane and 3d
as the catalytic system were tested and the results listed in Table 2. The results
indicate that the catalyst 3d showed excellent catalytic performance for the
hydrosilylation of linear alkenes. The conversion of 1-hexene was 94.4% with >99%
selectivity for the β-adduct when catalyzed using 0.02 mol% catalyst (entry 2, Table
2). Meanwhile, the selectivity for the β-adduct was 92.1% with a yield of 86.9% in the
hydrosilylation of 1-octene using (EtO)3SiH under similar conditions (entry 3, Table
2). In our previous report, the conversion was 100% but the selectivity was 92.3% and

91.0% in the hydrosilylation of 1-hexene or 1-octene, respectively [25]. In addition,
the selectivity for the β-adduct was 97.9% in the hydrosilylation of 1-dodecene using
(EtO)3SiH and the yield was 74.7%. As a comparison, an almost 100% conversion
with 90.2% selectivity in the hydrosilylation of 1-undecene was previous reported buy
our group [25]. Under the same reaction conditions, 85.7% of the β-adduct was
obtained when isobutyl vinyl ether was used as the substrate (entry 11, Table 2) and
77.8% of the β-adduct was obtained when butyl vinyl ether was used as the substrate
(entry 14, Table 2). A 90.1% yield was attained for the hydrosilylation of allyl phenyl
ether using (EtO)3SiH in the presence of 3d (entry 16, Table 2). When unsaturated
esters were used as the substrate, catalyst 3d showed excellent catalytic performance.
The yield of the β-adducts was 94.3% when methyl acrylate was used as the substrate
(entry 17, Table 2).
Hydrosilylation of styrene using silane catalyzed with 3d
Next, the hydrosilylation reactions of styrene with various hydrosilanes catalyzed
with 3d were investigated and the results summarized in Table 3. Using 0.02 mol%
catalyst based on styrene, a 90.3% yield of the adduct was obtained during the
hydrosilylation of styrene using (EtO)3SiH (entry 1, Table 3). When (EtO)2MeSiH
was used as the reagent, a yield of 79.9% was attained with β/α = 8.8 (entry 2, Table
3). However, the conversion of styrene was only 4.1% with a yield of 2.9% in the
hydrosilylation of styrene using (MeO)3SiH (entry 3, Table 3). Using Me2ClSiH and
MeCl2SiH as the hydrogen donor, the conversion was 97.7% and 97.3%, with yields
of 92.5% and 93.7%, respectively (entries 4 and 5, Table 3). A higher yield of adduct

was attained using Me2PhSiH as the reagent, the conversion and the yield of the
adduct was 99.9% and 97.2%, respectively (entry 6, Table 3). As a contrast, only a 7.0%
yield of adduct was obtained in the hydrosilylation of styrene using Et3SiH (entry 7,
Table 3). A 97.9% conversion and 96.0% yield were attained when styrene was
reacted with tetramethyldisiloxane (entry 8, Table 3).
Recyclability of catalyst 3d
In order to investigate the recyclability of catalyst 3d, the hydrosilylation of
1-octene using triethoxysilane was conducted. When the reaction was complete, the
reaction mixture was centrifuged and the upper liquid was decanted. Subsequently,
the next run was conducted by adding fresh substrates without adding fresh catalyst.
Figure 4 illustrates the results of the catalyst recovery efficiency. Under the same
reaction conditions, the catalyst can be recycled 27 times without an obvious loss of
activity and the yield of the β-adduct. The stability of the Pt-NHC catalyst was much
better than the catalyst system comprised of the polyethylene glycol functionalized
ionic liquid rhodium complex or platinum catalyst reported in a previous paper [25].
Hydrosilylation of alkynes catalyzed using 3d
We next turned our attention to the hydrosilylation of alkynes catalyzed by the
complexes prepared in this paper. The NHC-Pt complex 3d was tested as the catalyst
for the hydrosilylation of a terminal alkyne with various silanes and the results are
listed in Table 4. In the hydrosilylation of phenylacetylene using triethylsilane
catalyzed by 3d, the conversion of phenylacetylene was only 14.5% and the α-adduct
was the major product (entry 1, Table 4). However, when an alkoxy silane was used as

the reagent, the β-adduct became the major product and an excellent conversion was
obtained. Among the cases, a 97.8% conversion was obtained in the hydrosilylation of
phenylacetylene using (EtO)2MeSiH and a 97.2% yield was obtained (entry 4, Table
4). Using tetramethyldisiloxane as the reagent, catalyst 3d showed poor activity (entry
5, Table 4). However, both Me2ClSiH and Me2PhSiH were very suitable reagents for
this reaction with a 97.7% and 97.5% yield of adduct being produced, respectively
(entries 7 and 8, Table 4). The ratio of β/α reached 60.8 in the hydrosilylation of
phenylacetylene using Me2ClSiH (entry 7, Table 4). We also examined methylbutynol
as a substrate and a 99.0% conversion with 98.4% yield were obtained (entry 9, Table
4).
CONCLUSIONS
In summary, mPEG-NHC-Pt complexes functionalized with a polyether chain
and silyl group have been synthesized and used as the catalyst in the hydrosilylation
reaction. We have shown that complex 3d was highly active and very stable during
the hydrosilylation reactions of both alkenes and alkynes. The best yield obtained for
the desired adducts was 99.7% in the hydrosilylation of alkenes and 98.1% in the
hydrosilylation of alkynes catalyzed by the NHC-Pt complex 3d. Furthermore, Pt was
firmly bonded to the N-heterocyclic carbene, so the catalyst exhibited excellent
recyclability.
EXPERIMENTAL
General methods and equipment
1H NMR (400 MHz) and 13C NMR (100.6 MHz) spectra were recorded on a Bruker

Advance spectrometer. X-ray photoelectron spectroscopy (XPS) spectra were
performed using a PHI 5000C ESCA system. IR data were obtained using a Nicolet
5700 FTIR spectrometer. TG data were obtained using a T-25 thermogravimetric
analyzer. Elemental analyses were performed on a Vario EL analyzer. The platinum
content was determined by ICP using an M6 atomic absorption spectrophotometer.
Chemicals and solvents were purchased from SCRC (Sinopharm Chemical Reagent
Co.,Ltd) or Aldrich Chemical Co.. Toluene and tetrahydrofuran were dried using
standard methods and distilled. Other chemical were used without further purification.
Preparation of mPEG-functionalized ionic liquids
The methanesulfonate salt of mPEG was synthesized using a literature procedure
[24,25].
Synthesis of 1-(TMSCH2-)-1H-imidazole (1)
Imidazole (10.2 g, 0.15 mol) was dissolved in dry tetrahydrofuran (80 mL) in a
250 mL three-necked flask and then, sodium hydride (4.8 g, 0.2 mol) was added. The
resulting mixture was stirred at room temperature until no air bubbles were observed
and then (chloromethyl)trimethylsilane (18.4 g, 0.15 mol) was injected to the mixture.
After the resulting mixture was stirred for 10 h at 60 C it was cooled to room
temperature, filtered, washed with a small amount of tetrahydrofuran and the filtrate
concentrated in vacuo. The residue was distilled under high vacuum to afford 21.21 g
of the desired product as a pale yellow liquid in 91.7% yield (purity 99.5%).
NMR: (1H, CDCl3) δ (ppm): 7.34 (s, 1H, NCHN), 7.10 (s, 1H, NCHCHN), 6.79 (s,
1H, NCHCHN), 3.65 (s, 2H, NCH2Si), 0.04 (s, 9H, Si(CH3)3). (13C, CDCl3) δ (ppm):

137.2 (s, NCHN), 128.8 (s, NCHCHN), 119.9 (s, NCHCHN), 38.7 (s, NCH2Si), -2.8
(s, Si(CH3)3). (29Si, CDCl3) δ (ppm): -135.9 (s, Si(CH3)3).
Synthesis of the imidazolium salts (mPEGImin, 2)
1-((Trimethylsilyl)-methyl)-1H-imidazole (1.54 g, 0.01 mol) and monomethoxy
PEG2000 methanesulfonate (mPEG2000-OMs) (21.6 g, 0.01 mol) were dissolved in
toluene (30 mL) in a 100 mL three-necked flask. The mixture was stirred at 100 C
under an argon atmosphere for 24 h and then, the phases were separated. The lower
phase was washed with toluene (2 × 10 mL) and diethyl ether (3 × 10 mL). Residual
solvents were evaporated under reduced pressure to obtain the crude product, which
was dissolved in dichloromethane (100 mL) and washed with water (2 × 30 mL). The
organic layer was dried over anhydrous Na2SO4 and solvent was removed under
reduced pressure to afford the imidazolium salt (20.9 g, 90.3% yield).
1H NMR (400 MHz, CDCl3) (ppm): 8.67 (s, 1H, NCHN), 7.20 (s, 1H, NCHCHN),
7.11 (s, 1H, NCHCHN), 4.51 (t, 2H, NCH2CH2), 3.84 (t, 2H, NCH2CH2), 3.79 (s, 2H,
-
NCH2Si), 3.67 (m, nH, OCH2CH2O), 3.57 (m, nH, OCH2CH2), 3.40 (s, 3H, CH3SO3 ),
3.31 (s, 3H, OCH3), 0.07 (s, 9H, Si(CH3)3). 13C NMR (100 MHz, CDCl3) δ ppm:
137.9 (s, NCHN), 125.3(s, NCHCHN), 120.9 (s, NCHCHN), 71.9 (s, NCH2Si), 71.1
(s, NCH2CH2O), 70.7 (s, NCH2CH2O), 59.0 (s, CH2CH2O), 42.7 (s, OCH3), 37.1 (s,
-
CH3SO3 ), -2.8 (s, Si(CH3)3). (29Si, CDCl3) δ ppm: -135.9 (s, Si(CH3)3). Anal. Calc.
for C99H200N2O48Si, C, 53.7; H, 9.0; N, 1.3%. Found: C, 53.2; H, 8.9; N, 1.4%.
The mPEG150Imin(2a), mPEG350Imin(2b), mPEG1000Imin(2c) and mPEGBImin
(complexe with butyl instead of silyl group) were synthesized follow the same

method.
2a (mPEG150Imin): 1H NMR (400 MHz, CDCl3) (ppm): 8.48 (s, 1H, NCHN),
7.22 (s, 1H, NCHCHN), 7.05 (s, 1H, NCHCHN), 4.38-4.33 (t, 2H, NCH2CH2),
3.77-3.73 (t, 2H, NCH2CH2), 3.68 (s, 2H, NCH2Si), 3.50-3.47 (m, 12H, (OCH2CH2)3),
3.35 (s, 3H, CH3SO3), 3.22 (s, 3H, OCH3), 0.04 (s, 9H, Si(CH3)3). 13C NMR (100
MHz, CDCl3) δ ppm: 136.5 (s, NCHN), 123.3 (s, NCHCHN), 122.1 (s, NCHCHN),
71.7 (s, NCH2Si), 70.1 (s, NCH2CH2O), 68.9 (s, NCH2CH2O), 58.8 (s, CH2CH2O),
41.6 (s, OCH3), 39.5 (s, CH3SO3), -3.4 (s, Si(CH3)3). Anal. Calc. for C15H32N2O6Si, C,
42.8; H, 8.8; N, 7.7%. Found: C, 43.2; H, 8.7; N, 7.9%.
2b (mPEG350Imin): 1H NMR (400 MHz, CDCl3) (ppm): 8.56 (s, 1H, NCHN),
7.12 (s, 1H, NCHCHN), 7.07 (s, 1H, NCHCHN), 4.39-4.32 (t, 2H, NCH2CH2),
3.79-3.74 (t, 2H, NCH2CH2), 3.66 (s, 2H, NCH2Si), 3.56-3.52 (m, nH, (OCH2CH2)n),
3.44 (s, 3H, CH3SO3), 3.26 (s, 3H, OCH3), 0.08 (s, 9H, Si(CH3)3). 13C NMR (100
MHz, CDCl3) δ ppm: 136.7 (s, NCHN), 125.8 (s, NCHCHN), 120.5 (s, NCHCHN),
71.8 (s, NCH2Si), 71.2 (s, NCH2CH2O), 70.7 (s, NCH2CH2O), 58.8 (s, CH2CH2O),
42.6 (s, OCH3), 39.1 (s, CH3SO3), -3.1 (s, Si(CH3)3). Anal. Calc. for C23H48N2O10Si,
C, 46.7; H, 8.9; N, 5.2%. Found: C, 46.2; H, 8.8; N, 5.4%.
2c (mPEG1000Imin): 1H NMR (400 MHz, CDCl3) (ppm): 8.60 (s, 1H, NCHN),
7.12 (s, 1H, NCHCHN), 7.03 (s, 1H, NCHCHN), 4.46-4.41 (t, 2H, NCH2CH2),
3.81-3.77 (t, 2H, NCH2CH2), 3.73 (s, 2H, NCH2Si), 3.61-3.51 (m, nH, (OCH2CH2)n),
3.41 (s, 3H, CH3SO3), 3.24 (s, 3H, OCH3), 0.03 (s, 9H, Si(CH3)3). 13C NMR (100
MHz, CDCl3) δ ppm: 137.3 (s, NCHN), 125.2 (s, NCHCHN), 120.8 (s, NCHCHN),

71.9 (s, NCH2 Si) , 71.2 (s, NCH2CH2O), 70.3 (s, NCH2CH2O), 58.8 (s, CH2CH2O),
41.5 (s, OCH3), 36.7 (s, CH3SO3), -2.9 (s, Si(CH3)3). Anal. Calc. for C53H108N2O25Si,
C, 51.0; H, 9.0; N, 2.3%. Found: C, 50.2; H, 8.9; N, 2.4%.
mPEGBImin:1H NMR (400 MHz, CDCl3),  ppm): 8.72 (s, 2H, 2NCHN), 7.36
(s, 4H, 2CHCH), 4.37-4.33 (t, 4H, 2NCH2), 4.19-4.18 (t, 4H, NCH2), 3.86 (s,
6H,NCH3), 3.79-3.76 (m, 4H, OCH2CH2N), 3.66-3.59 (m,(OCH2CH2)n),1.89-1.85 (t,
4H, CH2), 1.39-1.36 (t, 4H, CH2), 0.98 (t, 6H, CH3).13C NMR (100 MHz, CDCl3),
(ppm): 136.2 (s, NCHN), 122.2 (s, NCHCHN), 121.8 (s, NCHCHN), 71.4 (s,
NCH2CH2O), 70.7 (s, NCH2CH2O), 70.6 (s, NCH2CH2O), 70.4 (s, CH2CH2O), 70.2,
49.7 (s, OCH3), 42.7 (s, NCH2CH2), 30.9 (NCH2CH2), 19.4 (CH2CH3), 13.3
(CH2CH3). Anal. Calc. for C99H198N2O48, C, 54.4; H, 9.1; N, 1.3%. Found: C, 53.9; H,
9.0; N, 1.2%.
Synthesis of the mPEG-NHC-Pt complexes 3
The mPEG2000-(trimethylsilyl)methyl imidazolium salt (0.8 g) was placed into a
100 mL three-neck flask and the flask was evacuated for 1 h. A solution of potassium
tert-butoxide (0.06 g) in tetrahydrofuran (50 mL) was added to the reaction mixture
via a syringe. After the mixture was stirred for 3 h at room temperature, K2PtCl4
(0.083 g) was added under a flow of argon and stirred for 3 days at room temperature.
Finally, the mixture was filtered and the solid product was washed twice with water
and tetrahydrofuran, respectively, dried under vacuum at 60 C for 12 h to obtain the
desired product as a pink powder (0.53 g, 52.4% yield). Anal. Calc. for (C99
H199N2O48Si)2PtCl2, C 50.7; H 8.5; N 1.2; Pt 4.3%. Found: C 50.8; H 8.4; N 1.25; Pt

4.6%.
Catalysis hydrosilylation
All the catalytic reactions were performed in a 10 mL flat-bottomed tube without
protection from air. The alkene (4.0 mmol) and the requisite amount of catalyst were
placed in a dried tube and the reaction mixture was stirred for 5 min. Thereafter, the
silane (4.4 mmol) was added and the resulting mixture was heated and stirred for the
requisite time and then cooled to room temperature. The product phase was separated
by decantation and the alkene conversion and selectivity of the reaction were
determined by GC-MS analysis on an Agilent 26890N/59731 apparatus equipped with
a DB-5 column (30 m × 2.5 mm × 0.25 mm).
ACKNOWLEDGMENTS
We are grateful to the National Natural Science Foundation of China (21303034)
and Natural Science Foundation of Zhejiang Province (LY14B030007) for financial
support.

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Table 1 Comparison of the various platinum catalysts for hydrosilylation
Selectivity[%]
Conversion
Entry
Catalysts
β/α
[%]
1-Ethyl- Dehydrogenative
β-adduct
α-adduct
benzene
silylation
1
2
K2PtCl4
K2PtCl4/2a
K2PtCl4/2b
K2PtCl4/2c
K2PtCl4/2d
3a
61.1
25.3
64.0
77.3
46.8
96.4
97.9
99.0
94.9
32.3
51.7
76.8
97.0
99.2
92.9
77.7
44.7
22.8
45.4
53.4
91.9
91.0
92.2
89.4
93.0
90.6
90.8
90.5
86.1
83.3
18.2
32.0
73.6
44.9
33.0
2.8
2.6
3.6
4.8
/
2.5
1.6
4.3
1.4
20.5
3.6
8.3
10.7
5.3
6.4
4.2
5.8
7.0
6.0
5.9
6.9
7.1
8.9
2.8
3
/
0.3
4
1.4
1.0
5
2.9
1.6
6
/
32.8
35
7
3b
/
8
3c
/
25.6
18.6
/
9
3d
/
10
11
12
13
14
15
3a[a]
/
3b[a]
3.4
3.3
2.6
5.5
7.8
/
26.6
27.5
34.8
15.7
10.7
3c[a]
/
/
3d[a]
3d[b]
1.3
/
3d[c]
o
Reaction conditions: styrene 4.0 mmol, silane 4.4 mmol, Pt catalyst 0.1 mol % based on styrene, 90 C, 12 h
[a] Pt catalyst 0.02 mol % based on styrene
[b] Pt catalyst 0.01 mol % based on styrene
[c] Pt catalyst 0.005 mol % based on styrene

Table 2 Hydrosilylation of alkenes with triethoxysilane
[Pt]
Entry
alkenes
Conversion[%]
88.2
β/α
Yield[%][a]
88.2
(mol%)
1
2
0.1
25
38
0.02
0.1
94.4
92.1
87.9
67.8
75.9
62.2
94.4
86.9
83.1
66.4
74.7
60.9
[b]
/
3
4
5
6
7
0.02
/
/
245
/
0.1
0.02
0.1
0.02
0.1
77.6
99.2
100
/
/
/
76.0
98.9
99.7
8
9
10
0.02
0.1
85.8
40.0
80.4
78.0
94.4
94.3
96.1
67.7
74.3
38.8
28
/
85.7
38.1
76.9
77.8
84.0
90.1
94.3
67.3
68.6
32.0
11
12
13
14
15
16
17
18
19
20
0.02
73
141
147
118
69
/
0.1
0.02
0.1
0.02
0.1
0.02
0.1
13
13
0.02
Reaction conditions: alkene 4.0 mmol, silane 4.4 mmol, Pt catalyst based on alkenes, 90 oC, 10 h
[a] Yield of β-adduct，the NMR data see ref [31,32].
[b] no alpha product

Table 3 Hydrosilylation ofstyrene with various silanes
Entry
R3SiH
(EtO)3SiH
(EtO)2MeSiH
(MeO)3SiH
Me2ClSiH
MeCl2SiH
Me2PhSiH
Et3SiH
Conversion[%]
β/α
34.8
8.8
Yield[%][a]
90.3
1
2
3
4
5
6
7
97.0
81.0
4.1
79.9
2.0
2.9
97.7
93.7
99.9
14.8
7.2
92.5
249
93.7
[b]
97.2
/
11.2
1.5
7.0
8
97.9
96.0
Reaction conditions: styrene 4 mmol, silane 4.4 mmol, 3d 0.02 mol % based on styrene, 90 oC, 10 h
[a] Yield of β-adduct.
[b] no alpha product

Table 4 Hydrosilylation of alkyne with various silane
Conversion
[%]
Yield[a]
[%]
Entry
1
R
R’3SiH
β(E+Z)/α
Ph
Et3SiH
14.5
24.0
13.9
23.8
0.8
2
3
4
Ph
Ph
Ph
(MeO)3SiH
(EtO)3SiH
1.8
1.7
1.2
76.8
97.8
71.0
97.2
(EtO)2MeSiH
5
Ph
10.7
10.4
0.8
6
7
8
Ph
Ph
Ph
Me2ClSiH
MeCl2SiH
Me2PhSiH
87.9
98.8
98.0
86.4
97.7
97.5
7.3
60.8
1.9
9
(CH3)2COH
(EtO)3SiH
99.0
98.4
37
Reaction conditions: alkyne 4 mmol, silane 4.4 mmol, catalyst 0.02 mol % based on alkynes, 90 oC, 10 h
[a] Yield of (β(E)+β(Z))

ACCEPTED MANUSCRIPT
Si(2p) 104.5
(b)
(a)
Pt(4f7/2) 74.4
Pt(4f5/2) 77.8
complexe 3d
Si(2p) 102.4
complexe 3d
Imidazolium salts
110 115
95
100
105
66
68
70
72
74
76
78
80
82
84
86
Binding Energy (e.V)
Binding Energy (e.V)
(c-1)
C(1s) 286
C(f3) 294.4
Cl(2p3/2) 200.6
(d)
complexe 3d
C(1s) 286
(c-2)
202.4
C(f3) 293.3
Imidazolium salt
194
196
198
200
202
204
206
208
210
276 278 280 282 284 286 288 290 292 294 296 298 300
Binding Energy (e.V)
Binding Energy (e.V)
Figure 1 X-ray photoelectron spectroscopy (XPS) analysis of NHC-Pt catalyst
(a) Pt; (b) Si; (c) C; (d) Cl
23
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100
80
60
40
20
mPEG-NHC-Pt
mPEGImin
0
200
400
600
800
T / oC
Figure 2 TG curves of mPEGImin and mPEG-NHC-Pt
24
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ACCEPTED MANUSCRIPT
mPEG-NHC-Pt
mPEGImin
mPEG-NHC-Pt
mPEGImin
1200
1250
1300
1000
1500
2000
2500
3000
3500
4000
Wave number/ cm-1
Figure 3 IR spectra of mPEGImin and mPEG-NHC-Pt
25
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100
80
60
40
20
0
0
2
4
6
8
10 12 14 16 18 20 22 24 26 28
Runs
Figure 4 Recylability of the catalyst in the hydrosilylation of 1-octene
Reaction conditions:1-octene 4 mmol, silane 4.4 mmol, catalyst 0.1 mol % based on1-octene, 90
oC, 10 h
26
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Scheme 1 Synthesis of imidazolium salts
27
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ACCEPTED MANUSCRIPT
Scheme 2 Synthesis of the platinum-NHC complexes
28
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