Synthesis of novel poly(ethylene glycol)-containing imidazolium-functionalized phosphine ligands and their application in the hydrosilylation of olefins

Article abstract of DOI:10.1002/aoc.4296

A series of polyethylene glycol-containing imidazolium-functionalized phosphine ligands (mPEG-im-PPh₂) were successfully synthesized and used in the rhodium-catalyzed hydrosilylation of olefins. The results indicate that the RhCl₃/mPEG-im-PPh₂ catalytic system exhibits both excellent activity and selectivity for the β-adduct. In addition, the catalytic system may be recycled at least six times.

Full text of DOI:10.1002/aoc.4296

Received: 16 October 2017
DOI: 10.1002/aoc.4296
Revised: 29 December 2017
Accepted: 2 January 2018
F U L L P A P E R
Synthesis of novel poly(ethylene glycol)‐containing
imidazolium‐functionalized phosphine ligands and their
application in the hydrosilylation of olefins
Guodong Zhang | Jiayun Li
Jiajian Peng
| Chuang Yang | Congbai Niu | Ying Bai
| Yu Liu |
Key Laboratory of Organosilicon
A series of polyethylene glycol‐containing imidazolium‐functionalized phos-
phine ligands (mPEG‐im‐PPh2) were successfully synthesized and used in the
rhodium‐catalyzed hydrosilylation of olefins. The results indicate that the
RhCl3/mPEG‐im‐PPh2 catalytic system exhibits both excellent activity and
selectivity for the β‐adduct. In addition, the catalytic system may be recycled
at least six times.
Chemistry and Material Technology of
Ministry of Education, Hangzhou Normal
University, Hangzhou 311121, China
Correspondence
Jiayun Li and Jiajian Peng, Key Laboratory
of Organosilicon Chemistry and Material
Technology of Ministry of Education,
Hangzhou Normal University, Hangzhou
311121, China.
KEYWORDS
Email: jiayun1980@hznu.edu.cn;
jjpeng@hznu.edu.cn
diphenylphosphine salts, hydrosilylation, poly(ethylene glycol) (PEG)
Funding information
Natural Science Foundation of Zhejiang
Province, Grant/Award Number:
LY18B020012; Science and Technology
Project of Zhejiang Province, Grant/
Award Number: 2017C31105
1 | INTRODUCTION
Mukaiyama aldol reaction[6,7] and Mitsunobu reaction,[8–
10]
have been intensively developed along with thorough
Poly(ethylene glycol) (PEG) has attracted a great amount
of interest as a reusable solvent medium for organic syn-
theses and catalytic processes because it is non‐volatile,
inexpensive and non‐toxic. Furthermore, the properties
of PEG can be tuned upon its modification with functional
groups. Conjugates combining some of the properties of
both the starting substrate and PEG can be produced when
PEG is used as a covalent modifier for various substrates.
In homogeneous catalytic processes, in addition to the
metal center used, the ligand also plays an important role
in the reactions.[1–3] Generally, the electronic, geometric
and steric properties of the ligands have a significant
effect on the catalytic activity of their corresponding metal
complexes. In particular, organic phosphine ligands have
played a crucial role in transition metal catalysis. Numer-
ous catalytic reactions, such as Wittig ylide formation,[4,5]
research on transition metal complexes coordinated with
organic phosphine ligands.[11–13]
The hydrosilylation of alkenes is one of the most
important methods used for the preparation of
organosilicon compounds. It has been reported that the
hydrosilylation of alkynes or alkenes can be effectively cat-
alyzed using Wilkinson's catalyst (Rh(PPh3)3Cl).[14,15] In
this catalytic process, the organic phosphine ligands play
a significant role in the hydrosilylation reaction.[16–20]
A
series of rhodium catalysts with PEG‐based ionic liquids
have been used as efficient and recyclable catalyst systems
for hydrosilylation reactions.[21,22]
In the present paper, we report the preparation of
PEG‐containing imidazolium‐functionalized phosphine
ligands (mPEG‐im‐PPh2) and their application in the rho-
dium‐catalyzed hydrosilylation of olefins.
Appl Organometal Chem. 2018;e4296.
wileyonlinelibrary.com/journal/aoc
Copyright © 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4296

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ZHANG ET AL.
was washed with toluene (2 × 15 ml) and dried in vacuo.
The synthesis route is shown in Scheme 1.
2 | EXPERIMENTAL
2.1 | General
1a Yield: 88.0%. 1H NMR (400 MHz, DMSO‐d6, δ,
ppm): 8.24 (s, 1H, imidazol), 7.66 (s, 1H, imidazol),
7.51–7.76 (m, 10H, Ph), 4.31 (m, 2NCH2), 3.81 (s, 3H,
NCH3), 3.72 (t, J = 8 Hz, 2H, OCH2CH2N), 3.21 (s, 3H,
OCH3). 13C NMR (100 MHz, DMSO‐d6, δ, ppm): 141.5
(imidazol), 139.7 (Ph), 132.5 (Ph), 128.9 (Ph), 125.1 (Ph),
123.4 (imidazol), 123.2 (imidazol), 68.7 (NCH2CH2O),
59.1 (OCH3), 49.3 (NCH2CH2O), 36.5 (NCH3). 31P NMR
(DMSO‐d6, δ, ppm): −31.5.
Styrene was washed with 5% NaOH and dried with
Na2SO4. After filtration, the styrene was distilled under
reduced pressure. All other substances were purchased
from Aldrich and were used as received.
Gas chromatography: Trace DSQ GC column = DB‐5
30 m × 2.5 mm × 0.25 μm, split = 50:1, flow = 1 ml min−1
constant flow, inlet temperature = 260 °C, column temper-
ature = 50 °C (hold 1 min) then 15 °C min−1 up to 260 °C
(hold 10 min).
2a Yield: 85.7%. 1H NMR (400 MHz, DMSO‐d6, δ,
ppm): 7.97 (s, 1H, imidazol), 7.67 (s, 1H, imidazol),
7.50–7.77 (m, 10H, Ph), 4.33 (m, 2NCH2), 3.87 (s, 3H,
NCH3), 3.71 (t, J = 8 Hz, 2H, OCH2CH2N), 3.51 (s, 4H,
(OCH2CH2)), 3.21 (s, 3H, OCH3). 13C NMR (100 MHz,
DMSO‐d6, δ, ppm): 141.1 (imidazol), 139.7 (Ph), 132.5
(Ph), 128.1 (Ph), 125.1 (Ph), 123.8 (imidazol), 123.2
(imidazol), 69.4 (CH2CH2O), 68.1 (NCH2CH2O), 59.1
(OCH3), 49.5 (NCH2CH2O), 35.9 (NCH3). 31P NMR
(DMSO‐d6, δ, ppm): −31.8.
1H NMR, 13C NMR and 31P NMR spectra were mea-
sured using a Bruker AV400 spectrometer operating at
400.13, 100.62 and 161.97 MHz, respectively. Chemical
1
shifts for H NMR and 13C NMR spectra were recorded
in ppm relative to residual proton of deuterated
dimethylsulfoxide (DMSO‐d6) (1H, 2.50 ppm; 13C
39.5 ppm). 31P NMR chemical shifts are relative to 85%
H3PO4 external standard.
3a Yield: 86.1%. 1H NMR (400 MHz, DMSO‐d6, δ,
ppm): 7.91 (s, 1H, imidazol), 7.64 (s, 1H, imidazol),
7.51–7.76 (m, 10H, Ph), 4.30 (m, 2NCH2), 3.80 (s, 3H,
NCH3), 3.75 (t, J = 8 Hz, 2H, OCH2CH2N), 3.53 (s,
(OCH2CH2)6), 3.21 (s, 3H, OCH3). 13C NMR (100 MHz,
DMSO‐d6, δ, ppm): 141.6 (imidazol), 139.3 (Ph), 132.8
(Ph), 128.0 (Ph), 125.1 (Ph), 123.5 (imidazol), 123.4
(imidazol), 69.5 ((CH2CH2O)6), 68.1 (NCH2CH2O), 59.1
(OCH3), 49.3 (NCH2CH2O), 36.7 (NCH3). 31P NMR
(DMSO‐d6, δ, ppm): −33.1.
2.2 | Preparation of mPEG‐im‐PPh2
Monomethoxy PEG (0.1 mol) was dissolved in toluene
(100 ml) in a 250 ml three‐necked flask and the stirred
solution was heated at reflux for 2 h to remove the water
contained in the PEG by azeotropic dehydration. After
cooling, dried pyridine (0.125 mol) was added to the solu-
tion and then thionyl chloride (0.125 mol) was added
dropwise with stirring. The color of the solution changed
from faint yellow to reddish brown. The reaction mixture
was stirred for 24 h at 80 °C. After cooling to room tem-
perature, a mixture of hydrochloric acid (8 ml) and water
(16 ml) was added and stirred, and the layers were
allowed to separate, and the lower layer was twice
extracted with toluene. The extracts were combined with
the upper organic phase and the solvent was removed
under vacuum to afford monomethoxy PEG chloride. A
mixture of monomethoxy PEG chloride (10.0 mmol) and
1‐alkylimidazole (11.0 mmol) was diluted in 1,1,1‐
trichloroethane (10.0 ml), and the solution was refluxed
for 36 h and the phases were separated. The lower phase
was washed twice with 5 ml of 1,1,1‐trichloroethane and
once with 10.0 ml of ethyl ether. Residual solvents were
removed by rotary evaporation. Removal of the solvent
under vacuum afforded a yellow oil (mPEGBImCl). A
solution of LiPPh2, freshly prepared from Li (0.8 g,
0.11 mol) and PPh3 (13.1 g, 0.05 mol), in tetrahydrofuran
(THF; 50 ml), was added to a solution of mPEGBImCl
(0.05 mol) in THF (50 ml). The mixture was stirred for
1 h at room temperature, then the supernatant was
decanted off and the remaining solid mPEG‐im‐PPh2
4a Yield: 84.7%. 1H NMR (400 MHz, DMSO‐d6, δ,
ppm): 7.89 (s, 1H, imidazol), 7.67 (s, 1H, imidazol),
7.49–7.77 (m, 10H, Ph), 4.31 (m, 2H, 2NCH2), 3.83 (s,
3H, NCH3), 3.77 (t, J = 8 Hz, 2H, OCH2CH2N), 3.50 (s,
(OCH2CH2)10), 3.23 (s, 3H, OCH3). 13C NMR (100 MHz,
DMSO‐d6, δ, ppm): 140.6 (imidazol), 139.1 (Ph), 132.3
(Ph), 128.4 (Ph), 125.7 (Ph), 123.1 (imidazol), 123.5
(imidazol), 69.1 ((CH2CH2O)10), 67.9 (NCH2CH2O), 58.1
(OCH3), 45.3 (NCH2CH2O), 35.7 (NCH3). 31P NMR
(DMSO‐d6, δ, ppm): −33.9.
5a Yield: 83.6%. 1H NMR (400 MHz, DMSO‐d6, δ,
ppm): 7.93 (s, 1H, imidazol), 7.67 (s, 1H, imidazol),
7.51–7.73 (m, 10H, Ph), 4.31 (m, 2NCH2), 3.85 (s, 3H,
NCH3), 3.73 (t, J = 8 Hz, 2H, OCH2CH2N), 3.51 (s,
(OCH2CH2)15), 3.25 (s, 3H, OCH3). 13C NMR (100 MHz,
DMSO‐d6, δ, ppm): 141.7 (imidazol), 139.3 (Ph), 132.9
(Ph), 128.3 (Ph), 125.1 (Ph), 123.7 (imidazol), 123.1
(imidazol), 69.1 ((CH2CH2O)15), 68.5 (NCH2CH2O), 59.3
(OCH3), 49.1 (NCH2CH2O), 36.7 (NCH3). 31P NMR
(DMSO‐d6, δ, ppm): −34.7.
6a Yield: 83.1%. 1H NMR (400 MHz, DMSO‐d6, δ,
ppm): 7.91 (s, 1H, imidazol), 7.61 (s, 1H, imidazol),

ZHANG ET AL.
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SCHEME 1 Synthesis of 2‐
diphenylphosphine Polyethylene‐glycol
functionalized imidazolium (mPEG‐
im‐PPh2)
7.51–7.73 (m, 10H, Ph), 4.33 (m, 2NCH2), 3.87 (s, 3H,
NCH3), 3.71 (t, J = 8 Hz, 2H, OCH2CH2N), 3.51 (s,
(OCH2CH2)41), 3.23 (s, 3H, OCH3). 13C NMR (100 MHz,
DMSO‐d6, δ, ppm): 141.3 (imidazol), 139.1 (Ph), 132.7
(Ph), 128.1 (Ph), 125.3 (Ph), 123.9 (imidazol), 123.3
(imidazol), 69.7 ((CH2CH2O)41), 68.5 (NCH2CH2O), 59.1
(OCH3), 49.3 (NCH2CH2O), 36.3 (NCH3). 31P NMR
(DMSO‐d6, δ, ppm): −35.9.
2H, NCH2), 3.71 (t, J = 8 Hz, 2H, OCH2CH2N), 3.54 (s,
(OCH2CH2)41), 3.21 (s, 3H, OCH3), 1.31–1.89 (m, 4H,
CH2), 0.89 (t, J = 8 Hz, 3H, CH3C3H6N). 13C NMR
(100 MHz, DMSO‐d6, δ, ppm): 142.3 (imidazol), 138.9
(Ph), 133.4 (Ph), 127.3 (Ph), 126.1 (Ph), 125.7 (imidazol),
123.1 (imidazol), 69.7 ((CH2CH2O)41), 68.1 (NCH2CH2O),
59.7 (OCH3), 49.1 (NCH2CH2O), 50.2 (NCH2), 31.7, 19.1
(CH3C2H4CH2N), 13.8 (CH3C2H4CH2N). 31P NMR
(DMSO‐d6, δ, ppm): −36.9.
1b Yield: 81.1%. 1H NMR (400 MHz, DMSO‐d6, δ, ppm):
7.93 (s, 1H, imidazol), 7.67 (s, 1H, imidazol), 7.51–7.73 (m,
10H, Ph), 4.63 (m, 2H, NCH2), 4.31 (m, 2H, NCH2), 3.73
(t, J = 8 Hz, 2H, OCH2CH2N), 3.55 (s, (OCH2CH2)41), 3.23
(s, 3H, OCH3), 0.84 (t, J = 8 Hz, 3H, CH3CH2N). 13C NMR
(100 MHz, DMSO‐d6, δ, ppm): 142.1 (imidazol), 138.1
(Ph), 133.7 (Ph), 127.1 (Ph), 126.3 (Ph), 125.9 (imidazol),
123.3 (imidazol), 69.1 ((CH2CH2O)41), 68.3 (NCH2CH2O),
59.3 (OCH3), 49.1 (NCH2CH2O), 45.3 (NCH2), 15.9
(NCH2CH3). 31P NMR (DMSO‐d6, δ, ppm): −36.3.
1
1d Yield: 80.1%. H NMR (400 MHz, DMSO‐d6, δ,
ppm): 7.89 (s, 1H, imidazol), 7.65 (s, 1H, imidazol),
7.47–7.77 (m, 10H, Ph), 4.65 (m, 2H, NCH2), 4.19 (m,
2H, NCH2), 3.73 (t, J = 8 Hz, 2H, OCH2CH2N), 3.55 (s,
(OCH2CH2)41), 3.27 (s, 3H, OCH3), 1.29–1.67 (m, 8H,
CH2), 0.86 (t, J = 8 Hz, 3H, CH3C3H6N). 13C NMR
(100 MHz, DMSO‐d6, δ, ppm): 142.1 (imidazol), 139.0
(Ph), 133.7 (Ph), 127.9 (Ph), 126.5 (Ph), 125.9 (imidazol),
123.3 (imidazol), 69.9 ((CH2CH2O)41), 68.7 (NCH2CH2O),
59.7 (OCH3), 49.5 (NCH2CH2O), 50.1 (NCH2), 22.3, 29.8,
30.4, 31.0 (CH3C4H8CH2N), 14.1 (CH3C2H4CH2N). 31P
NMR (DMSO‐d6, δ, ppm): −37.1.
1c Yield: 80.3%. 1H NMR (400 MHz, DMSO‐d6, δ,
ppm): 7.87 (s, 1H, imidazol), 7.73 (s, 1H, imidazol),
7.51–7.79 (m, 10H, Ph), 4.61 (m, 2H, NCH2), 4.23 (m,

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ZHANG ET AL.
The solid 6a (0.05 mol) was dissolved in 15 ml of water
2c Yield: 37.1%. 1H NMR (400 MHz, DMSO‐d6, δ,
ppm): 8.82 (s, 1H, imidazol), 8.67 (s, 1H, imidazol),
7.50–7.75 (m, 10H, Ph), 4.32 (m, 2NCH2), 3.84 (s, 3H,
NCH3), 3.69 (t, J = 8 Hz, 2H, OCH2CH2N), 3.51 (s,
(OCH2CH2)41), 3.22 (s, 3H, OCH3). 13C NMR (100 MHz,
DMSO‐d6, δ, ppm): 142.3 (imidazol), 139.7 (Ph), 132.1
(Ph), 128.5 (Ph), 125.1 (Ph), 123.3 (imidazol), 123.1
(imidazol), 69.9 ((CH2CH2O)41), 68.3 (NCH2CH2O), 59.7
(OCH3), 49.1 (NCH2CH2O), 36.1 (NCH3). 31P NMR
(DMSO‐d6, δ, ppm): −36.7.
and then mixed with KPF6 (0.06 mol) in 10 ml of water.
The mixture was stirred for 24 h at room temperature.
After decantation, the crude product was washed twice
with 20 ml of water and dried under vacuum. Product
2b was obtained.
1
2b Yield: 53.4%. H NMR (400 MHz, DMSO‐d6, δ,
ppm): 8.21 (s, 1H, imidazol), 7.89 (s, 1H, imidazol),
7.49–7.77 (m, 10H, Ph), 4.31 (m, 2NCH2), 3.85 (s, 3H,
NCH3), 3.69 (t, J = 8 Hz, 2H, OCH2CH2N), 3.48 (s,
(OCH2CH2)41), 3.22 (s, 3H, OCH3). 13C NMR (100 MHz,
DMSO‐d6, δ, ppm): 141.9 (imidazol), 132.9 (Ph), 132.5
(Ph), 128.3 (Ph), 125.1 (Ph), 123.4 (imidazol), 123.1
(imidazol), 69.9 ((CH2CH2O)41), 68.7 (NCH2CH2O), 59.3
(OCH3), 49.1 (NCH2CH2O), 36.7 (NCH3). 31P NMR
(DMSO‐d6, δ, ppm): −39.7, −143.0 (PF6−, J = 706.8 Hz).
The solid 6a (0.05 mol) was dissolved in 15 ml of ace-
tone and then mixed with NaBF4 (0.06 mol) in 10 ml of
acetone. The mixture was stirred for 24 h at room temper-
ature. After decantation, the crude product was diluted in
30 ml of methylene chloride, washed twice with 20 ml of
water and dried under vacuum. Product 2c was obtained.
2.3 | Catalytic Hydrosilylation of Alkene
with Triethoxysilane
A 10 ml three‐necked flask equipped with a magnetic stir-
rer was charged with RhCl3⋅3H2O (8.0 × 10−3 mmol) and
phosphine ligand (4.0 × 10−2 mmol) under argon atmo-
sphere. Then alkene (4 mmol) and silane (4.87 mmol)
were added via syringe. The hydrosilylation reaction
(Scheme 2) was conducted with constant stirring at an
appropriate temperature for 5 h. At the end of the reac-
tion, the conversion of alkene and the selectivity of prod-
uct were determined using GC.
3 | RESULTS AND DISCUSSION
3.1 | Effect of Length of PEG Chain on
Hydrosilylation Reaction
The catalytic properties of RhCl3/mPEG‐im‐PPh2 in the
hydrosilylation reaction of styrene with triethoxysilane
were investigated, and the results are listed in Table 1.
SCHEME 2 The hydrosilylation reaction of alkenes catalyzed
a
TABLE 1 Effect of molecular weight on hydrosilylation catalyzed with RhCl3
Selectivity (%)
Entry
Ligand
Conv. (%)
β
α
Ethylbenzene
Dehydrogenative silylation
1
—
1a
2a
3a
4a
5a
6a
1b
1c
1d
2b
2c
85.2
95.1
95.9
94.2
93.8
93.5
91.1
89.9
87.2
86.5
93.4
82.4
57.8
70.1
75.4
80.3
82.5
85.6
90.4
87.1
86.1
86.4
92.1
90.3
22.2
17.1
13.2
12.1
9.8
13.0
7.4
6.3
3.4
3.3
3.1
2.6
6.3
7.8
8.6
2.8
2.6
7.0
5.4
5.1
4.2
4.4
4.5
4.7
4.5
4.2
3.9
3.6
4.9
2
3
4
5
6
6.8
7
2.3
8
2.1
9
1.9
10
11
12
1.1
1.5
2.2
aReaction conditions: styrene 4.0 mmol, (EtO)3SiH 4.4 mmol, 5 h, 70 °C, RhCl3 0.001 mmol, n(RhCl3):n(mPEG‐im‐PPh2) = 1:3.

ZHANG ET AL.
5 of 6
An 85.2% conversion of styrene and 57.8% selectivity for
the β‐adduct were obtained in the absence of a phosphine
ligand (Table 1, entry 1). When RhCl3 was mixed with
mPEG‐im‐PPh2, it exhibited enhanced catalytic activity
and selectivity (Table 1, entries 2–7). In addition, it was
found that the catalytic activity of RhCl3/mPEG‐im‐PPh2
decreased slightly upon increasing the length of the PEG
chain. In contrast, the ratio of the β‐adduct to α‐adduct
(β/α) clearly increased. When RhCl3/6a was used as the
catalyst, the β‐adduct selectivity improved to 90.4%
(Table 1, entry 7). The results demonstrate that
mPEG‐im‐PPh2 is an effective promoter in the rhodium‐
catalyzed hydrosilylation reaction.
The effect of the length of the alkyl chain in the
imidazolium ring was investigated. When RhCl3 was
mixed with mPEG‐im‐PPh2 (6a, 1b, 1c and 1d), it exhib-
ited higher catalytic activity and β‐adduct selectivity. At
the same time, the catalytic activity of the RhCl3/mPEG‐
im‐PPh2 (6a, 1b, 1c and 1d) catalysts slightly decreased
upon increasing the length of the alkyl chain in the
imidazolium ring, while the ratio of the β‐adduct to the
α‐adduct (β/α) slightly increased (Table 1, entries 7–10).
This demonstrates that the substituents on the
imidazolium ring have a significant impact on the cata-
lytic process. Different substituents attached to the cation
result in different steric hindrance observed at the cata-
lytic center.
3.2 | Effect of Amount of mPEG‐im‐PPh2
on Hydrosilylation Reaction
The effect of the amount of mPEG‐im‐PPh2 on the
hydrosilylation reaction was also investigated, and the
results are listed in Table 2. The conversion of styrene
and the β‐adduct selectivity were 90.7 and 81.6% using
the catalyst with a ratio of n(mPEG‐im‐PPh2):n(RhCl3)
= 1:1 (Table 2, entry 2). When the ratio of n(mPEG‐im‐
PPh2):n(RhCl3) = 5:1, the conversion of styrene and the
β‐adduct selectivity were 94.7 and 90.5%, respectively
(Table 2, entry 4). This shows that a certain amount of
mPEG‐im‐PPh2 ligand was conducive to improving the
catalytic activity. Upon increasing the ratio from 5:1 to
80:1, the conversion of styrene and the β‐adduct selectiv-
ity decreased (Table 2, entries 4–8). This suggests that
too many ligands around the Rh center have a negative
impact on the catalytic activity.
3.3 | Catalyst Recycling
In general, RhCl3/mPEG‐im‐PPh2 shows excellent stability
in the hydrosilylation reaction of styrene and
triethoxysilane. For example, the RhCl3/6a catalyst system
can be reused more than six times without any noticeable
loss in the catalytic activity and selectivity. The results of
the catalyst recycling experiments are shown in Figure 1.
The effect of the anion in the imidazolium was inves-
tigated. When RhCl3 was mixed with mPEG‐im‐PPh2
(2b), it exhibited enhanced catalytic activity and β‐adduct
selectivity when compared to 6a. When RhCl3 was mixed
with mPEG‐im‐PPh2 (2c), it exhibited a lower catalytic
activity than with 6a. However, due to the complexity of
the preparation process, the separation yield of 2b was
low. Therefore, 6a was selected as the representative
catalyst.
3.4 | Hydrosilylation Reaction of Other
Aliphatic Alkenes
When aliphatic alkenes such as 1‐hexene, 1‐octene,
(vinyloxy)butane and ethoxyethene were used as the sub-
strates in the hydrosilylation reaction, excellent conver-
sions and selectivities were obtained with the RhCl3/6a
catalyst system (Table 3).
a
TABLE 2 Effect of amount of 6a on hydrosilylation catalyzed with RhCl3
Selectivity (%)
Entry
Ligand
Conv. (%)
β
α
Ethylbenzene
Dehydrogenative silylation
1
2
3
4
5
6
7
8
—
1:1
85.2
90.7
91.1
94.7
89.9
73.8
63.6
55.6
57.8
81.6
90.4
90.5
77.3
70.4
67.7
64.5
22.2
6.3
13.0
5.2
7.0
6.9
3:1
2.3
2.6
4.7
5:1
3.4
2.2
3.9
8:1
6.6
10.2
10.8
10.5
10.7
5.9
25:1
40:1
80:1
9.1
9.7
11.2
15.7
10.6
9.1
aReaction conditions: styrene 4.0 mmol, (EtO)3SiH 4.4 mmol, 5 h, 70 °C, RhCl3 0.001 mmol.

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ZHANG ET AL.
Ying Bai http://orcid.org/0000-0001-5630-5565
Conversion
Selectivity
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Number of cycles
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FIGURE 1 Reuse of RhCl3/6a catalytic system. (Reaction
conditions: styrene, 4.0 mmol; (EtO)3SiH, 4.4 mmol; 5 h; 70 °C;
n(RhCl3):n(mPEG‐im‐PPh2) = 1:5; RhCl3, 0.001 mmol)
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TABLE 3 Hydrosilylation of alkene and triethoxysilane catalyzed
with RhCl3/6aa
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Selectivity (%)
Entry Substrate
Conv. (%)
β
α
Other
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1
2
3
4
CH3(CH2)3CH═CH2
99.2
98.8
99.8
99.9
>99.9
>99.9
>99.9
>99.9
—
—
—
—
—
—
—
—
CH3(CH2)5CH═CH2
CH3(CH2)3OCH═CH2
CH3CH2OCH═CH2
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aReaction conditions: styrene 4.0 mmol, (EtO)3SiH 4.4 mmol, 5 h, 70 °C,
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n(RhCl3):n(mPEG‐im‐PPh2) = 1:5, RhCl3 0.001 mmol.
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4 | CONCLUSIONS
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In summary, a series of mPEG‐im‐PPh2 ligands have been
successfully synthesized and used in the hydrosilylation
reaction of alkenes catalyzed using the RhCl3/mPEG‐im‐
PPh2 catalyst system. The RhCl3/mPEG‐im‐PPh2 catalyst
showed excellent activity and selectivity for the β‐adduct.
The catalytic system can be recycled six times without any
noticeable loss in catalytic activity and selectivity.
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ACKNOWLEDGMENTS
This work was supported by Science and Technology
Project of Zhejiang Province (grant no. 2017C31105) and
Natural Science Foundation of Zhejiang Province
(LY18B020012).
How to cite this article: Zhang G, Li J, Yang C,
et al. Synthesis of novel poly(ethylene glycol)‐
containing imidazolium‐functionalized phosphine
ligands and their application in the hydrosilylation
of olefins. Appl Organometal Chem. 2018;e4296.
https://doi.org/10.1002/aoc.4296
ORCID
Jiayun Li http://orcid.org/0000-0001-7800-5686