Application of polyethyleneglycol (PEG) functionalized ionic liquids for the rhodium-catalyzed hydrosilylation reaction of alkenes

Article abstract of DOI:10.1016/j.jorganchem.2015.06.024

Abstract Rh(PPh₃)₃Cl-polyethyleneglycol (PEG) functionalized ionic liquids with various anions were used as a catalytic system for the hydrosilylation reaction of alkenes. The influence of the anion of the ionic liquid has been investigated. It was found that the anion has an impact on the catalytic activity and selectivity. [PEG₄₀₀DIL][PF₆]-[Rh(PPh₃)₃Cl] shows an improved catalytic performance towards the hydrosilylation reaction of alkenes. The scope of alkenes and recycling of the catalytic system have been investigated.

Full text of DOI:10.1016/j.jorganchem.2015.06.024

Journal of Organometallic Chemistry 794 (2015) 65e69
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Communication
Application of polyethyleneglycol (PEG) functionalized ionic liquids
for the rhodium-catalyzed hydrosilylation reaction of alkenes
Ying Bai*, Fengxiang Zhang, Jiayun Li, Yisong Xu, Jiajian Peng**, Wenjun Xiao
Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, Hangzhou 311121, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Rh(PPh3)3Clepolyethyleneglycol (PEG) functionalized ionic liquids with various anions were used as a
catalytic system for the hydrosilylation reaction of alkenes. The influence of the anion of the ionic liquid
has been investigated. It was found that the anion has an impact on the catalytic activity and selectivity.
[PEG400DIL][PF6]-[Rh(PPh3)3Cl] shows an improved catalytic performance towards the hydrosilylation
reaction of alkenes. The scope of alkenes and recycling of the catalytic system have been investigated.
© 2015 Published by Elsevier B.V.
Received 2 April 2015
Received in revised form
9 June 2015
Accepted 15 June 2015
Available online 24 June 2015
Keywords:
Hydrosilylation
Rh(PPh3)3Cl
PEG functionalized ionic liquids
1. Introduction
group reported that a polyethylene glycol functionalized ionic
liquid with [PF6]ꢀ anion can be used as the ligand in the hydro-
Hydrosilylation is one of the most powerful methods used for
the synthesis of functionalized organosilicon compounds. Although
a number of catalysts have been tested in the hydrosilylation pro-
cess, most research and industrial syntheses have been carried out
using platinum or rhodium complexes due to the fact that these
complexes often exhibit high catalytic activity [1e3]. In addition, to
promote the activity of the catalyst and selectivity of the adduct, a
variety of ligands such as new phosphine ligands [4e8] and
nitrogen-based ligands [9e11] have been used in the hydro-
silylation process.
silylation reaction of alkenes catalyzed by a Rh catalyst [20]. Herein,
we report the influence of the anions of novel polyethylene glycol
functionalized ionic liquids (Fig. 1) on the hydrosilylation reaction
of alkenes catalyzed using Rh(PPh3)3Cl.
2. Experimental
2.1. Procedure for the synthesis of [PEG400DIL][X] [X ¼ PF6, BF4,
SO3CF3 and N(SO2CF3)2]
Ionic liquids as ligands or reaction media have been applied in
many chemical fields [12e14]. Ionic liquids can promote the activity
of a rhodium catalyst and the selectivity of the adducts in the
hydrosilylation reaction of alkenes as well as improving there
cyclability of the catalytic system [15e18]. Monomethoxy poly-
ethylene glycol functionalized ionic liquids and transition metal
complexes can form co-catalytic systems, which can increase the
activity of the catalyst, promote the selectivity of the products and
allow the recycling of the catalyst system [19]. Very recently, our
The chlorination of PEG400 and PEG400-functionalized double
imidazolium chloride (PEG400DI) was accomplished using a litera-
ture procedure [20].
PEG400DIL[PF6]: PEG400DI (3.0 g, 5 mmol) was dissolved in
deionized H2O (10 mL) and added to a solution of NH4PF6 (1.6 g,
10 mmol) in H2O (5 mL). The reaction mixture was stirred at room
temperature for 6 h. After decantation, the oily crude product ob-
tained was diluted with dichloromethane (30 mL), washed with
H2O (4 ꢁ 20 mL) and then dried over anhydrous magnesium sulfate.
Removal of the solvent under vacuum afforded PEG400-DIL[PF6]
(3.8 g, 92%) as a yellow oil. 1H NMR (400 MHz, CD3OD),
d (ppm):
8.90 (s, 2H, 2NCHN), 7.63 (s, 4H, 2CHCH), 4.37 (t, J ¼ 13.4 Hz, 4H,
* Corresponding author. Hangzhou Normal University, Haishu Road 58, Hang-
zhou 311121, China.
** Corresponding author. Hangzhou Normal University, Haishu Road 58, Hang-
zhou 311121, China.
2NCH2), 3.85 (s, 6H, NCH3), 3.77e3.74 (m, 4H, OCH2CH2N),
3.66e3.60[m, (OCH2CH2)n]. 13C NMR (100.6 MHz, CD3OD),
d
(ppm):
137.2(NCHN), 123.1(NCHCHN), 122.7(NCHCHN), 70.1[(CH2CH2O)n],
70.0[(CH2CH2O)n], 69.9[(CH2CH2O)n], 68.3(NCH2CH2O),
E-mail addresses: baiying0912@163.com (Y. Bai), jjpeng@hznu.edu.cn (J. Peng).
http://dx.doi.org/10.1016/j.jorganchem.2015.06.024
0022-328X/© 2015 Published by Elsevier B.V.

66
Y. Bai et al. / Journal of Organometallic Chemistry 794 (2015) 65e69
49.4(NCH2CH2O), 35.2(NCH3).
PEG400DIL[BF4]: The PEG400DI (3.0 g, 5 mmol) obtained was
dissolved in deionized H2O (10 mL) and added to a solution of
NH4BF4 (1.1 g, 10 mmol) in H2O (5 mL). The mixture was stirred at
room temperature for 6 h. After decantation, the oily crude product
obtained was diluted with dichloromethane (30 mL), washed with
H2O (4 ꢁ 20 mL), and then dried over anhydrous magnesium sul-
fate. Removal of the solvent under vacuum afforded a yellow oil
PEG400-DIL[BF4] (2.8 g, 78% yield). 1H NMR (400 MHz, CD3OD),
d
(ppm): 8.90 (s, 2H, 2NCHN), 7.63 (s, 4H, 2CHCH), 4.37 (t,
J ¼ 13.4 Hz, 4H, 2NCH2), 3.85(s, 6H, NCH3), 3.77e3.74(m, 4H,
OCH2CH2N), 3.66e3.60[m, (OCH2CH2)n]. 13C NMR (100.6 MHz,
CD3OD),
70.1[(CH2CH2O)n],
68.3(NCH2CH2O), 49.4(NCH2CH2O), 35.2(NCH3).
d
(ppm): 137.2(NCHN), 123.1(NCHCHN), 122.7(NCHCHN),
70.0[(CH2CH2O)n], 69.9[(CH2CH2O)n],
PEG400DIL[SO3CF3]: The PEG400DI (3.0 g, 5 mmol) obtained was
dissolved in deionized H2O (10 mL) and added to a solution of
NH4SO3CF3 (1.7 g, 10 mmol) in H2O (5 mL). The mixture was stirred
at room temperature for 6 h. After decantation, the oily crude
product obtained was diluted with dichloromethane (30 mL),
washed with H2O (4 ꢁ 20 mL), and then dried over anhydrous
magnesium sulfate. Removal of the solvent under vacuum afforded
a yellow oil PEG400-DIL[SO3CF3] (3.3 g, 78% yield). 1H NMR
Fig. 1. Structure of ionic liquids.
reaction catalyzed by Rh(PPh3)3Cl was investigated and the results
summarized in Table 1. A styrene conversion of 78.4% was achieved
in the hydrosilylation reaction catalyzed using [Rh(PPh3)3Cl] and
the selectivity for the
Under the same reaction conditions, the catalytic activity of
[PEG400DIL][PF6]-Rh and the selectivity for the -adduct were
increased [20]. When [PEG400DIL][BF4]-[Rh(PPh3)3Cl] was used as
the catalyst, the best selectivity for the -adduct was 85.9% with a
b-adduct was only 64.9% (Table 1, entry 1).
(400 MHz, DMSO),
d (ppm): 9.05 (s, 2H, 2NCHN), 7.68(s, 4H,
b
2CHCH), 4.34(t, J ¼ 9.7 Hz, 4H, 2NCH2), 3.87(s, 6H, NCH3),
3.78e3.76(m, 4H, OCH2CH2N), 3.55e3.50[m, (OCH2CH2)n]. 13C NMR
b
(100.6 MHz, CD3OD),
d (ppm): 136.7(NCHN), 123.2(NCHCHN),
90.7% conversion of styrene (Table 1, entry 9). Furthermore, using
[PEG400DIL][SO3CF3]-[Rh(PPh3)3Cl] and [PEG400DIL][N(SO2CF3)2]-
[Rh(PPh3)3Cl] as the catalyst, the best selectivity was 80.4% and
76.4% with conversions of styrene of 91.0% and 86.6%, respectively
(Table 1, entry 16 and 22). The presence of the PEG chain in the ionic
liquids molecules suppressed the hydrogenation and dehydrogen-
ative silylation side reactions [20]. The type of anion can also in-
fluence the activity of catalyst and the selectivity of adduct.
The effect of the anion in the polyethylene glycol(400) func-
tionalized ionic liquid on the reaction was investigated and the
curve of reaction with time shown in Fig. 2. In the initial stage of the
reaction, the three catalytic systems of [PEG400DIL][X]-
[Rh(PPh3)3Cl] except [PEG400DIL][N(SO2CH3)]-[Rh(PPh3)3Cl] gave
high initial turnover rates and the activity of [PEG400DIL][SO3CF3]-
[Rh(PPh3)3Cl] found to be highest. Meanwhile, the Rh(PPh3)3Cl
catalyst without an ionic liquid was lower than the other catalytic
systems studied. During the intermediate stage of the reaction,
[PEG400DIL][PF6]-[Rh(PPh3)3Cl] showed better activity than the
other catalysts studied. However, both [PEG400DIL][PF6]-
[Rh(PPh3)3Cl] and [PEG400DIL][BF4]-[Rh(PPh3)3Cl] displayed similar
122.6(NCHCHN), 70.5[(CH2CH2O)n], 69.7[(CH2CH2O)n], 69.5
[(CH2CH2O)n], 68.0(NCH2CH2O), 48.7(NCH2CH2O), 35.4(NCH3).
PEG400DIL[N(SO2CF3)2]: The PEG400DI (2.9 g, 5 mmol) obtained
was dissolved in deionized H2O (10 mL) and added to a solution of
LiN(SO2CF3)2 (2.9 g, 10 mmol) in H2O (5 mL). The mixture was
stirred at room temperature for 6 h. After decantation, the oily
crude product obtained was diluted with dichloromethane (30 mL),
washed with H2O (4 ꢁ 20 mL), and then dried over anhydrous
magnesium sulfate. Removal of the solvent under vacuum afforded
a yellow oil PEG400DIL[N(SO2CF3)2] (3.2 g, 62% yield). 1H NMR
(400 MHz, CD3OD),
d (ppm): 8.72(s, 2H, 2NCHN), 7.47(s, 4H,
2CHCH), 4.31(t, J ¼ 9.1 Hz, 4H, 2NCH2), 3.85(s, 6H, NCH3),
3.79e3.77(m, 4H, OCH2CH2N), 3.70e3.64[m, (OCH2CH2)n]. 13C NMR
(100.6 MHz, CD3OD),
121.6(NCHCHN), 71.4[(CH2CH2O)n],
d
(ppm): 136.8(NCHN), 123.4(NCHCHN),
70.7[(CH2CH2O)n], 70.4
[(CH2CH2O)n], 68.5(NCH2CH2O), 49.8(NCH2CH2O), 36.3(NCH3).
2.2. The catalytic hydrosilylation reaction
All catalytic reaction was performed in a 10 mL flat-bottomed
tube without protection from air. The alkenes (4.0 mmol) and a
requisite amount of catalyst and ionic liquid were placed in a dried
tube and the reaction mixture stirred for 5 min. Thereafter, the
silane (4.4 mmol) was added, the resulting reaction mixture heated
with stirring for a requisite time and then allowed to cool to room
temperature. The product phase was separated by decantation and
the conversion of the alkenes and selectivity determined by GC-MS
analysis using an Agilent 26890N/59731 apparatus equipped with a
selectivity for the
liquids tested can increase the activity of the rhodium catalyst and
the selectivity towards the -adduct in the hydrosilylation reaction
of styrene using triethoxysilane, the [PEG400DIL][SO3CF3]-
[Rh(PPh3)3Cl] catalyst system showed the best activity, but the final
yield of adduct was lower.
b-adduct. Though all the PEG functionalized ionic
b
3.2. The effect of reaction temperature on the hydrosilylation
reaction
DB-5 column (30 m ꢁ 2.5 mm ꢁ 0.25
mm).
3. Results and discussion
With different anions, the ionic liquids have different properties
including solubility, melting point and mobility. These properties
have certain relationships with temperature. The effect of tem-
perature on the hydrosilylation reaction of alkenes was investi-
gated and the results shown in Fig. 3. Using an ionic liquid with the
PFꢀ6 anion and rhodium catalytic system, the reaction yield reached
its maximum at 80 ꢂC. However, the [PEG400DIL][N(SO2CF3)2]-
[Rh(PPh3)3Cl]system needed the highest reaction temperature for
3.1. The effect of the anion on the rhodium-catalyzed
hydrosilylation reaction of styrene
Initially, the hydrosilylation reaction of styrene catalyzed using
Rh(PPh3)3Cl in the presence of various ionic liquids was conducted.
The effect of the amount of ionic liquid on the hydrosilylation

Y. Bai et al. / Journal of Organometallic Chemistry 794 (2015) 65e69
67
Table 1
Effect of anions of ionic liquids on hydrosilylation catalyzed by Rh(PPh3)3Cl.
Entry
Ionic liquid
Rh(PPh3)3Cl/Ionic liquid
Conv. (%)
Selectivity (%)
b
/a
TON
b
a
1-Ethyl-benzene
Dehydrogenative silylation
1
2
3
4
5
6
7
8
e
e
78.4
98.5
100
64.9
77.7
83.1
83.6
84.9
78.9
75.8
76.2
85.9
79.7
79.5
84.5
79.9
65.2
65.5
80.4
80
79.3
73.5
69.8
72.0
76.4
75.4
65.6
62.5
12.0
8.4
7.8
5.4
4.8
7.6
13.6
9.0
4.8
12.6
6.9
5.0
4.6
11.2
7.8
3.8
4.4
4.2
5.7
7.4
7.3
6.6
6.8
5.6
10.1
11.0
6.7
4.8
5.4
4.9
6.6
3.9
7.7
5.5
3.3
7.5
5.8
8.2
14.3
19.6
10.9
12.2
12.5
27.8
14.7
11.6
8.9
12.1
7.2
4.3
5.6
5.4
6.8
6.7
7.0
3.7
4.4
5.9
4.7
6.8
9.2
6.9
4.7
3.5
4.1
5.5
8.1
9.2
8.1
10.3
9.7
9.3
5.4
9.2
1568
1970
2000
1978
1904
1792
1582
1772
1814
1678
1726
1354
994
1992
1994
1820
1950
1794
1306
1754
1670
1732
1928
1794
1630
[PEGDIL][PF6]
1:2
1:3
1:5
1:10
1:30
1:80
1:2
1:3
1:5
1:10
1:30
1:80
1:2
1:3
1:5
1:10
1:30
1:80
1:1
1:3
1:5
10.7
15.5
17.7
10.3
5.6
8.5
17.9
6.3
11.5
16.9
17.4
5.8
98.9
95.2
89.6
79.1
88.6
90.7
83.9
86.3
67.7
49.7
99.6
99.7
91.0
97.5
89.7
65.3
87.7
83.5
86.6
96.4
89.7
81.5
[PEGDIL][BF4]
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
[PEGDIL][SO3CF3]
[PEGDIL][N(SO2CF3)2]
8.4
20.9
18.1
18.7
13.0
9.4
9.7
11.6
11.1
11.7
6.2
1:10
1:30
1:80
7.5
19.1
18.3
Reaction conditions: styrene 4.0 mmol, (EtO)3SiH 4.4 mmol, 5 h, 90 ꢂC, Rh is 0.05 mol% based on styrene.
attaining the maximum of yield in the hydrosilyaltion reaction of
styrene.
results indicated that different anions in the polyethylene glycol
functionalized ionic liquid exhibited different effects on the activity
and selectivity in the hydrosilylation reaction of various alkenes
(Table 2).
For the hydrosilylation of 1-hexene, the [PEG400DIL]
[N(SO2CF3)2] based catalyst system (Table 2, entry 4) was superior
to the other ionic liquids studied. All the ionic liquids bearing
different anions showed excellent catalytic performance for the
hydrosilylation of 1-octene. When [PEG400DIL][SO3CF3]-
3.3. The hydrosilylation reaction of alkenes using triethoxysilane
To investigate the effect of ionic liquids with various anions on
hydrosilylation reaction of different alkenes, a series of alkenes in
the presence of triethoxysilane were investigated in the hydro-
silylation reaction catalyzed by PEG400DIL[X]- [Rh(PPh3)3Cl]. The
Fig. 3. Temperature-dependence curve for the hydrosilylation of styrene using
different IL. Reaction conditions: styrene 4.0 mmol, (EtO)3SiH 4.4 mmol, 5 h, Rh is
0.05 mol% based on styrene.
Fig. 2. Reaction curve with different ionic liquid-[Rh(PPh3)3Cl]. Reaction conditions:
styrene 4.0 mmol, (EtO)3SiH 4.4 mmol, 5 h, 90 ꢂC, Rh is 0.05 mol% based on styrene.

68
Y. Bai et al. / Journal of Organometallic Chemistry 794 (2015) 65e69
Table 2
Hydrosilylation of different alkenes with triethoxysilane.
Entry
Alkenes
Ionic liquids
Conv. (%)
Selec. of
b
-adduct (%)
TON
1
2
3
4
5
6
7
8
1-Hexene
[PEGDIL][PF6]
[PEGDIL][BF4]
[PEGDIL][SO3CF3]
[PEGDIL][N(SO2CF3)2]
[PEGDIL][PF6]
100
100
93.5
95.8
89.2
97.9
98.2
100
99.5
96.4
100
2000
2000
1816
1846
1852
1824
1924
1822
1698
2000
1628
1432
1908
1916
1998
2000
2000
1896
1970
1928
1824
1940
1638
1794
1958
2000
1990
1998
1884
1986
2000
1848
90.8
92.3
92.6
92.1
96.2
91.1
84.9
100
82.9
71.6
95.4
98.0
99.9
100
1-Octene
[PEGDIL][BF4]
[PEGDIL][SO3CF3]
[PEGDIL][N(SO2CF3)2]
[PEGDIL][PF6]
9
1-Decene
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
[PEGDIL][BF4]
98.7
100
100
[PEGDIL][SO3CF3]
[PEGDIL][N(SO2CF3)2]
[PEGDIL][PF6]
3,3- Dimethyl-1-butene
Styrene
100
[PEGDIL][BF4]
99.7
99.9
99.6
82.7
84.1
86.3
75.4
100
[PEGDIL][SO3CF3]
[PEGDIL][N(SO2CF3)2]
[PEGDIL][PF6]
100
[PEGDIL][BF4]
94.8
98.5
96.4
91.2
97.0
83.4
89.7
97.9
100
99.5
99.9
94.2
99.3
100
[PEGDIL][SO3CF3]
[PEGDIL][N(SO2CF3)2]
[PEGDIL][PF6]
Allylbenzene
Ethyl vinyl ether
Isobutyl vinyl ether
[PEGDIL][BF4]
100
[PEGDIL][SO3CF3]
[PEGDIL][N(SO2CF3)2]
[PEGDIL][PF6]
90.3
98.7
99.4
99.9
99.5
99.9
100
100
96.4
99.0
[PEGDIL][BF4]
[PEGDIL][SO3CF3]
[PEGDIL][N(SO2CF3)2]
[PEGDIL][PF6]
[PEGDIL][BF4]
[PEGDIL][SO3CF3]
[PEGDIL][N(SO2CF3)2]
92.4
Reaction conditions: alkene 4.0 mmol, (EtO)3SiH 4.4 mmol, 5 h, 90 ꢂC, Rh(PPh3)3Cl is 0.05 mol% based on alkene, n(Rh)/n(PEG400DIL[X]) ¼ 1:10.
[Rh(PPh3)3Cl] was used as the catalyst system, a 96.2% conversion
was obtained with 99.5% selectivity for the -adduct. Meanwhile, a
92.1% conversion with 100% selectivity for the -adduct was ob-
ionic liquid was more capable of protecting the [Rh(PPh3)3Cl]
catalyst from leaching out of the reaction system.
b
b
tained using [PEG400DIL][BF4]-[Rh(PPh3)3Cl] as the catalyst. For 3,3-
dimethyl-1-butene, a >99% selectivity and >98% conversion were
attained by the catalyst system comprised of four kinds of ionic
liquids and Rh(PPh3)3Cl, respectively. For aromatic alkenes, allyl-
4. Conclusions
In summary, polyethylene glycol(400) functionalized imidazo-
lium ionic liquids bearing different anions have been synthesized
and used in the hydrosilylation reaction of alkenes catalyzed using
a rhodium complex. All of the catalyst systems can be applied in the
hydrosilylation reaction of different linear aliphatic and aromatic
benzene as substrate gave better selectivity for the b-adduct when
compared to styrene, which was attributed to the electronic effects
of the benzene ring and the conjugation effect of the allyl substit-
uent that can influence the electron density of the olefinic bond to
favor the anti-markovnikov addition reaction to give the b-adduct.
Similar excellent results were obtained in the hydrosilylation re-
action of vinyl ether catalyzed using different ionic liquids and
Rh(PPh3)3Cl. The best conversion and selectivity was 100% and
99.9%, respectively, which was obtained in the hydrosilylation re-
action of ethyl vinyl ether in the presence of triethoxysilane using
[PEG400DIL][BF4]-[Rh(PPh3)3Cl] as the catalyst system.
3.4. Recycling of PEG400DIL[X]e[Rh(PPh3)3Cl] in the hydrosilylation
reaction of 1-octene
In recycling experiments, the ionic liquids and catalyst phase
were allowed to separate from the reaction system by gravity after
each run. The catalytic system without any further treatment was
used for the next cycle. The results are listed in Fig. 4. The PEG400DIL
[PF6]-[Rh(PPh3)3Cl] catalyst can be recycled 5 times with no sig-
nificant loss in activity. However, PEG400DIL[N(SO2CF3)2]-
[Rh(PPh3)3Cl] could only be reused 3 times and its catalytic activity
declined rapidly. The other two systems can be recycled 3 and 4
times, respectively. The results showed that the PEG400DIL[PF6]
Fig. 4. Recyclability of catalyst systems.

Y. Bai et al. / Journal of Organometallic Chemistry 794 (2015) 65e69
69
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Appendix A. Supplementary data
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