Effect of carboxyl-functionalized imidazolium salts on the rhodium-catalyzed hydrosilylation of alkene

Article abstract of DOI:10.1016/j.jorganchem.2012.12.016

A series of carboxyl-functionalized imidazolium salts were synthesized. Hydrosilylation reaction of carboxyl-functionalized imidazolium salts (1b-4b, 1c-3c) exhibited higher levels of styrene conversion and higher levels of β-adduct selectivity. In particular, no ethylbenzene as hydrogenation product could be yielded at all when Rh(PPh₃)₃Cl/carboxyl- functionalized imidazolium inner salts (1c-3c), respectively, were used as the catalyst. The Rh(PPh₃)₃Cl/carboxyl-functionalized imidazolium salts catalyst system can be reused without noticeable loss of catalytic activity.

Full text of DOI:10.1016/j.jorganchem.2012.12.016

Journal of Organometallic Chemistry 727 (2013) 28e36
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Effect of carboxyl-functionalized imidazolium salts on the rhodium-
catalyzed hydrosilylation of alkene
*
**
Chao Ma, Jiayun Li , Jiajian Peng , Ying Bai, Guodong Zhang, Wenjun Xiao, Guoqiao Lai
Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, Hangzhou 310012, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of carboxyl-functionalized imidazolium salts were synthesized. Hydrosilylation reaction of
carboxyl-functionalized imidazolium salts (1be4b, 1ce3c) exhibited higher levels of styrene conversion
and higher levels of b-adduct selectivity. In particular, no ethylbenzene as hydrogenation product could
be yielded at all when Rh(PPh3)3Cl/carboxyl-functionalized imidazolium inner salts (1ce3c), respec-
tively, were used as the catalyst. The Rh(PPh3)3Cl/carboxyl-functionalized imidazolium salts catalyst
system can be reused without noticeable loss of catalytic activity.
Received 16 November 2012
Received in revised form
10 December 2012
Accepted 13 December 2012
Keywords:
Ó 2012 Elsevier B.V. All rights reserved.
Carboxyl-functionalized imidazolium salts
Hydrosilylation
Rhodium complex
Recyclable
1. Introduction
separation, the preparation of fluorous room temperature ionic liquid
as well as fluorous version of Wilkinson’s catalyst was very difficult.
Hydrosilylation reaction was usually performed to synthesize
functionalized silane, polysilane and other organosilicon
compounds [1e3]. Hydrosilylation of carbonecarbon double bonds
catalyzed by transition metal was one of the most important
commercial processes [4,5]. However, low conversion and low
selectivities of the product were usually observed with some
particular terminal alkenes [6e8]. In particular, catalysis hydro-
silylation of styrene with hydrosilane, a model reaction often used
to check the catalytic activity of catalysts, has widely been reported,
to have unsatisfactory catalytic activity of transition metal and
selectivity of the product [9,10].
Recently, our group [16,17] reported that Rh(PPh3)3Cl/ionic liquid
(molten salt) could be applied in hydrosilylation process as a ther-
moregulated and recyclable catalyst system. The Rh(PPh3)3Cl/ionic
liquid (molten salt) catalyst system reported the advantages of ionic
liquid with convenient product separation. But catalytic activity of
Rh(PPh3)3Clandselectivityoftheproductwerestillunsatisfactory. On
the other hand, organic fatty acids could be used as promoters in the
hydrosilylation processes [18,19]. In this paper, we reported the
synthesis ofa series ofcarboxyl-functionalized imidazolium salts, and
their application on hydrosilylation reaction (Scheme 1).
Muchattentionhasbeenfocusedonhomogeneousorliquid/liquid
biphasic reactions with ionic liquids employed as media, inwhich the
catalysts were dissolved and immobilized in ionic liquids [11e13].
Weyershausen et al. [14] reported a platinum catalyzed hydro-
silylation reaction in ionic liquid, with the recyclable catalyst/ionic
liquid system. Broeke et al. [15] reported that hydrosilylation reaction
could be conducted in a novel fluorous ionic liquid in the presence of
fluorous version of Wilkinson’s catalyst. Though the fluorous ionic
liquid/Wilkinson’s catalyst system was simply recycled by biphasic
2. Experimental
2.1. General information
Styrene was washed with 5% NaOH and dried with Na2SO4, and
then was distilled under reduced pressure after filtration. All other
substances were purchased from Aldrich and were used as received.
Gas chromatography: Trace DSQ GC Column
¼
DB-5
30 m ꢀ 2.5 mm ꢀ 0.25
m
m, split ¼ 50:1, flow ¼ 1 mL minꢁ1 constant
flow, inlet temperature ¼ 260 ꢂC, column temperature ¼ 50 ꢂC
(hold 1 min) then 15 ꢂC minꢁ1 up to 260 ꢂC (hold 10 min).
1H, 13C and 29Si NMR spectra were measured using a Bruker
AV400 MHz spectrometer operating at 400.13, 100.62 and 79 MHz,
respectively.
* Corresponding author. Tel.: þ86 571 28865136.
** Corresponding author. Tel.: þ86 571 28865136; fax: þ86 571 28865135.
E-mail addresses: tougaos@hotmail.com, jiayun1980@hotmail.com (J. Li),
jjpeng@hznu.edu.cn (J. Peng), gqlai@hznu.edu.cn (G. Lai).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2012.12.016

C. Ma et al. / Journal of Organometallic Chemistry 727 (2013) 28e36
29
Si(R1)3
2.2.2. Synthesis of 1-(2-carboxyethyl)-3-methylimidazolium
bromide 2a
α-adduct
R
R
3-Bromopropionic acid (7.65 g, 50 mmol) was dissolved in THF
(50 mL) at room temperature under a nitrogen atmosphere by
adding 1-methylimidazole (4.11 g, 4.0 mL, 50 mmol). Then the
mixture was refluxed for 8 h at 75 ꢂC. Evaporation of the solvent
under vacuum yielded the crude ionic liquid, which was purified by
washing with Et2O (3 ꢀ 10 mL) and then dried in vacuo obtaining
Si(R1)3
Rh Complex
HSi(R1)3
R
β-adduct
+
alkane
R
dehydroganative
silylation product
91% yield. 1H NMR (CD3OD)
d
(ppm): 9.03 (s, 1H, im), 7.63 (brs, 2H,
Si(R1)3
R
im), 4.49 (t, J ¼ 6.3 Hz, 2H, CH2), 3.95 (s, 3H, CH3), 2.96 (t, J ¼ 6.3 Hz,
2H, CH2). 13C NMR (CD3OD)
d (ppm): 171.36, 135.97, 122.39, 121.44,
R: Ph, CH3Ph, CH3OPh, FPh, C4H9, C6H13, C10H21, OC2H5, OC4H9
R1: OEt, Et
44.20, 34.77, 33.16. IR (KBr) 1731.6, 1574.7, 1404.5, 1167.6 cmꢁ1. Anal.
Calc. for 2a (C7H11BrN2O2): C, 35.76; H, 4.72; N, 11.92; O, 13.61.
Found: C, 35.77; H, 4.71; N, 11.91; O, 13.61. r.t.: liquid.
Scheme 1. Hydrosilylation of alkenes with triethoxysilane or triethylsilane catalyzed
with rhodium complex.
2.2.3. Synthesis of 1-(4-carboxybenzyl)-3-methylimidazolium
chloride 3a
Elemental analyses were performed on a VARIO EL-3 elemental
analyzer and IR spectra were recorded on a Nicolet 5700 instru-
ment. GCeMS was tested Trace DSQ GCeMS Column.
A solution of 4-(chloromethyl) benzoic acid (8.53 g, 50 mmol) in
THF (50 mL) was added by adding 1-methylimidazole (0.52 g,
0.5 mL, 50 mmol) at room temperature under nitrogen atmosphere.
Then the mixture was heated for 8 h at 75 ꢂC. Evaporation of the
solvent under vacuum yielded the crude ionic liquid as white solid,
which was purified by washing with Et2O and dried in vacuo giving
2.2. Synthesis of carboxyl-functionalized imidazolium salts (Scheme
2)
83% yield. 1H NMR (CD3OD)
im), 7.71e7.45 (m, 4H, Ph), 5.50 (s, 2H, CH2), 3.94 (s, 3H, CH3). 13
NMR (CD3OD) (ppm): 166.34, 137.59, 135.67, 130.08, 128.94,
d (ppm): 9.05 (s, 1H, im), 8.09 (brs, 2H,
2.2.1. Synthesis of 1-carboxymethyl-3-methylimidazolium bromide
1a
C
d
To stirring solution of 1-methylimidazole (4.0 mL, 50 mmol) in
THF (50 mL) at 0 ꢂC was added dropwise methyl bromoacetate
(5.5 mL, 60 mmol) under a nitrogen atmosphere. The reaction
mixture was stirred at 0 ꢂC for 1 h, and then warmed at room
temperature for another 3 h. The resulting mixture was filtered
yielding the white solid that was washed with diethyl ether
(3 ꢀ 10 mL). The product was dried at 60 ꢂC in vacuo. Thereafter, the
prepared intermediate and 16.7% HCl (10 mL) were refluxed for 2 h
at 100 ꢂC then the solvent was removed under reduced pressure
yielding 89% of 1-carboxymethyl-3-methylimidazolium bromide as
126.99, 122.81, 121.19, 50.84, 34.11. IR (KBr) 1693.6, 1613.3, 1566.5,
1399.0, 1160.4 cmꢁ1. Anal. Calc. for 3a (C12H13ClN2O2): C, 57.04; H,
5.19; N, 11.09; O, 12.66. Found: C, 57.03; H, 5.19; N, 11.11; O, 12.65.
r.t.: solid.
2.2.4. Synthesis of 1,3-di(carboxymethyl)imidazolium bromide 4a
A solution of trimethylsilylimidazole (1.40 g, 1.5 mL, 0.010 mol)
and ethyl bromoacetate (3.34 g, 2.2 mL, 0.020 mol) in THF (50 mL)
was stirred at 60 ꢂC under nitrogen atmosphere for 24 h. The
precipitate was filtrated and washed with diethyl ether (3 ꢀ 10 mL),
and then the product was dried at 60 ꢂC in vacuo. Thereafter,
a mixture of the product and 16.7% HCl (10 mL) was refluxed for 2 h
at 100 ꢂC. The solvent was removed under reduced pressure and the
remaining product was washed with diethyl ether yielding 87% of
oil liquid. 1H NMR (CD3OD)
d
(ppm): 9.02 (s, 1H, im), 7.64 (brs, 2H,
(ppm):
im), 5.16 (s, 2H, CH2), 3.98 (s, 3H, CH3). 13C NMR (CD3OD)
d
171.74, 141.77, 127.65, 127.11, 53.37, 39.36. IR (KBr) 1734.9, 1581.7,
1403.8, 1190.3 cmꢁ1. Anal. Calc. for 1a (C6H9BrN2O2): C, 32.60; H,
4.10; N, 12.67; O, 14.48. Found: C, 32.61; H, 4.10; N, 12.66; O, 14.48.
r.t.: solid (Fig. 1).
the product as oil liquid. 1H NMR (CD3OD)
d
(ppm): 9.19 (s, 1H, im),
(ppm):
7.73 (brs, 2H, im), 5.26 (s, 4H, CH2). 13C NMR (CD3OD)
d
167.65, 138.57, 123.35, 49.58. IR (KBr) 1736.1, 1580.7, 1409.7,
1174.4 cmꢁ1. Anal. Calc. for 4a (C7H9BrN2O4): C, 31.72; H, 3.42; N,
10.57; O, 24.14. Found: C, 31.74; H, 3.42; N, 10.56; O, 24.16. r.t.: solid
(Fig. 2).
2.2.5. Synthesis of carboxyl-functionalized imidazolium
hexafluorophosphate salts 1be4b
According to general method the above 1a, 2a, 3a, or 4a
prepared (10 mmol), respectively, were dissolved in 15 mL of H2O
and then mixed with NH4PF6 (10.9 mmol) in 10 mL of H2O. The
mixture was stirred for 2 h at room temperature. After decantation,
the oily crude product was diluted in 30 mL of methylene chloride,
washed twice with 20 mL of H2O and then dried over anhydrous
magnesium sulfate. Removal of the solvent under vacuum afforded
1be4b, respectively.
2.2.5.1. 1-Carboxymethyl-3-methylimidazolium hexafluorophosphate
Fig. 1. Crystal structure of 1a. Some molecular dimensions: O(2)-C(6) 1.202(6) Å, C
(4)-N (2) 1.307 (5) Å, C (4)-N (1) 1.329(5) Å, C(2)-C(3) 1.362(6) Å, C(2)-N(1) 1.369(5) Å,
N(2)-C(3) 1.380(5) Å, N(2)-C(5) 1.463(4) Å, N(1)-C(1) 1.455(5) Å, C(5)-C(6) 1.507(6) Å,
C(6)-O(1) 1.307(5) Å, N(2)-C(4)-N(1) 109.0(3)ꢂ, C(3)-C(2)-N(1) 107.6(4)ꢂ, C(4)-N(2)-
C(3) 109.7(3)ꢂ, C(4)-N(2)-C(5) 125.6(3)ꢂ, C(3)-N(2)-C(5) 124.7(3)ꢂ, C(4)-N(1)-C(2)
108.3(3)ꢂ, C(4)-N(1)-C(1) 125.3(4)ꢂ, C(2)-N(1)-C(1) 126.3(4)ꢂ, N(2)-C(5)-C(6) 111.4(3)ꢂ,
C(2)-C(3)-N(2) 105.5(4)ꢂ, O(2)-C(6)-O(1) 125.0(4)ꢂ, O(2)-C(6)-C(5) 124.9(4)ꢂ, O(1)-
C(6)-C(5) 110.1(4)ꢂ.
1b. 1H NMR (DMSO)
d
(ppm): 9.13 (s, 1H, im), 7.69 (brs, 2H, im),
5.08 (s, 2H, CH2), 3.87 (s, 3H, CH3). 13C NMR (DMSO)
d
(ppm):
168.81, 137.97, 124.05, 123.48, 50.21, 36.25. IR (KBr) 1744.0, 1579.5,
1177.4, 1384.4, 886.4 cmꢁ1. Anal. Calc. for 1b (C6H9F6N2O2P): C,
25.19; H, 3.17; N, 9.79; O, 11.18. Found: C, 25.20; H, 3.16; N, 9.80; O,
11.19. Yield: 93%. r.t.: liquid.

30
C. Ma et al. / Journal of Organometallic Chemistry 727 (2013) 28e36
1a
2a
3a
4a
H2O
NH4PF6
+
N
N
N
N
R2
R1
x
R2
R1
PF
a
b
R1=-CH3,-CH2COOH
R2=-CH2COOH,-CH2CH2COOH,-CH2PhCOOH
X=Br, Cl
1b: R1=-CH3 R2=-CH2COOH
2b: R1=-CH3 R2=-CH2CH2COOH
3b: R1=-CH3 R2=-CH2PhCOOH
4b: R1=-CH2COOH R2=-CH2COOH
Anion exchange resins in chloride form ,CH3OH
N
N
N
N
R2
R1
x
R
R1
a
c
R1=-CH3,-CH2COOH
R2=-CH2COOH,-CH2CH2COOH,-CH2PhCOOH
R-=-CH2COO-,-CH2CH2COO-,-CH2PhCOO-
X=Br,Cl
1c: R1=-CH3 R-=-CH2COO-
2c: R1=-CH3 R-=-CH2CH2COO-
3c: R1=-CH3 R-=-CH2PhCOO-
a
d
R1=-CH3,-CH2COOH
R2=-CH2COOH,-CH2CH2COOH,-CH2PhCOOH
X=Br,Cl
1d: R1=-CH3 R2=-CH2COOH
2d: R1=-CH3 R2=-CH2CH2COOH
3d: R1=-CH3 R2=-CH2PhCOOH
4d: R1=-CH2COOH R2=-CH2COOH
Scheme 2. Synthesis of carboxyalkyl-imidazolium salts.

C. Ma et al. / Journal of Organometallic Chemistry 727 (2013) 28e36
31
13C NMR (CD3OD)
d
(ppm): 173.59, 135.91, 122.13, 121.19, 45.30,
35.40, 33.99. IR (KBr) 1584.6, 1402.1, 1166.3 cmꢁ1. Anal. Calc. for 2c
(C7H10N2O2): C, 54.54; H, 6.54; N,18.17; O, 20.76. Found: C, 54.55; H,
6.54; N, 18.16; O, 20.75. Yield: 86%. r.t.: liquid.
2.2.6.3. 1-(4-Carboxybenzyl)-3-methylimidazolium inner salt 3c.
1H NMR (CD3OD)
d
(ppm): 9.04 (s, 1H, im), 7.87 (brs, 2H, im), 7.36e
7.61 (m, 4H, Ph), 5.42 (s, 2H, CH2), 3.92 (s, 3H, CH3). 13C NMR
(CD3OD) (ppm): 172.80, 138.69, 135.74, 129.75, 127.57, 123.87,
d
122.33, 121.19, 52.29, 35.15. IR (KBr) 1673.6, 1598.3, 1555.0, 1407.4,
1163.8 cmꢁ1. Anal. Calc. for 3c (C12H12N2O2): C, 66.65; H, 5.59; N,
12.96; O, 14.80. Found: C, 66.67; H, 5.59; N, 12.95; O, 14.79. Yield:
89%. r.t.: solid.
Fig. 2. Crystal structure of 4a. Some molecular dimensions: O(1)-C(7) 1.207(6) Å, N(2)-
C(1) 1.330(6) Å, N(2)-C(3) 1.379(6) Å, N(2)-C(4) 1.462(6) Å, C(1)-N(1) 1.331(6) Å, C(3)-
C(2) 1.345(7) Å, O(3)-C(5) 1.209(6) Å, O(4)-C(5) 1.313(6) Å, C(2)-N(1) 1.381(6) Å, O(2)-
C(7) 1.317(5) Å, C(6)-N(1) 1.463(6) Å, C(6)-C(7) 1.494(6) Å, C(4)-C(5) 1.511(7) Å, C(1)-
N(2)-C(3) 108.9(4)ꢂ, C(1)-N(2)-C(4) 125.9(4)ꢂ, C(3)-N(2)-C(4) 125.0(4)ꢂ, N(2)-C(1)-N(1)
108.0(4)ꢂ, C(2)-C(3)-N(2) 107.3(4)ꢂ, C(3)-C(2)-N(1) 106.7(4)ꢂ, N(1)-C(6)-C(7) 112.4(3)ꢂ,
C(1)-N(1)-C(2) 109.1(4)ꢂ, C(1)-N(1)-C(6) 126.5(4)ꢂ, C(2)-N(1)-C(6) 124.4(4)ꢂ, N(2)-C(4)-
C(5) 110.5(4)ꢂ, O(3)-C(5)-O(4) 124.9(5)ꢂ, O(3)-C(5)-C(4) 124.1(4)ꢂ, O(4)-C(5)-C(4)
111.0(4)ꢂ, O(1)-C(7)-O(2) 125.4(4)ꢂ, O(1)-C(7)-C(6) 124.6(4)ꢂ, O(2)-C(7)-C(6) 109.9(4)ꢂ.
2.2.7. Synthesis of carboxyl-functionalized imidazolium
trifluoromethanesulfonate 1de4d
Applying general method a stoichiometric amount of tri-
fluoromethanesulfonate acid was added into 4a prepared
(10 mmol), respectively, by dropwise and the mixture stirred for 6 h
at 80 ꢂC. The obtained yield was washed thrice with ether and dried
in vacuum.
2.2.5.2. 1-(2-Carboxyethyl)-3-methylimidazoliumhexafluorophosphate
2b. 1H NMR (CD3OD)
d (ppm): 8.84 (s, 1H), 7.56 (brs, 2H, im), 4.42 (t,
2.2.7.1. 1-Carboxymethyl-3-methylimidazolium trifluoromethanesul-
J ¼ 6.3 Hz, 2H), 3.90 (s, 3H, CH3), 2.83 (t, J ¼ 6.3 Hz, 2H). 13C NMR
fonate 1d. 1H NMR (CD3OD)
d
(ppm): 9.04 (s, 1H, im), 7.73 (brs, 2H,
(ppm):
im), 5.29 (s, 2H, CH2), 4.09 (s, 3H, CH3). 13C NMR (CD3OD)
d
(CD3OD) d (ppm): 173.78,136.96,123.30,122.31, 45.74, 34.99, 34.97. IR
(KBr) 1728.9, 1570.0, 1156.0, 1394.7, 831.1 cmꢁ1. Anal. Calc. for 2b
(C7H11F6N2O2P): C, 28.01; H, 3.69; N, 9.33; O, 10.66. Found: C, 28.03;
H, 3.70; N, 9.34; O, 10.56. Yield: 92%. r.t.: liquid.
167.17,137.80,123.60,123.27,121.95 (q, 1JCeF ¼ 316 Hz), 49.39, 35.49.
IR (KBr) 1748.3, 1581.0, 1253.1, 1412.0, 1174.6 cmꢁ1. Anal. Calc. for 1d
(C7H9F3N2O5S): C, 28.97; H, 3.13; N, 9.65; O, 27.56. Found: C, 28.99;
H, 3.13; N, 9.66; O, 27.57. Yield: 91%. r.t.: liquid.
2.2.5.3. 1-(4-Carboxybenzyl)-3-methylimidazolium hexafluorophos-
phate 3b. 1H NMR (CD3OD)
d
(ppm): 9.21 (s, 1H, im), 7.45e7.94 (m,
4H, Ph), 7.74 (brs, 2H, im), 5.48 (s, 2H, CH2), 3.84 (d, J ¼ 4.1 Hz, 3H,
CH3). 13C NMR (CD3OD)
(ppm): 170.43, 137.95, 136.65, 131.04,
130.94, 127.56, 123.18, 122.91, 51.56, 34.67. IR (KBr) 1703.7, 1638.7,
1580.6, 1171.5, 1383.8, 835.3 cmꢁ1
Anal. Calc. for 3b
2.2.7.2. 1-(2-Carboxyethyl)-3-methylimidazolium trifluoromethane-
sulfonate 2d. 1H NMR (CD3OD)
d (ppm): 8.91 (s, 1H, im), 7.59 (brs,
d
2H, im), 4.46 (t, J ¼ 6.2 Hz, 2H, CH2), 3.92 (s, 3H, CH3), 2.95 (t,
J ¼ 6.2 Hz, 2H, CH2). 13C NMR (CD3OD)
d
(ppm): 171.26, 137.02,
1
.
123.60, 122.54, 122.08 (q, JCeF ¼ 318 Hz), 44.92, 35.46, 33.64. IR
(KBr) 1732.1, 1577.0, 1255.9, 1409.05, 1166.4 cmꢁ1. Anal. Calc. for 2d
(C8H11F3N2O5S): C, 31.58; H, 3.64; N, 9.21; O, 26.29. Found: C, 31.59;
H, 3.64; N, 9.20; O, 26.30. Yield: 93%. r.t.: liquid.
(C12H13F6N2O2P): C, 39.79; H, 3.62; N, 7.73; O, 8.83. Found: C, 39.77;
H, 3.61; N, 7.74; O, 8.83. Yield: 89%. r.t.: solid.
2.2.5.4. 1,3-Di(carboxymethyl)imidazolium hexafluorophosphate 4b.
1H NMR (CD3OD)
d (ppm): 8.90 (s, 1H, im), 7.50 (brs, 2H, im), 5.73 (s,
2.2.7.3. 1-(4-Carboxybenzyl)-3-methylimidazolium trifluoromethane-
4H, CH2). 13C NMR (CD3OD) (ppm): 168.49, 138.73, 123.88, 49.57. IR
(KBr) 1605.3, 1573.3, 1473.6, 1178.9, 1408.0, 832.1 cmꢁ1. Anal. Calc.
for 4b (C7H9F6N2O4P): C, 25.47; H, 2.75; N, 8.49; O, 19.39. Found: C,
25.48; H, 2.75; N, 8.50; O, 19.40. Yield: 94%. r.t.: solid.
sulfonate 3d. 1H NMR (CD3OD)
d
(ppm): 9.00 (s, 1H, im), 8.06 (brs,
2H, im), 7.66e7.46 (m, 4H, Ph), 5.49 (s, 2H, CH2), 3.93 (s, 3H, CH3). 13
NMR (CD3OD) (ppm): 167.61, 138.95,136.86,129.98,128.37, 128.33,
C
d
1
124.13, 122.41, 122.08 (q, JCeF ¼ 317 Hz), 52.13, 35.49. IR (KBr)
1715.7, 1615.7, 1577.1, 1414.8, 1257.3, 1164.9 cmꢁ1. Anal. Calc. for 3d
(C13H13F3N2O5S): C, 42.62; H, 3.58; N, 7.65; O, 21.84. Found: C, 42.63;
H, 3.58; N, 7.66; O, 21.85. Yield: 93%. r.t.: liquid.
2.2.6. Synthesis of carboxyl-functionalized imidazolium inner salts
1ce3c
With the help of general method the above 1a, 2a, or 3a
prepared (10 mmol), respectively, were dissolved in 15 mL of
CH3OH and then mixed with anion exchange resin in 10 mL of
CH3OH. The mixture was stirred for 2 h at room temperature. After
decantation, evaporation of the solvent under vacuum yielded the
crude ionic liquid, which was purified by washing with Et2O.
Removal of the solvent under vacuum afforded 1ce3c, respectively.
2.2.7.4. 1,3-Di(carboxymethyl)imidazolium trifluoromethanesulfonate
4d. 1H NMR (CD3OD)
d (ppm): 9.02 (s, 1H, im), 7.67 (brs, 2H, im),
5.21 (s, 4H, CH2). 13C NMR (CD3OD)
d (ppm): 167.17, 137.80, 123.72,
1
121.95 (q, JCeF ¼ 316 Hz), 49.52. IR (KBr) 1747.3, 1573.3, 1412.4,
1252.4, 1177.1 cmꢁ1. Anal. Calc. for 4d (C8H9F3N2O7S): C, 28.75; H,
2.71; N, 8.38; O, 33.51. Found: C, 28.76; H, 2.71; N, 8.39; O, 33.53.
Yield: 88%. r.t.: liquid.
2.2.6.1. 1-Carboxymethyl-3-methylimidazolium inner salt 1c. 1HNMR
(CD3OD)
d (ppm): 8.87 (s,1H, im), 7.52 (brs, 2H, im), 5.50 (s, 2H, CH2),
2.3. Preparation of carboxyl-functionalized imidazolium salts
supported catalysts
3.92 (s, 3H, CH3). 13C NMR (CD3OD)
d
(ppm): 170.00, 137.23, 123.46,
122.57, 51.86, 34.89. IR (KBr) 1627.8,1570.6,1405.7,1174.2 cmꢁ1. Anal.
Calc. for 1c (C6H8N2O2): C, 51.42; H, 5.75; N,19.99; O, 22.83. Found: C,
51.43; H, 5.75; N, 19.98; O, 22.84. Yield: 87%. r.t.: solid.
The typical procedure for preparation of carboxyl-
functionalized imidazolium salts supported by catalysts is as
follows: 0.4 g of the required carboxyl-functionalized imidazolium
salt (1ae4a, 1be4b, 1ce3c, 1de4d) was mixed with 2.0 mg of
Rh(PPh3)3Cl. After heating the mixture at 80e100 ꢂC, it was stirred
for 2 h under nitrogen and then cooled at room temperature. The
2.2.6.2. 1-(2-Carboxyethyl)-3-methylimidazolium inner salt 2c.
1H NMR (CD3OD)
d
(ppm): 8.93 (s, 1H, im), 7.65 (brs, 2H, im), 4.43 (t,
J ¼ 6.3 Hz, 2H, CH2), 3.92 (s, 3H, CH3), 2.75 (t, J ¼ 6.3 Hz, 2H, CH2).

32
C. Ma et al. / Journal of Organometallic Chemistry 727 (2013) 28e36
Table 1
Preparation of carboxyalkyl-imidazolium salts.
Product
Yielda (%)
89
Product
Yielda (%)
93
Br
-
PF6
COOH
COOH
N
N
N
N
N
1b
1a
Br-
-
PF6
91
83
92
89
N
N
N
COOH
COOH
2b
2a
COOH
COOH
Cl-
-
PF6
N
N
N
N
3a
3b
-
Br-
N
PF6
COOH
COOH
HOOC
HOOC
87
87
94
91
N
N
N
4a
4b
-
CF3SO3
COO-
COOH
N
N
N
N
N
N
1c
1d
-
CF3SO3
86
89
93
93
N
N
N
COO-
COOH 2d
2c
COO-
COOH
-
CF3SO3
N
N
N
3d
3c
-
CF3SO3
COOH
HOOC
88
N
N
4d
a
Isolated yields.
yielded solid was ground up and used as a catalyst for the hydro-
silylation of alkylene with triethoxysilane (Table 1).
2.4.1.2. a
-Adduct [triethoxy(1-phenylethyl)silane]. 1H NMR (CDCl3)
d
(ppm): 1.18 (t, J ¼ 8 Hz, 9H, CH3),1.33 (d, J ¼ 8 Hz, 3H, CH3), 3.65 (q,
J ¼ 8 Hz, 1H, SieCH), 3.76 (q, J ¼ 8 Hz, 6H, OeCH2), 7.12e7.19 (m, 5H,
Ph). MS (EI) m/z (%): 269 (Mþ, 17), 268 (100). Anal. Calc. for [trie-
thoxy(1-phenylethyl)silane] (C14H24O3Si): C, 62.64; H, 9.01; O,
17.88. Found: C, 62.63; H, 9.03; O, 17.87.
2.4. Catalytic hydrosilylation of alkene with triethoxysilane
Typical hydrosilylation reaction procedures were as follows: A
given amount of catalyst and ionic liquid was added to a 10 mL
round bottomed flask equipped with a magnetic stirrer and then
the alkene and silane were added. After heating the mixture at the
appropriate temperature, the hydrosilylation reaction was
preceded with constant stirring for 5 h. At the end of the reaction,
the product phase was separated from the catalyst by decantation
and the conversion of alkene and the selectivity were determined
by GC. The catalyst was recharged with fresh alkene and silane for
the next catalytic run.
2.4.1.3. Ethylbenzene. 1H NMR (CDCl3)
CH3), 2.64 (q, J ¼ 8 Hz, 2H, CH2), 7.11e7.25 (m, 5H, Ph).
d
(ppm): 1.15 (t, J ¼ 8 Hz, 3H,
2.4.2. Hydrosilylation of 2-methyl-styrene with triethoxysilane
2.4.2.1.
(CDCl3)
b
-Adduct [triethoxy(2-methylphenethyl)silane]. 1H NMR
(ppm): 1.05 (t, J ¼ 8.5 Hz, 2H, SieCH2), 1.37 (t, J ¼ 7.0 Hz, 9H,
d
CH3), 2.42 (s, 3H, CH3), 2.77 (t, J ¼ 8.6 Hz, 2H, CH2), 3.87 (q, J ¼ 7.0 Hz, 6H,
OeCH2), 7.08e7.35 (m, 4H, Ph).13C NMR (CDCl3)
d(ppm): 142.77,135.32,
130.11, 128.06, 126.11, 125.82, 58.40, 26.34, 19.07, 18.36, 11.53. 29Si NMR
2.4.1. Hydrosilylation of styrene with triethoxysilane [20]
(CDCl3, 79 MHz)
d
(ppm): ꢁ46.09. MS (EI) m/z (%): 283 (Mþ, 16), 282
2.4.1.1.
b
-Adduct [triethoxy(phenethyl)silane]. 1H NMR (CDCl3)
(100). Anal. Calc. for [triethoxy(2-methylphenethyl)silane] (C15H26O3Si):
C, 63.78; H, 9.28; O, 16.99. Found: C, 63.75; H, 9.27; O, 17.00.
d
(ppm): 1.00 (t, J ¼ 8 Hz, 2H, SieCH2),1.24 (t, J ¼ 8 Hz, 9H, CH3), 2.74
(t, J ¼ 8 Hz, 2H, CH2), 3.84 (q, J ¼ 8 Hz, 6H, OeCH2), 7.16e7.27 (m, 5H,
Ph). MS (EI) m/z (%): 269 (Mþ, 20), 268 (100). Anal. Calc. for [trie-
thoxy(phenethyl)silane] (C14H24O3Si): C, 62.64; H, 9.01; O, 17.88.
Found: C, 62.62; H, 9.00; O, 17.89.
2.4.3. Hydrosilylation of 3-methyl-styrene with triethoxysilane
2.4.3.1.
(400 MHz, CDCl3)
b
-Adduct [triethoxy(3-methylphenethyl)silane]. 1H NMR
d
(ppm): 1.10 (t, J ¼ 8.5 Hz, 2H, SieCH2), 1.36 (t,

C. Ma et al. / Journal of Organometallic Chemistry 727 (2013) 28e36
33
J ¼ 7.0 Hz, 9H, CH3), 2.43 (s, 3H, CH3), 2.79 (t, J ¼ 8.6 Hz, 2H, CH2), 3.94
(q, J ¼ 7.0 Hz, 6H, OeCH2), 7.15e7.22 (m, 4H, Ph). 13C NMR (101 MHz,
29.48, 29.29, 29.20, 22.69, 22.60, 18.16, 13.94, 10.33. 29Si NMR
(CDCl3)
d
(ppm): ꢁ44.84. MS (EI) m/z (%): 333(Mþ, 20), 332 (100).
CDCl3)
d
(ppm): 144.60, 137.59, 128.65, 128.27, 126.38, 124.91, 58.33,
Anal. Calc. for [triethoxy(dodecyl)silane] (C18H40O3Si): C, 65.00; H,
12.12; O, 14.43. Found: C, 64.99; H, 12.11; O, 14.44.
28.99, 21.32,18.34,12.85. 29Si NMR (CDCl3, 79 MHz)
d
(ppm): ꢁ46.24.
MS (EI) m/z (%): 283 (Mþ, 15), 282 (100). Anal. Calc. for [triethoxy(3-
methylphenethyl)silane] (C15H26O3Si): C, 63.78; H, 9.28; O, 16.99.
Found: C, 63.77; H, 9.28; O, 16.98.
2.4.10. Hydrosilylation of ethylvinylether with triethoxysilane
2.4.10.1.
b
-Adduct [triethoxy(2-ethoxyethyl)silane]. 1H NMR (CDCl3)
d
(ppm): 0.75 (t, J ¼ 8 Hz, 2H, SieCH2), 0.85e0.99 (m, 12H, CH3),
2.4.4. Hydrosilylation of 4-methyl-styrene with triethoxysilane
3.09e3.29 (m, 4H, OeCH2), 3.59 (q, J ¼ 8 Hz, 6H, OeCH2). 13C NMR
2.4.4.1.
b
-Adduct [triethoxy(4-methylphenethyl)silane]. 1H NMR
(CDCl3)
(CDCl3)
d
d
(ppm): 65.78, 65.09, 57.84, 17.77, 14.74, 12.62. 29Si NMR
(400 MHz, CDCl3)
d
(ppm): 1.03 (t, J ¼ 8.5 Hz, 2H, SieCH2), 1.28 (t,
(ppm): ꢁ47.85. MS (EI) m/z (%): 236 (Mþ, 11), 237 (100).
J ¼ 7.0 Hz, 9H, CH3), 2.31 (s, 3H, CH3), 2.70 (t, J ¼ 8.6 Hz, 2H, CH2),
Anal. Calc. for [triethoxy(2-ethoxyethyl)silane] (C10H24O4Si): C,
50.81; H, 10.23; O, 27.07. Found: C, 50.82; H, 10.23; O, 27.08.
3.87 (q, J ¼ 7.0 Hz, 6H, OeCH2), 7.07e7.11 (m, 4H, Ph). 13C NMR
(101 MHz, CDCl3)
d (ppm): 141.66, 134.97, 129.02, 127.82, 58.80,
28.53, 20.96, 18.12, 12.08. 29Si NMR (CDCl3, 79 MHz)
2.4.11. Hydrosilylation of isobutylvinylether with triethoxysilane
d
(ppm): ꢁ45.96. MS (EI) m/z (%): 283 (Mþ,16), 282 (100). Anal. Calc.
2.4.11.1.
b-Adduct
[triethoxy(2-isobutoxyethyl)silane]. 1H
NMR
for [triethoxy(4-methylphenethyl)silane] (C15H26O3Si): C, 63.78; H,
9.28; O, 16.99. Found: C, 63.79; H, 9.27; O, 16.99.
(CDCl3)
d
(ppm): 0.66 (d, J ¼ 6.8 Hz, 6H, SieCH2), 0.79 (t, J ¼ 8 Hz,
2H, SieCH2), 0.97 (t, J ¼ 8 Hz, 9H, CH3), 1.59 (Septet, J ¼ 6.8 Hz, 1H,
CH), 2.90 (d, J ¼ 6.6 Hz, 2H, OeCH2), 3.27 (d, J ¼ 6.6 Hz, 2H, OeCH2),
2.4.5. Hydrosilylation of 4-methoxy-styrene with triethoxysilane
3.57 (q, J ¼ 8 Hz, 6H, OeCH2). 13C NMR (101 MHz, CDCl3)
d (ppm):
2.4.5.1.
b
-Adduct [triethoxy(4-methoxyphenethyl)silane]. 1H NMR
78.05, 66.22, 57.86, 28.22, 19.03, 17.84, 12.55. 29Si NMR (CDCl3,
(400 MHz, CDCl3)
d
(ppm): 1.02 (t, J ¼ 8.5 Hz, 2H, SieCH2), 1.24 (t,
79 MHz)
d
(ppm): ꢁ47.82. MS (EI) m/z (%): 265 (Mþ, 19), 264 (100).
J ¼ 7.0 Hz, 9H, CH3), 2.70 (t, J ¼ 7.1 Hz, 2H, CH2), 3.70 (s, 3H, OeCH3),
Anal. Calc. for [triethoxy(2-isobutoxyethyl)silane] (C12H28O4Si): C,
54.50; H, 10.67; O, 24.20. Found: C, 54.49; H, 10.66; O, 24.21.
3.79 (q, J ¼ 7.0 Hz, 6H, OeCH2), 6.95e7.26 (m, 4H, Ph). 13C NMR
(101 MHz, CDCl3)
d (ppm): 157.79, 136.57, 128.58, 113.65, 58.21,
54.84, 28.05, 18.23, 12.92. 29Si NMR (CDCl3)
d
(ppm): ꢁ46.29. MS
2.4.12. Hydrosilylation reaction of styrene with triethylsilane
(EI) m/z (%): 299 (Mþ, 22), 298 (100). Anal. Calc. for [triethoxy(4-
methoxyphenethyl)silane] (C15H26O4Si): C, 60.37; H, 8.78; O,
21.44. Found: C, 60.35; H, 8.78; O, 21.45.
2.4.12.1.
CDCl3)
CH3), 0.98 (t, J ¼ 8 Hz, 2H, SieCH2), 2.71 (t, J ¼ 8 Hz, 2H, CH2), 7.11e
7.27 (m, 5H, Ph). 13C NMR (CDCl3)
(ppm): 144.62, 128.30, 127.79,
b
-Adduct [triethyl(phenethyl)silane]. 1H NMR (400 MHz,
d
(ppm): 0.66 (q, J ¼ 8 Hz, 6H, SieCH2), 092 (t, J ¼ 8 Hz, 9H,
d
2.4.6. Hydrosilylation of 4-fluoro-styrene with triethoxysilane
125.61, 30.44, 13.99, 7.74, 3.66. 29Si NMR (CDCl3)
d
(ppm): ꢁ42.89.
2.4.6.1.
b
-Adduct [triethoxy(4-fluorophenethyl)silane]. 1H NMR
(ppm): 1.01 (t, J ¼ 8.5 Hz, 2H, SieCH2), 1.21 (t, J ¼ 7.0 Hz, 9H,
MS (EI) m/z (%): 265 (Mþ, 19), 264 (100). Anal. Calc. for [triethyl(-
phenethyl)silane] (C12H24Si): C, 76.28; H, 10.97. Found: C, 76.29; H,
10.66; O, 10.96.
(CDCl3)
d
CH3), 2.70 (t, J ¼ 7.1 Hz, 2H, CH2), 3.78 (q, J ¼ 7.0 Hz, 6H, OeCH2), 6.84e
7.24 (m, 4H, Ph). 13C NMR (CDCl3)
d
(ppm): 162.36 (s, 1JCeF ¼ 241 Hz,
4
3
para), 139.65 (d, JCeF ¼ 3.0 Hz, ipso), 129.04 (d, JCeF ¼ 6.0 Hz,
2.5. X-ray structure determinations of complexes 1 and 2
2
ortho), 114.72 (d, JCeF ¼ 21 Hz, meta), 58.29, 28.15, 18.17,12.76. 29Si
NMR (CDCl3)
d
(ppm): ꢁ46.55. MS(EI)m/z(%): 287(Mþ, 20), 286 (100).
Colorless single crystals of the compounds (dimensions: 1:
0.35 ꢀ 0.25 ꢀ 0.25 mm, 2: 0.31 ꢀ 0.35 ꢀ 0.23 mm) were produced
by slow evaporation of the solvents from solutions in hexane/
dichloromethane solvent mixtures at 25 ꢂC. Diffraction data were
Anal. Calc. for [triethoxy(4-fluorophenethyl)silane] (C14H23FO3Si): C,
58.71; H, 8.09; O, 16.76. Found: C, 58.83; H, 8.08; O, 16.77.
2.4.7. Hydrosilylation of 1-hexene with triethoxysilane
collected at room temperature by the 4-scan and
on Smart Apex Duo diffractometer with graphite-
monochromated Mo-Ka radiation (
were solved by direct methods (SHELXTL-PLUS) [21] and subse-
quent Fourier difference syntheses, and were then refined by full-
matrix least-squares on F2 (SHELXL-97) [22]. All non-hydrogen
atoms were refined anisotropically, while hydrogen atoms were
placed in geometrically idealized positions. Crystal data and details
of the structures have been given in Table 2.
u-scan technique
2.4.7.1.
b
-Adduct [triethoxy(hexyl)silane]. 1H NMR (CDCl3)
d
(ppm):
a
ꢀ
0.64 (t, J ¼ 6 Hz, 2H, SieCH2), 0.89 (t, J ¼ 8 Hz, 3H, CH3), 1.22e1.42
l
¼ 0.71073 A). The structures
(m, 17H, CH2CH3), 3.81 (q, J ¼ 8 Hz, 6H, OeCH2). 13C NMR (CDCl3)
d
(ppm): 58.13, 32.74, 31.41, 22.63, 22.45, 18.14, 13.91, 10.31. 29Si
NMR (CDCl3)
d
(ppm): ꢁ44.86. MS (EI) m/z (%): 249 (Mþ, 18), 248
(100). Anal. Calc. for [triethoxy(hexyl)silane] (C12H28O3Si): C, 58.01;
H, 11.36; O, 19.32. Found: C, 58.03; H, 11.35; O, 19.34.
2.4.8. Hydrosilylation of 1-octene with triethoxysilane
2.4.8.1.
b
-Adduct [triethoxy(octyl)silane]. 1H NMR (400 MHz, CDCl3)
3. Results and discussions
d
(ppm): 0.63 (t, J ¼ 6 Hz, 2H, SieCH2), 0.81 (t, J ¼ 6.5 Hz, 3H, CH3),
1.04e1.43 (m, 21H, CH2CH3), 3.77 (q, J ¼ 8 Hz, 6H, OeCH2). 13C NMR
The high melting point molten organic salts N-alkylpyridinium
hexafluorophosphates and N, N-dialkylimidazolium hexa-
fluorophosphates have been used as thermoregulated supports
[23e25]. The use of Rh(PPh3)3Cl/ionic liquid (molten salt) as
a thermoregulated and recyclable catalytic system for hydro-
silylation, was investigated. It was found that both conversion and
selectivity were likely to be influenced by the alkyl chains attached
to the pyridinium and imidazolium cations. And the use of organic
acids in hydrosilylation as promoters was also investigated [26].
And mono-carboxyl-functionalized imidazolium bromide salts, for
example 1a [27], 2a [28], and 3a [29], have been already reported.
(101 MHz, CDCl3)
d (ppm): 58.14, 33.09, 31.83, 29.34, 29.14, 22.62,
22.52, 18.15, 13.92, 10.31. 29Si NMR (CDCl3, 79 MHz)
d
(ppm): ꢁ44.81. MS (EI) m/z (%): 276 (Mþ, 16), 277 (100). Anal. Calc.
for [triethoxy(octyl)silane] (C14H32O3Si): C, 60.82; H, 11.67; O, 17.36.
Found: C, 60.81; H, 11.65; O, 17.37.
2.4.9. Hydrosilylation of 1-dodecene with triethoxysilane
2.4.9.1.
b
-Adduct [triethoxy(dodecyl)silane]. 1H NMR (CDCl3)
d
(ppm): 0.57 (t, J ¼ 6 Hz, 2H, SieCH2), 0.82 (t, J ¼ 6.7 Hz, 3H, CH3),
0.92e1.44 (m, 29H, CH2CH3), 3.76 (q, J ¼ 8 Hz, 6H, OeCH2). 13C NMR
(101 MHz, CDCl3)
d
(ppm): 58.13, 33.09, 31.86, 29.61, 29.60, 29.59,
In this paper,
a
series of mono-carboxyl-functionalized

34
C. Ma et al. / Journal of Organometallic Chemistry 727 (2013) 28e36
Table 2
Table 3
Crystal data, data collection, and structure refinement details.
Effect of carboxyalkyl-imidazolium salts on the hydrosilylation reaction.
Entry Catalyst Conv. Selectivity (%)
Unsaturated Ethylbenzene
1a
4a
b/a
Empirical formula
Formula weight
Crystal system
Space group
C6H9BrN2O2
221.06
Orthorhombic
Pca2(1)
C7H9BrN2O4
265.07
Monoclinic
P2(1)/n
b
a
1
2
3
4
5
6
7
8
Rh(PPh3)3Cl/BmimPF6 81.9 80.9 15.9 e
2.3
26.9
29.5
26.6
26.4
15.6
16.9
15.3
10.3
e
5.1
Rh(PPh3)3Cl/1a
Rh(PPh3)3Cl/2a
Rh(PPh3)3Cl/3a
Rh(PPh3)3Cl/4a
Rh(PPh3)3Cl/1b
Rh(PPh3)3Cl/2b
Rh(PPh3)3Cl/3b
Rh(PPh3)3Cl/4b
Rh(PPh3)3Cl/1c
Rh(PPh3)3Cl/2c
Rh(PPh3)3Cl/3c
Rh(PPh3)3Cl/1d
Rh(PPh3)3Cl/2d
Rh(PPh3)3Cl/3d
Rh(PPh3)3Cl/4d
51.8 70.0 3.1 e
54.4 67.8 2.7 e
50.9 61.5 1.9 e
55.6 70.8 2.8 e
83.4 81.5 2.9 e
86.7 81.1 2.0 e
80.9 83.2 1.4 e
87.0 87.7 2.0 e
94.8 96.6 3.5 e
95.1 97.6 2.4 e
93.1 99.0 1.0 e
62.9 37.9 46.5 e
68.3 37.1 44.0 e
61.4 44.0 38.3 e
78.9 38.0 45.7 e
94.7 97.7 2.3 e
94.8 97.5 2.5 e
94.7 97.8 2.2 e
94.6 97.7 2.3 e
94.1 97.8 2.2 e
22.6
25.1
32.4
25.3
28.1
40.6
59.4
43.9
27.6
40.7
99.0
Unit cell dimensions
ꢀ
a (A)
13.5224(15)
6.5096(8)
9.9467(12)
90
90
90
875.56(18)
4, 1.677 Mg/m3
4.650
10.3407(19)
9.2205(16)
10.7519(19)
90
108.641(2)
90
ꢀ
b (A)
ꢀ
c (A)
Alpha (ꢂ)
Beta (ꢂ)
9
Gamma (ꢂ)
10
11
12
13
14
15
16
3
ꢀ
Volume (A )
971.4(3)
e
Z, calculated density
4, 1.813 Mg/m3
4.223
e
Abs. coeff. (mmꢁ1
)
15.6
18.9
17.7
16.3
e
0.82
0.84
1.1
F(000)
440
528
Reflections collected/
unique
3201/1650 [R(int) ¼
5098/1715 [R(int) ¼
0.0207]
0.0206]
0.83
Goodness-of-fit on F2
1.019
1.245
17a Rh(PPh3)3Cl/2c
18b Rh(PPh3)3Cl/2c
19c Rh(PPh3)3Cl/2c
20d Rh(PPh3)3Cl/2c
21e Rh(PPh3)3Cl/2c
Final R indices [I > 2
s(I)]
R1 ¼ 0.0301,
wR2 ¼ 0.0871
R1 ¼ 0.0371,
wR2 ¼ 0.0911
R1 ¼ 0.0440,
wR2 ¼ 0.1526
R1 ¼ 0.0613,
wR2 ¼ 0.1876
e
e
R indices (all data)
e
e
Reaction conditions: styrene: 40 mmol, triethoxysilane: 44 mmol, Catalyst: 1%
Rh(PPh3)3Cl/support: 0.2 g, Rh(PPh3)3Cl 0.05 mol% based on styrene. 90 ꢂC, 5 h.
a
Second run.
Third run.
Fourth run.
Fifth run.
imidazolium salts and multi-carboxyl-functionalized imidazolium
salts are synthesized. Infrared spectroscopy proves to be instru-
mental for confirming the chemical modifications proposed. Two
bands present in the diffuse reflection infrared Fourier-transform
spectra of 2a at 1574.7 and 1167.6 cmꢁ1, are due to the presence
of imidazolium cation cycle coupling [30]. The band present in the
diffuse reflection infrared Fourier-transform spectra of 2a at
1404.5 cmꢁ1, depends on the presence of carboxyl group [31]. The
new band in the spectra of 2b at 835.3 cmꢁ1 is bound to the
presence of the hexafluorophosphate [32]. The new bands in the
spectra of 2d at 1255.9 and 1166.4 cmꢁ1 depend on the presence of
the trifluoromethanesulfonate [33]. And all of these carboxyl-
functionalized imidazolium salts were characterized by NMR
spectroscopy, and the structures of complexes 1a and 4a were also
determined by X-ray analysis (Figs. 1 and 2). All of the prepared
complexes showed a correlation between the 1H NMR and 13C NMR
spectroscopic data and the proposed structures. Elemental analysis
data and theoretical values for the complexes 1ae4d were also
b
c
d
e
Sixth run.
found to be in accordance. These results were obtained after the
synthesis of a series of carboxyl-functionalized imidazolium salts
(Fig. 3).
Hydrosilylation reaction of the styrene with triethoxysilane
performed by Wilkinson’s catalyst [Rh(PPh3)3Cl] in 1-butyl-3-
methylimidazolium hexafluorophosphate (BMimPF6), exhibited
some levels of catalytic activity and b-adduct selectivity. A series of
carboxyl-functionalized imidazolium salts were synthesized, and
hydrosilylation reactions were conducted in different carboxyl-
functionalized imidazolium salts in the presence of Rh (PPh3)3Cl
(Table 3). In comparison with BMimPF6, the hydrosilylation reac-
tions performed in carboxyl-functionalized imidazolium hexa-
fluorophosphate salts (1be4b), presented higher conversion of
styrene and higher b-adduct selectivity. Although the interaction
between the central rhodium metal and carboxyl-functionalized
imidazolium salts remained unclear, there lies a possibility of
strong interaction between the carboxyl-functionalized imidazo-
lium salts and the rhodium complex. Interaction between carboxyl-
functionalized imidazolium salts and the central metal rhodium
CF SO
CF SO
2d
2c
Si(OEt)3
-SIC+
R
im
im
R
[Rh]
[Rh]
Si(OEt)3
-SIC+
[Rh]
R
PF
-SIC+
R
HSi(OEt)3
R
2b
+
C
I
-SIC+
-
S
Si(OEt)3
R
R
+
[Rh]
C
[Rh]
2a
I
S
-
Si(OEt)3
H
Si(OEt)3
R
]
h
R
[
-SIC+
[Rh]
R
-SIC+
[Rh]
1800
1600
1400
1200
1000
800
Si(OEt)3
Si(OEt)3
-SIC+: Carboxyalkyl-imidazolium salts (1a-4d)
(
cm-1
)
Wave numbers
Fig. 3. IR spectra (750e1800 cmꢁ1) of 2a, 2b, 2c, 2d.
Scheme 3. The reaction mechanism.

C. Ma et al. / Journal of Organometallic Chemistry 727 (2013) 28e36
35
Table 4
Results of the hydrosilylation reaction of aliphatic alkylenes with triethoxysilane.
Entry
Alkene
Silane
Conv.
Selectivity (%)
b
a
Un
Alkane
1
2
3
4
5
6
7
8
2-Methyl-styrene
3-Methyl-styrene
4-Methyl-styrene
4-Methoxy-styrene
4-Fluoro-styrene
1-Hexene
1-Octene
1-Dodecene
Ethylvinylether
Isobutylvinylether
Styrene
Triethoxysilane
100
100
97.7
94.9
94.8
99.8
99.5
>99.9
>99.9
>99.9
>99.9
>99.9
85.3
2.3
5.1
5.2
0.2
0.5
e
e
e
e
e
e
e
e
e
e
e
e
e
88.0
98.8
98.7
96.0
99.9
71.5
99.9
93.7
96.9
e
e
e
e
e
e
e
e
9
10
11
e
e
e
e
Triethylsilane
2.6
12.1
Reaction conditions: alkene: 40 mmol, silane: 44 mmol, Catalyst: 1% Rh(PPh3)3Cl/2c, support 2c: 0.2 g, Rh(PPh3)3Cl 0.05 mol% based on alkene, 90 ꢂC, 5 h.
could weaken the complexation abilities of other ligands, such as
Clꢁ, etc., that could facilitate the activation of the alkene. At the
same time, the carboxyl-functionalized imidazolium salts could
stabilize the intermediate states, maximizing the activity of the
central metal Rh. The different substituents attached to the cation
reported different steric hindrances of the catalytic center. There-
Rh(PPh3)3Cl exhibited a pronounced solubility in 2c. Since they
are specially designed to be used in ionic liquid biphasic systems
they have been employed to combat catalyst problems. Rh(PPh3)3Cl
in 2c can be reused without noticeable loss of catalytic activity and
selectivity.
fore, the ratio of the
b-adduct/a-adduct selectivity (b/a) clearly
4. Conclusion
increase with increasing of the steric structure of substituents
attached to the cation of carboxyl-functionalized imidazolium. But
hydrosilylation reaction of the styrene with triethoxysilane per-
formed by Rh(PPh3)3Cl in 3b, exhibited lower catalytic activity. The
styrene conversion was found to be 80.9%.
Hydrosilylation reaction of the styrene with triethoxysilane
performed in 1ae4a in the presence of Rh(PPh3)3Cl showed lower
catalytic activity and b-adduct selectivity, respectively. It therefore
In summary, a series of carboxyl-functionalized imidazolium
salts were synthesized. In comparison with BMimPF6, when the
hydrosilylation reaction was performed in carboxyl-functionalized
imidazolium salts (1be4b, 1ce3c), higher conversion of styrene
and higher b-adduct selectivity were obtained. In particular, no by-
product (ethylbenzene) could be detected at all when Rh(PPh3)3Cl/
1ce3c, respectively, was used as catalyst. There is a possibility of
strong interaction between the carboxyl-functionalized imidazo-
lium salts and the rhodium complex. It could weaken the
complexation abilities of other ligands, such as Clꢁ, etc., then that
could help to activate the alkene. At the same time, the carboxyl-
functionalized imidazolium salts could stabilize the intermediate
states that help in maximizing the activity of the central metal Rh.
The different substituents attached to the cation resulted in
different steric hindrances of the catalytic center. Therefore, the
can be assumed that the counter ions had some impact on the
hydrosilylation reaction. The counter ion Brꢁ is more nucleophilic
than PF6ꢁ, and it was found to have reduced the solubility of silane
in the hydrophilic carboxyl-functionalized imidazolium salts 1ae
ꢁ
4a, respectively. The counter ion CF3SO3 is similar to the
counter ion Brꢁ. Results of hydrosilylation of the styrene with
triethoxysilane performed in 1de4d also revealed low catalytic
activity and
b-adduct selectivity respectively but it obtained the
higher -adduct selectivity, the b/a
a
was found to be close to 1. Both
ratio of the
b-adduct/a-adduct selectivity (b/a) clearly increase
the substituents attached to the imidazolium salt cations and the
counter ions showed important impact on the catalytic process.
A series of carboxyl-functionalized imidazolium inner salts were
synthesized. Hydrosilylation reactions were conducted in 1ce3c in
the presence Rh(PPh3)3Cl (Table 3). Both higher catalytic activity
with increasing of the steric structure of substituents attached to
the cation of carboxyl-functionalized imidazolium. Rh(PPh3)3Cl in
2c can be reused without noticeable loss of catalytic activity and
selectivity.
and selectivity for the b-adduct were obtained. In particular, no by-
Acknowledgments
product (ethylbenzene) could be detected at all when Rh(PPh3)3Cl/
1ce3c, respectively, was used as catalyst. On the basis of these data,
they proposed the following reaction mechanism [34] (Scheme 3).
A possible reaction between carboxyl-functionalized imidazolium
and the central metal Rh could weaken the complexing ability of
other ligands such as chloride, which would help to activate the
alkene, and carboxyl-functionalized imidazolium could stabilize
the intermediate states. It can also be speculated that steric
hindrance of carboxyl-functionalized imidazolium salts had some
effect on the reaction pathway and the selectivity for the formation
We are grateful to the Natural Science Foundation of China
(21203049), the Fund of Zhejiang Province (Y4100248), and the
Technologies R&D Program of Hangzhou city (20100331T16) for
financial support.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2012.12.016.
of the b-adduct was increased.
When other alkenes such as 1-hexene, 1-octene, 1-dodecene, 2-
methyl-styrene, 3-methyl-styrene, 4-methyl-styrene, 4-methoxy
styrene, 4-fluoro-styrene, ethylvinylether and isobutylvinylether,
were used as one of the substrates, high levels of conversion and
selectivity were obtained in the 2c with Rh(PPh3)3Cl as catalyst
(Table 4). Also, when triethylsilane replaced triethoxysilane as
hydrogen donor, unsaturated adduct triethyl (styryl) silane was
found.
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