Hydrosilylation reactions catalyzed by rhodium complexes with phosphine ligands functionalized with imidazolium salts

Article abstract of DOI:10.1016/j.jorganchem.2010.09.023

Hydrosilylation reactions of styrene with triethoxysilane catalyzed by rhodium complexes with phosphine ligands functionalized with imidazolium salts are reported. In comparison with Wilkinson's catalyst, Rh(PPh₃) ₃Cl, all of the present rhodium complexes with phosphines functionalized with imidazolium salts exhibit higher catalytic activity and selectivity.

Full text of DOI:10.1016/j.jorganchem.2010.09.023

Journal of Organometallic Chemistry 696 (2011) 263e268
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Journal of Organometallic Chemistry
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Hydrosilylation reactions catalyzed by rhodium complexes with phosphine
ligands functionalized with imidazolium salts
*
*
Jiayun Li, Jiajian Peng, Diliang Wang, Ying Bai, Jianxiong Jiang , Guoqiao Lai
Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, Hangzhou 310012, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 July 2010
Received in revised form
7 September 2010
Accepted 7 September 2010
Available online 17 September 2010
Hydrosilylation reactions of styrene with triethoxysilane catalyzed by rhodium complexes with phos-
phine ligands functionalized with imidazolium salts are reported. In comparison with Wilkinson’s
catalyst, Rh(PPh3)3Cl, all of the present rhodium complexes with phosphines functionalized with imi-
dazolium salts exhibit higher catalytic activity and selectivity.
Ó 2010 Elsevier B.V. All rights reserved.
Keywords:
Hydrosilylation
Catalyst
Phosphines functionalized with
imidazolium salts
Rhodium complexes
1. Introduction
advantages of an IL and convenient product separation. The substit-
uents attached to the cation of the molten salt were found to have an
Hydrosilylationprocesses, particularlyof carbonecarbon multiple
bonds, have beenextensivelyapplied inthe fields of organic synthesis
and material science in the last two decades [1e3]. Although a wide
range of catalysts has been tested for hydrosilylation, most research
and industrial syntheses have been carried out in the presence of
platinum complexes or rhodium complexes. Phosphine complexes of
rhodiumeffectivelycatalyzethehydrosilylationof1-alkenes[3e6]. In
this catalytic process, besides the Rh center used, the phosphine
ligands also play an important role in the hydrosilylation [7]. The
primary role of the phosphines is to support the metal in the form of
stable species that can subsequently enter the catalytic cycle and
thereby help prevent the formation of inactive metal aggregates. On
the other hand, room temperature ionic liquids (ILs), which are
entirely constituted of ions, have attracted great interest as novel and
environmentally friendly benign media and catalyst systems [8,9].
Moreover, the physical and chemical properties of dia-
lkylimidazolium salts can also be specifically altered by changing the
attached substituents and/or associated anions. There have been
a few examples of hydrosilylations with the use of ionic liquids
[10e13]. Recently, our group [7,14] has reported that Rh(PPh3)3Cl/IL
(molten salt) may be used in the hydrosilylation process as a ther-
moregulated and recyclable catalyst system that combines the
impact on the catalytic process [7,14]. On the other hand, our studies
have also revealed that phosphines with 2-imidazolium ligands
(Scheme 1) enhance the catalytic activity and selectivity of rhodium
complexes for hydrosilylation reactions [15]. Consequently, it was
speculatedthatphosphinesfunctionalizedwithionicliquidsmightbe
good candidates as ligands for rhodium-catalyzed hydrosilylation
reactions. For the present study, we have synthesized several phos-
phine ligands functionalized with imidazolium salts (Scheme 2), and
the application of these ligands in the rhodium-catalyzed hydro-
silylation of styrene with silanes has been investigated.
2. Experimental
2.1. General methods
Styrene was washed with 5% aqueous NaOH solution 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. All reactions were carried out under a dry argon atmosphere
using Schlenk glassware and vacuum-line techniques. Solvents for
synthesis were dried and degassed by standard methods before use.
Gas chromatography: trace DSQ GC column: DB-5
* Corresponding authors. Tel.: þ86 571 28865136; fax: þ86 571 28865135.
E-mail addresses: hsdyjg@163.com (J. Jiang), gqlai@hznu.edu.cn (G. Lai).
30 m ꢀ 2.5 mm ꢀ 0.25
m
m, split: 50:1, flow: 1 mL minꢁ1 constant
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.09.023

264
J. Li et al. / Journal of Organometallic Chemistry 696 (2011) 263e268
R1
removed under vacuum, and the solid was dissolved in dichloro-
methane (30 mL). This solution was washed with H2O (2 ꢀ 20 mL)
and dried over anhydrous magnesium sulfate. Removal of the
solvent under vacuum afforded a white solid. The prepared
compound showed spectroscopic data (1H NMR and 13C NMR) in
accordance with the assigned structure (8b).
N
-
PF6
Ph2P
N
R2
R1: CH3, C2H5, C4H9, C6H13, C8H17
R2: C2H5, C4H9, C6H13, C8H17
2.2.2. 1-(2-Chloroethyl)-3-methylimidazolium
hexafluorophosphate (1b)
1H NMR (DMSO-d6)
d
(ppm): 3.43 (m, 3H, CH3), 3.83 (t, J ¼ 8 Hz,
2H, CH2Cl), 4.57 (m, 2H, NCH2), 7.56 (brs, 1H, imidazol), 7.74 (brs,
1H, imidazol), 8.95 (s, 1H, imidazol). 13C NMR (DMSO-d6)
(ppm):
Scheme 1. 2-Imidazolium phosphines.
flow, inlet temperature: 260 ꢂC, column temperature: 50 ꢂC (hold
1 min) then 15 ꢂC minꢁ1 up to 260 ꢂC (hold 10 min).
d
36.9 (NCH3), 42.1(ClCH2), 49.5(NCH2), 122.7(imidazol), 123.2(imi-
dazol), 137.1 (imidazol). Anal. Calc. for 1b (C6H10ClF6N2P): C, 24.80;
H, 3.47; N, 9.64. Found: C, 24.75; H, 3.43; N, 9.61. Yield: 85%
1H, 13C and 31P NMR spectra were measured using a Bruker
AV400 spectrometer operating at 400.13 MHz, 100.62 MHz and
161.97 MHz, respectively. Chemical shifts for 1H and 13C spectra are
given in ppm relative to the residual proton signal of [d6] DMSO
2.2.3. 1-(2-Chloroethyl)-3-butylimidazolium hexafluoro-
phosphate (2b)
(1H:
d d
2.50; 13C: 39.5). 31P NMR chemical shifts are specified
1H NMR (DMSO-d6)
d
(ppm): 0.89 (t, J ¼ 8 Hz, 3H, CH3),1.31e1.89
relative to 85% H3PO4 as an external standard.
(m, 4H, CH2), 4.07 (t, J ¼ 8 Hz, 2H, CH2Cl), 4.37 (m, 2H, NCH2), 4.64
(m, 2H, NCH2), 7.74 (brs, 1H, imidazol), 7.81 (brs, 1H, imidazol), 9.17
2.2. Synthesis of imidazolium salts
(s, 1H, imidazol). 13C NMR (DMSO-d6)
d (ppm): 13.8(CH3), 19.3
(CH2), 33.1 (CH2), 41.9 (ClCH2), 49.2 (NCH2), 50.2 (NCH2), 122.1
(imidazol), 123.3 (imidazol), 136.8 (imidazol). Anal. Calc. for 2b
(C9H16ClF6N2P): C, 32.50; H, 4.85; N, 8.42. Found: C, 32.40; H, 4.84;
N, 8.41. Yield: 81%
2.2.1. General procedure for the synthesis of 1be8b
A solution of the appropriate N-substituted imidazole (0.05 mol)
in tetrahydrofuran (THF; 20 mL) was treated with a solution of an
equivalent amount of Br(CH2)nCl (0.05 mol) in THF (20 mL). The
mixture was stirred at 50 ꢂC for 12 h. During this time, a cream-
colored solid precipitated in the flask. The suspension was cooled to
room temperature, the supernatant was decanted off, and the solid
was washed with THF (2 ꢀ 15 mL). A white solid was obtained.
The white solid obtained (0.03 mol) was dissolved in H2O (30 mL)
and this solution was treated with a solution of NH4PF6 (0.033 mol)
in H2O (10 mL). The resulting mixture was stirred for 2 h at room
temperature. After decanting the supernatant, the oil salt was
diluted with dichloromethane (30 mL), and this solution was
washed with H2O (2 ꢀ 20 mL) and dried over anhydrous magnesium
sulfate. Removal of the solvent under vacuum afforded a white solid.
All of the prepared compounds showed spectroscopic data (1H NMR
and 13C NMR) in accordance with the proposed structures (1be7b).
The white solid (0.03 mol) obtained as described above was
dissolved in acetone (30 mL) and this solution was treated with
a solution of NaBF4 (0.033 mol) in acetone (10 mL). The resulting
mixture was stirred for 2 h at room temperature. The white
precipitate was then collected by filtration, the solvent was
2.2.4. 1-(2-Chloroethyl)-3-hexylimidazolium
hexafluorophosphate (3b)
1H NMR (DMSO-d6)
d
(ppm): 0.84 (t, J ¼ 8 Hz, 3H, CH3),
1.34e1.62 (m, 8H, CH2), 4.19 (t, J ¼ 8 Hz, 2H, CH2Cl), 4.23 (m, 2H,
NCH2), 4.85 (m, 2H, NCH2), 7.74 (brs, 1H, imidazol), 7.83 (brs, 1H,
imidazol), 9.23 (s, 1H, imidazol). 13C NMR (DMSO-d6)
d (ppm): 14.3
(CH3), 22.1(CH2), 29.7 (CH2), 30.4 (CH2), 31.2 (CH2), 42.1(ClCH2),
50.1 (NCH2), 50.4 (NCH2), 123.1 (imidazol), 124.1 (imidazol), 136.3
(imidazol). Anal. Calc. for 3b (C11H20ClF6N2P): C, 36.63; H, 5.59; N,
7.77. Found: C, 36.61; H, 5.59; N, 7.72. Yield: 83%.
2.2.5. 1-(2-Chloroethyl)-3-octylimidazolium hexafluoro-
phosphate (4b)
1H NMR (DMSO-d6)
d
(ppm): 0.82 (t, J ¼ 8 Hz, 3H, CH3),1.22e1.83
(m, 12H, CH2), 4.12 (m, 2H, NCH2), 4.21 (t, J ¼ 8 Hz, 2H, CH2Cl), 4.95
(m, 2H, NCH2), 7.67 (brs, 1H, imidazol), 7.91 (brs, 1H, imidazol), 8.97
(s,1H, imidazol).13C NMR (DMSO-d6)
d (ppm): 14.1(CH3), 22.8 (CH2),
25.9(CH2), 28.2 (CH2), 30.5 (CH2), 31.6(CH2), 31.7 (CH2), 42.1 (ClCH2),
50.3 (NCH2), 50.5 (NCH2), 122.2 (imidazol), 123.5 (imidazol), 137.1
(imidazol). Anal. Calc. for 4b (C13H24ClF6N2P): C, 40.16; H, 6.22; N,
7.21. Found: C, 40.11; H, 6.21; N, 7.19. Yield: 78%
X-
N
N
R1
(CH2)nPPh2
2.2.6. 1-(3-Chloropropyl)-3-octylimidazolium hexafluoro-
phosphate (5b)
1c: R1=CH3, n=2, X=PF6
−
1H NMR (DMSO-d6)
d
(ppm): 0.83 (t, J ¼ 8 Hz, 3H, CH3),1.21e1.83
(m, 12H, CH2), 2.63 (q, J ¼ 4 Hz, 2H, CH2), 3.84 (t, J ¼ 8 Hz, 2H,
−
2c: R1=C4H9, n=2, X=PF6
CH2Cl), 4.21e4.56 (m, 4H, NCH2), 7.56 (brs, 1H, imidazol), 7.81 (brs,
1H, imidazol), 9.19 (s, 1H, imidazol). 13C NMR (DMSO-d6)
d (ppm):
3c: R1=C6H13, n=2, X=PF6
4c: R1=C8H17, n=2, X=PF6
5c: R1=C8H17, n=3, X=PF6
6c: R1=C8H17, n=4, X=PF6
7c: R1=C8H17, n=5, X=PF6
−
14.1 (CH3), 22.7 (CH2), 25.7 (CH2), 28.1 (CH2), 30.4 (CH2), 31.4 (CH2),
31.6 (CH2), 34.0 (CH2), 41.9 (ClCH2), 49.8 (NCH2), 50.3 (NCH2), 122.1
(imidazol), 122.4 (imidazol), 136.8 (imidazol). Anal. Calc. for 5b
(C14H26ClF6N2P): C, 41.75; H, 6.51; N, 6.95. Found: C, 41.73; H, 6.48;
N, 6.95. Yield: 75%.
−
−
−
−
2.2.7. 1-(4-Chlorobutyl)-3-octylimidazolium hexafluoro-
phosphate (6b)
8c: R1=C8H17, n=2, X=BF4
−
1H NMR (DMSO-d6)
1.23e2.07 (m, 16H, CH2), 3.88 (t, J ¼ 8 Hz, 2H, CH2Cl), 4.23e4.26 (m,
d
(ppm): 0.79 (t, J ¼ 8 Hz, 3H, CH3),
Scheme 2. Phosphine ligands functionalized with ionic liquids.

J. Li et al. / Journal of Organometallic Chemistry 696 (2011) 263e268
265
4H, NCH2), 7.63 (brs, 1H, imidazol), 8.01 (brs, 1H, imidazol), 9.23 (s,
1H, imidazol). 13C NMR (DMSO-d6)
(ppm): 14.3 (CH3), 22.4 (CH2),
(JPeC ¼ 13 Hz, PPh), 137.1 (imidazol). 31P NMR (DMSO-d6)
d
(ppm):
d
ꢁ22.1, ꢁ143.1 (PFꢁ6 , JPF
¼
706.8 Hz). Anal. Calc. for 1c
25.8 (CH2), 26.1 (CH2), 28.3 (CH2), 30.2 (CH2), 30.9 (CH2), 31.5 (CH2),
31.9 (CH2), 43.9 (ClCH2), 49.9 (NCH2), 50.7 (NCH2), 122.3 (imidazol),
123.4 (imidazol), 136.8 (imidazol). Anal. Calc. for 6b
(C15H28ClF6N2P): C, 43.22; H, 6.77; N, 6.72. Found: C, 43.18; H, 6.74;
N, 6.71. Yield: 77%.
(C18H20F6N2P2): C, 49.10; H, 4.58; N, 6.36. Found: C, 49.05; H, 4.57;
N, 6.37. Yield: 92%.
2.3.3. 1-(2-Diphenylphosphinoethyl)-3-butylimidazolium
hexafluorophosphate (2c)
1H NMR (DMSO-d6)
d
(ppm): 0.87 (t, J ¼ 8 Hz, 3H, CH3), 2.54 (t,
2.2.8. 1-(5-Chloropentyl)-3-octylimidazolium hexafluoro-
phosphate (7b)
J ¼ 12 Hz, 2H, CH2P), 1.35e1.82 (m, 4H, CH2), 4.39 (m, 2H, NCH2), 4.61
(m, 2H, NCH2), 7.41e7.49 (m, 10H, Ph), 7.71 (brs, 1H, imidazol), 7.89
1H NMR (DMSO-d6)
d
(ppm): 0.81 (t, J ¼ 8 Hz, 3H, CH3),1.21e2.17
(brs,1H, imidazol), 9.34(s,1H, imidazol).13C NMR (DMSO-d6)
d (ppm):
(m, 18H, CH2), 3.81 (t, J ¼ 8 Hz, 2H, CH2Cl), 4.29e4.31 (m, 4H, NCH2),
13.7 (CH3), 19.1 (CH2), 28.7 (JPeC ¼ 8 Hz, PCH2), 33.4 (CH2), 47.5
(JPeC ¼ 20 Hz, NCH2), 50.8 (NCH2), 123.1 (imidazol), 123.3 (imidazol),
128.2 (JPeC ¼ 6 Hz, PPh), 130.2 (JPeC ¼ 7 Hz, PPh), 130.8 (PPh), 133.2
7.73 (brs, 1H, imidazol), 8.23 (brs, 1H, imidazol), 9.23 (s, 1H, imi-
dazol). 13C NMR (DMSO-d6)
d (ppm): 14.1 (CH3), 22.8 (CH2), 24.6
(CH2), 26.8 (CH2), 27.4 (CH2), 28.3 (CH2), 30.1 (CH2), 30.7 (CH2), 31.9
(CH2), 32.8 (CH2), 44.8 (ClCH2), 50.1 (NCH2), 50.5 (NCH2), 122.3
(imidazol), 123.4 (imidazol), 137.1 (imidazol). Anal. Calc. for 7b
(C16H30ClF6N2P): C, 44.60; H, 7.02; N, 6.50. Found: C, 44.63; H, 7.05;
N, 6.51. Yield: 73%.
(JPeC ¼ 13 Hz, PPh), 137.8 (imidazol). 31P NMR (DMSO-d6)
d (ppm):
ꢁ21.1, ꢁ143.1 (PF6ꢁ, JPF ¼ 706.8 Hz). Anal. Calc. for 2c (C21H26F6N2P2): C,
52.29; H, 5.43; N, 5.81. Found: C, 52.30; H, 5.44; N, 5.83. Yield: 81%.
2.3.4. 1-(2-Diphenylphosphinoethyl)-3-hexylimidazolium
hexafluorophosphate (3c)
2.2.9. 1-(2-Chloroethyl)-3-octylimidazolium tetrafluoroborate (8b)
1H NMR (DMSO-d6)
(m, 8H, CH2), 2.55 (t, J ¼ 12 Hz, 2H, CH2P), 4.21 (m, 2H, NCH2), 4.39
(m, 2H, NCH2), 7.36e7.49 (m, 10H, Ph), 7.84 (brs, 1H, imidazol), 7.91
(brs, 1H, imidazol), 9.37 (s, 1H, imidazol). 13C NMR (DMSO-d6)
(ppm): 14.2 (CH3), 22.5 (CH2), 28.7 (CH2), 29.6 (JPeC ¼ 8 Hz, PCH2),
30.2 (CH2), 31.6 (CH2), 48.7 (JPeC ¼ 20 Hz, NCH2), 50.7 (NCH2), 122.3
(imidazol), 122.8 (imidazol), 128.6(JPeC Hz, PPh), 130.3
d
(ppm): 0.83 (t, J ¼ 8 Hz, 3H, CH3),1.31e1.63
1H NMR (DMSO-d6)
d
(ppm): 0.81 (t, J ¼ 8 Hz, 3H, CH3),
1.32e1.89 (m, 12H, CH2), 4.17 (t, J ¼ 8 Hz, 2H, CH2Cl), 4.57 (m, 2H,
NCH2), 4.81 (m, 2H, NCH2), 7.61 (brs, 1H, imidazol), 7.87 (brs, 1H,
imidazol), 9.12 (s, 1H, imidazol). 13C NMR (DMSO-d6)
d
(ppm): 13.9
d
(CH3), 22.1 (CH2), 26.1 (CH2), 28.4 (CH2), 30.3 (CH2), 31.5 (CH2), 31.9
(CH2), 42.5 (ClCH2), 50.6 (NCH2), 50.9 (NCH2), 123.2 (imidazol),
124.4 (imidazol), 138.2 (imidazol). Anal. Calc. for 8b
(C13H24ClF4N2B): C, 47.32; H, 7.32; N, 8.47. Found: C, 47.31; H, 7.31;
N, 8.45. Yield: 71%.
¼
6
(JPeC ¼ 9 Hz, PPh), 130.8(PPh), 133.0(JPeC ¼ 14 Hz, PPh), 136.3
(imidazol). 31P NMR (DMSO-d6)
d
(ppm): ꢁ20.6, ꢁ143.1 (PF-6,
JPF ¼ 706.8 Hz). Anal. Calc. for 3c (C23H30F6N2P2): C, 54.12; H, 5.92;
N, 5.49. Found: C, 54.09; H, 5.94; N, 5.47. Yield: 87%.
2.3. Synthesis of phosphines functionalized with imidazolium salts
(Scheme 3)
2.3.5. 1-(2-Diphenylphosphinoethyl)-3-octylimidazolium
hexafluorophosphate (4c)
1H NMR (DMSO-d6)
(m, 12H, CH2), 2.56 (t, J ¼ 12 Hz, 2H, CH2P), 4.25 (m, 2H, NCH2), 4.85
(m, 2H, NCH2), 7.33e7.51 (m, 10H, Ph), 7.74 (brs, 1H, imidazol), 8.01
(brs, 1H, imidazol), 9.37 (s, 1H, imidazol). 13C NMR (DMSO-d6)
d
(ppm): 0.85 (t, J ¼ 8 Hz, 3H, CH3), 1.19e1.73
2.3.1. General procedure for the synthesis of 1ce8c
The ligands (1ce8c) employed in this study were prepared as
shown in Scheme 3. A solution of LiPPh2, freshly prepared from Li
(0.8 g, 0.11 mol) and PPh3 (13.1 g, 0.05 mol), in THF (50 mL), was
added to a solution of the imidazolium salt (1be8b) (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 was
washed with toluene (2 ꢀ 15 mL) and dried in vacuo.
d
(ppm): 14.2 (CH3), 22.4 (CH2), 26.2 (CH2), 28.1 (CH2), 29.2
(JPeC ¼ 8 Hz, PCH2), 30.5 (CH2), 31.4 (CH2), 31.7 (CH2), 49.7
(JPeC ¼ 20 Hz, NCH2), 51.2 (NCH2),122.3 (imidazol),123.2 (imidazol),
128.9 (JPeC ¼ 7 Hz, PPh), 130.3 (JPeC ¼ 9 Hz, PPh), 131.0 (PPh), 132.8
(JPeC ¼ 12 Hz, PPh), 136.6 (imidazol). 31P NMR (DMSO-d6)
d (ppm):
ꢁ20.1, ꢁ143.1 (PF6- , JPF ¼ 706.8 Hz). Anal. Calc. for 4c (C25H34F6N2P2):
2.3.2. 1-(2-Diphenylphosphinoethyl)-3-methylimidazolium
C, 55.76; H, 6.36; N, 5.20. Found: C, 55.71; H, 6.37; N, 5.23. Yield: 83%.
hexafluorophosphate (1c)
1H NMR (DMSO-d6)
d
(ppm): 2.48 (t, J ¼ 12 Hz, 2H, CH2P), 3.82
2.3.6. 1-(3-Diphenylphosphinopropyl)-3-octylimidazolium
(m, 3H, CH3), 4.72 (m, 2H, NCH2), 7.46e7.57 (m, 10H, Ph), 7.70 (brs,
1H, imidazol), 7.85 (brs, 1H, imidazol), 9.28 (s, 1H, imidazol). 13C
hexafluorophosphate (5c)
1H NMR (DMSO-d6)
1.21e2.61 (m, 14H, CH2), 2.87 (t, J ¼ 12 Hz, 2H, CH2P), 4.76 (m, 2H,
NCH2), 4.84 (m, 2H, NCH2), 7.31e7.48 (m, 10H, Ph), 7.74 (brs, 1H,
imidazol), 7.97 (brs, 1H, imidazol), 9.51 (s, 1H, imidazol). 13C NMR
d
(ppm): 0.79 (t, J ¼ 8 Hz, 3H, CH3),
NMR (DMSO-d6)
d
(ppm): 27.6(JPeC ¼ 8 Hz, PCH2), 36.9 (NCH3), 46.5
(JPeC ¼ 20 Hz, NCH2), 122.7 (imidazol), 123.2 (imidazol), 127.5
(JPeC ¼ 6 Hz, PPh), 128.4 (JPeC ¼ 7 Hz, PPh), 129.5 (PPh), 132.3
(DMSO-d6)
d
(ppm): 14.4 (CH3), 22.8 (CH2), 24.4 (JPeC ¼ 10 Hz,
Br-
PCH2CH2), 25.9 (CH2), 27.3 (JPeC ¼ 18 Hz, PCH2CH2), 28.3 (CH2), 30.1
(CH2), 31.6 (CH2), 34.3 (CH2), 50.6 (JPeC ¼ 19 Hz, NCH2), 51.3 (NCH2),
122.1 (imidazol), 123.4 (imidazol), 128.8 (JPeC ¼ 7 Hz, PPh), 130.8
(JPeC ¼ 9 Hz, PPh), 132.0 (PPh), 132.9 (JPeC ¼ 12 Hz, PPh), 137.6
+ Br(CH2)nCl
N
N
N
N
(CH2)nCl
R1
R1
R1
a
X-
NH4PF6
Br-
N
N
(imidazol). 31P NMR (DMSO-d6)
d
(ppm): ꢁ17.1, ꢁ143.1 (PFꢁ6 ,
N
N
(CH2)nCl
-
X-: PF6-; BF4
or NaBF4
(CH2)nCl
(CH2)nCl
R1
b
JPF ¼ 706.8 Hz). Anal. Calc. for 5c (C26H36F6N2P2): C, 56.52; H, 6.57;
N, 5.07. Found: C, 56.55; H, 6.57; N, 5.06. Yield: 81%.
X-
N
X-
LiPPh2
Ar
N
N
N
X-: PF6-; BF4
-
2.3.7. 1-(4-Diphenylphosphinobutyl)-3-octylimidazolium
(CH2)nPPh2
R1
R1
hexafluorophosphate (6c)
c
1H NMR (DMSO-d6)
d
(ppm): 0.79 (t, J ¼ 8 Hz, 3H, CH3),
Scheme 3. Preparation of phosphine ligands functionalized with imidazolium salts.
1.21e2.09 (m, 16H, CH2), 2.95 (t, J ¼ 12 Hz, 2H, CH2P), 4.44e4.61 (m,

266
J. Li et al. / Journal of Organometallic Chemistry 696 (2011) 263e268
4H, NCH2), 7.33e7.47 (m,10H, Ph), 7.83 (brs,1H, imidazol), 7.94 (brs,
1H, imidazol), 9.09 (s, 1H, imidazol). 13C NMR (DMSO-d6)
(ppm):
d
14.3 (CH3), 22.4 (CH2), 25.1 (JPeC ¼ 10 Hz, PCH2CH2CH2), 25.9 (CH2),
28.1 (CH2), 28.3 (JPeC ¼ 12 Hz, PCH2CH2CH2), 30.5 (CH2), 31.7 (CH2),
32.5 (JPeC ¼ 12 Hz, PCH2CH2CH2), 34.1 (CH2), 51.1 (NCH2), 52.5
(NCH2), 122.6 (imidazol), 123.3 (imidazol), 128.9 (JPeC ¼ 7 Hz, PPh),
130.2 (JPeC ¼ 9 Hz, PPh), 131.8 (PPh), 132.3 (JPeC ¼ 12 Hz, PPh), 137.3
N
N
(2)
N
N
Br-
Br-
(imidazol). 31P NMR (DMSO-d6)
d
(ppm): ꢁ15.2, ꢁ143.1 (PFꢁ6 ,
JPF ¼ 706.8 Hz). Anal. Calc. for 6c (C27H38F6N2P2): C, 57.24; H, 6.76;
N, 4.94. Found: C, 57.26; H, 6.74; N, 4.99. Yield: 86%.
PPh2
Br
2.3.8. 1-(5-Diphenylphosphinopentyl)-3-octylimidazolium
(1)
hexafluorophosphate (7c)
1H NMR (DMSO-d6)
d
(ppm): 0.77 (t, J ¼ 8 Hz, 3H, CH3),1.21e2.19
(m, 18H, CH2), 2.97 (t, J ¼ 12 Hz, 2H, CH2P), 4.23e4.35 (m, 4H,
NCH2), 7.26e7.45 (m, 10H, Ph), 7.56 (brs, 1H, imidazol), 7.61 (brs, 1H,
imidazol), 8.87 (s, 1H, imidazol). 13C NMR (DMSO-d6)
d (ppm): 14.1
N
N
N
N
(3)
(4)
(CH3), 22.5 (CH2), 25.7 (CH2), 27.3 (JPeC ¼ 10 Hz, PCH2CH2CH2), 28.1
(CH2), 28.3 (JPeC ¼ 12 Hz, PCH2CH2CH2), 28.5 (JPeC ¼ 12 Hz,
PCH2CH2CH2), 30.5 (CH2), 31.1 (CH2), 31.9 (CH2), 34.3 (CH2), 50.9
(NCH2), 51.5 (NCH2), 122.6 (imidazol), 123.6 (imidazol), 128.8
(JPeC ¼ 7 Hz, PPh), 130.2 (JPeC ¼ 9 Hz, PPh), 131.9 (PPh), 132.5
X-
Br-
N
N
PPh2
PPh2
(JPeC ¼ 12 Hz, PPh), 137.3 (imidazol). 31P NMR (DMSO-d6)
d (ppm):
(5)
O
ꢁ13.8, ꢁ143.1 (PFꢁ6 , JPF
¼
706.8 Hz). Anal. Calc. for 7c
(C28H40F6N2P2): C, 57.93; H, 6.94; N, 4.83. Found: C, 57.91; H, 6.92;
N, 4.84. Yield: 82%.
2.3.9. 1-(2-Diphenylphosphinoethyl)-3-octylimidazolium
tetrafluoroborate (8c)
1H NMR (DMSO-d6)
(m, 12H, CH2), 2.69 (t, J ¼ 12 Hz, 2H, CH2P), 4.21 (m, 2H, NCH2), 4.83
(m, 2H, NCH2), 7.35e7.48 (m, 10H, Ph), 7.84 (brs, 1H, imidazol), 8.11
(brs, 1H, imidazol), 9.57 (s, 1H, imidazol). 13C NMR (DMSO-d6)
d
(ppm): 0.79 (t, J ¼ 8 Hz, 3H, CH3),1.21e1.89
N
(6)
N
N
(7)
Br-
Br-
Br-
N
N
N
d
(ppm): 14.3 (CH3), 22.1 (CH2), 26.5 (CH2), 28.7 (CH2), 28.9
(JPeC ¼ 8 Hz, PCH2), 30.1 (CH2), 31.6 (CH2), 31.9 (CH2), 50.1
(JPeC ¼ 20 Hz, NCH2), 51.7 (NCH2), 123.3 (imidazol), 123.8 (imida-
zol), 129.9 (JPeC ¼ 7 Hz, PPh), 130.9 (JPeC ¼ 9 Hz, PPh), 131.5 (PPh),
132.9 (JPeC ¼ 12 Hz, PPh), 138.6 (imidazol). 31P NMR (DMSO-d6)
PPh2
OH
Br
Scheme 4. Synthesis of phosphines functionalized with imidazolium salts. Reagents and
condition: (1) 1,2-dibromoethane (4.4 equiv.), THF, r.t., 2 d(23 %); (2) HPPh2 (1.1 equiv.),
tBuOK (1.05 equiv.), DMSO, r.t.,1 h (91 %); (3)Ph2P(=O)(CH2)2Br,150e160 ꢂC, 4e5 d (83 %);
(4) HSiCl3, chlorobenzene,120 ꢂC, 3 h(75 %); (5) 1-bromoethanol, toluene,120 ꢂC,18 h (91
%); (6)PBr3, CH2Cl2, 0 ꢂC,15 h (78%); (7) HPPh2 (1.1 equiv.), tBuOK(1.05 equiv.), DMSO, r.t.,1
h (95%).
d
(ppm): ꢁ21.8. Anal. Calc. for 8c (C25H34F4N2PB): C, 62.51; H, 7.13;
N, 5.83. Found: C, 62.49; H, 7.11; N, 5.80. Yield: 77%.
All of the prepared compounds showed spectroscopic data (1H,
13C and 31P NMR) in accordance with the proposed structures.
on quaternization of N-mesitylimidazole with 1-bromoethanol to
give 1-hydroxyethylene-3-mesitylimidazolium bromide (Scheme 4).
Our synthetic method is based on the quaternization of N-alkylimi-
dazoles with Br(CH2)nCl (n ¼ 2 or 3) to give 1-(n-chloroalkyl)-3-alkyl-
2.4. Hydrosilylation of alkenes with triethoxysilane
Typical hydrosilylation reaction procedures were as follows: The
requisite amounts of RhCl3 catalyst, the phosphine functionalized
with an ionic liquid, and the ionic liquid were added to a 10 mL
round-bottomed flask equipped with a magnetic stirrer, and the
mixture was stirred at 90 ꢂC for 30 min. The mixture was then
cooled to room temperature, whereupon the alkene and silane
were added. The resulting mixture was stirred for 5 h at the
appropriate temperature. At the end of the reaction, the product
phase was separated by decantation and the conversion of alkene
and the selectivity were determined by GC. The catalytic phase was
recharged with fresh alkene and silane for the next catalysis run.
719
1434
3. Results and discussion
1172
1584
1600
840
Nolan et al. [16] described the first synthetic method for the
phosphineeimidazolium cation 1-(2-diphenylphosphinoethyl)-3-
mesityl-imidazolium, which was obtained in only 21% overall yield.
The second method, described by Tsoureas et al. [17], involved
a phosphine oxide intermediate that had to be reduced under harsh
conditions. A synthetic method reported by Poli et al. [18] was based
1400
1200
1000
800
Wave numbers(cm-1)
Fig. 1. IR spectra (680e1700 cmꢁ1) of 1b and 1c.

J. Li et al. / Journal of Organometallic Chemistry 696 (2011) 263e268
267
increasing length of the alkyl chain attached to the imidazolium
cation, higher catalytic activities of the complex of RhCl3-phos-
phines functionalized with imidazolium salt were achieved, while
- adduct
- adduct
RCH2CH2Si(OEt)3
the
b
/
a
ratio increased (Table 1, entries 2e3, 5e6). However, the
ratio of the RhCl3-phosphines
catalytic activities and the
b/a
RCHSi(OEt)3
CH3
functionalized with imidazolium salts/BMimPF6 catalyst systems
decreased with increasing length of the alkyl chain between the
imidazolium ring and the diphenylphosphine group (Table 1,
entries 6e9). Phosphines bearing imidazolium moieties may
function as ambivalent P, C-donor systems, with the electron-rich
imidazolium moiety providing a suitable modification that stabi-
lizes the Rh-phosphine, which may be due to formation of Rh-N-
heterocyclic carbine (NHC) complex during the catalytic process
[19,20]. Although the rhodium complexe employing phosphines
with 2-imidazolium as ligands (d) resulted in the higher chemo-
+
(EtO)3SiH
R
R
R= Ph, n-C4H9, n-C5H11, n-C6H13, n-C9H19
Scheme 5. Hydrosilylation of olefins with triethoxysilane.
selectivity for the b-adduct than that of present catalyst system
(RhCl3-2c), the conversion was excellent in the presence of the
simple catalyst system derived from RhCl3 and phosphine ligands
functionalized with imidazolium salts (2c). Based on the screening
of phosphine ligands, it was concluded that the best catalytic
imidazolium salts, followed by nucleophilic substitution with LiPPh2
to produce the desired ligands. A series of phosphine ligands func-
tionalized with imidazolium salts (1ce8c) was synthesized and
characterized [16e18]. Infrared spectroscopy is a useful tool for con-
firming the proposed chemical modifications. A band appearing in
the diffuse reflection infrared Fourier-transform spectra of 1b and 1c
at 1584 cmꢁ1 can be assigned to ring-stretching of the imidazolium
cation (Fig. 1). Two bands appearing in the diffuse reflection infrared
Fourier-transform spectrum of 1c at 1434 and 719 cmꢁ1 may be
assigned to PePh and Ph stretching modes, respectively (Fig.1). All of
activity and selectivity in favor of the
b-adduct were obtained
when 1-(2-diphenylphosphinoethyl)-3-octylimidazolium hexa-
fluorophosphate (4c) was used as the ligand.
It is well known that the nature of the anion has a strong impact
on the physicochemical properties of imidazolium based ionic
liquid, which could result in pronounced effect between the
rhodium complexes and the reactants. In this case, it was observed
that nucleophilic BFꢁ4 anion could reduce the solubility of the silane
in the hydrophilic ionic liquid BMimBF4. Therefore, low catalytic
activity was observed when the hydrosilylation reaction of styrene
with triethoxysilane was conducted in BMimBF4 in the presence 8c,
and the conversion of styrene was just 64.2%. And this phenom-
enon is consistent with the former report [15].
When other alkenes, such as 1-hexene, 1-octene, or 4-chlor-
ostyrene, were used in place of styrene as the substrate, excellent
conversions and selectivities were obtained with the RhCl3-4c/
BMimPF6 catalyst system (Table 1, entries 11e13).
Catalyst systems of RhCl3 with phosphineeimidazolium salts
(1ce7c) as ligands show a pronounced solubility in BMimPF6. For
ease of reuse of the catalysts, they were specially designed to be
used in ionic liquid biphasic systems. It was verified that RhCl3 with
the prepared compounds showed spectroscopic data (1H, 13C and 31
P
NMR)in accordance with the proposed structures. Elemental analysis
data and theoretical values for the 1-(n-chloroalkyl)-3-alkylimida-
zolium hexafluorophosphates (1be8b) and phosphineeimidazolium
salts (1ce8c) were in close agreement (Scheme 5).
By using these phosphine ligands functionalized with imida-
zolium salts, rhodium-catalyzed hydrosilylations of styrene with
silanes in ionic liquids were tested. The results listed in Table 1
indicate that Wilkinson’s catalyst RhCl(PPh3)3 in BMimPF6
(1-methyl-3-butylimidazolium hexafluorophosphate) displayed
low catalytic activity and selectivity (Table 1, entry 1). When RhCl3
was mixed with the synthesized phosphine ligands functionalized
with imidazolium salts (1ce7c) in BMimPF6, higher catalytic
activity and selectivity in favor of the b-adduct were seen. With
Table 1
Hydrosilylation reactions of styrene with triethoxysilane.
Entry
Catalyst (% substrate mol)
Ligand
Substrate
Conversion %
Selectivity %
b/a
b
a
Ethylbenzene
1
2
Rh(PPh3)3Cl 0.1
RhCl3 0.02
RhCl3 0.02
d
e
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
4-Chloro-styrene
1-Hexene
1-Octene
Styrene
81.9
96.2
97.5
95.7
98.8
99.9
98.1
95.3
94.2
64.2
100
100
100
98.9
97.6
95.4
80.9
84.7
91.1
96.6
92.2
94.3
90.6
82.7
78.0
93.9
95.6
97.5
97.4
94.1
94.2
94.0
15.9
13.2
6.8
1.9
5.7
3.5
2.5
2.1
2.1
3.6
2.8
e
3.2
2.1
2.1
1.5
2.1
2.2
6.9
15.2
19.9
2.5
1.6
2.5
2.6
2.4
2.3
2.6
5.1
6.4
1c
2c
3
13.4
50.8
16.2
26.9
36.2
39.4
37.1
26.1
34.1
e
4a
5
RhCl3 0.02
RhCl3 0.02
RhCl3 0.02
RhCl3 0.02
RhCl3 0.02
RhCl3 0.02
RhCl3 0.02
RhCl3 0.01
RhCl3 0.01
RhCl3 0.02
RhCl3 0.02
RhCl3 0.02
3c
4c
5c
6c
7c
8c
4c
4c
4c
4c
4c
4c
6
7
8
9
10
11
12
13
14b
15c
16d
e
e
3.5
3.5
3.4
26.9
26.9
27.6
Styrene
Styrene
Reaction conditions: styrene 2.5 mmol; triethoxysilane 3.0 mmol; 90 ꢂC, 2 h; ligand/RhCl3: 1:5; BMimPF6: 0.5 mL.
a
70 ꢂC, 5 h; Catalyst d: Tri[1-ethyl-2-diphenylphosphino-3-butylimidazolium hexafluorophosphate] rhodium chloride [13].
Second run.
Third run.
b
c
d
Fourth run.

268
J. Li et al. / Journal of Organometallic Chemistry 696 (2011) 263e268
4c as ligand in BMimPF6 could be reused without significant loss of
catalytic activity or selectivity (Table 1, entries 14e16).
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We are grateful to the Fund of Zhejiang province (Y4100248)
and Technologies R&D Program of Hangzhou city (20100331T16)
for financial support.