Phosphines with 2-imidazolium ligands enhance the catalytic activity and selectivity of rhodium complexes for hydrosilylation reactions

Article abstract of DOI:10.1016/j.jorganchem.2009.10.029

Phosphines with 2-imidazolium ligands can specifically vary their physical and chemical properties by altering the attached substituents. Rhodium complexes (1b-7b) exhibited excellent catalytic activity and selectivity for hydrosilylation of olefins. The selectivity of the β-adduct clearly increased when the length of the alkyl chain bound to the imidazolium cation increased. Rhodium complex 1b in BMimPF₆ can be reused without noticeable loss of catalytic activity and selectivity.

Full text of DOI:10.1016/j.jorganchem.2009.10.029

Journal of Organometallic Chemistry 695 (2010) 431–436
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Phosphines with 2-imidazolium ligands enhance the catalytic activity
and selectivity of rhodium complexes for hydrosilylation reactions
Jiayun Li , Jiajian Peng , Ying Bai , Guodong Zhang , Guoqiao Lai b,*, Xiaonian Li
a,b
b
b
b
a,*
a
Resources and Environment Catalysis Institute of Zhejiang University of Technology, State Key Laboratory Breeding Base of Green Chemistry Synthesis Technology,
Hangzhou 310032, People’s Republic of China
Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, Hangzhou 310012, People’s Republic of China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 31 August 2009
Received in revised form 19 October 2009
Accepted 23 October 2009
Available online 27 October 2009
Phosphines with 2-imidazolium ligands can specifically vary their physical and chemical properties by
altering the attached substituents. Rhodium complexes (1b–7b) exhibited excellent catalytic activity
and selectivity for hydrosilylation of olefins. The selectivity of the b-adduct clearly increased when the
length of the alkyl chain bound to the imidazolium cation increased. Rhodium complex 1b in BMimPF
6
can be reused without noticeable loss of catalytic activity and selectivity.
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
Rhodium complex
Hydrosilylation
2
-Imidazolium phosphine ligand
1
. Introduction
the hydrosilylation of olefins with triethoxysilane (Scheme 1).
Phosphines with 2-imidazolium ligands can specifically vary their
physical and chemical properties by altering the attached substit-
uents of the imidazolium cation and it is therefore expected that
different reaction performances will be exhibited by using this
kind of novel catalyst (see Schemes 2 and 3).
Hydrosilylation is one of the most important Si–C bond forma-
tion reactions within organosilicon chemistry. Many organosilicon
monomers containing functional groups have been synthesized via
this reaction [1]. Transition metal complexes, such as tertiary
phosphine complexes of rhodium, palladium, platinum and nickel
have been applied as homogeneous catalysts for hydrosilylation
reactions due to the stereo-, regio- and/or enantioselectivity of this
reaction [2,3]. In view of homogeneously catalytic processes, apart
from the metal center used, these ligands also play an important
role in the reaction. Phosphines bearing 2-imidazolyl moieties
are interesting ligands and may function as ambivalent P, N-donor
systems which are capable of binding both soft and hard transition
metals [4–8].
Dialkylimidazolium salts can also specifically alter their physi-
cal and chemical properties by changing the attached substituents
and associated anions [9,10]. It is therefore to be expected that
phosphines bearing 2-imidazolium ligands should exhibit different
effects on reaction processes. Furthermore, because of the hetero-
cyclic groups, these ligands are expected to enhance the solubility
of metal complexes in ionic liquids.
2
. Experimental
2.1. General methods
Styrene was washed with 5% NaOH and dried with Na
2 4
SO .
After filtration the styrene was distilled under reduced pressure.
All other substances were purchased from Aldrich and were
used as received.
R
1
R
2
imPF
: C
, R : C
6
(R
1
: CH
: C
3
, R
2
: C
2
H
5
; R
1
: CH
: C
3
, R
2
: C
4
H
9
; R
1
: CH
: C
3
, R
2
:
;
C
R
6
H11; R
1
2
5
H , R
2
4
9
H ; R
1
: C
4
9
H , R
2
4 9
H ; R
1
: C
4
H
9
, R
2
H
6 11
1
: C
4
H
9
2
8
H
17) and 1-methyl-3-butylimidazolium tetrafluoro-
4
borate (BMimBF ) were, respectively, prepared according to litera-
ture procedures [11].
Gas chromatography: Trace DSQ GC Column = DB-5
The synthesis of a series of 2-imidazolium phosphines and their
application in hydrosilylation is reported here. The activity and
selectivity influenced by rhodium complexes employing 2-imi-
dazolium phosphines as ligands in ionic liquid are investigated in
À1
3
0 m  2.5 mm  0.25
l
m, split = 50:1, flow = 1 mL min
con-
stant flow, inlet temperature = 260 °C, column temperature = 50 °C
hold 1 min) then 15 °C min up to 260 °C (hold 10 min).
À1
(
1
13
31
H, C and P NMR spectra were measured using a Bruker
AV400 MHz spectrometer operating at 400.13, 100.62 and
1
1
61.97 MHz, respectively. Chemical shifts for H and 13C spectra
*
Corresponding authors. Fax: +86 571 28865135 (G. Lai).
E-mail addresses: gqlai@hznu.edu.cn (G. Lai), xnli@zjut.edu.cn (X. Li).
1
were recorded in ppm relative to residual proton of CDCl
3
( H: d
0
022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.10.029

4
32
J. Li et al. / Journal of Organometallic Chemistry 695 (2010) 431–436
CH
4
8
3
), 1.38 (m, 2H, CH
.18 (m, 2H, CH ), 7.38–7.57 (m, 10H, Ph), 7.74 (brs, 1H, imidazol),
.57 (brs, 1H, imidazol). C NMR (DMSO-d
2 2 3
), 1.63 (m, 2H, CH ), 3.56 (m, 3H, CH ),
RCH
2
CH
2
Si(OEt)
3
β- adduct
α- adduct
2
1
3
6
) d (ppm): 13.6, 19.1,
RCHSi(OEt)3
CH
32.4, 37.8 (J = 7 Hz), 50.0 (J = 11 Hz), 126.0, 128.2, 128.5 (J = 6 Hz),
130.2 (J = 9 Hz), 130.8, 133.1 (J = 14 Hz), 142.3 (J = 50 Hz).
NMR (DMSO-d
31
P
3
+
3
(EtO) SiH
R
À
6
) d (ppm): À25.5, À143.1 (PF , JPF = 705.2 Hz).
6
R
Anal. Calc. for 2a: C, 51.29; H, 5.16; N, 5.98. Found: C, 51.13; H,
5
.17; N, 5.97%.
-Methyl-2-diphenylphosphino-3-hexylimidazolium hexafluoro-
RCH=CHSi(OEt)3
unsaturated- adduct
1
1
phosphate (3a): H NMR (DMSO-d
CH
CH
6
) d (ppm): 0.86 (t, J = 8 Hz, 3H,
), 3.58 (m, 3H, CH ), 4.18 (m, 2H,
), 7.38–7.58 (m, 10H, Ph), 7.74 (brs, 1H, imidazol), 8.60 (brs,
R= Ph, n-C
4
H
9
, n-C
5
H11, n-C
6
H
13, n-C
9
H
19
3
), 1.36–1.60 (m, 8H, CH
2
3
2
Scheme 1. Hydrosilylation of olefins with triethoxysilane.
13
1
H, imidazol). C NMR (DMSO-d
6
) d (ppm): 14.1, 22.3, 29.8,
3
0.4, 31.0, 37.8 (J = 7 Hz), 50.2 (J = 11 Hz), 126.0, 128.3, 128.6
(
J = 6 Hz), 130.3 (J = 9 Hz), 130.8, 133.0 (J = 14 Hz), 142.3
3
1
À
R1
(J = 50 Hz). P NMR (DMSO-d
PF = 706.8 Hz). Anal. Calc. for 3a: C, 53.23; H, 5.69; N, 5.64. Found:
C, 53.02; H, 5.71; N, 5.65%.
-Ethyl-2-diphenylphosphino-3-butylimidazolium
6
) d (ppm): À30.0, À143.1 (PF
6
,
R1
R1
X-
a
X-
X-
J
nBuLi
N
N
N
Ph PCl
2
N
N
Ph2P
H
1
hexafluoro-
) d (ppm): 0.84 (t, J = 8 Hz, 3H,
N
R2
1
R2
phosphate (4a): H NMR (DMSO-d
CH ), 0.87 (t, J = 8 Hz, 3H, CH
.65 (m, 4H, CH ), 7.38–7.58 (m, 10H, Ph), 7.74 (brs, 1H, imidazol),
.59 (brs, 1H, imidazol). C NMR (DMSO-d
9.1, 32.2, 45.8 (J = 10 Hz), 50.2 (J = 11 Hz), 126.0, 128.1, 128.4
6
R2
3
3 2
), 1.34–1.61 (m, 4H, CH ), 4.18–
4
8
1
2
-
-
X: PF ; BF
6
4
13
6
) d (ppm): 13.6, 14.1,
Scheme 2. Preparation of 2-imidazolium phosphines.
(
(
J = 6 Hz), 130.4 (J = 7 Hz), 131.0, 132.7 (J = 12 Hz), 142.3
3
1
À
J = 50 Hz). P NMR (DMSO-d
6
) d (ppm): À27.5, À143.1 (PF
,
6
JPF = 706.8 Hz). Anal. Calc. for 4a: C, 52.29; H, 5.43; N, 5.81. Found:
R1
R
1
C, 52.28; H, 5.44; N, 5.83%.
X-
a
X-
1,3-Butyl-2-diphenylphosphino-imidazolium
hexafluorophos-
N
N
N
1
Ph2P
RhCl
3
·3H
2
O
RhCl Ph
2
P
phate (5a): H NMR (DMSO-d
6
) d (ppm): 0.89 (t, J = 8 Hz, 6H,
), 4.24 (m, 4H, CH ), 7.44–7.63 (m,
10H, Ph), 8.20 (s, 2H, imidazol). C NMR (DMSO-d ) d (ppm):
3.8, 19.1, 31.7, 50.2 (J = 11 Hz), 126.0, 130.2 (J = 6 Hz), 131.3
3
N
3
CH ), 1.31–1.89 (m, 8H, CH
2
2
1
3
R2
R
2
b
6
1
-
-
31
X: PF ; BF
6
4
(J = 8 Hz), 132.6, 133.0 (J = 12 Hz), 142.2 (J = 50 Hz).
P NMR
À
(
DMSO-d
6
) d (ppm): À28.5, À143.1 (PF , JPF = 706.8 Hz). Anal.
6
Scheme 3. Preparation of rhodium complexes employing the 2-imidazolium
Calc. for 5a: C, 54.12; H, 5.92; N, 5.49. Found: C, 54.13; H, 5.94;
phosphines as ligands.
N, 5.51%.
1
-Butyl-2-diphenylphosphino-3-hexylimidazolium
hexafluoro-
.24; 13C d 77.0) and DMSO-d
(1H: d 2.50; 13C d 39.5). 31P NMR
PO external standard.
1
6
7
6
phosphate (6a): H NMR (DMSO-d
CH ), 0.92 (t, J = 8 Hz, 3H, CH
.26 (m, 4H, CH ), 7.46–7.62 (m, 10H, Ph), 7.79 (brs, 1H, imidazol),
.24 (brs, 1H, imidazol). C NMR (DMSO-d
) d (ppm): 0.86 (t, J = 8 Hz, 3H,
chemical shifts are relative to 85% H
3
4
3
3 2
), 1.30–1.90 (m, 12H, CH ), 4.20–
4
8
2
1
3
6
) d (ppm): 13.7, 14.1,
2
.2. Preparation of 2-imidazolium phosphines
19.1, 22.5, 25.7, 30.6, 31.3, 32.4, 50.2 (J = 11 Hz), 50.3 (J = 11 Hz),
26.2, 128.4, 129.4 (J = 7 Hz), 130.5 (J = 9 Hz), 131.3, 133.4
1
3
1
To a solution of R
20 mL) (dried over P
hexane) at À78 °C, within a period of 15 min. After stirring for
5 min, the reaction mixture was charged, within 20 min, with
Ph
1
R
2
imPF
6
(3.0 mmol) dissolved in CH
2
Cl
2
(J = 12 Hz), 142.2 (J = 50 Hz). P NMR (DMSO-d
6
) d (ppm): À31.4,
n
À
(
4
O
10), was added BuLi (3.0 mmol, 15% in n-
À143.1 (PF , JPF = 706.8 Hz). Anal. Calc. for 6a: C, 55.76; H, 6.36;
6
N, 5.20. Found: C, 55.75; H, 6.37; N, 5.19%.
4
1-Butyl-2-diphenylphosphino-3-octylimidazolium hexafluorophos-
1
2
PCl (3.0 mmol) at À78 °C. The reaction mixture was warmed
phate (7a): H NMR (DMSO-d
6
) d (ppm): 0.83 (t, J = 8 Hz, 3H, CH
), 1.31–1.92 (m, 16H, CH ), 4.20–4.25 (m,
), 7.40–7.58 (m, 10H, Ph), 7.78 (brs, 1H, imidazol), 8.74
3
),
up gradually to room temperature over night. Thereafter the solu-
tion was extracted with three aliquots of deaerated water (10 mL).
The organic phase was dried over Na
0.94 (t, J = 8 Hz, 3H, CH
4H, CH
6
(brs, 1H, imidazol). C NMR (DMSO-d ) d (ppm): 13.6, 14.2, 19.1,
3
2
2
1
3
2
SO
4
. After evaporation of the
solvent in vacuo the cream-colored solid obtained was dried. The
spectroscopic data ( H NMR, C NMR and P NMR) of the pre-
pared compounds were in agreement with the assigned structures.
22.7, 25.8, 28.8, 30.1, 31.5, 31.6, 32.2, 50.1 (J = 11 Hz), 50.3
(J = 11 Hz), 125.0, 126.5, 128.9 (J = 7 Hz), 130.3 (J = 9 Hz), 131.0,
1
13
31
3
1
132.8 (J = 12 Hz), 142.0 (J = 50 Hz). P NMR (DMSO-d
6
) d (ppm):
À
1
-Methyl-2-diphenylphosphino-3-ethylimidazolium hexafluoro-
À34.4, À143.1 (PF , JPF = 706.8 Hz). Anal. Calc. for 7a: C, 57.24;
6
1
phosphate (1a): H NMR (DMSO-d
CH ), 3.86 (m, 3H, CH ), 4.67 (m, 2H, CH
Ph), 7.72 (brs, 1H, imidazol), 8.24 (brs, 1H, imidazol). C NMR
DMSO-d ) d (ppm): 15.9, 37.9 (J = 7 Hz), 45.6 (J = 10 Hz), 125.6,
28.3, 129.0 (J = 6 Hz), 130.3 (J = 7 Hz), 131.6, 132.9 (J = 13 Hz),
6
) d (ppm): 0.84 (t, J = 8 Hz, 3H,
H, 6.76; N, 4.94. Found: C, 57.23; H, 6.79; N, 4.94%.
3
3
2
), 7.51–7.76 (m, 10H,
To a solution of BMimBF
4 2 2
(3.0 mmol) dissolved in CH Cl
13
n
(20 mL) (dried over P 10), was added BuLi (3.0 mmol, 15% in n-
4
O
(
1
1
6
hexane) at À78 °C, within a period of 15 min. After stirring for
45 min, the reaction mixture was charged, within 20 min, with
3
1
42.1 (J = 50 Hz). P NMR (DMSO-d
6
) d (ppm): À23.8, À143.1
Ph
2
PCl (3.0 mmol) at À78 °C. The reaction mixture was warmed
À
(
PF6 , JPF = 706.8 Hz). Anal. Calc. for 1a: C, 49.10; H, 4.58; N, 6.36.
up gradually to room temperature over night. Thereafter the solu-
tion was extracted with three aliquots of deaerated water (10 ml).
Found: C, 49.21; H, 4.56; N, 6.33%.
-Methyl-2-diphenylphosphino-3-butylimidazolium hexafluoro-
1
The organic phase was dried over Na
2 4
SO . After evaporation of the
1
6
phosphate (2a): H NMR (DMSO-d ) d (ppm): 0.86 (t, J = 8 Hz, 3H,
solvent in vacuo the cream-colored solid obtained was dried. The

J. Li et al. / Journal of Organometallic Chemistry 695 (2010) 431–436
433
spectroscopic data ( H NMR, 13C NMR and 31P NMR) of the pre-
1
JPF = 706.8 Hz). Anal. Calc. for 4b: C, 47.70; H, 4.92; N, 5.30. Found:
pared compounds were in agreement with the assigned structures.
C, 47.89; H, 4.93; N, 5.31%.
1
-Methyl-2-diphenylphosphino-3-butylimidazolium tetrafluorobo-
Tri[1,3-dibutyl-2-diphenylphosphinoimidazolium
phosphate]rhodium chloride (5b): H NMR (DMSO-d
hexafluoro-
) d (ppm):
), 4.26 (m,
1
1
rate (8a): H NMR (DMSO-d
.16 (m, 2H, CH
H, CH
6
) d (ppm): 0.76 (t, J = 8 Hz, 3H, CH
), 1.60 (m, 2H, CH ), 3.63 (m, 3H, CH ), 4.38 (m,
), 7.31–7.47 (m, 10H, Ph), 8.40 (brs, 1H, imidazol), 8.90
3
),
6
1
2
(
2
2
3
0.86 (t, J = 8 Hz, 18H, CH
12H, CH ), 7.44–7.60 (m, 30H, Ph), 7.98 (brs, 6H, imidazol).
NMR (DMSO-d ) d (ppm): 13.7, 19.2, 31.8, 50.1(J = 11 Hz), 126.1,
3
), 1.30–1.88 (m, 24H, CH
2
13
2
2
C
1
3
brs, 1H, imidazol). C NMR (DMSO-d
6
) d (ppm): 13.3, 19.5, 33.1,
6
3
8.7 (J = 5 Hz), 50.4 (J = 12 Hz), 126.2, 128.4(J = 6 Hz), 128.8, 130.2
128.4, 130.3, 132.3, 133.1, 136.0, due to overlapping of signals,
3
1
(J = 9 Hz), 130.9, 132.6 (J = 18 Hz), 142.2 (J = 52 Hz).
P NMR
the carbon resonances from d 125 to 137 were listed without iden-
3
1
31
(
DMSO-d
6
) d (ppm): À26.7. Anal. Calc. for 8a: C, 58.57; H, 5.86;
tification of the P splitting. P NMR (DMSO-d
6
) d (ppm): À25.7
À
N, 6.83. Found: C, 58.56; H, 5.90; N, 6.83%.
(JPRh = 132 Hz), À143.0 (PF , JPF = 706.8 Hz). Anal. Calc. for 5b: C,
6
4
9.61; H, 5.39; N, 5.03. Found: C, 49.63; H, 5.41; N, 5.03%.
2
.3. Preparation of rhodium complexes employing the 2-imidazolium
Tri[1-butyl-2-diphenylphosphino-3-hexylimidazolium hexafluoro-
1
phosphines as ligands
phosphate] rhodium chloride (6b): H NMR (DMSO-d
6
) d (ppm):
), 1.31–1.88
2
), 7.46–7.61 (m, 30H, Ph),
0
.78 (t, J = 8 Hz, 9H, CH
(m, 36H, CH ), 4.18–4.23 (m, 12H, CH
7.77 (brs, 3H, imidazol), 8.72 (brs, 3H, imidazol).
(DMSO-d ) d (ppm): 13.7, 14.3, 19.2, 22.8, 25.9, 30.9, 31.5, 32.1,
3 3
), 0.89 (t, J = 8 Hz, 9H, CH
A solution of 2-imidazolium phosphine (a) (2.5 mmol) in
2
13
CH
3
OH (10 mL) was treated with RhCl
3
2
Á3H O (0.5 mmol). The mix-
C NMR
ture was stirred at 70 °C for 3 h. After filtration, the solid was
washed with diethyl ether, purified by silica gel column chroma-
tography and then dried in vacuo. All the prepared compounds
showed spectroscopic data ( H NMR, C NMR and P NMR) in
accordance with the assigned structures.
6
50.1 (J = 11 Hz), 50.3 (J = 11 Hz), 125.7, 127.7, 128.5, 131.0, 132.8,
134.7, 142.2, due to overlapping of signals, the carbon resonances
1
13
31
31
from d 125 to 137 were listed without identification of the
P
3
1
splitting. P NMR (DMSO-d
6
) d (ppm): À28.9 (JPRh = 148.1 Hz),
À
Tri[1-methyl-2-(diphenylphosphino)-3-ethylimidazolium
hexa-
fluorophosphate] rhodium chloride (1b): H NMR (DMSO-d ) d
ppm): 0.84 (t, J = 8 Hz, 9H, CH ), 3.84 (m, 9H, CH ), 4.65 (m, 6H,
CH ), 7.51–7.76 (m, 30H, Ph), 7.72 (br, 3H, imidazol), 8.29 (br,
À143.0 (PF , JPF = 706.8 Hz). Anal. Calc. for 6b: C, 51.34; H, 5.82;
6
1
6
N, 4.79. Found: C, 51.47; H, 5.85; N, 4.81%.
(
3
3
Tri[1-butyl-2-diphenylphosphino-3-octylimidazolium hexafluoro-
1
2
phosphate] rhodium chloride (7b): H NMR (DMSO-d
6
) d (ppm):
), 3.34–4.13 (m,
), 7.38–7.48 (m, 30H, Ph), 7.78 (brs, 3H, imidazol), 8.20
1
3
3
4
H, imidazol). C NMR (DMSO-d
6
) d (ppm): 14.2, 37.1 (J = 7 Hz),
0.67–0.82 (m, 18H, CH
12H, CH
6
(brs, 3H, imidazol). C NMR (DMSO-d ) d (ppm): 13.7, 14.4, 19.3,
3 2
), 1.31–1.52 (m, 48H, CH
4.6 (J = 6 Hz), 125.6, 127.9, 128.9, 130.2, 131.1, 134.3, 141.8, due
2
1
3
to overlapping of signals, the carbon resonances from d 125 to
35 were listed without identification of the 31P splitting. 31
1
P
22.5, 25.9, 28.8, 30.2, 31.6, 31.7, 32.2, 50.1 (J = 11 Hz), 50.3
(J = 11 Hz), 123.0, 126.8, 128.6, 130.3, 131.0, 132.9, 141.9, due to
overlapping of signals, the carbon resonances from d 125 to 133
À
NMR (DMSO-d
6
) d (ppm): À18.8 (JPRh = 161 Hz), À143.0 (PF
,
6
J
PF = 707 Hz). Anal. Calc. for 1b: C, 44.42; H, 4.11; N, 5.76. Found:
3
1
31
C, 44.53; H, 4.14; N, 5.79%.
were listed without identification of the P splitting. P NMR
À
Tri[1-methyl-2-diphenylphosphino-3-butylimidazolium
hexa-
) d
), 3.55
), 7.38–7.70 (m, 30H, Ph), 8.20
(DMSO-d
6
) d (ppm): À30.5 (JPRh = 132 Hz), À143.0 (PF , JPF
=
6
1
fluorophosphate] rhodium chloride (2b): H NMR (DMSO-d
6
706.8 Hz). Anal. Calc. for 7b: C, 52.92; H, 6.21; N, 4.57. Found: C,
(ppm): 0.76 (t, J = 8 Hz, 9H, CH
(m, 9H, CH ), 4.18 (m, 6H, CH
(brs, 3H, imidazol), 8.62 (brs, 3H, imidazol). C NMR (DMSO-d
3
), 1.26–1.75 (m, 12H, CH
2
53.17; H, 6.24; N, 4.59%.
3
2
Tri[1-methyl-2-diphenylphosphino-3-butylimidazolium tetrafluo-
13
1
6
)
roborate] rhodium chloride (8b): H NMR (DMSO-d
6
) d (ppm):
), 3.51 (m, 9H,
), 7.33–7.69 (m, 30H, Ph), 8.69 (brs, 3H, imi-
d (ppm): 13.7, 19.2, 31.8, 37.9 (J = 7 Hz), 50.1 (J = 11 Hz), 125.2,
26.0, 128.3, 130.3, 131.1, 134.9, 142.3, due to overlapping of sig-
nals, the carbon resonances from d 125 to 135 were listed without
0.83 (t, J = 8 Hz, 9H, CH
CH ), 3.84 (m, 6H, CH
dazol), 8.82 (brs, 3H, imidazol). C NMR (DMSO-d
3 2
), 1.10–1.79 (m, 12H, CH
1
3
2
1
3
6
) d (ppm): 13.1,
3
1
31
identification of the P splitting. P NMR (DMSO-d
6
) d (ppm):
19.2, 32.2, 37.8 (J = 6 Hz), 50.4 (J = 12 Hz), 125.2, 127.5, 128.1,
130.3, 131.3, 132.9, 142.1, due to overlapping of signals, the carbon
resonances from d 125 to 135 were listed without identification of
À
À21.7 (JPRh = 177.1 Hz), À143.0 (PF6 , JPF = 706.8 Hz). Anal. Calc.
for 2b: C, 46.67; H, 4.67; N, 5.44. Found: C, 46.87; H, 4.69; N, 5.46%.
3
1
31
Tri[1-methyl-2-diphenylphosphino-3-hexylimidazolium
hexa-
fluorophosphate] rhodium chloride (3b): H NMR (DMSO-d ) d
), 3.57
), 7.38–7.57 (m, 30H, Ph), 7.74
the
P
splitting.
P
NMR (DMSO-d
6
)
d
(ppm): À22.6
1
6
(JPRh = 161 Hz). Anal. Calc. for 8b: C, 52.64; H, 5.30; N, 6.14. Found:
(
(
(
d
(
ppm): 0.78 (t, J = 8 Hz, 9H, CH
m, 9H, CH ), 4.18 (m, 6H, CH
brs, 3H, imidazol), 8.61 (brs, 3H, imidazol), C NMR (DMSO-d
(ppm): 14.2, 22.2, 28.8, 30.9, 31.2, 37.9 (J = 7 Hz), 50.3
J = 11 Hz), 125.3, 126.1, 128.3, 130.2, 131.3, 136.5, 142.3, due to
3
), 1.32–1.64 (m, 24H, CH
2
C, 52.61; H, 5.26; N, 6.13%.
3
2
13
6
)
2.4. Hydrosilylation of alkene with triethoxysilane
Typical hydrosilylation reaction procedures were as follows: a
given amount of catalyst and ionic liquid were added to a 10 mL
round bottomed flask equipped with a magnetic stirrer and the al-
kene and silane were then added. This mixture was heated to the
appropriate temperature and the hydrosilylation reaction was al-
lowed to proceed 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.
overlapping of signals, the carbon resonances from d 125 to 137
were listed without identification of the 31P splitting. P NMR
31
À
(
DMSO-d
6
)
d
(ppm): À27.8 (JPRh = 132 Hz), À143.0 (PF6
,
J = 706.8 Hz). Anal. Calc. for 3b: C, 48.68; H, 5.16; N, 5.16. Found:
C, 48.91; H, 5.18; N, 5.17%.
Tri[1-ethyl-2-diphenylphosphino-3-butylimidazolium hexafluoro-
phosphate] rhodium chloride (4b): 1H NMR (DMSO-d
) d (ppm):
), 1.36–1.60
2
), 7.38–7.58 (m, 30H, Ph),
6
0
(
7
.86 (t, J = 8 Hz, 9H, CH
m, 12H, CH ), 4.18–4.64 (m, 12H, CH
.74 (brs, 3H, imidazol), 8.60 (brs, 3H, imidazol).
) d (ppm): 13.7, 14.1, 19.2, 31.8, 45.8 (J = 10 Hz), 50.1
J = 11 Hz), 125.4, 126.2, 128.2, 129.4, 132.1, 135.2, 142.2, due to
3 3
), 0.89 (t, J = 8 Hz, 9H, CH
2
1
3
C NMR
(
DMSO-d
6
2.4.1. Hydrosilylation of styrene with triethoxyslane
1
(
b-Adduct [triethoxy(phenethyl)silane]: H NMR (CDCl
3
, 400 MHz)
),
2
), 7.16–7.27
overlapping of signals, the carbon resonances from d 125 to 136
d (ppm): 1.00 (t, J = 8 Hz, 2H, Si–CH
2
), 1.24 (t, J = 9 Hz, 9H, CH
), 3.84 (q, J = 8 Hz, 6H, O–CH
3
were listed without identification of the 31P splitting. P NMR
31
2.74 (t, J = 8 Hz, 2H, CH
2
(
DMSO-d
6
)
d
(ppm): À23.4 (JPRh = 132 Hz), À143.0 (PF6À
,
(m, 5H, Ph).

4
34
J. Li et al. / Journal of Organometallic Chemistry 695 (2010) 431–436
a
-Adduct [triethoxy(1-phenylethyl)silane]: 1H NMR (CDCl
3
,
4
3
00 MHz) d (ppm): 1.18 (t, J = 8 Hz, 9H, CH ), 1.33 (d, J = 8 Hz,
1
b
1
565.8
3H, CH
3
), 3.65 (q, J = 8 Hz, 1H, Si–CH), 3.76 (q, J = 8 Hz, 6H, O–
CH ), 7.12-7.19 (m, 5H, Ph).
2
1
Ethylbenzene: H NMR (CDCl
3
, 400 MHz) d (ppm): 1.15 (t,
), 7.11–7.25 (m, 5H, Ph).
1
a
J = 8 Hz, 3H, CH ), 2.64 (q, J = 8 Hz, 2H, CH
3
2
1
433.8
2
.4.2. Hydrosilylation of 1-hexene with triethoxyslane
1
b-Adduct (hexyltriethoxysilane): H NMR (CDCl
ppm): 0.64 (t, J = 6 Hz, 2H, Si–CH ), 0.89 (t, J = 8 Hz, 3H, CH
), 3.81 (q, J = 8 Hz, 6H, O–CH ).
3
, 400 MHz) d
(
2
3
),
1
568.1
1
.22–1.42 (m, 17H, CH
2
CH
3
2
1
437.8
1450
3
. Results and discussion
Infrared spectroscopy is a useful tool to confirm the chemical
1600
1575
1550
1525
1500
1475
1425
-
1
Wave numbers (cm )
modifications proposed. Two bands present in the diffuse reflec-
tion infrared Fourier-transform spectra of 1a at 1568.1 cm and
À1
Fig. 1. IR spectra (1415–1600 cm ) of 1a and 1b.
À1
Table 1
Preparation of 2-imidazolium phosphines and rhodium complexes employing the 2-imidazolium phosphines as ligands.
Entry
1
Product a
Yielda (%)
90
Product b
Yielda (%)
92
H C
H3C
3
PF -
PF6-
6
N
Ph2P
N
N
Rh Cl Ph2P
3
3
N
C H
2
5
1
a
C H
2
5
1
b
2
H C
88
H C
88
3
3
PF 6-
PF -
N
N
N
6
Ph 2P
Rh Cl Ph2P
C H
N
C H
4
9
2
a
4
9
2
b
3
4
H C
88
86
H 3
Rh Cl Ph 2 P
C
90
90
3
PF 6-
PF 6-
N
N
N
N
Ph 2P
3
3
3
C 6H 13
C H
6
13
3b
3a
C H
C H
5
2
5
2
PF -
PF -
6
N
N
6
N
Ph2P
Rh Cl Ph2P
N
C H
4
9
C H
4a
4
9
4
5
6
b
5
6
C H
85
81
C H
9
87
83
4
9
4
PF 6-
PF6-
N
N
Ph 2P
Rh Cl Ph2P
C H
N
N
C H
4
9
4
9
5a
b
C H
C H
4 9
6
13
PF -
PF6-
6
N
N
Ph2P
Rh Cl Ph2P
3
3
N
N
C H
C H
6
13
4
9
6a
b
7
8
C H
83
87
C H
9
77
92
8
17
4
PF -
PF 6-
6
N
N
N
Ph 2P
Rh Cl Ph 2P
N
C H
C8H17
4
9
7a
7
b
H C
H C
3
3
BF 4-
BF 4-
N
N
N
Ph 2P
C H
Rh Cl Ph 2P
C H
9
3
N
4
9
4
8
a
8b
a
Isolated yields.

J. Li et al. / Journal of Organometallic Chemistry 695 (2010) 431–436
435
Table 2
Effect of b on the hydrosilylation reaction.
Entry
Catalyst (% substrate mol)
Substrate
Conversion (%)
Selectivity (%)
TON
b
a
Alkane
Un-saturated
1
2
3
4
5
6
7
8
9
RhCl(PPh
1b 0.1
3
)
3
0.1
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
1-Hexene
1-Heptene
1-Octene
1-Undene
Styrene
Styrene
Styrene
78.1
100
100
88.7
100
99.4
96.1
95.7
94.5
92.1
90.4
66.7
100
100
100
100
98.7
98.8
98.5
81.2
90.0
90.1
89.3
89.8
91.6
94.9
96.6
97.3
99.4
97.7
90.8
99.1
98.7
99.0
98.8
89.9
89.8
89.8
16.5
4.1
4.1
4.2
4.1
3.1
1.6
1.9
1.2
–
–
3.4
–
–
–
2.3
5.9
5.8
6.5
6.1
5.3
3.5
1.5
1.5
0.6
2.3
5.8
0.9
1.3
1.0
1.2
6.0
6.1
6.2
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
781
1000
2000
8870
5000
4970
4805
4785
4725
4605
4520
3335
20,000
20,000
20,000
20,000
4935
1b 0.05
1b 0.01
1b 0.02
2b 0.02
3b 0.02
4b 0.02
5b 0.02
6b 0.02
7b 0.02
8b 0.02
1b 0.005
1b 0.005
1b 0.005
1b 0.005
1b 0.02
1b 0.02
1b 0.02
10
11
12
13
14
15
16
17
18
19
a
–
b
c
4.1
4.1
4.0
4940
4925
d
6
Reaction conditions: alkene 2.5 mmol, triethoxysilane 3.0 mmol, 70 °C, 5 h, BMimPF 0.5 mL.
a
4
BMimBF 0.5 mL.
Second run.
Third run.
b
c
d
Fourth run.
À1
1
b at 1565.8 cm , are assigned to the presence of imidazolium
drances may be more than the effect of electronic properties and
so the selectivity of the b-adduct increased with increasing length
of alkyl chain.
cation cycle coupling [12] (Fig. 1). The band presents in the diffuse
reflection infrared Fourier-transform spectra of 1a at 1437.8 cm
À1
,
is assigned to the presence of P–Ph stretching [13]. The spectrum
also shows the band for 1b presents at 1433.8 cm (Fig. 1). Intro-
From Table 2 (entries 2–5) it is shown that the conversion of
styrene increases with increasing amounts of 1b used; the selectiv-
ity remains constant.
À1
duction of Rh into 1a causes a low-field shift in the infrared spec-
3
1
trum demonstrating that Rh is linked to 1a. Moreover, in the
P
Hydrosilylation reaction of styrene with triethoxysilane was
NMR spectra the 2-imidazolium phosphines (1a–7a) shows sing-
lets (À21.8 to À34.4 ppm) in a shift range typical for tertiary aryl-
conducted in BMimBF
4
in the presence 8b. However, 8b in
BMimBF shows low catalytic activity, and the conversion of sty-
4
3
1
alkyl phosphines bearing C-bound heterocyclic substituents.
P
rene is 66.7%. Therefore, we can conjecture that the counter ions
had some impact on the hydrosilylation reaction. The counter ion
chemical shifts at high frequency occur with an increasing alkyl
3
1
À
À
chain length and P chemical shifts at low frequency occur when
Rh links to the ligands Elemental analysis data and theoretical
BF4 is more nucleophilic than PF6 , and it reduced the solubility
of silane in the hydrophilic ionic liquid BMimBF
.
4
.
values for 2-imidazolium phosphines (1a–8a) and rhodium com-
plexes employing the 2-imidazolium phosphines as ligands (1b–
When aliphatic alkenes, such as 1-hexene, 1-heptene, 1-octene
and 1-undecene, replace styrene as one of the substrates, excel-
lent conversions and selectivities are obtained with the 1b
catalyst.
8
b) are in close agreement. (Table 1)
6
Wilkinson’s catalyst RhCl(PPh in BMimPF (1-methyl-3-buty-
3
)
3
limidazolium hexafluorophosphate) has low catalytic activity and
selectivity (Table 2, entry 1). However, Rh complexes employing
Rhodium complexes employing the 2-imidazolium phosphines
as ligands (1b–7b) show a pronounced solubility in BMimPF . They
6
2
-imidazolium phosphines as ligands (1b–7b) exhibit greater cat-
are specially designed to be used in ionic liquid biphasic systems
alytic activity and selectivity. The electron-rich heterocycle pro-
vides a suitable framework that stabilizes the Rh-phosphine
center located between the two nitrogen atoms. It is possible that
close proximity of the positive charge to the phosphorus atom
greatly enhances the catalytic activity, affording highly efficient
catalytic activity and stable metal centers. Although the catalytic
activities of Rh complexes employing the 2-imidazolium phos-
phines as ligands (1b–7b), slightly decreased with increasing
length of alkyl chain, the selectivity of the b-adduct clearly in-
and have been employed to circumvent catalyst problems. 1b in
6
BMimPF can be reused without noticeable loss of catalytic activity
and selectivity (Table 2, entries 5, 17–19).
4
. Conclusion
-Imidazolium phosphines can specifically vary their physical
2
and chemical properties by altering the attached substituents. Rho-
dium complexes employing 2-imidazolium phosphines as ligands
creased and no
a-adduct can be detected at all when 6b and 7b
are used as catalysts. This demonstrates that the attached substit-
uents on the nitrogen atoms have a significant impact on Rh com-
plexes as catalysts and that fine tuning the steric and electronic
properties of the substituents on the nitrogen atoms affords differ-
ent catalytic activity. It is possible that the Rh complexes employ-
ing the 2-imidazolium phosphines as ligands (1b–7b) can stabilize
the intermediate states. The different substituents on the nitrogen
atoms result in different steric hindrances of the catalytic center
and different electronic properties. The effect of the steric hin-
(
1b–7b) exhibited greater catalytic activity and selectivity. The
electron-rich heterocycle provides a suitable framework that stabi-
lizes the Rh-phosphine center located between the two nitrogen
atoms. It is possible that close proximity of the positive charge to
the phosphorus atom greatly enhances the catalytic activity and
can afford highly efficient catalytic activity. The selectivity of the
b-adduct clearly increased with increasing length of alkyl chain.
1
6
b in BMimPF can be reused without noticeable loss of catalytic
activity and selectivity.

4
36
J. Li et al. / Journal of Organometallic Chemistry 695 (2010) 431–436
[
[
4] D.J. Brauer, K.W. Kottsieper, C. Liek, O. Stelzer, H. Waffenschmidt, P.
Wasserscheid, J. Organomet. Chem. 630 (2001) 177–184.
5] S.S. Moore, G.M. Whitesides, J. Org. Chem. 47 (1982) 1489–1493.
Acknowledgment
We thank the Foundation of Zhejiang Educational Committee
[6] C. Kimblin, G. Parkin, Inorg. Chem. 35 (1996) 6912–6913.
[7] M. Azouri, J. Andrieu, M. Picquet, P. Richard, B. Hanquet, I. Tkatchenko, Eur. J.
Inorg. Chem. (2007) 4877–4883.
(
20070466) for financial support.
[
[
8] Y. Canac, N. Debono, L. Vendier, R. Chauvin, Inorg. Chem. 48 (2009) 5562–5568.
9] J. Dupont, R.F. de Souza, P.A.Z. Suarez, Chem. Rev. 102 (2002) 3667–3691.
References
[
10] J.J. Peng, J.Y. Li, Y. Bai, W.H. Gao, H.Y. Qiu, H. Wu, Y. Deng, G.Q. Lai, J. Mol. Catal.
A: Chem. 278 (2007) 97–101.
[
1] J. van den Broeke, F. Winter, B.J. Deelman, G. van Koten, Org. Lett. 22 (2002)
851–3854.
[11] P.A.Z. Suarez, J.E.L. Dullius, S. Einloft, R.F. de Souza, J. Dupont, Polyhedron 15
(1996) 1217–1219.
3
[
[
2] B. Marciniec, J. Gulinski, J. Organomet. Chem. 253 (1983) 349–362.
3] A. Onopchenko, E.T. Sabourin, D.L. Beach, J. Org. Chem. 48 (1983) 5101–5105.
[12] J.D. Holbrey, K.R. Seddon, Dalton Trans. (1999) 2133–2139.
[13] A.E. Senear, W. Valient, J. Wirth, J. Org. Chem. 25 (1960) 2001–2006.