Effect of silylated triarylphosphine ligands on rhodium-catalyzed hydrosilylation

Article abstract of DOI:10.1002/aoc.3519

A series of silylated triarylphosphines was synthesized. Hydrosilylation reactions of styrene with triethoxysilane catalyzed by RhCl₃/silylated triarylphosphine complexes were investigated. The complexes RhCl₃/phenylbis(4-trimethylsilylphenyl)phosphine and RhCl₃/tris(4-trimethylsilylphenyl)phosphine exhibited higher activity as well as greater β-adduct selectivity, and no unsaturated product was obtained. The results suggest that the silyl moieties have a significant impact on the catalytic process. Copyright

Full text of DOI:10.1002/aoc.3519

Full paper
Received: 24 February 2016
Revised: 26 April 2016
Accepted: 28 April 2016
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.3519
Effect of silylated triarylphosphine ligands on
rhodium-catalyzed hydrosilylation
Jiayun Li*, Mei Xue, Ying Bai, Jiajian Peng* and Wenjun Xiao
A series of silylated triarylphosphines was synthesized. Hydrosilylation reactions of styrene with triethoxysilane catalyzed by
RhCl3/silylated triarylphosphine complexes were investigated. The complexes RhCl3/phenylbis(4-trimethylsilylphenyl)phosphine
and RhCl3/tris(4-trimethylsilylphenyl)phosphine exhibited higher activity as well as greater β-adduct selectivity, and no unsatu-
rated product was obtained. The results suggest that the silyl moieties have a significant impact on the catalytic process.
Copyright © 2016 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web site.
Keywords: hydrosilylation; rhodium complex; silylated triarylphosphine ligands; β-adduct selectivity
complexes. We expected that silyl groups would have particular
electronic and steric effects on phosphine ligands, and that the over-
Introduction
Phosphorus ligands are a significant class of ligands in catalyzed
reactions. Numerous catalytic reactions, such as Mukaiyama redox
condensation,[1] Mitsunobu reaction[2–4] and Wittig ylide
formation,[5–7] have been extensively developed along with re-
search on transition metal complexes coordinated by phosphorus
ligands..[8,9] Generally, the steric, electronic and geometric proper-
ties of phosphorus ligands bearing functional groups have very sig-
nificant effects on the catalytic activities and selectivities of the
corresponding metal complexes.[10–15]
all effects of silylated triarylphosphine ligands would influence catal-
ysis by metal complexes.
In the study reported here, a series of silylated triarylphosphine
ligands was designed (Fig. 1), and the catalytic properties of rho-
dium complexes coordinated by these ligands were compared with
those of with the classic Wilkinson’s catalyst.
Experimental
Hydrosilylation is one of the most important reactions for Si–C
bond formation in organosilicon chemistry.[16,17] Many organosilicon
compounds bearing functional groups have been synthesized in this
way. Transition metal complexes, such as Wilkinson’s catalyst (Rh
(PPh3)3Cl), as well as tertiary phosphine complexes of palladium, plat-
inum, and nickel, have been applied as catalysts for hydrosilylation. In
this catalytic process, the phosphine ligands play important
roles.[18–20] Their chief role is to keep the metal in the form of a stable
species that can enter the catalytic cycle and to prevent the produc-
tion of inactive metal aggregates.[21–29]
General remarks
Styrene was washed with 5% NaOH and dried with Na2SO4, and
then was distilled under reduced pressure after filtration. All other
materials were purchased from Aldrich and were used as received.
All reactions were carried out under an argon atmosphere, using
common Schlenk techniques and dry solvents. Diethyl ether and
tetrahydrofuran (THF) were dried over sodium wire and dichloro-
methane over calcium hydride, and further purified by subsequent
distillation.
Ochida and Sawamura[19] reported that a novel bulky phosphine
ligand incorporating an alkyne group exhibited excellent catalytic
properties in the rhodium-catalyzed hydrosilylation of ketones.
Another bulky bowl-shaped phosphine ligand was also shown to
markedly improve catalytic activity in rhodium-catalyzed
hydrosilylation reactions as compared with conventional phos-
phine ligands such as PPh3 and PtBu3.[30] We reported that rhodium
complexes bearing functionalized triarylphosphine ligands are
characterized by very high catalytic efficiencies in the hydrosilylation
of alkenes, in comparison with the classic Wilkinson’s catalyst. Using
these triarylphosphine ligands for the rhodium-catalyzed
hydrosilylation of styrene, both higher conversions of the alkene
and higher β-adduct selectivities were obtained.[10,11] The electronic
properties of phosphine-based ligands are highly influenced by
modifying substituents attached to the phosphine, and are also im-
portant for the catalytic properties of the corresponding metal
GC: Trace DSQ GC Column, DB-5, 30 m × 2.5 mm × 0.25 μm; split
=50:1; flow =1 ml minÀ1 constant flow; inlet temperature = 260 °C;
column temperature = 50 °C (hold 1 min) then 15 °C minÀ1 up to
260 °C (hold 10 min). GC–MS: Trace DSQ GC–MS column.
1H NMR, 13C NMR, 29Si NMR and 31P NMR spectra were measured
using a Bruker AV400 spectrometer operating at 400.13, 100.62,
79.49 and 161.97 MHz, respectively. Infrared (IR) spectra were re-
corded with a Nicolet 5700 instrument. Elemental analyses were
performed with a VARIO EL-III elemental analyzer.
*
Correspondence to: Jiayun Li or Jiajian Peng, Key Laboratory of Organosilicon
Chemistry and Material Technology of Ministry of Education, Hangzhou Normal
University, Hangzhou 310012, China. E-mail: tougaos@hotmail.com
Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry
of Education, Hangzhou Normal University, Hangzhou 310012, China
Appl. Organometal. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.

Li J. et al.
Diphenyl(2-trimethylsilylphenyl)phosphine (1a). 1H NMR (CDCl3, δ, ppm):
7.72–7.66 (m, 1H, P–C6H4–Si), 7.41–7.31 (m, 2H, C6H5–P; 4H, C6H5–P;
1H, P–C6H4–Si; 1H, P–C6H4–Si), 7.31–7.26 (m, 4H, C6H5–P), 7.24–7.20
(m, 1H, P–C6H4–Si), 0.44 (s, 9H, Si–CH3), due to overlapping of sig-
nals, the proton assignments are listed without distinct identifica-
tion. 13C NMR (CDCl3, δ, ppm): 148.21 (1C, o-C, P–C6H4–Si), 143.13
(1C, P–C, P–C6H4–Si), 138.38 (1C, m-C, P–C6H4–Si), 135.38 (1C, o-C,
P–C6H4–Si), 134.73 (2C, P–C, C6H5–P), 133.35 (4C, o-C, C6H5–P),
129.21 (1C, m-C, P–C6H4–Si), 128.45 (4C, m-C, C6H5–P), 128.38 (2C,
p-C, C6H5–P), 128.24 (1C, p-C, P–C6H4–Si), 1.49 (3C, CH3). 29Si NMR
(CDCl3, δ, ppm): À3.53. 31P NMR (CDCl3, δ, ppm): À9.78. IR (cmÀ1):
692 (P–Ph), 740 (P–Ph), 755 (Si–C), 835 (Si–C), 1430 (Ar–Si), 2857
(CH3), 3046 (Ph). MS: 334.21 (M+).
Typical synthesis of phosphine ligands containing silica-based group (Schemes 2
and 3)
Figure 1. Structures of silylated triarylphosphine ligands.
An oven-dried 100 ml Schlenk tube equipped with a magnetic stir
bar was evacuated and refilled with argon three times before
adding a solution of 1-bromo-4-iodobenzene (or 1-bromo-3-
iodobenzene) (0.78 ml, 6.1 mmol) in THF (30 ml) under argon atmo-
sphere. The reaction Schlenk tube was cooled to À78 °C and a so-
lution of n-BuLi in hexane (1.6 M, 6.1 mmol) was added dropwise
slowly. After the addition was completed, the reaction mixture
was stirred at the same temperature for 1 h, and then chlorosilane
(3.10 ml, 6.7 mmol) was added at À78 °C. The resulting mixture was
gradually warmed to ambient temperature for 4 h. The mixture was
quenched with water and extracted with Et2O (30 ml). The com-
bined organic layers were dried over magnesium sulfate, filtered
and evaporated under reduced pressure to afford 1-bromo-
4-(alkylsilyl)benzene (or 1-bromo-3-(alkylsilyl)benzene) as a color-
less liquid. A solution of the 1-bromo-4-(alkylsilyl)benzene (or 1-
bromo-3-(alkylsilyl)benzene) (5 mmol) in Et2O (30 ml) was added
slowly to a solution of n-BuLi (2.5 M in hexane, 5 mmol) in 15 ml
of hexane at À78 °C. The resulting mixture was stirred at À78 °C
followed by the addition of a solution of chlorodiphenylphosphine
(0.89 ml, 5.0 mmol) for 2 h and then allowed to warm to room tem-
perature. After stirring overnight, the reaction mixture was
Synthesis of silylated triarylphosphines
Diphenyl(2-trimethylsilylphenyl)phosphine (1a; Scheme 1)
A 100 ml three-necked flask equipped with a magnetic stir bar, a
rubber septum and a reflux condenser was charged with NaOAc
(1.30 g, 15.8 mmol) and Pd(OAc)2 (17.5 mg, 0.07 mmol) and was
evacuated and refilled with argon three times before adding N,N-
dimethylacetamide (35 ml), 1-bromo-2-iodobenzene (2.50 ml,
19.5 mmol) and diphenylphosphine (2.5 ml, 19.5 mmol). The reac-
tion mixture was stirred at 130 °C for three days. The reaction mix-
ture was cooled to room temperature and diluted with water
(30 ml) and extracted with CHCl3 (20 ml × 3). The combined organic
extracts were dried over Na2SO4. The filtrate was concentrated in
vacuo, and purified by recrystallization from ethanol to afford a
yellow solid. Further purification was done using flash chromatog-
raphy (1:2 EtOAc–hexane) to yield a white precipitate of (2-
bromophenyl)diphenylphosphine in 92% yield.
The (2-bromophenyl)diphenylphosphine thus prepared (3.41 g,
9.99 mmol) was dissolved in degassed Et2O (30 ml) under argon at-
mosphere. The reaction flask was cooled to 0 °C and a solution of n-
BuLi in hexane (1.6 M, 10.1 mmol) was added dropwise slowly using
a drop funnel. After the addition was complete, the reaction mix-
ture was stirred at room temperature for
2 h, then
chlorotrialkylsilane (1.40 ml, 11.1 mmol) was added at 0 °C. The
resulting mixture was gradually warmed to ambient temperature
for 3 h and quenched by a saturated aqueous solution of NH4Cl
(30 ml). The mixture was extracted with Et2O (30 ml × 3). The com-
bined organic layers were dried over magnesium sulfate, filtered
and evaporated under reduced pressure. The solution was concen-
trated in vacuo, and the residue was subjected to column chroma-
tography on silica gel with hexane (Rf = 0.40) to give 1a as white
solid (2.73 g, 82% yield).[10,31]
Scheme 2. Synthesis of 1b, 1d and 1 f.
Scheme 1. Synthesis of 1a.
Scheme 3. Synthesis of 1c, 1e and 1 g.
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Appl. Organometal. Chem. (2016)

Effect of silylated triarylphosphine ligands on hydrosilylation
Diphenyl(3-triethylsilylphenyl)phosphine (1f). Yield 1.28 g (68%). 1H NMR
(CDCl3, δ, ppm): 7.55–7.54 (m, 1H, P–C6H4–Si), 7.52–7.50 (m, 1H, P–
C6H4–Si), 7.44–7.33 (m, 10H, P–C6H5; 2H, m-H, P–C6H4–Si), 0.98 (t,
J = 7.9 Hz, 9H, Si–CH3), 0.80 (q, J = 7.9 Hz, 6H, Si–CH2), due to over-
lapping of signals, the proton assignments are listed without dis-
tinct identification. 13C NMR (CDCl3, δ, ppm): 139.90 (1C, m-C,
P–C6H4–Si), 137.57 (1C, P–C, P–C6H4–Si), 134.60 (1C, o-C, P–C6H4–
Si), 134.19 (1C, p-C, P–C6H4–Si), 134.02 (1C, o-C, P–C6H4–Si), 133.86
(2C, P–C, P–C6H5), 133.67 (4C, o-C, P–C6H5), 128.72 (1C, m-C,
P–C6H4–Si), 128.53 (4C, m-C, P–C6H5), 127.96 (2C, p-C, P–C6H5),
7.46 (3C, CH3), 3.42 (3C, CH2). 29Si NMR (CDCl3, δ, ppm): 2.30. 31P
NMR (CDCl3, δ, ppm): À4.84. IR (cmÀ1): 699 (P–Ph), 741 (P–Ph),
811 (Si–C), 1439 (Ar–Si), 2871 (CH3), 2941 (CH2), 2952 (CH3), 3051
(Ph). MS: 376.15 (M+). Anal. Calcd for 1 f (C24H29PSi) (%): C, 76.55;
H, 7.76. Found (%): C, 76.53; H, 7.77.
quenched with water and extracted with CH2Cl2. The organic
phases were dried over Na2SO4 and evaporated in vacuum. The
crude product was purified by silica gel column chromatography
(5% EtOAc–hexanes) to afford the ligand as a colorless viscous oil.
Diphenyl(3-trimethylsilylphenyl)phosphine (1b). Yield 1.10 g (66%). 1H
NMR (CDCl3, δ, ppm): 7.68–7.66 (m, 1H, P–C6H4–Si), 7.61–7.59 (m,
1H, P–C6H4–Si), 7.44–7.33 (m, 10H, P–C6H5; 2H, P–C6H4–Si), 0.32 (s,
9H, Si–CH3), due to overlapping of signals, the proton assignments
are listed without distinct identification. 13C NMR (CDCl3, δ, ppm):
140.81 (1C, m-C, P–C6H4–Si), 139.38 (1C, P–C, P–C6H4–Si), 137.64
(1C, o-C, P–C6H4–Si), 136.50 (1C, p-C, P–C6H4–Si), 134.27(1C, o-C,
P–C6H4–Si), 134.00 (2C, P–C, P–C6H5), 133.84 (4C, o-C, P–C6H5),
128.91(1C, m-C, P–C6H4–Si), 128.72 (4C, m-C, P–C6H5), 128.20 (2C,
p-C, P–C6H5), À0.86 (3C, CH3). 29Si NMR (CDCl3, δ, ppm): À3.60. 31
P
NMR (CDCl3, δ, ppm): À4.64. IR (cmÀ1): 698 (P–Ph), 743 (P–Ph),
751 (Si–C), 837 (Si–C), 1437 (Ar–Si), 2863 (CH3), 3050 (Ph). MS:
334.21 (M+). Anal. Calcd for 1b (C21H23PSi) (%): C, 75.41; H, 6.93.
Found (%): C, 75.43; H, 6.93.
Diphenyl(4-triethylsilylphenyl)phosphine (1 g). [10] Yield 0.84 g (45%). 1H
NMR (CDCl3, δ, ppm): 7.57–7.26 (m, 4H, P–C6H4–Si; 10H, C6H5–P),
0.98 (t, J = 7.4 Hz, 9H, CH3), 0.86 (q, J = 7.4 Hz, 6H, CH2), due to over-
lapping of signals, the proton assignments are listed without dis-
tinct identification. 13C NMR (CDCl3, δ, ppm): 138.21 (1C, p-C,
P–C6H4–Si), 137.48 (1C, P–C, P–C6H4–Si), 137.10 (2C, m-C, P–C6H4–
Si), 134.28 (2C, o-C, P–C6H4–Si), 133.89 (2C, P–C, C6H5–P), 132.73
(4C, o-C, C6H5–P), 128.80 (4C, m-C, C6H5–P), 128.54 (2C, p-C, C6H5–
P), 7.49 (3C, CH3), 3.35 (3C, CH2). 29Si NMR (CDCl3, δ, ppm): 2.02.
31P NMR (CDCl3, δ, ppm): À5.02. IR (cmÀ1): 696 (P–Ph), 744 (P–Ph),
809 (Si–C), 1434 (Ar–Si), 2873 (CH3), 2933 (CH2), 2952 (CH3), 3052
(Ph). MS: 376.15 (M+). Anal. Calcd for 1 g (C24H29PSi) (%): C, 76.55;
H, 7.76. Found (%): C, 76.54; H, 7.76.
Diphenyl(4-trimethylsilylphenyl)phosphine (1c). Yield 0.9 g (54%). 1H
NMR (CDCl3, δ, ppm): 7.54 (dd, J = 7.8, 1.4 Hz, 2H, P–C6H4–Si),
7.38–7.36 (m, 10H, P–C6H5), 7.33 (dd, J = 1.4, 7.8 Hz, 2H, P–C6H4–
Si), 0.31 (s, 9H, Si–CH3), due to overlapping of signals, the proton as-
signments are listed without distinct identification. 13C NMR (CDCl3,
δ, ppm): 141.15 (1C, p-C, P–C6H4–Si), 137.12 (1C, P–C, P–C6H4–Si),
133.95 (2C, P–C, P–C6H5), 133.76 (2C, m-C, P–C6H4–Si), 133.46 (2C,
o-C, P–C6H4–Si), 132.92 (4C, o-C, P–C6H5), 128.83 (4C, m-C, P–C6H5),
128.58 (2C, p-C, P–C6H5), À1.05 (3C, CH3). 29Si NMR (CDCl3, δ,
ppm): À3.82. 31P NMR (CDCl3, δ, ppm): À4.93. IR (cmÀ1): 699 (P–
Ph), 741 (P–Ph), 758 (Si–C), 831 (Si–C), 1435 (Ar–Si), 2858 (CH3),
3058 (Ph). MS: 334.21 (M+). Anal. Calcd for 1c (C21H23PSi) (%): C,
75.41; H, 6.93. Found (%): C, 75.42; H, 6.94.
Diphenyl(2-triethoxysilylphenyl)phosphine (1 h; Scheme 4)
A 100 ml three-necked flask equipped with a magnetic stir bar, a
rubber septum and a reflux condenser was charged with NaOAc
(1.30 g, 15.8 mmol) and Pd(OAc)2 (17.5 mg, 0.07 mmol) and was
evacuated and refilled with argon three times before adding N,N-
dimethylacetamide (35 ml), 1-bromo-2-iodobenzene (2.50 ml,
19.5 mmol) and diphenylphosphine (2.5 ml, 19.5 mmol). The reac-
tion mixture was stirred at 130 °C for three days. The reaction mix-
ture was cooled to room temperature and diluted with water
(30 ml) and extracted with CHCl3 (20 ml × 3). The combined organic
extracts were dried over Na2SO4. The filtrate was concentrated in
vacuo, and purified by recrystallization from ethanol to give a yel-
low solid. Further purification was done using flash chromatogra-
phy (1:2 EtOAc–hexane) to yield a white precipitate of (2-
bromophenyl)diphenylphosphine in 92% yield.
An oven-dried 100 ml Schlenk tube equipped with a magnetic
stir bar was evacuated and refilled with argon three times before
adding a solution of (2-bromophenyl)diphenylphosphine (0.78 ml,
6.1 mmol) in THF (30 ml) under argon atmosphere. The reaction
Schlenk tube was cooled to À78 °C and a solution of n-BuLi in hex-
ane (1.6 M, 6.1 mmol) was added dropwise slowly. After the addi-
tion was complete, the reaction mixture was stirred at the same
temperature for 1 h. The reaction mixture was quenched with Si
(OEt)4 (3.10 ml, 6.7 mmol) at À78 °C. The resulting mixture was
gradually warmed to ambient temperature for 4 h. The mixture
Diphenyl(3-dimethylphenylsilylphenyl)phosphine (1d). Yield 1.01 g (51%).
1H NMR (CDCl3, δ, ppm): 7.71–7.69 (m, 1H, P–C6H4–Si), 7.59–7.43 (m,
3H, P–C6H4–Si; 10H, P–C6H5; 5H, C6H5–Si), 0.61 (s, 6H, Si–CH3), due to
overlapping of signals, the proton assignments are listed without
distinct identification. 13C NMR (CDCl3, δ, ppm): 139.95 (1C, o-C,
P–C6H4–Si), 138.04 (1C, o-C, P–C6H4–Si), 134.68 (2C, P–C, P–C6H5),
134.48 (4C, o-C, P–C6H5), 134.24 (1C, P–C, P–C6H4–Si), 134.24 (1C,
m-C, P–C6H4–Si), 133.95 (1C, Si–C, Si–C6H5), 133.76 (1C, p-C,
P–C6H4–Si), 129.28 (2C, o-C, Si–C6H5), 128.85 (1C, p-C, Si–C6H5),
128.63 (2C, p-C, P–C6H5), 128.56 (4C, m-C, P–C6H5), 128.14 (2C, m-
C, Si–C6H5), 127.99 (1C, m-C, P–C6H4–Si), À2.31 (2C, CH3). 29Si NMR
(CDCl3, δ, ppm): À7.80. 31P NMR (CDCl3, δ, ppm): À4.77. IR (cmÀ1):
698 (P–Ph), 743 (P–Ph), 751 (Si–C), 837 (Si–C), 1428 (Ph–Si), 1437
(Ar–Si), 2863 (CH3), 3050 (Ph). MS: 396.15 (M+). Anal. Calcd for 1d
(C26H25PSi) (%): C, 78.75; H, 6.35. Found (%): C, 78.73; H, 6.35.
Diphenyl(4-dimethylphenylsilylphenyl)phosphine (1e). Yield 1.29 g (65%).
1H NMR (CDCl3, δ, ppm): 7.88–7.86 (m, 2H, P–C6H4–Si), 7.59–7.24 (m,
2H, P–C6H4–Si; 10H, P–C6H5; 5H, C6H5–Si), 0.66 (s, 6H, Si–CH3), due to
overlapping of signals, the proton assignments are listed without
distinct identification. 13C NMR (CDCl3, δ, ppm): 139.91 (1C, P–C,
P–C6H4–Si), 137.45 (2C, P–C, P–C6H5), 137.14 (4C, o-C, P–C6H5),
135.65 (2C, o-C, P–C6H4–Si), 135.48 (1C, p-C, P–C6H4–Si), 134.95
(1C, Si–C, Si–C6H5), 133.71 (2C, m-C, P–C6H4–Si), 133.12 (2C, o-C,
Si–C6H5), 130.14 (1C, p-C, Si–C6H5), 129.26 (2C, p-C, P–C6H5), 128.54
(4C, m-C, P–C6H5), 128.04 (2C, m-C, Si–C6H5), À1.51 (2C, CH3). 29Si
NMR (CDCl3, δ, ppm): À7.96. 31P NMR (CDCl3, δ, ppm): À4.98. IR
(cmÀ1): 694 (P–Ph), 735 (P–Ph), 749 (Si–C), 827 (Si–C), 1421 (Ph–
Si), 1439 (Ar–Si), 2872 (CH3), 3062 (Ph). MS: 396.15 (M+). Anal. Calcd
for 1e (C26H25PSi) (%): C, 78.75; H, 6.35. Found (%): C, 78.74; H, 6.35.
Scheme 4. Synthesis of 1 h.
Appl. Organometal. Chem. (2016)
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Li J. et al.
Tri(4-trimethylsilylphenyl)phosphine (2b; Scheme 5)[32–34]
was quenched with water and extracted with Et2O (30 ml). The
combined organic layers were dried over magnesium sulfate, fil-
tered and evaporated under reduced pressure to afford 1 h as a col-
orless liquid. The crude product was purified by silica gel column
chromatography (5% EtOAc–hexanes) to afford 1 h as a colorless
liquid.
A solution of 1-bromo-4-(trimethlsilyl)benzene (15 mmol) in Et2O
(30 ml) was added slowly to a solution of n-BuLi (2.5 M in hexane,
5 mmol) in 15 ml of hexane at À78 °C. The resulting mixture was
stirred for 2 h at À78 °C followed by the addition of a solution of
trichlorophosphine (0.84 ml, 5.0 mmol) and then allowed to warm
to room temperature. After stirring overnight, the reaction mixture
was quenched with water and extracted by CH2Cl2. The organic
phases were dried over Na2SO4 and evaporated in vacuum. The
crude product was purified by silica gel column chromatography
(5% EtOAc–hexanes) to afford 2b as a colorless viscous oil.
Yield 1.53 g (59%). 1H NMR (CDCl3, δ, ppm): 8.25 (d, J = 4 Hz, 1H,
P–C6H4–Si), 7.40–6.96 (m, 10H, C6H5–P; 3H, P–C6H4–Si), 3.57(q,
J = 8 Hz, 6H, O–CH2), 1.28 (t, J = 8 Hz, 9H, CH3), due to overlapping
of signals, the proton assignments are listed without distinct identi-
fication. 13C NMR (CDCl3, δ, ppm): 143.67 (1C, P–C, P–C6H4–Si),
143.11 (1C, o-C, P–C6H4–Si), 138.53 (2C, P–C, C6H5–P), 138.28 (4C,
o-C, C6H5–P), 134.47 (1C, o-C, P–C6H4–Si), 133.27 (1C, m-C, P–C6H4–
Si), 129.87 (1C, m-C, P–C6H4–Si), 128.05 (2C, p-C, C6H5–P), 127.99
(1C, p-C, P–C6H4–Si), 127.83 (4C, m-C, C6H5–P), 58.53 (3C, O–CH2),
17.91 (3C, CH3). 29Si NMR (CDCl3, δ, ppm): À36.16. 31P NMR (CDCl3,
δ, ppm): À9.35. IR (cmÀ1): 692 (P–Ph), 740 (P–Ph), 1129 (Si–O–C),
1430 (Ar–Si), 2857 (CH3), 3046 (Ph). MS: 424.16 (M+). Anal. Calcd
for 1 h (C24H29O3PSi) (%): C, 67.90; H, 6.89; O, 11.31. Found (%): C,
67.91; H, 6.88; O, 11.30.
Yield 1.53 g (64%). 1H NMR (CDCl3, δ, ppm): 7.52–7.51 (d, J = 4 Hz,
6H, P–C6H4–Si), 7.33–7.36 (m, 6H, P–C6H4–Si), 0.30 (s, 27H, Si–CH3),
due to overlapping of signals, the proton assignments are listed
without distinct identification. 13C NMR (CDCl3, δ, ppm): 141.16
(3C, p-C, P–C6H4–Si), 133.41 (3C, P–C, P–C6H4–Si), 133.05 (6C, o-C,
P–C6H4–Si), 132.86 (6C, m-C, P–C6H4–Si), À1.15 (9C, CH3). 29Si NMR
(CDCl3, δ, ppm): À3.86. 31P NMR (CDCl3, δ, ppm): À5.75. IR (cmÀ1):
681 (P–Ph), 745 (P–Ph), 768 (Si–C), 857 (Si–C), 1445 (Ar–Si), 2861
(CH3), 3059 (Ph). MS: 478.21 (M+). Anal. Calcd for 2b (C27H39PSi3)
(%): C, 67.73; H, 8.21. Found (%): C, 67.72; H, 8.20.
Phenyldi(4-trimethylsilylphenyl)phosphine (2a; Scheme 5)
A solution of 1-bromo-4-(trimethlsilyl)benzene (10 mmol) in Et2O
(30 ml) was added slowly to a solution of n-BuLi (2.5 M in hexane,
5 mmol) in 15 ml of hexane at À78 °C. The resulting mixture was
stirred at À78 °C followed by the addition of a solution of
dichlorophenylphosphine (0.86 ml, 5.0 mmol) for 2 h and then
allowed to warm to room temperature. After stirring overnight,
the reaction mixture was quenched with water and extracted with
CH2Cl2. The organic phases were dried over Na2SO4 and evaporated
in vacuum. The crude product was purified by silica gel column
chromatography (5% EtOAc–hexanes) to afford 2a as a colorless
viscous oil.
Yield 1.52 g (75%). 1H NMR (CDCl3, δ, ppm): 7.50–7.48 (m, 4H, P–
C6H4–Si), 7.35–7.17 (m, 5H, P–C6H5; m, 4H, P–C6H4–Si), 0.28 (s, 18H,
Si–CH3), due to overlapping of signals, the proton assignments
are listed without distinct identification. 13C NMR (CDCl3, δ, ppm):
136.56 (2C, p-C, P–C6H4–Si), 135.42 (2C, P–C, P–C6H4–Si), 133.89
(1C, P–C, P–C6H5), 133.57 (4C, m-C, P–C6H4–Si), 133.50 (4C, o-C,
P–C6H4–Si), 132.73 (2C, o-C, P–C6H5), 129.03 (2C, m-C, P–C6H5),
128.71 (1C, p-C, P–C6H5), À1.13 (6C, CH3). 29Si NMR (CDCl3, δ,
ppm): À3.78. 31P NMR (CDCl3, δ, ppm): À6.15. IR (cmÀ1): 687 (P–
Ph), 736 (P–Ph), 763 (Si–C), 845 (Si–C), 1442 (Ar–Si), 2867 (CH3),
3061 (Ph). MS: 406.17 (M+). Anal. Calcd for 2a (C24H31PSi2) (%): C,
70.89; H, 7.68. Found (%): C, 70.88; H, 7.69.
Scheme 6. Hydrosilylation reaction of alkenes catalyzed by rhodium
complex.
Table 1. Effect of silylated triarylphosphine ligands on rhodium-cata-
lyzed hydrosilylation reactiona
Entry Ligand Conv. (%)
Selectivity (%)
β/α
β
α
Unsaturated 1-Ethylbenzene
0
1
PPh3
1a
94.3
95.4
97.7
94.5
92.1
91.7
97.1
93.8
96.8
93.4
92.1
65.9 5.5
84.8 6.2
80.4 8.9
87.4 4.5
83.1 5.4
90.7 3.2
77.5 8.4
83.2 3.8
61.6 4.2
93.7 3.1
92.7 2.4
13.6
—
15.0
9.0
12.0
13.8
9.0
2
1b
1c
—
10.7
8.1
3
—
19.4
15.4
28.3
9.2
4
1d
1e
5.4
3.1
6.4
5.8
9.8
—
6.1
5
3.0
6
1f
7.7
7
1 g
1 h
2a
7.2
21.9
14.7
30.2
38.6
8
24.4
3.2
9
10
2b
—
4.9
aReaction conditions: styrene, 4 mmol; triethoxysilane, 4.4 mmol;
catalyst, RhCl3 (0.2 mol%); ligand, 1.0 mol% based on styrene; 90 °C; 5 h.
Scheme 5. Synthesis of 2a and 2b.
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Effect of silylated triarylphosphine ligands on hydrosilylation
Table 2. Scope of hydrosilylation reactiona
Entry
Alkene
Silane
Conv.
(%)
Selectivity (%)
β
α
Other product
1
2
2-Methylstyrene
3-Methylstyrene
4-Methylstyrene
4-Methoxystyrene
1-Hexene
Triethoxysilane
94.5
92.1
90.4
95.6
94.5
92.7
100
93.1
92.9
2.9
1.8
2.4
1.3
—
4.0
5.3
3.7
5.1
—
3
93.9
4
93.6
5b
6b
7
>99.9
99.9
1-Octene
—
—
Styrene
Triethylsilane
66.5
1.2
32.3 (21.6 unsaturated +10.7 ethylbenzene)
aReaction conditions: alkene: 4 mmol; sliane: 4.4 mmol; catalyst: RhCl3 (0.2 mol%); 2a (1.0 mol% based on alkene); 90 °C; 5 h.
bRhCl3: 0.02 mol%; 2a: 0.1% mol based on alkene. Other product: alkane.
Catalytic hydrosilylation of alkene with triethoxysilane
(Scheme 6)
derivatives both promoted the hydrosilylation process and im-
proved the selectivity for the β-product (Table 1). The results indi-
cated that the silyl moieties attached to the triarylphosphine
exerted a strong influence on the catalytic process. When RhCl3
was mixed with 1a, or 1b, or 1c, no unsaturated product was ob-
tained. RhCl3–1b exhibited the highest conversion, whereas
RhCl3–1c exhibited the highest selectivity for the β-product. When
RhCl3 was mixed with 1c, or 1e, or 1g, RhCl3–1c exhibited the
highest conversion, whereas RhCl3–1g exhibited the highest se-
lectivity for the β-product. The results demonstrated that the
dual electronic and steric effects of the silylated phosphine li-
gands seemingly influence the Rh catalysis. The effect of steric
hindrance may be greater than that of the electronic properties,
and the selectivity for the β-adduct increased with increasing ste-
ric hindrance of the alkyl chain. Especially when 2a and 2b were
used as ligands, the catalytic activity was high, the selectivity for
the β-product was maximized and no unsaturated product was
obtained. RhCl3–1h gave higher conversion, but low selectivity
for the β-product and the highest selectivity for the unsaturated
product.
A 10 ml three-necked flask equipped with a magnetic stirrer was
charged with RhCl3Á3H2O (8.0 × 10À3 mmol) and silylated
triarylphosphine (4.0 × 10À2 mmol) prepared under argon atmo-
sphere. Then the alkene (4 mmol) and silane (4.87 mmol) were
added via syringe. The hydrosilylation reaction proceeded with
constant stirring under an appropriate temperature for 5 h. At the
end of the reaction, the conversion of alkene and the selectivity
were determined using GC. All data in the tables are average values
of three experiments. The spectroscopic data (1H NMR, 13C NMR,
29Si NMR) and elemental analysis data of the prepared compounds
were in agreement with the assigned structures and with those
found in the literature.[10]
Results and discussion
Synthesis of various silylated phosphine ligands
The efficient synthetic routes to the silylated triarylphosphines are
shown in Schemes 1–5. Ligand 1a was synthesized by the reaction
of (2-bromophenyl)diphenylphosphine with chlorotrimethylsilane.
Interestingly, 1g could not be obtained by the reaction of
(4-bromophenyl)diphenylphosphine with chlorotriethylsilane.
(4-Bromophenyl)triethylsilane was obtained by the reaction of
1-bromo-4-iodobenzene with chlorotriethylsilane, and then 1g
was synthesized by the reaction of (4-bromophenyl)triethylsilane
with chlorodiphenylphosphine. Unfortunately, diphenyl(2-
Scope of hydrosilylation reaction
Having established the optimal conditions, we proceeded to inves-
tigate hydrosilylation reactions of other alkenes with triethoxysilane
(Table 2). With 2-methylstyrene, 3-methylstyrene, 4-methylstyrene,
3-methoxystyrene, 1-hexene or 1-octene in place of styrene, excel-
lent conversions and selectivities were obtained with RhCl3–2b as
the catalytic system. However, when triethylsilane was used in
place of triethoxysilane, high selectivity for the unsaturated product
was obtained. This may be because triethylsilane has stronger re-
ducibility than triethoxysilane.
dimethylphenylsilylphenyl)phosphine
and
diphenyl(2-
triethylsilylphenyl)phosphine could not be obtained by methods
akin to those described above. It is possible that the steric and elec-
tronic properties of the substituents on the silicon moieties have a
significant impact on the syntheses of silylated triarylphosphines.
The ten products (1a–1h, 2a, 2b) were characterized using NMR
and IR spectroscopies, elemental analysis and MS, and the obtained
data were consistent with the assigned structures.
Conclusions
In summary, a series of silylated triarylphosphines (1a–1h, 2a, 2b)
has been synthesized. Hydrosilylation reactions of styrene with
triethoxysilane catalyzed by RhCl3/silylated triarylphosphine com-
plexes have been investigated. RhCl3 combined with 2a and RhCl3
combine with 2b exhibited higher activities as well as greater selec-
tivities for the β-adduct, and no unsaturated product was obtained.
The results suggest that the silyl moieties have a significant impact
on the catalytic process.
Effect of ligands on hydrosilylation reaction
The catalytic properties of RhCl3/silylated triarylphosphine com-
plexes in the hydrosilylation of styrene with triethoxysilane were
investigated, and the results are listed in Table 1. RhCl3–PPh3 gave
low selectivity for the β-product. Comparing these silylated
triarylphosphine ligands with PPh3, it was found that the silylated
Appl. Organometal. Chem. (2016)
Copyright © 2016 John Wiley & Sons, Ltd.
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Li J. et al.
[16] B. M. Trost, Z. T. Ball, J. Am. Chem. Soc. 2001, 123, 12726.
Acknowledgements
[17] A. Onopchenko, E. T. Sabourin, J. Chem. Eng. Data 1988, 33, 64.
[18] M. Xue, J. Li, J. Peng, Y. Bai, F. Chen, W. Xiao, G. Lai, Hangzhou Shifan
Daxue Xuebao. Ziran Kexueban 2014, 13, 1.
[19] A. Ochida, M. Sawamura, Chem. Asian. J. 2007, 2, 609.
[20] C. Reyes, A. Prock, W. P. Giering, J. Organometal. Chem. 2003, 671, 13.
[21] J. H. Kirchhoff, C. Dai, G. C. Fu, Angew. Chem. Int. Ed. 2002, 41, 1945.
[22] A. F. Littke, G. C. Fu, Angew. Chem. Int. Ed. 2002, 41, 4176.
[23] N. Kataoka, Q. Shelby, J. P. Stambuli, J. F. Hartwig, J. Org. Chem. 2002, 67,
5553.
[24] S. D. Walker, T. E. Barder, J. R. Martinelli, S. L. Buchwald, Angew. Chem.
Int. Ed. 2004, 43, 1871.
[25] L. K. Knight, Z. Freixa, P. W. N. M. van Leeuwen, J. N. H. Reek,
Organometallics 2006, 25, 954.
[26] Z. Liu, H. Du, Org. Lett. 2010, 12, 3054.
[27] L. Mei, Z. Yuan, M. Shi, Organometallics 2011, 30, 6466.
[28] D. Hou, K. Burgess, Org. Lett. 1999, 1, 1745.
[29] Y. Liu, Z. Cao, H. Du, J. Org. Chem. 2012, 77, 4479.
[30] O. Niyomura, T. Iwasawa, N. Sawada, M. Tokunaga, Y. Obora, Y. Tsuji,
Organometallics 2005, 24, 3468.
[31] A. Kawachi, T. Yoshioka, Y. Yamamoto, Organometallics 2006, 25, 2390.
[32] A. F. Ferris, K. W. McLean, I. G. Marks, W. D. Emmons, J. Am. Chem. Soc.
1953, 75, 4078.
We are grateful to the National Natural Science Foundation of China
(21203049, 21303034) and the Fund of Zhejiang Province
(LY14B030007) for financial support.
References
[1] D. D. Díaz, S. S. Gupta, J. Kuzelka, M. Cymborowski, M. Sabat, M. G. Finn,
Eur. J. Inorg. Chem. 2006, 22, 4489.
[2] K. A. Newlander, B. Chenera, D. F. Veber, N. C. F. Yim, M. L. Moore, J. Org.
Chem. 1997, 62, 6726.
[3] T. Ruhland, S. D. Nielsen, P. Holm, C. H. Christensen, J. Comb. Chem.
2007, 9, 301.
[4] T. Y. S. But, P. H. Toy, Chem. Asian. J. 2007, 2, 1340.
[5] G. Wittig, U. Schollkopf, Chem. Ber. 1954, 87, 1318.
[6] M. Mikołajczyk, W. Perlikowska, J. Omelańczuk, H. J. Cristau,
A. Perraud-Darcy, J. Org. Chem. 1998, 63, 9716.
[7] R. Robiette, J. Richardson, V. K. Aggarwal, J. N. Harvey, J. Am. Chem. Soc.
2006, 128, 2394.
[8] Y. H. Zhu, F. Yao, L. Lei, G. Q. Xiang, Chin. J. Org. Chem. 2007, 27, 545.
[9] P. Kočovský, A. V. Malkov, Chem. Eur. J. 2012, 18, 6873.
[10] M. Xue, J. Li, J. Peng, Y. Bai, G. Zhang, W. Xiao, G. Lai, Appl. Organometal.
Chem. 2014, 28, 120.
[33] S. O. Grim, A. W. Yankowsky, Phosphorus Sulfur 1977, 3, 191.
[34] M. A. Weiner, M. Lattman, S. O. Grim, J. Org. Chem. 1975, 40, 1292.
[11] J. Li, J. Peng, Y. Bai, G. Zhang, W. Xiao, G. Lai, X. Li, J. Organometal. Chem.
2010, 695, 413.
Supporting information
[12] J. Yang, X. Chen, Z. Wang, Tetrahedron Lett. 2015, 56, 5673.
[13] A. Khalafi-Nezhad, F. Panahi, J. Organometal. Chem. 2013, 741, 7.
[14] D. Lu, G. Salem, Coord. Chem. Rev. 2013, 257, 1026.
[15] N. Fey, A. G. Orpen, J. N. Harvey, Coord. Chem. Rev. 2009, 253, 704.
Additional supporting information may be found in the online ver-
sion of this article at the publisher’s web site.
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