Effect of triarylphosphane ligands on the rhodium-catalyzed hydrosilylation of alkene

Article abstract of DOI:10.1002/aoc.3092

A series of triarylphosphanes (1a, 2a, 3a, 4a, 5a, 6a, 7a, 8a, 9a, 10a, 11a) have been synthesized. An X-ray crystal structure analysis of (2-bromophenyl)diphenylphosphane (1a) unambiguously confirmed the constitution of the functionalized phosphane. The hydrosilylation reaction of styrene with triethoxysilane catalyzed with RhCl₃/triarylphosphane was studied. In comparison with the classic Wilkinson's catalyst, rhodium complexes with functionalized triarylphosphane ligands are characterized by a very high catalytic effectiveness for the hydrosilylation of alkene. Among these catalysts tested, RhCl₃/diphenyl(2-(trimethylsilyl)phenyl)phosphane (8a) exhibited excellent catalytic properties. Using this silicon-containing phosphane ligand for the rhodium-catalyzed hydrosilylation of styrene, both higher conversion of alkene and higher β-adduct selectivity were obtained than with Wilkinson's catalyst.

Full text of DOI:10.1002/aoc.3092

Full Paper
Received: 15 September 2013
Revised: 14 October 2013
Accepted: 14 October 2013
Published online in Wiley Online Library: 15 January 2014
(wileyonlinelibrary.com) DOI 10.1002/aoc.3092
Effect of triarylphosphane ligands on the
rhodium-catalyzed hydrosilylation of alkene
Mei Xue, Jiayun Li*, Jiajian Peng*, Ying Bai, Guodong Zhang,
Wenjun Xiao and Guoqiao Lai
A series of triarylphosphanes (1a–11a) have been synthesized. An X-ray crystal structure analysis of (2-bromophenyl)
diphenylphosphane (1a) unambiguously confirmed the constitution of the functionalized phosphane. The hydrosilylation re-
action of styrene with triethoxysilane catalyzed with RhCl3/triarylphosphane was studied. In comparison with the classic
Wilkinson’s catalyst, rhodium complexes with functionalized triarylphosphane ligands are characterized by a very high cata-
lytic effectiveness for the hydrosilylation of alkene. Among these catalysts tested, RhCl3/diphenyl(2-(trimethylsilyl)phenyl)
phosphane (8a) exhibited excellent catalytic properties. Using this silicon-containing phosphane ligand for the rhodium-
catalyzed hydrosilylation of styrene, both higher conversion of alkene and higher β-adduct selectivity were obtained than
with Wilkinson’s catalyst. Copyright © 2014 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web site.
Keywords: triarylphosphane; hydrosilylation; rhodium complex; alkene
to promote the metal in the form of stable species that can sub-
Introduction
sequently enter the catalytic cycle and prevent the production of
inactive metal aggregates.[22–25] However, Rh(PPh3)3Cl displayed
Phosphorus ligands are an important class of ligands in transition
metal catalysis reactions. In particular, triarylphosphanes
possessing functional groups, which can be easily attached to
organic compounds, have widely used applications. Numerous
catalytic reactions, such as Wittig ylide formation,[1–3] Mukaiyama
redox condensations[4] and Mitsunobu reactions,[5–7] have been
intensively developed along with thorough research into transi-
tion metal complexes coordinated with phosphorus ligands.[8,9]
Generally, geometric, steric and electronic properties of the
ligand including phosphane are important to the catalytic activity
and selectivity of the corresponding metal complex. Recently,
Niyomura[10] reported that a bulky bowl-shaped phosphane
ligand markedly improved the catalytic activity of rhodium-
catalyzed hydrosilylation reactions as compared with that of
conventional phosphane ligands such as PPh3 and PtBu3. Another
novel bulky phosphane ligand containing an alkyne group also
exhibited excellent catalytic properties for the rhodium-catalyzed
hydrosilylation of ketones.[11] By using a bulky ligand, resultant
rhodium complex bearing only one phosphane ligand was formed.
On the other hand, for phosphane-based ligands, the electronic
properties, which were highly influenced by modification of the
substituents attached to phosphane, are also important for the
catalytic properties of corresponding metal complexes.
low catalytic activity and selectivity in the hydrosilylation of
substituted alkenes.[18] In this paper, we now report a series of
triarylphosphane-based ligands (Scheme 1). Also, the catalytic
properties of rhodium complexes coordinated with these
triarylphosphane-based ligands with different substituents on
phosphane have been compared to classic Wilkinson’s catalyst.
Experimental
General Remarks
Styrene was washed with 5% NaOH and dried with Na2SO4, and was
then distilled under reduced pressure after filtration. All materials
were purchased from Aldrich and were used as received.
Gas chromatography: 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 (held for
1 min) then 15 °CminÀ1 up to 260°C (held for 10 min). GC-MS: Trace
DSQ GC-MS column.
Hydrosilylation is one of the most significant reactions for Si–C
bond formation in organosilicon chemistry.[12,13] Although a wide
range of catalysts have been tested for hydrosilylation, industrial
syntheses and most research studies have been carried out in the
presence of platinum complexes or rhodium complexes.[14–17]
It has been reported that Wilkinson’s catalyst, Rh(PPh3)3Cl,
effectively catalyzes the hydrosilylation of alkynes or alkenes.[18]
In this catalytic process, phosphane ligands play a significant role
in hydrosilylation.[19–21] The chief role of the phosphane ligands is
*
Correspondence to: Jiayun Li and Jiajian Peng, Key Laboratory of Organosilicon
Chemistry and Material Technology of Ministry of Education, Hangzhou Normal
University, Hangzhou 310012, China. Email: tougaos@hotmail.com
Key Laboratory of Organosilicon Chemistry and Material Technology of Minis-
try of Education, Hangzhou Normal University, Hangzhou 310012, China
The copyright line for this article was changed on 4 July 2014 after original
online publication.
Appl. Organometal. Chem. 2014, 28, 120–126
Copyright © 2014 John Wiley & Sons, Ltd.

Rhodium-catalyzed hydrosilylation of styrene
cooled to À78 °C and a solution of n-BuLi in hexane (1.6M, 6.5 mmol)
was added dropwise slowly. When the addition was complete, the
reaction mixture was stirred at the same temperature for 1 h. The
reaction mixture was quenched with chlorodiphenylphosphine
(1.10 ml, 6.1 mmol) 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 × 3). The com-
bined organic layers were dried over magnesium sulfate, filtered
and evaporated under reduced pressure. The residue was purified
by flash chromatography with hexane to yield 2a as a colorless
Scheme 1. Structures of triarylphosphane ligands. 1a: X = o-Br; 2a:
X = m-Br; 3a: X = p-Br; 4a: X = o-NH3; 5a: X = p-NH3; 6a: X = p-COOH; 7a:
X = o-Bu; 8a: X = o-SiMe3; 9a: X = p-SiEt3; 10a: X = o-Me; 11a: X = o-OMe.
1H, 13C, 29Si and 31P NMR spectra were measured using a
Bruker AV 400 MHz spectrometer operating at 400.13, 100.62,
79.49 and 161.97 MHz, respectively.
IR spectra were recorded on a Nicolet 5700 instrument and
elemental analyses were performed on a Vario EL-3 elemental
analyzer.
1
viscous oil; 74% yield. H NMR (CDCl3) δ: 7.73–7.68 (m, 1H, p-H,
P–C6H4–Br), 7.61–7.58 (m, 1H, m-H, P–C6H4–Br), 7.54 (m, 4H, m-H,
C6H5–P), 7.51–7.44 (m, 2H, p-H, C6H5–P; 4H, o-H, C6H5–P),
7.44–7.38 (m, 1H, m-H, P–C6H4–Br), 7.27 (m, 1H, o-H, P–C6H4-Br),
due to overlapping of signals, the proton assignment was
listed without distinct identification. 13C NMR (CDCl3) δ: 140.98
(J = 20.2 Hz, 1C, P–C, P–C6H4–Br), 136.66 (J = 10.8 Hz, 1C, o-C,
P–C6H4-Br), 136.28 (J= 20.2Hz, 2C, P–C, C6H5-P), 134.09 (J= 10.8Hz,
1C, o-C, P–C6H4–Br), 132.38 (1C, p-C, P–C6H4–Br), 131.96 (J= 10.8 Hz,
4C, o-C, C6H5–P), 130.35 (J= 6.5Hz, 1C, m-C, P–C6H4–Br), 129.36
(J= 6.5Hz, 4C, m-C, C6H5–P), 128.99 (2C, p-C, C6H5–P), 123.50
(J= 6.5Hz, 1C, m-C, P–C6H4–Br). 31P NMR (CDCl3) δ: À3.97. IR
(cmÀ1): 696 (P–Ph), 742 (P–Ph), 781 (m-Ph), 1476 (Ph), 1552 (Ph),
3070 (Ph). MS: 340.08 (M+). Anal. Calc. for 2a (C18H14BrP): C, 63.37;
H, 4.14. Found: C, 63.38; H, 4.15.
Synthesis of Triarylphosphane Ligands
Synthesis of (2-bromophenyl)diphenylphosphane 1a
A 100 ml three-necked flask equipped with a magnetic stir bar,
rubber septum and 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 3 days. The reaction mixture
was cooled to room temperature and diluted with water (30 ml)
and extracted with CHCl3 (20 ml × 3 ). The combined organic
extracts were dried using anhydrous Na2SO4. The filtrate was
concentrated in vacuo and purified by recrystallization in ethanol
to give a yellow solid. Further purification was done using flash
chromatography (1:2 EtOAc–hexane) to yield a white precipitate
Synthesis of (4-bromophenyl)diphenylphosphane 3a
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 (0.78 ml,
6.1 mmol) in Et2O (30 ml) under argon atmosphere. The reaction
Schlenk tube was cooled to À78 °C and a solution of n-BuLi
in hexane (1.6 M, 6.5 mmol) was added dropwise slowly. When
the addition was complete, the reaction mixture was stirred
at same temperature for 1 h. The reaction mixture was
quenched with chlorodiphenylphosphine (1.10 mL, 6.1 mmol)
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 × 3). The combined
organic layers were dried over magnesium sulfate, filtered
and evaporated under reduced pressure. The solution was
concentrated in vacuo, and the residue was purified by flash
chromatography with hexane to yield 3a as a white solid;
76% yield. These data of 1H, 13C, 29Si and 31P NMR spectra, IR
spectra and MS were consistent with those reported in the
literature.[30–32] See Scheme 2.
1
1a, 92% yield. The data of H, 13C, 29Si and 31P NMR spectra, IR
spectra and MS were consistent with those reported in the
literature (Fig. 1).[26–29]
Synthesis of (3-bromophenyl)diphenylphosphane 2a
A 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-3-iodobenzene (0.78 ml, 6.1 mmol) in Et2O
(30 ml) under argon atmosphere. The reaction Schlenk tube was
Synthesis of (2-aminophenyl)diphenylphosphane 4a
An oven-dried, 25 ml three-necked flask equipped with a
magnetic stir bar, rubber septum and reflux condenser was
charged with CuI (78 mg, 0.41 mmol), followed by anhydrous
toluene (0.887 ml), diphenylphosphine (1.42 ml, 8.2 mmol) and
N,N-dimethylethylenediamine (0.3 ml, 2.87 mmol) under Ar.
After 10–15 min of stirring, the 2-iodoaniline (1.80 g, 8.2 mmol)
and Cs2CO3 (513 mg, 1.64 mmol) were added at once, followed
by anhydrous toluene (1.15 ml) under Ar. The reaction mixture
was heated at 110 °C for 35 h, The resulting mixture from
the completed reaction was cooled to room temperature,
diluted with water (20 ml) and extracted with ethyl acetate
(40 ml × 4). The combined organic extracts were concentrated
in vacuo and purified by flash chromatography with EtOAc–
hexane (5% EtOAc–hexane) to yield 4a as a yellow solid;
Figure 1. Molecular structure of 1a drawn with 30% probability dis-
placement ellipsoids.
Appl. Organometal. Chem. 2014, 28, 120–126
Copyright © 2014 John Wiley & Sons, Ltd.
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M. Xue et al.
(10 mmol, 1.75 ml) and acetonitrile (30 ml). After the mixture was
refluxed at 95 °C for 40h, the reaction mixture was concentrated
in vacuo to give a light-yellow solid. The solid was dissolved in
0.1 N NaOH solution (60 ml) and the solution was extracted with
diethyl ether (10 ml× 3). On acidifying the aqueous phase with
3
N HCl, phosphane 6a was precipitated as a cream-colored
solid, then filtered and dried in vacuo; 50% yield. The data of
1H, 13C, 29Si and 31P NMR spectra, IR spectra and MS were con-
sistent with those reported in the literature.[39–41] See Scheme 4.
Synthesis of (2-butylphenyl)diphenylphosphane 7a
A 100 ml Schlenk tube equipped with a magnetic stir bar was
evacuated and refilled with argon three times before adding a
solution of 1 (1.51 g, 4.44 mmol) in THF (30 ml) under argon atmo-
sphere. The Schlenk tube was cooled to À78 °C and a solution of
n-BuLi in hexane (1.6 M, 5.33 mmol) was added dropwise slowly.
When the addition was complete, the reaction mixture was
stirred at the same temperature for 1 h. The reaction mixture
was quenched with DMF (0.68 ml, 8.84 mmol) at À78 °C. The
resulting mixture was gradually warmed to ambient temperature
for 2 h, then quenched with water and extracted with ethyl
acetate (30 ml × 3). The combined organic layers were dried over
magnesium sulfate, filtered and evaporated under reduced
pressure. The residue was purified by flash chromatography
with hexane to yield 7a as a white solid; 70% yield; m.p. 44 °C.
1H NMR (CDCl3) δ: 7.40–7.23 (m, 2H, p-H, C6H5–P; 4H, m-H,
C6H5–P; 4H, o-H, C6H5–P; 2H, m-H, P–C6H4–CH2), 7.14–7.07 (m,
1H, p-H, P–C6H4–CH2), 6.93–6.84 (m, 1H, o-H, P–C6H4–CH2),
2.91–2.82 (t, J= 7.3 Hz, 2H, C6H4–CH2CH2CH2CH3), 1.52–1.62 (m,
2H, C6H4–CH2CH2CH2CH3), 1.37–1.27 (m, 2H, C6H4–CH2CH2CH2CH3),
0.84 (t, J = 7.3Hz, 3H, C6H4–CH2CH2CH2CH3); due to overlapping
of signals, the proton assignments were listed without distinct
identification. 13C NMR (CDCl3) δ: 147.59 (J = 10.5 Hz, 1C, o-C,
P-C6H4-C), 136.89 (J = 20.5 Hz, 1C, P–C, P–C6H4–C), 135.09
(J= 10.5 Hz, 1C, o-C, P–C6H4–C), 133.93 (J=20.5Hz, 2C, P–C, C6H5–P),
133.65 (J=10.5Hz, 4C, o-C, C6H5–P), 129.13 (J=6.8Hz, 4C, m-C,
C6H5–P), 129.00 (2C, p-C, C6H5–P), 128.68 (1C, p-C, P–C6H4–C),
128.52 (J=6.8Hz, 1C, m-C, P–C6H4–C), 126.03 (J=6.8Hz, 1C, m-C,
P–C6H4–C), 34.29 (1C, C6H4–CH2CH2CH2CH3), 33.53 (1C, C6H4–
CH2CH2CH2CH3), 22.67 (1C, C6H4–CH2CH2CH2CH3), 13.97 (1C,
C6H4–CH2CH2CH2CH3). 31P NMR (CDCl3) δ: À14.70. IR (cmÀ1): 699
(P–Ph), 742 (P–Ph), 1432 (Ph), 1591 (Ph), 2858 (CH2), 2954 (CH3),
3052 (Ph). MS: 318.08 (M+). Anal. Calc. for 7a (C22H23P): C, 82.99;
H, 7.28. Found: C, 83.00; H, 7.27. See Scheme 5.
Scheme 2. Synthesis of 1a[26–29] to 3a.[30–32]
86%yield. The data of 1H, 13C, 29Si and 31P NMR spectra, IR
spectra and MS were consistent with those reported in
the literature.[33–35]
Synthesis of (4-aminophenyl)diphenylphosphane 5a
An oven-dried, 25 ml three-necked flask equipped with a mag-
netic stir bar, rubber septum and reflux condenser was charged
with CuI (78 mg, 0.41 mmol), followed by anhydrous toluene
(0.887 ml), diphenylphosphine (1.42 ml, 8.2 mmol) and N,N-
dimethylethylenediamine (0.3 ml, 2.87 mmol) under Ar. After stir-
ring for 10–15 min, 4-iodoaniline (1.80 g, 8.2 mmol) and Cs2CO3
(513 mg, 1.64 mmol) were added at once, followed by anhydrous
toluene (1.15 ml) under Ar. The reaction mixture was heated at
110 °C for 35 h. The resulting mixture from the complete reaction
was cooled to room temperature, diluted with water (20 ml) and
extracted with ethyl acetate (40 ml × 4). The combined organic
extracts were concentrated in vacuo, and purified by flash chro-
matography with EtOAc–hexane (5% EtOAc–hexane) to yield 5a
as a colorless viscous oil; 88% yield. The data of 1H, 13C, 29Si
and 31P NMR spectra, IR spectra and MS were consistent with
those reported in the literature.[36–38] See Scheme 3.
Synthesis of 4-diphenylphosphanylbenzoic acid 6a
A 50 ml Schlenk tube equipped with a magnetic stir bar, rubber
septum and reflux condenser was charged with 4-iodobenzoic
acid (10 mmol, 2.48 g) and Pd(OAc)2 (0.05 mmol, 12.5 mg), followed
by distilled triethylamine (10 mmol, 1.4 ml), diphenylphosphine
Synthesis of diphenyl(2-trimethylsilylphenyl)phosphane 8a
1a (3.41 g, 9.99 mmol) was dissolved in degassed Et2O (30 ml)
under argon atmosphere. 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. When the addition was complete, the reaction
mixture was stirred at room temperature for 2 h, then
chlorotrimethylsilane (1.40 ml, 11.1 mmol) was added at 0 °C.
The resulting mixture was gradually warmed to ambient
Scheme 3. Synthesis of 4a[33–35] and 5a.[36–38]
Scheme 4. Synthesis of 6a.[39–41]
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Appl. Organometal. Chem. 2014, 28, 120–126

Rhodium-catalyzed hydrosilylation of styrene
Scheme 5. Synthesis of 7a.
temperature for 3 h and quenched by a saturated aqueous solu-
tion of NH4Cl (30 ml). The mixture was extracted with Et2O
(30 ml × 3). The combined organic layers were dried over magne-
sium sulfate, filtered and evaporated under reduced pressure.
The solution was concentrated in vacuo, and the residue was
subjected to column chromatography on silica gel with hexane
Scheme 7. Synthesis of 9a.
1
(Rf = 0.40) to give 8a as a white solid; 82% yield. The data of H,
13C, 29Si and 31P NMR spectra, IR spectra and MS were consistent
with those reported in the literature.[42] See Scheme 6.
(CH3), 3052 (Ph). MS: 376.15 (M+). Anal. Calc. for 9a (C24H29PSi):
C, 76.55; H, 7.76. Found: C, 76.57; H, 7.76. See Scheme 7.
Synthesis of diphenyl(4-triethylsilylphenyl)phosphane 9a
Synthesis of diphenyl(2-tolyl)phosphane 10a
A 100 ml Schlenk tube equipped with a magnetic stir bar was
evacuated and refilled with argon three times before a solution
of 1-bromo-4-iodobenzene (0.78 ml, 6.1 mmol) in THF (30 ml)
was added under argon atmosphere. The Schlenk tube was
cooled to À78 °C and a solution of n-BuLi in hexane (1.6 M,
6.1 mmol) was added dropwise slowly. After the addition was
complete, the reaction mixture was stirred at the same tempera-
ture for 1 h, and then chlorotriethylsilane (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 × 3). The combined organic
layers were dried over magnesium sulfate, filtered and evapo-
rated under reduced pressure to give 1-bromo-4-(triethylsilyl)
Magnesium turnings (313 mg, 12.8 mmol) and a piece of I2 were
stirred under argon for 2 h and then overlaid with THF (30 ml).
Three drops of 1,2-dibromoethane were added, followed by a
few drops of a solution containing 2-bromotoluene (1.30 ml,
10.8 mmol) in THF (5 ml). Upon starting the reaction the
remaining solution of 2-bromotoluene in THF was added
dropwise. The reaction mixture was heated to reflux until all mag-
nesium was dissolved. A solution of diphenylphosphine chloride
(2.70 ml, 15.0 mmol) in THF (2 ml) was cooled to À78 °C and the
reaction mixture was added dropwise. The reaction mixture was
stirred overnight at room temperature and extracted twice with
saturated aqueous of NaCl and dried over MgSO4. The solvent
was removed under reduced pressure and the crude product
oil treated with EtOH. The formed solid was filtered and washed
with cold ethanol and the supernatant was concentrated and
purified by column chromatography (hexane–EtOAc, 1:0– > 5:1)
to give the title compound 10a as a white solid; 86% yield; m.p.
65 °C. 1H NMR (CDCl3) δ: 7.41–6.81 (m, 1H, p-H, P–C6H4–C; 2H,
m-H, P–C6H4–C; 2H, p-H, C6H5–P; 4H, m-H, C6H5–P; 4H, o-H,
C6H5–P; 1H, o-H, P–C6H4–C), 2.43 (s, 3H, CH3). Due to overlapping
of signals, the proton assignment was listed without distinct
identification. 13C NMR (CDCl3) δ: 142.25 (J = 10.5 Hz, 1C, o-C,
P–C6H4–C), 136.30 (J =19.8 Hz, 1C, P–C, P–C6H4–C), 136.01
(J = 10.5 Hz, 1C, o-C, P–C6H4–C), 134.16 (J =19.8 Hz, 2C, P–C,
C6H5–P), 133.97 (J = 10.5 Hz, 4C, o-C, C6H5–P), 132.79 (J = 6.4 Hz,
4C, m-C, C6H5–P), 130.11 (2C, p-C, C6H5–P), 128.78 (J = 6.4 Hz, 1C,
m-C, P–C6H4–C), 128.61 (1C, p-C, P–C6H4–C), 126.06 (J = 6.4 Hz,
1C, m-C, P–C6H4–C), 21.18 (1C, CH3). 31P NMR (CDCl3) δ: À12.68.
IR (cmÀ1): 694 (P–Ph), 742 (P–Ph), 1434 (CH3), 2846 (CH3), 3049
(Ph). MS: 275.1 (M+). Anal. Calc. for 10a (C19H17P): C, 82.59; H,
6.20. Found: C, 82.60; H, 6.21.
benzene as
a colorless liquid. A solution of 1-bromo-4-
triethylsilylbenzene (1.36 g, 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
hexane at À78 °C. The resulting mixture was stirred for 2 h at
À78 °C, followed by the addition of a solution of chloro-
diphenylphosphine (0.89 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 with Na2SO4 and evaporated in vacuo.
The crude product was purified by flash chromatography (5%
EtOAc–hexane) to give 9a as a colorless viscous oil; 45% yield.
1H NMR (CDCl3) δ: 7.57–7.26 (m, 2H, m-H, P–C6H4–Si; 2H, o-H,
P–C6H4–Si; 2H, p-H, C6H5–P; 4H, m-H, C6H5–P; 4H, o-H, C6H5–P),
0.98 (t, J = 7.4 Hz, 9H, CH3), 0.86 (q, J = 7.4 Hz, 6H, CH2). Due to
overlapping of signals, the proton assignments were listed
without distinct identification. 13C NMR (CDCl3) δ: 138.21 (1C,
p-C, P–C6H4–Si), 137.48 (J = 19.4 Hz, 1C, P–C, P–C6H4–Si),
137.10 (J = 6.4 Hz, 2C, m-C, P–C6H4–Si), 134.28 (J = 10.2 Hz, 2C,
o-C, P–C6H4-Si), 133.89 (J = 19.4 Hz, 2C, P–C, C6H5–P), 132.73
(J = 10.2 Hz, 4C, o-C, C6H5–P), 128.80 (J = 6.4 Hz, 4C, m-C, C6H5–P),
128.54 (2C, p-C, C6H5–P), 7.49 (3C, CH3), 3.35 (3C, CH2). 29Si NMR
(CDCl3) δ: 2.02. 31P NMR (CDCl3) δ: À5.02. IR (cmÀ1): 696 (P–Ph),
744 (P–Ph), 809 (Si–C), 1434 (Ar–Si), 2873 (CH3), 2933 (CH2), 2952
Synthesis of 2-methoxyphenyldiphenylphosphane 11a
Magnesium turnings (313 mg, 12.8 mmol) and a piece of I2 were
stirred under argon for 2 h and then overlaid with THF (30 ml).
Three drops of 1,2-dibromoethane were added, followed by a
few drops of a solution containing 2-bromotoluene (1.34 ml,
10.8 mmol) in THF (5 ml). Upon starting the reaction, the
remaining solution of 2-bromotoluene in THF was added
dropwise. The reaction mixture was heated to reflux until all
magnesium was dissolved. A solution of diphenylphosphine
chloride (2.70 ml, 15.0 mmol) in THF (2 ml) was cooled to À78 °C
and the reaction mixture was added dropwise. The reaction
mixture was stirred overnight at room temperature and extracted
twice with a saturated aqueous solution of NaCl and dried over
Scheme 6. Synthesis of 8a.[42]
Appl. Organometal. Chem. 2014, 28, 120–126
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M. Xue et al.
MgSO4. The solvent was removed under reduced pressure and
the crude product oil treated with EtOH. The formed solid was fil-
tered and washed with cold ethanol and the supernatant was
concentrated and purified by column chromatography (hex-
ane–EtOAc, 1:0– > 5:1) to give the title compound 11a as white
solid; 90% yield; m.p. 118 °C. 1H NMR (CDCl3) δ: 7.42–7.22 (m,
1H, p-H, P–C6H4–O) (m, 2H, p-H, C6H5–P; 4H, m-H, C6H5–P; 4H,
o-H, C6H5–P), 6.96–6.83 (m, 2H, m-H, P–C6H4–O), 6.74–6.65 (m,
1H, o-H, P–C6H4–O), 3.76 (s, 3H, OCH3). Due to overlapping of sig-
nals, the proton assignment was listed without distinct identifica-
tion. 13C NMR (CDCl3) δ: 161.19 (J = 10.2 Hz, 1C, o-C, P–C6H4–O),
136.61 (J = 10.2 Hz, 1C, o-C, P–C6H4–O), 134.03 (J =19.8 Hz, 2C,
P–C, C6H5–P), 133.76 (J = 10.2 Hz, 4C, o-C, C6H5–P), 130.42 (1C,
p-C, P–C6H4–O), 128.64 (J = 6.4 Hz, 4C, m-C, C6H5–P), 128.40 (2C,
p-C, C6H5–P), 125.50 (J =19.8 Hz, 1C, P–C, P–C6H4–O), 121.08
(J = 6.4 Hz, 1C, m-C, P–C6H4–O), 110.25 (J = 6.4 Hz, 1C, m-C,
P–C6H4–O), 55.72 (1C, OCH3). 31P NMR (CDCl3) δ: À16.06. IR
(cmÀ1): 696 (P–Ph), 748 (P–Ph), 1020 (C–O–C), 1431 (CH3), 1473
(Ph), 2841 (CH3), 3068 (Ph). MS: 292.1 (M+). Anal. Calc. for 11a
(C19H17OP): C, 78.07; H, 5.86; O, 5.47. Found: C, 78.08; H, 5.85; O,
5.48. See Scheme 8.
Scheme 9. Hydrosilylation reaction of alkenes catalyzed by rhodium
complex. R: Ph, CH3Ph, CH3OPh, C4H9, C6H13, C10H21; R1: OEt, Et.
Table 1. Crystal data, data collection and structure refinement de-
tails for 1a
Empirical formula
C18H14BrP
Formula weight
Crystal system
space group
341.17
Monoclinic
P, 21/c
Unit cell dimensions
a (Å)
9.2195(11)
17.155(2)
9.8057(12)
96.450(2)
1541.0(3)
4, 1.471 Mg mÀ3
2.758
b (Å)
c (Å)
Catalytic Hydrosilylation of Alkene with Triethoxysilane
β (°)
Volume (Å3)
Z, calculated density
A 10 ml three-necked flask equipped with a magnetic stirrer was
charged with RhCl3.3H2O (8.0 × 10À3 mmol) and prepared
triarylphosphane (4.0 × 10À2 mmol) under argon atmosphere.
The alkene (4 mmol) and silane (4.87 mmol) were then 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 selectivity were deter-
mined by GC. See Scheme 9.
Abs. coeff. (mmÀ1
)
F(000)
688
Reflections collected/unique
Goodness-of-fit on Fθ2max 25.2
Final R indices [I > 2σ(I)]
R indices (all data)
10607/2757 [R(int) = 0.0329]
1.03
R1 = 0.032, wR2 = 0.080
R1 = 0.053, wR2 = 0.089
X-Ray Structure Determinations of 1a
placed in geometrically idealized positions. Crystal data and de-
tails of the structures are given in Table 1.
Colorless single crystals of the compounds (dimensions: 1a:
0.26 × 0.20 × 0.17 mm) were produced by slow evaporation of
the solvents (hexane–dichloromethane) at 25 °C. Diffraction data
were collected at room temperature by the ϕ-scan and ω-scan
technique on a Smart Apex Duo diffractometer with graphite-
monochromated Mo-Kα radiation (λ = 0.71073 Å). The structures
were solved by direct methods (SHELXTL-PLUS)[43] and subse-
quent Fourier difference syntheses, and were then refined by
full-matrix least squares on F2 (SHELXL-97).[44] All non-hydrogen
atoms were refined anisotropically, while hydrogen atoms were
Results and Discussion
Synthesis of Various Types of Triarylphosphane[45,46]
A series of highly efficient protocols for the synthesis of
triarylphosphane are shown in Schemes 2–8. (2-Bromophenyl)
diphenylphosphane (1a) was synthesized by the reaction of 1-
bromo-2-iodobenzene and diphenylphosphine. The formation
of (2-aminophenyl)diphenylphosphane (4a), (4-aminophenyl)
diphenylphosphane (5a) and 4-diphenylphosphanylbenzoic acid
(6a), respectively, is similar to the formation of 1a. (2-
Butylphenyl)diphenylphosphane (7a) was synthesized by the
reaction of (2-bromophenyl)diphenylphosphane and n-BuLi.
(3-Bromophenyl)diphenylphosphane (2a) was synthesized by
the reaction of 1-bromo-3-iodobenzene and chlorodiphenyl-
phosphine. (4-Bromophenyl)diphenylphosphane (3a) is similar
to the formation of 2a. Diphenyl(2-trimethylsilylphenyl)
phosphane (8a) was synthesized by the reaction of 1a and
chlorotrimethylsilane. Interestingly, diphenyl(4-triethylsilylphenyl)-
phosphane (9a) was not obtained by the reaction of 1a and
chlorotriethylsilane. 4-Bromophenyltriethylsilane was obtained by
the reaction of 1-bromo-4-iodobenzene and chlorotriethylsilane;
9a was synthesized by the reaction of (4-bromophenyl)triethyl-
silane and chlorodiphenylphosphine. Diphenyl(2-tolyl)phosphane
Scheme 8. Synthesis of 10a and 11a.
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Copyright © 2014 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2014, 28, 120–126

Rhodium-catalyzed hydrosilylation of styrene
(10a) was synthesized by the reaction of 2-bromotoluene and
chlorodiphenylphosphine. Formation of (2-methoxyphenyl)
diphenylphosphane (11a) is similar to that of 10a. These 11 prod-
ucts are characterized by NMR, IR spectroscopy and MS. Further-
more, the NMR, IR spectroscopy and MS data of the prepared
compounds are in agreement with the assigned structures.
catalytic activity and highest selectivity of β-product with no
dehydrogenative silyation product were obtained. This suggests
that the silicon group had a significant impact on the catalytic
process. It was reported that organic fatty acids and amino acid
could be used as promoters in the hydrosilylation processes.[47]
Unfortunately, low conversion and low selectivities of the prod-
uct were usually observed by the use of RhCl3–4a, RhCl3–5a
and RhCl3–6a, respectively, as a catalytic system. RhCl3–10a and
RhCl3–11a catalytic systems showed higher conversion and
lower selectivity of β-product. To compare all these ligands with
PPh3, it was found that triarylphosphane containing aliphatic
and silicon groups promoted the hydrosilylation processes;
furthermore, triarylphosphane ligands containing silicon and/or
halogen group improved the selectivity of β-product (Table 2).
Effect of different ligands on the hydrosilylation reaction
The catalytic properties of RhCl3–triarylphosphane in the
hydrosilylation reaction of styrene with triethoxysilane were
investigated and the results are listed in Table 2. It is seen that
RhCl3–1a had low catalytic activity. RhCl3–3a had higher conver-
sion and low selectivity of β-product. The structure of 2a was
similar to those of 1a and 3a. Interestingly, when RhCl3 was
mixed with 2a, it exhibited greater catalytic activity and higher
selectivity of β-product. This result indicates that the substituent
attached to the benzene ring of triarylphosphane has a strong
impact on the catalytic process. When 7a was used as ligand,
highest catalytic activity, selectivity of β-product and a small
quantity of dehydrogenative silyation product were detected.
The RhCl3–9a catalytic system showed higher catalytic activity,
selectivity of β-product and lower dehydrogenative silyation
product. In particular, when 8a was used as ligand, higher
Scope of the Hydrosilylation Reaction
With preferred conditions in hand, we next carried out the
hydrosilylation reaction of other alkenes with triethoxysilane.
When another alkene such as 2-methylstyrene, 3-methylstyrene,
4-methylstyrene, 3-methoxystyrene, 1-hexene or 1-octene re-
placed styrene as one of the substrates, excellent conversions
and selectivities were obtained with the RhCl3–2a catalytic
system. However, when triethylsilane replaced triethoxysilane as
Table 2. Effect of triarylphosphane ligands on the rhodium-catalyzed hydrosilylation reaction
Entry
Ligands
Conv. (%)
Selectivity (%)
Unsaturated
β/α
β
α
1-Ethylbenzene
0
PPh3
1a
94.3
69.0
100
65.9
73.4
79.1
61.4
55.2
53.3
49.4
83.0
84.8
83.2
54.5
65.3
5.5
3.5
13.6
8.7
5.45
14.4
13.6
14.7
24.9
23.2
30.7
5.7
12.1
21.1
30.2
7.5
1
2
2a
2.6
4.6
3
3a
80.7
6.8
8.2
15.7
13.5
18.0
11.0
4.4
4
4a
6.4
8.6
5
5a
61.8
68.3
>99.9
95.4
95.8
99.0
96.9
5.5
9.7
6
6a
9.0
5.5
7
7a
6.7
12.4
13.8
29.7
1.9
8
8a
6.2
—
9.0
9
9a
2.8
5.8
8.2
10
11
10a
11a
28.0
14.2
9.1
8.4
11.4
9.1
4.6
Reaction conditions: styrene 4 mmol, triethoxysilane 4.4 mmol; catalyst: RhCl3 0.2 mol%, ligand 1.0 mol% based on styrene; 90 °C; 5 h.
Table 3. Scope of the hydrosilylation reaction
Entry
Alkene
Silane
Conv. (%)
Selectivity (%)
β
α
Unsaturated product
1
2-Methylstyrene
3-Methylstyrene
4-Methylstyrene
4-Methoxystyrene
1-Hexene
Triethoxysilane
95.8
87.3
83.2
88.6
91.0
89.7
100
87.4
86.6
2.8
1.6
2.6
1.4
—
3.4
4.7
3.4
5.6
—
2
3
82.5
4
86.5
5a
6a
7
>99.9
99.9
1-Octene
—
—
Styrene
Triethylsilane
48.5
2.1
32.6
Reaction conditions: alkene, 4 mmol; silane, 4.4 mmol; catalyst: RhCl3 0.2 mol%, 2a 1.0 mol% based on alkene; 90 °C, 5 h.
a2a 1.0 %mol based on alkene.
Appl. Organometal. Chem. 2014, 28, 120–126
Copyright © 2014 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

M. Xue et al.
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