Suzuki reactions in water catalyzed by an active and reusable PMO-type Pd(II) organometal catalyst with cage-like mesoporous structure

Article abstract of DOI:10.1002/cjoc.201200597

A novel Pd(II) organometal catalyst with three-dimensional (3D) cage-like Ia3d cubic mesoporous structure and high surface area was prepared. In comparison with the corresponding catalyst with two-dimensional (2D) P6mm hexagonal mesoporous structure, the as-prepared catalyst exhibited higher activities in the water-medium Suzuki coupling reactions owing to the diminished diffusion limit. It showed comparable efficiencies with the Pd(PPh ₃)₂Cl₂ homogeneous catalyst and could be easily recycled and reused for five times without significant loss of activity.

Full text of DOI:10.1002/cjoc.201200597

FULL PAPER
DOI: 10.1002/cjoc.201200597
Suzuki Reactions in Water Catalyzed by an Active and Reus-
able PMO-Type Pd(II) Organometal Catalyst with Cage-Like
Mesoporous Structure†
Zhu, Fengxiaa,b(朱凤霞)
Li, Hexing*,b(李和兴)
a Jiangsu Key Laboratory for Chemistry of Low-Dimensional Materials, School of Chemistry and Chemical
Engineering, Huaiyin Normal University, Huaian, Jiangsu 223300, China
b The Education Ministry Key Lab of Resource Chemistry, Shanghai Key Laboratory of Rare Earth Functional
Materials, Shanghai University of Electric Power, Shanghai 200049, China
A novel Pd(II) organometal catalyst with three-dimensional (3D) cage-like Ia3d cubic mesoporous structure and
high surface area was prepared. In comparison with the corresponding catalyst with two-dimensional (2D) P6mm
hexagonal mesoporous structure, the as-prepared catalyst exhibited higher activities in the water-medium Suzuki
coupling reactions owing to the diminished diffusion limit. It showed comparable efficiencies with the Pd(PPh3)2Cl2
homogeneous catalyst and could be easily recycled and reused for five times without significant loss of activity.
Keywords Pd(II) organometal catalyst, PMO, cage-like bicontinuous cubic mesostructure, water-medium clean
organic reactions, the Suzuki reaction
Introduction
recycled, many were still expensive besides the re-
quirement of higher reaction temperatures, long reaction
times and inert gas conditions. Recently, immobilization
of organometallic catalysts on supports with ordered
mesoporous channels and high surface area could con-
siderably improve the catalytic performance.[22] Mean-
while, functionalization with organic groups could fur-
ther promote the catalytic activity owing to the en-
hanced surface hydrophobility favoring diffusion and
adsorption of organic molecules on catalysts, especially
in aqueous medium.[23-25] However, organometals and
organic functionalities terminally bonded to pore sur-
face usually cause pore blockage and also are easily
leached off during reaction, leading to the poor activity
and durability.
Incorporation of organometals into silica walls leads
to the new-type of immobilized homogeneous catalysts
with the structure similar to periodic mesoporous or-
ganosilicas (PMOs),[26,27] which possess benefits of ad-
justable chemical microenvironment of active sites by
surface chemistry modification, combined with a high
surface area and strong stability against leaching.[28-32]
Up to date, all the reported organometal-bridged PMOs
are present in two-dimensional (2D) P6mm hexagonal
mesoporous structures.[33,34] Herein, we report for the
first time the synthesis of Pd(II) organometal catalyst
integrally incorporated into silica framework of the
Organometal catalysts are widely used in modern
organic synthesis.[1] Among them, Pd(II) organometal-
catalyzed coupling reactions between arylboronic acids
and aryl or alkenyl halides, known as the Suzuki reac-
tion, are of fundamental significance in constructing C
—C bonds[2-4] and also of great industrial importance in
producing fine chemicals, agrochemicals, pharmaceuti-
cal intermediates, and precursors of natural products.[5-7]
Recently, they are also used as homogeneous catalysts
with high activity and selectivity in water-medium or-
ganic reactions, which could be regarded as one impor-
tant branches of green chemistry since the replacement
of volatile organic solvents by water could greatly re-
duce the environmental pollution.[8-12] However, such
homogeneous catalyst is difficult to be separated from
the reaction system, which limits its recycle and reuse,
leading to the high cost and even the environmental
pollution from heavy metallic ions.[13] Heterogeneous
catalysts could be easily recycled and reused, but they
usually display lower activity than their corresponding
homogeneous catalysts due to the enhanced steric hin-
drance for both the diffusion and adsorption of reactant
molecules onto the catalysts.[14-18] In recent years, many
efficient polymer-supported palladium complexes have
been developed for the purpose.[19-21] Although these
complexes exhibited high catalytic activity and could be
*
E-mail: hexing-li@shnu.edu.cn; Tel.: 0086-021-64322272; Fax: 0086-021-64322272
Received June 19, 2012; accepted July 11, 2012.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201200597 or from the author.
Dedicated to the 80th Anniversary of Chinese Chemical Society.
†
Chin. J. Chem. 2012, 30, 2151—2157
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Zhu & Li
FULL PAPER
phenyl (Ph)-bridged PMO with a cage-like Ia3d cubic
mesoporous structure, denoted as Pd(II)-PMO(Ph)-3D.
Obviously, such catalyst is superior over the corre-
sponding one with 2D mesoporous structure owing to
the facilitated diffusion and adsorption of reactant
molecules inside pore channels.[35] As a result, this
catalyst exhibited greatly enhanced activity which was
comparable with the Pd(PPh3)2Cl2 homogeneous cata-
lyst in various organic reactions. It also displayed strong
durability and could be easily recycled and reused
without significant deactivation.
and TEM image in Figure S2) was also prepared by
surfactant-directed co-condensation of BTEB and
Pd[PPh2(CH2)2Si(OCH2CH3)3]2Cl2 according to the
procedure reported previously.[32] Briefly, 1.0 g P123
and 3.0 g KCl are dissolved in 40 mL 0.20 mol/L HCl
aqueous solution and stirred for 2 h, followed by mixing
with 1.0 g BTEB and 0.21 g Pd[PPh2(CH2)2Si(OCH2-
CH3)3]2Cl2. The mixture was stirred for 24 h at 40 ℃
and kept under hydrothermal conditions at 100 ℃ for
another 24 h. The solid product was extracted in 500 mL
0.50 mol/L HCl/ethanol solution at 80 ℃ for 24 h. The
Pd(II) loading was determined as 0.97 wt% by ICP
analysis.
Experimental
Characterization
Catalyst preparation
The compositions and Pd(II) loadings were deter-
mined by elemental analysis (Elementar Vario ELIII,
Germany) and/or inductively coupled plasma optical
emission spectrometer (ICP-OES, Varian VISTA-MPX).
Fourier transform infrared (FTIR) spectra were col-
lected on a Nicolet Magna 550 spectrometer by using
the KBr method. Solid-state NMR spectra were re-
corded on a Bruker AV-400 spectrometer. Low-angle
X-ray powder diffraction (XRD) patterns were obtained
on a Rigaku D/maxr B diffractometer with Cu Ka. N2
adsorption-desorption isotherms were measured at 77 K
on a Quantachrome NOVA 4000e analyzer, from which
the specific surface area (SBET) was calculated by multi-
ple-point Brunauer-Emmett-Teller (BET) model.
Meanwhile, the average pore diameter (DP) and total
pore volume (VP) were calculated from the adsorption
isotherms using Barrett-Joyner-Halenda (BJH) model.
Surface morphologies and porous structures were ob-
served through a transmission electron microscopy
(TEM, JEOL JEM2011). The surface electronic states
were analyzed by X-ray photoelectron spectroscopy
(XPS, Perkin-Elmer PHI 5000C). All the binding energy
(BE) values were calibrated by using the standard BE
value of contaminant carbon (C1s＝284.6 eV) as a ref-
erence.
Scheme 1 briefly illustrated the preparation of
Pd(II)-PMO(Ph)-3D. Firstly, the Pd[PPh2(CH2)2Si-
(OEt)3]2Cl2 was synthesized by coordinating Pd(II) ions
with PPh2CH2CH2Si(OEt)3. Their compositions and
purities are determined by both ICP analysis and 31P CP
MAS NMR spectra (Figure S1 in the Supporting Infor-
mation). Then, a certain amount of bis(triethoxysilyl)-
benzene (BTEB) was dissolved in 22 g of 0.14 mol/L
HCl aqueous solution containing 0.60 g P123 and 0.55 g
butanol. After being prehydrolyzed for 1.0 h under stir-
ring at 35 ℃ , the as-prepared Pd[PPh2(CH2)2Si-
(OEt3)3]2Cl2 was added into the above solution, fol-
lowed by rapidly stirring at 35 ℃ for 24 h and subse-
quently treating under hydrothermal conditions at 100
℃ for another 72 h. Then, the precipitate was filtrated
and vacuum dried overnight. Finally, the surfactants and
other organic substances were extracted by refluxing in
500 mL 0.50 mol/L HCl/ethanol solution at 80 ℃ for
24 h. The initial molar ratio in the mother solution was
fixed as Si∶P123∶HCl∶KCl∶H2O＝1.0∶0.010∶
0.085∶0.74∶105, where Si refers to the total silica
source. The Pd(II) loading was adjusted by changing the
amount of Pd[PPh2(CH2)2Si(OEt)3]2Cl2 in the initial
mixture and assigned as Pd(II)-PMO(Ph)-3D-1, Pd(II)-
PMO(Ph)-3D-2, and Pd(II)-PMO(Ph)-3D-3, respec-
tively. The ICP analysis determined the real Pd(II)
loadings as 0.67, 0.92, and 1.3 wt% in these three cata-
lysts.
Activity test
The reaction between arylboronic acids and aryl
halide (Eq. 1) was employed to evaluate the catalytic
performances. Each reaction was conducted in a 10 mL
round-bottomed flask at 100 ℃ under vigorous stirring.
In a typical run of the reactions, 1.0 mmol aryl halide,
1.5 mmol arylboronic acids, 2.0 mmol K2CO3, 5.0 mL
H2O, and a catalyst containing 0.0050 mmol Pd(II) were
mixed and allowed to react at 100 ℃ for 5 h. After
stirring for 5 h, the products were extracted by ethyl
acetate, followed by analysis on a gas chromatograph
(SHIMADZU, GC-17A) equipped with a JWDB-5, 95%
dimethyl 1-(5%)-diphenylpolysiloxane column and an
FID detector. The column temperature was programmed
from 80 to 250 ℃ at a ramp speed of 10 ℃/min. N2
was used as carrier gas, and n-decane was used as an
internal standard. The reproducibility was checked by
Scheme 1 Illustration of preparing Pd(II)-PMO(Ph)-3D
Cl
Ph
(EtO)3SiCH2CH2P
Cl
Ph
PCH2CH2Si(OEt)3
Ph
Pd
Ph
Self-assembly
Co-condensation
(EtO)3Si
Si(OEt)3
P123 surfactant
P123 micelle
Pd(II)
PPh2-ligand
Ethanol
Extraction
Ph-bridged silica wall
P123 surfactant
-Si-O-Si-CH2-CH2-PPh2-Pd(II)-PPh2-CH2-CH2-Si-O-Si-Ph-Si-O-Si-
For comparison, the Pd(II)-PMO(Ph)-2D with 2D
P6mm hexagonal mesoporous structure (see the low-
angle XRD pattern, N2 adsorption-desorption isotherm
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Chin. J. Chem. 2012, 30, 2151—2157

Suzuki Reactions in Water Catalyzed by an Active and Reusable PMO-Type Pd(II) Organometal Catalyst
repeating each result at least three times and found to be
within ±5%.
Catalyst
(1)
X
+
B(OH)2
R
K2CO3, H2O
R
In order to determine the durability, the catalyst was
allowed to centrifuge after each run of reactions and the
clear supernatant liquid was decanted slowly. The cata-
lyst was washed thoroughly with distilled water and
ethanol, followed by drying at 80 ℃ for 8 h under
vacuum condition. Then, the catalyst was reused with
fresh charge of reactants for subsequent recycle under
the identical reaction conditions.
Results and discussion
The FTIR spectra (Figure 1) revealed that the
Pd(II)-PMO(Ph)-3D-2 displayed no absorbance bands
characteristic of P123 molecules, indicating the com-
plete removal of surfactant template. Three peaks were
－
1
observed at around 650, 1458 and 3049 cm , corre-
sponding to δ(C—H), ν(C—C) and ν(C—H) vibrations
in benzene ring.[36] Two peaks at 1095 and 1162 cm－
1
were designated to the ν(Si—O) and ν(Si—C) vibra-
－
1
tions,[37] and other two peaks at 2891 and 2992 cm to
the ν(C—H) vibrations from the CH2CH2 group. [38] An-
other peak around 1526 cm－1 corresponded to the ν(P—
C) vibration.[39,40] These results demonstrated the suc-
cessful presence of both the Pd(II) organometallic com-
plexes and the PMO(Ph), which could be further con-
firmed by solid NMR. As shown in Figure 2, the 29Si
MAS NMR spectrum revealed that the Pd(II)-PMO(Ph)-
3D-2 displayed three peaks down-field corresponding to
T1 (δ＝－63), T2 (δ＝－73) and T3 (δ＝－81), where Tm
＝RSi(OSi)m-(OH)3 m, m＝1—3. No Qn peaks were
－
observed, where Qn＝Si(OSi)n-(OH)4 n, n＝2—4, indi-
－
cating that all the Si species were covalently bonded
with carbon atoms.[40] Meanwhile, two peaks around δ
13 and 30 were observed in the 13C CP MAS NMR
spectrum, corresponding to two C atoms in the CH2CH2
group connecting with the PPh2-group[41]. An intense
peak around δ 131 could be assigned to the C atoms in
Figure 2 Solid NMR spectra of the Pd(II)-PMO(Ph)-3D-2.
the benzene ring.[42] A weak peak around δ 55 could be
attributed to the C atoms in the C2H5O-group connect-
ing with silicon due to the incomplete hydrolysis.[42]
Other peaks denoted by asterisks were attributed to rota-
tional sidebands.[43] The 31P CP MAS NMR spectrum
displayed a single signal at δ 44, corresponding to P
atom in the PPh2-groups, indicating the unique coordi-
nation model between PPh2 and Pd(II). All these results
further demonstrated the integral incorporation of both
the Pd(II) organometals and the Ph groups into the silica
framework.
The XPS spectrum (Figure 3) demonstrated that all
the Pd species in the Pd(II)-PMO(Ph)-3D-2 were pre-
sent in＋2 oxidation state,[44] corresponding to the
binding energy around 343.3 eV in Pd3d5/2 level. The
unique XPS peak in Pd3d/2 level further verified only
4000 3500 3000 2500 2000 1500 1000 500
Wavenumber/cm-1
Figure 1 FTIR spectra of the Pd(II)-PMO(Ph)-3D-2 sample.
Chin. J. Chem. 2012, 30, 2151—2157
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one kind of coordination model between Pd(II) and
PPh2-ligand, in good accordance with that observed by
31P CP NMR. In comparison with the Pd(PPh3)Cl2, the
slightly negative shift of binding energy might be as-
cribed to the stronger electron-donating ability of P in
the PPh2(CH2CH2) than that in the PPh3, taking into
account that ∏ conjugated system between P and three
phenyl groups in the PPh3 could dilute the electron den-
sity on the P atom.[45]
Two small additional peaks at bigger 2θ were also ob-
served, corresponding to the (420) and (332) planes.
These results demonstrated the presence of well ordered
cage-like mesosoprous structure belonging to cage-like
Ia3d cubic mesoporous structure,[47] which could be
further confirmed by TEM images (Figure 6). The d(211)
reflection gradually decreased with the increase of the
Pd(II) loading, indicating the enhanced wall thickness,
leading to the gradual decrease in surface area (see Ta-
ble 1). However, no significant change in the pore di-
ameter was found with the increase of Pd(II) loading.
These results clearly demonstrated that the Pd(II) or-
ganometallic complexes were mainly integrated into the
silica walls rather terminally bonded to the pore surface.
Figure 3 XPS spectra of different samples.
Figure 4 demonstrated that all the Pd(II)-PMO(Ph)-
3D catalysts with different Pd(II) loadings displayed
type-IV nitrogen adsorption-desorption isotherms with
H1-type hysteresis loop indicative of the mesoporous
structure.[46] An abrupt step in the relative pressure at
p/p0＝0.6—0.7 was observed due to the capillary con-
densation of nitrogen in mesopores. The increase of the
Pd(II) loading had no significant influence on the shape
of H1-type hysteresis loop, suggesting the preservation
of the original mesoporous structure.
Figure 5 Low-angle XRD patterns of Pd(II)-PMO(Ph)-3D. (a)
Pd(II)-PMO-3D-1, (b) Pd(II)-PMO-3D-2, and (c) Pd(II)-PMO-3D-3.
Figure 6 TEM images of the Pd(II)-PMO(Ph)-3D-2.
Table 1 summarized the catalytic activities of vari-
ous catalysts in the water-medium Suzuki reaction be-
tween iodobenzene and phenyl boronic acid. No side
products were detected by GC-MS, indicating that these
reactions were absolutely selective toward target prod-
uct. The Pd(II)-PMO(Ph)-3D-2 exhibited higher activity
than the Pd(II)-PMO-2D with the similar Pd(II) load-
ings. Taking into that the Pd(II)-PMO(Ph)-3D was pre-
sent in the cage-like Ia3d cubic mesporous structure
while Pd(II)-PMO(Ph)-2D was present in the P6mm
hexagonal mesporous structure (see Scheme 2), the
higher activity of the Pd(II)-PMO(Ph)-2D could be
mainly due to the opened mesoporous channels, which
Figure 4 N2 adsorption-desorption isotherms.
The XRD patterns (Figure 5) revealed that all the
Pd(II)-PMO(Ph)-3D catalysts with different Pd(II)
loadings showed an intense peak at 2θ＝0.90o corre-
sponding to (211) plane and a hump for (220) plane.
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Suzuki Reactions in Water Catalyzed by an Active and Reusable PMO-Type Pd(II) Organometal Catalyst
Table 1 Structural parameters and catalytic performances of different catalystsa
－
－
1
1
Catalyst
S
BET/(m2•g )
VP/(cm3•g )
DP/nm
/
Pd loading/wt%
Conversion/%
Pd(PPh3)2Cl2
/
/
/
96
88
83
98
91
89
Pd(II)-PMO-2D
Pd(II)-PMO-3D-1
Pd(II)-PMO-3D-2
Pd(II)-PMO-3D-3
Used Pd(II)-PMO-3D-2b
790
922
893
846
867
0.83
1.2
6.2
6.8
6.8
6.8
6.8
0.97
0.67
0.92
1.3
0.95
0.98
0.98
0.90
a Reaction conditions: a catalyst containing 0.0050 mmol Pd(II), 5.0 mL H2O, 1.0 mmol iodobenzene, 1.5 mmol phenyl boronic acid, 2.0
mmol K2CO3, reaction temperature＝100 ℃, reaction period＝5 h. b The catalyst after being used repetitively for 5 times.
facilitated both the diffusion and the adsorption of reac-
tant molecules. For the Pd(II)-PMO(Ph)-3D series cata-
lysts, the activity first increased and then decreased with
the increase of Pd(II) loading. The optimum catalyst
was determined as Pd(II)-PMO(Ph)-3D-2 with Pd(II)
loading of 0.92 wt%. The Pd(II)-PMO(Ph)-3D-1 cata-
lyst with very low Pd(II) loading (0.67 wt%) exhibited
poor activity due to the relatively long distance between
the two neighboring Pd(II) active sites. Taking into ac-
count that the Suzuki reaction needs two kinds of
molecules adsorbed on the neighboring Pd(II) active
sites, the long distance between two neighboring Pd(II)
active sites would retard their cross-coupling reactions.
Meanwhile, the Pd(II)-PMO(Ph)-3D-3 with very high
Pd(II) loading (1.3 wt%) also displayed lower activity,
possibly due to the steric hindrance that retarded the
diffusion and the adsorption of reactant molecules on
the Pd(II) active sites. The Pd(II)-PMO(Ph)-3D-2 ex-
hibited equivalent catalytic efficiencies with the corre-
sponding Pd(PPh3)2Cl2 homogeneous catalyst. To make
sure whether the Pd(II) anchored on the support or Pd(II)
leached from the support was the real catalyst, then fol-
lowing experiments were carried out according to the
procedure proposed by Sheldon et al.[48] After reaction
for 3 h with the conversion exceeding 60%, the catalyst
was filtered out from the reaction system and liquid so-
lution was kept at the same reaction conditions for an-
other 5 h. No significant increase in either the conver-
sion or the product yield was found, suggesting that the
catalysis was purely heterogeneous in nature rather than
the dissolved Pd(II) species leached off from the solid
Pd(II)-PMO(Ph)-3D-2 catalyst.
between substituted aryl halides and phenyl boronic
acid. As shown in Table 2, iodobenzene could easily
react with phenyl boronic acid with very high product
yield. Bromobenzene could also react with phenyl bo-
ronic acid in good yield. However, the cross-coupling
reaction between chlorobenzene and phenyl boronic
acid displayed very poor product yield since chloroben-
zene was difficult to be activated. It was also found that
the bromobenzene with an electron-withdrawing group
such as NO2 exhibited higher activity in cross-coupling
reaction with phenyl boronic acid than that containing
an electron-donating group such as CH3, which could be
easily understood by considering the mechanism of the
Suzuki coupling reaction.[49] Furthermore, the 2-sub-
stituted bromobenzene exhibited much lower activity
than the 4-substituted one, obviously due to enhanced
steric hindrance.
Table 2 The water-medium Suzuki reactions on the Pd(II)-
PMO(Ph)-3D-2 catalysta
Catalyst
+
R2
X
X
B(OH)2
R1
R
K2CO3, H2O
Entry
R1
H
H
H
X
I
R2
H
H
H
H
H
H
H
Conversion/%
Yield/%
98
1
2
98
93
11
77
99
69
42
91
62
68
43
Br
Cl
93
3
11
4
4-CH3 Br
4-NO2 Br
2-NO2 Br
2-CH3 Br
77
5
99
6
69
7
42
We also examined the catalytic performances of
Pd(II)-PMO(Ph)-3D-2 in the Suzuki coupling reactions
8
H
H
H
H
Br 4-CH3
Br 2-CH3
91
9
62
10
11
Br 4-CF3
Br 2-CF3
68
Scheme 2 Picture of (a) P6mm hexagonal and (b) Ia3d cubic
mesporous structure
43
a Reaction conditions are the same as described in Table 1.
Pd(II)-PMO(Ph)-3D-2 also showed high activity for
the Suzuki couplings of other arylboronic acids with
different substituents. For p-methylphenylboronic acid
90% yield could be obtained. For arylboronic acid with
electron-withdrawing groups such as CF3, 68% yield
Chin. J. Chem. 2012, 30, 2151—2157
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Zhu & Li
FULL PAPER
was still afforded. When these substituents changed to
o-position, within the same reaction time as that for
p-substituted arylboronic acid, the yields for o-sub-
stituted products were lower than those of the corre-
sponding p-substituted products. The decreased reaction
rate may reflect the steric hindrance effects caused by
neighboring groups.
thermal stability owing to the presence of Pd(II) organ-
metals in silica walls,[25] corresponding to the preserva-
tion of surface area, pore diameter and pore volume (see
Table 1). Accordingly, the Pd(II)-PMO(Ph)-3D-2 dis-
played strong durability owing to the strong stability
against both the leaching of Pd(II) active sites and the
damage of ordered mesoporous structure.
The most important advantage of the heterogenous
catalysts was that they could be easily recycled and re-
used. As shown in Figure 7, the Pd(II)-PMO(Ph)-3D-2
catalyst could be used repetitively for more than 5 times
without significant loss of activity in the water-medium
Suzuki coupling reaction between iodobenzene and
phenyl boronic acid. According to the ICP analysis,
only 2.2% Pd(II) active sites were leached off from the
Pd(II)-PMO(Ph)-3D-2 catalyst after being used for 5
times (see Table 1), which could be attributed to the
strong interaction between Pd(II) organometal and the
support, taking into account that the Pd(II) organometal
was incorporated into silica walls. Meanwhile, the
low-angle XRD pattern and TEM image in Figure 8
demonstrated that the Pd(II)-PMO(Ph)-3D-2 preserved
well defined Ia3d cubic mesporous structure after being
used repetitively for 5 times, showing strong hydro-
Conclusions
In summary, this work developed a new cage-like
structured mesoporous PMO-type Pd(II) organometal
catalyst with both the Pd(II) organometals and phenyl
groups integrated into silica walls, which was superior
over the corresponding one with hexagonal mesporous
structure in the water-medium Suzuki reactions owing
to the facilitated diffusion and adsorption of organic
reactant molecules. The as-prepared solid catalyst dis-
played comparable activity with the corresponding
Pd(PPh3)2Cl2 homogeneous catalyst and could be easily
recycled and reused, which offered more opportunities
for industrial applications of water-medium clean or-
ganic reactions.
Acknowledgements
100
80
60
40
20
0
This work was supported by the National Natural
Science Foundation of China (20825724) and Shanghai
local government (S30406 and 10dj1400100).
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