Pd on surface-modified NiFe2O4 nanoparticles: A magnetically recoverable catalyst for Suzuki and Heck reactions

Article abstract of DOI:10.1021/ol702064x

This communication reports on the use of NiFe₂O ₄-DA-Pd, a complete magnetically separable catalyst for Suzuki and Heck coupling reactions of aromatic halide derivatives. The catalyst efficiency for the coupling of chloro derivatives is as good as bromo and iodo derivatives. Catalytic efficiency remains unaltered even after three repeated cycles.

Full text of DOI:10.1021/ol702064x

ARTICLE
pubs.acs.org/JPCC
Magnetically Recyclable Pd Nanoparticles Immobilized on Magnetic
Fe3O4@C Nanocomposites: Preparation, Characterization, and Their
Catalytic Activity toward Suzuki and Heck Coupling Reactions
Maiyong Zhu and Guowang Diao*
College of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou, 225002, People's Republic of China
ABSTRACT: An efficient magnetic carbon nanocomposite supported Pd nano-
particle catalyst has been prepared by a three-step process in this report. The
morphology, inner structure, and magnetic properties of all products were
studied with transmission electron microscopy, X-ray powder diffraction, Fourier
translation infrared spectroscopy, X-ray photoelectron spectroscopy, and vibrating sample magnetometer. The Suzuki and
Heck coupling reactions were used to demonstrate the catalytic efficiency of the as-prepared Pd/Fe3O4@C (Pd/MFC)
nanocomposite catalyst. The results showed that the catalyst is completely recoverable with the simple application of an
external magnetic field and the catalytic efficiency shows no obvious loss for Suzuki and Heck coupling reactions even after five
repeated cycles.
nanoparticles, the catalytic activity of Pd nanoparticles can be
retained, and the stability also can be improved to some
extent.35À37
1. INTRODUCTION
Conventionally, heterogeneous catalysis is favored over
homogeneous catalysis because they have more advantages, such
as the simplicity in recovery and regeneration.1À8 Despite the
easy synthesis procedures, heterogeneous catalysts are often
suffered from lower efficiency than their homogeneous
counterparts.9 Nowadays, metal nanoparticles are highly attrac-
tive tools for catalysis because of their high surface area-to-
volume ratio. A key challenge in the application of such materials
in catalysis is agglomeration of nanoparticles, which may lead to
deactivation.10,11 Furthermore, they have drawbacks of homo-
geneous catalyst such as difficulty in separation from the product
and any reaction medium and hence product purification,
recovery, and regeneration of catalyst.12
In this paper, we demonstrated the construction of a magnet-
ically separable Pd nanocatalyst based on magnetic Fe3O4@C
(MFC) nanocomposites as supports. Pd nanoparticles were
immobilized on a MFC support using a precipitationÀdeposition
method. To evaluate the activity and the stability of the supported
Pd nanocatalysts, Suzukiand Heckcoupling reactions werechosen
as the model reactions for testing. The results showed that this
catalyst could be easily separated from the reaction medium by
employing an external magnetic field because of the superpar-
amagnetic behavior of Fe3O4 and can be reused with sustained
selectivity and activity.
Attempts have been made to overcome these issues, including
thermal stability (high reaction temperature), separation, and
recovery of catalyst, by immobilizing the active species on inert or
relatively active support.13 Many materials with high surface area,
such as metal oxide,14À16 silica,17,18 carbon,19À21 zeolite,22 poly-
mer resins,23,24 and nanocomposites,25 have been developed to
be candidates for nanoparticle catalyst support. Recently, mag-
netic separable catalysts have emerged as the bridges between
homogeneous and heterogeneous catalysts.26 On one hand, the
magnetic nanocomposite matrices serve both as the support
as well as the stabilizer of the nanoparticles thus providing a
mechanism to prevent aggregation. On the other hand, magnetic
separation is an alternative to filtration or centrifugation as it
prevents loss of catalyst and increases the reusability.27À29
Palladium-based catalysts, in particular Pd nanoparticle catalysts,
have attracted much attention owing to their versatile role in
many catalytic reactions involving carbonÀcarbon formation,30
hydrogenation of many organic compounds,19,20,31 oxidation of
hydrocarbon,32 isomerization,33 and decomposition of nitrogen
monoxide.34 There have been a variety of reports describing the
use of magnetic nanocomposites for the immobilization of Pd
2. EXPERIMENTAL SECTION
2.1. Chemicals. FeCl3 6H2O, anhydrous sodium acetate,
3
poly-N-vinylpyrrolle-2-one (PVP, K-30), ethylene glycol, ethanol,
glucose, and NH2NH2 H2O were purchased from Sinopharm
3
Co. Other chemicals were purchased from Aladdin Reagent Co.
All chemical were used as received. Deionized water was used for
all experiments.
2.2. Preparation of Pd/Fe3O4@C (Pd/MFC) Nanocompos-
ite Catalyst. 2.2.1. Synthesis of Fe3O4 Nanoparticles. Fe3O4
nanoparticles were prepared with the solvothermal method
according to our previous work.38 Briefly, 1.5 g of FeCl3 6H2O,
3
1 g of PVP, and 2 g of NaAc were added into 30 mL of ethylene
glycol. The mixture was stirred vigorously for 2 h to make all
materials dissolve completely. Then, the mixture was transferred
to a Teflon-lined stainless-steel autoclave and sealed to heat at
Received: June 28, 2011
Revised:
October 22, 2011
Published: November 14, 2011
r
2011 American Chemical Society
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200 °C for 8 h. The precipitated black products were collected
from the solution by an external magnet and washed with ethanol
several times. Finally, the black products were dried in a vacuum
for 24 h at 60 °C.
Figure 1. Synthesis route to Pd/MFC nanocomposites.
2.2.2. Synthesis of Magnetic Fe3O4@C (MFC) Composites.
Fe3O4@C composites were synthesized by in situ carbonization
of glucose in the presence of Fe3O4 nanoparticles under hydro-
thermal condition.39 Typically, 100 mg of Fe3O4 nanoparticles
were dispersed in 30 mL of water containing 2 g of glucose by
ultrasonic irradiation. The mixture was transformed into a
Teflon-lined stainless-steel autoclave with 40 mL capacity. The
autoclave was placed in a oven and kept at 200 °C for 12 h. After
being cooled to room temperature, the precipitated black solid
products (MFC) were collected from the solution by an external
magnet and washed with water several times. Finally, the black
products were dried in a vacuum for 24 h at 60 °C.
2.2.3. Synthesis of Pd/MFC Microspheres. Pd/MFC micro-
spheres were prepared by the depositionÀprecipitation method.
All the procedures were carried out under ultrasonication.
Typically, 100 mg of MFC was dispersed in ethanol, and then,
100 mg of PdCl2 (g60%) was quickly added under ultrasonica-
tion. Finally, 1 mL of 80% NH2NH2 H2O was dropped into the
3
mixture. About half an hour later, the solid products were
collected by applying a magnet and were washed with water
and ethanol several times. The products were dried in vacuum.
The solid product was dissolved in concentrated nitric acid
and analyzed by inductively couple plasma mass spectrometry
(ICP-MS) to determine the content of Pd (0.308 mol %).
2.3. Characterizations. The morphology of all products was
investigated by transition electron microscopy (TEM; Tecnai-
12, Philip, The Netherlands). The composition and crystalline of
all products were characterized by X-ray diffraction (XRD; D8
Advance, Bruker, Germany). The Fourier transform infrared
(FT-IR) spectra were recorded with a Tensor 27 spectrometer
(Bruker, Germany) using a KBr wafer with wavenumber ranging
4000À400 cmÀ1. The oxidation state of the surface element of
Pd/MFC was determined by X-ray photoelectron spectroscopy
(XPS; Thermo Escalab 250 system using Al Kα radiation (hν =
1486.6 eV)). The magnetic measurements were carried out on a
vibrating sample magnetometer (VSM; EV7, ADE, USA) with an
applied field between À8000 and 8000 Oe at room temperature. The
Pd loading amount was determined by inductively couple plasma
mass spectrometry (ICP-MS, Elan DRC-e, PerkinElmer Com.)
2.4. Catalytic Reaction. For Suzuki cross-coupling reactions,
30 mg of Pd/MFC catalyst, arylhalide (1.5 mmol), phenylboronic
acid or 4-vinylphenboronic acid (3 mmol), and K2CO3 (6 mmol)
were added to the solvent (30 mL). The reactions were carried out
at reflux condition for 1 h. Then, the catalysts were collected by an
external magnet, and the reaction system was analyzed by gas
chromatography mass spectrometry (GC-MS; Trace DSQ II,
Thermo Co., USA). For Heck cross-coupling reactions, arylhalide
(1.5 mmol), methyl acrylate or styrene (3 mmol), K2CO3
(6 mmol), and catalyst (30 mg) were added to 30 mL of DMF.
The reactions were performed at 120 °C for definite time. The other
procedures are similar to Suzuki reactions. For recycling, the
recovered catalysts were washed with ethanol and distilled water
several times, respectively, and dried under vacuum at 50 °C.
Figure 2. TEM images of (a) Fe3O4 nanospheres, (b) MFC nanocom-
posites, (c, d) Pd/MFC nanocomposites with different magnifications.
prepared by a robust solvothermal reaction based on high
temperature reduction of Fe (III) salts with ethylene glycol
serving as both the solvent and the reducing agent in the presence
of PVP and NaAc as the precipitation agent. Second, a thin layer
of carbon was coated on the surface of the magnetite particles
through the carbonization of glucose under hydrothermal con-
dition. The thin shell layer has two functions: (1) it could protect
the magnetite particles from being corrupted and oxidized by
acids and oxygen; (2) there were amounts of functional groups
on the surface, such as ÀCOOH, ÀOH, and ÀCdO, which were a
benefit to immobilize the catalytic active species. Third, the noble
metal salt (PdCl2) was used as precursor, and it was first absorbed by
MFC in ethanol, followed by NH2NH2 H2O reduction, generating
3
Pd(0) nanoparticles decorated MFC composites.
Figure 2 shows the typical TEM images of magnetite cores,
MFC supports, and the resulting Pd/MFC nanocomposite
catalysts. It is easily observed in Figure 2a that the diameter of
the as-prepared Fe3O4 nanoparticles was about 300 nm with a
narrow size distribution. From Figure 2b, the catalyst support,
MFC spheres, consists of a Fe3O4 core and a carbon shell. The
thickness of the shell carbon layer is about 30 nm. As illustrated in
Figure 2c, numerous monodispersed nanoparticles were uniformly
decorated on the MFC. It was found that every MFC composite
sphere was decorated with uniform nanoparticles and that nearly all
the nanoparticles were attached on to MFC composite. Figure 2d
provided the higher magnification TEM image of Pd/MFC; it is
easy to find that the particle size was about 15 nm.
3. RESULTS AND DISCUSSION
The crystallinity and phase composition of the resulting
products were investigated by X-ray powder diffraction (XRD).
Figure 3 exhibited the wide angle XRD patterns of the samples.
The whole preparation route to Pd/MFC includes three steps
as illustrated in Figure 1. First, the magnetite particles were
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The Journal of Physical Chemistry C
ARTICLE
Figure 3. XRD patterns of (a) Fe3O4 nanospheres, (b) MFC spheres,
and (c) Pd/MFC (c). 2 stands for Fe3O4 and b stands for Pd
nanoparticles.
Figure 5. XPS spectra of sample Pd/MFC: (a) survey spectrum and
(b) high-resolution XPS Pd 3d spectrum in Pd/MFC.
Figure 4. FT-IR spectra of PVP stabilized (a) Fe3O4 nanospheres,
(b) Fe3O4@C spheres, and (c) Pd/MFC.
As shown in Figure 3a, all the peaks were in agreement of face
centered cubic (fcc) Fe3O4. There is a broad diffraction peak at
2θ < 20° assigned to amorphous carbon coated on the surface
of Fe3O4 nanospheres in Figure 3b. On the XRD patterns of
Pd/MFC nanocomposites, it was found that the Pd/MFC nano-
composites showed the characteristic diffraction peaks indexed
to the Pd(0), which suggested the presence of Pd(0) on MFC
composites. According to the DebyeÀScherrer equation, the
diameter of Pd(0) nanoparticles is calculated to be 14.6 nm, well
in agreement with that observed from TEM.
Figure 4 exhibits the FT-IR spectra of the magnetite nano-
particles, MFC catalyst supports, and the Pd/MFC nanocompo-
site catalysts synthesized in this work. On the spectrum of
magnetite nanoparticles (Figure 4a), the characteristic peaks
centered at around 584, 1425, and 1626 cmÀ1 were assigned to
FeÀO, CdO bound stretching, and pyrrole ring framework
stretching, respectively. From Figure 4b, for MFC, the bands at
577, 1700, and 3126 cmÀ1 were assigned to FeÀO, CdO, and
the —COOH bond, respectively, demonstrating the existence of
some functional groups on the surface of the MFC, which
resulted from the uncompleted carbonization of glucose. These
groups are critical for the immobilization of Pd nanoparticles. As
illustrated in Figure 4c, Pd/MFC shows absorption peaks related
to the presence of MFC at 580 and 1700 cmÀ1. It is worthy to
note that the intensity of absorption peaks for FeÀO, CdO,
and —COOH was obviously weaker than that of MFC.
Figure 6. Field-dependent magnetization and enlarged partial (inset)
curves of (a) Fe3O4, (b) MFC, and (c) Pd/MFC.
XPS spectroscopy, one of the most important techniques to
determine the oxidation state of surface element in materials, was
used to characterize the Pd/MFC composites. Figure 5 shows the
survey spectrum of the Pd/MFC composites. The signal of Pd is
slightly weaker than that of O (Figure 5a), because the MFC was
not fully covered by Pd nanoparticles. Besides Pd, O, and C, there
was a small amount of the element Cl detected, which originated
from PdCl2. The XPS spectrum of Pd 3d can be flitted into a main
doublet peak, as shown in Figure 5b. The binding energy of the
doublet peak at 335.4 eV (assigned to Pd 3d / ) and 340.7 eV
5
2
(assigned to Pd 3d /
3
) can be attributed to the Pd(0) state.40 The
2
above result indicated that the oxidation state of Pd species on
the MFC composite was Pd(0).
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Table 1. Main Magnetic Parameters of Samples
Table 3. Heck Reactions Catalyzed by Pd/MFC
Nanocompositea
sample
parameter
Fe3O4
MFC
Pd/MFC
Ms (emu/g)
Hc (Oe)
74.3
37.38
9.80
44.2
27.16
3.19
37.9
58.28
2.99
entry
R1
X
R2
t (h)
yield (%)
TOF
Mr (emu/g)
1
H
H
H
I
COOCH3
C6H5
1
100
66
16.67
5.50
2
I
I
I
I
I
I
2
3
C6H5
4
100
99
4.17
Table 2. Suzuki Reactions Catalyzed by Pd/MFC
Nanocompositesa
4
CH3O
CH3O
CH3CO
CH3CO
H
COOCH3
C6H5
1
16.5
5
4
100
94
4.17
6
COOCH3
C6H5
1
15.67
3.83
7
4
92
8
Br COOCH3
Br C6H5
2
98
8.17
entry
R1
X
R2
solvent t (h) yield (%)b
TOFc
9
H
2
65
5.42
1
2
3
4
5
6
7
8
9
H
H
H
I
H
EtOH
1
1
2
1
1
1
1
3
1
2
3
1
1
2
3
1
2
1
3
1
3
3
4
5
100
72.3
97
16.67
12.05
8.08
10
11
12
13
14
15
16
17
18
19
CH3O
CH3O
Br COOCH3
Br C6H5
2
97
8.08
I
CH2dCH EtOH
CH2dCH EtOH
4
91
3.79
I
CH3CO Br COOCH3
CH3CO Br C6H5
2
92
7.67
CH3O
CH3CO
H
I
H
H
H
EtOH
EtOH
EtOH
98
16.33
15.95
16.33
10.83
5.33
4
87
3.62
I
95.7
98
H
H
H
H
Cl COOCH3
Cl COOCH3
Cl C6H5
4
13(21)
59
0.54(0.87)
0.98
Br
10
4
H
Br CH2dCH EtOH
Br CH2dCH EtOH
65
4.3(17)
58
0.18(0.71)
0.96
H
96
Cl C6H5
10
10
10
CH3O
Br
Br
Br
Br
H
H
H
H
H
H
H
H
H
H
H
EtOH
EtOH
EtOH
DMF
EtOH
EtOH
EtOH
DMF
DMF
EtOH
DMF
54
9.00
CH3CO Cl COOCH3
CH3CO Cl C6H5
a Reaction conditions: arylhalide (1.5 mmol), alkene (3 mmol), K2CO3
58
0.96
10 CH3O
11 CH3O
12 CH3O
81
6.75
47
0.78
83
4.61
94
15.67
8.67
(6 mmol), catalyst (30 mg, Pd: 0.308 mol %), DMF (30 mL), 120 °C.
13 CH3CO Br
14 CH3CO Br
15 CH3CO Br
16 COCH3 Br
17 COCH3 Br
52
77
6.42
80
4.44
89
14.83
7.92
95
18
19
21
H
H
H
Cl
Cl
24(46) 4.00(7.67)
95
5.28
Cl CH2dCH EtOH
6(20)
À
1.00(3.33)
À
22 CH3CO Cl
23 CH3CO Cl
24 CH3CO Cl
25 CH3CO Cl
H
H
H
H
EtOH
DMF
DMF
DMF
36
2.00
62
2.58
Figure 7. Photograph of the catalyst (a) dispersed in reaction mixture,
and (b) magnetic separation of the catalysts from the reaction medium.
62
2.07
a Reaction conditions: arylhalide (1.5 mmol), phenylboronic acid
(3 mmol), K2CO3 (6 mmol), catalyst (30 mg, Pd: 0.308 mol %), solvent
(30 mL), reflux for 1 h. b The number of yields in brackets was obtained
by adding 0.3 mmol KI to the reaction systems. Elsewhere is the
same meaning withÀou1t special instruction. c TOF was defined as
the saturated magnetization was undoubtedly related to the
surface coating of magnetic Fe3O4 nanoparticles (Fe3O4f
MFC). Owing to the limited amount of Pd immobilized on
MFC, the saturated magnetization value of Pd/MFC was not
much smaller than that of MFC.
molproduct molÀ1Pd h
.
To evaluate the catalytic ability of the composites, Suzuki
cross-coupling reaction and Heck reaction were carried out as
model reactions. It is well-known that the Suzuki cross-coupling
reaction of arylhalides and phenylboronic acid provides an
efficient route to form CÀC bound under relatively mild
conditions.41 The reactions were conducted using ethanol as
the solvent and K2CO3 as the base. As shown in Table 2,
iodobenzene and bromobenzene showed good results due to
their high reactivity (Table 2, entries 1À4). As for chloroben-
zene, a small amount of KI added to the reaction system could
improve the yields to some extent (Table 2, entries 5 and 6). By
the way, the effect of substituted groups in substrates was also
Magnetic measurements of the samples were investigated by a
vibrating sample magnetometer (VSM) at room temperature in
the applied magnetic field ranging from À8000 to 8000 Oe. As
illustrated in Figure 6, the isothermal magnetization of all
samples showed a rapid increase with increasing the applied
magnetic field. In order to make out whether the samples are
paramagnetic magnet, the partial enlarged curves were given in
the inset of Figure 6, which can clearly indicate that all of them
show ferromagnetic behavior. Meanwhile, some magnetic para-
meters of these samples were listed in Table 1. The saturated
magnetization values, Ms, of Fe3O4, MFC, and Pd/MFC are 74.3,
44.1, and 37.9 emu/g, respectively. The systematic decrease of
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Table 4. Catalytic Performance of Pd/MFC Catalyst and Recovered Pd/MFC Catalyst in Successive Suzuki and Heck Reaction
Runs
run
1
2
3
4
5
Pd leached after 5 cycles (%)a
iodobenzene + phenylboronic acid
iodobenzene + methyl acrylate
100
100
100
100
100
98
100
98
100
95
0.2
0.5
a Pd content in product phase in % of initial Pd loading of the catalysts.
Table 5. Catalytic Performance of Different Magnetically Pd-Based Catalysts in the Coupling Reaction of Iodobenzene and
Phenylbronic Acid
entry
catalyst
Pd@Mag-MSNa
Xerogel g1-MNPsb
solvent
CH2Cl2
base
temp (°C)
time (h)
yield (%)
ref
1
K2CO3
Na2CO3
Na2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Na2CO3
Na2CO3
K2CO3
K2CO3
80
6
85
37
42
43
44
45
46
47
48
49
50
2
CH3OH
60
2
99
3
Pd/NiFe2O4
DMF
90
2
50
c
4
Fe3O4ÀBpy-Pd(OAc)2
Fe@FexOy/Pd
PdÀFe3O4
toluene
80
6
>99
98
5
H2O/EtOH = 1:1
DMEd/H2O = 3:1
toluene/H2O = 2:1
DME/H2O = 1:1
THF/H2O = 1:2
NMPf/H2O = 10:4
ethanol
rt
2
6
reflux
85
48
16
À
2
92
7
C/Co@PNIPAMeÀPPh2ÀPd
MP@NiSiO/Pd
99
8
110
65
>95
96
9
Co@C@Pd complex
Pd/NiFe2O4
10
80
4
97
11
Pd/MFC
reflux
1
100
this work
a Pd@Mag-MSN = Pd nanoparticles supported on magnetic mesoporous silica nanocomposites. b Xerogel g1-MNPs = Fe3O4 nanoparticles supported
gel nanofibers + Pd2+. c Fe3O4ÀBpy-Pd(OAc)2 = Fe3O4 nanoparticles-supported palladium-bipyridine complex. d DME = 1,2-dimethoxyethane.
e PNIPAM = poly-N-isopropylacrylamide. f NMP = 1-methyl-2-pyrrolidinone.
Table 6. Catalytic Performance of Different Magnetically Pd-
Based Catalysts in the Coupling Reaction of Iodobenzene and
Styrene
investigated. The whole trend shows that the conversions of
substituted substrates are lower than unsubstituted ones. For-
tunately, by increasing reaction temperature (changing solvent)
and reaction time, most of them can get satisfactory yields.
The Pd/MFC catalysts also showed a high activity for Heck
reactions in a DMF solution, since the as-prepared MFC spheres
can tolerate many organic solvents with their microstructure
preserved. Two alkenes, styrene and methyl acrylate, were
chosen to react with arylhalide. As illustrated in Table 3, the
results were similar with Suzuki reactions. Iodobenzene and
bromobenzene showed better results than chlorobenzene. As
for alkenes, methyl acrylate gives higher yields than styrene,
which may be related to their molecule structure. Substituted
substrates give lower yields. Especially, less reactive aryl halides
such as bromo-chlorobenzene resulted in low yield (no more
than 60%) even after prolonging the reaction time to 10 h.
Isolation and reuse of the catalyst, a crucial requirement for
any practical application in terms of cost and environmental
protection, are the greatest merits in this study. In our systems,
the catalysts can be easily recovered by an external magnet as is
shown in Figure 7. In order to test the reusability of the catalyst,
two reactions (Table 2, entry 1; and Table 4, entry 1) were
chosen to be test. As illustrated in Table 3, the catalyst can be
reused for five times with no obvious decrease of conversion and
selectivity, by a simple magnetic separation. It is well-known that
magnetic separation renders the recovery of catalysts from a
liquid reaction system much easier than the traditional separation
procedures, such as filtration and centrifugation.
temp time
yield
(%)
entry
catalysta
solvent
base
(°C) (h)
ref
1
2
3
4
5
6
Pd/MCPPYa
Pd/N-MCNPsd
DMAb TBAc
DMANe TEAf
120
120
120
3
97
51
3
97.6 35
100 52
>99 53
Pd-biomagnetite DMF
TEA
3
Fe3O4ÀNH2ÀPd NMPg K2CO3 130
Pd/NiFe2O4
10
4
DMF
TEA
80
97
50
Pd/MFC
DMF
K2CO3 120
4
100 this work
a Pd/MCPPY = Pd/Fe3O4@Polypyrrole. b DMA = N,N-dimethylaceta-
mide. c TBA = tributylamine; d Pd/N-MCNPs= Pd/N-dopand magnetic
carbon nanopartocles. e DMAN = dimethylacrylonitrile. f TEA = triethyl-
amine. g NMP = N-methyl-2-pyrrolidone.
reactions show determinable Pd loss, but the loss amount is trace.
In the Suzuki reaction, the Pd loss amount is 0.2%, while it is 0.5%
in the Heck reaction. This result may partly explain the yield
decreasing slightly with increasing the recycles for the coupling of
iodobenzene with methyl acrylate. The trace amount of Pd loss
indicates the high affinity palladium-support, the good perfor-
mance of the magnetic separation in the present catalytic system.
As a comparison, we compared the results achieved in this
work with those reported elsewhere over magnetically recover-
able Pd-based catalysts.Take iodobenzene reacting with phenyl-
bronic as an example; the results were listed in Table 5. It can be
seen that the results obtained in this study are superior to others
except for entry 5. Although some of them also can obtain high
yield, toxic solvents (such as toluene, CH2Cl2, or THF) were
used. These chemicals are less favorable to ethanol used in this
Another key factor to be investigated is the stability of
the catalyst: leaching of active species into the reaction mixture.
To address this possibility, the catalysts after five cycles were
analyzed by ICP-MS. The results were also listed in Table 4. Both
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The Journal of Physical Chemistry C
ARTICLE
work. Furthermore, some even used Pd complexes, whose
synthesis might be a great challenge for many groups. As for
the Heck reaction, taking iodobenzene reacting with styrene as
an example, the comparison results were listed in Table 6. At a
glance, we can conclude that the result obtained in this work has
at least two advantages: base (K2CO3) used here is much more
preferred to both TBA and TEA used elsewhere. Although the
yield obtained in entry 4 by using K2CO3 as base is as high as that
in this work, reaction time is much longer than this work.
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’ AUTHOR INFORMATION
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Corresponding Author
*E-mail: gwdiao@yzu.edu.cn.
’ ACKNOWLEDGMENT
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This work was supported by the National Natural Science
Foundation of China (Grant no. 20973151), Specialized Re-
search Fund for the Doctoral Program of Higher Education
(SRFDP, 20093250110001), a Project Funded by the Priority
Academic Program Development of Jiangsu Higher Education
Institutions, and the Foundation of Jiangsu Key Laboratory of
Fine Petrochemical Technology. The authors also acknowledge
the Foundation of the Educational Committee of Jiangsu Provincial
General Universities Graduate Student Scientific Research Inven-
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