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 nanoparticle 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.
1. INTRODUCTION Conventionally, heterogeneous catalysis is favored over homogeneous catalysis because they have more advantages, such as the simplicity in recovery and regeneration.1 8 Despite the easy synthesis procedures, heterogeneous catalysts are often suffered from lower efficiency than their homogeneous counterparts.9 Nowadays, metal nanoparticles are highly attractive tools for catalysis because of their high surface area-tovolume 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 homogeneous catalyst such as difficulty in separation from the product and any reaction medium and hence product purification, recovery, and regeneration of catalyst.12 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,14 16 silica,17,18 carbon,19 21 zeolite,22 polymer resins,23,24 and nanocomposites,25 have been developed to be candidates for nanoparticle catalyst support. Recently, magnetic 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.27 29 Palladium-based catalysts, in particular Pd nanoparticle catalysts, have attracted much attention owing to their versatile role in many catalytic reactions involving carbon carbon 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 r 2011 American Chemical Society
nanoparticles, the catalytic activity of Pd nanoparticles can be retained, and the stability also can be improved to some extent.35 37 In this paper, we demonstrated the construction of a magnetically separable Pd nanocatalyst based on magnetic Fe3O4@C (MFC) nanocomposites as supports. Pd nanoparticles were immobilized on a MFC support using a precipitation deposition method. To evaluate the activity and the stability of the supported Pd nanocatalysts, Suzuki and Heck coupling reactions were chosen 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 superparamagnetic behavior of Fe3O4 and can be reused with sustained selectivity and activity.
2. EXPERIMENTAL SECTION 2.1. Chemicals. FeCl3 3 6H2O, anhydrous sodium acetate, poly-N-vinylpyrrolle-2-one (PVP, K-30), ethylene glycol, ethanol, glucose, and NH2NH2 3 H2O were purchased from Sinopharm 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) Nanocomposite 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 3 6H2O, 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 24743
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The Journal of Physical Chemistry C 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. 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 hydrothermal 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 microspheres were prepared by the deposition precipitation 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 ultrasonication. Finally, 1 mL of 80% NH2NH2 3 H2O was dropped into the 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; Tecnai12, 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 4000 400 cm 1. 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 8000 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), K 2CO3 (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.
3. RESULTS AND DISCUSSION The whole preparation route to Pd/MFC includes three steps as illustrated in Figure 1. First, the magnetite particles were
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Figure 1. Synthesis route to Pd/MFC nanocomposites.
Figure 2. TEM images of (a) Fe3O4 nanospheres, (b) MFC nanocomposites, (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 condition. 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 COOH, OH, and CdO, 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 3 H2O reduction, generating 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. 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. 24744
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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 nanocomposites showed the characteristic diffraction peaks indexed to the Pd(0), which suggested the presence of Pd(0) on MFC composites. According to the Debye Scherrer 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 nanoparticles, MFC catalyst supports, and the Pd/MFC nanocomposite catalysts synthesized in this work. On the spectrum of magnetite nanoparticles (Figure 4a), the characteristic peaks centered at around 584, 1425, and 1626 cm 1 were assigned to Fe O, CdO bound stretching, and pyrrole ring framework stretching, respectively. From Figure 4b, for MFC, the bands at 577, 1700, and 3126 cm 1 were assigned to Fe O, 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 cm 1. It is worthy to note that the intensity of absorption peaks for Fe O, 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 3d5/2) and 340.7 eV (assigned to Pd 3d3/2) can be attributed to the Pd(0) state.40 The above result indicated that the oxidation state of Pd species on the MFC composite was Pd(0). 24745
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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)
74.3
44.2
37.9
Hc (Oe)
37.38
27.16
58.28
entry
Mr (emu/g)
9.80
3.19
2.99
1 2
Table 2. Suzuki Reactions Catalyzed by Pd/MFC Nanocompositesa
entry
R1
X
R2
solvent t (h) yield (%)b
TOFc
X
R2
t (h)
H
I
COOCH3
1
100
16.67
H
I
C6H5
2
66
5.50
3
H
I
C6H5
4
100
4.17
4
CH3O
I
COOCH3
1
99
16.5
5
CH3O
I
C6H5
4
100
4.17
6 7
CH3CO CH3CO
I I
COOCH3 C6H5
1 4
94 92
15.67 3.83
8
H
Br
COOCH3
2
98
8.17
9
H
Br
C6H5
2
65
5.42
R1
yield (%)
TOF
1
H
I
H
EtOH
1
100
16.67
10
CH3O
Br
COOCH3
2
97
8.08
2
H
I
CH2dCH
EtOH
1
72.3
12.05
11
CH3O
Br
C6H5
4
91
3.79
3 4
H CH3O
I I
CH2dCH H
EtOH EtOH
2 1
97 98
8.08 16.33
12
CH3CO
Br
COOCH3
2
92
7.67
13
CH3CO
Br
C6H5
4
87
3.62
5
CH3CO I
H
EtOH
1
95.7
15.95
6
H
Br H
EtOH
1
98
16.33
14 15
H H
Cl Cl
COOCH3 COOCH3
4 10
13(21) 59
0.54(0.87) 0.98
7
H
Br CH2dCH
EtOH
1
65
10.83
16
H
Cl
C6H5
4
4.3(17)
0.18(0.71)
8
H
Br CH2dCH
EtOH
3
96
5.33
17
H
Cl
C6H5
10
58
0.96
9
CH3O
Br H
EtOH
1
54
9.00
18
CH3CO
Cl
COOCH3
10
58
0.96
10
CH3O
Br H
EtOH
2
81
6.75
19
CH3CO
Cl
C6H5
10
47
0.78
11 12
CH3O CH3O
Br H Br H
EtOH DMF
3 1
83 94
4.61 15.67
13
CH3CO Br H
EtOH
1
52
8.67
14
CH3CO Br H
EtOH
2
77
6.42
15
CH3CO Br H
EtOH
3
80
4.44
16
COCH3 Br H
DMF
1
89
14.83
17
COCH3 Br H
DMF
2
95
7.92
18
H
Cl H
EtOH
1
24(46)
4.00(7.67)
19 21
H H
Cl H Cl CH2dCH
DMF EtOH
3 1
95 6(20)
5.28 1.00(3.33)
22
CH3CO Cl H
EtOH
3
23
CH3CO Cl H
DMF
3
36
2.00
24
CH3CO Cl H
DMF
4
62
2.58
25
CH3CO Cl H
DMF
5
62
2.07
a
Reaction conditions: arylhalide (1.5 mmol), alkene (3 mmol), K2CO3 (6 mmol), catalyst (30 mg, Pd: 0.308 mol %), DMF (30 mL), 120 °C.
Figure 7. Photograph of the catalyst (a) dispersed in reaction mixture, and (b) magnetic separation of the catalysts from the reaction medium.
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 without special instruction. c TOF was defined as molproduct mol 1Pd h 1.
Magnetic measurements of the samples were investigated by a vibrating sample magnetometer (VSM) at room temperature in the applied magnetic field ranging from 8000 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 parameters 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
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. 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 C C 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 1 4). As for chlorobenzene, 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 24746
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Table 4. Catalytic Performance of Pd/MFC Catalyst and Recovered Pd/MFC Catalyst in Successive Suzuki and Heck Reaction Runs
a
Pd leached after 5 cycles (%)a
run
1
2
3
4
5
iodobenzene + phenylboronic acid
100
100
100
100
100
0.2
iodobenzene + methyl acrylate
100
100
98
98
95
0.5
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 a
solvent
base
temp (°C)
time (h)
yield (%)
ref
1
Pd@Mag-MSN
CH2Cl2
K2CO3
80
6
85
37
2
Xerogel g1-MNPsb
CH3OH
Na2CO3
60
2
99
42
3
Pd/NiFe2O4
DMF
Na2CO3
90
2
50
43
4
Fe3O4 Bpy-Pd(OAc)2c
toluene
K2CO3
80
6
>99
44
5
Fe@FexOy/Pd
H2O/EtOH = 1:1
K2CO3
rt
2
98
45
6
Pd Fe3O4
DMEd/H2O = 3:1
K2CO3
reflux
48
92
46
7
C/Co@PNIPAMe PPh2 Pd
toluene/H2O = 2:1
K2CO3
85
16
99
47
8 9
MP@NiSiO/Pd Co@C@Pd complex
DME/H2O = 1:1 THF/H2O = 1:2
Na2CO3 Na2CO3
110 65
2
>95 96
48 49
10
Pd/NiFe2O4
NMPf/H2O = 10:4
K2CO3
80
4
97
50
11
Pd/MFC
ethanol
K2CO3
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 Fe3O4 Bpy-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.
investigated. The whole trend shows that the conversions of substituted substrates are lower than unsubstituted ones. Fortunately, 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. 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
Table 6. Catalytic Performance of Different Magnetically PdBased Catalysts in the Coupling Reaction of Iodobenzene and Styrene entry
catalysta
solvent
temp
time
yield
base
(°C)
(h)
(%)
ref
1
Pd/MCPPYa
DMAb
TBAc
120
3
97
2
Pd/N-MCNPsd
DMANe TEAf
120
3
97.6 35
3
Pd-biomagnetite
DMF
TEA
120
3
100
4
Fe3O4 NH2 Pd NMPg
K2CO3
130
10
>99 53
5
Pd/NiFe2O4
DMF
TEA
80
4
97
50
6
Pd/MFC
DMF
K2CO3
120
4
100
this work
51 52
a
Pd/MCPPY = Pd/Fe3O4@Polypyrrole. b DMA = N,N-dimethylacetamide. c TBA = tributylamine; d Pd/N-MCNPs= Pd/N-dopand magnetic carbon nanopartocles. e DMAN = dimethylacrylonitrile. f TEA = triethylamine. 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 performance 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 recoverable Pd-based catalysts.Take iodobenzene reacting with phenylbronic 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 24747
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The Journal of Physical Chemistry C 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.
4. CONCLUSIONS In summary, we have developed a highly efficient Pd(0) nanocatalyst immobilized on MFC nanocomposite highly suitable for carbon carbon coupling reactions. More significantly, the catalyst could be easily recovered and reused by a convenient magnetic separation technique, which is desirable in terms of cost and environmental protection. The activity of the Pd/MFC catalyst shows no obvious decrease. The Pd/MFC catalyst not only solves the basic problems of catalyst separation and recovery but also avoids the use of phosphine ligands which are dangerous for environment and widely used in homogeneous Pd catalyst system. ’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected].
’ ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (Grant no. 20973151), Specialized Research 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 Invention Plan. ’ REFERENCES (1) Zhao, M.; Crooks, R. M. Angew. Chem., Int. Ed. 1999, 38, 364. (2) Grunes, J.; Zhu, J.; Somorjai, G. A. Chem. Commun. 2003, 2257. (3) Narayanan, R.; El-Sayed, M. A. J. Am. Chem. Soc. 2003, 125, 8340. (4) Choudary, B. M.; Kantam, M. L.; Ranganath, K. V. S.; Mahendar, K.; Sreedhar, B. J. Am. Chem. Soc. 2004, 126, 3396. (5) Choudary, B. M.; Ranganath, K. V. S.; Pal, U.; Kantam, M. L.; Sreedhar, B. J. Am. Chem. Soc. 2005, 127, 13167. (6) Choudary, B. M.; Ravichandra, S. M.; Klabunde, K. J. J. Am. Chem. Soc. 2005, 127, 2020. (7) Yin, L.; Liebscher, J. Chem. Rev. 2007, 107, 133. (8) Jin, M. J.; Lee, D. H. Angew. Chem., Int. Ed. 2010, 49, 1119. (9) Abu-Reziq, R.; Alper, H.; Wang, D.; Post, M. L. J. Am. Chem. Soc. 2006, 128, 5279. (10) Lewis, L. N. Chem. Rev. 1993, 93, 2693. (11) Underhill, R. S.; Liu, G. J. Chem. Mater. 2000, 12, 3633. (12) Beller, M.; Fisher, H.; Kuhlein, K.; Reisinger, C. P.; Herrmann, W. A. J. Organomet. Chem. 1996, 520, 257. (13) Fan, J.; Gao, Y. J. Exp. Nanosci. 2006, 1, 457. (14) Zorn, K.; Giorgio, S.; Halwax, E.; Henry, C. R.; Gr€onbeck, H.; Rupprechter, G. J. Phys. Chem. C 2011, 115, 1103.
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