Palladium immobilized on Fe3O4/ZnO nanoparticles: A novel magnetically recyclable catalyst for Suzuki-Miyaura and heck reactions under ligand-free conditions

Article abstract of DOI:10.1007/s13738-015-0710-0

Magnetically separable Pd(0)/Fe₃O₄/ZnO catalyst was easily synthesized by immobilizing Pd on the surface of magnetic Fe₃O₄-ZnO nanoparticles. The nano-Pd/Fe₃O₄/ZnO was found as a magnetically separable and highly active catalyst for Suzuki-Miyaura as well as Heck cross-coupling reactions under ligand-free conditions. Under appropriate conditions, all reactions afforded the desired products in moderate to excellent yields. Moreover, this catalyst can be easily recovered using simple magnet and directly reused without significant loss of its activity.

Full text of DOI:10.1007/s13738-015-0710-0

J IRAN CHEM SOC
DOI 10.1007/s13738-015-0710-0
ORIGINAL PAPER
Palladium immobilized on Fe3O4/ZnO nanoparticles: a novel
magnetically recyclable catalyst for Suzuki–Miyaura and heck
reactions under ligand‑free conditions
Mona Hosseini‑Sarvari1 · Ameneh Khanivar1 · Fatemeh Moeini1
Received: 21 February 2015 / Accepted: 23 July 2015
© Iranian Chemical Society 2015
Abstract Magnetically separable Pd(0)/Fe3O4/ZnO cata-
lyst was easily synthesized by immobilizing Pd on the
surface of magnetic Fe3O4–ZnO nanoparticles. The nano-
Pd/Fe3O4/ZnO was found as a magnetically separable and
highly active catalyst for Suzuki–Miyaura as well as Heck
cross-coupling reactions under ligand-free conditions.
Under appropriate conditions, all reactions afforded the
desired products in moderate to excellent yields. Moreover,
this catalyst can be easily recovered using simple magnet
and directly reused without significant loss of its activity.
for palladium-catalyzed cross-coupling reactions. The use
of ligands is undesirable because of their toxicity, air, and
moisture-sensitivity, and consequent conversion into phos-
phine oxide species. Recently, phosphine ligand-free cross-
coupling reactions were reported [8, 9]. Although these
reported papers are incentive, there are considerable meth-
ods for improvement in term of substrate scope, reaction
conditions and reusability of the catalyst.
While traditional and homogeneous catalysts show
higher catalytic activities than their heterogeneous coun-
terparts, the problem lies in being costly and less green.
So, chemists pay more attention to the designing of a cata-
lyst that can be efficient and recoverable. Therefore, het-
erogeneous Pd-based catalysts will be a good alternative,
owing to their air-stability, recoverability, reusability, and
no residual properties [10]. In the past few years, numerous
solid supports, such as mesoporous silica [11–13], metal
oxides [14], clays [15], and carbon nanofibers [16], have
been used for Pd-based heterogeneous catalysts. In this
regard, magnetic nanoparticles (MNPs) as catalyst supports
have been attracting more and more attention and they are
very promising due to their large specific surface area and
magnetic property [17–25]. It can be easily recovered from
the reaction mixture simply using an external magnet to
prevent loss of the catalyst. Thus, using MNPs eliminates
the necessity of tedious centrifugation, filtration, or mem-
brane separation steps [26–32]. Recently, numerous func-
tioned MNPs have been employed in a range of organic
transformations, showing excellent catalytic activities in
C–C coupling [33–38].
Keywords Pd(0)/Fe3O4/ZnO · Magnetically separable
catalyst · Cross-coupling reactions · Heterogeneous catalyst
Introduction
The carbon–carbon bond formation is among the most
fundamental reactions in organic chemistry. In many of
these reactions, transition metals or their complexes have
been used as a catalyst. Among the transition metals [1,
2], supported Pd catalysts have been found enormous
applications in the Mizoroki–Heck [3, 4] and the Suzuki–
Miyaura reactions [5]. These cross-coupling reactions
have been recognized as fundamental tools and impor-
tant area of interest in multiple organic transformations
for industrial and academic processes [6, 7]. Generally,
phosphine ligands are used to complex and active the pal-
ladium species, and excellent results have been reported
ZnO-based magnetic semiconductors (MS) have
received significant attention because of their unique prop-
erties and potential applications in electronic and light elec-
tronic devices such as gas sensors, light emitting diodes
(LED), and solar cells [39, 40]. Many doping attempts into
* Mona Hosseini-Sarvari
hossaini@shirazu.ac.ir
1
Department of Chemistry, College of Science, Shiraz
University, Shiraz 71454, Islamic Republic of Iran
1 3

J IRAN CHEM SOC
Table 1 Characterization data
for nano-Pd/Fe3O4/ZnO
XRD
Crystallite sizes are 25.9 nm
62.79 m2/g
BET surface area
XPS
TEM
ICP
Binding energy (BE) of the Pd3d3/2 and Pd3d5/2 were 335.4 and 340.7, respectively
21.5–25.0 nm
Contents of Pd and Zn were 47.01 and 21.77 % (w/w)
Table 2 Optimization the amount of catalyst and solvent for the
reaction between 4-bromoacetophenone 1a and boronic acid 2a
Pd/ Fe3O4/ ZnO
Br
B(OH)2
O
O
3a
1a
2a
Entry Amount of catalyst
(mol% of Pd)a
Solvent
Time (h) Yield (%)
1
0.0005 (1.6 × 10−5
)
H2O
2
95
95
95
95
63
66
Trace
68
35
42
0
2
0.001 (3.2 × 10−5
0.002 (6.5 × 10−5
0.003 (9.7 × 10−5
0.003 (9.7 × 10−5
0.003 (9.7 × 10−5
0.003 (9.7 × 10−5
0.003 (9.7 × 10−5
0.003 (9.7 × 10−5
0.003 (9.7 × 10−5
No catalyst
)
)
)
)
)
)
)
)
)
H2O
1.6
1.3
1
3
H2O
4
H2O
5
DMSO
DMF
CH2Clb2
EtOHb
Toluene
10
12
11
5
6
7
8
9
7
10
11
Ethane-1,2 diol 7
H2O 24
Reaction condition: 4-bromoacetophenone (0.5 mmol), phenylbo-
ronic acid (0.5 mmol), K2CO3 (0.5 mmol), nano-Pd/Fe3O4/ZnO, sol-
vent (1 mL), 100 °C
a
The mol% of Pd was determined by ICP
Fig. 1 a SEM and b XPS of nano-Pd/Fe3O4/ZnO
b
Under reflux conditions
In addition, the free hydroxyl groups attached to the sur-
face of ZnO nanoparticles were protonated and then Pd (II)
was reduced to Pd (0) and located on the surface of ZnO
via a surface interaction. So, ZnO could act as a reductant
[46]. Thus new catalyst system can be well dispersed in the
reaction medium, conveniently separated from the reaction
mixture by using an external magnet, reused for several
times without significant loss of its activity, and ligand-free
conditions.
ZnO to form MS have been carried out, such as Co, Fe, and
Ni [41]. However, there are still many difficult problems in
ZnO-based MS, including the technique for crystal growth
and film fabrication, the quality of materials, p-type doping
and so on [42]. Alternatively, ZnO-based MS could also be
achieved by fabricating hybrid nanoparticles. Meanwhile,
the ZnO can prevent the aggregation of the Fe3O4 particles
and provide surface Zn-OH groups for further modification.
More recently, we reported for the first time a simple
and low-cost method for the synthesis of Pd/Fe3O4/ZnO
nanoparticles as a new catalyst and its application in the
synthesis of benzoxazoles and 2-oxazolines [43]. Herein,
we use this new catalyst for Suzuki and Heck coupling
reactions. Previously immobilize Pd nanoparticles on
Fe3O4 nanoparticles for C–C cross coupling reaction have
been reported [44, 45]. According to the literature ZnO in
this new catalyst system could play two roles. As described
in the previous paragraph, ZnO can prevent the aggrega-
tion of Fe3O4 particles and provide surface Zn-OH groups.
Experimental section
Chemicals were obtained from Fluka or Merck chemical
company. Catalysts were characterized by power X-ray dif-
fraction (XRD) on a Bruker D8-advance X-ray diffractometer
with Cu Ka (1.54, 178 Å) incident radiation. The distribu-
tion and morphology of the product were analyzed by Leica
Cambridge, model s360, version V03.03 scanning electron
1 3

J IRAN CHEM SOC
Table 3 Optimization of base and temperature in the reaction
between 4-bromoacetophenone 1a and boronic acid 2a
After completion of the reaction, the catalyst was removed
by a magnet and the resulting mixture was quenched with
water and extracted with EtOAc (2 × 10 mL). The com-
bined organic layer was dried over anhydrous sodium sul-
fate (Na2SO4) and evaporated in a rotary evaporator under
reduced pressure. Resulting product was purified by col-
umn chromatography on silica gel using n-hexane/ethyl
acetate (5:1) as eluent to afford the pure product.
Entry
Base (mmol)
Time (h)
Temp. (°C)
Yield (%)
1
K2CO3 (0.5)
K2CO3 (0.25)
K2CO3 (0.12)
KOH (0.5)
1
100
100
100
100
100
100
100
80
95
95
95
71
28
22
95
64
55
40
0
2
3.5
5
3
4
4
5
KF.2H2O (0.5)
Na2CO3.H2O (0.5)
Cs2CO3 (0.5)
K2CO3 (0.5)
K2CO3 (0.5)
K2CO3 (0.5)
Without base
12
10
1
6
General procedure for the synthesis of (E)‑ethyl
cinnamate
7
8
1
9
2
60
A mixture of aryl halide (1 mmol), ethylacrylate (1 mmol),
K3PO4 (1 mmol), nano-Pd/Fe3O4/ZnO (0.003 g), and DMF
(1.0 mL) was put into a preheated oil bath at 100 °C for
an appropriate period of time. Then, the reaction mixture
was diluted with EtOAc and the catalyst was removed
by a magnet. The filtrate was extracted with water and
the organic layer dried over CaCl2 and evaporated under
reduced pressure. Resulting products were purified by col-
umn chromatography over silica gel using n-hexane/ethyl
acetate (5:1) as eluent to give the desired pure product with
excellent yield.
10
11
3.5
24
rt
100
Reaction condition: 4-bromoacetophenone (0.5 mmol), phenylbo-
ronic acid (0.5 mmol), nano-Pd/Fe3O4/ZnO (0.003 g), H2O (1 mL),
and base
microscope (SEM) and transmission electron microscopy
(Zeiss EM10C TEM) using an accelerating voltage of 80 kV.
The amount of palladium on supports was determined by ICP
analyzer (Varian, Vista-pro) and atomic absorption spectros-
copy (AAS). X-ray photoelectron spectroscopy (XPS) meas-
urements were conducted with a XR3E2 (VG Microtech)
twin anode X-ray source using AlKα = 1486.6 eV). The
specific surface areas [SSABET; (m2/g)] of the nanopowders
were determined with the nitrogen adsorption measurement
applying the BET method at 77 K (BELsorp-mini II). FT-IR
spectra were run on a Shimadzu FTIR-8300 spectrophotom-
eter. Melting points were determined in open capillary tubes
in a Buchi-510 oil melting point apparatus.
General procedure for the synthesis of (E)‑stilbene
A mixture of aryl halide (1 mmol), styrene (1 mmol),
K3PO4 (1 mmol), nano-Pd/Fe3O4/ZnO (0.035 g), and DMF
(1.0 mL) was put into a preheated oil bath at 100 °C for
an appropriate period of time. All reactions were performed
under inert atmosphere of N2. Then, the reaction mixture
was diluted with EtOAc and the catalyst removed by a
magnet. The filtrate was extracted with water, the organic
layer dried over CaCl2 and evaporated under reduced pres-
sure. The resulting products were purified by column chro-
matography over silica gel using n-hexane/ethyl acetate
(5:1) as eluent to give the desired pure product with excel-
lent yield. All compounds are known and were character-
ized by comparison of their physical and spectroscopic data
with the authentic described in the literature.
Preparation of nano‑Pd/Fe3O4/ZnO catalyst
Nano-Pd/Fe3O4/ZnO was synthesized as reported in our
previous work [43]. The nitrate solution of palladium
(0.0025 g/mL) and Fe3O4/ZnO (0.01 g/mL) were sonicated
for 5 min. Then two solutions were mixed under vigorous
stirring at room temperature. Subsequently, Na2CO3 solu-
tion (0.1 M) was added drop-wise to the mixed solution
until the final pH of the solution was about 6.8. The prod-
ucts were washed with deionized water and ethanol two
times and dried at 80 °C for 3 h.
Results and discussion
Characterization of the catalyst
General procedure for the Suzuki–Miyaura coupling
reaction
Recently we reported the efficiency of nano-Pd/Fe3O4/
ZnO in the synthesis of benzoxazoles and 2-oxazolines
[43]. This catalyst was synthesized and fully characterized
by powder X-ray diffraction (XRD), transmission electron
microscopy (TEM), scanning electron microscopy (SEM),
X-ray photoelectron spectroscopy (XPS), BET surface
area measurement, FT-IR spectroscopy, and ICP analysis
A mixture of aryl halide (0.5 mmol), phenylboronic acid
(0.5 mmol), K2CO3 (0.5 mmol), and nano-Pd/Fe3O4/ZnO
(0.003 g, contain 9.7 × 10−5 mol% Pd), and H2O (1 mL)
was stirred at 100 °C in an oil bath under air atmosphere.
1 3

J IRAN CHEM SOC
Table 4 Nano-Pd/Fe3O4/ZnO catalyzed the synthesis of biaryls in water
Pd/Fe3O4/ZnO (0.003g)
X
B(OH)2
R1
R2
K2CO3 (0.5 mmol)
o
R1
R2
3
H O (1 mL)
1
2
,100 C
2
Entry
1
R1
X
R2
Product 3
Time (h)
1
Yield (%)
95
TONa (molproduct/molPd)
97,938
TOF (molproduct/molPd h)
97,938
4-COMe
Br
H
3a
1a
2
4-Cl
1b
Br
Br
Br
Br
Br
Br
Br
Br
I
H
H
H
H
H
H
3b
3c
3d
3e
3f
2
82
86
83
85
70
70
90
94
94
95
95
79
25
50
40
53
50
84,536
88,660
85,567
87,629
72,165
72,165
92,784
96,907
96,907
97,938
97,938
81,443
25,773
51,546
41,237
54,639
51,546
42,268
88,660
64,175
75,111
14,433
24,055
61,856
83,063
83,063
97,938
97,938
24,432
1718
3
4-NO2
1c
1
4
4-F
1d
1:20
1:10
5
5
4-CN
1e
6
4-Me
1f
7
H
1g
3g
3h
3i
3
8
4-COMe
1a
3,4,5-F
1:30
1:10
1.:10
1
9
4-COMe
1a
4-Et
H
10
11
12
13
14
15
16
17
18
H
1h
3g
3c
3d
3j
4-NO2
1i
I
H
4-F
1j
I
H
1
4-NH2
1k
I
H
3:20
15
10
14
7
H
1l
Cl
Cl
Cl
Cl
Cl
H
3g
3e
3k
3l
4-CN
1m
H
5155
4-CF3
1n
H
2946
2-Pyridin
1o
H
7806
4-NO2
H
3c
10
5155
1p
Reaction condition: 4-bromoacetophenone (0.5 mmol), phenylboronic acid (0.5 mmol), H2O (1 mL), K2CO3 (0.5 mmol), nano-Pd/Fe3O4/ZnO
(0.003 g), 100 °C under open air
a
Calculated according to mol% of Pd (9.7 × 10−5
)
and some of these results are shown in Table 1 [42]. Using
Debye–Scherrer formula: D = 0.9λ/βcosθ (where D is the
average crystallite size, λ is the wavelength of Cu Ka, β is
the full width at half maximum (FWHM) of the diffraction
peaks, and θ is the Bragg’s angle), the average sizes of Pd/
Fe3O4/ZnO is estimated to be about ~25.9 nm. The TEM
image and XPS spectra of Pd3d of the synthesized nano-
Pd/Fe3O4/ZnO are shown in (Fig. 1). Calculating the size
particles of Pd by XRD or TEM was impossible because of
very small amounts of Pd loaded on Fe3O4/ZnO; so accord-
ing to XRD the peak of Pd(0) is not strong.
Catalytic activity of nano‑Pd/Fe3O4/ZnO
Suzuki–Miyaura
Initially, the catalytic activity of nano-Pd/Fe3O4/ZnO was
tested in Suzuki–Miyaura reaction of boronic acids and
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J IRAN CHEM SOC
Table 5 Selected catalysts and conditions used for Suzuki–Miyaura cross-couplings
Entry Catalyst
Substrates
Condition
TON/TOF
References
1
Nano-Pd/Fe3O4/ZnO
I-C6H5/C6H5B(OH)2
Cat. [0.003 g, mol% of Pd
(9.7 × 10−5)], 100 °C/H2O under
open air
96,907/83,063 This study
2
3
Fe3O4 NP with Pd(0) on surface Br-C6H5/C6H5B(OH)2
Cat. (0.816 mol%), K3PO4, MeOH 11.6/0.65
[47]
[48]
Mag-IL-Pd
I-C6H5/C6H5B(OH)2
Cat. (0.025 mol%)
3800/633.3
K2CO3 (0.75 mmol), and 3 mL H2O,
under an argon atmosphere, 6 h
4
5
6
Pd/Fe3O4@C (Pd/MFC)
Pd/Fe3O4/G
I-C6H5/C6H5B(OH)2
K2CO3 (6 mmol), catalyst (30 mg, –/16.67
Pd: 0.308 mol %), EtOH
[49]
(30 mL), reflux for 1 h, (X = I)
p-Br-C6H4CHO/p-MeSC6H4B(OH)2 Cat. (0.3 mol%)
8100/97,500 [50]
K2CO3 (0.96 mmol), (H2O:EtOH)
(1:1), 80◦C microwave, 10 min
γ-Fe2O3@Cat-Pro(Pd)
p-I-C6H4NO2/p-MeC6H4B(OH)2
Cat. (0.01 mol%), Na2CO3,
(H2O:EtOH), 80◦C 30 min
–/18,000
[45]
Table 6 Condition screening of reaction between iodobenzene and
ethyl acrylate
observed in the yield of product 3a (almost 95 %) but the
reaction time was decreased (Table 2, entries 1–4). Obvi-
ously, there was no reaction without the use of any catalyst
(Table 2, entry 11). As known, solvent plays a crucial role
in the rate and the product distribution of Suzuki coupling
reactions. So, we screened various solvents in the model
reaction. Experiments carried out in DMSO, DMF, DCM,
EtOH, Toluene, and Ethane-1,2 diol yielded only trace
to 68 % of the cross-coupling product and ~30–95 % the
undesired homocoupling by-product. However, when we
switched to H2O, complete conversion of 4-bromoaceto-
phenone was observed, with only 1–2 % of the homocou-
pling by-product. So, we found that H2O was more effec-
tive than other solvents (Table 2, entries 4–10).
Then a series of bases and also the temperature were
taken into consideration. The results are shown in Table 3.
The base was found to have a pronounced effect in this
reaction, and both K2CO3 and Cs2CO3 were found more
effective, with KOH being almost as good, and KF.2H2O
and Na2CO3.H2O gave the product in low yield. So,
because K2CO3 is cheaper than Cs2CO3, K2CO3 was cho-
sen. As expected, no reaction occurred without using of a
base (Table 3, entry 11). The temperature of the reaction
is also an important parameter. The best temperature was
found at 100 °C (Table 3, entry 1).
Entry
Base
Solvent
Time (h)
Yield (%)
1
K2CO3
K2CO3
K3PO4
Cs2CO3
KOH
H2O
10
7
Trace
20
2
DMF
DMF
DMF
DMF
DMF
DMF
H2O
3
4
85
4
7
40
5
8
Trace
Trace
33
6
Na2CO3
NaOt−Bu
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
10
7
7
8
10
8
26
9
DMSO
EtOH
CH3CN
THF
18
10
11
12
8
10
10
10
Trace
Trace
Reaction condition: Phenyl iodide (1 mmol), ethyl acrylate (1 mmol),
base (1 mmol), solvent (1 mL), nano-Pd/Fe3O4/ZnO (0.003 g) at
100 °C under open air
aryl halides under ligand-free conditions. To standardize
the reaction conditions, we performed a series of reactions
with several bases, solvents, temperatures, and catalyst
concentration to obtain the best possible combination using
the reaction of 4-bromoacetophenone and phenylboronic
acid as model compounds (Tables 2, 3).
According to Table 2, different catalyst loadings
between 0.0005 and 0.003 g were investigated. When the
amount of the catalyst was increased no changes were
To investigate the generality of the catalytic proto-
col, we performed reactions using various aryl halides
with arylboronic acids under the optimized conditions.
The results are shown in Table 4. Various substituted aryl
iodides, and bromides with deactivated (electron rich) and
activated (electron poor) groups were converted efficiently
to the desired products in good to excellent yields within
0.8–3.3 h (Table 4, entries 1–13). Also, the coupling reac-
tion could be efficiently carried out using arylboronic acids
1 3

J IRAN CHEM SOC
Table 7 Synthesis of ethyl cinannamates 5 in the presence of nano-
Pd/Fe3O4/ZnO
under the same conditions. In this case, the corresponding
products were obtained in poor or moderate yields (Table 4,
entries 14–18).
According to Table 4, the turnover number (TON) and
turnover frequency (TOF) values were determined on the
basis of the yield of formation of final product. These
results showed very high efficiency of this nanocatalyst
compared to that in the literature (see Table 5).
Entry
1
R1
H
X
I
Time (h)
4
Product
Yield (%)
85
CO2Et
Mizoroki–Heck
1h
5a
5b
5c
5d
5e
5f
Having established the efficacy of the nano-Pd/Fe3O4/
ZnO in the Suzuki–Miyaura coupling reactions, we next
turned our attention to Heck coupling reaction. In an effort
to develop a good catalytic system, the coupling of iodo-
benzene and ethyl acrylate was investigated to optimize the
reaction conditions (Table 6). Efficiency of this reaction is
mainly affected by the amount of catalyst, temperature, and
reaction time. For getting the best conditions, initially we
started the condensation of iodobenzene and ethyl acrylate
in the presence of nano-Pd/Fe3O4/ZnO (0.003 g) as a cata-
lyst and K2CO3 (0.5 mol) H2O as solvent, at 100 °C, which
led to a trace amount of product 5a. To enhance the yield
of the desired product the base and solvent were changed.
Different bases (Cs2CO3, KOH, Na2CO3, NaOt−Bu, and
K3PO4) and solvents (DMSO, DMF, EtOH, CH3CN, THF,
and DMF) were investigated. The results are summarized
in Table 5. According to Table 6, K3PO4 is the most effec-
tive base in terms of the yield (85 %) and DMF indeed gave
the best value for the reaction. Under the optimized reac-
tion conditions, the reaction of ethyl acrylate with different
aromatic halides was investigated (Table 7). The reaction
proceeded smoothly with the formation of E-isomers with
60–90 % yields. The E-isomers products, as confirmed by
1H NMR spectroscopic analysis due to coupling constant,
were obtained exclusively in all cases and comparing to the
authentic results reported in the literature. In addition, it
was found that aromatic halides with withdrawing groups
were more active than that of electron donating groups.
Then we tried to study the Heck reaction between aryl
halides and styrene to synthesize stilbene derivatives. Ini-
tially, we started the reaction of iodobenzene (1 mmol) and
styrene (1 mmol) using K3PO4 (1 mmol) as base, DMF
(1 mL) as solvent, and nano-Pd/Fe3O4/ZnO (0.003 g) as
catalyst at 100 °C under air atmosphere (the same reac-
tion conditions between 1h and 4a), which led to low yield
(7 %) of E-1,2-diphenylethene. To enhance the yield of
the desired product the reaction was carried out under N2
atmosphere. So, the reaction time decreased and the pro-
ductivity of the reaction increased but was not very high.
Hence, it was thought worthwhile to carry out the reac-
tion in the presence of higher amount of the catalyst. As
indicated in Table 8, maximum yield was obtained (73 %)
CO2Et
CO2Et
CO2Et
2
3
4
5
6
7
8
9
4-NO2
I
I
2.5
2.5
5
91
92
60
67
80
83
85
69
O2N
1i
4-F
F
1j
4-NH2
I
H2N
1k
CO2Et
Ph
Br
7
1e
CO2Et
4-NO2 Br 4.25
O2N
1c
CO2Et
4-F
Br 4
F
1d
5g
5h
5i
CO2Et
CO2Et
4-CN Br 3.45
NC
Cl
1e
4-Cl
5.5
Br
1b
Reaction condition: aryl halide (1 mmol), ethyl acrylate (1 mmol),
K3PO4 (1 mmol), DMF (1 mL), nano-Pd/Fe3O4/ZnO (0.003 g),
100 °C under open air
bearing either electron-rich or electron-poor substituted
groups (Table 4, entries 8, 9). We also investigated whether
aryl chlorides were active for the Suzuki–Miyaura reaction
1 3

J IRAN CHEM SOC
Table 8 Optimization of the amount of nano-Pd/Fe3O4/ZnO in the
Table 9 Synthesis of stilbenes in the presence of nano-Pd/Fe3O4/
reaction between iodobenzene and styrene
ZnO
Pd/ Fe3O4/ ZnO
Ph
X
+
R1
Ph
4b
R1
K3PO4/ DMF
100 °C, N2
1
6
X= I, Br
Entry
Amount of catalyst [g]
Yield [%]
1
2
3
4
0.045
0.035
0.02
73
73
25
10
Entry
1
R1
X
I
Product
6a
Yield (%)
73
H
0.008
1h
Reaction condition: phenyliodide (1 mmol), styrene (1 mmol), K3PO4
(1 mmol), DMF (1 mL), 100 °C, under N2, 22 h
2
3
4
5
6
7
8
4-NO2
I
I
85
82
50
73
67
75
66
O2N
1i
when the reaction was loaded with 0.035 g of the catalyst
(entry 2). A further increasing of catalyst loading does
not affect the yield (entry 1). Detailed observations of all
the reactions are given in Table 9. We observed that the
catalyst was very active for the Heck reaction under such
conditions.
6b
4-F
F
1j
6c
For practical applications of heterogeneous catalysts,
especially in industry, the heterogeneity and level of reus-
ability are very important. To clarify this, the heterogene-
ity of the catalyst was evaluated to study whether the reac-
tion using solid Pd catalysts occurred on the Fe3O4/ZnO
surface or was catalyzed by Pd species in the liquid phase.
To address this issue, two separate experiments were con-
ducted with 4-bromotoluene and phenylboronic acid. In the
first experiment, the reaction was terminated after 2 h; at
this juncture, the catalyst was separated from the reaction
mixture by an external magnet and the reaction was con-
tinued with the filtrate for an additional 3 h. In the second
experiment, the reaction was terminated after 2 h. In both
cases, the desired product was obtained in the same yield
(30 %). Pd was not detected in the filtrate in either experi-
ment by ICP analyzer. These studies demonstrate that only
the Pd in the surface of Fe3O4/ZnO during the reaction is
active, and the reaction proceeds on the heterogeneous
surface.
The recovery and reusability of nano-Pd/Fe3O4/ZnO
catalyst were also investigated in the Suzuki reaction of
4-bromoacetophenone and phenylboronic acid and Heck
reaction of iodobenzene with ethyl acrylate. The results
are shown in Fig. 2. In both reactions, after completion for
the first reaction to afford the corresponding product, the
catalyst was recovered magnetically, washed with EtOAc
and water, and finally dried at 80 °C. A new reaction was
then performed with fresh solvent and reactants under the
same conditions. As can be seen in Fig. 3, nano-Pd/Fe3O4/
ZnO catalyst could be used more than four times without
H
Br
1g
6a
4-NO2 Br
O2N
1c
6b
4-F
Br
F
1d
6c
4-CN Br
NC
1e
6d
4-Cl
Br
Cl
1b
6e
6f
9
4-CH3 Br
28
H3C
1f
Reaction condition: Aryl halide (1 mmol), styrene (1 mmol), K3PO4
(1 mmol), DMF (1 mL), nano-Pd/Fe3O4/ZnO (0.035 g), 100 °C,
under N2, 22 h
1 3

J IRAN CHEM SOC
exhibited excellent activities for the Suzuki–Miyaura and
Heck reactions. The catalyst has the advantage to be com-
pletely recoverable with the simple application of an exter-
nal magnet, while without considerable deactivation in
catalytic activity during the reuse process. Furthermore, the
Pd/Fe3O4/ZnO catalyst not only solves the basic problems
of catalyst separation and recovery but also avoids the use
of phosphine ligands in comparison with the homogeneous
Pd catalyst system.
91
91
85
85
85
85
82
83
78
78
Acknowledgments We are grateful to Shiraz university research
council for the support of this work.
Cycle
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