Fe3O4@SiO2-polymer-imid-Pd magnetic porous nanosphere as magnetically separable catalyst for Mizoroki-Heck and Suzuki-Miyaura coupling reactions

Article abstract of DOI:10.1007/s13738-014-0443-5

The activity of palladium nanoparticles supported on poly (N-vinylpyrrolidone) grafted Fe₃O₄@SiO₂ was investigated in the cross-coupling reactions. We have applied this catalyst under low loading of the supported palladium nanoparticles for the coupling of aryl halides with alkenes (Mizoroki-Heck reaction) and organoboronic acids (Suzuki-Miyaura reaction) in the absence of phosphorous ligands. Short reaction times and excellent yields of the products express the effectiveness of this catalyst. The nanocatalyst can be separated from the reaction mixture by applying a permanent magnet externally and can be reused for six times without appreciable change in catalytic activity. Also, the amount of leaching of Pd nanoparticles has been determined by ICP analysis and results showed low leaching of the metal into solution from the supported catalyst.

Full text of DOI:10.1007/s13738-014-0443-5

J IRAN CHEM SOC
DOI 10.1007/s13738-014-0443-5
ORIGINAL PAPER
Fe3O4@SiO2-polymer-imid-Pd magnetic porous nanosphere
as magnetically separable catalyst for Mizoroki–Heck
and Suzuki–Miyaura coupling reactions
•
Mohsen Esmaeilpour Jaber Javidi
•
•
Fatemeh Nowroozi Dodeji Hamed Hassannezhad
Received: 4 September 2013 / Accepted: 22 February 2014
Ó Iranian Chemical Society 2014
Abstract The activity of palladium nanoparticles sup-
ported on poly (N-vinylpyrrolidone) grafted Fe3O4@SiO2
was investigated in the cross-coupling reactions. We have
applied this catalyst under low loading of the supported
palladium nanoparticles for the coupling of aryl halides
with alkenes (Mizoroki–Heck reaction) and organoboronic
acids (Suzuki–Miyaura reaction) in the absence of phos-
phorous ligands. Short reaction times and excellent yields
of the products express the effectiveness of this catalyst.
The nanocatalyst can be separated from the reaction mix-
ture by applying a permanent magnet externally and can be
reused for six times without appreciable change in catalytic
activity. Also, the amount of leaching of Pd nanoparticles
has been determined by ICP analysis and results showed
low leaching of the metal into solution from the supported
catalyst.
Introduction
Palladium-catalyzed carbon–carbon cross-coupling reac-
tions exemplify one of the important processes in organic
chemistry [1–4]. Recent progress in palladium catalysis has
revealed that Pd in nanoparticle forms can catalyze
numerous reactions such as Sonogashira–Hagihara [5–7],
Mizoroki–Heck [8, 9], Suzuki–Miyaura [10] and Stille [11]
reactions. Coupling of aryl halides with alkenes (Mizoroki–
Heck reaction) and organoboronic acids (Suzuki–Miyaura
reaction) has significant importance, and is a well-estab-
lished methodology in modern organic synthesis. These
Pd-catalyzed coupling reactions are ranked today among
the most general transformations in organic synthesis, and
have great industrial potential for the synthesis of bioactive
compounds, natural products, chemicals and advanced
materials [12].
Keywords Cross-coupling Á Suzuki–Miyaura Á Mizoroki–
Heck Á Palladium Á Magnetic nanoparticles Á Heterogeneous
catalysis
The Heck reaction is a powerful and modern palladium-
catalyzed method for generation of carbon–carbon bonds
between unsaturated entities, and it has been extensively
utilized in arylation and vinylation of olefins [13–15].
The reaction has been applied to many areas, including
natural products, bioactive compounds, UV absorbers, drug
intermediates, antioxidants, fine chemicals syntheses, and
industrial applications [16].
Also, the palladium catalyzed cross-coupling of aryl
halides with arylboronic acids, the Suzuki reaction [17–
20]. Among the traditional protocols, aryl iodides, bro-
mides have been found to be the more reactive and are
therefore commonly employed [21]. However, the more
economic aryl chlorides have been rarely employed as
coupling partners in palladium catalyzed Suzuki coupling
because the oxidative addition of C–Cl bond to Pd(0)
species is usually difficult [21]. In past decades, significant
research effort has been focused on the preparation and use
M. Esmaeilpour
Chemistry Department, College of Science, Shiraz University,
Shiraz, Iran
J. Javidi (&) Á F. N. Dodeji
Department of Pharmaceutics, School of Pharmacy, Shaheed
Beheshti University of Medical Sciences, Tehran, Iran
e-mail: jaberjavidi@gmail.com
H. Hassannezhad
Department of Chemistry, Payame Noor University,
PO Box 74515-161, Estahban, Iran
123

J IRAN CHEM SOC
of catalysts capable of activating aryl chloride substrates.
Complexes containing palladacyclic complexes [22] or N-
heterocyclic carbenes [23] and bulky phosphines [24], have
proved to be unique, highly efficient catalysts for Suzuki
cross-coupling reactions of aryl chlorides.
homogeneous catalysts for industrial reaction processes
[40]. To overcome this problem, great efforts have been
devoted to develop heterogeneous catalysts.
Because of these reasons and also as a part of our
ongoing research program on the application of magnetic
catalysts for the development of useful new synthetic
methodologies [41] herein, we report the use of polymer-
imid-Pd functionalized Fe3O4@SiO2 nanoparticle (Fe3-
O4@SiO2-polymer-imid-Pd) without added phosphine
ligands in Mizoroki–Heck and Suzuki–Miyaura cross-
coupling reactions with.
Unfortunately, most of these catalysts are expensive and
difficult to synthesize, which significantly limited their
industrial applications.
Phosphines and phosphinites as important phosphorous-
based ligands in organometallic chemistry are of current
interest and their metal complexes have been used in many
catalytic reactions [25]. However, Phosphorus ligands are
very often moisture and air sensitive, which creates prob-
lems in the catalytic system [26].
Experimental
Phosphine ligands are comparatively difficult to make or
rather more expensive [27] and often lead to competitive
degradation of the Pd catalyst through the P–C bond
cleavage of a coordinated phosphine ligand [15]. In addi-
tion, there is a strong tendency to avoid application of these
ligands because of their possibly negative impact on the
natural environment [25]. Consequently, the development
of economical, accessible phosphine-free palladium cata-
lytic systems to overcome these difficulties is still of
desirable goal.
General
The chemicals were obtained from Fluka or Merck chem-
ical companies and used without further purification.
Transmission electron microscopy (TEM) image was
obtained on a Philips EM208 TEM with an accelerating
voltage of 100 kV. X-ray photoelectron spectroscopy
(XPS) of catalyst was performed with XR3E2 (VG Mic-
rotech) twin anode X-ray source using AlKa = 1486.6 eV.
The progress of the reactions was followed with TLC using
silica gel SILG/UV 254 plates or GLC on a Shimadzu
model GC-10A instrument. IR spectra were run on a Shi-
Nanomagnetism is a vivid and highly interesting topic of
modern solid state magnetism and nanotechnology [28–
30]. This is not only due to the ever-increasing demand for
miniaturization, but also due to novel phenomena and
effects which appear only on the nanoscale: e.g., spin
structures, superparamagnetism, coupling phenomena, new
types of magnetic domain walls and interactions between
electrical current and magnetism [31]. Fe3O4 magnetic
nanoparticles have been used in various fields such as
sealing, oscillation damping, information storage and
electronic devices [32–34]. One of the rapidly developing
applications of Fe3O4 magnetic nanoparticles in recent
years is in biomedical areas, including rapid biologic sep-
aration and drug delivery and such as catalysts [35–37].
Recently, magnetic core–shell nanostructures have
attracted more attention due to their unique magnetic
properties [37]. In contrast to the difficulty observed in
recovering and reusing most solid catalysts, core–shell
nanostructure magnetic catalysts can be easily retrieved
under the influence of a magnetic field and used in sub-
sequent reactions. Due to this property, using magnetic
core–shell structure composites as catalysts has been rec-
ommended in the literature [38, 39].
1
madzu FTIR-8300 spectrophotometer. The H NMR and
13C NMR spectra were recorded on a Bruker Avance DPX
250 MHz Spectrometer in CDCl3 or DMSO-d6 solvents
using TMS as an internal standard. Mass spectra were
obtained at 70 eV. Pd loading and leaching test was carried
out with an inductively coupled plasma (ICP) analyzer
(Varian, vista-pro). Melting points were determined with a
Buchi 510 instrument in open capillary tubes and are
uncorrected. Evaporation of solvents was performed at
reduced pressure, with a Buchi rotary evaporator. All
products were identified by comparison of their spectral
data and physical properties with those of the authentic
sample and all yields refer to isolated products.
General procedure
Preparation of Fe3O4@SiO2 core–shell
The core–shell Fe3O4@SiO2 nanospheres were prepared by
a modified Stober method in our previous work [41]. In a
typical procedure, the mixture of FeCl3Á6H2O (1.3 g,
4.8 mmol) in water (15 ml) was added to the solution of
polyvinyl alcohol (PVA 15000) (1 g), as a surfactant, and
FeCl2Á4H2O (0.9 g, 4.5 mmol) in water (15 mL), which
was prepared by completely dissolving PVA in water fol-
lowed by addition of FeCl2Á4H2O. The resultant solution
Homogeneous catalysis is superior to heterogeneous
catalysis, making possible highly active and selective
organic transformations. However, the separation and
recovery of homogeneous catalysts are not easy and so it is
still significant to prepare more active heterogeneous cat-
alysts and to find effective ways of heterogenizing
123

J IRAN CHEM SOC
was left to be stirred for 30 min in 80 °C. Then, hexame-
thylentetraamine (HMTA) (1.0 mol/l) was added dropwise
with vigorous stirring to produce a black solid product
when the reaction media reaches pH 10. The resultant
mixture was heated on water bath for 2 h at 60 °C and the
black magnetite solid product was filtered and washed with
ethanol three times and was then dried at 80 °C for 10 h.
Then, Fe3O4 nanoparticle (0.50 g, 2.1 mmol) was dis-
persed in the mixture of ethanol (50 mL), deionized water
(5 mL) and tetraethoxysilane (TEOS) (0.20 mL), followed
by the addition of 5.0 mL of NaOH (10 wt%). This solu-
tion was stirred mechanically for 30 min at room temper-
ature. Then, the product, Fe3O4@SiO2, was separated by an
external magnet, and was washed with deionized water and
ethanol three times and dried at 80 °C for 10 h.
NaCl solution (5 %) (30 mL) at room temperature for 24 h.
The mixture was filtered off, washed thoroughly with
excess H2O and then dried in an oven under vacuum at
70 °C for 8 h (Fe3O4@SiO2-polymer-imid-S). The chlo-
ride ion capacity of imidazolium type Fe3O4@SiO2-poly-
mer was found using argentimetric titration method (0.1 g
of Fe3O4@SiO2-polymer-imid-S was suspended in 10 mL
of 0.1 M HNO3). After adding 1 mL of 0.1 M AgNO3, the
mixture was stirred for 10 h at room temperature. The
chloride counter ions precipitated as AgCl. The amount of
remaining Ag? was back titrated using 0.1 M HCl. The
permanent charge density of imidazole groups was calcu-
lated to be 1.31 mmol/g. The resulting Fe3O4@SiO2-
polymer-imid-S (1.0 g) was reacted with PdCl2 (3 mmol)
in the presence of Et3N (6 mmol) as a base and DMF
(15 mL) as a solvent at 80 °C for 16 h. The mixture
(Fe3O4@SiO2-polymer-imid-Pd) was filtered by an exter-
nal magnetic field and washed thoroughly with DMF
(2 9 5 mL) and H2O (2 9 5 mL) and dried at 70 °C for
8 h (Scheme 1) [42].
Synthesis of poly (N-vinylimidazole) functionalized
Fe3O4@SiO2 nanoparticle (Fe3O4@SiO2-polymer-imid)
Fe3O4@SiO2 (1 g) was added to the solution of 3-amino-
propyl (triethoxy) silane (1 mmol, 0.176 g) in ethanol
(10 mL) and the resultant mixture was under reflux for
12 h. The solvent was removed and the resulting solid
(Fe3O4@SiO2-NH2) was dried at 80 °C overnight. The
product was washed with ethanol and water to remove
unreacted species and dried at 80 °C for 6 h. Fe3O4@SiO2-
NH2 (1 g) was suspended in dry THF (15 mL) and sus-
pension cooled down to 0 °C. Triethylamine (0.151 g,
1.5 mmol) was added, followed by addition of acryloyl
chloride (0.109 g, 1.2 mmol) over a period of 1 h. Then,
the resultant mixture was stirred at 0 °C for a further 4 h
and the modified Fe3O4@SiO2 was isolated by external
magnetic field and washing with THF (10 mL), water
(2 9 10 mL) and acetone (10 mL). The solid obtained was
then dried at 80 °C for 12 h. To the resultant mixture
(1.0 g), N-vinylimidazole (2 mL) and recrystallized ben-
zoyl peroxide (0.025 g) were added and the mixture was
heated at 80 °C for 12 h. The poly (N-vinylimidazole)
functionalized Fe3O4@SiO2 nanoparticle (Fe3O4@SiO2-
polymer-imid) was separated by an external magnet, and
was washed with deionized water and ethanol three times
and dried at 80 °C for 10 h [42].
General procedure for Heck cross-coupling reactions
using Fe3O4@ SiO2-polymer-imid-Pd magnetic
nanocatalyst
Fe3O4@SiO2-polymer-imid-pd
(0.03 g),
K2CO3
(2.0 mmol), olefin (1.2 mmol), aryl halide (1.0 mmol)
were placed in a 25-mL flask equipped with a magnetic
stirring bar in NMP and heated at 110 °C. On completion
of the reaction determined by TLC or GC, the catalyst was
easily recovered using magnetic field and the filtrate was
poured into water (50 mL) and extracted with EtOAc
(3 9 10 mL). The combined organic phases were dried
over Na2SO4, filtered and evaporated in vacuum. The
mixture was then purified by column chromatography over
silica gel or recrystallization to afford a product with high
purity.
General procedure for Suzuki–Miyaura reactions using
Fe3O4@SiO2-polymer-imid-Pd magnetic nanocatalyst
A
suspension of aryl halide (1.0 mmol), K2CO3
(2.0 mmol), Fe3O4@SiO2-polymer-imid-pd nanocatalyst
(0.025 g) and NMP (3 mL) were mixed in a reaction flask
and phenylboronic acid (1.2 mmol) was added. The reac-
tion mixture was stirred at 90 °C in the air for an appro-
priate time. The completion of the reaction was monitored
by TLC. After completion of the reaction, the catalyst was
easily recovered using magnetic field and the mixture was
diluted with n-hexane and water. The organic layer was
washed with brine, dried over Na2SO4, and concentrated
under reduced pressure. Further purification, if it was
necessary, was performed on a silica gel column eluted
Synthesis of polymer-imid-Pd functionalized Fe3O4@SiO2
nanoparticle (Fe3O4@SiO2-polymer-imid-Pd)
Fe3O4@SiO2-polymer-imid (1 g) was dispersed in the
DMF solution (15 mL), ultrasonically for 15 min. Then,
methyl iodide (2.5 mmol, 0.155 mL) was added and the
mixture was stirred at 80 °C for 16 h and filtered by an
external magnet field and the product was washed with
DMF and ethanol to remove no reacted species and dried at
70 °C for 6 h. The resultant solid product was stirred in
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J IRAN CHEM SOC
Scheme 1 Process for preparation of polymeric N-heterocyclic carbene/Pd functionalized Fe3O4@SiO2 nanoparticle
Fig. 1 TEM (a) and XPS (b) of Fe3O4@SiO2-Polymer-imid-Pd
with n-hexane/ethyl acetate to give the pure biphenyl
The catalyst was characterized by XPS to ascertain the
oxidation state of Pd species. As shown in Fig. 1b, the
peaks located around 335.6 and 340.6 eV were assigned to
the Pd 3d5/2 and Pd 3d3/2 level in the Pd (0) metallic form
in agreement with the literature report [43]. The binding
energy clearly showed the fact that the Pd nanoparticles in
our catalyst contained only Pd (0) species.
product in high to excellent yields.
Results and discussion
TEM image of Fe3O4@SiO2-polymer-imid-pd nanocata-
lyst is presented in Fig. 1a. According to this figure, Pd
nanoparticle has a diameter around 10 nm.
Determination of the Pd content was carried out by ICP
analysis on the digested catalyst in refluxing HCl (37 %).
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J IRAN CHEM SOC
According to the ICP analysis, the Pd content in the
magnetic Fe3O4@SiO2-polymer-imid-Pd catalyst was
0.33 mmol/g.
To show the merit of application of these nanoparticles
in organic synthesis, we applied them as the catalysts in the
Mizoroki–Heck reaction (Scheme 2).
Scheme 2 Mizoroki–Heck
cross-coupling reactions
Table 1 Optimization of different proportions of Fe3O4@SiO2-polymer-imid-pd nanocatalyst and also effect of amount of catalyst,
solvents, temperature and using different bases upon the reaction of iodobenzene with n-butyl acrylate
Entry
Solvent
Catalyst amount (g)
Bases
Temperature (°C)
Yielda (%)
1
NMP
DMF
DMSO
CH3CN
EtOH
H2O
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
–
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
None
110
110
110
110
110
110
110
110
140
110
110
110
110
110
110
150
110
110
110
110
110
r.t
96
83
74
52
41
22
25
31
–
2
3
4
5
6
7
Toluene
THF
8
9
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Et3N
50
81
76
63
38
59
–
NaOAc
Cs2CO3
NaOH
nPr3N
KF
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
0.01
0.02
0.025
0.04
0.05
0.03
0.03
0.03
26
76
87
96
96
24
93
96
100
120
Reaction conditions: 1.0 mmol iodobenzene, 1.2 mmol n-butyl acrylate, 2 mmol base in 3.0 ml of solvent for 4.0 h
a
Isolated yield
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J IRAN CHEM SOC
Table 2 Heck–Mizoroki coupling of different aryl halides with n-butyl acrylate or styrene in the presence of Fe3O4@SiO2-Polymer-imid-Pd
catalyst and K2CO3 as base
Entry
1
Aryl halide
I
R1
Time
(h)
Isolated Yield
(%)b
TONc
97
TOF
(h-1)d
[Refs.]
[45]
CO2Bun
0.5
96
194
CO2Bun
CO2Bun
CO2Bun
CO2Bun
Me
I
1.0
95
96
96
[45]
2
3
4
5
MeO
O2N
O2N
I
1.0
0.5
93
97
93
94
98
94
94
[46]
[45]
[48]
I
I
196
125
0.75
CH3
I
6
CO2Bun
1.0
2.0
92
92
93
93
93
[45]
[46]
CO2Bun
CO2Bun
CO2Bun
CO2Bun
Br
46.5
7
8
Me
Br
Br
4.0
89
92
93
90
93
94
22.5
124
125
[46]
[48]
[48]
NC
O2N
0.75
0.75
9
Br
10
Br
Br
CO2Bun
CO2Bun
2.0
2.0
88
90
89
91
44.5
45.5
[48]
[48]
11
12
N
N
N
CO2Bun
CO2Bun
Cl
Br
4.0
86
87
78
21.75
7.8
[47]
[47]
13
14
10.0
77e
Cl
81e
90e
82
91
8.2
[47]
[47]
CO2Bun
CO2Bun
Me
Cl
10.0
1.5
15
16
O2N
Cl
60.7
I
1.0
95
96
96
[46]
17
Ph
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J IRAN CHEM SOC
Table 2 continued
Entry
Aryl halide
R1
Time
(h)
Isolated Yield
(%)b
TONc
TOF
(h-1)d
[Refs.]
MeO
I
1.5
2.0
95
89
96
90
64
45
[46]
[46]
18
19
Ph
Ph
I
CH3
Br
2.0
93
94
47
[46]
20
21
22
Ph
Ph
Ph
Me
NC
Br
5.0
1.0
91
90
92
91
18.4
91
[46]
[46]
Br
O2N
Cl
Br
1.0
4.0
2.5
94
85
87
95
86
88
95
[45]
[47]
[47]
23
24
25
Ph
Ph
Ph
Br
21.5
35.2
Br
N
N
Br
Cl
N
2.0
91
92
46
[45]
26
Ph
12.0
12.0
2.5
73e
75e
88e
74
76
89
6.2
6.3
[47]
[47]
[47]
27
28
29
Ph
Ph
Ph
Me
Cl
O2N
Cl
35.6
All reactions were carried out with Ar-X (1 mmol), alkene (1.2 mmol), and K2CO3 (2 mmol) in the presence of the Fe3O4@SiO2-polymer-imid-
pd catalyst (0.03 g) in 3.0 mL of NMP at 110 °C
a
Isolated yield
b
TON = Nproduct/Npalladium, N denotes molar numbers
c
TOF = Nproduct/(Npalladium 9 t), N denotes molar numbers, and t denotes reaction time (h)
d
With additional tetrabutylammonium bromide (TBAB) (0.04 mmol)
Initial studies were performed upon the reaction of
iodobenzene with n-butyl acrylate as a model reaction and
the effects of amount of catalyst, different solvents, bases
and temperature were studied for this reaction (Table 1). A
controlled experiment indicated that no cross-coupling
product was observed in the absence of the base or catalyst
and the reaction did not proceed even at a high temperature
(Table 1, entries 9, 16).
with (0.03 g:1 mmol:1.2 mmol:2 mmol) ratio of catalyst,
iodobenzene, n-butyl acrylate and K2CO3 in NMP at
110 °C (Table 1, entry 1). Decreasing the catalyst con-
centration resulted in lower yields under the same condi-
tions (Table 1, entries 17–19). On the other hand, higher
amounts of catalyst did not improve the yield or reaction
rate (Table 1, entries 20 and 21). Furthermore, we exam-
ined different reaction conditions in common organic sol-
vents such as DMF, DMSO, CH3CN, EtOH, H2O, Toluene
and THF at 110 °C (Table 1, entries 2–8) and excellent
yields of the product were observed in NMP (Table 1,
entry 1). The effect of temperature was studied by carrying
out the model reaction at different temperatures in NMP in
For such a purpose, firstly the influences of the catalytic
amount on the yield were investigated. The reaction was
performed with different amounts of Fe3O4@SiO2-poly-
mer-imid-pd as catalyst. The results are listed in Table 1.
The best result was achieved by carrying out the reaction
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J IRAN CHEM SOC
Fe3O4@SiO2-polymer-imid-pd nanocatalyst exhibited
higher activity with electron-withdrawing substituents
(Table 2, entries 4, 5, 9, 10, 16, 22, 23, 29) relative to
electron-donating substituents on the aryl halides
(Table 2, entries 2, 3, 8, 15, 18, 19, 21, 28). Also, the
coupling reaction of n-butyl acrylate or styrene with both
electron-releasing and electron-withdrawing aryl bromides
afforded the desired products in high yields (Table 2,
entries 7–13, 20–26).
The more easily accessible and cheaper aryl chlorides
have not been employed much, in palladium-catalyzed
coupling reactions, because the oxidative addition of C–
Cl bond to Pd (0) species is usually difficult. Although
aryl chlorides are not as reactive as aryl iodides and
bromides and are less likely employed in coupling
reactions, Heck reactions could be carried out by this
catalyst in the presence of tetrabutylammonium bromide
(TBAB) (Jeffery Catalyst) as an additive (Table 2,
entries 14–16 and entries 27–29) which increased the
conversion rate by formation and stabilization of Pd
colloids.
Fig. 2 Conversion of aryl chlorides with various Pd amount catalyst
the presence of K2CO3 (room temperature, 100, 110 and
120 °C) (Table 1, entries 1 and 22–24) and the best result
was obtained at 110 °C (Table 1, entry 1). The yield of the
product was negligible at room temperature, and only a
trace amount of the product was obtained (Table 1, entry
22). Moreover, a high temperature appears to be essential
for the Heck reaction to take place (Table 1, entries 1, 23
and 24). Also, the coupling of iodobenzene and n-butyl
acrylate was carried out in NMP with the Fe3O4@SiO2-
polymer-imid-pd catalyst at 110 °C in the presence of 2
equiv of different bases (Table 1). The results indicate that
K2CO3 was the best base for this reaction (Table 1, entry
1). The coupling with triethylamine, sodium carbonate,
cesium carbonate, sodium hydroxide, tripropylamine and
potassium fluoride gave n-butyl cinnamate in 50, 81, 76,
63, 38 and 59 % yield, respectively (Table 1, entries
10–15). Therefore, the best results for the Heck reaction of
iodobenzene with n-butyl acrylate were obtained using
0.03 g of the catalyst in NMP as the solvent and K2CO3 as
the base at 110 °C.
To investigate the possibility of conversion of aryl
chlorides with less Pd amount, a case reaction (n-butyl
acrylate with chlorobenzene) was carried out with various
amount of catalyst (0.01, 0.02, 0.025 and 0.30 g) in NMP
and K2CO3 at 110 and progress of reaction was monitored
by GC. The percent of conversion versus time of reaction
for four amounts is presented in Fig. 2. As shown the best
result attributed to 0.03 g of catalyst although the result of
0.025 g of catalyst is also significant.
Also, the efficiency of catalyst was evaluated in the
Suzuki coupling reaction as a versatile method for C–C
bond formation in organic synthesis. (Scheme 3).
We initially studied the coupling of iodobenzene with
phenylboronic acid as a model reaction under different
reaction conditions (Table 3). The optimized reaction
conditions were: 1 mmol of aryl halides, 1.2 mmol of
arylboronic acids, 0.025 g of Fe3O4@SiO2-polymer-imid-
Pd, 2 mmol of K2CO3 and 3 mL of NMP at 90 °C
(Table 3, entry 1).
The C–C cross coupling reaction of functional substi-
tuted aryl halides has much attention. Under the deter-
mined reaction conditions, a wide range of aryl halides
bearing electron-donating and electron-withdrawing
groups reacted with n-butyl acrylate and styrene effi-
ciently to produce the corresponding cross-coupling pro-
ducts in good to excellent yields. Nevertheless,
Under our optimized reaction conditions, the desired
products were obtained in good to excellent yields for a
Scheme 3 Suzuki–Miyaura
cross-coupling reactions
123

J IRAN CHEM SOC
Table 3 Optimization of different parameters of iodobenzene and phenylboronic acid in the Suzuki reaction
Entry
Solvent
Catalyst amount (g)
Bases
Temperature (oC)
Yielda (%)
1
NMP
DMF
DMSO
CH3CN
EtOH
H2O
0.025
0.025
0.025
0.025
0.025
0.025
0.025
0.025
0.025
0.025
0.025
0.025
0.025
0.025
0.025
0.025
0.025
–
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
None
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
90
140
90
90
90
90
90
r.t
97
84
2
3
57
4
61
5
87
6
13
7
Dioxane
THF
22
8
Trace
Trace
0
9
Toluene
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
NaOH
K3PO4
CS2CO3
Et3N
78
66
71
61
DBU
64
NaOAc
Na2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
16
89
0
0.01
28
0.015
0.02
54
73
0.03
96
0.035
0.025
0.025
0.025
97
Trace
85
80
100
96
Iodobenzene (1.0 mmol), phenylboronic acid (1.2 mmol), base (2 equiv.), solvent (3 ml), 3 h
a
Isolated yield
wide array of aryl halides. The results are shown in
Table 4.
reaction was performed under milder reaction condition
(90 °C) and less palladium catalyst. Moreover, similar to
Heck reaction, aryl chlorides can also give the coupling
products in the presence of TBAB (Table 4, entries
16–21).
However, aryl iodides were reacted efficiently with
phenylboronic acid in excellent isolated yields (Table 4).
Since aryl iodides are more expensive than their corre-
sponding bromides and chlorides, the use of iodides for
large-scale reactions is not economically encouraged.
Therefore, we applied this catalytic system for the reac-
tion of aryl bromides and chlorides with phenylboronic
acid (Table 4, entries 3–21). As it is evident from the
results in Table 4, different aryl bromides were reacted
with phenylboronic acid at 90 °C in appropriate reaction
times. The desired biphenyl compounds were isolated in
80–95 % yields (Table 4, entries 3–15). Compared to
Heck reaction described in the previous paragraph, Suzuki
To investigate the formation of biphenyl as side reaction
product by oxidative coupling of phenyl boronic acid, the
reaction of 4-methoxyiodobenzene with phenylboronic
acid in test condition (NMP as solvent, 0.025 g catalyst,
90 °C) was carried out (Scheme 4). The reaction mixer was
analyzed by GC during and after reaction. According to GC
results, just substance A is produced and substance B does
not form. So we can say that oxidative coupling of phenyl
boronic acid will not occur because biphenyl B was not
observed in GC result.
123

J IRAN CHEM SOC
Table 4 Suzuki reaction of phenylboronic acid with aryl halides in the presence of Fe3O4@SiO2-polymer-imid-pd catalyst
Time Isolated Yield TONc TOF [Refs]
Aryl halide
I
Product
(h)
(%)b
(h-1)d
0.5
1.0
1.0
1.5
97
93
88
86
118
113
107
104
236
113
107
69
[49]
[50]
[50]
[50]
1
2
3
4
MeO
Me
MeO
I
Br
Me
Br
CH3
Br
Me
2.5
2.5
85
81
103
98
41
39
[50]
[50]
5
6
H3C
Me
Br
MeO
OHC
Br
Br
MeO
OHC
2.0
1.5
1.5
85
87
85
103
105
103
51.5
70
[51]
[49]
[49]
7
8
9
H3COC
Br
H3COC
69
NC
O2N
Cl
Br
Br
Br
NC
O2N
Cl
0.75
0.75
0.75
1.0
94
95
91
86
114
116
110
104
152
155
147
104
[49]
[50]
[50]
[52]
10
11
12
13
Br
N
N
N
Br
N
1.0
1.5
88
83
107
101
107
67
[52]
[52]
14
15
N
S
N
S
Br
77e
79e
93
96
15.5
24
[52]
[52]
Cl
6.0
4.0
16
17
Me
Me
Cl
For great certainty, reaction of 4-metoxychlorobenzene
with phenylboronic acid in such condition (NMP as sol-
vent, 0.025 g catalyst, 90 °C) was examined (Scheme 4).
The progress of reaction was monitored by GC. In this
reaction, just substance A is produced also.
Fe3O4@SiO2-polymer-imid-pd magnetic catalyst dis-
persed in NMP can be easily separated by external mag-
netic field within several minutes without the need for a
filtration step, and then can be readily redispersed with
slight shake, indicating directly that the nanoparticles
123

J IRAN CHEM SOC
Table 4 continued
Time Isolated Yield TONc TOF [Refs]
Aryl halide
Product
(h)
(%)b
(h-1)d
86e
92e
89e
104
111.5
108
11.5
45
[50]
[50]
[50]
MeO
OHC
MeO
OHC
Cl
Cl
9.0
2.5
2.5
18
19
20
H3COC
H3COC
Cl
43
91e
110
55
[52]
O2N
Cl
O2N
2.0
21
All reactions were carried out with Ar-X (1 mmol), phenylboronic acid (1.2 mmol), and K2CO3 (2 mmol) in the presence of the Fe3O4@SiO2-
polymer-imid-pd catalyst (0.025) in 3.0 mL of NMP at 90 °C
a
Isolated yield
b
TON = Nproduct/Npalladium, N denotes molar numbers
c
TOF = Nproduct/(Npalladium 9 t), N denotes molar numbers, and t denotes reaction time (h)
d
With additional tetrabutylammonium bromide (TBAB) (0.04 mmol)
Scheme 4 Reaction of
4-methoxyiodobenzene or
4-metoxychlorobenzene with
phenylboronic acid in NMP as
solvent, 0.025 g catalyst, 90 °C
conditions
H3CO
O
O
I
HO
HO
A
0.025g Catalyst
NMP, 90oC
+
B
or
Cl
B
possess magnetic properties (Fig. 3). Such magnetic sepa-
ration performance makes the nanoparticles more effective
and convenient in application.
Conclusions
Surface of Fe3O4@SiO2 was covered with polymeric shell
and then Pd nanoparticles were loaded in polymeric chins.
The polymeric layer caused Pd nanoparticle faraway from
surface of Fe3O4@SiO2. Additionally Pd particles which
supported in polymer chin have a distinct distance between
themselves. Therefore Pd nanoparticles not aggregate and
provide better accessibility for reactants. The formation of
the carbene–Pd bond leads to leaching of Pd nanoparticles
reduces. Polymer chains act as spacer between Fe3O4@-
SiO2 and Pd and lead to the increased catalytic activity of
Pd.
Afterward, to investigate the recycling of the catalyst,
the reaction of iodobenzene and 1-chloro-4-nitrobenzene
with n-butyl acrylate (Heck reaction) (Fig. 4a, c, respec-
tively), and also iodobenzene and 1-chloro-4-nitrobenzene
with phenylboronic acid (Suzuki reaction) (Fig 4b, d,
respectively) in optimum condition was tested.
After the completion of reaction, the magnetic catalyst
could be conveniently and efficiently recovered from the
reaction mixture with an external magnet, it can be used in
the next run after washing with ethanol and drying. The
results revealed that the recovered catalyst had not signif-
icantly lost its activity after six cycles for two substrates
(iodobenzene and 1-chloro-4-nitrobenzene) (Fig. 4).
The amount of leached Pd in the reaction solution was
measured by the ICP technique. The amount of palladium
leaching after the first run was determined by ICP analysis
to be only 0.6 and 0.3 % for Mizoroki–Heck reaction and
Suzuki–Miyaura reaction, and after 6 repeated recycling
was 6 and 4 %, respectively.
Using Fe3O4@SiO2-polymer-imid-Pd nanoparticles as
an efficient catalyst for Mizoroki–Heck and Suzuki–Mi-
yaura coupling reaction of aryl iodides, aryl bromides and
aryl chlorides in the absence of phosphorous ligands was
reported. Heterogeneous nature and easy separation of the
catalyst, easy preparation, short reaction times, easy puri-
fication, excellent yields and very low Pd leaching are the
main characteristics of the process. These special features
make this method a facile tool in direct coupling reactions.
123

J IRAN CHEM SOC
Fig. 3 Catalyst ability to effective recovery at the end of reactions by external magnetic field
Fig. 4 Recycling of the catalyst
for the reaction of Heck–
Mizoroki coupling (a, c) and
Suzuki coupling reaction (b, d)
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