Synthesis and characterization of a Pd(0) Schiff base complex anchored on magnetic nanoporous MCM-41 as a novel and recyclable catalyst for the Suzuki and Heck reactions under green conditions

Article abstract of DOI:10.1016/S1872-2067(17)62865-1

A Pd Schiff base complex was immobilized onto the surface of magnetic MCM-41 (Fe₃O₄@MCM-41@Pd(0)-P2C) as a novel, eco-friendly, and recyclable heterogeneous nanocatalyst and fully characterized by FT-IR, VSM, EDS, transmission electron microscopy, scanning electron microscopy, thermogravimetric analyses, ICP-OES, and X-ray powder diffraction analysis. The Fe₃O₄@MCM-41@Pd(0)-P2C was investigated as a catalyst for the one-pot Suzuki and Heck reactions in PEG as a green solvent to provide the target products in excellent yields. The main advantages of using this catalyst include a short reaction time, green reaction conditions, a simple experimental procedure, non-use of hazardous organic solvents, low loading of the catalyst, and the ability to use various substrates. More importantly, the catalyst could be easily separated from the reaction mixture with the assistance of an external magnet and could be recovered and reused several times without significant loss of stability and activity.

Full text of DOI:10.1016/S1872-2067(17)62865-1

Chinese Journal of Catalysis 38 (2017) 1413–1422
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Synthesis and characterization of a Pd(0) Schiff base complex
anchored on magnetic nanoporous MCM‐41 as a novel and
recyclable catalyst for the Suzuki and Heck reactions
under green conditions
Mohsen Nikoorazm a,*, Farshid Ghorbani b, Arash Ghorbani‐Choghamarani a, Zahra Erfani a
a Department of Chemistry, Faculty of Science, Ilam University, P. O. Box69315516, Ilam, Iran
b Department of Environment, Faculty of Natural Resource, University of Kurdistan, Sanandaj 66177‐15177, Iran
A R T I C L E I N F O
A B S T R A C T
A Pd Schiff base complex was immobilized onto the surface of magnetic MCM‐41
Article history:
Received 7 April 2017
Accepted 16 May 2017
Published 5 August 2017
(Fe3O4@MCM‐41@Pd(0)‐P2C) as a novel, eco‐friendly, and recyclable heterogeneous nanocatalyst
and fully characterized by FT‐IR, VSM, EDS, transmission electron microscopy, scanning electron
microscopy, thermogravimetric analyses, ICP‐OES, and X‐ray powder diffraction analysis. The
Fe3O4@MCM‐41@Pd(0)‐P2C was investigated as a catalyst for the one‐pot Suzuki and Heck reac‐
tions in PEG as a green solvent to provide the target products in excellent yields. The main ad‐
vantages of using this catalyst include a short reaction time, green reaction conditions, a simple
experimental procedure, non‐use of hazardous organic solvents, low loading of the catalyst, and the
ability to use various substrates. More importantly, the catalyst could be easily separated from the
reaction mixture with the assistance of an external magnet and could be recovered and reused sev‐
eral times without significant loss of stability and activity.
Keywords:
MCM‐41
Magnetic nanoparticles
Suzuki reaction
Heck reaction
Polyethylene glycol (PEG)
Palladium
© 2017, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
and mechanical stability [11], which has opened up new possi‐
bilities for the design of novel heterogeneous catalysts. Mag‐
Molecular sieves and mesoporous materials with regular
geometries have attracted much attention owing to their re‐
markable characteristics such as high surface area, high effi‐
ciency, large pore volume, and recyclability compared with
nonporous objects [1–4]. Mobil composition of matter No. 41
(MCM‐41) as a member of a family of mesoporous molecular
sieves, which was reported by Beck et al. [5], consists of meso‐
porous‐structured SiO2 formed by a hexagonal array of unidi‐
rectional pore structures [6,7]. These materials possess unique
structural features such as high surface area [8], very narrow
pore size distribution [9], and excellent thermal [10], chemical,
netic nanoparticles (MNPs) are an important class of com‐
pounds that have received significant attention because of the
broad spectrum of biological and medical applications such as
drug delivery, biomolecular sensors, magnetic resonance im‐
aging, bioseparation, and magneto‐thermal therapy as well as
in catalysis, environmental depollution, and in vitro/in vivo
applications [12,13]. MNPs have been widely used in catalytic
reactions as heterogeneous catalysts. The advantages of using
magnetic nanoparticles as heterogeneous catalysts include ease
of recovery from the reaction mixture using an external magnet
[14], their large surface area ratio, and ease of preparation.
* Corresponding author. Tel/Fax: +98‐843‐2227022; E‐mail: e_nikoorazm@yahoo.com
DOI: 10.1016/S1872‐2067(17)62865‐1 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 38, No. 8, August 2017

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Mohsen Nikoorazm et al. / Chinese Journal of Catalysis 38 (2017) 1413–1422
MNPs have been used as a core for the support of catalyst used
in organic transformations owing to coupling with organic lig‐
ands and inorganic compounds [10]. The design and synthesis
of efficient and recoverable catalysts has become an important
environmental and economical consideration for industrial
applications [15]. One strategy in this area has focused on the
consolidation of functionalized mesoporous silica materials
with magnetic nanoparticles to form a porous magnetic nano‐
composite. These types of magnetic nanocomposites have the
properties and advantages of both mesoporous silica and
magnetic nanoparticles [16] and have been used for magnetic
storage and recording, catalytic applications, sensors, envi‐
ronmental, and biomedical applications [12]. Reactions leading
to the formation of C–C bonds catalyzed by palladium com‐
plexes, such as Suzuki and Heck coupling reactions, have be‐
come powerful methods in modern synthetic organic chemistry
for the preparation of natural products, ultraviolet (UV)
screens, pharmaceuticals, biologically active compounds, hy‐
drocarbons, polymers, liquid crystal materials, and advanced
materials [17–19]. Homogeneous palladium catalysts have
been extensively studied in synthetic organic chemistry be‐
cause of their high selectivity and catalytic activity [20]. Ho‐
mogeneous catalytic reactions have many disadvantages such
as poor reusability and separation of the catalysts from the
reaction mixture. These disadvantages can be minimized by
immobilizing homogenous catalysts on polymeric organic or
inorganic supports [21,22]. In this study, Pd complexes were
anchored to porous magnetic nanocomposites as a catalyst
support and employed as excellent and reusable heterogeneous
organometallic nanocatalysts for C–C Suzuki and Heck coupling
reactions. The main advantage of this catalytic system was the
use of PEG as a green solvent to provide the target products in
excellent yields in short reaction times. The nanoparticles could
be easily isolated from the product solution by using an exter‐
nal magnet after completing the reactions.
were performed using a vibrating sample magnetometer (VSM)
MDKFD. Magnetization measurements were carried out using
an external field of up to 15 kOe at several temperatures. The
Pd content was measured using inductively coupled plas‐
ma‐optical emission spectrometry (ICP‐OES).
2.2. Preparation of Fe3O4@MCM‐41
Magnetic Fe3O4 nanoparticles were prepared as follows. A
mixture of FeCl3·6H2O (2 g) and FeCl2·4H2O (0.8 g) were dis‐
solved in 10 mL of deionized water under a N2 atmosphere. The
mixture was added to 100 mL of 1.0 mol/L NH3 solution con‐
taining 0.4 g of CTAB under sonication and a N2 atmosphere.
After 30 min, the reaction was completed, the Fe3O4 nanoparti‐
cles were isolated by magnetic decantation and dried at 80 ˚C
under vacuum [23]. The Fe3O4@MCM‐41 was prepared by the
following method. First, Fe3O4 nanoparticles (0.05 g) were dis‐
persed in ethanol (20.0 mL) for 30 min by using ultrasoni‐
cation. Then, the suspension was centrifuged and the solid was
re‐dispersed in a mixture of deionized water (10 mL), ethanol
(20 mL), and NH3 (0.5 mL). The system was kept under vigor‐
ous mechanical stirring for 30 min, and then TEOS (0.03 g) was
added dropwise. The mixture was stirred at room temperature
for 6 h. The coated nanoparticles (Fe3O4@nSiO2) were sepa‐
rated by decantation with the aid of a magnet and washed with
ethanol and water several times. In the second step, the coated
Fe3O4@nSiO2 nanoparticles were dispersed in a mixture of
deionized water (40 mL), ethanol (30 mL), NH3 (0.6 mL), and
CTAB (0.15 g). After stirring at room temperature for 30 min,
0.4 g of TEOS (as a silica source) was added slowly to the solu‐
tion and stirring was continued for another 6 h. After comple‐
tion of the reaction, the solid products were collected by mag‐
netic separation, washed with plenty of ethanol/deionized wa‐
ter, and subsequently dried in a vacuum oven at 80 °C for 12 h.
To remove the CTAB template, ethanol (100 mL) and 5 mL of 2
mol/L HCl were added to 0.1 g of the produced nanocomposite,
then the mixture was stirred at room temperature for 48 h. The
solid products were collected by magnetic separation and sub‐
sequently dried in a vacuum oven at 80 °C for 24 h. The result‐
ing solid was referred to as Fe3O4@MCM‐41.
2. Experimental
2.1. Materials and characterization
The cetyltrimethylammonium bromide (CTAB; 98%), tetra‐
ethyl orthosilicate (TEOS), 3‐aminopropyltriethoxysilane
(3‐APTES), FeCl3·6H2O, FeCl2·4H2O, palladium acetate, phenyl‐
boronic acid, and solvents were purchased from Aldrich, Merck,
and Flucka and were used as received without further purifica‐
tion. The nanostructures were identified using a Holland
Philips X’pert X‐ray powder diffraction (XRD) diffractometer at
a scanning speed of 2°/min from 1° to 80°. Fourier transform
infrared (FT‐IR) spectra were recorded with KBr pellets utiliz‐
ing a VRTEX 70 model Bruker FT‐IR spectrometer. Thermo‐
gravimetric analyses (TGA) of the samples were carried out
between 30 and 800 °C using a Shimadzu DTG‐60 automatic
thermal analyzer. The particle size and morphology were ex‐
amined by scanning electron microscopy (SEM) using a
FESEM‐TESCAN MIRA3, as well by high‐resolution transmis‐
sion electron microscopy (TEM) with a JEOL JEM‐2100F, 200kV
transmission electron microscope. The VSM measurements
2.3. Preparation of 3‐APTES functionalized Mag‐mesoporous
silica (Fe3O4@MCM‐41‐NH2)
To a suspension of Fe3O4@MCM‐41(4.8 g) in n‐hexane, 4.8 g
of 3‐aminopropyltriethoxysilane (3‐APTES) was added slowly
under a N2 atmosphere at 80 °C and refluxed for 24 h. The sep‐
arated solid Fe3O4@MCM‐41‐(SiCH2CH2CH2NH2)x was collected
by magnetic separation, washed with n‐hexane, and dried un‐
der vacuum.
2.4. Preparation of heterogeneous Pd Schiff base complex
grafted in Mag‐mesoporous silica (Fe3O4@MCM‐41@Pd(0)‐P2C)
For the preparation of Fe3O4@MCM‐41@P2C, a solution of
0.5 g Fe3O4@MCM‐41@nPr‐NH2 and pyrrole‐2‐carbaldehyde
(1.2 mmol) in ethanol was refluxed under a N2 atmosphere for

Mohsen Nikoorazm et al. / Chinese Journal of Catalysis 38 (2017) 1413–1422
1415
3 h. The resulting solid was washed with ethanol, collected by
magnetic separation and dried under vacuum and designated
as Fe3O4@MCM‐41@P2C. Ultimately, the
Fe3O4@MCM‐41@Pd(0)‐P2C was prepared by refluxing a solu‐
tion of Pd(OAc)2 (0.63 mmol, 0.168 g) with 0.250
(1)
(2)
(3)
g
Fe3O4@MCM‐41@P2C in ethanol (20 mL) for 20 h. Finally,
Pd(II) was reduced with NaBH4 (0.057 mmol, 0.022 g) under
the same conditions for another 2 h. The resulting black solid
impregnated with the metal complex was separated by a mag‐
net and washed with ethanol to give the Pd(0) complex. The
detailed preparation route for Fe3O4@MCM‐41@Pd(0)‐P2C is
shown in Scheme 1.
(4)
(5)
4000 3500 3000 2500 2000 1500 1000 500
Wavenumber (cm1)
2.5. General procedure for the Suzuki coupling reaction
Fig. 1. FT‐IR spectra of Fe3O4 (1), Fe3O4@MCM‐41 (2),
Fe3O4@MCM‐41@nPr‐NH2 (3), Fe3O4@MCM‐41@P2C (4), and
Fe3O4@MCM‐41@Pd(0)‐P2C (5).
A mixture of an aryl halide (1 mmol), phenylboronic acid (1
mmol), K2CO3 (3 mmol), and Fe3O4@MCM‐41@Pd(0)‐P2C
(0.004 g, 0.66 mol%) was added to a reaction vessel. The re‐
sulting mixture was stirred in PEG‐400 at 60 °C and the pro‐
gress of the reaction was monitored by thin‐layer chromatog‐
raphy (TLC). After completion of the reaction, the catalyst was
separated using an external magnet and washed with ethyl
acetate. The reaction mixture was extracted with ethyl acetate
and water, and the organic layer was dried over anhydrous
Na2SO4 (1.5 g). The solvent was evaporated and pure products
were obtained in good to excellent yields.
diethyl ether. The reaction mixture was extracted with water
and diethyl ether. The organic layer was dried over Na2SO4 (1.5
g) and the solvent was evaporated to obtain the pure products
in good to excellent yields.
3. Results and discussion
3.1. Characterization of Fe3O4@MCM‐41@Pd(0)‐P2C
2.6. General procedure for the Heck reaction
The structure of the Palladium Schiff base complex an‐
chored onto
the surface of magnetic MCM‐41
A mixture of an aryl halide (1 mmol), an alkene (1.2 mmol),
K2CO3 (3 mmol), and Fe3O4@MCM‐41@Pd(0)‐P2C (0.006 g,
0.99 mol%) was stirred in PEG‐400 at 120 °C and the progress
of the reaction was monitored by TLC. After completion of the
reaction, the mixture was cooled to room temperature. The
catalyst was separated by an external magnet and washed with
(Fe3O4@MCM‐41@Pd(0)‐P2C) was studied and fully charac‐
terized by FT‐IR, VSM, EDS, TEM, SEM, XRD, and TGA analysis.
Fig. 1 shows the FT‐IR spectra of the synthesized Fe3O4,
Fe3O4@MCM‐41, Fe3O4@MCM‐41‐NH2, Fe3O4@MCM‐41@P2C,
and Fe3O4@MCM‐41@Pd(0)‐P2C. The FT‐IR spectrum of the
Fe3O4 nanoparticles (Fig. 1(1)) displayed strong absorptions at
Scheme 1. Synthesis of Fe3O4@MCM‐41@Pd(0)‐P2C.

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Mohsen Nikoorazm et al. / Chinese Journal of Catalysis 38 (2017) 1413–1422
400
300
200
100
0
500
(a)
(b)
400
Fe3O4@MCM-41
Fe3O4@MCM-41@Pd(0)-P2C
300
200
100
0
30
40
50
60
70
80
90
1
3
5
7
9
11
2/(o )
2/(o )
Fig. 2. (a) Wide angle XRD patterns of Fe3O4@MCM‐41 and Fe3O4@MCM‐41@Pd(0)‐P2C; (b) Small angle XRD pattern of Fe3O4@MCM‐41.
579 cm−1 and 3000–3500 cm−1, which were assigned to the
Fe–O and O–H stretching vibrations [22]. The FT‐IR spectrum
of the Fe3O4@MCM‐41 sample (Fig. 1(2)) displayed peaks at
460, 958, and 1081 cm−1, which corresponded to bending,
symmetric, and asymmetric stretching of the Si–O–Si vibra‐
tions, respectively [25]. The presence of the peak at 1550 cm−1,
mainly from NH2 symmetric bending vibrations, indicated suc‐
cessful attachment of an organic amine onto the
Fe3O4@MCM‐41 surface. The broad band at 3443 cm−1 was
assigned to the hydrogen bonding between the silanol groups
and adsorbed water, and the band at approximately 2939 cm−1
was associated with the CH2 vibrations corresponding to C–H
stretching (Fig. 1 (3)). The Fe3O4@MCM‐41@P2C exhibited a
ν(C=N) stretch at 1637 cm−1, which shifted to 1629 cm−1 in the
FT‐IR spectrum of Fe3O4@MCM‐41@Pd(0)‐P2C, indicating the
formation of Pd‐ligand bonds [2].
The crystalline structures of the catalyst were analyzed by
XRD. The wide angle XRD of the Fe3O4@MCM‐41 and
Fe3O4@MCM‐41@Pd(0)‐P2C samples are shown in Fig. 2(a).
The characteristic peaks at 2θ = 30.0°, 35.4°, 43.3°, 54.5°, 57.0°,
and 62.8° assigned to magnetite were observed, which is con‐
sistent with the standard Fe3O4 XRD spectrum and demon‐
strated that the catalyst had been successfully synthesized
without damaging the crystal structure of Fe3O4 [25]. Further‐
more, the XRD pattern of Fe3O4@MCM‐41@Pd(0)‐P2C con‐
tained a series of peaks (39.4°, 45.9°, and 66.9°) which were
indexed to Pd camouflaged on the surface of Fe3O4@MCM‐41
[8]. The comparison study of the XRD patterns of
Fe3O4@MCM‐41 and Fe3O4@MCM‐41@Pd(0)‐P2C showed that
after grafting of Pd through the formation of a complex with
Fe3O4@MCM‐41, reflections with weaker intensities were ob‐
served. As seen from the small angle XRD patterns in Fig. 2(b),
The XRD pattern of Fe3O4@MCM‐41 showed the presence of
three reflection peaks corresponding to d100, d110, and d200
planes at 2θ = 2.36°, 3.94°, and 4.38°, respectively, confirming
the presence of the ordered hexagonal mesoporous structure of
MCM‐41 [23].
Fig.
3 are the SEM images of Fe3O4@MCM‐41 and
Fe3O4@MCM‐41@Pd(0)‐P2C. The Fe3O4@MCM‐41 and
Fe3O4@MCM‐41@Pd(0)‐P2C materials were composed of
nearly spherical agglomerations composed of regular uniform
nanoparticles.
The energy dispersive spectrum (EDS) indicated the pres‐
ence of Pd, Fe, Si, O, N, and C species in the catalyst (Fig. 4).
TEM images of the Fe3O4@MCM‐41@Pd(0)‐P2C are shown
in Fig. 5. The HRTEM micrograph demonstrated the ordered
mesostructures with uniform pore dimension and hexagonal
symmetry and agglomeration of many ultrafine spherical‐like
particles that displayed dark magnetite cores surrounded by a
shell.
The magnetic properties of Fe3O4@MCM‐41 and
Fe3O4@MCM‐41@Pd(0)‐P2C were investigated using VSM at
1500
(a)
(b)
PdL
1000
500
0
N K
FeK
FeL
C K
PdL
FeK
keV
10.00
0
Fig. 3. SEM images of Fe3O4@MCM‐41 (a) and Fe3O4@MCM‐41@
Fig. 4. EDS spectrum of Fe3O4@MCM‐41@Pd(0)‐P2C.
Pd(0)‐P2C (b).

Mohsen Nikoorazm et al. / Chinese Journal of Catalysis 38 (2017) 1413–1422
1417
(b)
(a)
(c)
Fig. 5. HRTEM images of Fe3O4@MCM‐41@Pd(0)‐P2C. (a) 80 nm; (b, c) 200 nm.
room temperature (Fig. 6). VSM measurements of the
Fe3O4@MCM‐41 nanoparticles showed that the saturation
magnetization (Ms) of Fe3O4@MCM‐41@Pd(0)‐P2C was 9.42
emu/g (Fig. 6(2)), which is lower than the Ms of
Fe3O4@MCM‐41 (13.02 emu/g) (Fig. 6(1)). Based on these re‐
sults, the successful grafting of organic layers containing a pal‐
ladium complex on Fe3O4@MCM‐41 was verified [26].
below 125 °C owing to the removal of physically adsorbed wa‐
ter and solvent inside the pore channels. The other weight
losses was in the region of 200–550 °C (approximately 22%),
which was mainly related to the decomposition of the organi‐
cally modified moieties on Fe3O4@MCM‐41@Pd(0)‐P2C [27];
and above 600 °C (about 6%) as a result of the condensation of
the silanol groups.
The thermogravimetric analysis (TGA) curves of
Fe3O4@MCM‐41and Fe3O4@MCM‐41@Pd(0)‐P2C are shown in
Fig. 7. The TGA of the synthesized Fe3O4@MCM‐41 showed a
3% weight loss in one step at a temperature below 100 °C ow‐
ing to the desorption of water. The Fe3O4@MCM‐41@
Pd(0)‐P2C sample showed a mass loss of approximately 2%
Finally, the exact amount of Pd in the nanostructured cata‐
lyst was determined by ICP‐OES. The amount of Pd in the im‐
mobilized catalyst on Fe3O4@MCM‐41 was found to be 1.65
mmol/g.
3.2. Evaluation of the catalytic activity of
Fe3O4@MCM‐41@Pd(0)‐P2C in Suzuki‐Miyaura and
Mizoroki‐Heck reactions
After full characterization of the Fe3O4@MCM‐41@
Pd(0)‐P2C structure, the catalytic activity of this magnetic
mesoporous compound was examined for C–C coupling reac‐
tions, namely Suzuki and Heck reactions. To optimize the reac‐
tion conditions, the Suzuki coupling reaction of iodobenzene (1
mmol) with phenyl boronic acid (1 mmol) was examined using
different amounts of catalyst and solvent at a temperature
range of 25–60 °C (Table 1). When the reaction was carried out
Table 1
Optimization of the Suzuki reaction between iodobenzene and phenyl
boronic acid under different conditions.
Catalyst
amount (mg) (min)
Time Yield*
Fig. 6. Magnetic curves of Fe3O4@MCM‐41 (1) and Fe3O4@MCM‐41@
Pd(0)‐P2C (2).
Entry T (°C)
Solvent
Base
(%)
Trace
94
94
85
15
Trace
90
85
92
86
90
Trace
92
66
1
2
3
4
5
6
7
8
60
60
60
60
60
60
60
60
60
60
60
60
50
40
25
PEG‐400
PEG‐400
PEG‐400
PEG‐400
K2CO3
K2CO3
K2CO3
K2CO3
None
5
4
3
4
4
4
4
4
4
4
4
4
4
4
360
20
20
20
20
20
20
20
20
20
20
20
20
20
20
100
80
1,4‐dioxane K2CO3
H2O
DMF
EtOH
PEG‐400
PEG‐400 NaHCO3
PEG‐400 Na2CO3
PEG‐400
PEG‐400
PEG‐400
PEG‐400
K2CO3
K2CO3
K2CO3
Et3N
60
9
Fe3O4@MCM-41@Pd(0)-P2C
10
11
12
13
14
15
40
20
0
Fe3O4@MCM-41
KOH
K2CO3
K2CO3
K2CO3
20
25
225
425
625
825
Reaction conditions: iodobenzene (1 mmol), phenyl boronic acid (1
mmol), base (3 mmol), Fe3O4@MCM‐41@Pd(0)‐P2C (4 mg), and
PEG‐400 (2 mL).
Temperature (oC)
Fig. 7. TGA thermograms of Fe3O4@MCM‐41 and Fe3O4@MCM‐41@
Pd(0)‐P2C.
* Isolated yield.

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Mohsen Nikoorazm et al. / Chinese Journal of Catalysis 38 (2017) 1413–1422
Table 2
Results
Fe3O4@MCM‐41@Pd(0)‐P2C.
Table 3
of
the
Suzuki
reaction
catalyzed
by
Optimization of the Heck reaction between iodobenzene and n‐butyl
acrylate under different conditions.
Fe O @MCM-41@Pd-P2C
3
4
X
B(OH)
2
Temperature
(°C)
Catalyst Time Yield *
Entry
Solvent
Base
K CO , PEG, 60 ° C
2
3
(mg)
(min)
(%)
R
R
1
2
3
4
5
6
120
120
120
120
120
120
120
120
120
120
120
110
100
80
PEG‐400
PEG‐400
PEG‐400
PEG‐400
PEG‐400
PEG‐400 NaHCO3
PEG‐400 Na2CO3
PEG‐400
H2O
DMF
EtOH
PEG‐400
PEG‐400
PEG‐400
K2CO3
K2CO3
K2CO3
K2CO3
Et3N
None
3
4
6
6
1440 Trace
X= I, Br, Cl
25
25
25
25
25
25
25
25
25
25
25
25
25
62
85
96
90
75
88
35
—
83
78
87
68
54
Time Yield *
(min) (%)
m.p. (°C)
Entry
Aryl halide
Found
64–67
Reported [Ref.]
1
2
I
20
40
94
96
67–68 [28]
6
H3C
I
44–46
Oil
44–46 [29]
Oil [28]
7
8
9
10
11
12
13
14
6
6
6
6
6
6
I
KOH
3
35
98
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
OCH3
H3CO
H2N
I
4
5
55
65
91
88
83–85
53–54
84–85 [28]
50–53 [30]
I
6
6
Br
6
7
8
40
35
50
93
94
90
67–68
42–44
80–83
67–68 [28]
44–47 [28]
84–85 [28]
Reaction conditions: Ar‐X (1 mmol), n‐butyl acrylate (1.2 mmol), base
(3 mmol), Fe3O4@MCM‐41@Pd(0)‐P2C (6 mg), and PEG‐400 (2 mL).
* Isolated yield.
H3C
H3C
H2N
Br
Br
Br
9
70
40
50
50
90
93
92
94
51–53
79–81
50–53 [30]
82–83 [28]
To demonstrate the efficiency and the scope of
Fe3O4@MCM‐41@Pd‐P2C as a catalyst, various aryl halides
were reacted with phenyl boronic acid under the optimal reac‐
tion conditions to produce the corresponding biphenyls in ex‐
cellent yields and short reaction times (Table 2). As shown in
Table 2, the reaction with chlorobenzene was slower than of
iodobenzene or bromobenzene and required a much higher
temperature and more Fe3O4@MCM‐41@Pd(0)‐P2C catalyst (6
mg, 0.99 mol%) (Table 2, entries 14–16). The aryl halides con‐
taining electron‐donating and electron‐withdrawing functional
groups were converted to the corresponding biphenyls in short
reaction times with good yield. As shown in Table 2, for the aryl
iodides containing electron‐donating functional groups, such as
Me and OMe, the reaction was completed after shorter reaction
times compared with those containing electron‐withdrawing
substituents.
NC
O2N
Cl
Br
Br
Br
Br
10
11
12
112–114 112–114 [29]
69–71
Oil
70–71 [28]
Oil [31]
13
30
80
93
94
F3C
14 b
15 b
16 b
64–66
81–83
67–68 [28]
82–83 [28]
Cl
Cl
NC
200 90
240 92
O2N
Cl
111–112 112–114 [29]
Reaction conditions: various aryl halides (1 mmol), phenyl boronic acid
(1 mmol), K2CO3 (3 mmol), 60 °C.
* Isolated yield.
b Conditions were as follows: Fe3O4@MCM‐41@Pd(0)‐P2C (6 mg) at
100 °C.
To
extend
the
catalytic
applications
of
the
Fe3O4@MCM‐41@Pd(0)‐P2C catalyst, we investigated its abil‐
ity to catalyze the Heck C–C coupling reaction. The reaction of
aryl halides with two types of vinylic substrates (n‐butyl acry‐
late and acrylonitrile) were employed as the model reaction.
The effect of the amount of catalyst, solvent (DMF, 1,4‐dioxane,
H2O, EtOH, or PEG), temperature (room temperature to 120
°C), and the nature of the base (Et3N, K2CO3, KOH, NaHCO3, or
Na2CO3) on the outcome of the coupling of iodobenzene with
n‐butyl acrylate or acrylonitrile was examined. A summary of
the results is shown in Table 3. The reaction did not occur in
the absence of Fe3O4@MCM‐41@Pd(0)‐P2C (Table 3, entry 1).
Among the different amount of catalyst tested, 6 mg (0.99
mol%) was found to be the most effective amount because it
gave the highest product yield. Among the different solvents,
the best yields were obtained with PEG‐400 using 0.006 g (0.99
mol%) of Fe3O4@MCM‐41@Pd(0)‐P2C (Table 3, entry 4). The
reaction was significantly affected by the nature of the base; the
best result was obtained using K2CO3. The coupling reaction
in the absence of catalyst, the reaction was slow and resulted in
no product, even after 6 h (Table 1, entry 1). The best result
was obtained when the reaction was carried out in presence of
4 mg of catalyst in PEG‐400 at 60 °C (Table 1, entry 3). In the
next step, we studied the influence of the solvents PEG‐400,
EtOH, DMF, 1,4‐dioxane, and H2O, at 60 °C (Table 1, entries 3,
5–8). The best results were obtained when PEG‐400 was used.
We then investigated the effects of the base on the reaction in
the PEG solvent at 60 °C. Different bases including (Et)3N, Na‐
HCO3, Na2CO3, KOH, and K2CO3 were studied (Table 1, entries 3,
9–12). A high yield and shorter reaction time were obtained
when K2CO3 was employed as base. Therefore, we chose K2CO3
as the base in all of the subsequent coupling reactions. We also
studied the effect of temperature (Table 1, entries 3, 13–15).
The optimum results were obtained at 60 °C.

Mohsen Nikoorazm et al. / Chinese Journal of Catalysis 38 (2017) 1413–1422
1419
Table 4
Results of the Heck reaction catalyzed by Fe3O4@MCM‐41@Pd(0)‐P2C.
X
R2
Fe3O4@MCM-41@Pd-P2C
K2CO3, PEG-400, 120 o
R1
R1
R2
C
X=Br, Cl, I
Alkene
R2= COOBU, CN
m.p. (°C )
Entry
Aryl halide
Time (min)
Yield* (%)
Found
Oil
Reported [Ref.]
1
2
I
Butyl acrylate
Butyl acrylate
25
35
96
94
Oil [32]
H3C
I
Oil
Oil [32]
I
3
4
5
Butyl acrylate
Butyl acrylate
Butyl acrylate
85
40
80
88
90
92
Oil
Oil
Oil
Oil [32]
Oil [32]
Oil [32]
OCH3
H3CO
I
I
CH3
Br
6
Butyl acrylate
Butyl acrylate
Butyl acrylate
Butyl acrylate
Butyl acrylate
90
90
86
80
92
91
87
Oil
Oil
Oil [32]
Oil [32]
H3C
Cl
Br
Br
Br
7
8
120
80
Oil
Oil [33]
NC
9
40–43
Oil
40–43 [34]
Oil [32]
Cl
I
10
360
11
Acrylonitrile
65
94
Oil
Oil [35]
H3C
H3C
I
12
13
14
Acrylonitrile
Acrylonitrile
Acrylonitrile
100
180
190
93
95
92
70–73
Oil
72–73 [36]
Oil [35]
Br
Br
70–73
72–73 [36]
* Isolated yield.
yields were susceptible to temperature changes (Table 3, en‐
tries 4, 11–14). The highest product yield was achieved at 120
°C.
After optimization of the reaction conditions, we examined
the catalytic activity of Fe3O4@MCM‐41@Pd(0)‐P2C for other
substrates (Table 4). The optimized reaction conditions were
applied to a wide range of aryl halides using n‐butyl acrylate or
acrylonitrile. The aryl bromides and aryl iodides required a
shorter reaction time compared with the corresponding aryl
chloride (Table 4, entry 10).
ported in the literature, we investigated the results of the Suzu‐
ki‐Miyaura reaction between iodobenzene and phenylboronic
acid (Table 5) and the Heck‐Mizoroki cross‐coupling reactions
between iodobenzene and butyl acrylate (Table 6) in the pres‐
ence of various catalysts with respect to the temperature, the
yield of the products, solvent, and reaction time. As shown in
Tables 5 and 6, in this work, C–C bond forming through the
Suzuki and Heck reaction was carried out in PEG‐400 with
short reaction times and in good to excellent yields. The new
catalyst is also non‐toxic, stable, cheap and easy to separate.
The recoverability and recyclability of this catalyst was faster
and easier than that of the other reported catalysts.
To
compare
the
catalytic
properties
of
Fe3O4@MCM‐41@Pd(0)‐P2C with those of other catalysts re‐
Table 5
Comparison of the effect of catalyst with other catalysts for the Suzuki‐Miyaura reaction between iodobenzene and phenylboronic acid.
Entry
Catalyst
Conditions
Et3N, DMF, 100 °C
Et3N, DMF, 100 °C
Time (h)
Yield (%)
95
Ref.
[35]
[36]
[37]
[38]
[39]
[40]
[41]
[42]
1
2
3
4
5
6
7
8
9
10
Pd‐imino‐Py‐γ‐Fe2O3
γ‐Fe2O3‐acetamidine‐Pd
Pd‐Py‐MCM‐41
0.5
0.5
2
10
6
1
6
3
24
96
97
96
98
98
99
98
99
Na2CO3, PEG, 80 °C
K2CO3, 1,4‐dioxane‐H2O, 80 °C
K2CO3, DMF‐H2O, 80 °C
Et3N, DMF, 100 °C
LDH–Pd(0)
MCM‐41‐S‐Pd(0)
Pd‐BIP‐γ‐Fe2O3@SiO2
Fe3O4‐Bpy‐Pd(OAc)2
Fe3O4@SiO2@mSiO2‐Pd (II)
Pd(II)‐NHC complex
Fe3O4@MCM‐41@Pd(0)‐P2C
K2CO3, Toluene, 80 °C
K2CO3, EtOH, 80 °C
Cs2CO3, DMF, 100 °C
K2CO3, PEG, 60 °C
[43]
this work
20 min
96

1420
Mohsen Nikoorazm et al. / Chinese Journal of Catalysis 38 (2017) 1413–1422
Table 6
Comparison of the effect of catalyst with other catalysts for Heck‐Mizoroki cross‐coupling reactions from iodobenzene with butyl acrylate.
Entry
Catalyst
Fe3O4@SiO2/Schiff base/Pd(II)
Pd‐NPs
Conditions
K2CO3, DMF, 110 °C
Et3N, IL, 100 °C
Time (h)
Yield (%)
97
Ref.
[44]
[45]
[46]
[47]
[48]
[49]
[50]
[51]
1
2
3
4
5
6
7
8
9
10
0.75
3
5
87
99
97
96
99
97
95
97
Pd/Fe3O4
Pd/6c complex
Fe3O4/DAG/Pd
NHC‐Pd(II)
K2CO3, NMP, 130 °C
K2CO3, DMAc, 120 °C
Et3N, DMF, 110 °C
Na2CO3, DMA, 160 °C
Et3N, DMF, 100 °C
Et3N, solvent‐free, 100 °C
K2CO3, DMF, 100 °C
K2CO3, PEG, 120 °C
2
0.5
18
1
0.5
8
Pd(OAc)2@MNP
Pd‐isatin Schiff base‐γ‐Fe2O3
SiO2@Fe3O4‐Pd
[52]
this work
Fe3O4@MCM‐41@Pd(0)‐P2C
25 min
96
Heck reaction
Suzuki reaction
4. Conclusions
100
90
80
70
60
50
Fe3O4@MCM‐41@Pd(0)‐P2C was prepared and used as a
novel, environmentally benign, and heterogeneous nanocata‐
lyst and fully characterized using FT‐IR, VSM, EDS, TEM, SEM,
XRD, and TGA. The catalyst was successfully used for the Suzuki
and Heck reactions under mild experimental conditions. The
advantages of this system include the simple experimental
procedure, utilization of an inexpensive and readily available
catalyst, non‐chromatographic purification of the products,
simple recrystallization from diethyl ether, and avoiding the
use of organic solvents, which is in agreement with green
chemistry principles. In addition, this catalyst was easily sepa‐
rated from the reaction mixture by an external magnet and
reused seven times without any significant loss of stability and
activity.
1
2
3
4
5
6
7
Run
Fig. 8. Recyclability of catalyst in the Suzuki‐iyaura and Heck‐izoroki
model reaction.
The recovery and reusability of the catalysts is of major im‐
portance in green chemistry and heterogeneous catalysis. We
investigated the recovery and reusability of the
Fe3O4@MCM‐41@Pd(0)‐P2C in the Suzuki‐Miyaura reaction
between iodobenzene (1 mmol) with phenylboronic acid (1
mmol) in PEG at 60 °C, and Heck‐Mizoroki cross‐coupling reac‐
tion between iodobenzene (1 mmol) and butyl acrylate (1.2
mmol) in PEG‐400 at 120 °C. After completion of the reaction,
as monitored by TLC, the reaction mixture was cooled to room
temperature, the catalyst was easily and rapidly separated
from the reaction mixture using an external magnet and
washed several times with diethyl ether, then used in next run.
As shown in Fig. 8, the Fe3O4@MCM‐41@Pd(0)‐P2C could be
recycled over seven runs without any significant loss of its cat‐
alytic activity.
The heterogeneity of the Fe3O4@MCM‐41@Pd(0)‐P2C cata‐
lyst and the leaching of metal in the reaction mixture was ex‐
amined by carrying out a hot filtration test during the Suzuki
reaction between iodobenzene and phenylboronic acid. The
yield of the product in half the reaction time (15 min) was 54%.
The reaction was repeated and the catalyst was separated from
the reaction mixture by hot filtration after 15 min. The filtrate
was allowed to react further. The yield of the product under
these conditions was 57%. The results from the hot filtration
test indicated that no Pd leaching from the sample occurred
during the catalytic reaction.
Acknowledgment
The authors gratefully acknowledge Ilam University Re‐
search Council for partial financial support of this study.
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1421
Graphical Abstract
Chin. J. Catal., 2017, 38: 1413–1422 doi: 10.1016/S1872‐2067(17)62865‐1
Synthesis and characterization of a Pd(0) Schiff base complex
anchored on magnetic nanoporous MCM‐41 as a novel and
recyclable catalyst for the Suzuki and Heck reactions under
green conditions
Mohsen Nikoorazm *, Farshid Ghorbani,
Arash Ghorbani‐Choghamarani, Zahra Erfani
Ilam University, Iran; University of Kurdistan, Iran
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可重复使用的新型催化剂的合成、表征及在绿色条件下催化Suzuki和Heck反应:
锚合在磁性纳米多孔的MCM-41上Pd(0)希夫碱络合物
Mohsen Nikoorazm a,*, Farshid Ghorbani b, Arash Ghorbani-Choghamarani a, Zahra Erfani a
a伊拉姆大学科学学院化学系, 伊拉姆, 伊朗
b库尔德斯坦大学自然资源学院环境系, 萨南达杰66177-15177, 伊朗
摘要: 将Pd希夫碱络合物固定在磁性的MCM-41表面上, 做为环境友好且可循环使用的新型多相纳米催化剂, 并采用红外
光谱、振动探针式磁强计、能量散射谱、透射电镜、扫描电镜、热重、电感耦合等离子体发射光谱和X-射线衍射等对其
进行了全面的表征. 然后将该催化剂用于以PEG为绿色溶剂的一步法Suzuki和Heck合成反应中, 均以较高收率得到目标产
物. 该法主要优点为反应时间短、反应条件绿色友好、操作简便、无需使用有毒的有机溶剂、催化剂使用量低, 且底物适
用性广. 更为重要的是, 通过外部磁场即可方便地将催化剂从反应混合物中分离出来, 可重复使用数次而活性和稳定性未
见明显下降.
关键词: MCM-41; 磁性纳米颗粒; Suzuki反应; Heck反应; 聚乙二醇; 钯
收稿日期: 2017-04-07. 接受日期: 2017-05-16. 出版日期: 2017-08-05.
*通讯联系人. 电话/传真: +98-843-2227022; 电子信箱: e_nikoorazm@yahoo.com
本文的英文电子版由Elsevier出版社在ScienceDirect上出版(http://www.sciencedirect.com/science/journal/18722067).