Hybrid Pd/Fe3O4 nanowires: Fabrication, characterization, optical properties and application as magnetically reusable catalyst for the synthesis of N-monosubstituted ureas under ligand-free conditions

Article abstract of DOI:10.1016/j.materresbull.2014.03.038

This paper reports the synthesis and use of Pd/Fe₃O₄ nanowires, as magnetically separable catalysts for ligand-free amidation coupling reactions of aryl halides with benzylurea under microwave irradiation. Then, the in situ hydrogenolysis of the products was performed to afford the N-monosubstituted ureas from good to excellent yields. This method has the advantages of high yields, simple methodology and easy work up. The catalyst can be recovered by using a magnet and reused several times without significant loss of its catalytic activity. The catalyst was characterized using the powder XRD, SEM, EDS and UV-vis spectroscopy. Experimental absorbance spectra was compared with results from the Gans theory.

Full text of DOI:10.1016/j.materresbull.2014.03.038

Materials Research Bulletin xxx (2014) 168–175
Contents lists available at ScienceDirect
Materials Research Bulletin
journal homepage: www.elsevier.com/locate/matresbu
Hybrid Pd/Fe3O4 nanowires: Fabrication, characterization, optical
properties and application as magnetically reusable catalyst for the
synthesis of N-monosubstituted ureas under ligand-free conditions
b
a
c
Mahmoud Nasrollahzadeh a, , Abbas Azarian , Ali Ehsani , S.Mohammad Sajadi ,
*
Ferydon Babaei b
a
Department of Chemistry, Faculty of Science, University of Qom, Qom 37185-359, Iran
b
Department of Physics, University of Qom, Qom, Iran
c
Department of Petroleum Geoscience, Faculty of Science, Soran University, PO Box 624, Soran, Kurdistan Regional Government, Iraq
A R T I C L E I N F O
A B S T R A C T
Article history:
This paper reports the synthesis and use of Pd/Fe3O4 nanowires, as magnetically separable catalysts for
ligand-free amidation coupling reactions of aryl halides with benzylurea under microwave irradiation.
Then, the in situ hydrogenolysis of the products was performed to afford the N-monosubstituted ureas
from good to excellent yields. This method has the advantages of high yields, simple methodology and
easy work up. The catalyst can be recovered by using a magnet and reused several times without
significant loss of its catalytic activity. The catalyst was characterized using the powder XRD, SEM, EDS
and UV–vis spectroscopy. Experimental absorbance spectra was compared with results from the Gans
theory.
Received 13 November 2013
Received in revised form 24 February 2014
Accepted 31 March 2014
Available online xxx
Keywords:
Metals
Nanostructures
Optical materials
Optical properties
ã 2014 Elsevier Ltd. All rights reserved.
1. Introduction
long reaction times, low yields, several-step methods, environ-
mental pollution caused by formation of side products [13–16].
N-Monosubstituted urea compounds constitute a very impor-
tant class of organic compounds playing a significant role in a
number of natural products and bioactive molecules [1–4].
The classical approaches to substituted ureas are based on the
reaction of primary amines with toxic phosgene or its derivatives
[5,6], reaction of primary or secondary amines with isocyanates or
reaction with sodium or potassium cyanate in aqueous solution in
the presence of one equivalent of HCl [7,8], insertion of CO or CO2
into amino compounds in the presence of different catalysts in
organic solvents (at high pressure and temperature) [9–12], acid or
base-catalyzed hydration of cyanamides or reaction of S,S-
dimethyl dithiocarbonate with ammonia in water-dioxane [13–
16].
Thus, due to safety considerations, it is desirable to develop a more
efficient and convenient method for the synthesis of N-mono-
substituted ureas that reduce or eliminate the use and generation
of hazardous compounds is essential.
Palladium-catalyzed C–N cross-coupling reactions have
evolved into
a highly versatile and synthetically attractive
technique for targeting pharmaceutically useful intermediates
[17–19]. While a number of C–N cross-coupling methods to
synthesize symmetrical and unsymmetrical diarylureas exist,
methods for the formation of monoarylureas are sparse [20,21].
As an alternative approach, we believed a mild and efficient cross-
coupling method might be utilized to greatly expand the inventory
of available monoarylureas.
However, each of these methods suffer from different draw-
backs such as employing expensive, toxic, hazardous and moisture
sensitive reagents, harsh reaction conditions, tedious work-ups,
Nanotechnology is emerging as a cutting edge technology
interdisciplinary with biology, chemistry and material science.
Metal nanoparticles have been used widely in recent years due to
their unique electronic, optical, mechanical, magnetic and chemi-
cal properties which differ greatly from the bulk substances [22].
For these reasons, metallic nanoparticles have been found to be of
use in many applications in different fields, such as catalysis,
photonics, and electronics. Palladium (Pd) is able to catalyze a wide
variety of chemical reactions that are homogeneous and hetero-
geneous under conditions and therefore it is one of the most
Abbreviations: XRD, X-ray Powder Diffraction; SEM, Scanning Electron
Microscopy; EDS, Energy Dispersion X-ray Spectroscopy; FT-IR, Fourier transform
infrared spectroscopy; NMR, Nuclear Magnetic Resonance.
* Corresponding author. Tel.: +98 25 32850953; fax: +98 25 32103595.
E-mail address: mahmoudnasr81@gmail.com (M. Nasrollahzadeh).
http://dx.doi.org/10.1016/j.materresbull.2014.03.038
0025-5408/ã 2014 Elsevier Ltd. All rights reserved.

M. Nasrollahzadeh et al. / Materials Research Bulletin xxx (2014) 168–175
169
widely used metal catalysts [23]. Due to a higher available catalytic
surface, use of heterogeneous catalysts in the form of nanoparticles
is increasing. Recently, a variety of magnetic nanoparticles that are
amenable for easy separation and recovery have been synthesized
and applied as heterogeneous catalysts to a range of chemical
reactions [24–27].
In the course of our researches on the applications of
heterogeneous catalysts [28–35], herein we report a simple,
inexpensive and two-steps protocol for the preparation of
Pd/Fe3O4 nanowires by arc discharge of Fe in deionized (DI) water
and electroless deposition of palladium. The main advantage of the
present method is the direct formation of Fe nanowires from
discharge of iron electrodes in water. The catalyst is heterogeneous
and reusable, which provides an advantage over the homogeneous
Pd-catalyst.
Several methods for preparation of Fe nanowires have been
reported. Classical methods for the synthesis of Fe nanowires have
involved epitaxy [36], chemical deposition [37], self-assembly [38]
and electrochemical methods [39]. In spite of these methods, there
are no reports on the preparation of iron nanowires by the
electrical arc discharge method. The early works on arc discharge
method in liquids were based on the production of carbonaceous
nanostructures such as MWCNTs, SWCNTs, SW-CNHs and nano
onions [40–43]. In general, electrical arc discharge in water has the
advantage in this regard as it produces self-crystallized nano-
particles due to the high temperature caused by joule heating.
Moreover, compared with other techniques, electrical arc dis-
charge in water is an attractive method because of the simplicity of
the experimental set up, lack of complicated equipment, low
impurity and less production steps leading to a high-throughput
and cost-effective procedure to generate high yields of nano-
particles.
In the next step, we hereby describe the development of Pd/
Fe3O4 nanowires as a novel and stable heterogeneous catalyst for
the amidation of aryl halides with benzylurea (Scheme 1). The
amidation of aryl halides with benzylurea, followed by hydro-
genolysis, provides the corresponding N-monosubstituted ureas in
high yields.
During this study, we also introduce the effective medium
optical constant for decorated nanowires (Fe3O4 nanowires
decorated by Pd nanoparticles) thin films by comparing the
experimental data and calculation results in the spectral range of
300–700 nm. Gans theory and these effective optical constants
were used for calculation of extinction cross section of dispersed
above nanostructures in water. Our simulation results show that
this approach can be used for prediction of optical spectra of
decorated nanowires.
points. The NMR spectra were recorded in acetone and DMSO. 1H
NMR spectra were recorded on a Bruker Avance DRX 250, 300 and
400 MHz instrument. The chemical shifts (d) are reported in ppm
relative to the TMS as internal standard. J values are given in Hz. IR
(KBr) spectra were recorded on a PerkinElmer 781 spectropho-
tometer. Melting points were taken in open capillary tubes with a
BUCHI 510 melting point apparatus and were uncorrected. The
elemental analysis was performed using Heraeus CHN-O-Rapid
analyzer. TLC was performed on silica gel polygram SIL G/UV 254
plates. X-ray diffraction measurements were performed with a
Philips powder diffractometer type PW 1373 goniometer. It was
equipped with a graphite monochromator crystal. The X-ray
wavelength was 1.5405 Å and the diffraction patterns were
recorded in the 2u
range (10–60) with scanning speed of 2ꢀ min.
Morphology and particle dispersion were investigated by scanning
electron microscopy (SEM) (Cam scan MV2300). The chemical
composition of the prepared nanostructures was measured by EDS
performed in SEM. UV–vis spectral analysis was recorded on a
double-beam spectrophotometer (Hitachi, U-2900).
2.2. Preparation of Pd/Fe3O4 nanowires
Fe nanowires were prepared using a system consisting of two
main parts: a high current DC power supply and a reactor including
an anode, cathode and a micrometer, which moves the anode in
contact with the cathode. In this method, an 8 V DC voltage and 5 A
current are applied between two metallic iron electrodes; it was
found that the voltage dropped to 5 V during arcing but the current
remained constant. Both the anode and cathode were Fe, wire
shaped, 2 mm in diameter and 99.99% in purity. Initially we
brought the two electrodes into contact, leading to a small contact
cross section and thus to a high current density. As more iron was
ablated from the anode, the plasma expanded and pushed the
liquid away, and a gaseous bubble was formed. Melted species can
react with plasma and then condense into the liquid. In order to
extract the dispersed wires, the solution was dried at a pressure of
10ꢁ1 Torr and centrifuged several times and then dispersed on a
glass substrate. Deposition of Pd on the surface of Fe nanowires
was accomplished via a simple drop-drying process by dropping
PdCl2 solution onto Fe nanowires films and drying them at room
temperature. This solution was prepared by ultrasonically solving
0.02 g of PdCl2 powder (5 N), 99.9 mL DI water and 0.1 mL HCl. After
Pd deposition, samples were washed with DI water several times
and then dried in air. However, Fe nanowires are very air-sensitive
and easily oxidize to Fe3O4 nanowires in water.
2.3. General experimental procedure for the synthesis of N-
monosubstituted ureas
2. Experimental
A Smith process vial was charged with 1.0 mol% Pd/Fe3O4
nanowires, 1.0 mmol of phenylurea, 1.0 mmol of aryl halide and
Cs2CO3 (1.5 mmol). After sealing the cap and twice purging with N2,
the vial was irradiated by microwave at 120 ꢀC for 1 h in the Smith
Synthesizer. After completion of the reaction (as monitored by
TLC), the reaction mixture was cooled to room temperature, and a
small volume of MeOH (4 mL) was added; the catalyst was
2.1. Instruments and reagents
All reagents were purchased from the Merck and Aldrich
chemical companies and used without further purification.
Products were characterized by different spectroscopic methods
(FT-IR and 1H NMR spectra), elemental analysis (CHN) and melting
Scheme 1. Synthesis of N-monosubstituted ureas.

170
M. Nasrollahzadeh et al. / Materials Research Bulletin xxx (2014) 168–175
separated by a magnetic separator and the reaction mixture was
filtered through a pad of Celite and MeOH (6 mL/mmol), conc. HCl
and an equal weight of Pd black were added and the reaction vessel
was connected to
a
Parr medium pressure hydrogenation
apparatus (40–50
c); then it was stirred at room temperature
for 20 h.
The mixture was quenched with 2 M NaOH, filtered, diluted
with 30 mL of ethyl acetate and washed with 2 M NaOH. Then the
mixture was extracted three times with ethyl acetate (30 mL each).
The organic layer was dried over Na2SO4 and the solvent was
removed under reduced pressure. The residue was subjected to gel
permeation chromatography to afford pure products.
The elemental analysis (CHN), IR, 1H NMR and 13C NMR data of
the unknown substituted ureas is given as below:
N-(2,5-Dichlorophenyl) urea (Table 3, entry 4): white color; M.
p. 222–224 ꢀC; FT-IR (KBr, cmꢁ1) 3495, 3417, 3364, 3340, 3308,
3206, 2826, 1676, 1610, 1586, 1535, 1466, 1410, 1385, 1351, 1263,
1089, 1056, 873, 805, 792, 764, 583, 557, 475, 440, 418; 1H NMR
(300 MHz, DMSO-d6) dH = 8.24 (s, 2H), 7.38 (d, J = 8.1 Hz, 1H), 6.96
(d, J = 8.1 Hz, 1H), 6.55 (s, 2H); 13C NMR (75 MHz, DMSO-d6)
dC = 154.7, 137.7, 131.7, 129.9, 121.5, 119.5, 118.8; Anal. Calcd for
C7H6N2OCl2: C, 41.00; H, 2.95; N, 13.66. Found: C, 39.84; H, 2.89; N,
13.80.
N-(4-Acethylphenyl) urea (Table 3, entry 5): white color; M.p.
297–298 ꢀC; FT-IR (KBr, cmꢁ1) 3407, 3307, 3215, 1672, 1613, 1584,
1536,1508,1410,1357,1310, 1273, 1117, 1013, 963, 874, 835, 766, 747,
718, 632, 655, 594, 494, 410; 1H NMR (300 MHz, DMSO-d6)
dH = 8.93 (s, 1H), 7.80 (d, J = 8.4 Hz, 2H), 7.50 (d, J = 8.4 Hz, 2H), 6.02
(s, 2H), 2.47 (s, 3H); 13C NMR (75 MHz, DMSO-d6) dH = 196.6, 156.0,
145.7, 130.2, 130.0, 117.0, 26.7; Anal. Calcd for C9H10N2O2: C, 60.66;
H, 5.66; N, 15.72. Found: C, 60.47; H, 5.45; N, 15.59.
N-(1-Naphthyl) urea (Table 3, entries 6 and 7): white color; M.
p. 221–222 ꢀC; FT-IR (KBr, cmꢁ1) 3444, 33055, 3206, 3052, 2922,
1651, 1608, 1555, 1530, 1505, 1360, 1335, 1278, 1101, 785, 772, 608,
530; 1H NMR (250 MHz, DMSO-d6) dH = 8.70 (s, 1H), 8.17 (s, 1H),
8.00 (d, J = 7.3 Hz, 1H), 7.85 (s, 1H), 7.73–7.37 (m, 4H), 6.22 (s, 2H);
13C NMR (62.5 MHz, DMSO-d6) dC = 157.1, 135.9, 134.5, 128.9, 126.6,
126.4, 126.0, 122.7, 122.3, 117.5; Anal. Calcd for C11H10N2O2: C,
70.95; H, 5.41; N, 15.04. Found: C, 70.82; H, 5.34; N, 14.91.
N-(2-Methylphenyl) urea (Table 3, entries 8 and 9): white
color; M.p. 196–198 ꢀC; FT-IR (KBr, cmꢁ1) 3438, 3315, 3218, 1650,
1613, 1582, 1547, 1459, 1354, 1289, 1258, 1117, 1041, 844, 747, 596,
480; 1H NMR (250 MHz, DMSO-d6) dH = 7.79 (t, J = 6.4 Hz, 1H), 7.69
(s,1H), 7.13–7.07 (dd, J = 8.0 Hz, J = 7.6 Hz, 2H), 6.88 (d, J = 7.4 Hz,1H),
6.03 (s, 2H), 2.19 (s, 3H); 13C NMR (62.5 MHz, DMSO-d6) dH = 156.6,
138.6, 130.5, 127.4, 126.4, 122.5, 121.4, 18.36; Anal. Calcd for
C8H10N2O: C, 63.98; H, 6.71; N, 18.65. Found: C, 63.85; H, 6.61; N,
18.52.
Fig. 1. Typical SEM image of Pd/Fe3O4 nanowires.
leads to the formation of a temperature gradient and fast
condensation process. In fact, rapid cooling of the products
reduces the growth rate of the created nuclei and they do not
have enough time to form wire-shaped structures before
stabilization. Hence, due to fast condensation there are also other
shapes rather than nanowires in our samples. Scanning electron
microscopy image illustrate Pd/Fe3O4 nanowires with size ranging
from 1 to less than 20 mm in length and about 100 nm in diameter.
In addition, Pd particles appear as bright dots over the surface of
Fe3O4 nanowires with average size of less than 30 nm.
The crystalline structure and phase composition of catalyst was
confirmed by X-ray diffraction measurement. The X-ray diffraction
pattern revealed that Fe nanoparticles are very oxygen-sensitive
and easily oxidized to Fe3O4 (Fig. 2). All of the peaks in the X-ray
diffraction (XRD) pattern could also be assigned to the corre-
sponding lattice planes of face-centered-cubic (fcc) Pd and Fe3O4
crystals in accordance with the bimetallic heterodimer structure.
We used energy dispersive X-ray spectroscopy (EDS) to
determine chemical composition of our samples. In the EDS
spectrum of catalyst, peaks related to O, Fe and Pd were observed.
The atomic and weight ratios are listed in Table 1. The excess
amount of oxygen is due to physical absorption of oxygen from
environment during sample preparation.
3. Results and discussion
3.2. Optical properties
3.1. Characterization of catalyst
For non-spherical metallic particles, to calculate the light
absorption by them, the orientation with respect to the oscillating
electric field must be taken into account. In 1912, Gans derived the
extinction cross-section for nanowires, when the dipole approxi-
mation holds [44].
In recent years, many papers have been published about surface
plasmon resonance (SPR) of nanowires. In most of these articles,
the Gans theory was widely used because SPR properties of
nanowires is in good agreement with the results of this theory [45].
In this work, we introduce the effective medium optical
constant of these thin films by comparing the experimental data
and calculation results and then Gans theory which these optical
constants were used for the calculation of extinction cross section
of dispersed Fe nanowires decorated by Pd nanoparticles in water.
The catalyst was characterized using the powder XRD, SEM, EDS
and UV–vis spectroscopy.
Fe3O4 nanowires decorated by Pd nanoparticles were fabricated
in two-steps using a simple process. Fe3O4 nanowires of several
micron lengths were synthesized through arc discharge of iron
electrodes in DI water and then they were dispersed on glass
substrates and dried in air. Palladium nanoparticles were overlaid
on the surface of Fe3O4 nanowires via a simple drop-drying process
by dropping PdCl2 solution onto Fe nanowires films and drying
them at room temperature. Fig. 1 illustrates typical morphologies
of Pd/Fe3O4 nanowires obtained at 5 A arc currents. In general Fe
tends to form wire-like structures due to its lattice geometry. The
presence of a high temperature region and DI water in the reactor

M. Nasrollahzadeh et al. / Materials Research Bulletin xxx (2014) 168–175
171
Fig. 2. XRD pattern of Pd/Fe3O4 nanowires.
aext ¼ expðꢁ4
p
Kd=
l
Þ
(4)
Table
1
Atomic and weight ratios of Pd/Fe3O4.
where, n0, ns, nf are real parts of the refraction indices of the thin
film, the substrate and the air, respectively. Moreover, d is the film
thickness and K is the imaginary part of the refraction index of Pd/
Fe3O4 thin films. To obtain the values of K, using the extinction
coefficient equation as [48]:
Element
Series
Norm. C (wt%)
Atom. C (at%)
Iron
Palladium
Oxygen
K series
K series
K series
26.07
6.18
42.35
9.00
1.12
51.05
ꢀ
ꢁ
ꢁ4
p
l
kd
T
aext ¼ exp
¼
(5)
1 ꢁ R
A typical UV–vis spectrum of the Pd/Fe3O4 thin films on glass
substrates is shown in Fig. 3.
In order to obtain the real part of refraction indices (nf) of the
Pd/Fe3O4 thin films, we have used the prescription given in [46,47]
where it is suggested that the following equation may be used to
obtain the optical constants of low absorption thin films:
The effective real and imaginary parts of refraction indices of
Pd/Fe3O4 thin films are shown in Fig. 4. We used these effective
values as input data at Gans theory for the calculation of extinction
cross section of dispersed Pd/Fe3O4 in water.
Details of the Gans theory can be found in literature [49].
16n0nsn2f aext
C12 þ C22ae2xt þ 2C1C2aextCOSð4
According to the Gans theory, the extinction coefficient
g
for N
T ¼
(1)
p
nf d=lÞ
particles of volume V is given by the following equation.
"
#
3=2
2
2
2
p
NVem
ð2=px
Þ
e2
ð1=px Þe2
2
C1 ¼ ðn0 þ nf Þðnf þ nsÞ
C1 ¼ ðn0 ꢁ nf Þðnf ꢁ nsÞ
(2)
(3)
g
¼
þ
2
(6)
2
2
3
l
ð
e1 þ kxemÞ þ e2
ðe1 þ kzemÞ þ e2
Fig. 3. A typical UV–vis absorption spectrum of the Pd/Fe3O4 thin films on glass substrates.

172
M. Nasrollahzadeh et al. / Materials Research Bulletin xxx (2014) 168–175
Fig. 4. Investigated effective optical constants of Pd/Fe3O4.
where
l
the wavelength of the light,
e
m the dielectric constant of
Table
2
Optimization of reaction conditions in amidation reaction of 2,5-dichlorobromo-
the medium and e1 and e2 the real and complex part of copper
dielectric function related to interacting light.In this theory for
each dimension, a geometrical factor (Pi) are given by
benzene with benzylureaa.
Entry
Pd/Fe3O4 nanowires (mol.%)
Base
Yieldb (%)
ꢀ
ꢀ
ꢁ
ꢁ
1 ꢁ e2
1
2e
1 þ e
1 ꢁ e
1
2
3
4
5
6
7
8
1.0
1.0
1.0
1.0
1.0
0
Cs2CO3
Na2CO3
K3PO4
K2CO3
0
Cs2CO3
Cs2CO3
Cs2CO3
89
50
80
82
0
0
88
72
pz ¼
1n
ꢁ 1
(7)
(8)
e
1
px ¼ py ¼ ð1 ꢁ pzÞ
2
2.0
0.7
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
L2 ꢁ d2
e ¼
(9)
a
Reaction condition: 1.0 equiv of aryl halide, 1.0 equiv of benzylurea, 1.0 mol.% of
catalyst and 1.5 equiv of base, 120 ꢀC, 1 h.
L
where
L and d is the nanowires length and diameter,
respectively. For each dimension the screening parameter is
b
Isolated yield.
1
pi
Ki ¼ ð1 ꢁ piÞ
(10)
3.3. Activity of Pd/Fe3O4 nanowires catalyst for the preparation of N-
monosubstituted ureas
Here Ki (i = 1, 2, 3) are the same Kx, Ky and Kz in Eq. (6). The result
of this process is shown in Fig. 5. It is clear that there is good
agreement between calculation and experimental values of
absorption spectra of Pd/Fe3O4 dispersed in water.
The catalytic behavior of the Pd/Fe3O4 nanowires was studied
for the synthesis of N-monosubstituted ureas. Reaction conditions
Fig. 5. Experimental and calculated absorption spectra by effective optical constants of Pd/Fe3O4 dispersed in water.

M. Nasrollahzadeh et al. / Materials Research Bulletin xxx (2014) 168–175
173
Table
3
Formation of N-monosubstituted ureas.
Entry
1
Aryl halide
Product
Yielda (%)
Reference
[16]
87
89
2
3
[16]
[16]
85
4
89 (88,88,87)b
This work
5
6
85
82
This work
This work
7
85
This work
8
9
87
86
This work
This work
10
11
12
13
84
86
83
85
Commercial
Commercial
[16]
[16]
a
Yields are after work-up.
Yield after the fourth cycle.
b

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M. Nasrollahzadeh et al. / Materials Research Bulletin xxx (2014) 168–175
Fig. 6. FT-IR spectrum (KBr, cmꢁ1) of N-(2-methylphenyl) urea.
were optimized for the amidation reaction using 2,5-dichloro-
bromobenzene as a substrate, and benzylurea and Pd/Fe3O4
nanowires as heterogeneous catalysts in the presence of various
bases under microwave conditions at 120 ꢀC (Table 2). Control
experiments show that there is no effective reaction in the absence
of catalyst (Table 2, entry 6). However, addition of the Pd/Fe3O4
nanowires to the mixture has rapidly increased the amidation of
aryl halides in high yields. Our experiments showed that the base
was necessary for the amidation reaction. Among the selected
bases, Cs2CO3 acted as the most effective one (Table 2, entry 1).
Reaction without base did not give any product. The effect of
catalyst loading was probed. Catalyst loads of 1.0 mol% were
typically required to achieve quantitative conversion with most
substrates. The use of lower catalyst loadings resulted in
incomplete reactions (entry 8).
catalyst Pd/Fe3O4 in comparison with Fe3O4. In the other word, the
high activity of Pd/Fe3O4 catalyst for the synthesis of N-
monosubstituted ureas could be attributed to the formation of
small active Pd nanoparticles on the surface of Fe3O4.
After removal of the solvent and purification, the products were
characterized by melting points, elemental analysis (CHN), IR, 1H
NMR and 13C NMR. Appearance of the two absorption bands in the
range of 3200–3400 cmꢁ1 (NH stretching bands) and one
absorption band in the range of 1640–1670 cmꢁ1 (CQO) in the
IR spectrum confirmed formation of the N-monosubstituted ureas
(Fig. 6). The 1H NMR spectra of the products showed one NH proton
signal and another signal for the NH2 protons. The 13C NMR spectra
of the products showed one signal for the carbonyl carbon.
3.4. Catalyst recyclability
We then used the optimal reaction conditions (catalyst (1.0 mol
%), aryl halide (1.0 mmol), benzylurea (1.0 mmol) and Cs2CO3
(1.5 mmol)) for amidation of different aryl halides under micro-
wave conditions at 120 ꢀC) for 1 h and the results are shown in
Table 3. Then, the in situ hydrogenolysis of 1-benzyl-3-arylureas in
MeOH and in the presence of conc. HCl and Pd black yielded the
desired N-monosubstituted ureas from good to excellent yields.
To study the effects of the nature of the substituents, various 1-
benzyl-3-arylureas were synthesized from the reaction between
different aryl halides containing both electron-releasing and
electron-withdrawing groups with benzylurea in good to excellent
yields. As shown in Table 3, 1-bromo and 1-iodonaphthyl gave the
corresponding adduct in good yield (Table 3, entries 6 and 7).
To the best of our knowledge, Pd/Fe3O4 nanowires are one of the
most general and active catalysts reported so far for the synthesis
of N-monosubstituted ureas. These results represent a significant
advancement in the C–N coupling reaction. Although the mecha-
nism of Pd-catalyzed coupling is not obvious and further studies to
elucidate the detailed reaction mechanism are ongoing in our
laboratory. It should be noted that Pd/Fe3O4 nanowires were
absolutely necessary for this reaction as verified by a control
experiments where no reaction occurred in the absence of Pd/
Fe3O4 nanowires or in the presence of only Fe3O4 even at a higher
reaction temperature for a prolonged reaction time. Based on the
most accepted coupling reaction mechanism, Pd nanoparticles are
expected to be the reasons for the high catalytic activity of the
The reusability of the catalyst was checked in the reaction of
benzylurea with iodobenzene under the present reaction con-
ditions (Table 3, entry 4). After the completion of the reaction, the
insoluble catalyst was separated from the reaction mixture by the
application of an external magnet. The catalyst was washed with
ethyl acetate several times, dried in a hot air oven at 100 ꢀC for 2 h
and employed for the next reaction. The catalytic activity did not
decrease considerably after four catalytic cycles. The reusability of
the catalysts is one of the most important benefits and makes them
useful for commercial applications.
4. Conclusions
In conclusion, we have developed an efficient protocol for the
preparation of Pd/Fe3O4 nanowires. The catalyst was characterized
by SEM, XRD, EDS and UV–vis spectroscopy and exhibited good
activities in ligand-free coupling reactions of aryl halides with
benzylurea. This system allows the coupling of electron-rich,
-neutral, and -deficient aryl halides from good to excellent yields.
This method leads to the advantages of high yields, elimination of
homogeneous catalysts, simple methodology and easy work up.
The catalyst is eco-friendly catalyst because it produces little
waste, and can be recovered by a magnet and successively reused
without the significant loss of activity. The optical properties of the
catalyst were also studied.

M. Nasrollahzadeh et al. / Materials Research Bulletin xxx (2014) 168–175
175
[24] M.A. Willard, L.K. Kurihara, E.E. Carpenter, S. Calvin, V.G. Harris, International
Materials Reviews 49 (2004) 125.
Acknowledgments
[25] M. Zhu, G. Diao, The Journal of Physical Chemisty C 115 (2011) 24743.
[26] M. Zhu, C. Wang, D. Meng, G. Diao, Journal of Materials Chemisty A 1 (2013)
2118.
We gratefully acknowledge the Iranian Nano Council and
University of Qom for the support of this work.
[27] M. Zhu, G. Diao, Nanoscale 3 (2011) 2748.
[28] P. Fakhri, B. Jaleh, M. Nasrollahzadeh, Journal of Molecular Catalysis A:
Chemical 383-384 (2014) 17.
[29] D. Habibi, M. Nasrollahzadeh, H. Sahebekhtiari, Journal of Molecular Catalysis
A: Chemical 378 (2013) 148.
References
[1] K. Matsuda, Medicinal Research Reviews 14 (1994) 271.
[2] N.N. Melnikov, J.D. Gunther, Chemistry of Pesticides, Springer-Verlag, Berlin,
1971, pp. 225.
[30] M. Nasrollahzadeh, A. Ehsani, A. Rostami-Vartouni, Ultrasonics Sonochemisty
(2014) 21 275.
[31] A. Ehsani, F. Babaei, M. Nasrollahzadeh, Applied Surface Science 283 (2013)
1060.
[32] A.R. Modarresi-Alam, M. Nasrollahzadeh, F. Khamooshi, Sci. Iran. 15 (2008)
[3] A. Tsopmo, D. Ngnokam, D. Ngamga, J.F. Ayafor, O. Sterner, Journal of Natural
Products 62 (1999) 1435.
[4] Y. Funabashi, S. Tsubotani, K. Koyama, N. Katayama, S. Harada, Tetrahedron 49
(1993) 13.
[5] V. Papesch, E.F. Schroeder, Journal of Organic Chemistry 16 (1951) 1879.
[6] R.L. Clark, A.A. Pessolano, Journal of American Chemical Society 80 (1958)
1658.
[7] E.A. Jefferson, E.E. Swayze, Tetrahedron Letters 40 (1999) 7757.
[8] S. Knapp, J.J. Hale, M. Bastos, A. Molina, K.Y. Cheng, Journal of Organic Chemisty
57 (1992) 6239.
452.
[33] D. Habibi, S. Heydari, M. Nasrollahzadeh, Journal of Chemical Research 36
(2012) 573.
[34] D. Habibi, M. Nasrollahzadeh, L. Mehrabi, S. Mostafaee, Monatshefte für
Chemie 144 (2013) 725.
[35] A. Ehsani, S. Adeli, F. Babaei, H. Mostaanzadeh, M. Nasrollahzadeh, Journal of
Electroanalytical Chemistry 713 (2014) 91.
[36] H.M. Hwang, J.H. Kang, J. Lee, J.Y. Choi, H.H. Lee, Electrochemical and Solid-
State Letters 11 (2008) K7.
[37] W.-S. Lin, Z.-J. Jian, H.-M. Lin, L.-C. Lai, Journal of Chinese Chemical Society 60
(2013) 85 et all.
[9] X. Peng, F. Li, C. Xia, Synlett (2006) 1161.
[10] B. Zhu, R.J. Angelici, Journal of American Chemical Society 128 (2006) 14460.
[11] Y. Nishiyama, H. Kawamatsu, N. Sonoda, Journal of Organic Chemisty 70 (2005)
2551.
[12] F. Bigi, R. Maggi, G. Sartori, Green Chemisty 2 (2000) 140.
[13] V.D. Jadhav, E. Herdtweck, F.P. Schmidtchen, Chemisty: A European Journal 14
(2008) 6098.
[38] D.J. Sellmyer, M. Zheng, R. Skomski, Journal of Physics: Condensed Matter 13
(2001) R433.
[39] J. Zhang, W.M. Tong, H. Ding, H.B. Wang, H. Wang, Integrated Ferroelectics 141
(2013) 24.
[40] I. Alexandrou, H. Wang, N. Sano, G.A.J. Amaratunga, Journal of Chemical
Physics 120 (2004) 1055.
[41] D. Bera, G. Johnston, H. Heinrich, S. Seal, Nanotechnology 17 (2006) 1722.
[42] D. Bera, S.C. Kuiry, M. McCutchen, S. Seal, H. Heinrich, G.C. Slane, Journal of
Applied Physics 96 (2004) 5152.
[43] N. Sano, Materials Chemisty and Physics 88 (2004) 235.
[44] R. Gans, Annals of Physics 37 (1912) 881.
[45] S. Eustis, M. El-Sayed, The Joural of Physical Chemistry B 109 (2005) 16350.
[46] S.Z. Shang, K. Yi, Z.X. Fan, Applied Surface Science 242 (2005) 437.
[47] S. Wang, X. Fu, G. Xia, J. Wang, J. Shao, Z. Fan, Applied Surface Science 252
(2006) 8734.
[14] D. Schade, K. Topker-Lehmann, J. Kotthaus, B. Clement, Journal of Organic
Chemisty 73 (2008) 1025.
[15] E. Artuso, I. Degani, R. Fochi, C. Magistris, Synthesis (2007) 3497.
[16] S.H. Kim, B.R. Park, J.N. Kim, Bulletin of the Korean Chemical Society 32 (2011)
716.
[17] S.A. Lawrence, Amines, Synthesis Properties, and Application, Cambridge
University Press, Cambridge, 2004.
[18] S. Breitler, N.J. Oldenhuis, B.P. Fors, S.L. Buchwald, Organic Letters 13 (2011)
3262.
[19] A.G. Sergeev, G.A. Artamkina, I.P. Beletskaya, Russian Journal of Organic
Chemisty 38 (2002) 538.
[20] B.J. Kotecki, D.P. Fernando, A.R. Haight, K.L. Lukin, Organic Letters 11 (2009) 947.
[21] A.G. Sergeev, G.A. Artamkina, V.S. Velezheva, I.N. Fedorova, I.P. Beletskaya,
Russian Journal of Organic Chemisty 41 (2005) 860.
[22] M.C. Daniel, D. Astruc, Chemical Society Reviews 104 (2004) 293.
[23] A. Molnar, Chemical Reviews 111 (2011) 2251.
[48] J.R. Reitz, F.J. Milford, Foundations of Electromagnetic Theory, Addison-Wesley,
Reading, MA, 1960.
[49] C.F. Bohren, D.R. Huffman, Absorption and Scattering of Light by Small
Particles, John Wiley & Sons, New York, 1983.