Synthesis and characterization of Fe3O4@SiO 2-polymer-imid-Pd magnetic porous nanospheres and their application as a novel recyclable catalyst for Sonogashira-Hagihara coupling reactions

Article abstract of DOI:10.1007/s13738-013-0323-4

We demonstrate herein the modification of magnetic nanoparticles and their use as a magnetic nanocatalyst in direct coupling reactions of aryl halides with terminal alkynes. Magnetite particles were prepared by simple co-precipitation method in aqueous me

Full text of DOI:10.1007/s13738-013-0323-4

J IRAN CHEM SOC
DOI 10.1007/s13738-013-0323-4
ORIGINAL PAPER
Synthesis and characterization of Fe3O4@SiO2–polymer-imid–Pd
magnetic porous nanospheres and their application as a novel
recyclable catalyst for Sonogashira–Hagihara coupling reactions
•
•
•
Esmaeilpour Mohsen Javidi Jaber Mokhtari Abarghoui Mehdi
Nowroozi Dodeji Fatemeh
Received: 27 May 2013 / Accepted: 27 July 2013
Ó Iranian Chemical Society 2013
Abstract We demonstrate herein the modification of
magnetic nanoparticles and their use as a magnetic nano-
catalyst in direct coupling reactions of aryl halides with
terminal alkynes. Magnetite particles were prepared by
simple co-precipitation method in aqueous medium, and
then Fe3O4@ SiO2 nanosphere was synthesized by using
nano-Fe3O4 as the core, TEOS as the silica source and
PVA as the surfactant. Fe3O4@SiO2 was coated with
polymeric N-heterocyclic carbene/Pd. The samples were
characterized by X-ray diffraction, Fourier transform
infrared spectroscopy, transmission electron microscopy,
field emission scanning electron microscopy, dynamic light
scattering, thermogravimetric analysis, vibration sample
magnetometer and N2 adsorption–desorption isotherm
analysis. Poly (N-vinyl imidazole) functionalized
Fe3O4@SiO2 nanoparticle was found to be an efficient
nanocatalyst in Sonogashira–Hagihara cross-coupling
reactions. The nanocatalyst can be easily recovered by a
magnetic field and reused for six runs without appreciable
loss of its catalytic activity.
Keywords Core–shell Á Nanocatalyst Á
Sonogashira–Hagihara Á Superparamagnetic Á
Catalyst reuse
Introduction
During the past decade, scientists have developed techniques
for synthesizing and characterizing many new materials with
at least one dimension on the nanoscale, including nano-
particles, nanolayers and nanotubes [1]. Nanostructured
materials, a new branch of materials research, are attracting a
great deal of attention because of their potential applications
in areas such as catalysis [2], electronics [3], ceramics [4],
optic [5], magnetic data storage [6] and nanocomposites.
One of the most fundamental characteristics of nanometer-
sized particles is their very high surface-to-volume ratio.
This can lead to novel and unexpected atomic arrangements
and may also have dramatic effects on other physical or
chemical attributes [7].
In recent years, the synthesis of superparamagnetic
nanoparticles has been intensively developed not only for its
fundamental scientific interest, but also for many techno-
logical applications: catalytic [8], biosensing [9], magnetic
storage media [10], medical applications, such as contrast
agents in magnetic resonance imaging (MRI) [11–14], tar-
geted drug delivery [15, 16], magnetic inks for jet printing
[17], tissue repairing [18], immunoassay and [18] hyper-
thermia treatment of cancer cells [19], detoxification of
biological fluids [18] and cell separation [18]. These appli-
cations are mainly based on the magnetic feature of the solid
phase that enables achieving a rapid and easy separation
from the reaction medium in a magnetic field [20].
E. Mohsen Á N. D. Fatemeh
Chemistry Department, College of Science, Shiraz University,
Shiraz, Iran
e-mail: m1250m551085@yahoo.com
J. Jaber (&)
Department of Pharmaceutics, School of Pharmacy, Shaheed
Beheshti University of Medical Sciences, Tehran, Iran
e-mail: jaberjavidi@gmail.com
M. A. Mehdi
Department of Chemistry, Isfahan University of Technology,
Isfahan, Iran
Nanoscale magnetite (Fe3O4) is cheap, non-toxic, bio-
compatible and easy to prepare [21]. Many methods have
123

J IRAN CHEM SOC
been developed for the preparation of Fe3O4 such as
sonochemical synthesis [22], thermal decomposition [23],
microemulsions [24] and chemical co-precipitation [25,
26]. Among these methods, chemical co-precipitation may
be the most promising, because of its simplicity and
productivity.
procedure for the Pd-catalyzed Sonogashira–Hagihara
reaction is still a desirable goal.
In this work, we report the preparation of Fe3O4@SiO2–
polymer-imid–Pd nanocatalyst as illustrated in Scheme 1
and its use as a magnetic nanocatalyst in direct coupling
reactions of aryl halides with terminal alkynes.
Recently, magnetic core–shell nanostructures have
attracted more attention due to their unique magnetic
properties. These core–shell nanostructure magnetic cata-
lysts can be easily retrieved under the influence of a
magnetic field and used in subsequent reactions. Due to this
property, using magnetic core–shell structure composites
as catalysts has been recommended in many studies [27].
Also, several methods have been developed to prepare
polymer coatings on magnetite nanoparticles such as
physical adsorption of polymers and emulsion polymeri-
zation in the presence of nanoparticles, the so-called
‘‘grafting-to’’ and ‘‘grafting-from’’ methods [28, 29].
Obviously, homogeneous catalysts show higher catalytic
activities than their heterogeneous counterparts because of
their solubility in reaction media, which increases catalytic
site accessibility for the substrate. However, recycling
homogeneous catalysts is often tedious and time consuming
and there is also the issue of product contamination observed
when these catalysts are used [27]. Immobilization of
homogeneous catalysts on various insoluble supports,
especially porous materials with high surface areas, is usu-
ally the method of choice, since the immobilized catalysts
can be facilely recovered via a simple filtration process after
reactions [30]. Therefore, a number of functionalized Fe3O4
nanoparticles have been employed in a range of organic
transformations, and several studies on immobilization of
metal and organo-catalysts on silica-coated iron oxide
nanoparticles have been reported [31–34].
Experimental
General
All the chemicals reagents used in our experiments were
purchased from the Merck Chemical Company in high pur-
ity. All the solvents were distilled, dried and purified by
standard procedures. Fourier transform infrared (FT-IR)
spectra were obtained using a Shimadzu FT-IR 8300 spec-
trophotometer. NMR spectra were recorded on a Bruker
Avance DPX 250 MHz spectrometer in CDCl3 or DMSO-d6
using tetramethylsilane (TMS) as an internal reference.
X-ray powder diffraction (XRD) spectra were taken on a
Bruker AXS D8-advance X-ray diffractometer with Cu Ka
radiation (k = 1.5418). Transmission electron microscopy
(TEM) images were obtained on a Philips EM208 trans-
mission electron microscope with an accelerating voltage of
100 kV, and field emission scanning electron microscopy
(FE-SEM) images were obtained on HITACHI S-4160. The
BET surface area and porosity of catalysts were determined
from nitrogen physisorption measured on a Micromeritics
ASAP 2000 instrument at 196 °C. TGA thermograms were
recorded on an instrument of Perkin Elmer with N2 carrier
gas and with the rate of temperature change of 20 °C min-1
.
Magnetic properties were obtained on a BHV-55 vibrating
sample magnetometer (VSM) and dynamic light scattering
(DLS) was recorded on a HORIBA-LB550. Pd loading and
leaching test was carried out with an inductively coupled
plasma (ICP) analyzer (Varian, vista-pro). Mass spectra
were obtained at 70 eV. 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. The progress of the reaction was moni-
tored by TLC and purification was achieved by silica gel
column chromatography.
Palladium-catalyzed Sonogashira–Hagihara cross-cou-
pling is one of the most widely used carbon–carbon forming
reactions [35, 36] and has been widely applied in areas such
as natural products [37], pharmaceuticals [38] and biologi-
cally active molecules [39]. It provides an efficient route to
obtain materials for nonlinear optical and molecular elec-
tronics [40], alkenyl- and arylacetylenes, substituted alkynes
[41], conjugated oligomers and polymers [42] and sym-
metrical diynes [43]. The Sonogashira coupling reaction of
terminal alkynes with aryl halides can occur in the presence
of catalysts such as MCM-41-S–Pd(0) [44], Pd/C [45],
CELL–Pd(0) [46], Pd(dmba)Cl(PTA) [47], PdCl2(PCy3)2
[48] and PdCl2(PPh3)2 [49]. In addition, the use of transition
metals such as Co [50], Fe [51, 52], Ni [53], In [54] and Ru
[55] has been also reported for these reactions. Although
these methods are valuable, many of these procedures have
significant drawbacks such as tedious workup procedures,
low yields, long reaction times, high temperatures and non-
recoverable catalysts. Thus, the development of a new
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 [27]. 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), as a surfactant, and
123

J IRAN CHEM SOC
Scheme 1 Process for preparation of polymeric N-heterocyclic carbene/Pd functionalized Fe3O4@SiO2 nanoparticle
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
was left to be stirred for 30 min in 80 °C. Then, hexam-
ethylenetetraamine (HMTA) (1.0 mol/L) was added drop-
wise with vigorous stirring to produce a black solid product
when the reaction media reached pH 10. The resultant
mixture was heated on a water bath for 2 h at 60 °C, 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.
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 the 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-viny-
limidazole (2 mL) and recrystallized benzoyl 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 sep-
arated by an external magnet, washed with deionized water
and ethanol three times and dried at 80 °C for 10 h.
Synthesis of poly (N-vinylimidazole) functionalized
Fe3O4@SiO2 nanoparticle (Fe3O4@SiO2–polymer-imid)
Synthesis of polymer-imid–Pd functionalized Fe3O4@SiO2
nanoparticle (Fe3O4@SiO2–polymer-imid–Pd)
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 kept under reflux for
Fe3O4@SiO2–polymer-imid (1 g) was dispersed in the
DMF solution (15 mL), ultrasonically for 15 min. Then,
123

J IRAN CHEM SOC
methyl iodide (2.5 mmol, 0.155 mL) was added, the mix-
ture was stirred at 80 °C for 16 h and filtered in an external
magnetic field. The product was washed with DMF and
ethanol to remove any reacted species and dried at 70 °C
for 6 h. The resultant solid product stirred in 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 chloride ion capac-
ity of imidazolium-type Fe3O4@SiO2-polymer was found
using an argentometric 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 counterions precipitated as AgCl. The remaining
Ag? was back titrated using 0.1 M HCl. The permanent
charge density of imidazole groups was calculated 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 in an external magnetic field, washed
thoroughly with DMF (2 9 5 mL) and H2O (2 9 5 mL)
and dried at 70 °C for 8 h.
General procedure for the Sonogashira–Hagihara
reaction using Fe3O4@SiO2–polymer-imid–Pd
magnetic nanocatalyst
Fig. 1 FT-IR spectra: a Fe3O4, b Fe3O4@SiO2, c Fe3O4@SiO2–
NH2, d Fe3O4@SiO2–polymer-imid, e Fe3O4@SiO2–polymer-imid-
S and Fe3O4@SiO2–polymer-imid–Pd
A mixture of ArX (1.0 mmol), alkyne (1.2 mmol), Fe3O4@
SiO2-polymer-imid–Pd magnetic nanocatalyst (0.03 g),
Et3N (2 mmol) and DMF (4.0 mL) was stirred at 80 °C in
an oil bath. The progress of the reaction was monitored by
TLC or GC. After completion of the reaction and separa-
tion of Fe3O4@SiO2–polymer-imid–Pd using a magnetic
field, 15 mL of water was added and the mixture extracted
with Et2O. The combined organic phases were washed with
water (2 9 5 mL) and dried over anhydrous Na2SO4.
Then, the solvent was removed under reduced pressure.
The resulting crude product was purified by flash chro-
matography to give the desired pure coupling products in
high to excellent isolated yields.
sample. The surfaces of pure Fe3O4 nanoparticles were
readily covered with SiO2 layers. In Fig. 1b, the presence of
vibration bands at 561, 1,000–1,150 and 3,400 cm-1, due to
Fe–O, Si–O–Si, and –OH, respectively, demonstrates the
existence of Fe3O4@ SiO2. Figure 1c shows the FT-IR
spectrum of Fe3O4@SiO2–NH2 nanoparticles; the peaks at
560, 1,000–1,150, 1,400–1,410 and 1,543 cm-1 are attrib-
uted to Fe–O (stretching vibration), Si–O–Si (asymmetric
stretching), C–N(stretching vibration) and N–H (bending),
respectively. Also, the presence of several bands with med-
ium intensity in 28,010–2,986 cm-1 and 3,050–3,250
regions are allocated to C–H stretching of the propyl group
and N–H stretching (Fig. 1c). The presence of vibration
bands at 559, 1,000–1,150, 1,445, 1,649 and 2,792–2,985,
due to Fe–O, Si–O–Si, C=N, C=O and CH, respectively,
demonstrates the existence of Fe3O4@SiO2–polymer-imid
in the spectrum (Fig. 1d). The FT-IR spectrum of
Fe3O4@SiO2–polymer-imid–S exhibits a band at 1,518
cm-1 assigned to the C–H bending of the imidazolium group
(Fig. 1e). The absorption bands at 562, 1,000–1,150, 1,653
and 2,850–3,000 cm-1 are in correspondence with
Results and discussion
The FT-IR spectrum of Fe3O4, Fe3O4@SiO2, Fe3O4@SiO2–
NH2, Fe3O4@SiO2–polymer-imid, Fe3O4@SiO2–polymer-
imid–S and Fe3O4@SiO2–polymer-imid–Pd nanoparticles
are shown in Fig. 1a–f. In Fig. 1a, the absorption band at
559 cm-1 is assigned to the stretching vibration of the Fe–O
band of Fe3O4. Also, the peaks at around 3,400 and
1,620 cm-1 in Fig. 1a are due to the adsorbed water in the
123

J IRAN CHEM SOC
vibrations of Fe–O, Si–O–Si, C=O and C–H stretching in
Fe3O4@SiO2–polymer-imid–Pd (Fig. 1f). It also shows a
band in the region of 790 cm-1 which confirms the presence
of C–Pd absorption frequency in Fe3O4@SiO2–polymer-
imid–Pd (Fig. 1f).
broadening of each peak in XRD mean crystallite size was
calculated by applying Scherrer’s equation: D = 0.9 k/b
cosH, where D is the average diameter in A°, k is the
wavelength of the X-rays, b is the broadening of the dif-
fraction line measured at half of its maximum intensity in
radians and H is the Bragg diffraction angle. The mean
crystallite size superparamagnetic nanocatalyst was found
to be around 80 nm.
Structural investigation of samples was carried out by
powder X-ray diffraction (XRD) technique. Figure 2 shows
the XRD patterns for pure Fe3O4, Fe3O4@SiO2 and
Fe3O4@SiO2-polymer–Pd nanoparticles. As shown in
Fig. 2a, the Fe3O4 nanoparticle has highly crystalline cubic
spinel structure, which agrees with the standard Fe3O4
(cubic phase) XRD spectrum (PDF#88-0866). The char-
acteristic peaks at 2H = 30.1°, 35.4°, 43.1°, 53.4°, 57° and
62.6° for pure Fe3O4 nanoparticles, which were marked,
respectively, by their indices (220), (311), (400), (422),
(511) and (440), were also observed for Fe3O4@SiO2 and
Fe3O4@SiO2-polymer–Pd nanoparticles (reference JCPDS
card no.19-629). This revealed that the surface modifica-
tion and conjugation of the Fe3O4 nanoparticles do not lead
to their phase change. From Fig. 2b, we can see the XRD
pattern of Fe3O4@SiO2 showing an obvious diffusion peak
at 2H = 15–25°, generally considered as the diffusion
peak of amorphous silica. For Fe3O4@SiO2–polymer-
imid–Pd nanoparticles, the broad peak was transferred to
lower angles due to the synergetic effect of amorphous
silica and polymer. Also, the XRD pattern of Fe3O4@-
SiO2–polymer-imid–Pd nanocatalyst, showing the peaks of
both Fe3O4 and Pd and the diffraction peak at 39.79°,
indicates that the Pd particles are in a metallic state. The
The morphology and sizes of (a) Fe3O4 and
(b) Fe3O4@SiO2 particles were observed by transmission
electron microscopy (TEM) as shown in Fig. 3. As shown
in Fig. 3a, the Fe3O4 nanoparticles prepared by the
chemical coprecipitation are quasi spherical with an aver-
age of about 12 nm. Figure 1b clearly displays that Fe3O4
nanoparticles have been successfully encapsulated into the
SiO2 shell, and Fe3O4@SiO2 nanoparticles were obtained
with a diameter of about 20 nm due to the agglomeration of
Fe3O4 inside nanospheres and surface growth of silica on
the shell. The mesoporous silica shell on the surface of
Fe3O4 is quite homogeneous and exhibits good monodis-
persity with an estimated thickness of 8 nm.
The morphology of Fe3O4@SiO2–polymer-imid–Pd
nanoparticle was also observed by FE-SEM (Fig. 3c). The
Fe3O4@SiO2–polymer-imid–Pd nanoparticles are spheri-
cal in shape with a smooth surface morphology. The
diameter of the nanoparticles is found to be approximately
90 nm. The FE-SEM images indicate the successful coat-
ing of the magnetic Fe3O4 particles.
The hydrodynamic diameter of Fe3O4, Fe3O4@SiO2
and Fe3O4@SiO2–polymer-imid–Pd nanoparticles is
determined by the DLS technique (Fig. 3). This size
distribution is centered at a value of 12, 20 and 85 nm for
Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2–polymer-imid–Pd,
respectively (Fig. 3d–f). The theoretical curve of standard
distribution from our studies was calculated by means of
Microsoft Excel.
N2 adsorption–desorption isotherm analysis provides
information on the specific surface area and porosity of the
prepared samples. The surface areas and average pore
radius were measured by N2 adsorption and results are
shown in Table 1.
The results of magnetization measurements as a function
of applied magnetic field are shown in Fig. 4a. It indicated
that all products had superparamagnetism. The magneti-
zation curve and demagnetization curve are coincident, no
hysteresis phenomenon is found, and remanent magneti-
zation and coercivity are equal to zero. As shown in
Fig. 4a(a), the saturation magnetization of Fe3O4 is
65.8 emu/g, while for Fe3O4@SiO2–polymer-imid–Pd
with a 75 nm shell 27.3 emu/g at 300 K [Fig. 4a(b)]. These
results indicated that the magnetization of Fe3O4 decreased
considerably with the increase of SiO2 and polymer.
Nevertheless, the polymer–Pd supported on Fe3O4@SiO2
Fig. 2 XRD patterns of a Fe3O4 [27], b Fe3O4@SiO2 [27] and c
Fe3O4@SiO2–polymer-imid–Pd
123

J IRAN CHEM SOC
Fig. 3 TEM and DLS images of Fe3O4 (a, d) [27], Fe3O4@SiO2 (b), e [27] and FE-SEM and DLS images Fe3O4@SiO2–polymer-imid–Pd (c,
f), respectively
Table 1 BET result of Fe3O4, Fe3O4@SiO2, Fe3O4@SiO2–poly-
mer-imid–Pd and recovered catalystsa
analysis, the Pd content in the magnetic nanocatalyst was
determined, which revealed the presence of 0.33 mmol/g
Catalyst/cycle
reusability
Specific surface
area (m2/g)
Pore volume
(cm3/g)
Average pore
radius (nm)
for this catalyst.
Thermal analysis was performed to confirm coating
formation on the surface of Fe3O4@SiO2. As shown in
Fig. 4b, the TGA curve of Fe3O4@SiO2–polymer-imid–
Pd shows first weight loss of 2.6 % below 120 °C, which
might be due to the loss of adsorbed water in the sample.
The mass loss of about 27.74 % by weight in the range of
200–500 °C is attributed to the decomposition of pure
polymer and the temperature of the maximum weight loss
is 487 °C (Fig. 4b). Below 200 °C, the rate of weight loss
is relatively slow owing to the loss of residual water
adhering to the sample surface. Thus, the TGA curve
confirmed the successful grafting of polymer molecules on
the magnetic surface.
Fe3O4
480
350.3
270
264
260
258
255
240
0.803
0.755
0.639
0.635
0.633
0.636
0.678
0.696
1.254
1.787
3.768
4.810
4.880
4.930
5.323
5.800
Fe3O4@SiO2
Cat.
Cat./first
Cat./second
Cat./third
Cat./fourth
Cat./fifth
a
Calculated by the BJH method
can still be separated from the solution by using an external
magnetic field [Fig. 4a(b)].
The photographs of the dispersions of the Fe3O4@-
SiO2–polymer-imid–Pd nanoparticles are given in Fig. 5a,
which was well dispersed in DMF under normal condi-
tions. On the contrary, the nanoparticles rapidly gathered
Determination of Pd content was performed by induc-
tively coupled plasma (ICP) analyzer. According to the ICP
123

J IRAN CHEM SOC
Fig. 4 a Magnetization curves at 300 K for a Fe3O4 and b Fe3O4@SiO2–polymer-imid–Pd nanoparticles nanoparticles. b Thermogravimetric
analysis of Fe3O4@SiO2–polymer-imid–Pd nanoparticles
The use of a higher amount of nanocatalysts did not
improve the yield (Table 2, entry 14), while a decrease in
the amount of nanocatalysts decreased the yield (Table 2,
entries 12 and 13). In the absence of a magnetic nanocat-
alyst, the reaction did not proceed even after a long reac-
tion time (10 h) (Table 2, entry 17).
The results showed that among the tested solvents, DMF
was more efficient and the desired product was obtained in
shorter reaction times (30 min) and higher yields (Table 2,
entry 6) than the other solvents under study (Table 2, entries
1–5). In the reactions employing tetrahydrofuran, toluene,
water, acetonitrile and dimethyl sulfoxide as solvents, the
reactions did not progress efficiently and after 2 h the desired
product was obtained in only 66, 41, 79, 83 and 86 % yields,
Fig. 5 Catalyst ability for effective recovery at the end of reactions
respectively, at 80 °C (Table 2, entries 1–5).
by an external magnetic field
The effect of different bases on the reaction of iodo-
benzene (1 mmol) with phenylacetylene (1.2 mmol) in the
on the sidewall of the cylinder under a magnetic approach
(Fig. 5b). This result indicated that the Fe3O4@SiO2-
polymer–Pd nanoparticles can be easily manipulated by an
external magnetic field.
presence of Fe3O4@SiO2-polymer–Pd magnetic nanopar-
ticles (0.03 g) in DMF (4 mL) at 80 °C was studied
(Table 2, entries 6, 15-21). We have presented the results
of this study in Table 2, which indicates that Et3N is the
most suitable among the different bases studied for this
purpose (Table 2, entry 6).
To show the merit of application of these magnetic
nanoparticles in organic synthesis, we applied them as the
catalysts in the Sonogashira–Hagihara cross-coupling
reactions. Initial studies were performed upon the reaction
of iodobenzene with phenylacetylene as a model reaction
and the effects of different solvents, temperature, bases and
amount of catalyst were studied for this reaction (Table 2).
To elucidate the role of the catalyst, initially the reaction
between iodobenzene and phenylacetylene was examined
in the presence of varying amounts of the nanocatalysts and
the results are presented in Table 2. The best result was
achieved by carrying out the reaction with
(0.03 g:1:1.2 mmol) ratio of nanocatalyst, iodobenzene
and phenylacetylene in DMF at 80 °C (Table 2, entry 6).
Also, the effect of temperature was studied by carrying
out the model reaction at different temperatures (room
temperature, 40, 60, 80 and 90 °C) in DMF in the presence
of Et3N and the best results were obtained at 80 °C
(Table 2, entries 6–10). Therefore, we continued the
reactions under optimum conditions (Table 2, entry 6).
The generality of the reaction of phenylacetylene with
diverse aryl halides was studied under optimum conditions,
that is, Fe3O4@SiO2-polymer–Pd (0.03 g), DMF (4 mL)
and 2 mmol of Et3N and the results are summarized in
Table 3. As expected, the reaction of aryliodides bearing
electron-donating groups was completed with longer
123

J IRAN CHEM SOC
Table 2 Optimization of different proportions of nanocatalyst and also effect of solvents, temperature and using different bases upon the
reaction of iodobenzene with phenylacetylene as a model reactiona
Entry
Solvent
Catalyst
amount (g)
Bases
Temperature
(°C)
Yieldb
(%)
1
THF
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
Et3N
80
80
80
80
80
80
r.t
66
41
79
83
86
96
Trace
79
84
95
–
2
Toluene
H2O
Et3N
3
Et3N
4
CH3CN
DMSO
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
Et3N
5
Et3N
6
Et3N
7
Et3N
8
Et3N
40
60
90
80
80
80
80
80
80
80
80
80
80
80
9
Et3N
10
11
12
13
14
15
16
17
18
19
20
21
a
Et3N
c
–
Et3N
0.01
0.02
0.04
0.03
0.03
0.03
0.03
0.03
0.03
0.03
Et3N
22
73
95
23
87
91
64
66
87
90
Et3N
Et3N
Na2CO3
K2CO3
CS2CO3
NaOH
KOH
CsOH
DBU
Reactions were run in 4 ml solvent with 1 mmol iodobenzene, 1.2 mmol phenylacetylene and 2 mmol base for 2 h
b
c
Isolated yield
Time: 10 h
reaction times (Table 3, entries 2–4) than those with
To confirm the reusability and stability of the magnetic
nanocatalyst, it was separated from the reaction mixture
after its first use in the Sonogashira–Hagihara reaction. The
recovered catalyst was found to be reusable for six cycles
with a slight loss in activity (Fig. 6).
electron-withdrawing groups (Table 3, entries 5, 6, 8 and
9). The coupling of ortho- and meta-substituted iodo-
benzenes having ortho-methyl, ortho-chloro and meta-
chloro groups took place with phenylacetylene to give the
corresponding products in 87, 87, and 90 % yield,
respectively (Table 3, entries 3, 8 and 9). The coupling
reaction of phenylacetylene with both electron- releasing
and electron-withdrawing aryl bromides afforded the
desired products in high yields (Table 3, entries 10–17).
Also, 3-bromopyridine, 5-bromopyrimidine and 2-thio-
phenyl iodide led to the corresponding arylated alkynes in
good yields (Table 3, entries 15–17). Although aryl chlo-
rides are not as reactive and are less likely employed in
palladium-catalyzed coupling reactions, Sonogashira–
Hagihara reactions could take place using phenylacetylene
and aryl chlorides in the presence of catalytic amount of
Fe3O4@SiO2–polymer-imid–Pd nanoparticles (Table 3,
entries 18-21).
Conclusions
Fe3O4 was successfully prepared by co-precipitation with
FeCl2 and FeCl3 as reaction substrate, polyvinyl alcohol
(PVA 15000) as surfactant and hexamethylenetetraamine
as precipitant. The core–shell Fe3O4@SiO2 nanospheres
were prepared by a modified Stober method. Then,
Fe3O4@SiO2 was coated with polymeric N-heterocyclic
carbene/Pd. The nanocatalyst was successfully synthesized
and structural, surface, morphological and magnetic prop-
erties of these nanoparticles were evaluated. TEM
microscopy revealed a very fine layer of SiO2 and polymer
123

J IRAN CHEM SOC
Table 3 Sonogashira–Hagihara coupling of different aryl halides with phenylacetylene in DMF in the presence of the catalyst using Et3N as a
basea
Entry
1
Aryl halide
Product
Time (h)
0.5
Yield (%)b
96
References
[56]
I
2
3
2.5
3
93
87
[56]
[56]
Me
I
Me
Me
Me
I
4
5
6
7
3
91
93
94
90
[56]
[56]
[56]
[56]
MeO
NC
I
I
MeO
NC
1.2
1.5
3
I
O2N
O2N
I
S
S
8
9
2
87
90
[57]
[57]
Cl
Cl
I
1.5
Cl
Cl
I
10
11
2
4
93
90
[56]
[56]
Br
Me
Br
Me
123

J IRAN CHEM SOC
Table 3 continued
Entry
12
Aryl halide
Product
Time (h)
3
Yield (%)b
References
[56]
92
92
93
91
NC
Br
NC
13
14
15
3
[56]
[56]
[56]
H
3COC
Br
H3COC
O2N
2.5
3
O2N
Br
Br
Br
N
N
N
16
17
3
4
92
89
[56]
[56]
N
N
N
Br
S
S
18
19
20
21
a
7
78
76
87
90
[56]
[56]
[58]
[56]
Cl
10
4
Me
NC
Me
NC
Cl
Cl
Cl
3
O2N
O2N
Reactions were performed with ArX (1 mmol), phenylacetylene (1.2 mmol) and Et3N (2 mmol) catalyst (0.03 g) in DMF (4 mL) at 80 °C
on the Fe3O4. The size of the prepared nanoparticles with
roughly spherical shapes and core–shell structures was
about 20 nm in diameter. Moreover, magnetization curves
demonstrated a high degree of superparamagnetism.
Magnetic nanocatalyst with saturation magnetization value
of about 27.3 emu/g can be readily recovered under an
external magnetic field. The amount of polymer capsulated
around the magnetite nanoparticles in the prepared mag-
netic nanocatalyst was estimated to be 27.74 % by weight.
The crystallite size obtained from X-ray line profile fitting
is comparable with the particle size obtained from TEM.
Therefore, considering the importance of this catalyst, we
have shown that Fe3O4@SiO2–polymer-imid–Pd is an
efficient and stable nanocatalyst and is strongly active in
coupling reactions of aryl halides with terminal alkynes.
This method gives notable advantages such as easy prep-
aration, heterogeneous nature and easy separation of the
catalyst by external magnetic field, excellent yields, short
reaction times and simplicity of operation, making it a
facile tool in the Sonogashira–Hagihara cross-coupling
reaction. In addition, the novel catalyst used is easily
recovered by using a permanent magnet and reused without
123

J IRAN CHEM SOC
14. S. Boutry, S. Laurent, L. Vander Elst, R.N. Muller, Contrast Med.
Mol. Imaging. 1, 15 (2006)
15. I. Chourpa, L. Douziech-Eyrolles, L. Ngaboni-Okassa, J.F. Fou-
quenet, S. Cohen-Jonathan, M. Souce, H. Marchais, P. Dubois,
Analyst. 130, 1395 (2005)
16. J. Javidi, M. Esmaeilpour, Colloid. Surface B. 102, 265 (2013)
17. S.W. Charles, J. Popplewell, Endeavour. 6, 153 (1982)
18. A.K. Gupta, M. Gupta, Biomaterials. 26, 3995 (2005)
19. H. Pardoe, P.R. Clark, T.G. St Pierre, P. Moroz, S.K.A. Jones,
Magn. Reson. Imag. 21, 483 (2003)
20. L. Lei, X. Liu, Y. Li, Y. Cui, Y. Yang, G. Qin, Mater. Chem.
Phys. 125, 866 (2011)
21. B. Sahoo, S.K. Sahu, P. Pramanik, J. Mol. Catal. B Enzym. 69, 95
(2011)
22. K. Suslick, M. Fang, T. Hyeon, J. Am. Chem. Soc. 118, 11960
(1996)
23. S. Veintemillas-Verdaguer, M.P. Morales, C.J. Serna, Mater.
Lett. 35, 227 (1998)
24. P. Tartaj, C. Serna, Chem. Mater. 14, 4396 (2002)
25. D. Kim, Y. Zhang, W. Voit, K. Rao, M. Muhammed, J. Magn.
Magn. Mater. 225, 30 (2001)
Fig. 6 Recycling of the catalyst for the reaction of iodobenzene with
phenylacetylene in the presence of Et3N. Reaction conditions:
iodobenzene (1 mmol), phenylacetylene (1.2 mmol), catalyst
(0.03 g), Et3N (2 mmol), in DMF (4 mL) at 80 °C
26. R. Massart, E. Dubois, V. Cabuil, E. Hasmonay, J. Magn. Magn.
Mater. 149, 1 (1995)
27. M. Esmaeilpour, A.R. Sardarian, J. Javidi, Appl. Catal. A
445–446, 359 (2012)
28. K. Ohno, K.M. Koh, Y. Tsujii, T. Fukuda, Macromolecules. 35,
8989 (2002)
29. S. Sun, S. Anders, H.F. Hamann, J.U. Thiele, J.E.E. Baglin, T.
Thomson, E.E. Fullerton, C.B. Murray, B.D. Terris, J. Am.
Chem. Soc. 124, 2884 (2002)
30. P.D. Stevens, J. Fan, H.M.R. Gardimalla, M. Yen, Y. Gao, Org.
Lett. 7, 2085 (2005)
31. S. Shylesh, V. Schunemann, W.R. Thiel, Angew. Chem. Int. Ed.
49, 3428 (2010)
any noticeable loss of activity after at least six times. The
formation of the carbene–Pd bond leads to leaching of
reduced Pd nanoparticles. Polymer chains acts as spacer
between Fe3O4@SiO2 and Pd and leads to the increased
catalytic activity of Pd. The ICP analysis does not show
any Pd leaching at this stage. This experiment confirmed
the heterogeneous character of the catalytically active
species.
32. A. Schatz, M. Hager, O. Reiser, Adv. Funct. Mater. 19, 2109
(2009)
33. V. Polshettiwar, R. Luque, A. Fihri, H. Zhu, M. Bouhrara, J.M.
Basset, Chem. Rev. 111, 3036 (2011)
34. A. Schatz, O. Reiser, W.J. Stark, Chem. Eur. J. 16, 8950 (2010)
35. K. Sonogashira, Y. Tohda, N. Hagihara, Tetradron. Lett. 16, 4467
(1975)
Acknowledgments The authors are grateful to the council of Iran
National Science Foundation and University of Shiraz for their
unending effort to provide financial support to undertake this work.
36. R. Chinchilla, C. Najera, Chem. Rev. 107, 874 (2007)
37. I. Paterson, R.D.M. Davies, R. Marquez, Angew. Chem. Int. Edit.
40, 603 (2001)
References
1. C.C. Koch, Nanostructured materials, processing, properties and
applications (Norwich, New York, 2002)
2. J.M. Cowley, Diffraction physics (North-Holland, New York,
1981)
3. J.M. Cowley, Appl. Phys. Lett. 15, 58 (1969)
4. J.M. Cowley, Ultramicroscopy. 49, 4 (1993)
5. E. Zeitler, M.G.R. Thomson, Optik. 31, 258 (1970)
6. J.M. Rodenburg, R.H.T. Bates, Philos. Trans. R. Soc. 339, 521
(1992)
7. D. Zanchet, B.D. Hall, D. Ugarte, Characterization of nanophase
materials (Wiley, Germany, 2000)
8. E.W. Wong, M.J. Bronikowski, M.E. Hoenk, R.S. Kowalczyk,
B.D. Hunt, Chem. Mater. 17, 237 (2005)
38. G. Amiet, H.M. Hugel, F. Nurlawis, Synlett. 41, 495 (2002)
39. N.D.P. Cosford, L. Tehrani, J. Roppe, E. Schweiger, M. Wash-
burn, M.A. Varney, J. Med. Chem. 46, 204 (2003)
40. P. Li, L. Wang, H. Li, Tetrahedron. 61, 8633 (2005)
41. G. Altenhoff, S. Wurtz, F. Glorius, Tetrahedron Lett. 47, 2925
(2006)
42. A. Nagy, Z. Nova’k, A. Kotschy, J. Organomet. Chem. 690, 4453
(2005)
43. F. Yang, X. Cui, Y. Li, J. Zhang, G. Ren, Y. Wu, Tetrahedron. 63,
1963 (2007)
44. M. Cai, Q. Xu, J. Sha, J. Mol. Catal. A Chem. 272, 293 (2007)
45. M.B. Thathagar, G. Rothenberg, Org. Biomol. Chem. 4, 111
(2006)
9. M.M. Miller, G.A. Prinz, S.F. Cheng, S. Bounnak, Appl. Phys.
Lett. 81, 2211 (2002)
46. K.R. Reddy, N.S. Kumar, P.S. Reddy, B. Sreedhar, M.L. Kantam,
J. Mol. Catal. A Chem. 252, 12 (2006)
10. S. Sun, C.B. Murray, D. Weller, L. Folks, A. Moser, Science.
287, 1989 (2000)
47. J. Ruiz, N. Cutillas, F. Lopez, G. Lopez, D. Bautista, Organo-
metallics. 25, 5768 (2006)
11. M.M.J. Modo, J.W.M. Bulte, Molecular and cellular MR imaging
(CRC Press, Boca Raton, 2007)
12. C. Burtea, S. Laurent, A. Roch, L. Vander Elst, R.N. Muller, J.
Inorg. Biochem. 99, 1135 (2005)
13. J.W. Bulte, Methods Mol. Med. 124, 419 (2006)
48. C. Yi, R. Hua, J. Org. Chem. 71, 2535 (2006)
49. Y. Liang, Y.X. Xie, J.H. Li, J. Org. Chem. 71, 379 (2006)
50. L. Feng, F. Liu, P. Sun, J. Bao, Synlett. 10, 1415 (2008)
51. X. Xie, X. Xu, H. Li, X. Xu, J. Yang, Y. Li, Adv. Synth. Catal.
351, 1263 (2009)
123

J IRAN CHEM SOC
52. M. Carril, A. Correa, C. Bolm, Angew. Chem. Int. Ed. 47, 4862
(2008)
56. H. Firouzabadi, N. Iranpoor, M. Gholinejad, J. Mol. Catal.
A Chem. 321, 110 (2010)
53. M. Bakherad, A. Keivanloo, S. Mihanparast, Synth. Commun. 40,
179 (2010)
57. T. Suzuka, Y. Okada, K. Ooshiro, Y. Uozumi, Tetrahedron. 66,
1064 (2010)
54. H.N. Borah, D. Prajapati, R.C. Boruah, Synlett. 655, 2823 (2005)
55. S. Park, M. Kim, D.H. Koo, S. Chang, Adv. Synth. Catal. 346,
1638 (2004)
58. H. Firouzabadi, N. Iranpoor, F. Kazemi, M. Gholinejad, J. Mol.
Catal. A Chem. 357, 154 (2012)
123