Palladium nanoparticle supported on cobalt ferrite: An efficient magnetically separable catalyst for ligand free Suzuki coupling

Article abstract of DOI:10.1016/j.molcata.2011.10.022

Synthesis of Pd nanoparticle supported on cobalt ferrite magnetic nanoparticles has been achieved by direct addition of Pd nanoparticles during synthesis of cobalt ferrite nanoparticles by ultrasound assisted co-precipitation in the absence of any surface stabilizers or capping agent. The catalytic performance of the Pd incorporated cobalt ferrite nanoparticles was examined in Suzuki coupling reaction in ethanol under ligand free condition. The reaction undergoes with low catalyst loading (1.6 mol%) and the catalyst could be recovered using an external magnet and reused for multiple cycles with sustained catalytic activity.

Full text of DOI:10.1016/j.molcata.2011.10.022

Journal of Molecular Catalysis A: Chemical 352 (2012) 128–134
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Palladium nanoparticle supported on cobalt ferrite: An efficient magnetically
separable catalyst for ligand free Suzuki coupling
Kula Kamal Senapati, Subhasish Roy, Chandan Borgohain, Prodeep Phukan∗
Department of Chemistry, Gauhati University, Guwahati 781014, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 August 2011
Received in revised form 26 October 2011
Accepted 28 October 2011
Available online 7 November 2011
Synthesis of Pd nanoparticle supported on cobalt ferrite magnetic nanoparticles has been achieved by
direct addition of Pd nanoparticles during synthesis of cobalt ferrite nanoparticles by ultrasound assisted
co-precipitation in the absence of any surface stabilizers or capping agent. The catalytic performance of
the Pd incorporated cobalt ferrite nanoparticles was examined in Suzuki coupling reaction in ethanol
under ligand free condition. The reaction undergoes with low catalyst loading (1.6 mol%) and the catalyst
could be recovered using an external magnet and reused for multiple cycles with sustained catalytic
activity.
Keywords:
Magnetic nanoparticle
Pd–cobalt ferrite
Heterogeneous catalyst
Co-precipitation
Suzuki coupling
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
applications [18]. However, other paramagnetic or ferromagnetic
nanoparticles are less studied [19–23]. Although, the Fe3O4 could
Recently, magnetic nanoparticles (MNPs) supported catalyst
have been efficiently employed as heterogeneous catalysts for var-
ious organic transformations [1,2]. In particular, various magnetic
nanoparticle-supported Pd-catalyst has been widely employed for
promoting different organic reactions [3–11]. However, in most
cases, palladium is immobilized on to the modified surface of the
MNPs. The magnetic cores of these particles are generally capped
with suitable capping agents rendering their stability and dis-
persibility to organic solvent. The catalysts species can be loaded
onto the magnetic supports either by post modification of MNP
shells or by co-precipitation during the MNPs synthesis [12]. The
use of these magnetic nanoparticle catalysts can address the iso-
lation and re-cycling problem encountered in many heterogenous
and homogenous catalytic reactions [13–17]. Most importantly, the
MNPs-supported catalysts show not only high catalytic activity but
also a high degree of chemical stability and they do not swell in
organic solvents. It is noteworthy that, although the surface coated
MNPs offers good catalytic activity in many organic reactions, the
coating may decrease magnetization and stability of the magnetic
core by altering interparticle interactions which in turn reduce
effective surface area and hence catalytic efficacy [2]. Iron oxide
nanoparticles such as magnetite (Fe3O4) and maghemite (␥-Fe2O3)
are commonly used for both catalyst supports and biomedical
be easily prepared and has been efficiently utilized in many organic
reactions [4,10,24,25], it is fairly reactive to acidic environment
[9] and ␥-Fe2O3 is also not thermally stable [26] and hence coat-
ing on the magnetic core is mandatory. On contrary, the CoFe2O4
is a typical ferromagnetic oxide with spinel structure which has
high thermal stability, large magnetic anisotropy, moderate satura-
tion magnetization, remarkable chemical stability and mechanical
hardness [27,28]. Although the CoFe2O4 magnetic core as catalyst
or support has been used recently [13,29–32], the surface of the
CoFe2O4 magnetic particles was coated with the catalytic species in
the presence of surface capping agents. Recently, we have reported
the synthesis of highly stable CoFe2O4 MNPs without using organic
capping agent or surface stabilizer [33]. Herein, we wish to prepare
Pd incorporated CoFe2O4 nanoparticles by addition of Pd NPs to the
reaction mixture during synthesis of CoFe2O4 by co-precipitation
method under ultrasonic irradiation without using any surface
stabilizer. The catalytic property of the synthesized magnetic pal-
ladium particles was evaluated for Suzuki coupling reaction.
The palladium-catalyzed Suzuki coupling reaction is generally
performed under an inert atmosphere because the catalytic species
are sensitive to oxygen or moisture [34]. There are also several
reports in the literature for the Suzuki coupling reaction which
have the attractive attributes such as the commercial availability,
the air and water stability, and the nontoxic nature of boronic acids
and catalysts [35]. Normally, homogenous catalysts used for Suzuki
reaction are based on various Pd complexes [36–38] along with
some ligands, such as phosphines [39], dibenzylideneacetone (dba)
∗
Corresponding author. Tel.: +91 361 2570535; fax: +91 361 2700311.
E-mail address: pphukan@yahoo.com (P. Phukan).
1381-1169/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2011.10.022

K.K. Senapati et al. / Journal of Molecular Catalysis A: Chemical 352 (2012) 128–134
129
[40] and carbenes [41]. Some homogeneous Pd catalyzed method-
ologies for Suzuki reaction under ligand free condition have also
been developed [42–46]. However, high cost of the Pd complexes
and difficulty in recovery of the catalyst make these procedures
embarrassing. Due to the inherent advantages of recovery and
reuse, several Pd-based heterogeneous catalysts for Suzuki reaction
have been developed. Various supports such as carbon [47], clays
[48,49], zeolites [50–52], mesoporous silica [53] and metal oxides
[54] were used for immobilization of Pd complexes or nanoparti-
cles for Suzuki coupling reactions. The serious drawback in many
of these cases is that additional steps must be taken to remove the
leached metals and ligands released from the decomposed cata-
lyst. The use of magnetic nanoparticle supported Pd-catalysts have
also been addressed in recent times for the Suzuki coupling reaction
[4,5,11,55–59] so that the catalysts can be easily separated magnet-
ically and reused. However, the use of toxic organic chemicals such
toluene, DMF, dioxane and xylene is required either in preparation
of the catalyst or to catalyze the reactions. Moreover, in most cases,
specific functionalization procedures were inevitably adopted to
anchor the active Pd species onto the magnetic support. Therefore,
developing an efficient and ligand free Suzuki coupling reaction
with Pd-based MNPs in a green chemical process is of our special
interest. In this article, we report the direct use of CoFe2O4 MNPs
to support Pd NPs without using any protecting or functionalizing
agent and useful in Suzuki cross-coupling reaction under ligand
free and aerobic conditions. The new catalyst is well-dispersed
in reaction medium (ethanol), highly efficient, environmentally
benign, magnetically recoverable and reusable without consider-
able change in activity.
were mixed in a 200 mL flat bottom flask and placed in an ultra-
sonic bath. An aqueous NaOH solution (3 M, 25 mL) was added
drop-wise under argon atmosphere with continuous ultrasonic
irradiation (frequency 40 kHz and power of 40 kW). Prior to mix-
ing, all these three solutions were sonicated for 30 min to remove
dissolved oxygen. The temperature of the sonicator bath was raised
up to 60 ◦C and the mixture was further sonicated for 30 min in air
atmosphere. The black precipitate formation was observed during
that time. To the reaction mixture, was then added the dispersion
of the as-synthesized Pd NPs in ethanol and the reaction temper-
ature was slowly brought to 80 ◦C. The mixture was further kept
under sonication for 1 h and then slowly cooled down to room
temperature. The black precipitate was then separated by centrifu-
gation at 15,000 rpm for 15 min, washed several times with both
distilled water and ethanol and kept overnight in an incubator at
60 ◦C. The precipitate was then further dried in an oven at 100 ◦C
for nearly an hour and subsequently kept in highly evacuated envi-
ronment (10−2 bar) for another 1 h. At this stage the product (Pd
doped CoFe2O4) contains some associated water which was then
removed by heating the product at 200 ◦C for 6 h and preserved in
desiccator for further analysis. The whole procedure was repeated
twice to check the reproducibility. The synthesized sample by this
method was denoted as Pd–CoFe2O4 MNPs.
2.3. Characterization
The as-synthesized nanoparticles were characterized by scan-
ning electron microscopy (SEM, LEO 1430 VP), field emission
scanning microscopy (FESEM, Carl Zeiss, ꢀIGMA), transmission
electron microscopy (200KV TEM, JEOL JEM2100) and X-ray diffrac-
tion measurement (XRD, Bruker AXS D8). The formation cobalt
ferrite particles were first ascertained by electron dispersive X-ray
(EDX, Oxford INCA X-ray microanalysis) analysis combined with
the scanning electron microscope (SEM). For SEM or FESEM analy-
sis, the sample in ethanol dispersion was fixed on aluminum stub,
air dried and then mounted in the instrument. In SEM analysis, the
sample was scanned by electron beam at an accelerating voltage of
10–20 kV and a working distance of 10–15 mm using secondary
electron detector. The image was captured at the resolution of
1–100 nm with the magnification of 15–30K×. In FESEM, the sam-
ple was scanned by electron beam at low accelerating voltage of
2–5 kV at a working distance of 2–4 mm using inlens detector. The
image was taken at the resolution of 300–100 nm with the max-
imum magnification of 200K×. The sample for TEM analysis was
prepared by taking a micro drop of dilute ethanolic solution of the
particles deposited on a carbon-coated copper grid (400 mesh size)
and allowed to dry in air. The nanoparticle formed was observed
at bright field TEM images at the resolution of 300–20 nm with
the magnification of 50–200K×. The crystalline nature of the nan-
particles formed was further investigated by HRTEM and SAED
pattern. The magnetic properties of the Pd–CoFe2O4 MNPs were
analyzed in a vibrating sample magnetometer (VSM, Lakeshore
7410). The VSM measurement was done by taking 0.02 g of solid
sample fixed to the tips of the vibrating rod and analyzed at room
temperature. The IR spectrum was recorded in the range from 400
to 4000 cm−1, using FT-IR spectrophotometer (Perkin Elmer Spec-
trum One) on KBr pellet. The UV–vis measurement was done using
a Varian made Carry 50 UV–vis Spectrophotometer. The specific
surface area and porosity were measured in a Backman Coulter
Surface Area and Pore Size Analyzer (SA 3100). For this, the sam-
ple was first degassed for 2 h at 200 ◦C and then BET analysis was
performed.
2. Experimental
The chemicals and solvents used are of reagent grade purchased
from Merck Chemicals and used as purchased. The palladium
acetate was purchased from Sigma–Aldrich Pvt. Ltd.
2.1. Synthesis of Pd NPs
Prior to incorporation of palladium into CoFe2O4 MNPs, palla-
dium nanoparticles (Pd NPs) were synthesized. Then the Pd NPs
were incorporated into CoFe2O4 MNPs during their synthesis by
ultrasonication assisted co-precipitation method.
Pd NPs with narrow size distribution were synthesized follow-
ing the method reported by Wang et al. [60]. Pd(OAc)2 (0.05 g, of
2.2 × 10−4 M) was added into poly (ethyleneglycol) (4 g of PEG-
400, 2.0 × 10−4 M). The reaction mixture was then stirred in a
magnetic stirrer at 80 ◦C for 1 h. The resulting light yellow homoge-
neous solution was further stirred for 2 h at the same temperature
during which the color of the solution slowly turned from light
yellow to gray dark, indicating the formation of Pd NPs. The as-
synthesized PEG stabilized Pd NPs was then solidified by cooling at
room temperature. The Pd NPs were then dispersed in dry ethanol
by sonication. The dispersion was further centrifuged at 14,000 rpm
at 10 ◦C and the separated particles were washed properly with
ethanol. The particles were dried under vacuum and preserved for
further use.
2.2. Synthesis of Pd incorporated CoFe2O4 magnetic
nanoparticles (Pd–CoFe2O4 MNPs)
The Pd incorporated CoFe2O4 nanoparticles were synthesized
by adding Pd NPs in to the reaction mixture of CoFe2O4 during its
synthesis. The CoFe2O4 NPs were synthesized following our pre-
viously reported sonochemical assisted co-precipitation method
[33,61]. For this, two aqueous solutions of FeCl3 (9.3 mmol, 50 mL)
and CoCl2·6H2O (4.2 mmol, 50 mL) in distilled de-ionized water
The products in Suzuki reaction were characterized by compar-
ing the NMR (Varian 400 MHz FT-NMR) and Mass (LCMS; Waters
Q-Tof Premier) spectra with those reported in literature.

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reflux condition in oil bath for 6–12 h. The reaction was monitored
by thin layer chromatography (TLC). After completion of reaction,
the reaction mixture was cooled to room temperature and the cat-
alyst (MNPs) was recovered by external magnet and washed with
ethanol. The combined organic layer was dried over anhydrous
sodium sulfate (Na2SO4) and evaporated in a rotary evaporator
under reduced pressure. The crude product was purified by flash
chromatography on silica gel (230–400 mesh) with hexane as elut-
ing solvent.
3. Results and discussion
3.1. Synthesis of Pd incorporated CoFe2O4 MNPs
The formation of Pd NPs was observed from UV–vis spec-
trophotometric measurement (200–600 nm) as shown in Fig. 1 and
subsequently by FESEM and TEM (Fig. 2(a–d)). The complete disap-
pearance of peak at 400 nm in the UV–vis measurement revealed
the full conversion of Pd (II) to palladium nanoparticles (Pd NPs).
The SEM morphology visualized the presence of PEG-stabilized
very uniform narrow size distributed Pd NPs of spherical mor-
phology with the elemental contributions from Pd, C and O in the
EDX spectra (Fig. 2b). The high magnification TEM image of Pd NPs
showed that Pd NPs of 5–10 nm sizes were formed and clustered
together.
Fig. 1. UV–vis spectra of (a) Pd(OAc)2 in PEG-400, and (b) Pd NPs in PEG-400.
2.4. General procedure for Suzuki reaction catalyzed by
Pd–CoFe2O4 MNPs
In a typical reaction, to a solution of 0.5 mmol of the aryl halide
in 5 mL of dry ethanol was added 0.75 mmol of phenyl boronic
acid, 133 mg of Na2CO3 (1.25 mmol) followed by 2 mg of the as-
synthesized catalyst (1.6 mol%). The mixture was then stirred under
The CoFe2O4 MNPs were synthesized by a combined sonochem-
ical and co-precipitation technique in aqueous medium without
any surfactant or organic capping agent. The synthesis was car-
ried out in an alkaline pH with repeated ultrasonic irradiation.
Fig. 2. SEM with EDX (a and b) and TEM image with SAED (c and d) of Pd NPs.

K.K. Senapati et al. / Journal of Molecular Catalysis A: Chemical 352 (2012) 128–134
131
with 1% Pd incorporation. Similarly, the EDX analysis for CoFe2O4
MNPs (Fig. 3a) gave the elemental distribution of Co = 12.38%,
Fe = 24.27%, O = 62.09% with the nearly same atomic ratios as in
CoFe2O4 molecule.
We studied the morphology of the Pd–CoFe2O4 MNPs in FESEM
and TEM measurements (Fig. 4a and b). Fig. 4b shows the TEM image
of Pd–CoFe2O4 MNPs deposited on carbon coated copper grid at
100 nm resolution. The average particle sizes were measured in
FESEM and TEM micrographs and were found to be in the range of
40–50 nm.
The XRD measurement of CoFe2O4 MNPs (Supporting
Information) indicates the presence of all the characteristic
peaks with relative intensities of all patterns matching well with
a cubic spinel structure (JCPDS – International center diffraction
data, PDF cards 3-864 and 22-1086) [62,63]. XRD measurement
˚
was carried out using Cu K␣ radiation (ꢁ = 1.54178 A) giving a scan
from 10◦ to 70◦ (2Â) at a speed of 5◦/min. The crystallite size for
the nanoparticles obtained from the XRD pattern using scherer’s
formula [64] was found to be 40 5 nm which was consistent
with the particle size obtained from the FESEM and TEM micro-
graphs. The crystalline nature of the synthesized nanoparticles
was inferred from HRTEM and SAED patterns (Fig. 4c and d).
The magnetic properties of the as prepared Pd–CoFe2O4 MNPs
were investigated by VSM measurement. Fig. 5 shows the M–H
loop taken at room temperature with a maximum applied field
of 2 T. From the hysteresis loop both saturation magnetization
(Ms) and coercivity values (Hc) were extracted. Coercivity, Hc of
1409 Oe with the corresponding saturation magnetization, Ms of
52.6 emug−1 was obtained which indicates the ferromagnetism of
the nanoparticles.
Fig. 3. EDX analysis of (a) CoFe2O4 MNPs and (b) Pd–CoFe2O4 MNPs.
After determining the elemental composition of the black parti-
cles of CoFe2O4 formed at the initial stage by EDX analysis, the
as-synthesized Pd NPs were added. The EDX analysis of Pd incor-
porated CoFe2O4 MNPs (Pd–CoFe2O4 MNPs) (Fig. 3b) showed that
the distribution of the elements (atomic percent) in the product was
Co = 11.03%, Fe = 22.77%, O = 65.06% and Pd = 1.13%. The iron/cobalt
ratio in the nanoparticles by EDX was found to be 2.06 which
is very much close to the atomic ratio in the formula CoFe2O4
Next, the surface area and porosity of the Pd–CoFe2O4 MNPs
were measured using Brunauer–Emmett–Teller (BET) equation
[65] following the Barrett–Joyner–Halanda (BJH) method [65].
Fig. 4. (a) FESEM and (b) TEM image of Pd–CoFe2O4 MNPs with the (c) SAED pattern and (d) HRTEM image.

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K.K. Senapati et al. / Journal of Molecular Catalysis A: Chemical 352 (2012) 128–134
stable for longer period which is evident from the micrographs
of electron microscopy analyzed after one month. The catalyst
surface were further examined with the help of FT-IR spectra
(Supplementary file), which shows two broad absorption peaks
centered around 3419 cm−1 and 1620 cm−1 along with other char-
acteristic peaks of spinel ferrite. These two peaks are due to
excessive hydroxyl ions entrapped in the surface of the MNPs and
create surface polarity. This may happen due to ultrasonic treat-
ment during synthesis of the MNPs in aqueous medium and this
surface property of the MNPs accounts for stable dispersion in
ethanol. This behavior of the catalyst surface in case of CoFe2O4
MNPs synthesized by the same protocol has been reported in details
in our previous report [33].
3.2. Suzuki reaction catalyzed by Pd incorporated CoFe2O4 MNPs
Fig. 5. M–H loop in VSM measurement of Pd–CoFe2O4 MNPs at room temperature.
The catalytic activity of the synthesized Pd incorporated
CoFe2O4 MNPs were examined for Suzuki cross-coupling reaction.
Initial experiments were performed for the reaction of iodoben-
zene with phenyl boronic acid in the presence of a catalytic amount
of CoFe2O4 MNPs. In general, phospines are used as a promoting
ligand for many Pd-catalyzed reactions [68]. We have carried out
the reaction under phosphine-free condition in ethanol at reflux
temperature in the presence of Na2CO3 under aerobic conditions.
To standardize the reaction conditions, we performed a series
of reactions with several bases, solvents, temperatures and catalyst
concentration to obtain the best possible combination. Initially, the
reaction was performed using 0.5 mmol of iodobenzene, 0.75 mmol
of phenyl boronic acid, and 1.25 mmol Na2CO3 in the presence of
1.6 mol% of Pd–CoFe2O4 MNPs by refluxing in ethanol and moni-
tored by TLC. The reaction was completed in 12 h with a yield of
81%. When the reaction was carried out in water and ethylene gly-
col (EG) under the same reaction conditions, yields were very low
i.e. 30% and 20% respectively. The reactions were also carried out
under the same conditions using different bases such as K2CO3,
K3PO4 and CsCO3 and the yields were 80%, 68% and 30% respec-
tively (Table 1: entries 4, 5, 6). The yields were not satisfactory in
water and aqueous ethanol under the same reaction condition. The
reaction at room temperature was found to be very slow and com-
pletion of reaction was observed only after 52 h with 72% yield. The
results for optimum reaction condition are summarized in Table 1.
Hence, an optimum of 1.6 mol% (0.16 mol% of Pd) of Pd–CoFe2O4
catalyst (based on iodobenzene) in the reaction mixture was ideal
for achieving the best yield. We have analyzed the formation of
biphenyl in the Suzuki reaction by using LCMS (Waters Q-Tof Pre-
mier LC MSMS system) equipped with TUV detector using duel
wavelengths of 215 nm and 254 nm. We observed the 100% con-
version of product and the TON for this conversion was found to be
6250.
Fig. 6. (a) BET surface area and inset, (b) pore size distribution of Pd–CoFe2O4 MNPs.
From the N2 adsorption–desorption isotherm of Pd–CoFe2O4 MNPs
in Fig. 6, the BET surface area of the particles is 102 m2 g−1 as cal-
culated by linear part of the BET plot, which is much higher than
CoFe2O4 nanoparticles [33,66]. The total pore volume at P/Po = 0.98
is 0.5427 cm3g−1. The BET isotherm is of type II and H3 hysteresis
loop (BDDT/IUPAC classification) is the characteristic of meso-
porous adsorbents [67].
The as synthesized MNPs and their ethanolic dispersion formed
by this ultrasound promoted co-precipitation methods are quite
Table 1
Suzuki reaction catalyzed by Pd incorporated CoFe2O4 MNPs (Pd–CoFe2O4 MNPs).a
Entry
Catalyst concentration
Solvent
Base
Temperature (◦C)
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
9
1.6 mol%
2.4 mol%
0.8 mol%
1.6 mol%
1.6 mol%
1.6 mol%
1.6 mol%
1.6 mol%
1.6 mol%
1.6 mol%
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
aq.Ethanol
Water
Ethylene glycol
Ethanol
Na2CO3
Na2CO3
Na2CO3
K2CO3
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
30
12
12
12
12
12
12
12
12
12
52
81
81
78
80
68
30
60
30
20
72
K3PO4
Cs2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
10
a
Reaction condition: iodobenzene (0.5 mmol), phenyl boronic acid (0.75 mmol), base (133 mg), solvent (5 mL).
Isolated yield by column chromatography.
b

K.K. Senapati et al. / Journal of Molecular Catalysis A: Chemical 352 (2012) 128–134
133
Table 2
Suzuki reaction catalyzed by Pd–CoFe2O4 MNP.a
Entry
Aryl halide
Boronic acid
Time (h)
Product(s)
Yield (%)b
I
B(OH)2
1
2
3
12
12
6
81
79
88
Br
B(OH)2
B(OH)2
I
I
B(OH)2
B(OH)2
4
5
12
12
79
92
O2N
Br
O2N
NO2
O2N
O2N
B(OH)2
I
6
7
16
12
83
75
NO2
O2N
Br
Br
B(OH)2
O2N
Br
Br
B(OH)2
8
9
12
12
79
84
O2N
B(OH)2
B(OH)2
O2N
10
11
12
12
12
70
85
80
Br
Br
B(OH)2
B(OH)2
MeO
OMe
12
a
Reaction condition: 0.5 mmol of aryl halide, 0.75 mmol of boronic acid, 1.25 mmol of Na2CO3, 2 mg of Pd–CoFe2O4 MNPs, 5 mL ethanol, reflux.
Isolated yield by column chromatography.
b
After optimizing reaction conditions, the scope of the catalyst
centrifugation of the liquid and no elemental contributions present
in the Pd–CoFe2O4 MNPs was detected. We also checked for the Pd-
leaching in the ethanolic mixture by the method of flame atomic
absorption spectrometry (FAAS) [69] and did not get any contri-
bution for leached Pd in the organic liquor (Procedure is given in
Supplementary file).
The reusability of the magnetic catalyst was also examined
by carrying out repeated runs on the same batch of the used
1.6 mol% Pd–CoFe2O4 MNPs catalyst in Suzuki reaction of 4-
methyl iodobenzene and phenyl boronic acid (Table 3). After
each cycle, nanoparticles were magnetically separated, washed,
dried and used directly for the next round of reaction. The yield
was not significantly decreased in the regenerated catalyst even
was further investigated for a variety of aryl halidies and boronic
acids (Scheme 1) and the results are summarized in Table 2.
After completion of the reaction, an external magnet was
applied to concentrate the catalyst on the side of the reaction vessel.
The reaction mixture was decanted holding the magnet on outside
of the flask. Thereafter, the flask was washed with ethanol and com-
bined ethanol layer was concentrated in a rotary evaporator under
reduced pressure. The crude product was purified by flash chro-
matography in 230–400 mesh size silica using hexane as eluent.
The products were characterized by using IR, NMR and mass (ESI-
MS) spectroscopy data. After separation, the catalyst was dried in
an oven at 120 ◦C for 6 h and kept under vacuum before next cycle
of reaction.
To ensure complete removal of the magnetic catalyst we
measured the EDX analysis in the ethanolic mixture after
Table 3
Recyclability of Suzuki reaction with 1.6 mol% regenerated Pd–CoFe2O4 MNP
catalyst.a
Cycle
Yield at 6 h (%)b
Pd-CoFe2O4 MNPs
X
B(OH)2
+
1
2
3
4
87
86
83
81
R
R'
R'
Na2CO3, EtOH
reflux, 6-12 h
R
R:H, Ph, CH3, NO2
X: I, Br
R' : H, NO2
a
Reaction condition: 0.5 mmol 4-methyl iodobenzene, 0.75 mmol phenyl boronic
acid, 1.25 mmol Na2CO3, 5 mL dried ethanol, reflux.
b
Isolated yield after column purification.
Scheme 1. Suzuki reaction catalyzed by Pd–CoFe2O4 MNPs.

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K.K. Senapati et al. / Journal of Molecular Catalysis A: Chemical 352 (2012) 128–134
after four consecutive cycles. It was also evident from the FESEM
that, the morphology of the recovered MNPs remains unaltered
(Supplementary file).
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4. Conclusion
In conclusion, a facile magnetic catalyst of Pd incorporated
CoFe2O4 NPs (40–50 nm) was developed and efficiently employed
for Suzuki cross-coupling reactions. The reactions can be carried
out using ethanolic dispersion of the catalyst under ligand free and
aerobic conditions with low catalyst loading (1.6 mol%). The cata-
lyst could be recovered by simple magnetic decantation and reused
for multiple cycles with no significant loss of activity which will be
of immense importance in industrial processes. Hence, these MNPs
as catalysts are new development in using heterogenous catalysts
for production of fine chemicals in liquid phase reactions.
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Financial Support from DST, India (Grant No. SR/S1/RFPC-
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Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molcata.2011.10.022.
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