Pd Nanoparticles Immobilized on Supported Magnetic GO@PAMPS as an Auspicious Catalyst for Suzuki–Miyaura Coupling Reaction

Article abstract of DOI:10.1007/s10562-017-2089-2

A novel catalytic system based on palladium nanoparticles (Pd-NPs) immobilized onto the surface of graphene oxide (GO) modified by poly 2-acrylamido-2-methyl-1-propansulfonic acid decorated with magnetic Fe₃O₄ was designed, prepared and fully characterized. It was successfully examined as a highly efficient heterogeneous catalyst in the Suzuki–Miyaura cross coupling reaction. The results showed excellent catalytic activity for the cross coupling of aryl bromides, alkyl iodides as well as aryl chlorides as the challenging substrates. It was easily separated by an external magnet and reused without any pre-activation at least in seven consecutive runs without any loss in its catalytic activity as well as any detectable Pd leaching. This study demonstrates the great potential of polymeric-functionalized GO as a support owing to its high loading and suitable dispersing of Pd-NPs, for the development of metal–graphene nanocomposites in industrial scale. Graphical Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-017-2089-2

Catal Lett
DOI 10.1007/s10562-017-2089-2
Pd Nanoparticles Immobilized on Supported Magnetic GO@
PAMPS as an Auspicious Catalyst for Suzuki–Miyaura Coupling
Reaction
Shima Asadi1 · Roya Sedghi2 · Majid M. Heravi1
Received: 12 March 2017 / Accepted: 21 May 2017
© Springer Science+Business Media New York 2017
Abstract A novel catalytic system based on palladium
nanoparticles (Pd-NPs) immobilized onto the surface of
graphene oxide (GO) modified by poly 2-acrylamido-2-me-
thyl-1-propansulfonic acid decorated with magnetic Fe3O4
was designed, prepared and fully characterized. It was suc-
cessfully examined as a highly efficient heterogeneous cat-
alyst in the Suzuki–Miyaura cross coupling reaction. The
results showed excellent catalytic activity for the cross cou-
pling of aryl bromides, alkyl iodides as well as aryl chlo-
rides as the challenging substrates. It was easily separated
by an external magnet and reused without any pre-activa-
tion at least in seven consecutive runs without any loss in
its catalytic activity as well as any detectable Pd leaching.
This study demonstrates the great potential of polymeric-
functionalized GO as a support owing to its high loading
and suitable dispersing of Pd-NPs, for the development of
metal–graphene nanocomposites in industrial scale.
Graphical Abstract
Keywords Graphene oxide (GO) · Palladium
nanoparticles (Pd-NPs) · Suzuki–Miyaura reaction ·
Heterogeneous catalyst · Magnetic nanoparticles ·
Pd-catalyzed reaction
1 Introduction
Historically, from the date discovered, Pd-catalyzed C–C
bond formation has always attracted much intention and
stirred up the interest of synthetic organic chemists [1–9].
In addition, it has a significant impact on the academia as
well as chemical industries, especially those working on
the total synthesis of natural products or producing inter-
mediates for the currently prescribed drugs, respectively
[10, 11]. Transition metal-catalyzed cross-coupling reac-
tions undoubtedly, are the most important processes for
constructing carbon–carbon bonds [12]. Among them, the
Pd-catalyzed cross-coupling reactions, and in particular
* Roya Sedghi
r_sedghi@sbu.ac.ir
* Majid M. Heravi
mmh1331@yahoo.com
1
Department of Chemistry, Alzahra University, Tehran, Iran
2
Faculty of Chemistry and Petroleum Sciences, Department
of Polymer & Materials Chemistry, Shahid Beheshti
University, G.C., 1983969411, Tehran, Iran
Vol.:(0123456789)
1 3

S. Asadi et al.
“Suzuki–Miyaura reaction” [13–15] is the most admired
and practically employed which led to awarding the 2010
Nobel Prize in Chemistry to Professor Akira Suzuki, shared
with Richard Heck and Ei-ichi Negishi [16].
porous ionic copolymer [43] and biopolymer complex [44,
45] were also used in the Suzuki–Miyaura reaction. Despite
these noticeable achievements obtained in the field of poly-
meric stabilizers, the development of hydrophilic polymeric
networks with functional groups such as –SO3H, –COOH,
–CONH2, –OH, and –NH2 for the protection of Pd-NPs has
still remained a great challenge, especially in the case of
Suzuki coupling reaction.
The increasing trend in Suzuki–Miyaura coupling is
mostly due to the commercially or readily availability of
the starting materials which are mostly non-toxic and easy
to handle [17]. The biaryls as the products of Suzuki reac-
tion are the involved as scaffold in various natural products.
They are frequently used as suitable ligands and also are
the key intermediates in the productions of different drugs,
herbicides etc. [18–21].
We are interested in Pd-catalyzed reactions [46–48]. We
recently immobilized PdCl2 on modified poly(styrene-co-
maleic anhydride) and used it as a highly active and recy-
clable catalyst for the Suzuki–Miyaura and Sonogashira
reactions [49]. Very recently we disclosed the superiority
of Pd(0) encapsulated nanocatalysts as an efficient catalytic
systems for Pd-catalyzed organic transformations [50]. We
also used the easily separable magnetic Fe3O4 as a compo-
nent in our nano-catalytic systems [51–53].
The original Suzuki reaction is generally performed in
the presence of relatively large amounts of palladium and
copper in organic solvents which are cost-effective and
environmentally inadmissible. However, this palladium-
catalyzed reaction has been extensively investigated during
the years to improve the reaction conditions, thus a wide
variety of modifications has been reported so far, including
the utilization of Pd-nanoparticles (Pd-NPs) as the catalyst.
Catalysts based on Pd-NPs often suffer from two main
drawbacks. The first one is extensive leaching of the active
metal species during reactions which eventually leads the
less catalytic activity. Secondly, aggregation of the MNPs
which leads to increase the size of MNPs and their rela-
tive surface area becomes smaller, thus, their activities
are reduced significantly. Therefore, choosing an appro-
priate support to obtain suitable sized Pd-NPs in order to
avoid their leaching is still in much demand. Graphene has
been proven as one of the best support for different metals
because of its large specified surface area, excellent elec-
trical conductivity and high chemical and thermal stability
[22–24]. Many ongoing attempts are focused on deposi-
tion of various MNPs, metal oxides, polymers and chalco-
genides on graphene oxide (GO) sheets due to its superior
functionality [25–31].
Armed with these experiences, herein, we wish to reveal
the design of a highly dispersed catalytic system in green
environment which could be separated from the reaction
mixture and recycled easily several times without appreci-
able loss of its catalytic activity.
In this line, we wish to introduce a novel catalytic sys-
tem, denoted as Pd/GO/Fe3O4/PAMPS including, Pd-NPs
immobilized onto the surface of graphene oxide (GO)
modified by poly 2-acrylamido-2-methyl-1-propansulfonic
acid (PAMPS), decorated with magnetic Fe3O4. This cata-
lytic system was used successfully in Suzuki cross coupling
reaction.
2 Experimental
2.1 Characterization
All chemicals were purchased from international com-
mercial suppliers. The solvents were purified and dried
using standard procedures. X-ray photoelectron analysis
(XPS) was performed using a VG multilab 2000 spec-
trometer (ThermoVG scientific) in an ultrahigh vacuum.
A Shimadzu model AA-680 atomic absorption spectrom-
eter equipped with deuterium background correction was
employed for the determination of amount of Pd. The ele-
mental evaluation was performed using Energy-dispersive
X-ray spectroscopy (EDX) (Philips XL-30). Transmission
electron microscope (TEM) image of GO/Fe3O4/PAMPS/
Pd nanocomposite was taken using Philips CM-30 trans-
mission electron microscope with an accelerating volt-
age of 150 kV. The crystalline phases of the nanoparti-
cles were measured by X-ray powder diffraction (XRD)
measurements (Siemens D5000 diffractometer). Fourier
transform infrared (FT-IR) spectra were recorded using
a BOMEM MB-series FT-IR spectrometer in the form
The recovery of expensive Pd based catalysts by mag-
netic nanoparticles (Mag) without losing their catalytic
activity is a prominent feature in the maintainable catalytic
processes and green chemistry [32, 33].
In addition to the advantages of GO and Mag in cata-
lytic systems, development of a suitable stabilizer for uni-
formly distribution of nanoparticles sizes as well as cap-
ping agent gives nanoparticles a high desirable stability.
Consequently, to this purpose a variety of stabilizers were
examined. In 2000, the first Pd(0) species immobilized
onto a polymer was reported by El-Sayed et al. [34]. They
prepared and applied PVP as catalysts in the coupling of
aryl iodides with phenylboronic acid in aqueous media via
Suzuki reaction. Furthermore, other polymeric stabiliz-
ers such as poly(amido-amine) dendrimers [34–38], poly-
vinylpyrrolidone [39], poly(amino acetanilide) composite
[40], polypyrrole [41], poly(p-phenyleneethynylene) [42],
1 3

Pd Nanoparticles Immobilized on Supported Magnetic GO@PAMPS as an Auspicious Catalyst for…
of KBr pellets. Thermogravimetric analysis (TGA) was
performed by a thermal analyzer instrument (TGA/DTA
BAHR: STA 503) from 25 to 1000 °C at a heating rate
of 10 °C/min under air. For investigation of the magnetic
property, a vibrating sample magnetometer (VSM) from
−10,000 to +10,000 Oe at room temperature was meas-
ured by Meghnatis Daghigh Kavir Company (MDK) Iran.
1H-NMR spectra were recorded on a BRUKERDRX-300
AVANCE spectrometer. CDCl3 and TMS were used as
the solvent and internal standard, respectively. Melting
points were measured on an Electrothermal 9100 appa-
ratus and are uncorrected. Gas chromatography was per-
formed on a Trace GC ultra from the Thermo Company
equipped with FID detector and Rtx®-1 capillary column.
2.2.3 Synthesis of Magnetic GO Grafted by MAPTMS
In order to increase the stability and impeding the agglom-
eration of NPs, surface of GO/Fe3O4 sheets (1 g) was modi-
fied by 3-(trimethoxysilyl)propyl methacrylate (MAPTMS)
(1.9 mL) as a silane coupling agent [55]. For this purpose, the
above amounts of magnetic GO and MAPTMS was stirred in
20 mL toluene under a continuous flow of N2 gas at ambient
temperature for 24 h. Finally, the prepared surface modified
GO sheets were collected by an external magnet and repeat-
edly washed with toluene for the total elimination of the extra
MAPTMS and then dried overnight in an oven under vacuum
at 35°C for 24 h.
2.2.4 Polymerization and Synthesis of GO/Fe3O4/PAMPS
Nanocomposite
2.2 Preparation of the Catalyst System
For the polymerization of the desired monomers on the sur-
face of modified GO, in a typical experiment, 2-acrylamido-
2-methyl-1-propansulfonic acid (AMPS) (1.0 g) and meth-
ylenbisacrylamide (MBA) (0.147 g) were added to a flask
containing 1 g GO suspended in 12 mL deionized water.
Then, the mixture was purged under N2 gas for 15 min to
remove dissolved oxygen. Subsequently, 0.053 g azobisisobu-
tyronitrile (AIBN) as an initiator was added to the reaction
mixture, kept at 60°C for 24 h to complete the polymeriza-
tion. Finally, washing the synthesized polymer with ethanol
and water (three times) and drying under a vacuum oven for
24 h at 50°C afforded the GO/Fe3O4/PAMPS nanocomposite.
2.2.1 Synthesis of GO
Graphene oxide was prepared via a modified Hummers’
method from graphite powder, in accordance with pre-
viously reported method [54]. In brief, graphite powder
(5 g) was suspended in deionized water (100 mL) and
dispersed for 3 h using an ultrasonic bath. Then, KMnO4
(1 g) was added to this suspension gradually under stir-
ring for 15 min. This solution was stirred for 4 h then,
diluted by addition of deionized water (250 mL) while
the temperature kept below 50 °C. Then, H2O2 30%
(10 mL) was added to this mixture till the color of the
mixture changed into golden yellow. Finally, the obtained
product was filtered and washed several times with HCl
(0.1 M) for the removal metal ions, followed by addition
of deionized water (250 mL) to decrease the acidity. The
resulting GO solid was dried at 70 °C in a vacuum oven.
2.2.5 Synthesis of GO/Fe3O4/PAMPS/Pd Nanocomposite
For decoration of Pd-NPs, the mixture of GO/Fe3O4/
PAMPS (0.5 g) and PdCl2 (0.1 g) was dispersed in H2O
(50 mL) using ultrasonic bath. After being sonicated about
30 min, the reaction left to stir for 12 h at room tempera-
ture. Then, excess amount of sodium borohydride (NaBH4)
solution as reducing agent was added dropwise to convert
Pd(ΙΙ) ions to Pd(0). Ultimately, GO/Fe3O4/PAMPS/Pd
nanocomposite was obtained by an external magnet and
washed several times with distilled water, ethanol and ace-
tonitrile to remove unanchored Pd-NPs and finally dried
in vacuum oven at 60°C for 24 h. The content of Pd was
estimated to be 1.1150 mmol/g based on atomic absorption
spectroscopy (AAS).
2.2.2 Synthesis of Magnetic GO
Magnetic GO was synthesized by dispersion of GO
(1.5 g) and deionized water (150 mL) using an ultrasonic
bath for 1 h. Then, the iron salt (1.2 g FeCl3·6H2O) was
introduced to the mixture under vigorous stirring and
purging of N2 gas for 30 min. Following, FeCl2·4H2O
(1.8 g) was added under N2 atmosphere to the above mix-
ture. Finally, to this mixture an ammonia solution (25%,
120 mL) was added, diluted by addition of 200 mL water
and the suspension was refluxed for 2 h. The resultant
GO/Fe3O4 as a black precipitate was separated by an
external magnetic field and washed repeatedly with the
water and ethanol, and then dried at 35 °C under vacuum
overnight.
2.3 Investigations on the Catalytic Activity
2.3.1 GO/Fe3O4/PAMPS/Pd Catalyzed Suzuki–Miyaura
Reaction: General Procedure
To a 10 mL flask an appropriate aryl halide (1 mmol), suit-
able arylboronic acid (1.2 mmol), K2CO3 (3 mmol), the
1 3

S. Asadi et al.
above-mentioned catalyst (0.2–1 mol% Pd based on aryl
halide) and 5 mL EtOH/water (1:1 V/V) were added. The
mixture was stirred at reflux temperature (80°C) for appro-
priate time. Upon completion of the reaction, the reaction
mixture was cooled down to room temperature. Then, the
solution was diluted with deionized water, and the catalyst
was separated by using an external permanent magnet. The
reaction solution was extracted with ethyl acetate and the
organic phase was dried over MgSO4, filtered and then the
solvent was evaporated off under reduced pressure. The
resulting residual was purified by column chromatogra-
phy on silica gel (n-hexane/ethyl acetate) to give the cor-
responding pure products. All products were known and
The characterization was started by measuring the Pd
content of GO/Fe3O4/PAMPS/Pd nanocomposite based on
AAS analysis which found being 1.1150 mmol/g. The full
characterization for proving the structure of the nano-size
particles were achieved using FT-IR, XRD, XPS, TGA,
TEM, VSM and EDX analysis.
For the better understanding how Pd-NPs immobilized
on the surface of catalyst, another schematic was illustrated
in Scheme 2. As one can see, modification the surface of
GO with cross linked PAMPS carrying CONH2 and SO3H
functional groups could immobilize Pd-NPs. PAMPS are
believed to work as ligands, through nitrogen and oxygen
atoms, thereby avoiding the need of additional ligand. In
addition, hydrophilicity of this polymer was another impor-
tant character for choosing PAMPS as polymeric segment.
Figure 1 shows the FT-IR spectra of the GO (a), GO/
Fe3O4 (b), GO/Fe3O4/MAPTMS (c), GO/Fe3O4/PAMPS
(d) and GO/Fe3O4/PAMPS/Pd (e) nanocomposite. The
spectra of GO (Fig. 1a) demonstrates a broad band around
3400 cm−1, which results from –OH groups of GO. Also,
C–O stretching group of alkoxy and C=O stretching vibra-
tion of carbonyl were assigned at 1093 and 1623 cm−1
respectively. In the magnetic GO (Fig. 1b), the band at
570 cm−1 is attributed to Fe–O stretching vibration. The
spectra of modified GO using MAPTMS (Fig. 1c) showed
a broad peak between 1060 and 1110 cm−1, which was
assigned to Si–O–Si. The bands at 1144 cm−1 (C–O),
1645 cm−1 (C=C), and 1725 cm−1 (C–O) are character-
istic of MAPTMS, and indicated the successful linkage
of MAPTMS to the surface of GO sheet. After polymeri-
zation process, the presence of bands at 1644 cm−1 and
3250–3400 cm−1 is due to CONH2 and NH, respectively
(Fig. 1d). In addition, the peak around 1109–1120 cm−1 is
attributed to S=O stretching of sulfonic acid. In Fig. 1e, the
intensity of the peak at about 1644 cm−1 is weaker than that
of GO/Fe3O4/PAMPS (Fig. 1d) due to the formation of a
metal–ligand bond.
1
identified by FT-IR and H NMR spectra with those of
authentic samples which were found identical.
2.3.2 The Reusability Test
In order to investigate the reusability of desired nanocata-
lyst, the separated catalyst was washed with ethanol and
water and reused in a model reaction involving 4-bromotol-
uene and phenyl boronic acid under already secured opti-
mal optimized conditions.
3 Results and Discussion
Unsupported Pd-NPs have been extensively employed in
various Pd catalyzed name reactions such as Suzuki [13],
Heck [41], Sonogashira [56] and Negishi [57]. However,
the utilization of supported Pd-NPs scarcely can be found
in the chemical literature, although, the inherent tendency
toward particle agglomeration makes the use of stabilizing
agents or solid supports mandatory in most cases.
The purpose of this study is developing a new Pd-NPs
immobilized onto a suitable support which is decorated
with magnetic Fe3O4 for the ease of its separation by just
an external magnet. In this line, we decided to design a
novel magnetic Pd-NPs using GO and stabilizing it by the
polymer.
The crystalline structures of GO/Fe3O4 (a), GO/Fe3O4/
PAMPS (b) and GO/Fe3O4/PAMPS/Pd (c) were character-
ized by powder X-ray diffraction (XRD) (Fig. 2). All these
species have six strong diffraction peaks at 2θ=30.37,
35.71, 43.42, 53.79, 57.41, 63.05 corresponding to the
crystal face (220), (311), (400), (422), (511) and (440) of
Fe3O4 lattice [58]. The appearance of diffraction peaks at
2θ=40.12, 46.52 and 68.27 (weak peak) are due to the Pd
(111), Pd (200) and Pd (220) lattice planes, respectively.
The XPS survey scan spectra of the GO/Fe3O4/PAMPS/
Pd catalyst, Fe and Pd 3d region is shown in Fig. 3. As dis-
played in Fig. 3a, the peaks corresponding to C 1s, N 1s, O
1s, Fe 2p and Pd 3p & 3d was clearly observed in the XPS
survey spectrum. Figure 3b, c present the curve fitted Fe
2p and Pd 3d respectively. As shown in Fig. 3b, two peaks
at 711.75 and 725.42 eV, related to Fe 2p3/2 and Fe 2p1/2
Initially, water dispersed GO was performed from graph-
ite, according to Hummer’s method [54]. Then, magnetic
GO was prepared by introducing iron salts as illustrated
in Scheme 1. The surface of magnetic GO was modified
using MAPTMS to provide the reactive C=C bonds. Sub-
sequently, AMPS as monomer and MBA as cross–linker
were polymerized onto the modified magnetic GO using
AIBN as initiator for radical polymerization to produce the
desired polymeric network. Finally, to this polymeric seg-
ment, Pd(ΙΙ) salt was added with subsequent addition of
NaBH4 as reducing agent to obtain the expected GO/Fe3O4/
PAMPS/Pd catalyst.
1 3

Pd Nanoparticles Immobilized on Supported Magnetic GO@PAMPS as an Auspicious Catalyst for…
Scheme 1 General route for the synthesis of GO/Fe3O4/PAMPS/Pd nanocomposite
O
O
S O
Pd
O
Pd
N
O
S O
O
O
N
O
O
N
N
H
H
O
H
N
Pd
O
O
S
HN
O
O
O
O
O
S
O
Pd
O
H
N
Pd
O
O
S
HN
O
Pd
O
S
O
O
O
O
O
O
Si
O
O
O
O
O
O
Scheme 2 Immobilization of Pd-NPs on the surface of PAMPS
1 3

S. Asadi et al.
of GO and polymeric moieties. In addition, VSM meas-
ured by homemade instrument (Meghnatis Daghigh Kavir
Company, Iran), does not show any hysteresis loop and
perfect Langevin behavior which indicates its superpara-
magnetic characteristics. The magnetic character of GO/
Fe3O4/PAMPS/Pd catalyst also facilitates the removal of
the catalyst by a simple permanent magnet (See the photo
in Fig. 4).
Thermogravimetric analysis (TGA) of GO/Fe3O4 (a) and
GO/Fe3O4/PAMPS/Pd nanocomposite (b) was further used
to study the composition of the resultant nanocomposite.
The TGA of both materials show three main weights
loss. The first weight loss was occurred under 100°C which
attributed to desorption of water. The second weight loss
from 200 to 300°C is due to the dehydration process of sur-
face oxygen and hydroxyl groups in GO. The final weight
loss around 400–450°C is related to the decomposition
of graphene structure as well as decomposition of immo-
bilized organic moieties on the surface of nanocomposite.
Interestingly, the total mass loss of catalyst (Fig. 5b) was
only 6.8% at temperatures below 200°C and 20% at 650°C
which shows good thermal stability of the nanocompos-
ite. The percentage of the remaining mass of GO/Fe3O4/
PAMPS/Pd was also compared with GO/Fe3O4. It was
found about 17% which revealed the amount of loaded Pd
and polymeric moieties in the structure of catalyst.
Fig. 1 FT-IR spectra of a GO, b GO/Fe3O4, c GO/Fe3O4/MAPTMS,
d GO/Fe3O4/PAMPS and e GO/Fe3O4/PAMPS/Pd nanocomposite
Transmission electron microscopy (TEM) images
(Fig. 6) of GO (Fig. 6a, b) and GO/Fe3O4/PAMPS/Pd nano-
composite (Fig. 6c, d) were illustrated. The TEM images of
GO sheets (Fig. 6a, b) demonstrated the flake-like shapes
of graphene oxide. The high transparency of GO showed
a few layers proved thin film of GO. As shown in figure
(Fig. 6c, d), GO was successfully exfoliated in water and
also show that the Fe3O4 nanoparticles are quasi-spherical,
with average diameters of 16 nm. The Pd-NPs with mean
size of 5 nm were dispersed in close contact with the sur-
face of GO sheet. As shown in TEM images, Pd-NPs are
not found outside the modified GO because of polymer net-
work prevents the aggregation or agglomeration of Pd-NPs
on the GO sheets. Owing to the high density of polymeric
network and the presence of spherical Fe3O4 NPs, it is dif-
ficult to recognize Pd-NPs. In this regard, we tried to illus-
trate a closer sight of Pd-NPs at the bottom of the Fig. 6. In
addition, EDX image (Fig. 7), also indicates the successful
incorporation and presence of all the elements (O, C, N, Fe,
Si and Pd) onto the GO sheets.
Fig. 2 XRD patterns of a GO/Fe3O4, b GO/Fe3O4/PAMPS and c
GO/Fe3O4/PAMPS/Pd nanocomposite
respectively, which reveals the presence of Fe2+ in Fe3O4
[59]. The high-resolution XPS spectra of Pd 3d was col-
lected and peaks at 335.48 and 340.94 eV were ascribed to
Pd0 3d5/2 and 3d3/2 respectively (Fig. 3c).
The magnetic property of the GO/Fe3O4/PAMPS/Pd
catalyst was measured with a vibrating sample magnetom-
eter (VSM) from −10,000 to +10,000 Oe at room tempera-
ture (Fig. 4). As expected, the saturation magnetization
value (Ms) of resultant nanocomposite is 50 emu/g, which
is lower than that of pure Fe3O4 NPs because the presence
3.1 Catalytic Performance of GO/Fe3O4/PAMPS/Pd
Nanocomposite
Heterogeneous palladium catalysts stabilized by polymers
are extensively studied for the Suzuki–Miyaura cross-
coupling reaction [60, 61]. However, to the best of our
1 3

Pd Nanoparticles Immobilized on Supported Magnetic GO@PAMPS as an Auspicious Catalyst for…
Fig. 3 a Full range XPS
spectrum of GO/Fe3O4/PAMPS/
Pd nanocomposite. b Fe 2p and
c Pd 3d
Fig. 4 Room-temperature magnetization curve of magnetic GO/
Fig. 5 TGA diagram of (a) GO/Fe3O4 and (b) GO/Fe3O4/PAMPS/Pd
nanocomposite
Fe3O4/PAMPS/Pd nanocomposite
1 3

S. Asadi et al.
Fig. 6 Representative TEM images of GO (a, b) and GO/Fe3O4/PAMPS/Pd nanocomposite dispersed in water (c, d)
α
FeK
To study the effects of solvent, optimal amount of cat-
alyst and required time, we selected a model reaction. To
the purpose, 4-bromotoluene was reacted with phenyl
boronic acid in the presence our new catalytic system,
using different amounts of catalysts, the required base and
solvents diversel, finding the required times for each runs
under examination (Table 1). As shown in Table 1, the best
result was obtained in a mixture of H2O and EtOH as sol-
vent. This mixture of solvent provides a good interaction
of hydrophilic polymer stabilized Pd-NPs with water solu-
ble boronic acid and hydrophobic aryl halides which leads
to an improvement in Suzuki reaction. With the previous
experiments in hand, K2CO3 was selected as the most effi-
cient base for the present catalytic system. Amount of cata-
lyst and time of the reaction are two prominent parameters
which investigated precisely in this work. The better con-
version of 4-bromotoluene to the corresponding biphenyl
was occurred with 0.4 mol% of catalyst in 2 h.
3500
3000
2500
2000
1500
1000
500
α
α
O K
N K
β
PdL
β
α
AuM
α
PdL
AuM
α
FeL
β
FeK
α
C K
α
SiK
AuLl
keV
8.852
0
0
Fig. 7 EDX spectra of GO/Fe3O4/PAMPS/Pd nanocomposite
knowledge there are only a few reports on the application
of magnetically separable Pd stabilized by hydrophilic pol-
ymers which catalyze the Suzuki reaction under green con-
ditions [62–66].
To screen the efficiency and limitation of our novel
nanocatalyst, different substituted aryl halides and aryl
boronic acids, bearing either electron- donating or
1 3

Pd Nanoparticles Immobilized on Supported Magnetic GO@PAMPS as an Auspicious Catalyst for…
Table 1 Optimization of the reaction conditions for Suzuki reaction
of 4-bromotoluene with phenyl boronic acid catalyzed by GO/Fe3O4/
PAMPS/Pd
entries 8–9) and superior result with aryl chloride (entry
10) in term of yield (75%) without using harmful solvents
such as DMF or tetra butyl ammonium bromide (TBAB) or
excess amount of catalyst. After completion of each reac-
1
tion, all products were analyzed by H NMR and FT-IR
techniques and the corresponding peaks were observed.
3.2 Leaching
Another catalytic experiment was further conducted to esti-
mate the impact of palladium leaching. For the purpose, a
certain amount of catalyst was dispersed in the presence of
K2CO3 and solvents (EtOH:H2O). The mixture was stirred
and then filtered to obtain a transparent solution. In the next
step, the Suzuki coupling substrates such as phenyl boronic
acid and bromobenzene were introduced to the above
clean supernatant and the solution was heated to 80°C and
stirred. It was found that no biphenyl was detected even
after 5 h, indicating that the coupling reaction catalyzed by
heterogeneous catalyst not homogeneous leaching Pd.
Entry Amount
of catalyst
T (°C) Solvent
Time (h) Conver-
sion
(mol%)
(%)a
1
2
0.4
1.2
80
80
80
60
80
80
80
80
80
80
80
H2O
H2O
H2O
5
5
10
2
50
28
35
5
3
4
2.8
0.4
Toluene:H2O
EtOH:H2O
EtOH:H2O
EtOH:H2O
EtOH:H2O
EtOH:H2O
EtOH:H2O
EtOH:H2O
5
6
7
1.2
0.56
0.4
5
5
2
5
2
2
3.5
100
95
95
85
35
10
25
8
9
10
11
0.2
0.16
0.10
0.05
3.3 Comparison
To evaluate the efficiency of the GO/Fe3O4/PAMPS/Pd cat-
alyst, its catalytic activity was compared with some other
Pd supported catalysts reported, previously. The results
revealed that PAMPS cross linked by MAPTMS is a supe-
rior ligand to some of the previously reported catalysts in
terms of using green solvent, less reaction times, ease of
separation, recyclability, less Pd leaching and also better
isolated yields (Table 3).
Reaction conditions: phenyl boronic acid (1.2 mmol), 4-bromotoluene
(1 mmol), K2CO3 (3 mmol), GO/Fe3O4/PAMPS/Pd as catalyst, sol-
vent (5 mL)
aCalculated by GC
electron withdrawing groups were reacted under secure
optimal reaction conditions. These reactions all, proceeded
smoothly, resulted in the desired corresponding cross cou-
pled products in high to excellent yields. The results are
summarized in Table 2. As it can be seen, when iodoben-
zene, 4-iodoanisole and 4-iodotoluene were used as reac-
tants, desired coupling products were obtained in only 2 h
with excellent yields (95–98%) in the presence of 0.2 mol%
catalyst (Table 1, entries 1–3). Aryl bromides with elec-
tron-donating and electron-withdrawing groups such as
4-nitro, 4-methyl as well as bromobenzene, gave the cou-
pling products in excellent yields (up to 95%) (entries
4–6). It is noteworthy to mention that the Suzuki reaction
of aryl chlorides is more difficult than aryl bromides and
aryl iodides because of strong C–Cl bond than that of C–Br
and C–I and longer reaction time is required. However, by
increasing the amount of catalyst loading to 1 mol% and
extending the reaction time, the Suzuki reaction of aryl
chlorides was completed in good yields (52–68%) within
24 h (entries 7–10). Furthermore, 4-tolylboronic acid as a
coupling partner was subjected to various aryl halides and
the results were mentioned in entries 11–16. Surprisingly,
compare with phenyl boronic acid, 4-tolylboronic acid
showed less efficient result with aryl bromides (Table 2,
3.4 Recycles
The reusability of the GO/Fe3O4/PAMPS/Pd catalyst was
evaluated by using it in the coupling of 4-bromotoluene
with phenyl boronic acid as the model reaction under opti-
mized reaction conditions. After completion of each cycle,
the catalyst was separated easily by an external magnetic
field and the residue was analyzed by GC. Next, fresh start-
ing materials were then introduced to the flask containing
magnetic catalyst and a new Suzuki coupling was started.
The catalyst was recovered and reused for seven consecu-
tive runs without any significant loss of its activity (Fig. 8).
4 Conclusion
In summary, we have developed a novel Pd NPs compos-
ite as denoted by GO/Fe3O4/PAMPS/Pd. It was efficiently
used in Suzuki reaction of aryl halides with boronic acid in
green media to give the cross-coupled products in high to
excellent yields in relatively short reaction times. Worthy
1 3

S. Asadi et al.
Table 2 Suzuki reaction of various aryl halides with aryl boronic acids catalyzed by GO/Fe3O4/PAMPS/Pd
Entry
R1
R2
X
Amount of catalyst
(mol%)
Time (h)
Yield (%)a
TON/TOF (h−1 b
)
1
2
3
4
5
6
7
8
H
H
H
H
H
H
H
H
H
I
I
I
0.2
0.2
0.2
0.4
0.4
0.4
1
1
1
1
0.2
0.2
0.2
0.4
0.4
1
2
2
2
2
2
100
100
98
96
96
95
60
65
52
68
95
95
70
62
30
75
500/250
500/250
490/245
240/120
240/120
237.5/118.7
60/3.3
65/2.7
52/2.2
68/2.8
475/237.5
475/237.5
350/175
155/22.1
75/10.7
75/3.1
4-Me
4-OMe
H
4-NO2
4-Me
H
Br
Br
Br
Cl
Cl
Cl
Cl
I
I
I
Br
Br
Cl
2
18
24
24
24
2
2
2
7
7
24
H
9
4-Me
4-NO2
H
4-Me
4-OMe
H
H
H
10
11
12
13
14
15
16
Me
Me
Me
Me
Me
Me
4-Me
H
Reaction conditions: aryl boronic acid (1.2 mmol), aryl halide (1 mmol), K2CO3 (3 mmol), GO/Fe3O4/PAMPS/Pd as catalyst, EtOH:H2O
(5 mL), 80°C
aIsolated yield
bThe TOF was defined as mol product mol−1 Pd h−1
Table 3 Comparison the results of selected coupling products using GO/Fe3O4/PAMPS/Pd as catalyst with those obtained by some previous
literatures
Entry
Catalyst (Pd loading mol%)
Reaction conditions
Yield (%)
Time (h)
Refs.
1
2
3
4
5
6
7
8
9
Poly(NIPAM-co-4-VP)-Pd (1)
PNIPAM-HNT-Pd (1)
G/MWCNTs/Pd (0.5)
rGO/Pd (0.5)
MWCNTs/Pd (0.5)
GO-NHC-Pd (1)
GO-2N-Pd(II) (0.5)
GO-NH2-Pd(II) (1)
GO-NHC-Pd(II) (0.25)
GO/Fe3O4/PAMPS/Pd (0.4)
K2CO3, H2O, 60°C
K2CO3, H2O, 70°C
95
82
90
71
65
89
77
71
94
95
5
4
1.5
1.5
1.5
1
4
4
20
2
[63]
[67]
[65]
[65]
[65]
[68]
[69]
[70]
K2CO3, EtOH:H2O, 60°C
K2CO3, EtOH:H2O, 60°C
K2CO3, EtOH:H2O, 60°C
Cs2CO3, DMF:H2O, 50°C
K2CO3, EtOH, 80°C
K2CO3, EtOH:H2O, 80°C
K2CO3, EtOH:H2O, 60°C
K2CO3, EtOH:H2O, 60°C
[71]
This work
10
11
12
13
14
Poly(NIPAM-4-VP-AC)-Pd (0.05)
GO-NH2-Pd(II) (1)
GO-NHC-Pd(II) (0.25)
K2CO3, H2O, Ar atmosphere, 90°C
K2CO3, EtOH:H2O, 80°C
K2CO3, EtOH:H2O, 60°C
K2CO3, EtOH:H2O, 60°C
92
73
93
96
1
4
3
2
[72]
[70]
[71]
This work
GO/Fe3O4/PAMPS/Pd (0.4)
1 3

Pd Nanoparticles Immobilized on Supported Magnetic GO@PAMPS as an Auspicious Catalyst for…
12. Corbet J-P, Mignani G (2006) Chem Rev 106:2651–2710
13. Miyaura N, Yamada K, Suzuki A (1979) Tetrahedron Lett
20:3437–3440
14. Heravi MM, Hashemi E (2012) Tetrahedron 68:9145–9178
15. Heravi MM, Hashemi E (2012) Monatshefte für Chemie
143:861–880
16. Suzuki A (2011) Angew Chem Int Ed 50:6722–6737
17. Suzuki A (2002) J Organomet Chem 653:83–90
18. Kim J, Swager TM (2001) Nature 411:1030–1034
19. Fang Y-Q, Karisch R, Lautens
72:1341–1346
M (2007) J Org Chem
20. Bringmann G, Rüdenauer S, Bruhn T, Benson L, Brun R (2008)
Tetrahedron 64:5563–5568
21. Hassan J, Sevignon M, Gozzi C, Schulz E, Lemaire M (2002)
Chem Rev 102:1359–1470
22. Wu J, Pisula W, Müllen K (2007) Chem Rev 107:718–747
23. Moussa S, Siamaki AR, Gupton BF, El-Shall MS (2011) ACS
Catal 2:145–154
24. Qu K, Wu L, Ren J, Qu X (2012) ACS Appl Mater Interfaces
4:5001–5009
Fig. 8 Reusability of GO/Fe3O4/PAMPS/Pd catalyst in the Suzuki
25. Takamura T, Endo K, Fu L, Wu Y, Lee KJ, Matsumoto T (2007)
Electrochim Acta 53:1055–1061
reaction of 4-bromotoluene with phenyl boronic acid
26. Zhu C, Dong S (2013) Nanoscale 5:1753–1767
27. Zhang N, Zhang Y, Pan X, Yang M-Q, Xu Y-J (2012) J Phys
Chem C 116:18023–18031
to mention, this novel catalytic system worked equally well
with less reactive aryl chlorides compared with the corre-
sponding aryl bromides and aryl iodides. Furthermore, GO
sheet provided a high surface area for uniform distribution
of Fe3O4 NPs and magnetic character led to easy separation
of the catalyst from the reaction mixture by using a sim-
ple external magnet. The catalyst was reused at least seven
times without appreciable loss in its catalytic activity. Lack
of metal leaching is a promising advantage for our novel
catalyst proved by leaching test.
28. Scherer F, Anton M, Schillinger U, Henke J, Bergemann C, Kru-
ger A, Gansbacher B, Plank C (2002) Gene Ther 9:102–109
29. Gersting SW, Schillinger U, Lausier J, Nicklaus P, Rudolph
C, Plank C, Reinhardt D, Rosenecker J (2004) J Gene Med
6:913–922
30. Muthana M, Scott S, Farrow N, Morrow F, Murdoch C, Grubb S,
Brown N, Dobson J, Lewis C (2008) Gene Ther 15:902–910
31. Yang X, Wang Y, Huang X, Ma Y, Huang Y, Yang R, Duan H,
Chen Y (2011) J Mater Chem 21:3448–3454
32. Baig RN, Varma RS (2013) Chem Commun 49:752–770
33. Cheng T, Zhang D, Li H, Liu
16:3401–3427
G (2014) Green Chem
34. Li Y, Hong XM, Collard DM, El-Sayed MA (2000) Org Lett
2:2385–2388
Acknowledgements Sh. Asadi and M. M. Heravi are grateful to
Iran National Science Foundation (INSF) for financial support pro-
vided by the post-doctoral project (94026040). We also appreciate
Alzahra University and Shahid Beheshti University Research Council
for their help and supports.
35. Li Y, El-Sayed MA (2001) J Phys Chem B 105:8938–8943
36. Narayanan R, El-Sayed MA (2004)
108:8572–8580
J Phys Chem B
37. Narayanan R, El-Sayed MA (2005) Langmuir 21:2027–2033
38. Narayanan R, El-Sayed MA (2005) J Catal 234:348–355
39. de Luna Martins D, Alvarez HM, Aguiar LC (2010) Tetrahedron
Lett 51:6814–6817
References
40. Islam RU, Witcomb MJ, Scurrell MS, Van Der Lingen E, Van
Otterlo W, Mallick K (2011) Catal Sci Technol 1:308–315
41. Heck RF (2004) Palladium-Catalyzed Vinylation of Organic
Halides. In: Organic Reactions. John Wiley & Sons, Inc.
doi:10.1002/0471264180.or027.02
1. Johansson Seechurn CCC, Kitching MO, Colacot TJ, Snieckus V
(2012) Angew Chem Int Ed 51:5062–5085
2. Balanta A, Godard C, Claver C (2011) Chem Soc Rev
40:4973–4985
42. Daves GD Jr, Hallberg A (1989) Chem Rev 89:1433–1445
43. Bedford RB, Cazin CS, Coles SJ, Gelbrich T, Horton PN, Hurst-
house MB, Light ME (2003) Organometallics 22:987–999
44. Vilar R, Mingos DMP, Cardin CJ (1996) J Chem Soc Dalton
Trans 23:4313–4314
3. Farina V (2004) Adv Synth Catal 346:1553–1582
4. Li H, Johansson Seechurn CC, Colacot TJ (2012) ACS Catal
2:1147–1164
5. Kohler K, Prockl S, Kleist
10:1585–1601
W (2006) Curr Org Chem
45. Durà-Vilà V, Mingos DMP, Vilar R, White AJ, Williams DJ
(2000) J Organomet Chem 600:198–205
6. Colacot TJ (2011) Platin Met Rev 55:84–90
46. Heravi MM, Kivanloo A, Rahimzadeh M, Bakavoli M,
7. Heravi MM, Hashemi E, Nazari
18:441–472
N (2014) Mol Divers
Ghassemzadeh M, Neumüller
46:1607–1610
B (2005) Tetrahedron Lett
8. M. Heravi M, Hashemi E, Ghobadi N (2013) Curr Org Chem
17:2192–2224
47. Oskooie H, Heravi MM, Behbahani F (2007) Molecules 12:1438
48. Heravi MM, Keivanloo A, Rahimizadeh M, Bakavoli M, Ghas-
semzadeh M (2004) Tetrahedron Lett 45:5747–5749
9. Heravi MM, Hashemi E, Azimian F (2014) Tetrahedron 70:7–21
10. Nicolaou KC, Chen JS (2011) Classics in total synthesis III,
vol 3. Wiley, Weinheim
49. Heravi MM, Hashemi E, Beheshtiha YS, Ahmadi S, Hosseinne-
jad T (2014) J Mol Catal A 394:74–82
11. Magano J, Dunetz JR (2011) Chem Rev 111:2177–2250
1 3

S. Asadi et al.
50. Sadjadi S, Heravi MM (2016) RSC Adv 6:88588–88624
51. Nemati F, Heravi MM, Saeedi Rad R (2012) Chin. J Catal
33:1825–1831
63. Lee Y, Hong MC, Ahn H, Yu J, Rhee H (2014) J Organomet
Chem 769:80–93
64. Sivudu KS, Reddy NM, Prasad MN, Raju KM, Mohan YM,
Yadav J, Sabitha G, Shailaja D (2008) J Mol Catal A 295:10–17
65. Song H-q, Zhu Q, Zheng X-j, Chen X-g (2015) J Mater Chem A
3:10368–10377
52. Nemati F, Heravi MM, Elhampour
5:45775–45784
A (2015) RSC Adv
53. Ayati A, Heravi MM, Daraie M, Tanhaei B, Bamoharram FF,
Sillanpaa M (2016) J Iran Chem Soc 13:2301–2308
66. Sheldon RA, Wallau M, Arends IW, Schuchardt U (1998) Acc
Chem Res 31:485–493
54. Hummers WS, Offeman RE (1958)
80:1339–1339
J Am Chem Soc
67. Hong MC, Ahn H, Choi MC, Lee Y, Kim J, Rhee H (2014) Appl
Organomet Chem 28:156–161
55. Gao P, Ng K, Sun DD (2013) J Hazard Mater 262:826–835
56. Sonogashira K (2002) J Organomet Chem 653:46–49
57. Negishi E-i, Hu Q, Huang Z, Qian M, Wang G, Brown H (2005)
Aldrichim Acta 38:71–87
68. Park JH, Raza F, Jeon S-J, Kim H-I, Kang TW, Yim D, Kim J-H
(2014) Tetrahedron Lett 55:3426–3430
69. Bai C, Zhao Q, Li Y, Zhang G, Zhang F, Fan X (2014) Catal Lett
144:1617–1623
58. Wan J, Cai W, Feng J, Meng X, Liu E (2007) J Mater Chem
17:1188–1192
70. Shang N, Feng C, Zhang H, Gao S, Tang R, Wang C, Wang Z
(2013) Catal Commun 40:111–115
59. Zhang X, Niu Y, Meng X, Li Y, Zhao J (2013) CrystEngComm
15:8166–8172
71. Shang N, Gao S, Feng C, Zhang H, Wang C, Wang Z (2013)
RSC Adv 3:21863–21868
60. Paul S, Islam MM, Islam SM (2015) RSC Adv 5:42193–42221
61. Yin, Liebscher J (2007) Chem Rev 107:133–173
62. Sakai T, Matsunaga T, Yamamoto Y, Ito C, Yoshida R, Suzuki
S, Sasaki N, Shibayama M, Chung U-i (2008) Macromolecules
41:5379–5384
72. Zhang Y, Yang J, Zhang X, Bian F, Yu W (2012) React Funct
Polym 72:233–241
1 3