Cobalt supported on dendronized magnetic nanoparticles: A new highly efficient and recyclable catalyst for the Mizoroki–Heck cross-coupling reaction

Article abstract of DOI:10.1002/aoc.4823

Polyamidoamine (PAMAM) is one of the most interesting types of hyperbranched polymers that carry a large number of amino groups on its surface. PAMAM has gained significant attention from synthetic organic chemists due to its structural characteristics, controllable structure, inner porosity, and ability to trap a wide range of ions and molecules. So, in this work, the PAMAM dendrimer was synthesized, grafted onto the surface of magnetite nanoparticles, and the resulting hybrid nanoparticles were then employed as suitable host for immobilizing cobalt nanoparticles. The newly developed catalyst was well characterized by Fourier transform-infrared, X-ray diffraction, thermogravimetric analysis, field emission-scanning electron microscopy, transmission electron microscopy, atomic absorption spectroscopy, element mapping and energy-dispersive X-ray analysis. The efficiency of the as-prepared nanocatalyst was evaluated for the Mizoroki–Heck cross-coupling reactions. The MNP@PAMAM-Co represented perfect catalytic efficiency and high selectivity for the Mizoroki–Heck cross-coupling reaction compared with previously reported catalysts. The catalyst separation from the reaction mixture was easily achieved with the assistance of an external magnetic field, and its recycling was also investigated for five consecutive runs. Hot filtration confirmed no leaching of the active metal during the Heck coupling.

Full text of DOI:10.1002/aoc.4823

Received: 29 August 2018
DOI: 10.1002/aoc.4823
Revised: 14 October 2018
Accepted: 24 October 2018
F U L L P A P E R
Cobalt supported on dendronized magnetic nanoparticles:A
new highly efficient and recyclable catalyst for the
Mizoroki–Heck cross‐coupling reaction
Maryam Arghan
| Nadiya Koukabi
| Eskandar Kolvari
Department of Chemistry, Semnan
University, P.O. Box 35195‐363, Semnan,
Iran
Polyamidoamine (PAMAM) is one of the most interesting types of
hyperbranched polymers that carry a large number of amino groups on its
surface. PAMAM has gained significant attention from synthetic organic
chemists due to its structural characteristics, controllable structure, inner
porosity, and ability to trap a wide range of ions and molecules. So, in this
work, the PAMAM dendrimer was synthesized, grafted onto the surface of
magnetite nanoparticles, and the resulting hybrid nanoparticles were then
employed as suitable host for immobilizing cobalt nanoparticles. The newly
developed catalyst was well characterized by Fourier transform‐infrared,
X‐ray diffraction, thermogravimetric analysis, field emission‐scanning electron
microscopy, transmission electron microscopy, atomic absorption spectros-
copy, element mapping and energy‐dispersive X‐ray analysis. The efficiency
of the as‐prepared nanocatalyst was evaluated for the Mizoroki–Heck cross‐
coupling reactions. The MNP@PAMAM‐Co represented perfect catalytic effi-
ciency and high selectivity for the Mizoroki–Heck cross‐coupling reaction
compared with previously reported catalysts. The catalyst separation from
the reaction mixture was easily achieved with the assistance of an external
magnetic field, and its recycling was also investigated for five consecutive
runs. Hot filtration confirmed no leaching of the active metal during the Heck
coupling.
Correspondence
Nadiya Koukabi, Department of
Chemistry, Semnan University, P.O. Box
35195‐363, Semnan, Iran.
Email: n.koukabi@semnan.ac.ir
Funding information
Semnan University
KEYWORDS
cobalt nanoparticles, magnetite, Mizoroki–Heck cross‐coupling reaction, PAMAM dendrimers
1 | INTRODUCTION
considerable attention and become an active research
field.[1–6] The Mizoroki–Heck coupling reaction of olefins
Formation of carbon–carbon bonds is the key transforma-
tion of synthetic organic chemistry for setting up the car-
bon backbone of organic molecules as well as extending a
carbon framework, which has extensive applications in
agrochemical synthesis, fine chemical synthesis, natural
products synthesis and medicinal chemistry. Therefore,
improvement of efficacious methodologies for the forma-
tion of carbon–carbon bonds has been drawing
with aryl halide is particularly a versatile method for gen-
erating carbon–carbon bonds due to its atom economy
and high efficiency. The standard Heck reaction is carried
out using soluble palladiums, usually phosphine palla-
dium complexes, but it suffers from disadvantages that
limit its application in the industry.[7] Due to the toxicity
and high cost of palladium complexes, researches have
replaced them with affordable transition metal catalysts,
Appl Organometal Chem. 2019;e4823.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4823

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ARGHAN ET AL.
containing Ni,[8] Fe,[9] Cu[10] and Co.[11] On the other
hand, phosphine ligands are toxic, expensive, sensitive
to oxygen and water, and also unrecoverable. So, to
overcome these limitations, designing and applying a
novel catalyst is required. Most of the supported catalysts
that have been already applied are based on inorganic
silica, charcoal, synthetic polystyrene and alumina. For
example, carbon nanotubes, despite having unique fea-
tures,[7,12] are known to be hazardous to the environ-
ment.[13] Moreover, although mesoporous silica exhibits
many benefits, it is unstable in the conditions required
for coupling reactions, such as basic and aqueous condi-
tions.[14] In this regard, application of biocompatible
dendrimers as support is very promising due to their
phenomenal and adjustable physicochemical features.[15]
Dendrimers are an attractive type of macromolecules
with homogeneous, hyperbranched and spherical struc-
ture, with distinguished properties including nanoscale
size, multifunctional terminal surfaces, monodispersity,
high density of accessible active sites, intensive internal
porosity, host–guest potential, and moderate biocompati-
bility.[16,17] Attaching functional groups, such as
hydroxyl, carboxyl and amine as terminal groups of the
dendrimers can result in a considerable enhancement in
binding capacity to a diversity of ions.[15] These special
features make dendrimers promising candidates for
effective supports.[18] One of the most common types
of dendrimer is polyamidoamine (PAMAM) because
of its unique properties, such as imitating the three‐
dimensional structure of biomacromolecules, globular
structure, convenient synthesis method, good biocompat-
ibility and highly reactive primary amine terminal sur-
faces, which make them appropriate for any desired
application.[17] It is noteworthy to mention that the high
surface‐to‐volume ratio of PAMAM can supply more
active sites for chemical modifications to make a suitable
platform for efficient catalytic processes. Currently, the
use of magnetic nanoparticle (MNPs) supports has
become a subject of intense investigation due to providing
a beneficial separation approach with an external mag-
net. Simultaneously, the development of the more effi-
cient, user‐friendly and stable catalysts is observed in
coupling reactions using several metal complexes sup-
ported on MNPs.[19] To date there are rare examples of
the usage of metal–PAMAM anchored to MNPs with
the catalytic demeanor in the organic transforma-
tions.[20–25] So, inspired by the advantages of magnetic
PAMAM and the drawbacks of palladium complexes,
we were persuaded to immobilize first‐row transition
metal–PAMAM complexes on MNPs to ameliorate more
affordable and eco‐friendly heterogeneous palladium‐free
catalysts for carbon–carbon cross‐coupling reaction.
Cobalt‐catalyzed couplings have recently been very much
considered, because cobalt is non‐toxic, readily available,
stable in air, low cost and reveals powerful catalytic activ-
ities.[7] Nevertheless, the use of a cobalt catalyst for the
Mizoroki–Heck reaction is rare, and there are very few
examples of its application as a catalyst in this coupling
reaction.[7,11,26–28] Although none of these reported cobalt
catalysts can compete with palladium in synthetic versa-
tility, they have several benefits, including excellent
chemical and good mechanical stabilities, and better eco-
logical and economic features compared with palladium
catalysts. Therefore, the use of low‐cost heterogeneous
catalysts such as cobalt is very desirable. In line with
our efforts to develop and expand environmentally
benign and effective heterogeneous catalysts,[29–32] in this
work we wish to reveal a novel and green strategy for the
Mizoroki–Heck coupling reaction. For this purpose,
PAMAM‐Co complex was supported on MNPs and its
activity as a nanocatalyst was verified in the Mizoroki–
Heck coupling reaction in which superior catalytic activ-
ity of the nanocatalyst without needing protection of
inert atmosphere was obtained.
2 | EXPERIMENTAL
2.1 | General
All the chemicals (reagents and solvents) were purchased
from Merck and Sigma‐Aldrich, and were employed with-
out further purification. The Fourier transform‐infrared
(FT‐IR) spectra were recorded on a Shimadzu 8400 s
spectrometer using KBr pressed powder discs. X‐ray dif-
fraction (XRD) analysis was performed on a Siemens
D5000 (Siemens AG, Munich, Germany) using Cu‐Ka
radiation of wavelength 1.54 Å. Field emission‐scanning
electron microscopy (FE‐SEM)–energy‐dispersive X‐ray
(EDX) analyses were performed using TESCAN MIRA
II digital scanning microscope. Thin‐layer chromatogra-
phy (TLC) on commercial plates coated with silica gel
60 F254 was applied to determine the purity of the prod-
ucts and the progress of the reactions. Thermogravimetric
analysis (TGA) was accomplished using a Du Pont 2000
thermal analysis apparatus heated from 25°C to 1000°C
at ramp 5°C/min under air atmosphere. The amount of
cobalt in the catalyst was evaluated using an Agilent
model 240 AA Shimadzu (USA) flame atomic adsorption
spectrometer. All measurements were carried out in an
air/acetylene flame, and the Co hollow cathode lamps
were used as the radiation sources. The NMR spectra
were provided on Brucker Avance 400 MHz instruments
(1H‐NMR 400 MHz and 13C‐NMR 125 MHz) in pure
dimethyl sulfoxide.

ARGHAN ET AL.
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vigorous magnetic stirring and inert atmosphere. Then,
a dispersed mixture containing 1 g acrylamide, 10 ml dis-
tilled water and 20 ml ethanol was added to the above
reaction medium dropwise and the reaction continued
for 4 hr at 70°C with continuous stirring under inert
atmosphere. The obtained Fe3O4@PAM was collected by
an external magnet and washed with ethanol (several
times), and then dried under a vacuum oven at 80°C. In
the following, Hofmann degradation was carried out
to convert polyacryl amide to PVAm. Typically, 0.1 g of
Fe3O4@PAM nanocomposite and 0.08 g of Ca(OCl)2 were
put together into a round‐bottom flask and dispersed in
15 ml of deionized water with a water‐bath sonicator
for10 min. The suspension was stirred under reflux for
6 hr. The amine functionalized MNP was separated by a
permanent magnet and washed well with deionized
water and dried under vacuum at 60°C overnight.
2.2 | Catalyst preparation
2.2.1 | Synthesis of Fe3O4 nanoparticles
The magnetic (Fe3O4) nanoparticle was synthesized fol-
lowing a reported procedure:[32] 3 ml of FeCl3 solution
(2 M dissolved in 2 M HCl) was mixed with 10.33 ml of
ultrapure water. Then, 2 ml of Na2SO3 solution (1 M)
was added dropwise into the previous solution in 1 min
under magnetic stirring. In this step, after completion of
mixing the two solutions, a complex of SO32−and Fe3+
is formed, which changes the color of the mixture from
light yellow to red. After that, the solution was kept
under stirring to turn the color of the solution back again,
and then 80 mL NH3·H2O solution (0.85 M) was added. A
black precipitate was rapidly formed, which was stirred
for another 30 min to complete the crystallization. The
obtained MNPs were then purified by applying a magnet,
decantation and washing several times with deionized
water (to pH < 7.5). The precipitates were dried in a vac-
uum oven at 60°C for 12 hr.
2.2.4 | Preparation of PAMAM
dendrimer‐coated Fe3O4 nanoparticles
(MNP@PAMAM)
2.2.2 | Synthesis of VTES‐modified Fe3O4
nanoparticles (MNP@VTES)
The construction of hyperbranched PAMAM on magnetic
support was achieved by repeating two steps:[33] (1) for-
mation of methyl ester surface groups derived from the
Michael addition of MA to the surface amino groups;
and (2) amidation reaction of the resulting ester moieties
with EDA. The general procedure for the Michael addi-
tion of MA to the surface amino groups was as follows:
a mixture of the amine functionalized MNP (0.1 g) and
MA (5 mmol) was dispersed in 5 ml of ethanol, and the
resulting mixture was allowed to reflux for 12 hr under
vigorous stirring under the protection of N2. The desired
product was separated with a magnetic field, washed sev-
eral times with water to remove redundant, and dried
under vacuum at 65°C. The resulting product was
marked as MNP@PVAm‐MA‐G0.5 (Scheme 1). The gen-
eral procedure for the amidation of the resulting ester
moieties with EDA was as follows: 10 mmol EDA was
added into the flask containing 0.1 g MNP@PVAm‐MA
and 5 ml ethanol, and the reaction mixture was stirred
for a period of time under reflux conditions and N2 atmo-
sphere. The desired product was obtained after magnetic
separation, washing with water several times to remove
the unreacted EDA, and vacuum drying at 65°C. The
resulting product was marked as MNP@PVAm‐MA‐
EDA‐G1 (Scheme 1). For construction of the third gener-
ation of PAMAM dendrimer (G3) on the surface of MNP,
in order to yield MNP@PAMAM, two reactions of
Michael addition and amidation were repeated two more
times.
Modification of MNP surface with vinyl triethoxysilicane
(VTES) was performed to impede the agglomeration of
NPs, increase the stability and provide reactive C=C
bonds, and this is carried out through the reaction
between VTES and hydroxyl surface groups of MNPs.
Generally, 1.0 g of Fe3O4 nanoparticles was well dis-
persed in 60 ml of ethanol with a water‐bath sonicator
for 1 hr, then NH3·H2O (12 ml) was added and homoge-
neously dispersed by ultrasonic vibration for 10 min, then
6.0 ml of VTES was added to the reaction mixture at 50°C
under vigorous magnetic stirring. After 8 hr of stirring,
the modified MNP@VTES was obtained by magnetic
separation. The resultant product was washed well with
deionized water and ethanol until neutralization, and
dried under vacuum at room temperature for 12 hr.
2.2.3 | Synthesis of polyvinyl
amine‐coated Fe3O4 nanoparticles
(MNP@PVAm)
The surface modification of MNPs with polyvinyl amine
(PVAm) was performed to generate amine groups on
the surface of Fe3O4 nanoparticles. In a typical protocol,
a mixture of modified Fe3O4 nanoparticles (1 g) and
ammonium persulfate (0.02 g) was homogeneously dis-
persed in 30 ml ethanol and 10 ml distilled water, and
was sonicated for 30 min and then heated at 70°C under

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ARGHAN ET AL.
SCHEME 1 Schematic of the process for the synthesis of MNP@PAMAM‐Co

ARGHAN ET AL.
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cobalt supported on dendronized MNPs, a schematic
illustration was designed (Scheme 1). For assisting the
PAMAM dendrimer, MNPs were functionalized with
PVAm to generate amine groups on the surface of MNPs.
The main incentive of the choice of PVAm relies on the
fact that it provides the advantage that more amine
groups can be grafted onto the surface of the MNPs,
due to its multilayer and polymeric identity, whereas
in the normal grafting of other materials, such as
3‐(trimethoxysilyl)‐propylamine, just one layer of them
can be coated onto the surface. But before coating of the
polymer onto the surface of Fe3O4, the surface of the
MNPs was modified with VTES to achieve reactive groups
C=C onto the Fe3O4 surface to facilitate the polymeriza-
tion by surface‐initiated radical polymerization and to
graft the polymer onto the surface of Fe3O4 nanoparticles
via a covalent bond.[39] In the next step, generation
of MNP@PAMAM was produced by repeating and
alternating utilization of the Michael addition reaction
and amidation condensation reaction. Eventually, the
resulting MNP@PAMAM was synergized with cobalt salt
to form the catalyst MNP@PAMAM‐Co. The loading
amount of Co onto the MNP@PAMAM was determined
by atomic absorption spectroscopy (AAS) analysis to be
1.86 mmol g−1. The proof of the structure of the catalyst
and its stability before and after the catalytic reaction
were confirmed using FT‐IR, XRD, TGA, FE‐SEM, trans-
mission electron microscopy (TEM), AAS, element map-
ping and EDX analysis.
2.2.5 | Synthesis of Co‐nanoparticles sup-
ported on PAMAM dendrimer‐coated Fe3O4
nanoparticles (MNP@PAMAM‐Co)
In order to obtain the final MNP@PAMAM‐Co, 4.2 mmol
of Co(OAc)2·4H2O solved in ethanol (10 ml) was added to
a dispersed mixture of MNP@PAMAM (1 g) in ethanol
(5 ml). The reaction mixture was left for 18 hr under
stirring conditions at 60°C. The resulting complex was
separated, washed several times with ethanol and dried
at room temperature.
2.3 | Studies on catalytic activity
2.3.1 | General procedure for Mizoroki–
Heck reaction catalyzed by
MNP@PAMAM‐Co
In a round‐bottom flask charged with a mixture of
DMF (1.5 ml) and H2O (1.5 ml) as solvent, a mixture of
olefin (1.5 mmol), aryl halide (1.0 mmol) and K3PO4
(4.0 mmol), and MNP@PAMAM‐Co (0.55 mol%) as
catalyst was added. The reaction was under mechanical
agitation for an appropriate amount of time at 100°C. Fol-
lowing completion of the reaction (monitored by TLC)
and separation of the catalyst, the reaction mixture was
cooled to room temperature, the organic layer extracted
with ethyl acetate and then dried over anhydrous MgSO4.
The structures of some of the known products were char-
acterized by comparing their 1H‐NMR and 13C‐NMR
spectra with those found earlier in the literature.
3.1.1 | Fourier transform‐infrared spectra
In order to prove the modification of the magnetite sur-
face, the FT‐IR spectra of MNP@PVAm, MNP@PVAm‐
MA‐EDA and MNP@PAMAM‐Co nanocomposites were
recorded (Figure 1a–c). The strong adsorption bands at
3 | RESULTS AND DISCUSSION
3.1 | Fabrication and characterization of
MNP@PAMAM‐Co
For appropriate Co‐immobilization and stabilization,
MNPs were chosen as proper support and the first core
due to their magnetic properties, which provided a conve-
nient route for separating the synthesized catalyst in each
step of synthesis and a high surface to volume aspect ratio
in combination with PAMAM as an effective stabilizer
for Co. In recent years, many studies on the structure
of PAMAM supporting different metals for catalytic use
have been reported.[21,34,35] However, to the best our
knowledge, only a few reports refer to the application of
such complexes in coupling reactions[36–38] and, as far
as we know, this is the first report of synthesis using mag-
netic PAMAM‐supported Co catalyst in the Heck cou-
pling reaction without any additives and co‐catalyst. In
order to visually summarize the process of preparing the
FIGURE 1 Fourier transform‐infrared (FT‐IR) spectra of (a)
MNP@PVAm, (b) MNP@PVAm‐MA‐EDA, and (c)
MNP@PAMAM‐Co

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ARGHAN ET AL.
about 551 and 626 cm−1 indicated the presence of MNPs,
attributing to the Fe–O vibrations (Figure 1a–c). The
peaks at about 444 and 900–1200 cm−1 are related to the
stretching vibration of Si–O–metal, Si–OR and O–Si–O
(Figure 1a–c). For MNP@PVAm, the new band located
at 1639 cm−1 can be related to the bending vibration
absorption of the N–H bond (Figure 1a). In the FT‐IR
spectrum of MNP@PVAm‐MA‐EDA (Figure 1b), after
amidation of MA with EDA on the surface of the
MNP@PVAm, the characteristic absorption peak of an
ester group, which is commonly existent at about 1740
cm−1, disappeared, and the absorption peaks at 1602
and 1668 cm−1 related to N–H bending vibrations and
the C=O stretching of amide groups, respectively,
appeared. This demonstrated that amidation has
completely occurred. Furthermore, the bands at 1400,
2850–2950 and 3200–3500 cm−1 correspond to the bend-
ing vibration absorption of the CH2, stretching vibration
of the methylene groups and N–H stretching vibrations,
respectively (Figure 1a–c). In the spectrum of
MNP@PAMAM‐Co (Figure 2c), it is observed that the
locations of two bands were changed. The peaks at about
1602 cm−1 assigned to N–H bending vibrations and 1668
cm−1 related to carbonyl bonds of the hyperbranched
polymer were shifted to lower wavenumbers (1541 cm−1
and 1558 cm−1, respectively). These observations are pos-
sibly due to the strong interaction of functional groups
with the Co nanoparticles.[34] A closer inspection of the
spectrum of MNP@PAMAM‐Co (Figure 2c) showed that
the intensities of the methylene and amide peaks were
increased in comparison to those of MNP@PVAm‐MA‐
EDA resulting from the propagation of hyperbranched
dendritic PAMAM from the MNP@PVAm surface.[34]
Therefore, the overall results indicate that construction
of the hyperbranched polymer on the surface of the
MNP@PVAm and synthesis of MNP@PAMAM‐Co were
successfully achieved.
3.1.2 | Thermogravimetric analysis
The thermal degradation of MNP@PAMAM and
MNP@PAMAM‐Co were studied to further investigate
the effectiveness grafting of the dendrimer onto the MNPs
and also weight loss percentages at various decomposi-
tion temperatures (Figure 2). According to Figure 2, both
curves describe three decomposition stages. The weight
loss under 200°C is attributed to the evaporation of phys-
ically adsorbed water. In the second region, there is a sig-
nificant reduction in weight loss from 200 to 440°C
(about 3–4%), which is related to the decomposition of
VTES groups (Figure S1), and about 28–30% is related
to the degradation of dendrimers layer and the stable
functional groups.[40] As can be seen, the amount of
organic moieties bonded on the surface of the MNPs is
relatively high, which indicates the successful construc-
tion of the dendrimer on the surface.[41] The final weight
loss (about 630–680°C) is attributed to the degradation of
the PVAm polymer chains.[42] A closer inspection of the
TGA curve of MNP@PAMAM‐Co shows slightly lower
thermal stability after the immobilization of cobalt,
which can be due to the interaction of the cobalt species
with the ligands[43] and the catalytic effect of them in
the decomposition of the dendritic structure.[44] However,
this thermal stability is very acceptable for the catalytic
application in C–C coupling reactions, which are carried
out at high temperatures. Also, compared with the
remaining mass percentage of MNP@PAMAM (~48%;
Figure 4a), MNP@PAMAM‐Co has higher undecom-
posed content (~60%). This amount of difference (~12%)
can be attributed to the amount of loaded Co, which is
relatively consistent with the result of AAS analysis.
3.1.3 | X‐ray diffraction spectra
In order to provide further evidence for the existence of
iron and cobalt in the catalyst, XRD characterization
analysis was performed (Figure 3). As shown in
Figure 3, both samples have characteristic peaks at 2θ
about 30.5°, 35.9°, 43.5°, 53.9°, 57.2° and 63° related to
[45]
the inverse cubic spinel structure of Fe3O4.
As can be
seen in Figure 3b, after introducing the synthetic catalyst,
the intensity of the Fe3O4 peaks was reduced due to the
chemical modifications but the phase of Fe3O4 nanoparti-
cles was not altered. As illustrated in Figure 3b, the crys-
talline nature of the cobalt species was confirmed with
characteristic diffraction peaks at about 2θ = 30.08°,
37.43°, 57.5° and 62.81°, which correspond to the cubic
spinel structure of cobalt ferrite nanoparticles (PDF data
22–1086).[11,46]
FIGURE 2 Thermogravimetric analysis (TGA) curve of (a)
MNP@PAMAM and (b) MNP@PAMAM‐Co

ARGHAN ET AL.
7 of 17
FIGURE 3 X‐ray diffraction (XRD) pattern of (a) n‐Fe3O4 and (b)
MNP@PAMAM‐Co
3.1.4 | Field emission‐scanning electron
microscopy
The outer topography of MNP@PAMAM‐Co was
observed by SEM (Figure 4). The SEM image demon-
strates that MNP@PAMAM‐Co are spherical but the sur-
faces were not smooth in comparison to the MNPs, which
is due to the presence of PAMAM dendrimer. On the
other hand, as is clear from Figure 4, the morphology of
MNP@PAMAM‐Co is completely varying from those of
PAMAM[47] and n‐Fe3O4 (Figure 4a). These observations
illustrate that PAMAM was successfully linked to magne-
tite nanoparticles and the cobalt nanoparticles are coated
with the dendrimer.
FIGURE 4 Field emission‐scanning electron microscopy (FE‐
SEM) images of (a) n‐Fe3O4 and (b) MNP@PAMAM‐Co
3.1.5 | Energy dispersive X‐ray spectros-
copy mapping
Co nanoparticles in a relatively uniform dispersion in
n‐Fe3O4.
The density and spatial distributions of the grafted
PAMAM on n‐Fe3O4 and cobalt nanoparticles coated
with the dendrimer are evaluated by quantitative
energy‐dispersive X‐ray spectroscopy (EDS) element map-
ping (Figure 5). Figure 5a–f clearly defines the spatial dis-
tributions of Fe, C, Si, O, N and Co in individual shells
that are consistent with MNP@PAMAM‐Co structure.
As can be seen in Figure 5e, N is relatively homoge-
neously distributed over the whole surface, suggesting
the successful grafting of PAMAM dendrimer.[48] More-
over, Figure 3f clearly reveals the uniform dispersion of
Co nanoparticles, indicating that aggregation of cobalt
nanoparticles did not occur upon its immobilization on
MNP@PAMAM. All these observations depict that
PAMAM dendrimer can effectively entrap and stabilize
3.1.6 | Energy dispersive X‐ray analysis
The grafting of PAMAM dendrimers to n‐Fe3O4 and
immobilization of cobalt on the support were further con-
firmed by EDX studies. Figure 6 shows the EDX spectra
of MNP@PAMAM‐Co, in which the peak of iron is
ascribed to Fe3O4, the peak of carbon is ascribed to VTES,
PVAm and PAMAM, the peak of silicon is attributed to
VTES, the peak of oxygen is ascribed to Fe3O4, VTES
and PAMAM, and the peak of nitrogen is ascribed to
amino functional groups. The EDX spectrum (Figure 6)
proved the appearance of the cobalt as well as C, N, O,
Si and Fe in the body of the catalyst. The amount of Co

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ARGHAN ET AL.
FIGURE 5 Energy‐dispersive X‐ray spectroscopy (EDS) element mapping of (a) Fe, (b) C, (c) Si, (d) O, (e) N and (f) Co
FIGURE 6 Energy‐dispersive X‐ray
analysis (EDX) spectra of MNP@PAMAM‐
Co
supported onto the PAMAM grafted MNPs was found to
be 11.2% (based on EDX results). Moreover, Table 1
shows an enhancement in the proportion of N and C with
increasing the generations of the PAMAM (based on the
results of elemental analysis). These results prove that
grafting of PAMAM of diverse generations onto the sur-
face of n‐Fe3O4 by repeated Michael addition and
amidation reactions was successful.

ARGHAN ET AL.
9 of 17
TABLE 1 Elementary analysis of PAMAM‐grafted n‐Fe3O4
3.2 | Application of MNP@PAMAM‐Co in
C–C coupling reactions
Elemental proportion in PAMAM‐
grafted n‐Fe3O4
After full characterization of this novel nanocomposite,
the effectiveness of the prepared catalyst was investigated
in C─C bond formation via Mizoroki–Heck cross‐
coupling reaction (Scheme 2).
Generation
N (%)
C (%)
G1
G2
G3
3.30
3.91
4.96
19.01
23.34
27.56
3.2.1 | Optimization of the reaction
parameters for the Mizoroki–Heck cross‐
coupling reaction
3.1.7 | Transmission electron microscopy
Before performing the catalytic activity test of the cat-
alyst, our initial concern centered on the critical
parameters that affect the outcome of the reaction
(yield and time), such as amount of catalyst, solvent,
base system and temperature, to achieve the best reac-
tion conditions. The coupling reaction of iodobenzene
(1.0 mmol) and methyl acrylate (1.5 mmol) was chosen
as a model reaction to find out the optimized reaction
conditions.
Further characterization of the morphology and structure
of the catalyst was performed by TEM (Figure 7). The
TEM images showed well‐defined spherical Co particles
and good distribution of them in the catalyst, which have
good agreement with FE‐SEM and EDS results. Very sim-
ilar morphology observation has been previously
reported.[11]
3.1.8 | Atomic absorption spectroscopy
3.2.2 | Effect of catalyst loading
analysis
As the catalyst is the main factor in the progress of this
type of reaction, the C–C coupling reaction of
iodobenzene with methyl acrylate was optimized in the
presence of different amounts of catalyst. As shown in
Table 2, by raising the catalyst amount, the yield of
desired product increased accordingly (Table 2, entries
The cobalt loading on MNP@PAMAM was calculated
using AAS analysis after dissolution in nitric acid hydro-
chloric acid. The amount of cobalt in the catalyst was cal-
culated as 1.86 mmol g−1,which is in consistent with the
results of EDX analysis.
FIGURE 7 Transmission electron microscopy (TEM) images of MNP@PAMAM‐Co
SCHEME 2 MNP@PAMAM‐Co‐
catalysed Mizoroki–Heck reaction

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ARGHAN ET AL.
TABLE 2 Optimization of the reaction conditions for the Mizoroki–Heck reaction
Molar ratio of
iodobenzene/
base
Time
[hr
(min)]
Amount of
catalyst (% mol)
Temperature
(°C)
Yield
(%)
Entry
Base
Solvent
1
0.33
0.44
0.55
0.66
–
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
–
KOH
H2O
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
60
100
(70)
(65)
(60)
(60)
24
55
65
70
75
–
2
KOH
H2O
3
KOH
H2O
4
KOH
H2O
5
KOH
H2O
6
0.005(g)a
0.005(g)b
0.55c
0.55
0.55
0.55
0.55
0.55
0.55
0.55
0.55
0.55
0.55
0.55
0.55
0.55
0.55
0.55
0.55
0.55
KOH
H2O
24
10
Trace
35
–
7
KOH
H2O
24
8
KOH
H2O
24
9
–
H2O
24
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/2
1/3
1/4
1/5
1/4
1/4
K2CO3
Na2CO3
NaOH
K3PO4
Et3N
H2O
(60)
(60)
(60)
(55)
(60)
(55)
(80)
(60)
(60)
(80)
(55)
(55)
(55)
(55)
(65)
(50)
75
70
60
80
65
82
60
70
65
65
85
87
90
92
90
90
H2O
H2O
H2O
H2O
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
DMF
DMSO
MeOH
EtOH
PEG
DMF:H2O (1/1)
DMF:H2O (1/1)
DMF:H2O (1/1)
DMF:H2O (1/1)
DMF:H2O (1/1)
DMF:H2O (1/
1)
26
27
0.55
0.55
1/4
1/4
K3PO4
K3PO4
DMF:H2O (1/1)
DMF:H2O (1/1)
120
RT
(50)
6
93
–
The optimum conditions are shown in bold.
aReaction was performed in the presence of Fe3O4NPs.
bReaction was performed in the presence of MNP@PAMAM.
cReaction was performed in the presence of Co(OAc)2·4H2O.
1–4). As can be seen in Table 2, the most suitable amount
of catalyst for the Mizoroki–Heck coupling reaction was
0.55 mol%. In addition, in a set of experiments, the model
reaction was examined in the absence of the catalyst, as
well as in the presence of Fe3O4 NPs, MNP@PAMAM
and Co(OAc)2·4H2O to prove the catalytic activity of the
as‐prepared MNP@PAMAM‐Co in the Mizoroki–Heck
coupling reaction. As can be seen, in all cases, poor yield
of product was obtained even after a long period of time
(Table 2, entries 5–8).
3.2.3 | Effect of different bases
The role of base in the Mizoroki–Heck coupling reaction is
in preventing homo‐coupling product formation as well as

ARGHAN ET AL.
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TABLE 3 Mizoroki–Heck coupling reactions of aryl halides with olefinsa
Entry
Aryl halide
Olefin
Product
Time (min)b
Yield (%)c
TON
TOF
1
50
90
163
196
2
3
4
5
40
66
93
75
80
91
169
136
145
165
256
123
159
78
55
130
6
7
100
50
85
87
154
158
96
190
8
60
65
88
87
74
70
90
160
158
134
127
163
160
146
67
9
10
11
12
2 (hr)
3 (hr)
65
42
151
13
14
15
3 (hr)
50
71
89
93
129
162
169
43
195
225
45
16
17
45
60
80
86
145
156
193
156
aReaction conditions: aryl halide (1.0 mmol), olefin (1.5 mmol), K3PO4 (4.0 mmol), catalyst (0.55% mol) and DMF:H2O (1:1) (3 ml), at 100°C.
bDetected by TLC.
cIsolated yield.
TOF, turnover frequency, TON/time of reaction (hr); TON, turnover number, yield of product/per mol of Co.
neutralizing hydrogen halides.[45] Therefore, due to its cru-
cial role, it should exhibit high efficiency. So, the model
reaction was carried out in the presence of various bases
in order to find the best performance (Table 2, entries 3,
9–14). According to Table 2, K3PO4 showed better perfor-
mance than the rest of the bases.

12 of 17
ARGHAN ET AL.
24–27). According to the results, the desired product
was obtained in highest yield at 100°C.
3.2.4 | Effect of molar ratio of
iodobenzene/base
Undoubtedly, the amount of used base also has a great
effect on the results. So, by applying different amounts
of K3PO4, it was found that 4 equivalents of K3PO4 pro-
vides the highest yield of the corresponding product
(Table 2, entries 20–23).
3.2.7 | Performance of the catalyst on sev-
eral substrates for Mizoroki–Heck reaction
To further widen the generality and scope of this new cat-
alytic system in the Mizoroki–Heck cross‐coupling reac-
tion, a range of aryl halides with various olefins were
applied (Scheme 2) under the optimized reaction condi-
tions (Table 2, entry 25). These obtained results are sum-
marized in Table 3. By analyzing Table 3, it was found
that electronic effect has a considerable impact on yields
as aryl halides including electron‐withdrawing groups
on the aromatic ring usually favor the reaction in shorter
times than those with electron‐donating substituents.
Another result that can be obtained from these data is
that the coupling reactions with different substituted aryl
iodides are faster than aryl bromide and aryl chloride.
The first step of this catalytic coupling reaction is oxida-
tive addition, so the reactivity of C‐halogen bond has def-
inite influence. Because chlorides have a high bond
dissociation energy, the coupling reaction is not favored
with aryl chloride substrates. But from another perspec-
tive, aryl chlorides are an ideal substrate for coupling
reactions and their use in the reactions are significant
because they are inexpensive and widely available. In
3.2.5 | Effect of solvent
Several common solvents were tested for the Mizoroki–
Heck cross‐coupling reaction in the presence of
MNP@PAMAM‐Co to access the best optimal conditions
(Table 2, entries 13, 15–20). This reaction proceeded in
higher yields, more cleanly and faster when the reactions
were conducted in a mixture of DMF and H2O in 1:1 ratio
as solvent.
3.2.6 | Effect of temperature
In the final stage of optimizing the reaction parameters,
the effect of temperature on the Mizoroki–Heck reaction
was investigated. Therefore, the model reaction was car-
ried out at different temperatures (Table 2, entries 22,
SCHEME 3 Plausible mechanism for
the Mizoroki–Heck cross‐coupling
reactions in the presence of
MNP@PAMAM‐Co

ARGHAN ET AL.
13 of 17
most reported methods, harsh conditions and high load-
ings of palladium catalyst are required, nevertheless,
those catalysts show little or no activity with aryl chloride
substrates. Therefore, to enhance the efficiency and value
of this method, the cross‐coupling of aryl chloride with
methyl acrylate as olefin was checked under the same
conditions. Aryl chloride reacts more slowly than aryl
bromide and aryl iodide, but it should be noted that the
reported cobalt catalytic systems were totally inactive
for aryl chlorides in the Heck reaction.[49–51] The high
activity of MNP@PAMAM‐Co is probably due to good
dispersion of cobalt nanoparticles and good synergistic
effects of cobalt nanoparticles with ligands that are
grafted on MNP. The structure of the selected compounds
was further checked by applying their high‐field 1H‐NMR
and 13C‐NMR spectra, and comparing their melting
points with those reported in the literature. In all of the
reactions, E‐isomers were produced predominantly as
evident from the 1H‐NMR spectrum of product. Turnover
numbers (TON) and turnover frequency (TOF) were also
calculated, and the results are depicted in Table 3.
The beginning of the reaction was thought to be based
upon an in situ reduction of CoII complexes to CoI or 0
species (A) using K3PO4. It is apparent from the previous
study[55] that the formation of the active CoI species
would advance the cross‐coupling reaction. In the follow-
ing step, the low valent CoI was added oxidatively into
the aryl halide to afford aryl cobalt intermediate (B). In
the next steps, olefin coordination with (B) and migratory
insertion lead to the formation of adducts (C) and (D),
respectively. Hydridocobalt (F) and a new olefin were
afforded following β‐hydride elimination. Finally, the
active CoI species (A) were regenerated by a reductive
elimination in the presence of K3PO4. To complete the
catalytic cycle for the Mizoroki–Heck cross‐coupling
3.3 | Plausible mechanism for the
MizorokiHeck reaction catalyzed by
MNP@PAMAM‐Co
According to previous reports,[52–54] and also depending
on our results, a possible explanation for the Mizoroki–
Heck cross‐coupling reactions is proposed in Scheme 3.
FIGURE 8 Recyclability in the Mizoroki–Heck reaction of
iodobenzene with methyl acrylate under the optimized reaction
conditions. TOF, turnover frequency; TON, turnover number
TABLE 4 Comparison of results for MNP@PAMAM‐Co with those for other catalysts in the coupling of iodobenzene with methyl acrylate
Entry
Catalyst
Solvent
Temperature (°C)
Time (hr)
Yield (%)
Ref.
[7]
1
Co–NHC@MWCNTsa
SiO2‐Fe (acac)
Co‐MS@MNPs/CSb
Co@MNPs/CS
Nano Co
PEG
80
130
80
5
85
85
88
53
85
73
56
98
87
97
90
90
[9]
2
PEG
1.5
[11]
[11]
[26]
[27]
[28]
[49]
[50]
[57]
[58]
3
PEG
1
4
PEG
80
1
5
NMP
140
130
150
130
100
100
120
100
16
6
Co hollow nanospheres
Co/Al2O3
NMP
16
7
NMP
24
8
Co‐B
water/DMF (5/5)
Toluene
DMF
12
9
Co‐IL@MWCNTsc
Ni (II)–DABCO@SiO2
Nano Co
3
10
11
12
3
NMP
8
MNP@PAMAM‐Co
water/DMF (1:1)
50 (min)
This work
aMulti‐walled carbon nanotubes supported N‐heterocyclic carbene–cobalt (ΙΙ).
bCobalt immobilized on MNPs‐chitosan functionalized with methyl salicylate (Co‐MS@MNPs/CS).
cCobalt nanoparticles supported on ionic liquid‐functionalized multi‐wall carbon nanotubes.

14 of 17
ARGHAN ET AL.
reaction, aerobic oxidation of the CoI species (A) to the
CoII complexes was carried out.[56]
times with ethanol and deionized water, and dried in an
oven at 60°C. Then the recovered catalyst was conducted
squarely to the subsequent cycle without any extra treat-
ment. The results showed that this dendritic polymer
magnetic catalyst can be reused five times with no signif-
icant loss of activity, and the desired products were
obtained in high yields. In order to confirm that the prop-
erties of MNP@PAMAM‐Co nanocomposite including
3.4 | Comparison of MNP@PAMAM‐Co
results with those obtained by other
workers for the Mizoroki–Heck reaction
Comparison of the catalytic activity of MNP@PAMAM‐
Co in the coupling of iodobenzene with methyl acrylate
(Table 4) with some of the reported heterogeneous (Co,
Ni and Fe) catalysts was performed to examine the effi-
ciency of the presented procedures. This catalytic system
can perform the reactions in significantly shorter reaction
time, lower temperature and greener media (moderate
temperature and safe metal and green media) in compar-
ison with those for other catalysts. In addition, the pres-
ent protocol has the advantages of using low weight
percentage of the catalyst, magnetic recyclability, no use
of additional instrument, such as microwave oven, and
high product yield. Therefore, as is obvious, the
MNP@PAMAM‐Co is a very advantageous and beneficial
catalyst in the Mizoroki–Heck cross‐coupling reaction.
3.5 | Recyclability of MNP@PAMAM‐Co
As an aspect of green chemistry and industrial applicabil-
ity, the reusability of the catalyst was tested under the
optimized conditions of respective MNP@PAMAM‐Co
catalyst for the Mizoroki–Heck reaction of iodobenzene
with methyl acrylate as the model reaction (Figure 8).
After the completion of each cycle, the catalyst separation
was carried with a permanent magnet, washed several
FIGURE 10 Field emission‐scanning electron microscopy (FE‐
SEM) images of the recovered MNP@PAMAM‐Co nanocomposite
FIGURE 9 Energy‐dispersive X‐ray
analysis (EDX) spectra of the recovered
MNP@PAMAM‐Co nanocomposite

ARGHAN ET AL.
15 of 17
FIGURE 11 Energy‐dispersive X‐ray spectroscopy (EDS) element mapping of MNP@PAMAM‐Co nanocomposite before use (a) and after
being reused five times (b)
chemical composition, morphology, shape, particle size,
density and spatial distributions of cobalt nanoparticles
were preserved in the reaction media even after five recy-
cle runs, EDX, FE‐SEM and EDS techniques have been
applied. According to Figure 9, it was found that the cat-
alyst retains its structure in comparison to the fresh one,
indicating its proper stability in the liquid reaction. On
the other hand, EDX analysis of the recovered catalyst
confirmed the existence of Co after five cycles, and Co‐
leaching was negligible. As seen in Figure 10, no consid-
erable change in the morphology of the recycled catalyst
was observed, which demonstrates that the catalytic
activity was maintained after five cycles. EDS element
mapping demonstrates that the nano‐sized particles are
uniformly dispersed in the recovered catalyst, and no
agglomeration is observed even after five consecutive
recycle runs (Figure 11).
occurred, indicating a negligible leaching of active species
during the reaction process. The results are consistent
with the heterogeneous nature of the catalyst,[45] and
establish the strong attachment of cobalt nanoparticles
to the MNP@PAMAM surface.
4 | CONCLUSIONS
In the present study, a method for homogenizing hetero-
geneous catalyst is reported. The procedure is based on
construction of PAMAM dendrons on the surface of
MNPs. The dendritic polymer is a spherical three‐
dimensional macromolecule that has multiple internal
and external functional groups. So, due to its structure,
it can act as a suitable host for a wide range of ions and
molecules. After the dendronizing process, we have pre-
pared Co NPs immobilized on this solid support that
make the catalyst recyclable and reusable, and minimize
the leaching of the particles. This auspicious catalyst
can be used for the Mizoroki–Heck cross‐coupling reac-
tions with various substrates. This new catalyst is proven
to be highly reactive and selective, and the required
energy and time for the Heck reaction is extremely mini-
mized in comparison with those of previously reported
cobalt‐catalyzed Heck cross‐coupling reactions as an
unavoidable trend in development of green chemistry. It
is noteworthy that demonstration of the combination of
cobalt and organic ligands is very rare, so this phosphine
and palladium‐free catalyst can be introduced as a high
effective and recyclable catalyst that can be reused more
than five times without loss of activity.
3.6 | Leaching
In general, when using a supported metal catalyst,
leaching of metal ions is a serious problem. Therefore,
the proof of heterogeneity of the catalyst is an essential
task. In this regard, the reaction between methyl acrylate
and iodobenzene was carried out under the optimized
conditions, the reaction was paused at half the reaction
time (25 min) and the MNP@PAMAM‐Co was separated
from the reaction mixture applying a magnet. Then, the
reaction was kept back under the same optimized condi-
tions to continue for 2 hr (as though without addition of
fresh catalyst). The reaction progress was checked by
TLC. It was found that no further coupling reaction

16 of 17
ARGHAN ET AL.
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