NiFe2O4@SiO2@ZrO2/SO42-/Cu/Co nanoparticles: A novel, efficient, magnetically recyclable and bimetallic catalyst for Pd-free Suzuki, Heck and C-N cross-coupling reactions in aqueous media

Article abstract of DOI:10.1039/d0nj06208a

The novel heterogeneous bimetallic nanoparticles of Cu-Co were synthesized based on magnetic nanoparticles, and the magnetic nanocatalyst was characterized by XRD, FE-SEM, EDX mapping, BET, TEM, HRTEM, FTIR, TGA, and VSM. This catalyst was successfully applied as a recyclable magnetically catalyst in Heck, Suzuki, and C-N cross-coupling reactions with various aryl halides (iodides, bromides, and chlorides as challengeable substrates), with olefins, phenylboronic acid, and amines, respectively. We considered the rise of synergetic effects from the different Lewis acid and Br?nsted acid sites present in the catalyst. The catalyst was synthesized with cheap, available materials and a simple synthesis method. The catalyst can be separated easily using an external magnet. It was recycled for more than ten runs without a sensible loss of its catalytic activity, and no significant leaching of the Cu and Co quantity was observed. The significant benefits of the method are high-level generality, simple operation, and there are no heavy metals and toxic solvents. This is a quick, easy, efficacious and environmentally friendly protocol, and no by-products are formed in the reaction. These features make it an appropriate practical alternative protocol. In comparison with recent works, the other advantage of this catalyst is the synthesis of a wide variety of C-C and C-N bond derivatives (more than 40 derivatives). The other significant advantage is the low temperature of the reaction and the use of the least possible amount of the catalyst (0.003 g). The efficiency was good to excellent and the catalyst selectivity has been high. We aspire that our study inspires more interest to design novel catalysts based on using low-cost metal ions (such as cobalt and copper) in the cross-coupling reactions. This journal is

Full text of DOI:10.1039/d0nj06208a

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NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co nanoparticles:
a novel, efficient, magnetically recyclable and
bimetallic catalyst for Pd-free Suzuki, Heck and
C–N cross-coupling reactions in aqueous media†
Cite this: New J. Chem., 2021,
45, 7741
Seyyedeh Ameneh Alavi G., * Mohammad Ali Nasseri,
Ali Allahresani and Mahdi HussainZadeh
Milad Kazemnejadi,
The novel heterogeneous bimetallic nanoparticles of Cu–Co were synthesized based on magnetic
nanoparticles, and the magnetic nanocatalyst was characterized by XRD, FE-SEM, EDX mapping, BET,
TEM, HRTEM, FTIR, TGA, and VSM. This catalyst was successfully applied as a recyclable magnetically
catalyst in Heck, Suzuki, and C–N cross-coupling reactions with various aryl halides (iodides, bromides,
and chlorides as challengeable substrates), with olefins, phenylboronic acid, and amines, respectively.
We considered the rise of synergetic effects from the different Lewis acid and Brønsted acid sites
present in the catalyst. The catalyst was synthesized with cheap, available materials and a simple
synthesis method. The catalyst can be separated easily using an external magnet. It was recycled for
more than ten runs without a sensible loss of its catalytic activity, and no significant leaching of the Cu
and Co quantity was observed. The significant benefits of the method are high-level generality, simple
operation, and there are no heavy metals and toxic solvents. This is a quick, easy, efficacious and
environmentally friendly protocol, and no by-products are formed in the reaction. These features make
it an appropriate practical alternative protocol. In comparison with recent works, the other advantage of
this catalyst is the synthesis of a wide variety of C–C and C–N bond derivatives (more than 40 derivatives).
The other significant advantage is the low temperature of the reaction and the use of the least possible
amount of the catalyst (0.003 g). The efficiency was good to excellent and the catalyst selectivity has been
high. We aspire that our study inspires more interest to design novel catalysts based on using low-cost
metal ions (such as cobalt and copper) in the cross-coupling reactions.
Received 22nd December 2020,
Accepted 30th March 2021
DOI: 10.1039/d0nj06208a
rsc.li/njc
Pd,6 Ru,7 Au–Pd,8 Au–Ag–Pd,9 and Pd–Ni.10 The metals (such as
palladium) are not recommended, because Pd cannot be indus-
1. Introduction
The cross-coupling reaction is one of the basic reactions in the trialized exclusively due to its high cost and other important
pharmaceutical industry and organic synthesis. The Heck and factors, such as scarce storage capacities. The toxicity and high
Suzuki reactions are the most convenient and efficient mechanisms cost of Pd catalysts restrict their applications.11 Recent studies
to form C–C bonds.1 These reactions are used to synthesize suggest that metal cobalt has a unique reactivity.12,13 The metal
pharmaceutical, natural products, materials science, biological, cobalt changes its oxidation states and easily undertakes radical
medicinal, supramolecular chemistry, coordination chemistry, reactions.
polymer synthesis, complex molecules, and are also used in
Hence, it is not surprising that the cobalt metal is also widely
catalysis.2,3 Typically, Heck and Suzuki reactions are catalyzed involved in catalysis. There are many applications for metal
by homogeneous catalysts, and this should be performed in cobalt, such as cross-couplings,13 carbonylation reactions,14
high temperatures and toxic solvents.4 The synthesis of efficient hydrogenations,15 and functionalizations.16
green catalysts has received more recent attention. These reactions
Likewise, metal cobalt and copper catalysts have attracted
are usually catalyzed by noble and transition metals, such as Ni,5 the attention of researchers because of their applications. Copper
catalysts have major advantages both economically and environ-
mentally. They are available, cheap, and environment-friendly.3
In comparison with other transition metal catalytic systems,
there have been numerous investigations for Cu and Co-catalyzed
cross-coupling reactions, such as Heck and Suzuki. The latest
Department of Chemistry, Faculty of Science, University of Birjand,
P. O. Box 97175-615, Birjand, Iran. E-mail: saalavi.g64@gmail.com
† Electronic supplementary information (ESI) available: 1H-NMR and 13C-NMR
spectra of coupling products. See DOI: 10.1039/d0nj06208a
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examples consist of Fe3O4@SiO2@PrNCu,17 MNP@PAMAM-Co,12 Another surprising thing is that due to the high aspect ratio,
Cu-NH2-GO,18 and Cu@MCOP19 as catalysts for these reactions. MNPs can strongly enhance the catalytic activity of a catalyst. In
Bimetallic catalysis is an awesome way to perform chemical this article, NiFe2O4 NPs were used to support protocols. These
reactions that cannot be performed using single metal catalysis. NPs are popular and one of the most applicable nanomaterials,
The bimetallic catalyst procedure is different from single metal which consist of nickel and iron nanoparticles. They are widely
catalysts because both metals use special cycles that refer to used for various reactions due to their oxidation resistance,
transmetalation.20 It is obvious that constructing a core–shell high thermal stability, high impregnation magnetization, low
structure with another metal could change the electronic char- cost, flexibility in design, and low toxicity.13 According to the
acteristics of the metal catalyst. This is mainly due to the previous result of our research team’s publication, which consisted
relevance between the two separate metals. In addition to the of the Sonogashira3 coupling reaction, the synthesis of heterocyclic
relevance between metals, it provides more active sites for the compounds (including xanthene11 and quinolines32) from various
catalysis mechanism in bimetallic nanoparticles.21 Therefore, it starting materials and wide range of catalytic properties of the
has a great effect on the properties of the catalyst, especially on the selected catalyst and its excellent performance in coupling
performance of the catalyst. Consequently, bimetallic catalysts reactions, we decided to extend the catalyst and investigate its
demonstrate a significant enhancement in catalytic activity in application in other coupling reactions, such as Heck, Suzuki
comparison with monometallic catalysts.22 On the other hand, and also C–N coupling in a heterogeneous and bimetallic
there is an incredible advantage for heterogeneous bimetallic catalytic system due to the importance of using two metals in
catalysts, and it is tuning the catalytic activity. By controlling a system. The results have already been published, and the
the dispersity, chemical composition, size, and shape of the present study indicates the special properties of this catalyst
metal nanoparticles, you can synthesize your choice based on and its extraordinary effectiveness in organic syntheses. In the
the catalytic activity.23
present work, bimetallic nanoparticles were supported on magnetic
Additionally, in this method, aryl chlorides were used as NiFe2O4 NPs, and this catalyst was used for green Heck and Suzuki–
substrates. Aryl chlorides have advantages compared to bromides Miyaura coupling reactions under moderate conditions. This
and iodides, such as availability, low cost, and they are more bimetallic system awarded higher activity compared to its
favourable and convenient in the Suzuki–Miyaura reactions.24 monometallic counterparts. Moreover, the effects of the Cu/Co
Another incredible novelty is that these reactions led to the product ratio on the catalytic activity were investigated. After the recovery
with no palladium. The recent strategies are mainly related to the tests, it was shown that the catalyst did not significantly lose
extensive use of organic solvents in organic transformations. One catalytic activity.
may expect that the organic solvents have undeniable destructive
effects on human health and the environment. The cross-coupling
reactions in aqueous environments is a difficult challenge that has
2. Experimental
2.1. Instrumentation and materials
attracted the attention of the synthetic community.2 Thus, these
reactions have restrictions, such as the catalytic system, mass
transfer, and especially high temperature.25 However, researchers All chemicals were bought from Merck, Sigma, and Fluka chemical
are now trying to explore new low-temperature coupling strategies in companies. There was no need for further purification. The
aqueous systems.
chemical solvents should be dried and distilled under a noble
One of the most applied solid acids with substantial catalytic atmosphere before use. The progress of the reactions was mon-
activity is zirconium. It is used extensively as one of the best itored by thin-layer chromatography (TLC). The spectrum of FTIR
acid catalysts in many industries, such as petrochemical industries was recorded by a JASCO FT/IR 4600 spectrophotometer with a KBr
and oil refineries. This acid catalyst is used for processes like pellet. The NMR analyses (1H and 13C) were conducted by a Bruker
alkylation, cracking, esterification, and isomerization. Additionally, Avance DPX-250 spectrometer, and CDCl3 and DMSO-d6 were used
the activity of zirconium can be enhanced by sulfates.26,27 as a solvent. The TMS was an internal standard. The images of
Consequently, sulfated zirconium oxide (ZrO2/SO42À) can be scanning electron microscopy (FE-SEM) were taken with a TESCAN
produced with a great promotion in the catalytic activity. The MIRA3 apparatus. The mapping with transmission electron micro-
sulfated zirconia has incredible features, such as outstanding scopy (TEM) was done with a Philips EM208 microscope, and the
catalytic activities, high thermal stability, high acidity, durability, operation was conducted at 100 kV. The samples’ magnetic
and stability in various organic solvents. Under harsh reaction behavior was determined at room temperature with Lake Shore
conditions, these characteristics rendered the sulfated zirconia as Cryotronics 7407 (VSM). EDX spectra were recorded by a field
a suitable choice for more changes. It can also be industrialized emission scanning electron microscope (FE-SEM, JEOL 7600F),
and the catalytic aspects can be modified.28 The catalytic activity equipped with an energy dispersion of X-ray spectrometer from
has been examined in various organic reactions, for example, Oxford instruments. The samples (TGA) have been captured with a
towards multicomponent reactions, benzylation reactions, and NETZSCH STA 409 PC/PG in N2 atmosphere in the temperature
synthesis of a-aminophosphonates (Scheme 1).29,30
range of 25–850 1C, and with a heating rate of 10 1C minÀ1. The
On the other hand, this fantastic sulfated zirconia can be perusal of the magnetic properties of the samples was performed
magnetized by magnetic nanoparticles (MNPs). Magnetization at room temperature by the Lake Shore Cryotronics 7407 vibrating
via MNPs makes these supports magnetically recoverable. sample magnetometer (VSM). Finally, ICP analysis was carried out
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Scheme 1 The catalytic activity of metal incorporated into sulfated zirconium oxide for C–C and C–N cross-coupling reactions.
by VARIAN VISTA-PRO CCD simultaneous ICP-OES instrument. hydrothermal method. The final product was washed several
The surface area, pore diameter and pore volume of the nano- times with DI water and ethanol. At the end, it was dried at
particles were determined by Belsorp mini II instrument, and high 60 1C in a vacuum oven.
resolution transmission electron microscopy (HRTEM) studies
NiFe2O4@SiO2 MNPs were prepared by the sol–gel method.
were performed on a FEI Tecnai G2 F20 Super Twin TEM with a NiFe2O4 (2.0 g, 8.5 mmol) was dispersed in ethanol (25 mL) in
field emission gun at 200 kV.
an ultrasonic bath for 2 h at 60 1C. Then, the aqueous solution
of ammonia (10 mL) was added to the mixture and was stirred
at room temperature for at least 30 min. Subsequently, tetra
2.2. Preparation of NiFe2O4@SiO2 MNPs
In a general process, 2.13 g Fe(NO3)3Á9H2O and 0.8 g Ni(NO3)2Á ethoxy orthosilicate (TEOS, 1.0 mL) was added to the stirring
6H2O were dissolved in 150 mL DI water, and were stirred for at mixture. The NiFe2O4@SiO2 MNPs were separated from the
least 10 min. Eventually, the aqueous solution of NH3 was solution by a magnetic field, washed with DI water (3 Â 5 mL)
added to the solution, and this process was ended at pH = and EtOH (2 Â 5 mL), and then dried in a vacuum oven for at
11. The obtained solution was stirred for 15 min, and then least 1 day. The final product NiFe2O4@SiO2 MNPs were
was treated at 180 1C for 12 h under static conditions by the calcined at 400 1C for 4 h (at a heating rate of 20 1C minÀ1).31
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2.3. Preparation of NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co NPs
by a magnetic field, washed with water, and was dried in a vacuum
oven for 12 h. The full path to prepare the catalyst is shown
in Scheme 2.
The preparation proceeded according to the prepared sulfated
zirconium oxide protocol that was previously reported, except
with a modification.3 First of all, ZrCl4 (2.3 g, 10 mmol) was
dissolved as a precursor in 10 mL water. Thus, an ammonia
aqueous solution was added (10 mL, 1 N) drop by drop for
30 min until the pH was adjusted to 11. The provided suspended
solution was aged for 24 h at room temperature. Then, the pre-
cipitation was washed with water using a centrifuge (5 Â 10 mL).
This process was ended after neutralization (pH = 7). The gained
Zr(OH)4 was dried at 100 1C for at least 1 day. The separated yield of
Zr(OH)4 was calculated to be 96% (1.5 g). Eventually, Zr(OH)4 (1.0 g)
was plunged with a mixing ratio of 1 : 3, Zr : S in (NH4)2SO4 solution
(2.5 g in 50 mL distilled water). The obtained solution was dried at
100 1C for 24 h. After drying, the precipitate was calcined at 650 1C
for 3 h, and the rate of temperature was 10 1C minÀ1. The resulting
2.4. General procedure for the Suzuki–Miyaura and
Heck–Mizoroki C–C coupling reactions using
NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co nanoparticles
A mixture of alkene/phenylboronic acid (1.5 mmol), aryl halide
(1.0 mmol), NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co magnetic nano-
catalyst (0.003 g, (0.005 mol% Cu, 0.01 mol% Co)), K3PO4 (1.0 mmol)
and water (1.0 mL) was stirred in an oil tub at 60 1C. The progress of
the reaction was observed by TLC. According to the completion of
the reaction, the mixture was extracted with 10 mL of ethyl acetate
and the catalyst was removed magnetically. The merged organic
layers were dried with Na2SO4. Then, under reduced pressure
that was provided by rotary evaporator, the solvent was
removed. The coupling pure favourable product was gained
from the crude product by flash chromatography.
2À
ZrO2/SO4 (1.0 g) was saturated by Cu(OAc)2 solution (0.05 g
in 50 mL distilled water) to obtain a Cu content of 5 wt%.
This process was followed by drying at 100 1C for 12 h, and
calcination at 400 1C for 3 h under air atmosphere (at a heating
rate of 10 1C minÀ1). The final obtained ZrO2/SO42À/Cu was
washed with water (3 Â 10 mL), and then dried in an oven
(50 1C) for 8 h.32 The resultant ZrO2/SO42À/CU (1.0 g) was
impregnated in Co(OAc)2 solution (0.05 g in 50 mL distilled
water) in order to obtain a Co content of 5 wt%. The mixture
was dried at 100 1C for 12 h, and subsequently calcinated at 400 1C
for 3 h under air atmosphere (at a heating rate of 10 1C minÀ1). The
obtained ZrO2/SO42À/Cu/Co was washed with water (3 Â 10 mL),
and then dried in the vacuum oven (50 1C) for 8 h.
3. Results and discussion
3.1. Catalyst characterization
Different instruments conducted the characterization of synthe-
2À
sized catalyst. FTIR spectra of Zr(OH)4, ZrO2/SO42À, ZrO2/SO4
/
Cu, ZrO2/SO42À/Co, ZrO2/SO42À/Cu/Co, NiFe2O4, NiFe2O4@SiO2,
and NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co are shown in Fig. 1. A
wide and settled peak at 3403 cmÀ1 relating to the O–H stretch
vibrations confirms the zirconium chloride hydration by using
ammonia. Also, the 640–750 cmÀ1 absorptions relating to Zr–O–Zr
The synthesized ZrO2/SO42À/Cu/Co NPs were reinforced by
NiFe2O4@SiO2 magnetic nanoparticles. A mix of NiFe2O4@SiO2
NPs (0.2 g) was dispersed in an ultrasonic bath in an aqueous
solution of ethanol with a mixing ratio (15 mL, 1 : 3 v/v) for
10 min at room temperature. Another dispersed ethanolic
solution of ZrO2/SO42À/Cu/Co (0.4 g) was added to the mixture,
and was dispersed for more than 10 min at room temperature.
NaOH 10% w/w (15 mL) should be added drop by drop to the
solution for 30 min during dispersion.
2À
can be seen at Fig. 1a. The FTIR spectra of ZrO2/SO4 illustrates
the particular peaks at 1143, 1044, and 994 cmÀ1 (shoulder), which
correspond to the symmetric and asymmetric stretch vibrations of
SQO or S–O (Fig. 1b).33 These vibrations introduce bidentate
coordinated sulfate ions. Several peaks at 467–747 cmÀ1 are
assigned to the Zr–O–Zr asymmetric stretch vibrations.34 Also, a
wide peak at 3421 cmÀ1 and a moderate peak at 1636 cmÀ1 were
appointed to the O–H stretching and bending vibrations of
the coordinated or adsorbed water with the sulfate groups,
respectively. A sharp peak near 500 cmÀ1 was connected with
the Cu–O stretching vibration. This illustrates that the
Finally, the solution was stirred for at least 1 day. The
resulting NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co NPs were separated
Scheme 2 Synthesis of the NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co nanoparticles.
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2À
Fig. 2 XRD pattern of (a) ZrO2/SO42, (b) ZrO2/SO42À/Cu, (c) ZrO2/SO4
Cu/Co, (d) NiFe2O4, (e) NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co.
/
Fig. 1 FTIR spectra of (a) Zr(OH)4, (b) ZrO2/SO42, (c) ZrO2/SO42À/Cu, (d)
ZrO2/SO42À/Co, (e) ZrO2/SO42À/Cu/Co, (f) NiFe2O4, (g) NiFe2O4@SiO2, (h)
NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co.
the monoclinic structure of zirconia. It is a valuable notice that the
existence of sulfated groups did not lead to the phase change of
compilation of Cu ions took place through the oxygen atoms of zirconia. This can be related to the strong interaction between the
the sulfate ions in ZrO2/SO42À/Cu, and eventually accepted that sulfate ions and zirconia. In addition, the presence of strong peaks
2À
the Cu cation was coordinated successfully in the catalyst in ZrO2/SO4 proves the trigonal structure, and it should be
framework (Fig. 1c).32 The stretching vibrations relating to added that the saturation of the sulfate ions strongly affected
Zr–O–Zr are hidden because of strong absorption. A sharp peak the phase modification of zirconia from thermodynamically more
at 566 cmÀ1 was put down to the Co–O stretching vibration, and stable monoclinic to the metastable tetragonal phase. Incorpora-
it offers that the insertion of the Co ions took place through the tion of Cu into the structure of ZrO2/SO42À causes a tiny shift in the
oxygen atoms of the sulfate ions in ZrO2/SO42À/Co. This also position of the peaks relating to the crystal structure of sulfated
affirms the successful coordination of the Co cations on the zirconia at 2y = 31.71, 35.61, 38.81, 48.41, 58.21, 61.81, 66.01 and
catalyst framework (Fig. 1d).35
68.081. Thus, the peaks at 2y = 35.61, 38.81, 48.41, 66.01, and 68.081
In Fig. 1e, the presence of two strong peaks at 502 and have great matching with the indices (002), (111), (202), (311), and
602 cmÀ1 indicates the coordination of both copper and cobalt (113), respectively, which corresponds to the thermal prepared
metals. In the NiFe2O4 spectra of FTIR, two adsorption peaks at structure of the CuO powder (Fig. 2b).28,29,32 Moreover, the sulfated
1629 and 3374 cmÀ1 are attributed to the H–O–H bending and zirconium oxide peaks were situated in the much lower intensities
free O–H stretching vibrations, respectively. This is due to the near the baseline (Fig. 2b). The addition of Co into the structure of
water molecule adsorption on the surface of the NiFe2O4 NPs ZrO2/SO42À leads to a new XRD pattern. These results suggest that
with a great aspect proportion.36 There are two kinds of the cobalt ions were successfully incorporated into the ZrO2/SO4
2À
absorption bands at 476 and 596 cmÀ1 that were attributed to framework, and they took place through the sulfate ions according
the Ni–O and Fe–O stretching vibrations (Fig. 1f).36 A sharp to the previous article.35 In addition, new peaks appeared at
absorption at 1084 cmÀ1 relating to the Si–O vibrations accepts
the coating of NiFe2O4 NPs by silica shell (Fig. 1g).31 The
existence of vibrational bands near 481, 601, 1001 cmÀ1 showed
Fe–O, (Cu–O and Co–O broad peak), and Si–O–Si respectively,
and demonstrated that ZrO2/SO42À/Cu/Co was supported on
NiFe2O4@SiO2 (Fig. 1h). Moreover, there were multiple medium
bands in the 1261–1624 cmÀ1 region connected with the ZrO2/
SO4 stretch vibrations (Fig. 1f).3
2À
The XRD patterns of ZrO2/SO42À, ZrO2/SO42À/Cu, ZrO2/
SO42À/Cu/Co, NiFe2O4, and NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co
2À
are shown in Fig. 2. ZrO2/SO4 demonstrates three specific
peaks with strong intensities at 2y = 30.41, 50.31, and 60.21,
2À
which indicates the tetragonal structure of ZrO2/SO4 with
great crystallinity (JCPDS 17-0923) (Fig. 2a).37 Indeed, a mixture
of tetragonal and monoclinic phases can be seen in the spectra
(Fig. 2a), which affirms the reported ZrO2/SO42À crystal structure.38
The low intensity peaks at 2y = 24.11 and 28.31 were attributed to
Fig. 3 Magnetic behavior of (a) NiFe2O4 and (b) NiFe2O4@SiO2@ZrO2/
SO42À/Cu/Co.
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Fig. 4 EDX spectra of (a) ZrO2/SO42À/Cu/Co, (b) NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co.
Fig. 5 TGA-DTG curves of (a) ZrO2/SO42À/Cu/Co, (b) NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co.
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2y = 38.31, 43.61, 62.091, 75.51, and 78.11. These are in agreement
with indices (111), (200), (220), (311), and (222), respectively, in
accordance with the thermally prepared CoO powder structure.
2À
The addition of ionic metals into the ZrO2/SO4 matrix changes
the XRD pattern of the matrix, and accepts the incorporation of the
metal. The results show a proper dispersion of cobalt ions in the
matrix of ZrO2/SO42À. The results offer a Co-O bond formation
between the sulfate groups on ZrO2/SO42À/Co and Co ions.35
The results demonstrate a Cu–O and Co–O bonding among the
sulfated groups on ZrO2/SO42À/Cu/Co (Fig. 2c), and the Cu and Co
ions are quite in accordance with its FTIR spectrum.
In the NiFe2O4 XRD pattern (Fig. 2d), the most severe peak
was related to the (311) plane of the NiFe2O4 nanoparticles in
2y = 35.621.39 Diffraction peaks were considered with 2y values
of 30.621, 36.051, 37.721, 43.721, 54.121, 57.721, 63.321, which is
compatible with the crystal planes (220), (311), (222), (400),
(422), (511), (440) of the crystalline NiFe2O4, respectively, and
the broad peak in the 10–301 region is related to NiFe2O4
covered by SiO2.40
Fig. 2e shows the crystal structure of the catalyst, NiFe2O4@
SiO2@ZrO2/SO42À/Cu/Co supported by ZrO2/SO42À on the NiFe2O4@
SiO2 surface, resulting in the peaks with lower intensities
related to the NiFe2O4 crystal structure. The results accept the
functionalization of NiFe2O4 and did not lead to a changing
phase. Furthermore, the sharp peak at 2y = 38.21 illustrates
the coordination of Cu and Co in the catalyst. The peaks at
Fig. 7 (a) N2 gas adsorption and desorption isotherms, and (b) the
diameter distribution of the pores of NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co.
2y = 60.01, 50.31, 30.21, and 50.71 might be appointed with the
2À
ZrO2/SO4
crystal structure. The NiFe2O4 functionalization
with zirconium groups occurred successfully. The presence of
Fig. 6 TGA-DTG curves of (a) ZrO2/SO42À/Cu/Co, (b) NiFe2O4@SiO2@
ZrO2/SO42À/Cu/Co.
Fig. 8 (a) TEM and (b) FE-SEM images of ZrO2/SO42À/Cu/Co.
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2À
peaks related to the crystalline structure of NiFe2O4 confirms Cu, Ni, Si, S, Fe, Zr and O for the NiFe2O4@SiO2@ZrO2/SO4
/
the change in the XRD pattern from the crystalline state to the Cu/Co sample. The results ensure the presence of all of these
amorphous state of NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co.
elements in the sample, which are evenly distributed in the
The magnetic properties of NiFe2O4 and NiFe2O4@SiO2@ study section.
ZrO2/SO42À/Cu/Co were calculated by VSM analysis (Fig. 3). As
Accordingly, the successful association of Zr at the surface of
shown in Fig. 3, these materials exhibited a superparamagnetic NiFe2O4@SiO2 was also confirmed by EDS map analysis.
treatment, and no hysteresis loop was found in their spectra.
The resultant NiFe2O4 saturation of magnetization was about can be seen in Fig. 6. The thermal stability of ZrO2/SO42À/Cu/Co
57.1 emu gÀ1 (Fig. 3a).41
is considerable, and 7.5% weight loss at a temperature range of
The thermal treatment of ZrO2/SO42À/Cu/Co and the catalyst
The magnetization was largely reduced to 11.5 emu gÀ1 for 25–1000 1C was observed (Fig. 6a). This degradation happened in a
NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co, which strongly affirms the four-stage process. The first and second decreases could be
surface functionalization (Fig. 3b). Thus, there is a sufficient appointed to the dehydration of the water adsorption from the
magnetization for the complete separation of the nanoparticles surface of the catalyst (0.26% weight loss at 210 1C), and the
from the mixture. The figures show the separation of NiFe2O4@ evaporation of the trapped water in the network of the catalyst by
SiO2@ZrO2/SO42À/Cu/Co from the mixture in 2 minutes with an sulfate groups (1.19% weight loss at 350 1C), respectively. The third
external magnet after the dispersion.
weight loss was situated at the temperature range of 530–665 1C,
The preparation of ZrO2/SO42À/Cu/Co was accepted with and it is related to the oxidation of copper and cobalt, and the
the presence of Cu, Co, Zr, O, and S elements, and the detection formation of CuO and Co–O. The final weight loss appeared at the
was done by EDX analysis (Fig. 4a). Furthermore, the existence temperature range of 680–860 1C. This is because of sulfate
of the elements in the catalyst was checked and certified by decomposition and the structural OH-groups. In the presence of
EDX analysis. As shown in Fig. 4b, the presence of Zr, Cu, Co, O, ZrO2/SO42À/Cu/Co on NiFe2O4@SiO2, the thermal stability of the
S, Fe, Si, and Ni elements in the catalyst was confirmed.
catalyst was maintained and 25.5% weight loss up to 1000 1C was
In order to better identify the sample composition, elemental observed. The first weight loss with a mild slope proceeded to
mapping analysis was performed. Fig. 5 shows the energy- 747 1C, and this is because of water adsorption in the catalyst
dispersive X-ray spectroscopy (EDX) mapping analysis of Co, crystal structure. The last weight loss was assigned to the
Fig. 9 (a) and (b) FE-SEM and (c) and (d) TEM images of NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co.
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Fig. 10 HRTEM images of NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co.
decomposition of Cu and Co, and was incorporated with sulfate transition metal inclusions (Fig. 8b and 9a, b). In comparison
groups. This weight loss is around 19% (Fig. 6b). with their TEM images (Fig. 8a and 9c, d), this compression is
The adsorption and desorption isotherms of nitrogen gas of more obviously shown. Based on Fig. 8b and 9a, b, the size of the
2À
the synthetic sample are shown in Fig. 7a. According to the particles has an average range of 12 nm and 42 nm for ZrO2/SO4
IUPAC classification, the adsorption and desorption isotherms Cu/Co and NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co, respectively.
/
of nitrogen gas is type IV, which is the characterization of
mesoporous materials. It also has an H3 hysteresis ring, which morphology and structure of the NiFe2O4@SiO2@ZrO2/SO4
HRTEM characterizations were measured to obtain a closer
2À
/
is the characteristic of plate-shaped porous materials. The specific Cu/Co composites. As shown in Fig. 10, the crystal planes of the
surface area of the synthetic sample was measured using the BET different used metals in the catalyst rising from Cu and Co
method with an average surface area of 50.60 m2 gÀ1. The size moieties incorporated in the ZrO2/SO4 framework have been
2À
distribution of the sample cavities through the BJH desorption distinguished by two different crystal structures. These two
curve is shown in Fig. 7b. The highest pore volume is 0.24 cm3 gÀ1
,
phases are clearly shown with two different crystal structures
in Fig. 10. Also, the images were in agreement with the TEM
in which the pore diameter is 2.3 nm.42,43
The morphology and shape of ZrO2/SO42À/Cu/Co and and SEM images in terms of the average diameter, shape, and
NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co were extrapolated by SEM morphology.44,45
and TEM techniques (Fig. 8 and 9). The SEM images of ZrO2/
SO42À/Cu/Co and NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co demon-
3.2. Optimization of the reaction parameters
strated an irregular amorphous morphology shape that arises
from the expected accumulation in activated ZrO2/SO4 with
In the coupling reaction of C–C, the determination of the
optimized criteria was done by iodobenzene and styrene as a
2À
2À
Table 1 Optimization of the reaction parameters for the reaction of styrene and iodobenzene catalyzed by NiFe2O4@SiO2@ZrO2/SO4
Entry Solvent Base Catalyst (g) T. (1C) t. (min) Yield (%) Entry Solvent Base
Catalyst (g) T. (1C) t. (min) Yield (%)
1
2
3
4
5
6
7
8
EtOH
CH3CN
THF
CH2Cl2
Toluene K3PO4 0.003
CHCl3
DMSO
MeOH
Dioxane K3PO4 0.003
DMF
-
K3PO4 0.003
K3PO4 0.003
K3PO4 0.003
K3PO4 0.003
60
60
60
60
60
60
60
60
60
60
60
60
60
60
50
50
50
50
50
50
50
50
50
50
50
50
50
50
88
62
48
62
77
33
90
89
53
70
trace
93
92
67
15
16
17
18
19
20
21
22
23
24
25
26
27
28
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
NaOH
NaOAC
LiHMDS 0.003
Et3N
HMTA
t-BuOK
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
0.003
0.003
60
60
60
60
60
60
60
60
60
60
R.T.
80
Ref.
R.T.
50
50
50
50
50
50
50
50
50
50
50
50
50
240
88
89
60
77
58
90
67
88
94
86
70
96
90
78
0.003
0.003
0.001
0.001
0.004
0.006
0.008
0.003
0.003
0.003
0.003
K3PO4 0.003
K3PO4 0.003
K3PO4 0.003
9
10
11
12
13
14
K3PO4 0.003
K3PO4 0.003
K3PO4 0.003
H2O
H2O
H2O
KOH
0.003
K2CO3 0.003
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Table 2 Mizoroki–Heck and Suzuki cross-coupling reaction catalyzed by the NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co NPsa,b
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Table 2 (continued)
a
The reaction conditions: Aryl halide (1.0 mmol), alkene/phenylboronic acid (1.5 mmol), K3PO4 (1.0 mmol), H2O (1 mL), catalyst (0.003 g,
b
(0.005 mol% Cu, 0.01 mol% Co)), 60 1C. Isolated yields were reported.
model reaction. The effects of the reaction parameters, such as have investigated carefully. The results can be seen in Table 1.
type of solvent, temperature, type of base, and catalyst amount, As shown in the results in polar protic solvents, such as EtOH,
Table 3 C–N cross-coupling reaction of phenylboronic acid with various amines catalyzed by the NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co NPsa,b
a
The reaction conditions: phenylboronic acid (1.0 mmol), N-heterocyclic compound (1.5 mmol), K3PO4 (1.0 mmol), H2O (1 mL), catalyst (0.003 g,
b
(0.005 mol% Cu, 0.01 mol% Co)), 60 1C. Isolated yields were reported.
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MeOH, and water (Table 1, inputs 1, 8, and 12), the reaction was evaluated. The results presented in Table 2 show that the NiFe2O4@
carried out at a constant time with a higher efficiency, which is SiO2@ZrO2/SO42À/Cu/Co catalyst has an impressive efficiency in the
in complete agreement with the structure of the catalyst con- synthesis of various diaryl derivatives.
taining the hydrophilic groups. The other solvents showed low
The clear results show that the reaction efficiency of styrene
to medium yields. Water was selected as the best solvent, and with aryl iodides, including lethal electron groups such as NO2,
90% efficiency was recorded in 50 minutes at 60 1C. Then, the CN, and electron donor groups such as CH3, and NH2, are
effect of various bases was investigated over the model reaction desirable (14, 16, 18, 29). The reaction efficiency is comparable
in the presence of 0.003 g of NiFe2O4@SiO2@ZrO2/SO42À/Cu/ with the lethal electron group and the donor electron group aryl
Co, and the effective temperature and varying amounts of the ions, and the efficiency was higher and the time was shorter for
catalyst in optimal conditions were studied. The highest efficiency the lethal electron group aryl ions (comparison of compounds
was obtained in 50 minutes in the presence of water solvent and 16 and 29, and others). The coupling reaction of the aryl iodides
base K3PO4 at 60 1C and 0.003 g of catalyst. (Table 1, entry 12).
and aryl bromides was performed in a short time with appropriate
The Heck carbon–carbon coupling reaction was investigated efficiency, while the reaction of aryl chlorides in the longer
in the presence of various aryl halides, including electron donor reaction time produces a product with desired efficiency, which
and electron acceptor groups. After various studies and reaction can be due to less reactivity, the C–Cl bond and the difference in
optimization, in order to evaluate the range of reaction efficiency, the halogen cracking ability (I 4 Br 4 Cl) (comparison of
its application in several different aryl halide derivatives was compounds 18a and 18c, and others).
Table 4 C–C cross-coupling reaction of phenylboronic acid with (bromoethynyl)benzene catalyzed by the NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co NPsa,b
a
The reaction conditions: phenylboronic acid (1.0 mmol), (bromoethynyl)benzene (1.5 mmol), K3PO4 (1.0 mmol), H2O (1 mL), catalyst (0.003 g,
b
(0.005 mol% Cu, 0.01 mol% Co)), 60 1C. Isolated yields were reported.
Table 5 Control experiments for the reaction of styrene and phenylboronic acid with iodobenzene catalyzed by NiFe2O4@SiO2/ZrO2/SO42À/Cu/Co
Yield (%)
Entry
Cat. (0.003 g)
Time (h)
10aa
34ab
1
2
3
4
5
6
7
8
No Catalyst
ZrCl4
24
24
24
24
24
24
24
24
1
1
1
1
0.8
No reaction
No reaction
No reaction
No reaction
No reaction
No reaction
21
15
53
71
68
81
93
No reaction
No reaction
No reaction
No reaction
No reaction
No reaction
26
19
55
78
72
83
94
(NH4)2SO4
2À
ZrO2/SO4
Cu(OAC)2
Co(OAC)2
NiFe2O4
NiFe2O4@SiO2
9
NiFe2O4@SiO2/SO42À/Cu/Co
2À
10
11
12
13
ZrO2/SO42À/Cu
ZrO2/SO4 /Co
ZrO2/SO42À/Cu/Co
NiFe2O4@SiO2/ZrO2/SO42À/Cu/Co
a
b
Reaction conditions: iodobenzene (1.0 mmol), styrene (1.5 mmol), Cat. (0.003 g), H2O (1 mL), 60 1C. Reaction conditions: iodobenzene
(1.0 mmol), phenylboronic acid (1.5 mmol), Cat. (0.003 g), H2O (1 mL), 60 1C.
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In order to expand the work and evaluate the high efficiency 3.3. Control experimental
Paper
of the NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co catalyst, the carbon–
carbon coupling reaction with various substrates, including
butyl acrylate and methyl acrylate, was investigated. The results
are shown in Table 2, which showed excellent results.
Due to the excellent results obtained from the Heck coupling
reaction and the high performance of the NiFe2O4@SiO2@ZrO2/
SO42À/Cu/Co catalyst, the optimal conditions obtained for the
Heck reaction, the Suzuki coupling reaction, and the carbon-
nitrogen coupling were also investigated. The results are shown
in Tables 2 and 3. A specific type of carbon–carbon coupling was
obtained by reacting (bromoethynyl)benzene with boronic acid
under optimal conditions (Section 3-2) and in the presence of
nitrogen gas, which leads to the synthesis of 1,2-diphenylethyne
compounds to the range of activities that the NiFe2O4@SiO2@
ZrO2/SO42À/Cu/Co catalyst was also added (compounds 53, 54,
and 55 (Table 4)).
In order to reassure the performance of the specific catalytic
activity of the catalyst, the reaction was carried out in the absence
of catalysts and the individual components of the catalyst for the
synthesis of 1,2-diphenylethene (10a) (Table 5). The results showed
that all parts of the catalyst could work together effectively
(synergistic effect). In the absence of a catalyst and in the presence
of compounds ZrCl4, (NH4)2SO4, ZrO2/SO42À, Cu(OAC)2, Co(OAC)2,
no product was observed over 24 hours. The NiFe2O4 and
NiFe2O4@SiO2 efficiencies were about 21% and 15%, respectively.
By coordinating copper or cobalt ZrO2/SO42À/Cu, ZrO2/SO42À/Co,
the efficiency was increased to 71% and 68%, respectively.
In the bimetallic system, the efficiency was increased to 81%,
which represents an increase in the catalytic activity. In entry 9,
it can be seen that despite all the parts of the catalyst except
zirconium, high efficiency has not been achieved, which shows
the significant effect of zirconium. Finally, by connecting
Table 6 Comparison of the catalytic activity of NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co NPs with literature examples for 10b, 36c, 22a, 50a, 25b
Run
Catalyst
Condition
Time (h) Yield (%) Ref.
1
2
3
4
5
6
7
8
9
10b Fe3O4@OA-Pd (0.38 mol%)
MNPs-Mel-Pd (20 mg)
DMF/t-BuOK/120 1C
DMF/K2CO3/100 1C
NMPa/K2CO3/120 1C
CH3CN/K2CO3/Reflux
DMF/K2CO3/110 1C
H2O/[ADPPy][OH]b/80 1C
7
8
5
3
4
2
20
10
24
1
96
93
70
92
91
98
65
78
70
92
46
47
6
48
49
50
51
52
HMS-OPPh2-Pd (0.5 mol%)
Fe3O4@O2PO2(CH2)2NH2 (10 mg)
Fe3O4@SiO2/Schiff base/Pd(II) (0.3 mol%)
Pd(OAc)2 (2 mol%)
palladium(II)-exchanged zeolite-Y (EPdL1-Y) (0.7 mol%) DMF/Na2CO3/140 1C
Pd/MOP-I (0.0174 mol%)
CuI (8.0 mol%)
DMF/n-dodecane/Et3N/110 1C
DMSN/K3PO4/110 1C
H2O/K3PO4/60 8C
53
10
NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co
(0.005 mol% Cu, 0.01 mol% Co)
36c Fe3O4/P(GMA-AA-MMA)-Schiff base-Pd (0.1 mol%)
CL-Sc-Pd (0.005 mol%)
Present study
11
12
13
14
15
16
17
DMF/H2O/K2CO3/80 1C
MW/K2CO3/50 1C
MW/K2CO3/400w
DMF/H2O/K2CO3/70 1C
H2O/K3PO4/80 1C
H2O/TEAc/50 1C
3
43
39
52
48
88
62
79
54
55
56
57
0.1
0.13
6
1
6
AC-Pd (0.06 mol%)
MNP@SPGMA@AP@Pd (0.1 mol%)
HCP-Pd-I (40 mg)
58
Pd@COF-QA (1.7 mol%)
59d
NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co
(0.005 mol% Cu, 0.01 mol% Co)
22a Silica-supported NHC-Pd/IL (1 mol%)
Pd@NaY (1 mol%)
H2O/K3PO4/60 8C
2.5
Present study
18
19
20
21
22
23
NMPa/NaOAc/Ar atmosphere/140 1C
n-Butyl levulinate/Et3N/150 1C
NMPa/K2CO3/120 1C
DMF/Et3N/120 1C
CH3CN/K2CO3/80 1C
9
6
1
0.75
8
95
95
88
95
85
92
60
61
6
62
Si-OPPh2-Pd (0.5 mol%)
Fe3O4@SiO2-Se-T/Pd(II) (5 mg)
Pd-MOT (1 mol%)
63
NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co
(0.005 mol% Cu, 0.01 mol% Co)
50a MnCl2Á4H2O (5 mol%) L-proline (10 mol%)
NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co
(0.005 mol% Cu, 0.01 mol% Co)
25b Pd–DABCO@SiO2 (1 mol%)e
Co@MicroCS (3 mol%)f
H2O/K3PO4/60 8C
0.7
Present study
24
25
DMSO/NaOt-Bu/135 1C
H2O/K3PO4/60 8C
24
1.9
72
89
64
Present study
26
27
28
29
30
DMF/K2CO3/100 1C
DMAcg/Et3N/140 1C
DMF/K2CO3/100 1C
PEG/K2CO3/60 1C
H2O/K3PO4/60 8C
6
8
8
9
91
82
88
68
87
65
66
67
68
MNPs-Mel-Pd (20 mg)
Co-out-CNTs (20 mg)
NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co
(0.005 mol% Cu, 0.01 mol% Co)
b
3.2
Present study
a
c
d
e
N-Methyl-2-pyrrolidone. 1-(4-Chlorophenyl)-3-methyl-4-phenyl-1,2,3-triazolium iodide. Triethylamine. R = OMe. 1,4-Diazabicyclo[2.2.2]octane.
f
g
Aryl halide is iodobenzene. Dimethylacetamide.
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zirconium nanoparticles to magnetic nanoparticles, a signifi- depend on the transition metal electropositivity or electronegativity
cant increase in the efficiency was observed (Table 5, entry 13). of the latter rates of the distinct steps of the mono catalytic cycle
To confirm the advantage of the catalytic properties of (e.g., reductive elimination or oxidative addition).69 The interaction
NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co for the Heck, Suzuki, and may be increased with the organic linker, which bridges to the
C–N coupling reactions, this was compared with the works of different metal centers and plays a sensitive charge transfer role.
other researchers. The results are shown in Table 6.
The predicted result of this cooperation would be an enhancement
Of the advantages of the NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co of the overall reaction rate, so an increase in the activity of the
catalyst over other previous reports, mentions could be made of heterobimetallic catalysts can be seen.70
the short time, high efficiency, green solvent, low metal toxicity,
and easy catalyst recycling.
This perspective contribution is timely, as the bimetallic
catalysis for C–C and C–N coupling is a growing area that plays an
important role in contributions to the synthetic implement.71,72
3.4.1. 1,2-Diphenylethene derivatives (10a-33c):. Based on
the previous reports,67,73 and also according to our results, we
put forward a possible explanation for the Mizoroki–Heck
cross-coupling reactions in Scheme 3a. The start of the reaction
was assumed to be based upon an in situ reduction of Cu(II)
3.4. Mechanism study
The incorporation of Cu with various transition metals in
heterobimetallic Cu complexes appears in the newest generation
structures. The synergetic interactions between the active metal
sites that have emerged as an effective approach in cross-couplings
Scheme 3 A plausible mechanism for the (a) Mizoroki–Heck cross-coupling, (b) Suzuki coupling, (c) synthesis of internal alkynes, and (d) N-arylation of
imidazole using NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co.
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sites, which resulted in the Cu(I) species (I). This reduction was friendly are prominent and important factors for the catalysts.
made by the copper(I) species responsible for the coupling The rigid mineral structure of sulfated zirconium oxide com-
reaction being begotten by an electron transfer from cobalt(II) bined with the magnetic properties of NiFe2O4 make the catalyst
and oxidation to cobalt(III), while in the opposite case, the formation recyclable and reusable, and minimizes any metal leaching. The
of the copper(III) species at first seems unlikely. It was clear catalyst recyclability was tested in the Heck reaction. The reac-
from the previous study that the active Cu(I) species would tion of styrene and iodobenzene in the presence of K3PO4 base
proceed with the cross-coupling reaction. In the following level, at 60 1C in each catalyst cycle was recovered. The recovered
the low valent Cu(I) was oxidatively added into the aryl halide catalyst was washed with EtOH (2 Â 5 mL) and was reused in the
to cope with the aryl cobalt intermediate (II). In the next next step without any purification or pre-activation. Fig. 11
levels, olefin coordination with (II) and migratory insertion shows the corresponding results for more than ten consecutive
led to the shaping of adducts (III) and (IV), respectively. periods without significant loss of efficiency (catalyst perfor-
Hydridocobalt(VI) and a new olefin were compatible with, mance and reaction performance). Finally, after 11 consecutive
following b-hydride elimination. In the end, the active Cu(I) periods, the product yield reached 87% (6% decrease) (Heck
species (I) were regenerated by a reductive elimination in the coupling). Also, FE-SEM, TEM, and FTIR analyses were taken
presence of K3PO4. To complete the catalytic cycle for the from the recycled catalyst after 11 consecutive runs. The results
Mizoroki–Heck cross-coupling reaction, aerobic oxidation of have shown the stability of the NiFe2O4@SiO2@ZrO2/SO42À/Cu/
the Cu(I) species (I) to the Cu(II) complexes were conducted. Co catalyst in organic and aqueous environments. These results
Similar mechanisms for the synthesis of other compounds are have indicated a rigid and durable structure for the NiFe2O4@
shown in Scheme 3b–d.
SiO2@ZrO2/SO42À/Cu/Co catalyst as a magnetic heterogeneous
nanocatalyst. Another benefit of the cobalt copper catalyst is its
high recycling frequency and low leaching. The results were
3.5. Recoverability studies
Sustainability, durability, and recycling of a heterogeneous compared with other catalysts mentioned in the existing litera-
catalyst, as well as being energy-saving and environmentally ture (Table 7).
Fig. 11 (A) Recovery and reusability of NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co in the Mizoroki–Heck cross-coupling reaction under optimized reaction
conditions. (B) FTIR spectrum, (C) FE-SEM, and (D) TEM images of the recovered catalyst after the 11th run.
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Table 7 Reproducibility of the different Cu and Co catalysts in the Heck reactions
Entry
Catalyst
Recycle
Yield (%)
Ref.
1
2
3
4
5
6
7
8
9
Fe3O4@SiO2@PrNCu
MNP@PAMAM-Co
Co-MS@MNPs/CS
Cu-NH2-GO
Schiff Base/CuI
Co-DMM@MNPs/Cs
6
5
5
6
5
6
7
6
5
91–83
90–85
88–83
88–66
93–86
82–62
91–89
92–87
98–92
93–87
17
12
67
18
74
2
75
67
Fe3O4@SiO2@Im[Cl]Co(III)-melamine nanocomposite
Magnetic Chitosan Cobalt
Fe3O4@SiO2-Isa Cu(II)
76
10
NiFe2O4@SiO2@ZrO2/SO42À/Cu/Co
11
This work
4. Conclusion
References
In the end, we synthesized a magnetically recyclable bimetallic
nanocatalyst consisting of various Lewis acid and Brønsted acid
active sites. The catalyst can be used as a special catalyst in the
Heck-Suzuki reaction and the coupling of C–N cross-couplings.
The reactions can be performed from various precursors by a
green solvent, short reaction times, and with high efficiency
(49–94%), without the formation of any by-products. These
results were viewed as irrespective of the presence of electron-
donating and electron-withdrawing groups in the evaluated
(pre)catalyst structures. The transfer of an electron between
the Cu, Co, and Zr metal sites can be responsible for
the oxidation addition and reductive elimination proposed
mechanism, which is in line with the reported mechanisms.
Moreover, via adsorption of the cation, a surface-mediated/
facilitated interconversion was made among the sulfate ions on
the catalyst with the function of the base in water. The running
methodology can be replaced with the expensive Pd catalytic
systems with highly toxic and expensive phosphine ligands to
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Conflicts of interest
There are no conflicts to declare.
Acknowledgements
The authors are grateful to the University of Birjand for financial 22 A. Berrichi, R. Bachir, S. Bedrane, N. Choukchou-Braham
support.
and K. Belkacemi, Res. Chem. Intermed., 2019, 45, 3481–3495.
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