Magnetic covalently immobilized nickel complex: A new and efficient method for the Suzuki cross-coupling reaction

Article abstract of DOI:10.1002/aoc.6158

In this study, an efficient procedure was reported to prepare Fe₃O₄@SiO₂ magnetic nanoparticles (MNPs) with immobilized nickel NPs. In order to increase the activity of this catalyst, creatine as a ligand with high content of nitrogen atoms was linked onto the magnetic core–shell structure. Then, Ni(II) ions were coordinated on the surface of the silica-coated MNPs and reduced to Ni(0) NPs to obtain the final catalyst. The catalytic activity of the prepared catalyst was studied for the synthesis of biaryl derivatives via the Suzuki–Miyaura cross-coupling reaction in high yields. The catalyst could also be recovered and reused with no loss of activity over five successful runs.

Full text of DOI:10.1002/aoc.6158

Received: 29 August 2020
DOI: 10.1002/aoc.6158
Revised: 21 December 2020
Accepted: 28 December 2020
F U L L P A P E R
Magnetic covalently immobilized nickel complex: A new
and efficient method for the Suzuki cross-coupling reaction
Mahdi Keyhaniyan
| Amir Khojastehnezhad
| Hossein Eshghi
| Ali Shiri
Department of Chemistry, Faculty of
Science, Ferdowsi University of Mashhad,
Mashhad, Iran
In this study, an efficient procedure was reported to prepare Fe3O4@SiO2
magnetic nanoparticles (MNPs) with immobilized nickel NPs. In order to
increase the activity of this catalyst, creatine as a ligand with high content of
nitrogen atoms was linked onto the magnetic core–shell structure. Then,
Ni(II) ions were coordinated on the surface of the silica-coated MNPs and
reduced to Ni(0) NPs to obtain the final catalyst. The catalytic activity of the
prepared catalyst was studied for the synthesis of biaryl derivatives via the
Suzuki–Miyaura cross-coupling reaction in high yields. The catalyst could also
be recovered and reused with no loss of activity over five successful runs.
Correspondence
Ali Shiri, Department of Chemistry,
Faculty of Science, Ferdowsi University of
Mashhad, Mashhad, Iran.
Email: alishiri@um.ac.ir
Funding information
Ferdowsi University of Mashhad, Grant/
Award Number: 3/41331
K E Y W O R D S
cross-coupling, magnetic nanoparticles, nickel, organometallic chemistry, Suzuki reaction
1 | INTRODUCTION
Recently, the construction of carbon–carbon bond is
one of the most important challenges in organic
Green chemistry is one of the most branches of chemistry
that deals with sustainable and environmentally friendly
materials to achieve better human life. This partly new
emerging field has attracted vast interest these days due
to the decrease and removal of hazardous materials and
introduces sustainable and useful processes. Green chem-
istry is also defined as the careful and accurate planning
for molecular design and organic synthesis to eliminate
adverse consequences and improve human health and
the environment.[1] Green chemistry has a framework of
a cohesive set of 12 principles that the use of green cata-
lysts and reagents is the most important one.[2] Catalysts
undoubtedly are the main part of green chemistry, and
their separation procedures after the end of the reaction
are the huge challenge.[3] Recently, magnetic
nanoparticles (MNPs), particularly Fe3O4, have become
popular among the researcher, because they can be used
as a catalyst with some simple modifications.[4] These
amazing materials can be easily separated from the
reaction mixture with an external magnetic field, and
because of their heterogeneous nature, they have the
ability to be reused.[5]
synthesis,[6] and generally, the best and popular
procedure to access the C–C bond is the cross-coupling
reactions.[7] Suzuki–Miyaura reaction is one of the well-
known cross-coupling reactions that form C–C bond
through the reaction of a boronic acid and an orga-
nohalide in the presence of a kind of palladium
catalyst.[8] During recent years, different palladium
catalysts have been applied for the synthesis of biaryl
compounds via the Suzuki–Miyaura cross-coupling reac-
tion.[9] Considering the high cost of Pd catalysts, the use
of more inexpensive and available transition-metal cata-
lysts containing Fe,[10] Cu,[11] Co, and Ni[12] has attracted
the researchers' interests. Nickel-catalyzed Suzuki–
Miyaura cross-coupling reaction was initially reported by
Percec and coworkers in 1995.[13] In their study, the
Ni(0) generated from NiCl2(dppf) and Zn and the differ-
ent aryl sulfonates with arylboronic acids have been
reacted to obtain various biaryl derivatives in good yields.
After that, a number of homogeneous Ni-based cata-
lysts[14] have been reported for the synthesis of biaryl
derivatives via Suzuki–Miyaura cross-coupling reaction.
Many of them have problems to separate the Ni catalyst
Appl Organomet Chem. 2021;35:e6158.
wileyonlinelibrary.com/journal/aoc
© 2021 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.6158

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KEYHANIYAN ET AL.
from the reaction mixture due to the homogeneous
nature of the Ni catalyst and present that a new heteroge-
neous nickel-based catalyst for the Suzuki–Miyaura
cross-coupling reaction is highly recommended.
2 | RESULTS AND DISCUSSION
The organometallic heterogeneous catalyst has been pre-
pared according to Scheme 1. The silica-coated magnetic
Fe3O4 nanoparticles (NPs) (Fe3O4@SiO2) were prepared
based on the literature,[18] and then, the creatine (Crt) as
an amino acid was covalently immobilized on the surface
of Fe3O4@SiO2, and finally, the nickel ion was coordi-
nated on the creatine organic ligand to access the hetero-
geneous nickel-based catalyst (Fe3O4@SiO2–Crt–Ni). The
prepared catalyst has been fully characterized by different
analyses including Fourier transform infrared (FT-IR),
transmission electron microscopy (TEM), scanning elec-
tron microscopy (SEM), EDS, TGA, XRD, inductively
coupled plasma (ICP), VSM, and dynamic light scattering
(DLS).
The FT-IR of all steps for the synthesis of the catalyst
has been studied and compared with each other
(Figure 1). In the FT-IR of Fe3O4 MNPs (Figure 1a), the
broad absorption peak at 3350 cm−1 is assigned to the
O–H stretching bands of hydroxyl functional groups, and
the sharp and broad peak at 555 cm−1 is attributed to
Fe–O bonds on the structure of Fe3O4 MNPs.[19] In the
second spectrum related to Fe3O4@SiO2 (Figure 1b), the
In our previous study, the heterogeneous nickel cata-
lyst has been prepared by covalent immobilization of
nickel porphyrin on the surface of graphene oxide, and a
wide variety of biaryl compounds have been synthesized
via Suzuki–Miyaura cross-coupling reaction.[15] Also,
very recently, the new heterogeneous functionalized
magnetic Ni(II) catalyst has been reported by Dinarloo
et al. They synthesized a wide variety of biaryl com-
pounds via cross-coupling reaction of some aryl carba-
mates or aryl sulfamates with arylboronic acid in good to
excellent yields.[16] Thus, there is a pressing need to
develop some new heterogeneous Ni catalysts for cross-
coupling reactions. In this respect, in continuation of our
attempts in organic synthesis and catalysis,[17] a new het-
erogeneous nickel-based catalyst has been developed by
the covalent immobilization of nickel–creatine complex
on the surface of silica-coated Fe3O4 MNPs (Scheme 1),
and after the full characterization of catalyst structure, its
catalytic applications have been investigated in the
Suzuki–Miyaura cross-coupling reaction (Scheme 2).
SCHEME 1 Preparation of the catalyst (Fe3O4@SiO2–Crt–Ni)
SCHEME 2 Suzuki–Miyaura cross-coupling
reaction in the presence of catalyst

KEYHANIYAN ET AL.
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FIGURE 1 FT-IR spectra of
(a) Fe3O4, (b) Fe3O4@SiO2,
(c) Fe3O4@SiO2–Ni(0),
(d) creatine, (e) creatine–Ni(0),
(f) Fe3O4@SiO2–Crt–Ni(0)
appearance of the new bonds at 934 and 1096 cm−1 are
As shown in this spectrum, there are no significant differ-
ences between this spectrum and previous one that shows
the Ni are physically adsorbed on the surface of
Fe3O4@SiO2 MNPs. In the FT-IR spectrum of creatine
(Figure 1d), two absorption peaks at 3156 and 3205 cm−1
correspond to the stretching vibrations of NH2, and a
assigned to the stretching vibration of Si–O–Si and Si–O–H,
respectively, and the broad peak at 3352 cm−1 confirms the
[18]
existence of hydroxyl group on the surface of SiO2.
The
next spectrum (Figure 1c) is assigned to the
Ni(0) immobilized on the surface of Fe3O4@SiO2 MNPs.
FIGURE 2 XRD patterns of (a) Fe3O4 and
(b) Fe3O4@SiO2–Crt–Ni

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KEYHANIYAN ET AL.
broad absorption peak at 3072 cm−1 is assigned to the
stretching vibrations of OH. The week peaks at around
2900 cm−1 are allocated to the stretching vibrations of CH
in structure of creatine, and finally, sharp absorption
peaks at 1666 and 1411 cm−1 are attributed to the
stretching and bending vibrations of CO and OH func-
tional groups, respectively.[20] In the FT-IR spectrum of
creatine–Ni(0) complex (Figure 1e), the two absorption
peaks at 3156 and 3205 cm−1 are shifted to 3147 and
3195 cm−1 (blue shift), and another blue shift of carbonyl
peak was happened from 1666 to 1650 cm−1 that confirms
the successful coordination of Ni on the creatine organic
ligand. In the final spectrum that corresponds to the
nickel-coordinated catalyst (Figure 1f), the appearance of
all creatine–Ni(0) complex peaks in the structure of the
catalyst as well as blue shifts of the NH and CO peaks
from 3205 to 3196 and 1666 to 1652 cm−1, respectively,
confirms the successful preparation of the catalyst.[21]
The XRD patterns of Fe3O4 and final catalyst
(Fe3O4@SiO2–Crt–Ni) have been analyzed and compared
in Figure 2. As shown in Figure 2a, sharp peaks at
2Ɵ = 30.2, 35.5, 43.2, 53.3, 57.2, and 62.1 are attributed to
the (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1), and (4 4 0) lat-
tice planes of cubic Fe3O4 MNPs (JCPDS card
no. 19-0629),[22] and in the second XRD pattern
FIGURE 3 TEM image of Fe3O4@SiO2–Crt–Ni
FIGURE 4 SEM image of (a) Fe3O4@SiO2–
Crt–Ni and (b) EDX pattern of Fe3O4@SiO2–Crt–Ni

KEYHANIYAN ET AL.
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(Figure 2b), in addition to peaks related to Fe3O4 MNPs,
the new peaks at 2Ɵ = 43.6 and 54.0 appeared, which
confirm the successful formation of nickel complex.[23]
According to the Debye–Scherrer equation (d = Kλ/βcos θ),
the average size of Fe3O4 MNPs was 19.7 nm, which is in
agreement with DSL analysis.
(Figure 3).[24] SEM analysis also confirmed the spherical
morphology for the catalyst (Figure 4a). Moreover, the
EDS technique approves the presence of all elements,
especially Ni, in the structure of catalyst (Figure 4b).
These analyses are in agreement with ICP and DSL
observations.[25]
TEM, SEM and EDS analyses have been performed
for the understanding of morphology, size, and elemental
analysis of our samples. In the TEM image of the catalyst
(Fe3O4@SiO2–Crt–Ni), there are some tiny black
circles that are attributed to the Ni NPs immobilized on
the surface of Fe3O4 MNPs. Also, this image demon-
strated the successful core–shell of silica-coated Fe3O4
MNPs, and the average size of MNPs is about 30 nm
TGA analysis is the best analysis for the evaluation of
the catalyst functionalization. Thus, the TGA analysis
was used for the investigation of the thermal behavior of
the catalyst (Fe3O4@SiO2–Crt–Ni) (Figure 5). This figure
showed two main weight losses in which the first one
starts from 50ꢀC and stretches to 150ꢀC allocated to phys-
ically absorbed water and organic ligand on the surface
of Fe3O4@SiO2 and the second weight loss begins at
FIGURE 5 TGA curve of catalyst (Fe3O4@SiO2–Crt–Ni)
FIGURE 6 Magnetization curves of
(a) Fe3O4 and (b) Fe3O4@SiO2–Crt–Ni

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KEYHANIYAN ET AL.
FIGURE 7 Particles size
distribution of (a) Fe3O4 and
(b) Fe3O4@SiO2–Crt–Ni
about 200ꢀC and continues to 300ꢀC attributed to organic
molecules and nickel complex.[26]
analysis in the structure of the catalyst, the ICP technique
has been studied to estimate the amount of Ni in
the fresh and reused catalyst. According to ICP analysis,
the amounts of nickel in fresh and reused catalyst were
2.20 and 2.11 wt%, respectively. These observations
strongly confirm the successful coordination of Ni in
creatine amino acid immobilized on the surface of
Fe3O4@SiO2 MNPs, and no significant leaching of
metal or metal complex has been occurred during the
reaction.
In the second step, in order to optimize the reaction
condition, the reaction of iodobenzene and phe-
nylboronic acid was chosen as a model reaction
(Table 1). At first, the Suzuki–Miyaura cross-coupling
reaction was carried out without the catalyst, and no
biaryl product was observed after 5 h running the reac-
tion (entry 1). Then, the influence of solvents like DMF,
toluene, water, and 1,4-dioxane has been investigated on
the synthesis biaryl compounds via Suzuki–Miyaura
cross-coupling reaction (entries 25). The best solvent was
The magnetic properties of our Fe3O4 and final catalyst (-
Fe3O4@SiO2–Crt–Ni) have been investigated by VSM
analysis (Figure 6). As demonstrated in this figure, the satu-
ration magnetization of Fe3O4 and Fe3O4@SiO2–Crt–Ni is
around 64 and 35 emu/g, respectively, that approves the
proper coating of Fe3O4 MNPs with silica and nickel com-
plex and shows superparamagnetic properties of the catalyst
(Fe3O4@SiO2–Crt–Ni).[24] In addition to SEM and TEM
analyses for finding the catalyst size, the DLS technique has
been also applied for the estimation of the particle size distri-
bution (Figure 7). As shown in Figure 7, the particle size dis-
tribution of Fe3O4 and final catalyst (Fe3O4@SiO2–Crt–Ni)
has been analyzed. This analysis demonstrated that the
average size of Fe3O4 MNPs is 22 nm (Figure 7a) and
after the coating of these MNPs with SiO2 and organic
complex, the average size of MNPs has been increased to
55 nm (Figure 7b). Moreover, plus to energy-dispersive
X-ray (EDX) analysis for the evaluation of elemental

KEYHANIYAN ET AL.
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1,4-dioxane, and the yield of the reaction was very higher
than other solvents (entry 5). Base was a critical factor for
proceeding the Suzuki–Miyaura cross-coupling reaction.
Thus, the effects of various bases like K2CO3, BaCO3,
Cs2CO3, KOH, Ba (OH)2, Mg (OH)2, and K3PO4 were also
studied on the model reaction (entries 6–12). The yield of
the reaction in the presence of potassium phosphate was
the highest amount compared with other bases (Entry 5).
After finding the best solvent and base, the amount of the
catalyst was examined (entries 13 and 14). With 2.0 mol%
of the catalyst, the highest amount of biaryl product was
obtained in shorter reaction time (entry 5), and with
decrease of this amount to 1.0 mol %, the yield of the
reaction was reduced (entry 14). Besides, the model reac-
tion was carried out in different temperatures (entries
15–17), and 70ꢀC was found to be the optimum tempera-
ture (entry 5). Eventually, the model reaction has been
performed in the presence of other structures of
catalyst such as creatine-coordinated Ni(0) complex,
Fe3O4@SiO2–Ni(0), NiCl2, Fe3O4, and Fe3O4@SiO2
(entries 18–21). Interestingly, the progress of the reaction
was excellent in the presence of the creatine–Ni(0) com-
plex and Ni(0) immobilized on Fe3O4@SiO2 MNPs and
NiCl2, and more than 80% of biaryl products have been
obtained (entries 18–20). However, the bare Fe3O4 and
Fe3O4@SiO2 without Ni sources did not have convenient
effects on the synthesis of biaryl compounds, and no
product has been observed even after 3 h running the
reaction (entry 21).
According to the optimized reaction conditions, dif-
ferent biaryl compounds have been synthesized via
Suzuki–Miyaura cross-coupling reaction in the presence
of 2 mol % of the catalyst (Scheme 2). A wide variety of
aromatic and heteroaromatic halides including iodo,
bromo, and chloro derivatives with phenylboronic acid
derivatives have been examined. As expected, the
iodobenzene derivatives had better isolated yields and
reaction times in comparison with bromo- and
TABLE 1 The optimization of reaction conditionsa
Entry
1
Base
Solvent
Catalyst (mol%)
Time (h)
5.0
Temp (ꢀC)
Yieldb (%)
----
76
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K2CO3
BaCO3
Cs2CO3
Na2CO3
KOH
1,4-Dioxane
DMF
----
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
3.0
1.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
70
70
70
70
70
70
70
70
70
70
70
70
70
70
RT
50
Ref
70
70
70
70
2
0.7
3
Toluene
0.7
69
4
H2O
0.7
78
5
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
0.7
0.7
97
6
74
7
4.0
25
8
0.7
80
9
1.5
75
10
11
12
13
14
15
16
17
18
19
20
21
4.0
15
Ba (OH)2
Mg (OH)2
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
4.0
20
6.0
Trace
97
0.7
0.7
82
2.0
Trace
70
2.0
0.7
97
0.7
85c
89d
81e
---f
0.7
0.7
3.0
aReaction conditions: 4-Br-anisole (1.0 mmol) and phenylboronic acid (1.2 mmol).
bIsolated yield.
cCreatine–Ni(0) complex.
dFe3O4@SiO2–Ni(0) MNPs.
eNiCl2 salt.
fFe3O4 and Fe3O4@SiO2 MNPs.

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KEYHANIYAN ET AL.
TABLE 2 The Suzuki–Miyaura cross-coupling reactions catalyzed by Fe3O4@SiO2–Crt–Ni
Notes: Reaction conditions: halobenzene derivatives (1.0 mmol), phenylboronic acid derivatives (1.2 mmol), K3PO4 (2.0 mmol), 1,4-dioxane (2.0 ml), and
catalyst (2.0 mol %) at 70ꢀC. Time is hour.
chlorobenzene derivatives. All biaryl derivatives were
achieved in good to excellent yields in short reaction
times.
and probably no leaching and release of Ni or Ni complex
occurs during the reaction.
Another examination that was used to study the cata-
lyst stability and leaching of nickel was XRD analysis
(Figure 9). As demonstrated in this figure, all significant
peaks related to Fe3O4 MNPs and particular Ni NPs exist,
and there are not any significant differences between
XRD pattern of fresh and reused catalyst. This result is in
agreement with reusability test of the catalyst (previous
section) and confirms no leaching of the catalyst occurred
during the reaction.
The reusability of catalyst was also examined in the
model reaction. Thus, the model reaction of iodobenzene
and phenylboronic acid was carried out in the presence
of 2 mol% of the catalyst, and after the finalization of the
reaction, the catalyst has been separated from the reac-
tion mixture by an external magnetic field and washed
with acetone and ethanol and dried in a vacuum oven at
60ꢀC. Then, it was used in the other same model reaction
for five times. As seen in Figure 8, after five times reusing
the catalyst, the yield of the reaction decreased to only
4%, and it confirms that the catalyst has stable structure
The hot filtration test was also investigated in order to
test the catalyst stability. For this purpose, the reaction of
iodobenzene (1.0 mmol), phenylboronic acid (1.2 mmol),
FIGURE 8 Reusability test of catalyst
FIGURE 9 XRD pattern of catalyst after five-time reuse

KEYHANIYAN ET AL.
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TABLE 3 The comparison of our catalyst with other nickel-based catalysts in Suzuki–Miyaura cross-coupling reaction
Entry
Catalyst (mol%)
Solvent
Dioxane
Toluene
THF
Temp. (ꢀC)
Time (h)
Yield (%)
Reference
[14f]
[14e]
[14b]
[27]
1
NiCl2Á6H2O
NiCl2(PPh3)2
130
80
12
2.0
3.0
22
18
8.0
1.0
5
65
92
99
83
97
88
95
98
99
98
2
3
Ni (PPh3)2(1-naph)Cl
70
4
NiCl2(dppe)/dppe
Toluene
THF
100
60
[14g]
[14a]
[15]
5
Phosphine dendrimer stabilized nano-Ni particles
Nickel(II) complexes with Schiff base liganda
Ni-coordinated porphyrin GOb
Pd–Ni@TiO2
6
Dioxane
Dioxane
H2O/EtOH
Toluene
Dioxane
110
80
7
[28]
8
50
[29]
9
Ni(II)–diimine–POPc
100
70
8
10
Fe3O4@SiO2–Crt–Ni
1.0
This work
aSchiff base of o-phenylenediamine and salicylaldehyde.
bGraphene oxide.
cPorous organic polymer.
and catalyst (2.0 mol%) was heated at 70ꢀC in dioxane for
30 min, and 50% progress the reaction. Then, the catalyst
was removed from the reaction, and afterward, the
reaction was continued for another 30 min. The reaction
did not move forward during this time, which was
monitored by TLC. These observations truly confirm that
the catalyst has a strong stable structure and no leaching
of Ni or Ni–creatine complex has happened during the
reaction.
The merit of our sample was compared with other
nickel-based catalysts (Table 3). According to this
table, our catalyst and method had better results com-
pared with homogeneous (1–4) and heterogeneous
(5–7) nickel catalysts in the case of yield, condition,
and time of the reaction. Our nickel catalyst could
catalyze the synthesis of 3a via Suzuki–Miyaura cross-
coupling reaction with 98% isolated yield in 1 h. The
structure of all synthsized products were confirmed
using 1H NMR and 13C NMR and mass spectroscopy
(see supporting information).
to obtain a wide variety of biaryl derivatives in good to
excellent yields.
4 | EXPERIMENTAL
4.1 | General
All the materials and reagents were purchased from
Sigma-Aldrich and Merck without any further purifica-
tion. Melting points of products were recorded with an
Electrothermal type 9100 melting point apparatus. FT-IR
spectra were recorded with a Thermo Nicolet Avatar
370 FT-IR spectrometer. TEM was performed with a Leo
912AB (120 kV) microscope (Zeiss, Germany). SEM anal-
ysis was done using a MIRA3 TESCAN scanning electron
microscope operated at an accelerating voltage of 30 kV.
EDX analysis was performed using a SAMX instrument.
ICP analysis was carried out with a Varian VISTA-PRO,
CCD (Australia). TGA was performed with a Shimadzu
thermogravimetric analyzer (TG-50) under air atmo-
sphere at a heating rate of 10ꢀC min−1
.
3 | CONCLUSION
In summary, the silica-coated Fe3O4 MNPs has been
prepared by chemical procedure, and then, the creatine
amino acid has been immobilized on the surface of silica-
coated Fe3O4 MNPs, and eventually, the Ni NPs have
been coordinated on the amine groups of creatine organic
ligand. Then, its catalytic applications have been
investigated for the synthesis of biaryl derivatives via
Suzuki–Miyaura cross-coupling reaction. Different aryl
halides with various aryl boronic acids have been reacted
4.2 | Synthesis of catalyst (Fe3O4@SiO2–
Crt–Ni(0))
The organometallic heterogeneous catalyst has been pre-
pared according to Scheme 1. The silica-coated magnetic
Fe3O4 NPs (Fe3O4@SiO2) were prepared based on the
literature,[18] and then, the creatine amino acid and
nickel complex were prepared according to method
described below. A 0.1-g Fe3O4@SiO2 was dispersed in

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KEYHANIYAN ET AL.
40-mL ethanol ultrasonically for 30 min, and then, 0.2 g
of creatine amino acid in 20-mL deionized water was
added to this mixture and for another 20 min was dis-
persed under the ultrasound condition and then was
refluxed for 6 h. After the completion of the reaction, the
prepared Fe3O4@SiO2-Crt was separated from the solu-
tion by external magnetic field, and after three times
washing with ethanol, it was dried in a vacuum oven at
50ꢀC for 12 h. Then, in order to prepare the final catalyst,
0.2 g of Fe3O4@SiO2-Crt was dispersed in 20-mL ethanol
under the ultrasound condition for 20 min, and then,
5.0-mL aqueous solution of NiCl2 (0.5 M) was added to
this mixture and for another 20 min was dispersed under
the ultrasound condition. Then, the mixture was stirred
for 6 h at room temperature, and after the completion of
the reaction, the prepared Ni(II) coordinated catalyst was
separated from the solution by external magnetic field,
and after three times washing with ethanol, it was dried
in a vacuum oven at 50ꢀC for 12 h. Finally, for reduction
of the Ni(II) to Ni(0), 0.1 g of Fe3O4@SiO2–Crt–Ni
(II) was dispersed in 30-mL water under the ultrasound
condition for 20 min, and then, 5.0-mL aqueous solution
of NaBH4 (1.0 M) was droopingly added to this mixture
for 1 h in ice bath condition. Then, the mixture was
stirred at room temperature for 12 h, and after the com-
pletion of the reaction, the prepared Ni(0) catalyst
(Fe3O4@SiO2-Crt-Ni) was separated from the solution by
external magnetic field, and after four times of washing
with water and ethanol, it was dried in a vacuum oven at
60ꢀC for 12 h.
external magnetic field, and after four times washing
with water and ethanol, it was dried in a vacuum oven at
60ꢀC for 12 h.
4.4 | Synthesis of creatine–Ni(0) complex
An ethanolic solution of creatine amino acid (0.464 g,
1.0 mmol) was added dropwise to a clear solution of
NiCl2 (1.0 mmol, 0.129 g) in ethanol (10 mL). The
solution was stirred at room temperature for 2 h, and
then, it remained for 8 h and the resultant precipitate
of Ni(II) complex was filtered and dried in vacuum
over anhydrous CaCl2. Then, for reduction of the
Ni(II) to Ni(0), 0.1 g of creatine Ni(II) complex was
dissolved in 10-mL water/ethanol and stirred for
30 min, and then, 5.0-mL aqueous solution of NaBH4
(1.0 M) was droopingly added to the mixture for
30 min in ice bath condition and stirred for 2 h. Then,
the resulting precipitate of creatine-coordinated
Ni(0) complex was filtered and dried in vacuum over
anhydrous CaCl2.
4.5 | General procedure for the Suzuki–
Miyaura reaction catalyzed by Fe3O4
@SiO2–Crt–Ni
To a mixture of phenylboronic acids (1.2 mmol), aryl
halides (1.0 mmol), potassium phosphate (2.0 mmol), and
dioxane (2.0 ml), 2.0 mol % of Fe3O4@SiO2–Crt–Ni was
added and stirred at 70ꢀC in oil bath. After the comple-
tion of the reaction, the Fe3O4@SiO2–Crt–Ni was
separated from the reaction mixture by external magnetic
field, washed with and acetone and ethanol, and dried at
60ꢀC in a vacuum oven for 6 h. Then, the solvent was
removed from the mixture, and the synthesized biaryl
derivatives were purified by column chromatography
using ethyl acetate/n-hexane (1:6).
4.3 | Synthesis of Fe3O4@SiO2–Ni
(0) MNPs
Fe3O4@SiO2 (0.2) was dispersed in 20-mL ethanol under
the ultrasound condition for 20 min, and then, 5.0-mL
aqueous solution of NiCl2 (0.5 M) was added to this mix-
ture and for another 20 min was dispersed under the
ultrasound condition. Then, the mixture was stirred for
6 h at room temperature, and after the completion of the
reaction, the prepared Ni(II) immobilized Fe3O4@SiO2
MNPs were separated from the solution by external mag-
netic field, and after three times washing with ethanol, it
was dried in a vacuum oven at 50ꢀC for 12 h. Finally, for
reduction of the Ni(II) to Ni(0), 0.1 g of Fe3O4@SiO2–Ni
(II) was dispersed in 30-mL water under the ultrasound
condition for 20 min, and then, 5.0-mL aqueous solution
of NaBH4 (1.0 M) was droopingly added to this mixture
for 1 h in ice bath condition. Then, the mixture was
stirred at room temperature for 12 h, and after the com-
pletion of the reaction, the prepared Ni(0) immobilized
Fe3O4@SiO2 MNPs were separated from the solution by
ACKNOWLEDGMENTS
The authors gratefully acknowledge Ferdowsi University
of Mashhad (3/41331). We are thankful to Dr. Ali Samie
for the advices in preparation of Ni complex structures.
AUTHOR CONTRIBUTIONS
Mahdi Keyhaniyan: Formal analysis; methodology.
Amir Khojastehnezhad: Formal analysis; investigation;
project administration; validation; visualization. Hossein
Eshghi: Project administration; supervision; validation.
Ali Shiri: Conceptualization; data curation; investiga-
tion; project administration; supervision; validation;
visualization.

KEYHANIYAN ET AL.
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DATA AVAILABILITY STATEMENT
The data that support the findings of this study are avail-
able in the supplementary material of this article.
ORCID
Mahdi Keyhaniyan https://orcid.org/0000-0003-2104-
8372
Amir Khojastehnezhad https://orcid.org/0000-0002-
9078-7323
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How to cite this article: Keyhaniyan M,
Khojastehnezhad A, Eshghi H, Shiri A. Magnetic
covalently immobilized nickel complex: A new and
efficient method for the Suzuki cross-coupling
reaction. Appl Organomet Chem. 2021;35:e6158.
https://doi.org/10.1002/aoc.6158
SUPPORTING INFORMATION
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in the Supporting Information section at the end of this
article.