Preparation of magnetic chitosan-supported palladium-5-amino-1H-tetrazole complex as a magnetically recyclable catalyst for Suzuki-Miyaura coupling reaction in green media

Article abstract of DOI:10.1016/j.molstruc.2021.130873

The utilization of various tetrazoles as efficient ligands is a promising method for the functionalization of tetrazole-based heterogeneous catalysts. Their combination with magnetic species and natural supports exposes huge opportunities for the practical applications of heterogeneous catalysts. In this study, a green and novel strategy is applied to synthesize Fe₃O₄ magnetic nanoparticles (MNPs) incorporated with chitosan (CS) and 5-amino-1H-tetrazole with a long tail ((3-chloropropyl)trimethoxysilane) to immobilize palladium catalyst designated as Fe₃O₄–CS@tet-Pd(II). The prepared Fe₃O₄–CS@tet-Pd(II) was used as an efficient and magnetically recyclable catalyst for the Suzuki-Miyaura cross-coupling reaction (SMCR) using a mixture of EtOH/H₂O as green media under aerobic conditions. All the expected products were obtained in high yields, indicating the high efficiency of this catalyst for the preparation of various biaryls by SMCR. Various latest techniques were used to characterize Fe₃O₄–CS@tet-Pd(II), e.g., Fourier-transform infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy (EDS) elemental mapping, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning TEM (STEM), high resolution TEM (HR-TEM), vibrating sample magnetometer (VSM), fast Fourier transform (FFT), thermogravimetric analysis (TGA), etc. This study presents a unique example of 5-amino-1H-tetrazole grafted on Fe₃O₄–CS, which can easily be separated using an external magnet and reused five times without significant decrease of catalytic activity. In addition, the introduced method has significant advantages such as the utilization of natural and inexpensive materials, easy work-up, high yields of products, and high catalytic activity.

Full text of DOI:10.1016/j.molstruc.2021.130873

Journal of Molecular Structure 1244 (2021) 130873
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Preparation of magnetic chitosan-supported
palladium-5-amino-1H-tetrazole complex as a magnetically recyclable
catalyst for Suzuki-Miyaura coupling reaction in green media
a,∗
a
a
Mahmoud Nasrollahzadeh , Raziyeh Bakhshali-Dehkordi , Taghi A. Kamali ,
c,∗
b,∗
Yasin Orooji , Mohammadreza Shokouhimehr
a
Department of Chemistry, Faculty of Science, University of Qom, PO Box 37185-359, Qom, Iran
b
Jiangsu Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, International Innovation Center for Forest Chemicals and Materials,
College of Materials Science and Engineering, Nanjing Forestry University, Nanjing 210037, China
c
Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
The utilization of various tetrazoles as efficient ligands is a promising method for the functionalization
of tetrazole-based heterogeneous catalysts. Their combination with magnetic species and natural sup-
ports exposes huge opportunities for the practical applications of heterogeneous catalysts. In this study,
a green and novel strategy is applied to synthesize Fe3O4 magnetic nanoparticles (MNPs) incorporated
with chitosan (CS) and 5-amino-1H-tetrazole with a long tail ((3-chloropropyl)trimethoxysilane) to im-
mobilize palladium catalyst designated as Fe3O4–CS@tet-Pd(II). The prepared Fe3O4–CS@tet-Pd(II) was
used as an efficient and magnetically recyclable catalyst for the Suzuki-Miyaura cross-coupling reaction
Received 19 April 2021
Revised 29 May 2021
Accepted 6 June 2021
Available online 12 June 2021
Keywords:
Fe3O4 MNPs
Chitosan
(SMCR) using a mixture of EtOH/H O as green media under aerobic conditions. All the expected products
2
5
-Amino-1H-tetrazole
were obtained in high yields, indicating the high efficiency of this catalyst for the preparation of various
Palladium complex
Suzuki-Miyaura
Green media
biaryls by SMCR. Various latest techniques were used to characterize Fe3O4–CS@tet-Pd(II), e.g., Fourier-
transform infrared spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy (EDS) elemental mapping,
X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning TEM (STEM), high resolution
TEM (HR-TEM), vibrating sample magnetometer (VSM), fast Fourier transform (FFT), thermogravimetric
analysis (TGA), etc. This study presents a unique example of 5-amino-1H-tetrazole grafted on Fe3O4–CS,
which can easily be separated using an external magnet and reused five times without significant de-
crease of catalytic activity. In addition, the introduced method has significant advantages such as the
utilization of natural and inexpensive materials, easy work-up, high yields of products, and high catalytic
activity.
©
2021 Elsevier B.V. All rights reserved.
1
. Introduction
synthesis of various homogeneous or heterogeneous Pd-based
catalysts and their catalytic applications to promote the afore-
mentioned coupling reactions [11-13]. Indeed, heterogeneous Pd
catalysts have better reusability and durability than homogeneous
catalysts. Therefore, they are generally utilized for large-scale
catalytic organic processes and industrial applications [14-16].
The incorporation of solid supports with magnetic nanoparticles
(NPs) provides convenient catalyst recycling. Magnetically recy-
clable catalysts have various advantages including cost efficiency,
environmentally benign, non-toxicity, high surface area, easy sepa-
ration, etc. [17-20]. In contrast, unsupported catalyst NPs have low
stability and agglomerate quickly in the reaction mixture, losing
their efficiency [21-23]. To avoid their inevitable aggregation and
resolve the issues of stability, leaching, separation, and recovery,
many inorganic materials have been utilized as steady support
Metal-catalyzed Suzuki-Miyaura coupling reaction (SMCR) is
one of the most important organic reactions for the synthesis of
various biaryl compounds expediting the reaction between aryl
halides and arylboronic acids [1-3]. SMCR has been applied for
the synthesis of polymers, pharmaceuticals, advanced materials,
etc. [4,5]. Among transition metals, palladium (Pd)-based catalysts
have often been utilized in the carbon-carbon bond formations,
e.g., Negishi, Heck, Hiyama, Stille, Sonogashira, and, in particular,
SMCR [6-10]. Consequently, there are many reports related to the
∗
Corresponding authors.
E-mail
addresses:
mahmoudnasr81@gmail.com
(M.
Nasrollahzadeh),
yasin@njfu.edu.cn (Y. Orooji), mrsh2@snu.ac.kr (M. Shokouhimehr).
https://doi.org/10.1016/j.molstruc.2021.130873
0
022-2860/© 2021 Elsevier B.V. All rights reserved.

M. Nasrollahzadeh, R. Bakhshali-Dehkordi, T.A. Kamali et al.
Journal of Molecular Structure 1244 (2021) 130873
Fig. 1. Structures of chitin and chitosan.
for the immobilization of catalysts, e.g., clinoptilolite [24], sodium
borosilicate [25], graphene oxide [26], etc.
Among the available supports, biopolymers such as chitosan
(
CS) are used for the immobilization of metal NPs due to their
excellent stability, low cost, and high surface area [27-30]. CS
is a linear polysaccharide composed of randomly distributed β-
(
1→4)-linked d-glucosamine (deacetylated unit) and N-acetyl-d-
glucosamine (acetylated unit) generally obtained from alkaline
deacetylation of chitin which is widely available in the exoskele-
ton of certain crustacea such as crab, shrimp, and crawfish [31].
Fig. 1 demonstrates the structure of chitin and chitosan [32]. In
addition, CS has high biocompatibility, adsorption properties, and
biodegradability [29-31,33-35]. Butnariu and co-workers investi-
gated the Fourier-transform infrared spectroscopy (FT-IR) of chi-
tosan and chitin extract as biomass sources, confirming the pres-
ence of OH and NH2 groups [32]. CS also contains hydroxyl and
amine groups, which can chelate with metal NPs [36-38]. Recently,
the use of tetrazoles as efficient ligands in catalysis has garnered
huge attention [,39,40]. Tetrazoles and their anion (tetrazolate)
have several coordination modes (Fig. 2), functioning as multiden-
Fig. 2. Coordination modes of tetrazoles and their anion.
tate ligands in coordination chemistry for the synthesis of effective
catalysts via the complexation with metal ions [41-45].
In continuation of our study on the synthesis of tetrazole-based
catalysts, we described a facile and effective synthesis of magnetic
chitosan-supported tetrazole-Pd(II) complex (Fe O –CS@tet-Pd(II)).
3
4
Scheme 1. Synthesis procedure for the preparation of Fe3O4–CS@tet-Pd(II) catalyst.
2

M. Nasrollahzadeh, R. Bakhshali-Dehkordi, T.A. Kamali et al.
Journal of Molecular Structure 1244 (2021) 130873
Scheme 2. Preparation procedure for Fe3O4–CS@tet-Pd(II) catalyst.
The prepared catalyst exhibited high catalytic activity for the SMCR
the functional groups using a Perkin-Elmer 781 instrument. X-
ray diffraction (XRD) and vibrating sample magnetometer (VSM)
under green reaction conditions in ethanol:water (1:1) at 90 °C
(
Scheme 1).
measurements were performed using
˚
a Philips PW1373 (Cu
Kα = 1.5406 A, 2θ range = 10–90°) and Lake Shore VSM-7410,
respectively. The shape, size, composition, and elemental distribu-
tion of Fe O –CS@tet-Pd(II) were analyzed by transmission elec-
2
. Experimental
3
4
tron microscopy (TEM), scanning TEM (STEM), high resolution
TEM (HR-TEM) using a JEM-F200 JEOL microscope equipped with
energy-dispersive X-ray spectroscopy (EDS). The thermal analysis
2
.1. Reagents and methods
All the chemicals and solvents applied in this work were
of Fe O –CS@tet-Pd(II) was carried out by thermogravimetric anal-
purchased from Aldrich company and directly employed as re-
ceived without further purification. FT-IR analysis determined
3
4
ysis (TGA, Discovery USA) under nitrogen atmosphere. A Bruker
Fig. 3. FT-IR of Fe3O4–CS@tet-Pd(II).
3

M. Nasrollahzadeh, R. Bakhshali-Dehkordi, T.A. Kamali et al.
Journal of Molecular Structure 1244 (2021) 130873
Advance DRX500 MHz spectrometer was used to record 1H NMR
spectra. Melting points were measured on a BUCHI 510 melting
point apparatus.
2
.2. Synthesis of Fe O -chitosan
3 4
Fe O -chitosan (Fe O –CS) was prepared following the proce-
3
4
3
4
dure of our recently published article [30]. To prepare Fe O –CS
3
4
(
0.25 g) was dissolved in acetic acid solution (1%, 50 mL) and
mixed with Fe O4 NPs (2 g). The mixture was stirred for ~1 h.
3
Then, NaOH solution (50 mL, 1.0 M) was added slowly to the mix-
ture while stirring. The solid product (Fe O –CS) was isolated by
3
4
an external magnet.
2
.3. Synthesis of Fe O –CS@5-amino-1H-tetrazole
3
4
(
Fe O –CS@tet)
3 4
The synthetic procedure for the preparation of Fe O –CS@tet
3
4
is shown in Scheme 2. 5-amino-1H-tetrazole (5 mmol) was dis-
solved in ethanol (50 mL), and (3-chloropropyl)trimethoxysilane
(
5 mmol) was added to the mixture under stirring. The mixture
was stirred for 24 h under reflux conditions (solution A). Subse-
quently, Fe O –CS (1.5 g) was dispersed in ethanol (70 mL) us-
3
4
ing sonication for 20 min and mixed with solution A and K CO
2
3
(
5 mmol). The obtained mixture was stirred for 24 h at 60 °C.
Then, Fe O –CS@tet was collected with an external magnet and
3
4
thoroughly washed with ethanol several times, and finally dried in
a vacuum oven at 60 °C for 12 h.
2
.4. Synthesis of Fe O –CS@tet-Pd(II)
3 4
To prepare Fe O –CS@tet-Pd(II), a mixture of the as-prepared
3
4
Fe O –CS@tet (1 g) and PdCl (0.5 g) in ethanol (50 mL) was
3
4
2
stirred under reflux conditions for 24 h. The obtained solid
product was collected with an external magnet, washed with
ethanol several times, and dried in a vacuum oven at 60 °C.
The prepared nanostructured catalyst was utilized in SMCR
(
Scheme 2).
2
.5. General procedure for the Suzuki-Miyaura coupling
reaction
A mixture of aryl halide (1 mmol), C H B(OH) (1.1 mmol),
6
5
2
K2CO3 (2.0 mmol), and Fe O –CS@tet-Pd(II) catalyst (0.07 g) in
3
4
8
mL EtOH:H O (1:1) was stirred at 90 °C. The reaction progress
2
was monitored by thin-layer chromatography (TLC). After com-
pletion of the reaction, the catalyst was removed by an external
magnet, washed with ethanol and dried at 70 °C, and reused for
the subsequent reaction cycle. The synthesized compounds were
purified using column chromatography on silica gel and charac-
terized by nuclear magnetic resonance (NMR) and melting point
analysis.
2
.6. Characterization data of selected product
Biphenyl
1
HNMR (500 MHz, CDCl ) δ = 7.67 (d, J = 9.1 Hz, 2H), 7.52
3
H
(
t, J = 9.1 Hz, 2H), 7.43 (d, J = 8.8 Hz, 1H).
Fig. 4. EDS spectrum and elemental mapping of Fe3O4–CS@tet-Pd(II) catalyst.
3
. Results and discussion
catalyst. A sharp peak appeared at 1644 cm 1 presents the C = N
−
3
.1. Characterization of Fe O –CS@tet-Pd(II) catalyst
stretching vibration. As shown in Fig. 1, the broad peak at 3200–
3
4
3
500 cm 1 is related to the stretching vibrations of -OH and/or -
−
Fe O –CS@tet-Pd(II) catalyst was characterized precisely using
NH in chitosan. The construction peak of Fe O4 is observed at 536
3
3
4
cm 1, where the Fe-O stretching vibration is clear for Fe O MNPs
−
FT-IR, EDS, elemental mapping, XRD, STEM, HR-TEM, VSM, and TGA
techniques. Fig. 3 shows the FT-IR spectrum of Fe O –CS@tet-Pd(II)
3
4
−
1
[46]. The absorption peaks at 1026, 790, and 434 cm
indicate
3
4
4

M. Nasrollahzadeh, R. Bakhshali-Dehkordi, T.A. Kamali et al.
Journal of Molecular Structure 1244 (2021) 130873
Fig. 5. XRD pattern of Fe3O4–CS@tet-Pd(II) catalyst.
Fig. 6. (a) TEM and HR-TEM, (b) FFT, and (c) STEM images of Fe3O4–CS@tet-Pd(II) catalyst.
the Si-O-Si stretching, Si-O bending, and Si-O-Si bending, respec-
The structure of Fe O –CS@tet-Pd(II) catalyst was determined
3 4
−
1
tively. The characteristic absorption bands ~2800–3000 cm
and
by XRD study, confirming the presence of Fe O4 and Pd NPs. As
3
400–1500 cm 1 are attributed to C–H stretching and bending vi-
−
1
seen in Fig. 5, the sharp diffraction peaks indicate the high crys-
tallinity of Fe O –CS@tet-Pd(II) catalyst. The characteristic peaks at
brations of CH2 [40]. In addition, the band at 1450 cm 1 is ascribed
to the N = N stretching vibration in the structure of 5-amino-1H-
tetrazole.
−
3
4
2θ = 30.2°, 35.7°, 43.4°, 53.8°, 57.4°, and 63.1° can be assigned to
(220), (311), (400), (422), (511) and (440) reflection planes, respec-
tively, which are in good agreement to the cubic magnetite phase
(JCPDS#01–075–0449) of The peaks observed at 40.1° (111), 46.7°
(200), and 68.2° (220) are corresponding to the face-centered cubic
structure of Pd NPs in Fe O –CS@tet-Pd(II) catalyst, assuring their
The chemical composition of Fe O –CS@tet-Pd(II) catalyst was
3
4
characterized by EDS elemental mapping analysis (Fig. 4). Dis-
tinct peaks of Fe, C, N, Si, O, Pd, and Cl are clearly observed
in the EDS spectrum, indicating the formation and integrity of
Fe O –CS@tet-Pd(II) catalyst. Furthermore, the presence of Pd and
3
4
immobilization on Fe O –CS.
3
4
3
4
other elements existing in Fe O –CS@tet-Pd(II) confirms the graft-
The morphology of Fe O –CS@tet-Pd(II) catalyst was studied
3 4
3
4
ing of the palladium(II)-N-heterocyclic complex onto the surface of
by TEM, HR-TEM, STEM, and fast Fourier transform (FFT) analyses
(Fig. 6a-c). Fig. 6a demonstrates the TEM and HR-TEM images of
Fe O –CS.
3
4
5

M. Nasrollahzadeh, R. Bakhshali-Dehkordi, T.A. Kamali et al.
Journal of Molecular Structure 1244 (2021) 130873
Fig. 7. TGA curve of Fe3O4–CS@tet-Pd(II) catalyst.
Fig. 8. VSM curve of Fe3O4–CS@tet-Pd(II).
the as-prepared Fe O –CS@tet-Pd(II) with different magnifications.
the STEM image unambiguously demonstrates a homogeneously
assembled nanostructured catalyst.
3
4
It can be clearly seen from Fig. 6a that the obtained Pd NPs possess
spherical shape and are moderately uniform, dispersing with an
average diameter of ~10 nm. To further verify the crystallinity and
well-dispersion of Pd NPs on the surface of Fe O –CS@tet, STEM
Thermal stability of Fe O –CS@tet-Pd(II) catalyst was analyzed
3
4
by TGA analysis. Fig. 7 illustrates the comparative weight loss of
Fe O –CS magnetic NPs and Pd(II)−5-amino-1H-tetrazole complex
3
4
3
4
and FFT images were investigated (Fig. 6b). As shown in Fig. 7c,
immobilized on the modified magnetic NPs. The TGA curve depicts
6

M. Nasrollahzadeh, R. Bakhshali-Dehkordi, T.A. Kamali et al.
Journal of Molecular Structure 1244 (2021) 130873
Table 1
Optimization of the reaction conditions for SMCR.a.
Entry
Solvent
Catalyst (g)
Base
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
9
H2O
Fe3O4–CS@tet-Pd(II) (0.05)
Fe3O4–CS@tet-Pd(II) (0.05)
Fe3O4–CS@tet-Pd(II) (0.05)
Fe3O4–CS@tet-Pd(II) (0.05)
Fe3O4–CS@tet-Pd(II) (0.05)
Fe3O4–CS@tet-Pd(II) (0.05)
Fe3O4–CS@tet-Pd(II) (0.05)
Fe3O4–CS@tet-Pd(II) (0.07)
Fe3O4–CS@tet (0.05)
K2CO3
K2CO3
K2CO3
K2CO3
Na2CO3
Et3N
4.5
3.5
3.5
1.5
3
48
67
79
81
76
77
77
92
0
EtOH
Glycerol
EtOH/H2O
EtOH/H2O
EtOH/H2O
EtOH/H2O
EtOH/H2O
EtOH/H2O
EtOH/H2O
EtOH/H2O
EtOH/H2O
2:45
4:35
1:10
4
NaOH
K2CO3
K2CO3
K2CO3
–
1
1
1
0
1
2
Fe3O4–CS@tet-Pd(II) (0.04)
Fe3O4–CS@tet-Pd(II) (0.05)
Fe3O4–CS@tet-Pd(II) (0.08)
4
74
Trace
92
4
K2CO3
1:10
a
Reaction conditions: PhB(OH)2 (1.1 mmol), iodobenzene (1.0 mmol), base (2.0 mmol), and solvent
(
8.0 mL) at 90 °C.
b
Isolated yields.
Table 2
SMCR of phenylboronic acid with different aryl halides catalyzed by Fe3O4–CS@tet-Pd(II) catalyst.a.
Entry
R
X
Time (min)
Yield (%)b
1
2
3
4
5
6
7
8
9
H
I
70
92
88
89
88
85
90
91
87
87
78
86
82
76
65
2-OMe
4-OMe
4-Me
3-NO2
4-COMe
H
I
70
I
70
I
70
I
70
I
70
Br
Br
Br
Br
Br
Br
Cl
Cl
130
130
130
130
130
130
5 h
5 h
4-OMe
4-Me
3-NO2
4-COMe
4-CN
H
1
1
1
1
1
0
1
2
3
4
4-OMe
a
Reaction conditions: PhB(OH)2 (1.1 mmol), aryl halide (1.0 mmol), Fe3O4–CS@tet-Pd(II) (0.07 g), and K2CO3 (2.0 mmol) in EtOH:H2O (1:1, 8.0 mL) at 90
Isolated yields.
°
C.
b
−
1
several weight loss steps at a heating rate of 2 °C min
in flow-
3.2. Catalytic activity of Fe3O4–CS@tet-Pd(II) for the synthesis of
biaryl derivatives
ing air for Fe O –CS@tet-Pd(II). The maximum thermal degradation
3
4
of Fe O –CS@tet-Pd(II) catalyst was observed at 263 °C. The initial
3
4
weight loss, from the room temperature to 210 °C, is related to the
removal of physically adsorbed molecular water and organic sol-
vents on the surface of the catalyst. Most weight loss occurs above
The efficiency of Fe3O4–CS@tet-Pd(II) catalyst was tested for
the ligand-free SMCR. This catalyst eliminates the need for ex-
pensive and moisture-sensitive ligands for SMCR achievement. To
optimize the reaction conditions, the reaction between iodoben-
zene (1 mmol) and phenylboronic acid (1.1 mmol) was chosen
as a model reaction using Fe3O4–CS@tet-Pd(II) catalyst at 90 °C
(Table 1). Several experiments were performed under different re-
action conditions (nature of the base, effect of solvent, amount of
catalyst, etc.). The efficiency of the catalyst loading on the produc-
tion of biphenyl was studied by various amounts of Fe3O4–CS@tet-
Pd(II) in the presence of various bases (e.g., K2CO3, Na2CO3, NEt3,
and NaOH) and solvents (e.g., Glycerol, EtOH, H2O, and EtOH/H2O).
According to the obtained results, no product was obtained in the
absence of Fe3O4–CS@tet-Pd(II) or the presence of Fe3O4–CS@tet
(entry 9). It was found that the best yield was produced us-
ing K2CO3 (2 mmol) and EtOH/H2O (1:1, 8.0 mL) as the base
and solvent, respectively, as presented in Table 1. The amount of
Fe3O4–CS@tet-Pd(II) varied in the range of 0.04–0.07 g in the pres-
ence of K CO3 and EtOH/H O at 90 °C. The maximum yield of the
2
30 °C (between 230 and 600 °C), which is related to the degra-
dation of organic functional groups such as tetrazole and modi-
fied magnetic NPs. In addition, a weight loss is observed above
6
00 °C, which is assigned to the complete decomposition of the
catalyst.
The magnetic properties of Fe O –CS@tet-Pd(II) catalyst wae
3
4
examined using VSM technique at room temperature in a field
4
4
sweeping from −10 to +10 Oe (Fig. 8). Fe O –CS@tet-Pd(II) cat-
3
4
alyst presents a sensitive magnetic response so that it can easily
be separated from the reaction mixture by using an external mag-
net. The magnetization of Fe O NPs is higher than Fe O –CS@tet-
3
4
3
4
Pd(II) catalyst due to the modification of Fe O NPs with chitosan
3
4
support and tetrazole ligand. However, the magnetic property of
Fe O –CS@tet-Pd(II) catalyst is sufficiently high to provide efficient
3
4
separation and recycle.
2
2
7

M. Nasrollahzadeh, R. Bakhshali-Dehkordi, T.A. Kamali et al.
Journal of Molecular Structure 1244 (2021) 130873
Fig. 9. Reusability of Fe3O4–CS@tet-Pd(II) catalyst for SMCR of PhB(OH)2 and
iodobenzene.
desired product was obtained in the presence of Fe O –CS@tet-
3
4
Pd(II) catalyst (0.07 g) (Table 1, entry 8). No further improvement
in the yield of the product was discerned by increasing the amount
of Fe O –CS@tet-Pd(II) to 0.08 g (entry 13). Based on these obser-
3
4
vations, it was concluded that the optimum reaction condition was
K2CO3 (2 mmol) and catalyst (0.07 g) in EtOH/H O at 90 °C tem-
2
perature (Table 1, entry 8).
Under the optimized conditions, the catalytic activity, gen-
erality, and scope of the as-prepared Fe O –CS@tet-Pd(II) cat-
3
4
alyst was explored for the synthesis of biaryl derivatives us-
ing a variety of aryl halides and phenylboronic acid (Table 2).
The reaction of PhB(OH)2 with various aryl halides containing
electron-withdrawing and electron-donating groups provided dif-
ferent derivatives of biaryls yielding 82–92% within 70 min to
5
8
h using 0.07 g of Fe O –CS@tet-Pd(II) catalyst in EtOH:H O (1:1,
3 4 2
.0 mL) at 90 °C (Table 2). In addition, iodobenzenes were obtained
in good yields (Table 2, entry 1–6). To further investigate the ef-
ficacy of Fe O –CS@tet-Pd(II) catalyst, the reaction of chloroben-
3
4
zene and 4-methylchlorobenzene with phenylboronic acid was ex-
amined. Under the optimized reaction conditions, the correspond-
ing products were obtained in good yields (Table 2, entries 13 and
14).
Fig. 10. EDS image and elemental mapping of recycled Fe3O4–CS@tet-Pd(II) catalyst.
3
.3. Catalyst reusability
The recyclability of Fe O –CS@tet-Pd(II) catalyst was studied in
tivity even after five runs without any significant loss of activity
(Fig. 9), indicating the high stability and efficiency of the catalyst
under the applied reaction conditions. The EDS elemental mapping,
TEM, and HRTEM analyses of the recovered Fe O –CS@tet-Pd(II)
3
4
a model reaction of iodobenzene and phenylboronic acid in the
presence of K CO as an effective base in EtOH:H O at 90 °C. After
2
3
2
completion of the reaction as monitored by TLC, the reaction mix-
ture was cooled down to room temperature and the catalyst was
separated by an external magnet, washed with ethanol, and dried
in an oven at 70 °C. Then, the catalyst was reused for the next
cycles. It was found that the catalyst exhibited superb catalytic ac-
3
4
catalyst after five runs are shown in Figs. 10 and 11. These results
indicate that the size and shape of the catalyst are retained with-
out obvious detectable changes in the morphology and chemical
structure.
8

M. Nasrollahzadeh, R. Bakhshali-Dehkordi, T.A. Kamali et al.
Journal of Molecular Structure 1244 (2021) 130873
Fig. 11. TEM and HR-TEM images of the recycled Fe3O4–CS@tet-Pd(II) catalyst.
4. Conclusions
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