Synthesis of novel benzimidazoles and benzothiazoles via furan-2-carboxaldehydes, o-phenylenediamines, and 2-aminothiophenol using Cu(II) Schiff-base@SiO2 as a nanocatalyst

Article abstract of DOI:10.1002/aoc.6330

2-(5-Substituted phenyl)furan-2-carboxaldehyde derivatives were prepared by using an efficient copper(II) complex of tetradentate Schiff-base ligand immobilized onto silica as a heterogeneous nanocatalyst [Cu(II) Schiff-base@SiO₂] (5.0?mol%) using anilines, sodium nitrite, and furan-2-carboxaldehyde. Furthermore, attractive di-heteroaryl benzo-fused systems such as benzimidazole and benzothiazole derivatives were synthesized using this nanocatalyst (5.0?mol%) via the reaction of o-phenylenediamines and 2-aminothiophenol with 2-(5-substituted phenyl)furan-2-carboxaldehydes in EtOH. The catalyst was characterized by Fourier transform infrared (FT-IR), field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD), and inductively coupled plasma (ICP) techniques. The advantages of the present catalytic system are short reaction times, mild conditions, good to excellent yields, and low amount of nanocatalyst. Moreover, to the best of our knowledge, this is the first time of using the same catalyst in two steps including synthesis of 2-(5-substituted phenyl)furan-2-carboxaldehyde and benzimidazole or benzothiazole derivatives. In addition, the synthesized catalyst was recycled very well and reused several times without significant loss of its catalytic activity.

Full text of DOI:10.1002/aoc.6330

Received: 29 November 2020
DOI: 10.1002/aoc.6330
Revised: 20 May 2021
Accepted: 22 May 2021
F U L L P A P E R
Synthesis of novel benzimidazoles and benzothiazoles via
furan-2-carboxaldehydes, o-phenylenediamines, and
2-aminothiophenol using Cu(II) Schiff-base@SiO2 as a
nanocatalyst
Hashem Sharghi1
| Elahe Mashhadi1
| Mahdi Aberi1,2
| Jasem Aboonajmi1
1Department of Chemistry, College of
Sciences, Shiraz University, Shiraz, Iran
2Department of Chemical and Materials
Engineering, Faculty of Shahid Rajaee,
Shiraz Branch, Technical and Vocational
University (TVU), Shiraz, Iran
2-(5-Substituted phenyl)furan-2-carboxaldehyde derivatives were prepared by
using an efficient copper(II) complex of tetradentate Schiff-base ligand
immobilized onto silica as a heterogeneous nanocatalyst [Cu(II) Schiff-base@-
SiO2] (5.0 mol%) using anilines, sodium nitrite, and furan-2-carboxaldehyde.
Furthermore, attractive di-heteroaryl benzo-fused systems such as benzimid-
azole and benzothiazole derivatives were synthesized using this nanocatalyst
(5.0 mol%) via the reaction of o-phenylenediamines and 2-aminothiophenol
with 2-(5-substituted phenyl)furan-2-carboxaldehydes in EtOH. The catalyst
was characterized by Fourier transform infrared (FT-IR), field emission scan-
ning electron microscope (FESEM), energy-dispersive X-ray spectroscopy
(EDX), X-ray powder diffraction (XRD), and inductively coupled plasma (ICP)
techniques. The advantages of the present catalytic system are short reaction
times, mild conditions, good to excellent yields, and low amount of
nanocatalyst. Moreover, to the best of our knowledge, this is the first time of
using the same catalyst in two steps including synthesis of 2-(5-substituted
phenyl)furan-2-carboxaldehyde and benzimidazole or benzothiazole deriva-
tives. In addition, the synthesized catalyst was recycled very well and reused
several times without significant loss of its catalytic activity.
Correspondence
Hashem Sharghi, Department of
Chemistry, College of Sciences, Shiraz
University, Shiraz 7194684795, Iran.
Email: shashem@susc.ac.ir;
hashemsharghi@gmail.com
Funding information
Research Council of University of Shiraz
K E Y W O R D S
benzimidazole, benzothiazole, copper(II) complex, di-heteroaryl, heterogeneous
nanocatalyst
1 | INTRODUCTION
derivatives are more attractive motifs found in a wide
range of pharmaceuticals such as Nexium (esomeprazole)
Heterocycles are an important class of compounds
because of their widespread appearance in drugs, natural
products, and biologically active compounds.[1–9] Also,
these compounds have reactive sites that allow for fur-
ther functionalization.[10] Between various kinds of het-
erocyclic compounds, di-heterocycles benzo-fused
systems including benzimidazole and benzothiazole
antiulcerant (1), PARP-1 inhibitor (2), zopolrestat (for the
treatment of diabetes) (3), and aldose reductase inhibitor
(4) (Figure 1).[11–14] Moreover, these compounds have
unique properties. The basic core structures are used to
produce drugs with different properties like anticancer,
antimicrobial, anthelmintic, antiulcer, antiallergic,
human glucagon receptor antagonistic, and anti-
Appl Organomet Chem. 2021;e6330.
wileyonlinelibrary.com/journal/aoc
© 2021 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.6330

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SHARGHI ET AL.
FIGURE 1 Structures of bioactive
substituted benzimidazoles and
benzothiazoles
infectives.[15–21] Due to their wide range of applications,
various different synthetic paths have been developed
using catalytic systems.[22,23]
Heterogeneous catalytic systems are of particular
importance because they demonstrate excellent levels of
stability, are easily separated from the reaction mixture
by filtration, the catalysts can be reused several times,
possess high catalytic activity through increased interac-
tion with reactants, and have lots of application in het-
erocyclic chemistry and pharmaceutical industry.[59–70]
In continuation of our interest in exploring efficient
and diverse copper catalysts for organic processes,[71–78]
and as a result of our interest in the preparation of organic
compounds,[79–82] in the present study, first, we synthesized
and characterized copper(II) complex of tetradentate Schiff-
base ligand immobilized onto silica as a heterogeneous
nanocatalyst and applied it for the synthesis
of 2-(5-substituted phenyl)furan-2-carboxaldehyde and
One of the most common methods for
synthesizing
benzimidazole
and
benzothiazole
derivatives is through oxidative cyclization reaction
between o-phenylenediamines and 2-aminothiophenol
with benzaldehyde. In recent years, the syntheses of
benzimidazoles and benzothiazoles were reported using
a plethora of catalysts, such as metal–organic framework
(MOF) MIL-101(Cr),[24] NH2-MIL-125(Ti),[25] MgCl2,[26]
Ce(NO3)3.6H2O,[27] copper metallovesicles (CuMVs),[28]
Ni-MCM-41,[29]
Yb(OTf)3,[30]
H2O2/Fe(NO3)3,[31]
vanadium–salen nanoparticles supported on silica,[32]
cobalt–salen complex supported on activated carbon,[33]
copper nanoparticles on charcoal,[34] Co2+ complex
of [7-hydroxy-4-methyl-8-coumarinyl]glycine ([Co(MCG)
(H2O)3]),[35] iron-doped multi-walled carbon nanotubes
(Fe/MWCNTs),[36] chromium (III)–salen complex
nanoparticles on AlPO4,[37] CoFe2O4@SiO2@PAF-IL,[38]
and 2,6-dimethyl-1-nitropyridin-1-ium trinitromethanide
di-heteroaryl
molecules
including
2-(5-substituted
phenylfuran-2-yl)-1H-benzo[d]imidazole and benzothiazole
derivatives from furan-2-carboxaldehyde, anilines, sodium
nitrite, o-phenylenediamines, and 2-aminothiophenol in
EtOH solvent.
[39]
[2,6-DMPy-NO2]C(NO2)3.
Nowadays, metal catalysts play a vital role in enhanc-
ing the life quality of human society and support the
global economy. Copper catalysts have some interesting
physical and chemical properties such as having a cheap
and ubiquitous metal, which is one of the most abundant
transition metals present in living systems.[40] Cu-based
compounds have been used as catalysts for a wide range
of organic transformations such as multicomponent reac-
tions, reduction and oxidation reactions, cross-coupling,
click chemistry, C–H functionalization, and oxidative
coupling.[41–46] Also, there are various reports about
metal complexes stabilized on inorganic supports for the
preparation of heterocyclic compounds.[47–58]
2 | EXPERIMENTAL SECTION
Melting points and infrared (IR) spectra were measured
on an Electrothermal 9100 apparatus and a JASCO FT-
IR-460 plus spectrometer, respectively. All reagents and
solvents were purchased from Merck, Fluka, or Sigma-
Aldrich. The 1H NMR (400 MHz) and 13C NMR
(100 MHz) were obtained on Bruker DRX-400 Avance
instruments with DMSO-d6 and CDCl3 as a solvent. The
X-ray diffraction (XRD) patterns were recorded on a
Bruker D8 ADVANCE X-ray diffractometer using nickel-
filtered Cu Kα radiation (k = 1.5406 Aꢀ). Field emission
scanning electron micrograms (FESEM) were obtained

SHARGHI ET AL.
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using a KYKY-EM3200 instrument. The inductively
coupled plasma (ICP) analysis data were obtained using a
Varian Vista-Pro analyzer.
and nanocatalyst in EtOH (5.0 mL) was stirred at 25ꢀC or
78ꢀC. The progress of the reaction was monitored by thin-
layer chromatography (TLC). After completion of the reac-
tion, the reaction mixture was centrifuged to separate the
nanocatalyst. The organic layer was washed with
deionized water (3 ꢁ 10 mL) and was evaporated in vac-
uum. The crude product was purified by silica gel column
chromatography.
2.1 | Synthesis of copper(II) Schiff-base
complex
The Schiff-base N,N0-bis-(pyridin-2-ylmethylene)-ethane-
1,2-diamine was prepared via reaction of pyridine-
2-carbaldehyde with ethylenediamine in EtOH.
Copper(II) Schiff-base complex was synthesized by N,N0-
2.4 | Characterization data of
synthesized compounds
bis-(pyridin-2-ylmethylene)-ethane-1,2-diamine
with
CuCl2.2H2O (1.0 mmol) in ethanol solvent (10.0 mL) at
room temperature for 4 h. After completion of the reac-
tion, the thick precipitate was filtered off and washed
with ethanol (3 ꢁ 5 mL) and obtained dark green solid
copper(II) Schiff-base complex.[83–87]
2.4.1 | N,N0-bis-(pyridin-2-ylmethylene)-
ethane-1,2-diamine (Schiff-base)
Isolated yield: 90%. Brown solid, mp: 66–67ꢀC; IR (KBr):
1
1644 (C═N); H NMR (250 MHz, CDCl3): δ (ppm) 4.06
(s, 4H), 7.30 (ddd, J = 7.5, 5.0, 2.5 Hz, 2H), 7.68–7.75
(m, 2H), 7.97 (d, J = 7.5 Hz, 2H), 8.41 (s, 2H), 8.61
(d, J = 5.0 Hz, 2H).
2.2 | Anchoring of copper(II) Schiff-base
complex onto silica
3-Aminopropyl-functionalized silica gel (1.0 g) was added
to copper(II) Schiff-base complexes (1.5 mmol) in ethanol
solvent (10.0 mL) under stirring at room temperature for
24 h. The solid product was separated by centrifuging
and washed three times with EtOH (3 ꢁ 5 mL). Finally,
the solid product was dried at 60ꢀC in a vacuum.
2.4.2 | 2-(5-(4-Chlorophenyl)furan-2-yl)-1H-
benzo[d]imidazole (3a)
Purified by column chromatography on silica gel and
eluted with ethyl acetate/petroleum ether. Isolated yield:
81%. Dark brown solid, mp: 225–227ꢀC; IR (KBr): 3440
1
(NH); H NMR (400 MHz, DMSO-d6): δ (ppm) 7.21–7.26
(m, 2H), 7.25 (d, J = 4.0 Hz, 1H), 7.31 (d, J = 4.0 Hz,
1H), 7.57 (d, J = 8.0 Hz, 2H), 7.59–7.62 (m, 2H), 7.96
(d, J = 12.0 Hz, 2H); 13C NMR (100 MHz, DMSO-d6): δ
(ppm) 108.9, 112.4, 112.5, 122.3, 122.4, 125.5, 128.3, 128.9,
128.9, 132.5, 145.3, 152.9. Anal. Calcd for
C17H11ClN2O: C, 69.28; H, 3.76; N, 9.50; Found: C,
69.02; H, 3.54; N, 9.65.
2.3 | General procedure for the synthesis
of 5-phenylfuran-2-carbaldehydes,
2-(5-arylfuran-2-yl)-1H-benzo[d]imidazole,
and 2-(5-arylfuran-2-yl) benzothiazole in
the presence of cu(II) complex
nanoparticles onto silica
4-Substituted aniline (7.0 mmol) was dissolved in a mix-
ture of H2O (1.2 mL) and concentrated HCl (1.7 mL). The
solution was cooled to 0ꢀC and diazotized at 0–5ꢀC with
NaNO2 (7.0 mmol) dissolved in H2O (1.3 mL). The solu-
tion was stirred for 15 min, filtered, and then, furan-
2-carboxaldehyde (8.5 mmol) in H2O (2.5 mL) was added
along with a solution of nanocatalyst Cu(II) Schiff-base@-
SiO2 (5.0 mol%) in H2O (1.3 mL) at a temperature of 10–
15ꢀC. The reaction mixture was slowly warmed up to 40ꢀC
and stirred at this temperature for 4 h. The precipitate was
filtered and washed with water and an aqueous solution of
NaHCO3 (5.0%). The 5-phenylfuran-2-carbaldehydes and
nanocatalyst were dried at room temperature. Next,
a solution of o-phenylenediamines/2-aminothiophenol
(1.0 mmol), 5-phenylfuran-2-carbaldehydes (1.0 mmol),
2.4.3 | 2-(5-(4-Bromophenyl)furan-2-yl)-1H-
benzo[d]imidazole (3b)
Purified by column chromatography on silica gel and
eluted with ethyl acetate/petroleum ether. Isolated yield:
81%. Dark brown solid, mp: 243–245ꢀC; IR (KBr): 3438
1
(NH); H NMR (400 MHz, DMSO-d6): δ (ppm) 7.21–7.24
(m, 2H), 7.26 (d, J = 4.0 Hz, 1H), 7.31 (d, J = 4.0 Hz,
1H), 7.59–7.64 (m, 2H), 7.71 (d, J = 8.0 Hz, 2H), 7.89
(d, J = 12.0 Hz, 2H), 13.12 (s, 1H); 13C NMR (100 MHz,
DMSO-d6): δ (ppm) 108.9, 111.3, 112.6, 118.7, 121.1,
121.9, 122.8, 125.8, 128.7, 131.8, 134.2, 143.2, 143.7, 145.1,
153.0. Anal. Calcd for C17H11BrN2O: C, 60.20; H, 3.27; N,
8.26; Found: C, 60.05; H, 3.13; N, 8.34.

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2.4.4 | 2-(5-(4-Methoxyphenyl)furan-2-yl)-
(NH); H NMR (400 MHz, CDCl3): δ (ppm) 2.41 (s, 3H),
6.69 (d, J = 4.0 Hz, 1H), 7.03 (d, J = 8.0 Hz, 1H), 7.17
(d, J = 4.0 Hz, 1H), 7.28 (d, J = 8.0 Hz, 2H), 7.34 (s, 1H),
7.47 (d, J = 8.0 Hz, 1H), 7.56 (d, J = 8.0 Hz, 2H); 13C
NMR (100 MHz, DMSO-d6): δ (ppm) 21.4, 109.7, 114.4,
121.7, 122.3, 122.6, 125.4, 125.9, 126.8, 128.2, 132.0, 133.7,
147.6, 153.3, 154.3, 156.3. Anal. Calcd for
C18H13ClN2O: C, 70.02; H, 4.24; N, 9.07; Found: C,
69.68; H, 4.09; N, 8.81.
1H-benzo[d]imidazole (3c)
Purified by column chromatography on silica gel and
eluted with ethyl acetate/petroleum ether. Isolated yield:
72%. Brown solid, mp: 262–263ꢀC; IR (KBr): 3435 (NH);
1H NMR (400 MHz, DMSO-d6): δ (ppm) 3.81 (s, 3H),
7.03–7.11 (m, 3H), 7.19–7.22 (m, 2H), 7.28
(d, J = 4.0 Hz, 1H), 7.59 (d, J = 12.0 Hz, 2H), 7.87
(d, J = 12.0 Hz, 2H); 13C NMR (100 MHz, DMSO-d6): δ
(ppm) 55.7, 106.8, 113.2, 114.9, 122.6, 122.8, 126.0, 127.7,
144.5, 154.8, 159.7. Anal. Calcd for C18H14N2O2: C,
74.47; H, 4.86; N, 9.65; Found: C, 74.19; H, 4.65; N, 9.79.
2.4.8 | 2-[5-(4-Bromophenyl)-2-furanyl]-
5-methyl-1H-benzimidazole (3g)
Purified by column chromatography on silica gel and
eluted with ethyl acetate/petroleum ether. Isolated yield:
57%. Pale brown solid, mp: 270–271ꢀC; IR (KBr): 3455
(NH); 1H NMR (400 MHz, DMSO-d6): δ (ppm) 2.38
(s, 3H), 6.95–7.01 (m, 1H), 7.19 (d, J = 4.0 Hz, 1H), 7.26
(s, 1H), 7.36 (d, J = 8.0 Hz, 1H), 7.45 (d, J = 8.0 Hz, 1H),
7.64 (d, J = 8.0 Hz, 2H), 7.81 (d, J = 12.0 Hz, 2H), 12.91
(s,1H); 13C NMR (100 MHz, DMSO-d6): δ (ppm) 21.3,
108.9, 110.8, 111.0, 112.2, 112.3, 118.3, 118.4, 121.0, 123.4,
124.2, 125.7, 128.7, 131.8, 145.3, 152.8. Anal. Calcd for
C18H13BrN2O: C, 61.21; H, 3.71; N, 7.93; Found: C,
61.52; H, 3.40; N, 8.02.
2.4.5 | 2-(5-(2-Chlorophenyl)furan-2-yl)-1H-
benzo[d]imidazole (3d)
Purified by column chromatography on silica gel and
eluted with ethyl acetate/petroleum ether. Isolated yield:
82%. Orange solid, mp: 251–253ꢀC; IR (KBr): 3437 (NH);
1H NMR (400 MHz, DMSO-d6): δ (ppm) 7.23–7.26
(m, 2H), 7.36–7.39 (m, 2H), 7.42 (dd, J = 1.2, 7.6 Hz, 1H),
7.53 (t, J = 7.6 Hz 1H), 7.59–7.64 (m, 3H), 7.42
(dd, J = 1.6, 8.0 Hz, 1H), 13.15 (s, 1H); 13C NMR
(100 MHz, DMSO-d6): δ (ppm) 112.4, 113.2, 122.3, 122.4,
122.5, 127.5, 127.6, 128.1, 129.2, 129.4, 130.7, 143.1, 145.0,
150.1. Anal. Calcd for C17H11ClN2O: C, 69.28; H, 3.76; N,
9.50; Found: C, 68.95; H, 3.47; N, 9.31.
2.4.9 | 2-(5-(4-Bromophenyl)furan-2-yl)-
5-chloro-1H-benzo[d]imidazole (3h)
2.4.6 | 2-(5-(3-Chlorophenyl)furan-2-yl)-1H-
benzo[d]imidazole (3e)
Purified by column chromatography on silica gel and
eluted with ethyl acetate/petroleum ether. Isolated yield:
56%. Brown liquid, mp: 167–168ꢀC; IR (KBr): 3451 (NH);
1H NMR (400 MHz, DMSO-d6): δ (ppm) 7.23–7.26
(m, 1H), 7.28 (d, J = 4.0 Hz, 1H), 7.33 (d, J = 4.0 Hz,
1H), 7.56–7.68 (m, 2H), 7.72 (d, J = 8.0 Hz, 2H), 7.88
(d, J = 8.0 Hz, 2H), 13.26 (s, 1H); 13C NMR (100 MHz,
DMSO-d6): δ (ppm) 109.0, 110.9, 112.5, 113.2, 113.3,
118.0, 119.9, 121.3, 122.3, 122.8, 125.8, 128.6, 131.9, 144.6,
153.3. Anal. Calcd for C17H10BrClN2O: C, 54.65; H,
2.70; N, 7.50; Found: C, 54.32; H, 2.50; N, 7.44.
Purified by column chromatography on silica gel and
eluted with ethyl acetate/petroleum ether. Isolated yield:
55% Dark brown solid, mp: 232–234ꢀC; IR (KBr): 3412
(NH); 1H NMR (400 MHz, DMSO-d6): δ (ppm) 7.23
(d, J = 4.0 Hz, 2H), 7.33 (q, J = 4.0 Hz, 2H), 7.43
(d, J = 8.0 Hz, 1H), 7.53 (t, J = 8.0 Hz, 1H), 7.59–7.64
(m, 2H), 7.90 (d, J = 8.0 Hz, 1H), 8.05 (s, 1H), 13.16
(s, 1H); 13C NMR (100 MHz, DMSO-d6): δ (ppm) 109.6,
112.5, 122.3, 122.4, 123.3, 123.4, 127.7, 130.8, 131.4, 133.9,
143.2, 145.4, 152.4. Anal. Calcd for C17H11ClN2O: C,
69.28; H, 3.76; N, 9.50; Found: C, 69.02; H, 3.49; N, 9.38.
2.4.10 | 5-Chloro-2-(5-(2-chlorophenyl)
furan-2-yl)-1H-benzo[d]imidazole (3i)
2.4.7 | 2-(5-(4-chlorophenyl)furan-2-yl)-
5-methyl-1H-benzo[d]imidazole (3f)
Purified by column chromatography on silica gel and
eluted with ethyl acetate/petroleum ether. Isolated
yield: 80%. Dark orange solid, mp: 224–226ꢀC; IR
(KBr): 3432 (NH); 1H NMR (400 MHz, DMSO-d6): δ
(ppm) 7.25–7.70 (m, 8H), 8.19 (s, 1H), 13.32 (s, 1H); 13C
NMR (100 MHz, DMSO-d6): δ (ppm) 112.9, 113.3, 116.0,
Purified by column chromatography on silica gel and
eluted with ethyl acetate/petroleum ether. Isolated yield:
68%. Dark brown solid, mp: 215–217ꢀC; IR (KBr): 3442

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118.1, 120.0, 122.8, 126.8, 127.5, 127.5, 127.6, 128.2,
129.3, 129.5, 130.8, 131.2, 144.6, 150.5. Anal. Calcd for
C17H10Cl2N2O: C, 62.03; H, 3.06; N, 8.51; Found: C,
62.22; H, 3.15; N, 8.74.
2.4.14 | 2-[5-(4-Chlorophenyl)-2-furanyl]-
benzothiazole (3m)
Purified by column chromatography on silica gel and eluted
with ethyl acetate/petroleum ether. Isolated yield: 85%.
Pale brown solid, mp: 182–183ꢀC; 1H NMR (400 MHz,
DMSO-d6): δ (ppm) 7.35 (d, J = 4.0 Hz, 1H), 7.47
(d, J = 8.0 Hz, 1H), 7.51 (d, J = 4.0 Hz, 1H), 7.56
(d, J = 8.0 Hz, 1H), 7.60 (d, J = 12.0 Hz, 2H), 7.90
(d, J = 8.0 Hz, 2H), 8.06 (d, J = 8.0 Hz, 1H), 8.17
(d, J = 8.0 Hz, 1H); 13C NMR (100 MHz, DMSO-d6): δ (ppm)
109.7, 114.5, 122.3, 122.6, 125.5, 125.8, 126.5, 127.9, 129.3,
134.3, 147.5, 155.6, 156.3. Anal. Calcd for C17H10ClNOS: C,
65.49; H, 3.23; N, 4.49; Found: C, 65.31; H, 3.11; N, 4.34.
2.4.11 | 2-[5-(3-Chlorophenyl)-2-furanyl]-
5-chlor-1H-benzimidazole (3j)
Purified by column chromatography on silica gel and
eluted with ethyl acetate/petroleum ether. Isolated yield:
55%. Dark brown, mp: 231–233ꢀC; IR (KBr): 3431 (NH);
1H NMR (400 MHz, CDCl3): 6.68 (d, J = 4.0 Hz, 1H),
7.11–7.19 (m, 5H), 7.38 (d, J = 8.0 Hz, 1H), 7.45
(d, J = 8.0 Hz, 1H), 7.52 (s, 2H); 13C NMR (100 MHz,
CDCl3): δ (ppm) 108.5, 112.9, 122.3, 123.2, 123.5, 124.0,
126.6, 127.9, 129.3, 130.0, 131.5, 134.7, 137.0, 144.8, 145.1,
153.6. Anal. Calcd for C17H10Cl2N2O: C, 62.03; H,
3.06; N, 8.51; Found: C, 61.86; H, 3.017; N, 8.46.
2.4.15 | 2-(5-(4-Bromophenyl)furan-2-yl)
benzo[d]thiazole (3n)
Purified by column chromatography on silica gel and eluted
with ethyl acetate/petroleum ether. Isolated yield: 80%. Dark
orange solid, mp: 189–190ꢀC; IR (KBr): 1H NMR (400 MHz,
DMSO-d6): δ (ppm) 7.36 (d, J = 4.0 Hz, 1H), 7.46 (d, J =
8.0 Hz, 1H), 7.50 (d, J = 4.0 Hz, 1H), 7.57 (t, J = 8.0 Hz, 1H),
7.72 (d, J = 8.0 Hz, 2H), 7.82 (d, J = 8.0 Hz, 2H), 8.05
(d, J = 8.0 Hz, 1H), 8.16 (d, J = 8.0 Hz, 1H); 13C NMR
(100 MHz, DMSO-d6): δ (ppm) 109.7, 114.4, 121.7, 122.3,
122.6, 125.4, 125.9, 126.8, 128.2, 132.0, 133.7, 147.6, 153.3,
154.3, 156.3. Anal. Calcd for C17H10BrNOS: C, 57.32; H,
2.83; N, 3.93; Found: C, 57.41; H, 2.98; N, 4.05.
2.4.12 | 2-[5-(4-Chlorophenyl)-2-furanyl]-
5-chlor-1H-benzimidazole (3k)
Purified by column chromatography on silica gel and
eluted with ethyl acetate/petroleum ether. Isolated yield:
80%. Pale brown solid, mp: 210–212ꢀC; IR (KBr): 3434
1
(NH); H NMR (400 MHz, DMSO-d6): δ (ppm) 7.21–7.27
(m, 1H), 7.28 (d, J = 4.0 Hz, 1H), 7.34 (d, J = 4.0 Hz,
1H), 7.59 (d, J = 8.0 Hz, 2H), 7.63–7.71 (m, 2H), 7.96
(d, J = 8.0 Hz, 2H), 13.28 (s, 1H); 13C NMR (100 MHz,
DMSO-d6): δ (ppm) 109.0, 110.7, 113.2, 119.9, 122.5,
125.6, 128.3, 129.0, 132.7, 136.4, 144.6, 147.6, 153.2. Anal.
Calcd for C17H10Cl2N2O: C, 62.03; H, 3.06; N, 8.51;
Found: C, 61.73; H, 2.95; N, 8.59.
2.4.16 | 2-(5-(2-Chlorophenyl)furan-2-yl)
benzo[d]thiazole (3o)
Purified by column chromatography on silica gel and
eluted with ethyl acetate/petroleum ether. Isolated yield:
77%. Pale brown solid, mp: 208–210ꢀC; H NMR (400 MHz,
DMSO-d6): δ (ppm) 7.39 (d, J = 4.0 Hz, 1H), 7.46–7.50
(m, 2H), 7.53–7.56 (m, 2H), 7.58–7.60 (m, 1H), 7.64
(dd, J = 0.8, 7.6 Hz, 1H), 7.98 (dd, J = 1.6, 8.0 Hz, 1H),
8.07 (d, J = 8.0 Hz, 1H), 8.17 (d, J = 8.0 Hz, 1H); 13C NMR
(100 MHz, DMSO-d6): δ (ppm) 113.7, 113.8, 122.4, 122.7,
125.5, 126.8, 127.3, 127.8, 128.4, 129.6, 130.0, 130.9, 133.8,
147.5, 151.6, 153.3, 156.2. Anal. Calcd for C17H10BrNOS: C,
65.49; H, 3.23; N, 4.49; Found: C, 65.31; H, 3.12; N, 4.57.
2.4.13 | 2-(5-(2-Chlorophenyl)furan-2-yl)-
5-methyl-1H-benzo[d]imidazole (3l)
Purified by column chromatography on silica gel and
eluted with ethyl acetate/petroleum ether. Isolated
yield: 79%.brown oil, mp: 240–241ꢀC; IR (KBr): 3440
(NH); 1H NMR (400 MHz, CDCl3): δ (ppm) 2.64
(s, 3H), 6.66 (t, J = 8.0 Hz, 1H), 6.98 (t, J = 8.0 Hz,
1H), 7.11 (d, J = 4.0 Hz, 1H), 7.14 (s, 1H), 7.23
(t, J = 8.0 Hz, 1H), 7.29 (t, J = 4.0 Hz, 2H), 7.33
(d, J = 8.0 Hz, 1H), 7.57 (d, J = 8.0 Hz, 1H) 12.15
(s, 1H); 13C NMR (100 MHz, CDCl3): δ (ppm) 17.6,
112.6, 113.2, 123.3, 123.8, 125.7, 126.5, 127.6, 127.9,
128.4, 130.0, 130.5, 138.5, 138.7, 143.9, 144.5, 151.5.
Anal. Calcd for C18H13ClN2O: C, 70.02; H, 4.24; N,
9.07; Found: C, 70.21; H, 4.17; N, 9.14.
2.4.17 | 2-(5-(3-Chlorophenyl)furan-2-yl)
benzo[d]thiazole (3p)
Purified by column chromatography on silica gel and
eluted with ethyl acetate/petroleum ether. Isolated yield:

6 of 12
SHARGHI ET AL.
72%. Pale brown solid, mp: 204–206ꢀC; 1H NMR
(400 MHz, CDCl3): δ (ppm) 6.80 (d, J = 3.6 Hz, 1H),
7.22–7.25 (m, 2H), 7.31 (t, J = 7.6 Hz, 2H), 7.42–7.46
(m, 1H), 7.59–7.62 (m, 1H), 7.72 (t, J = 1.6 Hz, 1H), 7.84
(d, J = 8.0 Hz, 1H), 7.99 (d, J = 8.0 Hz, 1H); 13C NMR
(100 MHz, CDCl3): δ (ppm) 108.8, 113.4, 119.1, 121.6,
122.4, 123.1, 123.9, 124.3, 125.2, 126.5, 128.3, 128.8, 130.1,
131.3, 134.9, 153.8, 154.5. Anal. Calcd for
C17H10ClNOS: C, 65.49; H, 3.23; N, 4.49; Found: C,
65.31; H, 3.15; N, 4.42.
produced by adding 3-aminopropyl-functionalized silica
gel to copper(II) Schiff-base complex in EtOH solvent at
room temperature for 24 h.[75] Copper(II) Schiff-base
complex was prepared via the reaction of N,N0-bis-
(pyridin-2-ylmethylene)-ethane-1,2-diamine in the pres-
ence of CuCl2.2H2O and EtOH at room temperature
(Scheme 1).[83–87] The catalyst was characterized by FT-
IR, FESEM, energy-dispersive X-ray spectroscopy (EDX),
XRD, and ICP.
Figure 2 shows the Fourier transform infrared
(FT-IR) spectra of Schiff-base, Cu(II) Schiff-base complex,
and Cu(II) Schiff-base@SiO2. The observed peaks at
1644 cmꢂ1 represent the stretching band of imine (C═N)
nitrogen groups of Schiff-base (Figure 2a).[85] The shift of
the (C═N) stretching band to around 1604 cmꢂ1 suggests
the coordination of ligand to the copper ion
(Figure 2b).[85] The appearance of a peak in ꢃ471 cmꢂ1 is
related to the formation of Cu–N during the immobiliza-
tion of the Cu(II) Schiff-base@SiO2 (Figure 2c).[85] The
peaks at 797 and 1103 cmꢂ1 are related to the symmetric
and asymmetric stretching vibration of Si–O groups.[75]
Figure 3a shows the morphology of the nanoparticles
of copper(II) complex onto silica substrate in spherical
features. A little aggregation may be due to the hydrogen
bonds from the site of NH connected to the propyl group.
Figure 3b with a higher magnification shows a rough and
porous structure suggesting the improvement of the
surface area resulting in high catalytic activity. Figure 3b
also shows the nanoparticles size is in the range of
15–20 nm approximately. This feature could improve
catalytic activity, as well.
3 | RESULTS AND DISCUSSION
Copper(II) complex of tetradentate Schiff-base ligand
immobilized onto silica [Cu(II) Schiff-base@SiO2] was
The catalyst composition was surveyed by EDX analy-
sis. The obtained result is shown in Figure 4. The result
SCHEME 1 Copper(II) complex of tetradentate Schiff-base
ligand immobilized onto silica [Cu(II) Schiff-base@SiO2]
FIGURE 2 Fourier transform
infrared (FT-IR) spectra of Schiff-base
(a), Cu(II) Schiff-base complex (b), and
Cu(II) Schiff-base@SiO2 (c)

SHARGHI ET AL.
7 of 12
FIGURE 3 Field emission scanning electron microscope (FESEM) images of Cu(II) Schiff-base@SiO2
confirms the presence of Cu, Si, O, and N elements in the
synthesized sample composition.
Figure 5 shows the XRD pattern of Cu(II) Schiff-
base@SiO2. As shown in the Figure 5, the pattern
includes the indexed peaks attributed to the different
phases of (111), (110), (200), (222), and (400) planes of Cu
[78,88]
from the Cu(II) Schiff-base@SiO2.
Also, the content of copper in the Cu(II) Schiff-
base@SiO2 was determined by ICP analysis. Based on the
ICP results, the quantity of copper nanoparticles was
evaluated to be 3.37 wt%.
In what continues, we synthesized 5-phenylfuran-
2-carbaldehyde derivatives[89] via reaction of aniline
derivatives with sodium nitrite, HCl, furan-
2-carbaldehyde in the presence of 5.0 mol% Cu(II) Schiff-
base@SiO2 as nanocatalyst (Scheme 2). After completion
FIGURE 4 Energy-dispersive X-ray spectroscopy (EDX) of
Cu(II) Schiff-base@SiO2
FIGURE 5 X-ray diffraction (XRD)
patterns of Cu(II) Schiff-base@silica as a
nanocatalyst

8 of 12
SHARGHI ET AL.
was obtained under the catalyst-free conditions (Table 1,
Entry 1). Also, when the reaction was screened in the
presence of Cu(II) Schiff-base@SiO2 (5.0 mol%) under
solvent-free conditions, only 25% product was obtained
after 12 h (Table 1, Entry 2). In the following, we exam-
ined the effect of various solvents such as EtOH, DMSO,
DMF, CH3CN, EtOAc, and DCM on the model reaction,
and the best yield was achieved in EtOH at 25ꢀC
(Table 1, Entries 3–8). So, 5 mol% Cu(II) Schiff-
base@SiO2 in EtOH solvent was found to be the optimal
condition to push the reaction forward (Table 1, Entry 3).
Moreover, the reaction was also tested at reflux using the
catalyst, and it was found that the temperature has a
reverse effect on the yield of model reaction (Table 1,
Entry 9). Eventually, Schiff-base-Cu(II) was applied as a
catalyst, and lower yield of desired product (88%) was
obtained (Table 1, Entry 10). The solubility of Schiff-
base-Cu(II) in ethanol makes the catalyst separation and
recycling process difficult. This observation proves the
role necessity of heterogeneous nano-Cu(II) Schiff-
base@SiO2 for this reaction.
SCHEME 2 Synthesis of 5-phenylfuran-2-carbaldehyde
derivatives
of the reaction, the thick precipitate was filtered off and
washed with water and an aqueous solution of NaHCO3
(5%) and water. The 5-phenylfuran-2-carbaldehyde and
Cu(II) Schiff-base@SiO2 were dried at room temperature.
After synthesis of 5-phenylfuran-2-carbaldehyde and
characterization of the Cu(II) Schiff-base@SiO2 as
nanocatalyst, its catalytic ability was studied in the syn-
thesis of benzimidazole and benzothiazole derivatives. To
find out the suitable condition for the reaction, a series of
experiments for different parameters such as solvent and
temperature were performed with the standard reaction
After optimization of the reaction conditions, a series
of new 2-(5-substituted phenylfuran-2-yl)-1H-benzo[d]
imidazole and benzothiazole derivatives were synthesized
via the reaction of heterocyclic aromatic aldehydes with
o-phenylenediamines/or 2-aminothiophenol in the pres-
ence of 5 mol% Cu(II) Schiff-base@SiO2 as a heteroge-
neous nanocatalyst, and the desired products were
of
o-phenylenediamine
1a
(1.0
mmol)
and
5-(4-chlorophenyl)furan-2-carbaldehyde 2a (1.0 mmol)
for the synthesis of 2-(5-(4-chlorophenyl)furan-2-yl)-1H-
benzo[d]imidazole 3a (Table 1). At first, the reaction was
tested in the absence of catalyst, and no product
TABLE 1 Optimization of the
reaction conditions for synthesis of
2-(5-(4-chlorophenyl)furan-2-yl)-1H-
benzo[d]imidazolea,b
Entry
Catalyst/mol%
Solvent
EtOH
-
Temp.
25ꢀC
25ꢀC
25ꢀC
25ꢀC
25ꢀC
25ꢀC
25ꢀC
25ꢀC
Reflux
25ꢀC
Time (h)
Yielda %
Trace
25
1
-
12
12
2
2
Schiff-base-Cu(II)@SiO2/5
Cu(II)Schiff-base@SiO2/5
Schiff-base-Cu(II)@SiO2/5
Schiff-base-Cu(II)@SiO2/5
Schiff-base-Cu(II)@SiO2/5
Schiff-base-Cu(II)@SiO2/5
Schiff-base-Cu(II)@SiO2/5
Schiff-base-Cu(II)@SiO2/5
Schiff-base-Cu(II)/5
3
EtOH
DMSO
DMF
90
4
5
60
5
5
72
6
CH3CN
EtOAc
DCM
EtOH
EtOH
6
65
7
6
51
8
8
44
9
2
75
10
2
88
Note: The best optimization condition is bold.
aGeneral conditions: o-phenylendiamine (1.0 mmol), 5-(4-chlorophenyl)furan-2-carbaldehyde (1.0 mmol),
solvent (5.0 mL), air.
bIsolated yield.

SHARGHI ET AL.
9 of 12
obtained in good to excellent yields. The structures of the
new synthesized organic compounds were confirmed by
FT-IR, 1H NMR, 13C NMR, and elemental analysis
(Scheme 3, 3a–p).
As shown in Scheme 3, heterocyclic aromatic alde-
hydes containing different groups such as Cl, Br, and
OMe reacted with o-phenylenediamine and afforded the
desired benzimidazole derivatives in good to excellent
yields (Scheme 3, 3a–e).
Also, o-phenylenediamines, including Cl and Me
groups, participated in the reaction with different het-
erocyclic aromatic aldehydes to achieve corresponding
products in good yields at room temperature
(Scheme 3, 3f–l).
To further highlight the usefulness of this protocol,
2-aminothiophenol reacted with heterocyclic aromatic
aldehydes and led to the synthesis of benzothiazole deriv-
atives with good yields (Scheme 3, 3m–p).
SCHEME 3 Synthesis of
benzimidazole and benzothiazole
derivatives.a,b aGeneral conditions:
1 (1.0 mmol), 2 (1.0 mmol),
Cu(II) Schiff-base@SiO2 (5 mol%),
EtOH (5.0 mL), air, r.t. bIsolated
yield. c78ꢀC

10 of 12
SHARGHI ET AL.
Herein, according to the literature,[24,33,38,39] a plausi-
catalyst could be recovered 10 times, and a slight loss of
catalytic activity was observed for each reaction
(Figure 6). It is noteworthy that the catalyst recovery was
performed after its application in two steps of
the reaction, including synthesis of 5-phenylfuran-
ble mechanism for the synthesis of benzimidazole in the
presence of Cu(II) Schiff-base@SiO2 is demonstrated in
Scheme 4. First, 5-(4-chlorophenyl)furan-2-carbaldehyde
(I) was activated using Cu(II) Schiff-base@SiO2. Next, o-
phenylenediamine (II) attacks to the carbonyl group,
which after the elimination of H2O leads to the formation
of Schiff-base (III). Subsequently, intermediate (IV) is
generated via intramolecular cyclization. Finally, product
(V) is produced through the oxidative dehydrogenation
of intermediate (IV) in the presence of air and
Cu(II) Schiff-base@SiO2 (Scheme 4).
As the last study, the catalyst reusability was investi-
gated for the synthesis of product 3a under optimized
conditions. After the completion of the reaction,
Cu(II) Schiff-base@SiO2 was separated by centrifuging
from the reaction mixture and washed with EtOH (3 mL,
three times), dried, and utilized directly in the next cycle.
The study showed that the Cu(II) Schiff-base@SiO2
FIGURE 7 Infrared (IR) spectrum for the Cu(II) Schiff-
base@SiO2 after the 10 cycles
SCHEME 4 A plausible
mechanism for the synthesis of
2-(5-(4-chlorophenyl)furan-2-yl)-1H-
benzo[d]imidazole in the presence of
Cu(II) Schiff-base@SiO2
FIGURE 6 Reusability of Cu(II) Schiff-
base@SiO2 for the synthesis of product 3a

SHARGHI ET AL.
11 of 12
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[6] E. K. Moltzen, J. Perregaard, E. Meier, J. Med. Chem. 1995, 38, 2009.
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2-carbaldehydes, benzimidazole, and benzothiazole
derivatives. Figure 6 shows the high activity of the cata-
lyst after 10 runs. Additionally, the IR spectrum for the
Cu(II) Schiff-base@SiO2 after the 10 cycles are displayed
in Figure 7. Therefore, after 10 times of recovery, the cat-
alyst is stable and shows high activity.
4 | CONCLUSION
In summary, copper(II) complex of tetradentate Schiff-
base ligand immobilized onto silica [Cu(II) Schiff-base@-
SiO2] has been successfully synthesized and characterized
by the several techniques such as FT-IR, FE-SEM, EDX,
XRD, and ICP. Cu(II) Schiff-base@SiO2 was used as an
efficient catalyst for a two-step reaction including synthe-
sis of 5-phenylfuran-2-carbaldehydes and di-heteroaryl
molecules including benzimidazole and benzothiazole
derivatives via reaction of anilines, sodium nitrite,
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furan-2-carboxaldehyde,
o-phenylenediamines,
and
2-aminothiophenol. The significant advantages of this
protocol include short reaction times, mild conditions,
good to excellent yields, and low amount of nanocatalyst.
Also, to the best of our knowledge, this is the first time of
using the same catalyst in two steps including synthesis
of 2-(5-substituted phenyl)furan-2-carboxaldehyde and
benzimidazole or benzothiazole derivatives. In addition,
this synthesized catalyst was recycled very well and
reused several times after use in two steps of the reaction
without significant loss of its catalytic activity.
[17] T. C. Chien, S. S. Saluja, J. C. Drach, L. B. Townsend, J. Med.
Chem. 2004, 47, 5743.
[18] M. L. Richards, S. C. Lio, A. Sinha, K. K. Tieu, J. C. Sircar,
J. Med. Chem. 2004, 47, 6451.
ACKNOWLEDGMENT
[19] H. Nakano, T. Inoue, N. Kawasaki, H. Miyataka, H.
Matsumoto, T. Taguchi, N. Inagaki, H. Nagai, T. Satoh, Bioorg.
Med. Chem. 2000, 8, 373.
We gratefully acknowledge the support of this work by
the Research Council of University of Shiraz.
ꢀ
ꢀ
[20] C. Guigon-Lopez, F. Vargas-Albores, V. Guerrero-Prieto, M.
AUTHOR CONTRIBUTIONS
Ruocco, M. Lorito, Fungal Biol. 2015, 119, 264.
Hashem Sharghi: Conceptualization; supervision.
Elahe Mashhadi: Conceptualization; formal analysis;
investigation. Mahdi Aberi: Conceptualization. Jasem
Aboonajmi: Conceptualization.
[21] Z. Zhang, K. K. Ojo, S. M. Johnson, E. T. Larson, P. He, J. A.
Geiger, A. Castellanos-Gonzalez, A. C. White, M. Parsons,
E. A. Merritt, D. J. Maly, C. L. M. J. Verlinde, W. C. van
Voorhis, E. Fan, Bioorg. Med. Chem. Lett. 2012, 22, 5264.
[22] C. S. Digwal, U. Yadav, A. P. Sakla, P. V. Sri Ramya, S.
Aaghaz, A. Kamal, Tetrahedron Lett. 2016, 57, 4012.
ORCID
[23] D. Khalili, R. Evazi, A. Neshat, J. Aboonajmi, F. Osanlou,
Inorg. Chim. Acta 2020, 506, 119470.
[24] E. Niknam, F. Panahi, F. Daneshgar, F. Bahrami, A. Khalafi-
Nezhad, ACS Omega 2018, 3, 17135.
Hashem Sharghi https://orcid.org/0000-0001-6772-3332
Elahe Mashhadi https://orcid.org/0000-0002-0891-454X
Mahdi Aberi https://orcid.org/0000-0002-2095-8828
Jasem Aboonajmi https://orcid.org/0000-0003-0022-
9908
[25] V. Sankar, P. Karthik, B. Neppolian, B. Sivakumar, New
J. Chem. 2020, 44, 1021.
[26] Y. Nagasawa, Y. Matsusaki, T. Hotta, T. Nobuta, N. Tada, T.
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SUPPORTING INFORMATION
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How to cite this article: H. Sharghi,
E. Mashhadi, M. Aberi, J. Aboonajmi, Appl
Organomet Chem 2021, e6330. https://doi.org/10.
1002/aoc.6330