Catalytic activity of Co(II) Salen&at;KCC-1 on the synthesis of 2,4,5-triphenyl-1H-imidazoles and benzimidazoles

Article abstract of DOI:10.1016/j.inoche.2020.108137

The synthesis, reactions and biological properties of imidazoles and benzimidazole make up the bulk of the ring chemistry. In this study, the reaction between different types of aromatic aldehydes and ammonium acetate with diphenylethanedione, in ethanol solvent, using the Co(II) Salen complex&at;KCC-1 catalyst which is produced from Co (II) complex which is supported onto the KCC-1 was studied. The results showed that the products were synthesized in good to excellent yields. The products were identified with IR and NMR spectroscopy. Also, the catalyst was identified by FT-IR, TGA, TEM, and XRD. Finally, the catalyst was reused several times without lack of catalytic activity.

Full text of DOI:10.1016/j.inoche.2020.108137

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Short communication
Catalytic activity of Co(II) Salen@KCC-1 on the synthesis of 2,4,5-triphen-
yl-1H-imidazoles and benzimidazoles
Ali Allahresani, Elaheh Naghdi, Mohammad Ali Nasseri
PII:
S1387-7003(20)30727-9
DOI:
https://doi.org/10.1016/j.inoche.2020.108137
INOCHE 108137
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Inorganic Chemistry Communications
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19 July 2020
Please cite this article as: A. Allahresani, E. Naghdi, M. Ali Nasseri, Catalytic activity of Co(II) Salen@KCC-1
on the synthesis of 2,4,5-triphenyl-1H-imidazoles and benzimidazoles, Inorganic Chemistry Communications
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Catalytic activity of Co(II) Salen@KCC-1 on the synthesis of 2,4,5-triphenyl-
H-imidazoles and benzimidazoles
1
Ali Allahresani*, Elaheh Naghdi, Mohammad Ali Nasseri
Department of chemistry, Collage of Science, University of Birjand, Birjand 97175-615, Iran
E-mail: a_allahresani@birjand.ac.ir
Abstract:
The synthesis, reactions and biological properties of imidazoles and benzimidazole make up the
bulk of the ring chemistry. In this study, the reaction between different types of aromatic aldehydes
and ammonium acetate with diphenylethanedione, in ethanol solvent, using the Co(II) Salen
complex@KCC-1 catalyst which is produced from Co (II) complex which is supported onto the
KCC-1 was studied. The results showed that the products were synthesized in good to excellent
yields. The products were identified with IR and NMR spectroscopy. Also, the catalyst was
identified by FT-IR, TGA, TEM, and XRD. Finally, The catalyst was reused several times without
lack of catalytic activity.
Keywords: Co(II) Salen complex · Heterogeneous catalyst · 2,4,5-triphenyl-1H-imidazoles ·
benzimidazole · Multicomponent reaction

1
. Introduction
All imidazoles have the same annular ring but have different complementarities; imidazoles can
be used as bases or weak acid. Imidazole was first synthesized in 1858, but its different derivatives
were discovered in 1840 [1]. Since, imidazoles and benzimidazoles can bind to biological
molecules, such as triazoles, they have important biological activities and therefore they widely
used in medicine, pharmacy, and agriculture. Various applications of these compounds have been
reported, including several anti-inflammatories, anti-tumor, anti-allergic, antiviral and anti-
bacterial activities and other central applications of imidazole in biological systems [2-11]. They
use toxic reagents to produce heterocyclic compounds that involve many processes, and they can
also produce toxic waste. There are several ways to synthesize 2,4,5-triphenyl-1H-imidazoles
today, many of them have disadvantages such as long reaction time, low efficiency, use of
expensive and that require more reactions to synthesize better. These agents can lead to the
production of alternative imidazoles to take dangerous solvents and catalysts [12-21].
The multi-component reactions using heterogeneous catalysts under solvent conditions are an
efficient method that can be of great use in the field of drugs. Also, many supports were used for
the immobilization of homogeneous catalysts, but fibrous silica nanoparticles (KCC-1) are
generally used as catalyst, adsorbent and catalyst support [22]. These materials are chemically
inert silicate framework and have relatively low acidity. To improve acidity of KCC-1,
incorporation of one or more heteroatoms like metal complexes are necessary in the inert silica
framework [23-28] and the functionalized materials are good heterogeneous catalysts for chemical
reactions [29-31].
Herein, in continuation of our previous work for the development of new and benign
heterogeneous metal complexes for the synthesis of organic compounds, we synthesized

homogeneous Co (II) complex and immobilized onto the KCC-1 and the corresponding
heterogeneous Co (II) complex@KCC-1 was characterized by different techniques and the
synthesis of 2,4,5 triarylimidazoles via one-pot multicomponent method was studied in the
presence of heterogeneous Co (II) complex@KCC-1 catalyst in EtOH at 80 ◦C (Scheme 1).
Scheme 1. Schematic illustration for the preparation of Co (II) Salen complex
In this article, we report an easy and dramatic method for the synthesis of three-membered
imidazoles using complex Co-Salen nanoparticles as heterogeneous nanoparticles in solvent
ethanol at 80 °C. The can be said that this method has catalyst recyclability, mild reaction
conditions, including substrate generality, catalyst recyclability, large-scale synthesis and high
yields to identify the desired compound. The combination of these properties makes our method
an attractive way on the synthesis of 2,4,5- trisubstituted imidazoles [32-36]. Compound with the

RC=N imine group resulting from the condensation reaction of a first type amine and a carbonyl
compound is called Schiff base. Schiff bases also have biological activity, many clinical,
pharmacological and biochemical properties. Too Schiff base ligands are conveniently prepared,
known as privileged ligands. The synthesis of these compounds is shown in (Scheme 1). These
compounds are easily formed and decomposed. The heterogeneous catalyst causes stable, easy to
separate from the reaction mixture, and capable of reversible. Schiff base complexes have been
heterogeneous and their application as 2,4,5-triphenyl-1H-imidazoles reaction catalysts has been
investigated [37-48]. Nanostructures with diverse morphologies and a wide range is of dendritic
forms. The most prominent feature of nano-materials is their high surface to volume ratio, which
has led to an increase in the percentage of atoms on the surface and an increase in their surface
activity. These materials are widely used in various industries such as electronics, pharmaceuticals,
agriculture, biotechnology and more. Because of their extremely high surface area and the size of
the adjustable cavities, nanoporous materials are widely used in various fields. Herein, ongoing to
the previous works on the nanocatalysts [49-53], we report the design and synthesis of a complex
composed of the KCC-1 as a substrate with the Co(II) Salen schiff-base to serve as a catalyst for
the synthesis 2,4,5- trisubstituted imidazoles and benzimidazole derivatives [54-57] (Scheme 2).
Scheme 2. Schematic illustration for the preparation of Co(II) Salen complex@KCC-1

2
. Experimental
2
.1. Synthesis of KCC-1
In brief, the amount of (2g CTAB) cetyltrimethylammonium bromide and (2.4 g) of urea was
stirred (1500 rpm) in (300 ml) of water for 15 min. Tetraethyl orthosilicate (TEOS, 10 ml) and
cyclohexane (100 ml) were added dropwise to the above solution, stirred for 15 min, followed by
addition of 1-pentanol (6 ml). This dissolve was stirred at room temperature for 30 min, and next
transferred into a 1 L microwave reactor. This mixture was stirred in MW irradiation (800 W
power) under a moderate stirring rate under 120 °C by 4h. After completion of the reaction mixture,
the mixture was centrifuged with water and ethanol and then placed in Oven for 6 h at 80 °C. The
withe powder materials were then heated at 550 °C by a rate of 2.5 °C/min for 6 h in air to get
KCC-1[31].
2
.2. Synthesis of Salen ligand
Schiff- base was ready as follows. 3-aminopropyltrimethoxysilsn (1.2 mmol) was added to the 2-
hydroxybenzaldehyde (1.0 mmol) mixture in ethanol (10 ml) solution and refluxed for 3 h. the
color of the reaction solution changed to yellow due to the formation of imine. The solvent of the
mixture was easily removed at 70 °C to obtain an oily product [58].
2
.3. Synthesis of Cobalt (II) Salen Complex
The salen ligand (1.0 mmol) was solvable into ethanol (20 ml) and sodium hydroxide (1.67 mmol)
is added by Co(II) acetate one hydrate (1 mmol) then the reaction mixture was refluxed for 3 h. A

mixture was washed and filter three times by water, methanol, and diethyl ether, these solvents
was vaporizing and then a green solid were formed followed out desiccating at 80 °C in the oven
under vacuum [58].
2
.4. Synthesis of Cobalt (II) Salen Complex@KCC-1
KCC-1 (0.25 g) was washed with 30 ml of dry toluene. Then, (0.7 g) homogeneous Co(II) salen
complex was added to the mixture and refluxed for 20 hours. The catalyst was recovered after
filtration with a G4 filter by toluene, ethanol, and dichloromethane and then was dried under
vacuum at 80 °C for 8h. The Co(II) complex was characterized by FT-IR, TEM, XRD, TGA, and
SEM-EDX.
2
.5. Synthesis of 2,4,5-triphenyl-1H-imidazoles
The synthesis of 2,4,5-trisubstituted imidazole was studied as follows. Co(II) salen
complex@KCC-1 (0.004 g) as an impressive nanocatalyst was added to a mixture of
diphenylethanedione: benzaldehyde: ammonium acetate (1: 1: 4) in ethanol solvent. This mixture
was heated at 80 ºC by 10 min. The reaction was progressed via thin-layer chromatography using
a 20: 2 ratio of n-Hexane: ethyl acetate solvent. The product was then isolated by centrifugation
with 3 ml of ethyl acetate and the catalyst was quenched as a solid phase and dried at 80 °C in an
1
13
oven vacuum. The product was crystallized and detected by H-NMR and C-NMR spectroscopy.
.6. Synthesis of benzimidazole
A mixture of benzaldehyde (2 mmol) and O-phenylene diamine (1 mmol) in 3 ml ethanol and
.003 g of cobalt (II) salen Complex@KCC-1 was placed in a 25 ml magnetic stirrer. The resulting
2
0
mixture was then heated in an oil bath at 80 ºC for 5 min and then separated by the same procedure
as described in the previous section. Finally, a solid product was obtained at a 98% yield.

Spectral data
2
,4,5-triphenyl-1H-imidazoles (Table 4, Entry 1)
-1 1
mp: 267-269 °C. FT-IR (KBr): 3424 (NH), 3036 (CH), 1634-1597 (C=C, C=N) cm . H NMR
1
3
(
500 MHz, DMSO-d ): δ 12.52 (s, NH); 8.11-7.59 (m, 15H); C NMR (125 MHz, DMSO-d ): d
6
6
1
46.8, 130.83, 128.7, 128.5, 128.4, 128.3, 128.2, 127.6, 127.5, 125.6.
2
-(2-nitrophenyl)-4,5-diphenyl-1H-imidazoles (Table 4, Entry 4)
mp: 299 °C. FT-IR (KBr): 3423 (NH), 3028 (CH), 1590-1447 (C=C, C=N), 1524-1349 (N=O) cm-
1. 1
H NMR (500 MHz, DMSO-d ): δ 13.05 (s, NH); 8.05-7.40 (m, 14H); C NMR (125 MHz,
13
6
DMSO-d6): d 149.940, 147.241, 138.065, 135.256, 133.051, 129.550, 128.757, 128.507, 128.016,
26.949, 125.513, 123.301
-(2-methoxyphenyl)-4,5-diphenyl-1H-imidazoles (Table 4, Entry 11)
mp: 188 °C. FT-IR (KBr): 3176 (NH), 2837 (CH), 1582-1400 (C=C, C=N), 1180-1015 (Ar-O-C),
1
2
-1 1
1
300 (CH ) cm . H NMR (500 MHz, DMSO-d ): δ 8.10-6.09 (m, 14H); 3.94 (s, CH )
3 6 3
2
-(4-chlorophenyl)-4,5-diphenyl-1H-imidazoles (Table 4, Entry 5)
mp: 263-265 °C. FT-IR (KBr): 3024 (NH), 2835 (CH), 1663-1435 (C=C, C=N), 1089 (Ar-Cl) cm-
1. 1
H NMR (500 MHz, DMSO-d ): δ 12.82 (s, NH); 8.17-7.37 (m, 14H); C NMR (125 MHz,
13
6
DMSO-d6): d 176.990, 138.143, 134.468, 132.466, 130.055, 129.880, 128.690, 127.101
-(4-chlorophenyl)-1H-benzo[d]imidazole (Table 9, Entry 5)
2

-1
mp: 295-297 °C. FT-IR (KBr): 3450 (N–H), 3051 (C-H), 1584-1539 (C=N, C=C) cm . 1H NMR
500 MHz, DMSO-d6): δ 13 (s, NH); 8.22-7.19 (m, 8H).
-(4-Hydroxyphenyl)-1H-benzimidazole (Table 9, Entry 13)
(
2
-1
mp: 239–242 °C. FT-IR (KBr): 3438 (O–H, N–H), 3252 (C-H), 1609-1500 (C=N, C=C) cm . 1H
NMR (500 MHz, DMSO-d6): δ 12.46 (s, NH); 9.95-6.90 (m, 8H).
2
-(4-Methylphenyl)-1H-benzimidazole (Table 9, Entry 10)
mp: 275-276 °C. FT-IR (KBr): 3445 (N–H), 3053 (C-H), 1619-1550 (C=N, C=C), 2917 (CH3)
-1
cm . 1H NMR (500 MHz, DMSO-d6): δ 12.82 (s, NH); 8.9-7.16 (m, 8H).
3
. Results and discussion
The structure of Co(II) salen complex@KCC-1 as a new nanostructured and catalyst was studied
1
13
and identified by H NMR, C NMR, FT-IR, TGA, XRD and TEM analyses.
FT-IR analysis
Infrared spectra of all stages of Co(II) salen complex@KCC-1 which is synthesized in our lab are
shown in figure 1. The KCC-1 (Fig. 1 a), shows the peaks at 1091, 915 and 805 which are
belonging to Si-O and Si-OH, respectively. The peak at 3425 is assigned to OH. The above
vibrations emphasize the synthesis of KCC-1. Figure 1 b shows the infrared spectrum of the ligand
whose vibrations are in zones of 1079 and 1633 which are assigned to Si and C=N respectively.
Figure 1 c shows the infrared spectrum of the cobalt salen complex, in which, the peaks at 1076
and 2923 are related to the Si and methylene ring, respectively, as well as tensile vibrations of
C=N, are observed in 1620. The peak at 1616 appeared in the heterogeneous catalysts along with

the peak 1089 of Si-O-Si, indicating the successful fixation of the homogeneous cobalt complex
on the KCC-1 surface (Figure 1 d).
Figure 1. Fourier transform infrared (FT-IR) spectra of (a) KCC-1, (b) Salen ligand, (c) Cobalt (II) Salen
complex, (d) Cobalt (II) Salen complex@KCC-1
TGA analysis
The thermal gravimetric analysis (TGA) of KCC-1 and Co(II) salen complex@KCC-1 were done
at ambient temperature to 850 °C (Figure 2). In figure 2a, the deletion of H O appeared at the
2
temperatures below 130 ℃ (KCC-1). In figure 2b, the reason for weight loss of 4% is in the range
below 253 °C due to water removal. The weight loss in the temperature ranges of 250-450 °C,
about 10% was due to the removal of the oxygen from the functional groups of the Co(II) salen
and the weight loss in the temperature range of 450-700 °C which is evaluated 15% could be for
carbon removal. The whole weight loss of the organic sections was evaluated in 29% and there
was no additional weight loss above 700 °C (Figure 2 b).

Figure 2. Thermogravimetric analysis (TGA) pattern of (a) KCC-1, and (b) Cobalt (II) Salen
complex@KCC-1
XRD analysis
KCC-1 and Co(II) salen Complex@KCC-1 were studied by an X-ray diffractometer (XRD)
(Figure 3). KCC-1 silica nano indicated the attendance by fibers and was ordered dendritic fibers
and was distributed uniformly in all directions and the sample includes area particles with uniform
sizes (Figure 3 a). In figure 3b, the peak observed between 2θ = 20-30 corresponds to amorphous
silica. The dispersion of the nano-sample pattern with the desired sample of this complex indicates
the structural similarity between them. The structure of the complex and the nanostructure due to
the similarity of the peaks are the same and have an amorphous state and just because of the
reduction in the size of the particle width of the courier has changed.

Figure 3. X-ray diffraction (XRD) of (a) KCC-1, and (b) Cobalt (II) Salen complex@KCC-1
TEM analysis
In the TEM image of KCC-1, the presence of dendritic fibers distributed uniformly, coming out
from the center of the particle in all directions shows the structural features of the KCC-1
nanocatalyst (Figure. 4 a). The immobilization of Cobalt (II) Complex onto the KCC-1 is shown
in Figure 4 b. The image of the heterogeneous catalyst revealed that the fibrous nano-silica
(KCC-1) was loaded with Cobalt (II) complex.
Figure 4. TEM images of (a) KCC-1, and (b) Cobalt (II) Salen complex@KCC-1
EDX analysis

The EDX elemental analysis confirms that Co(II) salen complex@KCC-1 is composed of Si, Co,
O, N and C. These peaks suggest complexation of Cobalt with the Schiff-base of mesoporous
support (Figure 5).
Figure 5. Energy-dispersive X-ray (EDX) spectrum of Cobalt (II) Salen complex@KCC-1
Reaction optimization
After the synthesis of Cobalt(II) salen complex@KCC-1 as a nanostructured catalyst, it was used
as catalyst, and the reaction of diphenylethanedione, benzaldehyde, and ammonium acetate for the
synthesis of 2,4,5-triphenyl-1H-imidazoles derivatives in ethanol as a green medium (Scheme 1,
Scheme 3).
Scheme 3. 2,4,5-triphenyl-1H-imidazoles synthesis

To investigate the optimization of the catalyst, 2, 3, 4 and 5mg of catalyst were applied in separate
reactions in ethanol and the optimum amount of catalyst was 4mg (Table 1, 95%).
Table 1. Optimization of catalyst value
Co(II) Salen@KCC-1
a
Entry
1
Product
Time (min)
10
Yield (%)
(mg)
N
2
60
N
H
N
2
3
4
3
4
5
10
10
10
68
80
78
N
H
N
N
H
N
N
H
N
5
6
10
75
N
H
Reaction conditions: Diphenylethanedione (1 mmol); Benzaldehyde (1 mmol); ammonium
o
acetate (4 mmol), EtOH (3 cc), 80 C
a) Reported yield based on quantity of product isolated
After the optimization of the catalyst, the effect of solvent investigated the reaction conditions. As
the results showed, the solvent has grate effect on the reaction conditions. Deferent solvent such
as n-Hexane, CH CN, CH Cl , Ethyl acetate, CHCl , EtOH and H O as well as solvent-free were
3
2
2
3
2
applied on the reaction and EtOH was chosen as the best solvent (Table 2, 95%).

Table 2. Solvent optimization
Entry
Solvent
Time (min)
Yield (%)b
1
2
3
4
5
6
7
8
9
MeCN
EtOH
10
10
10
10
10
10
10
10
10
45
80
30
15
55
58
40
20
10
Ethyl acetat
H O
2
CH Cl
2
2
CHCl3
DMF
Solvent-free
n-Hexane
Reaction conditions: benzaldehyde (1 mmol), diphenylethanedione (1 mmol), ammonium
o
acetate (4 mmol) in 3 mL of solvent (in solution experiment), 80 C, b) yield refers to isolated
and pure product.
The effect of temperature and molar ratio of the reagent was tested in the model reaction and 80
°
C and molar ratio of 1:2:4 of diphenylethanedione, benzaldehyde, and ammonium acetate were
chosen as the best result (Table 3).

Table 3. Optimization of temperature and molar ratio of the reactants
Molar ratio
Diphenylethanedione :
aldehyde : ammonium
acetate
Temperature.
(°C)
a
Entry
Time (min)
Yield (%)
1
2
3
4
5
6
7
1.0:1.0:2.0
80
80
80
25
60
50
40
120
90
10
10
20
30
45
50
70
80
53
78
75
65
1.0:1.0:2.5
1.0:1.0:4.0
1.0:1.0:4.0
1.0:1.0:4.0
1.0:1.0:4.0
1.0:1.0:4.0
Reaction conditions: 3 cc EtOH, 4 mg of Co(II) Salen complex@KCC-1
a) Reported yield based on quantity of product isolated
After optimizing the reaction conditions, the reactions were evaluated using a variety of aldehydes.
Different aldehydes consist of electron-withdrawing and electron-releasing phenyl group was
tested and the results showed that both electron-withdrawing and electron-donating groups have a
good to excellent yield (Table. 4). Furthermore, other compounds like furan-2-carbaldehyde were
tested and lower yield at longer times was observed.
Table 4. 2,4,5-triphenyl-1H-imidazoles using of aryl aldehydes, diphenylethanedione and ammonium
acetate in the prycens of catalyst in EtOH
Entry
1
Aromatic aldehydes
Time (min)
% Yieldb
M.P. (℃)
CHO
10
80
267-269
CHO
2
15
86
238-240
O2N

Countinued table 4. 2,4,5-triphenyl-1H-imidazoles using of aryl aldehydes,
diphenylethanedione and ammonium acetate in the prycens of catalyst in EtOH
CHO
1
5
3
87
261-263
NO2
CHO
O N
2
4
5
10
15
89
85
325-327
268-270
CHO
Cl
CHO
6
7
8
20
15
10
80
81
85
198-199
204-205
273-275
Cl
CHO
OH
CHO
HO
CHO
CHO
9
5
87
272-273
H C
3
H C
3
1
0
1
10
10
83
88
297-298
222-224
CHO
1
1
H3C
O
CHO
O
2
H C
3
5
90
210-211
O
CHO
CHO
H3C
1
1
1
3
4
5
15
15
20
80
80
63
258-259
257-259
283-285
Br
O
CHO
a) Reaction conditions: 0.004 g of Cobalt (II) Salen Complex@KCC-1 at 80 °C, diphenylethanedione
1 mmol), aldehyde (1 mmol), ammonium acetate (4 mmol) and ethanol (3 mL), b) yield refers to pure
(
product.
The mechanism of the production of substituted imidazoles mediated by the Co(II) salen
Complex@KCC-1 catalyst was given in Scheme 4. At first, ammonium acetate detaches from

ammonia which is needful in the primary condensation. After the formation of, amine the reaction
was performed by attack of aldehyde in the presence of Co(II) salen complex catalyst (Intermediate
A). Then, this intermediate attacked to diphenylethanedione to produce intermediate B. This
intermediate produce the product with an 80% yield.
Scheme 4. Proposed mechanism for the 2,4,5-triphenyl-1H-imidazoles formation using of aryl
aldehydes, benzyl and ammonium acetate.

Catalyst reuse
The reusability of the catalyst for the synthesis of 2,4,5-triphenyl-1H-imidazoles was studied.
After 8 consecutive reuses, the results (Figure 6) showed that the yield of the products was almost
constant and this is shown the reusability of the reactions.
Figure 6. Reusability of catalyst for the synthesis of 2,4,5-triphenyl-1H-imidazoles.
To prove the high potency of cobalt (II) salen complex@KCC-1 catalyst compared to other
catalysts in similar synthesis, the results obtained from different catalysts were compared in a
comparative (Table 5) [59-64].

Table 5. Study of different catalysts on the synthesis of 2,4,5-triphenyl-1H-imidazole
Entry
Catalyst
Condition
Solvent free
Time
20
Yield (%)
[ref.]
59
1
2
3
4
5
6
7
Fe O @SiO /bipyridinium
90
82
91
95
93
96
80
3
4
2
iodine/DMSO
EtOH/100℃
120
34
60
(CTSA)
Solvent free/90℃
Ethanol, reflux
Solvent free/110℃
61
NanoNiCoFe O
20
62
2
4
‐SO H
90
63
3
20% H PMo V O / KSF Solvent free/110℃
35
64
5
10
2
40
Co (II) Salen
Ethanol, reflux
10
This
work
Complex@KCC-1
0
.004 g of Cobalt (II) Salen Complex@KCC-1 at 80 °C, diphenylethanedione (1 mmol),
aldehyde (1 mmol), ammonium acetate (4 mmol).
Synthesis of Benzimidazole
Benzimidazole derivatives are synthesized from benzaldehyde derivatives and o-
phenylenediamine. In order to optimize the reaction of benzimidazole, the benzaldehyde and o-
phenylenediamine was selected as the standard model reaction (Scheme 5).
Scheme 5. Synthesis of 2-phenyl-1H-benzo[d] imidazole.
We select the appropriate amount of o-phenylenediamine (1 mmol), benzaldehyde (2 mmol) in
ethanol (3 ml) solvent at 80 ºC with different amounts of cobalt (II) salen complex@KCC-1
catalyst and the products were separated. The conclusion is reported in (Table 6) and 3 mg of
catalyst was selected as the optimum amount of catalyst.

Table 6. Optimization of catalyst amount
Time
Yielda
(%)
Entry
Product
Cobalt (II) Salen complex@KCC-1
(min)
(mg)
N
1
2
3
4
5
2
10
75
84
85
86
N
H
N
3
4
5
6
10
10
10
10
N
H
N
N
H
N
N
H
N
87
N
H
0
Reaction conditions: o-phenylendiamine (1mmol), benzaldehyde (2mmol), EtOH (3 ml), 80 C
a) Reported yield based on quantity of product isolated
Then, the reaction of o-phenylenediamine (1 mmol), benzaldehyde (2 mmol) and cobalt (II) salen
complex @ KCC-1 were investigated in different solvents as well as solvent-free conditions. The
conclusion is presented in table 7. According to the results, the reaction yield was optimum in
ethanol therefor ethanol was selected as the optimum solvent (Table 7).

Table 7. Solvents optimization
Entry
solvent
MeCN
temp (°C)
Time (min)
yield (%)b
1
2
3
4
5
6
80
80
80
80
80
80
10
10
10
10
10
10
51
84
47
35
20
60
EtOH
Ethyl acetate
H O
2
CH Cl
2
2
Solvent-free
Reaction conditions: benzaldehyde (2 mmol), o-phenylendiamine (1 mmol), in 3 ml of solvent,
b) yield refers to pure product.
The reaction of o-phenylenediamine and benzaldehyde with different molar ratios in ethanol under
reflux conditions was carried out in the presence of cobalt (II) salen complex@KCC-1 and the
product was separated. The results are reported in table 8 and the optimum amount of reactants
(aldehyde to o-phenylenediamine) was 2:1.
Table 8. optimization of molar ratio of reactants
a
Entry
Aldehyde : o-phenylendiamine Temperature. (°C)
Time (min)
Yield (%)
1
2
3
4
5
1.0:1.0
1.5:1.0
2.0:1.0
2.0:1.0
2.0:1.0
80
80
80
60
40
60
40
10
30
55
75
78
84
70
68
Reaction conditions: EtOH (3 cc), 3 mg of Co(II) Salen@KCC-1
a) Reported yield based on quantity of product isolated

Also, the temperature was investigated in the model reaction and reflux conditions were selected
as optimum temperature (not listed).
Under optimized conditions (catalyst amount 3 mg, ethanol (3 ml), the ratio of benzaldehyde
derivatives to o-phenlenediamine (2:1) and temperature 80 ºC), the generality of the reactions was
investigated. Several phenylene releasing and withering groups were tested as reactants. As the
table shows, electron releasing and withdrawing groups have a good to excellent yield but the
reactions with electron-withdrawing groups have a little higher yield than electron resing groups.
The results are shown in table 9. These results are according to the 44, 45, 48 and 59.
Table 9. Synthesis of 2-Phenyl-1H-benzo[d]imidazole using aromatic aldehydes and o-phenylendiamine
using Catalyst in ethanol.
Entry
Aromatic aldehydes
Time (min)
10
% Yieldb
84
m.p℃
CHO
1
2
.
.
262-264
CHO
5
5
88
90
260-263
237-238
NO2
CHO
3
.
O2N
O N
2
CHO
CHO
4
5
.
.
5
95
80
320-323
290-291
10
Cl
CHO
Cl
6
.
15
78
190-194
O
O
CHO
H3C
7
8
.
.
10
5
90
83
257-259
222-224
CHO
H3C
CHO
O
9
.
H C
3
10
87
223-224

Countinued table 9. Synthesis of 2-Phenyl-1H-benzo[d]imidazole using aromatic aldehydes and o-
phenylendiamine using Catalyst in ethanol.
CHO
1
0.
10
83
272-273
H C
3
H C
3
CHO
1
1
1
1
1
1.
2.
3.
4.
5.
10
10
10
5
78
80
85
90
75
297-299
205-206
238-240
255-257
285-287
CHO
OH
CHO
HO
Br
CHO
O
CHO
20
a) Reaction conditions: 0.003 g of Cobalt (II) Salen Complex@KCC-1 at 80 °C, aldehyde (2 mmol), O-
Phenylenediamine (1 mmol) and EtOH (3 cc); b) yield refers to pure and isolated products.
A plausible mechanism was introduced for the synthesis of benzimidazoles from o-
phenylenediamine and benzaldehyde derivatives using cobalt(II) salen complex@KCC-1 catalyst
(Scheme 6). Benzaldehyde first activated with catalyst and attacked to times by o-phenylendiamine
and after [1,5] H-shift the product was achieved.

Scheme 6. Proposed mechanism for the 2-phenyl-1H-benzo[d] imidazole formation using aryl aldehydes
and O-phenylendiamine
In addition, the reusability of the catalyst was investigated in the reactions. Therefore, the reaction
was proceeded 8 times and from time 2 to 8 with a reuse catalyst and no negligible decrease was
achieved in the model reaction (Figure 7).
Figure 7. Reusability of the catalyst for the synthesis of 2-phenyl-1H-benzo[d]imidazole

Also, the reaction of benzaldehyde and o-phenylenediamine in ethanol at 80 °C was compared
with the literature [65-69]. As the result showed, this catalyst has better activity in time and solvent
(Table 10).
Table 10. Study of different catalysts on the synthesis of 2-Phenyl-1H-benzo[d]imidazole
Entry
Catalyst
TiCl3
Condition
EtOH/r.t.
Time
50-130 min
24 h
Yield (%)
70-90
62-92
85
[ref.]
65
1
2
3
4
5
TAP−Cu
CH CN/80℃
66
3
HNO @nano SiO (0.01 g) solvent-free/ 90 °C
2.30 h
1.30
67
3
2
Cp ZrCl (5 mol%)
EtOH/r.t
94
68
2
2
Yb(OTf) (0.5 mol%)
Solvent-free/ 90°C
1-6 h
40-92
69
3
Co(II) Salen
This
work
6
EtOH/80°C
10 min
84
complex@KCC-1
0
.003 g of Cobalt (II) Salen Complex@KCC-1 at 80 °C, aldehyde (2 mmol), O-Phenylenediamine
(1 mmol).
Conclusion
Imidazoles and benzimidazoles are important heterocyclic compounds which are used in medicine.
Compounds with imidazole skeleton have various pharmacological properties such as anti-
inflammatory, anti-clotting, fungicidal and insecticidal properties. In this project, Co(II) Salen
complex was synthesized by immobilizing of Cobalt(II) onto the salen. Then, Co(II) salen complex
was supported on the KCC-1 which is synthesized from TEOS. The heterogeneous catalyst (Co(II)
salen complex@ KCC-1) was characterized by different techniques such as TEM, XRD, FT-IR,
TGA, EDX, and AAS. This catalyst applied for the synthesis of 2,4,5-triphenyl-1H-imidazoles.
The results show that this catalyst has good activity on the synthesis of the desired products and

all products were the synthesis of good to excellent yields (80-90%). In addition, the synthesis of
benzimidazoles was investigated whit this catalyst at optimum reaction conditions. Many
compounds of benzimidazoles were synthesis with this catalyst and as the results shown all
compounds were synthesized in good excellent yields (84-95%). Also, the reusability of Co (II)
salen complex@ KCC-1 is checked and after 8 times a little negligible was found in the catalytic
activity of the catalyst. Furthermore, easy workup, a single-step multicomponent density and not
requireing intermediate separation, thus saving time, energy and cost are the advantageous of this
catalyst.

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