Aerobic {Mo72V30} nanocluster-catalysed heterogeneous one-pot tandem synthesis of benzimidazoles

Article abstract of DOI:10.1002/aoc.4638

A novel heterogeneous one-pot protocol is developed for tandem aerobic synthesis of benzimidazoles through dehydrogenative coupling of primary benzylic alcohols and aromatic diamines co-catalysed by Keplerate-type {Mo₇₂V₃₀} polyoxometalate and N-hydroxyphthalimide (NHPI). The catalytic system also works well for the synthesis of benzimidazoles using benzaldehydes, as commonly used starting materials, in the absence of NHPI. The high activity of the solid nanocluster provides standard conditions avoiding current limitations of oxidation methods including high catalyst loadings. The spectral results and leaching experiments revealed that the nanocapsule preserved its structural integrity after being reused in consecutive runs.

Full text of DOI:10.1002/aoc.4638

Received: 27 May 2018
DOI: 10.1002/aoc.4638
Revised: 31 August 2018
Accepted: 19 September 2018
F U L L P A P E R
Aerobic {Mo72V30} nanocluster‐catalysed heterogeneous
one‐pot tandem synthesis of benzimidazoles
Ashkan Khoshyan | Mehrdad Pourtahmasb | Fahimeh Feizpour
Abdolreza Rezaeifard
| Maasoumeh Jafarpour
|
Catalysis Research Laboratory,
A novel heterogeneous one‐pot protocol is developed for tandem aerobic syn-
thesis of benzimidazoles through dehydrogenative coupling of primary ben-
zylic alcohols and aromatic diamines co‐catalysed by Keplerate‐type
{Mo72V30} polyoxometalate and N‐hydroxyphthalimide (NHPI). The catalytic
system also works well for the synthesis of benzimidazoles using benzalde-
hydes, as commonly used starting materials, in the absence of NHPI. The high
activity of the solid nanocluster provides standard conditions avoiding current
limitations of oxidation methods including high catalyst loadings. The spectral
results and leaching experiments revealed that the nanocapsule preserved its
structural integrity after being reused in consecutive runs.
Department of Chemistry, Faculty of
Science, University of Birjand, Birjand
97179‐414, Iran
Correspondence
Abdolreza Rezaeifard and Maasoumeh
Jafarpour, Catalysis Research Laboratory,
Department of Chemistry, Faculty of
Science, University of Birjand, Birjand
97179‐414, Iran.
Email: rrezaeifard@birjand.ac.ir;
rrezaeifard@gmail.com;
mjafarpour@birjand.ac.ir
KEYWORDS
{Mo72V30}, benzimidazoles, heterogeneous catalyst, Keplerate, tandem synthesis
1 | INTRODUCTION
Mo2O2(μ‐X)2 dimers. They are recognized as
nanomaterials that allow a variety of research options in
Polyoxometalates (POMs), a class of versatile and discrete
anionic metal oxides with unique properties, have
attracted researchers’ attention for several decades. They
have been applied to many fields, such as catalysis,[1,2]
materials[3–6] and medicine.[7] The application of POMs
to catalysis is stimulated by their fascinating properties,
including strong acidity, strong oxidizing ability, an
unmatched range of molecular structures, efficient
adsorption, inherent resistance to oxidative decomposi-
tion, high thermal stability and impressive sensitivity to
light and electricity.[1]
In some cases, the shape of the POM framework is
such that it forms inner cavities, which are usually filled
with other molecular species. These two characteristics
are found in the family of Keplerates, spherical capsules
that can assemble either 102 or 132 metal atoms. For
the largest members, with general formula [M72M′
60O312(μ‐X)60]12− (M = Mo(VI), W(VI); M′ = Mo(V);
X = O, S), pentagonal building blocks are linked by 30
several disciplines such as electronic and magnetic appli-
cations and various aspects of materials science, includ-
ing catalysis.[8,9]
In the line of our research interest in catalytic applica-
tions of Keplerates,[10–14] quite recently the heteroge-
neous catalytic efficiency of {Mo72V30} nanocluster was
exploited[15] in selective aerobic oxidation of benzylic
alcohols and hydrocarbons co‐catalysed by N‐
hydroxyphthalimide (NHPI) in EtOAc.[16] Herein, we
report that the method is also capable of dehydrogenation
of alcohols followed by coupling with aromatic diamines
producing benzimidazoles which are known as important
building blocks for the construction of pharmaceuticals,
natural products, functional materials and agrochemical
compounds.[17–20] Among the methods used for the syn-
thesis of benzimidazoles, the use of alcohols as starting
materials is a suitable alternative considering economic
viability and environmental integrity because of the wide
availability of alcohols.[21–30]
Appl Organometal Chem. 2018;e4638.
wileyonlinelibrary.com/journal/aoc
© 2018 John Wiley & Sons, Ltd.
1 of 9
https://doi.org/10.1002/aoc.4638

2 of 9
KHOSHYAN ET AL.
In the study reported here, initially we explored the
water at room temperature. The mixture was acidified
to pH 2.0 with H2SO4 (2 M, 14 ml) and then treated with
N2H6SO4 (0.9 g, 6.9 mmol). The solution turned dark vio-
let and the pH increased to 2.8. After stirring for 3 h a
solution of KCl (3 g, 40.2 mmol) in 20 ml of water was
added to the mixture. Finally, the solution was filtered
and the filtrate (solution) was left standing at room tem-
perature. Black‐purple hexagonal plates were formed
overnight. The FT‐IR, Raman and UV–visible spectra as
well as XRD and TGA results of as‐prepared {Mo72V30}
are given in the supporting information (Figures S1–S5).
possibility of aerobic benzimidazole synthesis via the
reaction of 1,2‐diaminobenzenes and benzylic alcohols
using {Mo72V30} nanocluster co‐catalysed by NHPI in
EtOAc (Scheme 1). Subsequently, the possibility of using
benzaldehydes as commonly used starting materials for
condensation with diaminobenzenes for the synthesis of
benzimidazoles is also described. The heterogeneous cat-
alyst showing sustainable stability under oxidative condi-
tions could be recovered and reused at least five times.
2 | EXPERIMENTAL
2.1 | General remarks
2.3 | Typical procedure for synthesis of
benzimidazoles from benzylic alcohols and
1,2‐phenylenediamines (method A)
All chemicals were purchased from commercial sources.
Powder X‐ray diffraction (XRD) was performed using a
Bruker D8 Advance X‐ray diffractometer with Cu Ka
(λ = 1.5406 Å) radiation. Fourier transform infrared
(FT‐IR) spectra were recorded with a Shimadzu 800 FT‐
IR system using a KBr pellet. UV–visible spectra were
recorded with a SPECORD® 210 PLUS. Thermogravimet-
ric analysis (TGA) was conducted with a TGA‐50
(Shimadzu) at a heating rate of 10°C min−1 under 20
ml min−1 flowing air. Progress of the reactions was mon-
itored by TLC using silica‐gel SIL G/UV 254 plates and by
GC with a Shimadzu GC‐16A instrument using a 25 m
CBP1‐M25 (0.32 mm inner diameter, 0.5 mm coating)
capillary column.
To a mixture of 0.1 g of benzylic alcohol (1.0 mmol) and
10 mg of {Mo72V30} nanocluster (0.5 μmol, 0.05 mol%)
in 2.0 ml of EtOAc was added 15 mg of NHPI (0.1 mmol,
10 mol%) and the reaction mixture was stirred under
1 atm O2 (balloon) at 70°C for the required time. Then
1,2‐phenylenediamine (0.13 g, 1.2 mmol) was added.
The progress of the reaction was monitored by TLC and
conversion determined by GC based on the starting alco-
hol. After completion of the reaction, excess amount of
EtOAc was added to the mixture and the catalyst was sep-
arated by centrifugation followed by decantation
(3 × 5 ml of EtOAc). Desired products were purified by
plate silica chromatography eluted with n‐hexane–ethyl
acetate (10/2). Assignments of products were made from
chemophysical properties as well as NMR spectral data
(see supporting information).
2.2 | Synthesis of {Mo72V30}
The {Mo72V30} nanocluster was synthesized according to
the literature.[15] A solution of NaVO3 (2.6 g, 21.3 mmol)
dissolved in 55 ml of water at 70°C and then cooled to
2.4 | Typical procedure for synthesis of
benzimidazoles from benzaldehydes and
1,2‐phenylenediamines (method B)
room temperature was added to
a
solution of
Na2MoO42H2O (6 g, 24.8 mmol) dissolved in 75 ml of
To a mixture of 0.1 g of benzaldehyde (1 mmol) and 1,2‐
phenylenediamine (0.13 g, 1.2 mmol) in 2 ml of EtOH
was added 20 mg of {Mo72V30} nanocluster (1.0 μmol,
0.1 mol%) and the reaction mixture was stirred under
1 atm O2 at 60°C for the required time. The progress of
the reaction was monitored by TLC and conversion deter-
mined by GC based on the starting benzaldehyde. After
completion of the reaction, excess amount of EtOH was
added to the mixture and the catalyst was separated by
centrifugation followed by decantation (3 × 5 ml of etha-
nol). Desired products were purified by plate silica chro-
matography eluted with n‐hexane–ethyl acetate (10/2).
Assignments of products were made from chemophysical
properties as well as NMR spectral data (see supporting
information).
SCHEME 1 One‐pot synthesis of benzimidazoles from primary
alcohols catalysed by {Mo72V30} nanocapsule

KHOSHYAN ET AL.
3 of 9
5–9) revealed a solvent‐ and temperature‐dependent
product yield for the formation of benzimidazole. The
best performance (>99%) was achieved at 70°C in EtOAc
(Table 1, entry 5) and yield was significantly reduced on
decreasing the temperature, reaching 5% at room temper-
ature (Table 1, entries 6–9). Screening of the amount of
catalyst and NHPI in the model system was performed
with a further set of experiments. The blank reaction (cat-
alyst‐free) did not proceed in the absence or presence of
NHPI. Therefore, the use of catalyst as well as NHPI for
the promotion of the reaction is essential. Entries 5 and
10–14 in Table 1 show the effect of the amount of catalyst
on the reaction performance. While the reaction
2.5 | Recycling procedure for synthesis of
benzimidazoles
After performing the reactions using the procedures of
methods A and B, the residual catalyst was washed with
EtOAc three times (3 × 5 ml) and dried under vacuum.
It was weighed and then reused for subsequent runs.
3 | RESULTS AND DISCUSSION
3.1 | Synthesis of benzimidazoles using
method A
Initially, we tried to synthesize benzimidazole derivatives
using dehydrogenation of benzylic alcohols followed by
coupling with aromatic diamines. The data for the opti-
mization of a model reaction using benzyl alcohol
(1.0 mmol) and phenylenediamine (1.2 mmol) in the
presence of molecular oxygen (1 atm, balloon) are given
in Table 1. Inspection of the results in Table 1 (entries
TABLE 1 Screening of factors in the synthesis of benzimidazole
by reaction of benzyl alcohol and 1,2‐phenylenediamine catalysed
by {Mo72V30}a
Temp. Catalyst NHPI
Yield
Entry Solvent
(°C)
(mol%)
(mol%) (%)b
SCHEME 2 Proposed mechanism for aerobic synthesis of 2‐
phenylbenzimidazole from benzyl alcohol catalysed by {Mo72V30}
1
2
Solvent free 70
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
—
10
10
10
10
10
10
10
10
10
10
10
10
10
10
—
5
24
31
38
86
>99
78
50
27
5
Water
EtOH
70
70
70
70
60
50
40
25
70
70
70
70
70
70
70
70
70
70
TABLE 2 Screening of catalyst type in synthesis of benzimid-
azole by reaction of benzyl alcohol and 1,2‐phenylenediaminea
3
4
MeCN
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
Catalyst amount
(mol%)
Yield
(%)b
5
Entry Catalyst
6
1
3NaVO3
1.5c
3.6c
48
0
7
2
NaMoO4·2H2O
8
3
NaVO3 + NaMo4·2H2O 1.5% V + 3.6% Moc
37
50
36
0
9
4
VOSO4
1.5c
0.05
0.05
0.05
0.05
0.05
0.05
0.05
10
11
12
13
14
15
16
17
18
19
15
67
82
57
36
—
42
65
74
67
5
{Mo132}
0.01
0.02
0.5
6
{Mo72Fe30}
7
{Mo72V30}
>99
89
68
84
68
8
{Mo72Cr30}
1
9
{W72V30}
0.05
0.05
0.05
0.05
0.05
10
11
{mimC18‐Mo72V30}
{DODA‐Mo72V30}
7.5
aReactions were run at 70°C for 4 h under O2 (balloon) in 2.0 ml of EtOAc
containing 1.0 mmol of benzyl alcohol, 1.2 mmol of 1,2‐phenylenediamine
and 0.1 mmol of NHPI.
12.5
15
aReactions were run for 4 h under O2 (balloon) in 2.0 ml of solvent contain-
bGC yield based on starting alcohol.
cThe mol% of simple salts are the same as metal concentration in Keplerate
POMs, i.e. 72 times Mo and 30 times V.
ing 1.0 mmol of benzyl alcohol and 1.2 mmol of 1,2‐phenylenediamine.
bGC yield based on starting alcohol.

4 of 9
KHOSHYAN ET AL.
proceeded well with 0.05 mol% catalyst, increasing the
catalyst loading up to 0.5 and 1 mol% decreased the corre-
sponding yield to 57 and 36%, respectively. The formation
of blackberry structures in concentrated solution of
{Mo72V30} macroanion reduces markedly the active
sites.[31] The high dispersity of the solid nanocluster pro-
vides standard conditions avoiding current limitations of
oxidation methods including high catalyst loadings.
Next, the amount of NHPI was screened. Entries 5
and 16–19 in Table 1 reveal that increasing the amount
of NHPI improved the product yield, reaching a quantita-
tive yield (95%) using 10 mol% of NHPI. These results
demonstrated a co‐catalyst role for NHPI in combination
with {Mo72V30}. We also conducted the reaction under air
as oxidant and found it slightly less effective than
molecular oxygen (88%). Thus, the reaction exhibited
the best efficiency using molecular oxygen (balloon) and
a molar ratio of 2:2.4:1 for benzyl alcohol/diamine/NHPI
with 0.05 mol% of catalyst in EtOAc (0.4 ml) at 70°C.
According to our previous report on alcohol oxida-
tion,[16] a radical mechanism is reasonable for the investi-
gated oxidative coupling reaction using NHPI and
Keplerate catalyst including active Lewis acid and redox
sites (Scheme 2). NHPI catalyses the oxidation reaction
through initial generation of the phthalimide‐N‐oxyl
(PINO) radical by abstraction of the O―H hydrogen in
NHPI. The PINO radical then abstracts a hydrogen atom
from a target substrate.[32,33] More evidence for hydrogen
abstraction mechanism was obtained by using 2,2,6,6‐
tetramethylpiperidine‐1‐oxyl (TEMPO) as the most
widely used nitroxide radical.[34] The reaction proceeded
with a modest yield of pertinent benzimidazole (46%) at
the same time reflecting the steric hindrance about the
catalytic centre involving TEMPO and transition metals
of Keplerate catalyst.[16] To clarify whether NHPI is nec-
essary for the final step of the reaction, 4‐
chlorobenzaldehyde (1 mmol) and 1,2‐phenylenediamine
(1.2 mmol) were mixed in the absence of NHPI in EtOAc
under the same conditions. Benzimidazole was produced
selectively in desired yield within 1 h. Thus, the method
is amenable for the coupling of benzaldehydes, as com-
monly used starting materials, with aromatic diamines
TABLE 3 Aerobic synthesis of benzimidazoles using benzyl
alcohols catalysed by {Mo72V30}a
Time Yield
Entry
X
R
Product
(h)
(%)b
1
H
H
4
95
2
3
4‐Cl
2‐Cl
H
H
4
5
86
90
TABLE 4 Screening of various factors in synthesis of benzimid-
azole using 4‐chlorobenzaldehyde and 1,2‐phenylenediamine
catalysed by {Mo72V30}a
4
5
6
7
4‐NO2
4‐OMe
4‐Me
H
H
H
H
8
68c
92
89
88
Temp.
(°C)
Catalyst
(mol%)
Time
(min)
Yield
(%)b
Entry
Solvent
6
1
Solvent free
EtOH
Water
EtOAc
MeCN
DCE
360
60
60
60
60
60
25
40
70
80
60
60
60
0.1
135
45
97
98
96
90
97
90
60
98
96
90
90
90
98
2
0.1
0.1
6
3
150
45
4
0.1
2‐Me
6.5
5
0.1
95
6
0.1
145
100
70
8
9
4‐t‐Bu
4‐Me
H
5
7
90
7
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
0.1
8
0.1
NO2
42c
9
0.1
55
10
11
12
13
0.1
120
80
0.015
0.03
0.05
10
4‐Me
Me
6.5
87
70
60
aReactions were run using 1.0 mmol of primary alcohols and 1.2 mmol of
phenylenediamine in 2 ml of EtOAc under O2 (1 atm, balloon) at 70°C in
the presence of 0.05 mol% of catalyst, 10 mol% of NHPI.
aRreactions were run under O2 (7 ml min−1, bubbling) in 2.0 ml of solvent
containing mmol of 4‐chlorobenzaldehyde and 1.2 mmol of 1,2‐
1
bYield of isolated products.
phenylenediamine.
cRemainder is unreacted materials.
bGC yield based on starting 4‐chlorobenzaldehyde.

KHOSHYAN ET AL.
5 of 9
for quantitative production of benimidazoles, which is
the subject of next section of this work. It should be noted
that, to elucidate our radical mechanism, 2,6‐di‐tert‐butyl‐
4‐methylphenol as a common radical scavenger was
added to the reaction mixture, and significant retardation
of benzimidazole production was observed.[16]
The catalytic potential of simple Mo and V salts as
well as other Keplerate‐type POMs was also evaluated
in the oxidative dehydrogenation of benzyl alcohol and
1,2‐phenylenediamine (Table 2). According to the results
presented in entries 1–4, simple Mo and V salts were
inferior catalysts for this transformation. Among various
Keplerates used in this study (entries 5–9),[35–38]
{Mo72Fe30} was actually an inactive catalyst (entry 6),
whereas {Mo72Cr30} exhibited desired activity under the
same conditions (entry 8). As observed for alcohol oxida-
tion in our previous report,[16] by modification of
{Mo72V30} with organic cations such as 1‐methyl‐3‐
octadecaneimidazolium
(C18mim)
and
dioctadecyldimethylammonium (DODA) producing
organic–inorganic nanohybrids, the yield of the corre-
sponding products decreased to 84 and 68% (entries 10
TABLE 5 Aerobic synthesis of benzimidazoles using benzaldehydes catalysed by {Mo72V30}a
Entry
X
R
Product
Time (min)
Yield%b
1
4‐Cl
H
45
95
2
2‐Cl
H
90
94
3
4
4‐OH
2‐OH
H
H
110
190
94
80
5
6
4‐NO2
2‐NO2
H
H
180
170
90
96
7
8
9
4‐OMe
4‐Me
H
H
H
150
90
96
95
95
65
10
H
60
94
11
12
13
4‐Cl
4‐Cl
4‐Cl
4‐Me
4‐Cl
90
55
93
95
62
4‐NO2
150
aReactions were run using 1.0 mmol of aldehydes and 1.2 mmol of 1,2‐phenylenediamine in 2.0 ml of EtOH under O2 (1 atm, 7 ml min−1, bubbling) at 60°C in
the presence of 0.1 mol% of catalyst.
bYield of isolated products.

6 of 9
KHOSHYAN ET AL.
and 11), respectively. Protection of active sites by the long
chains of organic counter ions of the {Mo72V30}
surfactant‐encapsulated cluster was proposed to be a
good reason for such a reduction in activity.[16,39]
of 4‐chlorobenzaldehyde (1.0 mmol) with 1,2‐
phenylenediamine (1.2 mmol) in ethanol (2.0 ml) con-
taining 0.1 mol% {Mo72V30} proceeded quantitatively
within 45 min under a continuous stream of O2 at 60°C
with no need for NHPI.
With an improved procedure in hand, we then
focused on the evaluation of the substrate scope for syn-
thesis of benzimidazoles. First, a set of structurally
In order to establish the general applicability of the
method, various benzyl alcohols were subjected to this
protocol under the catalytic influence of the {Mo72V30}
nanocluster (Table 3). According to the results, benzimid-
azole derivatives were successfully produced with moder-
ate to high yields. It was observed that the reaction rate
was affected by electronic demands of substrates. Benzyl
alcohols bearing electron‐donating groups were effi-
ciently converted to the corresponding benzimidazoles
(Table 3, entries 5 and 6). Nevertheless, strong electron‐
withdrawing nitro group on the phenyl ring of both alco-
hol and amine molecules significantly retarded the reac-
tion (Table 3, entries 4 and 9). It should be mentioned
that the production of benzimidazoles using aliphatic
alcohols failed, resulting from their poor oxidation reac-
tivity for formation of aldehyde intermediates under the
optimized conditions of this work.[16]
diverse
aldehydes
was
coupled
with
1,2‐
phenylenediamine under O2 stream (Table 5). A broad
range of benzimidazole derivatives was successfully
formed with good to excellent yield using this protocol.
The results indicated that an electron‐withdrawing group
on the phenylenediamine induced a negative influence
on the reaction efficiency in this catalytic system (entry
13). It is noteworthy that, in all experiments, excellent
selectivity was observed for benzimidazole formation.
3.2 | Synthesis of benzimidazoles using
method B
Next, the possibility of benzimidazole synthesis via the
reaction of 1,2‐diaminobenzenes and benzaldehydes as
starting materials under the catalytic influence of the
{Mo72V30} nanocluster was examined. To optimize the
reaction conditions, various factors were screened.
According to data summarized in Table 4, the reaction
FIGURE 1 Recycling of catalytic system for synthesis of
benzimidazoles (methods A and B) using {Mo72V30} nanocluster
according to procedures mentioned in the experimental section.
Conversions were obtained using GC based on starting benzyl
alcohol and 4‐chlorobenzalaldehyde for methods A and B,
respectively
FIGURE 2 (a) UV–visible and (b) FT‐IR spectra of fresh (black)
and recovered (red) {Mo72V30} in the synthesis of benzimidazole
by method A

KHOSHYAN ET AL.
7 of 9
that the reaction had no effect on the structure and prop-
erties of the catalyst. Moreover, to determine the amount
of Mo and V released during the reaction, atomic absorp-
tion spectrometric measurements were performed after
filtration of solid particles. The amount of elements in fil-
trate was not detectable using this analysis (<1 ppm)
demonstrating that the {Mo72V30} nanocluster rather than
the products of its degradation acts as an active catalyst in
these transformations.
3.3 | Reusability and stability
The reusability and stability of a catalyst are imperative
factors for practical applications of a heterogeneous sys-
tem. In this line, the recyclability of the catalyst was
investigated in the synthesis of benzimidazoles based on
model reactions (methods A and B). After completion of
the reactions, the {Mo72V30} nanocluster was separated
easily by centrifugation followed by decantation. The
recovered catalyst was dried under air, weighed and used
for subsequent runs. The catalyst gave remarkable results
without noticeable loss of activity (Figure 1). Minor loss
of activity in method A after the third run can be related
to contamination of the catalyst surface by organic com-
pounds. Sonication of the residual catalyst in EtOAc
followed by filtration and drying under vacuum enhanced
the conversion to 96% in the fifth run. Moreover, the sta-
bility of the catalyst was investigated by comparison of
FT‐IR and UV–visible spectra of used catalyst with those
of fresh one (Figure 2). These results clearly revealed that
the structure of the catalyst remained almost intact so
3.4 | Comparison with previously
reported methods
Finally, the merit of these operationally catalytic proto-
cols in the synthesis of benzimidazoles was compared
with previously reported methods in terms of catalyst
loading, temperature, reaction time and yields of prod-
ucts with both benzyl alcohol (Table 6, method A) and
benzaldehyde (Table 7, method B) as starting materials.
Therefore, the title catalytic system is environmentally
TABLE 6 Comparison of catalytic activity of {Mo72V30} nanocluster with that of other previously reported catalysts for synthesis of
benzimidazole using benzyl alcohol and 1,2‐phenylenediamine
Catalyst amount (mol
%)
Time Yield
Entry Catalyst
Conditions
(h)
(%)
Ref.
1
2
3
4
5
6
7
8
9
{Mo72V30}
0.05
5
EtOAc/O2/NHPI/70°C
Solvent free/O2/120°C
Mesitylene/Ar/120°C
KOtBu/diglyme/110°C
Water/air/t‐BuONa/75°C
Toluene/Ar/150°C
4
6
95
96
97
85
96
74
72
89
80
This work
[40]
Co3O4@Al2O3/SiO2
Ir/TiO2–500
[41]
[42]
[43]
[44]
[23]
[45]
[26]
1
18
24
8
[Ir(cod)2,6‐DiAmPy(iPr)2]
TEMPO‐PEG4000‐NHC‐Cu(II)
dppf [1,1‐bis(diphenylphosphino)ferrocene]
2‐Iodoxybenzoic acid
FePC
1.4
5
5
24
5
1
DMSO/air/25°C
1
Toluene/t‐BuONa/120°C 36
Toluene/Ar/200°C 20
RuCl2(PPh3)3
3.3
TABLE 7 Comparison of catalytic activity of {Mo72V30} nanocluster with that of other previously reported catalysts for synthesis of
benzimidazole using 4‐chlorobenzaldehyde and 1,2‐phenylenediamine
Entry Catalyst
Catalyst amount (mol%) Conditions
Time (min) Yield (%) Ref.
1
2
3
4
5
6
7
8
9
{Mo72V30}
0.1
10
EtOH/O2/60°C
Methanol/air/RT
DMF/air/RT
45
240
90
95
98
88
91
79
83
89
85
91
This work
[46]
Cu(OH)2
[47]
[48]
[49]
[50]
[51]
[52]
[53]
Thiamine hydrochloride
LaCl3
3
10
19
2
CH3CN/air/RT
Solvent free/air/75°C
EtOH/air/50°C
EtOH/80 C/reflux
Water/air/RT
150
45
p‐Toluenesulfonic acid/graphite
Na3AlF6
960
480
35
Zn(OTf)2
10
10
100
NaC15H25SO4
Fe(HSO4)3
Water/RT
60

8 of 9
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4 | CONCLUSIONS
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tain. Chem. Eng. 2014, 2, 942.
The catalytic efficiency of {Mo72V30} nanocluster was
exploited in dehydrogenative coupling of primary ben-
zylic alcohols and aromatic diamines in the presence of
NHPI as hydrogen acceptor for direct synthesis of benz-
imidazoles. The method is also capable of oxidative cou-
pling of benzaldehydes with aromatic diamines
producing benzimidazoles in high to excellent yields.
The reactions exhibited high performance using low cata-
lyst loading because of high dispersity of the solid
nanocluster providing standard conditions avoiding cur-
rent limitations for scale‐up applications. The methods
use molecular oxygen as oxidant and ethyl acetate or eth-
anol as safe solvents affording environmentally friendly
reaction conditions for the synthesis of benzimidazoles
as medicinally and pharmaceutically important com-
pounds. Moreover, the stability of the catalyst and its
potential for efficient recyclability along with easy
workup procedure for isolation of products in good to
excellent yields are further advantages of these proce-
dures, highlighting their merits for applied purposes.
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ACKNOWLEDGEMENTS
[22] Y. Shiraishi, Y. Sugano, S. Tanaka, T. Hirai, Angew. Chem.
2010, 122, 1700.
Support of this work by the Research Council of Univer-
sity of Birjand is much appreciated. We thank the Iran
Science Elites Federation for partial support of this work.
[23] J. N. Moorthy, I. Neogi, Tetrahedron Lett. 2011, 52, 3868.
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148, 30.
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ORCID
[26] A. Eskandari, M. Jafarpour, A. Rezaeifard, M. Salimi, New J.
Chem. 2018, 42, 6449.
Fahimeh Feizpour http://orcid.org/0000-0001-7180-8822
Maasoumeh Jafarpour
5013
Abdolreza Rezaeifard
http://orcid.org/0000-0002-9946-
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Nandeesh, K. Mantelingu, K. S. Rangappa, Tetrahedron Lett.
2011, 52, 5571.
http://orcid.org/0000-0002-8717-
9036
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SUPPORTING INFORMATION
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How to cite this article: Khoshyan A,
Pourtahmasb M, Feizpour F, Jafarpour M,
Rezaeifard A. Aerobic {Mo72V30} nanocluster‐
catalysed heterogeneous one‐pot tandem synthesis
of benzimidazoles. Appl Organometal Chem. 2018;
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