A versatile synthesis of arylaminotetrazoles by a magnetic Fe@Phendiol@Mn nano-particle catalyst and its theoretical studies

Article abstract of DOI:10.1002/aoc.3826

The Fe₃O₄ magnetic nano-particles were modified with 1,10-phenanthroline-5,6-diol and the relevant Mn complex (Fe@Phendiol@Mn) synthesized as a nano-magnetic heterogeneous catalyst to be used for the synthesis of various arylaminotet

Full text of DOI:10.1002/aoc.3826

Received: 18 January 2017
DOI: 10.1002/aoc.3826
Revised: 28 February 2017
Accepted: 6 March 2017
F U L L PA P E R
A versatile synthesis of arylaminotetrazoles by a magnetic
Fe@Phendiol@Mn nano‐particle catalyst and its theoretical
studies
Davood Habibi
| Somayyeh Heydari | Mina Afsharfarnia | Zahra Rostami
Department of Organic Chemistrty, Faculty
of Chemistry, Bu‐Ali Sina University,
Hamedan 6517838683, Iran
The Fe3O4 magnetic nano‐particles were modified with 1,10‐phenanthroline‐5,6‐diol
and the relevant Mn complex (Fe@Phendiol@Mn) synthesized as a nano‐magnetic
heterogeneous catalyst to be used for the synthesis of various arylaminotetrazoles from
various arylcyanamides and sodium azide in DMF at 120 °C. Also, the nano‐catalyst
characterized by different methods such as the elemental analysis (CHN), ICP, FT‐IR,
XRD, EDX, SEM, TEM, TG‐DTA, VSM and XPS. In addition, the theoretical study of
the Fe@Phendiol@Mn nano‐catalyst was performed using the Gausian software. The
calculated results showed that the Gibbs free energy and the standard enthalpy values
are negative; therefore the complex is stable. Incidentally, the computational chemistry
descriptions including the electronic chemical potential, global hardness, electrophi-
licity index, energy gap, global softness and electronegativity were calculated.
Correspondence
Davood Habibi, Department of Organic
Chemistrty, Faculty of Chemistry, Bu‐Ali
Sina University, Hamedan, 6517838683 Iran.
Email: davood.habibi@gmail.com
KEYWORDS
1,10‐Phenanthroline‐5,6‐diol, arylaminotetrazoles, Fe3O4 magnetic nano‐particle, heterogeneous catalyst,
Mn complex, theoretical study
1 | INTRODUCTION
5‐aryl/alkyl aminotetrazoles, respectively.[20–26] Also,
cyanamides may be converted to aminotetrazoles using
Tetrazoles have several applications in biological and
pharmaceutical industries,[1–3] due to their antiallergic and
anti‐asthmatic,[4] antiviral and anti‐inflammatory,[5] anti‐
neoplastic,[6] and cognition disorder activities.[7] Tetrazoles
were used as explosives and rocket propellants,[8–10] and
applied in coordination chemistry,[11–13] preparation of
imidoylazides,[14] and also in agriculture farms as
plant growth regulators, herbicides, and fungicides stabi-
lizers.[15–17] So, the chemistry of tetrazoles has gained increas-
ing attention since the early 1980s.[18] The anionic tetrazoles
are almost ten times more lipophilic than corresponding
carboxylates, which is an important factor for designing drug
molecules to pass through the cell membranes.[19] There are
several methods for preparation of tetrazoles, for example
addition of the azide anion to nitriles, cyanates and
cyanamides which is the most common route for preparing
5‐substituted tetrazoles, 5‐aryl/alkyl oxytetrazoles and
hydrazoic acid, which often result in a mixture of isomers.[27]
In addition, 5‐monosubstituted‐amino‐1H‐tetrazoles were
synthesized by thermal isomerization of 1‐substituted‐5‐
amino‐1H‐tetrazoles in boiling ethylene glycol or melt.[28,29]
Another possible method of obtaining the 5‐
monoalkylaminotetrazoles was an adaption of the von Braun
degradation of tertiary amines with cyanogens bromide. In
this way, it might be possible to eliminate an alkyl group
from a 5‐dialkylamino‐tetrazoles.[30,31]
These methods suffer from one or more disadvantages, such
as low yield, long reaction times, harsh reaction conditions,
difficult obtaining and/or preparation of starting materials, use
of expensive and toxic reagents, and the in situ generation of
hydrazoic acid which is highly toxic and explosive.[32–36]
Congreve has reported a two‐step synthesis of 1‐aryl‐5‐
amino‐1H‐tetrazoles from the corresponding 1‐aryltetrazoles
via cyanamide intermediates.[37] Vorobiov and co‐workers
Appl Organometal Chem. 2017;e3826.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.3826

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published a three‐step synthesis of 1‐aryl‐5‐amino‐1H‐
tetrazoles in low yields from the corresponding aromatic
amines via isolation of cyanamide intermediates.[38]
FeCl2.4H2O (4.3 g) was dissolved in water (100 ml), and
the solution stirred for 0.5 h in 80 °C. The solution of 37%
ammonia was then added dropwise with vigorous stirring
which a black solid product obtained when a reaction media
reached to pH 10. The mixture was heated for 0.5 h at 70 °
C and the black solid product filtered, washed with water
(3 × 20 ml) and dried at 80 °C for 12 h.
Incidentally, several regiospecific syntheses of
arylaminotetrazoles have been reported through the [3 + 2]
cycloaddition of cyanamides using NaN3 in the presence of
[39]
[40]
catalysts such as ZnCl2,
AlCl3
and Iranian natrolite
zeolite.[41] ZnCl2 and AlCl3 are homogeneous catalysts
which are very difficult to be separated from the reaction
mixture. Thus, development of the useful catalytic systems
for tetrazole synthesis still remains as active research area.
Industry favors application of heterogeneous catalysts over
homogeneous processes in view of the ease of handling,
simple work‐up, and separations.[42]
Among catalysts, application of the nano‐catalysts has
received considerable attention in recent decades as heteroge-
neous catalysts for organic synthesis due to their unique
physical surfaces and catalytic properties.[43,44]
The surface area to volume ratio increases with the
decrease in radius of the sphere and vice versa. Therefore
as particle size decreases, a greater portion of the atoms are
found at the surface compared to those inside. Thus, nanopar-
ticles have a much greater surface area per unit volume com-
pared with the larger particles.
Also, as growth and catalytic chemical reaction occurs at
surfaces, therefore a given mass of nano‐material will be
much more reactive than the same mass of material made
up of large particles.
2.1.2 | Stage 2: Synthesis of a ligand
First: Synthesis of 1,10‐phenanthroline‐5,6‐dione
1,10‐Phenanthroline‐5,6‐dione was prepared according to the
literature.[46] Briefly, an ice cold mixture of concentrated H2SO4
(40 ml) and HNO3 (20 ml) was added to 1,10‐phenanthroline
(4.0 g, 22.2 mmol) and KBr (4.0 g, 33.6 mmol). The mixture
was heated at reflux for 4 h. The hot yellow solution was
poured over ice (500 ml) and neutralized carefully with NaOH
until neutral to slightly acidic pH. Extraction with CHCl3
followed by drying with Na2SO4 and removal of solvent gave
4.5 g (96%) of 1,10‐phenanthroline‐5,6‐dione.
Second: Synthesis of 1,10‐phenanthroline‐5,6‐diol (Phendiol)
1,10‐Phenanthroline‐5,6‐diol was prepared according to the
literature.[47] Briefly, a mixture of 1,10‐phenanthroline‐5,6‐
dione (0.70 g, 3.33 mmol) and rubeanic acid (dithiooxamide,
0.480 g, 3.99 mmol) was refluxed in ethanol (25 ml) for 16 h.
Upon cooling of the reaction mixture to room temperature,
the yellow‐brown precipitate was separated by filtration,
washed with ethanol (20 ml) and dried in Vacuo.
So, we interested to design the Mn nano‐catalyst with
better reactivity compared to the pure Mn(II)(Phendiol)
complex, and hereby would like to report application of the
Fe@Phendiol@Mn nano‐catalyst for the one‐pot two‐com-
ponent selective synthesis of various arylaminotetrazoles
(A. or B) from different arylcyanamides with sodium azide
in DMF at 120 °C (Scheme 1).
2.1.3 | Stage 3: Surface modification of Fe3O4
MNPs with Phendiol (Fe@Phendiol)
Surface modification of Fe3O4 MNPs with Phendiol was
preformed according to the literature.[45] Briefly, Fe3O4
MNPs prepared from the stage one (0.5 g) were dispersed
in water/ethanol solution (50 ml, 1:1) by sonication at room
temperature for 20 min. Then, Phendiol prepared from the
stage two (0.25 g, 1.8 mmol) dissolved in ethanol (5 ml)
was added and placed under ultrasound for 3 hours.
Fe@Phendiol was separated by external magnet, washed
with ethanol (20 ml) and dried under vacuum at 50 °C for
2 h.
2 | EXPERIMENTAL
2.1 | Synthesis of a Fe@Phendiol@Mn nano‐
catalyst
2.1.1 | Stage 1: General procedure for prepa-
ration of Fe3O4 magnetic nano particles (Fe3O4
MNPs)
The Fe3O4 MNPs was prepared according to the literature.[45]
Briefly, the mixture of FeCl3.6H2O (11.44 g) and
2.1.4 | Stage 4: General procedure for prepa-
ration of the Fe@Phendiol@Mn nano‐catalyst
The Mn nano‐catalyst was prepared according to the litera-
ture.[45] Briefly, Fe@Phendiol prepared from the stage three
(0.2 g) and Mn(CH3COOH)2.4H2O (0.735 g, 3 mmol) were
mixed in ethanol (30 ml) and placed in an ultrasonic bath
for 3 h at room temperature. The resulting catalyst was
SCHEME 1 Synthesis of arylaminotetrazoles

HABIBI ET AL.
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separated with an external magnet, washed with ethanol
(20 ml), dried in vacuum at 70 °C for 6 h, and kept in a
desiccator.
2.2 | Apparatus and reagents
The IR spectra (KBr) were recorded on Perkin–Elmer GX
Fourier transform infrared spectrometer (FT‐IR). The NMR
spectra were recorded on a Bruker Ultra‐Shield 500
spectrometer. The TEM images were recorded on a Zeiss‐
EM10C‐80 KV transmission electron microscope, and the
SEM images were recorded on a Philips XL‐30 scanning
electron microscope. The XRD measurements were done by
a Bruker D8 Advance powder diffractometer, using Cu Kα
(λ = 1.54 A°) as the incident radiation.
SCHEME 2 Schematic synthesis of the Fe@Phendiol@Mn nano‐
For counting the nanoparticles, size distributions were
measured by the Zetasizer Nano‐ZS‐90 (ZEN 3600,
MALVERN) instrument. In addition, the ICP measurements
for the metal content evaluation were performed using a
Perkin‐Elmer ICP/6500. Magnetic measurements were car-
ried out using an Iranian Meghnatis Daghigh Kavir Co. The
chemical surface composition of the Mn complex was deter-
mined by XPS (BesTec, Germany).
catalyst
3.2 | Characterization of a Fe3O4
MNPs@Phendiol@Mn nano‐catalyst
Formation of the Fe@Phendiol@Mn nano‐catalyst was veri-
fied using the CHN analysis, FT‐IR, X‐ray diffraction
(XRD), dispersive X‐ray spectroscopy (EDX), scanning elec-
tron microscope (SEM), transmission electron microscope
(TEM), thermogravimetry‐differential thermal analysis
(TG‐DTA), vibrating sample magnetometer (VSM) and
XPS (X‐ray photoelectron spectroscopy).
Chemicals and solvents were purchased from the Merck
and Aldrich chemical companies and used without further
purification.
2.3 | Stage 5: Application of the Mn nano‐
catalyst for preparation of various
arylaminotetrazole
3.2.1 | Characterization of the nano‐catalyst
by the elemental analysis (CHN)
The elemental analysis report for C, H and N, and the ICP infor-
mation for Mn are presented in Table 1. These data indicated
the fact that the CHN content increased with increasing the
Phendiol ligand attached to the surface of Fe3O4 MNPs. The
loading of Mn was determined by the EDX analysis and
the ICP information which the final Mn content measurement
was around 0.43 mmol/g, indicating that %54.7 of the
Phendiol ligands were complexed with the Mn ions.
A mixture of arylcyanamide (2 mmol), sodium azide
(0.195 g, 3 mmol), and the Fe@Phendiol @Mn nano‐catalyst
(50 mg) was stirred at 120 °C in DMF (10 ml) until the TLC
monitoring showed no further progress in the conversion.
When the reaction mixture came to room temperature, the
nano‐catalyst was separated by a strong magnet, 4 N HCl
(20 ml) and ethyl acetate (35 ml) were added to the filtrate
and the organic layer extracted with decanting. The aqueous
layer was washed with ethyl acetate (2 x 25 ml) and the
organic layers combined. The resulting solution was then
dried over anhydrous MgSO4, the solvent evaporated and
the resulting solid recrystallized in ethanol.
3.2.2 | Characterization of the nano‐catalyst
by the IR spectroscopy
Figure 1 shows the three FT‐IR spectra of: Fe3O4 MNPs
(blue), Fe@Phendiol (green), and Fe@ Phendiol@Mn (red).
Fe3O4 MNPs exhibits basic characteristic peak at approxi-
mately 580 cm−1 which is attributed to the presence of the
Fe–O stretching vibrations. The FT‐IR spectrum of
Fe@Phendiol shows several original signals located at the
3020–3066 cm−1 (C‐H of the pyridine ring), the peaks at
1434–1437 cm−1 (C = C of the pyridine ring) and 1670
(C = N of the Phendiol ligand). It could be concluded from
the above results that the Fe3O4 MNPs was modified
3 | RESULTS AND DISCUSSION
3.1 | Synthesis of a Fe@Phendiol@Mn nano‐
catalyst
Synthesis of a Fe@Phendiol@Mn nano‐catalyst was carried
out via the four stages which were comprehensively
described in the experimental section (Scheme 2):

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HABIBI ET AL.
TABLE 1 Chemical composition of the immobilized Mn nano‐catalyst on the Fe3O4
CHN analyses (wt%)
Fe@Phendiol@
Mn (g/mmol)
% of coordinated
No
Sample
C
N
Mn
Fe@Phendiol (g/mmol)
ligand to Mn2+
1
2
Fe3O4 MNPs
Fe@Phendiol
–
–
–
–
–
–
–
–
–
24.65
1.05
1.05 ÷ 14 = 0.075 x 10 (since
we took 0.1 g for CHN) = 0.75
3
Fe@Phendiol@Mn
19.11
0.11
1.83
0.11 ÷ 14 = 0.00786
0.43 (from ICP)
0.43 ÷ 0.00786 = 54.70
nano‐catalyst exhibited broadened pattern due to its non‐
crystalline nature at 2θ = 15–30 and also 30.2, 35.6, 43.3,
53.6, 57.3 and 62.8 which corresponded to the Mn catalyst
structure (Figure 2, red). Finally, the XRD patterns represent
similar diffraction peaks which indicate that the coating agent
does not significantly affect the crystal structure of the mag-
netite nanoparticles, and the Fe3O4 MNPs particles were suc-
cessfully coated with the ligand.
FIGURE 1 The IR spectra of Fe3O4 MNPs (blue), Fe@Phendiol
(green), and the Fe@Phendiol@Mn nano‐catalyst (red)
3.2.4 | Characterization of the nano‐catalyst
by the EDX analysis
successfully. Comparison of the two IR spectra (blue and
green) confirms anchoring of the Phendiol ligand on the surface
of the magnetic nanoparticles. Furthermore, after complexing of
Mn with Fe@Phendiol, the weak absorption peak at 413 cm−1
was appeared which is attributed to the Mn‐N bands.
The chemical composition of the Fe@Phendiol@Mn nano‐
catalyst was determined by the EDX analysis (Figure 3).
The survey scan provided the presence of the anticipated
elements in the structure of the nano‐catalyst, namely iron,
oxygen, nitrogen, manganese and carbon.
3.2.3 | Characterization of the catalyst by the
XRD patterns
3.2.5 | Characterization of the nano‐catalyst
by the SEM and the TEM images
In addition, the crystalline phase and purity of the synthe-
sized material was determined by the XRD patterns
(Figure 2). The particle size was calculated by means of
the Debye Scherrer formula based on the full width at half‐
maximum of the highest intensity diffraction peak at
2θ = 35.6° and was found to be about 18 nm. The XRD pat-
tern exhibited peaks at 2θ of 31, 35, 43, 54, 57 and 62.5 cor-
respond to the spinal structure of Fe3O4 MNPs which
attributed to (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1) and
(4 4 0) faces of crystal. The diffraction peaks in this pattern
can be well indexed to the cubic spinel phase of Fe3O4 MNPs
(Figure 2, blue). The XRD pattern of the Fe@Phendiol@Mn
The morphology and the particle size distribution of the
Fe@Phendiol@Mn catalyst were determined by the SEM
and TEM images (Figure 4 and 5). According to these
figures, the nanoparticles appearance and their sizes are
similar, indicating that the Fe@Phendiol@Mn nano‐catalyst
have good mechanical stability and have not been destroyed
during the whole modification.
FIGURE 2 The XRD patterns of Fe3O4 MNPs (blue), and the
Fe@Phendiol@Mn nano‐catalyst (red)
FIGURE 3 The EDX analysis of the Fe@Phendiol@Mn nano‐catalyst

HABIBI ET AL.
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FIGURE 5 The TEM images of the Fe@Phendiol@Mn nano‐catalyst
3.2.6 | Characterization of the nano‐catalyst
by the TG‐DTA technique
The
thermogravimetric
analysis
curves
of
the
Fe@Phendiol@Mn nano‐catalyst show the mass loss of the
organic materials as they decompose upon heating
(Figure 6). It can be observed that the nano‐catalyst shows
two weight loss steps in the temperature range of the DTG
analysis. The initial weight loss at 200–220 °C is probably
due to the complex decomposition, and the second step at
about 320 °C is contributed to the thermal decomposition
of the coated layer in the nano‐catalyst.
On the basis of these results, the well grafting of ligand
groups on the support is verified and indicated that the
nano‐catalyst has a good thermal stability which is probably
due to the strong interaction between the Phendiol ligand
and Fe3O4 MNPs.
FIGURE 4 The SEM images of Fe@Phendiol (left) and the
Fe@Phendiol@Mn nano‐catalyst (right)
3.2.7 | Characterization of the catalyst by the
VSM technique
The VSM analysis of Fe@Phendiol (Figure 7, left) and the
Fe@Phendiol@Mn nano‐catalyst (Figure 7, right) were
performed in order to demonstrate their magnetic properties.
As can be seen, both have magnetic properties, however,
magnetization of the Fe@Phendiol@Mn nano‐catalyst was
decreased to some extent in comparison with Fe@Phendiol.
This can be explained by considering the reduction in the
dipolar–dipolar interactions between the magnetic
According to the nanoparticle size and the ligand capping
to prevent any agglomeration, the Fe@Phendiol@Mn nano‐
catalyst could be used as a suitable catalyst for the synthesis
of various tetrazoles. However, the presence of Mn ions in
the Fe@Phendiol@Mn nano‐catalyst purposely coated to
increase the electrical conduction and hence to improve the
quality of the SEM micrographs.

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HABIBI ET AL.
nanoparticles after their modification with the Phendiol
ligand and complexation with the Mn ions which cause the
more coating of Fe3O4 MNPs.
3.3 | Optimization of the reaction conditions
Most cyclization reactions are carried out in high tempera-
tures and most organic solvents are not stable at these temper-
atures, so DMF was chosen as an optimum solvent. Then, the
reaction of 2,5‐dichlorophenylcyanamide (2 mmol) and
sodium azide (3 mmol) was carried out as a model reaction
in different temperatures and the optimum temperature was
about 120 °C. The results showed that the reaction is specific
in the presence of the Mn complex, since only the product A
or B were obtained, while with the other reagents, the mixture
of products (A + B) produced (Table 2).[49]
Also, in the other series of experiments with the model
reaction, different amounts of the catalyst were used which
the 50 mg of the Mn nano‐catalyst was an optimum amount
(Entry 8). Further increasing of the catalyst concentration
had no effect on the rate and yield. Also the reaction had no
progress in the absence of the catalyst even after 4 h.
3.2.8 | Characterization of the nano‐catalyst
by the XPS spectroscopy
The XPS spectrum relating to the core level presence of the
Mn 2p is shown in Figure 8. The binding energy shows two
peaks at 644.0 and 653.2 eV which are attributed to the
presence of the Mn 2p3/2 and Mn 2p1/2, respectively. These
data confirm the formation of the Fe@Phendiol@Mn nano‐
catalyst as well as the Mn(II) oxidation state.[48]
It should be noted that from the XPS spectrum, not only
the presence of Mn was concluded, but also we concluded
the structure of the complex due to the oxidation state of
Mn. We did not know which structure the Mn complex
had, structure A, or B. The oxidation state of Mn(II) showed
us that the structure A is correct, not B.
3.4 | Synthesis of arylaminotetrazole derivatives
According to the optimized reaction conditions, the synthesis
of various arylaminotetrazole derivatives were carried out
from the reaction of arylcyanamides (2.0 mmol) with sodium
azide (3.0 mmol) in DMF at 120 °C by the application of Mn
nano‐catalyst (50 mg) (Table 3).
Also, in a new reaction, the pure Mn(II)(Phendiol)
complex was applied for the synthesis of 1‐(4‐nitrophenyl)‐
1H–tetrazole‐5‐amine (2a) from the reaction of N‐(4‐nitrophe-
nyl)cyanamide (1a) with sodium azide in DMF at 120 °C.
FIGURE 6 TG‐DTA patterns of the Fe@Phendiol@Mn nano‐catalyst in N2 atmosphere

HABIBI ET AL.
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FIGURE 7 The VSM analysis of Fe@Phendiol (left), and the VSM analysis of the Fe@Phendiol@Mn nano‐catalyst (right)
3.5 | Characterization of the
arylaminotetrazole compounds
All known compounds were characterized by comparing
their physical and spectral data with those reported in the lit-
erature. In the IR spectra of the 1‐H substituted tetrazoles, the
NH2 peaks were disappeared and one strong absorptions
band was detected (C‐N stretching band, ̴
1640–1690 cm−1).
The 1H–substituted tetrazoles are generally acidic substances
and the relevant proton signal will be shifted to downfield, so
the peak at δ = 7.80–8.30 ppm can be attributed to the proton
of the tetrazole ring.
FIGURE 8 The XPS spectrum of the Mn(II) nano‐catalyst
3.6 | The catalyst reusability
Recovery of the catalyst is an important criterion because of
the environmental and economical aspects, so the reusability
of the Fe@Phendiol@Mn nano‐catalyst was investigated as
well. Therefore, the Mn nano catalyst was separated by filtration
Interestingly, as we expected the reaction was completed
with longer reaction time (235 min) and less yield (63%)
compared with the application of the Mn nano‐catalyst.
TABLE 2 Comparison of different catalyst in the synthesis of arylaminotetrazoles at 120 °C
Entry
Catalyst
Solvent
DMF
Time (min)
Yield %
Product [49]
1
PPh3
LiCl
120
100
25
75
70
85
86
90
87
77
80
76
73
70
65
A + B
A + B
A + B
A + B
A + B
A + B
A or B
A or B
A or B
A or B
A or B
A or B
2
DMF
3
SiO2‐HClO4
Solvent‐free
Solvent‐free
Solvent‐free
Glacial HOAc
DMF
4
Al2O3‐SO3H
30
5
Fe(HSO4)3
30
6
Glacial HOAc
30
7
Fe@Phendiol@Mn (140 mg)
Fe@Phendiol@Mn (50 mg)
Fe@Phendiol@Mn (50 mg)
Fe@Phendiol@Mn (80 mg)
Fe@Phendiol@Mn (70 mg)
Fe@Phendiol@Mn (60 mg)
100
85
8
DMF
9
DMSO
100
100
100
100
10
11
12
DMF
DMF
DMF

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HABIBI ET AL.
TABLE 3 Synthesis of arylaminotetrazoles in DMF at 120 °C
Entry
Cyanamide (1a–k)
Product (2a–k)
Time (min)
Yield (%)
1
115
75
2
3
100
90
82
78
4
40
73
5
6
55
55
75
77
7
8
9
30
95
80
77
79
100
10
11
60
50
73
75

HABIBI ET AL.
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after the first run, washed with ethanol and dried at 120 °C
under vacuum and then reused for the next successive runs
under the same conditions (Scheme 3). No significant loss of
the activity was observed, indicating that the Mn nano‐catalyst
is capable and has the high stability during the synthesis of
various arylaminotetrazoles.
3.8 | Frequency calculations
The standard enthalpies (H) and the Gibbs free energy (G)
values of the Mn complex were obtained by theoretical
methods using the B3LYP/6‐31G (d) level to obtain the min-
ima of the potential energy. The calculated results show that
both the Gibbs free energy [G (hartree) = −1910.8261] and
the standard enthalpy [H (hartree) = −1910.7713] values
are negative; therefore the complex is stable.
3.7 | Theoretical studies
All the atomic geometrical parameters of the structure were
allowed to relax in the optimization at the density functional
theory (DFT) level of B3LYP exchange‐functional and
6‐31G (d) standard basis set. For the Mn atom, the standard
LANL2DZ basis set was used.[50] All of the calculations have
been carried out using a locally modified version of the
GAMESS electronic structure program.[51] The geometry
optimization, natural bond orbital (NBO), density of state
(DOS), highest occupied molecular orbital (HOMO) and
lowest unoccupied molecular orbital (LUMO) were investi-
gated, respectively. The energy difference between the
HOMO and LUMO is termed as the HOMO–LUMO gap
and also the density of state (DOS) plot was obtained from
the Gauss Summ program. Dipole moment (μ), optimization
energy (Eopt) and the point group of the Mn complex were
obtained using the B3LYP/6‐31G level.
3.9 | Electrostatic potential maps
Electrostatic potential maps are especially useful for
considering the charge redistribution, and changes in the
reactive site, when molecules acquire and lose different
functional groups. Molecular electrostatic potential (MEP) is
capable of revealing the subtle changes observed in the spatial
electronic distribution due to the changes in the molecular
framework by locating and characterizing the critical points
(CPs).[55] The MEP for the Mn complex which is in its
optimized geometry was calculated using the Gauss view
5.0 W and sampled over the entire accessible surfaces of a
molecule (corresponding to a van der Waals contact surface).
This color coded surface provides information about the
region of negative valued potential (deep green color), and
the susceptible region (red color) likely to be attacked by
nucleophiles. The topography map resulted from the MEP
surface of the Mn complex has been shown in Scheme 4.
By using the B3LYP/6‐31G level, the obtained results for
dipole moment (μ), optimization energy (Eopt) and the point
group of the Mn complex are 2.6354, −1910.9720 and C1,
respectively.
3.10 | Atomic and bonding properties
For the Mn complex, the computational chemistry
descriptions[52,53] including the electronic chemical potential
(μ), global hardness (ɳ), electrophilicity index (ω),[54] energy
gap (Egap), global softness (s) and electronegativity (χ) were
calculated by the following equations: [μ = − χ = − (I + A)/2],
Natural bonding orbital (NBO) calculations are important for
describing the charge transfer, and also for understanding the
delocalization of the electron density between the filled
(bonding (BD) or lone pair (LP)) Lewis type NBOs and the
empty (antibonding and Rydberg) non‐Lewis acceptor
NBOs.
[ɳ = (I – A)/2], [ω = μ[2]/2ɳ], and [s = 1/2ɳ] where I (−EHOMO
)
is the first vertical ionization energy and A (−ELUMO) is the
electron affinity of the Mn complex. The electrophilicity index
is a measure of the electrophilic power of a molecule. The
obtained results for I, A, Egap, χ, η and s are −5.38852,
−1.8028, −3.58573, −1.79286, 3.595658 and1.607178,
respectively.
The interaction energy of filled and empty orbitals can be
predicted by the second‐order perturbation theory.[55] Also,
SCHEME 3 Reusability of the Fe@Phendiol@Mn nano‐catalyst in
SCHEME 4 The molecular electrostatic potential surface of the Mn
the synthesis of arylaminotetrazoles
complex

10 of 12
HABIBI ET AL.
for each donor NBO(i) and the acceptor NBO(j), the stabiliza-
tion energy E(2) related to the electron delocalization i ! j is
estimated using the following equation[56]: E(2) = ΔEi,j = ni
[Fi,j[2]/ (Ɛi ‐ Ɛj)], where ni is the donor orbital occupancy, Ɛi
and Ɛj are the diagonal elements (orbital energies) and Fi,j
is the off diagonal NBO Fock matrix element. The larger
interaction energy E(2) shows the stronger interaction
between the electron donor atoms and the electron acceptor
atoms. In this work, the NBO analysis was performed at the
B3LYP/6‐31G (d) level based on the stability energies E(2),
occupation numbers and delocalization of the electron
density for LP electrons of Mn atom for the most stable
configuration. The results obtained in indicated that the total
energy for the Mn LP (σ* or π*) delocalization increases with
increasing the π character of the LP electrons of Mn for each
donor acceptor atoms (Table 4). In addition, with increasing
the π character.
SCHEME 5 Optimized models for the stable configuration of the
Mn complex and their DOS plots. Distances are in Å
of LP (Mn), there is decrease occupancy of the LP of Mn.
The DOS plots obtained from the Gauss Summ program
for the Mn complex has been shown in Scheme 5. The big
distance between the HOMO and LUMO levels indicates that
the Mn complex is not a good conductive compound.
3.11 | The plausible mechanism
The plausible mechanism for the synthesis of different
arylaminotetrazoles is shown below (Scheme 6). The pro-
posed mechanism is probably due to the Lewis acidity of
the Mn nano‐catalyst which can catalyze the cyclization
reaction by activation of the C‐N bond to produce the final
product.
SCHEME 6 The plausible mechanism for the synthesis of different
arylaminotetrazoles
Calcd for C7H6N6O2: C, 40.78; H, 2.93; N, 40.77; Found: C,
40.88; H, 3.01; N, 40.67.
N‐(2‐Chlorophenyl)‐2H–tetrazole‐5‐amine (2b): M.p.
228–230 °C; FT‐IR (KBr, cm−1) 3329, 3157, 1660, 1595,
1578, 1499, 1460, 1317, 1130, 1081, 1040, 992, 760, 726,
712, 656, 559, 448; 1H NMR (500 MHz, DMSO‐d6):
δH = 14.86 (s, br, 1H), 9.12 (s, 1H), 8.00 (d, J = 8.2 Hz,
1H), 7.46 (d, J = 7.9 Hz, 1H), 7.33 (t, J = 8.4 Hz, 1H),
7.04 (t, J = 7.7 Hz, 1H); 13C NMR (125 MHz, DMSO‐d6):
δC = 154.8, 136.7, 129.6, 127.9, 123.5, 122.6, 120.2; Anal.
Calcd for C7H6N5Cl: C, 42.98; H, 3.09; N, 35.80. Found:
C, 43.10; H, 3.19; N, 35.68.
3.12 | Selected spectral data of some
synthesized arylaminotetrazoles
1‐(4‐Nitrophenyl)‐1H–tetrazole‐5‐amine (2a): M.p. 187–188 °C;
FT‐IR (KBr, cm−1): 3389, 3302, 3124, 1651, 1611, 1598,
1577, 1523, 1506, 1466, 1348, 1315, 1296, 1131, 1108,
1074, 867, 858, 751, 690, 588, 506, 449; 1H NMR
(500 MHz, DMSO‐d6): δH = 8.43 (d, J = 7.2 Hz, 2H), 7.91
(d, J = 7.2 Hz, 2H), 7.19 (s, 2H); 13C NMR (125 MHz,
DMSO‐d6): δC = 154.9, 147.1, 138.6, 125.3, 124.6; Anal.
TABLE 4 The most important second order perturbation energies (kcal/mole) for the acceptor–donor atoms of the Mn complex obtained from the
NBO calculations
Ɛi ‐ Ɛj
E(2)
Fi,j
Acceptor
Donor
Structure
0.01
0.01
0.65
0.61
3.9
0.022
0.022
0.020
0.036
BD* (N10‐Mn18)
BD* (N17‐Mn18)
BD* (C16‐N17)
BD* (C7‐N17)
BD (C11‐C12)
BD (C15‐C16)
LP (2) Mn18
LP (2) Mn18
Mn complex
3.9
0.39
1.35

HABIBI ET AL.
11 of 12
N‐(2,5‐Dichlorophenyl)‐2H–tetrazol‐5‐amine (2c): M.p.
J = 8.6 Hz, 2H), 7.62 (d, J = 8.6 Hz, 2H), 6.94 (s, 2H);
13C NMR (125 MHz, DMSO‐d6): δC = 155.8, 134.6,
133.2, 130.6, 126.9.
272–274 °C; FT‐IR (KBr, cm−1) 3330, 3170, 1659, 1588,
1568, 1492, 1457, 1396, 1311, 1250, 1142, 1100, 1080,
1030, 989, 885, 825, 813, 757, 737, 689, 671, 590, 499,
482, 449; 1H NMR (500 MHz, DMSO‐d6): δH = 14.72
(s, br, 1H), 9.38 (s, 1H), 8.19 (s, 1H), 7.48 (d, J = 8.5 Hz,
1H), 7.06 (d, J = 8.5 Hz, 1H); 13C NMR (125 MHz,
DMSO‐d6): δC = 154.4, 137.8, 132.3, 130.8, 122.5, 120.3,
118.7; Anal. Calcd for C7H5N5Cl2: C, 36.52; H,2.17; N,
30.43. Found: C, 36.66; H, 2.22; N, 30.56.
1‐(4‐Methoxyphenyl)‐1H–tetrazol‐5‐amine (2j): M.p.
211–213 °C; FT‐IR (KBr, cm−1): 3282, 3194, 3068, 2962,
1622, 1588, 1542, 1512, 1467, 1307, 1243, 1187, 1109,
1
1056, 1034, 996, 831, 790, 767, 725, 675, 566, 521; H
NMR (500 MHz, acetone‐d6): δH = 7.49 (d, J = 8.9 Hz,
2H), 7.14 (d, J = 8.9 Hz, 2H), 6.14 (s, 2H), 3.89 (s, 3H);
13C NMR (125 MHz, acetone‐d6): δC = 161.5, 156.2,
127.7, 127.1, 115.9, 56.19; Anal. Calcd for C8H9N5Ο: C,
50.25; H, 4.74; N, 36.63. Found: C, 50.21; H, 4.81; N, 36.75.
1‐(2,6‐Dimethylphenyl)‐1H–tetrazol‐5‐amine (2 k): M.p.
147–149 °C; FT‐IR (KBr, cm−1): 3441, 3383, 3351, 2952,
2921, 1697, 1651, 1604, 1583, 1558, 1526, 1486, 1442,
1‐p‐Tolyl‐1H‐tetrazol‐5‐amine (2d): M.p. 178–179 °C;
FT‐IR (KBr, cm−1) 3310, 3146, 2920, 1655, 1594, 1572,
1519, 1466, 1321, 1306, 1287, 1180, 1141, 1091, 1017,
1
919, 889, 819, 765, 739, 709, 672, 636, 618, 545, 483; H
NMR (500 MHz, DMSO‐d6): δH = 7.43 (d, J = 8.2 Hz,
2H), 7.39 (d, J = 8.2 Hz, 2H), 6.80 (s, 2H), 2.38 (s, 3H);
13C NMR (125 MHz, DMSO‐d6): δC = 155.8, 139.8,
131.8, 131.1, 124.8, 21.6.
1
1247, 1228, 1194, 1168, 1032, 987, 938, 780; H NMR
(500 MHz, DMSO‐d6): δH = 7.03 (s, 3H), 5.24 (s, 2H),
2.25 (s, 6H); 13C NMR (125 MHz, DMSO‐d6): δC = 157.5,
137.1, 136.6, 128.3, 126.3, 18.6; Anal.Calcd for C9H11N5:
C, 57.12; H, 5.86; N, 37.02. Found: C, 57.18; H, 5.90; N,
37.09.
1‐o‐Tolyl‐1H‐tetrazol‐5‐amine (2e): M.p. 191–192 °C;
FT‐IR (KBr, cm−1) 3323, 3160, 1656, 1593,
1576, 1504, 1473, 1378, 1313, 1293, 1139, 1091, 1027,
994, 773, 758, 716, 674, 565, 486, 445; 1H NMR
(300 MHz, DMSO‐d6): δH = 7.51–7.36 (m, 4H), 6.74 (s, 2H),
2.06 (s, 3H).
4 | CONCLUSION
1‐(2,4‐Dimethylphenyl)‐1H–tetrazol‐5‐amine (2f): M.p.
199–201 °C; FT‐IR (KBr, cm−1) 3312, 3152, 1954, 2922,
1655, 1593, 1576, 1509, 1460, 1378, 1355, 1315, 1237,
1137, 1091, 1030, 1091, 997, 870, 829, 617, 565, 496,
In conclusion, the Fe@Phendiol@Mn nano‐catalyst was
prepared, characterized by different methods and the Mn
nano‐catalyst used for the selective synthesis of various
arylaminotetrazole derivatives (A or B).
Also, the theoretical study of the Fe@Phendiol@Mn
nano‐catalyst by the Gausian software showed that the com-
plex is stable. In addition, some physicochemical parameters
were calculated, and the big distance between the HOMO
and LUMO levels indicated that the Mn complex is not a
good conductive compound.
1
444; H NMR (500 MHz, DMSO‐d6): δH = 7.28 (s, 1H),
7.22 (d, J = 8.2 Hz, 1H), 7.19 (d, J = 8.2 Hz, 1H), 6.63
(s, 2H), 2.36 (s, 3H), 1.99 (s, 3H); 13C NMR (125 MHz,
DMSO‐d6): δC = 155.6, 140.0, 134.9, 131.7, 129.4, 127.6,
127.1, 20.6, 16.7.
1,1′‐(1,4‐Phenylene)bis(1H–tetrazol‐5‐amine) (2 g): M.p.
264–266 °C; FT‐IR (KBr, cm−1) 3321, 3145, 1659, 1587,
1522, 1447, 1427, 1325, 1292, 1142, 1120, 1088, 1019,
1
852, 843, 737, 651, 575; H NMR (500 MHz, DMSO‐d6)
ACKNOWLEDGEMENTS
δH = 7.83 (s, 4H), 7.03 (s, 4H); 13C NMR (125 MHz,
DMSO‐d6) δC = 155.9, 134.6, 126.3; Anal. Calcd for
C8H8N10: C, 39.35; H, 3.30; N, 57.35. Found: C, 39.46; H,
3.42; N, 57.23.
We are thankful to the Bu‐Ali Sina University, Hamedan
6517838683 Iran, for the financial support of this work.
N‐(4‐Bromophenyl)‐2H–tetrazol‐5‐amine (2 h): M.p.
249–250 °C; FT‐IR (KBr, cm−1): 3266, 3128, 3074, 1626,
1578, 1545, 1486, 1246, 1070, 1009, 835, 784, 728, 584,
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How to cite this article: Habibi D, Heydari S,
Afsharfarnia M, Rostami Z. A versatile synthesis of
arylaminotetrazoles by a magnetic Fe@Phendiol@Mn
nano‐particle catalyst and its theoretical studies. Appl
Organometal Chem. 2017:e3826. https://doi.org/
10.1002/aoc.3826
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