Biosynthesis of Pd/MnO2 nanocomposite using Solanum melongena plant extract and its application for the one-pot synthesis of 5-substituted 1H-tetrazoles from aryl halides

Article abstract of DOI:10.1002/aoc.4698

In this work, for the first time, Solanum melongena plant extract was used for the green synthesis of Pd/MnO₂ nanocomposite via reduction osf Pd(II) ions to Pd(0) and their immobilization on the surface of manganese dioxide (MnO₂) nanoparticles (NPs) as an effective support. The synthesized nanocomposite were characterized by various analytical techniques such as Fourier transform infrared (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and UV–Vis spectroscopy. The catalytic activity of Pd/MnO₂ nanocomposite was used as a heterogeneous catalyst for the one-pot synthesis of 5-substituted 1H-tetrazoles from aryl halides containing various electron-donating or electron-withdrawing groups in the presence of K₄[Fe (CN)₆] as non-toxic cyanide source and sodium azide. The products were obtained in good yields via a simple methodology and easy work-up. The nanocatalyst can be recycled and reused several times with no remarkable loss of activity.

Full text of DOI:10.1002/aoc.4698

Received: 10 September 2018
DOI: 10.1002/aoc.4698
Revised: 17 October 2018
Accepted: 18 October 2018
F U L L P A P E R
Biosynthesis of Pd/MnO2 nanocomposite using Solanum
melongena plant extract and its application for the one‐pot
synthesis of 5‐substituted 1H‐tetrazoles from aryl halides
Mahmoud Nasrollahzadeh1
| Fatemeh Ghorbannezhad1 | S. Mohammad Sajadi2
1 Department of Chemistry, Faculty of
Science, University of Qom, Qom 37185‐
359, Iran
2 Department of Petroleum Geoscience,
Faculty of Science, Soran University, PO
Box 624, Soran, Kurdistan Regional
Government, Iraq
In this work, for the first time, Solanum melongena plant extract was used for
the green synthesis of Pd/MnO2 nanocomposite via reduction osf Pd(II) ions to
Pd(0) and their immobilization on the surface of manganese dioxide (MnO2)
nanoparticles (NPs) as an effective support. The synthesized nanocomposite
were characterized by various analytical techniques such as Fourier transform
infrared (FT‐IR), X‐ray diffraction (XRD), transmission electron microscopy
(TEM), field emission scanning electron microscopy (FESEM), energy disper-
sive X‐ray spectroscopy (EDS) and UV–Vis spectroscopy. The catalytic activity
of Pd/MnO2 nanocomposite was used as a heterogeneous catalyst for the
one‐pot synthesis of 5‐substituted 1H‐tetrazoles from aryl halides containing
various electron‐donating or electron‐withdrawing groups in the presence of
K4[Fe (CN)6] as non‐toxic cyanide source and sodium azide. The
products were obtained in good yields via a simple methodology and easy
work‐up. The nanocatalyst can be recycled and reused several times with no
remarkable loss of activity.
Correspondence
Mahmoud Nasrollahzadeh, Department of
Chemistry, Faculty of Science, University
of Qom, Qom 37185‐359, Iran.
Email: mahmoudnasr81@gmail.com
Highlights:
• Green synthesis of Pd/MnO2 nanocomposite using Solanum melongena
extract.
• Pd/MnO2 nanocomposite was characterized by FT‐IR, XRD, FESEM, EDS
and TEM.
• One‐pot synthesis of 5‐substituted 1H‐tetrazoles from aryl halides using
Pd/MnO2 nanocomposite.
• The catalyst can be easily recycled and reused several times without sensible
loss in its catalytic efficiency.
KEYWORDS
5‐substituted 1H‐tetrazole, aryl nitriles, Pd/MnO2 nanocomposite, sodium azide, Solanum melongena
Appl Organometal Chem. 2018;e4698.
wileyonlinelibrary.com/journal/aoc
© 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4698

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NASROLLAHZADEH ET AL.
conditions.[35–37] Among cyanide sources, K4[Fe (CN)6]
is attractive candidate in synthetic chemists as non‐toxic
cyano source.[38–40] There are several methods for the
synthesis of aryl nitriles using K4[Fe (CN)6] in the
presence of homogeneous catalysts.[38–40]
1 | INTRODUCTION
The field of heterocyclic synthesis has detected as enor-
mously important field in recent years. Tetrazoles as one
of the important five‐membered ring compounds are clas-
sified into heterocycles. This nitrogen‐rich heterocyclic is
represent an increasingly popular functionality owing to
their multi‐connectivity abilities and various applications
in medicinal as well as synthetic chemistry.[1] Among het-
erocycles, tetrazoles have been used as carboxylic acid
isosters[2] hence biological properties can be reclaimed
by replacement of C‐terminal amino acid with a tetrazole.
The N‐containing rings heterocyclic comprehensively are
applied in molecular design and synthesis of modified
amino acids and peptidomimetics due to metabolically
stable alteration in compared with the carboxylic acid
group.[3,4] Furthermore, tetrazole moieties are beneficial
to approachability more complex heterocycles through
various rearrangements.[5,6] In a quest for investigation
on high energy‐density materials (HEDM), N‐containing
heterocycles are promising candidates. Tetrazoles ener-
getic can be acquired of extrusion of nitrogen gas as an
end product and avoiding environmental pollution.[7–10]
Because of advantage the tetrazoles, several synthetic
paths have expanded due to their construction of
frameworks. 5‐Substituted 1H‐tetrazoles are the most N‐
containing heterocyclic compounds favorite. Standard
method for the synthesis of 5‐substituted 1H‐tetrazoles
is the [3 + 2] cycloaddition of organometallic between
nitriles and azides.[11–13] In generally, aluminium
azide,[13] tin azide[13–16] or silicon azide[17–20] were used
as the sources of azide which have follow drawbacks
including toxic organometallic reactants, difficult to
obtain and/or prepare starting materials, tedious workup
procedures and expensive materials. In 2001, Sharpless
and co‐workers[21] had introduced sodium azide for syn-
thesis of 5‐substituted 1H‐tetrazoles with stoichiometric
amounts of zinc salts as catalyst under aqueous condi-
tions. In recent years, [3 + 2] cycloaddition of nitriles
and azides enormously have been studied via homoge-
In recent years, there has been an immense upsurge
interest of separation of the catalyst and its reusability
in further runs as heterogeneous catalysis in various
chemical transformations. Metal nanoparticles (MNPs)
as heterogeneous catalysts are being employed because
of their high surface‐to‐volume ratio and the fact that
are exceedingly active upon their surfaces.[41–44] Biosyn-
thesis of MNPs as green nanobiotechnology are devel-
oped with growing concern use of environmental‐risk
substances. Biological‐based synthesis of nanoparticles is
utilized an ambient aqueous, plant extracts, biological
systems and microwave assisted synthesis.[45–47] The bio-
logical synthesis as a simple and environmentally safe
method have advantages such as utilization of non‐toxic
solvents, simple methodology, mild reaction conditions
(avoidance of the high pressure and temperature), easy
work‐up, long‐term stability, elimination of expensive
and toxic reducing agents, avoidance of expensive
capping agents and organic surfactants. However, the
agglomeration of MNPs is inevitable. To circumvent this
drawback, an ideal support is needed to decrease MNPs
agglomeration and suitable catalytic activity.[48–51]
Therefore, the importance of synthetic methods is to
establish environment friendly benign methods by choos-
ing suitable nanocatalyst to avoid all harm conditions and
give good results. Herein, in continuation of our efforts to
develop eco‐friendly synthetic methodologies, we are
used Solanum melongena plant extract for the synthesis
of Pd NPs on MnO2 NPs.
Solanum melongena (Eggplant), commonly known as
melongene (Figure 1) plays an important role in the
neous and heterogeneous catalysts[22–30]
. However,
despite wide advances for synthesis of 5‐substituted 1H‐
tetrazoles, there is no report on their in situ preparation
from aryl halides using metal nanocomposites.[31,32] So,
it is more desirable to develop a more efficient and simple
catalytic system for the one‐pot synthesis of 5‐substituted
1H‐tetrazoles from aryl halides via the formation of
benzonitriles as intermediate.
Aryl nitriles are important key constituents of
pharmaceuticals, agrochemicals, dyes, and natural prod-
ucts.[33,34] The successful examples for the synthesis of
benzonitriles were reported using superstoichiometric
amount of toxic cyanide sources under harsh reaction
FIGURE 1 Image of Solanum melongena plant

NASROLLAHZADEH ET AL.
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treatment of human disease since ancient time.[52–56] The
phytochemical constituents like tannins, proteins, alka-
loids, flavonoids and saponins of these species in dry
and shady areas were investigated qualitatively.[52–55]
Thus, through this research we decided to use the
Solanum melongena aqueous extract as a biomedia and
bioreducing agent to phytosynthesis of Pd NPs.
N
N
N
X
C
N
Pd/MnO2 nanocomposite
NaN3, Na2CO3, DMF, 120 o
H
R
+
K4Fe(CN)6
R
C
SCHEME 1 One pot synthesis of 5‐substituted 1H‐tetrazole from
aryl halides in the presence of bio‐catalyst
nFlO (radical) + nPd0
nFlOH + Pd+2
So, having the above point in mind, we have chosen a
biological procedure for preparation of the Pd/MnO2
nanocomposite using Solanum melongena aqueous
extract and its application as a heterogeneous catalyst
for the one‐pot synthesis of 5‐substituted 1H‐tetrazoles
from aryl halides by using K4[Fe (CN)6] as non‐toxic
cyano source and sodium azide as a azide source
(Scheme 1). The Pd/MnO2 nanocomposite was prepared
via immobilization of Pd NPs onto MnO2 nanostructure
using Solanum melongena aqueous extract.
nFlO (Radical) + Pd+2
nFlOX + nPd0 (Nucleation)
nPd0 + Pd+2
Pdn+2 (Growth)
+2
Pdn+2 + Pdn
+2n
Pd2n
(Pd2n+2n)n + (FlOH)n
Palladium NZV
SCHEME 2 Reducing ability of antioxidant phenolics to produce
Pd NPs where FlOH and NZV are flavonoid and nano zero valent,
respectively
2 | RESULTS AND DISCUSSION
2.1 | Characterization of Solanum
melongena plant extract and biosynthesized
Pd NPs
During this work, with the aim of improving the syn-
thetic methods we successfully introduced the Pd/MnO2
nanocomposite as a nanocatalyst heterogeneous using
Solanum melongena plant extract for conversion aryl
halides to aryl tetrazoles without aryl nitriles intermedi-
ate separation. The Pd2+ ions are reduced to Pdo in the
presence of the Solanum melongena plant extract as
reducing agent instead of the conventional environmen-
tally polluting ones. Nanocomposite are generally
characterized by their shape, size, and dispersity by
XRD, TEM, EDS, FESEM and FT‐IR.
FIGURE 2 UV–Vis spectrum of plant extract and green synthesis
Pd NPs at different times
In this work, we have employed Solanum melongena
plant extract as a reducing agent and efficient stabilizer.
As shown in Scheme 2, metal ions were reduced to
nano zero valent (NZV) metallic particles using flavonoid
(FlOH) contents of the plant as green chemical
component.
FIGURE 3 FT‐IR spectrum of green synthesized Pd NPs
FIGURE 4 The XRD powder pattern of
the Pd/MnO2 nanocomposite

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NASROLLAHZADEH ET AL.
The progression of the formation and stability of Pd
NPs were investigated by UV–Vis. Figure 2 shows the
UV bonds of the extract at 340 nm (bond Ι) and
255 nm (bond ΙΙ) due to the cinnamoyl and benzoyl
systems, respectively. In fact, they are concerned to the
π → π* transitions of polyphenolics. The UV–vis
spectrum of biosynthesized Pd NPs shows the effect of
surface Plasmon resonance following the appearance of
maximum wavelength around 305 nm. Also, the study
of stability of nanoparticles revealed that they have a
good stability even for more than one month because
the wavelength of nanoparticles shows no significant
deviation or disruption during this time and keeps
its symmetry. This stability is for possible adsorption of
FIGURE
nanocomposite
5
FT‐IR spectrum of biosynthesized Pd/MnO2
FIGURE 6 FESEM images of the Pd/MnO2 nanocomposite

NASROLLAHZADEH ET AL.
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antioxidant phytochemicals on nanosurface and
their protection effect to prevent decomposition and
deformation processes on nanostructures for a special
period of time.
Figure 3 shows the FT‐IR signals of Pd NPs synthe-
sized by Solanum melongena plant extract. The main
signals around 3600, 1790 and 1495–1580 cm−1 are
assigned to the OH, carbonyl group (C=O) and C=C
aromatic ring vibrations, respectively. The sharp peak
about 1100 cm−1 attributed to C‐O stretching vibrations.
These signals clearly confirm the presence of plant
phytochemicals on the surface of Pd NPs and their effect
on protection and stability of nanoparticles.
2.2 | Characterization of the Pd/MnO2
nanocomposite
The bioreduction process of Pd (II) ions to Pd NPs
and their immobilization on MnO2 NPs surface was
carried out by Solanum melongena plant extract. The
nanocatalyst formation was fully characterized by XRD,
TEM, FESEM, EDS and FT‐IR.
Phase investigation of the crystallized product was
carried out by powder XRD measurements. According
to XRD analysis of Pd/MnO2 nanocomposite as shown in
FIGURE 9 Histogram of particle size distribution of the Pd/
FIGURE 7 EDS spectrum of the Pd/MnO2 nanocomposite
MnO2 nanocomposite
FIGURE 8 TEM images of the Pd/MnO2 nanocomposite

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NASROLLAHZADEH ET AL.
Figure 4, strong and sharp peaks at 2θ values 40.05°, 46.5,
68.2° can be indexed to (111), (200) and (220) Bragg's
reflections of face‐centered cubic (fcc) Pd NPs (JCPDS
No. 89–4897).[45] To confirm presence MnO2 in sample,
the typical XRD pattern show diffraction peaks at 9.8°,
18.6°, 24.0°, 29.0°, 35.1°, 41.1°, 46.0°, 47.0°, 50.6°, and
68.7° corresponding to (110), (200), (220), (310), (400),
(420), (321), (510), (411), (541), respectively (JCPDS No.
44–0141).[57]
For confirmation of the polyphenolics present in Sola-
num melongena plant extract as reduction agent of metal
salt, analysis of FT‐IR spectrum was used (Figure 5).
Oxides and hydroxides of metal nanoparticles generally
gives absorption peak in the finger print region i.e. below
wavelength of 1000 nm arising from inter‐atomic
vibrations. Absorption band observed at 856 cm−1 is
corresponded to the surface –OH groups of Mn–OH for
colloidal MnO2 NPs.[58] The absorption peaks appearing
at 3346, 1621, 1384 and 1047 cm−1 are assigned to the
stretching vibrations of OH, carbonyl group (C=O),
stretching C=C aromatic ring and C‐O stretching vibra-
tions, respectively. The adsorption of organic compounds
in the extract on the surface of metal nanoparticles,
feasibility by interaction through π‐electrons interaction.
The morphology and uniformity of the Pd/MnO2
nanocomposite were ascertained by FESEM. As shown in
Figure 6, monodispersed spherical particles were
produced extracellular by the Solanum melongena plant
extract.
EDS analysis was used for more confirmation of the
Pd/MnO2 nanocomposite. As a result, the fabrication of
the Pd NPs and their immobilization on the MnO2 sur-
face was confirmed through elemental analysis. As
shown in Figure 7, the biosynthesized Pd/MnO2 nano-
composite is composed of O, Mn and Pd elements.
The shape and size of nanoparticles are finest
observed with the assistance of the TEM. TEM micro-
scopic analysis showed the deposition of Pd NPs on the
MnO2 surface and formation of regularly spherical
shaped nanoparticles with particle size distribution in
nanoscale (Figure 8). As shown in Figure 9, the average
size of particles is 12 nm.
2.3 | Preparation of 5‐substituted 1H‐
tetrazoles using Pd/MnO2 nanocatalyst via
a one‐step method
TABLE 1 Optimization of the reaction conditions for the syn-
thesis of 5‐phenyl‐1H‐tetrazole
Pd/MnO2
Entry (g)
Temperature Yield
In continuation of our recent effort on application of
heterogeneous nanocatalysts for the development of syn-
thetic methodologies, we introduced a green protocol for
the preparation of Pd/MnO2 nanocatalyst using Solanum
melongena plant aqueous extract and its application for
synthesis 5‐substituted 1H‐tetrazoles. To test this idea,
we have focused our investigation on conversion
iodobenzene to 5‐phenyl 1H‐tetrazole in the presence of
the potassium hexacyanoferrate (II), sodium azide and
Pd/MnO2 nanocatalyst without benzonitrile intermediate
work‐up in present bio‐catalyst. The reaction was not car-
ried out in the absence of catalyst (Table 1, entry 1). The
reaction conditions briefly were optimized and the best
conditions were achieved with 0.05 g of the Pd/MnO2
nanocomposite, 0.2 mmol of K4[Fe (CN)6], 1.5 mmol of
NaN3, 1.0 mmol of iodobenzene, 1.0 mmol of sodium
carbonate (Na2CO3) as base and 7.0 mL of DMF as
solvent and the results are summarized in Table 1.
Solvent Base
(°C)
(%)
1
0
DMF
DMF
DMF
DMF
DMF
Na2CO3
K2CO3
120
120
0
2
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.02
0.08
85
3
Piperidine 120
37
4
Et3N
120
120
120
120
110
80
48
5
Na2CO3
90
6
DMSO Na2CO3
NMP Na2CO3
87
7
52
8
Toluene Na2CO3
MeCN Na2CO3
Trace
Trace
72
9
10
11
DMF
DMF
Na2CO3
Na2CO3
120
120
90
Reaction conditions: Iodobenzene (1.0 mmol), K4Fe(CN)6 (0.22 mmol), base
(1.0 mmol), DMF (7.0 ml), NaN3 (1.5 mmol), 12 hr.
bYields are after work‐up.
X = I & Br
ArX
K4Fe(CN)6, Na2CO3, DMF, 120 oC
Pd/MnO2 nanocomposite
Cat
N
N
N
N
HN
Pd/MnO2 catalyst
N
C
H
Ar
C N
+
N
N
N
Ar
N
SCHEME 3 Proposed mechanism for
the preparation of 5‐substituted 1H‐
tetrazoles using Pd/MnO2 nanocatalyst
A
Ar
N
5-Substituted 1H-tetrazole
B

NASROLLAHZADEH ET AL.
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TABLE 2 One‐pot synthesis of 5‐substituted 1H‐tetrazoles from aryl halides using Pd/MnO2 nanocomposite
Entry
Aryl halide
Product
Time (h)
Yield (%)
1
12
90
2
3
4
5
12
12
12
12
87
85
83
85
6
7
12
12
84
82
8
9
12
12
80
83
10
11
12
12
18
18
85
83
80
13
18
80
14
15
18
18
81
80
(Continues)

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NASROLLAHZADEH ET AL.
TABLE 2 (Continued)
Entry
Aryl halide
Product
Time (h)
Yield (%)
16
18
78
Reaction conditions: Catalyst (0.05 g), aryl halide (1.0 mmol), K4Fe(CN)6 (0.22 mmol), NaN3 (1.5 mmol), Na2CO3 (1.0 mmol), DMF (5.0 ml), 120 °C.
bYields are after work‐up.
TABLE 3 Comparison of the Pd/MnO2 nanocomposite with
other previously reported catalysts in the synthesis of 5‐(4‐
methoxyphenyl)‐1H‐tetrazole
To extend the scope and applicability of the heteroge-
neous catalysis, we examined a wide divertimento of
substrates (Scheme 3). The optimal reaction conditions
were applied to synthesis of 5‐aryl 1H‐tetrazoles and the
results are summarized in Table 2. This strategy was
general for a range of aryl halides having electron
donating and withdrawing groups on benzene ring as
well as heterocyclic ring. The reaction time and yields
for aromatic nitriles bearing electron withdrawing and
electron donating groups have no significant difference.
As shown in Table 2, in comparison with aryl iodides,
aryl bromides require much longer time. In all cases,
the products were obtained in good yields under the
standard reaction conditions.
Time Yield
Entry Reaction conditions
(h)
(%)
Ref.
1
2
3
4
(4‐Methoxyphenyl) methanol, Cu 24
63
59
(NO3)2, TEMPO/NH3(aq.)/O2,
NaN3, DMSO
4‐Methoxybenzaldehyde, Cu
(NO3)2, TEMPO/NH3(aq.)/O2,
NaN3, DMSO
24
16
24
61
65
60
59
59
32
4‐Methoxybenzonitrile, Cu
(NO3)2, TEMPO/NH3(aq.)/O2,
NaN3, DMSO
A plausible mechanism is represented in Scheme 3. It
is proposed that initially aryl halide was converted to aryl
nitrile intermediate (A) by K4[Fe (CN)6] in the presence
of the Pd/MnO2 nanocomposite. Then the tetrazole prod-
uct was prepared from the [3 + 2] cycloaddition reaction
between aryl nitrile intermediate with NaN3 via the inter-
mediate B in the presence of the Pd/MnO2 nanocompos-
ite. The catalytic reaction is supplemented by acidic
work‐up to afford the desired products.
1‐Bromo‐4‐methoxybenzene,
K4[Fe (CN)6], NaN3,
[Pd (OAc)2], Na2CO3,
dabco, ZnBr2, DMF
5
4‐methoxybenzaldehyde
oxime, (PhO)2P(O)N3,
16
81
60
DPPA, DBU, toluene, 110 °C
6
7
4‐Methoxybenzonitrile,
NaN3 zinc salt, H2O
48
8
86
65
21
61
1
The products were characterized by FT‐IR, H NMR
4‐Methoxybenzaldehyde,
NH2OH, NaN3,
and 13CNMR. The disappearance of an CN stretching
band in the range of 2225–2370 cm−1 in the intermediate
B and the appearance of NH stretching band in product
structure in the FT‐IR spectra confirmed the formation
of the 5‐substituted 1H‐tetrazoles. 13CNMR spectra
showed one peak at 154–158 ppm corresponding to
carbon of the tetrazole ring.
(NH4)2Ce(SO4)4.2H2O, DMF
8
4‐Methoxybenzonitrile, Cu2O,
12
24
14
31
84
69
84
68
18
62
63
64
TMSN3, MeOH/DMF, 80 °C
9
4‐Methoxybenzonitrile, NaN3,
Yb (OTf)3.xH2O, DMF, 120 °C
10
11
4‐Methoxybenzonitrile, NaN3,
B(C6F5)3, DMF, 120 °C
A comparison of the catalytic activities of various cata-
lysts for the synthesis of 5‐(4‐methoxyphenyl)‐1H‐tetrazole
is given in Table 3. It is clearly axiomatic from the Table 3
that the Pd/MnO2 nanocomposite outperformed other
catalysts that are reported in the literature.[18,21,59–64]
The reaction was carried out in the presence of the
Pd/MnO2 nanocomposite in shorter time. The high yield
of 5‐(4‐methoxyphenyl)‐1H‐tetrazole obviously have dem-
onstrated excellent catalytic performance of the Pd/MnO2
nanocomposite. The nanocomposite synthesized by a
biological method which is a simple, green and ecofriendly
procedure using aqueous extract of the leaves of
Solanum melongena without using any harmful reducing
1‐Bromo‐4‐methoxybenzene,
Zn (CN)2, Pd (PPh3)4, NaN3,
NH4Cl, DMF, 120 °C
12
1‐Iodo‐4‐methoxybenzene,
K4[Fe (CN)6], NaN3, Pd/MnO2
nanocomposite, Na2CO3,
DMF, 120 °C
12
85
This
work
Yields are after work‐up.
or surfactant template. In addition, in comparison with
some of the reported catalysts, the proposed nanocatalyst
can be easily recovered and recycled for several times.

NASROLLAHZADEH ET AL.
9 of 13
Compared with the other literature works on the
synthesis of 5‐substituted 1H‐tetrazoles, the notable
features of our method are:
• The reaction system is simple;
• The yields of the products are high;
• The use of plant extract as an economic and effective
alternative represents an interesting, fast and clean
synthetic route for the synthesis of the Pd/MnO2
nanocatalyst;
• Elimination of toxic ligands and homogeneous
catalysts;
• Avoidance of in situ formation of dangerous and
harmful hydrazoic acid in reaction mixture
• The use of heterogeneous catalysts which can be
easily recovered and reused;
• The synthesized Pd NPs by this method is quite stable
and can be kept for one month.
I
Yield %
First Run
87 %
Me
First Recycle
87 %
Second Recycle
Pd/MnO2 nanocomposite, K4Fe(CN)6
Third Recycle
87 %
87 %
86 %
85 %
DMF, Na2CO3, 120 °C
2.4 | Catalyst reusability
Fourth Recycle
Fifth Recycle
N
N
N
In addition, we studied the reusability of the Pd/MnO2
nanocomposite. The catalyst was recovered by simple
filtration after completion of the reaction and re‐used
up to five times under the optimal reaction conditions
(Figure 10). The recovered catalyst showed good
N
H
Me
FIGURE 10 Reusability of Pd/MnO2 nanocomposite for the
synthesis of 5‐(4‐methylphenyl)‐1H‐tetrazole
FIGURE 11 The FE‐SEM images of recycled Pd/MnO2 nanocomposite

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NASROLLAHZADEH ET AL.
FIGURE 12 The EDS spectrum of
recycled Pd/MnO2 nanocomposite
FIGURE 13 TEM images of recycled Pd/MnO2 nanocomposite
reusability and catalytic activity with a slight decrease in
yield. The FE‐SEM, EDS and TEM analysis after the 5th
recycle exhibited no obvious change in the size, shape
and chemical composition of the reused Pd/MnO2
nanocomposite (Figure 11–13).
synthesis of 5‐aryl‐1H‐tetrazoles from aryl halides. The
catalyst was characterized by FT‐IR, FESEM, TEM, EDS
and XRD. The experimental results suggest that the
MnO2 NPs play critical role in stabilizing the Pd NPs,
which also prevent the Pd NPs from aggregating and
leaching during the reactions. This synthetic method
has the advantages of high yields, easy and simple prepa-
ration, the use of K4[Fe (CN)6] as a non‐toxic cyanide
source, avoidance of the formation of dangerous and
harmful hydrazoic acid, simple work‐up procedure, sim-
ple preparation and availability of the MnO2 as support.
3 | CONCLUSIONS
Pd/MnO2 nanocomposite synthesized using Solanum
melongena plant extract is a good catalyst for the

NASROLLAHZADEH ET AL.
11 of 13
In addition, the biosynthesized catalyst was stable
and easily recycled and reused several times without
remarkable loss in its catalytic activity.
4.4 | Preparation of MnO2 nanoparticles
MnO2 nanoparticles were prepared according to the
literature.[65]
4 | EXPERIMENTAL
4.5 | Green synthesis of the Pd/MnO2
nanocomposite using aqueous extract of
Solanum melongena plant
4.1 | Instruments and reagents
All reagents used in the present work were purchased
from Merck and Aldrich Chemical Companies without
further purification. FT‐IR (KBr) spectra were recorded
In a 250 ml flask, 50 mL of the aqueous extract of Sola-
num melongena plant was added to the MnO2 NPs
(1.0 g) and magnetically stirred for 15 min at 80 °C.
Then, 0.1 g of PdCl2 dissolved in 10 mL of water by
hydrochloric acid (37%) gradually added to the above
mixture under the continuous stirring and heated for
3 hr. The formed Pd/MnO2 nanocomposite was then cen-
trifuged, washed with ethanol and dries in an oven and
then characterized.
1
using a Varian model 640 spectrophotometer. H NMR
and 13C NMR spectra were recorded on a Bruker Avance
DRX spectrometer at 400 and 100 MHz, respectively.
Melting points were taken with a BUCHI 510 melting
point apparatus that are uncorrected. A Philips model
X'PertPro diffractometer X‐ray diffraction equipped with
a graphite monochromator crystal was used to perform
X‐ray diffraction (XRD) measurements (λ = 1.5405 Ao).
The scanning rate was 2o/min in the 2θ range from 10
to 80o. For investigation morphology and particle disper-
sion was used Scanning electron microscopy (SEM)
(Cam scan MV2300). The chemical compositions of the
prepared nanostructures were determined by EDS
(energy dispersive X‐ray spectroscopy) performed in
SEM. The chemical analysis of prepared nanostructures
was carried out by EDS (S3700 N). Transmission electron
microscope (TEM) was used to identify the Ag/Feldspar
shape and size using aPhilips‐EM‐2085 transmission elec-
tron microscope with an accelerating voltage of 100.0 kV.
4.6 | General procedure for the synthesis
of 5‐substituted 1H‐tetrazoles
The synthesis of tetrazole derivative are follow by typical
procedure. A mixture of aryl halide (1.0 mmol), K4[Fe
(CN)6] (0.22 mmol), sodium carbonate (1.0 mmol) and
0.05 g Pd/MnO2 nanocomposite was stirred in 7 mL
DMF at 120 °C. Then, to the benzonitrile generated in
situ (as indicated by TLC), then was added NaN3
(1.5 mmol) and the mixture magnetically stirred at
120 °C for appropriate time. The reaction progress was
monitored by TLC till completion. The catalyst was
removed by filtration, the reaction mixture was acidified
by 20 mL of HCl (4.0 M) and the solution diluted with
25 ml ethyl acetate and stirred vigorously. The organic
layer was separated, and the aqueous layer was extracted
with ethyl acetate twice. The combined organic layers
were concentrated to give a crude product. All products
are pure enough for IR and NMR spectroscopic analysis.
However, the products were further purified by recrystal-
lization from aqueous ethanol.
4.2 | Preparation of the Solanum
melongena plant extract
20 g of dried powdered of Solanum melongena plant and
150 mL double distillated water well mixed on magnetic
heating stirrer at 80 °C for 30 min and then the mixture
was centrifuged in 7000 rpm and filtered. Finally, the
green extract was kept at refrigerator to use further.
ACKNOWLEDGEMENTS
We gratefully acknowledge from the Iranian Nano Coun-
cil and University of Qom for the support of this work.
4.3 | Biogenic synthesis of Pd NPs using
Solanum melongena plant extract
10 ml of extract was added dropwise to 50 mL of 0.005 M
PdCl2 solution at 80 °C. Bio‐reduction process to form the
nano‐palladium (Pdo) finished around 4 min as solution
color changed to dark brown and monitored by UV–Vis
spectroscopy. Then the colored solution centrifuged at
7000 rpm for 45 min to completely separation.
ORCID
Mahmoud Nasrollahzadeh
4539-3544
S. Mohammad Sajadi
5178
http://orcid.org/0000-0002-
http://orcid.org/0000-0001-8284-

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NASROLLAHZADEH ET AL.
[29] D. Amantini, R. Beleggia, F. Fringuelli, F. Pizzo, L. Vaccaro,
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How to cite this article: Nasrollahzadeh M,
Ghorbannezhad F, Sajadi SM. Biosynthesis of
Pd/MnO2 nanocomposite using Solanum
melongena plant extract and its application for the
one‐pot synthesis of 5‐substituted 1H‐tetrazoles
from aryl halides. Appl Organometal Chem. 2018;
e4698. https://doi.org/10.1002/aoc.4698
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