The anchoring of a Cu(ii)-salophen complex on magnetic mesoporous cellulose nanofibers: green synthesis and an investigation of its catalytic role in tetrazole reactions through a facile one-pot route

Article abstract of DOI:10.1039/d1ra01913a

Today, most synthetic methods are aimed at carrying out reactions under more efficient conditions and the realization of the twelve principles of green chemistry. Due to the importance and widespread applications of tetrazoles in various industries, especially in the field of pharmaceutical chemistry, and the expansion of the use of nanocatalysts in the preparation of valuable chemical reaction products, we decided to use an (Fe₃O₄@NFC@NSalophCu)CO₂H nanocatalyst in this project. In this study, the synthesis of the nanocatalyst (Fe₃O₄@NFC@NSalophCu)CO₂H was explained in a step-by-step manner. Confirmation of the structure was obtained based on FT-IR, EDX, FE-SEM, TEM, XRD, VSM, DLS, TGA, H-NMR, and CHNO analyses. The catalyst was applied to the synthesis of 5-substituted-1H-tetrazole and 1-substituted-1H-tetrazole derivatives through multi-component reactions (MCRs), and the performance was assessed. With advances in science and technology and increasing environmental pollution, the use of reagents and methods that are less dangerous for the environment has received much attention. Therefore, following green chemistry principles, with the help of the (Fe₃O₄@NFC@NSalophCu)CO₂H salen complex as a nanocatalyst that is recyclable, cheap, safe, and available, the use of water as a green solvent, and reduced reaction times, the synthesis of tetrazoles can be achieved.

Full text of DOI:10.1039/d1ra01913a

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The anchoring of a Cu(II)–salophen complex on
magnetic mesoporous cellulose nanofibers: green
synthesis and an investigation of its catalytic role in
tetrazole reactions through a facile one-pot route†
a
Cite this: RSC Adv., 2021, 11, 19203
and Ghodsieh Bagherzade*b
Pouya Ghamari kargar
Today, most synthetic methods are aimed at carrying out reactions under more efficient conditions and the
realization of the twelve principles of green chemistry. Due to the importance and widespread applications
of tetrazoles in various industries, especially in the field of pharmaceutical chemistry, and the expansion of
the use of nanocatalysts in the preparation of valuable chemical reaction products, we decided to use an
(
Fe
3
O
4
@NFC@NSalophCu)CO
2
H
nanocatalyst in this project. In this study, the synthesis of the
H was explained in a step-by-step manner. Confirmation of
nanocatalyst (Fe
O
3 4
@NFC@NSalophCu)CO
2
the structure was obtained based on FT-IR, EDX, FE-SEM, TEM, XRD, VSM, DLS, TGA, H-NMR, and
CHNO analyses. The catalyst was applied to the synthesis of 5-substituted-1H-tetrazole and 1-
substituted-1H-tetrazole derivatives through multi-component reactions (MCRs), and the performance
was assessed. With advances in science and technology and increasing environmental pollution, the use
of reagents and methods that are less dangerous for the environment has received much attention.
Received 10th March 2021
Accepted 24th April 2021
3 4 2
Therefore, following green chemistry principles, with the help of the (Fe O @NFC@NSalophCu)CO H
DOI: 10.1039/d1ra01913a
salen complex as a nanocatalyst that is recyclable, cheap, safe, and available, the use of water as a green
solvent, and reduced reaction times, the synthesis of tetrazoles can be achieved.
rsc.li/rsc-advances
5
photography, information-recording systems, in materials
engineering as anti-corrosion agents, and many other areas. In
Introduction
Multi-component reactions are reactions that start by addition, they are widely used in the elds of medicinal and
6
combining several reagents at the same time and create the agricultural chemistry. 1-Substituted-1-H-tetrazoles and 5-
target molecule in the same pot; they reduce energy consump- substituted-1H-tetrazoles, which represent signicant classes of
tion and solvent loss, and also show reduced reaction times, heterocycles, have attracted considerable interest in recent
7
ultimately having the advantages of efficiency, simplicity, and years because of their wide utility and because of their hopeful
1
8
9
atom economy. Nitrogen-containing heterocyclic and aromatic biological properties, particularly their antifungal, antiulcer,
10
11
12
13
compounds are necessary and important structural compo- antinociceptive, anti-HIV, antiallergic, anti-inammatory,
14
15
16
nents in chemical and biochemical compounds, and these antiproliferative,
hormonal,
18
carboxylic acid isostere,
17
19
heterocyclic compounds have acquired immense importance herbicidal, diuretic, and anticancer potential (Scheme 1).
2,3
recently. Tetrazoles are a group of nitrogen-rich heterocyclic Due to the many benets that these compounds have shown,
compounds that have a high specic heat density due to the various synthesis approaches for tetrazole derivatives have been
presence of C]N and C–N bonds. These compounds are highly well-documented in the literature. In general, the easiest and
regarded as high-energy green materials for use in engines, gas most versatile method for the synthesis of 5-substituted-1H-
production, and explosive propellants due to their high poten- tetrazoles is the [3 + 2] cyclization of nitriles and azide in the
tial energies and low impact and friction sensitivities. Tetra- presence of appropriate catalysts and various solvents. Several
4
20
zoles are used in coordination chemistry, explosives, new catalysts have been investigated, such as zinc salts, b-
21
22
23
24
25
cyclodextrin, Fe(OAc) , CdCl2, AgNO , SiO –H BO , Cu–
MCM-41, PCl5, Zn/Al hydrotalcite, Pd(OAc) /ZnBr, Fe3-
2
3
2
3
3
26
27
28
29
2
a
Department of Chemistry, Faculty of Sciences, University of Birjand, Birjand,
30
31
O
4
@MCM-41–SB–Cu,
Fe
3
O
4
@L-lysine–Pd(0),
and copper
9
7175-615, Iran. E-mail: P.ghamari71@gmail.com
32
b
triates.
Department of Chemistry, Faculty of Sciences, University of Birjand, Birjand, 97175-
6
15, Iran. E-mail: gbagherzade@gmail.com; bagherzade@birjand.ac.ir; Fax: +98 56
2345192; Tel: +98 56 32345192
Although these methods have good advantages, some of
them also have drawbacks, including the use of dime-
thylformamide as a solvent, the need for harsh reaction
3
†
1
Electronic supplementary information (ESI) available. See DOI:
0.1039/d1ra01913a
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Scheme 2 The synthesis of differently structured 5-substituted-1H-
tetrazoles and 1-substituted-1H-tetrazoles in the presence of (Fe
3
-
O
4
@NFC@NSalophCu)CO H in aqueous media and without solvent.
2
Scheme 1 Drugs on the market with a tetrazole moiety.
conditions and long reaction times, the use of toxic and corro- plants, bacteria, tunicates, and algae, making it a green polymer
39–41
sive reagents, difficulties in the separation and recovery of suitable for use in sustainable materials engineering.
catalysts, low yields, the need for tedious work-up procedures
From a “green chemistry” perspective, substantial attempts
and expensive moisture-sensitive reaction conditions, and the to nd alternatives to organic solvents, such as solvent-free
presence of hydrazoic acid, which can be highly toxic and methods or those carried out in the presence of water, have
explosive, as well as volatile. Thus, the development of a simple, been made, due to the reduced pollution, low cost, safety, and
convenient, and environmentally benign method for synthe- ease of processing and use. They are of industrial importance.
sizing tetrazoles remains necessary. However, to achieve good The rst 11 principles of green chemistry state that preventing
results in the reaction process, it is crucial to choose a suitable the generation of waste is better than rening or cleaning-up
heterogeneous catalyst and an environmentally benign method waste aer generation. Here, our research team has presented
that can overcome all these problems. For minimizing chemical a simple and efficient method for the preparation of 1-H-tetra-
waste, increasing energy efficiency, and obtaining better zole and 5-H-tetrazole derivatives, considering the importance
economy, the use of nanocatalysts that comply with the prin- of green chemistry and the issues mentioned above. We have
ciples of green chemistry is recommended. These heteroge- illustrated it via forming successive C–N and N–N bonds cata-
neous catalysts can be easily recovered from the reaction lyzed by a new heterogeneous (Fe O @NFC@NSalophCu)CO H
3
4
2
medium, but the activity and selectivity of the catalysts can catalyst. The interesting thing is that (Fe O @-
3
4
decrease due to the existence of limited active sites on the NFC@NSalophCu)CO H has shown good catalytic activity. We
2
surfaces. Nanoscale supports can be used to solve this problem. reacted a wide range of aromatic amines and aromatic alde-
Due to the non-toxicity of Fe O , it is more oen used as hydes with electron-donating and electron-withdrawing groups
3
4
a magnetic substance in catalyst supports than other metallic to obtain the desired products. We also reported the use of
33,34
counterparts.
It is notable that nanomagnetic compounds recyclable heterogeneous catalysts with an aqueous solvent as
have had major effects on the development of other areas, such a green solvent for the synthesis of 5H-tetrazoles and under neat
35
as medications, drug delivery, and chemical modications.
A
conditions for obtaining 1H-tetrazole derivatives. The ease of
clear path in organic chemistry synthesis has been created due operation, short time required, and high efficiency are other
to the modications of the surfaces of magnetic nanoparticles. features of this method, which provides an efficient way to
Also, their physical properties, comprising high surface areas, synthesize different heterocycles (Scheme 2).
a superparamagnetic nature, low toxicity, give them potential
applications in various elds, such as biotechnology, medicine,
36
Results and discussion
drug delivery, and environmental science. However, pure
magnetic particles oxidate in the presence of air and the
magnetic properties are altered. Therefore, proper coverage is
The (Fe
prepared in multiple steps. In the rst step, Fe
magnetic nanoparticles were synthesized via a sol–gel method.
Then, the Fe @NFC core–shell particles were reacted with (3-
aminopropyl)triethoxysilane (APTES) as a spacer to obtain Fe
3
O
4
@NFC@NSalophCu)CO
2
H
nanocatalyst was
3 4
O
@NFC
37,38
important to prevent such an issue.
Thus, much consider-
ation has been paid to the synthesis of magnetic core–shell
structures via the use of a cellulose layer around the synthesized
nanoparticles. Nanober cellulose (NFC) coatings can give
magnetic nanoparticles an easily adjustable surface, which may
be used to gra various desirable functional groups. Cellulose is
abundantly available from diverse natural sources, such as
3 4
O
3
-
O @NFC@APTES. Aer the reux of an ethanolic solution of
4
copper acetate with a Schiff base ligand, the salen complex was
prepared. In this procedure, 5-chloromethyl salicylaldehyde was
used to form 3,5-bis(((E)-5-(chloromethyl)-2-hydroxybenzylidene)
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amino)benzoic acid as the novel ligand, and this was then reacted using various standard physicochemical techniques, such as
with copper acetate to obtain complex V (Scheme 3). Finally, the Fourier-transform infrared spectroscopy (FT-IR), powder X-ray
salen complex [(5-Cl-Saloph)Cu(II)]CO H was added to Fe O @- diffraction analysis (PXRD), transmission electron microscopy
2
3 4
NFC@APTES to generate the (Fe O @NFC@NSalophCu)CO H (TEM), scanning electron microscopy (SEM), thermogravimetric
3
4
2
nanocatalyst (Scheme 3). Aer the successful synthesis of the salen analysis (TGA), inductively coupled plasma optical emission
catalyst (Scheme 3), the magnetic nanocatalyst was characterized spectrometry (ICP-OES), dynamic light scattering (DLS), vibrating-
3 4 2
Scheme 3 The preparation of the catalyst (Fe O @NFC@NSalophCu)CO H.
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characteristic absorption bands observed at 731, 1107, 1450–1580,
ꢀ1
1
652, 2809, 2980, 3100, and 3250 cm are related to C–Cl, C–O,
C]C aromatic, C]O, C–H aldehyde, C–H aliphatic, C–H
aromatic, and O–H bonds in 2-hydroxy-5-chloromethyl benzalde-
hyde. Additionally, in Fig. 1b, the signals located at around 1650
ꢀ
1
(
C]N), 1710 (C]O; carboxylic acid), and 2500–3410 cm (O–H;
carboxylic acid) can be attributed to the structure of the Schiff base
5-Cl-Saloph)CO H. What was expected to be observed is that the
formation of the metal complex would cause the strong adsorption
(
2
ꢀ1
of the C]N and O–H groups at 1650 and 3250 cm seen in the
spectrum in Fig. 1b to be moved to lower wavenumbers.
As observed in Fig. 1c, the positions of these adsorption
peaks (C]N and O–H) are reduced by 17 cm . This indicates
the participation of azomethine nitrogen in bonding with metal
ions. It also conrms the coordination of C-based double bonds
with the metal through nitrogen. Also, the two absorption
bands at 448 and 641 cm could be assigned to Cu–O and Cu–
N stretching, respectively (Fig. 2g), because the connection of
each atom to the metal transmits electric charge to the metal
and the empty orbitals of the metal-containing layer. This
weakens the other bonds involving the corresponding atom.
ꢀ
1
ꢀ
1
Fig. 1 FT-IR spectra of the synthesized nanocomposites: (a) 5-
chloromethyl salicylaldehyde, (b) (5-Cl-Saloph)CO
2
H, and (c) (5-Cl-
The FT-IR spectrum of Fe
teristic peaks at 3402 cm and 578 cm related to O–H and
Fe–O stretching bands, respectively, conrms the formation of
3
O
4
nanoparticles with two charac-
Saloph)Cu(II) CO H.
2
ꢀ
1
ꢀ1
sample magnetometer (VSM), and energy-dispersive X-ray (EDS)
3 4
Fe O nanoparticles (Fig. 2d). As mentioned earlier, NFC is
analysis. FT-IR spectroscopy analysis, for investigating the steps of a natural product, therefore, in the IR spectrum of Fe O @NFC
3
4
catalyst synthesis and to conrm the formation of the expected
(Fig. 2e), the stretching vibrations of C–O and C–H bonds,
functional groups, has been done. The spectra of 5-chloromethyl
hydroxyl functional groups, and the Fe–O bonds of Fe O4
3
salicylaldehyde, the salen Schiff base, [(5-Cl-Saloph)Cu(II)]CO H,
2
should be observed.
Fe
3 4 3 4 3 4 2
O , Fe O @NFC, and the (Fe O @NFC@NSalophCu)CO H
Thus, in the Fe
absorption bands at 1100 and 2990 cm
3 4
O @NFC spectrum (Fig. 2e), there are the
ꢀ
1
nanocomposite are presented in Fig. 1 and 2. In Fig. 1a, the
(the stretching
Fig. 2 FT-IR spectra of the synthesized nanocomposites: (d) Fe
Fe @NFC, (f) Fe @NFC@APTES, and (g) (Fe
NFC@NSalophCu)CO H.
3
O
4
, (e)
@- Fig. 3 Low angle X-ray diffraction patterns of Fe
(Fe @NFC@NSalophCu)CO H nanocatalyst.
O
3 4
O
3 4
3
O
4
3 4
O , Cu(II), and the
2
3
O
4
2
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ꢀ1
vibrations of C–O and C–H from cellulose), and 574 and 3200 cm
3 4 3 4
The crystalline structures of the Fe O particles, Fe O @-
(the stretching vibrations of Fe–O and O–H in Fe O ). As envisaged NFC, and (Fe O @NFC@NSalophCu)CO H were determined via
3 4 3 4 2
(
3
Fig. 2f), several new bands become apparent at 1100, 1200, and powder X-ray diffraction (PXRD) studies. As shown in Fig. 3, it
200 cm that correspond to the stretching vibrations of the C–N can be seen that the characteristic broad diffraction peaks
ꢀ
1
and Si–O functional groups and NH
2
bonds, respectively, shown in the wide-angle PXRD patterns can be indexed to the
demonstrating the surface chemical modication of Fe
3
O
4
@NFC cubic spinel magnetite Fe
3 4
O crystal structure, which shows
with (3-aminopropyl)triethoxysilane (APTES).
diffraction peaks indicating a crystallized structure at 2q values
3 4 3 4 3 4 2
Fig. 4 FE-SEM (left) and EDX (right) images of the different materials: (a) Fe O , (b) Fe O @NFC, and (c) (Fe O @NFC@NSalophCu)CO H.
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ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
of 30.3 , 35.8 , 43.6 , 54.8 , 57.3 , and 63.2 , which can be that the crystal structure of the (Fe
3
O
4
@NFC@NSalophCu)
assigned to the (220), (311), (400), (422), (511), and (440) planes CO H nanoparticles is not changed upon modication with [(5-
2
4
2 43
respectively. , Also, the XRD pattern of CuO (Fig. 3) shows Cl-Saloph)Cu(II)]CO H, which means that the copper sites are in
2
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
peaks at 2q values of 32.07 , 35.47 , 35.82 , 48.72 , 52.97 , their Cu(II) state. With these explanations, these results imply
8.02 , 62.47 , 67.87 , and 69.32 , corresponding to the (110), that the spinel structure of Fe
ꢁ
ꢁ
ꢁ
ꢁ
5
3 4
O and the existence of Cu(II)
(
111), (022), (202), (202), (113), (022), (220), and (222) crystallo- have been retained during the process of catalyst preparation.
44,45
graphic phases.
The low-angle PXRD pattern of (Fe
H was also investigated, as depicted in images of the supported catalyst and to nd out the shape,
Fig. 3. The PXRD pattern of (Fe @NFC@NSalophCu)CO morphology, and particle distribution; also, EDX analysis was
3
O
4
@-
SEM and DLS analysis were employed to obtain visual
NFC@NSalophCu)CO
2
3
O
4
2
H
prepared via the St ¨o ber process shows pronounced diffuse conducted to qualitatively determine the elements in the
ꢁ
peaks from 20–25 that appear because of amorphous cellu- prepared samples. The SEM images, as shown in Fig. 4, reveal
46
lose. The PXRD pattern of (Fe O @NFC@NSalophCu)CO H, that Fe O (magnetic), Fe O @NFC (core–shell), and (Fe O @-
3
4
2
3
4
3
4
3 4
with immobilized Fe
3 4 2
O and Cu(II), shows characteristic peaks NFC@NSalophCu)CO H (the salen complex nanocatalyst) have
whose relative intensities match well with the reported PXRD almost uniform and spherical morphologies, ranging in size
pattern of Fe
3
O
4
magnetite. In addition, these results indicate from 4 to 31 nm, indicating good agreement with the calculated
results from the Debye–Scherrer equation. Some aggregation
occurs due to the magnetic properties of the nanoparticles.
From the EDX analysis of Fe O (Fig. 4a; magnetic particles),
3
4
Fe O @NFC (Fig. 4b; core–shell particles), and (Fe O @-
3
4
3 4
NFC@NSalophCu)CO H (Fig. 4c; the salen complex nano-
2
catalyst), the results displayed the presence of Cu, Fe, Si, O, N,
and C elements, which could be acceptable evidence of the
modication of the Fe
Therefore, it can be inferred that the expected elements were
loaded onto the magnetic surface (Fe in (Fe @-
3 4
O surface by the nanocatalyst.
3
O
4
)
3 4
O
NFC@NSalophCu)CO H (Fig. 4c). According to the results from
2
ICP and EDX analysis, the amount of copper in the (Fe O @-
3
4
NFC@NSalophCu)CO H nanocatalyst was calculated to be
2
ꢀ1
1
.47 mmol g . Also, the analyses gave heavy-metal percentages
of 45.57 wt%, 2.35 wt%, and 6.95 wt% for Fe, Si, and Cu,
respectively. In this study, to examine the size distributions of
these nanoparticles, particle-size histograms were prepared via
DLS analysis (Fig. 5a–c).
The average diameters of the particles are evaluated to be
about 17 nm for Fe O (Fig. 5a), 18 nm for Fe O @NFC (Fig. 5b),
3
4
3 4
and 23 nm for (Fe O @NFC@NSalophCu)CO H (Fig. 5c).
3
4
2
The thermal behaviors of the synthesized samples in the
nal catalyst preparation pathway were studied using TGA

Fig. 6 The TGA curves of the (a) Fe
(NFC), (c) Fe @NFC, and (d) the (Fe
nanocatalyst.
3
O
4
support, (b) nanofiber cellulose
Fig. 5 DLS analysis of (a) pure Fe
@NFC@NSalophCu)CO H.
O
3 4
3
, (b) Fe O
4
@NFC, and (c) (Fe
3
-
O
3 4
O
3 4
@NFC@NSalophCu)CO
2
H
O
4
2
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47,48
nanoparticles (Fig. 6a).
From analysis, it is evident that the
nanober cellulose structure degrades in three stages. In the
ꢁ

rst stage, at temperatures below 200 C, degradation occurs
due to the loss of water. The second stage involves signicant
ꢁ
weight loss that occurs between approximately 200 and 400 C.
This can generally be attributed to the destruction of the
structure of natural cellulose under oxidation conditions.
ꢁ
Decomposition at temperatures above 400 C occurs due to the
49,50
oxidation of rotten cellulose products (Fig. 6b).
Fig. 6c also
shows the thermal decomposition diagram of Fe O @NFC. At
3
4
ꢁ
temperatures below 140 C, gradual weight loss is shown, which
can be attributed to the removal of water adsorbed on the
nanocomposite surface. The second stage involves a sharp drop
ꢁ
in weight from 150–450 C, which is observed due to the
decomposition of the cellulose structure; this form has good
Fig. 7 The magnetization curves at 300 K for Fe
3 4
O
, Fe O
3 4
@NFC,
ꢁ
resistance up to about 650 C. However, at temperatures above
Fe O
3 4
@NFC-APTES, and the (Fe
O
3 4
@NFC@NSalophCu)CO
2
H
ꢁ
6
50 C, slight weight loss occurs, which may be due to the
nanocatalyst.
rupturing of the bonds between the nanober cells and the
Fe O nanoparticles, based on the thermal and mechanical
3
4
51,52
properties of Fe O @NFC.
In the thermogram of (Fe O @-
3 4
3
4
analysis, and the obtained results are illustrated in Fig. 6. The
total weight loss of uncoated Fe is 11% over the whole
temperature range, which can be assigned to the removal of OH
3 4
groups and water molecules from the surfaces of the Fe O
NFC@NSalophCu)CO
occurs in the temperature range of 25 to 280 C, which is related
to the volatilization of absorbed water on the surface of
2
H (Fig. 6d), weight loss of less than 11%
3 4
O
ꢁ
Table 1 Optimization of the reaction conditions for the synthesis of 5-
phenyl-1H-tetrazole
ꢁ
a
Entry Solvent Catalyst (mol%) Temp. ( C) Time (min) Yield (%)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
Water 0.4
EtOH 0.4
CH CN 0.4
80
15
60
30
30
120
240
45
98
40
55
80
20
0
70
98
Trace
35
55
75
10
60
82
97
98
95
Reux
Reux
80
80
80
80
80
80
80
80
80
R.T.
40
50
60
70
90
3
DMF
Neat
0.4
0.4
Water No catalyst
Water 0.2
Water 0.6
15
b
Water
Water
Water
Water
—
—
—
—
180
180
180
60
90
60
45
15
15
15
c
0
1
2
3
4
5
6
7
8
d
e
Water 0.4
Water 0.4
Water 0.4
Water 0.4
Water 0.4
Water 0.4
a
Reaction conditions: aldehyde (1.0 mmol), hydroxylamine (1.2 mmol),
and sodium azide (1.5 mmol). The catalyst was prepared using 0.4 mol%
b
catalyst, as explained in the experimental section. Reaction was
c
performed in the presence of Fe
performed in the presence of Fe
was performed in the presence of Cu(OAc)
was performed in the presence of [(5-Cl-Saloph)Cu(II)]CO
Fig. 8 A TEM image (top) and particle size distribution histogram catalyst.
bottom) of the (Fe @NFC@NSalophCu)CO H nanocatalyst.
3
O
4
as the catalyst. Reaction was
d
3 4
O @NFC as the catalyst. Reaction
e
2
as the catalyst. Reaction
H as the
2
(
3
O
4
2
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Fe @NFC@NSalophCu)CO
Paper
(
3
O
4
2
H. The next stage of weight loss of Fe
3
O
4
aer coating with cellulose, APTES, and the [(5-Cl-
ꢁ
in the temperature range of 325 to 475 C is associated with the Saloph)Cu(II)]CO H salen complex decreases signicantly from
2
thermal decomposition of cellulose groups, an organic section. about 63.5 emu per g to 41.97 emu per g. The cellulose shell and
The weight loss of about 13% with a gentle slope at tempera- silica that surround the Fe O nanoparticles reduce the inter-
3
4
ꢁ
tures of 475–800 C was assigned to the decomposition of actions between these particles. However, despite the reduction
immobilized organic moieties on the surfaces of the Fe
3
O
4
@- of the saturation magnetization, the catalyst can still be rapidly
NFC core–shell nanoparticles.
and easily separated from solution media via applying an
Magnetic studies of all the prepared materials were carried external magnetic eld.
out using a vibrating sample magnetometer (VSM) at room The morphology and structure of the (Fe
temperature and in an applied magnetic eld, sweeping from NFC@NSalophCu)CO H salen complex were also observed
3 4
O @-
2
ꢀ
20 000 to +20 000 Oe. The magnetization of the prepared using TEM (Fig. 8). TEM imaging reveals that the catalyst is
samples based on the applied magnetic eld can be observed in made up of well-shaped spherical particles. The diameter of the
Fig. 7. It is reported that the saturation magnetization (M ) value NPs in the particle-size-distribution histogram is found to be
of bare Fe nanoparticles is 63.50 emu per g. The saturation about 17 nm (Fig. 8). In addition, spherically structured NPs
magnetization (M values of Fe @NFC, Fe @- with a diameter of about 17 nm are evident in the image in
NFC@APTES, and (Fe @NFC@NSalophCu)CO H are 51.93, Fig. 8.
6.84, and 41.97 emu per g, respectively. Therefore, the M value
s
3 4
O
s
)
3
O
4
3 4
O
3
O
4
2
4
s
a
Table 2 The synthesis of 5-substituted-1H-tetrazoles catalyzed by (Fe
O
3 4
2
@NFC@NSalophCu)CO H
b
ꢁ
Entry
Aldehyde
Time (min)
Tetrazole
Yield (%)
Mp ( C)
217–218
258–259
TON
TOF
970
970
Ref. (lit)
60
1
2
a
15
15
97
97
242.5
242.5
b
60
3
4
5
c
15
20
10
97
90
98
220–221
233–234
232–233
242.5
225
970
60
60
60
d
e
682
245
1476
6
7
f
15
30
98
85
154–156
220–221
245
980
425
60
60
g
212.5
8
9
h
i
10
15
98
92
133–134
187–189
245
230
1476
920
60
53
1
0j
10
75
214–215
187.5
1130
60
a
b
ꢁ
Reaction conditions: aldehyde (1.0 mmol), hydroxylamine (1.2 mmol), sodium azide (1.5 mmol), catalyst (0.4 mol%), and H
Isolated yield.
2
O (5 mL); 60 C.
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The activity of the new (Fe
RSC Advances
3
O
4
@NFC@NSalophCu)CO
2
H
To determine the optimum conditions for MCRs between
magnetic nanocatalyst for the synthesis of imidazole derivatives aromatic amines, triethyl orthoformate, and sodium azide at
and tetrazoles was investigated. The reaction between benzal- dened molar ratios, various solvents, temperatures, and cata-
dehyde, hydroxylamine hydrochloride, and sodium azide in the lytic quantities were tested. Practical information about the
presence of the mentioned catalyst was used as a model. The optimization process is provided in Table 3. At rst, the reaction
effects of various parameters on the catalytic efficiency of (Fe
3
-
was carried out in various solvents. The data showed that the
O
4
@NFC@NSalophCu)CO H were examined (Table 1). As reaction efficiency aer 100 min was negligible in all solvents in
2
shown in Table 1, the nature of the solvent was observed to this experiment, and we continued the reaction for 180 minutes
profoundly affect both the catalyst activity and the product to observe the changes in the reaction efficiency. The details of
yield. CH CN, DMF, and EtOH gave moderate yields, whereas these experiments are presented in Table 3 (entries 1–4). The
3
solvent-free conditions were not suitable for this reaction (Table catalyst has the effect of assisting and boosting this reaction.
1, entry 5). Further screening of the solvents revealed that when
The reaction was then carried out under solvent-free condi-
the reaction was carried out in H
2
O, the yield of the desired tions in the presence of different quantities of catalyst. The
product increased signicantly (Table 1, entry 1). Therefore, results showed that 0.3 mol% of catalyst was adequate to obtain
water, as the cheapest, safest, and most environmentally green a response; lower values resulted in reduced reaction efficiency
solvent, is the best choice for this reaction. In the next step, the and increasing the catalyst content to 0.5 mol% did not increase
inuence of the catalyst amount was investigated. The sample the reaction efficiency: instead it decreased slightly. In addition,
ꢁ
reaction was performed with different levels of catalyst at 80 C. in the presence of Fe O NPs, Fe O @NFC, Cu (OAc) , and [(5-
3
4
3
4
2
ꢁ
It was detected that 0.4 mol% catalyst was effectual at providing Cl-Saloph)Cu(II)]CO H at 80 C, the demanded product was
2
a high yield. Increasing the catalyst loading did not improve the synthesized in low and good yields (Table 3, entries 9–12). To
production efficiency or lower the reaction time, while a lower acquire the optimum temperature, the model reaction was done
catalyst loading decreased the reaction yield, even aer a longer at different temperatures (Table 3, entries 13–18). A tempera-
ꢁ
reaction time. Also, when the sample reaction was performed ture of 80 C led to the best results (Table 3, entry 17); the model
without catalyst or in the presence of Fe
3
O
4
NPs, Fe
3
O
4
@NFC,
ꢁ
or Cu(OAc)
2
at 80 C, the product was obtained but with very low
efficiency.
Table 3 The optimization of the reaction conditions for the synthesis
The use of the [(5-Cl-Saloph)Cu(II)]CO H salen complex of 1-phenyl-1H-tetrazole
2
showed a higher product yield than the other cases (Table 1,
entries 9–12). Subsequently, the effects of temperature on the
reaction were explored, and a series of experiments was carried
out at different temperatures (Table 1, entries 13–18). At room
temperature, poor results are observed (Table 1, entry 13). The
ꢁ
best relative performance was obtained at 60 C (Table 1, entry
ꢁ
a
Entry Solvent Catalyst (mol%) Temp. ( C) Time (min) Yield (%)
16).
Aer several experimental optimization studies, the optimal
1
2
3
4
5
6
7
8
9
10
Water 0.3
EtOH 0.3
CH CN 0.3
Reux
Reux
Reux
100
100
100
100
100
100
100
100
100
R.T.
50
180
180
180
180
20
300
45
15
180
180
180
60
120
75
90
82
50
75
98
0
75
95
Trace
30
50
77
40
70
85
92
98
98
reaction conditions for the construction of tetrazole derivatives
ꢁ
are given as follows: 0.4 mol% catalyst in H
2
O at 60 C (Table 1,
3
entry 16). Aer optimizing the reaction conditions, we further
explored the scope and generality of the developed protocol for
synthesizing 5-substituted-1H-tetrazoles. Various aldehydes
with both electron-donating and electron-withdrawing substit-
uents were employed, producing the corresponding tetrazoles
in high to excellent yields (Table 2).
Generally, all the substrates resulted in products with high
yields (Table 2, entries 1a–10j), but aldehydes with electron-
donating substituents, due to the less electrophilic properties
of the carbonyl group, required longer reaction times (Table 2),
DMF
Neat
Neat
Neat
Neat
Neat
Neat
Neat
Neat
Neat
Neat
Neat
Neat
Neat
Neat
0.3
0.3
—
0.1
0.5
b
—
c
—
d
1
1
1
1
1
1
2
3
4
5
—
e
—
0.3
0.3
0.3
0.3
0.3
0.3
60
70
80
90
45
30
20
20
while electron-withdrawing groups had little effect on the 16
1
1
7
8
reaction progress and showed the best performance. Moreover,
steric effects were seen in this procedure. For example, 2-
hydroxy and 2-methoxy benzaldehyde were transformed to the
demanded products aer a long time and with low yields in
comparison with 4-hydroxy and 4-methoxy benzaldehyde (Table
, entries 4d, 7g, 5e and 6f). Encouraged by the results from the performed in the presence of Fe
-substituted-1H-tetrazole reactions, multi-component reac-
tions leading to tetrazole compounds were investigated via
reactions obtaining 1-substituted-1H-tetrazoles from amines.
a
Reaction conditions: amine (1.0 mmol), triethyl orthoformate (1.2
mmol), and sodium azide (1.2 mmol). 0.3 mol% catalyst was primarily
used, as explained in the experimental section. Reaction was
performed in the presence of Fe
b
c
3
O
4
as the catalyst. Reaction was
d
2
5
3 4
O @NFC as the catalyst. Reaction
e
was performed in the presence of Cu(OAc)
was performed in the presence of [(5-Cl-Saloph)Cu(II)]CO
catalyst.
2
as the catalyst. Reaction
2
H as the
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reaction gave the best results when it was performed in intermediary [II]. Aer that, the oxime undergoes rearrange-
ꢁ
a solvent-free fashion and at 80 C in the presence of 6.5 mg ment followed by water removal to provide the corresponding
(0.3 mol%) of catalyst (Table 3, entry 17). With the optimized nitrile intermediate [III]. Subsequently, the coordination of the
reaction conditions in hand, we then studied the general use of nitrogen atom of the nitrile with the (Fe O @NFC@NSalophCu)
3
4
2
our new catalytic system in the 1-substituted-1H-tetrazole CO H nanocatalyst activates it toward azide ion attack at the
reactions of some arylamines with triethyl orthoformate and electron-decient carbon atom [IV]. Interplay between the Cu(II)
sodium azide (Table 4). Under the optimized reaction condi- catalyst and the nitrogen atom of the nitrile increases the
tions, different arylamines (electron-withdrawing and electron- electrophilic character of the nitrile.
donating groups) could be successfully converted to the corre-
Subsequently, [3 + 2]-cycloaddition involving the activated
53,54
sponding tetrazole products. Based on previous reports
and nitrile and NaN3 results in the respective intermediate [V].
our observations, a suggested mechanism for the synthesis of 5- Finally, protonolysis of the intermediate [V] under the acidic
substituted-1H-tetrazole derivatives catalyzed by the (Fe O @- conditions present in the reaction mixture produces the more
3
4
NFC@NSalophCu)CO
. Initially, the coordination of the oxygen atom of the aldehyde Due to Lewis acidity, rst, the azide group coordinated with the
with a catalyst acidic hydrogen increases the electrophilicity of copper nanocatalyst.
2
H nanocatalyst is represented in Scheme stable product, a 5-substituted-1H-tetrazole, as a white solid.
4
the aldehyde [I]. Then, nucleophilic attack involving the
For the synthesis of 1-substituted-1H-tetrazoles, it is believed
3 4
nitrogen atom of hydroxylamine and the activated aldehyde that the ethoxy group of TEOF is activated by (Fe O @-
causes the expulsion of water and the formation of an oxime NFC@NSalophCu)CO H to initiate nucleophilic attack
2
a
Table 4 The synthesis of 1-substituted-1H-tetrazoles catalyzed by (Fe
3
O
4 2
@NFC@NSalophCu)CO H
b
ꢁ
Entry
Aldehyde
Time (min)
Tetrazole
Yield (%)
Mp ( C)
TON
TOF
Ref. (lit)
1
a
20
30
98
90
63
326.6
300
990
600
61
61
2
b
155
3c
4d
5e
6f
30
15
15
45
95
90
97
80
176–177
92–93
316.6
300
633
61
61
61
61
682
114–115
200
323.3
266.6
1293
355.4
7g
8h
9i
50
60
30
90
90
97
139–140
78–79
55
300
360
62
1
300
300
323.3
646.5
63
1
0j
30
97
67–68
323.3
646.5
64
a
Reaction conditions: aniline (1.0 mmol), triethyl orthoformate (1.2 mmol), sodium azide (1.2 mmol), catalyst (0.3 mol%), and solvent-free
ꢁ
b
conditions; 80 C. Isolated yield.
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Scheme
substituted-1H-tetrazoles
NFC@NSalophCu)CO H.
4
The suggested mechanism for the synthesis of 5-
in the presence of (Fe @-
3 4
O
Fig.
9
Catalyst recovery studies involving the use of (Fe
3 4
O @-
2
NFC@NSalophCu)CO
2
H for the preparation of tetrazoles.
(
3 4 2
Fe O @NFC@NSalophCu)CO H was separated from the reac-
involving an amino-group nitrogen atom (Scheme 5). This
facilitates the sequential removal of two ethanol molecules. The
tion mixture using a permanent magnet, washed with hot
ethanol, and dried at 60 C under vacuum. Aerward, the recycled
ꢁ
3 4 2
(Fe O @NFC@NSalophCu)CO H-supported removal of ethanol
catalyst was added to another vessel containing the starting
materials and the next reaction cycle was carried out under the
same conditions as discussed before. As exhibited in Fig. 9, the
catalyst could be recovered and reused for at least seven consec-
utive runs. The yields of the 5-Ph-1H-tetrazole and 1-Ph-1H-tetra-
zole reactions reached 90% and 92% on the 7th run, meaning that
only 7% and 6% drops in efficiency were observed compared to the
corresponding fresh catalyst (97% for 5-Ph-1H-tetrazole and 98%
for 1-Ph-1H-tetrazole). Also, the amounts of Cu that leached into
solution aer the 5-Ph-1H-tetrazole and 1-Ph-1H-tetrazole reac-
tions in each cycle were measured via ICP.
in the presence of the nanocatalyst leads to the synthesis of the
tetrazole. In a continuation of this research, the reusability and
recyclability of the catalyst were investigated.
Catalyst recovery is considered necessary from various
perspectives, such as environmental and commercial
55,56
concerns.
Therefore, the reusability of the (Fe O @-
3 4
NFC@NSalophCu)CO H nanocatalyst was studied under the
2
optimized conditions using the tetrazole model reaction. To
investigate the stability of the nanocatalyst, aer the rst cycle,
The catalyst showed leaching in each cycle, with 3% metal
leaching detected for the 4a and 7a reactions aer the 7th run,
reecting the stability under the reaction conditions (Fig. 9,
cylinders). In addition, the recovered catalyst from the 5-
substituted-1H-tetrazole reaction was characterized via FT-IR,
XRD, FE-SEM, and VSM analyses (Fig. 10a–d). FTIR and XRD
spectra conrm that the structure of the recovered catalyst
remained intact during recycling (Fig. 10a and c), which reects
its stability and durability.
In addition, ICP analysis of the reusable catalyst demonstrated
insignicant changes in the weight percentages of the elements
compared with the corresponding fresh values, with values as
follows: Fe, 45.54 wt%, Si, 2.33 wt%, and Cu, 6.8 wt%. In another
3 4
study, to show the heterogeneous nature of the (Fe O @-
NFC@NSalophCu)CO H magnetic nanocatalyst, hot ltration
2
testing was applied during the preparation of a tetrazole under the
optimum conditions. The reaction to obtain 5-substituted-1H-tet-
razole was started in the presence of the catalyst.
Aer the reaction was half-completed, the reaction was
stopped, and the catalyst was removed using an external
Scheme
substituted-1H-tetrazoles
NFC@NSalophCu)CO H.
5
The suggested mechanism for the synthesis of 1-
in the presence of (Fe @-
3 4
O
2
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Fig. 11 Leaching experiments involving the use of (Fe
3 4
O @-
NFC@NSalophCu)CO H to obtain a 5-substituted-1H-tetrazole.
2
This conrms the nature of the heterogeneous catalyst. To
prove the efficiency of the catalyst for the production of 5-
phenyl-1H-tetrazoles and 1-phenyl-1H-tetrazoles, we compared
the results with other catalysts in the literature (Tables 5 and 6).
The new proposed catalyst has high yields and short reaction
times and, unlike some catalysts, does not require toxic and
expensive solvents. In addition, the synthesized magnetic
catalyst has properties such as recyclability and the ability to be
separated using an external magnet. In recent years, various
methods have been proposed for the synthesis of tetrazoles
(
(
(
Scheme 6, eqn (1)–(10)). From the viewpoint of atom economy
AE) and atom efficiency (AE ), the present methodology
Scheme 6, eqn (5) and (10)) was compared with those reported
f
53
in the literature (Scheme 6, Tables 7 and 8). Each of the
analyzed reactions has disadvantages, including high amounts
of catalyst use, low efficiency, prolonged reaction times (24 h),
harsh reaction conditions, and the use of high-boiling-point
organic solvents (DMF and DMSO), leading to complicated
isolation and recovery methods. Therefore, it is complicated to
work with these materials. The advantages of the reactions
demonstrated here are that none of the above disadvantages are
observed (Scheme 7). Also, the use of (Fe
3 4
O @NFC@ NSa-
lophCu)CO H as a natural, benign, cheap, and non-corrosive
2
natural heterogeneous catalyst represents an interesting
synthetic method with relatively high nuclear economy. Ethanol
is the only by-product of this reaction. This solvent can be
classied as a green solvent.
Experimental
All chemical reagents and solvents were procured from Merck
and Sigma-Aldrich and were used as received without further
3
Fig. 10 (a) FT-IR, (b) VSM, (c) XRD, and (d) Fe-SEM analysis of (Fe -
O @NFC@NSalophCu)CO H after seven cycles.
4 2

ltration. The purity of products and the progress of reactions
were established based on TLC on silica gel Polygram STL G/UV
54 plates. The melting points of products were determined
2
magnet. The remaining mixture was maintained under opti-
mized reaction conditions in the absence of catalyst. Aer 1 h,
only small amounts of the product were formed (Fig. 11).
with electrothermal-type C14500 melting point apparatus.
Fourier-transform infrared (FT-IR) spectra were recorded in
pressed KBr pellet form using a JASCO FT/IR 4600 spectrometer
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Table 5 A comparison of the catalytic activity of the (Fe
3
O
4 2
@NFC@NSalophCu)CO H catalyst with some reported catalysts for 5-substituted-
1H-tetrazole multi-component reactions
a
Reaction Catalyst
Reaction conditions
Time (h)
Yield (%)
Ref.
b
ꢁ
5
-Substituted-1H-tetrazole
CuNO
Nano-Cu
Cu–MCM-41
Copper(II) Schiff base
3
$3H
2
O
DMSO/120 C
24
8
12
7
24
12
5
4
1.5
0.25
78
92
90
91
87
96
72
92
96
97
65
66
67
53
68
69
70
71
ꢁ
2
O-MFR
DMF/100 C
DMF/140 C
DMF/110 C
DMF/120 C
ꢁ
ꢁ
ꢁ
ꢁ
Bi(OTf)
Cu(OAC)
NH Ce(SO
Humic acid
Fe –CNT–TEA–Cu(II)
Fe @NFC@NSalophCu)CO
3
2
DMF/120 C
(
4
)
4
4
)
4
–2H
2
O
DMF/reux
ꢁ
H
2
O/100 C
ꢁ
3
O
4
DMF/70 C
54
ꢁ
(
3
O
4
2
H
H
2
O/60 C
This work
a
b
Isolated yield. Reaction conditions: benzaldehyde (1.0 mmol), hydroxylamine (1.2 mmol), and sodium azide (1.5 mmol).
Table 6 A comparison of the catalytic activity of the (Fe
3
O
4 2
@NFC@NSalophCu)CO H catalyst with some reported catalysts for tetrazole multi-
component reactions
a
Reaction
Catalyst
Reaction conditions
Time (h)
Yield (%)
Ref.
b
ꢁ
ꢁ
1
-Substituted-1H-tetrazole
Natrolite zeolite
Neat/120 C
4
1.5
5
82
89
95
96
92
92
95
78
93
98
72
73
74
7
75
76
77
78
In(OTf)
Silica sulfuric acid
3
Neat/100 C
ꢁ
Neat/120 C
ꢁ
Fe
Fe
3
O
O
4
@SiO
2
@salen@Cu
Neat/100 C
1
ꢁ
3
4
@quindiol@Cu
Neat/100 C
0.66
0.5
1
4.5
3
ZnS nanoparticles
Fe @HT@AEPH
DMF/R.T.
II
ꢁ
3
O
4
2
–Co
H
2
O/90 C
ꢁ
ZnS nanoparticles
Cu NPs/bentonite
Neat/130 C
ꢁ
Neat/120 C
79
ꢁ
(
Fe
3
O
4
@NFC@NSalophCu)CO
2
H
Neat/80 C
0.33
This work
a
b
Isolated yield. Reaction conditions: aniline (1.0 mmol), triethyl orthoformate (1.2 mmol), and sodium azide (1.2 mmol).
ꢀ1
in room temperature range from 400–4000 cm . NMR spectra triethoxysilane (APTES, 1.0 mmol) was added slowly to the
ꢁ
were captured with a Bruker Avance DPX-250 spectrometer at mixture. The mixture was then stirred for 12 h at 80 C. Fe
3
-
3
00 MHz, using DMSO-d solvent in the presence of tetrame- O @NFC@APTES was separated using an external magnet,
6
4
ꢁ
thylsilane as the internal standard. Thermogravimetric analysis washed with toluene and Et O, and dried at 75 C in an oven
2
(
TGA) was carried out using a TGA Q600 TA thermogravimetric under vacuum.
ꢁ
analyzer in the temperature range of 25–800 C at a heating rate
of 10 C min
ꢁ
ꢀ1
under an air atmosphere. High-resolution
Preparation of the 3,5-bis(((E)-5-(chloromethyl)-2-
transmission electron microscopy (HRTEM) analysis was
accomplished using a Tescan MIRA3 microscope. ICP experi-
ments were carried out using a Varian Vista Pro CCD simulta-
neous ICP-OES instrument. Room-temperature magnetization
isotherms were obtained using vibrating sample magnetometry
hydroxybenzylidene)amino)benzoic acid complex and its
reaction with Cu(OAc)
2 2
: [(5-Cl-Saloph)Cu(II)]CO H
5
-chloromethyl salicylaldehyde (1) was synthesized via
55
a method as reported earlier by us. Briey, a mixture of sali-
cylaldehyde (0.16 mol), paraformaldehyde (0.1 mol), and
(VSM; LakeShore Cryotronics 7407). Field-emission scanning
1
7
00 mL of conc. HCl was reuxed under an air atmosphere at
electron microscopy (FE-SEM) images were obtained using
Tescan MIRA3 apparatus. EDX spectroscopy was performed
ꢁ
0 C for 24 h. A small amount of H SO (2–3 drops) as a catalyst
2
4
was added to the reaction mixture. Aer the reaction, the
reaction mixture was cooled to room temperature and distilled
using
JEOL7600F). The powder X-ray diffraction (XRD) studies were
performed with Philips PW1730 apparatus with Cu Ka (l ¼
.154 nm) radiation.
a
eld-emission scanning electron microscope
(
water and CH
mixture to separate the organic phase from the aqueous phase.
Then the organic layer was separated and dried over MgSO
2 2
Cl (ratio 1 : 1) were added to the reaction
0
4
,
and the solvent was removed under reduced pressure. The
purple sediment was washed with sodium bicarbonate (50 mL)
3 4
Preparation of Fe O @NFC@APTES core–shell NPs
Fe O @NFC was synthesized via a sol–gel method as reported and then dried under an air atmosphere. The pure product, 5-
3
4
5
7–59
earlier by us.
1
The Fe
3
O
4
@NFC product (1 g) was sonicated in chloromethyl salicylaldehyde (1), was obtained via recrystalli-
ꢁ
5 mL of dry toluene for 30 min, and then (3-aminopropyl) zation from EtOH (mp: 85–87 C, 95% isolated yield). The
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3,5-bis(((E)-5-(chloromethyl)-2-hydroxybenzylidene)amino)
benzoic acid ((5-Cl-Saloph)CO H) was washed with dichloro-
2
methane and crystallized with ethanol. Then, for the formation
of Cu(II) and the complex (5-Cl-Saloph)CO H, the ligand (1.0
2
mmol) was dissolved in 15 mL of ethanol and then Cu(OAc)
2
-
$H
2
O (1.5 mmol) was added to the reaction mixture. The reac-
tion mixture was stirred for 6 h under reux conditions. The
solution was allowed to cool to room temperature and then the
resultant [(5-Cl-Saloph)Cu(II)]CO
washed with cold ethanol.
2
H complex was ltered off and
Preparation of [(5-Cl-Saloph)Cu(II)]CO
Fe @NFC@APTES [(Fe @NFC@NSalophCu)CO
The synthesized Fe @NFC-APTES (1.5 g) was sonicated in dry
toluene (15 mL) for 30 min. [(5-Cl-Saloph)Cu(II)]CO H (4 mmol)
2
H supported on
3
O
4
3
O
4
2
H]
3 4
O
2
was dissolved in dry toluene (15 mL) and added dropwise to the
ꢁ
dispersed mixture, which was stirred at 70 C for 24 h. The solid
was separated using an external magnet, washed with distilled
ꢁ
water and diethyl ether, and dried at 70 C in an oven under
vacuum for 12 h.
Typical procedure for the synthesis of 5-substituted-1H-
tetrazoles derivatives
An aldehyde (1.0 mmol), hydroxylamine (1.2 mmol), and
sodium azide (1.5 mmol) were added to a 5 mL round-
bottomed ask containing a magnetic stirrer, water (5 mL),
and (Fe O @NFC@NSalophCu)CO H (0.4 mol%; 8 mg). The
3
4
2
ꢁ
reaction mixture was stirred at 60 C, and the reaction
progress was monitored via thin-layer chromatography. Upon
the completion of the reaction, the catalyst was removed
using an external magnet. The solvent was removed under
reduced pressure and, for the removal of soluble impurities
Scheme
catalysts.
6 The synthesis of tetrazole derivatives with different
product 1 (2.0 mmol) was dissolved in 15 mL of dichloro-
methane, and then 3,5-diaminobenzoic acid (1.0 mmol) was
added slowly to the mixture. The mixture was then stirred for
trapped in the solid, it was washed with water (5 mL). Then,
0 mL of hot ethanol (50 C) was added and the mixture was
stirred to afford the tetrazole in powder form. Aer
completing the reaction, the precipitate formed was ltered
ꢁ
1
6
h at room temperature. Aer the completion of the reaction,
Table 7 A comparison of the atom economy and atomic efficiency of the present methodology with other methods for the synthesis of 5-
substituted-1H-tetrazole derivatives
a
Entry
Equation
Desired product
Time (h)
Yield (%)
AE (%)
AE
f
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
8
7
4
78
91
92
96
97
88
92
96
96
97
—
90
90
87
98
51.24
65.13
65.85
68.71
69.43
67.51
70.58
73.65
73.65
74.41
—
1
71.58
1 h 30 min
15 min
9
8
2
3
76.72
75.23
1 h 20 min
15 min
—
8
67.07
67.07
65.45
73.72
3
5
2 h 30 min
10 min
a
Isolated yield.
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Table 8 A comparison of the atom economy and atomic efficiency of the present methodology with other methods for the synthesis of 1-
substituted-1H-tetrazole derivatives
a
Entry
Equation
Desired product
Time (h)
Yield (%)
AE (%)
AE
f
6
7
8
9
5
1
67
92
92
78
98
77
75
92
—
80
92
96
93
—
97
31.95
43.88
43.88
37.20
46.74
41.88
40.80
50.04
—
43.52
48.18
50.27
48.70
—
1
40 min
4 h 30 min
20 min
4
47.70
1
6
7
8
9
1
6
7
8
9
1
0
0
0
3
2
1 h 10 min
—
45 min
6
1
1
54.40
52.37
3
—
15 min
50.79
a
Isolated yield.
EtOAc/n-hexane (ratio, 1 : 2). The products were characterized
via a comparison of their melting points with the reported ones.
The spectral data for selected compounds are given below.
Spectral data
1
5
-Phenyl-1H-tetrazole (4a). HNMR (DMSO, 400 MHz):
d (ppm) ¼ 6.15 (s, 1H, NH), 7.60–7.65 (t, 2H, H
m
-Ar), 7.73–7.78 (t,
1
H, H -Ar), 8.07–8.10 (d, 2H, H -Ar). Calcd for C H N : C, 57.47;
p
o
7
6 4
ꢁ
H, 4.16; N, 38.37; found: C, 57.53; H, 4.14; N, 38.34. Mp ( C):
17–218.
-(4-Chlorophenyl)-1H-tetrazole (4b). HNMR (DMSO, 400
-Ar),
: C, 46.57; H,
2
1
5
MHz): d (ppm) ¼ 6.21 (s, 1H, NH), 7.63–7.65 (d, 2H, H
m
8
2
(
o 7 5 4
.10–8.13 (d, 2H, H -Ar). Calcd for C H ClN
.80; N, 31.10; found: C, 46.56; H, 2.79; Cl, 19.63; N, 31.02. Mp
ꢁ
C): 258–259.
1
5
-(4-Nitrophenyl)-1H-tetrazole (4c). HNMR (DMSO, 400
Scheme
3 4 2
7 An overview of the (Fe O @NFC@NSalophCu)CO H-
catalyzed tetrazole reaction.
MHz): d (ppm) ¼ 6.22 (s, 1H, NH), 8.05–8.08 (t, 2H, H -Ar), 8.28–
o
8
p 7 5 5 2
.31 (t, 2H, H -Ar). Calcd for C H N O : C, 43.91; H, 2.66; N,
3
(
6.59; O, 16.84; found: C, 43.98; H, 2.64; N, 36.64; O, 16.74. Mp
and puried via recrystallization from ethanol to afford the
desired product (Table 3).
ꢁ
C): 220–221.
1
4-(1H-Tetrazol-5-yl)phenol (4d). HNMR (DMSO, 400 MHz):
d (ppm) ¼ 6.15 (s, 1H, NH), 7.60–7.65 (t, 2H, H
m
-Ar), 7.73–7.78 (t,
General procedure for the synthesis of 1-substituted-1H-
tetrazoles from amines
1H, H
p
-Ar), 8.07–8.10 (d, 2H, H
o
-Ar). Calcd for C O: C,
7 6 4
H N
5
1.85; H, 3.71; N, 34.49; O, 9.93; found: C, 51.85; H, 3.73; N,
ꢁ
An aniline (1.0 mmol), triethyl orthoformate (1.2 mmol), and 34.55; O, 9.87. Mp ( C): 233–234.
1
sodium azide (1.2 mmol) were added to a test tube containing
magnetic stirrer and (Fe @NFC@NSalophCu)CO
0.3 mol%; 6.5 mg). The reaction mixture was stirred at 80 C (d, 2H, H
5-(4-Methoxyphenyl)-1H-tetrazole (4e). HNMR (DMSO, 400
MHz): d (ppm) ¼ 3.98 (s, 3H, CH ), 6.00 (s, 1H, NH), 7.04–7.07
-Ar), 8.00–8.02 (d, 2H, H -Ar). Calcd for C O: C,
a
3
O
4
2
ꢁ
H
3
(
o
m
8 8 4
H N
without solvent, and the reaction progress was monitored via 54.54; H, 4.58; N, 31.80; O, 9.08; found: C, 54.54; H, 4.58; N,
ꢁ
thin-layer chromatography. Upon the completion of the reac- 31.80; O, 9.08. Mp ( C): 232–233.
1
tion, the mixture was cooled to ambient temperature and
5-(2-Methoxyphenyl)-1H-tetrazole (4f). HNMR (DMSO, 400
diluted with ethyl acetate (10 mL). The catalyst was removed MHz): d (ppm) ¼ 3.53 (s, 3H, CH ), 6.35 (s, 1H, NH), 7.06–7.20
3
using an external magnet, and then the resulting solution was (m, 2H, H -Ar), 7.30–7.34 (t, 1H, H -Ar), 7.64–7.68 (t, 1H, H -Ar).
m
p
o
washed with water, dried over anhydrous Mg
rated. The residue was concentrated and recrystallized from 54.54; H, 4.58; N, 31.80; O, 9.08. Mp ( C): 154–156.
2
SO
4
, and evapo- Calcd for C
8
H
8
N
4
O: C, 54.53; H, 4.61; N, 31.75; O, 9.11; found: C,
ꢁ
©
2021 The Author(s). Published by the Royal Society of Chemistry
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1
2
-(1H-Tetrazol-5-yl)phenol (4g). HNMR (DMSO, 400 MHz): 7.72–7.76 (d, d, 2H, Ho,p-Ar), 9.38 (s, 1H, CH-tetrazole). Calcd for
d (ppm) ¼ 6.11 (s, 1H, NH), 7.28–7.38 (m, 2H, H
t, 1H, H -Ar), 7.86–7.88 (d, 1H, H
for C O: C, 51.87; H, 3.71; N, 34.50; O, 9.92; found: C,
1.85; H, 3.73; N, 34.55; O, 9.87. Mp ( C): 220–221.
N,N-Dimethyl-4-(1H-tetrazol-5-yl)aniline (4h).
m
-Ar), 7.55–7.57
C
7
H
5
BrN
4
: C, 37.40; H, 2.26; Br, 35.48; N, 24.87; found: C, 37.36;
ꢁ
(
p
o
-Ar), 9.21 (s, 1H, O–H). Calcd H, 2.24; Br, 35.51; N, 24.90. Mp ( C): 78–79.
1
1-(m-Tolyl)-1H-tetrazole (7i). HNMR (DMSO, 400 MHz):
d (ppm) ¼ 2.25 (s, 3H, CH ), 7.31–7.32 (d, 2H, H -Ar), 7.54–7.58
HNMR (d, 2H, H -Ar), 9.57 (s, 1H, CH-tetrazole). Calcd for C : C,
7
6 4
H N
ꢁ
5
3
m
1
m
8 8 4
H N
(
DMSO, 400 MHz): d (ppm) ¼ 3.05 (s, 6H, 2CH ), 6.31 (s, 1H, 59.90; H, 5.10; N, 35.00; found: C, 59.99; H, 5.03; N, 34.98. Mp
3
ꢁ
NH), 7.05–7.08 (d, 2H, H -Ar), 7.75–7.78 (d, 2H, H -Ar). Calcd for ( C): 55.
m
o
1
C
9
H
11
N
5
: C, 57.09; H, 5.84; N, 37.07; found: C, 57.13; H, 5.86; N,
1-(3-Methoxyphenyl)-1H-tetrazole (7j). HNMR (DMSO, 400
MHz): d (ppm) ¼ 4.01 (s, 3H, CH ), 6.90–6.96 (d, s, 2H, Ho,p-Ar),
ꢁ
37.01. Mp ( C): 133–134.
3
1
4
-(1H-Tetrazol-5-yl)benzaldehyde (4i). HNMR (DMSO, 400 7.20–7.22 (d, 2H, Ho,m-Ar), 9.35 (s, 1H, CH-tetrazole). Calcd for
MHz): d (ppm) ¼ 6.00 (s, 1H, NH), 7.85–7.87 (t, 2H, H -Ar), 7.97–
O: C, 54.49; H, 4.60; N, 31.75; O, 9.16; found: C, 54.54; H,
.00 (t, 1H, H
-Ar), 10.01 (s, 1H, H-aldehyde). Calcd for 4.58; N, 31.80; O, 9.08. Mp ( C): 67–68.
C H N O: C, 55.10; H, 3.44; N, 32.22; O, 9.24; found: C, 55.17; H,
C H N
8 8 4
o
ꢁ
8
m
8
6 4
ꢁ
3
.47; N, 32.17; O, 9.19. Mp ( C): 187–189.
-(1H-Tetrazol-5-yl)benzene-1,2-diol (4j). HNMR (DMSO,
00 MHz): d (ppm) ¼ 6.30 (s, 1H, NH), 6.78–6.81 (m, 1H, H -Ar),
.88 (s, 1H, H -Ar), 7.63–7.65 (d, 1H, H -Ar), 9.49 (s, 2H, 2O–H).
Conclusions
1
4
4
6
m
In conclusion, a facile methodology was developed for the
o
o
preparation of tetrazole derivatives using (Fe
3 4
O @-
Calcd for C
7
H
6
N
4
O
2
: C, 47.22; H, 3.41; N, 31.42; O, 17.94; found:
NFC@NSalophCu)CO H nanoparticles as an efficient hetero-
2
ꢁ
C, 47.19; H, 3.39; N, 31.45; O, 17.96. Mp ( C): 214–215.
geneous catalyst. The nanocatalyst presents outstanding activity
under simple conditions. Good-to-high yields of products were
obtained using a wide variety of substrates within short reaction
times. The catalyst was characterized via FT-IR, EDX, FE-SEM,
TEM, XRD, VSM, DLS, and TGA analyses. Hot ltration testing
revealed the heterogeneous nature of the catalyst with low levels
of metal leaching. The catalyst could be recycled for at least
seven consecutive cycles with a negligible loss of efficiency.
There are myriad advantages to using this method, such as the
thermal stability, heterogeneous nature, short reaction times,
clean and simple procedure, excellent yields, easy workup, eco-
friendly nature, cost-effectiveness, and easy product separation
and purication, making the nanocatalyst a suitable alternative
for the preparation of tetrazole derivatives. Benecially, this
catalyst can easily be separated from the reaction environment
using an external magnetic eld and reused several times
without signicant loss of catalytic stability or activity.
1
1
-Phenyl-1H-tetrazole (7a). HNMR (DMSO, 400 MHz):
d (ppm) ¼ 7.54–7.87 (m, 5H, H-Ar), 9.41 (s, 1H, CH-tetrazole).
Calcd for C H N : C, 57.50; H, 4.14; N, 38.37; found: C, 57.53;
7
6 4
ꢁ
H, 4.14; N, 38.34. Mp ( C): 63.
-(4-Chlorophenyl)-1H-tetrazole (7b). HNMR (DMSO, 400
MHz): d (ppm) ¼ 7.76–7.77 (d, 2H, H -Ar), 7.53–7.55 (d, 2H, H
Ar), 9.26 (s, 1H, CH-tetrazole). Calcd for C ClN : C, 46.52; H,
1
1
m
m
-
7
H
5
4
2
3
.81; Cl, 19.60; N, 31.07; found: C, 46.56; H, 2.79; Cl, 19.63; N,
1.02. Mp ( C): 155.
ꢁ
1
1-(4-Bromophenyl)-1H-tetrazole (7c). HNMR (DMSO, 400
MHz): d (ppm) ¼ 7.48–7.49 (d, 2H, H -Ar), 7.83–7.85 (d, 2H, H -
o
o
Ar), 9.37 (s, 1H, CH-tetrazole). Calcd for C H BrN : C, 37.30; H,
7
5
4
2
2
.27; Br, 35.53; N, 24.91; found: C, 37.36; H, 2.24; Br, 35.51; N,
4.90. Mp ( C): 176–177.
ꢁ
1
1-(p-Tolyl)-1H-tetrazole (7d). HNMR (DMSO, 400 MHz):
d (ppm) ¼ 2.47 (s, 3H, CH
3
), 7.10–7.12 (d, 1H, H
-Ar), 7.53–7.55 (d, 1H, H -Ar), 7.63 (s, 1H, H
s, 1H, CH-tetrazole). Calcd for C H N : C, 60.02; H, 5.06; N,
p
-Ar), 7.27–7.29
(
(
t, 1H, H
m
o
o
-Ar), 9.37
8
8 4
ꢁ
Author contributions
35.04; found: C, 59.99; H, 5.03; N, 34.98. Mp ( C): 92–93.
1
1
-(4-Methoxyphenyl)-1H-tetrazole (7e). HNMR (DMSO, 400
MHz): d (ppm) ¼ 6.15 (s, 1H, NH), 7.60–7.65 (t, 2H, H -Ar), 7.73–
.78 (t, 1H, H -Ar), 8.07–8.10 (d, 2H, H -Ar). Calcd for C O:
Pouya Ghamari Kargar: investigation, methodology, soware,
writing – original dra. Ghodsieh bagherzade: project admin-
istration, data curation, writing – review and editing.
m
7
p
o
8 8 4
H N
C, 54.52; H, 4.55; N, 35.80; O, 9.09; found: C, 54.54; H, 4.58; N,
ꢁ
31.80; O, 9.08. Mp ( C): 114–115.
1
1
-(4-Nitrophenyl)-1H-tetrazole (7f). HNMR (DMSO, 400 Conflicts of interest
MHz): d (ppm) ¼ 8.08–8.10 (d, 2H, H -Ar), 8.62–8.63 (d, 2H, H -
o
m
There are no conicts to declare.
Ar), 9.42 (s, 1H, CH-tetrazole). Calcd for C H N O : C, 43.90; H,
7
5 5 2
2
1
.69; N, 36.62; O, 16.79; found: C, 43.98; H, 2.64; N, 36.64; O,
ꢁ
6.74. Mp ( C): 200.
Acknowledgements
1
1-(3-Chlorophenyl)-1H-tetrazole (7g). HNMR (DMSO, 400
The authors appreciate the University of Birjand and nancial
support from the Research Council.
MHz): d (ppm) ¼ 7.20–7.23 (d, s, 1H, H
Ar), 7.45–7.47 (d, 1H, H -Ar), 7.84 (s, 1H, H
tetrazole). Calcd for C ClN : C, 46.51; H, 2.82; Cl, 19.67; N,
1.00; found: C, 46.56; H, 2.79; Cl, 19.63; N, 31.02. Mp ( C): 139–140.
m
-Ar), 7.31–7.37 (t, 1H, H
p
-
o
o
-Ar), 9.41 (s, 1H, CH-
7
H
5
4
ꢁ
3
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1 H.
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