Immobilization of a nickel complex onto functionalized Fe3O4 nanoparticles: a green and recyclable catalyst for synthesis of 5-substituted 1H-tetrazoles and oxidation reactions

Article abstract of DOI:10.1007/s11164-017-3172-4

Abstract: In the present research, a magnetically recoverable catalyst was easily prepared by anchoring nickel onto the surface of organically modified magnetite nanoparticles. Characterization of the prepared nanostructure was performed by various physico-chemical techniques such as Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma optical emission spectroscopy, X-ray diffraction, thermal gravimetric analysis and vibrating sample magnetometer measurements. The catalytic behavior of the prepared nanohybrid as an efficient catalyst was successfully probed in the oxidation of sulfides, oxidative coupling of thiols and synthesis of 5-substituted 1H-tetrazoles. This method was found to have significant advantages, including high yield, green reaction conditions, short reaction time, easy separation and workup, as well as the ability to tolerate a wide variety of substitutions in the reagents. Graphical Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s11164-017-3172-4

Res Chem Intermed
DOI 10.1007/s11164-017-3172-4
Immobilization of a nickel complex onto functionalized
Fe3O4 nanoparticles: a green and recyclable catalyst
for synthesis of 5-substituted 1H-tetrazoles
and oxidation reactions
Taiebeh Tamoradi1 Bita Mehraban-Esfandiari1
•
•
Mohammad Ghadermazi1 Arash Ghorbani-Choghamarani2
•
Received: 8 August 2017 / Accepted: 6 October 2017
Ó Springer Science+Business Media B.V. 2017
Abstract In the present research, a magnetically recoverable catalyst was easily pre-
pared by anchoring nickel onto the surface of organically modified magnetite
nanoparticles. Characterization of the prepared nanostructure was performed by various
physico-chemical techniques such as Fourier transform infrared spectroscopy, scanning
electron microscopy, transmission electron microscopy, energy-dispersive X-ray spec-
troscopy, inductively coupled plasma optical emission spectroscopy, X-ray diffraction,
thermal gravimetric analysis and vibrating sample magnetometer measurements. The
catalytic behavior of the prepared nanohybrid as an efficient catalyst was successfully
probed in the oxidation of sulfides, oxidative coupling of thiols and synthesis of
5-substituted 1H-tetrazoles. This method was found to have significant advantages,
including high yield, green reaction conditions, short reaction time, easy separation and
workup, as well as the ability to tolerate a wide variety of substitutions in the reagents.
&
&
&
Taiebeh Tamoradi
t.tabss@yahoo.com
Mohammad Ghadermazi
mghadermazi@yahoo.com
Arash Ghorbani-Choghamarani
arashghch@gmail.com; a.ghorbani@mail.ilam.ac.ir
1
2
Department of Chemistry, Faculty of Science, University of Kurdistan, Sanandaj, Iran
Department of Chemistry, Faculty of Science, Ilam University, P.O. Box, 69315516, Ilam, Iran
123

T. Tamoradi et al.
Graphical Abstract
Keywords Nickel Á Sulfides Á Thiols Á 5-Substituted 1H-tetrazoles
Introduction
Among organic sulfur compounds, disulfides and sulfoxides have found widespread
application as precursors or intermediates in the synthesis of natural products and
valuable physiologically and pharmacologically active molecules as well as
important integral and supplementary parts in many pharmaceutical and biological
active molecules such as cystine, DTNB [Ellman’s reagent or 5,50-dithio-bis(2-
nitrobenzoic acid)], omeprazole and fipronil [1–11]. Among a large variety of
N-containing heterocyclic compounds, tetrazoles have attracted a great deal of
attention since they are extensively employed in organic synthesis, material science,
photography, information recording systems and explosives; and in organometallic
chemistry as effective stabilizers of metallopeptide structures, as well as use as
ligands in coordination chemistry, stable surrogates for carboxylic acids and
medicinal chemistry [12–22]. In the last few years, various catalysts have been
employed for the synthesis of 5-substituted 1H-tetrazoles, the oxidative coupling of
thiols and the oxidation of sulfides [23–25]. Despite these solutions, some of these
procedures have various disadvantages, including hazardous reaction conditions,
toxic chemicals, tedious workup, operational costs, product purity, use of strong
acids, high temperature, difficulty of separating the catalyst from the products, poor
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Immobilization of a nickel complex onto functionalized…
yields and long reaction times. The drawbacks mentioned above can be solved via
the development of a more versatile and also environmentally benign method. In
this regard, magnetic nanocatalysts offer a significant research area for the synthesis
of organic molecules due to their large specific surface areas and easy separation of
the catalyst upon reaction completion [26–29]. Interestingly, the design of novel
magnetically separable systems has created a significant potential in the develop-
ment of innovative systems with improved activities and selectivities [30–34].
Hence, in the development of greener and sustainable processes for organic
synthesis and nanocatalysis, we report the synthesis of a recoverable and efficient
Fe3O4@AMPD@Ni complex by coordination of nickel with 2-amino-2-methyl-1,3-
propanediol (AMPD) supported on Fe3O4 magnetic nanoparticles, which shows a
highly catalytic nature, easy to handle procedure, short reaction time, recycle
exploitation and excellent isolated yields in the oxidation of sulfides, oxidative
coupling of thiols and synthesis of 5-substituted 1H-tetrazoles.
Experimental
General
Ferric chloride hexahydrate, ferrous chloride tetrahydrate, ammonia (25% w/w),
3-chloropropyltrimethoxysilane (CPTMS), triethylamine, ethanol, hydrofluoric
acid, ethyl acetate, acetonitrile, H2O2 (33%), n-Hexane and toluene were supplied
from Merck (www.merckmillipore.com). Dimethyl sulfoxide, dimethylformamide,
nickel(II) nitrate, AMPD, poly(ethylene glycol) (PEG) and all reagents were pur-
chased from Fluka (www.sigmaaldrich.com). Powder X-ray diffraction (XRD)
patterns were collected to obtain the crystallographic structure of the catalyst using
˚
a Co radiation source with a wavelength l = 1.78897 A, at 40 kV. The size and
morphology of the as-synthesized nanoparticles were determined by scanning
electron microscopy (SEM) and transmission electron microscopy (TEM) tech-
niques using an FESEM-TESCAN MIRA3 and Zeiss-EM10C transmission electron
microscope, respectively. Supermagnetic properties of the catalyst were measured
in a vibrating sample magnetometer (VSM; 244; MDKFD) at room temperature. IR
spectra were examined for characterization of prepared samples by KBr disc using a
VRTEX 70 model BRUKER FT-IR spectrophotometer. Inductively coupled plasma
optical emission spectrometry (ICP-OES) of the catalyst was also performed to
determine the content of Ni of the obtained catalyst. The thermal stability of the
nanocatalyst was also studied by thermo-gravimetric analysis (TGA) using a Shi-
madzu DTG-60 instrument in the temperature range of 50–750 °C.
General procedure for the preparation of (Fe3O4@AMPD@Ni)
The Fe3O4 nanoparticles have been successfully prepared according to the very
recently reported method [35]. Then, 1 g of the obtained magnetic nanoparticles
with 1.5 mL of CPTMS were refluxed in dry toluene (20 mL) for 24 h. The final
product was separated with assistance of a magnetic device, washed with hexane
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T. Tamoradi et al.
and dried at 50 °C to give the Fe3O4 coated with CPTMS. Fe3O4-AMPD
nanoparticles were subsequently produced by the reaction of the CPTMS supported
on Fe3O4 nanoparticles (1 g) with 0.21 g of AMPD and triethylamine (1.5 mmol) in
dry toluene under reflux conditions for 48 h. The final product (Fe3O4@AMPD) was
separated by applying a simple magnet, washed with deionized water and ethanol
and dried at 50 °C. In the final step, Fe3O4@AMPD@Ni nanocatalyst was
successfully prepared through coordination of Fe3O4@ AMPD ligand to nickel. It
should be noted that Fe3O4@AMPD@Ni nanocatalyst was obtained by refluxing of
Ni(NO3)2Á6H2O (0.727 g) with the Fe3O4@AMPD (1 g) in ethanol (20 mL) for
16 h. Ultimately, the product easily collected by means of a magnet, eluted with
ethanol and dried at 50 °C to obtain Fe3O4@AMPD@Ni nanohybrid.
General procedure for the oxidation of sulfides
In this study, as a typical procedure, hydrogen peroxide solution (0.5 mL) was
added to suspension of sulfide (1 mmol) and Fe3O4@AMPD@Ni (0.005 g) in a
round-bottomed flask, and the mixture was stirred under solvent-free condition at
room temperature for an appropriate time period. After completion of the reaction
[monitored by thin-layer chromatography (TLC)], the catalyst was removed by
means of a magnet to be reused in subsequent reactions and washed with ethyl
acetate to obtain the pure sulfoxides.
General procedure for the oxidative coupling of thiols
In a typical procedure, a solution of thiol (1 mmol) and Fe3O4@AMPD@Ni
(0.005 g) was added to a round-bottomed flask containing H2O2 (0.5 mL) and 2 mL
of ethanol and stirred at room temperature for an appropriate time. After completion
of the addition, Fe3O4@AMPD@Ni catalyst was easily separated by a simple
magnet, and then the product was extracted with ethyl acetate and dried over
anhydrous Na2SO4 to give the pure disulfides.
Results and discussion
Catalyst preparation
Scheme 1 illustrates the preparation of a Fe3O4@AMPD@Ni nanocatalyst through
loading nickel AMPD complex on the surface of magnetic iron oxide nanoparticles
(Scheme 1). In order to immobilize the nickel complex, CPTMS was first loaded on
the surface of magnetic nanoparticles via coordination bonding through hydroxyl
group interaction, to achieve Fe3O4 nanoparticles coated with CPTMS. Fe3O4@-
AMPD nanostructure was subsequently prepared by the reaction of chloride groups
of CPTMS supported on Fe3O4 nanoparticles and AMPD ligand as a green and
available diol. Then, treatment of Fe3O4@AMPD with Ni(NO3)2.6H2O provides
Fe3O4@AMPD@Ni through a stable interaction between the metal ions and
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Immobilization of a nickel complex onto functionalized…
Scheme 1 Synthesis of Fe3O4@AMPD@Ni nanocatalyst
functional groups of the diol. Afterward, the structure of obtained catalyst was
characterized by FT-IR, TGA, EDS, ICP-OES, TEM, XRD and SEM.
SEM images of the Fe3O4 and Fe3O4@AMPD@Ni provided evidence that the
prepared nanoparticles comprised uniform nanometer-sized particles (Fig. 1). It
should be noted that Fe3O4@AMPD@Ni was synthesized without significant
changes in the surface structure and morphology of Fe3O4.
Fig. 1 SEM micrographs of a Fe3O4 and b Fe3O4@AMPD@Ni
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T. Tamoradi et al.
Fig. 2 EDX pattern of Fe3O4@AMPD@Ni nanocatalyst
As shown in Fig. 2, the presence of the expected elements in the structure of the
catalyst, namely iron, nitrogen, oxygen, carbon and nickel, is verified using the
energy-dispersive X-ray spectroscopy (EDX) analysis of Fe3O4@AMPD@Ni. It
should be noted that the exact amount of nickel loaded on modified magnetic
nanoparticles was found to be 0.34 mmol g-1 by ICP-OES analysis.
Figure 3 illustrates the quantitative determination of the organic groups
supported on the surface of Fe3O4 magnetic nanoparticles by TGA. It should be
noted that the small amount of weight loss below 200 °C which is due to removal of
physically adsorbed solvent and surface hydroxyl groups, and the other weight loss
of about 2% between 200 and 600 °C, is related to decomposition of functional
Fig. 3 The TGA diagrams of Fe3O4 nanoparticles (a) and Fe3O4@AMPD@Ni (b)
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Immobilization of a nickel complex onto functionalized…
groups chemisorbed onto the surface of magnetic nanoparticles [36, 37]. According
to the TGA results, the TGA curve of catalyst shows the first weight loss (4%)
below 200 °C is assigned to the loss of adsorbed water molecules or surface
hydroxyl groups, and the second loss (15%) at the temperature range of 200–600 °C
is attributed to the decomposition of the organic part on the surface of the magnetic
phase. Based on this result, the good grafting of nanocatalyst onto the surface of
magnetic nanoparticles is verified.
TEM images of Fe3O4@AMPD@Ni are depicted in Fig. 4. According to these
images, the particle size of synthesized catalyst is found to be approximately 20 nm.
TEM images of the catalyst also provided further evidence that the ordered
organizations of the magnetic nanoparticles were retained after loading copper
AMPD complex on the surface of the magnetic nanoparticles. Therefore,
interpretations made on the basis of SEM images are further supported by the
TEM images.
The XRD pattern of Fe3O4@AMPD@Ni is investigated to achieve a better
reorganization of the major properties of the magnetite structure (Fig. 5). It was
found that the Fe3O4 phase was identified by six characteristic peaks positions at 2h
values at 31.91, 36.85, 46.66, 54.95, 57.96 and 63.79 which is in agreement with
standard XRD pattern of Fe3O4 nanoparticles in the literature [38–40]. As shown in
Fig. 5, it is verified that the Fe3O4 phase has not changed during the grafting of
organic groups including Ni complex on the magnetic nanoparticles.
Figure 6 shows the FT-IR spectra of bare Fe3O4 nanoparticles, Fe3O4 coated with
CPTMS, Fe3O4@AMPD and Fe3O4@AMPD@Ni within the range of
400–4000 nm. The FT-IR analyses of Fe3O4 nanoparticles exhibit the characteristic
peaks around 602 and 3000–3500 cm-1 which can be attributed to symmetrical and
asymmetrical modes of the Fe–O bond of iron oxide and hydroxyl groups surface,
respectively [41]. The broad bands around 950–1000 and 2830–2960 cm-1 are due
to the Si–O and C–H stretching vibration modes in the FT-IR spectrum of Fe3O4
coated with CPTMS, respectively [42]. As shown in the FT-IR spectrum of
Fig. 4 TEM images of Fe3O4@AMPD@Ni at different magnifications
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T. Tamoradi et al.
Fig. 5 XRD pattern of Fe3O4@AMPD@Ni
Fe3O4@AMPD, the loading of catalyst on the modified surface of magnetic
nanoparticles is also verified through the presence of absorption bands in the range
of 1500–1650 and 1112 cm-1 which is assigned to to N–H and C–N vibration
bands, respectively [43].
As seen in Fig. 7, the magnetic properties of Fe3O4@AMPD@Ni and Fe3O4
were recorded at room temperature using a VSM technique. As a result of this
analysis, the magnetization of pure Fe3O4 (73 emu g-1) is higher than Fe3O4@-
AMPD@Ni (47.6 emu g-1) by which the effective grafting of catalyst on the Fe3O4
nanoparticles is verified.
Catalytic studies
After synthesis and characterization of the catalyst, we were interested in
investigation of catalytic activity in the oxidation of sulfides (Scheme 2), the
oxidative coupling of thiols (Scheme 4) and the synthesis of 5-substituted 1H-
tetrazoles (Scheme 6) using Fe3O4@AMPD@Ni as a green and efficient magnet-
ically retrievable heterogeneous nanocatalyst. In order to investigate the possibility
of the oxidation of sulfides using the obtained catalyst, methylphenylsulfoxide was
prepared as a model compound in various solvents in the presence of different
amount of catalyst and using different amounts of hydrogen peroxide (H2O2) to
achieve optimized condition (Table 1). As shown in Table 1, the solvent-free
condition in the presence of Fe3O4@AMPD@Ni (0.005 g) and H2O2 (0.5 mL) at
room temperature was found to be an ideal reaction condition for the conversion of
methylphenylsulfide to methylphenylsulfoxide.
As shown in Table 2, a wide range of sulfides with different functional groups
were converted to their corresponding products in the presence of Fe3O4@-
AMPD@Ni as catalyst under the optimized condition. All products were prepared
in the short reaction time and in good to excellent yields.
A plausible reaction mechanism for the oxidation of sulfides is shown in
Scheme 3. The intermediate
A is obtained by reaction of H2O2 with
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Immobilization of a nickel complex onto functionalized…
Fig. 6 FT-IR spectrum of bare Fe3O4 (a), Fe3O4 coated with CPTMS (b), Fe3O4@AMPD (c) and
Fe3O4@AMPD@Ni (d)
Fe3O4@AMPD@Ni, which is converted to active oxidant B. Then, nucleophilic
attack of the sulfide on this intermediate (C) produces corresponding sulfoxide
[48, 49].
It should be mentioned that the catalytic activity of Fe3O4@AMPD@Ni was also
investigated in the oxidative coupling of thiols. In order to optimize the reaction
conditions, the oxidative coupling of mercaptosuccinic acid substrate was selected
in the absence and presence of various solvents and in the presence of different
amount of Fe3O4@AMPD@Ni using different amounts of hydrogen peroxide
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T. Tamoradi et al.
Fig. 7 Vibrating sample magnetometry curves of Fe3O4 (a) and Fe3O4@AMPD@Ni (b)
Scheme 2 Fe3O4@AMPD@Ni catalyzed the oxidation of sulfides to sulfoxides
Table 1 Optimization of oxidation of sulfides to the corresponding sulfoxides using Fe3O4@AMPD@Ni
nanoparticles under various conditions at room temperature
Entry
Solvent
H2O2 (mL)
Catalyst (mg)
Time (min)
Yield (%)a
SDb
1
2
3
4
5
6
7
8
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Ethanol
0.5
0.5
0.5
0.4
0.5
0.5
0.5
0.5
3
7
5
5
5
5
5
0
20
82
2.5
3
7
98
9
98
3
17
88
3.5
2.5
3.5
4
55
91
Ethyl acetate
Acetonitrile
Solvent-free
260
320
10 h
88
87
Tracec
3
aIsolated yields (mean value)
bStandard deviation
cReaction proceeds in the absence of catalyst
(H2O2). As shown in Table 3, Fe3O4@AMPD@Ni (0.005 g) as catalyst in the
presence of H2O2 (0.5 mL) in ethanol at room temperature was found to be ideal the
reaction condition for the oxidative coupling of mercaptosuccinic acid (Schemes 4,
5, 6).
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Immobilization of a nickel complex onto functionalized…
Table 2 Oxidation of sulfides to sulfoxides in the presence of Fe3O4@AMPD@Ni under optimized
reaction conditionsa
Entry
Substrate
Product
Time (min)
Yield (%)b
SDc
M.p. (°C)
1
2
Dodecyl methylsulfide
Dipropylsulfide
2a
2b
2c
2d
2e
2f
35
23
12
5
92
95
92
93
97
96
98
94
98
94
3.5
3
60–63 [44]
Oil [45]
3
Dibenzylsulfide
3.5
3
130–132 [46]
Oil [45]
4
Tetrahydrothiophene
Propylenesulfide
5
43
37
9
4
Oil [44]
6
Dimethylsulfide
3.5
3
Oil [44]
7
Methylphenylsulfide
Allyl sulfide
2g
2h
2i
Oil [45]
8
38
52
48
4
Oil [44]
9
2-(Methylthio)ethanol
2-(Phenylthio)ethanol
3
Oil [47]
10
2j
3.5
Oil [45]
aReaction condition: sulfide (1 mmol), H2O2 (0.5 mL) and Fe3O4@AMPD@Ni (0.005 g) under solvent-
free condition at room temperature
bIsolated yields (mean value)
cStandard deviation
Scheme 3 Proposed mechanism for oxidation of sulfides in the presence of Fe3O4@AMPD@Ni as
catalyst
After optimization of the reaction parameters, we also decided to examine the
wider applicability of the catalyst for oxidation of a variety of substituted aromatic
and aliphatic thiols. The results are summarized in Table 4.
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T. Tamoradi et al.
Table 3 Optimization of oxidative coupling of thiols into disulfides using Fe3O4@AMPD@Ni under
various conditions at room temperature
Entry
Solvent
H2O2 (mL)
Catalyst (mg)
Time
Yield (%)a
SDb
1
2
3
4
5
6
7
8
EtOH
0.5
0.5
0.5
0.4
0.5
0.5
0.5
0.5
3
7
5
5
5
5
5
0
13 min
9 min
78
4
EtOH
99
2.5
2
EtOH
10 min
17 min
20 min
45 min
85 min
10 h
98
EtOH
93
3.5
4.5
3
Solvent-free
Ethyl acetate
Acetonitrile
EtOH
91
94
83
Tracec
3.5
2.5
aIsolated yields (mean value)
bStandard deviation
Reaction proceeds in the absence of catalyst
4a-4h
3a-3h
Scheme 4 Fe3O4@AMPD@Ni catalyzed the oxidative coupling of thiols into disulfides
Scheme 5 Proposed mechanism for oxidative coupling of thiols in the presence of Fe3O4@AMPD@Ni
as catalyst
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Immobilization of a nickel complex onto functionalized…
6a-6j
5a-5j
Scheme 6 Fe3O4@AMPD@Ni catalyzed the one-pot synthesis of 5-substituted 1H-tetrazoles
The proposed mechanism for this process using H2O2 as oxidant in the presence
Fe3O4@AMPD@Ni catalyst is outlined in Scheme 5 [48, 49].
Initially, in order to optimize the reaction conditions, we investigated the model
cyclocondensation reaction between 4-hydroxybenzonitrile and sodium azide in the
presence of the nanocatalyst under the effect of various parameters such as solvent,
catalyst concentration and temperature. It should be noted that the nature of the
temperature and solvent was observed to have a profound effect on both the activity
of the catalyst and the yield of product. As shown in Table 5, we observed that the
best results were obtained in PEG at 120 °C in the presence of 0.005 g of catalyst.
In order to generalize the scope of the reaction under the optimized conditions, a
series of substituted nitriles were chosen for the synthesis of 5-substituted 1H-
tetrazoles, with the results presented in Table 6.
A plausible reaction mechanism for the synthesis of tetrazoles derivatives in the
presence of Fe3O4@AMPD@Ni as catalyst is shown in Scheme 7 [56]. Initially,
interaction of a nitrogen atom of nitrile with Ni(II) forms compound A, which
accelerates the cyclization step. In fact, Ni(II) nanoparticles acts as a Lewis acid and
activates the nitrile group via coordination. Hence, it enhances the electrophilic
Table 4 Oxidative coupling of thiols into disulfides using H2O2 in the presence of Fe3O4@AMPD@Ni
under optimized reaction conditionsa
Entry
Substrate
Product
Time (min)
Yield (%)b
SDC
M.p. (°C)
1
2
3
4
5
6
7
8
Mercaptosuccinic acid
2-Mercaptobenzoic acid
Benzo[d]thiazole-2-thiol
2-Mercaptoethanol
4a
4b
4c
4d
4e
4f
10
5
99
95
94
85
93
94
98
94
2.5
3.5
3
105–108 [50]
280–282 [51]
171–1174 [52]
Oil [53]
10
5
2.5
3.5
3
Benzyl mercaptan
120
120
30
50
55–57 [26]
133–135 [26]
95 [46]
Naphthalene-2-thiol
Benzo[d]oxazole-2-thiol
4-Methylbenzenethiol
4g
4h
3.5
4
40 [26]
aReaction condition: thiol (1 mmol), H2O2 (0.5 mL) and Fe3O4@AMPD@Ni (0.005 g) in EtOH (2 mL)
at room temperature
bIsolated yields (mean value)
cStandard deviation
123

T. Tamoradi et al.
Table 5 Optimization of reaction conditions for synthesis of 5-substituted 1H-tetrazole derivatives in the
presence of Fe3O4@AMPD@Ni
Entry
Solvent
Temp (°C)
Catalyst (mg)
Time
Yield (%)a
SDb
1
2
3
4
5
6
7
8
9
EtOH
DMSO
DMF
H2O
80
120
120
100
100
120
120
120
120
4
4
4
4
4
3
4
5
0
130 min
20 min
50 min
120 min
50 min
50 min
15 min
14 min
10 h
92
3
89
4
87
3.5
3.5
2.5
3
92
PEG
PEG
PEG
PEG
PEG
95
92
97
3
98
Tracec
3.5
3.5
aIsolated yields (mean value)
bStandard deviation
cReaction proceeds in the absence of catalyst
Table 6 Synthesis of 5-substituted 1H-tetrazole derivatives in the presence of Fe3O4@AMPD@Ni under
optimized reaction conditionsa
Entry
Substrate
Product
Time (min)
Yield (%)b
SDc
M.p. (°C)
1
2
3
4
5
6
7
8
9
10
Phthalonitrile
4a
4b
4c
4d
4e
4f
50
180
150
9
91
97
94
90
89
97
96
96
96
93
4
202–205 [54]
249–251 [55]
153–154 [28]
175–178 [54]
220–223 [55]
114–117 [54]
230–233 [54]
252–255 [28]
219–221 [55]
209 [55]
4-Borobenzonitrile
3-Nitrobenzonitrile
2-Chlorobenzonitrile
2-Hydroxybenzonitrile
Malononitrile
3.5
4
2.5
3
175
15
3.5
4
4-Hydroxybenzonitrile
4-Chorobenzonitrile
4-Nitrobenzonitrile
Benzonitrile
4g
4h
4i
15
180
160
180
4.5
2.5
3
4j
aReaction condition: nitrile (1 mmol), sodium azide (1.2 mmol) and Fe3O4@AMPD@Ni (0.004 g) in
PEG (2 mL)
bIsolated yields (mean value)
cStandard deviation
character of the cyanide group, which then reacts with sodium azide to form the
intermediate B. Acidic work up affords compounds C and D. The equilibrium leads
to formation of the more stable tautomer D (5-substituted-1H-tetrazole).
The recovery and reusability of catalyst is an outstanding issue in modern
catalysis research, which makes them suitable for environmental concerns and
commercially applicable processes. In this regard, the performance of the catalyst
was successfully investigated after magnetic isolation and separation of the catalyst
upon reaction completion for six successive times (Fig. 8). Accordingly, one of the
123

Immobilization of a nickel complex onto functionalized…
Scheme 7 The proposed mechanism of synthesis of 5-substituted-1H-tetrazole derivatives in the
presence of Fe3O4@AMPD@Ni as catalyst
Fig. 8 Reusability of Fe3O4@AMPD@Ni in the oxidation of methylphenylsulfide
123

T. Tamoradi et al.
Table 7 Comparison of Fe3O4@AMPD@Ni for the oxidation of methylphenylsulfide with previously
reported procedure
Entry
Substrate
Catalyst
Time (min)
Yield (%)a
1
2
3
4
5
6
7
8
Methylphenylsulfide
Methylphenylsulfide
Methylphenylsulfide
Methylphenylsulfide
Methylphenylsulfide
Methylphenylsulfide
Methylphenylsulfide
Methylphenylsulfide
Fe3O4-SA-PPCA
VO2F(dmpz)2
DSA@MNPs
NBS
80
300
180
270
240
360
600
9
97 [57]
95 [58]
98 [59]
93 [60]
O(IV)–MCM-41
Mn–ZSM-5
95 [61]
83 [62]
Fe3O4@AMPD
Fe3O4@AMPD@Ni
42 [this work]
97 [this work]
aIsolated yields
outstanding features of this novel nanomagnetic reusable catalyst is the simple,
rapid and efficient separation of the catalyst by means of a magnet, which minimizes
the loss of catalyst using magnetic decantation.
Comparison of catalyst
In continuation of our studies in the introduction of novel and green catalysts, we
compared the results for the oxidation of methylphenylsulfide in the presence of
described catalyst with previously reported catalysts in the literature (Table 7).
Furthermore, the obtained catalyst showed shorter reaction time and better yield
than other catalysts. Also, operation and separation of the catalyst is easier and
faster than the other catalysts. Additionally, in comparison with other catalysts,
cheap and commercially available materials are advantages of this organometallic
catalyst.
Conclusion
Superparamagnetic nanoparticles (MNPs) were synthesized by a chemical copre-
cipitation method and coated with CPTMS by covalent bonds. Afterward, the
surface of magnetic nanoparticles were coated using AMPD ligand to achieve
functionalized magnetic nanoparticles. Then, Fe3O4@AMPD@Ni nanocatalyst was
prepared by coordination of nickel with AMPD supported on Fe3O4 magnetic
nanoparticles. Then, this nanohybrid was carefully characterized by FT-IR, XRD,
TGA, TEM, VSM, SEM, EDX and ICP-OES techniques. High surface area, the use
of commercially available, eco-friendly, cheap and chemically stabile reagents,
good reaction times, operational simplicity, high efficiency, convenient recovery
and ease of use all make Ni(II) immobilized on Fe3O4@AMPD a promising
candidate for potential applications in the synthesis of 5-substituted 1H-tetrazoles
and the oxidation reactions.
123

Immobilization of a nickel complex onto functionalized…
Acknowledgements The authors are deeply grateful to the University of Kurdistan and University of
Ilam for financial support of this research project.
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