Ni(II)-Adenine complex coated Fe3O4 nanoparticles as high reusable nanocatalyst for the synthesis of polyhydroquinoline derivatives and oxidation reactions

Article abstract of DOI:10.1002/aoc.3974

In the present study, Fe₃O₄ nanoparticles were prepared via simple and versatile procedure. Then, a novel and green catalyst was synthesized by the immobilization of Ni on Fe₃O₄ nanoparticles coated with adenine. The activity of this nanostructure compound was examined for the oxidation of sulfides, oxidative coupling of thiols and synthesis of polyhydroquinolines. The prepared catalyst was characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray Diffraction (XRD), thermal gravimetric analysis (TGA), and vibrating sample magnetometer (VSM) measurements. This organometallic catalyst was recovered by the assistance of an external magnetic field from the reaction mixture and reused for seven continuous cycles without noticeable change in its catalytic activity.

Full text of DOI:10.1002/aoc.3974

Received: 8 January 2017
DOI: 10.1002/aoc.3974
Revised: 28 May 2017
Accepted: 17 June 2017
F U L L P A P E R
Ni(II)‐Adenine complex coated Fe3O4 nanoparticles as high
reusable nanocatalyst for the synthesis of
polyhydroquinoline derivatives and oxidation reactions
Taiebeh Tamoradi1
| Mohammad Ghadermazi1 | Arash Ghorbani‐Choghamarani2
1 University of Kurdistan, Department of
Chemistry, Faculty of Science, Sanandaj,
Iran
2 Department of Chemistry, Faculty of
Science, Ilam University, PO Box,
69315516 Ilam, Iran
In the present study, Fe3O4 nanoparticles were prepared via simple and versa-
tile procedure. Then, a novel and green catalyst was synthesized by the immo-
bilization of Ni on Fe3O4 nanoparticles coated with adenine. The activity of this
nanostructure compound was examined for the oxidation of sulfides, oxidative
coupling of thiols and synthesis of polyhydroquinolines. The prepared catalyst
was characterized by Fourier transform infrared spectroscopy (FT‐IR), scanning
electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDS), induc-
tively coupled plasma optical emission spectroscopy (ICP‐OES), X‐ray Diffrac-
tion (XRD), thermal gravimetric analysis (TGA), and vibrating sample
magnetometer (VSM) measurements. This organometallic catalyst was recov-
ered by the assistance of an external magnetic field from the reaction mixture
and reused for seven continuous cycles without noticeable change in its cata-
lytic activity.
Correspondence
Mohammad Ghadermazi, University of
Kurdistan, Department of Chemistry,
Faculty of Science, Sanandaj, Iran.
Email: mghadermazi@yahoo.com
Arash Ghorbani‐Choghamarani,
Department of Chemistry, Faculty of
Science, Ilam University, P.O. Box,
69315516, Ilam, Iran.
Email: arashghch@gmail.com; a.
ghorbani@ilam.ac.ir
Funding information
University of Kurdistan and Ilam
University
KEYWORDS
adenine, Fe3O4, polyhydroquinoline, sulfide, thiol
1 | INTRODUCTION
area, high dispersion resulting in high catalyst loading
capacity, outstanding stability, easy separation of the cat-
The target of science is recently shifted toward preserving
environment, thus catalyst recovery and reusability are
important properties in catalytic processes.[1,2] Homoge-
neous catalysts have complicated recovery process; there-
fore heterogeneous catalysts have been proposed as a
primary solution in catalysis. In general, homogeneous
catalysts can be easily recovered via surface grafting to
heterogeneous supports, such as carbon, metal oxides,
molecular sieves (SBA‐15 and MCM‐41), ionic liquids
and polymers.[3–8] However, during the tedious recycling
in these heterogeneous systems via filtration and the inev-
itable loss of solid in the recovery process, similar prob-
lems are encountered.[9–11] Nowadays, magnetic
nanoparticles (MNPs) are considered as ideal supports
for the heterogenization of homogeneous catalysts sup-
port because of their easy preparation and high surface
alyst through an external magnet, and simple and inex-
pensive procedure.[12–20] In the last few years, several
procedures including various magnetic catalysts have
been reported for the synthesis of polyhydroquinoline
derivatives and oxidation reactions.[21–23] Organic sulfox-
ides are vital in laboratory and are useful in chemical
industries. Selective oxidation of sulfides to sulfoxides
and sulfones under adjusted reaction has been the subject
of various studies for the past two decades because it has
extensive applications for production of organosulfurous
compounds and some medicines.[24–27] Besides,
polyhydroquinoline (PHQ) derivatives are important
compounds because they have emerged as one of the most
important classes of drugs for treatment of cardiovascular
diseases. They are also geroprotective, bronchodilator and
have the ability to modulate calcium channels.[28–32]
Appl Organometal Chem. 2017;e3974.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.3974

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TAMORADI ET AL.
Although a few reagents and catalysts have recently been
reported for these reactions,[33–37] there are major disad-
vantages of these methods such as long reaction times,
operational costs and product purity, low product yields,
difficulty in preparation and/or storage of reagents or cat-
alysts, toxic chemicals and tedious workup. Hence, an
environmentally benign process and development of
new catalysts remains in great demand to overcome these
drawbacks.
Adenine is a nucleobase, and used in synthesis of pro-
tein. This important organic compound as a chemical
component of DNA and RNA is complementary to either
thymine in DNA or uracil in RNA. Adenine and its deriv-
atives have a variety of roles in the central and peripheral
nervous systems and in the immune, anti‐infection, car-
diovascular, renal, musculo‐skeletal systems, agonists
and antagonists. These compounds have an important
role to generate coordination complexes and polymers as
natural multisided ligands.[38–45] In recent years, nickel
compounds have been widely studied because of their
potential applicability in biochemistry and industry.
These compounds has been recognized as catalysts and
widely utilized for the synthesis of polyhydroquinoline
derivatives and oxidation reactions. Recently, there has
coupled plasma optical emission spectrometry (ICP‐
OES). Melting points were recorded by an Electrothermal
9100 apparatus. TEM analysis of the catalyst was recorded
using Zeiss‐EM10C transmission electron microscope.
2.2 | Preparation of the Fe3O4‐adenine
Superparamagnetic nanoparticles (MNPs) were synthe-
sized with chemical coprecipitation method and coated
with 3‐chloropropyltrimethoxysilane (CPTMS) by cova-
lent bonds.[49,50] According to this method, 2.35 g of
FeCl3.6H2O and 0.86 g of FeCl2.4H2O were dissolved in
40 ml deionized water under nitrogen gas with vigorous
stirring at 80 ̊C. Then 5 ml of NH4OH solution was
injected into the reaction mixture and immediately black
precipitate was formed. The black magnetite nanoparti-
cles were separated by magnetic decantation, washed sev-
eral times with deionized hot water and ethanol. Finally,
MNPs were dried in vacuum at 60 ̊C. To prepare Fe3O4‐
Cl, 1 g of MNPs powder was suspended in toluene
(20 ml) and 1.5 ml of CPTMS was added into the reaction
mixture. Then the mixture was refluxed for 24 h. Fe3O4‐Cl
was separated by an external magnet and washed with
hexane and dried at room temperature. Finally, 1 g of
Fe3O4‐Cl powder and 3 ml of triethylamine were added
in toluene (20 ml) then 0.27 g of adenine was added into
the reaction mixture and refluxed for 48 h. The final prod-
uct (Fe3O4‐Adenine) was separated by an external mag-
net, washed with deionized water and ethanol several
times and dried at room temperature.
been considerable effort in the ability of adenine to form
[46–48]
complexes with nickel.
Therefore, our studies have
been done on the synthesis of a magnetically recoverable
nanocatalyst using complex formation of adenine with
nickel.
In the current paper, we report the synthesis of a novel
and magnetically separable nanocatalyst by the immobili-
zation of a Ni complex onto Fe3O4, and successfully dem-
onstrate its application as a heterogeneous catalyst in the
oxidation of sulfides, oxidative coupling of thiols and syn-
thesis of polyhydroquinolines.
2.3 | Preparation of the Ni(II)
immobilized on Fe3O4‐adenine
In this step, Fe3O4‐Adenine was employed as support.
Briefly, Fe3O4‐Adenine (1 g) and Ni(NO3)2.6H2O
(0.727 g) were mixed in 30 ml ethanol, and then the mix-
ture was refluxed for 16 h. The nanosolid Fe3O4‐Adenine‐
Ni was separated from the solution by an external magnet.
Finally, the magnetic catalyst was washed with copious
amounts of ethanol and dried under vacuum at room
temperature.
2 | EXPERIMENTAL
2.1 | Materials
All reagents and solvents are commercially available from
Sigma‐Aldrich and Merck chemical companies and are
used without further purification. The particle size and
morphology were investigated by measuring SEM using
FESEM‐TESCAN MIRA3. VSM measurement was
recorded by a Vibrating Sample Magnetometer (VSM)
MDKFD. TGA was carried out on Shimadzu DTG‐60
instrument. IR spectra were examined by KBr disc using
a VRTEX 70 model BRUKER FT‐IR spectrophotometer.
Powder X‐ray diffraction (XRD) measurements were
investigated using Co Kα radiation (λ = 1.78897 Å nm)
with operating at 40 keV, and a cathode current of
40 Ma. The content of Ni was investigated by inductively
2.4 | General procedure for the oxidation
of sulfides
To a mixture of sulfide (1 mmol) and 33% H2O2 (0.5 mL),
Fe3O4‐Adenine‐Ni (0.005 g) as catalyst was added; and
then the mixture was stirred at room temperature under
solvent‐free condition and the progress of the reaction
was monitored by TLC. Then, Fe3O4‐Adenine‐Ni catalyst
was separated by an external magnet and the product
was extracted with ethyl acetate, and then dried over

TAMORADI ET AL.
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anhydrous Na2SO4. Finally, the solvent was evaporated to
obtain the pure products.
3.2 | Catalyst characterization
The morphology of the Fe3O4, Fe3O4‐Adenine, Fe3O4‐
Adenine‐Ni catalyst and recovered catalyst were obtained
using scanning electron microscopy (SEM) technique.
SEM images of these nanoparticles are given in Figure 1.
As shown in this figure, the synthesized materials were
formed with uniform nanometer‐sized particles. It should
be mentioned that the prepared samples were obtained
with approximately spherical shape.
2.5 | General procedure for the oxidation
of thiols to disulfides
Fe3O4‐Adenine‐Ni (0.005 g) was added to a mixture of sul-
fides (1 mmol) and H2O2 (0.5 ml) under solvent‐free con-
ditions with stirring at room temperature. After
completion of the reaction (monitored using TLC), the
catalyst was separated by applying an external magnet.
In order to observe the kinds of elements in Fe3O4‐
Adenine‐Ni, the energy‐dispersive X‐ray spectroscopy
(EDS) analysis of Fe3O4‐Adenine‐Ni was performed;
which EDS patterns of this catalyst shows the presence
of Fe, O, Si, N, C and Ni specie in the catalyst (Figure 2).
Also, in order to determine the exact amount of Ni loaded
on modified magnetic nanoparticles, ICP‐OES analysis
2.6 | General procedure for the synthesis
of Polyhydroquinolines
Fe3O4‐Adenine‐Ni as catalyst (0.05 g) was added to a mix-
ture of dimedone (1 mmol), aldehyde (1 mmol), ethyl
acetoacetate (1 mmol), and ammonium acetate (1.2 mmol)
in ethanol (2 ml) as solvent. Then the mixture was stirred
was performed and it was found to be 0.35 mmol g−1
.
Figure 3 shows TEM image of Fe3O4‐Adenine‐Ni
nanocatalyst. This study showed particle size of approxi-
mately 10–30 nm for the synthesized catalyst.
for the appropriate time at 80 ̊C, and the progress of the
reaction was monitored by TLC. Finally, the catalyst was
separated by an external magnet and solvent was evapo-
rated. A crude solid was obtained and the pure product
was prepared through crystallization from ethanol.
Quantitative determination of the organic groups sup-
ported on the surface of Fe3O4 magnetic nanoparticles
was investigated by thermo‐gravimetric analysis (TGA)
(Figure 4). The TGA curve shows a small amount of
weight loss (about 2%) below 200 °C that is due to removal
of hydroxyl groups and adsorbed solvents.[53] In the all
samples, the first step of weight loss below 200 °C corre-
sponds to the removal of the physically and chemically
adsorbed solvents or surface hydroxyl groups, and the
other weight loss in the range of 250–650 °C is related to
the decomposition of the organic layers on the surface of
Fe3O4 magnetic nanoparticles.[54] TGA curve of the
Fe3O4‐Adenine‐Ni shows a weight loss of about 16% from
250 to 650 °C, resulting from the decomposition of
immobilized organic spaces on the Fe3O4 surface. Mean-
while, weight loss of about 17% from 250 to 650 °C is
observed for Fe3O4‐Adenine.
3 | RESULTS AND DISCUSSION
3.1 | Catalyst preparation
Scheme 1 illustrates the preparation of a novel magnetic
nanoparticle catalyst. Fe3O4 nanoparticle was prepared
according to our recently reported procedure.[51,52]
Briefly, the surface of magnetic nanoparticles were coated
using adenine ligand to achieve functionalized magnetic
nanoparticles. Then, Fe3O4‐Adenine‐Ni nanocatalyst was
prepared using stable interaction between the N7 atom
of adenine and Ni2+ [45]
.
SCHEME 1 Synthesis of Fe3O4‐
Adenine‐Ni nanocatalyst

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TAMORADI ET AL.
FIGURE 1 SEM images of Fe3O4 (a),
Fe3O4‐Adenine (b), Fe3O4‐Adenine‐Ni
catalyst (c, d) at different magnifications
and recovered Fe3O4‐Adenine‐Ni catalyst
(e)
The X‐ray diffraction analysis (XRD) pattern of Fe3O4‐
measurements for Fe3O4 nanoparticles (77 emu g−1 [55]
)
Adenine and Fe3O4‐Adenine‐Ni are shown in Figure 5 in
which the Fe3O4 phase was identified by the peak posi-
tions of 2θ values at 35.69, 41.72, 51.05, 63.91, 67.94 and
74.83 which is in agreement with standard XRD pattern
of Fe3O4 nanoparticles.[53] Also, the XRD pattern of cata-
lyst shows that the Fe3O4 phase has not been changed
during the modifications.
The magnetic property of Fe3O4‐Adenine‐Ni has been
compared with bare Fe3O4 nanoparticles using vibrating
sample magnetometer (VSM) technique (Figure 6). VSM
is higher than Fe3O4‐Adenine‐Ni (57.31 emu g−1).
Decrease in magnetic property of Fe3O4‐Adenine‐Ni is
due to the grafting of organic layers and nickel complex
on Fe3O4 nanoparticles.[56] On the basis of VSM results,
the well grafting of organic layers including nickel com-
plex on the Fe3O4 is verified.
FT‐IR spectra for bare Fe3O4 nanoparticles, Fe3O4‐Cl,
Fe3O4‐Adenine and Fe3O4‐Adenine‐Ni are shown in
Figure 7. FT‐IR spectrum of Fe3O4 nanoparticles (Spec-
trum a) shows a stretching vibration at 3401 and 579 cm

TAMORADI ET AL.
5 of 11
FIGURE 4 The TGA diagrams of Fe3O4 nanoparticles (a), Fe3O4‐
Adenine (b) and Fe3O4‐Adenine‐Ni (c)
FIGURE 2 EDX spectrum of Fe3O4‐Adenine‐Ni
FIGURE 5 The XRD pattern of Fe3O4 (blue), Fe3O4‐Adenine
(red) and Fe3O4‐Adenine‐Ni catalyst (green)
FIGURE 6 Magnetization curves for Fe3O4‐Adenine‐Ni at room
temperature
−1
which incorporates the contributions from both sym-
metrical and asymmetrical modes of the surface hydroxyl
groups and Fe‐O bonds of iron oxide, respectively.[57] In
FT‐IR spectra of Fe3O4‐Cl (spectrum b), the presence of
the anchored (3‐choloropropyl) trimethoxysilane is identi-
fied by C–H stretching vibrations that appear at 2974 cm
−1
and also O–Si stretching vibration modes that appear
at 1009 and 1070 cm−1 [58]
.
In the FT‐IR spectra of
FIGURE 3 TEM images of Fe3O4‐Adenine‐Ni catalyst at different
Fe3O4‐Adenine (spectrum c), stretching vibrations of
magnifications (a, b)

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TAMORADI ET AL.
C = C and C = N has been identified by adsorption bands
at 1306–1418 and 1603–1667 cm−1. All of those bands
reveal that the surface of Fe3O4 nanoparticles is success-
fully modified with organic layers.
3.3 | Catalytic studies
In this research, our studies were directed towards the
outreach of practical and eco‐friendly procedures for
chemical synthesis.[59,60] We developed the preparation
of a stable, recyclable and efficient Fe3O4‐Adenine‐Ni
nanocatalyst. The catalytic activity of this nanocatalyst
was examined with excellent activity in oxidation of sul-
fides to sulfoxides (Scheme 2), oxidative coupling of thiols
into disulfides (Scheme 3) and synthesis of
polyhydroquinoline derivatives (Scheme 6). In order to
optimize the reaction conditions, methylphenylsulfoxide
was prepared as a model compound in various solvents
in the presence of different amount of catalyst and using
different amount of hydrogen peroxide (H2O2). The
results can be seen in Table 1. As shown in Table 1, the
solvent‐free condition in the presence of Fe3O4‐Adenine‐
Ni (0.005 gr) and H2O2 (0.5 ml) at room temperature
was found to be ideal reaction conditions for the conver-
FIGURE 7 FT‐IR spectrum for bare Fe3O4 nanoparticles (a),
Fe3O4‐Cl (b), Fe3O4‐Adenine (c) and Fe3O4‐Adenine‐Ni (d)
sion
of
methylphenylsulfide
to
the
methylphenylsulfoxide.
In this study, a variety of sulfides with different func-
tional groups were successfully employed to prepare the
corresponding sulfoxides in high to excellent yields in a
short reaction time. The results are shown in Table 2.
A plausible reaction mechanism for the oxidation of
sulfides is shown in Scheme 4. The intermediate A is
obtained by reaction of H2O2 with Fe3O4‐Adenine‐Ni,
which is converted to active oxidant B. Then, nucleophilic
attack of the sulfide on this intermediate (C1) produces
corresponding sulfoxide.[61]
SCHEME 2 Fe3O4‐Adenine‐Ni catalyzed the oxidation of sulfides
to sulfoxides
In continuation of this research work, the catalytic
activity of Ni‐Adenine complex in comparison with
Fe3O4‐Adenine‐Ni investigated for the conversion of
SCHEME 3 Proposed mechanism for oxidation of sulfides in
presence of Fe3O4‐Adenine‐Ni as catalyst
TABLE 1 Optimization of oxidation of sulfides to the corresponding sulfoxides using Fe3O4‐adenine‐Ni nanoparticles under various
conditions
Entry
Solvent
H2O2
Catalyst (mg)
Time (min)
Yield (%)a
1
Solvent‐Free
0.5
3
80
78
2
3
4
5
6
7
Solvent‐Free
Solvent‐Free
Solvent‐Free
Ethanol
0.5
0.5
0.4
0.5
0.5
0.5
4
5
5
5
5
5
70
55
75
70
85
95
85
98
93
90
88
83
Ethyl acetate
Acetonitrile
aIsolated yields.

TAMORADI ET AL.
7 of 11
TABLE 2 Oxidation of sulfides to the sulfoxides in the presence of Fe3O4‐Adenine‐Ni
Entry
Substrate
Product
Time (min)
Yield (%)a
M.p. (°C)
1
Dipropylsulfide
2a
65
95
Oil
2
Diethylsulfide
2b
2c
2d
2e
2f
60
30
90
12
85
55
65
70
65
96
95
97
98
95
98
94
97
94
Oil
3
Dibenzylsulfide
128–129
115–117
Oil
4
Benzylphenylsulfide
Tetrahydrothiophene
Dodecyl methylsulfide
Methylphenylsulfide
Ethylphenylsulfide
2‐(Methylthio)ethanol
2‐(Phenylthio)ethanol
5
6
63–65
Oil
7
2 g
2 h
2i
8
Oil
9
Oil
10
2j
Oil
aIsolated yields.
peroxide (H2O2) (Table 4). As shown in Table 4, Fe3O4‐
Adenine‐Ni (0.005 g) in the presence of H2O2 (0.5 ml) in
ethanol at room temperature was found to be the ideal
reaction conditions for the oxidative coupling of 4‐
methylbenzenethiol.
As shown in Table 5, a wide range of thiols with differ-
ent functional groups were converted to their correspond-
ing products in the presence of Fe3O4‐Adenine‐Ni as
catalyst in ethanol at room temperature. All products
were prepared in the short reaction time and in good to
excellent yields.
The proposed mechanism for this process using H2O2
as oxidant in the presence Fe3O4‐Adenine‐Ni catalyst is
outlined in Scheme 5.[50]
SCHEME 4 Fe3O4‐Adenine‐Ni catalyzed the oxidative coupling
of thiols into disulfides
We finally studied the synthesis of polyhydroquinoline
derivatives. In order to optimize the reaction conditions,
we examined the reaction of 4‐chlorobenzaldehyde
(1 mmol), dimedone (1 mmol), ethyl acetoacetate
(1 mmol) and ammonium acetate (1.2 mmol) as a model
methylphenylsulfide to the methylphenylsulfoxide under
optimized conditions (Table 3). The results of this com-
parison show that the products were obtained in 97 and
98% yield in the presence of Ni‐Adenine complex and
Fe3O4‐Adenine‐Ni, respectively. Therefore to make an
easily recoverable and efficient catalyst, the Ni‐Adenine
complex has been anchored on Fe3O4 nanoparticles. It
should be mentioned that the Ni content of Ni‐Adenine
reaction
to
synthesize
the
corresponding
polyhydroquinoline. The effect of various parameters
such as solvent, catalyst concentration and temperature
was investigated for the model reaction. The reaction con-
ditions for the one‐pot synthesis of polyhydroquinoline
derivatives were carried out for above mentioned reaction
in EtOH, H2O and PEG as solvents. As shown in Table 6,
Fe3O4‐Adenine‐Ni is much more reactive in EtOH
complex was found to be 0.65 mmol g−1
.
Also we examined the oxidative coupling of 4‐
methylbenzenethiol as a model substrate in various
solvents and in the presence of different amount of
Fe3O4‐Adenine‐Ni using different amount of hydrogen
TABLE 3 Effect of Ni‐Adenine complex in comparison with Fe3O4‐Adenine‐Ni in oxidation of methylphenylsulfide as model compound
under optimized conditions
Entry
Substrate
Catalyst
Time (min)
Yield (%)a
1
Methylphenylsulfide
Ni‐Adenine complex
60
97
2
Methylphenylsulfide
Fe3O4‐adenine‐Ni
55
98 [this work]
aIsolated yields.

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TAMORADI ET AL.
TABLE 4 Optimization of oxidative coupling of thiols into disulfides using Fe3O4‐Adenine‐Ni under various conditions
Entry
Solvent
H2O2
Catalyst (mg)
Time (min)
Yield (%)a
1
EtOH
0.5
3
85
78
2
3
4
5
6
7
EtOH
0.5
0.5
0.4
0.5
0.5
0.5
4
5
5
5
5
5
70
70
85
75
95
110
79
97
90
96
88
79
EtOH
EtOH
Solvent‐free
Ethyl acetate
Acetonitrile
aIsolated yields.
TABLE 5 Oxidative coupling of thiols into disulfides using H2O2 in the presence of Fe3O4‐adenine‐Ni
Entry
Substrate
Product
Time (min)
Yield (%)a
M.p. (°C)
1
Phenylmethanethiol
4a
85
90
57–59
2
4‐Methylbenzenethiol
Naphthalene‐2‐thiol
2‐Mercaptobenzoic acid
Benzo[d]thiazole‐2‐thiol
2‐Mercaptoethanol
4b
4c
4d
4e
4f
70
55
90
48
25
45
80
35
70
97
91
87
96
93
93
95
93
87
38–40
134–136
275–278
174–175
Oil
3
4
5
6
7
2‐Mercaptoacetic acid
4‐Bromothiophenol
4 g
4 h
4i
Oil
8
88–90
94–96
55–57
9
Benzo[d]oxazole‐2‐thiol
2‐Mercaptopyridine
10
4j
aIsolated yields.
in the presence of 50 mg of catalyst. The reaction temper-
ature was also optimized and 80 °C was chosen as reac-
tion temperature. The results of this study can be seen in
Table 6.
Finally, a variety of aromatic and aliphatic aldehydes
were employed to synthesis the corresponding
polyhydroquinoline derivatives in high to excellent yields
in a short time (Table 7 and Scheme 6).
A plausible reaction mechanism for the synthesis of
polyhydroquinoline derivatives in the presence of Fe3O4‐
Adenine‐Ni as catalyst is shown in Scheme 7. As shown
in this scheme, the role of catalyst comes in the
Knoevenagel coupling of aldehydes with active methylene
compounds to produce an α, β‐unsaturated compound
and in the Michael addition of intermediates to obtain
the polyhydroquinoline.[62]
SCHEME 5 Proposed mechanism for oxidative coupling of thiols
in presence of Fe3O4‐Adenine‐Ni as catalyst
compared with H2O and PEG. Moreover, this reaction
was optimized under the influence of different amounts
of Fe3O4‐Adenine‐Ni as a reusable nanocatalyst in EtOH.
We observed that the best results were obtained in EtOH
SCHEME 6 Fe3O4‐Adenine‐Ni
catalyzed the one‐pot synthesis of
polyhydroquinoline derivatives

TAMORADI ET AL.
9 of 11
TABLE 6 Optimization of amount of catalyst, solvent and tem-
perature for the synthesis of polyhydroquinolines via the conden-
sation of 4‐chlorobenzaldehyde (1 mmol), dimedon (1 mmol), ethyl
acetoacetate (1 mmol) and ammonium acetate (1.2 mmol) as a
model reaction at 80 °C
Catalyst Temperature Time
Yield
Entry Solvent (mg)
(°C)
(min) (%)a
1
2
3
4
5
6
EtOH
EtOH
EtOH
EtOH
PEG
30
40
50
50
50
50
80
230
165
145
195
350
320
83
87
96
91
83
87
80
80
40
80
80
SCHEME
7
The proposed mechanism of synthesis of
H2O
polyhydroquinoline derivatives in presence of Fe3O4‐Adenine‐Ni
aIsolated yields.
as catalyst
3.4 | Recyclability of the catalyst
The reusability of magnetic catalysts is one of their note-
worthy advantages, which makes them useful for envi-
ronmental concerns and commercially applicable
processes. In this study, the reusability of Fe3O4‐Ade-
nine‐Ni catalyst was investigated after completion of the
reaction. Fe3O4‐Adenine‐Ni catalyst could be easily sepa-
rated using application of an external magnet then
washed with ethanol and double distilled water. As
shown in Figure 8, this catalyst was recycled and reused
at least for seven consecutive cycles without considerable
decrease of its catalytic activity. Since leaching of nickel
from Fe3O4‐Adenine‐Ni is very negligible for these reac-
tions, the catalytic activity has been slightly decreased.
Also, in order to determine the exact amount of Ni loaded
on modified magnetic nanoparticles for the conversion of
methylphenylsulfide to the methylphenylsulfoxide at
least for seven consecutive cycles, ICP‐OES analysis was
FIGURE 8 Reusability of Fe3O4‐Adenine‐Ni in the oxidation of
methyl phenyl sulfide (blue column), coupling of 4‐
methylthiophenol (red column) and condensation of 4‐
chlorobenzaldehyde, dimedone, ethylacetoacetate and ammonium
acetate (green column)
found to be 0.34 mmol g−1
.
TABLE 7 Synthesis of various polyhydroquinolines in the presence of Fe3O4‐Adenine‐Ni (50 mg) under the standard reaction conditions
Entry
Aldehyde
Product
Time (min)
Yield (%)a
M.p. (°C)
1
Benzaldehyde
6a
165
91
217–219
2
4‐Bromobenzaldehyde
4‐Methylbenzaldehyde
4‐Chlorobenzaldehyde
4‐Fluorobenzaldehyde
4‐Methoxybenzaldehyde
4‐Hydroxybenzaldehyde
3‐Nitrobenzaldehydel
3,4‐Di(methoxy)benzaldehyde
Isobutyraldehyde
6b
6c
6d
6e
6f
205
195
145
160
235
195
210
255
230
95
97
96
97
96
91
93
93
91
251–253
250–253
148–150
183–185
248–250
226–228
176–179
203–205
162–163
3
4
5
6
7
6 g
6 h
6i
8
9
10
6j
aIsolated yields.

10 of 11
TAMORADI ET AL.
TABLE 8 Comparison of Fe3O4‐Adenine‐Ni for the oxidation of methylphenylsulfide with previously reported procedure
Entry
Substrate
Catalyst
Time (min)
Yield (%)a
[63]
1
Methylphenylsulfide
Ni‐salen‐MCM‐41
156
95
[64]
2
3
4
5
6
7
Methylphenylsulfide
Methylphenylsulfide
Methylphenylsulfide
Methylphenylsulfide
Methylphenylsulfide
Methylphenylsulfide
VO2F(dmpz)2
VO‐2A3HP‐MCM‐41
NBS
300
120
270
300
360
55
95
[65]
96
93[66]
[67]
Zr‐oxide@MCM‐41
DSA@MNPs
98
[68]
98
Fe3O4‐Adenine‐Ni
98 [this work]
aIsolated yields.
Arash Ghorbani‐Choghamarani
0002-7212-1317
http://orcid.org/0000-
3.5 | Comparison of the catalyst
In order to evaluate the efficiency of Fe3O4‐Adenine‐Ni
nanocatalyst, we compared the results for the oxidation
of sulfides in the presence of described catalyst with previ-
ously reported catalysts in the literature (Table 8). The
results of this research project verified short reaction time
and higher yield than the other catalysts. Furthermore,
compared with other catalysts, ease of operation, simple
and inexpensive procedure, easy separation of the catalyst
through an external magnet, non‐toxicity and low cost are
several advantages of this organometallic catalyst.
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How to cite this article: Tamoradi T,
Ghadermazi M, Ghorbani‐Choghamarani A. Ni(II)‐
adenine complex coated Fe3O4 nanoparticles as
high reusable nanocatalyst for the synthesis of
polyhydroquinoline derivatives and oxidation
reactions. Appl Organometal Chem. 2017;e3974.
https://doi.org/10.1002/aoc.3974
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