Nickel(II) Schiff base complex supported on nano-titanium dioxide: A novel straightforward route for preparation of supported Schiff base complexes applying 2,4-toluenediisocyanate

Article abstract of DOI:10.1002/aoc.4956

For the first time, a novel, straightforward and inexpensive route for immobilization of metals in Schiff base complex form is reported applying 2,4-toluenediisocyanate as a precursor of primary amine group. A nickel(II) Schiff base complex supported on nano-TiO₂ was designed and synthesized as an effective heterogeneous nanocatalyst for organic reactions, and well characterized using various techniques such as Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray analysis and thermogravimetric analysis. The catalytic efficiency of the complex was evaluated in selective oxidation of sulfide to sulfoxide by hydrogen peroxide as an oxidant under solvent-free conditions at room temperature, which successfully resulted in high yield and high conversion of products. Effective factors including solvent type, oxidant and catalyst amount were also optimized. The catalyst shows outstanding reusability and could be impressively recovered for six consecutive cycles without significant change of its catalytic efficiency.

Full text of DOI:10.1002/aoc.4956

Received: 10 January 2019
DOI: 10.1002/aoc.4956
Revised: 10 March 2019
Accepted: 23 March 2019
F U L L P A P E R
Nickel(II) Schiff base complex supported on nano‐titanium
dioxide: A novel straightforward route for preparation of
supported Schiff base complexes applying 2,4‐
toluenediisocyanate
Ali Amoozadeh
| Elham Tabrizian
| Saeedeh Shahjoee
Department of Organic Chemistry,
Faculty of Chemistry, Semnan University,
Semnan 35131‐19111, Iran
For the first time, a novel, straightforward and inexpensive route for immobi-
lization of metals in Schiff base complex form is reported applying 2,4‐
toluenediisocyanate as a precursor of primary amine group. A nickel(II) Schiff
base complex supported on nano‐TiO2 was designed and synthesized as an
effective heterogeneous nanocatalyst for organic reactions, and well character-
ized using various techniques such as Fourier transform infrared spectroscopy,
field emission scanning electron microscopy, transmission electron micros-
copy, X‐ray diffraction, energy‐dispersive X‐ray analysis and thermogravimetric
analysis. The catalytic efficiency of the complex was evaluated in selective oxi-
dation of sulfide to sulfoxide by hydrogen peroxide as an oxidant under
solvent‐free conditions at room temperature, which successfully resulted in
high yield and high conversion of products. Effective factors including solvent
type, oxidant and catalyst amount were also optimized. The catalyst shows out-
standing reusability and could be impressively recovered for six consecutive
cycles without significant change of its catalytic efficiency.
Correspondence
A. Amoozadeh, Department of Organic
Chemistry, Faculty of Chemistry, Semnan
University, Semnan 35131‐19111, Iran.
Email: aamozadeh@semnan.ac.ir
Funding information
Faculty of Chemistry of Semnan
University
KEYWORDS
heterogeneous nanocatalyst, nano metal oxides, Schiff base complexes, 2,4‐toluenediisocyanate,
oxidation
1 | INTRODUCTION
and (3) costly recycling of these homogeneous systems.[8]
So, for improving the efficiency of their catalytic activity
Schiff base ligands and their corresponding metal com-
plexes have gained significant attention.[1–5] Schiff bases
have played a main role in the development of coordina-
tion chemistry,[6,7] as they form stable complexes simply
with most of the transition metals and can stabilize a wide
variety of metals in various oxidation states, therefore con-
trolling their performances. Schiff base complexes are
often used as efficient homogeneous catalysts in a wide
range of catalytic transformations like oxidation reac-
tions;[3] however, some problems often occur in these types
of oxidations, such as (1) catalyst deactivation, (2) frailty
and ease of separation from reaction media, scientists have
tried to convert them into heterogeneous systems in
various ways. In this light, several methods can be used,
such as: (1) linking onto metal oxides such as silica,
Fe3O4 and so on,[9–11] (2) immobilizing on organic sup-
ports like graphene oxide[12,13] and carbon nanotubes,[14]
(3) copolymerizing and incorporating into an organic
polymer like chitosan or porous polydivinylbenzene[15–19]
and (4) encapsulating in various zeolites.[20–22]
Organosulfur compounds such as sulfoxides and
sulfones are very important compounds in organic
Appl Organometal Chem. 2019;e4956.
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© 2019 John Wiley & Sons, Ltd.
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AMOOZADEH ET AL.
chemistry.[23] In particular, sulfoxides are good chemicals,
medicine and valuable intermediates in the synthesis of
advantageous chemically and biologically active mole-
cules.[24] Various types of oxidants have been used for the
oxidation reaction of sulfides. Because of high cost,
formation of by‐products and low amount of reactive and
efficacious oxygen, most of the oxidants used are not
adequate for large‐scale synthesis. Among them, aqueous
hydrogen peroxide (H2O2) is the most attractive one, as it
is both environmentally safe and economical.[25] Further-
more, being inexpensive, readily available, having high
atom efficiency and generating water as the only
by‐product are advantageous properties of hydrogen
peroxide over other oxidants.[26]
2.2 | Preparation of nano‐TiO2
The TiO2 nanoparticles were synthesized by a hydrother-
mal method.[35] At first, NH3⋅H2O was added dropwise to
TiCl4 solution until a pH value of 1.8 was obtained. Then
the mixture was stirred and heated at 70°C for 2 h to a
final pH of 6. Thereupon, the mixture was kept at ambi-
ent temperature for 24 h, filtered and washed with
NH4Ac–HOAc. This was continued until no Cl− was
observed. The mixture was centrifuged and the precipi-
tate was obtained. Finally, it was washed with ethanol
and dried in vacuum and, after 2 h treatment at 650°C,
nano‐TiO2 was obtained.
In continuation of our efforts towards expanding the
application of 2,4‐toluenediisocyanate (TDI) in heteroge-
neous catalyst synthesis,[27–34] in the work reported in
this paper, for the first time, we successfully synthesized
a novel nickel(II) Schiff base complex, applying TDI as
a covalently bound linker and precursor of amine groups
immobilized on nano‐titania support. TDI is highly
accessible, of low cost and very active due to its reactive
unsaturated bonds and was used as a bridge between
the surface of nano‐titania and nickel(II) ion to improve
the recyclability and life span of the inorganic–organic
hybrid catalyst. Moreover, the catalytic performance of
the complex was studied in the selective oxidation of
sulfides to sulfoxides using H2O2 as green oxidant.
2.3 | Functionalization of TiO2
nanoparticles with TDI (nano‐TiO2‐NCO)
Nano‐TiO2‐NCO was prepared following a reported
procedure.[36] At first, 1.0 g of TiO2 nanoparticles and
1.40 g of TDI were dispersed in 50 ml of dried toluene.
After that, the mixture was placed in an ultrasonic bath
for 10–15 min. Then, the reaction was heated for 6 h at
95°C under magnetic stirring and an atmosphere of nitro-
gen. In order to remove the unreacted and physically
absorbed TDI, the powder was washed with dried toluene
several times and collection of the powder product was
achieved using centrifugation. Finally, the product was
dried in an oven at 80°C for 24 h.
2.4 | Preparation of amine‐functionalized
nano‐TiO2 (nano‐TiO2‐NH2)
2 | EXPERIMENTAL
2.1 | Materials and instrumentation
An amount of 1.0 g of nano‐TiO2‐NCO was dispersed in
50 ml of water–acetone at a mass ratio of 1:1. The mixture
was held at 30°C using a thermostatically controlled
water bath and stirred for 2 h. The final precipitate was
centrifuged to separate the solid and washed with acetone
and then dried at 110°C in an oven to afford a powder
product.[32]
All chemicals and solvents were purchased from Merck
or Aldrich. Industrial‐grade TDI with 80:20 mixture of
2,4‐ and 2,6‐isomers and was used as received. TLC with
silica gel 60 F245 was used to monitor the completeness
and progress of the reaction using nano‐hexane–ethyl
acetate as mobile phase. Fourier transform infrared
(FT‐IR) spectra (KBr pellets) were recorded with a
Shimadzu FT/IR‐8400 instrument. Powder X‐ray diffrac-
tion (XRD) data were obtained with a D5000 (Siemens
AG, Munich, Germany) using Cu Kα radiation at a wave-
length of 1.54 Å. Field emission scanning electron micros-
copy (SEM) and transmission electron microscopy (TEM)
images were obtained with a Philips XL30 instrument
(Royal Philips Electronics, Amsterdam, The Netherlands)
and a Philips EM 208S, respectively. Thermogravimetric
analysis (TGA) was performed with a DuPont 2000 ther-
mal analysis system at a heating rate of 10°C min−1 under
an air atmosphere.
2.5 | Preparation of Schiff
base‐functionalized nano‐TiO2 (nano‐TiO2‐
SA)
Salicylaldehyde (0.9 g) was added dropwise to a solution
of nano‐TiO2‐NH2 (1.0 g) dispersed in 50 ml of ethanol.
The mixture was reflux for 48 h at 70°C to obtain the
imine product. The resulting Schiff base ligand, as a
bright yellow precipitate, was separated by centrifugation
and washed with ethanol and then dried in an oven at
80°C to afford a powder product.

AMOOZADEH ET AL.
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efficient and recyclable nanocatalyst. For the first time,
TDI was employed as a precursor of amine groups for
preparation of the Schiff base ligand.
2.6 | General procedure for preparation of
Ni(II) Schiff base complex (nano‐TiO2‐SA‐
Ni(II))
The concise route for the preparation of the
nanocatalyst is outlined in Scheme 1. After synthesis of
nano‐TiO2 (by hydrothermal method), TiO2 nanoparti-
cles were reacted with TDI. Due to the presence of steric
hindrance in the TDI molecule[38] and therefore various
reactivity of the two isocyanate groups, para‐isocyanate
group of TDI was reacted with accessible surface hydroxyl
of nano‐TiO2 to form urethane bond[39,40] and left an
ortho‐isocyanate group unreacted which was changed to
amine by treating it with water. Next, salicylaldehyde
underwent a condensation reaction with the prepared
amine to afford the Schiff base ligand. The Schiff base
was then treated with a solution of Ni(NO3)2 under reflux
conditions to afford the supported complex. The structure
of nano‐TiO2‐SA‐Ni(II) as a heterogeneous nanocatalyst
was studied and identified using FT‐IR spectroscopy,
TGA, SEM, TEM, XRD and energy‐dispersive X‐ray
(EDX) analysis.
To a solution of the Schiff base ligand (1.0 g) in ethanol
(50 ml), nickel nitrate salt (1.0 g) was added and the
mixture was refluxed for 48 h to complete the reaction.
After the completion of complex formation, a colour
change was observed. Resulting product was centrifuged
and washed several times with ethanol and dried at
80°C in an oven to afford the product.
2.7 | General procedure for recycling of
nano‐TiO2‐SA‐Ni(II)
Reusability of the nanocatalyst was investigated in the
oxidation of methylphenyl sulfide under optimized condi-
tions. After the reaction was complete, the catalyst was
separated via centrifugation and washed with ether
(2 × 5 ml) and acetone (2 × 5 ml) and dried at 70°C for
1 h to be reused in the next cycle.
3 | RESULTS AND DISCUSSION
3.1 | Characterization of nano‐TiO2‐SA‐
Ni(II)
In continuation of our current programmes for the pro-
curement of novel heterogeneous catalysts for organic
reactions by applying TDI,[27–34,37] we report the synthe-
sis and application of Ni(II)–Schiff base complex sup-
ported on nano‐TiO2 (nano‐TiO2‐SA‐Ni(II)) as a novel,
3.1.1 | FT‐IR spectra
In order to verify the immobilization of functional groups
on nano‐TiO2 surface, FT‐IR spectra of the nano‐TiO2
SCHEME 1 Preparation of Ni(II) Schiff base complex supported on nano‐titania

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AMOOZADEH ET AL.
and product of every step of the synthesis reaction were
analysed (Figure 1). The FT‐IR spectrum of nano‐TiO2
(Figure 1a) exhibited strong characteristic bands at 1623
and 3355 cm−1, attributed to the surface hydroxyl groups
of TiO2 and the broad peak below 1200 cm−1 is assigned
to Ti─O─Ti.[41] The FT‐IR spectrum of TDI (Figure 1b)
shows an absorption peak at 2243 cm−1 owing to
stretching vibration of NCO, which is the main character-
istic peak, and the peak at 1550 cm−1 is attributed to the
phenyl ring of TDI.[42] On comparing the FT‐IR spectra
of TiO2 (Figure 1a) and nano‐TiO2‐NCO (Figure 1c), four
new additional peaks appeared in the latter at 2266,
1649, 1595 and 1533 cm−1, respectively. The peak at
2266 cm−1 can be ascribed to the unreacted
ortho‐isocyanate groups of TDI attached to the nano‐
TiO2 surface, while the bands at 1649 and 1595 cm−1
can be assigned to the C═O and C─N stretches indicating
the formation of a urethane bond (OCONH)[43] through
the reaction of TDI with titania, and the peak at
1553 cm−1 is attributed to the phenyl ring of TDI. These
results obviously confirmed that TDI had reacted chemi-
cally with nano‐TiO2. According to Figure 1d, using
water, the peak at 2266 cm−1 in Figure 1c disappeared
and changed to an amine group band which is overlapped
with N─H band of urethane bond at 3267 cm−1. Schiff
base reaction of nano‐TiO2‐NH2 with salicylaldehyde
produces nano‐TiO2‐SA (Figure 1e), in which the pres-
ence of (C═N) is indicated by the absorptions in the range
1632–1639 cm−1 and phenolic C─O is indicated by the
absorption peak at 1220 cm−1. As shown in Figure 1f,
on formation of the complex between ligand and Ni
metal, the (C═N) band at 1632 cm−1 is shifted to lower
frequency and appears at 1617 cm−1 due to the
coordination of nitrogen with nickel.[44] Bands in the
range 1480–1600 cm−1 are attributed to the aromatic
rings. Accordingly, the FT‐IR spectra confirm the success-
ful immobilization of Ni(II) on nano‐TiO2.
3.1.2 | Thermogravimetric analysis
TGA is a method that allows us to investigate the bond
formation between inorganic TiO2 and organic
chemicals. Figure 2 shows the TGA curves of nano‐TiO2
and nano‐TiO2‐SA‐Ni(II) in temperature range
30–800°C. As shown in Figure 2a, the nano‐TiO2 exhib-
ited weight losses below 100°C due to the physically
adsorbed water and then had slight weight loss (1 wt%)
between 100 and 800°C, which could be attributed to
the dehydroxylation of nano‐TiO2 according to the litera-
ture.[45] Figure 2b shows the TGA curve for the as‐
prepared Ni(II) Schiff base complex, presenting several
weight losses from 100 to 600°C. The (10 wt%) weight loss
below 220°C was is due to the loss of adsorbed water and
organic solvents. The (12 wt%) weight loss at 220–301°C
is mainly related to TDI.[36,46] Weight loss (6 wt%) in
the range 301–660°C is attributed to the decomposition
of both TDI[46] and salicylaldehyde group.[47–49] On the
basis of the results obtained, the good grafting of TDI
and Ni(II) complex is verified.
FIGURE 1 FT‐IR spectra of (a) nano‐TiO2, (b) TDI, (c) nano‐
TiO2‐NCO, (d) nano‐TiO2‐NH2, (e) nano‐TiO2‐SA and (f) nano‐
TiO2‐SA‐Ni(II)
FIGURE 2 TGA curves of (a) nano‐TiO2 and (b) nano‐TiO2‐SA‐
Ni(II)

AMOOZADEH ET AL.
5 of 9
corresponding anatase TiO2 nanoparticles with the
documented XRD data of anatase TiO2 (JCPD card
number 89‐4921). The diffraction patterns and position
of the sets of characteristic peaks were also observed for
nano‐TiO2‐SA‐Ni(II), indicating the stability of the crys-
talline phase of TiO2 nanoparticles during the formation
of the complex. Furthermore, the average sizes of TiO2
and nano‐TiO2‐SA‐Ni(II) nanoparticles were estimated
at about 21.88 and 25.48 nm, respectively, using the
Debye–Scherrer equation, D = kh/βcos θ, where k is a
constant (generally considered as 0.94), h is the wave-
length of Cu Kα (1.54 Å), β is the corrected diffraction line
full width at half maximum and θ is the Bragg angle.[50]
3.1.3 | Field emission scanning electron
microscopy
The morphology and particle size of nano‐TiO2‐SA‐Ni(II)
were investigated using SEM. According to Figure 3,
nano‐TiO2‐NH2 exhibits particles of a spherical shape
(Figure 3b), similar to the morphology of pristine
nano‐TiO2 (Figure 3a), indicating that nano‐TiO2 was
not deformed significantly after grafting of organic mole-
cules. Such spherical‐shaped structure of nano‐TiO2‐NH2
is highly beneficial due to its high active surface area for
anchoring other molecules. The observed SEM image of
nano‐TiO2‐SA‐Ni(II) (Figure 3c) exhibits no distinct
morphological difference between nano‐TiO2‐NH2 and
the metal‐loaded catalyst, but the presence of Ni caused
slight changes, demonstrated by the disappearance of
the roughness of the TiO2‐NH2 nanoparticles. However,
the catalyst efficiency is still good enough for catalysing
reactions. Moreover, an enlargement in particle diameter
of nano‐TiO2‐NH2 and nano‐TiO2‐SA‐Ni(II) compared to
nano‐TiO2 is obviously observed which are still of
nanometric size. Aggregation of nanoparticles in
nano‐TiO2‐SA‐Ni(II) is clearly seen.
3.1.6 | EDX analysis
EDX analysis as an efficient analytical technique was
used for the elemental analysis of the nanoparticles. The
functionalization of nano‐TiO2 with the Schiff base and
the formation of its complex with Ni metal are confirmed
by the presence of C, O, N, Ti and Ni signals in the EDX
patterns of the products (Figure 6).
3.2 | Evaluation catalytic activity of
nano‐TiO2‐SA‐Ni(II) for selective oxidation
of sulfides to sulfoxides
3.1.4 | Transmission electron microscopy
Figure 4 displays the TEM images of nano‐TiO2‐SA‐Ni(II)
which confirm the spherical‐like and nanometre‐sized
particles of the catalyst.
In continuation of the exploration of novel and straight-
forward methodologies in selective oxidation of sulfides
to sulfoxides,[51,52] the catalytic efficiency of the synthe-
sized nanocatalyst was studied in this reaction using
H2O2 as the oxidant under solvent‐free conditions at
room temperature, which successfully resulted in high
yield and high conversion of products (Scheme 2).
Primary experiments were done to investigate the
effect of parameters on reaction time and yield. Other fac-
tors including the amount of oxidant and catalyst were
3.1.5 | XRD analysis
The crystal phases of nano‐TiO2 and nano‐TiO2‐SA‐Ni(II)
were scanned using the powder XRD technique. As
shown in Figure 5a, diffraction signals corresponding to
(101), (103), (004), (112), (200), (105), (211), (204), (116),
(220), (215) and (224) can be attributed to the
FIGURE 3 SEM images of (a) nano‐TiO2, (b) nano‐TiO2‐NH2 and (c) nano‐TiO2‐SA‐Ni(II)

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AMOOZADEH ET AL.
FIGURE 4 TEM images of nano‐TiO2‐SA‐Ni(II)
also optimized. Initially, we performed experiments in
order to find the required catalyst load. The results are
summarized in Table 1. The best yield was obtained in
the presence of 40 mg of catalyst which led to lowest reac-
tion time and highest reaction yield (Table 1, entry 5).
Afterwards, we determined the optimum amount of
H2O2. As evident from Table 1, the optimum amount of
H2O2 giving the highest product yield was 2 eq. (Table 1,
entry 8). In the next step, the effect of solvent on the
reaction was investigated to compare the efficiency of
solvent‐free versus solvent conditions. The reaction was
performed under optimum conditions in the presence of
ethanol, water, CH3CN and toluene. The results showed
that the best yield in shorter reaction time was achieved
under solvent‐free conditions which adhere to green
chemistry. Briefly, the best reaction yield was obtained
FIGURE 5 XRD patterns of (a) nano‐TiO2 and (b) nano‐TiO2‐
SA‐Ni(II)
TABLE 1 Optimization of conditions for synthesis of
methylphenyl sulfoxidea
Catalyst
(mg)
H2O2
(eq.)
Time
(min)
Yield
(%)b
Entry
Solvent
1
0
2
—
1440 (24 h)
90
70
77
85
94
92
90
94
94
70
75
60
70
2
10
20
30
40
50
40
40
40
40
40
40
40
2
—
50
3
2
—
50
4
2
—
38
5
2
—
20
6
2
—
32
7
1.5
2
—
54
8
—
30
9
2.5
2
—
33
10
11
12
13
H2O
ETOH
Toluene
CH3CN
140
150
175
180
FIGURE 6 EDX analysis of nano‐TiO2‐SA‐Ni(II)
2
2
2
aReaction conditions: methyl sulfide (1 mmol), room temperature.
bIsolated yield.
SCHEME 2 Nano‐TiO2‐SA‐Ni(II)‐catalysed selective oxidation of
sulfides to sulfoxides

AMOOZADEH ET AL.
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under solvent‐free conditions at room temperature with
2 eq. of H2O2 and 40 mg of nano‐TiO2‐SA‐Ni(II).
which is converted to an active oxidation species (B). In
the next step, nucleophilic attack of the sulfide on this
intermediate gives a cation (C), which, in turn, produces
the corresponding sulfoxide products.
These results prompted us to study the domain and
generality of this protocol for various sulfides (aliphatic
and aromatic) under the optimized conditions. As evident
from Table 2, a variety of sulfides such as dialkyl sulfides
(Table 2, entries 1 and 2), alkylaryl sulfides (Table 2,
entries 3–5) and sulfides with other functional groups
could be easily transformed to corresponding sulfoxides
with high reaction rate and excellent selectivity, and no
over‐oxidation products such as sulfones were detected
in the reaction mixtures. Moreover, the influence of steric
effects could be observed in this catalytic system. For
example, the oxidation of diphenyl sulfide required much
longer reaction time in comparison to isopropylphenyl
sulfide and its product yield was also much lower. The
structures of some of the synthesis products were well
characterized from their 1H NMR spectral data
(supporting information).
3.3 | Recycling and leaching of catalyst
Reusability of a nanocatalyst is one of the most important
criteria for catalytic systems, which provides useful infor-
mation about the immobilization process and makes it
useful for commercial applications. For addressing this
important concern, the recyclability of the catalyst was
examined in the oxidation reaction of methylphenyl sul-
fide under the optimized conditions, which showed all
reactions led to the desired product without significant
changes in reaction time or yield which clearly indicates
the practical recyclability of nano‐TiO2‐Ni(II). Moreover,
the results show that the nanocatalyst does not lose its
activity and Ni(II) is successfully immobilized on the sup-
port. This result shows that the nanocatalyst can be
recovered and reused for at least six consecutive cycles
A suggested reaction mechanism of this selective oxi-
dation is depicted in Scheme 3.[53,54] Reaction of H2O2
with nano‐TiO2‐SA‐Ni(II) leads to an intermediate (A)
TABLE 2 Oxidation of sulfides to sulfoxides in presence of nano‐TiO2‐Ni(II)a
Entry
Sulfide
Sulfoxide
Time (min)
Yield (%)b
Selectivity (%)
1
27
90
100
2
3
180
49
92
90
100
100
4
100
93
100
5
6
7
30
94
80
85
100
100
100
300
300
8
9
300
240
87
83
100
100
aReaction conditions: sulfide (1 mmol), nano‐TiO2‐Ni(II) (40 mg), H2O2 (2 eq.), solvent‐free at room temperature.
bIsolated yield.

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AMOOZADEH ET AL.
SCHEME 3 Probable mechanism in
selective oxidation of sulfides to sulfoxides
catalysed by nano‐TiO2‐SA‐Ni(II)
with only a modest decrease in its catalytic activity
(Figure 7). Additionally, as can be clearly seen in
Figure 8, the EDX pattern of the recovered catalyst
confirmed the presence of Ni after six cycles.
4 | CONCLUSIONS
In summary, a Ni(II) Schiff base complex supported on
nano‐TiO2 as a novel type of heterogeneous nanocatalyst
was successfully synthesized through the use of TDI as a
regioselective linker and precursor of primary amine
groups, and was well characterized using FT‐IR spectros-
copy, XRD, SEM, TEM, TGA and EDX analysis. This
novel heterogeneous nanocatalyst showed high catalytic
activity in selective oxidation of sulfides to their
corresponding sulfoxides with high yield and under mild
conditions. Moreover, the prepared catalyst could be
recovered by centrifugation and reused for at least six
runs without leaching of Ni metal nor significant loss of
catalytic activity. Low cost, non‐toxic nature, high yield
of products, high catalytic activity, easy separation and
good recyclability are the main advantage of our new
nanocatalyst.
FIGURE 7 Reusability of nano‐TiO2‐SA‐Ni(II) for the synthesis
of methylphenyl sulfoxide. Reaction conditions: methylphenyl
sulfide (1 mmol), H2O2 (2 eq.), catalyst (40 mg), reaction time of
15 min at room temperature under solvent‐free conditions
ACKNOWLEDGEMENTS
We gratefully acknowledge the Faculty of Chemistry of
Semnan University for supporting this work.
ORCID
Ali Amoozadeh https://orcid.org/0000-0002-9405-2412
Elham Tabrizian https://orcid.org/0000-0003-3603-6518
FIGURE 8 EDX spectrum of recycled nano‐TiO2‐SA‐Ni(II) after
six reuse cycles

AMOOZADEH ET AL.
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[33] E. Tabrizian, A. Amoozadeh, T. Shamsi, React. Kinet. Mech.
Catal. 2016, 119, 245.
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How to cite this article: Amoozadeh A,
Tabrizian E, Shahjoee S. Nickel(II) Schiff base
complex supported on nano‐titanium dioxide: A
novel straightforward route for preparation of
supported Schiff base complexes applying 2,4‐
toluenediisocyanate. Appl Organometal Chem.
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