Preparation, characterization and catalytic application of molybdenum Schiff-base complex immobilized on silica-coated Fe3O4 as a reusable catalyst for the synthesis of pyranopyrazole derivatives

Article abstract of DOI:10.1002/aoc.4723

A recoverable molybdenum Schiff-base complex immobilized on silica-coated Fe₃O₄ nanoparticles was prepared and characterized. This superparamagntic nanocatalyst, which is separable using an external magnet, can be used as an efficien

Full text of DOI:10.1002/aoc.4723

Received: 31 July 2018
DOI: 10.1002/aoc.4723
Revised: 1 October 2018
Accepted: 30 October 2018
F U L L P A P E R
Preparation, characterization and catalytic application of
molybdenum Schiff‐base complex immobilized on silica‐
coated Fe3O4 as a reusable catalyst for the synthesis of
pyranopyrazole derivatives
Seyedeh Aghigh Hamrahian | Sadegh Salehzadeh
Farshid Haji babaei | Niloofar Karami
| Jamshid Rakhtshah |
Faculty of Chemistry, Bu‐Ali Sina
University, Hamedan 6517838683, Iran
A recoverable molybdenum Schiff‐base complex immobilized on silica‐coated
Fe3O4 nanoparticles was prepared and characterized. This superparamagntic
nanocatalyst, which is separable using an external magnet, can be used as an
efficient catalyst for the promotion of the synthesis of pyranopyrazole deriva-
tives. A variety of desired products were obtained in high to excellent yields
within short times. In comparison with other catalysts employed in the con-
densation of various aromatic aldehydes, malononitrile and 3‐methyl‐1‐
phenyl‐2‐ pyrazoline‐5‐one, the present catalyst showed a much higher activity
in terms of mild conditions and short reaction time. The catalyst can be reused
for several times without significant loss of activity.
Correspondence
Sadegh Salehzadeh, Faculty of Chemistry,
Bu‐Ali Sina University, Hamedan
6517838683, Iran.
Email: saleh@basu.ac.ir
KEYWORDS
immobilized complex, multicomponent reaction, pyranopyrazoles, solvent‐free
1 | INTRODUCTION
free type of these reactions have received substantial
levels of consideration. The synthesis of pyranopyrazoles
In recent years, there has been intense research on fused
heterocyclic compounds with pharmacological impor-
tance. Substituted pyranopyrazoles are much sought after
class of heterocyclic compounds, which play a significant
role in pharmaceutical field and biologically active com-
pounds.[1–3] These compounds possess a variety of thera-
peutic and biological activities, for instance anti‐
inflammatory,[4] antimicrobial,[5] anticancer,[6] inhibitors
of human Chk1 kinase,[7] and analgesic.[8] Synthetic
strategies of substituted pyrano[2,3‐c] pyrazoles have
evolved a long way from the early multistep proto-
cols[1,9–11] to present‐day multicomponent reactions.
Multi‐component reactions (MCRs) increase intrinsic
atom economy, structural diversity, simplicity and syn-
thetic efficiency on the conventional organic synthesis.[12]
Recently, the expansions of green protocols in pollution‐
by using nanoparticles has been already reported in the
presence of various catalysts such as MgO,[13] Ni(0),[14]
[15]
SnO2,
[nano‐Fe3O4@SiO2@(CH2)3‐Imidazole‐SO3H]
Cl[16] and ZrO2.
[17]
A literature search reveals that we[18] and others[19–21]
have explored different usages of magnetic Fe3O4 nano-
particles as magnetically recoverable catalysts in organic
reaction processes. Additionally, transition metal Schiff‐
base complexes[22,23] have attracted much interest in the
field of catalysis because of the extensive variety of appli-
cability, like chemical stability, controlling the perfor-
mance of metals in a large diversity of valuable catalytic
transformations and stabilization of different metals in
various oxidation states.[24,25] Immobilization of above
compounds on the surface of solid supports and their
applications as heterogeneous catalysts have received
Appl Organometal Chem. 2018;e4723.
wileyonlinelibrary.com/journal/aoc
© 2018 John Wiley & Sons, Ltd.
1 of 12
https://doi.org/10.1002/aoc.4723

2 of 12
HAMRAHIAN ET AL.
special attention. Several examples of heterogenization of
The IR spectra of SB@silica‐Fe3O4 and SBMo@silica‐
Fe3O4 compounds are shown in Figure 1. In accordance
with literature data,[33] the characteristic absorption
bands for SB@silica‐Fe3O4 (Figure 1a) appear at 3407,
2981, 1524 and 1069 cm−1 for O − H, C − H, C − N
and Si − O stretching vibrations, respectively. The C=N
stretching band in the IR spectrum of SB@silica‐Fe3O4
(Figure 1a) is appeared at 1637 cm−1 and indicates the
attachment of the Schiff base to nanoparticles. The above
band for SBMo@silica‐Fe3O4 (Figure 1b) is shifted to a
lower frequency (1626 cm−1) upon the complexation with
the molybdenum.
Schiff‐base complexes by immobilization of homogeneous
ones onto some supports, such as MCM‐41,[26,27] SiO2–
[28,29]
Al2O3
and nano magnetite particles[21,30,31] have
been reported.
In continuation of our work in developing new sup-
ported Schiff‐base catalysts,[32–34] we report here a molyb-
denum Schiff‐base complex immobilized on silica‐coated
Fe3O4 nanoparticles. We explore the effectiveness of
above nanoparticles as a reusable and inexpensive Lewis
acid catalyst for the synthesis of pyranopyrazole deriva-
tives (Scheme 1).
The presence of crystalline structure of initial Fe3O4
(Figure 2a) and final SBMo@silica‐Fe3O4 nanoparticles
(Figure 2b) was confirmed by XRD analysis which
showed several distinct peaks at 18.6°, 30°, 35.3°, 43 °,
53.7°, 57.1°, 62.9° and 74.7°. There was no visual differ-
ence detected between the magnetic nanoparticles with-
out and with immobilized complex, thus the crystal
structure of initial iron oxide NPs has not been destroyed.
There are eight diffraction peaks for Fe3O4 and
SBMo@silica‐Fe3O4: (1 1 1), (2 2 0), (3 1 1), (4 0 0), (4 2
2), (5 1 1), (4 4 0) and (5 5 3) which is the standard pattern
for crystalline magnetite with spinel structure (JCPDS
2 | RESULT AND DISCUSSION
A schematic representation for the synthesis of molybde-
num Schiff base complex immobilized on silica‐coated
magnetic nanoparticles is shown in Scheme 2.
Fourier transform infrared (FT‐IR), X‐ray powder dif-
fraction (XRD), scanning electron microscopy (SEM),
energy dispersive X‐ray (EDX), transmission electron
microscopy (TEM), vibrating sample magnetometry
(VSM) and inductively coupled plasma atomic emission
spectroscopy (ICP‐AES) were used to characterize the
SBMo@silica‐Fe3O4.
SCHEME 1 The synthesis of pyranopyrazole derivatives using
molybdenum Schiff base complex supported on functionalized
Fe3O4magnetite nanoparticles
FIGURE 1 FT‐IR spectra of (a) SB@silica‐Fe3O4 and (b)
SBMo@silica‐Fe3O4
SCHEME 2 The sequence of events in the preparation of SBMo@silica‐Fe3O4

HAMRAHIAN ET AL.
3 of 12
FIGURE
2
XRD diffraction pattern of Fe3O4 MNPs (a),
SBMo@silica‐Fe3O4 (b) and SBMo@silica‐Fe3O4 (reused after
catalytic reaction)
FIGURE
5
Transmission electron microscopy image of
SBMo@silica‐Fe3O4 NPs
FIGURE 6 The magnetic hysteresis loops of Fe3O4 MNPs (a)
and SBMo@silica‐Fe3O4 (b)
FIGURE 3 SEM image of SBMo@silica‐Fe3O4
FIGURE 4 EDX diagram of the SBMo@silica‐Fe3O4
FIGURE 7 TGA and DTG analysis of SBMo@silica‐Fe3O

4 of 12
HAMRAHIAN ET AL.
No. 85–1436).[35] Moreover, a XRD broadened pattern at
2θ = 20–30° appeared in the SBMo@silica‐Fe3O4, which
could be related to the amorphous silica formed around
the Fe3O4 NPs (Figure 2b). The width of the peak at
2θ = 35.3° (311) was used to estimate the average
crystallite size of the magnetic nanoparticles by Scherrer's
formula. The crystallite size of the magnetic nanoparticle
is calculated to be ~15 nm which are in good accordance
with the average particle size seen from scanning electron
microscopy.
The morphology and nanoparticle size of
SBMo@silica‐Fe3O4 was investigated by field emission
scanning electron microscopy (FE‐SEM) (Figure 3). It
can be seen that the resulting magnetic nanoparticles
were almost spherical and the complex matrix is uni-
formly covered on the surface of Fe3O4 NPs.
TABLE 1 The effect of the amount of the catalyst and tempera-
ture on the three‐component reaction of benzaldehyde,
malononitrile and 3‐methyl‐1‐phenyl‐2‐ pyrazolin‐5‐one under sol-
vent‐free conditionsa
To identify the elemental composition of
SBMo@silica‐Fe3O4, Energy‐dispersive X‐ray spectros-
copy (EDX) was used. According to Figure 4, chemical
characterization of as‐prepared product reveals that it is
composed of iron, silicon, oxygen, carbon, nitrogen, chlo-
rine and molybdenum elements.
Reaction
Amount of
Entry catalyst (mg)
temperature (° Reaction
Yieldc
(%)
C)b
time (min)
1
—
—
2
r.t.
100
r.t.
100
r.t.
50
45
50
5
30
35
68
70
95
95
95
95
95
95
95
95
90
90
90
90
TEM image of SBMo@silica‐Fe3O4 nanocatalyst is
presented in Figure 5. The resulting magnetic nanoparti-
cles were almost spherical or ellipsoidal and the average
particle size of nanoparticles was found to be ~10 nm in
diameter. However, there is a little aggregation in the
iron oxide nanoparticles coated with molybdenum
Schiff‐base complexes.
Magnetic measurements were carried out by
employing vibrating sample magnetometer (VSM) at room
temperature (Figure 6). The magnetization of samples
could be completely saturated at high fields and the Ms of
samples changed from 48.85 to 37.95 emu g−1. The results
of VSM show that the saturation magnetization value of
SBMo@silica‐Fe3O4 is lower than that of Fe3O4 NPs, due
to the formation of silica shell, Si‐linker and finally
Schiff‐base complex around the Fe3O4 core. However, the
nanocatalyst can still be quickly and easily separated from
the reaction mixture by using an external magnet.
The stability of the SBMo@silica‐Fe3O4 as catalyst
under N2 atmosphere was determined by thermogravi-
metric analysis (TGA) and derivative thermogravimetry
(DTG) (Figure 7). As can be seen, the catalyst shows a
good thermal stability, with two weight loss steps in the
2
3
4
2
5
5
4
5
6
4
5
7
4
75
5
8
4
100
r.t.
50
5
9
6
5
10
11
12
13
14
15
16
6
5
6
75
5
6
100
r.t.
50
5
8
10
10
10
10
8
8
75
8
100
aReaction conditions: benzaldehyde (1 mmol), malononitrile (1 mmol) and 3‐
methyl‐1‐phenyl‐2‐ pyrazolin‐5‐one (1 mmol).
bThis is the temperature of oil bath and not inside the reaction medium.
cIsolated yield.
TABLE 2 Solvent effect in the reaction between benzaldehyde, malononitrile and 3‐methyl‐1‐phenyl‐2‐pyrazolin‐5‐one at room temper-
ature using 4 mg catalysta
Solvent‐free
H2O
C2H5OH
CH3CN
CH2Cl2
Toluene
n‐Hexane
Yield (%)b
95
5
90
15
80
10
50
40
40
60
30
60
30
60
Reaction time (min)
aReaction conditions: benzaldehyde (1 mmol), malononitrile (1 mmol) and 3‐methyl‐1‐phenyl‐2‐pyrazolin‐5‐one (1 mmol) under room temperature;
bIsolated yield.

HAMRAHIAN ET AL.
5 of 12
TABLE 3 Three‐component reaction of pyranopyrazole derivatives using 4 mg catalyst under solvent‐free conditionsa
Entry
Product
Time (min)
Yieldb (%)
M.p (°C) [Lit.]
1
5
95
167–169[36]
2
8
90
175–177[36]
3
12
89
172–174[36]
4
5
90
225–227[16]
5
5
92
168–170[37]
6
5
90
175–177[36]
7
8
88
178–180[36]
(Continues)

6 of 12
HAMRAHIAN ET AL.
TABLE 3 (Continued)
Entry
Product
Time (min)
Yieldb (%)
M.p (°C) [Lit.]
8
5
93
187–189[36]
9
15
88
210–212[36]
10
15
85
172–174[38]
11
15
83
260–262[39]
12
10
85
210–212[16]
(Continues)

HAMRAHIAN ET AL.
7 of 12
TABLE 3 (Continued)
Entry
Product
Time (min)
Yieldb (%)
M.p (°C) [Lit.]
13
14
5
5
92
90
198–200[16]
190–192[36]
15
5
94
194–196[37]
16
15
87
188–190[39]
a: Reaction conditions: different aldehydes (2 mmol), benzaldehyde (1 mmol), malononitrile (1 mmol) and 3‐methyl‐1‐phenyl‐2‐pyrazolin‐5‐one (1 mmol), nano
catalyst (4 mg), solvent free and room temperature.
b: Isolated yield.
temperature range of 160–600 °C. The release of physi-
cally adsorbed solvent molecules takes place between 23
and 160 °C. From 160 °C up to 360 °C, the curve shows
a weight which is ascribed to the decomposition of the
coating organic layer on the surface of nanocomposite.
The second peak represent the Fe3O4 nanoparticles
decomposition. Furthermore, the DTG curve shows that
the decomposition of the organic structure mainly occurs
at 300 °C and the desired catalyst is stable around or
below 200 °C.

8 of 12
HAMRAHIAN ET AL.
Due to the ability of SBMo@silica‐Fe3O4 as a mild,
products in high yields. The type of substituent on the
aromatic ring showed strongly understandable effects in
terms of time and yields. As Table 3 shows, aldehydes
containing electron‐withdrawing groups furnished good
to excellent yields of the corresponding products in the
shorter reaction times, but aromatic aldehydes containing
electron donating groups carried out the reaction at lon-
ger reaction times and lower yields.
efficient and recoverable acid catalyst, we decided to
examine its catalytic activity for the synthesis of
pyranopyrazole derivatives. In order to optimize the reac-
tion conditions, we studied the reaction of benzaldehyde
malononitrile and 3‐methyl‐1‐phenyl‐2‐ pyrazolin‐5‐one
as a simple model substrate in various conditions. First,
we evaluated the effect of different amounts of the cata-
lyst from 25 to 100 °C under solvent‐free conditions and
yields. As shown in Table 1, the small amount of product
is formed in the absence of catalyst. It was found that
decreasing the amount of the catalyst from 0 to 2 mg,
increases the yield of reaction from 30 to 68% (entry 3)
and on further increase up to 4 mg an obvious increase
in the yield was observed again. The use of 4 mg of
SBMo@silica‐Fe3O4 keeping the yield at 95%, so this
amount is sufficient to promote the reaction. We also
tested the effect of temperatures by carrying out the
model reaction. Increasing the reaction temperature did
not improve the rate of the reaction at different amounts
of catalyst. Then the model reaction was further opti-
mized by detecting the efficiency of solvents in the pres-
ence of 4 mg of catalyst. The represented data in
Table 2 showed that the reaction proceeds efficiently in
solvent free condition and results in high yields of the
desired product.
The capability and efficiency of this catalyst was dem-
onstrated by the comparison between recently reported
catalysts, and the results of these catalysts for the synthe-
sis of pyranopyrazole were tabulated in Table 4. The
model reaction was also checked in presence of
MoO2(acac)2 as an acid catalyst. The represented data
established the important role of investigated substrate
in reaction time and the high yield of the desired product.
The data clearly shows that the present method is more
efficient and both the reaction time and the yield in the
present methodology are better in comparison with those
reported in the literature. In addition, considering this
fact that our catalyst is used with minimum amount at
room temperature and solvent‐free conditions, we can
conclude that it is in the first rank among all catalysts
which have been reported so far. Furthermore,
SBMo@silica‐Fe3O4 is easily prepared from inexpensive
and accessible starting materials via simple procedure.
In another study, in order to establish the generality
of this catalytic system, we extended the scope of the reac-
tion to the synthesis of various polysubstituted pyrrole
derivatives. We used the mentioned optimized condition
to estimate the reaction of aniline, ethyl acetoacetate
and nitromethane with a series of aromatic aldehydes.
Table 5 illustrates that the reaction is effective in the pres-
ence of a wide variety of functional groups on the
After optimizing the reaction conditions, to explore
the scope of the reaction catalyzed by SBMo@silica‐
Fe3O4, we next examined the application of catalyst in
synthesis of pyranopyrazole derivatives under the opti-
mized conditions. Various aromatic aldehydes carrying
either electron donating or electron‐withdrawing substit-
uents reacted successfully with malononitrile and 3‐
methyl‐1‐phenyl‐2‐ pyrazolin‐5‐one and gave the
TABLE 4 Comparison of various catalysts in the synthesis of pyranopyrazole with our catalysta
Entry
Amount of catalyst
Solvent
Temp (°C)
Time (min)
Yieldb (%)
Ref
[40]
1
Poly(4‐vinylpyridine)(PVP) (100 mg)
CuO–CeO2 nanocomposite (50 mg)
Nano‐titania sulfuric acid(n‐TSA) (10 mg)
Tungstate sulfuric acid (10 mol%)
CsF (5 mol%)
CH3CH2OH
Solvent free
CH3CH2OH
CH3CH2OH
CH3CH2OH
Solvent free
H2O
Reflux
80
9
12
15
10
360
3
96
94
96
95
70
98
99
89
91
90
98
[36]
[37]
[38]
[39]
[41]
[42]
[43]
[16]
2
3
40
4
Reflux
Reflux
80
5
6
Cl3CCOOH (10 mol%)
7
Triethylbenzylammonium chloride (TEBA) (150 mg)
Hexadecyltrimethylammonium bromide (HTMAB)
[nano‐Fe3O4@SiO2@(CH2)3‐Imidazole‐SO3H] Cl (7 mg)
MoO2(acac)2 (4 mg)
90
360
‐
8
H2O
85
9
Solvent free
Solvent free
Solvent free
r.t
30
15
5
10
11
r.t
‐
‐
SBMo@silica‐Fe3O4 (4 mg)
r.t
aReaction conditions: benzaldehyde (1 mmol), malononitrile (1 mmol) and 3‐methyl‐1‐phenyl‐2‐pyrazolin‐5‐one (1 mmol).
bIsolated yield.

HAMRAHIAN ET AL.
9 of 12
TABLE 5 Four‐component reaction of polysubstituted pyrrole
derivatives using 4 mg catalyst under solvent‐free conditions.a
The mechanism begins with the activation of the car-
bonyl group of the aldehyde (I) with the Mo complex
immobilized on Fe3O4 (II) and follows via initial forma-
tion of dicyanoalkene (IV) from the Knoevenagel conden-
sation of arylaldehyde (I) and malononitrile (III). The
next step may involve Michael addition of the methylene
group of 3‐Methyl‐1‐phenyl‐2‐pyrazolin‐5‐one (V) to an
electron deficient carbon of dicyanoalkene (IV) to form
(VI) which may undergo cyclisation to form the target
product (VII) after proton transfer and tautomerization.
The reusability of the catalysts is highly preferable for
greener process and makes them useful for commercial
applications. To investigate reusability of the catalyst,
the same model reaction was again studied under opti-
mized conditions. After completion of reaction the sepa-
rated catalyst was easily recovered by magnet and
washed with ethanol and dried at 60 °C. The recovered
catalyst was used repetitively for six cycles with only a
slight loss (~5%) of catalytic activity (Figure 8). The
recovered catalyst had no noticeable change in structure,
referring to the FT‐IR spectrum and XRD pattern
(Figure 2c.) of the catalyst in comparison with fresh cat-
alyst after six runs.
Time
(min)
Yieldb
(%)
M.p (°C)
[Lit.]
Entry
Product
1
25
25
25
86
83
85
Oil[44]
Oil[45]
Oil[44]
2
3
Moreover, molybdenum leaching in SBMo@silica‐
Fe3O4 catalyst was determined by ICP‐AES analysis of
the final product and no leaching was observed. This
experiment confirmed the heterogeneous character of
the catalytically active species.
4
5
20
20
92
90
Oil[45]
3 | EXPERIMENTAL
All organic products were characterized by comparison of
their spectroscopic data (FT‐IR) and physical properties
with those reported in the literature. Chemicals were pur-
chased from Fluka and Merck chemical companies.
Oil[45]
3.1 | Preparation of Fe3O4 nanoparticles
a: Reaction conditions: different aldehydes (1 mmol), different amines
(1 mmol), ethyl acetoacetate (1 mmol), nitromethan (1 mmol), nano catalyst
(4 mg), solvent‐free and room temperature.
Naked nanoparticles were prepared by chemical
coprecipitation of Fe3+ and Fe2+ ions with a molar ratio
of 2:1. described by Massart.[46] Briefly, 5.838 g of
FeCl3.6H2O and 2.147 g of FeCl2.4H2O were added into
55 mL of deionized water at room temperature and the
mixture was stirred vigorously for 10 min to make all
materials dissolve completely. Then, 15 ml of 25%
NH4OH was quickly added into the reaction mixture in
one portion. After stirring at 80 °C for 4 hr, the nanopar-
ticles were separated with an external magnet and
washed with ethanol, deionized water and 0.02 M solu-
tion of NaCl through magnetic decantation then finally
dried in vacuum at 60 °C for 8 hr.
b: Isolated yield.
aromatic aldehydes, giving good to excellent conversions
to the corresponding products.
A plausible reaction mechanism for the synthesis of 1‐
aminoalkyl‐2‐naphthol derivatives is outlined in
Scheme 3. We know that the surface of our catalyst plays
an important role for the synthesis of desired derivatives.
The surface of catalyst possibly contains active hydroxyl,
oxide and Mo Schiff‐base complex, which are well
reported in the literature to act as Lewis acids or bases.

10 of 12
HAMRAHIAN ET AL.
SCHEME 3 The plausible mechanism
for the SBMo@silica‐Fe3O4 catalyzed
formation of pyranopyrazole derivatives
temperature for 30 min and then the suspension was
carried out at reflux condition for 4 hr under nitrogen
atmosphere. Subsequently, the precipitates were collected
and washed with xylene three times.
3.4 | Preparation of Schiff‐base ligand
A mixture of diethylenetriamine (4 mmol, 0.412 g) and
pyrrole‐2‐carboxaldehyde (8 mmol, 0.680 g) in ethanol
(50 ml) was heated under reflux condition for 4 hr. The
resulting precipitate was allowed to cool, washed with
ethanol and dried (yield: 73%).
FIGURE
8
Reusability of SBMo@silica‐Fe3O4 as
a
heterogeneous catalyst in 20 minutes
3.5 | Synthesis of Mo complex
immobilized on magnetic Fe3O4
nanoparticles (SBMo@silica‐Fe3O4)
3.2 | Preparation of silica‐coated Fe3O4
nanoparticles
The silica coated magnetic nanoparticles were prepared
through a modified Stober method.[47] Considering the
aggregation tendency of the naked nanoparticles, coating
the magnetic nanoparticles with silica layer should be a
good solution. The powder of Fe3O4 NPs (1 g) was dis-
persed in 100 ml ethanol/deionized water solution (vol-
ume ratio, 10:1) by sonication for 20 min and then
2.5 ml of 25 wt% concentrated aqueous ammonia and
tetraethylorthosilicate (TEOS) (2 ml) solutions were
added dropwise into the above solution under mechanical
stirring. The precipitated brown products were collected
from the solution by a magnet and washed with ethanol
three times.
The Fe3O4 nanoparticles coated by CPTMS (0.4 g) was
dispersed in ethanol by ultrasonic vibration for 20 min,
subsequently, this suspension was added into the solution
of Schiff‐base in ethanol and stirred at 60 °C for 24 hr.
The solid was recovered by magnet and air‐dried at room
temperature overnight. Then, an excess amount of
MoO2(acac)2 and above solid product were dispersed in
ethanol solution containing
a
few drops of
trimethylamine. The mixture was refluxed in 60 °C for
3 hr under strong stirring. After separation by magnet,
washing with ethanol and deionized water and finally
drying, the functionalized Fe3O4 was obtained and
denoted as SBMo@silica‐Fe3O4.
3.3 | Synthesis of magnetite Fe3O4
nanoparticles coated by
3.6 | General procedure for the
preparation of pyranopyrazole derivatives
3‐chloropropyltrimethoxysilane (CPTMS)
A mixture of various aromatic aldehydes (1 mmol),
malononitrile (1 mmol), 3‐methyl‐1‐phenyl‐2‐pyrazolin‐
5‐one (1 mmol) and SBMo@silica‐Fe3O4 in a round bot-
tom flask was stirred magnetically under solvent‐free
0.5 g dried silica‐coated nanoparticles were dispersed to
the mixture of 3 mL (3‐chloropropyl)‐trimethoxysilane
and 100 ml xylene. The mixture was sonicated at room

HAMRAHIAN ET AL.
11 of 12
[7] N. Foloppe, L. M. Fisher, R. Howes, A. Potter, A. G. S. Robert-
conditions at room temperature. The progress of the reac-
tion and the disappearance of aldehyde was monitored by
TLC. The reaction mixture was purified with ethyl acetate
and n‐hexane. Furthermore, all the compounds were
characterized by FT‐IR spectroscopy data (supporting
information).The catalyst was easily separated from the
reaction mixture with an external magnet and washed
twice with ethyl acetate.
son, A. E. Surgenor, Bioorg. Med. Chem. 2006, 14, 4792.
[8] S. C. Kuo, L. J. Huang, H. Nakamura, J. Med. Chem. 1984, 27,
539.
[9] J. Zhu, Eur. J. Org. Chem. 2003, 7, 1133.
[10] A. Arabanian, M. Mohammadnejad, S. Balalaie, J. H. Gross,
Bioorg. Med. Chem. Lett. 2009, 19, 887.
[11] G. Rashinkar, R. Salunkhe, J. Mol. Catal. A: Chem. 2010, 316,
146.
[12] S. B. Patil, P. R. Singh, M. P. Surpur, S. D. Samant, Synth.
Commun. 2007, 37, 1659.
4 | CONCLUSION
[13] M. Babaie, H. Sheibani, Arabian. J. Chem. 2011, 4, 159.
[14] J. M. Khurana, K. Vij, Synth. Commun. 2013, 43, 2294.
In conclusion, we have shown that immobilization of
Silica‐coated Fe3O4 nanoparticles with a Schiff‐base
ligand and subsequent complexation with molybdenum
affords a truly heterogenized molybdenum catalysis sys-
tem. An efficient, recoverable, cost‐effective and opera-
tionally simple protocol for the synthesis of
pyranopyrazole derivatives under room temperature in
solvent free condition has been developed. Finally, the
data suggested that in comparison to previously reported
methods, this method is the best alternative for the syn-
thesis of pyranopyrazoles in the presence of
SBMo@silica‐Fe3O4 as a heterogeneous catalyst.
[15] S. Paul, K. Pradhan, S. Ghosh, S. K. De, A. R. Das, Tetrahedron
2014, 70, 6088.
[16] M. A. Zolfigol, R. Ayazi‐Nasrabadi, S. Baghery, V. Khakyzadeh,
S. Azizian, J. Mol. Catal. A: Chem. 2016, 418, 54.
[17] A. Saha, S. Payra, S. Banerjee, Green Chem. 2015, 17, 2859.
[18] J. Rakhtshah, S. Salehzadeh, E. Gowdini, F. Maleki, S. Baghery,
M. A. Zolfigol, RSC Adv. 2016, 6, 104875.
[19] Y. Li, F. Ma, X. Su, C. Sun, J. Liu, Z. Sun, Y. Hou, Catal.
Commun. 2012, 26, 231.
[20] M. M. Mojtahedi, M. S. Abaee, A. Rajabi, P. Mahmoodi, S.
Bagherpoor, J. Mol. Catal. A: Chem. 2012, 361, 68.
[21] T. Azadbakht, M. A. Zolfigol, R. Azadbakht, V. Khakyzadeh, D.
ACKNOWLEDGMENTS
M. Perrin, New J. Chem. 2015, 39, 439.
We are grateful to the Bu‐Ali Sina University for financial
support.
[22] S. Salehzadeh, M. D. Ward, H. Adams, Inorg. Chem. Commun.
2009, 12, 433.
[23] S. Salehzadeh, R. Golbedaghi, I. S. Tidmarsh, N. K. Al‐Rasbi,
H. Adams, M. D. Ward, Polyhedron 2008, 27, 3549.
ORCID
[24] P. G. Cozzi, Chem. Soc. Rev. 2004, 33, 410.
Sadegh Salehzadeh https://orcid.org/0000-0003-2840-1896
[25] K. C. Gupta, A. K. Sutar, Coord. Chem. Rev. 2008, 252, 1420.
[26] S. Tangestaninejad, M. Moghadam, V. Mirkhani, I.
Mohammadpoor‐Baltork, K. Ghani, Catal. Commun. 2009, 10,
853.
REFERENCES
[1] A. A. Fadda, A. El‐Mekabaty, K. M. Elattar, Synth. Commun.
2013, 43, 2685.
[27] M. Masteri‐Farahani, F. Farzaneh, M. Ghandi, Catal. Commun.
2007, 8, 6.
[2] A. I. Ilovaisky, M. G. Medvedev, V. M. Merkulova, M. N.
[28] M. Ghiaci, B. Rezaei, M. Arshadi, Sens. Actuators B. Chem.
2009, 139, 494.
Elinson, G. I. Nikishin, J. Heterocyclic Chem 2014, 51, 523.
[3] M. A. Zolfigol, F. Afsharnadery, S. Baghery, S. Salehzadeh, F.
[29] M. Arshadi, M. Ghiaci, A. Gil, Ind. Eng. Chem. Res. 2011, 50,
Maleki, RSC Adv. 2015, 5, 75555.
13628.
[4] (a) M. E. A. Zaki, H. A. Saliman, O. A. Hickal, A. E. Z. Rashad,
A. E. Z. Naturforsch, C. Biosci. 2006, 61, 1. (b) C. K. Sheng, J. H.
Li, N. Hideo, J. Med. Chem. 1984, 27, 539.
[30] X. Caia, H. Wanga, Q. Zhanga, J. Tonga, Z. Lei, J. Mol. Catal. A:
Chem. 2014, 383, 217.
[31] P. B. Bhat, B. R. Bhat, New J. Chem. 2015, 39, 4933.
[5] (a) W. P. Smith, L. S. Sollis, D. P. Howes, C. P. Cherry, I. D.
Starkey, N. K. Cobley, J. Med. Chem. 1998, 41, 787. (b) K.
Mazaahir, S. Shilpi, R. K. Khalilur, S. T. Sharanjit, Bioorg.
Med. Chem. Lett. 2005, 15, 4295.
[32] J. Rakhtshah, S. Salehzadeh, M. A. Zolfigol, S. Baghery, Appl.
Organometal. Chem. 2017, 31, e3560.
[33] J. Rakhtshah, S. Salehzadeh, Res. Chem. Intermed. 2017, 43,
6973.
[6] (a) J. L. Wang, D. Liu, Z. J. Zheng, S. Shan, X. Han, S. M.
Srinivasula, C. M. Croce, E. S. Alnemri, Z. Huang, Proc. Natl.
Acad. Sci. U. S. A. 2009, 97, 7124. (b) M. E. A. Zaki, E. M.
Morsy, F. M. Abdul‐Motti, F. M. E. Abdel‐Megeid, Heterocycl.
Commun. 2004, 10, 97.
[34] J. Rakhtshah, S. Salehzadeh, M. A. Zolfigol, S. Baghery,
J. Coord. Chem. 2017, 70, 340.
[35] H. Moghanian, A. Mobinikhaledi, A. G. Blackmanc, E.
Sarough‐Farahanib, RSC Adv. 2014, 4, 28176.

12 of 12
HAMRAHIAN ET AL.
[36] J. Albadi, A. Mansournezhad, Z. Derakhshandeh, Chin. Chem.
Lett. 2013, 24, 821.
[47] W. Stober, A. Fink, E. J. Bohn, J. Colloid Interface Sci. 1968, 26,
62.
[37] D. Azarifar, S. M. Khatami, M. A. Zolfigol, R. Nejat‐Yami,
J. Iran. Chem. Soc. 2014, 11, 1223.
SUPPORTING INFORMATION
[38] M. Farahi, B. Karami, I. Sedighimehr, H. Mohamadi‐
Tanuraghaj, Chin. Chem. Lett. 2014, 25, 1580.
Additional supporting information may be found online
in the Supporting Information section at the end of the
article.
[39] V. N. Bhosale, J. A. Angulwar, G. S. Khansole, G. S. Waghmare,
J. Chem. Pharm. Res. 2014, 6, 733.
[40] J. Albadi, A. Mansournezhad, F. A. Balout‐Bangan, Acta Chim.
Slov. 2014, 61, 185.
[41] Z. Karimi‐Jaberi, M. M. ReyazoShams, Heterocycl. Commun.
2011, 17, 177.
How to cite this article: Hamrahian SA,
Salehzadeh S, Rakhtshah J, Haji babaei F, Karami
N. Preparation, characterization and catalytic
application of molybdenum Schiff‐base complex
immobilized on silica‐coated Fe3O4 as a reusable
catalyst for the synthesis of pyranopyrazole
derivatives. Appl Organometal Chem. 2018;e4723.
https://doi.org/10.1002/aoc.4723
[42] D. Shi, J. Mou, Q. Zhuang, L. Niu, N. Wu, X. Wang, Synth.
Commun. 2004, 34, 4557.
[43] T. S. Jin, A. Q. Wang, Z. L. Cheng, J. S. Zhang, T. S. Li, Synth.
Commun. 2005, 35, 137.
[44] A. B. Atar, Y. T. Jeong, Tetrahedron Lett. 2013, 54, 5624.
[45] F. M. Moghaddam, B. K. Foroushani, H. R. Rezvani, RSC Adv.
2015, 5, 18092.
[46] R. Massart, IEEE. Trans. Magn. 1981, 17, 1247.