Synthesis of pyrazole derivatives in the presence of a dioxomolybdenum complex supported on silica-coated magnetite nanoparticles as an efficient and easily recyclable catalyst

Article abstract of DOI:10.1039/c6ra20988b

Efficient synthesis of pyrazole derivatives catalyzed by a dioxomolybdenum complex supported on functionalized Fe₃O₄ magnetite nanoparticles containing a Schiff base ligand is reported. The synthesized catalyst was characterized by X

Full text of DOI:10.1039/c6ra20988b

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Synthesis of pyrazole derivatives in the presence of
dioxomolybdenum complex supported on silica-coated magnetite
nanoparticles as an efficient and easily recyclable catalyst
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Jamshid Rakhtshah, Sadegh Salehzadeh*, Ehsan Gowdini, Farahnaz Maleki, Saeed Baghery and
Mohammad Ali Zolfigol
www.rsc.org/
3 4
Efficient synthesis of pyrazole derivatives catalyzed by dioxomolybdenum complex supported on functionalized Fe O
magnetite nanoparticles containing Schiff base ligand is reported. The synthesized catalyst was characterized by X-ray
powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), vibrating sample
magnetometry (VSM), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and Fourier transform infrared
(FT-IR). This heterogeneous catalyst can be reused several times without significant loss of its catalytic activity. The
described catalyst was efficiently tested in the synthesis of pyrazole derivatives via three-component condensation of
aromatic aldehydes, malononitrile and phenylhydrazine with short reaction times, good yields, ease of separation,
recycling and reusability of metal-complex immobilized on MNPs. Besides, the catalyst could be recovered in a facile
manner from the reaction mixture and recycled eight times without loss in activity. Also, a new mechanistic approach was
proposed for the final step of the synthesis of pyrazole derivatives which was supported by theoretical studies.
10-13
Introduction
paramagnetic character of the support.
However, an
unavoidable problem associated with particles in this size
range is their intrinsic instability, which tends to lead to
formation of agglomerates when exposed to physiological
Schiff bases are able to stabilize many different metals in
various oxidation states, controlling the performance of metals
in a large variety of efficient catalysts both in homogeneous
14-15
1
environment and aqueous solutions.
However, in terms of
and heterogeneous reactions. The activity of these complexes
stability, naked metallic nanoparticles are chemically highly
active and are very sensitive to oxidation and agglomeration
varied with the type of ligands, coordination sites and metal
2
ions. Metal Salen oxo species are stable to moisture and can
1
6
due to their magnetic nature. For many cases it is thus
necessary to provide protection technics to chemically stabilize
this nanoparticles. Silica is an ideal robust coupling layer
material to integrate MNPs because of its excellent chemical
affinity and thermal stability. An advantage of the silica coating
is that this surface is terminated with abundant Si–OH bonds
which can react with various coupling agents to covalently
be used for catalytic reactions in environmentally friendly
3
catalytic conditions. However, these catalysts are generally
homogeneous and are not easily recoverable after use. Taking
into account the price of the catalysts and ligands, the
problematic separation of the catalyst from the product is
4
important. one of the solutions of these problems is the
immobilization of the catalyst on the different solid supports.
Recently, the use of nanoparticles as heterogeneous catalyst
supports have received increasing attention because their
small diameters provide large external surface areas for
1
7-22
attach linkers, ligands, metals and/or complexes.
Transition metal catalyzed carbon–heteroatom bond
formations via multicomponent reactions (MCRs) are of most
2
3
5
-8
importance in organic synthesis. Multi-component reactions
achieve important role in modern combinatorial chemistry due
to the ability to prepare target compounds in organic and
medicinal chemistry with more efficiency and atomic economy
via one pot reaction of three or more compounds together in a
catalysis.
Metal complexes immobilized onto metal
nanoparticles are a category of relatively new promising
9
materials for catalytic processes and analytical chemistry.
3 4
Fe O nanoparticles have unique physical properties such as
high surface-to-volume ratios and also can be easily separated
from reaction mixture by using an external magnet due to the
2
4
single step.
Through the above mentioned aspects, we have chosen
pyrazole moiety due to its significance in the context of
pharmaceutical chemistry and agriculture. Pyrazoles belong to
an significant kind of heterocyclic compounds which exhibit a
2
5
wide range of biological activities such as anticancer,
2
antioxidant,
6,27
28
anti-depressant activities, antibacterial and
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antifungal, and anti HIV. The conventional synthetic of the Fe
RSC Advances
2
6
29
3
O
4
@Si@MoO
2
is calculated to be 10 nm using Scherrer's
method for the preparation of pyrazole derivatives is a three- equation, which is smaller than the size determined by field
component reaction of aromatic aldehydes, malononitrile and emission scanning electron microscopy (FE-SEM) analysis. The
phenylhydrazine under various reaction conditions. A variety observed disagreement can be ascribed to the reality that XRD
3
0
31
32
of reagents such as {[HMIM]C(NO
2
)
3
}, CuO/ZrO
2
,
Sc(OTf)
3
,
measurements investigate crystallite sizes as sizes of
3
3
34
35
Ti(NMe
triethylbenzylammonium chloride,
been used to catalyze the above mentioned reactions. To the Fig.
best of our knowledge, synthesis of pyrazole derivatives in the Fe
2
)
2
(PyPyr)
2
,
[BMIM]OH,
ZrO
2
nanoparticles,
“coherently diffracting domains” of crystals while grains may
3
6
37
38
8
I
2
,
and LiOH, have contain several of these domains.
shows the
@Si@dioxomolybdenum. As can be seen, SEM image
3
typical
FE-SEM
image
of
3
O
4
presence of transition-metal Schiff base complexes is not yet indicated that most of the prepared nanoparticles are spherical
reported. Herein we report the synthesis and characterization shaped and have average diameter about 30 nm. Interestingly, the
of a dioxomolybdenum complex supported on the surface of magnetic core is visible as a dark spot inside the bright spherical
MNPs through a Si-linker. We report also the efficient, rapid SiO thin shell in this image.
2
and green synthesis of pyrazole derivatives in the presence of
catalytic amounts of this catalyst under solvent-free conditions
(Scheme 1). In comparison with the other catalysts, our
catalyst is among the best ones with respect to efficiency.
Additionally it can be easily separated magnetically in the end
of reaction and have shown great reusability.
Results and discussion
Characterization of dioxomolybdenum complex supported on
MNPs as a heterogeneous catalyst
The structure of dioxomolybdenum complex supported on
MNPs as a heterogeneous catalyst was studied, considered
and identified by FT-IR, XRD, SEM, EDX, ICP and VSM analysis.
-1
Scheme 1. The synthesis of pyrazole derivatives using molybdenum complex
The infrared absorption values (cm ) of significant valence
vibrations, which are collected in Figure 1, are helpful for
identification of the immobilized complex. The presence of
magnetite nanoparticles was confirmed by the strong
3 4
supported on functionalized Fe O magnetite nanoparticles containing Schiff base
ligand.
-1
absorption band at around 585 cm which corresponds to the
3
9
-1
Fe–O bond. A Si–O peak at 1062 cm confirms the silane
modification on the nanoparticle. The presence of the
anchored alkyl groups in Fe O @Si-Cl is confirmed by the weak
3
4
aliphatic C–H symmetric and asymmetric stretching vibrations
-1
at 2920-2965 cm (Fig. 1c). Thus the above results indicate
that the Si-Cl moiety were successfully grafted onto the
surface of the magnetic Fe O @SiO nanoparticles. As shown
3
4
2
in Fig. 1d, the FT-IR spectrum of Fe O @Si–H azosaldien
3
4
2
-1
exhibit the C=N stretching vibration band at 1638 cm . The
-
1
band at 1638 cm due to reaction with Mo shifted to lower
Fig. 1. FT-IR spectra of (a) Fe
3 4 3 4 2 3 4
O , (b) Fe O @SiO , (c) Fe O @Si–Cl, (d)
-1
Fe
3
O
4
@Si–H azosaldien, e) Fe @Si@MoO .
2
3
O
4
2
frequency 1621 cm in Curve of Fig. 1e. The observation of
-1
band at 943 cm in the infrared spectrum of Fe O @Si@MoO
2
3
4
(Fig. 1e) is characteristic of the presence of Mo=O bond.
XRD patterns of the as-synthesized initial magnetite, silica coated
and catalysts were illustrated in Fig. 2. All samples showed eight
peaks at 18.3, 30.5, 35.9, 43.3, 53, 57, 62 and 74.5◦, which can be
ascribed to the reflection of (1 1 1), (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5
1
1), (4 4 0) and (5 3 3) diffractions of Fe
that the Fe particles are pure and have a cubic spinel structure
JCPDS NO. 85-1436). The X-ray diffraction (XRD) pattern of Silica
3 4
O , respectively, indicating
3
O
4
8
(
coated magnetite nanoparticles (Figure 2b) exhibited XRD
◦
broadened pattern because of its non-crystalline at 2θ= 20-30
3 4 2
which confirm Fe O @SiO structure. The XRD data of metal
complexes immobilized on MNPs was same as raw MNPs and silica
coated MNPs, clearly indicating that crystallinity and morphology
were not altered after grafting (Fig. 2c) and also, the crystallite size
Fig. 2. XRD diffraction pattern of Fe
3 4 3 4 2
O MNPs (a), Fe O @SiO (b) and
Fe @Si@MoO (c).
O
3 4
2
2
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The elemental composition of the Fe O @Si@MoO samples and
3
4
2
functionalization process of the MNPs with the Schiff-base and the
formation of its complex were determined by energy dispersive X-
ray spectroscopy (EDS) analysis. The EDS results, obtained from
SEM analysis of above nanomaterial, are shown in Fig. 4, and clearly
show the presence of Mo in this catalyst. Moreover, the further
confirmed presence of C, O, N, Si, Cl and Fe and also the higher
intensity of the Si peak compared with the Fe peaks indicates that
3 4 2
the Fe O nanoparticles were trapped by SiO . The Mo content of
the catalysts was also measured by ICP, which showed value of
about 0.82 mmol/g for immobilized complex supported on MNPs.
Magnetic measurements were carried out by employing vibrating
sample magnetometer at room temperature. The magnetization
Fig. 5. The magnetic hysteresis loops of Fe
3 4 3 4 2
O MNPs (a), Fe O @SiO (b) and
Fe @Si@MoO (c).
O
3 4
2
curves measured for Fe
compared in Fig. 5. It can be seen that the values of the saturation
magnetization were 58.31 emu/g for Fe , 48 emu/g for
Fe @SiO and 45 emu/g for Fe @Si@MoO respectively. This is
probably due to the formation of non-crystalline silica on the
surface of Fe nanoparticle as well as the restriction of domain
wall motion by the magnetic dilution effect of inert silica. Although
with this reduction in the saturation magnetization, strong
magnetization of the nanoparticles was also revealed by simple
attraction with an external magnet and the catalyst still can be
efficiently separated easily from the solution with the help of an
external magnetic force.
3 4 3 4 2 3 4 2
O , Fe O @SiO and Fe O @Si@MoO are
Application of dioxomolybdenum complex supported on Fe
a heterogeneous catalyst:
3 4
O as
3 4
O
3
O
4
2
3
O
4
2
After the characterization and identification of the catalyst, in order
to find the best reaction conditions for the synthesis of 5-amino-
pyrazole-4-carbonitrile derivatives, the one-pot three-component
condensation of 4-methoxybenzaldehyde, malononitrile and
phenylhydrazine with equimolar ratio were used as the model
reactants and the effect of catalyst and temperature was
3
O
4
3 4 2
investigated in presence of various amounts of Fe O @Si@MoO
°
°
(
(
0.001 to 0.05 g) at temperatures ranging from 25 C to 100 C
Table 1). As Table 1, show that, the best results were attained
when the reaction was achieved in the presence of 0.02 g catalyst
at room temperature (Table 1, entry 11). In the absence of catalyst
a low yield of the products was achieved after 60 min (Table 1,
entries 1 and 2). Increasing the reaction temperature did not
improve the rate of the reaction.
Table 1. The effect of amount of the catalyst and temperature on the
condensation reaction between 4-methoxybenzaldehyde, phenylhydrazine and
a
malononitrile under solvent-free conditions.
Amount of
catalyst (g)
Reaction
temperature ( C)
Reaction
time (min)
Yield (%)
Entry
o
1
2
3
3
3
8
1
1
1
8
1
2
3
4
5
6
7
8
9
—
r.t.
100
r.t.
60
60
60
60
60
60
45
45
30
30
20
20
20
20
20
20
—
0.001
0.001
0.002
0.002
0.005
0.005
0.01
0.01
0.02
0.02
0.02
0.02
0.05
Fig. 3. SEM image of Fe
O
3 4
@Si@MoO
2
.
100
r.t.
O Kα
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
100
r.t.
38
4
4
7
7
9
3
3
8
8
0
100
r.t.
FeLα
SiKα
1
1
1
1
1
1
1
0
1
2
3
4
5
6
100
r.t.
N Kα
FeKα
90
50
9
0
75
MoLβ
MoLα
ClKβ
ClKα
90
90
90
100
r.t.
C Kα
FeKβ
keV
0
5
10
0.05
100
Fig. 4. EDS diagram of the Fe
3
O
4
@Si@MoO
2
.
a
Reaction conditions: 4-methoxybenzaldehyde (1 mmol), phenylhydrazine (1
b
mmol), malononitrile (1 mmol),; Isolated yield.
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Then, we optimized the reaction conditions for the three- preparation of pyrazole derivative under optimized conditions. The
component condensation with respect to yield and reaction rate by catalyst was recovered by an external magnet and the remaining
varying the solvent (Table 2). Several solvents, such as H O, ethanol, solid was washed with hot ethanol (2×10 mL). Then, the recovered
2
°
CH
3
CN, CH
2
Cl
2
,
Toluene, CH
3
CO
2
Et and n-Hexane were also catalyst was dried under vacuum at 60 C. The performance of the
surveyed by using Fe O @Si@MoO as catalyst. The reaction that recycled catalyst in reaction up to eight successive runs was shown
3
4
2
used at room temperature under solvent-free conditions led to in Fig. S33. These bar diagrams shows that the desired products
higher yields and shorter reaction time than those using above were obtained in high yields with only a slight decrease in catalytic
mentioned solvents (entry 1).
activity of the nano-catalyst. The general methods to check the
presence or absence of leached soluble Mo in the reaction solution
are a hot filtration test or elemental analysis of the recovered
catalyst. The heterogeneity of this catalyst in solvent free condition
and room temperature is clear and in such condition the hot
filtration is unhelpful. Analysis by ICP-AES of molybdenum in the
product after isolation of catalyst showed no loss of metal during
the catalytic reaction, indicating that no metal leaching occurred.
Table 2. The effect of various solvents on the reaction between 4-
methoxybenzaldehyde, phenylhydrazine and malononitrile.
a
Reaction time
Theoretical study
Entry
Solvent
Yield (%)
(
min)
All of the calculations were performed with the Gaussian09
program. Full geometry optimization was carried out with the
1
2
3
4
5
6
7
8
Solvent-free
20
60
30
30
45
60
45
60
90
25
88
84
55
31
59
27
40
H
2
O
B3LYP hybrid density functional and the SVP basis set for all atoms.
Frequency calculations at the same level of theory have also been
performed to identify all of the stationary points as minima (zero
imaginary frequencies) or transition structure (one imaginary
frequency). In order to investigate the mechanism of the synthesis
of 5-amino-pyrazole-4-carbonitrile derivatives in the presence of
Fe O @Si@MoO we used the total electronic energies (E +ZPE)
2
C H
5
OH
CH
CH
Toluene
CH CO Et
3
CN
2
Cl
2
3
2
3
4
2
el
n-Hexane
and the Gibbs free energies. To make the calculations possible and
less expensive the H atom was used as a model for Fe @Si
a
O
3 4
Reaction conditions: 4-methoxybenzaldehyde (1 mmol), phenylhydrazine (1
mmol), malononitrile (1 mmol), room temperature; Isolated yield.
b
moiety. The energy and Cartesian atomic coordinates of all
compounds involved in our suggested mechanism are available in
Supporting Information. To investigate the oxidation process in the
To estimate the efficiency and scope of the nano-catalyst, we final step of proposed mechanism for the synthesis of 5-amino-
extended our study using Fe @Si@MoO (0.02 g) in the absence pyrazole-4-carbonitrile derivatives with Fe O @Si@MoO similar to
3
O
4
2
3
4
3
2
0
of solvent with different aromatic aldehydes to prepare a series of our previous study on a different catalyst , density functional
pyrazoles (Table 3). A broad range of structurally diverse aromatic theory was used. Starting from intermediate 11, two different
aldehydes (electron-releasing substituents, electron-withdrawing orientations of adjacent N–H and C–H groups on pyrazole ring with
substituents and halogens on their aromatic ring) were used respect to each other give cis and trans like isomers that the trans-
prosperity in the reaction, and gave the corresponding products in like isomer is 0.8 kcal/mol more stable than cis one. As illustrated in
high yields and in short reaction times without formation of any Fig. 6, by addition of Fe O @Si@MoO and through the formation
3
4
2
byproducts. According to the suggested mechanism and the nature of transition structures (TS) and then removing the molecular
of electron donating substituted on the phenylhydrazine ring, hydrogen (H ) the intermediate 12 will be formed. Our calculations
2
phenylhydrazine reacted faster than 4-bromophenylhydrazine and showed that the suitable transition structure obtained by addition
4
-chlorophenylhydrazine (see Table 3).
In Scheme 3 we present a probable mechanism for the synthesis of
-amino-pyrazole-4-carbonitrile derivatives (4) in the presence of
Fe @Si@MoO The reaction happens via initial creation of
3 4 2
of Fe O @Si@MoO to cis isomer, so Fig. 6 shows energy profile for
cis one. According to values of calculated Gibbs free energies, this
reaction is about -34.72 kcal/mol exothermic. In the final step of the
reaction the intermediate 12 converts into 5-amino-pyrazole-4-
carbonitrile (4) through an endothermic process (ꢀG = 11.70
kcal/mol).
5
3
O
4
2
arylidene malononitrile (8) by the Knoevenagel addition of activated
malononitrile (3) to the activated aromatic aldehyde (1) and
followed by loss of water molecules. The formation of the 5-amino- In conclusion, the whole process of conversion of 11 to 4 through
pyrazole-4-carbonitrile derivatives (4) is proposed to contain the the releasing molecular hydrogen is exothermic (ꢀG is -23.02
reaction between arylidene malononitrile (8) and phenylhydrazine kcal/mol for cis isomers). Thus the above theoretical studies
(3), followed through Michael addition, intermolecular cyclisation. support previous suggestion that releasing molecular hydrogen (H2)
Conversion of 5-amino-pyrazolidine-4-carbonitrile (12) to its during the reaction progress is quite possible. The important step of
corresponding 5-amino-pyrazole-4-carbonitrile (4) might be oxidation is the direct elimination of H molecule from intermediate
2
occurred by uncommon hydride transfer and releasing molecular 11 and Fe O @Si@MoO (Fig. 6) in which the C‒H bond in
3
4
2
3
0, 41-43
hydrogen (H
2
).
compound 11 is so weakened due to the delocalization of lone pair
of nitrogen atom and the π electron of adjacent double bond to σ*
The possibility of recycling the catalyst are important issues,
especially when the reactions use solid catalysts. Thus, the recovery
and reusability of catalyst were examined using the reaction of 4-
methoxybenzaldehyde, malononitrile and phenylhydrazine for the
3
0
C-H bond in intermediate 11 and therefore the activation energy is
relatively small. It should be noted that the Fe @Si@MoO in
3
O
4
2
30
comparison with the other used catalysts has significantly reduced
4
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‡
the value of ꢀG . The optimized structures of al lcompounds involved in our suggested mechanism are shown in Fig. 7.
a
Table 3. The three-component synthesis of 5-amino-pyrazole-4-carbonitrile derivatives in the presence of 0.02 g of nano catalyst.
b
o
Ref.
Entry
Aldehyde
Phenylhydrazine Derivatives
Time (min)
Yield (%)
M.p ( C) [Lit.]
3
0
1
2
3
4
5
6
7
8
9
4-Nitrobenzaldehyde
4-Chlorobenzaldehyde
Phenylhydrazine
Phenylhydrazine
Phenylhydrazine
Phenylhydrazine
Phenylhydrazine
Phenylhydrazine
Phenylhydrazine
Phenylhydrazine
Phenylhydrazine
Phenylhydrazine
Phenylhydrazine
Phenylhydrazine
Phenylhydrazine
Phenylhydrazine
Phenylhydrazine
4-Bromophenylhydrazine
4-Chlorophenylhydrazine
Phenylhydrazine
10
15
15
25
10
25
20
25
20
20
25
25
25
20
20
30
25
25
95
93
92
88
94
88
90
88
89
90
89
87
87
90
90
85
85
88
175-177 (Yellow)
3
0
221-223 (White)
30
1-naphthaldehyde
163-165 (Yellow)
3
0
Cinnamaldehyde
235-237 (Orange)
2,3,4,5,6-pentafluorobenzaldehyde
Ferrocene-carbaldehyde
5-fluoro-2-hydroxybenzaldehyde
pyrrole-2-carbaldehyde
2-hydroxy-3-methoxybenzaldehyde
3-ethoxy-4-hydroxybenzaldehyde
4-Pyridinecarboxaldehyde
Furan-2-carbaldehyde
158-160 (Orange)
>300 (Violet)
161-163 (Brown)
260-262 (Brown)
3
0
0
284-286 (Orange)
3
1
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
8
225-227 (Orange)
44
218-220 (Brown)
168-170 (Brown)
163-165 (Brown)
Thiophene-2-carbaldehyde
4-Methoxybenzaldehyde
3,4-Dimethoxybenzaldehyde
Benzaldehyde
4
4
112-114 (Red)
4
4
4
125-127 (Orange)
4
5
180-182 (Brown)
5
4-Methoxybenzaldehyde
210-212 (Orange)
44
Benzaldehyde
158-160 (Brown)
a
b
Reaction conditions: Aldehyde (1 mmol), phenylhydrazine derivatives (1 mmol), malononitrile (1 mmol), room temperature, solvent-free; Isolated yield.
Scheme 2. The sequence of events in the preparation of immobilized dioxomolybdenum complex supported on MNPs.
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.
3 4 2
Scheme 3. The offered mechanism for the synthesis of pyrazole derivatives using Fe O @Si@MoO
6
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Mo
Mo
Mo
SiO
Fe
2
TS
Mo
3
O
4
Mo
O
Mo
H
O
H
R
H
N
N
N
NH
2
1
8.18
Mo
Mo
Mo
(
5.84)
SiO
Fe
2
Mo
3
O
4
Mo
H
Mo
TS
H
2
0
.00
Mo
Mo
Mo
SiO
Fe
2
Mo
3
O
4
Mo
-
23.02
H
R
(-16.32)
H
N
Mo
H
N
N
NC
-34.72
-40.07)
NH2
R
(
2
H N
Mo
Mo
N
N
11-cis
SiO2
Fe
Mo
3
O
4
Mo
N
R
Mo
Mo
H
N
N
NH
2
12
Reaction Coordinate
3 4 2
Fig. 6. Energy profile calculated for synthesis of 5-amino-pyrazole-4-carbonitrile derivatives by Fe O @Si@MoO beginning from compound 11 (see scheme 3). The
relative Gibbs free energies and the gas phase total electronic energies (Eel+ZPE, figures in parentheses) obtained from the B3LYP/SVP calculations both are given in
kcal/mol.
1
1-cis
11-trans
4
TS
12
Catalyst
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Fig. 7. The optimized structure of all compounds involved in conversion of 11 to 4 according to the mechanism suggested in Figure 6.
magnetic particles were washed several times with water until the
Experimental
Materials
°
pH of the runoff was around 7 and dried at 60 C under vacuum.
Synthesis of silica-coated iron oxide nanoparticle (Fe O @SiO
3 4 2
MNPs)
All of the reagents and solvents involved in synthesis were of
analytically grade and used as received without further purification.
Azo-coupled aldehyde (5-(4-chlorophenylazosalicylaldehyde)) was
3 4 2
The Fe O @SiO core-shell nanoparticles were prepared according
4
7
4
6
to the Stober method. Magnetic nanoparticles (1.0 g) were
dispersed by ultrasonic vibration in a mixture of 100 mL of ethanol,
prepared as described previously.
Instrumentation
1
0 mL of deionised water, and 2.5 mL of 25 wt% concentrated
Reaction progress and purity determination of the compounds were aqueous ammonia solution, followed by the addition of 2 mL of
checked by TLC using silica gel SIL G/UV 254 plates. Infrared spectra tetraethylorthosilicate (TEOS). After stirring for 12 h at room
2
were recorded on Jusco 300 FT-IR Spectrometer using compressed temperature under an N atmosphere, the brown precipitate was
1
13
KBr discs. The H NMR (400.13) and C NMR (100.62 MHz) were collected from the solution using a magnet, and then washed
°
recorded on a Bruker spectrometer (δ in ppm). Nanostructure several times with water and ethanol and dried at 25 C under
8
observations were conducted with a field emission scanning vacuum.
electron microscope (FESEM). Melting points are uncorrected and
were recorded on a Buchi B-545 apparatus in open capillary tubes.
Mass spectra of new compounds were obtained on Agilent
Technologies 5975C VL MSD spectrometer. Magnetic
dispersed in 100 mL ethanol solution, then, 2.5 mL 3-
measurement of materials was investigated with a vibrating
sample magnetometer (VSM-4 inch, Daghigh Meghnatis
Synthesis of magnetite nanoparticles coated by 3-
chloropropyltrimethoxysilane (CPTMS)
Briefly, 1.0 g silica-coated metal nanoparticle samples were
chloropropyltrimethoxysilane was added using a syringe into the
system under an N
2
atmosphere. After 24 h stirring at room
Kashan Co., Kashan, Iran) at room temperature. XRD patterns were
collected using a Bruker, D8ADVANCE diffractometer. The samples
temperature, the CPTMS-modified Fe O particles were collected
3
4
◦
◦
◦
using a magnet, and subsequently washed with ethanol, followed
by D.I. water for two times and denoted as Fe O @Si-Cl.
were scanned at a rate of 0.05 / min from 10 to 90 of 2
θ.
Scheme summarizes the reactions which leading to
2
3 4
dioxomolybdenum complex supported on MNPs.
General procedure for synthesis of azo–azomethine ligand, H2L
Synthesis of iron oxide nanoparticle
A solution of diethylenetriamine (1 mmol, 0.103 g) in absolute EtOH
All the involved chemical agents were analytical grade and used
without further purification. The Fe NPs were prepared using a
published method with a slight modification. An aqueous solution
of (0.9941g, 5 mmol) FeCl .6H O and (2.7029 g, 10 mmol)
FeCl .4H O was added to a three-necked round bottomed flask (250
(
(
20 mL) was added to a stirring solution of azo-coupled aldehyde (5-
3
O
4
4-chlorophenylazosalicylaldehyde)) (2 mmol, 0.52 g) in absolute
3
9
°
EtOH (60 mL) during a period of 15 min at 50 C. The solution was
then heated for 4 h at 80 °C with stirring. The mixture was
separated and the obtained solid was washed with hot ethanol
3
2
2
2
mL) and then, the mixture solution was heated to 80 ºC. Finally, 15
mL of concentrated ammonia (25%) was added rapidly to the
solution, and it immediately turned black. The reaction was kept at
(
three times) and then with diethyl ether. The resulted product was
46
dried in air.
this temperature for 180 min. The black precipitate was obtained Synthesis of Fe
3
O
4
@Si–H
2
azosaldien and its metal complex
°
with the help of a magnet and dried at 50 C overnight. The resulted
Triethylamine was added to dry ethanol solution (60 ml) of the
H
2
azosaldien and then chloropropylsilyl modified MNPs was added
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Organic Chemistry Frontiers
PleaseRd So Cn oA t da vd aj un s ct ems argins
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DOI: 10.1039/C6RA20988B
ARTICLE
to the above solution and the reaction mixture under ultrasonic NMR (400 MHz, DMSO-d6): δppm 7.90 (d,
J
= 7.6 Hz, 1H), 7.71 (t,
J =
°
irradiation in N
metal salt (MoO
Fe @Si–H
azosaldien in methanol (100 ml) containing a few MHz, DMSO-
2
atmosphere was refluxed at 60 C for 24 h. Thus, 7.5 Hz, 1H), 7.50 (d,
J
= 7.6 Hz, 1H), 7.46 (d,
= 7.5 Hz, 2H), 6.51 (d, = 7.8 Hz, 1H); C NMR (100
): δppm 139.21, 132.81, 131.63, 128.91, 127.69,
J
= 8.0 Hz, 1H), 7.33 (s,
1
3
) (excess) was added to a mixture of 1H), 6.64 (t,
J
J
2
(acac)
2
O
4
2
d
6
3
drops of triethylamine and the resulting mixture was refluxed and 127.63, 127.26, 126.43, 125.96, 125.62, 125.43, 124.89, 120.52,
+
irradiated with ultrasonic for 24 h. The resulted precipitate was 72.73; MS: m/z = 237 [M] .
filtered and washed with hot-water and ethanol until solution
became colorless. The obtained product was dried and stored in a
vacuum desiccator.
5
-amino-1-phenyl-3-(thiophen-2-yl)-1H-pyrazole-4-carbonitrile
o
(
Table 3, entry 13): Brown solid; M.p: 163-165 C; Yield: 87%; IR
-1
(
KBr): υ 3395, 3097, 3033, 2943, 2227, 1584, 1489, 1407, 1291 cm ;
H NMR (400 MHz, DMSO-
1
General procedure for the synthesis of 5-amino-pyrazole-4-
carbonitrile derivatives
d
6
): δppm 7.92 (d,
J
= 7.2 Hz, 5H), 7.56 (d,
= 7.4 Hz, 3H), 7.34 (d,
6
= 7.2 Hz, 1H), 7.06 (s, 1H); C NMR (100 MHz, DMSO-d ): δppm
J
= 7.3 Hz, 2H), 7.50 (t, = 7.3 Hz, 8H), 7.40 (t,
J
1
1
J
J
13
A mixture of various aromatic aldehydes (1 mmol), malononitrile (1
mmol), phenylhydrazine (1 mmol) and dioxomolybdenum
complexes supported on MNPs as nano-catalyst (0.02 g) in a round
bottom flask was placed and the subsequent mixture was firstly
stirred magnetically under solvent-free conditions at room
temperature. After completion of the reaction, as monitored by TLC
51.78, 133.98, 132.93, 124.67, 122.33, 119.33, 118.40, 116.54,
15.45, 115.36, 114.75, 114.67, 112.94, 62.15; MS: m/z = 266 [M] .
+
Conclusions
n-hexane/ethyl acetate (5:3), ethyl acetate (10 mL) was added to In summary we have reported a reusable and heterogeneous
reaction mixture, stirred and refluxed for 3 min, and then by catalyst for the one-pot three-component synthesis of
external magnet to separate catalyst from the other materials. The pyrazole derivatives. The use of magnetite nanoparticles
remained catalyst was used for alternative reaction. The solvent of attracted a lot of attention in the field of catalysis due to
organic layer was evaporated and the crude product was purified by unique advantages such as chemical stability, strong
recrystallization from ethanol/water (10:1).
magnetization, high activities and easily separated in
heterogeneously catalytic processes. From the fifteen
synthesized derivatives of pyrazoles six ones are new
compounds. Interestingly, one of the new pyrazole derivatives
contains a ferrocene moiety. Numerous main advantages of
this study are reasonably cleaner reaction profile, high yield,
short reaction time, low cost, recyclability of magnetic nano-
catalyst and simplicity of product isolation.
Spectral data analysis for compounds
5-amino-3-(perfluorophenyl)-1-phenyl-1H-pyrazole-4-carbonitrile
o
(Table 3, entry 5): Orange solid; M.p: 158-160 C; Yield: 94%; IR
-
1
(
KBr): υ 3382, 3328, 3221, 2980, 2190, 1677, 1650, 1598, 1417 cm ;
1
H NMR (400 MHz, DMSO-
d
6
): δppm 8.71 (s, 1H), 8.09 (d,
= 22.1, 7.8 Hz, 4H), 7.51 (t, = 6.7 Hz, 2H), 7.42 (t,
= 7.9 Hz, 1H); C NMR (100 MHz, DMSO-
J = 8.3 Hz,
2
7
H), 7.79 (dd,
.3 Hz, 1H), 7.16 (d,
J
J
J
=
):
1
3
J
d
6
δppm 165.60, 146.72, 139.18, 133.62, 132.26, 131.64, 131.20,
Acknowledgements
1
5
5
28.47, 128.31, 128.23, 128.17, 127.99, 127.49, 127.40, 123.41,
8.09; MS: m/z = 350 [M] .
+
We are grateful to the Bu-Ali Sina University for financial support.
-amino-1-phenyl-3-(ferrocene-yl)-1H-pyrazole-4-carbonitrile
o
(Table 3, entry 6): Violet solid; M.p: >300 C; Yield: 88%; IR (KBr): υ
3
1
619, 3440, 3345, 3224, 2983, 2938, 2217, 1679, 1640, 1598, 1571, Notes and references
-
1
+
497 cm ; MS: m/z = 368 [M] . Due to paramagnetic nature of
1
2
P. G. Cozzi, Chem. Soc. Rev., 2004, 33, 410.
K. C. Gupta and A. K. Sutar, Coord. Chem. Rev., 2008, 252
1420.
ferrocene moiety a useful NMR spectrum of this compound was not
obtained.
,
3
4
5
6
7
Y. N. Belokon, B. Green, N. S. Ikonnikov, T. Parsons and V. I.
Tararov, Tetrahedron, 2001, 57, 771.
5
-amino-3-(5-fluoro-2-hydroxyphenyl)-1-phenyl-1H-pyrazole-4-
o
carbonitrile (Table 3, entry 7): Brown solid; M.p: 161-163 C; Yield:
0%; IR (KBr): υ 3621, 3437, 2989, 2217, 1598, 1571, 1497, 1347
A. Hu, G. T. Yee and W. Lin, J. Am. Chem. Soc., 2005, 127
2486.
,
9
1
-1 1
cm ; H NMR (400 MHz, DMSO-d6): δppm 8.82 (s, 2H), 8.40 (s, 2H),
B. Rac, A. Molnar, P. Forgo, M. Mohai and I. Bertoti, J.
Mol.Catal. A: Chem., 2006, 244, 46.
M. A. Nasseri and M. Sadeghzadeh, J. Chem. Sci., 2013, 125,
537.
S. Safaei, I. Mohammadpoor-Baltork, A. R. Khosropour,M.
Moghadam, S. Tangestaninejad and V. Mirkhani, Catal.Sci.
7
2
d
1
5
.20 (d,
H), 6.60 (t,
): δppm 153.19, 148.36, 132.12, 129.83, 129.69, 124.41, 124.21,
22.64, 121.85, 121.53, 117.12, 116.00, 115.54, 115.15, 109.92,
5.49; MS: m/z = 294 [M] .
J
= 7.8 Hz, 2H), 7.00 (t,
J = 7.6 Hz, 2H), 6.76 (d, J = 7.9 Hz,
1
3
J
= 7.5 Hz, 2H), 5.26 (s, 1H); C NMR (100 MHz, DMSO-
6
+
Technol., 2013,
H. Moghanian, A. Mobinikhaledi, A. G. Blackmanc and E.
Sarough-Farahanib, RSC Adv., 2014, , 28176.
3, 2717.
5-amino-1-phenyl-3-(1H-pyrrol-2-yl)-1H-pyrazole-4-carbonitrile
8
9
o
(Table 3, entry 8): Brown solid; M.p: 260-262 C; Yield: 88%; IR
4
(KBr): υ 3405, 3334, 3224, 3116, 2929, 2231, 2200, 1677, 1604,
M. B. Gawande, P. S. Branco and R. S. Varma, Chem. Soc.
Rev., 2013, 42, 3371.
-1 1
1
8
7
δ
1
2
6
580, 1521, 1344, 1213 cm ; H NMR (400 MHz, DMSO-d ): δppm
.06 (s, 1H), 7.88 (d,
.6 Hz, 1H), 6.62 (d,
ppm 165.82, 147.53, 147.50, 147.03, 146.66, 133.48, 133.43,
31.75, 128.33, 128.00, 127.56, 123.50, 123.44, 58.28; MS: m/z =
49 [M] .
J
J
= 7.8, 3H), 7.09 (t,
= 7.9 Hz, 1H); C NMR (100 MHz, DMSO-
J
= 7.6 Hz, 1H), 6.76 (t,
J
=
):
10 M. Y. Zhu, C. J. Wang, D. H. Meng and G. W. Diao, J. Mater.
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M. Basset, Chem. Rev., 2011, 111, 3036.
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3
1
1 V. Polshettiwar, R. Luque, A. Fihri, H. Zhou, M. bouhara and J.
d
6
+
5
3
3
-amino-3-(furan-2-yl)-1-phenyl-1H-pyrazole-4-carbonitrile (Table 13 J. Zhou, Z. Dong, P. Wang, Z. Shi, X. Zhou and R. Li, J. Mol.
o
, entry 12): Brown solid; M.p: 168-170 C; Yield: 87%; IR (KBr): υ
Catal. A: Chem, 2014, 382, 15.
-1
1
334, 3204, 2981, 2206, 1639, 1602, 1585, 1410, 1286 cm ; H
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Table of contents
Synthesis of pyrazole derivatives in the presence of dioxomolybdenum complex supported on
silica-coated magnetite nanoparticles as an efficient and easily recyclable catalyst
Jamshid Rakhtshah, Sadegh Salehzadeh*, Ehsan Gowdini, Farahnaz Maleki, Saeed Baghery
and Mohammad Ali Zolfigol
Dioxomolybdenum complex supported on functionalized Fe O magnetite nanoparticles as a heterogeneous
3
4
catalyst was synthesized, characterized and used in the synthesis pyrazole derivatives.