Copper Schiff base complex immobilized on silica-coated Fe3O4 nanoparticles: a recoverable and efficient catalyst for synthesis of polysubstituted pyrroles

Article abstract of DOI:10.1002/aoc.4501

In this work, a copper Schiff base complex immobilized on silica-coated Fe₃O₄ nanoparticles is synthesized, and studied as a highly efficient, recyclable, green and heterogeneous catalyst for the preparation of polysubstituted pyrroles under solvent-free and mild conditions. This new catalyst was characterized by different techniques, such as Fourier transform infrared (FT-IR), X-ray powder diffraction (XRD), field-emission scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), inductively coupled plasma (ICP) and vibrating sample magnetometry (VSM). The simple and environmentally one-pot multicomponent condensation of nitromethane, an aryl aldehyde, a 1,3-dicarbonyl compound and an amine in the presence of above catalyst affords the title compounds at room temperature. At the end, we compared the results for the synthesis of polysubstituted pyrroles in the presence of our nanocatalyst with previously reported catalysts in the literature.

Full text of DOI:10.1002/aoc.4501

Received: 22 February 2018
DOI: 10.1002/aoc.4501
Revised: 16 May 2018
Accepted: 12 June 2018
F U L L P A P E R
Copper Schiff base complex immobilized on silica‐coated
Fe O nanoparticles: a recoverable and efficient catalyst for
3
4
synthesis of polysubstituted pyrroles
Seyedeh Aghigh Hamrahian | Jamshid Rakhtshah | Seyedeh Mohadeseh Mousavi Davijani |
Sadegh Salehzadeh
Faculty of Chemistry, Bu‐Ali Sina
University, Hamedan, Iran
In this work, a copper Schiff base complex immobilized on silica‐coated Fe O
3 4
nanoparticles is synthesized, and studied as a highly efficient, recyclable, green
and heterogeneous catalyst for the preparation of polysubstituted pyrroles
under solvent‐free and mild conditions. This new catalyst was characterized
by different techniques, such as Fourier transform infrared (FT‐IR), X‐ray
powder diffraction (XRD), field‐emission scanning electron microscopy
(SEM), energy‐dispersive X‐ray spectroscopy (EDX), inductively coupled
plasma (ICP) and vibrating sample magnetometry (VSM). The simple and envi-
ronmentally one‐pot multicomponent condensation of nitromethane, an aryl
aldehyde, a 1,3‐dicarbonyl compound and an amine in the presence of above
catalyst affords the title compounds at room temperature. At the end, we com-
pared the results for the synthesis of polysubstituted pyrroles in the presence of
our nanocatalyst with previously reported catalysts in the literature.
Correspondence
Sadegh Salehzadeh, Faculty of Chemistry,
Bu‐Ali Sina University, Hamedan, Iran.
Email: saleh@basu.ac.ir
Funding information
Bu‐Ali Sina University
KEYWORDS
immobilized cu complex, multicomponent reaction, polysubstituted pyrroles, Schiff bases, solvent‐
free
1
| INTRODUCTION
antifungal, antitumor, antibacterial, anti‐oxidant and
anti‐inflammatory. Because of their enormous impor-
Multicomponent reactions (MCRs) have emerged as a
vital field of chemistry and a powerful tool in modern
tance in chemical as well as pharmaceutical research,
highly polysubstituted pyrroles have fascinated remark-
able sympathy in organic synthesis and a number of syn-
[1–3]
synthetic organic chemistry.
Such reactions represen-
[
5]
tation a number of practical, environmental, and eco-
nomical advantages over classical stepwise methods.
The combination of the privileges of multicomponent
reactions and active catalysts can be considered to result
in a highly efficient synthesis of polysubstituted pyr-
thetic methods have been developed. Different methods
for the synthesis of polysubstituted pyrroles include Paal‐
Knorr condensation reaction, Knorr reaction and
[
6]
Hantzsch reaction. These reactions have considerable
drawbacks such as limited scope, multisteps synthetic
operations and harsh reaction conditions, which limit
[4]
roles. Pyrrole derivatives are the important class of
N‐heterocyclic compounds and have been used as signifi-
cant building blocks in organic synthesis as well as in the
drug exploration. They have been widely used due to
interesting biological properties such as antianginal,
[
1]
their use. Polysubstituted pyrroles are generally synthe-
sized in the presence of various catalysts, such as nano
[
1]
[7]
[8]
copper oxide, nickel ferrite nanoparticles, FeCl3,
[
9]
gluconic acid aqueous solution,
nano‐CoFe O
2
4
Appl Organometal Chem. 2018;e4501.
wileyonlinelibrary.com/journal/aoc
© 2018 John Wiley & Sons, Ltd.
1 of 12
https://doi.org/10.1002/aoc.4501

2
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HAMRAHIAN ET AL.
[
4]
[6]
[10]
supported molybdenum,
β‐cyclodextrin,
NiCl ,
vibrations of alkyl groups in Cl@silica‐Fe O . The band
appeared at 1645 cm also confirms attachment the
2
3 4
[11]
[12]
−1
ionic liquid,
heterogenized tungsten complex,
Amberlyst 15,
and catalyst free conditions.
Fe‐
[
13]
[14]
[15]
MIL‐101,
p‐TSA,
ChCl‐malonic acid,
Schiff base (C=N) on the nanoparticle. In accordance
[
16]
[17]
[23]
with previously reported data,
comparison of
The development of heterogeneous catalysts of Schiff
Figures 1d and 1e indicates that the C=N stretching band
base complexes and the analysis of their effects on chem-
ical synthesis have become a primary area of research.
in SB@silica‐Fe O (Figure 1d) is shifted to a lower fre-
3
4
−1
[
18]
quency (1632 cm ) upon complexation with Cu (OAc) .
2
In recent years, many attempts have been made to immo-
bilize Schiff base complexes on different solid supports
like magnetic nanoparticles (MNPs) for catalysis of
organic reactions. Magnetic nanoparticles (MNPs) have
attracted increasing sympathy for the immobilization of
homogeneous catalysts because of their inimitable prop-
erties including a low toxicity, large surface‐to‐volume
Figure 2 shows the XRD patterns of synthesized initial
magnetite and Cu (II) Schiff base supported on MNPs in
the range 10–90°. Sharp peaks confirm the good crystal-
linity of Fe O The eight peaks for initial MNPs corre-
3
4
spond well with the cubic spinel structure for Fe O
3
4
[
23]
nanoparticles (JCPDS, 85–1436).
The observed intense
peaks at 18.3, 30.5, 35.9, 43.3, 53, 57, 62 and 74.5° repre-
sent, the (111), (220), (311), (400), (422), (511), (440) and
(533) Bragg reflections, respectively. The XRD data of
metal complexes immobilized on MNPs was the same as
raw MNPs, clearly indicating that crystallinity and mor-
phology were not altered after grafting (Figure 2b). Also,
the crystallite size of the SBCu@silica‐Fe O was calcu-
[19–21]
ratio and magnetism.
Following our continued interest in the heterogeneous
[22–24]
catalysts
herein, we report the synthesis of a copper
Schiff base complex immobilized on silica‐coated Fe O4
3
nanoparticles. We show that it is a highly efficient and eas-
ily recoverable catalyst for the synthesis of polysubstituted
pyrroles via the one‐pot four‐component reaction of nitro-
methane, aryl aldehyde, 1,3‐dicarbonyl compound and
amine under solvent‐free at room temperature (Scheme 1).
3
4
lated using Scherrer'sequation, which was smaller than
the size determined by field emission scanning electron
microscopy (FE‐SEM) analysis. The observed disagree-
ment can be ascribed to the reality that XRD measure-
ments investigate crystallite sizes as sizes of ‘coherently
diffracting domains’ of crystals while grains may contain
several of these domains. The peak width (FWHM), size
and interplanar distance from the XRD pattern of catalyst
in the range 11.95–55.44° were obtained and the results
are summarized in Table 1.
2
| RESULTS AND DISCUSSION
FT‐IR spectra were obtained on the substances pressed
−
1
into KBr pellets in the range 400–4000 cm . Figure 1
shows the FT‐IR spectra of Fe O (a), silica‐Fe O (b),
3
4
3 4
Cl@silica‐Fe O4
(c),
SB@silica‐Fe O4
(d),
and
The morphology of nanocatalyst was studied by scan-
ning electron microscopy (SEM) (Figure 3), and the result
indicated that the most of the particles have a spherical
shape. As can be seen, most of the prepared nanoparticles
have a mean diameter of about 20 nm which show a close
agreement with the values calculated by XRD analysis.
The EDX spectrum of the attained SBCu@silica‐Fe O
3
3
SBCu@silica‐Fe O (e). The presence of Fe‐O bond in
3
4
the magnetic nanoparticles is confirmed by the particular
strong peak at 585 cm . Comparing with the IR
spectrum (a), the bands at 1079 cm are attributed to
Si‐O stretching bands in Figure 1b. Also, Figure 1c.
−
1
−
1
confirms
the
successful
reaction
between
3
4
3
‐chloropropyltrimethoxysilane and silica‐coated MNPs.
as nanocatalyst indicates the presence of the anticipated
elements in the structure of the catalyst, for iron (Fe), sil-
icon (Si), carbon (C), oxygen (O), nitrogen (N), chlorine
−
1
The weak peak at 2920–2965 cm corresponds to ali-
phatic C–H symmetric and asymmetric stretching
(
Cl) and copper (Cu) (Figure 4). The higher severity of
the Si peak compared with the Fe peaks shows that the
Fe O nanoparticles are trapped by SiO .
3
4
2
The magnetic properties of the nanocatalyst were stud-
ied using vibrating sample magnetometer (VSM) at room
temperature. The saturation magnetization values for
Fe O and SBCu@silica‐Fe O are compared in Figure 5.
3
4
3 4
According to the magnetization curves, the saturation
magnetization of the nanoparticles decreases from
−
1
−1
4
8 emu g for the initial Fe O sample to 37 emu g for
3 4
the final SBCu@silica‐Fe O nanoparticles. The above
3
4
SCHEME
SBCu@silica‐Fe
1
The synthesis of pyrrole derivatives using
3 4
O as a highly efficient nanocatalyst
results indicated that the decrease in saturation magneti-
zation of the nanocatalyst compared to the bare

HAMRAHIAN ET AL.
3 of 12
3 4
FIGURE 1 FT‐IR spectra of Fe O (a),
silica‐Fe
SB@silica‐Fe
Fe (e)
3
O
4
(b), Cl@silica‐Fe
3 4
O (c),
3 4
O
(d), and SBCu@silica‐
3 4
O
FIGURE 2 XRD diffraction pattern of
Fe (a) and SBCu@silica‐Fe (b)
3
O
4
3 4
O
TABLE 1 X‐ray diffraction (XRD) data for the SBCu@silica‐
Fe as a nanocatalyst
thermostability of nanocatalyst. The weight loss at tem-
peratures below 202 °C (3%) indicates the removal of
water from the surface of the nanoparticles. The curve
shows a weight loss of about 4–8% from 285 °C to
3 4
O
Peak width
FWHM]
(degree)
Inter planer
distance
[nm]
[
Size
[nm]
536 °C, which is ascribed to the demolition of organic
Entry
2θ
structure. Higher than 700 °C, the sample weight has no
noticeable change, indicating that the organic structure
had decomposed already. Thus, the thermostability of
nanocatalyst is very excellent.
1
2
3
4
5
6
7
35.60
43.10
53.60
57.10
62.70
73.40
84.30
0.70
0.50
0.60
0.80
0.80
0.30
0.20
11.95
17.32
14.87
11.42
11.74
33.15
55.44
0.256666
0.213888
0.171111
0.163829
0.148076
0.130508
0.118461
UV–visible spectroscopy was another technique
applied in the range 200–850 nm for proving the structure
of SBCu@silica‐Fe O as a nanocatalyst. The samples for
3
4
above spectral investigation were prepared in ethanol sol-
vent and a concentration of 0.003 g of nanocatalyst was
studied (via dispersing process). This analysis was used
to compare alterations in the various steps of catalyst
synthesis. We are able to detect the presence of an
additional part on the main structure of the MNPs,
especially at =278 nm (Figure 7). These step‐by‐step
changes in the UV spectra indicate that the nanocatalyst
is formed. The purpose is to change the absorption
nanoparticles may be ascribed to the formation of silica
shell and functionalized groups during the modification
process. However, the nanocatalyst can still be separated
from the solution by using an external magnetic force.
The curve of thermogravimetric analysis (Figure 6)
which is determined under N atmosphere, shows the
2

4
of 12
HAMRAHIAN ET AL.
3 4
FIGURE 6 TGA analysis of SBCu@silica‐Fe O
synthesized catalyst in refluxing HCl (37%) and it was
−
1
found to be 0.23 mmol g .
After successful preparation of SBCu@silica‐Fe O
3
4
nanoparticles, we used them in the synthesis of
polysubstituted pyrrole derivatives. In order to investigate
the catalytic performance of the SBCu@silica‐Fe O and
FIGURE 3 SEM image of SBCu@silica‐Fe
3
O
4
3 4
the effect of media, the reaction of aniline, benzaldehyde,
ethyl acetoacetate and nitromethane was initially exam-
ined as a model reaction. Initial research was focused
on the above reaction in solvent‐free condition using dif-
ferent amount of catalysts (0.002–0.01 g) at temperatures
ranging from 25 °C to 100 °C. In the absence of catalyst, a
low yield of the products was achieved after 60 min
(
Table 2, entries 1 and 2) and also the reaction tempera-
ture did not have significant impact on reaction rate. As
shown in Table 2, the best results were achieved when
the reaction was attained in the presence of 0.008 g cata-
lyst at room temperature (Table 2, entry 9). Also, the rep-
resented data showed the desired product was obtained in
30 min as a best time with excellent yield.
The effect of different solvents on the catalytic activity
3 4
FIGURE 4 EDS diagram of the SBCu@silica‐Fe O
of the SBCu@silica‐Fe O was investigated in the synthe-
3
4
sis of polysubstituted pyrrole derivatives. While several
solvents such as toluene, dichloromethane, acetonitrile,
water, ethanol, n‐Hexane and ethyl acetate were tested,
but the highest yield in the shortest reaction time was
obtained in the solvent‐free condition (Table 3).
After optimization of the reaction conditions, the scope
and generality of the reaction were illustrated with respect
to various aromatic aldehydes and amines including
benzylamine, aniline and substituted anilines (Table 3).
Benzaldehyde and substituted benzaldehydes containing
electron‐donating or electron‐withdrawing functionalities
and some heteroaromatic aldehydes underwent facile
reactions giving very good to excellent yields. Various aro-
matic aldehydes having substituents such as H, Me, MeO,
FIGURE 5 The magnetic hysteresis loops of Fe
SBCu@silica‐Fe (b)
3 4
O (a) and
3 4
O
intensity at =267 nm during the synthesis of the
nanocatalyst in each stage.
NO and Cl in the aromatic ring were examined with
benzylamine and methyl acetoacetate in the presence of
2
Determination of the copper content was carried out
by inductively coupled plasma (ICP) analysis on the
SBCu@silica‐Fe O nanocatalyst in similar reaction con-
ditions and the products (Table 4, entries 1–5) were
3
4

HAMRAHIAN ET AL.
5 of 12
FIGURE 7 UV–visible absorption
curves of SBCu@silica‐Fe O as a
3 4
nanocatalyst
TABLE 2 The effect of amount of the catalyst and temperature on the four‐component reaction of aniline, benzaldehyde, ethyl
a
acetoacetate and nitromethane under solvent‐free conditions
b
c
Entry
Amount of catalyst (mol% Cu)
Reaction temperature (°C)
Reaction time (min)
Yield (%)
1
2
3
4
5
6
7
8
9
—
r.t.
100
r.t.
100
r.t.
100
r.t.
100
r.t.
50
60
60
60
60
60
60
40
40
30
30
30
30
30
30
20
25
33
33
43
43
54
55
92
92
92
92
92
92
—
2 (0.046)
2 (0.046)
4 (0.092)
4 (0.092)
6 (0.138)
6 (0.138)
8 (0.184)
8 (0.184)
8 (0.184)
8 (0.184)
10 (0.23)
10 (0.23)
1
1
1
1
1
0
1
2
3
4
75
100
r.t.
100
a
Reaction conditions: benzaldehyde (1 mmol), aniline (1 mmol), ethyl acetoacetate (1 mmol) and nitromethane (1 mmol).
b
This is the temperature of oil bath and not inside the reaction medium.
c
Isolated yield.
obtained in good yields. Also, using above aldehydes, ethyl
acetoacetate and aniline the desired products (Table 4,
entries 6–9) were isolated in good yields. Heteroaromatic
aldehydes furnished good yields of the corresponding
products in shorter reaction times (entries 10–11). Then a
series of polysubstituted pyrrole derivatives were synthe-
sized by using different aldehydes, substituted anilines
and ethyl acetoacetate or methyl acetoacetate in the
presence of SBCu@silica‐Fe O nanocatalyst in solvent‐
3
4
free condition (Table 4, entries 12–17). It should be noted
that the yield of the reaction with aldehydes having an
electro‐withdrawing group was a little higher than that
for those with an electron‐releasing group (Table 4, entries
4, 5, 8 and 9). Also, according to the metal content turn
over number (TON) and turn over frequency (TOF) of
the catalyst were calculated.

6
of 12
HAMRAHIAN ET AL.
a
TABLE 3 Solvent effect in the reaction between aniline, benzaldehyde, ethyl acetoacetate and nitromethane at room temperature using
0
.184 mol% catalyst
Solvent‐free
H
2
O
C
2
H
5
OH
CH
3
CN
CH
2
Cl
2
Toluene
n‐Hexane
b
Yield (%)
90
30
27
60
65
35
68
40
44
50
29
60
29
50
Reaction time (min)
a
benzaldehyde (1 mmol), aniline (1 mmol), ethyl acetoacetate (1 mmol) and nitromethane (1 mmol) under room temperature;
b
Isolated yield.
The reusability of the catalyst is one of the most
We studied the condensation reaction of nitromethane,
aryl aldehyde, 1,3‐dicarbonyl compound and amine
under optimized conditions and in the presence of all
above catalysts (see Table 5). The results show that
important advantages and makes it beneficial for com-
mercial applications. The reusability of the catalyst is
one of the most important advantages and makes it ben-
eficial for commercial applications. Recycling and reus-
ability of the catalysts were also examined upon the
condensation between aniline, benzaldehyde, ethyl
acetoacetate and nitromethane. After finishing each run,
SBCu@silica‐Fe O4 nanocatalyst synthesized here can
3
act as effective catalyst, with respect to reaction times,
simple conditions and yields of the obtained products
in model reaction. Thus, in addition to having the
general advantages attributed to the inherent magnetic
3
ml hot ethyl acetate was added to the reaction mixture
and stirred and heated to dissolve the crude product.
Then, the nanocatalyst was separated from the reaction
mixture by an external magnet and washed with ethanol
for alternative reaction. The results of reusability studies,
summarized in Figure 8, indicated that the catalyst was
stable and reusable six times without any significant loss
of activity and even after the six runs, the yields remained
still high.
properties of SBCu@silica‐Fe O4 nanocatalyst, it is a
more efficient catalyst for the four‐component reaction
studied here.
3
3
| EXPERIMENTAL
.1 | Materials
3
The structure of reused catalyst was also confident
via IR spectra and XRD pattern after its application in
the reaction. Also, in order to determine the copper spe-
cies leached into the reaction mixture, ICP analysis was
performed and Cu metal was not detected in the reaction
mixture after 6 repeated recycling which confirms the
fact that Schiff base moieties provide strong coordinating
sites on the surface of magnetic nanoparticles and
prevent metal leaching, and enable efficient catalyst
recycling.
All reagents used were commercially available and were
used without further purification. The preparation of
nanocatalyst, SBCu@silica‐Fe O , is summarized in
3
4
Scheme 2.
3
.2 | Synthesis of magnetite Fe O4
3
nanoparticles
A mixture of FeCl .6H O (2 mmol, 7.8 g) and FeCl .4H O
3
2
2
2
(
1 mmol, 2.9 g) in deionized water (55 ml) was charged
2
.1 | Comparison of catalytic activity of
[
25]
into a 250 mL round‐bottom flask.
The mixture was
SBCu@silica‐Fe O with other known
catalysts
3
4
stirred for 10 min at 80 °C until a red solution was
obtained. Then, 90 ml of ammonia (25%) was added rap-
idly to the solution. The black mixture was stirred under
Finally, the efficiency of SBCu@silica‐Fe O nanocatalyst
3
4
in synthesis of polysubstituted pyrroles was compared
with that of previously known catalysts such as
Amberlyst‐15, heterogenized tungsten Complex, nickel
N atmosphere for another 2 h and then cooled at room
2
temperature. The resulting black precipitate was isolated
by an external magnet, exhaustively washed with a solu-
tion of NaCl (10%wt) and ethanol for several times and
dried under vacuum.
(
II) chloride hexahydrate, FeCl , nickel ferrite nanoparti-
3
cles, nano Copper oxide, nano‐CoFe O and ionic liquid.
2
4

HAMRAHIAN ET AL.
7 of 12
a
TABLE 4 Four‐component reaction of polysubstituted pyrrole derivatives using 0.184 mol% nanocatalyst under solvent‐free conditions
b
−1
°
Entry
Product
Time (min)
Yield (%)
TON
TOF (min
)
M.p C [Lit.]
1
30
80
433.78
14.49
Oil [12]
2
30
85
461.95
15.39
Oil [7]
3
4
30
20
87
90
472.82
489.13
15,76
Oil [12]
24.45
Oil [7]
5
25
88
478.26
19.13
Oil [7]
6
7
30
35
85
80
461.95
433.78
15.39
12.42
Oil [12]
Oil [1]
(Continues)

8
of 12
HAMRAHIAN ET AL.
TABLE 4 (Continued)
b
−1
°
Entry
Product
Time (min)
Yield (%)
TON
TOF (min
)
M.p C [Lit.]
8
30
93
505.43
16.84
Oil [1]
9
25
90
489.13
16.30
Oil [7]
10
11
12
30
30
35
90
88
93
489.13
478.26
505.43
16.30
15.94
14.44
130–132 [10]
122–124 [10]
Oil [11]
1
3
40
90
489.13
12.22
140–142 [9]
(Continues)

HAMRAHIAN ET AL.
9 of 12
TABLE 4 (Continued)
b
−1
°
Entry
14
Product
Time (min)
Yield (%)
TON
TOF (min
)
M.p C [Lit.]
30
88
478.26
15.94
127–129 [c]
1
5
30
30
30
85
461.95
489.13
467.39
15.39
16.30
15.57
120–122 [c]
130–132 [7]
108–110 [c]
1
6
90
1
7
86
a
Reaction conditions: different aldehydes (2 mmol), different amines (2 mmol), methyl or ethyl acetoacetate (2 mmol), nitromethan (2 mmol), nanocatalyst
0.184 mol%), solvent‐free and room temperature.
(
b
Isolated yield.
c
New derivatives.
3
.3 | Synthesis of silica‐coated magnetite
precipitate was obtained which was separated from the
solution by a magnet, and was then washed several times
with ethanol and dried under vacuum.
Fe O nanoparticles
3
4
The silica‐Fe O core‐shell nanoparticles were prepared
according to the Stober method.
3
4
[26]
For coating magnetite
nanoparticles with a layer of silica, 2 g Fe O in mixture
3
4
3
.4 | Synthesis of magnetite Fe O4
3
of 20 ml H O and 200 ml of ethanol was dispersed by
2
nanoparticles coated by 3‐
chloropropyltrimethoxysilane (CPTMS)
ultrasonic vibration for half an hour. Consequently,
4
2
ml of tetraethylorthosilicate (TEOS) and 5 ml of
5 wt% concentrated aqueous ammonia solutions were
2 g of silica‐Fe O nanoparticles, synthesized in previous
3
4
injected dropwise into the reaction mixture and the pH
value was controlled in the range 11 ≤ pH ≤ 12. After stir-
section, were dispersed in 80 ml of xylene solution by
ultrasonic vibration for 20 min, then using a syringe
2.5 ml of CPTMS was added and the mixture stirred at
ring for 12 h at 60 °C under an N atmosphere, a brown
2

10 of 12
HAMRAHIAN ET AL.
3 4
FIGURE 8 Reusability of SBCu@silica‐Fe O as a heterogeneous
catalyst in 20 minutes
8
0 °C under N Atmosphere and reflux condition for 12 h.
2
The resulting precipitate was separated from solution by a
magnet and washed several times with ethanol and dried
[27]
under vacuum.
SCHEME 2 The sequence of events in the preparation of
3 4
SBCu@silica‐Fe O
3.5 | Synthesis of Schiff base ligand
To
a
round bottom flask (100 ml) containing
dropwise over a period of 20 min at room temperature.
After the addition was completed, the reaction mixture
was stirred for 5 h under reflux at 40 °C. The residue
diethylenetriamine (4 mmol, 0.412 g) in ethanol (50 ml),
pyrrole‐2‐carboxaldehyde (8 mmol, 0.680 g) was added
3 4
TABLE 5 Comparison of the SBCu@silica‐Fe O catalytic activity with those of reported catalysts
°
a
Catalyst
Solv.
Temp ( C)
Time (min)
Yield (%)
R
1
R
2
[Ref.]
[
[
[
[
[
[
5]
Amberlyst‐15
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
‐
r.t.
30
270
240
480
720
420
25
80
85
96
78
78
80
90
92
78
81
90
82
95
OMe
OMe
OMe
OMe
OMe
OMe
OMe
OEt
C
C
C
C
C
C
C
C
C
C
C
C
C
6
6
6
6
6
6
6
6
6
6
6
6
6
H
H
H
H
H
H
H
H
H
H
H
H
H
5
5
5
5
5
5
5
5
5
5
5
5
5
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
2
2
2
2
2
2
2
2
2
2
2
12]
7]
Heterogenized Tungsten Complex
Nickel ferrite nanoparticles
Nickel (II) chloride hexahydrate
Nano Copper oxide
Reflux
100
10]
1]
r.t.
100–105
Reflux
r.t.
8]
FeCl
3
SBCu@silica‐Fe
3
O
4
‐
[
[
[
7]
Nickel ferrite nanoparticles
Nickel (II) chloride hexahydrate
Nano Copper oxide
100
240
600
720
25
10]
1]
r.t.
OEt
100–105
r.t.
OEt
SBCu@silica‐Fe
Nano‐CoFe
Ionic liquid
3
O
4
OEt
‐
[
4]
2
O
4
90
300
180
OEt
[
11]
90–95
OEt
Reaction conditions: 4‐chloro benzaldehyde (1 mmol), amine (1 mmol), ethyl or methyl acetoacetate (1 mmol) and nitromethane (1 mmol).
a
Isolated yield.

HAMRAHIAN ET AL.
11 of 12
was washed with ethanol and dried under vacuum to give
the Schiff base ligand in 70% yield.
(400 MHz, DMSO‐d ) δ
8.32 (s, 1H, ArH), 7.87
ppm
6
[28]
(d, J = 8.0 Hz, 2H, ArH), 7.58 (t, J = 8.0 Hz, 1H, ArH),
.46 (d, J = 8.0 Hz, 2H, ArH), 7.34 (d, J = 8.0 Hz, 4H,
ArH), 3.75 (q, J = 8.0 Hz, 2H, −CH ), 2.19 (s, 3H,
7
2
3
.6 | Synthesis of Schiff base ligand
13
−
CH ), 1.14 (t, J = 8.0 Hz, 3H, −CH ); C NMR
3
3
immobilized on magnetic Fe O4
3
(
101 MHz, DMSO‐d ) δ
179.1, 168.2, 166.2, 161.8,
ppm
6
nanoparticles (SB@silica‐Fe O )
3
4
157.9, 153.4, 147.9, 144.6, 136.4, 132.7, 130.8, 127.1,
Triethylamine was added to dry ethanol solution (100 ml)
of 0.25 g Schiff base ligand and then the as‐prepared
123.9, 123.1, 119.5, 116.3, 115.4, 46.2, 32.3, 26.0.
MS: m/z = 339 [M] (Figures S1–S4).
+
Cl@silica‐Fe O4 (2 g) were dispersed by ultrasonic
3
vibration for 20 min, subsequently stirred at 60 °C under
reflux for 24 h. The resulting precipitate was separated
from the solution by a magnet and washed several times
with ethanol and dried in air.
3
.8.2 | Ethyl 1‐(4‐chlorophenyl)‐2‐methyl‐
‐(p‐tolyl)‐1H‐pyrrole‐3‐carboxylate
4
(
Table 4, entry 15)
White solid; M.p: 120‐122 °C; Yield: 85%; IR (KBr): υ
−
1 1
2
980, 2950, 2860, 1714, 1493 cm ; H NMR (400 MHz,
3
.7 | Synthesis of copper Schiff base
DMSO‐d ) δ 7.91 (d, J = 8.0 Hz, 2H, ArH), 7.76
6
ppm
complex immobilized on magnetic Fe O4
nanoparticles (SBCu@silica‐Fe O )
3
(
(
3
d, J = 8.0 Hz, 1H, ArH), 7.74 (s, 1H, ArH), 7.72
d, J = 8.0 Hz, 1H, ArH), 7.45 (d, J = 8.0 Hz, 4H, ArH),
.83 (q, J = 8.0 Hz, 2H, −CH ), 2.18 (s, 3H, −CH ), 1.67
3
4
Following careful purification, resulting nanoparticles
coated with Schiff base ligand, SB@silica‐Fe O , were dis-
2
3
13
3
4
(s, 3H, −CH ), 1.23 (t, J = 8.0 Hz, 3H, −CH ); C NMR
3
3
persed in 100 ml ethanol solution by ultrasonic vibration
for 20 min and finally the suspension was mixed with
(
1
101 MHz, DMSO‐d ) δ
61.2, 157.6, 152.4, 148.6, 139.0, 137.1, 133.4, 131.1,
180.1, 169.1, 167.5, 164.4,
ppm
6
excess amount of Cu (OAc) in ethanol containing a few
2
128.1, 124.0, 122.9, 119.6, 115.5, 45.3, 35.8, 31.4, 28.1.
MS: m/z = 353 [M] (Figures S5–S8).
+
drops of triethylamine and refluxed for 6 h at room tem-
perature. The resulting precipitate was separated from the
solution by a magnet and washed several times with eth-
anol and dried and stored in a vacuum desiccator.
3
.8.3 | Ethyl 4‐(4‐methoxyphenyl)‐2‐
methyl‐1‐phenyl‐1H‐pyrrole‐3‐carboxylate
Table 4, entry 17)
(
3
.8 | General method for the synthesis of
White solid; M.p: 108‐110 °C; Yield: 86%; IR (KBr): υ
polysubstituted pyrrole derivatives
−
1
1
2
933, 2880, 1712, 1599, 1522, 1442 cm ; H NMR
To a mixture of required amine (2 mmol), suitable alde-
hyde (2 mmol), ethyl acetoacetate (2 mmol) and nitro-
(
(
7
400 MHz, DMSO‐d ) δ 8.11 (s, 1H, ArH), 7.89
6
ppm
d, J = 8.0 Hz, 2H, ArH), 7.60 (t, J = 8.0 Hz, 1H, ArH),
.35 (d, J = 8.0 Hz, 2H, ArH), 7.30 (d, J = 8.0 Hz, 2H,
ArH), 7.17 (d, J = 8.0 Hz, 2H, ArH), 3.73 (s, 3H, −CH3),
.36 (q, J = 8.0 Hz, 2H, −CH ), 1.88 (s, 3H, −CH ), 1.26
methane (2 mmol), the nanocatalyst SBCu@silica‐Fe O4
3
(0.008 g) was added in a small test tube and stirred mag-
netically under solvent‐free conditions at room tempera-
ture (Scheme 1). The completion of the reaction
monitored by TLC n‐hexane/ethyl acetate (5:3). After
completion of the reactions, boiling ethyl acetate was
added to the reaction mixtures to dissolve the target prod-
ucts and unreacted starting materials. Then, the undis-
solved nanocatalyst was collected from the reaction
mixture using a magnet and washed with ethanol succes-
sively and preserved. The resulting crude products were
purified using CH Cl and n‐hexane.
3
(
2
3
13
t, J = 8.0 Hz, 3H, −CH3); C NMR (101 MHz, DMSO‐
d6) δppm 179.1, 167.1, 164.4, 159.9, 155.6, 152.4, 149.3,
1
1
45.6, 140.9, 131.2, 129.4, 128.5, 127.6, 124.0, 123.1,
19.3, 115.5, 44.0, 35.7, 30.0, 27.1. MS: m/z = 335 [M]
+
(
Figures S9–S12).
4 | CONCLUSION
2
2
In summary, a copper Schiff base complex was
immobilized on magnetic Fe O4 nanoparticles and
3
3
4
.8.1 | Ethyl 1‐(4‐chlorophenyl)‐2‐methyl‐
‐phenyl‐1H‐pyrrole‐3‐carboxylate (Table 4,
characterized. Then a green, facile, and convenient
method was developed for the one‐pot synthesis of
polysubstituted pyrrole derivatives from the coupling of
various aldehydes with different amine derivatives, nitro-
methane and methyl or ethyl acetoacetate using above
entry 14)
Yellow solid; M.p: 127‐129 °C; Yield: 88%; IR (KBr): υ
−
1 1
3
058, 2898, 1689, 1622, 1596, 1492, 1452 cm ; H NMR

12 of 12
HAMRAHIAN ET AL.
nanoparticles as an efficient heterogeneous catalyst. All
[15] H. C. Hu, Y. H. Liu, B. L. Li, Z. S. Cui, Z. H. Zhang, RSC Adv.
1
2
015, 5, 7720.
[16] R. Ballini, S. Gabrielli, A. Palmieri, M. Petrini, RSC Adv. 2014,
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[18] P. G. Cozzi, Chem. Soc. Rev. 2004, 33, 410.
the new products were characterized using H NMR,
13
C NMR, and FT‐IR spectroscopies. This simple syn-
4
thetic procedure has the advantages of simple methodol-
ogy, easy work‐up, high yields, and inexpensive, air
stability of catalyst and also easy separation and handling
of the nanocatalyst.
2
[
19] M. Esmaeilpour, A. R. Sardariana, J. Javidi, Appl. Catal. A. Gen.
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2
ACKNOWLEDGEMENTS
[20] Z. M–Shoeili, M. Zare, M. Bagherzadeh, S. Özkar, S. Akbayrak,
J. Coord. Chem. 2016, 69, 668.
We are grateful to the Bu‐Ali Sina University for financial
support.
[21] Q. Zhou, Z. Wan, X. Yuan, J. Luo, Appl. Organomet. Chem.
016, 30, 215.
2
[
22] J. Rakhtshah, S. Salehzadeh, Appl. Organomet. Chem. 2017, 31,
ORCID
e3560 1.
Sadegh Salehzadeh http://orcid.org/0000-0003-2840-1896
[23] J. Rakhtshah, S. Salehzadeh, E. Gowdini, F. Maleki, S. Baghery,
M. A. Zolfigol, RSC Adv. 2016, 6, 104875.
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