Synthesis and characterization of Co (III) salen complex immobilized on cobalt ferrite-silica nanoparticle and their application in the synthesis of spirooxindoles

Article abstract of DOI:10.1002/aoc.4743

The preparation, characterization and catalytic application of Co (III) salen complex loaded on cobalt ferrite-silica nanoparticle [CoFe₂O₄@SiO₂@ Co (III) salen complex] are described. Co (III) salen complex loaded on ferr

Full text of DOI:10.1002/aoc.4743

Received: 18 September 2018
DOI: 10.1002/aoc.4743
Revised: 24 October 2018
Accepted: 5 November 2018
F U L L P A P E R
Synthesis and characterization of Co (III) salen complex
immobilized on cobalt ferrite‐silica nanoparticle and their
application in the synthesis of spirooxindoles
Mohammad A. Nasseri
| Kaveh Hemmat
| Ali Allahresani
Department of Chemistry, College of
Sciences, University of Birjand, Birjand
97175‐615, Iran
The preparation, characterization and catalytic application of Co (III) salen com-
plex loaded on cobalt ferrite‐silica nanoparticle [CoFe2O4@SiO2@ Co (III) salen
complex] are described. Co (III) salen complex loaded on ferrite cobalt‐silica
nanoparticles is characterized by transmission electron microscopy, scanning
electron microscopy coupled with energy‐dispersive X‐ray, vibrating‐sample mag-
netometer and Fourier transform‐infrared analyses. The thermal stability of the
material is also determined by thermal gravimetric analysis. An average crystallite
size is determined from the full‐width at half‐maximum of the strongest reflection
by using Scherrer's approximation by powder X‐ray diffractometry. The efficiency
of CoFe2O4@SiO2@Co (III) salen complex is investigated in the synthesis of
spirooxindoles of malononitrile, various isatins with 1,3‐dicarbonyles. The
nanocatalyst demonstrated excellent catalytic activity that gave the corresponding
coupling products in good to excellent yields. Moreover, the recoverability and
reusability of CoFe2O4@SiO2@Co (III) salen complex is investigated where
nanocatalyst could be recovered and reused at least five times without any appre-
ciable decrease in activity and selectivity, which confirmed its high efficiency and
high stability under the reaction conditions and during recycling stages.
Correspondence
M. A. Nasseri, Department of Chemistry,
College of Sciences, University of Birjand,
Birjand 97175‐615, Iran.
Email: manaseri@birjand.ac.ir
KEYWORDS
Co (III) salen complex, cobalt ferrite, nanoparticle, spirooxindole
1 | INTRODUCTION
separation/recycling and products separation.[10,11]
Heterogenization of metal complexes has been carried
Schiff base ligands with more flexible structures are easily
synthesized and form complexes with almost all metal
ions. Many salen complexes show excellent catalytic
activity in various reactions.[1–9] Salen complexes are
one out of 10 superior catalysts synthesizing organic
material. On the other hand, immobilizing them on
nanomagnetic substrates could create a new methodology
of organic material. One of the most important challenges
in catalysis is to transform a successful homogeneous cat-
alyst into a heterogeneous one, due to the intrinsic advan-
tages of heterogeneous systems, namely easy catalyst
out using supports, such as zeolite, clays, silicious mate-
rials and activated carbon.[12–20] With the advancement
of nanoscience, magnetic nano‐sized particles are becom-
ing increasingly interesting due to their unique applica-
tions, such as their uses for cell separation, magnetic
resonance imaging, drug delivery systems, protein separa-
tion and cancer treatments through hyperthermia.[21–28]
Also, magnetic nanoparticles (MNPs) can be good candi-
dates as support materials for heterogeneous catalysts,
because of easy synthesis, high surface area, excellent
thermal and chemical stability, surface modification
Appl Organometal Chem. 2019;e4743.
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© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4743

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NASSERI ET AL.
ability, and low toxicity and cost. Moreover, the applica-
tion of an external magnet readily separates the catalyst‐
loaded MNPs from the reaction products to eliminate
the need for filtration and facilitate catalyst recycling.
This improvement highlights the advantages of both
homogeneous (selectivity, activity) and heterogeneous
(separation, recovery, recycling) catalysts.[29–34] CoFe2O4
nanoparticles have been studied extensively by the scien-
tific community due to applications in areas such as high‐
density information storage, electromagnetic wave
absorption and biomedicine.[35,36] Compared with some
magnetic platforms such as Fe3O4, which is fairly reactive
to acidic and oxidative environments, and γ ‐Fe2O3,
which is not thermally stable, CoFe2O4 is stable in acidic
environments and thermal conditions.[37–43]
this paper, we introduce Co (III) salen complex
immobilized on cobalt ferrite‐silica nanoparticle
[CoFe2O4@SiO2@Co (III) salen complex] as an efficient,
active and recyclable magnetic nano‐catalyst that can be
used for different organic functional group transforma-
tions in green processes. Then, we studied its catalytic
activity in the synthesis of spirooxindoles by the coupling
of various isatins with 1,3‐dicarbonyles and
malononitrile. The yield and selectivity of the correspond-
ing delivered products were also found to be high to
excellent. Also, the present study shows unique advan-
tages, such as high magnetic properties, simple synthesis
of the catalyst, easy separation of catalyst with a perma-
nent magnet, and the application of inexpensive and
available precursors. Moreover, the catalytic systems
exhibited high durability and reusability under the
applied reaction conditions. The reactivity, reusability
and stability of the catalyst against the reaction processes
have also been improved (Scheme 1).
On a different note, oxindoles occupy an important
place in the area of heterocyclic chemistry because they
are frequently found in numerous natural and synthetic
products along with useful biological activities. Oxindole
derivatives often appear as important structural compo-
nents in biologically active and natural compounds, which
include antibacterial, antiprotozoal, anti‐inflammatory
activities, and progesterone receptors (PRs) agonists.[44–48]
Several procedures of this strategy, which have been
recently reported in the literatures, are reaction of isatin,
malononitrile and dimedone in the presence of
GN/SO3H,[49] ZnFe2O4,[50] borax,[51] Al‐ITQ‐HB,[52]
sodium stearate,[53] TEBA,[54] AIUM,[55] B‐CD,[56]
2 | EXPERIMENTAL
2.1 | Chemicals
Reagents and solvents were purchased from Merck or
Fluka chemical companies. Purity determinations of the
products were accomplished by thin‐layer chromatogra-
phy (TLC) on silica‐gel polygram SILG/UV 254 plates.
Melting points were measured on an Electro thermal
9100 apparatus. IR spectra were taken on a Perkin Elmer
781 spectrometer in KBr pellets and reported in cm−1. 1H‐
NMR and 13C‐NMR spectra were measured on a Bruker
DPX‐250 Avance instrument at 250 MHz and 62.9 MHz
DES,[57] Ni NPS,[58] SBA‐PR‐NH2
and NEt3.
[59]
[60]
In continuation of our ongoing research on the devel-
opment of eco‐friendly organic synthesis, particularly by
nano‐catalysts,[61–71] up to now, salen complexes that
are stabled on a magnetic nano‐substrate have not been
used in multi‐component synthesis of spirooxindole. In
SCHEME 1 Synthesis of spirooxindole
derivatives catalyzed by
CoFe2O4@SiO2@Co (III) salen complex

NASSERI ET AL.
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in CDCl3 or DMSO‐d6 with chemical shift given in ppm
relative to TMS as internal standard. The morphology of
the products was determined by using CMPhilips10 model
transmission electron microscopy (TEM) at an accelerat-
ing voltage of 100 kV. Power X‐ray diffraction (XRD) was
performed on a Bruker D8‐advance X‐ray diffractometer
with Cu Kα (λ = 0.154 nm) radiation. The thermal gravi-
metric analysis (TGA) curves were recorded under air
atmosphere using TGA/DTA Shimadzu‐50 with platinum
pan. The samples were heated in air from 25 to 800°C with
a heating rate of 10°C per min. The weight losses as a func-
tion of temperature were recorded. The magnetic proper-
ties were determined by using vibrating‐sample
magnetometer (VSM) leak shore 7200 at 300 kVsm leak
shore. Scanning electron microscopy coupled with
energy‐dispersive X‐ray (SEM‐EDX) spectra were recorded
by MIRA 3TESCAN‐XMU and SAMx spectrometer.
mL) was added drop by drop to the mixture, and then
stirred for 6 h at 0°C. The crude solid yellow product was fil-
tered, and salicylaldehyde (0.52 mL, 5 mmol) in dry EtOH
(10 mL) was added. Then the reaction mixture was stirred
for 2 h under reflux conditions under N2 atmosphere. Upon
completion, the solvent was filtered and dried at 80°C for
12 h to obtain 4‐[(E)‐{(2‐[(E)‐2‐hydroxybenzylidene)
amino]phenyl)imino}methyl]benzene‐1,3‐diol.
2.2.4 | Procedure for the synthesis of Co
(III) salen complex
Co (OAC)2·4H2O (0.249 g, 1 mmol) in ethanol (10 mL)
was added to a suspension of ligand (0.332 g, 1 mmol)
and NaOH (67 mg, 1.67 mmol) in ethanol (20 mL). This
suspension was stirred under reflux conditions for 1.5 h.
Then, LiCl (5.8 mmol, 0.247 g) was added to the reaction
mixture and stirred for 1 h, and the product was filtered
and washed with hot water and methanol. The product
was dried at 80°C for 12 h to obtain Co (III) salen complex.
2.2 | Catalyst preparation
2.2.1 | Preparation of CoFe2O4
nanoparticles
2.2.5 | Preparation of CoFe2O4@SiO2@Co
(III) salen complex
n a balloon containing 100 mL of distilled water, 0.002 mol
(0.808 g) of Fe (NO3)3·9H2O and 0.001 mol (0.291 g) of Co
(NO3)2·6H2O were dissolved. Then, 1 M NaOH solution (20
mL) was added drop by drop to the previous solution and
sonicated (60 W, 30 min). The mixture was then heated for
2 h at 80°C. CoFe2O4 nanoparticles (black precipitate) were
separated using an external magnet, rinsed with distilled
water and ethanol, and dried in an oven at 80°C for 10 h.[72]
Co (III) salen complex was synthesized as reported in the
literature. The homogeneous Co (III) salen complex was
chemically grafted onto the surface of CoFe2O4@SiO2.
In 100 mL of dry toluene, 1.5 g of CoFe2O4@SiO2 was
sonicated for 2 h. Then, homogeneous Co (III) salen com-
plex was added. The mixture was stirred under reflux
conditions in an inert atmosphere for 48 h. After the reac-
tion completed, the corresponding Co (III) salen complex
was washed with dry toluene and EtOH. Under vacuum,
the corresponding nanocatalyst (1.95 g) was dried in an
oven for 10 h at 80°C.[74]
2.2.2 | Preparation of CoFe2O4@SiO2
core‐shell
An appropriate amount of CoFe2O4 nanoparticles (0.150
g) was dispersed in EtOH/H2O (4:1, 100 mL) for 30 min.
Then, tetraethylorthosilicate (0.5 mL) was added drop‐
wise to the mixture followed by addition of ammonia
solution (0.8 mL). For 24 h, the mixture was stirred. Using
a permanent magnetic, the achieved CoFe2O4@SiO2
nanoparticles were separated. Then, they were washed
with distilled water and dried under vacuum.[73]
2.3 | Catalytic activity
2.3.1 | General procedure for the prepara-
tion of oxindole derivatives
To a mixture of 1,3‐dicarbonyl compounds (1.0 mmol), isatin
(1.0 mmol) and malononitrile (1.0 mmol) in water/ethanol
mixture (1:1), was added CoFe2O4@SiO2@Co (III) salen
complex (10 mg). The mixture was stirred at 80°C for an
appropriate reaction time (Table 1), and the progress of the
reaction was monitored by TLC. After completion of the
reaction, the mixture was dissolved in ethyl acetate, and
CoFe2O4@SiO2@Co (III) salen complex MNPs were sepa-
rated by external magnet. Then the solvent was removed
from solution under reduced pressure, and the resulting
2.2.3 | Preparation of 4‐[(E)‐{(2‐[(E)‐(2‐
hydroxybenzylidene)amino]phenyl)imino}
methyl]benzene‐1,3‐diol
2,4‐ Dihydroxyl benzaldehyde (0.690 g, 5 mmol) was dis-
solved in dry chloroform (35 mL). Then, o‐
phenylenediamine (5 mmol, 0.54 g) in dry chloroform (30

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NASSERI ET AL.
TABLE 1 The synthesis of oxindole derivatives by CoFe2O4@SiO2@Co (III) salen complex
Isatin
Entry
R
R1
Cyclic ketone
Product
Time (min)
Yield (%)
TON
1
H
H
3a
3a
3a
3a
3a
3a
3a
3a
3b
3b
3b
3b
3b
3b
3b
3b
3c
3c
3c
3c
3c
3c
3c
3c
4a
4a
4a
4a
4a
4a
4a
4a
4b
4b
4b
4b
4b
4b
4b
4b
4c
4c
4c
4c
4c
4c
4c
4c
10
10
10
25
10
25
10
10
2
98
95
98
82
92
85
83
87
98
98
93
85
93
87
82
88
98
98
95
84
93
81
85
90
296.96
287.87
296.96
248.48
278.78
257.57
251.51
263.63
296.96
296.96
281.81
257.57
281.81
263.63
248.48
266.66
296.96
296.96
287.87
254.54
281.81
245.45
257.57
272.72
2
NO2
Cl
H
3
H
4
H
PhCH2
Et
5
NO2
OMe
Me
Br
6
H
7
H
8
Me
H
9
H
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
NO2
Cl
H
2
H
2
H
PhCH2
Et
10
2
NO2
OMe
Me
Br
H
5
H
5
Me
H
2
H
2
NO2
Cl
H
2
H
2
H
PhCH2
Et
10
2
NO2
OMe
Me
Br
H
5
H
5
Me
5
Reaction conditions: isatin (1.0 mmol), 1,3‐dicarbonyl (1.0 mmol) in EtOH:H2O (1:1), at 80°C, 10 mg CoFe2O4@SiO2@Co (III) salen complex.
product was purified by recrystallization using ethanol to
afford the pure oxindole product in excellent purity and
yield. Structural assignments of the products are based on
their 1H‐NMR, 13C‐NMR and IR spectra (for the NMR spec-
trum of the products, see SI, PP. S1‐S6).
2‐Amino‐2′,5‐dioxo‐5,6,7,8‐tetrahydrospiro‐
[chromene‐4,3′‐indoline]‐3‐carbonitrile (Compound 9,
1
Table 1): white solid, mp > 250°C. H‐NMR (250 MHz,
DMSO‐d6) 1.92 (2H, m, CH2), 2.12 (2H, m, CH2), 2.58
(2H, m, CH2), 6.66 (d,1H, J = 7.39 Hz, Ph), 6.89 (t, 1H,

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J = 7.39 Hz, Ph), 7.13 (d, 1H, J = 7.39 Hz, Ph), 7.23 (t, 1H,
J = 7.39 Hz, Ph), 7.36 (s, 2H, NH2), 10.66 (s, 1H, NH).
13C‐NMR (62.9 MHz, DMSO‐d6) 195.11 (C=O), 178.21
(C=O), 166.11 (C), 158.71 (C), 142.1 (C), 134.59 (C),
128.51 (CH), 123.31 (CH), 121.81 (CH), 117.41 (CH),
112.91 (C ≡ N), 109.21 (C), 57.61 (C), 46.91 (C), 36.41
(CH2), 26.81 (CH2), 19.81 (CH2). IR (KBr, cm−1) 3352,
3295, 3175, 2952, 2204, 1713, 1655, 1352, 1216, 1076.
Anal. calcd for C17H13N3O3: C, 66.44; H, 4.26; N,
13.67%. Found: C, 66.42; H, 4.31; N, 13.72%.
3 | RESULTS AND DISCUSSION
CoFe2O4 was synthesized from Fe (NO3)3·9H2O and Co
(NO3)2·6H2O. Then, an appropriate amount of CoFe2O4
nanoparticles was dispersed in EtOH/H2O followed by
drop‐wise addition of tetraethylorthosilicate to achieve
CoFe2O4@SiO2 nanoparticles. Finally, homogeneous Co
(III) salen complex was immobilized on to the
CoFe2O4@SiO2
[corresponding
heterogeneous
CoFe2O4@SiO2@ Co (III) salen complex; Scheme 2].
Co (III) salen complex loaded on ferrite cobalt‐silica
nanoparticles is characterized by TEM, SEM–EDX,
VSM, Fourier transform‐infrared (FT‐IR) analyses, TGA
and XRD.
2‐Amino‐7,7‐dimethyl‐2′,5‐dioxo‐5,6,7,8‐
tetrahydrospiro‐[chromene‐4,3′‐indoline]‐3‐
carbonitrile (Compound 17, Table 1): white solid, mp >
1
250°C. H‐NMR (250 MHz, DMSO‐d6) 1.00 (3H, s, CH3),
1.14 (3H, s, CH3), 2.08–2.11 (2H, m, CH2), 2.55 (2H, m,
CH2), 6.69 (d,1H, J = 7.3 Hz, Ph), 6.89 (t, 1H, J = 7.3 Hz,
Ph), 7.09 (d, 1H, J = 7.3 Hz, Ph), 7.21 (t, 1H, J = 7.4 Hz,
Ph), 7.34 (s, 2H, NH2), 10.64 (s, 1H, NH) .13C‐NMR
(62.9 MHz, DMSO‐d6) 195.29 (C=O), 178.49 (C=O),
166.57 (C), 159.19 (C), 152.39 (C), 142.47 (C), 134.82
(CH), 128.58 (CH), 123.39 (CH), 122.15 (CH), 117.75
(C), 112.21 (C ≡ N), 109.69 (C), 57.95 (C), 50.44 (CH2),
47.22 (C), 32.34 (CH2), 28.01 (CH3), 27.09 (CH3). IR
(KBr, cm−1): 3376, 3312, 3144, 2928, 2196, 1724, 1656,
1348, 1224, 1056. Anal. calcd for C19H17N3O3: C, 68.05;
H, 5.11; N, 12.53%. Found: C, 67.86; H, 5.14; N, 12.65%.
FT‐IR spectroscopy
The FT‐IR at 4000 to 400 cm−1 for (a) CoFe2O4, (b)
CoFe2O4@SiO2, and (c) CoFe2O4@SiO2@Co (III) salen
complex nanoparticles were studied by FT‐IR
spectroscopy, and the results are shown in Figure 1. The
broadening absorption peak at 3347 cm−1 belongs to
OH‐stretching of absorbed water molecules. The peak
located at 605 cm−1 is attributed to the bending mode of
Co‐O and Fe‐O. In spectrum 1b, the absorption band
present at about 1099 cm−1 is due to the stretching band
vibrations of Si‐O‐Si. The absorption band present at
about 467 cm−1 is due to the bending of Si‐O‐Si or O‐Si‐
O. In spectrum 1c, the absorption peak at 1611 cm−1
belongs to C=N stretching band vibrations in
CoFe2O4@SiO2@Co (III) salen complex.
2’‐Amino‐2,5′‐dioxo‐5’H‐spiro
[indoline‐3,4′‐
pyrano[3,2‐c]chromene]‐3′‐carbonitrile (Compound 1,
1
Table 1): white solid, mp > 250°C. H‐NMR (250 MHz,
DMSO‐d6): 6.82 (1H, d, J = 7.59 Hz, Ph), 6.91 (1H, t, J =
7.58 Hz, Ph), 7.16 (1H, d, J = 7.22 Hz, Ph), 7.31 (1H, d, J
= 7.61 Hz, Ph), 7.43 (1H, t, J = 7.5 Hz, Ph), 7.47 (1H, t,
J = 8.1 Hz, Ph), 7.51 (1H, d, J = 8.3 Hz, Ph), 7.52 (2H, s,
NH2), 7.94 (1H, d, J = 8.1 Hz, Ph), 10.64 (1H, s, NH).
13C‐NMR (62.9 MHz, DMSO‐d6) 177.41 (C=O), 158.9
(C=O), 155.7 (C), 155.5 (C), 152.39 (CH), 142.59 (CH),
134.09 (CH), 133.49 (CH), 129.38 (C), 125.39 (C), 124.49
(CH), 123.11 (CH), 122.51 (CH), 117.41 (CH), 117.08 (C),
112.89 (C ≡ N), 109.89 (C), 101.89 (C), 70.19 (C), 57.49
(C). IR (KBr, cm−1): 3415, 3241, 3260, 2218, 1719, 1679,
1623, 1581. Anal. calcd for C20H11N3O4: C, 67.23; H,
3.10; N, 11.76%. Found: C, 67.39; H, 3.12; N, 11.65%.
Transmission electron microscopy
The grain sizes of (a) CoFe2O4, (b)CoFe2O4@SiO2, and
CoFe2O4@SiO2@Co (III) salen nanoparticles were inves-
tigated by TEM. They have a narrow distribution of sizes,
from 18 to 30 nm (Figures 2 and 3).
SCHEME 2 Preparation of catalyst
CoFe2O4@SiO2@Co (III) salen complex

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NASSERI ET AL.
FIGURE 3 Particle size distribution of CoFe2O4@SiO2@Co (III)
salen complex nanoparticle
FIGURE 1 Fourier transform‐infrared (FT‐IR) spectra of (a)
CoFe2O4, (b) CoFe2O4@SiO2 and (c) CoFe2O4@SiO2@Co (III)
salen complex
X‐ray diffraction analysis
Figure 4 shows the XRD patterns of synthesized (a)
CoFe2O4 and (b) CoFe2O4@SiO2 nanoparticles. All the
peaks correspond to the CoFe2O4 phase, which shows
the formation of cobalt ferrite and cobalt ferrite‐silica
structure. The average grain sizes of the samples are cal-
culated using the Debye–Scherrer formula, where λ is
the X‐ray wavelength, θ is the Bragg's angle and β is the
full‐width of the diffraction line at the half‐maximum
intensity. The average crystallite size of synthesized prod-
ucts was thus calculated at about 14.5 and 17.2 nm.
Vibrating‐sample magnetometer
The magnetic properties of (a) CoFe2O4, (b)
CoFe2O4@SiO2, and (c) CoFe2O4@SiO2@Co (III) salen
complex nanoparticles were studied by a VSM at 300 K
(Figure 5). Figure 5 shows the absence of hysteresis phe-
nomenon, and indicates that the product has super‐
paramagnetism at room temperature. The saturation
FIGURE 4 Powder X‐ray diffractometry (XRD) pattern of (a)
CoFe2O4 and (b) CoFe2O4@SiO2
FIGURE 2 Transmission electron microscopy (TEM) image of (a) CoFe2O4, (b) CoFe2O4@SiO2 and (c) CoFe2O4@SiO2@Co (III) salen complex

NASSERI ET AL.
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magnetization values for CoFe2O4, CoFe2O4@SiO2 and
CoFe2O4@SiO2@Co (III) salen nanoparticles were
39.124, 30.387 and 27.348 emu g−1
.
Thermal gravimetric analysis
The thermal behavior of CoFe2O4@SiO2@Co (III) salen
nanoparticles is shown in Figure 6. Significantly, the
TGA curve of CoFe2O4@SiO2 shows a weight loss over
the range of 90–165°C. This weight loss can be attributed
to the loss of adsorbed water and dehydroxylation of
internal ‐OH groups. The second weight loss step is over
the range 250–460°C, which can be ascribed to even fur-
ther decomposition of the materials (Figure 6a). As
shown in Figure 6b, the amount of water decreased after
the incorporation of Co (III) salen complex onto the
CoFe2O4@SiO2, indicating that the Co (III) salen complex
has been successfully immobilized onto the
CoFe2O4@SiO2. The TGA curve of CoFe2O4@SiO2@Co
(III) salen complex shows a weight loss over the range
of 90–160°C and 250–650°C, which is similar to the
TGA curve of CoFe2O4@SiO2, and the organic parts were
decomposed completely at 460–800°C (Figure 6b).
FIGURE 5 Vibrating‐sample magnetometer (VSM) pattern of (a)
CoFe2O4, (b) CoFe2O4@SiO2 and (c) CoFe2O4@SiO2@Co (III) salen
complex
Scanning electron microscopy coupled
with energy‐dispersive X‐ray
Figures 7–9 show EDX of CoFe2O4, CoFe2O4@SiO2 and
CoFe2O4@SiO2@Co (III) salen complex nanoparticles.
These are recorded to investigate the elemental composi-
tion of nanoparticles. The results demonstrate that Co, Fe
and O appear in CoFe2O4 sample, and Co, Fe, Si and O
appear in CoFe2O4@SiO2 sample. Also, the results dem-
onstrate that Co, Fe, Si, O, N and C appear in
FIGURE 6 Thermal gravimetric analysis (TGA) pattern of (a)
CoFe2O4@SiO2 and (b) CoFe2O4@SiO2@Co (III) salen complex
FIGURE 7 Scanning electron microscopy coupled with energy‐dispersive X‐ray spectroscopy (SEM–EDX) of CoFe2O4

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FIGURE 8 Scanning electron microscopy coupled with energy‐dispersive X‐ray spectroscopy (SEM–EDX) of CoFe2O4@SiO2
FIGURE 9 Scanning electron microscopy coupled with energy‐dispersive X‐ray spectroscopy (SEM–EDX) of CoFe2O4@SiO2@Co (III)
salen complex
CoFe2O4@SiO2@Co (III) salen nanoparticles. Note that
no impurity is present in the products.
Scanning electron microscopy analysis of the products
(Figure 7–9) provided information on the size and
FIGURE 10 The effect of different solvents in the synthesis of
oxindole by CoFe2O4@SiO2@Co (III) salen complex. Reaction
conditions: isatin (1.0 mmol), 4‐hydroxycoumarin (1.0 mmol) in
EtOH:H2O (1:1), at 80°C, 10 min, 10 mg CoFe2O4@SiO2
FIGURE 11 The effect of the amount of CoFe2O4@SiO2@Co
(III) salen complex in the synthesis of oxindole. Reaction
conditions: isatin (1.0 mmol), 4‐hydroxycoumarin (1.0 mmol) in
EtOH:H2O (1:1), at 80°C

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morphology
of
CoFe2O4,
CoFe2O4@SiO2
and
cobalt ferrite‐silica nanoparticles [CoFe2O4@SiO2@Co
(III) salen complex] was used for the first time as an effi-
cient and recyclable nanocatalyst for the synthesis of
spirooxindoles by the coupling of various isatins with
1,3‐dicarbonyls and malononitrile. For this purpose,
isatins, 4‐hydroxycoumarin and malononitrile were taken
as model substrates. We examined this reaction in various
solvents (Figure 10). The results indicate that different
solvents affected the efficiency of the reaction. Acetoni-
trile and dichloromethane afforded low yields (50–56%),
while the use of solvents such as water, ethanol, DMF
and DMSO could improve the yields. Finally, when a
mixture of ethanol and water (1:1) was used, the yield
increased to 98% better than any other solvents examined
here. In the absence of solvent, the yield of model reac-
tion decreased to 35%.
CoFe2O4@SiO2@Co (III) salen nanoparticles. The results
showed that the average product sizes of CoFe2O4,
CoFe2O4@SiO2 and CoFe2O4@SiO2@Co (III) salen com-
plex nanoparticles were 11.76–15.00 nm.
According to ICP‐AES analysis, the Co loading was
found to be 0.33 mmol g−1
.
3.2 | Catalytic activity of
CoFe2O4@SiO2@co (III) salen complex for
the synthesis of oxindoles
In order to show the merit of synthesized nanocatalyst in
organic reactions, Co (III) salen complex immobilized on
Electrophilic reaction of isatin with two different
nucleophiles is a fundamental strategy for constructing
MCRs. As well as its action as a solvent, water and protic
solvent also help in the enolization of dimedone by mak-
ing hydrogen bonds with the OH and, thus, it increases
the nucleophilic character of the methylene carbon (C‐
2) of dimedone. As a result, it helps to increase the reac-
tion rate.[75]
We also changed the amount of catalyst. The results
are summarized in Figure 11. Our results showed that
the reaction yield was affected crucially by the catalyst
concentration. Decreasing the catalyst concentration
resulted in lower yields under the same conditions. With
catalyst concentration increasing (> 10 mg), product
decreased significantly. Consequently, this condensation
was best catalyzed by 10 mg of CoFe2O4@SiO2@Co (III)
FIGURE 12 The effect of time in the synthesis of oxindole by
CoFe2O4@SiO2@Co (III) salen complex. Reaction conditions:
isatin (1.0 mmol), 4‐hydroxycoumarin (1.0 mmol) in EtOH:H2O
(1:1), at 80°C
TABLE 2 Comparison of results using CoFe2O4@SiO2@Co (III) salen complex with various catalysts
Entry
Catalyst
Solvent/T (°C)
Time (min)
Yield (%)
Reference
[46]
1
Sodium stearate
TEBA
H2O/60°C
180
120
120
480
240
20
95
88
40
88
88
88
80
80
86
94
95
91
98
[47]
[48]
[49]
[50]
[51]
[52]
[53]
[43]
[44]
[42]
[45]
2
H2O/90°C
3
AIUM (10 mol%)
B‐CD
DMSO/60°C
H2O/60°C
4
5
DES (0.5 mL)
Ni NPS
Urea: CHCl3/80°C
Ethylene glycol
H2O/ref.
6
7
SBA‐PR‐NH2
NEt3
5
8
EtOH/ref.
30
9
ZnFe2O4
H2O/ref.
8
10
11
12
13
Borax (10 mol%)
GN/SO3H
EtOH/ref.
120
40
EtOH/water (1:1)/ref.
CDCl3/r.t.
Al‐ITQ‐HB (10 mol%)
120
2
CoFe2O4 @ SiO2 @
Co (III) salen complex
EtOH/water (1:1) /
80°C
This work
Malononitrile (1 mmol), isatin (1 mmol), dimedone (1 mmol).

10 of 13
NASSERI ET AL.
SCHEME 3 A plausible mechanism for
the synthesis of spirooxindole in the
presence of CoFe2O4@SiO2@Co (III) salen
complex
salen complex as the reaction was completed within a
high yield. The effect of time of reaction was studied by
carrying out the model reaction at different times, and
the best result was obtained within 10 min (Figure 12).
In order to study the catalytic activity of
CoFe2O4@SiO2@Co (III) salen complex, this coupling
was carried out in the absence of catalyst. In this case,
the reaction proceeded in low yield (16%) over model
reaction time. Oxindole was achieved with excellent yield
(98%), using 10 mg catalyst within 10 min in a mixture of
ethanol and water as solvent.
summarized in Table 1. In all cases, the reaction
proceeded readily to afford the corresponding oxindoles
in good to excellent yields (81–98%) in very short reaction
times. TON showed the catalytic activity of the catalysts.
Therefore, the TON of the catalyst was calculated and
added to the main text, and the results showed that
CoFe2O4@SiO2@Co (III) salen complex is highly active
in the synthesis of spirooxindole (296.96). As can be seen
in Table 2, this catalyst showed good catalytic activity and
good yields (98%) in shorter times compared with most of
the reported works (Table 2).
Co (III) complex showed that the system with the het-
erogeneous catalyst exhibits high catalytic efficiency with
TON (296.96).
To further explore the scope and limitation of this
protocol under the optimized conditions, particularly in
regard to library construction, we evaluated using various
1,3‐dicarbonyl and isatin compounds. The results are
FIGURE 13 Recyclability of CoFe2O4@SiO2@Co (III) salen
FIGURE 14 Transmission electron microscopy (TEM) image of
complex in the synthesis of oxindole
recovered CoFe2O4@SiO2@Co (III) salen complex after 2nd run

NASSERI ET AL.
11 of 13
Herein, we proposed a mechanism for the Co (III)
salen complex nanoparticles supported on
At the end of the reaction, the catalyst could be recov-
ered by external permanent magnet. The recycled catalyst
was washed with ethanol and subjected to a second reac-
tion process. The results show that the yield of product
after five runs was only slightly reduced (Figure 13).
For further investigation, the characterization of the
recycled catalyst after two runs [TEM image (Figure 14),
XRD spectrum (Figure 15) and SEM image (Figure 16)]
was obtained and the results showed that the recovered
catalyst did not show significant differences in the structure.
CoFe2O4@SiO2‐catalyzed preparation of spirooxindole in
Scheme 3. Thus, we proposed that the cobalt (III) in Co
(III) salen complex induces the polarization of the car-
bonyl group of isatin followed by the nucleophilic addi-
tion of malononitrile to isatin after this intermediate
subsequently undergoes elimination via Knoevenagel
condensation. The addition of dimedone to the interme-
diate afforded the spirooxindole derivatives.
4 | CONCLUSION
In
conclusion,
the
present
work
provided
CoFe2O4@SiO2@Co (III) salen complex for potential syn-
thetic application. CoFe2O4@SiO2@Co (III) salen com-
plex is an efficient and reusable nanocatalyst for the
synthesis of oxindoles, and is comparable with some
other applied catalysts. The reaction was completed in a
short period of time with small amounts of catalyst. In
addition, it is easy to separate and recover the catalyst
for catalytic recycling.
ACKNOWLEDGEMENTS
The authors gratefully acknowledge support for this work
from the Birjand University Research Council.
FIGURE 15 Powder X‐ray diffractometry (XRD) pattern of
recovered CoFe2O4@SiO2@Co (III) salen complex after 2nd run
ORCID
Mohammad A. Nasseri
https://orcid.org/0000-0002-2371-
6680
Kaveh Hemmat https://orcid.org/0000-0002-3973-383X
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How to cite this article: Nasseri MA, Hemmat
K, Allahresani A. Synthesis and characterization of
Co (III) salen complex immobilized on cobalt
ferrite‐silica nanoparticle and their application in
the synthesis of spirooxindoles. Appl Organometal
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