Copper-based Schiff Base Complex Immobilized on Core-shell Fe3O4@SiO2 as a magnetically recyclable and highly efficient nanocatalyst for green synthesis of 2-amino-4H-chromene derivatives

Article abstract of DOI:10.1002/aoc.5359

Fe₃O₄-supported copper (II) Schiff-Base complex has been synthesized through post-modification with 1,3-phenylenediamine followed by further post-modification with salicylaldehyde and coordination with Cu(II) ion. The resulted Fe

Full text of DOI:10.1002/aoc.5359

Received: 18 July 2019
DOI: 10.1002/aoc.5359
Revised: 17 September 2019
Accepted: 20 September 2019
F U L L P A P E R
Copper-based Schiff Base Complex Immobilized on Core-
shell Fe3O4@SiO2 as a magnetically recyclable and highly
efficient nanocatalyst for green synthesis of 2-amino-4H-
chromene derivatives
Hakimeh Ebrahimiasl
| Davood Azarifar
Department of Chemistry, Bu-Ali Sina
University, Hamedan, 65178, Iran
Abstract
Fe3O4-supported copper (II) Schiff-Base complex has been synthesized through
post-modification with 1,3-phenylenediamine followed by further post-modifi-
cation with salicylaldehyde and coordination with Cu(II) ion. The resulted
Fe3O4@SiO2-imine/phenoxy-Cu(II) magnetic nanoparticles (MNPs) were char-
acterized by various techniques including SEM, TEM, XRD, XPS, EDX, VSM,
FT-IR, and ICP. The catalytic activity as a magnetically recyclable heteroge-
neous catalyst for one-pot, three-component synthesis of 2-amino-4H-
chromene derivatives was examined. The catalyst is efficient in the reaction
and can be recovered by magnetic separation and recycled several times with-
out significant loss in the catalytic activity.
Correspondence
Davood Azarifar, Department of
Chemistry, Bu-Ali Sina University, Zip
Code 65178, Hamedan, Iran.
Email: azarifar@basu.ac.ir
Funding information
Research Council of Bu-Ali Sina
University
K E Y W O R D S
2-amino-4H-chromene, Fe3O4-immobilized-Cu (II) Schiff-Base complex, magnetic nanoparticles,
nanocatalyst, three-component reaction
1 | INTRODUCTION
potential of recyclability.[8–13] As previously reported, the
use of various magnetic metal oxides and hybrid metal
In the last few decades, scientists have greatly concerned
about the environmental health issues originating from
catalytic processes and have made considerable efforts for
development of eco-friendly recyclable catalysts for
organic transformations such as multi-component reac-
tions (MCRs) in the synthetic and industrial fields.[1–6] In
recent years, immobilization of different homogeneous
catalysts onto various nanoparticles has emmerged as a
promising strategy for improving the catalytic efficiency
and stability.[7] The last few decades have witnessed a
considerable progress in the development of various mag-
netic nanoparticles (MNPs) as sustainable and efficient
supports or catalysts in organic synthesis and industrial
fields due to their interesting physical and chemical char-
acteristics such as large surface to volume ratio, high
atom efficiency, easy magnetic separation and high
oxide nanoparticles such as Fe2O3, Fe3O4, TiO2, Al2O3,
ZnO, and La0.7Sr0.3MnO3 have attracted a massive atten-
tion both in industry and organic reactions as catalysts
and/or supports.[14,15] Magnetic Fe3O4 nanoparticles have
emerged as a privileged support for immobilization of
various ligands and functional groups such as phospho-
rous, nitrogen and organic moieties owing to the pres-
ence of high density hydroxyl groups on their surface,
high surface area, high stability, facile magnetic separa-
tion, environmental benignity and high loading
capacity.[13,16–25] Among different nitrogen-based ligands,
Schiff-Base ligands supported on magnetic nanoparticles
immobilize in excellent state through the coordination to
a variety of transition metals with improved catalytic
activity and stability.[26–31] This is because the ligands
containing N-donors exhibit a high performance by a
Appl Organometal Chem. 2019;e5359.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5359

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EBRAHIMIASL AND AZARIFAR
stable hosting a range of metal cations and as a result,
these materials become excellent candidates in catalysis
design as well as analytical, industrial and medicinal
applications.[32–36] In comparison, the Cu-based catalysts
have offered excellent alternatives to other noble-metal-
based catalysts due to their interesting features including
low price, facile separation and high catalytic
performance.[37–39]In addition, another environmentally
important synthetic approach is the use of multi-compo-
nent reactions (MCRs) that have attracted enormous
interest as convergent and high atom-economy
processes.2f, h, 41–46
(TGA) was recorded in air using TGA/DTA PYRIS DIA-
MOND instrument. Magnetic measurement of the cata-
lyst was performed using
a
vibrating sample
magnetometer (VSM) instrument MDKFT. Moreover,
high resolution transmission electron microscopy (TEM)
was conducted on the nanoparticles using a HRTEM
Philips CM30, (300KV) instrument. Inductively coupled
plasma optical emission spectroscopy (ICP-OES) was per-
formed by Arcos EOP, 32 Linear CCD simultaneous ICP
analyzer. X-ray photoelectron spectral (XPS) analysis was
performed using a K-Alpha spectrometer. To gain an
accurate understanding of the molecular structures of 2-
amino-4H-chromene derivatives, geometry optimization
and conformational analysis were performed in the gas
phase with the Gaussian 09 suite of programs and the
Beck's three-parameter hybrid method B3LYP with the 6-
31G (d,p) basis set. Vibrational frequency analysis was
also performed at the same level to ensure the structures
are local minima. The natural bond orbital (NBO)
method on the wave functions was obtained at the same
level of theory by NBO 3.1 program.[61–64] The characteri-
zation data for the catalyst and the titled products are
available online in the supporting information section at
the end of the article (Scheme 1).
Among the heterocyclic compounds, chromenes and
their derivatives are well-documented compounds of
important biological and pharmacological importance
which perform anticancer, spasmolytic, diuretic, anti-
HIV,
antimalarial,
and
anti-anaphylactic
activities.[31,46–50] A large group of chromenes have been
widely used as therapeutically useful agents such as
acenocoumarol which functions as an anticoagulant and
is used for the treatment of bronchial asthma.[51] Also, a
wide variety of chromenes are naturally occurring prod-
ucts contained in many secondary metabolites, as pig-
ments, flavonoids, and anthocyanin.[52,53] In addition, a
variety of chromenes have found wide applications as
pigments, cosmetics, and biodegradable agrochemi-
cals.[54] The methods reported in the literatures for the
synthesis of chromenes utilize various catalytic systems
such as ionic liquids,[54] hexadecyltrimethyl ammonium
2.2 | Preparation of Fe3O4-supported
copper (II) Schiff-base complex,
Fe3O4@SiO2-imine/phenoxy-Cu(II) (MNPs)
bromide,[55]
diammonium
hydrogen
phosphate
(DAHP),[56] Mg/La mixed metal oxides,[57] α-Fe2O3
nanoparticles,[58] silica-grafted ionic liquid,[59] and
H6P2W18O62.18H2O.[60]
The Fe3O4@SiO2-imine/phenoxy-Cu(II) core-shell mag-
netic nanoparticles were successfully prepared in six
steps as depicted in Scheme 2 and explained bellow.
2 | EXPERIMENTAL
2.1 | General
2.2.1 | Synthesis of SiO2-modified core-
shell Fe3O4 MNPs
Fe3O4 magnetic nanoparticles were synthesized by co-
Chemicals were purchased from Merck Chemical Com-
pany and used without further purification. Melting
points were determined in open capillary tubes using a
BUCHI 510 apparatus. Fourier transform infrared (FT-
IR) spectra were recorded from KBr pellets on a Perkin
precipitation of Fe3+ and Fe2+ ions with [Fe3+]/[Fe2+
]
molar ratio of 2:1 as described in the literature.[65]
Shortly, FeCl3.6H2O (5.4 g, 0.02 mol) and FeCl2.4H2O
(2.0 g, 0.01 mol) were dissolved in deionized water
(80 ml) under nitrogen atmosphere with vigorous stir-
ring. Then, 25% aqueous NH4OH solution (10 ml) was
added dropwise atꢀthe constant rate of 1 ml per min to
the mixture at 80 C in N2 atmosphere that resulted in
the formation of uniform black Fe3O4 magnetic
nanoparticles. Then, these black particles were cooled to
room temperature, washed twice with deionized water
and 0.02 M aqueous NaCl solution consecutively, and
decanted using an external magnet. In the following step,
the as-prepared Fe3O4 nanoparticles (1 g) were dispersed
1
Elmer GX FT-IR spectrometer. H NMR and 13C NMR
spectra were recorded for samples in CDCl3 or DMSO-d6
on 90, 250 and 400 MHz BRUKER AVANCE instruments
at ambient temperature using tetramethylsilane (TMS) as
internal standard. Scanning electron microscopy (SEM)
images were obtained on EM3200 instrument operated at
30 kV accelerating voltage. Energy-dispersive X-ray
(EDX) analysis was carried out using a FESEM-SIGM
(German) instrument. Thermo-gravimetric analysis

COPPER-BASED SCHIFF BASE COMPLEX IMMOBILIZED ON …
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SCHEME 1 Three-component synthesis of
various 2-amino-4H-chromene-3-carbonitrile
derivatives catalyzed by Fe3O4@SiO2-imine/
phenoxy-Cu(II) MNPs
SCHEME 2 Stepwise preparation of
Fe3O4@SiO2-Imine/Phenoxy-Cu(II) MNPs
in a mixture of ethanol (100 ml) and deionized water
(10 ml) containing 25% ammonia solution (2.5 ml). Then,
tetraethyl orthosilicate (TEOS) (2 ml) was added
dropwise and the stirring was continued for 2 hr at 60 ꢀC.
The resulted product was magnetically separated, washed
repeatedly with deionized water and ethanol, and then
dried in air for 4 hr.[66]
2.2.3 | Immobilization of 1,3-
phenylenediamine on Fe3O4@SiO2-(CH2)3-
Cl MNPs
To a solution of 1,3-phenylenediamine (1.3 g, 0.012 mol)
and a few drops of triethylamine as a base in ethanol
(70 ml), Fe3O4@SiO2-(CH2)3-Cl (1 g) was added to obtain
a suspension in 15 min. The resulting mixture was
refluxed in N2 for 24 hr and the final precipitate as the
product was separated with a magnet, washed three
times with ethanol and dried at room temperature.
2.2.2 | Chloro-functionalization of
Fe3O4−SiO2
The prepared core-shell Fe3O4@SiO2 (1 g) was added to a
solution of (3-chloropropyl)triethoxysilane (CPTES)
(3 ml) in dry toluene (100 ml) followed by stirring at
2.2.4 | Conversion of Fe3O4@SiO2-(CH2)3-
NH-(3-NH2C6H4 into iminomethyl/phenol
Schiff-base derivative (Fe3O4@SiO2-
iminomethyl/phenol)
ꢀ
90 C for 12 hr in N2 atmosphere. Finally, chloropropyl-
bonded magnetic nanoparticles (Fe3O4@SiO2-(CH2)3-Cl)
at the end of the reaction were repeatedly washed with
toluene, separated by using a magnet and dried under
reduced pressure.
Above-prepared Fe3O4@SiO2-(CH2)3-NH-(3-NH2C6H4)
nanoparticles (1 g) were dispersed in 50 ml of methanol

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EBRAHIMIASL AND AZARIFAR
TABLE 1 X-ray diffraction (XRD) data for and Fe3O4-SiO2-
in 15 min and was heated to reflux point. Then, to this
Schiff base complex of Cu(II)-MNPs
suspension was added dropwise
a
solution of
salicylaldehyde (2.93 g, 24 mmol) in ethanol (30 ml)
using a decanter funnel. The reaction mixture was
refluxed for 24 hr and the precipitated Fe3O4@SiO2-
Iminomethyl/phenol nanoparticles were separated using
a magnet, washed repeatedly with ethanol, and dried in
an oven.
Peak width
[FWHM]
(degree)
interplanar
spacing of the
(nm) crystal (nm)
Size
Entry 2θ
1
2
3
4
5
6
6.8 0.5
9.2 0.2
15.89
40.75
27.76
26.72
16.10
9.24
1.30
0.96
0.77
0.70
0.40
0.25
11.9 0.3
12.7 0.3
22
0.5
2.2.5 | Preparation of the Fe3O4-
immobilized Schiff-base Cu(II) complex
Fe3O4@SiO2-imine/phenoxy-Cu(II)
35.7 0.9
(90 MHz, DMSO-d6) δ: 8.30–8.12 (m, 3H, H-Ar), 7.93–
7.57 (m, 7H, H-Ar), 7.31–7.09 (m, 3H, H-Ar and NH2),
5.20 (s, 1H, C-H) ppm.
To a dispersion of previously prepared Fe3O4@SiO2-
iminomethyl/phenol nanoparticles (1 g) in ethanol
(50 ml) was added dropwise a 5% (w/v) solution of Cu
(OAc)2 in ethanol (5 ml) and the resulting mixture was
refluxed for 48 hr. After the reaction completed, the
expected Fe3O4@SiO2-iminomethyl/phenol nanoparticles
were magnetically separated by using a magnet. Finally,
the isolated nanoparticles were washed repeatedly with
ethanol and water to remove the remaining unreacted
materials, and dried at 80 ꢀC for 6 hr.
2.4.2 | 3-Amino-4-(2,6-dichlorophenyl)-
4H-benzo[h]chromene-2-carbonitrile (7 b)
ꢀ
Brown; m.p. 212–214 C; yield 96%; FT-IR (KBr) ν: 3591,
3476, 3328, 3196, 2192, 1662, 1637, 1557, 1437, 1292,
1
1103, 845, 747 cm−1; H-NMR (90 MHz, DMSO-d6) δ:
8.26–7.24 (m, 9H, Ar-H), 6.82 (s, 2H, NH2), 5.95 (s, 1H,
C-H) ppm.
2.3 | General procedure for synthesis of
2-amino-4H-chromene derivatives 7–10
2.4.3 | 3-Amino-4-(4-chloro-3-
nitrophenyl)-4H-benzo[h]chromene-2-
carbonitrile (7 c)
To a mixture of aromatic aldehyde 1 (1.0 mmol),
malononitrile 2 (0.067 g, 1 mmol) and phenolic reagent
(α-naphthol 3, β-naphthol 4, resorcinol 5 or 2-hydroxy-
naphthalene-1,4-dione 6) (1.0 mmol), catalyst,
Fe3O4@SiO2-imine/phenoxy-Cu(II) (0.02 g), was added.
The mixture was stirred with a magnetic stirrer and
heated at 80 ꢀC under solvent-free conditions for an
appropriate time until the mixture turned into solid
(Table 1). After completion of the reaction, judged by
TLC, the resulting reaction mixture was cooled to room
temperature, diluted with hot ethanol (20 ml), and the
catalyst was separated by an external magnet. The precip-
itated product was isolated by filtration and purified by
recrystallization in hot ethanol.
ꢀ
Light brown; m.p. 212–214 C; yield 97%; FT-IR (KBr) ν:
3473, 3328, 3196, 3068, 2194, 1669, 1603, 1570, 1535,
1411, 1377, 1260, 1190, 806, 754 cm−1
;
1H-NMR
(400 MHz, DMSO-d6) δ: 8.25 (d, J = 8.24 Hz, 1H, Ar-H),
8.03 (d,, J = 1.7 Hz, 1H, Ar-H), 7.90 (d, J = 8.01 Hz, 1H,
Ar-H), 7.72 (d, J = 8.01 Hz, 1H, Ar-H), 7.66–7.57 (m, 4H,
Ar-H), 7.34 (s, 2H, NH2), 7.13 (d, J = 8.52 Hz, 1H, Ar-H),
5.15 (s,1H, C-H) ppm; 13C-NMR (100 MHz, DMSO-d6) δ:
160.3, 147.6, 146.6, 142.9, 133.2, 132.9, 132.1, 127.7, 127.0,
126.8, 125.8, 124.5, 124.2, 123.5, 122.7, 120.8, 120.1,
116.2 ppm. ESI-MSM/Z = 376.9 [M]+.
2.4 | Selected data
2.4.4 | 3-Amino-4-(4-methoxyphenyl)-4H-
benzo[h]chromene-2-carbonitrile (7 d)
2.4.1 | 3-Amino-4-phenyl-4H-benzo[h]
chromene-2-carbonitrile (7 a)
ꢀ
Cream; m.p. 198–200 C; yield 90%; FT-IR (KBr) ν: 3417,
3326, 3203, 2907, 2837, 2194, 1606, 1509, 1408, 1290,
Light brown; m.p. 220–222 C; yield 91%; FT-IR (KBr) ν:
1191, 1024, 809, 743 cm−1; H-NMR (90 MHz, DMSO-d6)
1
ꢀ
3474, 3305, 3189, 3055, 3021, 2202, 1711, 1656, 1632,
δ: 8.28–6.91 (m, 10H, Ar-H), 6.82 s, 2H, NH2), 4.8 (s, 1H,
C-H), 3.71 (s, 3H, OCH3) ppm.
1574, 1375, 1262, 1186, 1012, 742 cm−1
;
1H-NMR

COPPER-BASED SCHIFF BASE COMPLEX IMMOBILIZED ON …
5 of 20
1
2.4.5 | 3-Amino-4-(4-hydroxyphenyl)-4H-
benzo[h]chromene-2-carbonitrile (7 e)
792 cm−1; H-NMR (90 MHz, DMSO-d6) δ: 9.78 (s, 1H,
OH), 8.04–6.82 (m, 7H, Ar-H), 6.47 (s, 2H, NH2), 4.93 (s,
1H, C-H) ppm.
ꢀ
Brown; m.p. 241–243 C; yield 97%; FT-IR (KBr) ν: 3457,
3316, 3192, 2198, 1630, 1511, 1448, 1261, 1039, 854,
1
749 cm−1; H-NMR (90 MHz, DMSO-d6) δ: 9.32 (s, 1H,
2.4.10 | 2-Amino-4-(2,4-dichlorophenyl)-
7-hydroxy-4H-chromene-3-carbonitrile (9 c)
OH), 8.26–6.37 (m, 10H, Ar-H), 6.64 (s, 2H, NH2), 4.77 (s,
1H, C-H) ppm.
ꢀ
White solid; m.p. 263–265 C; yield 97%; FT-IR (KBr) ν:
3480, 3341, 3276, 3216, 2194, 1642, 1587, 1412, 1153,
1
2.4.6 | 3-Amino-4-phenyl-1H-benzo[f]
chromene-2-carbonitrile (8 a)
844 cm−1; H-NMR (400 MHz, DMSO-d6) δ: 9.80 (s, 1H,
OH), 7.57 (d, J = 2 Hz, 1H, Ar-H), 7.39 (dd, J = 8.4, 2 Hz,
1H, Ar-H), 7.21 (d, J = 8.4 Hz, 1H, Ar-H), 6.98 (s, 2H,
NH2), 6.71 (d, J = 8.5 Hz, 1H, Ar-H), 6.48 (dd, J = 8.4,
2.4 Hz, 1H, Ar-H), 6.41 (d, J = 2.2 Hz, 1H, Ar-H), 5.12 (s,
1H, C-H) ppm; 13C NMR (100 MHz, DMSO-d6) δ: 160.5,
157.4, 149.0, 141.8, 132.8, 132.2, 129.2, 129.1, 128.0, 120.1,
120.1, 112.6, 111.9, 102.3 ppm.
ꢀ
Light brown; m.p. 270–272 C; yield 93%; FT-IR (KBr) ν:
3434, 3339, 3193, 3022, 2885, 2183, 1639, 1517, 1284, 815,
1
610 cm−1; H-NMR (90 MHz, DMSO-d6) δ: 8.29–8.17 (d,
1H, Ar-H), 7.89–7.83 (d, 1H, Ar-H), 7.61–7.53 (m, 3H, Ar-
H), 7.04–7.25 (m, 9H, Ar-H and NH2), 4.88 (s, 1H, C-
H) ppm.
2.4.11 | 2-Amino-7-hydroxy-4-(thiophen-
2-yl)-4H-chromene-3-carbonitrile (9 d)
2.4.7 | 3-Amino-4-(2,4-dichlorophenyl)-
1H-benzo[f]chromene-2-carbonitrile (8 b)
ꢀ
Cream solid; m.p. 240–242 C; yield 97%; FT-IR (KBr) ν:
ꢀ
Light Brown; m.p. 228–230 C; yield 96%; FT-IR (KBr) ν:
3476, 3423, 3332, 3219, 2195, 1654, 1588, 1506, 1327,
1
3463, 3324, 3190, 2200, 1662, 1557, 1408, 1260, 1187,
1290, 1150, 1043, 867 cm−1; H-NMR (400 MHz, DMSO-
1
1046, 846, 741 cm−1; H-NMR (400 MHz, DMSO-d6) δ:
d6) δ: 9.78 (s, 1H, OH), 7.34 (d, J = 4.9 Hz, 1H, Ar-H),
6.96 (d, J = 4.6 Hz, 2H, Ar-H), 6.95 (s, 2H, NH2), 6.91 (t,
J = 4 Hz, 1H, Ar-H), 6.53 (dd, J = 8.3, 2.1 Hz, 1H, Ar-H),
6.39 (d, J = 2.1 Hz, 1H, Ar-H), 4.98 (s, 1H, C-H) ppm; 13C
NMR (100 MHz, DMSO-d6) δ: 160.3, 157.3, 151.5, 148.5,
129.8, 126.8, 125.0, 124.0, 120.5, 120.5, 113.5, 112.4,
102.2 ppm.
7.94 (dd, J = 22.6, 8 Hz, 2H, Ar-H), 7.62 (d, J = 1.7 Hz,
1H, Ar-H), 7.56 (d, J = 8.3 Hz, 1H, Ar-H) 7.49–7.40 (m,
2H, Ar-H), 7.33 (d, 1H, J = 8.9 Hz, Ar-H), 7.26 (dd,
J = 10,1.7 Hz, 1H, Ar-H), 7.11 (s, 2H, NH2), 7.00 (d,
J = 8.2 Hz, 1H, Ar-H), 5.69 (s, 1H, C-H) ppm; 13C-NMR
(100 MHz, DMSO-d6) δ: 159.8, 147.1, 141.6, 132.0, 131.9,
131.4, 130.7, 130.0, 129.9, 128.9, 128.7, 128.4, 127.5, 125.1,
122.5, 119.6, 116.8, 114.1 ppm.
2.4.12 | 2-Amino-4-(4-fluorophenyl)-7-
hydroxy-4H-chromene-3-carbonitrile (9 e)
2.4.8 | 2-Amino-7-hydroxy-4-phenyl-4H-
chromene-3-carbonitrile (9 a)
ꢀ
Brown solid; m.p. 202–204 C; yield 96%; FT-IR (KBr) ν:
3432, 3344, 3281, 2187, 1646, 1505, 1407, 1094, 865,
1
ꢀ
Brown; m.p. 238–240 C; yield 92%; FT-IR (KBr) ν: 3495,
779 cm−1; H-NMR (90 MHz, DMSO-d6) δ: 9.71 (s, 1H,
3424, 3220, 2193, 1654, 1506, 1454, 1302, 1114, 806,
OH), 7.19–6.51 (m, 7H, Ar-H), 6.41 (s, 2H, NH2), 4.65 (s,
1H, C-H) ppm.
1
623 cm−1; H-NMR (90 MHz, DMSO-d6) δ: 9.69 (s, 1H,
OH), 7.24–7.19 (m, 5H, Ar-H), 6.86–6.75 (m, 3H, Ar-H),
6.51–6.41 (s, 2H, NH2), 4.61 (s, 1H, C-H) ppm.
2.4.13 | 2-Amino-7-hydroxy-4-(4-tolyl)-
4H-chromene-3-carbonitrile (9 f)
2.4.9 | 2-Amino-7-hydroxy-4-(3-
nitrophenyl)-4H-chromene-3-carbonitrile
(9 b)
ꢀ
Brown solid; m.p. 202–204 C; yield 90%; FT-IR (KBr) ν:
3440, 3339, 3049, 2972, 2191, 1641, 1589, 14.64, 1113,
1
1045, 858 cm−1; H-NMR (90 MHz, DMSO-d6) δ: 9.33 (s,
ꢀ
Dark brown; m.p. 165–167 C; yield 94%; FT-IR (KBr) ν:
1H, OH), 8.46–6.50 (m, 7H, Ar-H), 6.41 (s, 2H, NH2), 2.25
3472, 3342, 3104, 2195, 1643, 1588, 1460, 1156, 855,
(s, 3H, CH3) ppm.

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EBRAHIMIASL AND AZARIFAR
2.4.14 | 2-Amino-5,10-dioxo-4-phenyl-
5,10-dihydro-4H-benzo[g]chromene-3-
carbonitrile (10 a)
NMR (400 MHz, DMSO-d6) δ: 8.04 (dd, J = 5.7, 3.3 Hz,
1H, Ar-H), 7.95–7.84(m, 3H, Ar-H), 7.53(d, J = 1 Hz, 1H,
Ar-H), 7.43 (s, 2H, NH2), 6.36 (dd, J = 3.1, 1.9 Hz, 1H,
Ar-H), 6.29 (d, J = 3.18 Hz, 1H, Ar-H), 4.76 (s, 1H, C-H)
ppm; 13C-NMR (100 MHz, DMSO-d6) δ: 182.2, 176.8,
159.2, 154.5, 149.2, 142.7, 134.7, 130.9, 130.5, 126.2, 125.9,
119.8, 119.7, 119.2, 119.2, 110.7, 106.4 ppm.
ꢀ
Brown solid; m.p. 263–265 C; yield 91%; FT-IR (KBr) ν:
3400, 3323, 3191, 3021, 2198, 1670, 1405, 1244, 984,
1
754 cm−1; H-NMR (90 MHz, DMSO-d6) δ: 8.02–7.84 (m,
4H, Ar-H), 7.30–6.87 (m, 7H, Ar-H and NH2), 4.61 (s, 1H,
C-H) ppm.
2.4.19 | 2-Amino-4-(4-
dimethylaminophenyl)-5,10-dioxo-5,10-
dihydro-4H-benzo[g]chromene-3-
carbonitrile (10 f)
2.4.15 | 2-Amino-5,10-dioxo-4-(4-
nitrophenyl)-5,10-dihydro-4H-benzo[g]
chromene-3-carbonitrile (10 b)
Dark-orange solid; m.p. 241–243 ꢀC; yield 94%; FT-IR
(KBr) ν: 3336, 3323, 3193, 2798, 2199, 1667, 1524, 1403,
Dark-brown solid; m.p. 232–234 ꢀC; yield 97%; FT-IR
(KBr) ν: 3397, 3331, 3196, 3075, 2203, 1670, 1521, 1411,
1
1244, 715 cm−1; H-NMR (400 MHz, DMSO-d6) δ: 8.04–
1
1246, 1183, 859, 780 cm−1; H-NMR (90 MHz, DMSO-d6)
8.02 (m, 1H, Ar-H),7.88–7.81 (m, 3H, Ar-H), 7.25 (s, 2H,
NH2), 7.08 (d, J = 8 Hz, 2H, Ar-H), 6.63 (d, J = 8.7 Hz,
2H, Ar-H), 4.48 (s, 1H, C-H), 2.83 (s, 6H, CH3) ppm; 13C-
NMR (100 MHz, DMSO-d6) δ: 182.6, 176.9, 158.2, 149.5,
148.1, 134.5, 134.1, 131.1, 131.0, 130.5, 128.3, 126.0, 125.0,
122.6, 122.6, 119.5, 119.5, 112.4 ppm. ESI-MS-M/
Z = 371 [M]+.
δ: 8.21–7.60 (m, 8H, Ar-H), 7.47 (s, 2H, NH2), 4.82 (s, 1H,
C-H) ppm.
2.4.16 | 2-Amino-4-(2,4-dichlorophenyl)-
5,10-dioxo-5,10-dihydro-4H-benzo[g]
chromene-3-carbonitrile (10 c)
Red-brown solid; m.p. 280–282 ꢀC; yield 97%; FT-IR
(KBr) ν: 3467, 3341, 3167, 3073, 2202, 1670, 1592, 1248,
2.4.20 | 2-Amino-5,10-dioxo-4-(4-tolyl)-
5,10-dihydro-4H-benzo[g]chromene-3-
carbonitrile (10 g)
1
1199, 847, 717 cm−1; H-NMR (90 MHz, DMSO-d6) δ:
8.35–7.25 (m, 9H, Ar-H and NH2), 5.12 (s, 1H, C-H) ppm.
ꢀ
Dark-brown; m.p. 243–245 C; yield 94%; FT-IR (KBr) ν:
3407, 3327, 3195, 3247, 2199, 1661, 1593, 1408, 1243, 950,
1
2.4.17 | 2-amino-4-(4-chloro-3-
nitrophenyl)-5,10-dihydro-5,10-dioxo-4H-
benzo[g]chromene-3-carbonitrile (10 d)
734 cm−1; H-NMR (90 MHz, DMSO-d6) δ: 7.99–7.14 (m,
10H, Ar-H and NH2), 4.44 (s, 1H, C-H), 2.25 (s, 6H,
CH3) ppm.
Red-brown solid; m.p. 255–257 ꢀC; yield 98%; FT-IR
(KBr) ν: 3410, 3330, 3218, 2193, 1660, 1593, 1530, 1412,
1245, 716 cm−1; 1H-NMR (400 MHz, DMSO-d6) δ: 8.08 (s,
1H, Ar-H), 8.06 (dd, J = 6.5, 2 Hz, 1H, Ar-H) 7.88–7.71
(m, 5H, Ar-H), 7.50 (s, 2H, NH2), 4.81 (s, 1H, C-H) ppm;
13C-NMR (100 MHz, DMSO-d6) δ: 182.6, 176.9, 158.2,
149.5, 148.1, 134.5, 134.1, 131.1, 131.0, 130.5, 128.3, 126.0,
125.7, 122.6, 122.6, 119.5, 119.5, 112.4 ppm. ESI-MS-M/
Z = 406.9 [M]+.
3 | RESULTS AND DISCUSSION
3.1 | Preparation of the Fe3O4@SiO2-
imine/phenoxy-Cu(II) catalyst
Herin, we report the stepwise synthesis of hitherto
unexplored Fe3O4-supported copper (II) Schiff-base com-
plex Fe3O4@SiO2-imine/phenoxy-Cu(II) as an efficient
and recyclable nanocatalyst as explained above
(Scheme 2).
2.4.18 | 2-Amino-4-(furan-2-yl)-5,10-
dioxo-5,10-dihydro-4H-benzo[g]chromene-3-
carbonitrile (10 e)
First, the silica-coated Fe3O4 MNPs were prepared by
co-precipitation of ferrous (Fe2+) and ferric (Fe3+) ions
followed by the reaction of dispersion of the resulted
nanoparticles in ethanol and deionized water with
tetraethyl orthosilicate (TEOS) in the presence of 25%
ammonia solution to obtain the core-shell Fe3O4@SiO2
ꢀ
Orange solid; m.p. 257–259 C; yield 97%; FT-IR (KBr) ν:
1
3414, 3330, 2197, 1665, 1592, 1420, 1201, 708 cm−1; H-

COPPER-BASED SCHIFF BASE COMPLEX IMMOBILIZED ON …
7 of 20
nanoparticles. In the next step, the Fe3O4@SiO2
nanoparticles were reacted with (3-chloropropyl)
triethoxysilane (CPTES) in dry toluene under nitrogen
atmosphere to obtain the chloro-functionalized
Fe3O4@SiO2-(CH2)3-Cl MNPs. Then, the reaction of
Fe3O4@SiO2-(CH2)3-Cl nanoparticles with 1,3-phe-
nylenediamine in ethanol containing few drops of
triethylamine under nitrogen atmosphere and refluxed
condition furnished the Fe3O4@SiO2-(CH2)3-NH-(3-
NH2C6H4) nanoparticles. Conversion of the Fe3O4@SiO2-
(CH2)3-NH-(3-NH2C6H4 nanoparticles into iminomethyl/
phenol Schiff-base derivative Fe3O4@SiO2-Iminomethyl/
phenol was accomplished via the reaction of
Fe3O4@SiO2-(CH2)3-NH-(3-NH2C6H4) nanoparticles as a
dispersion in methanol with salicylaldehyde in ethanol
under refluxed condition and nitrogen atmosphere to
obtain the Fe3O4@SiO2-Iminomethyl/phenol MNPs.
Finally, the dispersion of Fe3O4@SiO2-Iminomethyl/phe-
nol nanoparticles in ethanol was treated with 5% (w/v)
solution of Cu(OAc)2 in ethanol to afford the Fe3O4-
immobilized Schiff-base Cu(II) complex Fe3O4@SiO2-
imine/phenoxy-Cu (II). The structure of Fe3O4@SiO2-
imine/phenoxy-Cu(II) MNPs was fully established by dif-
ferent analytical techniques as described below.
3.2.1 | FT-IR analysis
The FT-IR spectra of the naked Fe3O4 NPs (a), silica-
coated Fe3O4@SiO2 NPs (b), Fe3O4@SiO2-(CH2)3-Cl (c),
Fe3O4@SiO2-(CH2)3-NH-(3-NH2C6H4 (d), Fe3O4@SiO2-
iminomethyl/phenol (e) and Fe3O4@SiO2-imine/
phenoxy-Cu(II) (f) presented in Figure 1 are compared.
Appearance of the characteristic absorption bands at
about 566 and 637 cm−1 corresponding to the Fe-O vibra-
tions in all the spectra 1a-f indicated the successful
immobilization of the organic moieties and Cu species on
the surface of the Fe3O4 nanoparticles. In addition, a
broad peak at 3000–3600 cm−1 exhibited by these spectra
along with another peak at about 1612 cm−1 are associ-
ated with the O-H stretching vibrations.[67,68] The absorp-
tion band observed at about 1084 cm−1 with a small
shoulder at 1180 cm−1 in the spectra 1b-f can be attrib-
uted to the symmetric and asymmetric stretching vibra-
tions of the Si-O-Si groups which clearly confirm the
silica-modification of the nanoparticles. Moreover, the
presence of σ-bonded propyl groups on the surface of the
Fe3O4 was confirmed by the aliphatic C-H stretching
vibrations at 2949–2878 cm−1 observed in the spectra 1c-
f. Immobilization of the 1,3-phenylendiamine on the sur-
face of the silica-coated Fe3O4 nanoparticles was
evidenced by the presence of the characteristic N-H
stretching band at 3292 cm−1 overlapped with the O-H
group in the spectrum 1 d. Formation of the immobilized
iminomethyl/phenol Schiff-base ligand and its Cu (II)
complex were approved by the N-H and C=N characteris-
tic vibrational bands at about 3292 and 1629 cm−1 respec-
tively as observed in the spectra 1 e and 1 f. Moreover,
the absorption band observed at 459 cm−1 in the
3.2 | Characterization of the
Fe3O4@SiO2-imine/phenoxy-Cu(II) catalyst
The structure of Fe3O4@SiO2-imine/phenoxy-Cu (II) cat-
alyst was fully established by different analytical tech-
niques as described below. The characterization data for
the catalyst are available at the end of the article.
FIGURE 1 FT-IR spectra of (a) naked
Fe3O4, (b) Fe3O4@SiO2, (c) Fe3O4@SiO2-(CH2)3-
Cl, (d) Fe3O4@SiO2-(CH2)3-NH-(3-NH2C6H4,
(e) Fe3O4@SiO2-iminomethyl/phenol and (f)
Fe3O4@SiO2-Imine/Phenoxy-Cu(II)

8 of 20
EBRAHIMIASL AND AZARIFAR
spectrum 1 f can be attributed to the Cu-O stretching
vibration. Appearance of additional bands in the range
1170–1600 cm−1 can be assigned to the stretching vibra-
tions of the C=C, C-N, and C-O bonds which further con-
firm the formation immobilized Schiff-base ligand and its
related Cu (II) complex. The slight shift of the C=N
absorption frequency to a lower frequency shown in the
spectrum 1 f is likely due to the successful co-ordination
of the imminomethyl/phenol Schiff-base ligand to Cu(II)
ion.[69]
3.2.2 | XRD analysis
FIGURE 2 XRD patterns of (a) naked Fe3O4 MNPs and
(b) Fe3O4@SiO2-imine/Phenoxy-Cu(II) MNPs
The crystalline nature and the size of the Fe3O4@SiO2-
imine/phenoxy-Cu(II) nanoparticles were determined by
X-ray diffraction (XRD) analysis. As indicated in the
resulted XRD pattern of the Fe3O4@SiO2-imine/phenoxy-
Cu(II) nanoparticles in Figure 2a, the intense Bragg's
peaks observed at 2θ = 18.5ꢀ, 30.5ꢀ, 35.7ꢀ, 43.3ꢀ, 53.8ꢀ,
57.1ꢀ, 62.8 and 73.8ꢀ (2 a) correspond to the (111), (220),
(311), (400), (422), (511) and (531) reflection planes,
respectively. These peaks are related to the crystal
planes in the Fe3O4 lattice. The positions and relative
intensities of these peaks clearly match with the literature
data from the Joint Committee on Powder Diffraction
System of Fe3O4 (JCPDS Card No. 65–3107). Comparison
of the XRD pattern of Fe3O4@SiO2-imine/phenoxy-Cu(II)
nanoparticles (2 a) with that of the blank Fe3O4
nanoparticles (2 b) proved that the crystalline structure
was retained in the Fe3O4@SiO2-imine/phenoxy-Cu(II)
nanoparticles after coatation with SiO2 layer and
immobilization with the Schiff-base Cu (II) complex.[70]
From the XRD pattern can be ascertained the average
crystallite size of nanoparticles by applying the Debye–
Scherer equation that can be written as: ((D = (Kλ)/
(βcosθ)).[71] In this equation, D is the average crystalline
and K is a dimensionless shape factor. The shape factor
has a typical value of about 0.9, which varies with the
actual shape of the crystallite; λ is the X-ray wavelength,
β is the line broadening at half the maximum intensity
(FWHM) after subtracting the instrumental line broaden-
ing in radians, and also θ is the Bragg angle. Eventually,
Bragg equation (dhkl = λ/2sinθ) was employed to calcu-
late the distance between the layers (Table 1).
The presence of Fe, Si, O, N, C and Cu elements with
the corresponding weight percent (0.81%, 77%, 0.32%,
0.20%, 0.18%, 0.7%) is clearly evidenced by the EDX spec-
trum presented in Figure 3. Formation of the
Iminomethyl/Phenol Schiff-base and its Cu(II) complex
grafted on the surface of the nanoparticles was confirmed
by appearance of the peaks due to the N and Cu atoms.
In addition, the Cu content of the catalyst was detected
and evaluated by ICP-OES which was found to be
11.36 wt%.
3.2.4 | Scanning electron microscopy
(SEM) and transmission electron
microscopy (TEM)
The morphology and particle size of the Fe3O4@SiO2-
imine/phenoxy-Cu(II) nanoparticles were studied by
field-emission scanning electron microscopy (FE-SEM)
and TEM, respectively. It can be observed from the TEM
images shown in Figure 4a that, the encapsulated
Fe3O4@SiO2-imine/phenoxy-Cu(II) complex are made up
of nanometer-sized particles exhibiting
a regularly
spherical morphology with the diameters in the range
15–20 nm. Moreover, on the basis of the TEM image
shown in Figure 4b, the core-shell structure and the
nanometer-sized nature of the Fe3O4@SiO2-imine/
phenoxy-Cu(II) particles were obvious. Also, the core-
shell structure of the nanoparticles was further
approved by the presence of dark spots inside the bright
spherical thin silica shell. However, it should be noted
that, due to aggregation of the particles with paramag-
netic nature, the exact evaluation of the particle size is
difficult.
3.2.3 | Energy dispersive X-ray (EDX)
and inductively coupled plasma (ICP)
analyses
The elemental composition of Fe3O4@SiO2-imine/
phenoxy-Cu(II) nanoparticles was determined by EDX.

COPPER-BASED SCHIFF BASE COMPLEX IMMOBILIZED ON …
9 of 20
used to determine quantitative atomic composition and
chemistry of the Fe3O4@SiO2-imine/phenoxy-Cu(II)
nanoparticles. The discrete peaks observed in the XPS
spectra determined in the regions for Si, Fe, N, Fe (Fig-
ure 5) correspond to ionization from the core electron
orbitals of the atoms in the outermost 10–50 Å of the sur-
face. The results obtained from the analysis of the Si 2p
spectra confirmed the presence of binding energies at
103.28 and 103.88 eV corresponding to Si-O-Si and Si-O
bonds respectively. Also, the presence of carbon atom in
the structure of the nanoparticles was approved by the
peaks related to C 1 s at the binding energies of 284.88
(C-O-C), 286.18 (C-O) and 287.58 (C=N) eV.[72] The
nitrogen atoms contained in the grafted Schiff-base group
exhibited their N 1 s peaks at the related binding energies
398.68 and 400.28 eV corresponding to C-N and C=N
bonds respectively.[73] Appearance of the Fe 2p3/2 and
Fe 2p1/2 peaks binding energies at 712.68 and 725.38 eV
respectively correspond to Fe3+ present in the Fe3O4
phase. The XPS spectrum resulted in the Fe 2 pv region
presented two main binding energy peaks at 710.68 and
FIGURE 3 The energy dispersive X-ray (EDX) spectrum of
Fe3O4@SiO2-imine/Phenoxy-Cu(II) MNPs
3.2.5 | Study of X-ray photoelectron
spectroscopy (XPS) of the synthesized
Fe3O4@SiO2-imine/phenoxy-Cu(II)
nanoparticles
724.6 eV which were related to Fe2+ [74]
.
XPS spectrum in the Cu2p region showed a doublet
peak located at approximately 933.48 and 952.18 eV
which are attributed to Cu 2p3/2 and Cu 2p1/2
X-ray photoelectron spectroscopy (XPS), also known as
electron spectroscopy for chemical analysis (ESCA), is
FIGURE 4 (a) SEM and (b) TEM
images of the Fe3O4@SiO2-imine/
Phenoxy-Cu(II) MNPs

10 of 20
EBRAHIMIASL AND AZARIFAR
respectively Also, the doublet peaks with binding ener-
gies of 935.08 and 954.58 eV were assigned to Cu 2p3/2
and Cu 2p1/2 in Cu (II_ On the other hand, two shake-
up satellite peaks at 941.28 and 944.48 eV are related to
Cu (II) species.[75]
3.2.6 | Vibrating-sample magnetometer
(VSM) analysis of Fe3O4@SiO2-imine/
phenoxy-Cu(II) nanoparticles
In addition to the above-mentioned XRD, SEM and TEM
analyses, the room temperature magnetization behavior
was also studied by conducting vibrating-sample magne-
tometer (VSM) on Fe3O4@SiO2-imine/phenoxy-Cu(II)
nanoparticles. The magnetization curves obtained for the
naked Fe3O4 and Fe3O4@SiO2-imine/phenoxy-Cu(II)
nanoparticles are illustrated in Figure 6. As seen in these
curves, the specific saturation magnetizations (Ms) of
uncoated Fe3O4 and Fe3O4@SiO2-imine/phenoxy-Cu(II)
nanoparticles are measured to be 54 and 26 emu g−1
respectively. The slight decrease (28 emu g−1) observed in
the saturation magnetization value (Ms) of the
Fe3O4@SiO2-imine/phenoxy-Cu(II) nanoparticles com-
pared to the Ms value of the bare Fe3O4 nanoparticles
was most likely attributed to the existence of the coated
SiO2 and Schiff-base Cu(II) (11.36 wt.%) materials on the
surface of the Fe3O4 nanoparticles.
FIGURE 6 Magnetization curves of (a) bare Fe3O4 and
(b) Fe3O4@SiO2-imine/phenoxy-Cu(II)
ꢀ
steps in thermal range 25–800 C. ꢀThe first small weight
loss of about 7% occurs below 150 C which is likely due
to the removal of the adsorbed water and remaining
organic solvents. The second weight loss of almost 12% in
the range 150–450 ꢀC is possibly attributed to the removal
of the Fe3O4-grafted organic materials and Cu (II) Schiff
base complex. Complete decomposition of the catalyst
and the possible change of the crystal phase from Fe3O4
to γ-Fe2O3 happen in the final thermal step beyond
450 ꢀC.[76] These results clearly confirm the successful
immobilization of the imine/phenoxy derived Schiff-base
Cu (II) complex on the surface of the silica-coated
Fe3O4 MNPs.
3.2.7 | Thermal gravimetric
analysis (TGA)
Thermal gravimetric analysis (TGA) was applied to the
Fe3O4@SiO2-imine/phenoxy-Cu(II) catalyst in order to
investigate its thermal stability and verify the existence of
the materials immobilized on the surface of the
nanoparticles. According to the TGA pattern presented in
Figure 7, weight loss takes place in three consecutive
3.3 | Catalyst activity of Fe3O4@SiO2-
imine/phenoxy-Cu(II) MNPs
In order to evaluate the catalytic activity of the synthe-
sized Fe3O4@SiO2-imine/phenoxy-Cu(II) nanoparticles,
we chose to study three-component condensation
FIGURE 5 The X-ray photoelectron spectroscopy (XPS) spectra of the synthesized Fe3O4@SiO2-Imine/Phenoxy-Cu(II) nanoparticles

COPPER-BASED SCHIFF BASE COMPLEX IMMOBILIZED ON …
11 of 20
TABLE 3 Comparative catalytic activity of Fe3O4@SiO2-
Imine/phenoxy-Cu(II) nanoparticles under optimal conditions
Time
(min)
Yield
(%)
Entry Catalyst
1
Fe3O4@SiO2-Imine/
10
98
Phenoxy-Cu (II)
2
Fe3O4@SiO2-Iminomethyl/
Phenol
30
80
3
4
Fe3O4@SiO2
Fe3O4
120
35
58
70
FIGURE 7 TGA curve of Fe3O4@SiO2-imine/phenoxy-Cu
α-naphthol as the model reaction. According to the
experimental results summarized in Table 2, the best
results in terms of the reaction yield and rate for the
selected model reaction were observed when the reaction
was performed at 70 ꢀC under solvent-free condition
using the catalyst loading of 20 mg (entry 10). Indispens-
able use of the catalyst Fe3O4@SiO2-imine/phenoxy-Cu
(II) in the reaction was established by conducting the
reaction under the optimized conditions in the absence of
the catalyst and noticed that no detectable amount of the
product was produced after a long reaction time (entry
13). Moreover, the catalytic activity of the Fe3O4@SiO2-
(II) MNPs
reactions between the aldehydes, malononitrile, and dif-
ferent phenolic reagents like α-naphthol, β-naphthol, res-
orcinol, and 2-hydroxynaphthalene-1,4-dione to synthesis
various derivatives of 2-amino-4H-chromene-3-car-
bonitrile
using
Fe3O4@SiO2-imine/phenoxy-Cu(II)
nanoparticles as the catalyst (Scheme 1). At first, the
effects of different reaction parameters such as catalyst
loading, solvent, and temperature on the reaction were
screened to establish the conditions of the reactions using
the reaction between benzaldehyde, malononitrile and
TABLE 2 Screening the reaction parameters for the synthesis of 2-amino-4-phenyl-4H-benzo[h]chromene-3-carbonitrile (7a)a
Entry
Catalyst (mg)
Solvent
Temperature (ꢀC)
Time (min)
Yield (%)b
1
10
H2O
25
25
80
80
80
80
60
60
60
40
40
10
15
15
120
38
46
2
10
EtOH
3
10
CH3CN
25
43
4
10
Solvent-free
H2O
25
58
5
10
reflux
reflux
reflux
70
45
6
10
EtOH
62
7
10
CH3CN
68
8
10
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
72
9
10
100
70
70
10
11
12
13
20
98
40
60
70
85
70
80
No catalyst
70
trace
aConditions: benzaldehyde (1 mmol), malononitrile (1 mmol), α-naphthol (1 mmol), solvent (5 ml).
bIsolated pure yield.

12 of 20
EBRAHIMIASL AND AZARIFAR
TABLE 4 Fe3O4@SiO2-imine/phenoxy-Cu (II)-catalyzed synthesis of 2-amino-4H-chromene derivativesa
Mp (ꢀC)
Entry
Ar
Phenols 3–6
Products 7–10
Time (min)
Yield (%)b
Found
Reported
1
C6H5
3
10
98
210
205[77]
2
2,6-Cl2C6H3
3
3
8
8
96
97
212
214–216[27]
3new
4-Cl-3-NO2C6H3
258
-
4
4-MeOC6H4
3
12
90
200
195–196[29]
5
4-HOC6H4
3
12
92
241
245[77]
(Continues)

COPPER-BASED SCHIFF BASE COMPLEX IMMOBILIZED ON …
13 of 20
TABLE 4 (Continued)
Mp (ꢀC)
Entry
Ar
Phenols 3–6
Products 7–10
Time (min)
Yield (%)b
Found
Reported
6
C6H5
4
10
93
270
274[77]
7
2,6-Cl2C6H3
4
5
5
5
8
12
13
10
96
92
94
97
230
238–240
165
222–224[29]
8
C6H5
234–237[30]
169–170[31]
256–258[71]
9
3-NO2C6H4
10
2,4-Cl2C6H3
263–265
(Continues)

14 of 20
EBRAHIMIASL AND AZARIFAR
TABLE 4 (Continued)
Mp (ꢀC)
Entry
Ar
Phenols 3–6
Products 7–10
Time (min)
Yield (%)b
Found
Reported
11
Thiopen-2-yl
5
10
96
240–242
230–232[71]
12
13
14
4-FC6H4
4-MeC6H4
C6H5
5
5
6
9
14
10
96
90
91
202
178–180
265
186–188[78]
183–186[30]
260–26[79]
9f
15
4-NO2C6H4
6
9
97
232
233–234[79]
(Continues)

COPPER-BASED SCHIFF BASE COMPLEX IMMOBILIZED ON …
15 of 20
TABLE 4 (Continued)
Mp (ꢀC)
Entry
Ar
Phenols 3–6
Products 7–10
Time (min)
Yield (%)b
Found
Reported
252–254[80]
16
4-ClC6H4
6
8
97
250
17new
4-Cl-3-NO2C6H3
6
8
98
255
-
18
Furan-2-yl
6
8
97
262
266–268[76]
19new
4-Me2NC6H4
6
10
94
243
-
(Continues)

16 of 20
EBRAHIMIASL AND AZARIFAR
TABLE 4 (Continued)
Mp (ꢀC)
Entry
Ar
Phenols 3–6
Products 7–10
Time (min)
Yield (%)b
Found
245
Reported
20
4-MeC6H4
6
12
89
242–244[80]
aConditions: aldehyde (1 mmol), malononitrile (1 mmol), phenolic reagent (1 mmol), catalyst (0.02 g), 80 ꢀC.
bIsolated pure yield.
imine/phenoxy-Cu(II) nanoparticles was compared with
the catalytic activities of the bare Fe3O4, Fe3O4@SiO2 and
Fe3O4-supported Schiff-base nanoparticles in separate
experiments conducted under the same optimal condi-
tions. The resulting yields given in Table 3 clearly
indicated that the Fe3O4@SiO2-imine/phenoxy-Cu(II)
nanoparticles perform relatively higher catalytic activity
compared with other three nanoparticles.
With the optimized reaction conditions in hand, the
scope and generality of the reaction was investigated
using a divers series of aromatic aldehydes carrying dif-
ferent substituent groups and various phenolic com-
pounds 4–6. According to the experimental results
summarized in Table 4, all the tested aldehydes reacted
smoothly irrespective of the nature of the substituent
groups and the resulted 2amino-4H-chromene derivatives
7a-e, 8a-b, 9a-f and 10a-g were produced in excellent
yields and short reaction times. The products were struc-
turally characterized by their physical properties and
using FT-IR, 1H NMR, 13C NMR, and ESI-MS (in the case
of new compounds) spectral analyses and compared with
the reported data.
condensation reaction between the aldehyde and
malononitrile in the presence of Fe3O4@SiO2-imine/
phenoxy-Cu(II) as a Lewis acid catalyst to generate
arylidenemalononitrile (I). In the following step, the
resulted intermediate (I) undergoes a Michael-type
addition reaction with the phenolic species (α-naph-
thol, β-naphthol, resorcinol or 2-hydroxynaphthalene-
1,4-dione) under the catalytic acceleration to produce
the adduct (II). Finally, enolization of (II) occur to
yield the intermediate (III) which undergoes intramo-
lecular nucleophilic cyclization to afford the respective
products 7–10.[71]
3.5 | Catalyst recyclability
We examined the recycling and reusability of the
Fe3O4@SiO2-imine/phenoxy-Cu(II) catalyst for the model
reaction between benzaldehyde, malononitrile and
α-naphthol under the optimized conditions. After com-
pletion of the reaction, the catalyst was separated
magnetically using a magnet. The isolated nanoparticles
were washed with ethanol and water several times, oven-
ꢀ
dried at 60 C, and reused for five successive runs with
3.4 | Proposed catalytic reaction
no significant loss of activity (Figure 8).
A plausible mechanism for three-component reaction
of aldehydes, malononitrile and different phenolic
compounds for the synthesis of the corresponding 2-
amino-4H-chromene derivatives is suggested in
Scheme 3. Likely, the initial step involves the
4 | THEORETICAL STUDIES
Theoretical calculations were performed to analyze the
optimization of the molecular structures of 2-amino-4H-

COPPER-BASED SCHIFF BASE COMPLEX IMMOBILIZED ON …
17 of 20
chromene derivatives by using density functional theory
(DFT)/B3LYP method. The most important geometrical
parameters of the target compounds are quoted in
Table 5. The frontier molecular orbitals, i.e. the highest
occupied molecular orbital (HOMO) and the lowest
unoccupied molecular orbital (LUMO), of 2-amino-4H-
chromene derivatives are presented as Figure 1 in
supplementary data. In addition, some considerable elec-
tronic features such as calculated bond lengths, dipole
moments and energies of the HOMO and LUMO for all
2-amino-4H-chromene derivatives are listed in Table 5.
As can be seen from this table, the higher negative charge
density in the HOMO molecular orbitals, was found to be
around the nitrogen atoms of the NH2 and CN groups in
2-amino-4H-chromene derivatives. This observation
implies the increased probability of nucleophilic attack of
these groups at the metal ion. Moreover, the negative
charge density of LUMO molecular orbitals has been
nearly delocalized over the entire molecule. The higher
energy of HOMO and the lower energy of LUMO facili-
tate the interaction between the electron-donor and elec-
tron-acceptor units.
5 | CONCLUSIONS
In the present research, we report for the first time the
preparation of
immobilized
nanoparticles.
a new Cu(II) Schiff-base complex
on
The
silica-coated
prepared
Fe3O4
Fe3O4@SiO2-imine/
magnetic
phenoxy-Cu(II) catalyst was structurally characterized by
FT-IR, SEM, TEM, EDX, XRD, TGA, XPS, VSM and ICP-
OES analytical techniques. These newly prepared
nanoparticles were explored as efficient heterogeneous
Lewis acid catalyst for the synthesis of various 2-amino-
4H-chromene derivatives via one-pot three-component
reactions between aldehydes, malononitrile and phenolic
reagents such as α-naphthol, β-naphthol, resorcinol and
2-hydroxynaphthalene-1,4-dione under green solvent-free
condition. Moreover, this catalyst can be easily recycled
and reused for five times without significant loss of cata-
lytic activity.
SCHEME 3 A plausible pathway for one-pot synthesis of 2-
amino-4H-chromenes catalyzed by Fe3O4@SiO2-imine/phenoxy-Cu
(II) MNPs
FIGURE 8 Recyclability of the Fe3O4@SiO2-imine/phenoxy-
Cu(II) catalyst

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EBRAHIMIASL AND AZARIFAR

COPPER-BASED SCHIFF BASE COMPLEX IMMOBILIZED ON …
19 of 20
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ACKNOWLEDGMENTS
The authors wish to thank the Research Council of Bu-
Ali Sina University for financial support to carry out this
research.
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Hakimeh Ebrahimiasl https://orcid.org/0000-0001-
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Davood Azarifar https://orcid.org/0000-0002-7331-2748
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SUPPORTING INFORMATION
Additional supporting information may be found online
in the Supporting Information section at the end of this
article.
How to cite this article: Ebrahimiasl H,
Azarifar D. Copper-based Schiff Base Complex
Immobilized on Core-shell Fe3O4@SiO2 as a
magnetically recyclable and highly efficient
nanocatalyst for green synthesis of 2-amino-4H-
chromene derivatives. Appl Organometal Chem.
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