Copper(II) Schiff Base Complex Immobilized on Superparamagnetic Fe3O4@SiO2 as a Magnetically Separable Nanocatalyst for Oxidation of Alkenes and Alcohols

Article abstract of DOI:10.1002/aoc.3726

A new heterogeneous catalyst containing a copper(II) Schiff base complex covalently immobilized on the surface of silica-coated Fe₃O₄ nanoparticles (Fe₃O₄@SiO₂-Schiff base-Cu(II)) was synthesized. Characterization of this catalyst was performed using various techniques. The catalytic potential of the catalyst was investigated for the oxidation of various alkenes (styrene, α-methylstyrene, cyclooctene, cyclohexene and norbornene) and alcohols (benzyl alcohol, 3-methoxybenzyl alcohol, 3-chlorobenzyl alcohol, benzhydrol and n-butanol) using tert-butyl hydroperoxide as oxidant. The catalytic investigations revealed that Fe₃O₄@SiO₂-Schiff base-Cu(II) was especially efficient for the oxidation of norbornene and benzyl alcohol. The results showed that norbornene epoxide and benzoic acid were obtained with 100 and 87% selectivity, respectively. Moreover, simple magnetic recovery from the reaction mixture and reuse for several times with no significant loss in catalytic activity were other advantages of this catalyst.

Full text of DOI:10.1002/aoc.3726

Received: 19 August 2016
Revised: 25 November 2016
Accepted: 3 December 2016
https://doi.org/10.1002/aoc.3726
F U L L PA P E R
Copper(II) Schiff Base Complex Immobilized on
Superparamagnetic Fe3O4@SiO2 as a Magnetically Separable
Nanocatalyst for Oxidation of Alkenes and Alcohols
Marzieh Sarkheil | Maryam Lashanizadegan
Department of Chemistry, Faculty of Physics and
A new heterogeneous catalyst containing a copper(II) Schiff base complex
Chemistry, Alzahra University, PO Box
1993893973, Tehran, Iran
covalently immobilized on the surface of silica‐coated Fe3O4 nanoparticles
(Fe3O4@SiO2‐Schiff base‐Cu(II)) was synthesized. Characterization of this catalyst
was performed using various techniques. The catalytic potential of the catalyst was
investigated for the oxidation of various alkenes (styrene, α‐methylstyrene,
cyclooctene, cyclohexene and norbornene) and alcohols (benzyl alcohol, 3‐metho-
xybenzyl alcohol, 3‐chlorobenzyl alcohol, benzhydrol and n‐butanol) using tert‐
butyl hydroperoxide as oxidant. The catalytic investigations revealed that
Fe3O4@SiO2‐Schiff base‐Cu(II) was especially efficient for the oxidation of
norbornene and benzyl alcohol. The results showed that norbornene epoxide and
benzoic acid were obtained with 100 and 87% selectivity, respectively. Moreover,
simple magnetic recovery from the reaction mixture and reuse for several times with
no significant loss in catalytic activity were other advantages of this catalyst
Correspondence
Maryam Lashanizadegan, Department of
Chemistry, Faculty of Physics and Chemistry,
Alzahra University, PO Box 1993893973, Tehran,
Iran.
Email: m_lashani@alzahra.ac.ir
KEYWORDS
Alcohol, alkene, copper(II) Schiff base complex, magnetic nanoparticles, oxidation
catalyst
1
|
INTRODUCTION
many strategies involving entrapment of homogeneous
catalysts inside the pores of solid supports[17,18] or grafting
them on the surface of organic[19–21] or inorganic[22–24]
supports have been employed to heterogenize the homoge-
neous catalysts. One of the best solid supports are magnetic
nanoparticles which enable a catalyst to be readily separated
from reaction media by means of an external magnet.[25] Since
magnetic nanoparticles tend to aggregate in a liquid due to the
anisotropic dipolar attraction and being unstable under acidic
conditions, the magnetic core is usually protected with an
outer shell such as silica[26,27] or polymers.[28] Among them,
silica is a suitable candidate which provides appropriate prop-
erties such as preventing aggregation and improving thermal
and chemical stability. Also, its surface contains silanol
groups that can be modified by various coupling agents and
consequently specific ligands can be covalently anchored on
the surface of the magnetic support.[29]
Catalytic oxidation of organic substrates into useful products
is a fundamental synthetic method in chemical industries
and laboratory researches.[1] Among the oxidation catalysts,
Schiff base transition metal complexes represent a very useful
class of compounds because their structures are similar to that
of the porphyrin ring and they are good at loading oxygen and
mimicking enzymes.[2] Therefore, homogeneous or heteroge-
neous catalytic activities of various Schiff base transition
metal complexes such as Cu(II),[3–5] Co(II),[6–8] V(V),[9,10]
Mo(VI),[11,12] Mn(II)[13,14] and Ni(II)[15,16] complexes in the
oxidation of organic substrates have been extensively investi-
gated. Although homogeneous catalysts often show high cat-
alytic performances, they are associated with some
drawbacks including difficulty of separation from products,
deactivation of catalyst via dimerization and instability at high
temperatures. These drawbacks are in contrast with economic
and environmental concerns in industrial applications. So,
In the past few decades, great interest has been paid to cat-
alytic oxidation of alkenes for the production of several
Appl Organometal Chem 2017;e3726.
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Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.3726

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SARKHEIL AND LASHANIZADEGAN
important products such as epoxides, aldehydes, ketones and
alcohols, which are essential intermediates in pharmaceutical
and chemical industries.[30] The catalytic oxidation of alcohols
into corresponding carbonyl or acid compounds has also been
attracting the attention of chemical researchers. Although the
partial oxidation of primary alcohols to aldehydes is of great
importance owing to the application of aldehydes in agricul-
tural and fine chemicals, the complete and direct oxidation
of them to carboxylic acids also is also of great importance
in industry.[31–33] Thus to date, many efforts have been made
to design clean, reusable and efficient catalysts for the oxida-
tion of alkenes and alcohols. In this regard, many articles that
focus on the catalytic role of Schiff base complexes
immobilized on magnetic nanoparticles in the oxidation of
alkenes[34–38] and alcohols[39–42] have been published.
Also, coating of magnetic nanoparticles with silica
(Fe3O4@SiO2) was performed based on
a literature
method.[44]
To functionalize Fe3O4@SiO2 with amine groups, a
mixture of Fe3O4@SiO2 (0.1 g) with 3‐aminopropyltri-
methoxysilane (APTMS; 0.8 mmol, 0.14 ml) was refluxed
in dry toluene under nitrogen atmosphere for 48 h. The
obtained solid (Fe3O4@SiO2‐APTMS) was washed with
30 ml of toluene and ethanol and dried at 60 °C for 10 h.
Afterwards, to synthesize the Schiff base on the surface of
Fe3O4@SiO2‐APTMS, 2′‐hydroxypropiophenone (0.75 g,
1
mmol) was added to a suspended solution of
Fe3O4@SiO2‐APTMS (0.1 g) in dry toluene (15 ml). After
refluxing under nitrogen atmosphere for 48 h, the resultant
material (Fe3O4@SiO2‐Schiff base) was washed with toluene
and dried at 60 °C for 10 h. Finally, Fe3O4@SiO2‐Schiff
base‐Cu(II) was prepared by adding an ethanolic solution
(20 ml) of Cu(CH3COO)2⋅H2O (0.19 g, 1 mmol) to
Fe3O4@SiO2‐Schiff base (0.1 g). The resulting mixture was
sonicated and then refluxed under nitrogen atmosphere for
around 17 h (Scheme 1). Then, the catalyst was recovered
by magnetic decantation, washed several times with absolute
ethanol to remove unreacted copper and dried at 60 °C for
10 h.
Herein, we report the synthesis, characterization and
catalytic application of a copper(II) Schiff base complex
covalently anchored on the surface of silica‐coated Fe3O4
nanoparticles (Fe3O4@SiO2‐Schiff base‐Cu(II)) for the
oxidation of various alkenes and alcohols.
2
| EXPERIMENTAL
2.1 | Materials and instrumentation
Solvents and starting materials were purchased from Acros
Organics, Merck or Sigma‐Aldrich and were used without fur-
ther purification. Fourier transform infrared (FT‐IR) spectra
(KBr discs, 500–4000 cm−1) were recorded using a Bruker
FT‐IR Tensor 27 spectrometer. X‐ray diffraction (XRD) pat-
terns were collected using a Philips X'Pert diffractometer
using Cu Kα radiation (λ = 1.54 Å). Elemental analyses were
realized with a 2400 Series II CHN analyser (PerkinElmer,
USA). Scanning electron microscopy (SEM) images were
obtained using a KYKY‐EM3200 microscope. Transmission
electron microscopy (TEM) images were obtained with a
Philips CM120 electron microscope. Magnetic properties
were determined using a vibrating sample magnetometer
(BHV‐55, Riken, Japan) in the magnetic field range of
−8000 to +8000 Oe at room temperature. The amount of cop-
per in the catalyst was determined using an inductively
coupled plasma optical emission spectroscopy (ICP‐OES)
instrument (Varian, Vista‐Pro, Australia). Thermogravimetric
analysis (TGA) was conducted with a TGA/DSC1 (Mettler
Toledo). The oxidation products were analysed by GC and
GC–MS using an Agilent 6890 Series with a flame ionization
detector, an HP‐5% phenylmethylsiloxane capillary and an
Agilent 5973 Network, mass selective detector, HP‐5MS
6989 Network GC system, respectively.
2.3 | General procedure for oxidation of alkenes and
alcohols
All oxidation reactions of alkenes and alcohols were
performed in a 10 ml round‐bottom flask equipped with a
water condenser. In a typical run, to a solution of catalyst
(0.01 g) and substrate (5 mmol) in CH3CN (3 ml), tert‐
butyl hydroperoxide (TBHP; 20 mmol) was added. The
resulting mixture was refluxed for an appropriate time
(2 h for alkenes, 6 h for alcohols). At the end of the
reaction, the catalyst was collected using an external mag-
net and the reaction mixture was subjected to GC and
GC–MS analyses. Conversion of substrates was calculated
from GC data and the oxidation products were identified
from GC–MS results.
2.2 | Preparation of Fe3O4@SiO2‐Schiff base‐Cu(II)
Catalyst
Fe3O4 magnetic nanoparticles were prepared by the co‐
precipitation method according to a reported procedure.[43]
SCHEME 1 Preparation of Fe3O4@SiO2‐Schiff base‐Cu(II)

SARKHEIL AND LASHANIZADEGAN
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3
| RESULTS AND DISCUSSION
3.1 | Characterization of Fe3O4@SiO2‐Schiff base‐
Cu(II) Catalyst
The FT‐IR spectra of Fe3O4, Fe3O4@SiO2, Fe3O4@SiO2‐
APTMS, Fe3O4@SiO2‐Schiff base and Fe3O4@SiO2‐Schiff
base‐Cu(II) are presented in Figure 1. In the FT‐IR spectrum
of Fe3O4 (Figure 1a), the bands appearing at 587 and 631 cm
−1
correspond to Fe─O vibrations. Also, the bands seen at
3417 and 1616 cm−1 should be related to the stretching and
bending vibrations of adsorbed water or FeOH groups of
the surface.[45,46] The FT‐IR spectrum of Fe3O4@SiO2
(Figure 1b) shows two peaks at around 1086 and 816 cm−1
corresponding to Si─O─Si asymmetric and symmetric
vibrations, respectively. This observation confirms the coat-
ing of silica on the surface of the Fe3O4 nanoparticles. As
shown in Figure 1(c), two peaks at 2920 and 2860 cm−1
due to the C─H stretching vibrations corroborate the pres-
ence of anchored propyl groups in Fe3O4@SiO2‐APTMS.[47]
After the reaction of 2‐hydroxypropiophenone with
Fe3O4@SiO2‐APTMS, a band is observed at 1609 cm−1 in
its FT‐IR spectrum (Figure 1d) due to C═N vibration. The
C═N vibration of Fe3O4@SiO2‐Schiff base‐Cu(II) (Fig-
ure 1e) shows a lower frequency in comparison to the corre-
sponding vibration in the spectrum of Fe3O4@SiO2‐Schiff
base. This indicates the involvement of azomethine nitrogen
in coordination to the metal centre.
FIGURE
2
XRD patterns of (a) Fe3O4, (b) Fe3O4@SiO2, (c) fresh
Fe3O4@SiO2‐Schiff base‐Cu(II), (d) Fe3O4@SiO2‐Schiff base‐Cu(II)
recovered after first cycle and (e) Fe3O4@SiO2‐Schiff base‐Cu(II) recovered
after fourth cycle
The XRD patterns of Fe3O4, Fe3O4@SiO2 and
Fe3O4@SiO2‐Schiff base‐Cu(II) are exhibited in Figure 2.
As seen in Figure 2(a), the position and relative intensities
of all diffraction peaks of prepared Fe3O4 match with the
standard Fe3O4 XRD pattern (JCPDS no. 75–0033). After
coating the magnetite with silica and immobilizing the
copper(II) complex on the silica‐coated Fe3O4 (Figure 2a–
c), the similar characteristic peaks of Fe3O4 with change in
intensity are observed. This indicates the retention of the
magnetite phases during surface modification of Fe3O4.
However, the change in the peak intensities can be related
to the shielding effect of shell on magnetite core.[37] Based
on the XRD results, the average crystallite size of Fe3O4,
Fe3O4@SiO2 and Fe3O4@SiO2‐Schiff base‐Cu(II) is calcu-
lated to be around 11.7, 13.1 and 13.2 nm, respectively, by
applying the Debye–Scherrer equation.
The TEM image of Fe3O4@SiO2‐Schiff base‐Cu(II)
(Figure 3a) indicates that most of the nanoparticles have an
almost spherical shape. Also, the core–shell structure of the
catalyst is confirmed by revealing the Fe3O4 cores as dark
spots embedded in bright SiO2‐Schiff base‐Cu(II) shells.
The size of each nanoparticle is around 15 nm which is in
accordance with the value obtained from XRD analysis.
The surface morphologies of Fe3O4, Fe3O4@SiO2 and
Fe3O4@SiO2‐Schiff base‐Cu(II) were further studied using
SEM. As seen in Figure 3(b)–(d), these compounds have
spherical morphology and aggregation causes an increase of
the nanoparticle sizes.
TGA curves of Fe3O4@SiO2 and Fe3O4@SiO2‐Schiff
base‐Cu(II) are illustrated in Figure 4. In the TGA curve of
Fe3O4@SiO2 (Figure 4a), the weight loss around 200 °C is
FIGURE
1
FT‐IR spectra of (a) Fe3O4, (b) Fe3O4@SiO2, (c)
Fe3O4@SiO2@APTMS and (d) Fe3O4@SiO2‐Schiff base; and
Fe3O4@SiO2‐Schiff base‐Cu(II) (e) before use and (f) after use as catalyst

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SARKHEIL AND LASHANIZADEGAN
FIGURE 4 TGA curves of (a) Fe3O4@SiO2 and (b) Fe3O4@SiO2‐Schiff
base‐Cu(II)
related to removal of physically adsorbed water molecules
and surface hydroxyl groups on the magnetic surface.[44] As
seen in Figure 4(b), the TGA curve of Fe3O4@SiO2‐Schiff
base‐Cu(II) shows a weight decrease below 200 °C, which
is ascribed to loss of physically adsorbed water molecules
of the catalyst. Also, the weight loss (17.79%, 0.9 mmol g
−1) in the range 250–600 °C can be attributed to destruction
of organic groups. Elemental analysis of Fe3O4@SiO2‐Schiff
base‐Cu(II) was performed and the amount of nitrogen is
obtained as 1.14%. Thus, based on the obtained nitrogen,
the amount of grafted organic groups is estimated to be
0.8 mmol g−1, these data being consistent with the TGA
results.
The copper content of Fe3O4@SiO2‐Schiff base‐Cu(II)
was determined using ICP‐OES. The result shows the amount
of copper is 5.1 wt%. Moreover, the energy‐dispersive X‐ray
analysis of Fe3O4@SiO2‐Schiff base‐Cu(II) (Figure S1 in the
supporting information) indicates the existence of Cu, Si, Fe
and O in the catalyst. These are other data that indicate the
copper complex was successfully immobilized onto
Fe3O4@SiO2.
The magnetization curves of Fe3O4 and Fe3O4@SiO2‐
Schiff base‐Cu(II) are depicted in Figure 5. Both types of
nanoparticles have good magnetic properties and show no
remanence effect (superparamagnetic property). Comparison
of the magnetic saturation value of Fe3O4 (74 emu g−1) with
that of Fe3O4@SiO2‐Schiff base‐Cu(II) (39 emu g−1) shows
a decrease in the catalyst magnetic saturation value. This
observation provides clear evidence of the existence of some
organic matter on the surface of the magnetic core.
Although the magnetic saturation value of Fe3O4@SiO2‐
Schiff base‐Cu(II) is decreased, it can still be efficiently sep-
arated from solution with an external magnet and also can
be rapidly redispersed after removal of the external magnet.
3.2 | Catalytic activity studies
The catalytic performance of Fe3O4@SiO2‐Schiff base‐
Cu(II) for the oxidation of alkenes and alcohols with TBHP
was studied. In search of optimum reaction conditions, the
FIGURE 3 (a) TEM image of Fe3O4@SiO2‐Schiff base‐Cu(II). SEM
images of (b) Fe3O4, (c) Fe3O4@SiO2 and (d) Fe3O4@SiO2‐Schiff
base‐Cu(II)

SARKHEIL AND LASHANIZADEGAN
5 of 8
TABLE 1 Effect of mole ratio of TBHP to styrene on styrene oxidationa
Mole ratio
(TBHP:styrene) Conversion
Selectivity (%)
Benzaldehydec Styrene epoxidec
Entry
(%)b
1
2
3
2
3
4
68
85
95
50
44
63
50
56
37
aReaction conditions: catalyst (0.01 g), styrene (5 mmol), acetonitrile (3 ml), 2 h
under reflux.
bDetermined by GC.
cDetermined by GC–MS.
TABLE 2 Effect of amount of catalyst on styrene oxidationa
Selectivity (%)
Catalyst
FIGURE 5 Magnetization curves of (a) Fe3O4 and (b) Fe3O4@SiO2‐Schiff
base‐Cu(II)
amount
Conversion
Styrene
Entry
(g)
(%)b
Benzaldehydec
epoxidec
Others
influence of various factors, such as reaction time, solvent
and amount of oxidant and catalyst, were investigated. Also,
a series of blank experiments (Table S1) were carried out
and the results indicate that the presence of both catalyst
and oxidant is necessary for an effective catalytic
performance.
1
2
3
0.005
0.01
0.02
91
95
97
59
63
54
41
37
35
—
—
11
aReaction conditions: styrene (5 mmol), acetonitrile (3 ml), 2 h.
bDetermined by GC.
cDetermined by GC–MS.
of various alkenes, namely norbornene, styrene, α‐methyl-
styrene, cyclohexene and cyclooctene, was carried out
under the optimized conditions (Table 3). Based on the
obtained data, the catalyst shows high catalytic performance
in the alkene oxidation reaction.
3.2.1
| Oxidation of alkenes
The catalytic activity of the catalyst in the oxidation of
styrene, as a model substrate, with TBHP as oxidant was
evaluated. This reaction was monitored in various solvents
such as acetonitrile, ethanol, chloroform and dichlorometh-
ane (Figure 6). The results show that the highest styrene con-
version is obtained in acetonitrile within 2 h. The higher
catalytic performance in acetonitrile may be attributed to its
high dielectric constant and boiling point.[48] The effects of
different mole ratios of TBHP to styrene (Table 1) and cata-
lyst amounts (Table 2) were also investigated. According to
the experimental results, the best catalytic performance is
achieved using TBHP and styrene in a mole ratio of 4:1
and in the presence of 0.01 g of the catalyst during 2 h.
To determine the general applicability of Fe3O4@SiO2‐
Schiff base‐Cu(II) in the oxidation reaction, the oxidation
In order to study the reaction mechanism, the oxidation of
styrene was performed in the presence of diphenylamine as
an efficient radical scavenger. It is found that the addition
of diphenylamine inhibits the styrene oxidation and the reac-
tion proceeds via a radical mechanism.[49,50] So, it seems that
decomposition of TBHP to tert‐butoxyl and tert‐butylperoxyl
radicals is catalysed by Cu2+ in one‐electron transfer pro-
cesses.[51] According to the radical mechanism operation,
the behaviour of the alkenes used is depicted in Scheme 2.
The main reason for different product selectivity in the oxida-
tion of cyclic alkenes is due to competition between oxidation
of the double bond and the allylic site. In the case of alkenes
with double bonds attached to benzene ring, the oxidation
may predominantly occur through the double bond because
no allylic hydrogen is present. Styrene oxidation gives sty-
rene epoxide and benzaldehyde. In this reaction, styrene
epoxide is firstly formed and production of benzaldehyde
may be due to the ring opening of styrene epoxide followed
by cleavage of C─C bond[52] (Scheme 2a). Significantly,
the sole product of norbornene oxidation is norbornene epox-
ide. The high selectivity of epoxide reveals that only double
bond undergoes oxidation. Since the allylic site oxidation
through abstraction of α‐hydrogen leads to formation of
unstable bridgehead radical, the oxidation via this route
may not occur[53] (Scheme 2b). In the case of cyclooctene
and cyclohexene, both undergo epoxidation and allylic oxida-
tion concomitantly (Scheme 2c,d). The selectivity towards
FIGURE 6 Effect of time and solvent on styrene oxidation. (Reaction
conditions: styrene (5 mmol), catalyst (0.01 g), TBHP (15 mmol), solvent
(3 ml) and reflux)

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SARKHEIL AND LASHANIZADEGAN
TABLE 3 Oxidation of alkenes in the presence of Fe3O4@SiO2‐Schiff base‐Cu(II)a
Entry
Alkene
Conversion (%)b
Major productc (selectivity, %)
TONd/TOFe (h−1
)
1
2
3
4
5
Norbornene
Styrene
82
95
Norbornene epoxide (100)
Benzaldehydef (63)
Acetophenoneg (54)
2‐Cyclohexene‐1‐oneh (65)
Cyclooctene epoxidei (77)
494/247
572/286
602/301
386/193
392/196
α‐Methylstyrene
Cyclohexene
Cyclooctene
100
64
65
aReaction conditions: catalyst (0.01 g), alkene (5 mmol), TBHP (20 mmol), acetonitrile (3 ml), 2 h under reflux.
bDetermined by GC.
cDetermined by GC–MS
dTON: moles of product converted per mole of metal in the catalyst.
eTOF: moles of product converted per mole of metal in the catalyst per unit time.
fBenzaldehyde (37%) was also identified as by‐product.
g2‐Phenyl‐1,2‐propanediol (36%) was also identified as by‐product.
hCyclohexene epoxide (26%) was also identified as by‐product.
i2‐Cyclooctene‐1‐one (23%) was also identified as by‐product.
FIGURE 7 Reusability of Fe3O4@SiO2‐Schiff base‐Cu(II) for oxidation of
styrene under optimized conditions
from 95 to 85% after five runs. Also, ICP‐OES analysis
shows that the copper content of used catalyst (3.9 wt%) is
less than that of fresh catalyst (5.1 wt%). This is may be
attributed to the release of surface‐adsorbed copper complex.
So, the partial decrease in the activity may be due to some
leaching and chiefly inevitable loss of the catalyst during
the catalyst collection process. Based on the obtained results,
the catalyst has good reusability and stability in the optimized
reaction conditions. Also, the similarity of the FT‐IR spectra
(Figure 1) and XRD patterns (Figure 2) of Fe3O4@SiO2‐
Schiff base‐Cu(II) before and after use as a catalyst confirms
the stability of the catalyst.
SCHEME
2
Proposed mechanism for oxidation of (a) styrene, (b)
norbornene, (c) cyclooctene and (d) cyclohexene
epoxide in cyclooctene oxidation is higher than in cyclohex-
ene oxidation. Such behaviour may be attributed to
cyclooctene chair conformation in which the double bond lies
in a different plane from all other carbons,[54] whereas cyclo-
hexene has half‐chair conformation and its double bond lies
in the plane of allylic hydrogens.[55] Thus, less reactivity is
observed for allylic hydrogens of cyclooctene in comparison
to those of cyclohexene.
The reusability of the catalyst in the oxidation of styrene
was investigated for five consecutive runs (Figure 7). After
each run, the catalyst was separated by magnetic decantation,
washed with acetonitrile and dried. Then it was reused for
subsequent reactions under optimized conditions. As seen
in Figure 7, the conversion of styrene oxidation decreases
3.2.2
| Oxidation of alcohols
In order to evaluate the catalytic performance of
Fe3O4@SiO2‐Schiff base‐Cu(II) in the oxidation of alcohols,
the oxidation of benzyl alcohol as representative substrate
with TBHP as oxidant was investigated. In this study, the
experimental results show that the best catalytic performance
of this system is achieved under the following conditions: 6 h
is estimated as reaction time (Figure S2), TBHP and benzyl
alcohol in a mole ratio of 4:1 (Table S2) and amount of cata-
lyst is determined as 0.01 g (Table S3). The influence of

SARKHEIL AND LASHANIZADEGAN
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TABLE 4 Oxidation of alcohols in the presence of Fe3O4@SiO2‐Schiff base‐Cu(II)a
Entry
Alcohol
Conversion (%)b
Major productc (selectivity, %)
TON/TOF (h−1
)
1
2
3
4
5
Benzyl alcohol
100
86
Benzoic acid (87)
602/100
518/86
380/63
602/100
283/47
3‐Methoxybenzyl alcohol
3‐Chlorobenzyl alcohol
Benzhydrol
3‐Methoxybenzoic acid (85)
3‐Chlorobenzoic acid (84)
Benzophenone (100)
Butanoic acid (100)
63
100
47
n‐Butanol
aReaction conditions: catalyst (0.01 g), alcohol (5 mmol), TBHP (20 mmol), acetonitrile (3 ml), 6 h under reflux.
bDetermined by GC.
cDetermined by GC–MS.
[2] M. P. Doyle, D. C. Forbes, Chem. Rev. 1998, 98, 911.
various solvents such as acetonitrile, methanol, ethyl acetate
and chloroform on the benzyl alcohol oxidation was also
studied. The results are listed in Table S4 and the best conver-
sion and selectivity are obtained in acetonitrile.
[3] H. Hosseini‐Monfared, E. Pousaneh, S. Sadighian, S. Weng Ng, E. R. T.
Tiekink, Z. Anorg. Allg. Chem. 2013, 639, 435.
[4] P. Gogoi, M. Kalita, T. Bhattacharjee, P. Barman, Tetrahedron Lett. 2014, 55,
1028.
The results of the oxidation of various alcohols, namely
benzyl alcohol, 3‐methoxybenzyl alcohol, 3‐chlorobenzyl
alcohol, benzhydrol and n‐butanol, under the optimized con-
ditions are presented in Table 4. The major products for oxi-
dation of primary and secondary alcohols are the
corresponding carboxylic acid and ketone, respectively. Also,
the least reactivity is shown by the aliphatic alcohol, and the
presence of electron‐withdrawing and electron‐donating sub-
stituents on the benzene ring may affect the reactivity of the
aromatic alcohols.[41]
[5] A. Ghorbani‐Choghamarani, B. Ghasemi, Z. Safari, G. Azadi, Catal.
Commun. 2015, 60, 70.
[6] S. Menati, H. Amiri‐Rudbari, B. Askari, M. Riahi‐Farsani, F. Jalilian, G.
Dini, C. R. Chim. 2016, 19, 347.
[7] L. Chen, B.‐D. Li, Q.‐X. Xu, D.‐B. Liu, Chin. Chem. Lett. 2013, 24, 849.
[8] S. Shit, D. Saha, D. Saha, T. N. Guru Row, C. Rizzoli, Inorg. Chim. Acta
2014, 415, 103.
[9] G. Romanowski, J. Kira, M. Wera, J. Mol. Catal. A 2014, 381, 148.
[10] G. Romanowski, J. Kira, Polyhedron 2013, 53, 172.
[11] G. Romanowski, J. Kira, Polyhedron 2016, 117, 352.
[12] J. Zhang, P. Jiang, Y. Shen, W. Zhang, X. Li, Micropor. Mesopor. Mater.
2015, 206, 161.
[13] O. Erdem, B. Guzel, Inorg. Chim. Acta 2014, 418, 153.
4
| CONCLUSIONS
[14] A. Mavrogiorgou, M. Papastergiou, Y. Deligiannakis, M. Louloudi, J. Mol.
Catal. A 2014, 393, 8.
A new magnetic catalyst (Fe3O4@SiO2‐Schiff base‐Cu(II))
was synthesized by reacting copper(II) acetate with silica‐
coated magnetite nanoparticles functionalized with Schiff
base groups. The catalytic activity of this catalyst
was evaluated for the oxidation of various alkenes
(styrene, α‐methylstyrene, cyclooctene, cyclohexene and
norbornene) and alcohols (benzyl alcohol, 3‐methoxybenzyl
alcohol, 3‐chlorobenzyl alcohol, benzhydrol and n‐butanol)
with TBHP as oxidant. Based on the optimized results, the
best catalytic performances were obtained in acetonitrile
using 0.01 g of catalyst. It was found that the catalyst success-
fully catalysed the epoxidation of norbornrne with 82% con-
version and 100% selectivity during 2 h. Also, catalytic
oxidation of benzyl alcohol gave 100% conversion with
87% selectivity for benzoic acid within 6 h. Some advantages
including rather high yield and selectivity, easy separation
and recyclability demonstrate that Fe3O4@SiO2‐Schiff base‐
Cu(II) is an efficient heterogeneous catalyst.
[15] S. Bhunia, S. Koner, Polyhedron 2011, 30, 1857.
[16] F. Heshmatpour, S. Rayati, M. Afghan‐Hajiabbas, B. Neumüller, Z. Anorg.
Allg. Chem. 2011, 637, 1224.
[17] G. Willingh, H. S. Abbo, S. J. J. Titinchi, Catal. Today 2014, 227, 96.
[18] D. R. Godhani, H. D. Nakum, D. K. Parmer, J. P. Mehta, N. C. Desai, J. Mol.
Catal. A 2016, 415, 37.
[19] K. C. Gupta, A. K. Sutar, C.‐C. Lin, Coord. Chem. Rev. 2009, 253, 1926.
[20] R. Antony, S. T. D. Manickam, K. Saravanan, K. Karuppasamy, S.
Balakumar, J. Mol. Struct. 2013, 1050, 53.
[21] A. K. Sutar, T. Maharana, Y. Das, P. Rath, J. Chem. Sci. 2014, 126, 1695.
[22] A. Mavrogiorgou, M. Baikousi, V. Costas, E. Mouzourakis, Y.
Deligiannakis, M. A. Karakassides, M. Louloudi, J. Mol. Catal. A 2016,
413, 40.
[23] M. J. Taghizadeh, H. Karimi, H. Sadeghi‐Abandansari, Res. Chem.
Intermed. 2016, 42, 8201.
[24] Z. Li, S. Wu, H. Ding, D. Zheng, J. Hu, X. Wang, Q. Huo, J. Guan, Q. Kan,
New J. Chem. 2013, 37, 1561.
[25] M. B. Gawande, P. S. Brancoa, R. S. Varma, Chem. Soc. Rev. 2013, 42,
3371.
[26] M. Mohammadikish, M. Masteri‐Farahani, S. Mahdavi, J. Magn. Magn.
Mater. 2014, 354, 317.
ACKNOWLEDGEMENTS
[27] X. Li, Y. Fang, X. Zhou, J. Ma, R. Li, Mater. Chem. Phys. 2015, 156, 9.
[28] X. Cai, H. Wang, Q. Zhang, J. Tong, Z. Lei, J. Mol. Catal. A 2014, 384, 217.
Financial support from Alzahra University is acknowledged.
[29] M. B. Gawande, Y. Monga, R. Zboril, R. K. Sharma, Coord. Chem. Rev.
2015, 288, 118.
REFERENCES
[1] R. G. Sheldon, B. J. Kochi, Metal‐Catalyzed Oxidations of Organic Com-
pounds, Academic Press, New York 1981.
[30] B. Fredrich, W. Gerhartz, Ullmann's Encyclopedia of Industrial Chemistry,
Vol. A3, Wiley‐VCH, Weinheim 1985.

8 of 8
SARKHEIL AND LASHANIZADEGAN
[31] M. B. Smith, J. March, Advanced Organic Chemistry: Reactions, Mecha-
nisms and Structure, Wiley‐Interscience, New York 2001.
[48] J. Rydberg, C. Mussikas, G. R. Choppin, Principles and Practices of Solvent
Extraction, Marcel Dekker, New York 1992.
[32] R. C. Larock, Comprehensive Organic Transformations: A Guide to Func-
tional Group Preparations, Wiley‐VCH, New York 1999.
[49] L. M. Slaughter, J. P. Collman, T. A. Eberspacher, J. I. Brauman, Inorg.
Chem. 2004, 43, 5198.
[33] R. A. Sheldon, H. Van Bekkum, Fine Chemicals through Heterogeneous
Catalysis, Wiley‐VCH, New York 2001.
[50] F. Farzaneh, J. Taghavi, R. Malakooti, M. Ghandi, J. Mol. Catal. A 2006,
244, 252.
[34] A. Bezaatpour, S. Khatami, M. Amiri, RSC Adv. 2016, 6, 27452.
[51] U. Junghans, C. Suttkus, J. Lincke, D. Lässig, H. Krauyscheid, R. Gläser,
Micropor. Mesopor. Mater. 2015, 216, 151.
[35] M. Afshari, M. Gorjizadeh, S. Nazari, M. Naseh, J. Magn. Magn. Mater.
2014, 363, 13.
[52] R. Ghosh, Y.‐C. Son, V. D. Makwana, S. L. Suib, J. Catal. 2004, 224, 288.
[53] J. March, Advanced Organic Chemistry, John Wiley, New York 1985.
[54] U. Neuenschwander, I. Hermans, J. Org. Chem. 2011, 76, 10236.
[36] M. Zare, Z. Moradi‐Shoeili, M. Bagherzadeh, S. Akbayrak, S. Ozkar, New J.
Chem. 2016, 40, 1580.
[37] M. Ghorbanloo, A. Mohamadi, M. Amini, J. Tao, Transition Met. Chem.
2015, 40, 321.
[55] E. L. Eliel, S. H. Wilen, Stereochemistry of Organic Compounds, John
Wiley, New York 1994.
[38] J. Sun, G. Yu, L. Liu, Z. Li, Q. Kan, Q. Huo, J. Guan, Catal. Sci. Technol.
2014, 4, 1246.
SUPPORTING INFORMATION
[39] A. R. Judy‐Azar, E. Safaei, S. Mohebbi, Mater. Res. Bull. 2015, 70, 753.
[40] A. R. Judy‐Azar, S. Mohebbi, J. Mol. Catal. A 2015, 397, 158.
Additional Supporting Information may be found online in
the supporting information tab for this article.
[41] Q. Zhou, Z. Wan, X. Yuan, J. Luo, Appl. Organometal. Chem. 2016, 30, 215.
[42] P. B. Bhat, R. Rajarao, V. Sahajwall, B. R. Bhat, J. Mol. Catal. A 2015, 409,
42.
How to cite this article: Sarkheil M, Lashanizadegan
M. Copper(II) Schiff base complex immobilized on
superparamagnetic Fe3O4@SiO2 as a magnetically
separable nanocatalyst for oxidation of alkenes and
alcohols. Appl Organometal Chem. 2017;e3726.
https://doi.org/10.1002/aoc.3726
[43] X. Liu, Z. Ma, J. Xing, H. Liu, J. Magn. Magn. Mater. 2004, 270, 1.
[44] M. Tajbakhsh, M. Farhang, R. Hosseinzadeh, Y. Sarrafi, RSC Adv. 2014, 4,
23116.
[45] H. Cao, J. He, L. Deng, X. Gao, Appl. Surf. Sci. 2009, 255, 7974.
[46] M. Yamaura, R. L. Camilo, L. C. Sampaio, M. A. Macdo, N. Nakamura,
H. E. Toma, J. Magn. Magn. Mater. 2004, 210, 217.
[47] M. Esmaeilpour, A. R. Sardarian, J. Javidi, Appl. Catal. A 2012, 445–446,
359.