Olefins oxidation with molecular O2 in the presence of chiral Mn (III) salen complex supported on magnetic CoFe2O4@SiO2@CPTMS

Article abstract of DOI:10.1002/aoc.4937

In the present study, CoFe₂O₄@SiO₂@CPTMS nanocomposite was synthesized and the homogeneous chiral Mn-salen complex was anchored covalently onto the surface of CoFe₂O₄@SiO₂@CPTMS nanocomposite. The heterogeneous Mn-salen magnetic nanocatalyst (CoFe₂O₄@SiO₂@CPTMS@ chiral Mn (III) Complex) was characterized by different techniques including transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), vibrating sample magnetometer (VSM), scanning electron microscopy (SEM), powder X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Then, the aerobic enantioselective oxidation of olefins to the corresponding epoxide was investigated in the presence of magnetic chiral CoFe₂O₄@SiO₂@Mn (III) complex at ambient conditions within 90?min. The results showed the corresponding products were synthesized with excellent yields and selectivity. In addition, the heterogeneous CoFe₂O₄@SiO₂@ CPTMS@ chiral Mn (III) complex has benefits such as high selectivity and comparable catalytic reactivity with its homogeneous analog as well as mild reaction condition, facile recovery, and recycling of the heterogeneous catalyst.

Full text of DOI:10.1002/aoc.4937

Received: 27 November 2018
DOI: 10.1002/aoc.4937
Revised: 16 February 2019
Accepted: 7 March 2019
F U L L P A P E R
Olefins oxidation with molecular O2 in the presence of
chiral Mn (III) salen complex supported on magnetic
CoFe2O4@SiO2@CPTMS
Kaveh Hemmat
| Mohammad A. Nasseri
| Ali Allahresani
Department of Chemistry, College of
Sciences, University of Birjand, Birjand
97175‐615, Iran
In the present study, CoFe2O4@SiO2@CPTMS nanocomposite was synthesized
and the homogeneous chiral Mn‐salen complex was anchored covalently onto
the surface of CoFe2O4@SiO2@CPTMS nanocomposite. The heterogeneous
Mn‐salen magnetic nanocatalyst (CoFe2O4@SiO2@CPTMS@ chiral Mn (III)
Complex) was characterized by different techniques including transmission
electron microscopy (TEM), Fourier transform infrared (FT‐IR), vibrating sam-
ple magnetometer (VSM), scanning electron microscopy (SEM), powder X‐ray
diffraction (XRD) and thermogravimetric analysis (TGA). Then, the aerobic
enantioselective oxidation of olefins to the corresponding epoxide was investi-
gated in the presence of magnetic chiral CoFe2O4@SiO2@Mn (III) complex at
ambient conditions within 90 min. The results showed the corresponding prod-
ucts were synthesized with excellent yields and selectivity. In addition, the het-
erogeneous CoFe2O4@SiO2@ CPTMS@ chiral Mn (III) complex has benefits
such as high selectivity and comparable catalytic reactivity with its homoge-
neous analog as well as mild reaction condition, facile recovery, and recycling
of the heterogeneous catalyst.
Correspondence
Mohammad A. Nasseri, Department of
Chemistry, College of Sciences, University
of Birjand, Birjand 97175‐615, Iran.
Email: manaseri@birjand.ac.ir
KEYWORDS
aerobic oxidation, chiral Mn (III) salen complex, CoFe2O4@SiO2@CPTMS, olefins
1 | INTRODUCTION
catalytic epoxidation are carried out with toxic oxidants
at high temperature and extremely long reaction time.[8–
From green chemistry point of view, selective oxidation
reaction with low toxic oxidants is of high significance.
Recently, usage of nontoxic and green oxidants including
H2O2 and O2 in catalytic oxidation system has become very
popular.[1–3] Molecular oxygen particularly attracted great
attention due to its important advantages including low
cost, fast kinetics, and high active oxygen content, with
no byproducts.[4–6] However, molecular oxygen needs to
be activated and the oxidation reaction needs particular
reducing agents to activate the molecular oxygen by trans-
ferring electron and proton steps.[7] Recently, selective oxi-
dation of terminal alkenes is investigated. Usually, the
10] Therefore, proposing a strategy to conduct the reactions
using a nontoxic oxidant and short reaction in room tem-
perature which also saves energy is desirable. On the other
hand, metal salen complexes and especially Mn (III) salen
complexes could be used for the asymmetric epoxidation of
olefins.[11–13] Homogeneous metal salen complexes have
drawbacks such as tedious workup and recycling of the cat-
alysts, contamination of the product. Also, formation of
dimeric peroxo and m‐oxo species results in deactivation
of homogeneous catalysts.[14]
To resolve these drawbacks, homogeneous metal salen
complexes are converted to heterogeneous counterpart.
Appl Organometal Chem. 2019;e4937.
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© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4937

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HEMMAT ET AL.
Several insoluble solid supports such as zeolites, polymer
supports, mesoporous materials, clays, organic polymer‐
inorganic hybrid materials, SBA‐15, MCM‐41 and acti-
vated silica were employed for immobilizing of homoge-
neous metal‐salen complexes.[15–21]
30 m × 0.25 mm ×0.25 mm), were used for conversion
and yield of the products. For determination of
enantioselectivity, chiral GC column (HP 19091G‐B213,
30 m × 0.25 m × 0.25 mm) was used.
We have developed many catalytic systems using
metal‐salen complexes for various oxidative chemical
transformations.[13,22,23] To complete the previous study
on the metal‐salen complexes, chiral Mn (III) complex
was synthesized and immobilized on the surface of mag-
netic CoFe2O4@SiO2@CPTMS nanocomposite, in this
study, which has good stability and could be a good can-
didate for immobilizing of metal‐salen complexes. The
corresponding heterogeneous catalyst (CoFe2O4@
SiO2@ CPTMS@ chiral Mn (III) Complex) was applied
for aerobic epoxidation of olefins with molecular oxygen
at ambient temperature (Scheme 1).
2.2 | Catalyst preparation
2.2.1 | Synthesis of CoFe2O4 nanoparticles
In a balloon containing 100 ml of distilled water,
0.002 mol of Fe (NO3)3.9H2O and 0.001 mol Co (NO3)2.
6H2O are dissolved. Then, 1 M NaOH solution (20 ml)
was added drop by drop to the previous solution and son-
icated (60 W, 30 min). The mixture was then heated for
2 hr at 80 °C. CoFe2O4 nanoparticles (black precipitate)
was separated with external magnet and rinsed with dis-
tilled water, ethanol and dried in an oven at 80 °C for
8 h.[24]
2 | EXPERIMENTAL SECTION
2.2.2 | Synthesis of CoFe2O4@SiO2
2.1 | Materials and characterization
An appropriate amount of CoFe2O4 nanoparticles (0.04 g)
was dispersed in EtOH/H2O (4:1, 100 ml) for 30 min.
Then, tetraethylorthosilicate (1 ml) was added drop wise
to the mixture followed by addition of ammonia solution
(30%, 5 ml). The mixture was stirred for 20 hr at room
temperature. The achieved CoFe2O4@SiO2 nanocompos-
ite were separated by external magnet. Then, they were
washed with distilled water and dried under vacuum.[25]
techniques
The pure chemical materials were purchased from Merck.
The scanning electron microscope (SEM) (Mitra
3TEScan‐XMU) was used for recording surface morphol-
ogy and the elemental composition of the complex.
TEM image were recorded by transmission electron
microscopy (Philips EM208). TGA was also recorded
using a Perkin‐Elmer Diamond TG/DTA thermal ana-
lyzer in an argon flow rate (100 ml/min) with increasing
in the heating rate of 10 °C min−1. The X‐ray diffraction
of nanoparticles were recorded by modified GNR explorer
diffractometer. IR spectra were obtained by a Perkin
Elmer 781 with KBr pellets. Gas chromatography experi-
ments (Shimadzu GC‐17A) equipped with a FID (flame
ionization detector) and a capillary column (CBP‐1,
2.2.3 | Synthesis of
CoFe2O4@SiO2@CPTMS
A mixture of 1 g of CoFe2O4@SiO2 in 70 ml of dry toluene
was
dispersed
for
20
min.
Then,
3‐
chloropropyltrimethoxysilane (CPTMS) (3 ml of 3‐
chloropropyltrimethoxysilane in 20 ml dry toluene) was
added drop wise to the mixture. The mixture was stirred
at reflux continuous for 24 hr under nitrogen atmosphere.
The mixture then cooled and the magnetic nanoparticles
(black powder) was recovered by external magnet,
washed with toluene and EtOH, respectively. The solid
powder (CoFe2O4@SiO2@CPTMS) was dried in an oven
at 70 °C for 6 hr.[26]
2.2.4 | Synthesis of chiral Mn (III) salen
complex immobilized on
CoF2O4@SiO2@CPTMS
Chiral Mn (III) salen complex was synthesized as
reported in the literature.[27] The homogeneous chiral
SCHEME
epoxidation of olefins
1
The schematic illustration of asymmetric

HEMMAT ET AL.
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Mn (III) salen complex was chemically grafted onto the
surface of CoFe2O4@SiO2@CPTMS (Scheme 2).
3 | RESULTS AND DISCUSSION
Briefly, in 100 ml of dry toluene,
2
g
of
3.1 | Preparation and characterization of
CoFe2O4@SiO2@CPTMS was sonicated for 30 min. Then,
homogeneous Mn (III) salen complex (0.6 g) was added.
The mixture was stirred under reflux condition at inert
atmosphere for 24 hr. After the reaction completed, the
corresponding Mn (III) salen complex was washed with
dry toluene and EtOH, respectively. To ensure that the
homogeneous catalyst was removed, on a Soxhlet extrac-
tor, the mixture was repeatedly extracted with methanol
and dichloromethane. This was done until the washing
becomes colorless. The corresponding nanocatalyst was
dried in a vacuum oven for 6 hr at 70 °C.[13] Finally, the
characterization of the heterogeneous magnetic chiral
Mn (III) salen complex was done by different techniques
including SEM–EDX, TEM, ICP, FT‐IR, VSM and TGA.
magnetic chiral Mn (III) salen
CoFe2O4, CoFe2O4@SiO2 and CoFe2O4@SiO2@CPTMS
were synthesized according to the literature.[24–26] Then,
homogeneous chiral Mn (III) salen complex was grafted
onto the surface of CoFe2O4@SiO2@CPTMS. The mag-
netic characterization of chiral Mn (III) salen was done
using different techniques.
3.1.1 | TEM study
Figure 1A, belongs to the TEM image of CoFe2O4 which
shows the magnetic nanoparticles with average size of
17.49 nm. After the immobilization of homogeneous chi-
ral
Mn
(III)
salen
complex
onto
the
CoFe2O4@SiO2@CPTMS, the average size of the
nanocatalyst was 26.57 nm (Figure 1 C).
2.3 | Catalyst activity
2.3.1 | General procedure for the oxida-
tion reaction
3.1.2 | X‐ray diffraction study
X‐ray diffraction (XRD) patterns of CoFe2O4 and
CoFe2O4@SiO2 in the 2θ range between 10o and 80o are
shown in Figure 2. The diffraction peaks of all samples
at 18.14o, 30.27o, 35.76o, 43.47o, 53.91o, 57.17o and 63.71o
could be indexed to the (111), (220), (311), (400), (422),
(511) and (440) planes of the inverse spinel CoFe2O4,
respectively.[28] The XRD pattern of the CoFe2O4@SiO2
spheres has a broaden peak in the 2θ range of 20‐30o
which results from the amorphous silica.
Briefly, catalyst (0.02 mmol) was dispersed in CH3CN
(1 ml) for 30 min and then 0.95 mmol isobutyraldehyde
(IBA) and olefin (0.095 mmol) were added. The mixture
was stirred for 90 min at ambient temperature while
purged with oxygen (5 mL/min). The progress of the reac-
tion was monitored by TLC. Finally, the characterization
of the conversion, yield and enantioselectivity of the
products were done by GC.[27]
Using the Scherrer equation, Dc = Kλ/β cosθ, the crys-
tallite size was also measured. Where K is 0.9, b stands for
the width of the observed diffraction peak at its half max-
imum intensity (FWHM), and l stands for the X‐ray
wavelength (Cu Ka radiation, equals to 0.154 nm). The
estimated crystallite size of CoFe2O4@SiO2 is 12.8 nm.
3.1.3 | FT‐IR study
Figure 3 shows the FT‐IR spectra of CoFe2O4 (a),
CoFe2O4@SiO2 (b), CoFe2O4@SiO2@CPTMS (c), chiral
ligand (d), Mn (III) salen complex (e) and
CoFe2O4@SiO2@CPTMS@Mn (III) complex (f). The
broad peak at around 3396 cm−1 in all samples is associ-
ated with the stretching vibrations of O‐H bond. The peak
at 605 cm−1 confirmed the presence of Co‐O and Fe‐O
bonds in CoFe2O4 (Figure 3a) which shifts to 592 cm−1
after coating with silica (Figure 3b).[25] The bands at
1099 cm−1 is assigned to the stretching mode of the Si‐
SCHEME 2 The schematic immobilization of chiral Mn (III)
salen complex onto CoFe2O4@SiO2@CPTMS

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HEMMAT ET AL.
FIGURE 1 TEM image of CoFe2O4 (A) and Chiral Mn (III) salen (C) – Histogram of CoFe2O4 (B) and Chiral Mn (III) salen (D)
Figure 3d shows the IR spectra of the ligand. As can be
seen, C=N group stretching vibration is shown by a
strong band at 1626 cm−1. Mn‐metal coordination
through C=N functional groups was confirmed because
the band shifts to lower position (1580 cm−1) in homoge-
neous chiral Mn (III) complex (Figure 3e). Finally, homo-
geneous chiral Mn (III) complex grafting on the
CoFe2O4@SiO2@CPTMS is presented by the new bands
of vibration (1584 and 1231 cm−1) in Figure 3f.
3.1.4 | Vibrating sample magnetometer
(VSM) study
At 300 K, an investigation on the magnetic properties of
CoFe2O4, CoFe2O4@SiO2 and CoFe2O4@SiO2@ chiral
Mn (III) complex was carried out using the vibration
sample magnetometer (VSM). As can be shown, all nano-
particles showed superparamagnetism without hysteresis
phenomenon at 300 K (Figure 4). In addition, the satura-
tion magnetization values of 39.124, 30.387 and
27.348 emu/g was observed for CoFe2O4 (a),
FIGURE 2 XRD patterns of CoFe2O4 (a) and CoFe2O4@SiO2 (b)
O‐Si bond in silica and the bond at 467 cm−1 is belonging
to Si‐O‐Si bond (Fig. b).[29,30] By modification of CPTMS
onto the CoFe2O4@SiO2, the new peaks at 2850 and
2924 cm−1 is observed which are assigned to the
stretching vibration of C‐H alkane (Figure 3c).[31]
CoFe2O4@SiO2 (b) and CoFe2O4@SiO2@ chiral Mn (III)
salen complex catalyst (c), respectively. Furthermore,
the decrease in the saturation magnetization values of
CoFe2O4@SiO2 and chiral CoFe2O4@SiO2@ Mn (III)
salen complex catalyst confirmed the immobilization of

HEMMAT ET AL.
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FIGURE 3 FT‐IR spectra of CoFe2O4 (a) CoFe2O4@SiO2(b). CoFe2O4@SiO2@CPTMS (c) Chiral ligand(d) Mn (III) salen complex(e)
CoFe2O4@SiO2@CPTMS@Mn (III) salen complex (f)
FIGURE 5 TGA thermograms of (a) CoFe2O4@SiO2 and (b)
CoFe2O4@SiO2@CPTMS@chiral Mn (III) salen complex
FIGURE
4
Magnetization curves of (a) CoFe2O4 (b)
CoFe2O4@SiO2 (c) CoFe2O4@SiO2@CPTMS@chiral Mn (III) salen
complex at 300 K
3.1.6 | SEM–EDX study
The SEM image and elemental analysis of CoFe2O4@SiO2
and chiral CoFe2O4@SiO2@ Mn (III) salen complex were
characterized by SEM/EDX (Figure 6). The SEM images
of CoFe2O4@SiO2 and chiral CoFe2O4@SiO2@ Mn (III)
salen complex indicated the formation of the desired
complex (Figure 6 A ‐ D).
SiO2 and chiral Mn (III) salen complex on CoFe2O4,
respectively.
The distribution of elements in CoFe2O4@SiO2 and
chiral CoFe2O4@SiO2@ Mn (III) salen complex was stud-
ied by EDX analysis (Figure 6 B & D). As can be seen, the
percentage of Fe, Co, Si and O are 31.88, 14.76, 7.76 and
45.59, respectively. The presence of Si atom confirm the
successful synthesis of CoFe2O4@SiO2 (Figure 6 B). Fur-
thermore, the presence of Mn (3.44%) and C (22.75%) in
Figure 6 D shows the successful synthesis of chiral
CoFe2O4@SiO2@ Mn (III) salen complex. According to
ICP‐AES analysis, the Mn loading was found to be
3.1.5 | Thermal gravimetric analysis
(TGA)
In Figure 5, from 90 to 220 °C, a weight‐loss is shown by
TGA curve of CoFe2O4@SiO2. This is attributed to the
loss of –OH groups as well as the adsorb water. From
320 to 480 °C, another weight loss is observed. This could
be assigned to the further decomposition of the materials
(Figure 5a).[22]
0.54 mmol.g−1
.

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HEMMAT ET AL.
FIGURE 6 SEM‐EDS of CoFe2O4@SiO2 (A/B) CoFe2O4@SiO2@CPTMS@chiral Mn (III) salen complex (C/D)
FIGURE 7 (a) Adsorption/desorption isotherms; (b) BET and (c) BJH plot of CoFe2O4@SiO2@chiral Mn (III) salen complex

HEMMAT ET AL.
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one is the linear regression of multi‐point measurements.
The r which is the correlation coefficient of the linear
regression is approximately 0.999. Thus, the r2 is 0.999
which would confirm the data of BET analysis.
3.1.7 | BET study
For chiral CoFe2O4@SiO2@ Mn (III) salen complex, BET
analysis indicates that the available surface area is
48.46 m2.g−1. The average pore diameter according to
BJH analysis is 1.29 nm which indicates the micro‐
porosity of compound. The pore volume of chiral
CoFe2O4@SiO2@ Mn (III) salen complex according to
N2 adsorption/desorption is 11.134 cm3.g−1. There are
both straight and curved lines in Figures 7b. The straight
3.2 | Oxidation of olefins by the
heterogeneous catalyst
To investigate the catalytic efficiency of chiral
CoFe2O4@SiO2@ Mn (III) complex, the oxidation of
FIGURE 8 The catalytic system for the
epoxidation of styrene in CH3CN
catalyzed by
CoFe2O4@SiO2@CPTMS@chiral Mn (III)
salen complex. (Conditions of reaction:
chiral Mn (III) salen complex: IBA molar
ratio: styrene. is X: 450: 45 and O2
(balloon), reaction time: 90 min)
FIGURE 9 The solvents effect on the
styrene aerobic oxidation which is
catalyzed by
CoFe2O4@SiO2@CPTMS@chiral Mn (III)
salen complex at room temperature.
Conditions of the reaction: reaction time:
90 min, solvent: 1 ml, styrene: chiral Mn
(III) salen complex: isobutyraldehyde
molar ratio is 45: 1: 450 and O2 (balloon)
FIGURE 10 The effect of molar ratio of
the isobutyraldehyde/substrate on the
styrene aerobic oxidation which is
catalyzed by
CoFe2O4@SiO2@CPTMS@chiral Mn (III)
salen complex at room temperature.
Conditions of the reaction: styrene: chiral
Mn (III) complex: isobutyraldehyde is 45:
1: X and O2 (balloon), reaction time:
90 min; solvent: 1 ml, selectivities and
conversions were determined by GC

8 of 12
HEMMAT ET AL.
FIGURE 11 The effect of the time for
the styrene epoxidation in CH3CN which
is catalyzed by
CoFe2O4@SiO2@CPTMS@chiral Mn (III)
salen complex. (Conditions of the
reaction: IBA molar ratio: styrene: time is
450: 45: X and O2 (balloon), 0.03 g cat.)
FIGURE 12 The effect of the axial
ligand for the epoxidation of styrene in
CH3CN catalyzed by
CoFe2O4@SiO2@CPTMS@chiral Mn (III)
salen complex. (Conditions of the
reaction: IBA molar ratio: styrene: axial
ligand. is 450: 45: X and O2 (balloon),
reaction time: 90 min)
TABLE 1 The effect of the amount of molecular oxygen on the progress of the reaction
Entry
O2 (mL/min)
Yield (%)
ee (%)
1
2
3
4
1
3
5
7
32
75
17.87
21.32
24.84
18.62
100
100
Chiral Mn (III) salen complex: IBA: alkene molar ratio is 1:225: 45, reaction time: 90 min, solvent: 1 ml of CH3CN. Selectivity and conversions were determined
by GC.
TABLE 2 The effect of different oxidants on the asymmetric epoxidation of styrene catalyzed by chiral CoFe2O4@SiO2@ Mn (III) complex
Entry
Oxidant
Yield (%)
ee (%)
1
2
3
4
5
6
7
H2O2
18
21
18
32
45
61
97
25
30
32
24
23
26
35
PhIO
PhI (OAc)2
UHP
NaIO4
Oxone
m‐CPBA
Reaction conditions: styrene (1 mmol), oxidant (2 mmol), and chiral Mn (III) salen complex 25 °C. and duration 90 min

HEMMAT ET AL.
9 of 12
styrene with O2 and isobutyraldehyde in the presence of
the catalyst was studied at room temperature. In the
absence of the catalyst, the oxidation reaction did not pro-
ceed (blank experimental). Then, the effect of different
parameters which are affected on the conversion and yield
as well as the enantioselectivity (ee) of the products were
optimized to achieve suitable reaction conditions with
highest conversion, yields and ee. Therefore, the effects
of the solvent, the amount of the catalyst, time of the reac-
tion, the amount of molecular oxygen and the amount of
isobutyraldehyde (IBA, as a reducing agent) were studied
in detail. The model reaction was carried out using differ-
ent amounts of the heterogeneous magnetic Mn (III) cata-
lyst. The results suggest that 1.62 mol% catalyst (based on
Mn element) was the optimum concentration of the cata-
lyst (Figure 8). The optimum ee of the reaction was 24.83%.
The oxidation reaction of styrene with O2 was studied
in different solvents and the highest conversion (100%)
was obtained in acetonitrile after 90 min at room temper-
ature (Figure 9) which resulted that acetonitrile was cho-
sen as the best solvent.
The isobutyraldehyde is necessary to proceeded oxida-
tion reaction. This could be concluded from the catalyst
and the results (Figure 10). In the presence of different
amount of isobutyraldehyde, the model reaction was car-
ried out with molecular oxygen. Also, the optimum
amount of IBA as well as the ratio of IBA to substrate
was studied and the results showed that the ratio of IBA
to substrate 5:1 is needed for optimized reaction condi-
tion (Figure 10).
The reaction was carried out at various time intervals
and the best yields were observed in 90 min (Figure 11).
Due to the effect of additives in the asymmetric epox-
idation of olefins, various additives including NMO,
PNO and NH4OAc were applied in the epoxidation of
styrene in CH3CN/O2 system (Figure 12). As the results
TABLE 3 Various olefins oxidation with O2/isobutyraldehyde as the oxygen donor at room temperature in the presence of chiral Mn(III)
salen complex in CH3CN
Entry
Alkene
Conversion (%)
Selectivity to epoxide (%)
e.e (%)
TON
TOF (h‐1)
1
100
100
24.84
61.73
41.15
2
3
4
87.69
71.56
38.63
95.9
100
30.95
31.69
23.48
59.20
61.73
60.97
39.46
41.15
40.65
98.77
5
69.09
100
27.38
61.73
41.15
6
7
8
49.25
95.06
12.57
100
100
83
28.57
29.17
30
61.73
61.73
51.23
41.15
41.15
34.16
9
29.71
85.47
52
85
24.36
22.17
33
52.47
58.19
58.64
34.98
38.79
39.09
10
11
94.26
95
Chiral Mn(III) salen complex : IBA : alkene molar ratio is 1 :225: 45 and O2 (balloon), reaction time: 90 min, solvent: 1 ml of CH3CN. Selectivity and conversions
were determined by GC.

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HEMMAT ET AL.
shown, additives decreased the yield of the reaction, but
have great effects on the ee of the reactions. In the case
of PNO, the yield and ee of the reaction were decreased
compared with the model reaction, meanwhile, by using
NMO and NH4OAc the ee increased but the yields were
decreased.
The effect of molecular oxygen was investigated on the
progress of the reaction (Table 1) and the results showed
that 5 ml/min is the optimum amount for the oxidation
reaction.
In addition, various oxidants such as m‐CPBA, NaIO4,
H2O2, urea hydrogen peroxide (UHP), PhIO, Oxone, and
PhI (OAc)2 was used in the model reaction (Table 2).
The results showed that all of them have less efficiency
than molecular oxygen.
SCHEME 3 The mechanism that is proposed for the oxidation of
olefins with O2/IBA when the Chiral Mn (III) salen complex is
present
TABLE 4 Comparison of results using CoFe2O4@SiO2@CPTMS@Mn (III) salen complex with various catalysts
Entry
Catalyst
Oxidant
Solvent
Yield (%)
References
[34]
1
2
3
4
5
6
7
8
MNP@SiO2[Mn (III) TDCPP‐NH2]
MOF‐525‐Mn
O2/IBA
O2/IBA
O2/IBA
O2/IBA
O2/IBA
O2/iPrCHO
O2/IBA
O2/IBA
CH2Cl2
97.2
95
[35]
[36]
[37]
[38]
[39]
[40]
butyronitrile
CH3CN
Fe3O4/tart/Mn (TCPP)Cl
Fe (THPP)Cl@MWCNT
Mn (THPP)OAc@GO
67
DMF
89
CH3CN
85
Rd2(OAc)4
Acetone
88
CoO–MCM‐41
1,2‐dichloroethane
CH3CN
90
CoFe2O4@SiO2@CPMS@Mn (III) salen complex
100
This Work
Reaction conditions: Alkene (1 mmol) and O2 (balloon)
TABLE 5 The radical scavenger effect for styrene epoxidation in CH3CN which is catalyzed by chiral CoFe2O4@SiO2@ Mn (III) salen
complex
Entry
Condition
Conversion (%)
Selectivity to epoxide (%)
e.e (%)
TON
TOF (h−1
)
1
2
Radical Scavenger
0
0
0
0
0
Without Radical Scavenger
100
100
24.83
61.73
41.15
FIGURE 13 The catalytic system
recycling for the styrene oxidation in
CH3CN which is catalyzed by fresh
CoFe2O4@SiO2@CPTMS@chiral Mn (III)
salen complex (Conditions of the reaction:
chiral Mn (III) salen complex: IBA molar
ratio: substrate. is 1: 450: 45 and O2
(balloon), reaction time: 90 min)

HEMMAT ET AL.
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After that, peroxy acid convert the chiral Mn (III) salen
complex to high‐valent Mn salen complex intermediate.
Finally, when the active high‐valent metal‐oxo intermedi-
ate is present, the epoxide can be easily produced.
We compared the present results with some previously
reported data to evaluate the catalytic efficiency and reus-
ability of CoFe2O4@SiO2@ Mn (III) complex for aerobic
epoxidation of olefins with molecular oxygen (Table 4).
These results clearly show the catalytic activity of the
present work.
3.3 | Effect of radical scavenger
To confirmed the radical process of the reaction, 2,6‐di‐-
tert‐butyl‐4‐methylphenol (BHT), was added to the reac-
tion mixture as a radical scavenger (Table 5). As the
results shown, no yields were obtained in the presence
of the BHT which is confirmed the radical process in
the presence of IBA and O2.
FIGURE
14 FT‐IR
spectra
of
fresh
CoFe2O4@SiO2@CPTMS@chiral Mn (III) salen complex (a) and
after recovering from styrene (b)
3.4 | Recycling procedure of the chiral Mn
(III) complex
The efficiency of the heterogeneous catalyst was com-
pared with homogeneous counterpart and the results
showed that the heterogeneous catalyst is comparable in
terms of catalytic activity with a homogeneous catalyst
(Table not listed).
The reusability of the catalyst was investigated in the
epoxidation reaction. In each run, after the reaction was
completed, the catalyst was recovered and reused in the
next run. Interestingly, CoFe2O4@SiO2@ chiral Mn (III)
complex was reused for four times while its catalytic
activity wasn't lost (Figure 13). In addition, the FT‐IR
spectra of fresh and reused catalyst showed negligible
change in its spectra (Figure 14).
Under optimum reaction condition, the generality of
the oxidation reaction was studied by various olefins oxi-
dation with molecular oxygen and isobutyraldehyde
(Table 3). The oxidation of alkenes proceeded well and
the corresponding products were obtained in excellent
yields (83–100%). In the present study, olefins with the
functional group were also investigated. Due to the highly
active double bond with electron‐donating OH group,
85.42% conversion was obtained for 3‐methyl‐2‐buten‐1‐
ol (Table 3, entry 10). Much lower activity was observed
for 4‐methyl‐3‐penten‐2‐one with the electron‐
withdrawing carbonyl group with just 29.71% conversion
and 85% selectivity (Table 3, entry 9). Lower activity is
common for terminal olefins. For 1‐octene, 52% conver-
sion and 95% selectivity were obtained (Table 3, entry 11).
Based on the literature review, the epoxidation reac-
tion in the presence of chiral Mn (III) salen complex with
molecular oxygen and aldehyde oxidation is a free radical
reaction (scheme 3).[32,33] As it can be seen, by H abstrac-
tion from aldehyde, in the presence of Mn (III) salen
complex, an acyl radical was generated. Then, this radical
converted to acyl peroxy radical by reacting with O2.
Peroxy acid and another acyl radical were produced by
reacting the acyl peroxy radical with another aldehyde.
4 | CONCLUSIONS
In conclusion, the synthesis of CoFe2O4@SiO2@chiral
Mn (III) complex was prepared by immobilization of
homogeneous chiral Mn (III) salen complex onto the
CoFe2O4@SiO2@CPTMS. The corresponding magnetic
heterogeneous catalyst was characterized by different
techniques such as TEM, SEM, XRD, FT‐IR, VSM and
TGA. Then, the efficiency of CoFe2O4@SiO2@chiral Mn
(III) complex was studied in the aerobic oxidation reac-
tion of terminal olefins under mild conditions. The
results showed that, molecular oxygen, which can be con-
sidered as a standard “green” oxidant can oxidize the ole-
fins in a simple and reusable process. The advantageous
of this protocol includes cost‐effective, environment‐
friendly and simple reusability of the catalyst as well as
excellent yield and selectivity. These advantages make it
a worthy procedure for industrial points of view.

12 of 12
HEMMAT ET AL.
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ACKNOWLEDGMENTS
We gratefully acknowledge the support of this work by
the University of Birjand.
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ORCID
[24] J. Saffari, D. Ghanbari, N. Mir, K. Khandan‐Barani, J. Ind. Eng.
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Kaveh Hemmat https://orcid.org/0000-0002-3973-383X
Mohammad A. Nasseri
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