Modification of MnFe2O4 surface by Mo (VI) pyridylimine complex as an efficient nanocatalyst for (ep)oxidation of alkenes and sulfides

Article abstract of DOI:10.1016/j.molliq.2021.115690

In this current paper, we report a new type of heterogeneous molybdenum (+6) complex, prepared by covalent grafting of cis-dioxo?molybdenum (VI) pyridylimine complex on the surface of MnFe₂O₄ nanoparticles (NP) and characterized using various physicochemical techniques. The recyclable prepared nanocatalyst was tested for sulfoxidation of sulfides and epoxidation of alkenes under solvent-free condition. The catalyst exhibited high turnover frequency for the oxidization of cyclooctene and cyclohexene (10,850 h^?1) and thioanisole and dimethyl sulfide (41,250 h^?1). The synthesized catalyst was found highly efficient, retrievable and eco-friendly catalyst for the (ep)oxidation of alkenes and sulfides in excellent yields in a short time. Furthermore, the synthesized nanocatalyst can be reused for four runs without apparent loss of its catalytic activity in the oxidation reaction.

Full text of DOI:10.1016/j.molliq.2021.115690

Journal of Molecular Liquids 330 (2021) 115690
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Modification of MnFe O surface by Mo (VI) pyridylimine complex as an
2
4
efficient nanocatalyst for (ep)oxidation of alkenes and sulfides
a
a,
a
a
Narges Bouzari , Abolfazl Bezaatpour ⁎, Behnam Babaei , Mandana Amiri ,
b
b
Rabah Boukherroub , Sabine Szunerits
Department of Chemistry, Faculty of Basic Science, University of Mohaghegh Ardabili 179, Ardabil, Iran
Univ. Lille, CNRS, Centrale Lille, ISEN, Univ. Valenciennes, UMR 8520 - IEMN, F-59000 Lille, France
a
b
a r t i c l e i n f o
a b s t r a c t
Article history:
In this current paper, we report a new type of heterogeneous molybdenum (+6) complex, prepared by covalent
Received 4 December 2020
Received in revised form 5 February 2021
Accepted 14 February 2021
Available online 19 February 2021
2 4
grafting of cis-dioxo‑molybdenum (VI) pyridylimine complex on the surface of MnFe O nanoparticles (NP) and
characterized using various physicochemical techniques. The recyclable prepared nanocatalyst was tested for
sulfoxidation of sulfides and epoxidation of alkenes under solvent-free condition. The catalyst exhibited high
−
1
turnover frequency for the oxidization of cyclooctene and cyclohexene (10,850 h ) and thioanisole and di-
methyl sulfide (41,250 h− ). The synthesized catalyst was found highly efficient, retrievable and eco-friendly cat-
alyst for the (ep)oxidation of alkenes and sulfides in excellent yields in a short time. Furthermore, the synthesized
nanocatalyst can be reused for four runs without apparent loss of its catalytic activity in the oxidation reaction.
© 2021 Elsevier B.V. All rights reserved.
1
Keywords:
Solvent-free condition
Molybdenum (VI)
2 4
MnFe O
(Ep)oxidation
Olefins
Sulfides
1. Introduction
reports that have demonstrated catalyzed epoxidation of olefins
[
18,19]. Valencia and co-workers in 2020, reports a series of
pyridylimine ligands with variations of the substituent at the imine ni-
trogen that coordinated to the MoCl center and have used for epox-
Sulfoxides and epoxides (as valuable intermediates and precursors
in the synthesing of organic compounds) are prepared by oxidation of
sulfides and alkenes by strong organic oxidants such as meta-
chlorobenzoic acid and NaClO or mild oxidants such as TBHP and
2 2
O
idation of olefins as homogenous catalyst [20]. According to published
scientific reports, homogenous catalysts of transition metal complexes
may be deactivated in the reaction matrix through the formation of
oxo and peroxo dimeric species [21,22]. For this purpose, immobiliza-
tion of homogeneous metal complexes onto solid supports such as zeo-
lites, polymer, metal oxides, and especially magnetic nanoparticles has
attracted a lot of attention [8,23–29]. Nevertheless, physical and chem-
ical stability and recoverability of catalyst are one of the main chal-
2 2
H O in the presence of metal complex catalysts (V, Fe, Ni, Cu, Mo, Zn,
Mn and …) [1–4]. Among these metals, Mo has been highly regarded
by researchers due to its excellent roles in redox enzymes, such as xan-
thine oxidase, nitrate reductase, nitrogenase, aldehyde oxidase and
sulphite oxidase [5] and considered as a valuable trace element for
humans, animals, plants and microorganisms [6]. High oxidation state
6+
Mo complexes play an important role in oxygen transfer reactions
lenges. Therefore, using of magnetic nanoparticles such as Fe
3 4
O and
in chemical and biological environments such as sulfides into sulfoxides
MnFe nanoparticle was reported to overcome these limitations
2 4
O
[
7] and alkenes into epoxides [8–11] and providing access to surfac-
[30–38]. Most published scientific reports on the oxidation of organic
compounds carried out in the presence of hazardous, toxic and volatile
solvents. The use of harmful solvents poses a serious threat to human
health and the environment. Therefore, replacing and removing harm-
ful solvents in chemical processes is one of the great goals of researchers
[39]. Recently, with global scientific maturity, the design of solvent-free
green processes has been crucial in moving towards green chemistry
and environmental protection [40,41]. The published results show
that in the synthesis of organic compounds, avoiding the use of solvents
leads to increased efficiency, milder conditions, increased safety and re-
duced costs [42].
tants, chemical intermediates, epoxy resins [12], drugs [13], and anti-
fungal agents [14]. In most reports, the behavior of the catalyst is
influenced by the organic ligands around the molybdenum center. Nu-
merous molybdenum complexes based on bidentate N -type ligands
2
such as pyrazolylpyridines, bipyridines and diazabutadienes have been
reported as effective catalysts [15–17]. A group of suitable bidentate
N
2 2
-type ligands with MoO are pyridylimine that there are only a few
⁎
Corresponding author.
E-mail address: bezaatpour@uma.ac.ir (A. Bezaatpour).
https://doi.org/10.1016/j.molliq.2021.115690
167-7322/© 2021 Elsevier B.V. All rights reserved.
0

N. Bouzari, A. Bezaatpour, B. Babaei et al.
Journal of Molecular Liquids 330 (2021) 115690
2 4 2 4 2 4
Fig. 2. XRD patterns of (a) MnFe O , (b) MnFe O @PSB and (c) MnFe O @PSB-Mo(VI).
2 4
Scheme 1. Preparation of MnFe O @PSB-Mo(VI) as novel heterogeneous catalyst.
were collected with a magnet and washed several times with water
and ethanol.
Aimed at developing cleaner processes and eliminating harmful and
toxic solvents in this study we report the simple modification of
MnFe
MnFe
2
O
4
magnetic nanoparticles by molybdenum (+6) pyridylimine,
@PSB-Mo(VI), as an efficient and reusable catalyst for (ep)ox-
2.2.2. Preparation of MnFe O @PSB
2
4
2
O
4
2 4
To a suspension of MnFe O @APTES particles in 100 mL ethanol was
idation of various alkenes and sulfides under solvent-free conditions in
the shortest time. One of the important advantages of this study is the
removal of harmful solvents and escape from the reaction medium.
Other advantages of this study include high conversion rate and selec-
tivity compared to other similar published works. Also, the catalyst sep-
aration process is performed using a simple magnet without the need
for centrifugation and troubled filtration.
added dropwise an ethanoic solution of pyridine-2-carbaldehyde
(5 mmol) and the mixture was heated to reflux during 24 h. The pre-
pared MnFe O @PSB particles were collected using a magnetic field,
2
4
then washed thoroughly with ethanol and dried at 50 °C for 12 h.
2
.2.3. Preparation of MnFe
The preparation of MnFe
achieved as following: a solution of MoO
in 75 mL CH Cl [44] was slowly added to a suspension of 2 g
MnFe in ethanol. The mixture stirred and refluxed for 12 h. After
that, the obtained catalyst was separated by an external magnet,
washed with H O for four times and finally by ethanol, and then dried
at 40 °C for 8 h. IR (KBr, cm ): 1084 [S i\ \O], 586 [Fe\\O], 903 and
50 [O_Mo_O], 1648 [C_N].
2
O
4
@PSB-Mo(VI)
@PSB-Mo(VI) nanocatalyst was
Cl (DMF) (1.72 g, 5 mmol)
2 4
O
2
2
2
2
2
2. Experimental
2 2
O
2.1. Materials and instrument
2
−1
This section is presented in Electronic Supplementary Materials.
9
2
.2. Preparation of heterogeneous catalyst
2.3. Investigation of catalytic activity
2 4
The catalytic activity of MnFe O @PSB-Mo(VI) for the selective (ep)
oxidation of alkenes and sulfides was performed as follows. All glass-
wares were oven-dried prior to use and purged with argon gas. In the
2
.2.1. Preparation of MnFe
Manganese ferrite nanoparticles (MnFe
described in the literature [43]. In short, 2 g of prepared bare MnFe
2 4
O @APTES
O
2 4
NPs) were prepared as
O
2 4
NPs were dispersed in ethanol (100 mL) under ultra-sonication. To
the prepared suspension, was added dropwise 3-aminopropyl-
triethoxysilane (APTES, 5 mL) and ammonia (2 mL). After 48 h stirring
epoxidation processes olefins (1 mmol), MnFe
2
O
4
@PSB-Mo(VI)
−
4
(0.9 mg, 3.652 × 10
mmol based on Mo by XPS analysis), TBHP
(tert-Butyl hydroperoxide) (2 mmol) and chlorobenzene as internal
of the mixture at 80 °C, the resulting MnFe
2
O
4
@APTES nanoparticles
standard (1 mmol) was added in the 25 mL glass reactor at 95 °C. In
2 4 2 4 2 4 2 4
Fig. 1. FT-IR spectra of (a) MnFe O nanoparticles, (b) MnFe O @APTES, (c) MnFe O @PSB and (d) MnFe O @PSB-Mo(VI).
2

N. Bouzari, A. Bezaatpour, B. Babaei et al.
Journal of Molecular Liquids 330 (2021) 115690
2 4 2 4 2 4 2 4
Fig. 3. SEM image of (a) MnFe O , (b) MnFe O @PSB, (c) MnFe O @PSB-Mo(VI) and TEM image of MnFe O @PSB-Mo(VI) (d–f).
Si\\O\\Si bond vibration, respectively (Fig. 1b). Fig. 1c shows the
−
1
imine C_N band at 1649 cm , confirming the formation of Schiff
−
1
base on the surface of MnFe
assigned to the vibronic stretching of the cis MoO
Fig. 2 compares the XRD patterns of bare MnFe
and MnFe @PSB-Mo(VI). The XRD pattern of the MnFe
the diffraction peaks at 2θ = 30.2°, 35.1°, 36.7°, 43.0°, 53.5°, 56.8°, and
2.5° which are well indexed to the crystal plane of (220), (311),
222), (400), (422), (511) and (440), respectively [45]. So MnFe
PSB-Mo(VI) particles shows Bragg reflections of planes as same as the
2
O
4
. The bands at 903 and 950 cm are
group [44] (Fig. 1d).
, MnFe @PSB
showed
2
O
2 4
2 4
O
O
2 4
O
2 4
6
(
2 4
O @
MnFe
MnFe
phase of MnFe
and MnFe
2
O
O
4
. So the illustrated same diffraction peaks in MnFe
@PSB and MnFe @PSB-Mo(VI) confirm the crsystalline
. The particle size of MnFe , MnFe @PSB
@PSB-Mo(VI) were estimated about 21, 21 and 23 nm
2 4
O ,
2
4
2 4
O
2
O
4
2
O
4
2 4
O
2 4
O
respectively by using of Debye-Scherrer equation (L = Kλ/β.cosθ). Here
λ(=0.154 nm) is the wavelength of X-ray, θ is the diffraction angle
(
=17.61) of (311) crystal plan and k is a constant usually equal to 0.94.
Fig. 3a–c show the surface morphology of MnFe , MnFe @PSB
and MnFe @PSB-Mo (VI) which have been examined by scanning
O
2 4
2 4
O
2 4
O
2 4 2 4 2 4
Fig. 4. Magnetization response of MnFe O , MnFe O @PSB, MnFe O @PSB-Mo(VI) and
used catalyst after 4th run at 25 °C.
the oxidation process of sulfides, sulfides (1 mmol), MnFe
2
O
4
–Mo(VI)
mmol based on Mo by XPS analysis), H
2 mmol) and chlorobenzene as internal standard (1 mmol) was
−
4
(
0.7 mg, 2.88 × 10
2 2
O
(
added in the 25 mL glass reactor at 55 °C. In both catalytic processes,
the catalysts were removed by a magnet and product formation was
monitored by gas chromatography using a flame ionization detector at
certain intervals time.
3. Results and discussion
3.1. Preparation of catalyst
MnFe
pared according to the procedure in Scheme 1. Fig. 1 depicts the FT-IR
spectra of MnFe NPs (Fig. 1a), MnFe @APTES (Fig. 1b),
MnFe @PSB (Fig. 1c) and MnFe @PSB-Mo(VI) (Fig. 1d). As shown
in Fig. 1a, the FTIR spectrum displays peaks at 490 and 630 cm
which can be assigned to the characteristic vibration peaks of
MnFe structure . The FTIR spectrum of MnFe @APTES exhibits
characteristic peaks at 610 and 1084 cm attributed to Fe\\O and
2 4
O @PSB-Mo(VI) as a novel heterogeneous catalyst was pre-
2
O
4
2 4
O
2
O
4
2 4
O
−
1
Fig. 5. (A) EDAX spectrum of MnFe
2 4
O @PSB-Mo (VI). (B) Elemental mapping of
2
O
4
2 4
O
MnFe O @PSB-Mo (VI) aggregate using Mn Kα (b), Fe Kα (c), Si Kα (d), N Kα (e), Mo
2
4
−
1
Lα (f), C Kα (g) and Cl Kα (h).
3

N. Bouzari, A. Bezaatpour, B. Babaei et al.
Journal of Molecular Liquids 330 (2021) 115690
2 4
Fig. 6. (a) XPS survey spectrum of MnFe O @PSB-Mo(VI); (b) The core level spectrum of
Mo 3d.
+6
Fig. 9. Effect of a [Oxidant]/[substrate] ratio on the catalytic activity of MnFe
2 4
O @PSB-Mo
(VI) for cyclooctene epoxidation: cyclooctene (1 mmol), T = 95 °C, catalyst (0.9 mg)
reaction time = 15 min and solvent-free conditions; thioanisole sulfoxidation:
thioanisole (1 mmol), T = 55 °C, catalyst (0.7 mg), reaction time = 5 min and solvent-
free conditions.
Fig. 10. Optimization of catalytic reaction temperature on the catalytic activity of
MnFe
2 4
O @PSB-Mo(VI) for cyclooctene epoxidation]: cyclooctene (1 mmol), TBHP
(
2 mmol), catalyst (0.9 mg) reaction time = 15 min and solvent-free conditions;
thioanisole sulfoxidation: thioanisole (1 mmol), H
reaction time = 5 min and solvent-free conditions.
2 2
O (2 mmol) catalyst (0.7 mmol),
Fig. 7. Impact of solvent on the catalytic activity of MnFe2O4@PSB-Mo(VI) for cyclooctene
epoxidation: cyclooctene (1 mmol), TBHP (2 mmol), 95 °C, catalyst
3.652 × 10− mmol, 0.9 mg) reaction time = 15 min; and thioanisole sulfoxidation:
T
=
4
(
(2 mmol), T = 55 °C, catalyst (2.88 × 10− mmol, 0.7 mg),
4
thioanisole (1 mmol), H
O
2 2
W
reaction time = 5 min, mmol of catalys = (amount of catalyst (g) × (% of Mo)/M .
2 4 2 4 2 4
The magnetic properties of MnFe O , MnFe O @PSB and MnFe O @
PSB-Mo(VI) samples are assessed using vibrating sample magnetome-
ter (VSM). (Fig. 4). It is clearly obvious that saturated magnetization of
MnFe O NPs has been decreased from 60 to 9 emu/g after the modifi-
electron microscopy. Reconsideration in the SEM images shows the
spherical-like shape of MnFe , MnFe @PSB and MnFe @PSB-
Mo (VI). For the estimation of particle size of the final catalyst,
MnFe @PSB-Mo (VI), the images of transmission electron microscopy
TEM) was used (Fig. 3d–f). The TEM image (Fig. 3e and f) of the catalyst
2
O
4
2
O
4
2 4
O
2
4
cation of MnFe O surface. However, the saturation magnetization is
2
4
O
2 4
strong enough to magnetically separate the nanocatalyst from the reac-
tion mixture by using a small external magnetic field.
(
show a particle size of 13–20 nm with a relatively spherical shape that it
is in good agreement with the data (23 nm) obtained from the Debye-
Scherrer equation.
The elemental composition and dispersion in the samples were ex-
amined by energy dispersive X-ray (EDX) instrument. The EDX spec-
trum of the MnFe O @PSB-Mo(VI) nanocatalyst (Fig. 5) consists of
2
4
iron, manganese, silicon, carbon, nitrogen, molybdenum and chlorine
as the major elements on the catalyst surface. The element mapping im-
ages (Fig. 5b–h) are exhibited to identify the element distribution in the
MnFe
2
O
4
@PSB-Mo(VI) nanocatalyst, in which six elements: Fe Kα, Mn
@PSB-Mo(VI) nano-
Kα, Si Kα, C Kα, N Kα, Cl Kα and Mo Lα of MnFe
2 4
O
particles are distributed uniformly within the selected area.
Table 1
Effect of several oxidants on the catalytic activity under solvent-free.
Catalyst
Substrate
%Conversion of catalytic
process using various
oxidants
Time [Ox]/[Sub]
(min)
TBHP
MnFe O @PSB-Mo Cyclooctene 99
H
2
O
2
UHP NaIO
4
Fig. 8. Effect of catalyst amount on the (ep)oxidation catalytic activity of MnFe
Mo(VI) for cyclooctene epoxidation: cyclooctene (1 mmol), TBHP (2 mmol), reaction
time = 15 min, T = 95 °C and solvent-free conditions; thioanisole sulfoxidation:
2
O
4
@PSB-
2
2
2
2
15
5
2
2
2
4
(VI)
MnFe O @PSB-Mo Thioanisole 99
2
4
99
40
thioanisole (1 mmol), H
time = 5 min.
2
O
2
(2 mmol), T = 55 °C, solvent-free conditions and reaction
(VI)
4

N. Bouzari, A. Bezaatpour, B. Babaei et al.
Journal of Molecular Liquids 330 (2021) 115690
Table 2
2 4
Results of catalytic epoxidation of various olefins with TBHP as oxidant catalyzed by MnFe O
@PSB-Mo(VI)a.
Entry
Alkene
Conversion (%)
Productsb
Selectivity)
TOF(h−1)c
10850
(
1
99
2
3
96
74
10521
8110
4
24
2630
5
6
74
21
8110
2301
7
8
18
80
1972
8768
9
45
96
4932
1
1
0
1
10,521
75
8220
1
1
2
3
93
96
10192
10,521
a
Catalytic reaction condition: solvent free; [TBHP]:[alkenes] (2:1), catalyst = 0.9 mg, Reaction temperature = 95 °C, reaction time = 15 min.
All products were detected with using standard by GC-FID and GC-Mass.
Obtained as [mmol of product]/[mmol of catalyst] × hours.
b
c
In order to understand the surface composition and valence state of
(Fe2p), 639.5 eV (Mn2p), 529 (O1s), 397 (N1s), 285 (C1s), 232.9 and
the elements, XPS analyses were carried out (Fig. 6). Consistent with the
EDX results, XPS analysis confirmed the presence of bands at 709.8 eV
235.9 eV (Mo3d), 196.6 (Cl 2p) and 149 (Si2p) with atomic percent
for Mo, 3.9; Fe, 5.12; O, 22.57; C, 34.86; Cl, 7.82 and Mn, 2.53 and Fe/
5

N. Bouzari, A. Bezaatpour, B. Babaei et al.
Journal of Molecular Liquids 330 (2021) 115690
Table 3
Catalytic oxidation reaction of various sulfides with H
O
2 2
(30% aqueous) catalyzed by MnFe
O
2 4
@PSB-Mo(VI)a.
Sulfides
Oxidation product
Sulfide
mmol)
%Conversion
(Reaction
time)
Sulfoxide
Selectivity
(%)
TOF
(h 1)b
−
(
1.0
99 ≤ (5 min)
95c
41,250
1
1
.0
.0
99 ≤ (5 min)
100
100
41,250
39,558
95 (5 min)
1
1
.0
.0
99 (5 min)
27(5 min)
100
100
41,223
11,242
1
0
.0
.5
58(5 min)
0(30 min)
100
24,151
0
–
0
0
0
.5
.5
.5
6 (5 min)
38(5 min)
77 (5 min)
100
100
100
1250
7917
16,041
S
0.5
0(30 min)
–
0
HO
OH
a
b
c
2 2
Catalytic reaction condition: catalyst = 0.7 mg, solvent-free; [sulfides]:[H O ] (1:2), Reaction temperature = 55 °C.
Calculated as [mmol of product]/[mmol of catalyst] × hours.
Products were detected with using GC-Mass technique.
Mn = 2.02, C/Mo = 8.94 and Mo/Cl = 0.5, confirming that the Mo Schiff
base complex was supported onto the surface of MnFe . The peaks
with binding energies of 232.9 and 235.9 eV are ascribed to the Mo3d5/2
and Mo3d3/2 respectively [46].
The best molar ratio of oxidant to substrate was studied for the (ep)
oxidation of cyclooctene and thioanisole. As shown in Fig. 9, the best
ratio was 2 for both oxidation of cyclooctene and thioanisole.
As evident from Fig. 10, the best conversion of cyclooctene and
thioanisole to their corresponding oxidized products were obtained at
95 °C and 55 °C, respectively. It is to notice that in the catalytic oxidation
2 4
O
2 4
3.2. Catalytic activity of MnFe O @PSB-Mo(VI)
2 2
of sulfides, increasing the temperature to 55 °C leads to H O
Preliminary experiments were carried out for the (ep)oxidation of
cyclooctene and thioanisole (1 mmol) using TBHP (2 mmol) and H
2 mmol) as model reactions to determine the optimal catalytic condi-
decomposition.
2 2
O
(
tion, respectively. During optimization of the reaction conditions, the
best epoxidation and sulfoxidation results were obtained in solvent-
free condition, in which the highest conversion (>99%) was achieved
(Fig. 7). This result is influenced by problems such as the solubility of
the reactant components in non-polar solvents, the supply of the re-
quired temperature of the (ep)oxidation reaction, and the competition
between polar solvents and the reactant species for coordination to
the molybdenum center.
Next, the impact of different parameters such as amount of catalyst,
reaction temperature, reaction time, kind of oxidant and then molar
ratio of oxidant to substrate were investigated. Fig. 8 summarizes the ef-
fect of catalyst amount on the (ep)oxidation of cyclooctene and
thioanisole.The results indicate that 0.9 and 0.7 mg of catalyst are opti-
mal amounts for the epoxidation of cyclooctene and oxidation of
thioanisole respectively after 15 and 5 min under solvent-free
condition.
Fig. 11. Reusability of catalyst in the (ep)oxidation of cyclooctene and thioanisole using
the optimal catalytic reaction conditions and hot filtration test.
6

N. Bouzari, A. Bezaatpour, B. Babaei et al.
Journal of Molecular Liquids 330 (2021) 115690
Fig. 12. (a) FT-IR, (b) VSM analysis and (c) DRS spectra of fresh catalyst and catalyst after the 4th run of oxidation process.
Table 4
Comparison with literature data of the (ep)oxidation of cyclooctene and thioanisole under various conditions.
Catalyst
MoO (Salen) (piperazine)]n
SM-48ccg
DioxoMo(VI)acacAmpMCM141
Substrate
Reaction conditions
TBHP/C Cl /12 h
Conversion (%)
Ref.
[
2
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
Thioanisole
Thioanisole
Thioanisole
Thioanisole
Thioanisole
Thioanisole
Thioanisole
H
2 4
2
95
34
97
79
100
95
100
100
99
95
97
100
89
100
[49]
[47]
[54]
[55]
[19]
[50]
This work
[56]
[57]
[52]
[53]
[58]
[51]
TBHP/toluene/24 h
TBHP/CH
TBHP/CH
3
Cl/4 h
C
42
H
70Mo
2
N
4
O
9
·3C
2
H
6
OS
3
Cl/24 h
1
MoO
2
Cl
acacen@APTS NPs
@PSB-Mo(VI)
MoO(O2) @Bipy-PMO-IL
MRAMoO2(O2)]
SBA–15 + MoO
Fe @chit-based Cu complex
2
(L )
TBHP/Solvent-free/4.5 h
TBHP/CH Cl/8 h
TBHP/Solvent-free/15 min
MoO
2
3
MnFe
2
O
4
2
H
H
H
H
H
H
H
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
2
2
2
2
2
2
/Water/30 min
[
/Methanol/15 min
/Methanol/60 min
/Solvent-free/90 min
/Solvent-free/30 min
/Solvent-free/120 min
/Solvent-free/5 min
5
+ ImCl
3
O
4
Mo-DAPSH@APTES@SiO
Ti-MCM-41
2
MnFe
2
O
4
@PSB-Mo(VI)
This work
For choosing the suitable oxidant in the (ep)oxidation process, hy-
From the results in Table 3, thioanisole, diallyl sulfide, dibutyl sulfide
and dimethyl sulfide revealed excellent conversion via oxidation process
than diphenyl sulfide, bis(4-hydroxyphenyl) sulfide, benzyl phenyl sulfide
and well as benzothiophene. The low oxidation conversion of diphenyl
sulfide, bis(4-hydroxyphenyl) sulfide, benzyl phenyl sulfide and also
benzothiophene can be ascribed to steric effect of catalyst and sulfides.
Fig. 11 depicts the reusability and leaching of catalyst for epoxidation
of cyclooctene and oxidation of sulfides.. The catalyst was separated eas-
ily with a magnet and then used several times for subsequent epoxida-
tion and sulfoxidation reactions. As shown in Fig. 11, the catalyst can be
reused as an efficient catalyst for four runs without apparent loss of its
catalytic activity. So hot filtration experiments were carried out for
tests of stability and leaching of catalyst. For this goal, in epoxidation
process, after 10 min, the solid phase of catalyst can be removed from
the reaction mixture and the obtained product was analyzed by GC-
FID (about 75% conversion). After 60 min, the conversion showed no
significant increase and was determined to be 77%. In the same manner,
for the sulfoxidation process, after 3 min, the solid phase of catalyst was
separated from the reaction system and the product was analyzed by
GC-FID (85% conversion). After 60 min, the conversion did not show a
significant increase and was thereby determined to be 86%.
drogen peroxide–urea, TBHP (80% in decane solution), hydrogen perox-
ide (30%), and sodium periodate were tested under solvent-free
conditions. From the results of Table 1, it can be seen that the best re-
sults were recorded in the presence of TBHP (80% in decane solution)
for the epoxidation of cyclooctene and TBHP and H
of thioanisole. However, the oxidation of sulfides were optimized by
using H (30%) because, it is economically more viable, nontoxic,
2 2
O for the oxidation
2 2
O
and environmentally-friendly.
After optimization of the reaction conditions, we investigated the
substrate scope for the (ep)oxidation process using various alkenes
and sulfides. Table 2 summarizes the epoxidation results of several al-
−4
2 4
kenes using MnFe O @PSB-Mo(VI) (3.652 × 10 mmol, 0.9 mg), al-
kene (1 mmol), TBHP (2 mmol), catalyst reaction time = 15 min
under solvent-free conditions. In this catalytic process, we achieved de-
sired products with >99% conversion for cyclooctene and 96% for cyclo-
hexene, cis-cyclodecane, and tran-trans-cis-1,5,9-cyclododecatriene in
1
5 min. It is worth to notice that terminal alkenes did not show good
conversion. This is most likely due to electron density of internal olefins
and their ability to approach the Mo(VI) center. Table 3 depicts the cat-
alytic oxidation of various sulfides such as dimethyl sulfide,
benzothiophene, benzyl phenyl sulfide, methyl phenyl sulfide, dibutyl
sulfide, diphenyl sulfide, bis(4-hydroxyphenyl) sulfide, dipropyl sulfide,
and well as diallyl sulfide. All oxidation process of sulfides carried out
The chemical and physico-chemical properties of the catalyst after
4th run were examined using FT-IR, VSM and DRS analysis (Fig. 12).
The spectra of fresh catalyst and the same catalyst after the 4th oxida-
tion process run of cyclooctene indicated good physical and chemical
stability of the catalyst.
−4
using catalyst (2.88 × 10 mmol, 0.7 mg), H
2 2
O (2 mmol), reaction
time = 5 min, T = 55 °C, sulfide (1 mmol) and solvent-free conditions.
7

N. Bouzari, A. Bezaatpour, B. Babaei et al.
Journal of Molecular Liquids 330 (2021) 115690
Scheme 2. Proposed mechanism of epoxidation of cyclooctene loop (I) and oxidation of thioanisole loop (II).
Table 4 indicates the merit of this simple catalytic for (ep)oxidation
of cyclooctene and thioanisole as model substrates, respectively in com-
parison with other catalysts in terms of conversion rate, catalyst loading,
oxygen source, and especially catalytic reaction time. Our catalyst
achieved higher conversion percentage and faster epoxidation activity
for cyclooctene (%conversion/time: 99/15 min) than the literature re-
ports (34/24 h [47], 89/3 h [48], 95/12 h [49] and 95/8 h [50]) and higher
conversion percentage and faster sulfoxidation activity for thioanisole
APTS-AC/3 h) during cyclooctene epoxidation by TBHP. It is
(MnFe
alyst presented in Table 4 ([MRAMoO2(O2)]/15 min) during thioanisole
oxidation by H
2 4
O @PSB-Mo(VI)/5 min) also three times faster than the best cat-
2 2
O .
Declaration of Competing Interest
(
1
%conversion/time: 100/5 min) than the literature reports (89/
20 min [51] 95/60 min [52], 97/90 min [53]).
A plausible mechanism is proposed in Scheme 2. It is assumed that
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
the proposed mechanism in both catalytic oxidation processes may
occur via a seven-coordinate intermediate. Indeed, in the catalytic
cycle, the oxidation process starts with the generation of oxoeperoxo
Mo(VI) precursor. Then, the π electrons of cyclooctene (loop I) and elec-
tron pairs of sulfide (loop II) attack the sigma anti-bonding of O\\O lo-
cated on Mo(VI). Finally, after oxygen transfer from Mo center to
substrate, the catalyst is regenerated with production of epoxide and
sulfoxide.
Acknowledgement
We acknowledge the Research Council of University of Mohaghegh
Ardabili for financial support of the project.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.molliq.2021.115690.
4. Conclusion
In summary, we demonstrated the successful anchoring of a
molybdenium (VI) Schiff base complex on MnFe
O
2 4
nanoparticles sur-
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