Anchoring of a terpyridine-based Mo(VI) complex on manganese ferrite as a recoverable catalyst for epoxidation of olefins under solvent-free conditions

Article abstract of DOI:10.1080/00958972.2021.1904507

A magnetically separable heterogeneous nanocatalyst was obtained by anchoring a terpyridine-based Mo(VI) complex on modified MnFe₂O₄ nanoparticles and characterized by Fourier transform infrared (FT-IR), X-ray diffraction (XRD) and diffuse reflectance spectroscopies (DRS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), vibrating sample magnetometry (VSM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) analysis. The catalytic activity of the supported molybdenum based catalyst was evaluated in the selective epoxidation of various olefins (cyclooctene, limonene, 1-dodecane, 1-heptene, styrene, 1-indene, α-pinene, cyclohexene) with tert-butyl hydroperoxide (TBHP) as an oxidant under solvent-free conditions. This nanocatalyst was easily separated by using an external magnetic field and reused consecutively at least five times with no significant loss in selectivity and catalytic activity. The short reaction time, simple preparation, high conversion, good physicochemical stability and magnetic recycling of the catalysts are beneficial.

Full text of DOI:10.1080/00958972.2021.1904507

Journal of Coordination Chemistry
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/gcoo20
Anchoring of a terpyridine-based Mo(VI) complex
on manganese ferrite as a recoverable catalyst
for epoxidation of olefins under solvent-free
conditions
Mahsa Fadaei Sarabi, Abolfazl Bezaatpour & Ali Mahmoudi
To cite this article: Mahsa Fadaei Sarabi, Abolfazl Bezaatpour & Ali Mahmoudi (2021): Anchoring
of a terpyridine-based Mo(VI) complex on manganese ferrite as a recoverable catalyst for
epoxidation of olefins under solvent-free conditions, Journal of Coordination Chemistry, DOI:
10.1080/00958972.2021.1904507
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JOURNAL OF COORDINATION CHEMISTRY
https://doi.org/10.1080/00958972.2021.1904507
Anchoring of a terpyridine-based Mo(VI) complex on
manganese ferrite as a recoverable catalyst for
epoxidation of olefins under solvent-free conditions
a
b
a
Mahsa Fadaei Sarabi , Abolfazl Bezaatpour and Ali Mahmoudi
a
Faculty of Science, Department of Chemistry, Islamic Azad University North Tehran Branch, Tehran,
b
Iran; Faculty of Basic Science, Department of Chemistry, University of Mohaghegh Ardabili,
Ardabil, Iran
ABSTRACT
ARTICLE HISTORY
A
magnetically separable heterogeneous nanocatalyst was
Received 31 August 2020
Accepted 8 February 2021
obtained by anchoring a terpyridine-based Mo(VI) complex on
2 4
modified MnFe O nanoparticles and characterized by Fourier
KEYWORDS
transform infrared (FT-IR), X-ray diffraction (XRD) and diffuse reflect-
ance spectroscopies (DRS), transmission electron microscopy (TEM),
scanning electron microscopy (SEM), vibrating sample magnetom-
etry (VSM), X-ray photoelectron spectroscopy (XPS) and Brunauer-
Emmett-Teller (BET) analysis. The catalytic activity of the supported
molybdenum based catalyst was evaluated in the selective epoxida-
tion of various olefins (cyclooctene, limonene, 1-dodecane, 1-hep-
tene, styrene, 1-indene, a-pinene, cyclohexene) with tert-butyl
hydroperoxide (TBHP) as an oxidant under solvent-free conditions.
This nanocatalyst was easily separated by using an external mag-
netic field and reused consecutively at least five times with no sig-
nificant loss in selectivity and catalytic activity. The short reaction
time, simple preparation, high conversion, good physicochemical
stability and magnetic recycling of the catalysts are beneficial.
Epoxidation; olefins;
molybdenum; magnetic-
ally; MnFe O
2 4
CONTACT Abolfazl Bezaatpour
a_Bezaatpour@Yahoo.com
Faculty of Basic Science, Department of Chemistry,
University of Mohaghegh Ardabili, Ardabil, Iran.
ß 2021 Informa UK Limited, trading as Taylor & Francis Group

2
M. FADAEI SARABI ET AL.
1. Introduction
Epoxidation of olefins is a principal reaction to obtain epoxides which play an essential
role in pharmaceutical, epoxy resins production, cosmetics, and also plasticizers indus-
tries [1]. Various types of supported catalysts by loading Mo(VI) complexes on different
supports, such as silica [2], graphene, multiwall carbon nanotubes [3] and metal oxides
[4] have been reported in epoxidation of olefins. Schiff base complexes of Mo(VI) have
been extensively applied as a favorable homogeneous catalyst for epoxidation of
alkenes due to properties including facile preparation, stability, and commercial acces-
sibility [5–7]. Preparation of these complexes from inexpensive materials such as MoO3
is a major advantage of these complexes [7–9]. Although homogeneous catalysts are
commonly used for epoxide production, difficult separation of these catalysts from the
reaction mixture and subsequent environmental pollution limits further application [10,
11]. To solve this serious problem, heterogeneous catalysts by supporting a catalyst on
nanoparticles have been widely developed [12]. Magnetic nanoparticles have been
extensively used in immobilization of metal nanoparticles. Among different kinds of
nanoparticles, magnetic nanoparticles such as Fe O , MnFe O and MgFe O4 have
3
4
2
4
2
attracted attention due to their ease of separation, nontoxicity, high surface area and
more importantly high physicochemical stability [13, 14]. Surface functionalization of
various magnetic nanoparticles is an approach for synthesis of magnetically separable
heterogeneous catalysts [15, 16].
Solvent-less reactions offer many benefits in environmental protection, saving in
labor, lowering costs, and chemical waste reduction [17–19]. Application of tert-butyl
hydroperoxide (TBHP) as an eco-friendly oxidant in epoxidation is widely reported
[
20–22]. The advantages of TBHP over H O include thermal stability, selectivity, low
2 2
cost and its safety [23].
Following our previous attempts to investigate catalytic epoxidation of olefins by
Schiff base complex supported nanocatalysts [24–27], herein we present the anchoring
of a terpyridine based Mo(VI) complex onto the surface of chloro-modified magnetic
manganese ferrite nanoparticles. Complete characterization of the new heterogeneous
nanocatalyst (MnFe O @Phttpy-MoO ) was carried out via FT-IR, XRD, BET, SEM, EDX,
2
4
2
TEM, VSM, and also XPS analysis. Additionally, the catalytic activity of
MnFe O @Phttpy-MoO was assessed for green and selective epoxidation of several
2
4
2
olefins. It was noticed that the obtained MnFe O @Phttpy-MoO nanocatalyst could be
2
4
2
applied and recycled many times without apparent conversion reduction.
2. Experimental
2.1. Materials and instruments
Manganese chloride (MnCl ꢀ4H O), ferric chloride (FeCl ꢀ6H O), 4-hydroxybenzaldehyde,
2
2
3
2
toluene, 2-acetylpyridine, ammonia (25% w/w), hydrogen peroxide, urea hydrogen per-
oxide (UHP), cyclooctene, limonene, 1-dodecane, 1-heptene, styrene, 1-indene,
a-pinene, cyclohexene, MoO3 and all other chemicals were obtained from Merck
chemical company (Germany). tert-Butyl hydroperoxide (TBHP) and 3-

JOURNAL OF COORDINATION CHEMISTRY
3
chloropropyl)triethoxysilane (CPTES) were purchased from Sigma-Aldrich. All chemicals
were used without purification.
Fourier transform infrared (FT-IR) spectra were obtained as KBr disks on a Shimadzu
8400S spectrophotometer. Diffuse reflectance spectroscopy measurements were car-
ried out using a Scinco 4100 UV-Vis diffuse spectrophotometer within the 200-900 nm
range applying BaSO as reference material. An X-ray diffractometer (Philips X’Pert 1,
4
Netherlands) equipped with Cu-Ka radiation was applied for obtaining X-ray diffraction
patterns of products. BET analysis was performed using a BELSORP Mini II analyzer.
The surface morphology and mean particle size of nanoparticles were studied with
LEO 1430 VP scanning electron microscopy (SEM). Transmission electron microscopy
(TEM) micrographs were recorded via a Philips CM120 microscope. The magnetic prop-
erties of products were characterized by a Meghnatis Daghigh Kavir Co., Kashan Kavir
vibrating sample magnetometer (VSM). Monitoring of the oxidation products was car-
ried out by an Agilent 7890 A gas chromatograph equipped with a flame-ionization
detector (FID) and capillary column.
2
.2. Preparation of MnFe O @Si-(CH ) -Cl
2 4 2 3
MnFe O nanoparticles were synthesized according to the literature [28]. In brief, an
2
4
2
þ
3þ
aqueous solution of MnCl ꢀ4H O and FeCl ꢀ6H O containing Mn (0.01 M) and Fe
2
2
3
2
ꢁ
(
0.2 M) were prepared and then added slowly into 100 mL NaOH (3 M) at 95 C. After
continuous stirring for 2 h, the precipitate was collected, washed three times with
ꢁ
deionized water and calcined at 60 C for 12 h. First 2 g of the as-prepared MnFe O
2
4
nanoparticles were dispersed in toluene (100 mL) under ultrasonication and then
CPTES (5 mL) was added dropwise and refluxed for 48 h. The MnFe O @Si-(CH ) -Cl
2
4
2 3
ꢁ
particles were washed with DI water and ethanol and dried at 80 C for 24 h.
2.3. Synthesis of 4-(4-hydroxyphenyl)-2,2: 6, 2-terpyridine (4-OH-Phttpy)
4
-(4-Hydroxyphenyl)-2,2:6,2-terpyridine was prepared according to Oyetade et al. [29].
Into a 2:1 (v/v) mixture of water and ethanol (15 mL), 2-acetylpyridine (2.424 g) and 4-
hydroxybenzaldehyde (1.221 g) were added. After that, NaOH pellets (1.458 g) and NH3
(30 mL) were added and stirred for 8 h at room temperature until a creamy precipitate
was obtained. After filtration, the resulting solid was washed with deionized water and
ethanol to achieve the white product.
2
.4. Preparation of MnFe O @Si-(CH ) -O-Phttpy
2 4 2 3
A solution of 4-(4-hydroxyphenyl)-2,2:6,2-terpyridine was added to a suspension of
MnFe O @Si-(CH ) -Cl (0.5 g in 40 mL DMF). Then, the mixture was stirred and refluxed
2
4
2 3
ꢁ
for 72 h at 100 C. The obtained MnFe O @Si-(CH ) -O-Phttpy was recovered by a mag-
2
4
2 3
net and washed with DMF and water repeatedly.

4
M. FADAEI SARABI ET AL.
Scheme 1 Proposed preparation pathway for MnFe O @Phttpy-MoO heterogeneous nanocatalyst.
2
4
2
2
.5. Preparation of MnFe O @Phttpy-MoO
2
4
2
MoO Cl (DMF) was synthesized according to the method described [30]. Initially,
2
2
2
ethanolic solution of MoO Cl (DMF) (1.96 g) was added drop by drop to a suspension
2
2
2
of MnFe O @Si-(CH ) -O-Phttpy (2.0 g in 50 mL ethanol). In the next step, the reaction
2
4
2 3
ꢁ
mixture was refluxed for 24 h at 100 C. Finally, separation of the as-prepared catalyst
was performed using an external magnet and washed four times with DI water
and ethanol.
2.6. Catalytic activity
The catalytic activity of MnFe O @Phttpy-MoO was evaluated for epoxidation of vari-
2
4
2
ꢃ4
ous alkenes. Typically 0.005 mg (3.64 ꢂ 10 mmol determined based on XPS data) of
MnFe O @Phttpy-MoO , chlorobenzene as internal standard (0.5 mmol), alkenes
2
4
2

JOURNAL OF COORDINATION CHEMISTRY
5
Figure 1. FT-IR spectra of (a) MnFe2O4 NPs, (b) MnFe O @Si-(CH ) -O-Phttpy and
2
4
2 3
(
c) MnFe O @Phttpy-MoO .
2 4 2
Figure 2. XRD patterns of MnFe O NPs and MnFe O @Phttpy-MoO .
2
4
2
4
2
(
0.5 mmol) and TBHP (2 mmol) were added to the catalytic reactor. The catalytic
ꢁ
reactor was stirred at 95 C under solvent-free conditions and the oxidation products
were monitored by gas chromatography (FID).
3
. Results and discussion
.1. Characterization of catalyst
The preparation of MnFe O @Phttpy-MoO nanocatalyst is presented in Scheme 1.
3
2
4
2
Initially, the magnetic MnFe O nanoparticles were prepared by a chemical co-precipi-
2
4
tation route. Then the magnetic nanoparticles were modified with Phttpy-MoO . To
2
confirm the preparation of MnFe O @Phttpy-MoO , FT-IR analysis was applied. Figure
2
4
2

6
M. FADAEI SARABI ET AL.
Figure 3. XPS spectrum of (a) MnFe O @Phttpy-MoO and core level spectra of Mo3d.
2
4
2
Figure 4. (a) VSM graph of MnFe O and (b) MnFe O @Phttpy-MoO .
2
4
2
4
2
1
shows the FT-IR spectra of MnFe O nanoparticles, MnFe O @Si-(CH ) -O-Phtpy and
2 4 2 4 2 3
ꢃ1
MnFe O @Phttpy-MoO . As depicted in Figure 1(a), bands at 495 and 675 cm are
2
4
2
assigned to Mn-O and Fe-O stretching modes of manganese ferrite nanoparticles [31].
The MnFe O @Si-(CH ) -O-Phttpy sample (Figure 1(b)) shows additional vibrations of
2
4
2 3
ꢃ1
ꢃ1
the C ¼ N band at 1626 cm . In Figure 1(b), the absorption at 1114 cm is related to
ꢃ1
Si-O-Si vibrations. The two adjacent bands at 918 and 945 cm in Figure 1(c) are
attributed to the presence of cis O ¼ Mo ¼ O group in the supported catalyst [32].
Figure 2 reveals the X-ray powder diffraction patterns of MnFe O and
2
4
MnFe O @Phttpy-MoO . The emergence of diffraction peaks at 2⍜ ¼ 30.07, 35.17,
2
4
2
4
(
3.72, 53.27 and 56.47 were related to the Bragg reflections of (211), (311), (400),
422), (511), and (440) planes, respectively. The obtained characteristic diffraction peaks
in Figure 2 are assigned to the cubic centered geometry of manganese ferrite

JOURNAL OF COORDINATION CHEMISTRY
7
Figure 5. FE-SEM micrographs of (a) MnFe2O4 NPs and MnFe O @Phttpy-MoO in (b) 2 mm,
2
4
2
(c) 500 nm and (d) 200 nm.
nanoparticles in accord with standard JCPDS card NO. 74-2403. The particle size of
MnFe O @Phttpy-MoO was estimated at 32 nm by using the Debye-Scherrer equation
2
4
2
(
L ¼ Kk/b.cosh). Here k(¼ 0.154 nm) is the wavelength of X-ray, h is the diffraction
angle (¼ 17.61) of (311) crystal plane and K is a constant usually 0.94, FWHM is 0.28 in
degree and b is 0.00488 in radian.
The X-ray photoelectron spectrum (XPS) was employed to further identify the
chemical composition and chemical states of MnFe O @Phttpy-MoO (Figure 3). The
2
4
2
bands at 100 eV (Si2p), 234 eV (Mo3d), 296 eV (C1s), 400 (N1s), 414 (Mo3p) and 546
O1s) were assigned giving the atomic percentage for N, 2.3; O, 7.3; Fe, 1.4 and Mo,
.7, confirming that the terpyridine-based complex of dioxo-Mo(VI) was immobilized
onto the MnFe O surface. The Mo3d core level spectrum can be deconvolved into
(
0
2
4
two peaks at 232.90 and 235.85 eV, attributable to Mo3d5/2 and Mo3d3/2, respectively.
A vibration sample magnetometer (VSM) was applied to evaluate the magnetic
characteristics of the prepared samples. Figure 4 shows that saturation magnetization
ꢃ1
for MnFe O and MnFe O @Phttpy-MoO is obtained at 32.97 and 7.13 emu g
,
2
4
2
4
2
respectively. Furthermore, no hysteresis loop was observed in magnetization curves,
which indicates superparamagnetic behavior of the synthesized magnetic MnFe O4
2

8
M. FADAEI SARABI ET AL.
Figure 6. (a) Transmission electron microscopy image of MnFe O @Phttpy-MoO ; (b) DLS results of
2
4
2
MnFe O @Phttpy-MoO .
2
4
2
NPs. The results indicate immobilization of catalyst on magnetic NPs decreases mag-
netic saturation, but it is still enough to remove MnFe O @Phttpy-MoO from solution
2
4
2
by applying an external magnetic field.
The surface morphology and particle size of MnFe O @Phttpy-MoO were studied
2
4
2
via scanning electron microscopy. As illustrated in Figure 5, the magnetic catalyst was
composed of aggregated spherical particles. Also, the size distribution and shape of
the prepared supported catalyst was investigated using transmission electron micros-
copy. Figure 6 shows the TEM image and DLS analysis of MnFe O @Phttpy-MoO .
2
4
2
Figure 6(a) depicts TEM micrographs of magnetic MnFe O @Phttpy-MoO nanocatalyst,
2
4
2
showing uniform spherical nanoparticles obtained with an average diameter of 23-
0 nm. There may be two reasons for the difference in catalyst size obtained through
5
the Debye-Scherrer equation and TEM. One is the particles aggregation and the
second is that the Debye-Scherrer equation shows only an approximate size of
the crystalline phase of MnFe O and does not evaluate the modification layer on the
2
4
MnFe O . As shown in Figure 6(b), the DLS measurements performed on
2
4
MnFe O @Phttpy-MoO suspensions showed hydrodynamic radius of particles
2
4
2
about 79 nm.
The EDAX spectra (Figure 7) of catalyst provide clear evidence for presence of Mn
4.71%), Mo (1.19%,), Fe (11.42%), Si (1.11%), N (3.21%) and C (24.32%), consistent with
(
the chemical composition of the catalyst. Also, the EDX mapping mode (Figure 7)
showed that all elements were well distributed on the MnFe O @Phttpy-MoO
2
2
4
nanocatalyst.

JOURNAL OF COORDINATION CHEMISTRY
9
Figure 7. EDX spectrum and mapping micrographs of (a) C, (b) N, (c) O, (d) Mo, (e) Si, (f) Cl,
g) Mn and (h) Fe of MnFe O @Phttpy-MoO .
(
2
4
2
Figure 8. N adsorption-desorption isotherms of (a) MnFe O NPs and (b) MnFe O @Phttpy-MoO
2
2
4
2
4
2
nanocatalyst.

1
0
M. FADAEI SARABI ET AL.
Figure 9. Oxidation of cyclooctene (0.5 mmol) in various solvents (5 mL) and under solvent-free
ꢁ
ꢃ4
conditions at 95 C during 30 min, TBHP (1.5 mmol), MnFe O @Phttpy-MoO (3.64ꢂ 10 mmol).
2
4
2
Figure 10. Effect of temperature on epoxidation of cyclooctene (0.5 mmol) with TBHP (1.5 mmol)
under solvent-free conditions during 30 min, catalyst (3.64ꢂ 10ꢃ4 mmol).
ꢁ
Figure 11. Effect of [TBHP]/[cyclooctene] ratio on epoxidation process at 95 C under solvent-free
conditions during 30 min, catalyst (3.64ꢂ 10 mmol).
ꢃ4

JOURNAL OF COORDINATION CHEMISTRY
11
Table 1. Catalytic oxidation of different olefins by MnFe O @Phttpy-MoO under solvent-free
2
4
2
[
a]
conditions .
ꢃ1 [b]
Alkenes
Time
Oxidant
% conversion
% Selectivity
TOF [h
2719
]
Cyclooctene
30 min
TBHP
TBHP
99
90
0.0
0.0
0.0
99
92
67
95
54
96
95
100
100
–
[c]
60 min
60 min
60 min
60 min
1236
NaIO
4
–
–
–
2
H O
2
–
UHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
–
63
[
d]
Limonene
30 min
30 min
60 min
30 min
60 min
60 min
60 min
2719
2527
920
2609
741
1318
1304
1
1
-dodecene
-heptene
100
100
[
e]
Styrene
-indene
62
[
f]
1
60
a-Pinene
Cyclohexene
100
100
[
[
[
[
[
[
a]
Catalytic reaction condition: solvent-free; catalyst ¼ 3.64 ꢂ 10ꢃ4; 0.5 mmol alkene;.
b]
c]
Calculated as [mmol of epoxide]/[mmol of catalyst]ꢂtime (h).
Hot leaching test was studied of catalyst leaching in epoxidation of cyclooctene.
d]
e]
f]
1
,2-Limonene oxide is the desired product and 1,2,8,9-limonene dioxide is a byproduct.
Styrene oxide is the desired product and acetophenone is the other one.
H-inden-1-one 40%.
1
Figure 12. Effect of reaction time on oxidation rate of cyclooctene (0.5 mmol), catalyst
ꢃ4
ꢁ
(
3.64 ꢂ 10 mmol), TBHP (1.5 mmol), T ¼ 95 C.
The N2 adsorption-desorption isotherm of MnFe O4 and MnFe O @Phttpy-MoO ,
2
2
4
2
presented in Figure 8(a,b), reveal the mesoporous characteristic of the samples.
2
ꢃ1
Magnetic nanoparticles show a BET surface area of 32.14 m g and a total pore vol-
3
ꢃ1
ume of 0.0577 cm g ; after anchoring the Mo complex on the nanoparticle, BET sur-
2
ꢃ1
3
ꢃ1
face area and total pore volume rise to 42.45 m g and 0.1499 cm g , respectively.
3
.2. The catalytic epoxidation of olefins by MnFe O @Phttpy-MoO
2 4 2
The catalytic performance of heterogeneous MnFe O @Phttpy-MoO was investigated
2
4
2
for selective epoxidation of various alkenes using TBHP as oxidant. First, the effects of
parameters such as the amount of catalyst, kind of solvent, temperature, reaction
time, the type of oxidant and also the molar ratio of oxidant/substrate were optimized.
We have evaluated the catalytic behavior of MnFe O @Phttpy-MoO in different sol-
2
4
2
vents, including methanol, toluene, ethanol, dichloromethane, acetonitrile, and

1
2
M. FADAEI SARABI ET AL.
Figure 13. Reusability of MnFe O @Phttpy-MoO in epoxidation of cyclooctene (0.5 mmol) under
2
4
2
ꢁ
solvent-free conditions, TBHP (1.5mmol), T ¼ 95 C.
Figure 14. (a) FTIR spectra of MnFe O @Phttpy-MoO before (solid line) and after the fifth catalytic
2
4
2
run (dashed line). (b) DRS spectra of MnFe O @Phttpy-MoO nanocatalyst before (solid line) and
2
4
2
after the fifth catalytic epoxidation run (dashed line). (c) XRD pattern of MnFe O @Phttpy-MoO
2
4
2
nanocatalyst before (solid line) and after the fifth catalytic epoxidation run (dashed line).
chloroform. As seen in Figure 9, the best conversion of olefins to epoxides (100%) was
achieved under solvent-free conditions. To assess the effect of temperature on the
catalytic conversion of cyclooctene was examined. Increasing temperature of the cata-
ꢁ
lytic reactor from 55 to 95 C led to improvement of conversion percentage. As
ꢁ
depicted in Figure 10, the highest conversion (>99%) was attained at 95 C.
Additionally, the epoxidation of cyclooctene was performed in various [TBHP]/

JOURNAL OF COORDINATION CHEMISTRY
13
Table 2. Comparison of MnFe O @Phttpy-MoO nanocatalyst and some Mo-based catalysts used
2
4
2
for epoxidation of cyclooctene.
Entry
Catalyst
Oxidant
Time
2 h
6 h
8 h
8 h
2 h
8 h
30 min
Conversion
Ref.
[33]
[34]
[35]
[26]
[8]
[36]
This work
1
2
3
4
5
6
7
Mo-IFNP
Fe @C@MoO
@HSS-2
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
96
97.3
80
98
95
94.3
ꢄ 99
2
O
3
3
MoO
MoO
x
2
acacen@APTS
](acac) ]@HAP
RGO/Fe @C-SalenMoO
MnFe @Phttpy-MoO
[MoO
2
2
3
O
4
2
2
O
4
2
Scheme 2. Proposed mechanism for catalytic epoxidation of olefins via MnFe O @Phttpy-MoO
2
2
4
nanocatalyst.
[cyclooctene] ratios, 0.5, 1, 1.5, 2 and 2.5. As illustrated in Figure 11, maximum conver-
sion was achieved in 2.0 ratio of [TBHP]/[cyclooctene]. The type of oxidant plays a
major role in catalytic epoxidation of cyclooctene as a model olefin. The effects of
urea-hydrogen peroxide, H O , sodium periodate and TBHP on epoxidation rates were
2
2
examined. As evident from Table 1, the best epoxidation results were obtained in the
presence of TBHP.
For optimization of catalyst amount, epoxidation of cyclooctene was performed
under solvent-free conditions using 0.0, 1.0, 3.0, 5.0 and 7.0 mg of MnFe O @Phttpy-
2
4

1
4
M. FADAEI SARABI ET AL.
MoO . The optimum catalyst amount was 5.0 mg. Ultimately the highest conversion of
2
olefins to epoxides was achieved applying 5.0 mg of MnFe O @Phttpy-MoO , cyclooc-
2
4
2
ꢁ
tene (0.5 mmol) as substrate, TBHP as oxidant at 95 C under solvent-free conditions
(Figure 12).
The results of catalytic epoxidation of various olefins (cyclooctene, limonene, 1-
dodecene, 1-heptene, styrene, 1-indene, a-pinene, cyclohexene) under optimized con-
ditions are presented in Table 1. The obtained results reveal high conversion (>99%)
for cyclooctene, limonene, styrene and 1-dodecene using TBHP in 30 min. Also, we
obtained ꢄ 99 conversion and 100% epoxidation selectivity for cyclooctene under the
optimum and green conditions. The propensity of internal alkenes for catalytic epoxi-
dation is more than that of terminal ones. Hot filtration test was studied of catalyst
leaching in epoxidation of cyclooctene. For this purpose, after 10 min, the catalyst was
separated magnetically from the reactor with monitoring of products by gas chroma-
tography (89% conversion). After 60 min, the products were monitored to obtain final
conversion (90%) and there is no significant increase in conversion percent. This cata-
lyst can be recycled several times without obvious changes in physical and chemical
properties (Figure 13). The MnFe O @Phttpy-MoO nanocatalyst was separated mag-
2
4
2
netically and applied five times for successive catalytic epoxidation of olefins.
Comparing the FT-IR spectra (Figure 14) of the MnFe O @Phttpy-MoO nanocatalyst
2
4
2
before and after the fifth catalytic epoxidation run confirms the physico-chemical sta-
bility of MnFe O @Phttpy-MoO . Moreover, diffuse reflectance spectra (DRS) of
2
4
2
MnFe O @Phttpy-MoO before and after consecutive oxidation procedures reveals no
2
4
2
apparent changes.
Table 2 compares the catalytic epoxidation activity of MnFe O @Phttpy-MoO with
2
4
2
some previously reported molybdenum based nanocatalysts in the literature. In this
study, we report magnetically recoverable heterogeneous nanocatalyst
MnFe O @Phttpy-MoO ) for highly efficient epoxidation of olefins. The
a
(
2
4
2
MnFe O @Phttpy-MoO nanocatalyst achieved higher catalytic activity for cyclooctene
2
4
2
epoxidation (ꢄ99%) than other heterogeneous catalysts. Short reaction time is another
important advantage of our nanocatalyst in comparison with other supported Mo
catalytic systems. As expected, the catalytic epoxidation of olefins by
MnFe O @Phttpy-MoO nanocatalyst occurred through formation of a seven-coordin-
2
4
2
ate intermediate (Scheme 2). The proposed mechanism consists of coordination of t-
-
BuOO to molybdenum(VI) as
a Lewis acid center and formation of the
oxoperoxomolybdenum(VI) intermediate. The next step proceeds by approach of olefin
to coordinated oxygen. Finally forming a hydrogen bond between the (O) and coordi-
nated OH, releases epoxide and alcohol from the intermediate.
4. Conclusion
Preparation of a new heterogeneous nanocatalyst based on a terpyridine based Mo(VI)
complex supported on magnetic manganese ferrite nanoparticles is reported. This
magnetically separable nanocatalyst showed remarkable epoxide conversion and
selectivity. Furthermore, MnFe O @Phttpy-MoO heterogeneous nanocatalyst could be
2
4
2
applied and recovered during five runs without significant changes in its stability. The

JOURNAL OF COORDINATION CHEMISTRY
15
MnFe O @Phttpy-MoO nanocatalyst achieved higher cyclooctene conversion (ꢄ99)
2
4
2
ꢃ1
and turnover frequency (2719 h ) during 30 min under green and solvent-free reac-
tion conditions.
Disclosure statement
No potential conflict of interest was reported by the authors.
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