Cis-dioxo-Mo(VI) salophen complex supported on Fe3O4@SiO2 nanoparticles as an efficient magnetically separable and reusable nanocatalyst for selective epoxidation of olefins

Article abstract of DOI:10.1007/s13738-017-1147-4

In this work, paramagnetic Fe₃O₄/SiO₂ nanoparticles were synthesized, characterized and functionalized with dioxo-Mo(VI) tetradentate Schiff base complex and characterized using IR spectroscopy, X-ray powder diffraction spectroscopy, scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry, diffuse reflectance spectroscopy and atomic absorption spectroscopy. Catalyst was used for the selective epoxidation of cyclooctene, cyclohexene, styrene, indene, α-pinene, 1-hepten, 1-octene, 1-dodecen and trans-stilbene using tert-butyl hydroperoxide as oxidant in 1,2-dichloroethane. This catalyst is efficient for oxidation of cyclooctene with a 100% selectivity for epoxidation with 100% conversion in 1?h. After the reaction, the magnetic nanocatalyst was easily separated by simply applying an external magnetic field and was used at least five successive times without significant decrease in conversion.[Figure not available: see fulltext.].

Full text of DOI:10.1007/s13738-017-1147-4

J IRAN CHEM SOC
DOI 10.1007/s13738-017-1147-4
ORIGINAL PAPER
Cis‑dioxo‑Mo(VI) salophen complex supported on Fe3O4@SiO2
nanoparticles as an effcient magnetically separable and reusable
nanocatalyst for selective epoxidation of olefns
Abolfazl Bezaatpour1 · Sahar Khatami2 · Kamellia Nejati2
Received: 29 December 2016 / Accepted: 25 May 2017
© Iranian Chemical Society 2017
Abstract In this work, paramagnetic Fe3O4/SiO2 nano-
particles were synthesized, characterized and functional-
ized with dioxo-Mo(VI) tetradentate Schiff base complex
and characterized using IR spectroscopy, X-ray powder
diffraction spectroscopy, scanning electron microscopy,
transmission electron microscopy, vibrating sample mag-
netometry, diffuse refectance spectroscopy and atomic
absorption spectroscopy. Catalyst was used for the selec-
tive epoxidation of cyclooctene, cyclohexene, styrene,
indene, α-pinene, 1-hepten, 1-octene, 1-dodecen and
trans-stilbene using tert-butyl hydroperoxide as oxidant
in 1,2-dichloroethane. This catalyst is effcient for oxi-
dation of cyclooctene with a 100% selectivity for epoxi-
dation with 100% conversion in 1 h. After the reaction,
the magnetic nanocatalyst was easily separated by sim-
ply applying an external magnetic feld and was used at
least fve successive times without signifcant decrease in
conversion.
Electronic supplementary material The online version of this
article (doi:10.1007/s13738-017-1147-4) contains supplementary
material, which is available to authorized users.
* Abolfazl Bezaatpour
bezaatpour@uma.ac.ir
1
Department of Chemistry, Faculty of Basic Science,
University of Mohaghegh Ardabili, 179, Ardabil, Iran
2
Department of Chemistry, Payame Noor Universtiy, PO
Box 19395-3697, Tehran, Iran
1 3

J IRAN CHEM SOC
N
S
Fe3O4
SiO2
O
O
O
Si
O
O
O
Si
NH
HN
O
O
N
O
N
Mo O
Keywords Schiff base · Dioxomolybdenum(VI) ·
Epoxidation · Nanoparticles · Magnetically separable ·
Fe3O4
stability, decomposition and recycling of catalyst remain
a scientifc challenge. This problem may be solved by
immobilization of the homogeneous metal complex onto
solid supports. Therefore, supporting of metal complexes
has been the subject of a lot of research in catalytic felds
[3, 4, 7, 16, 17].
Introduction
A main idea for supporting of metal complexes is to
anchor the metal complex onto large surface area of inor-
ganic materials such as zeolite and metal oxide [18–22].
Nowadays, core–shell paramagnetic Fe3O4 nano-
particles have been used strongly as supporting surface
because of their unique properties including the high
surface area, low toxicity, separate-ability and biocom-
patibility [6, 23–25]. Magnetic separation renders the
recycling of catalysts from the solution by external mag-
netic felds much easier than fltration and centrifugation.
Meanwhile, using silica layer can prevent the occurrence
of aggregation of magnetic Fe3O4 nanoparticles [26].
Following of our previous research in catalytic activity of
Schiff base complexes, herein we report the immobilization
of N,N-bis(5-chloromethyl salicylidene)-1,2-phenylenedi-
amine dioxomolybdenum(VI) (CM–SalophMoO2) onto the
surface of amino-modifed core–shell paramagnetic nano-
Epoxidation of olefns is one of the fundamental reactions
in industrial organic synthesis [1, 2]. Recently, Schiff
base transition metal complexes have been extensively
studied as catalysts in a wide range of reactions [3–7].
There are many reports in synthesis and catalytic activ-
ity of molybdenum(VI) Schiff base complexes to be very
effective catalysts for the various oxidations of organic
compounds including sulfdes, alcohols and alkenes with
tert-butyl hydroperoxide (TBHP) as the oxidant [8–10].
It is noteworthy that tert-butyl hydroperoxide is environ-
ment-friendly organic peroxide widely used in a variety
of epoxidation processes with good thermal stability [11–
13]. Homogenous catalysts of transition metal complexes
are deactivated in the reaction matrix through the forma-
tion of oxo and peroxo dimeric species [14, 15]. Fur-
thermore, separation, insuffcient chemical and thermal
1 3

J IRAN CHEM SOC
particles (Fe3O4@APTMS/CM–SalophMoO2) (Scheme 1).
The resulted catalyst has been characterized by using dif-
ferent techniques and examined for the selective epoxi-
dation of cyclooctene, cyclohexene, styrene, indene,
α-pinene, 1-hepten, 1-octene, 1-dodecen and trans-stilbene
with tert-butyl hydroperoxide (70% aqueous) as oxidant.
The catalytic performances of supported catalyst have been
compared to homogeneous analogues. The reusability of
Fe3O4@APTMS/CM–SalophMoO2 was also studied in the
epoxidation of cyclooctene with TBHP (70% in water) in
1,2-dichloroethane.
iron(III) chloride(FeCl3·6H2O) and ammonium hydrox-
ide (25%[w/w]) were purchased from Merck Chemical
1
Company. HNMR spectra were recorded using a Bruker
FT NMR 500 (500 MHZ) spectrometer (CD3)2SO. Ele-
mental analyses (carbon, hydrogen and nitrogen) were
performed using a Heraeus Elemental Analyzer CHN-
O-Rapid (Elementar-Analysesysteme, GmbH). Atomic
absorption analysis was carried out on a Shimadzu 120
spectrophotometer. The purity of the solvents, cyclooc-
tene, cyclohexene, styrene, indene, α-pinene, 1-hepten,
1-octene, 1-dodecen, trans-stilbene and analysis of the oxi-
dation products was determined by gas chromatography
using Agilent 7890 with a capillary column and FID detec-
tor. Column temperature was programmed between 180
and 200 °C (2 °C/min). Nitrogen was used as carrier gas
(25 ml/min) at injection temperature. FT-IR spectra were
obtained by Shimadzu 8400S spectrophotometer in KBr
pellets. Diffuse refectance spectra (DRS) were taken on
a Scinco 4100 in the range 200–1100 nm using BaSO4 as
reference. VSM was recorded with MDKF-FORC/VSM)
MEGNATIS-DAGHIGH-KASHAN Co.). DRS data were
recorded by Scinco 4100 in the range 200–900 nm using
Experimental
Materials and physical measurements
5-chloromethyl salicylaldehyde [27] was prepared accord-
ing to literature procedures. Cyclooctene, 3-aminopro-
pyltrimethoxysilane
(APTMS),
o-phenylenediamine,
cyclohexene, styrene, indene, α-pinene, 1-hepten, 1-octene,
1-dodecen, trans-stilbene, iron(II) chloride (FeCl2·4H2O),
Scheme 1 Preparation of het-
erogeneous nanocatalyst
MeO
MeO
MeO
TEOS
Si
NH2
Fe3O4
Fe3O4
SiO2
H2N
NH2
OH HO
OH
Cl
Cl
Cl
O
H
N
N
Fe3O4
SiO2
O
O
O
O
O
O
Si
Si
NH
HN
O
O
O
Mo
O
N
N
1 3

J IRAN CHEM SOC
barium sulfate as reference. The powder small angle X-ray
diffraction patterns were recorded on ITALSTRUCTURE
X-ray diffractometer with CuKα (λ = 1.54 Å) radiation.
The voltage and current applied to the X-ray tube were
40 kV and 30 mA, respectively, with scanning speed as
0.001 min−1. Surface morphology and distribution of par-
ticles were studied via VEGA-TESCAN scanning electron
microscopy.
Preparation of Fe3O4@ APTMS
Nanoparticle of Fe3O4 and Fe3O4@SiO2 was synthesized
and characterized as described in the literature [28, 29].
Fe3O4@SiO2 (0.5 g) was suspended in ethanol (50 ml),
and 3-aminopropyltrimethoxysilane (APTMS) (2.5 ml)
dissolved in 50 ml ethanol was added dropwise to the
suspension. The mixture was stirred at 70 °C for 5 h.
Finally, the brown MNPs was separated magnetically and
washed with distilled water for several times to remove
any unbound APTMS. FT-IR (KBr, cm−1): 3406 [υ(O–
H)], 1033 [υ(Si–O–Si)], 575 [υ(Fe–O)].
Preparation of N,N′‑bis(5‑chloromethyl
salicylidene)‑1,2‑phenylenediamine (5‑CM‑saloph)
Fig. 1 FT-IR spectrum of (a) Schiff base ligand, (b) MoO2-Schiff
base complex, (c) Fe3O4@APTMS/CM–SalophMoO2
o-phenylenediamine (2.5 mmol, 0.27 g) was dissolved in
20 ml dichloromethane and added dropwise to the solu-
tion of 5-chloromethylsalicyaldehyde (5 mmol, 0.85 g) in
20 ml dichloromethane. The mixture was refuxed for 2 h.
The orange-colored precipitates were collected, washed
with dichloromethane and then dried in vacuum (yield 1 g,
96%). Anal. Calcd for C22H18N2O2Cl2.: C, 63.61; H, 4.81;
N, 6.71. Found: C, 63.81; H, 4.51; N, 6.49. IR (KBr, cm−1):
1654 [υ(C=N)], 3401 [υ(O–H)]. 1HNMR (500 MHz,
DMSO-d6) δppm: 11.2 (s, 2H, OH), 8.1 (s, 2H, Ar–CH=N),
6.8–7.5 (m, 10H, Ar), 4.22 (s, 4H, alkane) (supporting
information, Fig. S1). 13CNMR (500 MHz, CDCl3): 55.9,
115.2, 118.3, 118.8, 119.6, 120.8, 127.7, 142.5, 152.2,
155.6, 163.3 (supporting information, Fig. S2).
H, 2.97; N, 5.21. Found: C, 48.6; H, 3.20; N, 4.9. IR
(KBr, cm−1): 1620 [υ(C=N)], 944 and 912 [υ(Mo=O)].
1HNMR (500 MHz, DMSO-d6, 25 °C) δppm: 8.5, 8.6 (s,
2H, Ar–CH=N), 6.4–7.8 (m, 10H, Ar), 4.4, 4.6 (s, 4H,
alkane) (supporting information, Fig. S3). 13CNMR
(500 MHz, DMSO-d6): 56.2, 57.2, 111.3, 111.6, 112.6,
114.8, 116.2, 117.6, 118.5, 119.5, 121.3, 123.1, 124.5
143.3, 144.2, 155.5, 156.3, 161.3, 162.6, 166.4, 167.3,
169.6 (supporting information, Fig. S4). DRS (solid
phase, nm): 362 and 430 nm.
Preparation of Fe3O4@APTMS/CM–SalophMoO2
Preparation of 5‑CM‑salophen complex
of dioxomolybdenum(VI)
A
solution
containing
the
5-CM-salophen
dioxomolybdenum(VI) complex (5 mmol, in 50 ml tolu-
ene) was added to a suspension of amine-functionalized
Fe3O4 @APTMS (1.0 g in 50 ml toluene). The resulting
mixture was stirred at 70 °C for 24 h. After cooling, the
brown Fe3O4@APTMS/CM–SalophMoO2 nanocata-
lyst was separated using an external magnet and washed
several times with water and ethanol. 3.5% of Mo on
Fe3O4@APTMS was detected by atomic absorption and
EDAX.
An ethanol solution (25 ml) of [MoO2(acac)2] (2 mmol)
was added dropwise to the ligand 5-CM-saloph (2 mmol)
that was dissolved in absolute ethanol (25 ml), and the
mixture was refuxed for 3 h. Then, the desired orange
MoO2 complex was fltered and washed with cooled
absolute ethanol and dried at vacuum conditions (yield
0.6 g, 44%). Anal. Calcd for C22H16N2O4Cl2Mo.: C, 49.1;
1 3

J IRAN CHEM SOC
1.80
1.60
1.40
1.20
1.00
0.80
0.60
a mixture of 0.2 g of Fe3O4@APTMS/CM–SalophMoO2
(2.3 × 10−5 mol for unsupported complex), and 1,
2-dichloroethane (DCE) (5 ml), 5 mmol freshly distilled
olefns and 12.5 mmol of tert-butyl hydroperoxide was
refuxed for 1 h. The reaction was followed by a magnetic
separation of Fe3O4@APTMS/CM–SalophMoO2 using
an external magnetic feld. The separated catalyst washed
with absolute ethanol could be reused after drying at 80 °C
under vacuum. 1, 2-dichlorobenzene was used as an inter-
nal standard. The solution was injected to GC analysis,
fnally.
(b)
(a)
250
350
450
550
650
750
Wavelength
Result and discussion
Fig. 2 DRS spectrum of (a) Fe3O4@APTMS/CM–SalophMoO2 as
heterogeneous catalyst, (b) MoO2-Schiff base complex as homog-
enous catalyst
Synthesis and characterization
Dioxomolybdenum(VI) complex Schiff base (derived from
5-chloromethylsalicyaldehyde and o-phenylenediamine)
was prepared, characterized and immobilized on Fe3O4/
SiO2 core–shell nanoparticles as a heterogeneous recy-
clable nanocatalyst. Figure 1 compares the FT-IR spec-
tra of the Schiff base ligand in Mo complex and Fe3O4@
APTMS/CM–SalophMoO2. The FT-IR spectrum of free
ligand exhibits the C=N stretching vibration intense band
at 1654 cm−1, which shifts to 1620 and 1622 cm−1 in the
corresponding complex and Fe3O4@APTMS/CM–Sal-
ophMoO2, respectively, indicating coordination of azome-
thine nitrogen. The appearance of two adjacent bands of
molybdenum complex and Fe3O4@APTMS/CM–Sal-
ophMoO2 at 944 and 912 cm−1 was characteristic of
the presence of asymmetric and symmetric stretches of
cis-[O=Mo=O] group [30, 31]. Two bands in Fig. 1c at
1100 and 592 cm−1 can be assigned to Si–O–Si and Fe–O
stretching, respectively. Comparison of the FT-IR spectra
suggests that the MoO2 is bonded to the Schiff base ligand
and it is supported successfully on Fe3O4@ APTMS.
1H NMR and 13CNMR of Schiff base ligand and Mo
complex confrm the proposed structure of compounds.
1
In the H NMR spectra of the CM–Saloph, the signal at
11.2, 8.1 and 4.22 was assigned for H-phenol, H-imine and
1
Fig. 3 Small angle X-ray diffraction pattern of: a Fe3O4@APTMS/
CM–SalophMoO2, b Fe3O4 nanoparticles
H-methylene, respectively. By considering the H NMR
and 13CNMR spectra of Mo(VI) complex, it seems that
the more splitting is shown because of the non-equivalence
chelate ring (supporting information, Fig. S1-S4).
Catalytic activity of heterogeneous and homogeneous
complex in olefns epoxidation
As shown in Fig. 2, the diffuse refectance spectra
(DRS) of the net complex and Fe3O4@APTMS/CM–Sal-
ophMoO2 show two bands at 362 and 430 nm assigned
to n–π* of Schiff base ligand and ligand-to-metal charge
transfer (LMCT) transitions, respectively [8, 32]. The
comparison of diffuse refectance spectra (DRS) of the
Fe3O4@APTMS/CM–SalophMoO2 and MoO2(VI) Schiff
base complex shows that there is no geometrical change
Catalyst was used for the selective epoxidation of cyclooc-
tene, cyclohexene, styrene, indene, α-pinene, 1-hepten,
1-octene, 1-dodecen and trans-stilbene using tert-butyl
hydroperoxide as oxidant in 1,2-dichloroethane. The sys-
tem was purged with argon gas. In a typical experiment,
1 3

J IRAN CHEM SOC
Fig. 4 EDS spectrum of synthesized Fe3O4@APTMS/CM–SalophMoO2 heterogeneous nanocatalyst for epoxidation of olefns with TBHP in
1,2-dichloroethane
broad peak that appeared in the range from 2θ = 19° to
27° indicates the existence of amorphous silica. The crys-
tal size of Fe3O4 NPs and core–shell magnetic Fe3O4@
APTMS/CM–SalophMoO2 was estimated by using the
Debye–Scherrer equation (d{hkl} = 0.94 λ/βcosθ) where
β is the half-width of the highest intensity X-ray diffrac-
tion lines, d is the average crystalline diameter, 0.94 is the
Scherrer constant, θ is the Bragg angle in degree, and λ is
the X-ray wavelength. Here, the (311) peak of the highest
intensity was selected and d311 obtained 23 nm for Fe3O4
NPs. Comparing between X-ray diffraction patterns of
Fe3O4 NPs and Fe3O4@APTMS/CM–SalophMoO2 shows
that the coating of silica and dioxomolybdenum Schiff
base complex on Fe3O4 NPs did not signifcantly affect
the structure of NPs. As shown in Fig. 4, the EDX spectra
of catalyst provide existence of Mo, Si, C and the other
elements on catalyst surface. The plots of magnetization
versus magnetic feld show the absence of hysteresis phe-
nomenon and indicate that product appeared paramagnetic
at room temperature. The magnetic saturations of Fe3O4
and Fe3O4@APTMS/CM–SalophMoO2 are 57.8 and
37.02 emu/g, respectively. These results indicated that the
magnetization of Fe3O4 decreased considerably with the
formation of SiO2 shell and Mo(O)2 Schiff base complex
anchoring. However, we were able to separate the Fe3O4@
APTMS/CM–SalophMoO2 from the solution by using an
external magnetic feld (Fig. 5).
Fig. 5 Magnetization curves at 298 K for Fe3O4 (solid) and Fe3O4@
APTMS/CM–SalophMoO2 (dot)
in dioxomolybdenum(VI) complex after supporting on
Fe3O4@APTMS NPs.
The X-ray diffraction pattern of crystalline structures of
Fe3O4 NPs and core–shell magnetic Fe3O4@APTMS/CM–
SalophMoO2 (See Fig. 3) shows characteristic diffraction
peaks corresponding to (220), (311), (400), (422), (511)
and (440) refections of inverse spinel Fe3O4 NPs, respec-
tively. It showed the characteristic peaks, and the relative
intensities matched well with those of standard Fe3O4 nan-
oparticles (reference JCPDS card no. 87-2334). A weak
SEM (Fig. 6a, b) and TEM (Fig. 6c, d) images of Fe3O4
and Fe3O4@APTMS/CM–SalophMoO2 were utilized
for morphological studies. TEM images show that the
1 3

J IRAN CHEM SOC
Fig. 6 SEM images of a Fe3O4 NPs, b Fe3O4@APTMS/CM–SalophMoO2 and TEM images of c Fe3O4 NPs, d Fe3O4@APTMS/CM–Sal-
ophMoO2
Table 1 Results of catalytic epoxidation of cyclooctene solvent = 5 ml; catalyst = 2.3 × 10−5 mol; duration = 1 at refux; with the molar ratio
of cyclooctene: TBHP are 1:2.5
Entry
Catalyst
Solvent
Ultrasonication time (min)
Oxidant
Conversion (%)/selectivity (%)
1
2
3
4
5
6
7
8
9
Fe3O4@APTMS/CM–SalophMoO2
Fe3O4@APTMS/CM–SalophMoO2
Fe3O4@APTMS/CM–SalophMoO2
Fe3O4@APTMS/CM–SalophMoO2
Fe3O4@APTMS/CM–SalophMoO2
Fe3O4@APTMS/CM–SalophMoO2
Blank run/without cat.
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
CH3CN
–
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
UHP
32/100
61/100
100/100
80/100
63/100
60/100
16/100
52/100
32/100
10a
22a
22a
22a
22a
–
CH3OH
CH2Cl2
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
Fe3O4@APTMS/CM–SalophMoO2
Fe3O4@APTMS/CM–SalophMoO2
22a
22a
NaIO4
a
The catalyst ultrasonicated in DCE before adding the substrate and TBHP
1 3

J IRAN CHEM SOC
120
100
80
60
40
20
0
catalyst was optimized for epoxidation of cyclooctene. The
time of catalytic reaction, kind of solvent, the reaction tem-
perature and the molar ratio of [TBHP]/[cyclooctene] were
investigated. To choose the suitable solvent, dichlorometh-
ane, methanol, acetonitrile, 1,2-dichloroethane were exam-
ined and 1,2-dichloromethane has been selected, fnally.
The optimizing results are summarized in Table 1, which
shows dichloroethane to be the best solvent. Apparently,
highly coordinating solvents, such as methanol, cause a
signifcant decrease in the catalytic activity since they
compete with tert-butyl hydroperoxide for binding to the
metal center [33]. It seems the limitation of lower refux
reaction temperature is an important factor of least conver-
sion in dichloromethane (60%). The conversion increased
with increasing the reaction temperature from 25 to 80 °C
(Fig. 7). The percent of conversion increased with increas-
ing the molar ratio of [TBHP]/[cyclooctene] from 0.5 to
2.5, and the conversion of cyclooctene was maximum at
2.5:1 molar ratio of [TBHP]/[cyclooctene] (Fig. 8). In the
presented work, different oxidants such as NaIO4, UHP
(urea-H2O2) and TBHP (tert-butylhydroperoxide) were
examined in epoxidation of cyclooctene in 1, 2-dichloro-
ethane (DCE). Results in Table 1 show that TBHP is the
best oxidant for epoxidation of cyclooctene in DCE. It has
several advantageous such as high percent of conversion,
environment friendly and good thermal stability. The effect
of nanoparticles dispersion before reaction was investigated
on catalytic activity using ultrasonicating. It appears that
the dispersion of nanoparticles in solvent increased the cat-
alytic activity from 32 to 100% (See Table 1).
20
30
40
50
60
70
80
Temperature(°C)
Fig. 7 Effect of reaction temperature on conversion catalytic epoxi-
dation of cyclooctene by Fe3O4@APTMS/CM–SalophMoO2 catalyst
with TBHP as oxidant and 1,2-dichloroethane as solvent in 2:1 ratio
of [TBHP]/[cyclooctene]
120
100
80
60
40
20
0
0
0.5
1
1.5
2
2.5
3
Hence, typical catalytic rea◦ction conditions involve DCE
[ TBHP]/[ cycloocten]
(5 ml) solutions at 80
2 C, alkene (5 mmol), TBHP
(12.5 mmol) with the 1:2.5 molar ratio of cyclooctene:
TBHP and catalyst (2.3 × 10−5 mol, 0.2 g for Fe3O4@
APTMS/CM–SalophMoO2, complex loading on Fe3O4@
APTMS detected by atomic absorption and EDAX) stirred
for 1 and 2 h. The fnal solution exhibited no color. So,
no presence of metal was detected in the solution after
using heterogeneous catalyst (it was confrmed by atomic
absorption spectroscopy). The product distributions in the
epoxidation of various alkenes using homogeneous and
heterogeneous catalysts are shown in Table 2. Generally,
one of the main problems of homogeneous transition metal
complexes as catalysts is the formation of oxo and peroxo
dimeric and other polymeric species. The formation of
these compounds can deactivate catalysts irreversibly. As
summarized in Table 2, Fe3O4@APTMS/CM–SalophMoO2
gives higher percent of conversion of alkenes than the net
complex.
Fig. 8 Effect of [TBHP]/[cyclooctene] ratio on conversion catalytic
epoxidation of cyclooctene by Fe3O4@APTMS/CM–SalophMoO2
catalyst with TBHP as oxidant 1,2-dichloroethane as solvent at 80 °C
particle size has changed after immobilization of complex
on modifed MNPs. The synthesized catalysts are well dis-
persed, and the nanoparticles are almost spherical in shape.
The average particle size was estimated about 30 and
40 nm for Fe3O4 and Fe3O4@APTMS/CM–SalophMoO2,
respectively.
Catalytic activity
Selective epoxidation of cyclooctene, cyclohexene, sty-
rene, indene, α-pinene, 1-hepten, 1-octene, 1-dodecen and
trans-stilbene by using heterogeneous (Fe3O4@APTMS/
CM–SalophMoO2) and homogeneous (CM–SalophMoO2)
catalysts was tested with tert-butyl hydroperoxide (70%
aqueous) as oxidant. The catalytic testing of heterogeneous
The cyclooctene oxidation proceeds with a signifcant
selectivity (100%) of epoxidation with 100% conversion
in 1 h using Fe3O4@APTMS/CM–SalophMoO2, while the
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J IRAN CHEM SOC
Table 2 Results of catalytic epoxidation of various alkenes with TBHP catalyzed by Fe3O4@APTMS/CM–SalophMoO2 and net complex, 1,
2-dichloroethane = 5 ml; catalyst = 2.3 × 10−5 mola; duration = 1 and 2 h at refux; the molar ratio of cyclooctene/TBHP is 1:2.5
Alkene
% Conversion
% Epoxy
TONb
Fe3O4@SiO2-complex
Net complex
Fe3O4@SiO2-complex (net complex)
Fe3O4@SiO2-
complex
Net complex
1 h
2 h
1 h
60
2 h
70
100
100
100
56c
100
44d
218 (152)
100 (59)
76
82
50
62
66
44
48
68
70
78
62
76
47
26
44
52
58
35
54
63
100
>99
98
100
>97
98
152 (126)
168 (74)
132 (115)
165 (137)
100
100
58
50
35
64
65
40
32
42
32
48
46
36
100
100
100
100
100
100
139 (104)
142 (100)
87 (79)
a
The mole of catalyst in 0.2 g heterogeneous catalyst calculated by % Mo
TON: The mole of epoxide/mole of catalyst during 2 h
b
c,d
The by-products are verbenone and verbenol for heterogeneous system and homogeneous system
unsupported complex shows 60% conversion in the same
condition. This trend was illustrated for all alkenes in
Table 2. Catalytic reactions were not affected by the pres-
ence or absence of light. The catalytic oxidation of sub-
strate with TBHP in the absence of catalysts (blank run)
occurs with low conversion (~16%). We were able to sepa-
rate magnetically nanocatalyst by using external magnetic
feld and use the catalyst at least fve successive times with-
out signifcant decrease in conversion (Table 3).
Table 3 Results obtained from catalyst reuse in the epoxidation of
cyclooctene
Run
% Conversiona
% Epoxya
% Mo leachedb
1
2
3
4
5
100
100
99
100
100
100
100
100
0
0
0
0
0
99
98
As shown in Scheme 2, the observed results support a
proposed mechanism via a seven-coordinate intermediate
similar to the literature [34]. In the frst step, the mecha-
nism involves the transfer of TBHP’s proton to the ter-
minal of oxo atom of the MoO2 group and coordination
of t-BuOO− to molybdenum(VI) as a Lewis acidic metal
center and formation of the oxoperoxomolybdenum(VI)
intermediate. In the sequence, the next step proceeds by
approach of olefn to coordinated oxygen. Then, the form-
ing of hydrogen bond between the (O) and coordinated OH
releases epoxide and alcohol from the intermediate.
Table 4 illustrates the comparison of the most rele-
vant catalytic systems. Comparison and review of these
results indicate the effciency of the presented mag-
netic nanocatalyst in catalytic activity, selectivity, cata-
lytic reaction time and reusability and easy separation.
The presented nanocatalyst showed higher catalytic
a
GC conversion based on starting alkene
b
Determined by atomic absorption spectroscopy
activity than the [MoOCl(L)] [35], [Mo(CO)6@PS] [36],
[MoO2(py)2]-MCM41 [37], MoO2acpyAmpMCM-41
[38], MoO2–thio-SCMNPs [10], Mag-Mo-nanocatalyst
[39] and MoO2(L)(EtOH)ZBS-PVPA [40]. The epoxi-
dation reaction time of our catalyst (1 h) is consider-
able in comparison with the other reports (24 h) [10,
35], (8 h) [40], (7 h) [37] and (5 h) [39]. However, there
is some homogenous [MoO2(L)(CH3OH)] [41] and
[MoO2L1(CH3OH)] [42] catalysts with epoxidation reac-
tion time, 0.5 and 1 h, respectively, but our novel hetero-
geneous catalyst has more important advantages such as
easy magnetic separation for several times with suitable
reusability and stability of catalyst.
1 3

J IRAN CHEM SOC
Scheme 2 Proposed mecha-
nism for alkene epoxidation by
the Fe3O4@APTMS/CM–Sal-
ophMoO2
Table 4 Comparison of literature reports on the epoxidation of cyclooctene under various conditions
Catalyst
Substrate
Reaction conditions
Recoverability
% Epoxy
References
[MoOCl(L)]
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
Cyclohexene
Cyclooctene
Cyclooctene
Cyclooctene
Cyclooctene
TBHP/CDCl3/24 h
H2O2/CCl4/2.5 h
TBHP//DCE/0.5 h
TBHP/CHCl3/7 h
TBHP/CHCl3/4 h
CH3OH/CH2Cl2/1 h
TBHP/CHCl3/24 h
TBHP/CCl4/5 h
Non-recoverable
Filtration
100
96
[35]
[Mo(CO)6@PS]
[36]
[MoO2(L)(CH3OH)]
[MoO2(py)2]-MCM41
MoO2acpyAmpMCM-41
[MoO2L1(CH3OH)]
Non-recoverable
Filtration
99
[41]
89
[37]
Filtration
99
[38]
Non-recoverable
Magnetically
Magnetically
Filtration
100
100
99
[42]
MoO2–thio-SCMNPs
Mag-Mo-Nanocatalyst
MoO2(L)(EtOH)ZBS-PVPA
Fe3O4@APTMS/CM-salophMoO2
[10]
[39]
TBHP/DCE/8 h
100
100
[40]
TBHP/DCE/1 h
Magnetically
This work
complexes reported in the literature [10, 35–42]. The cat-
alyst can be separated by using a small external magnetic
feld from the reaction system and reused for at least fve
times without signifcant decrease in conversion. The cat-
alyst shows excellent conversion (100%) in 1 h.
Conclusion
In this research work, we successfully synthesized
the magnetically separable Fe3O4@APTMS/CM–Sal-
ophMoO2 nanocatalyst characterized by physicochemi-
cal methods. The homogeneous dioxomolybdenum(VI)
Schiff base complex and solids containing immobilized
Mo(VI) tetradentate Schiff base complex have been stud-
ied as catalyst for selective epoxidation of alkenes. Our
results showed that the conversion of heterogamous cat-
alyst was higher than that of unsupported Mo(VI) com-
plex. So novel heterogeneous catalyst has more important
advantages such as easy magnetic separation for sev-
eral times with suitable reusability, stability of catalyst
and short catalytic reaction time than the other Mo(VI)
Acknowledgements Authors are grateful to the Research Council of
University of Mohaghegh Ardabili for their fnancial support.
References
1. A. Zarrinjahan, M. Moghadam, V. Mirkhani, S. Tangestaninejad,
I. Mohammadpoor-Baltork, J. Iran. Chem. Soc. 13, 1509 (2016)
2. M. Fadhli, I. Khedher, J.M. Fraile, J. Mol. Catal. A Chem. 420,
282 (2016)
1 3

J IRAN CHEM SOC
3. C. Baleizão, B. Gigante, D. Das, M. Álvaro, H. Garcia, A.
Corma, J. Catal. 223, 106 (2004)
25. H. Eskandari, A. Bezaatpour, F. Eslami, J. Iran. Chem. Soc. 14,
457 (2017)
4. A. Bezaatpour, React. Kinet. Mech. Catal. 112, 453 (2014)
5. P.B. Bhat, B.R. Bhat, N. J. Chem. 39, 273 (2015)
6. L. Hamidipour, F. Farzaneh, C. R. Chim. 17, 927 (2014)
7. A. Bezaatpour, M. Amiri, V. Jahed, J. Coord. Chem. 64, 1837
(2011)
8. M. Bagherzadeh, M. Zare, J. Coord. Chem. 66, 2885 (2013)
9. A. Bezaatpour, S. Khatami, M. Amiri, RSC Adv. 6, 27452 (2016)
10. M. Mohammadikish, M. Masteri-Farahani, S. Mahdavi, J. Magn.
Magn. Mater. 354, 317 (2014)
26. W. Li, B. Zhang, X. Li, H. Zhang, Q. Zhang, Appl. Catal. A 459,
65 (2013)
27. T. Joseph, D. Srinivas, C.S. Gopinath, S.B. Halligudi, Catal.
Lett. 83, 209 (2002)
28. Z. Peng, K. Hidajat, M. Uddin, J. Colloid Interface Sci. 271, 277
(2004)
29. L. Chen, B. Li, D. Liu, Catal. Lett. 144, 1053 (2014)
30. M. Ghorbanloo, A. Mohamadi, M. Amini, J. Tao, Transit. Met.
Chem. (London) 40, 321 (2015)
11. A.S. Narula, Tetrahedron Lett. 23, 5579 (1982)
12. Y. Liu, H. Tsunoyama, T. Akita, T. Tsukuda, Chem. Commun.
(Cambridge, U. K.) 46, 550 (2010)
31. J. Topich, Inorg. Chem. 20, 3704 (1981)
32. W. Hill, N. Atabay, C. McAuliffe, F. McCullough, S. Razzoki,
Inorg. Chim. Acta 35, 35 (1979)
13. V.R. Choudhary, R. Jha, P. Jana, Green Chem. 8, 689 (2006)
14. C. Heinrichs, W.F. Hölderich, Catal. Lett. 58, 75 (1999)
15. K.J. Balkus, A.K. Khanmamedova, K.M. Dixon, F. Bedioui,
Appl. Catal. A 143, 159 (1996)
16. M. Bagherzadeh, M. Zare, M. Amini, T. Salemnoush, S. Akbay-
rak, S. Özkar, J. Mol. Catal. A Chem. 395, 470 (2014)
17. F. Farzaneh, Y. Sadeghi, J. Mol. Catal. A Chem. 398, 275 (2015)
18. A. Bezaatpour, M. Behzad, V. Jahed, M. Amiri, Y. Mansoori,
Z. Rajabalizadeh, S. Sarvi, React. Kinet. Mech. Catal. 107, 367
(2012)
33. M. Bagherzadeh, M. Zare, V. Amani, A. Ellern, L.K. Woo, Poly-
hedron 53, 223 (2013)
34. F.E. Kühn, M. Groarke, É. Bencze, E. Herdtweck, A. Prazeres,
A.M. Santos, M.J. Calhorda, C.C. Romão, I.S. Gonçalves, A.D.
Lopes, Chem. Eur. J. 8, 2370 (2002)
35. T. Heikkilä, R. Sillanpää, A. Lehtonen, J. Coord. Chem. 67, 1863
(2014)
36. S. Tangestaninejad, M. Moghadam, V. Mirkhani, I. Mohammad-
poor-Baltork, M. Torki, C. R. Chim. 14, 604 (2011)
37. A. Sakthivel, J. Zhao, G. Raudaschl-Sieber, M. Hanzlik, A.S.
Chiang, F.E. Kühn, Appl. Catal. A 281, 267 (2005)
38. M. Masteri-Farahani, F. Farzaneh, M. Ghandi, J. Mol. Catal. A
Chem. 248, 53 (2006)
19. C.A. McNamara, M.J. Dixon, M. Bradley, Chem. Rev. (Wash-
ington, DC, U. S.) 102, 3275 (2002)
20. S. Imamura, H. Sasaki, M. Shono, H. Kanai, J. Catal. 177, 72
(1998)
39. M. Shokouhimehr, Y. Piao, J. Kim, Y. Jang, T. Hyeon, Angew.
21. P. Eghbali, E. S¸ahin, M. Masteri-Farahani, J. Porous Mater. 24,
39 (2016)
22. S. Akbarpour, A. Bezaatpour, A. Elham, M. Amiri, Appl. Orga-
nomet. Chem. (2017). doi:10.1002/aoc.3804
Chem. Int. Ed. 46, 7039 (2007)
40. Y. Li, X. Fu, B. Gong, X. Zou, X. Tu, J. Chen, J. Mol. Catal. A
Chem. 55, 322 (2010)
41. Z. Moradi-Shoeili, M. Zare, M. Bagherzadeh, M. Kubicki, D.M.
23. S. Keshipour, N.K. Khalteh, J. Iran. Chem. Soc. 13, 1977 (2016)
24. J. Sun, G. Yu, L. Liu, Z. Li, Q. Kan, Q. Huo, J. Guan, Catal. Sci.
Technol. 4, 1246 (2014)
Boghaei, J. Coord. Chem. 68, 548 (2015)
42. A.-M. Li, J. Coord. Chem. 67, 1022 (2014)
1 3