Development of the catalytic reactiVIty of an oxo-peroxo Mo(VI) Schiff base complex supported on supermagnetic nanoparticles as a reusable green nanocatalyst for selective epoxidation of olefins

Article abstract of DOI:10.1039/c5ra27751e

A novel ancillary branch coated oxo-peroxo Mo(vi)tetradentate Schiff base complex on superparamagnetic nanoparticles was prepared and characterized by IR spectroscopy, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), diffuse reflectance spectra (DRS) and atomic absorption spectroscopy (AAS). The catalyst was used for the selective epoxidation of cyclooctene, cyclohexene, styrene, indene, α-pinene, 1-hepten, 1-octene, 1-dodecen and trans-stilben using tert-butyl hydroperoxide as an oxidant in 1,2-dichloroethane. This catalyst is efficient for the oxidation of cyclooctene, with a moderate 100% selectivity for epoxidation with 97% conversion in 30 min. We were able to separate the supermagnetic nanocatalyst by using an external magnetic field, and to use the catalyst at least five successive times without significant decrease in conversion. The proposed supermagnetic nanocatalyst has advantages in catalytic activity, selectivity, catalytic reaction time and reusability by easy separation.

Full text of DOI:10.1039/c5ra27751e

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PAPER
Development of the catalytic reactivity of an oxo–
peroxo Mo(VI) Schiff base complex supported on
supermagnetic nanoparticles as a reusable green
nanocatalyst for selective epoxidation of olefins†
Cite this: RSC Adv., 2016, 6, 27452
a
b
a
Abolfazl Bezaatpour,* Sahar Khatami and Mandana Amiri
A
novel ancillary branch coated oxo–peroxo Mo(VI)tetradentate Schiff base complex on
superparamagnetic nanoparticles was prepared and characterized by IR spectroscopy, X-ray powder
diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM),
vibrating sample magnetometry (VSM), diffuse reflectance spectra (DRS) and atomic absorption
spectroscopy (AAS). The catalyst was used for the selective epoxidation of cyclooctene, cyclohexene,
styrene, indene, a-pinene, 1-hepten, 1-octene, 1-dodecen and trans-stilben using tert-butyl
hydroperoxide as an oxidant in 1,2-dichloroethane. This catalyst is efficient for the oxidation of
cyclooctene, with a moderate 100% selectivity for epoxidation with 97% conversion in 30 min. We were
able to separate the supermagnetic nanocatalyst by using an external magnetic field, and to use the
catalyst at least five successive times without significant decrease in conversion. The proposed
supermagnetic nanocatalyst has advantages in catalytic activity, selectivity, catalytic reaction time and
reusability by easy separation.
Received 25th December 2015
Accepted 2nd March 2016
DOI: 10.1039/c5ra27751e
www.rsc.org/advances
This problem may be solved by immobilizing of the metal
complexes within the solid supports so it can separate
Catalytic epoxidation of olens is an interest of many complexes from each other. Meanwhile, the separation, recy-
researchers for the synthesis of ne chemicals. Because of their cling, insufficient stability of homogeneous catalysts and
versatility as intermediates, epoxies are of great value in both leaching of the active metal into the solvent are part of serious
Introduction
11
1
synthetic organic chemistry and chemical technology. Molyb- problems. Immobilization of the homogeneous metal complex
denum(VI) Schiff base complexes have been intensively used as onto solid supports has been the subject of a lot of research in
oxidation catalysts for a variety of organic substrates, because catalytic elds because of long catalytic lifetime, easy separa-
12–14
molybdenum complexes offer signicant advantages such as tion, thermal stability, high selectivity and easy recyclability.
being economic, environmentally friendly and commercially A main method for heterogenizing of homogenous catalyst is to
2
available. Oxo–peroxo molybdenum complexes investigated anchor the soluble catalyst on to large surface area inorganic
3
–6
15,16
particularly for epoxidation of olens. The catalytic activity of supports.
peroxido molybdenum complexes is related on the number of metal oxide can heterogenized homogeneous catalysts.
peroxido ligands attached to the catalyst and the nature of the Nowadays, core–shell superparamagnetic Fe nanoparticles
have been used strongly because of their unique properties
TBHP is environment-friendly and has good thermal including the high surface area, low toxicity, separability and
Many different solid catalysts such as zeolite and
17,18
O
3 4
7,8
remaining ligands in the coordination sphere.
9
19–21
stability. Moreover, one of the main problems of homogeneous biocompatibility.
Magnetic separation renders the recycling
transition metal complexes as catalysts is the formation of oxo of catalysts from the solution by external magnetic elds much
10
and peroxo dimeric and other polymeric species. The forma- easier than by ltration and centrifugation. Meanwhile, using of
tion of these compounds can deactivate catalysts irreversibly. core–shell can prevent the occurrence of aggregation of
magnetic Fe O nanoparticles, and endow the magnetic mate-
3
4
rials with favorable biocompatibility.
a
Department of Chemistry, Faculty of Basic Science, University of Mohaghegh Ardabili,
In this work we have reported the immobilization of N,N-bis(5-
1
79, Ardabil, Iran. E-mail: bezaatpour@uma.ac.ir
b
chloromethyl-salicylidene)-1,2-phenylenediamine
molybdenum(VI) (CM-salophMoO(O )) onto the surface of amino-
modied core–shell supermagnetic nanoparticles, Fe
APTMS/CM-salophMoO(O ). The resulting heterogeneous
oxoperoxo
Department of Chemistry, Payame Noor University (PNU), Tabriz, Iran
1
†
Electronic supplementary information (ESI) available: Fig. S1:
H
NMR of
2
1
N,N-bis(5-chloromethyl-salicylidene)-1,2-phenylenediamine (5-CM-salop), Fig. S2:
H
3 4
O @
13
NMR of 5-CM-salophMo(O
2 2
)O complex Fig. S3: C NMR of 5-CM-salophMo(O )O
2
complex. See DOI: 10.1039/c5ra27751e
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catalysis has been characterized by using different techniques. Preparation of N,N-bis(5-chloromethyl-salicylidene)-1,2-pheny-
We have been studying for selective alkene epoxidations, using lenediamine (5-CM-saloph) (4)
tert-butyl hydroperoxide (70% aqueous) as oxidant. The catalytic
5
-Chloromethyl-2-hydroxybenzaldehyde was prepared and
performances of supported catalyst have been compared to
homogeneous analogues. The reusability of prepared catalysis
based on core–shell supermagnetic nanoparticles was also
studied in the epoxidation of cyclooctene with tert-butyl hydro-
peroxide in 1,2-DCE.
25
characterized as described in literature. A mixture of salicy-
laldehyde (0.25 mol), paraformaldehyde (0.15 mol) and 150 ml
of conc. HCl was stirred at room temperature for 48 h. The white
3
solid was ltered, washed with 0.5% NaHCO solution, dried
and recrystallized in petroleum ether. The solution of (2.5
mmol, 0.27 g) 1,2-phenylenediamine in 20 ml dichloromethane
was added dropwise to the solution of 5-chloromethyl-
salicyaldehyde (5 mmol, 0.85 g) in 20 ml dichloromethane. The
mixture was reuxed for 2 h. The orange coloured precipitates
were collected, and washed with reaction solvent and then dried
Experimental section
Materials and physical measurements
All reagent used were puried using known procedures. 5-
in vacuum (yield 1 g, 96%). Anal. calcd for C22
18 2 2 2
H N O Cl : C,
22
Chloromethyl-salicylaldehyde have prepared according to
literature procedures. 1,2-Phenylenediamine, cyclooctene,
cyclohexene, styrene, indene, a-pinene, 1-hepten, 1-octene, 1-
dodecen, trans-stilben, 3-aminopropyltrimethoxysilane (APTMS),
63.61; H, 4.81; N, 6.71. Found: C, 63.81; H, 4.51; N, 6.49. IR (KBr,
ꢁ
1
1
cm ): 1654 [n(C]N)], 3401 [n(O–H)]. H NMR (500 MHz, CDCl ,
3
ꢀ
25 C) d
: 11.2 (s, 2H, OH), 8.1 (s, 2H, Ar-CH]N), 6.8–7.5 (m,
ppm
1
3
10H, Ar), 4.22 (s, 4H, alkane) (ESI, Fig. S1†). C NMR (500 MHz,
2 2 3 2
iron(II)chloride (FeCl $4H O), iron(III)chloride (FeCl $6H O), and
ammoniumhydroxide (25% [w/w]) were purchased from Merck
1
Chemical Company. H NMR spectra were recorded using
a Bruker FT NMR 500 (500 MHz) spectrophotometer (CD ) SO.
3
2
Elemental analyses (carbon, hydrogen and nitrogen) were per-
formed using a Heraeus Elemental Analyzer CHN-O-Rapid
(Elementar-Analysesysteme, GmbH). Atomic absorption anal-
ysis was carried out on a shimadzu 120 spectrophotometer. The
purity of the solvents, cyclooctene, cyclohexene, styrene, indene,
a-pinene, 1-hepten, 1-octene, 1-dodecen, trans-stilben and anal-
ysis of the oxidation products was determined by gas chroma-
tography using Agilent 7890 with a capillary column and FID
ꢀ
detector. Column temperature was programmed between 180 C
ꢀ
ꢀ
ꢁ1
and 200 C (2 C min ). Nitrogen was used as carrier gas (40 ml
ꢁ
1
min ) at injection temperature. FT-IR spectra were obtained by
Shimadzu 8400S spectrophotometer in KBr pellets. Diffuse
reectance spectra (DRS) were taken on a Scinco 4100 the range
2
00–1100 nm using BaSO as reference. The powder small angle
4
X-ray diffraction studies were done on ITALSTRUCTURE X-ray
Scheme
1
Preparation of heterogeneous nanocatalyst, (i) para-
/H (iv) FeCl
˚
diffractometer with CuKa (l ¼ 1.54 A) radiation. The voltage
formaldehyde/HCl (ii) O-phenylenediamine (iii) MoO
3
2
O
2
2
/
and current applied to the X-ray tube were 40 kV and 30 mA, FeCl /NH (v) APTMS (vi) reflux in toluene/24 h.
3
3
ꢀ
ꢁ1
respectively, with scanning speed as 0.001 min . Surface
morphology and distribution of particles were studied via VEGA-
TESCAN scanning electron microscopy, using an accelerating
voltage of 20 kV.
Preparation of Fe
3 4
O @APTMS
The chemical co-precipitation was used for preparation of Fe O
3
4
23
nanoparticles. Then silica coated Fe
3 4 3 4 2
O NPs (Fe O @SiO )
synthesized by the hydrolysis of tetraethylorthosilicate (TEOS)
24
3 4 2
using the sol–gel process. A suspension of Fe O @SiO (0.5 g)
was dispersed in ethanol (50 ml), and 3-amino-
propyltrimethoxysilane (APTMS) (2.5 ml) dissolved in 50 ml
ethanol was added dropwise to the suspension. The reaction
ꢀ
mixture was stirred at 70 C for 5 h. Finally the brown aminated
MNPs was separated magnetically and washed with distilled
water for several times to remove any unbound APTMS. FT-IR
Fig. 1 FT-IR spectrum of (a) 5-CM-saloph Schiff base ligand, (b)
MoO(O Schiff base complex, (c) Fe @APTMS/CM-
salophMoO(O ).
2
)
3 4
O
ꢁ1
(KBr, cm ): 3406 [n(O–H)], 1033 [n(Si–O–Si)], 575 [n(Fe–O)].
2
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3 4 2
Preparation of Fe O @APTMS/CM-salophMoO(O )
A solution containing the CM-salophMoO(O ) complex (5
2
mmol, in 50 ml toluene) was added to a suspension of amine-
functionalized Fe
resulting mixture was stirred at 70 C for 24 h. Aer cooling, the
3
O
4
@APTMS (1.0 g in 50 ml toluene). The
ꢀ
3 4 2
brown Fe O @APTMS/CM-salophMoO(O ) nanocatalyst was
separated using an external magnet and washed several times
with water and ethanol.
Epoxidation of alkenes by catalyst
Epoxidation of alkenes such as cyclooctene, cyclohexene,
styrene, indene, a-pinene, 1-hepten, 1-octene, 1-dodecen, trans-
stilben using homogeneous and heterogeneous form of catalyst
was carried out in a 25 ml Schlenk tube. All glassware's were
oven-dried prior to use. The system was purged with argon gas.
In a typical experiment, a mixture of 0.2 g of Fe O @APTMS/
2 3 4
Fig. 2 DRS spectrum of (a) salophMoO(O ) complex (b) Fe O @-
2 3 4
APTMS/CM-salophMoO(O ), (c) Fe O @APTMS/CM-salophMoO after
catalysis.
3
4
ꢁ
5
CM-salophMo(O )O (2.3 ꢂ 10 mol for net complex), and 1, 2-
2
dichloroethane (DCE) (5 ml), 5 mmol freshly distilled alkenes
and 12.5 mmol of TBHP was reuxed for 2 h. The reaction fol-
lowed by separation of the catalyst using an external magnetic

eld (for heterogeneous catalyst). The separated catalyst washed
ꢀ
with absolute ethanol could be reused aer drying at 80
C
under vacuum. 1,2-Dichlorobenzene was used as an internal
standard. The solution was then injected to GC analysis.
Fig. 3 Small angle X-ray diffraction pattern of: (blue) Fe
3 4
O @APTMS/
CM-salophMoO(O ), (red) Fe nanoparticles.
2
3 4
O
3
CDCl ): 55.9, 115.2, 118.3, 118.8, 119.6, 120.8, 127.7, 142.5,
152.2, 155.6, 163.3 (ESI, Fig. S2†).
Synthesis of 5-CM-salophen complex of
oxoperoxomolybdenum(VI)
The CM-salophMoO(O
2
) complex is synthesized by dissolving
Fig. 4 Magnetization curves at 298 K for Fe
APTMS/CM-salophMoO(O ) (solid).
3 4 3 4
O (dot) and Fe O @-
0
.72 g of MoO (5 mmol) in hydrogen peroxide (30%, 10 ml) by
3
2
stirring at room temperature. Then the N,N-bis(5-chloromethyl-
salicylidene)-1,2-phenylenediamine (5 mmol) dissolved in
a minimum volume of methanol and added the above solution
under stirring gave yellow solid. The solid was ltered off,
washed with water, methanol and nally with diethyl ether and
dried in vacuo (yield 55%). Anal. calcd for C22
H
16
N
2
O
5
Cl
2
Mo: C,
4
4
9
8
7.42; H, 3.26; N, 5.03; Mo, 17.23. Found: C, 47.01; H, 3.50; N,
ꢁ1
.7; Mo, 16.95. IR (KBr, cm ): 1620 [n(C]N)], 860 [n(O–O)] and
1
ꢀ
44 [n(Mo]O)]. H NMR (500 MHz, DMSO-d
.7 (s, 2H, Ar-CH]N), 6.8–7.8 (m, 10H, Ar), 4.3, 4.4 (s, 4H,
6
, 25 C) dppm: 8.6,
1
3
alkane) (ESI, Fig. S3†). C NMR (500 MHz, DMSO-d
6
): 56.1,
5
1
1
4
7.1, 111.2, 111.7, 112.8, 114.6, 116.1, 117.5, 118.6, 119.6, 121.4,
23.2, 124.6, 143.2, 144.3, 155.4, 156.4, 161.2, 162.7, 166.3,
67.2, 169.3 (ESI, Fig. S4†). DRS (solid phase, nm): 368 and
35 nm.
Fig. 5 TG curve of Fe
3 4 2
O @APTMS/CM-salophMoO(O ) (dash) and
CM-salophMoO(O ) (solid).
2
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Fe
3
O
4
NPs. Comparing between X-ray diffraction pattern of
Result and discussion
Synthesis and characterization
Fe O NPs and Fe O @APTMS/CM-salophMoO(O ) shows that
3
4
3
4
2
the coating of silica and salophMoO(O ) complex on Fe O NPs
2
3 4
Scheme 1 shows the synthesis of tetradentate Schiff base did not signicantly affect the structure of NPs.
derived from 5-chloromethylsalicyaldehyde and 1,2-phenyl-
As shown in Fig. 4, the plots of magnetization versus
enediamine) oxo–peroxomolybdenum(VI) complex and immo- magnetic eld show the absence of hysteresis phenomenon and
bilization of complex on Fe /SiO
core–shell nanoparticles as indicate that product has superparamagnetism at room
a heterogeneous recyclable nanocatalyst.
temperature. Fe and Fe @APTMS/CM-salophMoO(O
H NMR of Schiff base ligand and Mo complex conrm the show the magnetic saturation is 55.6 and 38.12 emu g
(
3
O
4
2
3
O
4
3
O
4
2
)
,
1
ꢁ1
1
formation of compounds 3 and 4. In the H NMR spectra of the respectively. These results indicated that the magnetization of
Schiff base ligand the signal at 11.2, 8.1 and 4.22 assigned for H- Fe
O decreased considerably with the increase of SiO and
4 2
3
phenol, H-imine and H-methylene respectively. By considering
1
13
of the H NMR and C NMR spectra of Mo(VI) complex it seems
that the more splitting is shown because of the non-equivalence
chelate ring.
There is some additional information from a comparison of
the infrared spectra of the Schiff base ligand, corresponding
MoO(O ) complex and Fe O @APTMS/CM-salophMoO (Fig. 1).
2
3
4
2
The FT-IR spectrum of CM-saloph Schiff base ligand exhibit the
ꢁ
C]N stretching vibration intense band at 1654 cm , which shi
ꢁ1
to 1632 and 1630 cm in the corresponding CM-salophMoO(O
2
)
complex and Fe @APTMS/CM-salophMoO(O ) respectively,
3
O
4
2
26
indicating coordination of azomethine nitrogen. Also the
n(Mo]O) and n(O–O) vibrations of CM-salophMoO(O ) complex
2
ꢁ
1
ꢁ1
27
appear around 929 cm
and 860 cm
respectively. The
appearance of two bands in Fig. 1(c) at 1100 and 592 cm can
ꢁ
1
be assigned to Si–O–Si and Fe–O stretching, respectively.
Comparison of all the FT-IR data suggest that the MoO(O
group is bonded to the Schiff base ligand and then supported
successfully on Fe @APTMS.
The diffuse reectance spectra (DRS) of the MoO(O
and Fe O @APTMS/CM-salophMoO(O ) in Fig. 2 show two bands
2
)
3 4
O
2
) complex
3
4
2
at 368 and 435 nm to assigned n–p* of Schiff base ligand and
14,28
ligand-to metal charge transfer transitions, respectively.
comparison of diffuse reectance spectra (DRS) of the Fe
APTMS/CM-salophMoO(O ) and CM-salophMoO(O ) show that
there is not any geometrical change in oxo–peroxomolybdenum(VI)
complex aer supporting on Fe @APTMS NPs.
So the
3 4
O @
2
2
3 4
O
The atomic absorption analysis gives the Mo content of
heterogeneous catalyst 3.5 wt%.
As shown in Fig. 3, the X-ray diffraction pattern of crystalline
structures of Fe O NPs and core–shell magnetic Fe O @
3
4
3 4
APTMS/CM-salophMoO(O
peaks correspond to (220), (311), (400), (422), (511) and (440)
reections of inverse spinel Fe NPs, respectively. It showed
characteristic peaks, and the relative intensity matched well with
those of standard Fe nanoparticles (reference JCPDS card no.
7-2334). The week broad peak appeared in the range from 2q ¼
9 to 27 indicates the existence of amorphous silica. The crystal
2
)
show characteristic diffraction
3 4
O
3 4
O
8
1
size of Fe O NPs and core–shell magnetic Fe O @APTMS/CM-
3
4
3 4
2
salophMoO(O ) were determined by using the Debye–Scherrer
(
d
{hkl} ¼ 0.94l/b cos q) equation where b is the half-width of the
highest intensity X-ray diffraction lines, d is the average crystal-
line diameter, 0.94 is the Scherrer constant, q is the Bragg angle
in degree and l is the X-ray wavelength. Here, the (311) peak of
Fig.
3 4 3 4
6 SEM images of (a) Fe O NPs, (b) Fe O @APTMS/CM-
the highest intensity was selected and d311 obtained 25 nm for salophMoO(O ) and TEM images of (c) Fe O NPs, (d) Fe O @APTMS/
2
3
4
3
4
2
CM-salophMoO(O ).
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Table 1 Optimization of Fe
3
O
4
@APTMS/CM-salophMoO(O
2
) catalytic tested for the selective epoxidation of cyclooctene, cyclohexene,
condition, solvent ¼ 5 ml; duration ¼ 30 min with the molar ratio of
styrene, indene, a-pinene, 1-hepten, 1-octene, 1-dodecen and
trans-stilben using tert-butylhydroperoxide (70% aqueous) as
cyclooctene : oxidant are 1 : 2
oxidant. The catalytic activities of Fe O @APTMS/CM-sal-
ophMoO(O ) were optimized for epoxidation of cyclooctene
2
Amount of
catalyst (g)
Conversion (%)/
selectivity (%)
3 4
ꢀ
Solvent
T ( C)
Oxidant
through investigation of the inuence of solvent, the reaction
temperature, the molar ratio of [TBHP]/[cyclooctene] and the
time of epoxidation reaction. For selecting the best solvent,
dichloromethane, methanol, acetonitrile, dichloroethane were
employed as solvents. The optimizing results in Table 1 show that
dichloroethane to be the best solvent. Apparently, highly coor-
1
1
1
1
1
1
1
1
CH
CH
CH
1
1
,2-DCE
,2-DCE
,2-DCE
,2-DCE
,2-DCE
,2-DCE
,2-DCE
,2-DCE
Without cat.
0.005
0.01
0.02
0.025
0.02
0.02
0.02
0.02
0.02
80
80
80
80
80
70
60
40
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
UHP
26/100
56/100
75/100
97/100
97/100
87/100
77/100
60/100
82/100
60/100
58/100
55/100
34/100
dinating solvents, such as CH OH, cause a signicant decrease in
3
the catalytic activity since they compete with TBHP for binding to
3
3
2
CN
OH
80
29
the Mo center. It seems that the lower reux reaction temper-
ature is the important reason of lowest conversion in CH Cl
(60%). The conversion increased with increasing the reaction
Reux
Reux
80
Cl
2
0.02
0.02
0.02
2
2
,2-DCE
,2-DCE
80
NaIO
4
ꢀ
ꢀ
temperature from 25 C to 80 C (Fig. 7).
Fig. 8 shows that the nanoparticles have good separation and
dispersion by ultrasonication. Aer of ultrasonication the
catalytic reactivity was tested and conversion increases during
ultrasonication time form 32–100%.
The percent of conversion increased with increasing the
molar ratio of [TBHP] : [cyclooctene] from 0.5 to 2 and the
conversion of cyclooctene was maximum at 2 : 1 molar ratio of
[TBHP] : [cyclooctene] (Fig. 9).
In this research work, different oxidants such as NaIO , UHP
4
(
urea–H O ) and TBHP (tert-butylhydroperoxide) were examined
2 2
in epoxidation of cyclooctene in variable solvents. TBHP has
some advantageous: (i) it can give high percent of conversion; (ii)
environment-friendly; (iii) it has good thermal stability. Table 1
shows that TBHP as the oxygen donor has the highest conver-
sion in the optimized reaction condition. Hence, typical catalytic
Fig.
cyclooctene.
7 The effect of reaction temperature on conversion of
Mo(O) Schiff base complex. However, the Fe O @APTMS/CM- reaction conditions involve 1,2-DCE (5 ml) solutions at 80 ꢃ
2
3 4
2
salophMoO can still be separated from the solution by using an
external magnetic eld.
Thermogravimetric analysis have been used to under-
standing of thermal stability of supported catalyst. As shown in
Fig. 5, the decomposition of the CM-salophMoO(O
2
) complex
and Fe O @APTMS/CM-salophMoO(O ) catalyst were began
3
4
2
ꢀ
ꢀ
1
50 C and 360 C respectively. These criteria indicate that the
Fe O @APTMS/CM-salophMoO(O ) catalyst is thermally stable
3
4
2
than CM-salophMoO(O
Fig. 6 illustrates the SEM (Fig. 6(a and b)) and TEM (Fig. 6(c
2
and d)) images of Fe and Fe @APTMS/CM-salophMoO .
2
).
3
O
4
3
O
4
Fig. 8 Effect of catalyst dispersion by ultrasonication before catalytic
The size and morphology of the nanoparticles were observed
using transmission electron microscopy (TEM). TEM images
show that the particle size has changed aer immobilization of
complex on modied MNPs. The synthesized catalysts are well
dispersed and most of the nanoparticles are almost spherical in
shape. The average particle size estimated about 29 nm and 41
process.
3 4 3 4 2
nm for Fe O and Fe O @APTMS/CM-salophMoO respectively.
Epoxidation catalytic reactivity of CM-salophMoO(O
Fe @APTMS/CM-salophMoO(O ) (8)
Catalytic reactivity of heterogeneous, Fe
MoO(O ) and homogeneous, CM-salophMoO(O
2
) (4) and
3
O
4
2
3 4
O @APTMS/CM-saloph-
Fig. 9 Effect of [TBHP]/[cyclooctene] ratio on cyclooctene conver-
ꢀ
) catalysts were sion at 80 C.
2
2
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of light. The catalytic oxidation of substrate with TBHP in the
absence of catalysts (blank run) occurs with low conversion
(
ꢄ26%). We were able to separate supermagnetically nano-
catalyst by using external magnetic eld and use the catalyst at
least ve successive times without signicant decrease in
conversion (Table 2).
Scheme 2 shows a proposed mechanism via an interaction
*
between the olen HOMO p(C]C) and the unoccupied s(O–O) orbital
40,41
of peroxo complex.
In the rst step, the electron density
is redistributed from the C–C bonding olen orbital to
*
s(
orbital via breaking of O–O bond and then epoxide is
O–O)
generated. Aer that, proton of TBHP is transferred to the
Fig. 10 Typical chromatogram taken during of catalytic process,
reaction time (a) 0 min, (b) 20 min and (c) 30 min with 100% selectivity.
ꢁ
terminal of oxo atom of the MoO
2
and t-BuOO is coordinated
to Mo(VI) as a Lewis acidic metal center. Finally, forming of
ꢁ
hydrogen bond between the coordinated t-BuOO and OH,
releases catalyst and alcohol. Table 3 compares the efficiency of
our catalyst with some found in the literature. The illustrated
Fe O @APTMS/CM-salophMoO(O ) catalytic system is one of
3
4
2
the fastest magnetically recoverable catalytic system for epoxi-
dation of alkenes. Our novel catalyst showed higher
3
0
catalytic activity than the [MoO(O
2
)
2
(H
2
32
O) (ONnDodec
3
)],
31
[MoO(O
2
)
2
(HMPT)],
[Mo(O)(O
2
)
2
(bipy)]
and [MoO
2
(py)
2
]-
MCM41(ref. 34) for the epoxidation of cyclooctene. So the
comparison of epoxidation reaction time of our catalyst (30
Table 2 The results obtained from catalyst reuse in the epoxidation of
a
cyclooctene
a
a
b
Run
% conversion
% epoxy
% Mo leached
1
2
3
4
5
100
100
99
99
99
100
100
100
100
100
0
0
0
0
0
Fig. 11 Product distributions in the epoxidation of various alkenes
using net complex and heterogeneous complex.
ꢀ
2
C, alkene (5 mmol), TBHP (12.5 mmol) with the molar ratio
a
Catalytic condition, solvent ¼ 5 ml; duration ¼ 30 min with the molar
b
of cyclooctene : TBHP and catalyst (0.0074 mmol), 0.02 g for ratio of cyclooctene : oxidant are 1 : 2. Detected by atomic absorption
Fe O @APTMS/CM-salophMoO(O ) stirred for 30 min for
3
spectroscopy.
4
2
cyclooctene and 60 min for the other olens. The nal solution
exhibited no color. So, no presence of metal was detected in the
solution aer using heterogeneous catalyst, (it was conrmed by
atomic absorption spectroscopy). The product distributions in
the epoxidation of various alkenes using net complex and
heterogeneous catalysts are shown in Fig. 11. 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 shown in Fig. 11, Fe
APTMS/CM-salophMoO(O ) gives higher percent of conversion
of alkenes than the CM-salophMoO(O ) complex.
3 4
O @
2
2
Fig. 10 shows the chromatograms of the cyclooctene oxida-
tion proceeds with a moderate 100% selectivity for epoxidation
with 97% conversion in 30 min for Fe O @APTMS/CM-
3
4
salophMoO(O2) catalyst. In the event that the CM-
salophMoO(O ) complex shows 75% conversion in the same
2
condition. This trend was illustrated for all alkenes in Fig. 11.
Catalytic reactions were not affected by the presence or absence
Scheme
2
Proposed mechanism for alkene epoxidation by the
)O.
Fe @APTMS/CM-salophMo(O
O
3 4
2
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Table 3 Comparison of literature reports on the epoxidation of
cyclooctene under various conditions
A. Bezaatpour, V. Jahed, G. Dutkiewicz, M. Kubicki and
M. Salehi, Polyhedron, 2011, 30, 2611–2618.
2
3
(a) A. Lazar, W. R. Thiel and A. P. Singh, RSC Adv., 2014, 4,
Reaction
conditions
%
14063–14073; (b) G. Fioroni, F. Fringuelli, F. Pizzo and
Catalyst
epoxy Ref.
L. Vaccaro, Green Chem., 2003, 5, 425–428; (c)
M. C.-Y. Tang, K.-Y. Wong and T. H. Chan, Chem.
Commun., 2005, 50, 1345–1347.
J. A. Brito, M. Go'mez, G. Muller, H. Teruel, J. Clinet,
E. Du n˜ ach and M. A. Maestro, Eur. J. Inorg. Chem., 2004,
4278–4285.
[
[
[
[
[
MoO(O
MoO(O
Mo(O)(O
Mo(O)(O
2
2
)
)
2
(H
(HMPT)]
2
O)(ONnDodec
3
)]
H
H
UHP/C
2
O
O
2
/CH
/DCE/5 h
mim(PF
/CH Cl/18 h
3
CN/24 h
75
14
90
86
89
99
96
100
99
100
97
30
31
32
33
34
35
36
37
38
39
This
work
2
2
2
2
)
)
2
2
(bipy)]
(dmpz)
4
6
)/8 h
2
2
]
H
2
O
2
3
MoO
2
(py)
acpyAmpMCM-41
Mo(O)(O (L-L)]SMNPs
-thio-SCMNPs
2
]-MCM41
TBHP/CHCl
TBHP/CHCl
3
/7 h
/4h
MoO
[
MoO
2
3
2
)
2
TBHP/CH
TBHP/CHCl
TBHP/CCl /5 h
TBHP/DCE/8h
TBHP/DCE/30 min
3
Cl/6 h
4 A. V. Biradar, M. K. Dongare and S. B. Umbarkar, Tetrahedron
Lett., 2009, 50, 2885–2888.
5
2
3
/24 h
Mag-Mo-nanocatalyst
4
R. J. Cross, P. D. Newman, R. D. Peacock and D. Stirling, J.
Mol. Catal. A: Chem., 1999, 144, 273–284.
MoO
Fe
2
(L)(EtOH)ZBS-PVPA
@APTMS/
3
O
4
CM-salophMoO(O
2
)
6 V. Conte, F. Di Furia and G. Modena, in Organic Peroxides, ed.
W. Ando, Wiley, Chichester, 1992, pp. 559–598.
7
R. Curci and J. O. Edwards, in Catalytic Oxidations with
Hydrogen Peroxide as Oxidant, ed. G. Strukul, Kluwer,
Dordrecht, 1992, pp. 57–60.
35
37
38
39
min) with the other reports (4 h), (24 h), (5 h) and (8 h) is
many considerable.
8
9
J. A. L. da Silva, J. J. R. F. da Silva and A. J. L. Pombeiro, Coord.
Chem. Rev., 2011, 255, 2232–2248.
(a) K. A. Jorgensen, Chem. Rev., 1989, 89, 431–458; (b)
J. M. Br ´e geault, J. Chem. Soc., Dalton Trans., 2003, 3289–3302.
Conclusions
As a part of our progressing studies on the catalyst, Novel 10 (a) K. J. Balkus Jr, A. K. Khanrnamedova, K. M. Dixon and
ancillary branch coated of oxo–peroxo Mo(VI) tetradentate
Schiff base complex on superparamagnetic nanoparticles
was prepared successfully and characterized by physico-
chemical methods. The solids containing immobilized
Mo(VI) tetradentate Schiff base complex has been studied as
efficient heterogeneous nanocatalyst for chemoselective
F. Bedioui, Appl. Catal., A, 1996, 143, 159–173; (b) R. Belal
and B. Meunier, J. Mol. Catal., 1988, 44, 187–190; (c)
M. Salavati-Niasari, M. Shakouri-Arani and F. Davar,
Microporous Mesoporous Mater., 2008, 116, 77–85; (d)
K. O. Xaviera, J. Chackoa and K. K. Mohammed Yusuff,
Appl. Catal., A, 1996, 258, 251–259.
epoxidation of olens. Oxidation result of Fe
CM-salophMoO(O was comparable with net CM-salo-
phMoO(O ). In this report the conversion of heterogeneous 12 (a) A. Bezaatpour, M. Amiri and V. Jahed, J. Coord. Chem.,
3
O
4
@APTMS/ 11 K. J. Ballus Jr, A. K. Khanmamedova, K. M. Dixon and
2
)
F. Bedioui, Appl. Catal., A, 1996, 143, 159–173.
2
catalyst was greater then the homogenous catalyst for all
2011, 64, 1837–1847; (b) A. Bezaatpour, React. Kinet., Mech.
of olens epoxidation. Also the Fe O @APTMS/CM-
Catal., 2014, 112, 453–465.
3
4
salophMoO(O ) can be separated by using a small external 13 A. Hu, S. Liu and W. Lin, RSC Adv., 2012, 2, 2576–2580.
2
magnetic eld from the reaction system and reused for at 14 (a) A. Bezaatpour, M. Behzad, V. Jahed, M. Amiri,
least 5 times without signicant decrease in conversion. Our
Y. Mansoori, Z. Rajabalizadeh and S. Sarvi, React. Kinet.,
Mech. Catal., 2012, 107, 367–381; (b) M. Bagherzadeh and
M. Zare, Coord. Chem., 2013, 66, 2885–2900.
novel catalyst showed higher catalytic activity than the other
3
0–39
Mo(VI) complexes reported in literature.
The illustrated
superparamagnetic catalyst shows excellent conversion (97%) 15 C. Baleiz ˜a o, B. Gigante, D. Das, M. A´ lvaro, H. Garcia and
in 30 min.
A. Corma, Catalysis, 2004, 223, 106–113.
16 C. A. McNamara, M. J. Dixion and M. Bradely, Chem. Rev.,
2
002, 102, 3275–3300.
Acknowledgements
1
7 H. V. Bekkum and J. C. Vander Waal, J. Mol. Catal. A: Chem.,
1997, 124, 137–146.
Authors are grateful to the Research Council of Mohaghegh-e-
Ardabili University for their nancial support.
18 S. Imamura, H. Sakai, M. Shono and H. Kanai, Catalysis,
998, 177, 72–81.
9 Y. S. Lin and C. L. Haynes, Chem. Mater., 2009, 21, 3979–
986.
1
1
Notes and references
3
1
(a) K. A. Srinivas, A. Kumar and S. M. S. Chauhan, Chem. 20 M. Mahmoudi, S. Sant, B. Wang, S. Laurent and T. Sen, Adv.
Commun., 2002, 2456–2457; (b) M. R. dos Santos,
Drug Delivery Rev., 2011, 63, 24–46.
J. R. Diniz, A. M. Arouca, A. F. Gomes, F. C. Gozzo, 21 M. Sevilla, T. Vald ´e s-Solis, P. Tartaj and A. B. Fuertes, J.
S. M. Tamborim, A. L. Parize, P. A. Z. Suarez and Colloid Interface Sci., 2009, 340, 230–236.
B. A. D. Neto, ChemSusChem, 2012, 5, 716–726; (c) 22 T. Joseph, D. Srinivas, C. S. Gopinath and S. B. Halligudi,
D. M. Boghaei, A. Bezaatpour and M. Behzad, J. Mol. Catal.
A: Chem., 2006, 245, 12–16; (d) J. Rahchamani, M. Behzad,
Catal. Lett., 2002, 83, 209–214.
27458 | RSC Adv., 2016, 6, 27452–27459
This journal is © The Royal Society of Chemistry 2016

View Article Online
Paper
RSC Advances
2
3 Z. G. Peng, K. Hidajat and M. S. Uddin, J. Colloid Interface 33 M. Herbert, F. Montilla and A. Galindo, J. Mol. Catal. A:
Sci., 2004, 271, 277–283. Chem., 2011, 338, 111–120.
4 L. Chen, B. Li and D. Liu, Catal. Lett., 2014, 144, 1053–1061. 34 A. Sakthivel, Y. Sakthivel, F. M. Pedro, A. S. T. Chiang and
2
2
5 A. Z. El-Sonbati, A. A. El-Bindary and I. G. Rashed,
Spectrochim. Acta, Part A, 2002, 58, 1411–1424.
F. E. Kuhn, Appl. Catal., A, 2005, 281, 267–273.
35 M. Masteri-Farahani, F. Farzaneh and M. Ghandi, J. Mol.
Catal. A: Chem., 2006, 248, 53–60.
2
2
2
2
6 W. E. Hill, N. Atabay, C. A. McAuliffe, F. P. McCullough and
S. M. Razzoki, Inorg. Chim. Acta, 1979, 35, 35–41.
36 S. Shylesh, J. Schweizer, S. Demeshko, V. Sch u¨ nemann,
S. Ernst and W. R. Thiel, Adv. Synth. Catal., 2009, 351,
1789–1795.
7 N. Gharah, S. Chakraborty, A. K. Mukherjee and
R. Bhattacharyya, Inorg. Chim. Acta, 2009, 362, 1089–1100.
8 M. Bagherzadeh, M. Zare, V. Amani, A. Ellern and L. K. Woo, 37 M. Mohammadikish and M. Masteri-Farahani, J. Magn.
Polyhedron, 2013, 53, 223–229. Magn. Mater., 2014, 354, 317–323.
9 F. E. K u¨ hn, M. Groarke, E. Bencze, E. Herdtweck, A. Prazeres, 38 Y. Shokouhimehr, J. Piao, Y. Kim and M. Jang, Angew. Chem.,
A. M. Santos, M. J. Calhorda, C. C. Rom ˜a o, I. S. Gonçalves,
2007, 119, 7169–7176.
A. D. Lopes and M. Pillinger, Chem.–Eur. J., 2002, 8, 2370– 39 Y. Li, X. Fu, B. Gong, X. Zou, X. Tu and J. Chen, J. Mol. Catal.
383. A: Chem., 2010, 322, 55–62.
0 G. Wahl, D. Kleinhenz, A. Schorm, J. Sundermeyer, 40 I. V. Yudanov, C. D. Valentin, P. Gisdakis and N. Rosch, J.
2
3
R. Stowasser, C. Rummey, G. Bringmann, C. Fickert and
W. Kiefer, Chem.–Eur. J., 1999, 5, 32–37.
1 M. Quenard, V. Bonmarin and G. Gelbard, Tetrahedron Lett.,
Mol. Catal. A: Chem., 2000, 158, 189–197.
41 M. Bagherzadeh, M. Amini, H. Parastar, M. Jalali-Heravi,
A. Ellern and L. K. Woo, Inorg. Chem. Commun., 2012, 20,
86–89.
3
3
1987, 28, 2237–2238.
´
2 M. Herbert, F. Montilla, R. Moyano, A. Pastor, E. Alvarez and
A. Galindo, Polyhedron, 2009, 28, 3929–3934.
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