New magnetic supported hydrazone Schiff base dioxomolybdenum (VI) complex: An efficient nanocatalyst for epoxidation of cyclooctene and norbornene

Article abstract of DOI:10.1002/aoc.4459

A new dioxomolybdenum (VI) complex with tridentate hydrazone Schiff base ligand (H₂L) derived from 2-hydroxy-5-nitrobenzaldehyde and benzhydrazide was synthesized and designated as [MoO₂L (DMF)]·2H₂O. The Fe₃O₄@SiO₂-CPS-L-MoO₂ (EtOH) nanocatalyst was successfully prepared by grafting H₂L ligand on modified Fe₃O₄ nanoparticles followed by reacting with MoO₂ (acac)₂. The complex and nanocatalyst were characterized by various techniques such as elemental analysis, mass, FT-IR, UV–Vis, ¹H NMR, ¹³C{¹H}-NMR, TGA, XRD, XPS, TEM, SEM and VSM. The catalytic activity of [MoO₂L (DMF)]2H₂O and Fe₃O₄@SiO₂-CPS-L-MoO₂ (EtOH) were evaluated for the oxidation of various alkenes (cyclooctene, norbornene, cyclohexene, styrene and α-methyl styrene) in the presence of tert-butylhydroperoxide as oxidant. The results revealed that the catalysts were especially efficient for oxidation of cyclooctene and norbornene with 100% selectivity towards corresponding epoxide product. Fe₃O₄@SiO₂-CPS-L-MoO₂ (EtOH) showed higher catalytic activity, shorter reaction time and higher turnover number (TON) compared with homogeneous complex [MoO₂L (DMF)]·2H₂O. Moreover, simple magnetic recovery from the reaction mixture and reuse for several times with no significant loss in activity were other advantages of the nanocatalyst.

Full text of DOI:10.1002/aoc.4459

Received: 28 February 2018
DOI: 10.1002/aoc.4459
Revised: 9 May 2018
Accepted: 13 May 2018
F U L L P A P E R
New magnetic supported hydrazone Schiff base
dioxomolybdenum (VI) complex: An efficient nanocatalyst
for epoxidation of cyclooctene and norbornene
Marzieh Sarkheil | Maryam Lashanizadegan
Department of Chemistry, Faculty of
A new dioxomolybdenum (VI) complex with tridentate hydrazone Schiff base
ligand (H2L) derived from 2‐hydroxy‐5‐nitrobenzaldehyde and benzhydrazide
was synthesized and designated as [MoO2L (DMF)]·2H2O. The Fe3O4@SiO2‐
CPS‐L‐MoO2 (EtOH) nanocatalyst was successfully prepared by grafting H2L
ligand on modified Fe3O4 nanoparticles followed by reacting with MoO2
(acac)2. The complex and nanocatalyst were characterized by various tech-
Physics and Chemistry, Alzahra
University, P. O. Box 1993893973 Tehran,
Iran
Correspondence
Maryam Lashanizadegan, Department of
Chemistry, Faculty of Physics and
Chemistry, Alzahra University P. O. Box
1993893973, Tehran, Iran.
niques such as elemental analysis, mass, FT‐IR, UV–Vis, H NMR, 13C{1H}‐
1
Email: m_lashani@alzahra.ac.ir
NMR, TGA, XRD, XPS, TEM, SEM and VSM. The catalytic activity of [MoO2L
(DMF)]2H2O and Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) were evaluated for the
oxidation of various alkenes (cyclooctene, norbornene, cyclohexene, styrene
and α‐methyl styrene) in the presence of tert‐butylhydroperoxide as oxidant.
The results revealed that the catalysts were especially efficient for oxidation
of cyclooctene and norbornene with 100% selectivity towards corresponding
epoxide product. Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) showed higher catalytic
activity, shorter reaction time and higher turnover number (TON) compared
with homogeneous complex [MoO2L (DMF)]·2H2O. Moreover, simple mag-
netic recovery from the reaction mixture and reuse for several times with no
significant loss in activity were other advantages of the nanocatalyst.
Funding information
Alzahra University
KEYWORDS
alkene, hydrazone ligand, magnetic nanoparticles, Mo complex, oxidation catalyst
1 | INTRODUCTION
synthesized and used in Mo coordination.[6–9] Among
various ligands, hydrazones, particularly acyl and aroyl
Catalytic oxidation of alkenes is of great interest in chem-
ical industries and laboratory researches due to produc-
tion of several valuable chemical intermediates and fine
chemicals.[1] During recent decades, inspired of enzy-
matic role of molybdenum in biological systems such as
oxotransferases (Xanthine oxidase, sulfite oxidase and
DMSO reductase),[2–5] significant attempts have been
made to design various biomimetic Mo complexes as oxi-
dation catalysts. In this regard, a number of ligands with
N, O and S donor atoms which mimic proteins were
hydrazones (‐CO‐NH‐N=CRR′; R and R′: H, alkyl, aryl)
have attracted grate attention owing to their facile syn-
thesis, structural diversities and chemical and biological
activities.[10] These ligands contain amide (HN‐C=O)
moiety which gives them the possibility of enol‐keto tau-
tomerism providing the ligands coordinate the metal ions
via neutral or anionic forms. Since hydrazone ligands can
induce various coordination numbers and geometries
around metal center, they can react with a wide variety
of transition metal ions.[11–17] The hydrazone transition
Appl Organometal Chem. 2018;e4459.
wileyonlinelibrary.com/journal/aoc
Copyright © 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4459

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SARKHEIL AND LASHANIZADEGAN
metal complexes have become increasingly popular class
of complexes not only for their catalytic properties,[18–20]
but also for their usage in various fields such as pharma-
cology,[10,21] sensors,[22,23] nonlinear optics[24] and
electrochromism.[25]
Perkin‐Elmer, Waltham, MA, USA. The amount of
molybdenum of the catalyst was determined by ICP‐
OES instrument (Varian, Vista‐Pro, Australia). X‐ray dif-
fraction patterns were recorded on a Philips X'Pert dif-
fractometer operated at 40 kV voltage and 30 mA
current using Cu Kα radiation (λ = 1.54 Å) in the 2θ
range 10–70° with step size of 0.02°/s. The 1H‐NMR
and 13C{1H]‐NMR spectra were recorded on the Bruker
DRX 500 and 125 MHz spectrometers, respectively.
Also, DMSO‐d6 and tetramethylsilane (TMS) were used
as the solvent and internal reference, respectively. Scan-
ning electron microscopy (SEM) images were obtained
using a KYKY‐EM3200 microscope. Transmission elec-
tron microscopy (TEM) image was taken by Zeiss
EM10C electron microscope. Magnetic properties were
taken on a vibrating sample magnetometer (VSM)
(BHV‐55, Riken, Japan) in the magnetic field range of
−8000 Oe to +8000 Oe at room temperature. The UV–
Vis absorption spectra were recorded on a Perkin‐Elmer
Lambda 35 spectrophotometer. XPS analysis was per-
formed on a Thermo Scientifi, ESCALAB 250 Xi with
Mg X‐ray resource. Thermogravimetric analyses (TGA)
were recorded on a TGA/DSC1 (Mettler Toledo). The
mass spectrum of the complex was obtained with an
HP (Agilent Technolgies) 593 Mass Selective Detector.
The oxidation products were analyzed by GC and GC–
mass spectrometry using an Agilent 6890 Series with a
FID detector, an HP‐5% phenylmethylsiloxane capillary
and an Agilent 5973 Network, mass selective detector,
HP‐5MS 6989 Network GC system, respectively.
It is well known that Mo (VI) complexes are useful
homogeneous catalysts for oxidation of alkenes.[26–29]
Despite the high catalytic potential of homogeneous cata-
lysts, they suffer from some disadvantages involving diffi-
culty in separation and recycling, instability at high
temperature and deactivation of the catalyst through for-
mation of oxo‐bridges by dimerization. To solve these
drawbacks which make them inappropriate for industrial
applications, attention is focused on the heterogenization
of homogeneous catalysts onto/in solid supports, such as
zeolites,[30–34] multi‐walled carbon nanotubes,[35,36]
boehmite,[37,38] polymers[39–44] and graphene oxide.[45–47]
The methods such as filtration and centrifugation which
are used to separate the heterogeneous catalysts from
the reaction mixture are time‐consuming and low effi-
cient. Recently, to avoid these problems, magnetic nano-
particles which are easily separated by an external
magnet are widely used as solid supports.
However, agglomeration of magnetic nanoparticles
causes the surface of them to be protected by inert mate-
rials such as carbon, silica and polymer. Among different
inert material, silica is an appropriate choice that not
only prevents aggregation and improves chemical and
thermal stability but also provides silanol groups for fur-
ther functionalization.[48–51] Regarding the application
of magnetically separable catalysts, there are several
reports that investigate the catalytic role of immobilized
Mo complex on magnetic nanoparticles in the oxidation
of alkenes.[52–56]
2.2 | Preparation of ligand (H2L)
An ethanolic solution (10 ml) of 2‐hydroxy‐5‐
nitrobenzaldehyde (334 mg, 2 mmol) was added dropwise
to an ethanolic solution (10 ml) of benzhydrazide
(272 mg, 2 mmol). The resulting mixture was refluxed
for about 1 hr (Scheme 1). Finally, the precipitate of the
ligand was recovered by filtration and washed several
times with absolute ethanol and dried. Yield 96%. m.p.
300 °C. FT‐IR (KBr pellet, cm−1): 1606 (C=N), 1633
(C=O), 3302 (NH2). UV–Vis (ethanol) (λmax, nm (ɛ, M
According to this background, in this study, we report
the synthesis and characterization of
a
new
dioxomolybdenum complex with tridentate hydrazone
Schiff base ligand ((2‐hydroxy‐5‐nitrobenzylidene)
benzhydrazide), followed by immobilization on the mod-
ified Fe3O4 nanoparticles. The catalytic activities of both
homogeneous and heterogeneous catalysts in the oxida-
tion of various alkenes are evaluated.
−1
cm−1)): 206 (21237), 221 (sh), 318 (21676), 378 nm
1
(14691). H NMR (500 MHz, DMSO‐d6, δ, ppm): 7.09–
2 | EXPERIMENTAL
8.58 (8H, m, Ar‐H), 8.73 (1H, s, HC=N), 12.25 (2H, s,
NH, OH). 13C{1H}‐NMR (125 MHz, DMSO‐d6, δ, ppm):
118–145.27 (Ar‐C), 163.5 (C=N), 163.98 (CO).
2.1 | Materials and instrumentation
Solvents and starting materials were purchased from
Acros Organics, Merck or Sigma‐Aldrich and were used
without further purification. The IR spectra (KBr discs,
500–4000 cm−1) were recorded using a Bruker FTIR
model Tensor 27 spectrometer. The elemental analyses
were realized in a 2400 Series II CHN analyzer,
2.3 | Preparation of complex ([MoO2L
(DMF)]·2H2O)
The complex was prepared by adding a DMF solution
(5 ml) of MoO2 (acac)2 (328 mg, 1 mmol) to a DMF

SARKHEIL AND LASHANIZADEGAN
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SCHEME 1 Preparation of [MoO2L
(DMF)]·2H2O complex
solution (5 ml) of ligand H2L (285 mg, 1 mmol). The
resulting mixture was refluxed for about 4 h. The mixture
was kept in air to allow the solvent to evaporate, whereby
the yellow solid of the complex were obtained (Scheme 1).
Yield 55%. d.p. > 310 °C. Anal. Calc. for C17H20N4O9Mo:
C, 39.23; H, 3.84; N, 10.76; Mo, 18.46%. Found: C, 38.84;
H, 4.19; N, 10.49; M, 18.79%. FT‐IR (KBr pellet, cm−1):
1614 (C=N), 1651 (C=O), 920, 940 (Mo = O). UV–Vis
(ethanol) (λmax, nm (ɛ, M−1 cm−1)): 202 (18657), 226
(sh), 286 (13672), 366 (12649), 400 (10981). 1H NMR
(500 MHz, DMSO‐d6, δ, ppm): 2.71 (3H, s, CH3 of
DMF), 2.81 (3H, s, CH3 of DMF), 7.93 (1H, HCO of
DMF), 7.14–8.79 (8H, m, Ar‐H), 9.14 (1H, s, HC=N).
13C{1H}‐NMR (125 MHz, DMSO‐d6, δ, ppm): 31.37,
36.39, 162.93 (DMF), 120.81–141.50 (Ar‐C), 164.57
(C=N), 170.01 (CO).
(5 ml). After refluxing under N2 atmosphere for 48 hr,
the resultant material (Fe3O4@SiO2‐CPS‐L) was washed
with DMF and ethanol and then dried at 60 °C for
10 hr. Finally, Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) was pre-
pared by the treatment of Fe3O4@SiO2‐CPS‐L (100 mg)
with an ethanolic solution of (15 ml) MoO2 (acac)2
(262 mg, 0.8 mmol). The mixture was then refluxed under
Nitrogen atmosphere for 24 hr (Scheme 2). The resulting
nanocatalyst was magnetically separated, washed several
times with absolute ethanol to remove unreacted molyb-
denum and dried at 60 °C for 10 hr.
2.5 | General procedure for the oxidation
of alkenes
All oxidation reactions were carried out in a 10 ml round
bottom flask equipped with a water condenser. In a typi-
cal procedure,
a
mixture of catalyst ([MoO2L
2.4 | Preparation of Fe3O4@SiO2‐CPS‐L‐
(DMF)]·2H2O complex (10 mg), Fe3O4@SiO2‐CPS‐L‐
MoO2 (EtOH) nanocatalyst (40 mg)), substrate (5 mmol),
solvent (1,2‐dichloroethane; 7 ml) and oxidant (TBHP,
70% in H2O (20 mmol)) was refluxed for an appropriate
time. The applicable reaction time for ([MoO2L
(DMF)]·2H2O and Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) cat-
alysts were 8 hr and 4 hr, respectively. At the end of the
reaction, the catalyst was magnetically collected and the
reaction mixture was analyzed by GC and GC–MS. Con-
version of substrates was calculated from GC data and
the oxidation products were identified by GC–MS results.
MoO2 (EtOH)
Fe3O4 magnetic nanoparticles were synthesized by the co‐
precipitation technique according to the published proce-
dure.[57] Next, Fe3O4 was covered with silica layer from
tetraethyl orthosilicate as source of silica to form core‐
shell Fe3O4@SiO2 structure under alkaline conditions.
Grafting of chloro groups on the surface of Fe3O4@SiO2
was
carried
out
by
refluxing
3‐
chloropropyltrimethoxysilane (CPS; 0.8 mmol, 0.14 ml)
with the suspension of Fe3O4@SiO2 (100 mg) in dry tolu-
ene (15 ml) under nitrogen atmosphere for 48 hr. The
resultant material (Fe3O4@SiO2‐CPS) was successively
washed with toluene and ethanol, and then dried at
60 °C for 10 hr.[58] Afterward, a DMF solution (10 ml)
of ligand H2L (227 mg, 0.8 mmol) was added to a
suspended solution of Fe3O4@SiO2‐CPS (0.1 g) in DMF
3 | RESULTS AND DISCUSSION
The H2L ligand was prepared by the condensation of 2‐
hydroxy‐5‐nitrobenzaldehyde with benzhydrazide. Then,

4 of 13
SARKHEIL AND LASHANIZADEGAN
SCHEME 2 Preparation steps of
Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH)
nanocatalyst
the reaction of H2L with MoO2 (acac)2 in N,N‐
dimethylformamide (DMF) gave [MoO2L (DMF)]·2H2O
complex (Scehme 1). The magnetically recoverable
Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) nanocatalyst was pre-
pared by grafting the ligand on modified Fe3O4 nanopar-
ticles followed by reacting with MoO2 (acac)2 (Scheme 2).
NMR spectra of the complex can be ascribed to the car-
bon atoms of coordinated DMF molecule.[60] These
observations confirm the proposed structure for the
ligand and complex (Scheme 1).
The FT‐IR spectra of free H2L and complex [MoO2L
(DMF)]·2H2O are shown in Figure 1. Free H2L displays
three bands at 1606, 1636 and 3302 cm−1 due to ν
(C=N), ν (C=O) and ν (NH), respectively.[59,61] The
absence of bands at 3302 (ν (NH)) and 1636 (ν (C=O))
cm−1 in the spectrum of the complex confirms that free
H2L exists in the keto form while in the complex, it coor-
dinates to the Mo center in the deprotonated enolate
form.[19] In the IR spectrum of the complex, the C=N
moiety shifts to higher wavenumber (1614 cm−1), indicat-
ing the involvement of azomethine nitrogen in
3.1 | Characterization of H2L and [MoO2L
(DMF)]·2H2O
The 1H NMR and 13C{1H}‐NMR spectra of the ligand
(H2L) and complex ([MoO2L (DMF)]·2H2O) are pre-
sented in Figures S1‐S4 (see supporting information).
1
In the H NMR spectrum of H2L, the sharp signal at
8.73 ppm is assigned to the azomethine proton
(HC=N) which is shifted downfield (9.14 ppm) in the
complex. This shift can be attributed to the involvement
of azomethine nitrogen in the coordination. Also in the
spectrum of free H2L, the phenolic OH and NH protons
are seen at 12.25 ppm. As seen in the Figure S2, the
spectrum of the complex dose not display any signals
corresponding to the phenolic OH and NH protons,
revealing that the ligand is coordinated to the Mo ion
as di‐negative ligand.[59] In the spectrum of [MoO2L
(DMF)]·2H2O complex, the peaks appearing at 2.71
(CH3), 2.78 (CH3) and 7.93 (HCO) indicate the coordina-
tion of DMF molecule to the metal center.[60] The aro-
matic protons of the ligand and complex are observed
as multiplets in the range 7.09–8.79 ppm. A comparison
of the 13C{1H}‐NMR spectra of the ligand with that of
complex shows Δδ for carbon atoms of azomethine and
phenolate which is due to their involvement in coordina-
tion. Also, the new peaks appearing at 31.37 (CH3),
36.39 (CH3) and 162.93 (HCO) ppm in the 13C{1H}‐
FIGURE 1 FT‐IR spectra of (a) ligand H2L, (b) complex [MoO2L
(DMF)]·2H2O

SARKHEIL AND LASHANIZADEGAN
5 of 13
TGA analysis of [MoO2L (DMF)]·2H2O complex was
carried out within a temperature range from 25 up to
700 °C (Figure 2, Table 1). TGA curve shows that the
complex decomposes in five steps. Removal of two mole-
cules of water (hydration) and coordinated DMF mole-
cule is occurred during first (30–120 °C) and second
(120–240 °C) steps (2H2O and DMF; obs.: 20.30%, calcd.:
20.96%). The third step appears in the range 240–
380 °C, revealing the decomposition of a part of the
ligand (C7N2O3H; obs.: 31.35%, calcd.: 31.53%). Then,
the remaining of the ligand (C7NOH5) is removed during
fourth (380–575 °C) and fifth (575–700 °C) steps (obs.:
22.58%, calcd.: 22.84%) and the residue is estimated to
be MoO2. The TGA results confirm the proposed struc-
ture of the complex.
FIGURE 2 TGA curves of complex [MoO2L (DMF)]·2H2O
coordination to the metal center.[59,61] Also, the new band
appears at 1663 cm−1 is assigned to the carbonyl
stretching vibration of the coordinated DMF mole-
cule.[62–64] In addition, two characteristic bands due to
the symmetric and asymmetric stretching modes of cis‐
3.2 | Characterization of Fe3O4@SiO2‐CPS‐
L1‐MoO2 (EtOH)
MoO2 are observed at 920 and 940 cm−1 [17]
.
The FT‐IR spectra of Fe3O4, Fe3O4@SiO2, Fe3O4@SiO2‐
CPS, H2L, Fe3O4@SiO2‐CPS‐L and Fe3O4@SiO2‐CPS‐L‐
MoO2 (EtOH) before and after using as catalyst are
depicted in Figure 3. In the FT‐IR spectrum of Fe3O4
(Figure 3a), observation of the bands at 587 and 631 cm
The electronic absorption spectra of the ligand and
the Mo complex in ethanol are illustrated in Figure S5.
In the spectrum of H2L, the bands appearing at 206 and
221 nm can be attributed to the π‐π* transitions of the
aromatic rings. Also, the other bands which observed at
318 and 387 nm may be related to π‐π* and n‐π* transi-
tions of the azomethine and amide moieties of the
ligand.[19] Comparison of the absorption bands of the
complex with that of free ligand shows a shift, indicating
the chelation of the ligand. In the spectrum of complex,
the band appearing at 400 nm is probably due to ligand
to metal charge transfer (LMCT) (O (p) → Mo (d)).[19,65]
The absence of d‐d transition bands in the visible region
verifies that the Mo center has 4d0 electronic configura-
tion (Mo (VI)).[66]
The mass spectrum of [MoO2L (DMF)]·2H2O complex
(Figure S6) shows the mass at m/z 520 corresponding to
the formula [MoO2L (DMF)]·2H2O. Observation of this
mass which is in agreement with elemental analysis con-
firms the suggested structure of the complex. The frag-
ments appearing at m/z 304, 135, 73 and 46 can be
attributed to the formulas of MoO2C7H4 (DMF),
C7N2OH5, DMF and NO2, respectively. The structures of
these fragments are illustrated in Figure S6.
−1
should be attributed to Fe‐O vibrations.[67] Also, the
band appearing at 3417 cm−1 corresponds to adsorbed
water or FeOH groups of the surface. As seen in
Figure 3b, the bands existing at around 1086 and
816 cm−1 due to Si‐O‐Si asymmetric and symmetric vibra-
tions corroborate the presence of SiO2 shell on the surface
of the Fe3O4 nanoparticles. Functionalization of
Fe3O4@SiO2 with 3‐chloropropyltrimethoxysilane reveals
new bands at 2856 and 2926 cm−1 which due to C‐H
stretching vibrations[58] (Figure 3c). After the reaction of
ligand H2L with Fe3O4@SiO2‐CPS, the bands displaying
at 1605 and 1642 cm−1 are ascribed to C=N and C=O
vibrations of ligand H2L (Figure 3e). Observation of these
bands indicates that H2L was successfully anchored on
the surface of Fe3O4@SiO2‐CPS. The NH stretching of
the free ligand displaying at 3302 cm−1 disappeared in
the spectrum of Fe3O4@SiO2‐CPS‐L due to the ligand
binding to the Fe3O4@SiO2‐CPS via the N atom of the
amide group.[68] Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) shows
two characteristic bands at 923 and 943 cm−1 which can
TABLE 1 TGA results for decomposition of complex [MoO2L (DMF)]·2H2O
Weight loss (%)
Calc.
Temperature
range (°C)
Removed
fragment
Compound
Steps
Obs.
Residue
[MoO2L (DMF)]·2H2O
1 + 2
3
4 + 5
30–240
240–380
380–700
2 H2O, DMF
C7N2O3H4
C7NOH5
20.96
31.53
22.84
20.30
31.35
22.58
MoO2

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SARKHEIL AND LASHANIZADEGAN
FIGURE 4 XRD patterns of (a) Fe3O4, (b) Fe3O4@SiO2 and (c)
Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) before using and (g) after using
as catalyst
Figure 4a, the peak positions and their relative intensi-
ties in XRD pattern of prepared Fe3O4 are in accordance
with the standard Fe3O4 XRD spectrum (JCPDS No. 75–
0033). The XRD patterns of Fe3O4@SiO2 and
Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) in comparison to that
of Fe3O4 exhibit the similar characteristic peaks with
change in intensities (Figure 4b and c). This indicates
the crystal structure of the Fe3O4 core is not destroyed
during surface modification of it. Also, the change in
the peak intensities can be ascribed to the shielding
effect of layer on magnetite core. According to the
Debye‐Scherer equation, the average crystallite size of
Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2‐CPS‐L‐MoO2
(EtOH) is estimated to be around 11.7, 13.1 and
14.1 nm, respectively.
TGA curves of Fe3O4@SiO2, Fe3O4@SiO2‐CPS,
Fe3O4@SiO2‐CPS‐L
and
Fe3O4@SiO2‐CPS‐L‐MoO2
(EtOH) are shown in Figure 5. In these curves, the weight
loss below 200 °C can be attributed to removal of
adsorbed water molecules. In the case of Fe3O4@SiO2‐
CPS, Fe3O4@SiO2‐CPS‐L and Fe3O4@SiO2‐CPS‐L‐MoO2
(EtOH), the weight decrease in the temperature range
200–700 °C is owing to decomposition of organic groups.
Based on the TGA data, the amount of organic groups
loading on the surface of Fe3O4@SiO2‐CPS,
FIGURE 3 FT‐IR spectra of (a) Fe3O4, (b) Fe3O4@SiO2, (c)
Fe3O4@SiO2@CPS, (d) ligand H2L, (e) Fe3O4@SiO2@CPS‐L, (f)
Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) before using and (g) after using
as catalyst
Fe3O4@SiO2‐CPS‐L
and
Fe3O4@SiO2‐CPS‐L‐MoO2
(EtOH) is approximately 13.59, 20.64 and 25.63%,
respectively.
The energy dispersive X‐ray spectrum of Fe3O4@SiO2‐
CPS‐L‐MoO2 (EtOH) (Figure S7) indicates the presence of
expected elements such as Mo, Si, Fe, N, C, Cl and O.
According to the data obtained from ICP‐OES, the Mo
be assigned to symmetric and asymmetric vibrations of
Mo = O[69] (Figure 3f).
The XRD patterns of Fe3O4, Fe3O4@SiO2 and
Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) before and after using
as catalyst are illustrated in Figure 4. As indicated in

SARKHEIL AND LASHANIZADEGAN
7 of 13
FIGURE 5 TGA curves of (a) Fe3O4@SiO2, (b) Fe3O4@SiO2‐CPS,
(c) Fe3O4@SiO2‐CPS‐L, (d) Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH)
content is 1.15% (0.12 mmol g−1). These are other data
that confirm the existence of molybdenum complex on
modified Fe3O4.
The TEM image of Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH)
(Figure 6) shows the core‐shell structure of it by revealing
the Fe3O4 cores as dark spots embedded in bright SiO2‐
CPS‐L‐MoO2 (EtOH) shells. Also, the average size of
nanoparticles is estimated around 17 nm which is in
agreement with the result obtained from XRD. The sur-
face morphologies of Fe3O4, Fe3O4@SiO2 and
Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) before and after using
as catalyst were characterized by SEM (Figure 7). As seen
in Figure 7, these compounds have spherical morphology.
The magnetic properties of Fe3O4 and Fe3O4@SiO2‐
CPS‐L‐MoO2 (EtOH) before and after using as catalyst
were measured by VSM. As shown in Figure 8, these
nanoparticles have good magnetic properties and show
no remanence effect (superparamagnetic property). The
magnetic saturation value of Fe3O4@SiO2‐CPS‐L‐MoO2
(EtOH) (41 emu g−1) is less than that of Fe3O4
(65 emu g−1). This reduction is probably due to the exis-
tence of some organic matter on the surface of magnetic
core. Despite the decrease in magnetic saturation value
of Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH), this value is still
FIGURE 7 SEM images of (a) Fe3O4, (b) Fe3O4@SiO2 and (c)
Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) before using and (d) after using
as catalyst
FIGURE 6 TEM image of Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH)

8 of 13
SARKHEIL AND LASHANIZADEGAN
in this catalyst (Figure S8). As seen in Figure 9a, two
major peaks with the binding energy at 235.3 and
235.2 eV are related to Mo 3d5/2 and Mo 3d3/2, respec-
tively, which revealed an oxidation state of Mo6 + .[70]
The XPS spectrum of C 1 s shows the peaks at 284.4,
285.9 and 291.8 eV, which can be attributed to C=C,
C=N and CO bonds, respectively[31,71] (Figure 9b). Also,
the peak for N 1 s appears at 397.9 eV. This peak may
be ascribed to N‐N=C.[71] In addition, XPS results show
1.15% loading of Mo on the surface of nanoparticles. This
result is in good agreement with the ICP result (1.15%
Mo). These observations confirm the supporting of Mo
complex on the surface of nanoparticles.
FIGURE
8
Magnetization curves of (a) Fe3O4 and (b)
Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) before using and (c) after using
as catalyst
3.3 | Catalytic study
The catalytic performance of [MoO2L (DMF)]·2H2O and
Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) for oxidation of
alkenes with TBHP were investigated. In search of opti-
mum reaction conditions, the influence of various factors
such as reaction time, solvent, the amount of oxidant and
catalyst were studied. Also, a series of blank experiments
(Tables S1 and S2) were conducted to evaluate the role of
catalyst and oxidant in the reaction. Based on these
experiments, it can be figured out that the presence of
both catalyst and oxidant is necessary for an effective cat-
alytic performance.
high enough to permit it efficiently separated from solu-
tion with an external magnet. Also after removal of the
magnetic field, Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) is rap-
idly redispersed.
To investigate the formation of Fe3O4@SiO2‐CPS‐L‐
MoO2 (EtOH), XPS technique was used. Based on this
analysis, the presence of C, N, O, Si and Mo are verified
3.3.1 | Catalytic study of [MoO2L
(DMF)]·2H2O
The effect of reaction time on the oxidation of
cyclooctene catalyzed by [MoO2L (DMF)]·H2O complex
is given in Figure 10. As seen in Figure 10, the best reac-
tion time is 8 h. Also, a variety of solvents including 1,2‐
dichloroethane, chloroform, acetonitrile, ethanol and N,
N‐dimethylformamide were examined for oxidation of
cyclooctene (Table 2). It was found that the highest
FIGURE 10 The influence of time on the cyclooctene oxidation;
Reaction condition: cyclooctene (5 mmol), [MoO2L (DMF)]·2H2O
(10 mg), TBHP (20 mmol), acetonitrile (7 ml) and reflux
FIGURE 9 Deconvoluted XPS spectra of (a) Mo 3d and (b) C 1 s
for Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH)

SARKHEIL AND LASHANIZADEGAN
9 of 13
TABLE 2 The effect of solvent on the cyclooctene oxidation in the presence of [MoO2L (DMF)]·2H2Oa
Entry
Time (h)
Solvent
Conversionb (%)
Selectivity of epoxidec (%)
1
2
3
4
5
6
6
8
8
8
8
8
1,2‐Dichloroethane
1,2‐Dichloroethane
Acetonitrile
62
97
37
30
60
32
100
100
100
100
100
100
Ethanol
Chloroform
N,N‐Dimethylformamide
aReaction conditions: catalyst amount (10 mg), cyclooctene (5 mmol), TBHP (20 mmol), solvent (7 ml) and reflux.
bDetermined by GC.
cDetermined by GC–MS.
TABLE 3 Oxidation of different alkenes in the presence of [MoO2L (DMF)]·2H2Oa
Entry
Alkenes
Conversionb (%)
Major productc (Selectivity (%))
TONd/TOFe (h−1
)
1
2
3
4
5
Cyclooctene
Norbornene
Cyclohexene
Styrene
97
100
74
Cyclooctene epoxide (100)
Norbornene epoxide (100)
Cyclohexene epoxidef (75)
Benzaldehydeg (67)
253/32
260/33
192/24
117/29
250/31
45
α‐Methyl styrene
96
Acetophenoneh (55)
aReaction conditions: catalyst (10 mg), alkene (5 mmol), TBHP (20 mmol), 1,2‐dichloroethane (7 ml), time (8 hr) and reflux.
bDetermined by GC.
cDetermined by GC–MS.
dTON: moles of product converted per moles of metal in the catalyst.
eTOF: moles of product converted per moles of metal in the catalyst per unit time.
f1,2‐Cyclohexanediol (25%) was also identified.
g1,2‐Ethandiol,1‐phenyl (27%) and styrene epoxide (6%) were also identified.
h2‐Phenyl‐1,2‐propanediol (32%) and α‐methyl styrene epoxide (13%) were also identified as byproduct.
SCHEME 3 Proposed mechanism for
oxidation of cyclooctene with TBHP
catalyzed by [MoO2L (DMF)]·2H2O
conversion was obtained in 1,2‐dichloroethane. It may be
described by hard‐soft acid–base theory. Since solvents
such as acetonitrile, ethanol and N,N‐dimethylformamide
have hard atom donors (N and O), they tend to coordi-
nate strongly to the hard Mo (VI) ion. This causes a com-
petition between these solvents and TBHP in

10 of 13
SARKHEIL AND LASHANIZADEGAN
coordination to Mo (VI) center that results the significant
decrease in the conversion. While, the noncoordinative
chlorinated solvents such as 1,2‐dichloroethane and chlo-
roform can facilitate the coordination of TBHP to Mo (VI)
center followed by transfer of oxygen to alkene.[53]
To optimize the reaction time, the oxidation of
cyclooctene was performed within different times
(Figure 11). The results indicate that the highest
cyclooctene conversion is achieved within 4 h. The
effects of catalyst amounts (Table S5) and mole ratios
of TBHP to cyclooctene (Table S6) were also tested.
Based on the experimental results, the best catalyst per-
formance is obtained in the presence of 40 mg of the
catalyst and using TBHP and cyclooctene in a mole
ratio of 4:1 during 4 h.
The reusability of Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH)
was investigated for five consecutive runs (Figure 12).
At the end of reaction, the catalyst was magnetically sep-
arated, washed several times with acetonitrile and dried.
Then, the recovered catalyst was consecutively used
under optimized reaction conditions. It was found that
the conversion of cyclooctene oxidation slightly dropped
from 100 to 97% after five runs. Also, ICP‐OES analysis
shows the Mo content of Fe3O4@SiO2‐CPS‐L‐MoO2
(EtOH) before and after using as catalyst are 1.15 and
1.14 wt%, respectively.
To further assess the stability of Fe3O4@SiO2‐CPS‐L‐
MoO2 (EtOH), the FT‐IR spectra (Figure 3), XRD patterns
(Figure 4), SEM images (Figure 7) and VSM curves
(Figure 8) of it before and after using as catalyst were
evaluated. The results obtained from recycled catalyst in
comparison to that of fresh catalyst are similar. Thus,
these observations clearly confirm the reusability and sta-
bility of the catalyst.
In the next step, the catalytic potential of
Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) for the oxidation of
various alkenes such as cyclooctene, norbornene, cyclo-
hexene, styrene and α‐methyl styrene was evaluated
under the optimized conditions (Table 4). Based on the
obtained data, the heterogeneous catalyst exhibits high
catalytic performance in the alkene oxidation reaction.
A comparison of Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) with
[MoO2L (DMF)]·H2O and other heterogeneous molybde-
num catalysts is reported in Table 5. As seen,
Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) as a heterogeneous
catalyst shows higher activity, shorter reaction time and
The influences of amounts of catalyst and oxidant on
the oxidation reaction of cyclooctene were evaluated and
the results are given in Tables S3 and S4, respectively.
As indicated in these Tables, 10 mg of catalyst in the pres-
ence of TBHP and cyclooctene in a mole ratio of 4:1 is suf-
ficient to achieve the best conversion (97%) and selectivity
(100%) toward the formation of cyclooctene epoxide.
To investigate the catalytic application of [MoO2L
(DMF)]·2H2O in the oxidation reaction, the oxidation of
different alkenes including cyclooctene, norbornene,
cyclohexene, styrene and α‐methyl styrene was performed
under the optimized conditions. The results are given in
Table 3. As indicated, the catalyst plays a considerable role
in the oxidation reaction of alkenes. Aiming at studying the
reaction mechanism, the oxidation reaction of cyclooctene
was performed in the presence of diphenylamine as a rad-
ical scavenger.[72] It was observed that cyclooctene oxida-
tion was not inhibited in the presence of diphenylamine,
thus the reaction dose not proceed via a radical mecha-
nism. Based on the literature, the suggested mechanism
is depicted in Scheme 3. The oxidation of cyclooctene
seems to have occurred through transferring of TBHP pro-
ton to one of the terminal oxygen atoms of MoO2 group and
coordinating of t‐BuOO− anion to the molybdenum center.
In the next step, the nucleophilic attack of cyclooctene to
the oxygen of peroxo ligand leads to the formation
of epoxide (major product) and t‐butanol (byproduct).[53]
Catalytic study of Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH)
The oxidation of cyclooctene with TBHP as an oxidant
was examined as a model reaction in the presence of
Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) in 1,2‐dichloroethane.
FIGURE 11 The influence of time on the cyclooctene oxidation;
Reaction condition: cyclooctene (5 mmol), Fe3O4@SiO2‐CPS‐L‐
MoO2 (EtOH) (50 mg), TBHP (20 mmol), 1,2‐dichloroethane (7 ml)
and reflux
FIGURE 12 Recycling experiments of Fe3O4@SiO2‐CPS‐L‐MoO2
(EtOH) for oxidation of cyclooctene under optimized conditions

SARKHEIL AND LASHANIZADEGAN
11 of 13
TABLE 4 Oxidation of different alkenes in the presence of Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH)a
Entry
Alkenes
Conversionb (%)
Major prductc (Selectivity (%))
TONd/TOFe (h−1
)
1
2
3
4
5
Cyclooctene
Norbornene
Cyclohexene
Styrene
100
68
Cyclooctene epoxide (100)
Norbornene epoxide (100)
1,2‐Cyclohexanediolf (55)
Benzaldehydeg (76)
1042/260
708/177
563/141
740/185
885/221
54
71
α‐Methyl styrene
85
Acetophenoneh (49)
aReaction conditions: catalyst (40 mg), alkene (5 mmol), TBHP (20 mmol), 1,2‐dichloroethane (7 ml), time (4 hr) and reflux.
bDetermined by GC.
cDetermined by GC–MS.
dTON: moles of product converted per moles of metal in the catalyst.
eTOF: moles of product converted per moles of metal in the catalyst per unit time.
fCyclohexene epoxide (45%) was also identified.
gStyrene epoxide (34%) was also identified.
h2‐Phenyl‐1,2‐propanediol (36%) and α‐methyl styrene epoxide (11%) were also identified as byproduct.
TABLE 5 Comparison of catalytic activity of Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) with [MoO2L (DMF)]·H2O and different heterogeneous
Mo catalysts for the oxidation of alkenes
Catalyst
Substratea
Oxidant
Conversion (%)
TOF (h−1
)
Ref.
Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH)
[MoO2L (DMF)]·H2O
I/II/III/IV/V
I/II/III/IV/V
I/III
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
100/68/54/71/85
97/100/74/45/96
95/62
260/177/141/185/221
32/33/24/29/31
180/110
This study
This study
[73]
MoO2salpr/SCMNPs
[74]
[53]
[75]
[76]
UiO‐66‐Mo (CO)3‐L
I/III/IV
98/96/95
19/18/9
Fe3O4@SiO2/[MoO2L (HOCH3)]b
ZPS‐PVPA‐Mo complex
Mo‐DAPSH@APTES@SiO2
I/II/III/IV/V
I/III/IV
77/62/82/67/58
100/100/89
100/95
―
80/73/28
I/III
28/27
aI = cyclooctene, II = norbornene, III = cyclohexene, IV = styrene, V = α‐methyl styrene.
bHL = 2‐[2‐hydroxy‐benzylidene)‐amino]‐3‐(4‐hydroxy‐phenyl)‐propionic acid.
higher TON and TOF than [MoO2L (DMF)]·2H2O com-
plex as a homogeneous one. Other advantages of it are
easy recovery by external magnet and efficient reusability
for several times. Also compared to other systems, the
higher TOF of Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) should
be considerable.
possesses higher catalytic performance than homoge-
neous catalyst. Magnetically separation, recyclability and
high conversion and TON of the nanocatalyst candidates
Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH) as a useful catalyst for
oxidation of alkenes.
ACKNOWLEDGEMENTS
The financial support from Alzahra University is
acknowledged.
4 | CONCLUSION
A new homogeneous dioxomolybdenum (VI) catalyst was
prepared with the tridentate 2‐hydroxy‐5‐nitrobenzylidene)
benzhydrazide ligand and MoO2 (acac)2 designated as
[MoO2L (DMF)]·2H2O. Also, grafting the ligand on
modified Fe3O4 nanoparticles followed by reacting with
MoO2 (acac)2 afforded Fe3O4@SiO2‐CPS‐L‐MoO2 (EtOH)
nanocatalyst (Scheme 2).
Both catalysts were found to efficiently catalyze the
oxidation reaction of different alkenes in the presence of
TBHP as oxidant. The heterogeneous nanocatalyst
ORCID
Maryam Lashanizadegan
9492-3495
http://orcid.org/0000-0001-
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SUPPORTING INFORMATION
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