Covalent supporting of novel dioxo-molybdenum tetradentate pyrrole-imine complex on Fe3O4 as high-efficiency nanocatalyst for selective epoxidation of olefins

Article abstract of DOI:10.1002/aoc.3804

A novel Mo(VI) tetradentate Schiff base complex based on two pyrrole-imine donors was anchored covalently on Fe₃O₄ nanoparticles and characterized using physicochemical techniques. The catalytic epoxidation process was optimized in t

Full text of DOI:10.1002/aoc.3804

Received: 13 January 2017
DOI: 10.1002/aoc.3804
Revised: 9 February 2017
Accepted: 23 February 2017
F U L L PA P E R
Covalent supporting of novel dioxo‐molybdenum tetradentate
pyrrole‐imine complex on Fe3O4 as high‐efficiency nanocatalyst
for selective epoxidation of olefins
Shadab Akbarpour1 | Abolfazl Bezaatpour1*
| Elham Askarizadeh2* | Mandana Amiri1
1 Department of Chemistry, Faculty of Basic
Science, University of Mohaghegh Ardabili
179, Ardabil, Iran
2 Department of Applied Chemistry, Faculty
of Pharmaceutical Chemistry,
Pharmaceutical Science Branch, Islamic
Azad University, Tehran, Iran
A novel Mo(VI) tetradentate Schiff base complex based on two pyrrole‐imine donors
was anchored covalently on Fe3O4 nanoparticles and characterized using physico-
chemical techniques. The catalytic epoxidation process was optimized in terms of
the effects of solvent, reaction temperature, kind of oxidant and amount of oxidant
and catalyst. Then the novel heterogeneous nanocatalyst was used for the efficient
and selective catalytic epoxidation of internal alkenes (cyclohexene, cyclooctene,
α‐pinene, indene and trans‐1,2‐diphenylethene) and terminal alkenes (n‐heptene,
n‐octene, n‐dodecene and styrene) using tert‐butyl hydroperoxide (70% in water)
as oxidant in 1,2‐dichloroethane as solvent. The prepared nanocatalyst is very effec-
tive for the selective epoxidation of cis‐cyclooctene with 100% conversion, 100%
selectivity and turnover frequency of 1098 h−1 in just 30 min. The magnetic
nanocatalyst was easily recovered using an external magnetic field and was used sub-
sequently at least six times without significant decrease in conversion.
Correspondence
Abolfazl Bezaatpour, Department of
Chemistry, Faculty of Basic Science,
University of Mohaghegh, Ardabili 179,
Ardabil, Iran.
Email: bezaatpour@uma.ac.ir
Elham Askarizadeh, Department of Applied
Chemistry, Faculty of Pharmaceutical
Chemistry, Pharmaceutical Science Branch,
Islamic Azad University, Tehran, Iran.
Email: Elhamaskarizadeh@gmail.com
KEYWORDS
Funding Information
Research Council of Mohaghegh‐e‐Ardabili
University
epoxidation, molybdenum, nanocatalyst, pyrrole‐imine, Schiff base
1 | INTRODUCTION
challenge.[11] These problems may be solved by replacement
of homogeneous oxidation catalysts by environmental
The transformation of olefins into epoxides gives valuable
starting chemical materials for access to industrially impor-
tant products such as drugs, intermediates, surfactants and
epoxy resins.[1] Schiff base complexes of Mo(VI) have been
intensively used as catalysts for their advantages such as
being economic, stable, environmental friendly and commer-
cially available.[2–6] tert‐Butyl hydroperoxide (TBHP) is
widely used in a variety of epoxidation processes with good
thermal stability.[7–10] The recovery of a homogeneous cata-
lyst from a reaction mixture is often difficult, has high costs
and causes additional waste. Furthermore, insufficient chem-
ical and thermal stability, leaching of the active metal into the
solvent and recycling of the catalyst remain a scientific
friendly heterogeneous catalysts.[12] Therefore, the support
of metal complexes has been the subject of much research
in catalytic fields.[13–16]
One of the main ideas for supporting of metal complexes
is to anchor them onto large‐surface‐area inorganic materials
such as zeolites and metal oxides.[17–23] Nowadays, magnetite
nanoparticles are applied widely because of their unique
properties including the high surface area, low toxicity,
ability to be separated and biocompatibility.[24–30] Magnetic
separation makes the recycling of catalysts from solution
using external magnetic fields much easier than filtration
and centrifugation.
Following our previous research on the catalytic activity
of Schiff base complexes, herein we report the immobiliza-
tion of a novel dioxomolybdenum N4‐type Schiff base
* These authors contributed equally to this work.
Appl Organometal Chem. 2017;e3804.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.3804

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AKBARPOUR ET AL.
complex, derived from 9,9‐bis(5‐formylpyrrole‐2‐yl)
fluorene, onto the surface of amino‐modified magnetite
nanoparticles. The novel catalyst (Fe3O4@APTMS/
fluorene‐SB‐MoO2) was characterized using infrared (IR)
spectroscopy, scanning electron microscopy (SEM), trans-
mission electron microscopy (TEM), diffuse reflectance
spectroscopy (DRS), vibrating sample magnetometry
(VSM), energy‐dispersive X‐ray spectroscopy (EDX), pow-
der X‐ray diffraction (XRD) and X‐ray photoelectron spec-
troscopy (XPS), and examined for the epoxidation of
internal alkenes (cyclohexene, cyclooctene, α‐pinene,
indene and trans‐1,2‐diphenylethene) and terminal alkenes
(n‐heptene, n‐octene, n‐dodecene and styrene) with TBHP
(70% aqueous) as oxidant. The reusability of
Fe3O4@APTMS/fluorene‐SB‐MoO2 was also studied in
the epoxidation of cyclooctene with TBHP (70% in water)
in 1,2‐dichloroethane for six reaction cycles.
APTMS (2.5 ml) dissolved in 50 ml of ethanol was added
dropwise to the suspension of Fe3O4 (0.5 g) in ethanol
(50 ml). After 12 h of stirring of the mixture at 70°C, the
aminated magnetic nanoparticles were collected with an
external magnetic field and washed with water three times.
IR (KBr, cm−1): 3406 [ν(O─H)], 1004 [ν(Si─O─Si)], 582
[ν(Fe─O)].
2.3 | Preparation of 9,9‐Bis(5‐formylpyrrole‐
2‐yl)fluorene
9,9‐Bis(5‐formylpyrrole‐2‐yl)fluorene was prepared as
reported in the literature.[32] First, 7.2 ml of fresh pyrrole
was added to 3.9 g of 9‐fluorenone with stirring at 0–3°C.
After 10 min, trifluoroacetric acid (five drops) was added to
reaction system as catalyst and the reaction mixture was kept
at 0°C with stirring for 10 min. Then the reaction was stopped
with the addition of 38 ml of 0.1 M sodium hydroxide and the
temperature of mixture increased to ambient. The mixture
was extracted with CH2Cl2 and dried with magnesium sul-
fate. Vacuum removal of CH2Cl2 and excess regent gave
85% yield of 9,9‐bis(pyrrole‐2‐yl)fluorene. Subsequently,
2 | EXPERIMENTAL
2.1 | Chemicals and measurements
9‐Flourenone, pyrrole, trifluoroacetic acid, phosphoryl
chloride, N,N′‐dimethylformamide, styrene, cyclohexene, α‐
pinene, cyclooctene, indene, 1‐dodecene, 1‐heptene, 1‐
octenee, trans‐1,2‐diphenylethene, ferrous chloride, ferric
chloride, 3‐aminopropyltrimethoxysilane (APTMS) and
ammonia (25% w/w) were purchased from Merck. Proton
nuclear magnetic resonance spectra were recorded using a
Bruker NMR 400 (400 MHz) spectrophotometer in CDCl3
solvent. CHNS analyses were performed using an elemental
analyser (CHNSO‐A PE 2400 series II system). Atomic
absorption analysis was carried out with a Jena Analytik
atomic absorption spectrometer. Analysis of oxidation prod-
ucts was conducted using GCs with an Agilent 7890 A with
a capillary column and flame ionization detector. Column
temperature was programmed between 180 and 200°C with
a rate of 2°C min−1. Nitrogen was used as carrier gas at
20 ml min−1. IR spectra were obtained with a Spectomrx 1
Fourier transform IR spectrometer in KBr pellets over the
range 400–4000 cm−1. VSM was conducted with an
MDKF‐FORC/VSM) Megnatis‐Daghigh‐Kashan Co.). DRS
data were recorded with a Scinco 4100 in the range
200–900 nm using barium sulfate as reference. Powder
small‐angle XRD studies were done using a Philips X'Pert
with Cu Kα radiation (k = 1.54 Å). Surface morphology
and distribution of nanoparticles were investigated via a
SEM instrument (LEO 1430 VP).
2.2 | Preparation of Fe3O4@APTMS
SCHEME
1
Preparation of heterogeneous nanocatalyst: (i)
Magnetite nanoparticles (Fe3O4) were synthesized using the
trifluoroacetic acid, (ii) POCl3, N,N′‐dimethylformamide, (iii) EtOH,
(iv) stirring at 70 °C for 48 h, (v) MoO2(acac)2/EtOH
chemical co‐precipitation method from the literature.[31]

AKBARPOUR ET AL.
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FIGURE 1 IR spectra: (a) Fe3O4
nanoparticles; (b) Fe3O4@APTMS; (c)
Fe3O4@APTMS/fluorene‐SB; (d)
Fe3O4@APTMS/fluorene‐SB‐MoO2; (e)
Fe3O4@APTMS/fluorene‐SB‐MoO2 (run
1); (f) Fe3O4@APTMS/fluorene‐SB‐MoO2
(run 6)
FIGURE 2 XRD patterns: (a)
Fe3O4@APTMS/fluorene‐SB‐MoO2; (b)
magnetite nanoparticles
phosphoryl chloride (1.40 ml, 14.85 mmol) and 9,9‐
bis(pyrrole‐2‐yl)fluorene (1.95 g, 6.66 mmol) were mixed
together in 20 ml of N,N‐dimethylformamide at 0°C. After
70 min of stirring at 25°C, the reaction was quenched with
addition of 38 ml of water. Then aqueous potassium hydrox-
ide (2 M) was added until reaction mixture became strongly
basic. The mixture was boiled for 50 min and a colourless
precipitate obtained by filtration. The solids were washed
with water three times and dried. Yield 2.06 g, 85% of 9,9‐
bis(5‐formylpyrrole‐2‐yl)fluorene; m.p. 262°C. Anal. Calcd
for C23H16N2O2 (%): C, 78.39; H, 4.58; N, 7.95. Found
(%): C, 78.11; H, 4.73; N, 8.20. IR (KBr, cm−1): 1649
1
[ν(C═O)], 3217 [ν(N─H)]. H NMR (500 MHz, CDCl3, δ,
ppm): 11.53 (br, 2H, NH), 9.03 (s, 2H, CHO), 8.02 (m, 2H,
fluorenyl), 7.78 (m, 2H, fluorenyl), 6.73 (d, 2H, pyrrole),
5.73 (d, 2H, pyrrole), 7.4–7.3 (m, 4H, fluorenyl) (supporting
information, Figure S1). MS, m/z: 352.2 (MA: 352.4 g mol−1
(supporting information, Figure S2).
)
FIGURE 3 Magnetization response of Fe3O4@APTMS/fluorene‐
SB‐MoO2 at 25°C

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AKBARPOUR ET AL.
APTMS. Considering these bands of the IR spectra confirms
the anchoring of Schiff base Mo(VI) complex on magnetic
nanoparticles.
2.4 | Preparation of Fe3O4@APTMS/
fluorene‐SB
A solution of 9,9‐bis(5‐formylpyrrole‐2‐yl)fluorene (2 g,
6 mol, in 50 ml of EtOH) was added to a suspension of
Fe3O4@APTMS (1.0 g in 50 ml of EtOH). The mixture
was stirred for 48 h at 70 °C. Then, Fe3O4@APTMS/
fluorene‐SB was collected using a magnet and washed with
water and ethanol several times. IR (KBr, cm−1): 586
[ν(Fe─O)], 1022 [ν(Si─O─Si)], 1640 [ν(C═N)], 2926
[C─H], 3224 [ν(N─H)], 3438 [ν(O─H)].
As expected in the XRD pattern (Figure 2) and compar-
ing with that of standard Fe3O4 nanoparticles (JCPDS card
no. 87–2334), diffraction peaks are observed (220,
2θ = 30.13°), (331, 2θ = 35.65°), (400, 2θ = 43.51°), (422,
2θ = 54.25°), (511, 2θ = 57.19°) and (440, 2θ = 63.13°)
for Fe3O4 nanoparticles and Fe3O4@APTMS/fluorene‐SB‐
MoO2. The broad peak (about 2θ = 20.85–32°) of
Fe3O4@APTMS/fluorene‐SB‐MoO2 is attributed to the pres-
ence of amorphous SiO2.
2.5 | Preparation of Fe3O4@APTMS/
fluorene‐SB‐MoO2
MoO2(acac)2 (1.96 g, 6 mol, in 20 ml of EtOH) was added
dropwise to a suspension of 2 g of Fe3O4@APTMS/
fluorene‐SB in 40 ml of EtOH and the mixture was refluxed
for 24 h. Then, the solid was separated using an external mag-
net and washed several times with water and ethanol. IR
(KBr, cm−1): 580 [ν(Fe─O)], 912, 946 [ν(cis, O═Mo═O)],
1052 [ν(Si─O─Si)], 1662 [ν(C═N)], 2926 [C─H], 3438
[ν(O─H)].
2.6 | Catalytic epoxidation of olefins
The catalytic activity of the heterogeneous Fe3O4@APTMS/
fluorene‐SB‐MoO2 catalyst was investigated in the epoxida-
tion of various olefins. For this, 0.05 g of Fe3O4@APTMS/
fluorene‐SB‐MoO2 was sonicated in 5 ml of dichloroethane
as solvent for 30 min. Then the substrate (0.5 mmol) and
TBHP (1.0 mmol) were added in a ratio of 1:2 to the catalyst
reaction. The catalytic reaction was refluxed for 30 min and
the catalyst was removed using a magnet and the residue
was subjected to GC analysis.
3 | RESULTS AND DISCUSSION
3.1 | Synthesis and characterization
The novel Fe3O4@APTMS/fluorene‐SB‐MoO2 catalyst was
prepared following the steps shown in Scheme 1. Figure 1
shows the IR spectra of Fe3O4 nanoparticles, Fe3O4@APTMS,
anchored Schiff base ligand and Fe3O4@APTMS/fluorene‐
SB‐MoO2. As shown in Figure 1(a,b), Fe─O and Si─O
stretching bands appear at 578 and 1006 cm−1. The band
assigned to imine stretching vibration of the anchored ligand
at 1638 cm−1 (Figure 1c) has shifted to 1660 cm−1 after coor-
dination with the Mo(VI) centre (Figure 1d).[33] The appear-
ance of two adjacent bands at 942 and 908 cm−1 is
characteristic of the presence of asymmetric and symmetric
stretches of cis‐[O═Mo═O] group (Figure 1d).[34] The band
at 2900 cm−1 can be assigned to aliphatic group (CH2) of
FIGURE 4 SEM images of (a) magnetite nanoparticles and (b)
Fe3O4@APTMS/fluorene‐SB‐MoO2. (c) TEM image of final catalyst

AKBARPOUR ET AL.
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Figure 3 shows the magnetization curves of Fe3O4 nano-
particles and Fe3O4@APTMS/fluorene‐SB‐MoO2. The
curves show no hysteresis loops and indicate magnetic satu-
ration at 57.67 and 36.84 emu g−1, respectively. The result
shows that the supporting of the catalyst on the magnetic
nanoparticles decreases the magnetic saturation, but also the
catalyst can be separated from the solution using a small
external magnetic field.
Figure 4 shows SEM and TEM images of magnetite nano-
particles and nanocatalyst. Comparison between the SEM
images of Fe3O4@APTMS/fluorene‐SB‐MoO2 and magne-
tite nanoparticles shows no change in morphology. The
TEM image of Fe3O4@APTMS/fluorene‐SB‐MoO2 shows
the particle size to be approximately 17–20 nm. The EDX
spectrum of the catalyst indicates the presence of Mo, Si, C
and the other elements on the catalyst surface (Figure 5).
The XPS spectrum of Fe3O4@APTMS/fluorene‐SB‐MoO2
catalyst is shown in Figure 6. The Fe 2p peak at 709.7 eV, O
1 s peak at 529.79 eV and Si 2p peak at 101.87 eV are as
expected for Fe3O4/SiO2 material. The peaks at 232.23 and
235.38 eV are assigned to Mo 3d5 and 3d3, respectively. In
addition to the Mo6+ peaks, the peaks for N 1 s at
400.07 eV and C 1 s at 284.36 eV confirm the supporting of
Mo Schiff base complex onto Fe3O4/SiO2 surface. Also,
XPS results of the catalyst show 3.66% loading of Mo on
the surface of nanoparticles. This result is in good agreement
with the atomic absorption spectrometry result (3.5% Mo).
3.2 | Epoxidation of olefins catalysed by
Fe3O4@APTMS/fluorene‐SB‐MoO2
The Fe3O4@APTMS/fluorene‐SB‐MoO2 catalyst was used
for epoxidation of internal alkenes and terminal alkenes using
TBHP. Initially, various parameters such as the kind of oxi-
dant and solvent, amount of catalyst, temperature, reaction
time and molar ratio of oxidant/substrate were optimized.
FIGURE 5 EDX spectrum of Fe3O4@APTMS/fluorene‐SB‐MoO2
FIGURE 6 XPS spectrum of
Fe3O4@APTMS/fluorene‐SB‐MoO2

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AKBARPOUR ET AL.
TABLE 1 Investigation of solvent, oxidant and temperature in
After running the catalytic process for epoxidation of
cyclooctene with TBHP and various solvents, it is found that
1,2‐dichloroethane is a suitable solvent among toluene, chlo-
roform, dichloromethane, methanol and acetonitrile, with
highest conversion (100%) during 30 min. By considering
the mechanism shown in Scheme 2, it seems that the compe-
tition between methanol, acetonitrile as a coordinator solvent
and (CH3)3COO− coordinated to Mo(VI) causes a marked
decrease in the catalyst activity.[35] Apparently, the lower
reflux reaction temperature is the reason for the lowest epox-
idation conversion in CH2Cl2 (37%). For optimization of
reaction temperature, epoxidation of cyclooctene was carried
out in 1,2‐dichloroethane using TBHP at four temperatures
(25, 40, 60, 80°C). As evident from Table 1, the best results
are obtained at 80 Æ 2°C. For selecting a suitable oxidant,
sodium periodate, hydrogen peroxide‐urea, hydrogen perox-
ide and TBHP (70% in water) were tested in cyclooctene
epoxidation in 1, 2‐dichloroethane. As evident from Table 1,
we obtained the best results in the presence of TBHP (70%
in water). SoTBHP has some significant advantages: (1) high
selectivity; (2) unreactive towards substrate without catalyst;
(3) high thermal stability. The epoxidation of cyclooctene
was performed at various [TBHP]/[cyclooctene] ratios. For
this, ratios of 0.5, 1, 1.5 and 2 were used in separate catalytic
reactions. Figure 7 shows that the catalytic activity increased
with increasing [TBHP]/[cyclooctene] ratio and the maximum
conversion was observed at a ratio of in 2.0. The amount of
catalyst was optimized for epoxidation of cyclooctene by
using 0, 0.005, 0.010, 0.020, 0.030, 0.040 and 0.050 g of
Fe3O4@APTMS/fluorene‐SB‐MoO2. As illustrated in
Figure 8, the conversion of catalyst increases with increasing
amount of catalyst. Finally, 1,2‐dichloroethane (5 ml) as sol-
vent, olefin (10 mmol) as substrate, TBHP (20 mmol) as oxi-
dant and 0.05 g of catalyst (1.82 × 10−2 mmol, determined by
atomic absorption spectroscopy) at 80 Æ 2 °C with stirring for
epoxidation of cyclooctene catalysed by Fe3O4@APTMS/fluorene‐SB‐
a
MoO2
Entry
Solvent
Oxidant
Temp. (°C)
Conversion (%)
1
C2H4Cl2
C2H4Cl2
C2H4Cl2
C2H4Cl2
C2H4Cl2
C2H4Cl2
C2H4Cl2
C2H4Cl2
C2H4Cl2
CH3CN
Toluene
CH3Cl
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
UHP
25
40
22
63
2
3
60
79
4
80
100
70b
71c
39
5
80
6
80
7
80
8
NaIO4
H2O2
80
35
9
80
45
10
11
12
13
14
TBHP
TBHP
TBHP
TBHP
TBHP
80
41
80
34
Reflux
Reflux
Reflux
80
CH3OH
CH2Cl2
10
37
aReaction conditions: solvent =5 ml; catalyst =1.82 × 10−2 mmol; 10 mmol
alkene and 20 mmol oxidant; reaction time = 30 min.
bReaction time = 15 min.
cHot filtration test: after 15 min, catalyst removed from reaction mixture and con-
version calculated after next 15 min.
30 min were selected. By monitoring the catalyst reactor, the
final solution exhibited no colour and no Mo leaching (deter-
mined by atomic absorption spectroscopy) in the solution
after the catalytic procedure.
The results of catalytic epoxidation of olefins are summa-
rized in Table 2. Our results demonstrate 100% conversion
and 100% epoxidation selectivity for cyclooctene in 30 min.
So the turnover frequency of catalyst for cyclooctene
SCHEME 2 Proposed mechanism for
catalytic oxidation of olefins

AKBARPOUR ET AL.
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FIGURE 9 DRS spectrum of Fe3O4@APTMS/fluorene‐SB‐MoO2
before oxidation process (solid) and Fe3O4@APTMS/fluorene‐SB‐
MoO2 after six recycles (dotted)
FIGURE 7 Effect of molar ratio of TBHP and cyclooctene on
conversion in 1,2‐dichloroethane as solvent at reflux temperature
TABLE 3 Recycling of cyclooctene epoxidation catalyst with TBHPa
Run
Conversion (%)
Leaching of Mo (%)b
1
2
3
4
5
6
100
99
99
99
98
97
0.02
0
0.01
0
0
0
aCatalytic reaction conditions: 1,2‐dichloroethane =5 ml; catalyst
FIGURE 8 Effect of catalyst amount on cyclooctene epoxidation in
1,2‐dichloroethane as solvent at reflux temperature with TBHP as
oxidant
=1.82 × 10−2 mmol; 10 mmol alkene and 20 mmol TBHP.
bMonitored by atomic absorption spectroscopy.
a
TABLE 2 Results of catalytic epoxidation of various alkenes with TBHP catalysed by Fe3O4@APTMS/fluorene‐SB‐MoO2
Alkene
Conversion after 30 min (%) Conversion (%) (reaction time, min) Selectivity of epoxy (%) TOF (h−1 b
)
100
68
100 (30)
90 (60)
100
100
1098
747
32
53
60 (120)
84 (120)
100
100
351
583
51
40
92 (120)
50 (60)
100c (58, 42)
100
561
440
35
26
26
86 (120)
97 (180)
97 (150)
100
100
100
385
286
286
aCatalytic reaction conditions: 1,2‐dichloroethane =5 ml; catalyst =1.82 × 10−2 mmol; 10 mmol alkene and 20 mmol TBHP.
bCalculated as [mmol of product]/[mmol of catalyst] × time.
ccis‐Epoxy product: 52% and trans‐epoxy product: 42%.

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AKBARPOUR ET AL.
TABLE 4 Comparison of literature reports on epoxidation of cyclooctene under various conditions
Catalyst
Reaction conditions
Conversion (%)
Ref.
[27]
MoO2–thio‐Schiff base
[MoO(O2)2(4‐MepyO)2].H2O
[MoO(O2)2(4‐MepyO)2].H2O
[MoO(O2)2(H2O)](ONnDodec3)
SBA‐15‐MoO2
TBHP/CHCl3/24 h
UHP/C4mim(PF6)/18 h
H2O2/CH3Cl/18 h
H2O2/CH3Cl/2 h
TBHP/C2H4Cl2/1 h
TBHP/C2H4Cl2/12 h
TBHP/toluene/24 h
TBHP/CH3Cl/8 h
TBHP/CH3Cl/4 h
TBHP/DCE/24 h
TBHP/CCl4/2 h
36
90
[37]
[38]
[39]
[40]
[15]
[41]
[5]
86
25
96
[MoO2(Salen)(piperazine)]n
SM‐48ccg
95
34
MoO2‐Salen‐GO
91.7
97
[42]
[43]
[6]
Dioxo‐Mo(VI) acac‐AmpMCM‐141
[MoO2Cl2(oep‐H2saldpen)]
Mo‐IFBNPs
100
95
[44]
[45]
[46]
[47]
Mag‐Mo‐Nano catalyst
Schiff base Mo(VI) catalysts
ZPS‐PVPA‐MoO2
TBHP/CCl4/5 h
99
TBHP/DCE/8 h
100
100
75
TBHP/DCE/3 h
MoO2pyprMCM‐41
TBHP/CHCl3/4 h
TBHP/DCE/30 min
Fe3O4@APTMS/fluorene‐SB‐MoO2
100
This work
epoxidation (1098 h−1) is remarkable. It seems that the incli-
nation of internal alkenes for epoxidation is more than that of
terminal alkenes. The catalytic oxidation of substrate with
TBHP in the blank run (without catalyst) occurs with 26%
conversion. The chemical and physical stability of the cata-
lyst allows its recycling and reuse several times (six times).
The catalyst was separated easily with a magnet and used
several times for the epoxidation process. As shown in
Figure 1(d–f), there are no changes in the IR spectra of the
catalyst before oxidation, after the second run and after the
sixth run, respectively. So comparison between DRS spectra
of the catalyst before and after the epoxidation process shows
no change (Figure 9). The use of catalyst for several times
without significant decrease in conversion and without sig-
nificant leaching is evident (Table 3). Hot filtration test was
performed for further investigation of catalyst leaching. For
this purpose, after 15 min, the catalyst was removed from
the reaction mixture and the conversion was calculated after
another 15 min. As illustrated in Table 1 (entry 6), the con-
version shows no significant increase. Considering the con-
version results, solvent optimization and compared with
previous works,[36] it seems that the proposed mechanism
occurs via a seven‐coordinate intermediate (Scheme 2). In
respect to the mechanism in Scheme 2, it may the competi-
tion between methanol, acetonitrile as a coordinator solvent
and (CH3)3COO− coordinated to Mo(VI) in step (II) that
causes a marked decrease in the catalyst activity.[35]
epoxidation of olefins. The novel presented catalyst showed
higher epoxidation catalytic activity for cyclooctene (100%
conversion) than the others (36%,[27] 90%,[37] 86%[38] and
75%[39]) Finally, a comparison of catalytic reaction time and
conversion of previous reports (1 h,[40] 12 h,[15]
1 day,[27,41,43] 4 h,[42] 5 h[44] and 8 h[5,45]) with that for
Fe3O4@APTMS/fluorene‐SB‐MoO2 (30 min) shows that
the present catalyst is efficient and time‐saving.
4 | CONCLUSIONS
We have reported the successful covalent anchoring of a
novel Mo(VI) tetradentate Schiff base complex based on
two pyrrole‐imine donors on Fe3O4 nanoparticles following
our pervious researches on catalytic activity. The novel para-
magnetic recoverable catalyst has been studied as a
nanocatalyst for selective oxidation of alkenes. The catalyst
was recovered successfully using a magnet and reused as a
catalyst six times without decrease in conversion and selec-
tivity. The Fe3O4@APTMS/fluorene‐SB‐MoO2 catalyst
showed higher epoxidation catalytic activity[27,37–39] and
markedly shorter catalytic reaction time than other reported
catalysts.[15,27,40–45,47] The Fe3O4@APTMS/fluorene‐SB‐
MoO2 catalyst shows a highest conversion in 0.5 h.
ACKNOWLEDGEMENT
Table 4 compares the present catalyst with those previ-
ously reported in the literature. In this work, we introduced
a suitable magnetically separable catalytic system for
We acknowledge the Research Council of Mohaghegh‐e‐
Ardabili University for financial support of the project.

AKBARPOUR ET AL.
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Askarizadeh E, Amiri M. Covalent supporting of
novel dioxo‐molybdenum tetradentate pyrrole‐imine
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