Amine-functionalized boehmite nanoparticle-supported molybdenum and vanadium complexes: Efficient catalysts for epoxidation of alkenes

Article abstract of DOI:10.1016/S1872-2067(16)62451-8

Boehmite nanoparticles with a high surface area and a high degree of surface hydroxyl groups were covalently functionalized by 3-(trimethoxysilyl)-propylamine to support vanadium-oxo-sulfate and molybdenum hexacarbonyl complexes. These supported catalysts were then characterized by Fourier-transform infrared spectroscopy, powder X-ray diffraction, thermogravimetry and differential thermal analysis, X-ray-photoelectron spectroscopy, elemental analysis, inductively coupled plasma, and transmission electron microscopy techniques. The catalysts were subsequently used for the epoxidation of cis-cyclooctene, and the experimental procedures were optimized. The progress of the reactions was investigated by gas-liquid chromatography. Recycling experiments revealed that these nanocatalysts could be repeatedly used several times for a nearly complete epoxidation of cis-cyclooctene. The optimized experimental conditions were also used successfully for the epoxidation of some other substituted alkenes.

Full text of DOI:10.1016/S1872-2067(16)62451-8

Chinese Journal of Catalysis 37 (2016) 1263–1274
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Amine‐functionalized boehmite nanoparticle‐supported
molybdenum and vanadium complexes: Efficient catalysts for
epoxidation of alkenes
Mahdi Mirzaee*, Bahram Bahramian, Marieh Mirebrahimi
Department of Chemistry, Shahrood University of Technology, Shahrood, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
Boehmite nanoparticles with a high surface area and a high degree of surface hydroxyl groups were
covalently functionalized by 3‐(trimethoxysilyl)‐propylamine to support vanadium‐oxo‐sulfate and
molybdenum hexacarbonyl complexes. These supported catalysts were then characterized by Fou‐
rier‐transform infrared spectroscopy, powder X‐ray diffraction, thermogravimetry and differential
thermal analysis, X‐ray‐photoelectron spectroscopy, elemental analysis, inductively coupled plasma,
and transmission electron microscopy techniques. The catalysts were subsequently used for the
epoxidation of cis‐cyclooctene, and the experimental procedures were optimized. The progress of
the reactions was investigated by gas‐liquid chromatography. Recycling experiments revealed that
these nanocatalysts could be repeatedly used several times for a nearly complete epoxidation of
cis‐cyclooctene. The optimized experimental conditions were also used successfully for the epoxida‐
tion of some other substituted alkenes.
Received 26 March 2016
Accepted 30 April 2016
Published 5 August 2016
Keywords:
Boehmite nanoparticles
Heterogeneous catalysts
Hexa‐carbonyl molybdenum
Oxo‐sulfate vanadium
Epoxidation
© 2016, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
lysts is a very important aspect from an economic and ecologi‐
cal viewpoint. Furthermore, immobilization of the catalysts on
Epoxides are well known as one of the most valuable inter‐
mediates for the production of commercially important chemi‐
cals such as polyglycols, polyamides, polyurethanes and many
other polymers, pharmaceuticals, food additives, epoxy paints,
dye‐stuffs, flavour and fragrance compounds [1–8], and
non‐toxic PVC‐plasticizers and stabilizers [8–10]. They are also
valuable additives to lubricants and adhesives [8,11,12].
In addition to conventional Mo complexes, several other
soluble complexes of V, W, Re, Mn, Ru, Co, Fe, and Ti have been
employed as active homogenous catalysts for the epoxidation
of alkenes [2,13–15]. However, these catalysts are toxic and
expensive, and they must be completely separated from the
products and waste. In this respect, the development of heter‐
ogeneous systems for improving the recovery of valuable cata‐
supports with a high surface area in heterogeneous systems
can efficiently improve the catalyst reactivity and enhance the
turnover number (TON) of the catalytic procedure [2]. An‐
choring catalysts on a solid surface disperses the active sites
uniformly and protects them from dimerization by oxo‐bridge
formation [16]. Accordingly, various organic and inorganic
materials have been used as insoluble supports in heterogene‐
ous catalytic procedures. The organic insoluble supports in‐
clude different types of polymers such as polybenzimidazole
[13,17], polystyrene [13,18,19], polymethacrylate [13], polyan‐
iline [20], and poly‐divinylbenzene‐allylamine [21]. In addition,
ion exchange and epoxy resins [13,22], graphene oxide [23],
multi‐walled carbon nanotubes [16,24], ordered mesoporous
carbon [25], silica [7,13,26], titanium silicate [13], MCM‐41
* Corresponding author. Tel/Fax: +98‐23‐32395441; E‐mail: mmirzaee@shahroodut.ac.ir
DOI: 10.1016/S1872‐2067(16)62451‐8 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 37, No. 8, August 2016

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Mahdi Mirzaee et al. / Chinese Journal of Catalysis 37 (2016) 1263–1274
[26–29], MCM‐48 [29], SBA‐15 [1,16,26,30,31], alumina [32],
montmorillonite K‐10 [13,33], coated magnetic particles
[13,34], zeolites [16,35–37] and layered bimetal hydroxides [5]
have been used as insoluble supports. Generally, inorganic
supports have a higher chemical stability and surface area than
organic ones. Additionally, the surface of some metal oxides
and metal hydroxides is covered with hydroxyl groups. These
groups create hydrophilic surfaces that provide valuable sites
for grafting a wide range of functionalities. Subsequently, sup‐
porting various transition metals on these functionalities can
produce active and stable catalysts for liquid‐phase organic
reactions.
Boehmite (γ‐AlOOH) is an inorganic insoluble support that
contains extra hydroxyl groups on its surface. It has been used
as an absorbent, flame retardant [38], and an important pre‐
cursor for preparing advanced catalysts, alumina, and alumi‐
na‐derived ceramics [38,39]. We have used pure boehmite for
the successful multi‐component synthesis of highly substituted
imidazoles [40]. Choudhary et al. [41] have also used pure
boehmite for the catalytic epoxidation of styrene, although they
reported that it was deactivated by the production and accu‐
mulation of water, and so it required continuous removal of
water. Consequently, in this work, we used grafted boehmite
nanoparticles (BNPs) with 3‐(trimethoxysilyl)‐propylamine
(MSPA) to support two complexes of molybdenum and vana‐
dium.
ESCA 2000 system from VG Microtech using a monochroma‐
tized aluminum Kα anode.
2.2. Preparation of BNPs
Aluminium 2‐butoxide was prepared by the reaction of al‐
uminium with 2‐butanol according to the general preparation
procedure for aluminium alkoxides [43]. The prepared alu‐
minium alkoxide was vacuum‐distilled to obtain a high‐quality
aluminium alkoxide precursor. For a hydrothermal‐assisted
hydrolysis, according to our previous report [44], aluminium
2‐butoxide was diluted in 2‐butanol to 50%, and then loaded in
a glass container. The glass container was placed in a 300‐mL
stainless steel autoclave. The gap between the autoclave
chamber and the glass container was covered with 50 mL of
distilled water, and then the autoclave was heated at 100 °C.
Aluminium 2‐butoxide was hydrolysed by diffusion of water
vapour into the solution in the hydrothermal chamber. All ma‐
nipulations of the aluminium alkoxides were performed on a
Schlenk line. Their transfer into the autoclave was performed in
a moisture‐free atmosphere to prevent the hydrolysis of alu‐
minium alkoxides prior to introducing it into the hydrothermal
chamber. After 5 h, the autoclave was cooled down and the
powder produced (BNPs) was filtered off and dried at 100 °C
overnight.
This strategy has been used for anchoring various metal
complexes on different solid supports. However, almost all of
them have changed the terminal amine group in MSPA to a
Schiff base and then used it for the supporting metal complex‐
es. We have also used this approach in our previous work [42].
In this work, grafted MSPA was used for the straight anchoring
of metal complexes and then the supported catalysts were used
in the epoxidation of various alkene substrates.
2.3. Preparation of supported molybdenum and vanadium
complexes on BNPs and amine‐functionalized BNPs
For the preparation of amine‐functionalized BNPs (AF‐
BNPs), 1.00 g of BNPs was refluxed with MSPA (61 µL, 0.35
mmol) in dry toluene (50.0 mL) for 24 h (Scheme 1). The solid
substance obtained was filtered off, washed three times with
dry toluene, and dried at 100 °C overnight.
The Mo(CO)6 and VOSO4·H2O complexes were used to sup‐
port on BNPs or AFBNPs (Scheme 1). For this purpose,
Mo(CO)6 (0.276 g, 1.05 mmol) was activated under ultraviolet
light in tetrahydrofuran (THF, 20.0 mL) for 30 min. This acti‐
vated molybdenum complex was then added to dry BNPs or
AFBNPs, and the mixture was subsequently refluxed for 6 h.
The mixture was then cooled down and filtered off, and the
resulting precipitate was washed several times with THF and
dried at 100 °C overnight. In a similar procedure, VOSO4·H2O
(0.200 g, 1.05 mmol) was refluxed with BNPs or AFBNPs in
ethanol (20 mL) for 7 h. The resulting powder was washed
several times with ethanol and dried at 100 °C overnight.
2. Experimental
2.1. Materials and methods
The required solvents and reagents were purchased from
Merck or Fluka, and used without further purification. Fouri‐
er‐transform infrared (FT‐IR) spectra were recorded on a
Bomem MB series FT‐IR instrument at 4 cm−1 resolution using
KBr pellets. 1H NMR spectra were obtained in d6‐DMSO using a
Bruker AVANCE 300 MHz spectrometer. Powder X‐ray diffrac‐
tion (PXRD) patterns were collected on a Phillips PW‐1800 or
STOE diffractometer with Cu Kα irradiation. Thermogravimetric
(TG) analyses were performed in a Rheometric Scientific
STA‐1500 or BAHR Thermoanalyse GmbH with a heating rate
of 10 °C min−1 in air. A 400‐W Hg lamp was used for activation
of the hexacarbonyl molybdenum complex. Elemental analyses
were performed in a Hereans CHN‐O‐Rapid Analyzer. Trans‐
mission electron microscopy (TEM) was performed on a JEOL
JSM‐6360LV transmission electron microscope. Gas‐liquid
chromatography (GLC) was performed on a Shimadzu GC‐16A
instrument using a 2‐m column packed with silicon DC‐200.
X‐ray photoelectron spectroscopy (XPS) was performed on an
2.4. Catalytic epoxidation of alkenes
In a typical process, an appropriate round bottom flask
equipped with a magnetic stirrer bar and a condenser was
charged with an alkene, an oxidant, the catalyst (Mo‐AFBNPs or
V‐AFBNPs), and solvent, and the mixture was then refluxed. All
the reactions were performed at least two times, and the reac‐
tion progress was monitored by GLC. Because different alkenes
have different reactivities toward oxidation, these reactions
were continued until no further progress was observed. The

Mahdi Mirzaee et al. / Chinese Journal of Catalysis 37 (2016) 1263–1274
1265
characterizations of the main products and by‐products were
(020)
performed by comparison of their retention times with those
for the standard samples. The alkene conversions and product
selectivities were calculated using their peak areas by the
standard addition method. In the case of cis‐ and trans‐stilbene,
1H NMR was also used to analyze the products.
(051, 200)
(120)
(140, 031)
(3)
2.5. Catalyst recycling
(2)
(1)
In a typical experiment, after recovering the catalyst from
the reaction mixture, it was washed several times with CCl4,
and then used in the same procedure under the same condi‐
tions.
10 15 20 25 30 35 40 45 50 55 60
2/(o )
3. Results and discussion
Fig. 2. PXRD patterns for BNPs (1), Mo‐AFBNPs (2), and V‐AFBNPs (3).
There are different methods that have been used for the
preparation of BNPs. Among them, a hydrothermal‐assisted
sol‐gel process on aluminum alkoxide was used here [44]. This
method has some advantages such as preparation in a one‐pot
process and processing at a low temperature. The BNPs ob‐
tained were then grafted with MSPA because they showed no
acceptable interaction with the molybdenum or vanadium
complexes. The supported molybdenum and vanadium AF‐
BNPs catalysts were then used in the epoxidation of
cis‐cyclooctene, and the experimental conditions were opti‐
mized for the parameters involved, such as the catalyst, solvent,
and oxidant. Hot filtration was also used to confirm the hetero‐
genic character of both catalytic procedures. In addition, recy‐
cling experiments were performed to determine if these cata‐
lysts could be reused. Both catalysts were then used for the
epoxidation of different alkenes under the optimum experi‐
mental conditions.
The most promising property of these hydrothermally pro‐
cessed BNPs is the formation of a crystalline single‐phase
product with no organic residue [44]. This was confirmed by
the FT‐IR spectrum, PXRD pattern, and TG/DSC thermogram of
this sample.
In the FT‐IR spectrum of BNPs (Fig. 1), there are two different
stretching vibrations at 3280 and 3075 cm−1, which were as‐
signed to the bridged and terminal hydroxyl groups of BNPs,
respectively. These stretching vibrations were accompanied by
two bending vibrations for the bridged and terminal hydroxyl
groups at 1150 and 1075 cm−1, respectively. BNPs also had
some distinguishable Al–O related vibrations at 740, 610, and
480 cm−1 in the IR spectrum. The PXRD pattern for BNPs (Fig.
2) also confirmed the crystallization of single‐phase boehmite
by comparison with JCPDS card No. 21‐1307. In the TG/DSC
curve of BNPs (Fig. 3(a)), there were two endothermic peaks:
3.1. Preparation and characterization of supported
molybdenum and vanadium complexes on BNPs and AFBNPs
5
0
0
(c)
-20
-40
-60
-80
-5
BNPs were prepared by the hydrothermal‐assisted sol‐gel
processing of an aluminum 2‐butoxide solution in 2‐butanol.
-10
-15
-20
-25
0
-10
-20
-30
-40
-50
-60
-70
10
(4)
(3)
(b)
-5
-10
-15
-20
(2)
-25
0
(1)
(a)
8
-5
-10
-15
-20
-25
6
4
2
0
-2
4000 3500 3000 2500 2000 1500 1000 500
Wavenumber (cm1)
100
200
300
400
500
600
Temperature (oC)
Fig. 3. Thermal analysis curves for BNPs (a), Mo‐AFBNPs (b), and
V‐AFBNPs (c).
Fig. 1. FT‐IR spectra for BNPs (1), AFBNPs (2), Mo‐AFBNPs (3), and
V‐AFBNPs (4).

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Mahdi Mirzaee et al. / Chinese Journal of Catalysis 37 (2016) 1263–1274
(a)
(b)
(c)
Fig. 4. TEM images for BNPs (a), Mo‐AFBNPs (b), and V‐AFBNPs (c).
one below 100 °C and the other one at approximately 450 °C.
The first one was attributed to the elimination of the physically
adsorbed water, and the other one was attributed to the dehy‐
droxylation of boehmite and crystallization of γ‐alumina. The
absence of the C–H stretching vibrations in the IR spectrum and
an exothermic peak at approximately 250 °C in the TG/DSC
curve of BNPs, respectively, confirmed the loss of all organic
residues in the hydrothermally processed BNPs. Calculation of
the particle size using the PXRD pattern according to the
Scherer equation shows an average particle size of 10 nm for
BNPs. This was confirmed by TEM image of BNPs (Fig. 4(a)). In
this image, needle‐shaped BNPs were seen with a length of
over 50 nm and a width of up to 10 nm. According to the BET
analysis, the efficient surface area for BNPs was 326 m2 g−1.
BNPs themselves have promising catalytic properties for
multi‐component synthesis of highly substituted imidazoles, as
performed by our research team and reported elsewhere [40].
In addition, it has been shown that for an efficient epoxidation
of alkenes under mild conditions, the presence of a catalyst
containing an active metal site is vital. The oxidant could coor‐
dinate to this site, and be activated for the epoxidation process.
However, BNPs showed no reactivity in the epoxidation of al‐
kenes (Table 1, entry 30), similar to the report by Choudhary
and co‐workers [41]. Furthermore, supporting the molyb‐
denum and vanadium complexes on BNPs failed (Scheme 1).
The IR spectra and inductively coupled plasma (ICP) analyses
showed no evidence to confirm an interaction between them
even after 6–7 h reflux. Consequently, we tried to functionalize
BNPs using MSPA. The functionalization was performed by
refluxing BNPs and MSPA in dry toluene for 24 h. During this
process, the –O3Si(CH2)3NH2 group was grafted on the hydrox‐
yl‐covered surface of BNPs by the elimination of methanol
(Scheme 1), which produced AFBNPs. The IR spectrum for
AFBNPs (Fig. 1) showed a new band at 1553 cm−1, which was
assigned to the N–H stretching vibration of the grafted amine
groups in addition to the BNPs characteristic bands. Elemental
analysis showed that the nitrogen content of AFBNPs was
0.46%, which means that 0.33 mmol of the pending amine
BNPs
OH
OH
Mo(CO)6 + THF
OH
OC
Mo CO
CO
OH
OH
hv (30 min)
OH
H2N
OC
CO
O
O
OH
OH
Si
Mo(CO)5THF
Reflux
6 h
OH
Reflux
6 h
Mo-AFBNPs
MeO
Si
OH
OH
NH2
O
NH2
OH
OH
OH
MeO
MeO
Si
O
OH
OH
BNPs
OH
OH
Reflux, 24 h
-MeOH
O
V
AFBNPs
Reflux
7 h
OH
H2N
O
S
O
O
O
OH
Reflux
7 h
Si
O
OH
O
VOSO4 . H2O
OH
OH
OH
OH
OH
OH
V-AFBNPs
BNPs
Scheme 1. Attempt to support molybdenum and vanadium complexes on BNPs and AFBNPs.

Mahdi Mirzaee et al. / Chinese Journal of Catalysis 37 (2016) 1263–1274
1267
groups were covalently bonded to the surface of 1.00 g of BNPs.
AFBNPs also showed no reactivity in the catalytic epoxidation
of alkenes (Table 1, entry 31), as it was predictable according to
the above‐mentioned discussion. The efficient BET surface area
of AFBNPs was 321 m2 g−1, which does not show a significant
change in comparison with BNPs.
AFBNPs were then used to support molybdenum and vana‐
dium complexes. For this purpose, Mo(CO)6 and VOSO4·H2O
were used. However, Mo(CO)6 is not labile in the ligand substi‐
tution reaction, so its solution in THF was activated by irradia‐
tion with ultraviolet light. This process resulted in the for‐
mation of a Mo(CO)5(THF) complex, which substituted its THF
ligand with the grafted amine group on BNPs after reflux for 6 h
(Mo‐AFBNPs). The VOSO4·H2O complex was also refluxed with
AFBNPs in ethanol for 7 h to support vanadium on AFBNPs
(V‐AFBNPs).
In the FT‐IR spectrum of Mo‐AFBNPs (Fig. 1), the carbonyl
stretching vibration band for the coordinated molybdenum
complex was covered by the characteristic broad band of the
BNPs in the region of 1900–2500 cm−1. This was attributed to
the small amount of catalyst that was loaded on AFBNPs. The
ICP analysis showed that approximately 90% of the nitrogen
sites on AFBNPs were used to anchor 0.3 mmol of the molyb‐
denum complex on 1.00 g of Mo‐AFBNPs. The PXRD pattern of
Mo‐AFBNPs (Fig. 2) confirms the retention of the BNPs crystal‐
line structure after functionalization and metal loading. There
are two endothermic peaks in the TG/DTA curves for
Mo‐AFBNPs (Fig. 3(b)). One of them is below 100 °C, and the
other is above 200 °C. The first was attributed to the elimina‐
tion of physically adsorbed water, and the second could be at‐
tributed to the elimination of carbonyl ligands from the coor‐
dinated molybdenum complex. There is also an exothermic
peak at approximately 300 °C owing to the ignition of the or‐
ganic parts of the pending groups on the BNPs. This thermo‐
gram also shows another weight loss in the range of 400–500
°C, which was accompanied with an endothermic peak in the
DTA curve owing to the dehydroxylation of boehmite and crys‐
tallization of γ‐alumina, similar to BNPs. The total weight loss
of this sample up to 600 °C was about 24%. Calculation of the
particle size using the PXRD pattern for Mo‐AFBNPs according
to the Scherer equation shows no change in the particle size in
comparison to BNPs, and this was confirmed by the TEM image
(Fig. 4(b)). The efficient surface area for Mo‐AFBNPs was 323
m2 g−1, which does not show a significant variation in compari‐
son with BNPs and AFBNPs.
The IR spectrum of V‐AFBNPs (Fig. 1) shows a new band at
956 cm−1 owing to the V=O stretching vibration of the VOSO4
complex, which confirms the coordination of the vanadium
complex to the functionalized BNPs. The ICP analysis also
showed that over 80% of the nitrogen sites on AFBNPs were
used to anchor 0.28 mmol of the vanadium complex on 1.00 g
of V‐AFBNPs, which is lower than the metal loading in
Mo‐AFBNPs. The PXRD pattern of V‐AFBNPs (Fig. 2) also con‐
firms retention of the crystalline structure of the BNPs after
metal loading. In the TG/DTA curve of V‐AFBNPs (Fig. 3(c)),
there is an endothermic peak below 100 °C with 6% weight
loss in the TG curve owing to the elimination of the physically
adsorbed water. Similar to the molybdenum counterpart, there
is an exothermic peak at approximately 300 °C owing to the
ignition of the organic parts of AFBNPs. Additionally, and simi‐
lar to BNPs and Mo‐AFBNPs, this thermogram shows a weight
loss in the range of 400–500 °C, accompanied by an endother‐
mic peak in the DTA curve, which was similarly assigned as
resulting from dehydroxylation of boehmite and crystallization
of γ‐alumina. The total weight loss of V‐AFBNPs up to 600 °C
was about 24%, similar to Mo‐AFBNPs. Calculation of the parti‐
cle size using the PXRD pattern for V‐AFBNPs according to the
Scherer equation, and similar to the molybdenum counterpart,
shows no change in the particle size in comparison to BNPs.
This was also confirmed by the TEM image (Fig. 4(c)).
The efficient surface area for V‐AFBNPs was 318 m2 g−1,
which does not show a significant variation in comparison with
BNPs, AFBNPs, and Mo‐AFBNPs. The XPS analysis was also
performed for further evidence of the surface compositions of
both the Mo‐AFBNPs and V‐AFBNPs catalysts inferred by the
FT‐IR and ICP analyses. Wide scan XPS spectra of both catalysts
over a wide binding energy range from 0 to 600 eV are dis‐
played in Fig. 5. In the case of Mo‐AFBNPs catalyst (Fig. 5), the
XPS Mo 3d5/2 and Mo 3d3/2 peaks were observed at 232 and
236 eV, respectively, indicating the presence of a molybdenum
complex on the surface of this catalyst. However, in the case of
the V‐AFBNPs catalyst (Fig. 5), the XPS V 2p3/2 and V 2p1/2
O 1s
80
900
600
300
0
4000
O 1s
Mo 3d5/2
Mo 3d3/2
(3)
3000
C 1s
40
0
215
Al 2s
Si 2p
V 2p3/2
V 2p1/2
(4)
2000
1000
0
(2)
(1)
235
255
510
520
530
540
Al 2p
0
50
100
150
200
250
300
350
400
450
500
550
600
Binding energy (eV)
Fig. 5. XPS analysis of Mo‐AFBNPs (1), V‐AFBNPs (2), Mo 3d region (3) of Mo‐AFBNPs, and V 2p and O 1s region (4) of V‐AFBNPs.

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Mahdi Mirzaee et al. / Chinese Journal of Catalysis 37 (2016) 1263–1274
peaks at 517 and 522 eV, respectively, indicates the presence of
a vanadium complex on the surface of this catalyst. The XPS Si
2p and C 1s peaks at 99 and 284 eV, respectively, confirmed the
attachment of the silylpropyl amine group on the surface of
boehmite nanoparticles in both catalysts. In addition, the XPS
Al 2p, Al 2s, and O 1s peaks at 72, 117, and 530 eV, respectively,
owing to the BNPs, were present in the spectra of both cata‐
lysts. In brief, the surface compositions characterized by the
FT‐IR, ICP, and XPS analyses support each other.
Other oxygen sources such as hydrogen peroxide and sodium
periodate (in the presence of 0.01 g of tetrabutylphosphonium
bromide as the phase‐transfer reagent), and urea‐hydrogen
peroxide in CCl4 or CH3CN do not show an acceptable activity. It
seems that the protic solvents, which were inevitably present
with those oxidants, competed to bind to the metal complexes,
and blocked the catalytic sites. Furthermore, under mild condi‐
tions, the epoxidation of cis‐cyclooctene by TBHP did not pro‐
ceed in the absence of the catalyst.
As shown in Table 1 (entries 1–6 and 17–22), the use of dif‐
ferent solvents showed the same trend as other literature re‐
ports on homogeneous alkene epoxidation by the Mo(CO)6
catalyst [45]. Coordinating solvents such as CH3CN and CH3OH
compete with TBHP to occupy the coordination sites on the
transition metal catalyst. Therefore, in the presence of these
solvents, the observed yields are very low. Among other sol‐
vents, CCl4 has the highest yield of epoxide product for both the
Mo‐AFBNPs and V‐AFBNPs catalysts. This could be attributed
to the higher boiling point of CCl4 in comparison to the other
solvents.
3.2. Alkene epoxidation with tert‐butylhydroperoxide catalyzed
by Mo‐AFBNPs and V‐AFBNPs
Epoxidation of cyclooctene has been widely used as a model
reaction to demonstrate the catalytic activities of new synthe‐
sized catalysts. This reaction was chosen because cyclooctene
epoxide is the only product and it does not have any other by‐
product. Thus, we used this reaction to show and optimize the
catalytic activities of our catalysts. The optimization of the title
reaction was investigated by changing different parameters
including the solvent, oxidant, catalyst, and time. Our experi‐
ments showed that in the presence of these catalysts,
tert‐butylhydroperoxide (TBHP) was the only oxidizing system
that can promote the epoxidation of cis‐cyclooctene in CCl4.
We then determined how the amount of the amine group
anchored on BNPs influenced the progress of the reaction (Ta‐
ble 1, entries 6–8). For this purpose, different amounts of MSPA
(6:0.35, 7:0.7, and 8:0.23 mmol) were used to anchor 1.00 g of
Table 1
Epoxidation of cis‐cylooctene with TBHP under reflux conditions after 2 h.
Pending amine group
Catalyst loadinga
(mol %)
1.7
Oxidant/Substrate
Epoxide yieldb
(%)
No reaction
Entry
Catalyst (mg)
Solvent (mL)
(mmol)/BNPs (g)
0.35
0.35
0.35
0.35
0.35
0.35
0.70
0.23
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
0.35
molar ratio
1
2
3
4
5
6
7
8
Mo‐AFBNPs (40)
Mo‐AFBNPs (40)
Mo‐AFBNPs (40)
Mo‐AFBNPs (40)
Mo‐AFBNPs (40)
Mo‐AFBNPs (40)
Mo‐AFBNPs (40)
Mo‐AFBNPs (40)
Mo‐AFBNPs (30)
Mo‐AFBNPs (20)
Mo‐AFBNPs (10)
Mo‐AFBNPs (20)
Mo‐AFBNPs (20)
Mo‐AFBNPs (20)
Mo‐AFBNPs (20)
Mo‐AFBNPs (20)
V‐AFBNPs (20)
V‐AFBNPs (20)
V‐AFBNPs (20)
V‐AFBNPs (20)
V‐AFBNPs (20)
V‐AFBNPs (20)
V‐AFBNPs (10)
V‐AFBNPs (30)
V‐AFBNPs (40)
V‐AFBNPs (20)
V‐AFBNPs (20)
V‐AFBNPs (20)
V‐AFBNPs (20)
BNPs (20)
CH3CN (3)
CH3OH (3)
(CH3)2CO (3)
CH2Cl2 (3)
CHCl3 (3)
CCl4 (3)
CCl4 (3)
CCl4 (3)
CCl4 (3)
CCl4 (3)
CCl4 (3)
CCl4 (3)
CCl4 (3)
CCl4 (3)
CCl4 (2)
CCl4 (1)
CH3CN (3)
CH3OH (3)
(CH3)2CO (3)
CH2Cl2 (3)
CHCl3 (3)
CCl4 (3)
CCl4 (3)
CCl4 (3)
CCl4 (3)
CCl4 (3)
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1
2
2.5
2
2
2
2
2
2
2
2
2
2
2
1.7
1.7
1.7
1.7
1.7
2.0
0.8
1.29
0.86
0.43
0.86
0.86
0.86
0.86
0.86
0.8
0.8
0.8
0.8
0.8
No reaction
18
23
40
53
55
40
53
63
46
42
79
83
86
96
8
10
35
61
68
73
57
67
63
53
76
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
0.8
0.4
1.2
1.6
0.8
0.8
0.8
0.8
1
3
2
2
2
2
CCl4 (3)
CCl4 (2)
CCl4 (1)
CCl4 (3)
80
83
—
—
No reaction
No reaction
AFBNPs (20)
CCl4 (3)
a Calculated for 0.7 mmol cyclooctene. b GLC yields are based on the starting cyclooctene.

Mahdi Mirzaee et al. / Chinese Journal of Catalysis 37 (2016) 1263–1274
1269
BNPs. These functionalized BNPs were then used to support
Mo(CO)6. These catalysts were then used for the epoxidation of
0.7 mmol of cis‐cyclooctene with 1.05 mmol of TBHP. The re‐
sults obtained showed that after 2 h the conversions of entries
6 and 7 were the same and higher than entry 8, respectively.
Therefore, 0.35 mmol of the pending amine group per gram of
BNPs was selected for further investigations. According to the
ICP analysis, the amount of supported molybdenum complexes
on samples 6, 7, and 8 were 0.3, 0.35, and 0.14 mmol g−1, re‐
spectively. The same activities for entries 6 and 7 may be at‐
tributed to almost the same metal loading on AFBNPs.
The amount of catalyst used for the epoxidation of
cis‐cyclooctene with TBHP was also investigated. Fig. 6 and
Table 1 (entries 6, 9–11, and 22–25) confirm that increasing
the amount of both the Mo‐AFBNPs and V‐AFBNPs catalysts up
to 20 mg increased the cyclooctene epoxide yield.
The oxidant to substrate ratio is one of the most crucial pa‐
rameters in the catalytic epoxidation processes. The results
tabulated in Table 1 (entries 10, 12–14, 22, 26, and 27) show
that the optimum oxidant to substrate ratio for both catalysts
was 2. Increasing this ratio to 2.5 and 3 for Mo‐AFBNPs and
V‐AFBNPs, respectively, did not change the epoxidation yields
significantly, but decreasing the ratio to 1 lowered the yields
significantly.
The amount of solvent was also investigated. The results
(Table 1, entries 13, 15, 16, 22, 28, and 29) show that decreas‐
ing the amount of solvent from 3 to 1 mL increases the epoxide
yield.
Fig. 7 shows the effect of reaction time on the epoxidation of
cis‐cyclooctene with TBHP. A comparison between the reactivi‐
ties of the Mo‐AFBNPs and V‐AFBNPs catalysts reveals that the
supported molybdenum catalyst is more reactive, and after 90
min, its conversion reaches a maximum, and then becomes
constant. However, the supported vanadium complex requires
180 min to reach this goal.
96
100
80
60
40
20
93
Mo-AFBNPs
V-AFBNPs
30
60
90
120
Time (min)
150
180
210
Fig. 7. Epoxidation of 0.7 mmol of cis‐cyclooctene with 1.4 mmol of
TBHP catalyzed by 20 mg of Mo‐AFBNPs or V‐AFBNPs in 3 mL of CCl4
under reflux conditions.
been determined earlier. The reaction was then allowed to
continue and reach the optimum reaction time without the
presence of the catalyst. The results obtained showed that
when the catalyst was removed from the reaction medium, the
catalytic procedure stopped and did not continue anymore.
This test proves that the catalytic reactions proceeded in het‐
erogeneous conditions and the catalysts were not leached into
the reaction medium.
We also studied the reaction progress in the presence of the
related homogenous catalysts. The results showed that by us‐
ing Mo(CO)6 or VOSO4·H2O as the catalyst under the same ex‐
perimental conditions for the heterogeneous counterparts, the
reaction yields reduced to 85% and 55%, respectively. The
greater reactivities of the heterogeneous Mo‐AFBNPs and
V‐AFBNPs catalysts may be related to the homogenous disper‐
sion of the catalytic active sites onto the surface of BNPs, which
efficiently increased the effective collision of the reagents to the
metal sites, and consequently, increased the cyclooctene epox‐
ide yield in comparison to the homogeneous counterparts. In
addition, anchoring the molybdenum and vanadium complexes
onto the BNPs surface protect them from dimerization by
oxo‐bridge formation, which leads to the deactivation of the
catalytic sites and lowers the yields in homogenous reaction
conditions.
The new catalysts Mo‐AFBNPs and V‐AFBNPs can also be
used for the epoxidation of a wide range of substituted alkenes
(Table 2). The blank experiments, performed without catalysts,
with BNPs or AFBNPs, showed a very low conversion even
after 5 h reflux. In the presence of Mo‐AFBNPs and V‐AFBNPs, a
wide range of both the cyclic and linear alkenes could efficient‐
ly and selectively be converted to epoxides. Based on the epox‐
idation mechanisms suggested earlier [44], the higher elec‐
tron‐donating ability of an alkene double bond is expected to
show more epoxidation reactivity. Therefore, cyclooctene and
cyclohexene with inner double bonds should exhibit more ac‐
tivity in comparison with 1‐hexene and 1‐octene, which contain
terminal double bonds. In addition, cyclooctene is more reac‐
tive than cyclohexene owing to some cyclooctene confor‐
Moreover, the heterogenic character of these catalysts was
checked by a hot filtration test. For this purpose, each catalyst
was removed by centrifuging the catalytic reaction mixture at
the halfway point of the optimum reaction time, which had
100
80
60
73
63
40
Mo-AFBNPs
20
0
V-AFBNPs
0
10
20
30
40
50
Amount of catalyst (mg)
Fig. 6. Epoxidation of 0.7 mmol of cis‐cyclooctene with 1.4 mmol of
TBHP, catalyzed by Mo‐AFBNPs or V‐AFBNPs in 3 mL of CCl4 after 2 h
under reflux conditions.

1270
Mahdi Mirzaee et al. / Chinese Journal of Catalysis 37 (2016) 1263–1274
Table 2
Epoxidation of some alkenes with TBHP catalyzed by Mo‐AFBNPs or V‐AFBNPs under reflux conditions.
Mo‐AFBNPs a
V‐AFBNP
Epoxide b
Time
(h)
Epoxide b
Entry
Alkene
Conversion b (%)
96
Conversion b (%)
93
Time (h)
3
(%) (large scale c)
(%) (large scale c)
1
2
96 (92)
70 (67)
1.5
1.5
93 (88)
85 (81)
98d
92d
3
3
4
60
68
60 (55)
68 (63)
6
6
58
60
58 (54)
60 (55)
10
10
5
6
88e
98f
81 (77)
86 (81)
6
87e
89f
66 (61)
80 (76)
10
3
1.5
7
99g
92g
99 transh
3
3
98g
90g
98 transh
6
6
8
79 cis and 13 transi
79 cis and 11 transi
a GLC yield based on the starting alkenes.
b Reaction conditions: alkene 0.7 mmol, TBHP 1.4 mmol, catalyst 20 mg, CCl4 1 mL.
c Large scale reaction conditions: alkene 14 mmol, TBHP 28 mmol, catalyst 0.4 g, CCl4 20 mL.
d The byproduct (cyclohexanone) is 18% for Mo‐AFBNPs and 7% for V‐AFBNPs.
e The byproduct (benzaldehyde) is 7% for Mo‐AFBNPs and 21% for V‐AFBNPs.
f The byproduct (acetophenone ) is 12% for Mo‐AFBNPs and 9% for V‐AFBNPs.
g Both 1H NMR and GLC data approved the reported yields.
h Trans isomer is the only product, according to 1H NMR data.
i Cis and trans isomers are both produced, according to 1H NMR data.
mations that favor the formation of reaction intermediates that
decrease the activation energy [46]. In contrast, 1‐octene is
oxidized slower than 1‐hexene, and this observation could be
attributed to the more steric hindrance of the hexyl group con‐
nected to the double bond present in 1‐octene in comparison
with the butyl group in 1‐hexene. A larger hexyl group can ef‐
fectively hinder the approach of 1‐octene to the catalyst metal
center, and slow down the reaction. Cis‐ and trans‐stilbene
were also completely converted to epoxides by the Mo‐AFBNPs
and V‐AFBNPs catalysts. Surprisingly, trans‐stilbene gives only
a trans epoxide, and cis‐stilbene gives a mixture with a high
cis/trans epoxide molar ratio (Table 2). This shows the high
selectivities of these catalysts in the epoxidation of alkenes. In
addition, we scaled‐up the reaction and reported the results
obtained in Table 2. These results show only a 4%–6% reduc‐
tion in the epoxide yields of different alkenes in comparison to
the small‐scale experiment, and they confirmed the potential
use of these catalytic protocols in industrial procedures.
first‐order dependence on the catalyst and substrate concen‐
trations. There are also some crucial stages in these processes.
The V‐AFBNPs catalyst initially contains the oxo ligand on its
metal center but, for Mo‐AFNBPs, the pending molybdenum
complex is oxidized in the first step, and an oxo‐molybdenum
complex is formed. The next step for both catalysts involves the
transfer of the TBHP hydroxyl proton to a terminal oxygen
atom of these oxo complexes, which results in the coordination
of the tert‐butylperoxide anion to the Lewis acidic metal cen‐
ters. Then the alkene substrate is coordinated to the metal
center, and, as a nucleophile, is inserted into the metal oxygen
bond of the coordinated peroxide electrophile anion. This
mechanism easily explains the faster reaction of the elec‐
tron‐rich alkenes in comparison to the electron‐poor ones. In
the next step, the epoxide product is formed, and the
tert‐butylperoxide anion is converted to the tert‐butoxide ani‐
on. Then the peroxide product is released and the catalytic cy‐
cle is continued by substitution of a new tert‐butylperoxide
instead of the tert‐butoxide anion.
Based on the Sobczak’s report [47] and other experimental
and theoretical reports [2,7,15,45], probable mechanisms were
proposed for the epoxidation of cyclooctene with TBHP by the
Mo‐AFBNPs and V‐AFBNPs catalysts (Schemes 2 and 3). Ac‐
cording to our experimental results, the reaction rates display a
3.3. Catalyst recovery and reuse
As discussed earlier, the reusability of solid‐supported cata‐

Mahdi Mirzaee et al. / Chinese Journal of Catalysis 37 (2016) 1263–1274
1271
O
O
TBOH
II
OH H2N
O
O
Mo
O
HO
Si
III
O
TBHP
O
OH
OH
OH
O
O
OC
O
CO
Mo CO
CO
OH H2N
O
O
Mo
O
H2N
Mo
OH H2N
OH
O
O
HO
OC
O
O
O
HO
Si
O
Si
Si
O
H
OH
OH
OH
OH
OH
OH
OH
OH
OH
I
O
O
TBOH
V
OH H2N
O
O
Mo
IV
O
O
HO
Si
O
OH
OH
OH
Scheme 2. Proposed mechanism for epoxidation of alkenes with TBHP by Mo‐AFBNPs.
TBOH
TBHP
O
I
O
OH
OH
S
O
O
H
2
N
H
N
O
O
OH
OH
2
O
O
Si
HO
S
O
Si
HO
O
V
O
V
O
(V)
OH
OH
(IV)
O
O
O
TBHP
II
TBOH
IV
O
O
O
O
S
S
O
O
O
O
OH
OH
V
(V)
O
H
V
(V)
OH
O
O
OH
OH
O
O
Si
HO
N
2
Si
HO
N
H
H
2
O
O
O
O
OH
OH
C(Me)
C(Me)
3
3
III
Scheme 3. Proposed mechanism for epoxidation of alkenes with TBHP by V‐AFBNPs.
lysts is one of their most important benefits. Therefore, the
reusability of the Mo‐AFBNPs and V‐AFBNPs catalysts was
monitored by means of multiple sequential epoxidations of
cis‐cyclooctene with TBHP (Table 3). After each cycle, the reac‐
tion mixture was centrifuged, and the supernatant solutions
and recovered catalysts were analyzed by ICP. This analysis
showed that there was no metal contaminant in the superna‐
tant solution, and no decrease in the metal loading of the re‐
covered catalyst. It also confirmed that the metal ions did not
leach from the heterogeneous catalysts, and that the reactions
were performed entirely under heterogeneous conditions. In
addition, retention of the catalytic activity, up to five cycles, for
recovered Mo‐AFBNPs, makes it a better candidate for the
epoxidation of alkenes. The reason for the small gradual de‐
crease in the yields with V‐AFBNPs was attributed to the poi‐
soning effect of water vapor, which may be adsorbed during the
recovering process and blocks the catalytic sites on the metal
center.
Turnover frequency (TOF) is a virtuous parameter for the
comparison of the catalytic activities, so we used it to show the

1272
Mahdi Mirzaee et al. / Chinese Journal of Catalysis 37 (2016) 1263–1274
Table 3
Epoxidation of cis‐cylooctene with TBHP under reflux conditions using recycled catalysts.
Mo‐AFBNPs catalyst a
V‐AFBNPs catalyst b
Number of
cycles
Content f
(mmol/g)
Epoxide yield c
TOF d
(h–1)
Content f
(mmol/g)
Epoxide yield c (%) TOF d (h–1) Leached e (%)
Leached e (%)
(%)
93
91
90
87
85
1
2
3
4
5
96
92
90
90
90
75
72
70
70
70
ND
ND
ND
ND
ND
0.3
39
38
37
36
ND
ND
ND
ND
ND
0.28
0.28
0.27
0.27
0.28
0.29
0.29
0.3
0.29
35
a Reaction conditions: cyclooctene 0.7 mmol, TBHP 1.4 mmol, catalyst 20 mg, CCl41 mL, 90 min.
b Reaction conditions: cyclooctene 0.7 mmol, TBHP 1.4 mmol, catalyst 20 mg, CCl4 1 mL, 180 min.
c GLC yields are based on the starting cyclooctene.
d TOF = mole of reactant  yield/(100  mole of catalyst  time)
e Metal leached from catalyst into the catalytic solution medium determined by ICP.
f Metal content of recycled catalyst determined by ICP.
ND—Not detected
benefits of our catalytic systems over other reported catalytic
protocols. Very recently, Feng et al. [21] have supported a di‐
oxo‐molybdenum complex onto an organic copolymer and
reached a TOF of 5 in the epoxidation of cis‐cyclooctene with
TBHP. Sakthivel et al. [31] have supported Mo(CO)6 on SBA‐15
Acknowledgments
The authors would like to thank the vice‐president's office
for research affairs of Shahrood University of Technology for
the financial support of this work. We also would like to
acknowledge the kind helps of Ms. Adonis Amoli and Mr.
Mahmood Norouzi.
and reported
a TOF of 32 in the same reaction.
Moahmmadikish et al. [48] have supported a molybdenum
complex onto nanomagnetite and reported a TOF of 19 with the
same catalytic reaction conditions. Yang et al. [49] have also
supported a molybdenum Schiff base complex onto SBA‐15 and
reached a TOF of 25 in the same reaction. Moghadam et al. [50]
have reported a TOF of 55.4 for the catalytic epoxidation of
cis‐cyclooctene with TBHP by a molybdenum complex sup‐
ported onto multi‐walled carbon nanotubes. All of these re‐
ports have lower TOF values than the TOF value obtained for
Mo‐AFBNPs in the present research work. In addition, the TOF
values for Mo‐AFBNPs and V‐AFBNPs (75 and 39 h–1, respec‐
tively) in the present report are significantly greater than their
Schiff‐base counterparts, Mo‐IFBNPs and V‐IFBNPs (44 and 29
h–1, respectively), in our previous report [42].
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Mahdi Mirzaee et al. / Chinese Journal of Catalysis 37 (2016) 1263–1274
1273
Graphical Abstract
Chin. J. Catal., 2016, 37: 1263–1274 doi: 10.1016/S1872‐2067(16)62451‐8
Amine‐functionalized boehmite nanoparticle‐supported
molybdenum and vanadium complexes: Efficient catalysts for
epoxidation of alkenes
Mahdi Mirzaee*, Bahram Bahramian, Marieh Mirebrahimi
Shahrood University of Technology, Iran
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