MoO2(acac)2 supported on multi-wall carbon nanotubes: Highly efficient and reusable catalysts for alkene epoxidation with tert-BuOOH

Article abstract of DOI:10.1016/j.poly.2012.08.084

In the present work, the preparation, characterization and investigation of the catalytic activity of MoO₂(acac)₂ supported on multi-wall carbon nanotubes modified with 2-aminopyridine and 1,2-diaminobenzene are reported. The catalysts were characterized by elemental analysis, FT-IR and UV-Vis spectroscopic techniques and scanning electron microscopy (SEM). The catalytic activity of molybdenyl acetylacetonate supported on multi-wall carbon nanotubes, MoO₂(acac)@amine-MWCNTs, was investigated in the alkene epoxidation with tert-BuOOH. These heterogenized catalysts were successfully applied for efficient epoxidation of olefins with tert-BuOOH in 1,2-dichloroethane as the solvent. The prepared catalysts can be reused several times without significant loss of their catalytic activity.

Full text of DOI:10.1016/j.poly.2012.08.084

Polyhedron 48 (2012) 212–220
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
MoO2(acac)2 supported on multi-wall carbon nanotubes: Highly efficient and
reusable catalysts for alkene epoxidation with tert-BuOOH
⇑
⇑
Fariba Esnaashari, Majid Moghadam , Valiollah Mirkhani , Shahram Tangestaninejad,
Iraj Mohammadpoor-Baltork, Ahmad Reza Khosoropour, Maryam Zakeri, Shohreh Hushmandrad
Department of Chemistry, Catalysis Division, University of Isfahan, Isfahan 81746-73441, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
In the present work, the preparation, characterization and investigation of the catalytic activity of MoO2-
(acac)2 supported on multi-wall carbon nanotubes modified with 2-aminopyridine and 1,2-diaminoben-
zene are reported. The catalysts were characterized by elemental analysis, FT-IR and UV–Vis
spectroscopic techniques and scanning electron microscopy (SEM). The catalytic activity of molybdenyl
acetylacetonate supported on multi-wall carbon nanotubes, MoO2(acac)@amine-MWCNTs, was investi-
gated in the alkene epoxidation with tert-BuOOH. These heterogenized catalysts were successfully
applied for efficient epoxidation of olefins with tert-BuOOH in 1,2-dichloroethane as the solvent. The
prepared catalysts can be reused several times without significant loss of their catalytic activity.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 11 April 2012
Accepted 28 August 2012
Available online 13 September 2012
Keywords:
Heterogeneous catalyst
Epoxidation
Molybdenyl acetylacetonate
Multi-wall carbon nanotubes
Reusable catalyst
1. Introduction
approaches have been used in order to obtain heterogeneous
molybdenum catalysts for olefins epoxidation [6].
Catalytic olefin epoxidation in the liquid phase is one of the
most important topics for the synthesis of fine chemicals [1],
because these compounds are valuable intermediates both in lab-
oratory research and in industry for production of chemicals such
as polyethers, diols and aminoalcohols. In the last few decades,
several soluble metal salts or complexes have been reported as
active catalysts in the epoxidation of alkenes. Amongst them, the
homogeneous complexes of Mo, W and Ti have been applied as
catalysts for olefin epoxidation [2]. Molybdenum-containing com-
plexes have been particularly investigated because of their good
catalytic activity for selective oxidations [3,4].
Reusable heterogeneous catalysts have attracted a great deal of
interest from laboratory and industrial points of view [5]. Since
most of the catalysts are expensive and contaminate the environ-
ment, the development of efficient methods for recovery and reuse
of the catalysts is a very important aspect from an economical
point of view. One way to overcome this problem is to immobilize
the homogeneous catalysts on solid supports. The major advanta-
ges of solid-supported catalysts are the facile recovery from the
reaction mixture and possibility of reusing them. Furthermore,
supporting of the catalysts efficiently increases the surface area
and subsequently the reactivity of the catalysts. Different
In recent years, functionalized polymers and inorganic supports
have been used for the immobilization of homogeneous catalysts.
Sherrington group synthesized polystyrene, polymethacrylate,
polybenzimidazole and polysiloxane resins for the immobilization
of Mo(VI) catalysts, and investigated their catalytic activity in
alkene epoxidation with tert-butyl hydroperoxide [7–12]. Recently,
we reported the use of molybdenum hexacarbonyl immobilized on
functionalized polystyrene as an active and highly reusable alkene
epoxidation catalyst with tert-BuOOH [13–15]. However, com-
pared to organic supports, inorganic ones do not swell or dissolve
in organic solvents, and show better thermal and mechanical sta-
bilities. Immobilized molybdenum compounds on functionalized
inorganic supports via various mono- or bidentate ligands have
been reported for epoxidation of alkenes [16–20]. On the other
hand, several approaches have been reported for the immobiliza-
tion of molybdenum catalysts on silica [21–25], modified MCM-
41 [26–34], zeolites [35], layered double hydroxides [36] and
multi-wall carbon nanotubes [37–39].
Carbon nanotubes (CNTs) have attracted much attention with
regards to their synthesis, characterization and applications,
because of their unique structural, mechanical, thermal and elec-
tronical properties. Due to the above mentioned properties, and
also high surface area of CNTs and their insolubility in most sol-
vents, these materials can be used as catalyst supports [40,41].
For example, Pt nanoparticles supported on CNTs have been used
for methanol oxidation [42], palladium nanoparticles supported
⇑
Corresponding authors. Tel.: +98 311 7932712; fax: +98 311 6689732.
E-mail addresses: moghadamm@sci.ui.ac.ir (M. Moghadam), mirkhani@sci.ui.
ac.ir (V. Mirkhani).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.08.084

F. Esnaashari et al. / Polyhedron 48 (2012) 212–220
213
porphyrin and manganese(III) salophen supported on MWCNTs
for epoxidation of alkenes with NaIO4 [46–49] and molybdenum
and tungsten complexes supported on MWCNTs for alkenes epox-
idation with tert-BuOOH [37–39,50–52].
In this paper, we report on the preparation and characterization
of molybdenyl acetylacetonate supported on amine modified
multi-wall carbon nanotubes and an investigation of their catalytic
activity in the epoxidation of alkenes with tert-BuOOH (Scheme 1).
Scheme 1. Alkene epoxidation with tert-BuOOH catalyzed by [MoO2(acac)@DAB-
MWCNT] and [MoO2(acac)@APy-MWCNT].
2. Experimental
Table 1
The specification of MWCNT-COOH used in this study.
All materials were commercial reagent grade and obtained from
Merck and Fluka. Elemental analysis was performed on a Perkin-
Elmer 2400 instrument. Atomic absorption analysis was carried
out on a Shimadzu 120 spectrophotometer. Diffuse reflectance
spectra were recorded on a Shimadzu UV-265 instrument using
optical grade BaSO4 as a reference. FT-IR spectra were obtained as
potassium bromide pellets in the range 500–4000 cmÀ1 with a
Bomen-Hartmann instrument. Scanning electron micrographs of
the catalysts were taken on a SEM Philips XL 30. 1H NMR spectra
MWCNT- COOH
Inside
diameter
Outside
diameter
Length COOH
content
Specific surface
area
5–10 nm
20–30 nm
30
lm
1.5%
>110 m2/g
on CNTs for semi-hydrogenation of phenylacetylene [43], a chiral
vanadyl salen complex supported on single-wall CNTs for enantio-
selective cyanosilylation of aldehydes [44,45], manganese(III)
Scheme 2. Preparation of [MoO2(acac)@DAB-MWCNT] and [MoO2(acac)@APy-MWCNT].

214
F. Esnaashari et al. / Polyhedron 48 (2012) 212–220
were recorded on a Bruker-Avance AQS 400 MHz. The ICP analyzes
were performed on an ICP-Spectrociros CCD instrument. Gas
chromatography experiments (GC) were performed on a Shimadzu
GC-16A instrument using a 2 m column peaked with silicon DC-200
or Carbowax 20 m. In the GC experiments, n-decane was used as an
internal standard. MWCNTs (multiwall carbon nanotubes with
outside diameters between 20 and 30 nm containing –COOH
groups, purity 96%) were purchase from Shenzen NTP Factory
(China). Conversions and yields were obtained by GC experiments
and the products were identified after isolation and purification.
2.2. Preparation of MWCNT-DAB and MWCNT-APy
In a 100 mL round-bottom flask equipped with a magnetic stir-
ring bar, a mixture of MWCNT-COCl (2 g), 1,2-diaminobenzene or
2-aminopyridine (2 g) and Et3N (3 mL) in dimethyl formamide
(DMF) (50 mL) was heated at 80 °C for 72 h. Then, the reaction
mixture was filtered, washed with CH3CN and dried at 30–40 °C
[37]. CHN analysis for MWCNT-DAB: C, 93.20; H, 0.93; N, 1.67%.
CHN analysis of MWCNT-APy: C, 93.03; H, 0.82; N, 2.11%.
2.3. Preparation of the catalysts, [MoO2(acac)@DAB-MWCNT] and
[MoO2(acac)@APy-MWCNT]
2.1. Chlorination of MWCNT-COOH
In a 100 mL round-bottom flask equipped with a condenser and
a magnetic stirrer bar, MWCNT-COOH (5 g) and SOCl2 (30 mL)
were mixed and refluxed for 1 h under an argon atmosphere. After
that, the reaction mixture was cooled and the SOCl2 was
evaporated. The resulting precipitate was chlorinated multi-wall
carbon nanotubes, MWCNT-COCl [37].
MoO2(acac)2 was synthesized according to the published proce-
dure [53]. MoO2(acac)2 (1 g) was dissolved in methanol (CH3OH)
(60 mL) and then MWCNT-DAB or MWCNT-APy (1 g) was added
to this solution and refluxed for 48 h. At the end of the reaction,
the solution was filtered, washed thoroughly with CH3CN and
dried in vacuum.
Fig. 1. The FT-IR spectra of (A) MWCNT-COOH and (B) MWCNT-COCl.

F. Esnaashari et al. / Polyhedron 48 (2012) 212–220
215
Fig. 2. The FT-IR spectra of (A) MWCNT-DAB, (B) [MoO2(acac)@DAB-MWCNT], and (C) recovered [MoO2(acac)@DAB-MWCNT].
Fig. 3. The FT-IR spectra of (A) MWCNT-APy, (B) [MoO2(acac)@APy-MWCNT], and (C) recovered [MoO2(acac)@APy-MWCNT].

216
F. Esnaashari et al. / Polyhedron 48 (2012) 212–220
2.4. General procedure for epoxidation of alkenes with tert-BuOOH
catalyzed by [MoO2(acac)@DAB-MWCNT] and [MoO2(acac)@
APy-MWCNT]
In a 25-mL round-bottom flask equipped with a magnetic stirrer
bar, a mixture of alkene (1 mmol), tert-BuOOH (2 mmol), [MoO2
(acac)@DAB-MWCNT] (5 mg, 9.3 Â 10À4 mmol) or [MoO2(acac)
@APy-MWCNT] (5 mg, 2.7 Â 10À4 mmol) and 1,2-dichloroethane
(5 mL) was refluxed under stirring. The reaction progress was mon-
itored by GC. At the end of the reaction (since different alkenes have
different reactivity toward oxidation, therefore the reactions
were continued until no progress was observed), the reaction mix-
ture was diluted with Et2O (20 mL) and filtered. The catalyst was
thoroughly washed with Et2O and the combined washing and
filtrates were purified on a silica gel plate to obtain the pure product.
A blank experiment in the presence of oxidant and using the
same experimental conditions in the absence of catalyst was also
performed.
2.5. Reusability of the catalysts
Fig. 4. The UV–Vis spectrum of Mo(O)2(acac)2.
The reusability of the catalysts was studied in the repeated
epoxidation reaction of cis-cyclooctene. The reactions were carried
out as described above. At the end of each reaction, the catalysts
were filtered, washed thoroughly with Et2O, dried and reused.
3. Results and discussion
3.1. Preparation and characterization of the catalysts
The properties of MWCNTs bearing carboxylic acid groups
used as a support are listed in Table 1. Scheme 2 shows the prep-
aration procedure for the supported molybdenum catalysts. The
amine modified MWCNTs, DAB-MWCNT and APy-MWCNT, were
prepared by the reaction of MWCNT-COCl with 1,2-diaminoben-
zene and 2-aminopyridine, respectively. Reaction of DAB-MWCNT
or APy-MWCNT (as bidentate ligands) with a solution of Mo(O)2-
(acac)2 in methanol and under reflux conditions produced the
[MoO2(acac)@DAB-MWCNT] or [MoO2(acac)@APy-MWCNT] cata-
lyst via coordination of molybdenyl acetylacetonate to the
amine-modified MWCNT (Scheme 2). These catalysts were charac-
terized by elemental analysis, scanning electron microscopy, FT-IR
and diffuse reflectance UV–Vis spectroscopic methods. The nitrogen
content of [MoO2(acac)@DAB-MWCNT] was 1.24%. According to this
value, the degree of nitrogen, which is available for Mo
attachment, was 0.44 mmol/g of support. The metal loading of
[MoO2(acac)@DAB-MWCNT], measured by ICP, was 0.185 mmol/g.
The nitrogen content of [MoO2(acac)@APy-MWCNT] was 1.5%.
According to this value, the degree of nitrogen which is available
for Mo attachment was 0.54 mmol/g of support. The metal loading
of [MoO2(acac)@APy-MWCNT] measured by ICP was 0.053 mmol/g.
The FT-IR spectra of MWNT-COOH, MWNT-COCl, DAB-
MWCNT,
APy-MWCNT,
[MoO2(acac)@DAB-MWCNT]
and
[MoO2(acac)@APy-MWCNT] are shown in Figs. 1–3. In the parent
MWNT-COOH, the C@O stretching band appears at 1647 cmÀ1
(Fig. 1A), while upon conversion to MWNT-COCl, this band ap-
pears at 1639 cmÀ1 (Fig. 1B). In the FT-IR spectra of both supports
and catalysts (Figs. 2A, B and 3A and B), the C@O stretching band
of the amide group appears at 1630–1632 cmÀ1. The presence of
bands in the range 800–900 cmÀ1 in the supported catalysts,
which are attributed to Mo@O vibrations, is a good indication
for attachment of cis-MoO2 species to the support.
Fig. 5. The DR UV–Vis spectra of (A) [MoO2(acac)@DAB-MWCNT] and (B) recovered
[MoO2(acac)@DAB-MWCNT].
In the FT-IR spectrum of homogeneous MoO2(acac)2, the MoO2
species bands appear at 905 and 934 cmÀ1. The coordinated acac
ligand showed bands at 1589, 1504 and 1360 cmÀ1 (C@O),
however we could not observe these bands in the supported cata-
lysts. Two possible states can be considered. The most probable

F. Esnaashari et al. / Polyhedron 48 (2012) 212–220
217
one is that the corresponding acac bands are masked by the
3.3. The effect of catalyst amount on the epoxidation of cyclooctene
MWCNTs bands, and the less probable case is that both acac li-
gands are replaced by supported bidentate ligands and therefore
the lack of bands corresponds to the absence of acac ligands.
In the Mo-containing species, the nature of the ligands has an
important role in the intensity and energy of the electronic spectra
[54]. The UV–Vis spectrum of MoO2(acac)2 (Fig. 4) shows an
absorption band at 270 nm, which is attributed to a ligand to Mo
charge transfer band. This band also appears in the diffuse reflec-
tance UV–Vis spectra of the solid catalysts at 268–263 nm, which
confirms the attachment of MoO2(acac)2 to the MWCNTs
(Figs. 5A and 6A).
catalyzed by [MoO2(acac)@DAB-MWCNT] and [MoO2(acac)@APy-
MWCNT]
Different amounts of catalyst were used to optimize the catalyst
amount and the best results were obtained in the presence of 5 mg
The SEM images of these catalysts show that the nanotubes are
aggregated and have retained their nanotube nature (Fig. 7).
3.2. The effect of solvent on the epoxidation of cyclooctene with tert-
BuOOH catalyzed by [MoO2(acac)@DAB-MWCNT] and
[MoO2(acac)@APy-MWCNT]
First, the effect of different solvents on the catalytic activity of
the resulting catalyst was investigated in the epoxidation of cis-
cyclooctene with tert-butyl hydroperoxide. Among the solvents
1,2-dichloroethane, dichloromethane, chloroform, acetonitrile,
acetone and methanol, refluxing 1,2-dichloroethane was chosen
as reaction media because the highest epoxide yield was observed
(Table 2). This can be attributed to the non-coordinating nature of
this solvent. When the same reactions were performed at room
temperature, the systems were less efficient and the epoxide yield
was 19% and 28% for [MoO2(acac)@DAB-MWCNT] and [MoO2
(acac)@APy-MWCNT], respectively. This can be attributed to the
isolation of catalytic active sites on the high surface area MWCNTs.
Fig. 7. The SEM images of (A) [MoO2(acac)@DAB-MWCNT] and (B) [MoO2(-
acac)@APy-MWCNT].
Table 2
The effect of solvent on the epoxidation of cis-cyclooctene with tert-BuOOH under
reflux conditions.a
Solvent
[Mo(O)2(acac)@DAB-MWCNT]
[Mo(O)2(acac)@APy-MWCNT]
Epoxideb (%)
Time (h)
Epoxideb (%)
Time (h)
CH3CN
C2H5OH
CH3OH
1,2-DCE
CH2Cl2
CHCl3
10
5
25
99
20
30
2
2
2
2
2
2
12
8
30
96
21
28
2
2
2
2
2
2
a
Reaction conditions: cis-cyclooctene (1 mmol), tert-BuOOH (2 mmol), catalyst
(5 mg), 5 mL solvent.
Fig. 6. The DR UV–Vis spectra of (A) [MoO2(acac)@APy-MWCNT] and (B) recovered
[MoO2(acac)@APy-MWCNT].
b
GC yield based on the starting cyclooctene.

218
F. Esnaashari et al. / Polyhedron 48 (2012) 212–220
Table 3
Epoxidation of alkenes with tert-BuOOH catalyzed by [MoO2(acac)@DAB-MWCNT] under reflux conditions.a
Entry
1
Alkene
Conversionb (%)
99
Epoxide selectivity (%)
100
Time (h)
2
TOF (hÀ1
538.0
)
2
90
100
2
489.1
3
4
90
95
84c
85d
5
5
195.6
206.5
5
86
100
12
77.9
7
8
9
80
92
89
100
100
100
8
10
10
108.7
100.0
96.7
.
10
11
97
99
99 (trans)e
8
8
131.8
131.8
89 (cis), 10 (trans)e
a
b
c
Reaction conditions: alkene (1 mmol), tert-BuOOH (2 mmol), catalyst (5 mg, 0.00092 mmol) and 1,2-dichloroethane (5 mL).
GC yield based on starting alkene.
Benzaldehyde was produced as a by-product.
d
e
Acetophenone was produced as a by-product.
Both 1H NMR and GC data approved the reported yields.
(0.00093 mmol) of [MoO2(acac)@DAB-MWCNT] and 5 mg (0.00
027 mmol) of [MoO2(acac)@APy-MWCNT]. Note that in the absence
of catalyst, only less than 10% of epoxide was observed. When the
same reaction was carried out using the same amounts of homoge-
neous catalyst (0.001, equal to the amount of Mo in [MoO2(acac)
@DAB-MWCNT], and 0.0003 mmol, equal to the amount of Mo in
[MoO2(acac)@APy-MWCNT]), the epoxide yield was 45% for 0.0
01 mmol and 18% for 0.0003 mmol of MoO2(acac)2.
In comparison with the data reported in our previous works on
the epoxidation of alkenes with other molybdenum catalysts, these
catalytic systems show much higher efficiency in the oxidation of
alkenes (by comparison of their TOFs) (Table 5). One reason for this
behavior may be related to the nano-particle nature of the MWCNTs
with high specific surface area, which in turns increases the cata-
lytic activity. Compared to room temperature epoxidation catalysts,
such as manganese(III) porphyrins and manganese(III) salophen
supported on functionalized MWCNTs, [MoO2(acac)@DAB-MWC
NT] and [MoO2(acac)@APy-MWCNT] show higher catalytic activity.
3.4. Catalytic alkene epoxidation with tert-BuOOH in the presence of
[MoO2(acac)@DAB-MWCNT] and [MoO2(acac)@APy-MWCNT]
3.5. Catalyst reuse and stability
Under the optimized conditions, these catalytic systems were
applied for alkene epoxidation with tert-BuOOH (Tables 3 and 4).
The obtained results in the presence of [MoO2(acac)@DAB-MWCNT]
and [MoO2(acac)@APy-MWCNT] showed that these catalysts are
efficient catalysts in the epoxidation of a wide range of alkenes,
including cyclic and linear ones. 1-Octene, 1-decene and 1-dode-
cene as linear alkenes were epoxidized efficiently by these catalysts
in high yields. Cyclic olefins such as cyclohexene and cyclooctene
were also epoxidized in high yields and selectivity. In the case of
styrene, benzaldehyde was produced as a minor product and in
The reusability of a supported catalyst can be one of the most
important benefits and makes it useful for commercial
applications. The recovery and reusability of the supported
[MoO2(acac)@DAB-MWCNT] and [MoO2(acac)@APy-MWCNT] cat-
alysts were investigated in the sequential epoxidation of cis-cyclo-
octene with tert-BuOOH. At the end of the reaction, the catalysts
were separated by simple filtration and the catalysts were washed
with acetone and dried before using in the next run. The filtrates
were used for determining the catalyst leaching. The results
showed that only small amounts of Mo catalysts were leached after
the first run and no Mo was detected after the second run in the
reaction mixture (Table 6). Also, the catalytic behavior of the sep-
arated liquids was tested by addition of fresh olefin to the filtrates
after each run. The oxidation reaction under the same reaction
the epoxidation of
a-methylstyrene, acetophenone was also pro-
duced. Stilbenes (both cis and trans) were also epoxidized by these
heterogenized catalysts in high yields. trans-Stilbene gives only
trans-epoxide and cis-stilbene produces a mixture with a high
cis/trans-epoxide ratio.

F. Esnaashari et al. / Polyhedron 48 (2012) 212–220
219
Table 4
Epoxidation of alkenes with tert-BuOOH catalyzed by MoO2(acac)@APy-MWCNT under reflux conditions.a
Entry
1
Alkene
Conversionb (%)
96
Epoxide selectivity (%)
100
Time (h)
2
TOF (hÀ1
)
1777.8
2
90
100
3
1111.1
3
4
84
89
83c
84d
5
7
622.2
470.9
5
80
100
12
246.9
7
8
9
82
84
85
100
100
100
8
12
14
379.6
259.3
224.9
.
10
97
99 (trans)e
8
449.1
11
97
88 (cis), 11 (trans)e
8
449.1
a
b
c
Reaction conditions: alkene (1 mmol), tert-BuOOH (2 mmol), catalyst (5 mg, 0.00027 mmol) and 1,2-dichloroethane (5 mL).
GC yield based on starting alkene.
Benzaldehyde was produced as a by-product.
d
e
Acetophenone was produced as a by-product.
Both 1H NMR and GC data approved the reported yields.
Table 5
Comparison of the results obtained for epoxidation of cyclooctene catalyzed by [Mo(O)2(acac)@APy-MWCNT] and [Mo(O)2(acac)@DAB-MWCNT] with some of our previously
reported systems.
Entry
Catalyst
Support
Oxidant
Conditions (°C)/solvent
TOF (hÀ1
)
Ref.
1
2
3
4
5
6
7
8
9
10
11
12
13
MoO2(acac)2
MoO2(acac)2
Molybdenum hexacarbonyl
Molybdenum hexacarbonyl
MoO2(acac)2
APy-MWCNT
DAB-MWCNT
Polystyrene
Polystyrene
Silica
tert-BuOOH
tert-BuOOH
tert-BuOOH
tert-BuOOH
tert-BuOOH
tert-BuOOH
tert-BuOOH
tert-BuOOH
tert-BuOOH
tert-BuOOH
NaIO4
Reflux/DCE
Reflux/DCE
Reflux/CCl4
Reflux/CCl4
Reflux/DCE
Reflux/DCE
Reflux/DCE
Reflux/CCl4
Reflux/CCl4
Reflux/CCl4
RT/CH3CN/H2O
RT/CH3CN/H2O
RT/CH3CN/H2O
1777.8
535.1
31.3
55.2
16.0
15.5
14.7
67.6–83.9
78.4
55.4
This work
This work
[13]
[14]
[25]
[26]
[27]
[37]
[38]
[39]
[46]
[47]
[48,49]
MoO2(acac)2
MoO2(acac)2
MCM-41
MCM-41
Molybdenum hexacarbonyl
Molybdenum hexacarbonyl
Molybdenum hexacarbonyl
Mn(TNH2PP)OAc
Manganese(III) salophen
Mn(TPP)Cl
Amine-MWCNT
APy-MWCNT
APy-MWCNT
MWCNT
Amine-MWCNT
Amine-MWCNT
9.5
6.6–8.0
7.6–12.4
NaIO4
NaIO4
conditions, as with the catalysts, showed that the obtained results
are the same as the blank experiments. The results showed that the
Mo content of the recovered catalysts remains constant. The FT-IR
and UV–Vis spectra of the recycled [MoO2(acac)@DAB-MWCNT]
and [MoO2(acac)@APy-MWCNT] showed no changes in compari-
son with fresh catalysts (Fig. 1C and 2C).
Recently, it has been reported that upon immobilization of
Cu(acac)2 on amine modified activated carbon, one of the acac li-
gands reacts with amine and a Schiff base is prepared which coor-
dinates to the Cu center [55]. We found no evidence in this regard.
The higher Mo loading for [MoO2(acac)@DAB-MWCNT] in compar-
ison with [MoO2(acac)@APy-MWCNT] can be attributed to the
more suitable coordination bite for [MoO2(acac)@DAB-MWCNT]
(Fig. 8A). In the case of [MoO2(acac)@DAB-MWCNT],
a five
member ring is formed which has no ring strain, but in
[MoO2(acac)@APy-MWCNT], a four member ring is formed that
has ring strain. Therefore, it seems that coordination of Mo to the
bidentate 1,2-diaminobenzene is more suitable and catalyst
loading is higher, but in the case of 2-aminopyridine, the ring stain
can lead to higher catalyst leaching (Fig. 8B).

220
F. Esnaashari et al. / Polyhedron 48 (2012) 212–220
[14] G. Grivani, S. Tangestaninejad, M.H. Habibi, V. Mirkhani, M. Moghadam, Appl.
Table 6
Catal. A 299 (2006) 131.
[15] S. Tangestaninejad, M.H. Habibi, V. Mirkhani, M. Moghadam, G. Grivani, Inorg.
Chem. Commun. 9 (2006) 575.
Investigation of catalyst reuse and stability in the epoxidation of cis-cyclooctene with
tert-BuOOH under reflux conditions.a
Run
MoO2(acac)@DAB-MWCNT
MoO2(acac)@APy-MWCNT
[16] M. Jia, W.R. Thiel, Chem. Commun. (2002) 2392.
[17] M. Jia, A. Siefert, W.R. Thiel, Chem. Mater. 15 (2003) 2174.
[18] C.D. Nunes, A.A. Valente, M. Pillinger, A.C. Fernandes, C.C. Romao, J. Rocha, I.S.
Concalves, J. Mater. Chem. 12 (2002) 1735.
[19] C.D. Nunes, M. Pillinger, A.A. Valente, A.D. Lopes, I.S. Gonçalves, Inorg. Chem.
Commun. 6 (2003) 1228.
[20] M. Masteri-Farahani, F. Farzaneh, M. Ghandi, J. Mol. Catal. A 243 (2006) 170.
[21] P.C. Bakala, E. Briot, L. Salles, J.M. Brégeault, Appl. Catal. A 300 (2006) 91.
[22] J. Jarupatrakorn, M.P. Coles, T. Don Tilley, Chem. Mater. 17 (2005) 1818.
[23] G. Wang, L.S. Feng, R.L. Luck, D.G. Evans, Z.Q. Wang, X. Duan, J. Mol. Catal. A
241 (2005) 8.
[24] Q.H. Yang, C. Copéret, C. Li, J.M. Basset, New J. Chem. 27 (2003) 319.
[25] S. Tangestaninejad, M. Moghadam, V. Mirkhani, I. Mohammadpoor-Baltork, K.
Ghani, Inorg. Chem. Commun. 11 (2008) 270.
Epoxideb (%)
Mo leachedc (%)
Epoxideb (%)
Mo leachedc (%)
1
2
3
4
5
99
96
93
92
88
1.4
0
0
0
0
96
93
90
85
83
4.8
0
0
0
0
a
Reaction conditions: alkene (1 mmol), tert-BuOOH (2 mmol), MoO2(acac)@DAB-
MWCNT (5 mg, 0.00092 mmol), MoO2(acac)@APy-MWCNT (5 mg, 0.00027 mmol)
and 1,2-dichloroethane (5 mL).
b
GC yield based on starting alkene.
Determined by ICP.
c
[26] S. Tangestaninejad, M. Moghadam, V. Mirkhani, I. Mohammadpoor-Baltork, K.
Ghani, J. Iran. Chem. Soc. 5 (2008) S71.
[27] S. Tangestaninejad, M. Moghadam, V. Mirkhani, I. Mohammadpoor-Baltork, K.
Ghani, Catal. Commun. 10 (2009) 853.
[28] S.M. Bruno, J.A. Fernandes, L.S. Martins, I.S. Gonçalves, M. Pillinger, P. Ribeiro-
Claro, J. Rocha, A.A. Valente, Catal. Today 114 (2006) 263.
[29] M. Masteri-Farahani, F. Farzaneh, M. Ghandi, J. Mol. Catal. A 248 (2006) 53.
[30] A. Sakthivel, M. Abrantes, A.S.T. Chiang, F.E. Kühn, J. Organomet. Chem. 691
(2006) 1007.
[31] A. Sakthivel, J. Zhao, G. Raudaschl-Sieber, M. Hanzlik, A.S.T. Chiang, F.E. Kühn,
Appl. Catal. A 281 (2005) 267.
O
O
N
NH
NH2
NH
Mo
MWNT
MWNT
Mo
[32] A. Sakthivel, J. Zhao, M. Hanzlik, A.S.T. Chiang, W.A. Herrmann, F.E. Kühn, Adv.
Synth. Catal. 347 (2005) 473.
[33] M. Abrantes, S. Gago, A.A. Valente, M. Pillinger, I.S. Gonçalves, T.M. Santos, J.
Rocha, C.C. Romão, Eur. J. Inorg. Chem. (2004) 4914.
[34] M.J. Jia, A. Seifert, W.R. Thiel, Chem. Mater. 15 (2003) 2174.
[35] A. Sakthivel, J. Zhao, F.E. Kühn, Catal. Lett. 102 (2005) 115.
[36] S. Gago, M. Pillinger, A.A. Valente, T.M. Santos, J. Rocha, I.S. Gonçalves, Inorg.
Chem. 43 (2004) 5422.
[37] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-Baltork,
N.S. Mirbagheri, J. Organomet. Chem. 695 (2010) 2014.
A
B
Fig. 8. Coordination of MWCNT-DAB and MWCNT-APy to MoO2(acac)2.
4. Conclusions
In conclusion, molybdenyl acetylacetonate was supported on
MWCNT modified with 1,2-diaminobenzene and 2-aminopyridine
and characterized by elemental analysis, FT-IR and UV–Vis
spectroscopic techniques and SEM. These heterogeneous catalysts
were used as highly efficient catalysts for epoxidation of cyclic and
linear alkenes with tert-BuOOH. The [MoO2(acac)@DAB-MWCNT]
and [MoO2(acac)@APy-MWCNT] catalysts were highly reusable
and can be reused several times without any appreciable decrease
in their initial activity.
[38] M. Moghadama, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-Baltork, A.
Mirjafari, N.S. Mirbagheri, J. Mol. Catal. A 329 (2010) 44.
[39] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-Baltork,
N.S. Mirbagheri, Appl. Organomet. Chem. 708 (2010) 2014.
[40] D. Tasis, N. Tagmatarchis, A. Bianco, M. Prato, Chem. Rev. 106 (2006) 1105.
[41] J.N. Coleman, U. Khan, W.J. Balu, Y.K. Gunko, Carbon 44 (2006) 1624.
[42] J. Chen, M. Wang, B. Liu, Z. Fan, K. Cui, Y. Kuang, J. Phys. Chem. B 110 (2006)
11775.
[43] S. Domínguez-Domínguez, A. Berenguer-Murcia, B.K. Pradhan, A. Linares-
Solano, D. Cazorla-Amorós, J. Phys. Chem. C 112 (2008) 3827.
[44] C. Baleizão, B. Gigante, H. García, A. Corma, Tetrahedron 60 (2004) 10461.
[45] C. Baleizão, B. Gigante, H. García, A. Corma, J. Catal. 221 (2004) 77.
[46] M. Moghadam, I. Mohammadpoor-Baltork, S. Tangestaninejad, V. Mirkhani, H.
Kargar, N. Zeini-Isfahani, Polyhedron 28 (2009) 3816.
References
[47] S. Tangestaninejad, M. Moghadam, V. Mirkhani, I. Mohammadpoor-Baltork,
M.S. Saeedi, Appl. Catal. A 381 (2010) 233.
[48] M. Zakeri, M. Moghadam, I. Mohammadpoor-Baltork, S. Tangestaninejad, V.
Mirkhani, A.R. Khosrpour, J. Coord. Chem. 65 (2012) 1144.
[1] M. Beller, C. Bolm, Transition Metals for Fine Chemicals and Organic Synthesis,
vol. 2, Wiley-VCH, Weinheim, 1998. pp. 261–267.
[2] K.A. Jorgensen, Chem. Rev. 89 (1989) 431.
[49] M. Zakeri, M. Moghadam, I. Mohammadpoor-Baltork, S. Tangestaninejad, V.
Mirkhani, A.R. Khosrpour, M. Alizadeh, Transition Met. Chem. 37 (2012) 45.
[50] M. Nooraeipour, M. Moghadam, S. Tangestaninejad, V. Mirkhani, I.
Mohammadpoor-Baltork, S.M. Nabavizadeh, Transition Met. Chem. 36 (2011)
861.
[51] M. Nooraeipour, M. Moghadam, S. Tangestaninejad, V. Mirkhani, I.
Mohammadpoor-Baltork, N. Iravani, J. Coord. Chem. 65 (2012) 226.
[52] F. Esnaashari, M. Moghadam, V. Mirkhani, S. Tangestaninejad, I.
Mohammadpoor-Baltork, A.R. Khosropour, Mater. Chem. Phys. http://
dx.doi.org/10.1016/j.matchemphys.2012.08.027
[53] G.J.-J. Chen, J.W. McDonald, W.E. Newton, Inorg. Chem. 15 (1976) 2612.
[54] M.D. Hopkins, W.P. Schaefer, M.J. Bronikowski, W.H. Woodruff, V.M.
Miskowski, R.F. Dallinger, H.B. Gray, J. Am. Chem. Soc. 109 (1987) 408.
[55] A.R. Silva, M. Martins, M.M.A. Freitas, J.L. Figueiredo, C. Freire, B. de Castro, Eur.
J. Inorg. Chem. (2004) 2027.
[3] W.R. Thiel, T. Preimer, Angew. Chem., Int. Ed. Engl. 34 (1995) 1737.
}
[4] F.E. Kuhn, A.D. Lopes, A.M. Santos, E. Herdweck, J.J. Haider, C.C. Romao, J. Mol.
Catal. A 151 (2000) 147.
[5] A. Corma, M. Domine, J.L. Jorda, M.T. Navarro, F. Rey, J. Perez-Pariente, J. Tsuji,
B. Mc Culloch, L.T. Nemeth, Chem. Commun. (1998) 2211.
[6] R.A. Sheldon, I.W.C.E. Arends, H.E.B. Lempers, Catal. Today 41 (1998) 387.
[7] D.C. Sherrington, S. Simpson, J. Catal. 131 (1991) 115.
[8] D.C. Sherrington, S. Simpson, React. Polym. 19 (1993) 13.
[9] M.M. Miller, D.C. Sherrington, S. Simpson, J. Chem. Soc., Perkin Trans. 2 (1994)
2091.
[10] M.M. Miller, D.C. Sherrington, J. Catal. 152 (1995) 368.
[11] M.M. Miller, D.C. Sherrington, J. Catal. 152 (1995) 377.
[12] J.H. Ahn, D.C. Sherrington, Chem. Commun. (1996) 229.
[13] G. Grivani, S. Tangestaninejad, M.H. Habibi, V. Mirkhani, Catal. Commun. 6
(2005) 375.