Oxidation reactions catalysed by molybdenum(VI) complexes grafted on UiO-66 metal–organic framework as an elegant nanoreactor

Article abstract of DOI:10.1002/aoc.3958

A heterogeneous catalyst was synthesized by immobilizing Mo(CO)₃ in a UiO-66 metal–organic framework. The benzene ring of the organic linker in UiO-66 was modified via liquid-phase deposition of molybdenum hexacarbonyl, Mo(CO)₆, as starting precursor to form the (arene)Mo(CO)₃ species inside the framework. The structure of this catalyst was characterized using X-ray diffraction, and chemical integrity was confirmed using Fourier transform infrared and diffuse reflectance UV–visible spectroscopic methods. The metal content was analysed with inductively coupled plasma. Field emission scanning electron microscopy was used to measure particle size and N₂ adsorption measurements to characterize the specific surface area. This catalytic system was efficiently applied for epoxidation of alkenes and oxidation of sulfides. The Mo-containing metal–organic framework was reused several times without any appreciable loss of its efficiency.

Full text of DOI:10.1002/aoc.3958

Received: 14 February 2017
DOI: 10.1002/aoc.3958
Revised: 18 May 2017
Accepted: 17 June 2017
F U L L P A P E R
Oxidation reactions catalysed by molybdenum(VI)
complexes grafted on UiO‐66 metal–organic framework as
an elegant nanoreactor
1
1
1
1
Niloufar Afzali | Shahram Tangestaninejad
| Majid Moghadam
| Valiollah Mirkhani |
2
1
1
Adam Mechler | Iraj Mohammadpoor‐Baltork
| Reihaneh Kardanpour |
1
Farnaz Zadehahmadi
1
Department of Chemistry, Catalysis
A heterogeneous catalyst was synthesized by immobilizing Mo(CO) in a
Division, University of Isfahan, Isfahan
3
8
2
1746‐73441, Iran
UiO‐66 metal–organic framework. The benzene ring of the organic linker in
UiO‐66 was modified via liquid‐phase deposition of molybdenum
hexacarbonyl, Mo(CO) , as starting precursor to form the (arene)Mo(CO)
La Trobe Institute for Molecular Science,
La Trobe University, Bundoora, Victoria
086, Australia
6
3
3
species inside the framework. The structure of this catalyst was characterized
using X‐ray diffraction, and chemical integrity was confirmed using Fourier
transform infrared and diffuse reflectance UV–visible spectroscopic methods.
The metal content was analysed with inductively coupled plasma. Field
emission scanning electron microscopy was used to measure particle size and
Correspondence
Shahram Tangestaninejad, Majid
Moghadam and Valiollah Mirkhani,
Department of Chemistry, Catalysis
Division, University of Isfahan, Isfahan
81746‐73441, Iran.
N adsorption measurements to characterize the specific surface area. This
2
Email: stanges@sci.ui.ac.ir;
moghadamm@sci.ui.ac.ir; mirkhani@sci.
ui.ac.ir
catalytic system was efficiently applied for epoxidation of alkenes and oxidation
of sulfides. The Mo‐containing metal–organic framework was reused several
times without any appreciable loss of its efficiency.
KEYWORDS
3
alkenes, metal–organic framework, Mo(CO) , oxidation, sulfides, UiO‐66
1
| INTRODUCTION
complex‐based heterogeneous catalysts for industrial
applications.
[
6]
Complexes of early transition metals, especially molyb-
denum complexes (oxomolybdenum species), have
shown high catalytic activity and selectivity.
Metal–organic frameworks (MOFs) composed of
metal–oxo clusters and organic linkers have attracted
[
1–3]
[7–9]
increasing attention in recent years.
Due to their
However, as homogeneous catalysts, their applicability
is limited due to poor catalyst separation and reusability.
To solve this problem, the catalysts are ‘heterogenized’
by immobilization onto various organic and inorganic
extraordinarily effective surface areas, high porosity and
chemical tuneability, such MOFs are suitable for a wide
range of applications, for example in gas sorption or
[
6]
[10,11]
[12]
storage, drug delivery,
optoelectronics,
chemi-
[4,5]
[13]
[14]
supports.
However,
in
many
cases
the
cal sensing,
food preservation
and storage of
[
15]
heterogenization process is associated with the loss of
activity or with a slow but significant leaching of the
catalyst into the reaction slurry. Thus, there is a strong
impetus for the development of better transition metal
dangerous gases.
One of the promising applications
of MOFs is for catalysis; MOFs often have catalytic activ-
ity on their own, or else they provide ideal supports for
[
16–22]
catalysts.
The organic linkers in the structures of
Appl Organometal Chem. 2017;e3958.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
1 of 11
https://doi.org/10.1002/aoc.3958

2
of 11
AFZALI ET AL.
MOFs can be altered by post‐synthetic modification
PSM) to produce MOF‐based catalysts with improved
performance compared to that of the non‐supported cata-
(
[23]
lysts.
Immobilization on a MOF scaffold is a very pow-
erful tool for heterogenizing soluble inorganic catalysts
that combine the benefits of easy separation and recovery
of heterogeneous catalysts with the high catalytic activity
[24–33]
of soluble transition metal complexes,
oxomolybdenum species.
such as
One possibility for attaching organometallic species
to MOFs is coordination to a π‐donor arene ring of the
organic linker. Transition metal centres can be attached
6
to the benzene rings of MOFs in an η fashion. A large
SCHEME 1 Alkene epoxidation and oxidation of sulfides
6
catalysed by UiO‐66‐Mo(CO)
3
variety of (η ‐arene)M(CO) (M = Cr, Mo, W) types of
3
complexes can be produced under mild conditions which
are compatible with the framework stability. This
strategy has been successfully applied to the attachment
of Cr(CO)3 units through thermal decomposition of
2 | EXPERIMENTAL
2.1 | Materials
Cr(CO) precursor to various substrates such as MOF‐5
6
All reagents were purchased at ACS reagent grade.
Alkenes were obtained from Merck or Fluka and passed
through a column containing active alumina to remove
peroxidic impurities. Molybdenum hexacarbonyl was
obtained from Sigma‐Aldrich.
by grafting Cr(CO) units on the benzene ring of the
3
organic linker, and to inorganic–organic hybrid mesopo-
[34,35]
rous silica.
Two porous matrices of UiO‐66 MOF
and highly crosslinked polystyrene were also
[
36]
immobilized with Cr(CO)6 precursor.
No attempts
were made, however, to use the method for the attach-
ment of other catalysts.
6
Recently, η ‐arene Mo(CO)3 species have garnered
considerable attention owing to their potential applica-
2.2 | Synthesis of UiO‐66‐Mo(CO)3
tions in photochemical reactions in which a CO ligand
A solution of Mo(CO)
(8 ml) was prepared. Activated UiO‐66 (400 mg) was
added to the Mo(CO) solution and the resulting
6
(100 mg, 0.37 mmol) in MeOH
[34]
is replaced by N or H .
The resulting N and H2
2
2
2
complexes exhibit excellent stability because the metal
centres are attached to the rigid scaffold of the MOF. This
behaviour has opened interesting perspectives for the
6
suspension was heated at 70 °C for 48 h in an oil bath.
At the end of the reaction, the mixture was cooled to room
temperature, and the particulate product precipitate was
isolated with a suitable filter and dispersed in MeOH (ca
10 ml) at 70 °C for 24 h. Finally, the scaffold‐attached cat-
alyst was filtered and dried at 150 °C for 24 h (Scheme 2).
The chemical composition of sample was confirmed by
elemental analysis (Table 1).
[34]
storage of small molecules.
In the study presented here we investigated the
catalytic activity of these types of functionalized MOFs.
We applied the arene‐coordination strategy to the
functionalization of UiO‐66 that is noted for its excellent
[37,38]
chemical and thermal stability.
UiO‐66 is a cubic
close‐packed three‐dimensional MOF comprised of
zirconia‐based inorganic building blocks and 1,4‐
benzenedicarboxylic acid as the organic linker. The Zr
sites do not present any coordination vacancy. UiO‐66
was synthesized by the solvothermal method and also by
a new protocol reported by Hupp and co‐workers that
[
39];
uses ultrasonic conditions in the presence of HCl
the
effectiveness of these two methods was compared. Molyb-
denum hexacarbonyl was immobilized on the UiO‐66
scaffold from refluxing solutions of Mo(CO) in methanol.
6
The catalyst was used efficiently for the epoxidation of
alkenes with tert‐butyl hydroperoxide (TBHP) and the oxi-
dation of sulfides with H O2 as a green oxidant
2
(Scheme 1).
SCHEME 2 Preparation of catalyst

AFZALI ET AL.
3 of 11
TABLE 1 Elemental analysis of UiO‐66‐Mo(CO)
tion at 150 °C for 5 h
3
‐L after activa-
a 19096C006 80/100 WHP packed column and a flame
ionization detector. The particle size and microscopic
morphological features of the samples were obtained with
a Hitachi S‐4700 field emission scanning electron
microscopy (FE‐SEM) instrument.
Catalyst
C (%)
H (%)
Zr (%)
Mo (%)
UiO‐66‐Mo(CO)
3
‐L
27.2
3.1
27.5
0.112
2
.3 | Instrumental measurements
2
2
.4 | Catalytic tests
X‐ray diffraction (XRD) analysis was carried out with a
Bruker D8 Advance instrument using Cu Kα
.4.1 | Epoxidation of alkenes
(
λ = 1.5406 Å) radiation. The analysis of the chemical
In a 25 ml round‐bottom flask equipped with a magnetic
composition was carried out using inductively coupled
plasma (ICP) optical emission spectrometry, with a
Jarrell‐Ash 1100 ICP analyser. Specific surface area, pore
volume and pore size were measured by adsorption–
stirring bar, a mixture of alkene (1 mmol), TBHP
(2 mmol), acetonitrile (3 ml) and UiO‐66‐Mo(CO)
3
catalyst (100 mg, 0.0112 mmol Mo) was prepared and
refluxed with continuous stirring. The reaction progress
was monitored by GC.
desorption of N gas at 77.360 K using a Micrometrics
2
ASAP 2000 instrument. Fourier transform infrared
(
FT‐IR) spectra were obtained in the range 400–4000 cm
using a JASCO 6300D spectrometer. Diffuse reflectance
2.4.2 | Oxidation of sulfides
−
1
spectra were recorded with a JASCOV‐670 UV–visible
spectrophotometer. Substances were identified and
quantified by GC using an Agilent GC 6890 equipped with
In a 25 ml round‐bottom flask equipped with a magnetic
stirring bar, a mixture of methylphenyl sulfide (1 mmol),
H O (30%, 2 mmol), acetonitrile (3 ml) and UiO‐66‐
2
2
TABLE 2 BET and ICP analyses of prepared catalysts
2
−1
3
−1
−1
Sample
S
BET (m g
)
Total pore volume (cm g
)
Total pore diameter (nm)
ICP (Mo mmol g )
UiO‐66‐S
1200
1100
1315
1017
0.58
0.57
0. 55
0.51
1.69
—
UiO‐66‐Mo(CO)
3
3
‐S
1.905
2.04
2.20
0. 0106
—
UiO‐66‐L
UiO‐66‐Mo(CO)
‐L
0.0112
FIGURE 1 (a) XRD patterns of
activated UiO‐66‐S, UiO‐66‐L, UiO‐66‐
Mo(CO) ‐S and UiO‐66‐Mo(CO) ‐L and
b) UiO‐66‐Mo(CO) ‐L after four catalytic
3
3
(
3
cycles in the epoxidation reaction of
alkenes (red curve) and oxidation reaction
of sulfides (black curve)

4
of 11
AFZALI ET AL.
FIGURE 2 FT‐IR spectra of (a) UiO‐66,
(
b) UiO‐66‐Mo(CO)
3
‐S, (c)UiO‐66‐
Mo(CO) ‐L and (d) UiO‐66‐Mo(CO) ‐L
3
3
after four catalytic cycles in epoxidation of
alkenes
Mo(CO) catalyst (100 mg, 0.0112 mmol Mo) was stirred
species inside the framework. As shown in Figure 1, the
3
at room temperature. The reaction progress was
monitored by GC.
main diffraction peaks of the UiO‐66 framework at 2θ
[
37]
(°) = 5.10, 8.41, 9.02, 16.49
are not affected by the
PSM in either catalytic system. The Mo contents mea-
−
1
sured by ICP analysis were 0.0106 and 0.0112 mmol g
for UiO‐66‐Mo(CO) ‐S and UiO‐66‐Mo(CO) ‐L, respec-
2.4.3 | Cyclic tests
3
3
The oxidation of cyclooctene was chosen as a model
reaction for checking the reusability of UiO‐66‐Mo(CO)3.
At the end of the reaction, the catalyst was recovered by
tively (Table 2).
The FT‐IR spectrum of the Zr‐based MOF synthesized
according to the literature
[
37]
is shown in Figure 2(a). The
−
1
filtration washed with Et O and dried at 100 °C. The
peaks at 1550–1630 cm are assigned to C═O of carbox-
2
catalyst was consequently reused four times without any
loss of activity. After each experiment, the catalyst was
isolated from the reaction mixture and the amount of
Mo leaching was determined by ICP analysis. The reus-
ability of the catalyst was also confirmed in the oxidation
of methylphenyl sulfide using the same procedure.
ylates coordinated with the metal centres by oxygen dur-
[
20,21]
ing the deprotonation process.
the region 1450–1580 cm are assigned to the C─C
The weak peaks in
−
1
stretch in the aromatic rings of the organic linker. The
−
1
strong peak at around 1400 cm can be ascribed to
C─O bond of C─OH group of carboxylic acid. The
presence of MoO group in both UiO‐66‐Mo(CO) ‐S and
3
3
UiO‐66‐Mo(CO) ‐L was confirmed by the appearance
3
3
3
| RESULTS AND DISCUSSION
.1 | Synthesis and investigation of
−
1
of new absorption bands at 2017 and 1985 cm
[
36]
(
Figure 2b,c).
catalytic activity of Mo(CO) ‐UiO‐66
3
UiO‐66 was synthesized using a typical solvothermal
[
37]
method (UiO‐66‐S)
and by a large‐scale procedure
[39]
under ultrasonic condition (UiO‐66‐L).
Large‐scale
synthesis of UiO‐66 made with 4 g of ZrCl yielded 7.2 g
4
of pre‐activated UiO‐66, and hence it has a potential for
[39]
commercialization using a reactor.
The N adsorption–desorption experiments (Table 2).
2
demonstrate that in the HCl‐containing synthesis the pre-
pared MOF has a higher surface area than in the case of
the solvothermal method. Based on the results of Hupp
and co‐workers, this is due to the missing of four linkers
[39]
per node that are substituted by HCl.
The decrease in
pore diameter of UiO‐66‐S compared with UiO‐66‐L
(Table 2) is also consistent with this interpretation.
In the next step, molybdenum hexacarbonyl was
immobilized into the MOF to form (arene)Mo(CO)3
3
FIGURE 3 TGA curve of UiO‐66‐Mo(CO) ‐L.

AFZALI ET AL.
5 of 11
FIGURE 4 FE‐SEM images of (a) UiO‐66‐S, (b) UiO‐66‐Mo(CO)
3
‐S, (c) UiO‐66‐L, (d) UiO‐66‐Mo(CO)
3
‐L and (h) UiO‐66‐Mo(CO)
3
‐L after
four runs. Histograms of size distribution of (e) UiO‐66‐Mo(CO)
3
‐S, (f) UiO‐66‐Mo(CO) ‐L and (i) UiO‐66‐Mo(CO)
3
3
‐L after four runs

6
of 11
AFZALI ET AL.
TABLE 3 Effect of amount of catalyst on epoxidation of
transfer band and hence also proves the presence of the
Mo coordination complex (Figure S1).
a
[40]
cyclooctene with TBHP catalysed by UiO‐66‐Mo(CO)
3
‐L
Thermogravimetric analysis (TGA) results are shown
Amount of catalyst Epoxide yield
b
in Figure 3. The TGA curve of the UiO‐66‐Mo(CO) ‐L
Entry Catalyst
(mg)
(%)
3
catalyst exhibited initial solvent loss near 84 °C followed
by a drop at 179 °C, which is related to the removal of car-
bonyl ligands (Figure 3). The third weight loss situated at
1
2
3
4
—
—
1
UiO‐66
Mo(CO)
UiO‐66‐
Mo(CO)
UiO‐66‐
Mo(CO)
UiO‐66‐
Mo(CO)
UiO‐66‐
Mo(CO)
100
3
5
6
28
38
3
10 °C is attributed to the dehydration of the Zr O (OH)
6 4 4
25
nodes to Zr O . The final step near 500 °C is related to
6
6
3
3
3
3
‐L
‐L
‐L
‐L
[34,39]
decomposition of the 1,4‐benzenedicarboxylate.
5
6
7
50
98
98
98
FE‐SEM images of the catalysts (Figure 4).clearly
show that the small cubic intergrown crystals of UiO‐66
have diameters in the range 85 to 110 nm and immobiliza-
tion of the catalyst causes no appreciable change in the
morphology of the framework. The morphology and size
100
150
distribution of UiO‐66‐Mo(CO) ‐L after use in the
3
a
epoxidation of cyclooctene were also imaged. As shown in
Figure 4 the morphology of the framework is still
maintained.
Reaction conditions: cyclooctene (1 mmol), TBHP (2 mmol), catalyst (0.1 g,
.0112 mmol Mo) and acetonitrile as solvent (3 ml) for 4.5 h under reflux
0
condition.
b
GC yield based on starting alkene.
The results of N adsorption–desorption experiments
2
are shown in Figure S2 and summarized in Table 2. The
great decreases in surface area after PSM indicate that
the cavities of MOF are occupied by Mo(CO) complexes.
3
Also, UiO‐66‐Mo(CO) ‐L has lower Brunauer–Emmett–
3
Teller (BET) surface area and total pore volume than
UiO‐66‐Mo(CO) ‐S likely due to its higher content of
3
anchored Mo complex as suggested by ICP measure-
ments: the Mo content measured by ICP was 0.0106 and
−
1
0
.0112 mmol g for UiO‐66‐Mo(CO) ‐S and UiO‐66‐
3
Mo(CO) ‐L, respectively. The pore size distribution curves
3
(
calculated by the Barrett–Joyner–Halenda equation)
show that there was no change in the pore size distribu-
tion of UiO‐66‐Mo(CO) ‐L and UiO‐66‐Mo(CO) ‐S in
comparison to pure UiO‐66 (Figure S2).
3
3
FIGURE 5 Effect of solvent on epoxidation of cis‐cyclooctene
with TBHP catalysed by UiO‐66‐Mo(CO)
3
‐L under reflux conditions
TABLE 4 Effect of oxidant on epoxidation of cyclooctene
3.2 | Investigation of catalytic properties
a
catalysed by UiO‐66‐Mo(CO)
3
‐L
of Mo(CO) ‐UiO‐66
3
b
Entry
Solvent
Oxidant
Epoxide yield (%)
The catalytic activity of heterogeneous UiO‐66‐Mo(CO)3‐
L catalyst was investigated in the epoxidation of cis‐
cyclooctene as a model reaction (Scheme 1). At first, the
catalyst amount was optimized in the epoxidation of
c
1
CCl
CCl
CCl
CCl
4
4
4
4
–H
2
O
H
2
O
2
69
2
3
4
TBHP
NaIO
Na SO
98
12
14
4
2
4
a
Reaction conditions: cyclooctene (1 mmol), oxidant (2 mmol), catalyst (0.1 g,
0
4
b
.0112 mmol Mo) and acetonitrile as solvent (3 ml) under reflux condition for
.5 h.
GC yield based on starting cyclooctene.
c
A 3:1 mixture of organic solvent and water was used.
The compounds were also characterized with UV–vis-
ible spectroscopy; in the spectra of UiO‐66‐Mo(CO) ‐S
3
and UiO‐66‐Mo(CO) ‐L an extra shoulder is observed
FIGURE 6 Epoxidation of cyclooctene with various amounts of
3
around 270 nm that is attributed to the Mo ! CO charge
TBHP catalysed by UiO‐66‐Mo(CO) ‐L.
3

AFZALI ET AL.
7 of 11
a
TABLE 5 Epoxidation of alkenes with TBHP catalysed by UiO‐66‐Mo(CO)
3
‐L under reflux conditions
b
c
−1 d
Entry
Alkene
Epoxide
Time (h)
Selectivity (%)
Conversion (%)
TOF (h )
1
4.5
80
95
18.8
2
3
4.5
9
100
63
98
96
19.4
9.6
e
e
e
e
4
5
6
9.5[9.5]
89[84]
97[91]
9[9]
12
13
65
70
69
89
5.1
6
7
8
9
12.5
15
96
80
71
60
5.7
3.9
9.5
11
97
96
93
51
83
75
56
77
7.8
6.1
3.7
2.8
10
11
12
13.5
9
a
Reaction conditions: alkene (1 mmol), TBHP (2 mmol), catalyst (0.1 g, 0.0112 mmol Mo for UiO‐66‐Mo(CO)
3
‐L) and acetonitrile as solvent (3 ml) under reflux
condition.
b
By‐products were aldehydes.
c
GC yield based on starting alkene.
d
TOF calculated as the amount of reactant (moles) divided by amount of catalyst (moles) divided by time (h).
e
3
Result of reaction using UiO‐66‐Mo(CO) ‐S (0.1 g, 0.0106 mmol Mo).
cyclooctene (1 mmol) with TBHP (2 mmol). It was
observed that 100 mg of the catalyst affords the highest
yield (Table 3). In order to show the effect of Mo species
in the epoxidation reaction, a blank experiment in the
presence of UiO‐66 and oxidant was also performed and
a cyclooctene oxide yield of only 5% was detected by GC.
The effect of different solvents on the activity of the
catalyst was also investigated. Among 1,2‐dichloroethane,
chloroform, acetonitrile and carbon tetrachloride,
acetonitrile was chosen as the reaction medium because
this solvent afforded the highest epoxide yield (Figure 5).
The efficacy of various oxygen donors such as TBHP,
NaIO , Na SO and H O2 in the epoxidation of
4
2
5
2
cis‐cyclooctene was investigated. Although H O is a
2
2

8
of 11
AFZALI ET AL.
a
2 2 3
TABLE 6 Effect of amount of catalyst on oxidation of methylphenyl sulfide with H O catalysed by UiO‐66‐Mo(CO) ‐L
b
Entry
Catalyst
Amount of catalyst (mg)
Epoxide yield (%)
1
—
—
5
2
3
4
5
6
7
UiO‐66
100
3
6
Mo(CO)
6
40
60
68
98
98
UiO‐66‐Mo(CO)
UiO‐66‐Mo(CO)
UiO‐66‐Mo(CO)
UiO‐66‐Mo(CO)
3
3
3
3
‐L
‐L
‐L
‐L
25
50
100
150
a
2 2
Reaction conditions: methylphenyl sulfide (1 mmol), H O (2 mmol), catalyst (0.1 g, 0.0112 mmol Mo) and acetonitrile as solvent (3 ml) for 10 min at room
temperature.
b
GC yield based on starting sulfide.
green oxidant, the results show that TBHP was the best
choice for oxygen donor in this reaction (Table 4).
In the epoxidation of cis‐cyclooctene using different
amounts of TBHP, the optimum product yield was
obtained in the presence of 2 mmol of TBHP (Figure 6).
The reaction temperature was also optimized, and 50 °C
was chosen as the best reaction temperature (Table S1).
Under the optimized reaction conditions, the ability of
a
2 2 3
TABLE 7 Oxidation of sulfides with H O catalysed by UiO‐66‐Mo(CO) ‐L
b
c
−1 d
Entry
Sulfide
Sulfone
Time (min)
Selectivity (%)
Conversion (%)
TOF (h )
1
10
96
98
546
2
3
4
5
6
15
25
20
12
35
96
95
94
96
94
98
97
96
98
96
350
216
259
433
147
7
30
93
95
169
8
9
20
60
95
94
97
96
262
85
a
2 2
Reaction conditions: methyl henyl sulfide (1 mmol), H O (2 mmol), catalyst (0.1 g, 0.0112 mmol Mo) and acetonitrile as solvent (3 ml) under reflux condition.
b
c
By‐products were sulfoxides.
GC yield based on starting sulfide.
d
TOF calculated as the amount of reactant (mmol) divided by amount of catalyst (mmol) divided by time (h).

AFZALI ET AL.
9 of 11
TABLE 8 Comparison of catalysts proposed for epoxidation of cyclooctene
Condition (° TOF
−
1
Entry Catalyst
Support
Oxidant C)/solvent
(h ) Ref.
[
[
[
[
42]
43]
44]
19]
1
2
3
4
MoO
MoO
MoO
2
2
2
(acac)
(acac)
(acac)
2
2
2
Silica
TBHP
TBHP
TBHP
Reflux/DCE 16
MCM‐41
Reflux/DCE 15.5
Reflux/DCE 14.7
MCM‐41
Mn(TPyP)OAc
Cm‐mil‐101
NaIO
4
3
RT/CH CN/ 19.3
2
H O
[
[
[
[
45]
46]
46]
46]
5
6
7
8
Mo
2
O
4
(acac)
2
BOX
None
None
None
TBHP
TBHP
TBHP
TBHP
Reflux/DCE 16.7
[MoI
[MoI
2
2
(CO)
3
3
(trpH)]
55/DCE
55/DCE
55/DCE
9
2
(CO)
(pheH)]
HT–trp–Mo
Amino acid intercalated clay
10
materials (HT–trp)
[
[
46]
47]
9
1
1
HT–phe–Mo
Amino acid intercalated clay
materials (HT–phe)
TBHP
TBHP
TBHP
55/DCE
17
5
0
1
MoO
2
[1,2diphenylethylenebis(3oxyethylpyrrole) None
Reflux/DCE
salicylideneiminate]
Mo(CO)
3
UiO‐66‐L
Reflux/
acetonitrile
19.4 Present
work
this catalytic system was investigated in the epoxidation
of various alkenes (Table 5). The results demonstrate that
the catalyst is highly active in the epoxidation of a wide
range of alkenes including cyclic and linear ones. 1‐
Octene and 1‐decene as linear alkenes were efficiently
converted to their corresponding epoxides. Cyclic olefins
such as cyclohexene and cyclooctene were also oxidized
in high yields. Based on the mechanism of epoxidation
reported in previous works, increasing the electronic den-
sity on the C═C double bond results in increasing the
amount. A blank experiment was carried out in the
absence of the catalyst under the same conditions, and
the corresponding sulfone was produced in 5% yield.
The effect of different oxidants and amount of oxidant
was also optimized (Figures S4 and S5).
From a green chemistry standpoint, it is very impor-
tant to develop a ‘green’ oxidation system for chemical
manufacturing. Hydrogen peroxide is considered as an
ideal green oxidant because it is environmentally benign,
cheap and easy to handle and does not produce toxic
by‐products. As shown in Figure S5, H O was the best
[41]
reactivity of the olefin.
Olefins containing aromatic
2
2
groups such as indene were also converted to their corre-
sponding aromatic epoxides (entry 4). In order to show
the power of the MOF‐supported catalyst, complex sub-
strates such as stilbene were also investigated (entries 7
and 8). The epoxidation of trans‐stilbene was much faster
than that of its cis‐isomer, because of steric hindrance. In
order to investigate the effect of the method of synthesis of
UiO‐66 on the reactivity of the prepared catalysts, the
oxidation reaction of indene was carried out in the
presence of UiO‐66‐Mo(CO) ‐L and UiO‐66‐Mo(CO) ‐S.
choice for oxygen source at an amount of 2 mmol. To
avoid decomposition of hydrogen peroxide at high
temperature, the reaction was carried out at 25 °C. Under
optimized conditions, various types of sulfides, including
diaryl, arylbenzyl, dialkyl, cyclic and unsaturated sulfides,
were successfully oxidized to their corresponding sulfones
with high conversions and short reaction times. The
results are summarized in Table 7. The oxidation reaction
is a two‐step process. The first step is oxidation of sulfide
to sulfoxide and the second one is oxidation of sulfoxide
to sulfone. From an industrial perspective it is important
to achieve either the selective oxidation to sulfoxides or
the complete oxidation to sulfones. Thus it is important
to highlight that our catalyst converts sulfides to sulfones
with 98% selectivity.
3
3
As is evident from Table 4, the results are almost identical
with only negligible differences.
The catalytic activity of UiO‐66‐Mo(CO) ‐L catalyst
3
was also investigated in the oxidation of various sulfides.
As shown in Figure S3, the solvent environment was
optimized for the oxidation of methylphenyl sulfide
and the best result was achieved with acetonitrile.
The effect of catalyst amount on the oxidation of
methylphenyl sulfide was also investigated (Table 6).
and 100 mg of catalyst was found to be the optimal
3.3 | Catalyst reusability and stability
The stability and reusability of heterogeneous catalysts
are most important features for economic purposes.

10 of 11
AFZALI ET AL.
Thus, the reusability of the supported molybdenum
ACKNOWLEDGEMENT
catalyst UiO‐66‐Mo(CO) ‐L was investigated in the
sequential epoxidation of cis‐cyclooctene with TBHP.
At the end of the reaction, the catalyst was filtered
3
The financial support of this work by the Research Coun-
cil of the University of Isfahan is acknowledged.
and washed with Et O and dried before use in the next
2
experiment. The results showed that the catalyst can be
reused for four consecutive cycles (Table S2). The Mo
leaching was determined by ICP analysis, confirming
that only small amounts of Mo species were lost after
the first run, and no Mo leaching was detected
after the second run in the reaction mixture. The
amount of molybdenum leached after four runs was
only about 1.3%. Therefore, the catalyst is completely
stable under the reaction conditions. One of the routine
techniques to establish the heterogeneity of the reaction
in liquid phase is a hot filtering experiment. In this case,
the catalyst was filtered out after 135 min and the
reaction was continued at 80 °C. After separation of
the catalyst only 3% progress was observed. The recycla-
bility of the catalyst was also investigated in the
oxidation of methylphenyl sulfide. The results are
summarized in Table S3. The structural integrity of the
recovered catalyst was confirmed by XRD and FT‐IR
analysis. As shown in Figures 1(b) and 2(d), the basic
lattice structure of UiO‐66 was not altered after four
cycles. The specific surface area of the catalyst after
the final run was also measured by nitrogen
physisorption at low temperature. The BET surface area
ORCID
Shahram Tangestaninejad
263-9795
Majid Moghadam http://orcid.org/0000-0001-8984-1225
Iraj Mohammadpoor‐Baltork http://orcid.org/0000-0001-
998-5401
http://orcid.org/0000-0001-
5
7
REFERENCES
[
1] G. Wahl, D. Kleinhenz, A. Schorm, J. Sundermeyer, R.
Stowasser, C. Rummey, G. Bringmann, C. Fickert, W. Kiefer,
Chem. – Eur. J. 1999, 5, 3237.
[
[
2] F. E. Kühn, A. D. Lopes, A. M. Santos, E. Herdtweck, J. J. Haider,
C. C. Romão, A. G. Santos, J. Mol. Catal. A 2000, 151, 147.
0
3] R. Martos‐Calvente, V. A. de la Peña O Shea, J. M. Campos‐
Martin, J. L. G. Fierro, E. Gutiérrez‐Puebla, J. Mol. Catal. A
2004, 214, 269.
[4] X. Huang, W. Guo, G. Wang, M. Yang, Q. Wang, X. Zhang, Y.
Feng, Z. Shi, C. Li, Mater. Chem. Phys. 2012, 135, 985.
[5] S. V. Kotov, E. Balbolov, J. Mol. Catal. A 2001, 176, 41.
[6] U. Mueller, M. Schubert, F. Teich, H. Puetter, K. Schierle‐
Arndt, J. Pastre, J. Mater. Chem. 2006, 16, 626.
2
−1
2
−1
decreased from 1017 m g (Figure S2) to 1003 m g .
This negligible decrease can be attributed to residual
products and/or solvent blocking some pores leading to
the cavities.
Compared to other catalysts proposed for alkene epox-
idation with TBHP (Table 8). our catalysts are superior in
terms of reaction time, yield and epoxide selectivity, while
they are also easier to prepare.
0
[
[
[
7] O. M. Yaghi, M. O Keeffe, N. W. Ockwig, H. K. Chae, M.
Eddaoudi, J. Kim, Nature 2003, 443, 705.
8] S. Kitagawa, R. Kitaura, S. Noro, Angew. Chem. Int. Ed. 2004,
43, 2334.
9] G. Férey, Chem. Soc. Rev. 2008, 37, 191.
[
[
[
10] P. Horcajada, C. Serre, M. Vallet‐Regí, M. Sebban, F. Taulelle,
G. Férey, Angew. Chem. Int. Ed. 2006, 45, 5974.
11] M. D. Allendorf, C. A. Bauer, R. K. Bhakta, R. J. T. Louk, Chem.
Soc. Rev. 2009, 38, 1330.
12] L.Jiang, Z.‐X.Li,Y.Wang,G.‐D.Feng,W.‐X.Zhao,K.‐Z.Shao,C.‐
Y. Sun, L.‐J. Li, Z.‐M. Su, Inorg. Chem. Commun. 2011, 14, 1077.
4
| CONCLUSIONS
[
[
13] G. Lu, J. T. Hupp, J. Am. Chem. Soc. 2010, 132, 7832.
We have produced UiO‐66 MOF by two different
methods: solvothermal and ultrasonic. The latter allows
the synthesis of the framework on a large scale. Immobi-
lization of Mo complex into the framework of UiO‐66
has been achieved via liquid‐phase deposition of molybde-
num hexacarbonyl. The activity of the catalyst was evalu-
ated in the oxidation of alkenes and sulfides which
afforded excellent yields and the catalyst showed good
reusability. In the latter case, using environmentally
benign H O , corresponding sulfones were produced with
14] H. Wang, E. Lashkari, H. Lim, C. Zheng, T. J. Emge, Q. Gong, J.
Li, Chem. Commun. 2016, 52, 2129.
[15] D. Britt, D. Tranchemontagne, O. M. Yaghi, Proc. Natl. Acad.
Sci. U. S. A. 2008, 105, 11623.
[16] F. Zadehahmadi, F. Ahmadi, S. Tangestaninejad, M.
Moghadam, V. Mirkhani, I. Mohammadpoor‐Baltork, R.
Kardanpour, J. Mol. Catal. A 2015, 398, 1.
[17] A. D. Burrows, C. G. Frost, M. F. Mahon, M. Winsper, C. Rich-
ardson, J. P. Attfield, J. A. Rodgers, Dalton Trans. 2008, 47, 6788.
2
2
excellent yield and selectivity. Easy workup and mild
reaction conditions are unique features of this catalyst.
[18] A. D. Burrows, L. C. Fisher, C. Richardson, S. P. Rigby, Chem.
Commun. 2011, 47, 3380.

AFZALI ET AL.
11 of 11
[
19] F. Zadehahmadi, S. Tangestaninejad, M. Moghadam, V.
Mirkhani, I. Mohammadpoor‐Baltork, A. R. Khosropour, R.
Kardanpour, Appl. Catal. A 2014, 477, 34.
[39] M. J. Katz, Z. J. Brown, Y. J. Colón, P. W. Siu, K. A. Scheidt, R. Q.
Snurr, J. T. Hupp, O. K. Farha, Chem. Commun. 2013, 49, 9449.
[
40] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I.
Mohammadpoor‐Baltork, N. S. Mirbagheri, Appl. Organomet.
Chem. 2010, 24, 708.
[
20] R. Kardanpour, S. Tangestaninejad, V. Mirkhani, M.
Moghadam, I. Mohammadpoor‐Baltork, A. R. Khosropour, F.
Zadehahmadi, J. Organomet. Chem. 2014, 761, 127.
[41] R. Sheldon, J. Van Doorn, J. Catal. 1973, 31, 427.
[
21] S. Bhattacharjee, Y.‐R. Lee, P. Puthiaraj, S.‐M. Cho, W.‐S. Ahn,
Catal. Surv. Jpn. 2015, 19, 203.
[
42] S. Tangestaninejad, M. Moghadam, V. Mirkhani, I.
Mohammadpoor‐Baltork, K. Ghani, J. Iran. Chem. Soc. 2008,
5, S71.
[
22] F. Zadehahmadi, S. Tangestaninejad, M. Moghadam, V.
Mirkhani, I. Mohammadpoor‐Baltork, A. R. Khosropour, R.
Kardanpour, Appl. Organomet. Chem. 2015, 29, 209.
[
43] S. Tangestaninejad, M. Moghadam, V. Mirkhani, I.
Mohammadpoor‐Baltork, K. Ghani, Catal. Commun. 2009,
10, 853.
[
[
[
[
23] Z. Wang, S. M. Cohen, Chem. Soc. Rev. 2009, 38, 1315.
24] S. Das, H. Kim, K. Kim, J. Am. Chem. Soc. 2009, 131, 3814.
25] W. Li, G. Li, D. Liu, RSC Adv. 2016, 6, 94113.
[44] S. M. Bruno, J. A. Fernandes, L. S. Martins, I. S. Gonçalves, M.
Pillinger, P. Ribeiro‐Claro, J. Rocha, A. A. Valente, Catal. Today
2006, 114, 263.
26] D. M. Jiang, A. Urakawa, M. Yulikov, T. Mallat, G. Jeschke, A.
[
45] M. Moshref Javadi, M. Moghadam, I. Mohammadpoor‐Baltork,
S. Tangestaninejad, V. Mirkhani, H. Kargar, M. Nawaz Tahir,
Polyhedron 2014, 72, 19.
Baiker, Chem. – Eur. J. 2009, 15, 12255.
[
27] S. Natarajan, P. Mahata, Chem. Soc. Rev. 2009, 38, 2304.
[
28] J. Lee, O. K. Farha, J. Roberts, K. A. Scheidt, S. T. Nguyen, J. T.
[
[
46] C. I. Fernandes, N. U. Silva, P. D. Vaz, T. G. Nunes, C. D.
Hupp, Chem. Soc. Rev. 2009, 38, 1450.
Nunes, Appl. Catal. A 2010, 384, 84.
[
[
[
[
[
29] A. M. Shultz, O. K. Farha, J. T. Hupp, S. T. Nguyen, J. Am.
47] S. M. Bruno, S. S. Balula, A. A. Valente, F. A. A. Paz, M.
Pillinger, C. Sousa, J. Klinowski, C. Freire, P. Ribeiro‐Claro, I.
S. Goncálves, J. Mol. Catal. A 2007, 270, 185.
Chem. Soc. 2009, 131, 4204.
30] Y. Lu, M. Tonigold, B. Bredenkötter, D. Volkmer, J. Hitzbleck,
G. Langstein, Z. Anorg. Allg. Chem. 2008, 634, 2411.
31] S. Proch, J. Herrmannsdörfer, R. Kempe, C. Kern, A. Jess, L.
Seyfarth, J. Senker, Chem. – Eur. J. 2008, 14, 8204.
32] M. J. Ingleson, J. P. Barrio, J.‐B. Guilbaud, Y. Z. Khimyak, M. J.
Rosseinsky, Chem. Commun. 2008, 2680.
SUPPORTING INFORMATION
Additional Supporting Information may be found online
in the supporting information tab for this article.
33] C.‐D. Wu, A. Hu, L. Zhang, W. Lin, J. Am. Chem. Soc. 2005, 127,
8
940.
[
34] S. S. Kaye, J. R. Long, J. Am. Chem. Soc. 2008, 130, 806.
[
35] T. Kamegawa, T. Sakai, M. Matsuoka, M. Anpo, J. Am. Chem.
Soc. 2005, 127, 16784.
How to cite this article: Afzali N,
Tangestaninejad S, Moghadam M, et al. Oxidation
reactions catalysed by molybdenum(VI) complexes
grafted on UiO‐66 metal–organic framework as an
elegant nanoreactor. Appl Organometal Chem.
[
[
[
36] S. Chavan, J. G. Vitillo, M. J. Uddin, F. Bonino, C. Lamberti, E.
Groppo, K.‐P. Lillerud, S. Bordiga, Chem. Mater. 2010, 22, 4602.
37] J. H. Cavka, S. Jakobsen, U. Olsbye, N. Guillou, C. Lamberti, S.
Bordiga, K. P. Lillerud, J. Am. Chem. Soc. 2008, 130, 13850.
2017;e3958. https://doi.org/10.1002/aoc.3958
38] S. S. Kaye, A. Dailly, O. M. Yaghi, J. R. Long, J. Am. Chem. Soc.
2
007, 129, 14176.