New perspective to catalytic epoxidation of olefins by Keplerate containing Keggin polyoxometalates

Article abstract of DOI:10.1016/j.poly.2018.09.015

Different Keggin encapsulated in Keplerate polyoxometalates (Mo₇₂Fe₃₀, PMo₁₂ ? Mo₇₂Fe₃₀, SiMo₁₂ ? Mo₇₂Fe₃₀ and BW₁₂ ? Mo₇₂Fe₃₀) have been synthesized and their catalytic efficiency in the epoxidation of olefins with hydrogen peroxide investigated. Results were confirmed that Keggin encapsulated in Keplerates could show higher catalytic activity than parent ones. These POM catalysts lead to heterogeneous epoxidation of alkenes by hydrogen peroxide with green features of convenient recovery, steady reuse, high conversion and selectivity, and simple preparation.

Full text of DOI:10.1016/j.poly.2018.09.015

Accepted Manuscript
New perspective to catalytic epoxidation of olefins by Keplerate containing
Keggin polyoxometalates
Hamid Taghiyar, Bahram Yadollahi
PII:
S0277-5387(18)30567-9
https://doi.org/10.1016/j.poly.2018.09.015
POLY 13414
DOI:
Reference:
Polyhedron
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6 September 2018
Please cite this article as: H. Taghiyar, B. Yadollahi, New perspective to catalytic epoxidation of olefins by Keplerate
containing Keggin polyoxometalates, Polyhedron (2018), doi: https://doi.org/10.1016/j.poly.2018.09.015
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New perspective to catalytic epoxidation of olefins by Keplerate containing
Keggin polyoxometalates
Hamid Taghiyar, Bahram Yadollahi*
Department of Chemistry, University of Isfahan, Isfahan 81746-73441, Iran
Abstract
Different Keggin encapsulated in Keplerate polyoxometalates (Mo72Fe30, PMo12⊂Mo72Fe30,
SiMo12⊂Mo72Fe30 and BW12⊂Mo72Fe30) have been synthesized and their catalytic efficiency in
the epoxidation of olefins with hydrogen peroxide investigated. Results were confirmed that
Keggin encapsulated in Keplerates could show higher catalytic activity than parent ones. These
POM catalysts lead to heterogeneous epoxidation of alkenes by hydrogen peroxide with green
features of convenient recovery, steady reuse, high conversion and selectivity, and simple
preparation.
Keywords: Polyoxomolybdates; Keplerate; Keggin anions; host–guest chemistry; catalysis;
oxidation of olefins
*Corresponding Author. Tel: +98-31-37934934; fax: +98-31-36689732; e-mail: yadollahi@chem.ui.ac.ir,
yadollahi.b@gmail.com
Declarations of interest: none
1

1. Introduction
Oxidation reactions play an important role in both of fine and bulk chemicals manufacturing [1].
Epoxides, which are important intermediates in the synthesis of fine chemicals and
pharmaceuticals, form a particularly important and versatile class of products in chemical and
industrial processes for the production of epoxy resins, paints, and surfactants [2, 3]. Different
catalytic systems have been used for the synthesis of these valuable chemicals. Among them,
polyoxometalates (POMs) have been used extensively due to their unique properties and structural
variations.
POMs as anionic early transition metal oxygen clusters are unique in terms of molecular and
electronic structural versatility, catalysis, medicine, biology, material science, electron-transfer
processes and nanochemistry [4-9]. Keplerates with the formula of {(MVI)MVI }512(linker)30 (M =
5
Mo or W) are a highly symmetrical class of POMs that for the first time were synthesized and
defined by Müller [10-14]. Among them, {Mo72Fe30}-type species – comprising 12 molybdenum-
oxide-based pentagonal units linked by 30 FeIII spacers that span an icosidodecahedron – have
attracted considerable attention such as their magnetic and catalytic properties [15-19]. This
Keplerate can act as a unique host for the other POMs like Lindqvist- or Keggin-type POMs [20-
22].
Numerous organic processes could be catalyzed by POMs due to their acid/base characterization
or ability to readily accept electrons and form electrochemically reduced clusters [23-25].
Nowadays, requirements for green and clear oxidation of olefins caused a great number of studies
in the olefin epoxidation with POMs as cheap and effective catalysts and hydrogen peroxide as a
green oxidant [26-35].
2

Considering the importance of epoxides and high efficiency of Keplerate and Keggin POMs as
catalyst and in continuation of our previous works [8, 19, 25, 36], in this work the synthesis and
catalytic effect of three Keggin-type POM encapsulated in molybdenum-iron-type Keplerate have
been
investigated.
In
this
way,
following
1–4
POMs
1),
[Mo72Fe30O251(CH3COO)12{Mo2O7(H2O)}2{H2Mo2O8(H2O)}(H2O}91]
(Mo72Fe30
≡
[HxPMo12O40⊂H4Mo72Fe30O254(CH3COO)15(H2O)98]
Na6[SiMo12O40⊂Mo72Fe30O252(CH3CO2)16(H2O)100]
(PMo12⊂Mo72Fe30
(SiMo12⊂Mo72Fe30
≡
2),
≡
3)
and
Na3K4[BW12O40⊂H4Mo72Fe30O254(CH3COO)16(H2O)96] (BW12⊂Mo72Fe30 ≡ 4) were synthesized
and used as catalyst in the epoxidation of various olefins with hydrogen peroxide (Scheme 1).
Scheme 1. Epoxidation of olefins by Keggins encapsulated in molybdenum-iron-type Keplerate
as catalysts
2. Experimental Section
2.1. General remarks
The chemicals used in this work were purchased from Aldrich, Fluka and Merck chemical
companies and used without furth er purification. Melting points were determined with a Stuart
Scientific SMP2 apparatus. Conversion and yields of the products were accomplished by GC-FID
on a Shimadzu GC-16A instrument using a 2 m column packed with silicon DC-200 or Carbowax
20 m column and toluene as the internal standard. 1H NMR spectra were recorded in CDCl3 solvent
3

on a Bruker AC 400 MHz spectrometer using TMS as an internal standard. FT-IR spectra were
recorded using potassium bromide pellets from 400 to 4000 cm-1 by a Jasco FT/IR-6300
instrument. Powder X-ray diffraction patterns were obtained on a D8 Advanced Bruker using Cu
Kα radiation (2θ = 10–80°).
2.2. Preparation of Mo72Fe30 catalyst
This POM cluster was prepared according to the method reported by Müller and coworkers [15].
+
The NH4 salt of {Mo132} (1.4 g, 0.05 mmol) was added to a solution of FeCl3∙6H2O (1.1 g, 4.1
mmol) and CH3COONa∙3H2O (1.1 g, 8.1 mmol) in H2O (75 mL). The resulting solution was
vigorously stirred in open 100-mL Erlenmeyer flask for 24 h. After acidification with HCl (1 mL,
1 M) and addition of NaCl (2.0 g), the stirred reaction solution was heated to 90-95 ºC and then
filtered whilst still hot. The golden yellow filtrate was cooled to 20 ºC formed over a period of 2-
3 d. The crystals were collected by filtration through a glass frit, washed twice with a little iced
water, and dried in air. Elemental analysis for C24H526Fe30Mo78O547 (%); calcd: C, 1.54; Fe, 8.95;
Mo, 39.96; found: C, 1.50; Fe, 8.83; Mo, 38.67; Characteristic IR bands: ʋ=1622 (m, (H2O)),
ʋ=1535 (m, COO), ʋ=1402 (m, COO), ʋ=965 (m, Mo=O), ʋ=851 (m), ʋ=776 (vs), ʋ=621 (m),
ʋ=571 (s), ʋ=435 cm-1.
2.3. Preparation of PMo12⊂Mo72Fe30 catalyst
The PMo12⊂Mo72Fe30 cluster was prepared following previously reported protocol [20].
NaH2PO4∙2H2O (0.21 g, 1.35 mmol) was added to a solution of FeCl2∙4H2O (1.0 g, 5.03 mmol),
Na2MoO4∙2H2O (5.0 g, 20.66 mmol) and CH3COOH (100%, 10 mL) in H2O (75 mL). After
acidification to pH 2 with about 3 mL of 32% HCl, the solution was stirred for 15 min at 20 ºC
and filtered. The filtrate was kept for one week in an open 250 mL beaker for crystallization. The
crystals were filtered, washed with water, and dried at room temperature. Elemental analysis: calcd
4

(%) for C30H365Fe30Mo84O482P: C, 1.98; H, 2.02; Fe, 9.2; P, 0.17; found: C, 2.1; H, 2.8; Fe, 8.6; P,
0.2; Characteristic IR bands for PMo12⊂Mo72Fe30: ʋ=1617 (m, (H2O)), ʋ=1539 (m, COO), ʋ=1420
(m, COO), ʋ=1068 (w, PO4), ʋ=952 (m, Mo=O), ʋ=827 (s), ʋ=775 (vs), ʋ=630 (m), ʋ=566 (s),
ʋ=435 cm-1.
2.4. Preparation of SiMo12⊂Mo72Fe30 catalyst
The cluster was prepared according to previously procedure [21]. H4SiMo12O40∙xH2O (1.0 g, 0.5
mmol) was added to a solution of FeCl2∙4H2O (0.5 g, 2.5 mmol), Na2MoO4∙2H2O (2.0 g, 8.3 mmol)
and CH3COOH (100%, 10 mL) in H2O (30 mL). After acidification with about 2.5 mL of 1 M
hydrochloric acid (pH of the reaction mixture was ~2.0), the solution was stirred for 1 h at room
temperature. After adding NaCl (0.5 g, 8.6 mmol), the solution was stirred for 15 min more and
then kept in an open 100 mL flask for one week at room temperature. The crystals were filtered,
washed with water, and dried at room temperature. Elemental analysis: calcd (%) for
C32H364Fe30Mo84Na6O482Si: C, 2.09; H, 2.00; Fe, 9.12; Mo, 43.89; Na, 0.75; Si, 0.15; found: C,
2.3; H, 2.4; Fe, 8.3; Mo, 41.0; Na, 0.4; Si, 0.15; Characteristic IR bands for SiMo12⊂Mo72Fe30:
ʋ=1617 (m, (H2O)), ʋ=1539 (m, COO), ʋ=1420 (m, COO), ʋ=950 (m, Mo=O), ʋ= 975, 909 (s,
SiO4), ʋ=855 (s), ʋ=780 (vs), ʋ=629 (m), ʋ=565 (s), ʋ=440 cm-1.
2.5. Preparation of BW12⊂Mo72Fe30 catalyst
The cluster was prepared according to the literature procedure [22]. K5[BW12O40]∙11H2O (1.67 g,
0.5 mmol) was added to a solution of Na2MoO4∙2H2O (2.0 g, 8.3 mmol) and acetic acid (15 mL,
100%) with FeCl2∙4H2O (1 g, 5 mmol) in H2O (60 mL). After acidification with about 11.5 mL of
1 M hydrochloric acid (pH of the reaction mixture was ~2.0), the solution was stirred for 1 h at
room temperature and then kept in an open 100 mL flask for one week at room temperature. The
crystals were filtered off, washed with water and dried at room temperature under nitrogen.
5

Elemental analysis: calcd (%) for C32H364BFe30K4Mo72Na3O482W12: C, 1.97; B, 0.06; Fe, 8.60; K,
0.80; Mo, 35.45; Na, 0.35; W, 11.32. Found: C, 2.0; B, 0.05; Fe, 7.9; K, 0.5; Mo, 34.8; Na, 0.2;
W, 10.3. Characteristic IR bands for BW12⊂Mo72Fe30: ʋ=1623 (m, (H2O)), ʋ=1537 (m, COO),
ʋ=1420 (m, COO), ʋ=952 (m, Mo=O), ʋ= 905 (s), ʋ=831 (s), ʋ=776 (vs), ʋ=630 (m), ʋ=565 (s),
ʋ=440 cm-1.
2.6. General procedure for the epoxidation reaction
All reactions were performed in a 25 mL round-bottom flask equipped with a magnetic stirrer bar.
The catalyst (2 µmol) was added to a solution of olefin (1 mmol) in 2 mL of ethanol. Then, H2O2
(30%, 0.3 mL, 3 mmol) was added to the mixture and closed the flask under air at 75 °C for the
required time. The progress of the reaction was monitored by TLC and GC, and the yield of
products was determined by GC analysis using toluene as the internal standard. At the end of
reaction, the catalyst was filtered and washed with ethanol (5 mL).
3. Results and Discussion
Investigation on the catalytic efficiency of 1, 2, 3, and 4 POM compounds were initiated by testing
the effect of {Mo72Fe30}-type Keplerate (1) in the epoxidation of olefins with H2O2 30% using
cyclohexene as a model compound. Considering its importance, the influence of different solvents
such as n-hexane, acetonitrile, acetone, ethyl acetate, THF, chloroform, dichloromethane,
methanol, ethanol, and water in the oxidation of cyclohexene were studied. From the results in Fig.
1, the highest conversion was obtained in ethanol. Although, the oxidation reaction in some of the
other solvents such as acetone and methanol was a little more selective. Consequently, ethanol was
selected as optimal solvent in our catalytic epoxidation system.
6

As expected, solvents of higher polarity and high basicity such as ethanol gave higher conversion
in epoxidation of cyclohexene (Fig. 1). These are in agreement with previously reported Kamlet–
Taft plot for estimating the physicochemical properties of solvents [26, 37-39].
100
75
50
25
0
Solvent
Figure 1. The effect of different solvents (2 mL) on the epoxidation of cyclohexene (1 mmol) with
H2O2 (3 mmol) in the presence of 1 (2 µmol) after 5 h reaction under reflux (Conversion red and
selectivity for epoxide green)
In the next step, to obtain the optimum amount of catalyst 1 in the epoxidation of cyclohexene, the
effect of different catalyst amounts was investigated (Fig. 2). It was observed that the conversions
were increased by increasing in the catalyst 1 amounts. Further increments of catalyst slightly
improved conversions when the amount of catalyst 1 was over 2 µmol. Different amounts of
catalyst 1 were only shown a little change in the selectivity. As a result, 2 µmol catalyst was chosen
as the optimal catalyst amount for further catalytic studies.
In the oxidation of cyclohexene by different volumes of H2O2, the optimum amount of oxidant
was obtained in the presence of 2 μmol catalyst (Fig. 3). The results showed that 3 mmol of 30%
H2O2 is sufficient for completion of the reaction after 5 h oxidation reaction. Thus, 3 mmol of
hydrogen peroxide was chosen as the best amount of oxidant in this catalytic epoxidation system.
7

100
75
50
25
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
µmol catalyst
Figure 2. Epoxidation of cyclohexene (1 mmol) by H2O2 (3 mmol) in the presence of different
catalyst 1 amounts in ethanol (2 mL) under reflux conditions for 5 h (Conversion red and selectivity
for epoxide green)
100
75
50
25
0
1
1.5
2
2.5
3
3.5
4
mmol H2O2
Figure 3. Epoxidation of cyclohexene by various amounts of H2O2 in the presence of 2 µmol 1
under reflux conditions for 5 h (Conversion red and selectivity for epoxide green)
In order to establish the general applicability of the method, the catalytic system was extended to
the oxidation of other olefins by the optimal reaction conditions – 2 μmol of catalyst, 3 mmol of
30% H2O2, under reflux condition and ethanol as solvent. The results with Mo72Fe30 and Keggin
POMs encapsulated in Mo72Fe30 (1, 2, 3 and 4) as catalysts were shown in Table 1. From the
results, cyclic olefins such as cyclohexene and cyclooctene were converted with very good to
excellent yields into their corresponding epoxides (Table 1, entries 1 and 2). In homogeneously
catalyzed oxidation reaction of cyclohexene, selectivity for product is often low and cyclohexane-
8

1,2-diol and 2-cyclohexene-1-one are commonly generated byproducts [40, 41]. Moreover, in this
catalytic system 2-cyclohexene-1-one could be converted into the corresponding epoxide in high
to excellent conversion and selectivity especially with 3 (Table 1, entry 10). The major product in
the oxidation of styrene was benzaldehyde (Table 1, entry 3) and indene was converted into the
corresponding aromatic epoxide (Table 1, entry 4). Because of the using from limonene oxide as
a raw material for polycarbonate synthesis [42], this new green process of epoxidation was also
used for the epoxidation of limonene. Under optimized epoxidation reaction, 48-66% conversion
was obtained for different 1, 2, 3 and 4 catalysts and the major product was monoepoxide
(limonene oxide). After 6 h reaction, di-epoxide was the main product (Table 1, entries 5 and 6).
In the case of trans-stilbene, epoxidation was done in a stereospecific manner with complete
retention of configuration (Table 1, entry 7). Conversion and selectivity became less when the
bulkiness or chain length of the substrates is increased. This may be explained on the basis of steric
hindrance caused by the substrates. So, although terminal alkenes need higher activation energy,
highly conversion (73–93%) of these olefins was obtained in our catalytic systems (Table 1, entries
8 and 9). In general, the epoxidation of allylic alcohols and allylic chlorides compared to cyclic
olefins is difficult, since the C=C double bond in allyl moieties is relatively electron deficient by
the electron-withdrawing group of hydroxyl (–OH) and –Cl. But, this compounds in our catalytic
system were converted into the corresponding epoxides in high to excellent yields (Table 1, entries
11–13).
As it could be seen in Table 1, among 1, 2, 3 and 4 POM catalysts, SiMo12⊂Mo72Fe30 (3) and
BW12⊂Mo72Fe30 (4) under the same reaction conditions were shown higher catalytic activities in
the epoxidation of various olefins than two others. Moreover, at this reaction condition
PMo12⊂Mo72Fe30 (2) demonstrated a better catalytic activity respect to Mo72Fe30 (1), too [43].
9

Table 1. Catalytic epoxidation of various olefins using 30% aqueous H2O2 in the presence of 1,
2, 3, and 4 catalystsa
Conversion (%)b
[Selectivity (%)]
Entry
Olefin
Time (h)
3.5
1
2
3
4
64
74
95
89
1
2
[52] [59] [46] [71]
73
82
91
93
3.25
[97] [98] [99] [99]
69
75
89
85
3c
4
3.5
3.5
[91] [81] [85] [89]
45 57 66 82
[85] [93] [81] [85]
48
57
85
66
5d
3.5
[89] [85] [68] [79]
65
76
92
89
6e
6
9
[45] [54] [46] [58]
68
81
87
95
7
[92] [94] [99] [96]
73
[95] [94] [97] [97]
75 79 86 86
[97] [91] [87] [93]
87
85
93
8
9
3.75
4.25
65
86
95
93
10
11
3.5
8
[72] [88] [93] [85]
47
54
68
74
[91] [96] [97] [91]
10

79
[85] [69] [75] [79]
73 84 86 81
82
85
90
12
13
5
4
[76] [72] [91] [77]
aReaction conditions: olefin (1 mmol), H2O2 (3 mmol), and catalyst (2 μmol) in ethanol (2 mL)
under reflux.
bYields refer to GC yields.
cProduct was benzaldehyde.
dProduct was 1,2-epoxide.
eProduct was diepoxide.
By MoO3, Na2MoO4·4H2O, and (NH4)6MO7O24·4H2O as simple salts of Mo (VI) and FeCl3·6H2O
as a simple salt of Fe (III), epoxidation product was not observed even after 24 h reaction under
the same conditions. Furthermore, the catalytic effect of PMo12, SiMo12 and BW12 as Keggin
POMs were examined in this epoxidation system (Table 2, entries 1–3) and low to moderate
conversions and selectivity were observed.
Table 2. Catalytic epoxidation of cyclohexene in the presence of 1, PMo12, SiMo12, BW12 and the
a
physical mixture of 1 with PMo12, SiMo12, or BW12
Entry
Catalyst
Conversion (%)b
Selectivity (%)c
1
2
3
4
5
6
7
PMo12
SiMo12
BW12
Mo72Fe30 (1)
PMo12 + 1d
SiMo12 + 1d
BW12 + 1d
18
26
23
64
68
70
68
58
45
69
52
50
52
54
aReaction conditions: cyclohexene (1 mmol), H2O2 (3 mmol), and catalyst (2 μmol) in ethanol (2
mL) under reflux condition for 3.5 h.
bConversion based on olefin substrate.
cSelectivity for epoxy cyclohexane.
dReaction conditions: cyclohexene (1 mmol), H2O2 (3 mmol), and catalysts (2 + 2 μmol) in ethanol
(2 mL) under reflux condition for 3.5 h.
Another catalytic investigation was carried out by physical mixings of Mo72Fe30 Keplerate (1) and
PMo12, SiMo12 and BW12 with the same ratio. Results (Table 2, entries 5–7) indicated that the
mixtures of 1 and Keggin POMs have not been shown considerable improvement in the catalytic
11

epoxidation reaction. So, exceeded catalytic activity of Keggins encapsulated in Keplerate than
parent ones were confirmed by these results.
The inhibitory effect of radical scavengers such as 2,6-di-tert-butyl-4-methylphenol (BHT) and
diphenyl amine in this oxidation system was also studied. This purpose was done by cyclohexene
epoxidation in the presence of BHT or diphenyl amine (>10 equiv. rather than catalyst 1). In this
oxidation systems, cyclohexene epoxide was produced after 5 h reaction in 90 and 51% yields,
respectively. So, in the present system our results demonstrated that non-radical processes prevail
to a high extent, although some contribution of free radicals may be existed. This behavior of 1 is
also similar to previously reported works by {Mo132} [44, 45].
Interestingly, these POM catalysts are stable even for months in various solvents due to inertness
of the spherical solutes and the presence of hard FeIII and MoVI centers [46, 47]. Since the structure
of POMs is pH dependent, the effect of different pH values in the epoxidation of olefins was also
studied (Fig. 4). According to previous works, Mo72Fe30 (1) in dilute aqueous solutions can act as
a nanosized weak inorganic acid that deprotonate differently depending on the pH [47]. As follows,
their sizes decrease with increasing deprotonation, monotonically that is relevant to cluster surface
charges. Also, it should be noted that all POMs decomposes at high pH values while smaller
species are formed. From Fig. 4, when the pH value was adjusted to less than or equal to 6, the
same conversions and selectivity were obtained. However, owing to the lesser stability of 1, 2, 3
and 4 POM catalysts at higher pH values, lower oxidation activities were observed at pH > 6.
Additionally, these Keggins encapsulated in Keplerate catalysts could be easily recovered by
filtration and reused without loss of catalytic activities. At least eight times reusability of as
mentioned POM catalysts without any significant loss of catalytic activity is one of the major
12

advantages in these systems (Fig. 5). The XRD patterns and FT-IR spectra for 1, 2, 3 and 4 catalysts
after 8 times recycling were stated that the structure of catalysts are preserved.
2
1
100
75
50
25
0
100
75
50
25
0
2
4
6
8
10
2
4
6
8
10
pH
pH
4
3
100
75
50
25
0
100
75
50
25
0
2
4
6
8
10
2
4
6
8
10
pH
pH
Figure 4. The effect of pH in the epoxidation of cyclohexene by H2O2 in the presence of 1, 2, 3
and 4 as catalyst
Figure 5. The reusability of 1, 2, 3 and 4 catalysts in the epoxidation of cyclohexene by H2O2
13

4. Conclusion
In this work, Mo72Fe30 and encapsulated Keggin anions in Mo72Fe30 were prepared and used as
catalyst for epoxidation of olefins by hydrogen peroxide. Optimum reaction conditions such as the
type of solvent and catalyst, amount of oxidant and catalyst, pH and temperature were obtained
and the oxidation of various olefins was performed at this catalytic reaction conditions. Keggin
encapsulated Keplerates were shown higher catalytic activity than parent ones and among them,
by SiMo12⊂Mo72Fe30 (3) and BW12⊂Mo72Fe30 the highest conversions and selectivity were
obtained. These catalysts were also showed high reusability after eight times usage without any
appreciable decrease in catalytic activity and selectivity.
References
[1] J.W. Brown, Q.T. Nguyen, T. Otto, N.N. Jarenwattananon, S. Glöggler, L.-S. Bouchard,
Epoxidation of alkenes with molecular oxygen catalyzed by a manganese porphyrin-based metal–
organic framework, Catal. Commun., 59 (2015) 50-54.
[2] S. Bhadra, M. Akakura, H. Yamamoto, Design of a new bimetallic catalyst for asymmetric
epoxidation and sulfoxidation, J. Am. Chem. Soc., 137 (2015) 15612-15615.
[3] P. Farràs, C. Di Giovanni, J. Clifford, P. Garrido-Barros, E. Palomares, A. Llobet, Light driven
styrene epoxidation and hydrogen generation using H2O as an oxygen source in a
photoelectrosynthesis cell, Green Chem., 18 (2016) 255-260.
[4] M.T. Pope, A. Müller, Polyoxometalate chemistry: an old field with new dimensions in several
disciplines, Angew. Chem. Int. Ed., 30 (1991) 34-48.
[5] A. Müller, S. Roy, Multifunctional metal oxide based nanoobjects: spherical porous
capsules/artificial cells and wheel-shaped species with unprecedented materials properties, J.
Mater. Chem., 15 (2005) 4673-4677.
14

[6] L. Cronin, Inorganic molecular capsules: from structure to function, Angew. Chem. Int. Ed.,
45 (2006) 3576-3578.
[7] C. Schäffer, A. Merca, H. Bögge, A.M. Todea, M.L. Kistler, T. Liu, R. Thouvenot, P. Gouzerh,
A. Müller, Unprecedented and differently applicable pentagonal units in a dynamic library: a
keplerate of the type {(W)W5}12{Mo2}30, Angew. Chem. Int. Ed., 48 (2009) 149-153.
[8] E. Nikbakht, B. Yadollahi, M.R. Farsani, Green oxidation of alcohols in water by a
polyoxometalate nano capsule as catalyst, Inorg. Chem. Commun., 55 (2015) 135-138.
[9] D. Karimian, B. Yadollahi, V. Mirkhani, Harvesting visible light for aerobic oxidation of
alcohols by a novel and efficient hybrid polyoxometalate, Dalton Transactions, 44 (2015) 1709-
1715.
[10] A. Müller, E. Krickemeyer, H. Bögge, M. Schmidtmann, F. Peters, Organizational forms of
matter: an inorganic super fullerene and keplerate based on molybdenum oxide, Angew. Chem.
Int. Ed., 37 (1998) 3359-3363.
[11] A. Müller, Y. Zhou, H. Bögge, M. Schmidtmann, T. Mitra, E.T. Haupt, A. Berkle, “Gating”
the pores of a metal oxide based capsule: after initial cation uptake subsequent cations are found
hydrated and supramolecularly fixed above the pores, Angew. Chem. Int. Ed., 45 (2006) 460-465.
[12] A.M. Todea, A. Merca, H. Bögge, J. van Slageren, M. Dressel, L. Engelhardt, M. Luban, T.
Glaser, M. Henry, A. Mueller, Extending the {(Mo)Mo5}12M30 capsule Keplerate sequence: a
{Cr30} cluster of s= 3/2 metal centers with a {Na(H2O)12} encapsulate, Angew. Chem., 119 (2007)
6218-6222.
[13] A.M. Todea, A. Merca, H. Bögge, T. Glaser, J.M. Pigga, M.L. Langston, T. Liu, R. Prozorov,
M. Luban, C. Schröder, Porous capsules {(M)M5}12FeIII (M= MoVI, WVI): sphere surface
30
15

supramolecular chemistry with 20 ammonium ions, related solution properties, and tuning of
magnetic exchange interactions, Angew. Chem. Int. Ed., 49 (2010) 514-519.
[14] A.M. Todea, A. Merca, H. Bögge, T. Glaser, L. Engelhardt, R. Prozorov, M. Luban, A.
Müller, Polyoxotungstates now also with pentagonal units: supramolecular chemistry and tuning
of magnetic exchange in {(M)M5}12V30 Keplerates (M= Mo, W), Chem. Commun., (2009) 3351-
3353.
[15] A. Müller, S. Sarkar, S.Q.N. Shah, H. Bögge, M. Schmidtmann, S. Sarkar, P. Kögerler, B.
Hauptfleisch, A.X. Trautwein, V. Schünemann, Archimedean synthesis and magic numbers:
“sizing” giant molybdenum‐oxide‐based molecular spheres of the Keplerate type, Angew. Chem.
Int. Ed., 38 (1999) 3238-3241.
[16] G. Liu, T. Liu, Strong attraction among the fully hydrophilic {Mo72Fe30} macroanions, J. Am.
Chem. Soc., 127 (2005) 6942-6943.
[17] P.P. Mishra, J. Pigga, T. Liu, Membranes based on “Keplerate”-type polyoxometalates: slow,
passive cation transportation and creation of water microenvironment, J. Am. Chem. Soc., 130
(2008) 1548-1549.
[18] R. Mekala, S. Supriya, S.K. Das, Fate of a giant {Mo72Fe30}-type polyoxometalate cluster in
an aqueous solution at higher temperature: understanding related Keplerate chemistry, from
molecule to material, Inorg. Chem., 52 (2013) 9708-9710.
[19] F. Jalilian, B. Yadollahi, M.R. Farsani, S. Tangestaninejad, H.A. Rudbari, R. Habibi, New
perspective to Keplerate polyoxomolybdates: green oxidation of sulfides with hydrogen peroxide
in water, Catal. Commun., 66 (2015) 107-110.
[20] A. Müller, S.K. Das, P. Kögerler, H. Bögge, M. Schmidtmann, A.X. Trautwein, V.
Schünemann, E. Krickemeyer, W. Preetz, A new type of supramolecular compound: molybdenum‐
16

oxide‐based composites consisting of magnetic nanocapsules with encapsulated Keggin‐ion
electron reservoirs cross‐linked to a two‐dimensional network, Angew. Chem. Int. Ed., 39 (2000)
3413-3417.
[21] A.M. Todea, J. Szakács, S. Konar, H. Bögge, D.C. Crans, T. Glaser, H. Rousselière, R.
Thouvenot, P. Gouzerh, A. Müller, Reduced molybenum‐oxide‐based core–shell hybrids:“blue”
electrons are delocalized on the shell, Chem. Eur. J., 17 (2011) 6635-6642.
[22] A.M. Todea, A.J.M. Al-Karawi, T. Glaser, S. Walleck, L.-M. Chamoreau, R. Thouvenot, P.
Gouzerh, A. Müller, Encapsulation of Keggin-type anions in reduced molybdenum–iron-type
Keplerates as a general phenomenon, Inorg. Chim. Acta, 389 (2012) 107-111.
[23] M. Misono, Unique acid catalysis of heteropoly compounds (heteropolyoxometalates) in the
solid state, Chem. Commun., (2001) 1141-1152.
[24] O.A. Kholdeeva, M.N. Timofeeva, G.M. Maksimov, R.I. Maksimovskaya, W.A. Neiwert,
C.L. Hill, Aerobic oxidation of formaldehyde mediated by a Ce-containing polyoxometalate under
mild conditions, Inorg. Chem., 44 (2005) 666-672.
[25] F. Jalilian, B. Yadollahi, S. Tangestaninejad, H.A. Rudbari, Wheel-shaped copper containing
polyoxotungstate as an efficient catalyst in the three-component synthesis of 1, 2, 3-triazoles, RSC
Adv., 6 (2016) 13609-13613.
[26] A. Mouret, L. Leclercq, A. Mühlbauer, V. Nardello-Rataj, Eco-friendly solvents and
amphiphilic catalytic polyoxometalate nanoparticles: a winning combination for olefin
epoxidation, Green Chem., 16 (2014) 269-278.
[27] S.P. Maradur, C. Jo, D.H. Choi, K. Kim, R. Ryoo, Mesoporous polymeric support retaining
high catalytic activity of polyoxotungstate for liquid‐phase olefin epoxidation using H2O2,
ChemCatChem, 3 (2011) 1435-1438.
17

[28] G.S. Armatas, G. Bilis, M. Louloudi, Highly ordered mesoporous zirconia-polyoxometalate
nanocomposite materials for catalytic oxidation of alkenes, J. Mater. Chem., 21 (2011) 2997-3005.
[29] M. Araghi, V. Mirkhani, M. Moghadam, S. Tangestaninejad, I. Mohammdpoor-Baltork,
Synthesis and characterization of a new porphyrin–polyoxometalate hybrid material and
investigation of its catalytic activity, Dalton Transactions, 41 (2012) 3087-3094.
[30] E. Poli, R. De Sousa, F. Jerome, Y. Pouilloux, J.-M. Clacens, Catalytic epoxidation of styrene
and methyl oleate over peroxophosphotungstate entrapped in mesoporous SBA-15, Catalysis
Science & Technology, 2 (2012) 910-914.
[31] R. Ishimoto, K. Kamata, N. Mizuno, Investigation of the reaction mechanism for the
epoxidation of alkenes with hydrogen peroxide catalyzed by a protonated tetranuclear
peroxotungstate with NMR spectroscopy, kinetics, and DFT calculations, Eur. J. Inorg. Chem.,
2013 (2013) 1943-1950.
[32] E. Tebandeke, C. Coman, K. Guillois, G. Canning, E. Ataman, J. Knudsen, L.R. Wallenberg,
H. Ssekaalo, J. Schnadt, O.F. Wendt, Epoxidation of olefins with molecular oxygen as the oxidant
using gold catalysts supported on polyoxometalates, Green Chem., 16 (2014) 1586-1593.
[33] R. Yahya, M. Craven, E.F. Kozhevnikova, A. Steiner, P. Samunual, I.V. Kozhevnikov, D.E.
Bergbreiter, Polyisobutylene oligomer-bound polyoxometalates as efficient and recyclable
catalysts for biphasic oxidations with hydrogen peroxide, Catalysis Science & Technology, 5
(2015) 818-821.
[34] M.R. Farsani, B. Yadollahi, H.A. Rudbari, A. Amini, T. Caradoc-Davis, J.R. Price, First stable
nitrate-encapsulated sandwich type polyoxometalate: Synthesis, structural characterization, and
catalytic performance, Inorg. Chem. Commun., 43 (2014) 39-44.
18

[35] M.R. Farsani, F. Jalilian, B. Yadollahi, H.A. Rudbari, Comparison between various Keggin
and Wells–Dawson sandwich-type polyoxometalates in catalytic oxidation of cyclooctene and
cyclohexene with hydrogen peroxide, Appl. Organomet. Chem., 29 (2015) 7-11.
[36] F. Jalilian, B. Yadollahi, M.R. Farsani, S. Tangestaninejad, H.A. Rudbari, R. Habibi, Catalytic
performance of Keplerate polyoxomolybdates in green epoxidation of alkenes with hydrogen
peroxide, RSC Adv., 5 (2015) 70424-70428.
[37] B. Choudary, B. Bharathi, C.V. Reddy, M.L. Kantam, Tungstate-exchanged Mg-Al-LDH
catalyst: an eco-compatible route for the oxidation of sulfides in aqueous medium, J. Chem. Soc.,
Perkin Trans. 1, (2002) 2069-2074.
[38] T. Patonay, W. Adam, A. Lévai, P. Kövér, M. Németh, E.-M. Peters, K. Peters, Chemo-and
diastereoselectivity in the dimethyldioxirane oxidation of 2, 3-dihydro-4 H-1-benzothiopyran-4-
ones and 4 H-1-benzothiopyran-4-ones. unusual reactivity of 4 H-1-benzothiopyran-4-one 1-
oxides, J. Org. Chem., 66 (2001) 2275-2280.
[39] F. Gregori, I. Nobili, F. Bigi, R. Maggi, G. Predieri, G. Sartori, Selective oxidation of sulfides
to sulfoxides and sulfones using 30% aqueous hydrogen peroxide and silica-vanadia catalyst, J.
Mol. Catal. A: Chem., 286 (2008) 124-127.
[40] S.R. Amanchi, A.M. Khenkin, Y. Diskin-Posner, R. Neumann, Bismuth-substituted
“sandwich” type polyoxometalate catalyst for activation of peroxide: umpolung of the peroxo
intermediate and change of chemoselectivity, ACS Catal., 5 (2015) 3336-3341.
[41] R. Noyori, M. Aoki, K. Sato, Green oxidation with aqueous hydrogen peroxide, Chem.
Commun., (2003) 1977-1986.
[42] C.M. Byrne, S.D. Allen, E.B. Lobkovsky, G.W. Coates, Alternating copolymerization of
limonene oxide and carbon dioxide, J. Am. Chem. Soc., 126 (2004) 11404-11405.
19

[43] R. Fareghi-Alamdari, S.M. Hafshejani, H. Taghiyar, B. Yadollahi, M.R. Farsani, Recyclable,
green and efficient epoxidation of olefins in water with hydrogen peroxide catalyzed by
polyoxometalate nanocapsule, Catal. Commun., 78 (2016) 64-67.
[44] A. Rezaeifard, R. Haddad, M. Jafarpour, M. Hakimi, {Mo132} nanoball as an efficient and
cost-effective catalyst for sustainable oxidation of sulfides and olefins with hydrogen peroxide,
ACS Sustainable Chem. Eng., 2 (2014) 942-950.
[45] A. Rezaeifard, R. Haddad, M. Jafarpour, M. Hakimi, Catalytic epoxidation activity of
Keplerate polyoxomolybdate nanoball toward aqueous suspension of olefins under mild aerobic
conditions, J. Am. Chem. Soc., 135 (2013) 10036-10039.
[46] A.A. Verhoeff, M.L. Kistler, A. Bhatt, J. Pigga, J. Groenewold, M. Klokkenburg, S. Veen, S.
Roy, T. Liu, W.K. Kegel, Charge regulation as a stabilization mechanism for shell-like assemblies
of polyoxometalates, Phys. Rev. Lett., 99 (2007) 066104.
[47] T. Liu, B. Imber, E. Diemann, G. Liu, K. Cokleski, H. Li, Z. Chen, A. Müller, Deprotonations
and charges of well-defined {Mo72Fe30} nanoacids simply stepwise tuned by pH allow
control/variation of related self-assembly processes, J. Am. Chem. Soc., 128 (2006) 15914-15920.
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New perspective to catalytic epoxidation of olefins by Keplerate containing
Keggin polyoxometalates
Hamid Taghiyar, Bahram Yadollahi*
Department of Chemistry, University of Isfahan, Isfahan 81746-73441, Iran
21

New perspective to catalytic epoxidation of olefins by Keplerate containing
Keggin polyoxometalates
Hamid Taghiyar, Bahram Yadollahi*
Department of Chemistry, University of Isfahan, Isfahan 81746-73441, Iran
Different Keggin encapsulated in Keplerate polyoxometalates have been used as catalyst in the
epoxidation of olefins with hydrogen peroxide. These POM catalysts show higher catalytic activity
than parent ones with green features of convenient recovery, steady reuse, high conversion and
selectivity, and simple preparation.
22

Using from Keggin encapsulated in Keplerate polyoxometalates as catalyst
Green catalytic epoxidation by hydrogen peroxide
Higher catalytic activity of Keggin encapsulated Keplerates than parent ones
23