Nanohybrid Complexes with Molybdenyl Acetylacetonate, Schiff Base and Lacunary Keggin-Type Polyoxometalates: Synthesis and Catalytic Epoxidation of Olefins in the Presence of tert-Butyl Hydroperoxide

Article abstract of DOI:10.1007/s10562-018-2354-z

Abstract: Two new nanohybrid compounds as heterogenous catalyst were prepared by reaction of Lacunary Keggin-type polyoxometalate compounds ([SiW₁₁O₃₉]^8? and [PW₁₁O₃₉]^7?), molybdenyl acetylacetonate [MoO₂(acac)₂] and ethylenediamine (en), (1 and 2 respectively) species and characterized by elemental analysis and various routine techniques. The catalytic activities of these nanocatalysts examined for the epoxidation of linear, cyclic and phenyl-substituted olefins using tert-Butyl hydroperoxide (tert-BuOOH) as oxidants. The synergistic effect between molybdenyl acetylacetonate complex and lacunary Keggin-type polyoxometalate plays an important role in the promotion of catalytic activity. The catalysts were recovered and reused at least six times without obvious losing of activity and the yields for catalyst recovery are all above 91%. Graphical Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-018-2354-z

Catalysis Letters
https://doi.org/10.1007/s10562-018-2354-z
Nanohybrid Complexes with Molybdenyl Acetylacetonate, Schiff Base
and Lacunary Keggin-Type Polyoxometalates: Synthesis and Catalytic
Epoxidation of Olefins in the Presence of tert-Butyl Hydroperoxide
1
1
2
Samira S. Hosseinyzade · Farrokhzad M. Zonoz · Bahram Bahramian
Received: 27 December 2017 / Accepted: 10 March 2018
©
Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
Two new nanohybrid compounds as heterogenous catalyst were prepared by reaction of Lacunary Keggin-type polyoxo-
8
−
7−
metalate compounds ([SiW O ] and [PW O ] ), molybdenyl acetylacetonate [MoO (acac) ] and ethylenediamine
1
1
39
11 39
2
2
(
en), (1 and 2 respectively) species and characterized by elemental analysis and various routine techniques. The catalytic
activities of these nanocatalysts examined for the epoxidation of linear, cyclic and phenyl-substituted olefins using tert-Butyl
hydroperoxide (tert-BuOOH) as oxidants. The synergistic effect between molybdenyl acetylacetonate complex and lacunary
Keggin-type polyoxometalate plays an important role in the promotion of catalytic activity. The catalysts were recovered and
reused at least six times without obvious losing of activity and the yields for catalyst recovery are all above 91%.
Graphical Abstract
Keywords Keggin-type polyoxometalates · Molybdenyl acetylacetonate · Schiff base · Olefin · Epoxidation · Nanohybrid
1
Introduction
of alkenes is a considerable process in the chemical and
petrochemical industries [7, 8], because these compounds
are greatly used for the synthesis of a variety of organic
compounds like resins, surfactants, paints and are intermedi-
ates in pharmaceutical synthesis [9].
The preparations of new heterogeneous catalysts for selec-
tive oxidation of organic compounds are currently a notable
assay purpose [1–5]. Heterogeneous catalysts have signifi-
cant advantages over homogeneous catalysts such as stabil-
ity, facility of separation, and reusability [6]. The oxidation
Polyoxometalates (POMs) are soluble anionic metal-
oxide clusters with oxygen-rich surface, the intense tendency
for coordination and potential applications in many fields
such as catalysis, ion exchange, magnetism, photochemis-
try and material science [10–20]. Using POMs as acid and
oxidation catalysts is one of the important applications of
these compounds [21, 22]. Silicotungstic acid (H SiW O ),
*
Farrokhzad M. Zonoz
f.zonoz@hsu.ac.ir
1
2
Department of Chemistry, Hakim Sabzevari University,
Sabzevar 96179-76487, Iran
4
12 40
phosphotungstic acid (H PW O ) and their transition metal
3
12 40
College of Chemistry, Shahrood University of Technology,
Shahrood 36155-316, Iran
substituted of mono-defect fragments with Keggin structure
Vol.:(0
1
123456789)
3

S. S. Hosseinyzade et al.
have attracted much attention as oxidation catalysts due to
the redox and acid feature and structural characteristics
Lambda 25 spectrophotometer. Thermogravimetric analysis
(TGA) analyses were carried out on Netzsch—TGA 209 F1
−
1
[
23–29]. However, these compounds are soluble in polar
instrument under nitrogen atmosphere with 30 mL min
solvents and therefore, using these compounds as a catalyst
is associated with some restrictions [30, 31].
flow rate. The temperature range was 20–700 °C with the
−
1
heating rate of 10 °C min . Field emission scanning elec-
tron microscopy (FESEM) equipped by EDS microanalysis
was done with MIRA3TESCAN-XMU instrument.
Nowadays, POMs attract much attention as building
blocks for reaction with organic ligands due to their inter-
esting structures [32–34]. They are great models for mak-
ing hybrid compounds, which in recent years the notable
attempt has been assigned to the design of nanostructured
hybrid POMs [35–37]. Preparation of nanosized hybrid pol-
yoxometalates increases the porosity of the structure and
surface area. Moreover, solubility in polar solvent of these
compounds also disappears due to incorporation of organic
ligands as hydrophobic groups [38]. These compounds are
new types of POM-based catalysts having great potential in
heterogeneous catalysis in contrast to supported heterogene-
ous catalysts. The significant problem in supported catalysts
is created by a poor connection between the polyoxometa-
lates and the supports that causes loading these compounds
by the solvent [39–41].
2.2 Methods
2
.2.1 Preparation of Mono-lacunary Silicotungstate
Molybdenyl Acetylacetonato Schiff Base (1)
A 0.719 g of H SiW O (0.25 mmol) was dissolved in min-
4
12 40
imum of distilled water, and during stirring a 0.066 mL of
ethylenediamine (1 mol) was added with vigorous stirring.
After 30 min the methanol solution of 0.33 g [MoO (acac) ]
2
2
(
1 mmol) was added and the mixture was refluxed for 5 h at
8
0 °C. The light green color precipitate was filtered, washed
with methanol, and dried at 80 °C. IR (KBr disk): 3330,
3
7
1
263, 3188, 3103, 2926, 1604, 1533, 1442, 1323, 914, and
In this paper, we have successfully synthesized two new
nanostructure organic–inorganic hybrid compounds with the
sol–gel method, which characterized by instrumentals tech-
niques. Then, we have used this nanohybrid polyoxometa-
lates as heterogeneous catalyst for epoxidation of olefins
using tert-Butyl hydroperoxide as oxidants. Furthermore the
effects of different solvents, temperatures, content of oxidant
and catalyst, and time on the activity of the catalysts on cis-
cyclooctene as model reaction were investigated. And finally
epoxidation of several olefins including linear, cyclic and
phenyl-substituted olefins with tert-Butyl hydroperoxide as
oxidant were investigated.
−
1
88 cm . Elemental analysis results showed: C, 5.85; H,
.03; Mo, 3.10; N, 2.75; Si, 0.91; W, 64.37%. Calculations
for C H MoN O SiW (3132.51): C, 5.75; H, 1.08; Mo,
1
5
34
6
43
11
3
.06; N, 2.68; Si, 0.90; W, 64.56%.
2
.2.2 Preparation of Mono-lacunary Phosphotungstate
Molybdenyl Acetylacetonato Schiff Base (2)
According to the above method the compound of 2 can be
synthesized as similar method in which the H PW O was
3
12 40
used instead of H SiW O . IR (KBr disk): 3350, 3270,
4
12 40
3
8
6
193, 3105, 2933, 1620, 1592, 1533, 1436, 1317, 1080, 973,
−
1
85, and 796 cm . Elemental analysis results showed: C,
.16; H, 1.25; Mo, 3.08; N, 2.87; P, 0.90; W, 63.88%. Cal-
2
Experimental
culations for C H MoN O PW (3135.51): C, 5.74; H,
1
5
34
6
43
11
2.1 General
1
.08; N, 2.68; W, 64.50; Mo, 3.06; P, 1.00%.
All reagents were commercially obtained and used without
any further purification. [MoO (acac) ] was prepared by the
2.2.3 General Procedure for the Epoxidation of Alkenes
2
2
literature methods and identified by Fourier transform infra-
red (FT-IR) spectroscopy [42]. FT-IR spectra were obtained
using KBr pellets on a Shimadzu 8400S FT-IR spectrometer
All reaction performed in 10 mL round bottom flask
equipped with a magnetic stirrer bar and a condenser
under similar refluxed conditions. The mixture of alkene
(0.5 mmol), catalyst 1 (10 mg, 3 mmol) and for catalyst 2
(20 mg, 6 mmol), and tert-BuOOH (0.4 mL) were refluxed in
1,2-dichloroethane as solvent. The progress of reaction was
monitored by gas chromatography analysis. Blank experi-
ments were also performed in the absence of catalyst under
the same experimental conditions. Since different alkenes
have various reactivity toward oxidation the reactions were
continued until no further progress was observed.
−
1
in the range of 4000–400 cm . The elemental analyses of
carbon, hydrogen, and nitrogen were determined by a Per-
kin-Elmer CHN analyzer. The ICP analyses were performed
by an ICP-Spectrociros CCD instrument. Gas chromatog-
raphy (GC) was accomplished by a Shimadzu GC-16A
instrument using a 2 m column, packed with silicon DC-200.
X-ray powder diffraction (XRD) patterns were obtained by
using Phillips PW-1800 or STOE diffractometer with Cu Kα
radiation. UV–Vis spectra were recorded on a Perkin-Elmer
1
3

Nanohybrid Complexes with Molybdenyl Acetylacetonate, Schiff Base and Lacunary Keggin-Type…
3
Results and Discussion
3.1 Synthesis Compounds of 1, and 2
Compounds 1 and 2 were synthesized from the reaction
between Keggin-type POMs, ethylene diamine and molyb-
denyl acetylacetonate. By addition ethylenediamine to POMs
solution, the pH of media increases and then Keggin-type
POMs changing to mono-lacunary species. In 2014, Memon
et al. was reported preparation of a Schiff’s base in the reac-
tion of acetyl acetone and ethylene diamine [43]. Therefore
a combination of molybdenyl acetylacetonate Schiff base
complex and mono-lacunary POMs can be considered in
formation of 1 and 2 nanocatalysts (Scheme 1).
8−
Fig. 1 The FT-IR spectra of a [MoO (acac) ], b [SiW O ] and c
2
2
11 39
compound 1
3
.2 Characterization of Mono‑lacunary
Polyoxometalate Molybdenyl Acetylacetonato
Schiff Base Nanocatalysts (1, and 2)
[MoO (acac) ], the ʋ (C=O) peak of 1 overlap with ν (C=N)
2
2
−
1
band and cannot be seen. In the range of 960–700 cm , the
8
−
peaks of [MoO (acac) ] and [SiW O ] were overlap and
2
2
11 39
3.2.1 FT-IR Analysis
ʋ (W–O –W) peaks is well seen.
as
c
The FT-IR spectrum of 2 (Fig. 2) is similar to compound 1.
8
−
7−
The FT-IR spectrum of [MoO (acac) ], [SiW O ] , and
The characteristic peaks of [MoO (acac) ],[PW O ] ani-
2
2
11 39
2
2
11 39
1
are shown in Fig. 1. The characteristic peaks at 2929,
ons and imine group can be seen in this spectrum. With
−
1
7−
1
590, 1363, 934, and 906 cm in [MoO (acac) ] spectrum
increasing symmetry of [PW O ] by filling the cavity
2
2
11 39
(
Fig. 1a) are attributed to ʋ (C–H), ʋ (C=O), δ (C–H), and
with Schiff base ligand, the ʋ (P–O) of 2 shows one peak
as
8
−
−1
ʋ
(Mo=O) respectively [44]. The [SiW O ] POM
at 1080 cm [45].
as
11 39
spectrum (Fig. 1b) shows five characteristic peaks at 995
[
ʋ (Si–O)], 956 [ʋ (W–O )], 887 [ʋ (W–O –W)], 792
3.2.2 XRD Analysis
as
as
t
as
b
−
1
and 721 [ʋ (W–O –W)] cm [45]. In the FT-IR spectrum
as
c
8
−
of 1 (Fig. 1c), the characteristic peaks of [MoO (acac) ],
Figure 3 shows the XRD patterns of [SiW O ] ,
11 39
2
2
8−
[
SiW O ] and Schiff base can be seen. A very interesting
[MoO (acac) ], and 1. The hybrid material reveals differ-
11
39
2
2
−
1
point in this spectrum is related to a new peak at 1604 cm ,
ent structure compared to pure POM and [MoO (acac) ]
2 2
[
ʋ (C=N)], which represents the formation of the bond
compounds. The Keggin structure shows two typical
reflexing area in XRD patterns (2θ = 2°–10° and 25°–35°)
[24]. According to the XRD pattern, 1 has a crystal struc-
ture after metal loading. A comparison of XRD patterns of
between carbon and nitrogen atoms. This band may be attrib-
uted to the existence of imine group (Schiff base) in 1 which
more specific in compound 2 [46]. In comparison of free
Scheme 1 Reaction scheme for the synthesis of 1 and 2 nanocatalysts
1
3

S. S. Hosseinyzade et al.
7
−
Fig. 4 XRD pattern of a [PW O ] , b [MoO (acac) ] and c com-
1
1
39
2
2
pound 2
3
.2.3 FESEM Images
7
−
Fig. 2 The FT-IR spectra of a [MoO (acac) ], b [PW O ] and c
2
2
11 39
compound 2
The FESEM images of compound 1 and 2 are shown in
Fig. 5. These two compounds have a regular structure. This
images confirmed that [MoO (acac) ] has been successfully
2
2
supported on POMs. The results show that 1 possesses rod-
like (particle size in the range of 84–108 nm) and spheri-
cal shape (particle size in the range of 36–40 nm) particles
(
Fig. 5b). According to this figure, the morphology of 1 can
be considered as corn-like. This result is consistent with
XRD data. The size of particles is estimated to be 30–60 nm
for compound 1, and 50–70 nm for compound 2. The results
of FESEM and XRD techniques are in good agreement with
each other.
3
.2.4 EDX Spectra
Energy dispersive X-ray analysis (EDX) is a very good tech-
nique for achieving data about the elemental composition of
compounds. EDX analysis of 1 and 2 indicates the presence
of C, N, O, Si, P, Mo, and W elements (Fig. 6). Based on
these results, it is demonstrated the proposed structure of 1
and 2 nanocatalysts (Scheme 1).
8
−
Fig. 3 XRD pattern of a [SiW O ] , b [MoO (acac) ] and c com-
1
1
39
2
2
pound 1
8
−
[
SiW O ] , [MoO (acac) ], and catalyst 1 shows that the
1
1
39
2
2
structure of primary polyoxometalate has been maintained
during reaction. The structure of [MoO (acac) ] is largely
2
2
altered and the intensity of its characteristic diffractions
3.2.5 UV Analysis
(
2θ = 10°–20°) decreases, which indicates the conversion
of its structure and creation of a new composition like
Schiff base complex in 1. By using Williamson–Hall equa-
tion, the average particle size of the particles is of one has
been estimated about 38 nm [47].
The UV–Vis spectra of [MoO (acac) ], H SiW O
12 40,
2
2
4
1, H PW O , and 2 are shown in Fig. 7. As shown in
3
12 40
Fig. 7A a, B a, the characteristic absorption peaks at 263
and 256 nm for H SiW O and H PW O respectively,
4
12 40
3
12 40
7
−
The XRD patterns of [PW O ] , [MoO (acac) ] and
are attributed to the oxygen-to-metal (O → W) charge-
transfer bands of Keggin anions [48]. As can be seen in
this figure [MoO (acac) ] has a peak at 271 nm (Fig. 7A b,
1
1
39
2
2
2
are shown in Fig. 4. This XRD pattern shows similar
results in the case of crystal structure and existence of
polyoxometalate in compound 2. By using similar calcula-
tions, the average size of the particles is estimated about
2
2
B b), which is attributed to the O (pπ) → Mo (dπ) charge
transfer transition [49]. This peak is shifted to 321 and
315 nm in the 1 and 2 compounds (Fig. 7A c, B c). This
5
0 nm [47].
1
3

Nanohybrid Complexes with Molybdenyl Acetylacetonate, Schiff Base and Lacunary Keggin-Type…
Fig. 5 FESEM images of a, b 1 and c, d 2 nanocatalysts
suggests an intramolecular interactions between POMs and
molybdenyl acetylacetonate in 1 (Calc. 15.7%). The final
[
MoO (acac) ].
weight loss step (14.8%) is attributed to decomposition of
silicotungstate that occurs above 550 °C (Calc. 12.4%).
The DSC-TGA curve of 2 was shown in Fig. 9. This
curve shows three remarkable steps in 20–1000 °C. The
weight loss between 100 and 400 °C (6.1%) cab be attrib-
uted to the removal of imine groups (Calc. 5.36%). The
removal of molybdenyl acetylacetonate and oxides of tung-
sten, phosphorus, and molybdenum oxides occurs between
400 and 1000 °C (24.2%) which nearly in accordance with
the calculated values (27.9%).
2
2
3.2.6 DSC-TGA Analysis
The DSC-TGA curve of 1 (Fig. 8) was shown five step
weight loss in the temperature range of 20–1000 °C.
The first and second weight losses (4.61%) between 100
and 300 °C correspond to the removal of imine groups
in Schiff base in two steps (Calc. 5.36%). The third and
fourth weight losses (14.1%) exhibits in the temperature
range of 320–550 °C is attributed to decomposition of
1
3

S. S. Hosseinyzade et al.
Fig. 6 The EDX spectra of a compound 1 and b compound 2
Fig. 7 UV–Vis spectra of A a H SiW O , b [MoO (acac) ] and c 1. B a H PW O , b [MoO (acac) ] and c 2
4
12 40
2
2
4
12 40
2
2
Fig. 9 DSC-TGA analysis of 2
Fig. 8 DSC-TGA analysis of 1
3
.3 Catalytic Applications of 1 and 2
in the Epoxidation of Alkenes
The catalytic application of 1 and 2 nanoparticles in the
epoxidation of alkenes using of tert-BuOOH as oxidant was
investigated. Initially, in order to investigation of catalyst
effect, the oxidation of cis-cyclooctene (as model reaction)
The results of FT-IR spectra, XRD patterns and DSC-
TGA analysis can be confirm the proposed structure
(
Scheme 1).
1
3

Nanohybrid Complexes with Molybdenyl Acetylacetonate, Schiff Base and Lacunary Keggin-Type…
Table 1 Epoxidation of
cis-cyclooctene at refluxed
conditions
Entry Catalyst (mg) Solventa Oxidant
TOF (h−1
)
Catalyst
Oxidant/sub-
strate molar
ratio
Epoxide
b
c
loading
mol%)
yield (%)
(
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
Catalyst-free C H Cl TBHP
–
–
–
0.90
0.90
0.90
0.90
0.90
0.90
2.24
2.24
2.24
1.24
2.24
2.24
2.24
2.24
2.24
2.24
2.24
2.24
2.24
2.24
2.24
2.24
1.68
1.12
0.56
2.24
2.24
2.24
2.24
2.24
2.24
2.24
2.24
2.24
2.24
2.24
2.24
2.24
1.68
1.12
0.56
–
–
–
–
3
2
4
2
H SiW O
C H Cl TBHP
Trace
Trace
17
6
4
12 40
2
4
2
H PW O
C H Cl TBHP
3
12 40
2
4
2
1 (15)
CH OH TBHP
3
1 (15)
1 (15)
1 (15)
1 (15)
1 (15)
1 (15)
1 (15)
1 (15)
1 (10)
1 (7)
CH CN TBHP
12.4
157
163
206
107.4
66
3
CH Cl
CHCl3
TBHP
TBHP
76
79
99
52
32
Trace
99
99
72
39
99
70
31
28
5
2
2
C H Cl TBHP
2
4
2
C H Cl H O
2
4
2
2
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
C H Cl H O ·CON H 0.90
2 4 2 2 2 2 4
d
C H Cl NaIO4
0.90
0.90
0.60
0.42
0.30
0.60
0.60
0.60
0.60
1.24
1.24
1.24
1.24
1.24
1.24
–
2
4
2
C H Cl TBHP
206
309
318.6
242
309
216.7
96
86.7
1.3
1
8.3
14
26
10
4.7
–
2
4
2
C H Cl TBHP
2
4
2
C H Cl TBHP
2
4
2
1 (5)
C H Cl TBHP
2 4 2
1 (10)
1 (10)
1 (10)
1 (10)
2 (20)
2 (20)
2 (20)
2 (20)
2 (20)
2 (20)
2 (20)
2 (20)
2 (15)
2 (10)
2 (7)
C H Cl TBHP
2 4 2
C H Cl TBHP
2
4
2
C H Cl TBHP
2
4
2
C H Cl TBHP
2
4
2
CH OH TBHP
3
CH CN TBHP
4
3
CH Cl
CHCl3
TBHP
TBHP
32
54
99
39
18
Trace
78
53
37
25
99
68
43
22
2
2
C H Cl TBHP
2
4
2
C H Cl H O
2
2
4
2
2
C H Cl H O ·CON H 1.24
2
4
2
2
2
2
4
d
C H Cl NaIO4
1.24
0.92
0.61
0.43
0.31
1.24
1.24
1.24
1.24
2
4
2
C H Cl TBHP
27
2
4
2
C H Cl TBHP
27.5
27.4
26
2
4
2
C H Cl TBHP
2
4
2
2 (5)
C H Cl TBHP
2 4 2
2 (20)
2 (20)
2 (20)
2 (20)
C H Cl TBHP
26
2
4
2
C H Cl TBHP
17.6
11.2
5.7
2
4
2
C H Cl TBHP
2
4
2
C H Cl TBHP
2
4
2
Reaction times are 30 min for catalyst 1, and 180 min for catalyst 2
a
Amounts of solvent are 2 mL
Calculated for 0.5 mmol cyclooctene
GC yields are based on the starting cyclooctene
Tetra-butyl phosphonium bromide was used as phase transfer reagent
b
c
d
was carried out using tert-Butyl hydroperoxide in different
reaction media at refluxed conditions (Table 1). No prod-
uct was obtained in the absence of any catalyst (Table 1,
entry 1). The reaction was incomplete or exhibited extremely
low catalytic activities in the presence of H SiW O
entry 2 and 3). The effects of different solvents (Table 1,
entries 4–8), mg of catalyst (Table 1, entries 12–15), oxi-
dant type (Table 1, entries 8–11), mol% for catalyst load-
ing (0.3–0.9 mol%), and oxidant to substrate molar ratio
(0.56–2.24 molar ratio) for 1 and 2 catalyst were investi-
gated. The experiments show that with these catalysts,
4
12 40
and H PW O POMs homogeneous systems (Table 1,
3
12 40
1
3

S. S. Hosseinyzade et al.
TBHP is the only oxidizing system, which can proceed
the epoxidation of cyclooctene in C H Cl . Other oxygen
entries 12–15 and 28–31). The highest conversion rate
for 1 and 2 were 10 and 20 mg respectively. The reaction
temperature was also optimized by carrying out the reac-
tion in 90 °C and room temperature. At room tempera-
ture (25 °C), the product yields were low for compound
2 but the catalyst 1 showed 15% conversion. By increas-
ing the reaction temperature to 90 °C the conversion was
improved for both samples. Generally, catalytic reactions
are considered to take place at the surface of catalysts. In
the low temperature section, the reactants are not easy to
reach the catalyst surface, so an increase in conversion is
observed as the temperature goes up until the chemical
turnover at the surfaces is equal to the chemical reaction
rate on their surfaces. After that, the conversion does not
alter with temperature due to the fact that catalysts do
not have sufficient exposed surface area for the reactants
to carry out high rates of catalytic reactions. With the
viewpoint of practical production, the optimum reaction
temperature was fixed at 90 °C for further studies.
2
4
2
sources such as hydrogen peroxide, sodium periodate (in
the presence of 0.01 g tetra-butyl phosphonium bromide
as phase transfer reagent) and urea-hydrogen peroxide in
C H Cl do not show any activity (Table 1, entries 8–11
2
4
2
and 23–26).
In order to study the effects of solvent, protic and aprotic
solvents with different polarity and coordinating ability
were used in epoxidation of cyclooctene with TBHP. The
solvents of CH Cl, CH Cl , CH OH, CH CN and C H Cl
3
2
2
3
3
2
4
2
were used for oxidation of cyclooctene in the presence of
tert-BuOOH (Table 1, entries 4–8 and 19–23). For EtOH and
CH CN a detrimental effect on the reaction of cyclooctene
3
was observed, giving less than 7% conversion at 30 min for
catalyst 1 and 180 min for catalyst 2. The observed cata-
lytic activities do not correlate with the polar properties of
the solvents. Instead, the coordinating ability of the solvent
seems to have a major influence. Thus, the solvents EtOH
and CH CN may compete with TBHP for connection to
According to these data catalyst 1 as nanocatalyst gave
the highest yield in 10 mg of catalyst, C H Cl as solvent,
3
coordination sites on transition metal catalyst. According to
the results 1,2-dichloroethane showed the highest conversion
rates as the solvent.
2
4
2
0.6 mol% for catalyst loading, and 2.24 molar ratios for oxi-
dant to substrate (Table 1, entry 13). In the case of catalyst
2, these values in C H Cl are 20 mg of catalyst, 1.24 mol%
In the next step, to optimize the reaction time the
reflux was performed at different times 10, 20, 30, 60, 90,
2
4
2
for catalyst loading, and 2.24 molar ratios for oxidant to
substrate (Table 1, entry 24). Therefore, catalyst 1 exhibits
a more efficient activity in the epoxidation process. The high
catalytic activity of 1 in epoxidation reaction of olefins is
probably due to the less reduction potential of this com-
pound [50].
120,150,180 min. Figure 10 shows the effect of reaction time
on epoxidation of cyclooctene with TBHP. A comparison
reactivity of catalyst 1 and catalyst 2 reveals that 1 is more
reactive and after 30 min its conversion reaches to maxi-
mum and becomes constant. However, catalyst 2 needs 3 h
to reach this point.
Finally epoxidation of several olefins including lin-
ear, cyclic and phenyl-substituted olefins with tert-Butyl
hydroperoxide as oxidant were carried out in the pres-
ence of 1 and 2 as nanocatalyst in refluxed conditions.
The expected products were obtained with various yields
(Table 2). For all substrates, catalyst 1 behaves as a better
catalyst than catalyst 2. For epoxidation of styrene, the
conversions are found to be 87.0 and 85.0% with excellent
selectivity for epoxide formation in the presence of both
catalyst 1 and 2, respectively. Aside from epoxide, benza-
ldehyde has been detected as the minor product for these
reactions. For the epoxidation of cyclohexene, the conver-
sions are approximately 99.0 and 98.0% with high selec-
tivity for epoxide formation in the presence of catalyst 1
and 2, respectively. Apart from epoxide, 2-cyclohexen-1-ol
and 2-cyclohexen-1-one are the other by-products formed
during the reaction. 1-Octene and 1-Hexen shows low yield
in the epoxidation reaction (Table 2, entry 3 and 4). The
results show that electron-rich alkenes are more reactive
than other alkenes. According to the epoxidation mecha-
nism suggested earlier, we can also see that electron-rich
alkenes are more reactive than other alkenes [51]. Conse-
quently, cyclooctene and cyclohexene with cyclic structure
The ratio of oxidant to substrate is one of the most
crucial parameters in catalytic epoxidation processes. Dif-
ferent values of 0.1, 0.2, 0.3 and 0.4 mmol were selected
for the oxidant. The results in (Table 1, entries 16–19
and 32–35) for 1 and 2 respectively, show that the opti-
mum ratio of oxidant to substrate for catalyst 1 and cata-
lyst 2 is 2.24. In order to select a right value of catalyst,
we checked out values of 20, 15, 10 and 7 mg (Table 1,
Fig. 10 Epoxidation of 0.5 mmol cis-cyclooctene with 1.12 mmol
TBHP catalyzed by a 10 mg of 1 or b 20 mg of 2 in 2 mL C H Cl
2
2
4
under refluxed conditions
1
3

Nanohybrid Complexes with Molybdenyl Acetylacetonate, Schiff Base and Lacunary Keggin-Type…
Table 2 Epoxidation of some olefins with TBHP catalyzed by 1 and 2 in refluxed conditions
a
Catalyst 2a
Conversion
a
Entry Alkene
Catalyst 1
–1
Conversion Selectivity Time
epoxide)a (%)
TOF
Selectivity
Time (h) TOF (h )
–1
(
(
(min)
(h )
(epoxide) (%) (%)
%)
1
2
99 (99) 100
30
309
309
98 (98)
98 (87)
100
3
3
26
26
99 (91)b 92
30
88.77
3
4
54 (54) 100
61 (61) 100
90
90
55.7
63
48 (48)
56 (56)
100
100
5
5
7.5
8.7
5
87 (82)c 94.25
90
89.8
85 (75)
88.37
4
16.5
6
92 (85)d 92.39
60
142.4
90 (81)
90
3.5
20
7
8
87 (80) 92
60
60
134.7
147
82 (75)
91.46
3.5
6
18.2
12.3
95 (95)e 100 (trans)f
95 (95)e
100 (trans)f
9
(90)e
80 (cis), 10
60
139.3
(86)e
75 (cis), 11
(trans)g
6
11.2
g
(
trans)
Reaction conditions: alkene (0.5 mmol), TBHP (1.12 mmol), catalyst 1 (10 mg), catalyst 2 (20 mg), C H Cl , (2 mL)
2
4
2
a
b
c
d
e
f
GC yield based on the starting alkenes
The by-products are 8% for catalyst 1 and 11% for catalyst, 2
The by-product are 5% for catalyst 1 and 10% for catalyst, 2
The by-product are 7% for catalyst 1 and 9% for catalyst, 2
1
Both H NMR and GC data approved the reported yields
1
Trans isomer is only product according to H NMR data
Cis and trans isomers are produced according to H NMR data
g
1
1
3

S. S. Hosseinyzade et al.
Table 3 Catalytic activity of various catalysts for the epoxidation of cyclooctene
Entry Catalyst Substrate Solvent
Cyclooctene C H Cl
Time (h) TOF (h−1
)
Conv. (%) Sel. (%) References
1
2
3
4
5
6
7
1
0.5
3
6
24
9
309
26
6.4
−
99
98
77
100
100
28
This work
This work
[52]
2
4
2
2
2
Cyclooctene C H Cl
2
4
[Ni(salen)-POM]
PVMo-MCM/IBA/O2
[As V O (H O)][Cu(2,2′-bpy) ]
Cyclooctene CH CN
3
Cyclooctene C H Cl
63
65.4
33
100
100
100
97.0
[53]
[54]
[54]
[55]
2
4
2
Cyclooctene CH CN
−
8
14 42
2
2 4
3
[As V O (H O)][Cu(1,10-phen) ]
Cyclooctene CH CN
9
−
−
8
14 42
2
2 4
3
Au/BW11/Al O
Cyclooctene C H Cl :CH CN 24
53
2
3
2
4
2
3
display more activities than 1-hexene and 1-octene, which
contain terminal double bonds. The epoxidation reaction
of trans-stilbene has remarkable selectivity with excellent
conversion efficiency whereas, the epoxidation of cis-stil-
bene give a mixture of cis- and trans-stilbene oxide with
high cis/trans epoxide ratio (Table 2 entry 8 and 9). It is
obvious that electron rich olefins are more reactive than
electron poor ones.
of cis-cyclooctene as a model reaction using tert-Butyl
hydroperoxide at optimum conditions. In each experi-
ment, after completion the reaction, the catalysts were eas-
ily separated by centrifugation, washed several times with
1,2-dichloroethane, dried, and then reused in the subsequent
experiments under the same conditions. The recovered cata-
lyst showed an efficient recycling ability without giving any
change in the reaction time and the yield of the product.
The heterogenic character of these catalysts was checked by
the hot filtration test. Because of this reason, each catalyst
was removed by centrifuging the catalytic mixture in the
middle of the optimization process, and the manner was
continued to reach an optimum time of reaction comple-
tion. The obtained results showed that when the catalyst was
removed from the reaction medium, the catalytic procedure
stopped and did not continue anymore. This test proves that
the catalytic reactions are retained in heterogeneous con-
ditions, and the catalysts are not leached to the reaction
medium. Furthermore, ICP has been employed to detect/
determine the amount of metal that leached out into the
reaction mixture. No detectable molybdenum was found in
the reaction mixtures. The obtained results revealed that
the amount of Mo in catalyst 1 after six runs decreased to
3.06% and in catalyst 2 decrease to 3.05%. Moreover, the
IR spectra of recovered catalysts did not show any obvi-
ous differences with fresh catalysts (Fig. 11). The structural
integrity of the recovered catalyst was confirmed by XRD
analysis. As shown in Fig. 12, the basic lattice structure
of 1 and 2 nanocatalysts were not altered after six cycles.
The results are given in Table 4. As shown in Fig. 13 the
recovered catalysts were reused at least six times without
losing of activity.
3.3.1 Comparison with Other Catalysts
The comparison of catalysts 1 and 2 with previously
offered catalysts in the epoxidation of cyclooctene are
given in Table 3. Mirkhani et al. have demonstrated
that the epoxidation of cyclooctene could be done with
Ni(salen)–POM complex [52]. They performed the epoxi-
dation reaction in acetonitrile as a solvent and reported
7
7% conversion and 28% selectivity in epoxidation of
cyclooctene (Table 3, entry 3). In addition, Khenkin
et al. carried out the epoxidation of alkenes by PVMo-
MCM/IBA/O in 1,2-dichloroethane (Table 3, entry 4)
2
[
[
[
53]. Moreover, Guo et al. found out that two complexes
As V O (H O)][Cu(2,2′-bpy) ] and [As V O (H O)]
8
14 42
2
2 4
8
14 42
2
Cu(1,10-Phen) ] could be applied to the selective epoxi-
2
4
dation of olefins (Table 3, entries 5 and 6) [54]. Further-
more, Jameel et al. have reported that Au/BW /Al O
1
1
2
3
used as true heterogeneous catalyst, could be recycled
three times without loss of activity (Table 3, entry 7) [55].
In the present work, the 1 gives 99% conversion and 100%
selectivity and 2 shows 98% conversion and 100% selec-
tivity for epoxidation cyclooctene (Table 3, entries 1 and
2
). Therefore, the present catalysts display the desirable
catalytic activity for the epoxidation of alkenes compared
to other catalysts listed in Table 3.
4
Conclusions
3.3.2 Catalysts Recycling
In this study, we have successfully prepared two nano-
hybrid heterogeneous catalysts by anchoring molybde-
nylacetylacetonate complex and Schiff base with poly-
oxometalates. These catalysts characterized with routine
The catalyst recovery and reusability are the two most
important features for many catalytic processes. The reus-
ability of catalyst 1 and 2 were investigated for oxidation
1
3

Nanohybrid Complexes with Molybdenyl Acetylacetonate, Schiff Base and Lacunary Keggin-Type…
Fig. 11 The FT-IR spectra of recovered a 1 and b 2 nanocatalysts
Fig. 12 The XRD pattern of
1
and 2 nanocatalysts: a basic
XRD pattern and b after six
cycles
Table 4 Epoxidation of cis-cylooctene with TBHP in refluxed condi-
techniques. We have found that the catalytic activity of a
MoO (acac) ] complex can be improved by creation of
tions using recycled catalysts
[
2
2
Number of Catalyst 1a
Catalyst 2a
hybrid combinations with lacunary Keggin-type polyoxo-
metalates. Such catalytic systems combine the advantages
of biphasic and heterogeneous catalysis as they allow an
easy separation of products and catalysts, without their
drawbacks (e.g. high reaction time and catalyst leaching).
The catalyst 1 shows a better catalytic activity than 2. The
new heterogeneous nanocatalysts could be easily recovered
by centrifuge and reused at least six times without signifi-
cant loss of activity. These nanocatalysts display good and
desirable catalytic activity in the epoxidation of various
olefins under quite heterogeneous conditions compared to
other reported catalysts.
cycle
Epoxide
TOF (h−1
)
Epoxide
TOF (h−1
)
b
b
yield (%)
yield (%)
1
2
3
4
5
6
98
96
95
93
93
91
306.25
300
296.88
290.62
290.62
284.38
97
95
94
94
93
90
25.26
24.73
24.48
24.48
24.22
23.44
a
Reaction condition: 0.5 mmol cyclooctene, 1.12 mmol TBHP, 10 mg
catalyst 1 and 20 mg catalyst 2, 2 mL C H Cl , 30 min for catalyst 1
2
4
2
and 180 min for catalyst 2
b
GC yields are based on the starting cyclooctene
1
3

S. S. Hosseinyzade et al.
Fig. 13 The recycling experiment of a catalyst 1 and b catalyst 2 for oxidation of cis-cyclooctene at optimum conditions
2
2
8. Sousa JLC, Santos ICMS., Simões MMQ, Cavaleiro JAS, Nogue-
ira HIS, Cavaleiro AMV (2011) Catal Commun 12:459
9. Balula SS, Santos ICMS., Cunha-Silva L, Carvalho AP, Pires J,
Freire C, Cavaleiro JAS, de Castro B, Cavaleiro AMV (2013)
Catal Today 203:95
References
1
2
3
.
.
.
Mizuno N, Kamata K (2011) Coord Chem Rev 255:2358
Pathare SP, Akamanchi KG (2013) Tetrahedron Lett 54:6455
Maksimchuk NV, Timofeeva MN, Melgunov MS, Shmakov AN,
Chesalov YA. Dybtsev DN, Fedin VP, Kholdeeva OA (2008) J
Catal 257:315
3
3
3
0. Hill CL, Prosser-McCartha CM (1995) Coor Chem Rev 143:407
1. Kozhevnikov IV (1995) Catal Rev Sci Eng 37:311
2. Proust A, Matt B, Villanneau R, Guillemot G, Gouzerh P, Izzet G
4
5
.
.
Conte V, Floris B (2010) Inorg Chim Acta 363:1935
Brocas AL, Mantzaridis CH, Tunc D, Carlotti S (2013) Prog
Polym Sci 38:845
(
2012) Chem Soc Rev 41:7605
3
3
3
3. Izzet G, Ishow E, Delaire J, Afonso C, Tabet JC, Proust A (2009)
Inorg Chem 48:11865
6
7
8
9
.
.
.
.
Simonneaux G, Le Maux P, Ferrand Y, Rault-Berthelot J (2006)
Coord Chem Rev 250:2212
4. Izarova NV, Vankova N, Heine T, Biboum RN, Keita B, Nadjo L,
Kortz U (2010) Angew Chem Int Ed 49:1886
Cancino P, Paredes-García V, Aguirre P, Spodine E (2014) Catal
Sci Technol 4:2599
5. Cao GJ, Liu JD, Zhuang TT, Cai XH, Zheng ST (2015) Chem
Commun 51:2048
Luts T, Frank R, Suprun W, Fritzsche S, Hey-Hawkins E, Papp H
3
3
3
3
6. Gouzerh P, Proust A (1998) Chem Rev 98:77
(
2007) J Mol Catal A 273:250
7. Uchida S, Mizuno N (2007) Coord Chem Rev 251:2537
8. Ren Y, Wang M, Chen X, Yue B, He H (2015) Materials 8:1545
9. Aany Sofia LT, Krishnan A, Sankar M, Kala Raj NK, Manikan-
dan P, Rajamohanan PR, Ajithkumar TG (2009) J Phys Chem C
Xia QH, Ge HQ, Ye CP, Liu ZM, Su KX (2005) Chem Rev
1
05:1603
1
1
1
0. Long DL, Burkholder E, Cronin L (2007) Chem Soc Rev 36:105
1. Nyman M (2011) Dalton Trans 40:8049
1
13:21114
2. Compain JD, Mialane P, Dolbecq A, Mbomekallé IM, Marrot J,
Sécheresse F, Rivière E, Rogez G, Wernsdorfer W (2009) Angew
Chem Int Ed 48:3077
4
0. Yamaguchi K, Yoshida C, Uchida S, Mizuno N (2005) J Am
Chem Soc 127:530
4
4
4
1. Kovalchuk T, Sfihi H, Zaitsev V, Fraissard J (2007) J Catal 249:1
2. Chen GJJ, Mcdonald JW, Newton WE (1976) Inorg Chem 15:2612
3. Channa AM, Siyal AlN, Memon SQ, Parveen S (2014) Desalin
Water Treat 52:3664
1
1
1
3. Duan CY, Wei ML, Guo D, He C, Meng QJ (2010) J Am Chem
Soc 132:3321
4. Coronado E, Giménez-Saiz C, Gómez-García CJ (2005) Coord
Chem Rev 249:1776
4
4
4. Tayyari SF, Milani nejad (2000) Spectrochim Acta A 56:2679
5. Rocchiccioli-Deltcheff C, Thouvenot R, Franck R (1976) Spec-
trochim Acta A 32:587
5. Zhao JW, Shi DY, Chen LJ, Li YZ, Ma PT, Wang JP, Niu JY
(
2012) Dalton Trans 41:10740
1
1
6. Fukaya K, Yamase T (2003) Angew Chem Int Ed 42:654
4
6. Anbarasu G, Malathy M, Karthikeyan P, Rajavel R (2017) J Solid
State Chem 253:305
7. Chen LJ, Shi DY, Zhao JW, Wang YL, Ma PT, Wang JP, Niu JY
(
2011) Cryst Growth Des 11:1913
4
4
7. Williamson GK, Hall WH (1953) Acta Metall 1:22
8. Grama L, Boda F, Gaz Florea AS, Curticăpean A, Muntean DL
1
1
8. Mitchell SG, Streb C, Miras HN, Boyd T, Long DL, Cronin L
2010) Nat Chem 2:308
(
(
2014) Acta Medica Marisiensis 60:84
9. Yin P, Wu P, Xiao Z, Li D, Bitterlich E, Zhang J, Cheng P,
Vezenov DV, Liu T, Wei Y (2011) Angew Chem Int Ed 50:2521
0. Fang XK, Anderson TM, Hill CL (2005) Angew Chem Int Ed 44:3540
1. Mizuno N, Misono M (1998) Chem Rev 98:199
2. Pope MT, Muller A (1991) Angew Chem Int Ed 30:34
3. Wang L, Feng Z, Cai H (2009) J Electroanal Chem 636:36
4. Keggin JF (1933) Nature 131:908
4
5
5
9. Farias M, Martinelli M, Rolim GK (2011) Appl Catal A 403:119
0. Zonoz FM (2016) Electrocatalysis 7:215
2
2
2
2
2
2
2
1. Cornils B, Hermann WA (1996) Applied homogeneous catalysis
with organometallic compounds, vol 2.Wiley, Weinheim, p 636
2. Mirkhani V, Moghadam M, Tangestaninejad S, Bahramian B
5
(
2008) Catal Commun 9:2171
5
5
3. Khenkin AM, Neumann R, Sorokin AB (1999) Catal Lett 63:189
4. Guo HY, Li ZF, Zhao DC, Hu YY, Xiao LN, Cui XB, Guan JQ,
Xu JQ (2014) Cryst Eng Comm 16:2251
5. Zhao S, Jia Y, Song YF (2013) Appl Catal A 453:188
6. Jahier C, Mal SS, Al-Oweini R, Kortz U, Nlate S (2013) Polyhe-
dron 57:57
5
5. Jameel U, Zhu M, Chen X (2016) J Zhejiang Univ Sci A 17:1000
2
7. Zhang Z, Zhang F, Zhu Q, Zhao W, Ma B, Ding Y (2011) J Col-
loid Interface Sci 360:189
1
3