The Effect of Substituents on Catalytic Performance of bis-Thiosemicarbazone Mo(VI) Complexes: Synthesis and Spectroscopic, Electrochemical, and Functional Properties

Article abstract of DOI:10.1134/S002315841802012X

The preparation, characterization and electrochemical properties are reported for three new types of molybdenum(VI) complexes with bis-thiosemicarbazone ligands. All compounds were characterized by elemental analysis, electronic spectra, IR and ¹

Full text of DOI:10.1134/S002315841802012X

ISSN 0023-1584, Kinetics and Catalysis, 2018, Vol. 59, No. 2, pp. 203–210. © Pleiades Publishing, Ltd., 2018.
The Effect of Substituents on Catalytic Performance
of bis-Thiosemicarbazone Mo(VI) Complexes: Synthesis
and Spectroscopic, Electrochemical, and Functional Properties1
Z. Moradi-Shoeilia, * and M. Zareb
aDepartment of Chemistry, Faculty of Sciences, University of Guilan, P.O. Box 41335-1914, Rasht, Iran
bDepartment of Basic Sciences, Golpayegan University of Technology, P.O. Box 8771765651, Golpayegan, Iran
*e-mail: zmoradi@guilan.ac.ir
Received May 26, 2017
Abstract⎯The preparation, characterization and electrochemical properties are reported for three new types
of molybdenum(VI) complexes with bis-thiosemicarbazone ligands. All compounds were characterized by
1
elemental analysis, electronic spectra, IR and H NMR spectroscopies, thermogravimetric analysis, and
cyclic voltammetry. The bis-thiosemicarbazone Mo(VI) complexes were tested as a catalyst for the homoge-
neous oxidation of olefins using tert-butyl hydrogen peroxide as an oxidant. The catalysts showed efficient
reactivity in the olefins epoxidation reactions giving high yield and selectivity of the products, in most cases.
Results showed that the bis-thiosemicarbazone ligands introduced both electronic and steric effects on cata-
lytic performance of the prepared Mo(VI) complexes.
Keywords: dioxomolybdenum(VI) complex, bis-thiosemicarbazone, olefin epoxidation
DOI: 10.1134/S002315841802012X
Synthesis and characterization of molybdenum
compounds with sulfur donor atoms has been drawing
considerable attention ever since their relevance to the
active sites of different oxotransfer enzymes was dis-
covered [14–16]. The extended X-ray absorption fine
structure (EXAFS) spectroscopic studies on active
sites of molybdoenzymes such as sulfite oxidase,
nitrate reductase, and xanthine dehydrogenase have
shown that the coordination environment of Mo in
both oxidized and reduced forms, i.e. MoV1O2 and
Thiosemicarbazone derivatives represent an
important class of Schiff base ligands with wide phar-
macological versatility [1–3]. The chemistry of
thiosemicarbazones, mixed hard-soft nitrogen-sulfur
chelating ligands, bounded to metals have also
attracted considerable interest primarily due to their
medicinal properties including antibacterial, antitu-
mour, antiviral and antifungal properties [4–7]. Some
experimental evidences supported the relationship
between chemical structures and biological activities
of α-(N)-heterocyclic thiosemicarbazones and their
metal complexes [8]. Experimental results showed that
the changes in the ligand backbone can significantly
alter the biological activity of the thiosemicarbazones
[9]. bis-Thiosemicarbazones are subgroups of
thiosemicarbazones which have exhibited very inter-
esting pharmacological properties [10, 11]. They were
also investigated as potential nuclide carriers for med-
ical imaging [12]. Due to their higher denticity, bis-
thiosemicarbazones have ability to link metal ions
more strongly than thiosemicarbazones [13]. Because
of important chemical properties and potentially bio-
MoIVO2 units, involves at least two sulfur atoms in
form of thiolate rather than thioether ligands [17].
Apart from the biological significance, higher valent
Mo complexes are also well known for their useful
application in industrial redox processes such as epox-
idation of olefins, olefin metathesis and isomerization
of allylic alcohols [18, 19].
Recently, we have described the synthesis of diox-
omolybdenum(VI) complex with the formula
[MoO2L(CH3CN)] (L = 1-(2,4-dihydroxybenzylidene)-
N-methyl-N-phenylthiosemicarbazone)
which
exhibited high catalytic activity for epoxidation of ole-
fins [20]. In this study, the synthesis, characteristics,
logical activities of both the ligands and the com- and catalytic performance of three new molybde-
num(VI) complexes with bis-thiosemicarbazone
ligands have been described. We have aimed to study
the effect of ligand substituents on the spectroscopic,
electrochemical, and functional properties of Mo(VI)
plexes, the investigation of more effective thiosemi-
carbazone metal complexes is constantly progressing.
1
The article is published in the original.
203

204
MORADI-SHOEILI, ZARE
complexes. The catalytic properties of the reported
complexes are also described for the homogeneous
epoxidation of olefins using tert-butyl hydrogen per-
oxide (TBHP) as an oxidant.
2,6-Diacetylpyridine
bis-(4-methyl-4-phenylth-
iosemicarbazone) (L1). 0.180 g (1.1 mmol) of 2,6-dia-
cetylpyridine in 10 mL methanol was added to 40 mL
methanolic solution of 0.400 g (2.2 mmol) of 4-methyl-
4-phenyl-3-thiosemicarbazide. The solution mixture
was refluxed with vigorous stirring for 8 h and left for
slow evaporation for the final separation of a solid
compound. The bright yellow precipitate was filtered.
The crude product was recrystallized from a metha-
nol-ether mixture and dried in air. M.p.: 232°C, yield
0.296 g, 55%. For C25H27N7S2, %: calculated: C 61.32,
H 5.56, N 20.02; found: C 61.95, H5.67, N 20.39.
EXPERIMENTAL
Materials
Commercial reagents hydrazine hydrate (Merck) and
2,6-diacetylpyridine (Aldrich), N-methyl aniline
(Merck), carbone disulfide (Merck) were used as
received.
4-Methyl-4-phenyl-3-thiosemicarbazide
[21], 4-phenyl-3-thiocabazide and p-chlorophenylth-
iosemicarbazide [22] were prepared according to litera-
ture procedures. The starting complex, bis-(acetylace-
tato) dioxomolybdenum(VI) [MoO2(acac)2] was pre-
pared as described in the report [23].
Similar procedures were applicable to the prepara-
tions of L2 and L3.
2,6-Diacetylpyridine bis-(4-phenylthiosemicarba-
zone) (L2). M.p: 222°C, yield 0.330 g, 65%. For
C23H23N7S2, %: calculated – C 59.84, H 5.02, N
21.24; found – C 59.34, H 4.45, N 20.66.
Instrumentation and Physical Measurements
2,6-Diacetylpyridine bis-(4-parachlorophenylth-
iosemicarbazone) (L3). M.p: 215°C, yield 0.397 g, 68%.
For C23H21N7S2Cl2, %: calculated – C 52.07, H 3.99,
N 18.48; found – C 52.82, H 4.34, N 18.26.
Elemental analysis (C, H, N) data were performed
on a Perkin Elmer 2400 CHNS/O elemental ana-
lyzer. IR measurements of the solids were carried
out on a Unicam Matson 1000 FT-IR spectropho-
tometer (400–4000 cm–1). NMR spectra were
obtained on a Bruker 500-DRX Avance Spectrome-
ter in DMSO-d6.UV-vis spectra were recorded by
CARY 100 Bio VARIAN UV-vis spectrophotometer
using quartz cells having a 1.0 cm path in length. Melt-
ing points of the products were monitored on a
BUCHI Melting Point Modle B-540. Thermogravi-
metric (TG) analyses were measured on a NETZSCH
TG 209 F1 Iris thermobalance using aluminum cruci-
bles under nitrogen atmosphere with a heating rate of
10°C/min. For all experiments, the temperature
ranged from 20 to 900°C. The cyclic voltammetric
measurements were made on a Autolab/PGSTAT101
electrochemical analyzer utilizing the three-electrode
configuration of a Ag/AgCl as reference electrode, a Pt
auxiliary electrode, and Pt working electrode. NOVA
software was employed to carry out the experiments
and to acquire the data. The working electrode was
polished fresh before each experiment with alumina
and sonicated in deionised water. The tests were per-
formed in the potential region –0.8 to +1 V at ambient
temperature at a scan rate of 20 mV/s. Recrystallized
tetra(n-butyl)ammonium perchlorate (TBAP) (0.01
mol/dm3) was used as supporting electrolyte and
DMF as solvent.
Preparation of the Complexes
Complexes [MoO2L1] (1), [MoO2L2] (2) and
[MoO2L3] (3) were prepared in a similar way by refluxing
methanolic solutions of MoO2(acac)2 (0.6 mmol, 0.200 g)
with H2L1 (0.6 mmol, 0.294 g), H2L2 (0.6 mmol, 0.277 g)
and H2L3 (0.6 mmol, 0.318 g), respectively. Initially on
mixing, the solutions turn to brown color and after
refluxing for 4 h, the dark brown complexes separated.
The mother liquors were cooled and left for slow evap-
oration for the final separation of solid compounds.
The solids were washed with methanol and diethyl
ether and dried under vacuum. Our attempts to get
single crystals suitable for X-ray diffraction studies
were not successful. Scheme 1 illustrates the syntheses
of complexes.
[MoO2L1] ⋅ H2O (1): yield 0.220 g, 55%. For
C25H27N7S2MoO3, %: calculated: C 47.39, H 4.29, N
15.47; found: C 47.18, H 3.96, N 16.50.
[MoO2L2] ⋅ H2O (2): yield 0.100 g, 55%. For
C23H23N7S2MoO3, %: calculated: C 45.62, H 3.83, N
16.19; found: C 45.22, H 3.67, N 16.34.
Preparation of the Ligands
[MoO2L3] (3): yield 0.150 g, 55%. For C23H19N7S2-
Cl2MoO2, %: calculated: C 42.08, H 2.92, N 14.94;
found: C 42.62, H 2.66, N 14.86.
All Schiff base ligands L1, L2 and L3 were synthe-
sized in a similar way by the condensation reactions of
2,6-diacetylpyridine with corresponding thiosemicar-
bazide in a 1 : 2 ratio. A typical preparation of the
ligands is described as follow.
Schematic representation of bis-thiosemicarba-
zone ligands and complexes 1–3
KINETICS AND CATALYSIS
Vol. 59
No. 2
2018

THE EFFECT OF SUBSTITUENTS
205
(e)
S
S
O
O
X
N
N
X
N
Y
N
H
N
N
H
N
Y
Mo
CH3
CH3
(c)
S
S
MoO2(acac)2
(a)
N
N
(d)
H2L1: X = CH3
H2L2: X = H(b)
H2L3: X = H(b)
Y = H
Y = H
Y = Cl
Scheme 1.
strong band due to ν(C=N) appears at 1600 cm–1 in
the free ligands, and this band undergoes a bathochro-
mic shift by 4–10 cm–1 in the complexes, thereby indi-
cating the participation of azomethine nitrogens in
coordination. Characteristic strong bands in the spec-
tra of H2L2 and H2L3 observed in the region 3420–
Catalytic Reactions
1 mmol of TBHP (oxidant) was added to a solution
of alkene (1 mmol), [MoO2L1] (0.001 mmol) and
chlorobenzene (1 mmol), as internal standard in
appropriate solvent (1 mL). The system was stirred for
1–5 h at 75°C. The progress of the reaction was mon-
itored by GC. All the reactions were performed at least
two times and the products were compared with stan-
dard samples.
3340 cm–1 attributed to modes of the NH group which
remain at nearly the same position in the spectra of the
corresponding complexes, suggesting the non-involve-
ment of this amino group in bonding [26]. The ν(N–N)
of the thiosemicarbazone is found at ∼1119 cm–1. The
increase in the frequency of this band in the spectra of
the complexes, due to an increase in the bond
strength, again confirms coordination via the azome-
thine nitrogen [27]. The decrease in the stretching fre-
quency of the ν(C=S) band from ~816 cm–1 in the
thiosemicarbazones by 60–75 cm–1 upon complexation
indicates coordination via the thiolato sulfur, a commonly
observed feature of such ligands [28]. IR spectra of com-
RESULTS AND DISCUSSION
Synthesis of bis-Thiosemicarbazone Mo(VI) Complexes
The dioxomolybdenum(VI) complexes were syn-
thesized by the reaction of bis-(acetylacetonato)diox-
omolybdenum(VI) with a stoichiometric amount of
bis-thiosemicarbazone ligands derived from 2,6-dia-
cetylpyridine and corresponding N4-substituted
thiosemicarbazide, in methanol solution. These dark
brown complexes were found to be sparingly soluble in plexes 1–3 show sharp bands at ~1540 cm–1 due to
alcohol, CHCl3, and CH2Cl2, but fairly soluble in the newly formed ν(N=C) bond, indicating the coor-
dination of sulfur in the enolate form rather than in the
keto form [29, 30]. All monomeric neutral complexes
1–3 exhibit two bands at ~903–910 and 935–951 cm–1
assigned to symmetric and antisymmetric vibrations of
the cis-dioxomolybdenum(VI) moiety, respectively
[31]. IR spectra of compounds [MoO2L1] and
DMF and DMSO. In the investigated monomeric
[MoO2L] complexes, each of the Schiff base ligands
behaves in a dianionic tetradentate manner, bonded to
the cis-MoO22+ ion through the sulfur and azomethine
nitrogen atoms. The formulations are in accordance
with the data of elemental analysis and physicochem-
ical measurements.
[MoO2L2] show broad bands around 3430 cm–1 which
indicate the presence of lattice water.
FT-IR Spectra
NMR Spectra
Table 1 lists the tentative assignments of the main
IR bands of the dioxomolybdenum(VI) complexes for
the ligands H2L1, H2L2 and H2L3 in 4000–400 cm–1
region. The free ligands show medium-intensity bands
at 3230 cm–1 assigned to NH vibrations of the func-
tional group, which disappear in the corresponding
complexes, indicating possible deprotonation of the
functional group upon complexation [24, 25]. This
evidence is further confirmed by NMR spectra. A
1H NMR spectra of H2L1, H2L2 and H2L3 and their
molybdenum complexes were recorded in DMSO-d6
solvent and data with their assignments are listed in
1
Table 2. The H NMR spectra of all ligands exhibit
similar signals (δ, ppm) at (10.96, 2.42), (10.86, 2.64)
and (10.80, 2.54) which can be assigned to 2(NHa) and
c
2(CH3 ) protons, respectively. The signals correspond-
KINETICS AND CATALYSIS Vol. 59 No. 2 2018

206
MORADI-SHOEILI, ZARE
Table 1. Wavenumbers (cm–1) of the characteristic IR bands of the ligands and corresponding dioxomolybdenum(VI)
complexes
ν(Mo=O)
Compound
ν(N–H)
ν(C=N)
ν(N=C)
ν(N–N)
ν(C=S)
(sym)
–
(asym)
–
H2L1
[MoO2L1]
H2L2
[MoO2L2]
H2L3
[MoO2L3]
3222
–
1592
1596
1602
1598
–
1544
–
1113
1155
1129
1161
1116
1158
819
758
816
752
816
749
951
–
910
–
3232, 3422
3418
1551
–
951
–
903
–
3235, 3457
3396
1592
1515
935
910
Table 2. 1H NMR spectra of H2L1, H2L2 and H2L3 ligands and their molybdenum complexes recorded in DMSO-d6 as
solvent
δ, ppm
δ, ppm
Assignment
H2L1
H2L2
H2L3
[MoO2L1]
[MoO2L2]
[MoO2L3]
Ha (s, 2NH)
Hb (s, 2NH)
Hc (s, 2CH3)
Hd (s, 2CH3)
He (d, 2CH)
Hf (t, 2CH)
10.96
–
10.86
10.45
2.64
–
10.80
10.24
2.54
–
–
–
–
–
9.85
3.17
–
10.25
3.18
–
2.42
3.58
8.37
7.93
3.17
3.39
8.03
7.71
8.31
7.89
8.57
7.86
8.17
7.85
8.35
7.89
d
ing to NHb in H2L2 and H2L3 and also the signal of CH3
Electronic Spectra
in H2L1 are observed at 10.51, 10.24 and 3.58 ppm,
respectively. These observations prove the thione form
of the ligand in solution. Peaks of the aromatic protons of
the phenyl groups were found in the region 7–7.6 ppm. A
triplet signal at 7.93, 7.89, and 7.86 ppm and a doublet
at 8.37, 8.31, and 8.56 ppm for H2L1, H2L2 and H2L3,
respectively, correspond to the protons of the pyridine
moiety. In NMR spectra of the complexes, the signals
due pyridine moiety and NHb (in complexes
[MoO2L1] and [MoO2L2]) appeared mostly at the
same position as in the free ligands, indicating the
non-involvement of pyridine nitrogen and NHb in
coordination. The coordination of the C–S groups in
complexes is supported by absence of NHa proton sig-
nals in the spectra of the three complexes that is in
accordance with the formulation of thioenolization
and subsequent the replacement of the protons by
Electronic absorption bands of the ligands and
complexes were studied in a DMF solution. The com-
pounds are found to display similar absorption max-
ima in the range 200–350 nm which assigned to intra-
ligand transitions (Fig. 1). The complexes 1–3 exhibit
one low-energy electronic absorption band in the
region 400–500 nm which may be assigned to a
charge-transfer transition from pπ-orbital of sulfur
(HOMO) to the dπ-orbital of molybdenum (LUMO)
[20, 33]. The absence of a d–d-transition absorption
band in the visible region confirms the 4d0 electronic
configuration of Mo(VI). Complexes 1–3 show simi-
lar electronic spectra, suggesting that they have essen-
tially similar structure.
Electrochemical Studies
Cyclic voltammograms of the ligands (H2L1, H2L2
and H2L3) and their dioxomolybdenum(VI) com-
plexes 1–3 were recorded at a platinum electrode
using DMF as solvent and tetrabutylammonium per-
chlorate (TBAP) as supporting electrolyte at a scan
rate of 20 mV/s in the potential range +1 to –0.7 V vs.
Ag/AgCl reference. Ligands, L1, L2 and L3 exhibited
c
metal [32]. Signals due to CH3 protons show a
remarkable shift in complexes 1–3, suggesting the
involvement of the azomethine nitrogen in coordina-
tion to metal ions.
KINETICS AND CATALYSIS
Vol. 59
No. 2
2018

THE EFFECT OF SUBSTITUENTS
207
one irreversible oxidative peak around 0.3 V. Com-
Abs, a. u.
2.5
plexes 1–3 exhibited irreversible single-electron
reduction waves in their cyclic voltammograms attrib-
utable to a reduction at the molybdenum centers
(Fig. 2). Previously, it has been shown that the substit-
uent on the ligand has a significant effect on the
cathodic reduction potential [34, 35]. The effect of
these groups, although not intimately linked to the
molybdenum, is to alter the electron density on the
metal center. The more negative is the cathodic reduc-
tion potential, the more difficult is the molybdenum
complex reduction [36]. The electron donating group,
CH3 on azomethine carbon in L1 is probably the lead-
ing contributor to increasing electron density at the
Mo(VI) center in [MoO2L1]. In this case, the cathodic
reduction potential is the most negative of the series.
Again, since the Cl substitution at position 5 of the
phenyl ring in L3 is electron withdrawing, it is expected
that the electron density is shifted away from Mo(VI)
center, the complex [MoO2L3] becomes easily reduc-
ible and the cathodic peak potential (Epc) shifts
H2L3
H2L2
2.0
1.5
1.0
[MoO2L3]
[MoO2L1]
[MoO2L2]
H2L1
0.5
0
300
400
500
600
700
Wavelength, nm
1
2
3
Fig. 1. UV-vis spectroscopy of H L , H L and H L
ligands and their molybdenum complexes 1–3.
2
2
2
towards the anodic direction, compared to [MoO2L2].
This type of behavior was also noted earlier for other
dioxomolybdenum(VI) complexes [35].
Thermal Properties
(1)
(2)
(3)
The thermogravimetric analysis of the complexes
was carried out in the temperature range 20–900°C at
a heating rate of 10°C/min (Fig. 3). Complexes
[MoO2L1] and [MoO2L2] showed weight losses in the
temperature range 80–110°C that could be due to the
removal of lattice water molecule. In complex 3, there
was no weight loss in the region below 200°C which
showed the absence of water molecule. With further
elevation in temperature, the TG curves showed two
steps of weight losses. The first step of decomposition
observed in the range from 200 to 400°C may be
ascribed to the dissociation of the Schiff base ligand at
the C=N bond. The last stage at 630–720°C can be
ascribed to the complete removal of the fragment parts
of the ligand. Decomposition continued until the final
residue MoO3 was left [37].
–1.2
–0.8
–0.4
0
Potential, V, vs. Ag/AgCl
1
Fig. 2. Cyclic voltammogram of complexes [MoO L ] (1),
2
2
3
[MoO L ] (2), and [MoO L ] (3) in DMF (0.01 M TBAP
2
2
as supporting electrolyte, scan rate: 20 mV/s).
TG, %
100
90
80
70
Epoxidation of Olefins
The catalytic performance of [MoO2L1] ⋅ H2O was
first studied in the oxidation of cyclooctene, used as a
model substrate, with TBHP as the oxygen donor and
the results are shown in Table 3. The effect of various
reaction media on the oxidation of cycloctene has
been studied. It is apparent that the efficiency of the
catalyst in different solvents decreases in the order:
dichloroethane>dichloromethane > acetonitrile >
methanol > DMF. Apparently, highly coordinating
solvents such as CH3OH and DMF cause a significant
decrease in the catalytic activity, since they compete
with TBHP to bind to the molybdenum center [38].
60
3
2
1
50
40
30
10
210
410
610
810
Temperature, °C
Fig. 3. Thermogravimetric analysis of the complexes 1–3.
KINETICS AND CATALYSIS Vol. 59 No. 2 2018

208
MORADI-SHOEILI, ZARE
Table 3. Conversion of cyclooctene using [MoO2L1] as catalyst for 1 h of reaction time under different reaction conditions
Entry
Catalyst, mmol
Temperature, °C
Solvent
CH3CN
Conversion, %
Selectivity, %
1
2
0.005
0.005
0.005
0.005
0.005
0.001
0.0005
0.01
75
75
51
72
38
31
82
85
66
75
73
62
46
19
93
95
99
98
99
99
99
99
99
99
99
99
CH2Cl2
CH3OH
DMF
3
75
4
5
75
75
C2H4Cl2
C2H4Cl2
C2H4Cl2
C2H4Cl2
C2H4Cl2
C2H4Cl2
C2H4Cl2
C2H4Cl2
6
75
7
75
8
75
9
0.005
0.005
0.005
0.005
65
10
11
12
55
40
room
The effect of the catalyst amount on the conversion version showed a small reduction from 82 to 75%
(Table 3, entries 5 and 8). Effect of reaction tempera-
ture on cyclooctene oxidation was investigated. It was
inferred that 75°C was the best suited temperature for
the maximum oxidation of cyclooctene under the
above reaction conditions. Thus, optimized operating
reaction conditions for maximum oxidation of
cyclooctene were: cycloctene (1 mmol), [MoO2L1]
(0.001 mmol), TBHP (1 mmol), dichlroetane (1 mL),
and reaction temperature (75°C).
In order to verify the catalytic scope of the
[MoO2L1] catalyst, it has also been applied for epoxi-
dation of a wide variety of alkenes (Table 4). Good
results are found for cyclic alkenes such as cyclohexene
and cyclooctene, whereas terminal linear alkenes give
slightly lower yields. In the epoxidation reaction of
cyclohexene, no allylic oxidation products were
detected, thus catalytic reaction occurs via nonradical
processes [39]. In case of styrene oxidation the highest
selectivity has been achieved for benzaldehyde, and this is
possibly due to the nucleophilic attack of the oxidant to
styrene oxide following by decomposition of the peroxy-
styrene intermediate [40].
and selectivity is illustrated in Table 3. Four different
amounts of catalyst viz. 0.01, 0.005, 0.001, and
0.0005 mmol were considered while keeping a fixed
amount of cyclooctene (1 mmol) and TBHP
(1 mmol). The results show that the decrease in the
catalyst amount from 0.005 to 0.001 mmol did not
have a significant effect on the percent of conversion
under reaction conditions of this study (Table 3,
entries 5 and 6). However, further decrease in the cat-
alyst amount to 0.0005 mmol caused the conversion of
cyclooctene to reach 66%. With a further increase in
the catalyst amount from 0.005 to 0.01 mmol, the con-
Table 4. Catalytic oxidation of various alkenes with TBHP
by [MoO2L1] complex*
Selectivity
to epoxide, Time, h
%
Conversion,
Substrate
%**
85
99
1
The catalytic activities of the prepared catalysts
were studied through the oxidation of olefins with
TBHP in 1,2-dicholoroethane. As the results in Fig. 4
show, the catalytic performance of the complexes
decreased in the following order: MoO2L2 > MoO2L3 >
86
71
>99
38
5
4
MoO2L1.
Based on Kühnet al. report [41], olefins are oxi-
dized by TBHP in a catalytic cycle involving the nuc-
leophilic attack of the olefin to the coordinated oxygen
(*) in the heptacoordinated intermediate containing
coordinated peroxide and a protonated oxo ligand.
The epoxide product is obtained by transfer of the oxy-
gen atom of the –OOC(CH3)3 ligand to the olefin
23
26
>99
>99
4
4
* Reaction condition. The molar ratio for catalyst: alkene:
TBHP was 1 : 1000 : 1000. The reactions were run at 75°C in 1 mL
of 1,2-dichlroethane.
** GC conversion based on starting alkene.
KINETICS AND CATALYSIS
Vol. 59
No. 2
2018

THE EFFECT OF SUBSTITUENTS
Conversion, %
209
100
80
60
40
20
MoO2L1
MoO2L2
MoO2L3
0
10
20
30
40
50
60
Time, min
Fig. 4. Epoxidation of cyclooctene with TBHP using various catalysts (75°C for 60 min in 1 mL of 1,2-dichlroethane).
C=C double bond. Herein, the metal center acts as a expected the efficiency of the catalysts to decrease in
the order: [MoO2L3] > [MoO2L2] > [MoO2L1], while
in fact the order observed for epoxidation of cyclooc-
tene is: [MoO2L2] > [MoO2L3] > [MoO2L1]. This
observation can be due to both electronic and steric
effects of ligand substituents.
Lewis acid by removing charge from the O–O bond,
facilitating its dissociation, and activating the nearest
oxygen atom (*) for insertion into the olefin double
bond. At the final stage, the release of a tert-butanol
molecule from metal center leads to the formation of
complex (Scheme 2). As the presence of the electron-
withdrawing substituents on ligand induces more pos-
itive charge on the coordinated oxygen (*), we
Proposed mechanism for oxidation of alkene with
[MoO2L1] complex in the presence of TBHP
S
N
TBHP
O
O
Mo
N
CH3
S
H3C
S
CH3
C
O
(CH3)3COH
+
O
N
O
*
O
H
Mo
N
O
CH3
H3C
S
S
CH3
C
O
*
N
O
O
H
Mo
O
N
S
Scheme 2.
CONCLUSIONS
a tetradentate N2S2 donor set to the central metal atom
have been described. All compounds were character-
In this study, three new types of molybdenum(VI)
complexes with thiosemicarbazone ligands containing ized by physicochemical and spectroscopic techniques
KINETICS AND CATALYSIS Vol. 59 No. 2 2018

210
MORADI-SHOEILI, ZARE
14. Hine, F.J., Taylor, A.J., and Garner, C.D., Coord.
Chem. Rev., 2010, vol. 254, p. 1570.
including elemental analysis, electronic spectra, IR
and 1H NMR spectroscopies, thermogravimetric
analysis, and cyclic voltammetry. The thiosemicarba-
zone Mo(VI) complexes were also tested as catalysts
for the homogeneous oxidation of olefins. The cata-
lysts showed efficient reactivity in the olefins epoxida-
tion reactions with good yield and selectivity. In addi-
tion, results confirm that the variation of substituents
on the ligand structures can influence the spectro-
scopic, electrochemical, and functional properties of
the Mo(VI) complexes and the catalytic reaction rates
can be controlled by both electronic and steric factors.
15. Holm, R.H., Solomon, E.I., Majumdar, A., and Ten-
derholt, A., Coord. Chem. Rev., 2011, vol. 255, p. 993.
16. Majumdar, A. and Sarkar, S., Coord. Chem. Rev., 2011,
vol. 255, p. 1039.
17. Dobbek, H., Coord. Chem., 2011, vol. 255, no. 9,
p. 1104.
18. Keith, J.M., Tomić, Z.D., Zarić, S.D., and Hall, M.B.,
J. Mol. Catal. A: Chem., 2010, vol. 324, p. 15.
19. Mitchell, J.M. and Finney, N.S., J. Am. Chem. Soc.,
2001, vol. 123, p. 862.
20. Moradi-Shoeili, Z., Boghaei, D.M., Amini, M., Bagh-
erzadeh, M., and Notash, B., Inorg. Chem. Commun.,
2013, vol. 27, p. 26.
ACKNOWLEDGMENTS
21. Sreekanth, A., Fun, H.K., and Kurup, M.P., J. Mol.
The authors are grateful to the University of Guilan
and the Golpayegan University of Technology for
financial support.
Struct., 2005, vol. 737, p. 61.
22. Richardson, D.R., Sharpe, P.C., Lovejoy, D.B., Sen-
aratne, D., Kalinowski, D.S., Islam, M., and Bern-
hardt, P.V., J. Med. Chem., 2006, vol. 49, p. 6510.
23. Chen, G.J., McDonald, J.W., and Newton, W.E.,
REFERENCES
Inorg. Chem., 1976, vol. 15, p. 2612.
24. Ngan, N.K., Wong, Ch.S., Lo, and K.M., J. Chem.
1. Brodowska, K., Correia, I., Garribba, E., Marques, F.,
Klewicka, E., Lodyga-Chruscinska, E., Pessoa, J.C.,
Dzeikala, A., and Chruscinski, L., J. Inorg. Biochem.,
2016, vol. 165, p. 36.
2. Pape, V.F., Toth, S., Furedi, A., Szebenyi, K., Lovrics, A.,
Szabo, P., Wiese, M., and Szakacs, G., Eur. J. Med.
Chem., 2016, vol. 117, p. 335.
3. Thanh, N.D., Giang, N.T.K., Quyen, T.H., Huong, D.T.,
and Toan, V.N., Eur. J. Med. Chem., 2016, vol. 123,
p. 532.
4. Banerjee, S., Mondal, S., Chakraborty, W., Sen, S.,
Gachhui, R., Butcher, R.J., Slawin, A.M., and Man-
dal, C., and Mitra. S., Polyhedron, 2009, vol. 28,
p. 2785.
5. Fountoulaki, S., Perdih, F., Turel, I., Kessissoglou, D.P.,
and Psomas, G., J. Inorg. Biochem., 2011, vol. 105,
p. 1645.
6. Chellan, P., Stringer, T., Shokar, A., Dornbush, P.J.,
Vazquez-Anaya, G., Land, K.M., Chibale, K., and
Smith, G.S., J. Inorg. Biochem., 2011, vol. 105, no. 12,
p. 1562.
Crystallogr., 2011, vol. 41, p. 1700.
25. Vrdoljak, V., Pisk, J., Prugovečki, B., and Matković-
Čalogovic, D., Inorg. Chim. Acta, 2009, vol. 362,
p. 4059.
26. Garg, R., Fahmi, N., and Singh, R.V., Russ. J. Coord.
Chem., 2008, vol. 34, p. 198.
27. Seena, E.B. and Kurup, M.P., Polyhedron, 2007,
vol. 26, p. 3595.
28. Eierhoff, D., Tung, W.C., Hammerschmidt, A., and
Krebs, B., Inorg. Chim. Acta, 2009, vol. 362, p. 915.
29. Seena, E.B. and Kurup, M.R.P., Polyhedron, 2007,
vol. 26, p. 3595.
30. Vrdoljak, V., Ðilović, I., Cindrić, M., Matković-
Čalogović, D., Strukan, N., Gojmerac-Ivšić, A., and
Novak, P., Polyhedron, 2009, vol. 28, p. 959.
31. Basu, P., Nemykin, V.N., and Sengar, R.S., Inorg.
Chem., 2009, vol. 48, p. 6303.
32. Cindrić, M., Vrdoljak, V., Strukan, N., and Kamenar,
B., Polyhedron, 2005, vol. 24, p. 369.
33. Kim, H.J. and Koo, B.K., Bull. Korean Chem. Soc.,
7. Karaküçük-İyidoğan, A., Taşdemir, D., Oruç-Emre, E.E.,
1994, vol. 15, p. 766.
Balzarini, J., Eur. J. Med. Chem., 2011, vol. 46, p. 5616.
34. Bhattacharjee, S. and Bhattacharyya, R., J. Chem. Soc.,
8. Hussein, M.A., Iqbal, M.A., Asif, M., Haque, R.A.,
Ahamed, M.B.K., Majid, A.M.A., and Guan, T.S.,
Phosphorus, Sulfur Silicon Relat. Elem., 2015, vol. 190,
p. 1498.
Dalton Trans., 1993, p. 1151.
35. Topich, J. and Lyon, J.T., Inorg. Chem., 1984, vol. 23,
p. 3202.
36. Topich, J., Inorg. Chem., 1981, vol. 20, p. 3704.
9. Kowol, C.R., Reisner, E., Chiorescu, I., Arion, V.B.,
Galanski, M., Deubel, D.V., and Keppler, B.K., Inorg. 37. Lal, R.A., Choudhury, S., Ahmed, A., Borthakur, R.,
Asthana, M., and Kumar, A., Spectrochim. Acta, Part A,
Chem., 2008, vol. 47, p. 11032.
2010, vol. 75, p. 212.
10. Paterson, B.M., Donnelly, P.S., Chem. Soc. Rev., 2011,
vol. 40, p. 3005.
38. Bagherzadeh, M., Tahsini, L., Latifi, R., and Woo, L.K.,
Inorg. Chim. Acta, 2009, vol. 362, p. 3698.
11. Palanimuthu, D., Shinde, S.V., Somasundaram, K.,
and Samuelson, A.G., J. Med. Chem., 2013, vol. 56, 39. Mimoun, H., Catal. Today, 1987, vol. 1, p. 281.
p. 722.
40. Koola, J.D. and Kochi, J.K., J. Org. Chem., 1987,
12. Dilworth, J.R. and Hueting, R., Inorg. Chim. Acta,
vol. 52, p. 4545.
2012, vol. 389, p. 3.
41. Kühn, F.E., Groarke, M., Bencze, É., Herdtweck, E.,
Prazeres, A., Santos, A.M., Calhorda, M.J., Romão, C.C.,
Gonçalves, I.S., Lopes, A.D., and Pillinger, M., Chem.
Eur. J., 2002, vol. 8, p. 2370.
13. Bisceglie, F., Alinovi, R., Pinelli, S., Galetti, M., Pioli,
M., Tarasconi, P., Mutti, A., Goldoni, M., Pelosi, G.,
Metallomics, 2016, vol. 8, p. 1255.
KINETICS AND CATALYSIS
Vol. 59
No. 2
2018