Catalytic oxidation of olefins and sulfides in the presence of hydrazone-oxidovanadium(V) complex containing VOCl2+core

Article abstract of DOI:10.1016/j.ica.2016.07.058

A new oxidovanadium(V) complex, [VO(L)Cl₂] (1), is synthesized by the reaction of VOCl₃with (E)-N′-(phenyl(pyridin-2-yl)methylene)isonicotinhydrazide (HL) in chloroform as a solvent. The complex is characterized by elemental analysis, spectroscopic methods (FT-IR, UV–vis), and its structure is determined by single crystal X-ray diffraction analysis. X-ray studies reveal a mononuclear complex of V(V) with the hydrazone ligand coordinated to the V(V) center as a tridentate mononegative ligand. This complex is used as a catalyst precursor for oxidation of olefins and sulfides in the presence of hydrogenperoxide (H₂O₂) as a green oxidant. The effect of various parameters is studied including the amount of the catalyst, temperature and solvent. The results show the system corresponds to an active and selective catalyst for oxidation of cyclooctene and thioanisole.

Full text of DOI:10.1016/j.ica.2016.07.058

Accepted Manuscript
Research paper
Catalytic oxidation of olefins and sulfides in the presence of hydrazone-oxido-
vanadium(V) complex containing VOCl2 + core
Rahman Bikas, Massomeh Ghorbanloo, Solmaz Jafari, Vaclav Eigner, Michal
Dusek
PII:
S0020-1693(16)30439-X
http://dx.doi.org/10.1016/j.ica.2016.07.058
ICA 17193
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
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Accepted Date:
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28 June 2016
29 July 2016
Please cite this article as: R. Bikas, M. Ghorbanloo, S. Jafari, V. Eigner, M. Dusek, Catalytic oxidation of olefins
+
and sulfides in the presence of hydrazone-oxidovanadium(V) complex containing VOCl2 core, Inorganica Chimica
Acta (2016), doi: http://dx.doi.org/10.1016/j.ica.2016.07.058
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Catalytic oxidation of olefins and sulfides in the presence of hydrazone-oxidovanadium(V)
+
complex containing VOCl2 core
Rahman Bikas,a, Massomeh Ghorbanloo,a,** Solmaz Jafari,a Vaclav Eigner,b Michal
*
Dusek,b
a Department of Chemistry, Faculty of Science, University of Zanjan 45195-313, Zanjan, Iran
b
Institute of Physics of the Czech Academy of Sciences, Na Slovance 2,182 21 Prague, Czech
Republic
Abstract
A new oxidovanadium(V) complex, [VO(L)Cl2] (1), is synthesized by the reaction of VOCl3
with (E)-N'-(phenyl(pyridin-2-yl)methylene)isonicotinhydrazide (HL) in chloroform as a solvent.
The complex is characterized by elemental analysis, spectroscopic methods (FT-IR, UV-Vis),
and its structure is determined by single crystal X-ray diffraction analysis. X-ray studies reveal a
mononuclear complex of V(V) with the hydrazone ligand coordinated to the V(V) center as a
tridentate mononegative ligand. This complex is used as a catalyst precursor for oxidation of
olefins and sulfides in the presence of hydrogenperoxide (H2O2) as a green oxidant. The effect of
various parameters is studied including the amount of the catalyst, temperature and solvent. The
results show the system corresponds to an active and selective catalyst for oxidation of
cyclooctene and thioanisole.
+
Keywords: Oxidovanadium(V), Catalytic oxidation, Hydrazone ligand, Crystal structure, VOCl2
*
Corresponding author. Tel.: +98 243 3052583; Fax: +98 243 2283203. E-mail addresses:
bikas_r@yahoo.com (R. Bikas).
** Email: m_ghorbanloo@yahoo.com (M. Ghorbanloo)
1

Introduction
The coordination chemistry of vanadium is of interest for number of biological and
therapeutic reasons. Vanadium complexes have many attractive features that constitute the basis
for their utility as insulin-mimetic drugs stimulating the glucose uptake [1], potential anti-tumor
agents exerting preventive effects against carcinogenesis [2], or promising agents against some
of parasitic diseases [3]. Moreover, vanadium complexes in high-oxidation states have a high
relevance in oxidation catalysis [4]. Hydrazone ligands have a tendency to stabilize the vanadium
in its highest oxidation state [5]. Vanadium complexes with hydrazone ligands are good
candidates for catalytic oxidation studies because of their stability in oxidizing conditions. They
have been widely used as homogeneous or heterogeneous catalysts in oxidation processes in the
presence of a suitable oxidant, e.g., alkyl hydroperoxides, H2O2 or O2, under mild conditions [6].
The use of high valent vanadium complexes in oxidation catalysis is encouraged by the easily
interconvertible vanadium oxidation states (where +4 and +5 are the most stable ones under
aerobic conditions), various possible coordination numbers, high affinity of vanadium toward
oxygen and Lewis acid character of the vanadium centers [7]. In most cases, the active site
contains either of the two motifs, VO3+ or VO2+, coordinated by oxygen/nitrogen atoms provided
by the ligands or solvents. In most vanadium complexes prepared in alcoholic solvents (like
methanol or ethanol), the solvent is usually coordinated to the vanadium core as a neutral or
mononegative alkoxide ligand [8]. In addition, in some cases the oxidovanadium core changes to
dioxidovanadium [9]. Due to the high affinity of vanadium towards oxygen, the vanadium
complexes containing “VOCl2” are not frequently isolated, nevertheless some of them are
reported in the scientific literature: (CH3C5H5O)2VOCl2 [10], bpa(VOCl2), (where bpa = bis(2-
methypyridyl)amine) [11], [VOCl2(dpi)(THF)] (dpi = di-2-pyridylimine), [VOCl2(adpe)] (adpe =
2

aminodi-2-pyridyl-methyl ethyl ether), [VOCl2(adpm-/NH2)] and [VOCl2(adpm-/OMe)]•/MeOH
(adpm = amino-di-2-pyridyl-methyl methyl ether) [12].
Although the crystal structures of more than 300 oxidovanadium complexes with tridentate
hydrazone ligands have been reported until now, searching the literature and Cambridge
Structural Database (CSD) [13] indicates that surprisingly there is no report onvanadium
complexes of hydrazone ligand containing V−X (X = Halogen) group. In all of the reported
hydrazone-vanadium complexes available in CSD, the coordination environment around the
vanadium ion contains five or six atoms. Most of hydrazone ligands act as tridentate ligands [14]
and due to the presence of the V=O moiety, four equatorial coordination sites around the
vanadium are available for these ligands. Thus, by considering octahedral geometry around the
vanadyl ion, two vacant coordination sites are available (Scheme 1). In crystal structures of
previously reported hydrazone-vanadium complexes these two coordination sites are occupied by
N or O donors, and no other atom coordinated to these positions has been reported so far.
Selective oxidation of sulfides to sulfoxides is very important since sulfoxides are useful
building blocks as chiral auxiliaries in organic synthesis [15]. Sulfoxides possess a wide range of
biological activities, e.g. antimicrobial properties [16], ability to inhibit the biosynthesis of the
uric acid and gastric acid secretion [17] or to regulate the cholesterol catabolism [18]. Vanadium
complexes are efficient catalyst precursors for oxidation of sulfides to sulfoxides [19].
Additionally, vanadium complexes are useful compounds in oxidation of olefins [20]. Epoxides
are the key starting materials for a wide variety of products, and the epoxidation of alkenes is one
of the most widely studied reactions in organic chemistry. The importance of epoxides arises
mainly from their ring opening reactions. Some review articles that focus on the vanadium
3

catalysts (also in the form of complexes with Schiff base ligands) in epoxidation of olefinic
compounds have been published recently [6a,21].
To continue our studies on the coordination complexes of hydrazone ligands and their
applications in oxidation reactions [22], we aimed to prepare a vanadium-hydrazone complex
containing V−X moiety. Comparing with V−O and V−N bonds, the V−Cl bond can be easily
broken by attacking with the oxygen atom of oxidants like H2O2 or tBut-COOH. A variety of
oxo- and/or peroxovanadium complexes, containing V−Cl bond, such as [LV(O)X] [X = Cl; R =
H, L = Me2NCH2CH(R)N(CH2-2-O-3,5-C6H2tBu2)2] [23], Bis[µ-chloro-chloro(ƞ2-2-iso-
propoxyethanolato)-oxovanadium(V)],
propanolato)-oxovanadium(V)]
Bis[µ-chloro-chloro(ƞ2
-1-methoxy-2-methyl-2-
and
Bis[µ-chloro-chloro-oxo(ƞ2-2-
tetrahydrofuranylmethanolato)-vanadium(V)] [24] have been used as catalyst precursors for
oxidation reactions in the presence of various oxidants. Thus, it was predictable that the catalytic
activity of hydrazone-vanadium complexes containing V−Cl moiety might be higher than for
other hydrazone-vanadium complexes. In the present work, we report synthesis, characterization,
crystal structure and catalytic activity of a new oxidovanadium-hydrazone complex containing
+
VOCl2 moiety.
Scheme 1.
2. Experimental
2.1. Materials and instruments
All chemicals and solvents were purchased from Merck and used as received without further
purification. The ligand (E)-N'-(phenyl(pyridin-2-yl)methylene)isonicotinhydrazide (HL) was
synthesized by the reaction of 4-pyridinecarboxylic acid hydrazide with 2-benzoylpyridine in
methanol according to our previous reports [25]. IR spectra were recorded in KBr disks with the
4

Bruker FT–IR spectrophotometer. The elemental analyses (carbon, hydrogen and nitrogen) were
obtained from the Carlo ERBA Model EA 1108 analyzer. The atomic absorption analysis was
1
13
carried out using the Varian Spectra AA 220 equipment. H and C NMR spectra of the ligand
and complex in DMSO-d6 solution were recorded on a Bruker 250 MHz spectrometer and
chemical shifts were indicated in ppm relative to tetramethylsilane (TMS). The reaction products
of oxidation were determined and analyzed using the HP Agilent 6890 gas chromatograph
equipped with the HP-5 capillary column (phenyl methyl siloxane 30 m × 320 µm × 0.25 µm)
and the gas chromatograph-mass spectrometry (the Hewlett-Packard 5973 Series MS-HP gas
chromatograph with a mass-selective detector).
2.2. Synthesis of [VO(L)Cl2] (1)
Complex 1 was synthesized by the reaction of hydrazone ligand, HL, (0.302 g, 1.0 mmol) and
VOCl3·(0.173 g, 1.0 mmol) in chloroform solvent according to the previously reported method
[26]. The above mentioned amounts of materials were placed in the main arm of a branched tube.
Chloroform was carefully added to fill the arms, the tube was sealed and the reagents containing
arm immersed in an oil bath at 60 °C while the other arm was kept at ambient temperature. After
a week, dark brown crystals of complex 1 were deposited in the cooler arm. Yield: 88% (0.35 g).
Anal. Calc. for C18H13Cl2N4O2V (MW = 439.2): C, 49.23; H, 2.98; N, 7.29; V, 11.60%. Found:
C, 49.46; H, 3.01; N, 7.29; V, 11.54%. Selected FT-IR (KBr, cm-1): 3418 (br, w), 3085 (w), 2925
(w), 2871 (w), 1632 (vs), 1598 (m), 1587 (m), 1561 (m), 1530 (vs), 1498 (s), 1453 (s), 1372 (s),
1362 (s), 1333 (m), 1297 (w), 1255 (w), 1247 (w), 1195 (w), 1155 (m), 1148 (m), 1088 (s), 1080
(s), 1045 (w), 1029 (w), 1023 (w), 969 (s), 950 (vs), 931 (m), 918 (m), 837 (s), 794 (s), 778 (m),
755 (s), 742 (m), 705 (vs), 689 (s), 685 (s), 659 (m), 647 (w), 606 (w), 489 (w), 472 (m), 454
5

(w), 432 (m). UV-Vis (H2O): λmax , nm (ε, M-1cm-1): 280 (13647), 400 (10000). 1H NMR (250.13
MHz, DMSO-d6, 25 °C, TMS, ppm): δ = 7.43 (3H, m), 7.54 (2H, d, J = 6.25 Hz), 7.64 (2H, d, J
= 5.75 Hz), 7.81-7.96 (3H, m), 8.60 (3H, m). UV-Vis (H2O): λmax , nm (ε, M-1cm-1): 280 (13647),
400 (10000).
2.3. X-ray Crystallography
X-ray diffraction data for 1 were collected at 95 K by the ω-scan technique on the SuperNova
diffractometer of Rigaku Oxford Diffraction equipped with the Atlas S2 CCD detector using
mirror collimated Mo-Kα radiation (λ = 0.71073 Å). The data integration and numerical
absorption corrections were carried out with the CrysAlis program [27]. Two crystal structures
were obtained, the first one for the fresh sample containing the lattice water, and the second one
for an aged sample without the lattice water. The form with the lattice water had a primitive unit
cell while the other converted to a C-centered unit cell. Both solvatomorphs were solved by the
charge flipping method using the Superflip program [28] and refined using Jana2006 software
[29]. Symmetry analysis of the electron density maps resulting from the charge flipping clearly
indicated the lack of the symmetry centre for both structures. The crystal data and refinement
parameters are presented in Table 1.
Table 1
CCDC 1470224 and 1470225 contains the supplementary crystallographic data for both
polymorphs of 1. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supporting information
for this article is available on the DOI:
6

2.4. General oxidation procedure
Oxidation reactions were carried out under air in 3 mL of solvent, and aqueous H2O2 (30%) was
used as an oxidant. In a typical experiment, a mixture of 2.3 × 10-3 mmol of the complex 1, 3.0
mL of the solvent and 1.0 mmol of the substrate were placed in a 25 mL round bottomed glass
flask. The mixture was heated to reach to the desired temperature and after addition of H2O2 the
solution was placed in an oil bath to continue the reaction at the set temperature. At appropriate
intervals, aliquots were removed and analyzed immediately by GC. The oxidation products were
identified by comparison of their retention times with those of the authentic samples.
3. Results and Discussions
3.1. Synthesis and Characterization
The reaction of 2-benzoylpyridine with the equimolar amount of 4-pyridinecarboxylic acid
hydrazide gave the desired tridentate Schiff base ligand (HL) in high yield and purity (Scheme
1). Complex 1 was synthesized by the reaction of HL with VOCl3 in chloroform. Dark brown
crystals of 1 grew by thermal gradient method. 1H NMR and 13C NMR spectra of H2L in DMSO-
1
d6 (Figs. S1-S3) confirmed the proposed structure for the ligand (Scheme 1). In the H NMR
spectrum of the complex 1 (Figs. S4-S5)the absence of amidic N−H peak shows HL is
coordinated to the metal ion as a mono-anionic ligand. The infrared spectrum of HL displays the
characteristic bands at 3066, 1582 and 729 cm-1, which are assigned respectively to υ(N-H),
υ(C=N) and υ(C=O) functionality of the free Schiff base ligand. The N-H and C=O bands
indicate that the HL exists in the keto form. The N-H and C=O bands of the free ligand are not
detected in the FT-IR spectrum of the complex 1 which confirms the coordination of HL as a
7

mono-negative ligand in the enol form (see Fig. S6). In the IR spectra of the complex 1, the
presence of the V=O moiety is indicated by the strong band at 960 cm-1 [30]. In addition, the
infrared spectra of the complex 1 displays an FT-IR absorption band around 1597 cm-1 which
can be assigned to the C=N stretching frequency of the coordinated ligand [31].
3.2. Crystal structure of [VO(L)Cl2] (1)
In order to obtain structural details, single-crystal X-ray diffraction study was made on
previously prepared crystals. Molecular structure of complex 1 is shown in Fig. 1 and selected
bond lengths and angles are given in Table 2. The complex 1 is a mononuclear complex of V(V)
with the hydrazone ligand coordinated to the V center. The amidic N−H hydrogen atom is
eliminated during the complexation and as a result the Schiff base ligand is coordinated to the V1
ion as tridentate mono-negative ligand. The octahedral coordination environment of
vanadium(V) is formed by one oxygen and two nitrogen atoms provided by Schiff base ligand,
two chloride anions and the oxygen atom of the oxido group. Two chloride ligands oriented trans
with respect to each other (Cl1—V1—Cl2 = 167.18(2)°). Chloride ligands together with nitrogen
atom of the pyridine group (N4) and oxygen atom of hydrazone moiety (O1) form the equatorial
plane of the octahedron. The axial positions are occupied by nitrogen atom of the azomethine
group (N3) and the oxido atom, O1v. The V1−O1v bond length (1.6125(13) Å) is considerably
shorter than the other bond lengths. The V1−N3 and V1-N4 bond lengths are 2.1589(15) and
2.11135(14) Å, respectively. The V1−N4 bond length is close to the other V−Npyridine bond
lengths reported in the literature but the V1−N3 bond length which is located trans with respect
to the V=O moiety is abnormally long compared to the usual V−Nazomethine bond length because
8

of the trans influence of the oxido group. The V−Cl bond lengths (V1−Cl1 = 2.3368(5) and
V1−Cl2 = 2.4663(5)) are close to the previously reported V−Cl bond lengths [32].
Fig. 1.
Due to presence of V=O and V−Cl groups, hydrogen bonding is a predictable feature for this
complex. Although complex 1 doesn’t have strong hydrogen bonding donor groups like OH and
NH, there are some other intermolecular C−H···O and C−H···Cl hydrogen bonding interactions
(see Fig. 2 and Table 3).
Fig. 2.
Table 2.
Table 3.
3.3. Solvatomorphism
During our effort to select a single crystal suitable for X-ray diffraction, we found that for some
specimens C centering was violated by a presence of forbidden reflections 30-50 I/σ(I), i.e. by
weak but clearly observed reflections. When we applied anyway C centering for such data,
disorder of the phenyl ring appeared, while when taking the forbidden reflections into the
account using the symmetry Pc, we obtained two very similar molecules different by the phenyl
position and elongation of ADPs of one molecule (Fig. S7). Moreover, refinement in Pc revealed
two different types of channels, one of them filled with disordered weakly occupied water
molecules (Fig. 3), while the structure with C centering had only one kind of channel without
any lattice water. The sample with the symmetry Cc was taken from the same batch as the one
with symmetry Pc, but four years later. We assume that the weakly bounded lattice water
molecules simply left the channels of the structure over the time. The solvatomorph without C
centering has no relevance for the structural description which is based on the C-centered
9

structure. On the other hand, other physical measurements correspond to the structure containing
the lattice water because these measurements were done using the fresh sample
Fig. 3.
3.3. Catalytic activity
The oxidation of cyclooctene as a representative substrate of olefins with 30% aqueous H2O2 was
carried out in the presence of complex 1 as a homogeneous catalyst precursor. In order to find
the optimum conditions for the oxidation reactions, oxidation of cyclooctene in various
conditions was studied. As shown in Table 4, the conversion was increased with increasing the
hydrogen peroxide:cyclooctene molar ratio from 0.5 to 2 (Table 4, entries 1-3) while further
increasing of the amount of H2O2 could not improve the conversion. Thus, the hydrogen
peroxide:cyclooctene molar ratio of 2:1 was selected as the optimal molar ratio for the oxidation
reactions of olefins in the presence of complex 1.
Another important factor influencing the yield of cyclooctene epoxide was the amount of the
catalyst itself. With the use of 0.0005 g (1.18 × 10-3 mmol) and 0.001 g (2.36 × 10-3 mmol) of the
catalyst precursor, respectively, the conversion reached 66% and 90%, while further increasing
of the amount of the catalyst precursor was useless. In the blank reaction under similar
conditions with cyclooctene, only 5% of cyclooctene was oxidized after 24 hours [33]. Thus, the
presence of complex 1 as a catalyst precursor in running the oxidation reactions was essential.
Table 4.
Table 5.
Alternatively, the reaction was carried out at different temperatures. When temperature was
increased (from room temperature to 80 °C), the conversion increased correspondingly (from
10

15% to 83%). In order to further optimize the process to achieve the maximum oxidation of
cyclooctene, the effect of different solvents was studied (Table 5). The highest conversion was
obtained for ethanol (90% after 5 hours) while the lowest one for n-hexane (7% after 5 hours).
To establish the scope for the activity of [VOCl2L], this study was further extended to the
catalytic oxidation of other linear and cyclic olefins, namely styrene, α-methyl styrene, 1-octene,
1-decene, cyclohexene and indene, using [VOCl2L] (Table 6). Generally, good epoxide
selectivity was observed for the tested aliphatic substrates and cyclooctene (Table 6, entries 5-6).
Moreover, the present catalytic system was completely selective for the epoxidation of
cyclooctene, indene, 1-octene and 1-decene, while for styrene byproducts benzaldehyde (19%)
and benzoic acid (8%) were obtained, and for α-methyl styrene the byproduct acetophenone
(38%) was obtained. The production of benzaldehyde in the oxidation of styrene is due to the
over-oxidation of styrene epoxide in the presence of H2O2. The conversion of styrene and
selectivity for styrene epoxide were also affected by the reaction time. The selectivity for styrene
epoxide was increased from 73% to 91% upon decreasing the reaction time from 5 h to 2 h,
which prevented the overoxidation at higher reaction times [34]. The lower catalytic activity of
α-methyl styrene compared to styrene seems to be due to the steric hindrance of the methyl
substituent [35].
Table 6.
In comparison with the previously reported catalysts, the [VOCl2L] system exhibited superior
activity for the oxidation of hydrocarbons. The previously reported [VOL1Cl] (L1
=
t
Me2NCH2CH2N(CH2-2-O-3,5-C6H2 Bu2)2), [VOL2Cl] (L2= Me2NCH2CH(CH3)N(CH2-2-O-3,5-
11

t
C6H2 Bu2)2) and [(VOL1)2(µ-O)] showed lower catalytic activity for the oxidation of cyclooctene
in the presence of H2O2 as an oxidant [36].
The catalytic activity of complex 1 was also tested for the oxidation of methyl phenyl
sulfide (thioanisole). In these reactions, H2O2 should be used carefully, due to the possibility of
overoxidation reactions [37]. In control experiments without the catalyst precursor, the yield of
sulfoxide was low (Table 7, entry 5). The effect of different amounts of H2O2 was investigated
with a fixed amount of substrate (1 mmol) and the complex 1 (2.3 × 10-3 mmol) in 3 mL of
EtOH. The reactions were carried out at room temperature. As shown in Table 7, the conversion
and sulfoxide selectivity considerably increases with increasing molecular ratio of H2O2 to
thioanisole from 0.5 to 1. Any attempt to further increase the ratio of H2O2 actually resulted in
decreased yield, in consequence of sulfoxide to be further oxidized to the corresponding sulfone
[38].
Table 7.
In the next step, the catalytic oxidation was studied in various solvents (Table 8). The catalytic
activity decreases in the order acetonitrile (dielectric constant ε/ε0 = 37.5) > methanol (32.7) >
ethanol (24.3) > chloroform (5.5) at 25 ºC. Chloroform is not miscible with the aqueous H2O2
which could also be the reason for low catalytic efficiency in this case. In agreement with results
previously reported in the literature, solvents of high hydrogen bonding capacity, such as
methanol, favor the formation of sulfoxide [39]. However, the best performance was observed in
acetonitrile.
Table 8.
The oxidation of p-Br-C6H4SMe was investigated under the optimal condition. Additional
electron-withdrawing substituent (Br) in the para-position of the aromatic ring of sulfide reduces
12

the conversion but increases sulfoxide selectivity (95%). Similar observation has been reported
in literature [40,41].
Although the details of catalytic mechanism are not studied in the present work, on the basis of
the electronic absorption spectroscopy studies (Fig. S8) and also by considering the previous
studies on similar systems [33,42], it is predicted that the key step in this catalytic process is the
oxidation of substrates by a peroxo-vanadium-hydrazone Schiff base species. Although such
species are not identified in this study, electronic absorption spectroscopy indicates that the
solution of [VOCl2L] in methanol is sensitive towards addition of H2O2. By increasing H2O2 to
the methanolic solution of complex 1, the intensity of absorption band at about 400 nm increases.
Moreover, the shoulder at about 275 nm overlaps with the new band with high extinction
coefficients which observes below than 300 nm after H2O2 addition. These changes can be
attributed to the formation of peroxido-VO(L) species by addition of H2O2 to the solution of
complex 1 [33,41].
Conclusion
+
In summary, a new oxidovanadium(V) complex containing the VOCl2 core was synthesized and
characterized by various analyses and its structure was determined by single crystal X-ray
diffraction analysis. The complex was used as a catalyst precursor in the oxidation of olefins and
sulfides in the presence of hydrogen peroxide as a green oxidant. The results showed that this
system corresponds to an active and selective catalyst for the oxidation of olefins and methyl
phenyl sulfides in the presence of H2O2. Using this catalytic system in the oxidation of sulfides,
sulfoxides were obtained as the main products, together with variable amounts of sulfones,
depending on the nature of the substrate. The catalytic potential of complex 1 in the oxidation of
13

olefins was also studied, choosing the oxidation of cyclooctene, styrene, α-methyl styrene,
indene, cyclohexene, 1-octene and 1-decne as the model reactions.
Acknowledgments
The authors are grateful to the University of Zanjan for financial support of this study. The
crystallographic part was supported by the project 14-03276S of the Czech Science Foundation
using instruments of the ASTRA lab established within the Operation program Prague
Competitiveness - project CZ.2.16/3.1.00/24510.
References
[1] a) D.C. Crans, J.J. Smee, E. Gaidamauskas, L. Yang, Chem. Rev.104 (2004) 849;
b) J.C. Pessoa, E. Garribba, M.F.A. Santos, T. Santos-Silva, Coord. Chem. Rev. 301–302 (2015)
49;
c) H. Sakurai, Y. Yoshikawa, H. Yasui, Chem. Soc. Rev. 37 (2008) 2383.
[2] a) E. Kioseoglou, S. Petanidis, C. Gabriel, A. Salifoglou, Coord. Chem. Rev. 301-302 (2015)
87;
b) J.C. Pessoa, S. Etcheverry, D. Gambino, Coord. Chem. Rev. 301-302 (2015) 24;
c) T. Chakraborty, A. Chartterjee, M.G. Saralaya, M. Chartterjee, J. Biol. Inorg.Chem. 11 (2006)
855.
[3] D. Gambino, Coord. Chem. Rev. 255 (2011) 2193.
[4] a) V. Conte, A. Coletti, B. Floris, G. Licini, C. Zonta, Coord. Chem. Rev. 255 (2011) 2165;
b) M. Kirihara, Coord. Chem. Rev. 255 (2011) 2281;
14

c) G. Licini, V. Conte, A. Coletti, M. Mba, C. Zonta, Coord. Chem. Rev. 255 (2011) 2345;
d) M. Sutradhar, L.M.D.R.S. Martins, M.F.C.G. Silva, A.J.L. Pomberio, Coord. Chem. Rev. 301-
302 (2015) 200;
e) P. Schwendt, J. Tatiersky, L. Krivosudský, M. Šimuneková, Coord. Chem. Rev. 318 (2016)
135.
[5] a) A. Pohlmann, S. Nica, T.K.K. Luong, W. Plass, Inorg. Chem. Commun. 8 (2005) 289;
(b) W. Plass, Coord. Chem. Rev. 237 (2003) 205;
(c) S. Nica, A. Pohlmann, W. Plass, Eur. J. Inorg. Chem. (2005) 2032;
(d) R. Dinda, P. Sengupta, S. Ghosh, T.C.W. Mak, Inorg. Chem. 41 (2002) 1684.
[6] a) J.A.L. da Silva, J.J.R. Frausto da Silva, A.J.L. Pombeiro, Coord. Chem. Rev. 255 (2011)
2232;
b) T. Hirao, Chem. Rev. 97 (1997) 2707;
c) M.R. Maurya, A. Kumar, J.C. Pessoa, Coord. Chem. Rev. 255 (2011) 2315.
[7] M. Sutradhar, L.M.D.R.S. Martins, M.F.C. Guedes da Silva, A.J.L. Pombeiro, Coord. Chem.
Rev. 301 (2015) 200.
[8] a) M.R. Maurya, B. Uprety, N. Chaudhary, F. Avecilla, Inorg. Chim. Acta 434 (2015) 230;
b) S.Y. Ebrahimipour, I. Sheikhshoaie, A.C. Kautz, M. Ameri, H. Pasban-Aliabadi, H.A.
Rudbari, G. Bruno, C. Janiak, Polyhedron 93 (2015) 99;
c) N. Noshiranzadeh, R. Bikas, M. Emami, M. Siczek, T. Lis, Polyhedron 111 (2016) 167.
[9] a) H. Hosseini-Monfared, R. Bikas, P. Mahboubi-Anarjan, S.W. Ng, E.R.T. Tiekink, Z.
Anorg. Allg. Chem. 640 (2014) 243;
b) M.R. Maurya, S. Agarwal, C. Bader, M. Ebel, D. Rehder, Dalton Trans. (2005) 537;
15

c) M.R. Maurya, S. Agarwal, M. Abid, A. Azam, C. Bader, M. Ebel, D. Rehder, Dalton Trans.
(2006) 937.
[10] J. Honzıcek, I. Cısarova, J. Vinklarek, Appl. Organomet. Chem. 19 (2005) 692.
[11] R.K. Egdal, F.B. Larsen, A.D. Bond, C.J. McKenzie, Inorg. Chim. Acta 358 (2005) 376.
[12] H. Kumagai, M. Endo, M. Kondo, S. Kawata, S. Kitagawa, Coord. Chem. Rev. 237 (2003)
197.
[13] F.H. Allen, Acta Crystallogr. B 58 (2002) 380.
[14] a) R. Bikas, H. Hosseini Monfared, T. Lis, M. Siczek, Inorg. Chem. Commun. 15 (2012)
151.
b) H. Hosseini-Monfared, H. Falakian, R. Bikas, P. Mayer, Inorg. Chim. Acta 394 (2013) 526.
c) H. Hosseini-Monfared, R. Bikas, P. Mahboubi-Anarjan, A.J. Blake, V. Lippolis, N.B. Arslan,
C. Kazak, Polyhedron 69 (2014) 90.
d) H. Hosseini-Monfared, R. Bikas, J. Sanchiz, T. Lis, M. Siczek, J. Tucek, R. Zboril, P. Mayer,
Polyhedron 61 (2013) 45;
e) S. Mondal, S. Naskar, A.K. Dey, E. Sinn, C. Eribal, S.R. Herron, S. K. Chattopadhyay, Inorg.
Chim. Acta 398 (2013) 98;
f) R. Bikas, H. Hosseini-Monfared, L. Sieroń, A. Gutiérrez, J. Coord. Chem. 66 (2013) 4023.
[15] H. Pellissier, Tetrahedron 62 (2006) 5559.
[16] K.H. Kyung, D.C. Han, H.P. Fleming, J. Food Sci. 62 (1997) 406.
[17] H. Cotton, T. Elebring, M. Larsson, L. Li, H. Sörensen, S.V. Unge, Tetrahedron:Asymm. 11
(2000) 3819.
[18] W. Komatsu, Y. Miura, K. Yagasaki, Lipids 33 (1998) 499.
[19] a) G. Romanowski, T. Lis, Inorg. Chim. Acta 394 (2013) 627;
16

b) M. Schulz, R. Debel, H. Görls, W. Plass, M. Westerhause, Inorg. Chim. Acta 365 (2011) 349.
c) S. Hussain, D. Talukdar, S.K. Bharadwaj, M.K. Chaudhuri, Tetrahedron Lett. 53 (2012) 6512;
d) P. Adão, S. Barroso, F. Avecilla, M.C. Oliveira, J.C. Pessoa, J. Organomet. Chem. 760 (2014)
212.
[20] a) M.R. Maurya, N. Chaudhary, A. Kumar, F. Avecilla, J.C. Pessoa, Inorg. Chim. Acta 420
(2014) 24;
b) C. Cordelle, D. Agustin, J.-C. Daran, R. Poli, Inorg. Chim. Acta 364 (2010) 144.
[21] M.R. Maurya, A. Kumar, J.C. Pessoa, Coord. Chem. Rev. 255 (2011) 2315.
[22] M. Ghorbanloo, R. Bikas, G. Małecki, Inorg. Chim. Acta 445 (2016) 8.
[23] S. Barroso, P. Adao, F. Madeira, M.T. Duarte, J.C. Pessoa, A.M. Martins, Inorg. Chem. 49
(2010) 7452.
[24] E.C.E. Rosenthal, H. Cui, J. Koch, P.E. Gaede, M. Hummert, S. Dechert, Dalton Trans.18 (
2005) 3108.
[25] (a) R. Bikas, P. Aleshkevych, H. Hosseini-Monfared, J. Sanchiz, R. Szymczak, T. Lis,
Dalton Trans. 44 (2015) 1782;
(b) R. Bikas, H. Hosseini-Monfared, V. Vasylyeva, J. Sanchiz, J. Alonso, J.M. Barandiarand, C.
Janiak, Dalton Trans. 43 (2014) 11925;
(c) H. Hosseini-Monfared, R. Bikas, R. Szymczak, P. Aleshkevych, A.M. Owczarzak, M.
Kubicki, Polyhedron 63 (2013) 74;
d) R. Bikas, H. Hosseini-Monfared, G. Zoppellaro, R. Herchel, J. Tucek, A.M. Owczarzak, M.
Kubicki, R. Zboril, Dalton Trans. 42 (2013) 2803;
e) R. Bikas, N. Noshiranzadeh, L. Sieroń, H. Hosseini-Monfared, J.M. Barandiaran, T. Lis, J.
Alonso, Inorg. Chem. Commun. 67 (2016) 85.
17

[26] a) R. Bikas, H. Hosseini-Monfared, P. Aleshkevych, R. Szymczak, M. Siczek, T. Lis,
Polyedron. 88 (2015) 48.
b) N. Noshiranzadeh, R. Bikas, K. Slepokura, M. Shaabani, T. Lis, J. Fluorine Chem. 160 (2014)
34;
c) N. Noshiranzadeh, M. Emami, R. Bikas, K. Slepokura, T. Lis, Polyhedron 72 (2014) 56;
d) M.A. Kamyabi, F. Soleymani-Bonoti, R. Bikas, H.Hosseini-Monfared, N. Arshadi, M. Siczek,
T. Lis, Phys. Chem. Chem. Phys. 17 (2015) 32161;
e) R. Bikas, H. Hosseini-Monfared, M. Siczek, S. Demeshko, B. Soltani, T. Lis, Inorg. Chem.
Commun. 62 (2015) 60.
[27] Xcalibur CCD System, CrysAlis Software System, v. 1.171 Oxford Diffraction Ltd.
Abingdon, England (2012).
[28] L. Palatinus, G. Chapuis, SUPERFLIP, J. Appl. Cryst. 40 (2007) 786.
[29] V. Petricek, M. Dusek, L. Palatinus, Z. Kristallogr. 229 (2014) 345.
[30] a) N. Noshiranzadeh, M. Mayeli, R. Bikas, K. Slepokura, T. Lis, Transit. Met. Chem. 39
(2014) 33;
b) K. Yamashita, S. Tazawa, K. Sugiura, Inorg. Chim. Acta 439 (2016) 173;
c) M.L. Tarlton, A.E. Anderson, M.P. Weberski, X. Riart-Ferrer, B.M. Nelson, C.C.
McLauchlan, Inorg. Chim. Acta 420 (2014) 159;
d) D.C. Horton, D. VanDerveer, J. Krzystek, J. Telser, T. Pittman, D.C. Crans, A.A. Holder,
Inorg. Chim. Acta 420 (2014) 112.
[31] a) R. Bikas, H. Hosseini-Monfared, M. Korabik, M.S. Krawczyk, T. Lis, Polyhedron 81
(2014) 282.
18

b) N.A. Mangalam, S. Sivakumar, S.R. Sheeja, M.R. Prathapachandra Kurup, E.R.T. Tiekink,
Inorg. Chim. Acta 362 (2009) 4191;
c) X.T. Ma, N. Xing, Z.D. Yan, X.X. Zhang, Q. Wu, Y.H. Xing, New J.Chem. 39 (2015) 1067;
d) H. Hosseini-Monfared, R. Bikas, M. Siczek, T. Lis, R. Szymczak, P. Aleshkevych, Inorg.
Chem. Commun. 35 (2013) 172;
e) R. Bikas, H. Hosseini-Monfared, M. Siczek, A. Gutiérrez, M.S. Krawczyk, T. Lis, Polyhedron
67 (2014) 396.
[32] a) M.A. Fik, A. Gorczyński, M. Kubicki, Z. Hnatejko, A. Wadas, P.J. Kulesza, A.
Lewińska, M. Giel-Pietraszuk, E. Wyszko, V. Patroniak Polyhedron 97 (2015) 83;
b) L. Clowes, M. Walton, C. Redshaw, Y. Chao, A. Walton, P. Elo, V. Sumerin, D.L. Hughes
Cat. Sci. Tech. 3 (2013) 152;
c) C. Redshaw, L. Clowes, D.L. Hughes, M.R.J. Elsegood, T. Yamato, Organometallics 30
(2011) 5620.
[33] H. Hosseini Monfared, R. Bikas, P. Mayer, Inorg. Chim. Acta 363 (2010) 2574.
[34] Y. Deng, Y. Cai, Z. Sun, J. Liu, C. Liu, J. Wei, W. Li, C. Liu, Y. Wang, D. Zhao, J. Am.
Chem. Soc. 132 (2010) 8466.
[35] G. Grivani, S. Tangestaninejad, A. Halili Inorg. Chem. Commun. 10 (2007) 914.
[36] F. Madeira, S. Barroso, S. Namorado, P.M. Reis, B. Royo, A.M. Martins, Inorg. Chim. Acta
383 (2012) 152.
[37] R. Noyori, M. Aoki, K. Sato, Chem. Commum. (2003) 1977.
[38] F. Xie, Z. Fu, S. Zhong, Z. Ye, X. Zhou, F. Liu, C. Rong, L. Mao, D. Yin, J. Mol. Catal. A:
Chem. 307 (2009) 93.
19

[39] B.M. Choudary, B. Bharathi, C.V. Reddy, M.L. Kantam, J. Chem. Soc. Perkin Trans. 1
(2002) 2069.
[40] A.L. Nuzhdin, D.N. Dybtsev, V.P. Fedinb, G.A. Bukhtiyarova, Dalton Trans. 47 (2009)
10481.
[41] H. Liu, M. Wang, Y. Wang, Y. Wang, H. Sun, L. Sun, Catal. Commun. 11 (2009) 294.
[42] a) T. Joseph, D. Srinivas, C.S. Gopinath, S.B. Halligudi, Catal. Lett. 83 (2002) 209;
b) C.J. Chang, J.A. Labinger, H.B. Gray, Inorg. Chem. 36 (1997) 5927;
c) V. Hulea, E. Dumitriu, Appl. Catal. A: Gen. 277 (2004) 99.
20

Scheme, Figures and Tables Caption
Scheme 1. a) General structure of hydrazone ligands and their tautomeric forms, b) coordination
environment of oxidovanadium complexes with hydrazone ligands, c) structure of complex 1
Fig. 1. Molecular structure of complex 1.
Fig. 2. Hydrogen bonding interactions in the crystal structure of complex 1, hydrogen atoms not
involved in hydrogen bonding were omitted for the sake of clarity.
Fig. 3. The channels in direction of c axis in a) structure 1a b) structure 1b
Table 1. Crystal data and structure refinement parameters for 1.
Table 2. Selected bond lengths (Å) and angles (°) for 1
Table 3. Hydrogen-bond geometry (Å, °) in 1
Table 4. Catalytic activity of [VOCl2L] on cyclooctene oxidation a
Table 5. Effect of various solvents on cyclooctene oxidation by [VOCl2L]a
Table 6. Oxidation of alkenes with H2O2 catalyzed by the [VOCl2L] a
a
Table 7. Oxidation of thioanisole by the [VOCl2L]/H2O2
a
Table 8. Solvent effect on the oxidation of methyl phenyl sulfide with [VOCl2L]/H2O2
21

R'
R'
H
R''
R''
N
R
N
R
N
N
-H+
H+
a)
O
N/O
N
X
O
X
O
X = N or C-OH
R, R', R'' = Substituents
A1
V
O
Ph
N
N
O
N
O
N
V
b)
c)
or
N
Cl
O
A1
N/O
N/O
N
O
V
A2
A2
Cl
O
A1, A2: available coordination sites
Scheme 1. a) General structure of hydrazone ligands and their tautomeric forms, b) coordination
environment of oxidovanadium complexes with hydrazone ligands, c) structure of complex 1
22

Fig. 1. Molecular structure of complex 1.
23

Fig. 2. Hydrogen bonding interactions in the crystal structure of complex 1, hydrogen atoms not
involved in hydrogen bonding were omitted for the sake of clarity.
24

a)
b)
Fig. 3. The channels in direction of c axis in a) structure 1a b) structure 1b
25

Table 1. Crystal data and structure refinement parameters for 1. The structures 1a and 1b are
solvatomorphs, 1a corresponding to the aged product.
Identification code
Net formula
Formula weight, g mol-1
Radiation
1a
C18H13Cl2N4O2V
439.2
1b
C18H13Cl2N4O2V 0.369(H2O)
445.82
CuKα
MoKα
Diffractometer
SuperNova
95
Gemini ultra
121
T, K
Crystal size, mm
Crystal shape, color
Crystal system
Space group
a, Å
0.22 × 0.11 × 0.05 0.50 × 0.38 × 0.17
Prism, brown
Monoclinic
C c
Prism, brown
Monoclinic
P c
10.1605 (2)
19.2565 (4)
9.8426 (2)
97.0030 (17)
1911.39 (7)
4
10.2498 (2)
19.3887 (4)
9.8457 (2)
97.6495 (17)
1939.23 (7)
4
b, Å
c, Å
β, deg
Volume, Å3
Z
Density (calc.), g cm−3
1.526
1.525
Absorption coefficient, mm−1 0.82
7.02
F(000)
Θ range, deg
888
900
4.2 – 29.3
4696
4.3 – 67.0
6791
Independent reflections
Measured reflections
Reflections with I > 3σ(I)
Index ranges hkl
15906
4491
50266
6378
h = –13 → 13
k = –26 → 25
l = –12 → 12
0.024
h = –12 → 12
k = –22 → 22
l = –11 → 11
0.047
Rint
restraints/parameters
Goodness of fit on F2
R[F2 > 3σ(F2)]
0/245
0/518
1.18
2.37
0.024
0.049
wR(F2)
0.065
0.133
Max electron density/e·Å–3
Min electron density/e·Å–3
CCDC number
0.26
0.32
–0.22
–0.60
1470224
1470225
26

Table 2. Selected bond lengths (Å) and angles (°) for 1
Bond
Length
Bond
Angle
V1—Cl1
V1—Cl2
V1—O1v
V1—N4
V1—O1
V1—N3
N4—C8
N4—C12
O1—C6
2.3368 (5)
2.4663 (5)
1.6125 (12)
2.1135 (14)
2.0190 (12)
2.1589 (15)
1.360 (2)
Cl1—V1—Cl2
Cl1—V1—O1v
Cl1—V1—N4
Cl1—V1—O1
Cl1—V1—N3
Cl2—V1—O1v
Cl2—V1—N4
Cl2—V1—O1
Cl2—V1—N3
O1v—V1—N4
O1v—V1—O1
O1v—V1—N3
N4—V1—O1
N4—V1—N3
O1—V1—N3
167.18 (2)
100.39 (5)
88.94 (4)
88.18 (4)
87.33 (4)
92.12 (4)
92.19 (4)
83.95 (4)
80.84 (4)
97.64 (6)
115.05 (6)
167.58 (6)
147.17 (5)
72.59 (5)
74.60 (5)
1.345 (2)
1.295 (2)
27

Table 3. Hydrogen-bond geometry (Å, °) in 1
D—H···A
D—H
0.96
0.96
0.96
0.96
0.96
0.96
H···A
2.78
2.86
2.28
2.46
2.92
2.44
D···A
D—H···A
127
123
144
163
C1—H1c1···Cl1i
C2—H1c2···Cl1i
C4—H1c4···O1vii
C5—H1c5···O1ii
C10—H1c10···Cl2iii
C17—H1c17···O1viv
3.4491 (18)
3.4824 (18)
3.105 (2)
3.387 (2)
3.549 (2)
3.375 (2)
124
165
Symmetry codes: (i) x-1/2, −y+1/2, z+1/2; (ii) x, –y+1, z+1/2; (iii) x+1/2, –y+1/2, z–1/2; (iv) x–
1/2, y–1/2, z.
28

Table 4. Catalytic activity of [VOCl2L] on cyclooctene oxidation a
Entry
[H2O2]/[C8H12]
Molar ratio
Conversion (%)b
Epoxide
selectivity (%)
TONc
TOF(h-1)d
1
2
3
4
0.5
1
13
30
54
56
>99
>99
>99
>99
56.52
130.4
234.7
237
11.30
26
2
46.94
47.4
3
a Reaction conditions: catalyst ([VOCl2L]) (2.36 × 10-3 mmol); reaction temperature, 60 ˚C;
cyclooctene, 1 mmol; CH3CN (solvent), 3 mL; reaction time, 5 h.;
b Conversions are based on the starting substrate for homogeneous conditions;
c TON = (mmol of epoxide)/(mmol of catalyst);
dTOF = TON/time(h)
29