Synthesis, crystal structures of oxovanadium(V) complexes with hydrazone ligands and their catalytic performance for the styrene oxidation

Article abstract of DOI:10.1016/j.poly.2016.09.060

Four new oxovanadium(V) complexes, [VO(aha)L¹] (1), [VO(aha)L²] (2), [VO(aha)L³] (3), and [VO(aha)L⁴]·EtOH (4) (Haha?=?acetohydroxamic acid, H₂L¹?=?4-nitrophenyl 2-(2-hydroxybenzylidene)hyd

Full text of DOI:10.1016/j.poly.2016.09.060

Accepted Manuscript
Synthesis, crystal structures of oxovanadium(V) complexes with hydrazone li-
gands and their catalytic performance for the styrene oxidation
Yan Zhang, Ting Yang, Bo-Yang Zheng, Ming-Yang Liu, Na Xing
PII:
S0277-5387(16)30490-9
DOI:
http://dx.doi.org/10.1016/j.poly.2016.09.060
POLY 12248
Reference:
Polyhedron
To appear in:
Received Date:
Revised Date:
Accepted Date:
31 July 2016
23 September 2016
29 September 2016
Please cite this article as: Y. Zhang, T. Yang, B-Y. Zheng, M-Y. Liu, N. Xing, Synthesis, crystal structures of
oxovanadium(V) complexes with hydrazone ligands and their catalytic performance for the styrene oxidation,
Polyhedron (2016), doi: http://dx.doi.org/10.1016/j.poly.2016.09.060
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Synthesis, crystal structures of oxovanadium(V) complexes with
hydrazone ligands and their catalytic performance for the styrene
oxidation
Yan Zhanga , Ting Yangb, Bo-Yang Zhenga, Ming-Yang Liua and Na Xing*
a. College of Chemistry and Chemical Engineering. Liaoning Normal University, Dalian 116029,
P. R. China
b. Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 116023, P.R.
China.
Abstract: Four new oxovanadium(V) complexes, [VO(aha)L1] (1),
[VO(aha)L2] (2), [VO(aha)L3] (3), and [VO(aha)L4]·EtOH (4) (Haha =
acetohydroxamic
acid,
H2L1
=
4-nitrophenyl
H2L2
2-
=
(2-hydroxybenzylidene)hydrazinecarboxylate,
N'-(2-hydroxylbenzylidene)-4-methoxybenzohydrazide,
N'-(2-hydroxylbenzylidene)-4-methylbenzohydrazide,
H2L3
HL4
=
=
N'-(5-bromo-2-hydroxybenzylidene)-3- methyl benzohydrazide), have
been prepared and structurally characterized by physico-chemical
methods and X-ray diffraction. The V atoms in the complexes are in
octahedral coordination, with the three donor atoms of the hydrazone
ligand and the deprotonated hydroxyl O atom of the aha ligand defining
the equatorial plane, and with the carbonyl O atom of the aha ligand and
one oxo O atom occupying the axial positions. Crystal structures of the
complexes are stabilized by hydrogen bonds. In addition, the catalytic
performances for the peroxidative oxidation (with hydrogen peroxide) of
* Corresponding author: Professor, Na Xing.
E-mail: scarllet_na@163.com

complexes 1-4 and their starting materials VO(acac)2 were studied by the
reaction of styrene (St) to benzaldehyde (BzA) (the maximum total
turnover number is 667) under the mild conditions.
Introduction
Benzaldehyde is a valuable chemical that is usually applied in
perfumery, dyestuff, pharmaceuticals, resin additives and organic
synthesis. One effective method to produce benzaldehyde is the oxidation
of styrene (St), which is an important reaction as it represents a
significant role for the synthesis of fine chemicals and pharmaceuticals，
like styrene oxide, 1-phenylethane-1,2-diol, benzoicacid and
phenylacetaldehyde. [1] Therefore, the exploration on the mild reaction
conditions and suitable catalysts for styrene oxidation has been paid more
and more attention [2-7].
Most of the St oxidation reactions are carried out with heterogeneous
catalysts, such as zeolite-Y encapsulated V [8-10], polymer anchored Cu
and Mn complexes [11], La, V, Cr, Mn and Ti modified molecular sieves
[12-14] etc. However, the advantage of homogeneous catalysts is clearly
seen that the reaction can be carried out in the mild condition with high
activity, such as Schiff bases porphyrin complexes [15, 16]. This may be
attributed to easier spread of catalysts, which lead to more possibilities to
emerge more active sites [17].
2

Among those active metals for St oxidation reactions, vanadium
achieved increasing attention due to its potential catalytic ability [18, 19],
especially as an abundant element existing in various life bodies [20-23].
A plenty of oxovanadium complexes show high catalytic activity towards
various oxidation reaction, such as sulfides [24, 25], alcohols [26, 27] and
alkenes [28-32] oxidations, which happened by the easily changing of
vanadium oxidation states at the presence of oxygen, the various
possibilities of coordination numbers of oxovanadium complexes and
Lewis acid character of the vanadium centers.
Research results show that the complexes with different organic
ligands exhibited different catalytic activity. In general, the organic
ligands used in catalysts can be divided into five different types: (i) the
schiff based ligands; (ii) the tripodal scorpionate ligands; (iii) the pincer
chelate ligands; (iv) the triangular amine ligands and (v) the carboxylate
ligands [33]. Hydrazone ligands belongs to the first type (schiff based
ligands), which is easier to form stable complex with vanadium and
makes the structure of the complexes more diversified [34-38]. However,
the reports focusing on the catalytic performance of vanadium complexes
with hydrazone ligands as homogeneous catalysts in St oxidation are still
limited, though stable oxovanadium complexes with N-donor ligands
have been proved to be potential catalysts in St oxidation [39].
In this paper, four new oxovanadium(V) complexes, [VO(aha)L1] (1),
3

·EtOH (4) (Haha =
[VO(aha)L2] (2), [VO(aha)L3] (3), and [VO(aha)L4]
acetohydroxamic acid, H2L1 = 4-nitrophenyl 2-(2-hydroxybenzylidene)
hydrazinecaroxylate,
H2L2
H2L3
=
N'-(2-hydroxybenzylidene)-4-
N'-(2-hydroxybenzylidene)-4-
methoxybenzohydrazide,
=
methylbenzohydrazide, HL4 = N'-(5-bromo-2- hydroxybenzylidene)
-3-methyl benzohydrazide; (Scheme 1) were synthesized and structurally
characterized. Furthermore, these complexes were also used as catalysts
in St oxidation, using 30 % H2O2 solution as the oxidant.
H2L1
H2L2
H2L3
H2L4
Scheme 1 The structure schemes of the H2L
Experimental
Materials and methods
All Reagents and solvents were purchased from commercial suppliers
and used without further purification. The hydrazones were prepared
according to the literature method [40]. Elemental analyses were
performed on a Perkin-Elmer 240C elemental analyzer. IR spectra were
4

recorded on a Jasco FT/IR-4000 spectrometer as KBr pellets in the
4000–400 cm–1 region. UV-Vis spectra were recorded on a Lambda 900
instrument. X-ray diffraction was carried out on a Bruker SMART 1000
1
CCD area diffractometer. H NMR data were recorded on a Bruker 300
MHz instrument with d6-DMSO as solvent.
Synthesis of complexes
The complexes were prepared according to the same method. An
ethanolic solution (20 mL) of the hydrazone (1.0 mmol) was added with
stirring to an ethanolic solution (20 mL) of VO(acac)2 (1.0 mmol, 0.267
g) and acetohydroxamic acid (1.0 mmol, 0.075 g). The mixture was
stirred at room temperature for 30 min to give solution with color from
light yellow to deep brown. X-ray quality single crystals were formed by
slow evaporation of the solutions in air after a few days.
Synthesis of [VO(aha)L1] (1)
Deep brown single crystals. Yield: 45%. Anal. calcd. for
C17H15N4O8V: C, 45.0; H, 3.3; N, 12.3%. Found: C, 44.8; H, 3.4; N,
12.4%. IR data: 3126 (w), 1605 (s), 1512 (s), 1436 (w), 1338 (s), 1262
(m), 1217 (w), 1179 (w), 1113 (w), 1011 (w), 973 (m), 902 (w), 849 (w),
754 (m), 673 (w), 631 (w), 579 (m), 491 (w), 456 (w). UV-Vis spectra
data in acetonitrile [nm (ε, M-1 cm-1)]: 218 (2.65 × 104), 267 (1.95 × 104),
5

307 (1.89 × 104), 420 (5.49 × 103). 1H NMR (300 MHz, DMSO) δ 13.91
(s, 1H, NH), 9.02 (s, 1H, CH=N), 8.23 (d, 2H, ArH), 7.73 (d, 1H, ArH),
7.55 (t, 1H, ArH), 7.18 (d, 2H, ArH), 7.00 (t, 1H, ArH), 6.85 (d, 1H, ArH),
5.05 (t, 2H, CH ), 2.00 (s, 3H, CH ).
2
3
Synthesis of [VO(aha)L2] (2)
Deep brown single crystals. Yield: 53%. Anal. calcd. for
C17H16N3O6V: C, 49.9; H, 3.9; N, 10.3%. Found: C, 49.8; H, 4.1; N,
10.1%. IR data: 3232 (w), 1606 (s), 1547 (w), 1498 (s), 1449 (w), 1420
(w), 1377 (w), 1333 (m), 1260 (m), 1219 (w), 1163 (m), 1033 (w), 955
(m), 900 (w), 827 (w), 751 (m), 673 (w), 638 (w), 588 (m), 555 (w), 475
(w). UV-Vis spectra data in acetonitrile [nm (ε, M-1 cm-1)]: 218 (1.94 ×
104), 294 (1.72 × 104), 333 (1.33 × 104), 425 (6.33 × 103). 1H NMR (300
MHz, DMSO) δ 13.94 (s, 1H, NH), 9.07 (s, 1H, CH=N), 7.85 (d, 2H,
ArH), 7.75 (d, 1H, ArH), 7.55 (t, 1H, ArH), 7.04–6.88 (m, 3H, ArH), 6.87
(d, 1H, ArH), 3.81 (s, 3H, OCH ), 2.09 (s, 3H, CH ).
3
3
Synthesis of [VO(aha)L3] (3)
Deep brown single crystals. Yield: 37%. Anal. calcd. for
C17H16N3O5V: C, 51.9; H, 4.1; N, 10.7%. Found: C, 52.0; H, 4.1; N,
10.5%. IR data: 3145 (w), 1607 (s), 1540 (m), 1521 (m), 1472 (w), 1438
(m), 1391 (m), 1333 (m), 1277 (m), 1215 (w), 1175 (w), 1121 (m), 997
6

(w), 966 (m), 901 (w), 824 (w), 759 (w), 669 (w), 631 (w), 588 (m), 551
(w), 480 (w). UV-Vis spectra data in acetonitrile [nm (ε, M-1 cm-1)]: 218
1
(2.59 × 104), 280 (2.56 × 104), 333 (1.46 × 104), 431 (7.71 × 103). H
NMR (300 MHz, DMSO) δ 13.96 (s, 1H, NH), 9.10 (s, 1H, CH=N),
7.82–7.75 (m, 3H, ArH), 7.54 (t, 1H, ArH), 7.30 (d, 2H, ArH), 7.00 (t, 1H,
ArH), 6.88 (d, 1H, ArH), 2.37 (s, 3H, PhCH ), 2.10 (s, 3H, CH ).
3
3
Synthesis of [[VO(aha)L4]·EtOH (4)
Deep brown single crystals. Yield: 61%. Anal. calcd. for
C19H21BrN3O6V: C, 44.0; H, 4.1; N, 8.1%. Found: C, 44.2; H, 4.0; N,
8.2%. IR data: 3389 (w), 3177 (w), 1611 (s), 1512 (s), 1460 (w), 1408 (s),
1377 (s), 1344 (w), 1280 (s), 1219 (w), 1198 (w), 1124 (m), 1089 (w),
1039 (m), 1002 (m), 971 (m), 912 (w), 875 (w), 827 (m), 723 (w), 654
(w), 598 (s), 574 (w), 560 (w), 491 (w), 463 (w), 445 (w). UV-Vis spectra
data in acetonitrile [nm (ε, M-1 cm-1)]: 223 (2.32 × 104), 273 (2.34 ×
104), 335 (1.27 × 104), 436 (7.32 × 103). 1H NMR (300 MHz, DMSO) δ
14.08 (s, 1H, NH), 9.10 (s, 1H, CH=N), 8.00 (s, 1H, ArH), 7.72–7.64 (m,
3H, ArH), 7.38 (d, 2H, ArH), 6.86 (d, 1H, ArH), 2.37 (s, 3H, PhCH3),
2.11 (s, 3H, CH3).
X-ray Crystallographic Determination
Diffraction intensities for the complexes were collected at 298(2) K
7

using a Bruker SMART 1000 CCD area diffractometer with MoKα
radiation (λ = 0.71073 Å). The collected data were reduced using the
SAINT program [41], and multi-scan absorption correction was
performed using the SADABS program [42]. The structures were solved
by direct method and refined against F2 by full-matrix least-squares
method using the SHELXTL package [43]. All non-hydrogen atoms were
refined anisotropically. The amino H atoms in the complexes were
located from difference Fourier maps and refined isotropically, with N−H
distances restrained to 0.90(1) Å, and with U (H) set to 0.08 Å2. The
iso
remaining H atoms in the complexes were placed in calculated positions
and constrained to ride on their parent atoms. The crystallographic data
for the complexes are summarized in Table S1. Selected bond lengths
and angles are listed in Table 1.
Table 1 Selected bond lengths (Å) and angles (º) for the complexes
Complex 1
V1-O1
V1-O6
1.841(2)
2.188(2)
V1-O2
V1-O7
1.993(2)
1.8673(19)
2.069(2)
V1-O8
1.585(2)
V1-N1
O8-V1-O1
O1-V1-O7
O1-V1-O2
O8-V1-N1
99.85(12)
107.42(9)
150.84(10)
96.96(11)
O7-V1-N1
O8-V1-O6
O2-V1-O6
N1-V1-O6
163.30(10)
169.03(10)
80.36(8)
93.95(9)
Complex 2
V1-O1
V1-O4
1.836(2)
2.195(2)
1.571(2)
99.51(14)
V1-O2
V1-O5
1.962(2)
1.858(2)
2.076(3)
95.95(12)
V1-O6
V1-N1
O6-V1-O1
O6-V1-O5
8

O5-V1-N1
O1-V1-O2
O6-V1-O4
159.94(10)
156.69(11)
171.13(12)
O5-V1-O2
O1-V1-N1
O1-V1-O4
94.96(9)
84.78(10)
85.08(11)
Complex 3
V1-O1
V1-O3
1.843(4)
2.219(4)
V1-O2
V1-O4
1.959(3)
1.871(4)
V1-O5
1.582(4)
V1-N1
2.072(4)
O4-V1-O2
O1-V1-N1
O1-V1-O2
O1-V1-O3
90.94(15)
84.29(17)
155.23(16)
85.86(17)
O5-V1-O4
O4-V1-N1
O5-V1-O3
N1-V1-O3
97.3(2)
156.40(19)
171.79(19)
83.12(16)
Complex 4
V1-O1
V1-O3
1.8608(18)
2.2231(18)
1.579(2)
V1-O2
V1-O4
1.9379(17)
1.8524(17)
2.0853(19)
99.64(10)
154.56(8)
159.68(8)
82.34(7)
V1-O5
V1-N1
O4-V1-O3
O4-V1-O1
O1-V1-N1
O5-V1-O3
75.58(7)
O5-V1-O1
O1-V1-O2
O4-V1-N1
O2-V1-O3
104.53(8)
84.85(7)
171.90(9)
Catalytic oxidation reaction
The oxidation catalytic reactions were carried out under atmospheric
pressure in the glass flasks with condenser pipes in a water bath with
magnetic stirring. In a typical experiment, fixed amount of the catalysts
(complex 1 to 4) was dissolved in 3.00 mL of desired solvent. Then a
certain amount of styrene was added according to this order. At last, the
required amounts of H2O2 (30 % H2O2 solution) was added into the
solution. The formation of the main product is outlined in Scheme 2.
9

O
V complex
St
BzA
Scheme 2. Main product observed during the catalytic oxidation of styrene
For the products analysis, 0.03 g of methylbenzene (internal standard)
and 1.5 mL of diethyl ether (to extract the substrate and the organic
products from the reaction mixture) were added. The obtained mixtures
were stirred for 10 min and then a sample (0.2 µL) was taken from the
organic phase and analyzed by a GC equipped with a capillary column
and a flame ionization detector by the internal standard method. The
catalytic performance was evaluated in terms of the conversion of St
selectivity to the BzA and the turn over number (TON), according to the
following equations:
Stin - Stout
× 100
% St Conversion =
( 1 )
Stin
mols of BzA produced
mols of reacted St
% Selectivity to BzA =
× 100
( 2 )
mols of BzA produced
( 3 )
TON of BzA =
mols of catalyst
Results and Discussion
Synthesis
The hydrazones were synthesized by the reaction of equimolar
10

quantities of aldehydes with hydrazines in methanol. The complexes were
synthesized by reaction of ethanolic solution of the hydrazones with
VO(acac)2 and acetohydroxamic acid. The complexes were characterized
1
by elemental analysis, IR, UV-vis and H NMR spectra. Structures of the
complexes were further confirmed by X-ray crystallography.
Structural description of complexes 1-4
The molecular structures of the complexes 1-4 are shown in Figures
1-4, respectively. And molecular packing diagrams are shown in Figures
S1-S4. X-ray crystallography reveals that the complexes are similar
oxovanadium(V) compounds. It should be pointed out that the vanadium
in the starting materials is in Ⅴ(Ⅳ) oxidation state, but it appears to be
Ⅴ(Ⅴ) in compounds 1-4, indicating that it was oxidized by air since no
other oxidants existed during the reaction procedures.The difference
among the complexes is the variety of the hydrazone ligands. The
coordination sphere around the vanadium atoms is a distorted octahedral
configuration with a six-coordinated structure as a [VVO(ONO)(OO)]
type. The V atoms in the complexes are in octahedral coordination, with
the phenolate oxygen O1, imino nitrogen N1 and enolate oxygen O2 of
the hydrazone ligands, and the deprotonated hydroxyl oxygen (O7 for 1,
O5 for 2, O4 for 3 and 4) of the aha ligand defining the equatorial plane,
and with the carbonyl oxygen (O8 for 1, O4 for 2, O3 for 3 and 4) of the
11

aha ligand and one oxo oxygen (O8 for 1, O6 for 2, O5 for 3 and 4)
occupying the axial positions. The form of the hydrazone ligands is
consistent with the observed O2–C8 and N2–C8 bond lengths of
1.309(3) Å and 1.286(4) Å, respectively in 1, 1.316(3) Å and 1.295(4) Å
in 2, 1.319(6) Å and 1.298(7) Å in 3 and 1.298(3)Å and 1.304(3) Å in 4.
This is in agreement with the reported complexes containing the enolate
form of hydrazone ligands [44-46], whereas the O2–C8 bond is
considerably short for reported complexes with the coordinated keto form
of the hydrazone system. The acetohydroxamic serves as the bidentate
co-ligand to present the hydroxamate form. It is confirmed by the bond
lengths of C17–N4 is 1.324(4) Å for 1 and C17–N3 are 1.318(4) Å,
1.311(7) Å , 1.313(3) Å for 2, 3 and 4 ,while the bond lengths of C17–O6
is 1.251(3) Å for 1, C17–O4 is 1.239(4) Å for 2, C17–O3 are1.244(6) Å,
1.244(3) Å for 3 and 4 respectively, which are consistent with the
reported values of analogous complexes [1, 47] . The distances between V
atoms and the oxo oxygen are in the range of 1.57-1.59 Å, indicating they
are typical V=O bonds. The displacement of the V atoms from the
equatorial planes toward the axial oxo oxygen are 0.255(1) Å for 1,
0.272(1) Å for 2, 0.310(1) Å for 3, and 0.282(1) Å for 4. The coordinate
bond lengths in the complexes are comparable to each other, and also
comparable to those observed in other similar oxovanadium complexes
[48]. The distortion of the octahedral coordination can be observed by the
12

coordinate bond angles, ranging from 74.05(9) to 107.42(9)º (1), 74.78(9)
to 102.11(13)º (2), 74.66(16) to 104.15(17)º (3), and 74.52(7) to
104.53(8)º (4), for the perpendicular angles, and from 150.84(10) to
169.03(10)º (1), 156.69(11) to 171.13(12)º (2), 155.23(16) to 171.79(19)º
(3), and 154.56(8) to 171.90(9)º (4), for the diagonal angles. The ethanol
molecule of complex 4 is linked to the vanadium complex molecule
through an O−H···N hydrogen bond [O6−H6 = 0.82 Å, H6···N2 = 2.06 Å,
O6···N2 = 2.875(3) Å, O6−H6···N2 = 177.4°; symmetry code for i: 1/2 +
x, 3/2 – y, –1/2 + z].
Figure 1 A perspective view of the molecular structure of 1 with the atom labeling scheme. The
thermal ellipsoids are drawn at the 30% probability level.
13

Figure 2 A perspective view of the molecular structure of 2 with the atom labeling scheme. The
thermal ellipsoids are drawn at the 30% probability level.
Figure 3 A perspective view of the molecular structure of 3 with the atom labeling scheme. The
thermal ellipsoids are drawn at the 30% probability level.
14

Figure 4 A perspective view of the molecular structure of 4 with the atom labeling scheme. The
thermal ellipsoids are drawn at the 30% probability level. Hydrogen bond is show as a dashed line.
IR spectral studies
The IR spectra of the complexes are presented in the Fig. S5–S8
exhibiting weak and sharp bands in the region 3100–3250 cm–1, which
are assigned to the ν(N–H) vibrations. The broad and weak absorption
band centered at 3389 cm–1 in complex 4 is assigned to the ν(O-H)
vibration. The v(C=O) stretches are absent in the complexes, which is
consistent with the enolisation of the amide functionalities and
subsequent proton replacement by the vanadium atoms. The bands
appearing in the region 1260–1280 cm–1 are assigned to the ν(C–Oenolic
)
vibrations. The strong absorption bands at 1605 cm–1 in 1, 1606 cm–1 in 2,
1607 cm–1 in 3, and 1611 cm–1 in 4, are attributed to the ν(C=N) vibration
15

[49]. The bands observed at 973 cm–1 in 1, 955 cm–1 in 2, 966 cm–1 in 3,
and 971 cm–1 in 4, are assigned to the ν(V=O) stretches [50].
UV-Vis spectral studies
The UV-vis absorption spectra of complexes 1–4 in acetonitrile
solution are presented in the Fig. S5–S8. The spectral features of 1-4 are
quite similar. The lowest energytransition broad band is observed in
visible region at 420–425 and 431–436 nm for complexes 1–4, which is
attributed to the LMCT transition [51] as a charge transfer from a
p-orbital on the lone-pair of ligands oxygen atoms to the empty d-orbital
of the vanadium atom. The other strong band at 307 nm for 1, 333 nm for
2 and 3, 335 nm for 4 corresponds to the intraligand n→π* absorption
peak. The high energy absorptions at 218 nm, 223 nm and 267-294nm are
most likely due to a π→π*transition of conjugated system in ligands. [46]
Whereas the absence of the d-d transition band is indicative of the +5
oxidation state of V.
1H-NMR spectral studies
The 1H-NMR spectra in d6-DMSO at 300MHz of complexes are
shown in Fig. S5–S8. The singlet at δ = 13.91, 13.94, 13.96 and 14.08
ppm assignable to –NH and δ = 9.02, 9.07 and 9.10 ppm due to –CH=N–,
respectively. In addition, the methyl group at C-17 in aha ligand appears
16

as a singlet at δ = 2.00, 2.09, 2.10 and 2.11ppm (3H) and the singlets at δ
= 8.23-6.85 ppm assignable to ArH. A singlet at δ = 5.05 ppm(2H) for 1,
a singlet at δ = 3.81 ppm (3H) for 2 and a singlet at δ = 2.37 (3H) for 3
and 4 ,are ascribed to the –CH2, terminal –OCH3 and PhCH3,
respectively. The absence of a singlet from –OH confirms enolization
prior to complexation followed by deprotonation during complexation.
This is also evident from the X-ray crystal structure studies.
Catalytic activity
The effects of solvents on the St oxidation over complex 3 as catalyst
are investigated and results are shown in Figure 5. As we all known, the
solvent plays an important and sometimes decisive role in the catalytic
behavior of a catalyst. Thus, the effect of solvents, such as acetonitrile
(MeCN), ethanol (EtOH), methanol (MeOH), petroleum ether (PE), N,
N-dimethylformamide (DMF) and distilled water (H2O) on reactivity was
studied in current catalytic St oxidation system catalyzed by complex 3 in
the presence of H2O2. Blank experiment has showed that nearly no
product was detected without solvent. It was found that the vanadium
complex showed the highest reactivity only when the reaction was
performed in EtOH media (TON=534), which may be attributed to the
polarity of solvent, that can make different phases uniform to promote
mass transfer. This suggesting can be proved by using distilled water as
17

the solvent, in which, the react mixture is remained two phases and the
TON value was only 7. Although the conversion of St in MeOH is similar
to EtOH (about 40 %), the TON value is about half (284) of EtOH, which
means that more by-products were produced when the media was MeOH.
The reactivity was lower in the order of MeCN, DMF and PE with the
TON values of 124, 42 and 16, respectively. Among them, DMF has the
power of capturing free radicals, which may be the reason why lower
catalytic activity was shown in it, considering that the St oxidation is a
radical reaction.
Conv.%
Sel.%
500
TON
400
300
200
100
0
EtOH
MeOH
MeCN
DMF
PE
H2O
Solvent
Figure 5 Effect of solvent on the St oxidation. Reaction conditions: St (0.520 g, 5 mmol), H2O2
(0.57 g, 5 mmol), catalyst (0.0006 g), time (4 h), temperature (60 oC) and solvent (3 mL).
We explored the effect of the St to H2O2 molar ratio over complex 3
by keeping the amounts of St (0.7200 g, 9.170 mmol) and catalyst
o
(0.0006 g) in ethanol (3 mL) at 60 C for 4 h fixed. As shown in Fig. 6,
the amount of H2O2 has an interesting effect on the catalytic activity. The
18

TON and conversion increased with the St to H2O2 molar ratio to a
maximum value as 534 and 53 % at 1:1 and 2:1, respectively. After then,
they all decreased, which may be caused by the further oxidation of BzA
by H2O2, and the dilution of the reaction mixture by the presence of larger
amount of water molecules in excess H2O2 aqueous.
55
50
45
40
35
30
25
20
15
600
500
400
300
200
100
Cov.%
Sel.%
TON
3:1
2:1
1:1
1:2
1:3
n
/n
(styrene) (H2O2)
Figure 6 Effect of the styrene to H2O2 molar ratio on the St oxidation. Reaction conditions: St
(0.520 g, 5 mmol), catalyst (0.0006 g), time (4 h), temperature (60 oC) and ethanol (3 mL).
19

A
90
75
60
45
30
15
0
78℃
60℃
40℃
3
4
5
6
7
Time(h)
100
80
60
40
20
0
B
40℃
60℃
78℃
3
4
5
6
7
Time(h)
Figure 7 Effect of the temperature on the St oxidation. Reaction conditions: St (0.520 g, 5 mmol),
H2O2 (0.57 g, 5 mmol), catalyst (0.0006 g), ethanol (3 mL).
The effect of reaction temperatures on the conversion and selectivity
for the St oxidation catalyzed by complex 3 was studied and the results
are shown in Fig. 7. As can be seen, with the temperature increased from
o
40 to 78 C, the St conversion increased from 13 to 70%, but the
selectivity to BzA decreased from 66 to 14%. It is consistent with the fact
that the vinyl C-H bonds of St molecules are very active at a high
temperature. But more by-products produced when the reaction reacted at
the high temperature.
20

The effect of different catalysts on the St oxidation reactions were
o
carried out in 3 mL of ethanol for 4 h at 60 C with 1:1 molar ratio of St
to H2O2 and 0.0015 mmol catalysts. In the absence of any catalyst (Table
2), H2O2 alone was unable to oxidize St to a significant extent, indicating
that the reaction can occur only when a catalyst promoted it. Comparison
was made between complexes 1-4 (Table 2, entries 1-4), which
represented that the order of the catalytic activities was 3 >2 >1 >4,
which meant that complex 3 was the best catalyst for styrene oxidation
among the 1, 2, 4 and the starting material VO(acac)2. The reason why
different complexes exhibited different catalytic abilities is that the
ligands have caused the changes of the electronic states of center metal
which can provide active sites in the St oxidation. The high catalytic
ability of complex 3 may be attributed to the weak electron withdrawing
effect of the terminal group in hydrazone ligand which only containing
the benzyl group so that it is easier to provide active site of center metal
during the reaction. It is also the reason why complex 2 performed better
activity than 1. Complex 4 showed the lowest activity because of the
dissociative ethanol having an impeditive effect when the reaction reacted
in ethanol. We confirmed it by changing acetonitrile as the solvent.
Table 2 Effect of catalyst on the styrene oxidation. Reaction conditions: styrene (0.520 g, 5
mmol ), H2O2 ( 0.57 g, 5 mmol ), catalyst ( 0.0006 g ), time (4 h), temperature (60 oC) and ethanol
(3 mL).
21

Entry
Catalyst
Conv./%
Sel./%
TON
1
2
3
4
5
6
VO(aha)L1
VO(aha)L2
VO(aha)L3
VO(aha)L4·EtOH
VO(acac)2
-
53
48
42
43
50
26
25
31
39
27
25
2
424
497
534
381
401
-
Conclusions
In this work, four new complexes have been successfully synthesized
by the reaction of VO(acac)2 with the hydrazone and acetohydroxamic
acid in ethanol for the first time. The single-crystal X-ray diffraction
analyses reveal that the vanadium atoms are six-coordinate in the
complexes and in an octahedral environment. In the catalytic study of the
vanadium complex using H2O2 as oxidant for styrene oxidation, we found
that our four new oxovanadium (V) complexes can be considered as
potential catalysts, and the order of the catalytic activities is 3 >2 >1 >4,
which can be contributed to the difference of electronegativity of the
group in ligands. Parameters such as solvent, temperature and oxidant
concentration were changed and showed the different catalytic effects on
both activity and selectivity of the oxidative process. Under normal
conditions, St oxidation was carried out with excellent activity catalyzed
by the complexes 3 (TON of 667).
22

References：
[1] G. Romanowski, J. Kira, M. Wera, Journal of Molecular Catalysis A: Chemical
2014, 381,148-160.
[2] X. Yu, L. Xu, X. Yang, Y. Guo, K. Li, J. Hu, W. Li, F. Ma, Y. Guo, Applied
Surface Science 2008, 254, 4444–4451.
[3] J. Tong, X. Cai, H. Wang, Q. Zhang, Materials Research Bulletin 2014, 55,
205–211.
[4] Ulmann’s, Encyclopedia of Industrial Chemistry, fifth ed.,VCH, Weinheim, 1985,
pp. 469.
[5] E. T. Saka, I. Acar, Z. Biyiklio˘glu, H. Kantekin, I. Kani, Synthetic Metals 2013,
169, 12– 17.
[6] F. Adam, A. Iqbal, Chemical Engineering Journal 2011,171, 1379–1386.
[7] L. X. Zhang, Z. L. Hua, X. P. Dong, L. Li, H. R. Chen, J. L. Shi, Journal of
Molecular Catalysis A: Chemical 2007, 268, 155–162.
[8] M.R. Maurya, A.K. Chandrakar, S. Chand, Journal of Molecular Catalysis A 2007,
274, 192.
[9] M.R. Maurya, A.K. Chandrakar, S. Chand, Journal of Molecular Catalysis A 2007,
270, 225.
[10]V.K. Bansal, P.P. Thankachan, R. Prasad, Applied Catalysis A 2010, 381, 8.
[11] S. Sharma, S. Sinha, S. Chand, Industrial & Engineering Chemistry Research
2012, 51, 8806.
23

[12] W. Zhan, Y. Guo, Y. Wang, X. Liu, Y. Guo, Y. Wang, Z. Zhang, G. Lu, The
Journal of Physical Chemistry B 2007, 111, 12103.
[13] V. Hulea, E. Dumitriu, Applied Catalysis A 2004, 277, 99.
[14] S. Gómez, L.J. Garces, J. Villegas, R. Ghosh, O. Giraldo, S.L. Suib, Journal of
Catalysis 2005, 233, 60.
[15] F. Heshmatpour, S. Rayati, M. Afghan Hajiabbas, P. Abdolalian, B. Neumüller,
Polyhedron 2012, 31, 443.
[16] S.S. Kurek, P. Michorczyk, A.M. Balisz, Journal of Molecular Catalysis A 2003,
194, 237.
[17] J. Haber, M. Kłosowski, J. Połtowicz, Journal of Molecular Catalysis A:
Chemical 2003,201, 167–178.
[18] A. Dhakshinamoorthy, H. Garcia, Chem. Soc. Rev. 2012, 41, 5262.
[19] H. F. Yao, Y. Yang, H. Liu, F. G. Xi, E. Q. Gao, Journal of Molecular Catalysis A:
Chemical 2014, 394, 57–65.
[20] A.S. Tracey, G.R. Willsky, E.S. Takeuchi, Vanadium: Chemistry, Biochemistry,
Pharmacology, and Practical Applications, CRC Press, Boca Raton, FL, 2007
(Chapter 10).
[21] R.R. Eady, Coord. Chem. Rev. 2003, 237, 23.
[22] G. Romanowski, Journal of Molecular Catalysis A: Chemical 2013, 368– 369,
137– 144
[23] S. Rayati, F. Ashouri, C. R. Chimie 2012, 15, 679–687.
[24] R. Ando, S. Mori, M. Hayashi, T. Yagyu, M. Maeda, Inorg. Chim. Acta 2004,
24

357, 1177–1184.
[25] C. Bolm, Coord. Chem. Rev. 2003, 237, 245–256, and references therein.
[26] Y. Maeda, N. Kakiuchi, S. Matsumura, T. Nishimura, T. Kawamura, S. Uemura,
J.Org. Chem. 2002, 67, 6718–6724.
[27] Y. Maeda, N. Kakiuchi, S. Matsumura, T. Nishimura, T. Kawamura, S. Uemura,
Tetrahedron Lett. 2001, 42, 8877–8879.
[28] M.R. Maurya, A. Kumar, J. Mol. Catal. A: Chem. 2006, 250, 190–198.
[29] S. Rayati, N. Torabi, A. Ghaemi, S. Mohebbi, A. Wojtczak, A. Kozakiewicz,
Inorg.Chim. Acta 2008, 361, 1239–1248.
[30] S. Rayati, N. Sadeghzadeh, H.R. Khavasi, Inorg. Chem. Comm. 2007, 10,
1545–1548.
[31] M.R.Maurya, A.K. Chandrakar, S. Chand, J. Mol. Catal. A: Chem. 2007, 274,
192–201.
[32] M.R.Maurya, A.K. Chandrakar, S. Chand, J. Mol. Catal. A: Chem. 2007, 270,
225–235.
[33] N. Xing, L. T. Xu, F. Y. Bai, H. Shan, Y. H. Xing, Z. Shi, Inorganica Chimica
Acta 2014,409,360-366.
[34] S. T.Chew, K. M. Lo, S. K.Lee, M. P. Heng, W. Y. Teoh, K. S. Sim, K. W.Tan,
Eur. J. Med. Chem. 2014, 76, 397.
[35] R.Pal, V.Kumar, A. K.Gupta, V. Beniwal, Med. Chem. Res. 2014, 23, 3327.
[36] B. Shaabani, A. A.Khandar, H. Mobaiyen, N. Ramazani, S. S.Balula, L.Cunha
Silva, Polyhedron 2014, 80, 166.
25

[37] G.Murtaza, A.Badshah, M.Said, H.Khan, A.Khan, S.Khan, S.Siddiq, M. I.
Choudhary, J. Boudreau, F.-G. Fontaine, Dalton Trans. 2011, 40, 9202.
[38] A.-M.Li, J. Coord. Chem. 2014, 67, 2076.
[39] S.Rayati, M.Koliaei, F.Ashouri, S.Mohebbi, A.Wojtczak, A.Kozakiewicz,
Applied Catalysis A: General 2008, 346, 65–71.
[40] M. Zhang, D.-M. Xian, H.-H. Li, J.-C. Zhang, Z.-L. You, Aust. J. Chem. 2012,
65, 343.
[41] Bruker, SMART (Version 5.628) and SAINT (Version 6.02); Bruker AXS Inc:
Madison, Wisconsin, USA (1998).
[42] G.M. Sheldrick, SADABS Program for Empirical Absorption Correction of Area
Detector, University of Göttingen: Germany (1996).
[43] G.M. Sheldrick, SHELXTL V5.1. Software Reference Manual; Bruker AXS, Inc:
Madison, Wisconsin, USA (1997).
[44] H. Hosseini Monfared, Z. Kalantari, M.-A. Kamyabi, C. Janiak, Anorg. Allg.
Chem. 633 (2007) 1945.
[45] H. Hosseini Monfared, M. Nazari, P. Mayer, M.-A. Kamyabi, A. Erxleben, Z.
Asgari, Z. Naturforsch. 64b (2009) 409–414.
[46] H. H. Monfared, R. Bikas, P. Mayer, Inorganica Chimica Acta 2010, 363,
2574-2583.
[47] G. Romanowski, J. Kira, M. Wera, Polyhedron 2014, 67,529-539.
[48] (a) N.R. Sangeetha, V. Kavita, S. Wocadlo, J. Coord. Chem. 2000, 51, 55; (b) Y.
Zhao, X. Han, X.-X. Zhou, H.-H. Li, Z.-L. You, Chinese J. Inorg. Chem. 2013,
29, 867.
26

[49] Z.-L. You, D.-M. Xian, M. Zhang, CrystEngComm 2012, 4, 7133.
[50] J.-Q. Ren, Q.-Z. Jiao, Y.-N. Wang, F.-Y. Xu, X.-S. Cheng, Z.-L. You, Chinese J.
Inorg. Chem. 2014, 30, 640.
[51] R. Dinda, P. Sengupta, S. Ghosh, T.C.W. Mak, Inorg. Chem. 2002, 41,1684.
Declaration
It is not under consideration for publication elsewhere. Its publication is
approved by all authors and explicitly by the responsible authorities where the work
was carried out.
Appendix A. Supplementary data
CCDC 1472971 (1)，1472972 (2) , 1472973 (3) and 1472974 (4) contains the supplementary
crystallographic data for complexes 1- 4. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts /retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
Acknowledgements
We thank the support of this work by the grants of the National Natural Science
Foundation of China (No. 21306073) and the Basic research project of Key
Laboratory of Liaoning Province (No. LZ2015048) for financial assistance.
27

35