Synthesis, crystal structures, and catalytic properties of two oxidovanadium(V) complexes with tridentate Schiff bases

Article abstract of DOI:10.1134/S1070328417060045

Two new oxidovanadium(V) complexes, [VO₂L¹] (I) and [VO₂L²] (II), where L¹ and L² are the deprotonated forms of 4-methyl-2-[(2-morpholin-4-ylethylimino)methyl]phenol (HL¹) and 2-[(2-isopropylaminoethylimino) methyl]-4-trifluoromethoxyphenol (HL²), respectively, have been prepared and characterized by physico chemical methods and single crystal X-ray diffraction (CIF files CCDC nos. 1443671 (I), 1443672 (II)). The V atom in each complex is coordinated by the phenolate oxygen, imino nitrogen and amino nitrogen of the Schiff base ligand, and two oxo groups, forming trigonal-bipyramidal geometry. The oxidation of olefins with the complexes as catalyst was evaluated, which indicated that both complexes showed effective catalytic efficiency in oxidation of several aliphatic and aromatic substrates by using tert-butyl hydrogen peroxide as oxidant.

Full text of DOI:10.1134/S1070328417060045

ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2017, Vol. 43, No. 6, pp. 404–410. © Pleiades Publishing, Ltd., 2017.
Synthesis, Crystal Structures, and Catalytic Properties of Two
Oxidovanadium(V) Complexes with Tridentate Schiff Bases1
D. L. Penga, b
aKey Laboratory of Surface and Interface Science of Henan Province, School of Material and Chemical Engineering,
Zhengzhou University of Light Industry, Zhengzhou, 450001 P.R. China
bHenan Collaborative Innovation Center of Environmental Pollution Control and Ecological Restoration,
Zhengzhou University of Light Industry, Zhengzhou, 450001 P.R. China
e-mail: pengdonglai2015@sina.com
Received June 20, 2016
Abstract—Two new oxidovanadium(V) complexes, [VO2L1] (I) and [VO2L2] (II), where L1 and L2 are the
deprotonated forms of 4-methyl-2-[(2-morpholin-4-ylethylimino)methyl]phenol (HL1) and 2-[(2-isopro-
pylaminoethylimino)methyl]-4-trifluoromethoxyphenol (HL2), respectively, have been prepared and char-
acterized by physico chemical methods and single crystal X-ray diffraction (CIF files CCDC nos. 1443671
(I), 1443672 (II)). The V atom in each complex is coordinated by the phenolate oxygen, imino nitrogen and
amino nitrogen of the Schiff base ligand, and two oxo groups, forming trigonal-bipyramidal geometry. The
oxidation of olefins with the complexes as catalyst was evaluated, which indicated that both complexes
showed effective catalytic efficiency in oxidation of several aliphatic and aromatic substrates by using tert-
butyl hydrogen peroxide as oxidant.
Keywords: Schiff base, oxidovanadium complex, X-ray diffraction, catalytic property
DOI: 10.1134/S1070328417060045
INTRODUCTION
pylaminoethylimino)methyl]-4-trifluoromethoxy-
phenol (HL2), respectively, are presented.
The catalytic epoxidation of olefins has been a sub-
ject of growing interest in the production of chemicals
and fine chemicals since epoxides are key starting
materials for a wide variety of oily products [1–3].
Much work has been carried out to explore new and
efficient catalysts for these reactions. H2O2 has been
used as the first selected oxidant in these reactions
because of its environment-friendly characteristic.
The vanadium enzymes such as vanadium-nitroge-
nases and vanadate-dependent haloperoxidases, have
been found in nature [4–6]. In recent years, vanadium
complexes with various organic ligands have shown
interesting catalytic properties in many organic reac-
tions [7–10]. Schiff bases are a kind of versatile ligands
in coordination chemistry. The synthesis, characteri-
zation and reactivity studies of a number of vanadium
complexes with Schiff bases have been reported [11–
14]. Some of the complexes have shown interesting
catalytic properties [15–17]. In order to further study
the catalytic potentiality of vanadium complexes, in
this paper, two new oxidovanadium(V) complexes,
[VO2L1] (I) and [VO2L2] (II), where L1 and L2 are the
deprotonated form of 4-methyl-2-[(2-morpholin-4-
ylethylimino)methyl]phenol (HL1) and 2-[(2-isopro-
EXPERIMENTAL
Materials and methods. All the reagents and sol-
vents used in the synthesis were procured commer-
cially and used without subsequent purification.
Microanalyses (C, H, N) were performed using a Per-
kin-Elmer 2400 elemental analyzer. Infrared spectra
were carried out using the JASCO FT-IR model
420 spectrophotometer with KBr disk in the region
4000–400 cm–1. Electronic absorption spectra mea-
surement in acetonitrile was measured using a
Labda 900 spectrometer. 1H NMR spectra were mea-
sured in DMSO-d6 on Bruker 300 MHz spectrometer.
Synthesis of I. HL1 (0.248 g, 1.0 mmol) and
VO(Acac)2 (0.265 g, 1.0 mmol) were dissolved and
mixed in methanol (20 mL). The mixture was stirred
at room temperature for 30 min to give yellow solution.
After leaving the solution for a few days at room tem-
perature, fine yellow crystals were formed. The prod-
uct was filtered and washed with methanol. The yield
was 53%.
IR (KBr; νmax, cm–1): 1627 m ν(C=N), 950 s and
853 s ν(V=O). Absorption spectrum in acetonitrile
1
The article is published in the original.
404

SYNTHESIS, CRYSTAL STRUCTURES, AND CATALYTIC PROPERTIES
405
(λmax, nm (ε, L mol–1 cm–1)): 267 (15130), 322 (8210),
solved by direct methods and refined by full-matrix
least-squares analysis using anisotropic thermal
parameters for non-H atoms with the SHELXTL pro-
gram [19]. The amino hydrogen atom in complex II
was located from a difference Fourier map and refined
isotropically with N–H distance restrained to
0.90(1) Å. The remaining H atoms were calculated at
idealized positions and refined with the riding models.
Crystallographic data for the compounds are summa-
rized in Table 1. Selected bond lengths and angles are
given in Table 2.
Supplementary material for structures has been
deposited with the Cambridge Crystallographic Data
Centre (CCDC nos. 1443671 (I), 1443672 (II);
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.
ac.uk).
Catalytic epoxidation of olefins. Catalytic experi-
ments were carried out in a 50 mL glass round-bottom
flask fitted with a reflux condenser and placed in an oil
bath at prearranged temperature under continuous
stirring. The oxidation was carried out as follows. The
complexes (0.032 mmol) were dissolved 10 mL of 1,2-
dichloroethane. Then alkene (10 mmol) was added to
the reaction mixture and TBHP (30 mmol) was added.
The reaction mixture was refluxed for 1 h. The reac-
tion products were monitored at periodic time inter-
vals using gas chromatography. The oxidation prod-
ucts were identified by comparison with authentic
samples (retention times in GC).
413 (2350).
For C14H19N2O4V
anal. calcd., %:
Found, %:
C, 50.92;
C, 50.71;
H, 5.80;
H, 5.89;
N, 8.48.
N, 8.37.
Synthesis of II. HL2 (0.290 g, 1.0 mmol) and
VO(Acac)2 (0.265 g, 1.0 mmol) were dissolved and
mixed in methanol (20 mL). The mixture was stirred
at room temperature for 30 min to give yellow solution.
After leaving the solution for a few days at room tem-
perature, fine yellow crystals were formed. The prod-
uct was filtered and washed with methanol. The yield
was 65%.
IR (KBr; νmax, cm–1): 3111 w ν(NH), 1645 m,
ν(C=N), 950 s and 859 s ν(V=O). Absorption spec-
trum in acetonitrile (λmax, nm (ε, L mol–1 cm–1)): 270
(14320), 325 (9780), 425 (2160).
For C13H16N2F3O4V
anal. calcd., %:
Found, %:
C, 41.95;
C, 42.10;
H, 4.33;
H, 4.41;
N, 7.53.
N, 7.45.
X-ray structure determination. X-ray data for the
compounds were collected on a Bruker SMART
APEX II diffractometer equipped with graphite-
monochromated MoKα radiation (λ = 0.71073 Å). A
preliminary orientation matrix and cell parameters
were determined from three sets of ω scans at different
starting angles. Data frames were obtained at scan
intervals of 0.5° with an exposure time of 10 s frame–1.
RESULTS AND DISCUSSION
The Schiff bases were reacted with VO(Acac)2 in
The reflection data were corrected for Lorentz and methanol followed by slow vaporization to generate
polarization factors. Absorption corrections were car- fine yellow crystalline complexes, as shown in
ried out using SADABS [18]. The structures were Scheme 1:
O
N
N
N
V
+ VO(Acac)2
N
O
OH
O
O
O
(I)
H
N
O
O
F3C
N
F3C
N
V
+ VO(Acac)2
H
N
OH
O
O
O
(II)
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406
Table 1. Crystallographic data and refinement parameters for complexes I and II
Value
PENG
Parameter
I
II
Formula weight
330.25
0.15 × 0.13 × 0.13
298(2)
372.22
0.20 × 0.20 × 0.17
298(2)
Crystal size, mm
Temperature, °C
Crystal system
Monoclinic
P21/c
Orthorhombic
Pca21
Space group
a, Å
21.017(2)
6.0710(6)
11.4094(11)
97.855(2)
1442.1(2)
4
10.995(2)
b, Å
14.595(3)
c, Å
10.155(2)
β, deg
V, Å
1629.7(6)
Z
4
calcd, g cm–3
1.521
1.517
ρ
μ(MoKα), mm–1
0.705
0.659
F(000)
688
7208
2438
760
8095
2261
Number of measured reflections
Number of observations
(I > 2σ(I))
Unique reflections
Refinement parameters
Number of restraints
R1, wR2 (I > 2σ(I))*
R1, wR2 (all data)*
2685
191
2416
214
0
2
0.0277, 0.0790
0.0310, 0.0811
1.110
0.0437, 0.1135
0.0472, 0.1193
1.084
Goodness of fit of F2
2
2
2
2 1/2
2
* R = ∑||F | – |F ||/∑|F |, wR = [∑w(
–
) /∑w( ) ]
.
Fo
Fc
Fo
1
o
c
o
2
Crystals of the complexes are stabilized in air at V atom forming a five- and a sixmembered chelate
room temperature, and soluble in methanol, ethanol, rings with bite angles of 75.15(5)° and 83.15(5)° for I,
and acetonitrile.
and 77.50(11)° and 83.38(12)° for II, which are similar
to those observed in similar vanadium complexes [20,
21]. The displacement of the V atoms from the basal
mean planes toward the phenolate oxygen are
0.132(2) Å for I and 0.086(2) Å for II. The V–O, V–N,
and V=O bonds in the complexes are within normal
ranges and similar to those observed in oxidovana-
dium complexes [22, 23].
Molecular structures of complexes I and II are
shown in Fig. 1. The Schiff bases coordinate to the
V atoms through the phenolate oxygen, imino nitro-
gen, and amino nitrogen. The coordination geometry
around the V atom can be described as distorted trigo-
nal bipyramidal with the imino nitrogen of the Schiff
base ligand and two oxo groups defining the basal
plane, and with the phenolate oxygen and the amino
In the crystal structure of complex I, molecules are
nitrogen of the Schiff base ligand occupying the axial linked through C–H···O hydrogen bonds to form
positions. The Schiff base ligand coordinates to the dimers along the x axis. The dimers are futher linked
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SYNTHESIS, CRYSTAL STRUCTURES, AND CATALYTIC PROPERTIES
Table 2. Selected bond lengths (Å) and angles (deg) for complexes I and II
407
Bond
d, Å
Bond
d, Å
I
V(1)–O(1)
V(1)–O(4)
V(1)–N(2)
1.9085(13)
1.6248(14)
2.1594(14)
V(1)–O(3)
V(1)–N(1)
1.6091(13)
2.1419(13)
II
V(1)–O(1)
V(1)–O(3)
V(1)–N(2)
1.933(3)
1.622(3)
2.170(3)
V(1)–O(2)
V(1)–N(1)
1.626(3)
2.138(3)
Angle
ω, deg
Angle
ω, deg
I
O(3)V(1)O(4)
O(4)V(1)O(1)
O(4)V(1)N(1)
O(3)V(1)N(2)
O(1)V(1)N(2)
109.42(8)
98.80(7)
132.07(6)
94.81(6)
156.62(5)
O(3)V(1)O(1)
O(3)V(1)N(1)
O(1)V(1)N(1)
O(4)V(1)N(2)
N(1)V(1)N(2)
102.78(7)
116.83(7)
83.15(5)
89.57(6)
75.15(5)
II
O(3)V(1)O(2)
O(2)V(1)O(1)
O(2)V(1)N(1)
O(3)V(1)N(2)
O(1)V(1)N(2)
110.28(18)
95.98(15)
131.08(16)
94.51(14)
159.65(13)
O(3)V(1)O(1)
O(3)V(1)N(1)
O(1)V(1)N(1)
O(2)V(1)N(2)
N(1)V(1)N(2)
100.60(15)
117.93(15)
83.38(12)
91.42(14)
77.50(11)
Table 3. Hydrogen bond distances (Å) and bond angles (deg) for complexes I and II*
Distance, Å
D–H···A
Angle DHA, deg
137(4)
D–H
H···A
D···A
I
C(8)–H(8)···O(1)i
0.93
2.48(3)
3.222(3)
C(11)–H(11A)···O(4)
C(12)–(H12B)···O(2)ii
0.97
0.97
2.47(3)
2.57(3)
2.981(3)
3.483(4)
113(3)
156(4)
II
N(2)–H(2)···O(2)iii
C(7)–H(7)···O(1)iv
C(7)–H(7)···O(3)iv
C(8)–H(8A)···O(1)iii
0.90
0.93
0.93
0.97
2.03(2)
2.896(3)
3.224(3)
3.379(3)
3.422(4)
3.182(3)
161(3)
130(4)
154(4)
151(5)
123(4)
2.54(3)
2.52(3)
2.54(3)
C(12)–H(12C)···O(2)
0.96
2.55(2)
i
ii
iii
iv
* Symmetry codes: x, 1/2 – y, –1/2 + z; 1 – x, 1/2 + y, 1/2 – z; 1/2 – x, y, 1/2 + z; –1/2 + x, 1 – y, z.
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408
PENG
(a)
C(7)
C(5)
C(6)
C(8)
C(9)
C(10)
C(11)
C(12)
N(1)
C(1)
C(4)
O(2)
V(1)
N(2)
C(13)
C(14)
C(2)
C(3)
O(1)
O(4)
O(3)
(b)
C(13)
F(1)
N(1)
C(7)
C(8)
C(6)
C(9)
N(2)
F(3)
C(1)
O(4)
C(5)
C(11)
C(10)
F(2)
C(2)
V(1)
C(4)
O(3)
O(2)
O(1)
C(3)
C(12)
Fig. 1. Molecular structure of complex I (a) and II (b) with 30% probability thermal ellipsoids.
through C–H···O hydrogen bonds to form one-
dimensional bands along the z axis (Table 3, Fig. 2a).
In the crystal structure of complex II, molecules are
linked through C–H···O hydrogen bonds, to form
one-dimensional bands along the x axis (Table 3,
Fig. 2b).
In the electronic spectra of the complexes, the
bands at about 420 nm are attributed to ligand-to-
metal charge transfer [26]. The bands at about 325 nm
are assigned to n–π* transitions [27]. The
intense bands at about 270 nm are assigned to intra-
ligand π–π* transitions [27].
The weak and sharp band at 3111 cm–1 for II is
assigned to the ν(NH) vibration. The V=O stretching
modes occur as a pair of sharp strong bands at 950 and
853 cm–1 for I and 950 and 859 cm–1 for II, which are
assigned to the antisymmetric and symmetric stretch-
ing modes of the dioxovanadium(V) moieties [24].
The strong bands indicative of the C=N groups in the
complexes are observed at 1627 cm–1 for I and
1645 cm–1 for II [25]. The new weak peaks observed in
the range 400–800 cm–1 may be attributed to the V–O
and V–N vibrations in the complexes. The IR spectra
of the complexes are similar to each other, indicating
the complexes are similar structures, as evidenced by
the single crystal X-ray determination.
The catalytic results are listed in Table 4. Effective
epoxide yields and 100% selectivity were observed for
all aliphatic and aromatic substrates. In general, oxi-
dation of aromatic substrates gave the corresponding
epoxides in over 90% yields, while in the oxidation of
aliphatic substrates, the conversion is lower than 82%.
Based on this consideration, it can be observed that
the isolated double bonds are less reactive than the
conjugated ones. For the aliphatic substrates, the con-
version for the chloro-substituted methyloxirane is
higher than the methyl or ethyl substituted species. For
the aromatic substrates, the same phenomenon was
observed. Thus, it may be concluded that the com-
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SYNTHESIS, CRYSTAL STRUCTURES, AND CATALYTIC PROPERTIES
409
Table 4. Detailed information of the catalytic oxidation of olefins catalyzed by the complexes*
Conversion, %**
Substrate
Product
I
II
O
69
73
O
63
82
65
78
Cl
Cl
O
O
80
91
85
88
O
O
93
98
92
94
Cl
Cl
O
O
Cl
Cl
95
97
Cl
Cl
* The molar ratio of catalyst : substrate : TBHP is 1 : 300 : 1000. The reactions were performed in mixture of CH OH–CH Cl (V : V =
3
2
2
6 : 4; 1.5 mL).
** The GC conversion (%) was measured relative to the starting substrate after 1 h.
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PENG
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complexes with similar tridentate Schiff base ligands
have been synthesized and characterized by infrared
and electronic spectra, as well as single crystal X-ray
determination. The Schiff base ligands coordinate to
the V atoms through the phenolate oxygen, imino
nitrogen and amino nitrogen atoms. The V atoms in
the complexes are coordinated by the Schiff base
ligands and two oxo groups, forming trigonal-bipyra-
midal geometry. The complexes are effective catalyst
for the oxidation of various aliphatic and aromatic ole-
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