Synthesis, crystal structure, and catalytic epoxidation of a new oxovanadium(V) complex with benzohydrazone and benzohydroxamate mixed-ligands

Article abstract of DOI:10.1134/S1070328415110093

Synthesis, characterization, and catalytic properties for styrene epoxidation of a new oxovanadium(V) complex [VOLL′] · CH₃OH (I) derived from N′-(3-bromo-5-chloro-2-hydroxybenzylidene)-2-hydroxybenzohydrazide (H₂L) and benzohydroxam

Full text of DOI:10.1134/S1070328415110093

ISSN 1070ꢀ3284, Russian Journal of Coordination Chemistry, 2015, Vol. 41, No. 12, pp. 792–797. © Pleiades Publishing, Ltd., 2015.
Synthesis, Crystal Structure, and Catalytic Epoxidation
of a New Oxovanadium(V) Complex with Benzohydrazone
and Benzohydroxamate MixedꢀLigands1
F. Y. Wei
Department of Chemistry and Chemical Engineering, Baoji University of Arts and Sciences, Baoji, 721013 P.R. China
eꢀmail: weifenyan78@163.com
Received March 23, 2015
Abstract
um(V) complex [VOLL
droxybenzohydrazide (H2L) and benzohydroxamic acid (HL') are reported. Complex
elemental analyses, IR, UVꢀVis spectra and molar conductivity. Single crystal Xꢀray structure of complex
has been determined (CIF file CCDC no. 1034615). The V atom in the structure is in an octahedral coordiꢀ
nation. In the crystal structure, molecules are linked through intermolecular O–H⋅⋅⋅O, O–H⋅⋅⋅Br and N–
⋅⋅⋅O hydrogen bonds, to form 2D layers. Catalytic property for epoxidation of styrene by the complex using
—
Synthesis, characterization, and catalytic properties for styrene epoxidation of a new oxovanadiꢀ
CH3OH ( ) derived from N'ꢀ(3ꢀbromoꢀ5ꢀchloroꢀ2ꢀhydroxybenzylidene)ꢀ2ꢀhyꢀ
was characterized by
']
⋅
I
I
I
H
PhIO and NaOCl as oxidant has been studied.
DOI: 10.1134/S1070328415110093
1
INTRODUCTION
EXPERIMENTAL
Hydrazones are very popular ligands because they
Material and measurements. All chemicals and solꢀ
vents used for the synthesis are of analytical grade. 3ꢀBroꢀ
moꢀ5ꢀchlorosalicylaldehyde, 2ꢀhydroxybenzohydraziꢀ
de, benzohydroxamic acid, VO(Fcac)2, styrene and styꢀ
rene oxide were purchased from Aldrich and used withꢀ
out further purification. Iodosylbenzene (PhIO) was preꢀ
pared by the hydrolysis of iodobenzene diacetate. Infraꢀ
red spectra were recorded as KBr pellets on a JASCO
FTꢀIR 4100 spectrophotometer. Elemental analyses (C,
H, N) were carried out using a Perkin Elmer 2400 II eleꢀ
mental analyser. Electronic spectra were recorded on a
Perkin Elmer Lambda 40 (UV/Vis) spectrometer in aceꢀ
tonitrile. GC analysis was performed with Agilent 6890N
efficiently act as chelates generating a rich variety of coꢀ
ordination compounds, ranging from mononuclear to
polynuclear species. In recent years, a great number of
complexes with hydrazones have been reported, showꢀ
ing interesting structures and excellent properties, such
as catalytic [1–3], magnetic [4–6], and biological [7–
9], etc. Vanadium complexes with hydrazones are often
described as good epoxidation catalysts [10–13]. The
method is mild and is an environment friendly proꢀ
cess. As a further study of the catalytic epoxidation of
vanadium complexes, in this study, the synthesis,
characterization, crystal structure and catalytic epoxiꢀ
dation property of a new oxovanadium(V) complex,
Network GC systems. Molar conductivity of complex
I
in acetonitrile was measured with a DDSꢀ11A molar
conductivity meter.
[VOLL
'
] CH3OH (I), derived from the benzohydraꢀ
⋅
Synthesis of H2L. The yellow crystalline product of
the benzohydrazone ligand H2L was prepared by reaction
of equimolar quantities of 3ꢀbromoꢀ5ꢀchlorosalicylaldeꢀ
hyde (1.0 mmol, 0.235 g) with 2ꢀhydroxybenzohydrazide
(1.0 mmol, 0.152 g) in methanol and subsequent evapoꢀ
ration of the solvent. The yield was 91%.
zone ligand N'ꢀ(3ꢀbromoꢀ5ꢀchloroꢀ2ꢀhydroxybenꢀ
zylidene)ꢀ2ꢀhydroxybenzohydrazide (H2L) and benꢀ
zohydroxamic acid (HL'), are reported.
H
N
, cm–1): 1647 s
, nm (ε × 103, L mol–1 cm–1)): 240
ν
(C=O), 1614 s
Cl
IR data (KBr;
(C=N). UV (
(2.89), 295 (4.05), 308 (3.31), 340 (2.71).
ν
N
ν
λ
O
OH
OH
Br
For C14H10N2O3ClBr
(H2L)
anal. calcd., %:
Found, %:
C, 45.5;
C, 45.3;
H, 2.7;
H, 2.8;
N, 7.6.
N, 7.7.
1
The article is published in the original.
792

SYNTHESIS, CRYSTAL STRUCTURE, AND CATALYTIC EPOXIDATION
793
Table 1. Crystallographic data and experimental details for
complex
Synthesis of complex I. The appropriate quantity of
solid benzohydrazone ligand H2L (0.5 mmol, 0.184 g)
was dissolved in dry methanol (20 mL). A solution of
VO(Acac)2 (0.5 mmol, 0.133 g) in dry methanol (15 mL)
was added to this solution followed by the addition of
benzohydroxamic acid (0.5 mmol, 0.068 g) in dry
methanol (15 mL). The mixture was refluxed for 1 h.
The resulting brown solution was then filtered off and
the filtrate was left undisturbed. After a week fine deep
brown block shaped Xꢀray diffraction quality single
crystals separated out. They were filtered off, washed
with methanol and dried in vacuum over anhydrous
CaCl2. The yield was 53%.
I
Parameter
Value
Formula weight
Crystal size, mm
Crystal system
Space group
602.7
0.27
0.27
×
×
0.20
Triclinic
P
1
a
, Å
, Å
7.4392(7)
b
13.3602(12)
13.4119(12)
113.425(2)
93.809(3)
103.064(2)
1173.1(2)
2
c
, Å
, deg
, deg
, deg
IR data (KBr; ν
ν(C=N), 969 m,
, cm–1): 3454 br. m,
(V=O). UV (
ν(O–H), 1608 s
, nm (ε × 103,
α
ν
λ
L mol–1 cm–1)): 225 (7.56), 270 (6.54), 347 (3.61),
445 (2.21).
β
γ
V
Z
, Å3
For C22H18N3O7ClBrV
anal. calcd., %:
Found, %:
C, 43.8;
C, 44.0;
H, 3.0;
H, 2.9;
N, 7.0.
N, 6.9.
ρcalcd, mg cm–3
1.706
μ(MoK
), mm–1
2.289
α
Xꢀray structure determination. Intensity data of
complex were collected at 298(2) K on a Bruker
Smart 1000 CCD diffractometer with graphiteꢀmonoꢀ
chromated Mo radiation ( = 0.71073 ). A suitꢀ
able crystal was affixed to the end of a glass fiber using
silicone grease and transferred to the goniostat. The
unit cell parameters were obtained from SAINT; abꢀ
sorption corrections were performed with SADABS
F
(000)
604
I
Number of measured reflections
10418
K
λ
Å
α
Number of observations (
I
> 2σ(I
))
4107
Unique reflections
2485
Parameters refinement
Number of restraints
322
7
[14]. Structure of complex I was solved by the direct
method and refined by a fullꢀmatrix leastꢀsquares
method on F2 using the SHELXTL crystallographic
software package [15]. All the nonꢀhydrogen atoms are
refined anisotropically. The hydrogen atoms on the
carbon atoms were included in fixed calculated posiꢀ
tions, whereas the hydrogen atom of the amino group
was located in a difference Fourier map and refined as
riding on its N atom. Crystal data for the complex are
summarized in Table 1. Selected bond lengths and anꢀ
gles of the complex are given in Table 2.
R1
,
,
wR2
(
I
> 2
σ
(
I
))*
0.0479, 0.0811
0.1083, 0.0986
1.019
R1
wR2 (all data)*
Goodness of fit of F2
Largest difference peak and hole,
e
Å–3 0.383, –0.306
2
2 2
2 2 1/2
* R = Σ||F | – |F ||/Σ|F |, wR = [Σw(F – F ) /Σw(F ) ]
.
1
o
c
o
2
o
c
o
rene epoxide quantified by the internal standard methꢀ
od (chlorobenzene). Styrene oxide was used as stanꢀ
dard sample in GC analysis. All other products detectꢀ
Supplementary material for structure I has been deꢀ
posited with the Cambridge Crystallographic Data Cenꢀ
tre (CCDC no. 1034615; deposit@ccdc.cam.ac.uk or
http://www.ccdc.cam.ac.uk).
ed by GC were mentioned as others. For complex I the
reaction time for maximum epoxide yield was deterꢀ
mined by withdrawing periodically 0.10 mL aliquots
from the reaction mixture and this time was used to
monitor the efficiency of the catalyst on performing at
least two independent experiments. Blank experiꢀ
ments with each oxidant and using the same experiꢀ
mental conditions except catalyst were also perꢀ
formed.
General method for styrene epoxidation. The epoxiꢀ
dation reactions were carried out at room temperature
in acetonitrile under nitrogen atmosphere with conꢀ
stant stirring. The composition of the reaction mixture
was 2.00 mmol of styrene, 2.00 mmol of chlorobenꢀ
zene (internal standard), 0.10 mmol of the mangaꢀ
nese(III) complex (catalyst) and 2.00 mmol iodosylꢀ
benzene or sodium hypochlorite (oxidant) in 5.00 mL
acetonitrile. When the oxidant was sodium hypochloꢀ
rite, the solution was buffered to pH 11.2 with
NaH2PO4 and NaOH. The composition of reaction
RESULTS AND DISCUSSION
The tridentate benzohydrazone H2L was easily preꢀ
medium was determined by GC with styrene and styꢀ pared from the reaction between 3ꢀbromoꢀ5ꢀchloroꢀ
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 41
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2015

794
WEI
Table 2. Selected bond lengths (Å) and angles (deg) for complex
I
Bond
Angle
d
, Å
Bond
Angle
d, Å
V(1)–O(1)
V(1)–O(4)
V(1)–O(6)
1.909(3)
2.204(3)
1.572(3)
V(1)–O(2)
V(1)–O(5)
V(1)–N(1)
1.961(3)
1.858(2)
2.084(3)
ω
, deg
ω
, deg
O(6)V(1)O(5)
O(5)V(1)O(1)
O(5)V(1)O(2)
O(6)V(1)N(1)
O(1)V(1)N(1)
O(6)V(1)O(4)
O(2)V(1)O(4)
N(1)V(1)O(4)
93.47(13)
103.82(12)
93.94(11)
97.65(13)
83.91(12)
168.50(12)
81.99(11)
93.80(11)
O(6)V(1)O(1)
O(6)V(1)O(2)
O(1)V(1)O(2)
O(5)V(1)N(1)
O(2)V(1)N(1)
O(5)V(1)O(4)
O(1)V(1)O(4)
99.19(14)
100.03(14)
152.88(12)
165.30(12)
74.72(12)
75.07(11)
82.99(11)
salicylaldehyde and 2ꢀhydroxybenzohydrazide in absent in the spectrum of complex I, and new C–O
stretch appeared at 1260 cm–1. This suggests occurꢀ
rence of ketoꢀimine tautomerization of the ligand durꢀ
methanol with 1 : 1 stoichiometric ratio. Reaction of
VO(Acac)2 with H2L and benzohydroxamic acid in a
molar ratio of 1 : 1 : 1 in methanol, followed by slow
ing complexation. The
at 1614 cm–1 in the free benzohydrazone ligand shifted
to 1608 cm–1 for complex
upon coordination to the
ν
(C=N) absorption observed
evaporation, affords the single crystals of I. During the
synthesis performed under aerobic conditions, the reꢀ
action system exhibited an obvious color change from
light to deep brown. This suggest the occurrence of oxꢀ
I
V atom. The weak peaks in the low wave numbers at
492 and 589 cm–1 may be attributed to V–O and V–N
bonds in the complex. The electronic spectral data for
the complex in acetonitrile were recorded in the range
idation process (V(IV)
→
V(V)) induced by the oxygen
in air. Crystals of the complex are stable in air. The
molar conductivity of the complex in acetonitrile is
of 200–800 nm. UVꢀVis spectra of H2L and complex
I
15
–1 cm2 mol–1, indicating the nonꢀelectronic naꢀ
Ω
are shown in Fig. 1. The intense absorption bands at
240 nm for H2L and 225 nm for the complex may be
assigned to intraꢀligand π → π* transitions. The abꢀ
ture [16]. The infrared spectrum of the complex was
recorded within the 4000–400 cm–1 region. The benꢀ
zohydrazone ligand has stretching bands attributed to
C=O, C=N, C–OH, and NH at 1647, 1614, 1163 and
1221, and 3241 cm–1, respectively. The complex exꢀ
hibits typical bands at 969 cm–1, which is assigned to
sorption band centered at 445 nm in complex
assigned to the ligandꢀtoꢀmetal charge transfer transiꢀ
tion. The remaining absorption bands can be assigned
to the → π* transitions.
I may be
n
An ORTEP representation of the complex with atꢀ
om numbering scheme is depicted in Fig. 2. Xꢀray
crystallography reveals that the asymmetric unit of the
complex contains a mononuclear oxovanadium(V)
species and a methanol molecule. The V centre is six
coordinated by three donor atoms (NO2) of the coorꢀ
dinated benzohydrazone ligand L, two oxygen atoms
of the coordinated benzohyroxamate ligand, and one
oxo oxygen atom. In the octahedral coordination,
O(4) and O(6) are the axial ligand atoms, and O(1),
O(2), N(1), and O(5) form the equatorial plane. The
coordination environment of the V atom is slightly
distorted, as evidenced from the bond lengths and anꢀ
gles. In the equatorial plane, the metal–ligand bond
distance involving the imine nitrogen (V(1)–N(1)
the V=O vibration [17]. The band due to ν(C=O) was
1.00
0.75
H2L
0.50
Complex
I
0.25
0
2.084(3)
oxygens (V(1)–O(1) 1.909(3), V(1)–O(2) 1.961(3),
V(1)–O(5) 1.858(2) ). As expected due to Jahn–
Teller distortion, the bond distances involving the axial
donor atoms (V(1)–O(4) 2.204(3), V(1)–O(6)
Å is longer than the bond lengths involving
250 300 350 400 450 500 550 600
Wavelength, nm
Å
Fig. 1. UVꢀVis spectra of H L and complex I.
2
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 41
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SYNTHESIS, CRYSTAL STRUCTURE, AND CATALYTIC EPOXIDATION
795
C(12)
C(11)
C(13)
C(14)
C(9)
C(8)
C(10)
O(3)
O(2)
O(5)
N(3)
C(15)
N(2)
C(22)
O(6)
N(1)
C(16)
C(7)
V(1)
C(17)
C(21)
O(4)
O(7)
C(1)
C(20)
O(1)
C(18)
C(19)
C(2)
C(6)
C(3)
Br(1)
C(5)
Cl(1)
C(4)
Fig. 2. A perspective view of the molecular structure of complex
I with atom labeling scheme. Thermal ellipsoids are drawn at the
30% probability level. Hydrogen bond is shown as a dashed line.
1.572(3)
bond lengths involving the equatorial atoms. The trans
angles (152.9(1) , 165.3(1) , and 168.5(1) ) and the
cis angles (74.7(1)°–103.8(1) ) deviate much from the
Å
) significantly longer or shorter than the
Epoxidation of styrene was carried out at room
temperature with complex , as the catalyst and PhIO
or NaOCl as the oxidant. The brown solution containꢀ
ing complex and the substrate was intensified after
I
°
°
°
°
I
ideal values. The coordinate bond values are in agreeꢀ
ment with those observed in vanadium(V) complexes
with hydrazones [18, 19]. The average deviation
the addition of oxidant indicating the formation of
oxoꢀmetallic intermediates of the catalyst. After comꢀ
pletion of oxidation reaction of the alkene, the soluꢀ
tion regains its initial color which suggests that the reꢀ
generation of the catalyst takes place. The percentage
of conversion of styrene, selectivity for styrene oxide,
(0.0597
dplacement (0.248
Å
) of the equatorial donor atoms and the disꢀ
Å
) of the metal center from the
leastꢀsquares plane defined by the equatorial donor atꢀ
oms indicates that the NO3 cavity affords an almost
perfect plane to the metal center. The benzohydrazone
ligand is approximate planar with dihedral angel beꢀ
yield of styrene oxide for complex I and reaction time
to obtain maximum yield using both oxidants are listed
in Table 3. The data reveal that the complex as a cataꢀ
lyst converts styrene efficiently in the presence of both
oxidants. The catalyst is selective towards the formaꢀ
tion of styrene epoxide despite of the formation of byꢀ
products which have been identified by GCꢀMS as
benzaldehyde, phenylacetaldehyde, styrene epoxide
tween the two benzene rings of 2.0(5)
In the crystal structure of , mononuclear oxovanaꢀ
dium complex molecules are linked by methanol moꢀ
lecules through intermolecular O(3)–H(3
⋅⋅⋅O(6)i,
O(7)–H(7)⋅⋅⋅O(1)ii, O(7)–H(7)⋅⋅⋅Br(1)ii, and N(3)–
H(3)⋅⋅⋅O(7)iii hydrogen bonds (O(3)–H(3
) 0.82,
, O(3)–
; O(7)–H(7) 0.82, H(7)⋅⋅⋅O(1)ii
, O(7)–H(7)⋅⋅⋅O(1)ii
O(7)–H(7) 0.82, H(7)⋅⋅⋅Br(1)ii 2.84,
O(7)⋅⋅⋅Br(1)ii 3.385(4) , O(7)–H(7)⋅⋅⋅Br(1)ii 126
N(3)–H(3) 0.90(1), 1.89(2),
H(3)⋅⋅⋅O(7)iii
N(3)⋅⋅⋅O(7)iii 2.742(5) N(3)–H(3)⋅⋅⋅O(7)iii
159(4) , 1 – , 2 –
; symmetry codes: i – ; ii 1 –
1 – , 2 – ) to form 2D layers parallel to
iii x, 1 +
the xy plane (Fig. 3).
°.
I
A)
derivative, alcohols, etc. When the reactions are carꢀ
A
Å
ried out with PhIO, styrene conversions are 95%. With
NaOCl as oxidant, styrene conversion dropped to
82%. It is evident that PhIO acts as a better oxidant
with respect to both styrene conversion and styrene
epoxide selectivity.
H(3
A
)
)
⋅⋅⋅O(6)i 2.59, O(3)⋅⋅⋅O(6)i 3.088(4)
⋅⋅⋅O(6)i 121
H(3A
°
2.19, O(7)⋅⋅⋅O(1)ii 2.974(4)
Å
160°;
Å
°;
Å,
ACKNOWLEDGMENTS
°
x
y
z
x,
We acknowledge the Education Office of Shanxi
Province (project no. 11JK0601) and the Natural Sciꢀ
y
z;
y, z
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 41
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2015

796
WEI
x
z
0
y
Fig. 3. Molecular packing diagram of complex
I
, viewed along the
x
axis direction. Hydrogen bonds are shown as dashed lines.
Table 3. Epoxidation of styrene catalyzed by complex
I
Selectivity, %
Time, h
Oxidant
Conversion, %
Epoxide yield, %
epoxide
other
2.0
2.5
PhIO
NaOCl
95
82
81
62
87
82
13
18
5. Anwar, M.U., Dawe, L.N., Parsons, S.R., et al., Inorg.
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6. Bikas, R., Aleshkevych, P., HosseiniꢀMonfared, H.,
ence Foundation of China (project no. 21173003) for
supporting this work.
et al., Dalton Trans., 2015, vol. 44, no. 4, p. 1782.
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