Synthesis, Crystal Structure, and Catalytic Property of a Dioxomolybdenum(VI) Complex Derived from N'-(3-Bromo-5-Chloro-2-Hydroxybenzylidene)-4-Nitrobenzohydrazide

Article abstract of DOI:10.1134/S1070328418070084

New dioxomolybdenum(VI) complex [MoO₂(L)(CH₃OH)], where L is the dianionic form of N'- (3-bromo-5-chloro-2-hydroxybenzylidene)-4-nitrobenzohydrazide (H₂L), was prepared and characterized by IR and UV-Vis spectra, as well as single crystal X-ray diffraction (CIF file ССDС no. 1567063). The complex crystallizes as the monoclinic space group P2₁/c with unit cell dimensions a = 13.8471(10), b = 7.5618(6), c = 17.9445(12) ?, β = 90.107(2)°, V = 1878.9(2) ?³, Z = 4, R¹ = 0.0821, wR₂ = 0.0907, GOOF = 1.024. X-ray analysis indicates that the complex is a dioxomolybdenum(VI) species with the Mo atom in octahedral coordination. The catalytic oxidation property of the complex with tert-butylhydroperoxide in CH₂Cl₂ was studied.

Full text of DOI:10.1134/S1070328418070084

ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2018, Vol. 44, No. 7, pp. 421–424. © Pleiades Publishing, Ltd., 2018.
Synthesis, Crystal Structure, and Catalytic Property
of a Dioxomolybdenum(VI) Complex Derived
from N'-(3-Bromo-5-Chloro-2-Hydroxybenzylidene)-4-
Nitrobenzohydrazide1
X. W. Zhu*
Key Laboratory of Surface and Interface Science of Henan, School of Material and Chemical Engineering,
Zhengzhou University of Light Industry, Zhengzhou, 450002 P.R. China
*e-mail: zhuxuewen2017@126.com
Received September 9, 2017
Abstract—New dioxomolybdenum(VI) complex [MoO2(L)(CH3OH)], where L is the dianionic form of N'-
(3-bromo-5-chloro-2-hydroxybenzylidene)-4-nitrobenzohydrazide (H2L), was prepared and characterized
by IR and UV-Vis spectra, as well as single crystal X-ray diffraction (CIF file ССDС no. 1567063). The com-
plex crystallizes as the monoclinic space group P21/c with unit cell dimensions a = 13.8471(10), b = 7.5618(6),
c = 17.9445(12) Å, β = 90.107(2)°, V = 1878.9(2) Å3, Z = 4, R1 = 0.0821, wR2 = 0.0907, GOOF = 1.024. X-ray
analysis indicates that the complex is a dioxomolybdenum(VI) species with the Mo atom in octahedral
coordination. The catalytic oxidation property of the complex with tert-butylhydroperoxide in CH2Cl2 was
studied.
Keywords: hydrazone, dioxomolybdenum complex, crystal structure, catalytic property
DOI: 10.1134/S1070328418070084
INTRODUCTION
NO2
H
N
Schiff bases are readily synthesized and form vari-
ous complexes with most metal ions. Many Schiff base
complexes show excellent catalytic properties, such as
ring opening polymerization of cycloalkenes [1], oxi-
dation of hydrocarbons [2, 3], ring opening of large
cycloalkanes [4–6], reduction of ketones to alcohols
[7], alkylation of allylic substrates [8], improve enanti-
oselectivity in the cyclopropanation reactions [9, 10],
and so on. The ability of molybdenum to formation of
stable complexes with oxygen-, nitrogen-, and sulfur-
containing ligands led to development of molybdenum
Schiff base complexes which are efficient catalysts
both in homogeneous and heterogeneous reactions
[11–16]. The activity of these complexes varied obvi-
ously with the type of ligands and coordination sites.
Thus, herein we synthesized a new dioxomolybde-
num(VI) complex [MoO2(L)(CH3OH)] with hydra-
zone ligand and evaluated its catalytic property in the
oxidation of various olefins.
Cl
N
O
OH
Br
(H2L)
EXPERIMENTAL
Materials and methods. 3-Bromo-5-chloro-2-
hydroxybenzaldehyde, 4-nitrobenzohydrazide, and
MoO2(Acac)2 were purchased from Sigma-Aldrich
and used as received. All other reagents were of analyt-
ical reagent grade. Elemental analyses of C, H, and N
were carried out in a Perkin-Elmer automated model
2400 Series II CHNS/O analyzer. FT-IR spectra were
obtained on a Perkin-Elmer 377 FT-IR spectrometer
with samples prepared as KBr pellets. UV-Vis spectra
were obtained on a Lambda 900 spectrometer. X-ray
diffraction was carried out on a Bruker APEX II CCD
diffractometer.
Synthesis of the complex. 3-Bromo-5-chloro-2-
hydroxybenzaldehyde (0.01 mol, 2.35 g) and 4-nitro-
1
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421

422
ZHU
Table 1. Crystallographic and refinement data for the complex
matrix least-squares method using SHELXTL [19].
All of the non-hydrogen atoms were refined aniso-
tropically. The methanol hydrogen atom was located
from an electronic density map and refined isotropi-
cally with O–H distance restrained to 0.85(1) Å. The
remaining hydrogen atoms were placed in calculated
positions and constrained to ride on their parent
atoms. The crystallographic data and refinement
parameters for the complex are listed in Table 1.
Selected bond lengths and angles are listed in Table 2.
Supplementary material for structure I has been
deposited with the Cambridge Crystallographic Data
Centre (CCDC no. 1567063; deposit@ccdc. cam.
ac.uk or http://www.ccdc.cam.ac.uk/const/retriev-
ing.html).
Catalytic epoxidation of olefins. Epoxidation of
cyclooctene, cyclohexene, 1-octene and 1-hexene
catalyzed by the complex with tert-butylhydroperoxide
(TBHP) in CH2Cl2 was carried out according to the
following general procedure. To a 25 mL round bot-
tomed flask equipped with a magnetic stirring bar and
immersed into water thermo-stated bath, was added
10 mL CH2Cl2, 1.0 mmol TBHP, 0.01 mmol catalyst
and 1.0 mmol olefin. The mixture was refluxed with
vigorous stirring for 2 h at an appropriately chosen
temperature. The progress of the reaction was moni-
tored by carefully withdrawing aliquots of the sample
at different time intervals to determine concentrations
of the products by gаs chromatography analysis, using
n-hexane as an internal standard and was left to pro-
ceed until near complete conversion of TBHP. The
concentration of the TBHP was determined by iodo-
metric titration method [20]. The yield of epoxide (%)
was calculated according to the starting amount of ole-
fin. Assignments of the products were made by com-
parison with authentic samples. All the reactions were
run in triplicates. Control experiments showed that no
epoxide was formed in a measurable extent in the
Parameter
Formula weight
Crystal shape/color
Value
556.6
Block/yellow
298(2)
T, K
Crystal dimensions, mm
0.27 × 0.25 × 0.23
Monoclinic
P21/c
Crystal system
Space group
a, Å
13.847(1)
b, Å
7.5618(6)
c, Å
17.945(1)
β, deg
V, Å3
90.107(2)
1878.9(2)
Z
4
calcd, g cm–3
1.967
ρ
μ(MoKα), mm–1
3.011
F(000)
1088
17251
3487
Measured reflections
Unique reflections
Observed reflections (I ≥ 2σ(I))
Min and max transmission
Restraints/parameters
2770
0.4969 and 0.5443
3/257
Goodness of fit on F2
R1, wR2 (I ≥ 2σ(I))*
R1, wR2 (all data)*
1.028
0.0369, 0.0819
0.0532, 0.0904
2
2
2 1/2
* R = F – F /F , wR = [∑ w(
–
2)/∑ w( ) ]
.
Fo Fc
Fo
1
o
c
o
2
benzohydrazide (0.01 mol, 1.81 g) were dissolved in
methanol. Then, MoO2(Acac)2 (0.01 mol, 2.65 g) was
added and stirred for 1 h to give yellow solution. Single absence of catalyst.
crystals of the complex, suitable for X-ray diffraction,
were grown from the solution upon slowly evaporation
RESULTS AND DISCUSSION
for a few days. The yield was 2.38 g (43%).
The ligand H2L was readily prepared by the con-
densation reaction of 3-bromo-5-chloro-2-hydroxy-
benzaldehyde with 4-nitrobenzohydrazide in
methanol. The molybdenum(VI) complex was syn-
thesized by stirring equimolar quantities of H2L with
MoO2(Acac)2 in methanol at room temperature. The
chemical formula of the complex has been confirmed
by elemental analyses, IR spectra, and single crystal
X-ray diffraction.
IR data (ν, cm–1): 3445 w ν(O–H); 1608 s
ν(C=N); 936 m, 913 m ν(Mo=O). UV-Vis data
(CH3OH, λmax, nm): 273, 335.
For C15H11N3O7ClBrMo
Anal. calcd., %
Found, %
C, 32.37
C, 32.12
H, 1.99
H, 2.13
N, 7.55
N, 7.67
The band at 1617 cm–1 characteristic of the azome-
thine nitrogen atom present in the free ligand, was
X-ray crystallography. X-ray diffraction was carried
out at a Bruker APEX II CCD area diffractometer
equipped with MoKα radiation (λ = 0.71073 Å). The shifted to lower wave number at 1608 cm–1 after com-
plexation, indicating that the involvement the azome-
thine nitrogen atom in coordination. The band at
collected data were reduced with SAINT [17], and
multiscan absorption correction was performed using
SADABS [18]. The structure of the complex was 1277 cm–1 in the spectrum of H2L is ascribed to the
solved by direct method and refined against F2 by full- phenolic C–O stretching vibration. This band is found
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SYNTHESIS, CRYSTAL STRUCTURE, AND CATALYTIC PROPERTY
423
at 1287 cm–1 in the spectrum of the complex. These
changes suggest that the hydroxyl group of this Schiff
base moiety has taken part in complex formation. H2L
and the complex exhibit broad bands at 3450 and
3445 cm–1, respectively, which may be assigned to the
ν(OH). Further evidence of the bonding is also shown
by the observation that new bands in the IR spectrum
of the metal complex appear at 400–470 and 500–
550 cm–1 assigned to Mo–N and Mo–O stretching
vibrations that are not observed in the spectrum of the
ligand. The Mo=O stretching mode occur as double
bands at 936 and 913 cm–1, assigned to the symmetric
and asymmetric stretching modes of the MoO2 moi-
eties [21, 22].
Table 2. Selected bond distances (Å) and angles (deg) for
the complex
Bond
d, Å
Bond
d, Å
Mo(1)–O(1)
Mo(1)–O(5)
Mo(1)–O(7)
1.926(3) Mo(1)–O(2)
1.683(4) Mo(1)–O(6)
1.687(3) Mo(1)–N(1)
1.995(3)
1.683(4)
2.263(3)
Angle
ω, deg
Angle
ω, deg
O(6)Mo(1)O(7) 106.3(2) O(6)Mo(1)O(1) 98.3(2)
O(7)Mo(1)O(1) 102.5(1) O(6)Mo(1)O(2) 97.7(2)
O(7)Mo(1)O(2) 98.6(1) O(1)Mo(1)O(2) 148.7(1)
O(6)Mo(1)N(1) 93.6(1) O(7)Mo(1)N(1) 158.8(2)
O(1)Mo(1)N(1) 81.2(1) O(2)Mo(1)N(1) 71.1(1)
O(6)Mo(1)O(5) 169.6(1) O(7)Mo(1)O(5) 84.0(1)
O(1)Mo(1)O(5) 79.8(1) O(2)Mo(1)O(5) 79.7(1)
N(1)Mo(1)O(5) 76.1(1)
Electronic absorption spectra of the ligand and the
complex were obtained in methanol solutions. The
electronic absorption spectrum of H2L displayed two
bands at 275 and 370 nm, which are assigned for the
π → π* and n → π* transitions, respectively. In the
electronic spectrum of the complex, the strong
band centered at 335 nm is attributed to the intra-
ligand π → π* absorption band of the hydrazone
ligand. The LMCT and to some extent π → π* band
appears at 273 nm.
equatorial mean planes toward the apical oxo-group is
0.322(1) Å. The hydrazone ligand is coordinated in its
dianionic form, which is evident from the N(2)–C(8)
and O(2)–C(8) bond lengths. The abnormal bond val-
ues indicate the presence of the enolate form of the
ligand amide groups. The Mo–O, Mo–N, and
Mo=O bonds are within normal ranges and are similar
to those observed in similar molybdenum(VI) com-
plexes [11–16].
The molecular structure of the complex is shown in
Fig. 1. The coordination geometry around the Mo
atom can be described as distorted octahedron with
the phenolate-O, imino-N, and enolate-O of the
hydrazone ligand, and one oxo-group defining the
equatorial plane, and with the other oxo-group and
one methanol oxygen occupying the axial positions.
The hydrazone ligand coordinates to the Mo atom in a
meridional fashion forming five- and six-membered
chelate rings with bite angles of 71.07(11)° and
81.17(11)°. The dihedral angle between the two ben-
zene rings of the hydrazone ligand are 1.3(5)°. The
In the crystal structure of the complex, adjacent
two [MoO2(L)(CH3OH)] molecules are linked
through two intermolecular O–H···N hydrogen
bonds (O(5)–H(5) 0.85(1), H(5)···N(2)i 1.98(1),
O(5)···N(2)i 2.833(4) Å, O(5)–H(5)···N(2)i 174(5)°;
i
symmetry code: 1 – x, –y, –z), to form dimers
displacement of the Mo atom in the complex from the (Fig. 2).
C(5)
C(3)
C(6)
Cl(1)
C(4)
C(14)
C(7)
C(13)
N(2)
O(4)
O(3)
C(1)
C(9)
C(8)
C(12)
N(1)
N(3)
O(6)
C(2)
C(10)
C(11)
O(2)
O(1)
Mo(1)
Br(1)
O(5)
O(7)
C(15)
Fig. 1. A perspective view of the complex with the atom labeling scheme. Thermal ellipsoids are drawn at the 30% probability
level.
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