Synthesis, characterization, and X-ray structure of [cis-MoO2L(MeOH)] (L = N′-(5-chloro-2-hydroxybenzylidene)-3-chlorobenzohydrazide) and its catalytic property

Article abstract of DOI:10.1080/15533174.2013.841219

The synthesis and characterization of [cis-MoO₂L(MeOH)] (L = N′-(5-chloro-2-hydroxybenzylidene)-3-chlorobenzohydrazide) are described. The dioxomolybdenum complex was prepared from 1:1 reaction mixture containing the benzohydrazone ligand and M

Full text of DOI:10.1080/15533174.2013.841219

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Synthesis, Characterization, and X-Ray Structure
of [cis-MoO2L(MeOH)] (L = N′-(5-Chloro-2-
Hydroxybenzylidene)-3-Chlorobenzohydrazide) and Its
Catalytic Property
Chun-Lin Dua & Zhe Honga
a School of Chemical Engineering & Material Science, Eastern Liaoning University, Dandong,
P. R. China
Accepted author version posted online: 16 Jun 2014.Published online: 24 Oct 2014.
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To cite this article: Chun-Lin Du & Zhe Hong (2015) Synthesis, Characterization, and X-Ray Structure of [cis-MoO2L(MeOH)]
(L = N′-(5-Chloro-2-Hydroxybenzylidene)-3-Chlorobenzohydrazide) and Its Catalytic Property, Synthesis and Reactivity in
Inorganic, Metal-Organic, and Nano-Metal Chemistry, 45:4, 507-511, DOI: 10.1080/15533174.2013.841219
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry (2015) 45, 507–511
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2013.841219
Synthesis, Characterization, and X-Ray Structure of [cis-
MoO2L(MeOH)] (L D N0-(5-Chloro-2-Hydroxybenzylidene)-
3-Chlorobenzohydrazide) and Its Catalytic Property
CHUN-LIN DU and ZHE HONG
School of Chemical Engineering & Material Science, Eastern Liaoning University, Dandong, P. R. China
Received 26 June 2013; accepted 1 September 2013
The synthesis and characterization of [cis-MoO2L(MeOH)] (L D N0-(5-chloro-2-hydroxybenzylidene)-3-chlorobenzohydrazide) are
described. The dioxomolybdenum complex was prepared from 1:1 reaction mixture containing the benzohydrazone ligand and
MoO2(acac)2. Orange single crystals were obtained by slow evaporation of methanolic solution containing the complex, and were
characterized by elemental analysis, infrared spectroscopy, and single-crystal X-ray diffraction techniques. The geometry around the
molybdenum center is distorted octahedral in which a tridentate benzohydrazone ligand with two anionic oxygens and one neutral
imine nitrogen occupies meridional position. The octahedral geometry of the cis-dioxomolybdenum center is additionally completed
by a coordinated methanol solvent molecule. The complex was tested for the homogeneous oxidation of various olefins.
Keywords: molybdenum dioxo complex, synthesis, X-ray structure, catalytic property
Introduction
Experimental
Materials and Methods
Benzohydrazones prepared by the condensation of salicylal-
dehydes with benzohydrazides are an important class of ver-
satile ligands.[1–3] Transition metal complexes derived from
such ligands have been widely investigated due to their inter-
esting properties, such as magnetic exchange,[4] biological
activities,[1,5,6] and catalytic materials.[7,8] Molybdenum is an
important metal that is capable of forming various complexes
with organic ligands,[9–11] and usually shows essential cata-
lytic properties.[12–15] Yet, molybdenum complexes derived
from benzohydrazone ligands are rarely reported. Epoxides
are very important and versatile intermediates for
manufacturing a range of important commercial products
such as pharmaceuticals and polymers. In addition, it can be
easily transformed to a variety of functional groups.[16] Many
transition metal complexes including molybdenum complexes
have been reported for oxidation of olefins.[8,11,12,17–19] As a
continuation of the work, in this report, a new cis-dioxomo-
lybdenum(VI) complex is reported.
5-Chlorosalicylaldehyde, 3-chlorobenzohydrazide, and MoO2
(acac)2 of AR grade were purchased from Aldrich and used as
received. CHN elemental analyses were performed with a Per-
kin Elmer 240C elemental analyzer. IR spectra (KBr disks)
were recorded on a Perkin Elmer 257 spectrophotometer. The
oxidation products were analyzed with a gas chromatograph
(Shimadzu, GC-14B) equipped with a SAB-5 capillary column
(phenyl methyl siloxane 30 mm £ 320 mm £ 0.25 mm) and a
1
flame ionization detector. H NMR spectrum was obtained in
DMSO-d6 solution with a Bruker NMR 400 (400 MHz) spec-
trometer. Thermal decomposition was measured on Pyris 1 ther-
mogravimetric analyzer.
Preparation of the Molybdenum Complex
A mixture of 5-chlorosalicylaldehyde (0.78 g, 5 mmol) and 3-
chlorobenzohydrazide (0.86 g, 5 mmol) in 30 mL methanol
was heated to reflux for 1 h, which gave the benzohydrazone
ligand H2L. Then MoO2(acac)2 (1.63 g, 5 mmol) was added
and refluxed for another 1 h. A yellow solid was obtained by
concentrating the methanolic solution, washed with cold meth-
anol and recrystallized from methanol by slow evaporation.
Yield: 63%; 1H NMR (DMSO-d6, 400 MHz): d D 3.13 (s, 3H),
6.91(d, 1H, aromatic), 7.25–7.97(m, 6H, aromatic), 8.53 (s, 1H,
-CHDN-). IR (KBr pellet): n(CDN) 1622; n(MoO2) 917,
Address correspondence to Zhe Hong, School of Chemical Engi-
neering & Material Science, Eastern Liaoning University, Dan-
dong 118003, P. R. China. E-mail: hongzhe57@126.com
Color versions of one or more of the figures in the article can be
found online at www.tandfonline.com/lsrt.

508
Du and Hong
Table 1. Crystallographic and experimental data for the
complex.
Empirical formula
Formula weight
Temperature/K
C15H12Cl2MoN2O5
467.1
298(2)
ꢀ
Wavelength (MoKa)/A
Crystal shape/color
Crystal size/mm
0.71073
Block/yellow
0.23 £ 0.23 £ 0.22
Triclinic
P-1
Crystal system
Space group
ꢀ
a/A
7.880(2)
9.589(2)
11.754(2)
98.149(2)
104.888(2)
91.201(2)
848.1(3)
2
ꢀ
b/A
ꢀ
c/A
a/ꢀ
b/ꢀ
g /ꢀꢀ
V/A3
Fig. 1. TG-DTA curves of the complex.
Z
Calculated density/g cm¡3
Absorption coefficient/mm¡1
Theta range for data collection
Index ranges/h, k, l
Tmin
1.829
1.117
non-H atoms were refined anisotropically. The methanol H
2.15–25.10
¡9, 8; ¡11, 11; ¡13, 12
0.7832
atom was located from an electronic density map and refined
ꢀ
with O¢¢¢H distance restrained to 0.85(1) A. All other H
atoms of the complex were included in calculated positions,
and assigned isotropic thermal parameters, which were set to
ride on the parent atoms. All calculations were performed
using the SHELXTL-97 package.[20]
Tmax
0.7911
3006/230
2151
Reflections/parameters
Independent reflections
Restraints
1
F(000)
464
1.021
Goodness of fit on F2
Catalytic Oxidation Procedure
R1, wR2 [I ꢀ 2s(I)]a
0.0518, 0.1158
0.0890, 0.1327
0.791, ¡0.553
P
R1, wR2 (all data)a
Catalytic experiments were carried out in a 50 mL glass reac-
tion flask fitted with a water condenser. In a typical proce-
dure, 0.032 mmol dioxo-molybdenum(VI) complex was
dissolved in 10 mL CH2Cl2. Then 10 mmol alkene was added
to the reaction mixture and 30 mmol TBHP was added. The
reaction mixture was refluxed for 1 h. The reaction products
were monitored at periodic time intervals using gas chroma-
tography. The oxidation products were identified by compar-
ison with authentic samples (retention times in GC).
ꢀ
Largest diff. peak and hole/e A¡3
P
P
P
aR1 D jjFoj – jFcjj/ jFoj, wR2 D [ w(Fo2 – Fc2)2/ w(Fo2)2]1/2
.
886 cm¡1. Anal. Calcd. (%) for C15H12Cl2MoN2O5: C, 38.6;
H, 2.6; N, 6.0. Found (%): C, 38.5; H, 2.7; N, 5.9.
Crystal Structure Determination
Crystals suitable for X-ray measurement were grown from Results and Discussion
methanol by slow evaporation method. The single crystal of
the complex was chosen and glued to thin glass fibers by The benzohydrazone ligand used for the preparation of
epoxy glue in air for data collection. The diffraction data molybdenum complex was derived from condensation of 5-
were collected on aꢀ Bruker Apex2 CCD with Mo Ka radia- chlorosalicylaldehyde and 3-chlorobenzohydrazide. The
tion (λ D 0.71073 A) at 298(2) K using the v scan method. complex was prepared by simple ligand exchange reaction of
An empirical absorption correction was applied. The struc- the benzohydrazone ligand with MoO2(acac)2 in methanol
ture was solved by direct methods and difference Fourier syn- (Scheme 1). Single crystals of the complex were successfully
thesis. Crystal data collection, parameters, and refinement grown by slow evaporation of methanolic solution of the
statistics for the complex are listed in Table 1. All of the complex at room temperature.
Sch. 1. The synthesis procedure of the complex.

[cis-MoO2L(MeOH)] and Its Catalytic Property
509
Fig. 2. ORTEP diagram (30% thermal ellipsoid) of the complex
with atom labeling scheme.
Fig. 3. Intermolecular O–H¢¢¢N hydrogen bonds (dotted lines)
The complex was characterized by IR spectroscopy. Two
strong bands at 886 and 917 cm¡1 which can be assigned as
symmetric and asymmetric stretching frequencies due to cis-
dioxo moieties indicating the existence of monomeric com-
linked dimers of the complex.
plex.[15] The molar conductance of the complex is 13 V¡1 cm2 atom, O4, occupy the meridional plane. The Mo1 atom lies
ꢀ
mol¡1, indicating it is a nonelectrolyte.
0.329(2) A out from this plane in the direction of the other ter-
Figure 1 is TG-DTG curves at a heating rate of minal oxygen atom O5. Both O5 and O3, the latter from the
10ꢀC¢min¡1. It can be seen that there are three different coordinated methanol molecule, occupy the axial positions
decomposition stages. The first decomposition stage which forming an O3–Mo1–O5 angle of 170.34(17)ꢀ which indicate
occurs in the temperature range of 165–181ꢀC, was observed the distorted octahedral nature of the donor environment
as mass loss of 7.2%, corresponding to the loss of methanol around the Mo(VI) center. The MoO2 moiety has a cis configu-
ligand (calcd. 6.9%). The second stage, which occurs in the ration. The Mo1–O3 bond trans to the terminal oxygen atom
temperature range of 206–500ꢀC, corresponds to the slow O5 is significantly longer compared to the length of other
decomposition of the remainder, and the formation of molybdenum oxygen bonds, indicating that the methanol mol-
MoO2, which is stable up to 708ꢀC, then slowly evaporated.
ecule is weakly coordinated to the metal center and can behave
as a substrate-binding site. The coordinate bond parameters
are consistent with those reported in the literature.[14,15] In the
crystal, the molecules are linked via intermolecular O3–
X-Ray Structure Description of the Complex
ꢀ
H3¢¢¢N2 hydrogen bonds [O3–H3 D 0.85(1) A, H3¢¢¢N2i D
ꢀ
ꢀ
1.99(2) A, O3¢¢¢N2i D 2.826(6) A, O3–H3¢¢¢N2i D 169(7)ꢀ; sym-
metry code for i: 1 – x, 1 – y, – z], forming dimers, as shown in
Figure 3.
The molecular structure of the complex is shown in Figure 2
and the bond parameters are given in Table 2. The mononu-
clear complex has a distorted octahedral geometry with one
nitrogen atom and five oxygen atoms. Three atoms, O1, N1,
and O2 (from the tridentate ligand), and one terminal oxo
Catalytic Oxidation Results
ꢀ
Table 2. Selected bond lengths (A) and bond angles (o) for the
The catalytic property of the complex was investigated in the
epoxidation of cyclooctene, as a model substrate, and tert-
butyl hydroperoxide as the oxygen donor. In the absence of
catalyst, the reactions did not proceed even under reflux. The
results are presented in Table 3. Oxidation of 4-F-styrene, 4-
Cl-styrene, 4-Mestyrene, and 4-OMe-styrene gave the corre-
sponding epoxide as the sole product, while in the oxidation of
styrene some benzaldehyde was detected as a by-product.
From the results, it can be seen that the electron donating
group in the salicylidene ring can decrease the activity of the
catalyst, which results from the decreasing Lewis acidity of the
molybdenum center and therefore the deduction of TBHP
activation.[12] In the proposed catalytic cycle (Scheme 2), at
first step, TBHP is activated by coordination to the molybde-
num center and formation of hepta-coordinated molybdenum
complexes.
Bond lengths
Mo1-O5-
Mo1-O1
1.680(4)
1.911(4)
2.257(4)
Mo1-O4
Mo1-O2
Mo1-O3
1.690(4)
2.004(4)
2.344(4)
Mo1-N1
Bond angles
O5-Mo1-O4
O4-Mo1-O1
O4-Mo1-O2
O5-Mo1-N1
O1-Mo1-N1
O5-Mo1-O3
O1-Mo1-O3
N1-Mo1-O3
106.0(2)
101.9(2)
99.0(2)
95.9(2)
80.9(2)
170.3(2)
82.2(2)
74.7(2)
O5-Mo1-O1
O5-Mo1-O2
O1-Mo1-O2
O4-Mo1-N1
O2-Mo1-N1
O4-Mo1-O3
O2-Mo1-O3
99.0(2)
96.3(2)
149.5(2)
157.0(2)
71.3(2)
82.9(2)
78.5(2)

510
Du and Hong
Sch. 2. The catalytic procedure of the oxidation.
intermediate I. It seems that heterolytic cleavage of the comparison of the results obtained for this work with
TBHP occurs. Therefore catalysts with higher Lewis acid- those reported in the literature, which used TBHP as oxi-
ity character increase the efficiency of the coordinated per- dizing agent reveals that reaction time is lower than other
oxo group. Then olefin as a nucleophile will attack to the systems and higher conversion for epoxide formation will
electrophile oxygen atom of the coordinated TBHP. A be achieved.
b
Table 3. Epoxidation of olefins using TBHP catalyzed by the complex in CH2Cl2 .
Conversion
(%)c
Selectivity to
epoxides (%)
Time
(h)
TOF
Alkene
Product
(h¡1
)
37
100
1
102.5
34
17
100
100
1
1
87.2
45.3
11
23
100
100
1
1
21.7
61.9

[cis-MoO2L(MeOH)] and Its Catalytic Property
511
8. Barlan, A. U.; Basak, A.; Yamamoto, H. Enantioselective
oxidation of olefins catalyzed by a chiral bishydroxamic acid
complex of molybdenum. Angew. Chem. Int. Ed. 2006, 45,
5849–5852.
9. Amini, M.; Haghdoost, M. M.; Bagherzadeh, M. Oxido-peroxido
molybdenum(VI) complexes in catalytic and stoichiometric oxida-
tions. Coord. Chem. Rev. 2013, 257, 1093–1121.
Funding
The authors acknowledge Eastern Liaoning University for
funding this study.
Supplementary Material
10. Sarioz, O.; Oznergiz, S.; Kandemirli, F. Bis(amino)phosphines
derived from N-phenylpiperazine and N-ethylpiperazine: Synthesis,
oxidation reactions, and molybdenum complexes. Synth. React.
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CCDC 946363 contains the supplementary crystallographic
data for the two complexes. These data can be obtained free
of charge via http://www.ccdc.ac.uk/conts/retrieving.html,
or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: (C44)1223-
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