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Acta Chim. Slov. 2016, 63, 822-826
DOI: 10.17344/acsi.2016.2699
Scientific paper
Synthesis, Crystal Structure, and Catalytic Property of Dioxomolybdenum(VI) Complex Derived from 4-Bromo-N'-(4-diethylamino-2-hydroxybenzylidene)
benzohydrazide
Li Wang, Yong-Jun Han, Qing-Bin Li and Ling-Wei Xue*
College of Chemistry and Chemical Engineering, Pingdingshan University, Pingdingshan Henan 467000, P.R. China
* Corresponding author: E-mail: pdsuchemistry@ 163.com
Received: 25-06-2016
Abstract
A novel dioxomolybdenum(VI) complex, [MoO2L(MeOH)], where L is the anion of 4-bromo-W-(4-diethylamino-2-hydroxybenzylidene)benzohydrazide, has been synthesized and characterized by physico-chemical methods and single crystal X-ray determination. In the complex the Mo atom is in octahedral coordination, with three donor atoms of the hydrazone ligand, two oxo groups, and one methanol O atom. The complex exhibits catalytic property for the sulfoxidation reactions. In the presence of the complex a 93% conversion of the sulfide to the corresponding sulfoxide was observed within 60 min and the 100% conversion was achieved after 2 h.
Keywords: Dioxomolybdenum; Hydrazone; Crystal structure; Catalytic property; Sulfoxidation
1. Introduction
Molybdenum complexes with multi-dentate ligands have received remarkable attention in recent years for their catalytic properties1 and molecular structures.2 Catalytic oxo transfer properties especially epoxidation and sulfoxi-dation by dioxomolybdenum complexes are industrially important. Many types of ligands with various functional groups have been synthesized to prepare molybdenum complexes with the aim to explore new and efficient catalytic materials.3 Salicylaldehyde and its derivatives have been widely used as ligands for the preparation of metal complexes with various applications.4 A large number of molybdenum complexes with Schiff base ligands have been reported.5 Some of the dioxomolybdenum complexes have shown oxygen atom transfer properties as they were found to oxidize thiols, hydrazine, polyketones, and tertiary phosphines.6 Recently, we reported the catalytic property of a dioxomolybdenum(VI) complex.7 As a continuation of such work, we report in this paper the synthesis, structure, and catalytic property of a new dioxomolybde-num(VI) complex, [MoO2L(MeOH)], where L is the anion of 4-bromo-N'-(4-dimethylamino-2-hydroxybenzylide-ne)benzohydrazide (Scheme 1).
Scheme 1. The hydrazone H2L.
2. Experimental
2. 1. Materials and Methods
4-Diethylaminosalicylaldehyde, 4-bromobenzohy-drazide and MoO2(acac)2 were purchased from Fluka. Other reagents and solvents were analytical grade and used without further purification. The hydrazone was prepared according to the literature method.8 Elemental (C, H, and N) analyses were made on a Perkin-Elmer Model 240B automatic analyzer. IR spectra were recorded on an IR-408 Shimadzu 568 spectrophotometer. 1H NMR data was recorded on a Bruker 300 MHz spectrometer.
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2. 2. Synthesis of [MoO2L(MeOH)]
MoO2(acac)2 (0.1 mmol, 33.5 mg) was dissolved with methanol (10 mL), to which was added with stirring a methanolic solution (10 mL) of H2L (0.1 mmol, 39.0 mg). The mixture was stirred at reflux for 30 min to give a yellow solution. The solution was slowly evaporated in air to give yellow block-shaped single crystals, which were collected by filtration and dried in evacuated desiccator containing anhydrous CaCl2. The yield is 41 mg (75%). Elemental analysis found: C, 41.8; H, 4.1; N, 7.5%, C19H22BrMoN3O5 calcd: C, 41.6; H, 4.0; N, 7.7%.
2. 3. X-ray Diffraction
Crystal data of the complex were collected with a Bruker Apex II diffractometer using Mo Ka radiation (0.71073 À). The data were processed with SAINT9 and corrected for absorption using SADABS.10 Multi-scan absorption corrections were applied with y scans.11 Structure of the complex was solved by direct method using SHELXS-97 and refined by full-matrix least-squares
Table 1. Crystal and structure refinement data for the complex
Table 2. Selected bond lengths (A) and angles (°) for the complex
Bond lengths				
Mo1-O1	1.927(2)	Mo1-O2		2.0096(19)
Mo1-O3	1.686(2)	Mo1-O4		2.384(2)
Mo1-N1	2.228(2)	Mo1-O5		1.697(2)
Bond angles				
O1-Mo1-O2	149.61(9)	O1-Mo1-	N1	81.59(8)
O5-Mo1-O1	102.56(9)	O1-Mo1-	O4	82.21(9)
O3-Mo1-O1	99.68(10)	O3-Mo1-	O2	97.01(10)
O3-Mo1-O5	105.92(12)	O3-Mo1-	N1	96.89(10)
O5-Mo1-N1	155.60(10)	O5-Mo1-	O2	96.98(9)
O2-Mo1-N1	71.29(8)	O3-Mo1-	O4	171.34(10)
O5-Mo1-O4	81.75(9)	N1-Mo1-	O4	74.95(8)
O2-Mo1-O4	77.79(8)			
techniques on F using anisotropic displacement parameters.12 All of the non-hydrogen atoms of the complex were refined anisotropically. The H atom of the methanol li-gand were located from electronic density maps and refined isotropically. The other hydrogen atoms were located as riding model. Crystallographic data for the complex are summarized in Table 1. Selected bond lengths and angles are listed in Table 2.
Molecular formula
C19H22BrMoN3O5
Molecular weight Crystal system Space group
a /A b /A c /A
p/°, v /A3
Z
Dcalc (g cm-3)
^ (mm 1)
Reflections measured
Unique reflections
Observed reflections (I > 2a(I))
Parameters
Restraints
Goodness of fit on F2 Rv wR2 [I > 2o(T)]a Rp wR2 (all data)a
548.2
Monoclinic P21/c 13.9971(8) 7.4182(4) 21.409(1) 107.319(1) 2122.2(2) 4
1.716 2.536 19023
3927 [Rint = 0.0301] 3241 268 1
1.027
0.0299, 0.0673 0.0422, 0.0721
a R = 2 | Fo I - I Fl |/£ IF I , wR2 = EwF^-F/mwFo2)2]1
2. 4. Catalytic Oxidation
The dioxomolybdenum(VI) complex (0.001 M) and phenyl methyl sulfide (0.100 M) were dissolved in the mixture of CH2Cl2 and CH3OH (6:4) with 1,3,5-trimet-hoxybenzene (0.100 M) as the internal standard. The solution was cooled to 283(2) K, to which was added dropwi-se H2O2 (35% w/w, 0.125 M). An aliquot of the solution (2.0 mL) was quenched with Na2SO3 (0.100 M, 5 mL), then extracted for three times with CH2Cl2 (4 mL). The solvent of the organic phase was removed, and the residue was dissolved in CDCl3 (0.6 mL) and analyzed by 1H NMR to determine the yield.
3. Results and Discussion
The complex was prepared by the reaction of the hydrazone ligand with MoO2(acac)2 in a 1:1 molar ratio (Scheme 2). The crystals of the complex are soluble in
Scheme 2. The preparation of the complex.
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DMSO, DMF, MeOH, EtOH and MeCN. Well-shaped single crystals of the complex can be obtained from MeOH.
3. 1. Crystal Structure Description
of the Dioxomolybdenum Complex
The molecular structure of the dioxomolybdenum complex is shown in Figure 1. In the complex the Mo atom is coordinated by the phenolic oxygen, imino nitrogen, enolic oxygen of the hydrazone ligand, two oxo oxygen and one methanol oxygen, forming an octahedral coordination. The hydrazone ligand coordinates to the MoO2 moiety by forming a five- and a six-membered chelate rings. The methanol molecule is weakly coordinated to the Mo atom, as indicated by the long bond value. The equatorial plane defined by atoms O1, O2, N1 and O5
show a high degree of planarity, with mean deviation from the plane of 0.038(3) Á. The Mol atom deviates from the least-squares equatorial plane by 0.346(1) Á in the direction of the axial atom O3. The coordinate bond lengths are comparable to those observed in similar complexes.13 The distortion of the octahedral coordination is indicated by the bond angles, ranging from 71.29(8) to 105.92(12)° for the cis angles and from 149.61(9) to 171.34(10)° for the trans angles. The dihedral angle between the two benzene rings of the hydrazone ligand is 0.3(5)°.
In the crystal structure of the complex, the complex molecules are linked through intermolecular hydrogen bonds of types O4-H4-N21 [O4-H4 = 0.85(1) Á, H4-N21 = 2.01(2) Á, O4-N2 = 2.834(3) Á, O4-H4-N21 = 164(4)°; symmetry code for i: - x, 1 - y, - z], to form di-mers (Figure 2).
Figure 1. Molecular structure of the complex at 30% probability displacement.
Figure 2. The hydrogen bonds linked dimeric structure of the complex.
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3. 2. Infrared and Electronic Spectra
In the IR spectrum of the hydrazone compound (Figure S1) the stretching bands attributed to C=O, C=N, C-OH and NH at 1634, 1603, 1130 and 3183 cm1 are present, respectively. In the IR spectrum of the dioxo-molybdenum complex (Figure S2) two prominent bands at 948 and 850 cm-1 are present, which can be attributed to the MoO2 group.14 The bands due to vC=O and vNH are absent in the dioxomolybdenum complex. This suggests occurrence of keto-imino tautomerization of the hydrazone ligand during coordination to the Mo atom. The typical C=N absorption of the dioxomolybdenum complex is observed at 1595 cm-1.15 The weak bands in low wave numbers can be attributed to the Mo-O and Mo-N vibrations.
The electronic spectrum of the dioxomolybdenum complex recorded in MeCN display strong and medium absorption bands in the region 370-420 and 260-300 nm (Figure S3). These peaks are assigned as charge transfer transitions of the type N(pn)-Mo(dn) LMCT and O(pn)-Mo(dn) LMCT,16 as the ligand based orbitals are either N or O donor types. The slight change of Amax values within each set of peaks may be due to the difference of electron donating capacity of the hydrazone ligand.
3. 3. Catalytic Sulfoxidation
The catalytic oxidation test of the dioxomolybde-num complex as catalyst on the oxidation of sulfide under homogeneous conditions using methyl phenyl sulfide as the substrate is shown as Scheme 3. Hydrogen peroxide was used as oxidant in 1.25 equivalent based on the sulfide substrate. Reactions were run with 1 mol% of catalyst based on the substrate at 10 °C. NMR technique was used to monitor the formation of the sulfoxides with 1,3,5-tri-methoxybenzene (TMB) as internal standard. The reaction was started by the addition of H2O2. A control reaction under the same condition without the complex present leads to less than 1% sulfide conversion within 4 h. In the presence of the dioxomolybdenum complex a 93% conversion of the sulfide to the corresponding sulfoxide was observed within 60 min and the 100% conversion was achieved after 2 h.
Scheme 3. The sulfoxidation process.
4. Supplementary Mateiral
CCDC-1487659 contain the crystallographic data for the complex. The data can be obtained at
http://www.ccdc.cam.ac.uk/const/retrieving.html or from the Cambridge Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44(0)1223-336033 or e-mail: deposit@ccdc.cam.ac.uk.
5. Acknowledgments
This research was supported by the National Sciences Foundation of China (No. 20676057 and 20877036) and Top-class foundation of Pingdingshan University (No. 2008010).
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Povzetek
Sintetizirali smo nov dioksomolibdenov(VI) kompleks, [MoO2L(MeOH)], kjer je L anion 4-bromo-W-(4-dietilamino-2-hidroksibenziliden)benzohidrazida, in ga okarakterizirali s fizikalno-kemijskimi metodami in monokristalno rentgensko analizo. V kompleksu je Mo atom oktaedricno koordiniran s tremi donorskimi atomi hidrazonskega liganda, dvema okso skupinama in atomom kisika z molekule metanola. Kompleks ima kataliticne lastnosti za reakcijo sulfoksidacije. Ob prisotnosti kompleksa pride v casu 60 min do 93 % pretvorbe sulfida do ustreznega sulfoksida ter do 100% pretvorbe po 2 h.
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