Abstract
Two new cis-dioxomolybdenum(VI) complexes with general formula [MoO2L(MeOH)], where L = L1 = N'-(3,5-dibromo-2-hydroxybenzylidene)-4-trifluoromethylbenzohydrazide for complex 1, and L = L2 = N'-(3-bromo-5-chloro-2-hydroxybenzylidene)-4-trifluoromethylbenzohydrazide for complex 2, have been synthesized and fully characterized on the basis of elemental analysis, FT-IR, molar conductivity, and electronic spectra. The complexes are also characterized by single crystal X-ray diffraction. The complexes have distorted octahedral structures in which the aroylhydrazones behave as dianionic ligands. It is also revealed from the crystal structures that the Mo(VI) center adopts NO5 donor environment, and the octahedral coordination is furnished by two oxido groups and oxygen atoms of neutral methanol molecules. The catalytic properties were investigated for epoxidation of cyclooctene using aqueous tert-butyl hydroperoxide as the oxidant.
Highlights
In the last 60 years, Schiff base ligands and their transition metal complexes have attracted considerable attention, for their facile synthesis, and for potential biological, catalytic and industrial applications.[1]
The aroylhydrazone Schiff bases H2L1 and H2L2 were synthesized in a similar way by refluxing a methanolic solution (30 mL) of 4-trifluoromethylbenzohydrazide (10 mmol, 2.04 g) with 3,5-dibromosalicylaldehyde (10 mmol, 2.80 g) and 3-bromo-5-chlorosalicylaldehyde (10 mmol, 2.35 g), respectively
The aroylhydrazone Schiff bases and their complexes were synthesized in a facile and analogous way (Scheme 1)
Summary
In the last 60 years, Schiff base ligands and their transition metal complexes have attracted considerable attention, for their facile synthesis, and for potential biological, catalytic and industrial applications.[1] In recent years, vanadium complexes with hydrazones have been widely studied, either from the structural or catalytic aspect.[2] As we know, catalytic epoxidation of olefins is an important reaction in organic synthesis. Many transition metal complexes are active catalysts for this process.[3] Yet, among the complexes, molybdenum complexes have a unique place in coordination chemistry and have displayed very high catalytic activities in the oxidation of olefins and sulfides.[4] In the present work, two similar aroylhydrazone Schiff bases, N’-(3,5-dibromo-2hydroxybenzylidene)-4-trifluoromethylbenzohydrazide (H2L1) and N’-(3-bromo-5-chloro-2-hydroxybenzylidene)-4-trifluoromethylbenzohydrazide (H2L2), were prepared and used to prepare dioxomolybdemum(VI) complexes with [MoO2(acac)2] in methanol. The catalytic properties were investigated for epoxidation of cyclooctene using aqueous tert-butyl hydroperoxide as the oxidant
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