Sonochemical syntheses of nano-sized dioxomolybdenum complexes: An efficient, selective and reusable heterogeneous nanocatalyst for oxidation of alkenes

Two Schiff base ligands derived from 2-hydroxy-4-methoxyacetophenone and 2,2'-dimethylpropylenediamine (H2L1) or 1,2-cyclohexanediamine (H2L2) have been synthesized and characterized by physico-chemical and spectroscopic methods. Then dioxomolybdenum complexes have been prepared by reaction of Schiff base ligands and MoO2(acac)(2) under ultrasonic irradiation to give nanoparticles of MoL1 and MoL2. FT-IR, UV-vis, H-1 NMR and C-13 NMR spectroscopy, elemental analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), were used to characterize and investigate the nanocatalysts. A practical catalytic method for efficient and highly selective oxidation of wide range of olefins with anhydrous tert-butyl hydroperoxide over the prepared molybdenum nanocatalysts was investigated. Under mild reaction conditions, oxidation of cyclooctene led to the formation of corresponding epoxide with a yield of more than 90%. The catalysts were reused five consecutive times without detectable catalyst leaching or significant loss of activity. (C) 2013 Elsevier B.V. All rights reserved.