Catalytic oxidation of internal and terminal alkenes by oxidoperoxidomolybdenum(VI) and dioxidomolybdenum(VI) complexes

Reaction of oxidoperoxidomolybdenum(VI) species, generated in situ by the reaction of MoO3 in the presence of H2O2, with three Schiff bases H(2)hap-inh (I), H(2)hap-nah (II) and H(2)hap-bhz (III), (derived from the condensation of 2-hydroxyacetophenone with isonicotinoylhydrazide, nicotinoylhydrazide and benzoylhydrazide) results in the formation of oxidoperoxidomolybdenum(VI) complexes, [MoO(O-2) (hap-inh)(MeOH)] (1), [MoO(O-2)(hap-nah)(MeOH)] (2) and [MoO(O-2)(hap-bhz)(MeOH)] (3), respectively. Their dioxidomolybdenum(VI) analogues [MoO2(hap-inh)](n) (4) [MoO2(hap-nah)(MeOH)] (5) and [MoO2 (hap-bhz)(MeOH)] (6) have also been prepared by reacting equimolar ratio of [MoO2(acac)(2)] and corresponding ligands. These complexes have been characterized in the solid state as well as in solution namely by spectroscopic techniques (IR, electronic, H-1 and C-13 NMR), elemental and thermogravimetric analysis. Structures of complexes 3, 4, and 6a ([MoO2(hap-bhz)(DMSO)]) have been confirmed by single crystal X-ray study which reveals that ligands behave as a dibasic tridentate coordinating through ONO functionalities. Sodium bicarbonate assisted oxidation of styrene and cyclohexene using 30% H2O2 as oxidant has been carried out using these catalysts. Under the optimized reaction conditions styrene gave mainly styrene oxide and minor amount of phenylacetaldehyde. Oxidation of cyclohexene gave cyclohexene epoxide selectively. The corresponding dioxidomolybdenum(VI) complexes have relatively lower catalytic activities. (C) 2015 Elsevier B.V. All rights reserved.