Electrocatalytic epoxidation and oxidation with dioxygen using manganese(III) Schiff-base complexes

The electrocatalytic properties of different Mn-III Schiff-base complexes in acetonitrile solution in the presence of benzoic anhydride, an axial base and dioxygen have been investigated by cyclic voltammetry. Bulk electrolysis in the presence of cyclooctene yields cyclooctene oxide and shows that the best catalyst complexes (in terms of current efficiency and turnover) are based on ligands containing an ethano (Salen complexes) or a 1,2-cyclohexylidene (Salchx complexes) bridging unit and 5,5'-dichloro substituents. The effect of axial base such as pyridine, collidine, 1- and 2-methylimidazole is shown. The use of the latter base gave the best results for cycloctene epoxidation. Some investigation on tetraline and triphenylphosphine oxidation are also reported. (C) 1997 Elsevier Science Ltd.