Alcohol Oxidations by Schiff Base Manganese(III) Complexes

Abstract

Asymmetric Schiff base manganese(III) complexes involving salen ligands, N,N'‐bis(salicylidene)2,3‐diaminopyridine, N,N'‐bis(3‐methoxysalicylidene)2,3‐diaminopyridine, N,N'‐bis(3,5‐di‐ tert ‐butylsalicylidene)2,3‐diaminopyridine and N,N'‐bis(3,5‐di‐chloro‐salicylidene)2,3‐diaminopyridine were prepared and their catalytic activity was investigated in the oxidation of some primary and secondary alcohols. During optimization of oxidation reactions, Mn‐4 , bearing electron withdrawing N,N'‐Bis(3,5‐di‐chloro‐salicylidene)2,3‐diaminopyridine ligand, showed higher activity than other catalysts tested. The catalytic reactions were carried out in the presence of various oxidants such as oxygen, hydrogen peroxide or tert ‐butyl hydroperoxide (TBHP) and additives such as acetic acid and imidazole. The oxidant/additive combination of TBHP and imidazole was shown to be effective for the oxidation process and the degree of their impact on oxidation reaction was found highly dependent on a balanced ratio between them. Mn‐4 was selected as the most effective catalyst under optimized reaction conditions and revealed efficient for the oxidation of secondary alcohols.