Copper(ii) induced oxidative modification and complexation of a schiff base ligand: synthesis, crystal structure, catalytic oxidation of aromatic hydrocarbons and DFT calculation

Abstract

A mononuclear square planar complex [Cu^II(L^f)] (1) was synthesized and structurally characterized by single crystal X-ray diffraction studies. Though we have started with the Schiff base H₂L^a with two –CH₂OH groups for complexation with Cu²⁺, the final product appears to have two formyl groups where two carbinols were oxidized during the course of the reaction with Cu²⁺. It opens up the possibility of using this complex as a precursor for condensation with suitable amines to give symmetric/asymmetric cyclic/acyclic Schiff base complexes. Systematic studies on catalytic oxidation of aromatic hydrocarbons like toluene and xylenes by an environmentally benign oxidant, H₂O₂ in the presence of 1 as a catalyst reveals that it is an efficient catalyst leading to the formation of the corresponding alcohol as the major product with TON ∼300 and alcohol selectivity of ∼72%.