A cyclic tetranuclear cuboid type copper(ii) complex doubly supported by cyclohexane-1,4-dicarboxylate: molecular and supramolecular structure and cyclohexane oxidation activity

Abstract

Synthesis, characterization and catalytic study of the new bis(μ₄-(ae)-cyclohexane-1,4-dicarboxylato-O,O′,O′′,O′′′)-tetracopper(II) complex [(CuL)₂(μ₄-O,O′,O′′,O′′′-CDC)]₂·2H₂O (1) (HL = 2-(2-pyridylmethyleneamino)benzenesulfonic acid and CDC = cyclohexane-1,4-dicarboxylate) are described. Complex 1 contains four copper(II) centres connected by four Schiff base ligands (L⁻) and doubly bridged by two cyclohexane-1,4-dicarboxylate moieties. The axial-equatorial conformation of the carboxylate groups of CDC stabilizes a tetracopper di-CDC ring in a cuboid type fashion. Compound 1 is applied as an efficient pre-catalyst for the oxidation of cyclohexane by aqueous H₂O₂ under mild conditions (50 °C) in CH₃CN/H₂O medium. Without any promoter, a total yield (based on substrate) of cyclohexanol and cyclohexanone up to 35% was achieved.