Aerial oxidation of primary alcohols and amines catalyzed by Cu(ii) complexes of 2,2′-selenobis(4,6-di-tert-butylphenol) providing [O,Se,O]-donor atoms

Abstract

Seven copper(II)-complexes 1–7 with the ligand 2,2′-selenobis(4,6-di-tert-butylphenol) providing [O,Se,O]-donor atoms have been isolated and characterized. Three of them 1, 2 and 3 are mononuclear, two 4 and 7 dinuclear and 5, 6 are trinuclear. The crystal structures of the complexes were determined by X-ray diffraction and the electronic structures were established by various physical methods including EPR and variable temperature (2–290 K) susceptibility measurements. The magnetic behaviour of the compounds 4–6 exhibits antiferromagnetic exchange coupling resulting in well-isolated S_t = 1/2 ground state for 5 and 6 and a diamagnetic spin state for 4. Complexes 5 and 6 belong to the class of asymmetric trinuclear copper(II) complexes modelling the trinuclear copper site in multicopper oxidases. Complex 1 is a catalyst in the presence of a strong base for the aerial oxidation of primary alcohols to the corresponding aldehydes. A dinuclear complex, seemed to be 4, prepared in situ has been found to be a catalyst for the aerial oxidation of primary amines containing α-C–H atoms. Primary kinetic isotope effects show that H-abstraction from the α-carbon atom of a coordinated substrate (alcoholato or amine) is the rate-determining step in both cases. Two functional models for the metalloenzymes galactose oxidase and amine oxidases are thus described.