Characterization of one-electron oxidized copper(ii)-salophen-type complexes; effects of electronic and geometrical structures on reactivities

Abstract

One-electron oxidized salophen-type complexes, [Cu(salophen)]⁺ (H₂salophen = N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-diaminobenzene), and its methoxy derivatives, [Cu(MeO-salophen)]⁺ and [Cu(salophen-(MeO)₂)]⁺ (H₂MeO-salophen = N,N′-bis(3-tert-butyl-5-methoxysalicylidene)-1,2-diaminobenzene, H₂salophen-(MeO)₂ = N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-diamino-4,5-dimethoxybenzene), have been synthesized and structurally characterized, and their reactivities have been investigated. The solid state structures of the one-electron oxidized forms of these complexes suggested that [Cu(salophen)]⁺ and [Cu(MeO-salophen)]⁺ can be assigned to relatively localized Cu(II)-phenoxyl radical complexes, while [Cu(salophen-(MeO)₂)]⁺ is the diiminobenzene radical complex. On the other hand, [Cu(salophen)]⁺ in solution showed a different electronic structure from that of the solid sample, the radical electron being delocalized over the whole π-conjugated ligand. The reaction of these oxidized complexes with benzyl alcohol has been investigated in the presence of a large excess of substrate, which revealed the difference in the kinetic behavior between the complexes. The mechanisms of the oxidation have been discussed on the basis of the electronic and geometrical structures and the reaction kinetics.