Bidentate nitroxide ligands stable toward oxidative redox cycling and their complexes with cerium and lanthanum

Abstract

We report the synthesis of 1,3-bis[(2′-tertbutyl)hydroxyaminophenyl]benzene (H₂arene-diNOx) and its metal complexes, Ce(arene-diNOx)₂ (1) and [(py)₂K(18-crown-6)][La(arene-diNOx)₂] (2). Electrochemical studies demonstrated that the H₂arene-diNOx, bidentate nitroxide ligands significantly stabilized the Ce^IV/III redox couple to −1.74 V versus Fc/Fc⁺. Moreover, a reversible oxidation wave was observed for 1 at −0.37 V, leading to a novel, stable redox-active nitroxide ligand. DFT calculations confirmed that the observed oxidation is assignable to one of the nitroxide groups.