Redox activity and two-step valence tautomerism in a family of dinuclear cobalt complexes with a spiroconjugated bis(dioxolene) ligand

Abstract

A family of dinuclear cobalt complexes with bridging bis(dioxolene) ligands derived from 3,3,3′,3′-tetramethyl-1,1′-spirobis(indane-5, 5′,6,6′-tetrol) (spiroH4) and ancillary ligands based on tris(2-pyridylmethyl)amine (tpa) has been synthesized and characterized. The bis(dioxolene) bridging ligand is redox-active and accessible in the (spiro cat-cat)4-, (spiroSQ-cat)3-, and (spiroSQ-SQ)2- forms, (cat = catecholate, SQ = semiquinonate). Variation of the ancillary ligand (Mentpa; n = 0-3) by successive methylation of the 6-position of the pyridine rings influences the redox state of the complex, governing the distribution of electrons between the cobalt centers and the bridging ligands. Pure ..