pH-Triggered intramolecular electron transfer in asymmetric bis-dioxolene adducts

Abstract

The oxidation of the bis-dioxolene 3,3,3′,3′-tetramethyl-5,6,5′,6′-tetrahydroxy-1,1′-spiro-bis(indane) (CatH₂–CatH₂) in acidic solution yields the o-quinone-catecholate (Q–CatH₂) as a product. The mixed valence character of the molecule is removed on deprotonation yielding the paramagnetic bis-semiquinonato species due to a formally intramolecular electron transfer. Complexes of formula M(CTH)(SQ–CatH₂)(PF₆)₂ (M = Cr^III, Co^III; CTH = tetraazamacrocycle, SQ–CatH₂ = semiquinonato form of CatH₂–Q) were also prepared. They are six-coordinate, the semiquinonato being coordinated to the metal ion. Evidences are given that intramolecular electron transfer follows deprotonation of the non-coordinated catecholate, yielding the M^III(CTH)(Cat–SQ) species, the catecholato being coordinated to the metal ion. The obtained results provide significant examples of systems showing pH-controlled magnetic properties.