Lawsone Dimerization in Cobalt(III) Complexes toward the Design of New Prototypes of Bioreductive Prodrugs

Dimerization of lawsone occurs upon reaction with Co(BF4)2·6H2O and N,N′-bis(pyridin-2-ylmethyl)ethylenediamine (py2en) to produce the mononuclear complex [CoIII(bhnq)(py2en)]BF4·H2O (1). This complex has been investigated as a prototype of a bioreductive prodrug, where the bhnq2– ligand acts as a model for cytotoxic naphthoquinones. Cyclic voltammetry data in aqueous solution have shown a quasi-reversible CoIII/CoII process at E 1/2 = −0.26 V vs Fc/Fc+. Reactivity studies revealed the dissociation of bhnq2– from the complex upon reduction of 1 with ascorbic acid, and a dependence of the reaction rate on the oxygen concentration suggests the occurrence of redox cycling.