ChemInform Abstract: Properties, Structure and Reactivity of Cobaloximes

Cobaloximes are bis(dioximate) cobalt complexes with the metal ion having different oxidation and coordination numbers. The most common cobaloximes are octahedral complexes of formula trans-LCo(dioxH)2X, where dioxH is the dioxime monoanion, L a neutral ligand and X a monoanionic ligand. Due to the possibility to obtain and characterize CoIII compounds with a large variety of dioxH, X and L ligands, they constitute a unique system of octahedral cobalt complexes. The availability of a large number of complexes has allowed to rationalize their structural properties in solution and in the solid state and their reactivity in term of cis and trans influences and effects. These studies were also prompted by the widely accepted proposal that cobaloximes are model systems of cobalamins, the cofactors of B12 enzymes. Cobaloximes behave as functional models of cobalamin also towards the reductive dechlorination of chloroethylenes. Alkylcobaloximes have catalytic applications in organic chemistry and in polymerization reactions. Recently, inorganic cobaloximes have been studied as catalysts for the hydrogen evolution in the presence of a proton source. All these aspects of cobaloximes and of some related compounds, such as dioximate chlatrochelates, are presented in this chapter. Keywords: Cobaloximes; Structure; Properties; Reactivity; Cis Influence/effect; Trans influence/effect; B12 model systems; Polymerization catalysts; Hydrogen evolution