Reduction and Aerobic Oxidation of Hexaketocyclohexane (C6O6) by Reaction with Metallic Copper

Cyclic C6O6 has been reacted with metallic copper as a potential route to rhodizonate complexes of Cu(II). The product isolated under aerobic conditions has been found from crystallographic analysis to contain croconate C5O52- and oxalate C2O42- ligands bridging CuII(tmeda) centers in a linear polymer of formula [(tmeda)Cu(μ-C5O5)Cu(tmeda)(μ-C2O4)]n. Oxalate ligands are believed to result from O2 addition to a CuI(C6O6•-) species, formed initially in the reaction, in steps that give C5O52- and CO2•- radical anion by elimination and ring contraction.