HALIDE SUBSTITUTIONS IN THE [RH2(O2-)(OH)2(H2O)N]3+ COMPLEX

Transition metal complexes containing activated dioxygen continue to attract considerable attention and are widely used as models, either as oxygen carriers or as catalysts in biological and industrial oxidations (1,2). Cobalt complexes containing the coordinated O2 molecule are well known (3,4), but the rhodium analogues are rare (5-8). The known complexes with coordinated O2 are rhodium(III) compounds containing strong nitrogen donor ligands. Our recent studies have focused on a synthesis of dioxygen rhodium derivatives in which a superoxide anion (O2-) is bound to the [Rh(III)-Rh(III)] core surrounded by other donor molecules, e.g. H2O, RCO2-(7,8), to investigate the effect of a coordination sphere of the metal centre on the redox properties of the O2- radical combined to it(9). The [Rh2(O2-)(OH)2(H2O)n]3+ cation, the product of oxidative addition of dioxygen to the [Rh2(H2O)10]4+ dimer, was isolated by us and examined in aqueous HClO4(7,9). So far we have been unable to isolate its solid but the water molecules coordinated to the [Rh2(O2-)-(OH)2]3+ moiety were found to undergo substitution relatively easily(8).