The dioxoosmium(VI) complex [OsO2(H(2)biim)(2)](NO3)(2) as oxygen-transferreagent - Synthesis and solid-state structure of bis(2,2 '-biimidazole)-bis(triphenylphosphane oxide)osmium(III) nitrate

Treatment of OsO4 (1) with 2,2'-biimidazole (H(2)biim) (2) in a methanol/ac etone mixture, and in the presence of nitric acid produces the novel dioxoo smium(VI) complex [OsO2(H(2)biim)(2)](NO3)(2). CH3OH (3). Addition of 2 equ iv, of PPh3 (4) and 1 equiv, of nitric acid to 3 affords mononuclear [Os(H( 2)biim)(2)(O=PPh3)(2)](NO3)(3) (5) by a redox reaction which involves the t ransfer of oxygen from osmium to PPh3. The Xray crystal structure of 5 reve als an octahedral coordination sphere around the osmium(Ill) centre. This o ccurs as a result of the two H(2)biim chelating ligands in the equatorial p ositions and two datively bonded phosphane oxide groups O=PPh3 in the axial positions. Hydrogen bonds are responsible for the formation of a polymeric structure in the solid state. The latter complex reacts with KOH to form m onocationic [Os(Hbiim)(2)(O=PPh3)(2)]NO3 (8).