The Dioxoosmium(VI) Complex [OsO_2(H_2biim)_2](NO_3)_2 as Oxygen-Transfer Reagent — Synthesis and Solid-State Structure of Bis(2,2'-biimidazole)-bis(triphenylphosphane oxide)osmium(III) Nitrate

摘要

Treatment of 0_s0_4 (1) with 2,2'-biimidazole (H_2biim) (2) in a methanol/acetone mixture, and in the presence of nitric acid produces the novel dioxoosmium(VI) complex [OsO_2(H_2biim)_2](N0_3)_2 centre dot CH_3OH (3). Addition of 2 equiv, of PPh_3 (4) and 1 equiv. of nitric acid to 3 affords moponuclear [Os(H_2biim)_2(0=PPh_3)_2](N0_3)_3 (5) by a redox reaction which involves the transfer of oxygen from osmium to PPh_3. The x-ray crystal structure of 5 reveals an octahedral coordination sphere around the osmium(III) centre. This occurs as a result of the two H_2biim chelating ligands in the equatorial positions and two datively bonded phosphane oxide groups 0= PPh_3 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 monocationic [Os(Hbiim)_2(0=PPh_3)_2]N0_3 (6).