Reversible osmium(VI) nitrido to osmium(II) ammine interconversion in complexes containing polypyrazolyl ligands

This paper describes the 4e(-)/3H(+) interconversion between NH3 and N3-, w hich is reversible in the coordination spheres of Os complexes containing e ither tpm (tpm = tris(1-pyrazolyl)methane) or Tp (Tp = hydrotris(1-pyrazoly l)-borate anion) ligands. Electrochemical or chemical reduction of the nitr ido complexes [Os-VI(tpm)(Cl)(2)(N)(+) (1) and Os-VI(Tp)(Cl)(2)(N) (2) in a cidic asueous solution gives the corresponding Os-II-ammine complexes, whic h, after air oxidation and workup, are isolated and structurally characteri zed as [Os-III(tpm)(Cl)(2)(NH3)](PF6) (3) and Os-III(Tp)(Cl)(2)(NH3) (4). T he Os-III-ammine complexes are reoxidized electrochemically to the nitrido complexes by stepwise mechanisms involving the loss of both electrons and p rotons and sequential Os(III --> IV) and Os(IV --> VI) oxidations.