Preparation and reactivity of osmium(II) hydride complexes with phosphites and polypyridyls

Chloro-complexes OsCl(N-N)P₃]BPh₄ (1, 2) N-N=2,2^′-bipyridine (bpy) and 1,10-phenanthroline (phen); P=P(OEt)₃ and PPh(OEt)₂] were prepared by allowing OsCl₄(N-N) to react with zinc dust in the presence of phosphites. Treatment of the chloro-complexes 1, 2 with NaBH₄ yielded, in the case of bpy, the hydride OsH(bpy)P₃]BPh₄ (4) derivatives. Mono-phosphite OsCl(bpy)₂P]BPh₄ (3) complexes were also prepared by reacting the OsCl₂(bpy)₂]Cl compound with zinc dust in the presence of phosphite. Protonation reaction of the hydride OsH(bpy)P₃]⁺ (4) cations with Brønsted acid was studied and led to thermally unstable (above 0 °C) dihydrogen Os(η²-H₂)(bpy)P₃]²⁺ (4*) derivatives. The presence of the H₂ ligand is supported by variable-temperature NMR spectra and T_1min measurements. Carbonyl Os(CO)(bpy){P(OEt)₃}₃](BPh₄)₂ (5), nitrile Os(CH₃CN)(bpy){P(OEt)₃}₃](BPh₄)₂ (6), and hydrazine Os(bpy)(NH₂NH₂){P(OEt)₃}₃](BPh₄)₂ (7) complexes were prepared by substituting the H₂ ligand in the η²-H₂ (4*) derivatives. Aryldiazene complex Os(C₆H₅NNH)(bpy){P(OEt)₃}₃](BPh₄)₂ (8) was also obtained by allowing the hydride OsH(bpy)P₃]BPh₄ to react with phenyldiazonium cation.