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 T1min 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.