Chloro-complexes [OsCl(N-N)P 3 ]BPh 4 (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 OsCl 4 (N-N) to react with zinc dust in the presence of phosphites. Treatment of the chloro-complexes 1,2 with NaBH 4 yielded, in the case of bpy, the hydride [OsH(bpy)P 3 ]BPh 4 (4) derivatives. Mono-phosphite [OsCl(bpy) 2 P]BPh 4 (3) complexes were also prepared by reacting the [OsCl 2 (bpy) 2 ]Cl compound with zinc dust in the presence of phosphite. Protonation reaction of the hydride [OsH(bpy)P 3 ] + (4) cations with Bronsted acid was studied and led to thermally unstable (above 0 o C) dihydrogen [Os(η 2 -H 2 )(bpy)P 3 ] 2 + (4*) derivatives. The presence of the H 2 ligand is supported by variable-temperature NMR spectra and T 1 m i n measurements. Carbonyl [Os(CO)(bpy){P(OEt) 3 } 3 ](BPh 4 ) 2 (5), nitrile [Os(CH 3 CN)(bpy){P(OEt) 3 } 3 ](BPh 4 ) 2 (6), and hydrazine [Os(bpy)(NH 2 NH 2 ){P(OEt) 3 } 3 ](BPh 4 ) 2 (7) complexes were prepared by substituting the H 2 ligand in the η 2 -H 2 (4*) derivatives. Aryldiazene complex [Os(C 6 H 5 N NH)(bpy){P(OEt) 3 } 3 ](BPh 4 ) 2 (8) was also obtained by allowing the hydride [OsH(bpy)P 3 ]BPh 4 to react with phenyldiazonium cation.