Mixed-ligand hydride complexes OsHCl(CO)-(PPh3)(2)L (2) [L = P(OMe)(3), P(OEt)(3)] were prepared by OsHCl(CO)(PPh3)(3) (1) to react with an excess of phosphite P(OR)(3) in refluxing toluene. Dichloro compounds OSCl2(CO)(PPh3)(2)L (3, 4) were also prepared by reacting 1, 2 with HCl. Treatment of hydrides OsHCl(CO)(PPh3)(2)L (2), first with triflic acid and then with an excess of RN3 afforded organic azide complexes [OsCl(eta(1)-N3R)(CO)(PPh3)(2)L]BPh4 (5-7) [R = 4-CH3C6H4CH2, C6H5CH2, C6H5; L = P(OEt)(3)]. Benzylazide complexes react in CH2Cl2/ethanol solution, leading to the imine derivative [OsCl(CO){eta(1)-NH=C(H)C6H4-4-CH3}(PPh3)(2){P(OEt)(3)}]BPh4 (8b). Hydrazine complexes [OsCl(CO)(RNHNH2)(PPh3)(2)L]BPh4 (9-11) [R = H, CH3, C6H5; L = P(OMe)(3), P(OEt)(3)] were prepared by allowing hydride species OsHCl(CO)(PPh3)(2)L (2) to react first with triflic acid and then with an excess of hydrazine. Aryldiazene derivatives [OsCl(CO)(ArN=NH)(PPh3)(2)L]BPh4 (12, 13) were also prepared following two different methods: (i) by oxidizing arylhydrazine [OsCl(C6H5NHNH2)(CO)(PPh3)(2)L]BPh4 (11) with Pb(OAc)(4) in CH2Cl2 at -30 degrees C; (ii) by allowing hydride species OsHCl(CO)(PPh3)(2)L (2) to react with aryldiazonium cations ArN2+ (Ar = C6H5, 4-CH3C6H4) in CH2Cl2. The complexes were characterized spectroscopically and by X-ray crystal structure determination of OsHCl(CO)(PPh3)(2)[P(OEt)(3)] (2b) and [OsCl{eta(1)-NH=C(H)C6H4-4-CH3}(CO)(PPh3)(2){P(OEt)(3)}]BPh4 (8b).