Dinitrogen complexes [OsH(N-2)P-4]CF3SO3 [P = PPh(2)OMe, PPh(2)OEt, PPh(2)O(i)Pr, PPh-(OEt)(2)] were prepared and the substitution reactions with H-2, CO, and CNR studied. Dihydrogen derivatives [OsH(eta(2)-H-2)P-4](+) were also obtained and characterized by H-1 and P-31 NMR data, T-1 measurements and J(HD) values. Reactions of the dinitrogen complexes with the alkynes HC=CCO(2)R afforded the new alkenyl [Os{CH=C(H)CO(2)R}P-4]CF3SO3 (R = Me, Et) derivatives.