The reduction of the N C bond of benzonitriles promoted by OsH6((PPr3)-Pr-i)(2) (1) has been studied. Complex 1 releases a H-2 molecule and coordinates 2,6-dimethylbenzonitrile to afford the tetrahydride OsH4{kappa(1)-N-(N CC6H3Me2)}((PPr3)-Pr-i)(2) (2), which is thermally stable toward the insertion of the nitrile into one of the Os-H bonds. In contrast to 2,6-dimethylbenzonitrile, benzonitrile and 2-methylbenzonitrile undergo insertion, via Os(eta(2)-N CR) intermediates, to give the azavinylidene derivatives OsH3(=N=CC6H4R)((PPr3)-Pr-i)(2) [R = H (3) or Me (4)]. The analysis by means of computational tools (EDA-NOCV) of the bonding situation in these compounds suggests that the donor-acceptor nature of the osmium azavinylidene bond dominates over the mixed electron-sharing/donor-acceptor and pure electron-sharing bonding modes. The N atom is strongly nucleophilic, whereas one of the hydrides is electrophilic. In spite of the different nature of these centers, the migration of the latter to the N atom is kinetically prevented. However, the use of water as a proton shuttle allows hydride migration, as a consequence of a significant decrease in the activation barrier. The resulting phenylaldimine intermediates evolve by means of orthometalation to give OsH3{kappa(2)-N,C-NH=CHC6H3R)}((PPr3)-Pr-i)(2) [R = H (5) or Me (6)]. The presence of electrophilic and nucleophilic centers in 3 confers upon it the ability to activate sigma-bonds, including H-2 and pinacolborane (HBpin). The reaction with the latter gives OsH3{kappa(2)-N,C-[N(Bpin)=CHC6H4]}((PPr3)-Pr-i)(2) (7).