A cobalt-nitrosyl complex, [(BPI)Co(NO)(OAc)], 1 {BPI = 1,3-bis(2'-pyridylimino)isoindol} was prepared and characterized. Structural characterization revealed that the cobalt center has a distorted square pyramidal geometry with the NO group coordinated from the apical position in a bent fashion. The addition of dioxygen (O-2) to the dichloromethane solution of complex 1 resulted in the formation of nitro complex, [(BPI)Co(NO2)(OAc)], 2. It was characterized structurally. Kinetic studies suggested the involvement of an associative mechanism. FT-IR spectroscopic studies suggested the formation of the intermediate la [(BPI)Co-III(NO)(O-2(-)(OAc)] in the reaction. The intermediate la decomposed to complex 2 via a presumed peroxynitrite intermediate which was implicated by its characteristic phenol ring nitration reaction.