Geometric and electronic structure and reactivity of a mononuclear ‘side-on’ nickel(iii)–peroxo complex

Metal-dioxygen adducts, such as metal-superoxo and -peroxo species, are key intermediates often detected in the catalytic cycles of dioxygen activation by metalloenzymes and biomimetic compounds. The synthesis and spectroscopic characterization of an end-on nickel(II)-superoxo complex with a 14-membered macrocyclic ligand was reported previously. Here we report the isolation, spectroscopic characterization, and high-resolution crystal structure of a mononuclear side-on nickel(III)-peroxo complex with a 12-membered macrocyclic ligand, [Ni(12-TMC)(O2)]+ (1) (12-TMC = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane). In contrast to the end-on nickel(II)-superoxo complex, the nickel(III)-peroxo complex is not reactive in electrophilic reactions, but is capable of conducting nucleophilic reactions. The nickel(III)-peroxo complex transfers the bound dioxygen to manganese(II) complexes, thus affording the corresponding nickel(II) and manganese(III)-peroxo complexes. Our results demonstrate the significance of supporting ligands in tuning the geometric and electronic structures and reactivities of metal–O2 intermediates that have been shown to have biological as well as synthetic usefulness in biomimetic reactions. Compounds containing dioxygen bonded to metal atoms – such as metal-peroxo or -superoxo species – are models of enzymes that can activate oxygen. Now a mononuclear side-on nickel(III)-peroxo complex has been made, which is stabilized by a macrocyclic ligand. The complex can transfer the bound dioxygen to another metal, and conduct nucleophilic reactions.