Insertion of molecular oxygen in transition-metal hydride bonds, oxygen-bond activation, and unimolecular dissociation of metal hydroperoxide intermediates

Thermal activation of molecular oxygen is observed for the late-transition-metal cationic complexes [M(H)(OH)](+) with M = Fe, Co, and Ni. Most of the reactions proceed via insertion in a metal-hydride bond followed by the dissociation of the resulting metal hydroperoxide intermediate(s) upon losses of O, OH, and H2O. As indicated by labeling studies, the processes for the Ni complex are very specific such that the O-atoms of the neutrals expelled originate almost exclusively from the substrate O-2. In comparison to the [M(H)(OH)] cations, the ion-molecule reactions of the metal hydride systems [MH](+) (M = Fe, Co, Ni, Pd, and Pt) with dioxygen are rather inefficient, if they occur at all. However, for the solvated complexes [M(H)(H2O)](+) (M Fe, Co, Ni), the reaction with O-2 involving O-O bond activation show higher reactivity depending on the transition metal: 60% for the Ni, 16% for the Co, and only 4% for the Fe complex relative to the [Ni(H)(OH)]+/O-2 Couple.