Characterization, orbital description, and reactivity patterns of transition-metal oxo species in the gas phase

Metal-ore and -peroxo species play key roles in catalytic oxidations using transition metals. This contribution addresses gas-phase studies of diatomic metal-ore species and their properties which turn out to be of prime importance for the understanding of the observed reactivity patterns. A second topic concerns higher transition-metal oxides such as di- and trioxides. For these species there exists a structural dichotomy with the corresponding dioxygen complexes, e.g,, MO2 reversible arrow M(O-2). Most of the metal-based oxidations described involve crossings between surfaces of different spin as crucial steps, and the violation of spin conservation is proposed to determine the reactivity of the late transition-metal oxides. The ability of transition metals to mediate surface crossings via spin-orbit coupling is introduced as a key aspect in oxidation catalysis which has as yet not been fully appreciated. It is further outlined how these fundamental properties may relate to the properties of metal-ore catalysts in the condensed phase.