2-STATE REACTIVITY IN ORGANOMETALLIC GAS-PHASE ION CHEMISTRY

In contrast to organic reactions, which can almost always be described in terms of a single multiplicity, in organometallic systems, quite o ften more than one state may be involved. The phenomenon of two states of different multiplicities that determine the minimum-energy pathway of a reaction is classified as two-state reactivity (TSR). As an exam ple, the ion/molecule reactions of 'bare' transition-metal-monoxide ca tions with dihydrogen and hydrocarbons have been analyzed in terms of the corresponding potential-energy hypersurfaces. It turns out that, b esides classical factors, such as the barrier heights, the spin-orbit coupling factor is essential, since curve crossing between the high- a nd low-spin states constitutes a distinct mechanistic step along the r eaction coordinates. Thus, TSR may evolve as a new paradigm for descri bing the chemistry of coordinatively unsaturated transition-metal comp lexes. This concept may contribute to the understanding of organometal lic chemistry in general and for the development of oxidation catalyst s in particular.