Thermodynamic and kinetic studies of stable low valent transition metal radical complexes

Abstract

The majority of stable low valent transition metal organometallic complexes obey the familiar eighteen-electron rule. Oxidative addition reactions of these complexes normally proceed by initial generation of sixteen electron coordinatively unsaturated species. Low valent 17 electron transition metal radical complexes ML n can be generated thermally or photochemically. Since radical recombination to form metal-metal bonded dimers L n MML n is a rapid process, the absolute concentration of metal radicals that can be achieved in solution is normally quite low. In cases where either there is no stable metal–metal bonded dimer or the metalmetal bond is so weak that the complex is completely dissociated in solution, relatively high concentrations (ca. 1 mM) are readily achieved. Illustrative mechanisms for oxidative addition reactions of ML n are discussed with a focus on reaction mechanisms that are second order in total metal concentration.