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

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. (C) 2000 Elsevier Science S.A.