[Kinetics and mechanisms of the reactions of transition metal complexes]

With the objective of elucidating the mechanisms of dioxygen activation by transition metal complexes, we have investigated functional models of some metalloenzymes, such as phenoxazinone synthase and catechol oxidase, based on bisdimethylglyoximatocobalt(II) and -iron(II) complexes. Kinetic studies and the identification of intermediates permitted to establish a free radical mechanism. The catalytic cycle involves H-atom abstraction from the catechol by a superoxo complex, generating a semi-quinone anion radical, which coordinates to the metal, affording new complexes. Useful free-radical intermediates in biological systems are not impossible since tyrosinase has been shown to contain coordinated tyrosyl radical as an integral part of the active enzyme. We have interpreted the structure-reactivity relationship observed in the reaction of the [Pd2Cl2(dppm)2] dimer with arenesulfonyl azides.