LASER FLASH-PHOTOLYSIS STUDY OF THE MECHANISM OF PHOTOOXIDATION OF ALKANES CATALYZED BY DECATUNGSTATE ANION

Generated during light excitation, the O(2p) --> W(5d) ligand-to-metal charge transfer (LMCT) excited state of decatungstate anion (W10O324- ) relaxes for t < 30 ps to a transient X which persists for 5 ns. In t he nanosecond time domain, it reacts with all components of the photoc atalytic system (substrate, organic counter-ion and solvent) to give a one-electron reduced decatungstate species HW10O324- and an organic r adical R(.). The latter is quenched by dioxygen at a near diffusion-co ntrolled rate, forming a peroxyl radical ROO(.), In the solvent cage, the peroxyl radical ROO(.) reoxidizes HW10O324- to give the hydroperox ide ROOH and W10O324-, thus closing the catalytic cycle. The catalyst reoxidation is the rate-limiting step of the alkane oxidation.