Characterization of peroxo-Mo and superoxo-Mo intermediate adducts in Photo-Oxygen Atom Transfer with O2

After photo Oxygen Atom Transfer, the reduced Mo(IV)Cl2O(4,4′-dicarboxylato-2,2′-bipyridine)/TiO2-NT specie is formed, which under the O2 atmosphere generates the intermediary peroxo-Mo(VI) {Mo(VI)(O)(O2)} and superoxo-Mo(V) {Mo(V)(O)(O2-•)} species characterized by FT-IR, Raman and EPR (which evidences the formation of the superoxo-Mo(V)) also evidenced in IR by the isotopic shift with 18O. These species are highly reactive and difficult to characterize, but the complex anchored on TiO2 allows to observe them at room temperature. The intermediary peroxo-Mo has nucleophilic and the superoxo-Mo has electrophilic character. Oxidation of a mixture of organic molecules shows that the nucleophilic oxidation products are formed in a higher proportion than the electrophilic ones. During the reaction, an increase of the electrophilic products suggests that peroxo is transformed into the superoxo specie as corroborated by Raman, FT-IR, and EPR spectroscopies. The reaction formation patterns of the intermediary species are concomitant with the appearance of the superoxo species (suggested by the simultaneous formation pattern of Mo(V) and the radical production). Both tendencies are in accord with the electrophilic and nucleophilic reaction pattern suggesting that the peroxo-Mo species are formed first, and then it is partially transformed into the superoxo-Mo entities.