Electrochemical approach of the reductive activation of O 2 by a nonheme Fe II complex. Some clues for the development of catalytic oxidations †

We report an in-depth study of the reductive activation of O 2 by the nonheme [Fe II (L 5 2 )(MeCN)] 2+ complex carried out by cyclic Experimental evidence is obtained for the slow coordination of dioxygen to the ferrous center yielding an Fe II /O 2 adduct with a strong Fe II -O 2 character rather than an Fe III -superoxo one. Electron in Fe II -O 2 species occurs at a potential of ca. -700 mV vs. SCE, i.e. 200 mV above the O 2 to O 2 •-reduction, leading to the formati peroxo intermediate and then Fe III -hydroperoxo upon protonation by residual water. The experimental CVs recorded at variable variable Fe II concentration are well simulated taking into account a detailed mechanism initiated by the competitive reduction of O 2 O 2 adduct. Analysis of the concentration of the reaction intermediates generated as a function of the applied potential indicates t peroxo intermediate significantly accumulates at a potential of -650 mV. Oxidative bromination of anisole is assayed unde conditions at this potential to yield bromoanisole products. The low faradaic yields observed reveal that deleterious reactions s reduction of reaction intermediates likely occur. Based on the detailed mechanism elucidated, a number of improvements to a efficient catalytic reac-tions can be proposed.