A Manganese(IV)-Hydroperoxo Intermediate Generated by Protonation of the Corresponding Manganese(III)-Superoxo Complex

Earlier work revealed that metal-superoxo species primarily function as radicals and/or electrophiles. Herein, we present ambiphilicity of a Mn-III-superoxo complex revealed by its proton- and metal-coupled electron-transfer processes. Specifically, a Mn-IV-hydroperoxo intermediate, [Mn((BDPP)-P-Br)(OOH)](+) (1, (H2BDPP)-P-Br = 2,6-bis((2-(S)-di(4-bromo)phenylhydroxylmethyl-1-pyrrolidinyl)methyl)pyridine) was generated by treatment of a Mn-III-superoxo complex, Mn((BDPP)-P-Br)(O-2(center dot)) (2) with trifluoroacetic acid at -120 degrees C. Detailed insights into the electronic structure of 1 are obtained using resonance Raman and multi-frequency electron paramagnetic resonance spectroscopies coupled with density functional theory calculations. Similarly, the reaction of 2 with scandium(III) triflate was shown to give a Mn(IV)/Sc(III) bridging peroxo species, [Mn((BDPP)-P-Br)(OO)Sc(OTf)(n)]((3-n)+) (4). Furthermore, it is found that deprotonation of 1 quantitatively regenerates 2, and that one-electron oxidation of the corresponding Mn-III-hydroperoxo species, Mn((BDPP)-P-Br)(OOH) (3), also yields 1.