A Mechanistic Spectrum of O-H Bond Cleavage Observed for Reactions of Phenols with a Manganese Superoxo Complex.

ABSTRACT

Reaction of a rare and well-characterized MnIII-superoxo species, Mn(BDPBrP)(O2⋅) (1, H2BDPBrP=2,6-bis((2-(S)-di(4-bromo)phenylhydroxylmethyl-1-pyrrolidinyl)methyl)pyridine), with 4-dimethylaminophenol at -80 °C proceeds via concerted proton electron transfer (CPET) to produce a MnIII-hydroperoxo complex, Mn(BDPBrP)(OOH) (2), alongside 4-dimethylaminophenoxy radical; whereas, upon treatment with 4-nitrophenol, complex 1 undergoes a proton transfer process to afford a MnIV-hydroperoxo complex, [Mn(BDPBrP)(OOH)]+ (3). Intriguingly, the reactions of 1 with 4-chlorophenol and 4-methoxyphenol follow two routes of CPET and sequential proton and electron transfer to furnish complex 2 in the end. UV-vis and EPR spectroscopic studies coupled with DFT calculations provided support for this wide mechanistic spectrum of activating various phenol O-H bonds by a single MnIII-superoxo complex, 1.