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 Mn^III-superoxo species, Mn(BDP^BrP)(O₂⋅) (1, H₂BDP^BrP=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 Mn^III-hydroperoxo complex, Mn(BDP^BrP)(OOH) (2), alongside 4-dimethylaminophenoxy radical; whereas, upon treatment with 4-nitrophenol, complex 1 undergoes a proton transfer process to afford a Mn^IV-hydroperoxo complex, [Mn(BDP^BrP)(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 Mn^III-superoxo complex, 1.

Keywords: Hydroperoxo; Manganese; O2 activation; Superoxo; and Hydrogen atom abstraction (HAA).