Theory Revealing Unusual Non-Rebound Mechanisms Responsible for the Distinct Reactivities of O═MnIV═O and [HO–MnIV–OH]2+ in C–H Bond Activation

Abstract

This article uses theory to address the origins of the reactivity differences between MnIV═O and MnIV–OH complexes, having identical ligand spheres and metal oxidation states, toward 9,10-dihydroanthracene (DHA) under different pH conditions. Theory discovers different non-rebound mechanisms leading to unique products for the two complexes. One of these is a novel mechanism that operates under basic conditions and that rationalizes the formation of anthraquinone through an anthracene radical anion intermediate. In addition, the calculations reveal a rich mechanistic scheme having blended hydrogen atom transfer and proton-coupled electron transfer (HAT/PCET) with both proton transfer/electron transfer (PT/ET) and electron transfer/proton transfer (ET/PT) characters. The distinct nature of the transition states, such as PT/ET and ET/PT, for the second H-abstraction reactions from the substrate radical by the MnIV═O and MnIV–OH complexes accounts for the observed product distributions for these two species. ...