Modeling C–H Abstraction Reactivity of Nonheme Fe(IV)O Oxidants with Alkanes: What Role Do Counter Ions Play?

It is shown that the addition of ClO4– counterions to [N4PyFeO]2+ enables us to avoid the anomalies associated with the self-interaction error in DFT and to describe for the first time the entire trajectories for alkane hydroxylation and desaturation by this potent oxidant. The predicted reactivity trends for cyclohexadiene and cyclohexane reproduce the experimentally observed product selectivity and relative ease of oxidation. Furthermore, the advent of this well-behaved oxidant enables us to derive generalizing principles: (a) orbital selection rules that predict transition state structures and (b) the exchange-enhanced reactivity (EER) principle that predicts the dominance of the high-spin state during the entire oxidation process. It is shown that the orbital selection rules and EER principle are general descriptors of the reactivity of metal-oxo systems and appear to be fundamental principles of chemistry.