Alternative oxidants (e.g., O2 or H2O2 or 2,6-dichloropyridine 1-oxide, which was used in previous experimental studies ) would rigidly shift the reaction energetics without affecting relative energetics (Supporting Information Table ). The terminal M(IV)=O species is highly reactive and catalyzes a hydrogen atom transfer (HAT) step in which a hydrogen atom from the secondary carbon of propane is abstracted to form a metal-hydroxo intermediate (3) (i.e., M(III)-OH) and an isopropyl radical (Figure ). The reaction energy for this step, DE(HAT), is given by: