Nature has chosen high-spin iron(IV)=O oxidants for nonheme iron enzymes with mononuclear active sites to cleave strong substrate A 5000-fold Increase in the HAT Reactivity of a Nonheme Fe(IV)=O Complex

Nonheme iron enzymes utilize S = 2 iron(IV)-oxo intermediates as oxidants in biological oxygenations. In contrast, corresponding synthetic 10-Fold Increase in Hydrogen Atom Transfer Reactivity for a Series of S = 1 FeIV=O Complexes Over the S = 2 [(TQA)FeIV=O]2+ Complex via Entropic Lowering of Reaction Barriers by Secondary Sphere Cycloalkyl Substitution