Reactivity of High-Valent Iron–Oxo Species in Enzymes and Synthetic Reagents: A Tale of Many States

The Account discusses the phenomenon of two-state reactivity (TSR) or multistate reactivity (MSR) in high-valent metal–oxo reagents, projecting its wide-ranging applicability starting from the bare species, through the reagents made by Que, Nam, and collaborators, to the Mn(V)–oxo substituted polyoxometalate, all the way to Compound I species of heme enzymes. The Account shows how the behaviors of all these variegated species derive from a simple set of electronic structure principles. Experimental trends that demonstrate TSR and MSR are discussed. Diagnostic mechanistic probes are proposed for the TSR/MSR scenario, based on kinetic isotope effect, stereochemical studies, and magnetic- and electric-field effects.