Intrinsic properties and reactivities of mononuclear nonheme iron-oxygen complexes bearing the tetramethylcyclam ligand

► FeIVO, FeIII (η2O2), and FeIIIO2H complexes having a common ligand environment. ► Models of intermediates in oxygen activation by mononuclear nonheme iron enzymes. ► Axial ligands influence FeO bonding and spectroscopic properties of FeIVO complexes. ► Generation of FeIVO species by activating O implicates an FeIII-superoxo intermediate. ► Reactivity studies with model substrates establish catalytic potency of short-lived intermediates.