High-valent Fe-OH species are important intermediates in hydroxylation chemistry. Such complexes have been implicated in mechanisms of oxygen-activating enzymes and have thus far been observed in Compound II of sulfur-ligated heme enzymes like cytochrome P450. Attempts to synthetically model such species have thus far seen relatively little success. Here, the first synthetic (FeOHn)-O-IV complex has been generated and spectroscopically characterized as either [(LFeOH)-O-IV](-) or [(LFeOH2)-O-IV](0), where H4L = Me4C2(NHCOCMe2NHCO)(2)CMe2 is a variant of a tetra-amido macrocyclic ligand (TAML). The steric bulk provided by the replacement of the aryl group with the -CMe2CMe2- unit in this TAML variant prevents dimerization in all oxidation states over a wide pH range, thus allowing the generation of (FeOHn)-O-IV in near quantitative yield from oxidation of the [(LFeOH2)-O-III](-) precursor.