The equatorial ligand effect on the properties and reactivity of iron(V)‐oxo intermediates

High‐valent metal‐oxo oxidants are common catalytic cycle intermediates in enzymes and known to be highly reactive. To understand what features of these oxidants affect their reactivity, we synthesized and characterized a series of novel biomimetic iron(V)‐oxo oxidants with periphery substituted biuret‐modified tetraamidomacrocyclic ligand. We find major shifts in the UV‐Vis absorption as a result of replacing a group in the equatorial plane of the iron(V)‐oxo species. Further characterization using EPR, ESI‐MS and resonance Raman spectroscopy predict structural differences and the electronic configuration of these complexes. A systematic reactivity study with a range of substrates was performed and shows that the reactions are affected by electron‐withdrawing substituents in the equatorial ligand, which enhances the reaction rate by almost 16 orders of magnitude. As such, the long‐range electrostatic perturbations have a major influence on the rate constant. Finally, computational studies identify the various electronic contributions to the rate determining reaction step and explain how the equatorial ligand periphery affects the properties of the oxidant.