Longer arms, higher reactivity: equatorial coordination ring expansion boosts iron-oxo activity.

Equatorial sulfur coordination has been shown to be important in enzymatic reactivity. To understand its effect, we synthesized two N4S-bound pentadentate ligands that differ by an extra -CH2- substituent in the ligand scaffold. The results demonstrate a dramatic rate enhancement for oxygen atom transfer to the substrate due to an increased redox potential.