Impact of Secondary Sphere Hydrogen Bonds on O2 Reactivity within a Nonheme Iron Complex

A nonheme iron complex bearing the tris(6-phenylamino-pyridyl)methylamine (TPA NHPh ) ligand with appended hydrogen bond (H-bond) groups displays facile O 2 reactivity to form a monomeric Fe(III)OH complex, which can release •OH via rebound to a carbon radical. An analogous compound without H-bonds, based on tris(6-methylpyridyl)methylamine (TPA Me ), exhibits minimal O 2 reactivity, forming a Fe(III) 2 (μ-O)(μ–OH) dimer, which also reacts with carbon-based radicals. The H-bonding system enables O 2 binding and activation at weakly reducing nonheme iron complexes, highlighting a cooperative role of secondary sphere units to facilitate reactions at atypical redox environments.