Reversible O-O Bond Scission of Peroxodiiron(III) to High-Spin Oxodiiron(IV) in Dioxygen Activation of a Diiron Center with a Bis-tpa Dinucleating Ligand as a Soluble Methane Monooxygenase Model

The conversion of peroxodiiron(III) to high-spin S = 2 oxodiiron(IV) via reversible O-O bond scission in a diiron complex with a bis-tpa dinucleating ligand, 6-hpa, has been characterized by elemental analysis; kinetic measurements for alkene epoxidation; cold-spray ionization mass spectrometry; and electronic absorption, Mossbauer, and resonance Raman spectroscopy to gain insight into the O-2 activation mechanism of soluble methane monooxygenases. This is the first synthetic example of a high-spin S = 2 oxodiiron(IV) species that oxidizes alkenes to epoxides efficiently. The bistability of the peroxodiiron(III) and high-spin S = 2 oxodiiron(IV) moieties is the key feature for the reversible O-O bond scission.