Selective Photo-Induced Oxidation with O₂ of a Non-Heme Iron(III) Complex to a Bis(imine-pyridyl)iron(II) Complex

Non-heme iron(II) complexes of pentadentate N4Py ( N,N-bis(2-pyridylmethyl)- N-bis(2-pyridyl)methylamine) type ligands undergo visible light-driven oxidation to their iron(III) state in the presence of O₂ without ligand degradation. Under mildly basic conditions, however, highly selective base catalyzed ligand degradation with O₂, to form a well-defined pyridyl-imine iron(II) complex and an iron(III) picolinate complex, is accelerated photochemically. Specifically, a pyridyl-CH₂ moiety is lost from the ligand, yielding a potentially N4 coordinating ligand containing an imine motif. The involvement of reactive oxygen species other than O₂ is excluded; instead, deprotonation at the benzylic positions to generate an amine radical is proposed as the rate determining step. The selective nature of the transformation holds implications for efforts to increase catalyst robustness through ligand design.