High-valent iron complexes with tetraamido macrocyclic ligands: Structures, Mössbauer spectroscopy, and DFT calculations

Iron complexes of tetraamido macrocyclic ligands (TAML) are unique synthetic oxidation catalysts. In general, the central FeIII ion (S = 3/2) is surrounded by four, almost planar, deprotonated amide-N σ-donors although the full suite with new generation systems includes some substitution of amides with related donor functionalities. Oxidation under different conditions affords a variety of high-valent forms of iron–TAMLs. This review provides a summary and discussion of structural and spectroscopic features of complexes oxidized by one equivalent above the ferric state. These comprise FeIV–TAML high spin (S = 2) and intermediate spin (S = 1) systems, wherein the oxidation equivalent can be taken from the metal (FeIV) or the ligand (TAML radical-cation FeIII), and coupled spin (S = 0) systems of μ-oxoiron(IV) dimers. The discussion is principally based on data obtained by X-ray crystallography, Mössbauer spectroscopy, and density functional theory calculations.