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

Iron complexes of tetraamido macrocyclic ligands (TAML) are unique synthetic oxidation catalysts. In general, the central Fe-III ion (S = 3/2) is surrounded by four, almost planar, deprotonated amide-N sigma-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 Fe-IV-TAML high spin (S = 2) and intermediate spin (S = 1) systems, wherein the oxidation equivalent can be taken from the metal (Fe-IV) or the ligand (TAML radical-cation Fe-III), and coupled spin (S = 0) systems of mu-oxoiron(IV) dimers. The discussion is principally based on data obtained by X-ray crystallography, Mossbauer spectroscopy, and density functional theory calculations. (c) 2006 Elsevier Inc. All rights reserved.