Spectroscopic Characterization of an FeIV Intermediate Generated by Reaction of XO− (X = Cl, Br) with an FeII Complex Bearing a Pentadentate Non‐Porphyrinic Ligand − Hydroxylation and Epoxidation Activity

Abstract

AbstractMononuclear FeIV intermediates have been generated in MeOH upon reaction of sodium hypochlorite or hypobromite with a ferrous complex bearing the pentadentate ligands N‐methyl‐N,N′,N′‐tris(2‐pyridylmethyl)ethane‐1,2‐diamine (L52) or N‐methyl‐N,N′,N′‐tris(2‐pyridylmethyl)propane‐1,3‐diamine (L53). These highly unstable green complexes are characterized by an absorption band at ca. 750 nm. Mössbauer data indicate that the iron center is low spin (S = 1) with an axial electronic structure, allowing identification of the mononuclear FeIV complexes as [L5FeIVO]2+ or [L5FeIVOCH3]3+. In acetonitrile/dichloromethane solutions, the L53FeIV system exhibits very selective activities toward hydroxylation of cyclohexane or epoxidation of cyclooctene and cis‐stilbene. Computational studies performed on [L5FeIVO]2+ and on the model compound [(NH3)5FeIVO]2+ reveal that the ground state possesses two unpaired electrons in the two π* orbitals, as known for O2. Electronic spectra computed by time‐dependent DFT exhibit only one band in the visible region that is essentially due to d‐d transitions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)