No abstract

Mononuclear 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)

The green complex S=1 [(TPEN)FeO]2+ [TPEN=N,N,N',N'-tetrakis(2-pyridylmethyl)ethane-1,2-diamine] has been obtained by treating the [(TPEN)Fe]2+ precursor with meta-chloroperoxybenzoic acid (m-CPBA). This high-valent complex belongs to the emerging family of synthetic models of Fe(IV)=O intermediates invoked during the catalytic cycle of biological systems. This complex exhibits spectroscopic characteristics that are similar to those of other models reported recently with a similar amine/pyridine environment. Thanks to its relative stability, vibrational data in solution have been obtained by Fourier transform infrared. A comparison of the Fe=O and Fe=(18)O wavenumbers reveals that the Fe-oxo vibration is not a pure one. The ability of the green complex to oxidize small organic molecules has been studied. Mixtures of oxygenated products derived from two- or four-electron oxidations are obtained. The reactivity of this [FeO]2+ complex is then not straightforward, and different mechanisms may be involved.