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

Mononuclear Fe-IV 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 (L-5(2)) or N-methyl-N,N',N'-tris(2-pyridylmethyl)propane-1,3-diamine (L-5(3)). These highly unstable green complexes are characterized by an absorption band at ca. 750nm. Mossbauer data indicate that the iron center is low spin (S 1) with an axial electronic structure, allowing identification of the mononuclear FeIV complexes as [(L5FeO)-O-IV](2+) or [(L5FeOCH3)-O-IV](3+). In acetonitrile/dichloromethane solutions, the (L5FeIV)-Fe-3 system exhibits very selective activities toward hydroxylation of cyclohexane or epoxidation of cyclooctene and cis-stilbene. Computational studies performed on [(L5FeO)-O-IV](2+) and on the model compound [(NH3)(5)(FeO)-O-IV](2+) reveal that the ground state possesses two unpaired electrons in the two pi* orbitals, as known for O-2. Electronic spectra computed by time-dependent DFT exhibit only one band in the visible region that is essentially due to d-d transitions. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.