title: Axial ligand and spin-state influence on the formation and reactivity of hydroperoxo-iron(III) porphyrin complexes.
abstract: The present study focuses on the formation and reactivity of hydroperoxo-iron(III) porphyrin complexes formed in the [Fe(III)(tpfpp)X]/H(2)O(2)/HOO(-) system (TPFPP=5,10,15,20-tetrakis(pentafluorophenyl)-21H,23H-porphyrin; X=Cl(-) or CF(3) SO(3)(-)) in acetonitrile under basic conditions at -15 °C. Depending on the selected reaction conditions and the active form of the catalyst, the formation of high-spin [Fe(III)(tpfpp)(OOH)] and low-spin [Fe(III)(tpfpp)(OH)(OOH)] could be observed with the application of a low-temperature rapid-scan UV/Vis spectroscopic technique. Axial ligation and the spin state of the iron(III) center control the mode of O-O bond cleavage in the corresponding hydroperoxo porphyrin species. A mechanistic changeover from homo- to heterolytic O-O bond cleavage is observed for high- [Fe(III)(tpfpp)(OOH)] and low-spin [Fe(III)(tpfpp)(OH)(OOH)] complexes, respectively. In contrast to other iron(III) hydroperoxo complexes with electron-rich porphyrin ligands, electron-deficient [Fe(III)(tpfpp)(OH)(OOH)] was stable under relatively mild conditions and could therefore be investigated directly in the oxygenation reactions of selected organic substrates. The very low reactivity of [Fe(III)(tpfpp)(OH)(OOH)] towards organic substrates implied that the ferric hydroperoxo intermediate must be a very sluggish oxidant compared with the iron(IV)-oxo porphyrin π-cation radical intermediate in the catalytic oxygenation reactions of cytochrome P450.
authors.affiliation: Inorganic Chemistry, Department of Chemistry and Pharmacy, Erlangen, Germany.
authors.forename: Alicja
authors.initials: A
authors.lastname: Franke
authors.forename: Christoph
authors.initials: C
authors.lastname: Fertinger
authors.forename: Rudi
authors.initials: R
authors.lastname: van Eldik
mesh_terms: D002384:Catalysis; D005290:Ferric Compounds / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D008665:Metalloporphyrins / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D010084:Oxidation-Reduction; D005464:Fluorobenzenes; D005466:Fluorocarbons
chemical_list: D005290:Ferric Compounds; D007501:Iron; D008024:Ligands; D008665:Metalloporphyrins; C575769:5,10,15,20-tetrakis(pentafluorophenyl)-21H,23H-porphyrin-Fe(III); D005464:Fluorobenzenes; D005466:Fluorocarbons