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Axial Ligand and Spin‐State Influence on the Formation and Reactivity of Hydroperoxo–Iron(III) Porphyrin Complexes
Author(s) -
Franke Alicja,
Fertinger Christoph,
van Eldik Rudi
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201103036
Subject(s) - porphyrin , reactivity (psychology) , chemistry , heterolysis , photochemistry , ligand (biochemistry) , bond cleavage , catalysis , medicinal chemistry , acetonitrile , ferric , spin states , inorganic chemistry , organic chemistry , medicine , biochemistry , alternative medicine , receptor , pathology
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)‐21 H ,23 H ‐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 OO bond cleavage in the corresponding hydroperoxo porphyrin species. A mechanistic changeover from homo‐ to heterolytic OO 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.