High-valent oxo-metal complexes are involved in key biochemical processes of selective oxidation and removal of xenobiotics. The catalytic properties of cytochrome P-450 and soluble methane monooxygenase enzymes are associated with oxo species on mononuclear iron haem and diiron non-haem platforms, respectively. Bio-inspired chemical systems that can reproduce the fascinating ability of these enzymes to oxidize the strongest C-H bonds are the focus of intense scrutiny. In this context, the development of highly oxidizing diiron macrocyclic catalysts requires a structural determination of the elusive active species and elucidation of the reaction mechanism. Here we report the preparation of an Fe(IV)(µ-nitrido)Fe(IV) = O tetraphenylporphyrin cation radical species at -90 °C, characterized by ultraviolet-visible, electron paramagnetic resonance and Mössbauer spectroscopies and by electrospray ionization mass spectrometry. This species exhibits a very high activity for oxygen-atom transfer towards alkanes, including methane. These findings provide a foundation on which to develop efficient and clean oxidation processes, in particular transformations of the strongest C-H bonds.
International audienceNitrene transfer reactions are increasingly used to access various kinds of amine derivatives but the underlying mechanisms have not been unraveled in most cases. Fe-catalyzed aziridination of alkenes has appeared as a promising route to aziridines which are important derivatives both per se and as intermediates in many synthetic procedures. We report the strong activity and the mechanism of di-iron catalysts for aziridination of styrenes using phenyltosyliodinane (PhI[double bond, length as m-dash]NTs). In addition, we have developed a similar mono-iron catalyst which operates under the same mechanism albeit with a reduced activity. DFT calculations were performed to investigate the structure and electronic structure of the FeIVNTs species of the latter catalyst. They suggest that the reaction pathway leading to the nitrene transfer to the olefin involves a transient charge transfer on the way to a radical intermediate, which is totally consistent with the experimental results. Moreover, these calculations identify the electron affinity (EA) of the active species as one key parameter allowing rationalization of the observations, which opens the way to improving the catalyst efficiency on a rational basis
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