µ-Nitrido Diiron Platform: Particulate Structure for Particulate Catalyses
Résumé
The ultimate objective of bio-inspired catalysis is the development of efficient and clean chemical processes. Since cytochrome P-450 and methane monooxygenase enzymes efficiently catalyze challenging reactions, e.g., oxidation of strong C-H bonds, current approaches involve mononuclear metal porphyrin-like and diiron non-heme complexes. However, biomimetic catalysts capable of oxidizing CH4 are not yet known. We have proposed a new bio-inspired strategy using N-bridged diiron phthalocyanine and porphyrin complexes providing powerful oxidizing catalysts [1-3]. This platform is particularly suitable for stabilization of Fe(IV)Fe(IV) complexes. The ultra high-valent diiron oxo species (L)FeIV-N-FeIV(L+.)=O (L = porphyrin or phthalocyanine) have been prepared at low temperatures and characterized by cryospray MS, UV-vis, EPR and Mössbauer techniques. The highly electrophilic (L)FeIV-N-FeIV(L+.)=O species exhibit remarkable reactivity.
The catalytic applications of µ-nitrido diiron complexes in oxidation of methane and benzene, in transformation of aromatic C-F bonds in oxidative conditions, in oxidative dechlorination as well as in the formation of C-C bonds will be discussed. Importantly, all these reactions can be efficiently performed under mild and clean conditions. µ-Nitrido diiron species show the same mechanistic features as enzymes but exhibit unprecedented reactivity. They are capable of reacting with perfluorinated aromatics in oxidative conditions while the strongest oxidizing enzymes do not. Advanced spectroscopic, labelling and reactivity studies confirm the involvement of high-valent diiron oxo species in these catalytic reactions. Computational studies shed light on the origin of the remarkable catalytic properties, distinguishing Fe-N-Fe scaffold from Fe-C-Fe and Fe-O-Fe analogs. X-ray absorption and scattering assisted with DFT calculations allow deeper insight into electronic structure of these remarkable catalysts.