Novel concept for bio-inspired catalysts: from fundamentals to efficient catalytic applications
Résumé
The ultimate objective of the intensive research in the mimicking of biological oxidation is the creation of the practical bio-inspired chemical systems reproducing fascinating catalytic properties of enzymes. Cytochrome P-450 and methane monooxygenase (MMO) enzymes capable of oxidizing the strongest C-H bonds under ambient conditions represent especially exciting and challenging examples. To achieve this reactivity Nature utilizes mono-nuclear iron porphyrin sites in cytochromes P-450 and non-heme diiron construction in soluble MMO. In the search of powerful oxidizing catalysts we have recently proposed a novel concept: to use diiron catalytic site like in solu-ble methane monooxygenase but in macrocyclic ligand environment like in cytochrome P-450.
Contrary to traditional belief, such a binuclear construction was shown to be particular efficient in many reac-tions [2-6] including challenging oxidation of methane and oxidative degradation of highly fluorinated aromatic compounds. We present here selected examples of the catalytic activity of N-bridged diiron phthalocyanine (FePc)2N and porphyrin (FePor)2N complexes in the oxidation of methane [2,3], benzene [4] and alkylaromatic compounds as well as in C-C bond formation [5] and dehalogenation reactions [6]. Elusive high-valent diiron oxo species responsible for the remarkable catalytic properties have been prepared at low temperatures and character-ized by cryospray MS, UV-vis, EPR, Mössbauer, EXAFS and XANES techniques [2,7]. Mechanistic aspects of unusual reactivity of diiron macrocyclic complexes will be discussed.