Diiron macrocyclic complexes: novel catalysts for oxidation of methane, formation of C-C bonds and oxidative dehalogenation
Résumé
The ultimate objective in the mimicking of biological oxidation is the development of practical and efficient bio-inspired catalysts. Methane monooxygenases (MMO) and cytochromes P-450 capable of oxidizing the strongest C-H bonds under ambient conditions represent especially exciting and challenging examples. To achieve this reactivity Nature utilizes mononuclear 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 soluble MMO but in macrocyclic ligand environment like in cytochrome P-450. Contrary to traditional belief, such a binuclear construction was shown to be particularly efficient in many reactions[1-4] 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,[1,2] benzene[4a] as well as in C-C bond formation[4c] and dehalogenation reactions.[3] Elusive high-valent diiron oxo species responsible for the remarkable catalytic properties have been prepared at low temperatures and characterized by cryospray MS, UV-vis, EPR, Mössbauer, EXAFS and XANES techniques.[1,2,4b] Mechanistic aspects of unusual reactivity of diiron macrocyclic complexes will be discussed. [1] E.V. Kudrik, P. Afanasiev, L.X. Alvarez, P. Dubourdeaux, M. Clémancey, J.-M. Latour, G. Blondin, D. Bouchu, F. Albrieux, S.E. Nededov, A.B. Sorokin, Nature Chem., 2012, 4, 1024-1029. [2] A.B. Sorokin, E.V. Kudrik, D. Bouchu, Chem. Commun. 2008, 2562-2564; A.B. Sorokin, E.V. Kudrik, L.X. Alvarez, P. Afanasiev, J.M.M. Millet, D. Bouchu, Catal Today 2010, 157, 149-154. [3] P. Afanasiev, D. Bouchu, J.M.M. Millet, E.V. Kudrik, A.B. Sorokin, Dalton Trans. 2009, 9828-9836. [4] a) E.V. Kudrik, A.B. Sorokin, Chem. Eur. J. 2008, 14, 7123-7126. b) P. Afanasiev, E.V. Kudrik, J.M.M. Millet, D. Bouchu, A.B. Sorokin, Dalton Trans. 2011, 40, 701-710. c) L.X. Alvarez, E.V. Kudrik, A.B. Sorokin, Chem. Eur. J. 2011, 17, 9298-9301.