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Electrochemical O2 activation by Fe and Mn porphyrins. Towards electrocatalytic aerobic oxidations of organic substrates

  • Kostopoulos, Nikolaos
Publication Date
Nov 05, 2021
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The activation of dioxygen is at the center of current economic challenges, because oxygenation and halogenation reactions play a major role in the chemical industry. These current oxidation processes often use harmful chemical oxidants, or dioxygen under drastic temperature and pressure conditions in the presence of noble metal catalysts. This is due to the kinetic inertia of oxygen. The metalloenzymes of the Cytochrome-P450 superfamily are capable of carrying out oxidation reactions efficiently and selectively under mild conditions, through the so-called reductive activation of dioxygen. This process begins with the coordination of dioxygen on the Fe ion at the active site, and leads, through a succession of reduction and protonation steps, to the cleavage of the oxygen-oxygen bond and the formation of a high valent species, FeV= O, a highly reactive species capable of oxidizing an organic substrate. The Fe and Mn porphyrins have been widely studied as models of the active site of these enzymes; several reaction intermediates were generated chemically and characterized by spectroscopy, and their reactivity was studied. In this manuscript, we propose an alternative approach that applies electrochemistry for the generation and characterization of these species. The reaction of MII (M = Fe, Mn) of Fe (F20TPP) Cl, FeIII(TPP)Cl, FeIII(F20TPP)Cl, FeIII(T-(2-COOH)PP)Cl and MnIII(TPP)Cl complexes with dioxygen is studied. by cyclic voltammetry (CV), UV-Vis spectroelectrochemistry and scanning electrochemical microscopy (SECM), in the absence or presence of Bronsted or Lewis acids. Electrocatalysis studies are then proposed; in preparative electrolysis, Fe or Mn porphyrin activates dioxygen in a reducing potential, in the presence of an organic substrate, such as cyclooctene, for example, which can be oxygenated or halogenated depending on the reaction conditions chosen. Finally, studies in catalyst heterogenization with inexpensive materials, and Resonance Raman spectroelectrochemistry are presented as promising results of this work.

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