Département de Chimie Moléculaire

The electrochemical reductive deoxygenation of N$_2$O catalyzed by the iron tetraphenylporphyrin (TPPFe) is studied and compared to the electroreduction of CO$_2$ to CO by the same catalyst. We show that the electroreduction of N$_2$O is catalyzed by TPPFe(I) albeit at a slower rate compared to TPPFe(0). On a similar timescale, CO$_2$ does not react with TPPFe(I). The catalytic reduction of N$_2$O by TPPFe(I) is however endowed by a self-modulation process due to the production of hydroxide ions as co-product, that bind to TPPFe(II) and slow down the regeneration of the TPPFe(I) catalytic active species. Two catalytic cycles are thus intertwined when the electrocatalysis is run at a potential where TPPFe(0) is generated, and the resting state in solution is TPPFe(II)(OH) and not TPPFe(I), as opposed to the case of CO$_2$ catalytic reductive deoxygenation. Revealing the shift of the active catalysis from TPPFe(0) to TPPFe(I) opens the way toward the design of molecular catalysts for N2O reductive deoxygenation at lower overpotential.