Iron(I) Tetraphenylporphyrin Is an Active Catalyst in Reductive Deoxygenation when Switching from CO₂ to Isoelectronic N₂O

The electrochemical reductive deoxygenation of N2O catalyzed by iron tetraphenylporphyrin (TPPFe) is studied and compared to the electroreduction of CO2 to CO by the same catalyst. We show that the electroreduction of N2O is catalyzed by TPPFe(I), albeit at a slower rate compared to that of TPPFe(0). On a similar time scale, CO2 does not react with TPPFe(I). The catalytic reduction of N2O by TPPFe(I) is however endowed by a self-modulation process due to the production of hydroxide ions as a coproduct 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 CO2 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 a lower overpotential.