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.