Tetrapodal iron complexes invoke observable intermediates in nitrate and nitrite reduction

This study investigates the mechanistic pathways of nitrate and nitrite reduction by the tetrapodal iron complex [Py₂Py(afa^mcyp)₂Fe]OTf₂, revealing key intermediates to elucidate the reaction process. Using UV-Vis, IR, mass and NMR spectroscopies, stable binding of oxyanions to the iron centre was observed, supporting the formation of the iron(iii)-hydroxide intermediate [Py₂Py(afa^mcyp)₂Fe(OH)]OTf₂. This intermediate is less stable than in previous systems, providing insights into the behaviour of metalloenzymes. A bimetallic mechanism is proposed for nitrogen oxyanion reduction where additional iron is required to drive the complete reaction, resulting in the formation of the final nitrosyl complex, Py₂Py(pi^mcyp)₂Fe(NO), and water. Our findings enhance the understanding of iron-based reduction processes and contribute to the broader knowledge of oxyanion reduction mechanisms.