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 [PyPy(afa)Fe]OTf, 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 [PyPy(afa)Fe(OH)]OTf. 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, PyPy(pi)Fe(NO), and water. Our findings enhance the understanding of iron-based reduction processes and contribute to the broader knowledge of oxyanion reduction mechanisms.