The Effect\nof Intramolecular Proton Transfer on the\nMechanism of NO Reduction to N<sub>2</sub>O by a Copper Complex: A\nDFT Study

DFT calculations were performed to\nexplore the mechanism underlying\nthe reduction of NO to N<sub>2</sub>O by a Cu<sup>I</sup> complex.\nA nitrosyl complex reacts with another NO molecule and the Cu<sup>I</sup> complex, leading to the formation of a dicopper–hyponitrite\ncomplex (Cu<sub>2</sub>N<sub>2</sub>O<sub>2</sub>). The first steps\nfollow a common pathway until the formation of the intermediate [Cu<sup>II</sup>-N<sub>2</sub>O<sub>2</sub>]<sup>+</sup>, after which the\nreaction pathway diverges into three Cu<sub>2</sub>N<sub>2</sub>O<sub>2</sub> species: κ<sup>2</sup>-N,N′, κ<sup>2</sup>-O,O′, and κ<sup>3</sup>-N,O,O′. These species\nyield different products along their respective reaction pathways.\nIn the case of the κ<sup>2</sup>-N,N′ and κ<sup>3</sup>-N,O,O′ species, the subsequent steps involve a methanol-mediated\nproton transfer and N–O bond cleavage, resulting in the generation\nof N<sub>2</sub>O and [Cu<sup>II</sup>–OH]<sup>+</sup>. Conversely,\nfor the κ<sup>2</sup>-O,O′ species, two proton transfers\noccur without N–O bond cleavage, leading to the formation of\nH<sub>2</sub>N<sub>2</sub>O<sub>2</sub> and [Cu<sup>II</sup>]<sup>2+</sup>. H<sub>2</sub>N<sub>2</sub>O<sub>2</sub> spontaneously converts\ninto N<sub>2</sub>O and H<sub>2</sub>O. These computational results\nelucidate how the coordination mode of hyponitrite influences reactivity\nand provide insights into NO reduction via proton transfer. Notably,\nswitching of the N<sub>2</sub>O<sub>2</sub> coordination mode to metal\nions from N to O was not required, offering insights for more efficient\nNO reduction strategies in the future.