The Effect of Intramolecular Proton Transfer on the Mechanism of NO Reduction to NO by a Copper Complex: A DFT Study.

DFT calculations were performed to explore the mechanism underlying the reduction of NO to NO by a Cu complex. A nitrosyl complex reacts with another NO molecule and the Cu complex, leading to the formation of a dicopper-hyponitrite complex (CuNO). The first steps follow a common pathway until the formation of the intermediate [Cu-NO], after which the reaction pathway diverges into three CuNO species: κ-N,N', κ-O,O', and κ-N,O,O'. These species yield different products along their respective reaction pathways. In the case of the κ-N,N' and κ-N,O,O' species, the subsequent steps involve a methanol-mediated proton transfer and N-O bond cleavage, resulting in the generation of NO and [Cu-OH]. Conversely, for the κ-O,O' species, two proton transfers occur without N-O bond cleavage, leading to the formation of HNO and [Cu]. HNO spontaneously converts into NO and HO. These computational results elucidate how the coordination mode of hyponitrite influences reactivity and provide insights into NO reduction via proton transfer. Notably, switching of the NO coordination mode to metal ions from N to O was not required, offering insights for more efficient NO reduction strategies in the future.