A trans-Hyponitrite Intermediate in the Reductive Coupling and Deoxygenation of Nitric Oxide by a Tricopper–Lewis Acid Complex

The reduction of nitric oxide (NO) to nitrous oxide (N₂O) is a process relevant to biological chemistry as well as to the abatement of certain environmental pollutants. One of the proposed key intermediates in NO reduction is hyponitrite (N₂O₂^2–), the product of reductive coupling of two NO molecules. We report the reductive coupling of NO by an yttrium–tricopper complex generating a trans-hyponitrite moiety supported by two μ-O-bimetallic (Y,Cu) cores, a previously unreported coordination mode. Reaction of the hyponitrite species with Brønsted acids leads to the generation of N₂O, demonstrating the viability of the hyponitrite complex as an intermediate in NO reduction to N₂O. The additional reducing equivalents stored in each tricopper unit are employed in a subsequent step for N₂O reduction to N₂, for an overall (partial) conversion of NO to N₂. The combination of Lewis acid and multiple redox active metals facilitates this four electron conversion via an isolable hyponitrite intermediate.