Triazenide-supported [CuS] structural mimics of Cu that mediate NO disproportionation rather than reduction.

As part of the nitrogen cycle, environmental nitrous oxide (NO) undergoes the NO reduction reaction (NORR) catalyzed by nitrous oxide reductase, a metalloenzyme whose catalytic active site is a tetranuclear copper-sulfide cluster (Cu). On the other hand, heterogeneous Cu catalysts on oxide supports are known to mediate decomposition of NO (deNO) by disproportionation. In this study, a Cu model system supported by triazenide ligands is characterized by X-ray crystallography, NMR and EPR spectroscopies, and electronic structure calculations. Although the triazenide-ligated Cu(μ-S) clusters are closely related to previous formamidinate derivatives, which differ only in replacement of a remote N atom for a CH group, divergent reactivity with NO is observed. Whereas the formamidinate-ligated clusters were previously shown to mediate single-turnover NORR, the triazenide-ligated clusters are found to mediate deNO, behavior that was previously unknown to natural or synthetic copper-sulfide clusters. The reaction pathway for deNO by this model system, including previously unidentified transition state models for NO activation in N-O cleavage and O-O coupling steps, are included. The divergent reactivity of these two related but subtly different systems point to key factors influencing behavior of Cu-based catalysts for NORR (, Cu) and deNO (, CuO/CeO).