Triazenide-supported [Cu₄S] structural mimics of Cu_Z that mediate N₂O disproportionation rather than reduction

As part of the nitrogen cycle, environmental nitrous oxide (N2O) undergoes the N2O reduction reaction (N2ORR) catalyzed by nitrous oxide reductase, a metalloenzyme whose catalytic active site is a tetranuclear copper-sulfide cluster (Cu-Z). On the other hand, heterogeneous Cu catalysts on oxide supports are known to mediate decomposition of N2O (deN(2)O) by disproportionation. In this study, a Cu-Z 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-4(mu(4)-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 N2O is observed. Whereas the formamidinate-ligated clusters were previously shown to mediate single-turnover N2ORR, the triazenide-ligated clusters are found to mediate deN(2)O, behavior that was previously unknown to natural or synthetic copper-sulfide clusters. The reaction pathway for deN(2)O by this model system, including previously unidentified transition state models for N2O 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 N2ORR (i.e., Cu-Z) and deN(2)O (e.g., CuO/CeO2).