Triazenide-supported [Cu4S] structural mimics of CuZ 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 (CuZ). On the other hand, heterogeneous Cu catalysts on oxide supports are known to mediate decomposition of N2O (deN2O) by disproportionation. In this study, a CuZ model system supported by triazenide ligands is characterized by X-ray crystallography, NMR and EPR spectroscopies, and electronic structure calculations. Although the triazenide-ligated Cu4(μ4-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 deN2O, behavior that was previously unknown to natural or synthetic copper–sulfide clusters. The reaction pathway for deN2O 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., CuZ) and deN2O (e.g., CuO/CeO2).