N-Heterocyclic Carbene-Ligated Mixed-Valent Linear Cu₃ Cluster for Enhanced Electrocatalytic Nitrite Reduction

Multinuclear copper centers play a crucial role in biological electron transfer processes, with the CuA site in cytochrome c oxidase and nitrous oxide reductase exemplifying efficient mixed-valence copper cycling. However, the challenges of mimicking these biological systems for multielectron catalysis, such as nitrite reduction to ammonia, remain largely underexplored. Herein, we present the design and synthesis of a stable, mixed-valent linear Cu₃ cluster coordinated by an N-heterocyclic carbene (NHC) ligand. This NHC ligand stabilizes the Cu₃ core and facilitates an efficient electron transfer. Structural and electronic characterizations reveal temperature-dependent electron delocalization within the cluster. The Cu₃ cluster efficiently catalyzes the electrochemical reduction of nitrite to ammonia with a high selectivity under mild conditions. These findings provide valuable insights into the role of mixed-valence copper clusters in catalysis, offering a promising approach for sustainable nitrite reduction.