Dipropyne-Modified N-Heterocyclic Carbene Stabilized Atomically Precise Copper(I) Nanocluster Catalysts for CO₂ Electroreduction

Atomically precise copper(I) nanoclusters with stable active sites are highly sought-after catalysts for the electrocatalytic CO₂ reduction reaction (CO₂RR), providing an exceptional platform to elucidate structure–activity relationships. However, the rational synthesis of robust copper nanoclusters as effective electrocatalysts and understanding the relationship between a more realistic active site and its performance remain a significant challenge due to their inherent instability. Here, a novel dipropyne-modified NHC ligand is elaborately devised to synthesis two atomically precise copper nanoclusters, [Cu₁₇H₆(NHC^H)₄(dppm)₄]³⁺ (Cu17a) and [Cu₁₇H₆(NHC^Ph)₄(dppm)₄]³⁺ (Cu17b), both exhibiting a distinct unique square orthobicupola Cu₁₇H₆ core (J₂₈, Johnson solid). The robust σ- and π-bonding between copper and the NHC ligands imparts ultrahigh stability of nanoclusters, while the unique coordination pattern (μ₇-η_σ¹:η_σ¹:η_σ¹:η_σ¹:η_σ¹:η_π²:η_π²) of NHC ligands facilitates exposure of neighboring copper atoms, generating accessible catalytic sites. Electrocatalytic CO₂ reduction experiments show that Cu17a achieves the highest Faradaic efficiency for ethylene production among reported nanoclusters. The active sites and tandem catalytic reaction mechanism of the CO₂RR are elucidated through a combination of theoretical calculations with attenuated total reflection-surface-enhanced IR absorption spectroscopy (ATR-SEIRAS). This work not only introduces dipropyne-modified NHC ligands for synthesizing stable copper nanoclusters but also offers critical insights into molecular design principles for CO₂RR catalysts.