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(NHCH)(4)(dppm)(4)](3+) (Cu17a) and [Cu17H6(NHCPh)(4)(dppm)(4)](3+) (Cu17b), both exhibiting a distinct unique square orthobicupola Cu17H6 core (J(28), Johnson solid). The robust sigma- and pi-bonding between copper and the NHC ligands imparts ultrahigh stability of nanoclusters, while the unique coordination pattern (mu(7)-eta(1)(sigma):eta(1)(sigma):eta(1)(sigma):eta(1)(sigma):eta(1)(sigma):eta(2)(pi):eta(2)(pi)) 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.