Low-coordinated single-atom Cu and enhanced charge transfer from Cu-N to TiO2 on Cu1/CN/TiO2 for efficient Sonogashira cross-coupling

This work presents a Cu single-atom catalyst (SAC)-catalyzed Sonogashira coupling reaction of lodine benzene and phenylacetylene to manufacture diphenylacetylene, with a satisfactory yield employing Cu single atoms on N-doped carbon (CN) supported on TiO₂ (Cu₁/CN/TiO₂). Cu₁/CN/TiO₂ SACs with a low Cu loading (0.81 wt %) and a Cu-N₂ structure achieved ultra-high conversion efficiency (99%) and yield for the Sonogashira coupling reaction, outperforming conventional heterogeneous and homogeneous Cu catalysts. Characterizations and density functional theory (DFT) calculations indicate that the presence of TiO₂ not only alters the coordination environment of Cu to form the Cu-N₂ coordination structure, with charge accumulation lowering the barrier for the adsorption and activation of the substrate, but also speeds the charge transfer from Cu₁/CN to TiO₂, which is advantageous for the oxidation addition steps in the reaction process, substantially boosting the Sonogashira coupling reaction. This work significantly broadens the scope of Cu SAC-catalyzed Sonogashira coupling processes.