Engineering Single Ni Sites on 3D Cage-like Cucurbit[n]uril Ligands for Efficient and Selective CO Photocatalytic Reduction.

Solar-driven CO selective reduction with high conversion is a challenging task yet holds immense promise for both CO neutralization and green fuel production. Enhancing CO adsorption at the catalytic centre can trigger a highly efficient CO capture-to-conversion process. Herein, we introduce cucurbit[n]urils (CB[n]), a new family of molecular ligands, as a key component in the creation of a 3D cage-like metal (nickel, Ni)-complex molecular co-catalyst (CB[7]-Ni) for photocatalysis. It exhibits an unprecedented CO yield rate of 72.1 μmol ⋅ h with a high selectivity of 97.9 % under visible light irradiation. To verify the origin of the carbon source in the products, a straightforward isotopic tracing method is designed based on tandem reactions. The catalytic process commences with photoelectron transfer from Ru(bpy) to the Ni site, resulting in the reduction of Ni to Ni. The locally enriched CO molecules in the cage ligand CB[7] undergo selective reduction by the Ni nearby to form CO product. This work exemplifies the inspiring potential of ligand structure engineering in advancing the development of efficient unanchored molecular co-catalysts.