Spatial Confinement of Solution-Inaccessible Single-Site Cu(I) in a Molecular Titanium-Oxo Cage for Efficient...

We introduce a precisely engineered molecular titanium-oxo cage, Ti₁₆O₂₄Bz₂₄ (denoted as Ti₁₆; Bz = C₆H₅CO₂), designed to host a spatially confined Cu⁺ single-atom site, that enables efficient and selective C─N coupling from CO₂ and NO₃ ^- under photo-electrocatalytic (PEC) conditions, providing a molecular-level blueprint for multi-reactant coupling catalysis. Ti₁₆ features a large internal cavity assembled from TiO₆ octahedra shielded by a hydrophobic benzoate shell. Metalation of Ti₁₆ with CuCl₂/NaBH₄ incorporates Cu⁺ ions, displacing encapsulated H₃O⁺ and enabling the synthesis of Ti₁₆Cu_x (x = 0.25-8). Among the Ti₁₆Cu_x series, Ti₁₆Cu₂ demonstrates optimal performance under PEC conditions, achieving a high urea yield of 20 mmol g_cat ^-1 h^-1 with a Faradaic efficiency of 85% and a selectivity of 62% at -0.6 V versus RHE, outperforming most reported Cu-based systems. Spectroscopic and structural analyses reveal that C─N bond formation occurs via coupling of *CO and *NO species at the confined Cu sites, highlighting the essential role of the molecular cage in stabilizing reactive species and facilitating their interaction. This work establishes cage-like metal-oxo clusters as an atomically precise and versatile molecular platform for developing highly selective single-atom catalysts for challenging multi-reactant coupling reactions.