Fluorite‐Type Silsesquioxane‐Protected Cerium Cluster as Molecular Analog of Highly Reduced Nanoceria Fragment for Efficient Photocatalysis

The surface oxygen vacancy defects generated from the abstraction of lattice oxygen atoms of bulk ceria accompanied by the reduction of Ce IV to Ce III , are considered to play a pivotal role in photocatalysis. As ideal molecular models of nanoceria, atom‐precise cerium‐oxo clusters (COCs) hold great promise in determining the accurate Ce III /Ce IV ratio and disclosing the underlying catalytic mechanism. However, the number of COCs, especially those mixed‐valent COCs with high surface Ce III concentrations, is very limited on account of their formidable synthetic challenges. Herein, we report the first silsesquioxane‐protected COC, Ce13 , featuring a fluorite‐type Ce 13 O 8 core, which is structurally reminiscent of bulk ceria. The cluster exhibits a substantially high Ce III /Ce IV ratio with one central Ce IV encapsulated by twelve surface‐exposed Ce III atoms, serving as a molecular analogue of highly reduced ceria surfaces. This cluster shows strong light‐harvesting ability that covers the entire visible range and demonstrates high photocatalytic activity and selectivity for oxidative coupling of various amines, where superoxide radical was involved using O 2 as the oxidant at room‐temperature under visible light. The surface Ce III sites are proposed to significantly enhance the adsorption and activation of O 2 . These results highlight the potential of Ce13 as an efficient sustainable photocatalyst for organic transformations.