Uranyl Tris(benzoate) Photocatalysts for Site-Selective Hydrocarbon Functionalization

The uranyl dication ([UO₂]²⁺) is a highly active photocatalyst for the functionalization of inert C_sp3-H bonds by direct hydrogen atom abstraction (HAA). However, photocatalysis by the uranyl ion remains underexplored. Most reports are limited to reactions catalyzed by simple uranyl salts, such as uranyl nitrate [UO₂(NO₃)₂·6H₂O] (U^NO3). We report a set of uranyl tris(benzoate) complexes 1-R containing strongly coordinating and tunable equatorial ligands that resist photodamage and control access to the oxo groups. These catalyst variants with appropriate aryl substituents undergo catalytic reactions at C-H bonds by HAA. The selectivity and reactivity of this step depend on the ligand framework and are distinct from that of U^NO3 or other photoactive oxo complexes, such as decatungstate, that lack ancillary ligands. Finally, consistent with the strong, stable axial U-O bond, reaction with exogenous radical acceptors outcompetes radical rebound, enabling C-C and C-N bond formation from the alkyl radical intermediate. Regioselective alkylation and functionalization of a broad range of substrates results, and this photocatalysis shows that modulation of equatorial ligands on [UO₂]²⁺ can influence the reactivity and selectivity of photocatalytic C-H bond functionalization.