Uranyl-Polyoxometalate as a Heterogeneous Catalyst for Visible-Light-Driven Oxidation Coupling of Amines

Developing efficient heterogeneous visible-light-responsive photocatalysts to achieve organic oxidation reactions is essential. We synthesized the uranyl-polyoxometalate (POM) compound Na₃[H₁₉(UO₂)₂(μ₂-O)(Se₂W₁₄O₅₂)₂]·41H₂O (denoted as <b>U2</b>) by incorporating uranyl (VI) ions (UO₂²⁺) into the POM framework and conducted the photocatalytic oxidation reaction of the uranyl-POM compounds. Results revealed that the introduction of uranyl groups not only extended the light absorption range of <b>U2</b> to 500 nm but also promoted its carrier separation efficiency and charge transfer rate remarkably. Meanwhile, the synergistic effect among the components enhanced the catalytic activity notably. The U2-catalyzed oxidative coupling of the benzylamine reaction was completed within 6 h under a green solvent-free system with a high yield of 98.7%. The turnover number and turnover frequency reached 1974 and 329 h^-1, respectively, far exceeding the activity of uranyl or POM used alone. Furthermore, <b>U2</b> was demonstrated to exhibit excellent recyclability, maintaining its activity over five consecutive cycles without significant degradation. Incorporating uranyl into POMs to form <b>U2</b> achieves excellent catalytic performance in the heterogeneous photocatalytic oxidation coupling of benzylamine to N-benzylidenebenzylamine under solvent-free conditions (yield = 98.7%; turnover number = 1974; turnover frequency = 329 h^-1).