Ag₃PO₄ enables the generation of long-lived radical cations for visible light-driven [2+2] and [4+2] pericyclic reactions

Photocatalytic redox reactions are important for synthesizing fine chemicals from olefins, but the limited lifetime of radical cation intermediates severely restricts semiconductor photocatalysis efficiency. Here, we report that Ag₃PO₄ can efficiently catalyze intramolecular and intermolecular [2+2] and Diels-Alder cycloadditions under visible-light irradiation. The approach is additive-free, catalyst-recyclable. Mechanistic studies indicate that visible-light irradiation on Ag₃PO₄ generates holes with high oxidation power, which oxidize aromatic alkene adsorbates into radical cations. In photoreduced Ag₃PO₄, the conduction band electron (eCB−) has low reduction power due to the delocalization among the Ag-lattices, while the particle surfaces have a strong electrostatic interaction with the radical cations, which considerably stabilize the radical cations against recombination with eCB−. The radical cation on the particle's surfaces has a lifetime of more than 2 ms, 75 times longer than homogeneous systems. Our findings highlight the effectiveness of inorganic semiconductors for challenging radical cation-mediated synthesis driven by sunlight.

Lirong Guo, Rongchen Chu, Xinyu Hao, Yu Lei, Haibin Li, Dongge Ma, Guo Wang, Chen-Ho Tung, Yifeng Wang