Photocatalytic Chemoselective Transfer Hydrogenation of Quinolines to Tetrahydroquinolines on Hierarchical NiO/In2O3–CdS Microspheres

The pursuit of a powerful strategy to enable chemoselective transfer hydrogenation reaction of quinolines to their corresponding tetrahydroquinolines is of great significance, but it remains a challenge. Herein, we have realized heterogeneous photocatalytic chemoselective transfer hydrogenation reaction of quinolines to their corresponding tetrahydroquinolines over the developed hierarchical NiO/In2O3–CdS microspheres with high activity and selectivity under visible light irradiation and mild conditions, in which benzyl alcohol serves as a hydrogen donor to replace high-pressure flammable molecular hydrogen. More interestingly, the experimental and theoretical calculation results confirm that NiO acts as active sites for this photocatalytic transfer hydrogenation reaction, and it adsorbs and activates benzyl alcohol far more effectively than the metallic Ni. It breaks through the traditional concept that the metallic Ni serves as photocatalytically active sites for the effective activation of benzyl alcohol. This work not only presents an efficient strategy for the production of tetrahydroquinolines via heterogeneous photocatalytic chemoselective transfer hydrogenation reaction of quinolines but also paves a way for designing other heterogeneous photocatalytic systems toward chemoselective transfer hydrogenation reaction of diverse N-heterocycles.