Defect engineering of TiO2 for efficient photocatalytic transfer hydrogenation with palladium as cocatalyst and water as a hydrogen source

Photocatalytic transfer hydrogenation using water as the proton source has emerged as an attractive and green approach for the catalytic reduction of unsaturated bonds. Herein, we report an oxygen-defective TiO2-supported palladium catalyst (Pd-TiO2-Ov) for efficient photocatalytic water-donating transfer hydrogenation of anethole towards 4-n-propylanisole in a high yield of 99.9%, which is significantly higher compared to the pristine TiO2-supported palladium catalyst (Pd-TiO2, 74%). The enhanced performance is ascribed to the presence of oxygen vacancies, which facilitate light absorption and suppress the recombination of photogenerated electron-hole pairs. Furthermore, the Pd-TiO2-Ov is versatile in hydrogenating various alkene substrates including those with hydroxyl, ether, fluoride, and chloride functional groups in full conversion, thus offering a green method for transfer hydrogenation of alkenes. This study provides new insights and advances in current hydrogenation technology with water as the proton source.