Photocatalytic transfer hydrogenolysis of aryl ethers

Abstract

Aryl ethers greatly influence lignin depolymerization and the oxygen content in lignin products. Cleaving aryl ethers normally requires harsh conditions such as high-pressure hydrogen gas and elevated temperature. Herein, we developed a synergistic method that combines photocatalytic hydrogen transfer with acid catalysis for H₂-free hydrogenolysis of diphenyl ether and aromatic oxygenates at room temperature. The electron-enriched Pt/TiO₂ surface stored abundant hydrogen species under light irradiation and efficiently catalyzed hydrogen transfer from isopropanol to aryl ethers. The acid mediated the hydrogenation sequence into: hydrogenolysis of aryl C–O bonds > saturation of aryl rings ≫ hydrogenolysis of aliphatic C–O bonds. DFT calculations suggested the aryl ether bond adsorbed on the Pt surface was weakened through protonation. This method delivered 98% yield of aliphatic monomers (73% cyclohexane and 25% cyclohexanol) from cleavage of diphenyl ether, and converted aromatic mixtures into cycloalkanes (57%) and aliphatic alcohols (9%) under mild conditions.