Bifunctional 1-Hydroxypyrene Photocatalyst for Hydrodesulfurization via Reductive C(Aryl)-S Bond Cleavage

We developed the visible-light-induced hydrodesulfurization of alkyl aryl thioethers via the reductive cleavage of the C(aryl)-S bond using 1-hydroxypyrene as a Brønsted acid-reductant bifunctional photocatalyst. The hydrodesulfurization reaction proceeded under simple reaction conditions (1-hydroxypyrene and Et₃N in THF under purple LED illumination); this reaction did not require chemicals commonly used for hydrodesulfurization, such as hydrosilanes, transition metal catalysts, and/or stoichiometric amounts of metal reagents. Detailed mechanistic studies based on control experiments, spectroscopic measurements, and computational studies revealed that the cleavage of the C(aryl)-S bond and the formation of the C(aryl)-H bond proceeded via the formation of the ion pair between the radical anion of alkyl aryl thioether and Et₃N⁺H, resulting in the generation of a sulfur radical. In addition, the 1-hydroxypyrene catalyst was regenerated via hydrogen atom transfer (HAT) from Et₃N.