Facile synthesis of 2D covalent organic frameworks for cooperative photocatalysis with TEMPO: The selective aerobic oxidation of benzyl amines

Abstract Two-dimensional (2D) covalent organic frameworks (COFs) have recently emerged as versatile photoactive functional materials. Herein, three β-ketoenamine linked 2D COFs were assembled with 2,4,6-triformylphloroglucinol (Tp) and 4,7-bis(4-aminophenyl)-2,1,3-benzothiadiazole (BTD) as building blocks at 150, 120, and 25 ℃, leading to Tp-BTD-150, Tp-BTD-120, and Tp-BTD-25. In particular, the facile synthesis at 25 ℃ afforded Tp-BTD-25 that featured superior activity for the photocatalytic selective aerobic oxidation of amines than the other two assembled at higher temperatures. Most importantly, both the stability and activity of Tp-BTD-25 photocatalyst were augmented with exogenous 5 mol% 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) to ease the transfer of electrons and protons during the oxidation of amines. Preeminently, the selective aerobic oxidation of amines into imines was established by cooperative photocatalysis of Tp-BTD-25 with TEMPO irradiated by blue LEDs. This work underscores that crystalline 2D COFs via facile synthesis can cooperatively work with a redox mediator to steer photocatalytic selective reactions.