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

2D (two-dimensional) 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 the building blocks at 150, 120, and 25 ℃ respectively, 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 benzylamine to 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% TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) to ease the transfer of electrons and protons during the oxidation of benzyl amines. Preeminently, the selective aerobic oxidation of benzyl amines into imines was established by cooperative photocatalysis of Tp-BTD-25 with TEMPO irradiated by blue LEDs (light-emitting diodes). This work underscores that crystalline 2D COFs via facile synthesis can cooperatively work with a redox mediator to steer photocatalytic selective reactions.