Enhancing photocatalytic C-O/N coupling reaction over covalent organic frameworks by pull-push electron group regulation

Covalent organic frameworks (COFs) have emerged as novel materials in photocatalytic technology for green energy and chemicals production. However, exploring highly efficient and stable COFs based materials for photocatalytic aromatic ethers and amines synthesis is still urgent. Herein, olefin-linked COFs modified with or without –F/-OCH3 groups were constructed by Knoevenagel condensation reaction. In addition, Ni active sites were embedded in the frameworks through bipyridine units to afford highly efficient and repeatable photocatalytic C-O/N coupling reaction. Through this strategy, it was found that the -F group modification greatly elevated photogenerated carriers separation efficiency attributing to its strong electronegativity and electron-withdrawing properties. Photocatalytic experiments conveyed that sp2c-F-COFdpy-Ni displayed highest photocatalytic activity and catalyzed cross-coupling of aryl C-O/N both with high yield exceeding 99 %, and exhibited excellent substrate compatibility for aryl bromides substituted with electron-withdrawing/donating groups. This investigation provides new insights into structure design of COFs for photocatalytic organic transformation.