Post-Synthetic Modification of the C═C Linkage in a Vinylene-Linked COF for ROS-Mediated Enamine Dimerization

Vinylene-linked covalent organic frameworks (COFs) are attractive photocatalytic platforms owing to their chemical robustness and extended π-conjugation, yet linkage-level post-synthetic modification (PSM) at vinylene (C═C) linkages has remained challenging. Here, we report Ru-catalyzed arylation directly at the C═C linkage of a vinylene-linked COF using 4-bromobenzonitrile, yielding COF-PhCN. COF-PhCN shows increased signals of both ¹O₂ and O₂ ^·- relative to COF-H, and quenching experiments identify ¹O₂ as the dominant reactive species responsible for enamine dimerization. Accordingly, COF-PhCN reaches comparable conversion within 3 h, whereas pristine COF-H requires 12 h, and the catalyst can be readily recovered and reused with sustained performance over five cycles. The enhanced activity is attributed to restricted intramolecular rotation and promoted intersystem crossing after arylation while preserving the π-conjugated framework, and control experiments support that the improvement originates from covalent framework arylation. To the best of our knowledge, this work represents the first example of COF-catalyzed enamine dimerization and provides an effective route to functionalize vinylene-linked COFs at the C═C linkage for ROS-driven photocatalytic transformations.