3D Covalent Organic\nFrameworks with 16-Connectivity\nfor Photocatalytic C(sp³)–C(sp²) Cross-Coupling

Abstract

The connectivity (valency) of building blocks for constructing\n3D covalent organic frameworks (COFs) has long been limited to 4,\n6, 8, and 12. Developing a higher connectivity remains a great challenge\nin the field of COF structural design. Herein, this work reports a\nhierarchical expansion strategy for making 16-connected building blocks\nto construct 3D COFs with sqc topology. The [16 + 2] construction\nachieved by condensation between a 16-connected carbazolyl dicyanobenzene-based\nbuilding block (CzTPN) and linear diamino linkers (BD or Bpy) affords\ntwo 3D COFs (named CzBD COF and CzBpy COF). Furthermore, attributed\nto the well-organized donor–acceptor (D–A) heterojunction,\nthe Ni chelated CzBpy COF (Ni@CzBpy COF) exhibits excellent performance\nfor photoredox/Ni dual catalytic C(sp³)–C(sp²) cross-coupling of alkyltrifluoroborates with aryl halides,\nachieving a maximum 98% conversion and 94% yield for various substrates.\nThis work developed the first case of high-connectivity COFs bearing\n16-connected units, which is the highest connectivity reported until\nnow, and achieved efficient photocatalysis applications, thus greatly\nenriching the possibilities of COFs.