Engineering a Hydrazone-Linked Covalent Organic Framework as a Cooperative Macromolecular Ligand for Recyclable...

The design of robust heterogeneous catalysts that rival the performance of homogeneous systems remains a fundamental challenge. Herein, we report a hydrazone-linked covalent organic framework (DHPy-COF) engineered as a cooperative macromolecular ligand with preorganized (O,N,O)-tridentate chelation sites for Cu(II) immobilization, a coordination mode unequivocally validated by single-crystal X-ray diffraction of a salicylhydrazone model complex. The resulting Cu(II)@DHPy-COF efficiently catalyzes Chan-Lam coupling of arylboronic acids with diverse N-nucleophiles under ambient conditions (up to 98% yield) and exhibits exceptional recyclability over five cycles with negligible Cu leaching (<0.2%). A control study employing an OH-free analogue unequivocally demonstrates that the ortho-phenolic hydroxyl group is functionally essential for cooperative chelation and sustained catalytic stability. This work establishes a paradigm shift, from employing COFs as inert supports to using them as functional ligands, offering a generalizable strategy for robust heterogeneous catalysis.