Nitrogen ligands in two-dimensional covalent organic frameworks for metal catalysis

We introduced bipyridine ligands into a series of two-dimensional (2D) covalent organic frameworks (COFs) using 2,2′-bipyridine-5,5′-dicarbaldehyde (2,2′-BPyDCA) as a component in the mixed building blocks. The framework of the COFs was formed by the linkage of imine groups. The ligand content in the COFs was synthetically tuned by the content of 2,2′-BPyDCA, and thus the amount of metal, palladium(II) acetate, bonded to the nitrogen ligands could be manipulated. Both the bipyridine ligands and imine groups can coordinate with Pd(II) ions, but the loading position can be varied, with one ligand favoring binding in the space between adjacent COFs′ layers and the other ligand favoring binding within the pores of the COFs. The Pd(II)-loaded COFs exhibited good catalytic activity for the Heck reaction.