Nickel-embedded covalent organic frameworks for dual photocatalytic hydrogen evolution and cross-coupling catalysis

This work reports the design and synthesis of a novel imine-linked 2D covalent organic framework (COF), TPDA-BiPy-COF, constructed from [3,3′-bipyridine]-6,6′-dicarboxaldehyde (3,3′-BiPy) as an electron acceptor and tetrakis(4-aminophenyl)-1,4-phenylenediamine (TPDA) as a donor. The COF features pyridyl-imine linkages, i.e., N_imine-Ni-N_bipyridine, with active nitrogen sites that facilitate proton reduction to hydrogen. To improve photocatalytic hydrogen evolution performance, Ni(II) centers were introduced via post-synthetic metalation, forming TPDA-BiPy@NiX₂ COF (X = Cl, Br). The coordination of Ni(II) with the imine and bipyridine nitrogen atoms enhanced framework planarity and conjugation, thereby boosting photocatalytic activity. Notably, TPDA-BiPy@Ni(II) COF achieved an excellent hydrogen evolution rate of 34.13 mmol g⁻¹ h⁻¹ under visible light, without requiring a cocatalyst. Furthermore, the metallaphotoredox activity of TPDA-BiPy@Ni(II) displayed its promise for photocatalyzed C–S cross-coupling reaction. This dual-functional catalyst highlights the advantage of incorporating nickel into COFs, offering a cost-effective and sustainable alternative to noble-metal-based systems for photocatalysis and synthetic transformations.