Nickel-embedded three-in-one pyridyl-quinoline-linked covalent organic framework photocatalysts for universal C(sp2) cross-coupling reactions

Metallaphotocatalysis, integrating interlocked photocatalytic cycles and transition-metal catalysis, harmonizes the ground state and excited state reactivities, enabling cross-couplings under mild conditions and expanding the scope of accessible transformations. However, homogeneous dual metallaphotocatalysts often suffer from limitations such as low catalyst stability, high metal loading, and challenges in catalyst recycling. In this study, we engineered a class of nickel-incorporated pyridyl-quinoline-linked covalent organic frameworks (Ni-PQCOFs) serving as robust and efficient heterogeneous metallaphotocatalysts. These Ni-PQCOFs facilitate universal visible-light-driven C(sp²)-carbon and heteroatom (S, N, O, B, P, Se, and Cl) bond formations across a broad range of aromatic halides and nucleophiles, while maintaining low metal loading (1-2 mol%). The Ni-PQCOFs, featuring fully conjugated and tunable pyridyl-quinoline (PQ) motifs, exhibit exceptional (photo)chemical stability, broadened absorption wavelength range, and enhanced redox capability. Remarkably, these COF-based heterogeneous metallaphotocatalysts exhibited significantly enhanced catalytic efficiency compared to their homogeneous counterparts. The versatility and practicality of this photocatalytic system extend to diverse synthetic applications, including late-stage functionalization of complex molecules, sequential functionalizations, and decagram-scale synthesis assisted by an in-house-built high-speed circulation flow system. Moreover, the micrometer-sized Ni-PQCOF catalyst could be recycled over 10 times through direct filtration with minimal activity loss and negligible metal leaching. All these advantages establish Ni-PQCOFs as versatile, effective, and sustainable metallaphotocatalysts for cross-coupling reactions.