The position-tuned nitrogen atom in Ni(ii)-metalated covalent organic frameworks enables highly efficient and sustainable C–N coupling

Abstract

The utilization of covalent organic frameworks (COFs) for visible-light-driven C–N bond coupling represents a promising and environmentally sustainable approach to synthesize amine derivatives. However, inefficient metal–photoactive center synergy results in low catalytic efficiency and a high carbon footprint. Herein, we design a “three-in-one” strategy to address these challenges through positional tuning of nitrogen atoms in the COF building blocks, leading to enhanced synergistic catalytic efficiency, applicability to low-pollution substrates, and catalyst recyclability. The heterogeneous metallaphotocatalyst Ni@Bpma-COF, designed based on this strategy, demonstrates exceptional performance in Buchwald–Hartwig aminations of challenging aryl chlorides and weakly nucleophilic reagents (morpholine), achieving a turnover frequency (TOF) of 442 h⁻¹ (in a flow protocol), an 88-fold improvement over the previous system. Life cycle assessment (LCA) across four sustainability metrics reveals that our catalytic system reduces the environmental footprint by 48% compared to previous reports, showcasing unparalleled advantages in environmental sustainability. By combining in situ characterization with computational calculations, we demonstrate that the electron transfer distance and electron density of the metal centers are the primary factors influencing the synergistic catalytic efficiency. The reduced electron density at the metal center not only facilitates efficient electron acceptance but also lowers the activation barrier, enabling highly efficient C–N coupling with broad scope. Furthermore, nitrogen positional modulation optimizes the coordination environment of Ni atoms, forming a stable five-membered imine-coordinated ring that significantly enhances catalyst stability. This work provides a crucial basis for the design of future environmentally benign catalysts.