A Single-Site Cu(II)-Anchored Covalent-Organic Framework for SO2 Catalytic Conversion.

Sulfur dioxide (SO2) is a major atmospheric pollutant as well as an indispensable chemical raw material for the synthesis of sulfuric acid and fine chemicals. From the perspectives of efficiency, ecology, and economy, the catalytic SO2 conversion into high value-added chemicals is particularly fascinating, while developing robust catalysts capable of efficiently activating and converting SO2 remains extremely challenging. Herein, we report the rational construction of a single-site Cu(II)-anchored covalent-organic framework (COF), COFbpy-CuBr2, for the highly efficient catalytic conversion of SO2. The COFbpy-CuBr2 showed multiple favorable SO2 adsorption sites within the framework, including OSO···Cu, O2S···π, and OSO···N contacts, thus exhibiting remarkable SO2 selectivity and excellent SO2 adsorption capacity of 10.98 mmol/g at 298 K and 1 bar. The strong Cu-SO2 interactions promoted the enrichment of SO2 at the catalytic center, further facilitating the SO2 insertion in the coupling with aryl diazoniums and alcohols, thus enabling the highly efficient conversion into sulfonate esters. Moreover, COFbpy-CuBr2 could be applied to the late-stage functionalization for the gram-scale synthesis of a biologically active coumarin derivative. Mechanism investigations revealed a Cu(II)-catalyzed radical pathway for this catalytic process. This work provides a novel paradigm for the rational construction of next-generation COFs to achieve highly efficient and selective SO2 catalytic conversion.