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), COF_bpy-CuBr₂, for the highly efficient catalytic conversion of SO₂. The COF_bpy-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, COF_bpy-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.