Electron-withdrawing effect of polyoxometalates in Cu(I)-based metal–organic frameworks for enhanced azide-alkyne “click” reaction

Boosting the nucleophilicity of Cu(I) sites is an essential strategy to enhance the efficiency of Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. In this work, a Lindquist-type polyoxometalate (POM)-based metal–organic framework, [Cu^I₄(W₆O₁₉)₂(L)]·2H₂O (NEAU-1), was synthesized via an in-situ solvothermal method. Single-crystal X-ray diffraction results reveal that NEAU-1 exhibits a sandwich structure, with POMs intercalated between the two-dimensional layers formed by resorcin[4]arene ligands and Cu(I) ions. NEAU-1 possesses abundant Cu(I) active sites and high chemical stability, making it an effective heterogeneous catalyst for the CuAAC reaction. More importantly, the presence of POMs effectively reduces the electron cloud density around Cu(I) sites, significantly lowering the energy barrier for the formation of copper-acetylide compounds and facilitating subsequent nucleophilic reactions. The synergistic catalytic effect of POMs and Cu(I) can achieve a conversion rate of over 99 % for benzyl azide and phenylacetylene within 40 min. This work presents a sustainable molecular-level strategy to enhance the activity of the CuAAC reaction.