Alkyne Activation by a Porous Silver Coordination Polymer for Heterogeneous Catalysis of Carbon Dioxide Cycloaddition

The widely studied porous coordination polymers, possessing large pores to adsorb waste carbon dioxide gas and further transform it into valuable chemical products, have been attracting research interest, both industrially and academically. The active silver(I) ions endow the specific alkynophilicity to activate C≡C bonds of alkyne-containing molecules via π activation. Incorporating catalytic Ag metal sites into the porous frameworks represents a promising approach to construct heterogeneous catalysts that cyclize propargylic alcohols with CO2, which is highly desirable for the environmentally benign conversion of carbon dioxide to fine chemicals. We report the preparation of porous coordination polymers (PCPs) with active silver sites and efficient silver–silver bond formation by carefully modifying the coordination geometries of the silver sites. The decentralized silver(I) chains in the porous frameworks enable the efficient conversion of CO2 and derivatives of acetylene to α-alkylidene cyclic carbonates in a heterogeneous manner. X-ray structure analysis reveals two kinds of substrate molecules positioned within the pores of the framework, which correspond to trapping and activated modes through the multiple interactions with the functional Ag chains. The example of tandem conversion of simple alkynes and carbon dioxide to α-alkylidene cyclic carbonates is also presented. The well-positioned catalytic silver(I) sites and the crystalline properties of the frameworks facilitated the structural analyses of the intermediates of each catalytic step, providing knowledge of the synergistic nature of the σ and π activation of C≡C bonds. The successful catalysis of azide–alkyne cycloaddition and synthesis of propargylic alcohols via terminal alkynes could also give another indicator for the activation properties of Ag sites.