Polyoxometalate-Based Ag<sup>I</sup>-MOF for Promoting Catalytic Conversion of CO<sub>2</sub> and Propargylic Alcohols under Mild Conditions
Xue Bai, Maochun Zhu, Yifei Liu, Yanli Yang, Jun Geng, Ange Zhang, Ying Lü, Bin Li, Shuxia Liu
Abstract
The conversion of carbon dioxide to high-value chemicals is greatly significant to green chemistry. The cyclization reaction of CO 2 with propargyl alcohol to form α-alkylidene cyclic carbonates has attracted attention due to atomic economy. Silver (Ag I ) has emerged as one of the most effective activators for alkynes, attributed to its distinctive electronic configuration affording a specific affinity with alkynes. Herein, two novel Ag I -based metal–organic frameworks containing Keggin PMo 12 O 40 3– (abbreviated as {PMo 12 }), namely, {Ag 3 (btap) 3 [PMo 12 O 40 ]}·H 2 O ( Ag-1 ) and {Ag(Hbtap) 2 [PMo 12 O 40 ]} ( Ag-2, btap is 3,5-bis(1′,2′,4′-triazol-1′-yl)pyridine), were successfully synthesized. Ag-1 exhibits both exceptional thermal and solvent stability, along with high catalytic activity in CO 2 cyclization with various substituted propargylic alcohols into α-alkyl cyclic carbonates at room temperature and atmospheric pressure. The highly dispersed Ag I and {PMo 12 } sites are beneficial for the superior performance of Ag-1, by activating the C≡C bond and adsorbing carbon dioxide, respectively. Based on the catalytic results, structural analysis, and classical chemical bond theory, it is speculated that the three-coordinated silver in Ag-1 has higher Lewis acidity compared with Ag-2, making it easier to activate the substrate. Notably, the Ag-1 catalyst exhibits outstanding stability with negligible activity loss over at least five successive cycles.