Solvent-Free Carboxylative Cyclization of CO2 with Alkynol Catalyzed by Ag(I)-Functionalized Polyoxoniobate-Based Coordination Polymer at Room Temperature

Transforming gaseous waste CO2 as a C1 feedstock into fine chemicals is significant for green chemistry and sustainable development. Herein, the novel Ag(I)-functionalized polyoxoniobate-based coordination polymer {[Ag(tpy)]5[Nb10O28]}[Ag(H2O)]·5H2O (1, tpy = 2,2′:6′,2″-terpyridine) is successfully fabricated and fully characterized. Compound 1 not only displays excellent thermal and solvent stabilities but can also efficiently and selectively catalyze the solvent-free carboxylative cyclization of terminal propargylic alcohols with different substituents with CO2 to high-value-added α-alkylidene cyclic carbonates at room temperature. The prominent performance of 1 is attributed to the synergistic operation of Ag(I) and [Nb10O28] in its structure, which is responsible for activating the C≡C bond and hydroxyl group of propargylic alcohols, respectively. The catalyst exhibits outstanding sustainability; no obvious decrease in catalytic activity is observed during five successive cycles, and the yield of α-alkylidene cyclic carbonate in the gram-scale (100 mmol, 8.4 g) experiment is up to 61.7% (turnover number value = 5144). To the best of our knowledge, this represents the first example of polyoxometalate-based catalyst for catalyzing the solvent-free conversion of CO2 to value-added chemicals at room temperature.