Thiophene-Functionalized Zn-Based Metal–Organic Frameworks with Nanosheets/Nanopores as Heterogeneous Catalysts for CO2 Conversion

Two Zn(II) metal–organic frameworks (Zn-MOFs), namely [Zn2(DMTDC)1.5(OH)(ttmtb)]n (Zn-MOF-3) and {[Zn(DMTDC)(H2O)(bptb)]·DMF}n (Zn-MOF-4) (H2DMTDC = 3,4- dimethyl[2,3-b]thiophene-2,5-dicarboxylic acid, ttmtb = 1,3,5-tris(1,2,4-triazol-1-ylmethyl)-2,4,6-trimethylbenzene, bptb = 1,3-bis(5-(pyrid-4-yl)-1,2,4-triazol-3-yl)benzene), were obtained by the reaction of bithiophene carboxylic acid ligand H2DMTDC and two flexible N-containing ligands, ttmtb and bptb, respectively. These Zn-MOFs displayed a three-dimensional stacked structure with different binuclear Zn2 units. The frameworks exhibit notable catalytic performance in the cycloaddition reactions involving epoxides and CO2, achieving isolated yields of 89% and 90%, respectively. Zn-MOF-3 can effectively catalyze the carboxylation of propargylic amines with CO2 under milder conditions, higher than that of Zn-MOF-4, likely due to structural differences in the framework. Further control experiments validated the notable catalytic effectiveness of Zn2+ Lewis acid sites in two types of CO2 conversion processes. Our study will contribute to the development of effective bifunctional MOF catalysts for CO2 conversion.