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.