Enhancement of Two Types of CO2 Conversion by Regulating Functional Thiophene Groups within Zn-MOF

Sustainable conversion of epoxides and propargylic amines using CO2 could produce valuable chemical products. Efficient conversion generally requires harsh conditions such as noble-metal catalysts, cocatalysts, and toxic solvents, thereby underscoring the crucial need for environmentally friendly non-noble-metal metal–organic framework (MOF) catalysts. In this study, we designed a novel zinc-based metal–organic framework (MOF) with a 5-fold interpenetrating diamond framework, specifically {[Zn(DMTDC)(bpy)]·H2O}n (Zn-MOF-2), where H2DMTDC represents 3,4-dimethylthieno[2,3-b]thiophene-2,5-dicarboxylic acid and bpy denotes 4,4′-bipyridine. Zn-MOF-2 serves as a bifunctional heterogeneous catalyst to promote the cyclization reaction of epoxides and propargylamine with CO2 under mild conditions. The isolated yields of the resulting cyclic carbonates and oxazolidinones were 92% and 93%, respectively. Notably, the catalyst maintained good catalytic activity after five catalytic cycles in both types of CO2 conversion. Control experiments confirmed the effective catalytic activity of the Zn2+ Lewis acid sites in Zn-MOF-2. The isostructural CPO-5 assembled from 4,4′-biphenyldicarboxylic acid has also been demonstrated to catalyze the cycloaddition of epoxides and CO2 but with an inferior performance in catalyzing the carboxyl cyclization of propargylic amines. This result shows that the thiophene ring in the ligand plays a pronounced role in the catalytic performance. The research will enhance the development of effective MOF catalysts for the conversion of CO2.