Two cyclotriveratrylene metal–organic frameworks as effective catalysts for Knoevenagel condensation and CO2 cycloaddition with epoxides

Abstract

By using a novel imidazole-functional cyclotriveratrylene ligand, two isostructural frameworks, [Cd₃(HECTV)(bdc)₃]·DMF·6H₂O (1) and [Zn₃(HECTV)(OH-bdc)₃]·3DMF·4H₂O (2) (HECTV = 5,6,12,13,19,20-hexaimidazolium-ethoxy-cyclotriveratrylene), were constructed. The two compounds exhibit fascinating 4-fold interpenetration three-dimensional frameworks. There are still large void spaces in the structures despite the interpenetration, which were filled with solvent molecules. Interestingly, 1 demonstrates a single-crystal to single-crystal transformation with the guests changed by a cycloalkane solvent. Strikingly, 1 and 2 feature highly heterogeneous catalytic activities for Knoevenagel condensation and CO₂ cycloaddition, respectively. In particular, catalysts 1 and 2 could be reused with good catalytic performance.