A Cationic Zinc-Organic Framework with Lewis Acidic and Basic Bifunctional Sites as an Efficient Solvent-Free Catalyst: CO2 Fixation and Knoevenagel Condensation Reaction.

A novel two-dimensional cationic framework [Zn2(TCA)(BIB)2.5]·(NO3) (1) (H3TCA = tricarboxytriphenyl amine, BIB = 1,3-bis(imidazol-1-ylmethyl)benzene) was successfully achieved. Compound 1 not only presents a moderate affinity toward CO2 molecules, but it also displays good catalytic performance and substrate selectivity toward both CO2 conversion with epoxides and Knoevenagel condensation under solvent-free environments, taking advantage of the Lewis acidity endowed by lower four-coordinated Zn(II) centers and Lewis basicity originated from the amines within TCA3-. More importantly, the bifunctional heterogeneous catalyst compound 1 shows easy recovery and reuse without an obvious decrease of activity. Strikingly, compound 1 exhibits good catalytic efficiency for CO2 coupled with propylene oxide forming propylene carbonate even at ambient temperature under 1 atm pressure. To the best of our knowledge, compound 1 is presented to be the first cationic MOF holding great promise as a heterogeneous solvent-free catalyst toward both CO2 epoxidation and Knoevenagel condensation reaction.