Post-synthetic cation exchange in anionic metal–organic frameworks; a novel strategy for increasing the catalytic activity in solvent-free condensation reactions†
Abstract
In recent years anionic MOFs (metal–organic frameworks) have only been scarcely explored for application in heterogeneous catalysis. In this work an anionic metal–organic framework, [HDMA]2[Zn2(BDC)3(DMA)2]·6DMF, has been prepared and its cations, HDMA+, were exchanged by Ni2+, Na+, Li+, tetraethylammonium (TEA+) and tetrapropylammonium (TPA+) by a post-synthetic process. By the strategy developed here, we have been able to prepare cation exchanged anionic MOFs as novel heterogeneous catalytic systems for solvent-free Knoevenagel condensation reaction between benzaldehyde and malononitrile. These catalysts were easily isolated from the reaction mixture and were reused several times without a significant degradation in activity.