Application of an amino-functionalised metal-organic framework: an approach to a one-pot acid-base reaction

The amino-functionalised metal-organic framework, MIL-101(Al)-NH2, has been synthesized by using a solvothermal method and employed as a bifunctional acid-base catalyst for a one-pot, sequential deacetalization-Knoevenagel condensation reaction. In preliminary studies, the abilities of MIL-101(Al)-NH2 to serve as an acid and base catalyst were explored separately by two typical acid-and base-catalysed reaction, that is, deacetalization of benzaldehyde dimethylacetal and Knoevenagel condensation of benzaldehyde with malononitrile. MIL-101(Al)-NH2 was found to catalyse each of these reactions with high efficiency. MIL-101(Al)-NH2 was then employed as a catalyst for the one-pot sequential deacetalization-Knoevenagel condensation reaction between benzaldehyde dimethylacetal and malononitrile. Benzylidenemalononitrile as the final product was successfully generated with a high yield via benzaldehyde over MIL-101(Al)-NH2. In addition, the catalytic ability of MIL-101(Al)-NH2 was demonstrated to be superior to those of conventional heterogeneous, homogeneous as well as other functionalised metal-organic framework catalysts. Finally, the results show that MIL-101(Al)-NH2 can be reused as a catalyst for this process without significant loss of its activity.