Synthesis, post-modification and catalytic properties of metal-organic framework NH2-MIL-53(Al)

A postsynthetic modification method was used to prepare salicylaldehyde functionalized metal-organic frameworks through the nucleophilic addition of salicylaldehyde with the amine group present in the frameworks of NH2-MIL-53(Al). Hydroxyl groups were successfully grafted onto NH2-MIL-53(Al), and imine groups were formed. Importantly, these hydroxyl and imine groups of the resulting NH2-MIL-53(Al)-SA can be used as the anchoring group to stabilise Au3+ ions and Au0 nanoparticles(NPs). By doing this, Au3+ ions and Au0 NPs were successfully encapsulated in the cages of NH2-MIL-53(Al) by a simple impregnation method. The resulting gold functionalized NH2-MIL-53(Al) showed good catalytic activities in the one-pot synthesis of structurally divergent propargylamines by three-component coupling reactions of aldehydes, amines and alkynes. Various aromatic/aliphatic aldehydes, aromatic alkynes, and piperidine were able to undergo three-component coupling on NH2-MIL-53(Al)-Au. In addition, the catalyst NH2-MIL-53(Al)-Au was recovered easily by centrifugation and reused up to four times. Thus, it can be used for the environmentally friendly synthesis of propargylamines.