A mechanochemically active metal-organic framework (MOF) based on Cu-Bis-NHC-linkers : synthesis and mechano-catalytic activation

Abstract

Porous coordination polymers, more commonly known as metal-organic frameworks (MOFs), are constructed from metal ions and organic linkers which form a robust network-like structure similar to very dense polymeric networks. In this work the mechanochemical activation of a MOF is reported, based on the previous results on the mechanochemical activation of latent Cu(I)-based N-heterocyclic carbenes (NHCs) embedded covalently in various polymers. A mechanochemically triggered copper-catalyzed azide-alkyne cycloaddition (CuAAC) is achieved using an NHC-MOF, constructed from 1,3-bis(4-carboxyphenyl)imidazolium chloride as organic linker. A Cu(I) bis(NHC) is embedded into the MOF analogous to ([Zn4O{Cu(L)2}2]) using the organic bis-NHC ligand, in turn generating a largely amorphous MOF. On activation by ultrasound, the MOF containing 4.66% of Cu shows mechanochemical activation to obtain Cu(I), subsequently triggering a CuAAC with conversions up to 26.5% as monitored by the reaction of benzylazide and phenylacetylene to yield 1-benzyl-4-phenyl-1H-1,2,3-triazole over a period of 20 sonication cycles. With this knowledge in solution, there are prospects to transfer this mechanochemical activity into polymer networks with embedded MOFs to detect stress in hybrid materials.