A Facile and Versatile “Click” Approach Toward Multifunctional Ionic Metal–organic Frameworks for Efficient Conversion of CO₂

Ionic metal–organic frameworks (IMOFs) that integrate synergistic Lewis-acid sites (intrinsic metal centers of the frameworks) and nucleophilic anions (halides encapsulated within pores) are intriguing platforms for the design of fully heterogeneous catalytic systems for cycloaddition of CO₂ to epoxides. A new, facile and versatile synthetic approach has been used to fabricate triazolium-based IMOFs for the first time. The approach makes use of azide–alkyne click chemistry and subsequent N-alkylation to post-synthetically create a cationic triazolium ring and introduce exchangeable counteranions at the same time. The IMOFs are efficient and recyclable heterogeneous catalysts for CO₂ conversion under mild and cocatalyst-free conditions. In particular, the click-accessible triazolium ring provides a handle to incorporate further functionality. The MIL-101-tzmOH-Br catalyst, which integrates hydrogen-bonding hydroxy groups besides metal centers and bromide anions, shows superior catalytic performance under mild conditions.