Zinc Porphyrin/Imidazolium Integrated Multivariate Zirconium Metal–Organic Frameworks for Transformation of CO₂ into Cyclic Carbonates

Abstract

The design and synthesis of metal-organic frameworks (MOFs) enclosed with multiple catalytic active sites is favorable for cooperative catalysis, but is is still challenging. Herein, we developed a sequential postsynthetic ionization and metalation strategy to prepare bifunctional multivariate Zr-MOFs incorporating zinc porphyrin and imidazolium functionalities. Using this facile strategy, tetratopic [5,10,15,20-tetrakis(4-carboxyphenyl)porphyrinato]zinc(II) (ZnTCPP) ligands were successfully installed into the cationic Zr-MOF to obtain ZnTCPP⊂(Br^-)Etim-UiO-66. These MTV-MOFs, including TCPP⊂Im-UiO-66, TCPP⊂(Br^-)Etim-UiO-66, and ZnTCPP⊂(Br^-)Etim-UiO-66, were well characterized and used in CO₂ capture and conversion into cyclic carbonate from allyl glycidyl ether and CO₂ under cocatalyst-free and 1 bar CO₂ pressure conditions. It was found that the structural features and CO₂ affinity properties of these MTV-MOFs can be tuned by introducing imidazolium groups or doping zinc sites. Additionally, ZnTCPP⊂(Br^-)Etim-UiO-66 exhibited enhanced catalytic activities compared to other MTV-MOFs herein for obtaining the 3-allyloxy-1,2-proplyene carbonate product, which was attributed to the cooperative effect of Zn²⁺ sites and Br^- ions in this microporous ionic MTV-MOF. ZnTCPP⊂(Br^-)Etim-UiO-66 can be recycled easily and used at least three times.