Anthracene-triazole-dicarboxylate-Based Zn(II) 2D Metal Organic Frameworks for Efficient Catalytic Carbon Dioxide Fixation into Cyclic Carbonates under Solvent-Free Condition and Theoretical Study for the Reaction Mechanism

Abstract

Two ZnII-based metal organic frameworks (MOFs) [Zn2(L)2(1,2-bis(4-pyridyl)ethane)4]n [(ZnMOF1)] and [Zn2(L)2(1,2-bis(4-pyridyl)ethene)4]n [(ZnMOF2)] have been synthesized and crystallographically characterized. Due to the presence of Lewis acidic center Zn and basic functional groups (−N═N) in both complex [(ZnMOF1)] and [(ZnMOF2)], it is possible to efficiently fix carbon dioxide into epoxides to produce biosource cyclic carbonates. Under solvent-free and mild reaction conditions (60 °C temperature and 1 bar CO2 pressure), various types of epoxides (terminal as well as internal epoxides) effectively undergo this catalytic reaction and produced high yield of the corresponding cyclic carbonate products. High turnover frequency was obtained for this CO2 fixation reaction of different epoxides, and the values are in the range of 72–234 h–1. The theoretical calculations are made by density functional theory (DFT) theory to achieve the relative energy of the intermediates and transition state and product which are engaged in each step of the catalytic reaction cycle, and the detailed mechanism of the reaction is presented. Moreover, the two MOF catalysts are easily recoverable and recyclable in nature. The efficiencies of both catalysts regain even after seven consecutive catalytic cycles. Overall, the work demonstrates the design and syntheses of two Zn(II)MOF catalysts for effective addition of CO2 into epoxides to produce cyclic carbonates and DFT study for the catalytic reaction mechanism.