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

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.