(757g) Cycloaddition Reaction of Epoxides with CO2 in a Copper Metal-Organic Framework: A Density-Functional Theory Study

A large number of metal-organic frameworks (MOFs) have been reported to be efficient catalysts in Lewis acid catalyzed reactions such as the cycloaddition reaction of epoxides with CO₂ to carbonates under mild condition. Herein, we report a density functional theory (DFT) study to investigate the cycloaddition reaction in a Cu-MOF. Two competitive pathways are considered in the channel of the Cu-MOF associated with a co-catalyst tetrabutylammonium bromide (TBAB). Both pathways are found to be energetically more favorable compared with other systems. The intermediates and transition states have low free energies with high stability, as attributed to the long-range electrostatic interactions with the Cu-MOF. In both two pathways, the rate-determining step is revealed to be the ring opening of epoxide through the necleophilic attack of Br^- of TBAB. Furthermore, the concerted reaction by inserting CO₂ into the ring opening step has a lower energy barrier and is a preferential pathway. This theoretical study provides microscopic insight into the cycloaddition reaction mechanism, and could facilitate the rational screening and development of new catalysts.