M-BTC as Efficient Catalyst for the Synthesis of Cyclic Organic Carbonates Assisted Tandem by Olefin Epoxidation and CO2 Cycloaddition

The metal-organic frameworks (MOFs) with oxidative and acidic active sites demonstrate promising potential for tandem reactions involving olefin oxidation carboxylation. In this study, M-BTCs were synthesized via a solvothermal method, employing 1,3,5-benzenetricarboxylic acid (H3BTC) as a ligand in combination with various metals (Mn, Co, Cu, Ni). The good thermal stability and morphology of M-BTC was verified by various characterization techniques, and its catalytic performance was evaluated for oxidative carboxylation. The catalytic activity of Mn-BTC, with Mn3+/ Mn2+as the primary oxidation site, was found to be superior in both olefin epoxidation and CO2 cycloaddition. The effects of reaction conditions on both epoxidation of styrene and the cycloaddition reaction were investigated, respectively. Under optimal reaction conditions (epoxidation: 10 wt% Mn-BTC of styrene, 80 degrees C for 12 h; cycloaddition: 100 degrees C for 12 h with a CO2 flow rate of 15 ml/min and tetrabutylammonium bromide (TBAB) amount of 15 mol%), a 53% yield of styrene carbonate (SC) was obtained in the assisted tandem reactions. Furthermore, cycling experiments as well as XRD and FT-IR spectra of the catalysts after use demonstrated that Mn-BTC maintained its crystal structure and retained a yield of 49% SC after three cycles. Finally, a possible mechanism for assisted tandem catalytic reaction over Mn-BTC was proposed.