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 ℃ for 12 h; cycloaddition: 100 ℃ 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.