Insight into the Mechanism of CO Chemical Fixation into Epoxides by Windmill-Shaped Polyoxovanadate and -BuNX (X = Br, I).

Carbon dioxide (CO) coupled with epoxide to generate cyclic carbonate stands out in carbon neutrality due to its 100% atom utilization. In this work, the mechanism of CO cycloaddition with propylene oxide (PO) cocatalyzed by windmill-shaped polyoxovanadate, [(CNH)(CHO)VVO]·4CHOH (V-1), and -BuNX (X = Br, I) was thoroughly investigated using density functional theory (DFT) calculations. The ring-opening, CO-insertion, and ring-closing steps of the process were extensively studied. Our work emphasizes the synergistic effect between V-1 and -BuNX (X = Br, I). Through the analysis of an independent gradient model based on Hirshfeld partition (IGMH), it was found that the attack of -BuNX (X = Br, I) on C of PO triggers a distinct attractive interaction between the active fragment and the surrounding framework, serving as the primary driving force for the ring opening of PO. Furthermore, the effect of different cocatalysts was explored, with -BuNI being more favorable than -BuNBr. Moreover, the role of V-1 in the CO cycloaddition reaction was clarified as not only acting as Lewis acid active sites but also serving as "electron sponges". This work is expected to advance the development of novel catalysts for organic carbonate formation.