First Photocatalytic Synthesis of Cyclic Carbonates from CO2 Using Bromide-Functionalized Polyoxometalate without Additional Cocatalyst

Developing photocatalysts with low energy consumption and high efficiency for CO2 fixation without any cocatalyst is a highly sought-after goal, but it still presents a significant challenge. Herein, aiming at enhancing the efficiency of photodriven CO2 cycloaddition reactions, an imidazolium bromide ionic liquid-functionalized polyoxometalate photocatalyst ImBr-[Ru(C10N2H8)2]H[AsW12O40]·2H2O with Ru-based photosensitizer coordinated with ionic liquids via strong coupling between the metal active site and carboxy group is reported. The optimized ImBr-[Ru(C10N2H8)2]H[AsW12O40]·2H2O achieves efficient photocatalytic CO2 cycloaddition with epoxides at ambient temperature without additional cocatalyst and photosensitizer, which is much higher than most reported photocatalysts in the presence of TBAB cocatalyst. The experimental results indicated that imidazolium bromide ionic liquid facilitating the ring-opened reaction of epoxides, the radical mechanism, and a plausible reaction pathway for the epoxidation step was further proposed by in situ DRIFT and EPR. Remarkably, this is the first report on the photoeffect of polyoxometalate-based catalysts with ionic liquid-functionalized molecules for catalytic CO2 photofixation without any cocatalyst and sacrificial agent.