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

Abstract

Developing photocatalysts with low energy consumption and high efficiency for CO 2 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 CO 2 cycloaddition reactions, an imidazolium bromide ionic liquid-functionalized polyoxometalate photocatalyst ImBr-[Ru(C 10 N 2 H 8 ) 2 ]H[AsW 12 O 40 ]·2H 2 O 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(C 10 N 2 H 8 ) 2 ]H[AsW 12 O 40 ]·2H 2 O achieves efficient photocatalytic CO 2 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 CO 2 photofixation without any cocatalyst and sacrificial agent.