Efficient green solvent-free CO2/epoxide cycloaddition catalyzed by a β-cyclodextrin-imidazolium-based ionic liquid

The rising atmospheric carbon dioxide (CO) levels significantly contribute to climate change. Converting CO into valuable products offers an attractive strategy to mitigate its environmental impact. Here, we present a highly efficient, solvent-free method for CO₂ fixation into cyclic carbonates using a novel green catalyst, β-cyclodextrin, linked to an imidazolium-based ionic liquid (β-CD-ImBr). This catalyst facilitates the conversion of various terminal and internal epoxides into cyclic carbonates with exceptional performance. Notably, β-CD-ImBr achieves up to 98 % conversion of styrene oxide to its corresponding carbonate within 24 h at 120 °C, demonstrating significant activity without needing a co-catalyst. Operating under solvent-free conditions, this method avoids environmentally harmful synthetic pathways by utilizing the hydroxyl groups of cyclodextrins as hydrogen bond donors and employing the bromine counterion to facilitate epoxide ring opening. Mechanistic studies reveal that β-CD-ImBr enhances catalytic performance by lowering the activation energy of the rate-limiting step through its hydrogen bond acceptor properties. Importantly, the catalyst is both recyclable and reusable, highlighting its cost-effectiveness and environmental benefits. This approach represents a significant advancement in sustainable chemistry, offering a green alternative for CO₂ fixation.