Bifunctional Boron Phosphate as an Efficient Catalyst for Epoxide Activation to Synthesize Cyclic Carbonates with CO₂

Development of inexpensive, easily prepared, non-toxic, and efficient catalysts for the cycloaddition of CO₂ with epoxides to synthesize five-membered cyclic carbonates is a very attractive topic in the field of CO₂ transformation. In this work, we conducted the first work on the cycloaddition of CO₂ with epoxides to produce cyclic carbonates catalyzed by a binary catalyst system consisting of KI and boron phosphate (BPO₄ ), which are both inexpensive and non-toxic, and various corresponding cyclic carbonates could be produced with high yields (93-99 %) at 110 °C with a CO₂ pressure of 4 MPa under solvent-free conditions. In the BPO₄ /KI catalyst system, BPO₄ , a Brønsted and Lewis acid hybrid, played the role of activating the epoxy ring through the formation of hydrogen bonds with Brønsted acidic sites and the interaction with Lewis acidic sites simultaneously, and thus enhanced the activity of KI for the cycloaddition of CO₂ with epoxides significantly. Additionally, the activity of the BPO₄ /KI catalyst system showed no noticeable decrease after being reused five times, indicating that the BPO₄ was stable under the reaction conditions.