B-containing ionic liquid modified SBA-15 for CO₂-epoxide coupling reaction metal-free catalysis

A novel external-skeleton B-containing ionic liquid modified SBA-15 catalyst BBN-Imi-SBA-15-I (BBN denotes borabicyclo[3.3.1]nonane, Imi represents imidazolium ionic liquid) was successfully constructed by a post-modification method for efficiently catalyzing CO₂-epoxide coupling reaction under both metal- and solvent-free conditions. 5BBN-Imi-SBA-15-I (5 refers to the molar ratio of Si to B), thanks to its synergistic effects of Lewis acid, weak base sites from tertiary amine and quaternary ammonium, hydrogen bond group and nucleophilic group, displayed good catalytic activity with 97 % product yield and 99 % selectivity at 100 °C, 2 MPa in the absence of cocatalyst. The obtained catalyst demonstrated good recyclability during six consecutive catalytic runs, also presented generality for various mono-substitute epoxides. Through in-situ NH₃ diffuse reflectance infrared Fourier transform spectroscopy (NH₃-DRIFTS) characterization, the Lewis acidity of organo-boron was verified. Besides, kinetics research also proved the positive effect of multiple active components on efficient catalysis under milder conditions over SiO₂-based metal-free catalysts.