The quest for innovative hydrogen-bond donor (HBD) catalysts has led to a significant advancement in the field of organic synthesis. Considering the electron-withdrawing strength of imidazolium cations and the spatial requirements of hydrogen bond donors, a novel HBD catalyst based on the 1,1'-methylenediimidazolium scaffold by bridging two imidazolium cations with methylene was developed. The 1,1'-methylenediimidazolium-based catalysts exhibit excellent performance in the cycloaddition reaction of CO₂ and epoxides, achieving up to 99% yield and 99% selectivity under mild conditions (atmospheric pressure, 80 ℃ for 12 h, with 1 mol% catalyst). The geometric structure, atomic charge distribution, and synergistic effect of HBD catalysts were studied in detail through ¹H NMR spectroscopy and density functional theory (DFT) calculations. The research results indicate that the protons at positions C2-H, C2'-H, C5-H, and C5'-H on the imidazolium rings, as well as the protons on the bridged methylene, contribute to the formation of multiple hydrogen bonds with appropriate distance and synergistic effects, which are crucial for activating CO₂ and epoxides. This research highlights the distinctive attributes of 1,1'-methylenediimidazolium-based catalysts and offers valuable insights into the development of highly efficient multiple HBD catalysts.

Key words: 1,1'-methylenediimidazolium, multiple hydrogen-bond donor catalysts, cycloaddition of CO₂, cooperative effects, density functional theory (DFT) calculation