Single-component, metal-free, solvent-free HO-functionalized 1,2,3-triazole-based ionic liquid catalysts for efficient CO2 conversion

Abstract

A series of HO-functionalized 1,2,3-triazolic ionic liquids (1–9b) bearing different alkyl chains and counter-anions was evaluated as green, single-component, bifunctional catalysts for cycloaddition reactions involving CO2 and epoxides. They were prepared via a clean, facile, and high-yield three-step procedure using cheap, non-toxic, and widely available starting materials. Compounds 1–9b were characterized via spectroscopic techniques, and the molecular structure of 3b was also confirmed via single-crystal X-ray diffraction. The catalytic results evidenced that synergism between the hydroxyl group and the counter anion is essential for achieving excellent turnover frequencies (TOFs). In parallel, neutral triazoles showed very low activity under the same reaction conditions. Using the optimal reaction conditions (25 mmol of epoxide, 140 °C, 30 bar CO2, and 1 h), high conversion of all terminal epoxides was achieved, including in a scale-up experiment that produced an outstanding TOF value of 667 h−1. Moreover, a reaction using cyclohexene oxide achieved 85% conversion in only 6 h. In summary, our results show the attractive potential of HO-functionalized 1,2,3-triazole-based ionic liquid catalysts for efficient CO2 conversion to cyclic carbonates.