Hydrophobic mesoporous poly(ionic liquid)s towards highly efficient and contamination-resistant solid-base catalysts

Mesoporous poly(ionic liquid)s were synthesized by radical copolymerization of the ionic liquid 1-aminoethyl-3-vinylimidazolium bromide with divinylbenzene plus the ion exchange of bromide anions with hydroxyls. Characterizations revealed the high ionic liquid content, large surface area, and hydrophobicity for the sample prepared with equimolar amounts of ionic liquid and divinylbenzene, with good accessibility to organic compounds and resistance to CO₂/H₂O contamination. The mesoporous copolymer behaved as a superior and recyclable solid-base catalyst for solvent-free Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate, giving the much higher turnover frequency of 304 h^-1 (yield 99%, 0.5 h) than those of the nonporous analogues, commercial strong basic resins, and even homogeneous NaOH. The high activity was confirmed by Knoevenagel condensation with various substrates and Claisen-Schmidt condensation. A possible synergistic Lewis-Brønsted dual-base-center mechanism is proposed for understanding the catalytic behavior.