A series of dicationic styrene-functionalized imidazolium-based salts, in which the two imidazolium rings are bridged by a functionalized spacer, are prepared. The salts are polymerized to afford cross-linked imidazolium-based ionic polystyrene materials, which, owing to the presence of the functionalized spaces, should be highly active organocatalysts for the cycloaddition of CO2 to epoxides to afford cyclic carbonates (CCE reaction). The catalytic activities of the polymers are evaluated in the CCE reaction. The most active catalyst incorporates a diol functionality and is active at 80 °C and a pressure of 4 bar at a loading of 5 mol %, which is comparable to the most active organocatalysts. Moreover, high yields can be obtained under atmospheric pressure upon increasing the temperature to 120 °C. Under harsher conditions, the catalyst is highly active at a loading one order of magnitude lower, highlighting the importance of benchmark conditions for the CCE reaction. Moreover, the polymer catalysts are advantageous because they can be used at low catalyst loadings, the carbonate product is easily isolated in pure form, and loss of activity of the recovered polymer catalyst is not observed during reuse.
Keywords: carbon dioxide; cycloaddition; imidazolium salts; ionic polymers; sustainable chemistry.
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