Amino acid-paired dipyridine polymer as efficient metal- and halogen-free heterogeneous catalysts for cycloaddition of CO2 and epoxides into cyclic carbonates

A series of amino acid-paired dipyridine polymers were synthesized and firstly used as metal- and halogen-free heterogeneous organocatalysts for chemical fixation of CO2 into cyclic carbonates. Glutamic acid (Glu)-paired dipyridine polymer (Pbpy-Glu) possesses the highest catalytic efficiency for cycloaddition reaction under solvent-free conditions, and provides a reasonable recycled process. The mechanism investigation based on the FTIR analysis of catalyst intermediates suggests that the intermolecular synergistic effect involving the -N+ ions in pyridine, COO– groups in Glu, as well as the COO⋯H3N ion pairs contributes to the good catalytic performance of Pbpy-Glu.