Aminolysis of five-membered cyclic carbonate catalyzed by guanidines: Solvent effects on the formation of guanidine dimers

• The aminolysis reactions of five-membered cyclic carbonate (5CC) catalyzed by mono- or bi-cyclic guanidines were evaluated. • The effect of the solvent polarity on the catalytic efficiency was systematically investigated. • Extensive DFT calculations were further carried out to confirm the solvent polarity-dependent dimeric state of the guanidines. This paper presents an experimental and computational investigation on the aminolysis reactions of five-membered cyclic carbonate (5CC) catalyzed by mono- or bi-cyclic guanidines in various solvents. For both liquid and solid 5CC substrate employed, higher polar solvent favors the monomeric active guanidine responsible for the catalytic aminolysis reactions. The formation of the dimeric state of the guanidine catalyst, which is seemingly inert to catalytic activity, is prevented by the bulkier substituents connecting to the guanidine moiety. Extensive DFT calculations further confirm that the relative stabilities of dimeric guanidine is depended on both the polarities of the solvents and the bulkiness of the substituents connected to the guanidine moiety, which is consistent with the experimental kinetic results.