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A series of bis(pyridylcarbamate) ligands with the flexible diethylene glycol spacer and carbamate NH donors as catalysts have been designed and synthesized, and these can be used for the fixation of carbon dioxide with commercially sourced epoxides under mild conditions using alkali metal salts. It is worth noting that between the ligand and the alkali metal salt there is a synergetic effect, which plays an important role in accelerating the reaction rate. A detailed mechanistic insight into the effects of carbamate NH groups and the diethylene glycol spacer on the activation of the epoxides has been studied using density functional theory (DFT) methods. [ABSTRACT FROM AUTHOR]

A new type of pyrene-based ammonium bromides (PABs) was synthesized via the reaction of bromomethyl pyrene and tertiary amines with different alkyl chains combined with graphitic carbon nitride (g-C 3 N 4 ) through π-π stacking interactions. The new pyrene-based ammonium bromides were investigated both in homogenous phase and heterogeneous phase combining with g-C 3 N 4 for the CO 2 fixation reaction of epoxides under mild conditions. Obviously, the combination was proved to be an efficient system for the conversion of epoxides. The interaction between g-C 3 N 4 and PABs was confirmed by quantum chemical calculations. g-C 3 N 4 /Py-C 12 exhibited an excellent yield of cyclic carbonates (above 93%) at 80 °C, atmospheric pressure and solvent-free conditions. A preliminary kinetic study was performed using g-C 3 N 4 /Py-C 12 and the activation energy was calculated to be 61.5 kJ mol -1 ., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)