CO2 Fixation by Dual-Function Cu(triNHC) Catalysts as a Route to Carbonates and Carbamates via α-Alkylidene Carbonates

This study employed dual-functional Cu(triNHC) (triNHC = tri-N-heterocyclic carbene) catalysts for the efficient coupling of CO2 with alcohols and amines to form various carbonates and carbamates with good yields. The direct synthesis of carbonates and carbamates from CO2 was realized by the Cu(triNHC)-catalyzed carboxylative cyclization of CO2 and propargyl alcohol and subsequent reactions with an additional nucleophile (alcohols or amines). The free carbene dangled from the Cu(triNHC) catalysts deprotonated the propargyl alcohol to increase the nucleophilicity toward CO2 and the subsequent cyclization was accelerated by the coordination of the copper ion of Cu(triNHC). This dual function of Cu(triNHC) is critical to the reaction of alpha-alkylidene carbonates with nucleophiles, forming carbonates or carbamates.