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Four binuclear tridentate copper(I) complexes were synthesized based on the trans effect of the hybrid ligands. The catalytic performance and behavior of the prepared copper(I) complexes were evaluated in the carboxylative cyclization of propargylic amines with CO2. The combined use of copper(I) complexes and 1,5,7-triazabicyclo4.4.0dec-5-ene (TBD) provided a catalytic system for the synthesis of a wide range of oxazolidinones from various propargylic amines and CO2 under mild reaction conditions (room temperature—40 °C and 1 bar CO2). The key factor for the success of the protocol is the use of copper complexes possessing the quality of hemilabile properties between N-heterocyclic carbenes and nitrogen donors. NMR measurements, density functional theory (DFT) calculations, and previous reports for the coordination behavior of the nickel complexes support the existence of the trans effect between N-heterocyclic carbenes and nitrogen donors.
Chen et al. (Mon,) studied this question.