Redox‐Active N‐Heterocyclic Carbene‐Bearing Silver(I) Complexes: Synthesis and Novel Catalysts for CO 2 Utilization in the Carboxylative Cyclization of Propargyl Amines

In this study, we have synthesized a series of neutral and cationic silver complexes bearing two different redox‐active N‐heterocyclic carbene (NHC) ligands. Neutral complexes of the type Nq(IDipp)AgOCOR (R = CH 3 ( 2b ), Ph ( 2c ), CF 3 ( 2d )) were obtained via the reaction of imidazolium salts or the corresponding free carbenes with silver precursors. In contrast, cationic complexes of the general formula Nq(NHC) 2 Ag)X (NHC = IDipp, X = BF 4 ( 3a ), SbF 6 ( 3b ); NHC = IMes, X = BF 4 ( 3c ), SbF 6 ( 3d )) were prepared using AgX salts. The complex Nq(IDipp)AgOCOCH 3 ( 2b ) was used as a catalyst for the carboxylative cyclization of substituted propargyl amines with CO 2 gas and outperforms the nonredox active NHC‐silver complexes. This transformation enabled the development of a new and efficient catalytic protocol for the synthesis of a broad range of oxazolidine‐2‐ones in good to excellent yields. Notably, catalyst 2b exhibited excellent catalytic performance under mild conditions, operating effectively at low CO 2 gas concentrations and in the absence of bases or additives.