Modular Synthesis of Chiral NHC Precursors and Their Silver and Gold Complexes

The stereoselective synthesis of chiral heterocyclic carbene precursors and the structural features of their silver and gold complexes were investigated. The prepared compounds are all based on the imidazolidine scaffold and bear the bulky tert-butyl substituent on the backbone in a stereocontrolled manner. The majority of the synthesized carbene precursors carry an additional element of central chirality in the side chain, and for some of them on formation of their silver or gold complexes a third element of asymmetry, axial chirality through hindered rotation of the aromatic substituent, is also present. The systematic study of the stereoselective formation of the NHC precursors led to scalable routes without the need for chiral chromatography. The NHC precursors were transformed efficiently into their silver and gold complexes, whose structural features were studied in detail both in solution and in the solid phase.