C2-symmetric S/C/S ligands based on N-heterocyclic carbenes: a new ligand architecture for asymmetric catalysis.

Neutral, C2-symmetric S/C/S ligands based on N-heterocyclic carbenes and thioether functionalities were incorporated into transition metal complexes characterised by two direct metal-stereogenic sulfur bonds. This new ligand design was applied to 1,3-dipolar cycloadditions as the first example of the use silver of carbenes in asymmetric catalysis.