C 2 -Symmetric atropisomeric N-heterocyclic carbene-palladium(II) complexes: synthesis, chiral resolution, and application in the enantioselective α-arylation of amides.

The concept of atropisomeric N-heterocyclic carbene (NHC)-metal complexes was extended to NHCs possessing a C 2 -symmetry and implemented to prepare palladium-based complexes. An in-depth study of the NHC precursors and the screening of various NHC ligands enabled us to circumvent the issue associated with the formation of meso complexes. A set of 8 atropisomeric NHC-palladium complexes were prepared and then obtained with high enantiopurities, thanks to an efficient resolution by chiral HPLC at the preparative scale. These complexes displayed good activity in the intramolecular α-arylation of amides and various cyclic products were isolated with excellent enantioselectivities (up to 98% ee).