Chiral Sulfur Functional Groups as Definers of the Chirality at the Metal in Ir and Rh Half-Sandwich Complexes: A Combined CD/X-ray Study.

Mesoionic carbenes (MICs) derived from triazolium salts that contain chiral sulfoxide or sulfoximine functional groups were used to construct enantiopure chiral-at-metal Ir and Rh half-sandwich complexes through the synthetic sequence of MIC complexation/C-H aromatic activation. The process was efficient and diastereoselective for the formation of enantiopure five-membered metallacycles. The use of the enantiomers of the chiral sulfur groups allowed us to prepare complexes that had opposite configurations at the metal center. Complete retention of the configuration at the metal center was observed during the formation of cationic Ir complexes and upon insertion of alkynes into the Ir -C bond, as demonstrated by a combined circular dichroism/X-ray study. These results point to a vicinal-assisted S 1-like mechanism.