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 (MIC) derived from triazolium salts containing chiral sulfoxide or sulfoximine functional groups lead to enantiopure chiral-at-metal Ir(III) and Rh(III) half-sandwich complexes, through the sequence MIC complexation-C-H aromatic activation. The process is efficient and totally diastereoselective in the formation of enantiopure five membered metallacycles. The use of the enantiomers of the sulfur chiral groups allows to prepare complexes having opposite configurations at the metal. Complete retention of the configuration at the metal center is observed during the formation of cationic Ir(III) complexes and upon insertion of alkynes into the Ir(III)-C bond, as demonstrated by a combined Circular Dichroism (CD)-X-ray study. These results point to vicinal assisted SN-like processes.