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 S1-like mechanism.

Support for this work under grants CTQ2013-46459-C2-01-P, CTQ2016-77555-C2-1-R to M.A.S., CTQ2013-46459-C2-02-P, CTQ2016-77555-C2-2-R to M.C.T. and CTQ2014-51912-REDC Programa Redes Consolider, from the MINECO (Spain) is gratefully acknowledged. M.G.A. and M.F.P. thanks the MINECO for FPI grants.