Central (S) to Central (M=Ir, Rh) to Planar (Metallocene, M=Fe, Ru) Chirality Transfer Using Sulfoxide‐Substituted Mesoionic Carbene Ligands: Synthesis of Bimetallic Planar Chiral Metallocenes

• Published in: Chemistry : a European journal 2019-10, Vol.25 (58), p.13344-13353
• Main Authors: Avello, Marta G., Torre, María C., Sierra, Miguel A., Gornitzka, Heinz, Hemmert, Catherine
• Format: Article
• Language: English
• Subjects: Bimetals; Cadmium; Chemical Sciences; Chemistry; Chirality; chirality transfer; circular dichroism; Coordination chemistry; Electrochemistry; Iridium; Iron; Ligands; Metallocenes; Metals; Oxidation; Rhodium; Ruthenium; Stereoselectivity; sulfoxides; Sulfur
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201902102

Enantiopure bimetallic systems containing three different elements of chirality, namely a main‐group‐based chiral center (sulfur), a transition‐metal chiral center (rhodium or iridium), and a planar chiral element (ferrocene or ruthenocene), have been prepared by a sequence of diastereoselective reactions. The chirality of the chiral sulfur center attached to C‐5 of a 1,2,3‐triazolylidene mesoionic carbene (MIC) ligand coordinated to a metal (Ir, Rh) was transferred through the formation of bimetallic complexes having a chiral‐at‐metal center and a planar chiral metallocene by C−H activation of the sandwich moiety (M=Fe, Ru). The sense of the planar chirality formed in this sequence of reactions depended on the nature of the ligands at the metal center of the starting complex. The configurations of these species were assigned on the basis of a combination of X‐ray diffraction and CD measurements. An electrochemical study of these bimetallic complexes in coordinating solvents showed an equilibrium between the cationic complexes and the neutral species. The effect of the half‐sandwich moiety on the oxidation potentials of the system is remarkable, producing notable cathodic displacements. DFT calculations support these findings. Chirality transferred: Enantiopure bimetallic systems having three different elements of chirality, namely a main‐group‐based chiral center (sulfur), a transition‐metal chiral center (rhodium or iridium), and a planar chiral element (ferrocene or ruthenocene), have been prepared by a sequence of diastereoselective reactions that includes a C−H insertion step (see scheme).