From Prochiral N‑Heterocyclic Carbenes to Optically Pure Metal Complexes: New Opportunities in Asymmetric Catalysis
journal contributionposted on 2019-12-23, 19:41 authored by Lingyu Kong, Jennifer Morvan, Delphine Pichon, Marion Jean, Muriel Albalat, Thomas Vives, Sophie Colombel-Rouen, Michel Giorgi, Vincent Dorcet, Thierry Roisnel, Christophe Crévisy, Didier Nuel, Paola Nava, Stéphane Humbel, Nicolas Vanthuyne, Marc Mauduit, Hervé Clavier
Well-defined optically pure transition metal (TM) complexes bearing C1- and C2-symmetric N-heterocyclic carbene (NHC) ligands were prepared from prochiral NHC precursors. As predicted by DFT calculations, our strategy capitalizes on the formation of a metal-carbene bond which induces an axis of chirality. Configurationally stable atropisomers of various NHC-containing TM complexes were isolated by preparative HPLC on a chiral stationary phase in good yields and excellent optical purities (up to 99.5% ee). The carbene transfer from an optically pure Cu complex to a gold or palladium center reveals, for the first time, a full stereoretentivity, supporting the hypothesis of an associative mechanism for the transmetalation. The potential of these new chiral TM complexes was illustrated in asymmetric catalysis with up to 98% ee.