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From Prochiral N-Heterocyclic Carbenes (NHC) to Optically Pure Copper Complexes: New Opportunities in Asymmetric Catalysis
preprintsubmitted on 04.07.2019, 14:11 and posted on 05.07.2019, 15:57 by Lingyu Kong, Jennifer Morvan, Delphine Pichon, Marion Jean, Muriel Albalat, Thomas Vives, Sophie Colombel-Rouen, Michel Giorgi, Christophe Crévisy, Didier Nuel, Paola Nava, Stéphane Humbel, Nicolas Vanthuyne, Marc MAUDUIT, Hervé Clavier
Well-defined optically pure copper-complexes are obtained from prochiral N- Heterocyclic Carbene (NHC) ligands. As predicted by DFT calculations, our strategy capitalizes on the formation of a metal-carbene bond which induces axial chirality. Configurationally stable (Sa)- and (Ra)-atropisomers of various Cu-complexes are isolated by preparative chiral HPLC in nearly quantitative yields and excellent optical purities (>99.5%). Their catalytic performances are illustrated in asymmetric allylic alkylation with high regioselectivity and enantioinductions. Importantly, the carbene transfer from an optically pure Cu-complex to gold or palladium center reveals, for the first time, a full stereoretentivity, supporting the hypothesis of an associative mechanism for the transmetalation.