From Prochiral N-Heterocyclic Carbenes (NHC) to Optically Pure Copper Complexes: New Opportunities in Asymmetric Catalysis

05 July 2019, Version 1

Abstract

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.

Keywords

Prochiral NHCs
copper complexes
NHC catalyst
Atropisomeric complexes
DFT calculations
Asymmetric catalysis

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