From Prochiral N-Heterocyclic Carbenes to Optically Pure Metal Complexes: New Opportunities in Asymmetric Catalysis

J Am Chem Soc. 2020 Jan 8;142(1):93-98. doi: 10.1021/jacs.9b12698. Epub 2019 Dec 23.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't