Asymmetric Kumada-Tamao-Corriu Cross-Coupling Catalyzed by Chiral Pd(NHC) Complexes

The Kumada-Tamao-Corriu cross-coupling affording axially chiral biaryl compounds has been investigated with various chiral Pd(NHC) complexes (NHC = N-heterocyclic carbene). While the nature of the aryl halide partner did not have an influence on the enantioselectivity, the enantioenrichment of coupling products was found to be highly dependent on the structure of the arylmagnesium halide but also on the chiral Pd(NHC) complex used. Thus, up to 63% ee was achieved using an atropisomeric Pd(NHC) complex. These data, along with role reversal experiments of cross-coupling partners, suggest the reductive elimination step to be likely rate- and enantio-determining.