Chiral N-heterocyclic carbeneligands based on a biisoquinoline template

Abstract

New chiral imidazolinium salts with tunable steric features, based on a biisoquinoline template, have been developed and structurally characterised using single crystal X-ray crystallography. The trans PdI₂(NHC)₂ complex was prepared by reaction of the parent H₄ imidazolinium salt with Pd(OAc)₂ in the presence of NaI, and the solid state structure determined by X-ray crystallography. The rigid, chiral, biisoquinoline geometry of the H₄ imidazolinium salt was found to be maintained upon ligand complexation. The sterically unencumbered parent biisoquinoline ligand has been found to give high conversion with modest enantioselectivity in the copper-catalysed asymmetric addition of diethylzinc to cyclohexenone.