Chiral N-heterocyclic carbene ligands based on a biisoquinoline template

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