Modular Synthesis of a New Type of Chiral Bis(carbene) Ligand from L-Valinol and Iridium(I) and Rhodium(I) Complexes Thereof

New, chiral bis(imidazol-2-ylidene) ligands, and their rhodium(l) and iridium(I) complexes, have been prepared by a simple six-step synthesis starting from commercially available enantiomerically pure L-Valinol. The stepwise introduction of the imidazoles makes it possible to create chiral his(NHC) complexes with different substituents at the terminal nitrogen atoms. Formation of Ir-I and Rh-I complexes by a one-pot transmetallation reaction gives the endo and exo stereoisomers in different. ratios, depending on the metal and the reaction conditions. Diastereomerically pure material was obtained by crystallisation. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)