Asymmetric Twisting of C -Centered Octahedral Gold(I) Clusters by Chiral N -Heterocyclic Carbene Ligation.

Asymmetric induction of metal clusters by ligation of chiral ligands is intriguing in terms of the mechanism of chirality transfer and the stability of the resulting chiral structure. Here we report the asymmetric induction of C -centered hexagold(I) CAu I 6 clusters into an asymmetrically twisted structure through monodentate, chiral benzimidazolylidene-based N -heterocyclic carbene (NHC) ligands. X-ray diffraction analysis revealed that the NHC-ligated CAu I 6 cluster was diastereoselectively twisted with directionally selective, bond length expansion, and contraction of the Au···Au contacts and that the original cluster with high symmetry was transformed into an optically pure, asymmetric CAu I 6 cluster with C 1 symmetry. Moreover, the circular dichroism spectroscopy and the time-dependent density functional theory calculation confirmed that the asymmetrically twisted CAu I 6 structure was maintained even in solution. Such asymmetric induction of configurationally stable metal clusters would greatly expand the molecular design possibilities of asymmetric catalysts and chiroptical materials by utilizing library chiral NHC ligands.