Chiroptical Activity of BINAP-Stabilized Undecagold Clusters

Undecagold cluster compounds [Au11(BINAP)4X2]+ (X = Cl and Br) were synthesized by chemical reduction of the corresponding precursor complexes, Au2X2(BINAP), where BINAP represents the bidentate phosphine ligand 2,2‘-bis(diphenylphosphino)-1,1‘-binaphthyl. The circular dichroism spectra of Au11 stabilized by the enantiomers [Au11(R-BINAP)4X2]+ and [Au11(S-BINAP)4X2]+ exhibited intense and mirror-image Cotton effect, whereas those of Au11 3+ clusters stabilized by achiral monodentate phosphine ligands did not. The origin of the chiroptical activity of [Au11(BINAP)4X2]+ is discussed in the context of the structural deformation of the Au11 3+ core.