Chiroptical activity of BINAP-stabilized undecagold clusters

Undecagold cluster compounds [Au-11(BINAP)(4)X-2](+) ( 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 Au-11 stabilized by the enantiomers [Au-11(R-BINAP)(4)X-2](+) and [Au-11(S-BINAP)(4)X-2](+) exhibited intense and mirror-image Cotton effect, whereas those of Au-11(3+) clusters stabilized by achiral monodentate phosphine ligands did not. The origin of the chiroptical activity of [Au-11(BINAP)(4)X-2](+) is discussed in the context of the structural deformation of the Au-11(3+) core.