Ligand Exchange Reaction on Au38(SR)24, Separation of Au38(SR)23(SR′)1 Regioisomers, and Migration of Thiolates

The ligand exchange reaction between Au-38(2-PET)(24) (2-PET: 2-phenylethanethiolate) clusters and enantio-pure planar chiral [2.2]paracyclophane-4-thiol 1 (PCP-4-SH) was studied using high performance liquid chromatography (HPLC) and mass spectrometry. It is shown that even at the initial stage of the reaction at least three out of the four symmetry-unique sites are exchanged leading to different regioisomers of composition Au-38(2-PET)(23)(PCP-4-S)(1). Using HPLC it was possible to isolate one specific regioisomer. The latter is stable at room temperature and at slightly elevated temperatures. However, at 80 degrees C the adsorbed thiolate (PCP-4-S) moves between different symmetry-unique sites. These observations have implications for the preparation of mixed ligand shell clusters with specific ligand patterns.