Soft, Oxidative Stripping of Alkyl Thiolate Ligands from Hydroxyapatite-Supported Gold Nanoclusters for Oxidation Reactions

A strategy for the mild deprotection of alkyl-thiolated (6-mercaptohexanoic acid, MHA, and 3-mercaptopropanoic acid, MPA) gold nanoclusters (AuNCs) supported on hydroxyapatite (HAP) has been developed by employing a peroxide (tert-butyl hydroperoxide, TBHP, or hydrogen peroxide, H2O2) as an oxidant. The thiol ligands on the supported AuNCs were removed after oxidation, and the size and integrity of the supported clusters were well-preserved. The bare gold clusters on HAP after removal of the ligands were catalytically effective for the epoxidation of styrene and the aerobic oxidation of benzyl alcohol. These two reactions were also investigated on calcined AuNCs that were supported on HAP for comparison, and the resulting AuNCs that were prepared by using this new strategy showed superior catalytic activity.