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Pd2Au36(SC2H4Ph)24 clusters have been prepared, isolated and separated in their enantiomers. Compared to the parent Au38(SC2H4Ph)24 cluster, the doping leads to a significant change of the circular dichroism spectrum; however, the anisotropy factors are of similar magnitude in both cases. Isolation of the enantiomers allowed us to study the racemization of the chiral cluster, which reflects the flexibility of the ligand shell composed of staple motifs. The doping leads to a substantial lowering of the racemization temperature. The change in activation parameters due to the doping may be solely due to modification of the electronic structure.

We investigate the distinctly different interaction of thiolate-protected cluster Au 38 (SC 2 H 4 Ph) 24 with two diverse support materials Al 2 O 3 and CeO 2 . The catalytic surfaces have been heated in different atmospheres, and the removal of the thiolate ligands has been studied. Thermogravimetry (TG), temperature-programmed process coupled with mass spectrometer (TPRDO-MS), and X-ray absorption spectroscopy (XAFS) studies were performed to understand the desorption of thiol ligands depending on conditions and support material. Depending on the atmosphere and the support material the fate of the thiol ligands is different upon heating, leading to metallic Au in the case of Al 2 O 3 and to cationic Au with CeO 2 . The thiolate removal seems to be a two-step procedure. The catalytic activity of these Au 38 -supported clusters was studied for the aerobic oxidation of cyclohexane. Conversion was higher for the gold clusters supported on CeO 2 . Surprisingly, a significant amount of cyclohexanethiol was found, revealing the active participation of the thiolate ligand in catalytic reactions. The observation also indicates that breaking and formation of C−S bonds can be catalyzed by the gold clusters. ■ INTRODUCTIONHeterogeneous catalytic processes by supported thiolateprotected clusters (Au n (SR) m ) represent an emerging field stimulated by reports showing higher activity and selectivity in several oxidation reactions 1−4 in comparison with metal nanoparticle catalysts. These clusters consist of a symmetric metal core protected by multiple gold−thiolate staples −SR− (Au−SR−) n (n = 1,2) that present size-dependent physical chemical properties, related with their quantized electronic structure and unique geometrical structure. In comparison to bulk gold, which has a face-centered cubic (fcc) structure, clusters of sizes <2 nm often show icosahedral structure. 5

Thiolate protected metal clusters are valuable precursors for the design of tailored nanosized catalysts. Their performance can be tuned precisely at atomic level, e. g. by the configuration/type of ligands or by partial/complete removal of the ligand shell through controlled pre‐treatment steps. However, the interaction between the ligand shell and the oxide support, as well as ligand removal by oxidative pre‐treatment, are still poorly understood. Typically, it was assumed that the thiolate ligands are simply converted into SO2, CO2 and H2O. Herein, we report the first detailed observation of sulfur ligand migration from Au to the oxide support upon deposition and oxidative pre‐treatment, employing mainly S K‐edge XANES. Consequently, thiolate ligand migration not only produces clean Au cluster surfaces but also the surrounding oxide support is modified by sulfur‐containing species, with pronounced effects on catalytic properties.

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