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Gold clusters protected by terminal alkynes (1-octyne (OC-H), phenylacetylene (PA-H) and 9-ethynyl-phenanthrene (EPT-H)) were prepared by the ligand exchange of small (diameter <2 nm) Au clusters stabilized by polyvinylpyrrolidone. The bonding motif of these alkynes on Au clusters was investigated using various spectroscopic methods. FTIR and Raman spectroscopy revealed that terminal hydrogen is lost during the ligand exchange and that the C≡C bond of the alkynyl group is weakened upon attachment to the Au clusters. Acidification of the water phase after the ligand exchange indicated that the ligation of alkynyl groups to the Au clusters proceeds via deprotonation of the alkynes. A series of precisely defined Au clusters, Au34(PA)16, Au54(PA)26, Au30(EPT)13, Au35(EPT)18, and Au(41-43)(EPT)(21-23), were synthesized and characterized in detail to obtain further insight into the interfacial structures. Careful mass analysis confirmed the ligation of the alkynes in the dehydrogenated form. An upright configuration of the alkynes on Au clusters was suggested from the Au to alkyne ratios and photoluminescence from the excimer of the EPT ligands. EXAFS analysis implied that the alkynyl carbon is bound to bridged or hollow sites on the cluster surface.

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A Lewis acid-surfactant-combined catalyst (LASC) has been developed and applied to Lewis acidcatalyzed organic reactions in water. LASCs are composed of water-stable Lewis acidic cations such as scandium and anionic surfactants such as dodecyl sulfate and dodecanesulfonate and are easily prepared. These catalysts have been successfully used for various typical carbon-carbon bond-forming reactions such as aldol, allylation, and Mannich-type reactions in water. Furthermore, the results of aldol reactions in various solvents show that water is the best solvent for the LASC-catalyzed reactions. A preliminary kinetic study of the aldol reaction showed that the initial rate in water was 1.3 × 10 2 times higher than that in dichloromethane. In the workup procedure, it was demonstrated that centrifugation of the reaction mixture led to phase separation without addition of any organic solvents. The LASCs was found to form stable colloidal dispersions rapidly in the presence of reaction substrates in water, even when the substrates are solid. The characterization of the colloidal particles has been carried out by means of dynamic light scattering, light microscopy, transmission electron microscopy, and atomic force microscopy. These observations revealed the size of ∼1 µm and the spherical shape of the particles. It was suggested that most of the substrates and catalyst molecules were concentrated in the spherical particles, which acted as a hydrophobic reaction environment and enabled the rapid organic reactions in water. In light of the increased demand for reduction of organic solvents in industry, the surfactantaided Lewis acid catalysis described here may have practical consequences in organic synthesis.

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