Ultrafine Colloidal Metal Catalysts. —Preparation, Characterization and Application to Organic Synthesis—

Preparations and characterizations of ultrafine colloidal catalyst particles such as colloidal platinum and gold are reviewed, and the applications for organic syntheses are summarized. Stable, monodisperse, and ultrafine colloidal metals are formed by the reduction of the corresponding metal ions in the presence of protective reagents like synthetic polymers, or in the internal aqueous phases of microemulsions and artificial liposomes. Methods for characterization of ultrafine colloidal catalysts and properties of the colloids are summarized. Several examples of the application of the colloids to organic reactions are described. Colloidal platinum with hydrogen is especially important as reductase models to activate dioxygen or to carry out clean reductions by avoiding any inorganic contaminant.