Ligand-Free Buchwald-Hartwig Aromatic Aminations of Aryl Halides Catalyzed by Low-Leaching and Highly Recyclable Sulfur-Modified Gold-Supported Palladium Material

A stable heterogeneous catalyst precursor, sulfur-modified gold-supported palladium material (SAPd), has proved to be an excellent source of leached, ligand-free, Pd for the amination of aryl bromides and chlorides. The reaction-enabling catalyst is provided in situ as leached Pd in low catalyst loading (0.21 +/- 0.02 mol%). This allows the precatalyst (SAPd) to be filtered off and used for a minimum of ten reaction cycles without loss of catalytic activity. SAPd released only trace amounts, less than 0.6 ppm, of highly active Pd during the reaction without any aggregation.