Active Ruthenium Catalysts Based on Phosphine-Modified Ru/CeO<sub>2</sub> for the Selective Addition of Carboxylic Acids to Terminal Alkynes

The modification of ruthenium species supported on ceria in the presence of suitable phosphines under H<sub>2</sub> at 100 °C was found to generate catalytically active Ru species that were effective for the regio- and stereoselective addition of carboxylic acids to terminal alkynes. The reactions in the presence of a catalytic amount of Ru/CeO<sub>2</sub> modified with 1,4-bis­(diphenylphosphino)­butane gave the anti-Markovnikov adducts in high yields with excellent (<i>Z</i>)-isomer selectivities. On the other hand, the reactions with the trioctylphosphine-modified catalyst gave the Markovnikov adducts as major products. Among the catalysts examined, only ceria- or zirconia-supported catalysts were effective, and hot filtration tests using the phosphine-modified Ru/CeO<sub>2</sub> catalyst suggested that soluble ruthenium species showed quite a high catalytic activity. Very small amounts of ruthenium species were detected in the solution. The solid Ru/CeO<sub>2</sub> could be repeatedly used as a reservoir of active catalysts without a significant loss of activity.