Complex catalyzed hydrogenation and carbon-carbon bond formation in aqueous micelles

Two reactions have been investigated in an aqueous micellar system: the asymmetric hydrogenation of alpha-amino acid precursors by means bf optically active rhodium(I) phosphine complexes and the Suzuki reaction of aryl-, benzyl- and allylhalogenides, respectively, with arylboronic acids by means of water soluble palladium-phosphine complexes. Surfactants of different types. Significantly enhance both activity and enantioselectivity in the hydrogenation reaction, provided that the-concentration of the surfactant is above the critical micelle concentration (cmc). We also show the application of amphiphilized polymers and polymerized micelles as surfactants in order to facilitate the phase separation after the reaction. Assemblies of surfactants also accelerate the. Suzuki reaction but there is a limitation due to the low water solubility of the reaction products, and a high concentration of surfactant is necessary. As an effective alternative method a phase transfer system with water and toluene as the immiscible phases and long chain amphiphiles as phase transfer reagents has been investigated. The best results are observed with cationic and zwitterionic surfactants. (C) 1999 Elsevier Science S.A. All rights reserved.