Polymerized ionic amphiphiles: Synthesis and effects in the enantioselective hydrogenation of an amino acid precursor

A number of polymerizable ionic amphiphiles has been polymerized in water at various concentrations above their critical micelle concentration (cmc). Oligomeric and polymeric species are formed upon photochemical initiation. Depending on the position of the double bond within the monomer and polymerization conditions (temperature, concentration, use of radical starters) polymeric assemblies were obtained of different size and hence water-solubility. After separation of low-molecular components by dialysis water-soluble polymers have been characterized by their molecular weights (membrane and vapor pressure osmometry) and transmission electron microscopy (TEM). They showed different efficiency as promotors in the rhodium complex-catalyzed asymmetric hydrogenation of (Z)-methyl α-acetamidocinnamate in water and have been compared with their monomeric counterparts. As was demonstrated in one case, associates formed by intramicellar polymerization display an enhanced catalytic efficiency whereas clustered assemblies are inactive.