Internal vs. external ionic functionality - a comparative study in the asymmetric hydrogenation in water as solvent

Coupling of the benzoylsulfonate moiety to chiral hydroxy phosphines by acy lation with o-sulfobenzoic anhydride (SBA) affords unique ligands bearing o ne or two sulfonate groups in distinguished positions in the molecular fram ework. Rhodium complexes based on the new ligands have been proven in the a symmetric hydrogenation of functionalized chelating olefins in methanol and in water. Results observed are compared to those featured by the correspon ding non-sulfonated catalysts. In methanol as solvent only one of the compl exes bearing a sulfonate group in a flexible ligand differed significantly from its parent complex, while in water all sulfonated complexes were super ior. In the most cases, addition of the amphiphile sodium dodecylsulfate (S DS) improved the catalytic performance of the parent catalysts as well as t hat of the sulfonated complexes in water. Other ionic additives (e.g., Na2S O4, camphersulfonate, benzenesulfonate) which do not bear the long alkyl ch ain gave poor results illustrating the importance of the particular structu re of SDS. (C) 1999 Elsevier Science B.V. All rights reserved.