Impressive Enhancement of the Enantioselectivity for a Hydroxy-Containing Rhodium(I) Bisphosphine Catalyst in Aqueous Solution by Micelle-Forming Amphiphiles

A selectivity increase for asymmetric hydrogenation in aqueous solution from 1.5%ee (blank experiment) up to 78%ee (amphiphiles present) may be accounted for by inclusion of the catalyst into micellar aggregates. The relative enantioselectivity Qa/b is distinctly higher for the rhodium chelate 1, carrying a hydroxy group, than for the related DIOP complex 2. The effect is minimized in the presence of increasing amounts of methanol, which is known to prevent micelle formation.