1201890-90-5Relevant articles and documents
Asymmetrie transfer hydrogenation of ketones catalyzed by amino acid derived rhodium complexes: on the origin of enantioselectivity and enantioswitchability
Ahlford, Katrin,Ekstr?m, Jesper,Zaitsev, Alexey B.,Ryberg, Per,Eriksson, Lars,Adolfsson, Hans
supporting information; experimental part, p. 11197 - 11209 (2010/04/26)
Amino acid based thioamides, hydroxamic acids, and hydrazides have been evaluated as ligands in the rhodium-catalyzed asymmetric transfer hydrogenation of ketones in 2propanol. Catalysts containing thioamide ligands derived from L-valine were found to selectively generate the product with an R configuration (95 % ee), whereas the corresponding Lvaline-based hydroxamic acids or hydrazides facilitated the formation of the (S)-alcohols (97 and 91% ee, respectively). The catalytic reduction was examined by performing a structureactivity correlation investigation with differently functionalized or substituted ligands and the results obtained indicate that the major difference between the thioamide and hydroxamic acid based catalysts is the coordination mode of the ligands. Kinetic experiments were performed and the rate constants for the reduction reactions were determined by using rhodiumarene catalysts derived from amino acid thioamide and hydroxamic acid ligands. The data obtained show that the thioamide-based catalyst systems dem-onstrate a pseudo-first-order dependence on the substrate, whereas pseudozero-order dependence was observed for the hydroxamic acid containing catalysts. Furthermore, the kinetic experiments revealed that the rate-limiting steps of the two catalytic systems differ. From the data obtained in the structure-activity correlation investigation and along with the kinetic investigation it was concluded that the enantioswitchable nature of the catalysts studied originates from different ligand coordination, which affects the ratelimiting step of the catalytic reduction reaction.
