The application of single-enantiomer catalysts is one of the most widely used methods for the generation of enantiomerically enriched products. In an effort to circumvent the requirement for usually laborious preparation of enantiopure catalysts, several strategies have been investigated. Stereodynamic, hence racemic catalysts are promising starting points for this since they exhibit two distinct chiral energetic minima - each suitable for asymmetric catalysis. Additionally, their enantiomerization barriers ΔGǂ allow for room temperature alignment of chirality. Previous studies demonstrated the general applicability of stereodynamic catalysts in asymmetric catalysis when combined with matching chiral additives. Here we report an innovative concept based on stereodynamic catalysts modified with small auxiliaries that allow controlling the catalyst by external parameters. Key features are the beneficial synergy of nonlinearity, stereodynamics and asymmetric activation. Our catalyst consists of a substituted BIPHEP (2,2’-Bis(diphenylphosphino)-1,1’- biphenyl) ligand coordinated to rhodium(I). The catalyst’s enantioselectivity can be controlled solely by temperature. This enables access to both configurations (R or S) of a prochiral substrate’s ((Z)-α-acetamidocinnamate) product in high optical purity by either cooling the reaction mixture during catalysis or heating the catalyst prior to application in a model reaction, e.g. enantioselective hydrogenation. The applicability of our concept is further illustrated by the successful investigation of various derivatives of the model substrate.

Stereodynamic catalysts: Bidirectional enantioselectivity controlled by temperature

249th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.