Supramolecular Axial Chiral Ligands for Asymmetric Catalysis

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In this project a new class of supramolecular ligands based on complementary hydrogen-bonding will be prepared and evaluated in asymmetric catalysis. In these ligands an axial-chiral twist of the self-assembled backbone is controlled by chiral substituents on the ligand monomers. Preliminary catalysis experiments with first examples of this new type of ligand showed good stereoselectivity in the asymmetric hydrogenation of alpha-dehydroamino acids with up to 87 % ee. The structure of the transition metal complexes was investigated by a combination of computational studies, NMR spectrometry and circular dichroism spectroscopy. In the project presented here, we plan to prepare a library of supramolecular, axial-chiral ligands based on our previous experience in this field: homodimeric ligands as well as heterodimeric ligands based on the complementary hydrogen bonding observed in AT base pairs will be prepared and tested in asymmetric hydrogenation, hydroformylation and hydrocyanation reactions of prochiral alkenes. Furthermore, we plan to perform an in-depth structural study of the transition metal complexes of these new ligands: The structure of the catalytically active Rhodium complexes as well as model Platinum complexes shall be explored by NMR-spectroscopy, X-Ray analysis and CD-spectroscopy. A main focus lies on analysing the relationship between the structure of the active complex and the observed catalytic selectivity and activity. In this regard we will also use DFT methods to calculate the relative stability of atropisomers, and to investigate the stereo induction caused by the chiral substituents in asymmetric hydrogenation.