Synthesis of Enantiopure Ru(II) and Rh(III) Complexes and Investigation of Chirality in a Photoactivated Reaction

Details

Supervisors

Elias, Benjamin

Faculty

Faculté des sciences

Degree label

Master [120] en sciences chimiques, à finalité approfondie

Abstract

enChirality is a fundamental property of matter with profound implications in biology, medicine, and catalysis. While the influence of molecular handedness on ground-state interactions is well established, its role in photoactivated reactions and in particular on bimolecular electron transfer processes remains largely unexplored. This Master Thesis addresses this question through the synthesis of enantiopure octahedral transition metal complexes and the investigation of chirality effects in a photoactivated reaction. Enantiopure Delta- and Lambda-[Ru(bpy)3]PF6 were synthesized via diastereomeric salt crystallization, and enantiopure Delta- and Lambda-Rh-enolate complexes via a chiral auxiliary strategy. Chiral HPLC was employed to quantify the enantiomeric excess of the isolated complexes, and its implementation further demonstrated its preparative potential for future enantiopure syntheses. The photosystem was then comprehensively characterized by UV-vis absorption and emission spectroscopy, cyclic voltammetry, excited-state lifetime measurements, spectroelectrochemistry, and transient absorption spectroscopy. Quenching experiments revealed that the bimolecular quenching rate constant kq is essentially independent of the relative configuration of the partners, consistent with a diffusion-controlled mechanism. In contrast, the cage escape yield, which reflects the fate of the geminate radical pair within the solvent cage following electron transfer, proved chirality-dependent. These preliminary results suggest that molecular handedness selectively influences the fate of the geminate radical pair, rather than the electron transfer kinetics, providing a conceptually novel handle for controlling radical availability in asymmetric photoredox catalysis.