Catalysis and Spectroscopy

Our research in this direction focuses on a more rational design of heterogeneous asymmetric hydrogenation on chirally-modified metal catalysts based on operando spectroscopic characterization. The general strategy is illustrated in Figure 2, which highlights the design process consisting of four interrelated steps. The required molecular level information from the catalytic interface will be obtained by the application of operando spectroscopy (Characterization). The operando spectroscopic data will provide insight into the relevant surface processes, allowing to derive profound mechanistic understanding (Analysis). To steer the desired catalysis after formation of the maximum number of enantioselectivesites towards optimal enantioselectivity the fraction of the heterogeneous surface inaccessible to the bulky chiral modifier but accessible to the substrate has to be minimized. Blocking of these unmodified sites by small suitable co-adsorbates is crucial to obtain the intrinsic selectivity of the modified sites on the macroscopic level. 

In heterogeneous asymmetric catalysis established strategies focus on defining the stereochemistry at the active metal center (immobilization of transition metal complexes with chiral ligands or chiral modification of noble metal catalysts). However, the inherent heterogeneity of the solid surface has been a major stumbling block rendering the formation of a stereochemically well-defined environment difficult. To achieve enantioselective reactions on catalytic surfaces we are exploring a new approach based on translating chiral information to the prochiral substrate molecule. The idea originates from our recent finding that heterogeneous chiral catalysis can be achieved in the hydrogenation of the prochiral substrate isophorone, an α,β-unsaturated ketone, on supported Pd catalyst using the amino acid (S)-proline as stereoselective mediator (chiral auxiliary).