Kinetics of Selection Processes
Prof. Dr. Detlef Heller
Current research: asymmetric hydrogenation of α-, β-dehydroamino acid derivatives, itaconic acid derivatives and ketones.
In contrast to a huge number of selection inducing, mainly chiral ligands for homogeneous catalysis known there are only few investigations that deal with kinetic aspects of reactions. The asymmetric hydrogenation of prochiral olefins with cationic Rh(I)-complexes is one of the best understood selection processes. The resulting so-called major/minor principle – the in solution less stable minor substrate complex dominates the selectivity due to its high reactivity – is to be regarded as a basic concept of homogeneous catalysis.
Recently, we succeeded in supplying the evidence that also the dominating intermediate – the so called major substrate complex – can lead to the main product of the selection process. This corresponds in principle to the lock-and-key concept well known from enzyme kinetics.
In our surveys on the asymmetric hydrogenation as model reaction we investigate the extension of the model, the transformation of precatalysts into active species, the influence of intramolecular and pre-equilibria, the concentration ratio of the intermediates and the origin of different reactivities. In addition, the influence of solvent, temperature and pressure on selectivity and reactivity is of interest.
A better understanding of the mutual dependences on the one hand gives a deep insight into the phenomenon of catalysis and on the other hand provides a possibility for optimization.