The first part of my thesis concerns the use of heterogeneous acidic resins for racemization of tert-alcohols without any side-product formation. The focus was to develop a system which can be further extended to a DKR protocol consisting of an enzymatic KR reaction. Based on our knowledge of the resins, an unexpected migratory DKR protocol turned out to be an efficient method for the synthesis of carbocyclic allylic carbinols.

The development of enzyme and metal catalyst hybrids was already an ongoing theme in our group. A supporter-free biohybrid catalyst was developed which can be used in several different types of reactions. The Pd(0)-CalB CLEA catalyst was applied in a two-step-cascade transformation and in the DKR of benzylic primary amines. The catalyst was characterized by different analytical techniques, to understand its composition and structure.

The enzymes have always been the main focus of the studies and therefore wild type enzymes were initially utilized. However, these natural biocatalysts are associated with certain limitations. In contrast, protein engineering allows for enzymes to be modified and optimized. We have used the technique to create a subtilisin Carlsberg mutant, which was studied both by modeling and in vitro. The mutant was found to catalyze the (S)-selective transesterification of sec-alcohols containing long aliphatic carbon chains, and it also exhibited higher performance in organic solvent.

The last project concerned the protein engineering of CalA enzyme towards tert-alcohols. The kinetic resolution of tert-alcohols with this enzyme is very slow but it occurs with good enantioselectivity. The aim was therefore to improve the activity of CalA via protein engineering. Seven amino acids were mutated close to the active site and a library was created based on our prediction. Throughout the screening, a few variants showed higher activity, which were sequenced and further analyzed in the transesterification of tert-alcohols.

The main focus of this thesis lies in the development of new transition metal-catalyzed chemoenzymatic dynamic kinetic resolutions (DKR) of both alcohols and amines. The first part of the thesis deals with the development of new heterogeneous systems for the DKR of amines. The racemization catalysts in these different systems are all composed of palladium nanoparticles supported on either mesoporous silica or incorporated in a biocomposite that is composed of a bioactive cross-linked enzyme aggregate. 

The second part of the thesis deals with the development of a homogeneous iron catalyst in the racemization of sec-alcohols for the implementation in a chemoenzymatic DKR. Two protocols for the racemization of sec-alcohols are reported. The first one could not be combined with a chemoenzymatic kinetic resolution, although this was overcome in the second iron based protocol. 

Following the successful iron catalyzed chemoenzymatic DKR of sec-alcohols, the iron catalyst was used in the cyclization of α-allenic alcohols and N-protected amines to furnish 2,3-dihydrofurans and 2,3-dihydropyrroles, respectively. The cyclization is proceeding in a diastereoselective manner.

The last part of the thesis deals with attempts to further elucidate the mechanism of activation of a known ruthenium racemization catalyst. X-ray absorption spectroscopy using synchrotron radiation was used for this purpose.

The palladium (Pd) and ruthenium (Ru) species in several attractive catalysts have been probed using X-ray absorption spectroscopy (XAS). The study of catalyst evolution in suspension- and solution-based reactions was the primary aim. It was achieved by performing in situ XAS experiments on Pd and Ru over the course of the reactions. A custom-made reactor was employed which allowed the catalysts to be mixed with other reaction components under desired conditions.

The first system investigated was the Heck coupling reaction catalyzed by Pd(II) complexes embedded on metal-organic frameworks. It was realized that the as-synthesized catalysts go through an instant ligand substitution process when added to the reaction mixture. Mononuclear Pd complexes are the active species at the first stage of the measurement which then gradually transform into Pd nanoclusters. At a later stage of the measurement, chloride ligands start to bind to surface atoms of the Pd nanoclusters, leading to a deactivation of the catalyst. Following the first successful in situ XAS experiment, Pd(II) carbene complexes catalyzing undirected C–H acetoxylation of benzene in the presence of an oxidant were explored. A gradual ligand substitution occurs, and the mean oxidation state of Pd increases at the same time. At a later stage, Pd nanoclusters form, while the mean oxidation state of Pd returns to the start value. Deactivation of a heterogeneous Pd(II) catalyst during cycloisomerization of acetylenic acids was then investigated using in situ XAS. The choice of substrates showed to significantly influence the nature of Pd species, and the reduction of Pd(II) forming Pd(0) aggregates causes the deactivation. Moreover, strategies of reactivating the catalyst and prevention of the deactivation were developed and examined. In the end, the activation process of a Ru catalyst was studied and the structure of the intermediate was determined by in situ XAS. It was demonstrated that an electron-donating substituent on the cyclopentadiene ligand exhibits a promoting effect on the activation, while an electron-withdrawing substituent inhibits the activation.