Quantum Chemical Investigations in Homogeneous Catalysis: Dehydrogenation, Carbonylation and Vinylation

This thesis describes in-depth mechanistic investigations of homogeneously catalyzed reactions with industrial relevance. Three different reaction classes were studied with the means of density functional theory: dehydrogenation, carbonylation and vinylation. All projects were carried out in a highly integrated framework with continuous exchange between experimental and computational efforts to achieve a high level of accuracy and efficiency. Firstly, the investigations on the dehydrogenative coupling of alcohols to esters are described. The frequently used Ru-MACHO catalyst was shown to undergo degradation after base- induced activation of the pre-catalyst. Attempts to stabilize the highly active species were successful and were shown to lead to two different structural motifs based on the employed phosphine, both of which are active catalysts in base-free (de-)hydrogenation reactions. Quantum-chemical calculations were employed to gain insights into the phosphine-dependent behavior as well as the reaction mechanism. Secondly, the carbonylation of alcohols to carboxylic acids was explored in two project phases. The initial investigation focused on employing Ni complexes and simple phosphine ligands for the transformation of phenyl ethanol as a model compound for ibuprofen. After the computational studies had provided insights into a combination of two reaction mechanisms, which explain the experimental observations and the crucial role of LiI as an additive, the scope was expanded to tertiary Koch-type carbonylation targets. While the desired conversion for these systems was achieved, the observed selectivities and control experiments clearly indicated that different reaction pathways are responsible for the observed conversion. A second set of quantum-chemical investigations was able to provide relevant information about this adapted reaction mechanism and helped to evaluate the catalytic system. Finally, the vinylation of pyrrolidone to N-vinylpyrrolidone was investigated, which was achieved by phosphine organocatalysis and direct employment of acetylene gas at low pressure. The DFT calculations were used to explain the mechanistic details of the reaction as well as to evaluate several side reactions and degradation pathways. The methods were also able to support a modification of the reaction that employs suitable carbonyl compounds to perform Wittig-type reaction steps after the initial formation of an ylide intermediate