Maßgeschneiderte Ruthenium-Triphos Katalysatoren für die homogenkatalysierte Hydrierung von Carbonsäurederivaten
- Tailor-made Ruthenium-Triphos catalysts for the homogeneous hydrogenation of esters and amides
Meuresch, Markus; Klankermayer, Jürgen (Thesis advisor); Leitner, Walter (Thesis advisor)
Dissertation / PhD Thesis
Dissertation, RWTH Aachen University, 2016
The present thesis deals with the development of tailor-made ruthenium catalysts for the selective conversion of carboxylic acids, esters and amides, based on the [Ru(Triphos)TMM] catalyst lead structure (TMM = trimethylenemethane, Triphos = 1,1,1-tris(diphenylphosphinomethyl)ethan).Chapter 1 describes the state-of-the-art in hydrogenation with molecular catalysts and the importance of catalytic reduction as a tool for the chemical transformation of polar bonds in laboratory as well as in industrial scale. The [Ru(Triphos)TMM] complex is a universal catalyst for the catalytic conversion of carboxylic acid derivatives, for the di-rect hydrogenation of CO2 to methanol, as well as for the direct methylation of aromatic amines using CO2 as a C1 building block. However, mechanistic investigations revealed that the catalyst deactivates irreversibly by forming an inactive ruthenium dimer in all catalytic transformations, thus preventing a general applicability.In order to prevent the catalyst from deactivating via dimerization, the ligand was chemically modified as described in chapter 2. The dimer formation should be blocked by the introduction of sterically demanding substituents to the aromatic backbone of the ligand, for this reason, a library of 7 triphos derivatives and their corresponding ruthenium complexes could be established. The molecular structures from single-crystal x-ray diffraction of the complexes emphasized that the meta-substituents of the newly developed Triphos Xyl (1,1,1-tris(3,5-dimethylphenylphosphinomethyl)ethan) showed a significantly increased shielding of the ruthenium center in comparison to the usual triphos ligand, paving the way for application in challenging reductive transfor-mations. Chapter 3 contains the detailed mechanistic characterization of the different catalyst species. The activation of [Ru(Triphos)TMM] in the presence of hydrogen leads to the formation of the hydride complex [Ru(Triphos)(H)2], the cationic complex [Ru(Triphos)(H)(H2)][NTf2] is formed in the presence of HNTf2. Moreover, the XRD-analysis of a ruthenium dimer showed that the meta-substituents of the Triphos Xyl ligand should have a major influence on the dimer formation. In selected catalytic reactions (chapter 4) the novel catalyst demonstrated remarkable activities in the hydrogenation of carboxylic acids, esters and amides. Moreover, it was shown by NMR-analysis that the dimer formation was completely prevented in a cata-lytic reaction by the introduction of the Triphos-Xyl ligand. Thus, the Triphos-Xyl ligand significantly improves the chemical stability, catalytic activity and selectivity in the hydrogenation of dimethyl itaconate, itaconic acid and N-acetanilide.