Valorisation of lignocellulose using homogeneous catalysts : ligand design and application
- Homogene Katalysatoren für die Aufwertung von Lignocellulose : Ligandendesign und Anwendung
Charkovskiy, Andrey; Leitner, Walter (Thesis advisor); Klankermayer, Jürgen (Thesis advisor)
Dissertation / PhD Thesis
Dissertation, RWTH Aachen University, 2020
The work reported in the present thesis has been carried out within the SuBiCat innovative training network, focusing on the catalytic methods for the valorisation of lignocellulosic biomass. Along these lines, Chapter 1 introduces the current state of the fossil fuel-based economy, the challenges associated with switching to renewable resources and the role of lignocellulose and homogeneous catalysts in lignocellulose based processes. Chapter 2 introduces the Triphos ligand system and deals with synthesis of novel ligands and their role in hydrogenation reactions. The preparation of a series of Triphos- derivative ligands, incorporating an electron-rich diisopropylphosphine donor, followed by detailed spectroscopic analysis of the respective ruthenium complexes, is reported. The novel ligands were then applied in hydrogenation of biogenic cellulose-derived acids, where significant improvements in activity could be achieved. Finally, Chapter 3 introduces lignin - a key renewable resource for aromatic building blocks, and deals with development of new catalyst systems and reactions for its depolymerisation. Along these lines, Ru(Triphos)(OAc)Cl (VII) was found to be the most efficient catalyst for selective redox-neutral C-C bond cleavage in lignin model compounds, mimicking the β-O-4 and β-1 linkages. It was found to be stable at elevated temperatures reaching 220 °C, allowing employment of significantly lower catalyst loadings with only minor selectivity losses. Furthermore, the catalyst system showed remarkably high activity in acceptorless alcohol dehydrogenation (AAD) and dehydrogenative coupling of alcohols to amines. This consequentially paved the way for development of a one-pot multi-step transformation, combining the redox-neutral C-C bond cleavage reaction and amine coupling of 1,3-dilignol model compounds towards a direct pathway to high-value imines from lignin. The practical utility of the novel reaction was demonstrated by synthesis of a substituted monoamine patented for use in skin care compositions due to its melanin inhibiting properties.