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Dissertation, RWTH Aachen University, 2022; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, Diagramme (2022). = Dissertation, RWTH Aachen University, 2022, This work deals with the design and execution of linked catalytic reactions in the form of a tandem or cascade reaction. Cascade reactions involve the connection of two partial reactions in series in a continuously operated plant without intermediate work-up. This type of linkage makes it possible to reduce costs and waste from processes and contribute to sustainability when a tandem reaction is not possible. In two projects, the prerequisites for a cascade reaction and the best way to carry it out were worked out. Both projects dealt with a process consisting of two substeps that cannot be linked as a tandem reaction, but only as a cascade reaction. For the first project, the conversion of the biomass-derived compound furfuralacetone into the potential biofuel molecule 2-butyltetrahydrofuran (BTHF) was investigated. The conversion consists of the complete hydrogenation of furfural acetone and the subsequent deoxygenation to BTHF. Initially, the two substeps were studied separately, a common solvent was found, and suitable catalysts were compared, focusing on the use of commercial heterogeneous catalysts. After optimizing both reactions on a small scale, they were transferred to a continuous operation. The cascade reaction was successfully demonstrated in a tailor-made miniplant. The second project dealt with the preparation of branched long-chain amines – which are of interest for application as surfactants – starting from terminal olefins. First, a multiphase catalyst system for the hydroformylation/aldol condensation tandem reaction was developed, which allowed the conversion of the olefins to unsaturated aldehydes. The green solvent polyethylene glycol turned out to be crucial for the reaction, as it both enhanced the activity of the basic aldol catalyst and allowed recycling of the homogeneous catalyst system. Further conversion of the aldol products to the branched amines via reductive amination was also successfully carried out and a catalyst recycling was developed. The combination of the two tandem reactions was realized on a small scale and it was discussed how the cascade reaction could be carried out in continuous operation. The findings of both projects finally led to a decision tree for the general design of cascade reactions., Published by RWTH Aachen University, Aachen

Dissertation, RWTH Aachen University, 2020; Aachen : RWTH Aachen University 1 Online-Ressource (XV, 293 Seiten) : Illustrationen, Diagramme (2020). = Dissertation, RWTH Aachen University, 2020, In this thesis a catalytic cycle, postulated for the direct carboxylation of simple arenes with carbon dioxide, was investigated in detail. Therefore, at first palladium and platinum complexes bearing phosphine sulfonamido ligands were identified as a suitable complex system, applying experimental and computational methods. In contrast to the well-studied phosphine sulfonato ligand system, these show a monomeric structure of the carboxylato complexes, involved in the catalytic cycle as most stable intermediates. So, they reveal energy barriers small enough to enable an analysis of the catalytic cycle. For this reason, a portfolio of palladium and platinum complexes bearing different ligands of this type were synthesized and analyzed regarding to their structures and their dynamic behavior in solution. In this course, conformational and configurational differences were identified, which are related to the ligands fine structure and enable to effectively influence the energies of the intermediates and transition states, involved in the postulated catalytic cycle (chapter 3). Complexes of this kind can catalytically decarboxylate bis-methoxy substituted aromatic carboxylic acids at room temperature without the need of an external proton source. This is the back reaction of the analyzed carboxylation and proceeds via metal aryl intermediates. This could be shown by successful decarboxylative coupling with olefins at room temperature. As a consequence of the spatial structure of the utilized complexes, this results in selective formation of 1,1-disubstituted olefins (chapter 4).The activation and cleavage of an aromatic C-H-bond, which is a necessary partial step of the postulated cycle, was successfully shown by H/D-exchange experiments with anisole (chapter 6). The second partial step of the postulated cycle, migratory insertion of CO2, was successfully verified on a phosphine sulfonamido palladium complex with a para-anisyl ligand, that was synthesized therefor. It was shown that this reaction proceeds via a migratory insertion mechanism with pre-coordination of the CO2 molecule to the metal center (chapter 5).First experiments regarding the catalytic carboxylation of non-preactivated arenes suggest, that this reaction suffers under a thermodynamic hinderance, despite the addition of an amine base for product stabilization. First proposals to overcome this problem were given (chapter 7)., Published by RWTH Aachen University, Aachen

Dissertation, RWTH Aachen University, 2019; Aachen 1 Online-Ressource (VI, 196 Seiten) : Illustrationen, Diagramme (2019). = Dissertation, RWTH Aachen University, 2019, This thesis describes the development of a liquid-liquid multiphasic catalyst system (MPC-System) which is used for the homogenously catalyzed hydrogenation of CO₂ to formic acid and formic acid (FA) derivatives (formic acid-amine adducts). The synthesis of the employed catalysts is described and the optimization of the catalysis is shown. Additionally, the downstream conversion of the obtained products with methanol into methyl formate (MF) is discussed. Finally, product isolation is validated and different process strategies are envisioned. Conclusively, this work demonstrates the use of CO₂ as an alternative carbon source for the synthesis of methyl formate., Published by Aachen

Dissertation, RWTH Aachen University, 2019; Aachen 1 Online-Ressource (xiv, 232 Seiten) : Illustrationen, Diagramme (2020). = Dissertation, RWTH Aachen University, 2019, The present thesis deals with the development of novel metalorganic ruthenium complexes as well as their application as catalysts for the homogeneously catalyzed hydrogenation of carboxylic acid derivatives. The synthesized metal complexes were characterized and compared in respect to their electro and steric properties. Furthermore, the catalytic activity of the molecular complexes in the hydrogenation of carboxylic acid esters and amides is studied. Thereby, not only the classical hydrogenation based on molecular hydrogen but also the transfer hydrogenation employing alcohols as sacrificial hydrogen donors is investigated. Beyond, the reductive hydrogenolysis of polycondensation plastics as innovative recycling strategy is examined. In the sense of a circular economy the conversion of polyester, polycarbonates, and polyamides to value added building blocks is focused., Published by Aachen

Dissertation, RWTH Aachen University, 2018; Aachen 1 Online-Ressource (IX, 91 Seiten) : Illustrationen (2018). doi:10.18154/RWTH-2018-225391 = Dissertation, RWTH Aachen University, 2018, The utilisation of carbon dioxide and renewable resources as feedstocks for the chemical industry is highly desirable due to fossil fuel depletion and climate change. Chemicals directly produced from these substrates could lead to a circular economy. In this regard, the synthesis of organic carbonates directly from an alcohol and CO2 is a sustainable target transformation since alcohols are readily available from renewable resources. Organic carbonates then can be used as greener alternatives for existing high-boiling polar solvents, carbonation sources or monomers for polycarbonates. The present thesis investigated the direct synthesis of cyclic carbonates and, in particular, glycerol carbonate from glycerol and carbon dioxide by Brønstedt base catalysis. Glycerol is a trivalent alcohol that is a by-product from different biomass conversion processes especially of the biodiesel production and is currently considered as a waste product. The synthesis of the corresponding five-membered cyclic carbonate leads to a value-added compound as it possesses two different functional groups, a hydroxyl group and a 2-oxa-1,3-dioxolane group, leading to a wide reactivity and a broad range of industrial applications. The aim of this thesis is to provide a better understanding of the direct synthesis of glycerol carbonate from glycerol and CO2. The reaction produces water as by-product which should be removed to shift the equilibrium towards the product side. Two different approaches to remove H2O were investigated: I) the reactive dehydration by acetonitrile, and II) the water extraction by a continuous carbon dioxide flow. For both water removal methods, the influence of reaction parameters such as temperature, catalyst, CO2 pressure or additives on the product yield was studied. Furthermore, the reaction mechanism and the formation of side products were investigated. In the case of reactive water removal with acetonitrile as dehydration agent, glycerol carbonate was synthesised in 17 % yield from glycerol and carbon dioxide with potassium carbonate as catalyst. It was found that the glycerol carbonate yield reaches a maximum depending on the reaction conditions due to a complex reaction network leading to side and decomposition reactions. For the non-reactive water removal in the synthesis of glycerol carbonate, a new semi-continuous process was developed with CO2 acting both as reagent and stripping gas. Glycerol carbonate was synthesised in 13 % yield. Investigations on the reaction mechanism identified glycerol hemi-carbonate as intermediate and the subsequent cyclisation to the cyclic carbonate as rate-determining step., Published by Aachen

Aliphatische Carbonsauren werden in vielen industriellen Bereichen verwendet und ihre wirtschaftliche Bedeutung nimmt zu. Sie werden derzeit in gror.en Mengen hergestellt, indem das meistens nicht erneuerbare Kohlenmonoxid als C1-Synthon genutzt wird. Kohlendioxid ist ein potenziell umweltfreundlicher, erneuerbarer und abundanter C1-Baustein. Das Ziel dieser Arbeit ist die Entwicklung eines Protokolls zur katalytischen Umwandlung von C02, H2 und sauerstoffhaltigen Substraten, um nützliche Chemikalien, wie Carbonsauren zu erhalten. Zu diesem Zweck wird ein homogenes Rh-Katalysatorsystems zur Herstellung aliphatischer Carbonsauren aus sauerstoffhaltigen Substraten, C02 und H2 untersucht und optimiert. Das System besteht aus Rh-Prakursor, lodid-Additiv und PPh3 als Ligand, die in einem Batchreaktor unter C02 und H2 eingesetzt werden. Die Reaktionsbedingungen wurden für folgende Substratklassen optimiert: primare Alkohole, sekundare Alkohole, Ketone, Aldehyde und Epoxide. Es wurden insgesamt 30 verschiedene Substrate mit Ausbeuten bis zu 80% zu Carbonsauren umgesetzt. Darüber hinaus wurde das System mit einem ,,Statistische Versuchsplanung"-Ansatz untersucht, um zusatzliche lnformationen zu den untersuchten Parametern zu erhalten. Mechanismus und katalytisch aktive Spezies wurden durch verschiedene Experimente wie Konkurrenzreaktionen, NMR- und Markierungsexperimenten untersucht. Dies erschloss den Reaktionsweg, der aus mehreren nicht-katalytischen Transformationen und zwei katalytischen Schritten besteht. Die Reaktion verlauft durch eine ,,reverse Wassergas-Shift-Reaktion" (rWGSR), die C02 und H2 in C0 und H20 umwandelt. Diese werden wiederum bei der nachfolgenden Hydrocarboxylierung des in-situ gebildeten Alkens unter Bildung der Carbonsaure verbraucht. Das katalytische System ahnelt herkômmlichen Rh-Carbonylierungs- und WGSR-Katalysatoren. PPh3 fungiert als zusatzlicher Ligand, der es dem Katalysator ermôglicht unter den gleichen Reaktionsbedingungen mit minimaler Menge toxischen C0 als Liganden zu arbeiten. Zusatzlich wurde ein heterogenes katalytisches System für die gleiche Reaktion untersucht. ,,Single atom catalysts" (SACs) erhalten gror.e Aufmerksamkeit als neue Katalysatorklasse. Sie kombinieren die Selektivitat und hohe Aktivitat homogener und die einfache Abtrennung und Recycling heterogener Katalysatoren Verschiedene Katalysatoren aus auf N-dotiertem Graphen dispergierten Rh-Atomen, wurden synthetisiert und charakterisiert. Dadurch wurden lnformationen über die chemische und physikalische Struktur des Materials gewonnen und als Katalysatoren für C02-Aktivierung, Carbonsauresythese, Hydrierung und Hydrogenolyse getestet; Aliphatic carboxylic acids are used in many industrial sectors and their importance from an economical point of view is increasing. They are currently produced in large quantities, through processes exploiting the mostly non-renewable C0 as C1 synthon. Carbon dioxide is a potential environmentally friendly, renewable and abundant C1 building block. The aim of this work is to provide a catalytic protocol converting C02, H2 and oxygenated substrates to obtain useful chemicals, like carboxylic acids.To this end a homogeneous catalytic Rh system, used to produce aliphatic carboxylic acids starting from oxygenated substrates, C02 and H2 was investigated and optimized. The system consists of a Rh precursor, iodide additive and PPh3 ligand working in a batch reactor under C02 and H2 pressure. The reaction conditions were optimized for each class of investigated substrates: primary alcohols, secondary alcohols, ketones, aldehydes and epoxides. The reaction scope was investigated and 30 different molecules were converted into carboxylic acids, leading to yields of up to 80%. ln addition, the system was studied using a Design of Experiment approach, obtaining additional information regarding the studied parameters.The reaction mechanism and the catalytically active species were studied, by different experiments like competitive reactions, NMR and labelling experiments. This investigation resulted in a deeper knowledge of the reaction pathway, composed of some non-catalytic transformations and two catalytic steps. The reaction proceeds through a reverse Water Gas Shift Reaction (rWGSR) transforming C02 and H2 into C0 and H20, which are consumed in the following hydrocarboxylation of the in-situ formed alkene to give the final carboxylic acid product. The catalytic system is similar to traditional Rh carbonylation and Water Gas Shift catalysts. The PPh3 is needed to supply additional ligands allowing the catalyst to work in reaction conditions with a minimal amount of toxic C0 ligand. ln addition, a heterogeneous catalytic system was investigated for the same reaction. Single atom catalysts (SACs) are receiving much attention as catalytic solution, since they have both the advantages of homogeneous (selectivity, high activity) and heterogeneous (easy separation and recycling) catalysts. Single Rh atoms dispersed on N-doped graphene were synthesized and characterized, obtaining information regarding the chemical and physical structure of the material. Eventually, they were tested as catalysts for C02 activation, carboxylic acid production, hydrogenation and hydrogenolysis reactions; Les acides carboxyliques aliphatiques sont utilisés dans de nombreux secteurs industriels et leur importance économique augmente. Ils sont actuellement produits en grande quantité, grâce à des procédés utilisant le C0 qui est principalement non- renouvelable. L'anhydride carbonique est une molécule potentiellement écologique, renouvelable et abondante. Cette thèse décrit l'étude et l'optimisation d'un système catalytique homogène de Rh, utilisé pour produire des acides carboxyliques aliphatiques à partir de substrats oxygénés, C02 et H2. Le système consiste en un précurseur de Rh, un additif à base d'iodure et un ligand PPh3, fonctionnant dans un réacteur discontinu sous une pression de C02 et de H2. Les conditions de réaction ont été optimisées pour chaque classe de substrats étudiés: alcools primaires et secondaires, cétones, aldéhydes et époxydes. 30 molécules différentes ont été converties en acides carboxyliques, conduisant à des rendements jusqu'à 80%. En plus, le système a été étudié avec une approche de « Design of Experiment », ce qui a permis d'obtenir des informations supplémentaires concernant les paramètres étudiés. Le mécanisme de réaction et les espèces catalytiques actives ont été étudiés par différentes manipulations comme des réactions compétitives, des expériences de RMN et l'utilisation de molécules marquées. La réaction est composée de transformations non catalytiques et de deux étapes catalytiques. La réaction se déroule à travers une réaction de reverse Water Gas Shift (rWGSR) transformant le C02 et l'H2 en C0 et H20, qui sont consommés dans l'hydrocarboxylation suivante de l'alcène formé in situ pour livrer l'acide carboxylique. Le système catalytique est similaire aux catalyseurs traditionnels à base du Rh pour les réactions de carbonylation et de Water Gas Shift. Le PPh3 est nécessaire pour fournir des ligands supplémentaires, permettant au catalyseur de fonctionner avec une quantité minimale de ligand toxique de C0. En plus, un système catalytique hétérogène a été étudié pour la même réaction. « Single Atom Catalysts » (SACs) reçoit beaucoup plus d'attention que les solutions catalytiques, car il présente à la fois les avantages des catalyseurs homogènes (sélectivité, haute activité) et des catalyseurs hétérogènes (séparation et recyclage faciles). Des atomes de rhodium simples dispersés sur du graphène dopé avec l'N ont été synthétisés et caractérisés, obtenant des informations concernant la structure chimique et physique du matériau. Finalement, ils ont été testés ainsi que les catalyseurs pour l'activation du C02, la production d'acides carboxyliques, les réactions d'hydrogénation et d'hydrogénolyse

The research aim of the dissertation “Transition metal-catalyzed oxidative cleavage of lignin and lignin β-O-4 model compounds” was to study the oxidative cleavage of lignin with transition metal catalysts. Lignin is one of three main components of lignocellulosic biomass and it is considered a potential feedstock for chemicals and fuels. Due to the complexity of lignin and its challenging analytics every initial catalyst screening was performed with lignin model compounds. In the majority of these studies erythro 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol (1) was employed as model substrate.A superior protocol for the synthesis of 1 and other diastereomerically pure 1,3-dilignol model compounds was developed. The key step in this synthesis is the 1,2-addition of a tert-butyl aryloxy ester enolate to a benzaldehyde derivative. The corresponding erythro and threo β-hydroxy esters could completely be separated from each other by column chromatography which had been one of the main challenges in previous protocols. Two iron catalyzed homogeneous reaction systems were studied. Nonheme iron catalysts displayed high activity for the conversion of 1 but afforded low selectivity for the formation of cleavage products. FeCl3-derived catalysts also showed high activity but were significantly more selective than the tested nonheme iron catalysts. 2-Methoxyphenol and veratraldehyde were the main products in 42% and 35% yield. The reaction likely involves the formation of methyl radicals that are generated from dimethyl sulfoxide and H2O2.Furthermore, heterogeneous transition metal catalysts were screened. Supported gold nanoparticles displayed distinctly different activity for the cleavage of 1 depending on the support and the reduction method. The most active catalyst in the oxidative cleavage was 1-phenylethanol reduced gold on hydrotalcite. In reactions performed in dimethyl carbonate it was observed that basic supports could function as catalysts for the base-catalyzed cleavage of 1.Transition metal-containing hydrotalcite-like catalysts were employed in the cleavage of lignin model compounds and different lignin samples. Copper-vanadium hydrotalcite-like catalysts (HTc-Cu-V) showed high activity and good selectivity for the cleavage of 1. Veratric acid and veratraldehyde were the main products in a combined yield of over 70%. Leaching experiments with HTc-Cu-V revealed that it acts to a significant degree as dispenser of catalytically active homogeneous copper and vanadium species that are continuously released. Lignin cleavage studies with organosolv and kraft lignin showed that HTc-Cu-V cleaved the different lignin samples to dimer and trimer size products.During the leaching experiments conducted with HTc-Cu-V, V(acac)3 and Cu(NO3)2·3H2O were tested as homogeneous vanadium and copper sources. V(acac)3/Cu(NO3)2·3H2O showed high activity and good selectivity for the cleavage of 1 affording veratric acid and veratraldehyde in a combined yield of over 80%. Studies with organosolv and kraft lignin showed that V(acac)3/Cu(NO3)2·3H2O displays similar activity as HTc-Cu-V for the cleavage of lignin furnishing dimer and trimer size products.

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.

This thesis deals with the development and investigation of tailor-made Ruthenium Triphos catalysts for the selective hydrogenation of biogenic substrates. To enable a targeted application of tailor made catalysts, a deep understanding of the mechanistic aspects of molecular catalysts is required. Thus the activation behaviour of the [Ru(Triphos)TMM] catalyst has been investigated and identified with respect to various reaction parameters. It has been shown that the neutral hydride complex [Ru(Triphos)(S)(H)2] acts as the active species under neutral reaction conditions, while in presence of HNTf2 as acidic additive the ionic [Ru(Triphos)(S)(H2)H][NTf2] is the active species. Furthermore, it was shown that these two activation mechanisms are not independent from each other, in which the neutral complex can be transformed into the ionic complex by addition of an acid to the reaction mixture. Hence a control of the activation process and the desired reaction mechanism is possible, depending on the proton concentration.Having a detailed knowledge about the proceeding activation processes in hand, a molecular design via variation of the TMM ligand was conducted and the impact on the catalyst activation was investigated. Variations on the aromatic substitutens of the Triphos ligand lead to an inhibition of catalyst deactivation via dimerization and therefore a significant increase of the catalytic activity in the hydrogenation of methyl benzoate. The initial activities observed here, exceeded the original ones by far, reaching the range of the most active systems known from literature.For the additive free catalytic system [Ru(Triphos)(methylallyl)][NTf2], kinetic investigations have been made to extend the mechanistic understanding beyond the activation processes. For the [Ru(Triphos)TMM] catalyst itself, experimental data and DFT-based kinetic information combined, have been implemented in a DAE simulation model. Thereby a precise comparison of the proposed mechanism with experimental data was achieved.This versatile and flexible, molecular catalytic system has been transferred to a semicontinuous hydrogenation setup for the transformation of itaconic acid to 3 MTHF. Besides the development and optimization of a reactor concept, purification using distillation procedure allowed for the isolation of pure and water free 3 MTHF. Further, two potential process schemes have been proposed towards a continuous one- or two-step process.Initiated by the new accessibility of 3 MTHF as a potential biogenic solvent, it was compared against THF and 2 MTHF as solvent for various catalytic reactions. 3 MTHF possessed promising solvent properties in hydrogenation/dehydrogenation and C C coupling reactions.

In this Ph.D. project it was examined how a combined density functional theory (DFT) and experimental approach may enhance research on homogenously catalyzed reactions on the example of carbon dioxide transformations with late transition metal complexes as catalyst. Therefore three reaction systems I – III have been studied by computational and partly by experimental means.In system I a CO2 hydrogenation with sodium hydroxide as a base was examined with 1 or 2 as catalyst respectively. This system is quite well known as Yang did a computational study on a complex very similar to 1,[1] while Milstein investigated 1 as a catalyst in the CO2 hydrogenation under slightly different conditions though.[2] In the Ph.D. project those results where expanded by also using 2 as a catalyst for the CO2 hydrogenation. It was known previously that 2 may be transformed under reaction conditions to a ruthenium analogue of 1.The study of the complex reaction network of this system should give insights into mechanistic details of the iron and ruthenium catalyst systems. In order to evaluate the catalyst by the DFT calculations, the energy span model was applied to extract a DFT based catalyst activity (turn over frequency, TOF) for the iron as well as the ruthenium complex from the computations. Furthermore kinetic experiments have been conducted to determine an experimental catalyst activity. For better comparison the TOF was transformed to an effective activation barrier ΔG‡DFT and ΔG‡EXP. This showed, that the DFT based values match the experimental ones within experimental accuracy, which means that computations may yield accurate results even for challenging reaction systems. DFT as well as experiment also showed, that the catalytic activity of the iron system is very close to that of the ruthenium system.In system II the CO2 hydrogenation with triethylamine as base and 3 or 4 as catalyst was examined respectively. Both compounds were not known to catalyze this transformation previously. An initial DFT calculation predicted 3 to be an active catalyst but also being highly prone to deactivation by protonation of the phenylpyridinyl ligand. This could then be shown in NMR experiments. For compound 4 the DFT calculations predicted an effective activation barrier of 20.7 kcal/mol and no deactivation. In laboratory experiments 4 proved to be stable over 48 hours at reaction conditions and exhibited an effective activation barrier of 23.0 kcal/mol, again supporting DFT predictions.In system III it was investigated if the previously studied carboxylation of benzene may be adapted to a carboxylation of methane.[3] Therefore an analogue reaction mechanism was the base for a catalyst screening with 5 as lead structure. By varying key components like the ligand backbone, the halogen or the metal center in different solvent environments, several catalyst candidates could be generated and the energy span for each one was calculated by DFT simulations. Two candidates with energy spans of 30.5 kcal/mol and 34.5 kcal/mol in toluene could be found.An energy span of 30 kcal/mol equals a predicted TOF of about 0.1 per hour at 100 °C. This means that the first catalyst candidate might show an observable activity for the carboxylation of methane under presence of potassium-tert-butoxide as base at 100 °C. The structural motive of the second complex is known to be stable at reaction conditions of 200 °C, which would correspond to an activity of about 40 per hour based on an energy span of 34.5 kcal/mol. Those predictions are made with the assumption that the catalyst candidates are stable under the investigated conditions and no side reactions take place.Overall it could be shown that DFT calculations are a versatile tool in homogenous catalyst research especially when combined with selected experimental techniques. Smart combination of computations with experiments yield complementary results which may enhance the quality of the generated knowledge significantly.Literature[1]X. Yang, ACS Catal. 2011, 1, 849-854.[2]R. Langer et al., Angew. Chem. Int. Ed. 2011, 50, 9948-9952.[3]A. Uhe et al., Chem. - Eur. J. 2012, 18, 170-177.

In the coming decades replacing the depleting fossil resources will demand the development of integrated biorefinery concepts. This study focuses on the use of biomass as starting material to produce biomass-derived fuels and commodity chemicals. Initially, a conceptual biomass pretreatment/fractionation strategy called 1 step OrganoCat Process is shown and optimized. This biphasic process uses an aqueous reactive phase, with oxalic acid as catalyst to hydrolyze hemicellulose, and 2 MeTHF as the second phase for the in situ extraction of lignin. Different acids as catalyst as well as biomass sources showed how versatile the system is. Recycling the liquid phases and increasing the ratio of substrate to solvent and catalyst by fourfold made the process more economically feasible. A 3 L-scale reaction was conducted, showing that scale-up of the process is possible while maintaining the laboratory scale efficiency. Second, the newly designed 2 step OrganoCat Process is presented. In this process hemicellulose is hydrolyzed in seawater, catalyzed by oxalic acid. The resulting solid residue (cellulose and lignin) is extracted by different bio-based solvents to extract lignin. While the efficiency of the hydrolysis improved significantly, lignin extraction was not as efficient as observed in the 1 step OrganoCat Process, making the variation with two steps more suitable for biomass with low lignin content like algae. Finally, different strategies for the valorization of the sugar-containing fractions of lignocellulose are presented. The organic acid-catalyzed as well as the enzymatic hydrolysis of crystalline cellulose are shown to work efficiently in (concentrated) seawater as solvent. For further conversion of the resulting glucose, a chemo-enzymatic approach is presented. In the first step commercially available immobilized glucose isomerase (IGI) is used for the isomerization of glucose to fructose in seawater. In the second step dehydration of fructose to HMF is conducted in a biphasic seawater-2 MeTHF system with oxalic acid as catalyst. Consecutive operation of both steps afforded 64% HMF. Using the raw hemicellulose effluent from the 1 step OrganoCat Process for fermentation with U. maydis is proven to afford itaconic acid, not needing any further downstream processing. Also the iron(III) chloride-catalyzed dehydration of xylose from hemicellulose to furfural is shown to work successfully. Both reactions are examples for possible subsequent reaction steps in biorefineries.

In this thesis the synthesis of new mixed bidentate phosphine ligands and their application in selected enantioselective transformations is presented. Based on a phosphine-phosphoramidite lead structure, a modular synthetic pathway was used to synthesise different types of mixed bidentate phosphine ligands. Variation of the organic moiety at the amine or at the diol building block afforded three novel phosphine-phosphoramidites, while replacement of the diol by an aminoalcohol gave four different phosphine-phosphorodiamidites. Phosphine-phosphorodiamidites are not known in literature so far and this is the first study on their synthesis, purification, stability and application in asymmetric catalysis. The application of these new structures as ligands in selected enantioselective transformations enabled a systematic study of the influence of variations in the lead structure on the behaviour in catalytic reactions. The novel phosphine-phosphoramidites and -phosphorodiamidites were applied in different asymmetric hydrogenation reactions (C=C, C=N, C=O) using different active metal centres (Rh, Ir and Ru, respectively). In addition, the phosphine-phosphorodiamidites were applied in Rh-catalysed asymmetric hydroformylation and Pd-catalysed hydrophosphorylation. The results of the catalytic reactions prove a high versatility of the new structures and include one of the highest enantioselectivities for the hydrogenation of 2-substituted quinolines (using phosphine-phosphoramidites). Replacement of the diol bulding block in the phosphine-phosphoramidite lead structure by a diamine afforded the first phosphine-phosphortriamide ligand, whose application in enantioselective transformations needs to be explored in future research.