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ACS sustainable chemistry & engineering 10(11), 3749-3756 (2022). doi:10.1021/acssuschemeng.2c00419, Published by ACS Publ., Washington, DC

Nature chemistry 13(9), 916-922 (2021). doi:10.1038/s41557-021-00735-w, Published by Nature Publishing Group, London

Green chemistry 23(17), 6330-6336 (2021). doi:10.1039/D1GC01651B, Published by RSC, Cambridge

Angewandte Chemie / International edition 60(51), 26639-26646 (2021). doi:10.1002/anie.202107916, Published by Wiley-VCH, Weinheim

Green chemistry : GC 23(24), 9860-9864 (2021). doi:10.1039/D1GC02915K, Published by Royal Society of Chemistry, Cambridge

Angewandte Chemie / International edition International edition 59(1), 215-220 (2020). doi:10.1002/anie.201909035, Published by Wiley-VCH, Weinheim

Green chemistry 22(23), 8260-8270 (2020). doi:10.1039/D0GC02412K, Published by RSC, Cambridge

Green chemistry 21(23), 6307 - 6317 (2019). doi:10.1039/C9GC03006A, Published by RSC, Cambridge

RWTH-Themen : Berichte aus d. Rheinisch-Westfälischen Technischen Hochschule Aachen SS 2018, 6-7 (2018). special issue: "Profilbereich „Molecular Science & Engineering“ (MSE) / Redaktion: Rauke Xenia Bornefeld ; Angelika Hamacher ; Nives Sunara", Published by RWTH, Aachen

Small : nano micro 17(5), 2006683 (2020). doi:10.1002/smll.202006683, Published by Wiley-VCH, Weinheim

Dissertation, RWTH Aachen University, 2023; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, Diagramme (2023). = Dissertation, RWTH Aachen University, 2023, In this work, tailored ruthenium catalysts were developed for the reduction of carboxylic acid derivatives with the goal to utilize plastic waste, biomass, and carbon dioxide as alternative and renewable carbon feedstock. In the first chapter, the state-of-the-art is described with a focus on the role of chemical recycling in the transformation to a circular economy, particularly using homogeneous transition metal catalysts.The second chapter focuses on the production of cyclic acetals by combining different renewable carbon sources. Selective hydrogenation of biogenic acids, esters, polylactic acid and polyhydroxyalkanoates using [Ru(triphos)(tmm)] and HNTf2 as catalyst system yielded various 1,2- and 1,3-diols. These were converted in the second step with C1-building blocks to generate cyclic acetals. For this purpose, either carbon dioxide was reduced with molecular hydrogen using the same catalyst system as for the diol synthesis or polyoxymethylene was depolymerized with an acidic catalyst. By synthesizing selected acetals on a 50 g scale, the determination of initial combustion properties was enabled to estimate their potential as bio-hybrid fuels in cooperation with project partners. Based on the hydrogenolysis of polyesters with Ru-triphos derivatives, the transfer hydrogenation of polyesters is reported in the third chapter. The combination of [Ru(triphos-xyl)(tmm)] and HNTf2 was identified as a suitable catalyst system to successfully convert not only aliphatic polyesters such as polylactide and polycaprolactone, but also more challenging aromatic polyesters such as polyethylene terephthalate, polybutylene terephthalate, SpectarTM, and TritanTM to high-quality alcohols. The best results were obtained when ethanol was used as a hydrogen donor. In the fourth chapter, the depolymerization of polyamides to cyclic secondary and tertiary amines and 1,6-hexanediol is discussed. The conversion of polyamide 6 and 6.6 was achieved by combining the robust and highly active catalyst system [Ru(triphos-xyl(OMe)2)(tmm)] and B(CF5)3 with 1,1,1,3,3,3-hexafluoro-iso-propanol as solvent. The selectivity of the reaction to tertiary amines or 1,6-hexanediol was controlled by adding primary and secondary alcohols. Finally, commercially available polyamide products such as nylon tights, cable ties, and fishing line were selectively depolymerized without any influence of the contained dyes or additives on the catalytic activity., Published by RWTH Aachen University, Aachen

Dissertation, RWTH Aachen University, 2023; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, Diagramme (2023). = Dissertation, RWTH Aachen University, 2023, This work covers the development of three different reaction systems to produce synthetic fuel alcohols from olefin paraffin mixtures, which are derived from Fischer Tropsch processes operating with bio syngas from the gasification of non edible biomass. These alcohols represent an interesting and important component of drop in capable synthetic fuels which are applicable in the fleet of existing vehicles. Beneficial influence on the density of the mixture as well as the combustion behavior represent the main advantages of higher alcohols in diesel type fuels. The pathway chosen to produce alcohols from olefins in this work is a hydroformylation and hydrogenation sequence, converting a C5 to C10 substrate mixture into C6 to C11 primary alcohols with aldehyde intermediates. These aldehydes, obtained in hydroformylation, already represent important platform chemicals in today’s chemical industry to produce a wide variety of products. The first reaction system investigated in this work is based on a major milestone in the development of industrial hydroformylation processes: the Ruhrchemie/Rhône-Poulenc process for the hydroformylation of propene in a water based liquid/liquid multiphase system and its efficient recycling of the precious rhodium/TPPTS catalyst. As this catalyst system exclusively produces aldehydes, a subsequent hydrogenation step is necessary, which leads to a two step process. This work further contributes to previous investigations of the application of this process concept to higher olefins with low water solubility. The focus of the investigation is to find reaction conditions for high once through conversion of the substrate to avoid energy intensive separation steps in the process. Batch reactions and continuous flow with a specially developed pilot plant setup led to high catalytic activity and stability. In a potential fuel production process leading towards alcohols, the aldehydes are not used as isolated intermediates. Hence, a tandem catalytic approach may increase the efficiency of the process by combining both the hydroformylation and hydrogenation reaction in a single process step. While tandem catalytic production of alcohols from olefins is known for cobalt based catalysts under harsh conditions, rhodium based processes have received comparably low attention. In combination with tertiary amines, molecular rhodium catalysts are capable of auto tandem reductive hydroformylation. In the second reaction system included in this work, this tandem catalytic approach is combined with a multiphasic catalyst recycling concept. By the introduction of alkanolamines to the reaction, a water based second phase for catalyst immobilization like in the two step process is investigated. By optimizing the reaction conditions for this biphasic system, namely the syngas pressure and composition, temperature as well as a Design of Experiment investigation of the reaction mixture composition, high selectivity towards the one step production of alcohols was achieved. The catalyst recycling concept was proven to be feasible in continuous flow. The most important parameter of this system was found to be the ratio between the alkanolamine and water in the aqueous catalyst phase, which significantly determines the catalytic activity as well as the phase behavior of the reaction. The third catalytic system in this work utilizes the strong dependence of the phase behavior on the water/amine ratio observed in the previously described multiphase system. When the amine is applied in excess to water, the formation of amphiphilic alcohols in combination with also amphiphilic alkanolamines leads to the formation of a single phase during the reaction. Since tertiary alkanolamines are CO2 responsive, the ionic strength of the amine can be influenced by the addition of carbon dioxide, resulting in a so called “switchable solvent system”, where the reaction is carried out under monophasic conditions while the catalyst can be recycled by the formation of a biphasic mixture upon addition of CO2. As the monophasic behavior during the reaction eliminates liquid liquid mass transfer limitations, the reaction rate of the system was increased compared to the multiphase system. Furthermore, a high selectivity towards alcohols in combination with high yields of up to 99.6% were achieved. In summary, three different approaches to produce alcohols as fuel additives were successfully developed and compared regarding their catalytic activity and stability, while the latter is an important factor for the economic feasibility of a potential production process. During this work, various insights on a molecular as well as on a process level were gained and utilized., Published by RWTH Aachen University, Aachen

Dissertation, RWTH Aachen University, 2022; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, Diagramme (2022). = Dissertation, RWTH Aachen University, 2022, Direct C–H functionalization is one of the most desirable reactions in organic chemistry, but remains a challenging feat. The main challenge is controlling regioselectivity, because organic molecules tend to contain multiple C–H bonds, and complex molecules often have C–H bonds of varying reactivity due to different hybridizations of the C–H bonds. Established methods can typically target C–H bonds with different hybridizations (e.g. Csp2 vs. Csp3), but site selectivity remains an issue if there is more than one C–H bond exhibiting the same hybridization. In 2019, the Ritter group published a report on the highly selective C–H thianthrenation of arenes to prepare aryl electrophiles. These electrophiles have been used in many subsequent transformations, such as fluorination, amination, and hydroxylation. Additionally, in 2020 the Ritter group published a report on applying thianthrenation to alkenes to regio– and stereoselectively prepare alkenyl electrophiles. These electrophiles were then used either with photoredox catalysis or palladium catalysis to form new carbon–heteroatom bonds.Part I of this thesis focuses on using these alkenyl electrophiles in Giese type reactions and photoredox mediated radical/polar crossover. Alkenyl thianthrenium salts have already been shown to react with nucleophiles in substitution reactions; the goal of this work was to determine if these electrophiles are also able to react with alkyl radicals in the β position to the thianthrenium group. Part I also focuses on using vinyl thianthrenium salts, a special case of an alkene (C2H3), in cross coupling reactions with alkyl halides. This transformation currently only exists to form new C–C bonds between alkyl halides and monosubstituted olefins, yielding a disubstituted olefin as the final product. The goal of this project was to instead introduce the vinyl group to a broad scope of alkyl halides with palladium catalysis. Both of these transformations can be summed up as a type of carbofunctionalization, because the work with both the alkenyl and vinyl thianthrenium salts attempts to form new C–C bonds, specifically new C(sp2)–C(sp3) bonds. In addition to direct C–H functionalization, carbon–heteroatom bonds can be formed by a substitution reaction if an organic molecule contains a suitable leaving group. When the nucleophile attacks at an aromatic carbon, the mechanism is typically through a nucleophilic aromatic substitution, although the Ritter group has published substitution reactions of phenols with fluoride via a concerted nucleophilic aromatic substitution mechanism. This reactivity works with both fluoride–19 and fluoride–18, and the Ritter group has published several reports on this work. However, deoxyfluorination of electron rich phenols initally proved challenging and had to be modified to obtain the desired reactivity. Preparing a ruthenium phenol complex makes the arene electron deficient enough to undergo deoxyfluorination with both fluoride–19 and fluoride–18. In 2018, the Ritter group showed the ruthenium mediated deoxyfluorination of peptides using this chemistry and have also applied this chemistry to medically relevant molecules. Part II of this thesis focuses on the radio deoxyfluorination of borussertib, a covalent–allosteric Akt inhibitor used to treat cancer. Borussertib exhibits remarkable selectivity and introducing the fluorine–18 isotope would allow for the opportunity to use PET imaging to study the mechanism of how this molecule acts in the body. 18F–borussertib was successfully prepared via ruthenium mediated deoxyfluorination of a ruthenium phenol precursor and the successful synthesis and purification of this molecule allowed for imaging studies in mice to be done., Published by RWTH Aachen University, Aachen

Dissertation, RWTH Aachen University, 2022; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen (2023). = Dissertation, RWTH Aachen University, 2022, In this thesis the development of a system for the homogeneously catalysed hydrogenation of CO2 to methanol based on manganese complexes and the elucidation of the underlying reaction mechanism is presented. In Chapter 1, the current state of research on the hydrogenation of CO2 to methanol with transition metal complexes and the latest developments for 3d metal complexes such as manganese are presented. In addition, literature known mechanisms for the hydrogenation of carbonyl groups are presented along with computational chemistry methods for their exploration. In chapter 3.1, the suitability of a Mn-pincer complex for the hydrogenation of CO2 to methanol via the formate ester route is investigated. A particular focus is put on the identification of hindering factors, such as the characterization of potential resting states of the reaction and their elimination by the addition of additives. The designed system for methanol synthesis from CO2 is optimized in chapter 3.2 by varying all relevant reaction parameters and testing structurally related catalysts, additives, and alcoholic media.Subsequently, mechanistic aspects of the designed reaction are investigated experimentally in chapter 3.3. Atomic-scale processes are considered via isotopic labelling or stoichiometric reactions at the NMR scale, and kinetic data is collected via the kinetic isotope effect and a concentration-time profile. Finally, the experimental activation energy is determined in an Eyring-Auftragung. In the following chapter 3.4, the reaction network is investigated using the optimal computational chemistry methods at DFT and DLPNO-CCSD(T) level to find the minimal energy pathway and thus the intermediates and transition states that determine the activity. Based on these results, the calculated energy span is determined and a simplified kinetic model is derived, allowing the simulation of a concentration profile.Finally, a reliable picture of the actual molecular mechanism in place can be postulated from the comparison between the ab-initio calculated reaction mechanism and the experimental counterparts. This serves as a basis for the systematic improvement of catalysts in the hydrogenation of CO2 to methanol through computational screening or rational design., Published by RWTH Aachen University, Aachen

Dissertation, RWTH Aachen University, 2022; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen (2022). = Dissertation, RWTH Aachen University, 2022, In this thesis, a catalyst system for the one-pot CO2 hydrogenation with methanol to methyl formate under continuous-flow conditions has been developed. The one-pot approach is advantageous with respect to the good extractability of the highly volatile product methyl formate. Non-volatile ionic liquids were utilized as reaction medium for a homogeneous, Ru-based catalyst, thus allowing the application as catalyst phase under continuous-flow conditions. Novel imidazolium carboxylates were synthesized and investigated regarding their applicability as reaction medium. The fine-tuning of the hydrogen bonding properties of the imidazolium carboxylates was found to be decisive for harmonizing the opposing requirements of hydrogenation and esterification step in the synthesis of methyl formate. An automated continuous-flow set-up was constructed that enabled the implementation of a self-optimizing system utilizing a machine learning algorithm. The reaction conditions were optimized reaching a maximum methanol conversion to methyl formate of 23 % and a weight-time-yield of 38.7 gMFgRu−1h−1. Sustained stability and activity of the ionic liquid and the catalyst could be demonstrated for almost six days of continuous operation. Furthermore, the application of Lewis-acidic co-catalysts was tested and suitable reaction conditions were found that preserve their stability in the catalyst phase., Published by RWTH Aachen University, Aachen

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, 2022; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen (2022). = Dissertation, RWTH Aachen University, 2022, The catalytic reduction of carbon dioxide (CO₂) to value-added C1 products is central for establishing sustainable chemical industries and requires both highly active and selective catalysts. This dissertation focuses on 3d transition metal pincer complexes as catalysts for the reduction of CO₂ to derivatives of formic acid, formaldehyde, and methanol. The work connects the catalytic activity and the preferred product reduction level to both the catalyst architecture and the reaction conditions and aims to contribute to a rational catalyst design.A catalytic system based on a cobalt(II) triazine pincer complex was applied in the hydrosilylation of CO₂. Fine adjustment of the reaction conditions enabled the selective arrival at three product levels with the same catalyst and reducing agent, while high temperature, low pressure, and high concentrations favored the reduction beyond the formate level. Synthesis, characterization, and catalytic application of hydride, formate, and silyl complexes enabled the identification of kinetically competent catalytic intermediates. Quantum chemical studies revealed that the cascade reaction proceeds via a series of hydride transfer, oxidative addition, and reductive elimination steps. Increasing kinetic barriers of the three cycles, competing hydride transfer steps, and trapping of formaldehyde as acetal are the key factors for selectivity control and rationalize the influence of the reaction conditions. Molecular volcano plots constructed from a library of iron, cobalt, and nickel pincer complexes provided insight into structure-reactivity relationships. The catalyst activity and selectivity could be described by the hydride affinity as a catalyst property depending on the choice of the metal and the ligand. The relative energy spans of the three steps determine if the reaction rates within the hydrosilylation cascade reaction decrease or increase, leading either to a more controlled arrival at each product level or to a rapid complete reduction to the methanol level. The implications of the volcano plots were confirmed by experimental observations for selected catalyst candidates. In conclusion, this thesis provides insight into molecular control in the reduction of CO₂ to products on different reduction levels both by catalyst design and by the reaction environment and hopes to contribute to the development of future catalytic systems., Published by RWTH Aachen University, Aachen

Dissertation, RWTH Aachen University, 2022; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, diagramme (2022). = Dissertation, RWTH Aachen University, 2022, In the endeavor to substitute fossil resources for the production of energy and chemicals with renewable carbon feedstocks and energy sources, the electrochemical reduction of carbon dioxide is considered a “dream reaction”. It holds the potential to use CO2 from industrial waste streams or the atmosphere and recycle the C1 building block into the chemical value chain by adding electrons. Molecular coordination complexes, particularly those based on 3d transition metals, can be introduced as catalysts to enable the reaction and expand the scope of accessible products. Thus, the alleviation of the global climatic and socio-economic effects of the greenhouse gas CO2 is combined with producing industrially relevant carbon-containing compounds. In this context, the present study is dedicated to investigating the role of the 3d metal center and the coordinated auxiliary ligands on the structural and electrochemical properties of the corresponding complexes. The obtained results shall be used to conclude the effect of these components on the traversed catalytic mechanism in the electrochemical activation of CO2. A series of mid to late 3d transition metal complexes (from manganese to zinc) was synthesized from the redox-innocent pincer ligand N2,N6-bis(diphenylphosphaneyl)-N2,N6-diphenylpyridine-2,6-diamine. Metal precursors were chosen in their +II or +I oxidation states and coordinated by chloride or acetonitrile (MeCN) ligands. The application of various analytical techniques allowed the correlation of the observed coordination geometries to the electronic configuration of the metal via crystal field theory. A qualitative increase in electronic density at the metal center could be observed throughout the 3d row. Cyclic voltammetry (CV) analyses revealed metal-centered redox processes for iron, cobalt, and nickel down to the zero-valent state. While cobalt and nickel undergo several ligand exchange reactions during this pathway, iron is surmised to dimerize or disproportionate.NMR spectroscopic and CV experiments tracked the ligand exchange between chloride and acetonitrile at the metal center. It was found that a single acetonitrile ligand coordinates cobalt and nickel at the zero-valent state in MeCN, independent from the auxiliary ligand in the starting complex. The π back bonding of MeCN supposedly removes electron density from the metal center, decreasing the potential required to reduce the complex but also its reduction strength. The stability of the complexes was found to be higher when chloride rather than labile acetonitrile ligands are coordinated and increased from iron to nickel, explainable by shorter and, hence, stronger bonds for the later transition metals. Electrochemical analyses under CO2 atmosphere showed the substrate coordination at the oxidation state zero for each of the complexes, yet substantial electron transfer to CO2 is only proposed for iron and cobalt. CV under the addition of the Lewis acid magnesium triflate identified cobalt as promising for the reductive disproportionation of CO2. A CV-based proton source screening revealed methanol as a suitable Brönsted acid for CO2 reduction with the same metal. Controlled potential electrolysis experiments, however, showed hydrogen as the preferred product with only minor amounts of CO. Likely, the probed complexes disintegrate at the electrode surface under formation of heterogeneous species. The para position in the pyridine core of the ligand backbone was identified as a possible weakness of the complex, the protection and further improvement of which will constitute a perspective for this work. Overall, the present study elucidates how the metal center determines the activity and stability of otherwise redox-innocent systems in electroreduction reactions such as carbon dioxide conversion. The in-depth knowledge of the electrochemical behavior of the cobalt and nickel complexes under inert conditions, in contact with CO2, and combined with further co-catalysts provides the means to adjust the properties of the complexes for CO2 activation. These insights will be used to improve the so-far unsatisfactory long-term stability of the complexes under electrocatalytic conditions., Published by RWTH Aachen University, Aachen

The cleavage of aromatic carbamates with the final application in a continuous reactor was investigated for this thesis. First, potential solvents were tested in experiments with the model substrate N-methyl phenyl carbamate in a mmol-scale set-up. As a result, sulfolane and diphenyl ether (DPE) were chosen for further experiments. In the next step the cleavage of the target substrate toluene dicarbamate (TDC) to the bifunctional 2,4-toluene diisocyanate (TDI) was performed at different reaction temperatures in the mmol-scale set-up. In summary, the TDC cleavage achieves significant yields above 200°C. Furthermore, the selectivity towards isocyanates is decreased above 240 °C, as the isocyanate products are decomposed into carbodiimids. Besides the screening of reaction conditions in the mmol-scale set-up, a kg-scale continuous stirred tank reactor (CSTR) was designed based on previous work. In the first place, batch experiments were performed with the model and the target system. In both cases the results were reproducible. However, the carbamate conversion and the yield of isocyanate were decreased in comparison to the mmol-scale set-up. As a consequence of difficulties with the separation of the product-containing gas phase utilizing the model substrate, only the target system was transferred into continuous operation. To achieve significant conversions in continuous reactions high temperatures, long residence times and high amounts of stripping gas (Ar) were necessary. Best results were achieved at 228 °C reactor temperature, an average residence time of 350 minutes and an elevated stripping gas flow of 120 L/h. Furthermore, the yield of the target product TDI is limited, due to the complexity of the reaction network and the formation of urea side products. The majority of the converted TDC is detected as isocyanate in the product mixture, but mostly mono isocyanate intermediate products are formed. Besides, the reaction is very selective and only urea species occured as side products. In the final section, a model for the TDC conversion at the steady state of a continuous reaction was calculated based on kinetic data from mmol-scale experiments. The results were comparable to the experiments, although the model expected slightly higher conversions than the experiment achieved.

Dissertation, RWTH Aachen University, 2021; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, Diagramme (2021). = Dissertation, RWTH Aachen University, 2021, The catalytic selective hydrogenation of unsaturated moieties in aromatic substrates (e.g. aromatic ring, C=C, C=O, etc.) has been widely applied for several decades in all fields of the chemical industry (petrochemical, fine chemical, pharmaceutical, agrochemical, etc.). However, to cope with the increasing complexity of aromatic substrates, for example coming from biomass, the perpetual development of efficient, selective, and tunable catalytic systems is essential. A state-of-the-art is provided in chapter 1, summarizing the importance of the selective hydrogenation of various functionalities in aromatic substrates as well as the main catalyst families that are currently available. On this basis, the motivation and objectives of this work are described. In the following two chapters, we report the design, synthesis and characterization of multifunctional catalysts consisting of ruthenium nanoparticles (Ru NPs) immobilized on various molecularly modified supports as well as their application to the hydrogenation of substituted aromatic substrates in batch conditions and in continuous flow processes. Chapter 2 discusses the selective hydrogenation of benzofurans to dihydrobenzofuran derivatives using a multifunctional catalyst composed of Ru NPs immobilized on a Lewis Acid-functionalized supported ionic liquid phase (Ru@SILP-LA). Using a molecular approach, the individual components (metal NPs, ionic liquid with chlorozincate anions as Lewis acid, silica as support) of the catalytic system were assembled to bring the metal and acid sites in intimate contact on the support material. The resulting Ru@SILP-LA catalyst allows the hydrogenation of O-containing heteroaromatic rings while keeping the aromaticity of C6-rings untouched. [ZnCl4]2- anions were identified to be the predominant chlorozincate species using X-ray Photoelectron Spectroscopy, and were found to be in close interaction with the metal NPs according to STEM-HAADF-EDX. The Ru@SILP-[ZnCl4]2- catalyst was found to be highly active, selective, and stable for the selective catalytic hydrogenation of various benzofuran derivatives in batch and continuous flow conditions, delivering easy access to biologically relevant dihydrobenzofuran motifs. The concept of multifunctional catalysts was extended in Chapter 3 with the development of a NPs-based catalytic system with switchable reactivity, meaning that its reactivity can be changed at will during a reaction through the modification of the catalyst’s environment or the application of an external stimulus. In particular, a catalytic system composed of Ru NPs immobilized on an amine-functionalized polymer-grafted silica (Ru@PGS) has been designed to respond adaptively to the feed gas composition used in catalytic hydrogenation. The resulting Ru@PGS catalyst was found to be active and stable for the hydrogenation of biomass-derived furfuralacetone. In pure hydrogen (H2), the substrate’s unsaturations (furan ring, C=C, C=O) were fully hydrogenated forming the corresponding saturated alcohol. However, using a mixture of hydrogen and carbon dioxide (H2/CO2) the C=O hydrogenation step was selectively switched off, producing the saturated ketone in excellent yield and selectivity. This selectivity switch is fully reversible allowing switching back and forth between H2 and CO2/H2 in continuous flow reactor to produce in high yields either one product or the other. The change in selectivity is attributed to the reversible formation of an alkylammonium formate species coming from the Ru-catalysed hydrogenation of CO2 assisted by the amine-functionalized support. These studies highlight the great potential of NPs on molecularly modified supports for the production of multifunctional catalytic systems with tailor-made reactivity., Published by RWTH Aachen University, Aachen

Dissertation, RWTH Aachen University, 2021; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen (2021). = Dissertation, RWTH Aachen University, 2021, The use of fossil resources has to be limited in light of the scarce availability of oil in the future and the associated damages to the environment. Although fossil resources are used as feed stock in the chemical industry, the major share of fossil resources is used for energy production. Most prominently, fossil resources are used as fuels in the transportation sector. Thus, transitioning the transport sector from fossil resources to renewable resources will have a major impact on the environment. Oxymethylene ethers (OMEs) are currently investigated as a promising fuel additive. OMEs have the potential to be synthesized from renewables and further have significant advantages with regard to their fuel properties. The addition of OME to Diesel fuel leads to drastically reduced NOx and soot emissions. In this thesis, catalysts were developed for a new synthesis route of OMEs from methanol. This synthesis pathway utilizes methanol dehydrogenation to access the formaldehyde intermediate. In contrast to the oxidation of methanol, methanol dehydrogenation yields molecular hydrogen and therefore enables an advanced hydrogen management for the selective synthesis of OMEs. Catalysts for a base-free methanol dehydrogenation and transfer-hydrogenation were developed and mechanistically investigated. An iridium catalyst was designed to achieve TONs up to 204 for OME1. The use of operando NMR spectroscopy, quantum-chemical calculations and targeted experiments led to the proposition of a plausible mechanism. Ruthenium catalysts were investigated and tailored to achieve TONs up to 131 for OME1. The extensive use of quantum-chemical calculations enabled a rational design approach for the ruthenium catalysts. Quantum-chemically predicted activation and deactivation pathways were evaluated experimentally. In addition, the ruthenium catalysts showed reactivity not only in the dehydrogenation of methanol but also in a coupled dehydrogenation-hydrogenation reactions. Lastly, the concept which is developed for the noble metals iridium and ruthenium is transferred to more abundant iron and manganese catalysts. The results gained in the study of abundant-earth metals showed a general proof of concept for the synthesis of OME1 from methanol., 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, Rheinisch-Westfälische Technische Hochschule Aachen, 2020; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, Diagramme (2021). = Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020, The production of bio-based fuels and fine chemicals in bio-refineries is a key step in a future bioeconomy. Sustainably grown lignocellulosic feedstocks need to be converted and fully valorized to provide a maximized sustainability. In this thesis, existing Biorefinery concepts were investigated, optimized and new pretreatment concepts for the conversion of lignocellulose were designed. They aim at producing valuable product streams that provide a high purity and should be ready to use for further applications, potentially boosting the pretreatments efficiency.The current state of the OrganoCat pretreatment, a biphasic oxalic acid catalyzed pretreatment, was evaluated and a new catalyst, 2,5-furandicarboxylic acid (FDCA) was tested. FDCA showed similar efficiency compared to oxalic acid but enables a more straightforward recovery and provides sufficient thermal stability. Both reaction systems were scaled up to 7 L, highlighting the impact of agitation, but also that comparable efficiency as in lab scale can be achieved. OrganoCat was then applied to different lignocellulosic feedstocks such as perennial plants, agricultural residues and wooden biomasses. The OrganoCat pretreatment proved to be robust and to process all provided substrates with good efficiency. To transfer the concept of OrganoCat from a batch reactor to a flow through mode, a reaction system was designed that uses a fixed bed reactor with continuous solvent flow. Similar efficiencies as in batch mode were observed when applying flow through pretreatment. Shorter reaction times, reducing contact times of solvent and catalyst, resulted in less side reactions. The flow thorugh setup showed promising results for future upscaling and application of the process.A novel approach for lignocellulose valorization was proposed, using phosphoric acid, aiming at the conversion of xylan into the platform molecule furfural, while providing high quality lignin and highly accessible cellulose pulp. Lignocellulose is swollen in phosphoric acid and afterwards treated with diluted phosphoric acid and 2-MTHF. Lignin and cellulose enriched pulp are separated and recovered to boost the economy of the process, both showing promising properties. In a second biphasic reaction step, the xylose is converted to furfural, the main product of the described process. The residual aqueous phase is concentrated, to recover the phosphoric acid for consecutive reactions. The processing efficiency was observed to be stable over four consecutive cycles. Having the potential to be a high-value feedstock, strategies for the purification and fractionation of lignin were evaluated based on its precipitation. Lignin precipitation from 2-MTHF solutions was achieved using either antisolvents or CO2 expansion of the solvent phase. The precipitation led to lignin fractions with different structures and sizes while separating furfural, formed during pretreatment. To make lignin more accessible for subsequent conversion, a depolymerization strategy was developed that aims at cleaving the β-O-4 linkage in the extracted lignin. A Mn(I) complex was used to successfully cleave the β-O-4 bond in lignin model compounds with full conversion and high selectivity., Published by RWTH Aachen University, Aachen

Dissertation, RWTH Aachen University, 2020; Aachen 1 Online-Ressource (XIV, 170 Seiten) : Illustrationen, Diagramme (2020). = Dissertation, RWTH Aachen University, 2020, Efficient hydrodeoxygenation (HDO) catalysts have to feature sites for the activation of the dihydrogen molecule and the oxygenated moiety of the substrate. In the case of the presented bifunctional catalysts, these tasks are accomplished by metal nanoparticles (NPs) and acid-functionalized supported ionic liquid phases (SILPs), respectively. In previous studies, we discovered that intimate contact of the active sites within bifunctional Ru@SILP-SO3H catalysts was crucial for a high HDO activity. Interestingly, experiments discussed in this thesis revealed that the interactions resulting from the close proximity of the Ru NPs and the SILP's sulfonic acid groups within these bifunctional catalysts were not solely advantageous for their HDO activity. Testing a series of Ru@SILP-SO3H catalysts showed a clear correlation between their acid:metal ratios and their activity towards the HDO of the model substrate, benzylideneacetone. This emphasizes the importance of a well-balanced ratio of hydrogenation and dehydration sites within the bifunctional catalysts. Comparing the HDO activity of Ru@SILP-SO3H and Ru@SILP+IL-SO3H catalysts indicated that the unfavorable interactions between the acid and the metal sites were not only present within the bifunctional catalysts, but did also occur during NP synthesis. The synthesis of FeRu NPs on a SILP featuring a chemisorbed, non-functionalized IL and the post-synthesis physisorption of an acidic IL allowed to separate the stabilization effect of the SILP from its functionalization. This approach facilitated the synthesis of Fe containing NPs from the highly acid sensitive {Fe[N(Si(CH3)3)2]2}2 precursor and ensured intimate contact of the acid and metal active sites on the surface of the bifunctional catalyst. It also paves the way for the preparation of multimetallic NPs on SILP materials and the assembly of multifunctional catalytic systems with tailor-made reactivity for challenging catalytic transformations. The structural similarity of the chemisorbed and physisorbed IL molecules led to the formation of a stable Fe25Ru75@SILP+IL-SO3H catalyst, which combined high activity and selectivity for the formation of aromatic HDO products with a broad substrate scope. Furthermore, the catalyst exhibited a unique preference for the HDO of non-benzylic over benzylic ketones. In contrast to the Ru@SILP+IL-SO3H and Fe25Ru75@SILP+IL-SO3H catalysts, the post-synthesis functionalization of Fe25Ru75@SILP with IL-SO3- and Hf(OTf)4 did not result in the formation of a stable Fe25Ru75@SILP+IL-SO3-Hf(OTf)3 catalyst. Leaching of Hf(OTf)3+OH- during the HDO of 4-methylacetophenone indicated that the immobilization of the Lewis acid via an ionic bond between the hafnium cation and the sulfonate anion was unsuccessful., Published by Aachen

Dissertation, RWTH Aachen University, 2020; Aachen 1 Online-Ressource (xxii, 272 Seiten) : Illustrationen, Diagramme (2020). = Dissertation, RWTH Aachen University, 2020, Die vorliegende Dissertation befasst sich mit der Umsetzung neuer organischer Umwandlungen mittels Wasserstoff-Transfer-Reaktionen unter Verwendung von Mn(I)- und Ru(II)-Komplexen. Hauptaugenmerk liegt in der Untersuchung von Mn(I)- und Ru(II)-Komplexen und ihrem ähnlichen Reaktionsverhalten in Wasserstoff-Transfer-Reaktionen, sowie dem „Hydrogen Borrowing“-Konzept und Reduktionsreaktionen. Kapitel 1 gibt einen Überblick über den aktuellen Stand der Technik für Wasserstoff Transfer-Reaktionen mit Mn(I)-Komplexen und ihrem ähnlichen Reaktionsverhalten zu Ru(II)-Komplexen, welche bereits für diese Reaktionen etabliert sind. Kapitel 2 beschreibt die selektive β Methylierung von Alkoholen unter Verwendung von Methanol als C1 Baustein für die Synthese von Feinchemikalien, Arzneimitteln und alternativen Brennstoffen. Verschiedene Ruthenium-Komplexe wurden für diese Reaktion getestet, wobei sich der Ru-MACHO-BH-Pincer-Komplex als der geeignetste Katalysator herausstellte. Mechanistische Untersuchungen und DFT-Computerrechnungen bestätigten, dass die Reaktion über „Hydrogen Borrowing“-Reaktionspfade und mit Metall-Ligand-Kooperationen am Ruthenium Metallcenter verläuft. Kapitel 3 fokussiert ebenfalls auf die β Methylierung von Alkoholen unter Verwendung von Methanol als C1 Baustein. Allerdings wurden luftstabile 3d-Übergansmetall-Mangan-Pincer-Komplexe verwendet. Die Reaktivitäten der Mn(I)- und Ru(II)-Pincer-Komplexe wurden miteinander verglichen. Ausgewählte Mangan-Pincer-Komplexe wurden synthetisiert und in der Reaktion getestet, wobei der Mn-MACHO-iPr-Komplex ausgezeichnete Ergebnisse mit höchster Selektivität und Ausbeute zum gewünschten Produkt aufwies. Kapitel 4 stellt die Umsetzung von substituierten Cycloalkanen mit sekundären Alkoholen oder Ketonen und Diolen als Ausgangsstoffe dar. Dabei wurden die Ru-MACHO-BH- und Mn MACHO iPr-Komplexe als Präkatalysatoren eingesetzt. Untersuchungen zeigten, dass der Mn MACHO iPr-Komplex eine bessere Reaktivität aufwies als der Ru-MACHO-BH-Komplex. Unter Verwendung des Mn MACHO-iPr-Katalysators konnten verschieden substituierte Cycloalkane, wie substituierte Cyclopentane, Cyclohexane sowie Cycloheptane, synthetisiert werden. Mechanistische Untersuchungen ergaben, dass die Reaktion über „Hydrogen Borrowing“-Reaktionswege verläuft. In Kapitel 5 wird die selektive Deuterierung von primären, aliphatischen Alkoholen mit D2O als Deuteriumquelle herausgestellt. Der bereits etablierte Mn-MACHO-iPr-Komplex wurde für die Reaktion untersucht und zeigte die selektive Deuterierung von Benzylalkohol an α-Position, sowie die α- und β-Deuterierungen bei aliphatischen Alkoholen. Kapitel 6 erläutert die selektive Hydrierung von cyclischen Carbonaten zu den entsprechenden Diolen und Methanol. Ausgewählte Mangan Pincer Komplexe wurden synthetisiert und für die Reaktion getestet, wobei der luftstabile Mn-MACHO-iPr Pincer Komplex die höchste katalytische Produktivität und Selektivität aufwies. Das letzte Kapitel beschreibt die Herstellung von Methoxyboronatester mittels selektiver Reduktion von organischen, cyclischen und linearen Carbonaten, sowie CO2 mit Pinakolboran als Reduktionsmittel. Ein neuer Mangan Pincer Komplex wurde entwickelt und ermöglicht die effiziente, selektive Umsetzung der Reaktion., Published by Aachen

Dissertation, RWTH Aachen University, 2020; Aachen 1 Online-Ressource (vii, 122 Seiten) : Illustrationen, Diagramme (2020). = 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., Published by Aachen

Dissertation, RWTH Aachen University, 2020; Aachen : RWTH Aachen University 1 Online-Ressource (VI, 160 Seiten) : Illustrationen, Diagramme (2020). = Dissertation, RWTH Aachen University, 2020, This thesis describes the development, the construction and the functionality of a flexible automated reaction set-up for the semi continuous homogeneously catalyzed hydrogenation of CO$_{2}$ and organic carbonates in multiphase systems. The conversion of CO$_{2}$ to [FA·amine] adducts (FA = formic acid) using the set up is demonstrated. Additionally, the downstream process of the product by functionalization with methanol (MeOH) to methyl formate (MF) is presented. Finally, the hydrogenation of organic carbonates to MeOH is studied and possible process strategies are discussed., Published by RWTH Aachen University, Aachen

Dissertation, RWTH Aachen University, 2019; Aachen 1 Online-Ressource (X, 140 Seiten) : Illustrationen, Diagramme (2018). = Dissertation, RWTH Aachen University, 2019, The goal of this study is to identify new trimerization catalysts which are active at low temperatures (40 to 70 °C) for both trimerization and polyurethane formation. Ideally, these catalysts are characterized by low activation energy. In order to get closer to ideal catalysts, the project was divided into three areas of investigations (Figure 6). The first is about the mechanistic understanding, as a good understanding of the trimerization mechanism is required in order to define guidelines for a better selection of trimerization catalysts. In the second area of investigation, different catalysts were proposed, synthesized and tested using a model system of mono-functional alcohol and isocyanate instead of a real foam system. Additionally, kinetic measurements were carried out during testing to compare their activity towards trimerization. Finally, the best candidates were tested in a real foam system using polyols and polyisocyanate provided by the industrial partners, and the produced foams were characterized by different analytical methods., Published by Aachen

Dissertation, RWTH Aachen University, 2019; Aachen 1 Online-Ressource (XIX, 138 Seiten) : Illustrationen, Diagramme (2019). = Dissertation, RWTH Aachen University, 2019, In the present work, various mononuclear manganese and iron complexes were investigated in the context of water oxidation catalysis. The aim of the work was to understand how a change of the electronic properties of the ligand influences the fundamental electrochemical water oxidation behavior. In addition, the formation of the respective catalytically active species and the mechanism of water oxidation were studied in detail. At the beginning, mononuclear manganese-bipyridine complexes were used. However, they did not show catalytic water oxidation neither when using chemical oxidants nor electrochemically. In the second part of the work the dpaq ligand system was used, which has stronger σ-donor properties due to an anionic carboxamide group. Starting from the known [FeIII(dpaqH)(OH2)](ClO4)2-WOC, the influence of different substituents in the 5-position of the ligand on water oxidation was investigated. It was shown that electron-withdrawing substituents increase the catalytic current, but only with a simultaneous increase of the overpotential, while electron-donating substituents reduce the catalytic activity. An increased catalytic current with a concomitant decreased overpotential was finally achieved by the introduction of a pyrene group into the ligand framework which led to an increased π-conjugation. In addition to the Fe complexes, the analogous [MnII(dpaqR)](ClO4) complexes were investigated and also showed a catalytic current. The influence of the different substituents in the ligand framework on the overpotential followed the same trend. In contrast to the Fe complexes, however, no reversible reduction waves were visible, so that a fundamental structural change of the starting complexes must be assumed under the measurement conditions. In the third part of the work, the tetradentate dpqma ligand was used to synthesize a new mononuclear [MnII(dpqma)Br2] complex, which showed a catalytic current in CV measurements in a borate buffer. However, when using Cerium (IV) ammonium nitrate (CAN) as the oxidant, no evolution of oxygen could be detected. Using EPR spectroscopy, it was shown that the dpqma ligand presumably dissociates after the addition of CAN, followed by the formation of a μ-oxo bridged MnIIIMnIV dimer. After a longer reaction time, the EPR measurements indicated the formation of MnOx compounds. In addition, the formation of MnO4- ions was detected by UV/Vis spectroscopy. This showed that the [MnII(dpqma)Br2] complex is not a suitable water oxidation catalyst when using CAN as the oxidant due to the poor stability under the acidic oxidative reaction conditions., Published by 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, 2018; Aachen 1 Online-Ressource (XXIII, 296 Seiten) : Illustrationen, Diagramme (2018). = Dissertation, RWTH Aachen, 2018, The thesis at hand various different topics regarding the synthesis and properties of polyoxymethylene (POM) oligomers and copolymers. POM is an engineering plastics, that finds widespread applications. The general interest in POM polymers remains high, as formaldehyde can be produced from sustainable feedstocks. The present thesis is divided into 5 main chap-ters. Chapter 1 gives an overview on the history behind POM polymers, their application as materials, the cationic homopolymerisation of trioxane, the cationic copolymerisation of trioxane with other comonomers. Also the sustainability of formaldehyde and its polymers are dis-cussed. In Chapter 2, the ring-opening reaction of trioxane in the presence of acetic anhydride is discussed as a model reaction for the initial phase of the trioxane homopolymerisation. In situ IR spectroscopy was used as a tool to monitor the kinetic profile of multiple reactions per-formed with different Brønsted acidic and Lewis acidic catalysts. The role of these catalysts is discussed in the context of the mechanism of the ring-opening reaction of trioxane with acetic anhydride. Chapter 3 entails the synthesis of a series of low molecular weight oxymethylene diacetates. The crystallinity, melting- and crystallisation temperature of these com-pounds were determined. The effect of the composition of oxymethylene diacetate mixtures on their thermal properties is discussed in general. Moreover, the findings are discussed in the context of sustainable fuel applications for POM oligomers with relatively low molecular weight. In Chapter 4, the synthesis, thermal properties and the application of poly(acetalester) are discussed. Poly(acetalester) are novel and sustainable copolymers of trioxane and cyclic anhydride. The monomers are copolymerised in the presence of an open chain anhydride as chain transfer agent to achieve molecular weight control. Multiple aspects, like average length of oxymethylene segments, formation of cyclic poly(acetalester) as side products and the introduction of reactive moieties in the copolymer chain are discussed. In Chapter 5, the synthesis, the mechanism and the thermal properties of multi-block POM-PEG copolymers are dis-cussed. The control of the copolymer composition and the connection to their thermal proper-ties are explained. As outlook, the applications scope of POM in the fields of fuels, materials, lubricants and phase change materials are discussed., Published by Aachen

Dissertation, RWTH Aachen University, 2018; Aachen, 1 Online-Ressource (XVIII, 140 Seiten) : Illustrationen, Diagramme (2018). = Dissertation, RWTH Aachen University, 2018, This doctoral thesis deals with the ruthenium-catalyzed utilization of CO2 in combination with molecular hydrogen. In the first part of this work, the N-methylation of different nitrogen-containing compounds using the ruthenium complex [Ru(triphos)(tmm)] as a catalyst and CO2 and hydrogen for the construction of the methyl groups was investigated. Under optimized reaction conditions, the N-methylation of ammonia, ammonium chloride and nitrobenzenes was successful. In addition, the influence of different substituents in the multicomponent coupling of aldehyde, amine and CO2 was studied. The second part of this work deals with the acid-catalyzed alkylation of amines for the synthesis of phenylpyrrolidines from aromatic amines and cyclic ethers. HNTf2 and Al(OTf)3 were identified as catalysts for this reaction. Under optimized reaction conditions high yields of the corresponding phenylpyrrolidine were obtained starting from primary amines. In addition, an alkyl group transfer was observed using secondary amines and cyclic ethers as substrates. In the third part of this thesis, a novel catalytic synthesis was developed for the preparation of dimethoxymethane (DMM) from methanol, CO2 and hydrogen. The developed reaction pathway provides the first direct reductive access to DMM. A ruthenium triphos complex in combination with a Lewis and/or Brønsted acid as a co-catalyst was identified as a suitable multifunctional catalyst system for the complex reaction sequence. Under optimized reaction conditions a TON of 513 was achieved for DMM. In addition, the developed reaction protocol was successfully used for the synthesis of different dialkoxymethanes from CO2, H2 and the corresponding alcohol. Regarding the reaction pathway, methyl formate and methoxymethanol were identified as intermediates and the construction of the methylene group from CO2 and H2 was clarified by a 13C labeling experiment. Based on these results, the reaction was further investigated using formic acid as a C1 synthon. Under optimized reaction conditions, the TON for DMM could be increased to 1076 starting from formic acid., Published by Aachen

RWTH Aachen University und University of Nottingham, Diss., 2017; Aachen, 1 Online-Ressource (254 Seiten) : Illustrationen, Diagramme(2017). = RWTH Aachen University und University of Nottingham, Diss., 2017, The work described in this Thesis has been carried out within the Erasmus Mundus framework for Sustainable Industrial Chemistry (SINCHEM). The work concentrates on the possible utilisation of carbon dioxide as a solvent and as a starting material. Chapter 1 introduces carbon dioxide and its utilisation. In addition, the 12 Principles of CO2 Chemistry are presented, as well as continuous flow chemistry and self-optimising reactors. The relevant aspects of these reactors are discussed further in Chapter 2. The results of the research are presented in Chapters 3-6. A self-optimising reactor with FT-IR analysis was employed for the methylation of alcohols as explained in Chapter 3. Chapters 4-6 concentrate on N-alkylation reactions. In Chapter 4, the reactivity between aniline, tetrahydrofuran and dimethyl carbonate in supercritical carbon dioxide is discussed. This research led to the discovery of novel transformations.In Chapters 5 and 6, methanol was employed to methylate amines. A ruthenium triphosphate catalyst, which can produce methanol from carbon dioxide and hydrogen, was used to catalyse the reactions between methanol and aliphatic amines, as described in Chapter 5. Also the cyclisation and subsequent methylation of amino alcohols was studied. This reactivity is also the topic of Chapter 6, where γ-alumina was used as catalyst and supercritical carbon dioxide as solvent. Finally, Chapter 7 summarises the work described in this Thesis and evaluates the progress made towards achieving the aims that are introduced at the end of Chapter 1. One of these aims is to evaluate the work carried out in this Thesis according to the 12 principles of CO2 Chemistry. This evaluation is shown in Chapter 7., Published by Aachen

Dissertation, RWTH Aachen University, 2017; Aachen, 1 Online-Ressource (184 Seiten) : Illustrationen (2018). = Dissertation, RWTH Aachen University, 2017, The present thesis discusses aspects concerning the catalyzed synthesis of polyols. Polyols represent fundamental building blocks for polyurethanes beside isocyanates. For the synthesis of polyether polyols from epoxides, double-metal-cyanide (DMC) catalysts are in the focus, which are preferentially used in industrial applications due to their specific characteristics. CO2-based polyethercarbonate polyols (PECs), another category of polyols which can be synthesized by DMC catalyst and from highly interest in actual research topics, are the main focus in my thesis. The thesis is divided into four main chapters. Chapter one gives a general overview on polyurethanes with respect to properties and applications in dependence of the choice of the polyol and isocyanate components. Further, classic and modern synthesis routes for polyols, and the corresponding catalyst system, are described. The ring-opening polymerization of epoxides catalyzed by DMC catalysts is discussed in detail. In the following, chapter two describes the successful minimization of side-products, which are formed during polyol synthesis with DMC catalysts by copolymerization of epoxides and CO2 as well as the separation of the catalyst from the obtained product. By addition of phosphoric acid as additive in the final step of the polyol synthesis, the DMC catalyst is deactivated. Hence, further formation of cyclic carbonates as side-product is prevented. An almost quantitative separation of the DMC catalyst, which after the synthesis remains finely dispersed in the polyol, was achieved by treatment of the polyol with ethanol at elevated temperatures. Chapter three describes different methods for the synthesis of higher functional polyethercarbonate polyols based on DMC catalysis. The incorporation of functional, cyclic latent AxBy-type monomers into the polymer chain increases the average functionality of the polyol and allows controlling the polymer architecture. Developing methods to raise the sustainability of the polyols is another focus point. In this context, the successful synthesis of polyethercarbonate polyols based on sugar alcohols and citric acid as chain transfer reagent is described. Finally, in chapter four the polymer dynamics of classical polyether polyols and modern polyethercarbonate polyols is described. New application areas of polyethercarbonate polyols are discussed based on their distinct visco-elastic properties at relative low molecular weights., Published by Aachen

RWTH Aachen University und Université de Lyon, Diss., 2016; 180 pp. (2016). = RWTH Aachen University und Université de Lyon, Diss., 2016, Nowadays, terpenes represent an interesting class of biomass constituents as potential precursors for key building blocks in fine chemical industry. More in details, the production of a terpene such as limonene is exponentially increasing, already in the 2013, its yearly production was estimated over 70000 tons year-1 from citrus waste. The hydrogenation of this terpene is a suitable reaction to prepare selectively monohydrogenated molecules, like p-menthene, used in pharmaceuticals, agrochemical, perfume industries and in polymers field, while, the full hydrogenated products, cis- and trans-p-menthane, cover a relevant role as green additives into fuels. As reported in recent literature, the catalytic reactions involving limonene were conducted under high H2 pressure (from 5 to 50 bar) and high-temperature (from 80 to 140°C) conditions using heterogeneous metal based catalysts (Pt, Ni and Pd), with low selectivity towards (+)-p-1-menthene. Nevertheless, whenever mild conditions were used, a good selectivity in (+)-p-1-menthene was reached. However, a comparative study of different catalysts under mild reaction conditions for the limonene hydrogenation has not been reported in literature. Therefore, the goal of this PhD project was in an early stage to study the activities of several commercial metal nanoparticles based catalysts for the mild hydrogenation of limonene. The hydrogenation of limonene has been performed in neat limonene and under mild conditions, e.g. low temperature (30°C) and low molecular hydrogen pressure (3 bar), aiming at a sustainable production route for (+)-p-1-menthene. In our study, the active metal nanoparticles (Pt, Pd and Ru) and supports (carbon, silica and alumina) were systematically varied and tested. It was found that the heterogeneous catalyst Pt/C alongside Pt/Al2O3 under mild reaction conditions (room temperature and 3 bar H2) was highly active and selective in the reduction of R-(+)-limonene to the partial hydrogenation product (+)-p-1-menthene. Moreover, the catalytic activity and stability of Pt/C were maintained during recycling tests under batch conditions and thus allowed the implementation of this catalytic system into continuous flow operation. The selective hydrogenation of terminal C=C bond over the internal one in limonene was rationalized by detailed kinetic studies which revealed an 8-fold difference in reaction rate between the two reactions. This previous study with commercial catalysts gave the possibility to tune the synthesis of heterogeneous metal-based catalysts for the next step of the study, where different heterogeneous metal based catalysts (Pt, Ru, Pt3Sn, and Ni), developed from a colloidal-based approach were tested in the hydrogenation of limonene. Those catalysts contain the same metal loading and similar particle sizes (ca. 2 nm) homogeneously dispersed onto non structured oxides (silica and alumina), carbon, or embedded into the walls or at the pore surface of a mesostructured silica materials (SBA-15). All the catalysts from the Pt series were particularly active in the selective hydrogenation of limonene towards p-menthene with further conversion into p-menthane, showing a very high reaction rate. Among of all those catalysts, the one containing Pt nanoparticles embedded in the walls of the silica showed the highest TOF, of ca. 2200 h-1 after two hours of reaction and a maximum yield in p-menthene of ca. 85 % was obtained after 10 hours of reaction. The same catalyst was tested in a continuous flow system and a stable yield of ca. 80% during 6 hours of reaction was reached. No products of isomerization were detected in the crude mixture during the reaction. We could therefore conclude that, using either a heterogeneous commercial catalyst like Pt/C or using a heterogeneous metal based catalyst developed from a colloidal-based approach like SBA-15{walls}, it was possible to achievea selective conversion of limonene into p-menthene in batch and in continuous flow conditions., Published by Aachen