Search

Hydroxy-terminated polyoxymethylene-\(\it co\)-polyoxyalkylene multi-block telechels were obtained by a new methodology that allows for the formal substituting of ether units in polyether polyols with oxymethylene moieties. An interesting feature is that, unlike carbonate groups in polycar-bonate and polyethercarbonate polyols, homopolymer blocks of polyoxymethylene moieties can be formed. The regular nature of polyoxymethylene blocks imparts a certain crystallinity to the polymer that can give rise to new properties of polyurethanes derived from such telechels. The synthesis, reaction sequence and kinetics of the formation of oligomeric hydroxy-terminated mul-ti-block telechel polyoxymethylene moieties are discussed in this paper and the preparation of a polyurethane material is demonstrated.

Green chemistry : GC (2022). doi:10.1039/D1GC04189D, Published by Royal Society Chemistry, Cambridge

Chemistry - a European journal 28(23), (2022). doi:10.1002/chem.202104375 special issue: "Hot Topic: Carbon Dioxide", Published by Wiley-VCH, Weinheim

Green chemistry (2022). doi:10.1039/D2GC01252A, Published by RSC, Cambridge

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

The synthesis, characterization, and catalytic properties of bimetallic cobalt‐rhodium nanoparticles of defined Co:Rh ratios immobilized in an imidazolium‐based supported ionic liquid phase (Co$_x$Rh$_{100−x}$@SILP) are described. Following an organometallic approach, precise control of the Co:Rh ratios is accomplished. Electron microscopy and X‐ray absorption spectroscopy confirm the formation of small, well‐dispersed, and homogeneously alloyed zero‐valent bimetallic nanoparticles in all investigated materials. Benzylideneacetone and various bicyclic heteroaromatics are used as chemical probes to investigate the hydrogenation performances of the Co$_x$Rh$_{100−x}$@SILP materials. The Co:Rh ratio of the nanoparticles is found to have a critical influence on observed activity and selectivity, with clear synergistic effects arising from the combination of the noble metal and its 3d congener. In particular, the ability of Co$_x$Rh$_{100−x}$@SILP catalysts to hydrogenate 6‐membered aromatic rings is found to experience a remarkable sharp switch in a narrow composition range between Co$_{25}$Rh$_{75}$ (full ring hydrogenation) and Co$_{30}$Rh$_{70}$ (no ring hydrogenation).

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

ChemCatChem 13, (2021). doi:10.1002/cctc.202100649 special issue: "Hot Topic: Carbon Dioxide", Published by WILEY-VCH Verlag, Weinheim

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

Molecules 25(15), 3330 (2020). doi:10.3390/molecules25153330, Published by MDPI22525, Basel

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

Catalysis science & technology 9(22), 6370-6378 (2019). doi:10.1039/C9CY01738K, Published by RSC Publ., London

Green chemistry 21(23), 6299 - 6306 (2019). doi:10.1039/C9GC02555C, Published by RSC, Cambridge

This report provides perspectives on CO2 utilisation from a variety of angles: interviews with scientists, essays on business, environment and social impact, as well as stories from CO2-utilising companies. While the authors’ views differ on whether and how CO2 utilisation could be done, all agree that large-scale CO2 utilisation would have a significant impact: It could not only change the way fossil resources and renewable energies are used, but CO2 utilisation could even lead to market changes in chemicals, fuels and materials and to new value chains. Such a fundamental societal change requires favourable preconditions in the four fields of technology, market, societal impact and policy. The future impact of CO2 utilisation remains to be decided. Whether utilisation markets will be niche or large-scale is debated and dependent on the right requirements.

Beilstein journal of organic chemistry 11, 675-677 (2015). doi:10.3762/bjoc.11.76, Published by Beilstein-Institut zur Förderung der Chemischen Wissenschaften, Frankfurt, Main

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, 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

Early-Late heterobimetallic (ELHB) transition metal complexes offer unique perspectives in small molecules activation reactions due to the bifunctionality of the metal atoms involved. One identified strategy in order to direct and stabilize ELHB assemblies is to take profit of bifunctional bridging ligands featuring two distinct coordination motifs: one hard, able to form strong bonds with electrophilic early metal centers and one soft nucleophilic site featuring a strong affinity for electron rich late metal centers. In most examples of bifunctional ligands reported to date in the literature, the late-metal donor is a phosphine-derived moiety. N-Heterocyclic carbenes (NHCs) have evolved as a substitute to phosphine ligands due to their relatively easy synthesis and ability to form stable and strong metal complexes when compared to phosphines. Moreover, a versatile range of functionalized NHCs could be synthesized by incorporating wide variety of functional groups in the NHC backbone. Surprisingly, very few ELHB complexes supported by bifunctional NHC ligands have been reported to date. Hence, the aim of this PhD work is to report the synthesis of tantalum-rhodium ELHB complexes utilizing the bifunctional NHC ligands. The efficient, scalable, simple and versatile synthesis of a new unsymmetrical hydroxyl-tethered NHC has been developed. The exact structure of the free ligand platform has been investigated in detail: the analyses reveal that this ligand adopts a neutral hydroxyl-carbene form that features an unusual OH-carbene hydrogen-bonding interaction. This ligand platform was successfully used to yield rare examples of Ta-NHC complexes, as well as a series of Rh-NHC monometallic species. The potential of these derivatives for the preparation of Ta/Rh heterobimetallic assemblies was then explored through either i) the protonolysis reaction between the free hydroxyl pendant group in the monometallic Rh complex and the alkyl moiety from tantalum precursors or ii) the incorporation of Rh into Ta-NHC complexes through carbene transmetallation from Ta to Rh. Mitigated results were obtained in the case of tantalum alkylidene derivatives, likely due to the high reactivity of this chemical motif. However, well-defined NHC-based Ta/Rh heterobimetallic entities were obtained in the case of Ta-imido or Ta-siloxy alkyl derivatives. This showcases the utility of this bifunctional alcoxy-carbene motif to promote the assembly of the two metals, due to the preferred coordination of the “soft” carbene ligand moiety to Rh while the “hard” alkoxy ligand group is selective to Ta. The insight obtained from the reactivity in solution with molecular silanols was utilized to develop rare examples of silica-supported tantalum-rhodium ELHB complexes. Finally, as a prospective exploration of a potential reaction of interest; computational study for nitrogen activation to NH3 was carried out using the homogeneous bimetallic complex. The first few steps of the catalytic cycle involve the transfer of hydride from the rhodium center to the tantalum bound ƞ2-N2 and are energetically favorable i.e., the transition states and the local minima energies are below 30 kcal.mol-1. This work opens attractive perspectives for small molecules activation by ELHB species, and future work will focus on the implementation of the N2 activation in laboratory using the silica-supported complexes, Les complexes de métaux de transitions hétérobimétalliques “Early-Late“ (ELHB) offrent des perspectives uniques pour les réactions d’activation de petites molécules grâce à la bifonctionnalité des atomes métalliques mis en jeu. Une des stratégies identifiées afin de diriger et de stabiliser ces assemblages hétérobimétalliques “Early-Late” est de tirer parti de ligands pontants bifonctionnels se caractérisant par la présence de deux fonctions coordinnantes distinctes : une fonction dite “dure”, capable de former des liaisons fortes avec des métaux précoces électrophiles ; et une fonction dite “molle”, exhibant une forte affinité pour les métaux tardifs riches en électrons. Dans la plupart des exemples de ligands bifonctionnels reportés dans la littérature à ce jour, le site donneur pour les métaux tardifs est de type phosphine. Les Carbènes N-Hétérocycliques (NHCs) sont devenus un substitut aux ligands phosphines grâce à leur synthèse relativement aisée ainsi qu’à leur propension à former des complexes métalliques stables et robustes comparés aux phosphines. De plus, une gamme étendue de NHCs fonctionnalisés peut être obtenue par l’introduction d’une grande diversité de groupements fonctionnels sur le squelette du NHC. De manière surprenante, très peu de complexes ELHB supportés par des ligands NHC bifonctionnels ont été reportés dans la littérature jusqu’à présent. Par conséquent, l’objectif de ce travail de thèse est de reporter la synthèse de complexes ELHB à base de Tantale-Rhodium comportant des ligands NHC bifonctionnels. Une méthode efficace, extensive, simple et polyvalente d’un ligand NHC asymétrique présentant un bras hydroxyde a été développée. La structure exacte de ce ligand libre a été examinée : les analyses ont relevées que ce ligand adopte une forme neutre carbène-hydroxyde contenant une liaison hydrogène atypique Ccarbène-HO. Cette plateforme moléculaire a été utilisée avec succès pour la synthèse presque inouïe de complexes Ta-NHC, ainsi qu’une série de complexes Rh-NHC monométalliques. Le potentiel de ces dérivés pour la préparation d’assemblages hétérobimétalliques Ta/Rh a été exploré, soit par i) la réaction de protonolyse entre le groupement hydroxyle libre contenu dans le complexe monométallique de rhodium et le groupement alkyle des précurseurs de tantale, ou par ii) l’incorporation de Rh dans le complexe Ta-NHC via une transmétallation du carbène depuis le tantale vers le rhodium. Des résultats mitigés ont été obtenus dans le cas des dérivés de tantale- alkylidènes, probablement dus à la forte réactivité de cette entité chimique. Cependant, des édifices ELHB bien définis, à base de Ta/Rh et supportés par un NHC ont été obtenus dans le cas des dérivés de Tantale-imido ou siloxy-alkyle. Cela valorise l’utilité de ce motif alcoxy-carbène à promouvoir l’assemblage de ces deux métaux via la coordination préférentielle du ligand “mou” carbénique sur le Rh tandis que le groupement coordinant hydroxyle “dur” est sélectif vis-à-vis du tantale. Les informations obtenues à partir de la réactivité en solution avec des silanols moléculaires ont été utilisées pour développer des exemples rares de complexes ELHB tantale-rhodium supportés sur silice. Finalement, en tant que perspective exploratoire d’une réaction potentielle d’intérêt, une étude computationnelle de l’activation de diazote et sa conversion en ammoniac a été réalisée en utilisant le complexe bimétallique homogène. Les premières étapes du cycle catalytique impliquent le transfert d’hydrures depuis le rhodium vers la liaison η2-N2─tantale, ses étapes sont énergétiquement favorables c’est-à-dire que les états de transition ainsi que les minima locaux d’énergie sont en deçà de 30 kcal∙mol-1. Ces travaux ouvrent des perspectives intéressantes pour l’activation de petites molécules par des espèces ELHB. De futurs travaux se concentreront sur la mise en œuvre de l’activation de N2 au laboratoire en utilisant des complexes supportés sur silice

Dissertation, RWTH Aachen University, 2020; Aachen 1 Online-Ressource (XV, 188, X Seiten) : Illustrationen (2020). = Dissertation, RWTH Aachen University, 2020, The overriding topic of this dissertation is the correlation of computerchemical and experimental methods in homogeneous catalysis. A variety of Ru-PNP-pincer complexes are applied as pre-catalysts in three different hydrogen-transfer reactions. In addition to an experimental optimization, the aim is to uncover and understand reaction mechanisms and calculate the respective catalytic cycles. By comparison of experimental and computerchemical results, an evaluation of the computerchemical method in respect to the prediction of catalyst activities is performed. This contributes to the assessment of the reliability of the computerchemical method, which might be the foundation of further work in the field of predictive computation in homogeneous catalysis. The long-term goal is to predict the effects of electronic and steric modifications in catalysts in respect to their activity and selectivity. The reactions optimized in the course of this thesis differ from each other in the way of complexity, wherein product diversity and side reactions are the most prominent aspects: While the hydrogenation of CO2 in the presence of triethylamine to formate presents a relatively limited product variety, the complexity of the reactions in the ensuing chapters rises respectively. Already the hydrogenation of benzonitrile poses the difficulty of yielding the primary and secondary amine beside the imine and other side-products. Lastly, the hydrogen transfer reaction in the silylation of 4-methylpyridine shows a variety of products and also a more complex set of reactants, which poses a greater challenge in the computational work as well as the applied analysis of the reaction. An Evaluation of the reliability of the results of each reaction allows for an assessment of the applicability of the computerchemical method in comparable experiments., Published by 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 (XV, 240 Seiten) : Illustrationen, Diagramme (2020). = Dissertation, RWTH Aachen University, 2020, Aromatic dicarbamates provide a phosgene-free access to the corresponding diisocyanates which are utilized in large quantities as industrial important building blocks in polyurethane chemistry. It is particularly beneficial to use the thermodynamically stable greenhouse gas CO2 for carbamate synthesis. For this purpose methyl formate (MF) can be efficiently produced by CO2 hydrogenation integrated with the subsequent esterification of formic acid with methanol. In this thesis, the oxidative carbonylation of toluene-2,4-diamine (TDA) using MF was investigated in detail. An HPLC-analysis method has been developed which allows the quantification of the target product methyl-toluene-2,4-dicarbamate (TDC) separately from side products in the reaction mixture. An extensive analysis of the product spectrum has provided detailed insight into the complex reaction network, pointing out that the side products are caused by three different reaction paths: N-formylation by MF, electrophilic aromatic substitution/condensation with in situ formed formaldehyde, and N-methylation by in situ formed dimethyl carbonate (DMC). The most prominent side product has been identified as "TDCCH2TDC" (5), which is also an interesting precursor for applications in polyurethane chemistry. However, N-methylations are irreversible and lead to unproductive and undesired compounds, therefore the dual reactivity of DMC must be shifted towards carbamate synthesis. The influence of the catalyst on product distribution was evaluated for PdCl2/CuCl2 and eleven heterogeneous Pd-catalysts. Pd(5%)/ZrO2 showed the highest productivity, closely followed by Pd(5%)/CeO2. Both oxidic support materials were found to partially suppress undesired side reactions leading to higher yields of TDC. Additionally, it turned out that the ratio of TDC and "TDCCH2TDC" (5) is significantly affected by the choice of the support. Furthermore, this synthetic method was extended to the synthesis of dicarbamates from 4,4'-methylenedianiline (MDA) and 2,4-diaminomesitylene (17)., Published by Aachen

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020; Aachen 1 Online-Ressource (XXI,172,71 Seiten) : Illustrationen, Diagramme (2020). = Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020, This thesis deals with the synthesis of P-stereogenic phosphine-phosphorodiamidite-ligands based on chiral amino alcohols as well as their application in the synthesis of rhodium(I)-complexes and in asymmetric catalysis.In the first part, the synthesis of tridentate diphosphine-phosphorodiamidite ligands on the basis of Betti bases was envisaged. These BettiPhos ligands provide a stereogenic phosphorus as characteristic element. The introduction of a phosphine group into the Betti-Base backbone via the amine and the aldehyde building block was investigated first. Moreover, tridentate BettiPhos ligands were synthesized and isolated based on bis(diphenylphosphinophenyl)amines via a multi-step synthesis. The ligands were analyzed regarding their stereochemistry and the isomerization kinetics of the stereogenic phosphorus was investigated via VT-NMR spectroscopy to generate a general understanding concerning the stereochemistry of these compounds. The new ligands were tested in their complexation of rhodium(I) and [Rh(nbd)(PPP)]BF4 complexes were isolated. The complexes were characterized using XRD analysis and the absolute configuration around the stereogenic phosphorus was confirmed via their crystal structure. These complexes showed a distorted trigonal-bipyramidal or a distorted square-planar geometry, respectively, containing a facial coordinating P,P,P-ligand. Moreover, the conversion of the tridentate BettiPhos-ligands with [Rh(cod)Cl]2 led to a P N bond cleavage in the ligand backbone including a chloride-transfer from [Rh(cod)Cl]2 to the phosphorodiamidite group. Additionally, the bis(diphenylphosphinophenyl)amine fragment was coordinating to rhodium in the manner of a PNP-pincer ligand. One of these obtained [Rh(PNP)(P*)] type complexes could be crystallized showing a distorted square-planar structure. In the second part of this thesis, P-stereogenic, bidentate Phosphine-Phosphorodiamidite ligands were synthesized based on ephedrine, a naturally abundant chiral amino alcohol. These bidentate ligands could be obtained via condensation of ephedrine with PCl3 and a chiral phosphine amine. One ligand was successfully crystallized and the absolute configuration of the stereogenic phosphorus was confirmed via XRD analysis. The ligands were converted to the corresponding cationic [Rh(cod)(PP)]+ complexes using [Rh(acac)(cod)]BF4 or [Rh(cod)Cl]2 precursors and then applied in asymmetric catalysis. In rhodium-catalyzed asymmetric hydroformylation of styrene and vinyl acetate only low enantioselectivity of about 15% ee could be achieved. In rhodium-catalyzed asymmetric hydrogenation of dimethyl itaconate and methyl-2-acetamido acrylate good enantioselectivities of up to 95% ee could finally be reached., 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

The present Ph.D. thesis was focused on the development of advanced technics for ammonia synthesis with sustainable methods, i.e. electrocatalytic processes using N2, H2O and renewable energy as input sources. Implementing this technology will thus result in a breakthrough change towards a sustainable, low-carbon chemical production based on the use of renewable energy sources. There is thus a rising interest in fossil-fuel-free direct ammonia synthesis. A flow electrochemical cell was developed for ammonia synthesis directly from water and N2 at room temperature and atmospheric pressure. Iron supported on carbon nanotubes (CNTs) was used as the electrocatalyst in this hemi-cell. An ammonia formation rate of 2.2×10-3 gNH3·m-2·h-1 was obtained at room temperature and atmospheric pressure in a flow of N2, under an applied potential of -2.0 V vs. Ag/AgCl. This value is higher than the ammonia formation rate obtained using noble metals (Ru/C) under comparable reaction conditions. Furthermore, hydrogen gas with total Faraday efficiency as high as 95.1% was obtained. Reaction condition was optimised with Fe2O3-CNT used as electrocatalyst. A 30% wt iron-oxide loading was found to be optimal. The performances greatly depend on the cell design, where the possibility of ammonia crossover through the membrane has to be inhibited. The reaction conditions also play a significant role. The effect of electrolyte (type, pH, concentration) was investigated in terms of current density, rate of ammonia formation and Faradaic efficiency in continuous tests up to 24h of time on stream. A complex effect of the applied voltage was observed. An excellent stability was found for an applied voltage of -1.0 V vs. Ag/AgCl. At higher negative applied voltages, the ammonia formation rate and Faradaic selectivity are higher, but with a change of the catalytic performances, although the current densities remain constant for at least 24h. This effect is interpreted in terms of reduction of the iron-oxide species above a negative voltage threshold, which enhances the side reaction of H+/e- recombination to generate H2 rather than their use to reduce activated N2 species, possibly located at the interface between iron-oxide and functionalized CNTs. Active sites for ammonia synthesis was also explored. We show here that, contrary to expectations, iron-oxide (Fe2O3) nanoparticles (supported over carbon nanotubes - CNTs) result more active in the direct electrocatalytic synthesis of ammonia from N2 and H2O than the corresponding samples after reduction to form Fe or Fe2N supported nanoparticles. A linear relationship is observed between the ammonia formation rate and the specific XPS (X-ray- photoelectron spectroscopy) oxygen signal related to O2- in Fe2O3 species, which is proofed by both chemically and electrochemically reduced samples. HRTEM (high-resolution transmission electron microscopy) data on the changes during the electrocatalytic tests confirmed that in-situ activated sites for ammonia synthesis were formed, due to the reconstruction of iron oxide particles. This opens new possibilities to understand the reaction mechanism under working conditions and design more efficient electrocatalyst for ammonia synthesis. Homogenous catalysts for ammonia synthesis was also explored. A series of ruthenium complexes were tested using the same conditions. Ru(PNP)Cl2 (PNP: 2,6-Bis[(di-tert-butylphosphanyl)methyl]pyridine) was found to be the best catalyst for ammonia synthesis among the series of analyzed complexes. This complex was also tested using different conditions, and it was found that suitable amounts of acetic acid can increase its catalytic performance. Comparing different compositions of nitrogen and hydrogen loadings, it was found that the ammonia formation rate increases with increasing nitrogen loading, from which we can deduce that activation of hydrogen was not the rate limitation step in these conditions.

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 University, 2019; Aachen 1 Online-Ressource (150 Seiten) : Illustrationen (2019). = Dissertation, RWTH Aachen University, 2019, The purpose of the thesis is the catalyzed functionalization of alkynes, alkenes and arenes via hydroboration, hydrosilylation and borylation. Initial, several new ruthenium acriphos complexes were synthesized and characterized. The ruthenium acriphos complexes can catalyze Z-selective hydroboration of terminal alkynes with pinacolborane in the presence of potassium tert-butoxide as an activator. Moreover, they can catalyze stereodivergent hydroborations of terminal alkynes depending on the activation method to form a range of vinylboronate esters with high but opposite stereoselectivity. Mechanistic studies and proposed catalytic cycles in the stereodivergent hydroboration of terminal alkynes were investigated and proposed. Arenes can be also reactive with ruthenium acriphos complexes and form the corresponding products in 50%-70% yield. However, ruthenium acriphos complexes did not give any selectivity of the hydrosilylation in despite of complete conversion of model compound., 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 ( XVII, 193 Seiten) : Illustrationen (2018). = Dissertation, RWTH Aachen University, 2018, Central theme of this work is the homogeneously catalyzed use of carbon dioxide (CO2) as a raw material or synthesis component, especially in combination with a sustainable reducing agent such as hydrogen (H2). In the first chapter of the thesis, the synthesis of lower and higher carboxylic acids with molecular rhodium compounds starting from non-activated alkenes and in the beginning also with oxygenated substrates is discussed. To understand the reaction, a systematic reaction development is to be pursued by using a close link between optimization and understanding of the various parameters. The aim is to obtain as complete picture as possible of the transformation, which is the prerequisite for a later rational catalyst design. On that way e.g., the choice of ligands with their different steric and electronic properties and the central atom play a crucial role. In this chapter, additional aspects (solvents, partial pressures, additives, promoters) of the developed catalyst system for the formal hydrocarboxylation are explored to provide in-depth information on the course of the reaction. Here, the actual formal hydrocarboxylation is understood as a sequence of a reverse water gas shift reaction (rWGSR) and a conventional hydroxycarbonylation in two interlocking processes and studied systematically. Subsequently, investigations are carried out on potential involved molecular rhodium compounds. In the second chapter of this thesis, based on the combination of CO2 and H2, a formal hydromethylation of cyclohexene with molecular ruthenium compounds, which has not previously been realized in this form, is treated. Core aspect here is also, as in the first chapter, a reverse water-gas shift reaction, but this time in combination with a hydroformylation and the consecutive, complete reduction to the corresponding hydrocarbon compound (methylcyclohexane). In order to simplify the realization of this reaction initially, synthesis gas is used successively instead of CO2 and H2 and systematically optimized for an understanding of the reaction process. Subsequently, first investigations on this transformation are carried out in their entirety based on CO2 and H2., 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 (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

Dissertation, RWTH Aachen University, 2018; Aachen 1 Online-Ressource (VI, 166, xvii) : Illustrationen (2018). = Dissertation, RWTH Aachen University, 2018, Fe-air batteries provide a most promising, resource-efficient battery concept with superior power densities compared to state-of-the-art Li-O2- and potentially superior specific energies compared to Li-ion batteries. However, although alkaline Fe-air batteries have been under repeated consideration over the past five decades, they still require considerable research and development. Among other things, the limited rechargeability of the iron electrode imposes a considerable bottleneck for the broad implementation of commercial cells. Contributing to the development of rechargeable Fe-air batteries, in this dissertation the electrochemistry of model-like and applicable, i.e., plane and porous iron electrodes in concentrated alkaline electrolyte is investigated. At this, under-standing charge-transfer reactions at the anode-electrolyte interface as well as fundamental electrode processes for porous iron-anodes is the key to develop high-performance cells. Over the course of this thesis it is established that the performance of iron electrodes in concentrated alkaline electrolyte hinges on the existence and the continuance of the solute intermediate reaction products, which, eventually, produce a thin but essential redox-layer on the iron electrode surface. With respect to this, it is shown by the application of chelating agents for iron ions in aqueous media that the electrochemistry of iron becomes irreversible as soon as the intermediate reaction products are removed from the equilibrium between electrode and electrolyte. Furthermore, by a dedicated in-situ electrochemical atomic force microscopy (EC-AFM) study it is shown that the evolution of the precipitating redox-layer proceeds discontinuously on preferential precipitation sites during the oxidation and reduction of the iron electrode. The latter particularly explains the extraordinarily increasing discharge capacity of pristine iron electrodes upon repeated galvanostatic cycling, which is investigated for both plane and porous iron anodes. Given the repeated dissolution and precipitation of iron in concentrated alkaline electrolyte, the surface area of iron electrodes gradually increases in every cycle and may repeatedly be discharged, if the previous recharge step was complete. Due to that, comparatively simple, surface reaction-confined iron electrodes may store tremendous amounts of energy already (here: up to 225 mAh·gFe-1)) and may reversibly provide decent specific power of up to 280 mW·gFe-1., Published by Aachen

Dissertation, RWTH Aachen University, 2018; Aachen, 1 Online-Ressource (IX, 187 Seiten) : Illustrationen, Diagramme (2018). = Dissertation, RWTH Aachen University, 2018, Process analytical technology (PAT) provides powerful tools to gather inline data of chemical processes; this data is most commonly used to optimize the processes in the process industry. PAT is not yet frequently used as a resource in R&D despite the significant advantages of early process optimization. Particularly in the field of biomass valorization, early development is required in order to successfully develop reaction systems which have to compete with heavily optimized processes from the petrochemical value chain. A methodology to evaluate kinetic parameters of biomass transformations employing PAT is presented. These kinetic parameters are then used to optimize a reaction by means of reaction engineering. Hereby, the transformation reactions represent the value chain of a biorefinery based on lignocellulose. The first step is the conversion of biomass to platform chemicals and the second step are further conversions to higher value products with desired properties. The dehydration of xylose to furfural was chosen as model systems for the first step and the hydrodeoxygenation of 5-hydroxymethylfurfural (5-HMF) to 2,5-dimethylfuran (2,5-DMF) represents the second step. The salient feature of the presented strategy involves the determination of reaction rates and activation energies for biomass conversions under process conditions without influence from occurring side reactions or fouling of optical probes. PAT was applied to the dehydration of the C5-sugar xylose to the platform chemical furfural. The reaction was comprehensively monitored in situ with ATR mid-IR and Raman spectroscopy at different reaction temperatures. The reaction kinetics for the dehydration of xylose to furfural and the side reaction of humin formation were simultaneously evaluated by chemometric and kinetic modeling of the inline data. This insight allowed for the proposal for an optimized reactor concept: a continuous reactor design to maximize the yields of furfural and minimize the production of humins. This continuous reactor was implemented and resulted in an improved selectivity towards furfural while using high reaction temperatures and short residence times. ATR UV/Vis, ATR mid-IR and Raman spectroscopy were used to monitor the hydrodeoxygenation of 5-HMF to 2,5-DMF under process conditions at different temperatures. The suitable PAT tools provided kinetic data and the data was evaluated by chemometric and kinetic modeling to show the activation energies of this reaction system. The kinetic modeling of the three in-process spectral data revealed the activation energy of 5-HMF consumption. The same methodology was used to investigate the pathways to 2,5-DMF via the intermediates. The gained knowledge allowed to determine the preferred pathway of this reaction system, which is first the hydrogenolysis towards 5-methylfurfural and subsequently the hydration to (5-methyl-2-furyl)methanol and then the hydrogenolysis towards 2,5-DMF.By using PAT tools in the field of research, especially in the field of biomass valorization, a system cannot only be optimized by in-process data, but this methodology also leads to a proven concept regarding the use of PAT for a subsequent production plant., 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