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Abstract New liquid cobalt salts were synthesized and characterized during this master thesis. In order to synthesize these liquid cobalt salts, cobalt(II) was coordinated by neutral ligands and combined with weakly coordinating anions. Different types of neutral ligands were used. The most important ones were 1-alkylimidazoles with a varying alkyl chain length from C1 to C12, amides (N,N-dimethylacetamide, 1-ethyl-2-pyrrolidone) and diamines (1,10-phenantroline). Two different anions were used: bis(trifluoromethylsulfonyl)imide (bistriflimide, Tf2N-) and methanesulfonate (mesylate, OMs-). Bistriflimide was the most appropriate anion since the liquid cobalt salts with this anion had the lowest melting points and viscosities. Complexes with many different ligands and bistriflimide or mesylate anions were synthesized and characterized with CHN, DSC, IR, viscometry, XRD. One of the goals of this thesis was to investigate the influence of the alkyl chain length of the 1-alkylimidazole ligands on the melting point of [Co(AlkIm)6][Tf2N]2- and [Co(AlkIm)6][OMs]2-complexes A general trend can be observed for the melting points of the [Co(AlkIm)6][Tf2N]2-complexes. The melting points first decrease in the series (C1 to C8) because as the alkyl chain on the ligand becomes longer, the crystal packing becomes less compact and the cation-anion interactions become weaker. If the alkyl chains becomes even longer, the melting point increases again due to the Van der Waals interactions between those chains. A second trend that is observed is an alternating odd-even effect for the melting points of the [Co(AlkIm)6][Tf2N]2- and [Co(AlkIm)6][OMs]2-complexes. The complexes with odd-numbered alkyl chains systematically have a lower melting point than the complexes with even-numbered alkyl chains. For instance, the complexes with 1-propylimidazole ligands have a significantly lower melting point than the complexes with 1-ethylimidazole and1-butylimidazole ligands. For the [Co(AlkIm)6][Tf2N]2-complexes, the odd-even effect fades out at higher chain lengths. The liquid cobalt salts with the lowest melting points and viscosities were characterized with electrochemical methods. The possibility to deposit cobalt layers from these liquid cobalt salts was investigated as well as the reversibility of the Co(II)/Co(III) couple to test their potential use as electrolytes in redox flow batteries. Two liquid cobalt salts with amide ligands were characterized: [Co(NEP)6][Tf2N]2 and [Co(DMAc)6][Tf2N]2. It was possible to deposit smooth and homogeneous thick cobalt layers from these electrolytes. However, it was not possible to oxidize Co(II) to Co(III). Instead, the anodic decomposition of the ligand or anion was observed. Three liquid cobalt salts with 1-alkylimidazole ligands were characterized: [Co(PrIm)6][Tf2N]2, [Co(HeIm)6][Tf2N]2 and [Co(DoIm)6][Tf2N]2. It was possible to reduce Co(II) to Co(0) but only very thin and inhomogeneous cobalt layers could be obtained from these electrolytes. Instead, most of the cathodic current was used to form cobalt nanoparticles, which was verified by TEM experiments It was not possible to observe the Co(II)/Co(III) couple in [Co(HeIm)6][Tf2N]2 and [Co(DoIm)6][Tf2N]2. In [Co(PrIm)6][Tf2N]2, Co(II)/Co(III) couple could be observed but it was only partially reversible.

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Although the majority of scientists recognize the ecological impact of anthropogenic carbon dioxide, emissions are still increasing, mainly due to deforestation and burning of fossil fuels. In order to effectively reverse this process several parallel approaches are required. One interesting strategy consists in making carbon dioxide into a valuable resource for the production of fuels and chemicals, in an effort to close the carbon cycle. Carbon dioxide has a high thermodynamic stability, making it difficult to process in conventional thermocatalytic systems. However, an energy-efficient one-electron reduction allows to activate this highly stable molecule under mild and safe conditions. This work shows how carbon dioxide can be used as carbon source for the production of valuable carboxylic acids, through incorporation in organic substrates. The continuous and rapid improvement in electricity production from renewable resources (wind, water, sun, …) makes organic electrosynthesis into a very interesting and green alternative for traditional chemical processes. This synthetic strategy offers valorization routes for a wide range of renewable reactants.A first part focuses on the electrocarboxylation of conjugated dienes in the production of valuable dicarboxylic acids, which are potential polymer building blocks. The use of sacrificial anodes and careful optimization of reaction conditions allow to dicarboxylate internal conjugated dienes with good to excellent yields. Efficient CO2 fixation in conjugated linoleic acid is established for the first time, opening routes to other renewable dienes. The effect of molecular configuration and alkyl substitution on electrocarboxylation efficiency was studied.In a second part, an innovative, more sustainable, pathway was devised and elaborated for a related reaction, using an inert anode. A paired electrosynthesis of diacid and diol precursors from dienes and CO2 allows to increase the current and atom efficiency of the process. With tetraethylammonium trifluoroacetate both as electrolyte and reactant, 1,3-cyclohexadiene was converted to a dicarboxylate and diacetate product in a one-compartment setup. However, the reactivity of conjugated double bonds towards carboxylation and acetoxylation is highly dependent on alkyl substitution, complicating extension to other conjugated dienes.As a follow-up, a new paired electrosynthesis method was designed, allowing to convert carbon dioxide and alcohols into useful α-hydroxy acids, using inert electrodes. Anodic oxidation of alcohols to carbonyls and simultaneous cathodic carboxylation of these carbonyls with CO2 produces one sole product. Preliminary tests transformed 1-phenylethanol and benzhydrol to useful pharmaceutical intermediates in a one-compartment cell.A bromide-assisted decarboxylation of amino acids further demonstrates the potential of organic electrosynthesis in the valorization of renewable substrates. A wide range of naturally occurring amino acids can be converted efficiently to valuable nitriles in a single step, using bromide salts both as redox mediators and supporting electrolyte. Furthermore, the selectivity of the decarboxylation process can be tuned towards nitriles, amines or amides.In a last part, the electrochemical decarboxylation of amino acids with electrogenerated hypobromite was subjected to an electroanalytical study. By means of cyclic voltammetry, spectrophotometry and rotating ring disk electrode measurements, the effect of solvent, electrolyte and electrode material is confirmed and investigated. The water fraction and intrinsic acidity have a large effect on the hypobromite concentration. An efficient process is realized by finding a good balance between this concentration and the amino acid solubility.