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Abstract

This thesis deals with the study of the properties of bispidine iron(IV)-oxo complexes. These are biomimetic model compounds for non-heme iron enzymes. The first part describes the thermal spin crossover behavior of the tetradentate bispidine ligands’ iron(II) complexes. These compounds were precisely characterized using UV-vis-NIR and Mößbauer spectroscopy as well as Evans NMR spectroscopy and SQUID measurements. The tetradentate bispidine ligands’ iron(IV)-oxo complexes were characterized using UV-vis-NIR and Mößbauer spectroscopy. They were also analyzed computationally with DFT calculations. In addition, it was possible to characterize a high spin iron(IV)-oxo species by Mößbauer spectroscopy. This species’ electron transfer properties were analyzed. The second part of this study is about the photocatalytic generation of an iron(IV) oxo species with water as oxygen source. [RuII(bpy)3] 2+ was used as a photosensitizer. After irradiating it with visible light it was oxidized with [CoIII(NH3)5(MeCN)] 3+ to [RuIII(bpy)3] 3+, which catalytically generates in situ an iron(IV)-oxo species with water as source of oxygen. This reaction is also interesting with regard to environmental issues as it seems promising to use solar energy to produce highly energetic species. The third part of this study covers the redox properties of the pentadentate bispidine ligands’ ferryl complexes when the redox inactive metal ion Sc3+ is present. The presence of Sc3+ shifts the redox potential of the ferryl complex to higher potentials. This effect can be used to manipulate the electron transfer properties of the ferryl compound. This FeIV(O)- Sc3+ complex can serve as a model compound for the Mn4CaO5 cluster in the photosystem II. The last part of this study is about the non heme iron-oxo-catalyzed methanogenesis. The ferryl complexes of the tetra- and pentadentate bispidine ligands produce methane from methionine and other thioethers. In the first step of the process, methionine is oxidized to methionine sulfoxide. A bifurcation of the reaction pathway to a sulfone or methyl radical production marks the second step of the process. The generation of methyl radicals was confirmed by spin trapping experiments. By way of detailed DFT calculations it was possible to shed light on the mechanism of methane formation in a highly oxidative environment.