Oxidation reactions in nature are an interesting topic since these reactions occur under ambient conditions, which is the reason why modeling these systems for industrial use has become a lucrative and well investigated field of science. Metalloenzymes with iron or copper ions located in the active site are essential compounds in nature. Therefore, in recent years, a number of iron or copper complexes have been studied as functional model complexes for these enzymes. It turned out that investigation of these complexes can be complicated, because of the instability of the dioxygen adduct complexes . In contrast to that, handling of dioxygen adduct complexes of chromium proved to be less difficult and stable chromium peroxido and oxido complexes have been reported in literature. Therefore, chromium complexes with ligands of which iron and copper complexes are already known, were investigated in this thesis. Firstly, chromium(II) complexes with the following tripodal amine ligands based on the related tren system were synthesized. The complexes [Cr(tmpa)Cl2] and [Cr(tmpa)Cl]2(BPh4)2 could be prepared according to the literature. Furthermore, spectroscopic data for the reaction of [Cr(tmpa)Cl]2(BPh4)2 with dioxygen to form a chromium(III) µ-oxido complex were reported. A chromium(III) bis(µ-hydroxido) complex [Cr(tmpa)OH]2(OTf)4 was structurally characterized. This complex is already known in literature with different counter anions. Similar to the reported chromium(II) complexes, [Cr(Me2uns-penp)Cl]2(BPh4)2, [Cr(Me6tren)Cl]Cl and [Cr(Me4apme)Cl]BPh4 were synthesized and structurally characterized. Furthermore, a chromium(III) complex [Cr(Me4apme)Cl3] was structurally characterized. The oxidation behavior of these complexes towards organic substrates like toluene was investigated. By using the complex [Cr(Me4apme)Cl]BPh4 a maximum yield (25 %) of benzaldehyde could be observed. Low temperature stopped-flow measurements led to the suggestion that the reaction of [Cr(Me4apme)Cl]BPh4 with dioxygen formed an end-on superoxido intermediate.Another object of this thesis was the investigation of dioxygen adduct complexes of chromium(II) complexes with the ligand bztpen. The starting materials [Cr(bztpen)Cl]Cl and [Cr(bztpen)(CH3OH)](OTf)2 could be structurally characterized. Based on these compounds, the reactivity towards dioxygen was investigated using low temperature stopped-flow techniques. For the reaction with [Cr(bztpen)(CH3OH)](OTf)2 the decomposition of an unknown species could be tracked spectroscopically. However, the absorption maxima could not be clearly assigned to a dioxygen adduct complex . During the reaction of [Cr(bztpen)Cl]Cl with dioxygen strong support for the formation of an end-on superoxido complex [Cr(bztpen)(O2)Cl]Cl could be obtained.Due to the fact that NO and dioxygen are isoelectronic, a comparison of NO metal complexes with dioxygen adduct complexes is very interesting. During these investigations a chromium NO complex was structurally characterized and thus useful structural information about the presence of the dioxygen intermediates was obtained. [Cr(bztpen)(NO)Cl]Cl is the first structural characterized chromium NO complex with a simple organic ligand.Moreover, the reactivity of bis(benzene)chromium toward dioxygen using organic solvents was investigated in this work. The formation of a yellow oxidation product was repeatedly observed, the structural characterization, however, repeatedly failed due to the fact that the yellow precipitate was only stable at low temperatures and decomposed to a green species after a couple of days at room temperature. Different suggestions about the structure of the yellow precipitate were made. Elschenbroich suggested that the oxidation product might be similar to the reaction of cobaltocene and dioxygen. Herein it is proposed that the oxygen is bridged between two cyclopentadienyl groups. Holthausen suggested a chromium peroxido complex based of DFT calculations. The resulting yellow precipitate could be structurally characterized as a mixed-valence chromium salt [Cr(C6H6)2]2[Cr2O7] CH3CN. Furthermore, a reaction equation for the formation of the oxidation product was suggested. GC-MS measurements and a chromium(VI) detection proved the proposed equation.
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