Investigation of the Reactivity of Dioxygen with Copper Complexes in Homogeneous and Heterogeneous Phases
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Benzaldehyde is an important basic compound in the chemical industry. However, established synthetic processes still have some disadvantages such as high resource consumption and non-selective material conversion. In the context of advancing green chemistry, there is a necessity of a more resource-conserving method for selective syntheses. ... Biological systems for activating atmospheric oxygen, such as copper-containing enzymes, are promising models to be industrially used a selective oxygenation by means of model complexes. However, so far only a low material conversions and high catalyst consumption have been achieved, so that further research in this area is essential. For this reason Chapter 3 extends the concept of dioxygen activation by copper complexes with tripodal ligands. The ligand (2-aminoethyl)bis(2-pyridylmethyl)amine (uns-penp) was bound covalently to silica gel for this purpose. The immobilization should counteract the self-decomposition and promote the formation of a stable end-on superoxido species. Here, the resulting copper complexes showed reversible oxygen binding through the formation of a dark green solid at -80 °C. Oxygenation of toluene to benzaldehyde could be carried out by suspending the oxygen species in toluene. Mobile complexes with uns-penp derivatives as comparison resulted in higher conversions, but offered a lower purity of the product mixture. Chapter 4 deals with the derivatization of the uns-penp ligand at the terminal nitrogen atom and its influence on the oxygen activation. Identical aliphatic groups and the attachment of ferrocene as well caused a passivation of the solid complex. However, different aliphatic substituents usually led to a reversible oxygen attachment, though the resulting species could not be finally characterized. Substitution of an ethyl- and an isopropyl residue allowed the rapid formation of an end-on peroxido complex in the solid state. In contrast to similar compounds the crystal structure remained almost unchanged during the reaction, which allowed a characterization by X-ray crystallographic analysis.