Investigation of the Reactivity of Dioxygen with Copper Complexes in Homogeneous and Heterogeneous Phases

Abstract

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.