Selective oxidations of organic substrates using a catalyst and air as an oxidant play an important role and nature has demonstrated that these reactions in principle are possible. Therefore, chemists have been trying for some years to model the reactivity of the according metalloenzymes using low molecular weight complexes as catalysts instead. Thus hydroxylation reactions are important and are catalyzed for example by copper based enzymes such as the monooxygenase tyrosinase. This enzyme is responsible for the hydroxylation of monophenols to o-diphenols and the subsequent two-electron oxidation to o-quinones. However, so far a complete mechanism for this oxidation reaction could not be postulated. Therefore, to obtain a better understanding on this type of reaction, a Cu(I)bis(imine)complex [Cu2(DAPA)]2+ (DAPA = 1,3-bis-[(3-(N-dimethyl)propyl)iminomethyl]benzene) has been synthesized and the structure of its Cu(I) complex as well as the structure of the Cu(II) product complex exhibiting a hydroxylated ligand was analyzed and characterized. Besides the investigations on the activity of tyrosinase, efforts have been made to synthesize and characterize an oxo species in copper chemistry which is considered to be a highly reactive intermediate responsible for many oxidizing processes. However, isolation and characterization of such a species is lacking so far.
In that regard several Cu(I) complexes with nitrogen donor ligands such as bipyridine and phenanthroline and derivatives were synthesized. To further increase the reactivity of these complexes towards dioxygen olefin ligands as co ligands were used to allow facile substitution reactions. Considering "greener chemistry", there is great interest in transition metal complexes containing unsaturated compounds and their reaction behavior. In collaboration with the research group of Prof. A. deMeijere Cu(I) and Ni(0) complexes with the unsaturated hydrocarbons bicyclopropylidene and dicyclopropylacetylene were synthesized and characterized by X-ray analysis.
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