As described in Chapter 1, the cobalt(II) complex Bis[3-(salicylidenimino)-propyl]methylaminecobalt(II), [Co(salmdpt)] can bind dioxygen reversibly and forms a cobalt(III) superoxido complex during this process.One topic of the present work was the investigation of the dioxygen activation on cobalt complexes and the characterization of the dioxygen adduct complexes of the ligand saldptH2 and its derivatives.To synthesize the cobalt(III) superoxido complex of [Co(salmdpt)] different solvents were used. With acetonitrile, butyronitrile and dichloromethane only the cobalt(II) complex of the ligand salmdptH2 was obtained. From toluene the precursor complex could be crystallized with an additional solvent molecule in its molecular structure. Variation of the reaction conditions in toluene caused formation of a cobalt(III) hydroxido complex instead of the cobalt(III) superoxido complex. When benzene was used as solvent, a black powder could be obtained. Based on infrared spectra it is most likely that here the superoxido complex was formed (however, no crystals could be obtained in contrast to the report in the literature). It is interesting to note that even though the crystal structure of the superoxido complex had been obtained so far no spectroscopic characterization (IR or Resonance Raman) of this complex type has been reported. During further experiments in acetonitrile crystals of a cobalt(III) cyanido complex were obtained. Performing the reaction in butyronitrile, allowed furthermore to detect propionaldehyde as a product.In co-operation with the group of Prof. Maison it was tried to synthesize aldehydes from adamantane nitriles. The results demonstrated that these reactions are possible. However, there is still need for improvement in regard to yields and optimization of the reaction conditions.Due to the fact that the experiments did not allow to obtain the cobalt(III) superoxido complex the ligands saldptH2 and salmdptH2 were modified by adding two tert-butyl groups in 3rd and 5th position to the aldehyde group of each salicylaldehyde moiety. Here it was assumed that these additional steric effects might improve the formation of an end-on cobalt superoxido complex.Reactions of the cobalt(II) complex with the ligand 3,5-Di-tert-butyl-saldptH2 and dioxygen leads to a dimeric peroxido bridged complex. Keeping in mind that cobalt(II) complexes with the ligand saldptH2 only form peroxido complexes, this result is not surprising. In contrast [Co(3,5-Di-tert-butyl-salmdpt)] did not react with air or dioxygen and only crystals of the starting material, the cobalt(II) complex, could be obtained.As described in the introduction NO metal complexes are interesting in comparison with dioxygen adduct compounds. Thus it was clear to also react [Co(salmdpt)] with NO. In contrast to the reaction with dioxygen the reaction with nitrogen oxide led to crystals of [Co(salmdpt)NO] suitable for X-ray analysis. In comparison with a nitrogen monoxide complex of cobalt salen [Co(salen)NO] and the superoxido complex of [Co(salmdpt)] the selected bond lengths and angles are similar. Both complexes [Co(salen)NO] and [Co(salmdpt)O2] are already known in the literature.The formation of a cobalt(III) cyanido complex described above most likely is based on a cobalt(IV) oxido complex as a reactive intermediate. While such a species already has been fully-characterized in related iron chemistry the according cobalt complex could not be obtained so far. Therefore, it was tried to use known methods to isolate this species. For different metal complexes it has been possible to obtain oxido complexes from the according nitro, nitrate or ozonido complexes. Here for example radiation leads to loss of NO, NO2 or O2 and thus leaving the according oxido complexes. The cobalt nitrito complex, [Co(salmdpt)NO2], was synthesized and could be structurally characterized. Unfortunately in this complex the nitrite is coordinated through the nitrogen atom and not through the oxygen atom. Therefore this complex could not be used for this purpose.Furthermore, it was tried to obtain the according ozonido complex. While it was not possible to synthesize this complex in pure form low temperature stopped-flow measurements indicated the formation of this complex.
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