Untersuchungen zur Synthese und Reaktivität NHC-substituierter Cobalt-Komplexe (English shop)

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The focus of the present work was the development of the chemistry of low-valent cobalt complexes stabilised by the N-heterocyclic carbene 1,3-diisopropylimidazol-2-ylidene. With the synthesis of [Co(ImiPr)2(η4–C8H12)] and the half-sandwich compounds [(η5–C5R5)Co(ImiPr)(η2–C2H4)] (R = Me, H), three interesting starting materials were successfully prepared. Subsequent investigations showed, however, that starting from [Co(ImiPr)2(η4–C8H12)] no transfer of the [Co(ImiPr)2] complex fragment to substrates could be observed. For the preparation of suitable precursors, the incorporation of monoolefins such as cyclooctene or ethene to give complexes of the type [Co(ImiPr)2(η2–olefin)2] could prove successful in future work. The reactivity of half-sandwich compounds was investigated in detail and yielded a number of unusual results. On the one hand, the carbonyl complex [(η5–C5Me5)Co(ImiPr)(CO)] reacts smoothly with dioxygen to give the carbonate complex [(η5–C5Me5)Co(ImiPr)(κ2–CO3)]. Until recently, such reaction behaviour of metal-bound CO was without precedent in the literature. On the other hand, the reaction of [(η5–C5Me5)Co(ImiPr)(η2–C2H4)] with white phosphorus made it possible, for the first time, to document without gaps the stepwise degradation of the P4 tetrahedron to transition-metal-stabilised P2 units. Furthermore, with the synthesis of [{(η5–C5Me5)Co(μ2–η2–P2)}2] an interesting starting material for future investigations of P2 transfer to organic and inorganic molecules could be prepared in high yields. The reactions of [(η5–C5H5)Co(ImiPr)(η2–C2H4)] with perfluorinated aromatics afforded hitherto unknown arene complexes in which two [(η5–C5H5)Co(ImiPr)] complex fragments coordinate to one aromatic ring. These complexes should constitute interesting starting compounds for future investigations of cobalt-mediated C–F activation. Initial investigations already indicate that products of carbon–fluorine bond activation can be obtained from such complexes.