Nmr spektroskopie an paramagnetischen komplexen : XXVI. Paramagnetische peralkyl-metallocene. Synthese,stereochemie und elektronische eigenschaften

The paramagnetic metallocenes (EtMe₄)Cp₂M, M  V, VBr, Cr, Co, Ni have been synthesized starting from the THF adducts of MCl₂. A detailed ¹H and ¹³C NMR study shows that there are two main effects of peralkylation: a change in redox properties and steric repulsion. The reducing power for M  Co, Ni is enhanced and hindered rotation is found for the ethyl group with Cβ being turned away from the metal. Cβ allows to determine selectively the sign of the electron spin density in the ligand π-system. This offers a general way to investigate the spin delocalisation as shown for bent vanadocenes. The limits of the NMR analysis are discussed.