Synthesis, Properties and Crystal Structure of a Dicyclopentadienyl Tantalum Cyclooctatetraene Complex Cp2TaC3H7 · η2-C8H8

Reactions of endo hydride olefin complexes Cp2M(H)L (M = Ta, Nb; L = C3H6, C4H8) with C8H8 give the tantalocene and niobocene alkyls Cp2MR · C8H8. In solution these complexes partly dissociate giving free cyclooctatetraene and only endo hydride olefin complexes. Temperature-dependent 1H NMR measurements indicate that the C8H8 ligand is fluxional on the NMR time scale. The crystal structure of Cp2TaC3H7 · C8H8 shows dihapto coordination of the cyclooctatetraene ligand and further reveals the coplanarity of the tantalum atom, the α- and β-carbon atoms of the propyl group and the two coordinated carbon atoms of the C8H8 group. In addition there is an unusual planar conformation of the carbon skeleton of the C8H8 group.