The Synthesis and Olefin Reactivity of Neutral and Cationic Tantalum Amidinate−Pentamethylcyclopentadienyl Complexes

Cp*[MeC(NPr i ) 2 ]TaCl 3, 1, was prepared in a 60% yield by the reaction of Cp*TaCl 4 with 1 equiv of Li[MeC(NPr i ) 2 ] in THF. The structure is pseudo-octahedral with a plane of symmetry containing the amidinate ligand and bisecting the Cp*. Reaction of 1 with excess MeMgCl yielded the trimethyl derivative Cp*[MeC(NPr i ) 2 ]TaMe 3 . Reaction of 1 with AgSbF 6 yielded the cation [Cp*[MeC(NPr i ) 2 ]TaCl 2 ][SbF 6 ]. The amidinate orientation is changed with respect to 1 such that the amidinate and the Cp* are nearly parallel. Complex 1 polymerizes ethylene upon treatment with MAO in isobutane (470 (g PE)(mmol Ta) - 1 h - 1 atm - 1 ).