Synthesis of two tantalum complexes bearing cyclopentadienyl analogs

Reaction of Li[C5H5B-NMe2] with (TBM)TaMe2Cl (TBM = tribenzylidenemethane) gives (TBM)[C5H5B-NMe2]TaMe2 (1). A single crystal diffraction study revealed a metallocene-like environment with the metal binding more strongly to the boratabenzene ring carbons furthest from the boron atom. Cp∗[C4H4B-N(CHMe2)2]Ta(η4-C4H6) (2) (Cp∗ = C5Me5) is obtained from the reaction of Cp∗[C4H4B-N(CHMe2)2]TaCl2 and (C4H6Mg)(THF)2. The diene fragment binds in a trans configuration. The oxidation state of tantalum in 2 can be considered as I, III or V if all resonance contributions are taken into account.