Ethylene polymerization with half-sandwich allyl imido complexes of tantalum

The imido-based half-sandwich complex Cp*Ta(=N(2,6-diisopropylphenyl))(eta(1)-C3H5)(eta(3)-C3H5) (3) polymerizes ethylene in the presence of [(C6H5)(3)C](+)-[(C6F5)(4)B](-) or B(C6F5)(3), while chloride and alkyl derivatives are inactive in. the presence of MAO or alkyl abstraction reagents. In contrast, however, Cp*Ta(=NSi(tert-butyl)(3))Cl-2 (5) polymerizes ethylene in the presence of MAO while Cp*Ta(=NSi(tert-butyl)(3))(eta(1)-C3H5)(eta(3)-C3H5) (6) and Cp*Ta(=NSi(tert-butyl)(3))Me-2 (4) are essentially inactive in the presence of alkyl abstractors.