Silicon-bridged tetramethylcyclopentadienyl-phenoxy complexes of tantalum: Preparation and alkylation of Et_2Si(η~5-C _5Me_4)(3-~tBu-5-Me-2-C_6H _2O)TaCl_3 and generation of its cationic Complex

摘要

A tantalum complex of a silicon-bridged tetramethylcyclopentadienyl-phenoxy ligand, Et_2Si(η~5-C_5Me_4)(3- ~tBu-5-Me-2-C_6H_2O)TaCl_3 (2), was prepared by treating TaCl_5 with the dilithium salt generated by reaction of the corresponding ligand 1 with ~nBuLi in the presence of Et_3N in heptane. The molecular structure of 2, as confirmed by X-ray analysis, showed a four-legged piano-stool geometry around the tantalum atom and slightly twisted ligand architecture with a bridging diethylsilylene unit. The tantalum complex 2 exhibited moderate catalytic activities for copolymerization of ethylene and 1-hexene in the presence of ~iBu_3Al/Ph _3C[B(C_6F_5)_4]. The methylation reaction of the trichlorotantalum complex 2 afforded the corresponding trimethyltantalum complex 4. Cationic dimethyltantalum species were generated by treating 4 with an equimolar amount of Ph_3C[B(C_6F _5)_4] or B(C_6F_5)_3 and found to be thermally stable in o-dichlorobenzene-d_4, even at elevated temperature.