Synthesis and Reactivity of Neutral, Zwitterionic and Cationic Pentamethylcyclopentadienyl−Tantalum−Phosphinimide Complexes

This paper focuses on the synthesis and reactivity of Cp*Ta(V)−phosphinimide complexes. Reaction of stoichiometric mixtures of Cp*TaCl₄ and phosphinimine R₃PNSiMe₃ affords the complexes Cp*Ta(NPR₃)Cl₃, R = t-Bu 1, i-Pr 2. These species are readily derivatized to the alkylated complexes Cp*Ta(NPR₃)Me₃, R = t-Bu3, i-Pr 4; Cp*Ta(NPt-Bu₃)(CH₂Ph)Cl₂, 5; and Cp*Ta(NPt-Bu₃)(CH₂Ph)Me₂, 6. Reaction with 3 equiv of BnMgCl afforded the robust alkylidene species Cp*Ta(NPR₃)(CHPh)(CH₂Ph), R = t-Bu 7, i-Pr 8. Reaction of 7 with MeI gives the metallacycle Cp*Ta(NPt-Bu₃)(η²-CHPhCH₂)(CH₂Ph), 9. Alkylation of 1 and 2 with 2 equiv of EtMgCl results in formation of the complexes Cp*Ta(NPR₃)(η²-C₂H₄)Cl, R = t-Bu 10, i-Pr 11, while further reaction of 10 with EtMgCl affords Cp*Ta(NPt-Bu₃)(η²-C₂H₄)(CH₂CH₃), 12. Reaction of 1 with 1 equiv of B(C₆F₅)₃ results in generation of the salt [Cp*Ta(NPt-Bu₃)Cl₂][ClB(C₆F₅)₃], 13, while the analogous reaction with Ph₃C[B(C₆F₅)₄] affords the related salt [Cp*Ta(NPt-Bu₃)Cl₂][B(C₆F₅)₄], 14. The zwitterionic species Cp*Ta(NPR₃)Me₂(MeB(C₆F₅)₃) (R = t-Bu 15, i-Pr 16) are derived via reaction of 3 or 4 with B(C₆F₅)₃. The analogous reaction of 3 and 4 with [Ph₃C][B(C₆F₅)₄] affords the related salts [Cp*Ta(NPR₃)Me₂][B(C₆F₅)₄] (R = t-Bu 17, i-Pr 18). Treatment of 10 with Ph₃CB(C₆F₅)₄, Ph₃CBF₄, or B(C₆F₅)₃ gives the complexes [Cp*Ta(NPt-Bu₃)(Cl)CH₂CH₂CPh₃][B(C₆F₅)₄], 20, [Cp*Ta(NPt-Bu₃)(Cl)(CH₂CH₂CPh₃)][BF₄], 21 and the zwitterionic species [Cp*Ta(NPt-Bu₃)(Cl)(CH₂CH₂B(C₆F₅)₃)], 22, respectively. The relevance of this chemistry to the related group IV metal olefin polymerization catalysts is discussed and considered. X-ray structural studies of 1, 3, 5, 7, 9, 10, and 22 are reported.