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

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journal contribution
posted on 01.03.2001, 00:00 authored by Silke Courtenay, Douglas W. Stephan
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.