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)Cl-3, R = t-Bu 1, i-Pr 2. These species are readily derivatized to the alkylated complexes Cp*Ta(NPR3)Me-3, R = t-Bu 3, i-Pr 4; Cp*Ta(NPt-Bu-3)(CH2Ph)Cl-2, 5; and Cp*Ta(NPt-Bu-3)(CH2Ph)Me-2, 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-Bu-3)(eta (2)-CHPhCH2)(CH2Ph), 9. Alkylation of 1 and 2 with 2 equiv of EtMgCl results in formation of the complexes Cp*Ta(NPR3)(eta (2)-C2H4)Cl, R = t-Bu 10, i-Pr 11, while further reaction of 10 with EtMgCl affords Cp*Ta(NPt-Bu-3)(eta (2)-C2H4)(CH2-CH3), 12. Reaction of 1 with 1 equiv of B(C6F5)(3) results in generation of the salt [Cp*Ta(NPt-Bu-3)Cl-2] [ClB(C6F5)(3)], 13, while the analogous reaction with Ph3C[B(C6F5)(4)] affords the related salt [Cp*Ta(NPt-Bu-3)Cl-2] [B(C6F5)(4)], 14 The zwitterionic species Cp*Ta(NPR3)Me-2-(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)-Me-2] [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-Bu-3)(Cl)CH2CH2CPh3] [B(C6F5)(4)], 20, [Cp*Ta(NPt-Bu-3)(Cl)(CH2CH2CPh3)] [BF4], 21 and the zwitterionic species [Cp*Ta(NPt-Bu-3)(Cl)(CH2CH2B(C6F5)(3))] 22, respectively. The relevance of this chemistry to the related group TV metal olefin polymerization catalysts is discussed and considered. X-ray structural studies of 1, 3, 5, 7, 9, 10, and 22 are reported.