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*TaCl 4 and phosphinimine R 3 PNSiMe 3 affords the complexes Cp*Ta(NPR 3 )Cl 3, R = t -Bu 1, i- Pr 2 . These species are readily derivatized to the alkylated complexes Cp*Ta(NPR 3 )Me 3, R = t -Bu 3, i- Pr 4; Cp*Ta(NP t -Bu 3 )(CH 2 Ph)Cl 2, 5; and Cp*Ta(NP t -Bu 3 )(CH 2 Ph)Me 2, 6 . Reaction with 3 equiv of BnMgCl afforded the robust alkylidene species Cp*Ta(NPR 3 )(CHPh)(CH 2 Ph), R = t -Bu 7, i- Pr 8 . Reaction of 7 with MeI gives the metallacycle Cp*Ta(NP t -Bu 3 )(η 2 -CHPhCH 2 )(CH 2 Ph), 9 . Alkylation of 1 and 2 with 2 equiv of EtMgCl results in formation of the complexes Cp*Ta(NPR 3 )(η 2 -C 2 H 4 )Cl, R = t -Bu 10, i- Pr 11, while further reaction of 10 with EtMgCl affords Cp*Ta(NP t -Bu 3 )(η 2 -C 2 H 4 )(CH 2 CH 3 ), 12 . Reaction of 1 with 1 equiv of B(C 6 F 5 ) 3 results in generation of the salt [Cp*Ta(NP t- Bu 3 )Cl 2 ][ClB(C 6 F 5 ) 3 ], 13, while the analogous reaction with Ph 3 C[B(C 6 F 5 ) 4 ] affords the related salt [Cp*Ta(NP t- Bu 3 )Cl 2 ][B(C 6 F 5 ) 4 ], 14 . The zwitterionic species Cp*Ta(NPR 3 )Me 2 (MeB(C 6 F 5 ) 3 ) (R = t- Bu 15, i- Pr 16 ) are derived via reaction of 3 or 4 with B(C 6 F 5 ) 3 . The analogous reaction of 3 and 4 with [Ph 3 C][B(C 6 F 5 ) 4 ] affords the related salts [Cp*Ta(NPR 3 )Me 2 ][B(C 6 F 5 ) 4 ] (R = t- Bu 17, i- Pr 18 ). Treatment of 10 with Ph 3 CB(C 6 F 5 ) 4, Ph 3 CBF 4, or B(C 6 F 5 ) 3 gives the complexes [Cp*Ta(NP t- Bu 3 )(Cl)CH 2 CH 2 CPh 3 ][B(C 6 F 5 ) 4 ], 20, [Cp*Ta(NP t- Bu 3 )(Cl)(CH 2 CH 2 CPh 3 )][BF 4 ], 21 and the zwitterionic species [Cp*Ta(NP t- Bu 3 )(Cl)(CH 2 CH 2 B(C 6 F 5 ) 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.