alpha-H Abstraction Research Articles

Reactivity of Tantalum/Iridium and Hafnium/Iridium Alkyl Hydrides with Alkyl Lithium Reagents: Nucleophilic Addition, Alpha-H Abstraction, or Hydride Deprotonation?

Cp*IrH4 reacts with Hf(Np)4 (Np = CH2C(CH3)3) to yield the heterobimetallic complex [Hf(Np)3(μ-H)3IrCp*], 2. Treatment of 2 with neopentyl lithium (NpLi) results in the nucleophilic addition of a neopentyl moiety onto the Hf center, restoring Hf(Np)4 and displacing the Cp*IrH3– iridate fragment. By contrast, treatment of the tantalum/iridium analogue [Ta(Np)3IrH2(Cp*)], 1, with NpLi triggers the α-hydrogen abstraction at a Ta–neopentyl moiety and leads to the formation of the alkylidene -ate complex [Li][{Ta(CHtBu)(Np)2}{IrH2Cp*}], 4. The benzylidene analogue [K][{Ta(CHPh)(Np)2}{IrH2Cp*}], 5, is obtained upon reacting 1 with benzyl potassium. An unusual vinyl oxo species, [{Li(THF)3}Ta(O)(Np)2{μ-C2H3}IrH(Cp*)], 6, is formed when the reaction of 1 with NpLi is carried out in tetrahydrofuran (THF) due to THF fragmentation.