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.