Synthesis and reactivity of tantalocene zwitterions stabilized by ground-state α-agostic interactions via reaction of B(C6F5)3 with Cp′2Ta(=CH2)(CH3) (Cp′ = C5H5, C5H4Me)

Zwitterionic tantalocene derivatives are formed when the perfluorophenyl-substituted borane B(C6F5)(3) is reacted with the tantalocene methyl methylidene complexes Cp'Ta-2(=CH2)(CH3) (Cp' = C5H5, C5H4Me). The products arise from borane attack of the methylidene ligand and are characterized by a strong, ground-state alpha-agostic interaction, and insertion. of tert-butyl isocyanide occurs exclusively into the agostic Ta-C bond, producing iminoacyl zwitterions.