A Cationic Imido Complex of Permethyltantalocene:  H_2 and Carbon−Hydrogen Bond Activation, [2 + 2] Cycloaddition Reactions, and an Unusual Reaction with Carbon Dioxide That Affords Coordinated Isocyanate

The cationic imido complex [Cp*2Ta(=NCMe_3)(THF)][B(C_6F_5)_4] (1) (Cp* = (η^5-C_5Me_5)) reacts with σ bonds H−X to afford [Cp*_2Ta(NHCMe_3)X][B(C_6F_5)_4] (X = Cl, OH, C⋮CR). Intramolecular activation of a carbon−hydrogen bond of a Cp* methyl group ultimately yields [Cp*Ta(η^5-C_5Me_4CH_2NCMe_3)H][B(C_6F_5)_4]. Reaction with carbon dioxide leads to dealkylation of the imido group, liberating isobutylene and yielding the isocyanate complex [Cp*_2Ta(OH)(NCO)][B(C_6F_5)_4]