A Cationic Imido Complex of Permethyltantalocene: H2 and Carbon−Hydrogen Bond Activation, [2 + 2] Cycloaddition Reactions, and an Unusual Reaction with Carbon Dioxide That Affords Coordinated Isocyanate

Abstract

Treatment of the imido hydride complex Cp*2Ta(NCMe3)H (Cp* = (η5-C5Me5)) with [Ph3C][B(C6F5)4] in tetrahydrofuran solution yields the cationic imido complex [Cp*2Ta(NCMe3)(THF)][B(C6F5)4] (1). Cation 1 reacts cleanly with H2 to yield [Cp*2Ta(NHCMe3)H][B(C6F5)4]. Carbon−hydrogen bond-activation reactions are observed with propyne or phenylacetylene to afford [Cp*2Ta(NHCMe3)(C≡CR)][B(C6F5)4] (R = CH3, C6H5). In the reaction with propyne, an initial mixture of the [2 + 2] cycloaddition product and C−H activation product is thermally driven to the C−H activation product. The heterolytic cleavage reactions for 1 may be rationalized in terms of the presence of both electrophilic and nucleophilic sites of reactivity in the same molecule. Intramolecular activation of a carbon−hydrogen bond of a Cp* methyl group to ultimately C−H activation of the carbon−hydrogen bonds of methane. An unusual reaction occurs with carbon dioxide:  dealkylation of the imido group is observed, liberating isobutylene and yielding the i...