Diverse structure and reactivity of pentamethylcyclopentadienyl antimony(iii) cations

The pentamethylcyclopentadienyl (Cp*) antimony(iii) cations [Cp*₂Sb][B(C₆F₅)₄], [Cp₂*Sb][OTf], [Cp*SbCl][B(C₆F₅)₄] and [Cp*Sb][OTf]₂ have been isolated and structurally characterised. [Cp*SbCl]⁺ forms dimers in the solid state via an intermolecular Sb-Cl interaction. Initial screening shows that [Cp*SbCl][B(C₆F₅)₄] is significantly Lewis acidic and can catalyse the dimerisation of 1,1-diphenylethylene; [Cp₂*Sb][B(C₆F₅)₄] exhibits negligible Lewis acidity. Highly unstable [Cp*SbF][B(C₆F₅)₄] could not be isolated, but stabilisation with the IMes ligand allowed isolation of [Cp*SbF(IMes)][B(C₆F₅)₄]. Fluorodechlorination of CH₂Cl₂ and PhCCl₃ was observed in the presence of crude [Cp*SbF][B(C₆F₅)₄] in solution. A computational mechanistic investigation suggests that the latter proceeds via a carbocation intermediate.