Diverse structure and reactivity of pentamethylcyclopentadienyl antimony(iii) cations

The pentamethylcyclopentadienyl (Cp*) antimony(iii) cations [Cp*Sb-2][B(C6F5)(4)], [Cp-2*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; [Cp-2*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.