A geminal antimony(iii)/phosphorus(iii) frustrated Lewis pair.

The geminal Lewis pair (FC)SbCHP(Bu) (1) was prepared by reacting (FC)SbCl with LiCHP(Bu). Despite its extremely electronegative pentafluoroethyl substituents, the neutral 1 exhibits a relatively soft acidic antimony function according to the HSAB concept (hard-soft acid-base). These properties lead to a reversibility in the binding of CS to 1, as observed by VT-NMR spectroscopy, while no reaction with CO is observed. The reaction behaviour towards heterocumulenes and the specific interaction situation in the CS adduct were analysed by quantum chemical calculations. The FLP-type reactivity of 1 has also been demonstrated by reaction with a variety of small molecules (SO, PhNCO, PhNCS, (MePhP)AuCl). The reactions of 1 with PhNCO and PhNCS led to different types of cyclic addition products: PhNCO adds with its N[double bond, length as m-dash]C bond and PhNCS adds preferentially with its C[double bond, length as m-dash]S bond. The reaction of 1 with (MePhP)AuCl gave an adduct {[(FC)SbCH(Bu)P]Au} with a clamp-like structure binding a chloride anion by its two antimony atoms in chelate mode. Compound 1 and its adducts have been characterised by X-ray diffraction experiments, multinuclear NMR spectroscopy, elemental analyses and computational calculations (DFT, QTAIM, IQA).