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

The geminal Lewis pair (F 5 C 2 ) 2 SbCH 2 P( t Bu) 2 (1) was prepared by reacting (F 5 C 2 ) 2 SbCl with LiCH 2 P( t Bu) 2 . 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 2 to 1, as observed by VT-NMR spectroscopy, while no reaction with CO 2 is observed. The reaction behaviour towards heterocumulenes and the specific interaction situation in the CS 2 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 2 , PhNCO, PhNCS, (MePh 2 P)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 (MePh 2 P)AuCl gave an adduct {[(F 5 C 2 ) 2 SbCH 2 ( t Bu) 2 P] 2 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).