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

Abstract

The geminal Lewis pair (F₅C₂)₂SbCH₂P(tBu)₂ (1) was prepared by reacting (F₅C₂)₂SbCl with LiCH₂P(tBu)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 CS₂ to 1, as observed by VT-NMR spectroscopy, while no reaction with CO₂ is observed. The reaction behaviour towards heterocumulenes and the specific interaction situation in the CS₂ 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 (SO₂, PhNCO, PhNCS, (MePh₂P)AuCl). The reactions of 1 with PhNCO and PhNCS led to different types of cyclic addition products: PhNCO adds with its NC bond and PhNCS adds preferentially with its CS bond. The reaction of 1 with (MePh₂P)AuCl gave an adduct {[(F₅C₂)₂SbCH₂(tBu)₂P]₂Au}⁺ 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).