Synthesis and Reactivity of an Antimony(iii) Dication

The proximity effect, frequently encountered in enzyme catalysis, entails bringing two or more molecules close together, forcing a reaction to occur. The presence of multiple binding sites at the active centre is required to facilitate the preorganization of reactants prior to reaction. We investigate this concept in a main-group compound by accessing a tricoordinate antimony dication, [TpMe2Sb]2+, where TpMe2 = tris(3,5-dimethylpyrazolyl)borate, that is charge balanced by two [B(C6F5)4]- anions. [TpMe2Sb]2+ readily reacts with anionic (X) and neutral (L) donor ligands, resulting in stable disphenoidal geometry complexes of the types [TpMe2SbX]+ and [TpMe2SbL]2+, respectively. Consequently, [TpMe2Sb(HNPh2)]2+ was obtained upon the addition of HNPh2 to the dication. As evidenced by density functional theory calculations, further treatment of [TpMe2Sb(HNPh2)]2+ with styrene resulted in a weak van der Waals interaction between the arene ring and the 5s lone pair on the antimony centre, eventually facilitating a hydroamination reaction. Our investigations open avenues for exploring intermolecular processes promoted by low-oxidation-state heavier main-group compounds.