π‐Complexes of Main‐Group Metal Cations: Exploration of Lewis Acid Reactivity

A series of cationic nido ‐clusters [E( η 4 ‐IDP)] +/2+ was prepared from the imidazolium‐substituted diphosphate‐diide (IPr) 2 C 2 P 2 ( IDP ), including [ 1 ] + (E = Ga) and [ 2b, c ] 2+ (E = Sn, Pb). As analogues of the elusive pyramidane [C( η 4 ‐C 4 H 4 )], these species belong to the class of heteropyramidanes. However, UV–vis spectroscopy and quantum‐chemical calculations, including the previously reported germanium species [Ge( η 4 ‐ IDP )] 2+ ([ 2a ] 2+ ), suggest they are best described as monoatomic cationic main‐group centres stabilised by a neutral 6 π ‐donating ligand. This electronic structure confers significant Lewis acidity to the metal centers, enabling catalytic hydrophosphinations and the formation of monocationic halogenide adducts [ 6a‐d ] + (X = F, Cl). Our studies reveal these adducts to be 4 π ‐complexes of diatomic tetryliumylidenes [E−X] + , including the elusive fluoride cations [GeF] + and [SnF] + , characterised in both the solid‐state and solution.