π-Complexes of Main-group Metal cations: Exploration of Lewis acid reactivity

A series of cationic nido-clusters [E(η4-IDP)]+/2+ was prepared from the imidazolium-substituted diphosphate-diide (IPr)2C2P2 (IDP), including [1]+ (E = Ga) and [2b,c]2+ (E = Sn, Pb). As analogues of the elusive pyramidane [C(η4-C4H4)], these species belong to the class of heteropyramidanes. However, UV-vis spectroscopy and quantum-chemical calculations, including the previously reported germanium species [Ge(η4-IDP)]2+ ([2a]2+), suggest they are best described as monoatomic cationic main-group centres stabilized by a neutral 6π-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 4π-complexes of diatomic tetryliumylidenes [E−X]+, including the elusive fluoride cations [GeF]+ and [SnF]+, characterized in both the solid-state and solution.