A Crystalline Phosphorus-Substituted Borinium Cation: Double Dihydrogen Activation by an Ambiphilic Inorganic Allene

We report the synthesis and isolation of the first ambiphilic borinium cation. Bromide abstraction from a bromo(diphosphino)borane precursor affords a two-coordinate boron cation with a structure isolobal to allene. The presence of two phosphido substituents directly bonded to the boron center provides electronic stabilization, enabling the isolation of the P-substituted borinium cation in crystalline form. This compound readily forms adducts with N-heterocyclic carbenes, yielding diphosphinoborenium cations. The ambiphilic nature of the P-substituted borinium cation is demonstrated by its ability to activate dihydrogen under mild, catalyst-free conditions, highlighting its dual Lewis acidic and basic character.