The first phosphaphosphenium cation isolated

Researchers who spend their time seeking out strange new molecules made from main-group elements have enjoyed great success in recent years thanks to the discovery of N-heterocyclic carbenes (NHCs). These Lewis bases with a sturdy lone pair of electrons can bind and stabilize metals and molecule fragments in ways not possible before. In the latest example, Yuzhong Wang, Gregory H. Robinson, and coworkers of the University of Georgia have used the NHC-stabilization strategy to prepare the parent phosphaphosphenium cation, HP₂⁺, for the first time. The complexity of the cation’s name hints that chemists have had a complex time isolating the deceptively simple species, previously only detecting it in gas-phase experiments. To make HP₂⁺, Robinson and coworkers used pyridine hydrochloride (HCl•NC₅H₅) to protonate NHC-stabilized diphosphorus, P₂, another compound they previously tamed. Unlike its nitrogen analog, N₂, diphosphorus is unstable. The Georgia team further obtained the X-ray crystal structure of NHC-stabilized HP₂⁺ and conducted spectroscopic and computational bonding analyses (Chem. Commun. 2016, DOI: 10.1039/c6cc0175b). The findings could lead to better understanding of how to use diphosphorus in organic synthesis and materials science, for example, similar to how aryl diazonium cations RN₂⁺ are used in palladium-catalyzed cross-coupling reactions.