P⁺ addition and transfer involving a tetraphosphenium ion

Triphospha[3]ferrocenophane Fe(C₅H₄-PTip)₂PCl (Tip = 2,4,6-tri(isopropyl)phenyl) has been prepared and its suitability to generate the corresponding bisphosphanylphosphenium ion has been explored. By formal addition of P⁺ to the latter, an unprecedented tetraphosphenium ion forms which likewise is capable of P⁺ transfer and qualifies as Lewis superacid based on its computed fluoride ion affinity. As a solid, this species is stable and conveniently storable, featuring a remarkably long P-P bond (2.335(5) Å). From this tetraphosphenium ion, known and unprecedented triphosphenium ions have been generated via P⁺ transfer in solution, including a triphosphenium ion with P-H functionalities. Moreover, the latter has been obtained by tautomeric rearrangement from the corresponding hydrophosphane precursor. The bonding situation and details of the P⁺ transfer have been investigated by DFT calculations and experimental methods like multinuclear NMR spectroscopy and SC-XRD.