Stepwise Reduction of an α‐Phosphonio–Carbocation to a Crystalline Phosphorus Radical Cation and an Acridinyl–Phosphorus Ylide

We have synthesized the dicationic α‐phosphonio–carbocation 1 2+ , which can be regarded as a two‐electron oxidized phosphorus ylide. Carbocation 1 2+ exhibits two reversible reduction waves at −0.28 and −0.90 V (vs. Fc + /Fc) indicating that both the radical cation 1 . + and the neural phosphorus ylide 1 can be generated. Indeed, reduction of 1 2+ with Zn afforded 1 . + as a dark green solid that was characterized by XRD and EPR spectroscopy, and reduction with Mg(Ant)⋅(THF) 3 gave 1 , which was characterized by 1 H and 31 P NMR spectroscopy. Computational analyses reveal the stepwise population of a C−P π bonding orbital upon reduction of 1 2+ .