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+) .