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

• Published in: Chemistry : a European journal Vol. 22; no. 9; pp. 2882 - 2886
• Main Authors: Hudnall, Todd W., Dorsey, Christopher L., Jones, James S., Gabbaï, François P.
• Format: Journal Article
• Language: English
• Published: WEINHEIM Blackwell Publishing Ltd 24.02.2016; Wiley
• Subjects: Bonding; carbocation; Cations; Chemistry; Chemistry, Multidisciplinary; Crystal structure; main group elements; Orbitals; Phosphorus; Physical Sciences; radical; Radicals; Reduction; Science & Technology; Spectroscopy; ylide; carbocation; LOCALIZATION; NUMBER; DATA-STORAGE; radical; main group elements; STRUCTURAL-CHANGES; DEVICES; BASIS-SETS; ylide; phosphorus
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201504744

We have synthesized the dicationic α‐phosphonio–carbocation 12+, which can be regarded as a two‐electron oxidized phosphorus ylide. Carbocation 12+ 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 12+ 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 1H and 31P NMR spectroscopy. Computational analyses reveal the stepwise population of a C−P π bonding orbital upon reduction of 12+. The first synthesized α‐phosphonio–carbocation undergoes one‐electron reduction to afford a stable radical cation that features a one‐electron P−C π bond (see picture) and two‐electron reduction to the corresponding antiaromatic phosphorus ylide.