The Hexaphenyl-1,2-Diphosphonium Dication [Ph3P–PPh3]2+

The oxidation of triphenylphosphine by perfluorinated phenaziniumF aluminate in difluorobenzene affords the hexaaryl-1,2-di¬phosphonium dialuminate 1. Dication 12+ is isoelectronic with elusive hexaphenylethane, where instead the formation of a mixture of the trityl radical and Gomberg’s dimer is favored. Quantum-chemical calculations in combination with Raman/IR spectroscopies rationalize the stability of the P–P bonded dimer in 12+ and suggest, akin to the halogens, facile homolytic as well as heterolytic scission. Thus, 12+ serves as a surrogate of both the triphenylphosphorandiylium dication (Ph3P2+) and the triphenylphosphine radical monocation (Ph3P•+). Treating 1 with dimethylaminopyridine (DMAP) replaces triphenylphosphine under heterolytic P–P bond scission. Qualifying as a superoxidant (E vs. Fc/Fc+ = +1.44 V), 1 oxidizes trimethylphosphine. Based on halide abstraction experiments (−BF4, −PF6, −SbCl6, −SbF6) as well as the deoxygenation of triethylphosphine oxide, triflate anions as well as toluic acid, 1 also features Lewis superacidity. The controlled hydrolysis affords Hendrickson’s reagent, which itself finds broad use as dehydration agent. Formally homolytic P–P bond scis¬sion is induced by diphenyldisulfide (PhSSPh), dihydrogen, and the triple bond in acetonitrile. The irradiation by light cleaves the P–P bond homolytically and generates transient triphenylphosphine radical cations, which engage in H-atom abstraction as well as CH phosphoranylation.