Work

Hexaphenyl-1,2-Diphosphonium Dication [Ph 3 P–PPh 3 ] 2+ : Superacid, Superoxidant, or Super Reagent?

Year: 2025

Type: article

Abstract: High Resolution Image Download MS PowerPoint Slide The oxidation of triphenylphosphine by perfluorinated phenazinium F aluminate in difluorobenzene affords hexaaryl-1,2-diphosphonium dialuminate 1 . Dication 1 2+ is valence 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 1 2+ and suggest, akin to the halogens, facile homolytic as well as heterolytic scission. Thus, 1 2+ serves as a surrogate of both the triphenylphosphorandiylium dication (Ph 3 P 2+ ) and the triphenylphosphine radical monocation (Ph 3 P ·+ ). Treating 1 with dimethylaminopyridine (DMAP) or t Bu 3 P 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 ( – BF 4, – PF 6, – SbCl 6, – SbF 6 ) 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 a dehydration agent. Formally, homolytic P–P bond scission occurs with diphenyldisulfide (PhSSPh) and the triple bonds in benzo- and 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.

Source: Journal of the American Chemical Society

DOI: 10.1021/jacs.5c01271