Synthesis and EPR/UV/Vis-NIR spectroelectrochemical investigation of a persistent phosphanyl radical dication.

The reaction of the bis(imidazoliumyl)-substituted P(I)  cation [(2-Im(Dipp) )P(4-Im(Dipp) )](+) (10(+) ) (2-Im=imidazolium-2-yl; 4-Im=imidazolium-4-yl; Dipp=2,6-di-isopropylphenyl) with trifluoromethanesulfonic acid (HOTf) or methyl trifluoromethylsulfonate (MeOTf) yields the corresponding protonated [(2-Im(Dipp) )PH(4-Im(Dipp) )](2+) (11(2+) ) and methylated [(2-Im(Dipp) )PMe(4-Im(Dipp) )](2+) (12(2+) ) dications, respectively. EPR/UV/Vis-NIR spectroelectrochemical investigation of the low-coordinated P(I)  cation 10(+) predicted a stable and "bottleable" P-centered radical dication [(2-Im(Dipp) )P(4-Im(Dipp) )](2+.) (13(2+.) ). The reaction of 10(+) with the nitrosyl salt NO[OTf] yields the persistent phosphanyl radical dication 13(2+.) as triflate salt in crystalline form. Quantum chemical investigation revealed an exceptional high spin density at the P atom.