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 = imidazolium2-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 PI cation 10+ predicted a stable and "bottleable" P-centered radical dication [(2-Im(Dipp)) P(4-Im(Dipp))](2+center dot) (13(2+center dot)). The reaction of 10(+) with the nitrosyl salt NO[OTf] yields the persistent phosphanyl radical dication 13(2+center dot) as triflate salt in crystalline form. Quantum chemical investigation revealed an exceptional high spin density at the P atom.