HCB₁₁(CF₃)_nF_{11- n}^-: Inert anions with high anodic oxidation potentials

Cs salts of four of the title anions were prepared by fluorination of salts of partly methylated (n = 11, 10) or partly methylated and partly iodinated (n = 6, 5) CB₁₁H₁₂^- anions. The CH vertex is acidic, and in the unhindered anion with n = 6 it has been alkylated. Neat Cs⁺[1-H-CB₁₁(CF₃)₁₁]^- is as treacherously explosive as Cs⁺[CB₁₁(CF ₃)₁₂]^-, but no explosions occurred with the salts of the other three anions. BL3YP/6-31G* gas-phase electron detachment energies of the title anions are remarkably high, 5-8 eV. Treated with NiF₃⁺ in anhydrous liquid HF at -60 °C, anions with n = 11 or 10 resist oxidation, whereas anions with n = 6 or 5 are converted to colored EPR-active species, presumably the neutral radicals [HCB ₁₁(CF₃)_nF_11-n]•. These are stable for hours at -60 °C after extraction into cold perfluorohexane or perfluorotri-n-butylamine solutions. On warming to -20 °C in a Teflon or quartz tube, the color and EPR activity disappear, and the original anions are recovered nearly quantitatively, suggesting that the radicals oxidize the solvent.