High-spin cation radicals of methylenephosphoranes

Novel di(cation radical)s and tri(cation radical)s are prepared by oxidation of the corresponding 1,3-phenylenebis[[(4-tert-butylphenyl)methylene]triphenylphosphorane] and 1,3,5-benzenetriyltris[[(4-tert-butylphenyl)-methylene]triphenylphosphorane] precursors. The oligo(cation radical)s are investigated in frozen solutions using ESR spectroscopy. The di(cation radical) has a triplet state as evidenced from a Delta M-s = +/-2 ESR transition exhibiting hyperfine coupling to two identical phosphorus nuclei and is characterized by zero-field splitting parameters D = 350 MHz and E = 0 MHz. The corresponding tri(cation radical) possesses a quartet state with D = 262 MHz and E = 0 MHz and exhibits a Delta M-s = +/-3 transition. Temperature dependent studies (4-100 K) reveal that the ESR intensities follow Curie's law, consistent with high-spin ground states. The stability of these oligo(cation radical)s is assessed via cyclic voltammetry at room temperature in THF solution.