The synthesis and redox reactivity of pentacoordinate phosphorus compounds incorporating a redox-active ONO amidodi-phenoxide scaffold [ONO = N,N-bis(3,5-di-tert-buty1-2-phenoxide)-amide] are described. Dichloro- and diphenylphosphoranes, 2 center dot Cl-2 and 2 center dot Ph-2, respectively, are synthesized and crystallographically characterized. Cyclic voltammograihs of 2 center dot Cl-2 show only a single irreversible oxidation (E-pa = +0.83 V vs Cp2Fe0/+), while the diphenyl analogue 2 center dot Ph-2 is reversibly oxidized at lower applied potential (E-1/2 = +0.47 V vs Cp2Fe0/+). Chemical oxidation of 2 center dot Ph-2 with AgBF4 produces the corresponding radical cation [2 center dot Ph-2](center dot+), where electron paramagnetic resonance spectroscopy and density functional theory calculations reveal that the unpaired spin density is largely ligand-based and is highly delocalized throughout the ONO framework of the paramagnetic species. The solid-state structures indicate only minor geometrical changes between the neutral 2 center dot Ph-2 and oxidized [2 center dot Ph-2](center dot+) species, consistent with fast self- exchange electron transfer, as observed by NMR line-broadening experiments.