Complexes of (5,10,15-tri-X-phenyl-2,3,7,8,12,13,17,18-octamethylcorrolato)cobalt(III) triphenylphosphine, (OMTXPC)Co(PPh(3)), where X = p-OCH3, p-CH3, p-Cl, m-Cl, m-F, o-Cl, o-F, or H, were synthesized and characterized in nonaqueous media using electrochemical, spectroelectrochemical, and EPR techniques. The o-Cl derivative exists as different atropisomers in solution, and a thermal interconversion between them was achieved at 338 K in toluene. Activation parameters (Delta S-double dagger, Delta H-double dagger) for interconversion between the atropisomers were obtained from H-1 NMR measurements and were similar in magnitude to values reported for ortho-substituted tetraphenylporphyrin derivatives. Formation constants for pyridine binding to the pentacoordinate cobalt(III) corroles in benzene were obtained from W-visible spectrophotometric measurements and ranged between 20 and 193 M(-1), with the exact value depending upon the specific electron-donating or electron-withdrawing group on the three phenyl rings of the complex. The redox potentials of (OMTXPC)Co(PPh(3)) also shift with the nature of the phenyl ring substituents, and linear free-energy relationships are observed. Each cobalt(III) derivative undergoes two one-electron reductions, the first of which involves a Co(III)/Co(II) conversion add concomitant loss of the bound PPh(3) ligand. Four one-electron oxidations; are also observed for the investigated compounds, and this contrasts with the oxidative properties of related cobalt(II) porphyrins which undergo a maximum of three one-electron oxidations under similar solution conditions. The first one-electron oxidation of each cobalt(III) corrole is metal-centered and results in formation of a Co(IV) corrole as ascertained by EPR spectroscopic characterization of the electrogenerated species.