The chemical or electrochemical oxidations and coupled chemical reactions of (TPP)Co(R) and (TPP)Co(R)(L) where R = Bu, Et, Me, or Ph, L = a substituted pyridine, and TPP = the dianion of tetraphenylporphyrin were investigated in acetonitrile or dichloromethane. The homogeneous one- or two-electron oxidation of the Co(III) sigma-bonded complexes was accomplished using [Fe(phen)(3)](3+) (phen = 1,10-phenanthroline) as an oxidant. The products of the initial oxidation as well as that of the subsequent R group migration from (TPP)Co(R) or (TPP)Co(R)(L) to give the N-aryl or N-alkyl Co(II) porphyrins were characterized by ESR and UV-vis spectroscopies, while the rates of migration were determined using stopped flow kinetics. The rate constants of R group migration from the metal to nitrogen in [(TPP)Co(R)](+) were found to vary by 6 orders of magnitude upon going from (TPP)Co(Ph) (1.3 x 10(-3) s(-1)) to (TPP)Co(Bu) (1.2 x 10(3) s(-1)) at 298 K in acetonitrile, but no significant differences were observed between E-1/2 for the first oxidation of (TPP)Co(Ph) or (TPP)Co(Bu). ESR spectra of the transient singly oxidized porphyrins indicate that the six-coordinated derivatives, represented as [(TPP)Co(R)(MeCN)](+) or [(TPP)Co(R)(L)](+) (R = Ph and Me), have a significant d(5) cobalt(IV) character in acetonitrile, while the five-coordinate compounds, [(TPP)Co(R)](+), in dichloromethane can be formulated as Co(III) porphyrin pi cation radicals. The formation constants for conversion of (TPP)Co(R) to (TPP)Co(R)(L) were calculated spectroscopically and the logarithmic values vary linearly with the pK(a) of the sixth axial ligand. The E-1/2 values for the first oxidation of (TPP)Co(R)(L) in dichloromethane and the migration rate constants for the R group of [(TPP)Co(R)(L)](+) in acetonitrile are also related to the ligand pK(a). Cobalt-carbon bond dissociation enthalpies and entropies were determined for (TPP)Co(R) and [(TPP)Co(R)](+), and a comparison of these two sets of data reveals that the Co(IV)-carbon bond in the singly oxidized species is significantly weaker than the Co(III)-carbon bond in the neutral complex.