A series of cobalt β-substituted nitroporphyrins were investigated as to their electrochemistry, spectroelectrochemistry and reactivity with alkyl halides in nonaqueous media. Selected structures of the examined compounds are shown in Chart 1. Each porphyrin contains cobalt(II) in its neutral air-stable form and is characterized by multiple redox reactions, some of which involve the conjugated π-ring system and others, the central metal ion which can be converted to its Co(III) and Co(I) forms under the application of an applied oxidizing or reducing potential. The half-wave potentials for each redox reaction were measured by cyclic voltammetry and spectra of the oxidized and reduced compounds were obtained by thin-layer UV-visible spectroelectrochemistry under the same solution conditions. The electrogenerated Co(I) porphyrins are highly reactive in the presence of methyl iodide and a rapid reaction occurs to generate a new series of σ-bonded Co(III) methyl derivatives, which were also characterized as to their electrochemistry and spectroscopic properties in nonaqueous media. These data were then analyzed as a function of the solvent properties, the nature of the β-pyrrole substituents and the oxidation state of the central metal ion.