Density functional theory (DFT) has been applied to the analysis of the structural and electronic properties of the alkyl-cobalt(III) phthalocyanine complexes, [(CoPc)-Pc-III]-R (Pc = phthalocyanine, R = Me or Et), and their pyridine adducts. The BP86/6-31G(d) level of theory shows good reliability for the optimized axial bond lengths and bond dissociation energies (BDEs). The mechanism of the reductive cleavage was probed for the [(CoPc)-Pc-III]-Me complex which is known as a highly effective methyl group donor. In the present analysis, which follows a recent study on the reductive Co-C bond cleavage in methylcobalamin (J. Phys. Chem. B 2007, 111, 7638-7645), it is demonstrated that addition of an electron and formation of the pi-anion radical [Co-III(Pc-center dot)]-Me- significantly lowers the energetic barrier required for homolytic Co-C bond dissociation. Such BDE lowering in [Co-III(Pc-center dot)]-Me- arises from the involvement of two electronic states: upon electron addition, a quasi-degenerate pi*(Pc) state is initially formed, but when the. cobalt-carbon bond is stretched, the unpaired electron moves to a sigma*(Co-C) state and the final cleavage involves the three-electron (sigma)(2)(sigma*)(1) bond. As in corrin complexes, the pi*(Pc)-sigma*(Co-C) states crossing does not take place at the equilibrium geometry of [Co-III(Pc-center dot)]-Me- but only when the Co-C bond is stretched to similar to 2.3 angstrom. The DFT computed Co-C BDE of 23.3 kcal/mol in the one-electron-reduced phthalocyanine species, [Co-III(Pc-center dot)] -Me-, is lowered by similar to 37% compared to the neutral Py-[(CoPc)-Pc-III]-Me complex where BDE = 36.8 kcal/mol. A similar comparison for the corrin-containing complexes shows that a DFT computed BDE of 20.4 kcal/mol for [Co-III-(corrin(center dot))]-Me leads to similar to 45% bond strength reduction, in comparison to 37.0 kcal/mol for Im(-)[Co-III(corrin)]-Me+. These results suggest some preference by the alkylcorrinoids for the reductive cleavage mechanism.