A tridentate [PPP] ligand has been used to construct a series of dimeric cobalt complexes and explore cooperative multi-electron redox processes that are both metal- and ligand-centered. Reduction of ((PPP)-P-Cl)CoCl2 (1) with excess magnesium affords the (CoCoI)-Co-I N-heterocyclic phosphido (NHP-)-bridged symmetric dimer [(mu-PPP)Co](2) (2). Two-electron oxidation of 2 with FcPF(6) generates an asymmetrically bridged dication [(mu-PPP)Co](2)[PF6](2) (3) in which the oxidation has occurred in a delocalized fashion throughout the Co2P2 core. In contrast, [(mu-PPP)Co](2)(+) (5), which can be generated either by one-electron oxidation of 2 with FcPF(6) or comportionation of 2 and 3, features an asymmetric geometry and localized mixed valence. Treatment of 1 with the milder reductants CoCp2 and KBEt3H does not lead to formation of 2, 3, or 5 but instead generates dimeric species [(PPP)CoCl](2) (6) and [(PPP)CoH](2) (7). Unlike 2-5, where the phosphine side arms of the tridentate [PPP] ligand span the two Co centers, complex 6 and 7 are connected solely by NHP- ligands that bridge the two (PPP)Co fragments.