The reactivity of the reduced ZrIIICo0 heterobimetallic complex [(thf)Zr(MesNPiPr2)3CoN2] (1a) towards O–H, S–H, S–S, and O–O bonds has been investigated. Complex 1a reacts readily with PhOH, EtOH, and H2O to generate the one-electron-oxidized complexes [(RO)Zr(MesNPiPr2)3CoN2] [R = Et (2), Ph (3), H (4)]. In contrast, PhSH and PhS–SPh react by means of overall two-electron processes to form [(η2-MesNPiPr2)Zr(μ-SPh)(MesNPiPr2)2Co(SPh)] (5a). Addition of stoichiometric diethyl peroxide to 1a generates 2, but further equivalents lead to the two-electron oxidized product [(EtO)Zr(MesNPiPr2)3Co(OEt)] (6). More sterically hindered peroxides such as dicumyl peroxide or di-tert-butyl peroxide do not react with 1a under ambient conditions, but upon photolysis, di-tert-butyl peroxide reacts with 1a to form [(tBuO)Zr(MesNPiPr2)3CoN2] (7). These results imply that an inner-sphere electron-transfer process is occurring at the Zr site of 1a upon treatment with these chalcogen-based substrates, and a dissociative electron-transfer mechanism is proposed.