We have prepared a series of cobalt(III) complexes coordinated in a κ²N,S manner by substituted phenylthioether ligands. The preparation is a two-step process starting with trans-dichloridobis(ethylenediamine)cobalt(III) chloride. NMR spectroscopy was used to characterize the complexes. In addition, the presence of an intense ligand-to-metal charge-transfer transition in the UV region confirms that a sulfur atom is bonded to the cobalt(III) center. In basic solution, the Co–S bond is broken, presumably by the classical S_N1CB mechanism. The rate of the cleavage reaction increases as the electron-withdrawing ability of the phenyl substituent increases. (Image credit: Lee Roecker.)