The treatment of a ligand, 2,6-bis((4-(pyridin-2-yl)pyrimidin-2-ylthio)methyl)-4-chlorophenol (ClPPT2), with cuprous chloride under a weak base condition led to the formation of a neutral Cu-4(I)-centered cluster [Cu-4(PPT2)(4)], whose X-ray diffraction analysis indicated that C-S bonds of the ligand were cleaved in the course of the reaction. To explain the C-S bond cleavage, a reasonable mechanism has been proposed. In support of it, four additional ligands, 2,6-bis((4-(pyridin-2-yl)pyrimidin-2-ylthio)methyl)-4-methylphenol (MePPT2), 2,6-bis((4-(pyridin-3-yl)pyrimidin-2-ylthio)methyl)-4-methylphenol (MePPT3), 2,6-bis((4-(pyridin-3-yl)pyrimidin-2-ylthio)methyl)-4-chlorophenol (ClPPT3), and 5-((4-(pyridin-3-yl)pyrimidin-2-ylthio)methyl)-2-hydroxybenzaldehyde (HBPPT2) were further tested to undertake the analogous reaction, and the cleaved products in these experiments were detected by electrospray ionization mass spectrometry techniques to clarify the process.