[[Mo(Cp)(CO)(m-SMe)]2] (Cp = h5-cyclopentadienyl) is methylated in two steps by Me3OBF4 to give the stable cations [[Mo(Cp)(CO)]2(m-SMe)(m-SMe2)]+ and [[Mo(Cp)(CO)(m-SMe2)]2]2+. In the latter, one CO ligand was replaced by PMe3 or P(OMe)3. The x-ray structure of [(Cp)(CO)Mo(m-SMe2)2Mo(PMe3)(Cp)][BF4]2 shows a slightly lengthened Mo-Mo double bond [2.693(1) .ANG.] combined with a short Mo-S bond (ca. 2.34 .ANG.).