Attempts at methylating cis-[Mo2Cp2(μ-SMe)3L2](BF4) [Cp = η5-C5H5; L = CO (1a) CNxyl (1b), CNBut (1c), NCMe (1d)] with methyl triflate gave the corresponding thioether-bridged cations [Mo2Cp2(μ-SMe)2(μ-SMe2)L2]2+ (42+), except in the case of 1a which did not react at room temperature. The electronic properties of the ancillary ligands L thus have a crucial influence on the course of this reaction. The dimeric compounds [Mo2Cp2(μ-SMe)3(CNBut)(CN)] (2) and [Mo2Cp2(μ-SMe)3{μ-η1-Ndouble bond; length as m-dashC(CH3)CH2CN}] (3), which potentially offer the alternatives of S- or N-methylation, reacted with methylating agents to give mainly the S-methylated derivatives 5 and 7. Only in the case of the nucleophilic reactant 2 was N-methylation also observed and isomer 6 was obtained as a minor product together with 5. New complexes have been completely characterised by multinuclear NMR, IR and elemental analysis, supplemented for 5 by X-ray diffraction study at 100 K.