Reactions of the bis(nitrile) compound [Mo2Cp2 (MeCN)2(μ-SMe)3](BF4) (1) with terminal alkynes in a 1:1 ratio in dichloromethane at room temperature led to the alkyne adduct [Mo2Cp2(μ-SMe)3(RCCH)] (BF4) (2: R = Tol (2a), Ph (2b), CH3C=CH2 (2c), nPr (2d), CO2Me (2e), CF3 (2f)). Compounds 2a-d were readily deprotonated with Et3N to give neutral acetylide derivatives [Mo2Cp2(μ-η1:η2- C≡CR)(μ-SMe)3] (3). Protonation of 3 afforded exclusively the vinylidene complexes [Mo2Cp2(μ-η1: η2-C=CHR) (μ-SMe)3](BF3) (4). Reaction of 1 with an excess of terminal alkyne RCCH in dichloromethane gave either the six-membered metallacycle compounds [Mo2Cp2(μ- η2:η4-CR=CHCR=CHSMe)(μ-SMe)2] (BF4) (5) or the S-methylthiophenium derivatives [Mo2Cp2(μ-η2:η4- C4H2R2SMe)(μ-SMe)2] (BF4) (6), depending on the nature of the R groups. Further reactions of the alkyne adducts 2 with isocyanide and carbon disulfide led to the vinyl-thioether complexes [Mo2Cp2(μ- η1:η3-CR=CR′-SMe)-(μSMe)2 (RNC)](BF4) (7, 8) and to their CS2 adducts [Mo2Cp2(S2C-CR′=CRSMe)(μ- SMe)2]-(BF4) (9, 10), which arise from regioselective C-S coupling. A mechanism is proposed for the formation of the cyclic thiometalla compounds 5, 9, and 10 and of the thiophenium species 6 which assigns a key intermediate role to vinyl-thioether species. The molecular structures of 3a, 4b, and 7a have been established by X-ray diffraction studies.