Reactions are reported of sulfur-bridged incomplete cubane-type tungsten clusters having W-3(mu(3)-S)(mu-S)(3) cores with acetylene and its derivative dimethylacetylenedicarboxylate (DMAD). The reaction of the isothiocyanate tungsten cluster [W-3(mu(3)-S)(mu-S)(3)(NCS)(9)](5-) (5) with acetylene in 0.1 M HCl afforded a novel complex having two acetylene molecules in different adduct formation modes, [W-3(mu(3)-S)(mu(3)-SCH = CHS)(mu-SCH=CH2)(NCS)(9)](4-) (6), and the presence of two kinds of intermediates [W-3(mu(3)-S)(mu(3)-S)(mu(3)-SCH = CHS)(NCS)(9)](5-) (7) and [W-3(mu(3)-S)(mu-S)(2)(mu-SCH = CH2)(NCS)(9)](4-) (8) was observed. The reaction of the diethyldithiophosphate (dtp) tungsten cluster [W-3(mu(3)-S)(mu-S)(3)(mu-OAc)(dtp)(3)(CH3CN)] (10) with DMAD in acetonitrile containing acetic acid resulted in the formation of another complex having two DMAD molecules of different adduct formation modes, [W-3(mu(3)-S)(mu-SC(CO2) = CH(CO2CH3))(mu(3)-SC(CO2CH3) = C(CO2CH3)S)(mu-OAc)(dtP)(3)] (11), where hydrolysis of one of the four ester groups of the two DMAD groups occurred and. the resultant carboxylic group coordinated to tungsten. The conformation of the mu-SCH = CH2 moiety in 6 is different from that of the corresponding moiety in [W-3(mu(3)-S)(mu-O)(mu-S)(mu-SCH = CH2)(NCS)(9)](4-) (4). Introduction of the second acetylene molecule to the intermediate [W-3(mu(3)-S)(mu-S)(2)(mu-SCH = CH2)(NCS)(9)](4-) (8) resulted in the formation of 6. The clusters were characterized by UV-vis spectroscopy, H-1 NMR spectroscopy, and X-ray crystallography (for (HPY)(4)(.)6(.)1.33py(.)0.5H(2)O and 11(.)CH(3)CN), and the formation of 6 and 11 was examined in detail from a mechanistic point of view.