Abstract The reaction of sulfur-bridged incomplete cubane-type molybdenum complex [Mo3(µ-S)3(µ3-S)(dtp)3(CH3CN)(µ-OAc)] (1) (dtp: diethyl dithiophosphate) with dimethyl acetylenedicarboxylate (H3COOCC≡CCOOCH3, DMAD) in several kinds of solvents gave solvent-dependent adducts. The use of acetone, acetaldehyde, acetylacetone, ethyl acetoacetate, and acetophenone as reaction solvents gave the following adducts, respectively: [Mo3{µ-SCH(COCH3)}(µ3-S){µ3-SC(CO2CH3)=C(CO2CH3)S}(dtp)3(µ-OAc)] (2), [Mo3{µ-SCH(CHO)}(µ3-S){µ3-SC(CO2CH3)=C(CO2CH3)S}(dtp)3(µ-OAc)] (3), [Mo3{µ-SC(COCH3)(COCH3)}(µ3-S){µ3-SC(CO2CH3)=C(CO2CH3)S}(dtp)3(µ-OAc)] (4) (and [Mo3{µ-SC(COCH3)(COCH3)}(µ3-S){µ3-SC(CO2CH3)=C(CO2CH3)S}(dtp)2(acac)(µ-OAc)] (4′)), [Mo3{µ-SC(COCH3)(COOC2H5)}(µ3-S){µ3-SC(CO2CH3)=C(CO2CH3)S}(dtp)3(µ-OAc)] (5), and [Mo3{µ-SCH(COC6H5)}(µ3-S){µ3-SC(CO2CH3)=C(CO2CH3)S}(dtp)3(µ-OAc)] (6). X-ray crystallography and 1H NMR spectroscopy have revealed that in all six cases, the solvent adduct-formation resulted in the removal of two hydrogen atoms from the methyl (or methylene) group of the solvent used and in the formation of a carbon–sulfur bond; it also revealed that in some cases (2, 3, 4′, and 6) additional carbon–molybdenum bond formations occurred. Mass spectroscopy indicates that the presence of DMAD is indispensable in the two-hydrogen elimination reaction. Electronic spectra of 2, 3, and 6 have absorption bands in the visible and near-infrared region, and those of the two complexes 4 and 5 have significantly larger absorption bands in the longer wavelength region than the former group. The complex 4′, where one of the three dtp ligands is replaced by an acetylacetone anion also has a larger peak in the longer wavelength region, but the intensity is between those of the former and the latter groups. All six complexes show a chemically reversible one-electron-oxidation process corresponding to a V, IV, IV/IV, IV, IV couple and the oxidation products of these six complexes are stable under a time scale in CV measurements. The reduction processes of 2, 3, and 6 are chemically irreversible; those of 4, 4′, and 5 are reversible, and the processes correspond to a IV, IV, IV/IV, IV, III couple. A mechanism for the formation of the doubly-dehydrogenated species is suggested.