The reaction of [Mo-2(CO)(4){mu-C-2)(CO(2)Me)(2)}(eta-C5H5)(2)] with RSH produces the mu-vinyl complexes [Mo-2(CO)(2){mu-C(CO(2)Me) = CHCO(2)Me}(mu mu-SR)(eta-C5H5)(2)] when R = Et or Pr-i but, for R = (t)Bu, dealkylation of the thiol and further hydrogenation of the alkyne occurs to give [Mo-2(mu-S)(2)(mu-eta(2),eta(1),eta(1)-cis-MeO(2)CCH = CHCO(2)Me)(eta-C5H5)(2)] in which the alkene dimethyl maleate acts as a six-electron donor ligand through its double bond and the carbonyl oxygen atoms of both CO(2)Me groups. In contrast, treatment of [Mo-2(CO)(4)(mu-C(2)Me(2))(eta-C5H5)(2)] with RSH provides a convenient new route to compounds of the type [Mo-2(mu-S)(2)(mu-SR)(2)(eta-C5H5)(2)] when R = Et or(1)Pr.