Rational synthesis of tricobalt-molybdenum and -tungsten butterfly clusters with alkyne ligands

The heterometallic alkyne complexes [CoM(μ-R1CCR2)(CO)5Cp] (M=Mo, W; R1=R2=CO2Me, CO2Et; R1=H, R2=CO2Me) react with dicobalt octacarbonyl in refluxing toluene to give the 60-electron tetranuclear clusters [Co3M(μ4-R1C2R2)(CO)9Cp] in moderate to good yields. The clusters consist of a butterfly-type metal core in which the molybdenum (or tungsten) atom occupies a wing-tip position, as shown by X-ray analysis of three of the complexes.