The mixed-metal cluster [HIrRu₃(CO)₁₃] 1 reacts with one equivalent of disubstituted alkynes RCCR to give [HIrRu₃(CO)₁₁(µ₃-η²-RCCR)] (R = Ph 2; R = Me 3), with a second equivalent of the alkyne the clusters [IrRu₃(CO)₁₀(µ₄-η²-RCCR)(µ-η²-RCCHR)] (R = Ph 4; R = Me 5) are obtained. The single-crystal X-ray structure analyses of 2 and 3 show these clusters to have a tetrahedral Ru₃Ir framework containing the alkyne ligand coordinated in a parallel fashion over the Ru₃ face of the metal skeleton. In contrast, the clusters 4 and 5 consist of a butterfly arrangement of the Ru₃Ir framework with the alkyne ligand coordinated to all four metal atoms, giving an overall octahedral Ru₃IrC₂ skeleton, as demonstrated by the single-crystal structure analysis of 4. Cluster 1 is an excellent catalyst for the hydrogenation of diphenylacetylene to give stilbene (catalytic turnover number 990 within 15 min), clusters 2 and 4 are also catalytically active but seem to represent side-channels of the catalytic cycle.