The reaction between the mixed-metal tetrahedral cluster Co 2Rh 2(CO) 12 ( 1) and the electron-poor alkyne methyl propiolate in hexane at room temperature furnishes a mixture of products consisting of Co 3Rh(CO) 12 ( 2), Co 3Rh(CO) 10(μ-HCCCO 2Me) ( 3), Co 2Rh 2(CO) 10(μ-HCCCO 2Me) ( 4), and CoRh 3(CO) 9(μ-HCCCO 2Me) 3 ( 5). The isolation and solution spectroscopic data of these compounds are described, and the solid-state structure of Co 2Rh 2(CO) 10(μ-HCCCO 2Me) determined by X-ray diffraction analysis. The title cluster crystallizes in the triclinic space group. The solid-state structure of Co 2Rh 2(CO) 10(μ-HCCCO 2Me) provides proof for the regiospecific insertion of the methyl propiolate ligand into the Co–Co bond of the starting cluster Co 2Rh 2(CO) 12. The stability of clusters 3 and 4 in the presence of added methyl propiolate is discussed.