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Reactions of acetylide clusters M3H(C⋮CFc)(CO)9 (1a, M = Ru; 1b, M = Os; Fc = ferrocenyl) with Ru3(CO)12 in refluxing hexane yield the tetranuclear clusters RuM3H(C⋮CFc)(CO)12 (2a,b) with a butterfly metal core. The μ4-acetylide ligand of these complexes undergoes migration, indicated by variable-temperature 1H and 13C NMR studies. Compounds 2a and 2b are relatively unstable in solution as well as in the solid state and decompose with formation of corresponding trinuclear acetylide precursors and Ru3(CO)12. The molecular structures of 1a and 2a were established by the X-ray diffraction study of a mixed crystal, which contains both clusters in a 1:1 ratio.

In the title complex, the Cr(CO3) fragment is bonded to the six carbon atoms of the fulvene system, causing a significant distortion in planarity of the fulvene system, and a loss of C3v symmetry of the Cr(CO)3 fragment.