Os-3(CO)(9){mu(3)-eta(1)-eta(1)-eta(2)-eta(2)-C(SiMe(3))C(Me)C(H)C(Fc)}, the second example of a cluster with the ''face'' coordination of the metallacyclopentadiene fragment and its conversion to the Os-3(mu-H)(CO)(8){mu(3)-eta(1)-eta(1)-eta(4)-eta(1)-C(SiMe(3))C(Me)C(H)C(C5H3FeC5H5)} complex with the ortho-metallated ferrocene moiety

Os-3(mu-CO)(CO)(9)(mu(3)-Me(3)SiC(2)Me) alkyne complexes react with ferrocenylacetylene in hot benzene to form Os-3(CO)(9)(mu(3)-eta(1)-eta(1)-eta(2)-eta(2)-C(SiMe(3))C(Me)C(H)C(Fc)) and a small amount of the isomeric Os-3(CO)(9){mu-eta(1)-eta(1)-eta(4)-C(SiMe(3))C(Me)C(Fc)C(H)} complex. The sturcture of the major isomer was confirmed by X-ray structural analysis of the single crystal. Thermolysis of this complex in refluxing benzene affords the Os-3(mu-H)(CO)(8){mu(3)-eta(1)-eta(1)-eta(4)-eta(1)-C(SiMe(3))C(Me)C(H)C(C5H3FeC5H5)} complex with the ortho-metallated ferrocen moiety. The spectral characteristics of clusters with the mu(3)-eta(1)-eta(1)-eta(2)-eta(2) and mu-eta(1)-eta(1)-eta(4) coordinations of the metallacyclopentadiene fragment have been established, which made it possible to choose between the alternative modes of bonding of diene with the trimetallic core.