Reactions of alkynes with HFeCO₃(CO)₁₂. Crystal structure of FeCO₃(CO)₉[PhC₂(H)Ph] (PhC₂Ph)

The reaction of HFeCO₃(CO)₁₂ with alkynes follow different pathways depending on the solvent characteristics. In apolar water-free solvent the major product are the novel tetranuclear derivatives Fe Co₃(CO)₉[RC₂(H)R](RC₂R), in which hydrogen shift is occurred from the Co₃ face of the hydrido complex to an acetylenic moiety. The structure of the complex with R = Ph has been determined by X-ray method. The compound crystallizes in the space group P1 with Z = 2 in a unit cell of dimensions a = 13.259(7), b = 12.994(8), c = 11.681(8) Å, α = 114.26(4), β = 11066(3), γ 71.32(4)°. The Structure has been solvent from diffractometer data by direct and Fourier methods and refined by full-matrix least -squares to R = 4.4% for 1789 observed reflections. The complex is characterized by tetranuclear cluster of three Co and one Fe atoms, in a butterfly arrangement, coordinated by nine carbonyls (seven terminal and two asymmetrically bridging the two FeCo Sides). The two starting C₂Ph₂ molecules are bound to the cluster in a different way: the former interacts with all the metals in a μ₄-η² fashion being σ-bond to the Co and Fe Atoms on the hinge and π-bonded to the Co atoms on the wings; the latter, on which the hydridic hydrogen of the starting complex is shifted, interacts only with two Co Atoms on one side of the cluster through one σ and one π bond respectively.