Structures of some derivatives of bis-π-cyclopentadienyltetracarbonyl-di-iron

The i.r. spectra of a number of [(π-dienyl)Fe(CO)2]2 and [(π-dienyl)(π-C5H5)Fe2(CO)4] complexes [dienyl = CH3C5H4 and C9H7(indenyl)] have been investigated between 400 and 700, and 1700 and 2100 cm.–1. They are solvent-dependent, and it is proposed that these compounds, like [(π-C5H5)Fe(CO)2]2, exist as their trans-bridged isomers in the solid state, but as a mixture of cis- and trans-bridged forms, together with small amounts of non-bridged species, in solution. The spectra of solutions of [(π-C9H7)Fe(CO)2]2 in saturated hydrocarbon solvents show two well-resolved bands of comparable intensities at ca. 1790 cm.–1, thereby confirming that two bridged isomers of this compound exist in solution.