The crystal and molecular structure of the iron i r complex obtained from the reaction of methyllithium with tricarbonyl-8,8-dibromobicyclo[5.1.0]octa-2,4-dieneiron has been determined by a single-crystal three-dimensional X-ray diffraction study. The complex crystallizes in the monocdinic space group P2,/c with lattice parameters a = 10.740 f 0.003, b = 6.967 f 0.002; c = 13.154 f 0.004 A, and p = 97.64 * 0.01". The intensity data for 2280 reflections were collected o n a Picker automatic diffractometer, and the structure was solved from three-dimensional Patterson and Fourier syntheses. Full-matrix least-squares refinement, including anisotropic thermal parameters, gave a final conventional residual R = 0.052 for 1836 statistically retained reflections.The structure of the compound reveals a n unsymmetrically substituted ir-cyclohexadienyl ligand which is linked t o the iron atom by means of a propenoyl side chain. The presence of the ir-cyclohexadienyl ligand in the product is suggestive of a n extensive skeletal rearrangement in the ligand structure of the precursor. The most interesting feature of this intramolecular "head-to-tail" bonded iron u,ir complex is the positional shift of the iron atom out of the pseudomirror plane of the n-cyclohexadienyl ligand. Analysis of the bonding geometry reveals that considerable intramolecular strain accompanies the unusual side-chain linkage t o the iron atom.he reaction o f tricarbonyl-8,8-dibromobicyclo-(1) (a