Hexafluorobutadiene reacts with [RhCl(PPh3)3] in hot benzene to afford the 5-coordinate tetrafluorometallacyclopentenone (72-tetrafluorovinylketene) complex 7, in which a CF2 group has been hydrolyzed to a ketone by adventitious water. Complex 7 has been characterized by spectroscopic means and by an X-ray crystallographic study of its acetone solvate: C43HxF402P2-ClRh, monoclinic, P21/n, a = 18.5706(33) A, b = 10.2670(12) A, c = 21.8591(31) A, 8 = 107.793(13)O, V = 3968.3(10) A3,Z = 4. The corresponding 6-coordinate derivatives 9 and 10can be prepared by treatment of 7 with thallium acetylacetonate and trimethylphosphine, respectively. The initial reaction of hexafluorobutadiene with [RhCl(PPh3)3] is shown to proceed via the intermediacy of a 5-coordinate hexafluorometallacyclopentene complex 11 in which one a-CF2 group is remarkably sensitive to hydrolysis. Complex 12, a coordinatively saturated analogue of 11, can be isolated from the reaction of hexafluorobutadiene with the trimethylphosphine complex [RhCl(PMe&] and has also been characterized b X-ray crystallography: C I~H~T F~P~C~R~, monoclinic, Pbca, a = 17.951(4) A, b = 18.619(3) c = 25.466(4) A, V = 8512.1(29) A3, 2 = 16. Compound 12 is far less moisture sensitive than its coordinatively unsaturated analogue 11 but does not undergo reaction with water under more forcing conditions,' or upon chromatography, to give an isomeric metallacyclopentenone ligand in complex 13, which has also been characterized by X-ray crystallo raphy: C13H2,F40P3ClRh, monoclinic, m l / n , a = 8.688(3) A, b = 14.712(4) A, c = 16.129(5) 1, 8 = 92.12(2)O, V = 2060.3(12) A3, Z = 4. The crystal of 13 chosen for study was contaminated with a solid solution impurity, most probably 15, which is a proposed intermediate in the hydrolysis reaction. Mechanisms are proposed to account for the observed a-and 8-hydrolysis pathways.

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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

[2 + 2]-Cycloaddition of an Iminoborane to a Methylene-Titanium Coordination CompoundThe iminoborane tBuB= NiBu (lc) reacts with the short-lived titanaethene H,C =TiCp2 (3) to give the l-aza-2-bora-4-titanacyclobutane 4c by [2 + 21-cycloaddition. A corresponding reaction with the more reactive iminoboranes 1 a, b, d is indicated by NMR data. CpaTi-CH2n,'