A NEW TYPE OF METAL-OLEFIN COMPLEX - SYNTHESIS AND CHARACTERIZATION OF 4 COMPOUNDS THAT CONTAIN AN ETHYLENE BRIDGE PERPENDICULARLY BISECTING A METAL METAL AXIS

The edge-sharing bioctahedral dimers M2X6(PR3)4 (M = Zr, Hf; X = Cl, Br; R = Et) react readily with 1,2-dichloroethane and ethylene to yield a novel type of metal-olefin complex, M2X6(PR3)4(CH2CH2). The characteristic feature of these complexes is a symmetrical olefin bridge, in which the olefin plane is perpendicular to the metal-metal axis, with the midpoint of the olefin coinciding with the midpoint of the metal-metal axis. Each compound was characterized by single-crystal X-ray diffraction studies. Zr2Cl6(PEt3)4(CH2CH2) (1): orthorhombic space group Pbca; a = 12.444 (3) Å, b= 15.878 (2) Å, c = 21.394 (4) Å, V = 4227 (2) Å3, and dcalc. = 1.408 g/cm3 for Z = 4. The structure was refined to R = 0.0628 and Rw = 0.0760 for 1021 reflections having I > 3σ(I). Zr2Br6(PEt3)4(CH2CH2) (2): monoclinic space group P21/n; a = 1 1.538 (3) Å, b = 15.063 (5) Å, c = 13.010 (4) Å, β = 108.41 (2)°, V = 2145 (2) Å3, and dcalc = 1.800 g/cm3 for Z = 2. The structure was refined to R = 0.0543 and R., = 0.0697 for 1109 reflections having I > 3σ(I). Hf2Cl6(PEt3)4(CH2CH2) (3): orthorhombic space group Pbca\ a = 12.393 (3) Å, b = 15.922 (6) Å, c = 21.339 (6) Å, V = 4211 (4) Å3, and dcalc = 1.688 g/cm3 for Z = 4. The structure was refined to R = 0.0318 and Rw = 0.0480 for 1841 reflections having I > 3σ(I). Hf2Br6(PEt3)4(CH2CH2) (4): monoclinic space group P21/n; a = 11.482 (2) Å, b = 15.093 (1) Å, c = 12.979 (2) Å, β = 108.14 (1)°, V = 2137 (1) Å3, and dcalc = 2.034 g/cm3 for Z = 2. The structure was refined to R = 0.0393 and Åw = 0.0531 for 1109 reflections with I > 3σ(I). Molecular orbital calculations on Zr2Cl6(PH3)4(CH2CH2) by the Fenske-Hall method have been carried out to elucidate the bonding in the M2(μ-η4-olefin) unit. The calculations show a HOMO resulting from an overlap between suitable dπ orbitals on the metal atoms with the π* orbital of CH2CH2. © 1990, American Chemical Society. All rights reserved.