Bis(cyclooctatetraene) derivatives of zirconium(IV) and hafnium(IV): syntheses and Lewis base adducts. Crystal structures of [Zr(η8-C8H8)(η4-C8H8)], [Hf{η8-C8H6(SiMe3)2}{η4-C8H6(SiMe3)2}], [Zr(η8-C8H8)(η4-C8H8)(NH3)] and [Zr(η8-C8H8)(η4-C8H8)(CNBut)]

Abstract

The syntheses of [M(η⁸-C₈H₈)(η⁴-C₈H₈)](M = Zr, 2 or Hf, 3) and [M{η⁸-C₈H₆(SiMe₃)₂}{η⁴-C₈H₆(SiMe₃)₂}](M = Zr, 4 or Hf, 5) are reported. The η⁸ and η⁴ bonding modes for C₈H₈ were established in the solid state by X-ray analyses, while in solution a single C₈H₈ environment was observed by ¹H NMR spectroscopy even at low temperature in accord with fluxional behaviour for these compounds. Complexes 2–5 behave as Lewis acids toward tetrahydrofuran, NH₃ and Bu^tNC and the adducts [Zr(η⁸-C₈H₈)(η⁴-C₈H₈)(NH₃)]6 and [M(η⁸-C₈H₈)(η⁴-C₈H₈)(CNBu^t)](M = Zr, 7 or Hf, 8) have been isolated and characterized by X-ray analysis. Crystallographic details: 2, monoclinic, space group P2₁/c, a= 13.754(1), b= 7.798(1), c= 12.753(1)Å, β= 114.02(1)°, Z= 4 and R= 0.037 for 1267 independent observed reflections; 5, orthorhombic, space group Pca2₁, a= 14.418(1), b= 11.285(1), c= 18.898(1)Å, Z= 4 and R= 0.036 for 2239 independent observed reflections; 6, orthorhombic, space group P2₁2₁2₁, a= 9.815(1), b= 14.129(2), c= 9.561(1)Å, Z= 4 and R= 0.022 for 1556 independent observed reflections; 7, triclinic, space group P, a= 11.172(1), b= 13.469(1), c= 14.303(1)Å, α= 62.80(1), β= 78.01(1), γ= 77.26(1)°, Z= 4 and R= 0.028 for 2994 independent observed reflections.