BIS(CYCLOOCTATETRAENE) DERIVATIVES OF ZIRCONIUM(IV) AND HAFNIUM(IV) - SYNTHESES AND LEWIS BASE ADDUCTS - CRYSTAL-STRUCTURES OF [ZR(ETA-8-C8H8)(ETA-4-C8H8)], [HF(ETA-8-C8H6(SIME3)2)-(ETA-4-C8H6(SIME3)2)], [ZR(ETA-8-C8H8)(ETA-4-C8H8)(NH3)] AND [ZR(ETA-8-C8H8)(ETA-4-C8H8)(CNBUT)]

The syntheses of [M(eta-8-C8H8)(eta-4-C8H8)] (M = Zr, 2 or Hf, 3) and [M{eta-8-C8H6(SiMe3)2}{eta-4-C8H6(SiMe3)2}] (M = Zr, 4 or Hf, 5) are reported. The eta-8 and eta-4 bonding modes for C8H8 were established in the solid state by X-ray analyses, while in solution a single C8H8 environment was observed by H-1 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(t)NC and the adducts [Zr(eta-8-C8H8)(eta-4-C8H8)(NH3)] 6 and [M(eta-8-C8H8)(eta-4-C8H8)(CNBu(t))] (M = Zr, 7 or Hf, 8) have been isolated and characterized by X-ray analysis. Crystallographic details: 2, monoclinic, space group P2(1)/c, a = 13.754(1), b = 7.798(1), c = 12.753(1) angstrom, beta = 114.02(1)-degrees, Z = 4 and R = 0.037 for 1267 independent observed reflections; 5, orthorhombic, space group Pca2(1), a = 14.418(1), b = 11.285(1), c = 18.898(1) angstrom, Z = 4 and R = 0.036 for 2239 independent observed reflections; 6, orthorhombic, space group P2(1)2(1)2(1), a = 9.815(1), b = 14.129(2), c = 9.561(1) angstrom, Z = 4 and R = 0.022 for 1556 independent observed reflections; 7, triclinic, space group P1BAR, a = 11.172(1), b = 13.469(1), c = 14.303(1) angstrom, alpha = 62.80(1), beta = 78.01(1), gamma = 77.26(1)-degrees, Z = 4 and R = 0.028 for 2994 independent observed reflections.