ZIRCONECENOPHANE DICHLORIDES WITH DI-SILOXANE-BRIDGED AND TRISILOXANE-BRIDGED RING LIGANDS - CRYSTAL-STRUCTURE OF RAC-[1,1,3,3-TETRAMETHYLDISILOXANE-DIYL-BIS(3-TERT-BUTYL-ETA(5)-CYCLOPENTADIENYL)ZIRCONIUM(IV)DICHLORIDE]

The three novel zirconocenophane dichlorides [{O(Me(2)SiC(5)H(4))(2)}ZrCl2] (3), [{O(Me(2)SiC(5)H(3)-(C4H9)-C-t)(2)}ZrCl2] (4) and [{Me(2)Si(OMe(2)SiC(5)H(4))(2)}ZrCl2](n) (5) have been prepared and characterized by H-1 NMR spectroscopy. According to a successful single-crystal X-ray study, 4 crystallizes from n-hexane as a racemic mixture with exclusively 1,3-disubstituted cyclopentadienyl ligands and Cl-2 centres oriented transoid to the O atoms. 4: monoclinic; space group P2(1)/c, a = 1167.7(2), b = 1590.2(2), c = 1491.3(3) pm; beta = 104.64(2)degrees; R = 0.061 (R(w) = 0.058). In solution (room temperature), all three complexes are fluxional; moreover the NMR spectrum of 4 displays the resonances of two isomers (25:1). According to a mass spectrometry study of 5, the B-2/E-coupled scan of the molecular ion M(+) (m/z = 494) indicates at least four ''parent'' fragments with 509 less than or equal to m/z less than or equal to 1275, suggesting here dinuclear or even trinuclear precursors.