Lanthanocene (Ln = PrIII, YbIII) chlorides involving tetramethyldisiloxane-interlinked cyclopentadienyl ligands

Article abstract of DOI:10.1016/0022-328X(94)88111-1

Two new lanthanocenophanes <Pr^IIICl*THF>x (2; x=1 or 2) and <Yb^IIICl>2 (3), were made from LnCl3 (Ln=Pr or Yb) and K2 in THF.The 1H NMR spectra of THF-d₈ solutions of paramagnetic 2 (at +35 to -25 deg C) and 3 (at < 10 deg C) reflect an asymmetrical disposition of the siloxy linkage, while solutions of 2 in CD2Cl2 (at 20 deg C) and 3 in THF-d₈ (at > 10 deg C), respectively, display somewhat less complex 1H NMR spectra consistent with a virtually symmetrical position of the Me2SiOSiMe2 unit with respect to the cent-Ln-cent' plane (cent = C5H4Si centroid).A low temperature (-100 deg C) single-crystal X-ray study of 3 has confirmed the presence of centrosymmetric, Cl-bridged dimers in which the molecular configuration of the mononuclear Yb^IIICl2 units correspond to that of the previously described complex <IVCl2> (1).The high-resolution mass spectrum of 3 displays several signals from dinuclear fragments, the B/E-linked scans of which suggest, inter alia, intramolecular reorientation of at least one O(Me2SiC5H4)2 ligand from the chelating into a metal-bridging position.Key words: Ytterbium; Praseodymium; Metallocenes; Lanthanides; Chiral metallocenophanes; Crystal structure