LANTHANOCENE (LN = PRIII, YBIII) CHLORIDES INVOLVING TETRAMETHYLDISILOXANE-INTERLINKED CYCLOPENTADIENYL LIGANDS

Two new lanthanocenophanes [{O(Me2SiC5H4)2}PrIIICl.THF]x (2; x = 1 or 2) and [{O(Me2SiC5H4)2}YbIIICl]2 (3), were made from LnCl3 (Ln = Pr or Yb) and K2[O(Me2SiC5H4)2] in THF. The H-1 NMR spectra of THF-d8 solutions of paramagnetic 2 (at +35 to -25-degrees-C) and 3 (at < 10-degrees-C) reflect an asymmetrical disposition of the siloxy linkage, while solutions of 2 in CD2Cl 2 (at 20-degrees-C) and 3 in THF-d8 (at > 10-degrees-C), respectively, display somewhat less complex H-1 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-degrees-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 {O(Me2SiC5H4)2}YbIIICl2 units correspond to that of the previously described complex [{O(Me2SiC5H4)2TiIVCl2] (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.