18402-76-1Relevant academic research and scientific papers
Lanthanocene (Ln = PrIII, YbIII) chlorides involving tetramethyldisiloxane-interlinked cyclopentadienyl ligands
Graeper, Jens,Fischer, R. Dieter,Paolucci, Gino
, p. 87 - 96 (1994)
Two new lanthanocenophanes PrIIICl*THF>x (2; x=1 or 2) and YbIIICl>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 8 (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 YbIIICl2 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
Role of torsional strain in the ring-opening polymerisation of low strain [: N] nickelocenophanes
Musgrave, Rebecca A.,Hailes, Rebekah L. N.,Annibale, Vincent T.,Manners, Ian
, p. 9841 - 9852 (2019/11/13)
Ring-opening polymerisation (ROP) of strained [1]-and [2]metallocenophanes and related species is well-established, and the monomer ring-strain is manifest in a substantial tilting of the cyclopentadienyl ligands, giving α angles of ～14-32°. Surprisingly, tetracarba[4]nickelocenophane [Ni(η5-C5H4)2(CH2)4] (2) undergoes ROP (pyridine, 20 °C, 5 days) to give primarily insoluble poly(nickelocenylbutylene) [Ni(η5-C5H4)2(CH2)4]n (12), despite the lack of significant ring-tilt. The exoenthalpic nature of the ROP was confirmed by DFT calculations involving the cyclic precursor and model oligomers (ΔH0ROP =-14 ± 2 kJ mol-1), and is proposed to be a consequence of torsional strain present in the ansa bridge of 2. The similarly untilted disila-2-oxa[3]nickelocenophanes [Ni(η5-C5H4)2(SiMe2)2O] (13) and [Ni(η5-C5H4)2(SiMePh)2O] (14) were found to lack similar torsional strain and to be resistant to ROP under the same conditions. In contrast, 1-methyltricarba[3]nickelocenophane {Ni(η5-C5H4)2(CH2)2[CH(CH3)]} (15) with a significant tilt angle (α ～ 16°) was found to undergo ROP to give soluble polymer {Ni(η5-C5H4)2(CH2)2[CH(CH3)]}n (18). The reversibility of the process in this case allowed for the effects of temperature and reaction concentration on the monomer-polymer equilibrium to be explored and thereby thermodynamic data to be elucidated (ΔH0ROP =-8.9 kJ mol-1, ΔG0ROP =-3.1 kJ mol-1). Compared to the previously described ROP of the unsubstituted analogue [Ni(η5-C5H4)2(CH2)3] (1) (ΔH0ROP =-10 kJ mol-1, ΔG0ROP =-4.0 kJ mol-1), the presence of the additional methyl substituent in the ansa bridge appears to marginally disfavour ROP and leads to a corresponding decrease in the equilibrium polymer yield.
