This contribution discusses lanthanide hydrocarbyl and hydride chemistry based upon Me2SiCp″2 supporting ligation (Cp″ = η5-(CH3)4C5). The reaction of MCl3, M = Nd, Sm, or Lu, with Me2Si(Cp″Li)2 yields the precursor complexes Me2SiCp″2MCl2-Li(ether) 2+. A slightly different workup procedure yielded (Me2SiCp″2NdCl)2Cl -Li(THF)2+, which crystallizes in the monoclinic space group P2/n with two molecules in a unit cell of dimensions (-133°C) a = 11.666 (3) Å, b = 12.585 (3) Å, c = 17.765 (6) Å, and β = 94.91 (2)°. Least-squares refinement led to a value for the conventional R index (on F) of 0.045 for 3231 independent reflections having I > 3σ(I). The structure consists of two Me2Si(η5-Cp″)2Nd units bridged by a chloride ion and an Nd-Cl-⋯Li+⋯Cl-Nd linkage. The Nd-Cl distances are 2.802 (1) and 2.754 (2) Å, and 〈Cl-Nd-Cl = 97.1 (1)°. The (ring centroid)-Nd-(ring centroid) angle is 121.3°. The Nd-C(ring) distances vary from 2.647 (7) to 2.815 (7) Å, with the shorter distances being to those carbon atoms closest to the Me2Si bridge. The Me2SiCp″2MCl2 compounds react with LiCH[Si(CH3)3]2 to yield ether- and halide-free Me2SiCp″2MCH[Si(CH3)3] 2 derivatives. The M = Nd compound crystallizes in the monoclinic space group P21/n with four molecules in a cell of dimensions (-125°C) a = 10.229 (2) Å, b = 15.623 (3) Å, c = 19.687 (3) Å, and β = 105.41 (2)°. Least-squares refinement led to a value of the conventional R index (on F) of 0.044 for 3407 independent, absorption corrected reflections having I > 3σ(I). The molecular structure consists of monomeric Me2SiCp″2NdCH[Si(CH3)3] 2 units with η5-Cp″ coordination, and 〈(ring centroid)-Nd-(ring centroid) = 121.6°. The CH[Si(CH3)3]2 fragment is coordinated to the Me2SiCp″2Nd center in a highly unsymmetrical fashion with a Nd-C σ-bond distance of 2.506 (7) Å and a secondary interaction to one methyl group of Nd-C = 2.862 (8) Å. The Si-C distance to this carbon atom is significantly longer than the other Si-CH3 contacts. Approximate hydrogen atom locations argue against an important M⋯HC(methyl) interaction and reveal a bending of the hydrogen atom on the σ-bonded carbon atom toward the metal with 〈Nd-C-H ∼ 76°. Reaction of the Me2SiCp″2MCH[Si(CH3)3] 2 complexes with H2 yields the coresponding hydrides, which are formulated as Me2SiCp″2M(μ-H)2MCp″ 2SiMe2 dimers. These compounds are active agents for the polymerization of ethylene as well as for the oligomerization of propylene and 1-hexene. For a constant lanthanide ion, a (Me2SiCp″2MH)2 hydride is an ca. 10 times more active for this reaction than the corresponding (Cp′2MH)2 hydride. Deprotonation of Me2SiCp″2LuCH(TMS)2 with t-BuLi/TMEDA leads to a metallacycle formulated as Li(TMEDA)3+-Me2SiCp″2LuCH 2Si(CH3)2C(H)Si(CH2) 3-.
|Number of pages||8|
|Journal||Journal of the American Chemical Society|
|Publication status||Published - 1985|
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