Highly Reactive Organolanthanides. Synthesis, Chemistry, and Structures of 4f Hydrocarbyls and Hydrides with Chelating Bis(polymethylcyclopentadienyl) Ligands

This contribution discusses lanthanide hydrocarbyl and hydride chemistry based upon Me₂SiCp“₂supporting ligation (Cp“ = 7/⁵-(CFf_{3 4}C₅). The reaction of MC1₃, M = Nd, Sm, or Lu, with Me₂Si(Cp“Li)₂yields 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) A, with the shorter distances being to those carbon atoms closest to the Me₂Si bridge. The Me₂SiCp“₂MCl₂compounds react with LiCH[Si(CH_{3 3}]₂to yield ether- and halide-free Me₂SiCp“₂MCH[Si(CH_{3 3}]₂derivatives. 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(CH_{3 3}]₂units with η⁵-Cp“ coordination, and ∠(ring centroid)-Nd-(ring centroid) = 121.6°. The CH[Si(CH_{3 3}]₂fragment 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-CH₃contacts. 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(CH_{3 3}]₂complexes with H₂yields the coresponding hydrides, which are formulated as Me₂SiCp“₂M(μ-H)₂MCp“2SiMe₂dimers. 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)₂hydride is an ca. 10 times more active for this reaction than the corresponding (Cp'₂MH)₂hydride. Deprotonation of Me₂SiCp”₂LuCH(TMS)₂with t-BuLi/TMEDA leads to a metallacycle formulated as Li(TMEDA)₃ ⁺-Me₂SiCp_“2LuCH₂Si(CH_{3 2}C(H)Si(CH_{2 3} ^-.