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Abstract

Reactions of the anionic complex [(Cp-CMe₂-Flu)YCl₂]^-[Li(ether)₄]⁺ (1) (Cp = C₅H₄, Flu = 9-C₁₃H₈), prepared in situ from YCl₃(THF)_3.5 and 1 molar equiv of the dilithium salt [Cp-CMe₂-Flu]Li₂, with equimolar amounts of RLi give alkyl mono-THF complexes [(Cp-CMe₂-Flu)]Y(R)(THF) (R = CH(SiMe₃)₂, 3; CH₂SiMe₃, 4) in high yields. The solid-state structure of 3 was established by X-ray diffraction, showing the fluorenyl moiety symmetrically coordinated to yttrium in an intermediary η³-η⁵ mode. Hydrogenolysis of 3 and 4 with H₂ or PhSiH₃ gives the hydride {[(μ:η⁵,η⁵-Cp-CMe₂-Flu)]Y(μ-H)(THF)}₂ (5). The solid-state structure of 5 was determined by X-ray diffraction, revealing a dimeric structure with both bridging Cp-CMe₂-Flu and hydride ligands (Y−H = 1.99(4)−2.01(4) Å). Complex 5 is the first structurally characterized example of a group 3 metal hydride stabilized by a fluorenyl ligand. Reaction of 1 with PhCH₂MgBr gives, instead of a benzyl derivative, the neutral base-free bromo complex {[(η⁵,η⁵-Cp-CMe₂-Flu)]Y(μ-Br)}₂ (6), which shows a dimeric structure in the solid state with chelating Cp-CMe₂-Flu and bridging bromide ligands. Introduction of the bulky tert-butyl substituent on the Cp ring of the ligand system enabled the preparation of the neutral chloro complex [(3-^tBuCp)-CMe₂-Flu]YCl(THF) (7), using a salt elimination between the dilithium salt of the ligand and YCl₃(THF)_3.5. Reaction of 7 with LiCH(SiMe₃)₂ gives the alkyl complex {[(3-^tBuCp)-CMe₂-Flu)]Y(CH(SiMe₃)₂) (8), which contains no THF molecule in its coordination sphere in contrast to unsubstituted analogues 3 and 4. Preliminary studies of the catalytic activity of these new complexes for ethylene and MMA polymerization are reported.