Cs-Symmetric ansa-Lanthanocenes Designed for Stereospecific Polymerization of Methyl Methacrylate. Synthesis and Structural Characterization of Silylene-Bridged Fluorenyl Cyclopentadienyl Lanthanide Halides, Amides, and Hydrocarbyls

A series of new Cs-symmetric organolanthanocene chlorides, [R2Si(Flu)(R‘Cp)Ln(μ-Cl)]2 (Flu = C13H8, fluorenyl; Cp = C5H3) (R = Me, R‘ = H, Ln = Y (1), Lu (2), Dy (3), Er (4); R = Ph, R‘ = tBu, Ln = Y (5), Dy (6)), has been synthesized by the reaction of anhydrous lanthanide chloride with the dilithium salt of the ligand Me2Si(FluH)(CpH). Treatment of the resulting chlorides with ME(TMS)2 (M = Li or K, E = N, CH) gave the amide and hydrocarbyl derivatives Me2Si(Flu)(Cp)LnE(TMS)2 (E = N, Ln = Dy (7), Er (9); E = CH, Ln = Dy (8), Er (10)). X-ray structures of chloride compounds reveal unusual Cp−SiMe2−Cp bridging dimeric coordination. All of the amide and hydrocarbyl complexes show normal chelating structure and exhibit apparently intramolecular γ-agostic Ln−Me−Si interaction. These complexes are active for the polymerization of methyl methacrylate.