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

Article abstract of DOI:10.1021/om000276f

A series of new C_s-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.