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 C-s-symmetric organolanthanocene chlorides, [R2Si(Flu)(R'Cp)Ln(mu-Cl)](2) (Flu = C13H8 fluorenyl; Cp = C5H3) (R = Me, R' = H, Ln = Y (1), Lu (2), Dy (3), Er (4); R = Ph, R' = Bu-t, 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-SiMe2Cp bridging dimeric coordination. All of the amide and hydrocarbyl complexes show normal chelating structure and exhibit apparently intramolecular gamma-agostic Ln-Me-Si interaction. These complexes are active for the polymerization of methyl methacrylate.