Rare earth metal benzyl complexes bearing bridged-indenyl ligand for highly active polymerization of methyl methacrylate

The novel anionic bridged-indenyl rare earth metal benzyl complexes [{C9H6SiMe2(CH2)2SiMe2C9H6}Ln(CH2C6H4-p-tBu)2][Li(THF)4] (Ln = Y (1), Lu (2)) were synthesized by an acid–base reaction of C9H7SiMe2(CH2)2SiMe2C9H7 with one equiv. of rare earth metal trisbenzyl complexes, which were formed in situ from the reaction of anhydrous LnCl3 with LiCH2C6H4-p-tBu in 1:3 molar ratio in THF. The complexes were characterized by elemental analysis, NMR spectroscopy, FT-IR spectroscopy, and X-ray structural analysis in the case of 2. Both complexes are active for the polymerization of methyl methacrylate (MMA) to afford high molecular weight and narrow molecular weight distribution PMMA. The molecular weights of PMMA could be controlled using 1 as a polymerization initiator in chlorobenzene at −40 °C.