Synthesis and Characterization of a Series of New Lanthanide Derivatives Supported by Silylene-Bridged Diamide Ligands and Their Catalytic Activities for the Polymerization of Methyl Methacrylate

Abstract

The synthesis and structures of a series of new lanthanide complexes supported by silylene-bridged diamide ligands are described. The complex {[Me2Si(NPh)2]YbCl(TMEDA)}2 (1) can be synthesized by YbCl3 with PhLiNSiMe2NLiPh in 1:1 molar ratio in good yield. Treatment of {[Me2Si(NPh)2]LnCl(THF)n}2 in situ and Cp‘Na in 1:2 molar ratio afforded a series of new anionic complexes: {[Me2Si(NPh)2]LnCp‘2}{Li(DME)3} [Cp‘ = C5H5, Ln = Yb (2); Sm(3); Cp‘ = MeC5H4, Ln = Yb(4)]. Complexes 2 and 4 can also be synthesized by Cp‘2YbCl with PhLiNSiMe2NLiPh in 1:1 molar ratio in good yield. The complex 1 reacted with PhLiNSiMe2NLiPh in 1:1 molar ratio to yield an anionic amide complex, {[Me2Si(NPh)2]2Yb(THF)2Li(THF) (6). These complexes were characterized by elemental analysis, IR, and 1H NMR. The molecular structures of 2−4 and 6 were further determined by X-ray diffraction techniques. These anionic complexes showed high activity for the polymerization of methyl methacrylate (MMA) at rt, giving syndiotactic-rich polymers with high molecular weights (Mn > 104) and relatively narrow molecular weight distributions (Mw/Mn = 1.54−1.85).