Syntheses of bis- and tetra(trimethylsilyl) substituted lanthanocene methyl complexes and their catalyses for polymerizations of methyl methacrylate, ε-caprolactone and l-lactide

Bis- and tetra(trimethylsilyl) substituted lanthanocene methyl complexes, [(Me3SiC5H4)2SmMe]2 (2) {[1,3-(Me3Si)2C5H3]2SmMe}2 (4) and {[1,3-(Me3Si)2C5H3]2NdMe}2 (5) were prepared in high yield from trimethylsilyl- or bis(trimethylsilyl)cyclopentadienyllithium and LnCl3(THF)2 followed by the reaction with a stoichiometric amount of MeLi. The molecular structures of 2 and 4 as well as their precursors, [(Me3SiC5H4)2SmCl]2 (1) and [1,3-(Me3Si)2C5H3]2SmCl2Li(THF)2 (3) were determined by X-ray crystallographic analyses. The complexes 2, 4 and 5 perform the living polymerization of methyl methacrylate and the block copolymerizations of l-lactide with ε-caprolactone in high yields in the absence of any cocatalysts.