Synthesis, structure, and catalytic activity of benzyl thorium metallocenes

Treatment of the chloride metallocene [η5-1,3-(Me3C)2C5H3]2ThCl2 or [η5-1,2,4-(Me3C)3C5H2]2ThCl2 with 2 equiv of PhCH2K in diethyl ether at room temperature gives, after recrystallization from a benzene solution, the benzyl metallocenes [η5-1,3-(Me3C)2C5H3]2Th(CH2Ph)2 (1) and [η5-1,2,4-(Me3C)3C5H2]2Th(CH2Ph)2 (2), respectively, in good yields. Complexes 1 and 2 have been characterized by various spectroscopic techniques, elemental analyses, and X-ray diffraction analyses. They are active catalysts for the polymerization of rac-lactide, leading to the atactic polylactides with high molecular weights and narrow molecular weight distributions.