Synthesis of Rare-Earth Metal Amides Bearing an Imidazolidine-Bridged Bis(phenolato) Ligand and Their Application in the Polymerization of l-Lactide

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• 作者：Zhongjian Zhang ; Xiaoping Xu ; Wenyi Li ; Yingming Yao ; Yong Zhang ; Qi Shen ; Yunjie Luo
• 刊名：Inorganic Chemistry
• 出版年：2009
• 出版时间：July 6, 2009
• 年：2009
• 卷：48
• 期：13
• 页码：5715-5724
• 全文大小：828K
• 年卷期：v.48,no.13(July 6, 2009)
• ISSN：1520-510X

文摘

A series of neutral rare-earth metal amides supported by an imidazolidine-bridged bis(phenolato) ligand were synthesized, and their catalytic activity for the polymerization of l-lactide was explored. The amine elimination reactions of Ln[N(TMS)₂]₃(μ-Cl)Li(THF)₃ with H₂[ONNO] {H₂[ONNO] = 1,4-bis(2-hydroxy-3,5-di-tert-butyl-benzyl)-imidazolidine} in a 1:1 molar ratio in tetrahydrofuran (THF) gave the neutral rare-earth metal amides [ONNO]Ln[N(TMS)₂](THF) [Ln = La (1), Pr (2), Nd (3), Sm (4), Yb (5), and Y (6)] in high isolated yields. All of these complexes are fully characterized. X-ray structural determination revealed that complexes 1−6 are isostructural and have a solvated monomeric structure. The coordination geometry around each of the rare-earth metal atoms can be best described as a distorted trigonal bipyramid. It was found that complexes 1−6 are efficient initiators for the ring-opening polymerization of l-lactide, and the ionic radii of the central metals have a significant effect on the catalytic activity. A further study revealed that these rare-earth metal amides can initiate l-lactide polymerization in a controlled manner in the presence of 1 equiv of isopropyl alcohol.