Shanghai Key Laboratory of Functional Materials Chemistry and Laboratory of Organometallic Chemistry, School of Chemistry and Molecular Engineering , East China University of Science and Technology , 130 Meilong Road , Shanghai 200237 , P. R. China.
Inorg Chem. 2018 Sep 4;57(17):11240-11251. doi: 10.1021/acs.inorgchem.8b01839. Epub 2018 Aug 22.
A series of tridentate achiral benzoxazolyl-based aminophenolate zinc complexes, LZnN(SiMe) (L = 2-{[benzoxazoly-CHN(R)-]CH}-6-R-4-R-CHO, R = R = Cl, R = Bn (1); R = R = Bu, R = Bn (2); R = trityl, R = Me: R = Bn (3); R = phenethyl (4); R = 3-methylbutyl (7); R = n-hexyl (8); R = cyclopentyl (9); R = cyclooctyl (11); R = 1-adamantyl (12)), was synthesized via the reactions of Zn[N(SiMe)] and 1 equiv of the corresponding aminophenol proligands. All of the complexes were obtained as racemates, and the X-ray diffraction studies confirmed the monomeric structures of typical complexes 11 and 12, where the metal center is tetra-coordinated by three donors of the aminophenolate ligand and one silylamido group. All of the complexes proved to be efficient initiators for the ring-opening polymerization of rac-lactide ( rac-LA) at ambient temperature, and the polymerizations were better controlled in the presence of 2-propanol. The substituents on the ortho-position of the phenoxide unit of the ligand and the skeleton nitrogen atom show significant influences on the stereoselectivity of the corresponding complex toward the polymerization of rac-LA, leading to the production of heterotactic biased polylactide (PLA) by complexes 1 and 2 ( P = 0.40-0.44) and moderately to highly isotactic PLA by complexes 3-12 ( P = 0.74-0.89). Detailed mechanism studies and microstructure analysis of typical PLA samples revealed that these zinc initiators afforded isotactic stereoblock PLAs via a chain-end control mechanism, and there is no obvious polymer exchange process during the polymerization process.
一系列的三齿非手性苯并恶唑基氨苯酚锌配合物，LZnN(SiMe)（L = 2-[[苯并恶唑基-CHN(R)-]CH]-6-R-4-R-CHO，R = R = Cl，R = Bn（1）；R = R = Bu，R = Bn（2）；R = 三苯甲基，R = Me：R = Bn（3）；R = 苯乙基（4）；R = 3-甲基丁基（7）；R = 正己基（8）；R = 环戊基（9）；R = 环辛基（11）；R = 1-金刚烷基（12）），通过 Zn[N(SiMe)] 和 1 当量的相应氨苯酚配体前体的反应合成。所有的配合物均以外消旋体的形式获得，并且 X 射线衍射研究证实了典型配合物 11 和 12 的单体结构，其中金属中心由氨基苯酚配体的三个供体和一个硅氨基基团四配位。所有的配合物都被证明是室温下 rac-丙交酯（rac-LA）开环聚合的有效引发剂，并且在存在 2-丙醇时聚合得到更好的控制。配体中酚氧基单元的邻位取代基和骨架氮原子对相应配合物对 rac-LA 聚合的立体选择性有显著影响，导致配合物 1 和 2 产生杂同规取向的聚丙交酯（PLA）（P = 0.40-0.44），而配合物 3-12 则产生中等至高度全同规 PLA（P = 0.74-0.89）。详细的机理研究和典型 PLA 样品的微观结构分析表明，这些锌引发剂通过链端控制机制提供了全同规立构嵌段 PLA，并且在聚合过程中没有明显的聚合物交换过程。
