摘要
合成了一系列非对称β-二亚氨基镁硅氨基络合物,通过1H NMR、13C NMR和元素分析进行了表征,典型络合物经X-射线单晶衍射确定了其晶体结构.利用上述镁络合物在四氢呋喃中催化外消旋丙交酯开环聚合主要得到较低至中等杂规度的聚合物(Pr=0.64~0.80).镁络合物在室温、甲苯中对ε-己内酯开环聚合表现出中等的催化活性,得到较宽分子量分布的聚合物(Mw/Mn=1.37~1.67).利用典型镁络合物2进行催化L-丙交酯和ε-己内酯共聚的研究,采用分步加料法(两种不同加料顺序)以及一锅法均得到了两嵌段结构为主的共聚物.所得共聚物通过核磁氢谱、碳谱等测试,进一步确定了其微观链结构.
Magnesium silylamido complexes 1-7 bearing non-symmetric fl-diketiminate ligands were synthesized via the reactions of corresponding proligands I-IL1-7 with one equivalent of Mg[N（SiMe3）2]2 at 80 ℃ in toluene. All complexes were characterized by 1H NMR, 13C NMR and elemental analysis. The monomeric nature of complexes 1 and 5 in the solid state was further confirmed by X-ray diffraction studies. In both complexes, the metal center is tri-coordinated by the β-diketiminate ligand and one silylamido group. The very close bond lengths of two Mg-N bonds as well as close C-N distances of the chelate ring indicate significant delocalization. The apparent deviation of the magnesium center from the ligand backbone plane suggests a certain ηn-coordination nature of the ligand to the metal center. These magnesium silylamido complexes showed good catalytic activities for the ring-opening polymerization of rac-lactide under ambient conditions, and could polymerize 300 equivalents ofrac-lactide to high molecular weight polymers within short time in THF. The solvent effect played a critical role during the polymerization process. All complexes showed higher catalytic activity in THF than in toluene. Taking complex 2 as an example, a monomer conversion of 96% could be achieved within 10 min in THF, whereas a conversion of 80% could only be achieved within extended polymerization time of 210 min in toluene （Table 1, Entries 6 and 9, [LA]0/[Mg]0= 100）. Upon the addition of isopropanol, the activities of magnesium silylamido complexes 1-7 increased significantly. For instance, when the polymerization runs were carried in THF in the presence of isopropanol, the reaction time could be reduced to 10-20 min even with a high molar ratio of [LA]0/[Mg]0=300. Moreover, the type and location of the substituent（s） on the N-aryl group of the η-diketiminate ligand exerts a significant influence on the catalytic activity of the corresponding complex toward the polymerization of rac-lactide. In the absence of excess isopropanol,
出处
《化学学报》
SCIE
CAS
CSCD
北大核心
2018年第2期121-132,共12页
Acta Chimica Sinica
基金
国家自然科学基金(Nos.21074032
21474028)资助项目~~
关键词
β-二亚氨基配体
镁络合物
内酯
开环聚合
共聚
β-diketiminate ligand
magnesium complex
cyclic ester
ring-opening polymerization
copolymerization
