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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >beta-diketiminate aluminium complexes: synthesis, characterization and ring-opening polymerization of cyclic esters
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beta-diketiminate aluminium complexes: synthesis, characterization and ring-opening polymerization of cyclic esters

机译：β-二酮铝化合物：环酯的合成，表征和开环聚合

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摘要

A series of aluminium alkyl complexes ( DI) AlEt2 (3a- m) bearing symmetrical or unsymmetrical beta-diketiminate ligand (BDI) frameworks were obtained from the reaction of triethyl aluminium and the corresponding beta-diketimine. The monomeric structure of the aluminium complex 3k was confirmed by an X-ray diffraction study, which shows that the aluminium center is coordinated by both of the nitrogen donors of the chelating diketiminate ligand and the two ethyl groups in a distorted tetrahedral geometry. Attempt to synthesize beta-diketiminate aluminium alkoxide complexes by the reactions of monochloride complex "(BDI- 2a) AlMeCl" ( 4) with alkali salts of 2-propanol gave unexpectedly an aluminoxane [(BDI-2a)AlMe](2)(mu-O) ( 7) as characterized by X- ray diffraction methods. Complexes 3a-m and [(2,6-(Pr2C6H3NCMe)-Pr-i)(2)HC]AlEt2 (8) were found to catalyze the ring-opening polymerization ( ROP) of epsilon-caprolactone with moderate activities. The steric and electronic characteristics of the ancillary ligands have a significant influence on the polymerization performance of the corresponding aluminium complexes. The introduction of electron-donating substituents at the para-positions of the aryl rings in the ligand resulted in an apparent decrease in catalytic activity. Complex 3h showed the highest activity among the investigated aluminium complexes due to the high electrophilicity of the metal center induced by the meta-trifluoromethyl substituents on the aryl rings. The increase of steric hindrance of the ligand by introducing ortho-substituents onto the phenyl moieties also resulted in a decrease in the catalytic activity. Although the viscosity average molecular weights ( M-n) of the obtained poly( caprolactone) s increased with the enhancement of monomer conversion, the ROPs of e- caprolactone initiated by complexes 3a- m and 8 were not well-controlled, as judged from the broad molecular weight distributions (PDI = 1.66-3.74, M-w/M-n) of the obtained polymers and the nonlinear relationship of molecular weight versus monomer conversion.
机译：从三乙基铝和相应的β-二酮亚胺的反应中获得了一系列带有对称或不对称的β-二酮基配体（BDI）的烷基铝配合物（DI）AlEt2（3a-m）。 X射线衍射研究证实了铝配合物3k的单体结构，该研究表明铝中心是由扭曲的四面体几何形状的螯合二酮化配体的两个氮供体和两个乙基协调的。尝试通过一氯化物络合物“（（BDI-2a）AlMeCl”（4）与2-丙醇的碱金属盐的反应来合成β-二酮化铝醇盐络合物，出乎意料的是铝氧烷[（BDI-2a）AlMe]（2）（mu -O）（7），其通过X射线衍射法表征。发现配合物3a-m和[（2,6-（Pr2C6H3NCMe）-Pr-i）（2）HC] AlEt2（8）催化具有中等活性的ε-己内酯的开环聚合（ROP）。辅助配体的空间和电子特性对相应的铝配合物的聚合性能具有重要影响。在配体的芳基环的对位引入给电子性取代基导致催化活性明显降低。由于芳基环上的间三氟甲基取代基诱导了金属中心的高亲电性，因此配合物3h在研究的铝配合物中显示出最高的活性。通过将邻位取代基引入苯基部分而增加配体的空间位阻，也会导致催化活性的降低。尽管获得的聚己内酯的粘均分子量（Mn）随着单体转化率的提高而增加，但由配合物3a-m和8引发的ε-己内酯的ROP并未得到很好的控制，所得聚合物的分子量分布（PDI ＝ 1.66-3.74，Mw / Mn）以及分子量与单体转化率的非线性关系。

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