Metal influence on the iso- and hetero-selectivity of complexes of bipyrrolidine derived salan ligands for the polymerisation of rac-lactide.
Metal influence on the iso- and hetero-selectivity of complexes of bipyrrolidine derived salan ligands for the polymerisation of rac-lactide.
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DOI：
10.1039/c5sc01819f
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发表时间：
2015-08-01
期刊：
影响因子：
8.4
通讯作者：
Lowe JP
中科院分区：
文献类型：
--
作者：
Jones MD;Brady L;McKeown P;Buchard A;Schäfer PM;Thomas LH;Mahon MF;Woodman TJ;Lowe JP
合成了一系列基于2，2 ′-联吡咯烷salan配体的配合物，并制备了全同立构和异同立构聚乳酸。本文合成了一系列基于双吡咯烷salan前配体的Ti（iv）、Hf（iv）和Al（iii）配合物。Hf（iv）配合物均为固态，手性配体与Hf（iv）以α-cis方式配位，而meso配体以β-cis几何构型配位。Hf（IV）配合物都是活跃的ROP的外消旋丙交酯在熔体中，与fluxional内消旋配合物提供一个强大的全同立构偏差Pm = 0.84。正如预期的那样，Hf（3）（OiPr）2聚合l-LA的速度比rac-LA快（kapp = 5.9 × 10-3 min-1 vs. 3.8 × 10-3 min-1）。对于Ti（iv）络合物，形成无规立构PLA。salan前配体也已络合到Al（iii），和新的Al-Me和Al-OiPr配合物的特征在于在固体和溶液状态。Al（1）（OiPr）在NMR时间尺度上是流动的，而Al（3）（OiPr）被锁定在溶液中，没有交换。有趣的是，铝（iii）配合物的3 H2产生PLA具有非常强的杂同立构的偏见P r高达0.87，而无规立构的PLA与1H 2。Al（3）（OiPr）与Mn和转化率呈线性关系。还进行了实验，并进行了讨论与外消旋LA的选择性引发剂的当量的添加。
A series complexes based on 2,2′-bipyrrolidine based salan ligands have been prepared and either isotactic or heterotactic PLA have been prepared. In this paper we have prepared a series of Ti(iv), Hf(iv) and Al(iii) complexes based on bipyrrolidine salan pro-ligands. The Hf(iv) complexes have all been characterised in the solid-state, the chiral ligands coordinate to Hf(iv) in an α-cis manner whereas the meso ligand coordinates in a β-cis geometry. The Hf(iv) complexes are all active for the ROP of rac-lactide in the melt, with the fluxional meso complex affording a strong isotactic bias P m = 0.84. As expected Hf(3)(OiPr)2 polymerised l-LA faster than rac-LA (k app = 5.9 × 10–3 min–1 vs. 3.8 × 10–3 min–1). For Ti(iv) complexes atactic PLA was formed. The salan pro-ligands have also been complexed to Al(iii), and the novel Al–Me and Al-OiPr complexes were characterised in the solid and solution state. Al(1)(OiPr) was fluxional on the NMR timescale, whereas Al(3)(OiPr) was locked in solution with no exchange. Interestingly, the Al(iii) complexes of 3H2 produce PLA with a very strong heterotactic bias P r upto 0.87, whereas atactic PLA is produced with 1H2. For Al(3)(OiPr) a linear relationship is observed with M n and conversion. Experiments with the addition of an equivalent of rac-LA to the selective initiators have also been performed and are discussed.
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影响因子：
2.8
作者：
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作者：
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DOI：
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发表时间：
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影响因子：
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作者：
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通讯作者：
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