Jones Matthew D, Brady Lauren, McKeown Paul, Buchard Antoine, Schäfer Pascal M, Thomas Lynne H, Mahon Mary F, Woodman Timothy J, Lowe John P
Department of Chemistry , University of Bath , Claverton Down , Bath BA2 7AY , UK . Email:
Doctoral Training Centre in Sustainable Chemical Technologies , University of Bath , Bath BA2 7AY , UK.
Chem Sci. 2015 Aug 1;6(8):5034-5039. doi: 10.1039/c5sc01819f. Epub 2015 Jun 17.
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- manner whereas the ligand coordinates in a β- geometry. The Hf(iv) complexes are all active for the ROP of -lactide in the melt, with the fluxional complex affording a strong isotactic bias = 0.84. As expected Hf()(OPr) polymerised l-LA faster than -LA ( = 5.9 × 10 min 3.8 × 10 min). 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-OPr complexes were characterised in the solid and solution state. Al()(OPr) was fluxional on the NMR timescale, whereas Al()(OPr) was locked in solution with no exchange. Interestingly, the Al(iii) complexes of H produce PLA with a very strong heterotactic bias upto 0.87, whereas atactic PLA is produced with H. For Al()(OPr) a linear relationship is observed with and conversion. Experiments with the addition of an equivalent of -LA to the selective initiators have also been performed and are discussed.
在本文中,我们基于联吡咯烷水杨醛前体配体制备了一系列钛(IV)、铪(IV)和铝(III)配合物。铪(IV)配合物均已在固态下进行了表征,手性配体以α-方式与铪(IV)配位,而配体以β-几何构型配位。铪(IV)配合物在熔体中对丙交酯的开环聚合均具有活性,其中具有动态变化的配合物产生了强烈的全同立构偏向((P = 0.84))。正如预期的那样,铪((IV))((OPr))使左旋丙交酯的聚合速度比右旋丙交酯更快((k_{l-LA}=5.9×10^{-3} min^{-1}),(k_{d-LA}=3.8×10^{-3} min^{-1}))。对于钛(IV)配合物,则形成了无规立构聚乳酸。水杨醛前体配体也已与铝(III)形成配合物,新型的铝-甲基和铝-异丙氧基配合物在固态和溶液状态下均进行了表征。铝((III))((OPr))在核磁共振时间尺度上是动态变化的,而铝((III))((OPr))在溶液中是固定的,没有交换。有趣的是,含氢的铝(III)配合物产生的聚乳酸具有非常强的间同立构偏向,高达(0.87),而含氢的则产生无规立构聚乳酸。对于铝((III))((OPr)),观察到了(P)与转化率之间的线性关系。还进行了向选择性引发剂中加入等量右旋丙交酯的实验并进行了讨论。