Ligand-Controlled Stereoselective Synthesis of Heterotactic Polylactide with Titanium(IV) Complexes

Stereoselective synthesis of polylactic acid (PLA) was achieved using titanium­(IV) complexes. The NO3 ligands prepared from 2,2′-dihydroxybenzophenone and salicylaldehyde derivatives were used to control the stereoselectivity of Ti­(IV)-catalyzed polymerization of rac-lactide, in which a substituted ligand provided heterotactic PLA with high stereoselectivity. Density functional theory calculations revealed that the ligand structure is crucial for differentiating reaction pathways, and that the octahedral transition states are stabilized by the preorganized intermediates.

本研究利用钛(IV)配合物实现了聚乳酸（polylactic acid，PLA）的立体选择性合成。由2,2'-二羟基二苯甲酮与水杨醛衍生物制备得到的NO3型配体，可用于调控钛(IV)催化外消旋丙交酯（rac-lactide）聚合的立体选择性；其中带有取代基的配体能够制备得到具有高立体选择性的间规聚乳酸。密度泛函理论（Density functional theory，DFT）计算结果表明，配体结构对区分不同反应路径至关重要，且八面体过渡态可通过预组织中间体实现稳定化。