School of Chemistry, Tel Aviv University, Ramat Aviv, Tel Aviv 69978 (Israel).
Angew Chem Int Ed Engl. 2015 Dec 1;54(49):14858-61. doi: 10.1002/anie.201503111. Epub 2015 May 15.
Alkyl aluminum complexes of chiral salan ligands assembled around the 2,2'-bipyrrolidine core form as single diastereomers that have identical configurations of the N donors. Active catalysts for the polymerization of lactide were formed upon the addition of benzyl alcohol. Polymeryl exchange between enantiomorphous aluminum species had a dramatic effect on the tacticity of the poly(lactic acid) (PLA) in the polymerization of racemic lactide (rac-LA): The enantiomerically pure catalyst of the nonsubstituted salan ligand led to isotactic PLA, and the racemic catalyst exhibited lower stereocontrol. The enantiomerically pure catalyst of the chloro-substituted salan ligand led to PLA with a slight tendency toward heterotacticity, whereas the racemic catalyst led to PLA of almost perfect heterotacticity following an insertion/auto-inhibition/exchange mechanism.
手性沙兰配体的烷基铝配合物围绕 2,2'-联吡啶核心组装形成单一非对映异构体，其 N 供体具有相同的构型。加入苄醇后，形成了用于丙交酯聚合的活性催化剂。手性铝物种之间的聚合交换对旋光性丙交酯（rac-LA）聚合中聚乳酸（PLA）的立构规整性有显著影响：未取代沙兰配体的对映体纯催化剂导致全同立构 PLA，而外消旋催化剂则表现出较低的立体选择性。氯取代沙兰配体的对映体纯催化剂导致 PLA 具有轻微的间同立构倾向，而外消旋催化剂则导致 PLA 几乎具有完美的间同立构性，遵循插入/自动抑制/交换机制。
