Department of Chemistry, Washington University in St. Louis, Campus Box 1134, 1 Brookings Drive, St. Louis, Missouri 63130, United States.
School of Chemistry, Tel Aviv University, Ramat Aviv, Tel Aviv 69997801, Israel.
J Am Chem Soc. 2022 Nov 2;144(43):20047-20055. doi: 10.1021/jacs.2c09073. Epub 2022 Oct 18.
Aspects of the proposed pathway combining chain-end and enantiomorphic site control for the stereospecific polymerization of lactide (LA) were investigated through studies of aluminum complexes supported by enantiopure and racemic bipyrrolidine-based salan ligands, LigAlOBn and LigAlOBn. Spectroscopic analysis of stoichiometric initiation reactions and the definition of the stereochemistry of the selective formation of the "match" single-insertion products by X-ray crystallography led to key conclusions about the observed stereocontrol. Notably, it was determined to rely heavily on the preference for the trio of stereocenters around the metal to have a "match" formation (-ligand + -polymer), which works synergistically with the enantiomorphic site preference of the catalyst to ring-open next to a stereocenter of a monomer of the same chirality as that of the ligand, resulting in highly heterotactic or syndiotactic PLA from - or -LA, respectively.
通过对由手性和外消旋双吡咯烷基沙兰配体 LigAlOBn 和 LigAlOBn 支持的铝配合物的研究，探讨了结合链末端和对映选择性反应控制的立体定向聚合丙交酯 (LA) 的方案的各个方面。通过光谱分析等手段对计量引发反应进行研究，并通过 X 射线晶体学确定选择性形成“匹配”单插入产物的立体化学，从而得出了关于观察到的立体控制的关键结论。值得注意的是，它主要依赖于金属周围的立体中心三重体具有“匹配”形成（-配体+ -聚合物）的强烈偏好，这与催化剂的对映选择性反应控制协同作用，在与配体相同手性的单体的立体中心旁边开环，从而得到高异规或间规 PLA 来自 - 或 -LA。
