Mechanism of living lactide polymerization by dinuclear indium catalysts and its impact on isoselectivity.
Mechanism of living lactide polymerization by dinuclear indium catalysts and its impact on isoselectivity.
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DOI：
10.1021/ja3048046
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发表时间：
2012-07
影响因子：
15
通讯作者：
Insun Yu;Alberto Acosta-Ramírez;P. Mehrkhodavandi
中科院分区：
文献类型：
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作者：
Insun Yu;Alberto Acosta-Ramírez;P. Mehrkhodavandi
合成了一系列外消旋和对映体纯的铟配合物1-11，它们带有大体积的手性二氨基芳氧基配体H（NNO（R）），并进行了充分的表征。通过变温、2D NOESY和PGSE NMR光谱对单烷氧基和双烷氧基桥联配合物[（NNO（R））InX]（2）[μ-Y][μ-OEt]（5，R =（t）Bu，X = Y = Cl; 8，R = Me，X = I，Y = OEt）的研究证实了溶液中的双核结构与通过单晶X射线晶体学获得的类似。该类双核配合物是室温下丙交酯开环聚合制备聚乳酸的高活性催化剂。特别地，配合物5在大的分子量范围内表现出活性聚合行为。催化剂的立体选择性研究表明，虽然（R，R/R，R）-5对l-LA具有高选择性，但在外消旋LA的聚合中仅得到无规聚乳酸。对于络合物8没有观察到这样的选择性。重要的是，对于外消旋LA与（R，R/R，R）-5和（R，R/R，R）-8的ROP获得的选择性是不同的，并且沿着动力学研究，表明这些络合物的双核增长物种。
A family of racemic and enantiopure indium complexes 1-11 bearing bulky chiral diaminoaryloxy ligands, H(NNO(R)), were synthesized and fully characterized. Investigation of both the mono- and the bis-alkoxy-bridged complexes [(NNO(R))InX](2)[μ-Y][μ-OEt] (5, R = (t)Bu, X = Y = Cl; 8, R = Me, X = I, Y = OEt) by variable temperature, 2D NOESY, and PGSE NMR spectroscopy confirmed dinuclear structures in solution analogous to those obtained by single-crystal X-ray crystallography. The dinuclear complexes in the family were highly active catalysts for the ring-opening polymerization (ROP) of lactide (LA) to form poly(lactic acid) (PLA) at room temperature. In particular, complex 5 showed living polymerization behavior over a large molecular weight range. A detailed investigation of catalyst stereoselectivity showed that, although (R,R/R,R)-5 is highly selective for l-LA, only atactic PLA is obtained in the polymerization of racemic LA. No such selectivity was observed for complex 8. Importantly, the selectivities obtained for the ROP of racemic LA with (R,R/R,R)-5 and (R,R/R,R)-8 are different and, along with kinetics investigations, suggest a dinuclear propagating species for these complexes.