Pan Yu, Li Wenqiang, Wei Ning-Ning, So Yat-Ming, Lai Xiaoling, Li Yang, Jiang Kang, He Gaohong
State Key Laboratory of Fine Chemicals, School of Petroleum and Chemical Engineering, Dalian University of Technology, Panjin 124221, China.
Dalton Trans. 2019 Jun 25;48(25):9079-9088. doi: 10.1039/c9dt00541b.
Rare-earth metal complexes usually exhibit high activities in the ring-opening polymerization (ROP) of lactide, yet only a few scandium complexes have shown satisfactory activity. Herein, we report the synthesis of a series of chiral anilido-oxazoline-supported scandium and yttrium complexes that exhibit high activity in the ROP of racemic lactide (rac-LA). Complexes La-f-Ln(CH2SiMe3)2THF (La-f = 2-(2,6-R2PhN)-phenyl-4-(S)-R'-oxazoline; for 1a-f: L = La-f, Ln = Sc; for 2a-d: L = La-d, Ln = Y) were synthesized via the convenient one-pot reaction of Ln(CH2SiMe3)3(THF)2 (Ln = Sc, Y) with the corresponding proligands. The crystal structures of 1a, 1d, 1e, and 1f were isostructural, adopting a distorted trigonal bipyramidal configuration. Sc complexes 1 showed outstanding activity in the ROP of rac-LA with heteroselectivity. TOFs of up to 720 h-1 and 2910 h-1 were obtained in THF at room temperature and toluene at 60 °C, respectively. To our knowledge, these are the highest activities reported for Sc systems. Y complexes 2 showed higher activity and heteroselectivity than the Sc complexes, with TOFs of up to 1176 h-1 in THF at room temperature. Compared with the ortho-substituent on the anilido moiety, the bulky substituent at the chiral center of the oxazoline ring had a greater effect on controlling the heteroselectivity.
稀土金属配合物通常在丙交酯的开环聚合（ROP）中表现出高活性，但只有少数钪配合物显示出令人满意的活性。在此，我们报道了一系列手性苯胺基-恶唑啉支撑的钪和钇配合物的合成，这些配合物在消旋丙交酯（rac-LA）的ROP中表现出高活性。配合物La-f-Ln(CH2SiMe3)2THF（La-f = 2-(2,6-R2PhN)-苯基-4-(S)-R'-恶唑啉；对于1a-f：L = La-f，Ln = Sc；对于2a-d：L = La-d，Ln = Y）通过Ln(CH2SiMe3)3(THF)2（Ln = Sc，Y）与相应的前体配体的便捷一锅法反应合成。1a、1d、1e和1f的晶体结构是同构的，采用扭曲的三角双锥构型。钪配合物1在rac-LA的ROP中表现出出色的活性和对映选择性。在室温下的THF和60℃的甲苯中分别获得了高达720 h-1和2910 h-1的转化频率。据我们所知，这些是报道的钪体系的最高活性。钇配合物2显示出比钪配合物更高的活性和对映选择性，在室温下的THF中转化频率高达1176 h-1。与苯胺基部分的邻位取代基相比，恶唑啉环手性中心的大位阻取代基对控制对映选择性有更大的影响。
