Phosphinimino-amino Magnesium Complexes: Synthesis and Catalysis of Heteroselective ROP of rac-Lactide

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• 作者：Hongyan Xie ; Zehuai Mou ; Bo Liu ; Ping Li ; Weifeng Rong ; Shihui Li ; Dongmei Cui
• 刊名：Organometallics
• 出版年：2014
• 出版时间：February 10, 2014
• 年：2014
• 卷：33
• 期：3
• 页码：722-730
• 全文大小：396K
• ISSN：1520-6041

文摘

Alkane elimination reactions of phosphinimino-amine ligands HL^1鈥? ((2,6-Me₂-C₆H₃NH)C(Ph)鈺怌HPPh₂(NAr) (Ar = C₆H₅ (HL¹); 2,6-Me₂-C₆H₃ (HL²); 2,6-Et₂-C₆H₃ (HL³); 2,6-ⁱPr₂-C₆H₃ (HL⁴); 2-OMe-C₆H₄ (HL⁵); 2-Cl-C₆H₄ (HL⁶); 3-CF₃-C₆H₄ (HL⁷); 4-MeO-C₆H₄ (HL⁸)) with MgⁿBu₂, respectively, afforded a series of phosphinimino-amine-based complexes L^1鈥?MgⁿBu(THF) (1鈥?b>8) by releasing butane. Complexes 1鈥?b>8 are phosphinimino-amine-ligated THF-solvated mono(alkyl)s, among which 1鈥?b>4 adopt twisted tetrahedral geometries, whereas 5 contains a trigonal bipyramido geometry core. Complexes 1鈥?b>8 all display high activity for the ring-opening polymerization of rac-lactide. The molecular weights of the resulting PLA are close to the theoretic values, and the molecular weight distributions are narrow. Moreover, these complexes show medium to high heteroselectivity, which, interestingly, increases with the decrease of the ligand steric hindrance; thus, complex 1, bearing a less bulky ligand, exhibits a heteroselectivity of P_r = 0.98, the highest value of a magnesium-based initiator achieved to date. The kinetics study showed that the polymerization rate is first-order dependent on both monomer and initiator concentrations, and the overall rate equation is 鈭抎[LA]/dt = 3.78 M^鈥? s^鈥? [LA][Mg].