Stereoselective ROP of rac-Lactide Mediated by Enantiopure NNO-Scorpionate Zinc Initiators

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• 作者：Manuel Honrado ; Antonio Otero ; Juan Fern谩ndez-Baeza ; Luis F. S谩nchez-Barba ; Andr茅s Garc茅s ; Agustı ; &#769 ; n Lara-S谩nchez ; Ana M. Rodrı ; &#769 ; guez
• 刊名：Organometallics
• 出版年：2014
• 出版时间：April 14, 2014
• 年：2014
• 卷：33
• 期：7
• 页码：1859-1866
• 全文大小：331K
• 年卷期：v.33,no.7(April 14, 2014)
• ISSN：1520-6041

文摘

The reaction of the enantiopure NNO-scorpionate ligand (R,R)-bpzmmH with [ZnR₂] (R = Me, Et, CH₂SiMe₃) in a 1:2 molar ratio afforded the dinuclear tris-alkyls [Zn(R)(魏²-NN渭-O)Zn(R)₂] (R = Me (1), Et (2), CH₂SiMe₃ (3)). The reaction of the bimetallic tris-alkyls 1鈥?b>3 with an aromatic alcohol and thioalcohol yielded the dinuclear zinc complexes containing aryloxide/arylthioxide ligands [(ZnR)₂(魏N:魏N-渭-O)(渭-EAr)] (Ar = 2,6-C₆H₃Me₂; E = O, R = Me (4), Et (5), CH₂SiMe₃ (6); E = S, R = Me (7), Et (8), CH₂SiMe₃ (9)) by an alcoholysis or thioalcoholysis reaction. The structures of the different compounds were determined by spectroscopic methods and, in addition, the X-ray crystal structures of 2 and 5 were also unambiguously established. Alkyl- and aryloxide/thioaryloxide-containing enantiopure zinc complexes 3鈥?b>6 and 9 can act as single-component living initiators for the ring-opening polymerization of lactides, affording materials with low molecular weights under mild conditions in only a few hours. Interestingly, microstructural analysis of poly(rac-lactide) by ¹H NMR spectroscopy revealed that the most sterically hindered initiator, [(ZnCH₂SiMe₃)₂(R,R-bpzmm)(渭-OAr)] (6), is one of the first examples of a zinc complex capable of exerting a significant influence on the degree of enantioselectivity, with enriched-isotactic PLAs (P_i = 0.74) produced through an enantiomorphic site control mechanism.