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首页> 外文期刊>Chemistry: A European journal >Highly Stereocontrolled Ring-Opening Polymerization of Racemic Alkyl beta-Malolactonates Mediated by Yttrium [Amino-alkoxy-bis(phenolate)] Complexes
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Highly Stereocontrolled Ring-Opening Polymerization of Racemic Alkyl beta-Malolactonates Mediated by Yttrium [Amino-alkoxy-bis(phenolate)] Complexes

机译：钇[氨基-烷氧基-双（酚盐）]配合物介导的外消旋烷基β-丙二酸内酯的高度立体控制的开环聚合

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摘要

Yttrium [ amino-alkoxy-bis(phenolate)] amido complexes have been used for the ring-opening polymerization (ROP) of racemic alkyl beta-malolactonates (4-alkoxycarbonyl-2-oxetanones, rac-MLA(R)s) bearing an allyl (All), benzyl (Bz) or methyl (Me) lateral ester function. The nature of the orthosubstituent on the phenolate rings in the metal ancillary dictated the stereocontrol of the ROP, and consequently the syndiotactic enrichment of the resulting polyesters. ROP promoted by catalysts with halogen (Cl, Br)-disubstituted ligands allowed the first reported synthesis of highly syndiotactic PMLA(R)s (Pr >= 0.95); conversely, catalysts bearing bulky alkyl and aryl ortho-substituted ligands proved largely inef-fective. All polymers have been characterized by 1H and C-13{H-1} NMR spectroscopy, MALDI-ToF mass spectrometry and DSC analyses. Statistical and thermal analyses enabled the rationalization of the chain-end control mechanism. Whereas the stereocontrol of the polymerization obeyed a Markov first-order (Mk1) model for the ROP of rac-MLA(Bz) and rac-MLA(All), the ROP of rac-MLA(Me) led to a chain end-control of Markov second-order type (Mk2). DFT computations suggest that the high stereocontrol ability featured by catalysts bearing Cl-and Br-substituted ligands does not likely originate from halogen bonding between the halogen substituent and the growing polyester chain.
机译：钇[氨基-烷氧基-双（酚盐）]酰胺配合物已用于外消旋烷基β-丙二酸内酯（4-烷氧基羰基-2-氧杂环丁烷，rac-MLA®）的开环聚合（ROP）。烯丙基（全部），苄基（Bz）或甲基（Me）侧酯官能团。金属辅助物中酚盐环上的原取代基的性质决定了ROP的立体控制，因此决定了所得聚酯的间同富集。具有卤素（Cl，Br）-二取代配体的催化剂促进的ROP允许首次报道高度间同的PMLA（s）（Pr> = 0.95）的合成。相反，带有庞大的烷基和芳基邻位取代的配体的催化剂被证明是无效的。所有聚合物均已通过1H和C-13 {H-1} NMR光谱，MALDI-ToF质谱和DSC分析进行了表征。统计和热分析使链端控制机制合理化。聚合的立体控制遵循rac-MLA（Bz）和rac-MLA（All）的ROP的马尔可夫一阶（Mk1）模型，而rac-MLA（Me）的ROP导致链端控制马尔可夫二阶类型（Mk2）。 DFT计算表明，带有Cl-和Br-取代的配体的催化剂所具有的高立体控制能力不可能源自卤素取代基和增长的聚酯链之间的卤素键。

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