The Effect of Alkyl Substituents on the Formation and Structure of Homochiral (R*,R*)-[R2Ga(µ-OCH(Me)CO2R')]2 Species-Towards the Factors Controlling the Stereoselectivity of Dialkylgallium Alkoxides in the Ring-Opening Polymerization of rac-Lactide.
Magdalena Kaźmierczak, Łukasz Dobrzycki, Maciej Dranka, Paweł Horeglad
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引用次数: 0
Abstract
Building on our previous studies, which have demonstrated that homochiral propagating species-(R*,R*)-[Me2Ga(µ-OCH(Me)CO2R)]2-were crucial for the heteroselectivity of [Me2Ga(µ-OCH(Me)CO2Me)]2 in the ring-opening polymerization (ROP) of racemic lactide (rac-LA), we have investigated the effect of alkyl groups on the structure and catalytic properties of dialkylgallium alkoxides in the ROP of rac-LA. Therefore, we have isolated and characterized the rac-[R2Ga(µ-OCH(Me)CO2Me]2 (R = Et (1), iPr (2) and rac-[R2Ga(µ-OCH(Me)C5H4N]2 (R = Et (3), iPr (4)) complexes, to demonstrate the effect of alkyl groups on the chiral recognition induced the formation of the respective homochiaral species-(R*,R*)-[R2Ga(µ-OCH(Me)CO2Me)]2 and (R*,R*)-[R2Ga(µ-OCH(Me)C5H4N]2. Moreover, we have investigated the structure of (S,S)-[R2Ga(µ-OCH(Me)CO2Me]2 (R = Et ((S,S)-1, R = iPr ((S,S)-2,) and their catalytic activity in the ROP of rac-LA. With an increase in the bulkiness of alkyl substituents on gallium the following can be observed: (a) the tendency for the formation of homochiral complexes decreased, (b) the symmetry of homochiral (S,S)-[R2Ga(µ-OCH(Me)CO2Me]2 (M = Me, Et (S,S)-1), iPr (S,S)-2) changed, and both have resulted in (c) lower or no heteroselectivtity across these complexes in the ROP of rac-LA. Importantly, the results have confirmed the crucial role of the chiral-induced formation of homochiral asymmetric dimers on the heteroselectivity of dialkylgallium alkoxides in the ROP of rac-LA.
烷基取代基对同手性(R*,R*)-[R2Ga（µ- och (Me)CO2R'）]2的形成和结构的影响——探讨开环聚合中二烷基镓烷氧化物立体选择性的控制因素
在前人研究的基础上，我们研究了同手性繁殖物种-(R*,R*)-[Me2Ga（µ- och (Me)CO2R）]2在消旋丙交酯（rac-LA）开环聚合（ROP）中[Me2Ga（µ- och (Me)CO2Me）]2的异选择性对[Me2Ga（µ- och (Me)CO2Me）]2在rac-LA开环聚合（ROP）中的结构和催化性能的影响。因此，我们分离并表征了rac-[R2Ga(µ- och (Me)CO2Me]2 (R = Et （1), iPr(2)）和rac-[R2Ga(µ- och (Me)C5H4N]2 (R = Et （3), iPr(4)）配合物，以证明烷基对手性识别的影响，诱导形成各自的同手性物质-(R*,R*)-[R2Ga（µ- och (Me)CO2Me）]2和(R*,R*)-[R2Ga(µ- och (Me)C5H4N]2。此外，我们还研究了（S，S）-[R2Ga(µ- och (Me)CO2Me]2 (R = Et ((S，S)-1, R = iPr （(S，S)-2,）的结构及其在rac-LA ROP中的催化活性。随着镓上烷基取代基体积的增加，可以观察到以下现象：(a)同手性配合物的形成趋势降低，(b)同手性（S，S）-[R2Ga(µ- och (Me)CO2Me]2 (M = Me, Et （S，S)-1), iPr (S，S)-2）的对称性发生变化，并且两者都导致(c)这些配合物在rac-LA的ROP中具有较低的杂选择或没有杂选择。重要的是，这些结果证实了手性诱导形成的同手性不对称二聚体对rac-LA ROP中二烷基烷氧基镓的杂选择性的关键作用。
期刊介绍：
Molecules (ISSN 1420-3049, CODEN: MOLEFW) is an open access journal of synthetic organic chemistry and natural product chemistry. All articles are peer-reviewed and published continously upon acceptance. Molecules is published by MDPI, Basel, Switzerland. Our aim is to encourage chemists to publish as much as possible their experimental detail, particularly synthetic procedures and characterization information. There is no restriction on the length of the experimental section. In addition, availability of compound samples is published and considered as important information. Authors are encouraged to register or deposit their chemical samples through the non-profit international organization Molecular Diversity Preservation International (MDPI). Molecules has been launched in 1996 to preserve and exploit molecular diversity of both, chemical information and chemical substances.
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