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.
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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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