Thermally Induced Helical Conformational Change in Poly(aryl isocyanide)s with Optically Active Ester Groups
Thermally Induced Helical Conformational Change in Poly(aryl isocyanide)s with Optically Active Ester Groups
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DOI：
10.1021/ma047883p
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发表时间：
2005-01
期刊：
影响因子：
5.5
通讯作者：
F. Takei;K. Onitsuka;Shigetoshi Takahashi
中科院分区：
文献类型：
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作者：
F. Takei;K. Onitsuka;Shigetoshi Takahashi
螺旋聚合物因其独特的光学性质和分子识别能力而受到人们的广泛关注，有望成为新型功能材料的开发方向。1具有庞大取代基的聚异氰是在溶液中保持稳定螺旋构象的人造聚合物的一个例子。2虽然具有较小体积取代基的聚异腈的构象一直是基于理论和实验研究的争议的主题，3，4已经表明，具有适当手性取代基的聚异腈主要具有单手螺旋构象。5由于主链由亚氨基组成，聚异氰化物表现出立构规整性，这可能取决于聚合条件，这是由于CdN双键周围的构型（顺式和反式）。然而，据我们所知，迄今为止，立体规整性对螺旋构象的影响几乎没有研究过。以前，我们发现Pd-Pt µ-乙炔二基络合物有效地引发了芳基异腈的活性聚合6，并且通过异腈单体与手性酯基团的聚合产生了主要具有单手螺旋结构的多异腈。7因为聚合催化剂或引发剂预期会影响多异氰化物的立构规整性，所以使用不同催化剂或引发剂由相同手性异氰化物单体制备的聚合物的手性光学性质的比较是有意义的。因此，我们通过使用NiCl 2，这是一种常见的聚合催化剂的异腈，2，并检查其手性光学性能的手性单体制备聚异腈。本文介绍了用NiCl_2催化剂制备的多异氰酸酯的单手螺旋构象的选择性和不可逆变化。我们发现，在13 C-标记的聚异腈的构象变化是可检测的13 C NMR光谱，并讨论了变化的起源。
Increasing attention has been paid to helical polymers because of their unique optical properties and molecular-recognition ability, which may be applicable to the development of novel functional materials. 1 Polyisocyanides with bulky substituents are an example of artificial polymers that maintain stable helical conformation in solution. 2 Although the conformation of polyisocyanides having less bulky substituents has been a subject of controversy based on theoretical and experimental studies, 3, 4 it has been shown that polyisocyanides with appropriate chiral substituents have predominantly a one-handed helical conformation. 5 As the main chain consists of imino groups, polyisocyanides exhibit stereoregularity that is likely to be dependent on the polymerization conditions due to the configuration around the CdN double bonds (syn and anti forms). To the best of our knowledge, however, the influence of stereoregularity on helical conformation has been scarcely studied so far.Previously, we showed that Pd-Pt µ-ethynediyl complexes efficiently initiated the living polymerization of aryl isocyanides6 and that polyisocyanides having predominantly one-handed helical structures were produced by the polymerization of isocyanide monomers with chiral ester groups. 7 Because a polymerization catalyst or an initiator is expected to influence the stereoregularity of polyisocyanides, the comparison of the chiroptical properties of the polymers prepared from the same chiral isocyanide monomers using various catalysts or initiators is of interest. Thus, we prepared polyisocyanides from chiral monomers by using NiCl2, which is a common polymerization catalyst for isocyanides, 2 and examined their chiroptical properties. We present herein the selectivity for and the irreversible change of the one-handed helical conformation of the polyisocyanides prepared with the NiCl2 catalyst. We found that the conformational change in 13C-labeled polyisocyanides was detectable by 13C NMR spectroscopy and discussed the origin of the change.