Department of Organic and Polymeric Materials, Tokyo Institute of Technology, 2-12-1 (H126) Ookayama, Tokyo 152-8552, Japan.
Chemistry. 2011 Oct 17;17(43):12067-75. doi: 10.1002/chem.201101727. Epub 2011 Sep 16.
Directed helicity control of a polyacetylene dynamic helix was achieved by hybridization with a rotaxane skeleton placed on the side chain. Rotaxane-tethering phenylacetylene monomers were synthesized in good yields by the ester end-capping of pseudorotaxanes that consisted of optically active crown ethers and sec-ammonium salts with an ethynyl benzoic acid. The monomers were polymerized with [{RhCl(nbd)}(2)] (nbd=norbornadiene) to give the corresponding polyacetylenes in high yields. Polymers with optically active wheel components that are far from the main chain show no Cotton effect, thereby indicating the formation of racemic helices. Our proposal that N-acylative neutralization of the sec-ammonium moieties of the side-chain rotaxane moieties enables asymmetric induction of a one-handed helix as the wheel components approach the main chain is strongly supported by observation of the Cotton effect around the main-chain absorption region. A polyacetylene with a side-chain rotaxane that has a shorter axle component shows a Cotton effect despite the ammonium structure of the side-chain rotaxane moiety, thereby suggesting the importance of proximity between the wheel and the main chain for the formation of a one-handed helix. Through-space chirality induction in the present systems proved to be as powerful as through-bond chirality induction for formation of a one-handed helix, as demonstrated in an experiment using non-rotaxane-based polyacetylene that had an optically active binaphthyl group. The present protocol for controlling the helical structure of polyacetylene therefore provides the basis for the rational design of one-handed helical polyacetylenes.
通过将侧链上的轮烷骨架杂交，实现了聚乙炔动态螺旋的定向螺旋控制。通过酯封端由手性冠醚和带有乙炔基苯甲酸的 sec-铵盐组成的伪轮烷，得到了收率良好的轮烷键合苯乙炔单体。将这些单体与[{RhCl(nbd)}(2)]（nbd=norbornadiene）聚合，以高产率得到相应的聚乙炔。具有远离主链的手性轮部件的聚合物没有圆二色性，从而表明形成外消旋螺旋。我们的假设是，侧链轮烷部分的 sec-铵部分的 N-酰基化中性化能够使单螺旋作为轮部件接近主链时产生不对称诱导，这一假设得到了观察主链吸收区域周围的圆二色性的有力支持。尽管侧链轮烷部分具有铵结构，但具有较短轴部件的侧链轮烷聚乙炔显示出圆二色性，这表明轮和主链之间的接近对于形成单螺旋的重要性。本系统中的通过空间手性诱导被证明与通过键手性诱导一样强大，这在使用具有手性联萘基团的非轮烷聚乙炔的实验中得到了证明。因此，控制聚乙炔螺旋结构的本方法为合理设计单螺旋聚乙炔提供了基础。
