Highly Asymmetric and Anionic Polymerizations of Achiral Methacrylate by Using Axially Chiral Ligands

The asymmetric polymerization of achiral methacrylates having bulky ester groups was achieved successfully by using the following chiral anionic initiators。因此，我们将光学活性四甲基化胺（TMEDA）衍生物修改为C_2-手性物质，从含有不对称碳的鞑靼酸衍生物，或更好地从脂肪酸联苯和联苯化合物中衍生出来。这些配体对各种有机化合物具有复杂性和有效性。在toluene at-78 C中的结果chiral complexes polymerized triphenylmethyl methacrylate （TrMA）。产生的聚合物展示了高光学旋转产生于辅助构象，是由高立体声通过聚合化形成的。“聚合物的旋转价值观和感觉强烈地依赖于已使用的配体的结构。”Although reaher复杂的立体化学产品/配体相关性被观察到，他们一致地解释了立体电子相互作用在聚合物链和手性配体之间传播末端的扩散末端的术语。最有效的配体之一是一种双苯-单溴化TMEDA。它的锂复合体被用作聚合物的有效启动器，而不仅仅是TrMA，但也是其2-pyridyl衍生物。聚合物生产的数量几乎是纯粹的一种手工加工的，而且分子重量也是如此有限，以至于在四氢呋喃中很容易得到缓解。光学活性和可溶性聚合物作为HPLC中的手性包装材料是有用的。关于另一方，当更少的甲基和苯甲基酒精的散装甲基丙烯酸酯与上述启动器聚合化时，产生的等离子聚合物显示出负弹性旋转。从这个结果来看，我们现在认为这样的聚合物（ester）无法形成一个足够稳定的解决方案。

The asymmetric polymerization of achiral methacrylates having bulky ester groups was achieved successfully by using the following chiral anionic initiators. Thus, we synthesized optically active tetramethylethylenediamine (TMEDA) derivatives modified with C_2-chiral substituents derived from tartaric acid having asymmetric carbons, or more preferentially from atropisomeric biphenyls and binaphthyls. These ligands were complexed effectively to various organolithium compounds. The resulting chiral complexes polymerized triphenylmethyl methacrylate (TrMA) in toluene at -78゜C. The produced polymers showed high optical rotations owing to the helical conformation, which was formed with high stereosectivity through the polymerization. The rotation values and senses of the polymers were strongly depending upon the structures of the used ligands. Although reaher complicated stereochemical product/ligand correlations were observed, they were consistently explained in terms of the stereoelectronic interaction between the propagating end of the polymer chain and the chiral ligand complexed to the counter lithium cation. One of the most effective ligands was a biphenyl-monosubstituted TMEDA. Its lithium complexes served as effective initiators for the polymerization of not only TrMA but also its 2- pyridyl derivative. The polymers produced quantitatively had almost pure one-handed heliciy, and have so limited molecular weights as to be easily soluble in tetrahydrofuran. The optically active and solvent-soluble polymers were useful as chiral packing materials for HPLC. On the other hand, when less bulky methacrylates of methyl and benzyl alcohols were polymerized with the above initiators, the produced isotactic polymers showed negligible rotations. From this result, we now consider that such poly(ester)s can't form helical conformation being enough stable in solutions.