ASYMMETRIC POLYMERIZATION OF TRIPHENYLMETHYL METHACRYLATE LEADING TO A ONE-HANDED HELICAL POLYMER - MECHANISM OF POLYMERIZATION
ASYMMETRIC POLYMERIZATION OF TRIPHENYLMETHYL METHACRYLATE LEADING TO A ONE-HANDED HELICAL POLYMER - MECHANISM OF POLYMERIZATION
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DOI：
10.1021/ja00030a030
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发表时间：
1992-02-12
影响因子：
15
通讯作者：
HATADA, K
中科院分区：
文献类型：
--
作者：
NAKANO, T;OKAMOTO, Y;HATADA, K
在-78 ℃甲苯溶剂中，以9-芴基锂和手性配体的配合物为催化剂，进行了甲基丙烯酸三苯甲酯（TrMA）的不对称齐聚反应，并将所得齐聚物转化为甲酯。所得的低聚（甲基丙烯酸甲酯）首先通过凝胶渗透色谱法在聚合度方面分馏，并通过高效液相色谱法进一步分离成非对映异构体和光学异构体。低聚物的分布和异构体的比例在每个低聚物的不对称（螺旋正义选择性）聚合的TrMA的机制提供了重要的信息。每种低聚物阴离子的反应活性在很大程度上取决于其聚合度和立体结构。在9-芴基锂与（-）-金雀花碱的配合物体系中，不对称中心为R构型的低聚阴离子，以及在（+）-（2S，3S）-2，3-二甲氧基-1，4-双（二甲氨基）丁烷和（+）-（S）-1-（2-吡咯烷甲基）吡咯烷体系中，不对称中心为S构型的低聚阴离子主要向单手螺旋聚合物中扩散。稳定的螺旋在前一个体系中在聚合度9处开始，在后两个体系中在聚合度7处开始。一个螺旋圈似乎由三个或四个单体单元组成。在前一体系中所得聚合物的主链具有RPR-绝对构型，而在后一体系中所得聚合物的主链具有SSS-绝对构型，尽管这两种聚合物被认为具有相同的螺旋度P或M。这些结果表明，聚合物的螺旋性不是由主链的构型，而是由配体的手性。
Asymmetric oligomerization of triphenylmethyl methacrylate (TrMA) was carried out with complexes of 9-fluorenyllithium and chiral ligands in toluene at -78-degrees-C, and the oligomers obtained were converted into methyl esters. The resulting oligo(methyl methacrylate)s were first fractionated by gel permeation chromatography in terms of degree of polymerization and further separated into diastereomers and optical isomers by high-performance liquid chromatography. The distribution of oligomers and the ratio of isomers in each oligomer gave important information on the mechanism of the asymmetric (helix sense selective) polymerization of TrMA. The reactivity of each oligomer anion depended greatly on its degree of polymerization and stereostructure. The oligomer anions whose asymmetric centers have R configuration in the system with the complex of 9-fluorenyllithium and (-)-sparteine and those of S configuration in the systems with (+)-(2S,3S)-2,3-dimethoxy-1,4-bis(dimethylamino)butane and (+)-(S)-1-(2-pyrrolidinylmethyl)pyrrolidine as chiral ligands predominantly propagated to a one-handed helical polymer. A stable helix starts at degree of polymerization 9 in the former system and at degree of polymerization 7 in the latter two systems. One helix turn seems to consist of three or four monomeric units. The main chain of the resulting polymer in the former system possessed RPR--- absolute configuration and that in the latter systems SSS---, though both polymers are considered to be of the same helicity, P or M. These results indicate that the helicity of the polymer is not governed by the configuration of the main chain but by the chirality of the ligands.