Jung Kijung, Ahmed Tonia S, Lee Jaeho, Sung Jong-Chan, Keum Hyeyun, Grubbs Robert H, Choi Tae-Lim
Department of Chemistry , Seoul National University , Seoul 08826 , Republic of Korea . Email:
The Arnold and Mabel Beckman Laboratory of Chemical Synthesis , Division of Chemistry and Chemical Engineering , California Institute of Technology , Pasadena , California 91125 , USA.
Chem Sci. 2019 Jul 22;10(39):8955-8963. doi: 10.1039/c9sc01326a. eCollection 2019 Oct 21.
Cyclopolymerization (CP) of 1,6-heptadiyne derivatives is a powerful method for synthesizing conjugated polyenes containing five- or six-membered rings α- or β-addition, respectively. Fifteen years of studies on CP have revealed that user-friendly Ru-based catalysts promoted only α-addition; however, we recently achieved β-selective regiocontrol to produce polyenes containing six-membered-rings, using a dithiolate-chelated Ru-based catalyst. Unfortunately, slow initiation and relatively low catalyst stability inevitably led to uncontrolled polymerization. Nevertheless, this investigation gave us some clues to how successful living polymerization could be achieved. Herein, we report living β-selective CP by rational engineering of the steric factor on monomer or catalyst structures. As a result, the molecular weight of the conjugated polymers from various monomers could be controlled with narrow dispersities, according to the catalyst loading. A mechanistic investigation by kinetic studies using H NMR spectroscopy revealed that with appropriate pyridine additives, imposing a steric demand on either the monomer or the catalyst significantly improved the stability of the propagating carbene as well as the relative rates of initiation over propagation, thereby achieving living polymerization. Furthermore, we successfully prepared diblock and even triblock copolymers with a broad monomer scope.
1,6-庚二炔衍生物的环聚合反应（CP）是一种分别合成含有五元或六元环的共轭多烯的有效方法，通过α-或β-加成反应来实现。对CP长达十五年的研究表明，使用方便的钌基催化剂仅能促进α-加成反应；然而，我们最近使用二硫醇盐螯合的钌基催化剂实现了β-选择性区域控制，从而制备出含有六元环的多烯。不幸的是，引发反应缓慢以及催化剂稳定性相对较低不可避免地导致了聚合反应失控。尽管如此，这项研究为如何成功实现活性聚合反应提供了一些线索。在此，我们报告通过对单体或催化剂结构的空间因素进行合理设计来实现活性β-选择性CP。结果，根据催化剂负载量，可以控制各种单体生成的共轭聚合物的分子量，并使其具有较窄的分散度。通过使用1H NMR光谱进行动力学研究的机理研究表明，加入适当的吡啶添加剂后，对单体或催化剂施加空间要求可显著提高增长卡宾的稳定性以及引发反应相对于增长反应的相对速率，从而实现活性聚合反应。此外，我们成功制备了具有广泛单体范围的二嵌段甚至三嵌段共聚物。
