Ito Shunji, Inabe Haruki, Morita Noboru, Ohta Kazuchika, Kitamura Teruo, Imafuku Kimiaki
Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan.
J Am Chem Soc. 2003 Feb 12;125(6):1669-80. doi: 10.1021/ja0209262.
A series of poly(6-azulenylethynyl)benzenes substituted with n-hexyloxycarbonyl chains at 1,3-positions in azulene rings, i.e., hexakis-, 1,2,4,5-tetrakis-, 1,3,5-tris-, and 1,4-bis(6-azulenylethynyl)benzene derivatives 1, 2, 3, and 4b, have been prepared by a simple one-pot reaction involving repeated Pd-catalyzed alkynylation of halogenated arenes with substituted 6-ethynylazulene and/or ethynylated arenes with substituted 6-bromoazulene under Sonogashira-Hagihara conditions. The redox behavior of these novel poly(6-azulenylethynyl)benzene derivatives was examined by cyclic voltammetry (CV), which revealed the presumed multielectron redox properties. Compound 4b exhibited a one-step, two-electron reduction wave upon CV, which revealed the formation of the dianion stabilized by two 6-azulenylethynyl substituents under electrochemical reduction conditions. Four 6-azulenylethynyl substituents on a benzene ring in a 1,2,4,5 relationship increased the electron-accepting properties because of the formation of a stabilized closed-shell dianionic structure, whereas 3 was reduced at more negative reduction potentials. In contrast to the multistep redox behavior of 2, compound 1 was reduced in one step at -1.28 V upon CV. Compound 1 showed a wide temperature range of columnar mesophases (Col(ho) and Col(ro)) from 77.3 degrees C to the decomposition temperature at ca. 270 degrees C. Compounds 2, 3, and 4b exhibited columnar mesomorphism (Col(ro)) with crystalline polymorphs for 2, unusual triple-melting behavior for 3, and both double-melting behavior and columnar mesomorphism (Col(ho)) for 4b. Therefore, the investigated systems exemplify a new principle for multielectron redox behavior with liquid crystalline properties.
一系列在薁环的1,3位被正己氧基羰基链取代的聚（6 - 薁基乙炔基）苯，即六（6 - 薁基乙炔基）苯、1,2,4,5 - 四（6 - 薁基乙炔基）苯、1,3,5 - 三（6 - 薁基乙炔基）苯和1,4 - 二（6 - 薁基乙炔基）苯衍生物1、2、3和4b，已通过一种简单的一锅法反应制备，该反应涉及在Sonogashira - Hagihara条件下，卤代芳烃与取代的6 - 乙炔基薁和/或乙炔基化芳烃与取代的6 - 溴薁进行重复的钯催化炔基化反应。通过循环伏安法（CV）研究了这些新型聚（6 - 薁基乙炔基）苯衍生物的氧化还原行为，结果揭示了推测的多电子氧化还原性质。化合物4b在CV中表现出一步两电子还原波，这表明在电化学还原条件下，由两个6 - 薁基乙炔基取代基稳定的二价阴离子的形成。苯环上处于1,2,4,5关系的四个6 - 薁基乙炔基取代基由于形成了稳定的闭壳二价阴离子结构而增强了吸电子性质，而化合物3在更负的还原电位下被还原。与化合物2的多步氧化还原行为相反，化合物1在CV中于 - 1.28 V时一步被还原。化合物1显示出从77.3℃到约270℃分解温度的宽温度范围的柱状中间相（Col(ho)和Col(ro)）。化合物2、3和4b表现出柱状介晶性（Col(ro)），化合物2具有结晶多晶型，化合物3具有不寻常的三重熔融行为，化合物4b具有双重熔融行为和柱状介晶性（Col(ho)）。因此，所研究的体系例证了具有液晶性质的多电子氧化还原行为的新原理。
