Solvent-Dependent Switch of Helical Main-Chain Chirality in Sergeants-and-Soldiers-Type Poly(quinoxaline-2,3-diyl)s: Effect of the Position and Structures of the 鈥淪ergeant鈥?Chiral Units on the Screw-S

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• 作者：Yuuya Nagata ; Tetsuya Yamada ; Takumi Adachi ; Yuto Akai ; Takeshi Yamamoto ; Michinori Suginome
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：July 10, 2013
• 年：2013
• 卷：135
• 期：27
• 页码：10104-10113
• 全文大小：594K
• 年卷期：v.135,no.27(July 10, 2013)
• ISSN：1520-5126

文摘

Poly(quinoxaline-2,3-diyl) copolymers bearing various 鈥渟ergeant鈥?chiral units with common 鈥渟oldier鈥?achiral units have been synthesized to investigate the efficiency of screw-sense induction and its dependence on the nature of the solvents. Optically active 2-alkoxymethyl side chains located at the 6- and 7-positions of the quinoxaline ring induced a single-handed helical conformation more efficiently than 3-methylpentyl or 2-methylbutoxy chiral side chains. Among the 2-alkoxymethyl side chains, those bearing higher 2-alkoxy groups induced a single-handed screw sense more efficiently. For instance, a monomer unit bearing (R)-2-octyloxymethyl groups stabilized the P-helix by 1.01 kJ/mol, whereas the monomer bearing (S)-2-butoxymethyl groups stabilized the M-helix by 0.59 kJ/mol. The effect of the position of the sergeant units in the polymer main chain on the screw-sense induction was also investigated using copolymers in which the positions of the sergeant units were carefully controlled by their synthesis via living polymerization. Chiral units placed sparsely could induce single-handed helical structure efficiently. Chiral units bearing 2-alkoxymethyl, 3-methylpentyl, and 2-methylbutoxy groups showed solvent-dependent helix inversion in CHCl₃ and 1,1,2-trichloroethane. No helix inversion was observed in those solvents with chiral units bearing 2-butoxy or (2-methylbutoxy)methyl side chains. The 40-mer of the (R)-2-octyloxymethyl units showed P-helical structures in THF, t-BuOMe, and c-C₅H₁₁OMe, toluene, pyridine, Et₃N, 1-BuOH, CHCl₃, CH₂Cl₂, 1,4-dichlorobutane, 1,1,-dichloroethane, and 1,1,1-trichloroethane, whereas M-helical structures were induced in 1-BuCN, 1-PrCN, 1,2-dichloroethane, 1,3-dichloropropane, and 2-BuOH.