Lipidic Carbo-benzenes: Molecular Probes of Magnetic Anisotropy and Stacking Properties of α-Graphyne

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• 作者：Chongwei Zhu ; Arnaud Rives ; Carine Duhayon ; Valérie Maraval ; Remi Chauvin
• 刊名：Journal of Organic Chemistry
• 出版年：2017
• 出版时间：January 20, 2017
• 年：2017
• 卷：82
• 期：2
• 页码：925-935
• 全文大小：609K
• ISSN：1520-6904

文摘

Solubilization of the C₁₈ fundamental circuit of α-graphyne has been envisaged by decoration with aliphatic chains R = n-C_nH_2n+1. The synthesis and characterization of p-dialkyl-tetraphenyl-carbo-benzenes (n = 2, 8, 14, 20) are thus presented and compared to the monoalkyl series produced concomitantly. In both series, a dramatic enhancement of solubility in organic solvents (CH₂Cl₂, CHCl₃) is observed for n ≥ 8, and in the dialkyl series, the melting–decomposition temperature of the solid products is shown to decrease linearly from 208 °C for n = 2 to 149 °C for n = 20. Fluoroalkyl analogues with R = n-C₈H₄F₁₃ are also described. The products display classical UV–vis electronic spectra of carbo-benzenes in solution (λ_max = 445.5 ± 1 nm, ε ≈ 200 000 L·mol^–1·cm^–1). They are also characterized by UV–vis absorption in the solid state, which is found to be correlated with the color and crystal packing. The methylene groups of R provide an experimental probe of the magnetic anisotropy and aromaticity of the C₁₈ ring through the progressive NMR shielding of the ¹H nuclei from ca. 4.70 to 1.25 ppm going away from the border of the ring (as far as 8 Å away). All alkyl-carbo-benzenes were also found to be highly crystalline. Seven of them have been characterized by X-ray diffraction analysis and the C₁₈ columnar packing compared in a systematic manner. Crystals of the diethyl and bistetradecyl derivatives, containing no solvent molecule, provided the first examples of direct π-stacking of carbo-benzene rings, with inter-ring distances very close to calculated interlayer distances in AB and ABC α-graphityne (3.255 and 3.206 Å vs 3.266 and 3.201 Å, respectively).