Department of Chemistry, College of Chemistry and Chemical Engineering and the MOE Key Laboratory of Analytical Sciences, Xiamen University, Xiamen 361005, China.
Chem Asian J. 2010 Mar 1;5(3):543-9. doi: 10.1002/asia.200900519.
N-(o-methoxybenzamido)thioureas (2 X/2 Y) are found to show an enhanced anion binding affinity with binding constants over 10(7) mol(-1) L orders of magnitude for AcO(-) and a redshifted absorption of the anion binding complexes in acetonitrile (MeCN) relative to those of N-benzamidothioureas (1) that bear no o-OMe in the N-benzamide moiety, despite the electron-donating character of o-OMe. Absorption of the anion-2 X/2 Y complex was shown to be of the same charge-transfer nature as that of the anion-1 complex, but its dependence on substituent X is interestingly influenced by the o-MeOHNC=O six-membered-ring intramolecular hydrogen bond identified in 2 X/2 Y. Such an intramolecular hydrogen bond is suggested to be responsible for the enhanced anion binding affinity. In the presence of this intramolecular hydrogen bond, the anion binding constant of 2 X was found to be independent of substituent X at the N-phenyl ring, as in the case of 1, whereas that of 2 Y showed an amplified dependence on substituent Y at the N'-phenyl ring, but to a lower extent than that of 1. A similar ring intramolecular hydrogen bond was purported to exist in 2 Za, 2 Zd, and 2 Ze, which bear NHMe, F, and Cl as the ortho substituent in the N-benzamide moiety. In terms of the current roles of thiourea in not only anion recognition and sensing but also organocatalysis and crystal engineering, the present finding would be of significance for a wider structural diversity of smart thiourea derivatives with predesigned functions.
N-(邻甲氧基苯甲酰胺基)硫脲（2X/2Y）被发现对 AcO-具有增强的阴离子结合亲和力，结合常数超过 10(7)mol(-1)L 数量级，相对于没有邻甲氧基的 N-苯甲酰胺基的 N-苯甲酰胺基硫脲（1），其阴离子结合配合物在乙腈（MeCN）中的吸收红移。尽管邻甲氧基具有供电子性质，但 o-OMe 对阴离子结合亲和力的增强没有影响。阴离子-2X/2Y 配合物的吸收被证明具有与阴离子-1 配合物相同的电荷转移性质，但它对取代基 X 的依赖性有趣地受到在 2X/2Y 中鉴定的邻甲氧基苯甲酰胺基六元环分子内氢键的影响。这种分子内氢键被认为是增强阴离子结合亲和力的原因。在存在这种分子内氢键的情况下，发现 2X 的阴离子结合常数与 N-苯基环上的取代基 X 无关，与 1 相同，而 2Y 的阴离子结合常数则表现出对 N'-苯基环上取代基 Y 的依赖性增强，但程度低于 1。据称，在 2Za、2Zd 和 2Ze 中存在类似的环分子内氢键，它们在 N-苯甲酰胺基中具有 NHMe、F 和 Cl 作为邻位取代基。就硫脲在阴离子识别和传感、有机催化和晶体工程中的当前作用而言，这一发现对于具有预定功能的智能硫脲衍生物的更广泛结构多样性具有重要意义。
