Caballero-García Guillermo, Romero-Ortega Moisés, Barroso-Flores Joaquín
Centro Conjunto de Investigación en Química Sustentable UAEM - UNAM, Carretera Toluca-Atlacomulco km 14.5, Unidad San Cayetano, Personal de la UNAM, Toluca 50200, Estado de México, Mexico.
Facultad de Química, Universidad Autónoma del Estado de México, Paseo Colón/Paseo Tollocan, s/n, Toluca 50000, Estado de México, Mexico.
Phys Chem Chem Phys. 2016 Oct 5;18(39):27300-27307. doi: 10.1039/c6cp04321f.
σ-Holes are shown to promote the electrophilic behavior of chlorine atoms in a trichloromethyl group when bound to an electron-withdrawing moiety. A halogen bond-type non-covalent interaction between a chlorine atom and a negatively charged sulfur atom takes place, causing the abstraction of such a chlorine atom while leaving a carbanion, subsequently driving the chemical reduction of the trichloromethyl group to a sulfide in a stepwise process. The mechanism for the model reaction of trichloromethyl pyrimidine 1 with thiophenolate and thiophenol to yield phenylsulfide 4 was followed through H-NMR and studied using DFT transition state calculations, and the energy profile for this transformation is fully discussed. MP2 calculations of the electrostatic potential were performed for a series of trichloromethyl compounds in order to assess the presence of σ-holes and quantify them by means of the maximum surface electrostatic potential. Such calculations showed that the chlorine atoms behave as electrophilic leaving groups toward a nucleophilic attack, opening a new possibility in the synthetic chemistry of the trichloromethyl group.
当与吸电子部分结合时，σ-空穴被证明可促进三氯甲基中氯原子的亲电行为。氯原子与带负电荷的硫原子之间发生卤键型非共价相互作用，导致该氯原子被夺取，同时留下碳负离子，随后在一个逐步过程中将三氯甲基化学还原为硫化物。通过氢核磁共振跟踪了三氯甲基嘧啶1与硫酚盐和硫酚反应生成苯硫醚4的模型反应机理，并使用密度泛函理论过渡态计算进行了研究，且充分讨论了该转化的能量分布。为了评估σ-空穴的存在并通过最大表面静电势对其进行量化，对一系列三氯甲基化合物进行了MP2静电势计算。此类计算表明，氯原子对于亲核攻击表现为亲电离去基团，为三氯甲基的合成化学开辟了新的可能性。
