Gleiter Rolf, Haberhauer Gebhard
Organisch-Chemisches Institut, Universität Heidelberg , Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany.
J Org Chem. 2014 Aug 15;79(16):7543-52. doi: 10.1021/jo501277h. Epub 2014 Jul 28.
Quantum chemical calculations were carried out by applying density functional theory to study the two center-three electron (2c-3e) bonds between the sulfur centers of cyclic dithioethers. Calculated were the S-S distance, the stabilization energy, and the energy of the σ → σ* transition. The extension of the calculations to two (2c-3e) bonds in one molecule shows that a rearrangement to one σ bond and two lone pairs on sulfur is usually more favorable. Exceptions are [H2S2(+)]2, the dimer of the 1,2-dithia-3,5-diazolyl radical (27a), the dimer of the 1,2,4-trithia-3,5-diazolyl radical cation (26a(2+)), and its Selena congeners and derivatives. In the case of [H2S2(+)]2, the (4c-6e) bond between the chalcogen centers is a good description of this dimer. To describe the binding situation in the dimer 26a(2+) and 27a, the concept of a "simple" (4c-6e) bond was extended. Our calculations reveal a strong σ-aromaticity within the plane of the four sulfur centers in addition to a strong π-conjugation within the five-membered rings. The whole phenomenon can best be described as a three-dimensional σ/π-aromaticity within the 14π dimers.
通过应用密度泛函理论进行量子化学计算，以研究环状二硫醚硫中心之间的双中心三电子（2c-3e）键。计算了S-S距离、稳定化能和σ→σ*跃迁的能量。将计算扩展到一个分子中的两个（2c-3e）键表明，重排成一个σ键和硫上的两个孤对通常更有利。例外情况是[H2S2(+)]2、1,2-二硫杂-3,5-二氮杂环自由基（27a）的二聚体、1,2,4-三硫杂-3,5-二氮杂环自由基阳离子（26a(2+)）的二聚体及其硒类似物和衍生物。在[H2S2(+)]2的情况下，硫属元素中心之间的（4c-6e）键很好地描述了该二聚体。为了描述二聚体26a(2+)和27a中的键合情况，扩展了“简单”（4c-6e）键的概念。我们的计算揭示了四个硫中心平面内强烈的σ芳香性以及五元环内强烈的π共轭。整个现象最好描述为14π二聚体内的三维σ/π芳香性。
