Mauksch Michael, Tsogoeva Svetlana B
Department of Chemistry and Pharmacy, Institute of Theoretical Chemistry, Computer Chemistry Center, Nägelsbachstrasse 25a, 91052, Erlangen, Germany.
Department of Chemistry and Pharmacy, Organic Chemistry Chair I and Interdisciplinary, Center for Molecular Materials (ICMM), Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Nikolaus-Fiebiger Str. 10, 91058, Erlangen, Germany.
Chemistry. 2019 Jun 4;25(31):7457-7462. doi: 10.1002/chem.201900849. Epub 2019 May 9.
In sigma complexes, intermediates in nucleophilic and electrophilic aromatic substitution and other reactions, delocalization in the aromatic ring is formally disrupted. Unexpectedly, computational evidence is presented that favorable processes contain aromatic sigma complexes. Tetracoordinated carbon therein surprisingly employs orbitals that are more similar to sp than to sp hybrids in sigma bonds with adjacent ring atoms. Both leaving groups and nucleo- or electrophiles may donate electrons to the π-system depending on the availability of p-type orbitals to fulfill Hückel (4N+2) or Möbius (4N) rules of aromaticity in analogy to conjugated transition-metal metallacycles.
在σ络合物中，亲核和亲电芳香取代反应及其他反应的中间体，芳香环中的离域作用会被形式上破坏。出乎意料的是，计算证据表明有利的过程包含芳香σ络合物。其中四配位碳令人惊讶地采用了与相邻环原子形成σ键时，比sp杂化轨道更类似于sp轨道的轨道。离去基团和亲核试剂或亲电试剂都可以向π体系供电子，这取决于p型轨道的可用性，以类似于共轭过渡金属金属环的方式满足休克尔（4N+2）或莫比乌斯（4N）芳香性规则。
