Thomas Selina I, Falvey Daniel E
Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA.
J Org Chem. 2007 Jun 22;72(13):4626-34. doi: 10.1021/jo062578i. Epub 2007 May 31.
The reactive intermediates N,N-di(4-chlorophenyl)nitrenium ion and N,N-di(4-bromophenyl)nitrenium ion were generated through photolysis of the corresponding N-amino(2,4,6,-collidinium) ions. The behavior of these diarylnitrenium ions was characterized by laser flash photolysis, analysis of the stable photoproducts, and ab initio calculations with density functional theory. The latter predict these species to have singlet ground states. The halogenated diarylnitrenium ions are significantly longer lived than the unsubstituted diphenylnitrenium ion. Specifically, cyclization to form carbazole derivatives occurs negligibly, if at all, with the halogenated derivatives. They do, however, carry out most of the characteristic reactions of singlet arylnitrenium ions, including combining with nucleophiles on the aryl rings, adding to arenes, and accepting electrons from readily oxidized traps. Interestingly these species also abstract H atoms from 1,4-cyclohexadiene and various phenol derivatives. The implication of the latter process in relation to the computed singlet-triplet energy gaps of ca. -12.5 kcal/mol is discussed.
通过相应的N-氨基（2,4,6-可力丁鎓）离子的光解产生反应中间体N,N-二（4-氯苯基）氮鎓离子和N,N-二（4-溴苯基）氮鎓离子。这些二芳基氮鎓离子的行为通过激光闪光光解、稳定光产物分析以及密度泛函理论的从头算计算进行表征。后者预测这些物种具有单重态基态。卤代二芳基氮鎓离子的寿命明显长于未取代的二苯基氮鎓离子。具体而言，卤代衍生物即使发生环化形成咔唑衍生物，其发生率也可忽略不计。然而，它们确实会进行单重态芳基氮鎓离子的大多数特征反应，包括与芳环上的亲核试剂结合、加成到芳烃上以及从易于氧化的捕获剂接受电子。有趣的是，这些物种还会从1,4-环己二烯和各种酚类衍生物中夺取氢原子。讨论了后一过程与计算得到的约-12.5 kcal/mol的单重态-三重态能隙的关系。
