New Polyheterocyclic 4nπ-Electron Dianions: Paratropicity, Charge Delocalization, and Reactions

Yoram cohen, Amatzya Y. Meyer, Mordecai Rabinovitz*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

A novel class of anions, namely, nitrogen-containing polyheterocyclic dianions, is described. These species show a very interesting spectral and chemical behavior. 2,3-Diphenylquinoxaline (1), 1,4-diphenylphthalazine (2), 2,3,7,8-tetra-phenylpyrzo[2,3-g]quinoxaline (3), tribenzo[a,c,i]phenazine (4), and 2,3-diphenyldibenzo[f,h]quinoxaline (5) were reduced by alkali metals to the corresponding 4mr conjugated dianions. The 1H and 13C NMR spectra as well as theoretical calculations (ωß) are reported and discussed in terms of the mode of charge delocalization and its relevance to paratropicity in these systems. The proton NMR line shapes of these charged species correlate with the energy difference calculated between their ground and first excited states. The striking differences in the 1H and 13C spectra of the two apparently similar dianions 12- and 22- are rationalized by the calculated HOMO-LUMO energy gaps. A very unusual mode of charge delocalization is detected in the NMR spectrum of the doubly charged system 42-, rationalized by a partitioning of the conjugated system into an uncharged phenanthrene-like moiety and a benzo[g]quinoxaline dianion moiety. A thermal ring closure reaction of 12- and 52- has been observed, forming dibenzo[a,c]phenazine dianion 62- and phenanthrazine dianion 72-, respectively. This reaction opens up a new pathway to synthetic transformations of heterocycles.

Original languageEnglish
Pages (from-to)7039-7044
Number of pages6
JournalJournal of the American Chemical Society
Volume108
Issue number22
DOIs
StatePublished - 1986
Externally publishedYes

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