Complexation-Triggered Fluctuation of π-Conjugation on an Antiaromatic Dicyanoanthracene Dianion

The formation of Lewis pairs is an important chemical concept. Recently, the complexation of Lewis acidic tris(pentafluorophenyl)borane with Lewis basic moieties and subsequent reduction has emerged as a fascinating strategy for designing novel reactions and structures. The impact of the complexation and subsequent reduction of antiaromatic systems bearing Lewis base moieties has been investigated. We found how Lewis adduct formation stabilizes an antiaromatic system consisting of 9,10-dicyanoanthracene and tris(pentafluorophenyl)borane by using synthesis, X-ray crystallography, spectroscopic analysis, and quantum chemical calculations. The reduction of a bisboron complex consisting of 9,10-dicyanoanthracene and two equivalents of tris(pentafluorophenyl)borane has also been studied. X-ray crystallographic analysis and theoretical calculations revealed a decrease in antiaromaticity upon Lewis adduct formation. The outer rings acquired aromaticity upon reduction, and the central ring turned into a nonaromatic quinoidal structure. Furthermore, a B-N-C angle-dependent change in antiaromaticity was suggested by a scan of the NICS(1) calculation. Dianion 2 exhibited chemiluminescence upon exposure to an oxygen atmosphere.image

Automated summary

The formation of Lewis pairs is an important concept in chemistry. Recently, the complexation of Lewis acid tris(pentafluorophenyl)borane with Lewis base moieties and subsequent reduction has been explored as a strategy for designing new reactions and structures. Through synthesis, X-ray crystallography, spectroscopic analysis, and quantum chemical calculations, it was found that Lewis adduct formation stabilizes an antiaromatic system consisting of 9,10-dicyanoanthracene and tris(pentafluorophenyl)borane. The reduction of a bisboron complex also resulted in a decrease in antiaromaticity.