8-Bromo-4,5-bis(dimethylamino)quinoline: Synthesis, protonation, and the first structural studies of quinoline proton sponge as a base

Synthesized 8-bromo-4,5-bis(dimethylamino)quinoline is the simplest and at the same time the first representative of quinoline proton sponges, existing as a base in a crystalline form, and not as an oil. This allowed to perform the XRD study both for the title compound and its salt with HBF4. The results obtained revealed a significant conjugation of the cyclic nitrogen atom with peri-NMe2 groups, which initiates a noticeable planarization of the latter and lengthening the distance between them. As a result, the mono-protonated salts of the title quinoline, either in solid or in solution, exist completely in the quinolinium form. To compare the effect of peri-NMe2 groups on the stability of naphthalene and quinoline proton sponges, the structural index of their aromaticity was calculated for the first time.& COPY; 2023 Elsevier Ltd. All rights reserved.

Automated summary

The synthesized 8-bromo-4,5-bis(dimethylamino)quinoline is the simplest and first representative of quinoline proton sponges, existing in a crystalline form instead of oil. XRD study showed significant conjugation of the cyclic nitrogen atom with peri-NMe2 groups, leading to their planarization and increased distance. The mono-protonated salts of the quinoline exist exclusively in the quinolinium form. The structural index of aromaticity was calculated for the first time to compare the stability of naphthalene and quinoline proton sponges with peri-NMe2 groups. ©2023 Elsevier Ltd. All rights reserved.