Acid-Catalyzed Electron Transfer Processes in Naphthalene peri-Dichalcogenides.

Abstract

1,8-Naphthalene peri-dichalcogenides undergo protonation by Bronsted acids to produce electrophilic cations. Single electron transfer (SET) from the remaining unprotonated electron-rich peri-dichalcogenide to the cation then generates a radical cation and a radical. Thus, the formation of radical species results in severe peak broadening and coalescence of NMR signals when trifluoroacetic acid or other strong acids are added to the peri-dichalcogenide, and the process can be reversed by treatment with base. Further evidence for the formation of radicals stems from EPR, radical quencing with sodium dithionite, and computational experiments. The electron transfer is enhanced by the presence of 2,7-dialkoxy substituents that further increase the electron-donating ability of the dichalcogenides. This is an unusual example of a proton-coupled electron transfer process where an electron-rich molecule reacts with its own conjugate acid via a single electron transfer process.