One-electron oxidation-induced dimerising C–C coupling of a 2,5-diamino-1,4-benzoquinonediimine: a chemical and electrochemical investigation

Abstract

The one-electron oxidation of N,N′,N″,N‴-tetraneopentyl-2,5-diamino-1,4-benzoquinonediimine 3 has been carried out using Ag(I) as an oxidising agent and led to the formation of the postulated nitrogen-based radical cation B. This unstable species can evolve by following two competing pathways, either a hydrogen atom abstraction from a THF solvent molecule, which leads to the N,N′,N″,N‴-tetraneopentyl-2,5-diamino-1,4-benzoquinonemonoiminemonoiminium triflate 5, or a dimerisation of two carbon-based radical cations C, which affords the new dimer 4. An X-ray diffraction study of the latter established the presence of a centre of symmetry in the middle of the newly formed C_sp³–C_sp³ bond. Breaking of this bond upon reduction regenerates 3 under mild conditions. This type of chemically induced formation/breaking of a C–C single bond appears to be unprecedented in quinonoid chemistry. Electrochemical studies performed in THF confirm the proposed mechanism for the one-electron oxidation process.