Probing Delocalization across Alkyne-Containing Linkages: Synthesis and Cyclic Voltammetry of Bridged Phenylenediamines

Article abstract of DOI:10.1021/jo00127a011

This paper presents the synthesis of N,N,N',N'-tetraethyl-1,4-phenylenediamines bridged by ethynyl-phenyl-ethynyl and diethynyl linkages.These compounds are of interest to determine if the N,N,N',N'-tetraethyl-1,4-phenylenediamines exhibit delocalized mixed oxidation states when oxidized electrochemically. 1-Butoxy-2,5-bis(N,N-diethylamino)-4-ethynylbenzene was a key intermediate, and nucleophilic addition of lithium (trimethylsilyl)acetylide to 2,5-bis(N,N-diethylamino)-1,4-benzoquinone provided an efficient synthesis of this compound.This intermediate was then assembled into the redox assemblies of interest in high yield by use of palladium-catalyzed cross-coupling and copper-catalyzed oxidative homo-coupling protocols.Cyclic voltammetry of these compounds indicate that the N,N,N',N'-tetraethyl-1,4-phenylenediamine redox units behave independently and that the interactions are principally electrostatic.As a result, we conclude that the electrochemically generated radical cations and dications are highly localized.