Facile synthesis and characterization of naphthidines as a new class of highly nonplanar electron donors giving robust radical cations

Article abstract of DOI:10.1021/jo0517444

Naphthidines 2 were prepared by nickel-catalyzed amination of 1-chloronaphthalene followed by oxidative homocoupling of 1-naphthalene amines 1 using titanium(IV) tetrachloride. The electronic and magnetic properties of materials 2 were investigated by cyclic voltammetry and other electrochemical techniques, EPR and UV-visible spectroscopies, and magnetic susceptibility. It was demonstrated that compounds 2 could be easily and reversibly oxidized via a two-electron-transfer reaction into their bis(radical cation) 2^2.2+, which displays a substantial stability at room temperature (the half-life of 2^2.2+ estimated by EPR at 25 °C was 10 days). B3LYP/6-31G* optimized structures of N,N′-bis(4-methoxyphenyl)-(1,1′-binaphthyl)- 4,4′-diamine 2g shows significant differences in the torsion angle between the naphthalene moieties depending on its oxidation state. Twisted structures are preferred for neutral compounds, whereas more planar are favored for the oxidized forms 2g⁺ and 2g^2.2+ to realize spin and/or charge delocalizations over the whole π-system. Such conformation changes concerted with the electron transfers contribute to explain the unusual two-electron process observed in the electrochemical behavior of 2g instead of the two single-electron transfers that would have been expected in the case of two successive oxidations. It is finally shown that the oxidation of 2g in CH₂Cl₂ with thianthrenium perchlorate (ThClO4) generates the dication 2g^2.2+ with singlet spin-multiplicity.