Facile Synthesis and Characterization of Naphthidines as a New Class of Highly Nonplanar Electron Donors Giving Robust Radical Cations
2006-02-17T00:00:00Z (GMT) by
Naphthidines <b>2</b> were prepared by nickel-catalyzed amination of 1-chloronaphthalene followed by oxidative homocoupling of 1-naphthalene amines <b>1</b> using titanium(IV) tetrachloride. The electronic and magnetic properties of materials <b>2</b> were investigated by cyclic voltammetry and other electrochemical techniques, EPR and UV−visible spectroscopies, and magnetic susceptibility. It was demonstrated that compounds <b>2</b> could be easily and reversibly oxidized via a two-electron-transfer reaction into their bis(radical cation) <b>2</b><sup>2.2+</sup>, which displays a substantial stability at room temperature (the half-life of <b>2</b><b><sup>2.2+</sup></b><sup></sup> estimated by EPR at 25 °C was 10 days). B3LYP/6-31G* optimized structures of <i>N,N</i>‘-bis(4-methoxyphenyl)-(1,1‘-binaphthyl)-4,4‘-diamine <b>2g</b> 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 <b>2g</b><b><sup>•</sup></b><sup>+</sup> and <b>2g</b><b><sup>2.2+</sup></b><sup></sup> 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 <b>2g</b> 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 <b>2g</b> in CH<sub>2</sub>Cl<sub>2</sub> with thianthrenium perchlorate (ThClO<sub>4</sub>) generates the dication <b>2g</b><b><sup>2.2+</sup></b><sup></sup> with singlet spin-multiplicity.