Direct Crystallization of Diamine Radical Cations: Carbon-Nitrogen Bond Formation from the Reaction of Triphenylamine with TiCl₄, TiBr₄, or SnCl₄ versus Carbon-Carbon Bond Formation with SbCl₅

Direct synthesis of diamine radical cations in crystalline form proceeding through oxidation of triphenylamine followed by the formation of a new C-N bond is reported. Although the oxidative coupling of triphenylamine is well studied, diamine products are rarely captured in their radical cation state. The neutral diamine most frequently obtained from this reaction pathway is N,N,N',N'-tetraphenylbenzidine. Herein, the capture of radical cations of diamines in crystalline form in one step starting with neutral triphenylamine was demonstrated, and the formation of two products (the radical cations of N,N,N',N'-tetraphenyl-1,4-benzenediamine or N,N,N',N'-tetraphenylbenzidine) depending on the oxidizing agent used was observed. The radical species are characterized by single-crystal X-Ray diffraction, electron paramagnetic resonance spectroscopy, and optical spectroscopy.