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**

Abstract

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.

Reactions of Thianthrene and 10-Phenylphenothiazine with the Lewis Acids─Titanium Tetrachloride, Titanium Tetrabromide, Tin(IV) Tetrachloride, or Antimony(V) Pentachloride: The Competition between Coordination and Oxidation

“…Although the (thianthrene •+ ) free radical can be produced using the Ti(IV) halides, they are a suboptimal oxidant for this specific redox chemistry since the coordination complex (1) crystallizes from solution. In case of the role of Ti(IV) in oxidizing 10-phenylphenothiazine, an important distinction between the results observed here and those reported by us previously involving triphenyl amine oxidation 11 is the absence of any evidence of dimerization of the radical cation through either C−C or C−N bond formation in solution or in the solid that crystallizes from solution.…”

“…This laboratory recently reported the direct synthesis of diamine cation radicals in the crystalline form by oxidation of triphenylamine accompanied by the formation of either N , N , N ′, N ′-tetraphenyl-1,4-benzenediamine or N , N , N ′, N ′-tetraphenylbenzidine . The product that formed depended on the oxidizing agent used.…”

“…27 Additionally, phenylphenothiazine can be viewed as a modified triphenylamine and might be susceptible to coupling reactions like those observed for triphenylamine. 11 ■ RESULTS…”

“…Heterocycles with a phenothiazine core have been used to prepare various organic electro-optical materials. − The phenothiazine functionality is found in the antipsychotic drug, chlorpromazine . Additionally, phenylphenothiazine can be viewed as a modified triphenylamine and might be susceptible to coupling reactions like those observed for triphenylamine …”

A double-helical S,C-bridged tetraphenyl-para-phenylenediamine and its persistent radical cation

“…The radical cation of TPPD ( TPPD˙ + ) is relatively stable, and its electronic structure has been studied both spectroscopically and crystallographically. 10 During our research program on the chemistry of triarylamine radical cations (Fig. S1, ESI†), 4 c , d we developed the idea that the structural constraint of TPPD using partial bridging could be an effective strategy to synthesize stable, helical radical cations.…”