Oxidative Dimerization of Triarylamines Promoted by WCl₆, Including the Solid State Isolation and the Crystallographic Characterization of a Triphenylammonium Salt

The triphenylammonium salt [NHPh₃]­[WCl₆], 1, and the product of the C–C dimerization of triphenylamine, Ph₂N­(C₆H₄)₂NPh₂, 2, were afforded from the reaction between WCl₆ and NPh₃ in CH₂Cl₂. Compound 2 was isolated in 43% yield upon hydrolysis of the reaction mixture. The X-ray structure of 1 provides the first crystallographic characterization of the triphenylammonium ion. Combined EPR and DFT studies gave insight into the reaction mechanism, and allowed the identification of WCl₅···[Cl­(C₆H₄)­NPh₂] as a presumable key intermediate. The reactions of WCl₆ with 4-bromotriphenylamine, 4,4′-dimethyltriphenylamine, 9-phenylcarbazole, followed by hydrolytic treatment, led to the dimerization products 3–6, in admixture with variable amounts of the parent amines. N,N,N′,N′-tetrakis­(4-bromophenyl)-[1,1′-biphenyl]-4,4′-diamine, 3, was isolated in 60% yield from the reaction of WCl₆ with 4,4′-dibromotriphenylamine.