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.