Oxidative Dimerization of Triarylamines Promoted by WCI6, 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)(2)NPh2, 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 center dot center dot center dot[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.