Palladium-catalyzed amination of aryl dibromides with secondary amines: synthetic and mechanistic aspects

Diaminobenzenes are obtained starting from m- and p-dibromobenzenes and sec ondary amines in the presence of Pd(dba)(2)/P(o-tolyl)(3) and sodium tert-b utoxide in moderate to good yields. Reductive dehalogenation of aryl dibrom ides is a major side reaction under these conditions. The study of this rea ction has shown that the formation of reductive dehalogenation products occ urs according to two independent ways. The first one proceeds via the well- known beta-hydride elimination from amido-coordinated palladium complexes. The second one involves the formation of hydride palladium complexes from a mino-coordinated derivatives. Although our results do not allow us to propo se a detailed mechanistic scheme, they clearly show that the deprotonation step of the catalytic amination cycle has a major effect on the amine/arene ratio. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.