Amination of Polyhalogenated Aromatic Substrates

Multiple arylations of polybromobenzenes have been conducted to generate electron-rich arylamines. Tribromotriphenylamine and 1,3,5-tribromobenzene all react cleanly with A-aryl piperazines using either P(o-tolyl)3 or BINAP-ligated catalysts to form hexamine products [107]. Reactions of other polyhalogenated arenes have also been reported [108]. Competition between aryl bromides and iodides or aryl bromides and chlorides has been investigated for the formation of aryl ethers [109], and presumably similar selectivity is observed for the amination. In this case bro-mo, chloroarenes reacted preferentially at the aryl bromide position. This selectivity results from the faster oxidative addition of aryl bromides and is a common selectivity observed in cross-coupling. Sowa showed complete selectivity for amination of the aryl chloro, bromo, or iodo over aryl-fluoro linkages [110]. This chemistry produces fluoroanilines, whereas the uncatalyzed chemistry typically leads to substitution for fluoride. 

3 Third-Generation Catalysts with Alkylmonophosphines High Turnover Numbers, General Animation of Bromides at Room Temperature, and General Animation of Aryl Chlorides at Low Temperatures 

In general, alkylphosphines have been used less often than arylphosphines in crosscoupling chemistry. However, several studies pointed to the potential of such ligands in palladium-catalyzed animation of aryl halides. Most remarkable is the milder temperatures for animation of aryl bromides, improved yields with acyclic secondary amines, high turnover numbers for these reactions, and the ability to conduct mild animations of inexpensive aryl chlorides and tosylates. 

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