NH₃'s synthetic appeal gets a boost

Ammonia is cheap and plentiful but rarely used as a reagent in catalytic processes. In hopes of broadening the synthetic appeal of this atom-economical nitrogen source, Yale University chemists have used NH₃ in a catalytic process to make primary aromatic amines, an important class of chemical building blocks (J. Am. Chem. Soc., DOI: 10.1021/ja064005t). John F. Hartwig and Qilong Shen use NH₃ and a palladium catalyst bearing the commercial Josiphos ligand (shown) to convert aryl halides into primary arylamines. Previous palladium-catalyzed syntheses of primary arylamines have relied on ammonia surrogates. The catalytic system Hartwig and Shen report affords good yields and excellent selectivity with NH₃, but they will have to overcome a number of hurdles for the reaction to find commercial use, including lowering catalyst loads, reducing dilution requirements, and increasing functional group tolerance. That quest will be helped by further study of the reaction's mechanism, which involves a never-before-seen C-N bond-forming reductive elimination of an NH₂ complex, the authors report.