CONTEXT

Ammonia is one of the most abundant and least expensive synthetic inorganic chemicals. It is made industrially from dinitrogen and dihydrogen under harsh conditions (up to 550 °C and 350 atm) by the catalytic Haber-Bosch process. Production, which requires 1% of the energy consumed annually by humans, reaches 10⁸ tones. This scale is equivalent to that of the biological reduction of dinitrogen to ammonia by nitrogenase enzymes which represents the main source of nitrogen for living organisms. Ammonia is also the common nitrogen source for the industrial production of fertilizers and organic amino compounds. It is therefore evident that the development of new processes using NH₃ as feedstock constitutes a very important research target. N-H bond activation involving transition metals or singlet carbenes has attracted increasing attention but remains difficult. The other way to activate NH₃ involves the well known formation of Lewis acid-base adducts between transition metals and ammonia (Werner-type complexes). In this field, catalytic reactions consuming NH₃ are extremely rare.  Recently, palladium catalyzed amination of non activated aryl halides using ammonia has been reported by Hartwig and Buchwald in the presence of bulky ferrocene or electron-rich phosphine ligands. Here there are drawbacks: ammonia pressure in one of the two methods (5-6 bars), the use of strong bases, a toxic and expensive metal and sophisticated supporting ligands.