Nitrogen Fixation via Splitting into Nitrido Complexes

The large carbon footprint of the Haber-Bosch process, which provides ammonia for fertilizers but also the feedstock for all nitrogenous commercial products, has fueled the quest for alternative synthetic strategies to nitrogen fixation. Owing to the extraordinarily strong N≡N triple bond, the key step of the Haber-Bosch reaction, i.e., the dissociative adsorption of N₂, requires high temperatures. Since the first report in 1995, a wide variety of molecular transition metal and f-block compounds have been reported that can fully cleave N₂ at ambient conditions and form well-defined nitrido complexes. We here provide a comprehensive survey of the current state of N₂ splitting reactions in solution and follow-up nitrogen transfer reactivity. Particular emphasis is put on electronic structure requirements for the formation of suitable molecular precursors and their N-N scission reactivity. The prospects of N₂ splitting for the synthesis of nitrogen containing products will be discussed, ranging from ammonia and heterocumulenes to organic amines, amides or nitriles via proton coupled electron transfer, carbonylation, or electrophilic functionalization of N₂ derived nitrido complexes. Accomplishments and challenges for nitrogen fixation via N₂ splitting are presented to offer guidelines for the development of catalytic platforms.