Activation of Dinitrogen by Polynuclear Metal Complexes

Activation of dinitrogen plays an important role in daily anthropogenic life, and the processes by which this fixation occurs have been a longstanding and significant research focus within the community. One of the major fields of dinitrogen activation research is the use of multimetallic compounds to reduce and/or activate N₂ into a more useful nitrogen-atom source, such as ammonia. Here we report a comprehensive review of multimetallic-dinitrogen complexes and their utility toward N₂ activation, beginning with the d-block metals from Group 4 to Group 11, then extending to Group 13 (which is exclusively populated by B complexes), and finally the rare-earth and actinide species. The review considers all polynuclear metal aggregates containing two or more metal centers in which dinitrogen is coordinated or activated (i.e., partial or complete cleavage of the N₂ triple bond in the observed product). Our survey includes complexes in which mononuclear N₂ complexes are used as building blocks to generate homo- or heteromultimetallic dinitrogen species, which allow one to evaluate the potential of heterometallic species for dinitrogen activation. We highlight some of the common trends throughout the periodic table, such as the differences between coordination modes as it relates to N₂ activation and potential functionalization and the effect of polarizing the bridging N₂ ligand by employing different metal ions of differing Lewis acidities. By providing this comprehensive treatment of polynuclear metal dinitrogen species, this Review aims to outline the past and provide potential future directions for continued research in this area.