Coordination chemistry insights into the role of alkali metal promoters in dinitrogen reduction

The Haber-Bosch process is a major contributor to fixed nitrogen that supports the world's nutritional needs and is one of the largest-scale industrial processes known. It has also served as a testing ground for chemists' understanding of surface chemistry. Thus, it is significant that the most thoroughly developed catalysts for N₂ reduction use potassium as an electronic promoter. In this review, we discuss the literature on alkali metal cations as promoters for N₂ reduction, in the context of the growing knowledge about cooperative interactions between N₂, transition metals, and alkali metals in coordination compounds. Because the structures and properties are easier to characterize in these compounds, they give useful information on alkali metal interactions with N₂. Here, we review a variety of interactions, with emphasis on recent work on iron complexes by the authors. Finally, we draw conclusions about the nature of these interactions and areas for future research.