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

•Alkali metals promote the Haber-Bosch catalyst, but are incompletely understood.•Coordination compounds with alkali metals and N2 can show roles of alkali metals.•We review complexes in which transition metals, N2, and alkali metals interact.•Parallels between homogeneous and heterogeneous compounds motivate new research.

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.

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