Alkali Metal Cation Effects on Dinitrogen Complexes and Organometallic Compounds

Conspectus Alkali metal (AM) cations are often taken for granted as counterions in coordination chemistry and organometallic reactions. However, the AM cation can be more than a bystander in inorganic transformations. This Account focuses on research that has elucidated several types of AM cation effects and how these can be exploited to achieve novel structures and reactivity pathways. A particular focus is on AM cation effects in low-coordinate iron β-diketiminate complexes, though we address general trends and potential applications in systems with other supporting ligands. The Account is organized by several recurring motifs and trends in how AM cations interact with transition-metal compounds: (1) the AM cations can stabilize and favor the formation of N 2 -bridged compounds, (2) the choice of AM cations can influence N–N bond cleavage, (3) the AM cations can influence other bond forming and cleaving reactions, and (4) AM cations can affect ligand binding modes and electronic structure at the metal center. Various methods including X-ray crystallography, density functional theory (DFT) calculations, Mössbauer spectroscopy, and vibrational spectroscopy are leveraged to show how the AM cation affects a given system. The results of these studies have more general lessons as well. They offer insights into how ligand design can be leveraged to promote or discourage AM cation interactions. AM cations can be used to activate challenging bonds and/or stabilize highly reactive species. The cooperative interactions described in this Account may offer new paths to reactivity in organometallic chemistry and small molecule activation.