Combinations of electron and proton donors in transition-metal complex mediated nitrogen reduction reactions

Nitrogen fixation is a complex process involving the transfer of six electrons and protons. Diverging from the conventional Haber-Bosch process, which relies on hydrogen (H₂) to provide both electrons and protons to reduce nitrogen (N₂), homogeneous transition metal complex-catalyzed N₂ reduction reactions (NRR) employ an array of electron and proton donors or even electron donors combined with silanes. As the synthesis of diverse catalytic progress, the categories of donors have seen rapid expansion. However, existing literature only provides summaries regarding the metal, ligands, and mechanism. Despite the significance of electron and proton donor combinations in nitrogen reduction reactions, no literature has thoroughly reviewed this aspect. Therefore, we hereby compiled a comprehensive list of commonly used reagents in N₂ reduction and classified them according to their specific donor combinations. This review presents clear and organized information about these combinations, along with a summary of their general performance trend in NRR with related catalysts. Finally, we conclude the discussion by highlighting key points for researchers to consider when selecting catalysts and donor combinations, with the ultimate goal of advancing the field of nitrogen fixation. (Figure presented.)