Effect of Salt Additives on Dinitrogen Activation Mediated by Boron-Based Compounds: Insights from Theory

Dinitrogen (N₂) is an inert molecule, and its activation under metal-free conditions presents a longstanding challenge with potential for new pathways to transform N₂ into valuable products. Herein, we employ density functional theory (DFT) to investigate the reactivity and reaction mechanism of two boron-based compounds, cyclic (alkyl)(amino)carbene (CAAC), diboracumulene (1), and N-heterocyclic carbene (NHC)-diboryne (2) toward N₂. Interestingly, we demonstrated that noncovalently bound lithium chloride (LiCl) enhances the reactivity by acting as a promoter, creating a local electric field that facilitates N₂ binding and activation. While salts like LiCl are often used empirically in bond activation, their role as a local electric field source for N₂ activation is rarely explored. Our calculations reveal that the free energy barrier for N₂ coordination and activation is significantly reduced with the 1/LiCl combination, and a process that is endergonic without LiCl becomes exergonic in its presence. Furthermore, the effect of heavier alkali metal salts, such as KCl, and bulkier ion-pairs containing 1-butyl-1-methylpyrrolidinium cation, (I) [C₄mpyr]⁺[eFAP]^-, and (II) [C₄mpyr]⁺[PF₆]^- on N₂ coordination was explored to gain comparative insights into how variations in electrostatic environments influence N₂ binding to 1, relative to LiCl, as presented in the later sections.