Manipulating Reactivity of Ir(CH₂)_0-2⁺ Cations toward Dinitrogen at Room Temperature: A Unique Dependence on the Organic Ligand Structures

Nitrogen (N₂) activation at room temperature has long been a great challenge. Therefore, the rational design of reactive species to adsorb N₂, which is a prerequisite for cleavage of the strong N≡N triple bond in industrial and biological processes, is highly desirable and meaningful. Herein, the N₂ adsorption process is controlled by regulating the types and numbers of organic ligands, and the organic ligands are produced through the reactions of Ir⁺ with methane and ethane. CH₄ molecules dissociate on the Ir⁺ cations to form Ir(CH₂)_1,2⁺. The reaction of Ir⁺ with C₂H₆ can generate HIrC₂H₃⁺, which is different from the structure of Ir(CH₂)₂⁺ obtained from Ir⁺/CH₄. The reactivity order of N₂ adsorption is Ir(CH₂)₂⁺ > HIrC₂H₃⁺ ≫ HIrCH⁺ ≈ Ir⁺ (almost inert under similar reaction conditions), indicating that different organic ligand structures affect reactivity dramatically. The main reason for this interesting reactivity difference is that the lowest unoccupied molecular orbital (LUMO) level of Ir(CH₂)₂⁺ is much closer to the highest occupied molecular orbital (HOMO) level of N₂ than those of the other three systems. This study provides new insights into the adsorption of N₂ on metal-organic ligand species, in which the organic ligand dominates the reactivity, and it discovers new clues in designing effective transition metal carbine species for N₂ activation.