A Catalytic System for Preparation of Diazomethylenephosphoranes R₃P=C=N₂ from Mixed Phosphonium–Sulfonium Bisylide R₃P=C=SPh₂ and N₂

Currently, in almost all work on transition metal-mediated transformation of dinitrogen (N₂) into organic compounds, the C–N bond formation steps are fulfilled through the interaction between metal-dinitrogen M-N₂ complexes and carbon based substrates. The preparation steps of M-N₂ complexes are incompatible with the reaction conditions of the N−C bond formation, which has prevented catalysis. Herein, we report a chemical cycle that does not involve the preparation steps of M-N₂ complexes. In the presence of Ni(CO)₄ and SbF₅ catalysts, this chemical cycle can convert mixed phosphonium–sulfonium bisylide \mathrmR_3\mathrmP=\mathrmC=\mathrmSPh_2 and N₂ into diazomethylenephosphoranes \mathrmR_3 \mathrmP=\mathrmC=\mathrmN_2 . The C–N bond formation steps in this work are achieved through the direct reaction of N₂ molecules with carbene 3, which is a metal-carbon based M-C complex. The computed free energy barrier for the reaction between carbene 3 and N₂ is 24.06 kcal/mol, indicating that this reaction can occur at room temperature. Theoretical calculations show that the above chemical cycle is feasible in terms of kinetics and thermodynamics and is a true catalytic system for directly introducing N₂ into organic compounds under mild conditions. Additionally, compared to traditional carbenes CR₂ with two electron-sharing bonds between carbon and substituent R, the predicted carbene 3' () and carbene 3 () in this work have unique electronic structures, which feature two P→C and C→Ni donor-acceptor bonds. The weak C→Ni bonds of carbene 3' and carbene 3 are critical for the regeneration of transition metal catalysts Ni(CO)₄. This also means that the predicted carbene 3' and carbene 3 will have richer chemical properties to be discovered than traditional carbene CR₂. This work also preliminarily predicted that carbene 3' has the potential to activate CO, indicating that this work may open the door to activating other important small molecules.