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 R3P = C = SPh2 and N2 into diazomethylenephosphoranes R3P = C = N2. 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′(MeNi(CO)3|↑R2P→C:) and carbene 3(MeNi(CO)2|↑R2P→C:) 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.