N–N Bond Cleavage of Mid-Valent Ta(IV) Hydrazido and Hydrazidium Complexes Relevant to the Schrock Cycle for Dinitrogen Fixation

Chemical reduction of the Ta(V) hydrazido chloride 1 generates the open-shell, mononuclear Ta(IV) hydrazido complex 2, which upon N-methylation yields the corresponding structurally characterized Ta(IV) hydrazidium 6. Chemical reduction of 6 results in N-N bond cleavage to generate a cis/trans mixture of the [Ta(V),Ta(V)] bis(μ-nitrido) product 7 in tetrahydrofuran and the mononuclear Ta(V) parent imide 8 in toluene. These results serve to establish an important foundation for the pursuit of a group-5 metal variant of the Schrock cycle for dinitrogen fixation.