In this paper we explore several issues surrounding the catalytic reduction of dinitrogen by molybdenum compounds that contain the [(HIPTNCH₂CH₂)₃N]³^- ligand (where HIPT = 3,5-(2,4,6-i-Pr₃C₆H₂)₂C₆H₃). Four additional plausible intermediates in the catalytic dinitrogen reduction have now been crystallographically characterized; they are MoNNH (Mo = [(HIPTNCH₂CH₂)₃N]Mo), [Mo NNH₂][BAr‘₄] (Ar‘ = 3,5-(CF₃)₂C₆H₃), [Mo NH][BAr‘₄], and Mo(NH₃). We also have crystallographically characterized a 2,6-lutidine complex, Mo(2,6-Lut)⁺, which is formed upon treatment of MoH with [2,6-LutH][B(C₆F₅)₄]. We focus on the synthesis of compounds that have not yet been isolated, which include Mo NNH₂, Mo NH, and Mo(NH₂). Mo NNH₂, formed by reduction of [Mo NNH₂]⁺, has not been observed. It decomposes to give mixtures that contain two or more of the following: MoNNH, Mo⋮N, Mo(NH₃)⁺, Mo(NH₃), and ammonia. Mo NH, which can be prepared by reduction of [Mo NH]⁺, is stable for long periods in the presence of a small amount of CrCp*₂, but in the absence of CrCp*₂, and in the presence of Mo NH⁺ as a catalyst, Mo NH is slowly converted into a mixture of Mo⋮N and Mo(NH₂). Mo(NH₂) can be produced independently by deprotonation of Mo(NH₃)⁺ with LiN(SiMe₃)₂ in THF, but it decomposes to Mo⋮N upon attempted isolation. Although catalytic reduction of dinitrogen could involve up to 14 intermediates in a “linear” sequence that involves addition of “external” protons and/or electrons, it seems likely now that several of these intermediates, along with ammonia and/or dihydrogen, can be produced in several reactions between intermediates that themselves behave as proton and/or electron sources.

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