Studies relevant to catalytic reduction of dinitrogen to ammonia by molybdenum triamidoamine complexes

In this paper we explore several issues surrounding the catalytic reduction of dinitrogen by molybdenum compounds that contain the [(HIPTNCH2CH2)(3)N](3-) ligand (where HIPT = 3,5-(2,4,6-i-Pr3C6H2)(2)C6H3). Four additional plausible intermediates in the catalytic dinitrogen reduction have now been crystallographically characterized; they are MoN= NH (Mo = [(HIPTNCH2CH2)(3)N]Mo), [Mo=NNH2][BAr'(4)] (Ar' = 3,5-(CF3)(2)C6H3)[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: MoN=NH, 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 CrCP2*, but in the absence of CrCP2*, 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.