Synthesis and Reactions of Molybdenum Triamidoamine Complexes Containing Hexaisopropylterphenyl Substituents

We have synthesized a triamidoamine ligand ([(RNCH2CH2)3N]3-) in which R is 3,5-(2,4,6-i-Pr3C6H2)2C6H3 (hexaisopropylterphenyl or HIPT). The reaction between MoCl4(THF)2 and H3[HIPTN3N] in THF followed by 3.1 equiv of LiN(SiMe3)2 led to formation of orange [HIPTN3N]MoCl. Reduction of MoCl (Mo = [HIPTN3N]Mo) with magnesium in THF under dinitrogen led to formation of salts that contain the {Mo(N2)}- ion. The {Mo(N2)}- ion can be oxidized by zinc chloride to give Mo(N2) or protonated to give MoNNH. The latter was found to decompose to yield MoH. Other relevant compounds that have been prepared include {MoN−NH2}+ (by protonation of MoNNH), Mo⋮N, {Mo=NH}+ (by protonation of Mo⋮N), and {Mo(NH3)}+ (by treating MoCl with ammonia). (The anion is usually {B(3,5-(CF3)2C6H3)4}- = {BAr‘4}-.) X-ray studies were carried out on {Mg(DME)3}0.5[Mo(N2)], MoNNMgBr(THF)3, Mo(N2), Mo⋮N, and {Mo(NH3)}{BAr‘4}. These studies suggest that the HIPT substituent on the triamidoamine ligand creates a cavity that stabilizes a variety of complexes that might be encountered in a hypothetical Chatt-like dinitrogen reduction scheme, perhaps largely by protecting against bimolecular decomposition reactions.