Synthesis and Reactions of Molybdenum Triamidoamine Complexes Containing Hexaisopropylterphenyl Substituents

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Abstract
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 MoNNH. The latter was found to decompose to yield MoH. Other relevant compounds that have been prepared include {Mo N−NH2}+ (by protonation of MoNNH), 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)], MoNNMgBr(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.