Synthesis and reactions of molybdenum triamidoamine complexes containing hexaisopropylterphenyl substituents

We have synthesized a triamidoamine ligand ([(RNCH2CH2)(3)N](3-)) in which R is 3,5-(2,4,6-i-Pr3C6H2)(2)C6H3 (hexaisopropylterphenyl or HIPT). The reaction between MOCl4(THF)(2) and H-3[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(N-2)}(-) ion. The {Mo(N-2)}(-) ion can be oxidized by zinc chloride to give Mo(N-2) 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 equivalent to N, {Mo=NH}(+) (by protonation of Moequivalent toN), and {Mo(NH3)}(+) (by treating MoCl with ammonia). (The anion is usually {B(3,5-(CF3)(2)C6H3)(4)}(-) = {BAr'(4)}(-).) X-ray studies were carried out on {Mg(DME)(3)}(0.5)-[Mo(N-2)], MoN=NMgBr(THF)(3), Mo(N-2) Moequivalent toN, 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.