Synthesis of molybdenum complexes that contain "hybrid" triamidoamine ligands, [(hexaisopropylterphenyl-NCH2CH2)2NCH2CH2N-aryl]3-, and studies relevant to catalytic reduction of dinitrogen

In the Buchwald-Hartwig reaction between HIPTBr (HIPT = 3,5-(2,4,6-i-Pr3C6H2)2C6H3 = hexaisopropylterphenyl) and (H2NCH2CH2)3N, it is possible to obtain a 65% isolated yield of (HIPTNHCH2CH2)2NCH2CH2NH2. A second coupling then can be carried out to yield a variety of "hybrid" ligands, (HIPTNHCH2CH2)2NCH2CH2NHAr, where Ar = 3,5-Me2C6H3, 3,5-(CF3)2C6H3, 3,5-(MeO)2C6H3, 3,5-Me2NC5H3, 3,5-Ph2NC5H3, 2,4,6-i-Pr3C6H2, or 2,4,6-Me3C6H2. The hybrid ligands may be attached to Mo to yield hybrid]MoCl species. From the monochloride species, a variety of other species such as hybrid]MoN, {hybrid]MoN2}Na, and {hybrid]Mo(NH3)}+ can be prepared. Hybrid]MoN2 species were prepared through oxidation of {hybrid]MoN2}Na species with ZnCl2, but they could not be isolated. Hybrid]Mo=N-NH species could be observed as a consequence of the protonation of {hybrid]MoN2}- species, but they too could not be isolated as a consequence of a facile decomposition to yield dihydrogen and hybrid]MoN2 species. Attempts to reduce dinitrogen catalytically led to little or no ammonia being formed from dinitrogen. The fact that no ammonia was formed from dinitrogen in the case of Ar = 3,5-Me2C6H3, 3,5-(CF3)2C6H3, or 3,5-(MeO)2C6H3 could be attributed to a rapid decomposition of intermediate hybrid]Mo=N-NH species in the catalytic reaction, a decomposition that was shown in separate studies to be accelerated dramatically by 2,6-lutidine, the conjugate base of the acid employed in the attempted catalytic reduction. X-ray structures of (HIPTNHCH2CH2)2NCH2CH2N{3,5-(CF3)2C6H3}]MoCl and (HIPTNHCH2CH2)2NCH2CH2N(3,5-Me2C6H3)]MoN2}Na(THF)2 are reported.