Molybdenum triamidoamine complexes that contain hexa-tert-butylterphenyl, hexamethylterphenyl, or p-bromohexaisopropylterphenyl substituents.: An examination of some catalyst variations for the catalytic reduction of dinitrogen

Three new tetramines, (ArNHCH2CH2)(3)N, have been synthesized in which Ar = 3,5-(2,4,6-t-Bu3C6H2)(2)C6H3 (H-3[HTBTN3N]), 3,5-(2,4,6-Me3C6H2)(2)C6H3 (H-3[HMTN3N]), or 4-Br-3,5-(2,4,6-i-Pr3C6H2)(2)C6H2 (H-3[pBrHIPTN(3)N]). The diarylated tetramine, {3,5-(2,4,6-t-Bu3C6H2)(2)C6H3NHCH2CH2}(2)NCH2CH2NH2, has also been isolated, and the "hybrid" tetramine {3,5-(2,4,6-t-Bu3C6H2)(2)C6H3NHCH2CH2}(2)NCH2CH2NH(4-t-BuC6H4) has been prepared from it. Monochloride complexes, [(TerNCH(2)CH(2))(3)N]MoCl, have been prepared, as well as a selection of intermediates that would be expected in a catalytic dinitrogen reduction such as [(TerNCH(2)CH(2))(3)N]ModropN and {[(TerNCH(2)CH(2))(3)N]Mo(NH3)}{BAr'(4)} (Ter = HTBT, HMT, or pBrHIPT and Ar' = 3,5-(CF3)(2)C6H3)). Intermediates that contain the new terphenyl-substituted ligands are then evaluated for their efficiency for the catalytic reduction of dinitrogen under conditions where analogous [HIPTN3N]Mo species give four turnovers to ammonia under "standard" conditions with an efficiency of similar to65%. Only [pBrHIPTN(3)N]Mo compounds are efficient catalysts for dinitrogen reduction. The reasons are explored and discussed.