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

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Abstract
Three new tetramines, (ArNHCH2CH2)3N, have been synthesized in which Ar = 3,5-(2,4,6-t-Bu3C6H2)2C6H3 (H3[HTBTN3N]), 3,5-(2,4,6-Me3C6H2)2C6H3 (H3[HMTN3N]), or 4-Br-3,5-(2,4,6-i-Pr3C6H2)2C6H2 (H3[pBrHIPTN3N]). The diarylated tetramine, {3,5-(2,4,6-t-Bu3C6H2)2C6H3NHCH2CH2}2NCH2CH2NH2, has also been isolated, and the “hybrid” tetramine {3,5-(2,4,6-t-Bu3C6H2)2C6H3NHCH2CH2}2NCH2CH2NH(4-t-BuC6H4) has been prepared from it. Monochloride complexes, [(TerNCH2CH2)3N]MoCl, have been prepared, as well as a selection of intermediates that would be expected in a catalytic dinitrogen reduction such as [(TerNCH2CH2)3N]Mo⋮N and {[(TerNCH2CH2)3N]Mo(NH3)}{BAr‘4} (Ter = HTBT, HMT, or pBrHIPT and Ar‘ = 3,5-(CF3)2C6H3)). 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 ∼65%. Only [pBrHIPTN3N]Mo compounds are efficient catalysts for dinitrogen reduction. The reasons are explored and discussed.