Synthesis of [(DPPNCH2CH2)3N]3- molybdenum complexes (DPP = 3,5-(2,5-Diisopropylpyrrolyl)2C6H3) and studies relevant to catalytic reduction of dinitrogen.
Molybdenum complexes that contain a new TREN-based ligand [(3,5-(2,5-diisopropyl-pyrrolyl)(2)C(6)H(3)NCH(2)CH(2))(3)N](3-) ([DPPN(3)N](3-)) that are relevant to the catalytic reduction of dinitrogen have been prepared. They are [Bu(4)N]{[DPPN(3)N]MoN(2)}, [DPPN(3)N]MoN(2), [DPPN(3)N]MoN=NH, {[DPPN(3)N]MoN=NH(2)}[BAr(f)(4)], [DPPN(3)N]Mo[triple bond]N, {[DPPN(3)N]Mo[triple bond]NH}[BAr(f)(4)], and {[DPPN(3)N]MoNH(3)}[BAr(f)(4)]. NMR and IR data for [Bu(4)N]{[DPPN(3)N]MoN(2)} and [DPPN(3)N]MoN(2) are close to those reported for the analogous [HIPTN(3)N](3-) compounds (HIPT = hexaisopropylterphenyl), which suggests that the degree of reduction of dinitrogen is virtually identical in the two systems. However, X-ray studies and several exchange studies support the conclusion that the apical pocket is less protected in [DPPN(3)N]Mo complexes than in [HIPTN(3)N]Mo complexes. For example, (15)N/(14)N exchange studies showed that exchange in [DPPN(3)N]MoN(2) is relatively facile (t(1/2) approximately 1 h at 1 atm) and depends upon dinitrogen pressure, in contrast to the exchange in [HIPTN(3)N]MoN(2). Several of the [DPPN(3)N]Mo complexes, e.g., the [DPPN(3)N]MoN(2) and [DPPN(3)N]MoNH(3) species, are also less stable in solution than the analogous "parent" [HIPTN(3)N]Mo complexes. Four attempted catalytic reductions of dinitrogen with [DPPN(3)N]MoN yielded 2.53 +/- 0.35 equiv of total ammonia. These studies reveal more than any other just how sensitive a successful catalytic reduction is to small changes in the triamidoamine supporting ligand.
Reithofer
Michael R
MR
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Schrock
Richard R
RR
Müller
Peter
P
D002384:Catalysis; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D008982:Molybdenum / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D010084:Oxidation-Reduction; D011758:Pyrroles / Q000737:chemistry*
D008024:Ligands; D009942:Organometallic Compounds; D011758:Pyrroles; D008982:Molybdenum; D009584:Nitrogen