title: Protonation of the dinitrogen-reduction catalyst [HIPTN3N]Mo(III) investigated by ENDOR spectroscopy.
abstract: Dinitrogen is reduced to ammonia by the molybdenum complex of L = [HIPTN3N](3-) [Mo; HIPT = 3,5-(2,4,6-iPr3C6H2)2C6H3]. The mechanism by which this occurs involves the stepwise addition of proton/electron pairs, but how the first pair converts MoN2 to MoN ═ NH remains uncertain. The first proton of reduction might bind either at Nβ of N2 or at one of the three amido nitrogen (N(am)) ligands. Treatment of MoCO with [2,4,6-Me3C5H3N]BAr'4 [Ar' = 2,3-(CF3)2C6H3] in the absence of reductant generates HMoCO(+), whose electron paramagnetic resonance spectrum has greatly reduced g anisotropy relative to MoCO. (2)H Mims pulsed electron nuclear double-resonance spectroscopy of (2)HMoCO(+) shows a signal that simulations show to have a hyperfine tensor with an isotropic coupling, aiso((2)H) = -0.22 MHz, and a roughly dipolar anisotropic interaction, T((2)H) = [-0.48, -0.93, 1.42] MHz. The simulations show that the deuteron is bound to N(am), near the Mo equatorial plane, not along the normal, and at a distance of 2.6 Å from Mo, which is nearly identical with the (Nam)(2)H(+)-Mo distance predicted by density functional theory computations.
authors.affiliation: Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States.
authors.forename: R Adam
authors.initials: RA
authors.lastname: Kinney
authors.forename: Rebecca L
authors.initials: RL
authors.lastname: McNaughton
authors.forename: Jia Min
authors.initials: JM
authors.lastname: Chin
authors.forename: Richard R
authors.initials: RR
authors.lastname: Schrock
authors.forename: Brian M
authors.initials: BM
authors.lastname: Hoffman
mesh_terms: D002384:Catalysis; D056831:Coordination Complexes / Q000737:chemistry*; D060526:Magnetic Fields; D009682:Magnetic Resonance Spectroscopy; D008982:Molybdenum / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry*; D010084:Oxidation-Reduction; D011522:Protons
chemical_list: D056831:Coordination Complexes; D011522:Protons; D008982:Molybdenum; D009584:Nitrogen