Formatlon of ([HIPTN3N]Mo(III)H) by heterolytic cleavage of H2 as established by EPR and ENDOR spectroscopy

R. Adam Kinney, Dennis G.H. Hetterscheid, Brian S. Hanna, Richard R. Schrock, Brian M. Hoffman

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25 Scopus citations

Abstract

MoN2 (Mo=[(HIPTNCH2CH2)3N]Mo, where HIPT = 3,5-(2,4,6-i-Pr3C6H2) 2C6H3) is the first stage In the reduction of N2 to NH3 by Mo. Its reaction with dlhydrogen in fluid solution yields "MoH2", a molybdenum-dlhydrogen compound. In this report, we describe a comprehensive electron paramagnetic resonance (EPR) and 1/2H/14N electron nuclear double resonance (ENDOR) study of the product of the reaction between MoN2 and H 2 that is trapped in frozen solution, 1. EPR spectra of 1 show that it has a near-axial g tensor, g = [2.086, 1.961, 1.947], with dramatically reduced g anisotropy relative to MoN2. Analysis of the g values reveal that this anion has the Mo(III), [dxz dyz] 3 orbltal configuration, as proposed for the parent MoN2 complex, and that It undergoes a strong pseudo-Jahn-Teller (PJT) distortion. Simulations of the 2D 35 GHz 1H ENDOR pattern comprised of spectra taken at multiple fields across the EPR envelope (2 K) show that 1 is the [MoH]- anion. The 35 GHz Mims pulsed 2H ENDOR spectra of 1 prepared with 2H2 show the corresponding 2H- signal, with a substantial deuterium isotope effect In also. Radiolytic reduction of a structural analogue, Mo(IV)H, at 77 K, confirms the assignment of 1. Analysis of the 2D 14N ENDOR pattern for the ligand amine nitrogen further reveals the presence of a linear N ax-Mo-H- molecular axis that is parallel to the unique magnetic direction (g1). The ENDOR pattern of the three equatorial nitrogens Is well-reproduced by a model in which the Mo-Neq plane has undergone a static, not dynamic, PJT distortion, leading to a range of hyperflne couplings for the three Neq's. The finding of a nearly axial hyperfine coupling tensor for the terminal hydride bound Mo supports the earlier proposal that the two exchangeable hydrogenic species bound to the FeMo cofactor of the nitrogense turnover intermediate, which has accumulated four electrons/protons (E4), are hydrides that bridge two metal ions, not terminal hydrides.

Original languageEnglish (US)
Pages (from-to)704-713
Number of pages10
JournalInorganic chemistry
Volume49
Issue number2
DOIs
StatePublished - Jan 18 2010

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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