Catalytic Tuning of a Phosphinoethane Ligand for Enhanced C-H Activation

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Article discussing research on the catalytic tuning of a phosphinoethane ligand for enhanced C-H activation.

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8 p.

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Cundari, Thomas R., 1964-; Jimenez-Halla, J. Oscar C.; Morello, Glenn R. & Vaddadi, Sridhar September 5, 2008.

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Article discussing research on the catalytic tuning of a phosphinoethane ligand for enhanced C-H activation.

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8 p.

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Reprinted with permission from the Journal of the American Chemical Society. Copyright 2008 American Chemical Society.

Abstract: Hydrogen atom abstraction (HAA) from 1,4-cyclohexadiene (CD-H) by (dtbpe)Ni(NAr) to form a Niǀ-amide, (dtbpe)Ni(NHAr), and cyclohexadienyl radical is calculated to be thermodynamically reasonable, ∆Hʜᴀᴀ(dtbpe) = -1.3 kcal/mol, dtbpe = bis(di-tert-butylphosphino)ethane, Ar = 2,6-diisopropylphenyl. However, radical rebound to form a metal-bound amine is highly endothermic (∆Hreb(dtbpe) = +25.1 kcal/mol). Analysis of bond enthalpies indicates that weakening of the Ni-N bond (Ni-amide→Ni-amine) upon radical rebound is not compensated by the weak C-N bond formed. Hence, a ligand was sought that would enhance the metal-amine bond strength while diminishing the metal-amide bond strength. Reaction of (dfmpe)Ni(NAr) with CD-H was thus analyzed, dfmpe = bis(di(trivluoromethyl)phosphino)ethane. While there is a small change in the thermodynamics of HAA (∆Hʜᴀᴀ(dfmpe) = -5.7 kcal/mol), there is a profound change in the rebound step (∆Hreb(dfmpe) = -7.8 kcal/mol) upon replacing dtbpe by dfmpe. Regeneration of the nitrene active species by reaction of ArN3 with the metal-bound product is calculated to be highly exothermic, ∆Hreg = -36.7 kcal/mol. Two candidates for a precatalyst, (dfmpe)Ni(COD) and (dfmpe)Ni(bpy), COD = 1,5-cyclooctadiene and bpy = 2,2´-bipyridine, were calculated to undergo highly exothermic reactions with ArN3 to form the nitrene active species. The calculated enthalpic barrier for HAA of CD-H by (dfmpe)Ni(NAr) is 21.3 kcal/mol. Hence, consideration of the computed thermodynamics and kinetics suggests that nickel-nitrenes with fluorinated phosphine supporting ligation are promising candidates for catalytic amination of C-H bonds.

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  • Journal of the American Chemical Society, 2008, Washington DC: American Chemical Society, pp. 13051-13058

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  • Publication Title: Journal of the American Chemical Society
  • Volume: 130
  • Page Start: 13051
  • Page End: 13058
  • Pages: 8
  • Peer Reviewed: Yes

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The Scholarly Works Collection is home to materials from the University of North Texas community's research, creative, and scholarly activities and serves as UNT's Open Access Repository. It brings together articles, papers, artwork, music, research data, reports, presentations, and other scholarly and creative products representing the expertise in our university community. Access to some items in this collection may be restricted.

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  • September 5, 2008

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  • March 2, 2012, 11:47 a.m.

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  • May 12, 2014, 2:31 p.m.

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Cundari, Thomas R., 1964-; Jimenez-Halla, J. Oscar C.; Morello, Glenn R. & Vaddadi, Sridhar. Catalytic Tuning of a Phosphinoethane Ligand for Enhanced C-H Activation, article, September 5, 2008; [Washington, DC]. (digital.library.unt.edu/ark:/67531/metadc77145/: accessed May 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT College of Arts and Sciences.