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

Description:

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

Creator(s):
Creation Date: September 5, 2008
Partner(s):
UNT College of Arts and Sciences
Collection(s):
UNT Scholarly Works
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Total Uses: 161
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Creator (Author):
Cundari, Thomas R., 1964-

University of North Texas

Creator (Author):
Jimenez-Halla, J. Oscar C.

University of Girona

Creator (Author):
Morello, Glenn R.

University of North Texas

Creator (Author):
Vaddadi, Sridhar

University of North Texas

Publisher Info:
Publisher Name: American Chemical Society
Place of Publication: [Washington, DC]
Date(s):
  • Creation: September 5, 2008
Description:

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

Degree:
Department: Chemistry
Note:

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

Note:

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.

Physical Description:

8 p.

Language(s):
Subject(s):
Keyword(s): phosphinoethane ligand | C-H activation | catalytic tuning
Source: Journal of the American Chemical Society, 2008, Washington DC: American Chemical Society, pp. 13051-13058
Partner:
UNT College of Arts and Sciences
Collection:
UNT Scholarly Works
Identifier:
  • DOI: 10.1021/ja803176 |
  • ARK: ark:/67531/metadc77145
Resource Type: Article
Format: Text
Rights:
Access: Public
Citation:
Publication Title: Journal of the American Chemical Society
Volume: 130
Page Start: 13051
Page End: 13058
Pages: 8
Peer Reviewed: Yes