Effects of phosphine-carbene substitutions on the electrochemical and thermodynamic properties of nickel complexes

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Abstract

Nickel(II) complexes containing chelating N-heterocyclic carbene-phosphine ligands ([NiL2](BPh4)2, for which L = [MeIm(CH2)2PR2], MeIm = 1- methylimidizolylidene, and R = Ph or Et) have been synthesized for the purpose of studying how this class of ligand affects the electrochemical and thermodynamic properties compared to the nickel bis-diphosphine analogues. The nickel complexes were synthesized and then characterized by X-ray crystallography, electrochemical methods, and thermodynamic studies, including DFT calculations. On the basis of the reduction potentials (E°), substitution of an NHC for one of the phosphines in a diphoshine ligand resulted in negative shifts in potential by 0.6 to 1.2 V relative to the corresponding nickel bis-diphosphine complexes. From computational studies of the nickel hydride complex of the phenyl-substituted phosphine-carbene ligand, the hydride donor ability was determined to improve by 32 kcal/mol relative to the estimated hydride donor ability for the analogous nickel complex of the chelating diphosphine ligand 1,3-bis(diphenylphosphino)propane. The free energy for addition of H2 is presented, and the implications for catalysis are discussed. These quantitative results highlight the substantial effect that NHC ligands can have on the electronic properties of the metal complexes.

Original languageEnglish
Pages (from-to)2287-2294
Number of pages8
JournalOrganometallics
Volume33
Issue number9
DOIs
Publication statusPublished - May 12 2014

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phosphine
carbenes
Nickel
Electrochemical properties
phosphines
Substitution reactions
Thermodynamic properties
thermodynamic properties
nickel
substitutes
Ligands
ligands
Hydrides
hydrides
Chelation
Phosphines
X ray crystallography
Coordination Complexes
Discrete Fourier transforms
propane

ASJC Scopus subject areas

  • Organic Chemistry
  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

Cite this

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title = "Effects of phosphine-carbene substitutions on the electrochemical and thermodynamic properties of nickel complexes",
abstract = "Nickel(II) complexes containing chelating N-heterocyclic carbene-phosphine ligands ([NiL2](BPh4)2, for which L = [MeIm(CH2)2PR2], MeIm = 1- methylimidizolylidene, and R = Ph or Et) have been synthesized for the purpose of studying how this class of ligand affects the electrochemical and thermodynamic properties compared to the nickel bis-diphosphine analogues. The nickel complexes were synthesized and then characterized by X-ray crystallography, electrochemical methods, and thermodynamic studies, including DFT calculations. On the basis of the reduction potentials (E°), substitution of an NHC for one of the phosphines in a diphoshine ligand resulted in negative shifts in potential by 0.6 to 1.2 V relative to the corresponding nickel bis-diphosphine complexes. From computational studies of the nickel hydride complex of the phenyl-substituted phosphine-carbene ligand, the hydride donor ability was determined to improve by 32 kcal/mol relative to the estimated hydride donor ability for the analogous nickel complex of the chelating diphosphine ligand 1,3-bis(diphenylphosphino)propane. The free energy for addition of H2 is presented, and the implications for catalysis are discussed. These quantitative results highlight the substantial effect that NHC ligands can have on the electronic properties of the metal complexes.",
author = "Galan, {Brandon R.} and Eric Wiedner and Monte Helm and John Linehan and Aaron Appel",
year = "2014",
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T1 - Effects of phosphine-carbene substitutions on the electrochemical and thermodynamic properties of nickel complexes

AU - Galan, Brandon R.

AU - Wiedner, Eric

AU - Helm, Monte

AU - Linehan, John

AU - Appel, Aaron

PY - 2014/5/12

Y1 - 2014/5/12

N2 - Nickel(II) complexes containing chelating N-heterocyclic carbene-phosphine ligands ([NiL2](BPh4)2, for which L = [MeIm(CH2)2PR2], MeIm = 1- methylimidizolylidene, and R = Ph or Et) have been synthesized for the purpose of studying how this class of ligand affects the electrochemical and thermodynamic properties compared to the nickel bis-diphosphine analogues. The nickel complexes were synthesized and then characterized by X-ray crystallography, electrochemical methods, and thermodynamic studies, including DFT calculations. On the basis of the reduction potentials (E°), substitution of an NHC for one of the phosphines in a diphoshine ligand resulted in negative shifts in potential by 0.6 to 1.2 V relative to the corresponding nickel bis-diphosphine complexes. From computational studies of the nickel hydride complex of the phenyl-substituted phosphine-carbene ligand, the hydride donor ability was determined to improve by 32 kcal/mol relative to the estimated hydride donor ability for the analogous nickel complex of the chelating diphosphine ligand 1,3-bis(diphenylphosphino)propane. The free energy for addition of H2 is presented, and the implications for catalysis are discussed. These quantitative results highlight the substantial effect that NHC ligands can have on the electronic properties of the metal complexes.

AB - Nickel(II) complexes containing chelating N-heterocyclic carbene-phosphine ligands ([NiL2](BPh4)2, for which L = [MeIm(CH2)2PR2], MeIm = 1- methylimidizolylidene, and R = Ph or Et) have been synthesized for the purpose of studying how this class of ligand affects the electrochemical and thermodynamic properties compared to the nickel bis-diphosphine analogues. The nickel complexes were synthesized and then characterized by X-ray crystallography, electrochemical methods, and thermodynamic studies, including DFT calculations. On the basis of the reduction potentials (E°), substitution of an NHC for one of the phosphines in a diphoshine ligand resulted in negative shifts in potential by 0.6 to 1.2 V relative to the corresponding nickel bis-diphosphine complexes. From computational studies of the nickel hydride complex of the phenyl-substituted phosphine-carbene ligand, the hydride donor ability was determined to improve by 32 kcal/mol relative to the estimated hydride donor ability for the analogous nickel complex of the chelating diphosphine ligand 1,3-bis(diphenylphosphino)propane. The free energy for addition of H2 is presented, and the implications for catalysis are discussed. These quantitative results highlight the substantial effect that NHC ligands can have on the electronic properties of the metal complexes.

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