Ability of N-Heterocyclic Carbene Ligands to Promote Intermolecular Oxidative Addition Reactions at Unsaturated Ruthenium Centers

Richard A Diggle, Stuart A Macgregor, Michael K Whittlesey

Research output: Contribution to journalArticle

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Abstract

The results of d. functional calcns. on the reactivity of a series of coordinatively unsatd. mixed phosphine/N-heterocyclic carbene complexes of ruthenium of the type Ru(CO)(IR)3-n(PH3)n, where n = 1-3 and R = H (1,3-imidazol-2-ylidene) and R = Me (1,3-dimethylimidazol-2-ylidene) are reported. The oxidative addn. reactions of H2 and CH4 and the C-C bond activation of C2H6 have been studied. For all three processes, substitution of PH3 by IH results in minimal changes in the reaction energetics. In all cases H2 oxidative addn. is barrierless and is downhill by around 120 kJ/mol. With CH4 activation barriers of around 75 kJ/mol are computed and the reaction is approx. thermoneutral. With C2H6 activation barriers increase to around 260 kJ/mol and the reaction is disfavored by about + 35 kJ/mol. Introduction of the IMe ligand disfavors oxidative addn., esp. for the C2H6 reaction, and this trend is linked to increased steric bulk of the IMe ligand compared to IH. Computed Ru-PH3 and Ru-IR bond strengths and CO stretching frequencies indicate that PH3/IR substitution does create a more electron-rich metal center, and yet this does not facilitate oxidative addn. with these Ru species. A fragment anal. reveals that, as expected, PH3/IH substitution enhances the Lewis basicity of the metal reactant. However, a more important effect is a redn. in Lewis acidity, and this factor lies behind the similar reaction energetics computed for analogous PH3- and IH-contg. species.
LanguageEnglish
Pages1857-1865
Number of pages9
JournalOrganometallics
Volume23
Issue number8
StatusPublished - 2004

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Addition reactions
Ruthenium
carbenes
ruthenium
phosphine
Substitution reactions
Chemical activation
Carbon Monoxide
Ligands
ligands
Metals
activation
substitutes
Alkalinity
Acidity
Stretching
Electrons
imidazoles
phosphines
acidity

Keywords

  • Total energy
  • of reaction products of nitrogen-heterocyclic carbene ruthenium complex)
  • Potential barrier
  • Addition reaction (oxidative
  • Density functional theory (B3LYP
  • Bond (carbon-carbon
  • PRP (Properties)
  • DFT oxidative addn imidazolylidene ruthenium hydrogen methane ethane
  • PROC (Process)
  • RCT (Reactant)
  • Transition state structure (theor. anal. of ability of nitrogen-heterocyclic carbene ligands to promote intermol. oxidative addn. reactions at unsatd. ruthenium centers)
  • theor. anal. of ability of nitrogen-heterocyclic carbene ligands to promote intermol. oxidative addn. reactions at unsatd. ruthenium centers)
  • RACT (Reactant or reagent) (theor. anal. of ability of nitrogen-heterocyclic carbene ligands to promote in
  • nitrogen heterocyclic carbene ligand intermol oxidative addn unsatd ruthenium
  • PEP (Physical
  • Molecular structure (optimized
  • Carbene complexes Role
  • CPS (Chemical process)
  • activation
  • engineering or chemical process)

Cite this

Ability of N-Heterocyclic Carbene Ligands to Promote Intermolecular Oxidative Addition Reactions at Unsaturated Ruthenium Centers. / Diggle, Richard A; Macgregor, Stuart A; Whittlesey, Michael K.

In: Organometallics, Vol. 23, No. 8, 2004, p. 1857-1865.

Research output: Contribution to journalArticle

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N2 - The results of d. functional calcns. on the reactivity of a series of coordinatively unsatd. mixed phosphine/N-heterocyclic carbene complexes of ruthenium of the type Ru(CO)(IR)3-n(PH3)n, where n = 1-3 and R = H (1,3-imidazol-2-ylidene) and R = Me (1,3-dimethylimidazol-2-ylidene) are reported. The oxidative addn. reactions of H2 and CH4 and the C-C bond activation of C2H6 have been studied. For all three processes, substitution of PH3 by IH results in minimal changes in the reaction energetics. In all cases H2 oxidative addn. is barrierless and is downhill by around 120 kJ/mol. With CH4 activation barriers of around 75 kJ/mol are computed and the reaction is approx. thermoneutral. With C2H6 activation barriers increase to around 260 kJ/mol and the reaction is disfavored by about + 35 kJ/mol. Introduction of the IMe ligand disfavors oxidative addn., esp. for the C2H6 reaction, and this trend is linked to increased steric bulk of the IMe ligand compared to IH. Computed Ru-PH3 and Ru-IR bond strengths and CO stretching frequencies indicate that PH3/IR substitution does create a more electron-rich metal center, and yet this does not facilitate oxidative addn. with these Ru species. A fragment anal. reveals that, as expected, PH3/IH substitution enhances the Lewis basicity of the metal reactant. However, a more important effect is a redn. in Lewis acidity, and this factor lies behind the similar reaction energetics computed for analogous PH3- and IH-contg. species.

AB - The results of d. functional calcns. on the reactivity of a series of coordinatively unsatd. mixed phosphine/N-heterocyclic carbene complexes of ruthenium of the type Ru(CO)(IR)3-n(PH3)n, where n = 1-3 and R = H (1,3-imidazol-2-ylidene) and R = Me (1,3-dimethylimidazol-2-ylidene) are reported. The oxidative addn. reactions of H2 and CH4 and the C-C bond activation of C2H6 have been studied. For all three processes, substitution of PH3 by IH results in minimal changes in the reaction energetics. In all cases H2 oxidative addn. is barrierless and is downhill by around 120 kJ/mol. With CH4 activation barriers of around 75 kJ/mol are computed and the reaction is approx. thermoneutral. With C2H6 activation barriers increase to around 260 kJ/mol and the reaction is disfavored by about + 35 kJ/mol. Introduction of the IMe ligand disfavors oxidative addn., esp. for the C2H6 reaction, and this trend is linked to increased steric bulk of the IMe ligand compared to IH. Computed Ru-PH3 and Ru-IR bond strengths and CO stretching frequencies indicate that PH3/IR substitution does create a more electron-rich metal center, and yet this does not facilitate oxidative addn. with these Ru species. A fragment anal. reveals that, as expected, PH3/IH substitution enhances the Lewis basicity of the metal reactant. However, a more important effect is a redn. in Lewis acidity, and this factor lies behind the similar reaction energetics computed for analogous PH3- and IH-contg. species.

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KW - theor. anal. of ability of nitrogen-heterocyclic carbene ligands to promote intermol. oxidative addn. reactions at unsatd. ruthenium centers)

KW - RACT (Reactant or reagent) (theor. anal. of ability of nitrogen-heterocyclic carbene ligands to promote in

KW - nitrogen heterocyclic carbene ligand intermol oxidative addn unsatd ruthenium

KW - PEP (Physical

KW - Molecular structure (optimized

KW - Carbene complexes Role

KW - CPS (Chemical process)

KW - activation

KW - engineering or chemical process)

M3 - Article

VL - 23

SP - 1857

EP - 1865

JO - Organometallics

T2 - Organometallics

JF - Organometallics

SN - 0276-7333

IS - 8

ER -