A tungsten complex with a bidentate, hemilabile N-heterocyclic carbene ligand, facile displacement of the weakly bound W-(C=C) bond, and the vulnerability of the NHC ligand toward catalyst deactivation during ketone hydrogenation

Fan Wu, Vladimir K. Dioumaev, David J. Szalda, Jonathan Hanson, R Morris Bullock

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Abstract

The initial reaction observed between the N-heterocyclic carbene IMes (IMes = l,3-bis(2,4,6trimethylphenyl)imidazol-2-ylidene) and molybdenum and tungsten hydride complexes CpM(CO)2(PPh3)H (M = Mo, W) is deprotonation of the metal hydride by IMes, giving [(IMeS)H]+[CpM(CO) 2(PPh3)]. At longer reaction times and higher temperatures, the reaction of IMes with CpM(CO)2(PR3)H (M = Mo, W; R = Me, Ph) produces CpM(CO)2(IMeS)H. Hydride transfer from CpW(CO)2(EvIeS)H to Ph3C+B(C6F 5)4 - gives CpW(CO)2(IMeS) +B(C6F5)4 -, which was crystallographically characterized using X-ray radiation from a synchrotron. The IMes is bonded as a bidentate ligand, through the carbon of the carbene as well as forming a weak bond from the metal to a C=C bond of one mesityl ring. The weakly bound C=C ligand is hemilabile, being readily displaced by H2, THF, ketones, or alcohols. Reaction of CpW(CO)2- (IMes)+ with H2 gives the dihydride complex [CpW(CO)2(IMes)(H) 2]+. Addition of Et2CH-OH to CpW(CO) 2(IMeS)+B(C6F5)4 - gives the alcohol complex [CpW(CO)2(IMes)(Et 2CH-OH)]+[B(C6F5)4] -, which was characterized by crystallography and exhibits no evidence for hydrogen bonding of the bound OH group. Addition of H2 to the ketone complex [CpW(CO)2(IMes)(Et2C=O)] +[B(C6F5)4]- produces an equilibrium with the dihydride [CpW(CO)2(IMeS)(H)2]+ (Keq = 1.1 × 103 at 25° C). The tungsten ketone complex [CpW(CO)2(IMeS)(Et2C=O)I+[B(C6F 5)4]- serves as a modest catalyst for hydrogénation of Et2C=O to Et2CH-OH in neat ketone solvent. Decomposition of the catalyst produces [H(IMes)]+B(C 6F5)4 -, indicating that these catalysts with N-heterocyclic carbene ligands are vulnerable to decomposition by a reaction that produces a protonated imidazolium cation.

Original languageEnglish
Pages (from-to)5079-5090
Number of pages12
JournalOrganometallics
Volume26
Issue number20
DOIs
Publication statusPublished - Sep 24 2007

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Catalyst deactivation
Tungsten
vulnerability
carbenes
Carbon Monoxide
Ketones
ketones
deactivation
Hydrogenation
hydrogenation
tungsten
Ligands
catalysts
dihydrides
ligands
hydrides
alcohols
decomposition
metal hydrides
imidazoles

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Organic Chemistry

Cite this

@article{27428be8ca314bacb6f0900c8a37685d,
title = "A tungsten complex with a bidentate, hemilabile N-heterocyclic carbene ligand, facile displacement of the weakly bound W-(C=C) bond, and the vulnerability of the NHC ligand toward catalyst deactivation during ketone hydrogenation",
abstract = "The initial reaction observed between the N-heterocyclic carbene IMes (IMes = l,3-bis(2,4,6trimethylphenyl)imidazol-2-ylidene) and molybdenum and tungsten hydride complexes CpM(CO)2(PPh3)H (M = Mo, W) is deprotonation of the metal hydride by IMes, giving [(IMeS)H]+[CpM(CO) 2(PPh3)]. At longer reaction times and higher temperatures, the reaction of IMes with CpM(CO)2(PR3)H (M = Mo, W; R = Me, Ph) produces CpM(CO)2(IMeS)H. Hydride transfer from CpW(CO)2(EvIeS)H to Ph3C+B(C6F 5)4 - gives CpW(CO)2(IMeS) +B(C6F5)4 -, which was crystallographically characterized using X-ray radiation from a synchrotron. The IMes is bonded as a bidentate ligand, through the carbon of the carbene as well as forming a weak bond from the metal to a C=C bond of one mesityl ring. The weakly bound C=C ligand is hemilabile, being readily displaced by H2, THF, ketones, or alcohols. Reaction of CpW(CO)2- (IMes)+ with H2 gives the dihydride complex [CpW(CO)2(IMes)(H) 2]+. Addition of Et2CH-OH to CpW(CO) 2(IMeS)+B(C6F5)4 - gives the alcohol complex [CpW(CO)2(IMes)(Et 2CH-OH)]+[B(C6F5)4] -, which was characterized by crystallography and exhibits no evidence for hydrogen bonding of the bound OH group. Addition of H2 to the ketone complex [CpW(CO)2(IMes)(Et2C=O)] +[B(C6F5)4]- produces an equilibrium with the dihydride [CpW(CO)2(IMeS)(H)2]+ (Keq = 1.1 × 103 at 25° C). The tungsten ketone complex [CpW(CO)2(IMeS)(Et2C=O)I+[B(C6F 5)4]- serves as a modest catalyst for hydrog{\'e}nation of Et2C=O to Et2CH-OH in neat ketone solvent. Decomposition of the catalyst produces [H(IMes)]+B(C 6F5)4 -, indicating that these catalysts with N-heterocyclic carbene ligands are vulnerable to decomposition by a reaction that produces a protonated imidazolium cation.",
author = "Fan Wu and Dioumaev, {Vladimir K.} and Szalda, {David J.} and Jonathan Hanson and Bullock, {R Morris}",
year = "2007",
month = "9",
day = "24",
doi = "10.1021/om700694e",
language = "English",
volume = "26",
pages = "5079--5090",
journal = "Organometallics",
issn = "0276-7333",
publisher = "American Chemical Society",
number = "20",

}

TY - JOUR

T1 - A tungsten complex with a bidentate, hemilabile N-heterocyclic carbene ligand, facile displacement of the weakly bound W-(C=C) bond, and the vulnerability of the NHC ligand toward catalyst deactivation during ketone hydrogenation

AU - Wu, Fan

AU - Dioumaev, Vladimir K.

AU - Szalda, David J.

AU - Hanson, Jonathan

AU - Bullock, R Morris

PY - 2007/9/24

Y1 - 2007/9/24

N2 - The initial reaction observed between the N-heterocyclic carbene IMes (IMes = l,3-bis(2,4,6trimethylphenyl)imidazol-2-ylidene) and molybdenum and tungsten hydride complexes CpM(CO)2(PPh3)H (M = Mo, W) is deprotonation of the metal hydride by IMes, giving [(IMeS)H]+[CpM(CO) 2(PPh3)]. At longer reaction times and higher temperatures, the reaction of IMes with CpM(CO)2(PR3)H (M = Mo, W; R = Me, Ph) produces CpM(CO)2(IMeS)H. Hydride transfer from CpW(CO)2(EvIeS)H to Ph3C+B(C6F 5)4 - gives CpW(CO)2(IMeS) +B(C6F5)4 -, which was crystallographically characterized using X-ray radiation from a synchrotron. The IMes is bonded as a bidentate ligand, through the carbon of the carbene as well as forming a weak bond from the metal to a C=C bond of one mesityl ring. The weakly bound C=C ligand is hemilabile, being readily displaced by H2, THF, ketones, or alcohols. Reaction of CpW(CO)2- (IMes)+ with H2 gives the dihydride complex [CpW(CO)2(IMes)(H) 2]+. Addition of Et2CH-OH to CpW(CO) 2(IMeS)+B(C6F5)4 - gives the alcohol complex [CpW(CO)2(IMes)(Et 2CH-OH)]+[B(C6F5)4] -, which was characterized by crystallography and exhibits no evidence for hydrogen bonding of the bound OH group. Addition of H2 to the ketone complex [CpW(CO)2(IMes)(Et2C=O)] +[B(C6F5)4]- produces an equilibrium with the dihydride [CpW(CO)2(IMeS)(H)2]+ (Keq = 1.1 × 103 at 25° C). The tungsten ketone complex [CpW(CO)2(IMeS)(Et2C=O)I+[B(C6F 5)4]- serves as a modest catalyst for hydrogénation of Et2C=O to Et2CH-OH in neat ketone solvent. Decomposition of the catalyst produces [H(IMes)]+B(C 6F5)4 -, indicating that these catalysts with N-heterocyclic carbene ligands are vulnerable to decomposition by a reaction that produces a protonated imidazolium cation.

AB - The initial reaction observed between the N-heterocyclic carbene IMes (IMes = l,3-bis(2,4,6trimethylphenyl)imidazol-2-ylidene) and molybdenum and tungsten hydride complexes CpM(CO)2(PPh3)H (M = Mo, W) is deprotonation of the metal hydride by IMes, giving [(IMeS)H]+[CpM(CO) 2(PPh3)]. At longer reaction times and higher temperatures, the reaction of IMes with CpM(CO)2(PR3)H (M = Mo, W; R = Me, Ph) produces CpM(CO)2(IMeS)H. Hydride transfer from CpW(CO)2(EvIeS)H to Ph3C+B(C6F 5)4 - gives CpW(CO)2(IMeS) +B(C6F5)4 -, which was crystallographically characterized using X-ray radiation from a synchrotron. The IMes is bonded as a bidentate ligand, through the carbon of the carbene as well as forming a weak bond from the metal to a C=C bond of one mesityl ring. The weakly bound C=C ligand is hemilabile, being readily displaced by H2, THF, ketones, or alcohols. Reaction of CpW(CO)2- (IMes)+ with H2 gives the dihydride complex [CpW(CO)2(IMes)(H) 2]+. Addition of Et2CH-OH to CpW(CO) 2(IMeS)+B(C6F5)4 - gives the alcohol complex [CpW(CO)2(IMes)(Et 2CH-OH)]+[B(C6F5)4] -, which was characterized by crystallography and exhibits no evidence for hydrogen bonding of the bound OH group. Addition of H2 to the ketone complex [CpW(CO)2(IMes)(Et2C=O)] +[B(C6F5)4]- produces an equilibrium with the dihydride [CpW(CO)2(IMeS)(H)2]+ (Keq = 1.1 × 103 at 25° C). The tungsten ketone complex [CpW(CO)2(IMeS)(Et2C=O)I+[B(C6F 5)4]- serves as a modest catalyst for hydrogénation of Et2C=O to Et2CH-OH in neat ketone solvent. Decomposition of the catalyst produces [H(IMes)]+B(C 6F5)4 -, indicating that these catalysts with N-heterocyclic carbene ligands are vulnerable to decomposition by a reaction that produces a protonated imidazolium cation.

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U2 - 10.1021/om700694e

DO - 10.1021/om700694e

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