Facile thermal W-W bond homolysis in the N-heterocyclic carbene containing tungsten dimer [CpW(CO) 2(IMe)] 2

Edwin F. Van Der Eide, Tianbiao Liu, Donald M. Camaioni, Eric D. Walter, R Morris Bullock

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Abstract

The thermal W-W bond homolysis in [CpW(CO) 2(IMe)] 2 (IMe = 1,3-dimethylimidazol-2-ylidene) was investigated and was found to occur to a large extent in comparison to other tungsten dimers such as [CpW(CO) 3] 2. CpW(CO) 2(IMe)H was prepared by heating a solution of [IMeH] +[CpW(CO) 2(PMe 3)] -, and it exists in solution as a mixture of interconverting cis and trans isomers. The carbene rotation in CpW(CO) 2(IMe)H was explored by DFT calculations, and low enthalpic barriers (-1) are predicted. CpW(CO) 2(IMe)H has pK a MeCN = 31.5(3), and deprotonation with KH gives K +[CpW(CO) 2(IMe)] - (•MeCN). Hydride abstraction from CpW(CO) 2(IMe)H with Ph 3C +PF 6 - in the presence of a coordinating ligand L (MeCN or THF) gives [CpW(CO) 2(IMe)(L)] +PF 6 -. Electrochemical measurements on the anion [CpW(CO) 2(IMe)] - in MeCN, together with digital simulations, give an E 1/2 value of -1.54(2) V vs Cp 2Fe +/0 for the [CpW(CO) 2(IMe)] •/- couple. A thermochemical cycle provides the solution bond dissociation free energy of the W-H bond of CpW(CO) 2(IMe)H as 61.3(6) kcal mol -1. In the electrochemical oxidation of [CpW(CO) 2(IMe)] -, reversible dimerization of the electrogenerated radical CpW(CO) 2(IMe) occurs, and digital simulation provides kinetic and thermodynamic parameters for the monomer-dimer equilibrium: k dimerization ≈ 2.5 × 10 4 M -1 s -1, k homolysis ≈ 0.5 s -1 (i.e., K dim ≈ 5 × 10 4 M -1). Reduction of [CpW(CO) 2(IMe)(MeCN)] +PF 6 - with cobaltocene gives the dimer [CpW(CO) 2(IMe)] 2, which in solution exists as a mixture of anti and gauche rotamers. As expected from the electrochemical experiments, the dimer is in equilibrium with detectable amounts of CpW(CO) 2(IMe) . This species was observed by IR spectroscopy, and its presence in solution is also in accordance with the observed reactivity toward 2,6-di-tert-butyl-1,4-benzoquinone, chloroform, and dihydrogen.

Original languageEnglish
Pages (from-to)1775-1789
Number of pages15
JournalOrganometallics
Volume31
Issue number5
DOIs
Publication statusPublished - Mar 12 2012

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Tungsten
carbenes
Carbon Monoxide
Dimers
tungsten
dimers
digital simulation
dimerization
electrochemical oxidation
quinones
chloroform
hydrides
isomers
reactivity
monomers
free energy
dissociation
anions
thermodynamics
ligands

ASJC Scopus subject areas

  • Organic Chemistry
  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

Cite this

Facile thermal W-W bond homolysis in the N-heterocyclic carbene containing tungsten dimer [CpW(CO) 2(IMe)] 2 . / Van Der Eide, Edwin F.; Liu, Tianbiao; Camaioni, Donald M.; Walter, Eric D.; Bullock, R Morris.

In: Organometallics, Vol. 31, No. 5, 12.03.2012, p. 1775-1789.

Research output: Contribution to journalArticle

Van Der Eide, Edwin F. ; Liu, Tianbiao ; Camaioni, Donald M. ; Walter, Eric D. ; Bullock, R Morris. / Facile thermal W-W bond homolysis in the N-heterocyclic carbene containing tungsten dimer [CpW(CO) 2(IMe)] 2 In: Organometallics. 2012 ; Vol. 31, No. 5. pp. 1775-1789.
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abstract = "The thermal W-W bond homolysis in [CpW(CO) 2(IMe)] 2 (IMe = 1,3-dimethylimidazol-2-ylidene) was investigated and was found to occur to a large extent in comparison to other tungsten dimers such as [CpW(CO) 3] 2. CpW(CO) 2(IMe)H was prepared by heating a solution of [IMeH] +[CpW(CO) 2(PMe 3)] -, and it exists in solution as a mixture of interconverting cis and trans isomers. The carbene rotation in CpW(CO) 2(IMe)H was explored by DFT calculations, and low enthalpic barriers (-1) are predicted. CpW(CO) 2(IMe)H has pK a MeCN = 31.5(3), and deprotonation with KH gives K +[CpW(CO) 2(IMe)] - (•MeCN). Hydride abstraction from CpW(CO) 2(IMe)H with Ph 3C +PF 6 - in the presence of a coordinating ligand L (MeCN or THF) gives [CpW(CO) 2(IMe)(L)] +PF 6 -. Electrochemical measurements on the anion [CpW(CO) 2(IMe)] - in MeCN, together with digital simulations, give an E 1/2 value of -1.54(2) V vs Cp 2Fe +/0 for the [CpW(CO) 2(IMe)] •/- couple. A thermochemical cycle provides the solution bond dissociation free energy of the W-H bond of CpW(CO) 2(IMe)H as 61.3(6) kcal mol -1. In the electrochemical oxidation of [CpW(CO) 2(IMe)] -, reversible dimerization of the electrogenerated radical CpW(CO) 2(IMe) • occurs, and digital simulation provides kinetic and thermodynamic parameters for the monomer-dimer equilibrium: k dimerization ≈ 2.5 × 10 4 M -1 s -1, k homolysis ≈ 0.5 s -1 (i.e., K dim ≈ 5 × 10 4 M -1). Reduction of [CpW(CO) 2(IMe)(MeCN)] +PF 6 - with cobaltocene gives the dimer [CpW(CO) 2(IMe)] 2, which in solution exists as a mixture of anti and gauche rotamers. As expected from the electrochemical experiments, the dimer is in equilibrium with detectable amounts of CpW(CO) 2(IMe) •. This species was observed by IR spectroscopy, and its presence in solution is also in accordance with the observed reactivity toward 2,6-di-tert-butyl-1,4-benzoquinone, chloroform, and dihydrogen.",
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T1 - Facile thermal W-W bond homolysis in the N-heterocyclic carbene containing tungsten dimer [CpW(CO) 2(IMe)] 2

AU - Van Der Eide, Edwin F.

AU - Liu, Tianbiao

AU - Camaioni, Donald M.

AU - Walter, Eric D.

AU - Bullock, R Morris

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N2 - The thermal W-W bond homolysis in [CpW(CO) 2(IMe)] 2 (IMe = 1,3-dimethylimidazol-2-ylidene) was investigated and was found to occur to a large extent in comparison to other tungsten dimers such as [CpW(CO) 3] 2. CpW(CO) 2(IMe)H was prepared by heating a solution of [IMeH] +[CpW(CO) 2(PMe 3)] -, and it exists in solution as a mixture of interconverting cis and trans isomers. The carbene rotation in CpW(CO) 2(IMe)H was explored by DFT calculations, and low enthalpic barriers (-1) are predicted. CpW(CO) 2(IMe)H has pK a MeCN = 31.5(3), and deprotonation with KH gives K +[CpW(CO) 2(IMe)] - (•MeCN). Hydride abstraction from CpW(CO) 2(IMe)H with Ph 3C +PF 6 - in the presence of a coordinating ligand L (MeCN or THF) gives [CpW(CO) 2(IMe)(L)] +PF 6 -. Electrochemical measurements on the anion [CpW(CO) 2(IMe)] - in MeCN, together with digital simulations, give an E 1/2 value of -1.54(2) V vs Cp 2Fe +/0 for the [CpW(CO) 2(IMe)] •/- couple. A thermochemical cycle provides the solution bond dissociation free energy of the W-H bond of CpW(CO) 2(IMe)H as 61.3(6) kcal mol -1. In the electrochemical oxidation of [CpW(CO) 2(IMe)] -, reversible dimerization of the electrogenerated radical CpW(CO) 2(IMe) • occurs, and digital simulation provides kinetic and thermodynamic parameters for the monomer-dimer equilibrium: k dimerization ≈ 2.5 × 10 4 M -1 s -1, k homolysis ≈ 0.5 s -1 (i.e., K dim ≈ 5 × 10 4 M -1). Reduction of [CpW(CO) 2(IMe)(MeCN)] +PF 6 - with cobaltocene gives the dimer [CpW(CO) 2(IMe)] 2, which in solution exists as a mixture of anti and gauche rotamers. As expected from the electrochemical experiments, the dimer is in equilibrium with detectable amounts of CpW(CO) 2(IMe) •. This species was observed by IR spectroscopy, and its presence in solution is also in accordance with the observed reactivity toward 2,6-di-tert-butyl-1,4-benzoquinone, chloroform, and dihydrogen.

AB - The thermal W-W bond homolysis in [CpW(CO) 2(IMe)] 2 (IMe = 1,3-dimethylimidazol-2-ylidene) was investigated and was found to occur to a large extent in comparison to other tungsten dimers such as [CpW(CO) 3] 2. CpW(CO) 2(IMe)H was prepared by heating a solution of [IMeH] +[CpW(CO) 2(PMe 3)] -, and it exists in solution as a mixture of interconverting cis and trans isomers. The carbene rotation in CpW(CO) 2(IMe)H was explored by DFT calculations, and low enthalpic barriers (-1) are predicted. CpW(CO) 2(IMe)H has pK a MeCN = 31.5(3), and deprotonation with KH gives K +[CpW(CO) 2(IMe)] - (•MeCN). Hydride abstraction from CpW(CO) 2(IMe)H with Ph 3C +PF 6 - in the presence of a coordinating ligand L (MeCN or THF) gives [CpW(CO) 2(IMe)(L)] +PF 6 -. Electrochemical measurements on the anion [CpW(CO) 2(IMe)] - in MeCN, together with digital simulations, give an E 1/2 value of -1.54(2) V vs Cp 2Fe +/0 for the [CpW(CO) 2(IMe)] •/- couple. A thermochemical cycle provides the solution bond dissociation free energy of the W-H bond of CpW(CO) 2(IMe)H as 61.3(6) kcal mol -1. In the electrochemical oxidation of [CpW(CO) 2(IMe)] -, reversible dimerization of the electrogenerated radical CpW(CO) 2(IMe) • occurs, and digital simulation provides kinetic and thermodynamic parameters for the monomer-dimer equilibrium: k dimerization ≈ 2.5 × 10 4 M -1 s -1, k homolysis ≈ 0.5 s -1 (i.e., K dim ≈ 5 × 10 4 M -1). Reduction of [CpW(CO) 2(IMe)(MeCN)] +PF 6 - with cobaltocene gives the dimer [CpW(CO) 2(IMe)] 2, which in solution exists as a mixture of anti and gauche rotamers. As expected from the electrochemical experiments, the dimer is in equilibrium with detectable amounts of CpW(CO) 2(IMe) •. This species was observed by IR spectroscopy, and its presence in solution is also in accordance with the observed reactivity toward 2,6-di-tert-butyl-1,4-benzoquinone, chloroform, and dihydrogen.

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