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 language | English |
|---|---|
| Pages (from-to) | 1775-1789 |
| Number of pages | 15 |
| Journal | Organometallics |
| Volume | 31 |
| Issue number | 5 |
| DOIs | |
| Publication status | Published - Mar 12 2012 |
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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 journal › Article
}
TY - JOUR
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
PY - 2012/3/12
Y1 - 2012/3/12
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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U2 - 10.1021/om201162g
DO - 10.1021/om201162g
M3 - Article
VL - 31
SP - 1775
EP - 1789
JO - Organometallics
JF - Organometallics
SN - 0276-7333
IS - 5
ER -