Electron transfer activity of a cobalt crown carbene complex

Stuart R Park, Neil J Findlay, Jean Garnier, Sheng-Ze Zhou, Mark Spicer, John A Murphy

Research output: Contribution to journalArticle

35 Citations (Scopus)

Abstract

The novel cobalt(II) crown carbene complex 12(II) has been prepared and characterised by X-ray crystallography. This complex is reduced in a one-electron process to a cobalt(I) complex that acts as a powerful single electron donor, reducing aryl halides, including aryl chlorides and demonstrating the strong electron-enriching effect on cobalt of the crown carbene ligand. The metal ion is tightly held in a tetrahedral conformation by its enveloping crown liganddthis prevents what would otherwise be expected to be an easy oxidation to cobalt(III) under standard electrochemical conditions. Complex 12 is shown to be an effective catalyst in mediated electrochemical reductions of aryl iodides at room temperature and aryl bromides at 90 C. The electrochemically produced catalyst [from 10 mol % of added Co(II) complex] also triggers reduction of aryl chlorides, although this seems at the limit of its reactivity. However, when the cobalt(II) complex is reduced by sodium amalgam, this affords stoichiometric quantities of the active cobalt reducing agent, which affords reduction of aryl iodides and bromides as above, but also reduces aryl chlorides at elevated temperatures.
LanguageEnglish
Pages10756-10761
Number of pages6
JournalTetrahedron
Volume65
Issue number52
DOIs
Publication statusPublished - 26 Dec 2009

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Cobalt
Crowns
Electrons
Chlorides
Iodides
Bromides
Mercury amalgams
Catalysts
Temperature
X ray crystallography
X Ray Crystallography
Reducing Agents
Metal ions
Conformations
carbene
Metals
Sodium
Ions
Ligands
Oxidation

Keywords

  • electron transfer activity
  • cobalt
  • cobalt crown carbene

Cite this

Park, S. R., Findlay, N. J., Garnier, J., Zhou, S-Z., Spicer, M., & Murphy, J. A. (2009). Electron transfer activity of a cobalt crown carbene complex. Tetrahedron, 65(52), 10756-10761. https://doi.org/10.1016/j.tet.2009.10.090
Park, Stuart R ; Findlay, Neil J ; Garnier, Jean ; Zhou, Sheng-Ze ; Spicer, Mark ; Murphy, John A. / Electron transfer activity of a cobalt crown carbene complex. In: Tetrahedron. 2009 ; Vol. 65, No. 52. pp. 10756-10761.
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Park, SR, Findlay, NJ, Garnier, J, Zhou, S-Z, Spicer, M & Murphy, JA 2009, 'Electron transfer activity of a cobalt crown carbene complex' Tetrahedron, vol. 65, no. 52, pp. 10756-10761. https://doi.org/10.1016/j.tet.2009.10.090

Electron transfer activity of a cobalt crown carbene complex. / Park, Stuart R; Findlay, Neil J; Garnier, Jean; Zhou, Sheng-Ze; Spicer, Mark; Murphy, John A.

In: Tetrahedron, Vol. 65, No. 52, 26.12.2009, p. 10756-10761.

Research output: Contribution to journalArticle

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T1 - Electron transfer activity of a cobalt crown carbene complex

AU - Park, Stuart R

AU - Findlay, Neil J

AU - Garnier, Jean

AU - Zhou, Sheng-Ze

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N2 - The novel cobalt(II) crown carbene complex 12(II) has been prepared and characterised by X-ray crystallography. This complex is reduced in a one-electron process to a cobalt(I) complex that acts as a powerful single electron donor, reducing aryl halides, including aryl chlorides and demonstrating the strong electron-enriching effect on cobalt of the crown carbene ligand. The metal ion is tightly held in a tetrahedral conformation by its enveloping crown liganddthis prevents what would otherwise be expected to be an easy oxidation to cobalt(III) under standard electrochemical conditions. Complex 12 is shown to be an effective catalyst in mediated electrochemical reductions of aryl iodides at room temperature and aryl bromides at 90 C. The electrochemically produced catalyst [from 10 mol % of added Co(II) complex] also triggers reduction of aryl chlorides, although this seems at the limit of its reactivity. However, when the cobalt(II) complex is reduced by sodium amalgam, this affords stoichiometric quantities of the active cobalt reducing agent, which affords reduction of aryl iodides and bromides as above, but also reduces aryl chlorides at elevated temperatures.

AB - The novel cobalt(II) crown carbene complex 12(II) has been prepared and characterised by X-ray crystallography. This complex is reduced in a one-electron process to a cobalt(I) complex that acts as a powerful single electron donor, reducing aryl halides, including aryl chlorides and demonstrating the strong electron-enriching effect on cobalt of the crown carbene ligand. The metal ion is tightly held in a tetrahedral conformation by its enveloping crown liganddthis prevents what would otherwise be expected to be an easy oxidation to cobalt(III) under standard electrochemical conditions. Complex 12 is shown to be an effective catalyst in mediated electrochemical reductions of aryl iodides at room temperature and aryl bromides at 90 C. The electrochemically produced catalyst [from 10 mol % of added Co(II) complex] also triggers reduction of aryl chlorides, although this seems at the limit of its reactivity. However, when the cobalt(II) complex is reduced by sodium amalgam, this affords stoichiometric quantities of the active cobalt reducing agent, which affords reduction of aryl iodides and bromides as above, but also reduces aryl chlorides at elevated temperatures.

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Park SR, Findlay NJ, Garnier J, Zhou S-Z, Spicer M, Murphy JA. Electron transfer activity of a cobalt crown carbene complex. Tetrahedron. 2009 Dec 26;65(52):10756-10761. https://doi.org/10.1016/j.tet.2009.10.090