Determination of S - H bond strengths in dimolybdenum tetrasulfide complexes

Aaron Appel, Suh Jane Lee, James A. Franz, Daniel L DuBois, M. Rakowski DuBois, Brendan Twamley

Research output: Contribution to journalArticle

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Abstract

Homolytic solution bond dissociation free energies (SBDFE) for S - H bonds have been determined for soluble dimolybdenum tetrasulfide complexes through thermochemical cycles using electrochemical potentials and pK a values in acetonitrile. In spite of the importance and extensive use of metal sulfide catalysts, these S - H bond strengths are among the first experimentally determined values for metal sulfide systems. For [Cp *Mo(μ-S) (μ-SMe) 2(μ-SH)MoCp *] + (S 4Me 2H +), [Cp *Mo(μ-S)(μ- SMe)(μ-SH) 2MoCp *] + (S 4MeH 2 +), and [Cp *Mo(μ-S) (μ-SH) 3MoCp *] + (S 4H 3 +), the pK a values were determined to be 5.6 ± 0.4, 5.3 ± 0.3, and 4.9 ± 0.3, respectively. The E 1/2 values for S 4Me 2 •+/0, S 4MeH •+/0, and S 4H 2 •+/0 were measured to be - 0.02 ± 0.02, +0.04 ± 0.05, and +0.07 ± 0.07 V vs FeCp 2 +/0, respectively. Using these experimental values, the homolytic S - H SBDFE for S 4Me 2H + to S 4Me 2 •+, S 4MeH 2 + to S 4MeH •+, and S 4H 3 + to S 4H 2 •+ were determined to be 60.8 ± 1.0, 61.8 ± 1.6, and 61.9 ± 2.0 kcal/mol, respectively. These SBDFE values can be used to estimate gas phase bond dissociation enthalpies of 65.6, 66.6, and 66.7 kcal/mol, respectively. Solid state structures are presented for S 4MeH and S 4H 2.

Original languageEnglish
Pages (from-to)749-754
Number of pages6
JournalOrganometallics
Volume28
Issue number3
DOIs
Publication statusPublished - Feb 9 2009

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dissociation
Free energy
free energy
Sulfides
sulfides
Metals
metals
acetonitrile
Enthalpy
Gases
enthalpy
vapor phases
solid state
catalysts
cycles
Catalysts
estimates

ASJC Scopus subject areas

  • Organic Chemistry
  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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Determination of S - H bond strengths in dimolybdenum tetrasulfide complexes. / Appel, Aaron; Lee, Suh Jane; Franz, James A.; DuBois, Daniel L; DuBois, M. Rakowski; Twamley, Brendan.

In: Organometallics, Vol. 28, No. 3, 09.02.2009, p. 749-754.

Research output: Contribution to journalArticle

Appel, Aaron ; Lee, Suh Jane ; Franz, James A. ; DuBois, Daniel L ; DuBois, M. Rakowski ; Twamley, Brendan. / Determination of S - H bond strengths in dimolybdenum tetrasulfide complexes. In: Organometallics. 2009 ; Vol. 28, No. 3. pp. 749-754.
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abstract = "Homolytic solution bond dissociation free energies (SBDFE) for S - H bonds have been determined for soluble dimolybdenum tetrasulfide complexes through thermochemical cycles using electrochemical potentials and pK a values in acetonitrile. In spite of the importance and extensive use of metal sulfide catalysts, these S - H bond strengths are among the first experimentally determined values for metal sulfide systems. For [Cp *Mo(μ-S) (μ-SMe) 2(μ-SH)MoCp *] + (S 4Me 2H +), [Cp *Mo(μ-S)(μ- SMe)(μ-SH) 2MoCp *] + (S 4MeH 2 +), and [Cp *Mo(μ-S) (μ-SH) 3MoCp *] + (S 4H 3 +), the pK a values were determined to be 5.6 ± 0.4, 5.3 ± 0.3, and 4.9 ± 0.3, respectively. The E 1/2 values for S 4Me 2 •+/0, S 4MeH •+/0, and S 4H 2 •+/0 were measured to be - 0.02 ± 0.02, +0.04 ± 0.05, and +0.07 ± 0.07 V vs FeCp 2 +/0, respectively. Using these experimental values, the homolytic S - H SBDFE for S 4Me 2H + to S 4Me 2 •+, S 4MeH 2 + to S 4MeH •+, and S 4H 3 + to S 4H 2 •+ were determined to be 60.8 ± 1.0, 61.8 ± 1.6, and 61.9 ± 2.0 kcal/mol, respectively. These SBDFE values can be used to estimate gas phase bond dissociation enthalpies of 65.6, 66.6, and 66.7 kcal/mol, respectively. Solid state structures are presented for S 4MeH and S 4H 2.",
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AU - Lee, Suh Jane

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AU - Twamley, Brendan

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N2 - Homolytic solution bond dissociation free energies (SBDFE) for S - H bonds have been determined for soluble dimolybdenum tetrasulfide complexes through thermochemical cycles using electrochemical potentials and pK a values in acetonitrile. In spite of the importance and extensive use of metal sulfide catalysts, these S - H bond strengths are among the first experimentally determined values for metal sulfide systems. For [Cp *Mo(μ-S) (μ-SMe) 2(μ-SH)MoCp *] + (S 4Me 2H +), [Cp *Mo(μ-S)(μ- SMe)(μ-SH) 2MoCp *] + (S 4MeH 2 +), and [Cp *Mo(μ-S) (μ-SH) 3MoCp *] + (S 4H 3 +), the pK a values were determined to be 5.6 ± 0.4, 5.3 ± 0.3, and 4.9 ± 0.3, respectively. The E 1/2 values for S 4Me 2 •+/0, S 4MeH •+/0, and S 4H 2 •+/0 were measured to be - 0.02 ± 0.02, +0.04 ± 0.05, and +0.07 ± 0.07 V vs FeCp 2 +/0, respectively. Using these experimental values, the homolytic S - H SBDFE for S 4Me 2H + to S 4Me 2 •+, S 4MeH 2 + to S 4MeH •+, and S 4H 3 + to S 4H 2 •+ were determined to be 60.8 ± 1.0, 61.8 ± 1.6, and 61.9 ± 2.0 kcal/mol, respectively. These SBDFE values can be used to estimate gas phase bond dissociation enthalpies of 65.6, 66.6, and 66.7 kcal/mol, respectively. Solid state structures are presented for S 4MeH and S 4H 2.

AB - Homolytic solution bond dissociation free energies (SBDFE) for S - H bonds have been determined for soluble dimolybdenum tetrasulfide complexes through thermochemical cycles using electrochemical potentials and pK a values in acetonitrile. In spite of the importance and extensive use of metal sulfide catalysts, these S - H bond strengths are among the first experimentally determined values for metal sulfide systems. For [Cp *Mo(μ-S) (μ-SMe) 2(μ-SH)MoCp *] + (S 4Me 2H +), [Cp *Mo(μ-S)(μ- SMe)(μ-SH) 2MoCp *] + (S 4MeH 2 +), and [Cp *Mo(μ-S) (μ-SH) 3MoCp *] + (S 4H 3 +), the pK a values were determined to be 5.6 ± 0.4, 5.3 ± 0.3, and 4.9 ± 0.3, respectively. The E 1/2 values for S 4Me 2 •+/0, S 4MeH •+/0, and S 4H 2 •+/0 were measured to be - 0.02 ± 0.02, +0.04 ± 0.05, and +0.07 ± 0.07 V vs FeCp 2 +/0, respectively. Using these experimental values, the homolytic S - H SBDFE for S 4Me 2H + to S 4Me 2 •+, S 4MeH 2 + to S 4MeH •+, and S 4H 3 + to S 4H 2 •+ were determined to be 60.8 ± 1.0, 61.8 ± 1.6, and 61.9 ± 2.0 kcal/mol, respectively. These SBDFE values can be used to estimate gas phase bond dissociation enthalpies of 65.6, 66.6, and 66.7 kcal/mol, respectively. Solid state structures are presented for S 4MeH and S 4H 2.

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