Determination of S - H bond strengths in dimolybdenum tetrasulfide complexes

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

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26 Citations (Scopus)

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

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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