Determination of S-H Bond Strengths in Dimolybdenum Tetrasulfide Complexes

Journal Article · Mon Jan 12 00:00:00 EST 2009 · Organometallics

DOI:https://doi.org/10.1021/om800875n· OSTI ID:949061

Appel, Aaron M. ^[1]; Lee, Suh-Jane ^[1]; Franz, James A. ^[1]; DuBois, Daniel L. ^[1]; Rakowski DuBois, Mary ^[1]; Twamley, Brendan ^[2]

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1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
2. Univ. of Idaho, Moscow, ID (United States)

Homolytic solution bond dissociation free energies (sBDFE’s) for S-H bonds have been determined for soluble dimolybdenum tetrasulfide complexes through thermochemical cycles using electrochemical potentials and pK_a values, all measured in acetonitrile. For [Cp*Mo(μ S)(μ SMe)2(μ SH)MoCp*]+ (S₄Me₂H⁺), [Cp*Mo(μ S)(μ SMe)(μ SH)2MoCp*]+ (S₄MeH₂⁺), and [Cp*Mo(μ S)(μ SH)₃MoCp*]⁺ (S₄H₃⁺), the pKa 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 S₄Me₂•+/o, S₄MeH^•+/o, and S₄H₂^•+/o were measured to be -0.02 ± 0.02, +0.04 ± 0.05, and +0.07 ± 0.07 V vs FeCp₂^+/o, respectively. Using these experimental values, the homolytic S-H sBDFE for each S₄RR’H⁺ to S₄RR’^•+ reaction was determined to be 60.8 ± 1.0, 61.8 ± 1.6, and 61.9 ± 2.0 kcal/mol for S₄Me₂H⁺, S₄MeH²⁺, and S₄H₃⁺ 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. The gas phase bond dissociation enthalpy for the analogous complex, Cp₂Mo₂S₄Me₂H⁺ was determined to be 64.9 kcal/mol by electronic structure calculations. Solid state structures are presented for S₄MeH and S₄H₂. The Pacific Northwest National Laboratory is operated y Battelle for the U.S. Department of Energy.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 949061
• Report Number(s): PNNL-SA-61722; ORGND7; KC0302010; TRN: US200907%%297
• Journal Information: Organometallics, Vol. 28, Issue 3; ISSN 0276-7333
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
MOLYBDENUM COMPLEXES
SULFIDES
CHEMICAL BONDS
SULFUR
HYDROGEN
ELECTRONIC STRUCTURE
ENTHALPY
DISSOCIATION ENERGY