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Formation and Reactivity of a Persistent Radical in a Dinuclear Molybdenum Complex

Journal Article · · Journal of the American Chemical Society
DOI:https://doi.org/10.1021/ja078115r· OSTI ID:949088
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The reactivity of the S-H bond in Cp*Mo(μ-S)2(μ-SMe)(μ-SH)MoCp* (S4MEH) has been explored by hydrogen atom abstraction to form the radical Cp*Mo(μ-S)3(μ-SMe)MoCp* (S4ME∙), as well as hydrogen addition to the radical to reform the S-H complex. The rate expression for abstraction of hydrogen atom by benzyl radical has been determined, giving log(kabs/M-1 s-1) = (2.41 ? 0.37)/(2.303RT) + (7.88 ? 0.25) with kabs = 1.3 x 106 M-1 s-1 at 25ºC. The radical termination product of the Mo2S4 core was found to be the benzyl cross-termination product, Cp*Mo(μ-S)2(μ-SMe)(μ-SBz)MoCp*. Structures are presented for this complex as well as the cationic Cp*Mo(μ-S2)(μ-S)(μ-SMe)MoCp*(OTf), a precursor of the radical and the alkylated derivatives. The radical undergoes reversible dimerization to form the tetranuclear complex (Cp*Mo(μ-S)2(μ-SMe)MoCp*)2(μ-S2), as shown by the solid state structure. In solution, the radical and the dimer are in equilibrium, and the equilibrium constant for dimerization has been estimated from magnetic susceptibility and EPR data. The rate of dissociation of the dimer has been determined to be 640 s-1 at 25ºC, based on variable temperature 1H NMR data. The rate constant for dimerization of the radical has been estimated to be 6.5 x 107 M-1 s-1, based on the dimer dissociation rate constant and the lower limit of the equilibrium constant for dimerization.
Research Organization:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
Sponsoring Organization:
USDOE
DOE Contract Number:
AC05-76RL01830
OSTI ID:
949088
Report Number(s):
PNNL-SA-57391; KC0302010
Journal Information:
Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 28 Vol. 130; ISSN JACSAT; ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English

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Related Subjects

08 HYDROGEN
36 MATERIALS SCIENCE
ATOMS
BENZYL RADICALS
DIMERIZATION
DIMERS
DISSOCIATION
HYDROGEN
HYDROGEN ADDITIONS
MAGNETIC SUSCEPTIBILITY
MOLYBDENUM
PRECURSOR
RADICALS