Activation of the sulfhydryl group by Mo centers: Kinetics of reaction of benzyl radical with a binuclear Mo(μ-SH)Mo complex and with arene and alkane thiols

James A. Franz, Jerome C. Birnbaum, Douglas S. Kolwaite, John Linehan, Donald M. Camaioni, Michel Dupuis

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Abstract

This paper provides evidence from kinetic experiments and electronic structure calculations of a significantly reduced S-H bond strength in the Mo(μ-SH)Mo function in the homogeneous catalyst model, CpMo(μ-S) 2(μ-SH)2MoCp (1, Cp = η 5-cyclopentadienyl). The reactivity of 1 was explored by determination of a rate expression for hydrogen atom abstraction by benzyl radical from 1 (log(kabs/M-1 s-1) = (9.07 ± 0.38) - (3.62 ± 0.58)/θ) for comparison with expressions for CH3(CH2)7SH, log(kabs/M -1 s-1) = (7.88 ± 0.35) - (4.64 ± 0.54)/θ, and for 2-mercaptonaphthalene, log(kabs/M -1 s-1) = (8.21 ± 0.17) - (4.24 ± 0.26)/θ (θ = 2.303RT kcal/mol, 2σ error). The rate constant for hydrogen atom abstraction at 298 K by benzyl radical from 1 is 2 orders of magnitude greater than that from 1-octanethiol, resulting from the predicted (DFT) S-H bond strength of 1 of 73 kcal/mol. The radical CpMo(μ-S) 3(μ-SH)MoCp, 2, is revealed, from the properties of slow self-reaction, and exclusive cross-combination with reactive benzyl radical, to be a persistent free radical.

Original languageEnglish
Pages (from-to)6680-6691
Number of pages12
JournalJournal of the American Chemical Society
Volume126
Issue number21
DOIs
Publication statusPublished - Jun 2 2004

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Alkanes
Sulfhydryl Compounds
Paraffins
Hydrogen
Chemical activation
Atoms
Kinetics
Cross Reactions
Free radicals
Discrete Fourier transforms
Free Radicals
Electronic structure
Rate constants
Catalysts
Experiments
n-octanethiol

ASJC Scopus subject areas

  • Chemistry(all)

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Activation of the sulfhydryl group by Mo centers : Kinetics of reaction of benzyl radical with a binuclear Mo(μ-SH)Mo complex and with arene and alkane thiols. / Franz, James A.; Birnbaum, Jerome C.; Kolwaite, Douglas S.; Linehan, John; Camaioni, Donald M.; Dupuis, Michel.

In: Journal of the American Chemical Society, Vol. 126, No. 21, 02.06.2004, p. 6680-6691.

Research output: Contribution to journalArticle

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abstract = "This paper provides evidence from kinetic experiments and electronic structure calculations of a significantly reduced S-H bond strength in the Mo(μ-SH)Mo function in the homogeneous catalyst model, CpMo(μ-S) 2(μ-SH)2MoCp (1, Cp = η 5-cyclopentadienyl). The reactivity of 1 was explored by determination of a rate expression for hydrogen atom abstraction by benzyl radical from 1 (log(kabs/M-1 s-1) = (9.07 ± 0.38) - (3.62 ± 0.58)/θ) for comparison with expressions for CH3(CH2)7SH, log(kabs/M -1 s-1) = (7.88 ± 0.35) - (4.64 ± 0.54)/θ, and for 2-mercaptonaphthalene, log(kabs/M -1 s-1) = (8.21 ± 0.17) - (4.24 ± 0.26)/θ (θ = 2.303RT kcal/mol, 2σ error). The rate constant for hydrogen atom abstraction at 298 K by benzyl radical from 1 is 2 orders of magnitude greater than that from 1-octanethiol, resulting from the predicted (DFT) S-H bond strength of 1 of 73 kcal/mol. The radical CpMo(μ-S) 3(μ-SH)MoCp, 2, is revealed, from the properties of slow self-reaction, and exclusive cross-combination with reactive benzyl radical, to be a persistent free radical.",
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