Abstract
The reactivity of the S-H bond in Cp*Mo(μ-S)2(μ-SMe) (μ-SH)MoCp* (S4MeH) has been explored by determination of kinetics of hydrogen atom abstraction to form the radical Cp*Mo(μ-S) 3(μ-SMe)MoCp* (S4Me•), as well as reaction of hydrogen with the radical-dimer equilibrium to reform the S-H complex. From the temperature dependent rate data for the abstraction of hydrogen atom by benzyl radical, ΔH‡ and ΔS‡ were determined to be 1.54 ± 0.25 kcal/mol and -25.5 ± 0.8 cal/mol K, respectively, giving kabs = 1.3 × 106 M-1 s-1 at 25°C. In steady state abstraction kinetic experiments, the exclusive 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* (S4MeBz), consistent with the Fischer-Ingold persistent radical effect. S4Me• was found to reversibly dimerize by formation of a weak bridging disulfide bond to form the tetranuclear complex (Cp*Mo(μ-S)2(μ-SMe)MoCp*) 2(μ-S2) ((S4Me)2). The radical-dimer equilibrium constant has been determined to be 5.7 × 10 4 ± 2.1 × 104 M-1 from EPR data. The rate constant for dissociation of the dimer was found to be 1.1 × 103 s-1 at 25°C, based on variable temperature 1H NMR data. The rate constant for dimerization of the radical has been estimated to be 6.5 × 107 M-1 s-1 in toluene at room temperature, based on the dimer dissociation rate constant and the equilibrium constant for dimerization. Structures are presented for (S 4Me)2, S4MeBz, and the cationic Cp*Mo(μ-S2)(μ-S)(μ-SMe)MoCp*(OTf) (S 4Me+), a precursor of the radical and the alkylated derivatives. Evidence for a radical addition/elimination pathway at an Mo 2S4 core is presented.
| Original language | English |
|---|---|
| Pages (from-to) | 8940-8951 |
| Number of pages | 12 |
| Journal | Journal of the American Chemical Society |
| Volume | 130 |
| Issue number | 28 |
| DOIs | |
| Publication status | Published - Jul 16 2008 |
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ASJC Scopus subject areas
- Chemistry(all)
Cite this
Formation and reactivity of a persistent radical in a dinuclear molybdenum complex. / Appel, Aaron; Lee, Sun Jane; Franz, James A.; DuBois, Daniel L; DuBois, M. Rakowski; Birnbaum, Jerome C.; Twamley, Brendan.
In: Journal of the American Chemical Society, Vol. 130, No. 28, 16.07.2008, p. 8940-8951.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Formation and reactivity of a persistent radical in a dinuclear molybdenum complex
AU - Appel, Aaron
AU - Lee, Sun Jane
AU - Franz, James A.
AU - DuBois, Daniel L
AU - DuBois, M. Rakowski
AU - Birnbaum, Jerome C.
AU - Twamley, Brendan
PY - 2008/7/16
Y1 - 2008/7/16
N2 - The reactivity of the S-H bond in Cp*Mo(μ-S)2(μ-SMe) (μ-SH)MoCp* (S4MeH) has been explored by determination of kinetics of hydrogen atom abstraction to form the radical Cp*Mo(μ-S) 3(μ-SMe)MoCp* (S4Me•), as well as reaction of hydrogen with the radical-dimer equilibrium to reform the S-H complex. From the temperature dependent rate data for the abstraction of hydrogen atom by benzyl radical, ΔH‡ and ΔS‡ were determined to be 1.54 ± 0.25 kcal/mol and -25.5 ± 0.8 cal/mol K, respectively, giving kabs = 1.3 × 106 M-1 s-1 at 25°C. In steady state abstraction kinetic experiments, the exclusive 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* (S4MeBz), consistent with the Fischer-Ingold persistent radical effect. S4Me• was found to reversibly dimerize by formation of a weak bridging disulfide bond to form the tetranuclear complex (Cp*Mo(μ-S)2(μ-SMe)MoCp*) 2(μ-S2) ((S4Me)2). The radical-dimer equilibrium constant has been determined to be 5.7 × 10 4 ± 2.1 × 104 M-1 from EPR data. The rate constant for dissociation of the dimer was found to be 1.1 × 103 s-1 at 25°C, based on variable temperature 1H NMR data. The rate constant for dimerization of the radical has been estimated to be 6.5 × 107 M-1 s-1 in toluene at room temperature, based on the dimer dissociation rate constant and the equilibrium constant for dimerization. Structures are presented for (S 4Me)2, S4MeBz, and the cationic Cp*Mo(μ-S2)(μ-S)(μ-SMe)MoCp*(OTf) (S 4Me+), a precursor of the radical and the alkylated derivatives. Evidence for a radical addition/elimination pathway at an Mo 2S4 core is presented.
AB - The reactivity of the S-H bond in Cp*Mo(μ-S)2(μ-SMe) (μ-SH)MoCp* (S4MeH) has been explored by determination of kinetics of hydrogen atom abstraction to form the radical Cp*Mo(μ-S) 3(μ-SMe)MoCp* (S4Me•), as well as reaction of hydrogen with the radical-dimer equilibrium to reform the S-H complex. From the temperature dependent rate data for the abstraction of hydrogen atom by benzyl radical, ΔH‡ and ΔS‡ were determined to be 1.54 ± 0.25 kcal/mol and -25.5 ± 0.8 cal/mol K, respectively, giving kabs = 1.3 × 106 M-1 s-1 at 25°C. In steady state abstraction kinetic experiments, the exclusive 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* (S4MeBz), consistent with the Fischer-Ingold persistent radical effect. S4Me• was found to reversibly dimerize by formation of a weak bridging disulfide bond to form the tetranuclear complex (Cp*Mo(μ-S)2(μ-SMe)MoCp*) 2(μ-S2) ((S4Me)2). The radical-dimer equilibrium constant has been determined to be 5.7 × 10 4 ± 2.1 × 104 M-1 from EPR data. The rate constant for dissociation of the dimer was found to be 1.1 × 103 s-1 at 25°C, based on variable temperature 1H NMR data. The rate constant for dimerization of the radical has been estimated to be 6.5 × 107 M-1 s-1 in toluene at room temperature, based on the dimer dissociation rate constant and the equilibrium constant for dimerization. Structures are presented for (S 4Me)2, S4MeBz, and the cationic Cp*Mo(μ-S2)(μ-S)(μ-SMe)MoCp*(OTf) (S 4Me+), a precursor of the radical and the alkylated derivatives. Evidence for a radical addition/elimination pathway at an Mo 2S4 core is presented.
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U2 - 10.1021/ja078115r
DO - 10.1021/ja078115r
M3 - Article
C2 - 18564842
AN - SCOPUS:48949118180
VL - 130
SP - 8940
EP - 8951
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 28
ER -