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Volumn 132, Issue 48, 2010, Pages 17199-17210

Bridging the gap between electrochemical and organometallic activation: Benzyl chloride reduction at silver cathodes

Author keywords

[No Author keywords available]

Indexed keywords

CHEMICAL ACTIVATION; CHLORINE COMPOUNDS; DENSITY FUNCTIONAL THEORY; ELECTROLYTIC REDUCTION; FREE RADICAL REACTIONS; METAL COMPLEXES; METAL HALIDES; ORGANOMETALLICS; RAMAN SPECTROSCOPY; TRANSITION METAL COMPOUNDS; TRANSITION METALS;

EID: 78650125851     PISSN: 00027863     EISSN: 15205126     Source Type: Journal    
DOI: 10.1021/ja106049c     Document Type: Article
Times cited : (104)

References (81)
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    • In the classical view the nonconcerted reductive cleavage of aromatic halides proceeds by electron injection into the low energy π* aryl orbital. This is then transferred into the σ* C-Cl one when its energy becomes reduced following its vibrational elongation. However, this does not account for the requirement of a significant overlap between the two molecular orbitals which remain orthogonal in such a process. Thus, an out-of-plane bending of the C-Cl bond in PhCl was shown recently to be crucial for allowing the cleavage of the C-Cl bond. See the following
    • In the classical view the nonconcerted reductive cleavage of aromatic halides proceeds by electron injection into the low energy π* aryl orbital. This is then transferred into the σ* C-Cl one when its energy becomes reduced following its vibrational elongation. However, this does not account for the requirement of a significant overlap between the two molecular orbitals which remain orthogonal in such a process. Thus, an out-of-plane bending of the C-Cl bond in PhCl was shown recently to be crucial for allowing the cleavage of the C-Cl bond. See the following
  • 3
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    • In benzyl halides, the π* and σ* are nonorthogonal and have a sufficient overlap to allow a direct electron-transfer into the conjugated orbital hence leading to a "concerted" rupture of the carbon-halide bond
    • Burghardt, I., Laage, D., and Hynes, J. T. J. Phys. Chem. 2003, 107, 11292-11306. In benzyl halides, the π* and σ* are nonorthogonal and have a sufficient overlap to allow a direct electron-transfer into the conjugated orbital hence leading to a "concerted" rupture of the carbon-halide bond
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    • Burghardt, I.1    Laage, D.2    Hynes, J.T.3
  • 15
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    • The phenomena reported in Figures 2 and 4 of ref 6a after long specific preconditioning of the silver cathode in the presence of benzyl chloride were not observed under our normal electrochemical conditions, with the voltammetric wave exhibiting pure diffusional behavior (peak current proportional to the square root of the scan rate). Furthermore, during our related SERS investigations 7 we did not observe any change of the adsorbed species detected along the foot of the wave even after the electrode has been poised during ca. 4 min at each sampled potential. This shows that though of interest under the specific conditions explored in ref 6a the phenomena reported in this reference are not active under our conditions
    • The phenomena reported in Figures 2 and 4 of ref 6a after long specific preconditioning of the silver cathode in the presence of benzyl chloride were not observed under our normal electrochemical conditions, with the voltammetric wave exhibiting pure diffusional behavior (peak current proportional to the square root of the scan rate). Furthermore, during our related SERS investigations 7 we did not observe any change of the adsorbed species detected along the foot of the wave even after the electrode has been poised during ca. 4 min at each sampled potential. This shows that though of interest under the specific conditions explored in ref 6a the phenomena reported in this reference are not active under our conditions.
  • 17
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    • 2Cl weak adduct onto the silver surface was indicated by (i) the weakness of its SERS spectrum intensity, (ii) the fact that its peak frequencies differed only modestly from those of a free benzyl chloride, and (iii) the constancy of this signal with time all along the foot of the voltammetric wave. (7a)
    • 2Cl weak adduct onto the silver surface was indicated by (i) the weakness of its SERS spectrum intensity, (ii) the fact that its peak frequencies differed only modestly from those of a free benzyl chloride, and (iii) the constancy of this signal with time all along the foot of the voltammetric wave. (7a)
  • 20
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    • - by the acetonitrile solvent) onto the parent benzyl chloride. The same is true at silver cathodes since 3-phenylpropanenitrile is obtained with the same 20% yield, so that we use the same convenient formulation. Note, however, that in both cases this cannot be detected on the basis of voltammetry alone in the absence of extreme precision on the electrode surface area and diffusion coefficient of benzyl chloride
    • - by the acetonitrile solvent) onto the parent benzyl chloride. The same is true at silver cathodes since 3-phenylpropanenitrile is obtained with the same 20% yield, so that we use the same convenient formulation. Note, however, that in both cases this cannot be detected on the basis of voltammetry alone in the absence of extreme precision on the electrode surface area and diffusion coefficient of benzyl chloride.
  • 21
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    • For a discussion about absolute measurement of electron stoichiometries in transient electrochemistry see the following
    • For a discussion about absolute measurement of electron stoichiometries in transient electrochemistry see the following: Amatore, C., Azzabi, M., Calas, P., Jutand, A., Lefrou, C., and Rollin, Y. J. Electroanal. Chem. 1990, 288, 45-63
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    • Amatore, C.1    Azzabi, M.2    Calas, P.3    Jutand, A.4    Lefrou, C.5    Rollin, Y.6
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    • pp 519-532
    • pp 519-532
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    • p 223
    • p 223.
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    • pp 443-451
    • pp 443-451
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    • pp 454-455 and Figure 11.3.4 therein
    • pp 454-455 and Figure 11.3.4 therein.
  • 47
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    • The reduction potential of the benzyl radical in acetonitrile at a gold electrode has been reported to lie in between -1.43 and -1.45 V versus SCE. See the following
    • The reduction potential of the benzyl radical in acetonitrile at a gold electrode has been reported to lie in between -1.43 and -1.45 V versus SCE. See the following
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    • revision A.02; Gaussian, Inc.: Wallingford, CT
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    • For quantitative kinetic discussions about oxidative addition mechanistic pathways in homogeneous organometallic catalysis, see the following, e.g.: In;, Ed.; Wiley, New York,; chapter III.2.19
    • For quantitative kinetic discussions about oxidative addition mechanistic pathways in homogeneous organometallic catalysis, see the following, e.g.: Amatore, C. and Jutand, A. In Handbook of OrganoPalladium Chemistry for Organic Synthesis; Negishi, E. I., Ed.; Wiley, New York, 2002; chapter III.2.19, pp 943 - 972.
    • (2002) Handbook of OrganoPalladium Chemistry for Organic Synthesis , pp. 943-972
    • Amatore, C.1    Jutand, A.2    Negishi, E.I.3
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    • For an evaluation of electron-transfer pathways in organometallic oxidative additions, see the following, e.g.:, and references therein
    • For an evaluation of electron-transfer pathways in organometallic oxidative additions, see the following, e.g.: Amatore, C. and Pflüger, F. Organometallics 1990, 9, 2276-2282 and references therein
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    • For the importance of precomplexation during oxidative additions, see the following, e.g
    • For the importance of precomplexation during oxidative additions, see the following, e.g.: Amatore, C., Azzabi, M., and Jutand, A. J. Am. Chem. Soc. 1991, 113, 1670-1677
    • (1991) J. Am. Chem. Soc. , vol.113 , pp. 1670-1677
    • Amatore, C.1    Azzabi, M.2    Jutand, A.3
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    • For a general review on homogeneous versus heterogeneous organometallic catalysis in the context of palladium catalysis, see the following, e.g
    • For a general review on homogeneous versus heterogeneous organometallic catalysis in the context of palladium catalysis, see the following, e.g.: Phan, N. T. S., Van Der Sluys, M., and Jones, C. W. Adv. Synth. Catal. 2006, 348, 609-679
    • (2006) Adv. Synth. Catal. , vol.348 , pp. 609-679
    • Phan, N.T.S.1    Van Der Sluys, M.2    Jones, C.W.3
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    • All electron-transfers considered in this work do not obey the requirement of Marcus theory for outer-sphere electron-transfers, although this does not prevent using Marcus formulations for reorganization energies for the sake of comparison to the experimental values determined
    • All electron-transfers considered in this work do not obey the requirement of Marcus theory for outer-sphere electron-transfers, although this does not prevent using Marcus formulations for reorganization energies for the sake of comparison to the experimental values determined.
  • 57
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    • note
    • 0 provided that the product system has almost no vibronically excited states.
  • 58
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    • In;, Eds.; M. Dekker: New York,; chapter 1, p. For discussions about the reasons justifying the combination of "work terms" in the "effective" activation barrier, see and the following pages
    • Amatore, C. In Organic Electrochemistry; Lund, H. and Hammerich, O., Eds.; M. Dekker: New York, 2000; chapter 1, p 61 and the following pages. For discussions about the reasons justifying the combination of "work terms" in the "effective" activation barrier, see
    • (2000) Organic Electrochemistry , pp. 61
    • Amatore, C.1    Lund, H.2    Hammerich, O.3
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    • ref 17a
    • ref 17a.
  • 61
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    • These two latest works consider bimolecular homogeneous reactions, but the concepts involved are readily transposable to heterogeneous cases within the Marcus framework (upon considering the electrode as one infinite reactant plane). For a discussion of this latter point, see the following reference
    • Schlesener, C. J., Amatore, C., and Kochi, J. K. J. Phys. Chem. 1986, 90, 3747-3756. These two latest works consider bimolecular homogeneous reactions, but the concepts involved are readily transposable to heterogeneous cases within the Marcus framework (upon considering the electrode as one infinite reactant plane). For a discussion of this latter point, see the following reference
    • (1986) J. Phys. Chem. , vol.90 , pp. 3747-3756
    • Schlesener, C.J.1    Amatore, C.2    Kochi, J.K.3
  • 62
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    • Yet the metallic nature of the electrode introduces some electrostatic mirror effects not accounted for in bimolecular cases. See the following reference
    • Kojima, H. and Bard, A. J. J. Am. Chem. Soc. 1975, 97, 6317-6324. Yet the metallic nature of the electrode introduces some electrostatic mirror effects not accounted for in bimolecular cases. See the following reference
    • (1975) J. Am. Chem. Soc. , vol.97 , pp. 6317-6324
    • Kojima, H.1    Bard, A.J.2
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    • note
    • 0.
  • 65
    • 78650161163 scopus 로고    scopus 로고
    • This relationship may appear surprising at first glance but should be readily understood; the observation of a CV wave at a given scan rate (i.e., of a current flow compatible with a diffusion-limited supply at this scan rate) requires that the electron-transfer rate constant has the exact magnitude required for sustaining this precise current flow (compare eq 15). This condition may be fulfilled only when the potential-dependent effective activation barrier at the CV peak potential reaches a constant magnitude (compare eq 22) irrespective of the exact elementary steps under voltammetric scrutiny
    • This relationship may appear surprising at first glance but should be readily understood; the observation of a CV wave at a given scan rate (i.e., of a current flow compatible with a diffusion-limited supply at this scan rate) requires that the electron-transfer rate constant has the exact magnitude required for sustaining this precise current flow (compare eq 15). This condition may be fulfilled only when the potential-dependent effective activation barrier at the CV peak potential reaches a constant magnitude (compare eq 22) irrespective of the exact elementary steps under voltammetric scrutiny.
  • 66
    • 78650112123 scopus 로고    scopus 로고
    • note
    • ads = 5.4 kcal/mol reported in Table 1 is the minimum one, both results cannot be reconciled with the present DFT thermodynamic evaluations and with the SERS evidence. This definitively rules out both concerted mechanisms I.
  • 67
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    • For related examples, see also the following reference
    • Willett, B. C. and Peters, D. G. J. Electroanal. Chem. 1981, 123, 291-306. For related examples, see also the following reference
    • (1981) J. Electroanal. Chem. , vol.123 , pp. 291-306
    • Willett, B.C.1    Peters, D.G.2
  • 71
    • 77249169796 scopus 로고    scopus 로고
    • Note that there is a similar drastic positive shift of the reduction wave of aliphatic chloride at the silver electrodes when shifting from aprotic solvent to aqueous electrolytes; compare with the following
    • Note that there is a similar drastic positive shift of the reduction wave of aliphatic chloride at the silver electrodes when shifting from aprotic solvent to aqueous electrolytes; compare with the following: Scialdone, O., Guarisco, C., Galia, A., and Herbois, R. J. Electroanal. Chem. 2010, 641, 14-22
    • (2010) J. Electroanal. Chem. , vol.641 , pp. 14-22
    • Scialdone, O.1    Guarisco, C.2    Galia, A.3    Herbois, R.4


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