The cathodic behaviour of poly(alkyl) and (aryl) sulfones revisited. Mechanistic and theoretical approaches

Article abstract of DOI:10.1039/b308091a

A series of aromatic sulfones activated by 2, 3 or 4 sulfonyl groups were reduced electrochemically in aprotic media. The electrochemical behaviour is strongly directed by the nature and the number of the substituents bound to the aromatic ring. From the analyses of cyclic voltammetry experiments, the kinetics and thermodynamic parameters were evaluated for each system and a theoretical study at the B3LYP/6-31G* level was performed simultaneously to understand the reactivity of the radical anions stemmed from these aromatic sulfones.

Full text of DOI:10.1039/b308091a

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The cathodic behaviour of poly(alkyl) and (aryl) sulfones revisited.
Mechanistic and theoretical approaches
Jean-Francois Bergamini,a Philippe Hapiot,a Corinne Lagrost,*a Loredana Preda,b
Jacques Simoneta and Elena Volanschib
a
`
`
Synthese et Electrosynthese organique, Institut de Chimie, Campus de Beaulieu,
UMR 6510, 35042, Rennes, cedex, France. E-mail: corinne.lagrost@univ-rennes1.fr;
Fax: (+33) 22323 6732; Tel: (+33) 22323 5940
b
Department of Physical Chemistry, University of Bucarest, Bdul Elisabeta 4-12, RO-70346,
Bucarest, Romania
Received 17th July 2003, Accepted 4th September 2003
First published as an Advance Article on the web 24th September 2003
A series of aromatic sulfones activated by 2, 3 or 4 sulfonyl groups were reduced electrochemically in aprotic
media. The electrochemical behaviour is strongly directed by the nature and the number of the substituents
bound to the aromatic ring. From the analyses of cyclic voltammetry experiments, the kinetics and
thermodynamic parameters were evaluated for each system and a theoretical study at the B3LYP/6-31G*
level was performed simultaneously to understand the reactivity of the radical anions stemmed from these
aromatic sulfones.
stable radical anion owing to conformational changes asso-
ciated with a single electron-transfer.7
Introduction
Over the past two decades, the reduction of alkyl- or aryl- sul-
fonylbenzenes has been the subject of numerous investigations
because of interest in their use in organic synthesis1 and the
manifold of observed mechanisms (selective sulfur–carbon
bond cleavage, coupling reaction, self alkylation,. . .).1–8 After
the cleavage step, whose nature depends on experimental con-
ditions and selectivity, the produced radical may be involved in
a series of reactions like H-atom transfer, SRN1,. . .. Despite
this large literature, the factors governing the selectivity of
the S–C bond cleavage or more generally the changes in the
nature of the chemical steps are still not well understood.9,10
As a matter of fact, under electrochemical reduction, alkyl-
or aryl-sulfonylbenzenes lead first to radical anions that are
often unstable. The radical anion of the unsubstituted aryl
alkyl-monosulfone undergoes a fast selective cleavage (clea-
In the present paper, we especially focused on the first steps
of the global mechanisms to attempt a rationalization of the
variations in the chemical pathways for different aromatic
polysulfones (see Scheme 1 for the investigated compounds).
The cathodic reductions of several aromatic poly-sulfones
bearing two, three or four ethyl- and phenyl-sulfonyl groups
have been systematically investigated in aprotic solvent (aceto-
nitrile). Decays of the electrogenerated radical anions were
analyzed as a function of the number and the nature of the sul-
fonyl substituents. Density functional calculations at the
B3LYP/6-31G* level were performed and discussed in connec-
tion with the dissociative electron transfer model14 in agree-
ment with the electrochemical data: redox behaviour and
reactivities of electrogenerated radical anion.
vage kinetics rate constant around 105 ꢀ1) of the sulfur–
s
Experimental
carbon bond to yield aryl sulfinate ions and hydrocarbons
(b-cleavage).10,11 The reductive process for the aromatic poly-
sulfones (1–5) is more complex and the electrogenerated radi-
cal anions decay along very different chemical pathways.
Reduction of the o-bis(alkylsulfonyl)benzene 1a leads to the
the R-alkylated mono sulfone.1,10,12 The proposed mechanism
involves a regioselective b-cleavage reaction (formation of
the aromatic sulfinate and the alkyl radical Rꢁ) which is fol-
lowed by a coupling reaction between Rꢁ and the substrate
radical anion, then by an elimination.5,10 When R is a phenyl
(1b) group, the regioselectivity of the bond cleavage reaction
changes and the reduction simply leads to the formation of
the diphenylsulfone (selective cleavage of SO2Rꢀ). Surpri-
singly, completely different reactivities appear for the other
polysulfones. When tri-sulfones 3 are reduced, coupling pro-
ducts are isolated, such as the tetra- or penta-(alkylsulfonyl)
biaryls, depending on the nature of the alkyl groups.6
1,2,4,5-Tetrakis(phenylsulfonyl)benzene 52 and pentakis(phe-
nylsulfonyl)benzene13 could be reversibly reduced into highly
stabilized anion radical and dianion whereas hexakis(phenyl-
sulfonyl)benzenes showed a specific behavior of a particularly
Chemicals
All substrates were prepared according to previously published
procedures.15 Acetonitrile (ACN) from SDS contained less
than 50 ppm of water and was used without further
Scheme 1 General formula of poly-sulfones investigated in this work.
4846
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DOI: 10.1039/b308091a

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Table 1 Electrochemical data for aromatic poly-sulfones
Compounds Eꢂ/V vs. SCE ks/cm sꢀ1 Chemical rate constanta
purification. Tetra-n-butylammonium tetrafluoroborate was
from Fluka and used as received (puriss, electrochemical grade)
0.1 sꢀ1
Electrochemical experiments
1a
1b
2
ꢀ1.688
ꢀ1.591
ꢀ1.844
ꢀ1.55
0.08
0.3
1–2 sꢀ1
Electrochemical instrumentation consisted of
GSTP4 programmer and of home-built potentiostat
a Tacussel
0.15
0.07–0.08
0.2
5 ꢄ 105 L molꢀ1.sꢀ1
8 ꢄ 103 L molꢀ1.sꢀ1
1 ꢄ 102 L molꢀ1.sꢀ1
No reactiona
a
3a
3b
4
equipped with a positive-feedback compensation device.16
The voltammograms were recorded with a 310 Nicolet oscillo-
scope. Electrochemical investigations were carried out in a one
compartment, three-electrode cell, using a Pt wire as counter
electrode and a SCE electrode as reference. Ferrocene was
added to the electrolyte solution at the end of each series of
ꢀ1.351
ꢀ1.038
ꢀ0.607
0.3
0.2
5
No reactiona
a
First order rate constant for cleavage bond reactions. Second order
rate constants for dimerization.
experiments and the ferrocene/ferrocenium couple (Eꢂ
¼
0.405 V vs. SCE) served as an internal probe. The working
electrode was a glassy carbon disk (1.5 mm or 3 mm dia-
meter). The electrode was carefully polished before each
voltammetry experiment with 1 mm diamond paste and ultra-
sonically rinsed in absolute ethanol. Electrolyte solutions were
thoroughly purged and kept under a dry argon flow during
each run. Experiments were performed at room-temperature
(20 ꢃ 2 ꢂC). Numerical simulations of the voltammograms
were performed with the BAS DigiSim simulator 3.03, using
the default numerical options with the assumption of planar
diffusion and a Butler-Volmer law for the electron transfer.
The charge-transfer coefficient, a, was taken as 0.5 and the dif-
fusion coefficients were taken equal for all species (D ¼ 10ꢀ5
cm2 sꢀ1).
process but the voltammetric behaviour indicates that the first
chemical step following the formation of the radical anion is
the S–C bond cleavage. To measure the kinetics parameters
for both the heterogeneous electron transfer rate and its asso-
ciated chemical steps, the experimental voltammograms were
compared with theoretical curves calculated using the DigiSim
software.23 We obtained for ks (standard electron-transfer rate
constants uncorrected from the double layer effect) values of
0.08–0.1 cm sꢀ1 and 0.3 cm sꢀ1 for 1a and 1b, respectively, that
correspond to moderately slow redox couples.
From comparison with calculated curves, the voltammo-
gram reversibility versus the scan rate allow determination of
the kinetics parameters of the chemical step triggered by elec-
tron transfer. Thus, the kinetics rate constants for the C–S
bond cleavage were found to be k1 ¼ 0.1 sꢀ1 for 1a and
k1 ¼ 1–2 sꢀ1 for 1b. Both k1 values are rather modest, but it
is noticeable that the cleavage rate is more than 10 times higher
for 1b when the leaving group is a phenyl sulfinate. A very dif-
ferent behaviour from that described for 1a is observed for the
di-sulfone 2 (Fig. 1). Irreversible monoelectronic24 voltammo-
grams are recorded in the scan-rate range 0.1–20 V sꢀ1. A par-
tial reversibility becomes visible when the scan rate is greater
than 50 V sꢀ1 indicating a considerable decrease of the radical
Theoretical modeling
The calculations were performed using the Gaussian 98W
package.17 Gas phase geometries and electronic energies were
calculated by full optimization without imposed symmetry of
the conformations using the B3LYP18 density functional with
the 6-31G* basis set,19,20 starting from preliminary optimiza-
tions performed with semi-empirical methods. Geometries
were checked by frequency calculations except for the two lar-
gest polysulfone radical anions. Because of the difficulty in
running frequency calculations with these molecules, the
quality of the obtained minima were checked by restarting
the optimizations from other conformations. We checked that
the spin contamination remains low (s2 < 0.765) for all the
open-shell B3LYP calculations (radical anion). Total energies
were obtained after calculation of the frequencies. These values
were corrected by a scaling factor (0.9804) applied to the
zero-point energies and thermal energy corrections.21
Results
Disulfones
The radical anion decay kinetics were derived from scrutiny
analyses of the voltammetric current responses of the first
reduction wave. In acetonitrile (ACN) and at low sweep rate
(0.1 V sꢀ1), disulfones 1 display a partially reversible wave.
The reversibility increases with the scan rate and becomes total
for scan rates higher than 0.2 V sꢀ1 for 1a and 2 V sꢀ1 for 1b
(for a 2 ꢄ 10ꢀ3 mol Lꢀ1 concentration). The formal potentials
Eꢂ for the sulfone/sulfone radical anion couples were immedi-
ately derived as the half-sum between the forward and the
backward scan from these reversible voltammograms (see also
Table 1). For both compounds, we observed that the reversi-
bility did not change when the sulfone concentration was
increased by at least a factor of 10 for any investigated scan
rates, showing that the corresponding radical anions decay
according to a first-order kinetics.22 This observation corres-
ponds to a kinetic situation where the C–S bond cleavage is
the rate-determining step and agrees with the previously pub-
lished results.6 For 1a, the overall reaction is a self-alkylation
Fig. 1 Cyclic voltammetry of ꢅ10ꢀ3 mol Lꢀ1 1a (a) and 2 (b) in
ACN-0.1 mol Lꢀ1 Bu4NBF4 on a glassy carbon disk electrode at
0.5 (a) and 50 V sꢀ1 (b).
Phys. Chem. Chem. Phys., 2003, 5, 4846–4850
4847

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anion life-time from comparison with those from the ortho
disulfones.25 It is also noticeable that the Eꢂ ꢁꢀ value
2/2
(ꢀ1.844 V) is 200 mV more negative than those of 1a or 1b,
showing that 2 is more difficult to reduce than 1 in agreement
with a better stabilization of the radical anion by two conju-
gated sulfone groups. To characterize the nature of the fol-
low-up reaction to the electron-transfer step for 2, we
investigated the peak-potential variations in the irreversible
voltammograms as a function of scan rate and initial sulfone
concentration (Fig. 2).26 The peak potential (Ep) was found
to vary linearly as a function of log(v) with a slope @Ep/
@log(v) ¼ ꢀ19.5 mV decadeꢀ1 and the linear bulk concentra-
tion27 dependence of the peak potential was measured @Ep/
@log(c) ¼ 19.52 mV decadeꢀ1. These slopes show a second-
order character for the follow-up reaction and suggest a
DIM1 mechanism i.e. a fast electron transfer followed by a
coupling reaction between two electrogenerated radical anions
(see Scheme 2), leading to the formation of coupling pro-
ducts.26 However, the resulting coupling product is observed
to be very easily oxidized at low anodic potential (ꢀ0.70 V
vs. SCE). This behaviour has been already described in pre-
vious studies concerning tri-sulfones 3 for which the transient
formation of a dianion was demonstrated.6a By analogy, the
chemically reversible process can be written as in Scheme 2.
According to this coupling scheme, numerical simulations
give the standard electron-transfer rate constant ks ¼ 0.15
Scheme 2 DIM1 mechanism.
involving the corresponding anion radical 3ꢁꢀ. Because of
the long lifetime of 3 that is close to the longest available
experimental time in cyclic voltammetry,28 it was difficult to
obtain a clear-cut answer about the nature of the bimolecular
kinetic step as we did for 2. However in previous investiga-
tions, dihydro-dimer compounds were isolated from the catho-
ꢁ
ꢀ
dicꢀreduction ꢁof 3a and 3b and it is likely that the decay of
3aꢁ and 3b
follow the same radical–radical coupling
ꢀ
mechanism as obtained for 2.6a Both compounds behave simi-
larly regarding the variation of the voltammogram’s reversibil-
ity with concentration, but for the same scan rate and
concentrations, 3a displaysꢁa lower reversibility corresponding
to a higher reactivity for 3a ꢀ than that for 3bꢁꢀ. Assuming the
DIM1 mechanism, the calculated coupling rate constant kdim is
10 times higher for 3a (kdim ¼ 8 ꢄ 103 L molꢀ1
s
ꢀ1) than that
for 3b (kdim ¼ 1 ꢄ 102 L molꢀ1
s
ꢀ1) that can be explained
cm sꢀ1 and a second order dimerization rate constant kdim
¼
because of different steric bulk effects. Concerning the hetero-
geneous charge-transfer rate constants, the ks value is slightly
higher for 3b, ks ¼ 0.2 cm sꢀ1 than 3a (0.07–0.08 cm sꢀ1).
We also performed cyclic voltammetry experiments of tri-
sulfone 4. Despite a lower apparent steric hindrance (two
adjacent positions are free on the aromatic ring), reversible
voltammograms are obtained in the whole scan-rate range
0.1–200 V sꢀ1 for all used concentrations of 4 (1–10ꢁ mmol
5 ꢄ 105 L molꢀ1 sꢀ1
.
Trisulfones
We were then interested in the reduction of symmetrical tri-
sulfones 3a and 3b. Both of these compounds displayed rever-
sible (or quasi-reversible) voltammograms in the scan-rate
range 0.1–50 V sꢀ1. In contrast to what was observed for
di-sulfones 1, the reversibility of the voltammogram decreases
when the concentration of sulfone 3 is increased, indicating
that the rate-determining step is a bimolecular process
Lꢀ1 range) showing a longer life-time than those of 2 and
ꢀ
3ꢁꢀ. Similar observations were made for the cathodic reduction
of the tetra-sulfone 5 that also exhibits reversible voltammo-
grams in the scan-rate range 0.1–100 V sꢀ1, associated with a
quasi-Nernstian electrochemical behaviour. Values of ks ¼
ꢁ
ꢁ
ꢀ
ꢀ
0.3 cm sꢀ1 and ks ¼ 0.2 cm sꢀ1 for 4/4 and 5/5 couples,
respectively, were extracted from the peak to peak potential
difference.
Discussion
As a general trend, increasing the number of sulfonyl groups
onto the aromatic core induces a better stabilization of the
transient radical anion that can be partly ascribed to an
increasing delocalization of the unpaired electron in the radical
anion and steric hindrance. We also note that ks values are
higher for poly(arylsulfonyl)benzenes (1b and 3b, for instance)
than for the poly(alkylsulfonyl)benzenes (1a and 3a) (Table 1)
in agreement with a better delocalization of the charge in the
radical anion that results in a lower solvent reorganization
during the electron transfer. However, the stabilization of
the radical anion is not an ‘‘absolutꢁeꢀ’’ requisite as demon-
ꢁ
ꢀ
strated by the comparison between 3b and 4 on one hand
and between 1aꢁꢀ, 1bꢁꢀ and 2ꢁꢀ on the other hand. For the last
two types of sulfone, we observed for the o-disulfone radical
ꢁ
ꢀ
anion a bond cleavage contrary to the meta disulfone 2 for
which coupling reactions are observed. In a situation where
bond cleavage occurs, the other question concerns the factors
governing the regio-selectivity (a- or b-bond cleavage). To
explain these behaviours, we performed a series of theoretical
calculations using the B3LYP density functional method.
We first try to explain and predict the Eꢂ variations with the
number and position of sulfonyl groups. Theoretical Eꢂs were
estimated from the difference between the electronic energies
for the radical anion and the neutral sulfone in the gas phase.
Fig. 2 Cyclic voltammetry of 1.6 ꢄ 10ꢀ3 mol Lꢀ1 2 in ACN + 0.1 mol
L
ꢀ1 Bu4NBF4 at a glassy carbon disk electrode. sweep rate ¼ 0.1 V sꢀ1
(up). Variation of the reduction peak potential Ep with the logarithm
of the scan rates, v in V sꢀ1. Insert: Variations of the reduction peak
potential Ep with the logarithm of the concentration of 2, at 0.2 V
sꢀ1 (down).
4848
Phys. Chem. Chem. Phys., 2003, 5, 4846–4850

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Table 2 Comparison of electrochemical data with B3LYP calcula-
tionsa .
Table 3 Comparison of electrochemical data with B3LYP calcula-
tionsa
DEꢂ
/
theo
DEꢂ
eV
/
exp
Compounds
DAr-SR/kcal molꢀ1
DArS-R/kcal molꢀ1
Compounds Uneutral (a.u.)
Uradical anion (a.u.) eV
1a
1b
3a
3b
62.4
56.5
62.5
62.6
54.7
61.6
55.0
66.0
1a
1b
2
ꢀ1486.647692 ꢀ1486.664777
ꢀ1.36
ꢀ1.10
ꢀ1.45
ꢀ0.89
ꢀ0.79
ꢀ0.47
0.0
ꢀ1.081
ꢀ0.985
ꢀ1.237
ꢀ0.943
ꢀ0.744
ꢀ0.431
0.0
ꢀ1791.473968 ꢀ1791.500621
ꢀ1486.651817 ꢀ1486.665752
ꢀ2113.848332 ꢀ2113.882980
ꢀ2571.1023623 ꢀ2571.140571
ꢀ2571.090022 ꢀ2571.139942
ꢀ3350.693409 ꢀ3350.760573
3a
3b
4
charge will be taken by the SO2 moieties. Both effects are in
agreement with the inversion in the regioselectivity observed
when passing from the alkyl to the aromatic substituents.
The next point is the evolution of the reactivity i.e. passage
from a cleavage reaction to a coupling reaction. The most
remarkable fact is the change of reactivity as illustrated by
the change in the Ep vs. log(v) and Ep vs. log(cꢂ) curves that
corresponds to a dimerization reaction. As a possible explana-
tion, it was suggested that coupling reactions are simply
observed because of a decrease of the cleavage rate with the
number of the sulfonyl groups or positions makes it possible
for other slow reactions to occur. This explanation is not
entirely suitable, as the radical anion lifetimes are shorter for
2 (when the coupling reaction occurs) than for 1 (when the
cleavage reaction occurs). Radical–radical dimerizations are
strongly dependent on the localization and density of the
unpaired electron on the aromatic ring. It is therefore useful
to examine the spin delocalization in the radical anion espe-
cially on the aromatic carbon bearing the sulfone groups and
on the opposite position. Spin densities were calculated using
the B3LYP method and are displayed on Fig. 4. The EPR
spectrum for 1aꢁꢀ has previously been obtained, a good agree-
ment with the calculated spin density is observed.8 When
5
a
Eꢂ for compound 5 is taken as an internal reference.
As seen in Table 2 and Fig. 3, a good correlation is obtained
between the calculated values and the experimental data. The
slope value is lower than the unity (slope ¼ 0.83) that falls in
line with a lesser solvation of the radical anion when the size
of the molecule increases.
Concerning the reactivity of the radical anion, the first
addressed point concerns the higher bond cleavage rate and
the variation of the regioselectivity when R is an aliphatic or
aromatic group (see 1a and 1b for example). In the framework
of the dissociative ET model, the standard free energy of the
dissociation energy of the C–S bond is related to the various
characteristic standard potentials and to the dissociation
energy of the C–S bond.29
DGA0 rSR
¼ DArꢀSR ꢀ ES0Rꢁ=SRꢀ þ EArSR=ArSR
þ T SArSR ꢀSAr ꢀSSR
0
ꢁꢀ!ArꢁþSRꢀ
ꢁꢀ
À
Á
ꢀ
ꢀ
ꢀ
ꢀ
ꢁ
The two main factors governing the selectivity are the bond
dissociation energy D and the oxidation potential of the leav-
ing group. Concerning the bond dissociation energies, the D
values can be estimated by means of B3LYP density functional
calculations (see Table 3) for the disulfones 1a, 1b and trisul-
fones 3a, 3b. When R is an aliphatic group, the a-bond (Ar–
SR) is 7–8 kcal molꢀ1 stronger than the b- (ArS–R) bond.
When R is a phenyl group an opposite situation is observed,
the a-bond becomes weaker than the b-bond by around 3 kcal
molꢀ1. The same effect also affects the kinetics barrier as the
standard intrinsic energy, depends on D, a lower D value leads
to a lower intrinsic barrier.30 Concerning the oxidation poten-
ꢁ
ꢁ
passing from the disulfone 1a to 2 ꢀ, a large increase of the
spin localization on the para (to sulfonyl groups) aromatic
carbon (0.201 and 0.434) together with a large decrease on
the ring carbon adjacent between both sulfone groups (0.289
and 0.128) is observed. This result explains the increase of
the radical–radical coupling reactivity due to an orientation
and localization of the unpaired electron by the two meta
sulfone groups. The same results are expected and found for
the radical anion of trisulfones 3a and 3b.
However, if, in this last case, the radical–radical coupling
process is the most favored process from the spin localization
point of view, the simultaneous increase of the steric hin-
drances leads to a decrease of the dimerization rates. Another
illustration of the localization effect comes from the trisulfone
4, for which a reversible voltammogram is observed. This indi-
cates that the radical anion has a low reactivity versus both the
ꢀ
tial of the fragment that will take the charge, there are no pre-
cise determinations of all the Eꢂ
ꢁ
values. However, two
possibilities exist: the charge is taken either by the carbon
atoms (production of the carbanion) or by the group bearing
SR /SRꢀ
the SO2 (formation of a sulfinate RSO2ꢀ). Since the sulfinate
is always more difficult to oxidize than the carbanion, the
ꢀ
Fig. 3 Variations of experimental Eꢂ with DFT calculations
predictions.
Fig. 4 Spin densities from B3LYP/6-31G* calculations predictions
(iso spin density curves for 0.005 a.u).
Phys. Chem. Chem. Phys., 2003, 5, 4846–4850
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Advances in Electron Transfer Chemistry, ed. P. S. Mariano, JAI
Press, New York, 1994, vol. 4, p. 53 116
bond cleavage and the dimerization, despite the same number
of sulfone groups and an expected lower steric hindrance due
to two adjacent free aromatic carbons.
15 (a) V. W. Poules and R. Praefcke, Chem. Zeit., 1983, 107, 310; (b)
L. Testaferri, M. Tuigoli and M. Tiecco, J. Org. Chem., 1980, 45,
4376; (c) L. Testaferri, M. Tiecco, M. Tuigoli, D. Chianelli and M.
Montanucci, Synthesis, 1983, 751; (d ) D. D. MacNicol, P. R.
Mallison, A. Murphy and G. J. Sym, Tetrahedron Lett., 1982,
23, 4131.
Conclusion
The reactivity of electrogenerated radical anions of sulfone
follows a manifold of mechanisms. The specificity can be
explained by a subtle competition between bond cleavage influ-
ence, by the stability of the different fragments and their bond
energy on the one hand and by the localisation of the unpaired
electron on the other hand. All these parameters have to be
considered to explain a change in the mechanism when intro-
ducing or modifying the position of the sulfone group. A
detailed analysis of the electrochemical data with the help of
DFT calculations allows a clean rationalization of all these
observations.
´
16 D. Garreau and J. -M Saveant, J. Electroanal. Chem., 1972,
35, 309.
17 Gaussian 98 (Revision A.9), M. J. Frisch, G. W. Trucks, H. B.
Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, V. G.
Zakrzewski, J. A. Montgomery, R. E. Stratmann, J. C. Burant,
S. Dapprich, J. M. Millam, A. D. Daniels, K. N. Kudin, M. C.
Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi, R. Cammi,
B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski,
G. A. Petersson, P. Y. Ayala, Q. Cui, K. Morokuma, D. K.
Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman,
J. Cioslowski, J. V. Ortiz, B. B. Stefanov, G. Liu, A. Liashenko,
P. Piskorz, I. Komaromi, R. Gomperts, R. L. Martin, D. J.
Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara,
C. Gonzalez, M. Challacombe, P. M. W. Gill, B. G. Johnson,
M. W. ChenWong, J. L. Andres, M. Head-Gordon, E. S.
Replogle and J. A. Pople, Gaussian, Inc., Pittsburgh PA, 1998.
18 A. D. Becke, J. Chem. Phys., 1993, 98, 5648.
Acknowledgements
19 P. C. Hariharan and J. A. Pople, Chem. Phys. Lett., 1972, 16, 217.
20 (a) Hybrid density functional methods with the 6-31G* base have
been used previously for calculations on neutral and radical cation
of heterocycles containing sulfur atoms and on extended TTF and
found to give a good qualitative description of properties. See for
The authors thank Dr G. Alcaraz and Dr C. Martineau
(University of Rennes 1) for their help and fruitful discussions.
´
example refs. 20b,c and 21c; (b) V. Hernandez, H. Muguruma,
S. Hotta, J. Casado and J. T. Lopez Navarrete, J. Phys. Chem.
´
References
A, 2000, 104, 735; (c) T. Keszthelyi, M. M. -L Grage, J. F.
Offersgaard, R. Wilbrandt, C. Svendsen, O. S. Mortensen, J. K.
Pedersen and H. J. A Jensen, J. Phys. Chem. A, 2000, 104, 2808.
21 J. B. Foresman and A. Frisch, Exploring Chemistry with
Electronic Structure Methods, Gaussian Inc., Pittsburgh, PA,
1996.
1
2
3
J. Simonet, in The chemistry of Sulfones and Sulfoxides, ed.
S. Pata¨ı, Z. Rappoport and C. J. M. Stirling, John Wiley and
sons, New York, 1988, ch. 22, p. 1001.
J. Simonet, in The Chemistry of Sulfur-containing Functional
Groups, ed. S. Pata¨ı and Z. Rappoport, John Wiley and Sons,
New York, 1993, p. 462.
´
22 C. P. Andrieux and J.-M. Saveant, in Investigations of rates
B. Lamm and K. Ankner, Acta Chem. Scand. Ser. B, 1978,
32, 264.
Mechanism of reactions, ed. C. F. Bernasconi, Wiley, New York,
1986, vol. 6, 4/E, Part 2 p. 305–390.
4
5
N. Djeghidjegh and J. Simonet, Electrochim. Acta, 1989, 34, 1615.
(a) P. Cauliez, M. Benaskar, A. Ghanimi and J. Simonet, New J.
Chem., 1998, 253; (b) P. Cauliez, M. Benaskar and J. Simonet,
Electrochim. Acta, 1997, 42, 2191.
23 From reversible or quasi-reversible voltammograms, peak-
potential separations between the cathodic and anodic processes
give a measurement of the kinetics parameters for the heteroge-
neous electron transfer.
6
7
(a) M. Benaskar and J. Simonet, Tetrahedron Lett., 1994, 35,
1727; (b) J. Simonet and H. Lund, Acta Chem. Scand. Ser. B,
1977, 37, 909.
(a) A. Ghanimi, B. Fabre and J. Simonet, New J. Chem., 1998,
831; (b) B. Fabre, P. Hapiot and J. Simonet, J. Phys. Chem. A,
2002, 106, 5422.
M. Benaskar, PhD thesis, University of Rennes 1, France, 1994.
A. Botrel, E. Furet, O. Fourets and J. F. Pilard, New J. Chem.,
2000, 24, 815.
24 By comparison with the reversible one-electron oxidation wave
of ferrocene.
25 Concentration of 2 is 1.6 ꢄ 10ꢀ3 mol Lꢀ1
.
26 C. P. Andrieux, L. Nadjo and J.-M. Saveant, J. Electroanal.
Chem., 1973, 42, 223.
´
27 Concentrations were varied between 7ꢄ10ꢀ4 and 10ꢀ2 mol Lꢀ1
.
ꢁ
ꢀ
8
9
28 The reversibility for 3b/3b was almost total at 0.1 V sꢀ1 for
a 10ꢀ3 mol Lꢀ1 concentration of 3b.
29 (a) C. P. Andrieux, A. Le Gorande and J.-M. Saveant, J. Am.
´
Chem. Soc., 1992, 112, 6892; (b) J.-M. Saveant, J. Phys. Chem.,
´
1994, 98, 3716; (c) C. P. Andrieux, C. Combellas, F. Kanoufi,
10 J.-F. Pilard, O. Fourets, J. Simonet, L. J. Klein and D. G. Peters,
J. Electrochem. Soc., 2001, 148, E171.
´ ´
J.-M. Saveant and A. Thiebault, J. Am. Chem. Soc., 1997,
11 b-Cleavage (formation of the aryl radical and the alkyl sulfinate)
has also been reported for aryl alkyl suphone when the aromatic
ring is substituted by an electron-withdrawing group. (see ref. 10).
12 G. Mabon, M. Chaquid El Badre and J. Simonet, Bull. Soc. Chim.
Fr., 1992, 129, 9.
´
119, 9540; (d ) J.-M. Saveant, in Advances in Physical Organic
Chemistry, ed. T. T. Tidwell, Academic Press, New York, 2000,
vol. 35, p. 177–192 and references therein.
30 According to a development of the dissociative ET model to
the decomposition of radical anion, the standard activation
13 A. Ghanimi and J. Simonet, J. Electroanal. Chem., 1997, 425, 217.
14 (a) J.-M. Save´ant, J. Am. Chem. Soc., 1987, 109, 6788; (b) J.-M.
z
energy depends directly on the bond dissociation energy (DGꢂ
proportional to D/4) (ref. 14).
´
Saveant, Acc. Chem. Res., 1993, 26, 455; (c) J.-M. Saveant, in
´
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