Thiolate chemistry: A powerful and versatile synthetic tool for immobilization/functionalization of oligothiophenes on a gold surface

Article abstract of DOI:10.1002/chem.201003687

The synthesis and characterization of a series of quaterthiophenes (4Ts) with thiolate groups protected with 2-cyanoethyl (CNE), 2-trimethylsilylethyl (TMSE), and acetyl (Ac) groups are described. Sequential cleavage of these different protecting groups allows for the preparation of 4Ts derivatized with ferrocene and/or alkanethiol chains. The electrochemical behavior of these compounds has been analyzed in solution by cyclic voltammetry (CV). A ferrocene-derivatized dithiol 4T 14 and a dithiol 4T 15 with two TMSE-protected thiolate groups have been immobilized on a gold surface as monolayers that have been characterized by CV, ellipsometry, contact-angle measurement, and X-ray photoelectron spectroscopy (XPS). The results show that molecules 14 and 15 are doubly grafted with a horizontal orientation of the conjugated system relative to the surface. Furthermore, application of the deprotection/alkylation sequence of the remaining protected thiolate groups on a monolayer of 15 allows for efficient post-functionalization.

Full text of DOI:10.1002/chem.201003687

DOI: 10.1002/chem.201003687
Thiolate Chemistry: A Powerful and Versatile Synthetic Tool for
Immobilization/Functionalization of Oligothiophenes on a Gold Surface
Truong Khoa Tran,[a] Quentin Bricaud,[a] Maꢀtꢁna OÅafrain,[a] Philippe Blanchard,*[a]
Jean Roncali,*[a] Stꢁphane Lenfant,[b] Sylvie Godey,[b] Dominique Vuillaume,[b] and
David Rondeau[c, d]
Dedicated to Professor Jan Becher
Abstract: The synthesis and characteri-
zation of a series of quaterthiophenes
(4Ts) with thiolate groups protected
with 2-cyanoethyl (CNE), 2-trimethyl-
silylethyl (TMSE), and acetyl (Ac)
groups are described. Sequential cleav-
age of these different protecting groups
allows for the preparation of 4Ts deriv-
atized with ferrocene and/or alkane-
thiol chains. The electrochemical be-
havior of these compounds has been
analyzed in solution by cyclic voltam-
metry (CV). A ferrocene-derivatized
dithiol 4T 14 and a dithiol 4T 15 with
two TMSE-protected thiolate groups
have been immobilized on a gold sur-
face as monolayers that have been
characterized by CV, ellipsometry, con-
tact-angle measurement, and X-ray
photoelectron spectroscopy (XPS). The
results show that molecules 14 and 15
are doubly grafted with a horizontal
orientation of the conjugated system
relative to the surface. Furthermore,
application of the deprotection/alkyla-
tion sequence of the remaining protect-
ed thiolate groups on a monolayer of
15 allows for efficient post-functionali-
zation.
Keywords: conjugation · cyclic vol-
tammetry · molecular electronics ·
monolayers · thiophene
Introduction
[a] Dr. T. K. Tran,+ Dr. Q. Bricaud,+ Dr. M. OÅafrain, Dr. P. Blanchard,
Dr. J. Roncali
Self-assembled monolayers (SAMs) based on electroactive
p-conjugated systems are the subject of high interest on ac-
count of their applications in the fields of molecular elec-
tronics,[1–4] organic electronics,[5] photovoltaic conversion,[6–9]
sensors[10,11] and surfaces with magnetic properties.[12] These
SAMs are generally formed by chemisorption on a semicon-
ducting or metallic surface of a p-conjugated molecule that
bears a fixation group such as thiol, sulfide, thiocyanate, car-
boxylic/phosphonic acids, or silane directly grafted on the p-
conjugated system or through an alkyl linker.[13,14] Interac-
tions between p-conjugated chains reinforced by lipophilic
interactions between alkyl spacers contribute to ensure the
cohesion of the SAMs and the quasivertical orientation of
the conjugated chains on the surface of the substrate.
University of Angers, CNRS
Laboratoire MOLTECH-Anjou
Linear Conjugated Systems Group
2 Bd Lavoisier, 49045 Angers (France)
Fax : (+33)241-73-54-05
E-mail: Philippe.Blanchard@univ-angers.fr
Jean.Roncali@univ-angers.fr
[b] Dr. S. Lenfant, Dr. S. Godey, Dr. D. Vuillaume
Molecular Nanostructures and Devices Group
Institute for Electronics Microelectronics & Nanotechnology
CNRS, University of Sciences and Technologies of Lille
BP60069, Avenue Poincarꢀ
59652 Villeneuve d’Ascq (France)
[c] Dr. D. Rondeau
University of Angers
Service Commun d’Analyses Spectroscopiques
2 Boulevard Lavoisier, 49045 Angers (France)
Compared to the extensively investigated surface-chemis-
try of nonconjugated SAMs,[13,15] the functionalization of
SAMs based on p-conjugated systems is much less devel-
oped. For instance, the extension of p-conjugated systems
grafted onto metal surfaces has been achieved by imine con-
densations.[16] More recently, integration of molecules be-
tween two gold electrodes has been realized by stepwise
synthesis of molecular bridges by using click chemistry.[17]
Click chemistry was also used for covalent grafting of ferro-
cene onto monolayers of phenylethynyl.[18] Gold nanoparti-
cles have been covalently attached on the top of SAMs of
thiophene diblock oligomers.[3c] Donor–acceptor thiophene-
based conjugated systems immobilized on a diamond surface
[d] Dr. D. Rondeau
Current address: Universitꢀ Europꢀenne de Bretagne
Laboratoire de Chimie
ꢁlectrochimie Molꢀculaires et Chimie Analytique
UMR CNRS 6521 du CNRS, UFR Sciences et Techniques
6 avenue Victor Le Gorgeu, 29238 Brest Cedex 3 (France)
[+] These authors contributed equally to the work.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201003687. It includes the syn-
thesis of 3-methylsulfanylthiophene and 10, details on analytical tech-
1
niques, H NMR spectra of 3-methylsulfanylthiophene and com-
pounds 2–11 and 13–15, and potentiodynamic electrooxidation of di-
thiol 15.
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FULL PAPER
have been prepared by covalent grafting of an iodo inter-
mediate followed by a Suzuki coupling,[19a] whereas ferro-
cene redox probes have been introduced on biphenyl deriva-
tives adsorbed onto glassy carbon by electrochemical activa-
tion.[19b]
droxide ions, n-butyllithium),[37–39] and 2) a 2-trimethylsilyl-
ethyl (TMSE) group that is stable under the previous condi-
tions but that can be cleaved in the presence of fluoride
anions.[3c,40]
The synthesis of 7 is depicted in Scheme 1. Regioselective
bromination at the 2-position of 3-(2-cyanoethylsulfanyl)-
As reviewed recently,[20] SAMs that involve oligothio-
phenes have been widely investigated[3c,d,21–31] and used for
AHCTUNGTRENNUNG
thiophene (1)[38] by N-bromosuccinimide (NBS; 1 equiv) in
applications
in
molecular junctions,[25] diodes,[3c,d,f]
dimethylformamide (DMF)[41] led to compound 2. The CNE
protecting group of 2 was then replaced by a TMSE group.
switches,[26] field-effect transistors,[5d,e] mass spectrometry,[27]
chemosensors,[28] or photovoltaic devices.[6c,d,9a]
Whereas most of this work has concerned monolayers of
singly attached conjugated molecules in a quasivertical ori-
entation on the surface, few approaches have been devoted
to the elaboration of SAMs with oligothiophenes horizontal-
ly oriented with respect to the surface.[23,32–34] In particular,
the double fixation of a p-conjugated system with a con-
trolled horizontal orientation can be of both fundamental
and technical interest.[34,35] Besides an improved stability re-
lated to multiple anchoring sites,[5f,9a,34] such horizontal ori-
entation is considerably more efficient for absorption of in-
cident light.[6d] On the other hand, the possibility to achieve
a direct through-space charge transfer between the conjugat-
ed system and the metal electrode instead of the through-
bond transfer associated with the usual vertical fixation can
help to enrich the toolbox for the design of molecular-elec-
tronic devices.
We have recently shown that substitution of a p-conjugat-
ed 4T by two alkylthiol chains introduced at the internal b
positions of the two terminal thiophene rings allows for the
efficient horizontal double fixation onto a gold surface.[36]
As a further step, we present here a versatile synthetic strat-
egy for the preparation of functionalized surfaces based on
doubly fixed oligothiophenes. To this end, a series of 4Ts
functionalized with thiolate groups protected with 2-cya-
noethyl (CNE), 2-trimethylsilylethyl (TMSE), and acetyl
(Ac) groups has been synthesized. Sequential cleavage of
these different protecting groups leads to the stepwise prep-
aration of 4Ts functionalized with ferrocene units and/or
two alkanethiol chains.
The electrochemical properties of these compounds have
been analyzed in solution, and their immobilization as mon-
olayers on gold has been investigated. The structure and the
properties of the monolayers are discussed on the basis of
results of cyclic voltammetry, ellipsometry, contact-angle
measurement, and X-ray photoelectron spectroscopy (XPS).
Furthermore, surface chemistry on chemically active mono-
layers has been tested by means of thiolate deprotection
and subsequent S-alkylation by using a ferrocene probe.
Scheme 1. Synthesis of compound 7.
Thus deprotection of the thiolate group of 2 with CsOH
(1 equiv) and subsequent reaction with (2-bromoethyl)tri-
methylsilane 4 gave compound 3 in almost quantitative
yield. Symmetrical 2,2’-bithiophene 5 was prepared in 60%
yield from compound 3 after lithium–bromine exchange
with nBuLi (1 equiv) at low temperature and further oxida-
tive coupling of the resulting anion in the presence of
CuCl2.[42] Treatment of 5 with 2.5 equiv of nBuLi and subse-
quent addition of Bu3SnCl afforded the 5,5’-distannyl deriv-
ative 6, which was engaged in the following Stille reaction
without purification. Heating at reflux a mixture of 6 and
bromo derivative 2 (2.5 equiv based on 5) in the presence of
catalytic amount of tetrakis(triphenylphosphine)palladi-
um(0) in toluene led to the target 4T 7 in 72–80% yields
based on compound 5.
Results and Discussion
Compound 4 was readily synthesized according to an anti-
Markovnikov addition of HBr on vinyltrimethylsilane
(Scheme 2). Compared to previous synthetic procedures of
4,[43–45] HBr was generated in situ by reaction of PBr3 and
silica gel in CH2Cl2.[46]
Synthesis: The key to our strategy relies on the preparation
of 4T 7 in which each thiophene ring bears a masked thio-
late group at the 3- or 4-position. Two types of thiolate pro-
tecting groups have been used: 1) a 2-cyanoethyl (CNE)
group that can be deprotected in basic conditions (e.g., hy-
The deprotection conditions of the two different types of
masked thiolate group of compound 7 have been investigat-
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P. Blanchard, J. Roncali et al.
The synthesis of dithiol compounds 14 and 15 is described
in Scheme 5. Two alkylsulfanyl chains with terminal acetyl-
protected thiol were first introduced in compound 11. Selec-
tive cleavage of the CNE groups of 7 with CsOH (2 equiv)
and subsequent reaction of the resulting dithiolate salts with
an excess amount of S-4-bromobutyl ethanethioate 12 led to
11 in 72% yield. Thiol ester 12 was prepared in 63% yield
Scheme 2. Synthesis of (2-bromoethyl)trimethylsilane (4).
ed. As reported previously,[3c] fluoride anions can cleave the
CNE groups of 7 due to their basicity. In fact, treatment of
1 with Bu4NF in tetrahydrofuran (THF) followed by addi-
tion of CH3I gave 3-methylsulfanylthiophene in 60% yield
(see the Supporting Information). The sequential deprotec-
tion of the thiolate groups of 7 was tested as shown in
Scheme 3. Treatment of compound 7 with CsOH (2.2 equiv)
in methanol and reaction with an excess amount of CH3I af-
forded compound 8 in 69% yield. Treatment of 8 with
Bu4NF in THF[40a,b] led to a dithiolate compound, which,
upon addition of 4-bromobutylferrocene 10, gave the ferro-
cenyl-functionalized 4T 9 in 80% yield.
Scheme 3. Functionalization of 7.
Scheme 5. Synthesis of dithiols 14 and 15.
Reagent 10 was prepared
using a known procedure (see
the Supporting Information).[47]
To confirm the versatility of the
proposed synthetic approach,
monolayers of doubly attached
functionalized 4Ts were pre-
pared by two distinct routes,
(Scheme 4) namely, immobiliza-
tion of the ferrocenyl-function-
alized dithiol 14 (route 1) and
the post-functionalization of a
monolayer of dithiol 15 by
using the remaining TMSE-pro-
tected thiolate groups (route 2). Scheme 4. Different routes to ferrocenyl-functionalized 4T fixed on gold.
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Thiolate Chemistry
FULL PAPER
by treating potassium thioacetate with 1,4-dibromobutane
(1.5 equiv) as previously reported.[36,48]
Dithiol 14 was prepared in high yield from compound 13
after reduction of the thioester groups by using diisobutyl-
ACHTUNGTRENNUNGaluminum hydride (DIBAl-H) in anhydrous CH2Cl2 fol-
lowed by addition of HCl. Compound 13 was obtained after
treatment of 11 with Bu4NF in THF and subsequent alkyla-
tion reaction with an excess amount of ferrocenyl derivative
10. Although the yield remains modest (25%), the access to
dithioester 13 from 11 shows that it is possible to selectively
cleave the two TMSE groups of 11 in the presence of fluo-
ride anions while preserving the thioacetyl ester groups.[40a,49]
Dithiol 15 was synthesized by saponification of dithioester
11 in the presence of CsOH.
Electrochemical and optical properties in solution: The elec-
trochemical and optical properties of the 4Ts have been an-
alyzed by cyclic voltammetry and UV/Vis spectroscopy. The
anodic peak potentials (Epa) and absorption maxima are
listed in Table 1.
Figure 1. Cyclic voltammograms of compounds 8 and 9 (1 mm in 0.10m
Bu4NPF6 and CH2Cl2/CH3CN (1:1), scan rate 0.1 VsÀ1, Pt working elec-
trode, saturated calomel electrode (SCE) reference electrode).
with that of 13 reveals a slight broadening of the electro-
chemical response in the 0.70–1.20 V region, which can be
attributed to the oxidation of the thiol groups of 14.
Table 1. Absorption maxima (in CH2Cl2) and oxidation peak potentials
of 4Ts (1 mm in 0.10m Bu4NPF6 and CH3CN/CH2Cl2 (1:1 v/v), scan rate
100 mVsÀ1, Pt working electrode and SCE reference electrode).
In fact, application of recurrent potential scans between
À0.10 and 1.40 V to a solution of dithiol 14 leads to the pro-
gressive development of a broad redox system between 0.60
and 1.20 V with a sharp redox peak at around 0.45 V due to
Fc units (Figure 3). This behavior is indicative of the electro-
deposition of a polydisulfide material that results from the
oxidation of thiol groups, as previously observed.[36] Exami-
nation of the first CV traces of 14 (Figure 3, top) clearly
shows that in addition to the redox waves associated with
the 4T and Fc units, a new redox system appears around
0.75 V. This suggests that besides polydisulfide formation,
some coupling of the 4T radical cation that leads to more ex-
tended conjugated chains also occurs. This result contrasts
with the behavior of dithioesters 11 and 13 for which the
stability of the cation radical is confirmed by the reversibili-
ty of the oxidation process. A possible explanation for this
different behavior could involve a more favored coupling of
the 4T radical cation of 14 in the confined environment of
the polydisulfide film.
The CV of the polymer recorded in a monomer-free
medium (Figure 3, middle), shows a good stability upon cy-
cling between 0.2 and 1.2 V/SCE. In addition to the intense
oxidation peak at 0.47 V related to the Fc units and the
broad wave centered at 0.90 V due to the two oxidation
steps of the 4T backbone, the persistence of a redox system
at around 0.75 V confirms the presence of a more extended
conjugated system.
Fc
pa
SH
pa
Compound
lmax [nm]
E
[V]
E
[V]
E1pa [V]
E2pa [V]
7
8
9
11
13
14
15
275, 392
276, 388
299 (sh), 385
297, 390
295 (sh), 390
295 (sh), 389
298, 391
–
–
–
–
–
–
0.85
0.72
0.84
0.74
0.82
0.91
0.78
1.04
0.91
0.96
0.91
0.93
1.02
0.98
–
0.41
–
0.37
0.45
–
–
0.67
The CV results of all 4T derivatives exhibit two one-elec-
tron reversible oxidation waves at E1pa and Ep2a, which corre-
spond to the successive formation of the radical cation and
dication (Table 1). Replacement of the CNE groups of 7 by
methyl (8) produces a 130 mV negative shift of E1pa and Ep2a
due to the suppression of the electron-withdrawing effect of
the cyano groups.
The presence of the ferrocenyl (Fc) groups in 4T 9 is con-
firmed by the intense reversible oxidation wave of the Fc/
Fc+ couple at 0.41 V (Figure 1). The occurrence of a single
well-resolved oxidation peak for the two Fc units suggests
an absence of interaction between them. Replacement of
the TMSE groups of 8 by two Fc units (9) leads to 120 and
50 mV positive shifts of E1pa and Ep2a, respectively, probably
due to the suppression of the electron-donating effect of the
TMSE moiety.
Compounds 8 and 11 show close E1pa and Ep2a values that
are in agreement with their similar structures. As for 9, the
For dithiol 15, the CV shows an irreversible oxidation
peak that corresponds to the oxidation of the thiol groups at
SH
pa
CV of compound 13 exhibits the typical signature of the Fc
E =0.67 V (Figure 4). The oxidation of the 4T system in
units (E =0.37 V) and 4T core (E1pa =0.82 V and Ep2a =
radical cation and in dication occurs at E1pa =0.78 V and
E2pa =0.98 V, respectively. Interestingly, the passage from di-
thioester 11 to dithiol 15 leads to a 40 mV and a 70 mV posi-
tive shift of E1pa and Ep2a, respectively. These positive shifts
Fc
pa
0.93 V). Integration of the peaks of the deconvoluted CV of
13 gives results consistent with a ratio of two Fc units per
4T (Figure 2). Comparison of the CV results of dithiol 14
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5631

P. Blanchard, J. Roncali et al.
Figure 2. Cyclic voltammograms (top) and deconvoluted cyclic voltammograms (bottom) of dithioester 13 (left) and dithiol 14 (right) (1 mm in 0.10m
Bu4NPF6 and CH2Cl2/CH3CN (1:1), scan rate 0.1 VsÀ1, Pt working electrode, SCE reference electrode).
are even more pronounced when comparing the CV results
of dithioester 13 and dithiol 14 (Table 1). This phenomenon
may arise from the rapid modification of the electrode sur-
face by electrodeposition of polydisulfide (vide supra) or by
chemical adsorption of thiols 14 and 15 on Pt during CV
measurement. In fact, application of recurrent potential
scans between À0.10 and 1.40 V/SCE to solutions of dithiol
15 leads to the electrodeposition of a polydisulfide material
as in the case of dithiol 14 (see Figure S16 in the Supporting
Information).
solution. The sharp and symmetrical electrochemical re-
sponse of the Fc units shows that they do not interact
strongly after immobilization.[13e] The similarity of the sur-
face area of the two waves is consistent with two-electron
processes that correspond to Fc units on one hand, and the
radical cation and dication of 4T on the other. The linear
variation of the peak current versus scan rate confirms that
molecules 14 are immobilized on the electrode surface.
The surface coverage (G) of molecules 14 has been deter-
mined by integration of the voltammetric peak of the ferro-
cene or that of the 4T signal after correction for double
layer charge.[52] Values of G=2ꢃ10À10 molcmÀ2 (1.2ꢃ
1014 moleculescmÀ2 or 83.4 ꢄ2 per molecule) and G=2.5ꢃ
10À10 molcmÀ2 (1.5ꢃ1014 moleculescmÀ2 or 66.7 ꢄ2 per mole-
cule) were obtained. These results are in close agreement
with previous results for doubly fixed 4T[36] and consistent
with the horizontal orientation of the 4T chain expected for
a double grafting. The CV results of the monolayer of 14 re-
mained unchanged after 400 cycles between À0.10 and
1.40 V, thus confirming its good stability.
Preparation and cyclic voltammetry of monolayers of 4Ts 14
and 15: Dithiols 14 and 15 were subjected to chromatogra-
phy before monolayer preparation to avoid disulfide forma-
tion.[36,50,51] Monolayers were prepared under an argon at-
mosphere by immersion of cleaned gold-bead electrodes in
a millimolar solution of compound 14 or 15 in CH2Cl2 for a
period of 2 or 3 days. The resulting electrodes were then
rinsed with pure CH2Cl2 and CH3CN before immersion in
CH2Cl2 for 4 h to eliminate physisorbed molecules.
The CV results of monolayer of 14 shows a reversible
sharp oxidation peak at 0.45 V that corresponds to the oxi-
dation of the Fc units (Figure 5). A broad reversible wave
centered at 1.12 V is associated to the oxidation of the 4T
backbone. Thus, immobilization of 14 leads to a coalescence
of the two distinct one-electron oxidation waves observed in
The CV of the monolayer of 15 (Figure 6) exhibits a
broad reversible oxidation wave centered at 1.07 V; as for
monolayer of 14, this wave can be attributed to the two oxi-
dation processes of the 4T backbone. Again, the linear scan-
rate dependence of the peak current versus scan rate con-
firms the surface immobilization of the molecules, whereas
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Thiolate Chemistry
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Figure 4. Cyclic voltammograms of dithioester 11 and dithiol 15 (1 mm in
0.10m Bu4NPF6 and CH2Cl2/CH3CN (1:1), scan rate 0.1 VsÀ1, Pt working
electrode, SCE reference electrode).
Figure 5. Top: cyclic voltammogram of the monolayer of 14 in 0.10m
Bu4NPF6/CH3CN, scan rate=20 VsÀ1, SCE reference electrode. Bottom:
variation of the peak intensity related to the oxidation of ferrocene
versus scan rate.
Figure 3. Potentiodynamic electrooxidation of a 2 mm solution of dithiol
14 in 0.10m Bu4NPF6/CH2Cl2 (top) and a cyclic voltammogram of the re-
sulting material deposited on a Pt working electrode in 0.10m Bu4NPF6/
CH3CN, scan rate 0.1 VsÀ1 (middle), SCE reference electrode.
Structural characterization of monolayers of 14 and 15:
Monolayers of 14 and 15 were prepared on an evaporated
gold layer (200 nm) on silicon wafers recovered by a 10 nm
layer of titanium. The thickness of the monolayers was de-
termined by ellipsometry, which gave values of (19Æ2) ꢄ
and (16Æ2) ꢄ, respectively for 14 and 15. These values are
in good agreement with a monolayer formation and with the
calculated 21–22 and 18–19 ꢄ height for molecules 14 and
the absence of modification of the CV after 200 scans be-
tween À0.20 and 1.20 V indicates the good stability of the
monolayer. The estimated G value of 1.5ꢃ10À10 molcmÀ2 is
consistent with the formation of a monolayer.[53–55]
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P. Blanchard, J. Roncali et al.
Table 2. XPS binding energies (BE), full width at half-maximum
(FWHM), and assignment of emission peaks measured from high-resolu-
tion XPS of monolayers of 14 and 15 adsorbed on gold.
XPS
signal
BE
[eV]
FWHM
[eV]
Corrected area[a]
[A.U.]
Assignment
monolayer of 14
C 1s
S 2s
284.6
227.6
1.20
2.59
19610
3440
3416
1656
828
C 1s
S 2p[b]
band 1
band 2
band 3
band 4
Fe 2p
band 1
band 2
À
3
163.4
164.6
161.9
163.1
1.24
1.24
1.24
1.24
S 2p =
S 2p =
S 2p = Au
S 2p = Au
C
À
C
2
1
2
À
3
463
232
2
À
1
2
1
720.5
707.7
1.20
1.20
186
530
Fe 2p =
Fe 2p =
2
3
2
monolayer of 15
C 1s
S 2s
284.7
227.8
1.37
2.50
27057
6202
5665
3126
1563
898
C 1s
S 2p[b]
band 1
band 2
band 3
band 4
À
3
163.6
164.8
161.9
163.0
1.12
1.12
1.12
1.12
S 2p =
S 2p =
S 2p = Au
S 2p = Au
C
À
C
2
1
2
À
3
2
À
1
449
2
[a] The corrected areas were calculated using empirically derived sensi-
bility factors (C 1s: 0.3; S 2s: 0.4; S 2p: 0.57; Fe 2p: 2.7). Each measured
peak area was divided by this factor to obtain the corrected area. The
1
3
2
total corrected areas of each peak are in italics. [b] The ratio S 2p = /S 2p =
2
Figure 6. Top: cyclic voltammogram of the monolayer of 15 in 0.10m
Bu4NPF6/CH3CN, scan rate=20 VsÀ1, SCE reference electrode. Bottom:
variation of the intensity of the oxidation peak versus scan rate.
for the related shifts in binding energy were fixed to 0.52 and 1.17 eV, re-
spectively.[58]
15, respectively, in the conformation expected for double
fixation (Figure 7). These latter values have been estimated
spectra of the S 2p region of monolayers of 14 and 15 are
given in Figure 8.
À
with the MOPAC 3D software and assuming a S Au dis-
Comparison of the peak area of the S 2s or S 2p signals to
that of the C 1s signal provides an estimation of the S/C
ratio in the monolayer. In the case of monolayer of 14, the S
2p/C and S 2s/C ratios of 0.18 is very close to the theoretical
value of S/C=10:52=0.19. As expected, the spectrum
shows the presence of iron atoms with a Fe/C ratio of 0.037
for a theoretical value of Fe/C=2:52=0.038. The Fe 2p
tance of about 2 ꢄ.[56]
1
binding energies observed for the iron doublet Fe 2p = and
2
1
Fe 2p = at 720.5 and 707.7 eV, respectively, are in good
2
agreement with literature values.[57] For monolayer of 15,
the S 2p/C and S 2s/C ratios of 0.21 and 0.22, respectively,
deviate slightly from the theoretical value (S/C=10:34=
0.29). Thus the chemical composition determined by XPS
for each monolayer confirms the immobilization of 14 and
15 on the gold surface.
The high-resolution XPS spectra of the S 2p region
(Figure 8) are decomposed in individual contributions. The
curve-fitted high-resolution XPS spectra for the S 2p region
of monolayers of 14 and 15 show two doublets. Each dou-
blet results from spin–orbit splitting of the S 2p level and
Figure 7. Molecular structures of dithiols 14 (left) and 15 (right) drawn
from ellipsometry data in a conformation that leads to a double fixation
on gold (from MOPAC-ChemDraw 3D optimization).
The relatively high values of water contact angle for mon-
olayers of 14 (qH O =(87Æ2)8) and 15 (qH O =(91Æ2)8) show
2
2
3
that these surfaces present an hydrophobic character that
can be explained by the presence of the aromatic ferrocenyl
groups or the lipohilic TMSE groups on the top of the sur-
face.[3d,53]
consists of a high-intensity S 2p = peak at lower energy and
2
1
a low-intensity S 2p = peak at higher energy separated by
2
1.2 eV with an intensity ratio of 2:1.[58] The value of the S
3
2p = peak at around 161.9 eV for monolayers of 14 and 15 is
2
Monolayers of 14 and 15 have been analyzed by XPS. The
binding energies (BE) of C 1s, S 2s, S 2p, and Fe 2p signals
are reported in Table 2, whereas the high-resolution XPS
in excellent agreement with the binding energy for bound
alkanethiolate on gold (161.9–162.0 eV).[53,59] Thus, peaks at
3
1
161.9 and 163.1 eV of the lower-energy doublet S 2p = , = of
2
2
5634
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ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 5628 – 5640

Thiolate Chemistry
FULL PAPER
Figure 8. Curve-fitted, high-resolution XPS spectra for the S 2p region of molecules 14 (top) and 15 (bottom) adsorbed on gold.
monolayers of 14 (161.9 and 163.0 eV for 15) may be as-
THF for 0.5 h, and finally washed thoroughly with THF. The
signed to the thiol chemisorbed on the Au surface.[58–60]
post-functionalization process has been followed by CV
analysis (Figure 9). The CV results of monolayer of 15 after
treatments show a broad oxidation wave centered at approx-
imately 1.10 V/SCE, which is associated to the radical cation
and the dication of the 4T system. More importantly, a new
intense and reversible oxidation peak at around 0.40 V/SCE,
which corresponds to the oxidation of Fc units, is also ob-
served. The estimated 1:1 ratio between the areas of these
two oxidation waves suggests an efficient post-functionaliza-
tion process (Scheme 6). In a control experiment, monolay-
ers of 15 were treated with ferrocenyl derivative 10 in THF
and thoroughly washed with THF. In this case, the absence
of electrochemical signature of ferrocene indicates that mol-
ecules 10 do not physisorb on the monolayer, thus confirm-
ing that the functionalization of monolayer of 15 by Fc units
results from a nucleophilic substitution of molecules 10 by
thiolate groups generated from 15 on the surface.
3
1
The other doublet S 2p = , = at 163.4 and 164.6 eV for 14
2
2
(163.6 and 164.8 eV for 15) corresponds to the other sulfur
atoms of compound 14 (or 15). Comparison of the areas of
À
À
these two doublet signals leads to an estimated S C/S Au
ratio of g=3.6Æ1, which is in agreement with the expected
À
À
value (S C/S Au =4) for a double fixation of molecule 14
on gold by formation of two S Au bonds. For molecule 15,
À
À
À
a S C/S Au ratio of 3.5Æ1 has been obtained also relative-
ly close to the theoretical value expected for a double fixa-
À
À
tion (S C/S Au =4). The grafting of molecules 14 or 15 by
À
a single S Au bond would lead to a theoretical ratio of g=
9, which is quite far from experimental values. Thus, XPS re-
sults and ellipsometry measurements confirm that the major-
ity of molecules 14 and 15 are doubly fixed on the gold sur-
face as shown in Figure 7.
Post-functionalization of monolayer of 15: In a glovebox
(argon atmosphere), a monolayer of 15 on gold beads has
been immersed in a 1m solution of Bu4NF in anhydrous
THF for 20 min, then rapidly rinsed with THF, immediately
immersed in a 10 mm solution of ferrocenyl derivative 10 in
Finally, the similarity of the CV of the 4T system in the
monolayer of 15 and that observed after covalent grafting of
ferrocene in Figure 9 suggests that the surface coverage of
molecules is practically unaffected by the post-immobiliza-
tion functionalization. On the other hand, the calculated
Chem. Eur. J. 2011, 17, 5628 – 5640
ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5635

P. Blanchard, J. Roncali et al.
direct grafting of Fc-containing molecules or by post-func-
tionalization of monolayer of 15 by cleavage and S-alkyla-
tion of the remaining protected thiolates.
Characterization of the monolayers by cyclic voltammetry,
ellipsometry, water contact-angle measurements, and XPS
provide coherent results that indicate that the molecules are
doubly attached on the surface with a horizontal orientation
of the main axis of the 4T system. These results that illus-
trate the rich potentialities of the versatile thiolate chemis-
try can open interesting perspectives for future develop-
ments in sensors and molecular electronics.
Experimental Section
1H and 13C NMR spectra were recorded at 500.13 and 125.7 MHz, respec-
tively; chemical shifts (d) are given in ppm relative to TMS, and coupling
constants (J) are in Hz. IR spectra were recorded by using samples em-
bedded in KBr disks or thin films between NaCl plates. Melting points
are uncorrected. The synthesis of bromobutylferrocene is described in
the Supporting Information following a known procedure.[47]
Figure 9. Cyclic voltammograms of the monolayer of 15 before (dotted
line) and after treatment with Bu4NF and then compound 10 (solid line).
Cyclic voltammograms were recorded in 0.10m Bu4NPF6/CH3CN, scan
rate=20 VsÀ1, SCE reference electrode.
2-Bromo-3-(2-cyanoethylsulfanyl)thiophene (2): A solution of N-bromo-
succinimide (2.91 g, 17.7 mmol) in
DMF (15 mL) was added dropwise to
a
solution of compound 1 (3.0 g,
17.7 mmol) in DMF (20 mL) under N2
at 08C in the absence of light. The
mixture was stirred 4 h at 208C, con-
centrated in vacuo, and the residue
was diluted with CH2Cl2 (200 mL).
The organic phase was washed with
water, dried over Na2SO4, evaporated
in vacuo, and subjected to chromatog-
raphy on silica gel (1:1 CH2Cl2/petrole-
um ether (PE)) to give a white solid
(3.69 g, 84% yield). M.p. 40–418C;
1H NMR (500 MHz, CDCl3): d=2.57
3
3
(t, J=7.5 Hz, 2H), 3.05 (t, J=7.5 Hz,
2H), 7.00 (d, 3J=5.7 Hz, 1H),
7.32 ppm
(d,
3J=5.7 Hz,
1H);
Scheme 6. Formation of monolayer of 14 by means of post-functionalization of the monolayer of 15.
13C NMR (125 MHz, CDCl3): d=18.6,
30.8, 117.8, 118.5, 126.8, 129.6,
131.5 ppm; IR (KBr): n˜ =2246 cmÀ1
(CN); elemental analysis calcd (%) for
value of G (ꢀ1.5ꢃ10À10 molcmÀ2), which is slightly lower
C7H6BrNS2: C 33.88, H 2.44, S 25.84, N 5.64; found: C, 33.88, H, 2.38, S,
25.54, N, 5.62.
than that observed for the monolayer of 14 (G=2–2.5ꢃ
10À10 molcmÀ2) and the broadening of the electrochemical
response of post-functionalized monolayer of 15 compared
to that of the monolayer of 14 can be related to a weaker or-
ganization of the native monolayer of 15.
2-Bromo-3-(2-trimethylsilylethylsulfanyl)thiophene (3): Under an N2 at-
mosphere, a solution of CsOH.H2O (5.36 g, 31.9 mmol) in N2-degassed
MeOH (15 mL) was added dropwise to
a solution of 2 (7.20 g,
29.0 mmol) in degassed DMF (50 mL). The reaction mixture was stirred
for 1 h at 208C before addition of a solution of bromo derivative 4
(7.36 g, 40.6 mmol) in degassed DMF (15 mL). After 4 h of additional
stirring at 208C and evaporation of the solvents, the residue was dis-
solved in CH2Cl2 and the organic phase was washed with water, dried
over MgSO4, and concentrated under reduced pressure. Purification by
chromatography on silica gel (9:1 PE/CH2Cl2 as eluent) gave compound
3 as yellow oil (8.10 g, 95% yield). Note that 3 slowly decomposes when
stored at +48C, hence it is preferable to use it quite rapidly after synthe-
Conclusion
We have described a versatile synthetic approach that
allows for multiple functionalizations of oligothiophene de-
rivatives. Our strategy is based on the concomitant use of
different thiolate protecting groups. The different conditions
of deprotection of these groups allow for a sequential func-
tionalization of the 4T skeleton. To illustrate the potentiali-
ties of this approach, stable monolayers of 4T derivatives
functionalized with Fc units have been prepared either by
sis. 1H NMR (500 MHz, CDCl3): d=7.26 (d, 3J=5.4 Hz, 1H; H5thio), 6.92
3
(d, J=5.4 Hz, 1H; H4thio), 2.92–2.88 (m, 2H; CH2 S), 0.90–0.86 (m, 2H;
À
CH2 Si), 0.02 ppm (s, 9H; CH3 Si); 13C NMR (125 MHz, CDCl3): d=
133.2, 130.1, 125.8, 113.5, 31.0, 17.5, À1.8 ppm; MS (70 eV): m/z (%): 296
À
À
(100) and 294 (100) [M+ ], 268 (18) and 266 (18), 253 (46) and 251 (46);
C
elemental analysis calcd (%) for C9H15BrS2Si: C 36.74, H 5.14; found: C
37.55, H 5.13.
5636
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ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 5628 – 5640

Thiolate Chemistry
FULL PAPER
(2-Bromoethyl)trimethylsilane (4): Under an N2 atmosphere, a solution
of phosphorus tribromide (4.10 mL, 22.5 mmol) in anhydrous CH2Cl2 was
added dropwise to a mixture of vinyltrimethylsilane (10 mL, 67.8 mmol)
and silica gel (30 g) in anhydrous CH2Cl2 cooled to À108C. After 10 min
of stirring at À108C, the reaction mixture was allowed to warm to 208C
over a period of 0.5 h, after which silica gel was separated by filtration.
The filtrated solution was washed with a saturated aqueous solution of
Na2CO3, dried over Na2SO4, and concentrated to dryness to give pure 4
as slightly yellow oil (6.30 g, 51% yield). Note that 4 slowly decomposes
at room temperature or when stored at +48C, hence it is preferable to
organic phase was washed with water, dried over MgSO4, and concentrat-
ed under reduced pressure. Purification by chromatography on silica gel
(6:4 PE/CH2Cl2 as eluent) gave compound 8 as yellow oil (0.28 g, 69%
yield). 1H NMR (500 MHz, CDCl3): d=7.32 (s, 2H; Hthio), 7.23 (d, 3J=
5.3 Hz, 2H; Hthio), 7.05 (d, 3J=5.3 Hz, 2H; Hthio), 2.93–2.90 (m, 4H;
À
À
À
CH2 S), 2.49 (s, 6H; CH3 S), 0.94–0.90 (m, 4H; CH2 Si), 0.00 ppm (s,
18H; CH3 Si); 13C NMR (125 MHz, CDCl3): d=135.4, 132.9, 132.6,
À
131.9, 130.5, 130.2, 129.2, 123.9, 32.1, 18.8, 17.5, À1.7 ppm; UV/Vis
(CH2Cl2): l (loge)=276 (4.63), 388 nm (4.23); MS (MALDI): m/z: 686
[M+ ].
C
1
use it quite rapidly after synthesis. H NMR (500 MHz, CDCl3): d=3.59–
Compound 9: Under an N2 atmosphere, a solution of tetrabutylammoni-
um fluoride (1m) in THF (1.40 mL, 1.40 mmol) was added dropwise to a
solution of 8 (0.24 g, 0.35 mmol) in anhydrous THF (4 mL). The solution
turned rapidly from yellow to violet. The reaction mixture was stirred
under ultrasound for 1.5 h before the addition of compound 10 (0.56 g,
1.75 mmol) dissolved in anhydrous THF (5 mL) to afford an orange color
to the reaction mixture, which was left under stirring overnight. After
evaporation of the solvent and the subsequent addition of CH2Cl2, the so-
lution was washed with water, dried over MgSO4, and concentrated
under reduced pressure. Purification by chromatography on silica gel
(from an 8:2 to a 1:1 mixture of PE/CH2Cl2 as eluent) led to compound 9
À
À
3.55 (m, 2H; CH2 Br), 1.39–1.36 (m, 2H; CH2 Si), 0.04 ppm (s, 9H;
À
CH3 Si).
3,3’-Bis(2-trimethylsilylethylsulfanyl)-2,2’-bithiophene (5): Under an N2
atmosphere, a solution of nBuLi 1.6m in hexanes (13.2 mL, 21.1 mmol)
was added dropwise to a solution of 3 (5.95 g, 20.1 mmol) in anhydrous
Et2O (100 mL) cooled to À788C. After 0.5 h of additional stirring at
À788C, copper(II) chloride 99.995% (2.8 g, 20.8 mmol, Aldrich) was
added in one portion to the reaction mixture. The latter was further
stirred at À788C for 15 min, warmed to 208C, and stirred at 208C over-
night. After dilution with Et2O (150 mL), the organic phase was washed
with water, dried over MgSO4, and concentrated under reduced pressure.
Purification by chromatography on silica gel (8:2 PE/CH2Cl2 as eluent)
1
as brown oil (0.27 g, 80% yield). H NMR (500 MHz, CDCl3): d=7.34 (s,
2H; Hthio), 7.24 (d, 3J=5.2 Hz, 2H; Hthio), 7.05 (d, 3J=5.2 Hz, 2H; Hthio),
gave compound
5 as a
yellow oil (2.59 g, 60% yield). 1H NMR
3
4.13 (s, 10H; HFc), 4.09 (s, 4H; HFc), 4.07 (s, 4H; HFc), 2.85 (t, J=7.0 Hz,
(500 MHz, CDCl3): d=7.37 (d, 3J=5.3 Hz, 2H; Hthio), 7.07 (d, 3J=
3
À
À
À
4H; CH2 S), 2.49 (s, 6H; CH3 S), 2.24 (brt, J=6.6 Hz, 4H; CH2 Fc),
1.63 (m, 4H; CH2), 1.55 ppm (m, 4H; CH2); 13C NMR (125 MHz,
CDCl3): d=135.6, 132.9, 132.7, 131.7, 130.5, 130.3, 129.3, 124.0, 88.9, 68.4,
68.0, 67.0, 36.1, 30.1, 29.4, 29.1, 18.8 ppm; UV/Vis (CH2Cl2): l (loge)=
À
À
5.3 Hz, 2H; Hthio), 2.85–2.82 (m, 4H; CH2 S), 0.84–0.82 (m, 4H; CH2
Si), À0.02 ppm (s, 18H; CH3 Si); 13C NMR (125 MHz, CDCl3): d=132.2,
À
132.1, 130.5, 125.9, 31.7, 17.4, À1.8 ppm; UV/Vis (CH2Cl2): l=279 nm;
MS (MALDI): m/z: 447 [M+ +17], 430 [M ]; elemental analysis calcd
+
C
C
299 (sh), 385 nm (4.25); MS (MALDI): m/z: 966 [M+ ].
C
(%) for C18H30S4Si2: C 50.22, H 7.03; found: C 49.98, H 6.99.
Compound 11: Under a N2 atmosphere, a solution of CsOH.H2O (0.96 g,
5.76 mmol) in N2-degassed MeOH (5 mL) was added dropwise to a solu-
tion of 7 (2 g, 2.62 mmol) in degassed DMF (25 mL). The reaction mix-
ture was stirred for 1 h at 208C before addition of a solution of bromo
derivative 12 (1.40 g, 6.55 mmol) in degassed DMF (10 mL) . After 4 h of
additional stirring at 208C and evaporation of the solvents, the residue
was dissolved in CH2Cl2 and the organic phase was washed with water,
dried over MgSO4, and concentrated under reduced pressure. Purification
by chromatography on silica gel (1:2 PE/CH2Cl2 as eluent) gave com-
pound 11 as orange oil (1.73 g, 72% yield). 1H NMR (500 MHz, CDCl3):
d=7.34 (s, 2H; Hthio), 7.20 (d, 3J=5.2 Hz, 2H; Hthio), 7.04 (d, 3J=5.2 Hz,
Compound 6: Under an N2 atmosphere, a solution of nBuLi 1.6m in hex-
anes (6.7 mL, 10.75 mmol) was added dropwise to a solution of 5 (1.85 g,
4.3 mmol) in anhydrous THF (50 mL) cooled to À788C. The reaction
mixture was allowed to warm to 208C and stirred at this temperature for
1 h before addition of tributyltin chloride (2.6 mL, 9.5 mmol). The mix-
ture was heated to reflux for 1 h. At 208C, petroleum ether (150 mL) was
added, and the organic phase was washed with a saturated aqueous solu-
tion of NH4Cl and then with water. The organic phase was dried over
MgSO4 and concentrated to dryness to afford 6 as yellow oil (4.35 g),
1
which was engaged in the next step without further purification. H NMR
À
(500 MHz, CDCl3): d=7.06 (s, 2H; Hthio), 2.82 (m, 4H; CH2 S), 1.64–
À
À
À
2H; Hthio), 2.94–2.91 (m, 4H; S CH2 CH2 Si), 2.88–2.84 (m, 8H; SCH2),
1.56 (m, 12H), 1.38–1.28 (m, 12H), 1.11 (m, 12H), 0.93–0.85 (m, 18H),
À
À
2.29 (s, 6H; CH3 CO), 1.71–1.69 (m, 8H), 0.96–0.93 (m, 4H; CH2 Si),
À
À
0.85 (m, 4H; CH2 Si), À0.04 ppm (s, 18H; CH3 Si).
Compound 7: Under an N2 atmosphere, [Pd(PPh3)4] (0.50 g, 0.43 mmol)
0.02 ppm (s, 18H; CH3 Si); 13C NMR (125 MHz, CDCl3): d=195.8,
À
AHCTUNGTRENNUNG
135.6, 135.4, 132.7, 132.3, 131.7, 129.2, 127.9, 123.6, 35.5, 32.1, 30.6, 28.6,
was added in one portion to an N2-degassed solution of 6 (4.34 g) and
compound 2 (2.70 g, 10.88 mmol) in toluene (50 mL). The reaction mix-
ture was heated to reflux overnight. After evaporation of the solvent and
addition of CH2Cl2 (200 mL), the organic phase was washed with water
(2ꢃ75 mL), dried over MgSO4, and concentrated under reduced pressure.
Purification by chromatography on silica gel (9:1 CH2Cl2/PE as eluent)
led to compound 7 as orange oil, which slowly crystallized (2.37–2.63 g,
72–80% yield based on 5). M.p. 74–768C; 1H NMR (500 MHz, CDCl3):
28.5, 17.5, À1.7 ppm; IR (NaCl); n˜ =1690 cmÀ1 (C=O); UV/Vis (CH2Cl2):
l (loge)=297 (3.61), 390 nm (4.18); MS (MALDI): m/z: 918 [M+ ]; ele-
C
mental analysis calcd (%) for C38H54O2S10Si2: C 49.67, H 5.93; found: C
49.56, H 6.02.
Compound 13: Under an N2 atmosphere, a solution of tetrabutylammoni-
um fluoride (1m) in THF (1.75 mL, 1.75 mmol) was added dropwise to a
solution of 11 (0.40 g, 0.44 mmol) in anhydrous THF (6 mL). The reac-
tion mixture was stirred under ultrasound for 1.5 h before addition of
compound 10 (0.70 g, 2.18 mmol) in anhydrous THF (5 mL). The reaction
mixture was stirred for 2 h at 208C. After concentration and the addition
of CH2Cl2, the solution was washed with water, dried over MgSO4, and
concentrated under reduced pressure. Purification by chromatography on
silica gel (6:4 PE/Et2O as eluent) led to compound 13 as yellow oil
(0.13 g, 25% yield). 1H NMR (500 MHz, CDCl3): d=7.37 (s, 2H; Hthio),
7.22 (d, 3J=5.6 Hz, 2H; Hthio), 7.05 (d, 3J=5.6 Hz, 2H; Hthio), 4.11 (s,
d=7.36 (s, 2H; Hthio), 7.27 (d, 3J=5.3 Hz, 2H; Hthio), 7.09 (d, 3J=5.3 Hz,
3
À
À
À
2H; Hthio), 3.05 (t, J=7.4 Hz, 4H; S CH2 CH2 CN), 2.95–2.91 (m, 4H;
3
À
À
À
À
S CH2 CH2 Si), 2.58 (t, J=7.4 Hz, 4H; CH2 CN), 0.94–0.90 (m, 4H;
CH2 Si), 0.01 ppm (s, 18H; CH3 Si); 13C NMR (125 MHz, CDCl3): d=
138.8, 134.7, 133.4, 132.9, 132.2, 129.7, 124.5, 124.3, 117.9, 32.1, 31.6, 18.5,
17.5, À1.7 ppm; IR (KBr): n˜ =2251 cmÀ1 (CN); UV/Vis (CH2Cl2): l
À
À
(loge)=275 (4.53), 392 nm (4.23); MS (70 eV): m/z (%): 764 (30) [M+ ],
C
711 (16), 422 (15), 390 (22), 126 (100); MS (MALDI): m/z: 781
[M+ +17]; elemental analysis calcd (%) for C32H40N2S8Si2: C 50.26, H
À
C
10H; HFc), 4.06 (s, 8H; HFc), 2.88–2.83 (m, 12H; CH2 S), 2.30 (s, 6H;
3
5.28; found: C 49.96, H 5.39.
À
À
CH3 CO), 2.25 (t, J=7.7 Hz, 4H; CH2 Fc), 1.69–1.61 (m, 12H), 1.60–
1.52 ppm (m, 4H); 13C NMR (125 MHz, CDCl3): d=195.8, 135.5, 133.1,
132.4, 131.5, 129.5, 128.0, 123.7, 69.0, 68.5, 67.5, 36.1, 35.6, 30.7, 30.0, 29.3,
29.1, 28.58, 28.54, 28.50 ppm; IR (NaCl): n˜ =1690 cmÀ1 (C=O); UV/Vis
(CH2Cl2): l=295 (sh), 390 nm; HRMS (ESI): m/z: calcd for
C56H62Fe2O2S10: 1198.0656; found: 1198.0687; MS (MALDI): m/z: 1197
Compound 8: Under an N2 atmosphere, a solution of CsOH.H2O (0.22 g,
1.3 mmol) in N2-degassed MeOH (7 mL) was added dropwise to a solu-
tion of 7 (0.45 g, 0.6 mmol) in degassed DMF (15 mL). The reaction mix-
ture was stirred for 1 h at 208C before the addition of a solution of iodo-
methane (0.37 mL, 5.9 mmol). After 4 h of additional stirring at 208C
and evaporation of the solvents, the residue was dissolved in CH2Cl2. The
[M+ À1].
C
Chem. Eur. J. 2011, 17, 5628 – 5640
ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5637

P. Blanchard, J. Roncali et al.
Compound 14: Under an N2 atmosphere, a solution of DIBAL-H (1m) in
CH2Cl2 (0.7 mL, 0.7 mmol) was added dropwise to a solution of 13
(0.10 g, 0.08 mmol) in anhydrous CH2Cl2 (5 mL) cooled to 08C. After 2 h
of stirring at 08C, an aqueous solution (3m) of HCl (3 mL) was added to
the reaction mixture, which was further stirred at 208C for 0.5 h. The
mixture was washed with water, dried over MgSO4, and concentrated
under reduced pressure. Purification by chromatography on silica gel (1:1
PE/CH2Cl2 as eluent) led to compound 14 as orange oil (0.09 g, 97%
yield). 1H NMR (500 MHz, CDCl3): d=7.37 (s, 2H; Hthio), 7.22 (d, 3J=
Guꢀrin, F. Tran Van, C. Chevrot, S. Palacin, J.-P. Bourgoin, O. Bou-
loussa, F. Rondelez, D. Vuillaume, J. Phys. Chem. B 2006, 110,
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3
5.6 Hz, 2H; Hthio), 7.05 (d, J=5.6 Hz, 2H; Hthio), 4.07 (s, 10H; HFc), 4.02
À
À
(s, 8H; HFc), 2.88–2.85 (m, 8H; CH2 S), 2.52–2.47 (m, 4H; CH2 SH),
3
À
2.28 (t, J=7.7 Hz, 4H; CH2 Fc), 1.73–1.70 (m, 8H), 1.68–1.55 (m, 8H),
1.31 ppm (t, 3J=7.9 Hz, 2H; SH); 13C NMR (125 MHz, CDCl3): d=
135.5, 133.1, 132.4, 131.5, 129.5, 128, 123.7, 69.6, 68.2, 67.2, 36.1, 35.7,
32.8, 30.1, 29.4, 29.1, 28.2, 24.2 ppm; UV/Vis (CH2Cl2): l=295 (sh),
389 nm; MS (MALDI): m/z: 1114 [M+ ].
C
Compound 15: A solution of CsOH·H2O (0.16 g, 0.95 mmol) in N2-de-
gassed MeOH (5 mL) was added dropwise to a solution of compound 11
(0.35 g, 0.38 mmol) in N2-degassed THF (15 mL). The reaction mixture
was stirred for 2 h before addition of an aqueous solution of HCl (1m,
1 mL, 1 mmol). After 2 h of additional stirring, the reaction mixture was
concentrated and diluted with CH2Cl2 (100 mL). The organic phase was
washed with water, dried over MgSO4, and concentrated under reduced
pressure. Purification by chromatography on silica gel (1:1 CH2Cl2/PE as
eluent) gave compound 15 as yellow oil (0.20 g, 63% yield). 1H NMR
3
(500 MHz, CDCl3): d=7.34 (s, 2H; Hthio), 7.21 (d, J=5.2 Hz, 2H; Hthio),
7.05 (d, 3J=5.2 Hz, 2H; Hthio), 2.94–2.90 (m, 4H; S CH2 CH2 Si), 2.87
À
À
À
3
3
À
À
À
À
(t, J=6.7 Hz, 4H; S CH2 ACHTNUGTRNE(UGN CH2)3 SH), 2.50 (q, J=7.7 Hz, 4H; CH2
SH), 1.73–1.71 (m, 8H; CH2 ACTHNUTRGNEUNG
(CH2)2 CH2), 1.31 (t, 3J=7.9 Hz, 2H; SH),
À
À
0.94–0.91 (m, 4H; CH2 Si), 0.01 ppm (s, 18H; CH3 Si); 13C NMR
(125 MHz, CDCl3): d=135.6, 135.4, 132.7, 132.3, 131.8, 129.3, 128.0,
123.7, 35.7, 32.8, 32.1, 28.2, 24.2, 17.5, À1.7 ppm; IR (NaCl): n˜ =
À
À
2563 cmÀ1 (S H); UV/Vis (CH2Cl2): l (loge)=298 (4.17), 391 nm (4.23);
À
MS (MALDI): m/z: 834 [M+ ].
C
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Acknowledgements
The Ministꢅre de la Recherche is acknowledged for the PhD grant of
T. K. Tran. This work was financially supported by ANR-PNANO (OP-
TOSAM project ANR-06-NANO-016) and the CNANO Nord-Ouest.
The authors thank O. AlꢀvÞque (MOLTECH-Anjou) for technical assis-
tance and the PIAM of the University of Angers for the characterization
of organic compounds.
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Received: December 21, 2010
Published online: April 13, 2011
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