Ferrocenyl oligo(phenylene-vinylene) thiols for the construction of self-assembled monolayers

Article abstract of DOI:10.1002/ejic.200700266

A short and efficient preparation of conjugated oligo(phenylene-ethylene) thiols bearing redox-active ferrocene moieties is described. While minimising the number of synthetic steps, the proposed strategy permits the development of sets of oligomers with varying chain length. The redox properties of the compounds in solution are determined. Preliminary studies of self-assembled monolayers (SAMs) on gold electrodes are discussed, and indicate that electron transfer through the SAMs is indeed rapid. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200700266

FULL PAPER
DOI: 10.1002/ejic.200700266
Ferrocenyl Oligo(phenylene-vinylene) Thiols for the Construction of Self-
Assembled Monolayers
Christian Amatore,*[a] Stephen Gazard,[a] Emmanuel Maisonhaute,[a] Cécile Pebay,[a]
Bernd Schöllhorn,*[a] Jean-Laurent Syssa-Magalé,[a] and Jay Wadhawan[a]
Keywords: Molecular wires / SAMs / Ferrocenes / Thiols / Redox chemistry / Self-assembly
A short and efficient preparation of conjugated oligo(phen-
ylene-ethylene) thiols bearing redox-active ferrocene moie-
ties is described. While minimising the number of synthetic
steps, the proposed strategy permits the development of sets
of oligomers with varying chain length. The redox properties
of the compounds in solution are determined. Preliminary
studies of self-assembled monolayers (SAMs) on gold elec-
trodes are discussed, and indicate that electron transfer
through the SAMs is indeed rapid.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
lea[7] illustrate the tendency to use conjugated bridges be-
cause π-delocalisation increases the coupling between the
redox probe and the electrode. For this reason conjugated
π-systems are potentially the most adapted and most prom-
ising molecular wires, assuring fast electron transfer kinetics
over distances up to 20 Å and longer. Hitherto, oligo(p-
phenylene-trans-vinylene) chains have exhibited the fastest
electron transfer rates of all investigated systems.[5] Ferro-
cene has been used in various studies as a convenient elec-
troactive centre showing fast and reversible one-electron
oxidation. Furthermore, ferrocenes may act as a local mo-
lecular switch as their Cp/Cp conduction (Cp = cyclopen-
tadienyl ligand) is poor in the reduced state and effective in
the ferricinium cations. It is thus important to develop rapid
and efficient access for sets of ferrocenyl oligo(phenylene-
ethylene) thiols with varying chain length. Our synthetic
strategy described herein also permits the insertion of ad-
ditional ferrocenyl groups into the bridge itself and thus the
building of more complex structures leading eventually to
more sophisticated signal processing functions such as field-
effect transistors. We wish to report here the rapid access to
a set of three ferrocenyl oligo(p-phenylene-trans-vinylene)
derivatives, 1, 2 and 3, bearing a mercaptomethyl group on
the terminating phenyl ring. The peculiar electrochemical
properties of 3 will also be described.
Introduction
There is growing interest in nanotechnologies for at-
taching and wiring conductive molecules onto surfaces for
a wide series of applications. Electrochemical systems may
be promising for developing, for example, molecular elec-
tronic devices,[1] efficient artificial photosynthetic systems,[2]
organic liquid crystal light-emitting diodes[3] or biosensors.
The use of self-assembly allows easy formation of mono-
layers of a redox-active species over an electrode by soaking
an appropriate electrode surface in a nonaqueous solution
of the suitably derivatised redox-active compound to enable
it to tether to the surface. Typically, an electroactive moiety
is located at one end of the molecule, whilst the grafting
end is terminated by a Lewis base.[4] When using gold elec-
trodes, such compounds often terminate with thiol moieties,
owing to the exquisite affinity of sulfur groups for gold.
This methodology is also highly attractive for electroanalyt-
ical sensors, as this method requires little preparative work,
and furnishes a reagent-immobilised electrode relatively in-
expensively. The attached compounds are able to carry elec-
trons back and forth from the electrode to redox enzymes.
In this context, the investigation of electron transfer
through molecular bridges has revealed that the rates usu-
ally decrease exponentially as the distance to the electrode
decreases. The attenuation factor is typically 10 nm–1 (i.e.,
1 Å–1) for alkyl bridges, a value that may be too high for
fast signal processing over long distances. Recent contri-
butions by the groups of Chidsey,[5] Creager[6] and Fink-
[a] Ecole Normale Supérieure, Département de Chimie, UMR
CNRS 8640 “PASTEUR”, Université Pierre et Marie Curie-
Paris 6,
24 rue Lhomond, 75231 Paris cedex 05, France
Fax: +33-144-32-38-63
E-mail: christian.amatore@ens.fr
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C. Amatore, B. Schöllhorn et al.
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rectly (Scheme 2). The subsequent reduction of the latter
compound with sodium borohydride in a mixture of meth-
anol and tetrahydrofuran afforded the desired free thiol
(88%). The use of lithium aluminium hydride (LAH) as a
reducing agent gave thiol 1 in only a 46% yield. Even with
an excess of LAH, the aldehyde 9 was isolated as an unex-
pected sideproduct. Whilst the analytical characterisation
data of 9 are consistent with previously published data for
this compound,[11] it is important to note that in contrast
to the earlier work, we also prepared compound 9 by Heck
reaction of vinylferrocene with 4-iodobenzaldehyde, thus
unambiguously identifying the structure of 9.
Results and Discussion
Two main approaches are commonly used in the synthe-
sis of free thiol derivatives: either the use of a protective
group or the late introduction of the thiol group as a final
step so as to avoid interferences during the earlier synthetic
steps. In the case of benzyl derivatives, a possible approach
involves masking a hydroxy group by an aldehyde, which,
after reduction to the corresponding primary alcohol, can
be converted in several steps to the desired thiol. Com-
pounds 1 and 2 have been prepared in this way.[8] As an
alternative, we opted for the late introduction of a thioester
group. We chose the S-protected 4-iodobenzylthiol 4, as this
useful building block significantly reduces the number of
synthetic steps. In a more convergent approach, 4a can be
easily obtained by treatment of 4-iodobenzyl bromide with
sodium thioacetate.[9] As an alternative route, we tried to
exploit the 4-iodobenzyl alcohol as a starting material, thus
favouring the direct conversion of the generally more stable
and readily available alcohol into the corresponding thio-
ester without any preceding halogenation. The Mitsunobu
reaction of 4-iodobenzyl alcohol with thioacetic acid af-
fords 4a in only low yield (30%) (Scheme 1). Hughes and
Reamer[10] showed evidence for improved yields in the Mit-
sunobu esterification of alcohols in the presence of acids
stronger than acetic acid. Accordingly, we employed thio-
benzoic acid instead of thioacetic acid so that, under the
same conditions, the thiobenzoic acid ester 4b is obtained
in high yield (95%).
Scheme 2. Synthesis of compounds 1 and 2: (i) Pd(OAc)2, P(Tol)3,
tributylamine, dimethylacetamide; (ii) NaBH4, THF, MeOH, 0 °C;
(iii) LiAlH4, THF, 0 °C.
Access to the ferrocene thiol 2 is achieved in only 3 steps
starting from aldehyde 9 (Scheme 2). The Heck coupling of
the olefin 10 and 4a leads directly to the thioacetate 11,
which was subsequently converted into the free thiol 2
through reduction with lithium aluminium hydride.
Scheme 1. Synthesis of the precursors 4a and 4b: (i) AcSH (for 4a),
BzSH (for 4b), PPh3, DEAD, THF, 0 °C; (ii) LiAlH4, THF, 0 °C.
Taking into account our previous results, we performed
the synthesis of the bis(ferrocenyl) thiol 3 in only 6 steps
The thiobenzoates 6b and 7b are also formed in satisfac- involving Heck coupling, standard methyl Wittig conver-
tory yields (84 and 63%) from the respective hydroxymethyl sion and a final reduction (Scheme 3). Our synthetic strat-
derivatives 6a and 7a. The reaction of alcohol 8a to the egy is based on the monofunctionalisation of 1,1Ј-ferro-
thioacetate 8b[8] shows a low yield (20%) compared to the cenedicarbaldehyde leading, in two steps, to the key inter-
thiobenzoate 8c (75%), confirming the observed tendency. mediate 13. The methyl Wittig conversion of ferrocened-
All of the thiobenzoic acid esters discussed above were suc- icarbaldehyde in dioxane allows for its selective monoole-
cessfully converted into the respective free thiols 5, 6c, 7c fination. Upon using the less polar tetrahydrofuran as a
and
1 through reduction with sodium borohydride solvent, the reaction is faster (TLC analysis) but less selec-
(Scheme 1). Both of the building blocks 4a and 4b were tive, indicative of a strong kinetic control depending on the
employed in the following syntheses leading to the target solvent polarity. In the following Heck reaction of 12 with
compounds 1, 2 and 3.
a twofold excess of 1,4-diiodobenzene, the monoiodo deriv-
ative 13 was obtained as the major product. Only small
amounts of the symmetric bis(ferrocenyl) derivative 17 (2%)
are isolated. Inversion of the molar ratio of the starting
compounds should afford this potential precursor of a tris-
(ferrocenyl) derivative in reasonable yields. An alternative,
but longer and less efficient, synthesis of 13 involving a pro-
The preparation of the short ferrocenyl-vinylene-phenyl- tective group is described in the literature.[12,13] A second
ene thiol 1 was achieved in only two steps. The Heck coup- Heck reaction of compound 13 with vinylferrocene affords
ling of 4b with vinylferrocene afforded thiobenzoate 8c di- the dissymmetric bis(ferrocenyl) monocarbaldehyde 14. The
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Ferrocenyl Oligo(phenylene-vinylene) Thiols
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Rf values of starting material 13 and product 14 are very
similar, and it is difficult to monitor the reaction by TLC.
In order to obtain a complete conversion, a higher tempera-
ture has to be maintained during the reaction. The rela-
tively low yield (53%) is probably due to a competitive de-
gradation of either starting material or product under these
conditions. A methyl Wittig conversion of 14 leads to the
corresponding vinyl derivative 15. This highly conjugated
and relatively apolar compound displays low solubility in
solvents such as diethyl ether or chloroform. The use of
dichloromethane is necessary for the purification steps in
the workup following the reaction. Unreacted starting com-
pound 14 was recovered and the reaction repeated in order
to improve the total yield to 60%. The thiobenzoate 16 was
obtained by a third Heck reaction of 15 with 4b. In the final
step, 16 is reduced with sodium borohydride to the target
compound 3. The use of LAH as a reducing agent consider-
ably lowers the yield and affords the aldehyde 18 as a side
product, like in the reduction of 8c.
Exploring the Electron Transfer Properties of the
Ferrocene-Based Compounds in Homogeneous Solution
We resorted to cyclic voltammetry to explore the electro-
chemical properties of 1, 2, 3, 14, 16 and 17. Owing to the
low solubility of some of the compounds in conventional
electrochemical solvents, investigations were undertaken in
dichloromethane with tetrabutylammonium tetrafluoro-
borate (TBABF4) at 0.1  concentration as the supporting
electrolyte. In a preliminary study, we checked that 1 and 2,
bearing a single redox centre, behave similarly to ferrocene.
Each gave a monoelectronic reversible wave whose current
intensity was proportional to v1/2, where v is the scan rate.
This is typical of a diffusive behaviour. The average of the
forward and backward peak currents allows evaluation of
a standard potential of (0.55Ϯ0.01) V versus SCE for 1 and
(0.54Ϯ0.01) V versus SCE for 2. Figure 1a depicts a cyclic
voltammogram at a scan rate of 200 mVs–1 of a 0.38 m
solution of 14 at a glassy carbon electrode. This bis(ferro-
cenyl) monocarbonyl species gives rise to two apparently
reversible waves centred at E°1 = (0.54Ϯ0.01) V versus SCE
and (0.81Ϯ0.01) V versus SCE, both waves being of the
same height. Given that the first wave occurs at the same
potential as that of the nonderivatised ferrocene, we infer
that this wave represents the one-electron oxidation of the
ferrocene moiety within the conjugated chain to yield the
corresponding ferricinium cation. The second wave is re-
lated to oxidation of the terminal ferrocenyl group bearing
an electron-withdrawing substituent.
Conversely, the voltammetry of the thiobenzoate 16 (cf.
Figure 1b) reveals a single oxidation wave, despite the pres-
Scheme 3. Synthesis of compound 3: (i) methyltriphenylphospho-
nium bromide, tert-butoxide, dioxane/water; (ii) Pd(OAc)2, P(Tol)3,
tributylamine, dimethylacetamide; (iii) NaBH4, THF, MeOH, 0 °C. ence of two redox centres. Complex 16 is a larger molecule
Figure 1. Cyclic voltammogram of (a) 14 (3.8ϫ10–4 ), (b) 16 (2.5ϫ10–4 ), (c) 17 (2.7ϫ10–4 ) in dichloromethane containing 0.1 
TBABF4 at a scan rate of 0.2 Vs–1.
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C. Amatore, B. Schöllhorn et al.
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than 14, so that its diffusion coefficient is necessarily where ∆Ecoul is the electrostatic contribution, we can evalu-
smaller. Hence, we infer from the peak current intensities ate that:
that two electrons are involved in the oxidation. Unfortu-
E°2 – E°1 ≈ –2(1 – µ)IP + ∆Ecoul
(3)
nately, free thiol 3 adsorbs slightly even onto a carbon elec-
trode, which prevents its full characterisation in solution.
However, a single wave was also observed. This unusual be-
haviour may seem counterintuitive as the electrostatic repul-
sion should destabilise the dication and thus raise the po-
tential of the second oxidation. In fact, such behaviour has
already been observed by Launay et al. for polyvinylferro-
cenes,[14] and by Saveant et al. for carotenoids.[15] These au-
thors proposed a rationalisation of this effect. As the mono-
cationic species are in a mixed-valence state, the charge is
delocalised inside the large volume defined between both
redox centres, so that the solvation is necessarily weak.
Conversely, in the dication, because of coulombic repulsion,
the charges are localised onto the two redox centres, thus
minimising the electrostatic repulsion and also allowing a
much stronger stabilisation by the solvent. In some cases,
this effect may balance the electrostatic repulsion and may
result in a potential inversion. A single two-electron process
then occurs, being thermodynamically and kinetically con-
trolled by the first electron transfer. This effect corresponds
with previous observations by Amatore and Kochi, reveal-
ing that for common aromatic compounds, there is a linear
correlation between the standard potential E°1 and the
ionisation potential IP [Equation (1)],[16] where 0 Ͻ µ Ͻ 1
and Cte is a constant depending on the reference electrode:
This formulation leads to [Equation (4)]:
E°2 ≈ (2µ – 1)IP + ∆Ecoul + Cte
(4)
We can then predict that there is a potential inversion
when [Equation (5)]:
IP Ͼ ∆Ecoul/(2 – 2µ)
(5)
If the compound is dissymmetrical (for example 14), an-
other term, ∆Echim, should be added to Equation (2), taking
into account the different chemical nature of both elec-
troactive moieties. Agreeing with this analysis, the voltam-
metry of 17, which is totally symmetrical, also reveals a
single peak (cf. Figure 1c). The weak signal around 0.55 V
may be attributed to an impurity in the crude product 17.
In Figure 1b a second wave is observed as a shoulder on
the medium discharge, reflecting an oxidative degradation
of compound 16, probably due to the irreversible thioben-
zoate oxidation.
The electrochemical behaviour of 3 while attached to a
gold electrode will be described elsewhere.[17] As a prelimi-
nary result, Figure 2 illustrates typical cyclic voltammog-
rams for 3, coadsorbed with diphenyl disulfide or pen-
tanethiol diluents. A single two-electron wave is still ob-
served as anticipated. Although the scan rate is high (cf.
Figure 2b), the relatively low peak-to-peak potential differ-
ence confirms that electron transfer inside this molecule is
indeed very fast.
E° ≈ µIP + Cte
(1)
Here, µ reflects how the variations in IP are transmitted to
E°; µ = 1 would mean that any variation in IP is fully re-
flected in the condensed phase. In this study, the electroac-
tive moieties were normally solvated and µ = 0.71 was ob-
tained; (1 – µ) reflects the effects of solvation. For the
monocation, the charge is only poorly solvated, so that µ
should be close to 1 so that [Equation (2)]:
Conclusions
A particularly short and efficient preparation of conju-
gated oligo(phenylene-ethylene) thiols bearing redox-active
ferrocene moieties is described. The proposed strategy to
introduce the sulfur group by Heck reaction of a vinyl
E°1 ≈ IP + Cte
(2)
Conversely, in the dication, the charges are normally sol- group with the key synthone 4 readily yields a set of oligo-
vated, so that in a very approximate model [Equation (3)], mers with varying chain length in only 2 (compound 1) or 4
Figure 2. Cyclic voltammogram in 1  perchloric acid of 3 coadsorbed (a) with pentanethiol onto a 111 gold single-crystal electrode,
scan rate: 12 Vs–1; (b) with diphenyl disulfide onto a gold ball ultramicroelectrode, scan rate: 220000 Vs–1.
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Ferrocenyl Oligo(phenylene-vinylene) Thiols
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ments. Cyclic voltammograms (CV) were recorded at room tem-
perature [(22Ϯ1) °C] and at a potential sweep rate of 0.2 Vs–1. To
form self-assembled monolayers, we left gold electrodes to bathe
for one night in a mixture of 1 and pentanethiol or 1 and diphenyl
disulfide in chloroform. Either a 111 Au single crystal or a gold
ball ultramicroelectrode (made by melting a 10 µm diameter wire
in a blue flame)[17] were used. Cyclic voltammograms were then
recorded in H2O + 1  HClO4. For Figure 2b, a home-built po-
synthetic steps (compound 2). The preparation of the thio-
esters by Mitsunobu reaction of benzyl alcohol was im-
proved by replacing thioacedic acid with thiobenzoic acid.
The additional insertion of ferrocenyl units into the conju-
gated bridge can be easily achieved by the use of 1Ј-vinylfer-
rocene-1-carbaldehyde (12), a key intermediate in the syn-
thesis of the bis(ferrocenyl) derivative 3. For the bis(ferro-
cenyl) derivatives, the nature of the second side chain at-
tached to the second ferrocene species may have a signifi-
tentiostat allowing scan rates up to 2.5 MVs–1 was used.[20,21]
full analysis of the electrochemical behaviour of self-assembled
A
cant effect on the redox thermodynamics, leading to an in- monolayers will be described elsewhere.
verted series of electrode potentials, causing a single two-
electron wave to occur. The ultrafast cyclic voltammetry of
1, 2 and 3 when they are adsorbed onto gold electrodes
confirms that these compounds are indeed very efficient
molecular wires. A full kinetic analysis of electrochemical
results for monolayers of these compounds will be pub-
lished elsewhere.[17]
Synthesis
4-[(E)-2-Ferrocenylvinyl]benzylthiol (1). (a) A solution of 8b (45 mg,
0.12 mmol) in tetrahydrofuran (THF) (2 mL) was chilled with a
water/ice bath. A 1  solution of lithium aluminium hydride (LAH)
in diethyl ether (0.24 mL, 0.24 mmol) was added slowly. The reac-
tion mixture was stirred at room temperature for 30–60 min, and
the reaction progress was monitored by thin layer chromatography
(TLC). The mixture was neutralised with 1  hydrochloric acid,
and extracted with dichloromethane. The organic phase was
washed with water, brine and then dried with magnesium sulfate.
Purification by chromatography (silica gel, dichloromethane/petro-
leum ether using a solvent gradient of 20:80 to 50:50) yielded 1 as
a red solid (39 mg, 97%). (b) 8c (45 mg, 0.10 mmol) was dissolved
in a mixture of methanol (2 mL) and tetrahydrofuran (1 mL). So-
dium borohydride (8 mg, 0.21 mmol) was added. The reaction mix-
ture was stirred at room temperature for 12 h, and the reaction
progress was monitored by TLC. The mixture was neutralised with
1  hydrochloric acid, and extracted with dichloromethane. The
organic phase was washed with water, brine and then dried with
magnesium sulfate. Purification by chromatography (silica gel,
dichloromethane/petroleum ether using a solvent gradient of 20:80
to 50:50) yielded 1 as a red solid (32 mg, 93%). (c) Compound 1
(10 mg, yield 47%) was prepared from 8c (28 mg, 0.064 mmol) and
lithium aluminium hydride as described. Compound 9 was found
to be a sideproduct (7.4 mg, yield 36%).
Compound 1: 1H NMR (CDCl3, 250 MHz): δ = 7.39 (d, J = 8.2 Hz,
2 H, aromatic), 7.28 (d, J = 8.2 Hz, 2 H, aromatic), 6.86 (d, J =
16 Hz, 1 H, vinyl), 6.67 (d, J = 16 Hz, 1 H, vinyl), 4.46 (t, J =
1.7 Hz, 2 H, Cp), 4.28 (t, J = 1.7 Hz, 2 H, Cp), 4.13 (s, 5 H, unsub-
stituted Cp), 3.74 (d, J = 7.4 Hz, 2 H, CH2), 1.76 (t, J = 7.4 Hz, 1
H, SH) ppm. 13C NMR (CDCl3, 400 MHz): δ = 139.6, 136.8, 128.3,
127.0, 126.0, 125.5, 69.2, 69.1, 66.8, 28.8 ppm. MS (CI+, NH3): m/z
(%) = 335 (95) [M + 1], 303 (100). HRMS (CI+, CH4): calcd. for
[C19H19FeS]+ 335.0551; found 335.0546. UV (CH3Cl): λ (ε) = 456
(908) nm (br.).
Experimental Section
General: All reactions were performed with previously dried sol-
vents under argon, if not stated otherwise. The compounds ferro-
cene, ferrocenemonocarbaldehyde, ferrocenylmethanol (6a) and
ferrocene-1,1Ј-diyldimethanol (7a) were bought from Sigma/
Aldrich (France). The commercially available vinylferrocene was
obtained in larger quantities from ferrocenemonocarbaldehyde in
a Wittig reaction with methyltriphenylphosphonium bromide. Fer-
rocene-1,1Ј-dicarbaldehyde was prepared from freshly sublimed fer-
rocene.[18] Thin layer chromatography (TLC) was performed on al-
uminium sheets precoated with 60 F254 silica gel. Preparative flash
column chromatography was performed on silica gel 60 (0.040–
1
0.063 mm, Merck). H and 13C NMR spectra were recorded with
a Bruker AC 250 or a Bruker DRX 400 spectrometer. Chemical
shifts are reported using the deuterated (13C NMR) or the residual
monoprotonated (1H NMR) solvent signals as reference, based on
the values published by Gottlieb and Nudelman.[19] Mass spectra
were recorded with a Jeol JMS-700 spectrometer and UV/Vis spec-
tra with a Beckman DU 7400 spectrophotometer. Elemental analy-
ses were conducted at the University of Pierre and Marie Curie
(Paris, Jussieu, France) or the Centre Nationale de Recherche Sci-
entifique (Gif-sur-Yvette, France).
Electrochemistry: The electrochemical experiments in dichloro-
methane were conducted in an air-tight, three-electrode glass cell,
controlled by a commercially available computer-controlled po-
tentiostat (AUTOLAB PGSTAT 30, Eco Chemie, the Nether-
lands). A platinum wire and an aqueous saturated calomel elec-
trode (SCE) were used as a counter and a reference electrode,
respectively. The reference electrode was kept in a side arm sepa-
rated from the electrochemical cell by a porous frit. The side arm
was filled with the solvent/supporting electrolyte solution. A glassy
carbon disk electrode, having a disk radius of 0.5 mm, was used as
the working electrode. The working electrode was polished prior to
each experiment on successively finer grades of carborundum paper
(P1200 down to P4000), and then using a 0.3 µ aqueous alumina
slurry on a wetted, napped polishing cloth. The supporting electro-
lyte employed was a 0.1  solution of tetrabutylammonium tetra-
fluoroborate (TBAF4) in dichloromethane (distilled from barium
oxide). TBABF4 had been recrystallised and dried at 70 °C for at
least 24 h before use. Prior to experimentation, argon gas was
bubbled into the electrolyte solution to remove oxygen, and was
flushed over the cell solution during the electrochemical measure-
4-[(E)-2-{4-[(E)-2-Ferrocenylvinyl]phenyl}vinyl]benzylthiol (2): Com-
pound 2 (74 mg, yield 71%) was prepared from 11 (114 mg,
0.24 mmol) and lithium aluminium hydride as described for the
1
preparation of 1 (procedure a). H NMR (CDCl3, 250 MHz): δ =
7.45–7.19 (m, 10 H, aromatic, vinyl), 6.83 (d, J = 16 Hz, 1 H, vinyl),
6.62 (d, J = 16 Hz, 1 H, vinyl), 4.42 (d, J = 2.7 Hz, 2 H, Cp), 4.23
(d, J = 2.7 Hz, 2 H, Cp), 4.08 (s, 5 H, unsubstituted Cp), 3.68 (d,
J = 7.5 Hz, 2 H, CH2), 1.60 (t, J = 7.5 Hz, 1 H, SH) ppm. MS
(CI+, CH4): m/z (%) = 437 (50) [M + 1], 405 (100). HRMS (CI+,
CH4): calcd. for [C27H25FeS]+ 437.1021; found 437.1024.
4-[(E)-2-{1Ј-[(E)-2-{4-[(E)-2-Ferrocenylvinyl]phenyl}vinyl]ferrocen-1-
yl}vinyl]benzylthiol (3). (a) Compound 3 (14 mg, yield 81%) was
prepared from 16 (20 mg, 0.026 mmol) and sodium borohydride as
described for the preparation of 1 (procedure b). Compound 16 is
soluble in dichloromethane, whereas its solubility is very low in
diethyl ether. Chromatography (silica gel; dichloromethane/petro-
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C. Amatore, B. Schöllhorn et al.
leum ether gradient of 20:80 to 40:60) to yield pure compound 3. Compound 7b: Compound 7b (194 mg, yield 63%) was prepared
FULL PAPER
(b) Compound 3 (7 mg, yield 46%) was prepared from 16 (18 mg,
0.023 mmol) and lithium aluminium hydride as described for the
preparation of 1 (procedure a). Aldehyde 18 was isolated as a side-
from 7a (156 mg, 0.63 mmol) and thiobenzoic acid as described for
the preparation of 4b. H NMR (CDCl3, 250 MHz): δ = 7.96 (d, J
= 7.4 Hz, 4 H, aromatic), 7.56 (m, 2 H, aromatic), 7.44 (m, 4 H,
1
product {MS (CI; NH3): m/z (%) = 648 (37) [M + 1], 631 (33), 613 aromatic), 4.27 (s, 4 H, Cp), 4.18 (s, 4 H, Cp), 4.15 (s, 4 H, CH2)
(100)}.
ppm. MS (CI+, NH3): m/z (%) = 504 (62) [M + NH4], 349 (96),
213 (100).
Compound 3: 1H NMR (CD2Cl2, 400 MHz): δ = 7.25 (m, 6 H,
aromatic), 7.14 (m, 2 H, aromatic), 6.88 (d, J = 16Hz, 1 H, vinyl),
6.76 (d, J = 16 Hz, 1 H, vinyl), 6.73 (d, J = 16 Hz, 1 H, vinyl), 6.68
{4-[(E)-2-Ferrocenevinyl]phenyl}methanol (8a): Compound 8a
(436 mg, yield 85%) was prepared from 9 (510 mg, 1.61 mmol) and
(d, J = 16 Hz, 1 H, vinyl), 6.61 (d, J = 16 Hz, 1 H, vinyl), 6.59 (d, sodium borohydride as described for the preparation of 1 (pro-
J = 16 Hz, 1 H, vinyl), 4.48 (t, J = 1.8 Hz, 2 H, Cp), 4.42 (m, 4 H, cedure b). Chromatography (silica gel; dichloromethane) yielded a
Cp), 4.28 (t, J = 1.8 Hz, 2 H, Cp), 4.25 (m, 4 H, Cp), 4.13 (s, 5 H,
red-orange solid. 1H NMR (CDCl3, 250 MHz): δ = 7.44 (d, J =
unsubst. Cp), 3.68 (m, 2 H, CH2), 0.88 (t, J = 7.6 Hz, 1 H, SH) 8.1 Hz, 2 H, aromatic), 7.33 (d, J = 8.1 Hz, 2 H, aromatic), 6.89
ppm. MS (CI+, NH3): m/z (%) = 647 (100) [M + 1], 615 (65).
HRMS (FAB+, NH3): calcd. for [C39H35FeS]+ 647.1153; found
647.1157. UV (CH3Cl): λ (ε) = 463 (4311) nm (br.).
(d, J = 16.1 Hz, 1 H, vinyl), 6.69 (d, J = 16.1 Hz, 1 H, vinyl), 4.68
(d, J = 5 Hz, 2 H, CH2), 4.47 (s, 2 H, Cp), 4.29 (s, 2 H, Cp), 4.14
(s, 5 H, unsubstituted Cp), 1.61 (t, J = 5 Hz, 1 H, OH) ppm.
S-(4-Iodobenzyl) Thioacetate (4a): A solution of 4-iodobenzyl
alcohol (200 mg, 0.85 mmol), triphenylphosphane (448 mg,
1.71 mmol) and thioacetic acid (122 µL, 1.71 mmol) in tetra-
hydrofuran (3.5 mL) was cooled to 0 °C, and diethyl diazodi-
carboxylate (298 mg, 1.71 mmol, 40% mixture in toluene) was
added dropwise. The reaction mixture was stirred for 12 h. Diethyl
ether was added and the organic phase was washed with aqueous
sodium hydrogen carbonate solution, water and brine and then
dried with magnesium sulfate. After evaporation of the solvent, the
residue was purified by column chromatography (silica gel; 40%
dichloromethane in petroleum ether) to yield 4a as a colourless oil
(72 mg, 29%). 1H NMR (CDCl3, 250 MHz): δ = 7.62 (d, J =
8.3 Hz, 2 H, aromatic) 7.03 (d, J = 8.3 Hz, 2 H, aromatic), 4.04 (s,
2 H, CH2), 2.35 (s, 3 H, CH3) ppm.
S-{4-[(E)-2-Ferrocenylvinyl]benzyl} Thioacetate (8b): Compound 8b
(78 mg, yield 22%), a red solid, was prepared from 8a (300 mg,
0.94 mmol) and thioacetic acid as described for the preparation of
4a. Chromatography: silica gel; dichloromethane/petroleum ether,
1
40:60 v/v. H NMR (CDCl3, 250 MHz): δ = 7.36 (d, J = 8.2 Hz, 2
H, aromatic), 7.24 (d, J = 8.2 Hz, 2 H, aromatic), 6.85 (d, J =
16.1 Hz, 1 H, vinyl), 6.66 (d, J = 16.1 Hz, 1 H, vinyl), 4.45 (t, J =
1.6 Hz, 2 H, Cp), 4.29 (t, J = 1.6 Hz, 2 H, Cp), 4.13 (s, 5 H, unsub-
1
stituted Cp), 4.11 (s, 2 H, CH2), 2.35 (s, 3 H, CH3) ppm. The H
NMR data described in the literature[8] confirms the above data.
S-{4-[(E)-2-Ferrocenylvinyl]benzyl} Thiobenzoate (8c): A solution of
vinylferrocene (106 mg, 0.50 mmol), 4b (176 mg, 0.50 mmol), palla-
dium acetate (11 mg, 0.014 mmol) and tributylamine (180 µL,
0.75 mmol) in N,N-dimethylacetamide (10 mL) was stirred at room
temperature for 1 h. Tri(ortho-tolyl)phosphane (3 mg, 0.01 mmol)
was added. After 3 h of stirring at room temperature, the reaction
mixture was heated at 100 °C for 12 h. After extraction with diethyl
ether, the organic phase was washed with 1  hydrochloric acid,
water, brine and then dried with magnesium sulfate. After evapora-
tion of the solvent, the residue was purified by column chromatog-
raphy (silica gel; 50% dichloromethane in petroleum ether) to yield
S-(4-Iodobenzyl) Thiobenzoate (4b): A solution of 4-iodobenzyl
alcohol (200 mg, 0.85 mmol), triphenylphosphane (448 mg,
1.71 mmol) and thiobenzoic acid (222 µL) in tetrahydrofuran
(3.5 mL) was cooled to 0 °C, and diethyl diazodicarboxylate
(298 mg, 1.71 mmol, 40% mixture in toluene) was added dropwise.
The reaction mixture was stirred for 4–12 h (TLC control). Diethyl
ether was added and the organic phase was washed with aqueous
sodium hydrogen carbonate solution, water and brine and then
dried with magnesium sulfate. After evaporation of the solvent, the
residue was purified by column chromatography (silica gel; 40%
1
8c (138 mg, 63%). H NMR (CDCl3, 250 MHz): δ = 7.97 (d, J =
7.2 Hz, 2 H, aromatic), 7.31–7.57 (m, 7 H, aromatic), 6.85 (d, J =
16 Hz, 1 H, vinyl), 6.66 (d, J = 16 Hz, 1 H, vinyl), 4.46 (m, 2 H,
Cp), 4.31 (s, 2 H, CH2), 4.28 (m, 2 H, Cp), 4.12 (s, 5 H, unsubsti-
dichloromethane in petroleum ether) to yield 4b as a colourless oil
1
(287 mg, 95%). H NMR (CDCl3, 250 MHz): δ = 7.95 (d, 2 H, J tuted Cp) ppm. 13C NMR (CDCl3, 250 MHz): δ = 185.0, 133.4,
= 7.4 Hz, aromatic), 7.63 (d, 2 H, J = 8.2 Hz, aromatic), 7.58 (t, 1
H, J = 7.4 Hz, aromatic), 7.44 (t, 2 H, J = 7.4 Hz, aromatic), 7.12
(d, 2 H, J = 8.2 Hz, aromatic), 4.24 (s, 2 H, CH2) ppm. 13C NMR
(CDCl3, 250 MHz): δ = 191.0, 137.7, 137.4, 136.7, 133.6, 130.9,
128.7, 127.3, 32.8 ppm. MS (CI+, NH3): m/z (%) = 372 (100) [M +
NH4], 355 (8) [M + 1], 246 (33) [M – I + NH4]. C14H11IOS (354.21):
calcd. C 47.47, H 3.13; found C 47.40, H 3.13.
129.3, 128.6, 127.3, 127.1, 126.0, 125.5, 69.2, 69.1, 66.9, 33.3 ppm.
MS (CI+, NH3): m/z (%) = 456 (12) [M + NH4], 439 [17] [M + 1],
303 (100).
{4-[(E)-2-Ferrocenevinyl]phenyl}carbaldehyde (9): Compound
9
(406 mg, yield 56%) was prepared from vinylferrocene (486 mg,
2.30 mmol) and 4-iodobenzaldehyde (532 mg, 2.29 mmol) as de-
1
scribed for the preparation of 8c. H NMR (CDCl3, 250 MHz): δ
(4-Iodophenyl)methanethiol (5): Compound 5 (32 mg, yield 91%)
was prepared from 4b (50 mg, 0.14 mmol) and sodium borohydride
as described for the preparation of 1 (procedure b). 1H NMR
(CDCl3, 250 MHz): δ = 7.64 (d, J = 8.2 Hz, 2 H, aromatic), 6.96
(d, J = 8.2 Hz, 2 H), 3.54 (s, 2 H, CH2), 1.85 (s, 1 H, SH) ppm.
= 9.98 (s, 1 H, CHO), 7.84 (d, J = 8.2 Hz, 2 H, aromatic), 7.56 (d,
J = 8.2 Hz, 2 H, aromatic), 7.08 (d, J = 16.1 Hz, 1 H, vinyl), 6.72
(d, J = 16.1 Hz, 1 H, vinyl), 4.52 (s, 2 H, Cp), 4.36 (s, 2 H, Cp),
4.16 (s, 5 H, unsubstituted Cp) ppm. 13C NMR (CDCl3, 250 MHz):
δ = 191.6, 131.5, 130.3, 126.0, 124.6, 69.8, 69.5, 69.4, 67.4 ppm.
MS (CI+, NH3): m/z (%) = 317 (100) [M + 1].
S-(Ferrocenylmethyl) Thiobenzoate (6b): Compound 6b (208 mg,
yield 84%) was prepared from ferrocenylmethanol 6a (159 mg,
0.74 mmol) and thiobenzoic acid as described for the preparation
4-[(E)-2-Ferrocenylvinyl]styrene (10): Compound 10 (301 mg, yield
86%) was prepared from aldehyde 9 (352 mg, 1.11 mmol) as de-
1
1
of 4b. H NMR (CDCl3, 250 MHz): δ = 7.93 (d, J = 7.4 Hz, 2 H,
scribed for the preparation of 12. H NMR (CDCl3, 250 MHz): δ
aromatic), 7.54 (t, J = 7.4 Hz, 1 H, aromatic), 7.41 (t, J = 7.4 Hz,
2 H, aromatic), 4.33 (m, 2 H, Cp), 4.26 (m, 2 H, Cp), 4.22 (s, 5 H,
Cp), 4.13 (s, 2 H, CH2) ppm.
= 7.40 (s, 4 H, aromatic), 6.88 (d, J = 16.2 Hz, 1 H, vinyl), 6.70
(dd, J = 16.2, 10.7 Hz, 1 H, vinyl), 6.67 (d, J = 16.2 Hz, 1 H, vinyl),
5.75 (d, J = 17.5 Hz, 1 H, vinyl), 5.22 (d, J = 10.7 Hz, 1 H, vinyl),
4040
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Ferrocenyl Oligo(phenylene-vinylene) Thiols
FULL PAPER
4.46 (t, J = 1.6 Hz, 2 H, Cp), 4.3 (m, 2 H, Cp), 4.15 (s, 5 H, Cp)
ppm.
reaction mixture was extracted with dichloromethane. The organic
phase was washed with water and dried with magnesium sulfate.
After evaporation of the solvent, the brown solid residue was puri-
fied by column chromatography (silica gel; dichloromethane/petro-
leum ether, 35:65 v/v) to yield 15 (56 mg, 44%). Repetition of the
experiment with the recovered starting material afforded another
S-{4-[(E)-2-{1Ј-[(E)-2-{4-[(E)-2-Ferrocenylvinyl]phenyl}vinyl]-
ferrocen-1-yl}vinyl]benzyl} Thioacetate (11): Compound 11
(152 mg, yield 83%) was prepared from 10 (120 mg, 0.38 mmol)
and 4a (233 mg, 0.80 mmol) as described for the preparation of 8c.
1H NMR (CDCl3, 250 MHz): δ = 7.45 (m, 8 H, aromatic), 7.20
(2d, J = 17 Hz, 2 H, vinyl), 6.85 (2d, J = 16.1 Hz, 2 H, vinyl), 4.65
(s, 2 H, CH2) 4.45 (d, J = 2.67 Hz, 2 H, Cp), 4.30 (d, J = 1.6 Hz,
2 H, Cp), 4.15 (s, 5 H, unsubstituted Cp), 3.95 (s, 3 H, CH3) ppm.
The 1H NMR data described in the literature[8] confirms the above
data. MS (CI+, NH3): m/z (%) = 479 (20) [M + 1], 295 (100). MS
(FAB+): m/z (%) = 478 (10) [M], 295 (100).
1
37 mg of 15, increasing the total yield to 64%. H NMR (CDCl3,
250 MHz): δ = 7.4 (s, 4 H, aromatic), 6.9 (d, J = 16 Hz, 1 H, vinyl),
6.81 (d, J = 16 Hz, 1 H, vinyl), 6.68 (d, J = 16 Hz, 1 H, vinyl), 6.64
(d, J = 16 Hz, 1 H, vinyl), 6.38 (dd, J = 17.5, 10.7 Hz, 1 H,
CH=CH2), 5.24 (d, J = 17.5 Hz, 1 H, CH=CH2), 5.0 (d, J =
10.7 Hz, 1 H, CH=CH2), 4.47 (t, J = 1.3 Hz, 2 H, Cp), 4.39 (t, J
= 1.6 Hz, 2 H, Cp), 4.30 (t, J = 2.3 Hz, 4 H, Cp), 4.23 (t, J =
1.7 Hz, 2 H, Cp), 4.19 (t, J = 1.6 Hz, 2 H, Cp), 4.14 (s, 5 H, Cp)
ppm. MS (CI+, NH3): m/z (%) = 525 (100) [M + 1], 391 (5), 315
(7).
1Ј-Vinylferrocene-1-carbaldehyde (12): A solution of ferrocene-1,1Ј-
dicarbaldehyde (0.849 g, 3.51 mmol) and methyltriphenylphospho-
nium bromide (1.25 g, 3.51 mmol) in dioxane (20 mL) was treated
with potassium tert-butoxide (0.39 g, 3.5 mmol) and water
(100 µL). After stirring at room temperature for 3 h, the reaction
mixture was extracted with diethyl ether. The organic phase was
washed with water and dried with magnesium sulfate. Purification
by chromatography (silica gel; dichloromethane) yielded 12 as a
S-{4-[(E)-2-{1Ј-[(E)-2-{4-[(E)-2-Ferrocenylvinyl]phenyl}vinyl]-
ferrocen-1-yl}vinyl]benzyl} Thiobenzoate (16): Compound 16
(24 mg, 91%) was prepared from 15 (22 mg, 0.035 mmol) and 4b
(30 mg, 0.084 mmol) as described for the preparation of 8c
(chromatography: silica gel; 50% dichloromethane in petroleum
ether). 1H NMR (CD2Cl2, 400 MHz): δ = 7.99 (dd, J = 7.1, 1.4 Hz,
2 H, aromatic), 7.58 (tt, J = 7.4, 1.4 Hz, 1 H, aromatic), 7.45 (m,
2 H, aromatic), 7.29 (aromatic, J = 8.3 Hz, 2 H, d), 7.23 (s, 4 H,
aromatic), 7.21 (aromatic, J = 8.3 Hz, 2 H, d), 6.9 (d, J = 16 Hz,
1 H, vinyl), 6.75 (d, J = 16 Hz, 2 H, vinyl), 6.68 (d, J = 16 Hz, 1
H, vinyl), 6.60 (d, J = 16 Hz, 2 H, vinyl), 4.47 (t, J = 1.8 Hz, 2 H,
Cp), 4.41 (t, J = 1.8 Hz, 4 H Cp), 4.29 (s, 2 H, CH2), 4.27 (t, J =
1.8 Hz, 2 H, Cp), 4.25 (t, J = 1.8 Hz, 4 H, Cp), 4.12 (s, 5 H, Cp)
ppm. MS (CI+, CH4): m/z (%) = 751 (62) [M + 1], 242 (100), 186
(40). HRMS (CI+, NH3): calcd. for [C46H39Fe2OS]+ 751.1415;
found 751.1412.
1
brown oil (0.37 g, 44%). H NMR (CDCl3, 250 MHz): δ = 9.88 (s,
1 H, CHO), 6.37 (dd, J = 17.5, 10.7 Hz, 1 H, vinyl), 5.40 (d, J =
17.5 Hz, 1 H, vinyl), 5.14 (d, J = 10.7 Hz, 1 H), 4.72 (s, 2 H, Cp),
4.54 (s, 2 H, Cp), 4.51 (s, 2 H, Cp), 4.31 (s, 2 H, Cp) ppm. MS
(CI+, NH3): m/z (%) = 241 (100) [M + 1], 215 (12), 124 (7).
1Ј-[(E)-2-(4-Iodophenyl)vinyl]ferrocene-1-carbaldehyde (13): Com-
pound 13 (276 mg, 57%) was prepared from 12 (271 mg, 1.1 mmol)
and 1,4-diiodobenzene (0.74 g, 2.3 mmol), as described for the
preparation of 8c. However, the reaction mixture was not heated
but stirred at room temperature for 3 d (chromatography: silica gel;
1
dichloromethane). H NMR (CDCl3, 400 MHz): δ = 9.90 (s, 1 H,
CHO), 7.65 (d, J = 8.4 Hz, 2 H, aromatic), 7.17 (d, J = 8.4 Hz, 2
H, aromatic), 6.76 (d, J = 16.2 Hz, 1 H, vinyl), 6.63 (d, J = 16.2 Hz,
1 H, vinyl), 4.76 (t, J = 1.9 Hz, 2 H, Cp), 4.55 (multiplet, J =
1.9 Hz, 4 H, Cp), 4.38 (t, J = 1.9 Hz, 2 H, Cp) ppm. MS (CI+,
NH3): m/z (%) = 443 (100) [M + 1], 317 (33). Only a small amount
of the symmetrical bis(ferrocene) dicarbaldehyde 17 was isolated
(12 mg, 2%). 1H NMR (CDCl3, 250 MHz): δ = 9.90 (s, 2 H, CHO),
7.42 (s, 4 H, aromatic), 6.67 (s, 2 H, vinyl), 6.66 (s, 2 H, vinyl), 4.77
(t, J = 1.8 Hz, 4 H, Cp), 4.57 (m, 8 H, Cp), 4.39 (t, J = 1.8 Hz, 4
H, Cp) ppm. 13C NMR (CDCl3, 250 MHz): δ = 193.8, 136.4, 127.8,
126.4, 124.8, 85.5, 79.9, 74.4, 70.7, 70.5, 68.2 ppm. MS (CI+, CH4):
m/z (%) = 455 (15) [M + 1], 241 (100).
Acknowledgments
This work was supported by the CNRS, the Ecole Normale Supé-
rieure, the Universite Pierre et Marie Curie and the French Minis-
try of Research (ACI Nanosciences-Nanotechnologies). J. W. grate-
fully thanks The Leverhulme Trust, London, UK for financial sup-
port through a postdoctoral studentship (GR/N SAS/30105). We
gratefully thank Prof. Juan Feliu and Dr. Victor Climent (Univer-
sity of Alicante) for providing a 111 Au single crystal.
1Ј-[(E)-2-{4-[(E)-2-Ferrocenylvinyl]phenyl}vinyl]ferrocene-1-carb-
aldehyde (14): Compound 14 (180 mg, 55%) was prepared from
13 (276 mg, 0.63 mmol) and vinylferrocene (265 mg, 1.25 mmol) as
described for the preparation of 8c (chromatography: silica gel;
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1
dichloromethane/petroleum ether, 40:60 v/v). H NMR (CDCl3,
250 MHz): δ = 9.91 (s, 1 H, CHO), 7.40 (s, 4 H, aromatic), 6.90 (d,
J = 16 Hz, 1 H, vinyl), 6.72 (s, 2 H, vinyl), 6.66 (d, J = 16 Hz, 1
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4041

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