Calixarene-Poly(dithiophene)-based chemically modified electrodes

Article abstract of DOI:10.1002/1521-3765(20010803)7:15<3354::AID-CHEM3354>3.0.CO;2-U

The stepwise synthesis of cone and partial cone 1,3-bridged n-propoxy-calix[4]crown ethers ("monomers" 2 and 3) with an electropolymerizable 2,2′-dithiophene-3-yl-hexylene functionality at the lower rim, is described. The potential of 2 and 3 as sensing agents for alkali metal ions was investigated by ¹H NMR titration experiments with NaSCN and KSCN. The results obtained have confirmed that the presence of the heterocyclic subunit does not affect the well-known size-selectivity observed with calix[4]crowns. Monomers 2 and 3 were electropolymerized (Pt as a working electrode, CH₂Cl₂/CH₃CN, Bu₄NPF₆) to produce the title chemically modified electrodes (CMEs). After coating with a PVC membrane containing a lipophylic cation exchanger, CMEs based on calix[4]-crown-5 2b (cone) and 3b (partial cone) were tested for the potentiometric recognition of alkali metal ions in aqueous solution. In agreement with NMR titration studies, a satisfactory potentiometric response in terms of K⁺/Na⁺ selectivity was obtained only with CME 2b (pK_K/Na 1.51). The amperometric responses of PVC-uncoated CMEs were studied by cyclic voltammetry (CV) experiments in CH₃CN solution. High Na⁺ selectivity was found with the CME based on partial cone calix[4]crown-4 3 a, and frequency response analysis (FRA) measurements support this finding. Wiley-VCH Verlag GmbH, 2001.

Full text of DOI:10.1002/1521-3765(20010803)7:15<3354::AID-CHEM3354>3.0.CO;2-U

FULL PAPER
Calixarene ± Poly(dithiophene)-Based Chemically Modified Electrodes
Marco Giannetto,[b] Giovanni Mori,*[b] Anna Notti,[c] Sebastiano Pappalardo,*[a] and
Melchiorre F. Parisi[c]
Abstract: The stepwise synthesis of
cone and partial cone 1,3-bridged n-
propoxy-calix[4]crown ethers (ªmono-
mersº 2 and 3) with an electropolymer-
merized (Pt as a working electrode,
CH2Cl2/CH3CN, Bu4NPF6) to produce
the title chemically modified electrodes
(CMEs). After coating with a PVC
membrane containing a lipophylic cati-
on exchanger, CMEs based on calix[4]-
crown-5 2b (cone) and 3b (partial cone)
were tested for the potentiometric rec-
ognition of alkali metal ions in aqueous
solution. In agreement with NMR titra-
tion studies, a satisfactory potentiomet-
‡
‡
ric response in terms of K /Na selec-
tivity was obtained only with CME 2b
(pKK/Na 1.51). The amperometric re-
sponses of PVC-uncoated CMEs were
studied by cyclic voltammetry (CV)
experiments in CH3CN solution. High
izable
2,2'-dithiophene-3-yl-hexylene
functionality at the lower rim, is de-
scribed. The potential of 2 and 3 as
sensing agents for alkali metal ions was
investigated by 1H NMR titration ex-
periments with NaSCN and KSCN. The
results obtained have confirmed that the
presence of the heterocyclic subunit
does not affect the well-known size-
selectivity observed with calix[4]crowns.
Monomers 2 and 3 were electropoly-
‡
Na selectivity was found with the CME
based on partial cone calix[4]crown-4
3a, and frequency response analysis
(FRA) measurements support this find-
ing.
Keywords: calixarenes ´ conducting
materials
´
chemically modified
electrodes ´ electrochemistry ´ ion
recognition
pyrroles or thiophenes with suitable pendant functionalities is
currently being employed for the coating of electrode
surfaces.[3] Such electrodes are being extensively studied for
their potential in electrocatalysis,[4] or for their ability to sense
alkali metal ions.[5]
Introduction
Calixarene derivatives are nowadays among the most versa-
tile and effective synthetic receptors available for the selective
recognition of ions and neutral molecules.[1] Calixarene-based
receptors have thus emerged as leading sensing agents for the
development of advanced sensory devices (i.e., ion selective
electrodes, ISEs; chemically modified field effect transistors,
CHEMFETs; ion selective field effect transistors,
ISFETs).[1a, 2] At the same time, the electropolymerization of
We recently envisaged the possibility of combining the ion-
binding affinities of calix[4]arene crown ethers with the
electronic/redox properties of conducting polymers (CPs),[6]
in order to create new classes of molecular sensors able to
recognize and electrochemically respond to alkali metal ions.
A rational design of these materials requires the presence, on
the calixarene skeleton, of an appropriate moiety which
would easily undergo electrooxidative polymerization directly
providing CPs immobilized on the electrode surface.[7] The
ion-sensing properties of the resulting chemically modified
electrodes (CMEs)[8] could be tuned by varying the confor-
mation of the calixarene platform, the size of the crown ether
bridge, the nature of the substituents at both the upper and
lower rims, and the length of the connecting spacer on the
monomeric precursor.
To this end, we recently designed and synthesized several
conformers of 1,3-bridged calix[4]arene crown ethers 1 (m ˆ
0; p ˆ 2), bearing a potentially electropolymerizable 3-thienyl
functionality at the lower rim.[9] However, early attempts to
electropolymerize monomers 1 under a number of different
conditions, did not produce any CPs on the working electrode,
but only soluble oligomeric oxidized species.[10]
[a] Prof. S. Pappalardo
Dipartimento di Scienze Chimiche
Universita di Catania, Viale A. Doria 6
Á
95125 Catania (Italy)
Fax : (‡ 39)095-580138
E-mail: spappalardo@dipchi.unict.it
[b] Prof. G. Mori, Dr. M. Giannetto
Dipartimento di Chimica Generale, Inorganica,
Á
Analitica e Chimica Fisica, Universita di Parma
Parco Area delle Scienze 17/A, 43100 Parma (Italy)
Fax : (‡ 39)0521-905557
E-mail: mori@unipr.it
[c] Dr. A. Notti, Prof. M. F. Parisi
Dipartimento di Chimica Organica e Biologica
Universita di Messina, Salita Sperone 31
Á
98166 Messina (Italy)
Supporting information for this article is available on the WWW under
http://www.wiley-vch.de/home/chemistry/ or from the authors.
3354
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
0947-6539/01/0715-3354 $ 17.50+.50/0
Chem. Eur. J. 2001, 7, No. 15

3354±3362
D
C
A
B
Y = (CH2OCH2)n
OnPrO
Y
1 : m = 0; p = 2
O
O
HO
OH
nPrO
HO
O
OBn
OH
O
(CH2)p
S
4
8
X
i)
iv)
H
S
m
In order to promote the electropolymerization process and
minimize the steric interactions between the adjacent calix-
arene moieties on the resulting polymer, we have now
modified monomers 1 by replacing the 3-thienyl ethylene
moiety with a 2,2'-dithiophene-3-yl-hexylene functionality. In
this paper we describe the synthesis, structural character-
ization and binding studies of dithiophene-containing cone
and partial cone calix[4]crown ethers 2 and 3 (m ˆ 1, p ˆ 6),
and demonstrate that these monomers undergo electrochem-
ical polymerization to poly(dithiophenes) with pendant
calix[4]arene-crown-ether functionalities. These hybrid mate-
rials behave as useful CMEs for the electrochemical sensing of
alkali metal ions.
nPrO
O
nPrO
O
O
OH
OR
O
X
X
5: R = Bn
6: R = H
9
ii)
iii)
iii)
nPrO
nPrO
O
O
O
O
O
O
(CH2)6
(CH2)6
X
X
S
S
Results and Discussion
S
S
Cone calix[4]crown ether monomers 2 and partial cone
monomers 3, endowed with a pendant 2,2'-dithiophene-3-yl-
hexylene moiety at the lower rim, were synthesized using the
strategy presented in Scheme 1. Cone precursors 6 were
obtained by reaction of 4[9] with the appropriate oligoethylene
glycol ditosylate and NaH in dry THF to afford cone
calix[4]crown derivatives 5 (71 ± 75% yield), followed by
selective removal (Pd/C, H2; 1 atm) of the benzyl protecting
group. The Pd-catalyzed hydrogenolysis of 5 to produce 6 is
highly recommended over other methods (i.e., Me3SiCl[9]),
because the reaction is clean and proceeds smoothly in nearly
quantitative yield. The partial cone precursors 9 were
prepared in reasonable yield (30 ± 38%) by direct propylation
of 1,3-bridged calix[4]crowns 8[11] with nPrI and Cs2CO3 in
refluxing CH3CN. The final conversion of 6 and 9 into target
cone and partial cone monomers 2 and 3 was accomplished in
good yield (48 ± 70%) by alkylation with the known[12] 3-(6-
bromohexyl)-2,2'-dithiophene (7) and NaH in dry THF
(Scheme 1). The use of NaH as a base ensured that the
conformation of the precursors was retained upon derivatiza-
tion.
All new compounds were characterized by 1H and 13C NMR
spectroscopy, FAB-MS and elemental analysis. The cone
structures show the expected two AX pattern (Dd >1.2 ppm)
for the bridging methylene protons and two resonances
around d ˆ 31 for the relevant carbons, while their partial
cone counterparts display one AX (Dd ˆ 1.15 Æ 0.07 ppm) and
one AB system (Dd ˆꢀ 0.05 ppm) for the ArCH2Ar protons,
and two resonances close to d ˆ 31 and 39 for the correspond-
ing carbons. The 1H NMR spectra of 9 and 3 suggest that the
n-propoxy group attached to the inverted phenol residue is
3
2
a: X = (CH2OCH2)2
b: X = (CH2OCH2)3
Scheme 1. Synthesis of monomers
2 and 3. i) oligoethylene glycol
ditosylate, NaH, THF, reflux, 24 h; ii) H2 (1 atm), Pd/C, AcOEt, RT, 4 h;
iii) 3-(6-bromohexyl)-2,2'-dithiophene (7), NaH, THF, reflux, 24 h; iv) n-
PrI, Cs2CO3, CH3CN, reflux, 4.5 ± 22 h.
included inside the hydrophobic cavity generated by the three
remaining aryl rings.
1H NMR titration experiments of 2 and 3 with NaSCN and
KSCN (up to 2 equiv), carried out in CDCl3/CD3OD (1:1 v/v),
showed that the introduction of a 2,2'-dithiophene function-
ality at the lower rim of calixcrowns was not detrimental to
their binding abilities. In agreement with the known size-
selectivity displayed by calixcrowns,[13] calix[4]crown-4 mono-
mers 2a and 3a formed 1:1 complexes with NaSCN and did
‡
‡
not bind KSCN at all. Very high Na /K selectivity levels,
comparable to those reported by Shinkai for the structurally
related (1,3)-diethoxy-calix[4]crown-4 cone and partial cone
conformers,[11] were therefore expected for 2a and 3a. With a
NaSCN/calixcrown-4 molar ratio of 0.5, separate resonances
for the complex and free monomer are simultaneously present
in both cases, which indicates that 2a and 3a form strong
‡
complexes with Na with slow exchange kinetics on the NMR
time-scale.
On the other hand, the larger calix[4]crown-5 derivatives
2b and 3b are best adapted for the complexation of K (slow
exchange rate process on the NMR time-scale), but still allow
the inclusion of the smaller Na ion. The complexation
‡
‡
Chem. Eur. J. 2001, 7, No. 15
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
0947-6539/01/0715-3355 $ 17.50+.50/0
3355

G. Mori, S. Pappalardo et al.
FULL PAPER
‡
process with Na is in fast exchange regime with cone 2b, but
participation by the n-propoxy oxygen in the stabilization of
the complex, and consequently the calixarene framework is
believed to approach an almost flat partial cone conforma-
unexpectedly slow with partial cone 3b. The behavior of 3b
with Na ions apparently contrasts with the fast exchange
process previously found for the Na complexation with the
partial cone conformer of 1,3-bridged di-(a-picolyloxy)-p-tert-
butylcalix[4]crown-5,[13f] and may imply a different coordina-
tion geometry around the Na ion.
The solution structures of the alkali metal complexes with
monomers 2 and 3 in the stated solvent mixture were inferred
by a scrutiny of the complexation-induced shifts (CIS),
‡
‡
‡
tion. Obviously, the small Na ion is less tightly bound by the
1
larger crown-5 derivative 3b, and a H NMR experiment in
which one equivalent of KSCN was added to the preformed
‡
‡
‡
Na ꢁ 3b complex has shown that the Na ion can easily be
‡
displaced by the better fitting K ion (Figure 2c).
A comparison between the CIS values of the n-propoxy
‡
‡
group in Na ꢁ 3b and K ꢁ 3b complexes shows that the two
defined as Dd ˆ d[monomer´M
‡
d[monomer] in ppm, which are
ions have different binding modes. The ion ± dipole interac-
tion of the n-propoxy group with Na is now overcome by a
]
‡
summarized in Table 1. The remarkable downfield shifts
more effective cation ± p inter-
action with the softer K ion,[14]
which pushes the O-nPr group
‡
Table 1. 1H NMR complexation induced shifts [Dd ˆ d[monomer´M
‡
d[monomer] in ppm] of selected protons for
dithienyl calix[4]crown complexes with NaSCN and KSCN in CDCl3/CD3OD (1:1 v/v).
]
out of the calix cavity, as evi-
denced by the substantial
downfield shift experienced by
the protons of the inverted n-
propoxy-phenyl residue (Ta-
ble 1 and Figure 2b, c).
The electropolymerization of
2 and 3 on Pt disk electrodes
was achieved by repetitive scan
cyclic voltammetry (RSCV)[3]
under strictly controlled exper-
imental conditions. Unsubsti-
tuted poly(dithiophene) can be
obtained from acetonitrile or
dichloromethane solutions.[6, 15]
‡
‡
‡
‡
‡
‡
Protons
Na ꢁ 2a
Na ꢁ 2b
K ꢁ 2b
Na ꢁ 3a
Na ꢁ 3b
K ꢁ 3b
tBu (A,C-rings)
tBu (B,D-rings)[a]
OCH2CH2CH3
OCH2CH2CH3
OCH2CH2CH3
ArCH2Ar eq
ArCH2Ar ax
ArH (A,C-rings)
ArH (B,D-rings)
0.28
0.11
0.12
0.35
0.15
0.10
0.42
0.24
0.03
0.03, 0.15
0.01, 0.15
0.05, 0.11
0.04
0.05
0.09
0.13
0.02
0.51
0.07
0.04
0.03
1.25
0.32
1.07
[b]
[b]
[b]
0.89
1.06
1.25
0.32
0.03
0.59
0.10
0.28
0.04
0.70
0.04
0.28
0.02
0.78
0.06
0.27
0.21
0.13
0.12
0.04
0.09
0.15, 0.37
0.00, 0.13
0.09, 0.33
0.02, 0.05
0.21, 0.38
0.01, 0.09
[a] Aryl rings holding the polyether chain. [b] Not measured, because the relevant protons are buried under the
signals of the crown ether moiety.
observed for the aromatic (0.59 ± 0.78 ppm) and tert-butyl
protons (0.28 ± 0.42 ppm) of the alkylated A,C-rings in the
alkali complexes with cone monomers 2 are suggestive of a C2v
symmetry in the free ligands (A,C-rings in roughly parallel
planes), and a pseudo-four-fold C4v symmetry in the com-
plexes (A,C-rings markedly diverging, and B,D-rings holding
the polyether bridge slightly converging upon complexation).
In the complex, the alkali metal ion is believed to be sitting
inside the hydrophilic cavity defined by the crown ether and
phenoxy oxygens, with the calix[4]arene moiety adopting an
almost regular conic shape.
However, monomers 2 and 3 are not soluble in neat
acetonitrile, whereas neat dichloromethane readily solubilizes
the oligomers generated in the early stages of the process, thus
preventing the attainment of the critical solubility required
for the electrodeposition. Electropolymerization was there-
fore conducted in CH2Cl2/CH3CN (1:5 v/v) containing 10 1m
Bu4NPF6 as a supporting electrolyte with a silver wire
Å
pseudoreference electrode (Ep ferrocene ˆ 0.40 V). A typical
voltammogram showing the growth of the film from monomer
2b is depicted in Figure 3. The choice of the window potential
(E ˆ 0.0 ± 1.3 V) and particularly the anodic limit are ex-
tremely critical to obtain film deposition and to avoid over-
oxidation phenomena. The oxidation peak potential of
monomers 2a and 3a lies at 1.025 V, whereas 2b and 3b
show the peak at 1.035 V. The resulting films were greenish-
blue in color in the oxidized form, and deep red when
reduced. They were soluble in CHCl3 and THF, and insoluble
in CH3CN.
The n-propoxy group attached to the inverted phenol unit
in partial cone monomers 3 proved to be a useful probe for
assessing the binding sites and geometry of their complexes
with alkali metal salts. Undoubtedly the O-nPr substituent
shows a certain propensity to fill the hydrophobic cavity of the
free monomers, as shown by the upfield resonances close to
‡
d ˆ 0.0 (Figure 1, 2, traces a), but upon Na complexation it
intrudes more deeply inside the calix cup, as evidenced by the
A comparison of the structural features and electrochemical
behavior of monomers 1 ± 3 shows that the replacement of an
alkylthiophene with an alkyldithiophene calixcrown pendant
and an increase in the spacer length favor the electropolyme-
rization/deposition process. This trend closely parallels the
one previously reported for mono- and dithiophene crown-
ether-functionalized monomers.[5b] In that instance, steric
repulsion and/or solubility effects and more importantly the
lowering of the oxidation potential due to the more extended
p-system of the dithiophene moiety were invoked to account
for the electrooxidative polymerization outcome.
dramatic upfield CIS observed for the b-methylene group in
‡
the Na ꢁ 3a complex (Dd ˆ 1.25 ppm) (Figure 1c) and to a
‡
much lesser extent in the Na ꢁ 3b complex (Dd ˆ
0.32 ppm) (Figure 2b). The overall CIS values observed
‡
for the Na ꢁ 3a,b complexes (Table 1) are consistent with the
‡
formation of capsular complexes, with the Na ion bound
inside the hydrophilic crown ether cavity and the n-propoxy
group acting as a stopper from the upper rim side. The
remarkable upfield shift experienced by the b-methylene
‡
protons in the Na ꢁ 3a complex is suggestive of a strong
3356
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
0947-6539/01/0715-3356 $ 17.50+.50/0
Chem. Eur. J. 2001, 7, No. 15

Calixarene-Based Electrodes
3354±3362
Figure 1. Selected regions of the 1H NMR spectra (300 MHz, CDCl3/CD3OD 1:1 v/v, 228C) of partial cone monomer 3a a), and spectral changes upon
addition of 0.5 b) and 1.0 equiv c) of NaSCN. An asterisk indicates residual solvent peak. In the middle trace, a slow exchange rate between the free monomer
‡
‡
‡
and its Na complex accounts for peak doubling. The upper trace (Na ꢁ 3a complex) provides clear evidence that the Na ion is tightly encapsulated inside
the ionophoric cavity composed by the four crown ether oxygens and the ethereal oxygens of the lower rim substituents. The complexation induced shifts
(CIS) for the inverted O-nPr group indicate that this substituent intrudes very deeply inside the calix cup, acting as a stopper.
Initial studies on the CMEs 2b and 3b for the potentio-
metric recognition of K ions revealed that the electro-
determined by the fixed interference method[16] and calcu-
lated with a non-linear regression on a modified Nicolsky ±
Eisenman Equation[17] [Eq. (1)], where b is the slope (mV/pI),
ak is the activity of the primary ion to which the CME is
‡
chemical behavior of the polymeric films was extremely
sensitive to the oxygen dissolved in the tested aqueous
solution. Thus, the films of the CMEs were set into the
reduced form, using an aqueous solution of 10 1m KCl
containing traces of hydrazine, dried, and then coated with a
dibutyl sebacate membrane supported on poly(vinylchloride)
(PVC), in which only potassium tetrakis(4-chlorophenyl)bo-
rate (K(TCPB)) was dissolved. The potentiometric response
‡
reversible, KK,Na is the selectivity constant of the device for K
‡
vs Na ions, aNa is the activity of the interfering ion, and x is an
ªapparent activityº present on the electrode at the beginning
of the calibration in the absence of added ions. Equation (1)
allows the simultaneous interpolation of several calibration
curves obtained with different methods and with different
interferent concentrations (see Supporting Information).
‡
of PVC-coated CMEs 2b and 3b towards K ions (KCl) was
‡
measured in the presence of Na as interfering ions (NaCl).
Their characteristic parameters, shown in Table 2, were
E ˆ Econst‡blog(aK‡KK,Na ´ aNa‡x)
(1)
‡
‡
The potentiometric values of K /Na selectivity shown by
CMEs 2b and 3b, albeit moderate, are significantly higher
than those determined, under identical experimental condi-
Table 2. Electrochemical parameters for CMEs 2b and 3b.[a]
CME
Slope [mV/pK]
log x
logKK,Na
1.51(0.06)
tions, either by a PVC-coated bare Pt-electrode (pKK,Na
ˆ
2b
3b
49.3(1.6)
59.2(0.7)
4.6(0.1)
4.4(0.1)
0.18(0.05)) or a PVC-coated Pt-electrode modified with
unfunctionalized poly(dithiophene) (pKK,Na ˆ 0.20(0.03)).
This experimental evidence rules out the hypothesis that the
0.63(0.02)
[a] Standard deviations in parentheses.
Chem. Eur. J. 2001, 7, No. 15 ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
0947-6539/01/0715-3357 $ 17.50+.50/0
3357

G. Mori, S. Pappalardo et al.
FULL PAPER
Figure 2. The three spectral regions of the 1H NMR spectra (300 MHz, CDCl3/CD3OD 1:1 v/v, 228C) of 3b a), and spectral changes upon addition of
1.0 equiv NaSCN b), and then 1.0 equiv KSCN c). An asterisk indicates residual solvent peak. A comparison of traces b) and c) emphasizes the different
‡
‡
coordination geometry and binding sites around the encapsulated Na (ion ± dipole interaction with the n-propoxy group) or K (cation ± p interaction with
the inverted aryl unit) ions.
‡
‡
analyte ions (K or Na ) with different charge density, and
confirms that an active role is played by the calixcrown
moieties of the poly(dithiophene) films 2b and 3b. Further-
more, the lower selectivity of the partial cone CME 3b
(pKK,Na ˆ 0.63) with respect to the cone 2b (pKK,Na ˆ 1.51),
agrees with the results of NMR experiments.
Although the mechanism accounting for the potentiometric
ion recognition of PVC-coated CMEs 3b and 2b is not yet
fully understood and deserves further investigation, it is worth
mentioning that, to the best of our knowledge, this is the first
instance in which calixarene ± poly(dithiophene)-based CMEs
have successfully been employed for the recognition of alkali
metal ions in aqueous solution.[18]
The potentiometric behavior of CMEs 2a and 3a could not
be studied, as the PVC coating was hampered by the high
solubility of the film in the solvents (THF, DMF, cyclo-
hexanone) commonly used to solubilize PVC.
The amperometric selectivity of PVC-uncoated CMEs 3a
and 2b for alkali metal ions was studied in both aqueous and
organic media. Cyclic voltammetry (CV) experiments, per-
formed in monomer-free acetonitrile solutions, showed that
the complexation of alkali metal ions strongly influences the
voltammetric behavior of our electrodes. For instance, in the
Figure 3. Cyclic voltammograms recorded during the electropolymeriza-
tion of monomer 2b. The polymer was grown on a polished Pt disk
electrode of 1.35 mm radius by cycling the potential between 0.0 and 1.3 V
1
vs Ag/AgCl at a scan rate of 100 mVs of a solution of 2b (10 2 m) and
Bu4NPF6 (10 1m) in CH2Cl2/CH3CN (1:5 v/v).
observed selectivity might simply be due to unspecific
interactions between the ion-exchanger (K(TCPB)) and/or
the solvent (dibutyl sebacate) of the PVC membrane and the
3358
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
0947-6539/01/0715-3358 $ 17.50+.50/0
Chem. Eur. J. 2001, 7, No. 15

Calixarene-Based Electrodes
3354±3362
case of CME 3a the anodic peak current (Epa ˆ 1.05 V) of the
by the presence of alkali metal ions. Furthermore, since no
amperometric response was obtained for the model CME
based on the unsubstituted poly(dithiophene), the changes in
cyclic voltammograms recorded in solutions of NaClO4 in
‡
10 1m Bu4NPF6, decreased with the increase of Na concen-
tration, ranging from 1.0Â 10 5 to 2.2 Â 10 4 m (Figure 4). Con-
the electronic properties of CME 3a induced by Li and Na
‡
‡
ions can be attributed to specific host ± guest interactions
between the calixcrown units and the target analyte. Attempts
‡
to free the Na -containing film 3a from the bound ions by
rinsing with fresh CH3CN did not restore the original electro-
activity of the CME.
Calixcrown-5-based CME 2b was amperometrically re-
‡
sponsive to K ions, but the selectivity over other alkali metal
ions was poor.
‡
The selective recognition of Na ions by CME 3a was
further investigated by means of frequency response analysis
(FRA) experiments[19] in the 104 ± 10 1 Hz frequency range at
the open circuit potential, using solutions analogous to those
employed in the amperometric measurements. Nyquist dia-
grams obtained with CME 3a show how the resistance of the
Figure 4. Cyclic voltammograms (E vs Ag/AgCl) of PVC-uncoated CME
3a (scan rate 50 mVs 1) in 10 1m Bu4NPF6/CH3CN solution in the presence
of increasing concentrations of NaClO4 (1.0 Â 10 5 ± 2.2 Â 10 4 m).
‡
polymeric film decreases with the increase of Na ion
concentration (Figure 6). Conversely, the resistance of a
versely, CME 3a was voltammetrically inactive in water, where
‡
no oxidation peak could be detected. The effect of Na ions
on the CV response of CME 3a in CH3CN can presumably be
‡
ascribed to the accumulation of positive charges (Na ) in the
calixarene moieties of the polymeric film, which electrostati-
cally hamper the formation of positive charges on the
poly(dithiophene) backbone during the oxidation process.
Figure 5 shows that the amperometric response of calix-
‡
‡
crown-4-based CME 3a is highly selective for Na over K ,
‡
‡
‡
NH4 , and Cs ions, while Li ion strongly interferes, as its size
allows it to be included in the crown-4 moiety. Over the same
Figure 6. Nyquist diagrams (Z' indicates the real component of the
impedance, and Z'' the imaginary one) recorded with CME 3a by FRA
experiments, showing a progressive decrease in polymer resistance upon
‡
exposure to increasing amounts of Na ions (NaClO4).
second film based on 3a was substantially unchanged in the
‡
presence of increasing amounts of K ions (Figure 7). The
present data demonstrate that drastic changes in the film
‡
Figure 5. Correlation plots of anodic peak current vs ion concentration
(Li , Na , K , NH4 , and Cs ) obtained with CME 3a at the potential value
of 1.05 V.
resistance are only due to the selective Na ion recognition by
the calixcrown unit of the CME 3a.
‡
‡
‡
‡
‡
In conclusion, the present study shows that dithiophene-
substituted calix[4]arene-crown ethers can be conveniently
electropolymerized on Pt disks, regardless of their conforma-
tion and the length of the crown ether chain, to provide ion-
responsive sensory materials with interesting potentialities in
both potentiometric and amperometric recognition of alkali
metal ions. Fine tuning of the calixcrown monomers to
generate new materials with enhanced and/or different
analyte selectivities is currently in progress.
concentration range of ion added (as perchlorate salts), the
‡
‡
decrease of the peak current upon addition of Li and Na
‡
‡
‡
ions was about ten-fold that caused by K , NH4 , and Cs ions.
A control experiment carried out in an analyte-free solution
did not show, after a number of successive scans, any
appreciable changes in the cyclic voltammograms, thus
confirming that the redox chemistry of CME 3a is influenced
Chem. Eur. J. 2001, 7, No. 15
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
0947-6539/01/0715-3359 $ 17.50+.50/0
3359

G. Mori, S. Pappalardo et al.
FULL PAPER
4H), 6.49, 6.46 (s, 2H each), 4.72 (s, 2H), 4.40, 4.38 (d, J ˆ 12.4 Hz, 2H
each), 4.24 ± 4.16 (m, 2H), 4.06 ± 3.87 (m, 6H), 3.70 ± 3.62 (m, 4H), 3.43 ±
3.35 (m, 2H), 3.12, 3.11 (d, J ˆ 12.4 Hz, 2H each), 1.94 (sextet, J ˆ 7.4 Hz,
2H), 1.34, 0.83, 0.81 (s, ratio 2:1:1, 36H), 1.03 (t, J ˆ 7.4 Hz, 3H); 13C NMR:
d ˆ 154.7, 152.4, 151.2 (s, Csp2-O), 144.9, 144.3, 143.7 (s, Csp2 tBu), 137.8 (s,
Ph), 135.5, 135.4, 132.0, 131.8 (s, bridgehead-C), 129.9, 128.4, 128.0, 125.6,
125.5, 124.5, 124.3 (d, Ar, Ph), 78.2 (t, OCH2Ph), 77.6 (t, OCH2CH2CH3),
73.6, 70.6, 70.0 (t, OCH2CH2O), 34.1, 33.6, 33.5 (s, C(CH3)3), 31.7, 31.16,
31.10 (q, C(CH3)3), 30.6, 30.4 (t, ArCH2Ar), 23.4 (t, OCH2CH2CH3), 10.7
‡
(q, OCH2CH2CH3); FAB(‡) MS: m/z: 895 [MH] ; elemental analysis calcd
(%) for C60H78O6 (894.6): C 80.50, H 8.78; found: C 80.15, H 8.64.
a
a
5,11,17,23-Tetrakis(1,1-dimethylethyl)-25,27-(crown-4) -26-hydroxy -28-
a
propoxy -calix[4]arene (6a):[22] A suspension of 5a (0.447 g, 0.5 mmol) and
10% Pd/C (50 mg) in AcOEt (25 mL) was stirred for 4 h at room
temperature in the presence of H2 (1 atm). The mixture was filtered
through a bed of celite, and the filtrate was evaporated to dryness to give a
solid. Recrystallization from CHCl3/MeOH gave monohydroxy-crown-4 6a
1
(0.342 g, 85%). M.p. 218 ± 2208C; H NMR: d ˆ 7.14 (pseudo-s, 4H), 6.64
(s, 2H), 6.62 (s, 1H), 6.41 (s, 2H), 4.60 ± 4.53 (m, 2H), 4.55, 4.40 (d, J ˆ
12.7 Hz, 2H each), 3.77 ± 3.69 (m, 2H), 3.75 (t, J ˆ 7.4 Hz, 2H), 3.22, 3.15 (d,
J ˆ 12.7 Hz, 2H each), 1.97 (sextet, J ˆ 7.4 Hz, 2H), 1.33, 0.96, 0.71 (s, ratio
2:1:1, 36H), 1.11 (t, J ˆ 7.4 Hz, 3H); 13C NMR: d ˆ 154.2 (Â2), 152.2, 147.6
(s, Csp2-O), 145.8 (Â2), 144.3 (s, Csp2-tBu, alkylated rings), 142.3 (s, Csp2-tBu,
unalkylated ring), 135.9, 135.2, 131.7, 130.9 (s, bridgehead-C), 126.0, 125.2,
125.0, 123.8 (d, Ar), 77.7 (t, OCH2CH2CH3), 74.6, 71.0, 70.8 (t, OCH2-
CH2O), 34.1 (Â2), 33.6, 33.5 (s, C(CH3)3), 31.8 (t, ArCH2Ar), 31.6 (Â2),
31.2 (q, C(CH3)3), 31.1 (t, ArCH2Ar), 31.0 (q, C(CH3)3), 23.7 (t,
Figure 7. Nyquist diagrams (Z' indicates the real component of the
impedance, and Z'' the imaginary one) recorded with CME 3a by FRA
experiments in the presence of different amounts of K ions (KClO4). No
‡
changes in polymer resistance is observed.
‡
OCH2CH2CH3), 10.7 (q, OCH2CH2CH3); FAB(‡) MS: m/z: 805 [MH] ;
elemental analysis calcd (%) for C53H72O6 (804.5): C 79.05, H 9.02; found:
C 78.86, H 9.15.
a
a
Experimental Section
5,11,17,23-Tetrakis(1,1-dimethylethyl)-25,27-(crown-5) -26-hydroxy -28-
propoxy -calix[4]arene (6b):[22] Pd/C-catalyzed hydrogenolysis of 5b under
a
conditions analogous to those described for 5a, afforded monohydroxy-
crown-5 6b (93%). The physical and spectral data are coincident with those
reported in the literature.[9]
General: Melting points were determined on a Kofler hot stage and are not
corrected. Unless otherwise stated, 1H and 13C NMR spectra were recorded
in CDCl3 (TMS as an internal standard) with a Varian Gemini 300
spectrometer at 300 and 75 MHz, respectively. 13C NMR spectra were
acquired with the APT technique. FAB(‡) mass spectra were obtained
with a Finnigan MAT 90 spectrometer, using 3-nitrobenzyl alcohol as a
matrix. TLC was performed on silica gel coated plastic plates (Polygram
SIL G/UV254, Macherey ± Nagel), and column chromatography (CC) was
carried out with 230 ± 400 mesh, Merck Kieselgel 60 silica gel. All chemicals
were of the best grade commercially available and were used without
purification. Dry solvents were purchased from Fluka. Compounds 4,[9] 7,[12]
8a,[11] 8b,[13f] and oligoethylene glycol ditosylates[20] were prepared accord-
ing to literature procedures.
Propylation of 5,11,17,23-tetrakis(1,1-dimethylethyl)-25,27-(crown-4)-
26,28-dihydroxycalix[4]arene (8a):
A mixture of crown-4 diol 8a
(0.686 g, 0.9 mmol) and Cs2CO3 (0.293 g, 0.9 mmol) in dry CH3CN
(25 mL) was refluxed under stirring for 1 h. Then nPrI (0.595 g, 3.5 mmol)
was added and the mixture was heated at reflux. After 6 h, a second portion
of nPrI (0.595 g, 3.5 mmol) was added, and reflux was continued for a total
of 22 h. After cooling, the solvent was evaporated and the residue was
partitioned between 1n HCl and CH2Cl2. The organic layer was washed
with a dilute aqueous Na2S2O3, then with water and dried (Na2SO4). The
crude product obtained by evaporation of the solvent was purified by CC
(silica gel, eluent: hexanes/AcOEt 6:1 ! 2:1 v/v) to afford 9a (0.277 g,
38%). M.p. 200 ± 2028C (CH3CN/CH2Cl2); 1H NMR: d ˆ 7.32 (s, 1H), 7.14,
7.02 (s, 2H each), 7.17/6.95 (ABq, J ˆ 2.6 Hz, 4H), 4.38/3.30 (AX, J ˆ
12.5 Hz, 4H), 3.97 ± 3.49 (m, 16H), 1.92 (t, J ˆ 7.8 Hz, 2H), 1.42, 1.22, 1.21
(s, ratio 1:2:1, 36H), 0.05 (sextet, J ˆ 7.8 Hz, 2H), 0.59 (t, J ˆ 7.4 Hz, 3H);
Electropolymerizations and voltammetric studies were conducted using the
computerized Autolab PGSTAT 20 potentiostat (Ecochemie, Utrecht, The
Netherlands) connected to a 663 VA Stand (Metrohm, Herisau, Switzer-
land) and controlled by Ecochemie GPES 4.4 software. Polymeric films
were obtained by cycling potential for a number of 25 scans between 0 and
1.3 V in 5 Â 10 3 m monomer and 0.1m Bu4NPF6 solutions. The three-
electrode miniaturized cell (1 mL) was equipped with a platinum disk (rˆ
1.5 mm) working electrode and a platinum rod counter. All potential values
were measured against a silver/silver chloride pseudoreference electrode
with respect to which the ferrocene system showed an Ep ˆ 0.402 V. FRA
experiments were performed with the same equipment, controlled by
Ecochemie FRA 2.3 software. Potentiometric measurements were carried
13C NMR: d ˆ 154.3, 153.0 (Â2), 149.4 (s, Csp2-O), 146.0 (Â2), 144.1 (s, Csp2
-
tBu, alkylated rings), 141.8 (s, Csp2-tBu, unalkylated ring), 134.6, 133.7, 133.2,
129.1 (s, bridgehead-C), 126.5, 125.9, 125.5, 124.2 (d, Ar), 71.3 (t,
OCH2CH2CH3), 72.7, 70.2, 69.3 (t, OCH2CH2O), 39.6 (t, ArCH2Ar), 34.1,
34.0 (Â2), 33.8 (s, C(CH3)3), 31.9 (t, ArCH2Ar), 31.8, 31.6, 31.4 (Â2) (q,
C(CH3)3), 21.2 (t, OCH2CH2CH3), 8.6 (q, OCH2CH2CH3); FAB(‡) MS:
‡
m/z: 805 [MH] ; elemental analysis calcd (%) for C53H72O6 (804.5):
C 79.05, H 9.02; found: C 79.27, H 8.88.
out using
a Radiometer PHM84 digital potentiometer (Radiometer
Medical A/S, Copenaghen, Denmark). The PVC membrane is analogous
Propylation
26,28-dihydroxycalix[4]arene (8b):
of
5,11,17,23-tetrakis(1,1-dimethylethyl)-25,27-crown-5 ±
mixture of crown-5 diol 8b
to that previously used for ISEs.[21]
A
a
a
5,11,17,23-Tetrakis(1,1-dimethylethyl)-25-benzyloxy -26,28-(crown-4) -27-
(1.536 g, 1.9 mmol) and Cs2CO3 (0.620 g, 1.9 mmol) in dry CH3CN
(30 mL) was refluxed under stirring for 1 h. Then nPrI (0.258 g, 1.5 mmol)
in CH3CN (20 mL) was added dropwise and the mixture was heated at
reflux for 4.5 h. After cooling, the solvent was evaporated and the residue
was partitioned between 1n HCl and CH2Cl2. The organic layer was
washed with a dilute aqueous Na2S2O3, then with water and dried
(Na2SO4). The crude product obtained after evaporation of the solvent
was purified by CC (silica gel, hexanes/AcOEt 8:1 v/v) to give colorless
propoxy -calix[4]arene (5a):[22] A mixture of 4 (0.550 g, 0.704 mmol) and
a
NaH (0.090 g, 3.75 mmol) in dry THF (40 mL) was heated under reflux for
1.5 h under stirring. Triethylene glycol ditosylate (0.353 g, 0.77 mmol) in dry
THF (10 mL) was then added dropwise over 30 min, and reflux was
continued for additional 20 h. The reaction was quenched by cautious
addition of MeOH (2 mL), and the solvent was evaporated. The residue
was partitioned between acidified water and CH2Cl2. The organic layer was
dried (Na2SO4) and concentrated to leave a solid, which upon recrystal-
lization from CH3CN/CH2Cl2 gave crown-4 5a (0.450 g, 71%) as colorless
crystals. M.p. >2508C; 1H NMR: d ˆ 7.57 ± 7.36 (m, 5H), 7.13 (pseudo-s,
1
crystals of 9b (0.400 g, 30%). M.p. 238±2408C (MeOH/CH2Cl2); H NMR:
d ˆ 7.22, 7.04 (s, 2H each), 7.02 (s, 1H), 6.98/6.96 (ABq, J ˆ 2.4 Hz, 4H),
4.41/3.20 (AX, J ˆ 12.9 Hz, 4H), 4.12 (dt, J ˆ 10.1, 3.0 Hz, 2H), 4.00 ± 3.93
3360
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
0947-6539/01/0715-3360 $ 17.50+.50/0
Chem. Eur. J. 2001, 7, No. 15

Calixarene-Based Electrodes
3354±3362
(m, 2H), 3.86/3.81 (ABq, J ˆ 16.5 Hz, 4H), 3.78 ± 3.59 (m, 12H), 2.09 (t, J ˆ
8.2 Hz, 2H), 1.45, 1.28, 1.14 (s, ratio 1:1:2, 36H), 0.95 (sextet, J ˆ 7.5 Hz,
2H), 0.13 (t, J ˆ 7.4 Hz, 3H); 13C NMR: d ˆ 154.3, 152.4 (Â2), 150.3 (s,
Csp2-O), 145.7 (Â2), 143.7 (s, Csp2-tBu, alkylated rings), 141.0 (s, Csp2-tBu,
unalkylated ring), 133.9, 133.7, 133.4, 127.9 (s, bridgehead-C), 127.1, 126.1,
125.9, 124.7 (d, Ar), 73.8, 72.7, 71.3, 70.7, 70.3 (t, OCH2CH2O,
OCH2CH2CH3), 38.9 (t, ArCH2Ar), 34.1, 33.9 (Â2), 33.8 (s, C(CH3)3),
31.9, 31.7, 31.2 (Â2) (q, C(CH3)3), 30.9 (t, ArCH2Ar), 22.6 (t,
J ˆ 7.8 Hz, 2H), 1.90 (t, J ˆ 5.5 Hz, 2H), 1.81 (quin, J ˆ 7.4 Hz, 2H), 1.63
(quin, J ˆ 7.4 Hz, 2H), 1.44 ± 1.30 (m, 4H), 1.38, 1.28, 1.08 (s, ratio 1:2:1,
36H), 0.01 ± 0.10 (m, 5H); 13C NMR: d ˆ 154.8, 154.1 (Â2), 152.8 (s,
Csp2-O), 145.3 (Â2), 144.2, 143.9 (s, Csp2-tBu), 139.5 (s, ThTh), 136.1, 133.4,
133.1, 132.6 (s, bridgehead-C), 130.5 (s, ThTh), 129.8, 127.3, 126.1, 126.0,
125.8, 125.5, 125.3, 124.5, 123.7 (d, Ar, ThTh), 76.0 (t, OCH2(CH2)5ThTh),
72.5, 69.9, 69.3 (t, OCH2CH2O), 70.5 (t, OCH2CH2CH3), 38.7 (t, ArCH2Ar),
34.02 (Â2), 34.00, 33.9 (s, C(CH3)3), 31.7, 31.6 (Â2), 31.3 (q, C(CH3)3), 30.7,
30.4, 29.8, 29.4, 29.0, 25.9 (t, OCH2(CH2)5ThTh, ArCH2Ar), 22.2 (t,
‡
OCH2CH2CH3), 9.1 (q, OCH2CH2CH3); FAB(‡) MS: m/z: 849 [MH] ;
‡
elemental analysis calcd (%) for C55H76O7 (848.5): C 77.79, H 9.02; found: C
77.47, H 8.95.
OCH2CH2CH3), 10.1 (q, OCH2CH2CH3); FAB(‡) MS: m/z: 1053 [MH] ;
elemental analysis calcd (%) for C67H88O6S2 (1052.6): C 76.38, H 8.43, S
6.07; found: C 76.11, H 8.36, S 5.94.
Alkylation of monopropylated calix[4]crowns with 3'-(6-bromohexyl)-2,2'-
dithiophene (7)
a
5,11,17,23-Tetrakis(1,1-dimethylethyl)-25,27-(crown-5) -26-{[6-(2,2'-bithio-
a
b
phene-3-yl)hexyl]oxy} -28-propoxy -calix[4]arene (3b):[22] Purified by two
subsequent CC (eluent: first column, cyclohexane/AcOEt 9:1, v/v; second
column, hexanes/AcOEt 4:1 v/v); 70% yield. M.p. 125 ± 1278C (EtOH);
1H NMR: d ˆ 7.27 (dd, J ˆ 5.1, 1.2 Hz, 1H), 7.19/6.93 (ABq, J ˆ 2.4 Hz, 4H),
7.152 (d, J ˆ 5.2 Hz, 1H), 7.150 (s, 2H), 7.08 (dd, J ˆ 3.6, 1.2 Hz, 1H), 7.03
(dd, J ˆ 5.1, 3.6 Hz, 1H), 6.90 (d, J ˆ 5.2 Hz, 1H), 6.88 (s, 2H), 4.33/3.20
(AX, J ˆ 12.0 Hz, 4H), 3.91 ± 3.39 (m, 18H), 3.86 (pseudo-s, 4H), 2.74 (t,
J ˆ 7.6 Hz, 2H), 1.87 (quint, J ˆ 7.5 Hz, 2H), 1.76 (t, J ˆ 5.8 Hz, 2H), 1.65
(quint, J ˆ 7.5 Hz, 2H), 1.43, 1.27, 1.07 (s, ratio 1:2:1, 36H), 1.42 ± 1.30 (m,
4H), 0.02 ± 0.14 (m, 5H); 13C NMR: d ˆ 154.4, 154.1 (Â2), 152.4 (s,
Csp2-O), 145.2, 144.0 (s, Csp2-tBu), 139.3, 133.3 (s, ThTh), 135.9, 133.4, 133.2,
132.6 (s, bridgehead-C), 129.7, 128.8, 127.3, 126.0, 125.9, 125.7, 125.3, 124.8,
123.7 (d, Ar, ThTh), 76.1 (t, OCH2(CH2)5ThTh), 73.7, 71.2, 71.0, 70.5 (t,
OCH2CH2O), 70.8 (t, OCH2CH2CH3), 38.9 (t, ArCH2Ar), 34.0 (Â3), 33.8
(s, C(CH3)3), 31.7, 31.6 (Â2), 31.3 (q, C(CH3)3), 30.6, 30.3, 30.1, 29.7, 29.0,
25.9 (t, OCH2(CH2)5ThTh, ArCH2Ar), 22.3 (t, OCH2CH2CH3), 10.2 (q,
General procedure: A stirred suspension of the appropriate n-propoxy-
calix[4]crown (0.2 mmol) and NaH (14.4 mg, 0.6 mmol) in dry THF
(10 mL) was refluxed for 1 h under inert atmosphere. Then a solution of
7 (72 mg, 0.22 mmol) in THF (10 mL) was added through cannula, and
reflux was continued for 24 h. After cooling, the reaction mixture was
quenched with MeOH (2 mL), and concentrated to dryness. The crude
product was taken up in aqueous ethanol and heated under reflux for 12 ±
48 h. After extraction with CHCl3, the organic layer was dried over
anhydrous Na2SO4 and concentrated. The residue was purified either by
silica gel CC and/or recrystallization from EtOH.
a
5,11,17,23-Tetrakis(1,1-dimethylethyl)-25,27-(crown-4) -26-{[6-(2,2'-dithio-
a
a
phene-3-yl)hexyl]oxy} -28-propoxy -calix[4]arene (2a):[22] Purified by CC
1
(AcOEt/MeOH 95:5 v/v); 48% yield; foamy; H NMR: d ˆ 7.25 (dd, J ˆ
5.0, 1.3 Hz, 1H), 7.16 (d, J ˆ 5.1 Hz, 1H), 7.13 (s, 4H), 7.09 (dd, J ˆ 3.6,
1.3 Hz, 1H), 7.01 (dd, J ˆ 5.0, 3.6 Hz, 1H), 6.93 (d, J ˆ 5.1 Hz, 1H), 6.47 (s,
4H), 4.38, 4.37 (d, J ˆ 12.4 Hz, 2H each), 4.34, 4.03 (t, J ˆ 6.0 Hz, 4H each),
3.83 (s, 4H), 3.70 (t, J ˆ 7.1 Hz, 2H), 3.68 (t, J ˆ 7.2 Hz, 2H), 3.14, 3.13 (d,
J ˆ 12.4 Hz, 2H each), 2.77 (t, J ˆ 7.7 Hz, 2H), 2.03 ± 1.90 (m, 4H), 1.76 ±
1.40 (m, 4H), 1.34, 0.82 (s, ratio 1:1, 36H), 1.30 (m, 2H), 1.06 (t, J ˆ 7.5 Hz,
3H); 13C NMR: d ˆ 154.6 (Â2), 152.3 (Â2) (s, Csp2-O), 144.9 (Â2), 143.8
(Â2) (s, Csp2-tBu), 139.5 (s, ThTh), 135.5 (Â2), 131.8 (Â2) (s, bridgehead-C),
130.5 (s, ThTh), 129.9, 127.3, 126.0, 125.6 (Â2), 125.3, 124.3 (Â2), 123.7 (d,
Ar, ThTh), 77.7 (t, OCH2CH2CH3), 75.9 (t, OCH2(CH2)5ThTh), 73.6, 70.9,
70.2 (t, OCH2CH2O), 34.1 (Â2), 33.6 (Â2) (s, C(CH3)3), 31.7 (Â2), 31.1
(Â2) (q, C(CH3)3), 30.8, 30.5, 30.3, 29.7, 29.5, 29.1, 26.1 (t,
OCH2(CH2)5ThTh, ArCH2Ar), 23.5 (t, OCH2CH2CH3), 10.8 (q,
‡
OCH2CH2CH3); FAB(‡) MS: m/z: 1097 [MH] ; elemental analysis calcd
(%) for C69H92O7S2 (1096.6): C 75.50, H 8.45, S 5.83; found: C 75.33, H 8.36,
S 5.71.
Acknowledgements
Á
We thank Dr. P. Fallini (Universita di Parma) for help with the
experimental work, and MURST for financial support.
‡
OCH2CH2CH3); FAB(‡) MS: m/z: 1053 [MH] ; elemental analysis calcd
[1] a) C. D. Gutsche, Calixarenes Revisited in Monographs in Supra-
molecular Chemistry, Vol. 6 (Ed.: J. F. Stoddart), The Royal Society of
Chemistry, Cambridge, 1998; b) V. Böhmer, Angew. Chem. 1995, 107,
785 ± 818; Angew. Chem. Int. Ed. Engl. 1995, 34, 713 ± 745; c) Calix-
arenes, a Versatile Class of Macrocyclic Compounds (Eds.: J. Vicens, V.
Böhmer), Kluwer Academic, Dordrecht, 1991.
[2] D. Diamond, M. A. McKervey, Chem. Soc. Rev. 1996, 25, 15 ± 24; D. N.
Reinhoudt, Recl. Trav. Chim. Pays-Bas 1996, 115, 109 ± 118; K. M.
OꢁConnor, D. W. M. Arrigan, G. Svehla, Electroanalysis 1995, 7, 205 ±
215.
[3] S. J. Higgins, Chem. Soc. Rev. 1997, 26, 247 ± 257, and references
therein.
[4] F. Bedioui, J. Devynck, C. Bied-Charreton, Acc. Chem. Res. 1995, 28,
30 ± 36; A. Deronzier, J. C. Moutet, Coord. Chem. Rev. 1996, 147,
339 ± 371.
(%) for C67H88O6S2 (1052.6): C 76.38, H 8.43, S 6.07; found: C 76.27, H 8.33,
S 5.85.
a
5,11,17,23-Tetrakis(1,1-dimethylethyl)-25,27-(crown-5) -26-{[6-(2,2'-dithio-
a
phene-3-yl)hexyl]oxy}a-28-propoxy -calix[4]arene (2b):[22] Purified by di-
rect recrystallization of the crude reaction mixture; 58% yield. M.p. 173 ±
1768C (EtOH); 1H NMR: d ˆ 7.26 (dd, J ˆ 5.2, 1.3 Hz, 1H), 7.16 (d, J ˆ
5.3 Hz, 1H), 7.11 (s, 4H), 7.09 (dd, J ˆ 3.6, 1.3 Hz, 1H), 7.03 (dd, J ˆ 5.2,
3.6 Hz, 1H), 6.93 (d, J ˆ 5.3 Hz, 1H), 6.42 (s, 4H), 4.35, 4.34 (d, J ˆ 12.5 Hz,
2H each), 4.30 ± 4.18 (m, 8H), 3.78 ± 3.66 (m, 12H), 3.13, 3.12 (d, J ˆ
12.5 Hz, 2H each), 2.77 (t, J ˆ 7.7 Hz, 2H), 2.01 ± 1.89 (m, 4H), 1.73 ± 1.62
(m, 2H), 1.53 ± 1.42 (m, 4H), 1.34, 0.80 (s, ratio 1:1, 36H), 1.04 (t, J ˆ 7.5 Hz,
3H); 13C NMR: d ˆ 155.0, 152.3 (s, Csp2-O), 144.9 (Â2), 143.93, 143.90 (s,
Csp2-tBu), 139.41 (s, ThTh), 135.39, 135.35, 131.7 (Â2) (s, bridgehead-C),
130.5 (s, ThTh), 129.8, 127.3, 126.0, 125.5 (Â2), 125.3, 124.4 (Â2), 123.7 (d,
Ar, ThTh), 77.7 (t, OCH2CH2CH3), 75.9 (t, OCH2(CH2)5ThTh), 72.5, 71.9,
71.2, 70.1 (t, OCH2CH2O), 34.1 (Â2), 33.5 (Â2) (s, C(CH3)3), 31.7 (Â2),
31.1 (Â2) (q, C(CH3)3), 31.0 (Â3), 30.7, 30.3, 29.0, 26.1 (t,
OCH2(CH2)5ThTh, ArCH2Ar), 23.5 (t, OCH2CH2CH3), 10.7 (q,
[5] See for example: a) H. K. Youssoufi, M. Hmyene, F. Garnier, D.
Delabouglise, J. Chem. Soc. Chem. Commun. 1993, 1550 ± 1552; b) P.
Bäuerle, S. Scheib, Adv. Mater. 1993, 5, 848 ± 853.
[6] J. Roncali, Chem. Rev. 1992, 92, 711 ± 738.
‡
OCH2CH2CH3); FAB(‡) MS: m/z: 1097 [MH] ; elemental analysis calcd
[7] The chemical copolymerization and electrochemical properties of a
calixarene-functionalized dithiophene have recently been described:
M. J. Marsella, R. J. Newland, P. J. Carrol, T. M. Swager, J. Am. Chem.
Soc. 1995, 117, 9842 ± 9848.
(%) for C69H92O7S2 (1096.6): C 75.50, H 8.45, S 5.83; found: C 75.32, H 8.30,
S 5.95.
a
5,11,17,23-Tetrakis(1,1-dimethylethyl)-25,27-(crown-4) -26-{[6-(2,2'-dithio-
a
b
phene-3-yl)hexyl]oxy} -28-propoxy -calix[4]arene (3a):[22] Purified by two
subsequent CC (eluent: first column, cyclohexane/AcOEt 9:1 v/v; second
column, hexanes/AcOEt 4:1 v/v); 64% yield. M.p. 115 ± 1178C (EtOH);
1H NMR: d ˆ 7.26 (dd, J ˆ 4.9, 1.1 Hz, 1H), 7.21/6.94 (ABq, J ˆ 2.5 Hz, 4H),
7.15 (d, J ˆ 5.2 Hz, 1H), 7.09 (s, 2H), 7.08 (dd, J ˆ 3.6, 1.1 Hz, 1H), 7.03 (dd,
J ˆ 4.9, 3.6 Hz, 1H), 6.90 (d, J ˆ 5.2 Hz, 1H), 6.88 (s, 2H), 4.41/3.23 (AX,
J ˆ 12.1 Hz, 4H), 4.03 (dt, J ˆ 10.2, 6.0 Hz, 2H), 3.87 (pseudo-s, 4H), 3.80 ±
3.51 (m, 8H), 3.78 (t, J ˆ 7.5 Hz, 2H), 3.19 (dt, J ˆ 10.2, 6.0 Hz, 2H), 2.73 (t,
[8] R. D. McCullough, Adv. Mater. 1998, 10, 93 ± 116.
[9] G. Ferguson, J. F. Gallagher, A. J. Lough, A. Notti, S. Pappalardo,
M. F. Parisi, J. Org. Chem. 1999, 64, 5876 ± 5885; corrigendum: G.
Ferguson, J. F. Gallagher, A. J. Lough, A. Notti, S. Pappalardo, M. F.
Parisi, J. Org. Chem. 2000, 65, 930.
[10] No electrodeposition was observed by varying the solvent (CH2Cl2,
CH2Cl2/CH3CN mixtures), the monomer concentration (10 3 ± 10 1m),
the supporting electrolyte (Bu4NPF6, Bu4NBF4, Et4NBr), the working
Chem. Eur. J. 2001, 7, No. 15
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
0947-6539/01/0715-3361 $ 17.50+.50/0
3361

G. Mori, S. Pappalardo et al.
FULL PAPER
Á
electrode (Pt, Au, glassy carbon), and the conditions of potential
application (potentiodynamic, potentiostatic). The anodic current
peaks (Epa) occurred above 1.7 V vs Ag/AgCl, and progressively
decreased in intensity during scanning, indicating that the oxidation
only concerns the monomer diffusing to the electrode.
[16] C. Macca, Anal. Chim. Acta 1996, 321, 1 ± 10, and references therein.
[17] G. Mori, M. Giannetto, Ann. Chim. (Rome) 1999, 89, 601 ± 611; D.
Á
Diamond, F. J. Saez de Viteri, Analyst 1994, 119, 749 ± 758.
[18] Unsuccessful attempts have been made to use electropolymerized
pyrrole-containing calix[4]arene films for the detection of alkali metal
ions: A. Buffenoir, G. Bidan, Synth. Met. 1999, 102, 1300 ± 1301; Z.
Chen, P. A. Gale, P. D. Beer, J. Electroanal. Chem. 1995, 393, 113 ± 117.
[19] A. J. Bard, L. R. Faulkner, Electrochemical Methods: Fundamentals
and Applications, Wiley, New York, 1980, Chapter 9; Z. B. Stoynov,
B. M. Grafov, B. S. Savova-Stoynov, V. V. Elkin, Electrochemical
Impedance, Nauka, Moscow, 1991.
[20] M. Ouchi, Y. Inoue, T. Kanzaki, T. Hakushi, J. Org. Chem. 1984, 49,
1408 ± 1412.
[21] M. Giannetto, G. Mori, A. Notti, S. Pappalardo, M. F. Parisi, Anal.
Chem. 1998, 70, 4631 ± 4635; C. Bocchi, M. Careri, A. Casnati, G.
Mori, Anal. Chem. 1995, 67, 4234 ± 4638.
[11] H. Yamamoto, S. Shinkai, Chem. Lett. 1994, 1115 ± 1118.
[12] L. Huchet, S. Akoudad, J. Roncali, Adv. Mater. 1998, 10, 541 ± 545.
[13] a) E. Ghidini, F. Ugozzoli, R. Ungaro, S. Harkema, A. Abu El-Fadl,
D. N. Reinhoudt, J. Am. Chem. Soc. 1990, 112, 6979 ± 6985; b) Z.
Brzozka, B. Lammerink, D. N. Reinhoudt, E. Ghidini, R. Ungaro, J.
Chem. Soc. Perkin Trans. 2 1993, 1037 ± 1040; c) A. Casnati, A.
Pochini, R. Ungaro, C. Bocchi, F. Ugozzoli, R. J. M. Egberink, H.
Struijk, R. Lugtenberg, F. de Jong, D. N. Reinhoudt, Chem. Eur. J.
1996, 2, 436 ± 445; d) R. Ungaro, A. Casnati, F. Ugozzoli, A. Pochini,
J.-F. Dozol, C. Hill, H. Rouquette, Angew. Chem. 1994, 106, 1551 ±
1553; Angew. Chem. Int. Ed. Engl. 1994, 33, 1506 ± 1509; e) A. Casnati,
A. Pochini, R. Ungaro, F. Ugozzoli, F. Arnaud, S. Fanni, M.-J.
Schwing, R. J. M. Egberink, F. de Jong, D. N. Reinhoudt, J. Am. Chem.
Soc. 1995, 117, 2767 ± 2777; f) F. Arnaud-Neu, G. Ferguson, S.
Fuangswasdi, A. Notti, S. Pappalardo, M. F. Parisi, A. Petringa, J.
Org. Chem. 1998, 63, 7770 ± 7779.
[22] Notations
a and b were introduced by Shinkai to define the
stereochemistry of calix[4]arene atropisomers having mixed substitu-
ents at the lower rim: K. Iwamoto, K. Araki, S. Shinkai, Tetrahedron
1991, 47, 4325 ± 4342.
[14] F. Ugozzoli, O. Ori, A. Casnati, A. Pochini, R. Ungaro, D. N.
Reinhoudt, Supramol. Chem. 1995, 5, 179 ± 184.
[15] R. J. Waltman, J. Bargon, Can. J. Chem. 1986, 64, 76 ± 95; R. J.
Waltman, J. Bargon, A. F. Diaz, J. Phys. Chem. 1983, 87, 1459 ± 1463.
Received: August 8, 2000
Revised version: December 23, 2000 [F2659]
3362
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
0947-6539/01/0715-3362 $ 17.50+.50/0
Chem. Eur. J. 2001, 7, No. 15