A supramolecular approach for the formation of fullerene-phthalocyanine dyads

Article abstract of DOI:10.1039/b110270m

A supramolecular Pc-C₆₀ dyad with pseudorotaxane-like geometry has been assembled in solution by the threading of a dibenzylammonium unit attached to a fullerene through the crown ether of an unsymmetrically substituted phthalocyanine, which co

Full text of DOI:10.1039/b110270m

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A supramolecular approach for the formation of
fullerene–phthalocyanine dyads
M. Victoria Mart´ınez-D´ıaz,a Nicolette S. Fender,b M. Salome´ Rodr´ıguez-Morgade,a
Marcos Go´mez-Lo´pez,c Franc¸ois Diederich,c Luis Echegoyen,b J. Fraser Stoddartd and
Toma´s Torres*a
aDepartamento de Qu´ımica Orga´nica, Facultad de Ciencias, Universidad Auto´noma de
Madrid, Cantoblanco, 28049 Madrid, Spain
bDepartment of Chemistry, University of Miami, Coral Gables, FL 33124, USA
cLaboratorium fu¨r Organische Chemie, ETH-Zentrum, Universita¨tstrasse 16, 8092 Zu¨rich,
Switzerland
dDepartment of Chemistry and Biochemistry, University of California, Los Angeles,
405 Hilgard Avenue, Los Angeles, CA 90095, USA
Received 9th November 2001, Accepted 18th January 2002
First published as an Advance Article on the web 21st February 2002
A supramolecular Pc–C60 dyad with pseudorotaxane-like geometry has been assembled in solution by the
threading of a dibenzylammonium unit attached to a fullerene through the crown ether of an unsymmetrically
substituted phthalocyanine, which contains a DB24C8 moiety. Spectroscopic data as well as electrochemical
studies suggest a conformation for the complex in which the two bulky subunits are far apart from each other,
thus preventing electronic interactions between both electroactive subunits.
Here, we report the first example of a Pc–C60 pseudorotaxane-
Introduction
like complex formed in solution [1?2-H][PF6] (Fig. 1). This
inclusion complex consists of two components: an unsymme-
trically substituted phthalocyanine 1 containing a DB24C8 unit
attached to the Pc core, and a C60 derivative 2-H?PF6,5a in which
a secondary dibenzylammonium moiety has been linked to the
C60 by a modified Bingel reaction.10 These two components,
which both contain different electroactive subunits, can be
assembled in a CHCl3 solution by threading the dibenzyl-
ammonium chain of 2-H?PF6 through the DB24C8 ring of
component 1, thus forming the typical stable pseudorotaxane-
like complex.7 By arranging the two electroactive subunits
in such a geometry we expected them to be close enough to
exhibit electronic coupling between the Pc and C60 components.
For this reason, we have carried out electrochemical studies,
but these did not reveal a measurable interaction as reflected in
the redox properties upon complexation.
[60]Fullerenes are one of the acceptor units most frequently
used in the construction of photovoltaic devices on account
of their unique electrochemical properties—namely their
ability to reversibly accept up to six electrons.1 On the other
hand, phthalocyanines2 (Pcs) are the best known azapor-
phyrin analogues. They are very versatile and stable aromatic
chromophores with unusual physico-chemical properties that
can play a crucial role in different fields of materials science.
Therefore, much attention has been devoted to the study of
Pcs as organic building blocks applicable as active components
in gas sensors, electrochromic devices, field effect transistors
and photovoltaic cells. These two redox-active moieties have
been covalently linked following different synthetic strategies
to form phthalocyanine–fullerene hybrids.3 In the case of
the dyad reported by us in which the Pc and C60 subunits
are connected through a pyrrolidine spacer, the presence of
inter- and intramolecular electronic interactions in the ground
state has been ascertained for the first time by electrochemical
studies.3d
Supramolecular chemistry represents an elegant alternative
approach for the construction of functional systems by means
of noncovalent bonding interactions.4 Recently, supramolecu-
lar C605 and Pc6 dimers have been self-assembled via hydrogen
bonding between complementary recognition motifs. Some of
them5a,6 are based on the recognition motif developed by
one of us, involving medium-sized crown ether macrocycles,
such us dibenzo-24-crown-8 (DB24C8), and secondary dialkyl-
ammonium cations, e.g., dibenzylammonium (DBA1) as its
2
PF6 salt.7 These two components assemble in solution and
in the solid state to form stable complexes with a pseudo-
rotaxane superstructure. Although some complexes between
C60 and planar aromatic macrocycles such as porphyrins8 or
porphyrazines9 have been reported, there are no supramole-
cular hydrogen bonded Pc–C60 dyads described in the literature
to our knowledge.
Fig. 1 Structure of proposed [2]pseudorotaxane [1?2-H][PF6].
DOI: 10.1039/b110270m
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Scheme 1 Synthesis of the dicyano-24C8 derivative 8.
to their Q-bands. The 1H NMR spectra of compounds 1a
and 1b show well-resolved sets of resonances which, in agree-
ment with their UV–vis spectra, suggest that these DB24C8–
phthalocyanines do not form strong aggregates in solution. The
aromatic phthalocyanine protons appear at d ~ 8.3–8.2
and 9.0–8.9 for 1a and 1b, respectively.
Results and discussion
Synthesis
The dicyano-24C8 derivative 8 was prepared following a
standard stepwise procedure,11 the key step of which is the
formation (Scheme 1) of a crown ether, as a result of a
macrocyclization reaction of catechol with the diol 5 via its
bis(toluene-p-sulfonate) derivative 6. Under semi-high-dilution
conditions (Cs2CO3–MeCN, in the presence of CsOTs and
LiBr), the dibromo-DB24C8 derivative 7 was obtained in
80% yield. Further conversion into the dinitrile derivative by
means of the Rosenmund–von Braun reaction gave rise to
the Pc precursor 8 in 55% yield. This last step was highly
dependent on the experimental conditions, affording different
yields of compound 8 for each batch, and, in some cases,
variable amounts of a by-product which has been identified
as the mononitrile derivative 9.
The convergent synthesis of phthalocyanines 1a–c is outlined
in Scheme 2 and synthetic details are given in the Experimental
section. The three compounds were obtained in 16–30% yield
by the crossover condensation of the dicyano-24C8 8 and
4,5-bis(octyloxy)phthalonitrile (10)12 in the presence of the
corresponding metal salt. These reactions afforded mixtures
of all the possible phthalocyanines. In each case, they were
separated and purified by flash chromatography. Compounds
1a–c were characterized by mass spectrometry and by NMR
and UV–vis spectroscopy. Thus, Pcs 1a, 1b, and 1c showed
their corresponding molecular ions at m/z ~ 1708.8, 1715.1
and 1713.9, respectively. Their UV–vis spectra exhibited
absorptions in the range lmax ~ 671–678 nm that are assigned
Complexation studies
1H NMR spectroscopy has proven to be the best technique for
the characterization in solution of [2]pseudorotaxane com-
plexes formed between DB24C8 type macrocycles and
dibenzylammonium hexafluorophosphate derivatives.7 The
main reason is the unusually slow host–guest exchange on
1
the H NMR time-scale at room temperature, a phenomenon
which gives rise to three sets of resonances assigned to i) the
two free components and ii) the 1 : 1 complex. This situation
allows the determination of the stoichiometry and the
association constant (Ka) of the complex by integration of
the signals of the three species at equilibrium. Moreover, the 1H
NMR spectra of these types of complexes display some
diagnostic signals that help in their characterization, for
instance, for the CH2N1 protons of the complexed ammonium
salt and for the 1,2-dioxybenzene protons on the DB24C8
macrocycle. Since the pseudorotaxane-like superstructures of
some of these complexes, especially the one formed between
DB24C8 and DBA?PF6, have been determined by X-ray
crystallography and NOE studies,7 the superstructures of
complexes based on this particular recognition motif can be
shown to be similar by simply analyzing their 1H NMR spectra.
The 1H NMR spectrum (500 MHz, 298 K) of a 1 : 1 mixture
of 1a and 2-H?PF6 (c ~ 2.4 mM) in CDCl3 (Fig. 2) displays
some of the above-mentioned, characteristic resonances,
indicating that complexation is taking place by threading of
the fullerene-containing diammonium salt through the
DB24C8 subunit of compound 1a. In particular, the char-
acteristic high field shift and splitting of the resonances
assigned to the 1,2-dioxybenzene unit are observed. As in the
case of the phthalocyanine dimer already reported by us,6 the
signals of the Pc core become nonequivalent and strongly
upfield-shifted upon complexation. Fortunately, diagnostic
1
Fig. 2 Partial H NMR spectrum (500 MHz, 298 K, CDCl3) of a 1 : 1
mixture of 1a and 2-H?PF6.
Scheme 2 Synthesis of phthalocyanines 1a–c.
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Fig. 3 MALDI-TOF mass spectrum (matrix: dithranol) of a mixture of
1a and 2-H?PF6.
signals for both free and complexed ArCH2O subunits on the
fullerene component 2-H?PF6 were identified. The comparison
of the intensities of these two singlets allowed us to determine
the association constant (Ka ~ 15300 M21), which is similar in
magnitude to that reported for related complexes in the same
solvent.5a,7
Fig. 4 Cyclic voltammograms (sweep rate 100 mV s21) for a) 2-H?PF6
and b) a 1 : 1 mixture of 1b and 2-H?PF6 (6.4 6 1024 M), in CH2Cl2
(1 0.1 M TBAPF6) at room temperature.
Molecular modeling studies have confirmed that the fullerene-
containing diammonium salt can adopt several conformations
in the complex in which the carbon sphere is too far from the
The formation of the 1 : 1 complex [1a?2-H][PF6] was also
evidenced by matrix-assisted laser desorption ionization time-
of-flight (MALDI-TOF) mass spectrometry using dithranol
(anthracene-1,8,9-triol) as the matrix. The spectrum recorded
from a 1 : 1 mixture of the fullerene-containing diammonium
salt 2-H?PF6 and the crowned phthalocyanine 1a displays
an intense peak at m/z ~ 2769 (Fig. 3) which corresponds
1
phthalocyanine ring. Probably, and in agreement with the H
NMR spectrum of the complex, the C60 subunit prefers to be
far from the phthalocyanine ring of 1b for steric reasons.
2
to the supramolecular ion [1a?2-H]1 after loss of the PF6
counterion.
Conclusions
The UV–vis spectrum of a dilute solution (c ~ 3.2 6 1026 M)
of 1a in CH2Cl2 did not change significantly upon addition
of an equimolar amount of the fullerene derivative 2-H?PF6,
thus indicating negligible electronic interactions between the
chromophores in the ground state. This observation is con-
sistent with the electrochemical results discussed in the
following section.
A supramolecular approach has been applied successfully for
the first time to the preparation of fullerene–phthalocyanine
dyads. A supramolecular complex has been formed by attach-
ing covalently both electroactive subunits to a dibenzylammo-
nium hexafluorophosphate salt and a DB24C8 macrocycle,
respectively, to allow molecular recognition by hydrogen
bonding between these two recognition motifs, namely,
DB24C8 and (DBA)1. Electrochemical and UV–vis studies
failed to reveal measurable electronic interactions between the
Pc and the C60 subunits in the ground state. The preparation of
related noncovalent Pc–C60 dyads as targets for electron and
energy transfer processes is under investigation.
Similar results to those described above were obtained for
the complexation of 1b and 2-H?PF6 to yield [1b?2-H][PF6].
Complex [1c?2-H][PF6] could not be studied by H NMR due
1
to the presence of the paramagnetic central ion.
Electrochemical studies
The redox properties of both the individual components 1b and
2-H?PF6 and the [2]pseudorotaxane [1b?2-H][PF6] were studied
by cyclic voltammetry (CV) at room temperature in CH2Cl2
(1 0.1 M NBu4PF6). Potentials were measured (Table 1)
against the ferrocene/ferricinium (Fc/Fc1) couple as internal
reference. Since 1a and 1b have similar complexing abilities
with 2-H?PF6, compound 1b was selected for these studies
because of its better electron-donor character. As previously
Experimental
Chemicals were purchased from Aldrich Chemical Co. and
used as received without further purification. Compounds 3
and 4 were prepared according to refs. 13 and 11, respectively.
UV–vis spectra were recorded with a Hewlett-Packard 8453
instrument. IR spectra were recorded on a Bruker Vector 22
spectrophotometer. FAB-MS and HRMS spectra were deter-
mined on a VG AutoSpec instrument. MALDI-TOF MS were
recorded with a Bruker Reflex III spectrometer. NMR spectra
were recorded with Bruker WM-200-SY, Bruker AC-300 and
Bruker DRX-500 instruments. Column chromatography was
reported,5a two quasi-reversible reduction waves at EK
~
21.08 and 21.45 V were observed (Fig. 4) for the fullerene-
containing diammonium salt 2-H?PF6. Upon addition of the
crown ether phthalocyanine 1b, these waves did not change
significantly, revealing that complexation does not influence
the reduction properties of the fullerene component and
suggesting that the electroactive units are not close enough
to allow measurable electronic interactions between them.
˚
carried out on silica gel Merck-60 (230–400 mesh, 60 A),
neutral alumina 90 active and TLC on aluminium sheets
precoated with silica gel 60 F254 (E. Merck).
Table 1 Electrochemical dataa of compounds 1b and 2-H?PF6 and the supramolecular complex [1b?2-H][PF6]
1
2
3
4
Compound
Eox
Ered
Ered
Ered
Ered
1b
2-H?PF6
[1b?2-H][PF6]
10.03 (185)
—
—
21.56 (190)
21.08 (88)
21.05 (110)
21.87 (160)
21.45 (110)
21.42 (118)
21.97 (irrev.)
21.96 (irrev.)
22.13 (irrev.)
22.11 (irrev.)
aEK potential given in V vs. Fc/Fc1 observed by cyclic voltammetry on glassy carbon in CH2Cl2 solutions containing 0.1 M NB4PF6; DE
values in mV are in parentheses at v ~ 0.1 V s21
.
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1,2-Bis{2’-[2@-(2--hydroxyethoxy)ethoxy]ethoxy}-4,5-
dibromobenzene (5)
ammonia (30 ml). Air was bubbled through the blue solution
for 2 h, and afterwards the mixture was extracted with
dichloromethane, washed with water and dried over MgSO4.
After filtration and evaporation, the residue was chromato-
graphed on deactivated (5% H2O) neutral aluminium oxide
using ethyl acetate as eluent. Yield 762 mg (55%). Selected
A mixture of 313 (13.98 g, 45.94 mmol), 4,5-dibromocatechol
(4)11 (3.06 g, 11.4 mmol) and potassium carbonate (21.14 g,
153 mmol) in dimethylformamide (80 ml) was stirred under
argon at 100 uC for 2.5 days. The mixture was allowed to cool
down to room temperature and afterwards it was poured into
water. The organic layer was extracted with dichloromethane,
washed four times with water, and dried over MgSO4.
Chromatography on silica gel of the obtained oil using an
8 : 1 mixture of dichloromethane and methanol as eluent pro-
vided 5 as an oil. Yield 6.08 g (100%). Selected spectroscopic
data: 1H NMR d (CDCl3): 7.13 (s, 2H, arom.), 4.20–3.60
(4 6 m, 24H, OCH2). LSIMS-MS (m-NBA) m/z: 531 (M1H)1.
Found: C, 40.2; H, 5.0. Calc. for C18H28Br2O8: C, 40.6; H,
5.3%.
1
spectroscopic data: H NMR d (CDCl3): 7.11 (s, 2H, arom.),
6.89, 6.88 (AA’BB’ system, 4H, arom.), 4.22–4.11 (m, 8H,
OCH2), 3.96–3.87 (m, 8H, OCH2), 3.82 (s, 8H, OCH2). 13C
NMR d (CDCl3): 152.3, 148.8, 121.5, 116.4, 115.7, 114.0, 108.9,
71.6, 71.3, 70.0, 69.3. IR (KBr) n: 3127, 3062 (CH), 2930, 2892,
2874, 2838 (CH), 2231 (CN), 1591, 1520, 1507, 1451, 1356,
1291, 1253, 1228, 1216, 1134, 1100, 1058, 1035, 969 cm21
.
LSIMS-MS (m-NBA) m/z: 498 (M1), 499 (M1H)1,
521 (M1Na)1. Found: C, 62.3; H, 6.5; N, 5.4. Calc. for
C26H30N2O8: C, 62.6; H, 6.1; N, 5.6%.
2-Cyano-6,7,9,10,12,13,20,21,23,24,26,27-dodecahydrodibenzo-
[b,n][1,4,7,10,13,16,19,22]octaoxacyclotetracosine (9)
1,2-Bis{2’-[2@-(2--tosyloxyethoxy)ethoxy]ethoxy}-4,5-
dibromobenzene (6)
Compound 9 was obtained in variable yields during the
synthesis of the dicyano derivative 8, and isolated from the first
eluted fractions of the column chromatography. 1H NMR d
(CDCl3): 7.40 (dd, J ~ 4, 8.3 Hz, 1H, H3), 7.10 (d, J ~ 8.3 Hz,
1H, H4), 6.95–6.80 (m, 5H, H1 1 H catechol), 4.20–4.00 (2m,
8H, OCH2), 3.80–3.70 (m, 8H, OCH2), 3.65 (s, 8H, OCH2).
LSIMS-MS (m-NBA) m/z: 473 (M1), 474 (M 1 H)1, 496 (M 1
Na)1.
A mixture of the dibromide 5 (6.08 g, 11.4 mmol), tosyl chloride
(8.41 g, 44.1 mmol) and triethylamine (2.31 g, 22.8 mmol)
in dichloromethane (85 ml) was stirred at room temperature
for 24 h until the reaction was complete. The solution was
poured into dilute hydrochloric acid and the organic layer was
extracted, washed four times with water and dried over
magnesium sulfate. After evaporation of the solvent, the
residue was chromatographed on silica gel using a 1 : 1 mixture
of ethyl acetate and hexanes, and then ethyl acetate, as eluents.
Compound 6 was collected from the second fraction as an oil.
Yield 5.85 g (61%). Selected spectroscopic data: 1H NMR d
(CDCl3): 7.78 (d, J ~ 8.3 Hz, 4H, arom., tosyl ring), 7.32 (d, J ~
8.3 Hz, 4H, arom., tosyl ring), 7.12 (s, 2H, arom.), 4.18–4.05
(m, 8H, OCH2), 3.85–3.66 (2 6 m, 16H, OCH2), 2.43 (s, 6H,
CH3). LSIMS-MS (m-NBA) m/z: 839 (M1H)1. Found: C,
45.2; H, 5.1. Calc. for C32H40Br2O12S2: C, 45.5; H, 4.8%.
[9,10,16,17,23,24-Hexakis(octyloxy)-22,23,25,26,28,29,218,219,
221,222,224,225-dodecahydrobenzo[n][1,4,7,10,13,16,19,22]-
octaoxacyclotetracosino[2,3-b]phthalocyaninato]nickel(II) (1a)
A mixture of the phthalonitrile derivative 8 (30 mg, 0.06 mmol),
4,5-bis(octyloxy)phthalonitrile 10 (69 mg, 0.18 mmol) and
Ni(OAc)2?4H2O (18 mg, 0.07 mmol) in N,N-dimethylamino-
ethanol (0.5 ml) was stirred at 140 uC for 24 h. After addition
of methanol, the dark solid was filtered and washed with the
same solvent. Chromatography of the crude on silica gel using
CHCl3 and then a 50 : 1 mixture of CHCl3 and MeOH afforded
the nickel phthalocyaninate 1a which was collected as a green
solid from the second fraction. Yield 16 mg (16%). 1H NMR d
(CDCl3): 8.27–8.25 (2 6 br s, 8H, Pc ring), 6.84, 6.83 (AA’BB’
system, 4H, arom), 4.71–3.95 (6 6 m, 36H, OCH2), 2.25–2.15,
1.89–1.75, 1.65–1.25, 1.09–0.99 (5 6 m, 90H, aliphatic); UV–
vis (CHCl3) (log e/dm3 mol21 cm21) lmax 289 (4.89), 310 (4.78),
411 (4.36), 605 (4.39), 643 (sh, 4.45), 671 nm (5.21); MALDI-
TOF-MS (dithranol) m/z 1709 (M1).
2,3-Dibromo-6,7,9,10,12,13,20,21,23,24,26,27-dodecahydrodi-
benzo[b,n][1,4,7,10,13,16,19,22]octaoxacyclotetracosine (7)
To a mixture of Cs2CO3 (4.53 g, 13.90 mmol) in dry acetonitrile
(460 ml) a solution of catechol (383 mg, 3.48 mmol) in dry
acetonitrile (230 ml) was added dropwise at 75 uC under argon.
The reaction mixture was heated under reflux for 2 h and then a
solution of the bis(toluene-p-sulfonate) 6 (2.92 g, 3.48 mmol) in
acetonitrile (231 ml) was added dropwise. After addition of
CsOTs (1 g, 3.3 mmol) and LiBr (605 mg, 6.97 mmol), the
mixture was stirred at reflux temperature for 2.5 days to drive
the reaction to completion. The solvent was evaporated under
reduced pressure and the residue was suspended in dichloro-
methane, washed with water and dried over magnesium sulfate.
Filtration and evaporation of the solution gave a white
solid which was chromatographed on silica gel using ethyl
acetate as eluent. Yield 1.69 g (80%). Selected spectroscopic
data: 1H NMR d (CDCl3): 7.06 (s, 2H, arom.), 6.88 (br s, 4H,
arom.), 4.21–4.05 (m, 8H, OCH2), 3.99–3.85 (m, 8H, OCH2),
3.81 (s, 8H, OCH2). LSIMS-MS (m-NBA) m/z: 606 (M 1 H)1,
629 (M 1 Na)1. Found: C, 47.1; H, 5.2. Calc. for C24H30Br2O8:
C, 47.5; H, 5.0%.
[9,10,16,17,23,24-Hexakis(octyloxy)-22,23,25,26,28,29,218,219,
221,222,224,225-dodecahydrobenzo[n][1,4,7,10,13,16,19,22]-
octaoxacyclotetracosino[2,3-b]phthalocyaninato]zinc(II) (1b)
A mixture of 8 (30 mg, 0.06 mmol), 4,5-bis(octyloxy)phthalo-
nitrile 10 (69 mg, 0.18 mmol) and Zn(OAc)2?2H2O (16 mg,
0.07 mmol) in N,N-dimethylaminoethanol (0.5 ml) was stirred
at 140 uC under Ar for 24 h. After addition of methanol the
green solid was filtered and washed with the same solvent.
Chromatography of the crude material on silica gel using
CHCl3 and then a 100 : 1 mixture of CHCl3 and MeOH
afforded the zinc phthalocyaninate 1b which was collected as
a green solid from the second fraction. Yield 31 mg (30%).
1H NMR d (CDCl3): 8.94, 8.90 (2 6 br s, 8H, Pc ring), 6.72,
6.40 (AA’BB’ system, 4H, arom.), 4.70–4.55, 4.28–2.50, (6 6
m, 36H, OCH2), 2.25–2.02, 1.86–0.60 (5 6 m, 90H, aliphatic);
UV–vis (CHCl3) (log e/dm3 mol21 cm-1) lmax 355 (4.56), 612
(4.11), 656 (sh, 4.15), 678 nm (4.91); MALDI-TOF-MS
(dithranol) m/z: 1715 (M1).
2,3-Dicyano-6,7,9,10,12,13,20,21,23,24,26,27-dodecahydrodi-
benzo[b,n][1,4,7,10,13,16,19,22]octaoxacyclotetracosine (8)
A mixture of 7 (1.69 g, 2.78 mmol) and CuCN (996 mg, 11.12
mmol) was heated under reflux in dimethylformamide (42 ml)
under argon for 24 h. After this time the reaction was com-
plete and the solution was allowed to cool down to room
temperature and subsequently poured into 33% aqueous
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[9,10,16,17,23,24-Hexakis(octyloxy)-22,23,25,26,28,29,218,
219,221,222,224,225-dodecahydrobenzo[n][1,4,7,10,13,16,19,22]-
octaoxacyclotetracosino[2,3-b]phthalocyaninato]copper(II) (1c)
Thieme, Stuttgart, 1998, p. 717; (c) G. de la Torre, M. Nicolau and
T. Torres, in Phthalocyanines: Synthesis, Supramolecular Organi-
zation and Physical Properties (Supramolecular Photosensitive and
Electroactive Materials), ed. H. S. Nalwa, Academic Press, New
York, 2001.
(a) T. G. Linssen, K. Du¨rr, M. Hanack and A. Hirsch, J. Chem.
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T. Linssen, A. Hirsch and M. Hanack, Chem. Ber., 1997, 130,
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1999, 1, 1807; (d) A. Gouloumis, S. G. Liu, A. Sastre, P. Va´zquez,
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A mixture of 8 (31 mg, 0.062 mmol, 4,5-bis(octyloxy)phthalo-
nitrile 10 (120 mg, 0.31 mmol) and Cu(OAc)2?H2O (27 mg,
0.134 mmol) in pentanol (10 ml) was refluxed under Ar in the
presence of DBU (7 drops) for 48 h. The reaction mixture was
allowed to cool down to room temperature and subsequently
methanol (20 ml) was added. The resulting precipitate was
filtered, washed with methanol and dried. The green solid
was chromatographed on silica gel using chloroform as eluent.
3
Yield 23 mg (22%). UV–vis (CHCl3) (log e/dm3 mol21 cm21
)
max 292 (4.87), 339 (4.85), 401 (4.68), 627 (4.66), 678 nm (4.79);
4
5
l
MALDI-TOF-MS (dithranol) m/z: 1714 (M1).
Electrochemical studies
All electrochemical experiments were performed on a BAS
100W electrochemical analyzer (Bioanalytical Systems, West
Lafayette, IN) at room temperature with a three-electrode
configuration in CH2Cl2 containing 0.1 M tetrabutylammo-
nium hexafluorophosphate (TBAPF6) as the supporting
electrolyte, which was recrystallized twice from ethanol and
dried under vacuum. A glassy carbon (GC, 3 mm) was used
as the working electrode and the counter electrode was a
platinum wire ( 1 mm). A non-aqueous Ag/Ag1 electrode
served as reference and ferrocene served as internal reference.
Both the counter and the reference electrodes were directly
immersed in the electrolyte solution. The scan rate was
generally 100 mV s21 unless otherwise specified.
6
7
M. V. Mart´ınez-D´ıaz, M. S. Rodr´ıguez-Morgade, M. C. Feiters,
P. J. M. van Kan, R. J. M. Nolte, J. F. Stoddart and T. Torres,
Org. Lett., 2000, 2, 1057.
(a) P. R. Ashton, P. J. Campbell, E. J. T. Chrystal, P. T. Glink,
S. Menzer, D. Philp, N. Spencer, J. F. Stoddart, P. A. Tasker and
D. J. Williams, Angew. Chem., Int. Ed. Engl., 1995, 34, 1865;
(b) P. R. Ashton, E. J. T. Chrystal, P. T. Glink, S. Menzer,
C. Schiavo, N. Spencer, J. F. Stoddart, P. A. Tasker, A. J. P. White
and D. J. Williams, Chem. Eur. J., 1996, 2, 709; (c) S. J. Cantrill,
A. R. Pease and J. F. Stoddart, J. Chem. Soc., Dalton Trans., 2000,
3715.
8
9
(a) P. D. W. Boyd, M. C. Hodgson, C. E. F. Rickard, A. G. Oliver,
L. Chaker, P. J. Brothers, R. D. Bolskar, F. S. Tham and
C. A. Reed, J. Am. Chem. Soc., 1999, 12, 10487; (b) T. Da Ros,
M. Prato, D. Guldi, E. Alessio, M. Ruzzi and L. Pasimeni, Chem.
Commun., 1999, 635; (c) D. M. Guldi, C. Luo, T. Da Ros,
M. Prato, E. Dietel and A. Hirsch, Chem. Commun., 2000, 375.
D. H. Hochmuth, S. L. J. Michel, A. J. P. White, D. J. Williams,
A. G. M. Barrett and B. M. Hoffman, Eur. J. Inorg. Chem., 2000,
593.
Acknowledgement
This work was supported by CICYT (Spain) through grant
MAT99/0180. We also acknowledge the MEC (Spain) for a
research contract to MSR-M. LE and JFS wish to acknowledge
the US National Science Foundation (grant CHE 9816503
and CHE 9910199) for generous financial support.
10 (a) C. Bingel, Chem. Ber., 1993, 126, 1957; (b) J.-F. Nierengarten,
V. Gramlich, F. Cardullo and F. Diederich, Angew. Chem., Int.
Ed. Engl., 1996, 35, 2101.
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