Synthesis of dumbbell-shaped bis-(pyrazolino[60]fullerene)-oligophenylenevinylene derivatives

Article abstract of DOI:10.1016/S0040-4039(02)01769-0

Symmetrically substituted oligophenylenevinylene (OPV) derivatives bearing terminal p-nitrophenyl-hydrazone groups have been prepared and used for the synthesis of dumbbell-shaped bis-(pyrazolino[60]fullerene)-OPV systems.

Full text of DOI:10.1016/S0040-4039(02)01769-0

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 7507–7511
Synthesis of dumbbell-shaped
bis-(pyrazolino[60]fullerene)-oligophenylenevinylene derivatives
Mar´ıa J. Go´mez-Escalonilla,a Fernando Langa,a,* Jean-Michel Rueff,b Laurence Oswaldb and
Jean-Franc¸ois Nierengartenb,*
aFacultad de Ciencias del Medio Ambiente, Universidad de Castilla-La Mancha, 45071 Toledo, Spain
bGroupe des Mate´riaux Organiques, Institut de Physique et Chimie des Mate´riaux de Strasbourg, Universite´ Louis Pasteur et
CNRS, 23 rue du Loess, 67037 Strasbourg Cedex, France
Received 21 August 2002; accepted 23 August 2002
Abstract—Symmetrically substituted oligophenylenevinylene (OPV) derivatives bearing terminal p-nitrophenyl-hydrazone groups
have been prepared and used for the synthesis of dumbbell-shaped bis-(pyrazolino[60]fullerene)-OPV systems. © 2002 Elsevier
Science Ltd. All rights reserved.
The design of molecules bearing covalently linked elec-
tron donors to [60]fullerene (C60) have received increas-
ing attention in the past few years as these systems can
be used in artificial photosynthesis and for photoelec-
tronic applications.1 As part of this research, com-
pounds combining C60 with p-conjugated oligomers are
of particular interest.2–5 On one hand, they provide
entry into photoinduced intramolecular processes such
as energy and electron transfer.3 On the other hand,
such hybrid compounds can be used for the preparation
of solar cells allowing a detailed structure–activity
exploration for a better understanding of the photo-
voltaic system.4 As far as the synthesis of such fullerene
derivatives is concerned, the 1,3-dipolar cycloaddition
of C60 with an azomethine ylide generated in situ from
an oligomer containing an aldehyde functionality and
N-methylglycine is the most widely used strategy.2–5
The resulting fulleropyrrolidines are usually obtained in
good yields but an asymmetric C atom is generated
during the cycloaddition reaction. Therefore, the use of
this methodology for the preparation of p-conjugated
systems bearing more than one fullerene sphere yields
diastereomeric mixtures.5 In this communication, we
show that oligophenylenevinylene (OPV) derivatives
substituted with two fullerene moieties can be obtained
by a 1,3-dipolar cycloaddition of C60 with bis-nitril-
imines which were themselves generated in a one pot
procedure6 from the corresponding bis-hydrazones.
Since no stereogenic centers are produced during
the reaction, the dumbbell-shaped bis-(pyrazolino-
[60]fullerene) OPV derivatives are obtained in a pure
form.
The strategy employed for the preparation of the func-
tionalized OPV precursors is based upon Wittig–
Horner type chemistry.7 To this end, the key building
blocks 3 and 9 were prepared first (Scheme 1). Bro-
momethylation of 1,4-bis(octyloxy)benzene 1, by treat-
ment with paraformaldehyde and HBr in acetic acid at
65°C, afforded 2 in 70% yield. Compound 2 was then
converted to the bis-phosphonate 3 in 91% yield by a
Michaelis–Arbuzov reaction. Compound 4 was pre-
pared in two steps from 1 according to a previously
reported method.2e Reaction of 4 with 2,2-dimethyl-
propane-1,3-diol in refluxing benzene in the presence of
a catalytic amount of p-toluenesulfonic acid (TsOH)
gave the protected aldehyde 5 in 87% yield. Subsequent
treatment with n-BuLi in Et2O at 0°C followed by
quenching with dry DMF afforded aldehyde 6 in 86%
yield. LiAlH4 reduction then yielded alcohol 7 which,
after treatment with CBr4/PPh3, gave bromide 8. Phos-
phonate 9 was finally obtained in 99% yield by reaction
of 8 with triethylphosphite under Michaelis–Arbuzov
conditions.
Treatment of aldehyde 6 with bis-phosphonate 3 in
THF in the presence of t-BuOK afforded the targeted
OPV trimer, but as an E:Z isomer mixture (Scheme 2).
The latter observation is quite surprising, as the reac-
tion of benzylic phosphonates with aromatic aldehydes
under Wittig–Horner conditions is generally stereose-
* Corresponding authors. E-mail: flanga@amb-to.uclm.es; niereng@
ipcms.u-strasbg.fr
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)01769-0

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Scheme 1. Reagents and conditions: (i) HBr, paraformaldehyde, AcOH, 65°C, 2 h (70%); (ii) P(OEt)3, 150°C, 6 h (91%); (iii)
2,2-dimethylpropane-1,3-diol, TsOH (cat.), benzene, D, Dean Stark trap, 48 h (87%); (iv) n-BuLi, Et2O, 0°C, 1 h, then DMF, 0°C
to room temperature, 4 h (86%); (v) LiAlH4, THF, 0°C, 4 h (80%); (vi) CBr4, PPh3, THF, 0°C to room temperature, 4 h (85%);
(vii) P(OEt)3, 150°C, 4 h (99%).
Scheme 2. Reagents and conditions: (i) 6, t-BuOK, THF, 0°C, 1 h, then I2 (cat.), toluene, D, 12 h (80%); (ii) CF3CO2H, CH2Cl2,
H2O, room temperature, 4 h (95%); (iii) p-nitrophenylhydrazine, AcOH, EtOH, D, 3.5 h (99%).
lective, leading to the E isomer only.7 In the present
case, steric hindrance resulting from the presence of the
octyloxy group in the ortho position of the reactive
groups in both 3 and 6 may explain the lack of E:Z
selectivity. The isomerization of the isomeric mixture to
the all-E derivative 10 was easily achieved by treatment
with a catalytic amount of iodine in refluxing toluene
and trimer 10 was thus obtained in 80% yield. Subse-
quent deprotection with CF3CO2H in CH2Cl2/H2O
afforded bis-aldehyde 11 in 95% yield. The E configura-
tion of the double bonds in 11 was confirmed by a
coupling constant of ca. 17 Hz for the AB system
with phosphonate 9 under Wittig–Horner conditions
followed by treatment with a catalytic amount of iodine
in refluxing toluene gave the all-E OPV pentamer 13 in
51% yield. Deprotection, by treatment with CF3CO2H
in CH2Cl2/H2O, followed by reaction of the resulting
bis-aldehyde 14 with p-nitrophenylhydrazine in reflux-
ing ethanol in the presence of acetic acid afforded the
bis-hydrazone 15 in 83% yield.
Treatment of bis-hydrazone 12 with N-chlorosuccin-
imide (NCS) and pyridine in dry chloroform, followed
by reaction of the resulting bis-nitrilimine intermediate
with C60 in chlorobenzene in the presence of Et3N at
room temperature, afforded the desired dumbbell-
shaped derivative 16 in 27% yield (Scheme 4). Interest-
ingly, in addition to 16, the monosubstituted derivative
17 was also isolated from the reaction mixture; the
aldehyde group in 17 originates most probably from the
hydrolysis of unreacted hydrazone moieties during the
1
corresponding to the vinylic protons in the H NMR
spectrum. Bis-hydrazone 12 was then obtained in 99%
yield from aldehyde 11 and p-nitrophenylhydrazine in
refluxing ethanol in the presence of acetic acid.
The preparation of the corresponding OPV pentamer
15 is depicted in Scheme 3. Reaction of bis-aldehyde 11

M. J. Go´mez-Escalonilla et al. / Tetrahedron Letters 43 (2002) 7507–7511
7509
Scheme 3. Reagents and conditions: (i) 11, t-BuOK, THF, 0°C to room temperature, 2 h, then I2 (cat.), toluene, D, 12 h (51%);
(ii) CF3CO2H, CH2Cl2, H2O, room temperature, 3 h (88%); (iii) p-nitrophenylhydrazine, AcOH, EtOH, D, 3.3 h (83%).
Scheme 4. Reagents and conditions: (i) NCS, pyridine, CHCl3, 0°C to room temperature, then C60, Et3N, chlorobenzene, room
temperature, 1 h [from 12: 16 (27%) and 17 (57.5%); from 15: 18 (10%) and 19 (19%)].
work-up procedure. Following the same procedure, the
reaction of bis-hydrazone 15 with NCS and subsequent
reaction with C60 at room temperature gave the bis-
(pyrazolino[60]fullerene) OPV derivative 18 and the
monosubstituted compound 19 in 10 and 19% yields,
respectively. Due to the good solubility brought about
by the octyloxy groups, the C60-OPV derivatives 16–19
that there are no significant ground state interactions
between the different chromophores. As depicted in
Fig. 1, the UV–vis spectra of 16 recorded in CH2Cl2
shows the characteristic absorption features of a pyra-
zolino[60]fullerene derivative as well as the diagnostic
OPV trimer band at 416 nm. The UV–vis spectrum of
the higher homologue 18 is similar but due to the
increased length of the p-conjugated system, the
absorption maximum of the OPV moiety is shifted to
461 nm. Preliminary luminescence measurements in
CH2Cl2 solutions show a strong quenching of the OPV
fluorescence by the fullerene moieties in both 16 and 18
indicating the occurrence of intramolecular photo-
induced processes. Detailed photophysical studies are
1
were easily characterized by H and 13C NMR.8 The
structures of 16–19 were also confirmed by their
MALDI-TOF mass spectra showing the expected
molecular ion peaks.8
The absorption spectra of 16–19 correspond to the sum
of the spectra of their component subunits, indicating

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M. J. Go´mez-Escalonilla et al. / Tetrahedron Letters 43 (2002) 7507–7511
Figure 1. UV–vis spectra of 16 (—) and 18 (·····) in CH2Cl2 solutions at room temperature.
currently under investigation in collaboration with the
group of Nicola Armaroli (Bologna, Italy) and special
emphasis is placed on the detection of photo-induced
and long-lived charge-separated states.
2002, 656–657; (e) Gu, T.; Nierengarten, J.-F. Tetrahedron
Lett. 2001, 42, 3175–3178.
3. (a) Armaroli, N.; Barigelletti, F.; Ceroni, P.; Eckert, J.-F.;
Nicoud, J.-F.; Nierengarten, J.-F. Chem. Commun. 2000,
599–600; (b) Fujitsuka, M.; Ito, O.; Yamashiro, T.; Aso,
Y.; Otsubo, T. J. Phys. Chem. A 2000, 104, 4876–4881; (c)
Yamasshiro, T.; Aso, Y.; Otsubo, T.; Tang, H.; Harima,
Y.; Yamashita, K. Chem. Lett. 1999, 443–444; (d) Segura,
J. L.; Gomez, R.; Martin, N.; Guldi, D. M. Chem. Com-
mun. 2000, 701–702; (e) Apperloo, J. J.; Martineau, C.;
van Hal, P. A.; Roncali, J.; Janssen, R. A. J. J. Phys.
Chem. A 2002, 106, 21–31.
In conclusion, an efficient synthesis of symmetrically
substituted OPV derivatives has been developed,
enabling us to prepare building blocks for the construc-
tion of new dumbbell-shaped bis-(pyrazolino-
[60]fullerene) OPV derivatives. The electronic properties
of these compounds are under investigation and will be
reported in due time.
4. (a) Nierengarten, J.-F.; Eckert, J.-F.; Nicoud, J.-F.; Ouali,
L.; Krasnikov, V.; Hadziioannou, G. Chem. Commun.
1999, 617–618; (b) Eckert, J.-F.; Nicoud, J.-F.; Nieren-
garten, J.-F.; Liu, S.-G.; Echegoyen, L.; Barigelletti, F.;
Armaroli, N.; Ouali, L.; Krasnikov, V.; Hadziioannou, G.
J. Am. Chem. Soc. 2000, 122, 7467–7479; (c) Peeters, E.;
van Hal, P. A.; Knol, J.; Brabec, C. J.; Sariciftci, N. S.;
Hummelen, J. C.; Janssen, R. A. J. J. Phys. Chem. B 2000,
104, 10174–10190; (d) Guldi, D. M.; Luo, C.; Swartz, A.;
Gomez, R.; Segura, J. L.; Martin, N; Brabec, C.; Sariciftci,
N. S. J. Org. Chem. 2002, 67, 1141–1152; (e) Gu, T.;
Tsamouras, D.; Melzer, C.; Krasnikov, V.; Gisselbrecht,
J.-P.; Gross, M.; Hadziioannou, G.; Nierengarten, J.-F.
ChemPhysChem 2002, 124–127; (f) Armaroli, N.; Accorsi,
G.; Gisselbrecht, J.-P.; Gross, M.; Krasnikov, V.;
Tsamouras, D.; Hadziioannou, G.; Gomez-Escalonilla, M.
J.; Langa, F.; Eckert, J.-F.; Nierengarten, J.-F. J. Mater.
Chem. 2002, 12, 2077–2087.
Acknowledgements
This research was supported by the Spanish Ministry of
Science and Technology (Project BQU2001-1512, Feder
funds and Accio´n Integrada HF-2001-0016), ECODEV,
the French Ministry of Research (ACI Jeunes
Chercheurs) and the Picasso program (Project
04273UE).
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4H), 7.26 (s, 2H), 7.20 (s, 2H), 7.13 (s, 2H), 4.05–4.02 (m,
12H), 1.86–1.71 (m, 12H), 1.58–1.25 (m, 60H), 0.88–0.79
(m, 18H). IR (KBr): w 2852.5, 1733.0 (CꢀO), 1677.4,
1591.9 (CHꢀN), 1467.9, 1322.6, 1198.6, 852.3, 526.9; UV–
vis (CH2Cl2) umax/nm (log m) 420 (4.7), 325 (4.8), 255 (5.2),
231 (5.1); MALDI-TOF m/z 1959.8 (M+, calcd for
1
C
138H117N3O9: 1959.87). 18: H NMR (CDCl3) l 8.34 (d,
J=9.5 Hz, 4H), 8.26 (d, J=9.5 Hz, 4H), 7.58 (B of AB,
J=17 Hz, d, 4H), 7.48 (A of AB, J=17 Hz, d, 4H), 7.29
(s, 2H), 7.28 (s, 2H), 7.21 (s, 2H), 7.17 (s, 2H), 7.15 (s,
2H), 4.10–4.00 (m, 20H), 1.92–1.82 (m, 20H), 1.58–1.27
(m, 100H), 0.89–0.81 (m, 30H); 13C NMR (CDCl3): l
151.9, 150.9, 150.1, 147.6, 147.0, 146.3, 146.1, 146.0, 145.8,
145.5, 145.2, 145.1, 144.7, 144.3, 143.1, 142.9, 142.3, 142.2,
142.0, 140.7, 139.2, 137.1, 135.2, 130.4, 127.9, 126.8, 125.4,
123.3, 114.2, 110.5, 97.8, 89.3, 83.5, 69.9, 69.5, 32.2, 29.8,
29.7, 26.6, 26.5, 23.8, 23.0, 14.5, 14.4; IR (KBr): w 2921.3,
1636.3, 1616.5, 1588.1 (CHꢀN), 1495.5, 1319.9, 1262.9,
1020.9, 800.2, 527.3; UV–vis (CH2Cl2) umax/nm (log m) 461
(4.2), 324 (4.2), 255 (4.7), 230 (4.6); MALDI-TOF m/z
3529.8 (M+, calcd for C252H196N6O14: 3529.48). 19: 1H
NMR (CDCl3) l 10.4 (s, CHO, 1H), 8.32 (d, J=9.5 Hz,
2H), 8.26 (d, J=9.5 Hz, 2H), 7.66–7.44 (m, 8H), 7.33 (s,
2H), 7.21 (s, 2H), 7.18 (s, 2H), 7.17 (s, 2H), 7.15 (s, 2H),
4.07–4.04 (m, 20H), 1.89–1.86 (m, 20H), 1.59–1.27 (m,
100H), 0.90–0.85 (m, 30H). IR (KBr): w 2925.3, 2850.4,
1717.3 (CꢀO), 1636.7, 1618.5, 1587.3 (CHꢀN), 1496.3,
1322.1, 1257.1, 1197.3, 802.1, 526.6; UV–vis (CH2Cl2)
umax/nm (log m) 467 (4.0), 323 (3.9), 255 (4.3), 230 (4.2);
MALDI-TOF m/z 2676.5 (M+, calcd for C186H193N3O13:
2676.45).
7. Mu¨llen, K.; Wegner, G. Electronic Materials: the Oligomer
Approach; Wiley-VCH: Weinheim, 1998.
8. Selected spectroscopic data for 16: 1H NMR (CDCl3) l
8.34 (d, J=9.5 Hz, 4H), 8.26 (d, J=9.5 Hz, 4H), 7.57 (B
of AB, J=17 Hz, d, 2H), 7.48 (A of AB, J=17 Hz, d, 2H),
7.28 (s, 2H), 7.21 (s, 2H), 7.14 (s, 2H), 4.05–3.99 (m, 12H),
1.90–1.71 (m, 12H), 1.57–1.25 (m, 60H), 0.96–0.75 (m,
18H); 13C NMR (CDCl3): l 151.9, 151.0, 150.3, 150.0,
147.6, 147.0, 146.9, 146.6, 146.2, 146.1, 145.9, 145.8, 145.5,
145.3, 145.2, 145.1, 144.6, 144.3, 143.9, 143.1, 142.8, 142.7,
142.3, 142.1, 141.9 (2C), 141.8, 140.6, 139.2, 137.1, 135.0,
130.3, 127.2, 125.3, 123.1, 119.1, 119.0, 116.3, 110.7, 89.3,
84.3, 69.9, 69.5, 32.2, 30.0, 29.9, 29.8, 29.7, 26.7, 26.6, 26.5,
23.0, 14.5, 14.4; IR (KBr): w 2925.4, 1638.6, 1616.7, 1587.6
(CHꢀN), 1493.0, 1328.1, 1197.1, 1022.5, 845.4, 527.7; UV–
vis (CH2Cl2) umax/nm (log m) 416 (5.0), 327 (5.1), 257 (5.5);
MALDI-TOF m/z 2812.7 (M+, calcd for C204H120N6O10:
1
2812.90). 17: H NMR (CDCl3) l 10.4 (s, CHO, 1H), 8.32
(d, J=9.5 Hz, 2H), 8.24 (d, J=9.5 Hz, 2H), 7.55–7.44 (m,