Synthetic approaches to a variety of covalently linked porphyrin-fullerene hybrids

Article abstract of DOI:10.1021/jo010317x

There is substantial interest in dyads in which C₆₀ is covalently linked to electron donors, such as porphyrins, which absorb light strongly in the visible region. We present here the details of the syntheses of such compounds, which can be broadly organized into categories depending upon the nature of the linker joining the two chromophores. The structural aspects of intramolecular electronic interaction that we have sought to explore have dictated the synthetic strategies employed to generate these classes of molecules. Flexible glycol linkers were used to allow close approach between the fullerene and porphyrin, facilitating through-space interactions. These linkers also allowed studies of the effects of metal cation complexation. Naphthalene and alkyne linkers were used to examine the possible effects a conjugated or aromatic linker might have on photophysical properties. Finally, steroids were used as linkers in dyads expected to possess a large distance between the two chromophores, in which only through-bond interactions between the fullerene and porphyrin should be possible.

Full text of DOI:10.1021/jo010317x

J . Org. Chem. 2001, 66, 5449-5455
5449
Syn th etic Ap p r oa ch es to a Va r iety of Cova len tly Lin k ed
P or p h yr in -F u ller en e Hybr id s
Shaun MacMahon, Robert Fong II, Phil S. Baran, Igor Safonov, Stephen R. Wilson, and
David I. Schuster*
Department of Chemistry, New York University, 100 Washington Square East,
New York, New York 10003
david.schuster@nyu.edu
Received March 23, 2001
There is substantial interest in dyads in which C60 is covalently linked to electron donors, such as
porphyrins, which absorb light strongly in the visible region. We present here the details of the
syntheses of such compounds, which can be broadly organized into categories depending upon the
nature of the linker joining the two chromophores. The structural aspects of intramolecular electronic
interaction that we have sought to explore have dictated the synthetic strategies employed to
generate these classes of molecules. Flexible glycol linkers were used to allow close approach between
the fullerene and porphyrin, facilitating through-space interactions. These linkers also allowed
studies of the effects of metal cation complexation. Naphthalene and alkyne linkers were used to
examine the possible effects a conjugated or aromatic linker might have on photophysical properties.
Finally, steroids were used as linkers in dyads expected to possess a large distance between the
two chromophores, in which only through-bond interactions between the fullerene and porphyrin
should be possible.
In tr od u ction
Resu lts a n d Discu ssion
The photophysical properties of covalently linked por-
phyrin-fullerene hybrids have been a focus of recent
intense investigation. C60 has received a great deal of
interest as an electron acceptor due to its high electron
affinity and extremely low reorganization energy in
electron-transfer processes, which promotes forward-
electron transfer from photoexcited electron donors while
simultaneously retarding back-electron transfer.1 Poten-
tial applications of these dyads include use as photosen-
sitizers in photodynamic therapy through generation of
singlet molecular oxygen,2 as well as applications in
energy storage devices.1a A large variety of such donor-
acceptor systems have been synthesized by a number of
groups, including our own, and have proven useful in the
elucidation of energy transfer and charge separation
processes.1,3 We have previously reported the photophysi-
cal characterization of a variety of such hybrids.4
All dyads, as well as most synthetic intermediates,
1
were characterized by their H NMR and UV-vis spectra
and either FAB-MS or MALDI-MS. The 1H NMR spectra
were all consistent with the proposed structures. The 13
C
NMR spectra for all Hirsch-Bingel (methanofullerene)
and Prato (fulleropyrrolidine) addition products were
consistent with [6,6]-closed linkages on the fullerene cage.
The spectral evidence for the addition pattern of azafuller-
enes 12 and 13 is described below. Mass spectrometry
showed molecular ion peaks for all compounds examined.
In our first efforts to gain insight into excited-state
interactions between porphyrin and fullerene moieties in
covalently linked hybrid systems, flexible poly(ethylene
glycol) linkers were employed.4a These linkers allow
extremely close approach of the two chromophores, as
theoretical calculations suggested that conformations in
which the porphyrin and fullerene moieties are in close
proximity are preferred, attributed to van der Waals
interactions. This unique type of interaction has been
confirmed by Reed and co-workers, who showed that
porphyrins readily form ordered cocrystals with fullerenes.5
The efficient syntheses of these flexibly linked hybrids
were accomplished by the convergent strategy outlined
in Scheme 1.4a Sulfonium ylide addition to C60 and
subsequent hydrolysis afforded methanofullerene car-
boxylic acid 16 in high yield. DCC/DMAP coupling of 1
to mono-silyl-protected diols 3 and 4 in 5:1 bromobenzene/
DMSO, followed by acidic deprotection, yielded synthons
7 and 8 in 40-76% yield. EDCI-mediated coupling of
(1) (a) Imahori, H.; Sakata Y. Eur. J . Org. Chem. 1999, 10, 2445.
(b) Guldi, D. M. Chem. Commun. 2000, 5, 321. (c) Schuster, D. I.;
Cheng, P.; Wilson, S. R.; Prokhorenko, V.; Katterle, M.; Holzwarth, A.
R.; Braslavsky, S. E.; Klihm, G.; Williams, R. M.; Luo, C. J . Am. Chem.
Soc. 1999, 121, 11599.
(2) Bensasson, R. V.; Land, E. J .; Truscott, T. G. Excited States and
Free Radicals in Biology and Medicine; Oxford University Press: New
York, 1993.
(3) (a) Imahori, H.; Cardoso, S.; Tatman, D.; Lin, S.; Noss, L.; Seely,
G. R.; Sereno, L.; de Silber, J . C.; Moore A. L.; Gust, D. Photochem.
Photobiol. 1995, 62, 1009. (b) Sariciftci, N. S.; Wudl, F.; Heeger, A. J .;
Maggini, M.; Scorrano, G.; Prato, M.; Bourassa, J .; Ford, P. C. Chem.
Phys. Lett. 1995, 247, 510. (c) Linssen, T. G.; Durr, K.; Hanack, M.;
Hirsch, A. J . Am. Chem. Soc., Chem. Commun. 1995, 1, 103. (d)
Armspach, D.; Constable, E. C.; Diederich, F.; Housecroft, C. E.;
Nierengarten, J . F. Chem. Commun. 1996, 17, 2009. (e) Martin, N.;
Sanchez, L.; Illescas, B.; Perez, I. Chem. Rev. 1907, 7, 2527.
(4) (a) Schuster, D. I.; Baran, P. S.; Monaco, R. R.; Boulas, P.;
Echegoyen, L.; Wilson, S. R.; Khan, A. U. J . Am. Chem. Soc. 1997,
119, 8363. (b) Safonov, I. G.; Baran P. S.; Schuster, D. I. Tetrahedron
Lett. 1997, 38, 8133. (c) Fong, R.; Wilson, S. R.; Schuster, D. I. Proc.
Electrochem. Soc. 1998, 8, 262. (d) Fong, R.; Wilson, S. R.; Schuster,
D. I. Org. Lett. 1999, 1, 729. (e) MacMahon, S.; Wilson, S. R.; Schuster,
D. I. Proc. Electrochem. Soc. 2000, 10, 155. (f) Cheng, P.; Wilson, S.
R.; Schuster, D. I. Chem. Commun. 1999, 5, 89.
(5) (a) Boyd, P. D. W.; Hodgson, M. C.; Rickard, C. E. F.; Oliver, A.
G.; Chaker, L.; Brothers, P. J .; Bolskar, R. J .; Tham, F. S.; Reed, C. A.
J . Am. Chem. Soc. 1999, 121, 10487. (b) Olmstead M. M.; Costa D. A.;
Maitra K.; Noll B. C.; Phillips S. L.; Van Calcar, P. M.; Balch A. L. J .
Am. Chem. Soc. 1999, 121, 7090.
(6) Wang, T.; Cao, J .; Schuster, D. I.; Wilson, S. R. Tetrahedron Lett.
1995, 36, 6843.
10.1021/jo010317x CCC: $20.00 © 2001 American Chemical Society
Published on Web 07/12/2001

5450 J . Org. Chem., Vol. 66, No. 16, 2001
MacMahon et al.
Sch em e 3. Syn th esis of Aza -Lin k ed
Sch em e 1. Syn th esis of Glycol-lin k ed C60
P or p h yr in Dya d s
C60-Glycol-P or p h yr in Dya d
chloride and subsequent nucleophilic substitution with
NaN3 in DMSO generated mono-azide 11, which was
heated at reflux with C60 in chlorobenzene8 to give the
aza-linked synthon 12 in 55% yield. The 13C NMR
spectrum of 12 is consistent with a [5,6]-open aza-linked
fulleroid structure as there are no peaks for fullerene sp3
carbon atoms. This is in agreement with results of
previous studies of azide additions to fullerenes.9 Sub-
sequent EDCI mediated coupling of 12 to 2 proceeded in
63% yield to yield hybrid 13, which was characterized
Sch em e 2. Meta l Ion Com p lexa tion
1
spectroscopically by H NMR, MALDI-MS, and UV-vis.
In particular, the 1H NMR spectrum showed peaks
attributable to the glycol linker between 3.5 and 4 ppm,
as well as characteristic peaks for 2 between 7.5 and 9
ppm.
In pursuit of a porphyrin-fullerene hybrid with in-
creased solubility and superior cation complexation abili-
ties, hybrid 19 was prepared.4b The synthesis is outlined
in Scheme 4. Catechol was first reacted with excess
tetraethylene glycol mono-tosylate in the presence of
potassium carbonate to generate 15, which was subse-
quently monoprotected with trimethylsilyl chloride and
coupled to 1 using the DCC/DMAP protocol, generating
17. Hybrid 19 was generated after deprotection of 17 and
EDCI-mediated coupling of 18 to 2. While the dyad did
not show any conformational reorganization in the pres-
ence of metal cations, as indicated by fluorescence
quenching studies, it showed a surprisingly high quan-
tum yield (0.40) for photosensitized formation of singlet
oxygen.
Subsequent work sought to explore the effects of
conjugated and aromatic linkers on the photophysics of
fullerene-porphyrin hybrids. To this end, hybrids 23 and
27 were prepared using the strategy outlined in Schemes
5 and 6 in 16% and 20% yield, respectively.4c Mono-silyl
protection of 2-butyn-1,4-diol was accomplished as in
Scheme 1, while dihydropyran was employed for protec-
tion of 2,7-naphthalenediol as its mono-THP derivative.
The attachment of porphyrin and fullerene moieties was
these synthons with 5-(4′-carboxyphenyl)-10,15,20-tri-
phenylporphyrin 27 in 1:1 dry CH2Cl2/CS2 yielded hybrids
9 and 10 in 48-70% yield. The dyads were characterized
1
using H NMR, MS, UV-vis and fluorescence spectro-
scopy.
Complexation of hybrids 9 and 13 with metal cations
resulted in open-chain crown-ether host-guest mimics.4a
This approach, illustrated in Scheme 2, was exploited to
bring the two chromophores into even closer proximity,
as verified by computational studies.4a Complexation with
Na+ and K+ was accomplished with NaSCN and KSCN
in acetone. Indeed, stronger intramolecular electronic
interactions were observed for the complexed hybrids, as
evidenced by fluorescence quenching studies.
Compound 13, representing the first aza-linked fuller-
ene-porphyrin hybrid, was prepared to explore the
effects of changing the nature of the linkage to the
fullerene sphere on photophysics and complexation.4a
Scheme 3 outlines the strategy employed in its synthesis.
Monochlorination of tetraethylene glycol with thionyl
(8) Prato, M.; Li, Q.; Chan, Q.; Wudl, F.; Lucchini, V. J . Am. Chem.
Soc. 1993, 115, 1148.
(9) Hirsch, A. Top. Curr. Chem. 1999, 199, 1.
(7) Lindsey, J . S.; Schreiman, I. C.; Hsu, H. C.; Kearney, P. C.;
Marguerettaz, A. M. J . Org. Chem. 1987, 52, 827.

Synthetic Approaches to Porphyrin-Fullerene Hybrids
J . Org. Chem., Vol. 66, No. 16, 2001 5451
Sch em e 4. Syn th esis of Ca tech ol-Lin k ed
Sch em e 5. Syn th esis of Alk yn e-Lin k ed
C60-P or p h yr in Dya d
C60-P or p h yr in Dya d
that study, namely 3-keto-17-ols, were thought to be ideal
candidates for our purposes, providing a rigid polycyclic
spacer capable of separating covalently linked donor
(porphyrin) and acceptor (fullerene) well beyond the
range of van der Waals contact. This approach was
modeled on the classic work of Closs and co-workers, who
showed that long-range electron transfer occurred in
systems where the donor and acceptor were separated
by a steroid linker.11 However, because of the possibilities
of syn and anti conformations at the porphyrin ester
linkage, the porphyrin and fullerene chromophores in
these dyads may actually be in fairly close proximity or
very far apart. Insight II calculations place the center to
center distance between the porphyrin and the fullerene
moieties in the two conformations, at 6.55 and 21.94 Å,
respectively.12 In fact, the computations predict that the
syn conformation, which is energetically unfavorable in
most esters, is actually significantly more stable, due to
van der Waals attraction between the fullerene and the
porphyrin5 (the distance from the center of the porphyrin
to the nearest point on the surface of the fullerene in the
syn conformer is just over 3 Å). While the actual confor-
mational population in these steroid-linked dyads in
solution is not known, the fact that the porphyrin
fluorescence is quenched by only 52-74%,4d much less
than in the flexibly linked dyads, suggests that these
systems do not exist solely in the syn conformation.
accomplished using the methodology employed in the
syntheses of 9 and 10. Dyads 23 and 27 were character-
ized by 1H NMR, 13C NMR, MALDI-MS, UV-vis, and
fluorescence spectroscopy. Surprisingly, significant quench-
ing of porphyrin fluorescence was observed in 23 and 27,
indicating substantial interaction between the chro-
mophores in the excited state.4d Computational studies
indicated that these linkers were sufficiently flexible to
permit close approach between the porphyrin and fullerene
moieties.
Seeking to explore the contribution of through-bond
interactions to the excited-state conversion between the
porphyrin and fullerene moieties, a series of rigidly linked
hybrids with a large distance of separation between
fullerene and porphyrin moieties were needed to control
for through space effects. To this end, hybrids 34-36
were prepared4d using a synthetic approach inspired by
Maggini’s work on steroid-linked ruthenium tris-bipyridyl
fulleropyrrolidines.10 The steroid-derived linkers used in
(10) Maggini, M.; Guldi, D. M.; Mondini, S.; Scorrano, G.; Paolucci,
F.; Ceroni, P.; Roffia, S. Chem. Eur. J . 1998, 4, 1992.
(11) Calcaterra, L. T.; Closs, G. L.; Miller, J . R. J . Am. Chem. Soc.
1983, 105, 670.
(12) Kirschner, A. N.; J arowski, P. D.; Schuster, D. I.; Wilson, S.
R., manuscript in preparation.

5452 J . Org. Chem., Vol. 66, No. 16, 2001
MacMahon et al.
Sch em e 6. Syn th esis of Na p h th a len e-Lin k ed
Sch em e 8. Ster oid -Lin k ed C60-P or p h yr in Dya d
C60-P or p h yr in Dya d
Str u ctu r a l In ter m ed ia tes
facility of the Prato reaction. Reaction products in all
cases were generated as a 3:1 mix of diastereomers,
corresponding to the two possible orientations at the spiro
ring junction, as determined by 1H NMR and HPLC
analysis. Subsequent EDCI-mediated union of these
synthons with 2 as in Scheme 1 yielded hybrids 34-36
as a mix of diastereomers in 12-25% yield. These
isomeric mixtures were characterized by 1H NMR, MALDI-
MS, UV-vis, and fluorescence spectroscopy. The dyads
Sch em e 7. Syn th esis of Ster oid -Lin k ed
C60-P or p h yr in Dya d s
1
displayed H NMR spectra with characteristic peaks for
their respective steroid linkers between 1 and 2 ppm,
peaks between 3 and 4.5 ppm attributable to the protons
from the fulleropyrrolidine, as well as peaks between 7.5
and 9 ppm derived from porphyrin 2. An attempt was
made to chromatographically separate the diastereomers
of 34, the most abundant of these steroidal dyads, but
1
this was only partially successful, as both H NMR and
HPLC analysis of fractions indicated only moderate
enrichment of one or the other of the diastereomers. No
difference in the fluorescence spectra or intensities of
these enriched fractions was seen, suggesting no signifi-
cant difference in photophysical properties of the two
diastereomers.
Ongoing interest in soluble fullerenes, as well as the
difficulty of working with the relatively insoluble hybrids
that have thus far been made, prompted the use of
carboxylic acid 37 in place of 1. The synthesis of 37 has
been reported by Diederich and co-workers.13 Triethylene
and tetraethylene glycol linked hybrids 40 and 41 were
prepared by the procedure outlined in Scheme 9.4e
Increased solubility of 37 led to higher coupling yields
and enabled more facile collection of spectroscopic data.
Also, use of an excess of the diol precursor in the DCC
coupling step avoided the need for protecting groups, in
As outlined in Scheme 7, the synthetic route to steroid-
linked dyad 34 involved the addition of an azomethine
ylide derived from steroid precursor 28 to C60 in refluxing
toluene, yielding fulleropyrrolidine synthon 31 in 31%
yield (see Scheme 7). Similar Prato additions were carried
out using unsaturated steroids 29 and 30 to give analo-
gous fulleropyrrolidines 32 and 33 (see Scheme 8).
Consistent with the mechanism of addition, increased
conjugation in the steroid ketone decreased the yield and
(13) Nierengarten, J . F.; Herrmann, A.; Tywinski, R. R.; Ruttimann,
M.; Diederich, F.; Boudon, L.; Gisselbracht, J . P.; Gross, M. Helv. Chim.
Acta 1997, 80, 293.

Synthetic Approaches to Porphyrin-Fullerene Hybrids
J . Org. Chem., Vol. 66, No. 16, 2001 5453
chemicals were purchased from Aldrich. Reaction solvents
were distilled over calcium hydride prior to use. Flash chro-
matography was performed using 200-300 mesh silica gel
purchased from Natland. Concentration of reaction mixtures
was performed on a Bu¨chi rotary evaporator. 1H NMR spectra
were obtained on Varian 200-MHz and 300-MHz spectrom-
eters, with 13C NMR at 75 MHz and 125 MHz. Peaks are
reported relative to TMS. UV-vis spectra were recorded on a
Perkin-Elmer Lambda 2 spectrophotometer. Fluorescence
spectra were recorded on a Perkin-Elmer LS-50 fluorimeter.
MALDI mass spectra were recorded on a Kratos Kompact
MALDI I V4.0.0 spectrometer. FAB-MS were obtained at the
Michigan State University Mass Spectrometry Facility, which
is supported, in part, by a grant (DRR-00480) from the
Biotechnology Research Technology Program, National Center
for Research Resources, National Institutes of Health.
Sch em e 9. Syn th esis of Glycol-Lin k ed
C60-P or p h yr in Dya d s
Mon o-silyl P r otection of Diols: Gen er a l P r oced u r e for
P r ep a r a tion of 3, 4, 16, a n d 20. tert-Butyldimethylsilyl
chloride (1 equiv) was added in a dropwise manner to a
solution of the appropriate diol (5 equiv), 4-(dimethylamino)-
pyridine (0.2 equiv), and triethylamine (1 equiv) in dry CH2-
Cl2. After completion of the reaction, the mixture was washed
with water and saturated aqueous ammonium chloride and
then dried over sodium sulfate. The solvent was removed in
vacuo, and the products were purified by column chromatog-
raphy on silica. Com p ou n d 3: yield 72%; eluant ethyl acetate;
TLC Rf ) 0.5 (ethyl acetate); 1H NMR (CDCl3, 200 MHz) 1.0-
1.1 (21H, m), 2.8 (1H, bs), 3.5-4.0 (16H, m); 13C NMR (CDCl3,
50 MHz) 12.6, 18.3, 62.1, 64.0, 71.3, 71.4, 73.6. 4: yield 46%;
eluant ethyl acetate; TLC Rf ) 0.3 (ethyl acetate), 1H NMR
(CDCl3, 200 MHz) 0.0 (6H, s), 0.8 (9H, s), 3.5-3.9 (24H, m);
13C NMR (CDCl3, 50 MHz) 26.5, 62.2, 63.2, 70.9, 71.1, 73.1.
16: yield 33%; eluant ethyl acetate; TLC Rf ) 0.8 (2:8
1
methanol/ethyl acetate); H NMR (CDCl3, 200 MHz) 0.0 (6H,
s), 0.8 (9H, s), 3.0 (1H, s), 3.4-4.2 (24H, m), 6.8 (4H, s); 13C
NMR (CDCl3, 50 MHz) 4.6, 26.5, 62.1, 63.2, 69.4, 70.3, 70.9,
71.3, 73.1, 115.6, 122.1. 20: yield 72%; eluant 3:2 ethyl acetate/
petroleum ether; TLC Rf ) 0.7 (3:2 ethyl acetate/petroleum
ether); 1H NMR (CDCl3, 200 MHz) 0.1 (6H, s), 0.9 (9H, s), 3.3
(1H, s), 4.2 (2H, s), 4.3 (2H, s).
contrast to the protection-deprotection technique applied
in the synthesis of analogous hybrids 9 and 10. Dyads
40 and 41 were characterized by 1H NMR, FAB-MS, UV-
vis, and fluorescence spectroscopy (Scheme 9). Not sur-
prisingly, dyads 40 and 41 have been shown to exhibit
photophysical properties similar to those of related
hybrids 9 and 10,4a in particular almost complete quench-
ing of porphyrin fluorescence and very rapid generation
of charge-separated states. Details will be reported
elsewhere.
DCC/DMAP Cou p lin g of Meth a n ofu ller en eca r boxylic
Acid 1 to P r otected Alcoh ols: Gen er a l P r oced u r e for
P r ep a r a tion of 5, 6, 17, 21, a n d 25. A 5:1 mixture of
bromobenzene/DMSO was added to an Ar-purged flask con-
taining 1 (1 equiv), 4-(dimethylamino)pyridine (0.2 equiv),
1-hydroxybenzotriazole hydrate (1.1 equiv), and 1,3-dicyclo-
hexylcarbodiimide (3 equiv). The solution was sonicated for
30 min. The appropriate monoprotected alcohol (3 equiv) was
added, and the reaction was held at 50 °C with constant
stirring for 16 h. Bromobenzene was removed in vacuo, and
the mixture was diluted with CHCl3. Oxalic acid (10%) in
methanol was added, and the mixture was sonicated for 1 min.
The resulting solution was washed with water, 10% CaSO4,
and brine and dried over sodium sulfate. The solvent was
removed in vacuo, and the residue was dissolved in CS2,
filtered, and evaporated in vacuo to obtain the corresponding
ester in the form of shiny brown plates. Com p ou n d 5: yield
47%; 1H NMR. 6: yield 41%. 17: yield 50%; 1H NMR (CDCl3,
200 MHz) 0.0 (6H, s) 0.8 (9H, s) 3.4-4.3 (22H, m) 4.6 (2H, t)
4.8 (1H, s) 6.8 (4H, s); MALDI-MS (M+ ) 1255.6, calcd )
1249.6) 21: yield 53%; 1H NMR (CDCl3, 200 MHz) 0.1 (6H, s)
0.8 (9H, s) 4.3 (2H, s), 4.8 (1H, s) 5.1 (2H, s). 25: yield 49%.
Rem ova l of th e P r otectin g Gr ou p : Gen er a l P r oced u r e
for P r ep a r a tion of 7, 8, 18, 22, a n d 26. The appropriate
protected alcohol was stirred in a 5:1:0.25 CH2Cl2-0.05 N HCl/
EtOH-CS2 solution at room temperature for 8 h. The resulting
solution was diluted with CH2Cl2 and extracted with water
and brine, and the solvent was removed in vacuo. The residue
was subjected to flash chromatography on silica to yield the
corresponding alcohol. 7: Yield 95+%; eluant 5% acetic acid/
chloroform; TLC Rf ) 0.3 (5% acetic acid/chloroform); 1H NMR
(CDCl3, 200 MHz) 3.4-4.2 (16H, m), 4.6 (1H, t), 4.9 (1H, s). 8:
yield 95+%; eluant 5% acetic acid/chloroform; TLC Rf ) 0.2
(5% acetic acid/chloroform). 18: yield 52%; eluant chloroform;
TLC Rf ) 0.4 (20% acetic acid/toluene. 22: yield 95+%; eluant
Con clu sion s
Over the course of research into the dynamics of
excited-state interactions in porphyrin-fullerene hybrids,
a variety of synthetic approaches have been developed
to generate classes of compounds suited to the exploration
of theoretical questions that have arisen as our knowl-
edge of these interactions has grown.14 The various
schema presented here provide access to a large array of
flexibly and rigidly linked hybrid systems. Along with the
host of other synthetic approaches that have recently
been developed, including the synthesis by our group of
a semirigid “parachute-shaped” hybrid via Bingel chemis-
try,4f the possibilities are indeed great for the generation
of a myriad of novel hybrid systems for the further
elucidation of energy transfer and charge separation
processes occurring in these unique donor acceptor
hybrids, and larger supramolecular complexes derived
from them.
Exp er im en ta l Section
Gen er a l Meth od s. All reactions were performed under dry
nitrogen. All glassware was dried in an oven at 200 °C prior
to use. C60 was obtained from MER corporation; all other
(14) Schuster, D. I. Carbon 2000, 38, 1607.

5454 J . Org. Chem., Vol. 66, No. 16, 2001
MacMahon et al.
chloroform; TLC Rf ) 0.2 (chloroform), characterization by 1H
NMR (CDCl3, 200 MHz) 4.4 (2H, s), 4.8 (1H, s), 5.1 (2H, s).
26: yield 95+%; eluant chloroform; TLC Rf ) 0.2 (chloroform);
1H NMR (CDCl3, 200 MHz) 5.0 (1H, s), 7.1 (1H, d), 7.3 (1H,
d), 7.6-7.7 (3H, m), 7.9 (1H, s), 9.3 (1H, s).
plug of silica to yield 11, which was characterized as follows:
1H NMR (CDCl3, 200 MHz) 2.9 (1H, s), 3.3-3.7 (16H, m); 13
C
NMR (CDCl3, 50 MHz) 41.5, 51.2, 62.1, 70.5, 70.8, 71.1, 73.0.
Syn th esis of Aza fu ller en e 12. Mono-azide 11 dissolved
in 20 mL of chlorobenzene was added over 1 h to a solution of
EDC-Med ia ted Cou p lin g of F u ller en e Syn th on s to
P or p h yr in ca r b oxylic Acid 2: Gen er a l P r oced u r e for
P r ep a r a tion of 9, 10, 13, 19, 23, 27, 34-36, 40, a n d 41. A
solution of fullerene synthon (1 equiv) in CS2 was added to a
solution of porphyrin 2 (1.01 equiv), 1-(3-dimethylaminopro-
pyl)-3-ethylcarbodiimide hydrochloride (1.01 equiv), and 4-(di-
methylamino)-pyridine (1.01 equiv) in absolute CH2Cl2 at room
temperature. The mixture was stirred for 12 h, diluted with
CH2Cl2, washed with saturated aqueous ammonium chloride,
and brine, dried over sodium sulfate, and evaporated to give
the crude product, which was purified by flash chromatography
on silica to give the pure dyad. Com p ou n d 9: yield 53%;
eluant chloroform; TLC Rf ) 0.2 (chloroform); 1H NMR (CDCl3,
200 MHz) 3.5-4.0 (16H, m), 4.7 (1H, s), 7.5-9 (27H, m); FAB-
MS (M+ ) 1594.4, calcd ) 1594.3). 10: yield 60%; eluant
C60 (500 mg) in refluxing chlorobenzene (300 mL). Heating was
continued for 24 h, after which time the solution was evapo-
rated in vacuo. The product was purified (SiO2, benzene, then
CH2Cl2) to afford 70 mg of 12 (55% based on recovered C60),
which was characterized as follows: 1H NMR (CDCl3, 200
MHz) 3.6-4.4 (16H, m); 13C NMR (CDCl3, 125 MHz) 52.5, 71-
72 (5 peaks), 131.3, 138-149 (29 peaks), 167.1; MALDI-MS
(M+) 913.7, calcd ) 911.9).
P r ep a r a tion of Tr ieth ylen e Glycol Mon otosyla te 14.
P-Toluenesulfonyl chloride (1 equiv) dissolved in dry CH2Cl2
was added in a dropwise manner to a solution of triethylene
glycol (1 equiv) and pyridine (1 equiv) in dry CH2Cl2 at 0 °C.
After complete addition of tosyl chloride, the reaction mixture
was stirred for 3 h at room temperature, subsequently
extracted with 5% aqueous HCl, saturated aqueous sodium
bicarbonate, and water, and dried over sodium sulfate, and
the solvent was removed under reduced pressure. The crude
product was purified (SiO2, ethyl acetate, TLC Rf ) 0.4) to
afford the desired product 14 (54%), which was characterized
as follows: 1H NMR (CDCl3, 200 MHz) 2.4 (3H, s), 3.5-4.2
(12H, m), 7.3 (2H, d), 7.8 (2H, d); 13C NMR (CDCl3, 50 MHz)
22.1, 62.1, 69.1, 69.7, 70.7, 71.2, 72.9 128.4, 130.3.
1
chloroform; TLC Rf ) 0.1 (chloroform); H NMR (CDCl3, 200
MHz) 3.4-4.0 (24H, m), 4.7 (1H, s), 7.7-9.0 (27H, m); MALDI-
MS (M+ ) 1683.8, calcd ) 1682.4). 13: yield 53%; eluant 10%
1
acetic acid/chloroform; TLC Rf ) 0.65 (chloroform); H NMR
(CDCl3, 200 MHz) 3.4-4.2 (16H, m), 4.6 (1H, s), 7.5-9 (27H,
m); FAB-MS (M+) 1683.8). 19: yield 51%; eluant 20% acetic
acid/toluene; TLC Rf ) 0.56 (20% acetic acid/toluene); 1H NMR
(CDCl3, 200 MHz) 3.5-4.3 (18H, m), 4.5-4.7 (6H, m), 4.8 (1H,
s), 6.9 (4H, m), 7.7-8.9 (27H, m); MALDI-MS (M+ ) 1777.7,
calcd ) 1776.3). 23: yield 26%; eluant chloroform; TLC Rf )
0.4 (chloroform); 1H NMR (CDCl3, 200 MHz) 4.6 (1H, s), 5.2-
5.2 (2H, d), 5.3 (2H, d), 7.7-8.9 (27H, m); 13C NMR 14.1, 22.7,
29.4, 38.2, 53.8, 61.6, 70.0, 70.5, 72.9, 120.4, 126.7, 127.8, 128.2,
134.5, 142.0, 143.4, 144.3, 144.9; MALDI-MS (M+ ) 1488.1,
calcd ) 1487.5). 27: yield 20%; eluant chloroform; TLC Rf )
0.45 (chloroform); 1H NMR (CDCl3, 200 MHz) 4.9 (1H, s), 7.5-
7.6 (2H, m), 7.7 (10H, m), 8.0 (2H, m), 8.2 (9H, m), 8.4 (1H, d),
8.6 (1H, d), 8.9 (8H, m); 13C NMR (CDCl3, 125 MHz) 28.7, 38.8,
69.7, 70.3, 120.5, 126.8, 127.8, 128.4, 128.6, 130.9, 131.1, 134.6,
134.9, 136.3, 140.77, 140.9, 141.8, 141.9, 142.1, 142.6, 143.0,
143.4, 143.7, 144.4, 144.8, 144.9, 145.0, 145.4, 148.6, 148.2,
165.3, 166.1; MALDI-MS (M+ ) 1556.9, calcd ) 1561.6) 34:
yield 14%; eluant 1:10 ethyl acetate/toluene; TLC Rf ) 0.4 (1:
10 ethyl acetate/toluene); 1H NMR (CDCl3, 200 MHz) 0.8-2.2
(28H, m), 2.9 (3H, s), 4.6 (2H, s), 7.7-9.0 (27H, m). 35: yield
12%; eluant 1:10 ethyl acetate/toluene; TLC Rf ) 0.4 (1:10
ethyl acetate/toluene); 1H NMR (CDCl3, 200 MHz) 0.8-2.1
(25H, m) 2.8 (2H, s) 4.5 (2H, s) 5.7 (1H, s) 7.7-9.0 (27H, m).
36: yield 10%; eluant 1:10 ethyl acetate/toluene; TLC Rf )
0.4 (1:10 ethyl acetate/toluene); 1H NMR (CDCl3, 200 MHz)
0.8-2.2 (21H, m), 2.8 (3H, s), 4.5 (2H, s), 5.6-5.9 (2H, m), 6.1
(1H, m), 7.7-9.0 (27H, m). 40: yield 41%; eluant 1:9 ethyl
P r ep a r a tion of Glycol-Der ived Ca tech ol 15. Catechol
(1 equiv) in dry acetone containing K2CO3 was heated at reflux
for 15 h with triethylene glycol monotosylate 14 (2 equiv). The
mixture was filtered, the solvent was removed under reduced
pressure, and the crude product was redissolved in ether,
washed with 5% aqueous NaOH and water, dried over sodium
sulfate, and chromatographed (SiO2, 2:8 methanol: ethyl
acetate, TLC Rf ) 0.5) to afford the desired product 15 (55%),
which was characterized as follows: 1H NMR (CDCl3, 200
MHz) 3.1 (2H, s), 3.5-4.3 (24H, m), 6.9 (4H, s); 13C NMR
(CDCl3, 50 MHz) 62.2, 69.5, 70.3, 71.0, 71.4, 73.1, 115.6, 122.2.
THP P r otection : Syn th esis of 24. Dihydropyran (1.1
equiv) was added in a dropwise manner to p-toluenesulfonic
acid (0.2 equiv) and 2,7-dihydroxynaphthalene (1 equiv) in dry
CH2Cl2. After completion, the reaction mixture was washed
with water and saturated aqueous ammonium chloride and
then dried over sodium sulfate. The solvent was removed in
vacuo, and the product was purified by flash chromatography
(SiO2; 3:2 ethyl acetate/petroleum ether). 24: yield 76%; Rf )
1
0.7 (3:2 ethyl acetate/petroleum ether); H NMR (CDCl3, 200
MHz) 1.2-1.9 (6H, m), 3.5 (2H, t), 7.1 (3H, d), 7.6 (2H, t), 8.1
(1H, s), 9.6 (1H, s).
P r a to Ad d ition of Ster oid a l Azom eth in e Ylid es to
C60
: Gen er a l P r oced u r e for P r ep a r a tion of 31-33. A
solution of C60 (1 equiv), sarcosine (2 equiv), and the appropri-
ate steroid ketone (28-30) (5 equiv) was heated at reflux in
toluene for 12 h. The solvent was removed in vacuo, and the
product was purified by flash chromatography (SiO2, 1:4 ethyl
acetate/toluene). Com p ou n d 31: yield 31%; TLC Rf ) 0.3 (1:4
ethyl acetate/toluene); 1H NMR (CDCl3, 200 MHz) 0.8-2.2
(28H, m), 3.0 (3H, s), 4.6 (2H, s). 32: yield 22%; TLC Rf ) 0.3
1
acetate/toluene; TLC Rf ) 0.4 (1:9 ethyl acetate/toluene); H
NMR (CDCl3, 200 MHz) 1.5 (3H, t), 3.6-4.0 (8H, m), 4.3-4.7
(6H, m), 4.9 (2H, s), 7.6-8.9 (27H, m); FAB-MS (M+ ) 1745.1,
calcd ) 1745.8). 41: yield 47%; eluant 1:10 ethyl acetate/
1
toluene; TLC Rf ) 0.4 (1:10 ethyl acetate/toluene); H NMR
(CDCl3, 200 MHz) 1.5 (3H, t), 3.6-4.0 (12H, m), 4.3-4.7 (6H,
m), 4.9 (2H, s), 7.7-9.0 (27H, m); FAB-MS (M+) 1788.3, calcd
) 1789.8).
1
(1:4 ethyl acetate/toluene); H NMR (CDCl3, 200 MHz) 0.8-
2.1 (25H, m), 2.8 (2H, s), 4.6 (2H, s), 5.7 (1H, s). 33: yield 20%;
TLC Rf ) 0.3 (1:4 ethyl acetate/toluene); 1H NMR (CDCl3, 200
MHz) 0.8-2.2 (21H, m), 2.9 (3H, s), 4.6 (2H, s), 5.6-5.9 (2H,
m), 6.2 (1H, m).
P r ep a r a tion of Tetr a eth ylen e Glycol Mon o-a zid e 11.
Thionyl chloride (9 g) was added to a solution of tetraethylene
glycol (15 g) dissolved in dry toluene (70 mL) over 1 h. The
reaction mixture was then heated at reflux under argon for 2
h. After evaporation of the solvent in vacuo, 20 mL of dry
toluene was added, and again the solution was evaporated to
dryness. Purification by flash chromatography (SiO2, CH2Cl2,
followed by 5% CH3OH/ethyl acetate) provided 8.3 g of an oil
(51%). To a solution of the presumed monochloro derivative
in DMSO (10 mL) was added NaN3 (800 mg), and the mixture
was heated at 60 °C for 20 h. After cooling, the mixture was
poured into 100 mL of water and extracted with CH2Cl2 (5 ×
20 mL); the combined extracts were dried over sodium sulfate
and evaporated to furnish 700 mg of a tan oil (68%). Purifica-
tion of the product was accomplished by passing through a
DCC/DMAP Cou p lin g to Diols: P r ep a r a tion of 38 a n d
39. A 5:1 mixture of bromobenzene/DMSO was added to an
Ar-purged flask containing 37 (1 equiv), 4-(dimethylamino)-
pyridine (0.2 equiv), 1-hydroxybenzotriazole hydrate (1.1
equiv), and 1,3-dicyclohexylcarbodiimide (5 equiv). The diol (10
equiv) was added, and the reaction was held at 50 °C with
constant stirring for 16 h. Bromobenzene was removed in
vacuo, and the mixture was diluted with CHCl3. After addition
of 10% oxalic acid in methanol, the mixture was sonicated for
1 min. The resulting solution was washed with water, 10%
CaSO4, and brine. After being dried over sodium sulfate, the
solvent was removed in vacuo. The residue was purified by

Synthetic Approaches to Porphyrin-Fullerene Hybrids
flash chromatography (SiO2, 1:9 ethyl acetate/toluene). 38:
J . Org. Chem., Vol. 66, No. 16, 2001 5455
Kolbanovskiy for technical assistance and Professor
Michele Maggini at the University of Padova for details
of the synthesis and NMR spectra of the saturated
steroidal fulleropyrrolidines. Finally, we thank Peter
J arowski for the theoretical calculations on the steroid
dyad 34.
1
yield 61%; TLC Rf ) 0.3 (1:9 ethyl acetate/toluene); H NMR
(CDCl3, 200 MHz) 1.5 (3H, t), 3.5-4.1 (10H, m), 4.4 (2H, t),
4.6 (2H, q), 5.0 (2H, s). 39: yield 64%; TLC Rf ) 0.3 (1:9 ethyl
acetate/toluene); 1H NMR (CDCl3, 200 MHz) 1.5 (3H, t), 3.5-
3.9 (14H, m), 4.4 (2H, t), 4.6 (2H, q), 5.0 (2H, s).
Ack n ow led gm en t. We thank the National Science
Foundation for support of this research through Grant
No. CHE-9712735. We also wish to thank NYU for
supporting this research through the Dean’s Under-
graduate Research Fund (P.S.B., R.F.) and Dr. Nicholas
Geacintov at NYU for access to his UV-vis and fluo-
rescence spectrophotometers. We thank Dr. Aleksandr
1
Su p p or tin g In for m a tion Ava ila ble: Copies of H NMR
for all new compounds, as well as 13C NMR and mass spectral
data where appropriate. This material is available free of
charge via the Internet at http://pubs.acs.org.
J O010317X