Fullerene-coated beads as reusable catalysts

Article abstract of DOI:10.1021/jo025926z

New heterogeneous catalysts that use oxygen and light to generate singlet oxygen (102) have been prepared. The catalysts facilitate various types of singlet oxygenation reactions including the Ene reaction, the Diels-Alder reaction, and others. The catalysts are made by stirring a heterogeneous mixture of fullerene-C₆₀(dissolved in toluene) with aminomethylated poly(styrene-co-divinylbenzene) beads. Also, catalysts for aqueous photooxidations are made by reacting the initial catalysts with poly(allylamine) to create an outer layer that is more hydrophilic.

Full text of DOI:10.1021/jo025926z

VOLUME 68, NUMBER 2
J ANUARY 24, 2003
© Copyright 2003 by the American Chemical Society
F u ller en e-Coa ted Bea d s a s Reu sa ble Ca ta lysts
Anton W. J ensen* and Coreen Daniels
Department of Chemistry, Central Michigan University, Mount Pleasant, Michigan 48859
anton.w.jensen@cmich.edu
Received May 10, 2002
New heterogeneous catalysts that use oxygen and light to generate singlet oxygen (1O2) have been
prepared. The catalysts facilitate various types of singlet oxygenation reactions including the Ene
reaction, the Diels-Alder reaction, and others. The catalysts are made by stirring a heterogeneous
mixture of fullerene-C60 (dissolved in toluene) with aminomethylated poly(styrene-co-divinylbenzene)
beads. Also, catalysts for aqueous photooxidations are made by reacting the initial catalysts with
poly(allylamine) to create an outer layer that is more hydrophilic.
In tr od u ction
In 1973 Blossey et al. described the preparation of Rose
Bengal coated beads and their use as heterogeneous
catalysts for 1O2 reactions.10-12 These catalysts were
patented13 and commercially available for several years.
The ability to simply filter them out of the solution after
the reaction is complete is a major advantage to using
them. The initial catalysts that were made are used
primarily for reactions in organic solvents. Similar
catalysts have also been developed for singlet oxygen-
ations in aqueous solutions.14,15 More recently, other
heterogeneous 1O2 catalysts have been developed by using
clay,16 silica,17 and zeolite18,19 solid supports.
Singlet oxygen (1O2) is a reagent used for a variety of
organic reactions. These reactions include the Ene reac-
tion,1 the Diels-Alder reaction,2 and others.3 Singlet
oxygen may be made by the reaction of ozone with
triphenyl phosphite,4 hypochlorite oxidation of hydrogen
peroxide,5 or photosensitization of ground-state oxygen.6
The last method requires only a catalytic amount of
the photosensitizer. Various sensitizers are available
(fullerenes,7,8 Rose Bengal,9 methylene blue,9 and oth-
ers9).
* Author to whom correspondence should be addressed.
(1) (a) Adam, W.; Bottke, N.; Engels, B.; Krebs, O. J . Am. Chem.
Soc. 2001, 123, 5542. (b) Erden, I.; Song, J .; Cao, W. Org. Lett. 2000,
2, 1383. (c) Sevin, F.; McKee, M. L. J . Am. Chem. Soc. 2001, 123, 4591.
(d) Gollnick, K.; Kuhn, H. J . Ene-Reactions with Singlet Oxygen. In
Organic Chemistry, Singlet Oxygen; Wasserman, H. H., Murray, R.
W., Eds.; Academic Press: London, UK, 1979; Vol. 40, p 287.
(2) (a) Yao, G.; Steliou, K. Org. Lett. 2002, 4, 485. (b) Mehta, G.;
Uma, R. J . Org. Chem. 2000, 65, 1685. (c) Bloodworth, A. J .; Eggelte,
H. J . Endoperoxides. In Singlet Oxygen, Volume II: Reaction Modes
and Products, Part 1; Frimer, A. A., Ed.; CRC Press: Boca Raton, FL,
1985; Chapter 4, p 93.
(3) (a) Greer, A.; Vassilikogiannakis, G.; Lee, K.-C.; Koffas, T. S.;
Nahm, K.; Foote, C. S. J . Org. Chem. 2000, 65, 6876. (b) See
examples: Ene-Reactions with Singlet Oxygen. In Organic Chemistry,
Singlet Oxygen; Wasserman, H. H., Murray, R. W. Eds.; Academic
Press: London, UK, 1979; Vol. 40.
The aim of this research is ultimately to build hetero-
geneous 1O2 catalysts with chiral outer layers where
stereoselective oxidation reactions could occur.20 The first
step in developing such catalysts is to coat beads with a
1O2 sensitizer that may be easily covered with a material
to which chiral outer layers may later be attached.20
Buckminsterfullerene (C60) is an ideal sensitizer to ac-
(10) Blossey, E. C.; Neckers, D. C.; Thayer, A. L.; Schaap, A. P. J .
Am. Chem. Soc. 1973, 95, 5820.
(11) Schaap, A. P.; Thayer, A. L.; Blossey, E. C.; Neckers, D. C. J .
Am. Chem. Soc. 1975, 97, 3741.
(12) Paczkowska, B.; Paczkowski, J .; Neckers, D. C. Macromolecules
1986, 19, 863.
(4) Bartlett, P. D.; Mendenhall, G. D.; Durham, D. L. J . Org. Chem.
1980, 45, 4269.
(13) Neckers, D. C.; Blossey, E. C.; Schaap, A. P. Photosensitized
reactions utilizing polymer-bound photosensitizing catalysts, U.S.
Patent 4 315 998, Feb 1982.
(14) Schaap, A. P.; Thayer, A. L.; Zaklika, K. A.; Valenti, P. C. J .
Am. Chem. Soc. 1979, 101, 4016.
(15) Prat, F.; Foote, C. S. Photochem. Photobiol. 1998, 67, 626.
(16) Madhavan, D.; Pitchumani, K. Tetrahedron 2001, 57, 8391.
(17) Soggiu, N.; Cardy, H.; J iwan, J . L. H.; Leray, I.; Soumillon, J .
P.; Lacombe, S. J . Photochem. Photobiol. 1999, 124, 1.
(18) Li, X.; Ramamurthy, V. Tetrahedron Lett. 1996, 37, 5235.
(19) Zhou, W.; Clennan, E. L. J . Am. Chem. Soc. 1999, 121, 2915.
(20) J ensen, A. W. Singlet Oxygen Catalysts Including Condensed
Carbon Molecules; pending patent application (serial number 10/126,-
308), Filed April 2002.
(5) Foote, C. S.; Wexler, S. J . Am. Chem. Soc. 1964, 86, 3879.
(6) Kasha, M.; Brabham, D. E. Singlet Oxygen Electronic Structure
and Photosensitization. In Organic Chemistry, Singlet Oxygen; Wasser-
man, H. H., Murray, R. W., Eds.; Academic Press: London, UK, 1979;
Vol. 40, pp 1-33.
(7) Aborgast, J . W.; Darmanyan, A. P.; Foote, C. S.; Rubin, Y.;
Diederich F. N.; Alvarez, M. M.; Anz, S. J .; Whetten, R. L. J . Phys.
Chem. 1991, 95, 11.
(8) Arbogast, J . W.; Foote, C. S. J . Am. Chem. Soc. 1991, 113, 8886.
(9) Rabek, J . F. 1O2 Oxidation of Polymers and their Stabilization.
In Singlet O2, Volume IV. Polymers and Biomolecules; Frimer, A. A.,
Ed.; CRC Press: Boca Raton, FL, 1985; Vol. IV, p 36.
10.1021/jo025926z CCC: $25.00 © 2003 American Chemical Society
Published on Web 08/08/2002
J . Org. Chem. 2003, 68, 207-210
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J ensen and Daniels
complish this objective. It efficiently catalyzes the conver-
sion of 3O2 to 1O2 (even after derivatization with various
organic groups). It has multiple reactive units, which
provide a scaffolding to cover the fullerenes once they
have been added to beads. And it has good thermal and
photochemical stability.
C60 placed on a film can be used to photochemically
form 1O2.21 Unfortunately, films lack sufficient surface
1
area to be able to make enough O2 for those materials
to be as useful as bead-coated catalytic materials. In fact,
prior to our bead studies, we prepared fullerene films and
1
were unable to generate enough O2 to catalyze a signi-
1
ficant amount of even the most reactive O2 reactions.
Fullerene-coated beads have been made before. A
patent was filed in 1994 that describes the preparation
of various fullerene-coated beads.22 However, the main
derivatization reaction described in the patent is cumber-
some. It utilizes a three-step process that involves
reduction of the fullerene, addition of Br2 to a double
bond, and replacement of one of the fullerene bromines
with 8-bromo-1-octanol. Once prepared, this derivative
is added to an amine-coated bead, which the authors
suggest is able to displace the tethered primary bromine.
Other groups have connected fullerenes to beads coated
with dienes via Diels-Alder reactions.23,24 However, these
adducts undergo reverse Diels-Alder reactions at around
110 °C. A Prato reaction adduct has been made that
requires derivatization of commercially available beads
via a three-step process.24 Fullerenes have also been
linked to beads with Cryptand-22 (a macrocycle contain-
ing two amines).25
F IGURE 1. Digital photograph of Catalyst I.
SCHEME 1. Bea d -Coa tin g Rea ction (F or m a tion of
Ca ta lyst I)
Resu lts a n d Discu ssion
For this project, commercially available amine-coated
beads26 were reacted with fullerenes directly in one step.
Amines react quickly with fullerenes at or slightly above
ambient temperature.27 Thus, fullerene-coated beads
were easily prepared by adding the beads to a solution
of C60 in toluene and stirring the mixture overnight at
35 °C (see Scheme 1).20 A hydrophilic fullerene-coated
bead for aqueous photooxidations was also prepared by
stirring Catalyst I in a methanolic solution of poly-
(allylamine) for about 2 h (see Scheme 2).20
SCHEME 2. F or m a tion of Aqu eou s Ca ta lyst
(Ca ta lyst II)
During the initial reaction between C60 and the beads,
the solution visibly loses some of its purple fullerene color
as the beads are coated. From the color change, the
reaction is probably completed in just a few hours;
however, stirring overnight may increase the loading.
(21) Brandt, O.; Roth, P. Anwendungspotential Fullerene, Status-
semin 1996, 39.
(22) (a) Stalling, D. L.; Guo, C.; Kuo, K. C.; Kelly, K. P.; Saim, S.
Chemically bound fullerenes to resin and silica supports and their use
as stationary phases for chromatography; U.S. Patent 5 308 481, May
1994. (b) Stalling, D. L.; Guo, C.; Saim, S. J . Chromatogr. Sci. 1993,
31, 265.
(23) (a) Nie, B.; Hasan, K.; Greaves, M. D.; Rotello, V. M. Tetrahe-
dron Lett. 1995, 36, 3617. (b) Guhr, K. I.; Greaves, M. D.; Rotello, V.
M. J . Am. Chem. Soc. 1994, 116, 5997.
(24) Wilson, S. R.; Cao, J .; Chin, E.; Saneii, H.; Peterson, M. L.;
Healy, E. Proc. Electrochem. Soc. 1995, 95-10, 22.
(25) Chiou, C.-S.; Shih, J .-S. Anal. Chim. Acta 2000, 416, 169.
(26) Purchased from Aldrich (Aminomethylated poly(styrene-co-
divinylbenzene) beads).
After coating, the beads were briefly rinsed in toluene.
Further rinsing, sonication, and Soxhlet extraction in-
dicated that the initial washing had removed any fullerene
molecules that were loosely associated with the bead
surface. Before coating, the beads are clear. After coating
they are reddish-purple (see Figure 1).
(27) Hirsch, A.; Li, Q.; Wudl, F. Angew. Chem., Int. Ed. Engl. 1991,
30, 1309.
208 J . Org. Chem., Vol. 68, No. 2, 2003

Fullerene-Coated Beads as Reusable Catalysts
SCHEME 3. Ca ta lysis w ith Ca ta lyst I or Ca ta lyst II
complete after 2 h based on the ratios of starting material
to the internal standard.
The bead loading for the beads with C60 was deter-
mined to be between 3 and 4.0% (of available amine sites)
from direct bead counting of massed bead samples, as
well as spectroscopic analysis of the original fullerene
solutions used for coating. This is comparable to Rose
Bengal-coated beads.11 The low loading most likely occurs
because many of the amine groups are within the core of
the beads.
Bead reusability was checked by repeating the TME
oxidation several times. The same beads were rinsed each
time between uses with CHCl3 to remove any product
that may have adhered to the beads. The beads catalyzed
the reactions each time to yield the same amount of
product.
Con clu sion
Heterogeneous catalysis of singlet oxygenations can be
achieved with fullerene-coated polymer beads. The beads
are easily prepared by stirring a heterogeneous mixture
of C60 and the beads. Also, because only Catalyst II was
able to decompose histidine in D2O, it appears that poly-
(allylamine) did successfully coat the fullerene layer of
Catalyst I with hydrophilic amine groups. Thus, it should
be possible to coat Catalyst I with layered polyelectrolyte
structures or other architectures which may lead to
stereoselective catalysts. Studies directed toward that
end are in progress.20
Four reactions were carried out to test the catalytic
ability of the beads. The first three (a, b, and c in Scheme
3) are representative of classes of 1O2 reactions (Ene
reaction, Diels-Alder reaction, and oxidation of phenols).
The last reaction (d in Scheme 3) was chosen to test
Catalyst II because it is an aqueous reaction. All four
reactions proved to be successfully catalyzed by either
Catalysts I or II.
Exp er im en ta l Section
The first three reactions were all performed in CDCl3,
so that the progress of the reactions could be followed by
1H NMR. Tetramethylethylene (TME) is converted to
3-hydroperoxy-2,3-dimethyl-1-butene. Because the prod-
uct of the TME oxidation does not absorb light >280 nm,
this reaction could be irradiated through Pyrex. Under
these conditions, Catalyst I completely oxidizes TME to
product cleanly in less than 1 h and 20 min, an order of
magnitude faster than the previously reported irradiation
time.10 Irradiation of 1,3-cyclohexadiene forms 5,6-
dioxabicyclo[2.2.2.]oct-2-ene as the only product by NMR
after only 65 min. Rose Bengal catalysts give a 69% yield
of bicyclic product after 9.5 h of irradiation of 1,3-
cyclohexadiene.11 Photooxidation of 1-naphthol gives 64%
conversion to only 1,4-naphthoquinone (by NMR) after
only 35 min. Previously, this reaction had been done with
90% yield after 10 h of irradiation with dissolved meth-
ylene blue sensitizer.28
The L-histidine reaction is done in D2O. The reaction
of L-histidine with singlet oxygen forms multiple prod-
ucts.29 The success of catalysis was therefore determined
by 1H NMR through comparison of the integration of
histidine against an internal standard. Catalyst I was
unable to oxidize histidine in D2O; however, Catalyst II
did catalyze the reaction. When Catalyst II was used the
histidine reaction was 24% complete after 1 h and 37%
Sta r tin g Ma ter ia ls a n d Rea gen ts. Aminomethylpolysty-
rene resin (PL-AMS) beads (in the 50-100 mesh size) were
obtained from a commercial source. C60, ethyl acetate, DMF,
toluene, ethanol, methanol, chloroform-d, methylene chloride,
and deuterium oxide were high purity commercial samples.
The tetramethylethylene, 1-naphthol, 1,3-cyclohexadiene, and
L-histidine were also purchased from chemical suppliers and
used without further purification.
Gen er a l P r oced u r e for P r ep a r a tion of Ca ta lyst I. C60
(100.0 mg) was dissolved in 50.0 mL of toluene by heating to
35 °C while stirring and using a water condenser to ensure
no loss of toluene. (Sonication helps the C60 dissolve faster.)
When the C60 was dissolved, the solution was dark purple. To
this solution was added 500 mg of PL-AMS beads (50-100
mesh) with stirring for 20 h at 50 °C with a water condenser
attached. The beads were filtered through a fritted vacuum
funnel and washed with 2-100 mL aliquots of hot toluene (50
°C) until the color of the toluene passing through the filter
was clear. The beads were allowed to completely dry on the
vacuum funnel for 12 h. The vacuum funnel containing the
dry beads was then placed on a new flask and the beads were
rinsed with 200 mL of methylene chloride. (If the toluene is
still wet on the beads, addition of CH2Cl2 causes them to break.
When broken, the beads take on a brownish color, but still
appear to catalyze the reactions.) The beads were then placed
on a Petri dish and dried in a vacuum oven for 12 h at 45 °C.
Bea d Loa d in g. Bead loading was determined by two
different methods: Spec. 20 and direct counting. The procedure
for the Spec. 20 involved determining the concentration of the
C60 remaining in the solvent after bead coating. This amount
of C60 remaining was the amount that did not adhere to the
bead surface. A calibration curve was plotted with absorbances
at 600 nm. The absorbance of the washing was then measured
and its concentration was calculated from the equation of the
linear regression.
(28) Chawla, H. M.; Kaul, K.; Kaul, M. Indian J . Chem. Sect. B 1993,
32, 733.
(29) Wasserman, H. H.; Lipshutz, B. H. Reactions of Singlet Oxygen
with Heterocyclic Systems. In Organic Chemistry, Singlet Oxygen;
Wasserman, H. H., Murray, R. W., Eds.; Academic Press: London, UK,
1979; Vol. 40, p 429.
J . Org. Chem, Vol. 68, No. 2, 2003 209

J ensen and Daniels
The direct bead counting was carried out by counting a
measured mass of uncoated (and then coated) beads under a
40× power dissecting microscope. The difference in mass per
bead was determined, which is the value for the average
amount of dye that was coated onto each bead. From this mass,
the millimoles of C60 per bead was determined. The millimoles
of C60 per bead was then divided by the number of millimoles
of amine groups in the total mass of beads used. (The values
for millimoles of amine sites are provided by the manufacturer
of the beads.)
Gen er a l P h otoch em ica l Rea ction P r oced u r e. Within
a photochemical reaction chamber, the light source (450 W
medium-pressure Hg arc lamp) was placed inside of a cylindri-
cal Pyrex filter, which was then placed inside of a quartz
water-cooled jacket. A square filter was clamped next to the
jacket to block wavelengths below 330 nm (although it was
found that the TME reaction can be run without this filter,
vide supra). The reactants, solvent, and catalyst were placed
into a Pyrex test tube for each reaction. The test tube was
clamped against the square filter. Compressed air was bubbled
through the reactions at a constant rate to maintain a constant
supply of oxygen to the reaction and also to stir the beads,
ensuring even exposure to the light source. The entire setup
was submerged in an ice bath to keep each reaction at a
relatively constant temperature.
Tetr am eth yleth eyth len e P h otoch em ical Reaction . Tet-
ramethylethylene (TME, 2,3-dimethyl-2-butene; 0.14 mL) was
placed in a Pyrex test tube containing 100.0 mg of Catalyst I
and 5 mL of CDCl3. The reaction was complete by 1H NMR
(formed only 3-hydroperoxy-2,3-dimethyl-1-butene as deter-
mined by NMR)10 after 1 h and 20 min (without the 330 cutoff
filter). With the 330 cutoff filter, the conversion to product was
55% after 65 min (only 3-hydroperoxy-2,3-dimethyl-1-butene).
This reaction was also conducted five additional times, rinsing
the same beads with CHCl3 each time to verify reusability of
the beads. The reactivity each time was essentially the same.
1,3-Cycloh exa d ien e P h otoch em ica l Rea ction . 1,3-Cy-
clohexadiene (0.11 mL) was added to a test tube containing
100 mg of C60 Catalyst I and 5 mL of CDCl3. The reaction was
allowed to run for 65 min and was found to be 44% converted
to only 5,6-dioxabicyclo[2.2.2.]oct-2-ene as determined by 1H
NMR.11
1-Na p h th ol P h otoch em ica l Rea ction . 1-Naphthol (15
mg), 100 mg of C60 catalyst (Catalyst I), and 10 mL of CDCl3
were irradiated as described above. The reaction was 64%
converted to only 1,4-naphthoquinone after 35 min as deter-
mined by 1H NMR. When higher concentrations of 1-naphthol
are used, the solution darkens to the point were 1O2 generation
is inhibited.
Gen er a l P r oced u r e for P r ep a r a tion of Ca ta lyst II,
P oly(a llyla m in e)-Coa ted Ca ta lyst. Catalyst I beads (75 mg)
were stirred for 2 h in a solution of poly(allylamine) [1.9758 g
of poly(allylamine)/89.0 mL of methanol]. The mixture was
filtered through a fritted vacuum funnel and rinsed with 200
mL of H2O. The beads were allowed to dry on the funnel for 2
h. The beads appeared to disperse in water much better than
Catalyst I beads.
Histid in e P h otoch em ica l Rea ction . L-Histidine (35 mg)
and D2O (5 mL) were placed into a clean dry graduated
cylinder and stirred until the histidine dissolved. A 1.0-mL
portion was removed and spiked with 10 µL of acetone
1
(internal standard) for H NMR comparison. The remaining 4
mL of D2O and histidine mixture was transferred to a test
tube. Catalyst II beads (70 mg) were added to the mixture and
the reaction was allowed to run for 2 h. Samples (1 mL) were
removed after 1 h and 2 h, 10 µL of acetone was added to each
sample, and 1H NMR analysis was performed.
J O025926Z
210 J . Org. Chem., Vol. 68, No. 2, 2003