Photocatalytic oxygenation of anthracenes and olefins with dioxygen via selective radical coupling using 9-mesityl-10-methylacridinium ion as an effective electron-transfer photocatalyst

Article abstract of DOI:10.1021/ja048353b

Visible light irradiation of the absorption band of 9-mesityl-10- methylacridinium ion (Acr⁺-Mes) in an O₂-saturated acetonitrile (MeCN) solution containing 9,10-dimethylanthracene results in formation of oxygenation product, i.e., dimethylepidioxyanthracene (Me ₂An-O₂). Anthracene and 9-methylanthracene also undergo photocatalytic oxygenation with Acr⁺-Mes to afford the corresponding epidioxyanthracenes under the photoirradiation. In the case of anthracene, the further photoirradiation results in formation of anthraquinone as the final six-electron oxidation product, via 10-hydroxyanthrone, accompanied by generation of H₂O₂. When anthracene is replaced by olefins (tetraphenylethylene and tetramethylethylene), the photocatalytic oxygenation of olefins affords the corresponding dioxetane, in which the O-O bond is cleaved to yield the corresponding ketones. The photocatalytic oxygenation of anthracenes and olefins is initiated by photoexcitation of Acr⁺-Mes, which results in formation of the electron-transfer state: Acr^?- Mes^?+, followed by electron transfer from anthracenes and olefins to the Mes^?+ moiety together with electron transfer from the Acr^? moiety to O₂. The resulting anthracene and olefin radical cations undergo the radical coupling reactions with O ₂^?- to produce the epidioxyanthracene (An-O ₂) and dioxetane, respectively.

Full text of DOI:10.1021/ja048353b

Published on Web 11/16/2004
Photocatalytic Oxygenation of Anthracenes and Olefins with
Dioxygen via Selective Radical Coupling Using
9-Mesityl-10-methylacridinium Ion as an Effective
Electron-Transfer Photocatalyst
Hiroaki Kotani, Kei Ohkubo, and Shunichi Fukuzumi*
Contribution from the Department of Material and Life Science,
Graduate School of Engineering, Osaka UniVersity, CREST,
Japan Science and Technology Agency (JST), Suita, Osaka 565-0871, Japan
Received March 23, 2004; E-mail: fukuzumi@ap.chem.eng.osaka-u.ac.jp
Abstract: Visible light irradiation of the absorption band of 9-mesityl-10-methylacridinium ion (Acr+-Mes)
in an O2-saturated acetonitrile (MeCN) solution containing 9,10-dimethylanthracene results in formation of
oxygenation product, i.e., dimethylepidioxyanthracene (Me2An-O2). Anthracene and 9-methylanthracene
also undergo photocatalytic oxygenation with Acr+-Mes to afford the corresponding epidioxyanthracenes
under the photoirradiation. In the case of anthracene, the further photoirradiation results in formation of
anthraquinone as the final six-electron oxidation product, via 10-hydroxyanthrone, accompanied by
generation of H2O2. When anthracene is replaced by olefins (tetraphenylethylene and tetramethylethylene),
the photocatalytic oxygenation of olefins affords the corresponding dioxetane, in which the O-O bond is
cleaved to yield the corresponding ketones. The photocatalytic oxygenation of anthracenes and olefins is
initiated by photoexcitation of Acr+-Mes, which results in formation of the electron-transfer state: Acr•-
Mes•+, followed by electron transfer from anthracenes and olefins to the Mes•+ moiety together with electron
transfer from the Acr• moiety to O2. The resulting anthracene and olefin radical cations undergo the radical
•-
coupling reactions with O2 to produce the epidioxyanthracene (An-O2) and dioxetane, respectively.
using a classical concerted pathway.9-14 The radical ion pair
Introduction
formed in photoinduced electron transfer from anthracene to
Although radical coupling reactions between radical cations
and radical anions have profound fundamental and synthetic
interest, the difficulty of generating such highly reactive species
together had precluded the exploitation of such reactions until
Amatore et al.1 succeeded in generating an anthracene radical
cation and a superoxide anion in close proximity with use of a
pair of microband electrodes at the femtoliter scale. The radical
cation and the radical anion combine chemically to form
epidioxyanthracene (An-O2) before reacting with the electrolyte
solution.1 However, any reactions on the femtoliter scale have
no synthetic interest.
Alternatively radical cations and radical anions can be
produced photochemically by photoexcitation of the charge-
transfer complex between electron donors and acceptors.2-8 In
particular, photoinduced cycloadditions via photoinduced elec-
tron transfer provide a new potentially important pathway for
controlling synthetic processes which could not be exploited
(7) (a) Yoon, U. C.; Mariano, P. S.; Givens, R. S.; Atwater, B. W. In AdVances
in Electron-Transfer Chemistry; Mariano, P. S., Ed.; JAI Press: Greenwich,
CT, 1994; Vol. 4, pp 117-205. (b) Roth, H. D. In Topics in Current
Chemistry: Photoinduced Electron-Transfer IV; Mattay, J., Ed.; Springer-
Verlag: Berlin, 1992; Vol. 163, pp 131-245. (c) Saeva, F. D. In AdVances
in Electron-Transfer Chemistry; Mariano, P. S., Ed.; JAI Press: Greenwich,
CT, 1994; Vol. 4, pp 1-25.
(8) (a) Fukuzumi, S. In AdVances in Electron-Transfer Chemistry; Mariano,
P. S., Ed.; JAI Press: Greenwich, CT, 1992; Vol. 2, pp 67-175. (b)
Fukuzumi, S.; Itoh, S. In AdVances in Photochemistry; Neckers, D. C.,
Volman, D. H., Eds.; John Wiley & Sons: New York, 1999; Vol. 25, p
107. (c) Sancar, A. In AdVances in Electron-Transfer Chemistry; Mariano,
P. S., Ed.; JAI Press: Greenwich, CT, 1992; Vol. 2, pp 215-272.
(9) (a) Mattes, S. L.; Farid, S. Acc. Chem. Res. 1982, 15, 80. (b) Mattes, S. L.;
Farid, S. In Organic Photochemistry; Padwa, A., Ed.; Dekker: New York,
1983; Vol. 6, pp 233-326. (c) Mattay, J.; Vondenhof, M. In Topics in
Current Chemistry: Photoinduced Electron-Transfer III; Mattay, J., Ed.;
Springer-Verlag: Berlin, 1990; Vol. 159, pp 219-255. (c) Mu¨ller, F.;
Mattay, J. Chem. ReV. 1993, 93, 99.
(10) (a) Schmoldt, P.; Rinderhagen, H.; Mattay, J. Mol. Supramol. Chem. 2003,
9, 185. (b) Ulmer, L.; Siedschlag, C.; Mattay, J. Eur. J. Org. Chem. 2003,
3811.
(11) (a) Lewis, F. D. In Photoinduced Electron Transfer; Fox, M. A., Chanon,
M., Ed.; Elsevier: Amsterdam, 1988; Part C, pp 1-69. (b) Bauld, N. L. In
AdVances in Electron-Transfer Chemistry; Mariano, P. S., Ed.; JAI Press:
Greenwich; CT, 1992; Vol. 2, pp 1-66.
(12) (a) Gotoh, T.; Padias, A. B.; Hall, H. K., Jr. J. Am. Chem. Soc. 1991, 113,
1308. (b) Mattay, J.; Trampe, G.; Runsink, J. Chem. Ber. 1988, 121, 1991.
(c) Takahashi, Y.; Kochi, J. K. Chem. Ber. 1988, 121, 253. (d) Kim, E.;
Christl, M.; Kochi, J. K. Chem. Ber. 1990, 123, 1209.
(13) (a) Mikami, K.; Matsumoto, S.; Tonoi, T.; Okubo, Y.; Suenobu, T.;
Fukuzumi, S. Tetrahedron Lett. 1998, 39, 3733. (b) Mikami, K.; Matsumoto,
S.; Okubo, Y.; Fujitsuka, M.; Ito, O.; Suenobu, T.; Fukuzumi, S. J. Am.
Chem. Soc. 2000, 122, 2236. (c) Vassilikogiannakis, G.; Orfanopoulos, M.
Tetrahedron Lett. 1997, 38, 4323.
(14) (a) Bockman, T. M.; Perrier, S.; Kochi, J. K. J. Chem. Soc., Perkin Trans.
2 1993, 595. (b) Bockman, T. M.; Shukla, D.; Kochi, J. K. J. Chem. Soc.,
Perkin Trans. 2 1996, 1623.
(1) Amatore, C.; Brown, A. R. J. Am. Chem. Soc. 1996, 118, 1482.
(2) Photoinduced Electron Transfer; Fox, M. A., Chanon, M., Eds.; Elsevier:
Amsterdam, 1988; Part A-D.
(3) (a) Julliard, M.; Chanon, M. Chem. ReV. 1983, 83, 425. (b) Kavarnos, G.
J.; Turro, N. J. Chem. ReV. 1986, 86, 401.
(4) Whitten, D. G.; Chesta, C.; Ci, X.; Kellett, M. A.; Yam, V. W. W. In
Photochemical Processes in Organized Molecular Systems; Honda, K., Ed.;
Elsevier: Amsterdam, 1991. (b) Gaillard, E. R.; Whitten, D. G. Acc. Chem.
Res. 1996, 29, 292.
(5) Pandey, G. Topics in Current Chemistry; Photoinduced Electron-Transfer
V; Springer-Verlag: Berlin, 1993; Vol. 168, pp 175-221.
(6) (a) Mangion, D.; Arnold, D. R. Acc. Chem. Res. 2002, 35, 297. (b) Miyashi,
T.; Ikeda, H.; Takahashi, Y. Acc. Chem. Res. 1999, 32, 815.
9
10.1021/ja048353b CCC: $27.50 © 2004 American Chemical Society
J. AM. CHEM. SOC. 2004, 126, 15999-16006
15999

A R T I C L E S
Kotani et al.
dienophiles has been detected by laser flash photolysis stud-
ies.15,16 However, the photoexcitation of dienes often results in
formation of excimer intermediates which lead to the photoin-
duced dimerization, precluding the selective reactions between
dienes and dienophiles.17-19 Thus, it is highly desired to use a
photocatalyst which can catalyze cycloadditions via photoin-
duced electron transfer without involving the photoexcited states
of substrates.
Radical cations and radical anions may also be formed using
an electron donor-acceptor linked molecule, since the photo-
excitation results in formation of a radical cation and anion pair
which can oxidize and reduce substrates to generate radical
cations and radical anions, respectively.20-24 Unfortunately,
however, the lifetimes of charge-separated states of most donor-
acceptor linked molecules reported so far were too short to be
coupled with the oxidation and reduction of substrates.20-24 In
this context, we have recently found that the photoexcitation
of 9-mesityl-10-methylacridinium ion (Acr+-Mes) results in
formation of the electron transfer state (Acr•-Mes•+), which
has an extremely long lifetime (e.g., 2 h at 203 K) and a high
energy (2.37 eV).25
We report herein that Acr+-Mes acts as an efficient electron-
transfer photocatalyst for highly selective oxygenation of
anthracenes with O2 via selective radical coupling of anthracene
radical cations and O2•- to produce epidioxyanthracenes under
visible light irradiation. An-O2 is further oxidized to an-
thraquinone, accompanied by generation of H2O2 under the
photoirradiation. Epidioxyanthracenes, which are generally
produced by the reactions of anthracenes with singlet oxygen
(1O2), have merited significant interest in relation with reversible
oxygen storage and as a species responsible for causing
physiological damage.26,27 In the case of the present photocata-
lytic oxygenation of anthracenes, however, the epidioxyan-
thracenes are shown to be formed selectively by the radical
coupling reactions of anthracene radical cations with O2•- rather
than the reaction with O2. The radical coupling reaction is
expanded to dioxetane formation, when anthracene is replaced
by tetraphenylethylene or tetramethylethylene.
1
Experimental Section
Materials. Anthracene, 9-methylanthracene, 9,10-dimethylan-
thracene, tetraphenylethylene, and tetramethylethylene were purchased
commercially. 9-Mesityl-10-methylacridinium ion (Acr+-Mes) was
prepared by the reaction of 10-methylacridone in dichloromethane
with mesitylmagnesium bromide, followed by addition of perchloric
acid for the hydrolysis and sodium hydroxide for the neutralization,
and then purified by recrystallization from methanol-diethyl ether.
9-Mesityl-10-methylacridinium (Acr+-Mes) perchlorate: Anal. Calcd
for C23H22ClNO4‚0.15(H2O): C, 66.63; H, 5.42; N, 3.38. Found; C,
1
66.44; H, 5.22; N, 3.49. H NMR (300 MHz, CD3CN, δ ppm) δ 8.16
(d, J ) 9.0 Hz, 2H), 7.93 (t, J ) 9.0 Hz, 2H), 7.40 (s, 4H), 6.79 (s,
2H), 4.37 (s, 3H), 2.02 (s, 3H), 1.25 (s, 6H). Acetonitrile (MeCN) used
as solvent was purified and dried by the standard procedure.28
Deuterated [2H3]acetonitrile (CD3CN) and deuterated [2H6]benzene
(C6D6) were obtained from EURI SO-TOP, CEA, France, and used as
received.
Reaction Procedure. Typically, a CD3CN solution (0.6 mL)
containing Acr+-Mes (1.0 × 10-3 M) and anthracene (1.0 × 10-2 M)
in an NMR tube sealed with a rubber septum was saturated with oxygen
by bubbling with oxygen through a stainless steel needle for 5 min.
The solution was then irradiated with a xenon lamp (Ushio Optical
ModelX SX-UID 500XAMQ) through a color filter glass (Asahi Techno
Glass Y43) transmitting λ > 430 nm at room temperature. The irradiated
1
1
solution was analyzed periodically by H NMR spectroscopy. The H
NMR measurements were performed on a Japan Electron Optics JNM-
AL300 (300 MHz) NMR spectrometer. Matrix-assisted laser desorption/
ionization (MALDI) time-of-flight (TOF) mass spectra were measured
on a Kratos Compact MALDI I (Shimadzu). Gas chromatographic
analyses were performed on a Shimadzu GC-17A equipped with a DB-
5MS column (Agilient Technologies, 30 m) and a mass spectrograph
(Shimadzu QP-5050) as a detector. The products of the photooxygen-
ation were determined by 1H NMR, MALDI-TOF-MS, and GC-MS.
9,10-Dihydro-9,10-epidioxyanthracene (An-O2): 1H NMR (300 MHz,
CD3CN) δ 6.15 (s, 2H), 7.29-7.32 (m, 4H), 7.45-7.48 (m, 4H);29
MALDI-TOF-MS m/z 211 (M+ calcd for C14H10O2 211.0). Anal. Calcd
for C14H10O2: C, 79.98; H, 4.79. Found: C, 79.96; H, 4.65. 9-Methyl-
10-hydro-9,10-epidioxyanthracene: 1H NMR (300 MHz, CD3CN) δ
2.10 (s, 3H), 6.11 (s, 1H), 7.29-7.48 (m, 8H); MALDI-TOF-MS m/z
225 (M+ calcd for C15H12O2, 225.1). Anal. Calcd for C15H12O2‚
0.25H2O: C, 79.15; H, 5.95. Found: C, 78.88; H, 6.27. 9,10-Dimethyl-
9,10-epidioxyanthracene (Me2An-O2): 1H NMR (300 MHz, CD3CN)
δ 2.09 (s, 6H), 7.31-7.34 (m, 4H), 7.44-7.48 (m, 4H);27 MALDI-
TOF-MS m/z 239 (M+ calcd for C16H14O2, 238.1). Anal. Calcd for
C16H14O2‚0.25H2O: C, 79.15; H, 5.92. Found: C, 78.88; H, 6.27.
Tetraphenylethylene dioxetane: 1H NMR (300 MHz, CD3CN) δ 7.16-
7.22 (m, 12H), 7.26-7.31 (m, 8H). Tetramethylethylene dioxetane: 1H
NMR (300 MHz, CD3CN) δ 1.32 (s, 12H). The isolation of the
photocatalytic oxygenation product of dimethylanthracene in a prepara-
tive scale was performed using an O2-saturated MeCN solution (20
mL) containing Acr+-Mes (8.2 mg, 2.0 × 10-5 mol) and dimethyl-
anthracene (100 mg, 5.0 × 10-4 mol) in a Schlenck flask (20 mL)
after the photoirradiation with a xenon lamp through a color filter glass
transmitting λ > 430 nm for 6 h. After irradiation the solution was
evaporated to dryness and purified by silica gel column chromatography
(15) (a) Sun, D.; Hubig, S. M.; Kochi, J. K. J. Photochem. Photobiol., A 1999,
122, 87. (b) Sun, D.; Hubig, S. M.; Kochi, J. K. J. Org. Chem. 1999, 64,
2250.
(16) Fukuzumi, S.; Okamoto, T.; Ohkubo, K. J. Phys. Chem. A 2003, 107, 5412.
(17) (a) Stevens, B. AdV. Photochem. 1971, 8, 161. (b) Saltiel, J.; Townsend,
D. E.; Watson, B. D.; Shannon, P.; Finson, S. L. J. Am. Chem. Soc. 1977,
99, 884. (c) Bergmark, W. R.; Jones, G., II.; Reinhardt, T. E.; Halpern, A.
M. J. Am. Chem. Soc. 1978, 100, 6665. (d) Saltiel, J.; Marchand, G. R.;
Smothers, W. K.; Stout, S. A.; Charlton, J. L. J. Am. Chem. Soc. 1981,
103, 7159. (e) Charlton, J. L.; Dabestani, R.; Saltiel, J. J. Am. Chem. Soc.
1983, 105, 3473.
(18) Manring, L. E.; Peters, K. S.; Jones, G., II; Bergmark, W. R. J. Am. Chem.
Soc. 1985, 107, 1485.
(19) Schaefer, C.; Mattay, J. Photochem. Photobiol. Sci. 2004, 3, 331.
(20) (a) Gust, D.; Moore, T. A.; Moore, A. L. In Electron Transfer in Chemistry,
Balzani, V. Ed; Wiley-VCH: Weinheim, 2001; Vol. 3, pp 272-336. (b)
Gust, D.; Moore, T. A. In The Porphyrin Handbook; Kadish, K. M., Smith,
K. M., Guilard, R., Eds.; Academic Press: San Diego, CA, 2000; Vol. 8,
pp 153-190. (c) Gust, D.; Moore, T. A.; Moore, A. L. Acc. Chem. Res.
2001, 34, 40.
(21) (a) Wasielewski, M. R. Chem. ReV. 1992, 92, 435. (b) Debreczeny, M. P.;
Svec, W. A.; Wasielewski, M. R. Science 1996, 274, 584. (c) Osuka, A.;
Mataga, N.; Okada, T. Pure Appl. Chem. 1997, 69, 797.
(22) (a) Jordan, K. D.; Paddon-Row, M. N. Chem. ReV. 1992, 92, 395. (b)
Paddon-Row: M. N. Acc. Chem. Res. 1994, 27, 18. (c) Verhoeven, J. W.
AdV. Chem. Phys. 1999, 106, 603. (d) Paddon-Row, M. N. AdV. Phys. Org.
Chem. 2003, 38, 1.
(23) (a) Harriman, A.; Sauvage, J.-P. Chem. Soc. ReV. 1996, 25, 41. (b) Blanco,
M.-J.; Consuelo Jime´nez, M.; Chambron, J.-C.; Heitz, V.; Linke, M.;
Sauvage, J.-P. Chem. Soc. ReV. 1999, 28, 293. (c) Chambron, J.-C.; Collin,
J.-P.; Dalbavie, J.-O.; Dietrich-Buchecker, C. O.; Heitz, V.; Odobel, F.;
Solladie´, N.; Sauvage, J.-P. Coord. Chem. ReV. 1998, 178-180, 1299.
(24) Fukuzumi, S.; Guldi, D. M. In Electron Transfer in Chemistry; Balzani,
V. Ed.; Wiley-VCH: Weinheim, 2001; Vol. 2, pp 270-337. (b) Fukuzumi,
S. Org. Biomol. Chem. 2003, 1, 609.
(25) Fukuzumi, S.; Kotani, H.; Ohkubo, K.; Ogo, S.; Tkachenko, N. V.;
Lemmetyinen, H. J. Am. Chem. Soc. 2004, 126, 1600.
(26) ActiVe Oxygen in Chemistry; Foote, C. S., Valentine, J. S., Greenberg, A.,
Liebman, J. F., Eds.; Blackie Academic and Professional: New York, 1995;
Vol. 2.
(28) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of Laboratory
Chemicals, 4th ed.; Pergamon Press: Elmsford, NY, 1996.
(29) Foote, C. S.; Wexler, S.; Ando, W.; Higgins, R. J. Am. Chem. Soc. 1968,
90, 975.
(27) Donkers, R. L.; Workentin, M. S. J. Am. Chem. Soc. 2004, 126, 1688.
9
16000 J. AM. CHEM. SOC. VOL. 126, NO. 49, 2004

Photocatalytic Oxygenation of Anthracenes and Olefins
A R T I C L E S
(chloroform as an eluent) to afford Me2An-O2 as a white solid. The
isolated yield of Me2An-O2 was determined as 80%. The amount of
H2O2 was determined by titration by iodide ion by the following
procedure.30 An O2-saturated MeCN solution (3.0 mL) of Acr+-Mes
(1.0 × 10-4 M) and anthracene (1.0 × 10-4 M) was photoirradiated
for 2 h, and the photoirradiated product mixture was treated with an
excess amount of NaI. The amount of I3- formed was then determined
by the visible spectrum (λmax ) 361 nm, ꢀ ) 2.50 × 104 M-1 cm-1).31
Laser Flash Photolysis. An argon or O2-saturated MeCN solution
containing anthracene (1.6 × 10-6 - 2.8 × 10-4 M) and Acr+-Mes
(1.0 × 10-4 M) was excited by a Panther OPO pumped by Nd:YAG
laser (Continuum, SLII-10, 4-6 ns fwhm) at λ ) 430 nm with a power
of 10 mJ per pulse. The transient absorption measurements were
performed using a continuous xenon lamp (150 W) and an InGaAs-
PIN photodiode (Hamamatsu 2949) as a probe light and a detector,
respectively. The output from the photodiodes and a photomultiplier
tube was recorded with a digitizing oscilloscope (Tektronix, TDS3032,
300 MHz). The transient spectra were recorded using fresh solutions
in each laser excitation at 298 K. The quantum yields of formation of
the electron-transfer state (Acr•-Mes•+) and anthracene radical cations
upon laser photoexcitation were determined by comparing the transient
absorption due to Acr•-Mes•+ and anthracene radical cations with the
triplet-triplet absorption of C60 (λ ) 750 nm, ꢀ ) 1.8 × 104 M-1
cm-1) under the deaerated benzene solution of C60 (1.8 × 10-3 M) as
reported elsewhere.25,36,37
ESR Measurements. An oxygen-saturated MeCN solution of Acr+-
Mes (1.0 × 10-3 M) was irradiated at 233 K with a high-pressure
mercury lamp (USH-1005D) through a water filter focusing at the
sample cell in the ESR cavity. After the photoirradition, the sample
cell was immediately cooled to 123 K and the ESR spectra were taken
on a JEOL JES-RE1XE under nonsaturating microwave power condi-
tions. The magnitude of the modulation was chosen to optimize the
resolution and the signal-to-noise ratio (S/N) of the observed spectra.
The g values were calibrated using a Mn2+ marker.
1O2 Emission Measurements. An O2-saturated CD3CN solution
containing Acr+-Mes (2.0 × 10-4 M) and Me2An (1.0 × 10-2 M) in
a quartz cell (optical path length 10 mm) was excited at λ ) 400 nm
using a Cosmo System LVU-200S spectrometer. An O2-saturated C6D6
solution containing C60 (2.0 × 10-4 M) was also employed for
comparison. A photomultiplier (Hamamatsu Photonics, R5509-72) was
used to detect emission in the near-infrared region (band path 2 mm).
For the emission lifetime measurements, O2-saturated C6D6 solutions
containing C60 (2.0 × 10-4 M) in the presence of various concentrations
of Me2An were excited by the frequency-tripled output of Q-switched
Nd:YAG laser at λ ) 355 nm (Spectra Physics GCR-150-10) operating
at 10 Hz. Typical pulse energies at sample were in the range 1-2 mJ.
The emission was detected by a liquid nitrogen-cooled photomultiplier
(Hamamatsu Photonics, R5509-72). The signal was captured and
averaged by a digital storage oscilloscope (Tektronix TDS3032) and
transferred to a PC for analysis.
Quantum Yield Determination. Potassium ferrioxalate used as an
actinometer was prepared according to the literature and purified by
recrystallization from hot water.32 A standard actinometer (potassium
ferrioxalate) was used for the quantum yield determination of the
photocatalytic oxygenation of anthracene and its derivatives with O2.
A square quartz cuvette (10 mm i.d.) which contained a MeCN solution
(3.0 mL) of Acr+-Mes (2.0 × 10-4 M) and anthracene (3.0 × 10-5
-
7.0 × 10-4 M) was irradiated with monochromatized light of λ ) 430
nm from a Shimadzu RF-5300PC fluorescence spectrophotometer.
Under the conditions of actinometry experiments, both the actinometer
and Acr+-Mes absorbed virtually all the incident light. The light
intensity of monochromatized light of λ ) 430 nm was determined as
5.5 × 10-10 einstein s-1 with an illumination bandwidth of 1 cm.
The photochemical reaction was monitored by using a Hewlett-Packard
8453 photodiode array spectrophotometer. The quantum yields were
determined from a decrease in absorbance due to anthracene (λ ) 376
nm, ꢀ ) 6.7 × 103 M-1 cm-1), 9-methylanthracene (λ ) 387 nm, ꢀ )
6.7 × 103 M-1 cm-1), and 9,10-methylanthracene (λ ) 398 nm, ꢀ )
7.2 × 103 M-1 cm-1). To avoid the contribution of light absorption of
the products, only the initial rates were determined for determination
of the quantum yields.
Electrochemical Measurements. Electrochemical measurements
were performed on an ALS630B electrochemical analyzer in deaerated
MeCN containing 0.1 M Bu4NClO4 (TBAP) as supporting electrolyte
at 298 K. A conventional three-electrode cell was used with a platinum
working electrode (surface area of 0.3 mm2) and a platinum wire as
the counter electrode. The Pt working electrode (BAS) was routinely
polished with BAS polishing alumina suspension and rinsed with
acetone before use. The measured potentials were recorded with respect
to the Ag/AgNO3 (0.01 M) reference electrode. The second-harmonic
alternating current voltammetry (SHACV) measurements were carried
out with an ALS630B electrochemical analyzer in deaerated MeCN
containing 0.1 M Bu4NClO4 (TBAP) as supporting electrolyte. All
potentials (vs Ag/Ag+) were converted to values vs SCE by adding
0.29 V. All electrochemical measurements were carried out under an
atmospheric pressure of Ar.
Results and Discussion
Theoretical Calculations. Density-functional theory (DFT) calcula-
tions were performed on a COMPAQ DS20E computer. Geometry
optimizations were carried out using the Becke3LYP functional and
6-31G* basis set,33,34 with the unrestricted Hartree-Fock (UHF)
formalism and as implemented in the Gaussian 98 program.35 Graphical
outputs of the computational results were generated with the Cerius2
software program developed by Molecular Simulations Inc.
Photocatalytic Formation of Epidioxyanthracenes. Visible
light irradiation (λ > 430 nm) of the absorption band of Acr+-
Mes (1.0 × 10-3 M) in an O2-saturated acetonitrile (MeCN)
solution containing anthracenes (1.0 × 10-2 M) results in
formation of the oxygenation products, i.e., epidioxyanthracenes
(eq 1). The yields of epidioxyanthracenes derived from 9,10-
dimethylanthracene (Me2An), 9-methylanthracene (MeAn), and
anthracene (An) after 10 min photoirradiation are listed in Table
1. The photocatalytic oxygenation of Me2An with O2 in a
preparative scale (100 mg, 5.0 × 10-4 mol) with Acr+-Mes
(8.2 mg, 2.0 × 10-5 mol) was also performed to isolate
dimethylepidioxyanthracene (80% yield, see Experimental Sec-
tion). The lower yields of methylepidioxyanthracene (MeAn-
(30) Mair, R. D.; Graupner, A, J. Anal. Chem. 1964, 36, 194.
(31) (a) Fukuzumi, S.; Kuroda, S.; Tanaka, T. J. Am. Chem. Soc. 1985, 107,
3020. (b) Fukuzumi, S.; Ishikawa, M.; Tanaka, T. J. Chem. Soc., Perkin
Trans. 2 1989, 1037.
(32) Hatchard, C. G.; Parker, C. A. Proc. R. Soc. London, Ser. A 1956, 235,
518.
(33) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang, W.;
Parr, R. G. Phys. ReV. B 1988, 37, 785.
(34) Hehre, W. J.; Radom, L.; Schleyer, P. v. R.; Pople, J. A. Ab Initio Molecular
Orbital Theory; Wiley: New York, 1986.
(35) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M.
A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.; Stratmann,
R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin,
K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi,
R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.;
Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz,
J. V.; Baboul, A. G.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.;
Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham,
M. A.; Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.;
Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.;
Gonzalez, C.; Head-Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian
98, Revision A.7; Gaussian, Inc.: Pittsburgh PA, 1998.
(36) Luo, C.; Fujitsuka, M.; Watanabe, A.; Ito, O.; Gan, L.; Huang, Y.; Huang,
C.-H. J. Chem. Soc., Faraday Trans. 1998, 94, 527.
(37) Ohkubo, K.; Kotani, H.; Shao, J.; Ou, Z.; Kadish, K. M.; Li, G.; Pandey,
R. K.; Fujitsuka, M.; Ito, O.; Imahori, H.; Fukuzumi, S. Angew. Chem.,
Int. Ed. 2004, 43, 853.
9
J. AM. CHEM. SOC. VOL. 126, NO. 49, 2004 16001

A R T I C L E S
Kotani et al.
Table 1. Product Yields and Quantum Yields (ΦP) in
Photocatalytic Oxygenation of Anthracenes with Oxygen in the
Presence of Acr+-Mes (2.0 × 10-4 M) and Anthracenes (7.0 ×
10-4 M), One-Electron Oxidation Potentials of Anthracenes, Rate
Constants (ket) of Electron-Transfer Oxidation of Anthracenes by
Acr•-Mes•+, Quantum Yields for Formation of Anthracene Radical
Cations (ΦR) under Ar, and Quantum Yields (ΦR′) under O2 in the
Presence of Acr+-Mes (1.0 × 10-4 M) and Anthracenes (2.8 ×
10-4 M)
product
yielda
ΦP
(%)
ΦR
(%)
ΦR′
(%)
1
anthracene
(%)
E
°
b (V)
k
et (M-1 s-
)
ox
Me2An
MeAn
An
99
46
75
30
6
2
1.05
1.11
1.19
1.4 × 1010
1.3 × 1010
7.5 × 109
66
58
34
86
91
62
a Determined by 1H NMR after 10 min of photoirradiation. b vs SCE,
taken from ref 39.
Figure 1. Photoirradiation time profile of the photooxygenation of
anthracene (1.0 × 10-2 M) in the presence of Acr+-Mes (1.0 × 10-3 M)
in O2-saturated CD3CN; anthracene (O), An-O2 (b), 10-hydroxyanthrone
(9), and anthraquinone (2).
O2) and epidioxyanthracene (An-O2) as compared with Me2An-
O2 result from the further photochemical reactions (vide infra).
In the case of anthracene, the An-O2 is converted to
10-hydroxyanthrone38 with the further photoirradiation (λ > 430
nm) of an O2-saturated CD3CN solution of An-O2 and Acr+-
Mes (eq 2). When the reaction is started from the isolated
Figure 2. Dependence of the quantum yields (ΦP) of formation of
epidioxyanthracenes of Me2An (b), MeAn (O), and An (9) on concentra-
tions of anthracenes in photooxygenation of anthracenes in the presence of
Acr+-Mes (2.0 × 10-4 M) in O2-saturated MeCN.
An-O2, no photochemical reaction has occurred without Acr+-
Mes or no thermal reaction has taken place with Acr+-Mes.
The photochemical reaction time profile of the photocatalytic
oxygenation of An is examined by 1H NMR as shown in Figure
1. After An-O2 is converted to 10-hydroxyanthrone, the anthrone
is further oxidized under prolonged photoirradiation to yield
the final six-electron oxidation product, i.e., anthraquinone,
which is accompanied by generation of H2O2 (eq 3). The yield
of H2O2 was determined as 99% (see Experimental Section).
The oxygenated final product of 9-methylanthracene (MeAn)
was 10-hydroxy-10-methylanthrone as reported previously for
the electron-transfer oxidation of MeAn.38
ing Information Figure S1). This indicates that the two oxygen
atoms of anthraquinone come from O2.
The quantum yields (ΦP) of formation of epidioxyanthracenes
were determined from a decrease in absorbance due to an-
thracenes using an actinometer (see Experimental Section). The
dependence of ΦP on concentrations of anthracenes is shown
in Figure 2. In each case, the ΦP value increases with increasing
concentration of anthracene or its derivative to reach a constant
value (>10-4 M). Such a saturation behavior of ΦP at the low
concentration region indicates that the photooxygenation occurs
via the long-lived electron-transfer state (Acr•-Mes•+) produced
by photoinduced electron transfer from the Mes moiety to the
singlet excited state of the Acr+ moiety. The ΦP values at a
fixed concentration of anthracenes (7.0 × 10-4 M) are listed in
Table 1. The photocatalytic oxygenation mechanism is discussed
in the following section.
In the case of Me2An, the Me2An-O2 is stable under the
photocatalytic conditions. This indicates that the photocatalytic
conversion from An-O2 to 10-hydroxyanthrone (eq 2) requires
the migration of hydrogen. The further oxidation of 10-
hydroxyanthrone (eq 3) also requires photoirradiation in the
presence of Acr+-Mes (vide supra).
Photocatalytic Oxygenation Mechanism via Radical Cou-
pling. To elucidate the photocatalytic oxygenation mechanism,
the intermediate species are detected by laser flash photolysis
experiments. Nanosecond laser excitation at 430 nm of a
deaerated MeCN solution of Acr+-Mes results in formation
When 18O2 is employed instead of 16O2, 18O-labeled an-
thraquinone is produced as indicated by GC-MS (see Support-
(38) Fukuzumi, S.; Nakanishi, I.; Tanaka, K. J. Phys. Chem. A 1999, 103, 11212.
9
16002 J. AM. CHEM. SOC. VOL. 126, NO. 49, 2004

Photocatalytic Oxygenation of Anthracenes and Olefins
A R T I C L E S
Figure 3. (a) Transient absorption spectra of Acr+-Mes (1.0 × 10-4 M)
in deaerated MeCN at 298 K taken at 15 µs after laser excitation at 430
nm in the absence (O) and presence (b) of Me2An (5.0 × 10-5 M). (b)
Absorbance time profiles at 500 nm due to Mes•+ (O) and at 660 nm due
to Me2An•+ (b).
Figure 4. (a) Absorbance time profiles at 660 nm due to Me2An•+ in the
presence of various concentrations of Me2An. (b) Plot of the pseudo-first-
order rate constant (kobs) for electron transfer from Me2An to the Mes•+
moiety of Acr•-Mes•+ vs [Me2An].
increasing concentration of Me2An (Figure 4b). The second-
order rate constant (ket) of electron transfer from Me2An to
Acr•-Mes•+ is determined from the slope of the linear plot in
Figure 4b as 1.4 × 1010 M-1 s-1, which is close to be the
diffusion-limited value as expected from the exergonic electron
transfer. Transient absorption spectra of radical cations of An
and MeAn are also detected in the photoirradiation of Acr+-
Mes in the presence of An and MeAn (see Supporting
Information Figure S2). The ket values of anthracenes thus
determined are also listed in Table 1, together with the one-
electron oxidation potentials (E°ox) of anthracenes.
of the electron-transfer state (Acr•-Mes•+) via photoinduced
electron transfer from the Mes moiety to the singlet excited state
of the Acr+ moiety.25 The quantum yields for the formation of
the electron-transfer state (Acr•-Mes•+) has been previously
determined as almost quantitative (98%).25 Since the one-
electron reduction potential of Acr•-Mes•+ (E°red ) 1.88 V vs
SCE)25 is more positive than the one-electron oxidation potential
of Me2An (E°ox ) 1.05 V vs SCE),39 electron transfer from
Me2An to the Mes•+ moiety in Acr•-Mes•+ is energetically
feasible. Thus, the addition of Me2An to the MeCN solution of
Acr+-Mes and the laser photoirradiation result in formation
of the Me2An radical cation (Me2An•+: λmax ) 660 nm)38 with
a concomitant decrease in the absorption band due to the Mes•+
moiety as shown in Figure 3a and b. It is important to note that
the absorption band due to the Acr• moiety remains virtually
the same in the absence of O2 (Figure 3a). This indicates clearly
that Me2An•+ is formed by electron transfer from Me2An to
Acr•-Mes•+ rather than by direct photoinduced electron transfer
from Me2An to the singlet excited state of the Acr+ moiety in
Acr+-Mes. The rate of formation of Me2An•+ increases with
increasing concentration of Me2An as shown in Figure 4a. The
formation rate obeyed pseudo-first-order kinetics, and the
pseudo-first-order rate constant (kobs) increases linearly with
The quantum yields (ΦR) of formation of anthracene radical
cations were determined from the transient absorption and the
extinction coefficients using a comparative method (see Ex-
perimental Section). The dependence of ΦR on concentrations
of anthracenes is shown in Figure 5, where the ΦR value
becomes constant at a low concentration region of anthracene
or its derivative (>10-4 M) as in the case of the product
quantum yields (ΦP) in Figure 2. The quantum yields (ΦR) at
2.8 × 10-4 M anthracenes are also listed in Table 1.
Although the absorption band due to the Acr• moiety remains
virtually the same in the absence of oxygen (vide supra, see
Figure 3a), the absorption band due to the Acr• moiety decays
in the presence of O2 by electron-transfer reduction from the
Acr• moiety to O2. The decay of the transient spectrum at 500
nm due to the Acr• moiety obeys pseudo-first-order kinetics,
(39) Fukuzumi, S.; Ohkubo, K.; Okamoto, T. J. Am. Chem. Soc. 2002, 124,
14147.
9
J. AM. CHEM. SOC. VOL. 126, NO. 49, 2004 16003

A R T I C L E S
Kotani et al.
Figure 7. Decay time profile of absorbance at 660 nm due to Me2An•+
after laser excitation at 430 nm in an O2-saturated MeCN solution containing
Acr+-Mes (1.0 × 10-4 M) and Me2An (1.0 × 10-3 M). Inset: Second-
order plot.
Figure 5. Dependence of the quantum yields (ΦR) of formation of radical
cations of Me2An (b), MeAn (O), and An (9) on concentrations of
anthracenes after laser photoexcitation at 430 nm of Acr+-Mes (1.0 ×
10-4 M) in deaerated MeCN solution containing anthracenes.
Mes•+. Such a bimolecular decay obeys second-order kinetics.
•-
The formation of O2 was confirmed by the ESR spectrum
which was measured at 123 K immediately after the photoir-
radiation of an MeCN solution of Acr+-Mes (1.0 × 10-4 M)
at 233 K (g| ) 2.1050 and g ) 2.0032, see Supporting
Information Figure S3).40,41
In the presence of both Me2An and O2, the quantum yields
(ΦR′) of formation of anthracene radical cations were also
determined from the transient absorption and the extinction
coefficients using a comparative method, and the ΦR′ values at
1.0 × 10-3 M anthracenes are also listed in Table 1. The ΦR′
values of formation of anthracene radical cations in the presence
of O2 are larger than the corresponding ΦR values in the absence
of O2. This indicates that electron transfer from the Acr• moiety
to O2 prevents back electron transfer from the Acr• moiety to
anthracene radical cations, resulting in the increase in the ΦR′
values. The absorbance at 660 nm due to Me2An•+ decays
obeying second-order kinetics. The second-order plot in Figure
7 affords the second-order rate constant as 1.7 × 1010 M-1 s-1
which is close to the diffusion-limited value in MeCN. The
quantum yields of the formation of anthracene radical cations
(ΦR′) in the presence of O2 are significantly larger than those
of the epidioxyanthracenes formation (ΦP) (Table 1). This
indicates that the back electron transfer from O2•- to anthracene
radical cations to regenerate the reactant pair is also involved
in the second-order decay of anthracene radical cations in
addition to the radical coupling between anthracene radical
•-
cations and O2 to afford the corresponding epidioxyan-
thracenes.
On the other hand, An-O2 is known to be formed by the
reaction of anthracene with 1O2.26 To evaluate the contribution
of the singlet oxygen pathway, the rate constant of the reaction
of 1O2 with Me2An was determined by emission decay rates of
1O2 (λem ) 1270 nm)42 in the presence of various concentrations
of Me2An as 2.4 × 105 M-1 s-1 (Figure 8a and b). This value
is by far smaller than the second-order decay rate constant of
Me2An•+ (1.7 × 1010 M-1 s-1). It was confirmed that no singlet
Figure 6. (a) Absorbance time profiles at 500 nm due to Acr•-Mes•+ in
the presence of various concentrations of O2 in MeCN containing Acr+-
Mes (1.0 × 10-4 M). (b) Plot of the pseudo-first-order rate constant (kobs
)
for electron transfer from the Acr• moiety of Acr•-Mes•+ to O2 vs [O2].
and the pseudo-first-order rate constant increases linearly with
O2 concentration (Figure 6a and b). The rate constant of electron
transfer from the Acr• moiety to O2 (k′et) was determined from
the slope of Figure 6b as 6.8 × 108 M-1 s-1. The observed
residual absorption is attributed to the Mes•+ moiety of Acr+-
Mes•+, which decays at a prolonged reaction time by back
electron transfer (BET) from O2•- to the Mes•+ moiety of Acr+-
(40) Lind, J.; Shen, X.; Mere´nyi, G.; Jonsson, B. O¨ . J. Am. Chem. Soc. 1989,
111, 7654.
(41) (a) Bagchi, R. N.; Bond, A. M.; Scholz, F.; Sto¨sser, R. J. Am. Chem. Soc.
1989, 111, 8270. (b) Ohkubo, K.; Menon, S. C.; Orita, A.; Otera, J.;
Fukuzumi, S. J. Org. Chem. 2003, 68, 4720.
9
16004 J. AM. CHEM. SOC. VOL. 126, NO. 49, 2004

Photocatalytic Oxygenation of Anthracenes and Olefins
A R T I C L E S
Figure 9. Transient absorption spectra of Acr+-Mes (1.0 × 10-4 M) in
deaerated MeCN at 298 K taken 20 µs after laser excitation at 355 nm in
the presence of (O) An-O2 (1.0 × 10-3 M) and (b) 10-hydroxyanthrone
(3.3 × 10-4 M).
Scheme 1
Figure 8. (a) Decay of emission intensity of singlet oxygen at 1270 nm
generated by the laser irradiation (λ ) 355 nm) of an O2-saturated C6D6
solution of C60 (2.0 × 10-4 M) containing various concentrations of Me2-
An. Inset: Emission spectrum of singlet oxygen. (b) Plot of the pseudo-
first-order decay rate constant for the emission quenching of the singlet
oxygen by Me2An vs [Me2An].
present time scale of the measurements. This is consistent with
the redox potentials of An-O2 determined by the CV and
SHACV measurements (see Supporting Information Figure S4),
oxygen emission was observed during the photocatalytic
oxygenation of Me2An in an O2-saturated CD3CN. Thus, it can
be safely concluded that the An-O2 is formed exclusively by
since electron transfer from An-O2 (E0 vs SCE ) 2.05 V) to
•-
the radical coupling between anthracene radical cation and O2
ox
the Mes•+ moiety (E0red vs SCE ) 1.88 V) is thermodynamically
(kc) rather than the reaction of anthracene and 1O2 as shown in
Scheme 1. With regard to the radical coupling process, the fast
radical coupling process being close to being diffusion-limited
(vide infra) has precluded determining whether it is concerted
or stepwise.
much more favorable than that from the Acr• moiety (E0 vs
ox
SCE ) -0.57 V) to An-O2 (E0 vs SCE ) -0.94 V). The
red
rate of appearance of the absorption band at 650 nm due to
10-hydroxyanthrone obeys pseudo-first-order kinetics, and the
pseudo-first-order rate constant (kobs) increases linearly with
increasing concentration of An-O2 (see Supporting Information
Figure S5). The second-order rate constant (ket) of electron
transfer from An-O2 to the Mes•+ moiety of Acr•-Mes•+ is
determined from the slope of the linear plot of kobs vs
In order to elucidate the photocatalytic conversion of An-O2
to 10-hydroxyanthrone (vide supra), we examined the laser flash
photolysis of a deaerated MeCN solution of Acr+-Mes in the
presence of An-O2. The addition of An-O2 to a deaerated MeCN
solution of Acr+-Mes and laser photoirradiation result in
appearance of a new absorption band at 650 nm together with
an absorption band at 500 nm due to the Acr• moiety as shown
in Figure 9a. Virtually the same absorption band appears at 650
nm when An-O2 is replaced by 10-hydroxyanthrone (Figure 9b).
This indicates that An-O2 radical cation, which is initially
formed by electron transfer from An-O2 to Acr•-Mes•+, is rapidly
converted to 10-hydroxyanthrone radical cation within the
concentration of An-O2 as 1.2 × 108 M-1 s-1
.
The mechanism of the photocatalytic conversion of An-O2
to 10-hydroxyanthrone is shown in Scheme 2. The electron
transfer from An-O2 to the Mes•+ moiety of Acr•-Mes•+,
produced upon photoexcitation of Acr+-Mes, results in the
O-O bond cleavage of An-O2, followed by facile intramolecular
hydrogen transfer to produce 10-hydroxyanthrone radical cation.
This is supported by the DFT calculations using B3LYP/6-31G*
basis set (see Experimental Section), which indicate that the
10-hydroxyanthrone radical cation is 60 kcal mol-1 more stable
than the An-O2 radical cation. The back electron transfer from
(42) (a) Araki, Y.; Dobrowolski, D. C.; Goyne, T. E.; Hanson, D. C.; Jiang, Z.
Q.; Lee, K. J.; Foote, C. S. J. Am. Chem. Soc. 1984, 106, 4570. (b)
Fukuzumi, S.; Fujita, S.; Suenobu, T.; Yamada, H.; Imahori, H.; Araki,
Y.; Ito, O. J. Phys. Chem. A 2002, 106, 1241.
9
J. AM. CHEM. SOC. VOL. 126, NO. 49, 2004 16005

A R T I C L E S
Scheme 2
Kotani et al.
Scheme 3
the Acr• moiety to 10-hydroxyanthrone radical cation affords
10-hydroxyanthrone, accompanied by regeneration of Acr+-
Mes (Scheme 2).
The electron-transfer oxidation of 10-hydroxyanthrone by the
mesitylene radical cation moiety of Acr•-Mes•+ results in the
two-electron oxidation to yield anthraquinone by releasing two
protons, whereas the two-electron reduction of O2 by the
acridinyl radical moiety of Acr•-Mes•+ with two protons yields
H2O2 (Scheme 2).
Formation of Dioxetanes via Radical Coupling. The radical
coupling reaction between the anthracene radical cation and O2
Figure 10. (a) Photoirradiation time profile of photooxygenation of
tetraphenylethylene (1.0 × 10-2 M) in the presence of Acr+-Mes (2.0 ×
10-3 M) in O2-saturated CD3CN; tetraphenylethylene (O), tetraphenyleth-
ylene dioxetane (b) and benzophenone (9). (b) Photoirradiation time profile
of photooxygenation of tetramethylethylene (1.0 × 10-2 M) in the presence
of Acr+-Mes (2.0 × 10-3 M) in O2-saturated CD3CN; tetramethylethylene
(O), tetramethylethylene dioxetane (b) and acetone (9).
•-
to produce An-O2 in Scheme 1 can be expanded to the dioxetane
formation from olefins.43-46 Visible light irradiation (λ > 430
nm) to an O2-saturated MeCN solution of Acr+-Mes (2.0 ×
10-3 M) with tetraphenylethylene or tetramethylethylene (1.0
× 10-2 M) results in formation of the corresponding radical
cation and O2•-, followed by the radical coupling to afford the
dioxetane as shown in Scheme 3. The products were analyzed
In conclusion, the use of Acr+-Mes as an electron-transfer
photocatalyst in the presence of O2 provides a convenient
methodology to produce radical cations of electron donors of
anthracenes and olefins as well as O2•-, which can combine
together to yield the oxygenated products selectively in a
preparative scale.
1
by H NMR (see Experimental Section). The irradiation time
profiles are shown in Figure 10a and b, where tetraphenyl-
ethylene and tetramethylethylene are converted to the corre-
sponding dioxetanes, in which the O-O bond is cleaved at a
prolonged irradiation time to yield benzophenone and acetone,
respectively.47-49
Acknowledgment. This work was partially supported by a
Grant-in-Aid (No. 16205020) from the Ministry of Education,
Culture, Sports, Science and Technology, Japan.
(43) Eriksen, J.; Foote, C. S.; Parker, T. L. J. Am. Chem. Soc. 1977, 99, 6455.
(44) Kabe, Y.; Takata, T.; Ueno, K.; Ando, W. J. Am. Chem. Soc. 1984, 106,
8174.
Supporting Information Available: GC-MS spectra of
anthraquinone (Figure S1), transient spectra of MeAn (Figure
•-
(45) Akaba, R.; Sakuragi, H.; Tokumaru, K. J. Chem. Soc., Perkin Trans. 2
1991, 291.
S2), ESR spectrum of O2 produced in the electron transfer
from Acr•-Mes•+ to O2 (Figure S3), the CV of An-O2 and
Acr+-Mes (Figure S4), and a plot of the pseudo-first-order rate
constant (kobs) of formation of An-O2 radical cation vs concen-
tration of An-O2 (Figure S5). This material is available free of
charge via the Internet at http://pubs.acs.org.
(46) da Hora Mashado, A. E.; de Andrade, M. L.; Severino, D. J. Photochem.
Photobiol., A 1995, 91, 179.
(47) Fox M. A. In Electron Transfer in Chemistry; Balzani, V., Ed.; Wiley-
VCH: Weinheim, 2001; Vol. 1, pp 271-311.
(48) Fox, M. A.; Chen, C.-C. J. Am. Chem. Soc. 1981, 103, 6757.
(49) The photocatalytic O-O bond cleavage of the dioxetane may proceed via
electron transfer from the dioxetane to the Mes•+ moiety of Acr•-Mes•+
as in the case of An-O2 (Scheme 2). However, the detailed mechanism has
yet to be clarified.
JA048353B
9
16006 J. AM. CHEM. SOC. VOL. 126, NO. 49, 2004