Dehydrogenation versus oxygenation in two-electron and four-electron reduction of dioxygen by 9-alky-10-methyl-9,10-dihydroacridines catalyzed by monomeric cobalt porphyrins and cofacial dicobalt porphyrins in the presence of perchloric acid

Article abstract of DOI:10.1021/ja046422g

Dehydrogenation of 10-methyl-9,10-dihydroacridine (AcrH₂) by dioxygen (O₂) proceeds efficiently, accompanied by the two-electron and four-electron reduction of O₂ to produce H₂O ₂ and H₂O,

Full text of DOI:10.1021/ja046422g

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Published on Web 11/20/2004
Dehydrogenation versus Oxygenation in Two-Electron and
Four-Electron Reduction of Dioxygen by
9-Alkyl-10-methyl-9,10-dihydroacridines Catalyzed by
Monomeric Cobalt Porphyrins and Cofacial Dicobalt
Porphyrins in the Presence of Perchloric Acid
Shunichi Fukuzumi,*,† Ken Okamoto,† Yoshihiro Tokuda,† Claude P. Gros,‡ and
Roger Guilard*,‡
Contribution from the Department of Material and Life Science, Graduate School of
Engineering, Osaka UniVersity, CREST, Japan Science and Technology Agency, Suita,
Osaka 565-0871, Japan, and LIMSAG, UMR 5633, Faculte´ des Sciences Gabriel,
UniVersite´ de Bourgogne, 6, bd Gabriel, 21100 Dijon, France
Received June 17, 2004; E-mail: fukuzumi@ap.chem.eng.osaka-u.ac.jp; roger.guilard@u-bourgogne.fr.
Abstract: Dehydrogenation of 10-methyl-9,10-dihydroacridine (AcrH2) by dioxygen (O2) proceeds efficiently,
accompanied by the two-electron and four-electron reduction of O2 to produce H2O2 and H2O, which are
effectively catalyzed by monomeric cobalt porphyrins and cofacial dicobalt porphyrins in the presence of
perchloric acid (HClO4) in acetonitrile (MeCN) and benzonitrile (PhCN), respectively. The cobalt porphyrin
catalyzed two-electron reduction of O2 also occurs efficiently by 9-alkyl-10-methyl-9,10-dihydroacridines
(AcrHR; R ) Me, Et, and CH2COOEt) to yield 9-alkyl-10-methylacridinium ion (AcrR+) and H2O2. In the
case of R ) But and CMe2COOMe, however, the catalytic two-electron and four-electron reduction of O2
by AcrHR results in oxygenation of the alkyl group of AcrHR rather than dehydrogenation to yield 10-
methylacridinium ion (AcrH+) and the oxygenated products of the alkyl groups, i.e., the corresponding
hydroperoxides (ROOH) and the alcohol (ROH), respectively. The catalytic mechanisms of the dehydro-
genation vs the oxygenation of AcrHR in the two-electron and four-electron reduction of O2, catalyzed by
monomeric cobalt porphyrins and cofacial dicobalt porphyrins, respectively, are discussed in relation to
the C(9)-H or C(9)-C bond cleavage of AcrHR radical cations produced in the electron-transfer oxidation
of AcrHR.
undergo the reduction of O2 by NADH.7 In the former case,
activated dioxygen species such as singlet oxygen can oxidize
Introduction
Most organic compounds that have singlet ground states are
unreactive toward dioxygen, which has a triplet ground state,
because the reactions of triplet dioxygen (3O2) with singlet
molecules to produce singlet products are spin-forbidden.1 In
contrast, electron transfer from organic donors to O2 to produce
the radical cations of organic donors and the radical anion of
O2 (O2•-) is spin-allowed.2 In the respiratory chain, reduced
nicotinamide adenine dinucleotide (NADH) acts as the electron
source for the four-electron reduction of O2 to H2O via stepwise
electron transport, coupled to membrane-spanning proton trans-
port for ATP synthesis.3-6 NADH itself is stable against O2,
and thus, either dioxygen or NADH should be activated to
NADH to yield the two-electron oxidized form, i.e., NAD+.8-11
Photoinduced electron transfer from the singlet excited states
of NADH analogues to O2 also leads to the two-electron
reduction of O2.12 In the presence of acids, the thermal electron-
transfer reduction of O2 becomes energetically much more
(6) (a) Tsukihara, T.; Aoyama, H.; Yamashita, E.; Tomizaki, T.; Yamaguchi,
H.; Shinzawa-Itoh, K.; Nakashima, R.; Yaono, R.; Yoshikawa, S. Science
1995, 269, 1069. (b) Tsukihara, T.; Aoyama, H.; Yamashita, E.; Tomizaki,
T.; Yamaguchi, H.; Shinzawa-Itoh, K.; Nakashima, R.; Yaono, R.;
Yoshikawa, S. Science 1996, 272, 1136. (c) Yoshikawa, S.; Shinzawa-
Itoh, K.; Nakashima, R.; Yaono, R.; Yamashita, E.; Inoue, N.; Yao, M.;
Fei, M. J.; Libeu, C. P.; Mizushima, T.; Yamaguchi, H.; Tomizaki, T.;
Tsukihara, T. Science 1998, 280, 1723.
(7) (a) Fukuzumi, S. In Photoinduced Electron Transfer; Fox, M. A., Chanon,
M., Eds.; Elsevier: Amsterdam, 1988; Part C, Chapter 10. (b) Fukuzumi,
S. In AdVances in Electron Transfer Chemistry; Mariano, P. S., Ed.; JAI
press; Greenwich, CT, 1992; pp 67-175.
† Osaka University.
‡ Universite´ de Bourgogne.
(8) (a) Bodaness, R. S.; Chan, P. C. J. Biol. Chem. 1977, 252, 8554. (b) Land,
E. J.; Swallow, A. J. Biochim. Biophys. Acta 1971, 234, 34.
(1) Bonnett, R. Essays Biochem. 1981, 17, 1.
(2) Chanon, M.; Julliard, M.; Santamaria, J.; Chanon, F. New J. Chem. 1992,
16, 171.
(9) Czochralska, B.; Kawczynski, W.; Bartosz, G.; Shugar, D. Biochim.
Biophys. Acta 1984, 801, 403.
(3) (a) Mitchell, P. Science 1979, 206, 1148. (b) Michel, H.; Behr, J.; Harrenga,
A.; Kannt, A. Annu. ReV. Biophys. Biomol. Struct. 1998, 27, 329.
(4) (a) Babcock, G. T.; Wikstro¨m, M. Nature 1992, 356, 301. (b) Babcock, G.
T. Proc. Natl. Acad. Sci. U.S.A. 1999, 96, 12971.
(10) Fukuzumi, S.; Fujita, S.; Suenobu, T.; Imahori, H.; Araki, Y.; Ito, O. J.
Phys. Chem. A 2002, 106, 1465.
(11) For photosensitized one-electron reduction of O2 by NADH, see: (a)
Yamakoshi, Y.; Umezawa, N.; Ryu, A.; Arakane, K.; Miyata, N.; Goda,
Y.; Masumizu, T.; Nagano, T. J. Am. Chem. Soc. 2003, 125, 12803. (b)
Nakanishi, I.; Fukuzumi, S.; Konishi, T.; Ohkubo, K.; Fujitsuka, M.; Ito,
O.; Miyata, N. J. Phys. Chem. B 2002, 106, 2372.
(5) (a) Wikstro¨m, M.; Krab, K.; Saraste M. In Cytochrome Oxidase:
A
Synthesis; Academic Press: London, 1981. (b) Ferguson-Miller, S.;
Babcock, G. T. Chem. ReV. 1996, 96, 2889.
9
10.1021/ja046422g CCC: $27.50 © 2004 American Chemical Society
J. AM. CHEM. SOC. 2004, 126, 17059-17066
17059

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
A R T I C L E S
Fukuzumi et al.
favorable than that in the absence of acids.13 Thus, the thermal
reduction of O2 is made possible by an acid-stable NADH
analogue, i.e., 10-methyl-9,10-dihydroacridine (AcrH2)14-16 in
the presence of perchloric acid (HClO4) in acetonitrile (MeCN)
to yield H2O2 and the corresponding NAD+ analogue, 10-
methylacridinium ion (AcrH+).17 The thermal two-electron
reduction of O2 by AcrH2 has been reported to be catalyzed
Scheme 1
efficiently by metalloporphyrins such as Co(TPP)+ (TPP2-
)
tetraphenylporphyrin dianion) in the presence of HClO4 in
MeCN.18,19 In the respiratory chain, NADH is used as the
electron source in the terminal enzymes of the respiratory chains,
i.e., cytochrome c oxidases (CcO’s), which consist of the
bimetallic Fe/Cu core located in the inner mitochondrial
membrane and catalyze the four-electron reduction of O2 to H2O
by the soluble one-electron carrier, cytochrome c, without
formation of H2O2.3-6 In this context, we have recently reported
four-electron reduction of O2 by one-electron reductants such
as ferrocene derivatives, which is efficiently catalyzed by
cofacial dicobalt porphyrins in the presence of perchloric acid
(HClO4) in benzonitrile (PhCN).20 A number of synthetic models
of CcO’s have so far been synthesized to mimic the coordination
environment of the Fe/Cu core as well as the catalytic function
of the four-electron reduction of O2.21-24 Electrocatalytic four-
electron reduction has so far been studied extensively because
not only it is of great biological interest, but also it is of
technological significance such as in fuel cells.25-28 However,
the catalytic four-electron reduction of O2 by an NADH
analogue without formation of H2O2 has yet to be achieved.
We report herein that the four-electron reduction of O2 by
an acid-stable NADH analogue (AcrH2) occurs efficiently using
cofacial dicobalt porphyrins as effective catalysts in the presence
of HClO4 in benzonitrile (PhCN), as shown in Scheme 1, but
only the two-electron reduction of O2 by AcrH2 takes place using
monomeric cobalt porphyrins under otherwise identical experi-
mental conditions. When AcrH2 is replaced by 9-alkyl-10-
methyl-9,10-dihydroacridine (AcrHR),29,30 the monomeric cobalt
porphyrins catalyze two-electron reduction of O2 by AcrHR in
the presence of HClO4, resulting in oxygenation of the alkyl
group via the C(9)-C bond cleavage of AcrHR to yield AcrH+
and the dioxygenated product, i.e., alkyl hydroperoxide (ROOH),
instead of dehydration of AcrHR via the C(9)-H cleavage to
yield H2O2 depending on the type of R group. Similar selectivity
in the dehydration vs oxygenation of AcrHR by O2 is observed
for the cofacial dicobalt porphyrin catalyzed four-electron
reduction of O2 by AcrHR, in which the dehydration of AcrHR
yields H2O and AcrR+ whereas the oxygenation yields ROH
and AcrH+ (Scheme 1). The selectivities of the C-H vs C-C
bond cleavage as well as the reactivities of AcrHR in the
monomeric and dimeric cobalt porphyrin catalyzed reduction
of O2 are compared to those in the electron-transfer oxidation
of AcrHR with one-electron oxidants.29 Such comparison
provides valuable insight into the catalytic mechanism of the
dehydration vs oxygenation pathways in the monomeric and
dimeric cobalt porphyrin-catalyzed two-electron and four-
electron reductions of O2 by AcrHR.
(12) Fukuzumi, S.; Ishikawa, M.; Tanaka, T. J. Chem. Soc., Perkin Trans. 2
1989, 1037.
(13) (a) Sawyer, D. T.; Valentine, J. S. Acc. Chem. Res. 1981, 14, 393. (b)
Chin, D.-H.; Chiericato, G., Jr.; Nanni, E. J., Jr.; Sawyer, D. T. J. Am.
Chem. Soc. 1982, 104, 1296. (c) Lee-Ruff, E. Chem. Soc. ReV. 1977, 6,
195.
(14) Fukuzumi, S.; Koumitsu, S.; Hironaka, K.; Tanaka, T. J. Am. Chem. Soc.
1987, 109, 305.
(15) (a) Pestovsky, O.; Bakac, A.; Espenson, J. H. Inorg. Chem. 1998, 37, 1616.
(b) Pestovsky, O.; Bakac, A.; Espenson, J. H. J. Am. Chem. Soc. 1998,
120, 13422.
(16) NADH and the ordinary model compounds decompose in the presence of
acids. (a) Johnston, C. C.; Gardner, J. L.; Suelter, C. H.; Metzler, D. E.
Biochemistry 1963, 2, 689. (b) Kim C. S. Y.; Chaykin, S. Biochemistry
1968, 7, 2339. (c) van Eikeren, P.; Grier, D. L.; Eliason, J. J. Am. Chem.
Soc. 1979, 101, 7406.
(17) Fukuzumi, S.; Chiba, M.; Ishikawa, M.; Ishikawa, K.; Tanaka, T. J. Chem.
Soc., Perkin Trans. 2 1989, 1417.
(18) (a) Fukuzumi, S.; Mochizuki, S.; Tanaka, T. J. Chem. Soc., Chem. Commun.
1989, 391. (b) Fukuzumi, S.; Mochizuki, S.; Tanaka, T. Inorg. Chem. 1990,
29, 653.
(19) For the catalytic two-electron reduction of other NADH analogues by O2,
see: (a) Vol’pin, M. E.; Novodarova, G. N.; Kolosova, E. M.; Guzhova,
N. V.; Kononenko, A. A.; Lejkin, Y. N. Inorg. Chim. Acta 1981, 50, 21.
(b) Tabushi, I.; Kodera, M. J. Am. Chem. Soc. 1986, 108, 1101.
(20) Fukuzumi, S.; Okamoto, K.; Gros, C. P.; Guilard, R. J. Am. Chem. Soc.
2004, 126, 10441.
(21) Collman, J. P.; Boulatov, R.; Sunderland, C. J. In The Porphyrin Handbook;
Kadish, K. M., Smith, K. M., Guilard, R., Eds.; Elsevier Science: New
York, 2003; Vol. 11, pp 1-49.
(22) (a) Collman, J. P.; Fu, L.; Herrmann, P. C.; Zhang, X. M. Science 1997,
275, 949. (b) Collman, J. P. Inorg. Chem. 1997, 36, 5145. (c) Collman, J.
P.; Fu, L.; Herrmann, P. C.; Wang, Z.; Rapta, M.; Bro¨ring, M.; Schwen-
ninger, R.; Boitrel, B. Angew. Chem., Int. Ed. 1998, 37, 3397. (d) Boulatov,
R.; Collman, J. P.; Shiryaeva, I. M.; Sunderland, C. J. J. Am. Chem. Soc.
2002, 124, 11923.
(23) (a) Liang, H. C.; Dahan, M.; Karlin, K. D. Curr. Opin. Chem. Biol. 1999,
3, 168. (b) Ghiladi, R. A.; Ju, T. D.; Lee, D.-H.; Moe¨nne-Loccoz, P.;
Kaderli, S.; Neuhold, Y.-M.; Zuberbu¨hler, A. D.; Woods, A. S.; Cotter, R.
J.; Karlin, K. D. J. Am. Chem. Soc. 1999, 121, 9885. (c) Ghiladi, R. A.;
Hatwell, K. R.; Karlin, K. D.; Huang, H.-w.; Moe¨nne-Loccoz, P.; Krebs,
C.; Huynh, B. H.; Marzilli, L. A.; Cotter, R. J.; Kaderli, S.; Zuberbu¨hler,
A. D. J. Am. Chem. Soc. 2001, 123, 6183.
(24) (a) Sasaki, T.; Naruta, Y. Chem. Lett. 1995, 24, 663. (b) Sasaki, T.;
Nakamura, N.; Naruta, Y. Chem. Lett. 1998, 27, 351. (c) Chishiro, T.;
Shimazaki, Y.; Tani, F.; Tachi, Y.; Naruta, Y.; Karasawa, S.; Hayami, S.;
Maeda, Y. Angew. Chem., Int. Ed. 2003, 42, 2788.
Experimental Section
Materials. Cobalt(II) tetraphenylporphyrin [Co(TPP)] was prepared
according to the literature.31 Co(TPP) was oxidized by O2 in the
presence of HCl in methanol to obtain Co(TPP)Cl,32 which was purified
by recrystallization from methanol. Co(TPP)ClO4 was obtained by the
(26) (a) Anson, F. C.; Shi, C.; Steiger, B. Acc. Chem. Res. 1997, 30, 437. (b)
Liu, Z.; Anson, F. C. Inorg. Chem. 2001, 40, 1329. (c) Liu, Z.; Anson, F.
C. Inorg. Chem. 2000, 39, 274. (d) Chang, C. J.; Loh, Z.-H.; Shi, C.; Anson,
F. C.; Nocera, D. G. J. Am. Chem. Soc. 2004, 126, 10013.
(27) (a) Kingsborough, R. P.; Swager, T. M. Chem. Mater. 2000, 12, 872. (b)
Kingsborough, R. P.; Swager, T. M. AdV. Mater. 1998, 10, 1100.
(28) Vijayalatha, S.; Gomathi, H.; Prabhakara, R. Bull. Electrochem. 1992, 8,
222.
(29) Fukuzumi, S.; Tokuda, Y.; Kitano, T.; Okamoto, T.; Otera, J. J. Am. Chem.
Soc. 1993, 115, 8960.
(30) Fukuzumi, S.; Ohkubo, K.; Tokuda, Y.; Suenobu, T. J. Am. Chem. Soc.
2000, 122, 4286.
(25) (a) Collman, J. P.; Rapta, M.; Bro¨ring, M.; Raptova, L.; Schwenninger,
R.; Boitrel, B.; Fu, L.; L’Her, M. J. Am. Chem. Soc. 1999, 121, 1387. (b)
Collman, J. P.; Boulatov, R. Angew. Chem., Int. Ed. 2002, 41, 3487.
9
17060 J. AM. CHEM. SOC. VOL. 126, NO. 51, 2004

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Two- and Four-Electron Reduction of O2 by AcrHR
A R T I C L E S
metathesis of the corresponding chloride salt with AgClO4 and
recrystallized from toluene.33 Cobalt(II) octaethylporphyrin [Co(OEP)]
was purchased by Aldrich Co., USA. Details of the synthesis and
characterization of each cofacial dicobalt porphyrin [Co2(DPB), Co2-
(DPA), Co2(DPX), and Co2(DPD)] have been reported elsewhere.34-37
Acetonitrile (MeCN) and benzonitrile (PhCN) were purchased from
Tokyo Kasei Organic Chemicals, Japan, and distilled over P2O5 prior
to use.38 Perchloric acid (70%) and hydrogen peroxide were obtained
from Wako Pure Chemicals. 10-Methyl-9,10-dihydroacridine (AcrH2)
was prepared from 10-methylacridinium iodide (AcrH+I-) by reduction
with NaBH4 in methanol, and purified by recrystallization from
ethanol.39 10-Methylacridinium iodide was prepared by the reaction of
acridine with methyl iodide in acetone, and it was converted to the
perchlorate salt (AcrH+ClO4-) by the addition of magnesium perchlorate
to the iodide salt and purified by recrystallization from methanol.14
9-Alkyl-10-methyl-9,10-dihydroacridines (AcrHR; R ) Me, Et, CH2-
Ph) were prepared by the reduction of AcrH+I- with the corresponding
Grignard reagents (RMgX).29 AcrHR (R ) But) was prepared by the
photoreduction of AcrH+ClO4- with RCOOH in the presence of NaOH
in H2O-MeCN.40 AcrHR’s (R ) CH2COOEt and CMe2COOMe) were
prepared by the reduction of AcrH+ClO4- with the corresponding ketene
Figure 1. Spectral change observed in the oxidation of AcrH2 (1.2 × 10-4
M) with O2 (8.5 × 10-3 M), catalyzed by Co(OEP) (2.0 × 10-5 M) in the
presence of HClO4 (3.0 × 10-2 M) in PhCN.
silyl acetals (CH2dC(OEt)OSiEt3 and Me2CdC(OMe)OSiMe3, respec-
placed in a thermostated compartment at 298 K. An air-saturated PhCN
solution was used for the catalytic reduction of O2 by AcrHR. The O2
concentrations in an air-saturated PhCN solution (1.7 × 10-3 M) and
an air-saturated MeCN solution (2.6 × 10-3 M) were determined by
spectroscopic titration for the photooxidation of AcrH2 by O2 as reported
previously.12,20 Larger concentrations of AcrHR than those of O2 were
used for the catalytic reduction of O2 by AcrHR, when dioxygen was
the limiting reagent in the reaction cell which was filled with the reactant
solution.
tively).41 9-Substituted 10-methylacridinium perchlorate (AcrR+ClO4
;
-
R ) Me, Et, But) was prepared by the reaction of 10-methylacridone
in dichloromethane with RMgX and purified by recrystallization from
ethanol-diethyl ether.29
Reaction Procedure. Typically, an O2-saturated acetonitrile or
chloroform (CD3CN or CDCl3, 0.7 mL) solution containing HClO4 (5.0
× 10-2 M) was added to an NMR tube which contained AcrHR (5.6
× 10-3 mmol) and a catalyst (7.0 × 10-5 mmol). The oxidized products
were identified by comparing the 1H NMR spectra of the resulting
solution with those of the authentic samples, which were obtained
independently. 1H NMR (CD3CN): AcrH+ClO4- δ 4.76 (s, 3H), 7.9-
Kinetic Measurements. All kinetic measurements were performed
on a Shimadzu UV-2200 or UV-3100PC spectrophotometer at 298 K.
Rates of the oxidation of AcrHR were monitored by the rise of the
-
8.8 (m, 8H); AcrMe+ClO4 δ 3.48 (s, 3H), 4.74 (s, 3H), 7.9-8.9 (m,
absorption band due to AcrH+ and AcrR+ (λmax ) 358 nm, ꢀmax ) 1.8
-
8H); AcrEt+ClO4 δ 1.52 (t, 3H), 3.95 (q, 2H), 4.71 (s, 3H), 7.9-8.9
18,29
× 104 M-1 cm-1
)
in MeCN or (λmax ) 361 nm, ꢀmax ) 1.7 × 104
(m, 8H); AcrCH2Ph+ClO4- δ [4.79 (s, 3H), 5.35 (s, 2H), 7.5-8.6 (m,
M-1 cm-1; λmax ) 460 nm, ꢀmax ) 650 M-1 cm-1) in PhCN at 298 K.
The kinetic measurements were carried out under pseudo-first-order
conditions, where dioxygen concentrations were maintained at more
than 10 times excess the concentrations of AcrHR.
13H)]; AcrCH2COOEt+ClO4 δ 1.09 (t, 3H), 2.41 (q, 2H), 4.76 (s,
-
3H), 5.02 (s, 2H), 7.7-8.7 (m, 8H); ButOOH δ 1.18 (s, 9H); ButOH δ
1.16 (s, 9H); HOOCMe2COOMe δ 1.37 (s, 6H), 3.70 (s, 3H). The 1H
NMR measurements were performed using Japan Electron Optics JEOL
JNM-AL300 (300 MHz) and JNM-GSX-400 (400 MHz) NMR
spectrometers. The amount of hydrogen peroxide (H2O2) was deter-
mined by titration by iodide ion.42 The aliquots of the product mixture
in MeCN or PhCN were treated with excess NaI, and the amount of
Cyclic Voltammetry. Cyclic voltammetric measurements were
performed at 298 K on a BAS 100 W electrochemical analyzer in
deaerated PhCN containing 0.1 M tetra-n-butylammonium phosphate
(TBAPF6) as supporting electrolyte. 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 a 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.
All potentials (vs Ag/Ag+) were converted to values vs SCE by adding
0.29 V.43
-
I3 formed was determined by the UV-visible spectrum (λmax ) 365
42
nm, ꢀmax ) 28 000 M-1 cm-1
)
using a Hewlett-Packard 8453 diode
array spectrophotometer with a quartz cuvette (path length ) 10 mm)
at 298 K. Electronic absorption spectra during the cobalt porphyrin-
catalyzed oxidation of AcrHR by O2 in the presence of HClO4 in MeCN
or PhCN were recorded on a Shimadzu UV-2200 or UV-3100PC
spectrophotometer with a quartz cell (1 mm or 1 cm i.d.), which was
Results and Discussion
(31) Aldler, A. D.; Longo, F. R.; Varadi, V. Inorg. Synth. 1976, 16, 213.
(32) Sakurai, T.; Yamamoto, K.; Naito, H.; Nakamoto, N. Bull. Chem. Soc.
Jpn. 1976, 49, 3042.
Catalytic Two-Electron vs Four-Electron Reduction of O2
by AcrH2. No reduction of O2 by AcrH2 occurs in PhCN at
298 K. In the absence of HClO4, no catalytic oxidation of AcrH2
by O2 in the presence of Co(TPP)+ in MeCN is observed.18a In
the presence of a catalytic amount of Co(OEP) and more than
stoichiometric amount of HClO4, however, AcrH2 is readily
oxidized by O2 to yield AcrH+ (λmax ) 361 nm) as shown in
Figure 1, where Co(OEP) is oxidized to Co(OEP)+ (λmax ) 420
nm), the concentration of which remains the same during the
reaction. To determine the stoichiometry of the reaction, the
O2 concentration is fixed at 1.7 × 10-3 M and the catalytic
(33) Reed, C. A.; Mashiko, T.; Bentley, S. P.; Kastner, M. E.; Scheidt, W. R.;
Spartalian, K.; Lang, G. J. Am. Chem. Soc. 1979, 101, 2948.
(34) Collman, J. P.; Hutchison, J. E.; Lopez, M. A.; Tabard, A.; Guilard, R.;
Seok, W. K.; Ibers, J. A.; L’Her, M. J. Am. Chem. Soc. 1992, 114, 9869.
(35) Deng, Y.; Chang, C. J.; Nocera, D. G. J. Am. Chem. Soc. 2000, 122, 410.
(36) Guilard, R.; Lopez, M. A.; Tabard, A.; Richard, P.; Lecomte, C.; Brande`s,
S.; Hutchison, J. E.; Collman, J. P. J. Am. Chem. Soc. 1992, 114, 9877.
(37) Chang, C. J.; Deng, Y.; Heyduk, A. F.; Chang, C. K.; Nocera, D. G. Inorg.
Chem. 2000, 39, 959.
(38) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of Laboratory
Chemicals, 4th ed.; Pergamon Press: Elmsford, NY, 1996.
(39) Roberts, R. M. G.; Ostovic, D.; Kreevoy, M. M. Faraday Discuss. Chem.
Soc. 1982, 74, 257.
(40) Fukuzumi, S.; Kitano, T.; Tanaka, T. Chem. Lett. 1989, 18, 1231.
(41) Otera, J.; Wakahara, Y.; Kamei, H.; Sato, T.; Nozaki, H.; Fukuzumi, S.
Tetrahedron Lett. 1991, 32, 2405.
(42) Fukuzumi, S.; Kuroda, S.; Tanaka, T. J. Am. Chem. Soc. 1985, 107, 3020.
(43) DeSimone, R. E.; Drago, R. S. J. Am. Chem. Soc. 1970, 92, 2343.
9
J. AM. CHEM. SOC. VOL. 126, NO. 51, 2004 17061

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
A R T I C L E S
Fukuzumi et al.
O2 is H2O2 (Table 1). The smaller H2O2 yields than AcrR+
yields shown in Table 1 suggest that H2O2 decomposes partially
during the Co(TPP)+-catalyzed reactions. The Co(OEP)-
catalyzed reduction of O2 by AcrHR affords virtually the same
products (Table 1). This indicates that the dehydration of AcrHR
(R ) H, Me, Et, and CH2COOEt) occurs exclusively via the
C(9)-H bond cleavage (Scheme 2a). In contrast, the oxygen-
ation of R occurs selectively in the case of R ) But and CMe2-
COOMe to yield AcrH+ and ROOH via the C(9)-C bond
cleavage (Table 1). Thus, the dehydration pathway via the
C(9)-H bond cleavage of AcrHR (R ) H, Me, Et, and CH2-
COOEt) in Scheme 2a is changed to the oxygenation pathway
via the C(9)-C bond cleavage of AcrHR (R ) But and CMe2-
COOMe) in Scheme 2b. In the case of R ) CH2Ph, both the
dehydration and the oxygenation pathway occur to yield
AcrCH2Ph+ and AcrH+ together with the oxygenated product,
PhCHO, which may be formed via the decomposition of Ph2-
CHOOH.
Figure 2. Plots of the concentration of AcrH+ formed in the oxidation of
AcrH2 (3.0 × 10-3 M) by O2 (1.7 × 10-3 M), catalyzed by Co2(DPA),
Co2(DPX), Co2(DPB), Co2(DPD) (1.0 × 10-5 M), and Co(OEP) (2.0 ×
10-5 M) in PhCN, vs the ration of the concentration of AcrH2 to the initial
concentration of O2 in the presence of HClO4 (3.0 × 10-2 M).
The observed selectivities for the C(9)-H vs C(9)-C bond
cleavage in Table 1 agree with those reported for the C(9)-H
vs C(9)-C bond cleavage of radical cations of AcrHR (AcrHR•+)
produced in the electron-transfer oxidation of AcrHR with Fe-
(phen)33+ (phen ) 1,10-phenanthroline) depending on the type
of R substituent (Scheme 3).29 In the case of R ) Me, Et, and
CH2COOEt, the C(9)-H bond of AcrHR•+ is heterolytically
reduction of O2 is examined by changing the concentration of
AcrH2. The results of such spectral titration are shown in Figure
2 (O), which indicates that AcrH2 reacts with 1 equiv of O2 to
produce AcrH+ and H2O2 (eq 1). The stoichiometric formation
cleaved to produce AcrR• and H+ exclusively.29,44 AcrR• is
further oxidized by Fe(phen)3
to yield AcrR+. Such a
3+
deprotonation pathway is disfavored in the case of R ) But
and CMe2COOMe, when the C(9)-C bond of AcrHR•+ is
homolytically cleaved to produce AcrH+ and R• exclu-
sively.29,45,46 In the case of CH2Ph, both the C(9)-H and
C(9)-C bonds are cleaved to yield AcrCH2Ph+ and AcrH+.29
Such agreement in the competition of C(9)-H vs C(9)-C bond
cleavage indicates that the dehydrogenation vs oxygenation of
AcrHR depending on R in the cobalt porphyrin-catalyzed
reduction of O2 by AcrHR (Scheme 2) is determined by the
selectivities for C-H and C-C bond cleavages in the radical
cation (AcrHR•+), which may be produced by electron transfer
from AcrHR to cobalt(III) porphyrins as discussed in more detail
later.
of H2O2 (1.6 × 10-3 M) was confirmed by the iodometric
titration (see Experimental Section). Such catalytic two-electron
reduction of O2 by AcrH2 has previously been reported for the
Co(TPP)+-catalyzed reduction of O2 by AcrH2 in the presence
of HClO4 in MeCN.18
When Co(TPP)+ is replaced by a cofacial dicobalt porphyrin
[Co2(DPA)], the concentration of AcrH+ formed in the Co2-
(DPA)-catalyzed reduction of O2 by AcrH2 becomes 2 times
the O2 concentration (1.7 × 10-3 M), as shown in Figure 2
(b). Thus, the four-electron reduction of O2 by AcrH2 occurs
efficiently in the presence of a catalytic amount of Co2(DPA)
and HClO4 (2.0 × 10-2 M) in PhCN (eq 2). In this case, it was
When the monomeric cobalt porphyrin is replaced by a
cofacial dicobalt porphyrin in the reduction of O2 by AcrHBut,
the yield of the two-electron-reduced product of O2, i.e., But-
OOH, decreases in the order Co2(DPB)2, Co2(DPX), and Co2-
(DPA), accompanied by the formation of the four-electron-
reduced product of O2, ButOH, as shown in Table 1.47 In the
case of Co2(DPA), a significant amount of acetone is formed
with methanol. Such a change in the stoichiometry from the
confirmed that no H2O2 was formed by iodometric titration in
the catalytic reduction of O2 by AcrH2.
The other cofacial dicobalt porphyrins also catalyze the four-
electron reduction of O2 by AcrH2. However, the concentration
of AcrH+ formed in the catalytic reduction of O2 by AcrH2 in
Figure 2 decreases following the sequence Co2(DPX), Co2-
(DPB), and Co2(DPD), indicating that the contribution of the
two-electron-reduction pathway of O2 increases in this order.
Catalytic Dehydration vs Oxygenation of AcrHR by O2.
The catalytic two-electron reduction of O2 by 9-alkyl-10-methyl-
9,10-dihydroacridines (AcrHR) also proceeds efficiently using
Co(TPP)+ or Co(OEP) as a catalyst. The oxidized products of
AcrHR were examined by 1H NMR. The results are summarized
in Table 1. In the case of R ) H, Me, Et, and CH2COOEt, the
oxidized product in the Co(TPP)+-catalyzed reduction of AcrHR
by O2 in CD3CN is solely AcrR+ and the reduced product of
(44) Hapiot, P.; Moiroux, J.; Save´ant, J.-M. J. Am. Chem. Soc. 1990, 112, 1337.
(45) (a) Anne, A.; Fraoua, S.; Moiroux, J.; Save´ant, J.-M. J. Am. Chem. Soc.
1996, 118, 3938. (b) Anne, A.; Fraoua, S.; Moiroux, J.; Save´ant, J.-M. J.
Phys. Org. Chem. 1998, 11, 774.
(46) For C-C bond cleavage of radical cations of other NADH analogues, see:
(a) Anne, A.; Moiroux, J.; Save´ant, J.-M. J. Am. Chem. Soc. 1993, 115,
10224. (b) Takada, N.; Itoh, S.; Fukuzumi, S. Chem. Lett. 1996, 25, 1103.
(c) Fukuzumi, S.; Suenobu, T.; Patz, M.; Hirasaka, T.; Itoh, S.; Fujitsuka,
M.; Ito, O. J. Am. Chem. Soc. 1998, 120, 8060.
(47) In the presence of 1.0 × 10-4 M Co(OEP) as well as in the absence of
Co(OEP) or Co2(DPA), no decomposition of ButOOH (5 × 10-3 M) was
observed in the presence of 5.0 × 10-2 M HClO4 in air-saturated CDCl3
in 1.5 h. In the presence of 1.0 × 10-4 M Co2(DPA), only 9% ButOH was
formed by the catalytic decomposition of ButOOH (5 × 10-3 M) in the
presence of 5.0 × 10-2 M HClO4 in air-saturated CDCl3 in 1.5 h. Thus,
the catalytic decomposition pathway of ButOOH is negligible in the results
of Table 1.
9
17062 J. AM. CHEM. SOC. VOL. 126, NO. 51, 2004