Visible-light-induced oxygenation of benzene by the triplet excited state of 2,3-dichloro-5,6-dicyano-p-benzoquinone

Article abstract of DOI:10.1021/ja402303k

Photocatalytic oxygenation of benzene to phenol occurs under visible-light irradiation of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) in an oxygen-saturated acetonitrile solution of benzene and tert-butyl nitrite. The photocatalytic reaction is initiated by photoinduced electron transfer from benzene to the triplet excited state of DDQ.

Full text of DOI:10.1021/ja402303k

Supporting Information
Visible Light Induced Oxygenation of Benzene by the Triplet
Excited State of 2,3-Dichloro-5,6-dicyano-p-benzoquinone
Kei Ohkubo, Atsushi Fujimoto, and Shunichi Fukuzumi*
Department of Material and Life Science, Graduate School of
Engineering, Osaka University, ALCA, Japan Science and Technology
Agency (JST), Suita, Osaka 565-0871, Japan
Department of Bioinspired Science, Ewha Womans University, Seoul
120-750, Korea
E-mail: fukuzumi@chem.eng.osaka-u.ac.jp
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(a)
(b)
1.0
0.5
0
0
500
1000
Time, s
1500
Figure S1. (a) UV-vis spectral change of DDQH2 (0.10 mM) upon addition of TBN
(1.5 mM) in O2-saturated MeCN at 298 K. (b) Time profiles at 350 nm (red) and 400
nm (blue).
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(a)
100
80
60
40
20
0
OH
1
2
3
Time, min
4
5
(b)
100
80
60
40
20
0
16OH
18OH
90
92
94
96
98
100
m / z
Figure S2. (a) GC-MS chart of reaction mixture after photoirradiation and (b) GC-MS
spectra of phenol produced by photooxygenation of benzene with DDQ in nitrogen
saturated MeCN at 298K: [benzene] = 10 mM; [DDQ] = 5.0 mM; [H2O] = 1.0 M
16
18
[(blue) H2 O; (b) H2 O (98%, red)].
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3
2
1
0
10
5
0
0.1
0.2
[PhOH], mM
0
0
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4
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Time, µs
Figure S3. Decay time profiles of 3DDQ* in the presence of various concentrations of
phenol (0.50, 1.0 and 1.5 mM) after nanosecond laser excitation of an MeCN solution
of DDQ (1.2 mM) with phenol. Inset: Plot of kobs vs [PhOH].
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3
Figure S4. Decay time profiles of DDQ* (λ = 630 nm) in the presence of various
concentrations of phenol (red; 0.13 M, orange; 0.25, green; 0.50 and blue; 1.0 M) after
femtosecond laser excitation of an MeCN solution of DDQ (5.0 mM) with phenol.
Inset: Plot of kobs vs [PhOH].
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(a)
(b)
(c)
100
80
60
40
20
0
F
F
OH
F
OH
OH
2
3
Time, min
4
100
80
60
40
20
0
Cl
Cl
Cl
OH
OH
2
3
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5
Time, min
100
80
60
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20
0
Br
Br
Br
OH
OH
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3
4
Time, min
5
6
Figure S5. GC charts of reaction mixture obtained by photooxygenation of (a) fluoro-
(b) chloro- (c) bromobenzene with DDQ in nitrogen saturated MeCN at 298K after
photoirradiation.
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Experimental Section
Materials. Chemicals were purchased from commercial source and used without
purification, unless otherwise noted. 2,3-Dichloro-5,6-dicyano-p-benzoquinone (DDQ)
was obtained commercially and purified by recrystallization from hot
dichloromethane.S1 Potassium ferrioxalate used as an actinometer was prepared
according to the literature and purified by recrystallization from hot water.S2
Acetonitrile was of spectral grade, obtained commercially and used without further
purification. Deuterated [2H3] acetonitrile (CD3CN) was obtained from Euri SO-TOP,
CEA, France, and used as received.
Reaction Procedure. The stoichiometric photoreaction carried out by the following
procedure. A CD3CN solution (0.60 cm3) containing DDQ (40 mM) and D2O (0.5 M) in
an NMR tube sealed with a rubber septum was deaerated by bubbling with nitrogen
through a stainless steel needle for 5 min. In the case of photocatalytic reaction, the
DDQ solution (3.0 mM) with tert-butyl nitrite (TBN, 1.5 mM) and D2O (0.5 M) in an
NMR tube with rubber septum was saturated with oxygen by bubbling oxygen through
a stainless steel needle for 5 min. After the bubbling, benzene (1.80 µmol; 30 mM) or
halogenated benzene (1.80 µmol; 30 mM) was added to the solution. The solution was
then irradiated with a 500 W xenon lamp (Ushio Optical Module X SX-UID
500XAMQ) through color glass filter transmitting λ > 390 nm at room temperature.
After photoirradiation, the corresponding oxygenated product was identified and
quantified by comparison of the 1H NMR spectra with that of an authentic sample. The
1H NMR measurements were performed on a Japan Electron Optics JMN-AL300 (300
MHz) NMR spectrometer.
Quantum Yield Determinations. A standard actinometer (potassium ferrioxalate)
was used for the quantum yield determination of the DDQ photosensitized oxygenation
of benzene with water. A square quartz cuvette (10 mm i.d.) that contained an MeCN
solution (3.0 cm3) of DDQ (2.0 mM) and benzene or halogenated benzene (50 mM) was
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irradiated with monochromatized light of λ = 420 nm from a Shimadzu RF-5300PC
fluorescence spectrophotometer. Under the conditions of actinometry experiments,
DDQ absorbed essentially 75% incident light of λ = 420 nm (Abs420 = 0.70). The light
intensity of monochromatized light of λ = 420 nm was determined as 2.5 × 10–8
einstein s–1. The photochemical reaction was monitored using a Shimadzu GC-17A gas
chromatograph and Shimadzu MS-QP5000 mass spectrometer. The quantum yields
were determined from increase of phenol derivatives.
Phosphorescence Measurements. Phosphorescence of DDQ (0.75 mM) in
deaerated 2-methyltetrahydrofuran glass in a quartz tube (3 mm in diameter) was
measured at 77 K using a HORIBA Fluoromax-4 florescence spectrophotometer by
excitation at 400 nm.
Laser Flash Photolysis. The measurements of nanosecond transient absorption
spectra in the photochemical reactions of DDQ with benzene and H2O in MeCN were
performed according to the following procedures. Typically, a nitrogen saturated MeCN
solution containing benzene (1.0 × 10–2 – 1.0 M) and DDQ (1.2 mM) was excited by a
Nd:YAG laser (Continuum, SLII-10, 4-6 ns fwhm) at λ = 430 nm with the power of 10
mJ/pulse. Photoinduced events were estimated by use of a continuous Xe 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 for fresh solutions in each laser excitation. All experiments were
performed at 298 K.
Femtosecond transient absorption spectroscopy experiments were conducted using
an ultrafast source: Integra-C (Quantronix Corp.), an optical parametric amplifier:
TOPAS (Light Conversion Ltd.) and a commercially available optical detection system:
Helios provided by Ultrafast Systems LLC. The source for the pump and probe pulses
were derived from the fundamental output of Integra-C (λ = 786 nm, 2 mJ/pulse and
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fwhm = 130 fs) at a repetition rate of 1 kHz. 75% of the fundamental output of the laser
was introduced into a second harmonic generation (SHG) unit: Apollo (Ultrafast
Systems) for excitation light generation at λ = 393 nm, while the rest of the output was
used for white light generation. The laser pulse was focused on a sapphire plate of 3 mm
thickness and then white light continuum covering the visible region from λ = 410 nm
to 800 nm was generated via self-phase modulation. A variable neutral density filter, an
optical aperture, and a pair of polarizer were inserted in the path in order to generate
stable white light continuum. Prior to generating the probe continuum, the laser pulse
was fed to a delay line that provides an experimental time window of 3.2 ns with a
maximum step resolution of 7 fs. In our experiments, a wavelength at λ = 393 nm of
SHG output was irradiated at the sample cell with a spot size of 1 mm diameter where it
was merged with the white probe pulse in a close angle (< 10°). The probe beam after
passing through the 2 mm sample cell was focused on a fiber optic cable that was
connected to a CMOS spectrograph for recording the time-resolved spectra (λ = 410 -
800 nm). Typically, 1500 excitation pulses were averaged for 3 seconds to obtain the
transient spectrum at a set delay time. Kinetic traces at appropriate wavelengths were
assembled from the time-resolved spectral data. All measurements were conducted at
room temperature, 295 K.
Theoretical Calculations. Density functional theory (DFT) calculations were
performed with Gaussian09 (Revision C.02, Gaussian, Inc.).S3 The calculations were
performed on a 32-processor QuantumCubeTM at the B3LYP/6-31+G(d,p) level of
theory. Graphical outputs of the computational results were generated with the
GaussView software program (ver. 3.09) developed by Semichem, Inc.
References for SI
(S1)
Armarego, W. L. F.; Chai, C. L. L. In Purification of Laboratory Chemicals,
5th ed.; Butterworth-Heinemann: Oxford, 2003.
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(S2)
(S3)
(a) Hatchard, C. G.; Parker, C. A. Proc. R. Soc. London, Ser. A 1956, 235, 518.
(b) Calvert, J. G.; Pitts, J. N. Photochemistry; Wiley: New York, 1966; p 783.
Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.;
Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.;
Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino,
J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.;
Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.;
Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.;
Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.;
Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J.
B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.;
Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R.
L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg,
J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.;
Cioslowski, J.; Fox, D. J. Gaussian 09, revision A.02; Gaussian, Inc.:
Wallingford, CT, 2009.
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