Photocatalytic function of the B12 complex with the cyclometalated iridium(III) complex as a photosensitizer under visible light irradiation

Article abstract of DOI:10.1039/c7dt03742b

A visible light induced three-component catalytic system with the cobalamin derivative (B₁₂) as a catalyst, the cyclometalated iridium(iii) complex (Irdfppy, Irppy, Irpbt and [Ir{dF(CF₃)ppy}₂(dtbpy)]PF₆) as a photosensitizer and triethanolamine as an electron source under N₂ was developed. This catalytic system showed a much higher catalytic efficiency than the previous catalytic system using [Ru(ii)(bpy)₃]Cl₂ as the photosensitizer for the dechlorination reaction of 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT). Noteworthy is the fact that the remarkable high turnover number (over ten thousand) based on B₁₂, which ranks at the top among the reported studies, was obtained when Irdfppy was used as a photosensitizer. This photocatalytic system was also successfully applied to the B₁₂ enzyme-mimic reaction, i.e., the 1,2-migration of the phenyl group of 2-bromomethyl-2-phenylmalonate. The plausible reaction mechanism was proposed, which involved two quenching pathways, an oxidative quenching pathway and a reductive quenching pathway, to be responsible for the initial electron transfer of the excited-state photosensitizers during the DDT dechlorination reaction. Transient photoluminescence experiments revealed that the oxidative quenching of the photosensitizer dominated over the reductive quenching pathway.

Full text of DOI:10.1039/c7dt03742b

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DOI: 10.1039/C7DT03742B
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ARTICLE
Photocatalytic Function of B12 Complex with Cyclometalated
Iridium(III) Complex as Photosensitizer under Visible Light
Irradiation
†
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
b
b
b
a
DOI: 10.1039/x0xx00000x
Hui Tian, Hisashi Shimakoshi,* Sinheui Kim, Gyurim Park, Youngmin You* and Yoshio Hisaeda*
www.rsc.org/
A visible light induced threeꢀcomponent catalytic system with the cobalamin derivative (B12) as a catalyst, the
cyclometalated iridium(III) complex (Irdfppy, Irppy, Irpbt and [Ir{dF(CF )ppy} (dtbpy)]PF as a photosensitizer and
triethanolamine as an electron source under N was developed. This catalytic system showed a much higher catalytic
efficiency than the previous catalytic system using [Ru(bpy) ]Cl as the photosensitizer for the dechlorination reaction of
,1ꢀbis(4ꢀchlorophenyl)ꢀ2,2,2ꢀtrichloroethane (DDT). Noteworthy is the fact that the remarkable high turnover number
over ten thousand) based on B12, which ranks at the top among the reported studies, was obtained when Irdfppy was used as
3
2
6
2
3
2
1
(
a photosensitizer. This photocatalytic system was also successfully applied to the B12 enzymeꢀmimic reaction, i.e., the 1,2ꢀ
migration of the phenyl group of 2ꢀbromomethylꢀ2ꢀphenylmalonate. The plausible reaction mechanism was proposed,
which involved two quenching pathways, an oxidative quenching pathway and a reductive quenching pathway, to be
responsible for the initial electron transfer of the excitedꢀstate photosensitizers during the DDT dechlorination reaction.
Transient photoluminescence experiments revealed that oxidative quenching of the photosensitizer dominated over the
reductive quenching pathway.
reported smart dechlorination systems of 1,1ꢀbis(4ꢀ
chlorophenyl)ꢀ2,2,2ꢀtrichloroethane (DDT) catalyzed by the B12
Introduction
3 2
complex in the presence of a photosensitizer ([Ru(II)(bpy) ]Cl )
The cobalamin derivative (B12) has emerged in a variety of
enzymes, such as methylmalonl CoA mutase, methionine
synthase, ribonucleotide reductase, epoxyqueosine reductase
6
or its derivatives under visible light irradiation. In this system,
the supernucleophlic Co(I) species was generated from the
reduction of the Co(II) state of the B12 derivative by electron
transfer from the photosensitizer by visible light irradiation.
Although this reaction system worked well, low turnovers
based on the B12 complex were obtained even though an excess
amount of the photosensitizer was used. It is noted that Yoon
and coꢀworkers reported the decomposition pathway and fate of
1
and reductive dehalogenase as a cofactor. Inspired by the
unique dehalogenation function of
B12 in the reductive
dehalogenase, B12 model complexes have been widely studied
as excellent catalysts for the dehalogenation reactions since the
Co(I) species of the B12 complexes are supernucleophlic and
can react with alkyl halides to generate alkylated complexes
2
+
2
Ru(bpy)
3
during the photocatalytic reaction, in which rapid
which provide the dehalogenation products.
2
+
decomposition of the Ru(bpy)
irradiation was demonstrated.
revealed that the excited state of Ru(bpy)
3
complex under light
Furthermore, Sun’s work
Organic halides are indispensable chemicals that are widely
utilized as general organic solvents, useful reagents for organic
7
2
+
3
in the
synthesis etc., both in laboratory studies and industrial
3
photocatalytic system cannot be effectively reduced even with a
production.
It is noted that their wastes have caused
8
large excess of reductant.
The fast decomposition and
environmental contamination and several health problems due
to their accumulation in the environment and biomagnificaition
2
+
inefficient reductive quenching of Ru(bpy)
3
during the
4
catalytic reaction may be the factors that led to limited
turnovers of B12 combined the use with the Ru photosensitizer.
Therefore, there are still efforts that should be made to develop
more efficient and robust visible light responsible
photosensitizers to improve the catalytic efficiency of the B12
complex in the photocatalytic system.
properties in living organisms. To solve these problems, the
reductive dehalogenation of organic halides has been
5
intensively studied for decades . In recent years, our group
Cyclometalated iridium(III) complexes have been rapidly
developing due to their superior photophysical and
9
photochemical properties. Consequently, they have been
widely utilized as photoredox catalysts in organic synthesis as
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ARTICLE
Journal Name
1
0
well as serving as photosensitizers.
It has been recognized dithranol as the matrix. The cyclic voltammograms (CV) were
obtained using a BAS CV 50W electrochemical analyzer. A
+
that [Ir(C^N)
2
(N^N)] chromophores (C^
N=cyclometallating ligand and N^N=bidendate N2 ligand) threeꢀelectrode cell equipped with 1ꢀmm diameter platinum
display considerably higher efficiencies with remarkable high wires as the working and counter electrodes were used. An
turnovers in homogeneous H
working as photosensitizer than that obtained from the typical the presence of tetrabutylammonium perchlorate (
metal bipyridyl complexes such as the Ru(bpy)
Bernhard’s group systematically studied the catalytic efficiency ferrocenium (Fc
2
ꢀevolving photocatalytic systems Ag/AgCl (3.0 M NaCl aq.) electrode served as the reference in
ꢀBu NClO
as the supporting electrolyte. The E1/2 value of the ferrocene–
n
4
4
)
2
+
8,11
3
complex.
+
/
Fc ) was 0.41 V vs. Ag/AgCl with this setup.
improvement by evaluating the photophysical parameters and Fluorescence emission spectra were collected at room
pointed out the longer excitedꢀstate lifetimes and improved temperature by a Hitachi Fꢀ7000 fluorescence spectrometer at
+
stability of the [Ir(C^N)
their high efficiency.
2
(N^N)] complexes that contributed to the scan speed of 240 nm/min, and the slits were set at 5.0 nm
unless otherwise noted. The excitation wavelength was 264
1
2
In this study, a threeꢀcomponent catalytic system involving nm. An ASAHI SPECTRA MAXꢀ301 with bandꢀpass filters
the B12 complex as a catalyst, cyclometalated iridium(III) was used as monochromatic light source. The power of the
complexes as a photosensitizer, and triethanolamine (TEOA) as light source was measured by an Optical Power Meter, Model
a sacrificial reductant is reported. This catalytic system was 1916ꢀR (Newport).
applied to the visible lightꢀdriven dehalogenation of DDT, Photophysical studies of photosensitizers with B12 complex
which is one of the most problematic POPs (persistent organic A 100
pollutants).
ꢀ
M photosensitizer in Arꢀsaturated CH
A high catalytic efficiency with significantly the determination of the rate constant for quenching (
enhanced turnovers was obtained. The 1,2ꢀmigration of the photosensitizer. Photoluminescence decay traces of the
phenyl group of 2ꢀbromomethylꢀ2ꢀphenylmalonate was also photosensitizers were acquired based on timeꢀcorrelated singleꢀ
3
CN was used for
1
3
k
q
) of a
conducted as a model reaction of the B12 dependent enzyme.
photonꢀcounting (TCSPC) techniques using a FluoTime 200
instrument (PicoQuant, Germany) after a picosecond pulsed
laser excitation. A 377 nm diode laser (PicoQuant, Germany)
was used as the excitation source. The photoluminescence
signals at the emission peak wavelengths of the photosensitizers
Experimental
Materials
were
monochromator.
obtained
through
an
automated
motorized
All solvents and chemicals used in this study were of reagent grade.
Unless otherwise noted, commercial reagents, including
Photoluminescence decay profiles were
analyzed (OriginPro 8.0, OriginLab) using single or double
exponential decay models. In the case of the biphasic decays,
[
Ir{dF(CF
3
)ppy}
2
(dtbpy)]PF
6
([iridium bis(2ꢀ(2,4ꢀdifluorophenyl)ꢀ5ꢀ
trifluoromethylpyridinate)
butyl)bipyridine))]hexafluorophosphate) and [Ru(II)(bpy)
=
commercial suppliers and were used as received. Heptamethyl
cobyrinate perchlorate, the B12 complex, was synthesized by a
(2,2′ꢀ(4,4′ꢀdi(tꢀ
the photoluminescence lifetime (τobs) values were calculated
3 2
]Cl (bpy
2
from the relationship
are the preꢀexponential factor and the time constant,
respectively. The obs values were determined with the
obs i i i i i
τ = ΣA τ /ΣA τ (i = 1−2), where A and
2,2’ꢀbipyridine), were purchased from WAKO, Aldrich, and other
τ
i
τ
14,15
increasing concentration of the B12 complex or TEOA under a
pseudo first order condition. The quenching rates were
previously reported method.
Co(III)(DO)(DOH)Br , was prepared according to the literature.
Bicyclometalated iridium(III) complexes, Irdfppy ([iridium bis(2ꢀ
2,4ꢀdifluorophenyl)pyridinate) (9,10ꢀ
The cobalt complex,
16
2
calculated from the relationship, quenching rate = 1/
obs
τ −
1
/
τ
obs(0), where obs(0) correspond to the
τ
obs and
τ
(
photoluminescence lifetimes of
presence and absence of the
a
B
photosensitizer in the
12 complex or TEOA,
phnanthroline)]hexafluorophosphate), Irppy ([iridium bis(2ꢀ
phenylpyridinate) (9,10ꢀphnanthroline)]hexafluorophosphate), and
Irpbt
respectively. A linear fit of the quenching rate vs the
concentration of the B12 complex or TEOA yielded the k value.
q
([iridium
bis(2ꢀphenylbenzo[d]thiazolate)
(9,10ꢀ
phnanthroline)]hexafluorophosphate), were prepared following
1
7
General procedure of catalytic reaction
previously described methods (Scheme 1). 2ꢀBromomethylꢀ2ꢀ
phenylmalonate (1) and the authentic sample, diethyl 2ꢀmethylꢀ2ꢀ
phenylmalonate (3), were synthesized according to our previous
report. Diethylbenzylmalonate (2) was purchased from TCI.
Measurements
ꢀ5
A 10 mL ethanol solution of the B12 complex (1.0×10 M),
ꢀ
5
iridium(III) complex (0.128×10 M), TEOA (0.25 M) and DDT
ꢀ
3
18
(3.0×10 M) was degassed by N gas, then the solution was stirred at
2
room temperature under irradiation using a 200 W tungsten lump
with a 420 nm cutꢀoff filter (Sigma Koki, 42 L) and a heat cutꢀoff
filter (Sigma Koki, 30 H). After the reaction, the solution was first
The NMR spectra were recorded by a Bruker Avance 500
spectrometer at the Center of Advanced Instrumental Analysis
of Kyushu University, and the chemical shifts (in ppm) were
referenced relative to the residual protic peaks of the solvents.
evaporated to remove the solvent, then water (40 ml) and CHCl
ml) were added to the residue for extraction. The chloroform layer
was washed 3 times with water and dried with anhydrous Na SO
After filtration and vacuum drying, the residue was passed through a
silica gel short column eluting with CHCl to remove the B12 and
3
(30
4
.
The GCꢀmass spectra (GCꢀMS) were obtained using
a
2
Shimadzu GCꢀQP5050A equipped with a J&W Scientific DBꢀ1
column (length 30 m; ID 0.25 mm, film 0.25 ꢁm). The UVꢀvis
absorption spectra were measured by a Hitachi Uꢀ3300
spectrophotometer at room temperature. The MALDIꢀTOF
mass spectra were obtained by a Bruker autoflex II using
3
iridium(III) complexes. The product for the DDT dechlorination
1
reactions was analyzed by employing GCꢀMS or H NMR with 1,4ꢀ
dioxane as the internal standard.
2
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ARTICLE
(a)
B12 complex
Co(III)(DO)(DOH)Br2
Irdfppy
[
Ru(II)(bpy) ]Cl2
3
(
b)
Irpp
Irpbt
Ir{dF(CF )ppy} dtbpy)]PF
[
3
2(
6
Scheme
1
Structure of B12 complex, Co(III)(DO)(DOH)Br2,
Irppy, Irpbt, [Ir{dF(CF )ppy} (dtbpy)]PF and
]Cl
Irdfppy,
3
2
6
[
Ru(II)(bpy)
3
2
.
Fig.
Co(III)(DO)(DOH)Br
and [Ir{dF(CF )ppy}
1
UV-vis absorption spectra of
B
12 complex,
2
3 2
, [Ru(II)(bpy) ]Cl and Irdfppy (a), Irppy, Irpbt
-4
3
2
(dtbpy)]PF (b) in ethanol (1.28×10 M).
6
Results and discussion
In this study, heptamethyl cobyrinate perchlorate (B12 complex) and
another model compound of B12, Co(III)(DO)(DOH)Br , were
2
employed as catalysts for the dechlorination reaction. Four
iridium(III) complexes (i.e., Irdfppy, Irppy, Irpbt and
[
[
Ir{dF(CF
Ru(II)(bpy)
The UVꢀvis absorption spectra of the
Co(III)(DO)(DOH)Br
3
)ppy}
2
(dtbpy)]PF
were used as photosensitizers.
6
)
and
the
conventional
3
]Cl
2
B
12 complex,
2
, the cyclometalated iridium(III) complexes
i.e., Irdfppy, Irppy, Irpbt and [Ir{dF(CF )ppy} (dtbpy)]PF ) and
Ru(II)(bpy) ]Cl in ethanol are shown in Fig. 1. The B12 complex
(
[
3
2
6
3
2
showed the typical absorption band of the Co(II) species of the
cobalamin derivative around 480 nm (Fig. 1a) and all
-
5
1
9
Fig. 2 UV-vis spectral change of B12 complex (2.5×10 M) in
photosensitizers exhibited broad absorptions in the visible region
The groundꢀstate redox potentials of the B12 complex, Irdfppy,
Irppy, Irpbt, [Ir{dF(CF )ppy} (dtbpy)]PF and [Ru(II)(bpy) ]Cl as
well as the oxidation potential of a sacrificial reductant, TEOA, were
.
-5
ethanol in the presence of Irdfppy (0.32×10 M) and TEOA
(0.5 M) by visible light irradiation (λ≥420 nm): before
irradiation (yellow line) and after irradiation for 2 hours (green
line).
3
2
6
3
2
Table 1 Excited-state and ground state redox potentials of B12 complex, Irdfppy, Irppy, Irpbt, [Ir{dF(CF
3
)ppy}
2
(dtbpy)]PF
6
, [Ru(II)(bpy)
3
]Cl
2
and TEOA
Potenial/V
B12 complex
Irdfppy
Irppy
Irpbt
[Ir{dF(CF
3
)ppy}
2
(dtbpy)]PF
6
[Ru(II)(bpy)
3
]Cl
2
TEOA
a
b
E
ox
*
ꢀ
ꢀ
ꢀ1.17
1.47
1.63
ꢀ0.90
0.90
1.32
ꢀ1.12
1.21
1.49
ꢀ1.02
1.52
1.78
ꢀ0.73
ꢀ
a
b
Ered
*
0.73
ꢀ
c
III/II
E
ox
0.53(Co
)
0.95
0.93
c
II/I
Ered
ꢀ0.61(Co
)
ꢀ1.22
ꢀ1.28
ꢀ1.24
ꢀ1.28
ꢀ1.30
ꢀ
a
b
c
ꢀ3
ꢀ1
Reference (20). reference (11a). Condition: [complex] = 1.0×10 M, [nꢀBu
4
NClO
4
]= 1.0×10 M, [solvent]= acetonitrile, using a Pt wire as
counter electrode, Pt with 1 mm diameter as working electrode, Ag/AgCl (3.0 M NaCl aqueous ) as reference electrode at room temperature,
potential V vs. Ag/AgCl; ground state potentials were determined by CV measurement in CH CN.
3
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ARTICLE
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Irdfppy
Irdfppy + B12 (0.2 equiv.)
Irdfppy + B12 (8 equiv.)
+
[
Irdfppy]
= 752.8
B
M = 1037.10
12 complex
M
w
w
7
00
800
900
1000
m/z
1100
1200 1300
Fig. 4 MALDI-TOF mass spectrum of B12 complex and Irdfppy
Fig. 3 Emission spectra of Irdfppy (black line), and spectra change
after catalytic reaction.
with adding different amount of B12 complex: 0.2 equiv. mole
(
purple line), 8 equiv. mole (brown line) at room temperature with
-5
complex was reduced to the Co(I) species by photoinduced electron
transfer from Irdfppy. This notion is supported by the
a 37L filter in ethanol; λex=264 nm, [Irdfppy]= 0.128×10 M.
determined by cyclic voltammetry in acetonitrile solutions (Fig. S1). phosphorescence quenching experiments shown in Fig. 3 .
*
The results along with the excitedꢀstate redox potentials (Eox and
The phosphorescence intensity of Irdfppy in proportion to the
*
Ered ) of Irdfppy, Irppy, Irpbt and [Ir{dF(CF )ppy} (dtbpy)]PF are added concentration of B12 complex is displayed in Fig.3. Complete
3
2
6
summarized in Table 1. The electrochemical potentials reveal that quenching was observed in the presence of 8 equiv. of the B12
all the photosensitizers are capable of reduction of the B12 complex complex. The absence of any spectral shift in the phosphorescence
into a supernucleophilic Co(I) species by electron transfer from the spectra suggested diffusional quenching of Irdfppy by the B12
excited state (oxidative quenching) and the oneꢀelectronꢀreduced complex. Taken together, these spectroscopic behaviors indicated the
state (reductive quenching).
occurrence of oxidative quenching of Irdfppy by the B12 complex.
The reductive formation of the Co(I) species of the B12 complex Electron transfer processes between the two complexes will be
was monitored by UVꢀvis spectroscopy in the presence of Irdfppy discussed later (vide infra).
and TEOA under visible light irradiation (λ≥420 nm). After visible
The catalytic performance of this photoreaction system was
light irradiation for 2 hours, the peak of the Co(II) species (yellow evaluated using DDT as a substrate. The results are summarized in
line) disappeared and a strong absorption at 390 nm was observed Table 2. When DDT was irradiated with visible light in the presence
of the B12 complex, Irdfppy and TEOA, the dichlorination reaction
of DDT efficiently proceeded as shown in Entry 1 of Table 2. DDT
(
green line) as shown in Fig. 2, which is the typical peak of the Co(I)
5b
species of the B12 complex.
This result suggested that the B12
a
Table 2 Photocatalytic dechlorination of DDT by B12 complex with
Table 3 Dechlorination of DDT with different photosensitizers
a
Irdfppy as photosensitizer
Entry Photosensitizer Conversion(%) Yield (%) TON1 TON2
Entry
1
Conversion (%)
Yiled (%)
TON1
TON2
100
0
18
0
0
43
93
93
0
14
0
0
29
279
ꢀ
42
ꢀ
ꢀ
87
10880
2180
ꢀ
ꢀ
ꢀ
1
2
3
Irdfppy
Irppy
Irpbt
100
90
100
93
67
84
279
201
252
2180
1570
1968
b
2
3
4
5
b
c
c
d
[
Ir{dF(CF )ppy}
e
d
3
ꢀ
4
100
91
273
2132
(dtbpy)]PF
2 6
f
6
680
5
[Ru(II)(bpy) ]Cl 28
26
78
609
g
3
2
7
90
84375
a
ꢀ5
a
ꢀ5
ꢀ5
Condition:
[B12
complex]=1.0×10
(0.128
TEOA]=0.25 M, [DDT]=3.0×10 M (300 equiv. mole), solvent:
M,
Condition: [B12 complex]=1.0×10 M, [Irdfppy]=0.128×10
M
ꢀ5
ꢀ3
[photosensitizer]=0.128×10
[
M
ꢀ3
equiv.
mole),
(
0.128 equiv. mole), [TEOA]=0.25 M, [DDT]=3.0×10 M (300
equiv. mole), solvent: ethanol, reaction time: 3 hours, light
source: 200 W tungsten lump with L42 cutꢀoff filter (λ≥ 420
nm) at 5 cm distance. Conversion and yield were based on the
initial concentration of the substrate. Turnover number 1
ethanol, reaction time: 3 hours, light source: 200 W tungsten lump
with L42 cutꢀoff filter (λ≥ 420 nm) at 5cm distance. Conversion
and yield were based on the initial concentration of the substrate
1
and calculated by H NMR. Turnover number 1 (TON1) is based
(
TON1) is based on the B12 complex, TON2 is based on Irdfppy.
No B12 complex. No Irdfppy. No TEOA. In the dark.
b
on [B12 complex], TON2 is based on [photosensitizer].
DDA
b
c
d
e
c
(9%), TTBD(E) (7%), DDA (4%), TTBD(E) (4%), DDMU (1%),
f
Co(DO)(DOH)Br2 was used in place of the B12 complex.
d
DDA (3%), TTDB(E)(1%)..
g
[
TEOA]=2.5 M, [DDT]=0.12 M, reaction time was 36 hours.
4
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was almost completely dichlorinated to the monodechlorinated
Table 4 Catalytic reaction of 2-bromomethyl-2-phenylmalonate by
a
product, 1,1ꢀbis(4ꢀchlorophenyl)ꢀ2,2ꢀdichloroethane (DDD), after
B12 complex with Irdfppy as photosensitizer
‡
3
(
2
hours of visible light irradiation.
TONs) based on the B12 complex and Irdfppy reached 279 and
180, respectively. In contrast, the reaction almost did not
The turnover numbers
proceed under the conditions without B12, Irdfppy, TEOA, or
Entry Solvent Conversion Yield
2/3
TON1 TON2
visible light irradiation (Entries 2, 3, 4 and 5, respectively, in
§
(%)
(%)
Table 2). When Co(III)(DO)(DOH)Br
2
was conducted as a
2
3
catalyst in place of the B12 complex, the yield of DDD was only
1
2
3
EtOH
CH
PhCN
100
CN 100
95
8
85 0.09 270
211
234
2
9% (Entry 7 in Table 2) due to the poor stability of the
3
21 79 0.26 300
50 23 2.17 219
§§
2
Co(III)(DO)(DOH)Br .
171
a
ꢀ5
ꢀ5
Condition: [B12 complex]=1.0×10 M, [Irdfppy]=1.28×10
M
The stability of the B12 complex was confirmed by the detection
of the UVꢀvis spectral change before and after the catalytic
reaction (Fig. S2). The intensity of the Co(II) species peak of B12
complex showed a slight change, which indicated that most of the
ꢀ3
(
1.28 equiv. mole), [TEOA]=0.25 M, [substrate]=3.0×10 M (300
equiv. mole), reaction time: 12 hours, light source: 200 W tungsten
lump with L42 cutꢀoff filter (λ≥ 420 nm) at 5 cm distance.
Conversion and yield were based on the initial concentration of the
substrate and calculated by GCꢀMS. TON1 is based on [B12
complex], TON2 is based on [Irdfppy].
B
12 complex survived from the catalytic reaction. The MALDIꢀ
TOF mass spectrometric analysis was also conducted after the
catalytic reaction. Mass peaks ascribed to the B12 complex
together with Irdfppy were clearly detected as shown in Fig. 4.
Thus, the B12 complex and Irdfppy are very stable compounds
during the photocatalytic reactions. These results further suggested
that higher TONs might be achieved under the present reaction
conditions due to the high stability of both compounds. To confirm
this, the reaction was conducted for 36 hours with increasing
concentrations of DDT to 0.12 M and TEOA to 2.5 M. Noteworthy,
the TONs were significantly increased to 10,880 and 84,375 based
on the B12 complex and Irdfppy, respectively, among the highest
reported TONs (Entry 7, Table2).
The other iridium(III) complexes, Irppy, Irpbt and
Ir{dF(CF3)ppy}2(dtbpy)]PF6 and the most widely utilized visible
[
light harvesting photosensitizer, [Ru(II)(bpy) ]Cl , were used as
3
2
photosensitizers. The results are summarized in Table 3. Catalytic
efficiencies comparable to that of Irdfppy were obtained for Irpbt
3 2 6
and [Ir{dF(CF )ppy} (dtbpy)]PF (Entries 3 and 4 in Table 3). Some
further dechlorinated products, 1,1,4,4ꢀtetrakis(4ꢀchlorophenyl)ꢀ2,3ꢀ
dichloroꢀ2ꢀbutene
chlorophenyl)ethylene
(TTDB),
(DDMU)
1ꢀchloroꢀ2,2ꢀbis(4ꢀ
ethyl 2,2ꢀbis(4ꢀ
and
chlorophenyl)acetate (DDA) w¶ere obtained in low yield (Entries
, 3 and 4, in Table 3, Fig. S3). It is noted that the yield of DDD
sharply decreased to 26% when Irdfppy was replaced by
Ru(II)(bpy) ]Cl as a photosensitizer (Entry 5 in Table 3). This was
2
To confirm that the catalysis was due to photon absorption by
Irdfppy, we determined the action spectrum of the catalytic
dechlorination of DDT. A Xenon light source with bandꢀpath filters
was utilized to provide monochromatic lights at 350 nm, 365 nm,
[
3
2
probably due to the gradual decomposition of [Ru(II)(bpy)
3 2
]Cl
under visible light irradiation.
The photocatalytic system was applied to the B12 enzymeꢀmimic
reaction, the 1,2ꢀmigration of the phenyl group of 2ꢀbromomethylꢀ2ꢀ
4
00 nm, 490 nm, 540 nm and 600 nm with the same light intensity
2
of 1.9 mW/cm . The action spectrum, which plots the yields
determined at the irradiation wavelengths, was depicted together
with the UVꢀvis absorption spectra of the B12 complex (red line) and
Irdfppy (black line) in Fig. 5. The similarity between the action
spectrum and the spectral profiles of Irdfppy suggested that the
desired photosensitizing reaction by Irdfppy actually occurred to
allow the catalytic reaction.
phenylmalonate (
phenyl migrated product, diethylbenzylmalonate (
simply reduced product, 2ꢀmethylꢀ2ꢀphenylmalonate
obtained and the distribution of and were dependent on the
solvents. The ratio of was 0.09 in EtOH, 0.26 in CH CN and
.17 in PhCN. The ratio of significantly increased in poor
hydrogen radical donor solvents, which showed the same tendency
1
). The results are summarized in Table 4. The
), along with the
), were
2
(
3
2
3
2
/3
3
2
2
1
8
as in our previous report.
B
12
Table 5 Rate constants (keT) and driving forces (−ꢁGeT) for oxidative
or reductive quenching of the photosensitizers
oxidative quenching
by B12 complex
reductive quenching
by TEOA
k
eT
−ꢁGeT
(eV)
k
eT
−ꢁGeT
(eV)
10 M s−
8
−1
(10 M s−
8
−1
(
1
1
)
)
Irdfppy
26
23
0.56
9.4
7.7
0.54
0.59
[
(
Ir{dF(CF )ppy}
dtbpy)]PF
0.41
3
2
6
Irpbt
17
13
0.51
0.29
N.D.
N.D.
0.28
Fig. 5 Action spectrum of B12-Irdfppy catalytic system: UV-vis
spectra of B12 complex (red line) and Irdfppy (black line), yield of
DDD at corresponding wavelength (blue square).
Irppy
−0.03
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photoredox catalytic cycle of the iridium(III) photosensitizers.
The steadyꢀstate photophysical results provided strong evidence
that the B12 complex was reduced to a Co(I) species by the
photoexcited catalyst (i.e., Fig. 2). Two electronꢀtransfer
pathways can exist in this reduction step: 1) an oxidative
quenching of the photocatalyst by the B12 complex, and 2) a
reductive quenching of the photocatalyst by TEOA, followed
by transfer of the extra electron to the B12 complex. In the case
of the oxidative quenching pathway, the one electronꢀoxidized
photosensitizer is neutralized by electron donation by TEOA.
Inspection of the electrochemical potentials in Table 1 indicated
varying thermodynamic allowance of the quenching pathways.
3 2 6
Specifically, Irdfppy, [Ir{dF(CF )ppy} (dtbpy)]PF and Irpbt
0
2
4
6
8
10
0
2
4
6
8
10
are predicted to follow both oxidative and reductive quenching
pathways, whereas only an oxidative quenching pathway would
Time/μS
Time/μS
be available for Irppy. The driving force (−ꢁ
pathways was calculated assuming a oneꢀelectron transfer
process; the oxidative quenching pathway, −ꢁ =
GeT) for both
G
eT
II/I
e
⋅
[
E
*
ox(photocatalyst)
quenching pathway,
E*red(photocatalyst)]. In this equation,
charge. The calculated −ꢁ eT values are summarized in Table
. It was determined that Irdfppy possesses the highest −ꢁ
value for the oxidative quenching pathway, followed by Irpbt >
Ir{dF(CF )ppy} (dtbpy)]PF > Irppy. In the case of the
reductive quenching, [Ir{dF(CF )ppy} (dtbpy)]PF is predicted
to have the highest −ꢁ −ꢁ eT for the reductive quenching
of Irdfppy is lower than that for [Ir{dF(CF )ppy} (dtbpy)]PF
by 0.05 eV. Judging from the negative −ꢁ 0.03 eV), Irppy
−
E
red(Co )], and the reductive
−ꢁ ox(TEOA)
is the elementary
G
eT
=
e
⋅
[
E
−
e
G
5
G
eT
[
3
2
6
3
2
6
0
100
200
300
400
500
G
eT
.
G
Quencher/μM
Fig. 6 (a,b) Phosphorescence decay traces of 100 ꢀM Irdfppy
Ar-saturated CH CN) with increasing the concentration of B
3
2
6
eT
G (−
cannot undergo reductive quenching by TEOA. Note that
almost identical driving forces for the oxidative and reductive
quenching pathways exist in Irdfppy, and that other
photocatalysts have driving forces for the oxidative quenching
greater than those for the reductive quenching except for
(
3
12
complex (a) or TEOA (b).
(c) Pseudo first order fit of the
quenching rate as a function of the added concentrations of B12
complex (squares) and TEOA (triangles).
[
Ir{dF(CF
3 2 6
)ppy} (dtbpy)]PF .
To gain
a mechanistic insight, we investigated the
The quenching process of the photosensitizers was directly
Fig. 7 Plausible reaction mechanism for the dechlorination of DDT by B12 complex with Irdfppy photosensitizer.
6
| J. Name., 2012, 00, 1-3
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Plea sDe a dl t oo nn oT tr aa nd sj ua cs tt i om nasrgins
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ARTICLE
monitored by employing transient photoluminescence techniques. In summary, we have developed a threeꢀcomponent visible light
Photoluminescence decay traces of 100 ꢀM Irdfppy (Arꢀsaturated induced catalytic system with the B12 complex as a catalyst,
CH CN) were acquired after picosecond pulsed laser photoexcitation cyclometalated iridium(III) complex (Irdfppy, Irppy, Irpbt and
3
with the increasing concentration of the B12 complex or TEOA (Fig. [Ir{dF(CF )ppy} (dtbpy)]PF ) as a photosensitizer and TEOA as an
3
2
6
6a,b). Pseudo first order kinetics analyses yielded the rate constant electron source under a N2 atmosphere, in which an excellent
for the bimolecular oneꢀelectron transfer keT between the catalytic efficiency was obtained. The mechanistic study suggested
(
)
photoexcited Irdfppy and B12 complex (i.e., oxidative quenching that the choice of an oxidative quenching pathway or a reductive
pathway) or TEOA (i.e., reductive quenching pathway) (Fig. 6c). quenching pathway significantly depended on the photosensitizer.
Results for the other photosensitizers are shown in Figs. S4ꢀS6. The Transient photoluminescence experiments revealed that the oxidative
determined
that keT for the oxidative quenching (1.3−2.6 × 10
greater than those for the reductive quenching (7.7−9.4 × 10 M
s ) by two or three fold, a result consistent with the prediction based of 2ꢀbromomethylꢀ2ꢀphenylmalonate. Further application of this
on −ꢁGeT. This finding suggests that oxidative quenching is favored catalytic system to other reactions is currently in progress in our
over reductive quenching. keT for the oxidative quenching roughly laboratory.
keT values are included in Table 5. It was determined quenching of the photocatalyst dominated over the reductive
9
−1 −1
M
s ) are quenching. This photocatalytic system was also successfully applied
8
−1
to the B12 enzymeꢀmimic reaction, the 1,2ꢀmigration of phenyl group
−
1
increases with −ꢁGeT, indicative of the Marcusꢀnormal region of
electron transfer. Therefore, oxidative quenching will be further
dominated for a photocatalyst having a high bandgap energy or a
shallow oxidation potential. Among the tested photosensitizers,
Acknowledgements
Irdfppy displays the highest keT values of both the oxidative and
This study was partially supported by KAKENHI Grant
Numbers 23550125, JP16H01035, and JP16H04119 from the
Japan Society for the Promotion of Science (JSPS) and a Grant
from the Iwatani Naoji Foundation (No. 16ꢀ4313).
reductive quenching pathways. These kinetic behaviors may explain
the best catalytic performance of Irdfppy, although other catalysis
steps should be investigated for a complete understanding.
Based on these results, a plausible reaction mechanism involving
Irdfppy as a photosensitizer was constructed as shown in Fig. 7. The
reaction is assumed to proceed via two competitive pathways, the
oxidative quenching pathway (pathway A) and reductive quenching
pathway (pathway B). Under visible light irradiation, Irdfppy is
Notes and references
‡
ꢀ
Over 80% of Cl based on DDD was detected after the reaction
by spectrophotometric determination using the mercury(II)
promoted to an excited state through the metalꢀtoꢀligand chargeꢀ thiocyanate method (T. M. Florence and Y. J. Farrar, Anal. Chim.
Acta. 1971, 54, 373).
Probably due to the photosensitizing catalysis of the B12
complex without photosensitizer, 14% of DDD was produced
Entry 3 in Table 2). See H. Shimakoshi, L. Li, M. Nishi, Y.
Hisaeda, Chem. Commun., 2011, 47, 10921.
transfer (MLCT) transition. The excited state oxidation potential
§
(
ꢀ
E*ox) and the excited state reduction potential (E*red) of Irdfppy are
1.17 V vs. Ag/AgCl and 1.47 V vs. Ag/Ag/Cl, respectively (Table
(
1). In the case of the oxidative quenching pathway, the excited state
of Irdfppy is quenched to the oneꢀelectron oxidized species by the §§ Decomposition of Co(III)(DO)(DOH)Br was monitored by
2
reduction of the B12 complex from the Co(II) state to form the UVꢀvis (Fig. S7) and MALDIꢀTOF mass spectra (Fig. S8).
¶
II/I
Didechlorinated products, TTDB and DDMU could be formed
2d
supernucleophilic Co(I) species (E1/2(Co ) = ꢀ0.61 V vs. Ag/AgCl)
by reduction of substrate radical. The selectivity of products
distribution may be caused by
Table 1.
which is catalytically active. The corresponding alkylated complex
could then be generated along with leaving of the chloride anion by
the reaction of the supernucleopholic Co(I) species with the DDT
Ered of photosensitizer as shown in
#
In the present catalytic reaction condition with high TEOA
21
substrate.
The cobaltꢀcarbon bond of the alkylated complex concentration, reductive quenching pathway could be competing
to oxidative quenching pathway and possible to becomes
subsequently undergoes photolysis to form the substrate radical and
Co(II) species. The substrate radical reacts with hydrogen to form
the dechlorinated DDD product. In the case of the reductive
quenching pathway, the excited state of Irdfppy is quenched to the
oneꢀelectron reduced species by the oxidation of TEOA. The redox
potential of the reduced state Irdfppy is ꢀ1.22V vs. Ag/AgCl. Thus,
the Co(II) species would be reduced to the supernucleopholic Co(I)
species to catalyze the dechlorination of DDT. For these two
predominant pathway.
determined by the concentration of sacrificial reagent and its
redox potential.
The predominant pathway should be
1
W. Buckel and B. T. Golding, Chem. Soc. Rev., 1996, 25, 329;
b) Vitamin B12 and B12ꢀProtein, ed. B. Kraütler, D. Arigoni
(
and B. T. Golding, WileyꢀVCH, Weinheim, 1998; (c)
Chemistry and Biochemistry of B12, ed. R. Banerjee, Wileyꢀ
Interscience, New York, 1999; (d) R. Banerjee and S. W.
Ragsdale, Annu. Rev. Biochem., 2003, 72, 209; (e) T. Toraya,
Chem. Rev., 2003, 103, 2095; (f) B. Kraütler and S.
Ostermann, in The Porphyrin Handbook, ed. K. M. Kadish,
K. M. Smith and R. Guilard, Academic Press, 2003, 11, 229;
pathways, identical driving forces exist, but keT for the oxidative
9
−1 −1
quenching pathway (2.6 × 10
M
s ) is greater than that of the
reductive quenching pathway (9.4 × 10 M−1 s−1) (Table 5), thus
8
oxidative quenching of the photosensitizer dominated over the
(
g) J. BridwellꢀRabb and C. L. Drennan, Curr. Opinion Chem.
#
reductive queching pathway.
Biol., 2017, 37, 63; (h) K. Proinsia, M. Giedyk and D. Gryko,
Chem. Soc. Rev., 2013, 42, 6605.
(a) Y. Hisaeda and H. Shimakoshi, in Handbook of Porꢀ
phyrin Science, ed. K. M. Kadish, K. M. Smith and R.
2
Conclusion
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Guilard, World Scientific, 2010, 10, 313; (b) G. N. Schrauzer 21 H. Shimakoshi, Z. Luo, T. Inaba and Y. Hisaeda, Dalton
and E. Deutsch, J. Am. Chem. Soc., 1969, 91, 3341; (c) G. N.
Schrauzer, E. Deutsch and R. J. Windgassen, J. Am. Chem.
Soc., 1968, 90, 2441; (d) H. Shimakoshi, M. Tokunaga and Y.
Hisaeda, Dalton Trans., 2004, 878; (e) H. Shimakoshi, Y.
Maeyama, T. Kaieda, T. Matsuo, E. Matsui, Y. Naruta and Y.
Hisaeda, Bull. Chem. Soc. Jpn., 2005, 78, 859; (f) M. Giedyk,
K. Goliszewska and D. Gryko, Chem. Soc. Rev., 2015, 44,
Trans. 2016, 45, 10173.
3
391.
3
4
(a) R. L. Metcalf, New York, NY: Wiley. 1995, 14, 524. (b) K.
Kannan, S. Tanabe and R. J. Williams, Sci. Total Environ.,
1
994, 153, 29. (c) W. R. Kelce, C. R. Stone, S. C. Laws, L. E.
Gray, J. A. Kemppainen and E. M. Wilson, Nature, 1995,
75, 581.
A. Mansouri, M. Cregut, C. Abbes, M. J. Durand, A.
Landoulsi and G. Thouand. Appl. Biochem. Biotechnol.
017, 181, 309.
F. Alonso, I. P. Beletskaya and M. Yus, Chem. Rev. 2002, 102,
009.
3
ꢀ
,
2
5
6
4
(a) H. Shimakoshi, M. Tokunaga, T. Baba and Y. Hisaeda,
Chem. Comm., 2004, 9, 1806; (b) W. Zhang, H. Shimakoshi,
N. Houfuku, X. M. Song and Y. Hisaeda, Dalton Trans.
014, 43, 13972; (c) Y. Sun, W. Zhang, J. Tong, S. Wu, D.
Liu, H. Shimakoshi, Y. Hisaeda and X. M. Song, RSC Adv.,
017, 7, 19197.
,
2
2
7
8
9
U. S. Akhtar, E. L. Tae, Y. S. Chun, I. C. Hwang and K. B.
Yoon, ACS Catal., 2016, 6, 68361.
P. Zhang, M. Wang, Y, Na, X. Li, Y. Jiang and L. Sun, Dalton
Trans., 2010, 39, 1204.
(a) L. Flamigni, A. Barbieri, C. Sabatini, B. Ventura, F.
Barigelletti, in: V. Balzani, S. Campagna (Eds.),
Photochemistry and Photophysics of Coordination Comꢀ
pounds II, Springer, Berlin Heidelberg, 2007, 143; (b) Y. You
and W. Nam, Chem. Soc. Rev. 2012, 41, 7061; (c) A. Singh,
K. Teegardin, M. Kelly, K. S. Prasad, S. Krishnan and J. D.
Weaver, J. Organomet. Chem., 2015, 776, 51.
10 (a) D. M. Schultz and T. P. Yoon, Science, 2014, 343, 985; (b)
C. K. Prier, D. A. Rankic and W. C. MacMillian, Chem, Rev.
2
013, 113, 5322. (c) S. M. Senaweera, A. Singh and J. D.
Weaver, J. Am. Chem. Soc., 2014, 136, 3002. (d) K. Singh, S.
J. Staig and J. D. Weaver, J. Am. Chem. Soc., 2014, 136,
5
2
275. (e) A. Singh, A. Arora and J. D. Weaver, Org. Lett.,
013, 15, 5390.
1
1 (a)A. Fihri, V. Artero, A. Pereira and M. Fontecave, Dalton
Trans. 2008, 41, 5567. (b) M. S. Lowry, J. I. Goldsmith, J. D.
Slinker, R. Rohl, R. A. Pascal, Jr., G. G. Malliaras and S.
Bernhard, Chem. Mater., 2005, 17, 5713.
12 J. I. Goldsmith, W. R. Hudson, M. S. Lowry, T. H. Anderson
and S. Bernhard, J. Am. Chem. Soc. 2005, 127, 7502.
1
3 (a) S. Sudharshan, R. Naidu, M. Mallavarapu and N. Bolan,
Biodegradation, 2012, 23, 851; (b) W. G. Kiflom, S. O.
Wandiga and G. N. Kamau, Pure Appl. Chem., 2001, 73,
1
907.
1
1
1
1
1
1
2
4 L. Werthemann, ETH Zürich (No. 4097), Dissertation, Juris
Druck and Velag, Zürich, 1968.
5 Y. Murakami, Y. Hisaeda and A. Kajihara, Bull. Chem. Soc.
Jpn., 1983, 56. 3642.
6 Y. Murakami, Y. Hisaeda, S. D. Fan and Y. Matsuda, Bull.
Chem. Soc. Jpn., 1989, 62, 2219.
7 H. Woo, S. Cho, Y. Han, W.ꢀS. Chae, Y. You and W. Nam, J.
Am. Chem. Soc. 2013, 135, 4771.
8 H. Shimakoshi, M. Abiru, S. I. Izumi and Y. Hisaeda, Chem.
Commun., 2009, 42, 6427.
9 Y. Murakami and Y. Hisaeda, Bull. Chem. Soc. Jpn. 1985, 58,
2652.
0 S. Lee, Y. You, K. Ohkubo, S. Fukuzumi and W. Nam, Chem.
Sci. 2014, 5, 1463.
8
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