Mechanism of a one-photon two-electron process in photocatalytic hydrogen evolution from ascorbic acid with a cobalt chlorin complex

Article abstract of DOI:10.1039/c5cc05064b

A one-photon two-electron process was made possible in photocatalytic H₂ evolution from ascorbic acid with a cobalt(ii) chlorin complex [Co^II(Ch)] via electron transfer from ascorbate to the excited state of [Ru(bpy)₃]²⁺ followed by electron transfer from [Ru(bpy)₃]⁺ to Co^II(Ch) with proton to give the hydride complex, which reacts with proton to produce H₂. [Co^III(Ch)]⁺ was reduced by ascorbate to reproduce Co^II(Ch).

Full text of DOI:10.1039/c5cc05064b

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Mechanism of a one-photon two-electron process in
photocatalytic hydrogen evolution from ascorbic acid
with a cobalt chlorin complex†
Cite this: DOI: 10.1039/x0xx00000x
Received 00th February 2015,
Accepted 00th xxxx 2015
a
a
ab
*abc
Shoko Aoi, Kentaro Mase, Kei Ohkubo and Shunichi Fukuzumi
DOI: 10.1039/x0xx00000x
www.rsc.org/
ꢀ
A one-photon two-electron process was made possible in
photocatalytic H evolution from ascorbic acid with a solution (1:1 v/v) of [Ru(bpy)
cobalt(II) chlorin complex [Co (Ch)] via electron transfer ascorbic acid (AscH
Visible light irradiation of a deaerated (Ar-saturated) H
2
O/MeCN
2
+
2
3
]
(bpy = 2,2'-bipyridine) containing
II
–
2
) and ascorbate (AscH ) (Eox = 0.43 V vs. SCE)
2
+
II
from ascorbate to the excited state of [Ru(bpy)
3
]
followed as an electron donor and Co (Ch) (Ered = –0.96 V vs. SCE) [Fig. S1
+
II
by electron transfer from [Ru(bpy)
to give the hydride complex, which reacts with proton to
3
] to Co (Ch) with proton in the supplementary information (ESI)†] as a catalyst resulted in
–
H
2
evolution (Fig. 1, black line). When the ratio of AscH to AscH
. [Co (Ch)] was reduced by ascorbate to was changed as fixed total concentrations of AscH and AscH
reproduce Co (Ch).
2
–
III
+
produce H
2
2
II
–
([AscH ] + [AscH ] = 1.1 M), the largest H evolution activity was
2
2
–
attained with AscH (0.30 M) and AscH
2
(0.80 M) (Fig. S2 in ESI
–
2
Photocatalytic production of hydrogen (H ) has attracted increasing
†
). The smaller concentration of AscH results in less efficient
2
+
attention as a clean energy source because of the ever-increasing
3
reductive quenching of the [Ru(bpy) ] * emission (* denotes the
1
2
+
demand for energy and climate change on our planet. A number of
excited state). The quenching efficiency of [Ru(bpy)
3
] * (Ered
=
2
0
–
highly efficient hydrogen evolving systems have been developed
0
.77 V vs. SCE in MeCN) by AscH (0.30 M) with AscH
2
(0.80
2
-
including homogeneous and heterogeneous photocatalytic systems.
M) was determined to be 95% (Fig. S3 in ESI†). On the other hand,
the smaller concentration of AscH may retard H production due to
decreasing the acidity. When H O was replaced by D
1
3
Two electrons are required to produce H
one photon generates normally only one electron. A mechanism of
photocatalytic production of H was reported to clarify how
photoinduced electron transfer of a photosensitiser (a one-electron
2
from protons, although
2
2
2
2
2
O, D and HD
2
1
4-16
H O
D O
2
process) leads to H
2
production (a two-electron process).
2
50
40
30
20
10
0
Disproportionation of one-electron reduced species of metal
complexes resulted in formation of the two-electron reduced species
1
7
from which H
2
is formed. Bimolecular reactions of metal(III)-
accompanied by regeneration of
metal(II) complexes. In each case, the maximum quantum yield of
production per photon is 50%, because two photons are required
to produce two electrons. Thus there has so far been no example for
one photon to generate one H molecule.
We report herein photocatalytic H evolution from ascorbic acid
AscH ) with a cobalt(II) chlorin complex [Co (Ch)] (a chemical
structure shown in Scheme 1) in an aqueous acetonitrile solution
O/MeCN), which proceeds via a one-photon two-electron process.
The photocatalytic mechanism is clarified by nanosecond laser
transient absorption spectra and by examining each step in the saturatedꢀH
hydride complexes also generate H
2
1
8
H
2
2
2
II
(
2
1
9
0
5
10
15
20
(
H
2
Time, h
Fig.ꢀ1ꢀTimeꢀcoursesꢀofꢀH
2
ꢀevolutionꢀinꢀtheꢀphotocatalyticꢀreductionꢀofꢀprotonꢀinꢀanꢀAr-
O/MeCNꢀ(red)ꢀmixedꢀsolutionꢀ(1:1ꢀv/v)ꢀcontainingꢀ
2
2+
O/MeCNꢀ(black)ꢀandꢀD
2
II
II
[
Ru (bpy)
3 2
] ꢀ(2.0ꢀmM),ꢀAscH ꢀ(0.80ꢀM),ꢀAscHNaꢀ(0.30ꢀM)ꢀandꢀCo (Ch)ꢀ(25ꢀµM)ꢀunderꢀ
catalytic cycle independently.
irradiationꢀofꢀvisibleꢀlightꢀ(λꢀ>ꢀ420ꢀnm)ꢀatꢀ298ꢀK.ꢀꢀ
Thisꢀjournalꢀisꢀ©ꢀTheꢀRoyalꢀSocietyꢀofꢀChemistryꢀ2012ꢀ
J.ꢀName.,ꢀ2012,ꢀ00,ꢀ1-3ꢀ|ꢀ1ꢀ

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2
were produced without formation of H . Thus, hydrogen was
(
a) 1.2
(b)
6
4
2
0
produced from water and ascorbic acid as electron and proton
sources. The observed deuterium kinetic isotope effect (KIE) in Fig.
[Co
6
I
(Ch)]
–
6 ms
View Article Online
DOI: 10.1039/C5CC05064B
1
s
6
3
60 nm
COO)]
[
CoIII(H)(Ch)(CH
–
1
(k
cleavage of a cobalt hydride intermediate ([Co (H)(Ch)]) by proton
may be the rate-determining step for the photocatalytic H evolution
H D
/k = 1.8 in the initial stage) suggests that the Co-H bond
0
0
.8
.4
0
III
652 nm
[
Co (Ch)]+
III
2
6
60 nm
[Co (Ch)]
I
–
(
vide infra).
The concentration of Co (Ch) was optimised to be 50 µM for the
II
2
+
2 3
efficient photocatalytic H evolution. The absorption of [Ru(bpy) ]
II
3
00
400
500
600
700
0
0.5
1.0
1.5
is blocked by the larger concentration of Co (Ch) (Fig. S4 in ESI
Wavelength, nm
[CH
3
COOH], M
2
1
†
2
). The quantum yield of the photocatalytic H evolution was
I
–ꢀ
Fig.ꢀ 3ꢀ (a)ꢀ UV-visꢀ absorptionꢀ spectralꢀ changesꢀ ofꢀ [Co (Ch)] (30ꢀ µM)ꢀ uponꢀ additionꢀ ofꢀꢀ
CH COOHꢀ (0.30ꢀ M)ꢀ inꢀ dearatedꢀ MeCNꢀ atꢀ 298ꢀ K.ꢀ Theꢀ blackꢀ andꢀ blueꢀ linesꢀ showꢀ theꢀ
spectraꢀtakenꢀatꢀ66ꢀmsꢀandꢀ1ꢀsꢀafterꢀmixing,ꢀrespectively.ꢀTheꢀredꢀlineꢀshowsꢀUV-visꢀ
determined to be 12% using a ferric oxalate actinometer (see the
3
experimental section in ESI†). This value is similar to the highest
I
– ꢀ
value reported for photocatalytic H
2
evolution using a cobalt absorptionꢀspectrumꢀofꢀ[Co (Ch)] ꢀ (15ꢀµM)ꢀformedꢀbyꢀtheꢀelectron-transferꢀreductionꢀofꢀ
2
2
I
I
*
terpyridine complex (Φ = 0.13).
Co (Ch)ꢀ(15ꢀµM)ꢀwithꢀCoCp 2ꢀ(300ꢀµM)ꢀinꢀdearatedꢀMeCNꢀatꢀ298ꢀK.ꢀ(b)ꢀPlotꢀofꢀkobsꢀforꢀ
III
+ꢀ
3
theꢀrateꢀofꢀformationꢀofꢀ[Co (Ch)] vs.ꢀ[CH COOH].ꢀꢀ
(a)
(b)
4
3
2
1
0
1
4
3
2
1
0
[
Ru(bpy)3]+
00 nm
II
510 nm) decreased with increasing absorption band at 660 nm
(black line) at 66 ms after addition of acetic acid (CH3COOH)
(0.30 M). Then, this absorption band was finally blue shifted to
1
µs
[Co (Ch)] =
5
10 µs
5
9
0 µM
5.0 µM
0 µM
20 µM
0 µs
0 µs
1
III
+ 24,25
I
–
λmax = 652 nm, which is due to [Co (Ch)] .
Thus, [Co (Ch)]
may react with CH COOH to form the hydride complex
3
III
–
([Co (H)(Ch)(CH3COO)] : λmax = 660 nm), from which H2
was evolved by the reaction with CH3COOH to produce
III
+
I
–
–
3
[Co (Ch)] . The reaction of [Co (Ch)] with CH COOH was
monitored by the absorption change at 652 nm due to [Co (Ch)] as
III
+
4
00
500
600
700
0
0.1
0.2
0.3
0.4
0.5
Wavelength, nm
Time, ms
III
+
shown in Fig. 3, where the rate of the formation of [Co (Ch)]
Fig.ꢀ 2ꢀ (a)ꢀ Transientꢀ absorptionꢀ spectraꢀ afterꢀ laserꢀ excitationꢀ (λꢀ =ꢀ 450ꢀ nm)ꢀ ofꢀ obeyed first-order kinetics (Fig. S8 in ESI†). The first-order rate
II
2+
[
Ru (bpy)
deaeratedꢀH
atꢀ 500ꢀ nmꢀ dueꢀ toꢀ decayꢀ ofꢀ [Ru(bpy)
3
]
ꢀ (80ꢀ µM)ꢀ inꢀ theꢀ presenceꢀ ofꢀ AscH
2
ꢀ (0.80ꢀ M)ꢀ andꢀ AscHNaꢀ (0.30ꢀ M)ꢀ inꢀ aꢀ
constant increased with increasing concentration of CH
approach a constant value (Fig. 3b). Such a saturation behaviour
COOH is not involved in the rate-determining step
3
COOH to
2
O/MeCNꢀmixedꢀsolutionꢀ(1:1ꢀv/v)ꢀatꢀ298ꢀK.ꢀ(b)ꢀTimeꢀprofilesꢀofꢀabsorbanceꢀ
+
3
] ꢀ inꢀ theꢀ presenceꢀ ofꢀ variousꢀ concentrationsꢀ ofꢀ
Co (Ch)ꢀ (0ꢀ –ꢀ 20ꢀ µM)ꢀ inꢀ deaeratedꢀ H
O/MeCNꢀ mixedꢀ solutionsꢀ (1:1ꢀ v/v)ꢀ containingꢀ indicates that CH
ꢀ(0.80ꢀM),ꢀAscHNaꢀ(0.30ꢀM).ꢀ
II
2
3
II
2+
I
–
[
Ru (bpy)
3
]
ꢀ(80ꢀµM),ꢀAscH
2
and that the reaction of [Co (Ch)] with CH COOH proceeds via
3
III
–
formation of the hydride complex ([Co (H)(Ch)(CH
3
COO)] ),
III
2
Nanosecond transient absorption spectra of an H O/MeCN followed by the rate-determining heterolytic cleavage of the Co -H
solution of [Ru(bpy)
2
+
–
3
]
2
with AscH and AscH are shown in Fig. 2, bond. The subsequent reaction of the released hydride ion with
III
+
where appearance of the absorption band at 500 nm due to CH COOH to produce H and [Co (Ch)] may be fast as compared
Ru(bpy) ] is observed upon the nanosecond laser excitation. Thus, with the back reaction of the Co –H bond cleavage (Scheme 1). The
electron transfer from AscH to [Ru(bpy)
3
2
+
III
[
3
– 2+*
III
+
3
]
occurred to produce kinetic equation for the formation of [Co (Ch)] is given by eqn (1),
•
+
AscH and [Ru(bpy)
3
] . The rate constant of electron transfer from
–
2+*
8
–1 –1
III
+
III
–
AscH to [Ru(bpy)
3
]
(ket) was determined to be 8.0 × 10 M
s
d[[Co (Ch)] ]/dt = k[[Co (H)(Ch)(CH COO)] ]
(1)
3
2
–1
from a slope of Stern-Volmer plot (KSV = 3.5 × 10 M ) and the
2
+*
lifetime of [Ru(bpy)
3
]
(0.44 µs in water/MeCN 1:1 v/v) (Fig. S5 where k is the rate constant of the hydrogen evolution. From the
2
3
in ESI†). The decay rate of absorbance at 500 nm due to equilibrium constant (K), the concentration of a complex between
Ru(bpy)
+
I
–
I
–
[
3
]
obeyed the second-order kinetics of bimolecular back [Co (Ch)] and CH COOH is given by eqn (2), where [[Co (Ch)] ]
3
0
+
•
electron transfer from [Ru(bpy)
3
]
to AscH . In the presence of
II
+
3
Co (Ch), the decay of absorbance at 500 nm due to [Ru(bpy) ]
+
became much faster because of electron transfer from [Ru(bpy)
3
] to
CoI(Ch)]– + CH COOH
3
[
II
Co (Ch) as shown in Fig. 2b. The decay rate constant linearly
II
N
N
N
N
K
increased with increasing the concentration of [Co (Ch)] (Fig. S6 in
Co
+
ESI†). The rate constant of electron transfer from [Ru(bpy)
3
] to
[Co (Ch)(H)(CH3COO)]–
III
II
9
–1 –1
Co (Ch) was determined to be 2.5 × 10 M
s
from the slope of
CH COOH
3
k
dependence of the first-order decay rate constant on concentration of
O
H–
H2 + CH COO
–
II
3
Co (Ch) (Fig. S6b in ESI†).
O
OMe
fast
I
–
To examine the reaction of [Co (Ch)] that is produced by
[CoIII(Ch)]+ + CH COO–
3
Co(Ch)
+
II
I
–
electron transfer from [Ru(bpy)
3
]
to Co (Ch), [Co (Ch)] was
I
–
Scheme 1 Mechanism of hydrogen formation by the reaction of [Co (Ch)]
II
prepared by the one-electron reduction of Co (Ch) by
with CH COOH.
3
*
2
decamethylcobaltocene [Co(Cp ) ] in MeCN (Fig. S7 in ESI†). The
I
–
UV-vis absorption band of [Co (Ch)] (red line in Fig. 3a; λmax =
2
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III
–
[
=
[Co (H)(Ch)(CH
K[CH
3
COO)] ]
The photocatalytic cycle is summarized in Scheme 2.
I
–
III
+
2+
3
COOH]([[Co (Ch)] ]
0
– [[Co (Ch)] ])/(1 + K[CH
3
COOH]) Photoexcitation of [Ru(bpy)
3
]
resulted in electron transfer from
–
2+*
+
View Article Online
DOI: 10.103 9I /C5C C– 05064B
(
2)
AscH to [Ru(bpy)
transfer from [Ru(bpy)
reacts with AscH to produce [Co (H)(Ch)(AscH)] . Hydrogen is
generated by the reaction of [Co (H)(Ch)(AscH)] with AscH
3
]
to produce [Ru(bpy)
3
] , followed by electron
+
II
3
] to Co (Ch) to produce [Co (Ch)] , which
III
–
is the initial concentration. Equation (1) is rewritten by eqn (3).
2
III
–
2
via
which is
III
+
I
–
III
+
III
+ 28,29
d[[Co (Ch)] ]/dt = kK[CH
3
COOH]([[Co (Ch)] ]
COOH])
0
– [[Co (Ch)] ])
(3)
the Co-H bond heterolysis to produce [Co (Ch)] ,
–
II
/
(1 + K[CH
3
reduced by AscH to regenerate Co (Ch). In such a case, a one-
photon two-electron process is made possible, because one photon is
I
–
3 2
Under the conditions, the concentration of CH COOH is much required to produce [Co (Ch)] for H evolution and another electron
I
–
–
higher than that of [Co (Ch)] , the kobs value is given by eqn (4). To is provided thermally by AscH .
determine the k value, eqn (4) is rewritten by eqn (5), which predicts
AscH
2
[CoIII(Ch)(H)] + AscH–
AscH–
[Ru(bpy)
3
]2+*
[Co
I
(Ch)]
–
k
k
obs = kK[CH
3
COOH]/(1 + K[CH
3
COOH])
(4)
(5)
AscH
2
–
1
–1
hν
obs = 1/kK･[CH
3
COOH] + 1/k
H–
]2+
AscH
2
[Ru(bpy)
3
–
1
–1
a linear correlation between kobs and [CH
3
COOH] (Fig. S9 in ESI
H
2
+ AscH–
†
). The k and K values were determined from the intercept and
–
1
–1
–1
slope of the linear plot of kobs vs. [CH
3
COOH] to be 5.9 s and
]+
AscH•
[Ru(bpy)
II
[CoIII(Ch)]+ + AscH–
3
Co (Ch)
–
1
7
.1 M .
AscH– = Ascorbate anion
AscH•
When CH
3
COOH was replaced by CH COOD, the deuterium
3
2
6
–
kinetic isotope effect (KIE) was observed (Fig. S10 in ESI†),
Scheme 2 Mechanism of photocatalytic hydrogen evolution from AscH
2
+
II
indicating that the cleavage of the Co-H bond of and AscH with [Ru(bpy) ] and Co (Ch).
[
2
3
III
–
Co (H)(Ch)(CH
the rate-determining step of the reaction of [Co (Ch)] with
CH COOH. Because CH COOH is not involved in the rate- photocatalytic H evolution from ascorbic acid with [Ru(bpy) ] as
3 3
COO)] or O-H bond of CH COOH is involved in
I
–
II
In conclusion, Co (Ch) acts as an efficient catalyst for
2
+
3
3
2
3
determining step (vide infra), the cleavage of the Co-H bond of a photocatalyst to attain the high quantum yield via a one-photon
III
–
[
Co (H)(Ch)(CH
3
COO)] is the rate-determining step of the two-electron process in which the second electron is provided
–
reaction of [CoI(Ch)] with CH
3
COOH. The KIE value was 1.7 thermally from ascorbic acid.
which is virtually the same as observed for the photocatalytic H
evolution (KIE = 1.8, Fig. 1), indicating that the heterolytic Co-H This work was supported by Grants-in-Aid (nos. 26620154 and
2
III
–
bond cleavage of [Co (H)(Ch)(CH
determining step in the photocatalytic H
3
COO)] is also the rate- 26288037 to K.O.) and JSPS fellowship (No. 25•727 to K.M.) from
evolution.
the Ministry of Education, Culture, Sports, Science and Technology
2
III
+
III
[
Co (Ch)] produced by the reaction of [Co (H)(Ch)- (MEXT); ALCA and SENTAN projects from JST, Japan (to S.F.). ꢀ
–
–
(
CH
II
3
COO)] with CH
3
COOH is reduced by AscH to produce
.27
Co (Ch) as shown by stopped-flow measurements in Fig. 4 The
Notes and references
Department of Material and Life Science, Graduate School of
–
III
+
a
rate constant of electron transfer from AscH to [Co (Ch)] that was
II
prepared by the one-electron oxidation of Co (Ch) with (p- Engineering, Osaka University, ALCA and SENTAN, Japan Science
•
+
–
3
BrC
M
6
H
4
)
3
N SbCl
6
in H
2
O/MeCN was determined to be 1.5 × 10
and Technology Agency (JST), Suita, Osaka 565-0871, Japan. E-
mail: fukuzumi@chem.eng.osaka-u.ac.jp; Fax: +81-6-6879-7370
–
1 –1
s from the linear dependence of the first-order rate constant on
–
b
concentration of AscH (Fig. S11 in ESI†).
Department of Chemistry and Nano Science, Ewha Womans
University, Seoul 120-750, Korea.
c
(
a)
(b) 0.24
0
0
0
.6
.4
.2
0
Faculty of Science and Technology, Meijo University, ALCA and
7
0 ms
[AscHNa] =
5.0 mM
SENTAN, Japan Science and Technology Agency (JST), Nagoya,
Aichi 468-8502, Japan
118 ms
1
0 mM
6
52 nm
25 mM
50 mM
0.20
CoIII(Ch)]+
†
Electronic Supplementary Information (ESI) available:
[
Experimental details and cyclic voltammograms (Fig. S1), time
6
40 nm
II
courses of H evolution (Fig. S2), Photoluminescence spectra (Fig.
Co (Ch)
2
0.16
S3), UV-vis absorption spectra (Fig. S4) and kinetic data (Figs. S5 –
S11). See DOI: 10.1039/c000000x/
0.12
3
00
400
500
600
700
0
100
200
300
1
2
R. A. Kerr and R. F. Service, Science, 2005, 309, 101.
X. Song, H. Wen, C. Ma, H. Chen and C. Chen, New J. Chem.,
2015, 39, 1734.
Wavelength, nm
Time, ms
Fig.ꢀ 4ꢀ (a) UV-visꢀ absorptionꢀ spectralꢀ changesꢀ inꢀ theꢀ electron-transferꢀ reductionꢀ ofꢀ
III
+
[
Co (Ch)] ꢀ(15ꢀµM)ꢀwithꢀAscHNaꢀ(50ꢀmM)ꢀinꢀair-saturatedꢀH
2
O/MeCNꢀmixedꢀsolutionsꢀ
3
4
K. Kawano, K. Yamauchi and K. Sakai, Chem. Commun., 2014,
50, 9872.
X. Wang, S. Goeb, Z. Ji, N. A. Pogulaichenko and F. N.
Castellano, Inorg. Chem., 2011, 50, 705.
(
1:1ꢀv/v)ꢀatꢀ298ꢀKꢀtakenꢀatꢀ70ꢀmsꢀandꢀ118ꢀmsꢀafterꢀmixing. (b)ꢀDecayꢀtimeꢀprofilesꢀofꢀ
III
+
absorbanceꢀatꢀ652ꢀnmꢀdueꢀtoꢀ[Co (Ch)] ꢀinꢀtheꢀpresenceꢀofꢀvariousꢀconcentrationsꢀofꢀ
AscHNaꢀinꢀair-saturatedꢀH O/MeCNꢀmixedꢀsolutionsꢀ(1:1ꢀv/v)ꢀatꢀ298ꢀK.ꢀ
2
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L.-Z. Fu, L.-L. Zhou, L.-Z. Tang, Y.-X. Xhang and S.-Z. Zhan, J.
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S. Fukuzumi, Curr. Opin. Chem. Biol., 2015, 25, 18
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1 The photocatalytic H evolution in our optimized conditions, the
absorption at λ = 450 nm of [Ru(bpy) ] (2.0 mM, ε450nm = 1.4 ×
2
2
2
2+
3
4
–1
–1
II
1
0 M cm ) is not significantly blocked by that of Co (Ch)
4
–1
–1
(
Abs450 nm = 0.38; ε450 nm = 1.8 × 10
M
cm ) under this
experimental conditions.
2
2
2 C. V. Krishnan and N. Sutin, J. Am. Chem. Soc., 1981, 103, 2141.
2
+*
3 The emission lifetime of [Ru(bpy)
3
]
in water at 298 K was
reported to be 0.58 µs; see: J. V. Houten and R. J. Watts, J. Am.
Chem. Soc., 1976, 98, 4853.
III
+
I
–
2
2
4 The spectrum of [Co (Ch)] obtained by the reaction [Co (Ch)]
III
+
with CH
3
COOH was identical to that of [Co (Ch)] prepared by
the electron-transfer oxidation of Co (Ch) by a one-electron
oxidizing reagent of (p-BrC
II
•
+
–
6
H
4
)
3
N SbCl
6
(Ered = 1.05 V vs.
1
9
SCE).
III
+
III
5
[Co (Ch)] or [Co (H)(Ch)] species is not re-reduced by large
excess of Co(Cp*) , under the present reaction conditions
because Co (Ch) with 20 molar equiv. of Co(Cp*) is necessary
to quantitatively produce [Co (Ch)] as shown in ESI Fig. S7.
2
II
2
I
–
+
/0
Co(Cp*)
carefully degassed and dehydrated MeCN.
6 The KIE value was determined from the kobs values at
CH COOH] = [CH COOD] = 1.0 M.
2
(E 1/2 = –1.47 V vs. SCE) is unstable even in
2
2
2
2
[
3
3
III
+
7 Neither oxidation of [Co (Ch)] nor O
under the basic reaction conditions.
8 S. Mandal, S. Shikano, Y. Yamada, Y.-M. Lee, W. Nam, A.
Llobet and S. Fukuzumi, J. Am. Chem. Soc., 2013, 135, 15294.
9 No Co(II)-H complex is involved in the heterolysis of the Co-H
bond as reported in ref. 28.
2
reduction was observed
4
ꢀ|ꢀJ.ꢀName.,ꢀ2012,ꢀ00,ꢀ1-3ꢀ
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TOC
View Article Online
DOI: 10.1039/C5CC05064B
Photocatalytic H Evolutionꢀ
2
hνꢀ
N
N
Co
N
N
N
N
N
N
N
RuII
N
O
O
OMe
One-Photon Two-Electron Process ꢀ
Text for TOC
A one-photon two-electron process was made possible in
2
photocatalytic H evolution from ascorbic acid with a cobalt(II)
chlorin complex via electron transfer.
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