Photocatalytic Conversion of CO2 to CO by a Copper(II) Quaterpyridine Complex

Article abstract of DOI:10.1002/cssc.201701354

The invention of efficient systems for the photocatalytic reduction of CO₂ comprising earth-abundant metal catalysts is a promising approach for the production of solar fuels. One bottleneck is to design highly selective and robust molecular complexes that are able to transform the CO₂ gas. The Cu^II quaterpyridine complex [Cu(qpy)]²⁺ (1) is found to be a highly efficient and selective catalyst for visible-light driven CO₂ reduction in CH₃CN using [Ru(bpy)₃]²⁺ (bpy: bipyridine) as photosensitizer and BIH/TEOA (1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole/triethanolamine) as sacrificial reductant. The photocatalytic reaction is greatly enhanced by the presence of H₂O (1–4 % v/v), and a turnover number of >12 400 for CO production can be achieved with 97 % selectivity, which is among the highest of molecular 3d CO₂ reduction catalysts. Results from Hg poisoning and dynamic light scattering experiments suggest that this photocatalyst is homogenous. To the best of our knowledge, 1 is the first example of molecular Cu-based catalyst for the photoreduction of CO₂.

Full text of DOI:10.1002/cssc.201701354

Accepted Article
Title: Photocatalytic CO2-to-CO Conversion by a Copper(II)
Quaterpyridine Complex
Authors: Marc Robert, Zhenguo Guo, Fei Yu, Ying Yang, Chi-Fai
Leung, Siu-Mui Ng, Chiu-Chiu Ko, Claudio Cometto, and Tai-
Chu Lau
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10.1002/cssc.201701354
ChemSusChem
COMMUNICATION
Photocatalytic CO2-to-CO Conversion by a Copper(II)
Quaterpyridine Complex
Zhenguo Guo,[b]† Fei Yu,[a]† Ying Yang,[a] Chi-Fai Leung,*[a] Siu-Mui Ng,[b] Chi-Chiu Ko,[b] Claudio
Cometto,[c] Tai-Chu Lau*[b] and Marc Robert*[c]
Abstract: The invention of efficient systems for the photocatalytic
reduction of CO2 comprising earth-abundant metal catalysts is a
promising approach for the production of solar fuels. One bottleneck
is to design highly selective and robust molecular complexes able to
transform the gas. The Cu(II) quaterpyridine complex [Cu(qpy)]2+ (1)
is found to be a highly efficient and selective catalyst for visible-light
driven CO2 reduction in CH3CN using [Ru(bpy)3]2+ as photosensitizer,
BIH/TEOA as sacrificial reductant. The photocatalytic reaction is
greatly enhanced by the presence of H2O (1–4% v/v), and a TON of
>12,400 for CO production can be achieved with 97% selectivity,
which is among the highest of molecular 3d CO2 reduction catalysts.
Results from Hg-poisoning and dynamic light scattering (DLS)
experiments suggest that this photocatalysis is homogenous. To the
best of our knowledge 1 is the first example of molecular Cu-based
catalyst for the photoreduction of CO2.
[Cu(qpy)]2+ (1) of the planar tetradentate ligand 2,2':6',2":6",2"'-
quaterpyridine (qpy) is a highly efficient catalyst for visible-light
driven reduction of CO2 to CO using [Ru(bpy)3]2+ (RuPS) as
photosensitizer. To the best of our knowledge, [Cu(qpy)]2+ is
also the first example of molecular copper catalyst for the
photocatalytic reduction of CO2.
In recent years, tremendous efforts have been devoted by
chemists to convert solar energy into storable chemical forms.[1-
Regarding molecular based catalytic systems, 3d complexes
Scheme 1. Structure of the catalyst 1, photosensitizer (RuPS) and sacrificial
reductant (BIH).
7]
have been widely studied as viable catalysts for solar fuel
production by the splitting of water and the reduction of carbon
dioxide. A number of carbon dioxide reduction catalysts based
on Mn, Fe, Co and Ni have been reported.[8-32] On the other
hand, there are only very few reports on the use of molecular
copper complexes for the electrocatalytic reduction of CO2,[33-35]
although electrocatalytic, and more recently also photocatalytic,
CO2 reduction by Cu heterogeneous materials have been well
documented.[36-40] One example is given by the one electron
The structure of [Cu(qpy)](NO3)22H2O has been previously
reported to consist [Cu(qpy)(OH2)(NO3)]+ cation with a distorted
tetragonal pyramidal geometry, which bears an axial H2O ligand
-
(Cu–O = 2.286(3) Å) and a weakly bound NO3 (Cu–O =
2.695(3) Å).[41] We have also determined the X-ray crystal
structure of [Cu(qpy)](ClO4)2, which has a distorted square
-
planar structure with two weakly bound ClO4 ions (Cu–O =
2.518(2) Å and 2.470(2) Å) in the axial positions and a bent O–
Cu–O angle (169.86(9)) (Figure S1, Tables S1 and S2).
catalytic CO2-to-oxalate conversion with
a dinuclear Cu
complex,[33] and a second one involved the use of a Cu
porphyrin deposited on graphite electrode to produce CO along
with small amounts of methane and ethane[35], although in that
case demetalation of the catalyst and further formation of Cu
particles, which are, as noted above, highly active towards CO2
reduction. We report herein that the copper(II) complex
Photocatalytic CO2 reduction by 1 was investigated in CH3CN
(MeCN) by using [Ru(bpy)3]2+ (RuPS) as photosensitizer and
BIH/TEOA as sacrificial reductant (Scheme 1). BIH is an efficient
reductive quencher for the excited state of RuPS, while TEOA
(triethanolamine) mainly functions as proton acceptor of
BIH+•.[42,43] As shown in Figure 1 and in Table 1 (entry 4), CO is
produced upon visible light irradiation ( > 420 nm). The amount
of CO increases with irradiation time and then levels off after 3.5
h, with a turnover number (TON) of 2425. H2 is also produced
with a TON of 620, while only a trace amount of formate could
be detected (TON = 8). Hence the selectivity for CO production
is 80%. In the absence of BIH (Table 1, entry 6), the TON for CO
is much lower (210), while that of H2 is not much affected (590),
and there is a slightly larger amount of formate (TON 66). No
CO was detected in the absence of TEOA. Replacing TEOA with
triethylamine (TEA) resulted in immediate formation of a white
precipitate, probably BI+, and CO was not produced. On the
other hand, if 1 was omitted (Table 1, entry 1), essentially no CO
or H2 could be detected within the same irradiation time. When 1
was replaced by a simple Cu2+ salt such as Cu(ClO4)2 (Table 1,
entry 8), no CO or formate was detected, and only H2 was
produced (TON = 141). This result indicates that catalytic CO
production is not due to Cu2+ ion that may arise from
demetalation of 1. Since Cu nanoparticles are known to be CO2
photoreduction catalysts,[36] catalysis was also performed in the
[a]
[b]
Dr. C.-F. Leung
Department of Science and Environmental Studies
The Education University of Hong Kong
10 Lo Ping Road, Tai Po, Hong Kong, China
E-mail: cfleung@eduhk.hk
Prof. Dr. T.-C. Lau
Institute of Molecular Functional Materials and Department of
Biology and Chemistry
City University of Hong Kong
Tat Chee Avenue, Kowloon Tong, Hong Kong, China
E-mail: bhtclau@cityu.edu.hk
[c]
Prof. Dr. M. Robert
Université Paris Diderot, Sorbonne Paris Cité, Laboratoire
ďElectrochimie Moléculaire, Unité Mixte de Recherche Université–
CNRS no. 7591, Bâtiment Lavoisier, 15 rue Jean de Baïf, 75025
Paris Cedex 13, France.
E-mail: robert@univ-paris-diderot.fr
†
These two authors contributed equally to this work
Supporting information for this article is given via a link at the end of
the document.
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10.1002/cssc.201701354
ChemSusChem
COMMUNICATION
presence of mercury, which may form inactive amalgam with
any Cu(0) present. The yield of CO was found to be decreased
by around 10% (Figure 1 and Table 1). Dynamic light scattering
experiments did not reveal the formation of any particles during
photocatalysis (Figure S4). We conclude from all these results
that photocatalytic reduction of CO2 by this system is
predominately homogeneous.
As shown in Figure 2 and Table 1 (entries 2-4, 9), both the rate
and CO yield increase with catalyst concentration. The initial
rate shows a linear correlation with [1] (Figure S5), suggesting
that the rate-limiting step for CO2 reduction involves a single Cu
site. The photolysis was also investigated using 13C-labelled CO2
and 13CO was detected by GC-MS (Figure S6), indicating the
CO produced originates from the reduction of CO2.
Figure 3. Time trace of CO evolution during irradiation of
1
μM)/RuPS (2 mM)/BIH (0.1 M)/TEOA (15% v/v) in CO2-saturated MeCN
containing various concentrations of H2O (1 – 10 % v/v).
(1.0
The production of CO was found to be greatly enhanced by the
presence of a few % (v/v) of water (Figure 3 and Table S3). Both
the yield and rate for CO generation increased when H2O was
added (1-4%). At 1 M of 1, an optimum CO yield of 31.2 μmol
(TON = 12,400) was observed with 3% H2O after 3 h of
irradiation, and the yield of H2 has also increased similarly by
approx. four folds (1.0 μmol, TON = 410, Table S3) as compared
to dry MeCN, leading to a selectivity of 97% for CO production.
No CO was detected in the absence of 1, but some CO (TON =
664) was obtained with 3% H2O in the absence of TEOA.
Further increase in the amount of water added resulted in lower
CO production; the CO TON became 850 when 10% H2O was
added. On the other hand, the yield of H2 increased steadily with
[H2O], and at 10% H2O the yield is over 10 times higher than
without adding H2O. However, similar H2 yields were also
obtained in control experiments without 1 (Table S3). Thus, the
suppressed CO production at [H2O] > 4% may be partly due to
competitive H2 generation by RuPS. As discussed and analyzed
in details elsewhere,[44,45] adding a weak acid like e.g. H2O could
boost the CO2 binding step to the metal center by providing
thermodynamic stabilization of the intermediate through H-bonds
and/or protonation. It may also favor the cleavage of the C-O
bond leading to the release of CO and a water molecule.
However, when the concentration (or the strength) of the added
acid increases, competition for H2 evolution may occur, leading
to an optimized concentration for CO2 selective reduction.
Similar enhancement of photocatalytic CO2-to-CO conversion by
weak acid has been reported in several cases.[44-46] The
photocatalysis in the presence of H2O was also found to be
homogeneous, as indicated by Hg0 poisoning and DLS results
(Figure S7 and S8). The quantum yield (CO) for CO production
in optimized conditions (3% water) has been determined to be
1.2% by ferrioxalate actinometry (λ = 460 nm). The quenching
rate constant (kq) of the ruthenium excited state RuPS* by 1 was
found to be 2.15 ×108 M-1 s-1 by Stern-Volmer plot (Figure S9),
which is much lower than that by BIH (4.0 x 109 M-1 s-1 ).[19] Since
in addition BIH is more than 10 times more concentrated than 1
(see Table 1), reductive quenching of RuPS* by BIH should
Figure 1. Plot of CO amount and TON versus time during irradiation of a) 1 (5
μM)/RuPS (2 mM)/TEOA (15% v/v)/BIH (0.1 M) in CO2-saturated MeCN, b)
0.1 mL Hg added, c) no BIH added and d) Cu(ClO4)2 (5 µM) used as catalyst
instead of 1.
Figure 2. Time trace of CO evolution during irradiation of 1/RuPS (2
mM)/BIH(0.1 M)/TEOA (15% v/v) in CO2-saturated MeCN at various [1] (1.0 –
7.5 μM).
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10.1002/cssc.201701354
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COMMUNICATION
Table 1. Table Caption. Yields of H2, CO and HCOOH under various photocatalytic conditions in acetonitrile using RuPS (2 mM), BIH (0.1M) and 15% TEOA
(v/v). Irradiation time = 3.5 h (white light, λ > 420 nm). TONs obtained in the presence of catalyst are listed without background correction.
[Cu(qpy)2+]/ μM
H2
CO
HCOOH
Yield/μmol
0.3
TON
----
Yield/μmol
TON
----
Yield/μmol
TON
0
1
0
1
0
7.4
23.3
30.3
0
0
0
2
0.2
93
2939
3730
2425
0
0
3
2.5
5
3.0
490
623
14
0
0
4
7.8
0.1
0
8
5 [a]
6 [b]
7 [c]
8 [d]
9
5
0.18
7.4
0
5
592
35
2.6
29
210
2317
0
0.83
0
66
0
5
0.44
1.76
15.3
5
141
814
0
0
0
7.5
29.7
1582
0
0
[a] under Ar. [b] no BIH. [c] with 0.1 mL Hg0. [d] 1 replaced by 5 μM Cu(ClO4)2.
predominate and be the first step of the process. To explore the
reason for catalysis leveling off, fresh reagents were added in
different combinations after 120 min irradiation so as to identify
following a second reduction, see Figures S2 and S3). The
dimer is further reoxidised at +0.41 V vs. SCE on the oxidative
scan (Figure 4A). Upon adding 0.05 M BIH, the reduction wave
of the CuII species disappears (Figure 4B). These results
indicate that the CuII initial species ([Cu(qpy)]2+) is reduced to a
CuI species by BIH before irradiation, probably [Cu2(qpy)2]2+.
Note that redox induced formation of binuclear CuI complexes
with functionalized quaterpyridine have been reported.[47] We
thus propose that under photocatalytic conditions the dimeric
species formed upon spontaneous reduction by BIH is further
reduced to Cu0(qpy) or CuI(qpy-), which is the active species for
CO2 reduction.
the
limiting
reagents
(Figure
S14).
Addition
of
RuPS/BIH/TEOA/H2O produced essentially no CO during the
second photocatalysis experiment, pointing to decomposition of
1 into an inactive species. When 1 alone was added, only a
small amount of CO was produced (TON = 116) during the
second photocycle, showing that other components have been
depleted. Addition of 1/RuPS/TEAO together with H2O or BIH
resulted in a TON of CO <50% as compared to the first
photocycle. When 1/BIH/H2O were added together with RuPS or
TEOA more than 80% (TON > 2,200) of the original catalytic
activity was restored. All together, these results indicate that the
main limiting factor of the photocatalysis is related to the
deactivation of 1, as well as to the consumption of both BIH and
H2O.
To confirm these conclusions, the [CuI2(qpy)2]2+ dimer was
synthesized (see Experimental Section and Supporting
Information for details) and its photocatalytic activity was
investigated in acetonitrile with 3% H2O. CO was produced and
then leveled off after 3.5 h of irradiation, similarly to what has
been observed for 1. The amount of CO produced (TON =
23,000 vs [CuI2(qpy)2]2+ or 11,500 per Cu center) is twice that
obtained using the same mole amount of 1 (Figure S15), in
accordance with the initial conversion of [Cu(qpy)]2+ to
[Cu2(qpy)2]2+, the latter complex being further reduced to the
active catalyst species. Remarkably, 1 appears as one of the
most efficient molecular CO2-to-CO photocatalyst. Catalysts
based on earth abundant metals have been carefully reviewed
recently[7,32] and mainly include cyclams, polypyridines and their
derivatives (Ni, Co, Fe), porphyrins (Co, Fe) as well as carbonyl
complexes (Mn, Fe). From these data (see Table 2 in Ref. 7 and
Table S1 in Ref. 32) it appears that 1 is one of the most efficient
catalysts reported to date in terms of both selectivity for CO
formation (97%) and turnover number (12,400).
Electrospray ionization mass spectrometry (ESI/MS) of a blue
solution of 1 in CH3CN exhibits peaks at m/z 187 and 207 in the
mass spectrum, which are assigned to [Cu(qpy)]2+ and
[Cu(qpy)(CH3CN)]2+, respectively (Figure S10). Upon addition of
excess of BIH to 1, these peaks disappeared and new peaks at
m/z 223 and 373 appeared (Figure S11), which are assigned to
BI+ and [Cu2(qpy)2]2+, respectively. The UV/Vis spectrum of the
solution containing 1 and BIH also shows the presence of a new
species with max at 432 and 545 nm (Figure S12), which is
identical to that obtained upon direct one-electron
electrochemical reduction of 1 (Figure S13). That [Cu(qpy)]2+ is
spontaneously reduced by BIH is also confirmed by the
observation of its first electrochemical reduction (Figure 4).
Without added BIH, the CuII species is reduced at +0.1 V vs.
SCE and then dimerizes (note that the CO2 reduction occurs at
more negative potentials (onset potential at ca. -1.4 V vs. SCE)
In conclusion, [Cu(qpy)]2+ is a very efficient homogeneous
catalyst for the photocatalytic reduction of CO2 to CO in CH3CN
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10.1002/cssc.201701354
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COMMUNICATION
using Ru(bpy)32+/BIH/TEOA. The yield of CO is significantly
enhanced by the addition of 1-4 % water, and a TON of 12,400
can be achieved. To the best of our knowledge, 1 is the first
example of Cu molecular catalyst for CO2 photoreduction,
showing that molecular species including copper as metal and a
simple, easily synthesized ligand could serve as competent,
selective catalysts for CO2 catalytic reduction. Finally, 1 gives
top catalytic performance among molecular 3d metal catalysts
reported so far.
18300715), the Hong Kong University Grants Committee Area of
Excellence Scheme (AoE/P-03-08) and the Education University
of Hong Kong (RG95/2015-2016). PhD fellowship to C. C. from
Université Sorbonne Paris Cité (USPC) is gratefully
acknowledged. We thank Dr. Shek-Man Yiu for collecting the
crystal data.
Keywords: Photocatalysis • carbon dioxide reduction• transition
metals • homogeneous catalysis • copper catalyst
A
10
[1]
N. S. Lewis, D. G. Nocera, Proc. Natl. Acad. Sci. U. S. A. 2006, 103,
15729-15735.
5
0
[2]
[3]
P. Du, R. Eisenberg, Energy Environ. Sci. 2012, 5, 6012-6021.
M. Rakowski Dubois, D. L. Dubois, Acc. Chem. Res. 2009, 42, 1974-
1982.
-5
Under Ar
-10
-15
[4]
E. E. Benson, C. P. Kubiak, A. J. Sathrum, J. M. Smieja, Chem. Soc.
Rev. 2009, 38, 89-99.
[5]
[6]
H. Takeda, O. Ishitani, Coord. Chem. Rev. 2010, 254, 346-354.
J. Schneider, H. Jia, J. T. Muckerman, E. Fujita, Chem. Soc. Rev. 2012,
41, 2036-2051.
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
Potential (vs SCE) / V
[7]
H. Takeda, C. Cometto, O. Ishitani, M. Robert, ACS Catal. 2017, 7, 70-
88.
10
5
B
[8]
[9]
B. J. Fisher, R. Eisenberg, J. Am. Chem. Soc. 1980, 102, 7361-7363.
J.-M. Lehn, R. Ziessel, Proc. Natl. Acad. Sci. U. S. A. 1982, 79, 701-
704.
0
[10] S. Matsuoka, K. Yamamoto, T. Ogata, M. Kusaba, N. Nakashima, E.
Fujita, S. Yanagida, J. Am. Chem. Soc. 1993, 115, 601-609.
[11] T. Ogata, S. Yanagida, B. S. Brunschwig, E. Fujita, J. Am. Chem. Soc.
1995, 117, 6708-6716.
-5
-10
-15
Under Ar
Under Ar, + BIH 0.05 M
[12] T. Dhanasekaran, J. Grodkowski, P. Neta, P. Hambright, E. Fujita, J.
Phys. Chem. A 1999, 103, 7742-7748.
-0.4
-0.2
0.0
0.2
[13] J. Grodkowski, P. Neta, E. Fujita, A. Mahammed, L. Simkhovich, Z.
Gross, J. Phys. Chem. A 2002, 106, 4772-4778.
Potential (vs SCE) / V
[14] A. J. Morris, G. J. Meyer, E. Fujita, Acc. Chem. Res. 2009, 42, 1983-
1994.
Figure 4. CVs of the first reduction (CuII to CuI species) wave of 1 (1mM) in
Ar-saturated ACN solution + 0.1M nBu4NPF6 (A) and after addition of 0.05 M
BIH (B, red trace).
[15] S. Wang, W. Yao, J. Lin, Z. Ding, X. Wang, Angew. Chem. Int. Ed.
2014, 53, 1034-1038.
[16] A. Chapovetsky, T. H. Do, R. Haiges, M. K. Takase, S. C. Marinescu, J.
Am. Chem. Soc. 2016, 138, 5765-5768.
Experimental Section
[17] S. Roy, B. Sharma, J. Pécaut, P. Simon, M. Fontecave, P. D. Tran, E.
Derat, V. Artero, J. Am. Chem. Soc. 2017, 139, 3685-3696.
[18] L. Chen, Z. Guo, X. G. Wei, C. Gallenkamp, J. Bonin, E. Anxolabéhère-
Mallart, K. C Lau, T. C. Lau, M. Robert, J. Am. Chem. Soc. 2015, 137,
10918-10921.
Synthesis and materials: The ligand 2,2:6,2:6,2-quaterpyridine
(qpy) was prepared by a literature method.[48] BIH was synthesized using
a reported procedure.[49] [CuII(qpy)](ClO4)2 was prepared by the addition
of a chloroform (8 mL) solution of qpy (84 mg, 0.27 mmol) to a stirring
solution of Cu(ClO4)26H2O (100 mg, 0.27 mmol) in methanol (10 mL).
The mixture was stirred for 2 h at room temperature and the resulting
pale blue solid was filtered, washed with methanol and chloroform, and
then dried under vacuo. [CuI2(qpy)2](ClO4) was prepared similarly by
adding a chloroform (8 mL) solution of qpy (61 mg, 0.20 mmol) into a
stirring acetonitrile (10 mL) solution of [CuI(CH3CN)4]ClO4 (64 mg, 0.20
mmol) under an Ar atmosphere. The reddish brown solid formed after 1 h
was filtered, washed with chloroform and acetonitrile, and dried under
vacuum. All other chemicals were obtained commercially and used
without further purification unless otherwise stated. Detailed experimental
procedures can be found in the supporting information.
[19] Z. Guo, S. Cheng, C. Cometto, E. Anxolabéhère-Mallart, S. M. Ng, C. C.
Ko, G. Liu, L. Chen, M. Robert, T. C. Lau, J. Am. Chem. Soc. 2016, 138,
9413-9416.
[20] J. Bonin, M. Chaussemier, M. Robert, M. Routier, ChemCatChem 2014,
6, 3200-3207.
[21] J. Bonin, M. Robert, M. Routier, J. Am. Chem. Soc. 2014, 136, 16768-
16771.
[22] H. Takeda, K. Ohashi, A. Sekine, O. Ishitani, J. Am. Chem. Soc. 2016,
138, 4354-4357.
[23] P. G. Alsabeh, A. Rosas-Hernandez, E. Barsch, H. Junge, R. Ludwig,
M. Beller, Catal. Sci. Technol. 2016, 6, 3623-3630.
[24] V. S. Thoi, N. Kornienko, C. G. Margarit, P. Yang, C. J. Chang, J. Am.
Chem. Soc. 2013, 135, 14413-14424.
[25] J. D. Froehlich, C. P. Kubiak, J. Am. Chem. Soc. 2015, 137, 3565-3573.
[26] H. Takeda, H. Koizumi, K. Okamoto, O. Ishitani, Chem. Commun. 2014,
50, 1491-1493.
Acknowledgements
[27] E. Torralba-Peñalver, Y. Luo, J.-D. Compain, S. Chardon-Noblat, B.
Fabre, ACS Catal. 2015, 5, 6138-6147.
The work described in this project was supported by the Hong
Kong Research Grants Council (project number 28300014,
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10.1002/cssc.201701354
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COMMUNICATION
[28] H. Fei, M. D. Sampson, Y. Lee, C. P. Kubiak, S. M. Cohen, Inorg.
Chem. 2015, 54, 6821-6828.
[39] F. S. Roberts, K. P. Kuhl, A. Nilsson, Angew. Chem. Int. Ed. 2015, 54,
5179-5182.
[29] P. L. Cheung, C. W. Machan, A. Y. S. Malkhasian, J. Agarwal, C. P.
Kubiak, Inorg. Chem. 2016, 55, 3192-3198.
[40] Shown, H.-C. Hsu, Y.-C. Chang, C.-H. Lin, P. K. Roy, A. Ganguly, C. H.
Wang, J. K. Chang, C. I. Wu, L.-C. Chen, Nano Lett. 2014, 14, 6097-
6103.
[30] X. Zhang, Z. Wu, X Zhang, L. Li, Y. Li, H. Xu, X. Li, Xiaolu Yu, Z. Zhang,
Y. Liang, H. Wang, Nat. Commun. 2017, 8, 14675, DOI:
10.1038/ncomms14675.
[41] W. Henke, S. Kremer, D. Z. Reinen, Anorg. Allg. Chem. 1982, 491,
124-136.
[31] X.-M. Hu, M. H. Rønne, S. U. Pedersen, T. Skrydstrup, K. Daasbjerg,
Angew. Chem. Int. Ed. 2017, 56, 6468-6472.
[42] Y. Tamaki, K. Koike, T. Morimoto, O. Ishitani, J. Catal. 2013, 304, 22-
28.
[32] T. Ouyang, C. Hou, J.-W. Wang, W.-J. Liu, D.-C. Zhong, Z.-F. Ke, T.-B.
Lu, Inorg. Chem. 2017, 56, 7307-7311.
[43] Y. Tamaki, Y. Koike, O. Ishitani, Chem. Sci. 2015, 6, 7213-7221.
[44] C. Costentin, M. Robert, J.-M. Savéant, Acc. Chem. Res. 2015, 48,
2996-3006.
[33] R. Angamuthu, P. Byers, M. Lutz, A. L. Spek, E. Bouwman, Science
2010, 327, 313-315.
[45] C. Costentin, S. Drouet, G. Passard, M. Robert, J.-M. Savéant, J. Am.
Chem. Soc. 2013, 135, 9023-9031.
[34] R. J. Haines, R. E. Wittrig, C. P. Kubiak, Inorg. Chem. 1994, 33, 4723-
4728.
[46] T. Ouyang, H.-H. Huang, J.-W. Wang, D.-C. Zhong and T.-B, Lu,
Angew. Chem. Int. Ed., 2017, 56, 738-743.
[35] Z. Weng, J. Jiang, Y. Wu, Z. Wu, X. Guo, K. L. Materna, W. Liu, V. S.
Batista, G. W. Brudvig, H. Wang, J. Am. Chem. Soc. 2016, 138, 8076-
8079.
[47] T. Potts, M. Keshavarz-K, F. S. Tham, H. D. Abruῆa, C. R. Arana, Inorg.
Chem. 1993, 32, 4422-4435.
[36] Y. Hori, A. Murata, R. Takahashi, S. Suzuki, J. Chem. Soc. Chem.
Commun. 1988, 1, 17-19.
[48] E. C. Constable, S. M. Elder, M. J. Hannon, A. Martin, P. R. Raithby, D.
A. Tocher, J. Chem. Soc. Dalton Trans. 1996, 2423-2433.
[49] I.-S. H. Lee, E. H. Jeoung, M. M. Kreevoy, J. Am. Chem. Soc. 1997,
119, 2722-2728.
[37] Z. Chen, P. Kang, M.-T. Zhang, B. R. Stoner, T. J. Meyer, Energy
Environ. Sci. 2013, 6, 813-817.
[38] C. W. Li, M. W. Kanan, J. Am. Chem. Soc. 2012, 134, 7231-7234.
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10.1002/cssc.201701354
ChemSusChem
COMMUNICATION
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The photocatalytic reduction of CO2 to
CO by [Cu(qpy)]2+ is highly efficient
and selective. In MeCN solution in the
presence of Ru(bpy)32+, BIH and
TEOA and 3% H2O, a TON of 12,400
with 97% selectivity is obtained, which
is the highest among molecular 3d
metal catalysts reported so far.
Zhenguo Guo,[b]† Fei Yu,[a]† Ying Yang,[a]
Chi-Fai Leung,*[a] Siu-Mui Ng,[b] Chi-Chiu
Ko,[b] Claudio Cometto,[c] Tai-Chu Lau*[b]
and Marc Robert*[c]
Page No. – Page No.
Photocatalytic CO2-to-CO Conversion
by a Copper(II) Quaterpyridine
Complex
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