Lanthanide Ions Coupled with Photoinduced Electron Transfer Generate Strong Reduction Potentials from Visible Light

Article abstract of DOI:10.1002/chem.201701665

Metal ions can have beneficial effects on photoinduced electron transfer. Merging such metal-ion-coupled electron transfer (MCET) with consecutive photoinduced electron transfer (conPET) enables the one-electron reduction of chlorobenzene with blue light in the presence of diisopropylethylamine as an electron donor. The presence of the metal ions extends the substrate scope of the photoredox catalysis to extreme reduction potentials (beyond ?3 V vs. SCE).

Full text of DOI:10.1002/chem.201701665

A Journal of
Accepted Article
Title: Metal ion coupled consecutive photoinduced electron transfer
generates strong reduction potentials from visible light
Authors: Andreas Meyer, Tomas Slanina, Alexander Heckel, and
Burkhard König
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To be cited as: Chem. Eur. J. 10.1002/chem.201701665
Link to VoR: http://dx.doi.org/10.1002/chem.201701665
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COMMUNICATION
Metal ion coupled consecutive photoinduced electron transfer
generates strong reduction potentials from visible light
Andreas Uwe Meyer,[a] Tomáš Slanina,[b] Alexander Heckel,[b] and Burkhard König*[a]
Abstract: Metal ions can have beneficial effects on photoinduced
electron transfer. Merging such metal-ion coupled electron transfer
(MCET) with consecutive photoinduced electron transfer (conPET)
enables the one-electron reduction of chlorobenzene with blue light
in the presence of diisopropylethylamine as electron donor. The
presence of the metal ions extends the substrate scope of the
photoredox catalysis to extreme reduction potentials (beyond -3 V vs
SCE).
photoredox catalysis by consecutive photoinduced electron
transfer (conPET)[2] using the organic dye Rh6G (A) as
photocatalyst[3d] and N,N-diisopropylethylamine (DIPEA) as
sacrificial electron donor (Scheme 1c). Fukuzumi and Wolf have
described the beneficial effect of metal ion addition on the
photophysical properties of dyes for flavin photooxidations.[21]
The coordination of Lewis-acidic metal to the substrate or to the
reduced photocatalyst affects the rate of photoinduced electron
transfer.[22] Metal-induced electron transfer (MCET)[23] processes
were previously reported for acridine, pyrene and quinone
radical anions with scandium salts.[22, 24] We report here the first
example of metal ion coupled consecutive photoinduced
electron transfer (MCconPET), which allows the chemical
reduction of chlorobenzene by blue light.
Visible light photoredox catalysis has developed into a powerful
synthetic method in organic chemistry.[1] Besides redox active
metal complexes, organic dyes like PDI[2] and rhodamine 6G
(Rh6G)[3][4] are used, as they exhibit a strong reduction power
enabling photoinduced electron transfer to aryl bromides and
even aryl chlorides with electron withdrawing groups. However,
aryl chlorides with higher reduction potentials, such as chloro-
benzene (1a), chlorotoluene (1b) and chloroanisole (1c) are
beyond the scope of current visible light photoredox catalysis.
The reduction, however, would be of interest for
defunctionalization steps in synthesis[5] or the detoxification of
halogenated molecules in waste streams.[6] Reported methods
for the reduction of chlorobenzene (Ered = -3.11 V vs SCE in
MeCN, see ESI) use for example nickel(0)/N-heterocyclic
carbene/alkoxide (Scheme 1a)[7] at elevated temperatures or the
electrochemical dechlorination with naphthalene as mediator
(Scheme 1b).[8] Also some lanthanide(II) iodides are strong
enough to reduce aryl chlorides, but stoichiometric amounts are
required. The most important one-electron transfer reagent is
samarium diiodide (SmI2).[9] First introduced in 1977 by Henri
Kagan,[10] it has been used for many transformations,[11]
including the selective reductions of halides.[12] The reduction
potential of samarium diiodide (Ered = -1.73 V vs SCE in MeCN)
varies with additives (e.g. SmI2-HMPA mixture: Ered = -2.05 V vs
Ag/AgNO3 in THF).[13] The three non-classic lanthanide(II)
iodides (LnI2):[14] thulium(II) iodide[15] (TmI2, Ered = -2.35 V vs
SCE in MeCN), dysprosium(II) iodide[16] (DyI2, Ered = -2.47 V vs
SCE in MeCN) and neodymium(II) iodide[17] (NdI2, Ered = -2.86 V
vs SCE in MeCN) have even stronger reducing power. For a
catalytic use of lanthanide(II) iodides, stoichiometric amounts of
metal (magnesium or zinc in combination with further additives,
e.g. silanes,[18] or mischmetall) are added as co-reductants.[19]
The electrochemical regeneration of Ln(II) is another
approach.[20]
a. Nickel(0)/imidazolium chloride catalyzed reduction of chlorobenzene
Ni(0) (3 mol%)
IMes.HCl (6 mol%)
i-PrONa
Cl
H
THF, 65 °C, N2
1a
2a
(96%)
(IMes = 1,3-bis(2,4,6-trimethylphenylphenyl)imidazol-2-ylidene)
b. Electrochemical dechlorination with naphthalene as mediator
Ag/Zn/Pt electrode
-2.94 V (Ag/Ag+
Cl
H
)
0.1 M Et4NClO4
10 mM naphthalene (MeCN)
1a
2a
(10 mM
in MeCN)
c. This work: reduction of aryl chlorides by LnI2 (cat.) and photoredox catalysis
10 mol%
CO2Et
HCl
N
O
N
H
A
(Rh6G)
Cl
1
H
2
LnI2 (10 mol%)
DIPEA (2 equiv.), DMF (dry)
25 °C, 455 nm, N2
R
R
Scheme 1. Reactions for the reduction of aryl chlorides.
First, we optimized the reaction conditions by irradiating a
mixture of chlorobenzene (1a), Rh6G, LnI2, and DIPEA with blue
light at room temperature under nitrogen atmosphere. In a
typical reaction mixture for the reduction of chlorobenzene (1a),
10 mol% of Rh6G and DyI2, respectively, and two equivalents of
DIPEA in DMF with blue light irradiation were used to give 2a in
99% after 48 h of irradiation (Table 1, entry 1). Lower amounts
(5 mol%) of Rh6G and DyI2 led to 51% yield after the same
irradiation time (Table 1, entry 2). Control experiments with
green light irradiation or without light, photocatalyst, lanthanide
diiodide or base, confirmed that all components are necessary
for product formation (Table 1, entries 3-7). Thulium(II) iodide, a
lanthanide with slightly lower reduction power, led to 91% yield
of 2a (Table 1, entry 8). The strongest lanthanide diiodide, NdI2,
gave 99% of 2a (Table 1, entry 9), a yield comparable to DyI2.[2]
The reaction proceeds in other polar aprotic solvents (DMSO
and THF), but with lower yields. A Ln(III) salt can also be used
as electron mediator, but the yields (e.g. 35%, Table 1, entry 10)
We have combined the excellent reducing properties of
lanthanide(II) salts with their regeneration by visible light
[a]
M.Sc. Andreas Uwe Meyer, and Prof. Dr. Burkhard König
University of Regensburg, Faculty of Chemistry and Pharmacy
D-93040 Regensburg, Germany
E-mail: Burkhard.Koenig@ur.de
[b]
[*]
Dr. Tomáš Slanina, and Prof. Dr. Alexander Heckel
Institute of Organic Chemistry and Chemical Biology, Goethe
University Frankfurt, Frankfurt am Main, Germany
Corresponding author.
Supporting information for this article is given via a link at the end of
the document.
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10.1002/chem.201701665
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COMMUNICATION
are irreproducible due to lower purity of the available salts
containing undefined amounts of insoluble Ln(III) species, e.g.
Ln2O3.
C–C bond formation of 1a with N-Me-pyrrole (3) and the C–P
bond formation of 1cc with triethyl phosphite (5). The expected
product 4 was isolated in 81% yield (Scheme 2a). The carbon-
phosphorus product 6 was obtained in 48% (DyI2) and 50%
(NdI2), respectively (Scheme 2b). The reported yield for the
reaction using 4-bromo-anisole was 54%.[3g]
Table 1. Optimization of the reaction conditions.
Cl
H
Conditions
DIPEA (2 equiv.)
455 nm, N2, DMF (dry)
48 h @ 25 °C
a)
Cl
Rh6G (10 mol%)
DyI2 (10 mol%)
1a
2a
N
N
DIPEA (2 equiv.), DMSO (dry)
25 °C, 44 h, 455 nm, N2
yield
[%][a]
entry
conditions
1a
Cl
3
4
(20 equiv.)
(81%) [a]
1[b]
2
Rh6G (10 mol%), DyI2 (10 mol%)
Rh6G (5 mol%), DyI2 (5 mol%)
99
51
2
b)
OEt
O
P OEt
Rh6G (10 mol%)
LnI2 (10 mol%)
DIPEA (2 equiv.), DMSO (dry)
25 °C, 36 h, 455 nm, N2
3
Rh6G (10 mol%), DyI2 (10 mol%), no light
Rh6G (10 mol%), NdI2 (10 mol%), 535 nm
no Rh6G, DyI2 (10 mol%)
P(OEt)3
4
6
OMe
5
10
1
OMe
6
1cc
5
6
Rh6G (10 mol%), no DyI2
(3 equiv.)
(Ln = Dy: 48%
Ln = Nd: 50%)[b]
7
Rh6G (10 mol%), DyI2 (10 mol%), no base
Rh6G (10 mol%), TmI2 (10 mol%)
Rh6G (10 mol%), NdI2 (10 mol%)
Rh6G (10 mol%), DyCl3 . 6 H2O (10 mol%)
–
([a] Isolated yield. [b] Determined by GC analysis with naphthalene as internal standard.)
8
91
99
35
Scheme 2. a) C–C and b) C–P bond formation.
9
10
A series of control experiments (Table 1) has confirmed the role
of each component of the system. The reaction in absence of
rhodamine (entry 5) with 10 mol% of DyI2 led to 10% yield. This
indicates that DyI2 is able to reduce chlorobenzene, but it is not
regenerated. When catalytic amounts of Ln(III) salt are used
instead of Ln(II) (Table 1, entry 10), the reaction still occurs,
which suggests that Ln(II) could be produced in situ by a
MCconPET process. Blue light of 455 nm was used for the
reaction since both rhodamine 6G and its radical anion absorb at
this wavelength (the isosbestic point for Rh6G and the Rh6G
radical is at 460 nm; Figure S-2). The excitation of both species
is essential, which could be demonstrated by a negligible
conversion using green light (535 nm; Table 1, entry 4), which
cannot excite the rhodamine 6G radical anion.
[a] Determined by GC analysis with toluene as internal standard. [b] General
reaction conditions: 1a (0.1 mmol, 1 equiv.), Rh6G (10 mol%), DyI2 (10 mol%)
and DIPEA (0.2 mmol, 2 equiv.) in dry DMF (1.5 mL) was irradiated with blue
light for 48 h at 25 °C under nitrogen atmosphere.
The substrate scope of the reaction was explored using the
optimized reaction conditions (Table 1, entry 1): various aryl
chlorides 1, 10 mol% of Rh6G and DyI2, respectively, two
equivalents of DIPEA, DMF as solvent, and blue light irradiation
at room temperature under nitrogen atmosphere. The results are
depicted in Table 2. Chlorotoluenes (1b), chloroanisoles (1c)
and chlorobiphenyls (1d) were reduced in moderate to good
yields of 51-82%.[25]
Table 2. Substrate Scope.[a]
Rh6G (10 mol%)
DyI2 (10 mol%)
DIPEA (2 equiv.), DMF (dry)
25 °C, 72 h, 455 nm, N2
Cl
H
The photocatalytic reduction of aryl halides leads to the
defunctionalized compounds by hydrogen abstraction of the
intermediate aryl radicals from the solvent. This process was
1
(E0(red)
vs SCE)[i]
R
R
1
2
Cl
H
H
H
confirmed by the reaction of 1a in DMF-d7, which is an excellent
Me
26]
hydrogen atom donor for aryl radicals.[2,
GC-MS analysis
Me
revealed an increased amount (after 48 h: ratio 2a/2a’ = 54/46)
of deuterated benzene (2a’) compared to the natural ratio in
commercially available benzene (natural ratio 2a/2a’ = 94/6; see
Table S-1). The mechanism of C–C[3d] and C–P[3g] bond
formation between aryl radicals and appropriate substrates has
been described by some of us in earlier reports.
Me
Me
1bc
2ba
2bb
2bc
(77%)
(- 2.94 V)
(51%)
(70%)
Cl
H
H
H
OMe
OMe
OMe
OMe
Ln(III) salts are commonly used as Lewis acids in catalysis.[27]
We investigated the possibility of Ln(III) salt formed in situ acting
as a Lewis acid complexing with the substrate and thus
decreasing the reduction potentials of halogenated arenes. The
13C NMR study of 1a in presence and absence of DyCl3 . 6 H2O
(5 mol%), respectively, did not exhibit any change in the
resonance signal chemical shifts (see ESI). This indicates that
the Ln(III) salt and the substrate do not form a complex. A
ground state complex of Rh6G and Dy3+ ions has been observed
spectroscopically (Figure S-11; the absorption peak of Rh6G is
broadened and its molar absorption coefficient is lower). This
1cc
(- 2.96 V)
2ca
(61%)
2cb
(54%)
2cc
(82%)
H
Cl
1da
(- 2.75 V)
H
2da
(53%)
2db
(67%)
[i] Reduction potential vs SCE (in CH3CN; internally referenced to Fc/Fc+).
[a] Determined by GC analysis with internal standard.
Applying Rh6G for the debromination of aryl bromides and
subsequent C–C and C–P bond formation was intensively
studied in our group.[3d-g] The compatibility of the herein
described method with our previous reports was shown for the
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indicates the association of rhodamine and the lanthanide ion
suggesting the presence of a MCET mechanism.
3
4
5
Rh6G+DIPEA
22 ± 2[h] 5.3 ± 0.4
5.2 ± 0.4 60 ± 1
3.2 ± 0.2 93 ± 2
3.3 ± 0.3 90 ± 2
Rh6G+DIPEA+DyCl3 11 ± 2
10.0 ± 0.4
9.8 ± 0.2
Based on these findings and our previous mechanistic
2, 3d]
investigations,[1e,
we propose the following MCconPET
Rh6G+DIPEA+DyCl3+ 11 ± 2
PhCl
mechanism (Scheme 3). Rhodamine 6G forms a ground state
complex with Ln3+. This complex is excited by visible light and
subsequently reduced by the sacrificial electron donor, DIPEA.
The coordination of the metal ion prevents the back electron
transfer to the DIPEA radical cation, which is a mechanistic
pathway common for MCET.[22] The reduced radical/Ln3+
complex is consecutively excited by another photon, which
significantly increases its reduction power. The excited radical
complex reduces Ln3+ to Ln2+ weakening the complex as there is
no observed interaction between Ln2+ and Rh6G. Ln2+ transfers
an electron to the aryl chloride and the reduced aryl chloride
radical anion fragments the C–Cl bond generating an aryl radical,
which abstracts a hydrogen atom forming the product.
6
7
8
Rh6G+DIPEA+PhCl
Rh6G+DIPEA+NaCl
Rh6G+DIPEA+CsCl
25 ± 2
22 ± 1
17 ± 2
5.0 ± 0.3
4.2 ± 0.4
4.1 ± 0.4
4.9 ± 0.2 59 ± 1
4.1 ± 0.3 75 ± 2
3.9 ± 0.2 78 ± 1
[a] Degassed solutions in DMSO; Rh6G: rhodamine 6G (c = 1 × 10‒5 M),
DIPEA (c = 5 × 10‒2 M), DyCl3 • 6 H2O (c = 7 × 10‒2 M), PhCl (c = 2 × 10‒2 M),
NaCl (c = 7 × 10‒2 M), and CsCl (c = 7 × 10‒2 M). [b] Rate constant of the rise
of the rhodamine 6G radical at 420 nm. [c] Rate constant of the decay of the
signal of the rhodamine 6G radical at 420 nm. [d] Decay at irradiation by 420
nm light. [e] Decay in dark. [f] Recovery of the absorbance at 500 nm before
and after the irradiation experiment. [g] n. o. = radical not observed. [h]
Maximal values are shown in bold.
The experiments in absence of DIPEA (Table 3, entries 1 and 2)
did not yield any rhodamine 6G radical anion and no bleaching
was observed during the irradiation experiment. The experiment
using Rh6G and DIPEA (Table 3, entry 3) led to a quantitative
formation of rhodamine 6G radical anion after irradiation with
530 nm light (Figure S-2). The subsequent decay of the radical
did not depend on the presence/absence of 420 nm light, which
indicates that the decay of the signal corresponds to a dark
process. A significant bleaching (~60% recovery after one
irradiation experiment) indicates that the decay of rhodamine 6G
radical corresponds to further chemical reactions connected with
the decomposition of the photocatalyst. The presence of
[28]
DyCl3
(Table 3, entry 4) slows down the formation of the
Scheme 3. Proposed mechanism of the photocatalytic reduction of aryl
chlorides 1.
Rh6G radical anion and simultaneously accelerates its decay in
presence of 420 nm light (Figure 1 and S-10).
We performed a series of spectroscopic experiments with online
irradiation (for details of the experimental setup and used
concentrations, which differ from photocatalytic experiments,
see ESI) in order to further confirm the proposed mechanism
(Scheme 3). An irradiation procedure has been developed,
which enabled to separate the process of photoinduced
generation of the rhodamine 6G radical and to determine further
quenching by other components in presence and in absence of
light. While the photocatalytic system uses 455 nm light, where
both Rh6G and the corresponding radical anion absorb, the
irradiation procedure used 530 nm green light for generation of
the rhodamine 6G radical anion and subsequent periods of dark
and 420 nm blue light where only the Rh6G radical anion
absorbs (see ESI). The rate constants of raise/decay of the
rhodamine 6G radical anion at 420 nm were determined for a
series of solutions by fitting the decay curves (Figures S4-S10)
and the results are summarized in Table 3.
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
A
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
A
t/ s
0
100
200
300
400
500
Figure 1. Comparison of time dependence of absorbance at 420 nm (black
line), and 500 nm (red line) of a degassed solution of rhodamine 6G (c = 1 ×
10‒5 M), PhCl (c = 2 × 10‒2 M) and DIPEA (c = 5 × 10‒2 M) in DMSO in
presence (bottom) and in absence (top) of DyCl3 • 6 H2O (c = 7 × 10‒2 M),
irradiated by a standard irradiation procedure (see ESI for details).
Table 3. Rate constants of decay/rise of signal of rhodamine 6G radical at 420
nm and the recovery of the photocatalyst after a model experiment.
The slower formation of the Rh6G radical anion can be
explained by combination of (i) an external heavy atom effect of
ସଶ଴
݇
ସଶ଴
ௗ௘௖௔௬
݇
௥௜௦௘
[c]
Recovery
[%][f]
/10–3 [s–1
]
Conditions[a]
/10–3
dysprosium
ions
(and
hence
lower
population
of
Entry
[b]
[s–1
]
420 nm[d]
dark[e]
n. o.
n. o.
photocatalytically active singlet excited state of Rh6G in favor of
its triplet state)[29] and (ii) due to possible complex formation of
Lewis acidic Dy3+ ions with DIPEA (similar complexes with
tertiary amines have been already observed).[30] The external
heavy atom effect has been confirmed by the experiment in
1
2
Rh6G
n. o.[g]
n. o.
n. o.
n. o.
100 ± 0.1
99 ± 0.5
Rh6G+DyCl3
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10.1002/chem.201701665
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COMMUNICATION
presence of Cs+ (Table 3, entry 8), where slower formation of the
Rh6G radical anion was also observed. The control experiment
with Na+ ions (Table 3, entry 7) resulted in the same rate of
formation as in absence of salts. The decay of the rhodamine
6G radical anion in presence of Dy3+ ions was significantly faster
(by factor of ~3 under experimental conditions) in presence of
420 nm light in comparison to experiments in the dark (Table 3,
entries 4 and 5). Moreover, almost no bleaching of the
photocatalyst has been observed. This indicates that the
electron transfer to the Dy3+ salt must proceed from the excited
state of the Rh6G radical anion. The presence of chlorobenzene
(Table 3, entries 5 and 6) does not affect the raise/decay of the
Rh6G radical, which indicates that the direct electron transfer
from the excited Rh6G radical to chlorobenzene (1a) does not
occur. The stability of the Rh6G radical anion in the dark is
influenced by the ionic strength of the solution and is higher in
presence of inorganic salts (Table 3, entries 4, 5, 7 and 8).
Moreover, the bleaching of the photocatalyst is suppressed in
the presence of these salts. Increased ionic strength has been
demonstrated to increase the stability of organic radicals and
radical anions.[31]
Lanthanide salts form
photocatalyst and act as an electron mediator and bleaching-
protective agent.
a
ground state complex with the
In conclusion, we have developed an efficient photocatalytic
method for the reduction and C–C and C–P bond forming
reactions of aryl radicals produced from aryl halides. Aryl
chlorides with electron-donating groups have high reduction
potentials and are beyond the limit of known photocatalytic
reduction methods. The combination of consecutive photo-
induced electron transfer with metal catalysis, MCconPET,
allows the activation of such aryl chlorides. The cooperative
action of the organic photocatalyst, rhodamine 6G, and
lanthanide ions in photoinduced electron transfer processes
expands the scope of visible light photocatalysis.
Experimental Section
See supporting information.
We further investigated the mechanism by EPR coupled with
irradiation (for details see ESI). The EPR resonance signal of
the Rh6G radical anion[32] was observed upon irradiation with
green light (535 nm), which initiates PET from DIPEA (Figures
S-12 and S-13). The resonance signal remained unchanged
upon further excitation with blue light (455 nm) in the absence of
Dy(III) and decayed rapidly in the presence of Dy(III) indicating
that the excited Rh6G radical anion is oxidized by Dy(III) ions in
the complex (Figure 2).
Acknowledgements
This work was supported by the German Science Foundation (DFG) (GRK
1626, Chemical Photocatalysis). A.M. thanks the Fonds der Chemischen
Industrie for a scholarship. T.S. thanks the Experientia Foundation for a
postdoctoral fellowship. We thank Dr. Rudolf Vasold for his assistance in GC-
MS measurements and Regina Hoheisel (both University of Regensburg) for
her assistance in cyclic voltammetry measurements.
-15
Keywords: photoredox catalysis • lanthanides • aryl radical •
Rh6G+DIPEA-before irradiaion
Rh6G+DIPEA-after 10 min (455 nm)
Rh6G+DIPEA+DyCl3-before
photoreduction • C-C bond formation
-10
I / a. u.
Rh6G+DIPEA+DyCl3-after 5 min (455 nm)
[1]
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Rh6G+DIPEA+DyCl3-after 10 min (455 nm)
-5
g = 2.0026
0
g = 1.9900
5
10
15
B0 / mT
336
338
340
342
Figure 2. EPR spectra of a degassed solution of mixtures of rhodamine 6G (c
= 1 × 10‒3 M), DyCl3 • 6 H2O (c = 7 × 10‒2 M), and DIPEA (c = 1.1 × 10‒1 M) in
DMSO (after exhaustive irradiation with green light, 535 nm, e.g. formation of
Rh6G radical) before and after irradiation with blue light (455 nm).
Rh6G+DIPEA-before 455 nm irradiation (black line), Rh6G+DIPEA-after 10
min of 455 nm irradiation (red line), Rh6G+DIPEA+DyCl3-before 455 nm
[2]
[3]
It was not possible to regenerate LnI2 with perylene diimide (PDI),
which was already used for consecutive visible light–induced electron
transfer processes. I. Ghosh, T. Ghosh, J. I. Bardagi, B. König, Science
2014, 346, 725-728.
irradiation (dark blue line), Rh6G+DIPEA+DyCl3-after
5 min of 455 nm
irradiation (light blue line), Rh6G+DIPEA+DyCl3-after 10 min of 455 nm
irradiation (green line).
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The experiments confirm the suggested mechanism (Scheme 3).
The excitation of the Rh6G radical anion is essential for the
process. While the electron transfer from the excited Rh6G
radical anion to chlorobenzene (1a) is not feasible in the
absence of the metal ions, the lanthanide additive enables an
efficient photocatalytic reduction of aryl chlorides by MCconPET.
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The excited-state reduction potential of the radical anion Rh6G●
under blue light irradiation is approximately -2.4 V vs SCE.
*
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With a little help from a friend - in
this case a lanthanide metal ion – the
organic photoredox catalyst
Andreas Uwe Meyer, Tomáš Slanina,
Alexander Heckel and Burkhard König*
Page No. – Page No.
rhodamine 6G can do more. Catalytic
amounts of lanthanide salts enable
metal-ion coupled consecutive
electron transfer allowing reductions
of chloroarenes with potentials beyond
-3 V vs SCE and stabilize the
photocatalyst.
Metal ion coupled consecutive
photoinduced electron transfer
generates strong reduction potentials
from visible light
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Title
Text for Table of Contents
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