Photosensitizing Properties of Alkynylrhenium(I) Complexes [Re(-C≡C-R)(CO)3(N∩N)] (N∩N = 2,2′-bipy, phen) for H2 Production

Article abstract of DOI:10.1002/ejic.201402142

A series of complexes of the type [fac-Re(X)(CO)₃(N∩N)] (X = -C≡C-R, N∩N = 2,2′-bipy, 2,2′-phen) were synthesized and fully characterized. Their photophysical characteristics make them very convenient photosensitizers (PSs). Upon light irradiat

Full text of DOI:10.1002/ejic.201402142

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DOI:10.1002/ejic.201402142
Photosensitizing Properties of Alkynylrhenium(I)
Complexes [Re(–CϵC–R)(CO)3(NʝN)]
(NʝN = 2,2Ј-bipy, phen) for H2 Production
Miriam Oberholzer,[a] Benjamin Probst,[a] Dominik Bernasconi,[a]
Bernhard Spingler,[a] and Roger Alberto*[a]
Keywords: Hydrogen / Rhenium / Homogeneous catalysis / Luminescence / Alkynes
A series of complexes of the type [fac-Re(X)(CO)3(NʝN)] (X
= –CϵC–R, NʝN = 2,2Ј-bipy, 2,2Ј-phen) were synthesized
and fully characterized. Their photophysical characteristics
make them very convenient photosensitizers (PSs). Upon
light irradiation, H2 formation was observed for all alkynyl
complexes in the presence of a water-reducing catalyst
(WRC) and a sacrificial electron donor. Relative rates of H2
production indicate a dependency upon the diimine ligands
rather than upon the nature of the σ-bonded alkynyl deriva-
tives. The coordinated acetylene group induces a redshift of
the λmax of the MLCT band in UV/Vis spectroscopy as com-
pared to those of the corresponding halides, nitriles, or cat-
ionic ReI complexes, such as [fac-ReX(CO)3(NʝN)] (X = pyr-
idine, H2O, NʝN = bipy, phen).
chosen as a PS in particular.[3b–3e,4] Diimine units are incor-
porated in transition-metal-based PSs of the types [Ru(b-
ipy)3]2+, [Ir(ppy)2(bipy)]3+, or [PtX(terpy)]+.[3a,5] In trying
to avoid rare elements, light-emitting organic mo-
lecules such as rhodamine have also been shown to have
excellent photosensitizing properties.[6] Organic dye sensi-
tizers often suffer from photoinstability, as opposed to
metal-containing sensitizers, which are generally more ro-
bust but also display a limited spectral absorption range.[7]
Whereas PSs are often exclusively based on polypyridine
ligands such as bipy or phen, a wide structural variety of
water-reducing catalysts (WRCs) is found in photo- and
electrocatalytic studies. Highly active WRCs include glyox-
imato complexes of cobalt,[3c–3e,4b,5c,6,8] polypyridyl com-
plexes of cobalt and nickel or molybdenum,[3b,4a,9] as well as
heterogeneous molybdenum, platinum, gold, or palladium
compounds.[10]
Introduction
The photophysical properties of alkynyl rhenium(I) com-
plexes including a {Re(CO)3(NʝN)}+ core (NʝN = di-
imine) have already been intensively studied by Yam and
co-workers since 1995.[1] Successful incorporation of [Re-
(–CϵC–R)(CO)3(NʝN)] in electroluminescence applica-
tions, such as OLED devices, show the general applicability
of this system in the field of luminescent materials.[2] In
addition to the interesting luminescence properties of ReI–
alkynyl complexes, the strong σ-donating and π-accepting
properties of the alkynyl moieties make this M–C bond
strong and lead to a decrease of the HOMO–LUMO gap
and, accordingly, to a redshifted metal-to-ligand charge-
transfer (MLCT) band for a given {Re(CO)3(NʝN)} core.
Hence, these features are interesting for photocatalysis,
since previously reported ReI complexes, such as [ReX-
(CO)3(NʝN)] (NʝN = bipy, phen), exhibit high photocata-
lytic H2 formation activities but suffer from weak overlap
with the visible solar spectrum and lability of the axial
ligand X, entailing deactivation of the photosensitizer
(PS).[3]
Previously, we introduced [ReBr(CO)3(bipy)][3d] as PS for
photocatalytic proton reduction in the organic solvent
DMF [triethanolamine (TEOA) as sacrificial electron do-
nor, Co(dmgH)2 as WRC], with TONPS values of up to 300
(H/PS). In a similar system, with the more robust [Re(NC-
S)(CO)3(bipy)],[3e] TONPS values up to 6000 could be ob-
tained. Our group then introduced a series of water-soluble
In contrast, (modified) bipyridine (bipy) or phenanthrol-
ine (phen) ligands are crucial for luminescent transition-
metal-based PSs in photocatalytic H2 production. Because
of its photostability and efficient charge separation in the
excited state, the {Re(CO)3(NʝN)} fragment is frequently
[ReI]+[3c]
catalysts,
among
which
[Re(py)(CO)3-
(bipy)]+ did show a reasonable stability and good perform-
ance in photocatalytic H2 formation in pure H2O (TONPS
up to 500). Lately, we showed that, by replacing TEOA with
ascorbic acid, the stability of the system in H2O could be
further increased up to TONPS values of more than 5000.[4b]
Unfortunately, all these catalysts suffer from insufficient
light-harvesting properties, since the spectral absorption
[a] Department of Chemistry, University of Zürich,
Winterthurerstrasse 190, 8057 Zürich, Switzerland
E-mail: ariel@chem.uzh.ch
www.chem.uzh.ch
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201402142.
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range is limited to the upper UV region. Introducing [Re- troscopic studies, revealing the presence of Cs symmetry in
(–CϵC–R)(CO)3(NʝN)] complexes as PS increases the sta- 1–6. [M + H]+ and [M + Na]+ ions were the dominant
bility of the PS as compared to systems such as [Re- fragments detected by ESI mass spectrometry. After purifi-
(py)(CO)3(bipy)]+ or [Re(Br)(CO)3(bipy)].[3,4b] In addition, cation, the complexes were subjected to photophysical stud-
the MLCT band is redshifted, more towards the part of the ies (Figure 1, Tables 1 and 2) and used in photocatalytic H2
solar spectrum with more intense photon flux. We present production in DMF (Figure 3).
herein six novel PSs, [Re(–CϵC–R)(CO)3(NʝN)] (1–6),
comprising an alkynyl linker with different organic groups
Spectroscopic Properties
“R”. All complexes are fully characterized, and photocatal-
ysis in DMF with these PSs results in TON values of up
to400 (H/PS) with TEOA as sacrificial electron donor.
The coordination of the alkynyl ligands induces an ob-
servable redshift in absorption as compared to analogous
ReI complexes such as [ReX(CO)3(NʝN)] (X = Cl–, Br–,
py, H2O, NCS–, CN–) (Figure 1, Table 1).[3a,3c,4c] Since acet-
ylides are strong σ-donors, the ReI center becomes more
electron-rich, which raises the energy of the metal-centered
HOMO and decreases the MLCT transition energy.[1d] It is
well established that this transition displays a metal-to-
ligand charge transfer (3MLCT) dπ(Re)Ǟπ*(diimine), as
discussed for similar systems in the literature.[4e,4g,4h,4k,4l,11]
On the basis of computational studies, it is assumed that in
ReI alkynyl complexes [Re(–CϵC–R)(CO)3(NʝN)], mixing
with the [π(CϵC–R)Ǟπ*(diimine)] 3LLCT (ligand-to-li-
gand charge transfer) character can occur.[2a] The observed
redshifts of compounds 1–6 come close to the most intense
part of the sunlight spectrum (between 400 and 500 nm),
which is a promising feature for photocatalysis. Subtle
changes in the observed absorption spectra upon variation
of the substituents “R” in –CϵC–R only became obvious
after an analysis of the first derivative of the absorption
spectra (see Figure S1), indicating a slight increase in the
HOMO–LUMO gaps in the order 2 Ͼ 3, 4, 5, 6 Ͼ 1. The
most distinct effect was observed for 5 and 6, which display,
additionally to the charge transfer (CT) band at about
380 nm, a transition at 370 nm, attributable to the couma-
rin dye, which increases the molar absorptivity considerably.
The same behavior was observed for similar Pt-based
dyes.[12] Moreover, the replacement of phen by bipy does
not change the λmax, but slightly decreases the molar ab-
sorptivity of the CT band, while increasing the absorption
at 300 nm due to intraligand transitions.[13] In line with the
above observations, CO stretching frequencies indicate a de-
stabilization of the rhenium-based HOMO for the alkynyl
Results and Discussion
Six novel PSs (1–6, Scheme 1) were prepared by an
adapted literature procedure.[1a,2b] Heating at reflux
[ReBr(CO)3bipy] or [ReBr(CO)3phen], Tl[PF6], triethyl-
amine (TEA), and the corresponding arylalkyne HCϵC–R
in water-free, coordinating solvents such as THF or aceto-
nitrile gave 1–6 in 60–80% isolated yields. The structures of
complexes 1–4 and 6 were elucidated by single-crystal X-
ray crystallography (Table S1 and Figure 2) and NMR spec-
Scheme 1. Schematic drawings of PSs 1–6 and WRC 7.
Figure 1. Combined UV/Vis absorption spectra of 1–6 (left) and UV/Vis absorption spectra of 4 compared to those of [Re(NCS)(CO)3-
(bipy)] and [Re(py)(CO)3(bipy)]+ (right).
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complexes as compared to neutral or even halide-type li- pared to other ReI complexes, in line with the diminished
gands at the sixth position.[3c,3e,4c]
excited state reduction potential (PS*/PS–) of 1–6 (0.51–
0.60 V), as compared to [Re(X)(CO)3(bipy)]0/+ (X = Br–,
NCS– and pyridine, 0.83–1.15 V; see Table S3 and Fig-
ure S11) and the reported oxidation potential of TEOA
(0.6Ϯ0.1 V; all vs. Ag/AgCl).[10d,15]
Table 1. Photophysical properties of complexes 1–6 and
[Re(X)(CO)3(bipy)]0/+ (X = Br–, NCS–, and pyridine)[3c–3e] in DMF.
Compound
λMLCT [nm][a,b] λem [nm][c] τ [ns][c]
390 (2820) 650 67.7Ϯ2.0
ca. 385 (3590)[e] 654
ΦP (ϫ10–3)[d]
Unlike ReI–alkyl complexes, which undergo fast and ef-
ficient Re–C bond homolysis,[4j] rhenium–alkynyl com-
pounds are reported to be stable under irradiation for at
least 12 h.[1e] HPLC analysis of irradiated solutions, con-
taining 1–6 in DMF under Ar, evidenced 10–40% decom-
position after 8 h, and complete decomposition after 100 h
(Figure S12).
1
2
3.5
100.6Ϯ1.7 7.4
3
4
5
6
380 (2980)
395 (2490)
655
671
72.1Ϯ0.2
36.3Ϯ0.2
64.3Ϯ1.1
14.9Ϯ0.2
42.2Ϯ0.2
25.5Ϯ0.2
5.0
1.2
3.7
1.0
1.8
1.1
ca. 370 (4630)[e] 651
ca. 375 (4230)[e] 677
375 (3110)
375 (2760)
345 (3630)
Br–
NCS–
py[f]
600
602
567
201.5Ϯ0.4 9.8
[a] In DMF solution. [b] Molar absorptivities, ε, are given in round
brackets ([m–1 cm–1]). [c] In degassed DMF solution. [d] Photolumi-
nescence quantum yield determined with [Ru(bipy)3]2+ in H2O as
standard at 298 K (estimated uncertainty 15%). [e] Absorption
shoulder. [f] In H2O.
Electrochemistry
A pronounced anodic shift in oxidation potentials (200
to more than 400 mV) was observed between the alkynyl
complexes 1–6 and [Re(X)(CO)3(bipy)]0/+ (X = Br–, NCS–,
and pyridine). The reduction potential shifts by 60–300 mV
to more negative values (Table 3) mirror once again the in-
fluence of the strong σ-donating properties of the alkynyl
ligands on the Re-based HOMO, whereas only a small ef-
fect is observed on the diimine-based LUMO, in agreement
with the above findings. As observed before, the oxidation
of ReI at 0.1 V/s is completely irreversible.[16] All complexes
display a reversible one-electron reduction at 0.1 V/s in
DMF (E1/2,red ≈ –1.3 V vs. Ag/AgCl, Table 3). Variation of
“R” in [Re(CϵC–R)(CO)3(NʝN)] did not shift the re-
duction potential to a large extent, as observed for other
alkynyl–rhenium complexes.[1f,2a] The oxidation potential
clearly follows the trends as seen from absorption and IR
studies: complex 2, bearing the most electron-withdrawing
group on the alkynyl, displays the most positive oxidation,
whereas complex 1 is easiest to oxidize. With these argu-
ments, the oxidation potential of 5 and 6 are somehow
lower than expected, possibly implying an involvement of
the coumarin moiety in the first oxidation. No distinct dif-
ferences can be observed in the relative positions of the elec-
trochemical potentials when replacing bipy for phen.
While the substitution of phen for bipy had only a minor
impact on the absorption properties, the emission proper-
ties as well as the lifetime (τ) of the triplet state were dis-
tinctly influenced. Excitation at λmax of 1–6 led to broad,
long-lived orange emission centered at around 650 nm. Dif-
ferences in the emission spectra were clearly observed be-
tween bipy (λem ≈ 670 nm for 4 and 6) and phen (λem
≈
650 nm for 1–3 and 5) complexes, while no or little influ-
ence of the “R” substituent in –CϵC–R was detected. Life-
times of phen complexes 1, 2, 3, and 5 are greater than
60 ns, whereas those of bipy analogues 4 and 6 are lower,
37 and 15 ns, respectively. Accordingly, the contributions of
nonradiative decay must increase, since oxidation and re-
duction potentials for all compounds are very similar (vide
infra). This observation is in agreement with the literature,
assigning this behavior to an increased rigidity of the phen
ligand[4j] and to a lower-lying ligand-based state that only
weakly interacts with rhenium.[14] The quenching rate con-
stants, kq, of 1–6 with TEOA as electron donor (Table 2) are
relatively low (1–50ϫ106 m–1 s–1) and far away from being
diffusion-controlled. Reductive quenching is slower as com-
Table 2. Kinetic data of 1–6 and [Re(X)(CO)3(bipy)]0/+ (X = Br–,
NCS– and pyridine)[3c–3e] in the presence of 1 m TEOA as reductive
quencher in DMF.
Table 3. Electrochemical properties of complexes 1–6 and
[c]
[Re(X)(CO)3(bipy)]0/+ (X = Br–, NCS– and pyridine)[3c–3e] in DMF.
Compound
τq [ns][a]
kq (ϫ106 m–1s–1)[b] Φq,max
Compound
E1/2,red [V][a]
Epa [V][b]
ν(CϵO) [cm–1][c]
1
29.9Ϯ1.4
85.2Ϯ0.4
63.7Ϯ2.3
14.0Ϯ0.2
40.5Ϯ0.6
11.4Ϯ0.2
–
19Ϯ1.9
1.47Ϯ0.07
1.8Ϯ0.6
44Ϯ1.4
9.2Ϯ0.60
21Ϯ1.9
64.8Ϯ0.4
92Ϯ1.2
51Ϯ1
0.56Ϯ0.03
0.13Ϯ0.01
0.12Ϯ0.03
0.61Ϯ0.01
0.37Ϯ0.02
0.23Ϯ0.02
0.73Ϯ0.01
0.70Ϯ0.01
0.91Ϯ0.01
2
1
–1.33
–1.30
–1.31
–1.31
–1.30
–1.32
–1.24
–1.19
–1.04
1.17
1.28
1.21
1.25
1.17
1.19
1.49
1.49
Ͼ1.6
1886, 1921, 2012
1893, 1917, 2006
1891, 1922, 2009
1898, 1928, 2014
1890, 1902, 2008
1880, 1897, 2006
1881, 1902, 2011
1914, 1928, 2020
1907, 1923, 2026
3
2
4
3
5
4
6
5
Br–
NCS–
py[d]
6
Br–
NCS–
py
–
–
[a] In degassed DMF solution in the presence of 1 m TEOA. [b]
Quenching rate constant in the presence of 1 m TEOA. [c] Theoreti-
[a] Reversible one-electron reduction potentials in V vs. Ag/AgCl
(DMF solutions containing 0.1 m NBu4PF6 with Fc0/+ at +500 mV
as internal standard). [b] Anodic peak potentials, irreversible oxi-
dation wave. [c] KBr pellets.
kq[Q]
cal maximum yield of reduction, Φq,max
[TEOA] = 1 m. [d] In H2O.
=
, for
[Q] + knr + kr
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With respect to photocatalysis, the reduction potentials [1.123(6) Å, greater than 3σ] than those in 1, 3, 4, and 6.
are negative enough for the respective reduced PS to reduce This correlates well with spectroscopic and electrochemical
Co(III/II)
WRC 7 from CoII to CoI (E1/2,red
E1/2,red
= –0.07 V, results, indicating a stabilization of the HOMO for the lat-
ter as compared to 1 and 3–6, due to decreased σ-donation
of the 1-ethynyl-3,5-bis(trifluoromethyl)benzene moiety.
The axial Re–CO bond lengths of the most electron-rich
complexes 1, 3, and 4 are found to be slightly elongated
Co(II/I)
= –0.61 V vs. Ag/AgCl).[17]
X-ray Structures
The crystal structures of complexes 1–4 and 6 (Figure 2) [1.153(6), 1.143(7), and 1.150(2), respectively] as compared
depict octahedral geometry with a fac-{Re(CO)3} arrange- to free CO. Generally, the reported CO bond lengths of 1–
ment; the bidentate diimine ligand and the alkynyl ligand 4 and 6 coincide with their corresponding symmetric
are in the axial position. The carbonyl bond lengths [C1– stretching frequencies ν(CϵO)sym (Table S2). Angles Re1–
O1, C2–O2, and C3–O3, Table S2] are generally elongated C14–C15 and C14–C15–C16 deviate in all complexes
relative to that of
a
noncoordinating CO ligand slightly from the expected 180° (Table S2). We attribute
(1.128 Å),[18] which indicates a strong backbonding from these deviations to characteristics of the individual crystal
the rhenium center into the π*-orbital of the CO ligands. packing as observed in other complexes as well.[1a,1c,1f]
Bond C3–O3 in complex
2 is significantly shorter Bond lengths and angles around the metal centers are sim-
Figure 2. ORTEP drawings of 1–4 and 6 at 50% probability level with labeled nitrogen atoms, carbonyl groups, and metal–alkynyl bond.
Solvent molecules and hydrogen atoms are omitted for clarity.
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ilar for all structures and comparable to those in
closely related compounds such as [ReX(CO)3(NʝN)]
(X
=
Cl–, Br–, OH2)[4c,19] or [Re(–CϵC–R)(CO)3-
(NʝN)],[1a,1c,1e,1f,2a,2c] in which the angle N1–Re1–N2 is
found to be less than 90° as expected for the steric demand
of the bite angle of the chelating diimine unit (NʝN).
Photocatalysis
Since the excited states of PSs 1–6 can be quenched by
TEOA, and, additionally, the electrochemical reduction po-
tential is negative enough to ensure the reduction of [Co-
(DOH)Br2] (7) as a WRC (see Table 3), compounds 1–6
were subjected to photocatalytic H2 formation experiments
in DMF. Irradiation was performed at 385 nm with 0.9 m
TEOA as sacrificial electron donor, 0.1 m [HTEOA]BF4 as
proton source, 0.5 mm 7 as WRC, and 1–6 as PS. With all
complexes 1–6, H2 formation was observed, albeit to dif-
ferent extents. The highest TON was observed for 1 and 6,
achieving 400 TONH/Re after 30 h and 50 h, respectively.
Since the efficiency of excited PS quenching by TEOA de-
pends on the lifetime of PS*, the performance of 6 is unex-
pected. The lifetime of 6 is rather short (14.9 ns), and hence
the theoretical maximum yield of reduction Φq,max is lower
than those for compounds 1, 4, and 5 (Table 2). We em-
phasize that blank experiments, excluding either WRC or
PS, only showed traces of H2 (1Ϯ1 TONH/Re), which is
most likely formed by the decomposition of 1–6.
Figure 3. TONs (A) and rate profiles (B) for photocatalytic H2 pro-
duction in 10 mL of DMF, 0.9 m TEOA, 0.1 m [HTEOA]BF4, and
0.5 mm [Co(DOH)Br2] (7), at 385 nm and in the presence of 0.1 mm
1–6.
The rate profile of H2 formation reveals an initialization
phase before onset of H2 formation (Figure 3). As shown
earlier, CoIII in WRC 7 is first reduced to CoII and then to
CoI, the actual precatalyst for H2 formation.[4b] This “acti-
vation step” is dependent on PS concentration for 1–6 and
requires 10–90 min, followed by a steep increase of the rate
of H2 formation (H2/sec). A maximum rate was reached
after 2–3 h for 1–3 and 5 (phen), followed by an equally
rapid rate decrease. H2 formation ceases after 10–30 h.
Complexes 4 and 6 are more inert and a slow increase of the
H2 production rate to a maximum after 5–10 h, followed by
a slow decrease, was observed. The shape of the rate–time
curve mirrors the degradation of both WRC and PS over
time. HPLC measurements, performed before and after ca-
talysis, revealed degradation products but no pristine PS or
WRC anymore. Decomposition of PS was also evidenced
in blank DMF under irradiation as shown in Figure S12.
We hypothesize that loss of the CO ligand trans to the alk-
formation remained constant (1.7ϫ10–8 mol/s and
1.8ϫ10–8 mol/s, respectively), clearly demonstrating PS
concentration to be rate-limiting. Still, bleaching of the
catalytic solution during irradiation indicates decomposi-
tion of both PS and WRC. Furthermore, the reductive
quenching rate of the excited PS plays a key role in this
process as well, since the kq values of 1–6 (1.5–
43.8ϫ106 m–1 s–1) are far from diffusion-limited values
(Table 2). Furthermore, trends between theoretical Φq,max
and observed yields are not obvious, and different cage es-
cape yields (Φcage) of PS 1–6 are likely to play a significant
role in the actual reduction yields (Φred), thereby decisively
influencing the performance of catalysts.
Conclusions
Luminescent ReI–alkynyl complexes, based on [Re-
ynyl, as observed in other complexes with strong donors (–CϵC–R)(CO)3phen] and [Re(–CϵC–R)(CO)3bipy] (1–6),
such as phosphines, could lead to inactivation and finally are active PSs in photocatalytic H2 production. TONs up
decomposition.[20]
to 400 were achieved with TEOA as electron donor,
The rate profiles of H2 formation for phen (1–3, 5) and [HTEOA]BF4 as proton source, and compound 7 as WRC
bipy (4, 6) complexes are different (Figure 3A). The maxi- in DMF. These alkynyl ligands induce a slight redshift of
mum initial rates of 1–3 and 5 are up to five times higher the MLCT, exhibit increased excited state lifetimes and have
than those of 4 and 6, but the latter ones show more long- higher quantum yields. TOFmax are up to five times higher
term stability. To deduce rate- and performance-limiting for phen than for bipy complexes. There was no difference
factors, the concentration of WRC 7 was altered. Increasing in overall performance between the two diimine units or the
WRC 7 from 0.5 mm to 2 mm improved the TONH/Re of 2 alkynyl moieties. Thus, {Re(CO)3}-based complexes with
from 140 in 15 h to 270 in 45 h. The highest rate of H2 alkynyl ligands in the axial position do improve the spectro-
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[M + H]+, 574.9 (100) [M + Na]+. HPLC: 15.62. C23H13N2O3Re
(551.57): calcd. C 50.08, H 2.38, N 5.08; found C 49.96, H 2.66, N
4.81.
scopic properties by inducing a redshift of the MLCT,
which enables a more efficient conversion of solar light into
chemical energy. Still, photoinstability, as observed with
other ReI-based PSs, remains a concern.
[Re(CO)3(–CϵC–{3,5-(CF3)2(C6H3)})phen] (2): The same pro-
cedure as that for 1 was used with [ReBr(CO)3phen] (200 mg,
0.38 mmol), TlPF6 (134.5 mg, 0.385 mmol), 1-ethynyl-3,5-bis(tri-
fluoromethyl)benzene (151 μL, 0.86 mmol), and dry TEA (1 mL)
at 75 °C for 48 h. Purification by flash chromatography (neutral
aluminum oxide, hexane/ethyl acetate, 3:1). Yield: 151 mg of an
analytically pure, yellow powder (0.22 mmol, 58%). Crystals suit-
able for X-ray measurements were obtained by diffusion of diethyl
ether vapor into a concentrated solution of 2 in methanol. UV/Vis:
λmax (DMF) = 392 nm (ε = 3503 m–1 cm–1), λem (DMF) = 654 nm
Experimental Section
Experimental details for analytical instrumentation, measurements
and chemicals, as well as UV/Vis, emission, and CV spectra can be
found in the Supporting Information.
Hydrogen Evolution Measurements: Gas chromatograms were re-
corded with a Bruker 450 GC gas chromatograph by using argon
as carrier gas with a 3 mϫ2 mm packed molecular sieves 13X 80–
100 column. Automated measurements were performed as de-
scribed previously.[3c] Sample preparation for homogeneous cataly-
sis was performed by adding from stock solutions 0.5 mm 1–6,
0.5 mm [Co(DOH)Br2], and 0.1 m [HTEOA]BF4 to 1 m TEOA (re-
action volume = 10 mL). The reaction vessel was closed and di-
rectly degassed with argon in the automation system of the gas
chromatograph. This procedure was applied for all H2 evolution
experiments discussed. Irradiation was started when oxygen and
nitrogen had been depleted from the solution (as directly monitored
by gas chromatography). HPLC samples were taken before and af-
ter catalysis.
(ΦP = 0.0074; τ = 94 ns). IR (KBr): ν = 1893 (s), 1917 (s), 2006 (s)
˜
ν(CϵO), 2091 (w), 2121 (w) ν(CϵC) cm–1. 1H NMR (300 MHz,
[D4]methanol): δ = 9.46 (dd, J = 5.4 and 1.5 Hz, 2 H), 8.80 (dd, J
= 8.1 and 1.5 Hz, 2 H), 8.21 (s, 2 H), 8.00 (dd, J = 8.1 and 5.4 Hz,
2 H), 7.41 (s, 1 H), 7.08 (s, 2 H) ppm. ESI-MS (MeOH): m/z (%)
= 710.9 (100) [M + Na]+. HPLC: 20.70. C25H11F6N2O3Re (687.56):
calcd. C 43.67, H 1.61, N 4.07; found C 43.28, H 1.49, N 3.89.
[Re(CO)3(–CϵC–{2-(NC5H4)})phen] (3): The same procedure as
that for 1 was used with [ReBr(CO)3phen] (200 mg, 0.38 mmol),
TlPF6 (134.5 mg, 0.385 mmol), 2-ethynylpyridine (76 μL,
0.76 mmol), and dry TEA (1 mL) at 75 °C for 48 h. Purification
by flash chromatography (neutral aluminum oxide, gradient ethyl
acetate, 0–10% methanol). Precipitation of 3 in methanol with hex-
ane gave 174.8 mg of an analytically pure, yellow powder
(0.32 mmol, 84%). Crystals suitable for X-ray measurements were
obtained by diffusion of hexane vapor into a concentrated solution
of 3 in methanol (two water molecules have been co-crystallized).
UV/Vis: λmax (DMF) = 392 nm (ε = 2972 m–1 cm–1), λem (DMF) =
X-ray Crystallography: Crystallographic data for compounds 1–4
and 6 were collected at 183(2) K with an Oxford Diffraction
Xcalibur system having a ruby detector by using Mo-Kα radiation
(λ = 0.71073 Å) that was graphite-monochromated. Suitable crys-
tals were covered with oil (Infineum V8512, formerly known as
Paratone N), mounted on top of a CryoLoopTM (Hampton Re-
search), and immediately transferred to the diffractometer. The
program suite CrysAlisPro was used for data collection, multiscan
absorption correction, and data reduction.[21] Structures were
solved with direct methods by using SIR97[22] and were refined by
full-matrix least-squares methods on F2 with SHELXL-97.[23] All
hydrogen atoms were placed on calculated positions. The structures
were checked for higher symmetry with the help of the program
Platon.[24] CCDC-990010 (for 1), -990011 (for 2), -990012 (for 3),
-990013 (for 4), -990014 (for 4a), and -990015 (for 6) contain the
supplementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
655 nm (ΦP = 0.005; τ = 72 ns). IR (KBr): ν = 1891 (s), 1922 (s),
˜
2009 (s) ν(CϵO), 2086 (w) ν(CϵC) cm–1. 1H NMR (300 MHz, [D6]-
DMSO): δ = 9.47 (dd, J = 5.4 and 1.5 Hz, 2 H), 8.96 (dd, J = 8.4
and 1.5 Hz, 2 H), 8.34 (s, 2 H), 8.13–8.06 (m, 2 overlapping signals,
3 H), 7.33 (td, J = 7.8 and 1.8 Hz, 1 H), 6.92–6.87 (m, 1 H), 6.58–
6.55 (dt, J = 7.8 and 1.2 Hz, 1 H) ppm. ESI-MS (MeOH): m/z
(%) = 553.9 (100) [M + H]+, 575.9 (11) [M + Na]+. HPLC: 16.43.
C22H16N3O5Re [3 (588.6) + 2H2O]: calcd. C 44.89, H 2.74, N 7.14;
found C 45.02, H 2.92, N 7.01.
[Re(CO)3(–CϵC–{2-(C5H4N)})bipy] (4)
When the general procedure was followed, the synthesis resulted in
a mixture of 4 and its N-bridged dimeric form: [{Re(CO)3-
(bipy)}2(μ–CϵC–{2-(C5H4N)})]+ (approximately 1:1, as monitored
by HPLC and confirmed by ESI-MS and crystal structure; see
compound 4a in the Supporting Information). Therefore the reac-
tion protocol was modified, and the selectivity was optimized
towards the formation of 4.
[Re(CO)3{–CϵC–(C6H5)}phen] (1): In a Young Schlenk system
(under a N2 atmosphere), [ReBr(CO)3phen] (40 mg, 0.075 mmol)
and TlPF6 (26.6 mg, 0.076 mmol) were suspended in dry THF
(5 mL), then phenylacetylene (16.6 μL, 0.15 mmol) and dry TEA
(0.2 mL) were added. The Young Schlenk system was closed tightly
and heated up to 75 °C for 48 h. After completion of the reaction
(monitored by HPLC), TlBr was filtered off over Celite and washed
with additional THF. After the solvent was evaporated, the crude
product was purified by flash chromatography (silica gel, ethyl acet-
ate/hexane, 2:1). Yield: 25.4 mg of an analytically pure, orange
powder (0.046 mmol, 61%). Crystals suitable for X-ray measure-
ments were obtained by diffusion of pentane vapor into a concen-
In a Young Schlenk system (under a N2 atmosphere), [ReBr(CO)3-
bipy] (100 mg, 0.20 mmol) and TlPF6 (69.7 mg, 0.20 mmol) were
suspended in dry acetonitrile (10 mL), then 2-ethynylpyridine
(40.2 μL, 0.40 mmol) and dry TEA (0.5 mL) were added. The
Young Schlenk system was closed tightly and heated up to 80 °C
trated solution of 1 in CH2Cl2. UV/Vis: λmax (DMF) = 389 nm (ε for 20 h. After completion of the reaction (monitored by HPLC),
= 2817 m–1 cm–1), λem (DMF) = 650 nm (ΦP = 0.0035; τ = 82 ns).
TlBr was filtered off over Celite and washed with additional aceto-
nitrile. After the solvent was evaporated, the crude product was
purified by flash chromatography (neutral aluminum oxide, gradi-
ent ethyl acetate, 0–5% methanol). Yield: 85.3 mg of an analytically
pure, yellow powder (0.16 mmol, 80%). Crystals suitable for X-ray
IR (KBr): ν = 1886 (s), 1921 (s), 2012 (s) ν(CϵO), 2077 (w), 2091
˜
(w) ν(CϵC) cm–1. 1H NMR (300 MHz, CDCl3): δ = 9.46 (unre-
solved dd, 2 H), 8.52 (unresolved dd, 2 H), 8.03 (s, 2 H), 7.84 (dd,
J = 8.1 and 4.8 Hz, 2 H), 7.02–6.87 (m, overlapping signals, 3 H),
6.74–6.70 (m, 2 H) ppm. ESI-MS (MeOH): m/z (%) = 552.9 (28) measurements were obtained by diffusion of hexane vapor into a
Eur. J. Inorg. Chem. 0000, 0–0
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concentrated solution of 4 in methanol. UV/Vis: λmax (DMF) =
395 nm (ε = 2489 m–1 cm–1), λem (DMF) = 671 nm (ΦP = 0.0012; τ
[1]
a) B. J. Liddle, S. V. Lindeman, D. L. Reger, J. R. Gardinier,
Inorg. Chem. 2007, 46, 8484–8486; b) V. W.-W. Yam, S. H.-F.
Chong, K.-K. Cheung, Chem. Commun. 1998, 2121–2122; c)
V. W.-W. Yam, S. H.-F. Chong, K. M.-C. Wong, K.-K. Cheung,
Chem. Commun. 1999, 1013–1014; d) V. W.-W. Yam, Chem.
Commun. 2001, 789–796; e) V. W.-W. Yam, V. C.-Y. Lau, K.-K.
Cheung, Organometallics 1995, 14, 2749–2753; f) V. W.-W.
Yam, K. M.-C. Wong, S. H.-F. Chong, V. C.-Y. Lau, S. C.-F.
Lam, L. Zhang, K.-K. Cheung, J. Organomet. Chem. 2003,
670, 205–220.
a) W.-K. Chung, K. M.-C. Wong, W. H. Lam, X. Zhu, N. Zhu,
H.-S. Kwok, V. W.-W. Yam, New J. Chem. 2013, 37, 1753–1767;
b) S.-T. Lam, G. Wang, V. W.-W. Yam, Organometallics 2008,
27, 4545–4548; c) K. M.-C. Wong, S. C.-F. Lam, C.-C. Ko, N.
Zhu, S. Roué, C. Lapinte, S. Fathallah, K. Costuas, S. Kahlal,
J.-F. Halet, Inorg. Chem. 2003, 42, 7086–7097.
= 37 ns). IR (KBr): ν = 1898 (s), 1928 (m), 2014 (s) ν(CϵO), 2087
˜
(w) ν(CϵC) cm–1. 1H NMR (300 MHz, CDCl3): δ = 9.13 (unre-
solved dd, 2 H), 8.26–8.22 (m, 1 H), 8.18 (unresolved dd, 2 H),
8.06–8.00 (m, 2 H), 7.52–7.47 (m, 2 H), 7.36–7.33 (m, 1 H), 7.06–
7.03 (m, 1 H), 6.88–6.83 (m, 1 H) ppm. ESI-MS (MeOH): m/z (%)
= 529.9 (100) [M + H]+. HPLC: 16.18. C20H12N3O3Re (528.53):
calcd. C 45.45, H 2.29, N 7.74; found C 45.25, H 2.33, N 7.74.
[Re(CO)3(6-{CϵC–(coumarin)})phen] (5): The same procedure as
that for 1 was used with [ReBr(CO)3phen] (100 mg, 0.19 mmol),
TlPF6 (66.6 mg, 0.19 mmol), 6-ethynylcoumarin (67 mg,
0.39 mmol), and dry TEA (0.5 mL) at 75 °C for 48 h. Purification
by flash chromatography (silica gel, ethyl acetate/hexane, 2:1).
Yield: 89.3 mg of an analytically pure, yellow powder (0.143 mmol,
76%). UV/Vis: λmax (DMF) = 378 nm (ε = 4506 m–1 cm–1), λem
[2]
[3]
a) A. Fihri, V. Artero, M. Razavet, C. Baffert, W. Leibl, M.
Fontecave, Angew. Chem. Int. Ed. 2008, 47, 564–567; Angew.
Chem. 2008, 120, 574; b) M. Guttentag, A. Rodenberg, C.
Bachmann, A. Senn, P. Hamm, R. Alberto, Dalton Trans. 2013,
42, 334–337; c) B. Probst, M. Guttentag, A. Rodenberg, P.
Hamm, R. Alberto, Inorg. Chem. 2011, 50, 3404–3412; d) B.
Probst, C. Kolano, P. Hamm, R. Alberto, Inorg. Chem. 2009,
48, 1836–1843; e) B. Probst, A. Rodenberg, M. Guttentag, P.
Hamm, R. Alberto, Inorg. Chem. 2010, 49, 6453–6460.
a) C. Bachmann, M. Guttentag, B. Spingler, R. Alberto, Inorg.
Chem. 2013, 52, 6055–6061; b) M. Guttentag, A. Rodenberg,
R. Kopelent, B. Probst, C. Buchwalder, M. Brandstätter, P.
Hamm, R. Alberto, Eur. J. Inorg. Chem. 2012, 59–64; c) P.
Kurz, B. Probst, B. Spingler, R. Alberto, Eur. J. Inorg. Chem.
2006, 2966–2974; d) M. Wang, Y. Na, M. Gorlov, L. Sun, Dal-
ton Trans. 2009, 6458–6467; e) M. Wrighton, D. L. Morse, J.
Am. Chem. Soc. 1974, 96, 998–1003; f) J. K. Hino, L. Della Ci-
ana, W. J. Dressick, B. P. Sullivan, Inorg. Chem. 1992, 31, 1072–
1080; g) A. Juris, S. Campagna, I. Bidd, J. M. Lehn, R. Ziessel,
Inorg. Chem. 1988, 27, 4007–4011; h) A. J. Lees, Chem. Rev.
1987, 87, 711–743; i) D. J. Stufkens, J. W. M. van Outersterp,
A. Oskam, B. D. Rossenaar, G. J. Stor, Coord. Chem. Rev. 1994,
132, 147–154; j) D. J. Stufkens, A. Vlcˇek Jr., Coord. Chem. Rev.
1998, 177, 127–179; k) B. P. Sullivan, J. Phys. Chem. 1989, 93,
24–26; l) G. Tapolsky, R. Duesing, T. J. Meyer, Inorg. Chem.
1990, 29, 2285–2297.
a) E. D. Cline, S. E. Adamson, S. Bernhard, Inorg. Chem. 2008,
47, 10378–10388; b) P. Du, J. Schneider, F. Li, W. Zhao, U.
Patel, F. N. Castellano, R. Eisenberg, J. Am. Chem. Soc. 2008,
130, 5056–5058; c) P. Du, J. Schneider, G. Luo, W. W. Brennes-
sel, R. Eisenberg, Inorg. Chem. 2009, 48, 4952–4962; d) F.
Gärtner, B. Sundararaju, A.-E. Surkus, A. Boddien, B. Loges,
H. Junge, P. H. Dixneuf, M. Beller, Angew. Chem. Int. Ed. 2009,
48, 9962–9965; Angew. Chem. 2009, 121, 10147; e) C. Li, M.
Wang, J. Pan, P. Zhang, R. Zhang, L. Sun, J. Organomet.
Chem. 2009, 694, 2814–2819; f) S. Metz, S. Bernhard, Chem.
Commun. 2010, 46, 7551–7553; g) H. Ozawa, M.-a. Haga, K.
Sakai, J. Am. Chem. Soc. 2006, 128, 4926–4927; h) L. L. Tin-
ker, S. Bernhard, Inorg. Chem. 2009, 48, 10507–10511; i) X.
Wang, S. b. Goeb, Z. Ji, N. A. Pogulaichenko, F. N. Castellano,
Inorg. Chem. 2011, 50, 705–707.
(DMF) = 651 nm (ΦP = 0.0037; τ = 60.6 ns). IR (KBr): ν = 1727
˜
(m) ν(C=O), 1890 (s), 1902 (s), 2008 (s) ν(CϵO), 2089 (w), ν(CϵC)
cm–1. 1H NMR (300 MHz, CDCl3): δ = 9.48 (dd, J = 5.1 and
1.5 Hz, 2 H), 8.55 (dd, J = 8.1 and 1.5 Hz, 2 H), 8.06 (s, 2 H), 7.87
(dd, J = 8.1 and 5.1 Hz, 2 H), 7.40 (d, J = 9.6 Hz, 1 H), 6.98 (d, J
= 1.8 Hz, 1 H), 6.87 (d, J = 8.7 Hz, 1 H), 6.80 (dd, J = 8.7 and
1.8 Hz, 1 H), 6.25 (d, J = 9.6 Hz, 1 H) ppm. ESI-MS (MeOH): m/z
(%) = 642.9 (100) [M + Na]+. HPLC: 15.81. C26H13N2O5Re
(619.60): calcd. C 50.40, H 2.11, N 4.52; found C 50.22, H 2.08, N
4.41.
[4]
[Re(CO)3(6-{CϵC–(coumarin)})bipy] (6): The same procedure as
that for 1 was used with [ReBr(CO)3bipy] (100 mg, 0.20 mmol),
TlPF6 (69.7 mg, 0.20 mmol), 6-ethynylcoumarin (67 mg,
0.39 mmol), and dry TEA (0.5 mL) at 75 °C for 48 h. Purification
by flash chromatography (silica gel, ethyl acetate/hexane, 2:1).
Yield: 99.3 mg of an analytically pure, yellow powder (0.167 mmol,
84%). Crystals suitable for X-ray measurements were obtained by
diffusion of pentane vapor into a concentrated solution of 6 in
THF. UV/Vis: λmax (DMF) = 379 nm (ε = 4180 m–1 cm–1), λem
(DMF) = 677 nm (ΦP = 0.00096; τ = 14.1 ns). IR (KBr): ν = 1727
˜
(m) ν(C=O), 1880 (s), 1897 (s), 2006 (s) ν(CϵO), 2090 (w), ν(CϵC)
cm–1. 1H NMR (300 MHz, CDCl3): δ = 9.15 (unresolved dd, 2 H),
8.22 (unresolved dd, 2 H), 8.10–8.04 (m, 2 H), 7.55–7.50 (m, 2 H),
7.48 (d, J = 9.6 Hz, 1 H), 7.13 (d, J = 1.8 Hz, 1 H), 7.01 (dd, J =
8.7 and 1.8 Hz, 1 H), 6.94 (d, J = 8.7 Hz, 1 H), 6.29 (d, J = 9.6 Hz,
1 H) ppm. ESI-MS (MeCN): m/z (%) = 596.9 (47) [M + H]+, 618.9
[5]
(100) [M
+ +
Na]+, 634.9 (58) [M K]+. HPLC: 15.39.
C24H13N2O5Re (595.58): calcd. C 48.40, H 2.20, N 4.70; found C
48.08, H 2.28, N 4.49.
[Co(DOH)Br2] (7): The WRC was prepared according to our pub-
lished procedure.[3c]
Supporting Information (see footnote on the first page of this arti-
cle): Experimental details, absorption and emission plots, cyclic
voltammograms, photophysical plots, ORTEP drawings, crystallo-
graphic data, energy levels.
[6]
a) T. Lazarides, T. McCormick, P. Du, G. Luo, B. Lindley, R.
Eisenberg, J. Am. Chem. Soc. 2009, 131, 9192–9194; b) T. M.
McCormick, B. D. Calitree, A. Orchard, N. D. Kraut, F. V.
Bright, M. R. Detty, R. Eisenberg, J. Am. Chem. Soc. 2010,
132, 15480–15483; c) T. M. McCormick, Z. Han, D. J. Wein-
berg, W. W. Brennessel, P. L. Holland, R. Eisenberg, Inorg.
Chem. 2011, 50, 10660–10666.
K. Zeitler, Angew. Chem. Int. Ed. 2009, 48, 9785–9789; Angew.
Chem. 2009, 121, 9969.
a) J. L. Hawecker, J. M. R. Ziessel, New J. Chem. 1983, 7, 271–
277; b) X. Hu, B. S. Brunschwig, J. C. Peters, J. Am. Chem.
Soc. 2007, 129, 8988–8998; c) R. M. Kellett, T. G. Spiro, Inorg.
Acknowledgments
We would like to thank Prof. Dr. Rainer Winter and his group for
providing us 6-ethynylcoumarin. For financial support of this
work, we are grateful to the Swiss National Science Foundation
(Sinergia CRSII2-136205/1program). Financial support by the
University of Zurich through the University Research Priority Pro-
gram (URPP) “LightChEC” is gratefully acknowledged.
[7]
[8]
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Chem. 1985, 24, 2373–2377; d) S. Losse, J. G. Vos, S. Rau, Co-
ord. Chem. Rev. 2010, 254, 2492–2504.
[13] D. Guillaumont, M. P. Wilms, C. Daniel, D. J. Stufkens, Inorg.
Chem. 1998, 37, 5816–5822.
[9] a) J. P. Bigi, T. E. Hanna, W. H. Harman, A. Chang, C. J. [14] a) W. D. Bates, P. Chen, D. M. Dattelbaum, W. E. Jones, T. J.
Chang, Chem. Commun. 2010, 46, 958–960; b) H. I. Karunad-
asa, C. J. Chang, J. R. Long, Nature 2010, 464, 1329–1333; c)
C. V. Krishnan, B. S. Brunschwig, C. Creutz, N. Sutin, J. Am.
Chem. Soc. 1985, 107, 2005–2015; d) C. V. Krishnan, N. Sutin,
J. Am. Chem. Soc. 1981, 103, 2141–2142; e) H. A. Schwarz, C.
Creutz, N. Sutin, Inorg. Chem. 1985, 24, 433–439; f) W. M.
Singh, T. Baine, S. Kudo, S. Tian, X. A. N. Ma, H. Zhou, N. J.
DeYonker, T. C. Pham, J. C. Bollinger, D. L. Baker, B. Yan,
C. E. Webster, X. Zhao, Angew. Chem. Int. Ed. 2012, 51, 5941–
5944; Angew. Chem. 2012, 124, 6043; g) B. D. Stubbert, J. C.
Peters, H. B. Gray, J. Am. Chem. Soc. 2011, 133, 18070–18073;
h) Y. Sun, J. P. Bigi, N. A. Piro, M. L. Tang, J. R. Long, C. J.
Chang, J. Am. Chem. Soc. 2011, 133, 9212–9215.
Meyer, J. Phys. Chem. A 1999, 103, 5227–5231; b) S. Cam-
pagna, S. Serroni, S. Bodige, F. M. MacDonnell, Inorg. Chem.
1999, 38, 692–701.
[15] H. Sun, M. Z. Hoffman, J. Phys. Chem. 1994, 98, 11719–11726.
[16] P. J. Giordano, S. M. Fredericks, M. S. Wrighton, D. L. Morse,
J. Am. Chem. Soc. 1978, 100, 2257–2259.
[17] P.-A. Jacques, V. Artero, J. Pécaut, M. Fontecave, Proc. Natl.
Acad. Sci. USA 2009, 106, 20627–20632.
[18] J. E. Huheey, E. A. Keiter, R. L. Keiter, Anorganische Chemie –
Prinzipien von Struktur und Reaktivität, 3rd ed., Walter de
Gruyter, Berlin, 2003, p. 495.
[19] a) S. F. Haddad, J. A. Marshall, G. A. Crosby, B. Twamley,
Acta Crystallogr., Sect. E 2002, 58, m559–m561; b) N. J. Lun-
din, P. J. Walsh, S. L. Howell, J. J. McGarvey, A. G. Blackman,
K. C. Gordon, Inorg. Chem. 2005, 44, 3551–3560.
[20] a) K. Koike, N. Okoshi, H. Hori, K. Takeuchi, O. Ishitani, H.
Tsubaki, I. P. Clark, M. W. George, F. P. A. Johnson, J. J.
Turner, J. Am. Chem. Soc. 2002, 124, 11448–11455; b) K.
Koike, J. Tanabe, S. Toyama, H. Tsubaki, K. Sakamoto, J. R.
Westwell, F. P. A. Johnson, H. Hori, H. Saitoh, O. Ishitani, In-
org. Chem. 2000, 39, 2777–2783.
[10] a) D. Merki, S. Fierro, H. Vrubel, X. Hu, Chem. Sci. 2011, 2,
1262–1267; b) S. Y. Reece, J. A. Hamel, K. Sung, T. D. Jarvi,
A. J. Esswein, J. J. H. Pijpers, D. G. Nocera, Science 2011, 334,
645–648; c) S. Jones, J. Qu, K. Tedsree, X.-Q. Gong, S. C. E.
Tsang, Angew. Chem. Int. Ed. 2012, 51, 11275–11278; Angew.
Chem. 2012, 124, 11437; d) K. Kalyanasundaram, J. Kiwi, M.
Grätzel, Helv. Chim. Acta 1978, 61, 2720–2730; e) Z. Li, Y.
Chen, Y. Du, X. Wang, P. Yang, J. Zheng, Int. J. Hydrogen
Energy 2012, 37, 4880–4888; f) P. Shen, S. Zhao, D. Su, Y. Li,
A. Orlov, Appl. Catal. B 2012, 126, 153–160; g) X.-J. Zheng,
[21] Oxford Diffraction Ltd., 171.32 ed., Oxford, UK, 2007, p. Xca-
libur CCD system.
L.-F. Wei, Z.-H. Zhang, Q.-J. Jiang, Y.-J. Wei, B. Xie, M.-B. [22] A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano, C.
Wei, Int. J. Hydrogen Energy 2009, 34, 9033–9041.
Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori, R.
Spagna, J. Appl. Crystallogr. 1999, 32, 115–119.
[23] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122.
[24] A. L. Spek, J. Appl. Crystallogr. 2003, 36, 7–13.
Received: March 6, 2014
ˇ
[11] A. Cannizzo, A. M. Blanco-Rodríguez, A. El Nahhas, J. Seb-
era, S. Zálisˇ, J. A. n. Vlcˇek, M. Chergui, J. Am. Chem. Soc.
2008, 130, 8967–8974.
[12] M. Rank, M. Zabel, R. F. Winter, Z. Anorg. Allg. Chem. 2013,
639, 2565–2574.
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Photocatalysis
M. Oberholzer, B. Probst, D. Bernasconi,
B. Spingler, R. Alberto* .................... 1–9
Upon irradiation, luminescent alkynyl-
rhenium(I) complexes [Re(–CϵC–R)-
(CO)3(NʝN)] (NʝN = bipy, phen) allow
for TONs up to 400 (H/Re) in photocat-
alytic proton reduction in the presence of a
sacrificial electron donor and cobalt-based
water reduction catalyst. The acetylene
group induces a redshift in the UV/Vis
spectrum, ensuring a more efficient conver-
sion of solar light into chemical energy.
Photosensitizing Properties of Alkynyl-
rhenium(I) Complexes [Re(–CϵC–R)(CO)
3(NʝN)] (NʝN = 2,2Ј-bipy, phen) for H2
Production
Keywords: Hydrogen / Rhenium / Homo-
geneous catalysis / Luminescence / Alkynes
Eur. J. Inorg. Chem. 0000, 0–0
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