Evaluation of bis-cyclometalated alkynylgold(III) sensitizers for water photoreduction to hydrogen

Article abstract of DOI:10.1039/c6dt03044k

Well-defined gold sensitizers for hydrogen production from water remain extremely rare despite decades of interest, and are currently limited to systems based on ruthenium, iridium or platinum complexes. This report details the synthesis and characterization of a series of neutral cyclometalated gold(iii) complexes of the type [(RC^N^CR)Au(CC-R′)] (R = H or tert-butyl group; R′ = aryl groups) that have been found to be good candidates to function as harvesting materials in light-induced electron transfer reactions. We established the efficacy of systems with these gold(iii) complexes as photosensitizers (PSs) in the production of renewable hydrogen in the presence of [Co(2,2′-bipyridine)₃]Cl₂ or [Rh(4,4′-di-tert-butyl-2,2′-bipyridine)₃](PF₆)₃ as a H₂-evolved catalyst and triethanolamine (TEOA) as a sacrificial electron donor in acetone-water solution. All complexes are active, and there is a more than threefold increase over other candidates in photocatalytic H₂ generation activity. Under the optimal reaction conditions, hydrogen evolution took place through a photochemical route with the highest efficiency and with a turnover number (TON) of up to 1441.5 relative to the sensitizer over 24 hours. In the initial photochemical path, the reductive quenching of the excited gold(iii) complex by TEOA due to the latter's greater concentration in the system followed by electron transfer to the catalyst species is proposed to be the dominant mechanism. A photo-to-H₂ quantum yield of approximately 13.7% was attained when illuminated with monochromatic light of 400 nm. Such gold(iii) complexes have demonstrated significant utility in solar-to-hydrogen reactions and thus represent a new effective class of light-harvesting materials. These results open possibilities for pursuing more efficient photosensitizers featuring gold(iii) complexes in photocatalytic solar energy conversion.

Full text of DOI:10.1039/c6dt03044k

View Article Online
View Journal
Dalton
Transactions
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: Z.T. Yu, X. Liu, Y.
Yuan, Y. Li, G. Chen and Z. zou, Dalton Trans., 2016, DOI: 10.1039/C6DT03044K.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/dalton

Page 1 of 20
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT03044K
Evaluation of BisꢀCyclometalated Alkynylgold(III) Sensitizers for Water
Photoreduction to Hydrogen
Zhen-Tao Yu,a,b Xiao-Le Liu,c Yong-Jun Yuan,a Yong-Hui Li,a Guang-Hui Chen,c and Zhi-Gang Zoua,b
a National Laboratory of Solid State Microstructures and Collaborative Innovation Center of Advanced
Microstructures, Jiangsu Provincial Key Laboratory for Nanotechnology, Nanjing University, Nanjing,
Jiangsu 210093 (P. R. China)
b EcoꢀMaterials and Renewable Energy Research Center, College of Engineering and Applied Sciences,
Nanjing University, and Kunshan Innovation Institute of Nanjing University, Nanjing, Jiangsu 210093
(P. R. China)
c Department of Chemistry, Shantou University, Guangdong 515063 (P. R. China)
* Correspondence authors
Eꢀmail: yuzt@nju.edu.cn
RECEIVED DATE (to be automatically inserted after your manuscript is accepted if required
according to the journal that you are submitting your paper to)
1

Dalton Transactions
Page 2 of 20
View Article Online
DOI: 10.1039/C6DT03044K
ABSTRACT: Wellꢀdefined gold sensitizers for hydrogen production from water remain extremely rare,
despite decades of interest and are currently limited to systems based on ruthenium, iridium or platinum
complexes. This report details the synthesis and characterization of a series of neutral cyclometalated
gold(III) complexes of the type [(RC^N^CR)Au(C≡CꢀR')] (R = H or tertꢀbutyl group; R' = aryl groups)
that have been found to be good candidates to function as harvesting materials in lightꢀinduced electron
transfer reactions. We established the efficacy of systems with these gold(III) complexes as
photosensitizers (PSs) in the production of renewable hydrogen in the presence of [Co(2,2'ꢀ
bipyridine)3]Cl2 or [Rh(4,4'ꢀdiꢀtertꢀbutylꢀ2,2'ꢀbipyridine)3](PF6)3 as a H2ꢀevolved catalyst and
triethanolamine (TEOA) as a sacrificial electron donor in acetoneꢀwater solution. All complexes are
active, and there is a more than threefold increase over other candidates in photocatalytic H2 generation
activity. Under the optimal reaction conditions, hydrogen evolution took place through a photochemical
route with the highest efficiency with a turnover number (TON) of up to 1441.5 relative to the sensitizer
over 24 hours. In the initial photochemical path, the reductive quenching of the excited gold(III)
complex by TEOA due to the latter’s greater concentration in the system followed by electron transfer
to the catalyst species is proposed to be the dominant mechanism. A photoꢀtoꢀH2 quantum yield of
approximately 13.7% was attained when illuminated with monochromatic light of 400 nm. Such
gold(III) complexes have demonstrated significant utility in solarꢀtoꢀhydrogen reactions and thus
represent a new effective class of lightꢀharvesting materials. These results open possibilities for
pursuing more efficient photosensitizers featuring gold(III) complexes in photocatalytic solar energy
conversion.
Keywords: gold • hydrogen evolution • photochemistry • photosensitizer • water splitting
2

Page 3 of 20
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT03044K
INTRODUCTION
The solar generation of molecular hydrogen is an inspiring technology based on the direct reduction
of water that involves turning solar energy into clean chemical energy, and it has favorable longꢀterm
prospects for building a sustainable clean energy future.1 Among the various approaches that have been
developed toward this, artificial photosynthetic processes exploiting the principles of natural
photosynthesis are particularly intriguing, and they always start with the light energy being trapped by
specialized lightꢀharvesting chromophores acting similar to photosynthetic pigments such as
chlorophylls in multiꢀcomponent photochemical hydrogen evolution systems.2 For the efficient capture
of solar energy in solarꢀtoꢀfuel conversion devices,3 the capability of a light harvester, which funnels the
energy to the associated reaction centers (waterꢀreduction catalyst) for conversion into chemical fuel in
the form of hydrogen, plays a pivotal role.4 Transition metal compounds, especially based on the d6
Ru(II) metal ion with polypyridylꢀbased ligands as potent sensitizers, have been the focus of research
due to their advantageous photophysical and photochemical properties, such as intense absorption in the
visible range and long excited state lifetimes, thereby making them attractive in the context of
developing the lightꢀharvesting components of fuelꢀgenerating systems.5
Recently, Ir(III) complexes with excellent activity have emerged as exciting alternatives to be used in
this process.6 The potential of these complexes relies on the fact that their remarkable photoexcited
states are very tunable by varying the electronic structures of the ligands or the selection of special
ligands with relatively facile synthetic accessibility. Despite years of research and the achievement of
significant progress in recent years,7 solar fuel production is still at its experimental stage, and there are
many challenges that must be met. Indeed, upon irradiation, sensitizers are often limited by their
durability.8 This drawback is the consequence of the fact that the ligand dissociation of the complex
occurs during photolysis, hence giving rise to the functional inactivation of the complex. Against this
backdrop, several solutions have already been proven but require the further design and development of
novel metal complex sensitizers that show stability and activity to fulfill artificial photosynthesis.9,10
Comprehensively understanding the structural features of these sensitizers that determine the electronic
structures and excitedꢀstate molecular geometries is certainly important as part of the mechanistic
principles behind H2O reduction catalysis to apply this knowledge to the rational molecular design of
future efficient sensitizers for photosensitized reactions.
In contrast, reports of luminescent gold(III) complexes having longꢀlived excited states in fluid
solutions, which can lead to their utilization as functional sensitizers to perform lightꢀinduced electron
transfer reactions, are sparse due to the high electrophilicity of the gold(III) center and the presence of
the lowꢀenergy dꢀd ligand field states responsible for nonꢀemissive species.11 Moreover, as a
consequence of their relatively large positive reduction potentials and their consequent poor stability in
3

Dalton Transactions
Page 4 of 20
View Article Online
DOI: 10.1039/C6DT03044K
solution, the photochemistry of cyclometalated gold(III) complexes has not yet been extensively
investigated. It has been proposed that the gold(III) complexes, by use of the incorporation of both rigid
cyclometalating and strongly σ–donating carbon ligands such as acetylide or carbene, as they raise the
energies of the deactivating metalꢀcentered dꢀd excited states, making them thermally inaccessible and
thus leading to a reduction of nonꢀradiative deactivation, have been observed to emit even at room
temperature in various media.12ꢀ14 Additionally, the presence of the σ(M–C) bond to a correlated
gold(III) center improves the stability of the highꢀvalent metal compounds toward reduction. By analogy
to isoelectronic and isostructural alkynylplatinum(II) compounds, alkynylgold(III) complexes with longꢀ
lived emissive excited states and other attractive properties, such as low toxicity, inertness and an
environmentally benign nature, may open a wide range of unexplored possibilities as photosensitizers
for the prospect of photocatalytic hydrogen production. Despite these prospects, gold(III) complexes are
considerably less explored in such investigations. A cationic carbeneꢀcontaining gold(III) complex was
first found recently to lend itself to this type of application, with approximately 350 turnovers of
hydrogen after 4 h of irradiation,15 reinforcing the potential application of gold complexes in the
relevant photocatalytic process. This demonstration of their accessibility offers opportunities for the
development of new sensitizers in this series that bear new and specific structural features and might
display increasing reactivity.
Scheme 1. Chemical structures of gold compounds 1–4.
In continuation of our work on the design of transition metal complex sensitizers and their
application in the chemical conversion of light energy, we now anticipate to extend it to gold(III)
complexes for the construction of photochemical hydrogen production systems. In this study, we
4

Page 5 of 20
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT03044K
focused on bisꢀcyclometalated gold(III) complexes with acetylide coꢀligands, which have been
discovered to favor bright luminescence with a long lifetime in both the solid and solution states, which
is crucial for triggering efficient photocatalytic processes. A class of neutral luminescent
alkynylgold(III) complexes [(RC^N^CR)Au(C≡CꢀR')] (R = H or tertꢀbutyl group; R' = aryl groups) has
been synthesized and characterized (Scheme 1). Theoretical investigations based on density functional
theory (DFT) and timeꢀdependent DFT (TDꢀDFT) methods have elucidated the electronic structures and
electronic transition processes of the compounds. Their photosensitization behavior for hydrogen
production was investigated by adopting a threeꢀcomponent catalytic system in the presence of the
water reduction catalyst and triethanolamine (TEOA) as a sacrificial electron donor in a mixture of
acetone and water. The results demonstrate that the change of the microenvironment of the gold(III)
complex, such as the use of cyclometalating ligands with different electronic properties and ancillary
ligands, generates complexes with different photophysical and photochemical characteristics and also
shows different activities in photocatalytic systems for the production of hydrogen.
RESULTS AND DISCUSSION
Gold(III) complexes 1–4 were synthesized in 68.7ꢀ95.8% yields via a copper(I)ꢀcatalyzed route based
on the literature protocol for analogous compounds as executed with related molecules.16 The detailed
synthetic procedures are described in the Supporting Information.
40000
1
2
3
4
30000
20000
10000
0
300
350
400
450
500
Wavelength (nm)
Figure 1. Electronic absorption spectra of complexes 1–4 (5×10ꢀ5 M) in CH3CN.
Photophysical Properties. The studied complexes were first assessed for their photophysical properties
in airꢀsaturated acetonitrile at ambient temperature. The UV/vis profiles of complexes 1–4 are
illustrated in Figure 1. The photophysical data of complexes 1 and 3 that have previously been reported
are also shown for comparison.16 For all complexes, at concentrations of ca. 5×10ꢀ5 M, intense
absorption bands below 340 nm in the UV spectral region with molar extinction coefficients (ε) on the
order of 104 Mꢀ1 cmꢀ1 are observed and are in general assigned to the ligandꢀcentered π → π* intraligand
5

Dalton Transactions
Page 6 of 20
View Article Online
charge transfer (ILCT) transition located on the surrounding ligands. This UV absorpDtiOoI:n10i.1s03f9o/lCl6oDwT0e3d044bKy
a less intense vibronicꢀstructured absorption band (ε on the order of 103 Mꢀ1 cmꢀ1) at a longer
wavelength with some tailing into the visible region, giving rise to the paleꢀyellow to yellow colors of
the complexes. The lowerꢀenergy bands contribute to the transition, incorporating a mixed state
involving metalꢀperturbed π → π* IL transitions located in the tridentate C^N^C ligand and π → π*
ligandꢀtoꢀligand charge transfer (LLCT) transitions from the peripheral phenyl moieties to the central
pyridine unit. Such assignments are based on earlier reported studies of related similar gold(III)
complexes. A possibility of a metalꢀtoꢀligand charge transfer (MLCT) is less feasible due to the
electrophilic and redoxꢀinactive character of the gold(III) metal center, as predicted by the below
calculations. The intensity and onset of absorption in the visible spectral region account for the ability
of the lightꢀharvesting materials to capture solar energy and thus exert an influence on the
photocatalytic performance.
Table 1. Photophysical and electrochemical properties of studied gold(III) complexes 1ꢀ4.
Comp.
λem [nm][a]
478,504
τ [ns][a]
τavg [ns][a]
10.1
Φ[a] [%]
1.5×10ꢀ3
1.1×10ꢀ2
8.8×10ꢀ3
2.6×10ꢀ2
Eox [V][b]
+1.77
Ered [V][b]
ꢀ1.27
1
2
3
4
35.1 (44%)
19.6 (97%)
106.9 (88%)
3.8 (70%)
480,625
19.4
+1.29
ꢀ1.27
488,513
42.9
+1.87
ꢀ1.33
ꢀ1.35c
455,478(sh)
4.2
+1.44
[a] Measurements in a N2 atmosphere in CH3CN at room temperature (relative error for λem: ±3 nm); Decay profiles were satisfactorily fitted by three exponential functions and
only the dominant lifetime was shown (relative error for τ: ±5%). The percentage in parentheses indicates the contribution from that component; the luminescence quantum yield
was measured utilizing [Ru(bpy)3]Cl2 in aqueous in solution as a standard (relative error for Φ: ±10%). [b] Redox potentials measured in deoxygenated CH3CN with 0.1 M nꢀ
Bu4NPF6 as the supporting electrolyte; potentials (Eox refers to the peak potential for the irreversible oxidation waves; Ered = 1/2(Epa + Epc) for the reversible reduction) measured vs
Ag/AgCl coupled and converted to normal hydrogen electrode (NHE). [c] The value refers to the peak potential for the irreversible reduction wave.
For all complexes, emission was weak in the airꢀsaturated CH3CN solutions, probably because of
quenching by oxygen in air. However, in nitrogenꢀsaturated CH3CN, using an excitation wavelength of
350 nm, all complexes (at concentrations of ca. 5×10ꢀ5 M) exhibited intense emissions with a broad,
emission band with peak wavelengths of approximately 455–625 nm at room temperature, with solution
photoluminescence quantum yields (Φ) on the order of 10ꢀ2. The corresponding photophysical data are
collected in Table 1 and found to be qualitatively in agreement with those observed for gold(III)
complexes described in the literature,16 and the spectra are depicted in Figure S1. As anticipated, there
was an increase in the quantum yield of the carbazoleꢀcontaining complexes 2 and 4 compared to 1 and
3. The excitation spectra of each complex recorded at the maximum emission closely resemble the
corresponding electronic absorption spectra. With reference to previous studies, the luminescence was
derived from the metalꢀperturbed triplet [π → π*] IL excited state of the C^N^C ligand. The
luminescence of 3 is redꢀshifted with respect to that observed for complex 1. As in the absorption
spectra, this is due to the involvement of slight different HOMOꢀ1 in the related transition, as observed
6

Page 7 of 20
Dalton Transactions
View Article Online
from the corresponding TDꢀDFT data (vide infra). Complexes 2 and 4 displayed exDcOeIp: 1t0i.o10n3a9/lCe6DmT0is30s4io4Kn
profiles and wavelength maxima at wavelengths of 480 nm and 625 nm for 2, and 455 nm for 4,
respectively, which probably originated from a LLCT [π(C≡CꢀR') → π*(RC^N^CR)] excited state.17
The relatively weak emission peak at 480 nm persisted even after the most careful purifications of 2 by
repeated recrystallization, and thus is not attributed to a possible impact of impurity but to an intrinsic
electronic transition of this complex. The incorporation of tertꢀbutyl groups in the C^N^C ligand
resulted in a blue shift of the emission. This has also been observed in [Pt(II)C^N^N] alkynyl complex
by Che and coworkers previously.18 These differences in the emission maxima could arise from the
varying energies of the different cyclometalating surroundings, which provide orbitals that participate to
different extents in the excited state origin of the respective complexes. The spectral assignments have
been further substantiated by DFT/TDDFT calculations. For each complex in nitrogenꢀsaturated
CH3CN (5×10ꢀ5 M), the observed emission lifetimes (τ) upon excitation at 370 nm exhibit three
exponential component with an average lifetime (τavg) on the nanosecond time scale (4.2ꢀ42.9 ns),
following the order 3 > 2 > 1 > 4 (Figure S2). Three exponential components were necessary for fitting
adequately the luminescence decays. This result is similar to that obtained for emissive Au(III)
complexes.19 The lifetime data suggested the presence of more than one emitting species in these
complexes, which can not be resolved in energy in the steadyꢀstate emission spectra with our device.20
In the case of complex 4, it exhibits a relatively short lifetime. This is probable the result of mixed
singlet–triplet states,21,22 which could contain more singlet state mixing in the emission. That such a
mixing occurs is supported by the fact that the luminescence cannot be quench by oxygen. Under air
saturation, the emission spectral profiles of 1-3 remain unchanged but the intensities of the
luminescence, exhibiting the short lifetimes in aerated solution, were quenched an extent of ca. 20%ꢀ
30%, whereas no significant quenching effect was observed for 4 (Figure S3).17 The knowledge of these
photophysical parameters for complexes of these types provides valuable insights in evaluating the
potential applications of these materials in lightꢀinduced electron transfer reactions.
DFT Calculations. The above spectral/structure views are supported by the DFT/TDꢀDFT
calculations using the molecular orbital diagrams of the systems of interest.23 The spatial plots of the
highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) for
each complex are illustrated in Table S1, and they are consistent with previous reports on analogous
gold(III) complexes. The HOMO and LUMO are obviously separated, indicating intramolecular charge
separation interactions between the separated fragments in the complex. For the four complexes, the
HOMO consists primarily of the electron density on the ligand of πꢀ(C≡CꢀR'). The HOMOꢀ1 (secondꢀ
highest occupied molecular orbital) is of quite a different character, as is induced by the different
characters of the molecular environments of the individual complexes. It is interesting that the C^N^C
7

Dalton Transactions
Page 8 of 20
View Article Online
ligand in 1 and 3 contributes a large participation to the HOMOꢀ1 orbital, while theDHOOI: 1M0.10O39ꢀ/1C6iDnT0230a4n4Kd
4 is localized on the carbazole fragment. In contrast, the LUMO has nearly identical contours in all
complexes, being spread over both the π*ꢀ(RC^N^CR) with some contributions from the gold(III)
center.
Based on the results of TDꢀDFT calculations (Table S2), the orbitals involved in the lowest energy
transition (S0 → S1, S0 is the ground state) for complexes 1–4 are primarily HOMOꢀ1 and LUMO for 1
(by 97.35% contribution) and 3 (by 96.85% contribution), while that are HOMO and LUMO for 2 (by
96.50% contribution) and 4 (by 95.04% contribution). Thus, the vertical transitions imply an electron
density transfer, mainly from the oneꢀelectron excitations of HOMOꢀ1 → LUMO (1ILCT) for 1 and 3.
The presence of the carbazolyl group in 2 and 4 reduces the contribution of the C^N^C ligand and
enhances the participation of the C≡CꢀR' ligand; consequently, the origin of the first singlet transition,
which is clearly different from that of 1 and 3, can be described as the oneꢀelectron excitation of
HOMO → LUMO (1LLCT, also involving HOMOꢀ3).
Similar to the singlets, the lowest vertical triplet S0 → T1 transition is of the π → π* type, which does
not correspond to the triplet excited state derived from the HOMO → LUMO excitation but is defined
by the configuration HOMOꢀ1 → LUMO for both 1 and 3 (contribution: 82.80% for 1; 82.79% for 3),
lying at similar energies. This indicates that the excited state contains predominantly a tridentate ligand
with a 3ILCT character, although other transitions are also involved therein. In comparison to complexes
1 and 3, complexes 2 and 4 also only differ in the ligand of RC^N^CR (for 2, R = H; for 4, R = tertꢀ
butyl); however, owe to the large molecular architectures of these complexes, it is difficult to describe
the distribution calculated for their lowest triplet S0 → T1 transition, which is rather complicated, both
containing HOMO → LUMO (contribution: 40.77% for 2; 10.38% for 4) and being highly
multiconfigurational in character. This is likely accounted for the blueꢀshift of the emission band in 4
compared to that in 2. The result suggests a difference in the nature of the excited state of these
complexes.
Electrochemical Properties. The redox properties of all four complexes were evaluated by cyclic
voltammetry, conducted in anhydrous acetonitrile solvent containing 0.1 M tetraꢀnꢀbutylammonium
hexafluorophosphate (nꢀBu4NPF6) as the supporting electrolyte at room temperature, and the results are
summarized in Table 1. The cyclic voltammograms of the four compounds exhibit an irreversible
oxidative wave with anodic maxima at 1.29ꢀ1.87 V versus NHE (Epa) (Figure S4). They also show a
quasiꢀreversible reductive wave, except 4 (irreversible wave), with a halfꢀwave potential in a small
range of ꢀ1.27 V to ꢀ1.35 V vs NHE (for 4, Epc, cathodic peak). In analogy with previously published
works16 and the uncoordinated ligand under identical conditions (Figure S5), on the basis of the DFT
calculations, both processes could mainly be associated with ligandꢀcentered electrochemical events,
8

Page 9 of 20
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT03044K
concomitant with minor influences from the gold(III) center. For the reduction potentials occurring at
the π*ꢀ(RC^N^CR) orbital with only minor influences from the gold(III) center, there is only a small
variation in the cathodic peaks, indicating the limited influence of the tertꢀbutyl substituents on the aryl
ring of the RC^N^CR ligand in 3 and 4 on the LUMO orbitals. With reference to the other studies on
the related derivatives,16 the oxidation is considered the oxidation of the alkyne unit. The electronic
effects of the alkynyl ligands lead to the variation of the potential for the oxidation.
Photocatalytic Hydrogen Production. The photocatalytic reaction activities for hydrogen generation
were then examined to identify the applicability of these complexes as photosensitizers (PSs). The
studies were performed by adopting a threeꢀcomponent catalytic system in the presence of the water
reduction catalyst (WRC) and TEOA as a sacrificial electron donor in a media of an acetone/water
mixture (v/v = 4:1) (for details, see the Experimental Section).24 The reduction catalyst generally
includes cobalt, rhodium and platinum and so on.8ꢀ10 TEOA is chosen because according to the
comparison of the equilibrium redox potential of TEOA with the excitedꢀstate redox potentials E(S*/Sꢀ)
of the gold(III) complexes, the driving force for the reductive quenching of the excited state of the
complex using TEOA is generally thermodynamically favorable. The utility of acetone is due to
solubility reasons, as this type of gold(III) complex is sparingly soluble in water. In an earlier study,25 it
was found that the performance of the catalytic system is strongly affected by the media used in the
hydrogenꢀevolving reactions. Here, the ratio of coꢀsolvent is adopted based on optimizing experiments
previously described for similar multicomponent systems.10 The reaction turnover numbers [TONs =
n(H)/n(PS)] with respect to the photosensitizer were calculated according to oneꢀelectron transfer
processes.
An initial series of experiments was conducted for the comparison of the activities of the four
complexes in the photocatalytic production of hydrogen upon irradiating deaerated solutions containing
different complexes 1–4 acting as a PS, [Co(2,2'ꢀbipyridine)3]Cl2 (0.33 mM) or [Rh(dtbꢀbpy)3](PF6)3
(dtbꢀbpy = 4,4'ꢀdiꢀtertꢀbutylꢀ2,2'ꢀbipyridine) (0.33 mM) as a WRC,8ꢀ10 and TEOA (0.19 M) as a source
of electrons under irradiation with a Xeꢀarc lamp (300 W). The conditions were identical to those used
for hydrogen production according to the preceding results,10 which were optimized for the catalytic
performance. The pH value of the initial solution is adjusted to the desired value by the addition of
hydrochloric acid prior to addition of the PS and WRC, and the pH was selected based on the
optimization of the catalytic reaction to achieve the optimal performance of hydrogen production.
Figure 2 displays a plot of the amount of hydrogen produced in the photolysis at a specific pH in a
typical run, as quantitatively measured by gas chromatography, versus the irradiation time under UV
and visible light irradiation, and the results are summarized in Table 2. No hydrogen production could
be detected outside of experimental error in the control experiments in the absence of any of the
9

Dalton Transactions
Page 10 of 20
View Article Online
sensitizer, TEOA, or WRC in the system, demonstrating that all of the componentsDOmI:a1k0.e103a9n/C6eDsTs0e3n04ti4aKl
contribution in the reaction for the production of hydrogen. Moreover, the reaction did not proceed at
all when the reaction was conducted under identical reaction conditions but lacking light, suggesting
that light is a necessary component to provide the electrochemical driving force for electron transfer to
achieve a fuelꢀproducing catalysis. The experimental results suggest that the systems containing the
gold(III) complexes are capable of promoting the lightꢀdriven hydrogen production in the presence of an
electron donor.
2000
1
2
3
4
1
2
3
4
(A)
1600
1200
800
400
0
(B)
1500
1000
500
0
In the dark
0
12
24
36
48
60
72
0
4
8
12
16
20
24
Irradiation Time (h)
Irradiation Time (h)
Figure 2. Photoꢀinduced hydrogen evolution of 1–4 (40 ꢁM) with (A) 0.33 mM [Co(bpy)3]Cl2 (at pH
8.0) or (B) 0.33 mM [Rh(dtbꢀbpy)3](PF6)3 (at pH 7.0) and 0.19 M TEOA in acetone/water (4:1 v/v, 100
mL) upon irradiation (Xe arc lamp; 300 W).
In Figure 2A, for the cobalt catalyst employed (pH = 8.0), the hydrogen produced with no induction
period was observed to follow the order 3 > 4 > 1 > 2. Upon maintaining these conditions for 24 h, the
system with complex 3 produced up to 1716.9 µmol of H2 (TON = 858.5, ±10%), which is
approximately 3.3 times as much as that produced with complex 2 (515.7 µmol of H2). When the
photoproduction of H2 was accomplished in the presence of [Rh(dtbꢀbpy)3](PF6)3 (pH = 8.0), which
replaced [Co(bpy)3]Cl2 (bpy = 2,2'ꢀbipyridine) as a WRC, the hydrogen production occurs after a
measurable induction time. During the initial 4 h of irradiation (except for complex 4, with 6 h), no
reaction proceeded to yield H2, but the H2 produced increased with the continued irradiation time. This
is indicative of the formation of an active species from the reaction during the induction time, as
confirmed by the formation of the black solid after the photolysis. The observed long induction time
prior to hydrogen generation in the Rhꢀcatalyzed system is a feature about the formation of active
colloidal species in the reaction.26 The quenching behavior of these complexes will be further discussed
in the sections below. A similar induction time was previously observed in studies of the Rh catalyst for
water reduction,27 with the reduction of the initial Rh(III) species to the catalytically reactive state,
probably formally a colloidal Rh, which is a key species for hydrogen evolution. Similarly, under these
conditions, complex 3 led to the production of more H2 (TON = 745.5) after 72 h of illumination than
10

Page 11 of 20
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT03044K
did the other complexes (Figure 2B). These results indicate that there is no clear correlation between the
photophysical properties and the catalytic activity. For example, although complex 3 is by far the most
effective compared to the other complexes, it has no remarkable photophysical properties, except for
the excitedꢀstate lifetime compared to its analogues. The difference among the activities of these
complexes is difficult to rationalize because the hydrogen evolution activity depends in a complex way
on the sensitizer, the catalyst and the electron donor but also the interaction between them. It is clear
that the further exploration of the utility of such complexes for photoinduced electron transfer chemistry
would be helpful in understanding the underlying structure and function relationship.
Table 2. Photocatalytic H2ꢀproducing activity using different catalytic conditions.
Run
PS (Concn (µM))
1 (40 ꢁM)
2 (40 ꢁM)
3 (40 ꢁM)
4 (40 ꢁM)
3 (5 µM)
Catalyst
pH
8.0
8.0
8.0
8.0
8.0
8.0
8.0
7.0
7.0
7.0
7.0
7.0
7.0
7.0
8.0
8.0
8.0
7.0
Time (h)
TON[a]
394.2
257.9
858.5
633.1
1276.2
1441.5
1250.2
610.3
557.5
745.5
295.2
1246.3
1057.7
923.4
216.9
443.7
530.5
127.4
1
Co(bpy)3Cl2
24
2
Co(bpy)3Cl2
24
3
Co(bpy)3Cl2
24
4
Co(bpy)3Cl2
24
5
Co(bpy)3Cl2
24
6
3 (10 ꢁM)
3 (20 ꢁM)
1 (40 ꢁM)
2 (40 ꢁM)
3 (40 ꢁM)
4 (40 ꢁM)
3 (5 ꢁM)
Co(bpy)3Cl2
24
7
Co(bpy)3Cl2
24
8
Rh(dtbꢀbpy)3(PF6)3
Rh(dtbꢀbpy)3(PF6)3
Rh(dtbꢀbpy)3(PF6)3
Rh(dtbꢀbpy)3(PF6)3
Rh(dtbꢀbpy)3(PF6)3
Rh(dtbꢀbpy)3(PF6)3
Rh(dtbꢀbpy)3(PF6)3
Co(bpy)3Cl2 (0.08 mM)
Co(bpy)3Cl2 (0.17 mM)
Co(bpy)3Cl2 (0.33 mM)
K2PtCl4
72
9
72
10
11
12
13
14
15[b]
16[b]
17[b]
18
72
72
72
3 (10 ꢁM)
3 (20 ꢁM)
3 (20 ꢁM)
3 (20 ꢁM)
3 (20 ꢁM)
3 (40 ꢁM)
72
72
24
24
24
72
Photocatalytic conditions: PS, 0.33 mM catalyst and 0.19 M TEOA in acetone/water (4:1 v/v, 100 mL) upon irradiation (Xe arc lamp, 300 W).
[a] Error was less than 10% of stated values upon repeated experiments. [b] Upon irradiation (Xe lamp, 300 W, λ > 420 nm).
The activity of the hydrogenꢀevolving systems is determined by each electron transfer step which
depends on the redox potentials of the involved species in the reaction mixture. Based on the estimated
excitedꢀstate redox data, the excited state of gold(III) is likely to undergo an electron transfer of both
11

Dalton Transactions
Page 12 of 20
View Article Online
DOI: 10.1039/C6DT03044K
oxidative quenching by the catalyst with electron transfer from the photoexcited sensitizer to the
+
3+
catalyst [Co(bpy)3]2+ [E(Co(bpy)32+/Co(bpy)3 = ꢀ0.95 V vs. NHE]28 or Rh(dtbꢀbpy)3 [E(Rh(dtbꢀ
bpy)33+/Rh(dtbꢀbpy)32+ = ꢀ0.67 V vs. NHE]29 and reductive quenching by TEOA [E(TEOA+/TEOA) =
3+
+0.82 V vs. NHE].30 In such multicomponent systems with catalyst as [Co(bpy)3]2+ or Rh(dtbꢀbpy)3
,
because quenching processes are certainly thermodynamically favorable, the reductive and oxidative
quenching can take place at the same time. Experimentally, reductive quenching by TEOA is observed
for complexes 1–3, but not for complex 4, which suggests that the much shorterꢀlived singlet state of
the complex is not the species involved in the photoreduction event. Unlike TEOA, quenching by
3+
[Co(bpy)3]2+ or Rh(dtbꢀbpy)3 is observed at relatively low concentrations for all cases, as shown in
Figures. S7 and S8. All the quenching followed a linear SternꢀVolmer relationship between the
luminescence intensity of the complex and the quencher concentration (Figures S6ꢀ8), and the
quenching constant (kq) are presented in Table 3. Complex 3 has a smaller driving force for the
respective reaction and also has a relatively long lifetime than the other gold cyclometalated species
(Table 1), which make it low sensitivity to quenching by TEOA and other quenchers. The rate constant
3+
for complexes 1, 2 and 4 by [Co(bpy)3]2+ or Rh(dtbꢀbpy)3 is near the diffusionꢀlimited rate (in the
range of 109−1010 Mꢀ1sꢀ1), suggesting the presence of both static and dynamic quenching, which can be
attributed to electron transfer from the excited sensitizer to the Co or Rh species.31
Table 3. Quenching Kinetics of studied gold complexes.[a]
PS
1
kq Co(bpy)32+ (Mꢀ1sꢀ1)
kq Rh(dtbꢀbpy)3+ (Mꢀ1sꢀ1)
1.81×109
kq TEOA (Mꢀ1sꢀ1)
1.87×108
5.94×1010
2
6.73×1010
1.59×109
1.57×108
3
3.71×109
3.37×107
2.11×107
4
6.37×1010
2.24×1010
No quenching
[a] Measured in CH3CN at room temperature.
These results, combined with the fact that all complexes facilitated the hydrogenꢀevolution process to
some degree, suggest that quenching ability is not directly correlated with catalytic reactivity. The
3+
observation showed that the presence of the [Co(bpy)3]2+ or Rh(dtbꢀbpy)3 in the systems of 1–3
provided an anther quenching pathway that was the oxidative electron transfer from the sensitizer to the
catalyst and was fast as the reductive quenching by TEOA. To obtain the information of the excited
state reaction of the cyclometalated gold complex with Co or Rh catalyst in the presence of TEOA, the
lifetime of 3 in CH3CN were measured under the addition of [Co(bpy)3]2+ or Rh(dtbꢀbpy)33+ (Figure
S9). With TEOA, in the absence of the catalyst the decay time of the luminescence is almost half of that
12

Page 13 of 20
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT03044K
in the pure CH3CN solution, indicating that the quenching behavior by TEOA through electron transfer.
3+
If the [Co(bpy)3]2+ or Rh(dtbꢀbpy)3 was added, the decay time of the luminescence reduces further,
3+
respectively. The observation showed that the presence of the [Co(bpy)3]2+ or Rh(dtbꢀbpy)3 provided
an anther quenching pathway that was the oxidative electron transfer from the sensitizer to the catalyst
and was slow as the reductive quenching. In the photocatalysis, both pathway should occur in the same
time and contribute to the quenching process. In the photocatalysis, it could be considered that
hydrogen evolution may also occur by both pathway. However, these processes may be kinetically
competitive with the hydrogen generation reaction under the existing working conditions, where the
amount of TEOA is far more than that of the catalyst. Therefore, the pathway for electron transfer
accounting for the production reaction of hydrogen was assumed to proceed via reductive quenching
dominating over oxidative quenching. For the system containing complex 4, the results unambiguously
demonstrate that the hydrogen production appears to involve an oxidative quenching event.
Considering the aforementioned photocatalytic results, a possible photocatalytic pathway is briefly
documented below based on wellꢀestablished studies.32 Hydrogen generation starts with the quenching
of the excitedꢀstate of gold(III) of 1–3, which is longꢀlived enough for electron transfer between the
light harvesting and the electron donor. In the presence of an electron donor, the excited state of PS, that
is *[Au]3+ (most likely in the triplet excited state), is reductively quenched, providing a reduced
sensitizer, that is [Au]2+, which has a sufficiently strong reduction potential to effectively deliver an
electron to the catalyst unit, where dihydrogen can be produced. With complex 4, an oxidative
quenching pathway results in hydrogen production.
However, if the reaction was carried out with [Co(bpy)3]Cl2 or [Rh(dtbꢀbpy)3](PF6)3 under irradiation
with a Xeꢀarc lamp (300 W), the sensitizer was unstable. Complex 3 was used for all of the subsequent
lightꢀdriven hydrogen production experiments. After photoreduction reaction, the decomposition
products were extracted from the mixture solution and characterized. From the ESIꢀMS analysis (Figure
S10) for illuminated samples of the reaction mixture with 3, no peak of complex 3 (m/z = 662.33) was
observed, and the peak of RC^N^CR (R = tertꢀbutyl) was found at m/z = 343.33. The results indicated
that the neutral gold complex is still unstable under constant illumination. This is in part because a
reductive quenching pathway drives the photochemical reaction.33 In addition, when using
[Co(bpy)3]Cl2, no solid particle was observed in the solution after the photocatalytic reaction. There
was no evidence of the formation of metallic Co nanoparticles during photocatalysis for hydrogen
production. The Xꢀray photoelectron spectroscopy (XPS) measurements were used to get information
on metal oxidation state before and after the photocatalytic reaction. In Co 2p spectra, no peak appeared
for the 2p transition in the sample obtained from the reaction mixture compared with that of CoCl2 or
[Co(bpy)3]Cl2 (Figure S11, left),34 suggesting that the occurrence of the decomposition of the catalyst
13

Dalton Transactions
Page 14 of 20
View Article Online
under the photocatalytic conditions. In the case of [Rh(dtbꢀbpy)3](PF6)3, a dark DsOoI:li10d.10p39a/rCt6icDlTe030w44aKs
observed after photolysis. From the XPS measurements of this particle (Figure S11, right), much
broader and relative lower intensities were observed compared to the original compound. The catalytic
reaction seemed to not be homogeneous, as confirmed by the quantitative poisoning experiments with
carbon disulfide (CS2), which is a strong catalyst poison for rhodium(0).27b With the addition of 1
equivalents of CS2, the activity of the catalysis system was suppressed. The observation that the
catalytic system is deactivated in the presence of CS2 supported that the colloidal species participate in
the catalysis.35
2000
1500
1000
500
0
15
12
9
pH 5
pH 6
pH 7
pH 8
pH 9
(B)
(A)
400 nm
380 nm
6
350 nm
420 nm
3
450 nm
0
0
6
12
18
24
330
360
390
420
450
Irradiation Time (h)
Wavelength (nm)
Figure 3. (A) Influence of pH on photoinduced hydrogen evolution upon irradiation (300 W Xeꢀarc
lamp) using 3 (40 ꢁM). (B) The apparent quantum yield (AQY) of hydrogen production of 3 versus the
wavelength of the incident light (upon irradiation of 2 h, selected wavelengths: 350, 380, 400, 420, and
2+
450 nm). Conditions: Co(bpy)3 (0.33 mM) and TEOA (0.19 M) in acetoneꢀwater solution (4:1, v/v,
100 mL, pH = 8.0)
In the lightꢀinduced catalytic experiments, the pH value has a strong effect on the activity of the
catalytic system.36 A series of photocatalytic experiments based on the system containing complex 3 by
changing the pH of the solution was conducted to investigate the effect of the pH while keeping the
component concentrations of 40 ꢁM 3, 0.33 mM [Co(bpy)3]2+ and 0.19 M TEOA. The reaction has
been found to be sensitive to the pH; a clear optimum is observed at a pH value of 8.0, with an activity
~4ꢀfold higher than that observed at pH 5.0, as shown in Figure 3A. This agrees with previous
observations by others using [Co(bpy)3]2+ as a catalyst in hydrogen generation systems.37 At lower pH
values, the activity of the H2 production was decreased. This reduction in activity can be rationalized by
the decrease in the pH value, which may cause the protonation of TEOA to a considerable extent. At a
higher pH of 9.0, a reduced hydrogen production was also observed. The loss of activity can be
attributed to that the solution in this case does not favor the formation of the cobalt hydride species or
proton reduction to hydrogen at the metal center of a molecule catalyst. The effects of pH are complex,
and the observed pH optimum for the photocatalytic hydrogen production is the result of the balance of
these competing effects. The optimal hydrogenꢀproduction activity corresponds with the pH range at
14

Page 15 of 20
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT03044K
which the system shows its highest electron transfer ability, as confirmed by the quenching experiments
of complex 3 in the presence of TEOA at different values of pH (Figure S12). Further wavelengthꢀ
dependent experiments were carried out for the optimized system with complex 3 using bandpass filters
at 350, 380, 400, 420, and 450 nm under otherwise identical reaction conditions (Figure 3B). The
apparent quantum efficiency (AQY) of the hydrogen production was calculated to evaluate the photonꢀ
toꢀH2 efficiency. The AQY increased with increasing wavelength to a maximum at 400 nm, which
achieved a maximum AQY of 13.7%. After that, it decreased because of a decrease in the absorbance of
3 (Figure S13), and finally reached zero at the given wavelength of 450 nm.
When a 420ꢀnm cutꢀoff filter was used in the same xenon lamp to remove the UV irradiation,
complex 3 was still active, indicating that visible light is sufficient to promote hydrogen production.
However, the amount of evolved hydrogen upon visibleꢀlight irradiation decreased to 43% (530.5 ꢁmol,
2+
TON = 530.5) after irradiation for 24 h under otherwise identical conditions [3 (20 ꢁM), Co(bpy)3
(0.33 mM) and TEOA (0.19 M)]. Under this condition, the decomposition of 3 is much slower, and the
system durability increases, with a system lifetime of over 96 h to when the system produces minimal
further H2, with a total amount of hydrogen evolved of 933.0 ꢁmol. At the last stage of irradiation, the
H2 production rate decreases dramatically, with the turnover frequency (TOF) (3.7 hꢀ1) significantly
lower than that at 24 h (22.1 hꢀ1). The enhanced durability of the system under visible light irradiation is
mainly associated with the weak absorption ability at those wavelengths. Such catalysis would proceed
slowly and the process of decomposition would slow down as well. In a separate experiment, the
stability of 3 during photolysis was tested. At the end of a given hydrogenꢀproducing cycle, as shown in
Figure 4, after the readdition of an extra equiv of catalyst, approximately 502.0 µmol H2 was obtained
after an additional 30 h of irradiation, suggesting that the activity was almost recovered. The results
imply that the catalyst deactivation was the main reason for the cessation of hydrogen evolution under
illumination.
1500
1200
900
600
300
0
Re-addition of catalyst
0
30
60
90
120
Irradiation Time (h)
Figure 4. H2 production as a function of time showing the stability of the system with the reꢀaddition of
catalyst after 96 h of irradiation (λ > 420 nm). Conditions: 3 (20 ꢁM), Co(bpy)32+ (0.33 mM) and TEOA
15

Dalton Transactions
Page 16 of 20
View Article Online
DOI: 10.1039/C6DT03044K
(0.19 M) in acetoneꢀwater solution (4:1, v/v, 100 mL, pH = 8.0)
We also examined the concentration effect of the catalyst on the lightꢀinduced hydrogen production,
while the concentrations of TEOA (0.19 M) and sensitizer (20 ꢁM) were kept constant in the mixed
solvent solution of acetone/water (4:1 v/v, pH = 8.0) (Table 2). The amount of hydrogen production
increased with the concentration of the catalyst in the range of 0.08 to 0.33 mM (Figure S14), but the
initial rates of H2 generation are similar for the three catalyst concentrations; an analogous phenomenon
was also observed for other Coꢀbased catalytic systems.38 The H2 production efficiency of the system
reached its highest value, 530.5 ꢁmol of H2 after 24 h of irradiation in the presence of 0.33 mM
Co(bpy)32+, after which the system did not produce more hydrogen as the concentration of catalyst
increased further to 0.5 mM.
Conclusions
In this work, a class of bisꢀcyclometalated gold(III) acetylide complexes containing a tridentate 2,6ꢀ
diphenylpyridineꢀbased C^N^Cꢀtype ligand have been successfully utilized as sensitizers for application
in photocatalytic hydrogen production in the presence of a molecular cobalt or rhodium complex as the
proton reduction catalyst and TEOA as an electron donor in an acetone/water solvent mixture. These
threeꢀcomponent systems displayed a long lifetime of greater than 96 h under the operating conditions,
and a turnover number of H2 production as high as 1441.5 was achieved, 4ꢀfold higher than those
reported previously for water reduction using gold complexes. The highest singleꢀwavelength quantum
yield of 13.7% for water reduction was obtained at 400 nm and compares well to the values for lightꢀ
induced H2 production by other metal complexes. The photocatalytic hydrogen production process may
occur through the quenching of the excited states of the neutral Au(III) complexes via both an oxidative
quenching by the catalyst and a reductive quenching by TEOA, based on UV/vis and electrochemistry
data, but the latter likely plays a more significant role in the photocatalysis because the amount of the
catalyst is far less than that of the TEOA. On the basis of the present results, future research will focus
on deepening our understanding of the structure/function relationship, as well as the further exploration
of architectureꢀunique gold(III) complexes through modification of the ligand framework for the
construction of even more efficient lightꢀharvesting materials for use in direct solar fuel production.
EXPERIMENTAL SECTION
Syntheses. All of the gold complexes (1–4) were prepared via the similar procedure and were described
in the Supporting Information.
16

Page 17 of 20
Dalton Transactions
View Article Online
Theoretical Calculations. All calculations were performed using the Gaussian 09DpOrI:o1g0.r1a03m9/Cb6DaTs0e3d04o4Kn
the density functional theory (DFT) method and timeꢀdependent DFT (TDꢀDFT) calculations. The
numerical calculations in this paper were performed on the IBM Blade cluster system at the High
Performance Computing Center (HPCC) of Nanjing University.
H2 Evolution Experiments. All H2 production experiments were evaluated in a conventional closed
circulating system with a side visible light irradiation using a 300 W xenon lamp (CERMAX LX−300;
ILC Technology) equipped without or with a cutꢀoff filter (radiation wavelength > 420 nm, 300
mW/cm2).1c A typical sample for the photocatalytic reaction studied herein contained 5 µM
photosensitizer, 0.33 mM catalyst and 0.19 M TEOA solution in 100 mL of acetoneꢀwater (4:1, v/v).
The pH value of the mixed solution was adjusted with concentrated hydrochloric acid as required. Prior
to the light irradiation, the solution should be protected from light by an Al foil, and the system was
evacuated successively before being backfilled with 100% argon. Subsequently, the solution was
irradiated with magnetic stirring. At this point, the hydrogen evolved from the reactions was monitored
and quantified at each analysis time on an online gas chromatograph equipped with a thermally
conductive detector (Shimadzu GCꢀ8A, argon as a carrier gas and MSꢀ5A column). The variation in
hydrogen production was less than 10% upon repeated experiments.
ACKNOWLEDGMENT. This work was financially supported by the National Basic Research
Program of China (Grant No. 2013CB632400), the Natural Science Foundation of Jiangsu Province
(Grant No. BK20141233). We are also grateful to the Scientific Research Foundation for the Returned
Overseas Chinese Scholars, State Education Ministry.
Supporting Information. Synthetic procedures, additional data and details including CVs,
photocatalytic experiments and DFT calculations for all complexes in this work. This material is
available free of charge via the Internet at http://pubs.acs.org.
REFERENCES
(1) (a) S. Styring, Faraday Discuss., 2012, 155, 357–376; (b) Y. Tchibana, L. Vaysierres and J. R.
Durrant, Nat. Photonics, 2012, 6, 511–518; (c) A. Kudo and Y. Miseki, Chem. Soc. Rev., 2009, 38,
253–278; (d) V. Artero, M. ChavarotꢀKerlidou and M. Fontecave, Angew. Chem. Int. Ed., 2011, 50,
7238–7266.
(2) (a) M. Wang and L. Sun, ChemSusChem, 2010, 3, 551–554; (b) N. Armaroli and V. Balzani,
Angew. Chem. Int. Ed., 2007, 46, 52–66.
(3) T. C. B. Harlang, Y. Liu, O. Gordivska, L. A. Fredin, C. S. Ponseca Jr, P. Huang, P. Chábera, K.
17

Dalton Transactions
Page 18 of 20
View Article Online
S. Kjaer, H. Mateos, J. Uhlig, R. Lomoth, R. Wallenberg, S. Styring, P. Persson, V.DSOuI: n10d.1s0t3r9ö/Cm6DTa0n3d044KK.
Wärnmark, Nat. Chem., 2015, 7, 883–889.
(4) (a) W. T. Eckenhoff and R. Eisenberg, Dalton Trans., 2012, 41, 13004–13021; (b) S. P. Luo, E.
Mejía, A. Friedrich, A. Pazidis, H. Junge, A. E. Surkus, R. Jackstell, S. Denurra, S. Gladiali, S.
Lochbrunner and M. Beller, Angew. Chem. Int. Ed., 2013, 52, 419–423; (c) R. S. Khnayzer, C. E.
McCusker, B. S. Olaiya and F. N. Castellano, J. Am. Chem. Soc., 2013, 135, 14068–14070; (d) S.
Jasimuddin, T. Yamada, K. Fukuju, J. Otsuki and K. Sakai, Chem. Commun., 2010, 46, 8466–8468.
(5) (a) S. Fukuzumi, T. Kobayashi and T. Suenobu, Angew. Chem. Int. Ed., 2011, 50, 728–731; (b) T.
Stoll, M. Gennari, I. Serrano, J. Fortage, J. Chauvin, F. Odobel, M. Rebarz, O. Poizat, M. Sliwa, A.
Deronzier and M.ꢀN. Collomb, Chem. Eur. J., 2013, 19, 782–792.
(6) (a) J. I. Goldsmith, W. R. Hudson, M. S. Lowry, T. H. Anderson and S. Bernhard, J. Am. Chem.
Soc. 2005, 127, 7502–7510; (b) F. Gärtner, D. Cozzula, S. Losse, A. Boddien, G. Anilkumar, H. Junge,
T. Schulz, N. Marquet, A. Spannenberg, S. Gladiali and M. Beller, Chem. Eur. J., 2011, 17, 6998–
7006; (c) P. Zhang, M. Wang, Y. Na, X. Li, Y. Jiang and L. Sun, Dalton Trans., 2010, 39, 1204–1206;
(d) S. Hansen, M. M. Pohl, M. Klahn, A. Spannenberg and T. Beweries, ChemSusChem, 2013, 6, 92–
101.
(7) D. R. Whang, K. Sakai and S. Y. Park, Angew. Chem. Int. Ed., 2013, 52, 11612–11615.
(8) L. J. Tinker, N. D. McDaniel, P. N. Curtin, C. K. Smith, M. J. Ireland and S. Bernhard, Chem.
Eur. J., 2007, 13, 8726–8732.
(9) (a) S. Metz and S. Bernhard, Chem. Commun., 2010, 46, 7551–7553; (b) B. F. DiSalle and S.
Bernhard, J. Am. Chem. Soc., 2011, 133, 11819–11821.
(10) (a) Z. T. Yu, Y. J. Yuan, J. G. Cai and Z. G. Zou, Chem. Eur. J., 2013, 19, 1303–1310; (b) Y. J.
Yuan, Z. T. Yu, H. L. Gao, Z. G. Zou, C. Zheng and W. Huang, Chem. Eur. J., 2013, 19, 6340–6349; (c)
Y. J. Yuan, Z. T. Yu, J. G. Cai, C. Zheng, W. Huang and Z. G. Zou, ChemSusChem, 2013, 6, 1357–
1365.
(11) (a) C.ꢀW. Chan, W.ꢀT. Wong and C.ꢀM. Che, Inorg. Chem., 1994, 33, 1266–1272; (b) X. Zhu,
L.ꢀL. Hung, N. Zhu, V. W.ꢀW. Yam and H.ꢀS. Kwok, Chem. Commun., 2005, 2906–2908; (c) V. W.ꢀW.
Yam, K. M.ꢀC. Wong, L.ꢀL. Hung and N. Zhu, Angew. Chem. Int. Ed., 2005, 44, 3107–3110.
(12) (a) W.ꢀP. To, K. T. Chan, G. S. M. Tong, C. Ma, W. M. Kwok, X. Guan, K.ꢀH. Low and C.ꢀM.
Che, Angew. Chem. Int. Ed., 2013, 52, 6648–6652; (b) C.ꢀY. Sun, W.ꢀP. To, X.ꢀL. Wang, K.ꢀT. Chan,
Z.ꢀM. Su and C.ꢀM. Che, Chem. Sci., 2015, 6, 7105–7111.
(13) J. FernandezꢀCestau, B. Bertrand, M. Blaya, G. A. Jones, T. J. Penfold and M. Bochmann, Chem.
Commun., 2005, 51, 16629–16632.
(14) (a) V. K.ꢀM. Au, K. M.ꢀC. Wong, D. P.ꢀK. Tsang, M. Y. Chan, N. Zhu and V. W.ꢀW. Yam, J.
18

Page 19 of 20
Dalton Transactions
View Article Online
DOI: 10.1039/C6DT03044K
Am. Chem. Soc., 2010, 132, 14273–14278; (b) K. M.ꢀC. Wong, V. K.ꢀM. Au, D. Wu and V. W.ꢀW.
Yam, J. Am. Chem. Soc., 2015, 137, 4654–4657.
(15) W.ꢀP. To, G. S.ꢀM. Tong, W. Liu, C. Ma, J. Liu, A. L.ꢀF. Chow and C.ꢀM. Che, Angew. Chem.
Int. Ed., 2012, 51, 2654–2657.
(16) (a) K. M.ꢀC. Wong, L.ꢀL. Hung, W. H. Lam, N. Zhu and V. W.ꢀW. Yam, J. Am. Chem. Soc.,
2007, 129, 4350–4365; (b) V. K.ꢀM. Au, D. P.ꢀK. Tsang, K. M.ꢀC. Wong, M.ꢀY. Chan, N. Zhu and V.
W.ꢀW. Yam, Inorg. Chem., 2013, 52, 12713–12725.
(17) A. Szentkuti, J. A. Garg, O. Blacque and K. Venkatesan, Inorg. Chem., 2015, 54, 10748–10760.
(18) W. Lu, B. X. Mi, M. C. W. Chan, Z. Hui, C. M. Che, N. Zhu and S. T. Lee, J. Am. Chem. Soc.,
2004, 126, 4958–4971.
(19) M. P. Eng, T. Ljungdahl, J. Andréasson, J. Mårtensson and B. Albinsson, J. Phys. Chem. A, 2005,
109, 1776–1784.
(20) E. C. Glazer, D. Magde and Y. Tor, J. Am. Chem. Soc., 2007, 129, 8544–8551.
(21) K. Kalyanasundaram, Coord. Chem. Rev., 1982, 46, 159–244.
(22) E. Y.ꢀH. Hong, C. T. Poon and V. W.ꢀW. Yam, J. Am. Chem. Soc., 2016, 138, 6368–6371.
(23) (a) E. S.ꢀH. Lam, W. H. Lam and V. W.ꢀW. Yam, Inorg. Chem., 2015, 54, 3624–3630; (b) G. S.
M. Tong, K. T. Chan, X. Chang and C.ꢀM. Che, Chem. Sci., 2015, 6, 3026–3037.
(24) E. S. Andreiadis, M. ChavarotꢀKerlidou, M. Fontecave and V. Artero, Photochem. Photobiol.,
2011, 87, 946–964.
(25) J. G. Cai, Z. T. Yu, Y. J. Yuan, F. Li and Z. G. Zou. ACS Catal., 2014, 4, 1953–1963.
(26) L. E. Roy, G. Scalmani, R. Kobayashi and E. R. Batista, Dalton Trans., 2009, 6719–6721.
(27) (a) J. Xie, Q. Zhou, W. Wang, Y. Hou, B. Zhang and X. Wang, Inorg. Chem., 2012, 51, 6376–
6384; (b) E. D. Cline, S. E. Adamson and S. Bernhard, Inorg. Chem., 2008, 47, 10378–10388.
(28) H. A. Schwarz, C. Creutz and N. Sutin, Inorg. Chem., 1985, 24, 433–439.
(29) C. Creutz, A. D. Keller, N. Sutin and A. P. Zipp, J. Am. Chem. Soc., 1982, 104, 3618–3627.
(30) H. Sun and M. Z. Hoffman, J. Phys. Chem., 1994, 98, 11719–11726.
(31) (a) A. M. Kluwer, R. Kapre, F. Hartl, M. Lutz, A. L. Spek, A. M. Brouwer, P. W. N. M. van
Leeuwen and J. N. H. Reek, Proc. Natl. Acad. Sci. USA, 2009, 106, 10460–10465; (b) C. F. Wise, D.
Liu, K. J. Mayer, R. M. Crossland, C. L. Hartley and W. R. McNamara, Dalton Trans., 2015, 44,
14265–14271.
(32) S. Fukuzumi, Y. Yamada, T. Suenobu, K. Ohkubo and H. Kotani, Energy Environ. Sci., 2011, 4,
2754–2766.
(33) Z. Han, W. R. McNamara, M. S. Eum, P. L. Holland and R. Eisenberg, Angew. Chem. Int. Ed.,
2012, 51, 1667–1670.
19

Dalton Transactions
Page 20 of 20
View Article Online
DOI: 10.1039/C6DT03044K
(34) H. Chen, Z. Sun, S. Ye, D. Lu and P. Du, J. Mater. Chem. A, 2005, 3, 15729–15737.
(35) P. Lei, M. Hedlund, R. Lomoth, H. Rensmo, O. Johansson and L. Hammarström, J. Am. Chem.
Soc., 2008, 130, 26–27.
(36) (a) P. Du, J. Schneider, P. Jarosz and R. Eisenberg, J. Am. Chem. Soc., 2006, 128, 7726–7727; (b)
C. F. Leung, S. M. Ng, C. C. Ko, W. L. Man, J. Wu, L. Chen and T. C. Lau, Energy Environ. Sci.,
2012, 5, 7903–7907.
(37) (a) S. C. Marinescu, J. R. Winkler and H. B. Gray, Proc. Natl. Acad. Sci. USA, 2012, 109,
15127–15131; (b) T. Lazarides, T. McCormick, P. Du, G. Luo, B. Lindley and R. Eisenberg, J. Am.
Chem. Soc., 2009, 131, 9192–9194.
(38) T. M. McCormick, B. D. Calitree, A. Orchard, N. D. Kraut, F. V. Bright, M. R. Detty and R.
Eisenberg, J. Am. Chem. Soc., 2010, 132, 15480–15483.
Entry for the Table of Contents
hν
Gold(III) acetylide complexes actively catalyzed the lightꢀdriven evolution of hydrogen in water when
using [Co(2,2'ꢀbipyridine)3]Cl2 or [Rh(4,4'ꢀdiꢀtertꢀbutylꢀ2,2'ꢀbipyridine)3](PF6)3 as a H2ꢀevolved catalyst.
20