Aromatic TpyRu2+(L)2Cl derivatives as water oxidation catalysts (Tpy?=?2,2″:6″,2″-terpyridine, Ru?=?ruthenium, L?=?pyridine or isoquinoline)

Article abstract of DOI:10.1016/j.catcom.2018.12.021

Several mononuclear complexes with structure of [TpyRu²⁺(Py)₂Cl]⁺ and [TpyRu²⁺(Isoq)₂Cl]⁺ have been designed and synthesized. The structures of these complexes were confirmed by NMR and ESI

Full text of DOI:10.1016/j.catcom.2018.12.021

Accepted Manuscript
Aromatic TpyRu2+(L)2Cl derivatives as water oxidation catalysts
(Tpy=2,2′:6′,2″-terpyridine, Ru=ruthenium, L=pyridine or
isoquinoline)
Qianqian Liu, Linlin Wu, Mingzhao Chen, Yuan Guo, Tingzheng
Xie, Pingshan Wang
PII:
S1566-7367(18)30420-5
DOI:
Reference:
https://doi.org/10.1016/j.catcom.2018.12.021
CATCOM 5584
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
10 September 2018
2 November 2018
31 December 2018
Please cite this article as: Qianqian Liu, Linlin Wu, Mingzhao Chen, Yuan Guo, Tingzheng
Xie, Pingshan Wang , Aromatic TpyRu2+(L)2Cl derivatives as water oxidation catalysts
(Tpy=2,2′:6′,2″-terpyridine, Ru=ruthenium, L=pyridine or isoquinoline). Catcom
(2019), https://doi.org/10.1016/j.catcom.2018.12.021
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ACCEPTED MANUSCRIPT
Aromatic TpyRu2+(L)2Cl Derivatives as Water Oxidation
Catalysts (Tpy=2,2’:6’,2’’-terpyridine, Ru=ruthenium,
L=pyridine or isoquinoline)
Qianqian Liu,a Linlin Wu,b Mingzhao Chen,a Yuan Guo,a Tingzheng Xiec and Pingshan Wanga,c,*
AUTHOR ADDRESS：
a College of Chemistry and Chemical Engineering, Central South University, Changsha,
Hunan-410083, China.
bDepartment of Chemistry, The Hong Kong University of Science and Technology, Clear Water B
ay, Kowloon, Hong Kong, China.
cKey Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of
Education; Institute of Environmental Research at Great Bay, Guangzhou University, Guangzhou,
Guangdong-510006, China.
*To whom the correspondence should be addressed:
E-mail: chemwps@csu.edu.cn (P. Wang)
Graphical abstract:

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Abstract:
Several mononuclear complexes with structure of [TpyRu2+(Py)2Cl]+ and
[TpyRu2+(Isoq)2Cl]+ have been designed and synthesized. The structures of these complexes were
confirmed by NMR and ESI-MS, the properties of all catalysts were also characterized optically
and electrochemically. Water oxidation experiments were examined by turnover numbers (TONs),
which showed the catalytic properties of all catalysts. In comparison, pyridine functionalized
1a-1d have more catalytic activities than isoquinoline coordinated complexes 2a-2d. It was also
observed that attached polycyclic aromatic groups on the terpyridines had limited impact on
catalytic activities. Among these ruthenium complexes, Ph-TpyRu2+(Py)2Cl exhibited the highest
TON of 897.
Key words: mononuclear complex, turnover number, ruthenium, terpyridine, water oxidation
catalyst.
Highlight:
·Novel terpyridine-Ru catalysts were designed with aromatic moieties
·Structure-property relationship of functional units was systematically investigated
·[TpyRu2+(Py)2Cl]+ showed higher catalytic activities than [TpyRu2+(Isoq)2Cl]+
1. Introduction
Energy shortage is an extremely urgent issue need to be solved in the coming future, research
in energy is focused on designing effective materials and devices to generate the direct or indirect
renewable energy sources, such as electricity, hydrogen, biofuels and so on [1]. The holy
production of non-fossil-based, harmless and environmentally friendly biofuels is one of the
greatest challenges ever confronted by contemporary society [1-3]. In the past decades, artificial
water oxidation photosynthesis has received great amount of attention, the state-of-the art catalysts
mainly compose of pyridine/polypyridine ruthenium [4-6]. Although ruthenium related water
splitting catalysts need to confront the chemical challenges, the significant profiles and results still
encourage researchers to seek out valuable and economical materials [7]. The process of water
decomposed by Ru-based catalysts is showed in equation 1, will loss four electrons and coupled
with the formation of four protons and one oxygen in the oxidation step.
2
(
2
2
Ruthenium catalysts and other abundant transition metals have been widely researched in
this field [8-10], th first xampl of wat r oxidation of ruth nium catalysts was th “blu dim r”
developed by Meyer and co-workers in the early 1980s [11, 12], and then followed by Thummel,
Sun and other researchers [13, 14]. A mononuclear PolypyRu(py)2(H2O) as water oxidation
catalyst (WOC) was reported by Thummel groups in 2005 [13], turnover number of 390 for
evolved oxygen was achieved. Moreover, a number of Ru2+ bipyridine dicarboxylate complexes
have been reported by Sun [15-17] and Llobet [14, 18]. Mono-Ru complex of
[(tpyRu2+)(bpy)(OH2)]2+ (tpy = 2,2’;6,2’’-terpyridine; bpy = 2, 2’-bipyridine) scaffold have been

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comprehensively studied due to its preparing convenience and distinct structure (Chart 1).
Chart 1 Representativemononuclear TpyRu2+-based WOC structures and their comparative turnover numbers:
Thummel catalyst (390, left), 1a (897, middle) and 2a (135, right).
In this study, we designed and synthesized a series of terpyridine based ruthenium
complexes, and terpyridine were functionalized with various aromatic attachments to investigate
the influence on the catalytic efficiency. The ruthenium trichloride was firstly coordinated with
tridentateterpyridine, and then the rest three coordination sites were occupied by two axial
pyridine or isoquinoline ligands and one chloride. As showed in Chart 1and Chart 2, eight
complexes with structures of [trans-TpyRu2+(Py)2Cl]+ (py = pyridine; 1a, 1b, 1c and 1d) and
[trans-TpyRu2+(Isoq)2Cl]+ (Isoq = isoquinoline; 2a, 2b, 2c and 2d) were obtained. The water
oxidation catalytic properties of these eight complexes were examined by TONs, and the TON
results showed that the absence of the aromatic groups (e.g., phenyl, naphthyl, anthracenyl and
pyrenyl, respectively) on the tpy ligands and axial ligands in WOCs can increase the oxidation
potential of catalytic metal centers, which further leads to high water catalytic activity.
Furthermore, the introduction of the polyaromatic π-donating groups into mononuclear catalysts
can significantly decrease the O2 evolution initial rate of all systematic complexes, while
impacting the electronic density of the WOC, which in turn influences the intrinsic activity of the
metal centers at the same time.
Chart 2 Schematic functional aromatic mononuclear structures of TpyRu2+ complexes 1b-1d and 2b-2d.
2. Materials and methods
2.1 materials and regents
Solvents used in the experimental process were via a purification system prior to use. The raw
materials,
Benzaldehyde,
1-Naphthaldehyde,
9-Anthracenecarboxaldehyde,
pyrene-1-carboxaldehyde, pyridine, isoquinoline and RuCl3·3H2O were purchased through J
& K Chemical Technology and used without further purification. Analytical thin layer

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chromatography (TLC) was performed on aluminum backed sheets precoated with aluminum
150 F254 adsorbent (0.25 mm thick; Merck, Germany).
2.2 Apparatus and experimental procedure
2.2.1 Nuclear magnetic resonance apparatus
The NMR spectra was recorded at room temperature on a Bruker spectrometer operating at
1
500 for H NMR and 126 MHz for 13C NMR, respectively. 1H NMR assignments for
complexes 1a-1d and 2a-2d (Fig. S1) were based on 2D COSY NMR spectroscopy. Chemical
shifts were reported in parts per million (ppm) referenced to the residual solvent peak.
2.2.2 Ultraviolet visible absorption apparatus
UV-vis absorption spectra were recorded with a VARIAN Cary-50 UV-visible
spectrophotometer and were corrected for the background spectrum of the solvent.
2.2.3 Cyclic voltammetry apparatus
A glassy carbon disk was used as a working electrode, a platinum wire as a counter electrode,
and Ag/AgCl (sat. KCl) as a reference electrode fitted with a one-compartment cell. CV
experimental measurements in CH2Cl2, 0.1 M [(n-Bu)4N][PF6] solution.
2.2.4 High-resolution mass spectrum (HRMS) apparatus
Mass spectra (MALDI-TOF-MS) were determined on a Bruker BIFLEX III Mass
Spectrometer.
2.2.5 Oxygen Measurements apparatus
Oxygen measurements were mainly performed using a calibrated O2 probe (YSI 5300A
Biological Oxygen Monitor) and TONs measurements were calculated on a Shimadzu
GC-2014C.
2.2.6 Kinetic analysis of water oxidation catalysts
A 2.0 mM solution of ceric ammonium nitrate in 0.1 M CF3SO3H was mixed with an equal
amount of catalyst solution in 5:1 water/acetonitrile, with catalyst concentrations after mixing
ranging from 5 mM to 1 μM. Stopped-flow kinetic measurements were performed at 20 ±
0.1 °C with Agilent Technologies Cary 8454 UV-Vis equipped with stopped-flow.
2.3 General experimental procedure
The preparation of 1a-1d and 2a-2d was conducted first by reacting aromatic funtionalized
terpyridine with RuCl3 to give monoadduct TpyRuCl3 according to the reported method [19],
and then adding excess pyridine or isoquinoline to replace two axial chlorides (Scheme S1 in
ESI) afforded the pure corresponding catalysts after column chromatography.
RuCl3·3H2O (0.30 mmol) and terpyridines (0.30 mmol) were combined in 50 ml EtOH and
refluxed for 10 h. The mixture was cooled and collected as a brown solid upon filtration and
washed with MeOH. TpyRuCl3 (0.3 mmol) and Pyridine (0.9 mmol) or Isoquinoline (0.9
mmol) were mixed with N-ethylmor-pholine (0.2 mL) in 30 ml of EtOH. The mixture was

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then heated at reflux for 16h. The solvent was removed from the solution, and the crude
products were purified through column chromatography with neutral aluminium oxide using
MeOH/CH2Cl2 (1.5:100/v:v) as the eluent. The product was collected as a dark purple
powder.
3. Results and discussion
3.1 UV-vis spectrum analysis
[TpyRu2+(L)2]+ (L = Py or Isoq) were measured with UV-vis spectrophotometry and
found that the characteristic long wavelength absorption (metal to ligand charge transfer,
MLCT) were in the range of 556-565 nm (Fig. 1 and Table S1). 1a-1d include two axial
pyridines, the long wavelength absorbance ranged from 556 nm to 560 nm. 2a-2d with two
isoquinolines, the wavelength moved from 560 nm to 565 nm was surveyed. In contrast to the
polyaromatic framework, the aromatic 4”-substituted groups on the Tpy gave rise to a slightly
red shift, indicating that the peak of the band shifting as the polyaromatic substituted groups
became a better donor. For comparison of the type-1 complexes, the MLCT bands of type-2
were also somewhat red shift but follows the same general trend with variation of the axial
ligand [20].
Fig. 1 Electronic absorption spectra of complexes 1a-1d and 2a-2d recorded in CH2Cl2 (3.8×10-5 M).
3.2 Cyclic voltammetry (CV) analysis
Catalytic peak evolutions were observed for the freshly prepared [TpyRu2+(L)2]+ catalysts;
thus, the redox potentials of these peaks were systematically studied using glassy carbon
electrodes (GC) in CH2Cl2 solutions (Fig. 2). Cyclic voltammograms of complexes 1a-1d, which
the axial coordination motifs were functionalized with pyridines, provided a higher oxidation
potential and a better oxidation catalytic capacity compared to 2a-2d (Fig. S3). A higher reversible
oxidation wave of RuIII/II, RuIV/III and RuV/IV of complex 1a (Fig. 2) was observed at 1.02 V, 1.35
V and 1.75 V, respectively. The CV of complex 1b was measured under the same conditions,
showing a comparatively obvious oxidized wave of RuIV/III, and a large catalytic current starting
from 1.38 V. The RuIII/II, RuIV/III and RuV/IV couples of complex 1c appear at 1.02 V, 1.34 V and
1.54 V, respectively. A strong wave of electrochemically oxidation at 1.11 V (1d) was observed
versus Ag/AgCl in phosphate buffer at pH 7.0. As the number of aromatic groups on the
terpyridines increased, these peak potentials all shifted in the negative direction. The peak

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potential values were plotted against the functional aromatic groups, especially the terpyridine
ligand which was functionalized with aromatic pyrene, as shown in Fig. 3 and Fig. S3. The
dependency of the peak positions on the number of the aromatic groups on the terpyridines
confirmed proton-coupled electron transfer (PCET) in these processes. Electron removal is
typically associated with proton translocation in many electron-donating groups (EDGs) ligand
while increasing the electron density of the ruthenium center and thus lower the oxidation
potential [21]. Peaks with slightly different values on the potential versus isoquinoline axial
coordination motifs have been reported in the Table S1, which occurs because the valence band
potential is lower than that for water oxidation, indicating that catalysts 2a-2d must undergo a
harsher precatalytic oxidation process before oxidizing water. This result is also consistent with
the results of water oxidation studies.
Fig. 2 Measured with a glassy carbon electrode at 50 mV s-1 in CH2Cl2 containing 0.1 M NBu4PF6.
3.3 DFT calculations and proposed mechanism
To explain the higher chemical redox of 1a, DFT calculations show the electronic and
structural changes upon chemical redox of [TpyRu2+(Py)2Cl]+ platform with the ruthenium
centers and tpy ligands. The clorine-water ligand exchange for 1a at this oxidation state was
Ⅱ
investigated subsequently (Fig. S4). Similar to the HOMO-LUMO gap in complex Ru -Cl
(268.77 kJ/mol), the HOMO-LUMO gap of the equatorial clorine exchange to form aqua
Ⅱ
Ⅱ
complex Ru -OH2 is slightly higher by 312.28 kJ/mol. In comparison with Ru -OH2
Ⅲ
alternative (Scheme 1), the HOMO-LUMO gap of Ru -OH2 intermediates is 338.82 kJ/mol.
For the high oxidation state of ruthenium, that is, RuIV/RuV, complex coordination via
ruthenium-O bonds was calculated (229.63 kJ/mol). The essence of the intermediate state is
that RuV=O species that are accelerated the formation O- bond via th · coupling in forms
of [RuIVO·]2+, and then releasing O2 [22-24]. In the usual water nucleophilic attack (WNA)
pathway, “ -atom transf r” is a common and w ll-defined process for RuIV=O complexes
[25]. The mechanism for O2 evolution may involve conversion between intermediates
followed by intramolecular charge transfer and water attack. The I2M-pathways, for which
the calculated structure and proposed mechanism were shown in Figure S5. The HOMO and
LUMO levels of complex 1a was calculated (Table S2). The theoretically calculated the
HOMO-LUMO gap, which could be approximate to ΔΕɡ, of complex 1a (268.77 kJ/mol) is in
good agreement with the experimental values (274.65 kJ/mol). HRMS (Fig. S6) and UV-vis

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spectra (Fig. S7) was utilized to further confirm the mechanism of predicted intermediates, for
example, a peak at m/z: 585.10 matching the RuV intermediate [TpyRuV(Py)2(O)]+ (Fig. S11)
was observed and presumed to be converted from the [TpyRuIII(Py)2(OH2)]+ specie (m/z:
587.04) (Fig. S9) [26-29]. The fundamental catalytic intermediates, which were provided by
HRMS, are important for understanding the proposal catalytic mechanism of the complex 1a,
Ⅱ
including the competition between decomposition of [Ru (OH2)]+ and its further oxidation by
Ce(IV).
Scheme 1. Proposed mechanism of 1a in aqueous solution (pH 1.0) (HOMO-LUMO gap are gave in kJ/mol).
3.4 Water oxidation
Catalytic water oxidation studies of type-1 and -2 catalysts were carried out using the
reported method as a guide: Ce4+ (in excess) was utilized as the sacrificial oxidant in pH=1.0
CF3SO3H; O2 evolution was quantified with a syringe needle extract the gas which was
produced the headspace of the sealed reaction vessel [30-32].
To examine the possible effect in the presence of the aromatic groups (e.g., phenyl,
naphthyl, anthracenyl and pyrenyl, respectively) and axial ligands (e.g., pyridine and
isoquinoline), the currenttime TON and TOF responses for WOCs about 1a-1d and 2a-2d
were given in Table S1. The TON of 1awas calculated to be 897 with an initial rate of 0.0279
s-1 (Fig. 3), which was comparabl to th valu s d t rmin d with Thumm l’s ruth nium
catalysts (390), recorded under our reaction conditions to serve as a comparison [33]. The
comparative work on hydration indicates that the chloride in 1a was about 55% replaced by
water in 8 h. Hydration of the Thumm l’s cat was slower, requiring 15 h for 55% conversion
(Fig. S4). It was clear that for the complex 1a oxidized by (NH4)2Ce(NO3)6 considerably more
stability than Thumm l’s, which was provided by the UV-vis spectrum and 1H NMR analysis
(Fig. S15 and Fig. S16). The TONs and TOFs of the type-2 were lower than the values of the
studied counterparts type-1 (Table S1). For complex 2a, a low TON of 135 was found with an
initial rate of 0.0017 s-1. The data shown that complex 2a has a lower initial rate than complex
1a, which was lack of robustness than 1a. In comparison with complex 1a, the replacement of
Tpy ligand (e.g., phenyl) with other Tpy ligands (e.g., naphthyl, anthracenyl and pyrenyl)
gave complexes 1b-1d TONs and initial rate that were lower than 1a (Fig. S17). An
explanation of this trend can be rationalized by th incr as d pr s nc of π-donating groups to
the aromatic 4”-substituted groups caused by the EDGs on the tpy ligand and the similar
explanation could be applied to the axial coordination ligands [21].

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Fig. 3 indicated the rate profiles for the oxygen evolution at the first 30 minutes of
reaction with various concentrations for 1a. The initial rate results were obtained in the
concentration range (Fig. S18-S24) where the catalytic activity is purely controlled by
catalytic kinetics, and therefore, the low initial rate slope of the type with polycyclic aromatic
groups catalysts indicates a slow discharge WOCs process and suggests that WOCs rates with
low catalyst stability could be delivered in practical applications.
Fig. 3 Using various concentrations of 1a (25 μL, 50 μL,75 μL,100 μL) measured the rate of theproduction of
oxygen.
3.5 Kinetics of [ph-TpyRu2+(Py)2Cl]-Mediated Water Oxidation.
To gain further understanding of the mechanism for WOCs, the kinetics of 1a Ce-driven
catalyzed water oxidation was studied using stopped-flow kinetics measurements[34]. As the
[Ce] decrease, the reaction order for cerium(IV) is better fit to a linear zero-order dependence.
The rate laws for the first-order and zero-order regimes are represented by cerium using 1a at
1.0 μM and 1 mM, respectively in Fig. S25a and Fig. S25b. Shown in Fig. 4, the
reaction-order for 1a is clearly transition from about 1 (higher concentrations) to about 2
(lower concentrations), which indicates the change of reaction-order dependence on catalyst
concentration. The reaction order with respect to cerium(IV) is reflected in Fig. S25c,
revealing a first-order dependence on higher concentration. These results presented in this
data reveals that the rate-determining step depending on the catalyst concentration.

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Fig. 4 Plots of -log of the initial reaction rate vs -log[Ru] (log/log plots) for 1a, showing the
concentration-dependent rate law regimes when [Ru]0 = 0.5 mM and [CeIV]0 = 0.1 mM.
4. Conclusions
The synthesis of a series of terpyridinyl ruthenium WOCs (1a-1d and 2a-2d) using pyridine
and isoquinoline as coordinating ligands has been reported. The different oxidation catalyst
activity is derived from the mononuclear WOC structure changes. In the presence of Ce4+ as a
sacrificial chemical oxidant, the complexes showed the ability of decomposition of water to
O2. Complexes with pyridine appends ([TpyRu2+(Py)2Cl]+ d monstrat d high r W C’s
activities than with isoquinoline appends ([TpyRu2+(Isoq)2Cl]+). ([TpyRu2+(Py)2Cl]+)-type
catalysts showed good catalytic results for oxidation of water molecule to oxygen. Density
functional theory (DFT) has been used to calculate the HOMO-LUMO gap of each
intermediate in the possible catalytic mechanism. Introduction of aromatic species on the
4”-position of terpyridine ligands prevented the catalytic productivity of the catalysts and
decreased the catalytic stability. Systematic investigations on how terpyridinyl ligands tune
the reactivity and stability of WOCs are being carried out.
Acknowledgements
This research was supported by the National Natural Science Foundation of China (21274165),
the Distinguished Professor Research Fund from Guangzhou University. Authors
acknowledge the NMR measurements from The Modern Analysis and Testing Center of CSU.
References
[1] N.S. Lewis, D.G. Nocera, Powering the Planet: Chemical Challenges in Solar Energy
Utilization, Proc. Natl. Acad. Sci. USA., 103 (2006) 15729-15735.
[2] L. Sun, L. Hammarström, B. Åkermark, S. Styring, Towards artificial photosynthesis:
ruthenium–manganese chemistry for energy production, Chem. Soc. Rev., 30 (2001) 36-49.
[3] R. Eisenberg, H.B. Gray, Preface on Making Oxygen, Inorg. Chem., 47 (2008) 1697-1699.
[4] J.J. Concepcion, J.W. Jurss, J.L. Templeton, T.J. Meyer, One site is enough. Catalytic water
oxidation by [Ru(tpy)(bpm)(OH2)]2+ and [Ru(tpy)(bpz)(OH2)]2+, J. Am. Chem. Soc., 130
(2008) 16462-16463.
[5] H.W. Tseng, R. Zong, J.T. Muckerman, R. Thummel, Mononuclear ruthenium(II) complexes
that catalyze water oxidation, Inorg. Chem., 47 (2008) 11763-11773.
[6] J.F. Hull, D. Balcells, J.D. Blakemore, C.D. Incarvito, O. Eisenstein, G.W. Brudvig, R.H.
Crabtree, Highly Active and Robust Cp* Iridium Complexes for Catalytic Water Oxidation, J.
Am. Chem. Soc., 131 (2009) 8730.
[7] J.L. Fillol, Z. Codolà, I. Garcia-Bosch, L. Gómez, J.J. Pla, M. Costas, Efficient water oxidation
catalysts based on readily available iron coordination complexes, Nat. Chem., 3 (2011) 807.
[8] D.W. Shaffer, Y. Xie, D.J. Szalda, J.J. Concepcion, Manipulating the Rate-Limiting Step in
Water Oxidation Catalysis by Ruthenium Bipyridine–Dicarboxylate Complexes, Inorg. Chem.,
55 (2016).
[9] T. Wada, H. Ohtsu, K. Tanaka, Catalytic Four-Electron Oxidation of Water by Intramolecular
Coupling of the Oxo Ligands of a Bis(ruthenium–bipyridine) Complex, Chem. Eur. J., 18
(2012) 2374-2381.

ACCEPTED MANUSCRIPT
[10] Y. Liu, S.-M. Ng, W.W.Y. Lam, S.-M. Yiu, T.-C. Lau, A Highly Reactive Seven-Coordinate
Osmium(V) Oxo Complex: [OsV(O)(qpy)(pic)Cl]2+, Angew. Chem., Int. Ed., 55 (2016)
288-291.
[11]
S.J.
Raven,
T.J.
Meyer,
Reactivity
of
the
oxo-bridged
ion .mu.-oxobis[bis(2,2'-bipyridine)dioxodiruthenium](3+), Inorg. Chem., 27 (1988)
4478-4483.
[12]
E.L.
Lebeau,
S.A.
Adeyemi,
T.J.
Meyer,
Water
Oxidation
by
[(tpy)(H2O)2RuIIIORuIII(H2O)2(tpy)]4+, Inorg. Chem., 37 (1998) 6476-6484.
[13] R. Zong, R.P. Thummel, ANew Family of Ru Complexes for Water Oxidation, J. Am. Chem.
Soc., 127 (2005) 12802-12803.
[14] S. Maji, L. Vigara, F. Cottone, F. Bozoglian, J. Benet-Buchholz, A. Llobet, Ligand Geometry
Directs O-O Bond-Formation Pathway in Ruthenium-Based Water Oxidation Catalyst, Angew.
Chem., Int. Ed., 51 (2012) 5967-5970.
[15] L. Duan, L. Wang, F. Li, F. Li, L. Sun, Highly Efficient Bioinspired Molecular Ru Water
Oxidation Catalysts with Negatively Charged Backbone Ligands, Acc. Chem. Res., 48 (2015)
2084-2096.
[16] Y. Jiang, F. Li, B. Zhang, X. Li, X. Wang, F. Huang, L. Sun, Promoting the Activity of
Catalysts for the Oxidation of Water with Bridged Dinuclear Ruthenium Complexes, Angew.
Chem., Int. Ed., 52 (2013) 3398-3401.
[17] H. Li, F. Li, B. Zhang, X. Zhou, F. Yu, L. Sun, Visible Light-Driven Water Oxidation
Promoted by Host–Guest Interaction between Photosensitizer and Catalyst with A High
Quantum Efficiency, J. Am. Chem. Soc., 137 (2015) 4332-4335.
[18] L. Francàs, X. Sala, E. Escudero-Adán, J. Benet-Buchholz, L. Escriche, A. Llobet, Synthesis,
Structure, and Reactivity of New Tetranuclear Ru-Hbpp-Based Water-Oxidation Catalysts,
Inorg. Chem., 50 (2011) 2771-2781.
[19] J.J. Concepcion, M.-K. Tsai, J.T. Muckerman, T.J. Meyer, Mechanism of Water Oxidation by
Single-Site Ruthenium Complex Catalysts, J. Am. Chem. Soc., 132 (2010) 1545-1557.
[20] E. Jakubikova, W. Chen, D.M. Dattelbaum, F.N. Rein, R.C. Rocha, R.L. Martin, E.R. Batista,
Electronic Structure and Spectroscopy of [Ru(tpy)2]2+, [Ru(tpy)(bpy)(H2O)]2+, and
[Ru(tpy)(bpy)(Cl)]+, Inorganic Chemistry, 48 (2009) 10720-10725.
[21] D.J. Wasylenko, C. Ganesamoorthy, B.D. Koivisto, M.A. Henderson, C.P. Berlinguette,
Insight into Water Oxidation by Mononuclear Polypyridyl Ru Catalysts, Inorganic Chemistry,
49 (2010) 2202-2209.
[22] S. Maji, I. López, F. Bozoglian, J. Benet-Buchholz, A. Llobet, Mononuclear Ruthenium–
Water Oxidation Catalysts: Discerning between Electronic and Hydrogen-Bonding Effects,
Inorg. Chem., 52 (2013) 3591-3593.
[23] J.J. Concepcion, J.W. Jurss, M.R. Norris, Z. Chen, J.L. Templeton, T.J. Meyer, Catalytic
Water Oxidation by Single-Site Ruthenium Catalysts, Inorg. Chem., 49 (2010) 1277-1279.
[24] A. Lewandowska-Andralojc, D.E. Polyansky, R. Zong, R.P. Thummel, E. Fujita, Enabling
light-driven water oxidation via a low-energy RuIV=O intermediate, Phys. Chem. Chem. Phys.,
15 (2013) 14058-14068.
[25] J.J. Concepcion, M.-K. Tsai, J.T. Muckerman, T.J. Meyer, Mechanism of Water Oxidation by
Single-Site Ruthenium Complex Catalysts, Journal of the American Chemical Society, 132
(2010) 1545-1557.

ACCEPTED MANUSCRIPT
[26] A.F. Abdel-Magied, A. Shatskiy, R.-Z. Liao, T.M. Laine, W.A.A. Arafa, P.E.M. Siegbahn,
M.D. Kärkäs, B. Åkermark, E.V. Johnston, Chemical and Photochemical Water Oxidation
Mediated by an Efficient Single-Site Ruthenium Catalyst, ChemSusChem, 9 (2016)
3448-3456.
[27] C. Vergeiner, M. Ulrich, C. Li, X. Liu, T. Müller, B. Kräutler, Stereo- and Regioselective
Phyllobilane Oxidation in Leaf Homogenates of the Peace Lily (Spathiphyllum wallisii):
Hypothetical Endogenous Path to Yellow Chlorophyll Catabolites . Chem. Eur. J., 21 (2015)
136-149.
[28] C. Casadevall, Z. Codolà, M. Costas, J. Lloret-Fillol, Spectroscopic, Electrochemical and
Computational Characterisation of Ru Species Involved in Catalytic Water Oxidation:
Evidence for a [RuV(O)(Py2Metacn)] Intermediate, Chem. Eur. J., 22 (2016) 10111-10126.
[29] S. Neudeck, S. Maji, I. López, S. Meyer, F. Meyer, A. Llobet, New Powerful and Oxidatively
Rugged Dinuclear Ru Water Oxidation Catalyst: Control of Mechanistic Pathways by Tailored
Ligand Design, J. Am. Chem. Soc., 136 (2014) 24-27.
[30] K.M. Waldie, K.R. Flajslik, E. McLoughlin, C.E.D. Chidsey, R.M. Waymouth,
Electrocatalytic Alcohol Oxidation with Ruthenium Transfer Hydrogenation Catalysts, J. Am.
Chem. Soc., 139 (2017) 738-748.
[31] J. Creus, R. Matheu, I. Peñafiel, D. Moonshiram, P. Blondeau, J. Benet-Buchholz, J.
García-Antón, X. Sala, C. Godard, A. Llobet, A Million Turnover Molecular Anode for
Catalytic Water Oxidation, Angew. Chem., Int. Ed., 55 (2016) 15382-15386.
[32] H. Huang, B. Yu, P. Zhang, J. Huang, Y. Chen, G. Gasser, L. Ji, H. Chao, Highly Charged
Ruthenium(II) Polypyridyl Complexes as Lysosome-Localized Photosensitizers for
Two-Photon Photodynamic Therapy, Angew. Chem., 127 (2015) 14255-14258.
[33] N. Kaveevivitchai, R. Zong, H.-W. Tseng, R. Chitta, R.P. Thummel, Further Observations on
Water Oxidation Catalyzed by Mononuclear Ru(II) Complexes, Inorg. Chem., 51 (2012)
2930-2939.
[34] D.W. Shaffer, Y. Xie, D.J. Szalda, J.J. Concepcion, Manipulating the Rate-Limiting Step in
Water Oxidation Catalysis by Ruthenium Bipyridine–Dicarboxylate Complexes, Inorganic
Chemistry, 55 (2016) 12024-12035.

ACCEPTED MANUSCRIPT
Highlight:
·Novel terpyridine-Ru catalysts were designed with aromatic moieties
·Structure-property relationship of functional units was systematically investigated
·[TpyRu2+(Py)2Cl]+ showed higher catalytic activities than [TpyRu2+(Isoq)2Cl]+
Graphical abstract