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“This document is the Accepted Manuscript version of a Published Work that appeared in final form in Catalysis Science &
Technology, copyright © The Royal Society of Chemistry 2016 after peer review and technical editing by the publisher. To
access the final edited and published work see:

http://pubs.rsc.org/en/content/articlelanding/2016/cy/c6cy01077f#!divAbstract

Journal Name
ARTICLE
Incorporation of the ruthenium–bis(pyridine)pyrazolate (Ru-bpp)
water oxidation catalyst in a hexametallic macrocycle
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/

a

Craig J. Richmond and Antoni Llobet

a,b*

New terpyridine-functionalised analogues of the in,in-[{RuII(trpy)}2(μ-bpp)(H2O)2]3+ water oxidation catalyst (bpp = bis-(2pyridyl)pyrazolate) have been synthesised and used to create a hexametallic {Fe2Ru4} macrocycle. The macroyclic WOC
precursor contains two catalyst units linked by two {Fe(R-trpy)2} bridges and shows similar catalytic activity for water
oxygen when compared to the non-cyclic catalyst precursors. The synthesised complexes were fully characterised by
standard voltammetric and spectroscopic techniques (CV, DPV, NMR, MS, UV and IR) and the assessment of their
performance as WOCs was performed using a CeIV chemical oxidant in aqueous triflic acid.

Introduction
Molecular water oxidation catalysts (WOCs) based on
ruthenium have been an integral part of research into artificial
1-7
photosynthesis (AP) for a little over three decades now.
Within the vast number of molecular Ru-based WOCs
8-38
reported,
the Ru-bpp catalysts (bpp = 3,5-bis(2pyridyl)pyrazolato) have been of particular interest because of
their distinctive I2M mechanism; only the Ru-bda catalysts
(bda = 2,2’-bipyridine-6,6’-dicarboxylato) of Sun et al have
39-44
been reported to follow a similar oxo-coupling mechanism.
The major drawback with the Ru-bpp catalysts, as with most
organic ligand-based WOCs, is consumption of the ligands
during operation leading to catalyst degradation and
ultimately termination of the catalysis. Largely successful
attempts have been made to circumvent this problem by
removing the organic ligands altogether and replacing them
with inorganic ligands in the form of polyoxometallates
45-54
(POMs)
or by encapsulating or heterogenising the
55molecular catalyst in/on Metal Organic Frameworks (MOFs).
57
These strategies, however, have their own limitations such
as low catalyst accessibility, MOF degradation, nanoparticle
57-61
formation and pore clogging.
The most “stable”
homogeneous WOC that contains organic ligands, as judged by
turnover number (TON), is the bromophthalazine-Ru-bda
complex prepared by Sun et al and can achieve >100,000 TON
43
before catalysis ceases. These catalysts are believed to lose

their catalytic activity through decoordination of the axial
ligands under the harsh catalytic conditions and the high TONs
are largely attributed to their extraordinarily fast rates as
41
opposed to any enhanced ligand/complex stability. However,
a macrocyclic version of the Ru-bda WOC was very recently
reported by Würthner et al where catalyst stability was
62
increased through the chelate effect. Although this was the
first example of a macrocyclic WOC, macrocycles and
supramolecular cages/containers have a long history and have
been used to great effect in the catalysis of many organic
63-73
transformations.
Embedding the Ru-bpp catalyst in a
macrocycle was therefore proposed as a possible approach to
increase the catalyst lifetime by inhibiting the intermolecular
ligand oxidation pathway, where the activated Ru-oxo site of
one catalyst molecule “attacks” the ligand backbone of
31
another catalyst unit.
Herein, we report our attempts to use a macrocyclic
encapsulation strategy to overcome the degradative
intermolecular interactions between Ru-bpp catalysts through

a.

Institute of Chemical Research of Catalonia (ICIQ) Av. Països Catalans 16, E43007 Tarragona, Spain
Departament de Química, Universitat Autònoma de Barcelona, Cerdanyola del
Vallès, 08193 Barcelona, Spain
Electronic Supplementary Information (ESI) available: [Including compound spectra
and details of methods and instrumentation]. See DOI: 10.1039/x0xx00000x
b.

Figure 1. MM2 computer modelled representation of {M2Ru4}
macroyclic WOC. Colour scheme: H – white, C – grey, N – blue, O
– red, Ru – teal, M – orange.
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the formation of a hexanuclear {Fe2Ru4} macrocycle that
directs the catalyst active sites away from the sensitive ligand
backbone.

Results and discussion
After observing the oxidation products of the bpp ligand
31
backbone after catalysis, our attentions were focused on the
design of new catalyst structures that could minimize the
interactions between the Ru-oxo active site and the bpp
II
ligand. Consequently the [({Ru (trpy-O-trpy)}2(μ-bpp)(µ8+
Cl))2M2] structure shown in Figure 1 was designed. The fusion
of two catalyst units linked by two {M(R-trpy)2} bridges
generates a macrocyclic structure where the catalyst units are
“locked” in an orientation with the active Ru-oxo sites facing
into the central cavity and hence cannot interact with the
sensitive bpp ligand framework of other catalyst molecules.
Synthesis of the macroyclic WOC began with the modification
of the original Ru-bpp catalyst framework and ligands
(Schemes 1 and 2). A chlorinated terpyridine ligand (Cl-trpy)
II
was used to create catalyst precursor 1, [{Ru (Cl-trpy)}2(μbpp)(µ-Cl)](PF6)2, using an adaptation of the original Ru-bpp
6
catalyst preparation. The bridging chloro ligand was then
hydrolysed and converted to a bridging benzoate ligand to give
II
compound 2, [{Ru (Cl-trpy)}2(μ-bpp)(µ-PhCOO)](PF6)2. The
reasoning behind this conversion was in essence a protection
strategy, after discovering that only the µ-PhCOO bridge was
able to withstand the harsh substitution conditions in the
following step. Both the µ-Cl and µ-OAc analogues resulted in
complex mixtures upon refluxing in acetone with HO-trpy and
K2CO3. On the other hand, the conversion of 2 under these
conditions was clean and subsequently afforded the pendant
II
3,
[{Ru (trpy-O-trpy)}2(μ-bpp)(µterpyridine
complex
PhCOO)](PF6)2, in high yield. Initial attempts to cyclise
derivative 3 directly via reaction with RuCl3 led to precipitation
of a solid that was very poorly soluble in most common
solvents and difficult to unambiguously identify, although it
was suspected to be polymeric in nature. Iron has been
proposed as a suitable substitute for ruthenium in the context

74

of water oxidation before so it was thought that a similar
substitution to couple the pendant terpyridine groups through
the more easily formed {Fe(R-trpy)2} bridge could also help in
this case. This strategy partially worked and a soluble product
was obtained. UV-vis and NMR UV-vis and NMR spectroscopy

Scheme 2. Structures and synthetic steps for the preparation of
compound 1-5.
indicated formation of the {Fe(R-trpy)2}, however, the NMR
spectra and MS data did not match the cyclic structure but
instead suggested a mixture of non-cyclised/oligomeric
structures (ESI). At this point a return to the computer
generated models highlighted that the bridging benzoate
ligands were occupying much of the space within the cavity of
the hypothetical macrocyclic products and therefore were
most likely preventing cyclisation through steric hindrance (see
ESI). To overcome this, a “deprotection” strategy had to be
developed in order to replace the µ-PhCOO with a smaller yet
still hydrolysable bridging ligand. A procedure for the clean
conversion of the µ-PhCOO back to the µ-Cl was established
II
and gave complex 4 [{Ru (trpy-O-trpy)}2(μ-bpp)(µ-Cl)](PF6), in
high yield. Satisfyingly, the subsequent reaction of 4 with
II
FeCl2∙4H2O then afforded the target macrocycle 5, [({Ru (trpyII
O-trpy)}2(µ-Cl)(μ-bpp))2Fe 2](PF6)8.
Despite many efforts to crystallise complex 5 for single crystal
x-ray diffraction analysis, none of the attempts were successful
and so structure confirmation was achieved through
1
voltammetric and spectroscopic techniques. Firstly, the H
NMR spectrum of compound 5 was very sharp and clean,
indicating formation of a single discrete molecular product.
The large downfield shift of the characteristic singlet of the
pendant terpyridine and the large up-field shift of the doublet
adjacent to the pyridyl nitrogen also strongly indicated
coordination to Fe (See Figure 2). Further evidence for the

Scheme 1. Ligands prepared and used in this work.
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formation of macrocycle 5 was obtained through UV-vis
spectroscopy and CV (Figure 3): From the overlaid UV-vis
spectra of compounds 4 and

caused by adsorption on the glassy carbon electrode, an effect
commonly observed for Ru-bpp-type compounds. Finally, a
comparison of DOSY NMR spectra of macrocycle 5 and

1

Figure 2. Assigned H-NMR spectra of complexes 4 (bottom) and 5 (top) in d6-acetone. The most significant chemical shifts due to
coordination of Fe are indicated by the dotted pink lines.
5 with a sample of Fe(trpy)2(PF6)2 it can be seen clearly that
the catalyst units and the Fe(R-trpy)2 units are incorporated
within the structure of 5 in a 1:1 ratio. The CV and DPV data
for compound 5 also show a marked difference to those of 4
due to the formation of the two new redox active Fe centres.
The two redox processes in 4 are assigned to the two
II
II
II
III
reversible 1-electron oxidations for Ru /Ru – Ru /Ru and for
II
III
III
III
Ru /Ru – Ru /Ru and give an appropriate 1:1 peak area ratio
in the DPV. Two redox processes are also observed in the CV
and DPV of 5 instead of the three predicted but this is due to
the reversible 1- electron oxidation of the Fe(R-trpy)2 units
II
III
III
III
overlapping with the Ru /Ru – Ru /Ru peak. This overlay is
evidenced by the relative peak heights in the DPV. Note the
ratio is not a perfect 2:1 due to the distorted cathodic waves

precursor 2 gave a satisfactory ratio of 2.3:1 for their relative
hydrodynamic radii, calculated from the observed diffusion
coefficients using the Stokes-Einstein equation (see Figure 3
75,76
for spectra and ESI for calculations).
Having confirmed the structure of 5, its water oxidation
performance was tested against the non-cyclic precursor 4 in
order to investigate the influence the macrocyclic framework
IV
had on catalysis. A solution of Ce (NH4)2(NO3)6 (CAN) in 0.1 M
triflic acid was added to a solution of 5 in 0.1 M triflic acid
(with 25% TFE added to help dissolve the complex) and the
resulting gas evolution was monitored by manometry. As can
be seen in Figure 4, catalysis was observed for macrocycle 5
but the gas evolution profile was very similar to the
comparative control experiment, which contained twice the

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amount of 4 with respect to 5 but with all other variables the
same. The almost identical gas evolution profiles for the two

compounds could be explained by examining the strength of
the {Fe(R-trpy)2} link

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-5

-5

Figure 3. (Top) UV-vis spectra of 4 (1.0 × 10 M in propylene carbonate, dashed line), Fe(trpy)2(PF6)2 (1.1 × 10 M in propylene
-5
carbonate, dotted line) and 5 (0.5 × 10 M in propylene carbonate, solid line); (Middle) CV and DPV of (left) 4 (ca. 0.7 mM in DCM, 0.1 M
TBAPF6); (right) 5 (ca. 0.3 mM in DCM, 0.1 M TBAPF6). E vs MSE reference, GC Working, Pt counter). MSE = +0.640 vs NHE; (Bottom)
DOSY NMR spectra of 5 (left) and 2 (right) in acetone-d6. Note the X axis values are log(D) so larger molecules have larger values.

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within macrocycle 5: The kinetic stability of Fe(R-trpy)2 clusters
is relatively high at neutral pH, however, the ligand exchange
77,78
coefficient increases significantly at high and low pH.
II
2+
Additionally, the oxidation potential for [Fe (trpy)2] is 1.45 V
vs NHE, which allows it to be oxidised by the CAN oxidant.
Therefore, under the conditions employed for the catalysis
experiments, oxidation and hydrolysis of the {Fe(R-trpy)2} link
preceded water oxidation, thus producing two equivalents of
precursor 4 and an almost identical result to the control
experiment. Experiments to test catalyst 5 at neutral pH with
other chemical oxidants, where the {Fe(R-trpy)2} link may be
more stable, were considered, however, control experiments
II
with [Fe (trpy)2](PF6)2 and sodium periodate demonstrated
that hydrolysis still occurred at pH 7 upon oxidation, albeit
more slowly than at pH 1 (see ESI). Complete replacement of
the weak Fe link would therefore be necessary before the
desired “macrocyclic encapsulation effect” on catalysis could
be observed and so further efforts have been focused along
these lines. Attempts to form the more hydrolytically stable
{Ru(R-trpy)2} link as well as covalent links via “click chemistry”
are still ongoing in our labs.

Figure 4. Manometry traces for gas evolution during catalysis
for 5 (4.12 mg (0.25 mM), 112 mg CAN (50 mM), 3.0 mL 0.1 M
triflic acid + 1.0 mL TFE, grey dashed curve) and; 4 (3.42 mg
(0.5 mM), 112 mg CAN (50 mM), 3.0 mL 0.1 M triflic acid + 1.0
mL TFE, solid black curve).

Experimental
Materials: RuCl3∙xH2O was supplied by Precious Metals Online
PMO Pty Ltd. All other reagents were purchased from SigmaAldrich and Alfa Aesar chemical companies. 2,2'-(1H-pyrazole79-81
82
82
3,5-diyl)dipyridine (Hbpp),
HO-trpy and Cl-trpy were
prepared according to the their reported procedures. All
synthetic manipulations under N2/Ar were performed using
standard Schlenk tubes and vacuum-line techniques.
Synthesis and characterization of 1: In a 100 mL round bottom
flask, a suspension of (Cl-trpy)RuCl3 (500 mg, 1.05 mmol, 2.0
eq), LiCl (134 mg, 3.16 µmol, 6.0 eq) and TEA (219 µL, 1.575
mmol, 3.0 eq) in MeOH (40 mL) was degassed by bubbling N2
for ca.10 mins. Meanwhile in a separate vessel, a solution of
Hbpp ligand (117 mg, 0.535 mmol, 1.0 eq) and TEA (219 µL,
1.575 mmol, 3.0 eq) in MeOH (10 mL) was prepared and

degassed with N2. The ligand solution was added to the round
bottom flask and the blackish brown reaction mixture was
then heated to reflux under a N2 atmosphere for 14 hrs with
irradiation (100 W household lamp). The reaction mixture was
cooled to room temperature and filtered to remove insoluble
by-products. A saturated aqueous solution of NH4PF6 (ca. 1
mL) was added to the filtrate to produce a brown solid
precipitate which was subsequently collected by filtration. The
brown solid residue was then triturated with MeOH portions
(4×40 mL) and the MeOH triturates were then concentrated to
dryness to afford four separate batches of a brown powder of
varying purity. The original MeOH reaction filtrate was then
diluted with H2O (ca. 40 mL) to precipitate a fifth batch of
brown solid, collected by filtration and dried under vacuum.
Total yield of product 1 obtained was 394 mg (0.307 mmol,
1
58% based on Ru). H NMR (acetone-d6, 400 MHz): δ 8.80 (4H,
s), 8.62 (4H, d, J=6.9 Hz), 8.52 (1H, s), 8.42 (4H, d, J=6.9 Hz),
8.27 (2H, d, J=7.0 Hz), 7.99 (4H, t, J=6.9 Hz), 7.83 (2H, t, J=7.0
Hz), 7.66 (4H, t, J=6.9 Hz), 7.52 (2H, d, J=7.0 Hz), 6.81 (2H, t,
13
J=7.0 Hz); C NMR (acetone-d6, 100 MHz): δ 159.7 (C), 158.7
(C), 158.5 (C), 154.0 (CH), 153.6 (CH), 148.6 (C), 140.7 (C),
137.2 (CH), 137.1 (CH), 127.8 (CH), 124.2 (CH), 122.7 (CH),
19
122.2 (CH), 120.5 (CH), 103.3 (CH); F NMR (acetone-d6, 380
31
MHz): δ -72.3 (d, J=708.0 Hz); P NMR (acetone-d6, 160 MHz):
+
δ -141.1 (sep, J=708.0 Hz); MS (CH2Cl2, acetone, MALDI ): m/z
− +
1138.1 ([M − PF6 ] ); E1/2 (DCM, 0.1 M TBA(PF6), V vs SSCE):
-1
0.767, 1.114; IR (powder, cm ): 3641w, 3073w, 1603, 1501w,
1448w, 1420m, 1382, 1280w, 1246, 1109, 1041w, 830s, 783s,
II
752s, 554s; Anal. Calc. for [{Ru (Cl-trpy)}2(μ-bpp)(µCl)](PF6)2.H2O: C, 39.66; H, 2.40; N, 10.76; Found: C, 39.13; H,
2.73; N, 10.60.
Synthesis and characterization of 2: In a 100 mL round bottom
flask, a solution of benzoic acid (66 mg, 0.545 µmol, 2.0 eq)
and TEA (152 µL, 1.092 mmol, 4.0 eq) in an acetone-water
mixture (1:1, 30 mL) was added to a solution of 1 (350 mg,
0.273 mmol, 1.0 eq) in acetone (30mL). The dark brown
solution was then heated to reflux under for 3 hrs. The
reaction mixture was cooled to room temperature and a
saturated aqueous solution of NH4PF6 (ca. 1 mL) was added.
1
The solution was concentrated under vacuum to ca. /3 volume
to produce a purplish brown solid precipitate which was
subsequently collected by filtration. The solid residue was
washed well with water and Et2O to give a purplish brown
powder after drying under vacuum. Total yield of product 2
1
obtained was 337 mg (0.246 mmol, 90% based on Ru). H NMR
(acetone-d6, 500 MHz): δ 8.84 (4H, s), 8.61 (4H, d, J=6.9 Hz),
8.60 (1H, s), 8.55 (4H, d, J=6.9 Hz), 8.26 (2H, d, J=7.0 Hz), 8.00
(4H, t, J=6.9 Hz), 7.79 (2H, t, J=7.0 Hz), 7.57 (4H, t, J=6.9 Hz),
7.56 (2H, d, J=7.0 Hz), 7.10 (1H, t, J=7.9 Hz), 6.86 (2H, t, J=7.0
13
Hz), 6.71 (2H, t, J=7.9 Hz), 6.15 (2H, d, J=7.9 Hz); C NMR
(acetone-d6, 100 MHz): δ 185.4 (C), 161.3 (C), 158.8 (C), 156.4
(C), 153.9 (CH), 153.3 (CH), 152.0 (C), 140.8 (C), 137.5 (CH),
136.2 (CH), 134.5 (C), 131.0 (CH), 127.9 (CH), 127.4 (CH), 127.1
(CH), 124.2 (CH), 123.0 (CH), 122.3 (CH), 119.7 (CH), 104.1
19
(CH); F NMR (acetone-d6, 470 MHz): δ -72.5 (d, J=708.2 Hz);
31
P NMR (acetone-d6, 200 MHz): δ -144.2 (sep, J=708.2 Hz);
+
− +
MS (CH2Cl2, acetone, MALDI ): m/z 1224.2 ([M − PF6 ] ); E1/2

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(DCM, 0.1 M TBA(PF6), V vs SSCE): 0.778, 1.084; IR (powder,
-1
cm ): 3645w, 3079w, 1604m, 1526, 1382, 1248w, 1108w,
II
829s, 783, 752, 729, 555s; Anal. Calc. for [{Ru (Cl-trpy)}2(μbpp)(µ-PhCOO)](PF6)2.2H2O: C, 42.72; H, 2.72; N, 9.96; Found:
C, 40.93; H, 2.72; N, 10.24.
Synthesis and characterization of 3: In a 100 mL round bottom
flask, HO-trpy (227 mg, 0.913 µmol, 5.0 eq) and K2CO3 (252
mg, 1.826 mmol, 10.0 eq) were added to a solution of 2 (250
mg, 0.183 mmol, 1.0 eq) in acetone (50 mL). The dark brown
solution was then heated to reflux for 17 hrs. The reaction
mixture was cooled to room temperature and a saturated
aqueous solution of NH4PF6 (ca. 1 mL) was added, followed by
dilution with H2O (20 mL). The solution was concentrated
1
under vacuum to ca. /2 volume to produce a purplish brown
solid precipitate which was subsequently collected by
filtration. The solid residue was then washed well with water
and Et2O to give a purplish brown powder after drying under
vacuum. Total yield of product 3 obtained was 268 mg (0.149
1
mmol, 82% based on Ru). H NMR (acetone-d6, 400 MHz): δ
8.81 (4H, d, J=8.0 Hz), 8.74 (4H, s), 8.66 (4H, d, J=8.0 Hz),
8.55 (9H, m), 8.46 (4H, s), 8.25 (2H, d, J=7.1 Hz), 8.07 (4H, t,
J=8.0 Hz), 7.90 (4H, t, J=7.8 Hz), 7.79 (2H, t, J=7.1 Hz), 7.69 (2H,
d, J=7.1 Hz), 7.52 (8H, m), 7.14 (1H, t, J=7.6 Hz), 7.07 (2H, t,
13
J=7.6 Hz), 6.91 (2H, t, J=7.1 Hz), 6.40 (2H, d, J=7.6 Hz); C NMR
(acetone-d6, 100 MHz): δ 184.7 (C), 164.4 (C), 162.2 (C), 161.8
(C), 159.4 (C), 158.6 (C), 156.7 (C), 154.8 (C), 154.0 (CH), 153.3
(CH), 152.0 (C), 149.4 (CH), 137.4 (CH), 137.3 (CH), 136.0 (CH),
134.8 (C), 130.9 (CH), 127.7 (CH), 127.6 (CH), 127.5 (CH), 124.8
(CH), 124.2 (CH), 122.3 (CH), 121.2 (CH), 119.6 (CH), 114.0
19
(CH), 111.2 (CH), 104.0 (CH); F NMR (acetone-d6, 375 MHz):
31
δ -72.5 (d, J=707.8 Hz); P NMR (acetone-d6, 160 MHz): δ +
141.2 (sep, J=707.8 Hz); MS (CH2Cl2, acetone, MALDI ): m/z
− +
1651.4 ([M − PF6 ] ); E1/2 (DCM, 0.1 M TBA(PF6), V vs MSE):
-1
0.425, 0.717; IR (powder, cm ): 3643w, 3069w, 1605, 1580,
1562, 1531, 1399, 1352, 1202, 964w, 833s, 788, 753, 556s;
II
Anal.
Calc.
for
[{Ru (trpy-O-trpy)}2(μ-bpp)(µPhCOO)](PF6)2.4H2O: C, 47.72; H, 3.15; N, 11.13; Found: C,
47.92; H, 3.18; N, 11.63.
Synthesis and characterization of 4: In a 25 mL round bottom
flask, a saturated aqueous solution of NaCl (3.0 mL) was added
to a solution of 3 (150 mg, 0.084 mmol) in acetone (9.0 mL).
The dark purple brown solution was then heated to reflux for
18 hrs. The reaction mixture was cooled to room temperature
and a saturated aqueous solution of NH4PF6 (ca. 1 mL) was
added followed by dilution with water (10 mL). The brown
solid precipitate was subsequently collected by filtration and
washed well with water and Et2O to give a brown powder after
drying under vacuum. Total yield of product 4 obtained was
1
126 mg (0.074 mmol, 88% based on Ru). H NMR (acetone-d6,
400 MHz): δ 8.79 (4H, d, J=6.4 Hz), 8.69 (4H, s), 8.67 (4H, d,
J=6.4 Hz), 8.53 (4H, d, J=8.1 Hz), 8.50 (1H, s), 8.42 (8H, m), 8.27
(2H, d, J=7.5 Hz), 8.10 (4H, t, J=6.4 Hz), 7.88 (4H, t, J=8.1 Hz),
7.84 (2H, t, J=7.5 Hz), 7.62 (6H, m), 7.55 (4H, t, J=6.4 Hz), 6.87
13
(2H, t, J=7.5 Hz); C NMR (acetone-d6, 125 MHz): δ 164.5 (C),
161.7 (C), 160.4 (C), 159.1 (C), 158.9 (C), 158.4 (C), 154.6 (C),
154.0 (CH), 153.7 (CH), 148.8 (CH), 148.6 (C), 137.6 (CH), 137.0
(CH), 136.8 (CH), 127.6 (CH), 125.1 (CH), 124.2 (CH), 122.2

(CH), 121.5 (CH), 120.4 (CH), 113.7 (CH), 111.6 (CH), 103.3
19
(CH); F NMR (acetone-d6, 470 MHz): δ -72.4 (d, J=708.9 Hz);
31
P NMR (acetone-d6, 200 MHz): δ -144.2 (sep, J=708.9 Hz);
+
− +
MS (CH2Cl2, acetone, MALDI ): m/z 1565.3 ([M − PF6 ] ); E1/2
(DCM, 0.1 M TBA(PF6), V vs MSE): 0.400, 0.782; UV−vis
−1
−1
(propylene carbonate): λmax, nm (ε, L mol cm ); 513 (15534),
-1
479 (17047), 379 (26006); IR (powder, cm ): 3647w, 3086w,
1605, 1580, 1563, 1399, 1352w, 1203, 965w, 834s, 787, 753,
II
Anal.
Calc.
for
[{Ru (trpy-O-trpy)}2(μ-bpp)(µ553s;
Cl)](PF6).4NaCl.4H2O: C, 43.50; H, 2.85; N, 11.12; Found: C,
43.19; H, 2.89; N, 11.16.
Synthesis and characterization of 5: In a 25 mL round bottom
flask, a solution of KPF6 (26 mg, 0.142 mmol, 10.0 eq) and
FeCl2.4H2O (4.4 mg, 0.0219 mmol, 1.5 eq) in MeOH (2.5 mL)
were added to a solution of precursor 4 (25 mg, 14.6 µmol, 1.0
eq) in acetone (5.0 mL). The resulting deep purple solution was
heated to reflux with stirring for 14 hrs. The reaction mixture
was cooled to room temperature and filtered to remove
insoluble by-products. Dilution of the filtrate with water (5.0
mL) produced a purple precipitate which was subsequently
collected by filtration. The purple solid residue was redissolved
in acetone (2.0 mL), filtered, and then concentrated to dryness
to afford a dark purple powder (12 mg, 2.92 µmol, 20% based
1
on Ru). H NMR (acetone-d6, 500 MHz): δ 9.02 (8H, s), 8.98
(8H, s), 8.63 (8H, d, J=7.0 Hz), 8.59 (2H, s), 8.54 (8H, d, J=7.0
Hz), 8.38 (8H, d, J=6.9 Hz), 8.33 (4H, d, J=7.1 Hz), 8.04 (8H, t,
J=7.0 Hz), 7.90 (4H, t, J=7.1 Hz), 7.73 (8H, t, J=7.0 Hz), 7.69 (8H,
t, J=6.9 Hz), 7.68 (4H, d, J=7.1 Hz), 7.31 (8H, d, J=6.9 Hz), 7.02
13
(8H, t, J=6.9 Hz), 6.90 (4H, t, J=7.1 Hz); C NMR (acetone-d6,
125 MHz): δ 165.9 (C), 161.3 (C), 160.8 (C), 159.2 (C), 158.8 (C),
158.4 (C), 157.7 (C), 154.1 (CH), 153.7 (CH), 153.4 (CH), 148.7
(C), 138.4 (CH), 137.3 (CH), 137.0 (CH), 127.8 (CH), 127.5 (CH),
124.5 (CH), 123.8 (CH), 122.3 (CH), 120.5 (CH), 116.5 (CH),
19
112.5 (CH), 103.3 (CH); F NMR (acetone-d6, 470 MHz): δ 31
72.0 (d, J=709.2 Hz); P NMR (acetone-d6, 200 MHz): δ -144.3
+
(sep, J=709.2 Hz); MS (CH2Cl2, acetone, MALDI ): m/z 3967.2
− +
([M − PF6 ] ); E1/2 (DCM, 0.1 M TBA(PF6), V vs MSE): 0.399,
−1
0.809; UV−vis (propylene carbonate): λmax, nm (ε, L mol
−1
cm ); 559 (44835), 516 (50268), 476 (42741), 371 (64599); IR
-1
(powder, cm ): 3644w, 3083w, 1600, 1396, 1206, 964w, 829s,
II
786s, 753, 555s; Anal. Calc. for [({Ru (trpy-O-trpy)}2(µ-Cl)(μII
bpp))2Fe 2](PF6)8.10H2O: C, 40.86; H, 2.77; N, 10.44; Found: C,
40.41; H, 2.47; N, 10.11.

Conclusions
In summary, this work successfully functionalised the Ru-bpp
catalyst, post-synthesis, with free pendent trpy-O-trpy “arms”
following a protection-substitution-deprotection strategy. The
pendent trpy-O-trpy arms were subsequently exploited to
couple two catalyst units together via two {Fe(R-trpy)2} bridges
to form a novel macrocyclic WOC precursor. The catalytic
activity of the macrocyclic complex was assessed under
comparable conditions (CAN, pH 1) with the parent Ru-bpp
catalyst but the macrocycle was unfortunately not stable
enough to withstand the oxidative acidic environment and no
enhanced activity or stability was observed. Current efforts are

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focussed on replacing the {Fe(R-trpy)2} with a more robust
linker group and applying the macrocyclic encapsulation
strategy to other WOC systems that are also plagued by
intermolecular ligand oxidation.

Acknowledgements
We thank MINECO (CTQ-2013-49075-R, SEV-2013-0319; CTQ2014-52974-REDC) and “La Caixa” foundation for financial
support. COST actions, CM1202 and CM1205 from the EU are
also gratefully acknowledged and CR thanks the European
Commission for a Marie Curie IEF grant (298957).

Notes and references
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L. Francàs, R. Bofill, J. García-Antón, L. Escriche, X. Sala and A.
Llobet, Ru-Based Water Oxidation Catalysts in Molecular
Water Oxidation Catalysis: A Key Topic for New Sustainable
Energy Conversion Schemes, ed. A. Llobet, John Wiley & Sons
Ltd, Chichester UK, 2014.
S. Maji, I. Lopez, F. Bozoglian, J. Benet-Buchholz and A.
Llobet, Inorg. Chem., 2013, 52, 3591.
J. D. Blakemore, R. H. Crabtree and G. W. Brudvig, Chem.
Rev., 2015, 115, 12974.
R. Cao, W. Laia and P. Du, Environ. Sci., 2012, 5, 8134.
S. W. Gersten, G. J. Samuels and T. J. Meyer, J. Am. Chem.
Soc., 1982, 104, 4029.
C. Sens, I. Romero, M. Rodríguez, A. Llobet, T. Parella and J.
Benet-Buchholz, J. Am. Chem. Soc., 2004, 126, 7798.
L. Duan, A. Fischer, Y. Xu and L. Sun, J. Am. Chem. Soc., 2009,
131, 10397.
M. D. Kärkäs, T. Åkermark, E. V. Johnston, S. R.Karim, T. M.
Laine, B.-L. Lee, T. Åkermark, T. Privalov, B. Åkermark,
Angew. Chem., Int. Ed., 2012, 51, 11589.
Y. Xu, A. Fischer, L. Duan, L.Tong, E. Gabrielsson, B. Åkermark
and L. Sun, Angew. Chem. Int. Ed., 2010, 49, 8934.
T. M. Laine, M.D. Kärkäs, R.-Z. Liao, P. E. M. Siegbahn and B.
Åkermark, Chem. Eur. J., 2015, 21, 10039.
W. Rabten, T. Åkermark, M. D. Kärkäs, H. Chen, J. Sun, P. G.
Andersson and B. Åkermark, Dalton Trans., 2016, 45, 3272.
Y. Xu, T. Åkermark, V. Gyollai, D. Zou, L. Eriksson, L. Duan, R.
Zhang, B. Åkermark and L. Sun, Inorg. Chem., 2009, 48, 2717.
L.-Z. Zeng, C.-J. Wang, T.-T. Li, X. Gan, C. Li and W.-F. Fu,
Catal. Commun., 2015, 68, 84.
T.-T. Li, W.-L. Zhao, Y. Chen, F.-M. Li, C.-J. Wang, Y.-H. Tian,
W.-F. Fu, Chem. Eur. J., 2014, 20, 13957.
Z. Deng, H.-W. Tseng, R. Zong, D. Wang and R. Thummel,
Inorg. Chem., 2008, 47, 1835.
R.Zong and R. P Thummel, J. Am. Chem. Soc., 2005, 127,
12802.
N. Kaveevivitchai, R. Zong, H.-W. Tseng, R. Chitta and R. P.
Thummel, Inorg. Chem., 2012, 51, 2930.
N. Kaveevivitchai, L. Kohler, R. Zong, M. El Ojaimi, N. Mehta
and R. P Thummel, Inorg. Chem., 2013, 52, 10615.
H.-W. Tseng, R. Zong, J. T. Muckerman and R.Thummel,
Inorg. Chem., 2008, 47, 11763.
T. Wada, K. Tsuge and K. Tanaka, Inorg. Chem., 2001, 40,
329.
J. T. Muckerman, D. E. Polyansky, T. Wada, K. Tanaka and E.
Fujita, Inorg. Chem., 2008, 47, 1787.
A. C. Sander, A. Schober, S. Dechert and F. Meyer, Eur. J.
Inorg. Chem., 2015, 4348.
S. Neudeck, S. Maji, I. López, S. Meyer, F. Meyer and A.
Llobet, J. Am. Chem. Soc., 2014, 136, 24.

24 J. Mola, C. Dinoi, X. Sala, M. Rodriguez, I. Romero, T. Parella,
X. Fontrodona and A. Llobet, Dalton Trans., 2011, 40, 3640.
25 S. Maji, L. Vigara, F. Cottone, F. Bozoglian, J. Benet-Buchholz
and A. Llobet, Angew. Chem. Int. Ed., 2012, 51, 5967.
26 S. Roeser, M. Z. Ertem, C. Cady, R. Lomoth, J. BenetBuchholz, L. Hammarström, B. Sarkar, W. Kaim, C. J. Cramer
and A. Llobet, Inorg. Chem., 2012, 51, 320.
27 J. Mola, E. Mas-Marza, X. Sala, I. Romero, M. Rodríguez, C.
Viñas, T. Parella and A. Llobet, Angew. Chem. Inter. Ed.,
2008, 47, 5830.
28 L. Francàs, X. Sala, J. Benet-Buchholz, L. Escriche and A.
Llobet, ChemSusChem., 2009, 2, 321.
29 J. Aguilo, L. Francas, H. J. Liu, R. Bofill, J. Garcia-Anton, J.
Benet-Buchholz, A. Llobet, L. Escriche and X. Sala, Catal. Sci.
Technol. 2014, 4, 190.
30 L. Francàs, X. Sala and E. Escudero-Adán, J. Benet-Buchholz,
L. Escriche and A. Llobet, Inorg. Chem., 2011, 50, 2771.
31 F. Bozoglian, S. Romain, M. Z. Ertem, T. K. Todorova, C. Sens,
J. Mola, M. Rodríguez, I. Romero, J. Benet-Buchholz, X.
Fontrodona, C. J. Cramer, L. Gagliardi and Antoni Llobet, J.
Am. Chem. Soc., 2009, 131, 15176.
32 J. J. Concepcion, J. W. Jurss, J. L. Templeton and T. J. Meyer,
J. Am. Chem. Soc., 2008, 130, 16462.
33 Z. Chen, J. J. Concepcion and T. J. Meyer, Dalton Trans.,
2011, 40, 3789.
34 J. A. Gilbert, D. S. Eggleston, W. R. Murphy Jr., D. A.
Geselowitz, S. W. Gersten, D. J. Hodgson and T. J. Meyer, J.
Am. Chem. Soc., 1985, 107, 3855.
35 R. A. Binstead, C. W. Chronister, J. Ni, C. M. Hartshorn and T.
J. Meyer, J. Am. Chem. Soc., 2000, 122, 8464.
36 J. J. Concepcion, J. W. Jurss, M. R. Norris, Z. F. Chen, J. L.
Templeton and T. J. Meyer, Inorg. Chem., 2010, 49, 1277.
37 B. Radaram, J. A. Ivie, W. M. Singh, R. M. Grudzien, J. H.
Reibenspies, C. E. Webster and X. Zhao, Inorg. Chem., 2011,
50, 10564.
38 L. Bernet, R. Lalrempuia, W. Ghattas, H. Mueller-Bunz, L.
Vigara, A. Llobet and M. Albrecht, Chem. Commun., 2011, 47,
8058.
39 Y. Jiang, F. Li, B. Zhang, X. Li, X. Wang, F. Huang and L. Sun,
Angew. Chem. Int. Ed., 2013, 52, 3398.
40 L. Duan, F. Bozoglian, S. Mandal, B. Stewart, T. Privalov, A.
Llobet, and L. Sun, Nat. Chem., 2012, 4, 418.
41 L. Duan, C. M. Araujo, M. S. G. Ahlquist and L. Sun, Proc. Natl.
Acad. Sci. U.S.A., 2012, 109, 15584.
42 L. Duan, L. Wang, A. K. Inge, A. Fischer, X. Zou and L. Sun,
Inorg. Chem., 2013, 52, 7844.
43 L. Wang, L. Duan, Y. Wang, M. S. G. Ahlquist and L. Sun,
Chem. Commun., 2014, 50, 12947.
44 L. Wang, L. Duan, B. Stewart, M. Pu, J. Liu, T. Privalov and L.
Sun, J. Am. Chem. Soc., 2012, 134, 18868.
45 H. Lv, J.Song, Y. V. Geletii, J. W. Vickers, J. M. Sumliner, D. G.
Musaev, P.Kögerler, P. F. Zhuk, J. Bacsa, G. Zhu and Craig L.
Hill, J. Am. Chem. Soc., 2014, 136, 9268.
46 Y. V. Geletii, B. Botar, P. Kögerler, D. A. Hillesheim, D. G.
Musaev and C. L. Hill, Angew. Chem., Int. Ed., 2008, 47, 3896.
47 A. Sartorel, M. Carraro, G. Scorrano, R. D. Zorzi, S. Geremia,
N. D. McDaniel, S. Bernhard, M. Bonchio, J. Am. Chem. Soc.,
2008, 130, 5006.
48 C. Besson, Z. Huang, Y. V. Geletii, S. Lense, K. I. Hardcastle, D.
G. Musaev, T. Lian, A. Proust, C. L. Hill, Chem. Commun.,
2010, 46, 2784.
49 Q. Yin, J. M. Tan, C. Besson, Y. V. Geletii, D. G. Musaev, A. E.
Kuznetsov, Z. Luo, K. I. Hardcastle and C. L. Hill, Science,
2010, 328, 342.
50 G. Zhu, Y. V. Geletii, P. Kögerler, H. Schilder, J. Song, S. Lense,
C. Zhao, K. I. Hardcastle, D. G. Musaev, C. L. Hill, Dalton
Trans., 2012, 41, 2084.

8 | J. Name., 2012, 00, 1-3

This journal is © The Royal Society of Chemistry 20xx

Please do not adjust margins

Please do not adjust margins
Journal Name

ARTICLE

51 G. Zhu, E. N. Glass, C. Zhao, H. Lv, J. W. Vickers, Y.V. Geletii,
D. G. Musaev, J. Song and C. L. Hill, Dalton Trans., 2012, 41,
13043.
52 P.-E. Car, M. Guttentag, K. K. Baldridge, R. Alberto, G. R.
Patzke, Green Chem., 2012, 14, 1680.
53 S. Goberna-Ferrón, L. Vigara, J. Soriano-López, J. R. GalánMascarós, Inorg. Chem., 2012, 51, 11707.
54 X.-B Han,. Z.-M. Zhang, T. Zhang, Y.-G. Li, W. Lin, W. You, Z.M. Su, E.-B. Wang, J. Am. Chem. Soc., 2014, 136, 5359.
55 K. Meyer, M. Ranocchiari and J. A. van Bokhoven, Energy
Environ. Sci., 2015, 8, 1923.
56 C. Wang, J.-L. Wang and W. Lin, J. Am. Chem. Soc., 2012, 134,
19895.
57 R. E. Hansen and S. Das, Energy Environ. Sci., 2014, 7, 317.
58 S. Fukuzumi and D. Hong, Eur. J. Inorg. Chem., 2014, 4, 645.
59 A. Savini, P. Belanzoni, G. Bellachioma, C. Zuccaccia, D.
Zuccaccia and A. Macchioni, Green Chem., 2011, 13, 3360.
60 U. Hintermair, S. M. Hashmi, M. Elimelech and R. H.
Crabtree, J. Am. Chem. Soc., 2012, 134, 9785.
61 J. M. Thomsen, S. W. Sheehan, S. M. Hashmi, J. Campos, U.
Hintermair, R. H. Crabtree and G. W. Brudvig, J. Am. Chem.
Soc., 2014, 136, 13826.
62 M. Schulze, V. Kunz, P. D. Frischmann and F. Würthner, Nat.
Chem., 2016, Advance
Online Publication,
DOI:
10.1038/NCHEM.2503
63 P. Ballester, M. Fujita and J. Rebek, Chem. Soc. Rev., 2015,
44, 392.
64 J. Kang and J. Rebek, Nature, 1997, 385, 50.
65 F. Hof and J. Rebek, Proc. Natl. Acad. Sci. U.S.A., 2002, 99,
4775.
66 M. Yoshizawa, J. K. Klosterman and M. Fujita, Angew. Chem.
Int. Ed., 2009, 48, 3418.
67 S. Horiuchi, T. Murase and M. Fujita, Chem. Asian J., 2011, 6,
1839.
68 D. L. Caulder and K. N. Raymond, Acc. Chem. Res., 1999, 32,
975.
69 D. Fiedler, R. G. Bergman and K. N. Raymond, Angew. Chem.
Int. Ed., 2004, 43, 6748.
70 C. J. Brown, R. G. Bergman and K. N. Raymond, J. Am. Chem.
Soc., 2009, 131, 17530.
71 M. D. Pluth, R. G. Bergman and K. N. Raymond, Acc. Chem.
Res., 2009, 42, 1650.
72 C. J. Brown, G. M. Miller, M. W. Johnson, R. G. Bergman, K.
N. Raymond, J. Am. Chem. Soc., 2011, 133, 11964.
73 Z. J. Wang, C. J. Brown, R. G. Bergman, K. N. Raymond and F.
D. Toste, J. Am. Chem. Soc., 2011, 133, 7358.
74 A. Poater, Catal. Commun., 2014, 44, 2.
75 J. T. Edward, J. Am. Chem. Soc., 1970, 47, 261.
76 C.S. Johnson, Progress in Nuclear Magnetic Resonance
Spectroscopy, 1999, 34, 203.
77 R. Farina, R. Hogg and R. G. Wilkins, Inorg. Chem., 1968, 7,
170.
78 J. Burgess and R. H. Prince, J. Chem. Soc., 1965, 6061.
79 P. C. Andrews, G. B. Deacon, R. Frank, B. H. Fraser, P. C. Junk,
J. G. MacLellan, M. Massi, B. Moubaraki, K. S. Murray and M.
Silberstein, Eur. J. Inorg. Chem., 2009, 744.
80 P. W. Ball, A. B. Blake, J. Chem. Soc. A, 1969, 1415.
81 W. Zhang, J. Liu, H. Zhu, W. Gao and L. Sun, Synth. Commun.,
2007, 37, 3393.
82 E. C. Constable and M. D. Ward, J. Chem. Soc., Dalton
Trans., 1990, 1405.

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