A Ruthenium(II) Aqua Complex as Efficient Chemical and Photochemical Catalyst for Alkene and Alcohol Oxidation

Article abstract of DOI:10.1002/ejic.201801206

Different synthetic routes have been developed to obtain the aqua complex trans-[Ru^II(trpy)(pypz-H)(OH₂)](PF₆)₂, Ru6. This complex, together with the chlorido intermediate complexes cis- and trans-[Ru^IICl(pypz-H)(trpy)]⁺, Ru5a and Ru5b, have been fully characterized by analytical, spectroscopic, and electrochemical methods. Furthermore, the trans-Ru5b complex has been characterized in the solid state through single-crystal X-ray diffraction analysis. The aqua complex Ru6 was tested as catalyst in the photooxidation of alcohols in water and in the chemical oxidation of alkenes, displaying a good performance with high selectivity values in both catalytic processes.

Full text of DOI:10.1002/ejic.201801206

A Journal of
Accepted Article
Title: A Ruthenium(II) aqua complex as efficient chemical and
photochemical catalyst for alkene and alcohol oxidation
Authors: Ester Manrique, Xavier Fontrodona, Montserrat Rodríguez,
and M.Isabel Romero
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European Journal of Inorganic Chemistry
10.1002/ejic.201801206
FULL PAPER
A Ruthenium(II) aqua complex as efficient chemical and
photochemical catalyst for alkene and alcohol oxidation
Ester Manrique, [a] Xavier Fontrodona, [a] Montserrat Rodríguez* and Isabel Romero*
[a]
[a]
Dedication ((optional))
Abstract: Different synthetic routes have been developed to obtain
Since high-valent metal-oxo complexes have been identified to be
involved in the heme and non-heme metalloenzymes responsible
for the oxidation of organic substrates,[5] an artificial
photosynthetic system can also be applied to the oxidation of such
type of substrates. In this sense, the oxidation of alcohols [6] is a
thermodynamically uphill conversion that involves a two electron-
two proton coupled process (eq.1) This process has a practical
importance in the production of renewable clean energy as
hydrogen, because the anodic liberation of protons and electrons
could be coupled on a cathode for hydrogen fuel production in an
integrated photoelectrochemical cell. [7]
II
the aqua complex trans-[Ru (trpy)(pypz-H)(H
2
O)](PF
6 2
) , Ru6. This
complex, together with the chlorido intermediate complexes, cis- and
II
+
trans-[Ru Cl(pypz-H)(trpy)] , Ru5a and Ru5b, have been fully
characterized by analytical, spectroscopic and electrochemical
methods. Furthermore, the trans-Ru5b complex has been
characterized in the solid state through monocrystal X-ray diffraction
analysis. The aqua complex Ru6 was tested as catalyst in the
photooxidation of alcohols in water and in the chemical oxidation of
alkenes, displaying a good performance with high selectivity values in
both catalytic processes.
RCH(-OH)R’----- RC(=O)R’ +2 H + 2 e- (1)
+
Introduction
During the last decades, we have developed efficient
polypyridyl ruthenium-aqua complexes as catalysts for chemical
oxidation reactions.[8] These Ru aqua complexes can easily lose
protons and electrons to form reactive, high oxidation state Ru=O
species, and hence they have been widely used as redox
Oxidation of organic substrates as olefins, alcohols, and
sulfides, among others, mediated by transition metals, is a
relevant process from an industrial point of view since the
corresponding products play an important role as intermediates
and building blocks in synthesis and also in materials science.[1]
One of the challenges of this century is to design catalysts to
improve the control of the activity and selectivity of the chemical
processes and, at the same time, be compatible and respectful
with the environment. Solar energy combined with water are good
alternative energy sources for the development of non-fossil
based fuel. [2] Sunlight can be considered as an ideal reagent for
environmentally friendly, green chemical synthesis since visible
light is non-toxic, generates no waste and can be obtained from
renewable sources.
catalysts for the chemical oxidation of both organic and inorganic
[9]
substrates.
We believe that, from the perspective of
sustainability, the research and development of efficient artificial
photosynthetic systems is a great challenge for a potential
technological application. Moreover, to the best of our knowledge,
scarce reports on the photocatalytic oxidation of alcohols can be
found in the literature. [10]
With all this in mind, in this work we describe different synthetic
routes for obtaining a new family of ruthenium complexes of
II
n+
general formula [Ru (pypz-H)(trpy)(X)] , (pypz-H= 2-(3-
-
pyrazolyl)pyridine; trpy= terpyridine; X=Cl , n=1, cis-Ru5a and
In the photosystem II, water is oxidized by sunlight providing
electrons and protons for sustainable processes in nature through
the formation of manganese (V) oxo as active species, generated
by stepwise proton-coupled electron transfers (PCET). [3] Then,
most of the studies, carried out with transition metals as catalysts,
have tried to mimic the PSII aiming at water splitting into
molecular oxygen and hydrogen. [4]
2
trans-Ru5b; X=H O, n=2, Ru6 ) together with their complete
spectroscopic, and electrochemical characterization. The aqua
complex Ru6 has been tested as photocatalyst in the oxidation of
alcohols in water and as catalyst in the chemical oxidation of
alkenes.
Results and Discussion
[
a]
Dr. Ester Manrique, Xavier Fontrodona, Dr. Montserrat Rodríguez
and Dr. Isabel Romero
Synthesis and Spectroscopic properties
Department de Quimica , Serveis Cientifics Tècnics de Recerca
Universitat de Girona
C/ Mª Aurèlia Capmany 69, 17003 Girona
E-mail: marisa.romero@udg.edu; montse.rodriguez@udg.edu
http://www.udg.edu/depq/
Different synthetic pathways were followed for the preparation of
II
the Ru(II) complexes, cis- and trans-[Ru Cl(trpy)(pypz-H)](PF
6
)
II
(
(
Ru5a and Ru5b, respectively) and trans-[Ru (trpy)(pypz-H)
2 6 2
H O)](PF ) , Ru6, which are outlined in Scheme 1 (the
nomenclature trans- and cis- for complexes refers to the relative
position of the monodentate ligand with regard to the pyrazole ring
of the pypz-H ligand). Different complexes, cis(Cl),cis(S)-
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
II
],[11] P2, [Ru Cl
III
[12]
[
Ru Cl
2
(pypz-H)(dmso)
2
3
(trpy)]
,
P3 and
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European Journal of Inorganic Chemistry
10.1002/ejic.201801206
FULL PAPER
[
RuCl
2
(trpy)(dmso)],[13] P4, were used as precursors depending
on the synthetic strategy (pathways A, B or C) used. Compounds
II
P2 and P4 were first obtained by reaction of [Ru Cl
2
(dmso)
4
], P1,
with pypz-H or trpy ligand respectively, in EtOH at reflux.
In pathway A, P2 reacts with equimolar amounts of the
commercial trpy ligand in methanol at reflux (18 h) to generate a
II
mixture of Ru -Cl isomeric complexes, cis- and trans-
II
[
Ru Cl(pypz-H)(trpy)](PF
6
), Ru5a and Ru5b, in a 1:4 ratio, which
are separated and purified through crystallization and by column
chromatography. The use of absolute ethanol instead methanol
as solvent, along with a longer reflux time (up to 48 h), leads to
an increased final yield of the pure trans-isomer Ru5b (see the
experimental section). In pathway B, equimolar amounts of
III
[
Ru Cl
3
(trpy)], P3, and the bidentate pypz-H ligand in EtOH:H
2
O
(
9:1) in the presence of Et
3
N (1.2 equivalents) resulted in the
substitution of two chlorido ligands in P3 to generate the Ru(II)
complex Ru5b as a single trans-isomer together with other
secondary products, among which the dimeric species
[
Ru
2
IICl(trpy)
2
(µ-Cl)(µ-pypz)](PF
6
), Ru7, that contains
a
-
deprotonated pypz bridging ligand. Triethylamine, used as
ruthenium (III) reducing agent, might also play a base role by
deprotonating the pypz-H ligand, thus favouring the formation of
the dinuclear Ru7 species. Finally, in pathway C, P4 reacts with
equimolar amounts of pypz-H ligand in EtOH at reflux for 20 h and
leads to the major formation of Ru5b complex isolated after
column chromatography. In both pathways A and C, the formation
II
of the dmso complex trans-[Ru (pypz-H)(trpy)(dmso)](PF
6
)
2
, Ru8,
as a minor product was also observed. Treatment of the trans-
II
+
[
Ru Cl(pypz-H)(trpy)](PF
corresponding aqua
H)(trpy)(H O)](PF
6
) Ru5b complex with Ag generates the
II
complex,
trans-[Ru (pypz-
, Ru6. The corresponding cis-aqua complex
2
6
)
2
could not be obtained since the analogous reaction of cis-
II
Scheme 1. Schematic pathways for the synthesis of the Ru -chlorido
II
+
[
Ru Cl(pypz-H)(trpy)](PF
6
), Ru5a with Ag led to a new dimeric
](PF (Ru9, see below).
complexes Ru5a and Ru5b and the aqua-complex Ru6 (other minor products
were obtained in the different synthesis but are not displayed, see text for
details)
II
compound, [Ru (trpy)
2
(µ-pypz)
2
6 2
)
The IR spectra of compounds (SI) show bands around 3600-
-1
3
400, 3090 and 1412-1389 cm , that can be respectively
2
trans Ru-OH complex (Figure S5) the deshielding effect of the
H
2
O ligand over H(1) is not as strong as that observed in the
assigned to N-H, =C-H and C=N stretching modes of the
polypyridylic ligands. In the case of Ru6, the spectrum displays
an additional peak over 3350 cm-1 which corresponds to the υO-H
corresponding chlorido complex trans-Ru5b, thus leading to a
lower chemical shift ( = 9.4 ppm).
stretching of the aqua ligand. The one-dimensional (1D) and two-
dimensional (2D) NMR spectra of compounds were recorded in
methanol-d and are presented in Figure 1 and in the Figures S2-
4
In all the synthetic pathways, the obtaining of the trans isomer
Ru5b is favoured versus the cis Ru5a isomer. This fact could be
explained on the basis of electronic effects. In the trans Ru5b
isomer, the more sigma-donor pyrazolyl ring of the bidentate
pypz-H ligand is coordinated trans to the monodentate Cl ligand
(see Scheme 2), allowing a better distribution of the electronic
density through elongation of the Ru-Cl bond distance, as we
have observed in another family of complexes containing the
highly sigma-donor carbene CN-Me ligand.[15] In the
corresponding cis isomer, the chelate character of the trpy ligand
prevents such structural rearrangement. On the other hand, the
S5. All the resonances for the complexes are found in the
aromatic region (except for the methyl dmso signals in Ru8), and,
in the case of complexes Ru5b and Ru8, are consistent with the
solid-state structures determined through X-ray diffraction. The
combination of 1D and 2D NMR spectra allows to identifying all
the resonances for the complexes. The most interesting feature
of the spectra of chlorido-complexes Ru5a and Ru5b (Figure 1)
is the deshielding effect exerted by the chlorido ligand over the
pyridilic H(1) of the bidentate ligand in the trans isomer Ru5b ( =
trans isomer probably allows
a stronger hydrogen bond
10.03 ppm) with regard to Ru5a, where H(1) is influenced by the
interaction between the chloride ligand and the H proton in cis,
which has a pyridyl ring spatially closer to what the smaller
pyrazolyl ring would be (H(1)-Cl distance is 2.768 Å as inferred
from X-ray diffraction analysis, see below).
aromatic π electron density then appearing upfield with regard to
Ru5b ( = 7.2 ppm). Such an effect has been also observed in
other Ru compounds containing R-pypz-H ligands.[14] For the
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European Journal of Inorganic Chemistry
10.1002/ejic.201801206
FULL PAPER
a)
Figure 2. ORTEP plot and labelling scheme for the cationic moiety in the X-ray
structure of isomer Ru5b.
b)
a)
1
Figure 1. H-NMR spectra of complexes a) Ru5a and b) Ru5b in methanol
-d
4
b)
II
Scheme 2. Cl-H interaction in trans- and cis-Ru Cl(trpy)(pypz-H)](PF
6
)
complexes.
II
The crystal structures of complex trans-[Ru Cl(trpy)(pypz-
H)](PF
Cl)(µ-pypz)](PF
Ru8 and [Ru (trpy)
6
), Ru5b, and that of the minor products [Ru
2
IICl(trpy)
2
(µ-
II
6
), Ru7, trans-[Ru (pypz-H)(trpy)(dmso)](PF
6
)
2
,
c)
II
2
(µ-pypz)
2
](PF
6
)
2
Ru9, have been solved by
single crystal X-ray diffraction analysis. Figure 2 displays the
molecular structure for Ru5b, whereas Figure 3 shows those of
the three minor compounds. The main crystallographic data and
selected bond distances and angles can be also found in the
Supporting Information section. The structures of Ru5b (Figure 2)
and Ru8 (Figure 3b) show the Ru metal centres with an
octahedral distorted type of coordination where the trpy ligands
are bonded in a meridional manner and the pypz-H ligands act in
a bidentate fashion. The sixth coordination site is occupied by a
chlorido ligand placed in trans respect to the pyrazole ring in Ru5b
and by a dmso ligand placed in cis respect to the same ring in
Ru8. The cis conformation in complex Ru8 is probably favoured
by the higher volume (with regard to Cl) of the dmso ligand, which
Figure 3. ORTEP plots and labeling schemes for the cationic moieties in the X-
ray structures of complexes (a) Ru7 (b) Ru8 and (c) Ru9
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European Journal of Inorganic Chemistry
10.1002/ejic.201801206
FULL PAPER
is better accommodated close to the smaller pyrazolyl ring instead
of a pyridyl in cis. Also, a hydrogen bonding interaction between
the O atom of the dmso ligand and the pyrazolic N-H proton (bond
distance 2.339 Å) can help its formation. All bond distances and
angles are within the expected values for this type of
of the pyridylpyrazole and the chlorido ligands to the ruthenium,
leading to a greater stabilization of Ru(III) when the pyrazolyl ring
is placed in trans respect to the σ-donor chlorido ligand.
The redox properties of the the aqua complex Ru6 were studied
by means of DPV in aqueous phosphate buffer solution. Figure 5
displays the DPV of complex Ru6 at pH= 10.6, where several
distinctive processes can be observed: an initial oxidation process
complexes.[
15]
Regarding the two dimeric compounds (see SI),
their structures show again distorted octahedral geometries
around the metal centres, with the deprotonated pyrazole rings of
the corresponding pypz-H ligands bridging the two ruthenium
III
II
is found at 0 V corresponding to the Ru /Ru couple, followed by
another two one-electron oxidation waves at 0.4 and 1.1 V (vs.
-
IV/III
V/IV
atoms in both cases. The trpy and pypz arrangement around
SCE), which were attributed to Ru
and Ru redox couples,
each Ru metal centre corresponds to that of a cis isomer and this
leads to an additional hypothesis to explain the lower occurrence
of Ru5a in the synthesis of the chlorocomplex, as the easy
deprotonation of the pyrazolic proton in Ru5a could result in its
conversion into the dinuclear compounds described.
respectively, on the basis of other similar compounds previously
described. [
14c],[18]
DPV shows that the oxidation of complex Ru6
to Ru(V) oxidation state leads to the emergence of a large electro-
catalytic wave at 1.2 V, which is presumably indicative of
electrochemical water oxidation. A similar behaviour has been
also observed at neutral pH (see SI). Thus, the behaviour
displayed by this complex suggests that it can oxidize water after
The UV-Vis spectra of complexes Ru5a, Ru5b and Ru6,
V
2+
the generation of the active species [Ru =O] .
2 2
determined in CH Cl or aqueous phosphate buffer, are displayed
in Figure 4. The complexes exhibit ligand based π-π * bands
below 350 nm and relatively intense bands above 350 nm
assigned mainly to a series of dπ-π* MLCT transitions.[16] For the
Ru-Cl complexes the MLCT bands are shifted to the red with
7
6
,00E-02
,00E-02
regard to the corresponding Ru-OH
2
due to the relative
5,00E-02
destabilization of the dπ(Ru) levels provoked by the Cl ligand.[17]
4
3
,00E-02
,00E-02
1
,2
2,00E-02
1,00E-02
0,00E+00
1
0,8
0,6
0,4
0,2
0
-
0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4
Potential (V)
Figure 5. DPV for complex Ru6 registered in a phosphate buffer (pH= 10.6) vs
SCE.
220
320
420
520
620
720
λ / nm
The stability of the different ruthenium species generated from the
aquacomplex Ru6 as a function of the pH was evaluated and the
corresponding Pourbaix diagram (where pH-potential regions
arising from the multiple protonation sites in the complex are
defined) is displayed in Figure 6. All the redox waves are pH-
dependent except in three different regions of the diagram: at pH
values below 2.1 (where the wave observed at E1/2=0.64 V
Figure 4. UV-visible spectra of Ru5a (solid line), Ru5b (dotted line) in CH
and Ru6 (dashed line) in phosphate buffer (pH=7).
2 2
Cl
Electrochemical properties
III
3+
corresponds to the equilibrium between [Ru (pypzH)(OH
2
)] and
The redox properties of chlorido complexes Ru5a and Ru5b,
together with those of the aqua complex Ru6 were investigated
by means of cyclic voltammetry (CV) and differential pulse
voltammetry (DPV). The CV of the complexes Ru5a and Ru5b in
II
)]2+ through one-electron oxidation), at pH
[
Ru (pypzH)(OH
2
values above 11.8 (where the interconversion between
III
+
II
[
Ru (pypz)(OH)] and [Ru (pypz)(OH)] takes place at E1/2 = 0 V)
V
2+
and, finally, the exchange between Ru (pypz)(O)]
and
CH
process at E1/2= 0.88 V and E1/2= 0.80 V vs SCE, respectively
Figure S6). The lack of anionic current for free chloride ions
2 2
Cl exhibit a reversible one electron Ru(III)/Ru(II) redox
IV
+
[
Ru (pypz)(O)] along the basic pH range at 1.1 V.
(
+
Under acidic conditions (pH values in the range 2.1-6.0), a 1H /1e-
oxidation reveals the inertness of the Ru-Cl bond, giving evidence
for the high stability of the Ru5a and Ru5b complexes under
these experimental conditions. Despite presenting the same
coordination environment, higher potential values are obtained for
the cis chlorido complex Ru5a (0.88 V) when compared to the
analogous trans Ru5b (0.80 V). This redox behaviour evidences
that the oxidation state (III) is affected by the relative coordination
PCET
process
assigned
to
the
III
2+
II
)]2+ redox couple was
[
Ru (pypzH)(OH)] /[Ru (pypzH)((OH
2
observed. In the pH range 6.0-7.1 two redox processes are
detected. The lowest potential wave decreases 118 mV per pH
unit and this variation is consistent with a 2H /1e PCET process,
+
-
III
+
II
)]2+
which is assigned to the [Ru (pypz)(OH)] /[Ru (pypzH)((OH
2
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European Journal of Inorganic Chemistry
10.1002/ejic.201801206
FULL PAPER
redox couple. In this process, deprotonation of both aqua and
trans-[Ru(Hbpp)(trpy)(OH
2 2
)]2+ and trans-[Ru(Hbpa)(trpy)(OH )]2+
pypz-H ligands take place upon Ru(II)Ru(III) oxidation. A
second 1H /1e PCET process can be detected at higher E1/2
values with a slope of ~69 mV per pH unit attributed to the
complexes (entries 2 and 3) and thus the electron-withdrawing
substituents at the C5 position of the pyrazole ring do not exert a
significant effect (only a slight influence of such substituents is
+
-
IV
+
III
+
manifested the case of [Ru(Hbpa)(trpy)(OH
2
)]2+, entry 3,
[
7
to
[
Ru (pypz)(O)] /[Ru (pypz)(OH)] redox pair. Finally, in the range
+
-
.1-11.8 two 1H /1e PCET processes can be observed, assigned
containing a carboxylate group, as evidenced by the increase of
50 mV for the III/II couple redox and 40 mV for the IV/III with
respect to the analogous values for Ru6). However, substitution
III
+
II
)]+
the
[Ru (pypz)(OH)] /[Ru (pypz)((OH
III
2
and
IV
+
+
Ru (pypz)(O)] /[Ru (pypz)((OH)] redox couples.
at the N-position of the pyrazolyl ring, as is the case for complex
II
)]2+ (entry 4) has a more important
trans-[Ru (trpy)(pypz-Me)(OH
2
V
1
,2
1
Ru (pypz)(O)
effect on the Ru(III/II) redox couple which is increased by 160 mV,
in accordance with the higher electron-donor character of the
pypz-H ligand with regard to pypz-Me due to the acidity of the N-
H proton in Ru6. If bpy is used as bidentate ligand (entry 5), the
electron-donor ability of the bidentate ligand is even lower and
therefore a higher Ru(III/II) potential value is found. Finally,
III
Ru (pypz-H)(OH )
2
IV
0
0
0
0
,8
,6
,4
,2
0
Ru (pypz)(O)
III
Ru (pypz-H)(OH)
III
Ru (pypz)(OH)
coordination of
a strong σ-donor anionic ligand such as
II
Ru (pypz-H)(OH )
2
II
acetylacetonate (acac, entry 6) produces a stabilization of the
Ru(III) oxidation state and thus a strong decrease of the III/II
couple to values below to that observed in Ru6 takes place. The
IV/III couple is in general much less affected by the different
bidentate ligands present.
Ru (pypz)(OH)
II
Ru (pypz)(OH )
2
-
0,2
1
2
3
4
5
6
7
pH
8
9
10 11 12 13
Figure 6. Pourbaix diagram for complex Ru6. The pH-potential regions of
stability and the proton composition for the different redox species are indicated.
The pKa of each species is represented with a dashed vertical line.
Regarding the pKa values, complex Ru6 presents the highest
pka(II)aqua value (11.8) followed by that displayed by the acac
complex in entry 6. This is in accordance with the anionic nature
The Ru (IV/III) and Ru(V/IV) waves are not observed below pH=7
in the Pourbaix diagram but we tentatively propose that the
Ru(V/IV) process is pH-independent throughout the whole pH
range, due to the high acidity of Ru(V) that would presumably
drive the deprotonation of the pypz-H ligand even at acidic pH
values.[14c]
-
of acac and pypz ligands (that is deprotonated at this pH value),
which are strong -donor and thus make the Ru metal centre and
the coordinated aqua ligand less acidic. On the other hand, the
complexes bearing the less electron-donor bidentate ligands
(entries 4 and 5) are the ones displaying the lowest pKa values.
The pKa values for the deprotonation of pypz-H or H
2
O ligands in
Table 1. pKa and electrochemical data (pH= 7, E1/2 in V vs SCE) for aqua
the Ru(II) and Ru(III) species were determined from the changes
of slope in the Pourbaix diagram and are indicated with vertical
dashed lines. The corresponding equilibria for the Ru(II) species
are displayed in eq. 2 and 3:
complexes described in this work and others for purposes of comparison.
E
1/2
E
1/2
entry
compound
a
pK (II)
(III/II)
(IV/III)
1[a]
11.7 (7.1)[b]
11.1 (6.8)[b]
Ru6
0.23
0.24
0.60
0.61
[
[
Ru(pypz-H)(OH
2
)]2+  [Ru(pypz)(OH
2
)]+ + H+ (2)
)]  [Ru(pypz)(OH)]+ + H+ (3)
2
2[15a]
3[14c]
)]2+
)]2+
trans-[Ru(Hbpp)(trpy)(OH
trans-[Ru(Hbpa)(trpy)(OH
2
2
+
Ru(pypz)(OH
0.28
0.64 10.5 (4.75)[b]
II
In the case of Ru6, the pKa values for Ru(II) are pKa(Ru )pz= 7.1
and
II
4[19]
5[20]
)]2+ 0.39
0.49
pKa(Ru )aqua
=
11.8,
corresponding
to
the
trans-[Ru(trpy)(pypz-Me)(OH
[Ru(trpy)(bpy)(OH
)]2+
[Ru(trpy)(acac)(OH2)]
2
0.57
0.62
0.56
10.1
9.7
protonation/deprotonation of the pyrazole ring and the aqua
ligand, equations (2) and (3) respectively. In the case of Ru(III),
the subsequent increase of the Lewis acid character with regard
to Ru(II) has a notably higher influence on the pKa value of the
aqua ligand (which is directly coordinated to the Ru metal centre)
than on that of the pyrazolyl ligand. As a result, the deprotonation
sequence is reversed and the corresponding pKa values are
pKa(RuIII)aqua= 2.1 and pKa(RuIII)pz= 6.
2
[21]
+
6
0.19
11.2
[
a] This work. [b] pKa values corresponding to the deprotonation of the pyrazolyl
ligand. Ligand abbreviations: Hbpp is 3,5-bis(2-pyridyl)pyrazole; Hbpa is 1H-
pyrazole-3-carboxylic acid 5-(2-pyridinyl)-ethylester; acac is
acetylacetonate.(See SI for the structure of the ligands)
Photocatalytic oxidation of alcohols
2
Table 1 shows the redox potential of the Ru-OH complex Ru6
together with those of similar complexes previously reported in
the literature, for comparison purposes.[14a,c] [19-21] As can be
observed, the redox potentials of the Ru(III/II) and Ru(IV/III)
couples in Ru6 are very close to that displayed by the analogous
The photocatalytic oxidation of alcohols was performed in a
system containing [Ru(bpy) as
]2+ as photosensitizer, Na
oxidizing agent and the ruthenium aquacomplex Ru6 as catalyst,
3
2 2 8
S O
in a ratio complex:photosensitizer:substrate:oxidant of 1:10:100:
200, in phosphate buffer pH=7, at 25ºC. The samples were
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European Journal of Inorganic Chemistry
10.1002/ejic.201801206
FULL PAPER
irradiated with a xenon lamp (150, Hamamatsu L8253), equipped
with a 400-700 nm large band filter.
Table 2. Oxidation tests performed with complex Ru6. Conditions: Ru6 (0.5
mM), photosensitizer (5 mM), substrate (50 mM), Na S O (100 mM) in 2.5 ml
2 2 8
of 0.1M phosphate buffer solution at pH=7.2; light irradiation for 15 h.
TON=n(product)/n(catalyst).
Different reaction times were evaluated using 1-phenylethanol as
substrate in order to optimize the reaction time on the
photocatalytic oxidation of alcohols (Figure S8). We chose 15 h
as optimal time to perform the catalytic experiments. Then, after
irradiation for 15 h, the reaction products were extracted with
Entry
Substrate
Product
Conv.(%)
85
1
1
three portions of dichloromethane and evaluated by means of H-
NMR spectroscopy.
2
3
65
78
Blank experiments were performed under dark conditions and
with all reagents in the reaction vessel. After 15h, the oxidation
of alcohol was below 2%. The effect of light was also tested
and, after irradiation for 15h with visible light in the absence of
catalyst or oxidizing agent, the conversion values for the
oxidation of alcohols were below 5%. In all the catalytic
essays, the expected aldehyde or ketone was detected as
unique product of the oxidation reaction, and the selectivity
achieved was above 99%, similar to that displayed by other
5
6
9
4
5
6
compounds described in the literature.[22]
.
Table displays the conversion values obtained in the
2
Catalytic epoxidation of alkenes
photooxidation of different alcohols by Ru6. These results show
moderate to high yields for the corresponding aldehyde and
ketones. For the primary alcohols (entries 2-4), the TON is
enhanced by the presence of electron-donating substituents at
the aromatic ring of the benzylalcohol (entry 3) but is decreased
by the presence of electron withdrawing substituents, as chloro
The catalytic activity of Ru6 was checked in the epoxidation of
different alkenes in dichloromethane and using iodobenzene
diacetate as oxidant, with a catalyst:substrate:oxidant ratio of
1:100:200 at room temperature for 24 h. Blank experiments
evidenced that no epoxidation occurred in the absence of catalyst
under the same conditions.
(
entry 4). This behaviour is in accordance with the presence of an
electrophilic active species in the catalyst, which is also in
accordance with the better performance displayed by 1-
phenylethanol (entry 1) when compared to diphenylmethanol
Table 3 reports the conversion and selectivity values for the
epoxide product in each case. In general moderate to high
conversions and good selectivity values for the corresponding
epoxides are obtained for all the substrates tested. Both aliphatic
and aromatic alkenes are efficiently epoxidized and, among the
aromatic ones (entries 1-3), styrene (entry 1) displays a slightly
lower conversion degree. This would be in accordance with the
involvement of an electrophilic active species that would display
better reactivity towards the alkyl-substituted β-methylstyrenes
(entries 2 and 3) than for styrene. The conversion trend within
aliphatic olefins (entries 4-6) would also be in accordance with the
occurrence of such electrophilic active species, achieving slightly
lower conversion values for the monosubstituted 1-octene
substrate (entry 6) when compared to the alkyl-disubstituted
cyclic olefins.
(
entry 5).
Additional tests using acetone (2% volume) as co-solvent were
performed for the oxidation of 1-phenylethanol and
phenylmethanol (entries 1 and 2 respectively). The conversion
values were increased from 85 to 89% in the first case and
from 65 to 90% in the second, probably due to a better
solubility of the alcohols in the medium.
The activity of Ru6 with regard to the epoxidation of cis-β-
methylstyrene shows 78 % of cis-epoxide and 22 % of trans-
epoxide, and this fact must be caused by the involvement of a
relatively stable radical species in the catalytic cycle that
undergoes isomerization to the most thermodynamic stable trans
isomer.[23] It is interesting to compare the activity of complex Ru6
with regard to the previously reported trans-[Ru(trpy)(pypz-
2
+ [19]
2
Me)(OH )] , for which the isomerization to the trans-epoxide is
inexistent. Taking into account that both catalysts present similar
redox behaviour, their different stereoselectivity could be related
to structural factors associated to the presence of the additional
methyl group which could hinder the cis  trans rotation of the
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European Journal of Inorganic Chemistry
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FULL PAPER
Table 3. Ru-catalyzed alkene epoxidation mediated by complex Ru6.
Experimental Section
Conditions: Ru6:subs:PhI(OAc)
in CH Cl , 24 h at RT. Selectivity for epoxide (sel): [Yield/conversion]x100.
Conversion (conv) and selectivity (sel) values are given in %.
2
(catalyst:substrate:oxidant) ratio of 1:100:200
2
2
Materials and preparations: all reagents used in the present work were
obtained from Aldrich Chemical Co and were used without further
purification. Reagent grade organic solvents were obtained from “Carlo
Erba” and high purity de-ionized water was obtained by passing distilled
water through a nano-pure Mili-Q water purification system. All the
oxidation manipulations were performed under inert atmosphere.
Entry
Substrate
Conv
Sel
1
6
9
8
9
0
6
>99
2
3
4
>99 (78/22)a
Instrumentation and Measurements: IR spectra were recorded on an
ATR MK-II Golden Gate Single Reflection spectrometer. UV-Vis
82
spectroscopy was performed on
a
Cary 50 Scan (Varian)
>99 (100/0)b
>
99
spectrophotometer with 1 cm quartz cells. Cyclic voltammetry (CV) and
Differential Pulse Voltammetry (DPV) experiments were performed in an
IJ-Cambria IH-660 potentiostat using a three electrode cell. Glassy carbon
electrode (3 mm diameter) from BAS was used as working electrode,
platinum wire as auxiliary and SCE as the reference electrode. All cyclic
voltammograms presented in this work were recorded under nitrogen
5
6
9
4
>99
>99
66
aRatio [% cis epoxide/ % trans epoxide]. bRatio [% ring epoxide/ % vinyl
epoxide].
atmosphere. The complexes were dissolved in solvents containing the
+
-, TBAH, or
intermediate species in the catalytic cycle. Regarding the 4-
vinylcyclohexene substrate, Ru6 is specific towards the ring
oxidation, again in agreement with the formation of an
electrophilic catalytic species that would preferently epoxidize the
disubstituted ring double bond.
necessary amount of supporting electrolyte (n-Bu
4
NH PF
6
phosphate buffers) to yield a 0.1 M ionic strength solution. All E1/2 values
reported were estimated from cyclic voltammetric experiments as the
average of the oxidative and reductive peak potentials (Epa+Epc)/2, or
directly from DPV. Unless explicitly mentioned the concentration of the
complexes was approximately 1mM. The NMR spectroscopy was
performed on a Bruker DPX 300 and 400 MHz. Samples were run in
Conclusions
4 6
methanol-d or acetone-d with internal references (residual protons
and/or tetramethylsilane). Elemental analyses were performed using a
CHNS-O Elemental Analyser EA-1108 from Fisons. ESI-MS experiments
were performed on a Navigator LC/MS chromatograph from Thermo Quest
Finnigan, using methanol as a mobile phase. Gas chromatography
experiments were performed by capillary GC, using a GC-2010 Gas
Chromatograph from Shimadzu, equipped with an Astec CHIRALDEX G-
TA Column (30 m x 0.25 mm diameter) incorporating a FID detector. All
the product analyses in the catalytic experiments were performed by
means of GC using biphenyl as internal standard and were quantified from
calibration curves.
Through different synthetic routes, it has been possible to
II
synthesize
H)(trpy)(H
the
O)](PF
aquo
complex
trans-[Ru (pypz-
2
6
)
2
,
Ru6, that has been characterized
spectroscopic and electrochemically. We have also isolated its
II
precursor, the chlorido complex trans-[Ru (Cl)pypz-H)(trpy)](PF
6
),
Ru5b, that was successfully separated from the cis-isomer Ru5a
and from other secondary products that have been also fully
characterized. Ru6 can electrochemically oxidize water through
V
2+
the generation of a high oxidation state [Ru =O ] active species.
Ru6 has been used as catalyst in the photochemical oxidation of
alcohols in water at pH=7, at room temperature, using
Crystallographic Data Collection and Structure Determination
Measurement of the crystals were performed on a Bruker Smart Apex CCD
[
Ru(bpy)
3
]2+ as photosensitizer and as sacrificial electron
acceptor, demonstrating a good performance, with high selectivity
values. This study provides valuable information for the
development of new aqua-ruthenium molecular catalysts in the
photocatalytic oxidation of alcohols, in sustainability conditions.
Finally, we have also studied the chemical oxidation of alkenes
mediated by complex Ru6, evidencing moderate to high
conversions and good selectivity values for the corresponding
epoxides. The lack of stereospecificity in the epoxidation of cis-β-
methylstyrene is associated to the presence of the proton on the
pyrazolic nitrogen that would allow the isomerization to the most
thermodynamic stable trans isomer.
diffractometer using graphite-monochromated Mo Kα radiation (λ
.71073Å) from an X-Ray tube. Data collection, Smart V. 5.631
BrukerAXS 1997-02); data reduction, Saint+ Version 6.36A (Bruker AXS
001); absorption correction, SADABS version 2.10 (Bruker AXS 2001)
=
0
(
2
and structure solution and refinement, SHELXL-2013 (Sheldrick, 2013).
The crystallographic data as well as details of the structure solution and
refinement procedures are reported in supplementary information. CCDC
1870392 (Ru9), 1870393 (Ru5b), 1870394 (Ru7), 1870395 (Ru8) contain
the supplementary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/products/csd/request/
Preparations
2
-(3-pyrazolyl)pyridine (pypz-H, L1), ligand[24] and [RuCl
2
(dmso)
(P2),[11] [RuCl (trpy)] (P3),[12] or
3
4
]
(
P1),[25] [RuCl
2
(pypz-H)(dmso)
2
]
II
(trpy)(dmso)] (P4),[13] complexes were prepared according to
[
Ru Cl
2
literature procedures.
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European Journal of Inorganic Chemistry
10.1002/ejic.201801206
FULL PAPER
1
): δ 6.88 (ddd, 1H, H2, 3JH,H
For Ru5a: H-NMR (400 MHz, methanol-d
8.04, 6.66 Hz, 4
1.33 Hz, 5
4JH,H= 1.31 Hz), 7.53 (d, 1H, H7, 3JH,H= 2.89 Hz), 7.68 (ddd, 1H, H3, 3JH,H
8.04, 7.98 Hz, 4 H,H= 1.33 Hz), 7.76 (ddd, 2H, H9, H23, 3
H,H= 6.59 Hz,
4JH,H= 1.43 Hz, 5JH,H= 0.71 Hz), 7.95 (td, 2H, H11, H21, 3
H,H= 7.71 Hz,
4JH,H= 1.43 Hz), 8.08 (ddd, 1H, H4, 3 H,H= 7.98, 4 H,H= 1.45, 5
H,H= 0.80
Hz), 8.12 (t, 1H, H16, 3 H,H= 8.06 Hz), 8.38 (d, 1H, H8, 3
H,H= 2.89 Hz),
8.53 (dd, 2H, H12, H20, 3JH,H= 7.71 Hz, 4JH,H= 1.31 Hz), 8.65 (d, 2H, H15,
H17, 3JH,H= 8.06 Hz) ppm. 13C-NMR (400 MHz, Methanol-d
): δ 106 (C7),
4
=
II
J J J
H,H= 1.45 Hz), 7.18 (ddd, 1H, H1, 3 H,H= 6.66 Hz, 4
H,H
cis- and trans-[Ru Cl(pypz-H)(trpy)](PF
6
), Ru5a and Ru5b.
=
Pathway A
J
H,H= 0.80 Hz), 7.37 (ddd, 2H, H10, H22, 3JH,H= 7.53, 6.59 Hz,
II
A 0.558 g (1.179 mmol) sample of [Ru Cl
2
(pypz-H)(dmso)] complex (P2)
=
and 0.275 g (1.155 mmol) of trpy were refluxed in 150 mL of methanol for
8 h. Afterwards, the solution was evaporated to dryness in a rotary
evaporator and the residue redissolved in MeOH:NH OH (75:1). The
mixture was cooled in an ice bath until a brown precipitate was formed,
that was filtered on a frit and washed two times with cold MeOH:NH OH
75:1) mixture. At this point, the solid (PP1) and the filtrate (F1) were
J
J
1
J
4
J
J
J
J
J
4
(
4
treated separately. Brown solid PP1 was purified through recrystallization
by dissolving it in a mixture of MeOH:HCl (adjusting the pH to < 2), followed
123.1 (C4), 123.6 (C15, C17), 124.6 (C12, C20), 125.3 (C2), 128.5 (C10,
C22), 134.7 (C8), 134.9 (C16), 137.1 (C3), 138.1 (C11, C21), 152.7 (C1),
154 (C9, C23), 160.4(C14, C19), 160,6(C14,C18), 168.2(C6), 168.3(C5)
by addition of 1 mL of a saturated NH
00 mL of cold water under vigorous stirring. After cooling in an ice bath,
pure Ru5b complex precipitated (267 mg, 34 % yield) that was filtered off
and washed with cold H O and diethyl ether. On the other hand, filtrate F1
was reduced to dryness and purified by column chromatography (SiO
4 6
PF aqueous solution together with
-
1
1
ppm. IR (ν max, cm ): 3648, 3562, 1594, 1445, 1382, 838, 760. E1/2(III/II)
(CH Cl + 0.1 M TBAH): 0.88 V vs. SCE. UV-vis (CH Cl
) [λmax, nm (ε, M-1
2
2
2
2
-
1
2
cm )]: 238 (1480), 276 (1163), 318 (1198).
1
): δ 7.10 (d, 1H, H7, 3JH,H= 2.84
2
,
For Ru5b: H-NMR (400 MHz, methanol-d
4
2+
Hz), 7.33 (ddd, 2H, H10, H22, 3JH,H= 6.88, 6.57 Hz, 4JH,H= 1.30 Hz), 7.48
4
eluent MeOH:NH OH 30:1). The first orange fraction containing Ru(trpy)
2
was discarded together with a second purple fraction. Finally, a third
brownish fraction containing the cis-isomer was obtained that was
evaporated to dryness and redissolved in 10 mL of a MeOH:HCl mixture
(d, 1H, H8, 3JH,H= 2.84 Hz), 7.71 (ddd, 2H, H9, H23, 3JH,H= 6.57 Hz, 4JH,H
1.98 Hz, 5 H,H= 0.72 Hz), 7.83 (ddd, 1H, H2, 3 H,H= 6.54, 5.61 Hz, 4
1.4 Hz), 7.92 (td, 2H, H11, H21, 3 H,H= 6.88 Hz, 4
=
=
J
J
J
H,H
J
J
H,H= 1.98 Hz), 8.11 (t,
(
pH<2). Then a saturated aqueous NH
resulting solution was cooled until precipitation. The fine crystalline
precipitate was filtered off, washed twice with cold H O and diethyl ether
4
PF
6
solution was added and the
1H, H16, J = 8.10 Hz), 8.23 (ddd, 1H, H3, 3JH,H= 7.78, 6.54 Hz, 4JH,H= 1.46
Hz), 8.37 (dd, 1H, H4, 3JH,H= 7.78 Hz, 4JH,H= 1.41 Hz), 8.48 (ddd, 2H, H12,
H20, 3
3JH,H= 8.10 Hz), 10.03 (ddd, 1H, H1, 3JH,H= 5.61 Hz, 4JH,H= 1.46 Hz, 5JH,H
0.9 Hz) ppm. 13C-NMR (400 MHz, methanol-d
): δ 105.3 (C7), 123.2 (C4),
J J JH,H= 0.72 Hz), 8.59 (d, H15, H17,
H,H= 8.05 Hz, 4 H,H= 1.30 Hz, 5
2
and dried in vacuum obtaining 98.7 mg (13 % yield) of pure Ru5a complex.
A higher yield of Ru5b product can be obtained following the same
synthetic procedure but using absolute ethanol instead of methanol as
solvent, and maintaining the reflux throughout 48 h. Subsequent
=
4
123.3 (C15, C17), 124.1 (C12, C20), 125.3 (C2), 128.3 (C10, C22),
134.2(C8), 134.9 (C16), 137.9 (C11, C21), 138.0 (C3), 153.6 (C9, C23),
160.7 (C13,C19), 160.8 (C14, C18), 160.9 (C5,C6) ppm. Suitable crystals
for X-ray diffraction were grown as brownish-purple needles by diffusion of
precipitation with aqueous saturated NH
4
PF
6
solution and purification of
Cl :CH OH, 99:1
the solid by column chromatography (AlO
2
, eluent CH
2
2
3
mixture) leads to the obtaining of pure Ru5b in 48% yield.
2 2
diethyl ether into a CH Cl solution of the pure complex. For the NMR
Pathway B
assignments we use the same labelling scheme as for the X-ray structures.
III
A sample of [Ru Cl
3
(trpy)] (P3, 0.1 g, 0.23 mmol) was added to a solution
O (9:1) under
(0.07 mL, 0.52 mmol) was added and the
reaction mixture was stirred under N atmosphere at room temperature for
0 min. Afterwards, pypz-H (0.033 g, 0.23 mmol) was added and the
IR (ν max, cm-1): 3800-3000 (w), 3200-2800 (m), 1628, 1445, 1386, 1062,
of LiCl (22 mg, 0.52 mmol) dissolved in 15 mL of EtOH/H
magnetic stirring. Then, NEt
2
2 2
842, 760. E1/2(III/II) (CH Cl + 0.1 M TBAH): 0.80 V vs. SCE. UV-vis
-1
3
2 2
(CH Cl
) [λmax, nm (ε, M-1 cm )]: 236 (1477), 276 (1235), 322 (1146). ESI-
MS (m/z): 514.9 [Ru Cl(trpy)(pypz-H)]+
II
2
II
3
trans-[Ru (pypz-H)(trpy)(H
2
O)](PF
6
)
2
, Ru6. 0.08 g of AgPF
6
(0.32 mmol)
O, and
the mixture was heated at reflux for 2 h in the absence of light. Then, the
AgCl formed was filtered off through Celite. Afterwards, NH PF (1 mL)
mixture was refluxed for 2 h. The hot solution was then filtered off in a frit
and the volume was reduced in a rotary evaporator. After addition of a
were added to a solution of Ru7b (0.1 g, 0.15 mmol) in 30 mL of H
2
saturated NH
filtered off and washed with cold water. This solid was purified by column
chromatography (AlO , eluent CH Cl :CH OH, 99:1 mixture) and a purple-
reddish fraction, corresponding to complex Ru7b, was obtained (32 mg,
1 % yield) together with other secondary products.
Pathway C
A 150 mg (0.34 mmol) sample of complex [Ru Cl
9 mg (0.34 mmol) of pypzH were refluxed in 20 mL of absolute ethanol
4
PF
6
aqueous solution a precipitate was formed which was
4
6
was added to the filtrate and the volume reduced until a precipitate that
corresponded to the Ru6 aqua complex was formed, which was filtered on
a frit, washed with cold water and diethyl ether and dried at vacuum. Yield:
2
2
2
3
1
3
2
0.040 g (40 %). H-NMR (400 MHz, methanol-d4): δ 7.09 (d, 1H, H8, JH,H=
2.94 Hz), 7.42 (ddd, 2H, H10, H22, 3JH,H= 7.84, 5.53 Hz, 4JH,H= 1.31 Hz),
7.53 (d, 1H, H7, 3JH,H= 2.94 Hz), 7.78 (ddd, 2H, H9, H23, 3JH,H= 5.53 Hz,
J JH,H= 7.66, 6.65 Hz,
4JH,H= 1.51 Hz, 5 H,H= 0.76 Hz), 7.92 (ddd, 1H, H2, 3
II
2
(trpy)(dmso)] (P4) and
4
for 20 hours. After the reaction time, the mixture was cooled to room
temperature and the volume was reduced. Afterwards, a saturated
4JH,H= 1.44 Hz), 8.03 (ddd, 2H, H11, H21, 3JH,H= 8.06, 7.84 Hz, 4JH,H= 1.51
Hz), 8.25 (t, 1H, H16, 3JH,H= 8.14 Hz), 8.33 (ddd, 1H, H3, 3JH,H= 8.37, 7.66
aqueous solution of NH
formed, which was separated by filtration, washed with diethyl ether and
dried in vacuum. This solid was purified by column chromatography (AlO
eluent CH Cl :CH OH, 99:1 mixture), obtaining the pure Ru5b complex.
Yield: 128 mg (57%).
4
PF
6
was added and a brown precipitate was
Hz, 4 H,H= 1.47 Hz), 8.47 (ddd, 1H, H4, 3 H,H= 8.37 Hz, 4
J J JH,H= 1.44 Hz,
5JH,H= 0.89 Hz), 8.58 (ddd, 2H, H12, H20, 3JH,H= 8.06 Hz, 4JH,H= 1.31 Hz,
5JH,H= 0.76 Hz), 8.70 (d, 2H, H15, H17, 3JH,H= 8.14 Hz), 9.48 (ddd, 1H, H1,
2
,
J
3JH,H= 6.65 Hz, 4 H,H= 1.47 Hz, 5JH,H= 0.89 Hz) ppm. IR (ν max, cm-1):
2
2
3
3618, 3551, 1992, 1602, 1449, 820, 756. E1/2(III/II) (phosphate buffer
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201801206
FULL PAPER
pH=7): 0.26 V vs. SCE. E1/2(IV/II) (phosphate buffer pH=7): buffer pH= 7):
Acknowledgements
1.1 V (Ru(V/IV)) 0.62 V (Ru(IV/III)) and 0.25 V Ru(III/II)) vs SCE. UV-vis
(
(
[
phosphate buffer pH=7): [λmax, nm (ε, M-1 cm-1)]: 230 (18800), 270
This research has been financed by the Spanish Ministerio de Economía
y Competitividad (CTQ2015-66143-P), Generalitat de Catalunya (2017-
SGR-1720) and Universitat de Girona (MPCUdG2016/048).
16180), 315 (15060), 381 (3410), 460 (3654).
IICl(trpy)
Ru (µ-Cl)(µ-pypz)](PF ) Ru7. Complex Ru7 was obtained as
2 2 6
a minor product in the column chromatography carried out after the
synthesis of complexes Ru5a and Ru5b by following route B, as a deep
Keywords: ruthenium • photocatalysis• pyrazole ligands• oxidation •
purple fraction (12 mg, 5 % yield).
aqua-complex
1
): δ 6.65 (td, 1H, H17, 3JH,H= 5.8
H,H= 5.68 Hz, 4
H,H= 1.4 Hz,
H,H=7.6, 5.48 Hz, 4
H,H= 1.32
For Ru7: H-NMR (400 MHz, acetone-d
6
Hz, 4
J
H,H= 1.48 Hz), 7.04 (ddd, 1H, H16, 3
5JH,H= 0.76 Hz), 7.54 (ddd, 2H, H2, H14, 3
J
J
J
J
References
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H37, 3JH,H= 7.52, 5.04 Hz, 4JH,H= 1.4 Hz), 7.66 (t, 1H, H8, 3JH,H= 8.08 Hz),
[1]
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.68 (d, 1H, H22, 3JH,H= 2.32 Hz), 7.78 (td, 2H, H26, H36, 3JH,H= 7.68 Hz,
4JH,H= 1.56 Hz), 7.84 (td, 2H, H3, H13, 3JH,H= 7.76 Hz, 4JH,H= 1.56 Hz), 7.99
7
(
t, 1H, H31, 3
J
H,H= 8.08 Hz), 8.02 (ddd, 1H, H19, 3
J
H,H= 8.12 Hz, 4
H,H= 5.44 Hz, 4
J
J
H,H
=
=
=
1760; d) E. Manrique; X. Fontrodona, A. Poater, M. Sola, M.
1
1
1
2
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J
H,H
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.48 Hz, 5JH,H= 0.72 Hz), 8.26 (ddd, 2H, H27, H35, 3JH,H= 8.04 Hz, 4JH,H
.32 Hz, 5JH,H= 0.76 Hz), 8.28 (d, 2H, H7, H9, 3JH,H= 8.04 Hz), 8.36 (ddd,
H, H4, H12, 3JH,H= 8.08 Hz, 4JH,H= 1.20 Hz, 5JH,H= 0.80 Hz), 8.51 (d, 2H,
[2]
73–87.
H30, H32, 3JH,H= 8.08 Hz), 8.80 (ddd, 2H, H24, H38, 3JH,H= 5.4 Hz, 4JH,H
.48 Hz, 5JH,H= 0.68 Hz), 9.16 (d, 1H, H23, 3JH,H= 2.28 Hz) ppm. 13C-NMR
400 MHz, acetone-d ): δ 105.6 (C22), 120.5 (C19), 121.5 (C7, C9), 122.1
C17), 122.9 (C27, C30, C32, C35), 123.9 (C4, C12), 127.3 (C25, C37),
=
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(
(
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Cl(trpy)
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A glass vessel containing a pH 7.2 phosphate buffer aqueous solution
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2
2
2
[8]
II
)]+2 as catalyst (0.5 mM),
(
2.5ml) together with trans-[Ru (trpy)(pypz-H)(OH
]2+ (5 mM) as photosensitizer, substrate (50 mM) and Na
Ru(bpy)
100 mM) as sacrificial acceptor was stirred under N and exposed to
2
[
3
2 2 8
S O
(
2
continuous irradiation with a xenon lamp (150, Hamamtsu L8253),
equipped with a 400-700 nm large band filter, for 15 hours. The resulting
2 2
solution was extracted with CH Cl for three times. The solvent was
2
3, 4096-4107.
evaporated under reduced pressure. To check the reproducibility of the
reactions all of the experiments were carried out three times. The reaction
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1
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2 2
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European Journal of Inorganic Chemistry
10.1002/ejic.201801206
FULL PAPER
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European Journal of Inorganic Chemistry
10.1002/ejic.201801206
FULL PAPER
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FULL PAPER
We report a new aqua complex, trans-
Oxidation Catalysis*
II
[
Ru (trpy)(pypz-H)(H
2
O)](PF
)
6 2
that
has been proved as catalyst in the
photo oxidation of alcohols in water
and in the chemical oxidation of
Ester Manrique, Xavier Fontrodona,
Montserrat Rodríguez* and Isabel
Romero*
alkenes,
displaying
a
good
performance with high selectivity
values in both catalytic processes.
Page No. – Page No.
Title
*one or two words that highlight the emphasis of the paper or the field of the study
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