TiO2 modified with a Ru(ii)-N′NN′ 8-hydroxyquinolyl complex for efficient gaseous photoreduction of CO2

Article abstract of DOI:10.1039/c8cy00158h

A new rigid neutral Ru(ii) pincer complex [Ru(N′NN′)(ONO)] was synthesized from cationic [Ru(N′NN′)(MeCN)₂Cl]Cl (N′NN′, 2,6-bis(N-benzyl-benzimidazol-2-yl)pyridine) and 4,8-dihydroxyquiniline-2-carboxylic acid (ONO). The X-ray diffraction analysis indicates that the Ru(ii) center adopts a slightly distorted octahedral geometry, in which the two benzyl moieties of the N′NN′ ligand are located on the same side of the coordination plane, defined by three N atoms of N′NN′ and the Ru(ii) center, and the dihedral angles of the benzyl group and the Ru(ii)-N′NN′ plane are 89.1° and 74.9°, respectively. Upon loading onto TiO₂ nanoparticles (P25), this Ru(ii) complex exhibits an efficient CO₂ photoreduction ability with CO/CH₄ production activities of 26.6/17.2 μmol g^-1 h^-1 in a gaseous photocatalytic system containing CO₂ and H₂O vapor, which is much better than that of the pristine TiO₂ nanoparticles. This result gives a good example of TiO₂ nanoparticles loaded with the Ru(ii) pincer complex acting as a heterogeneous photocatalytic CO₂ reduction system, which could facilitate the development of a more feasible artificial photosynthesis system.

Full text of DOI:10.1039/c8cy00158h

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ISSN 2044-4753
PAPER
Qingzhu Zhang et al.
Catalytic mechanism of C–F bond cleavage: insights from QM/MM
analysis of fluoroacetate dehalogenase
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DOI: 10.1039/C8CY00158H
Journal Name
ARTICLE
TiO Modified with A Ru(II)–NNN 8-Hydroxyquinolyl Complex for
2
Efficient Gaseous Photoreduction of CO2
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
b
a
a,
a,
Wenjing Xiang, Lin Li, Zengjin Dai, Xianggao Meng, Renjie Li, Jing Zhang * and Tianyou Peng *
DOI: 10.1039/x0xx00000x
New Rigid neutral Ru(II) pincer complex [Ru(NNN)(ONO)] was synthesized from cationic [Ru(NNN)(MeCN)
2
Cl]Cl (NNN,
2
,6-bis(N-benzyl-benzimidazol-2-yl)pyridine) and 4,8-dihydroxyquiniline-2-carboxylic acid (ONO). The X-ray diffraction
www.rsc.org/
analysis indicates that the Ru(II) center adopts a slightly distorted octahedral geometry, in which the two benzyl moieties
of N’NN’ ligand are located in the same side of the coordination plane defined by three N atoms of N’NN’ and the Ru(II)
center, and the dihedral angels of the benzyl group and the Ru(II)–N’NN’ plane are 89.1° and 74.9°, respectively. Upon
loading onto TiO
production activities of 26.6/17.2 μmol g-1 h-1 in a gaseous photocatalytic system containing CO
much better than that of the pristine TiO nanoparticles. This result gives an good example of loading Ru(II) pincer complex
onto TiO nanoparticles acting as a heterogeneous photocatalytic CO reduction system, which would facilitate the
development of more feasible artificial photosynthesis system.
Keywords: Gaseous CO photoreduction; rigid Ru(II) pincer complex; TiO
2
nanoparticles (P25), this Ru(II) complex exhibits efficient CO
2
photoreduction ability with CO/CH
4
2
and H O vapor, which is
2
2
2
2
2
2
; CO/CH production
4
system for photocatalytic CO
developed.
2
reduction have been gradually
However, the search for cheaper
heterogeneous photocatalysts with sufficient activity and high
16 19
–
Introduction
Carbon dioxide (CO ) as fertile C1 source and generally
2
1,2
stability remains challenge in chemistry. Until now, the best
catalyst performed only with turnover numbers (TONs) of
produced by the combustion of fossil fuels and respiration of
organism. Due to the relatively inert nature of CO molecule,
reduction of CO to form useful chemicals or new energy
source is a challenging task, which normally requires
appropriate catalysts and energy input. In this context,
2
20
1000 and apparent quantum yields (AQYs) of
5%.
2
Ru(II) pincer complexes bearing pyridyl-based N

NN ligands
or quinolinyl-based ONO ligands have the rigid framework,
high thermal and light stability, and versatile but easily
modified structure with adjustable UV-vis absorption band,
which might be good candidates as photosensitizers or
photoreduction of CO
CO/CH or methanol, may provide a promising procedure to
solve the problem of the shortage about fossil fuels and global
2
to high energy products, such as
4
photocatalysts for CO
photosynthesis process. Herein, we report a rare example of
Ru(II) pincer complex bearing both N NN and ONO ligands
each, which displays efficient photocatalytic CO reduction
ability to produce CO/CH after combining with TiO
2
reduction through an artificial
1
,2
warming. Since the first CO
2
photoreduction catalyst was
3
reported by Lehn and co-workers, various types of transition
metal complexes based on Rh, Ni, Ru


4
5,6
7-11
12-14
and Co
were
2
reported as catalysts, which combining with a suitable
4
2
2
photosensitizer displayed high efficiency for CO reduction in
nanoparticles (P25) in a gas/solid system.
homogeneous system.
From the view of large-scale application and efficient solar
energy utilization, semiconductor-based heterogeneous
photocatalysts have more advantages than homogeneous
catalysts with their superior oxidation/reduction ability and
Results and discussion
Synthesis and characterization of Ru(II) pincer complex
1
5
potential recyclability. In the past decade, heterogeneous
Ligand 4,8-dihydroxyquinoline-2-carboxylic acid (ONO) was
prepared according to the literature with slightly
21,22
modification.
prepared from [RuCl
benzimidazol-2-yl)pyridine (N
Complex [RuCl(N
(p-cymene)]
NN ) through the procedure

NN
3 2
)(CH CN) ]·Cl was
a.College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072,
2
2
with 2,6-bis(N-benzyl-
P. R. China.


3
b.
Key Laboratory of Pesticide and Chemical Biology, Ministry of Education; School of
2
reported
[RuCl(N NN
by
)(CH
our
group.
Upon
refluxing
of
Chemistry, Central China Normal University, Wuhan 430079, P. R. China.
*
Corresponding authors. E-mail: jzhang03@whu.edu.cn (J. Zhang);


3
CN) ]·Cl and one equivalent of ligand ONO
2
typeng@whu.edu.cn (T. Peng)
Electronic Supplementary Information (ESI) available: [FTIR spectrum, MALDI-TOF
mass spectrum, cyclic voltammogram, and CIF file for Ru(II) pincer complex (CCDC
with two equivalents of LiOH in methanol, the neutral complex
Ru(N NN )(ONO)] was obtained in good yield (Scheme 1). The
[
1


1
536357)]. See DOI: 10.1039/x0xx00000x
H NMR spectrum of Ru(II) pincer complex shows one singlet
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signal with the integration of four protons at 6.10 ppm, which
Journal Name
Volume
4528(6) Å3
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3
DOI: 10.1039/C8CY00158H
can be assigned to the two CH
lack of any signal between 1.7
2
groups of N

NN

ligand. The
4.0 ppm in HNMR of Ru(II)
Z, Density (calculated)
Absorption coefficient
F(000)
Crystal size
Theta range for data
collection
4, 1.166 Mg/m
-
1
1
0.389 mm
1620

pincer complex clearly indicates the two acetonitrile ligands in
RuCl(N NN )(CH CN) ]·Cl were extracted by ONO pincer ligand.
The IR spectrum (Fig. S1 ) of Ru(II) pincer complex also
0.10 x 0.06 x 0.05 mm3
[


3
2
†
1.70 to 22.58°
-
1
displays a strong absorption at 1650 cm , indicating the
existence of coordinated carboxylate moiety of ONO ligand.
Moreover, the Ru(II) pincer complex was also characterized by
Index ranges
-13<=h<=12, 0<=k<=16,
0
<=l<=26
Reflections collected
Independent reflections
Completeness to theta
Absorption correction
Max. and min.
transmission
Refinement method
Data/restraints/parameter 5911/287/533
Goodness-of-fit on F
5911
MALDI TOF-MS (Fig. S2
†
), elemental analysis, UV-vis and
5911 [R(int) = 0.0000]
22.58 98.8 %
None
fluorescence spectra as described below.
+
Cl-
R
R
R
R
OH
0.9808 and 0.9622
Cl
N
N
N
N
N
N
N
Ru
2 equiv. LiOH
N
+
N
O
N
O
Full-matrix least-squares on F2
Ru
MeOH, reflux 6 h
CO2H
N
N
OH
N
O
2
0.832
R=benzyl; Yield 78.6%
OH
Final R indices [I>2sigma(I)] R1 = 0.0744, wR2 = 0.1868
Scheme 1 Synthesis procedure of Ru(II) pincer complex.
R indices (all data)
Largest diff. peak and hole
R1 = 0.1226, wR2 = 0.2145
-3
0.928 and -1.045 eÅ
For further investigation of the structure of the Ru(II) pincer
complex, single crystals suitable for X-ray diffraction analysis
were obtained by slow diffusion of diethyl ether into the
concentrated solution of the Ru(II) pincer complex in N-
methyl-2-pyrrolidinone (NMP). The crystal structure of the
Ru(II) pincer complex crystallizes in a monoclinic space group
P21/n (Table 1). The selected bond distances and angles are
listed in Fig. 1. Although there exists the disorder of ONO
ligand around the Ru(II)-NNN plane, the structure of the Ru(II)
pincer complex still clearly displays the metal centre adopting
a slightly distorted octahedral geometry which is configured by
three N atoms of NNN ligand and two O atoms and one N
atom of the ONO ligand (Fig. 1). The ONO ligand is
perpendicular to the coordination plane defined by Ru(II)-
NNN (the dihedral angel is 89.53°). Due to the stronger
coordination ability of the pyridine N atom than that of
benzimidazole N atom to Ru centre, the bond distance of Ru-
N(1) (pyridyl, 2.004(6) Å) is shorter than that of Ru-N(2) are omitted for clarity. Selected bond lengths (Å) and angles (
Fig. 1 The structure of the Ru(II) pincer complex with thermal
ellipsoids are drawn at the 30% probability level. All H-atoms
°
):
(
imidazole, 2.037(8) Å) and Ru-N(4) (imidazole, 2.063(8) Å), Ru(1)-N(1), 2.004(6); Ru(1)-N(2), 2.037(8), Ru(1)-N(4), 2.063(8);
24
which is consistent to the literature. The bond distances of Ru(1)-N(6), 1.900(9); Ru(1)-O(1), 2.072(13), Ru(1)-O(3),
2
.099(11). N(6)-Ru(1)-N(1), 172.4(4); N(2)-Ru(1)-N(4), 155.8(3);
Ru(II)-Npy and Ru(II)-Nbimz in the Ru(II) pincer complex match
well with the reported analogous Ru(II) complexes.25-31 It is
N(1)-Ru(1)-N(2), 78.7(3); N(1)-Ru(1)-N(4).
noted that the two benzyl groups of N
in the same side of the Ru(II)-N NN plane with the dihedral
angels between the benzyl and the N NN framework at 89.01
and 74.87 , respectively.
NN ligand are located
Spectroscopic/electrochemical analyses of Ru(II) complex




°
The UV-vis absorption spectra of the Ru(II) pincer complex in
DMF solution are shown in Fig. 2. There are fairly strong and
relatively broad absorption peaks with a maximum at 535 nm
°
4
-1
-1
Table 1 Crystallographic data and structure refinement (ε = 1.44 × 10 L mol cm ), which can be assigned to the
parameters for the Ru(II) pincer complex
1
metal-to-ligand charge-transfer (MLCT) transition to a MLCT
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
C
43
H
29
N
6
O
4
Ru
state. The other high energy transitions in the region 300390
794.79
100(2) K
0.71073 Å
Monoclinic
P2(1)/c
nm are normally attributed to the overlapped π–π* intraligand
transitions (ILCT) of the ligands. It is noted that this Ru(II)
pincer complex displays a low-energy shoulder in the range of
6
00

800 nm in their absorption spectra, which also arise from
32
MLCT transitions.
Unit cell dimensions
a = 12.139(9) Å = 90°; b=
1
2
5.53 (1) Å
4.30 (2) Å


= 98.77 (1)°; c =
= 90°
2
| J. Name., 2012, 00, 1-3
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1
0
0
0
0
.2
.9
.6
.3
.0
Photoreduction CO
loaded TiO
2
activity of the Ru(II) pincer complex-
nanoparticles
View Article Online
DOI: 10.1039/C8CY00158H
2
The Ru(II) pincer complex (denoted as Ru(N
loaded on TiO nanoparticles (P25, Degussa) through an
impregnation method. Typically, TiO nanoparticles (30 mg)
NN)(ONO)) was
2
2
was mixed with a due amount of Ru(II) complex in DMF
solution (20 mL) under stirring for 12 h, and then centrifugally
separated and dried in vacuum at 60°C overnight to obtain the
complex-loaded
Ru(N NN )(ONO)-TiO
showed that both photocatalyst and irradiation are necessary
for the CO photoreduction system. Gaseous CO were
Fig. 2 UV-vis absorption spectra of the Ru(II) pincer complex in reduced to CO/CH mixture using H O vapor as the hydrogen
source, and no other products such as CH OH, HCHO or
products,
which
is
denoted
as


2
.
The primary experimental results
300
400
500
600
700
800
900
Wavelength / nm
2
2
4
2
DMF solution.
3
HCOOH was observed in the gas or liquid phase detected by
using GC-FID method. The control experiment displayed
neither CO nor other carbon containing organic matters can be
The photoluminescence (PL) spectra of Ru(II) pincer complex
in DMF solution at room temperature are displayed in Fig. 3.
Upon excitation at their MLCT band, the Ru(II) pincer complex
exhibits one broad luminescent band with a maximum
emission at 590 nm. According to the previous reports,33,34 the
optical energy gap (E0–0) can be estimated by the intersection
point (λintersect.) of the normalized absorption and emission
spectra through the formula E0-0 = 1240/λintersect.. As shown in
Fig. 3, the intersection points for the Ru(II) pincer complex are
16
detected using N
2 2 4
instead of CO , demonstrating CO/CH
generation stemmed from the CO
2
photoreduction process.
3
3
2
5
0
5
250
CO
CH4
TCEN
200
150
100
5
78 nm, implying its E0–0 value can be calculated to be 2.15 eV.
20
The electrochemical characteristics of the Ru(II) pincer
15
complex were examined by cyclic voltammetry (CV) in DMF
solution. As shown in Fig. S3†, the first half-wave redox
potential values (vs. SCE) were summarized in Table 2. The
Ru(II) pincer complex exhibits a quasireversible oxidation at
10
5
50
0
E
1/2 = 0.77 V and a reduction at E1/2 = -0.75 V. According to
0
P25 0.05% 0.13% 0.25% 0.50% 1.00% 2.00%
Ru(N'NN')(ONO)-loading amount on TiO2
35,36
Leeuw’s experience formula,
the HOMO level of the Ru(II)
pincer complex could be estimated to be 0.98 V vs. NHE (the
same as below), while the LUMO level of can be estimated to
Fig. 4 Effect of the Ru(N

NN

)(ONO)-loading amount on the
NN )(ONO)-TiO
CO/CH production activities of Ru(N
4


2
.
be -1.16 V according to the formula ELUMO = EHOMO + E0–0
.
1
1
0
0
0
0
.5
.2
.9
.6
.3
.0
In the present gaseous photocatalytic CO2 reduction
system,16 the Ru(N
NN )(ONO)-loading amount has an obvious
effect on the CO/CH production activities of the
Ru(N NN )(ONO)-TiO under full spectrum irradiation of Xe-
lamp as shown in Fig. 4. As can be seen, the pristine TiO
shows very low CO/CH
production rates of 1.82/0.82 μmol g-1
h with an overall activity (TECN, total electron consumption
UV-vis spectrum
PL spectrum


4
5
78 nm


2
2
4
-1
2
,16
-1 -1
number for CO/CH
), whereas those Ru(N
different Ru(II) pincer complex-loading amount achieve much
higher CO/CH production activities. Among which, 0.25wt%
Ru(N NN )(ONO)-TiO gives a maximum CO/CH production
activities of 26.6/17.2 μmol g
4
production, ) of 10.2 μmol g h (Table
3

NN )(ONO)-TiO composites with

2
4
450
500
550
Wavelength / nm
600
650


2
4
-1
-1
h
h
with an overall activity
even though significant
Fig. 3 Normalized absorption and emission spectra of the Ru(II)
pincer complex (ex = 502 nm) in DMF solution.
-1
-1
(
TECN) up to 190.8 μmol g
4
decreases in the CO/CH production activities can be observed
Table 2 Electrochemical data of the Ru(II) pincer complex
with further enhancing the Ru(II) complex-loading amount
(Table S1). It indicates that loading the Ru(II) pincer complex
HOMOa /
LUMOb /
E
ox / V
E
ox / V
E
0-0
Complex
Ru(II)
vs. SCE vs. SCE / eV V vs. NHE V vs. NHE
0.77 −0.75
(Red
bearing pyridyl-based N
on TiO nanoparticles can effectively catalyse the CO
reduction reaction in the present heterogeneous
photocatalytic system. Moreover, the 0.25wt% Ru(N NN )(ONO)
NN and quinolinyl-based ONO ligands
2
2
2
.14
0.98
-1.16
complex (Oxd
1
)
1
)
a
Calculated with EHOMO = −(Eox + 4.71) eV. b Calculated with ELUMO = (EHOMO
0–0) eV.
+


E
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TiO shows gradually increasing trends of the CO/CH
4
Journal Name
two benzyl moieties of N’NN’ ligand lie in the samVeiewsiAdreticleofOntlhinee
-
2
production amounts with prolonging the irradiation time (Fig. coordination plane defined by three N atomDsOoIf: 1N0’.N10N3’9a/Cn8dCtYh0e01R5u8(HII)
S4†), indicating the Ru(II) pincer complex has a relatively good centre with the dihedral angels of the benzyl group and the Ru(II)–
stability during the 3 h light irradiation of Xe-lamp.
N’NN’ plane being 89.1° and 74.9°, respectively. The resultant Ru(II)
For understanding the charge transfer behaviours in the pincer complex displays high efficiency for gaseous CO2
present photocatalytic system, the photoluminescence (PL)
spectra were carried out with both pristine TiO and its
complex-loaded product. As shown in Fig. 5, the single TiO
film exhibits obvious PL peaks with maximum at 475 nm upon
excited by 330 nm wavelength, while those peaks of
photoreduction to produce CO/CH
nanoparticles in a gaseous photocatalytic system containing CO
and H
efficient artificial photosynthesis based on Ru(II) pincer complex-
loaded semiconductor.
4
upon loaded to TiO
2
2
2
2
2
O vapour. It demonstrates the feasibility of developing more
Ru(N
same condition. It could be ascribed to the good charge
transfer channel between the Ru(II) pincer complex and TiO
nanoparticles which made electron transfer from TiO to Ru(II)
2 2
NN)(ONO)-TiO are much weaker than that of TiO in the
Experimental section
General information
2
2
complex easily, and then the fluorescence quenching of All manipulations were carried out under purified Ar
Ru(N NN )(ONO)-TiO . The above calculated HOMO energy atmosphere using standard Schlenk techniques. Ligand 4,8-
level (0.98 V, Table 2) for the Ru(II) pincer complex is more dihydroxyquinoline-2-carboxylic acid (ONO) was prepared


2
3
7
21,22
positive than the TiO
benefit to the excited electrons of TiO
HOMO of Ru(N NN )(ONO), and then to its LUMO excited by cymene)]
) according to the procedure reported elsewhere.23 All
visible light for the CO reduction since the LUMO energy level (N
NN
2
’s conduction band (CB, -0.50 V ). It is a according to the literature with slightly modification.
transferring to the Complex [RuCl(N
NN )(CH CN) ]Cl was prepared from [RuCl
with 2,6-bis(N-benzyl-benzimidazol-2-yl)pyridine
2


3
2
2
(p-


2
2


(
-1.16 V) is sufficient negative than the reduction potentials of solvents were distilled under an Ar atmosphere over
2
CO
reduction for the CO/CH
in Ru(N NN )(ONO)-TiO
and CO reduction catalyst unit by accepting the
photogenerated electrons of TiO
2
/CO (-0.53 V) and CO
2
/CH
4
(-0.24 V) to drive to CO
2
appropriate agents, and stored in gas-tight solvent bulbs.
)(ONO) DMSO-d
was dried with CaH and vacuum-transferred by
4
formation. Namely, Ru(N

NN

6
2


2
might serve as both light harvester appropriate methods and vacuum-distilled prior to use.
1
13
2
H and C NMR spectra were recorded at 300 MHz, 75 MHz
1
2
’s CB, which is different from Varian Gemini 300 spectrometer. The H NMR chemical shifts
the traditional dye-sensitized semiconductor reported were referenced to the residual hydrogen signals of the
1
6
13
previously, where the excited dye molecules transfer the deuterated solvents or TMS, and the C NMR chemical shifts
13
electrons to TiO
irridiation. The detail photocatalytic mechanism for CO
2
’s CB for the CO
2
reduction under visible light are referenced to the C signals of the deuterated solvents.
MALDI-TOF-MS spectra were taken on a Bruker BIFLEX III
2
reduction in the present Ru(N
underway.

NN

)(ONO)-TiO
2
is investigated ultrahigh resolution Fourier transform ion cyclotron resonance
(FT-ICR) mass spectrometer with alpha-cyano-4-hydroxy-
cinnamic acid as a matrix. UV-Vis absorption spectra were
recorded on a TU-1810 spectrophotometer with scanning from
ex = 330 nm
Ru(N'NN')(ONO)-TiO2
TiO2
2
50 to 900 nm. Fluorescence spectra were recorded on a K2
ISIS spectrometer. Fourier transform infrared (FTIR) spectrum
was recorded by using a Nicolet iS10 spectrometer (Thermo
Electron).
Preparation of 4,8-dihydroxyquinoline-2-carboxylic acid (ONO)
To a solution of o-ansidine (2.46 g, 0.02 mol) in methanol (40
mL) was added dimethyl acetylenedicarboxylate (2.84 g, 0.02
mol) dropwisely and then heated to reflux for 3 h. Upon
cooling to room temperature, the solvent was removed by
evaporation and the residue (3.37 g, 63.6%) was added to
350
400
450
500
550
600
Wavelength / nm
stirred diphenyl ether (50 mL, which were preheated to 250
℃)
2
Fig. 5 Photoluminescence (PL) spectra of the pristine TiO and
its complex-loaded product.
for ten minutes. After cooling to room temperature,
petroleum ether (150 mL) was added to the mixture and the
brown precipitate formed, which was collected and dried
under vacuum to form a brown solid of methyl 4-hydroxy-8-
Conclusions
1
methoxyquinoline-2-carboxylate. Yield: 1.93 g (65.1%);
NMR (CDCl
H), 7.08 (s, 1H), 6.97 (d, 1H), 4.04 (d, 6H).
Methyl 4-hydroxy-8-methoxyquinoline-2-carboxylate (1.17 g,
H
A new Ru(II) complex bearing both conjugated NNN and ONO
pincer ligands were synthesized and fully characterized. The crystal
structure of Ru(II) pincer complex exhibits that the Ru(II) centre
3
, 300 MHz): δ = 9.42 (s, 1H), 7.89 (d, 1H), 7.31 (d,
1
adopts a slightly distorted octahedral geometry, in which two 0.005 mol) was dissolved in 48% hydrobromic acid (30 mL) and
pincer ligands are located perpendicularly to each other. And the the solution was heated in a sealed tube at 120
C for 72h.
°
4
| J. Name., 2012, 00, 1-3
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ARTICLE
After the solution was cooled, the precipitate was collected A Bruker SMART APEX II diffractometer wiVtihew AgrtricalepOhnitliene-
and put in the deionic water (15 mL), the mixture was adjusted monochromated Mo-Kα (λ= 0.71073 ÅDO) I:w10a.s103e9m/Cp8lCoYy0e0d158tHo
to pH2.5 with 6M NaOH to give a yellow powder, which was collect the intensity data for the single crystal of
collected and dried under vacuum to give a yellow solid of Ru(N

NN

)(ONO). The data was collected at about 100 K using
1
ligand ONO. Yield: 0.87 g (85%). H NMR (DMSO-d
6
, 300 MHz): ω-scan techniques. The structure was solved by direct
38
δ = 7.55 (d, 1H), 7.32 (s, 1H), 7.14 (d, 1H), 6.90(s, 1H). Which is methods using SHELXL-97. Multi-scan empirical absorption
22
consistent to the reported literature.
corrections were applied to the data set using the program
3
9
37
SADABS. The structure was refined with SHELXL-97.
Hydrogen atoms bound to carbon were placed at calculated
positions and refined using a riding mode. All non-hydrogen
Preparation of Ru(NNN)(ONO)
2
atoms were refined by full-matrix least squares on F using the
To a yellow solution of lithium 4,8-dihydroxyquinoline-2-
carboxylate prepared in situ from 4,8-dihydroxyquinoline-2-
40
SHELXTL grogram package. Cell refinement, data collection,
and reduction were done by Bruker SAINT.41 The
crystallographic data is available in the SI as CIF file and
deposited in CCDC number 1536357.
carboxylic acid (40 mg, 0.195 mmol) and LiOH
.390 mmol) in CH OH (10 mL), complex [RuCl(N
CH CN) Cl (138.5 mg, 0.195 mmol) was added at room
·
H
2
O (16.4 mg,
0
3

NN)
(
3
2
]·
temperature under Ar atmosphere. The mixture was then
refluxed for 12 h under Ar atmosphere, in which a violet solid
was precipitated. After cooling, the solvent was removed by
Conflicts of interest
filtration and the residues were washed sequentially with There are no conflicts to declare.
methanol (10 mL) and diethyl ether (2 × 10 mL). The solid was
dried under vacuum to give
a
violet powder of
Acknowledgements
Ru(N NN )(ONO). Yield: 0.1220 g (78.6%). A single crystal


suitable for X-ray diffraction analysis was obtained by slow
This work was supported by the Natural Science Foundation of
China (21171134, 21573166), the Natural Science Fund of
Hubei Province (2011CDB441), the Funds for Creative Research
Groups of Hubei Province (2014CFA007), and the Natural
Science Foundation of Jiangsu Province (BK20151247), China.
We also thank Prof. Xiaojun Wu for NMR support and analysis.
diffusion of diethyl ether into the saturated NMP (N-methyl-2-
1
pyrrolidinone) solution of Ru(N

NN

)(ONO). H NMR (DMSO-d
6
,
3
00 MHz): δ = 8.08 (s, 2H), 7.79 (s, 1H), 7.66 (s, 2H), 7.22
–7.45
(
m, 20H), 6.10 (s, 4H) (H in OH has not been found); IR(KBr
–
-1
pellets, cm ): 3433 (s, br), 3061 (m)
MS (m/z) calcd. for C43
Elemental analysis: calcd. for C43
0.56. Found: C 65.22, H 4.00, N 10.43.
，
1650 (s, br); MALDI TOF-
+
H N
29 6
O
4
Ru [M+H] 796.81, found 796.30;
29 6 4
H N O Ru: C, 64.90, H 3.80, N
1
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DOI: 10.1039/C8CY00158H
A rare example of Ru(II) pincer complex for efficient photoreduction of CO
2 4
to CO/CH in
gaseous system is developed.