Synthesis of six 8-quinolinate-based ruthenium complexes with high catalytic activity for nitroarene reduction

Article abstract of DOI:10.1016/j.poly.2018.06.054

Six ruthenium complexes were synthesized by treating different 2-substituted 8-hydroxyquinolinate ligands with [Ru(p-cymene)(μ-Cl)Cl]₂. Their structures were fully characterized by a variety of techniques, including ¹H and ¹³C NMR spectra, elemental analyses and infrared spectrometry. Additionally, single-crystal X-ray diffraction reveals that these ruthenium complexes possess similar half-sandwich structures. The mononuclear ruthenium building units are further linked into 1D or 2D supramolecular structures through non-covalent interactions, such as π?π stacking, hydrogen-bonding and C–H? halogen interactions. The catalytic activities of the six half-sandwich ruthenium complexes towards the hydrogenation of nitroarenes were explored under mild conditions. The ruthenium complexes displayed high catalytic activities in the synthesis of aromatic anilines from nitroarenes in the presence of NaBH₄.

Full text of DOI:10.1016/j.poly.2018.06.054

Accepted Manuscript
Synthesis of six 8-quinolinate-based ruthenium complexes with high catalytic activity for nitroarene reduction
Wei-Guo Jia, Ming-Xia Cheng, Qiu-Tong Xu, Li-Li Gao, Guozan Yuan
PII:
S0277-5387(18)30385-1
https://doi.org/10.1016/j.poly.2018.06.054
POLY 13263
DOI:
Reference:
To appear in:
Polyhedron
Received Date:
Revised Date:
Accepted Date:
8 March 2018
27 June 2018
27 June 2018
Synthesis of six 8-quinolinate-based ruthenium complexes
Please cite this article as: W-G. Jia, M-X. Cheng, Q-T. Xu, L-L. Gao, G. Yuan,
with high catalytic activity for nitroarene reduction
,
Polyhedron (2018), doi: https://doi.org/10.1016/j.poly.2018.06.054
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Synthesis of six 8-quinolinate-based ruthenium complexes
with high catalytic activity for nitroarene reduction
a,
a
a
a
b,
Wei-Guo Jia *, Ming-Xia Cheng , Qiu-Tong Xu , Li-Li Gao , Guozan Yuan *
a
College of Chemistry and Materials Science, The Key Laboratory of Functional
Molecular Solids, Ministry of Education, Anhui Laboratory of Molecular-Based
Materials (State Key Laboratory Cultivation Base), Anhui Normal University, Wuhu,
2
41002, China
E-mail: wgjiasy@mail.ahnu.edu.cn (W. -G. Jia)
b
School of Chemistry and Chemical Engineering, Anhui University of Technology,
Maanshan 243002, China.
E-mail: yuanguozan@163.com (G. Yuan)

Graphic Abstract
Highlights:



Half-sandwich ruthenium complexes containing 2-substituted quinolinate ligands
with different substituent groups have been synthesized and characterized.
The catalytic activities for nitroarene reduction using the Ru(II) complexes were
controlled by the organic ligands with different functional substituents.
1D or 2D supramolecular structures are formed through ππ stacking,
hydrogen-bonding and C-H halogen interactions.

ABSTRACT: Six ruthenium complexes were synthesized by treating different
-substituted 8-hydroxyquinolinate ligands with [Ru(p-Cymene)(-Cl)Cl] . Their
2
2
1
13
structures were fully characterized by a variety of techniques, including H and C
NMR spectra, elemental analyses and infrared spectrometry. Additionally,
single-crystal X-ray diffraction reveals that these ruthenium complexes possess
similar half-sandwich structures. The mononuclear ruthenium building units are
further linked into 1D or 2D supramolecular structures through non-covalent
interactions, such as ππ stacking, hydrogen-bonding and C-H halogen interactions.
The catalytic activities of the six half-sandwich ruthenium complexes towards the
hydrogenation of nitroarenes were explored under mild conditions. The ruthenium
complexes displayed high catalytic activities in the synthesis of aromatic anilines
from nitroarenes in the presence of NaBH4.
Keywords: Half-sandwich; Ruthenium; Complex; Structure; Catalyst; Nitroarene
reduction

1
. Introduction
Half-sandwich ruthenium complexes have been widely used as organic
transformation catalysts, exhibiting high catalytic activities and abundant
reactivities, particularly in the construction of carbon-carbon bonds through C-H
bond activation, during the past decades [1-3]. Therefore, remarkable efforts
have been devoted to the synthesis of functional half-sandwich ruthenium
complexes with various nitrogen [4], oxygen [5,6], sulfur [7-10], selenium
[
11-13], phosphorous [14-16] or N-heterocyclic carbene (NHC) [17-20] donors
and their application in organic syntheses [21-23]. 8-Hydroxyquinoline and its
derivatives are versatile coordination ligands due to the flexible coordination
modes of the nitrogen and oxygen atoms towards a wide range of transition metal
ions, resulting in some complexes with promising structures and photophysical
properties [24-45].
Aromatic anilines and their derivatives are useful precursors for the preparation of
many drugs and agrochemicals [46,47]. As a result, tremendous efforts have been
made toward the synthesis of this molecular scaffold. An efficient strategy for the
synthesis of aromatic anilines is the reduction of nitroarenes [48-51] and
half-sandwich ruthenium complexes showed high catalytic activities towards
nitroarene reduction in the presence of a reducting agent [7,12,52,53]. We have
developed a class of half-sandwich ruthenium complexes as active catalysts for the
hydrogenation of nitroarene to aromatic aniline in the presence of sodium
tetrahydroborate (NaBH ) as a reducing agent [6,54-56]. In continuation of our
4
interest in half-sandwich ruthenium complexes for their rich chemistry, we have tried

to prepare ruthenium complexes with 8-hydroxyquinoline derivatives ligands and
hope to exploit their catalytic applications in the hydrogenation of nitroarenes.
Herein, we have synthesized the half-sandwich ruthenium complexes 2a-2f with the
8
-hydroxyquinoline derivatives 1a-1f (Scheme 1) and have explored their catalytic
activities for the reduction of nitroarenes to aromatic anilines in the presence of
NaBH . The results indicate that the half-sandwich ruthenium complexes show
4
promising catalytic activities for nitroarene reduction, with high yields in ethanol.
Moreover, the molecular structures of 2a, 2b and 2f have been determined by X-ray
crystallography. Our results provide valuable insight into the non-covalent interactions,
such as ππ stacking, C-HCl, C-HF and C-HO intermolecular hydrogen
bonding, in half-sandwich ruthenium complexes. Novel 1D and 2D supramolecular
frameworks have been obtained through these non-covalent intermolecular
interactions.
2
. Experimental
2.1. Materials and physical measurements
All the operations were carried out under a pure nitrogen atmosphere using
standard Schlenk techniques. All solvents were purified and degassed by
standard procedures. The 8-hydroxyquinoline derivatives were synthesized
1
13
according to procedures described in previous literature [25,57-59]. H and C
NMR were recorded on a 300 MHz or 500 MHz NMR spectrometer at room
temperature. Chemical shifts (δ) are given in ppm relative to internal TMS and
1
13
are internally referenced to residual H and C solvent resonances. IR spectra

were recorded on a Niclolet AVATAR-360IR spectrometer. Elemental analyses
were performed on a PerkinElmer 2400 CHN analyzer.
2
.2 .Synthesis of the half-sandwich ruthenium complexes 2a-2f
A solution of [Ru(p-cymene)( -Cl)Cl] (153.0 mg, 0.25 mmol), the
-hydroxyquinoline derivatives (0.60 mmol) and K CO (96.5 mg, 0.60 mmol)
.

2
8
2
3
in MeOH (12 mL) was purged with N and then stirred at 85 ºC for 3 h. The
2
reaction mixture was separated from any unsoluble salts by filtration and dried in
vacuo. The crude material was subjected to silica gel chromatography with ethyl
acetate and petroleum ether (2:1) to give the dark red half-sandwich ruthenium
complexes.
2
.2.1. Half-sandwich ruthenium complex 2a.
1
Yield: (122.0 mg, 57%). H NMR (300 MHz, CDCl , ppm) δ: 7.89 (d, 1H),
3
7
2
0
1
8
.21 (m, 2H), 6.95 (d, J = 9Hz, 1H), 6.71 (d, J = 6Hz, 1H), 5.67 (d, 1H), 5.50 (t,
H), 5.26 (t, 1H), 3.15 (s, 3H), 2.62 (m, 1H), 2.29 (s, 3H), 1.08 (d, J = 6 Hz, 3H),
1
3
.95 (d, J = 6 Hz, 3H). C NMR (125 MHz, CDCl , ppm) δ: 168.42, 158.40,
3
44.48, 138.05, 129.24, 128.75, 123.55, 115.69, 110.89, 101.54, 100.70, 86.71,
1.28, 80.07, 79.78, 30.99, 28.92, 22.75, 22.40, 19.32. Anal. Calcd. for
C H ClNORu: C 55.94, H 5.17, N 3.26 Found: C 55.90, H 5.23, N 3.30%. IR
2
0
22
-
1
(
(
(
(
KBr, cm ): 3044 (vw), 2961 (vw), 2919 (vw), 2871 (vw), 1733 (vw), 1716
vw), 1700 (vw), 1683 (vw), 1652 (vw), 1646 (vw), 1635 (vw), 1602 (vw), 1560
vs), 1506 (s), 1464 (s), 1429 (s), 1374 (w), 1333 (w), 1287 (vw), 1110 (vw), 832
vw), 753 (vw), 624 (vw), 519 (vw).
2
.2.2. Half-sandwich ruthenium complex 2b.

1
Yield: (207.9 mg, 76%). H NMR (500 MHz, CDCl , ppm) δ: 7.95 (m, 2H),
3
7.62 (m, 3H), 7.26 (m, 2H), 6.99 (m, 3H), 6.73 (d, J = 5 Hz, 1H), 5.59 (d, J = 5
Hz, 1H), 5.49 (d, J = 10 Hz, 1H), 5.37 (d, J = 5 Hz, 1H), 5.11 (d, J = 5 Hz, 1H),
.87 (s, 3H), 2.54 (m, 1H), 2.30 (s, 3H), 0.99(d, J = 6.5 Hz, 3H), 0.90 (d, J = 6.5
3
1
3
Hz, 3H). C NMR (125 MHz, CDCl , ppm) δ: 168.81, 160.91, 156.65, 144.65,
3
1
1
1
6
37.71, 134.04, 129.81, 129.29, 129.20, 129.03, 128.84, 120.21, 116.01, 115.05,
10.94, 101.72, 100.49, 85.84, 81.38, 81.31, 80.71, 55.87, 31.21, 22.59, 22.41,
9.34. Anal. Calcd. for C H ClNO Ru: C 61.42, H 5.16, N 2.56 Found: C
2
8
28
2
-1
1.46, H 5.12, N 2.59%. IR (KBr, cm ): 3048 (vw), 2961 (w), 2930 (vw), 2870
(
vw), 2830 (vw), 1733 (vw), 1720 (vw), 1701 (vw), 1687 (vw), 1654 (vw), 1629
vw), 1604 (m), 1548 (s), 1513 (s), 1463 (m), 1440 (vs), 1374 (m), 1338 (w),
(
1318 (w), 1301 (m), 1259 (s), 1199 (vw), 1174 (s), 1104 (m), 1056 (w), 1025
(m), 965 (w), 871 (vw), 826 (m), 801 (w), 741 (w), 626 (vw), 516 (vw).
2
.2.3. Half-sandwich ruthenium complex 2c.
1
Yield: (219.2 mg, 78%) H NMR (500 MHz, CDCl , ppm) δ: 8.25 (m, 3H),
3
7.96 (d, J = 10 Hz, 1H), 7.75 (d, J = 5 Hz, 2H), 7.65 (d, J = 10 Hz, 1H), 7.37 (d, J
=
15 Hz, 1H), 7.26 (d, J = 15 Hz, 1H), 6.99 (d, J = 5 Hz, 1H), 6.72 (d, J = 5 Hz,
H), 5.59 (d, J = 5 Hz, 1H), 5.49 (d, J = 5 Hz, 1H), 5.30 (d, J = 5 Hz, 1H), 5.05 (d,
J = 5 Hz, 1H), 2.50 (m, 1H), 2.28 (s, 3H), 0.98(d, J = 5 Hz, 3H), 0.90 (d, J = 5 Hz,
1
1
3
3
1
1
H). C NMR (125 MHz, CDCl , ppm) δ: 169.08, 154.95, 148.01, 144.87,
3
42.47, 138.05, 135.13, 131.48, 130.65, 129.14, 128.17, 124.88, 120.15, 116.35,
11.05, 102.12, 100.61, 85.96, 81.39, 81.12, 80.91, 31.24, 22.53, 22.41, 19.33.
Anal. Calcd. for C H ClN O Ru: C 57.65, H 4.48, N 4.98 Found: C 57.63, H
2
7
25
2
3

-1
4
.52, N 4.96%. IR (KBr, cm ): 2961 (w), 2921 (w), 1733 (w), 1718 (w), 1700
w), 1683 (w), 1670 (w), 1652 (w), 1646 (w), 1635 (m), 1628 (m), 1624 (m),
615 (w), 1593 (w), 1558 (vw), 1549 (m), 1521 (m), 1514 (m), 1508 (w), 1490
w), 1473 (w), 1466 (w), 1455 (m), 1436 (m), 1418 (w), 1412 (m), 1394 (w),
383 (w), 1372 (m), 1339 (vs), 1298 (w), 1287 (w), 1267 (w), 1171 (vw), 1108
s), 1055 (w), 1035 (vw), 869 (w), 843 (w), 803 (vw), 762 (w), 746 (m), 696 (w),
(
1
(
1
(
670 (w), 620 (vw), 519 (w), 515 (w), 504 (w).
2
.2.4. Half-sandwich ruthenium complex 2d.
1
Yield: (260.2 mg, 96%) H NMR (500 MHz, CDCl , ppm) δ: 8.18 (d, J = 16
3
Hz, 1H), 8.03 (d, J = 8.5 Hz, 1H), 7.93 (d, J = 8Hz, 1H), 7.88 (s, 1H), 7.68 (t, 2H),
.61 (t, 1H), 7.33 (m, 2H), 7.01. (d, J = 7.5 Hz, 1H), 6.78 (d, J = 8 Hz, 1H), 5.59
d, J = 5.5 Hz, 1H), 5.49 (d, J = 6 Hz, 1H), 5.32 (d, J = 5.5 Hz, 1H), 5.06 (d, J = 6
Hz, 1H), 2.55 (m, 1H), 2.30 (s, 3H), 1.02 (d, J = 7 Hz, 3H), 0.92 (d, J = 7 Hz, 3H).
7
(
1
3
C NMR (125 MHz, CDCl , ppm) δ: 168.86, 155.21, 144.76, 138.10, 137.51,
3
1
1
2
33.55, 132.60, 131.59, 131.40, 131.12, 130.52, 130.49, 129.12, 120.18, 118.74,
16.28, 113.90, 111.15, 102.17, 100.46, 85.84, 81.52, 81.04, 80.90, 31.24, 22.56,
2.41, 19.28. Anal. Calcd. for C H ClN ORu: C 61.98, H 4.65, N 5.17 Found:
2
8
25
2
-1
C 62.04, H 4.70, N 5.23%. IR (KBr, cm ): 3048 (vw), 2963 (w), 2919 (w), 1735
w), 1718 (w), 1700 (w), 1685 (w), 1676 (w), 1670 (w), 1661 (m), 1652 (m),
646 (m), 1635 (m), 1628 (m), 1624 (m), 1617 (m), 1595 (w), 1578 (w), 1569
w), 1558 (m), 1549 (vs), 1532 (w), 1521 (w), 1508 (w), 1499 (w), 1490 (w),
473 (w), 1466 (w), 1458 (m), 1436 (w), 1418 (w), 1414 (w), 1372 (m), 1328
w), 1296 (w), 1158 (w), 1108 (m), 1055 (w), 972 (w), 873 (vw), 860 (w), 832
(
1
(
1
(

(w), 799 (w), 751 (w), 738 (w), 720 (vw), 694 (w), 674 (w), 670 (w), 661 (vw),
639 (vw), 615 (vw), 587 (vw), 510 (w).
2
.2.5. Half-sandwich ruthenium complex 2e.
1
Yield: (216.5 mg, 74%). H NMR (500 MHz, CDCl , ppm) δ: 8.18 (d, J = 17
3
Hz, 1H), 8.02 (d, J = 8.5 Hz, 1H), 7.90 (s, 1H), 7.85 (d, J = 7.5 Hz, 1H), 7.67 (m,
H), 7.35 (d, J = 17 Hz, 1H), 7.29 (t, 1H), 7.00 (d, J = 7.5 Hz, 1H), 6.77 (d, J = 7.5
Hz, 1H), 5.60 (d, J = 6 Hz, 1H), 5.49 (d, J = 6 Hz, 1H), 5.33 (d, J = 5.5 Hz, 1H),
.07 (d, J = 5.5 Hz, 1H), 2.56 (m, 1H), 2.30 (s, 3H), 1.02 (d, J = 7 Hz, 3H), 0.91
3
5
1
3
(
d, J = 7 Hz, 3H). C NMR (125 MHz, CDCl , ppm) δ: 168.97, 155.41, 144.73,
3
1
1
3
38.04, 137.02, 132.99, 132.49, 130.61, 130.34, 130.19, 129.11, 125.96, 124.35,
20.12, 116.88, 116.20, 111.02, 101.94, 100.64, 86.14, 81.48, 80.89, 80.67,
1.21, 22.62, 22.31, 19.23. Anal. Calcd. for C H ClF NORu: C 57.43, H 4.31,
28
25
3
-1
N 2.39 Found: C 57.48, H 4.36, N 2.41%. IR (KBr, cm ): 3048 (w), 2965 (w),
2
1
919 (w), 1549 (s), 1506 (m), 1455 (m), 1436 (s), 1370 (s), 1335 (vs), 1202 (m),
184 (m), 1167 (s), 1123 (s), 1097 (m), 1070 (m), 983 (m), 862 (m), 825 (m), 797
(m), 753 (m), 736 (m), 696 (m), 661 (m), 628 (w), 615 (vw), 563 (vw), 539 (m),
528 (vs), 512 (m).
2
.2.6. Half-sandwich ruthenium complex 2f.
1
Yield: (214.1 mg, 75%). H NMR (300 MHz, CDCl , ppm) δ: 8.32 (d, J = 18
3
Hz, 1H), 7.99 (d, J = 9Hz, 1H), 7.69 (d, J = 9Hz, 1H), 7.27 (m, 2H), 6.98 (d, J = 9
Hz, 1H), 6.78 (m, 3H), 5.61 (d, J = 6 Hz, 1H), 5.53 (s, 1H), 5.47 (d, J = 3 Hz, 1H),
1
3
5
.23 (d, J = 9 Hz, 1H), 2.46 (m, 1H), 2.30 (s, 3H), 0.94 (s, 3H), 0.92 (s, 3H). C
NMR (125 MHz, CDCl , ppm)δ: 169.08, 163.66, 162.79, 162.70, 162.59,
3

1
1
8
61.65, 160.77, 160.65, 160.57, 155.91, 144.72, 137.99, 136.03, 130.36, 129.21,
20.25, 119.79, 116.21, 110.96, 110.70, 101.79, 101.68, 101.57, 101.48, 101.36,
6.20, 81.80, 80.71, 79.96, 31.34, 22.67, 22.37, 19.42. Anal. Calcd. for
C H ClF NORu: C 56.74, H 4.06, N 2.45 Found: C 56.78, H 4.03, N 2.46%. IR
2
7
23
3
-1
(
KBr, cm ): 3062 (vw), 3048 (vm), 2772 (vm), 1636 (vw), 1613 (w), 1590 (m),
508 (vs), 1472 (vw), 1456 (w), 1437 (vs), 1369 (s), 1355 (m), 1336 (m), 1313
w), 1304 (w), 1204 (vw), 1174 (vw), 1122 (m), 1109 (w), 1035 (m), 998 (w),
81 (w), 893 (vw), 874 (vw), 849 (w), 819 (m), 788 (vw), 750 (w), 618 (vw), 517
vw).
.3. General procedure for the reduction of nitroarenes to anilines with the
1
(
9
(
2
half-sandwich ruthenium catalysts
The half-sandwich ruthenium complex (0.0015 mmol, 0.05 equiv.) was
dissolved in ethanol (2.0 mL), then the appropriate nitroarene (0.3 mmol, 1.0
equiv.) and NaBH (1.2 mmol, 4.0 equiv.) was added. Subsequently, the
4
resulting mixture was stirred at room temperature in a closed vial. After
completion of the reaction (monitored by TLC), the mixture was quenched with
water (2 mL) and extracted with EtOAc (3 × 2 mL). After the solvents were
removed in vacuo from the combined organic extracts, the crude products were
loaded directly onto a column of silica gel and purified by column
chromatography to yield the corresponding products.
2
.4. X-ray crystallography for 2a, 2b and 2f:
Diffraction data of 2a 2b and 2f were collected on a Bruker AXS SMART
APEX diffractometer, equipped with a CCD area detector using Mo Kα radiation
,

(λ = 0.71073 Å). All the data were collected at 298 K and the structures were
2
solved by direct methods and subsequently refined on F using full-matrix
least-squares techniques (SHELXL) [60]. SADABS [61] absorption corrections
were applied to the data, all non-hydrogen atoms were refined anisotropically
and hydrogen atoms were located in calculated positions. All calculations were
performed using the Bruker Smart program.
3
. Result and discussions
3
.1 Synthesis of the half-sandwich ruthium complexes
As outlined in Scheme 1, the 8-hydroxyquinoline derivatives ligands (1a-1f
)
were synthesized from the condensation of 8-hydroxyquinaldine with the
corresponding aromatic aldehyde in acetic anhydride according to the literature
methods [25,57-59]. Following the procedures as described previously by our
group, dark red ruthenium complexes (2a-2f) were obtained through the reaction
of [Ru(p-Cymene)(-Cl)Cl] with two equivalents of the 8-hydroxyquinoline
2
derivatives in modest to good yields [6]. All the complexes have been
characterized by IR, NMR spectroscopy as well as elemental analyses. The
ruthenium complexes 2a-2f are moderately soluble in common organic solvents,
such as MeCN and MeOH. They are stable in the solid state as well as in solution.

Cl
OH
Ru
Ru
N
R
Ru Cl
N
Reflux
MeOH
2
Cl
Cl
O
2
+
R
Cl
R = 2-substituted styrenyl group in the quinoline ring
Ligand/Pruduct
OMe
NO2 1c/2c
R: CH3 1a/2a
R:
1b/2b R:
CN
CF3
F
F
R:
R:
R:
1f/2f
1
d/2d
1e/2e
F
Scheme 1. Synthesis of the half-sandwich ruthenium complexes (2a-2f) with the
-hydroxyquinoline derivatives ligands (1a-1f)
8
3
.2 Structural description
X-ray diffraction data of single crystals for complexes 2a, 2b and 2f were
obtained. The crystals were grown by slow diffusion of diethyl ether into a
concentrated solution of the complexes in methanol solution. The
crystallographic data for the half-sandwich ruthenium complexes 2a
,
2b and 2f
are summarized in Table 1. The molecular structures of 2a
, 2b and 2f are shown
in Fig 1.
Table 1
Crystallographic data and structure refinement parameters for the ruthenium
complexes 2a, 2b and 2f

2
a
2b
2f
CCDC
1577530
C H ClNORu
1577531
1577532
Empirical formula
C H ClNO Ru
28 28
C H ClF NORu
27 23 3
2
0
22
2
Formula weight
428.90
547.03
570.98
Crystal syst., Space group
Triclinic, P-1
12.4058(6)
12.7432(6)
13.2158(7)
90.709(1)
Monoclinic, P2 /c
Monoclinic, P2 /c
1
1
a (Å)
b (Å)
c (Å)
α (°)
β (°)
γ (°)
13.7969(8)
7.4497(5)
24.9005(13)
90
17.6083(9)
7.4908(4)
19.1170(10)
90.00
95.315(1)
107.799(3)
90
111.6940(10)
90.00
117.900(1)
1834.81(16), 4
1.553
3
Volume (Å ), Z
2436.8(3), 4
1.491
2342.9(2), 4
1.619
3
D (Mg/m )
c
-
1
μ (Mo-Kα) (mm )
F(000)
1.006
0.778
0.828
872
1120
1152
θ range (°)
1.812 ~ 27.498
-16, 16; -16, 16; -17, 16
7984 / 5848 [0.0360]
7984 / 812 / 440
1.207
1.550 ~26.372
-17, 16; -9, 9; -31, 31
18829 / 4949 [0.0291]
4949 / 115 / 302
1.346
1.245 ~ 27.543
-22, 22; -9, 9; -21, 24
19448/5343 [0.0265]
5343 / 0 / 310
1.023
Limiting indices
Reflections/unique[R(int)]
Data/restraints/parameters
2
Goodness-of-fit on F
R1= 0.0760,
R1= 0.1180,
R1= 0.0276,
a
R , wR [I > 2(I)]
1
2
wR = 0.1916
wR = 0.2674
wR = 0.0633
2
2
2
R1= 0.1012,
R1= 1236,
R1= 0.0372,
R , wR (all data)
1
2
wR = 0.2019
wR = 0.2694
wR = 0.0676
2
2
2
a
2
2
2
2 2 1/2
R
1
o c o 2 o c o
= Σ||F |-|F ||/Σ|F |; wR = [Σw(|F |-|F |) /Σw|F | ] .
Table 2
Selected bond lengths (Å) and bond angles (°) for the ruthenium complexes 2a, 2b
and 2f
2
a
2b
2f
Ru1-O1
Ru1-N1
Ru1-Cl1
2.033(4)
2.140(5)
2.058(9)
2.103(10)
2.410(4)
2.0643(14)
2.1271(18)
2.4089(6)
2.4082(16)
N1-Ru1-O1
N1-Ru1-Cl1
O1-Ru1-Cl1
78.93(17)
83.51(13)
85.70(13)
79.2(5)
85.6(3)
88.1(3)
78.19(7)
85.16(5)
88.10(5)
As shown in Fig 1, the structures of the half-sandwich ruthenium complexes are

remarkably similar. In all cases, the coordination environment of the ruthenium atom
retains the classic half-sandwich geometry in which the p-cymene ligand occupies
half of the coordination sphere, assuming that the p-cymene ring serves as a
three-coordinated ligand. One chloride ligand along with oxygen and nitrogen donor
atom from the ligands complete the second half of the coordination sphere [62-64].
All the ruthenium centers have a six-coordinate geometry; the metal centers of 2a, 2b
and 2f exist in the three-legged piano-stool conformation with a five-membered
metallocycle formed by coordination of the bidentate 8-hydroxyquinoline derivatives
ligands to the metal centers. The Ru-N distances (2.140(5) Å in 2a, 2.103(10) Å in 2b,
and 2.1271(18) Å in 2f) and the Ru-O distances (2.033(4) Å in 2a, 2.058(9) Å in 2b,
and 2.0643(14) Å in 2f) (Table 2) are in the range for typical distances of reported
ruthenium complexes containing [N,O] anionic ligands [56,63,65-70].
(2a)
(2b)
(2f)
Fig. 1. Molecular structures of complexes 2a, 2b and 2f with thermal ellipsoids drawn
at the 30% level. All hydrogen atoms are omitted for clarity.

Fig. 2. 1D supramolecular structure of 2a mediated by weak C-HCl and C-HO
hydrogen bonding, the other hydrogen atoms are omitted for clarity.
In addition, the structural unit of 2a contains two independent molecules, and they
are a pair of racemic isomers (Fig. 1). Non-covalent hydrogen bonding, including a
non-polar C-H unit with suitable H-bond acceptors, for instance C-HX (X = O, N, S
or halogen) interactions play an important role in designing supramolecular
architectures due to their selectivity and directionality [71,72]. As seen in Fig. 2,
intermolecular non-classical hydrogen bonds (C-HO and C-HCl, Table 3) between
the oxygen atom of the ligand, hydrogen atoms of the cymene ring and the chloride
ligand form a 1D supramolecular structure in complex 2a. As shown in the Fig. S1,
the coordinated chlorine atoms and the oxygen atom of the ligand form two
non-classical C-HCl hydrogen bonds with adjacent molecules [C(7)Cl(1) = 2.87 Å;
C(7)-H(7)Cl(1) =145° and C(24)O(2) = 2.53 Å; C(24)-H(24)O(2) =146°] in 2b.
The molecular half-sandwich ruthenium complex units are linked into a helical chain
along the b axis via the intermolecular hydrogen bonds. Two intertwined helical
chains are generated around the crystallographic 2(1) axis with a pitch of 7.4497(5) Å,
which is equal to the b axis length. Each helix is linked by C-HO intermolecular
hydrogen bonds along the c axis to form a 2D architecture. Moreover, two complexes
adopt trans tropism and two ligands molecules are parallel to each other in the

packing structure; the distance between the two planes is 3.3992 Å, which shows a
π-π stacking interaction. Weak intermolecular interactions play a crucial role in the
construction of the packing structure in the solid state. There are two intermolecular
hydrogen bonds [C(4)F(2) = 2.53 Å; C(4)-H(4)F(2) =159° and C(14)F(3) = 2.63
Å; C(14)-H(14)F(3) =147°] between the ruthenium complexes, giving rise to a 1D
supramolecular structure in 2f (Fig. S2).
Table 3.
a
Hydrogen bond parameters for the half-sandwich ruthenium complexes 2a, 2b and 2f
Complex
D–HA
d(HA) (Å)
2.47
d(DA) (Å)
3.353(9)
D–HA ()
159
♯
1
2
a
C(17)–H(17)O(1)
C(37)–H(37)O(2)
2.28
3.197(15)
3.698(10)
3.595(14)
3.613(11)
3.34(2)
171
C(34)–H(34)C1(1)
C(27)–H(27)Cl(2)
C(36)–H(36)Cl(2)
2.78
169
2.81
142
2.79
148
♯
2
2
b
C(24)–H(24)O(2)
C(7)–H(7)C1(1)
2.53
146
2.87
3.6815(2)
3.411(4)
145
♯
3
2
f
C(4)–H(4)F(2)
C(14)–H(14)F(3)
2.53
159
2.63
3.441(1)
147
a: Complex 2a: ♯1: -x, -y, 1-z; Complex 2b: ♯2: 1-x, -0.5+y, 0.5-z; Complex 2f: ♯3: 1-x, 0.5+y, -0.5-z
3
.3. Catalytic reduction of nitroarenes
Initially, 1-chloro-4-nitrobenzene was chosen as the standard substrate for the
catalytic studies. The ruthenium complexes 2a-2f were screened as catalysts with 0.5
mol% and 4.0 equiv of NaBH in 2 mL ethanol at room temperature for 0.5 h. As
4
shown in Fig.3, the best reaction outcome was obtained with 2f. Furthermore, various
solvents were used for this transformation (Fig. 4). Ethanol was identified as the
optimal solvent for the 1-chloro-4-nitrobenzene reduction. In a control experiment, no
desired product was observed without the half-sandwich ruthenium catalyst. On the

basis of above investigations, the optimal reaction conditions for nitroarene
reduction are 0.5 mol% 2f catalyst, 0.5 h at room temperature in ethanol. A 51%
yield of 4-chloroaniline was observed using 0.5 mol% of a ruthenium complex
with a Schiff-base ligand under the same reaction conditions [6,55]. Thus the
catalytic efficiency has been improved greatly on comparing the half-sandwich
ruthenium complexes with the Schiff-base ligands catalysts.
4
eq NaBH , 0.5 h
4
EtOH, Room temperature
Ru Catalyst 0.5mol%
Cl
NO2
Cl
NH2
Fig. 3. Screening of half-sandwich ruthenium complexes as catalysts for
-chloro-4-nitrobenzene reduction. Reaction conditions: 0.3 mmol nitrobenzene, 1.2
mmol NaBH , Ru catalyst (0.5 mol %), ethanol (2 mL), room temperature, 0.5 h.
1
4
4
eq NaBH , 6 h
4
Solevent, 2f, 0.5mol%
Room temperature
Cl
NO2
Cl
NH2
Fig. 4. Screening of various solvents for 1-chloro-4-nitrobenzene reduction using the
2
f catalyst. Reaction conditions: 0.3 mmol nitrobenzene, 1.2 mmol NaBH , 2f (0.5
4
mol %), solvent (2 mL), room temperature, 6 h.

Table 4.
Screening of substrates for nitroarene reduction catalyzed by the ruthenium complex
2
f.
a
Entry
Substrate
Product
Time (min)
Yield (%)
NO2
NO2
NH2
90
1
2
120
Cl
Br
I
Cl
Br
I
NH2
NH2
NH2
24
93
3
4
NO2
NO2
20
14
91
94
NC
HO
NO2
NC
HO
NH2
5
6
90
92
6
0
0
NO2
NH2
4
60 (88)b
7
NO2
NH2
30
45 (90)c
89
8
9
NO2
NO2
NH2
NH2
3
0
30
O
HO
NO2
NH2
1
0
1
2
95
93
1
1
HOH C
NH2
HOH C
NO2
90
6
2
2
OHC
NO2
HOH C
NH2
1
2
2
94
91
HOOC
NO2
HOOC
NH2
1
1
3
4
8
H NOC
NO2
H NOC
2
NH2
4
2
10
97
92
1
5
120
NO2
NH2

,
a Reaction conditions: 0.3 mmol nitrobenzene, 1.2 mmol NaBH , 2f (0.5 mol %), EtOH (2 mL), room temperature
4
isolated yield; b 180 min; c 240 min.
With the optimal conditions established, the generality of the protocol was
subsequently investigated. Gratifyingly, a series of anilines with different substituent
groups on the phenyl ring were obtained in excellent yields and with shorter reaction
times compare to our previous studies [6,54-56]. Generally, both electron-donating
and -withdrawing groups on the phenyl ring were compatible with the catalytic
system.
However, reduction of nitrotoluene generally takes a longer time, with an
electron-donating group such as -CH . Also, substituents at the meta-, ortho- or para-
3
position influence the yields dramatically (Table 4, entries 7-9). The reduction of
2
-nitrotoluene takes a longer reaction time. Chemoselective reduction of the nitro
group in the presence of -CHO, -CH OH, -COMe, -COOH and -NHCOMe groups
2
were also carried out (Table 4, entries 10-14). For 4-nitroacetophenone and
4-nitrobenzaldehyde, the -CHO and -COMe groups were reduced together with the
nitro group. Under the same conditions, the -COOH and -NHCOMe groups were
unchanged. Notably, the highly sterically hindered 2,6-dimethylnitrobenzene was also
suitable for this catalytic system and it was transferred into the desired product in 92%
yield (Table 4, entry 15). According to previous observations [47,73-75], a
half-sandwich ruthenium hydride was proposed as the catalytically active species for
the reduction of nitrobenzene.
4
. Conclusions
In conclusion, we have synthesized and characterized a series of novel
half-sandwich ruthenium complexes with 8-hydroxyquinoline derivatives ligands. A

combination of spectroscopic studies and X-ray crystallography confirmed the
molecular structures of the ruthenium complexes. Accordingly, these results may
further enrich our knowledge of the structural topologies for supramolecular networks
with non-covalent interactions. These ruthenium complexes are highly efficient
catalysts for the hydrogenation of nitroarenes using NaBH as a reducing agent under
4
mild conditions. Interestingly, these Ru(II)-quinolinate complexes exhibit disparate
catalytic activities owing to their different Lewis acidities, as controlled by the
8
-quinolinate-based ligands. This unique capability may provide a useful synthetic
strategy to prepare new molecular catalysts with high catalytic activities.
Appendix A. Supplementary data
CCDC 1577530-1577532 contains the supplementary crystallographic data for 2a,
2
b
and 2f. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated
1
with this article can be found, in the online version.
Acknowledgment
We acknowledge financial support from the National Nature Science Foundation of
China (21671002 and 21102004), the Natural Science Foundation of Anhui Province
(1708085MB44) and the Natural Science Foundation of the Anhui Higher Education
Institutions of China (KJ2016A845), and the Special and Excellent Research Fund of
Anhui Normal University.

References
[
[
[
[
1] L. Ackermann, Org. Process Res. Dev. 19 (2015) 260-269.
2] P.B. Arockiam, C. Bruneau, P.H. Dixneuf, Chem. Rev. 112 (2012) 5879-5918.
3] B. Li, P.H. Dixneuf, Chem. Soc. Rev. 42 (2013) 5744-5767.
4] M.J. Chow, C. Licona, D. Yuan Qiang Wong, G. Pastorin, C. Gaiddon, W.H. Ang,
J. Med. Chem. 57 (2014) 6043-6059.
[
[
[
[
[
[
[
5] R.M. Lord, A.J. Hebden, C.M. Pask, I.R. Henderson, S.J. Allison, S.L. Shepherd,
R.M. Phillips, P.C. McGowan, J. Med. Chem. 58 (2015) 4940-4953.
6] W.-G. Jia, H. Zhang, T. Zhang, D. Xie, S. Ling, E.-H. Sheng, Organometallics 35
(
2016) 503-512.
7] O. Prakash, H. Joshi, K.N. Sharma, P.L. Gupta, A.K. Singh, Organometallics 33
2014) 3804-3812.
(
8] M. Carmona, R. Rodriguez, F.J. Lahoz, P. Garcia-Orduna, C. Cativiela, J.A. Lopez,
D. Carmona, Dalton Trans. 46 (2017) 962-976.
9] Z.-W. Xu, L. Han, C. Ji, R. Zhang, X.-J. Shen, H. Yan, Dalton Trans. 40 (2011)
6
992-6997.
10] J.-S. Zhang, S. Liu, G.-L. Wang, Y.-J. Lin, G.-X. Jin, Organometallics 27 (2008)
112-1118.
11] F. Saleem, G.K. Rao, A. Kumar, G. Mukherjee, A.K. Singh, Organometallics 32
2013) 3595-3603.
1
(
[
[
12] P. Singh, A.K. Singh, Organometallics 29 (2010) 6433-6442.
13] J. Hu, J. Wen, D. Wu, R. Zhang, G. Liu, Q. Jiang, Y. Li, H. Yan, Organometallics

3
0 (2011) 298-304.
[
[
14] D.V. Gutsulyak, A.L. Osipov, L.G. Kuzmina, J.A.K. Howard, G.I. Nikonov,
Dalton Trans. (2008) 6843-6850.
15] A.P. Shaw, J.R. Norton, D. Buccella, L.A. Sites, S.S. Kleinbach, D.A. Jarem,
K.M. Bocage, C. Nataro, Organometallics 28 (2009) 3804-3814.
[
[
16] C.A. Mebi, R.P. Nair, B.J. Frost, Organometallics 26 (2007) 429-438.
17] W.B. Cross, C.G. Daly, Y. Boutadla, K. Singh, Dalton Trans. 40 (2011)
9
722-9730.
[
18] V.H. Mai, L.G. Kuzmina, A.V. Churakov, I. Korobkov, J.A.K. Howard, G.I.
Nikonov, Dalton Trans. 45 (2016) 208-215.
[
[
[
[
[
[
[
19] B. Bagh, D.W. Stephan, Dalton Trans. 43 (2014) 15638-15645.
20] F.E. Fernández, M.C. Puerta, P. Valerga, Organometallics 30 (2011) 5793-5802.
21] H. Li, B. Zheng, K.-W. Huang, Coord. Chem. Rev. 293–294 (2015) 116-138.
22] C. Gunanathan, D. Milstein, Chem. Rev. 114 (2014) 12024-12087.
23] S.K. Singh, D.S. Pandey, RSC Adv. 4 (2014) 1819-1840.
24] J. Luo, C. Zhang, C. Li, H. Hu, B. Hu, RSC Adv. 4 (2014) 57393-57401.
25] J. Shi, C. Gong, X. Zeng, J. Zhang, C. Zhu, J. Xie, Polyhedron 102 (2015)
5
62-568.
[
[
[
26] Y. Huo, J. Lu, S. Hu, L. Zhang, F. Zhao, H. Huang, B. Huang, L. Zhang, J. Mol.
Struct. 1083 (2015) 144-151.
27] B. Yang, Y. Huo, L. Zhang, S. Hu, S. Wang, B. Huang, Tetrahedron 71 (2015)
4
015-4022.
28] Y. Huo, S. Wang, J. Lu, B. Yang, X. Li, C. Pan, J. Fluorine Chem. 180 (2015)

1
68-174.
29] Y. Huo, C. Pan, S. Wang, S. Ji, T. Kong, L. Gao, N. Cai, H. Zeng, Polyhedron
19 (2016) 175-183.
[
1
[
[
30] G. Yuan, W. Shan, J. Chen, Y. Tian, H. Wang, J. Lumin. 160 (2015) 16-21.
31] G. Yuan, Y. Huo, X. Nie, H. Jiang, B. Liu, X. Fang, F. Zhao, Dalton Trans. 42
(
2013) 2921-2929.
32] G. Yuan, L. Rong, X. Qiao, L. Ma, X. Wei, CrystEngComm 15 (2013)
307-7314.
33] G. Yuan, W. Shan, B. Liu, L. Rong, L. Zhang, H. Zhang, X. Wei, Dalton Trans. 43
2014) 9777-9785.
[
[
7
(
[
[
34] L. Zhang, L. Sun, X. Li, Y. Tian, G. Yuan, Dalton Trans. 44 (2015) 401-410.
35] G. Yuan, G. Hu, W. Shan, S. Jin, Q. Gu, J. Chen, Dalton Trans. 44 (2015)
1
7774-17783.
[
36] G. Yuan, Q. Zhang, Z. Wang, K. Song, X. Yuan, Y. Wang, L. Zhang, Inorg. Chem.
Front. 4 (2017) 764-772.
[
[
[
[
37] P. Hu, F. Wang, G.-X. Jin, Organometallics 30 (2011) 1008-1012.
38] P. Hu, Y.-L. Qiao, J.-Q. Wang, G.-X. Jin, Organometallics 31 (2012) 3241-3247.
39] M. Colle, R.E. Dinnebier, W. Brutting, Chem. Commun. (2002) 2908-2909.
40] K. Sokołowski, W. Bury, I. Justyniak, D. Fairen-Jimenez, K. Sołtys, D.
Prochowicz, S. Yang, M. Schröder, J. Lewiński, Angew. Chem. Int. Ed. 52 (2013)
1
3414-13418.
[
41] K. Sokołowski, I. Justyniak, W. Śliwiński, K. Sołtys, A. Tulewicz, A. Kornowicz,
R. Moszyński, J. Lipkowski, J. Lewiński, Chem. Eur. J. 18 (2012) 5637-5645.

[
[
[
[
42] E.V. Baranov, G.K. Fukin, T.V. Balashova, A.P. Pushkarev, I.D. Grishin, M.N.
Bochkarev, Dalton Trans. 42 (2013) 15699-15705.
43] S. Hossain, S. Das, A. Chakraborty, F. Lloret, J. Cano, E. Pardo, V.
Chandrasekhar, Dalton Trans. 43 (2014) 10164-10174.
44] W.-M. Wang, H.-X. Zhang, S.-Y. Wang, H.-Y. Shen, H.-L. Gao, J.-Z. Cui, B.
Zhao, Inorg. Chem. 54 (2015) 10610-10622.
45] P. Kathirgamanathan, S. Surendrakumar, J. Antipan-Lara, S. Ravichandran, V.R.
Reddy, S. Ganeshamurugan, M. Kumaraverl, V. Arkley, A.J. Blake, D. Bailey, J.
Mater. Chem. 21 (2011) 1762-1771.
[
[
46] A.M. Tafesh, J. Weiguny, Chem. Rev. 96 (1996) 2035-2052.
47] M.J. Vaidya, S.M. Kulkarni, R.V. Chaudhari, Org. Process Res. Dev. 7 (2003)
2
02-208.
[
[
[
[
[
48] A.K. Shil, P. Das, Green Chem. 15 (2013) 3421-3428.
49] T. Aditya, A. Pal, T. Pal, Chem. Commun. 51 (2015) 9410-9431.
50] H.K. Kadam, S.G. Tilve, RSC Adv. 5 (2015) 83391-83407.
51] R.S. Downing, P.J. Kunkeler, H. van Bekkum, Catal. Today 37 (1997) 121-136.
52] R.J. Lundgren, M.A. Rankin, R. McDonald, G. Schatte, M. Stradiotto, Angew.
Chem. Int. Ed. 46 (2007) 4732-4735.
[
[
[
53] A.K. Sharma, H. Joshi, K.N. Sharma, P.L. Gupta, A.K. Singh, Organometallics
3
3 (2014) 3629-3639.
54] W.-G. Jia, T. Zhang, D. Xie, Q.-T. Xu, S. Ling, Q. Zhang, Dalton Trans. 45 (2016)
4230-14237.
55] W.-G. Jia, H. Zhang, T. Zhang, S. Ling, Inorg. Chem. Commun. 66 (2016) 15-18.
1

[
[
[
[
[
[
56] W.-G. Jia, Z.-B. Wang, X.-T. Zhi, J.-Q. Han, Y. Sun, J. Coord. Chem. 70 (2017)
48-858.
8
57] G.-Z. Yuan, L.-L. Rong, X.-L. Qiao, Y.-P. Xia, T. Guo, X.-W. Wei, Chinese J.
Inorg. Chem. 29 (2013) 1769-1776.
58] G.-Z. Yuan, Y.-P. Huo, L.-L. Rong, X.-L. Nie, X.-M. Fang, Inorg. Chem.
Commun. 23 (2012) 90-94.
59] W. Shan, X. Shan, X. Li, J. Liu, L. Zhang, G. Yuan, Inorg. Chem. Commun. 48
(2014) 131-135.
60] G. Sheldrick, SHELXL-97, a program for refining crystal structures, University
of Göttingen, Germany, (1997).
61] G. Sheldrick, SADABS v. 2.01, Bruker/Siemens area detector absorption
correction program, Bruker AXS, Madison, WI, USA, (1998).
[
[
62] Y.-F. Han, G.-X. Jin, Chem. Soc. Rev. 43 (2014) 2799-2823.
63] Y.-F. Han, H. Li, Y. Fei, Y.-J. Lin, W.-Z. Zhang, G.-X. Jin, Dalton Trans. 39 (2010)
7
119-7124.
[
[
64] Y.-F. Han, G.-X. Jin, Acc. Chem. Res. 47 (2014) 3571-3579.
65] R. Schuecker, R.O. John, M.A. Jakupec, V.B. Arion, B.K. Keppler,
Organometallics 27 (2008) 6587-6595.
[
[
[
66] M. Kubanik, H. Holtkamp, T. Söhnel, S.M.F. Jamieson, C.G. Hartinger,
Organometallics 34 (2015) 5658-5668.
67] L. Gong, S.P. Mulcahy, D. Devarajan, K. Harms, G. Frenking, E. Meggers, Inorg.
Chem. 49 (2010) 7692-7699.
68] W.-G. Jia, S. Ling, S.-J. Fang, E.-H. Sheng, Polyhedron 138 (2017) 1-6.

[
[
69] C. Gemel, R. John, C. Slugovc, K. Mereiter, R. Schmid, K. Kirchner, Dalton
Trans. (2000) 2607-2612.
70] M. Gobec, J. Kljun, I. Sosic, I. Mlinaric-Rascan, M. Ursic, S. Gobec, I. Turel,
Dalton Trans. 43 (2014) 9045-9051.
[
[
[
71] A.M. Beatty, Coord. Chem. Rev. 246 (2003) 131-143.
72] S.J. Grabowski, Chem. Rev. 111 (2011) 2597-2625.
73] R.V. Jagadeesh, G. Wienhöfer, F.A. Westerhaus, A.-E. Surkus, H. Junge, K. Junge,
M. Beller, Chem. Eur. J. 17 (2011) 14375-14379.
[
[
74] A. Bolje, S. Hohloch, J. Kosmrlj, B. Sarkar, Dalton Trans. 45 (2016)
1
5983-15993.
75] W.-G. Jia, S. Ling, H.-N. Zhang, E.-H. Sheng, R. Lee, Organometallics 37 (2018)
0-47.
4

Graphic Content
Based on 2-substituted quinolinate ligands with different substituent groups, six half-sandwich ruthenium
complexes have been synthesized and characterized. The catalytic activities of the Ru(II)-quinolinate
complexes are controlled by the organic ligands with different functional substituents.