Half-Sandwich Ruthenium Complexes for One-Pot Synthesis of Quinolines and Tetrahydroquinolines: Diverse Catalytic Activity in the Coupled Cyclization and Hydrogenation Process

Article abstract of DOI:10.1021/acs.inorgchem.0c00955

Four types of half-sandwich ruthenium complexes with an N,O-coordinate mode based on hydroxyindanone-imine ligands have been prepared in good yields. These stable ruthenium complexes exhibited high activity in the catalytic synthesis of quinolines from the reactions of amino alcohols with different types of ketones or secondary alcohols under very mild conditions. Moreover, the methodology for the direct one-pot synthesis of tetrahydroquinoline derivatives from amino alcohols and ketones has been also developed on the basis of the continuous catalytic activity of this ruthenium catalyst in the selective hydrogenation of the obtained quinoline derivatives with a low catalyst loading. The corresponding products, quinolines and tetrahydroquinoline derivatives, were afforded in good to excellent yields. The efficient and diverse catalytic activity of these ruthenium complexes suggested their potential large-scale application. All of the ruthenium complexes were characterized by various spectroscopies to confirm their structures.

Full text of DOI:10.1021/acs.inorgchem.0c00955

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Article
Half-Sandwich Ruthenium Complexes for One-Pot Synthesis of
Quinolines and Tetrahydroquinolines: Diverse Catalytic Activity in
the Coupled Cyclization and Hydrogenation Process
Xue-Jing Yun, Jing-Wei Zhu, Yan Jin, Wei Deng, and Zi-Jian Yao*
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ABSTRACT: Four types of half-sandwich ruthenium complexes
with an N,O-coordinate mode based on hydroxyindanone-imine
ligands have been prepared in good yields. These stable ruthenium
complexes exhibited high activity in the catalytic synthesis of
quinolines from the reactions of amino alcohols with different
types of ketones or secondary alcohols under very mild conditions.
Moreover, the methodology for the direct one-pot synthesis of
tetrahydroquinoline derivatives from amino alcohols and ketones
has been also developed on the basis of the continuous catalytic
activity of this ruthenium catalyst in the selective hydrogenation of the obtained quinoline derivatives with a low catalyst loading.
The corresponding products, quinolines and tetrahydroquinoline derivatives, were afforded in good to excellent yields. The efficient
and diverse catalytic activity of these ruthenium complexes suggested their potential large-scale application. All of the ruthenium
complexes were characterized by various spectroscopies to confirm their structures.
harsh conditions. The preparation of quinoline under the
catalysis of transition metal complexes has attracted consid-
erable attention in recent years,22−34 and several Ru catalysis
methods also have been developed (see Figure 1 for a sampling
of previous work): (i) reactions between anilines and trialkyl-
amines catalyzed by RuCl3, SnCl2, and dppm with the hex-1-
enein as the additive,28 (ii) RuCl2(DMSO)4-catalyzed con-
densation of 2-aminophenyl ketone derivatives with alcohols
with benzophenone as the additive,29 (iii) reaction of 2-
aminobenzyl alcohol with ketones catalyzed by Grubbs catalyst
or the Ru(arene) complex,30 and (iv) reaction of amino alcohol
with secondary alcohol catalyzed by the ruthenium hydrido
complex.31,32 However, the drawbacks of these methods such as
the high reaction temperature and long reaction time, the high
catalyst loading, the instability of the ruthenium catalysts, and
the need for additives limited their application.
INTRODUCTION
■
Group 8 and 9 metal complexes with half-sandwich motifs
[[Cp#MCl2]2 (M = Ru, Ir, or Rh), where Cp# = Cp*, p-cymene]
have been widely studied because of their diverse catalytic
activity, good stability, and easy functionalization.1−4 Among
these compounds, half-sandwich ruthenium(II) arene motifs
were often used as building blocks in the synthesis of different
complexes that exhibited potential for application in catalysis,
supramolecular chemistry, and biochemistry.5−10 Recent
research showed that the half-sandwich ruthenium(II) com-
plexes bearing Schiff base ligands can serve as efficient catalysts
in various types of organic reactions.11−16 Nitrogen-donor Schiff
base ligands were often employed in the preparation of
coordination compounds because their steric and electronic
effects can be altered conveniently. One type of nitrogen-donor
ligand is the N,O-chelate mode Schiff base ligand, which was
frequently studied because different types of metal complexes in
various oxidation states can be formed by using the ligands.17,18
Therefore, the interaction between Schiff base ligands and the
half-sandwich ruthenium motif in N,O-chelate mode should be
examined.19,20
The preparation of quinoline derivatives has attracted
considerable attention in organic synthesis because they are
important intermediates in fine chemicals and pharmaceuticals,
so a number of synthetic methods have been developed to build
this N-heterocyclic structure because of its wide utilization in
antibacterial, anti-inflammatory, and other areas.21 The
application of these traditional reactions is limited due to the
low stereoselectivity and yields, multiple reaction steps, and
Because of the high catalytic efficiency of the half-sandwich
ruthenium catalysts, the preparation and application of the half-
sandwich ruthenium complexes with new structures should be
explored. We report herein four types of N,O-coordinate half-
sandwich ruthenium complexes bearing the hydroxyindanone-
imine motif. Preliminary results suggested good catalytic activity
Received: March 31, 2020
https://dx.doi.org/10.1021/acs.inorgchem.0c00955
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Scheme 1. Synthesis of N,O-Chelate Half-Sandwich Ru(II)
a
Complexes 1−4
a
Reaction conditions: (i) 4-methylphenol (1.1 equiv), γ-butyrolac-
tone (1.0 equiv), AlCl3 (1.5 equiv), NaCl (7.5 equiv), 200 °C, 2 min;
(ii) amines (1.2 equiv), HOAc (3 drops), 4 Å molecular sieves (0.1
g), EtOH, reflux, 24 h; (iii) [(p-cymene)RuCl2]2 (0.5 equiv), NaOAc
(2.0 equiv), CH3OH, reflux, 6 h.
The ultraviolet−visible spectra of the target ruthenium
complexes 1−4 in a CH3CN solution exhibited strong ligand-
centered (LC) π−π* and n−π* transitions located around 240−
270 nm and ligand-to-metal charge transfer (LMCT)
absorptions in the range of 310−360 nm (see the Supporting
Information).17 The broad stretching absorption in the range of
3300−3500 cm−1 in the infrared (IR) spectra of the ligands was
assigned to the hydroxyl group. The disappearance of the signals
in this region in the IR spectra of complexes 1−4 indicated Ru−
O bond formation through deprotonation of the −OH group.
The imine group vibration bands of the ligands (1630−1650
cm−1) are shifted to high fields (1610−1620 cm−1) because of
the formation of the N,O-chelate mode between the metal
center and the imine group. The singlet at δ 8.19 in the 1H NMR
spectra of the ligands was attributed to the −OH group. The
coordination of the Ru−O bond was further confirmed by the
disappearance of this signal. Groups of multiplets around δ
Figure 1. Sampling of Ru catalysis methods for quinoline synthesis.
of the ruthenium catalysts in the synthesis of quinoline through a
one-pot process under mild conditions. Additionally, the
ruthenium complex can continuously catalyze the selective
hydrogenation of the obtained quinolines under a H2
atmosphere. Therefore, the methodology for the one-pot
synthesis of tetrahydroquinoline derivatives has been also
developed, which combined cyclization and hydrogenation
based on the continuous catalytic activity of the ruthenium
catalyst in the selective catalytic hydrogenation of quinolines. All
of the prepared compounds were fully characterized, and the
structures of the ruthenium complexes were precisely confirmed
using single-crystal X-ray diffraction. In addition, the effects that
influenced the catalytic activity of the ruthenium complexes
were also discussed.
1
6.70−7.80 were observed in the H NMR spectra of the
ruthenium complexes, which can be assigned to the aromatic
protons of the ligands in 1−4.
RESULTS AND DISCUSSION
■
Synthesis of the Ligands and Half-Sandwich Ruthe-
nium Complexes. As shown in Scheme 1, the starting material
7-hydroxy-3,4-methylindan-1-one was prepared through the
AlCl3-catalyzed Friedel−Crafts reaction between 4-methylphe-
nol and γ-butyrolactone. NaCl was added to the reaction
mixture to decrease the fusing temperature of AlCl3.
Hydroxyindanone-imine ligands L1−L4 were obtained in
good yields through the reaction of indanone with arylamines
in an equimolar ratio in refluxing ethanol. It is noteworthy that
molecular sieves are essential for the preparation of the ligands.
New N,O-coordinate half-sandwich ruthenium(II) complexes
1−4 were formed in moderate yields by the interaction of the
ligands and [(p-cymene)RuCl2]2 in the presence of NaOAc in
refluxing CH3OH for 6 h (Scheme 1). All of the pure products
were isolated as brown powder that is air and moisture stable for
several weeks. Ru(II) complexes 1−4 exhibited only slight
solubility in chloroform, tetrahydrofuran, toluene, dichloro-
methane, and DMSO, affording brown-colored solutions that
were insoluble in nonpolar solvents. The characterization data
for all of the half-sandwich Ru(II) complexes match well with
the expected general molecular formula.
Crystal Structures of Ruthenium Complexes. X-ray
diffraction was performed to precisely elaborate the structure of
the obtained half-sandwich ruthenium complexes. Qualified
single crystals of the ruthenium complexes for X-ray
determination were obtained by liquid diffusion of n-hexane
into a saturated solution of the target products in CH2Cl2.
Complexes 1 and 4 crystallized in monoclinic space groups
P2(1)/n and P2(1)/c, respectively (Figure 2). Crystallographic
data are summarized in Table 1. The crystal structure showed
the N,O-chelate mode of the ruthenium center obviously in
which hydroxyindanone-imine served as a bidentate ligand. The
geometry of the metal center in the two complexes both showed
distorted octahedral conformations, supposing that half-
sandwich motif afforded three coordination points. The half-
sandwich metal corner was coordinated by N, O, and Cl atoms.
For complex 1, the Ru−Cl bond distance of 2.4353(5) Å is
inconsistent with other structurally similar (p-cymene)Ru(II)
complexes.35 The longer Ru−N bond distance of 2.0957(16) Å
in comparison with the Ru−O bond distance of 2.0649(15) Å
indicates the weaker interaction between the nitrogen atom and
metal center. The small dihedral angle between the N(1)−
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Figure 2. Molecular structures of 1 and 4 with thermal ellipsoids drawn at the 30% level. All hydrogen atoms have been omitted for the sake of clarity.
Selected bond lengths (angstroms) and angles (degrees). Complex 1: Ru(1)−N(1), 2.0957(16); Ru(1)−O(1), 2.0649(15); Ru(1)−Cl(1),
2.4353(5); C(3)−N(1), 1.300(3); C(1)−O(1), 1.305(3); O(1)−Ru(1)−N(1), 90.16(6); O(1)−Ru(1)−Cl(1), 85.49(5); Cl(1)−Ru(1)−N(1),
83.18(5); Ru(1)−O(1)−C(1), 126.82(13); Ru(1)−N(1)−C(3), 124.79(14). Complex 4: Ru(1)−N(1), 2.099(2); Ru(1)−O(1), 2.074(2); Ru(1)−
Cl(1), 2.4376(8); C(7)−N(1), 1.301(4); C(1)−O(1), 1.303(4); O(1)−Ru(1)−N(1), 90.01(9); O(1)−Ru(1)−Cl(1), 85.19(7); Cl(1)−Ru(1)−
N(1), 84.73(7); Ru(1)−O(1)−C(1), 126.87(19); Ru(1)−N(1)−C(7), 125.0(2).
oxidative cyclization reaction under catalysis of N,O-chelate
half-sandwich ruthenium complexes 1−4 was explored. The
reaction of acetophenone with 2-aminobenzyl alcohol under
open flask conditions catalyzed by complex 1 is considered as a
model reaction for screening various reaction factors such as
reaction temperature, time, catalyst loading, solvents, and bases
(Table 2). The initial reaction was performed in methanol with
1.0 equiv of KOH as the base at room temperature for 6 h (1 mol
% catalyst loading), and the expected product 5a was generated
in a moderate yield of 62% (Table 2, entry 1). Different bases
were employed in the reaction to increase the yield of the
product. The highest yield of 93% was obtained when CH3ONa
was used in the reaction (Table 2, entries 2−8). No products
were observed in the absence of a base (Table 2, entry 9). As
expected, the performance of inorganic bases was better than
that of organic bases probably because catalytic activity was lost
through the coordinate interaction between the N donor of the
organic bases and the Ru center of the catalyst.15 Low yields may
also be caused by the low basicity of the organic bases. 5a was
furnished in excellent yields in CH3OH after screening several
solvents (Table 2, entries 10−15). We next investigated the
catalyst loading to pursue the highest TON value because the
mole ratio of the catalyst and substrate (C/S) is important in
industrial application. No obvious change in yield was observed
when the catalyst loading was decreased from 1.0 to 0.1 mol %.
However, a serious decrease in the product yield was found with
a further decrease in the catalyst loading to 0.05 mol % (Table 2,
entries 16−18). Therefore, the optimal condition of the
reaction, in an open flask at room temperature, was obtained
after screening different reaction parameters. Target product 5a
was isolated in 93% yield under mild conditions (CH3OH/
CH3ONa, 0.1 mol % catalyst loading, room temperature, 6 h).
The catalytic activity of complexes 2−4 was also investigated
under the optimal conditions, which exhibited a similar
efficiency (Table 2, entries 19−21). A poor result was found
when [(p-cym)RuCl2]2 was employed as the catalyst (Table 2,
entry 22).
Table 1. Crystallographic Data and Structure Refinement
Parameters for 1 and 4
1
4
chemical formula
formula weight
T (K)
C27H30ClNORu
521.04
173(2)
C27H29BrClNORu
599.94
173(2)
λ (Å)
0.71073
monoclinic
P2(1)/n
10.0915(5)
14.0422(7)
17.4255(10)
90
106.140(2)
90
2372.0(2)
8
0.71073
monoclinic
P2(1)/c
10.6081(7)
13.5729(9)
17.8991(12)
90
102.774(2)
90
2513.4(3)
4
crystal system
space group
a (Å)
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
ρ (Mg m−3
)
1.459
1.585
μ (mm−1
F(000)
)
4.400
1072
5.400
1208
θ range (deg)
4.596−58.221
35639
5044/0/301
1.118
R1 = 0.0257,
wR2 = 0.0647
4.407−58.000
36419
5319/75/324
1.163
R1 = 0.0351,
wR2 = 0.0830
no. of reflections collected
data/restraints/parameters
goodness of fit on F2
a
final R indices [I > 2σ(I) ]
largest difference peak and hole 0.497 and −0.369
1.359 and −1.033
(e Å−3
)
a
R1 = ∑||Fo| − |Fc||/∑|Fo| (based on reflections with Fo2 > 2σF2). wR2
= {∑[w(Fo − Fc2)2]/∑[w(Fo )2]}1/2. w = 1/[σ2(Fo ) + (0.095P)2],
2
2
2
where P = [max(Fo , 0) + 2Fc2]/3 (also with Fo > 2σF2).
2
2
Ru(1)−O(1) and N(1)−C(3)−C(2)−C(1)−O(1) planes
suggests the planarity of the Ru(1)−O(1)−C(1)−C(2)−
C(3)−N(1) six-membered ring of complex 1. The structure of
complex 4 is similar to that of complex 1.
Quinoline Synthesis under [NO]Ru Catalysis. Transition
metal-catalyzed oxidative cyclization of ketones and amino
alcohol for the preparation of quinoline derivatives represented a
green and sustainable chemical process because no toxic
byproducts were generated in this reaction. Moreover, various
quinoline derivatives could be prepared by using different cheap
and readily available ketones as starting materials. Thus, the
We next explored the universality of this reaction under
optimized conditions. The oxidative cyclization of 2-amino-
benzyl alcohol with various types of ketones catalyzed by
complex 1 readily occurred, and the corresponding quinoline
derivatives were afforded in desirable yields. Ketones with
electron-donating and electron-withdrawing groups both gave
C
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On the basis of the results mentioned above, we were
encouraged to investigate quinoline derivatives from the
catalytic oxidative cyclization of 2-aminobenzyl alcohol and
alcohols that were used as an alternative to ketones, because the
preparation of quinoline derivatives from cheap alcohols is a
useful methodology in organic synthesis. In particular, the
employment of secondary alcohols in this protocol remains a
challenge. Fortunately, our catalytic system also showed good
efficiency for the synthesis of quinoline derivatives by a one-pot
procedure using amino alcohol and secondary alcohols as
starting materials under refluxing conditions. The reactions of
amino alcohol with various secondary alcohols were carried out,
and the products were furnished in moderate to good yields
[5a−n (Table 4)]. Linear aliphatic secondary alcohols also gave
the corresponding quinoline derivatives in lower yields (Table 4,
entries 6−9). The current catalyst showed an efficiency higher
than that of the Milstein catalyst.31
A gram-scale production of the oxidative cyclization of 2-
aminobenzyl alcohol with acetophenone was carried out with
0.1 mol % catalyst 1 under optimal conditions. Analytically pure
5a and 5k were obtained in 92% and 90% isolated yields,
respectively (Figure 3). The two examples suggest that our
methodology with stable ruthenium catalysts can be utilized in
industrial production.
Catalytic hydrogenation of N-heterocycles has attracted a
great deal of interest because of their wide use in the synthesis of
pharmaceuticals and agrochemicals. On the other hand, the
transition metal-catalyzed hydrogenation methodology using
clean H2 as the reductive reagent is a green and sustainable way,
which avoided the production of the large amount of waste.36
We have reported several half-sandwich ruthenium and iridium
complexes that were used for the catalytic hydrogenation
process.35,37 Therefore, we wonder if the N,O-chelate
ruthenium complexes reported here could also be catalytically
active in the hydrogenation of quinolones obtained in the
reactions described above. Different solvents were investigated
in the quinoline reduction by utilizing complex 1 (0.1 mol %) as
the catalyst at 60 °C under a H2 atmosphere (6 atm) (Table 5,
entries 1−6). To our delight, the catalytic hydrogenation
process occurred smoothly in CF3CH2OH. The high polarity
and low nucleophilicity of CF3CH2OH can facilitate the
dissociation of the chloride ligand of the catalyst, which is the
necessary step during the catalytic hydrogenation cycle.38
Increases in the catalyst loading showed little influence on the
yield of the product (Table 5, entry 7). No reaction was detected
when the reaction was conducted at room temperature (Table 5,
entry 8). The hydrogenation reaction hardly occurred with a
[(p-cymene)RuCl2]2 catalyst and without any catalyst (Table 5,
entries 9 and 10, respectively).
Table 2. Quinoline Synthesis under Catalysis of N,O-Chelate
Ruthenium Complexes
a
b
catalyst
yield
(%)
TOF
(h−1
entry
(mol %)
base
KOH
K2CO3
NaOH
solvent
TON
)
1
2
3
4
5
6
7
8
1 (1)
CH3OH
CH3OH
CH3OH
62
46
55
93
84
62
46
55
93
84
33
−
−
−
−
77
10.3
7.7
9.2
15.5
14.0
5.5
−
−
−
−
12.8
1 (1)
1 (1)
1 (1)
1 (1)
1 (1)
1 (1)
1 (1)
CH3ONa CH3OH
tBuONa
K3PO4
Et3N
pyridine
DBU
CH3OH
CH3OH
CH3OH
CH3OH
CH3OH
CH3OH
33
trace
trace
trace
−
9
10
1 (1)
1 (1)
−
CH3ONa 1,4-
dioxane
77
11
12
13
14
15
16
17
18
19
20
21
22
1 (1)
1 (1)
1 (1)
1 (1)
CH3ONa toluene
CH3ONa THF
CH3ONa DMF
65
81
83
72
58
92
93
79
92
93
93
8
65
81
83
72
58
184
930
1580
920
930
930
120
10.8
13.5
13.8
12.0
9.7
CH3ONa DMSO
CH3ONa CH2Cl2
CH3ONa CH3OH
CH3ONa CH3OH
CH3ONa CH3OH
CH3ONa CH3OH
CH3ONa CH3OH
CH3ONa CH3OH
CH3ONa CH3OH
1 (1)
1 (0.5)
1 (0.1)
1 (0.05)
2 (0.1)
3 (0.1)
4 (0.1)
30.7
155
263
153
155
155
20
[(p-cym)
RuCl2]2
(0.1)
a
Reaction conditions: 2-aminobenzyl alcohol (1.0 mmol), acetophe-
none (1.0 mmol), base (1.1 mmol), solvent (2 mL), room
b
temperature, open flask. The yield was determined by GC analysis,
and n-tridecane was used as the internal standard.
positive results [5a−e (Table 3, entries 1−5, respectively)]. The
substituent position indicated little influence on the yields of the
products by using o-, m-, and p-methylacetophenone as starting
materials in the oxidative cyclization reaction [5f and 5g (Table
3, entries 2, 6, and 7, respectively)]. Heteroaryl ketones were
also employed in the reaction under standard conditions. The
cyclization coupling of 2-aminobenzyl alcohol with 2-acetylfur-
an, 2-acetylthiophene, and 2-acetylpyridine afforded the desired
products in 88%, 91%, and 90% yields, respectively [5h−j,
respectively (Table 3, entries 8−10, respectively)]. This process
worked well with cyclic aliphatic ketones, and the products were
afforded in excellent yields. A slightly lower yield was observed
when the smaller cyclic aliphatic ketones were used [5k and 5l
(Table 3, entries 11 and 12, respectively)]. Linear aliphatic
ketones gave the corresponding quinoline derivatives in lower
yields (78−84%) [5m and 5n (Table 3, entries 13 and 14,
respectively)]. To our delight, this catalytic system showed good
stereoselectivity, and only one product (5n) was observed in
good yield when an asymmetric ketone was used in the reaction
in comparison with the results in which a mixture of two
quinolines was formed, as reported by Verpoort.30 Aminobenzyl
alcohols with both electron-donating and electron-withdrawing
groups also afforded positive results [5o and 5p (Table 3, entries
15 and 16, respectively)].
A variety of quinoline derivatives were employed in the
catalytic hydrogenation under the optimal conditions. Hydro-
genation was found to be tolerant of different functional groups,
and the tetrahydroquinoline derivatives were afforded in good
yields (Table 6, 6a−i). The phenyl rings in the substrates were
intact, suggesting the selectivity of the catalyst for the
hydrogenation of N-heterocycles. Additionally, the dehalogena-
tion of CAr−X bonds was not observed, hence making the
product valuable for further reactions (such as cross-coupling
reactions) (Table 6, 6c). 2-Heterocycle-substituted quinolines
were also efficiently and selectively hydrogenated in good yields
(Table 6, 6d−f).
Experimental results indicated that the N,O-chelate Ru
complexes can catalyze both cyclization coupling of amino-
D
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a
Table 3. Substrate Scope of Cyclization of Aminobenzyl Alcohols with Ketones
a
Reaction conditions: complex 1 (0.1 mol %), aminobenzyl alcohols (1.0 mmol), ketones (1.1 mmol), CH3ONa (1.2 mmol), CH3OH (2 mL),
b
room temperature, 6 h, open flask. The yield was determined by GC analysis, and n-tridecane was used as the internal standard. Isolated yields
(%) are provided in parentheses.
benzyl alcohol with ketones and selective hydrogenation of
quinoline derivatives. Inspired by the diverse catalytic activity of
the half-sandwich Ru complexes, we investigated one-pot
synthesis of tetrahydroquinoline derivatives by using amino-
E
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a
Table 4. Scope of the Reaction between 2-Aminobenzyl Alcohol and Secondary Alcohols
a
Reaction conditions: complex 1 (0.1 mol %), 2-aminobenzyl alcohol (1.0 mmol), secondary alcohols (1.2 mmol), CH3ONa (1.2 mmol), CH3OH
b
(2 mL), reflux, 3 h. The yield was determined by GC analysis, and n-tridecane was used as the internal standard. Isolated yields (%) are provided
in parentheses.
Figure 3. Gram-scale reaction study.
benzyl alcohol and ketones as starting materials that combined
two reactions together. Fortunately, the reaction of aminobenzyl
alcohol and ketones afforded the desired products smoothly
under the sequential catalysis of complex 1 in a H2 atmosphere
by using CF3CH2OH as the solvent. Both electron-donating and
electron-withdrawing substituents on the phenyl ring of ketones
were well tolerated in the reaction (Table 7, entries 1−11). This
homogeneous catalysis for the direct synthesis of tetrahydro-
quinoline derivatives complements quite well the heterogenen-
uous catalysis reported very recently.39
CONCLUSIONS
■
In summary, we have prepared a series of half-sandwich N,O-
chelate ruthenium complexes that exhibited excellent catalytic
activity in the synthesis of both quinoline and tetrahydroquino-
line derivatives. The synthesis of quinoline derivatives starting
from amino alcohols and ketones as well as secondary alcohols
has been accomplished under very mild conditions. On the other
hand, the ruthenium catalyst also exhibited good efficiency in
the hydrogenation of quinoline derivatives under a H2
F
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Table 5. Optimization for the Catalytic Hydrogenation of
Quinoline
EXPERIMENTAL SECTION
■
a
General Data. Half-sandwich ruthenium complexes 1−4 were
synthesized under an atmosphere of argon using standard Schlenk
techniques. Chemicals were used as commercial products without
further purification. 1H NMR (500 MHz) spectra were recorded with a
Bruker DMX-500 spectrometer. Elemental analysis was performed on
an Elementar vario EL III analyzer. IR (KBr) spectra were recorded
with the Nicolet FT-IR spectrophotometer.
Synthesis of 7-Hydroxy-3,4-methylindan-1-one. 4-Methyl-
phenol (11 mmol, 1.1 equiv), γ-butyrolactone (10 mmol, 1.1 equiv),
AlCl3 (15 mmol, 1.5 equiv), and NaCl (75 mmol, 7.5 equiv) were mixed
together, and the mixture was stirred at 200 °C for 2 min. After the
reaction mixture had cooled to room temperature, the mixture was
poured into the HCl (10 wt %) solution. Then the solution was
extracted with CH2Cl2 (3 × 20 mL). The combined organic layer was
dried and concentrated. The crude product was recrystallized in an n-
b
entry catalyst (mol %)
solvent
MeOH
THF
toluene
DMF
yield (%)
TON TOF (h−1
)
1
2
3
4
5
6
7
8
9
0.1
0.1
0.1
0.1
0.1
0.1
0.5
0.1
0.1
11
trace
−
trace
−
89
90
−
trace
110
−
13.8
−
−
−
−
−
CH2Cl2
−
−
CF3CH2OH
CF3CH2OH
CF3CH2OH
CF3CH2OH
CF3CH2OH
890
900
−
111
112
−
1
c
hexane/Et2O mixed solvent to give a white solid (yield of 41%): H
d
NMR (500 MHz, CDCl3) δ 9.00 (s, 1H, OH), 7.16 (d, J = 8.2 Hz, 1H,
ArH), 6.58 (d, J = 8.2 Hz, 1H, ArH), 3.39−3.33 (s, 1H, ArCH), 2.88
(dd, J = 7.5, 7.5 Hz, 1H, CH2), 2.25−2.21 (m, 1H, CH2, overlapped
with ArCH3), 2.22 (s, 3H, ArCH3), 1.25 (d, J = 7.0 Hz, 3H, CHCH3).
Elemental analysis calcd (%) for C11H12O2: C, 74.98; H, 6.86. Found:
C, 75.03; H, 6.80.
−
−
e
10
−
−
−
−
a
Reaction conditions: 5a (1.0 mmol), complex 1 (0.1 mol %), solvent
(2.0 mL), H2 (6 atm), 8 h, 60 °C. The yield was determined by GC
analysis, and n-tridecane was used as the internal standard. Reaction
b
c
d
at room temperature. [(p-cym)RuCl2]2 used as the catalyst.
Synthesis of Hydroxyindanone-imine Ligands L1−L4. The
mixture of 7-hydroxy-3,4-methylindan-1-one (1.0 mmol, 1.0 equiv),
corresponding aromatic amines (1.2 mmol, 1.1 equiv), and 4 Å
molecular sieves (0.1 g) in EtOH (10 mL) in a 25 mL Schlenk tube was
refluxed for 24 h. The reaction mixture was filtered, and the solvent was
removed under reduced pressure. Column chromatography of the
crude products (6:1 PE:EA) gave L1−L4 in good yields.
e
Without a catalyst.
Table 6. Scope of the Catalytic Hydrogenation of Quinoline
a,b
Derivatives
L1. Yellow solid; 81% isolated yield; 1H NMR (500 MHz, CDCl3) δ
8.19 (s, 1H, −OH), 7.38 (t, J = 7.7 Hz, 2H, ArH), 7.16−7.12 (m, 2H,
ArH), 7.03 (d, J = 7.5 Hz, 2H, ArH), 6.75 (d, J = 8.0 Hz, 1H, ArH),
3.47−3.44 (m, 1H, CH), 3.06 (dd, J = 7.5, 7.5 Hz, 1H, CH2), 2.40−2.37
(m, 1H, CH2), 2.29 (s, 3H, ArCH3), 1.27 (d, J = 7.0 Hz, 3H, CHCH3);
IR (KBr, disk) υ 3359 (υO−H), 2915 (υC−H), 1659 (υCN), 1023
(υC−O), 768 (υAr−H) cm−1. Elemental analysis calcd (%) for C17H17NO:
C, 81.24; H, 6.82; N, 5.57. Found: C, 81.32; H, 6.75; N, 5.66.
1
L2. Light yellow solid; 78% isolated yield; H NMR (500 MHz,
CDCl3) δ 8.19 (s, 1H, −OH), 7.19 (d, J = 8.0 Hz, 2H, ArH), 7.13 (d, J =
8.0 Hz, 1H, ArH), 6.95 (d, J = 8.0 Hz, 2H, ArH), 6.74 (d, J = 8.0 Hz, 1H,
ArH), 3.48−3.42 (m, 1H, CH), 3.10 (dd, J = 8.0, 8.0 Hz, 1H, CH2),
2.43−2.39 (m, 1H, CH2), 2.36 (s, 3H, ArCH3), 2.28 (s, 3H, ArCH3),
1.27 (d, J = 7.0 Hz, 3H, CHCH3); IR (KBr, disk) υ 3367 (υO−H), 2920
(υC−H), 1652 (υCN), 1018 (υC−O), 766 (υAr−H) cm−1. Elemental
analysis calcd (%) for C18H19NO: C, 81.47; H, 7.22; N, 5.28. Found: C,
81.41; H, 7.20; N, 5.37.
L3. Yellow solid; 72% isolated yield; 1H NMR (500 MHz, CDCl3) δ
8.19 (s, 1H, −OH), 7.34 (d, J = 8.5 Hz, 2H, ArH), 7.15 (d, J = 8.0 Hz,
1H, ArH), 6.97 (d, J = 9.0 Hz, 2H, ArH), 6.75 (d, J = 8.0 Hz, 1H, ArH),
3.49−3.43 (m, 1H, CH), 3.05 (dd, J = 8.0, 8.0 Hz, 1H, CH2), 2.38−2.34
(m, 1H, CH2), 2.29 (s, 3H, ArCH3), 1.28 (d, J = 7.0 Hz, 3H, CHCH3);
IR (KBr, disk) υ 3447 (υO−H), 2963 (υC−H), 1640 (υCN), 1080
(υC−O), 769 (υAr−H) cm−1. Elemental analysis calcd (%) for
C17H16ClNO: C, 71.45; H, 5.64; N, 4.90. Found: C, 71.52; H, 5.62;
N, 4.97.
a
Reaction conditions: quinolines (1.0 mmol), complex 1 (0.1 mol %),
b
CF3CH2OH (2.0 mL), H2 (6 atm), 8 h, 60 °C. The yield was
determined by GC analysis, and n-tridecane was used as the internal
standard.
L4. Yellow solid; 76% isolated yield; 1H NMR (500 MHz, CDCl3) δ
8.19 (s, 1H, −OH), 7.49 (d, J = 8.5 Hz, 2H, ArH), 7.15 (d, J = 8.0 Hz,
1H, ArH), 6.91 (d, J = 8.5 Hz, 2H, ArH), 6.75 (d, J = 8.0 Hz, 1H, ArH),
3.49−3.43 (m, 1H, CH), 3.05 (dd, J = 7.5, 7.5 Hz, 1H, CH2), 2.37−2.37
(m, 1H, CH2), 2.29 (s, 3H, ArCH3), 1.21 (d, J = 7.0 Hz, 3H, CHCH3);
IR (KBr, disk) υ 3403 (υO−H), 2960 (υC−H), 1643 (υCN), 1010
(υC−O), 761 (υAr−H) cm−1. Elemental analysis calcd (%) for
C17H16BrNO: C, 61.83; H, 4.88; N, 4.24. Found: C, 61.89; H, 4.93;
N, 4.15.
Synthesis of N,O-Chelate Half-Sandwich Ruthenium Com-
plexes 1−4. A mixture of [(p-cymene)RuCl2]2 (0.1 mmol, 0.5 equiv),
NaOAc (0.4 mmol, 2.0 equiv), and ligands L1−L4 (0.2 mmol, 1.0
equiv) was stirred at 60 °C in methanol (5 mL) for 6 h. The mixture was
atmosphere with a low catalyst loading, so the methodology for
the one-pot synthesis of tetrahydroquinoline derivatives has
been also developed, which combined the two reactions of
cyclization and hydrogenation together on the basis of the
continuous catalytic activity of the ruthenium catalyst in the
selective hydrogenation of quinolines. The stability, diverse
catalytic activity, and good efficiency made them attractive in
industrial applications.
G
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a
Table 7. One-Pot Synthesis of Tetrahydroquinoline Derivatives
a
Reaction conditions: aminobenzyl alcohols (1.0 mmol), ketones (1.1 mmol), CH3ONa (1.1 mmol), complex 1 (0.1 mol %), CF3CH2OH (2.0
b
mL), H2 (6 atm), 8 h, 60 °C. The yield was determined by GC analysis, and n-tridecane was used as the internal standard.
1
filtered and concentrated to give the crude products that were further
purified by silica gel column chromatography (6:1 CH2Cl2:EA) to
afford pure N,O-chelate half-sandwich ruthenium complexes.
2. Yellow brown solid; 58% isolated yield; H NMR (500 MHz,
CDCl3) δ 7.66−7.62 (m, ArH, 2H), 7.00 (d, J = 7.5 Hz, ArH, 2H), 6.75
(d, J = 7.5 Hz, ArH, 2H), 5.31 (d, J = 6.0 Hz, p-cymene-H, 1H), 5.18 (d,
J = 6.0 Hz, p-cymene-H, 1H), 5.10 (d, J = 6.0 Hz, p-cymene-H, 1H),
5.02 (d, J = 6.0 Hz, p-cymene-H, 1H), 3.17−3.09 (m, CHCH3, 1H),
2.90−2.85 [m, CH(CH3)2, 1H], 2.72−2.61 (m, CHCH2, 2H), 2.43 (s,
ArCH3, 3H), 2.09 (s, ArCH3, 3H), 1.69 (s, p-cymene-CH3, 3H), 1.40
(d, J = 7.5 Hz, 3H, CHCH3), 1.08 [d, J = 7.5 Hz, CH(CH3)2, 6H]; IR
1. Brown solid; 62% isolated yield; 1H NMR (500 MHz, CDCl3) δ
7.80 (d, J = 8.0 Hz, ArH, 1H), 7.51−7.45 (m, ArH, 2H), 7.32 (t, J = 7.5
Hz, ArH, 1H), 7.07−7.00 (m, ArH, 2H), 6.78 (d, J = 10.0 Hz, ArH,
1H), 5.32 (d, J = 6.0 Hz, p-cymene-H, 1H), 5.14−5.11 (m, p-cymene-
H, 2H), 5.04 (d, J = 6.0 Hz, p-cymene-H, 1H), 3.18−3.08 (m, CHCH3,
1H), 2.91−2.86 [m, CH(CH3)2, 1H], 2.71−2.61 (m, CHCH2, 2H),
2.09 (s, ArCH3, 3H), 1.68 (s, p-cymene-CH3, 3H), 1.45 (d, J = 7.5 Hz,
3H, CHCH3), 1.11 [d, J = 7.0 Hz, CH(CH3)2, 6H]; IR (KBr, disk) υ
2963 (υC−H), 1615 (υCN), 1015 (υC−O), 760 (υAr−H) cm−1. Elemental
analysis calcd (%) for C27H30ClNORu: C, 62.24; H, 5.80; N, 2.69.
Found: C, 62.18; H, 5.75; N, 2.79. MS (ESI, m/z): 486 [M − Cl]+.
(KBr, disk) υ 2965 (υC−H), 1612 (υCN), 1010 (υC−O), 768 (υAr−H
)
cm−1. Elemental analysis calcd (%) for C28H32ClNORu: C, 62.85; H,
6.03; N, 2.62. Found: C, 62.89; H, 6.10; N, 2.57. MS (ESI, m/z): 500
[M − Cl]+.
3. Brown solid; 54% isolated yield; 1H NMR (500 MHz, CDCl3) δ
7.45 (d, J = 7.5 Hz, ArH, 2H), 7.01 (d, J = 7.5 Hz, ArH, 2H), 6.75−6.73
(m, ArH, 2H), 5.33 (d, J = 6.0 Hz, p-cymene-H, 1H), 5.19 (d, J = 6.0
H
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Article
Hz, p-cymene-H, 1H), 5.10 (d, J = 6.0 Hz, p-cymene-H, 1H), 5.03 (d, J
= 6.0 Hz, p-cymene-H, 1H), 2.89−2.84 (m, CHCH3, 1H), 2.72−2.60
[m, CH(CH3)2 and CHCH2, 3H], 2.09 (s, ArCH3, 3H), 1.69 (s, p-
cymene-CH3, 3H), 1.21 (d, J = 7.5 Hz, 3H, CHCH3), 1.09 [d, J = 7.5
Hz, CH(CH3)2, 6H]; IR (KBr, disk) υ 2960 (υC−H), 1618 (υCN),
1019 (υC−O), 763 (υAr−H) cm−1. Elemental analysis calcd (%) for
C27H29Cl2NORu: C, 58.38; H, 5.26; N, 2.52. Found: C, 58.42; H, 5.25;
N, 2.60. MS (ESI, m/z): 520 [M − Cl]+.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c00955.
■
sı
1H NMR spectra of L1−L4 and ruthenium complexes 1−
4 and FT-IR spectra of the complex (PDF)
4. Brown solid; 59% isolated yield; 1H NMR (500 MHz, CDCl3) δ
7.60 (d, J = 7.5 Hz, ArH, 2H), 7.01 (d, J = 7.5 Hz, ArH, 2H), 6.77−6.73
(m, ArH, 2H), 5.33 (d, J = 6.0 Hz, p-cymene-H, 1H), 5.19 (d, J = 6.0
Hz, p-cymene-H, 1H), 5.10 (d, J = 6.0 Hz, p-cymene-H, 1H), 5.02 (d, J
= 6.0 Hz, p-cymene-H, 1H), 2.89−2.84 (m, CHCH3, 1H), 2.72−2.60
[m, CH(CH3)2 and CHCH2, 3H], 2.26 (s, ArCH3, 3H), 1.75 (s, p-
cymene-CH3, 3H), 1.51 (d, J = 7.5 Hz, 3H, CHCH3), 1.09 [d, J = 7.5
Hz, CH(CH3)2, 6H]; IR (KBr, disk) υ 2955 (υC−H), 1615 (υCN),
1021 (υC−O), 765 (υAr−H) cm−1. Elemental analysis calcd (%) for
C27H29ClBrNORu: C, 54.05; H, 4.87; N, 2.33. Found: C, 54.11; H,
4.82; N, 2.31. MS (ESI, m/z): 564 [M − Cl]+.
Accession Codes
CCDC 1966541−1966542 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Author
■
Zi-Jian Yao − School of Chemical and Environmental Engineering,
Shanghai Institute of Technology, Shanghai 201418, China;
State Key Laboratory of Structural Chemistry, Fujian Institute of
Research on the Structure of Matter, Chinese Academy of Sciences,
Fuzhou, Fujian 350002, China; orcid.org/0000-0003-
1833-1142; Phone: +86-21-60877231; Email: zjyao@
sit.edu.cn; Fax: +86-21-60873335
General Procedure for the Synthesis of Quinolines from
Amino Alcohols with Ketones. 2-Aminobenzyl alcohol (1.0 mmol),
ketone (1.1 mmol), CH3ONa (1.1 mmol), and complex 1 (0.001
mmol) were mixed in CH3OH (2 mL), and the mixture was stirred at
room temperature for 6 h. After the reaction, the mixture was diluted
with CH2Cl2 and washed with brine. Organic layers were combined,
dried over Na2SO4, filtered, and evaporated to give the crude products
that were further purified by silica gel column chromatography (5:1
PE:EA) to furnish pure products.
Authors
Xue-Jing Yun − School of Chemical and Environmental
Engineering, Shanghai Institute of Technology, Shanghai 201418,
China; State Key Laboratory of Transducer Technology,
Shanghai Institute of Microsystem and Information Technology,
Chinese Academy of Sciences, Shanghai 200050, China
Jing-Wei Zhu − School of Chemical and Environmental
Engineering, Shanghai Institute of Technology, Shanghai 201418,
China
Yan Jin − State Key Laboratory of Transducer Technology,
Shanghai Institute of Microsystem and Information Technology,
Chinese Academy of Sciences, Shanghai 200050, China; College
of Science, Shanghai Institute of Technology, Shanghai 201418,
China
General Procedure for the Synthesis of Quinolines from
Amino Alcohols with Secondary Alcohols. 2-Aminobenzyl alcohol
(1.0 mmol), secondary alcohol (1.1 mmol), CH3ONa (1.1 mmol), and
complex 1 (0.001 mmol) were mixed in CH3OH (3 mL), and the
mixture was refluxed for 3 h. After the reaction, the mixture was diluted
with CH2Cl2 and washed with brine. Organic layers were combined,
dried over Na2SO4, filtered, and evaporated to give the crude products
that were further purified by silica gel column chromatography (5:1
PE:EA) to furnish pure products.
General Procedure for the Hydrogenation of Quinolines. In a
typical run, quinoline (1.0 mmol), complex 1 (0.001 mol), and
CF3CH2OH (3 mL) were charged in a 5 mL vial. The vial was then
transferred to an autoclave. The autoclave was pressurized with H2 (6
atm) and disconnected from the H2 source. The autoclave was heated
to 60 °C. After the reaction, the resultant mixture was extracted with
diethyl ether (2 × 5 mL) and dried over anhydrous Na2SO4. The
organic solution was concentrated, and the residue was dissolved in
hexane and assessed by GC-MS.
Wei Deng − School of Chemical and Environmental Engineering,
Shanghai Institute of Technology, Shanghai 201418, China
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.inorgchem.0c00955
General Procedure for the One-Pot Synthesis of Tetrahy-
droquinolines. In a typical run, 2-aminobenzyl alcohol (1.0 mmol),
ketone (1.1 mmol), CH3ONa (1.1 mmol), complex 1 (0.001 mmol),
and CF3CH2OH (3 mL) were charged in a 5 mL vial. The vial was then
transferred into an autoclave. The autoclave was pressurized with H2 (6
atm) and disconnected from the H2 source. The autoclave was heated
to 60 °C. After the reaction, the mixture was extracted with diethyl ether
(2 × 5 mL) and dried over anhydrous Na2SO4. The organic solution
was concentrated, and the residue was dissolved in hexane and assessed
by GC-MS.
X-ray Crystallography. Diffraction data of the complex were
collected on a Bruker Smart APEX CCD diffractometer with graphite-
monochromated Mo Kα radiation (λ = 0.71073 Å). All of the data were
collected at room temperature, and the structure was determined by
direct methods and subsequently refined on F2 by using full-matrix
least-squares techniques (SHELXL).40 SADABS41 absorption correc-
tions were applied to the data; all non-hydrogen atoms were refined
anisotropically, and hydrogen atoms were located at calculated
positions. All calculations were performed using the Bruker program
Smart.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the National Natural Science
Foundation of China (21601125), the Chenguang Scholar of
Shanghai Municipal Education Commission (16CG64 and
18CG67), and the Shanghai Gaofeng & Gaoyuan Project for
University Academic Program Development.
REFERENCES
■
(1) (a) Han, Y.-F.; Jin, G.-X. Half-sandwich Iridium- and Rhodium-
based Organometallic Architectures: Rational Design, Synthesis,
Characterization, and Applications. Acc. Chem. Res. 2014, 47, 3571−
3579. (b) Sun, L.-Y.; An, Y.-Y.; Ma, L.-L.; Han, Y.-F. Single-Crystalline
Organoiridium Complex for Gas-Triggered Chromogenic Switches and
Its Applications on CO Detection and Reversible Scavenging. Chin. J.
Chem. 2019, 37, 763−768.
I
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Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
(2) Kumar, P.; Gupta, R. K.; Pandey, D. S. Half-sandwich arene
ruthenium complexes: synthetic strategies and relevance in catalysis.
Chem. Soc. Rev. 2014, 43, 707−733.
(3) Gichumbi, J. M.; Friedrich, H. B.; Omondi, B. Synthesis and
characterization of piano-stool ruthenium complexes with N, N′-
pyridine imine bidentate ligands and their application in styrene
oxidation. J. Organomet. Chem. 2016, 808, 87−96.
hydrogenation of ketones. Appl. Organomet. Chem. 2019, 33,
No. e5111.
(17) Małecki, J. G.; Kruszynski, R.; Jaworska, M.; Lodowski, P.;
Mazurak, Z. Synthesis, spectroscopic and electronic characterizations of
two half sandwich ruthenium(II) complexes with 2-(2′-hydroxyphen-
yl)-benzoxazole and 4-picolinic acid ligands. J. Organomet. Chem. 2008,
693, 1096−1108.
(18) (a) Huang, Y.-B.; Wang, Q.; Liang, J.; Wang, X.; Cao, R. Soluble
Metal-Nanoparticle Decorated Porous Coordination Polymers for the
Homogenization of Heterogeneous Catalysis. J. Am. Chem. Soc. 2016,
138, 10104−10107. (b) Huang, Y.; Liu, T.; Lin, J.; Lu, J.; Lin, Z.; Cao,
R. Homochiral Nickel Coordination Polymers Based on Salen(Ni)
Metalloligands: Synthesis, Structure, and Catalytic Alkene Epoxidation.
Inorg. Chem. 2011, 50, 2191−2198. (c) Huang, Y.-B.; Yu, W.-B.; Jin, G.-
X. Half-Sandwich Chromium(III) Catalysts Bearing Hydroxyindani-
mine Ligands for Ethylene Polymerization. Organometallics 2009, 28,
4170−4174.
(19) Nandhini, R.; Venkatachalam, G. Half-sandwich ruthenium(II)
complexes containing O, N bidentate azo ligands: Synthesis, structure
and their catalytic activity towards one-pot conversion of aldehydes to
primary amides and transfer hydrogenation of ketones. J. Organomet.
Chem. 2019, 895, 15−22.
(20) (a) Jiang, B.; Si, Y. Zn(II)-Mediated Alkynylation-Cyclization of
o-Trifluoroacetyl Anilines: One-Pot Synthesis of 4-Trifluoromethyl-
Substituted Quinoline Derivatives. J. Org. Chem. 2002, 67, 9449−9451.
(b) Linderman, R. J.; Kirollos, S. K. Regioselective synthesis of
trifluoromethyl substituted quinolines from trifluoroacetyl acetylenes.
Tetrahedron Lett. 1990, 31, 2689−2692.
(21) Chen, Y.-L.; Fang, K.-C.; Sheu, J.-Y.; Hsu, S.-L.; Tzeng, C.-C.
Synthesis and Antibacterial Evaluation of Certain Quinolone
Derivatives. J. Med. Chem. 2001, 44, 2374−2377.
(4) Mannancherril, V.; Therrien, B. Strategies toward the Enhanced
Permeability and Retention Effect by Increasing the Molecular Weight
of Arene Ruthenium Metallaassemblies. Inorg. Chem. 2018, 57, 3626−
3633.
(5) Betanzos-Lara, S.; Salassa, L.; Habtemariam, A.; Novakova, O.;
Pizarro, A. M.; Clarkson, G. J.; Liskova, B.; Brabec, V.; Sadler, P. J.
Photoactivatable Organometallic Pyridyl Ruthenium(II) Arene Com-
plexes. Organometallics 2012, 31, 3466−3479.
(6) Noyori, R.; Hashiguchi, S. Asymmetric Transfer Hydrogenation
Catalyzed by Chiral Ruthenium Complexes. Acc. Chem. Res. 1997, 30,
97−102.
(7) Yan, Y. K.; Melchart, M.; Habtemariam, A.; Sadler, P. J.
Organometallic chemistry, biology and medicine: ruthenium arene
anticancer complexes. Chem. Commun. 2005, 38, 4764−4776.
(8) Pike, R. D.; Sweigart, D. A. Electrophilic reactivity of coordinated
cyclic π-hydrocarbons. Coord. Chem. Rev. 1999, 187, 183−222.
(9) (a) Stubbs, J. M.; Hazlehurst, R. J.; Boyle, P. D.; Blacquiere, J. M.
Catalytic Acceptorless Dehydrogenation of Amines with Ru(PR2NR′2)
and Ru(dppp) Complexes. Organometallics 2017, 36, 1692−1698.
(b) Ma, L.-L.; An, Y.-Y.; Sun, L.-Y.; Wang, Y.-Y.; Hahn, F. E.; Han, Y.-F.
Supramolecular Control of Photocycloadditions in Solution: In Situ
Stereoselective Synthesis and Release of Cyclobutanes. Angew. Chem.,
Int. Ed. 2019, 58, 3986−3991. (c) Wang, L.-J.; Li, X.; Bai, S.; Wang, Y.-
Y.; Han, Y.-F. Self-Assembly, Structural Transformation, and Guest-
Binding Properties of Supramolecular Assemblies with Triangular
Metal-Metal Bonded Units. J. Am. Chem. Soc. 2020, 142, 2524−2531.
(d) Wang, Y.-S.; Feng, T.; Wang, Y.-Y.; Hahn, F. E.; Han, Y.-F. Homo-
and Heteroligand Poly-NHC Metal Assemblies: Synthesis by
Narcissistic and Social Self-Sorting. Angew. Chem., Int. Ed. 2018, 57,
15767−15771. (e) Li, Y.; Jin, G.-F.; An, Y.-Y.; Das, R.; Han, Y.-F. Metal-
Carbene-Templated Photochemistry in Solution: A Universal Route
towards Cyclobutane Derivatives. Chin. J. Chem. 2019, 37, 1147−1152.
(22) Jacob, J.; Jones, W. D. Selective Conversion of Diallylanilines and
Arylimines to Quinolines. J. Org. Chem. 2003, 68, 3563−3568.
(23) Michlik, S.; Kempe, R. A sustainable catalytic pyrrole synthesis.
Nat. Chem. 2013, 5, 140−144.
(24) Parua, S.; Sikari, R.; Sinha, S.; Das, S.; Chakraborty, G.; Paul, N.
D. A nickel catalyzed acceptorless dehydrogenative approach to
quinolines. Org. Biomol. Chem. 2018, 16, 274−284.
(25) Xu, X.; Zhang, X.; Liu, W.; Zhao, Q.; Wang, Z.; Yu, L.; Shi, F.
Synthesis of 2-substituted quinolines from alcohols. Tetrahedron Lett.
2015, 56, 3790−3792.
̈
(10) Malineni, J.; Keul, H.; Moller, M. A green and sustainable
phosphine-free NHC-ruthenium catalyst for selective oxidation of
alcohols to carboxylic acids in water. Dalton Trans. 2015, 44, 17409−
17414.
(26) Lee, S. Y.; Jeon, J.; Cheon, C.-H. Synthesis of 2-Substituted
Quinolines from 2-Aminostyryl Ketones Using Iodide as a Catalyst. J.
Org. Chem. 2018, 83 (9), 5177−5186.
(11) Kumar, K. N.; Venkatachalam, G.; Ramesh, R.; Liu, Y. Half-
sandwich para-cymene ruthenium(II) naphthylazophenolato com-
plexes: Synthesis, molecular structure, light emission, redox behavior
and catalytic oxidation properties. Polyhedron 2008, 27, 157−166.
(12) Gichumbi, J. M.; Friedrich, H. B.; Omondi, B. Synthesis and
characterization of piano-stool ruthenium complexes with N, N′-
pyridine imine bidentate ligands and their application in styrene
oxidation. J. Organomet. Chem. 2016, 808, 87−96.
(13) Azizi Talouki, S.; Grivani, G.; Crochet, P.; Cadierno, V. Half-
sandwich ruthenium(II) complexes with water-soluble Schiff base
ligands: Synthesis and catalytic activity in transfer hydrogenation of
carbonyl compounds. Inorg. Chim. Acta 2017, 456, 142−148.
(14) Gomez, J.; Garcıa-Herbosa, G.; Cuevas, J.; Arnaiz, A.; Carbayo,
A.; Munoz, A.; Falvello, L.; Fanwick, P. E. Diastereospecific and
Diastereoselective Syntheses of Ruthenium(II) Complexes Using N, N′
Bidentate Ligands Aryl-pyridin-2-ylmethyl-amine ArNH-CH2-2-
C5H4N and Their Oxidation to Imine Ligands. Inorg. Chem. 2006,
45, 2483−2493.
(27) Patil, T. N.; Raut, S. V. Cooperative Catalysis with Metal and
Secondary Amine: Synthesis of 2-Substituted Quinolines via Addition/
Cycloisomerization Cascade. J. Org. Chem. 2010, 75, 6961−6964.
(28) Cho, C. S.; Oh, B. H.; Kim, J. S.; Kim, T.-J.; Shim, S. C. Synthesis
of quinolines via ruthenium-catalysed amine exchange reaction
between anilines and trialkylamines. Chem. Commun. 2000, 1885−
1886.
́
(29) Martínez, R.; Ramon, D. J.; Yus, M. RuCl2(dmso)4 Catalyzes the
̈
Solvent-Free Indirect Friedlander Synthesis of Polysubstituted Quino-
lines from Alcohols. Eur. J. Org. Chem. 2007, 2007, 1599−1605.
(30) Vander Mierde, H.; Van Der Voort, P.; De Vos, D.; Verpoort, F.
̈
A Ruthenium-Catalyzed Approach to the Friedlander Quinoline
Synthesis. Eur. J. Org. Chem. 2008, 2008, 1625−1631.
(31) Srimani, D.; Ben-David, Y.; Milstein, D. Direct synthesis of
pyridines and quinolines by coupling of γ-amino-alcohols with
secondary alcohols liberating H2 catalyzed by ruthenium pincer
complexes. Chem. Commun. 2013, 49, 6632−6634.
(32) Pan, B.; Liu, B.; Yue, E.; Liu, Q.; Yang, X.; Wang, Z.; Sun, W.-H. A
Ruthenium Catalyst with Unprecedented Effectiveness for the
Coupling Cyclization of γ-Amino Alcohols and Secondary Alcohols.
ACS Catal. 2016, 6, 1247−1253.
(33) Cho, C.-S.; Kim, B. T.; Kim, T.-J.; Shim, S. C. Ruthenium-
catalysed oxidative cyclisation of 2-aminobenzyl alcohol with ketones:
modified Friedlaender quinoline synthesis. Chem. Commun. 2001,
2576−2577.
(15) Subramanian, M.; Sundar, S.; Rengan, R. Synthesis and structure
of arene ruthenium(II) complexes: One-pot catalytic approach to
synthesis of bioactive quinolines under mild conditions. Appl.
Organomet. Chem. 2018, 32, No. e4582.
(16) Satheesh, C. E.; Sathish Kumar, P. N.; Kumara, P. R.; Karvembu,
R.; Hosamani, A.; Nethaji, M. Half-sandwich Ru (II) complexes
containing (N, O) Schiff base ligands: Catalysts for base-free transfer
J
https://dx.doi.org/10.1021/acs.inorgchem.0c00955
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
(34) Motokura, K.; Mizugaki, T.; Ebitani, K.; Kaneda, K. Multifunc-
tional catalysis of a ruthenium-grafted hydrotalcite: one-pot synthesis of
quinolines from 2-aminobenzyl alcohol and various carbonyl
compounds via aerobic oxidation and aldol reaction. Tetrahedron
Lett. 2004, 45, 6029−6032.
(35) (a) Yao, Z.-J.; Li, K.; Li, P.; Deng, W. Mononuclear half-sandwich
iridium and rhodium complexes through C-H activation: Synthesis,
characterization and catalytic activity. J. Organomet. Chem. 2017, 846,
208−216. (b) Yao, Z.-J.; Zhu, J.-W.; Lin, N.; Qiao, X.-C.; Deng, W.
Catalytic hydrogenation of carbonyl and nitro compounds using an [N,
O]-chelate half-sandwich ruthenium catalyst. Dalton Trans. 2019, 48,
7158−7166.
(36) Yao, Z.-J.; Li, K.; Zhang, J.-Y.; Deng, W. [NO]- and [NN]-
coordination mode rhodium complexes based on a flexible ligand:
synthesis, reactivity and catalytic activity. New J. Chem. 2016, 40, 8753−
8759.
(37) Yao, Z.-J.; Lin, N.; Qiao, X.-C.; Zhu, J.-W.; Deng, W.
Cyclometalated Half-Sandwich Iridium Complex for Catalytic Hydro-
genation of Imines and Quinolines. Organometallics 2018, 37, 3883−
3892.
(38) (a) Wu, J.; Talwar, D.; Johnston, S.; Yan, M.; Xiao, J. L.
Acceptorless Dehydrogenation of Nitrogen Heterocycles with a
Versatile Iridium Catalyst. Angew. Chem., Int. Ed. 2013, 52, 6983−
6987. (b) Han, Y.-F.; Zhang, L.; Weng, L.-H.; Jin, G.-X. H2-Initiated
Reversible Switching Between Two-Dimensional Metallacycles and
Three-Dimensional Cylinders. J. Am. Chem. Soc. 2014, 136, 14608−
14615.
(39) Zhang, J.; An, Z.; Zhu, Y.; Shu, X.; Song, H.; Jiang, Y.; Wang, W.;
Xiang, X.; Xu, L.; He, J. Ni0/Niδ+ Synergistic Catalysis on a Nanosized
Ni Surface for Simultaneous Formation of C-C and C-N Bonds. ACS
Catal. 2016, 6, 1247−1253.
(40) Sheldrick, G. M. SHELXL-97, Program for the Refinement of
̈
̈
̈
Crystal Structures; Universitat Gottingen: Gottingen, Germany, 1997.
(41) Sheldrick, G. M. SADABS (2.01), Bruker/Siemens Area Detector
Absorption Correction Program; Bruker AXS: Madison, WI, 1998.
K
https://dx.doi.org/10.1021/acs.inorgchem.0c00955
Inorg. Chem. XXXX, XXX, XXX−XXX