NNN-Ruthenium Catalysts for the Synthesis of Pyridines, Quinolines, and Pyrroles by Acceptorless Dehydrogenative Condensation

Article abstract of DOI:10.1021/acs.organomet.8b00359

The bidentate ruthenium complex (HO-C₅H₃N-CO-C₅H₃N-C₅H₄N)Ru(CO)₂Cl₂ (2) could transform to a tridentate product (HO-C₅H₃N-CO-C₅H₃N-C₅H₄N)Ru(CO)Cl₂ (3), which further reacted with CH₃ONa in the presence of PPh₃ to convert to two complexes [(OC₅H₃N-CO-C₅H₃N-C₅H₄N)Ru(PPh₃)₂(CO)]Cl^- (4) and [(OC₅H₃N-CO-C₅H₃N-C₅H₄N)Ru(PPh₃)(CO)Cl] (5), via -OH deprotonation. The catalytic coupling cyclizations of secondary alcohols with amino alcohols were investigated, and complex 3 exhibited the highest activity. The coupling reactions proceeded in air with only 0.2 mol % catalyst loading and had a broad scope for the synthesis of pyridines, quinolones, and pyrroles.

Full text of DOI:10.1021/acs.organomet.8b00359

Article
Cite This: Organometallics XXXX, XXX, XXX−XXX
NNN-Ruthenium Catalysts for the Synthesis of Pyridines, Quinolines,
and Pyrroles by Acceptorless Dehydrogenative Condensation
Danfeng Deng, Bowen Hu, Min Yang, and Dafa Chen*
MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemical Engineering &
Technology, Harbin Institute of Technology, Harbin 150001, People’s Republic of China
S
* Supporting Information
ABSTRACT: The bidentate ruthenium complex (HO-C5H3N-CO-
C5H3N-C5H4N)Ru(CO)2Cl2 (2) could transform to a tridentate product
(HO-C5H3N-CO-C5H3N-C5H4N)Ru(CO)Cl2 (3), which further reacted
with CH3ONa in the presence of PPh3 to convert to two complexes
[(OC5H3N-CO-C5H3N-C5H4N)Ru(PPh3)2(CO)]Cl− (4) and
[(OC5H3N-CO-C5H3N-C5H4N)Ru(PPh3)(CO)Cl] (5), via −OH de-
protonation. The catalytic coupling cyclizations of secondary alcohols
with amino alcohols were investigated, and complex 3 exhibited the
highest activity. The coupling reactions proceeded in air with only 0.2
mol % catalyst loading and had a broad scope for the synthesis of
pyridines, quinolones, and pyrroles.
with such a moiety, which were mainly applied to the transfer
hydrogenation of ketones.17 As an extension, we herein report
new types of NNN-ruthenium complexes with a 2-hydroxypyr-
idyl fragment showing high catalytic efficiency for the synthesis
of pyridines, quinolones, and pyrroles; notably, the catalytic
reactions could be carried out in air.
INTRODUCTION
■
The synthesis of N-heterocycles has drawn wide attention, as
their motifs are applied in pharmaceuticals, dyes, and functional
materials.1 Nevertheless, classical approaches to these N-
heterocycles still suffer from deficiencies like scarcity of the
raw materials, complexity of the reaction steps and harsh
reaction conditions. From a green chemistry perspective, atom
economical, environment-friendly and effective methodologies
for synthesizing N-heterocycles are in urgent demand.
In recent years, the hydrogen autotransfer (HA) or borrowing
hydrogen (BH) reaction has become an elegant protocol for the
coupling of C−C and C−N bonds, which generates only water
as a byproduct.1d,2 Acceptorless dehydrogenation condensation
(ADC), which is mechanistically related to the HA/BH reaction,
enables the synthesis of aromatic N-heterocycles from
secondary alcohols with amino alcohols.3−15 For instance, the
groups of Kempe,4 Milstein,5 Saito,6 Beller,7 Sun,8 Yu,9 and
others10 reported efficient Ru- and Ir-catalyzed coupling
cyclization, and a series of pyridines, pyrroles, and quinolones
were synthesized. However, most of their catalysts were
synthesized on the basis of air-sensitive phosphine ligands. In
recent years, a few noble-metal-free catalysts, such as Fe,11 Mn,12
Cu,13 Co,14 and Ni15 complexes, were also developed for the
synthesis of N-heterocycles, while high catalyst loading (2−10
mol %) and long reaction time (16−24 h) were almost
inevitable. Therefore, it is still significative to explore the
relatively low cost ruthenium complexes with nonphosphine
ligands as the catalysts for such transformations.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of the Ligand and
Complexes. As shown in Scheme 1, ligand 1 was obtained by
the reaction of HBr (40% in water) with (6-methoxypyridin-2-
yl)(6-(pyridin-2-yl)pyridin-2-yl)methanone at reflux for 3 h in
Scheme 1. Synthesis of 1−3
Recently, Kundu and co-workers reported several NNN-Ru
complexes with a 2-hydroxypyridyl moiety for the synthesis of
N-alkylated amines and quinolones under an N2 atomsphere.16
In addition, over the past few years, our group has also designed
a range of ruthenium complexes bearing NNN tridentate ligands
Received: May 28, 2018
© XXXX American Chemical Society
A
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81% yield. When 1 was treated with [Ru(CO)2Cl2]n in refluxing
THF for 24 h, the yellow bidentate NN-Ru complex 2 was
isolated in 72% yield. The 1H NMR spectrum of 2 in d6-DMSO
shows nine signals between 9.24 and 6.86 ppm for its aromatic
protons. The IR spectrum of 2 exhibits two strong CO
absorptions at 2060 and 1998 cm−1 with equal intensity.
In refluxing xylene, 2 further transformed into the red complex
3, accompanied by the release of one molecule of CO (Scheme
1). 3 could be obtained by the reaction of 1 with [Ru(CO)2Cl2]n
in refluxing xylene as well. The IR spectrum of 3 reveals a CO
peak at 1965 cm−1.
trans Cl atoms, and one CO group coordinating with Ru(1).
The Ru(1)−N(1), Ru(1)−N(2), and Ru(1)−N(3) distances
are 2.053(3), 2.078(3), and 2.120(3) Å, respectively, com-
parable to those in complex 2.
Treatment of 3 with CH3ONa in the presence of PPh3 in
1
methanol generated complex 4 (Scheme 2). The H NMR
spectrum of 4 exhibits 40 protons at 9.62−6.85 ppm, suggesting
the existence of two PPh3 groups. A singlet at 28.9 ppm is
appeared in its 31P NMR, indicating the trans configuration of
the PPh3 groups. The IR spectroscopy analysis shows one CO
band at 1967 cm−1. From these data, the structure of 4 was
regarded as an ionic pincer complex with one Cl− anion.
One of the PPh3 groups could be replaced by a Cl− anion
when complex 4 was heated in refluxing toluene, generating
product 5 (Scheme 2). From the 1H NMR spectrum, there are
only 25 protons in 5, demonstrating one less PPh3 group in
comparison to 4. Together with the IR absorption (1958 cm−1
for one CO), 5 was concluded to be a neutral complex with a
Ru−Cl bond.
The molecular structures of 2 (Figure 1) and 3 (Figure 2)
were further confirmed by X-ray crystallography. The central Ru
The molecular structures of 4 (Figure 3) and 5 (Figure 4)
were also confirmed by X-ray crystallography. Complex 4 shows
a trans configuration of the PPh3 groups, and the P(1)−Ru(1)−
P(2) angle is 176.40°, consistent with its NMR data. The C−O
distances in the pyridonate groups (1.248(7) Å for 4 and
1.252(2) Å for 5) are consistent with CO double bonds,
indicating that the −OH group in 3 was deprotonated in the
presence of CH3ONa.
Catalysis. To find the optimal conditions for the synthesis of
N-heterocycles, the reaction of 3-aminobutan-1-ol with 1-
phenylethanol was selected as the model reaction (Table 1, top).
t-BuOK and complex 3 were chosen as the base and precatalyst,
respectively. The base amount and the ratio of amino alcohol to
secondary alcohol were explored first. Solvent and catalyst
amounts were also tested in the same way (for details see the
Supporting Information). The conditions for entry 2 in Table 1
were selected as the optimal conditions (2 mmol of 3-
aminobutan-1-ol, 4 mmol of 1-phenylethanol, 3 mmol of t-
BuOK, 3 mL of toluene, and 0.2 mol % of complex 3 for 6 h in
the air). It is worth noting that, when the amount of catalyst 3
was increased from 0.2% to 0.4%, an unstable unknown
byproduct which has not been identified appeared, decreasing
the yield from 84% to 70% (Table S4, entry 4).4b,8 Next,
complexes 2−5 were tested as catalysts and complex 3 showed
the best efficiency (Table 1, entries 1−4). Parts of the excess 1-
phenylethanol were dehydrogenated to the acetophenone
(Table 1, entry 2). Different bases were also explored, and t-
BuOK was the most suitable one, indicating that a stronger base
should be beneficial for the desired product (Table 1, entries 5−
8). The N2 atmosphere had almost no influence on the reaction
(Table 1, entry 9).
On the basis of the results above, various γ-amino alcohols
with secondary alcohols were tested for their reactivity (Table
2). When 1-phenylethanol was chosen as the secondary alcohol,
the corresponding pyridine and quinolone derivatives were
isolated in high yields, such as 80% for 2-methyl-6-phenyl-
pyridine (Table 2, entry 1), 87% for 2,6-diphenylpyridine (Table
2, entry 6), and 89% for 2-phenylquinoline (Table 2, entry 11).
An electron-donating group at the para position of 1-
phenylethanol increased the activity slightly (Table 2, entries
3, 8, and 13), while an electron-withdrawing group decreased
the yields notably (Table 2, entries 2, 7, and 12).4e 1-
Phenylpropanol was also tested for the reaction, and the yields
decreased slightly owing to steric hindrance (Table 2, entries 5,
Figure 1. Molecular structure of complex 2. Hydrogen atoms and
solvents have been omitted for clarity. Selected bond distances (Å) and
angles (deg): Ru(1)−N(1), 2.112(2); Ru(1)−N(2), 2.149(2);
Ru(1)−Cl(1), 2.3786(10); Ru(1)−Cl(2), 2.3811(9); Ru(1)−C(17),
1.876(3); Ru(1)−C(18), 1.895(4); N(1)−Ru(1)−C(17),
179.56(14); N(2)−Ru(1)−C(18), 171.41(11); Cl(1)−Ru(1)−
Cl(2), 172.79(3).
Figure 2. Molecular structure of complex 3. Hydrogen atoms have been
omitted for clarity. Selected bond distances (Å) and angles (deg):
Ru(1)−N(1), 2.053(3); Ru(1)−N(2), 2.078(3); Ru(1)−N(3),
2.120(3); Ru(1)−Cl(1), 2.4190(11); Ru(1)−Cl(2), 2.4076(10);
Ru(1)−C(17), 1.873(5); C(16)−O(1), 1.327(5); N(2)−Ru(1)−
C(17), 172.67(16); N(1)−Ru(1)−N(3), 169.63(13); Cl(1)−
Ru(1)−Cl(2), 173.27(4).
atoms of both complexes are in octahedral coordination
environments. In complex 2, Ru(1) is coordinated with two
pyridyl groups, two CO groups, and two Cl atoms. The two Cl
atoms are trans to each other, while the two CO groups are in cis
geometry, consistent with its IR data. The N(1)−Ru(1)−
C(17), N(2)−Ru(1)−C(18) and Cl(1)−Ru(1)−Cl(2) angles
are 179.56, 171.41, and 172.79°, respectively, implying their
almost linear arrangement. Different from complex 2, 3 is a
pincer type ruthenium complex, with three pyridyl rings, two
B
DOI: 10.1021/acs.organomet.8b00359
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Scheme 2. Synthesis of 4 and 5
Table 1. Optimization of Reaction Conditions for the
a
Synthesis of 2-Methyl-6-phenylpyridine
b
entry
Cat.
base
yield (%)
1
2
3
4
5
6
7
8
9
2
3
4
5
3
3
3
3
3
t-BuOK
t-BuOK
t-BuOK
t-BuOK
NaOH
K2CO3
NaOMe
KOH
64
84
59
67
72
0
c
Figure 3. Molecular structure of complex 4. Hydrogen atoms, phenyl
rings on PPh3 ligands, and solvents have been omitted for clarity.
Selected bond distances (Å) and angles (deg): Ru(1)−N(1), 2.081(4);
Ru(1)−N(2), 2.092(4); Ru(1)−N(3), 2.107(4); Ru(1)−P(1),
2.4572(13); Ru(1)−P(2), 2.4043(13); Ru(1)−C(17), 1.869(5);
C(1)−O(1), 1.248(7); N(2)−Ru(1)−C(17), 172.60(2); N(1)−
Ru(1)−N(3), 169.21(17); P(1)−Ru(1)−P(2), 176.40(5).
57
75
d
t-BuOK
85
a
Conditions unless specified otherwise: amino alcohol (2 mmol),
secondary alcohol (4 mmol), base (3 mmol), toluene (3 mL), air,
catalyst (0.2 mol %), 110 °C, 6 h. Yields determined by GC analysis
by using dodecane as the internal standard. The ratio of 1-
b
c
phenylethanol, acetophenone, and 2-methyl-6-phenylpridine is about
d
7:3:10 in the resulting mixture. The reaction was carried out under
an N2 atmosphere.
corresponding ketone transformed from the secondary alcohol,
and no pyrrole derivative was detected (Table 3, entries 10−12).
The reaction mechanism of our work might be consistent with
relevant literature reports (Scheme 3).4a,5a,b,8,10 First, the
secondary alcohol is functionalized by the catalyst to form the
corresponding ketone with loss of a molecule of hydrogen. Then
the amine group of the amino alcohol attacks the ketone to
generate an imine intermediate, after which a second hydrogen
is lost. Due to the promotion of base, C−C coupling occurs, and
the resulting cyclized intermediate dissociates water and
hydrogen to give the final product.
Figure 4. Molecular structure of complex 5. Hydrogen atoms and
phenyl rings on the PPh3 ligand have been omitted for clarity. Selected
bond distances (Å) and angles (deg): Ru(1)−N(1), 2.0666(14);
Ru(1)−N(2), 2.0892(14); Ru(1)−N(3), 2.1036(14); Ru(1)−P(1),
2.2959(5); Ru(1)−Cl(1), 2.4464(5); Ru(1)−C(17), 1.8672(18);
C(16)−O(1), 1.252(2); N(2)−Ru(1)−C(17), 171.33(7); N(1)−
Ru(1)−N(3), 167.55(6); P(1)−Ru(1)−Cl(1), 178.165(17).
CONCLUSIONS
■
In summary, four ruthenium complexes bearing NNN ligands
with a 2-hydroxypyridyl or 2-pyridonate fragment have been
synthesized and were applied to the synthesis of pyridines,
quinolones, and pyrroles via an ADC mechanism. These
bifunctional NNN-Ru complexes, especially complex 3, are
efficient for such transformations. It is also worth noting that
these one-step, environmentally benign, and atom-economical
ADC reactions were carried out in air. Our current work
provides alternative methods for the synthesis of N-heterocycles,
and other experimental studies are ongoing to explore more
active transition-metal catalysts.
10, and 14). In addition, secondary alcohols with only alkyl
substituents were also suitable for this reaction, and the products
were obtained in good yields (Table 2, entries 4 and 9).
In addition, the reactions of β-amino alcohols with secondary
alcohols were conducted, and a series of pyrrole derivatives were
obtained (Table 3). Similarly, 1-phenylethanol and 1-(4-
methoxyphenyl)ethanol reacted well with 2-amino-1-butanol
and 2-amino-3-methyl-1-pentanol, respectively (Table 3, entries
1, 3, 5, and 7), while 1-(4-chlorophenyl)ethanol gave moderate
yields (Table 3, entries 2 and 6). 1-Phenylpropanol and 2-
heptanol were also not as good as 1-phenylethanol (Table 3,
entries 4, 8, and 9). However, when 2-amino-2-phenylethanol
was selected as the β-amino alcohol, the major product was the
EXPERIMENTAL SECTION
■
All of the manipulations were carried out under an atmosphere of dry
nitrogen using vacuum-line and oven-dried standard Schlenk
techniques if not mentioned otherwise. All solvents were dried from
C
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a
Table 2. Synthesis of Pyridines and Quinolones Using Various γ-Amino Alcohols and Secondary Alcohols
a
Conditions: amino alcohol (2 mmol), secondary alcohol (4 mmol), t-BuOK (3 mmol), toluene (3 mL), air, catalyst (0.2 mol %), 110 °C, 6 h.
b
Yields of isolated product.
18
the appropriate drying agents under N2 before use. All reagents were
obtained from commercial suppliers and used without further
purification, with the exception of [Ru(CO)2Cl2]n and (6-
methoxypyridin-2-yl)(6-(pyridin-2-yl)pyridin-2-yl)methanone,17b
D
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a
Table 3. Synthesis of Pyrroles Using Various β-Amino Alcohols and Secondary Alcohols
a
Conditions: amino alcohol (2 mmol), secondary alcohol (4 mmol), t-BuOK (3 mmol), toluene (3 mL), air, catalyst (0.2 mol %), 110 °C, 12 h.
b
c
Yields of isolated product. Yields determined by GC analysis by using dodecane as the internal standard.
which were synthesized by the methods reported in the literature. The
High-resolution mass spectra (HR-MS) were recorded on a Varian 7.0
T FTICR-MS instrument by the ESI technique. IR spectra were
recorded on a Nicolet iS5 FT-IR spectrometer. For single-crystal X-ray
diffraction, suitable crystals were placed in a cooled N2 stream at 173(2)
K on an SuperNova X-ray single-crystal diffractometer (complexes 2−
4) or a Bruker D8 Quest X-ray diffractometer (complex 5). Data
collections were performed using four-circle κ diffractometers equipped
with CCD detectors. Data were reduced and then corrected for
1H, 31P, and 13C NMR spectra were recorded on a Bruker Avance 400
1
spectrometer. The H NMR chemical shifts were referenced to the
residual solvent as determined relative to Me4Si (δ 0 ppm). The
31P{1H} chemical shifts were reported in ppm relative to external 85%
H3PO4. The 13C{1H} chemical shifts were reported in ppm relative to
the carbon resonance of CDCl3 (77.0 ppm) or d6-DMSO (39.5 ppm).
Elemental analyses were performed on a PerkinElmer 240C analyzer.
E
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Scheme 3. Plausible Mechanism of Formation of Aromatic N-Heterocycles
absorption.19 Solution, refinement, and geometrical calculations for all
crystal structures were performed with SHELXTL.20 All of the GC
measurements were performed on Agilent GC7890A equipment using
an Agilent 19091B-102 (25 m, 220 μm) column.
Synthesis of 4. CH3ONa (0.045 g, 0.84 mmol) was added to a
solution of 3 (0.200 g, 0.42 mmol) and PPh3 (0.219 g, 0.84 mmol) in
dried methanol (10 mL) with stirring, and this mixture was then
refluxed for 3 h. After the mixture was cooled to room temperature, the
precipitate was collected, washed with ether, and dried under vacuum to
provide 4 as a red powder (0.350 g, 86%). Single crystals suitable for X-
ray crystallographic determination were grown with CH2Cl2/n-hexane
at ambient temperature. Mp: 232 °C. Anal. Calcd for
C53H40ClN3O3P2Ru: C, 65.94; H, 4.18; N, 4.35. Found: C, 65.82; H,
Synthesis of 1. A solution of (6-methoxypyridin-2-yl)(6-(pyridin-
2-yl)pyridin-2-yl)methanone (2.70 g, 9.28 mmol) in 15 mL of HBr
(40% in water) was heated at reflux for 3 h. After it was cooled to room
temperature, the yellow solution was neutralized by slow addition of a
saturated aqueous solution of NaOH. The aqueous solution was
extracted with CH2Cl2 (3 × 100 mL). The combined organic extracts
were dried over Na2SO4, filtered, and concentrated to afford 1 as a
yellow solid (2.20 g, 81%). Mp: 193 °C. HR-MS (ESI): calcd for
C16H11N3O2 + H, 278.0929; found, 278.0931. 1H NMR (400 MHz, d6-
DMSO, ppm): 11.82 (s, 1H), 8.76 (d, J = 4.4 Hz, 1H), 8.67 (d, J = 7.6
Hz, 1H), 8.30 (d, J = 8.0 Hz, 1H), 8.24 (t, J = 8 Hz, 1H), 8.10 (d, J = 7.6
Hz, 1H), 8.01 (t, J = 7.6 Hz, 1H), 7.71−7.67 (m,, 1H), 7.55−7.51 (m,
1H), 7.27 (d, J = 6.8 Hz, 1H), 6.77 (d, J = 8.4 Hz, 1H). 13C NMR (100
MHz, d6-DMSO, ppm): 181.5, 162.0, 155.5, 154.3, 152.8, 149.5, 139.8,
139.7, 138.9, 137.6, 127.7, 125.3, 125.1, 124.7, 121.3, 113.2.
Synthesis of 2. A solution of 1 (1.00 g, 3.61 mmol) and
[Ru(CO)2Cl2]n (0.823 g, 3.61 mmol) in dried THF (150 mL) was
refluxed with stirring for 24 h. The mixture was cooled to room
temperature, and the yellow precipitate was collected, washed with
ether, and dried under vacuum to provide 2 (1.31 g, 72%). Single
crystals suitable for X-ray crystallographic determination were grown
with CH2Cl2/CH3OH/n-hexane at ambient temperature. Mp: 224 °C.
Anal. Calcd for C18H11Cl2N3O4Ru: C, 42.79; H, 2.19; N, 8.32. Found:
C, 42.63; H, 2.34; N, 8.24. IR (νCO, KBr, cm−1): 2060 (s), 1998 (s). 1H
NMR (400 MHz, d6-DMSO, ppm): 11.95 (s, 1H), 9.24 (d, J = 5.2 Hz,
1H), 8.98 (d, J = 8 Hz, 1H), 8.90 (d, J = 8.4 Hz, 1H), 8.54 (t, J = 8 Hz,
1H), 8.42 (t, J = 7.2 Hz, 1H), 8.14 (d, J = 8 Hz, 1H), 7.90 (t, J = 6 Hz,
1H), 7.65 (t, J = 5.6 Hz, 1H), 6.86 (d, J = 9.2 Hz, 2H).
Synthesis of 3. Method a. A solution of 2 (0.507 g, 1.00 mmol) in
xylene (30 mL) was refluxed with stirring for 24 h. The mixture was
cooled to room temperature, and the brick red precipitate was collected,
washed with ether, and dried under vacuum to provide 3 (0.455 g,
90%). Single crystals suitable for X-ray crystallographic determination
were grown with CH2Cl2/CH3OH/n-hexane at ambient temperature.
Mp: 228 °C. Anal. Calcd for C17H11Cl2N3O3Ru: C, 42.78; H, 2.32; N,
8.80. Found: C, 42.74; H, 2.50; N, 8.74. IR (νCO, KBr, cm−1): 1965 (s).
1H NMR (400 MHz, d6-DMSO, ppm): 11.42 (s, 1H), 9.32 (d, J = 5.6
Hz, 1H), 8.91 (d, J = 7.6 Hz, 1H), 8.77 (d, J = 8.0 Hz, 1H), 8.44 (t, J =
8.0 Hz, 1H), 8.32 (t, J = 7.6 Hz, 1H), 8.14 (m, 2H), 7.85 (t, J = 6.8 Hz,
1H), 7.73 (d, J = 7.2 Hz, 1H), 7.30 (d, J = 8.4 Hz, 1H),.
Method b. A solution of 1 (1.00 g, 3.61 mmol) and [Ru(CO)2Cl2]n
(0.823 g, 3.61 mmol) in xylene (100 mL) was refluxed with stirring for
24 h. The mixture was cooled to room temperature, and the brick red
precipitate was collected, washed with ether, and dried under vacuum to
provide 3 (1.38 g, 80%).
1
4.31; N, 4.34. IR (νCO, KBr, cm−1): 1967 (s). H NMR (400 MHz,
CDCl3, ppm): 9.62 (d, J = 8.4 Hz, 1H), 9.46 (d, J = 7.6 Hz, 1H), 8.35−
8.28 (m, 2H), 8.11 (d, J = 7.6 Hz, 1H), 7.96 (t, J = 7.2 Hz, 1H), 7.35 (t, J
= 7.2 Hz, 6H), 7.13−6.99 (m, 15H), 6.91−6.85 (m, 13H). 31P NMR
(162 MHz, CDCl3, ppm): 28.95.
Synthesis of 5. Method a. A solution of 4 (0.200 g, 0.21 mmol) was
refluxed for 3 h in toluene. After the mixture was cooled to room
temperature, the precipitate was collected, washed with ether, and dried
under vacuum to provide 5 as a red powder (0.120 g, 82%). Single
crystals suitable for X-ray crystallographic determination were grown
with CH3OH/diethyl ether at ambient temperature. Mp: 229 °C. Anal.
Calcd for C35H25ClN3O3PRu: C, 59.79; H, 3.58; N, 5.98. Found: C,
59.77; H, 3.74; N, 5.97. IR (νCO, KBr, cm−1): 1958 (s). 1H NMR (400
MHz, CDCl3, ppm): 8.58 (br s, 1H), 8.48 (d, J = 4.8 Hz, 1H), 8.33 (br s,
1H), 8.15 (t, J = 8.0 Hz, 1H), 7.89 (d, J = 8.0 Hz, 1H), 7.76 (t, J = 7.6
Hz, 1H), 7.73−7.00 (m, 19H). 31P NMR (162 MHz, CDCl3, ppm):
48.71.
Method b. CH3ONa (0.023 g, 0.42 mmol) was added to a solution of
3 (0.200 g, 0.42 mmol) and PPh3 (0.109 g, 0.42 mmol) in dried toluene
(20 mL) with stirring, and this mixture was then refluxed for 12 h. The
mixture was cooled to room temperature, and the organic phase was
evaporated under vacuum. The crude product was purified by column
chromatography on silica gel to provide 5 as a red powder (0.150 g,
51%).
General Procedure for the Synthesis of Substituted
Pyridines, Quinolones, and Pyrroles. In air, the secondary alcohol
(4.0 mmol), amino alcohol (2.0 mmol), complex 3 (2 mg, 0.004
mmol), t-BuOK (0.336g, 3 mmol), and 3 mL of toluene were mixed and
stirred at 110 °C. After 6 or 12 h, the reaction mixture was cooled to
room temperature and 0.1 mL was sampled and immediately diluted
with 5 mL of CH2Cl2 precooled to 0 °C for GC analysis to calculate the
conversation and product selectivity of the reaction. After the reaction
was completed, the reaction mixture was condensed under reduced
pressure and subjected to purification by flash silica gel column
chromatography to afford the target product, which was identified by
NMR analyses. All analytical data of the known compounds are
consistent with those reported in the literature.
2-Methyl-6-phenylpyridine.8 1H NMR (400 MHz, CDCl3, ppm):
8.02 (d, J = 7.6 Hz, 2H), 7.65 (t, J = 7.6 Hz, 1H), 7.54 (d, J = 7.6 Hz,
1H), 7.50 (t, J = 7.2 Hz, 2H), 7.43 (t, J = 7.6 Hz, 1H), 7.12 (d, J = 7.6
F
DOI: 10.1021/acs.organomet.8b00359
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Hz, 1H), 2.67 (s, 3H). 13C NMR (100 MHz, CDCl3, ppm): 158.4,
157.0, 139.8, 136.9, 128.7, 127.0, 121.6, 117.6, 24.7.
= 7.2 Hz, 1H), 6.48 (t, J = 2.8 Hz, 1H), 6.04 (t, J = 2.8 Hz, 1H), 2.74 (q,
J = 7.6 Hz, 2H), 1.34 (t, J = 7.6 Hz, 3H). 13C NMR (100 MHz, CDCl3,
ppm): 135.7, 133.1, 130.6, 128.8, 125.7, 123.4, 106.3, 106.0, 21.0, 13.6.
2-Ethyl-5-(4-methoxyphenyl)-1H-pyrrole.12b 1H NMR (400 MHz,
CDCl3, ppm): 8.07 (s, 1H), 7.40 (d, J = 8.8 Hz, 2H), 6.93 (d, J = 12.8
Hz, 2H), 6.33 (t, J = 3.2 Hz, 1H), 6.00 (t, J = 2.8 Hz, 1H), 3.85 (s, 3H),
2.71 (q, J = 7.6 Hz, 2H), 1.32 (t, J = 7.6 Hz, 3H). 13C NMR (100 MHz,
CDCl3, ppm): 157.9, 134.9, 130.6, 126.2, 124.9, 114.3, 105.9, 104.8,
55.3, 21.0, 13.7.
2-Methyl-6-(4-chlorophenyl)pyridine.21 1H NMR (400 MHz,
CDCl3, ppm): 7.96 (d, J = 8.8 Hz, 2H), 7.65 (t, J = 7.6 Hz, 1H),
7.51 (d, J = 7.6 Hz, 1H), 7.45 (d, J = 8.4 Hz, 2H), 7.13 (d, J = 7.6 Hz,
1H), 2.65 (s, 3H). 13C NMR (100 MHz, CDCl3, ppm): 158.5, 155.6,
138.1, 137.1, 134.9, 128.8, 128.3, 121.9, 117.4, 24.7.
2-Methyl-6-(4-methoxyphenyl)pyridine.22 1H NMR (400 MHz,
CDCl3, ppm): 7.98 (d, J = 8.8 Hz, 2H), 7.62 (t, J = 7.6 Hz, 1H), 7.48 (d,
J = 8.0 Hz, 1H), 7.06 (d, J = 7.6 Hz, 2H), 7.01 (d, J = 9.2 Hz, 2H), 3.88
(s, 3H), 2.64 (s, 3H). 13C NMR (100 MHz, CDCl3, ppm): 160.4, 158.1,
156.6, 136.9, 132.3, 128.3, 120.9, 116.9, 114.1, 55.4, 24.7.
2-Methyl-6-pentylpyridine.23 1H NMR (400 MHz, CDCl3, ppm):
7.49 (t, J = 7.6 Hz, 1H), 6.98 (d, J = 2.8 Hz, 1H), 6.96 (d, J = 2.8 Hz,
1H), 2.77 (t, J = 8.0 Hz, 2H), 2.55 (s, 3H), 1.74 (m, 2H), 1.35 (m, 4H),
0.93 (m, 3H). 13C NMR (100 MHz, CDCl3, ppm): 161.9, 157.6, 136.5,
120.4, 119.5, 38.5, 31.7, 29.9, 24.5, 22.6, 14.0.
5-Ethyl-3-methyl-2-phenyl-1H-pyrrole.9 1H NMR (400 MHz,
CDCl3, ppm): 7.87 (s, 1H), 7.45−7.42 (m, 4H), 7.28−7.25 (m, 1H),
5.93 (s, 1H), 2.71 (q, J = 7.6 Hz, 2H), 2.323 (s, 3H), 1.342 (t, J = 7.6 Hz,
3H). 13C NMR (100 MHz, CDCl3, ppm): 134.0, 133.9, 128.7, 126.6,
126.0, 125.5, 116.3, 108.6, 20.9, 13.6, 12.6.
2-(1-Methylpropyl)-5-phenyl-1H-pyrrole.14a 1H NMR (400 MHz,
CDCl3, ppm): 8.22 (s, 1H), 7.55 (d, J = 8.0 Hz, 2H), 7.44 (t, J = 7.6 Hz,
2H), 7.27 (t, J = 7.0 Hz, 1H), 6.56 (t, J = 3.2 Hz, 1H), 6.11 (t, J = 3.2 Hz,
1H), 2.87−2.78 (m, 1H), 1.85−1.65 (m, 2H), 1.40 (d, J = 7.2 Hz, 3H),
1.05 (t, J = 7.6 Hz, 3H). 13C NMR (100 MHz, CDCl3, ppm): 139.4,
133.2, 130.4, 128.9, 125.7, 123.5, 106.0, 105.8, 34.6, 30.4, 20.2, 12.0.
2-(1-Methylpropyl)-5-(4-chlorophenyl)-1H-pyrrole. 1H NMR (400
MHz, CDCl3, ppm): 8.09 (s, 1H), 7.41−7.32 (m, 4H), 6.45 (t, J = 3.2
Hz, 1H), 6.02 (t, J = 3.2 Hz, 1H), 2.80−2.71 (m, 1H), 1.78−1.58 (m,
2H), 1.33 (d, J = 7.2 Hz, 3H), 0.97 (t, J = 7.6 Hz, 3H). 13C NMR (100
MHz, CDCl3, ppm): 139.7, 131.6, 131.0, 129.2, 128.9, 124.5, 106.5,
106.0, 34.5, 30.3, 20.1, 11.9. HR-MS (ESI): calcd for C14H16ClN + H,
234.7445; found, 234.7441.
3,6-Dimethyl-2-phenylpyridine.24 1H NMR (400 MHz, CDCl3,
ppm): 7.54−7.37 (m, 6H), 7.07 (d, J = 7.6 Hz, 1H), 2.66 (s, 3H), 2.31
(s, 3H). 13C NMR (100 MHz, CDCl3, ppm): 157.9, 155.3, 140.7, 138.9,
128.9, 127.9, 127.5, 121.8, 24.1, 19.5.
2,6-Diphenylpyridine.9 1H NMR (400 MHz, CDCl3, ppm): 8.25 (d,
J = 6.8 Hz, 4H), 7.86−7.82 (m, 1H), 7.74 (d, J = 8.4 Hz, 2H), 7.60−
7.49 (m, 6H). 13C NMR (100 MHz, CDCl3, ppm): 156.9, 139.6, 137.5,
129.1, 128.8, 127.1, 118.7.
2-(4-Chlorophenyl)-6-phenylpyridine.25 1H NMR (400 MHz,
CDCl3, ppm): 8.18−8.12 (m, 4H), 7.84 (t, J = 7.6 Hz, 1H), 7.74−
7.67 (m, 2H), 7.56−7.46 (m, 5H). 13C NMR (100 MHz, CDCl3, ppm):
157.0, 155.6, 139.2, 137.8, 137.7, 135.1, 129.2, 128.9, 128.8, 128.3,
127.0, 119.0, 118.4.
2-(1-Methylpropyl)-5-(4-methoxyphenyl)-1H-pyrrole. 1H NMR
(400 MHz, CDCl3, ppm): 8.05 (s, 1H), 7.41 (d, J = 8.8 Hz, 2H),
6.94 (d, J = 8.8 Hz, 2H), 6.35 (t, J = 3.2 Hz, 1H), 6.00 (t, J = 2.8 Hz,
1H), 3.86 (s, 3H), 2.80−2.71 (m, 1H), 1.74−1.61 (m, 2H), 1.33 (d, J =
7.2 Hz, 3H), 0.98 (t, J = 7.6 Hz, 3H). 13C NMR (100 MHz, CDCl3,
ppm): 157.9, 138.5, 130.3, 126.3, 124.9, 114.3, 105.4, 104.7, 55.3, 34.4,
30.3, 20.1, 11.9. HR-MS (ESI): calcd for C15H19NO + H, 230.3254;
found, 230.3256.
2-(4-Methoxyphenyl)-6-phenylpyridine.13 1H NMR (400 MHz,
CDCl3, ppm): 8.16 (t, J = 8.8 Hz, 4H), 7.81 (t, J = 8.0 Hz, 1H), 7.67 (d,
J = 7.2 Hz, 2H), 7.53 (t, J = 7.2 Hz, 2H), 7.46 (t, J = 7.2 Hz, 1H), 7.05
(d, J = 8.8 Hz, 2H), 3.908 (s, 3H). 13C NMR (100 MHz, CDCl3, ppm):
160.6, 156.7, 156.5, 139.4, 137.5, 132.0, 129.0, 128.7, 128.4, 127.1,
118.1, 114.1, 55.4.
2-(1-Methylpropyl)-3-methyl-5-phenyl-1H-pyrrole. 1H NMR (400
MHz, CDCl3, ppm): 7.82 (s, 1H), 7.44−7.38 (m, 4H), 7.24−7.20 (m,
1H), 5.88 (d, J = 3.2 Hz, 1H), 2.74−2.66 (m, 1H), 2.28 (s, 3H), 1.75−
1.54 (m, 2H), 1.30 (d, J = 7.2 Hz, 3H), 0.96 (t, J = 7.6 Hz, 3H). 13C
NMR (100 MHz, CDCl3, ppm): 137.6, 134.0, 128.6, 126.3, 125.9,
125.4, 116.1, 108.0, 34.3, 30.2, 20.0, 12.6, 11.9. HR-MS (ESI): calcd for
C15H19N + H, 214.3260; found, 214.3255.
2-Pentyl-6-phenylpyridine.5a 1H NMR (400 MHz, CDCl3, ppm):
8.03 (d, J = 7.2 Hz, 2H), 7.67 (t, J = 7.9 Hz, 1H), 7.55 (d, J = 8.0 Hz,
1H), 7.49 (t, J = 7.2 Hz, 2H), 7.42 (t, J = 7.2 Hz, 1H), 7.11 (d, J = 7.6
Hz, 1H), 2.89 (t, J = 7.6 Hz, 2H), 1.88−1.80 (m, 2H), 1.44−1.29 (m,
4H), 0.97−0.90 (m, 3H). 13C NMR (100 MHz, CDCl3, ppm): 162.4,
156.7, 136.9, 128.7, 128.6, 127.1, 121.0, 117.8, 38.4, 31.7, 29.5, 22.6,
14.1.
2-(1-Methylpropyl)-5-pentyl-1H-pyrrole. 1H NMR (400 MHz,
CDCl3, ppm): 7.66 (s, 1H), 5.85 (d, J = 2.8 Hz, 2H), 2.74−2.65 (m,
1H), 2.61 (d, J = 7.6 Hz, 2H), 1.73−1.55 (m, 4H), 1.43−1.39 (m, 4H),
1.30 (d, J = 6.8 Hz, 3H), 0.99−0.95 (m, 6H). 13C NMR (100 MHz,
CDCl3, ppm): 136.2, 131.1, 104.3, 103.3, 34.3, 31.7, 30.3, 29.4, 27.9,
22.5, 20.0, 14.1, 11.9. HR-MS (ESI): calcd for C13H23N + H, 194.3364;
found, 194.3361.
2,6-Diphenyl-3-methylpyridine.26 1H NMR (400 MHz, CDCl3,
ppm): 8.11 (d, J = 7.6 Hz, 2H), 8.01 (d, J = 7.2 Hz, 1H), 7.68 (d, J = 5.2
Hz, 2H), 7.53−7.43 (m, 7H), 2.44 (s, 3H). 13C NMR (100 MHz,
CDCl3, ppm): 158.2, 154.6, 141.0, 139.4, 139.3, 132.9, 129.3, 129.2,
128.6, 128.6, 128.5, 128.0, 126.9, 118.7, 19.9.
2-Phenylquinoline.8 1H NMR (400 MHz, CDCl3, ppm): 8.26−8.19
(m, 4H), 7.91 (d, J = 8.4 Hz, 1H), 7.86 (d, J = 8.0 Hz, 1H), 7.76 (t, J =
8.4 Hz, 1H), 7.59−7.48 (m, 4H). 13C NMR (100 MHz, CDCl3, ppm):
157.4, 148.2, 139.6, 136.9, 129.7, 129.6, 129.4, 128.9, 127.6, 127.5,
127.2, 126.3, 119.0.
4-Methoxyacetophenone.28 1H NMR (400 MHz, CDCl3, ppm):
7.93 (d, J = 8.8 Hz, 2H), 6.92 (d, J = 9.2 Hz, 2H), 3.85 (s, 3H), 2.54 (s,
3H). 13C NMR (100 MHz, CDCl3, ppm): 196.8, 163.5, 130.6, 113.7,
55.4, 26.3.
2-(4-Chlorophenyl)quinolone.13 1H NMR (400 MHz, CDCl3,
ppm): 8.25 (d, J = 8.8 Hz, 1H), 8.20−8.14 (m, 3H), 7.87−7.84 (m,
2H), 7.76 (t, J = 6.8 Hz, 1H), 7.58−7.51 (m, 3H). 13C NMR (100 MHz,
CDCl3, ppm): 156.0, 148.1, 137.9, 137.1, 135.6, 129.9, 129.6, 128.9,
127.5, 127.2, 126.6, 118.6.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00359.
2-(4-Methoxyphenyl)quinolone.13 1H NMR (400 MHz, CDCl3,
ppm): 8.18 (d, J = 8.8 Hz, 1H), 7.86−7.81 (m, 2H), 7.74 (t, J = 8.4 Hz,
1H), 7.52 (t, J = 8.0 Hz, 1H), 7.08 (d, J = 8.8 Hz, 2H), 3.91 (s, 3H). 13C
NMR (100 MHz, CDCl3, ppm): 160.9, 156.9, 148.3, 136.7, 132.2,
129.6, 129.5, 128.9, 127.5, 126.9, 125.9, 118.5, 114.3, 55.4.
3-Methyl-2-phenylquinolone.27 1H NMR (400 MHz, CDCl3,
ppm): 8.19 (d, J = 8.0 Hz, 1H), 8.06 (s, 1H), 7.82 (d, J = 8.0 Hz,
1H), 7.70 (t, J = 8.0 Hz, 1H), 7.62 (d, J = 8.0 Hz, 2H), 7.57−7.45 (m,
4H), 2.50 (s, 3H). 13C NMR (100 MHz, CDCl3, ppm): 160.3, 137.2,
129.3, 129.0, 128.9, 128.4, 128.3, 127.6, 126.7, 126.6, 20.6.
2-Ethyl-5-phenyl-1H-pyrrole.9 1H NMR (400 MHz, CDCl3, ppm):
8.18 (s, 1H), 7.49 (d, J = 7.2 Hz, 2H), 7.39 (t, J = 7.6 Hz, 2H), 7.21 (t, J
Crystallographic details for complexes 2−5, screening
reactions, and IR and NMR spectra of the new
compounds (PDF)
Accession Codes
CCDC 1845517−1845520 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-
G
DOI: 10.1021/acs.organomet.8b00359
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bridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Author
*E-mail for D. C.: dafachen@hit.edu.cn.
■
ORCID
Dafa Chen: 0000-0002-7650-4024
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
■
This work was supported by the National Natural Science
Foundation of China (No. 21672045), the China Postdoctoral
Science Foundation (2016M591519), the Heilongjiang Post-
doctoral Foundation (LBH-Z16069), and the National Natural
Science Foundation of Heilongjiang (Nos. B2018005 and
LC2018005).
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DOI: 10.1021/acs.organomet.8b00359
Organometallics XXXX, XXX, XXX−XXX