Nickel-Catalyzed Sonogashira Coupling Reactions of Nonactivated Alkyl Chlorides under Mild Conditions

Article abstract of DOI:10.1021/acs.organomet.0c00793

The two nickel chlorides1and2with [P,S] and [P,Se] bidentate ligands, respectively, were synthesized and used as catalysts for Sonogashira coupling reaction. Both1and2are efficient catalysts for Sonogashira C(sp³)-C(sp) coupling reactions. Comp

Full text of DOI:10.1021/acs.organomet.0c00793

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Nickel-Catalyzed Sonogashira Coupling Reactions of Nonactivated
Alkyl Chlorides under Mild Conditions
Qingqing Fan, Hongjian Sun, Shangqing Xie, Yanhong Dong, Xiaoyan Li,* Olaf Fuhr, and Dieter Fenske
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ABSTRACT: The two nickel chlorides 1 and 2 with [P,S] and [P,Se] bidentate ligands, respectively, were synthesized and used as
catalysts for Sonogashira coupling reaction. Both 1 and 2 are efficient catalysts for Sonogashira C(sp3)−C(sp) coupling reactions.
Complex 1 has better catalytic activity than complex 2. In a combination of 1 mol % catalyst loading of 1 and CuI/Cs2CO3/DMSO
at 25 °C for the coupling reactions of alkyl iodides with terminal alkynes, the corresponding coupling products were obtained in
moderate to excellent yields. This catalytic system is also suitable for alkyl bromides at 40 °C. It must be pointed out that with NaI as
an additive complex 1 could effectively catalyze the C(sp3)−C(sp) coupling of nonactivated alkyl chlorides with alkynes under mild
conditions (50 °C) with low catalyst loading (1 mol %). Complex 1 is easy to synthesize and has efficient catalytic activity, especially
for alkyl chlorides, under mild conditions.
addition of a C(sp3)−X bond of haloalkanes is very difficult;
INTRODUCTION
■
on the other hand, β-H elimination can easily occur.5
The formation of carbon−carbon bonds is the core of organic
chemistry.1 Traditionally, carbon−carbon bond coupling
mainly includes Heck, Suzuki, Kumada, Negishi, and
Therefore, it is challenging to synthesize functionalized
alkynes by C(sp3)−C(sp) coupling reactions. In 2003, Fu
disclosed for the first time a Pd/Cu-catalyzed C(sp3)−C(sp)
coupling reaction between primary bromo- or iodoalkanes and
alkynes.6 Glorius studied the first case of a Pd/Cu-catalyzed
C(sp3)−C(sp) coupling reaction between secondary bromoal-
kanes and alkynes.7 In comparison with palladium, nickel in
the same group is cheaper and less toxic. Therefore, the
Sonogashira coupling reaction catalyzed by nickel complexes
has gradually become the focus of chemists. In comparison
with the palladium catalyst system, nickel as a catalyst for
Sonogashira coupling is rare. In 2009, Hu realized the
C(sp3)−C(sp) coupling reaction of nonactivated haloalkanes
Sonogashira reactions. Through these reactions, C(sp2)−
C(sp2), C(sp3)−C(sp2), or C(sp2)−C(sp) coupling can be
realized. In comparison with other coupling reactions, the
Sonongashira coupling reaction has its own unique character-
istics, among which alkynes with various functions can be
constructed. Various functionalized alkynes are not only
important structural units of drug molecules, natural products,
and organic materials2 but also important intermediates in
organic synthesis.3 The transition-metal-catalyzed Sonogashira
coupling reaction is one of the important methods to
construct functional alkynes. Ever since the palladium-
catalyzed C(sp2)−C(sp) coupling reaction was first reported
by Heck, Cassar, and Sonogashira in 1975,4 the palladium-
catalyzed Sonogashira coupling reaction has attracted more
and more attention from scientists. There have been many
reports on the synthesis of alkynes by C(sp2)−C(sp) coupling
reactions, but there are few examples of alkynes synthesized
by C(sp3)−C(sp) coupling between haloalkanes and alkynes.
This is mainly because, on the one hand, the oxidative
Special Issue: Organometallic Solutions to Challenges
in Cross-Coupling
Received: December 21, 2020
https://dx.doi.org/10.1021/acs.organomet.0c00793
© XXXX American Chemical Society
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A

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Scheme 1. Nickel-Catalyzed Sonogashira Coupling Reactions
catalyzed by an [NNN] pincer nickel complex. This system
not only is suitable for iodoalkanes and bromoalkanes but also
has high catalytic yield for chloroalkanes at 140 °C (Scheme
1a).8 Our group reported that [CNN] pincer nickel
complexes could be used as catalysts for C(sp3)−C(sp)
coupling reactions and had a good catalytic effect for
secondary haloalkanes at 100 °C (Scheme 1b).9 This indicates
that the activation of a C−Cl bond needs higher reaction
temperature (>100 °C). Some other nickel catalysts are only
suitable for iodoalkenes and bromoalkanes and are not
suitable for chloroalkanes.10,11 Therefore, C(sp3)−C(sp)
coupling reactions between chlorinated alkanes and alkynes
under mild conditions need to be further explored. In
addition, most of the nickel catalysts used for Sonogashira
coupling reactions are pincer nickel complexes, while nickel
chelate complexes are rarely used. In comparison with pincer
complexes, chelate complexes are simple and easy to obtain.
As we know, [P,O]-chelate nickel complexes have been
successfully used in the SHOP process.12 Because O and S are
chalcogenide elements, we explored the [P,S] chelate system
and studied the interaction between the [P,S]-chelate nickel
hydrides and alkynes.13 We also found that the [P,S]-chelate
iron hydrides have good catalytic effects on the hydrosilylation
of aldehydes and ketones.14 Therefore, as a continuation of
our research work in this direction, we have synthesized [P,Y]
(Y = S, Se) chelate nickel complexes 1 and 2 and used them
to catalyze C(sp3)−C(sp) coupling reactions. Under mild
conditions (25−50 °C), complexes 1 and 2 could catalyze not
only the coupling reactions of iodoalkanes and bromoalkanes
but also the coupling reactions of chloroalkanes in high yields
with a low catalyst loading (Scheme 1c).
Scheme 2. Synthesis of Nickel Chlorides 1 and 2
single-crystal X-ray diffraction analysis confirmed that complex
1 has a distorted-square-planar structure with the Ni atom in
the center (Figure 1). The two coordinated P atoms are in
trans positions. Complex 2 has the spectroscopic and
structural characteristics similar to those of 1. Both 1 and 2
in the solid state are air-stable, but 1 is not stable at room
temperature in solution and transforms gradually into a bis-
chelated nickel complex.13b
RESULTS AND DISCUSSION
■
The nickel complex 1 or 2 was prepared from the reaction of
2-(diphenylphosphanyl)benzenethiol (L1) or 2-
(diphenylphosphanyl)benzeneselenol (L2) with
NiCl2(PMe3)2 in THF in a yield of 70% or 64%, respectively
(Scheme 2).15,16 In the 31P NMR spectrum of complex 1 a
signal for the −PPh2 group is situated at 48.95 ppm while the
resonance of PMe3 ligand is registered at −14.74 ppm. A
Figure 1. Molecular structure of complex 1. Thermal ellipsoids are
drawn at the 50% probability level. Hydrogen atoms have been
omitted for clarity. Selected bond lengths (Å) and angles (deg):
Ni1−Cl1 2.19(8), Ni1−S1 2.14 (9), Ni1−P1 2.17(9), Ni1−P2
2.21(9); Cl1−Ni1−S1 174.9(4), P1−Ni1−P2 179.3(4), Cl−Ni1−P1
90.1(3), P1−Ni1−S1 89.2(3), P2−Ni1−Cl1 90.3(4), S1−Ni1−P2
90.5(4).
B
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a
Table 1. Optimization for Sonogashira Coupling Reaction
b
c
entry
catalyst
loading (mol %)
base (1.5 equiv)
solvent
temp (°C)
time (h)
conversn (%)
yield (%)
1
2
3
4
5
6
7
8
1
1
1
1
2
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
K2CO3
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
dioxane
PhMe
CH2Cl2
Et2O
THF
CH3CN
DME
DMF
50
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
2
2
3
4
4
4
4
12
4
4
4
4
4
4
4
4
4
4
4
4
4
4
95
87
97
99
87
58
47
73
75
23
52
30
51
27
63
53
57
68
52
78
0
91
83
92
92
82
51
42
69
72
19
47
26
47
23
58
48
52
62
47
73
0
1
0.5
0.5
0.5
1
1
1
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Na2CO3
tBuOK
1
tBuONa
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
1
1
1
1
1
1
1
1
DMSO
DMSO
d
1
1
0
0
a
Reaction conditions unless specified otherwise: phenylacetylene (1.0 mmol), 1-iodooctane (1.1 mmol), base (1.5 mmol), and CuI (0.05 mmol) in
b
c
d
solvent (2.5 mL). Determined by GC with n-dodecane as an internal standard (1.0 mmol). Isolated yields. Without CuI.
Using phenylacetylene and 1-iodooctane as template
substrates with complex 1 or 2 as the catalyst, the reaction
conditions of Sonogashira coupling were investigated (Table
1). When the catalyst loading was 1 mol % with Cs2CO3 as a
base, 5 mol % CuI as a cocatalyst, and DMSO as the solvent
at 50 °C, 95% conversion could be achieved in 2 h (entry 1,
Table 1). When the temperature was reduced to 25 °C, 87%
conversion could be achieved in 2 h and the complete
conversion was finished in 4 h (entries 2−4, Table 1).
According to entries 5−7 in Table 1, the catalytic effect of
complex 1 is better than that of complex 2. When the amount
of complex 1 was reduced to 0.5 mol %, the conversion could
only reach 73% even when the reaction time was prolonged to
12 h (entry 8, Table 1). In comparison with other bases, such
as K2CO3, Na2CO3, tBuOK, and tBuONa, the conversion with
Cs2CO3 is the highest (entries 4 and 9−12, Table 1). In
comparison with other solvents, such as dioxane, PhMe,
CH2Cl2, Et2O, THF, CH3CN, DME, and DMF, the best
reaction medium for the catalytic system is DMSO (entries 4
and 13−20, Table 1). It can be seen that the greater the
polarity of the solvent, the higher the catalytic efficiency of the
system. The control experiments showed that the catalytic
reaction could not take place without complex 1 or CuI
(entries 21 and 22, Table 1). Therefore, it can be speculated
that the catalytic system is a complex 1/CuI synergetic
catalytic system, and Cu plays the role of a cocatalyst in the
catalytic system. Finally, we chose catalyst 1 as the catalyst (1
mol %), 150 mol % of Cs2CO3 as the base, 5 mol % CuI as
the cocatalyst, and DMSO as the solvent at 25 °C for 4 h as
the optimized conditions (entry 4, Table 1) to expand the
scope of the substrates.
For iodinated alkanes, the isolated yields could reach 88−
92% under the optimized reaction conditions (Table 2). The
reaction of 2-ethynylpyridine with 1-iodooctane provided the
C(sp3)−C(sp) coupling product in 88% yield. At 25 °C, the
catalytic yields with bromoalkanes are not as good as those
with iodoalkanes. When the reaction temperature was raised
to 40 °C and the reaction time was extended to 8 h, the
isolated yields with brominated substrates were 68−94%.
Under more demanding conditions (50 °C, 12 h) with the
addition of NaI, the catalytic effect with chloroalkane
substrates could reach 49−97% isolated yields. No matter
whether there was an electron-donating group (−OMe) or
electron-withdrawing group (−Cl) in the para position of the
phenyl ring, the substrates could achieve complete conversion.
For both secondary and tertiary chloroalkanes, the yields were
good. This catalytic system is also tolerant toward amino,
hydroxyl, and ester groups. For the aliphatic alkynes the yields
are relatively low (19−47%). In ccomparison with the
previously reported pincer nickel compexes,8−11 this catalytic
system has the following advantages: complex 1 is easy to
synthesize and has efficient catalytic activity with a lower
catalyst loading, especially for alkyl chlorides, under mild
conditions.
The gram-scale reaction between phenylacetylene and 1-
chlorooctane using 1 mol % of catalyst 1 could be smoothly
carried out to give rise to octylphenylacetylene (2a) in 91%
yield (Scheme 3).
C
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a
Table 2. Scope of Alkynes and Alkyl Halides
a
Reaction conditions for X = I: alkynes (1.0 mmol), alkyl iodides (1.1 mmol), Cs2CO3 (1.5 mmol), CuI (0.05 mmol), and 1 (0.01 mmol) in 2.5
mL of DMSO, 4 h, 25 °C. Isolated yields. Reaction conditions for X = Br: alkynes (1.0 mmol), alkyl bromides (1.1 mmol), Cs2CO3 (1.5 mmol),
CuI (0.05 mmol), and 1 (0.01 mmol) in 2.5 mL of DMSO, 8 h, 40 °C. Isolated yields. Reaction conditions for X = Cl: alkynes (1.0 mmol), alkyl
chlorides (1.1 mmol), Cs2CO3 (1.5 mmol), CuI (0.05 mmol), NaI (0.2 mmol), and 1 (0.01 mmol) in 2.5 mL of DMSO, 12 h, 50 °C. Isolated
yields.
Scheme 3. Gram-Scale Reaction of Phenylacetylene with 1-Chlorooctane
D
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were added. In the case of alkyl chloride, NaI (0.03 g, 0.2 mmol) was
added. The catalytic mixture was stirred for 4 h at room temperature
for alkyl iodide and heated for 8 h at 40 °C for alkyl bromide and for
12 h at 50 °C for alkyl chloride. After the reaction the solution was
cooled to room temperature and quenched with 15 mL of water and
1 mL of 1 mol/L HCl. The mixture was extracted with Et2O (3 × 20
mL), and a moderate amount of anhydrous Na2SO4 was added to the
extraction solution. The product could be obtained by flash
chromatography on silica gel.
X-ray Crystal Structure Determination. Intensity data and cell
parameters were recorded on a Stoe StadiVari diffractometer,
employing Ga Kα radiation (λ = 1.34143 Å). The structures were
solved using the charge-flipping algorithm, as implemented in the
program SUPERFLIP,18 and refined by full-matrix least-squares
techniques against F2 using the SHELXL19 program through the
OLEX220 interface. All non-hydrogen atoms were refined anisotropi-
cally, and all hydrogen atoms except for those of the disordered
solvent molecules were placed using AFIX instructions. Appropriate
restraints or constraints were applied to the geometry and the atomic
displacement parameters of the atoms. CCDC 1865451 (complex 1)
contains supplementary crystallographic data for this paper.
CONCLUSIONS
■
In conclusion, we have synthesized the [P,S]-chelated nickel
chloride 1 and the [P,Se]-chelated nickel chloride 2. The
structures of complexes 1 and 2 were confirmed by IR, NMR,
and single crystal X-ray diffraction analysis. Both complexes
could catalyze the Sonagashira C(sp3)−C(sp) coupling
reactions, but the catalytic effect of complex 1 is better than
that of complex 2. The reaction temperature is mild, and the
yields for both secondary and tertiary alkyl halides could reach
from above medium to an excellent level. Especially, complex
1 has a good catalytic effect on chloroalkanes under mild
conditions (50 °C) with low catalyst loading (1 mol %).
EXPERIMENTAL SECTION
■
General Considerations. All experiments and manipulations
were performed under a N2 atmosphere utilizing the standard
Schlenk techniques. THF, n-pentane, diethyl ether, toluene, and
dioxane were dried and freshly distilled by Na-benzophenone before
use under a nitrogen atmosphere. DMSO, DMF, DME, CH2Cl2, and
CH3CN were dried through molecular sieves. NiCl2(PMe3)2,17 L1,
and L2 were synthesized according to the literature methods.15,16
Alkynes and alkyl halides were purchased and used without further
purification. Melting points (mp) were measured on a WRR
instrument with samples sealed in capillaries. Infrared spectra
(4000−400 cm−1) were recorded on a a Bruker ALPHA Fourier
transform infrared (FT-IR) instrument from Nujol mulls between
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.0c00793.
■
sı
Spectroscopic data for complexes 1 and 2 and
characterization data for the catalytic products (PDF)
1
KBr disks. The H, 31P, and 13C NMR spectra were recorded with a
300 MHz Bruker instrument. Gas chromatography (GC) was carried
out with a Fuli 9790 spectrometer and performed with n-dodecane as
an internal standard.
Accession Codes
CCDC 1865451 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
Synthesis of Complex 1. A solution of ligand L1 (1.00 g, 3.40
mmol) in THF (35 mL) was mixed slowly with a solution of
NiCl2(PMe3)2 (1.10 g, 3.74 mmol) in THF (35 mL) at −78 °C
under a N2 atmosphere. The reaction solution was warmed to room
temperature and stirred overnight, and the red solution gradually
turned brown-yellow. After removal of the volatiles under vacuum,
the brown-yellow residue was extracted with n-pentane and diethyl
ether and filtered through Celite. Complex 1 (1.10 g) was obtained
as square brown-yellow crystals from diethyl ether in 70% yield at
−10 °C. Anal. Calcd for C21H23ClNiP2S (463.57 g mol−1): C, 54.41;
H, 5.00. Found: C, 54.00; H, 5.11. Mp: >195 °C. IR (Nujol mull,
KBr, cm−1): 951 (PMe3). 31P NMR (121 MHz, C6D6, 298 K, ppm):
δ 48.95 (d, J = 346 Hz, 1P, PPh2), −14.74 (d, J = 346 Hz, 1P,
AUTHOR INFORMATION
Corresponding Author
■
Xiaoyan Li − School of Chemistry and Chemical Engineering,
Key Laboratory of Special Functional Aggregated Materials,
Ministry of Education, Shandong University, 250100 Jinan,
People’s Republic of China; orcid.org/0000-0003-0997-
0380; Email: xli63@sdu.edu.cn
1
PMe3). H NMR (300 MHz, C6D6, 298 K, ppm): δ 7.74−7.28 (m,
11H, Ar-H), 7.11−6.83 (m, 3H, Ar-H), 1.34 (d, 9H, PCH3). 13C
NMR (75 MHz, C6D6, 298 K, ppm): δ 133.9, 133.7, 133.2, 132.0,
131.4, 130.3, 128.5, 128.3, 128.1, 127.8, 127.5, 29.9, 12.7, 12.4.
Synthesis of Complex 2. A solution of ligand L2 (1.00 g, 2.93
mmol) in THF (35 mL) was mixed slowly with a solution of
NiCl2(PMe3)2 (0.91 g, 3.22 mmol) in THF (35 mL) at −78 °C
under a N2 atmosphere. The reaction solution was warmed to room
temperature and stirred overnight, and the red solution gradually
turned brown-yellow. After removal of the volatiles under vacuum,
the brown-yellow residue was extracted with n-pentane and diethyl
ether and filtered through Celite. Complex 2 (0.96 g) was obtained
as square brown-yellow crystals from diethyl ether in 64% yield at
−10 °C. Anal. Calcd for C21H23ClNiP2Se (510.47 g mol−1): C,
49.41; H, 4.54. Found: C, 49.12; H, 4.72. Mp: >183 °C. IR (Nujol
mull, KBr, cm−1): 954 (PMe3). 31P NMR (121 MHz, C6D6, 298 K,
ppm): δ 54.79 (d, J = 276 Hz, 1P, PPh2), −16.11 (d, J = 290 Hz, 1P,
Authors
Qingqing Fan − School of Chemistry and Chemical
Engineering, Key Laboratory of Special Functional
Aggregated Materials, Ministry of Education, Shandong
University, 250100 Jinan, People’s Republic of China
Hongjian Sun − School of Chemistry and Chemical
Engineering, Key Laboratory of Special Functional
Aggregated Materials, Ministry of Education, Shandong
University, 250100 Jinan, People’s Republic of China;
orcid.org/0000-0003-1237-3771
Shangqing Xie − School of Chemistry and Chemical
Engineering, Key Laboratory of Special Functional
Aggregated Materials, Ministry of Education, Shandong
University, 250100 Jinan, People’s Republic of China
Yanhong Dong − School of Chemistry and Chemical
Engineering, Key Laboratory of Special Functional
Aggregated Materials, Ministry of Education, Shandong
University, 250100 Jinan, People’s Republic of China
1
PMe3). H NMR (300 MHz, C6D6, 298 K, ppm): δ 8.09−7.86 (m,
5H, Ar-H), 7.26−6.75(m, 9H, Ar-H), 1.08 (d, 9H, PCH3). 13C NMR
(75 MHz, C6D6, 298 K, ppm): δ 133.9, 133.7, 133.2, 132.0, 131.4,
130.3, 128.5, 128.3, 128.1, 127.8, 127.5, 29.9, 12.7, 12.4.
General Procedure for Sonogashira Coupling Reactions. A
25 mL dried Schlenk tube containing Cs2CO3 (0.49 g, 1.5 mmol)
and CuI (0.01 g, 0.05 mmol) was purged with N2, and alkyne (1.0
mmol), alkyl halide (1.1 mmol) and anhydrous solvent (2.5 mL)
Olaf Fuhr − Institut fur Nanotechnologie (INT) und
̈
Karlsruher Nano-Micro-Facility (KNMF), Karlsruher
E
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̈
Leopoldshafen, Germany
Dieter Fenske − Institut fu
Karlsruher Nano-Micro-Facility (KNMF), Karlsruher
Institut fur Technologie (KIT), 76344 Eggenstein-
̈
r Nanotechnologie (INT) und
̈
Leopoldshafen, Germany
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.organomet.0c00793
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We gratefully acknowledge the support by the natural science
foundation of Shandong province (ZR2019ZD46/
ZR2019MB065) and NSF China (21971151).
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https://dx.doi.org/10.1021/acs.organomet.0c00793
Organometallics XXXX, XXX, XXX−XXX