N, N -Dimethylformamide-stabilized copper nanoparticles as a catalyst precursor for Sonogashira-Hagihara cross coupling

Article abstract of DOI:10.1039/c6ra27910d

We report the catalysis of a Sonogashira-Hagihara cross-coupling reaction using a DMF-stabilized copper nanoparticle catalyst. The reaction proceeded with low catalyst loadings, and a turnover number of 4.0 × 10³ was recorded for 0.01 mol% cata

Full text of DOI:10.1039/c6ra27910d

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N,N-Dimethylformamide-stabilized copper
nanoparticles as a catalyst precursor for
Cite this: RSC Adv., 2017, 7, 22869
Sonogashira–Hagihara cross coupling†
a
Hideo Oka,a Katsuya Kitai,a Takeyuki Suzukib and Yasushi Obora
*
Received 8th December 2016
Accepted 20th April 2017
We report the catalysis of a Sonogashira–Hagihara cross-coupling reaction using a DMF-stabilized copper
nanoparticle catalyst. The reaction proceeded with low catalyst loadings, and a turnover number of 4.0 ꢀ
103 was recorded for 0.01 mol% catalyst loading. DMF-stabilized copper nanoparticles thus showed high
catalytic activity.
DOI: 10.1039/c6ra27910d
rsc.li/rsc-advances
supported on metal oxides have also been reported.26–29 Copper
NPs (Cu NPs) with various nanostructures have also been
Introduction
developed, and research into their applicability as catalysts has
been carried out.26,27,30 There are many reports of Sonogashira
coupling catalyzed by M NPs.31–37 However, in almost all cases,
these reports describe Pd NP catalyst systems.31–33,38–41 Cu NPs
are superior in terms of cost, but there are a limited number of
examples in which Cu NPs are used as catalysts for the Sono-
gashira reaction.34–37 In addition, a greater amount of catalyst is
required for Cu NP-catalyzed reactions, and multi-step proce-
dures are required for the synthesis of these catalysts.28,29,34–37
Rothenberg and co-workers were the rst to report a copper-
catalyzed palladium-free and ligand-free Sonogashira cross
coupling with various aryl iodides and bromides.35 For this they
used Cu nanoclusters prepared from chloride salt precursors by
using tetra-n-octylammonium formate (TOAF) as a stabilizer in
DMF at 65 ꢁC. However, a multi-step operation was required for
the synthesis of the Cu nanoparticles and the Sonogashira
reaction was carried out with 5 mol% of the Cu NP catalyst.35
Tang, Zhang, and co-workers reported that octahedral Cu2O
NPs could be used in a reusable Cu2O/PPh3/n-Bu4NBr (TBAB)
system to catalyze Sonogashira coupling.37 However, a multistep
synthesis is required to access Cu NPs in this system; this
includes the use of hazardous reductants, such as hydrazine Cu
NPs. Furthermore, this Cu NP system required a relatively large
amount of the Cu NP catalyst (10 mol%), and TBAB surfactant
was also needed.37 Therefore, the development of more effective
Cu NPs that require smaller catalytic amounts and less
demanding synthetic procedures is desired.
Transition metal catalysis is a very useful strategy for the
synthesis of a wide variety of compounds with carbon struc-
tures. Multiple catalytic reactions that use transition metal
catalysts have been reported; well-known examples include
Suzuki–Miyaura cross coupling, the Mizoroki–Heck reaction,
Negishi coupling, Migita–Kosugi–Stille coupling, and Sonoga-
shira coupling.1–3 Sonogashira coupling is a remarkably valu-
able approach to the synthesis of acetylene compounds with
unsaturated C^C bonds, which can be used as intermediates,
bioactive substances, pharmaceutical compounds, and elec-
tronic materials.4–6 However, the strategy originally reported by
Sonogashira and co-workers used expensive palladium and
copper as co-catalysts.7 In recent years, copper- or palladium-
free catalysis has been studied.8–13 Low-cost metals such as
iron and nickel have also been used as catalysts, but these
metals require copper to be used as a co-catalyst, complex
ligands, zinc additives, and harsh reaction conditions.14–21
Sonogashira coupling using a palladium-based catalyst system
proceeds with a low catalyst loading (0.07 mol%) and under
mild conditions. Copper, nickel, or iron catalysts with a cost
advantage have not yet been developed.22,23
Transition metal nanoparticles (M NPs) have been exten-
sively studied with regard to their application in catalytic reac-
tions, with the aim of identifying the specic advantages of their
high surface area and unique properties.24,25 The synthesis of
metal NPs commonly requires a metal precursor, reductant,
protectant, and solvent. M NPs stabilized by dendrimers and
We have reported the synthesis of Cu NPs using the DMF-
reduction method without the need for specialized reductants
or surfactants, as well as catalytic reactions using these Cu NPs.42
DMF-stabilized M NPs synthesized with this method have very
small (<10 nm) particle sizes. The specic surface area of the M
NPs increases as the particle diameter decreases, and this leads
to an improvement in the catalytic activity. We have previously
reported that DMF-stabilized Pd NCs catalyze Suzuki–Miyaura
aDepartment of Chemistry and Materials Engineering, Faculty of Chemistry, Materials
and Bioengineering, Kansai University, Suita, Osaka 564-8680, Japan. E-mail: obora@
kansai-u.ac.jp
bComprehensive Analysis Center, The Institute of Scientic and Industrial Research
(ISIR), Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0057, Japan
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c6ra27910d
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cross coupling,43 the Mizoroki–Heck reaction,43 and Migita–
Kosugi–Stille coupling,44 and that DMF-stabilized Cu NPs cata-
lyze the Ullmann coupling reaction.45 For these catalytic reac-
tions, we recorded higher turnover numbers (TONs), and thus
concluded that DMF-stabilized M NPs have high catalytic activity.
Herein, we report that DMF-stabilized Cu NPs can catalyze the
Sonogashira coupling reaction. DMF-stabilized Cu NPs prepared
by a simple methodology from CuCl2 and DMF (as solvent,
reductant, and stabilizer) promoted the reaction of terminal
alkynes with aryl halides at low catalyst loadings (0.01 mol%)
with a TON of 4.0 ꢀ 103. This is an improvement over previously
reported TBAB- and TOAF-protected Cu NPs, which require 5–10
mol% catalyst loadings.35,37
Table
1
Copper nanoparticle (Cu NP)-catalyzed Sonogashira
coupling reaction of iodobenzene (1a) with phenylacetylene (2a)a
Entry
Additive
Base
Solvent
Conv. (%)
Yieldb (%)
1
2
3
4
5
6
7
8
—
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Na2CO3
Cs2CO3
KOH
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
NMP
DMSO
H2O
9
7
PPh3
P(o-tol)3
PCy3
dppe
bpy
dbbpy
1,10-Phen
TMEDA
TMHD
acac
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
>99
73
47
65
>99
>99
82
63
84
60
66
65
27
<1
59
89
>99
>99
>99
84
3
>99 (96)
14
Trace
Trace
>99
>99
40
25
45
19
55
Trace
18
Trace
Trace
73
>99
88
>99
41
Results and discussion
9
First, we prepared Cu NPs by the DMF-reduction method,
according to the procedure reported in the literature.45 Char-
acterization of the Cu NPs was conducted by various instru-
mental analytical techniques.
The transmission electron microscopy (TEM) image and
particle size distribution of the prepared Cu NPs revealed that
10
11
12
13
14
15
16
NEt3
—
their diameters mainly ranged from 2 to 7 nm (Fig. 1). In 17
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
18
19
20
addition, X-ray diffraction (XRD) spectra showed that the NPs
had an amorphous nature (Fig. S1†).
Toluene
DMF
DMF
DMF
DMF
The FT-IR spectrum of the DMF-stabilized Cu NPs showed
a strong absorption at around 1670 cmꢂ1 (Fig. S2(a)†), which
corresponds to the n(C]O) vibration of the DMF molecules.
These results suggest that the DMF molecules interact with the
Cu NPs.46,47 Thermogravimetric analysis-differential thermal
analysis (TG-DTA) of the Cu NPs conrmed that the nano-
21c
22d
23e
24f
Trace
51
n.d.
64
<1
a
Conditions: 1a (0.5 mmol), 2a (0.75 mmol), Cu NPs (2 ꢀ 10ꢂ1 mol%),
additive (10 mol%), base (1.0 mmol), solvent (1 mL), 135 ꢁC, 48 h, under
b
Ar. GC yield. The number in parentheses shows the isolated yield.
ꢁ
particles are thermally stable up to around 150 C (Fig. S3†).
c
With 0.01 mol% Cu NPs. d At 80 ꢁC. e At 120 ꢁC. f Without catalyst.
The synthesis of acetylene by the coupling of aryl halides with
terminal alkynes has a wide scope, and is utilized in areas such as
the pharmaceutical and electronic materials elds. In terms of
cost advantage, it would be more useful to develop an M NP-
catalyzed version of this reaction than of any other reaction.
Furthermore, a wide variety of additives and solvents are toler-
ated in this reaction (Table 1). First, the Sonogashira reaction of
the model compounds iodobenzene (1a, 0.5 mmol) and phenyl-
low conversion and we only obtained a trace of the desired
product (entry 1). Addition of PPh3 promoted the reaction and
improved conversion; we obtained desired product 3a in quan-
titative yield (entry 2). We then examined other phosphine,
nitrogen, and diketone compounds because of the great
improvement observed when using the PPh3 additive. Phosphine
compounds other than PPh3, for example P(o-tolyl)3, PCy3, and
dppe did not promote the reaction (entries 3–5). In contrast,
nitrogen compounds such as bipyridine (bpy) and 4,40-di-tert-
butyl-2,20-bipyridine (dbbpy) were very effective and the reaction
proceeded quantitatively when these additives were used (entries
6 and 7). 1,10-Phenanthroline (1,10-phen) and N,N,N0,N0-tetra-
methylethylenediamine (TMEDA) improved the yield slightly
(entries 8 and 9), and using 2,2,6,6-tetramethyl-3,5-heptadione
(TMHD) gave the product in moderate yields (entry 10).
However, when acetylacetone (acac) was used instead of PPh3 the
product yield was 19% (entry 11).
ꢁ
acetylene (2a) was catalyzed by Cu NPs in DMF at 135 C for 48
hours, using K2CO3 as the base. However, this reaction showed
To investigate the effect of the DMF molecules on the surface
of the Cu NPs during the catalytic reaction, FT-IR measure-
ments featuring the DMF n(C]O) vibration peak at around 1670
cmꢂ1 were conducted on Cu NP samples that had undergone
Fig. 1 (a) Transmission electron microscopy image of DMF-stabilized
copper nanoparticles (scale bar ¼ 10 nm); (b) particle size distribution
of the nanoparticles.
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Table 2 Cu NP-catalyzed Sonogashira cross-coupling reactions of
various compounds
Yielda
Entry Ar-X (1)
Alkyne (2)
Product (3)
(%)
Fig. 2 (a) Transmission electron microscopy image (scale bar ¼ 10
nm) and (b) particle size distribution of the nanocatalyst after reaction
under the conditions shown in entry 2, Table 1.
1
57
2
2a
90
complete removal of the DMF solvent using an NaCl plate
method (Fig. S2†). These analyses indicated that DMF was
liberated from the Cu NPs aer catalytic reactions with PPh3
(entry 2 and Fig. S2(b) and (c)†) and bipyridine (entry 6 and
Fig. S2(d)†). However, the n(C]O) vibration peak remained for
a mixture of Cu NPs with PCy3 aer the reaction had nished.
This result indicates that addition of PCy3 did not induce the
liberation of DMF, probably owing to steric constraints (entry 4
and Fig. S2(e)†).
3
4
5
2a
2a
2a
97
84
93
We next measured the particle size distribution of the Cu NPs
by TEM and dynamic light scattering under the conditions shown
in entry 2 of Table 1 (Fig. 2 and S4†). A slight growth in the
particle size was observed aer the reaction. However, by inhib-
iting Ostwald ripening42,48,49 during the course of the catalytic
reaction, the nanoparticles retained their original size of <10 nm.
The Cu NPs are themselves inactive as catalysts in this
reaction owing to the strong coverage of DMF molecules on
their surfaces (Fig. S5† and entry 1, Table 1). The liberation of
the DMF molecules during the course of the reaction, which is
assisted by additives such as PPh3, generates the active NP
catalyst. PPh3 (or bipyridine) presumably serves to stabilize the
uncoordinated sites on the Cu nanoparticles during the course
of the reaction (Fig. 2 and S4†).
6
2a
2a
95
7
75
90
8b
2a
2a
9
3a
3e
n.d.c
84
As shown in entry 2 of Table 1, K2CO3 was a good choice of
base and gave excellent yields when used with the PPh3 additive.
We also investigated other carbonate salts under the same
conditions. Using a weak base, such as Na2CO3, gave the desired
product in moderate yield (entry 12), but strong bases, such as
Cs2CO3 or KOH, were not suitable for this reaction (entries 13
and 14). The substrates did not convert at all when using trie-
thylamine or base-free conditions (entries 15 and 16). We next
investigated the effect of changing the solvent and found that
aprotic polar solvents, such as N-methyl-2-pyrrolidone (NMP)
and dimethyl sulfoxide (DMSO), were most appropriate for this
catalytic system (entries 17 and 18). Using H2O as the solvent
gave good yields (entry 19), and quantitative yields of the
product were also obtained with toluene (entry 20), which is less
toxic than NMP and DMSO. Thus the reaction proceeded
smoothly with various solvents under these conditions (entries
2, 18–20).
10
11
12
1a
1a
92
57
87
13
1a
3g
a
Conditions: same as entry 2, Table 1. Yields of the isolated product
b
aer purication. Bromobenzene (2.0 mmol) and phenylacetylene
(0.5 mmol) were used. c Not detected by GC.
For this reaction, TONs of up to 4.0 ꢀ 103 were obtained by
reducing the amount of the catalyst to 0.01 mol% (entry 21),
although a small amount of a dehalogenated byproduct was
observed. The time–yield curves for the formation of 3a with the
Cu NP catalyst under the conditions in entry 2 of Table 1
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(Fig. S6†) show that the reaction was mostly complete aer only 3% yield and with low conversion (20%). This result indi-
about 24 h, and that the turnover frequency at the initial stage cates that PPh3-stabilized Cu NPs have more uncoordinated
of the reaction was 29 hꢂ1
.
active sites available on their Cu surfaces, whereas the DMF
The reaction temperature is another important factor in this seems to passivate the surface of the nanoparticles.
catalytic system. The reaction substrates did not convert at 80 ꢁC
The reusability of the Cu NP catalyst was examined in
(entry 22, Table 1) and only moderate yields were obtained at toluene, and the results showed that the catalyst could be
120 ꢁC (entry 23). The reaction did not proceed without the reused at least ve times without loss of activity (Fig. 3).
catalyst (entry 24).
We next attempted Cu NP-catalyzed Sonogashira cross-
coupling reactions using various reaction substrates (Table 2),
Conclusions
and found that DMF-stabilized Cu NPs had a broad scope in
We found that DMF-stabilized Cu NPs have high catalytic activity
Sonogashira coupling reactions when the optimized reaction
in the Sonogashira cross-coupling reaction and can be applied in
conditions were used. First, the reactivity of iodobenzene
the reactions of a wide range of substrates, including aryl halides
derivatives in reactions with phenylacetylene was studied
and alkynes bearing electron-donating and electron-withdrawing
substituents, as well as sterically hindered and heterocyclic
substrates. The reactions were successful with low catalyst load-
(entries 1–9). Sterically hindered substrates and iodobenzenes
bearing electron-donating or electron-withdrawing substituents
gave the corresponding internal alkyne in moderate-to-good
ings and it was possible to reuse the catalyst multiple times.
yields (3b–f, entries 1–5). Heteroaromatic iodides, such as 3-
iodopyridine or 2-iodothiophene, provided the corresponding
Experimental section
General
heteroaromatic internal alkynes (3g and 3h) in good yields (95%
and 75%, respectively, entries 6 and 7).
We also applied this catalytic system to the less reactive
substrates bromobenzene and chlorobenzene in an attempt to
extend the scope of the halide leaving group. Sonogashira
coupling products were obtained from bromobenzene by using
Transmission electron microscopy (TEM) images were recorded
by using a JEOL JEM-ARM200F at an acceleration voltage of 200
1
kV. H and 13C NMR were measured by using a JEOL JNM-ECA
400 spectrometer at 400 and 100 MHz, respectively, in CDCl3
excess aryl halide reagent. However, no coupling products were
with Me4Si as the internal standard. Thermogravimetric analysis
obtained from chlorobenzene. Both electron-donating and
(TG) was performed by using a Thremo plus EVO device (Rigaku,
electron-withdrawing groups were tolerated on the terminal
Japan) at a heating rate of 10 ꢁC minꢂ1 under nitrogen ow.
alkyne and gave desired products 3e and 3i in good yields
(entries 10 and 11). This is a result of the high acidity of the C–H
Typical reaction procedure for Cu NP-catalyzed Sonogashira
cross coupling of 1a with 2a (Table 1, entry 2)
bond attached to the electron-withdrawing alkyne group. In
contrast, because aliphatic terminal alkynes lower the acidity of
the C–H position, we obtained the internal alkyne with an
aliphatic moiety (3j) in only moderate yield (entry 12). In addi-
tion, heteroaromatic substrate 3-ethynylpyridine gave corre-
sponding heteroaromatic internal alkyne 3-(phenylethynyl)
pyridine (3g) in good yield (87%, entry 13).
A mixture of iodobenzene 1a (102 mg, 0.5 mmol), phenyl-
acetylene 2a (77 mg, 0.75 mmol), K2CO3 (138 mg, 1.0 mmol),
and PPh3 (13 mg, 10 mol%) were placed in a pressure container
and a suspension of Cu NPs in DMF (1 mM, 1.0 mL) was added
ꢁ
as the catalyst. The reaction mixture was stirred at 135 C for
To gain further insight into the function of PPh3 on the
catalytic activity of the Cu NPs, we carried out a poisoning test in
the presence of mercury (5 equiv.) under the conditions shown
in entry 2 of Table 1. This reaction gave coupling product 3a in
48 h under argon. The conversion of substrates and yields of the
products were calculated from their peak areas in the GC based
on an internal standard (n-tridecane). The reaction mixture was
extracted with water and n-hexane to separate the product from
the Cu NPs and K2CO3. Product 3a was isolated by column
chromatography (silica gel (230–400 mesh), n-hexane as eluent)
in 96% yield (86 mg).
Mercury poisoning test for Cu NP-catalyzed Sonogashira cross
coupling of 1a with 2a (Table 1, entry 2)
A mixture of iodobenzene 1a (102 mg, 0.5 mmol), phenyl-
acetylene 2a (77 mg, 0.75 mmol), K2CO3 (138 mg, 1.0 mmol),
PPh3 (13 mg, 10 mol%) and Hg (0.5 g, 2.5 mmol) were placed in
a pressure container and a suspension of Cu NPs in DMF
(1 mM, 1.0 mL) was added as the catalyst. The reaction mixture
ꢁ
was stirred at 135 C for 48 h under argon. The conversion of
substrates and yields of the products were calculated from their
peak areas in the GC based on an internal standard (n-
tridecane).
Fig. 3 Repeated runs of the same catalyst under the reaction condi-
tions shown in entry 20 of Table 1 (red: conversion of 1a; blue: yield of
3a).
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NMR (CDCl3, 100 MHz): d: 131.9 (CH), 131.4 (CH), 128.4 (CH),
128.4 (CH), 127.2 (CH), 127.1 (CH), 123.3 (C), 122.9 (C), 93.0 (C),
82.6 (C).
Reusability of the catalyst in Cu NP-catalyzed Sonogashira
cross coupling of 1a with 2a in toluene (Table 1, entry 20)
A mixture of iodobenzene 1a (102 mg, 0.5 mmol), phenyl-
acetylene 2a (77 mg, 0.75 mmol), K2CO3 (138 mg, 1.0 mmol) and
PPh3 (13 mg, 10 mol%) were placed in a pressure container and
a suspension of Cu NPs in toluene (1 mM, 1.0 mL) was added as
the catalyst. The reaction mixture was stirred at 135 ꢁC for 48 h
under argon. The conversion of the substrate and yield of the
product were calculated from their peak areas in the gas chro-
matogram based on an internal standard (n-tridecane). Then,
1a (102 mg, 0.5 mmol), phenylacetylene 2a (77 mg, 0.75 mmol),
K2CO3 (138 mg, 1.0 mmol) and PPh3 (13 mg, 10 mol%) were
added to the resulting mixture for the next reaction cycle.
1-Fluoro-4-(2-phenylethynyl)-benzene 3i.57 White solid. Mp ¼
109–110 ꢁC (lit.9 108–111 ꢁC) 1H-NMR (CDCl3) d: 7.52–7.50 (4H,
m), 7.34–7.33 (3H, m), 7.04–7.02 (2H, m); 13C-NMR (CDCl3, 100
MHz): d: 162.5 (CF, 1JF ¼ 248 Hz), 133.5 (CH, 3JF ¼ 9 Hz), 131.6
(CH), 128.4 (CH), 128.3 (CH), 123.1 (C), 119.3 (C), 115.6 (CH, 2JF
¼ 22 Hz), 89.0 (c), 88.3 (C).
1
1-Undecyn-1-yl-benzene 3j.57 Yellow oil. H-NMR (CDCl3) d:
7.40–7.38 (2H, m), 7.27–7.26 (3H, m), 2.39 (2H, t, J ¼ 7.1 Hz),
1.63–1.56 (2H, m), 1.40–1.33 (10H, m), 0.88 (3H, t, J ¼ 6.8 Hz);
13C-NMR (CDCl3, 100 MHz): d: 131.5 (CH), 128.2 (CH), 127.4
(CH), 124.1 (C), 90.5 (C), 80.6 (C), 31.9 (CH2), 29.2 (CH2), 29.2
(CH2), 29.0 (CH2), 28.8 (CH2), 22.7 (CH2), 19.4 (CH2), 14.1 (CH3).
1,10-(1,2-Ethynediyl)bis-benzene 3a.50 White solid. Mp ¼ 56–
1
58 ꢁC (lit.2 57–58 C) H-NMR (CDCl3, 400 MHz): d: 7.54–7.52
ꢁ
(2H, m), 7.33–7.31 (3H, m); 13C-NMR (CDCl3, 100 MHz): d: 89.4
Acknowledgements
(C), 123.3 (C), 128.2 (CH), 128.3 (CH), 131.6 (CH).
1-Methyl-2-(2-phenylethynyl)-benzene 3b.51 Colorless oil. 1H-
NMR (CDCl3, 400 MHz): d: 7.54–7.35 (3H, m), 7.34–7.16 (6H, m),
2.51 (3H, s); 13C-NMR (CDCl3, 100 MHz): d: 140.1 (C), 131.8 (CH),
131.5 (CH), 129.4 (CH), 128.7 (CH), 128.5 (CH), 128.3 (CH), 128.3
(CH), 128.1 (CH), 125.6 (CH), 123.5 (CH), 123.0 (CH), 93.3 (C),
88.3 (C), 20.7 (CH3).
This work was performed under the Research Program of
“Dynamic Alliance for Open Innovation Bridging Human,
Environment and Materials” in “Network Joint Research Center
for Materials and Devices”. We thank the members of the
Comprehensive Analysis Center, SANKEN (ISIR), Osaka
University for TEM analysis.
1-Methyl-3-(2-phenylethynyl)-benzene 3c.51 Colorless oil. 1H-
NMR (CDCl3, 400 MHz) d: 7.53–7.51 (2H, m), 7.35–7.31 (5H, m),
7.21 (1H, t, J ¼ 7.6 Hz), 7.12 (1H, d, J ¼ 7.3 Hz), 2.33 (3H, s); 13C-
NMR (CDCl3, 100 MHz): d: 138.0 (CH), 132.1 (CH), 131.5 (CH),
129.1 (CH), 128.6 (CH), 128.3 (CH), 128.2 (CH), 128.1 (CH), 123.3
(C), 123.0 (C), 89.5 (C), 89.0 (C), 21.1 (CH3).
Notes and references
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1-Methyl-4-(2-phenylethynyl)-benzene 3d.52 White solid. Mp
1
¼ 68–69 C (lit.4 67–69 C) H-NMR (CDCl3, 400 MHz) d: 7.44–
7.42 (2H, m), 7.34 (2H, d, J ¼ 7.8 Hz), 7.24–7.22 (3H, m), 7.05
(2H, d, J ¼ 7.8 Hz), 2.26 (3H, s); 13C-NMR (CDCl3, 100 MHz): d:
138.3 (CH), 131.5 (CH), 131.5 (CH), 129.0 (CH), 128.3 (CH), 128.0
(CH), 123.4 (C), 120.1 (C), 89.5 (C), 88.7 (C), 21.5 (CH3).
ꢁ
ꢁ
1-Methoxy-4-(2-phenylethynyl)-benzene 3e.53 White solid. Mp
1
¼ 54–57 C (lit.5 56–58 C) H-NMR (CDCl3, 400 MHz) d: 7.51–
7.46 (4H, m), 7.32–7.29 (3H, m), 6.85 (2H, d, J ¼ 7.3 Hz), 3.78
(3H, s); 13C-NMR (CDCl3, 100 MHz): d: 159.6 (CH), 133.0 (CH),
131.4 (CH), 128.2 (CH), 127.9 (CH), 123.5 (C), 115.3 (C), 113.9
(C), 89.4 (C), 88.7 (C), 55.2 (CH3).
ꢁ
ꢁ
1-(2-Phenylethynyl)-4-(triuoromethyl)-benzene 3f.54 White
solid. Mp ¼ 98–99 ꢁC (lit.6 99–101 ꢁC) 1H-NMR (CDCl3, 400 MHz)
d: 7.51–7.48 (6H, m), 7.28–7.27 (3H, m); 13C-NMR (CDCl3, 100
MHz): d: 131.8 (CH), 131.7 (CH), 129.9 (C, q, 2JCF ¼ 32 Hz), 128.8
(CH), 128.4 (CH), 127.1 (C, d, JCF ¼ 2 Hz), 125.2 (CH, d, 3JCF ¼ 4
1
Hz), 123.9 (CF3, d, JCF ¼ 271 Hz), 122.5 (C), 91.7 (C), 88.0 (C).
3-(2-Phenylethynyl)-pyridine 3g.55 White solid. Mp ¼ 46–
47 ꢁC (lit.7 47.8–49.0 ꢁC) 1H-NMR (CDCl3, 400 MHz) d: 8.77 (1H,
s), 8.54 (1H, s), 7.80 (1H, d, J ¼ 7.8 Hz), 7.56–7.55 (2H, m), 7.37–
7.35 (3H, m), 7.27–7.26 (1H, m); 13C-NMR (CDCl3, 100 MHz): d:
152.2 (CH), 148.5 (CH), 138.3 (CH), 131.6 (CH), 128.7 (CH), 128.4
(CH), 122.9 (CH), 122.4 (C), 120.4 (C), 92.6 (C), 85.9 (C).
11 K. Okuro, M. Furuune, M. Miura and M. Nomura,
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2-(2-Phenylethynyl)-thiophene 3h.56 White solid. Mp ¼ 48–
1
49 C (lit.8 45.3–48.2 C) H-NMR (CDCl3) d: 7.52–7.50 (2H, m),
ꢁ
ꢁ
7.36–7.33 (3H, m), 7.29–7.28 (2H, m), 7.01 (1H, t, J ¼ 5 Hz); 13C-
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