Bis(pyrazolyl)methane Copper Complexes as Robust and Efficient Catalysts for Sonogashira Couplings

Article abstract of DOI:10.1002/ejoc.201501117

A series of bis(pyrazolyl)methane copper complexes were found to catalyze a fast palladium-free Sonogashira coupling reaction of several iodoarenes with terminal alkynes such as phenylacetylene, propargyl benzyl ether, and (tert-butyl-dimethyl)silylacetyl

Full text of DOI:10.1002/ejoc.201501117

FULL PAPER
DOI: 10.1002/ejoc.201501117
Bis(pyrazolyl)methane Copper Complexes as Robust and Efficient Catalysts for
Sonogashira Couplings
[c]
[c]
[a]
Julian Moegling,[a,b] Andreas D. Benischke, Jeffrey M. Hammann, Nynke A. Veprek,
Florian Zoller,[a] Bettina Rendenbach,[a] Alexander Hoffmann,[a,b] Holger Sievers,[d]
Michael Schuster,[d] Paul Knochel,[c] and Sonja Herres-Pawlis*[a,b]
ˇ
Keywords: Homogeneous catalysis / Cross-coupling / C–C coupling / Copper / Alkynes / N ligands
A series of bis(pyrazolyl)methane copper complexes were
found to catalyze a fast palladium-free Sonogashira coupling
reaction of several iodoarenes with terminal alkynes such as
phenylacetylene, propargyl benzyl ether, and (tert-butyl-
CuCl2·2H2O (10 mol-%) under aerobic conditions and the
corresponding chelate ligand (10 mol-%), with its tailored fa-
cial coordination mode, is crucial for the success of the reac-
tion. The coupling can also be carried out in water with liquid
dimethyl)silylacetylene. These reactions proceed with aryl halides and a phase-transfer catalyst.
rich phenyl halides. The addition of AgOTf (2 mol-%) im-
Introduction
proves the coupling of aryl bromides.[6l]
The Sonogashira reaction[1] has been known since 1975
and allows the coupling of terminal alkynes with alkenyl
and aryl halides. The major drawbacks of the Sonogashira
reaction are the toxicity, the high cost of palladium salts,
and the requirement for inert gas conditions. Owing to the
importance of this coupling for the preparation of biolo-
gically[2] and synthetically[3] relevant acetylenes, there have
been numerous efforts to develop new synthetic protocols
for palladium-free Sonogashira cross-couplings. Nickel,[4]
cobalt,[5] and copper[6] have been successfully used to per-
form Sonogashira cross-couplings. Among these, copper-
catalyzed couplings have attracted most attention.[6] Some
synthetic protocols have been published with the focus on
microwave-assisted reactions[7] or on the use of copper
nanoparticles[8] as catalysts.[6n] Hwang et al. reported a
room temperature blue light (LED) induced coupling of
aryl iodides and aryl acetylenes. The copper acetylide is
suggested to undergo ligand to metal charge transfer
(LMCT), which facilitates nucleophilic attack of electron-
For all other homogeneous systems, the addition of a
ligand to copper(I) or copper(II) salts is mandatory to en-
able the coupling. Most of those ligands are commercially
available and contain nitrogen, phosphorus, or oxygen
donors such as DMEDA,[6o] 1,3-diphenylpropane-1,3-
dione,[6e]
1,4-diazabicyclo[2.2.2]octane
(DABCO),[6a]
Xantphos[6q] or salicylic acid.[6g] The most efficient bases
are K2CO3, Cs2CO3, NaOH, or KOH and it is noticeable
that for all thermal protocols, elevated temperatures (80–
145 °C) are required. Typical solvents are N,N-dimethyl-
formamide (DMF), dimethyl sulfoxide (DMSO), N-methyl-
2-pyrrolidinone (NMP), and toluene, which allow high re-
action temperatures. A remarkable protocol for the cou-
pling of aryl bromides and chlorides with phenyl acetylenes
has been reported by Bhargava et al. using bis(μ-iodo)bis-
[(–)-sparteine]dicopper(I) as catalyst.[6r]
Another procedure for carrying out the Sonogashira re-
action in water at 100 °C has been developed by Zhou et
al.[6i] With the utilization of a water-soluble bisulfonated
salen copper(II) catalyst under aerobic conditions, various
iodoarenes where coupled with phenylacetylene to afford
cross-coupled acetylenes and indoles. To our knowledge, be-
sides Zhou et al.,[6i] only one other report on aerobic Sono-
gashira cross-coupling has been published.[6d] Li et al. used
the catalytic system of copper(II) acetate/1,4-diphenyl-1,4-
diazabuta-1,3-diene with three equivalents of tetrabutyl-
ammonium fluoride (TBAF) as base for the coupling of
iodoarenes with phenylacetylene.[6d]
[a] Ludwig-Maximilians-Universität München, Fakultät Chemie
und Pharmazie Anorganische Chemie,
Butenandtstr. 5, 81377 München, Germany
[b] Rheinisch-Westfälische Technische Hochschule Aachen
University, Institut für Anorganische Chemie,
Landoltweg 1, 52074 Aachen, Germany
E-mail: Sonja.herres-pawlis@ac.rwth-aachen.de
http://www.bioac.ac.rwth-aachen.de/
[c] Ludwig-Maximilians-Universität München, Fakultät Chemie
und Pharmazie Organische Chemie,
Butenandtstr. 5, 81377 München, Germany
[d] Technische Universität München, Fakultät für Chemie,
Fachgruppe Analytische Chemie,
Results and Discussion
Herein, we report a copper-catalyzed Sonogashira reac-
tion of various iodoarenes with acetylenes under aerobic
Lichtenbergstraße 4, 85747 Garching, Germany
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201501117.
Eur. J. Org. Chem. 2015, 7475–7483
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S. Herres-Pawlis et al.
FULL PAPER
conditions. The reaction is carried out in DMF as solvent Table 1. Efficiency of bis(pyrazolyl)methane ligands in the cross-
coupling of phenylacetylene and 4-iodobenzotrifluoride.
and with K2CO3 as base. Given that the stabilizing N-donor
ligand is crucial for the catalysis, we chose strong facial
bis(pyrazolyl)methane ligands for the stabilization of cop-
per complexes. These hetero-scorpionate ligands can be eas-
ily electronically and sterically modified and therefore are
ideal compounds for ligand design.[9] Similar members of
this ligand class, namely (pyridin-2-yl)bis(tert-butylpyrazol-
1-yl)methane and (1-methylimidazol-2-yl)bis(tert-butylpyr-
azol-1-yl)methane have been utilized in the copper(I)-medi-
ated oxygen activation and catalytic transfer.[10] The unsub-
stituted ligands are known to form bis- and monofacial
complexes with copper(II) salts.[11]
During our investigations, we have used various CuII/
ligand systems (Table 1, ligand L1–7) to perform the cross-
coupling of iodoarenes. Hereby, we have varied the third
donor function and the steric encumbrance. Ligands L1,[12]
L2,[12,15] L3,[16] L5,[17] L6,[12] and L7[17] are known. Ligands
Entry[a]
FG[b]
Ligand
Time [h]
Yield [%][c]
L1, L2, and L3 turned out to be the most effective ligands,
and these have been tested on two substrates (ethyl 3-iodo-
benzoate and 4-iodobenzotrifluoride) (Table 1, entries 1–3
and 8–10), giving short reaction times and similar yields.
Ligands L4–7 are found to be less efficient in these Sonoga-
shira cross-couplings. This study shows the importance of
two factors: firstly, the steric encumbrance of the donor en-
tity should be as small as possible. This can be seen in the
catalysis (Table 1, entries 1 and 6) of 3-tert-butyl-substi-
tuted ligand L6 compared with that of the nonsubstituted
pyrazoles (ligand L1). Comparison of the activity of ligands
L3 and L4, in which the amine hydrogen atoms are replaced
by methyl groups, shows the same behavior (Table 1, entries
3 and 4). Secondly, the donor properties of the non-pyr-
azolyl donor are essential. Switching the pyridyl substituent
with an imidazolyl group led to the fastest coupling
(Table 1, entries 1–2 and 8–9), which may be a result of the
increased donor strength of the imidazole nitrogen. Never-
theless, the substitution of two pyrazoles with imidazoles
does not benefit the catalysis (Table 1, entries 1 and 7).
For the following reactions (1-methylimidazol-2-yl)-
bis(pyrazol-1-yl)methane (L2)[12] and CuCl2·2H2O were
used. We found that it was not necessary to work under an
inert atmosphere. The conversion of the iodoarene proceeds
fast and smoothly. Indeed the reaction is one of the fastest
reported palladium-free copper-catalyzed Sonogashira reac-
tions, allowing the coupling of iodoarenes with acetylenes
in very short reaction times (1.0–2.0 h) at 120 °C. Various
iodoarenes bearing electron-withdrawing or electron-donat-
ing groups have been used (Table 2, entries 1–12). It is pos-
sible to couple a range of acetylenes such as phenylacetyl-
ene, propargyl benzyl ether, and (tert-butyldimethyl)silyl-
acetylene.
1
2
3
4
5
6
7
8
9
4-CF3
4-CF3
4-CF3
4-CF3
4-CF3
4-CF3
4-CF3
3-CO2Et
3-CO2Et
3-CO2Et
L1
L2
L3
L4
L5
L6
L7
L1
L2
L3
1.5
1.0
1.0
2.5
2.5
2.0
2.5
2.5
1.0
1.5
79
77
74
77
8
trace
39
70
71
70
10
[a] See standard procedure for the preparation. [b] FG: functional
group. [c] Isolated yield.
Table 2. Coupling reactions of iodoarenes and acetylenes.
Entry[a] FG[b]
R1
Time [h] Yield [%][c]
1[d]
2[d]
3[d]
4[e]
3-CO2Et
Ph
Ph
Ph
Ph
1.5
1.0
1.0
2.0
1.0
1.0
1.0
2.0
1.0
1.0
1.0
1.0
70
74
87
84
74
68
75
66
74
62
62
61
4-CF3
4-OMe
–
3-CO2Et
4-OMe
4-CF3
5[d]
6[d]
7[d]
8[e]
CH2OBn
CH2OBn
CH2OBn
CH2OBn
Si(tBu)(Me)2
Si(tBu)(Me)2
Si(tBu)(Me)2
Si(tBu)(Me)2
–
9[d]
10[d]
11[d]
12[e]
3-CO2Et
4-OMe
4-CF3
–
[a] See standard procedure for the preparation. [b] FG: functional
group. [c] Isolated yield. [d] X = C. [e] X = N.
Under the aerobic conditions, the homo-coupling of the
acetylene[13,14] was found to be a controllable side-reaction. iodoarenes to bromoarenes, a large amount of homocou-
However, to avoid a reduction in yield, it was necessary to pling was observed. Only 4-nitrobromobenzene gave 50%
add 1.5 equiv. of the alkyne. Under these conditions, full yield under an air atmosphere within 3 h. When the reac-
conversion was rapidly reached and only small amounts of tion was performed under an inert gas atmosphere, the con-
homocoupled acetylenic byproducts were obtained (di- version stopped at 48% after 24 h, probably due to deacti-
acetylenes). When the substrates were changed from vation of the catalyst.
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Bis(pyrazolyl)methane Copper Catalysts for Sonogashira Couplings
It is remarkable that the use of copper(I) halides did not comparison to C2 [Cu(1)–N(Pz) 2.006(2) Å], which indi-
give any cross-coupling product under an inert gas atmo- cates that imidazolyl and pyrazolyl donors are stronger do-
sphere. However, performing the reaction under aerobic nating than the pyridinyl or amine groups. Additionally, the
conditions led to full conversion of the electrophile, afford- axial N–Cu bond varies from 2.500(3) (C1), 2.387(2) (C2),
ing the cross-coupling product. Using copper(II) chloride to 2.243(2) Å (C3) and plays an auxiliary role in the
under an inert gas atmosphere indeed enabled the cross- stabilization of the copper(II) complex, which is crucial for
coupling reaction, albeit at slightly reduced rate and with efficient catalysis.
lower conversion. We observe that initially the green DMF
solution of the catalyst CuCl2·2H2O/L2 turns orange after
Table 3. Selected bond length [Å] and angles [°] of C1 and C2.
C1
C2
the addition of K2CO3 and phenylacetylene. This is due to
an oxidative homocoupling,[13,14] which consequently gives
copper(I) and a diphenyldiacetylene. EPR spectroscopic
analysis verified the absence of copper(II) (EPR silence) af-
ter the addition of K2CO3 and phenylacetylene.
Cu(1)–N(Im/Pz*)
Cu(1)–N(Pz)
Cu(1)–N(PzЈ/Am)
Cu(1)–Cl(1,2)
N(Im/Pz*)–Cu(1)–Cl(1)
N(Pz)–Cu(1)–Cl(1)
N(PzЈ/Am)–Cu(1)–Cl(1)
N(Im/Pz*)–Cu(1)–Cl(2)
N(Pz)–Cu(1)–Cl(2)
N(PzЈ/Am)–Cu(1)–Cl(2)
N(Im/Pz*)–Cu(1)–N(Pz)
N(PzЈ/Am)–Cu(1)–N(Pz)
2.002(3)
2.021(4)
2.500(3)
2.260(1), 2.254 (1)
90.7 (1)
176.3 (1)
98.0(1)
161.9(1)
90.3(1)
2.006(2)
2.036(2)
2.387(2)
2.263(1), 2.263(1)
90.2(1)
173.3(1)
102.6(1)
166.6(1)
90.4(1)
103.9(1)
85.0(1)
82.1(1)
88.0(1)
93.2(1)
We interpret this data as follows: bis(pyrazolyl)methane
ligands with unsubstituted heteroarenes are known to form
easily both bisfacial and monofacial complexes with cop-
per(II) halides.[11] Thus, adding ligands L1–5 to the cop-
per(II) halides may lead to a catalytically inactive bisfacial
complex. We provide two molecular structures of bis(pyr-
azolyl)methane catalysts obtained from single-crystal X-ray
diffraction, which show monofacial ligand-coordination be-
havior (Figure 1). The reductive reaction medium for the
copper(II) complex may lead to an activated monofacial
copper(I) chloride complex. We assume that this copper(I)
complex is not a simple complex of type [CuILCl], because
the independently prepared copper(I) complex does not
show any activity. Moreover, we propose that this activated
species is an intermediate [CuIL(DMF)] complex, which is
formed during the first homocoupling step and possesses
superior reactivity.
113.5(1)
85.9(1)
80.4(1)
N(PzЈ/Am)–Cu(1)–N(Im/Pz*) 83.3(1)
Cl(1)–Cu(1)–Cl(2)
93.3(1)
0.24
[a]
τ5
0.11
α – β [18]
[a] τ5 =
.
60°
Table 4. Crystallographic data and parameters of C1 and C2.
C1
C2
Empirical formula
C11H12Cl2CuN6
362.71
0.16ϫ0.05ϫ0.03
100
C10H15Cl2CuN5
339.71
0.12ϫ0.10ϫ0.08
100
Formula mass [gmol–1]
Crystal size [mm]
T [K]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
monoclinic
P21/n
9.3266(4)
14.1665(6)
10.8849(5)
90
monoclinic
P21/n
9.8783(4)
13.4853(5)
9.9701(4)
90
α [°]
β [°]
97.8080(10)
90
1424.84(11)
4
1.691
1.906
92.4780(10)
90
1326.89(9)
4
1.701
2.037
γ [°]
V [Å3]
Z
ρcacld. [gcm–3
]
μ [mm–1
λ [Å]
]
0.71073
732
0.71073
692
F(000)
Figure 1. Molecular structures of [Cu(L2)Cl2] (C1) and [Cu(L4)Cl2]
(C2).
hkl range
Ϯ11, Ϯ17, Ϯ13
24194
2914
0.0564
2914
158
0.0467
0.1142
1.072
Ϯ12, Ϯ16, Ϯ12
22422
2708
0.0279
2708
165
0.0260
0.0602
1.122
Reflections collected
Independent reflections
Rint.
Reflections observed
Number of parameters
R1 [I Ն 2σ[I]]
Selected bond lengths and angles of [Cu(L2)Cl2] (C1)
and [Cu(L4)Cl2] (C2) are given in Table 3, with crystallo-
graphic details presented in Table 4. Another complex,
[Cu(L1)Cl2]·MeOH (C3), has been reported previously.[11]
These three complexes have the bispyrazolyl moiety in com-
mon and can be compared regarding the third donor. All
complexes C1–3 adopt pyramidal square-planar geometries
(τ5 = 0.05–0.24).[11] Exclusively in C1, the non-pyrazolyl do-
wR2 (all data)
Goodness-of-fit
Largest diff. peak, hole [eÅ–3] 1.770, –0.908
0.335, –0.273
A comparative study between the imidazolyl and pyr-
nor (imidazolyl) lies in the square-planar plane. Concerning azolyl nitrogen donors in copper(II)-bis(tert-butylpyrazol-
the smallest equatorial N–Cu bond length, C1 possesses a 1-yl)methanes has been performed by Herres-Pawlis et
shorter bond [Cu(1)–N(Im) 2.002(3) Å] compared with C3 al.[10b] They reasoned from NBO charges and charge-trans-
[Cu(1)–N(Pz) 2.032(2) Å] and an equal bond length by fer energies that the imidazolyl nitrogen lone-pair displays
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S. Herres-Pawlis et al.
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a slightly larger donor ability. As a result, a tremendous impurities in copper salts or alkali carbonates. Based on
increase in the catalytic oxygen transfer rate for the hydrox- the highly selective complexation[20] of palladium with the
ylation of phenols occurs, which could be deduced from the ligand NЈ-benzoyl-N,N-di-n-hexylthiourea (BDHT),[21]
a
increased donor strength of the imidazolyl nitrogen.
dry sample of a typical reaction mixture (1 mmol halo-
To verify the necessity of the ligand/CuCl2·2H2O combi- arene) was examined for traces of palladium (see the Sup-
nation for the catalysis, control experiments were carried porting Information for the calculation and procedure).
out (Scheme 1, reactions a and b), indicating both ligand Palladium separation and enrichment was performed by
and the degree of copper(II) oxidation to be pivotal for the cloud point extraction followed by electrothermal atomic
catalysis. Furthermore, the use of only the heterocyclic frag- absorption spectrometry (ET-AAS). Traces of palladium
ments, 1-methylpyrazole and pyridine, instead of the tri- (0.912Ϯ0.244 ppm; μmol Pd/mol haloarene) have been
dentate ligand L1, resulted in no cross-coupling product found in the dry mass of a typical reaction mixture (error
(Scheme 1, reaction c). Thus, the facial coordination of li- is in the standard derivation of three independent measure-
gand L1 is crucial for the success of the cross-coupling. To ments, N = 3). This small amount of palladium is not criti-
establish the role of the copper complex with respect to the cal for the reported series of reactions, considering that no
catalyst activity, a reaction with CuCl2·2H2O/L1 and coupling takes place in the absence of ligand (Scheme 1,
Cu(NO3)2·2.5H2O/L1 (Scheme 1, reaction d and e) was per- reaction a).
formed. No difference of activity could be identified, indi-
cating that the halide substituent does not play an impor-
tant role in the catalysis.
Conclusions
We have shown that bis(pyrazolyl)methane copper(II)
complexes are valuable new catalysts in the palladium-free
copper-catalyzed and aerobic Sonogashira reaction. A large
array of iodoarenes and terminal alkynes can be converted
into the desired cross-coupling products under air. Most
remarkable is the excellent reaction rate, resulting from the
use of the bis(pyrazolyl)methane copper catalysts. The pos-
sibility to perform the coupling in aqueous media with li-
quid substrates offers a viable alternative to the use of sol-
vent DMF. Further investigations will focus on the acti-
vation of bromo- and chloroarenes and on mechanistic
studies.
Scheme 1. Systematic variation of the catalyst composition.
For liquid (or solubilized under the reaction conditions)
aryl halides, it is possible to conduct the coupling in water
under an air atmosphere (Scheme 2). The addition of a
phase-transfer agent such as (nBu)4NBr is mandatory. In
this biphasic mixture, we assume the reaction to occur in
the organic substrate phase. The use of solid substrates does
not lead to any cross-coupling product. Besides the system
of Zhou et al.[6i] also Guan et al.,[6p] Wan et al.[7b] and Hu
et al.[6k] reported copper-catalyzed Sonogashira reactions in
water. Except for the group of Guan et al.,[6p] every system
Experimental Section
General Methods: Some manipulations were carried out under
nitrogen atmosphere. Nitrogen was dried by passage through P2O5.
NMR spectra were recorded with a JEOL EX-400-NMR spectrom-
required a phase-transfer catalyst. They used a simple CuI/ eter or a Varian NMR-system 300 MHz. 1H and 13C NMR spectra
data are given relative to deuterated solvent (CDCl3, 25 °C) as an
internal standard. Mass spectra data were measured with a Thermo
Finnigan MAT 95 and a Jeol MStation Sektorfeld spectrometer.
IR spectra were recorded with a Perkin–Elmer Spectrum BX II
FTIR Spectrometer with ATR technique. EPR measurements were
performed with a Magnettech MiniScope MS400 in DMF samples
at 10 mm. Gas chromatographic measurements were obtained with
a Hewlett-Packard 7890A Series (HP 5 capillary column; 5% phen-
ylmethylpolysiloxane, length: 15 m, diameter: 0.25 mm, film thick-
ness: 0.25 μm, flame ionization detector). Melting points were mea-
sured with a Büchi B-540 apparatus and are uncorrected. All chem-
icals were purchased from ABCR, Bayer, Riedel-de Haën, Sigma–
Aldrich or TCI. Benzyl propargyl ether[22] and 1-methylpyrazole[23]
have been synthesized according to reported procedures. The sol-
vents used were dried by standard procedures.[24]
PPh3 catalyst under N2 with KOH as base in water. Wan et
al.[7b] reported a similar system but with K2CO3 as base,
microwave radiation, and TBAB as additive. Hu et al.[6k]
used phenanthroline/CuI and TBAB at 120 °C under N2 for
the cross-coupling in water. We present the only system
beside Zhou et al.,[6i] which provides cross-coupling under
aerobic conditions and in water.
Determination of relative response factors for the gas chromato-
graphic analysis:
The relative response factors (fP)[25] were calculated as
Scheme 2. Coupling of liquid iodoarenes with phenylacetylene in
water.
Palladium is known to catalyze Sonogashira couplings at
the ppm level.[19] Thus, it is important to check for trace
Ap·[IS]
fP
=
AIS·[P]
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Bis(pyrazolyl)methane Copper Catalysts for Sonogashira Couplings
allowing the concentration of the product to be calculated as
Merck (Darmstadt, Germany). TritonX-114 was purchased from
AppliChem (Darmstadt, Germany). Palladium stock solution
[Pd(NO3)2 in 0.5 m HNO3, 1000 mgL–1, Merck] was used for palla-
dium serial dilution for AAS calibration. Ultrapure water (UPW)
was provided by a DirectQ 3 Ultrapure Water System (Millipore,
Billerica, MA, USA), the conductivity was always above
17.5 MΩcm–1. NЈ-Benzoyl-N,N-di-n-hexylthiourea (BDHT) was
synthesized according to a reported procedure[30] and recrystallized
from ethanol.
Ap·[IS]
[P] =
AIS·fP
where AP is the area of the product signal, AIS is the area of the
internal standard signal, [IS] is the concentration of the internal
standard, and [P] is the concentration of the product.
For a typical procedure, three mixtures of the product and the in-
ternal standard were analyzed by GC to give area ratios. Each mix-
ture was run three times. The value for the response factors was
obtained as average over all runs. For the product 4-trifluoro-
methyl-1-(2-phenylethynyl)benzene, a response factor of 2.08 was
estimated.
A Perkin–Elmer 4100 ZL atomic absorption spectrometer equipped
with Zeeman-effect background correction, a transversally heated
graphite atomizer (THGA), and an AS-70 furnace autosampler
was used for ET-AAS measurement. High purity argon (99.996%)
served as inert gas for THGA operation. A Photron hollow-cath-
ode lamp (Photron, Victoria, Australia) was employed as primary
source, the wavelength was set at 247.6 nm; the lamp current to
30 mA; the slit width (low) to 0.7 nm. The time-temperature pro-
gram for graphite furnace operation is given in Table 5.
For some samples, the GC-conversion of the electrophile is given.
These were obtained by comparison with an internal standard by
using the area ratios of the electrophile and the internal standard
at the start of the reaction (t = 0 s) and at a given time.
Standard Procedure:
A tube was charged with CuCl2·2H2O
Table 5. THGA time-temperature program.
(17.1 mg, 0.1 mmol, 0.1 equiv.) and the ligand (0.1 mmol,
0.1 equiv.) under an air atmosphere and sealed with a rubber sep-
tum. DMF (2 mL) was then added and the resulting suspension
was stirred for 15 min at room temperature. K2CO3 (0.40 g,
2.0 mmol, 2.0 equiv.), the haloarene (1.0 mmol, 1.0 equiv.), and 1,3-
dimethoxybenzene (100 μL, internal standard) were added and the
reaction mixture was heated to 120 °C. After stirring for 3 min at
120 °C, the acetylene (1.5 mmol, 1.5 equiv.) was added. Complete
conversion of the haloarene was indicated by GC analysis. The re-
action mixture was cooled to room temperature and filtered. NH3
solution (aq., 25%, 15 mL) was added and the mixture was ex-
tracted with ethyl acetate (3ϫ 10 mL). Evaporation of the solvent
gave the crude product, which was purified by column chromatog-
raphy (SiO2).
Temp.
[°C]
Ramp
[s]
Hold
[s]
Argon flow
[mLmin–1]
Step
80
130
1650
2380
2600
1
15
15
30
5
250
250
250
0
drying 1
drying 2
pyrolysis
measurement
clean out
15
30
0
1
6
250
Sample Preparation and Calibration Procedure: A constant-weight
dried sample of the catalytic mixture was homogenized by using a
mortar and three aliquots of 500 mg were taken. These aliquots
were digested in a mixture of nitric acid (65 wt.-%, 2 mL), hydro-
chloric acid (36 wt.-%, 3 mL) and hydrogen peroxide (30 wt.-%,
1 mL) for 24 h at 60 °C. After 10 h additional hydrogen peroxide
(30 wt.-%, 1 mL) was added. The digestion solution was then fil-
tered through a syringe filter (polystyrene, 0.45 μm). The filter was
rinsed with UPW, and the rinsing solution was added to the filtrate,
which was then filled up with UPW to a weight of 40.00 g. Cali-
bration was performed by means of the standard addition method.
For selective Pd enrichment, the sample and calibration solutions
were treated with 500 μL 10 wt.-% TritonX-114 (in UPW) and
100 μL of a solution containing BDHT (1.0 gL–1) dissolved in
methanol as highly selective complexing agent.[20] The solutions
were homogenized by a vortex mixer and incubated for 2 h at 62 °C
in a water bath. Phase separation was accelerated by centrifugation
at 3210 rcf for 20 min and the phase separated solution was then
cooled in ice water for 2 to 3 min to increase the viscosity of the
surfactant-rich phase. The aqueous supernatant was then removed
by decanting. The remaining surfactant droplet, containing Pd as
Pd(BDHT)2 complex was dissolved in a mixture of ethanol
(100 μL) and HCl (36 wt.-%, 100 μL) and then forwarded to ET-
AAS measurement. The correlation coefficient (R2) of the cali-
bration was 0.9987 and the limit of detection, calculated from the
confidence interval of the linear regression,[31] was 0.5 ng Pdg–1.
The arithmetic mean of the Pd content of the measured samples
was 0.164 μgg–1 and the standard derivation wasϮ0.044 μgg–1
(N = 3).
For coupling with water as solvent, (nBu)4NBr (48.4 mg,
0.15 mmol, 0.15 equiv.) was added in the same step as the catalyst
and DMF was replaced with water.
Crystallographic Data and Parameters of C1 and C2: The crystal
data for C1 and C2 are presented in Table 4. The data was collected
with a D8 Venture diffractometer with graphite monochromated
Mo-Kα radiation (λ = 0.71073 Å). Data reduction and absorption
correction was performed with SAINT and SADABS.[26] The struc-
ture was solved by direct and conventional Fourier methods and
all non-hydrogen atoms were refined anisotropically with full-ma-
trix least-squares based on F2 (XPREP,[27] SHELXS[28] and
ShelXle[29]). Hydrogen atoms were derived from difference Fourier
maps and placed at idealized positions, riding on their parent C
atoms, with isotropic displacement parameters Uiso(H) = 1.2Ueq(C)
and 1.5Ueq(C methyl). All methyl groups were allowed to rotate
but not to tip.
Full crystallographic data (excluding structure factors) have been
deposited with the Cambridge Crystallographic Data Centre as
supplementary no. CCDC-1045301 (for C1) and -1045302 (for C2).
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
Determination of Palladium Content
The palladium content of a typical reaction mixture (1 mmol
haloarene) for phenylacetylene and iodobenzene with the catalyst
L1/CuCl2·2H2O for a full conversion was determined as follows:
Chemicals and Instrumentation: All purchased chemicals were of
analytical grade or better. Moreover, all solvents and chemicals
were tested for Pd contamination by control blank measurements
with ET-AAS. Ethanol, 36 wt.-% hydrochloric acid, 30 wt.-%
hydrogen peroxide, and 65 wt.-% nitric acid were purchased from
The dry mass of such a mixture contains diphenylacetylene
(0.178 g, 1.00 mmol), K2CO3 (0.207 g, 1.50 mmol), KI (0.166 g,
Eur. J. Org. Chem. 2015, 7475–7483
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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S. Herres-Pawlis et al.
FULL PAPER
1.00 mmol), CuCl2 (13.4 mg, 0.10 mmol), and L1 (22.5 mg,
0.10 mmol) resulting in a dry mass of 0.59 g (KHCO3 decomposes
to K2CO3 during the drying procedure).
C11H12Cl2CuN6: C 36.43, N 23.17, H 3.33; found C 36.34, N 23.17,
H 3.33.
Synthesis of [CuCl2{HC(Pz)2(CH2N(Me)2)}] (C2)
The palladium content of the measured samples was
0.164Ϯ0.044 μgg–1, thus resulting in 91.2Ϯ24.4ϫ10–11 mol palla-
dium for a reaction mixture of 1 mmol iodobenzene. Division by
the amount of iodobenzene gives 0.912Ϯ0.244 ppm (μmol Pd/mol
iodobenzene) palladium.
Synthesis of Ligands and Complexes
Synthesis of Ligands L1–L7: Ligands L1,[12] L2,[12,15] L3,[16] L5,[17]
L6,[12] and L7[17] were synthesized according to reported pro-
cedures.
CuCl2·2H2O (43.3 mg, 0.3 mmol, 1.0 equiv.) was dissolved in
MeOH (3 mL) and added to a solution of {HC(Pz)2(CH2N(Me)2)}
(L4) (61.6 mg, 0.3 mmol, 1.0 equiv.) in CH2Cl2 (3 mL). After 2 h,
blue-green plates, crystals suitable for X-ray diffraction were ob-
Synthesis of N,NЈ-Dimethyl-2,2-dipyrazol-1-yl-ethanamine (L4)
tained (65.2 mg, 0.2 mmol, 64%). IR (ATIR, neat): ν = 3104 (w),
˜
2952 (vw), 1639 (vw), 1515 (m), 1438 (w), 1402 (m), 1284 (m), 1238
(w), 1210 (w), 1186 (w), 1159 (vw), 1086 (m), 1086 (m), 1071 (m),
1046 (m), 988 (w), 960 (m), 860 (m), 817 (m), 801 (s), 767 (s), 752
(vs), 693 (m), 670 (m), 658 (m) cm–1. MS (FAB+): m/z (%) = 307
(5)
[C10H1537Cl65CuN5]+,
305
(30)
[C10H1537Cl63CuN5,
2,2-Dipyrazol-1-yl-ethanamine (1.51 g, 8.34 mmol, 1.0 equiv.) was
dissolved in formalin (37%, 8 mL, 0.26 mol, 30 equiv.) and formic
acid (99%, 1 mL, 26.5 mmol, 3.2 equiv.). The solution was heated
to reflux for 24 h and cooled to room temperature. The volatiles
where removed under high vacuum and the residue was taken up
in water (10 mL). The reaction mixture was brought to pH 9 with
K2CO3 and extracted with CH2Cl2 (3ϫ 10 mL). Subsequent wash-
ing with brine (2ϫ 10 mL), drying over Na2SO4, and evaporation
C10H1535Cl65CuN5]+, 303 (35) [C10H1535Cl63CuN5]+, 268 (5)
[C10H1563CuN5]+, 206 (40) [C10H15N5] +. HRMS (FAB+): m/z
calcd. for C10H13N535Cl63Cu 303.0312; found 303.0287.
Analytical Data of the Cross-Coupled Compounds
Ethyl 3-(2-Phenylethynyl)benzoate
of the solvent afforded the product (1.78 g, 8.53 mmol, 98%) as a
3
slightly yellow solid. 1H NMR (400 MHz): δ = 7.65 [d, JH,H
=
3
2.4 Hz, 2 H, 5-HPz], 7.54 ppm [d, JH,H = 1.7 Hz, 2 H, 3-Hpz], 6.51
3
3
[t, JH,H = 7.2 Hz, CH], 6.27 [d, JH,H = 2.4 Hz, 2 H, 4-HPz], 3.43
[d, JH,H = 7.2 Hz, 2 H, CH2], 2.28 (s, 6 H, CH3) ppm. 13C NMR
3
(101 MHz): δ = 140.3 (2 C; 3-CPz), 128.9 (2 C; 5-CPz), 106.7 (2 C;
4-CPz), 73.9 (1 C; CH), 61.2 (1 C; CH2), 45.8 (2 C; CH3) ppm. IR
1
Rf = 0.3 (isohexane/Et2O, 19:1); m.p. 20 °C. H NMR (300 MHz):
(ATIR, neat): ν = 3113 (w), 2950 (w), 2869 (vw), 2830 (w), 2774
˜
δ = 8.22–8.20 (m, 1 H, Ph-H), 8.03–7.99 (m, 1 H, Ph-H), 7.72–7.68
(m, 1 H, Ph-H), 7.57–7.51 (m, 2 H, Ph-H), 7.46–7.40 (m, 1 H, Ph-
(w), 1731 (vw), 1513 (w), 1464 (w), 1437 (w), 1391 (m), 1344 (w),
1325 (m), 1293 (m), 1249 (w), 1204 (m), 1151 (w), 1090 (m), 1050
(m), 1034 (vs), 967 (w), 916 (w), 867 (m), 796 (s), 761 (v), 721
(m) cm–1. MS (70 eV, EI): m/z (%) = 204 (5) [M – H]+, 147 (34)
[C7H7N7]+. HRMS (70 eV, EI): m/z calcd. for C10H14N5 [M – H]
204.1248; found 204.1237.
3
H), 7.39–7.33 (m, 3 H, Ph-H), 7.40 [q, JH,H = 7.1 Hz, 2 H, C(O)
OCH2], 1.41 [t, JH,H = 7.1 Hz, 3 H, C(O)OCH2CH3] ppm. 13C
3
NMR (75 MHz): δ = 165.9, 135.6, 132.7, 131.7, 130.8, 129.2, 128.5,
128.5, 128.4, 123.7, 122.9, 90.2, 88.4, 61.2, 14.3 ppm. IR (ATIR,
neat): ν = 3064 (vw), 3036 (vw), 2981 (w), 2935 (w), 2905 (vw),
˜
Synthesis of [CuCl2{HC(Pz)2(MeIm)}] (C1)
2213 (vw), 1717 (s), 1602 (w), 1578 (w), 1493 (m), 1443 (w), 1428
(w), 1392 (w), 1367 (m), 1317 (m), 1280 (m), 1303 (m), 1280 (m),
1250 (vs), 1146 (m), 1100 (m), 1080 (m), 1025 (m), 914 (m), 750
(vs), 686 (s) cm–1. MS (70 eV, EI): m/z (%) = 250 (100) [M]+, 205
(80) [C15H9O1]+, 176 (45) [C14H8]+, 151 (25) [C12H7]+. HRMS
(70 eV, EI): m/z calcd. for C17H14O2 250.0994; found 250.0991.
4-Trifluoromethyl-1-(2-phenylethynyl)benzene
CuCl2·2H2O (85 mg, 0.5 mmol, 1.0 equiv.) was dissolved in MeOH
(5 mL) and added to a solution of {HC(Pz)2(MeIm)} (L2) (114 mg,
0.5 mmol, 1.0 equiv.) in CH2Cl2 (6 mL). After 2 h, blue plates, Rf = 0.6 (isohexane Ǟisohexane/Et2O, 19:1); m.p. 100.6 °C. 1H
crystals suitable for X-ray diffraction were obtained (0.11 g,
NMR (300 MHz): δ = 7.67–7.51 (m, 6 H, Ph-H), 7.41–7.33 ppm
(m, 3 H, Ph-H) ppm. 13C NMR (75 MHz): δ = 132.0, 131.9, 130.1
[q, JC,F = 32.7 Hz], 129.0, 128.6, 127.3 [q, JC,F = 1.0 Hz], 125.4 [q,
JC,F = 3.8 Hz], 124.3 [q, JC,F = 272.2 Hz], 122.7, 91.2, 88.1 ppm.
0.3 mmol, 62%). IR (ATIR, neat): ν = 3113 (w), 2950 (w), 2869
˜
(vw), 2830 (w), 2774 (w), 1731 (vw), 1513 (w), 1464 (w),
1437 (w), 1391 (m), 1344 (w), 1325 (m), 1293 (m), 1249 (w), 1204
(m), 1151 (w), 1090 (m), 1050 (m), 1034 (vs), 967 (w), 916 (w), 867 19F NMR (282 MHz): δ = –62.8 ppm. IR (ATIR, neat): ν = 3036
˜
(m), 796 (s), 761 (v), 721 (m) cm–1. MS (FAB+): m/z (%) =
(vw), 2925 (vw), 2200 (w), 1608 (m), 1572 (w), 1486 (w), 1442 (w),
330 (11) [C11H1237Cl65CuN6]+, 328 (61) [C11H1237Cl63CuN6, 1405 (w), 1322 (m), 1154 (m), 1129 (m), 1104 (vs), 1065 (s), 1018
C11H1235Cl65CuN6]+, 326 (72) [C11H1235Cl63CuN6]+, 291 (100)
[C11H1263CuN6]+;
elemental analysis calcd. (%)
(m), 920 (w), 842 (s), 757 (s), 689 (s), 596 (m) cm–1. MS (70 eV,
for EI): m/z (%) = 246 (100) [M]+, 202 (40) [C13H8F2]+, 149 (17)
7480
www.eurjoc.org
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2015, 7475–7483

Bis(pyrazolyl)methane Copper Catalysts for Sonogashira Couplings
[C9H3F2]+. HRMS (70 eV, EI): m/z calcd. for C15H9F3 246.0657; 1-[(3-Benzyloxy)prop-1-ynyl]-4-(trifluoromethyl)benzene
found 246.0659.
3-(2-Phenylethynyl)anisole
Rf
=
0.56 (isohexane/Et2O, 19:1); yellow liquid. 1H NMR
(300 MHz): δ = 7.61–7.53 (m, 4 H), 7.43–7.39 (m, 4 H), 7.37–7.31
=
0.15 (isohexaneǞCH2Cl2); m.p. 57.2 °C. 1H NMR
(m, 1 H), 4.70 (s, 2 H), 4.43 (s, 2 H) ppm. 13C NMR (75 MHz): δ
Rf
(300 MHz): δ = 7.51–7.45 (m, 4 H, Ar-H), 7.34–7.29 (m, 3 H, Ar-
H), 6.86 [d, JH,H = 8.8 Hz, 2 H, Ar-H], 3.81 (s, 3 H, OCH3) ppm.
13C NMR (75 MHz): δ = 159.8, 133.3, 131.7, 128.5, 128.1, 123.8,
2
= 137.4, 132.1, 130.3 [q, JC,F = 32 Hz], 128.6, 128.2, 128.1, 126.6
4
3
1
[q, JC,F = 1.4 Hz], 125.4 [q, JC,F = 3.8 Hz], 124.0 [q, JC,F
=
270 Hz], 87.8, 85.2 [q, JC,F = 1.4 Hz], 71.9, 57.9 ppm. 19F NMR
4
115.6, 114.2, 89.6, 88.3, 55.5 ppm. IR (ATIR, neat): ν = 3061 (vw),
˜
(282 MHz): δ = –118.0 ppm. IR (ATIR, neat): ν = 3071 (vw), 3036
˜
2993 (vw), 2960 (vw), 2835 (vw), 2216 (w), 1604 (w), 1593 (m),
1569 (w), 1508 (m), 1464 (w), 1454 (w), 1439 (w), 1288 (w), 1245
(s), 1179 (m), 1139 (w), 1108 (m), 1070 (w), 1027 (m), 917 (w), 840
(vs), 813 (m), 779 (w), 752 (s), 691 (s) cm–1. MS (70 eV, EI): m/z
(%) = 208 (100) [M]+, 193 (42) [C14H9O]+, 165 (32) [C13H9]+.
HRMS (70 eV, EI): m/z calcd. for C15H12O 208.0886; found
208.0877.
(vw), 2925 (vw), 2855 (vw), 1888 (vw), 1586 (w), 1498 (s), 1443 (m),
1229 (m), 1187 (m), 1111 (m), 918 (w), 893 (m), 826 (s), 752 (vs),
687 (s) cm–1. MS (70 eV, EI): m/z (%) = 210 (100) [M]+, 183 (10)
[C13H8F1]+. HRMS (70 eV, EI): m/z calcd. for C15H11F 210.0843;
found 210.0837.
4-[(3-Benzyloxy)prop-1-ynyl]anisole
3-(Phenylethynyl)pyridine
Rf = 0.18 (isohexane/EtOAc, 99:1); yellow liquid. 1H NMR
(300 MHz): δ = 7.46–7.29 (m, 7 H, Ph-H), 6.89–6.84 (m, 2 H, Ph-
H), 4.70 (s, 2 H, OCH2), 4.41 (s, 2 H, OCH2), 3.82 (s, 3 H,
OCH2) ppm. 13C NMR (75 MHz): δ = 159.8, 137.6, 133.3, 128.5,
128.1, 127.8, 114.8, 114.0, 86.4, 83.7, 71.6, 58.0, 55.3 ppm. IR
Rf = 0.15 (isohexane/Et2O, 9:1Ǟisohexane/Et2O, 6:4); yellow solid;
m.p. 51.2 °C. 1H NMR (300 MHz): δ = 8.78 [dd, JH,H = 2.1, 0.9 Hz,
1 H, 2-py], 8.56 [dd, JH,H = 5.0, 1.8 Hz, 1 H, 6-py], 7.84 [dt, JH,H
= 8.0, 1.9 Hz, 1 H, 4-py], 7.59–7.54 (m, 2 H, Ph-H), 7.41–7.36 (m,
3 H, Ph-H), 7.31 [ddd, JH,H = 8.0, 5.0, 1.0 Hz, 1 H, 5-py] ppm. 13
C
(ATIR, neat): ν = 3064 (vw), 3032 (vw), 2934 (w), 2838 (w), 2236
˜
(w), 1606 (m), 1568 (w), 1508 (vs), 1454 (m), 1353 (m), 1291 (m),
1246 (vs), 1172 (m), 1070 (s), 964 (w), 830 (vs), 799 (m), 736 (s),
697 (s), 604 (m) cm–1. MS (70 eV, EI): m/z (%) = 252 (15) [M]+,
146 (100) [C10H10O1]+, 131 (45) [C9H7O]+. HRMS (70 eV, EI): m/z
calcd. for C17H16O2 252.1153; found 252.1144.
NMR (75 MHz): δ = 152.1, 148.3, 138.6, 131.7, 128.8, 128.5, 123.1,
122.5, 120.6, 92.8, 85.8 ppm. 19F NMR (282 MHz):
δ
=
–118.0 ppm. IR (ATIR, neat): ν = 3005 (vw), 1558 (w), 1489 (m),
˜
1470 (m), 1442 (m), 1414 (m), 1189 (w), 1176 (w), 1145 (w), 1123
(w), 1071 (w), 1020 (m), 920 (w), 814 (m), 756 (s), 709 (s), 690
(vs) cm–1. MS (70 eV, EI): m/z (%) = 179 (100) [M]+, 151 (10)
[C12H8]+, 126 (18) [C10H6]+. HRMS (70 eV, EI): m/z calcd. for
C13H9N 170.0604; found 179.0729.
3-[(3-Benzyloxy)prop-1-ynyl]pyridine
Ethyl 3-[(3-Benzyloxy)prop-1-ynyl]benzoate
1
Rf = 0.47 (isohexane/Et2O, 5:5); yellow oil. H NMR (300 MHz):
δ = 8.70 [d, JH,H = 1.3 Hz, 1 H, 2-py], 8.56 [dd, JH,H = 4.9, 1.6 Hz,
1 H, 6-py], 7.76 [dt, JH,H = 7.9, 3.9 Hz, 1 H, 4-py], 7.43–7.26 (m,
6 H, Ph-H, 5-py), 4.69 (s, 2 H, OCH2), 4.43 (s, 2 H, OCH2) ppm.
13C NMR (75 MHz): δ = 152.3, 148.7, 138.8, 137.2, 128.5, 128.1,
128.0, 123.0, 120.0, 88.7, 83.0, 77.3, 77.2, 77.0, 76.7 ppm. IR
(ATIR, neat): ν = 3030 (vw), 2852 (vw), 1584 (vw), 1561 (vw), 1496
˜
(w), 1475 (m), 1453 (vw), 1407 (m), 1353 (m), 1261 (vw), 1206 (vw),
1187 (w), 1071 (s), 1023 (m), 961 (w), 804 (m), 737 (s), 696
(vs) cm–1. MS (70 eV, EI): m/z (%) = 222 (36) [C15H13NO]+, 117
(63) [C8H7N]+, 91 (100) [C7H7]+. HRMS (70 eV, EI): m/z calcd. for
C15H13N 222.0900; found 222.0914.
Rf = 0.24 (isohexane/Et2O, 19:1); light-yellow oil. 1H NMR
(300 MHz): δ = 8.15 [td, JH,H = 2.2, 0.5 Hz, 1 H, Ph-H], 8.01 [ddd,
JH,H = 7.9, 1.6, 1.3 Hz, 1 H, Ph-H], 7.63 [td, JH,H = 8.7, 1.5 Hz, 1
H, Ph-H], 7.44–7.28 (m, 7 H, Ph-H), 4.60 (s, 2 H, CH2), 4.42 (s, 2
H, CH2), 4.39 [q, JH,H = 7.1 Hz, 2 H, C(O)OCH2], 1.41 [t, JH,H
=
Ethyl 3-(2-{[(1,1-Dimethylethyl)dimethyl]silyl}ethynyl)benzoate
7.1 Hz, 3 H, C(O)OCH2CH3] ppm;13C NMR (75 MHz): δ = 165.8,
137.4, 135.8, 132.8, 130.8, 129.4, 128.5, 128.4, 128.1, 127.9, 123.0,
86.1, 85.5, 71.8, 61.2, 57.8, 14.3 ppm. IR (ATIR, neat): ν = 3066
˜
(vw), 3032 (vw), 2982 (w), 2938 (vw), 2853 (w), 1717 (vs), 1602 (w),
1580 (w), 1478 (w), 1454 (w), 1431 (w), 1367 (m), 1353 (m), 1289
(s), 1224 (vs), 1168 (w), 1103 (s), 1073 (vs), 1026 (s), 913 (m), 817
(w), 751 (vs), 736 (s), 697 (s), 683 (s) cm–1. MS (70 eV, EI):
m/z (%) = 265 (54) [C18H17O2]+, 191 (23) [C15H11]+, 143 (65)
[C10H7O1]+, 91 (100) [C7H7]+; HRMS (70 eV, EI): m/z calcd. for Rf = 0.42 (isohexane/Et2O, 99:1); light-yellow liquid. 1H NMR
C19H18O3 294.1257; found 294.1254.
(300 MHz): δ = 8.12 [td, JH,H = 1.7, 0.5 Hz, 1 H, Ph-H], 7.97 [ddd,
Eur. J. Org. Chem. 2015, 7475–7483
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7481

S. Herres-Pawlis et al.
FULL PAPER
JH,H = 7.9, 1.7, 1.3 Hz, 1 H, Ph-H], 7.63 [ddd, JH,H = 7.7, 1.6,
1.3 Hz, 1 H, Ph-H], 7.37 [td, JH,H = 7.0, 0.8 Hz, 1 H, Ph-H], 4.38
[q, JH,H = 7.1 Hz, 2 H, C(O)OCH2], 3.35 [t, JH,H = 7.1 Hz, 3 H,
C(O)OCH2CH3], 1.00 [s, 9 H, SiC(CH3)3], 0.19 [s, 6 H, Si(Me)
2] ppm. 13C NMR (75 MHz): δ = 165.9, 136.0, 133.0, 130.6, 129.4,
128.3, 123.6, 104.6, 93.6, 61.2, 26.1, 16.7, 14.3, –4.7 ppm. IR
Acknowledgments
Financial support by the Deutsche Forschungsgemeinschaft
(DFG) (SFB 749, project B10) is gratefully acknowledged.
(ATIR, neat): ν = 3069 (vw), 2954 (w), 2930 (m), 2886 (w), 2857
˜
[1]
K. Sonogashira, Y. Tohda, N. Hagihara, Tetrahedron Lett.
1975, 16, 4467–4470.
(w), 2162 (w), 1722 (s), 1600 (w), 1579 (w), 1471 (w), 1464 (w),
1428 (w), 1368 (w), 1281 (s), 1249 (m), 1204 (s), 1103 (m), 1079
(m), 1023 (m), 920 (m), 828 (vs), 810 (m), 774 (s), 752 (vs), 684 (s),
672 (m), 620 (m) cm–1. MS (70 eV, EI): m/z (%) = 288 (7) [M]+, 231
(100) [C13H15O2Si]+, 203 (15) [C11H11O2Si]+. HRMS (70 eV, EI):
m/z calcd. for C17H24O228Si 288.1543; found 288.1541.
[2]
[3]
D. Wang, S. Gao, Org. Chem. Front. 2014, 1, 556–566.
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Angew. Chem. Int. Ed. 2009, 48, 4300–4316; Angew. Chem.
2009, 121, 4364; c) A. M. Thomas, A. Sujatha, G. Anilkumar,
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874–922.
1-(2-{[(1,1-Dimethylethyl)dimethyl]silyl}ethynyl)-4-(trifluorometh-
yl)benzene
[4]
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Rf
=
0.72 (isohexane/Et2O, 99:1); yellow liquid. 1H NMR
(300 MHz): δ = 7.56 (s, 4 H), 1.01 (s, 9 H), 0.21 (s, 6 H) ppm. 13C
NMR (75 MHz): δ = 132.4, 130.3 [q, 2JC,F = 34 Hz], 127.2 [q, 4JC,F
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= 1.4 Hz], 125.3 [q, 3JC,F = 3.8 Hz], 124.1 [q, 1JC,F = 271 Hz], 104.3
[q, JC,F
=
1.4 Hz], 95.8, 26.3, 16.9, –4.6 ppm. 19F NMR
4
(282 MHz): δ = –62.9 ppm. IR (ATIR, neat): ν = 2954 (w), 2930
˜
(w), 2888 (vw), 2859 (w), 2162 (w), 1614 (m), 1471 (w), 1463 (w),
1404 (w), 1363 (vw), 1320 (vs), 1250 (m), 1221 (w), 1167 (s), 1127
(vs), 1104 (vs), 1066 (vs), 1017 (m), 1007 (vw), 939 (vw), 836 (vs),
821 (vs), 807 (vs), 774 (vs), 682 (vs) cm–1. MS (70 eV, EI): m/z (%) =
284 (3) [M]+, 227 (100) [C11H10F3Si]+, 197 (5) [C9H4F3Si]+. HRMS
(70 eV, EI): m/z calcd. for C15H11F 210.0843; found 210.0837.
4-(2-{[(1,1-Dimethylethyl)dimethyl]silyl}ethynyl)anisole
Rf
=
0.68 (isohexane/Et2O, 99:1); yellow liquid. 1H NMR
(300 MHz): δ = 7.42–7.39 (m, 2 H, Ph-H), 6.83–6.80 (m, 2 H, Ph-
H), 3.81 (s, 3 H, OCH3), 0.99 [s, 9 H, SiC(CH3)3], 0.18 [s, 6 H,
Si(Me)2] ppm. 13C NMR (75 MHz): δ = 159.7, 133.5, 115.4, 113.8,
105.8, 90.7, 55.3, 26.2, 16.7, –4.5 ppm. IR (ATIR, neat): ν = 2954
˜
(m), 2929 (m), 2896 (w), 2856 (m), 2154 (m), 1606 (m), 1571 (w),
1507 (s), 1463 (m), 1292 (m), 1246 (vs), 1171 (m), 1106 (w), 1034
(m), 1007 (w), 851 (s), 824 (vs), 807 (vs), 773 (vs), 754 (s), 676 (m),
589 (w) cm–1. MS (70 eV, EI): m/z (%) = 246 (18) [M]+, 189 (100)
[C11H13OSi]+, 174 (7) [C10H10OSi]+. HRMS (70 eV, EI): m/z calcd.
for C15H22O28Si 246.1440; found 261.1435.
3-(2-{[(1,1-Dimethylethyl)dimethyl]silyl}ethynyl)pyridine
1
Rf = 0.31 (isohexane/Et2O, 9:1); yellow oil. H NMR (300 MHz):
δ = 8.70 [d, JH,H = 1.3 Hz, 2-py], 8.53 [dd, JH,H = 4.8, 1.5 Hz, 1
H, 6-py], 7.77 [dt, JH,H = 7.7, 1.9 Hz, 1 H, 4-py], 7.26 [ddd, JH,H
= 8.0, 4.8, 1.0 Hz, 1 H, 5-py], 1.00 [s, 9 H, SiC(CH3)3], 0.20 [s, 6
H, Si(Me)2] ppm. 13C NMR (75 MHz): δ = 152.3, 148.3, 139.2,
123.0, 120.6, 101.9, 97.0, 77.3, 77.2, 77.0, 76.7, 26.1 ppm. IR
(ATIR, neat): ν = 2953 (w), 2929 (m), 2885 (vw), 2857 (w), 2161
˜
(w), 1559 (vw), 1473 (m), 1463 (m), 1406 (m), 1362 (w), 1249 (m),
1236 (w), 1183 (w), 1022 (w), 1007 (w), 833 (vs), 802 (vs), 774 (vs),
703 (s), 683 (s) cm–1. MS (70 eV, EI): m/z (%) = 217 (12) [M]+, 160
(100) [C9H10NSi]+, 130 (8) [C7H4NSi]+. HRMS (70 eV, EI): m/z
calcd. for C13H19N28Si 217.1299; found 217.1286.
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Received: September 1, 2015
Published Online: October 29, 2015
Eur. J. Org. Chem. 2015, 7475–7483
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
7483