Acetylene and terminal alkyne complexes of copper(i) supported by fluorinated pyrazolates: Syntheses, structures, and transformations

Article abstract of DOI:10.1039/c9dt03350e

Trinuclear {μ-[3,5-(CF₃)₂Pz]Cu}₃ reacts with acetylene to produce the 2:1 copper(i) acetylene complex, Cu₄(μ-[3,5-(CF₃)₂Pz])₄(μ-HCCH)₂. Related Cu₄(μ-[4-Br-3,5-(CF₃)₂Pz])₄(μ-HCCH)₂ and Cu₄(μ-[4-Cl-3,5-(CF₃)₂Pz])₄(μ-HCCH)₂ have also been isolated using the corresponding copper(i) pyrazolate and acetylene. The 1:1 adducts Cu₂(μ-[3,5-(CF₃)₂Pz])₂(HCCH)₂ and Cu₂(μ-[4-Br-3,5-(CF₃)₂Pz])₂(HCCH)₂ are significantly less stable to the acetylene loss and can be observed in solution at low temperatures under excess acetylene. The X-ray crystal structures of 2:1 and 1:1 complexes, Cu₄(μ-[3,5-(CF₃)₂Pz])₄(μ-HCCH)₂ and Cu₂(μ-[4-Br-3,5-(CF₃)₂Pz])₂(HCCH)₂ are reported. Raman data show a reduction in _CC stretching frequency by about ～340 and ～163 cm^-1 in the 2:1 and 1:1 Cu(i)/acetylene complexes, respectively, from that of the free acetylene. Copper(i) pyrazolate complexes of the terminal alkynes, phenylacetylene, 1,8-nonadiyne, and 1,7-octadiyne are also reported. They form adducts involving one copper atom on each alkyne moiety. The {μ-[3,5-(CF₃)₂Pz]Cu}₃ is also a very versatile and competent catalyst for alkyne transformations as evident from its ability to catalyze the alkyne C(sp)-H bond carboxylation chemistry with CO₂, azide-alkyne cycloadditions leading to 1,2,3-triazoles including the use of acetylene itself as a substrate, and thiol addition to phenylacetylene affording vinyl sulfides.

Full text of DOI:10.1039/c9dt03350e

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10.1039/C9DT03350E.
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Number 10
14 March 2017
Pages 3073-3412
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Acetylene and terminal alkyne complexes of copper(I) supported by
fluorinated pyrazolates: Syntheses, structures, and transformations
Devaborniny Parasar, Tharun T. Ponduru, Anurag Noonikara Poyil, Naleen B. Jayaratna, and H.
V. Rasika Dias*
Affiliations:
Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington,
Texas 76019, United States
*Correspondence to: dias@uta.edu (H.V.R.D.)
1

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Abstract. Trinuclear {-[3,5-(CF3)2Pz]Cu}3 reacts with acetylene to produce the 2:1 copper(I)
acetylene complex, Cu4(-[3,5-(CF3)2Pz])4(-HCCH)2. Related Cu4(-[4-Br-3,5-(CF3)2Pz])4(-
HCCH)2 and Cu4(-[4-Cl-3,5-(CF3)2Pz])4(-HCCH)2 have also been isolated using the
corresponding copper(I) pyrazolate and acetylene.
The 1:1 adducts Cu2(-[3,5-
(CF3)2Pz])2(HCCH)2 and Cu2(-[4-Br-3,5-(CF3)2Pz])2(HCCH)2 are significantly less stable to
the acetylene loss and can be observed in solution at low temperatures under excess acetylene.
The X-ray crystal structures of 2:1 and 1:1 complexes, Cu4(-[3,5-(CF3)2Pz])4(-HCCH)2 and
Cu2(-[4-Br-3,5-(CF3)2Pz])2(HCCH)2 are reported. Raman data show a reduction in ῡCC
stretching frequency by about ~340 and ~163 cm-1 in the 2:1 and 1:1 Cu(I)/acetylene complexes,
respectively, from that of the free acetylene. Copper(I) pyrazolate complexes of the terminal
alkynes, phenylacetylene, 1,8-nonadiyne, and 1,7-octadiyne are also reported. They form adducts
involving one copper atom on each alkyne moiety. The {-[3,5-(CF3)2Pz]Cu}3 is also a very
versatile and competent catalyst for alkyne transformations as evident from its ability to catalyze
the alkyne C(sp)-H bond carboxylation chemistry with CO2, azide-alkyne cycloadditions leading
to 1,2,3-triazoles including the use of acetylene itself as a substrate, and thiol addition to
phenylacetylene affording vinyl sulfides.
2

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Introduction
Trinuclear copper pyrazolates are of significant interest due to their fascinating
photophysical properties and tendency to self-assemble via Cu•••Cu contacts.1-16 For example, the
copper complex {-[3,5-(CF3)2Pz]Cu}3 (1) exhibits bright orange luminescence, which can be
fine- and coarse-turned to multiple bright visible colors by varying solvents, concentration,
temperatures, and excitation wavelength.1, 2 Dendritic, trinuclear Cu(I) pyrazolate complexes
carrying long alkyl chains have been utilized in the fabrication of rewritable phosphorescent
paper.4 Trinuclear copper pyrazolates also serve as good precursors to produce various mixed
ligand complexes or hybrid materials with different nuclearities and/or supramolecular structures.7,
9, 17-23
For example, dinuclear Cu2(-[3,5-(CF3)2Pz])2(2,4,6-collidine)2 obtained from {-[3,5-
(CF3)2Pz]Cu}3 and 2,4,6-collidine show ligand based blue emissions that are different from the
orange emissions of the precursor {-[3,5-(CF3)2Pz]Cu}3.24 Some of these copper complexes such
as {-[3,5-(CF3)2Pz]Cu}3 with electron-withdrawing fluoroalkyl groups on the ligand backbones
act as π-acidic units, and are known to associate with electron rich arenes (e.g., benzene,
mesitylene) and C60 leading to 2D- or 3D-stacks.18, 25, 26 In addition, copper pyrazolates also show
promise in catalysis,27-34 and adsorption and/or separation of small molecules,10, 20, 35, 36 but these
applications have received relatively less scrutiny.
Copper mediates many important transformations involving alkynes such as hetero atom-
hydrogen bond additions, cycloaddition chemistry, cyclopropenation, Csp-H bond
functionalizations, and alkyne coupling processes.37-53 Copper alkyne or alkynide complexes are
believed to be key intermediates in most of these reactions. Copper alkynes are also used as
precursors for the copper deposition.54, 55 Despite the importance of copper in alkyne chemistry
and the availability of a large number and a diverse group of binary copper(I) pyrazolates,
3

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coordination chemistry of copper pyrazolates with alkynes, or the use of copper-pyrazolates as
catalysts in alkyne transformations remain virtually unexplored. There was an isolated report in
2002 relevant to this topic concerning the synthesis Cu2(-[3,5-(CF3)2Pz])2(Me3SiCCSiMe3)2, as
a chemical vapor deposition (CVD) precursor for copper.56 As the first part of a detailed
investigation into this area, we reported the isolation of di- and tetra-nuclear copper complexes
such as 2 and 3 (Figure 1) resulting from the reaction between tri-nuclear {-[3,5-(CF3)2Pz]Cu}3
(1) and internal-alkynes, together with their structures (including molecules featuring bridged,
22-/4e-alkyne donors) and photophysical properties.57 Here we describe the coordination
chemistry of copper(I) pyrazolates with acetylene and terminal-alkynes, as well as the use of {-
[3,5-(CF3)2Pz]Cu}3 as a catalyst in the carboxylation, azide-cycloaddition and hydrothiolation of
alkynes. Recently, a communication appeared on the use of {-[3,5-(CF3)2Pz]Cu}3 in click-
chemistry, and the isolation of two mixed-valent copper alkyne complexes (resulting from the
partial oxidation of Cu(I) in the precursor).58 Their report complements the azide-alkyne
cycloaddition results described in this manuscript.
F3C
CF3
N
N
Cu
Cu
CF3
F3C
N
N
N
N
Cu
1
CF3
F3C
Et
Et
F3C
CF3
Et
CF3
Et
Cu
Cu
F3C
N
N
N
N
N
N
Et
Et
N
Cu
N
Cu
CF3
N
N
Cu
Cu
F3C
N
N
CF3
F3C
Et
F3C
CF3
F3C
CF3
2
Et
3
Figure 1. Diagram showing the structures of {-[3,5-(CF3)2Pz]Cu}3 (1), Cu2(-[3,5-
(CF3)2Pz])2(EtCCEt)2 (2), and Cu4(-[3,5-(CF3)2Pz])4(-EtCCEt)2 (3)
4

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Results and Discussion
Coordination chemistry of copper pyrazolates with acetylene:
R
F3C
CF3
N
N
Cu
Cu
CF3
R
F3C
R
N
N
N
N
Cu
CF3
F3C
Limited acetylene
Excess acetylene
H
H
H
H
CF3
F3C
Cu
Cu
CF3
Cu
CF3
H
Cu
F3C
H
N
N
N
N
F3C
N
N
R
R
R
R
R
R
N
N
N
N
N
N
F3C
CF3
Cu
Cu
CF3
F3C
CF3
F3C
H
H
R = H (5), Br (8)
R = H (4), Br (6), Cl (7)
4/3 {-[3,5-(CF3)2Pz]Cu}3 + 2 HCCH  Cu4(-[3,5-(CF3)2Pz])4(-HCCH)2 (4)
2/3 {-[3,5-(CF3)2Pz]Cu}3 + 2 HCCH  Cu2(-[3,5-(CF3)2Pz])2(HCCH)2 (5)
eq. 1
eq. 2
Figure 2. Structures and synthetic routes to tetra-nuclear complexes Cu4(-[3,5-(CF3)2Pz])4(-
HCCH)2 (4), Cu4(-[4-Br-3,5-(CF3)2Pz])4(-HCCH)2 (6), Cu4(-[4-Cl-3,5-(CF3)2Pz])4(-
HCCH)2 (7) and di-nuclear complexes and Cu2(-[3,5-(CF3)2Pz])2(HCCH)2 (5) and Cu2(-[4-
Br-3,5-(CF3)2Pz])2(HCCH)2 (8) from tri-nuclear copper(I) pyrazolates and acetylene.
The highly fluorinated {-[3,5-(CF3)2Pz]Cu}3 reacts with purified acetylene (~1 atm)53, 59
in CH2Cl2, affording Cu4(-[3,5-(CF3)2Pz])4(-HCCH)2 (4) as a white, crystalline solid in >90%
yield (Figure 2, eq. 1). The room temperature 1H NMR data of 4 in CDCl3 displayed the presence
of a 2:1 Cu:acetylene complex, and a large, down-field shift of acetylenic proton resonances
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(observed at  6.16 ppm) relative to the corresponding signal of the free acetylene ( 2.05 ppm).
The ῡCC band of solid 4 in the Raman spectrum was observed at 1638 cm-1, representing a
significant (336 cm-1) red shift relative to the corresponding stretching frequency of the free
acetylene (1974 cm-1).60
Although there is a long history of copper(I)-acetylene chemistry,61, 62 copper(I) acetylene
complexes with detailed structural and spectroscopic data are surprisingly scarce. This is perhaps
due to challenges such as facile loss of coordinated acetylene, copper acetylide formation, and the
potential explosion hazard associated with this work.62-64 The search of Cambridge Structural
Database65 revealed eight structurally characterized copper-acetylene complexes. These include,
[Cu{NH(Py)2}(HCCH)]BF4 and [Cu(phen)(HCCH)]ClO4 complexes with Cu(2-
HCCH) moieties,63, 66, 67 and polymeric or octanuclear, chloride bridged copper(I) adducts
containing
22-(HCCH)
moieties.68-70
Among
these,
compound
[Cu{NH(Py)2}(HCCH)]BF4 has 1H NMR and IR data available for comparison, and displays its
acetylenic proton resonance and ῡCC band at  5.59 ppm and 1796 cm-1, respectively.66 The CC
stretch of [Cu(phen)(HCCH)]ClO4 has been reported at 1800 cm-1.67 These two copper adducts
featuring 2-acetylene moieties show only about 174-179 cm-1 lowering of their acetylene CC
stretching frequency upon coordination to Cu(I). Both the NMR shifts and ῡCC data of the
acetylene ligands of Cu4(-[3,5-(CF3)2Pz])4(-HCCH)2 (4) are however, significantly different
from these adducts, and suggest the presence of a 22-acetylene group rather than the 2-
acetylene moiety. Note that even larger down field shifts of acetylenic proton resonance71 and
more significant reductions in CC stretching frequency have been reported for coordinated
acetylene (e.g., ῡCC band of Co2(CO)6(-HCCH) in IR was observed at 1402 cm-1, which is
6

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about 570 cm-1 lower than that of free acetylene),72 but they involve earlier transition metal ions
instead of Cu(I).
Figure 3. Molecular structure of Cu4(-[3,5-(CF3)2Pz])4(-HCCH)2 (4); ORTEP view with 50%
probability ellipsoids are shown. Disordered atoms of the minor occupancy (12%) component
have been removed for clarity.
The X-ray crystal structure of Cu4(-[3,5-(CF3)2Pz])4(-HCCH)2 (4) is illustrated in
Figure 3. It is a tetranuclear copper(I) complex with trigonal planar copper sites and sits on an
inversion center. Unfortunately, this molecule shows positional disorder over two orientations (at
88%:12% occupancy), which was rather challenging initially to recognize (see supporting
information), but was resolved satisfactorily. Although metrical parameters (Table 1) are not ideal
for a detailed analysis due to the disorder, the basic structural features and atom connectivities are
clear and indicate the presence of 22-(HCCH) moieties, consistent with the spectroscopic
data. There are close intramolecular Cu•••Cu contacts that are within the van der Waals separation
of two copper atoms.73 It is also interesting to note that during the formation of 4, copper
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pyrazolate moieties of {-[3,5-(CF3)2Pz]Cu}3 rearrange to form two separate six-membered,
Cu2N4 fragments, whereas in Cu4(-[3,5-(CF3)2Pz])4(-EtCCEt)2 (3), they form a large 12-
membered Cu4N8 metallacycle (see Figures 1 and 2).57
We could not isolate the 1:1 complex, Cu2(-[3,5-(CF3)2Pz])2(HCCH)2 (5) involving non-
bridging acetylene as a solid, from solutions containing even large excess of acetylene with {[3,5-
(CF3)2Pz]Cu}3 (Figure 2, eq. 2). This is however, not surprising based on the similar findings
reported by us and others involving alkynes like 2-butyne with {-[3,5-(CF3)2Pz]Cu}3 or
MeCCCO2Me with copper(I) trifluoroacetate.57, 74 Only the tetranuclear copper complexes
featuring bridging alkynes have been preferentially precipitated from these reactions, despite the
presence of an excess of alkyne. The VT-NMR data of {-[3,5-(CF3)2Pz]Cu}3 in the presence of
excess acetylene in CD2Cl2 indicated the likely presence of Cu2(-[3,5-(CF3)2Pz])2(HCCH)2 (5)
in solution, as evident from the appearance of a broad signal at  4.86 ppm corresponding to bound
acetylene, starting at about -35 ºC during the cooling process. It is still broad even at -70 ºC
indicating the presence of extremely labile copper-bound acetylene group in 5 that rapidly
exchanges with free acetylene on the NMR time scale.
The work involving CO and fluorinated copper(I) pyrazolates indicates that more weakly
coordinating pyrazolates such as [3,4,5-(CF3)3Pz] offer greater stability to, and allow relatively
easier isolation of the dinuclear Cu-CO adducts such as Cu2(-[3,4,5-(CF3)3Pz])2(CO)2 relative to
that of Cu2(-[3,5-(CF3)2Pz])2(CO)2.19 Accordingly, we also investigated the chemistry of {-[4-
75
Br-3,5-(CF3)2Pz]Cu}3,75 and {-[4-Cl-3,5-(CF3)2Pz]Cu}3 with acetylene (Figure 2). The
treatment of {-[4-Br-3,5-(CF3)2Pz]Cu}3 and {-[4-Cl-3,5-(CF3)2Pz]Cu}3 with acetylene in
1
CH2Cl2 followed by the cooling at -20°C afforded white crystalline solids. The H NMR and
8

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Raman spectroscopic data of these samples however, indicated the formation of Cu4(-[4-Br-3,5-
(CF3)2Pz])4(-HCCH)2 (6) and Cu4(-[4-Cl-3,5-(CF3)2Pz])4(-HCCH)2 (7) featuring bridging
acetylenes, respectively, rather than molecules with 2e-donor, 2-(HCCH) ligands.52, 63, 66, 67 For
example, copper-bound acetylene proton signal of 6 and 7 was observed at  6.03 and 6.04 ppm,
respectively, whereas their CC stretch in Raman spectra was detected at 1631 and 1632 cm-1,
respectively. These values are similar to those observed for the tetranuclear Cu4(-[3,5-
(CF3)2Pz])4(-HCCH)2 (4). The solubility of 6 and 7 in less polar solvents like hexanes are rather
limited once the solid is formed. Unfortunately, many attempts to grow acceptable crystals of 6
and 7 for X-ray crystallography failed. Twinning and the formation of badly inter-twined crystals
are common. Interestingly, solids obtained from certain batches of Cu4(-[4-Br-3,5-(CF3)2Pz])4(-
HCCH)2 (6) in CH2Cl2 solutions at -20 ºC indicated the presence of two types of crystals and
new-band at 1810 and 1811 cm-1 in the IR and Raman spectra, respectively (in addition to the ῡCC
band due to 6). These new peaks with relatively small changes in CC frequency (compared to
the free acetylene ῡCC) are indicative of a copper-bound, non-bridging acetylene moiety. Indeed,
a careful analysis of a needle-shaped crystal fragment (found as a minor product amongst diamond
shaped, and often badly twinned crystals) revealed the presence of 1:1 adduct, Cu2(-[4-Br-3,5-
(CF3)2Pz])2(HCCH)2 (8). It was later obtained as the major product (and as much better-quality
single crystals) using toluene as the solvent of crystallization. X-ray crystal structure of this
molecule is illustrated in Figure 4. It crystallizes with molecules of toluene in the crystal lattice,
and sits on a mirror plane. The copper sites adopt trigonal planar geometry and acetylenes bind to
copper atoms in an 2-fashion. The average CC bond distance of 8 (1.227 Å) is slightly longer
than the corresponding distance of free acetylene (1.2033(2) Å).60
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Figure 4. Molecular structure of Cu2(-[4-Br-3,5-(CF3)2Pz])2(HCCH)2 (8); ORTEP view with
50% probability ellipsoids are shown.
Table 1. Selected bond distances (Å) and angles (º) for Cu2(-[3,5-(CF3)2Pz])2(EtCCEt)2 (2),
Cu4(-[3,5-(CF3)2Pz])4(-EtCCEt)2 (3), Cu4(-[3,5-(CF3)2Pz])4(-HCCH)2 (4), Cu2(-[4-Br-
3,5-(CF3)2Pz])2(HCCH)2
(8),
Cu2(-[3,5-(CF3)2Pz])2(HCCPh)2
(9),
Cu2(-[3,5-
(CF3)2Pz])2(HCC(CH2)5CCH) (10), Cu4(-[3,5-(CF3)2Pz])4(HCC(CH2)4CCH)2 (11), and
Cu4(-[3,5-(CF3)2Pz])4(C2H5CC(CH2)4CCC2H5)2 (12). Average values are given below, and
specific bond distances and angles are presented in CIF and Supporting Information section.
Parameter\
Complex
3
4*
2
8
9
10
11
12
-
1.987
-
1.269
1.961
2.647
-
1.970
-
1.943
1.996
1.226
1.971
3.161
1.955
2.008
1.229
1.978
3.136
1.958
1.992
1.220
1.975
3.128
-
av. Cu-C(H)
av. Cu-C(C)
av. CC
av. Cu-N
Shortest
2.016
1.265
1.978
2.646
1.978
1.981
1.234
1.982
3.074
1.227 1.227
1.985 1.972
3.051 3.200
Cu•••Cu
av. C-Cu-C
av. C-CC
av. N-Cu-N
-CC- bonding
mode
36.57
155.2
108.99
37.24
-
103.04
36.13 36.28
36.23
161.4
100.05
2-
36.10
161.1
98.13
2-
35.97
163.7
100.04
2-
36.29
162.4
97.85
2-
161.2
-
97.49 98.95
22- 22-
2-
2-
57
This work
57
This work
This work
This work
This work
This work
ref
*Metrical parameters of 4 should be used with due caution considering the disorder. Only the bond distance/angle
values for major occupancy component are provided for compound 4.
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The Raman spectrum of solid samples of 8 displays a strong band at 1811 cm-1,
corresponding to the ῡCC. This represent a 163 cm-1 reduction in stretching frequency as a result
of copper-coordination, relative to that of the free acetylene.60 Solid samples of 8 (even with a
thin, hydrocarbon oil coating) lose acetylene upon standing at room temperature in air, as evident
from the gradual intensity loss of 1811 cm-1 band over several hours, and a complete disappearance
within a day. This process accompanies the gradual growth of the 1636 cm-1 band, pointing to the
formation of a bridged-acetylene species 6, which is relatively more stable to the loss of acetylene.
Notably, we could not observe the NMR signal of the coordinated acetylene in 8 in CD2Cl2 at
room temperature, as it rapidly loses some of the acetylene during the dissolution (can even
observe the release of bubbles when the NMR solvent is added to dissolve the crystals), and
establishes a fast equilibrium with the free acetylene on the NMR time scale. We can however
observe this resonance at low temperatures in the presence of excess acetylene. The copper bound
acetylenic proton signal of 8 was observed as a broad peak at  4.75 ppm in CD2Cl2. We have
not probed the acetylene chemistry of 4-chloro analog {-[4-Cl-3,5-(CF3)2Pz]Cu}3 in greater detail
apart from the isolation of 7, although it could also show similar chemistry as the 4-bromo analog,
{-[4-Br-3,5-(CF3)2Pz]Cu}3.
The solutions of 4 (in CH2Cl2) is notably sensitive and change color to brown on exposure
to air or upon removal of the solvent under reduced pressure or if purged with nitrogen. It however,
remains stable for a few days under acetylene atmosphere both in solution (in -20 °C freezer) and
in solid state but slowly decomposes over time. In contrast, solutions of compounds 6 and 7 are
comparatively stable, and do not show noticeable color changes upon exposure to air or if purged
with nitrogen briefly. Both these complexes remain stable for days in solution (in a freezer) and in
solid state under an acetylene atmosphere. In the presence of excess acetylene at room
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1
temperature, solutions of tetranuclear 4, 6 and 7 lose the bound acetylene signal in H NMR
spectrum indicating fast exchange with free acetylene, and perhaps the formation of 1:1 Cu:alkyne
adducts.
Coordination chemistry of copper(I) pyrazolates with terminal-alkynes:
F3C
CF3
N
N
Cu
Cu
CF3
F3C
N
N
N
N
Cu
CF3
F3C
1
PhCCH
HCC(CH2)5CCH
Ph
H2
C
H2
C
Ph
H2
C
C
C
H2
H2
H
Cu
CF3
CF3
H
Cu
F3C
N
N
Cu
CF3
H
Cu
F3C
H
N
N
N
N
10
N
N
F3C
9
CF3
F3C
Scheme 1. Synthetic routes to di-nuclear complexes Cu2(-[3,5-(CF3)2Pz])2(HCCPh)2 (9) and
Cu2(-[3,5-(CF3)2Pz])2(HCC(CH2)5CCH) (10) from tri-nuclear {[3,5-(CF3)2Pz]Cu}3 and the
corresponding alkyne.
We have also explored the chemistry of phenylacetylene and 1,8-nonadiyne with {-[3,5-
(CF3)2Pz]Cu}3. The treatment of the copper pyrazolate with slight excess of these terminal alkynes
in
CH2Cl2
led
to
Cu2(-[3,5-(CF3)2Pz])2(HCCPh)2
(9)
and
Cu2(-[3,5-
(CF3)2Pz])2(HCC(CH2)5CCH) (10) in high yield (Scheme 1). They show their CC stretch in
Raman at 1932 (average of three bands observed at 1918, 1928, 1950 cm-1) and 1946 cm-1,
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respectively, indicating the presence of typical, non-bridging, 2e donor, 2-alkynes on copper.
They represent a ~179 and 169 cm-1 reduction in stretching frequency upon Cu(I) coordination
(free phenylacetylene and 1,8-nonadiyne display their CC stretch in Raman at 2011 and 2015 cm-
1
,
respectively).
For comparison, the bis(pyrazolyl)borate complex [H2B(3,5-
(CF3)2Pz)2]Cu(HCCPh) exhibits its CC band at 1927 cm-1,76 while the mixed-valent Cu{(-
[3,5-(CF3)2Pz])2Cu(HCCPh)}2 and Cu{(-[3,5-(CF3)2Pz])2Cu(HCCC6H13)}2 show their CC
bands at 1910 and 1945 cm-1,58 respectively, in their IR spectra. Copper complexes featuring 2
and 22-bound, internal alkyne 3-hexyne, Cu2(-[3,5-(CF3)2Pz])2(EtCCEt)2 (2) and Cu4(-
[3,5-(CF3)2Pz])4(-EtCCEt)2 (3), show their ῡCC bands in Raman at 2050 and 1874 cm-1,
respectively, and about 210 and 386 cm-1 red shifts relative to the corresponding stretching
frequency of the free EtCCEt.57
Figure 5. Molecular structure of Cu2(-[3,5-(CF3)2Pz])2(HCCPh)2 (9); ORTEP view with 50%
probability ellipsoids are shown.
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X-ray crystal structures of 9 and 10 confirm the formation of dinuclear species containing
alkyne ligands bonded to copper in an 2-fashion. Compound Cu2(-[3,5-(CF3)2Pz])2(HCCPh)2
(9) crystallized in the P space group with two chemically similar but crystallographically different
1
molecules in the asymmetric unit. One of these molecules is depicted in Figure 5. In these
molecules, phenylacetylene ligands orient in a similar fashion with phenyl moieties pointing in the
same direction. The Cu2N4 metallacycle adopts the familiar boat shape.
Figure 6. Molecular structure of Cu2(-[3,5-(CF3)2Pz])2(HCC(CH2)5CCH) (10); ORTEP view
with 50% probability ellipsoids are shown.
The X-ray structure of Cu2(-[3,5-(CF3)2Pz])2(HCC(CH2)5CCH)(10) is shown in Figure
6. The 1,8-nonadiyne serves as an intramolecular bridge for two copper sites of the dinuclear
“Cu2(-[3,5-(CF3)2Pz])2” fragment, and the alkyne groups coordinate to copper atoms in an 2-
1
fashion. H NMR resonances corresponding to H-C protons of 9 and 10 in CDCl3 at room
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13
temperature appear as broad singlets at  3.17 and 4.33 ppm, respectively. The C NMR peaks
assignable to the CC carbons are also broad suggesting that the alkyne groups in these complexes
are rather labile in solution at ambient temperatures.
F3C
CF3
N
N
Cu
Cu
CF3
F3C
N
N
N
N
Cu
1
CF3
F3C
R'CC(CH2)4CCR'
R'
H2
C
H2
C
R'
CF3
F3C
C
C
CF3
H2
Cu
H2
F3C
Cu
N
N
N
N
N
N
N
N
CF3
Cu
R'
F3C
H2
C
Cu
H2
C
CF3
F3C
C
C
H2
H2
R'
R' = H (11), Et (12)
Scheme 2. Synthetic routes to Cu4(-[3,5-(CF3)2Pz])4(HCC(CH2)4CCH)2 (11) and Cu4(-[3,5-
(CF3)2Pz])4(C2H5CC(CH2)4CCC2H5)2 (12) from tri-nuclear {[3,5-(CF3)2Pz]Cu}3 and the
corresponding alkyne.
We have investigated the effect of alkyne moiety linker length on copper-alkyne adduct
formation by using a terminal bis-alkyne 1,7-octadiyne, as well as an internal bis-alkyne 3,9-
dodecadiyne ligands with {-[3,5-(CF3)2Pz]Cu}3 (Scheme 2). The X-ray crystal structures of the
resulting molecules Cu4(-[3,5-(CF3)2Pz])4(HCC(CH2)4CCH)2 (11) and Cu4(-[3,5-
(CF3)2Pz])4(C2H5CC(CH2)4CCC2H5)2 (12) are illustrated in Figure 7. In these 11 and 12, the
two alkyne moieties are linked by a four-carbon, –(CH2)2– linker, and they serve as a bridge to
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two-separate dinuclear “Cu2(-[3,5-(CF3)2Pz])2” fragments.
In contrast, the di-alkyne
HCC(CH2)5CCH with a five-carbon linker in 10 acts as in intramolecular bridge to a single
“Cu2(-[3,5-(CF3)2Pz])2” moiety (Scheme 1). Thus, it appears that anything shorter than the five-
carbon –(CH2)5– linker in these aliphatic bis-alkyne molecules is not long enough to bridge Cu
atoms of dinuclear “Cu2(-[3,5-(CF3)2Pz])2” fragments in an intra-dimer fashion.
Figure 7. Molecular structures of Cu4(-[3,5-(CF3)2Pz])4(HCC(CH2)4CCH)2 (11) (top) and
Cu4(-[3,5-(CF3)2Pz])4(C2H5CC(CH2)4CCC2H5)2 (12) (bottom); ORTEP views with 50%
probability ellipsoids are shown.
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A comparison of metrical parameters of 3 and 4 containing 4e-donor, 22-alkynes to
2, 8-12 featuring 2e-donor, 2-alkyne ligands (Table 1) show that the former group of molecules
have longer CC bonds, which is expected and consistent with the vibration spectroscopic data.77
Also, compound 3 shows a greater alkyne bending-back angle (deviation from linearity of the
alkyne C-CC bond angle) as a result of the coordination of two copper atoms compared to those
of the 2 and 9-12 that have only one copper atom on each alkyne. The structural data from 9-11
with terminal alkynes indicate that the Cu-C(H) bond is significantly shorter than the Cu-C(C)
bond length, which is probably a result of steric effects. The coordinated alkyne groups of 4 and
8-12 are co-planar with respect to the trigonal plane of copper (i.e., N2CuC2 atoms are in the same
plane; see Supporting information). These molecules represent a rare group of structurally
characterized, terminal alkyne complexes of copper, derived from binary copper(I) pyrazolates.
The
mix-valent,
Cu{(-[3,5-(CF3)2Pz])2Cu(HCCPh)}2
and
Cu{(-[3,5-
(CF3)2Pz])2Cu(HCCC6H13)}2 featuring Cu(I) and Cu(II) sites are the only copper-alkyne-
pyrazolates that are somewhat related to 8-11 in the literature.58
Copper(I) pyrazolates in alkyne transformations. Despite the importance of copper in alkyne
chemistry,37-53 and the ease of synthesis and availability of many copper(I) pyrazolates, they have
not been used widely as catalysts in alkyne transformations. We have been working on the
chemistry of highly fluorinated copper pyrazolates,2, 78 and copper-alkyne complexes for a number
of years.76, 79-81 Fluorinated copper pyrazolates serve as excellent Lewis acids and bind to
molecules with lone pairs (e.g., CO, pyridines) or -electrons (e.g., alkene, alkynes).19, 20, 23-26, 57
During this work, we noticed that they are also competent catalysts for several processes that
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transform alkynes. Here we report the use of fluorinated copper pyraolates as a catalyst in the
carboxylation, azide-cycloaddition and hydrothiolation of alkynes.
Carboxylation of the terminal alkynes: Incorporation of carbon dioxide into molecules is a
significant current interest.45, 47 One way to achieve this is via the insertion of CO2 into C(sp)-H
bonds of terminal alkynes leading to carboxylic acids. Copper is turning out to be an important
catalyst in this regard.45, 47 For example, CuCl with various ligands (e.g., TMEDA) in the presence
of K2CO3 have been reported to mediate CO2 insertion to phenylacetylene.47 We found that {-
[3,5-(CF3)2Pz]Cu}3 is also effective in this process. It does not require an external base and the
reactions proceed at 1 atm of CO2 at the room temperature (Table 2). For example, {-[3,5-
(CF3)2Pz]Cu}3 at 2 mol% level, catalyzes the reaction between phenylacetylene and CO2 at room
temperature and produces PhC2CO2H in 72% isolated yield (entry 1). In these reactions, molecules
resulting from an alkyne coupling were also observed as a minor product.
Table 2. Carboxylation of terminal alkynes using {-[3,5-(CF3)2Pz]Cu}3 (2 mol%)as the catalyst.
{[3,5-(CF3)2Pz]Cu}3 (2 mol%)
R
+
H
CO2
DMF, R.T., 1 atm
OH
R
+
R
R
O
Product A
Product B
Entry
R
Time
(h)
12
12
12
% Yield
(Product A) (Product B)
% Yield
1
2
3
H
CH3
Cl
72
80
64
10
2
5
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Azide-alkyne cycloaddition.
Copper catalyzed synthesis of 1,2,3-triazoles via the cycloaddition of azides to triple bonds of
alkynes is perhaps the most well-known process involving copper and alkynes.38, 40, 82-84 The
standard catalytic system uses copper(II) salts such as copper sulfate pentahydrate in the presence
of a reducing agent, such as sodium ascorbate.83 During our work involving copper(I) pyrazolates
and alkynes, we discovered that {-[3,5-(CF3)2Pz]Cu}3 is an excellent catalyst for the
cycloaddition of azides to terminal alkynes. Furthermore, it also mediates similar chemistry with
acetylene,85 which is rare (Scheme 3). It is important to note that a report appeared recently on the
use of {-[3,5-(CF3)2Pz]Cu}3 in click chemistry with 1-octyne and phenylacetylene with ortho-
fluorobenzyl azide.58 That work complements the findings reported below involving terminal
alkynes.
N
-Tol
p
{[3,5-(CF3)2Pz]Cu}3 (1 mol%)
CH2Cl2, R.T., 1 atm, 12 h
N
N
+
H
H
-TolNNN
p
99%
N
-Tol
p
N
N
{[3,5-(CF3)2Pz]Cu}3 (1 mol%)
CH2Cl2, R.T., 12 h
H
R'
+
+
-TolNNN
p
99%
R' = Ph or -hexyl
R'
n
{[3,5-(CF3)2Pz]Cu}3 (1 mol%)
Benzene, 80 oC, 12 h
TolNNN
p-
H
(CH2)5
H
N
N
-Tol
p
-Tol
p
N
N
N
N
(CH2)5
99%
Scheme 3. The {-[3,5-(CF3)2Pz]Cu}3 catalyzed alkyne-azide cycloaddition involving acetylene
or various terminal alkynes as the alkyne source and p-tolylazide
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Specifically, the trinuclear copper(I) pyrazolate {-[3,5-(CF3)2Pz]Cu}3 (1 mol%) catalyzes
the cycloaddition of p-tolylazide to acetylene (1 atm) to form the desired 1-substituted-1,2,3-
triazole in quantitative yield based on the NMR spectroscopic analysis of the product mixture
(Scheme 1). Reaction proceeds in CH2Cl2 under mild conditions and no heating or base is required.
The reactions ensue equally well with phenylacetylene or 1-octyne as the alkyne source affording
the corresponding 1,4-disubstituted 1,2,3-triazole.86 Mild reaction conditions of the copper
pyrazolate catalyzed process and the high yields are noteworthy, as also highlighted by Titov and
co-workers.58
We have also successfully converted 1,8-nonadiyne to the corresponding 1,4-disubstituted
1,2,3-triazole using p-tolylazide (Scheme 3). Although it produces the bis-triazole product in
quantitative yield, this reaction required the use of slightly elevated temperature (80 °C) and
benzene as the solvent. The control reaction at this temperature (with no copper catalyst) produces
the product in 19% yield. The -[3,5-(CF3)2Pz]Cu}3 catalyzed process at room temperature also
gives the product, but in low yield (13%). Overall, this work indicates that the trinuclear copper(I)
pyrazolate {-[3,5-(CF3)2Pz]Cu}3 can be used as an efficient catalyst to prepare 1-substituted-
1,2,3-triazoles and 1,4-disubstituted 1,2,3-triazoles using just the organic azide and an alkyne
source. Some of the isolable copper-alkyne complexes described earlier (e.g., Table 1), resulting
from the same alkynes and {-[3,5-(CF3)2Pz]Cu}3 combination may exist as intermediates in these
processes.
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Hydrothiolation of alkynes.
Copper also plays an important role as a catalyst in the alkyne hydrothiolation chemistry
which leads to an important class of compounds, vinyl sulfides.37, 87-92 We found that {-[3,5-
(CF3)2Pz]Cu}3 is an effective catalyst in this process involving phenylacetylene and thiophenol
(Table 3). For example, it catalyzes (1 mol%) the addition of thiol group of PhSH to the alkyne
moiety of PhCCH at room temperature under CO2 producing PhCHCHSPh in 70% isolated yield
(entry 1). Note that both the E- and Z-isomers are obtained, which is not unusual for a copper
catalyzed process.88 Interestingly, the control reaction without the catalyst also produces the
product,91 albeit in lower yield (e.g., 42% yield (with almost opposite E:Z of 30:70) at room
temperature after 3 h under CO2).
The E/Z stereoselectivity of {-[3,5-(CF3)2Pz]Cu}3 catalyzed reaction is somewhat
complicated, and dependent on reaction time, reaction temperature and the atmosphere. For
o
example, at 0 C and after 3 h of reaction time (entry 2), we have observed different
stereoselectivities for reactions carried out under CO2 (E/Z ratio = 26:74) and N2 atmosphere (E/Z
ratio = 10:90). At 90 oC and after 16 h of reaction time, a reversal in product stereoselectivity was
observed (E/Z ratio = 78:22) in the reaction performed under CO2 atmosphere compared to the 3h
reaction at 0°C (entries 4 and 2). The change in product ratio was less significant for the reaction
carried out under N2 atmosphere (E/Z ratio = 34:66 vs 10:90). The hydrothiolation chemistry
reported by Y. Zhang and coworkers using CuI (5 mol%) catalyst (in DMSO with K2CO3 as a
base)88 under similar reaction temperatures and time, also generated very different product ratios
under CO2 and argon (E/Z ratio = 10:90 and 84:16, with 92% and 68% yields, respectively). Note
also that the E/Z stereoselectivity is nearly opposite for the two copper catalysts (i.e., E/Z ratio =
10:90 and 78:22 for CuI and {-[3,5-(CF3)2Pz]Cu}3 catalyzed reactions, respectively). The
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isolated product yields of each {-[3,5-(CF3)2Pz]Cu}3 catalyzed experiment were relatively low,
when the reactions were performed under N2 instead of CO2. We have thus far not probed various
temperature, solvent, reaction time effects in detail. This work however, shows that copper
pyrazolates are competent catalysts for alkyne hydrothiolations.
Table 3. Hydrothiolation of terminal alkynes using {-[3,5-(CF3)2Pz]Cu}3 (1 mol %) as the
catalyst. Yields reported are isolated yields (average from two separate experiments). The E/Z
ratio was determined by 1H NMR analysis.
Ph
SPh
+
{[3,5-(CF3)2Pz]Cu}3 (1 mol%)
toluene
PhSH
Ph
SPh
Ph
Z-isomer
E-isomer
H
Entry Temp Time Under
Under
N2
Overall % yield Overall % yield
(oC)
(h)
CO2
under CO2
under N2
(E:Z)
63:37
26:74
30:70
78:22
(E:Z)
50:50
10:90
56:44
34:66
1
2
3
4
RT
0
90
90
3
3
3
16
70
65
78
90
56
48
62
81
Summary and Conclusions
Overall, we describe convenient routes to HCCH and terminal alkyne (phenylacetylene, 1,8-
nonadiyne, 1,7-octadiyne) complexes of copper(I) using readily available, fluorinated copper(I)
pyrazolates and the corresponding alkynes. The 2:1 copper:acetylene complexes Cu4(-[3,5-
(CF3)2Pz])4(-HCCH)2 (4), Cu4(-[4-Br-3,5-(CF3)2Pz])4(-HCCH)2 (6), and Cu4(-[4-Cl-3,5-
(CF3)2Pz])4(-HCCH)2 (7) are easier to isolate and relatively more stable in solid state and
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solution. They have bridging acetylene ligands as evident from the NMR and Raman
spectroscopic data and confirmed for 4 by X-ray crystallography. Low temperature NMR data
suggest the existence of 1:1 Cu:alkyne adducts, perhaps of the type Cu2(-[3,5-
(CF3)2Pz])2(HCCH)2 (5) and Cu2(-[4-Br-3,5-(CF3)2Pz])2(HCCH)2 (8) in solutions containing
excess acetylene. They are however, extremely labile in solution, and challenging to isolate than
4, 6, or 7. Compound 8 has been isolated in crystalline form, and characterized structurally but it
loses acetylene even in the solid state. Raman data show a reduction in ῡCC stretching frequency
from 1974 cm-1 in free acetylene to 1811 cm-1 in the 2-/2e-donor acetylene adduct 8 and, more
drastically, to 1631 cm-1 in the bridged 22-/4e-donor adduct 6. The terminal alkynes,
phenylacetylene, 1,8-nonadiyne, and 1,7-octadiyne easily form their 2-/2e-donor alkyne adducts
Cu2(-[3,5-(CF3)2Pz])2(HCCPh)2 (9), Cu2(-[3,5-(CF3)2Pz])2(HCC(CH2)5CCH) (10), and
Cu4(-[3,5-(CF3)2Pz])4(HCC(CH2)4CCH)2 (11) that have 1:1 Cu/alkyne stoichiometry.
Isolation of a copper(I)-pyrazolate 12 containing an internal alkyne is also reported. In addition
to alkyne coordination, the {-[3,5-(CF3)2Pz]Cu}3 is also a very versatile and competent catalyst
for alkyne transformations. We have presented its utility in C(sp)-H bond carboxylation with CO2,
facile azide-alkyne cycloaddition leading to 1,2,3-triazoles including the rare chemistry involving
acetylene itself, and S-H addition to alkyne moiety leading to vinyl sulfides. We are currently,
exploring further details on these copper-alkyne chemistry and additional transformations of
alkynes mediated by copper. Note that unlike the often used copper halide catalysts, these copper
pyrazolates can be more easily fine-tuned sterically and electronically via changes to pyrazolyl
ring substituents, which is a useful attribute for homogeneous catalysts.
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Experimental details.
General procedures. All manipulations were carried out under an atmosphere of purified
nitrogen using standard Schlenk techniques unless otherwise noted. Solvents were purchased from
commercial sources, and distilled prior to use. NMR spectra were recorded at 25 °C on a JEOL
Eclipse 500 spectrometer (1H, 500.16 MHz; 13C, 125.78 MHz; 19F, 470.62 MHz), unless otherwise
noted. Proton and carbon chemical shifts are reported in ppm versus Me4Si. 19F NMR values were
referenced to external CFCl3. Melting points were obtained on a Mel-Temp II apparatus and were
not corrected. Elemental analyses were performed using a Perkin-Elmer Model 2400 CHN
analyzer. Infrared spectra were recorded on a Shimadzu IR Prestige-21 spectrometer. Raman data
were collected on a Horiba Jobin Yvon LabRAM Aramin Raman spectrometer with a HeNe laser
source of 633nm. High-resolution mass spectra (HRMS) were recorded in Electron spray
ionization time-of-flight (ESI/TOF) mode. Samples were introduced as a solution in
dichloromethane. The {μ-[3,5-(CF3)2Pz]Cu}3, {μ-[4-Br-3,5-(CF3)2Pz]Cu}3, and {μ-[4-Cl-3,5-
(CF3)2Pz]Cu}3 were prepared according to reported literature procedures with slight
modifications.75, 78 p-Tolyl azide was prepared according to literature procedure.93 Acetylene gas
was freed from acetone and purified before use.59 All other reactants and reagents were purchased
from commercial sources.
Warning. Due care must be taken when working with acetylene gas. It is known to produce
explosive combinations with oxygen, and also form potentially explosive acetylides and other
materials with copper salts.53
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Synthesis of Cu4(μ-[3,5-(CF3)2Pz])4(μ-HC≡CH)2 (4)
{-[3,5-(CF3)2Pz]Cu}3 (1) (0.25 g, 0.312 mmol) was dissolved in 10 mL of dichloromethane and
stirred for ~10 min while bubbling acetylene as a steady stream (1 atm) through the solution. The
reaction mixture was concentrated with continuous flow of acetylene and kept at -20 °C to obtain
X-ray quality colorless crystals of Cu4(μ-[3,5-(CF3)2Pz])4(μ-HC≡CH)2. Yield: >90%. M.p.: 170
°C (decomp.). 1H NMR (in CDCl3): δ (ppm) 6.16 (s, 2H, CH), 6.84 (s, 2H, Pz-H). 19F NMR (in
13
CDCl3): δ (ppm) -60.1 (s). C{1H} NMR (in CDCl3): δ (ppm) 79.2 (br s, C≡C), 104.8 (s, C-4),
1
2
120.7 (q, JC-F =268.7 Hz, CF3), 143.0 (br q, JC-F = 37.8 Hz, C-3/C-5). Raman (cm-1), selected
peak: 1638 (C≡C). Anal. Calc. C24H8Cu4F24N8•0.4C15H3Cu3F18N6: C, 25.05%; H, 0.64%; N,
10.13%. Found: C, 25.68%; H, 0.74%; N, 10.02%. Compound 4 lose some acetylene under
reduced pressure leading to 1. Signals corresponding to {-[3,5-(CF3)2Pz]Cu}3 were also observed
1
in the solutions of resulting material. H NMR (in CDCl3): δ (ppm) 7.01 (br s, 2H, Pz-H). 19F
NMR (in CDCl3): δ (ppm) -61.0 (br s).
Generation of Cu2(-[3,5-(CF3)2Pz])2(HCCH)2 (5)
{µ-[3,5-(CF3)2Pz]Cu}3 (1) (4 mg) was dissolved in 1.5 mL CD2Cl2 in a NMR tube and acetylene
gas was bubbled for 30 to 60 s. The NMR tube was quickly sealed and the 1H and 19F NMR data
were collected at different temperatures (21 °C, -10 °C, -35 °C, -60 °C and -70 °C). A broad peak
started to appear around 4.8 ppm at -35 °C which is likely the signal from bound acetylene of
1
Cu2(µ-[3,5-(CF3)2Pz])2(HCCH)2. H NMR (in CD2Cl2 at -70 °C): δ (ppm) 6.92 (s, Pz-H), 4.86
(br s, CH). 19F NMR (in CD2Cl2 at -70 °C): δ (ppm) -59.7 (s). We could not isolate this molecule
as a solid, as all attempts even in the presence of excess acetylene led to the precipitation of 4.
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Synthesis of Cu4(-[4-Br-3,5-(CF3)2Pz])4(-HCCH)2 (6)
{-[4-Br-3,5-(CF3)2Pz]Cu}3 (0.25 g, 0.241 mmol) was dissolved in 10 mL of dichloromethane and
stirred for ~10 min while bubbling acetylene as a steady stream (1 atm) through the solution. The
reaction mixture was concentrated using an acetylene stream and kept at -20 °C to obtain Cu4(-
[4-Br-3,5-(CF3)2Pz])4(-HCCH)2 as a crystalline solid. Yield: 85%. M.p.: 180 °C (decomp.). 1H
NMR (in CDCl3): δ (ppm) 6.03 (s, 2H, CH). 19F NMR (in CDCl3): δ (ppm) -59.5 (s). Solid 6 does
not show good solubility in most NMR solvents to collect good 13C NMR data. 13C{1H} NMR (in
(CD3)2CO): δ (ppm) 74.0 (br s, C≡C), 92.8 (s, C-4), 121.7 (br, CF3), 142.6 (br, C-3/C-5). Raman
(cm-1), selected peaks: 1631 (C≡C). Anal. Calc. C24H4Br4Cu4F24N8: C, 20.09%; H, 0.28%; N,
7.81%. Found: C, 20.87%; H, 0.31%; N, 8.01%. Indicates minor acetylene loss leading to the
precursor copper pyrazolate. Also in solution, some Cu4(-[4-Br-3,5-(CF3)2Pz])4(-HCCH)2
dissociates into {-[4-Br-3,5-(CF3)2Pz]Cu}3 and free acetylene as evident from 19F and 1H NMR
data.
Generation and isolation of Cu2(-[4-Br-3,5-(CF3)2Pz])2(HCCH)2 (8)
{µ-[4-Br-3,5-(CF3)2Pz]Cu}3 (4 mg) was dissolved in 1.5 mL CD2Cl2 in a NMR tube and acetylene
gas was bubbled for 30 to 60 s. The NMR tube was quickly sealed and the 1H and 19F NMR data
were collected at different temperatures (21 °C, -10 °C, -35 °C, -60 °C and -70 °C). A broad peak
started to appear around 4.7 ppm at -35 °C which is likely the signal from bound acetylene of
1
Cu2(µ-[4-Br-3,5-(CF3)2Pz])2(HCCH)2. H NMR (in CD2Cl2 at -70 °C): δ (ppm) 4.75 (br s, 4H,
19
CH). F NMR (in CD2Cl2 at -70 °C): δ (ppm) -59.7 (s). X-ray quality crystals of Cu2(µ-[4-Br-
3,5-(CF3)2Pz])2(HCCH)2 was obtained in toluene at -20 °C. For that, 50 mg of {µ-[4-Br-3,5-
(CF3)2Pz]Cu}3 was dissolved in 8 mL of dry dichloromethane in 50 mL Schlenk flask and
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acetylene gas was bubbled until all dichloromethane was evaporated and white powder was
obtained. This white powder was dissolved in 10 mL of dry toluene under acetylene atmosphere
and kept at -20 °C refrigerator to obtain colorless crystals. Raman (cm-1), selected peak: 1811
(C≡C). IR (cm-1), selected peak: 1810. This molecule losees acetylene easily in solution or in the
solid.
Synthesis of Cu4(-[4-Cl-3,5-(CF3)2Pz])4(-HCCH)2 (7)
{-[4-Cl-3,5-(CF3)2Pz]Cu}3 (0.25 g, 0.276 mmol) was dissolved in 10 mL of dichloromethane,
and acetylene was bubbled as a steady stream (1 atm) through the solution for 10 mins. The
reaction mixture was concentrated using acetylene stream and kept at -20 °C to obtain Cu4(-[4-
Cl-3,5-(CF3)2Pz])4(-HCCH)2 as a white, crystalline solid. Yield: 87%. M.p.: 180 °C (decomp.).
1H NMR (in CDCl3): δ (ppm) 6.04 (s, 2H, CH). 19F NMR (in CDCl3): δ (ppm) -59.6 (s). Solid 7
13
13
does not show good solubility in most NMR solvents to collect good C NMR data. C{1H}
NMR (in (CD3)2CO): δ (ppm) 74.1 (br s, C≡C), 109.6 (s, C-4), 119.4 (br, CF3), 140.7 (br q, C-
3/C-5). Raman (cm-1), selected peaks: 1632 (C≡C). Anal. Calc. C24H4Cl4Cu4F24N8: C, 22.93%;
H, 0.32%; N, 8.92%. Found: C, 22.53%; H, 0.56 %; N, 8.45 %. Compound 7 tend to lose some
acetylene under reduced pressure. Also in solution, some Cu4(-[4-Cl-3,5-(CF3)2Pz])4(-
HCCH)2 dissociates into {-[4-Cl-3,5-(CF3)2Pz]Cu}3 and free acetylene as evident from 19F and
1H NMR data.
Synthesis of Cu2(-[3,5-(CF3)2Pz])2(HCCPh)2 (9)
Phenylacetylene (0.096 g, 0.936 mmol) was added dropwise to a solution of {-[3,5-
(CF3)2Pz]Cu}3 (1) (0.25 g, 0.312 mmol) in dichloromethane (~10 mL) at room temperature. The
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reaction mixture was stirred for 4 h under nitrogen, and the resulting solution was reduced to
dryness by evaporation of solvent under vacuum to obtain Cu2(-[3,5-(CF3)2Pz])2(HCCPh)2 as
an off-white solid. X-ray quality crystals were grown from dichloromethane at -20 C. Yield:
>90%. M.p.: 55-57 C. 1H NMR (in CDCl3): δ (ppm) 3.17 (br s, 2H, CH), 7.01 (s, 2H, Pz-H), 7.32
(m, J = 6.65 Hz, 6H, CH), 7.47 (d, J = 6.85 Hz, 4H, CH). 19F NMR (in CDCl3): δ (ppm) -61.0 (s).
1
13C{1H} NMR (in CDCl3): δ (ppm) 77.8 (br s, C≡C), 104.6 (s, C-4), 120.5 (q, JC-F = 268.3 Hz,
CF3), 122.4 (s, Phenyl-C), 128.8 (s, m-CH), 129.4 (s, p-CH), 132.3 (s, o-CH), 144.4 (br q, 2JC-F
=
13
37.2 Hz, C-3/C-5). The C{1H} NMR peak of the quaternary carbon atom of the triple bond of
phenylacetylene broadens into the base line at around 84-85 ppm and as a result, it is difficult to
pinpoint its exact position. Raman (cm-1), selected peaks: 1918, 1928 and 1950 (C≡C). Anal. Calc.
C26H14Cu2F12N4: C, 42.34%; H, 1.91%; N, 7.60%. Found: C, 42.37%; H, 1.94%; N, 7.69%.
Synthesis of Cu2(-[3,5-(CF3)2Pz])2(HCC(CH2)5CCH) (10)
{-[3,5-(CF3)2Pz]Cu}3 (1) (0.25 g, 0.312 mmol) was dissolved in the dichloromethane (~10 mL)
under nitrogen at room temperature. To this solution, 3 equivalents of 1,8-nonadiyne (0.11g, 0.936
mmol) was slowly added and stirred for ~ 4 h. The solution was then filtered and dried under
reduced pressure to obtain crude white Cu2(-[3,5-(CF3)2Pz])2(HCC(CH2)5CCH) as solid
product. X-ray quality crystals were grown from dichloromethane at -20°C. Yield: 82%. M.p.: 144
°C. 1H NMR (in CDCl3): δ (ppm) 1.31 (br s, 4H, CH2), 1.53 (m, J = 7.5 Hz, 2H, CH2), 2.61 (br s,
19
4H, CH2), 4.33 (br s, 2H, CH), 6.81 (s, 2H, Pz-H). F NMR (in CDCl3): δ (ppm) -60.54 (s).
13C{1H} NMR (in CDCl3): δ (ppm) 21.7 (br s, alkyne C-3/C-7), 26.4 (br s, alkyne C-4/C-5/C-6),
75.1 (br s, C≡C), 96.4 (br s, C-2/C-8), 103.6 (s, C-4), 121.6 (q, 1JC-F =268.3 Hz, CF3), 142.2 (br
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q, JC-F = 37.2 Hz, C-3/C-5). Raman (cm-1), selected peak: 1946 (C≡C). Anal. Calc.
C19H14Cu2F12N4: C, 34.92%; H, 2.16%; N, 8.57%. Found: C, 34.89%; H, 2.01%; N, 8.56%.
Synthesis of Cu4(-[3,5-(CF3)2Pz])4(HCC(CH2)4CCH)2 (11)
1,7- Octadiyne (0.080 g, 0.750 mmol) was added dropwise to a solution of {-[3,5-(CF3)2Pz]Cu}3
(1) (0.20 g, 0.250 mmol) in dichloromethane (~8 mL) in 3:1 molar ratio. The reaction mixture was
stirred for ~ 4 h under nitrogen at room temperature. The resulting mixture was filtered and dried
under reduced pressure to obtain Cu4(-[3,5-(CF3)2Pz])4(HCC(CH2)4CCH)2 as white solid. It
was recrystallized from dichloromethane at -20°C to obtain X-ray quality crystals of Cu2(µ-[3,5-
(CF3)2Pz])2(1,7-Octadiyne). Yield: 81%. Raman (cm-1), selected peak: 1952 (C≡C).
Synthesis of Cu4(-[3,5-(CF3)2Pz])4(C2H5CC(CH2)4CCC2H5)2 (12)
3,9-Dodecadiyne (0.091g, 0.561 mmol) was added dropwise to a solution of {-[3,5-
(CF3)2Pz]Cu}3 (1) (0.15 g, 0.187 mmol) in dichloromethane (~ 8 mL) in 3:1 molar ratio. The
reaction mixture was stirred for ~ 4 h under nitrogen at room temperature. The solution was then
filtered and dried under reduced pressure to obtain crude white Cu4(-[3,5-
(CF3)2Pz])4(C2H5CC(CH2)4CCC2H5)2 as solid product. X-ray quality crystals were grown from
dichloromethane at -20°C. Yield: 78%. M.p.: 118°C. 1H NMR (in CDCl3): δ (ppm) 1.11 (t, J = 7.2
Hz, 6H, CH3), 1.54 (br s, 4H, CH2), 1.57 (br s, 4H, CH2), 2.18 (br s, 4H, CH2), 7.01 (s, 2H, Pz-H).
13
19F NMR (in CDCl3): δ (ppm) -60.98 (s). C{1H} NMR (in CDCl3): δ (ppm) 13.1 (br s, CH3),
14.4 (br s, CH2), 19.1 (br s, CH2), 28.3 (br s, CH2), 80.3 (br s, C≡C), 83.2 (br s, C≡C), 104.3 (s,
C-4), 121.3 (br q, CF3), 143.9 (br q, C-3/C-5). Raman (cm-1), selected peaks: 2040 and 2070 (C≡C).
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