Interaction of a trinuclear copper(i) pyrazolate with alkynes and carbon-carbon triple bond activation

Article abstract of DOI:10.1039/c8cc08592g

The trinuclear copper(i) pyrazolate {[3,5-(CF₃)₂Pz]Cu}₃ forms η²-copper/alkyne triple bond coordinated structures in the presence of acetylenes. There is no coordination of copper atoms to the phenyl ring of phe

Full text of DOI:10.1039/c8cc08592g

Volume 55 Number 3 11 January 2019 Pages 259–418
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Aleksei A. Titov, Vladimir A. Larionov et al.
Interaction of a trinuclear copper(I) pyrazolate with alkynes
and carbon–carbon triple bond activation

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Interaction of a trinuclear copper(I) pyrazolate
with alkynes and carbon–carbon triple bond
activation†
Cite this: Chem. Commun., 2019,
5, 290
5
Received 26th October 2018,
Accepted 31st October 2018
a
ab
a
Aleksei A. Titov, ‡* Vladimir A. Larionov, ‡* Alexander F. Smol’yakov,
a
ab
a
Maria I. Godovikova, Ekaterina M. Titova, Victor I. Maleev
and
DOI: 10.1039/c8cc08592g
a
Elena S. Shubina
rsc.li/chemcomm
The trinuclear copper(I) pyrazolate {[3,5-(CF
)
3 2
Pz]Cu}
3
forms
2
g -copper/alkyne triple bond coordinated structures in the
presence of acetylenes. There is no coordination of copper atoms
to the phenyl ring of phenylacetylene and copper(I) acetylide
formation during the interaction. It was observed that the com-
plexes formed are the active catalytic species in click reactions.
In the last decade, copper(I) pyrazolate complexes have
1
–3
attracted wide attention due to their diverse structures, rich Fig. 1 Structure of complex {[3,5-(CF ) Pz]Cu} .
3
2
3
2,4–13
supramolecular chemistry,
in the areas of luminescence,
Being Lewis acids, trinuclear copper(I) pyrazolates have shown demonstrate the application of the complex as an efficient catalyst
and many potential applications
14–23
24–28
29
catalysis,
and adsorption.
3
0,31
interesting structural features forming infinite stacks by metallo- for alkyne–azide cycloaddition under mild conditions.
1
6,17
philic bonding
or by complexation with bases such as
The titration of 1-octyne or phenylacetylene solutions in
3
,10
5,9
init
p-electron systems of arenes
or sandwich compounds,
However, no data on the complexa- bands (3304 cm for 1 and 3307 and 3294 cm for 2) decrease,
tion of copper(I) pyrazolate macrocycles with compounds contain- while new low-frequency n(CH)
ing triple bonds have been reported so far. Furthermore, despite 3217 cm for 2) appear in the IR spectra (Fig. 2 and see Fig. S1 in
the fact that many copper(I) complexes are active catalysts in the ESI†). Simultaneously, similar changes are observed in the
certain types of reactions, e.g., the dimerization of acetylenes
a vast majority of the works on n(CRC) bands (2115 cm for 1 and 2110 cm for 2) decrease
macrocyclic copper(I) pyrazolates has been devoted towards the and new low-frequency n(CRC)
CH
2
Cl
2
with [CuL]
3
showed that the intensities of their n(CH)
6
,21
11,19
À1
À1
ketones
and halogens.
in compl
À1
bands (3222 cm for 1 and
À1
30
region of CRC stretching vibrations: the intensities of the initial
31,32
init
À1
À1
and alkyne–azide cycloaddition,
bonded
À1
bands (1945 cm for 1 and
À1
investigation of supramolecular aggregation and its influence on 1910 cm for 2) appear (see Fig. S2 in the ESI†). The coordination
the properties of the macrocycles, but without considering possible of the copper(I) salts to the carbon–carbon triple bond is known to
activation of the coordinated bonds of bases.
entail the appearance of new low-frequency bands in the n(CH)
3
3,34
Herein we report our results on the complexation of the tri- and n(CRC) regions.
Therefore, this spectral behavior
to the p-electron
3
); Fig. 1) with 1-octyne 1 and phenylacetylene 2 and system of the triple bond but not the formation of the copper(I)
nuclear copper(I) bis-(trifluoromethyl)pyrazolate ({[3,5-(CF
[CuL]
3
)
2
Pz]Cu}
3
evidences the coordination of macrocycle [CuL]
3
(
acetylide complex via proton elimination. Moreover, the absence of
the high frequency bands in both the regions of n(CH) and
n(CRC) stretching vibrations in the case of the complexation
a
A.N. Nesmeyanov Institute of Organoelement Compounds of Russian Academy of
Sciences (INEOS RAS), Vavilov St. 28, 119991 Moscow, Russian Federation.
E-mail: tit@ineos.ac.ru, larionov@ineos.ac.ru
of phenylacetylene with [CuL] suggests the absence of coordina-
3
b
Peoples’ Friendship University of Russia (RUDN University), Miklukho-Maklaya St. 6,
17198 Moscow, Russian Federation
tion of copper atoms to the phenyl ring that could be expected
based on the well-known affinity of trinuclear group 11 metal
1
†
Electronic supplementary information (ESI) available. CCDC 1871238 and
871239. For ESI and crystallographic data in CIF or other electronic format
3
,10
pyrazolates to aromatic hydrocarbons.
The Job plot for the
1
complexation of [CuL] with 1-octyne (obtained at a total
3
see DOI: 10.1039/c8cc08592g
‡
Both authors contributed equally to this work.
concentration of 0.05 M) has a maximum at 0.66 mole fraction
2
90 | Chem. Commun., 2019, 55, 290--293
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resonance of the quaternary carbon atom of the triple bond (C2)
broadens into a base line and it is impossible to establish its
position. The carbon resonance of the CH group of 1 close to the
2
CRC bond also undergoes low field shifting and broadening,
which confirms the complex formation. All the above mentioned
observations prove unequivocally that the interaction of the
copper(I) macrocycle with both acetylenes 1 and 2 in solution
yields intermolecular complexes, in which the p electron system of
2
the carbon–carbon triple bond is bound to copper via Z -type
coordination. Furthermore, despite the well-known high affinity of
3,10
trinuclear copper pyrazolates to arenes,
there is no interaction
with the phenyl ring of phenylacetylene 2 in the solution.
The structures of the complexes were unveiled by single crystal
X-ray diffraction analysis. Brownish crystals of both complexes
Fig. 2 IR spectra of 1-octyne 1 (c = 0.05 M, black) and 1 in the presence of
3 2 2
increasing amounts of [CuL] (0.5 equiv.: red, 1 equiv.: blue) in CH Cl ,
d = 2 mm, T = 298 K.
[
CuL]
slow solvent evaporation from equimolar reagent mixtures in
of 1-octyne (see Fig. S3 and S4 in the ESI†), suggesting that two CH Cl /hexane (1 : 1) solutions in air. Surprisingly, both complexes
acetylene molecules and one macrocycle molecule take part in appeared to contain two copper(I) atoms and one copper(II) atom
the complex formation.
linked by four pyrazolate ligands. The oxidation of copper(I) to
The titration of 1-octyne or phenylacetylene solutions in copper(II) corresponds to the presence of oxygen/moisture in the
3 3
/phenylacetylene 3 and [CuL] /1-octyne 4 were obtained by
2
2
1
CD
the acetylene group in 1 and 2 to a significantly low field, while and in the plane of four neighboring nitrogen atoms (Fig. 4).
other proton resonances (except for the CH group protons
In both complexes each copper(I) atom is coordinated to
2 2 3
Cl with complex [CuL]
shifts the H NMR resonances of reaction vessel. Copper(II) atoms are located on the inversion centers
2
close to the CRC of 1-octyne, vide infra) shift to a high field. an acetylene fragment via MÁ Á Áp interaction (the distances
Thus, the addition of one equivalent of the macrocycle [CuL] to between Cu and the CRC bond centroid are 1.879 Å for 3
3
a solution of phenylacetylene leads to a non-significant high and 1.890 Å for 4). Also, the C–C bond lengths are in the range
field shift of aromatic proton resonances (Dd = –0.06 to –0.12 ppm) typical for triple bonds, being 1.218 and 1.224 Å for 3 and 4,
3
5
and a considerable low field shift of an acetylene proton (Dd = respectively. Furthermore, the solid state IR spectra of crystals
0.54 ppm) (see Fig. S5 and S6 in the ESI†). The integration shows 3 and 4 are similar to the IR spectra in solution, meaning that
+
that the ratio of phenyl protons to a proton at the triple bond of 2 the structures of 3 and 4 are the same in the solid state and in
does not change upon macrocycle addition (remaining 5 : 1), which solution (see Fig. S9 and S10 in the ESI†). As the trinuclear
evidences the absence of the proton elimination and formation of macrocycles dissociate into mononuclear (MPz) and dinuclear
13
a copper(I) acetylide complex (see Fig. S6 in the ESI†). The
C
2 2
(M Pz ) species at low concentrations, this could be the driving
NMR resonances of the carbons at the triple bond broaden and force for their reorganization in the presence of alkynes, yield-
2
undergo significant low field shifts in the presence of an equi- ing the Cu Pz (Z -alkyne) complexes 3 and 4. Unfortunately,
3 4 2
molar amount of the macrocycle (Dd = +0.85 to +3.31 ppm; Fig. 3). the complexity of the equilibria in solution prevents the reliable
At the same time, the resonances of quaternary (C3) and ortho- estimation of the formation constants for 3 and 4.
carbon atoms (C4) drift to a high field (Dd = –0.18 to –0.27 ppm),
while the resonances of meta- and para-carbons undergo compar-
1
able low field shifts (Dd = +0.14 to +0.34 ppm; Fig. 3). The H and
1
3
C NMR signals of 1-octyne show similar behavior in the presence
13
of the macrocycle (see Fig. S7 and S8 in the ESI†). The C NMR
13
Fig. 3
the presence of different amounts of [CuL]
grey, 0.75 equiv.: magenta, 1 equiv.: olive) in CD
C NMR spectra of phenylacetylene 2 (c = 0.05 M, blue) and 2 in
(0.25 equiv.: green, 0.5 equiv.:
Cl , T = 298 K.
Fig. 4 Crystal structures of 3 (left) and 4 (right). Copper and nitrogen
atoms are ellipsoids (50% probability level), and other atoms are sticks.
Fluorine atoms are omitted for clarity.
3
2
2
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through the activation of the carbon–carbon triple bond.
The detailed study of this catalytic reaction is now ongoing in
our laboratory and will be reported elsewhere.
We are grateful for the financial support from the Russian
Science Foundation (RSF grant 14-13-00801). X-ray studies were
supported by the RUDN University Program 5-100.
Conflicts of interest
There are no conflicts to declare.
Notes and references
1
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Scheme 1 Alkyne–azide cycloaddition catalyzed by trinuclear copper(I)
3
pyrazolate complex [CuL] .
Next, we tested the ability of the trinuclear copper(I)
pyrazolate complex to catalyze the alkyne–azide cycloaddition
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addition of one equivalent of ortho-fluorobenzyl azide 5 to
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2
2
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,4-substituted 1,2,3-triazole in a quantitative yield by NMR
spectroscopy (Scheme 1a) (see Fig. S11 in the ESI†). The click
1
1
0 N. B. Jayaratna, C. V. Hettiarachchi, M. Yousufuddin and H. V.
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1
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12, 1001.
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1
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1
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