Discrete Benzotriazole-Copper(II) Complexes in Chelated and Non-Chelated Coordination Modes: Structural Analysis and Catalytic Application in Click and A3 Coupling Reactions

Article abstract of DOI:10.1002/ejic.202100103

Two copper(II) complexes with benzotriazole-based ligands having pyridyl and quinolinyl arms were synthesized in good yields and characterized fully via spectroscopic and crystallographic techniques. The crystal structures of the complexes revealed differ

Full text of DOI:10.1002/ejic.202100103

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doi.org/10.1002/ejic.202100103
Discrete Benzotriazole-Copper(II) Complexes in Chelated
and Non-Chelated Coordination Modes: Structural Analysis
and Catalytic Application in Click and A3 Coupling
Reactions
Sharmila Pandey*[a, b] and Tanmoy Mandal[a]
Two copper(II) complexes with benzotriazole-based ligands
having pyridyl and quinolinyl arms were synthesized in good
yields and characterized fully via spectroscopic and crystallo-
graphic techniques. The crystal structures of the complexes
revealed different coordination environments around copper(II)
centers. The difference in structure was due to the steric effect
of the ligands, which resulted in an octahedral and a square
pyramidal geometry of the resulting complexes in the solid
state. Both the air-stable complexes were utilized as precatalysts
in catalytic click reactions and A3 coupling.
Introduction
were found to be better catalysts than Cu(I)-NHC (NHC=N-
heterocyclic carbene) complexes in copper-catalyzed azide-
alkyne cycloaddition (CuAAC) reactions, probably due to
stronger σ-donating and π-accepting efficiency of the former
ligands than the later ones.[6] On the other hand, with regard to
the π-acceptor property, cyclic (alkyl)(amino)carbenes (CAACs)
are known to be very strong π-acceptor ligands.[7,8] Eventually,
catalytic CuAAC reactions were slow with CuÀ CAAC complexes,
and these ligands were even utilized to isolate Cu(I) acetylide
complexes which are potential catalytic intermediates in the
CuAAC reactions.[7,9]
Copper-catalyzed azide-alkyne cycloaddition (CuAAC), pop-
ularly known as “click reaction”[10] and aldehyde-amine-terminal
alkyne multicomponent reaction (MCR), popularly known as
“A3-coupling”,[11] are regarded as high-utility catalytic processes
in synthetic chemistry (Figure 1a). The products of these two
reactions – 1,2,3-triazoles and propargylamines respectively, are
extremely useful chemicals in various applications.[12,13,14] Pre-
vious studies disclosed that the click reaction, in the absence of
any catalyst, is sluggish, and requires harsh conditions, and
more importantly, it produces a mixture of both 1,4- and 1,5-
disubstituted 1,2,3-triazoles without any regioselectivity.[10]
However, the presence of a Cu(I) catalyst, results in a dramatic
improvement of both rate and regioselectivity of the same
reaction, yielding 1,4-disubstituted 1,2,3-triazoles under mild
reaction conditions. To avoid handling of unstable Cu(I) species,
often Cu(II) salts/compounds are used for in situ generation of
Cu(I) species. In further improvement, to overcome the
instability issues related to unprotected Cu(I) species, various
ligands are mixed with Cu(II) precursors. N-containing ligands,
and especially the nitrogen-containing heterocyclic ligands are
one of the most popular ligands in Cu-catalyzed click
reactions.[10] Similarly, as the A3-coupling reaction also proceeds
through a Cu(I) intermediate, the significance of N-heterocyclic
ligands is obviously very important in this reaction too. It is
noteworthy to mention that the application of pre-formed
Cu(II)-precursor complexes in these transformations are still
underexplored, in comparison to in situ protocols.[11]
The importance of N-donor ligands in the diverse and multi-
faceted chemistry of Cu is remarkable. The versatility of copper
chemistry stems from the easy access of a variety of oxidation
states such as Cu0, CuI, CuII, and CuIII which eventually facilitates
several catalytic processes involving radical as well as two-
electron routes.[1] The N-donor ligands possessing modular
electronic and steric properties are particularly suitable in
stabilizing such variable oxidation states of Cu, thus justifying
their immense significance in efficient operation of the relevant
catalytic cycles. Among several N-donor heterocyclic ligands,
benzotriazole-based motifs,[2,3,4,5] owing to some excellent
attributes such as inexpensive, simple, stable, and ready
accessibility, have been well-explored as suitable auxiliary
ligands in various Cu-catalyzed organic syntheses. In addition to
exhibiting very good σ-donor property, these nitrogen-enriched
benzotriazole ligands also act as excellent π-acceptors, and thus
they are able to stabilize low-valent Cu(I) intermediates which
are key to several catalytic reactions. In fact, recently Vargas and
Kostakis established the unique properties of this class of
ligands as efficient charge sinks due to the availability of
extended π-conjugation as well as uncoordinated N atoms
within the ligand backbone, which facilitates stabilization of
low oxidation states of Cu, such as Cu(I), during reductive
catalysis.[5] Notably, a balanced σ-donating and π-accepting
capability is expected to be the key in such reductive catalysis.
For example, Cu(I)-MIC (MIC=mesoionic carbene) complexes
[a] Dr. S. Pandey, T. Mandal
Department of Chemistry
Indian Institute of Science Education and Research (IISER) Bhopal
Bhopal 462 066, India
E-mail: sharmila.pandey@gmail.com
[b] Dr. S. Pandey
School of Sciences
SAGE University Bhopal
Bhopal 462 022, India
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/ejic.202100103
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Results and Discussion
Syntheses of ligands and complexes
Treatment of benzotriazole with 2-bromopyridine and 2-
choroquinoline, as per our previously reported protocol,
afforded the desired ligands
– 1-(pyridine-2-yl)-1H-benzo
[d][1,2,3]triazole (BTZ-2P) and 1-(quinoline-2-yl)-1H-benzo
[d][1,2,3]triazole) (BTZ-2Q) respectively, in excellent yields (>
90%).[2b] The air-stable Cu(II) complexes [Cu(BTZ-2P)2(ClO4)2] (1)
and [Cu(BTZ-2Q)2(CH3CN)2(H2O)](ClO4)2 (2) were isolated in
good yields (82% for 1 and 74% for 2) by reacting the ligands
BTZ-2P and BTZ-2Q respectively with Cu(ClO4)2.6H2O in CH3CN
(Scheme 1). These complexes were first analyzed by electron-
spray ionization mass spectrometry (ESI-MS) to get insight into
their probable structural formulations in solution. The ESI-MS
spectrum of complex 1 exhibited a major intense peak at m/z=
455.0808 with the expected isotopic pattern (Figure S5, Sup-
porting Information), which may be assigned to [CuI(BTZ-2P)2]+
fragment, plausibly generated under mass spectrometric con-
À
ditions through dissociation of the two ClO4 anionic ligands
and in situ reduction of Cu(II) to Cu(I). On the other hand,
complex 2 displayed three peaks at m/z=407.9712, m/z=
555.1128 and m/z=654.0608 with the expected isotopic
patterns (Figure S6), which may correspond to the [CuII(BTZ-
2Q)(ClO4)]+, [CuI(BTZ-2Q)2]+ and [CuII(BTZ-2Q)2(ClO4)]+ frag-
ments respectively, present under mass spectrometric condi-
tions. From the above studies, it was apparent that there were
two BTZ-2P and BTZ-2Q ligands attached to the Cu center in 1
and 2 respectively. To evaluate the exact binding modes
(monodentate or bidentate) of these ligands as well as the
exact geometry around the central metal center, single crystal
X-ray diffraction (SCXRD) studies were undertaken (vide infra).
Further, electronic and electron paramagnetic resonance (EPR)
spectroscopic analyses were performed to examine the struc-
tural integrity correlation of 1 and 2 both in solution and under
solid-state conditions.
Figure 1. (a) Model click reaction and A3 coupling; (b) reported Cu(II)-
benzotriazole-based coordination polymer used as catalyst; (c) two discrete
Cu(II)-benzotriazole based complexes 1 and 2 having variable ligand
coordination, used as catalysts in this study.
From the above perspectives, it would be interesting to
design and apply pre-formed well-defined benzotriazole-based
ligand-bound Cu(II) complexes as pre-catalysts for CuAAC and
A3-coupling reactions. Notably, Kostakis et al. recently used
coordination polymers of Cu(II) with substituted benzotriazole
ligands in these two high-utility catalytic reactions (Fig-
ure 1b).[3,4] Motivated by the above background, we sought to
explore discrete, molecular Cu(II)-benzotriazole complexes in
CuAAC and A3-coupling reactions. In this study, we utilized 1-
heteroaryl-substituted benzotriazole ligands, BTZ-2P and BTZ-
2Q, to synthesize two new Cu(II)-complexes – 1 with chelated
BTZ-2P and 2 with non-chelated BTZ-2Q coordination modes
and investigated their catalytic applications in these reactions
(Figure 1c).[5] Both the air-stable complexes were found to be
effective in the click as well as A3-coupling reactions. These
results are in support of the fact that benzotriazole-based
ligands are efficient to stabilize the low oxidation state Cu(I),
which is the key intermediate for these reactions.
Single crystal X-ray structures of 1and 2
The exact mode of coordination of the ligands and the structure
of the complexes were unambiguously confirmed via single
crystal X-ray structure determination of 1 and 2.
Scheme 1. Synthesis of the complexes 1 and 2.
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Features of [Cu(BTZ-2P)2(ClO4)2] (1): A perspective view of
ffNBTZÀ CuÀ NPY angle and the inter-ligand ffNBTZÀ CuÀ NPY angle of
the crystal structure of 1 is displayed in Figure 2. Some selected
bond distances and angles are collected in Table 1. The crystal
structure of 1 revealed a mononuclear complex where two BTZ-
2P ligands were coordinated to the Cu(II) ion in bidentate
fashion, occupying a square-based plane. The intra-ligand
the square-based plane around the Cu center showed the
°
°
values of 79.43(9) and 100.57(9) respectively. Two perchlorate
ions (ClO4 ) were attached to Cu through one of the oxygen
À
atoms of perchlorate anion in the axial positions thus making
the complex octahedral and charge-neutral. The CuÀ NBTZ and
CuÀ NPY distances were found to be 1.992(2) Å and 2.093(7) Å
respectively. The structural features are supported by similar
characteristics observed in a reported Cu(II) complex with
benzotriazole ligands.[2a] For example, the previously reported
CuÀ NBTZ and CuÀ NPY distances were 2.047(2) Å and 2.034(2) Å
respectively, whereas the intra-ligand ffNBTZÀ CuÀ NPY angle and
the inter-ligand ffNBTZÀ CuÀ NPY angle of the square-based plane
°
°
around the Cu center were reported as 80.34(8) and 99.66(8)
respectively. The CuÀ O1 (ClO4) bond distance in 1 is 2.413(2) Å
which is shorter than the CuÀ O (ClO4) distance of 2.453(2) Å
found in a similar Cu(II) complex with a fused benzotriazole
ligand.[15]
Features of [Cu(BTZ-2Q)2(CH3CN)2(H2O)](ClO4)2 (2): In con-
trast to the complex 1, the crystal structure of [Cu(BTZ-
2Q)2(CH3CN)2(H2O)](ClO4)2 (2) showed a square pyramidal geom-
etry around Cu(II) ion. A perspective view of the structure is
depicted in Figure 2, and some selected bond distances and
angles are tabulated in Table 1. Interestingly, the structure of 2
revealed that the mononuclear complex consisted of two BTZ-
2Q ligands bound to the central Cu(II) ion trans to each other
via a monodentate fashion through the most basic nitrogen
atom of the benzotriazole ring, farthest from the quinoline
motif of the ligand. The quinoline nitrogen remained free of
coordination to the Cu(II) ion plausibly due to the subtle steric
factor of the fused benzene ring adjacent to the nitrogen atom
of the quinoline scaffold.[2a] The formation of N2QÀ CuÀ NBTZ-type
chelate in 2 similar to the complex 1 was thus disfavored due
to the inhibition of coordination of the quinoline nitrogen to
the Cu center. It was also found previously by Steel et al. that
the nitrogen atom of the pendant isoquinoline of a similar
benzotriazole-based ligand did not coordinate to the Cu(II) ion
and remained free.[2a] Apart from the above distinguished
coordination features of the ligand BTZ-2Q in 2, there were
some additional salient characteristics present around the metal
center. One acetonitrile was attached to the Cu(II) ion at the
apical position while another coordinated acetonitrile and a
coordinated water molecule occupied the remaining two trans
positions of the square plane, thus leading to a square
pyramidal geometry around the metal center. The two
ffNBTZÀ CuÀ NCH3CN angles in the square plane were found to be
Figure 2. ORTEP of 1 (top) and 2 (bottom) with 30% and 50% ellipsoid
probability respectively. H atoms were removed for clarity.
°
Table 1. Selected bond lengths (Å) and bond angles ( ) in the X-ray
structures of 1 and 2.[a]
1
2
CuÀ N1BTZ
–
1.996(4)
–
2.004(4)
CuÀ N2BTZ
1.992(2)
–
2.093(7)
CuÀ N5BTZ
CuÀ N4PY
CuÀ O1
2.413(2)
CuÀ O1S
1.958(4)
2.190(3)
2.190(3)
°
°
89.08(17) and 89.59(17) while the two ffNBTZÀ CuÀ OH2O angles
CuÀ N1S
°
in the square plane showed the values of 88.04(17) and
CuÀ N2S
N2BTZÀ CuÀ N4PY
N1BTZÀ CuÀ N5BTZ
N2BTZÀ CuÀ O1
N1BTZÀ CuÀ N1S
N1BTZÀ CuÀ N2S
N1BTZÀ CuÀ O1S
N5BTZÀ CuÀ N1S
N5BTZÀ CuÀ N2S
N5BTZÀ CuÀ O1S
79.43(9)
°
90.42(17) , thus suggesting a very little deviation from the
169.58(13)
°
idealized value of 90 . In addition, the apical CH3CN ligand also
88.43(10)
°
maintained approximately 90 angles to each of the four
89.08(17)
97.56(17)
88.04(17)
89.59(17)
92.86(17)
90.42(17)
ligands occupying the square plane (Table 1). While the two
CuÀ NBTZ bond distances were almost equal 1.996(4) Å and
2.004(4) Å, the apical CuÀ NCH3CN bond (2.190(3) Å) was found to
be longer than the equatorial CuÀ NCH3CN bond (1.997(4)Å) as
expected.
[a] [NBTZ, and NPY indicate the coordinating N atoms associated with the
benzotriazole, and pyridine rings respectively in 1 and 2, as applicable.
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The CuÀ NBTZ bond distances were almost similar as reported
similar very weak and broad d-d band centered at 760 nm
(observed in ~1 M CH3CN). However, according to previous
literature reports, typical square pyramidal or distorted square
pyramidal Cu(II) complexes generally display a weak band over
for this type of copper complex with benzotriazole-based
ligand.[2a] Notably, unlike the coordination polymers reported in
literature with this kind of chelating ligand backbones,[3] the
compound 2 existed clearly as a discrete molecule as evident
from the presence of free quinoline nitrogen atoms in the
crystal packing diagram (Figure S4).
a
broad region of 550–650 nm,[17] while typical trigonal
bipyramidal Cu(II) systems generally feature a broad band at
λ>800 nm.[17] Based on these observations, it can be argued
that in CH3CN solution, the complex 2 likely existed in a
relatively more stable trigonal bipyramidal structure, although
in the solid state it maintained the square-pyramidal geometry.
EPR spectroscopy of 1and 2in the solid state
EPR spectrum of complex 1 in the solid state at room temper-
ature exhibited a shoulder at gjj �2.360 and an intense signal at
g⊥ �(Figure 3A). On the other hand, the EPR spectrum of
complex 2 consisted of a weak shoulder at gjj �2.230 accom-
Catalytic application of 1and 2
The complexes 1 and 2 were used as precatalysts for two
different types of catalytic reactions, namely click reaction and
A3-coupling. The two systems turned out to be highly efficient
precatalysts in both the catalytic processes, thus demonstrating
the successful application of the discrete molecular Cu(II)
complexes in such reactions. The similar reactivity and catalytic
efficiency of the two catalysts in both the reactions suggested
the involvement of similar Cu(I) catalytic intermediates with
little difference in electronic perturbation from the two ligands
BTZ-2P and BTZ-2Q to the metal centre during the catalytic
conditions. In accordance with the recent findings of Cu(I)-
catalyzed click reactions,[9,18] a bimetallic pathway along with a
traditional monometallic pathway were proposed in the present
CuAAC reactions by 1 and 2 (Figure S47, Supporting Informa-
tion). The generation of active Cu(I) species from the starting
Cu(II) complexes via single electron transfer (SET) pathway was
hypothesized in line with the proposal recently provided by
Vargas and Kostakis with similar Cu(II) complexes.[5] The active
Cu(I) intermediates might involve monodentate-coordinated
BTZ-2P and BTZ-2Q via the benzotriazole nitrogen, thus making
the two catalytic systems very similar in terms of activity. A
similar structural change during the reduction process might
plausibly be the main reason behind the similar catalytic activity
observed for both 1 and 2-catalyzed A3 coupling as well
(Figure S47, Supporting Information).
panied by an adjacent intense peak at g �2.066 (Figure 3B).
⊥
For both the complexes, the trend of gjj >g >ge (ge =2.0023)
⊥
suggested an axial symmetry of the Cu(II) ion having the
unpaired electron in the dx2-y2 orbital, thus confirming a
common square-based geometry around the metal center. The
difference in the patterns and g values were consistent with an
octahedral geometry for 1 and a square-pyramidal geometry for
2, in line with the literature reports.[16] These results were
therefore corroborated with the observed crystal structures for
1 and 2.
Absorption spectroscopy of 1and 2in solution
The absorption spectra of [Cu(BTZ-2P)2(ClO4)2] (1) and [Cu(BTZ-
2Q)2(CH3CN)2(H2O)](ClO4)2 (2) were recorded in CH3CN in the
range of 220–800 nm (Figure 3C, Figure 3D). The spectra of the
complexes exhibited very weak absorption bands originated
from d-d transitions, apart from the very intense bands
originated from the intra-ligand π-π* transitions. The spectrum
of 1 displayed a very weak and broad d-d band centered at
680 nm (observed in ~1 M CH3CN) plausibly from a combina-
tion of dz2!dx2-y2 and dxy!dx2-y2 and dxz,dyz!dx2-y2 transitions in
Oh geometry. On the other hand, the complex 2 showed a
Click reaction toward synthesis of 1,2,3-triazoles
As already mentioned, click reaction leads to synthesis of
various 1,4-disubstituted 1,2,3-triazoles which are not only used
to connect readily accessible building blocks containing various
functional groups but also used in pharmaceutical applications
for biological activity[12] as well as material sciences[13] For
conducting the azide-alkyne click reaction, the organic azide
partner was generated in situ in the reaction medium, by the
reaction of the corresponding alkyl halide with sodium azide.
Further reaction of the azide with the suitable alkyne partner in
the presence of 1 or 2 led to the formation of the desired
triazole products in good yields (Scheme 2). Reaction conditions
were chosen according to previous report by Kostakis et al.
using Cu(II)-coordination polymers as precatalysts.[3] A number
of para-substituted benzyl halides were successfully utilized in
Figure 3. Solid-state EPR (A–B) and solution-state electronic (C–D) spectra of
1 and 2.
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We employed previously reported reaction conditions utilized
for Cu(II)-coordination polymers.[4] In the present case, it was
seen that both the Cu-complexes and resulted in
1
2
significantly high yields (65–77%) of propargylamine products
4a–4l. Various para-substituted benzaldehydes (bromo, methyl,
methoxy) were employed in this reaction to furnish good yields
of the corresponding products (4b–4d, 4i–4k) which indicated
the the tolerance of these groups under the reaction conditions.
However, no electronic bias from the substituents of the
aromatic aldehyde was observed on the yields of the final
products. Moreover, the use of heteroarene aldehydes such as
4-pyridinecarboxaldehyde and 3-pyridinecarboxaldehyde also
resulted in successful product formation (4e, 4f, 4l) when
reacted with pyrrolidine and aromatic/aliphatic alkyne partners.
Notably, comparable yields (in the range of 68–76%) were
obtained with the heteroarene aldehydes as well similar to the
aromatic aldehydes (in the range of 65–77%). Saturated
aliphatic aldehyde also reacted efficiently to provide the
corresponding product (4g) in 65% (with 1) and 68% (with 2)
yields. Use of 1-octyne in place of aromatic alkyne, showed that
the Cu catalysts 1 and 2 were effective for aliphatic alkyne also
in the reaction with pyrrolidine and aldehyde resulting in the
formation of the corresponding propargyl products (4h, 4i, 4j,
4k, 4l) in good yields.
Scheme 2. Catalytic application of 1 and 2 in azide-alkyne click reaction.
Yields (%) are shown in parentheses with 1 and 2 respectively.
the reaction, thus tolerating the functional groups such as
methoxy, nitro and vinyl (3a–3d). Normal straight chain alkyl
halide also gave good yield of product with phenyl acetylene
(3e). In addition to aromatic alkyne, aliphatic alkyne was also
found to be successful in the reaction (3f–3h).
Conclusion
A3-coupling for the synthesis of propargylamines
In summary, pyridine- and quinoline-appended two benzotria-
zole-based N,N-chelating ligands, BTZ-2P and BTZ-2Q, were
utilized successfully to yield two diverse coordination com-
plexes of copper(II) – 1 and 2, wherein the BTZ-2P was bound
to the copper(II) center in a cheating bidentate mode in an
octahedral geometry whereas the BTZ-2Q was coordinated in a
non-cheating monodentate coordination mode in a square-
pyramidal structure in the solid state. X-ray crystal structures of
both the complexes confirmed the above proposition. Solid-
state EPR features of 1 and 2 were in good agreement with
their X-ray structures. Solution-state electronic spectroscopic
characteristics in CH3CN at ambient temperature suggested an
octahedral geometry for 1 while for 2, a likely conversion from
square-pyramidal to trigonal bipyramidal structure was sug-
gested. Finally, the catalytic application of both the copper
complexes was successfully explored in click and A3 coupling
reactions, thus suggesting the utility of these discrete Cu(II)
systems as efficient precatalysts. The similarity in their catalytic
performance in alcoholic solution under heating conditions
cannot rule out the involvement of a similar active Cu(I)-species,
both sterically and electronically, in both the cases. To the best
of our knowledge, these are the first examples of benzotriazole-
based discrete copper catalysts in click as well as A3 coupling
reactions.[5]
To further evaluate the catalytic activity of the Cu complexes 1
and 2, the A3-coupling reaction was also explored (Scheme 3).
Scheme 3. Catalytic application of 1 and 2 in A3 coupling reaction. Yields (%)
are shown in parentheses with 1 and 2 respectively.
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12 h. After completion, the slurry was filtered upon a short pad of
silica. The filtrate was collected and evaporated under vacuum. The
resulting residue was then loaded into silica-gel column
chromatograph and the product propargylamine was isolated using
a hexane/EtOAc mixture (10/1, v/v) as the eluent.
Experimental Section
Ligands BTZ-2P and BTZ-2Q were synthesized according to a
a
previously published procedure.[2b]
Synthesis of [Cu(BTZ-2P)2(ClO4)2] (1)
Deposition Numbers 2048478 (for 1) and 2048479 (for 2) contain
the supplementary crystallographic data for this paper. These data
are provided free of charge by the joint Cambridge Crystallographic
Data Centre and Fachinformationszentrum Karlsruhe Access Struc-
tures service www.ccdc.cam.ac.uk/structures.
BTZ-2P (100 mg, 0.50 mmol) was taken in a round-bottom flask
with 8 mL of CH3CN. After that Cu(ClO4)2.6H2O (92.5 mg, 0.25 mmol)
was added to it. The reaction mixture was stirred for 15 min at
room temperature. A green-colored precipitate appeared which
was filtered and washed with diethyl ether. The green solid thus
obtained was recrystallized from CH3CN/Et2O. Yield=135 mg (82%).
Anal. Calcd for C22H16N8CuCl2O8: C, 40.35; H, 2.46; N, 17.11. Found: C,
41.04; H, 2.23; N, 17.73. HRMS (ESI positive mode): m/z calcd for
[C22H16N8CuCl2O8]+: 455.0808, found: 455.0808 for [CuI(BTZ-2P)2]+
fragment, present under mass spectrometric conditions.
Acknowledgements
S.P. is the recipient of a research grant (grant no. SR/WOS-A/CS-
1070/2014(G)) under DST Women Scientists Scheme (WOS-A), and
thanks DST, Govt. of India, for supporting this research generously.
Infrastructural support from IISER Bhopal is gratefully acknowl-
edged. S.P. is highly thankful to her project mentor Professor Sanjit
Konar, Department of Chemistry, IISER Bhopal for all kinds of help
and support. T.M. sincerely acknowledges fellowship from CSIR,
Govt. of India, and thanks OSML, Department of Chemistry, IISER
Bhopal for performing experiments.
Synthesis of [Cu(BTZ-2Q)2(CH3CN)2(H2O)](ClO4)2 (2)
BTZ-2Q (100 mg, 0.40 mmol) was taken in a round-bottom flask
with 10 mL CH3CN and then Cu(ClO4)2.6H2O (74 mg, 0.20 mmol) was
added to it. The reaction mixture was stirred for 1 h at 60 C. The
°
mixture was then filtered on celite pad to remove any insoluble
material and the filtrate was evaporated. The green solid thus
obtained was washed with diethyl ether and then recrystallized
from CH3CN/Et2O. Yield=155 mg (74%). Anal. Calcd for
C34H28N10CuCl2O9: C, 47.76; H, 3.30; N, 16.38. Found: C, 48.32; H, 3.27;
N, 17.01%. HRMS (ESI positive mode): m/z calcd for
[C15H10N4CuClO4]+: 407.9681, found 407.9712 for [CuII(BTZ-
2Q)(ClO4)]+ fragment; m/z calcd for [C30H20N8Cu]+: 555.1101, found
555.1128 for [CuI(BTZ-2Q)2]+ fragment; and m/z calcd for
[C30H20N8CuClO4]+: 654.0587, found 654.0608 for [CuII(BTZ-
2Q)2(ClO4)]+ fragment.
Conflict of Interest
The authors declare no conflict of interest.
Keywords: Click reaction · Coordination chemistry · Copper · A3
coupling · Structure elucidation
Single crystal X-ray diffraction analysis of 1and 2
Single crystals of 1 and 2 suitable for X-ray diffraction studies were
grown by diffusion of diethyl ether into the concentrated
acetonitrile solution of the respective complexes. Data collection
was carried out on a Bruker SMART APEX II CCD diffractometer with
graphite monochromated Mo Kα (λ=0.71073 Å) radiation at low
temperature. Structures were solved with direct methods using
SHELXS-97 and refined with full-matrix least-squares on F2 using
SHELXL-97.[19]
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1,2,3-triazole derivatives
A mixture of organic chloride (1 mmol), sodium azide (1.1 mmol),
alkyne (1.2 mmol) and Cu catalyst (5 mol% based on organic halide)
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°
78 C for 24 h. After completion, the slurry was filtered through a
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Catalytic A3 coupling of aldehyde, amine, and acetylene
toward synthesis of propargylamine derivatives
A
mixture of aldehyde (1 mmol), amine (1.1 mmol), alkyne
(1.2 mmol) and Cu catalyst (2 mol% based on aldehyde) in 2-
°
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