Copper(II)-benzotriazole coordination compounds in click chemistry: a diagnostic reactivity study

Article abstract of DOI:10.1039/c8dt01256c

This diagnostic study aims to shed light on the catalytic activity of a library of Cu(ii) based coordination compounds with benzotriazole-based ligands. We report herein the synthesis and characterization of five new coordination compounds formulated as [Cu^II(L⁴)(MeCN)₂(CF₃SO₃)₂] (1), [Cu^II(L⁵)₂(CF₃SO₃)₂] (2), [Cu^II(L⁶)₂(MeCN)(CF₃SO₃)]·(CF₃SO₃) (3), [Cu^II(L⁶)₂(H₂O)(CF₃SO₃)]·(CF₃SO₃)·2(Me₂CO) (4), and [CuI4(L¹)₂(L^1′)₂(CF₃SO₃)₂]₂·4(CF₃SO₃)·8(Me₂CO) (5), derived from similar nitrogen-based ligands. The homogeneous catalytic activity of these compounds along with our previously reported coordination compounds (6-13), derived from similar ligands, is tested against the well-known Cu(i)-catalysed azide-alkyne cycloaddition reaction. The optimal catalyst [Cu^II(L¹)₂(CF₃SO₃)₂] (10) activates the reaction to afford 1,4-disubstituted 1,2,3-triazoles with yields up to 98% and without requiring a reducing agent. Various control experiments are performed to optimize the method and examine parameters such as ligand variation, metal coordination geometry and environment, in order to elucidate the behaviour of the catalytic system.

Full text of DOI:10.1039/c8dt01256c

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Trans., 2018, DOI: 10.1039/C8DT01256C.
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Copper(II)-benzotriazole coordination compounds in click chemistry: A
diagnostic reactivity study
a
a
b
c
d
Edward Loukopoulos, Alaa AbdulꢀSada, Gizella Csire, Csilla Kállay, Adam Brookfield,
e
e
f
a
Graham J. Tizzard, Simon J. Coles, Ioannis N. Lykakis* and George E. Kostakis*
a
Department of Chemistry, School of Life Sciences, University of Sussex, Brighton BN1
QJ, UK. Eꢀmail: G.Kostakis@sussex.ac.uk
9
b
Department of Inorganic and Analytical Chemistry, University of Debrecen, Hꢀ4032
Debrecen, Hungary.
c
MTAꢀDE Redox and Homogeneous Catalytic Reaction Mechanisms Research Group,
University of Debrecen, Hꢀ4032 Debrecen, Hungary
d
School of Chemistry, The University of Manchester, Manchester M13 9PL, UK.
e
UK National Crystallography Service, Chemistry, University of Southampton SO1 71BJ,
U.K
f
Department of Chemistry, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece.
lykakis@chem.auth.gr
ABSTRACT
This diagnostic study aims to shed light on the catalytic activity of a library of Cu(II) based
coordination compounds with benzotriazoleꢀbased ligands. We report herein the synthesis
and
characterization
of
five
new
coordination
compounds
formulated
II
4
II
5
[
[
(
Cu (L )(MeCN)
2
(CF
3
3
SO
3
3
)
2
]
(1),
[Cu (L )
2
(CF
3
SO
3
)
2
]
(2),
II
6
II
6
Cu (L )
2
(MeCN)(CF
SO
)]·(CF
3
SO
3
) (3), [Cu (L )
2
(H
2
O)(CF
3
SO )]·(CF SO )·2(Me CO)
3
3 3 2
I
4
1
1’
4), [Cu (L ) (L ) (CF SO ) ] ·4(CF SO )·8(Me CO) (5), derived from similar nitrogenꢀ
2
2
3
3 2 2
3
3
2
based ligands. The homogeneous catalytic activity of these compounds along with our
previously reported coordination compounds (6 ꢀ13), derived from similar ligands, is tested

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DOI: 10.1039/C8DT01256C
against the wellꢀknown Cu(I)ꢀcatalysed azideꢀalkyne cycloaddition reaction. The optimal
II
1
2 3 3 2
catalyst [Cu (L ) (CF SO ) ] (10) activates the reaction to afford 1,4ꢀdisubstituted 1,2,3ꢀ
triazoles with yields up to 98% and without requiring a reducing agent. Various control
experiments are performed to optimize the method as well as examine parameters such as
ligand variation, metal coordination geometry and environment, in order to elucidate the
behaviour of the catalytic system.
Introduction
In the constant search for efficient activation and optimization of organic reactions
with transition metal elements, copper remains one of the most attractive options due to many
1–3
advantages. Apart from its abundance and low cost, copper presents an incredibly versatile
0
I
II
III
chemistry and may be easily available in one of multiple (Cu , Cu , Cu , Cu ) oxidation
states. As a result, its salts and compounds can be powerful catalysts for reactions that
involve both one and twoꢀelectron (radical and bondꢀforming) mechanisms. Furthermore, it
can easily coordinate to heteroatoms as well as πꢀbonds to form organometallic intermediates
that are crucial promoters of these transformations.
4
,5
The Huisgen 1,3ꢀdipolar cycloaddition
of organic azides and alkynes is a
characteristic reaction in which the above principles are in full effect. In the absence of a
catalyst, the reaction proceeds very slowly and under harsh conditions to produce a mixture
of 1,4ꢀ and 1,5ꢀdisubstituted 1,2,3ꢀtriazoles with no regioselectivity (Scheme 1, pathway A).
I
6
However, the introduction of a Cu source, as found independently by the groups of Meldal
7
8
and Sharpless , greatly improves the rate and regioselectivity of the reaction to produce only
the 1,4ꢀdisubstituted analogue (Scheme 1, pathway B) under favourable conditions. The
resulting triazoles have considerable applications in various biological activities, and as a

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result the Cuꢀcatalysed azide–alkyne cycloaddition (CuAAC) reaction has been employed in
9
10–13
14
the fields of drug discovery , biochemistry
and materials science .
Scheme 1. General synthetic scheme of disubstituted 1,2,3ꢀtriazoles through azideꢀalkyne
cycloaddition.
Multiple studies have shown that the reaction proceeds using almost any copper
I
source as a catalytic precursor, as long as it generates catalytically active Cu species in the
8
,15–17
II
reaction medium
. The most popular method involves the use of an inexpensive Cu salt
7
18
and a reducing agent (e.g sodium ascorbate or hydrazine hydrate ) in large excess. The
choice of the ligand is also important in the CuAAC reaction; it has been shown that certain
1
9
20
21
22
nitrogenꢀcontaining ligands (e.g. amines , histidines , triazoles , benzimidazoles and
1
3,23,24
other polydentate chelators
) accelerate the transformation and enhance the stability of
I
the Cu state through coordination, which protects the metal centres from oxidation.
Therefore, the formation of unnecessary byꢀproducts is avoided.
In recent decades, there have been many attempts to bridge the fields of catalysis and
coordination chemistry, in an effort to provide valuable information towards the mechanism
of reactions as well as unveil the catalytic potential of coordination compounds. An important
step has been the use of coordination polymers (CPs) and metal organic frameworks
2
5–27
28–32
(MOFs)
, lowꢀ or porous threeꢀdimensional networks with possible catalytic activity
.
A common strategy for the construction of neutral CPs involves the use of metal centres and

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3
3–35
protic bridging spacers, such as polycarboxylic ligands
, to generate the framework and
complete the charge balance. Another synthetic strategy incorporates neutral bridging
36
37,38
39–41
ligands, mainly nitrogenꢀbased (e.g. derivatives of bipyridine , pyrazine
, triazole
,
41–44
imidazole
) along with metal centres to afford cationic CPs. Focusing on the latter
approach, we recently embarked in a series of studies that investigated the coordination and
catalytic capabilities of coordination compounds based, mainly, on the semiꢀrigid
1
2
3
benzotriazoleꢀbased organic ligand L and its derivatives L and L (Scheme 2). Our first
II
effort included isoskeletal Cu compounds that were found to promote the one pot synthesis
45
of Nꢀsubstituted dihydropyridines, from azines and ethyl propiolate, in methanol . Through
fine tuning we then isolated additional derivatives of this catalytic system and tested them
3
46
against the synthesis of propargylic amines through the A coupling as well as in the
47
multicomponent synthesis of polyꢀsubstituted pyrroles from aldehydes and nitrostyrenes , in
I
alcoholic media. Various results from these studies indicate the formation of a Cu
intermediate during the reaction, which acts as the catalytically active species. However,
more specific details on the mechanistic nature of the catalyst remained yet elusive to us.
Having all these in mind, in this work we performed a study with a twoꢀfold
character. Firstly, to evaluate the efficacy of the catalysts derived from the benzotriazoleꢀ
1
2
7
based organic ligand L against other isotypical nitrogenꢀbased ligands L ꢀ L (Scheme 2),
1
4
7
5
6
such as substituted benzotriazoles (L ꢀL and L ), benzimidazole (L ) or imidazole (L ), in a
given reaction system. Secondly, to shed light on the mechanistic aspects and performance of
the present catalytic library in the CuAAC reaction, a wellꢀrefined and known transformation
I
that is promoted exclusively by Cu sources. To perform this diagnostic study, we herein
report the synthesis and characterization of five new compounds formulated as
II
4
II
5
[
[
Cu (L )(MeCN) (CF SO ) ]
(1),
[Cu (L ) (CF SO ) ]
(2),
2
3
3 2
2
3
3 2
II
6
II
6
Cu (L ) (MeCN)(CF SO )]·(CF SO ) (3), [Cu (L ) (H O)(CF SO )]·(CF SO )·2(Me CO)
2
3
3
3
3
2
2
3
3
3
3
2

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I
1
1’
(
4 2 2 3 3 2 2 3 3 2
4), [Cu (L ) (L ) (CF SO ) ] ·4(CF SO )·8(Me CO) (5). We also report the catalytic
performance of 1ꢀ5 in the one pot synthesis of 1,4ꢀdisubstituted 1,2,3ꢀtriazoles (click
reaction). The tested methods employ either organic halides or phenylboronic acid as starting
materials, along with sodium azide to generate the organic azides in situ and avoid the
isolation of potentially unstable intermediates. We additionally evaluate the respective
catalytic performance of several suitable coordination compounds formulated as
II
1
II
1
I
1
[
(
[
[
Cu (L )
2
(MeCN)
2
]·2(ClO
4
)·MeCN (6), [Zn (L )
2
(H
2
O)
2
4
]·2(ClO )·2MeCN (7), [Cu (L )Cl]
II
1
II
1
8),
[Cu (L )
2
(MeCN)
2
]·2(BF (9),
4
)
[Cu (L )
2
(CF
3
SO
3
)
2
]
(10),
II
1
II
2
2
Zn (L ) (MeCN) ]·2(CF SO ) (11), [Cu (L ) (H O) ]·4(CF SO )·4Me CO (12) and
2
2
3
3
4
2
2
3
3
2
II
2
3
Cu (L ) (CF SO ) ]·2(CF SO )·Me CO (13) from our previously reported works, to
4
3
3 2
3
3
2
provide further comparisons and draw useful conclusions towards our targets.
1
7
Scheme 2. The organic ligands (L ꢀL ) used in this study.
EXPERIMENTAL
Materials. Chemicals (reagent grade) were purchased from Sigma Aldrich, Acros Organics
and Alfa Aesar. Materials and solvents were used with no further purification. Unless stated
1
4
7
in their chemical formula, the metal salts used were anhydrous. Ligands L ꢀL , L and

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4
5,46,48
compounds 6ꢀ13 were synthesized according to the reported procedures
. Colourless
1
6
7 49
block crystals of L , L and L
were also obtained; the relevant crystallographic parameters
may be found in the Supporting Information (Table S1). Safety note: Azides are potentially
explosive; such compounds should be used in small quantities and handled with caution and
the appropriate protection measures at all times.
ꢀ1
Instrumentation. IR spectra of the samples were recorded over the range of 4000ꢀ600 cm
on a Perkin Elmer Spectrum One FTꢀIR spectrometer fitted with a UATR polarization
accessory. EIꢀMS was performed on a VG Autospec Fissions instrument (EI at 70 eV). TGA
analysis was performed on a TA Instruments Qꢀ50 model (TA, Surrey, UK) under nitrogen
and at a scan rate of 10°C/min. NMR spectra were measured on a Varian VNMRS solutionꢀ
state spectrometer at 30°C. Chemical shifts are quoted in parts per million (ppm). Coupling
constants (J) are recorded in Hertz (Hz).
EPR Spectroscopy. 9 GHz continuousꢀwave Xꢀband electron paramagnetic resonance (EPR)
spectra were recorded on a Bruker Biospin EMX spectrometer with a Bruker ER4119HS
resonator. The spectra were obtained with 2.2mW microwave power and 2G modulation
under nonꢀsaturating conditions at 5K. Low temperature measurements were achieved using
5
0
an Oxford Instruments ESR900 cryostat. The Easyspin software package was used for all
simulations.
II
Cyclic voltammetry. The cyclic voltammograms of the Cu complexes were obtained by
means of a Metrohm VA 746 Trace Analyzer equipped with a 747 VA Stand driven by a
common PC. All the measurements were carried out in DMF and DMSO (0.10 M TBAP was
used as the supporting electrolyte). Argon gas was bubbled through the complex solutions
again to ensure the absence of oxygen. In each case, the voltammogram of the ligand was
registered and no peaks were found. The systems were analysed at 25°C with a three
electrode assembly. During the experiments, the working electrode was glassy carbon (glassy

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carbon electrode: CHI104). The reference electrode was a Vycor tip Ag/AgCl electrode
stored in 3 M NaCl (BASI Instr. REꢀ5B, MFꢀ2079), while the counter electrode was a
platinum electrode (distributed by ALS Co., Japan). The concentration of the complexes was
–
3
1
·10 M and the volume of the sample was 1 mL. Before each scan, the working electrode
was treated with alumina paste (0.1 micron ordered from Buehler Company) and the surface
was cleaned with the help of sandpaper. The electrochemical measuring system was
3
–
4–
6 6
calibrated with the [Fe(CN) ] /[Fe(CN) ] redox system. The redox potential was 0.462 V,
5
1
which is in good agreement with the published redox potential (0.458 V ). The potential
range was changed between +800 and –1200 mV. The voltammograms were recorded at 25,
100, 1000 mV/s sweep rates. For the analysis of the voltammograms, we used the CACYVO
program that was provided by the distributor of the instrument. The halfꢀwave potential (E1/2
)
values were calculated based on the following equation:
E pc + E pa
E
1/2
=
, where Epc and Epa are the cathodic and anodic peak potentials,
2
0
0
respectively. Considering that E1/2 = E , the E values throughout this work are referred to
0
0
NHE, taking into account that E Ag/AgCl versus E NHE (water) is +209 mV at 25 °C.
0
0
E = E1/2 + E Ag/AgCl
6
7
X-Ray crystallography. Data for L , L , compounds 1, 2 and triazoles 18aa – 18ad were
collected (ωꢀscans) at the University of Sussex using an Agilent Xcalibur Eos Gemini Ultra
diffractometer with CCD plate detector under a flow of nitrogen gas at 173(2) K and Cu Kα
radiation (λ = 1.54184 Å). CRYSALIS CCD and RED software was used respectively for
data collection and processing. Reflection intensities were corrected for absorption by the
1
multiꢀscan method. Data for L and compounds 3ꢀ5 were collected at the National
52
Crystallography Service, University of Southampton. All structures were determined using
53
54,55
56
Olex2 , solved using SHELXT
and refined with SHELXLꢀ2014 . All nonꢀH atoms were
refined with anisotropic thermal parameters, and Hꢀatoms were introduced at calculated

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positions and allowed to ride on their carrier atoms. Crystal data and structure refinement
parameters for all compounds are given in Tables S1ꢀS3. Geometric/crystallographic
5
7
53
56
calculations were performed using PLATON , Olex2 , and WINGX packages; graphics
5
8
were prepared with Crystal Maker and MERCURY . Each of the crystal structures has been
deposited at the CCDC 1831783 – 1831794.
SYNTHETIC PROCEDURES
5
Synthesis of 1-(2-((1H-benzo[d]imidazol-1-yl)methyl)benzyl)-1H-benzo[d]imidazole (L ).
5
59
L was synthesized according to the literature method with slight modifications: To a
solution of benzimidazole (3.0 g, 25 mmol) in DMF (50 ml) was added a solution of KOH
(
1.6 g, 25 mmol) in 20 ml H O. After 20 minutes of stirring, a,a'ꢀdichloroꢀoꢀxylene (2.19 g,
2
12.5 mmol), was added slowly and the mixture was stirred under room temperature for 4 hrs.
Then H
2
O (30 mL) was added to the reaction mixture, and stirring was continued for another
5
1
hr. The mixture was then filtered to provide L as a pale brown solid. Yield: 71% (2.98 g).
1
H NMR (500 MHz, CDCl ) δ 7.84 (d, J = 8.0 Hz, 2H), 7.77 (s, 2H), 7.35 – 7.21 (m, 6H),
3
1
3
7
1
.12 (d, J = 8.0 Hz, 2H), 7.06 – 7.03 (m, 2H), 5.28 (s, 4H). C NMR (126 MHz, CDCl ) δ
3
43.8, 142.8, 133.7, 132.9, 129.4, 129.0, 123.5, 122.7, 120.7, 109.7, 46.3. Selected IR peaks
ꢀ1
(
cm ): 3087 (w), 1615 (w), 1496 (m), 1458 (w), 1428 (w), 1402 (w), 1393 (w), 1385 (w),
366 (w), 1317 (w), 1287 (m) 1265 (m), 1230 (w), 1201 (s), 1006 (w), 963 (w), 937 (w), 891
m), 866 (w), 849 (w), 771 (m), 733 (s), 645 (w), 631 (w), 619 (m). HRMS for C H N [M
1
(
22
19
4
+
H]: theor. 339.1604 m/z, found 339.1611 m/z.
6
Synthesis of 1-(2-((1H-imidazol-1-yl)methyl)benzyl)-1H-imidazole (L ).
6
60
L was synthesized according to the literature method with slight modifications: a solution
containing imidazole (3.16 g, 46.4 mmol) and α,α′ꢀdichloroꢀoꢀxylene (0.78 g, 4.46 mmol) in
methanol (50 mL) was heated under reflux for 20 hrs. After cooling, the solvent was
evaporated to give a yellow syrup, which was then dissolved in 80 ml aqueous potassium

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carbonate (6.13 g). The resulting solution was left undisturbed to produce large crystals
6
1
which were identified as [L ]·2H
2
O. Yield: 1.0 g (82%). H NMR (500 MHz, CDCl
3
) δ 7.43
(s, 2H), 7.36 (dd, J = 5.7, 3.4 Hz, 2H), 7.09 (s, 2H), 7.07 (dd, J = 5.7, 3.4 Hz, 2H), 6.78 (s,
1
3
2
H), 5.01 (s, 4H). C NMR (126 MHz, CDCl ) δ 137.3, 133.7, 130.1, 129.4, 119.2, 117.7,
3
4
8.1. HRMS for C H N [M + H]: theor. 239.1291 m/z, found 239.1290 m/z.
14
15
4
II
4
2 3 3 2
Synthesis of [Cu (L )(MeCN) (CF SO ) ] (1)
4
0
.05 mmol (0.017 g) of L and 0.10 mmol (0.036 g) of Cu(OTf)
2
·H
2
O were dissolved in 10
mL of MeCN while stirring to produce a green solution. After 10 min of stirring, the solution
was stored in a glass vessel and heated at 95 °C for 18 h. After cooling down, the solution
was subjected to Et O using the vapour diffusion technique. Green block crystals were
2
ꢀ1
produced after 3 days. Selected IR peaks (cm ): 3564 (w), 3512 (w), 1651 (w), 1455 (m),
321 (m), 1283 (m), 1234 (w), 1172 (w), 1059 (s), 1020 (s), 954 (w), 880 (w), 794 (w), 758
s), 748 (s), 672 w), 626 (w). Yield: 16% (based on Cu). Elemental analysis for
C H CuF N O S : C 39.81, H 2.83, N 14.29; found C 39.96, H 2.82, N 14.38.
1
(
26
22
6
8
6 2
II
5
Synthesis of [Cu (L ) (CF SO ) ] (2)
2
3
3 2
4
0
2 2
.06 mmol (0.022 g) of L and 0.12 mmol (0.044 g) of Cu(OTf) ·H O were dissolved in 15
ml acetone while stirring to produce a dark green solution. Then the solution was filtrated and
layered over nꢀhexane in a 1:2 ratio to produce small blue block crystals after 3 weeks.
ꢀ1
Selected IR peaks (cm ): 3351 (br), 3125 (w), 1616 (w), 1558 (w), 1519 (m), 1484 (w), 1465
m), 1397 (w), 1241 (s), 1224 (s), 1175 (m), 1028 (s), 928 (w), 849 (w), 740 (s), 669 (m).
Yield: 9% (based on Cu). Elemental analysis for C46 : C 53.22, H 3.50, N
0.80; found C 53.36, H 3.42, N 10.83.
(
6 8 6 2
H36CuF N O S
1
II
6
Synthesis of [Cu (L )
2 3 3 3 3
(MeCN)(CF SO )]·(CF SO ) (3)
A 10 ml solution of Cu(OTf) ·H O (0.072 g, 0.2 mmol) in MeCN was dropwise added to a 10
2
2
5
ml solution of L (0.068 g, 0.2 mmol) in methanol. The resulting blue solution was filtered,

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DOI: 10.1039/C8DT01256C
then carefully layered over Et
2
O in a 1:2 ratio to produce blue block crystals after 1 week.
Selected IR peaks (cm ): 3462 (br), 3145 (m), 1659 (w), 1522 (m), 1459 (m), 1445 (w), 1258
s), 1244 (m), 1226 (s), 1174 (w), 1109 (m), 1089 (m), 1032 (s), 947 (w), 868 (w), 857 (w),
38 (w), 774 (m), 759 (m), 729 (s), 687 (w), 661 (s), 634 (m), 625 (m). Yield: 24% (based on
Cu). Elemental analysis for C H CuF N O S : C 43.73, H 3.56, N 14.35; found C 43.70, H
ꢀ1
(
8
32
31
6
9
6 2
3.72, N 14.43.
II
6
Synthesis of [Cu (L )
2
2 3 3 3 3 2
(H O)(CF SO )]·(CF SO )·2(Me CO) (4)
5
A 5 ml solution of L (0.038 mg, 0.16 mmol) in acetone was layered on a 8 ml solution of
Cu(OTf) ·H O (0.029 g, 0.08 mmol) in H O. Purple needles were obtained after 5 days.
2
2
2
ꢀ1
Selected IR peaks (cm ): 3516 (w), 3444 (w), 3135 (w), 1611 (w), 1523 (m), 1461 (m), 1441
(
(
(
w), 1277 (m), 1263 (m), 1244 (s), 1224 (s), 1155 (m), 1108 (m), 1090 (m), 1026 (s), 950
m), 842 (w), 827 (w), 773 (w), 758 (w), 734 (s), 667 (m), 655 (m), 634 (s). Yield: 31%
6 8 9 2
based on Cu). Elemental analysis for C36H42CuF N O S : C 44.46, H 4.35, N 11.52; found C
4
2.00, H 3.35, N 12.91. This result corresponds to the loss of two Me CO molecules (calcd.
2
C 42.08, H 3.43, N 13.08).
I
4
1
1’
Synthesis of [Cu
(L )
2
(L )
2
(CF
3
SO
3
)
2
]
2
·4(CF
3
SO
3
)·8(Me
2
CO) (5)
1
I
0
.06 mmol (0.022 g) of L and 0.12 mmol (0.045 g) of Cu (MeCN)
4
3 3
·CF SO were dissolved
in 17.5 ml acetone while stirring to produce a light yellow solution. Then the solution was
filtrated and layered over Et O in a 1:2 ratio to produce small yellow block crystals after 2
2
ꢀ1
days. Selected IR peaks (cm ): 3395 (br), 1608 (w), 1597 (w), 1499 (w), 1522 (m), 1457 (m),
275 (m), 1223 (s), 1165 (m), 1026 (s), 869 (w), 743 (m), 634 (s). Yield: 41% (based on Cu).
Elemental analysis for C96 : C 47.17, H 3.63, N 13.75; found C 46.89, H
.08, N 14.71. This result corresponds to the loss of four acetone molecules (calcd. C 46.77,
H 2.85, N 14.87).
1
4 12 24 16 4
H88Cu F N O S
3

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General Catalytic Protocol. To a sealed tube containing 0.5 mmol of sodium azide (0.033 g)
in 3 mL of ethanol, 0.5 mmol of organic halide or boronic acid, 0.5 mmol of alkyne and 5
mol% of the catalyst were added and the mixture was stirred at reflux for the appropriate
time. After completion of the reaction, the slurry was filtered upon a short pad of silica (to
withhold the catalyst) and the filtrate was evaporated under vacuum. The resulting residue
was then separated by column chromatography using silica gel and a mixture of
hexane/EtOAc (5/1 ratio for triazoles 18aa – 18ae, 18ba – 18be, 10/1 ratio for triazoles 18ca
–
18cd) as the eluent, to afford the corresponding triazole product in pure form.
RESULTS
2
7
Synthetic aspects. Due to the similar chemical nature and behaviour of ligands L ꢀL
1
compared to the prototype L , we employed similar methods and techniques to generate
frameworks that resemble the coordination geometry and environment of the main catalyst
4
6
1
0 . As a result, all newly reported compounds were synthesized under aerobic conditions
and analogous concentrations. The experiments were mainly conducted using acetonitrile or
acetone as the main solvent, in order to i) provide satisfying solubility for all ligands and
metal salts, ii) maintain the same synthetic method that were used during experiments with
1
L , iii) enable us to engineer the resulting coordination environment through the coordinating
2
(MeCN) or nonꢀcoordinating (Me CO) capabilities of the solvents. The main crystallization
technique that was used for all compounds in order to provide high diffraction quality crystals
was liquid or vapour diffusion. In regards to the secondary crystallization solvent, the nonꢀ
2 2
coordinating solvents Et O and nꢀhexane proved to be the best choices; nevertheless H O (a
coordinating solvent) also provided some success during the synthesis of 4 and allowed us to
II
slightly manipulate the coordination environment of Cu . Room temperature conditions were
4
8
employed in almost all compounds, with the exception of 1; it has been reported that the
4
temperature effect on L further promotes the formation and dimensionality of coordination

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polymers. For this reason, the mixture in this case was initially heated at 95 °C. All
compounds are soluble in DMF, less soluble in other common organic solvents (eg.
acetonitrile, methanol, THF) and insoluble in water.
Crystal structure description. The crystal structures of compounds 6 – 13 have already
45,46
been reported and described . Hence, only the structures of 1 – 5 will be discussed in detail
in this section. A summarizing table providing structural details for all compounds is given in
Table 1. Since compound 10 serves as the main catalyst and reference point in this study, a
brief description of its structural characteristics will also be included, prefacing the newly
reported compounds. The reference catalyst 10 was synthesized using the benzotriazoleꢀ
1
ꢁ
based L ligand; the compound crystallizes in the triclinic ꢀ1 space group and its asymmetric
II
1
unit contains a Cu centre, one L molecule and one triflate anion molecule. Due to the
generated symmetry, the structure propagates into a ribbonꢀlike oneꢀdimensional framework
1
with small cavities (Figure 1, left). The flexibility of the –CH
2
groups in L allow for a
coordination mode in which the planes of the benzotriazole molecules are found at an angle
of 118.44(7)° to each other. Due to this, the metal centres are fairly separated and the
II
corresponding CuꢀCu distance was measured at 9.0095(3) Å. Each Cu centre is coordinated
to a total of six atoms and possesses an octahedral geometry through a {N O } coordination
4
2
environment. The axial positions of the octahedron are occupied by triflate oxygen atoms as
1
the four nitrogen atoms from L molecules in the equatorial positions create an almost perfect
square plane. The mean CuꢀO distance was measured at 2.536(4) Å, while the CuꢀN bond
lengths are 2.009(5) and 2.013(7) Å. No strong hydrogen bonds or other supramolecular
interactions are observed. In addition, 10 has very similar structural characteristics
(coordination geometry of the Cu centre and coordination mode of the ligand) to compound
5
2
, which utilized the benzimidazoleꢀbased ligand L , containing an identical 1D framework
with small pores (Figure 1, right). For this reason, its structure will not be discussed further.

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Figure 1. Part of the oneꢀdimensional framework in compounds 10 (left) and 2 (right). The
two complexes are isostructural. Certain H atoms are omitted for clarity. Colour code Cu
(blue), C (black), H (light pink), N (light blue), O (red), S (yellow), F (light green).
4
II
ꢁ
1
was prepared using the L ligand and crystallizes in the triclinic ꢀ1 space group. One Cu
4
centre, one L molecule, two coordinating triflate anion molecules and two coordinating
4
acetonitrile molecules are contained in the asymmetric unit. The L ligand molecules in the
structure adopt a type of synꢀ conformation that promotes the formation of a oneꢀdimensional
4
chain as shown in Figure 2. The behaviour of the flexible unit of L is similar to the one of
1
L , with an angle of 123.96(4)° between the planes of the benzotriazole moieties. However,
4
due to the metaꢀsubstitution in L the resulting polymer in 1 shows a CuꢀCu distance of
II
9
.3801(5) Å, larger compared to 10. Each Cu centre possesses a slightly distorted octahedral
geometry and a {N O } coordination environment in which the axial positions of the
4
2
octahedron are occupied by the triflate oxygen atoms; relevant CuꢀO distances were
measured at 2.370(4) and 2.401(4) Å. The remaining four nitrogen atoms form a nearꢀperfect
square plane, as the mean CuꢀN distances range from 1.994(5) to 2.003(4) Å. While similar
coordination characteristics were found in the main catalyst 10, in this case only two of the
four nitrogen atoms that form the square plane derive from ligand molecules. The relevant Nꢀ

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CuꢀN angles were found to be in the range of 87.82(15) to 91.16(17)°. Finally, no π···π
interactions or strong hydrogen bonds were observed in the compound.
Figure 2. Part of the oneꢀdimensional chain in 1. H atoms are omitted for clarity. Colour
code Cu (blue), C (black), N (light blue), O (red), S (yellow), F (light green).
6
The imidazoleꢀbased L ligand was employed for the construction of compound 3. The
complex crystallizes in the monoclinic C2/c space group and its asymmetric unit contains one
II
6
Cu centre, two L molecules, two triflate anion molecules and one acetonitrile molecule. As
II
in the cases of the benzotriazole (10) and benzimidazole (2) analogues, the Cu centres
4
possess an octahedral geometry that also includes a {N } square plane with ligandꢀderiving
nitrogen atoms at distances ranging from 1.996(4) to 2.017(4) Å. As a result, 3 exhibits a
similar oneꢀdimensional framework as shown in Figure 3 (top). A triflate and an acetonitrile
molecule also coordinate through the axial positions in significantly larger distances (CuꢀO:
2.513(5) Å, CuꢀN: 2.549(6) Å respectively) to complete the octahedron, while a second
triflate anion is also present in the crystal lattice to account for the charge balance. In this
case the distance between the metal centres was measured at 9.7264(3) Å, which is the
highest relevant in the study. This may be attributed to the absence of the bulky phenyl
groups which limits potential steric effects and the possible formation of weak CꢀH···π
interactions. As a result of this increased flexibility, the angles between the planes of the

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imidazole moieties were measured at 100.1(2) and 111.5(3)°, differing significantly
compared to the previous compounds.
Figure 3. The oneꢀdimensional frameworks in 3 (top) and 4 (bottom). Certain H atoms are
omitted for clarity. Colour code Cu (blue), C (black), H (light pink), N (light blue), O (red), S
(yellow), F (light green).
6
Compound 4 was also synthesized using L and Cu(OTf)
2 2
·H O as the metal salt. Compared
to 3, compound 4 reveals an analogous oneꢀdimensional framework which consists of the
II
6
same [Cu (L ) (solvent)(CF SO )] units, however with some structural differences based on
2
3
3
2 2
the use of different crystallization solvents (H O/Me CO instead of MeCN). In this case, the
complex crystallizes in the monoclinic P2
1
/n space group and a water molecule acts as the
II
coordinating solvent (Figure 3, bottom). This accounts for octahedral Cu centres with
4 2
{N O } environment, slightly different compared to the case of compound 3, however the

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4
ligandꢀderived {N } square plane is present on both occasions. A second triflate anion along
with solvent molecules are also found in the crystal lattice. The structure of 4 is further
stabilized by the formation of two strong OꢀH···O hydrogen bonds between the oxygen from
the water molecule and an oxygen atom of either a triflate anion or a solvent molecule in each
case.
I
Determination of the structure of 5 by Xꢀray crystallography reveals a zeroꢀdimensional Cu
ꢁ
tetramer (Figure 4) which crystallizes in the triclinic space groupꢂꢀ1. All of the metal centres
1
in this Cu
4
unit appear aligned in a single plane. Four organic ligands derived from L are
also present. An interesting case of ligand isomerism is observed in two of these ligands, as
the ꢀCH linker is bonded to the central N atom of one of the benzotriazole moieties,
2
1
’
generating the 1,2ꢀdisubstituted benzotriazole analogue (L ) despite the fact that pure crystals
1
of L were used during the synthesis. This phenomenon is common in substituted
6
1,62
benzotriazole derivatives, as multiple studies by Katritzky’s group
have shown that both
the benzotriazolꢀ1ꢀyl and ꢀ2ꢀyl adducts exist in solution; the position of this equilibrium has
been found to be strongly dependant on parameters such as the polarity of the solvent, the
6
3–67
temperature or the bulkiness of the substrate
, however the 1ꢀyl adduct remains
predominant, which explains the presence of both species in the structure. Two triflate
molecules are also present in these tetramer units, each coordinating to one metal centre. All
I
Cu centres exhibit tetrahedral geometry; the two external centres have a {N
3
O} coordination
1
environment which involves nitrogen atoms from three different ligand molecules (two as L
1
’
and one as L ). Respective CuꢀN distances for these atoms were measured from 1.981(3) to
.010(3) Å. The remaining metal centres inꢀbetween are coordinated to nitrogen atoms from
2
1
1’
two as L and two L ligands, possessing an {N
4
} environment. In this case, the measured
CuꢀN distances were found to be slightly larger, ranging from 2.037(3) to 2.080(3) Å. In

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regards to the triflate coordination, the analogous CuꢀO distance was calculated at 2.173(3)
Å. Finally, the relevant angles for all tetrahedra were found to be in the range of 99.47(12)
and 112.74(12)°.
Figure 4. The structure of the tetrameric units in compound 5. Lattice solvent and anion
molecules, as well as H atoms are omitted for clarity. Colour code Cu (orange), C (black), N
(light blue), O (red), S (yellow), F (light green).

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Table 1. Structural summary of compounds 1ꢀ13.
Entry
Compound
Ligand
Coordination
Environment
M source
Dimensionality
(M = Cu/Zn)
4
1
1
L
Cu(OTf)
2
·H
2
O
1D
5
2
3
4
5
2
3
4
5
L
Cu(OTf) ·H O
1D
1D
2
2
2
2
2
2
2
2
6
L
Cu(OTf)
Cu(OTf)
Cu(OTf)
·H
·H
·H
O
O
O
6
L
1D
1
1’
L , L
0D (tetramer)
1
6
7
8
9
6
7
L
Cu(ClO
4
)
2
·6H
2
O
1D
1D
1D
1D
1D
1D
1
L
Zn(ClO ) ·6H O
4 2 2
1
8
L
4 2 2
Cu(ClO ) ·6H O
1
9
L
4 2 2
Cu(BF ) ·6H O
1
1
0
1
10
11
L
2 2
Cu(OTf) ·H O
1
1
L
Zn(OTf)
2
2
1
1
2
3
12
13
L
Cu(OTf) ·H O
0D (dimer)
0D (dimer)
2
2
3
L
Cu(OTf) ·H O
2 2

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1
X = ClO / L / MeCN
4
II
1
[
Cu (L ) (MeCN) ]—2(ClO )—MeCN (6)
2 2 4
1
X = BF / L / MeCN
4
II
1
[
[
[
Cu (L ) (MeCN) ]—2(BF ) (9)
2 2 4
1
X = OTf / L / Me CO
2
II
1
Cu (L ) (OTf) ] (10)
2
2
2
X = OTf / L / Me CO
2
II
2
Cu (L ) (H O) ]—4(OTf)—4Me CO (12)
2
4
2
2
2
3
X = OTf / L / Me CO
2
II
II
3
Cu X
[Cu 2(L )4(OTf)2]—2(OTf)—Me2CO (13)
2
4
X = OTf / L / MeCN / T
II
4
[
Cu (L )(MeCN) (OTf) ] (1)
2 2
5
X = OTf / L / Me CO
2
II
5
[
Cu (L ) (OTf) ] (2)
2 2
6
X = OTf / L / MeCN
II
6
[
Cu (L ) (MeCN)(OTf)]—(OTf) (3)
2
6
X = OTf / L / Me CO
2
II
6
[
Cu (L ) (H O)(OTf)]—(OTf)—2(Me CO) (4)
2
2
2
1
X = ClO / L / MeCN
4
II
1
[
Zn (L ) (H O) ]—2(ClO )—2MeCN (7)
2 2 2 4
II
Zn X
2
1
X = OTf / L / Me CO
2
II
1
[
Zn (L ) (MeCN) ]—2(OTf) (11)
2 2
X = Cl / L1
I
1
[
Cu (L )Cl] (8)
I
Cu X
1
X = OTf / L / Me CO
2
I
1
1'
[
Cu (L ) (L ) (OTf) ] —4(OTf))—8(Me CO) (5)
4 2 2 2 2 2
Scheme 3. A Schematic presentation of the synthesis of compounds 1ꢀ13

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Characterization of compounds.
We initially investigated the thermal stability of 1ꢀ5 through thermogravimetric analysis
TGA) experiments up to a temperature of 1000°C. The measurements revealed that the
(
polymeric compounds 1ꢀ4 are slightly more stable than the zeroꢀdimensional tetrameric
complex 5; the former retain their main metalꢀligand core until the region of 260ꢀ300°C after
which gradual decomposition to copper oxide begins. In complex 5, the same procedure
occurs at a slightly lower temperature region (~240°C). The TGA graphs are presented and
interpreted in detail in the Supporting Information (Figures S29ꢀS33).
ESIꢀMS (positiveꢀion mode) in methanolic solution for complexes 1ꢀ5 shows a variety of
peaks depending on their behaviour in solution as well as the ligand used. The most common
peaks can be found in all or almost all compounds and correspond perfectly to the respective
+
+
+
+
[
2 3 3 2 3 3
Cu(L)] , [Cu(L) ] , [Cu(L)(CF SO )] and [Cu(L) (CF SO )] fragments. Additional peaks
are also observed in each spectrum, which are consistent to various metal–ligandꢀanion
fragments. For example, 1 and 2 also contain peaks that correspond to the respective
+
+
[
Cu (L) (CF SO ) ] and [Cu (L) (CF SO ) ] fragments. Imidazoleꢀbased compounds 3 and
2 2 3 3 3 2 3 3 3 3
+
4
present additional peaks that match the theoretical values for the [Cu(L)
3
]
and
+
[
Cu(L)
3
(CF
3
SO
3
)] fragments. Finally, the ESIꢀMS spectrum of 5 reveals five main peaks
+
+
+
which are attributed to the corresponding [Cu(L)] , [Cu(L)
2
] , [Cu(L)
2 3 3
(CF SO )] ,
+
+
[
Cu (L) (CF SO )] and [Cu (L) (CF SO )] fragments. Overall, 1ꢀ5 appear to behave in
2
2
3
3
2
3
3
3
solution similarly to the already reported compounds 6ꢀ13. All ESIꢀMS spectra, along with a
detailed analysis of the fragments, are presented in Figures S24–S28.
Catalytic studies. In order to provide an ideal scheme for the reaction we focused on the
catalytic synthesis, which would avoid the isolation of the potentially unstable organic azides
1
5
(
especially azides with low molecular weights ). For these reasons, we adopted the
multicomponent reaction between organic halides, alkynes and sodium azide as our initial

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reaction scheme, in which the respective organic azide is generated in situ. The initial testing
catalytic protocol included the use of benzyl chloride, sodium azide and phenylacetylene, as
well as compound 10 as the homogeneous catalyst. After several catalytic tests (Table 2), it
was found that optimal results were obtained when the reaction takes place in ethanol for 24
hrs, under reflux and 5 mol% of the catalyst (Table 2, entry 2). Under these conditions, the
starting material is consumed and the reaction leads to the corresponding triazole 18aa in
93% yield. To our delight, this result was obtained in the absence of any external reducing
I
agent, providing substantial evidence towards the formation of a Cu intermediate during the
reaction.
Table 2. Optimization of the synthesis of triazole 18aa using 10 as the catalyst.
Entry Solvent Temperature Time Loading Conversion Yield Regioselectivity TON/TOF
o
a
b
ꢀ1
(
C)
(h) (mol %)
(%)
76
(%)
62
93
76
43
ꢀ
1,4/1,5ꢀproduct
(hr )
1
2
3
4
5
6
7
8
9
MeOH
EtOH
64
78
82
82
24
24
24
24
24
24
24
24
24
1
5
5
83:17
99:1
98:2
99:1
ꢀ
12.4/0.52
18.6/0.78
15.2/0.63
8.6/0.36
ꢀ
100
94
iPrOH
MeCN
Toluene
DMF
5
5
65
110
120
101
100
78
5
NR
96
5
46
ꢀ
98:2
ꢀ
9.2/0.38
ꢀ
1
,4ꢀDioxane
5
NR
NR
83
H
2
O
5
ꢀ
ꢀ
ꢀ
EtOH
EtOH
2.5
5
47
22
99:1
98:2
18.8/0.78
4.4/4.4
10
78
45

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c
1
1
EtOH
EtOH
EtOH
EtOH
EtOH
78
78
78
78
rt
24
24
24
1
5
5
5
5
5
93
87
82
87
93
92
ꢀ
97:3
99:1
99:1
99:1
ꢀ
16.4/0.68
17.4/0.73
18.6/0.78
18.4/18.4
ꢀ
d
1
1
1
2
e
3
100
99
e
4
1
5
24
NR
Reaction conditions: benzyl chloride (0.5 mmol), sodium azide (0.5 mmol), phenylacetylene
(0.5 mmol), 10, solvent (3 mL). [a]: based on benzyl chloride, [b]: calculated from the crude
1
mixture by HNMR. [c]: with 0.5 ml solvent. [d] with the addition of 15% P(Ph)
3
. [e] with
68 1
the addition of 15% Sodium Ascorbate. NR = no reaction. The reported HNMR peaks of
the 1,5ꢀanalogue were employed to determine regioselectivity.
I
II
Encouraged by this result, we then compared the performance of various Cu and Cu
salts under the same reaction conditions (Table S5) which demonstrated the better
performance of 10. In addition; in some of these cases, the starting material was not even
entirely consumed.
Having obtained the optimal conditions for our system, we then tested a number of
substrates in order to study the catalytic scope and limitations of 10. Initial substrate
screening included the use of organic halides as starting materials as well as a variety of
terminal alkynes (e.g. aromatic, alkyl, linear, containing hydroxyl or carboxylate groups).
The results are presented in Scheme 4. The reaction affords triazoles in excellent (88 ꢀ 99%)
yields when aromatic or substituted aliphatic alkynes are used. In regards to the organic
ꢀ
ꢀ
halide, increasing the strength of the leaving group from Cl (entries 18aa – 18af) to Br
(entries 18ba – 18be) led to improved results as expected. It is also worth noting that the
triazoles derived from benzyl halide proved to be very easy to crystallize. As such, XꢀRay
crystallography structures of representative triazoles 18aa – 18ad are additionally included.
Iodobenzene was also tested as a possible substrate in our attempts to generate the relevant

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aryl triazole analogues, however these efforts were unsuccessful. This was not surprising as
21,69,70
the azidonation of aryl halides
is generally a slow process that requires very harsh or
tedious conditions. We therefore employed the inexpensive and readily available
71
benzeneboronic acid in order to obtain the corresponding product . To our delight, the
resulting triazole 18ca was generated in a very good 80% yield, as seen in Scheme 5.
Additional screening of the arylboronic acid with other alkynes led to the formation of
triazoles 18cb – 18cd in poorer yields, whereas reactions with 2ꢀhydroxyphenylboronic acid
did not yield any product (18ce – 18cf). Nevertheless, these results provided us with another
potential pathway for our catalyst which avoids the isolation of unstable organic azide
intermediates.

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Scheme 4. Catalytic activity of 10 in the multicomponent synthesis of 1,4ꢀdisubstituted 1,2,3ꢀ
triazoles from organic halides.

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OH
B
1
0 (5 mol %)
N
R1
N
N
OH +
NaN3
+
R2
o
EtOH, 78 C
X
24 hrs
R2
X = H (18ca ꢀ 18cd)
OH (18ce-18cf)
N N
N
N
N
N
N
N
N
N
N
N
OH
OH
18ca (80%)
18cb (Trace)
18cc (27%)
18cd (34%)
N N
N
N
N
N
OH
OH
8cf (NR)
1
1
8ce (NR)
Scheme 5. Catalytic activity of 10 in the oneꢀpot synthesis of 1ꢀarylꢀ1,2,3ꢀtriazoles from
boronic acid.
Cyclic Voltammetry studies. As a first step, we performed cyclic voltammetric studies of
1
2
5
6
the ligands L , L , L , L . During this process, we neither did not observe any processes in the
negative nor in the positive potential range and only the CV of the TBAP was measurable.
Therefore, we could establish that the ligands are stable in DMSO and in DMF and they are
not oxidized. We then performed the CV studies for the Cu based compounds (Figures 5 and
6
). Compounds 2, 10 and 12 were selected for these purposes due to their structural
characteristics and catalytic performance. 2 and 10 can be reduced in the first step and can be
then oxidized back in the second step in the positive potential range. The I /I is ~1 and the
a
c
1
/2
v ꢀ|Ic| function is not linear whereas the potential difference of the anodic and cathodic peak
potential is more than 59 mV indicating a structural change. This can be rationalized to the
different coordination preference of the Copper element in different oxidation states (I or II),
therefore the intraꢀconversion (II to I to II) takes place in a slower manner, or the electron
crossing may be slower on the electrode surface. These results show that these processes are

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quasiꢀreversible. The redox potentials are positive in both cases and substantially different
when compared with the redox potential of Cu(NO , thus supporting that the measured
potential values correspond to Cu(II) complexes. The CV of compound 12 complex is similar
to the Cu(NO cyclic voltammogram in both solvents, indicating that compound 12, despite
having similar structural characteristics with 2 and 10, is not stable in DMF and in DMSO.
3 2
)
3 2
)
Figure 5. Voltammograms of 2 (black) and 10 (purple) in 0.1 M TBAP/DMF (Potential
range: 800ꢀ0 mV. Scan rate 100 mV/s). (right) Voltammograms of 12 (green) and Cu(NO
red) in 0.1 M TBAP/DMF (Potential range: 800ꢀ(ꢀ1200) mV for 12, 800ꢀ(ꢀ700) mV for
Cu(NO . Scan rate 100 mV/s).
3 2
)
(
3 2
)
Figure 6. (left) Voltammograms of 2 (black) and 10 (purple) in 0.1 M TBAP/DMSO
Potential range: 800ꢀ0 mV for 2, 800ꢀ(ꢀ400) mV for 10. Scan rate 100 mV/s). (right)
Voltammograms of 12 (green) and Cu(NO (red) in 0.1 M TBAP/DMSO (Potential range:
00ꢀ(ꢀ1200) mV for 12, 1000ꢀ(ꢀ1200) mV for Cu(NO ) . Scan rate 100 mV/s).
(
3 2
)
8
3
2

Page 27 of 43
Dalton Transactions
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DOI: 10.1039/C8DT01256C
EPR Studies. To gain further structural insights, Xꢀband EPR studies of characteristic
compounds 2, 10, 12 were performed. The spectra of polycrystalline samples in solidꢀstate or
in frozen alcoholic solution were recorded at a temperature of 5K. For compound 2, a
comparison between the spectra of the solidꢀstate sample and the one in frozen methanol
(Figure S35, right) shows similar signals in both case, however fewer hyperfine lines are
observed in the former. A closer look at the crystallographic parameters of the compound
reveals severe axial distortion in the octahedron due to JahnꢀTeller effects, with the CuꢀN and
CuꢀO distances at 2.022(3) and 2.549(3) Å respectively. Furthermore, a series of weak
intramolecular interactions (C–H⋯π, C–H⋯OOTf) involving the –CH group of the imidazole
moiety is observed. Both these phenomena contribute to weaker magnetic coupling between
neighbouring cations and eventually a narrowing of the hyperfine lines. The best simulation
x y z
(Figure S35, left) was obtained with (g , g , g ) = (1.92, 1.99, 2.3) ± 0.01 and A = 200 ± 30
MHz which is in agreement with the above observations. In contrast, the EPR signal of 2 in
methanolic solution provides much more defined hyperfine lines which are consistent to a
II
14
5
Cu (S=1/2) interaction with four N nuclei from L ligands in a square planar environment,
pointing to an eventual {N } octahedral geometry. A plausible hypothesis for the
4
O
2
difference in the clarity of the two spectra could be that, in solution, methanol molecules
II
replace the triflate anions and coordinate to the Cu centres, removing any potential
7
2,73
formation of C–H⋯O interactions
.
II
Similar studies for compound 10, as can be seen in Figure S36, show that Cu retains
the {N O } octahedral geometry in alcoholic solution, and the structure remains polymeric.
4
2
46
This result is consistent with previously conducted UVꢀVis studies which showed that the
compound retains a similar coordination environment in solution. It is worth noting that the
spectrum in this case is very well defined compared to the one of compound 2, as no weak C–

Dalton Transactions
Page 28 of 43
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DOI: 10.1039/C8DT01256C
H⋯O interactions are formed in the absence of the imidazolic moiety. A comparison of the
hyperfine lines shows slight changes in the coordination environment upon solvation but does
not alter, indicating once again potential replacement of the triflate anions with ethanol
molecules. A simulation with very good agreement for the polycrystalline sample at room
temperature provided the fitting parameters (g
x y z
, g , g ) = (2.08852, 2.03142, 2.29635) ± 0.01
2
2
and A = 520 ± 30 MHz, indicating that the unpaired electron is localized in the d
orbital.
x −y
II
Furthermore, they are in accordance to the corresponding values of similar Cu complexes
74–76
with a {N
While the crystallographic data for 12 could not be optimally refined, the Cu centres
clearly exhibited a square pyramidal geometry in the crystal structure, with a {N O}
4
O
2
} coordination environment
.
II
3
environment in the equatorial plane. The Xꢀband EPR studies (Figure S37) of the
polycrystalline sample at 5K further confirm this behaviour. Reasonable fits are obtained for
(g
x
, g
y z
, g ) = (1.96, 2.04, 2.28) ± 0.01 and A = 350 ± 30 MHz; these values are in satisfying
II
77,78
agreement to the ones of related Cu complexes with a {N
4
O} coordination sphere
. Once
again, a narrowing of the hyperfine lines is also observed, possibly due to the formation of
weak π⋯π and C–H⋯π interactions within the crystal structure.
Mechanistic studies
The aforementioned homogeneous catalytic performance of 10 in the azideꢀalkyne
cycloaddition provides us with yet another organic transformation in which our library of 1D
II
I
Cu CP catalysts may be applied. More importantly, the presence of a Cu source is
necessitated for this specific reaction to occur; this serves as an excellent blueprint, which
could shed light into the mechanistic function of our catalysts. Up to this point, we have
II
established that our polymeric Cu compounds retain their nature in alcoholic solution, and
I
can generate Cu species when tested as preꢀcursor catalysts in organic reactions under
alcoholic media which involve the formation of the important copperꢀacetylide intermediate.

Page 29 of 43
Dalton Transactions
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DOI: 10.1039/C8DT01256C
We embarked in an extensive set of control experiments and techniques which could enable
I
us to i) diagnose the exact nature of the generated Cu species, ii) find the limits of the present
II
catalytic system, iii) identify the importance of the Cu preꢀcursor in the catalytic activity, iv)
further examine the effect of parameters such as ligand variation, metal effect, polymeric
nature, dimensionality, geometry and coordination sphere.
Firstly, the importance of metal selection in the construction of the catalysts was
II
evaluated. Zn ꢀbased compounds 7 and 11 were tested as catalysts for the synthesis of 18aa,
as they are isostructural to 10, containing the same oneꢀdimensional framework; they also
79,80
behave similarly in solid and solution state. Recent investigations
on the feasibility of a
ZnAAC system have shown that the reaction is indeed possible. Albeit it requires the
presence of a reducing agent (none present in our proposed system) and is highly sensitive to
steric effects in regards to the choice of alkyne. However, no product was formed in both
cases (Table 4, entries 7 and 11). Given the inactivity of Zn centre towards the AAC reaction,
this experiment excludes the possibility that the reaction is promoted by the ligand.
I
The next step was to assess the performance of Cu complexes from our backlog of
related catalysts. Relevant compounds 5 and 8 were employed for these purposes, accounting
for average yields as seen in Table 4, entries 5 and 8. This allowed us to narrow our fineꢀ
II
tuning efforts to Cu compounds. Therefore, we then opted to study the effect of the choice
of metal ion during the catalytic process. The comparison tests in this case involved the
isoskeletal 1D catalysts 6, 9 and 10 (Table 4, entries 6, 9, 10) that differ in the counter anion
ꢀ
ꢀ
ꢀ
(
ClO
yield, with the OTf analogue exhibiting superior behaviour and the BF
for the lowest activity. In addition, lower conversion (90%) of the starting material was
4 4
, BF , OTf respectively). The results show significant differences in the afforded
ꢀ
ꢀ
4
analogue accounting
ꢀ
4
ꢀ
observed in both ClO and BF analogues. Furthermore, we have documented in previous
4
ꢀ
ꢀ
ꢀ
ꢀ
studies that an anion conversion of ClO to Cl (in 6) and BF to F (in 9) is also taking
4
4