Luminescent iridium(iii) complexes of N-heterocyclic carbene ligands prepared using the 'click reaction'

Article abstract of DOI:10.1039/c9dt01362h

A series of imidazolium salt, N-heterocyclic carbene (NHC) ligand precursors, combined with 1,2,3-triazoles were synthesized using the Cu(i) catalyzed azide-alkyne cycloaddition 'click reaction'. These pro-ligands were prepared from imidazolium molecules that were functionalized with either a terminal alkyne or azide group. Methylation of the triazole unit with methyl iodide produced a series of imidazolium/triazolium NHC pro-ligands. From these pro-ligands a family of luminescent Ir(iii) complexes of the general form [Ir(ppy)₂(C^N)]⁺ or [Ir(ppy)₂(C-C)]⁺ (where ppy is 2-phenylpyridine and C-N represents a bidentate imidazolylidene/triazole ligand and C-C represents a bidentate imidazolylidene/triazolylidene ligand) were prepared. The electrochemical, photophysical and electrochemiluminescence properties of the complexes have been evaluated and a preliminary study of two of these compounds as luminescent probes for cell imaging studies was conducted in A549 human lung adenocarcinoma basal epithelial cells. Co-localisation studies with the commercial dye MitoTracker CMXRos were consistent with mitochondrial uptake for these compounds.

Full text of DOI:10.1039/c9dt01362h

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Luminescent Iridium(III) Complexes of N-Heterocyclic Carbene Ligands
DOI: 10.1039/C9DT01362H
Prepared Using the ‘Click Reaction’
a
a
b
a
b
Rebecca E. Karmis, Serena Carrara, Amy A. Baxter, Conor F. Hogan, Mark D. Hulett and
Peter J. Barnard a *
aDepartment of Chemistry and Physics, La Trobe Institute for Molecular Science, La Trobe
University, Victoria, 3086, Australia, Fax: (+)61 3 9479 1266, E-mail: p.barnard@latrobe.edu.au
bDepartment of Biochemistry and Genetics, La Trobe Institute for Molecular Science, La Trobe
University, Victoria, 3086, Australia.
Abstract
A series of imidazolium salt, N-heterocyclic carbene (NHC) ligand precursors, combined with
1
,2,3-triazoles were synthesized using the Cu(I) catalyzed azide-alkyne cycloaddition ‘click
reaction’. These pro-ligands were prepared from imidazolium molecules that were functionalized
with either a terminal alkyne or azide groups. Methylation of the triazole unit with methyl iodide
produced a series of imidazolium / triazolium NHC pro-ligands. From these pro-ligands a family of
˄
+
˄
+
luminescent Ir(III) complexes of the general form [Irppy) (C N)] or [Ir(ppy) (C C)] (where ppy is
2
2
2
-phenylpyridine and C^N represents a bidentate imidazolylidene/triazole ligand and C^C represents
a bidentate imidazolylidene / triazolylidene ligand) were prepared. The electrochemical,
photophysical and electrochemiluminescence properties of the complexes have been evaluated and a
preliminary of two of these compounds as luminescent probes for cell imaging studies was conducted
in A549 human lung adenocarcinoma basal epithelial cells. Co-localisation studies with the
commercial dye Mitotracker CMXRos were consistent with mitochondrial uptake for these
compounds.
Introduction
N-heterocyclic carbene (NHC) ligands are well known for their synthetic versatility and
1
impressive electron donating properties and metal complexes of NHCs have been evaluated for a
variety of applications, including homogeneous catalysis,2-6 electroluminescent materials for the
development of organic light emitting diodes (OLEDs),7, 8 and for a variety of biological applications
such as antimicrobial and anticancer agents.9, 10 The versatility of NHCs is illustrated by the
incorporation of the naphthalimide chromophore into a series of NHC ligands to provide deep-red to
NIR emitting Ir(III) complexes.11, 12 Some ten years after the first isolation of a free imidazolylidene

Dalton Transactions
Page 2 of 26
1
3
by Arduengo in 1991, experimental and computational studies have shown that NHCs can behave
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DOI: 1 01 .41 ,0 13 59 /C9DT01362H
as carbenes not only at the ‘normal’ C-2 position but also at the ‘abnormal’ C-4 position.
In this
series of studies, ‘abnormal’ or mesoionic C-4 coordination was found to occur in preference to the
‘
normal’ NHC binding mode for steric and kinetic reasons.14, 16 Later, in 2009 Bertrand isolated and
characterized the first example of an ‘abnormal’ imidazole-based carbene.17
Since Sharpless and co-workers reported the Cu(I) azide-alkyne cycloaddition reaction
(CuAAC) or the ‘click reaction’, 1,2,3-triazoles and the mesoionic carbenes derived from these
species (1,2,3-triazolylidenes) are now well established as efficient donors for a range of metals.18-31
The 1,2,3-triazole moiety can coordinate to metals via either the N2 or N3 positions and experimental
observations in combination with DFT studies have shown coordination via the N3 position tends to
result in stronger metal-ligand binding.32, 33 The combination of 1,2,3-triazole donors with imidazole-
based NHCs has been previously examined34, 35 and Rh(I), Rh(III) and Ir(III) complexes with this
ligand system (e.g. I Figure 1) were evaluated as catalysts for the intramolecular hydroamination of
aminoalkynes.36 Mixed imidazolium/1,2,3-triazolium pro-ligand have been used to prepare
mononuclear dicarbene complexes (e.g. II Figure 1) and asymmetrical mixed-metal complexes.37, 38
CH3
N
N
H C
3
N
Ir
N
Cl
N
N
H C I Rh
3
N
I
Dipp
N
N
N
O
O
CH3
BPh -
4
II
I
Figure 1. I Ir(I) complex of a bidentate NHC / 1,2,3-triazole ligand and II a Rh(III) complex of a
bidentate imidazolylidene / triazolylidene ligand.
Attractive features often associated with luminescent Ir(III) complexes, such as large Stokes
shifts, high photostability and long excited state lifetimes have led to them being explored as probes
for cell imaging studies and the cellular distribution of a range of complexes has been previously
evaluated.39-42 Significantly, specific organellular uptake, including lysosomal , mitochondrial44-50
and phospholipid membrane51 labeling has been reported and in a highly pertinent study, a
luminescent Ir(III) complexes of biscarbene ligands were shown to specifically stain the endoplasmic
reticulum.52
43
We have a long-standing interest in the synthesis and evaluation of new luminescent
complexes of NHC ligands and have previously reported luminescent NHC complexes of the metals
5
3
54-56
Re57, 58 and Au.59, 60 In the present paper, the use of a one-pot ‘click reaction’ for the
Ru, Ir,
synthesis of a series of four pro-ligands that combine imidazolium units with 1,2,3 triazoles is

Page 3 of 26
Dalton Transactions
described. Utilizing these compounds, a second set of pro-ligands combining imidazolium and 1,2,3-
View Article Online
DOI: 10.1039/C9DT01362H
triazolium groups were prepared by methylation of the chosen 1,2,3-triazole with iodomethane. From
these pro-ligands, a series of five heteroleptic Ir(III) complexes of the general form [Ir(ppy) (N^C)]+
2
+
[
Ir(ppy) (C^C)] were prepared (where ppy represents 2-phenylpyridine and N^C represents a
2
bidentate triazole substituted imidazolylidene ligand and C^C represents a 1,2,3-triazolylidene /
imidazolylidene ligand). The complexes are luminescent and their photophysical and electrochemical
and electrochemiluminescent properties were evaluated. Finally, due to the synthetic versatility of
these ligand systems, a preliminary evaluation of the use of these compounds as luminescent probes
for cell imaging studies was conducted.
Results and Discussion
Ligand Synthesis
Two classes of imidazolium salt, N-heterocyclic carbene pro-ligands linked to 1,2,3-triazole units
were prepared and their structures are shown in Scheme 1 (class I = 3a, 3b and class II = 4a, 4b).
The preparation of ligands 3a and 3b involved the initial synthesis of an azide substituted azolium
salt. Due to safety concerns associated with the isolation of organic azides a one-pot synthetic
procedure was developed for the formation of the 1,2,3-triazole unit. In this procedure, the required
azide was generated in situ by the reaction of a 2-bromoethyl functionalized imidazolium salt
precursor (1a and 1b) with sodium azide. These synthetic reactions were monitored by TLC and upon
completion, the components for triazole formation (phenylacetylene, CuI, and the base Na CO ) were
2
3
1
8
added to the mixture. Initially, attempts were made to carry out the ‘click reactions’ using a Cu(II)
salt (e.g. CuSO or Cu(CH CO ) in the presence of the reducing agent ascorbic acid to generate the
4
3
2 2
Cu(I) catalyst in situ.18, 27, 61 This approach was unsuccessful as the cationic imidazolium salts formed
could not be isolated from the reaction mixtures. To allow for a simpler workup, the reactions were
instead conducted using CuI as the catalyst under an atmosphere of N to avoid oxidation of the
2
cuprous ion. Using this approach, the Cu(I) salts could be readily removed at the end of the reaction
by filtration.

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Page 4 of 26
Br-
View Article Online
DOI: 10.1039/C9DT01362H
Br-
Br-
N
1.5 eq NaN3
N
N
Br
N3
R
N
N
R
N
N
R
N
N
CuI
Na CO
3
RT, 12 h
DMF/water, N2
(3a) R= Ph (60%)
(
not isolated)
(
(
1a) R= Ph (80%)
o
2
5
0 C, 5 h
(3b) R= CH (43%)
3
1b) R= CH (96%)
3
X
X-
N3
R
N
N
R
N
N
N
N
N
-
CuI
Na CO
DMF/water, N2
RT, 12 h
(
(
2a) R= Ph (86%), X = PF6
-
2
3
2b) R= CH (42%), X = Cl
3
(4a) R= Ph (76%), X = PF6-
(4b) R= Ph (46%), X = Cl-
Scheme 1. (Upper panel) Synthesis of class I pro-ligands 3a and 3b (the azide functionalized
imidazolium salts were prepared in situ) and (lower panel) synthesis of class II pro-ligands 4a and
4
b.
The second class of pro-ligands (class II, 4a and 4b, Scheme 1) were prepared from the propargyl
functionalized imidazolium salts (2a and 2b), which were synthesized by the alkylation of either 1-
phenyl- or 1-ethyl-imidazole with propargyl p-toluenesulfonate. The 1,2,3-triazole functionalized
pro-ligands were then synthesized from 2a or 2b and benzyl azide, using the same azide-alkyne
cycloaddition conditions that were described for the preparation of 3a and 3b.
The second goal of this work was the generation of pro-ligands suitable for the formation of mesoionic
or ‘abnormal’ N-heterocyclic carbenes in combination with ‘normal’ NHCs. To this end, compounds
3
a, 3b, 4a and 4b were alkylated at the N3 position of the 1,2,3-triazole ring to generate the triazolium
6
2
containing pro-ligands 5a, 5b, 6a and 6b respectively (Scheme 2). Initial attempts to alkylate the
N3 position of the 1,2,3-triazole unit by refluxing a mixture of the chosen 1,2,3-triazole and an excess
1
of iodomethane in acetonitrile were unsuccessful with H NMR analysis showing only unreacted
starting material. After several additional attempts, it was found that the reactions could be
successfully carried out at elevated temperature in a sealed flask. Using this approach, a mixture of
the chosen 1,2,3-triazoles (either 3a, 3b, 4a, and 4b) and an excess of iodomethane (acting as both a
o
reactant and solvent) in a sealed reaction flask was heated to 80 C (Scheme 2). In the case of pro-
ligands 3b and 4b, a small amount of acetonitrile was also added to ensure the starting materials were
fully dissolved. A similar method for the alkylation of the N3 position of 1,2,3-triazoles with
6
3
iodomethane has been reported previously by Poulain and 1,2,3-triazoles have also been alkylated
at the N3 position using the methylating agent trimethyloxonium tetrafluoroborate.64

Page 5 of 26
Dalton Transactions
2X-
Br-
2
View Article Online
DOI: 10.1039/C9DT01362H
1
) CH I
3
o
80 C
N
N
N
N
R
N
N
N
for (5a):
) KPF6
R
N
N
N
2
-
(
5a) R= Ph (87%), X= PF
(
(
3a) R= Ph
3b) R= CH3
6
-
(5b) R= CH (74%), X= I
3
3
2
2X-
X-
1) CH I
o
80 C
R
N
N
R
N
N
N
N
N
N
N
N
for (6a):
) KPF6
2
(
4a) R= Ph, X= PF6-
(6a) R= Ph (25%), X= PF -
6
4b) R= CH , X= Cl-
(
-
3
(6b) R= CH (28%), X= I
3
Scheme 2: Alkylation at the N3 position of the triazole unit for class I ligands (3a and 3b) (Upper
panel) and class II ligands (4a and 4b) (Lower panel).
1
The H NMR spectra of the imidazolium salt pro-ligands were relatively simple with a characteristic
imidazolium pro-carbenic proton signal which resonated as a downfield shifted peak at 9.16, 9.08,
9
.35, 9.20, 9.19, 9.37 and 9.30 ppm for pro-ligands 3a, 3b, 4a, 5a, 5b, 6a and 6b respectively. For
pro-ligands 3a, 3b and 4a the C-H proton signals of the triazole group were in all cases the second
most downfield shifted signals, resonating at 8.54, 8.54 and 8.28 for these molecules respectively.
For pro-ligand 4b the carbenic proton signal was observed at 7.42 ppm. Formation of the 1,2,3-
triazolium unit resulted in a significant downfield shift of the triazolium C-H proton, with this proton
resonating at 9.08, 9.13, 9.03 and 9.06 ppm for pro-ligands 5a, 5b, 6a, and 6b respectively. In each
case, the base peak observed in the high-resolution mass spectra for the pro-ligands 3a-4b
+
corresponded to the mono-cationic imidazolium salt i.e. m/z 330.1713 [C H N ] for 3a. While for
2
0
20
5
the imidazolium / 1,2,3-triazolium pro-ligands 5b-6b, the base peak corresponded to a mono-cation
consisting of the di-cationic pro-ligand in combination with one counter anion e.g. m/z 490.1589
+
+
[
C H N ]PF for 5a and m/z 410.0837 [C H N ]I for 5b. The structures of pro-ligands 4a and
21 23 5 6 16 21 5
5
b were confirmed by X-ray crystallography (see Structural Studies section).
Iridium complex synthesis
The Ir(III) N-heterocyclic carbene complexes were prepared utilizing a silver trans-metalation
protocol. First developed by Lin and co-workers in 1998, the silver trans-metalation process involves
in situ deprotonation of the imidazolium / triazolium unit and formation of an intermediate Ag(I)
6
5, 66
complex using Ag O.
The Ir(III) complexes were synthesized by introduction of the Ir(III)
2
precursor [Ir(ppy) Cl] (where ppy is 2-phenylpyridine). Based on the ligand structures it is expected
2
2

Dalton Transactions
Page 6 of 26
upon binding to the metal centre that pro-ligands 3a and 3b would produce seven-membered chelate
View Article Online
DOI: 10.1039/C9DT01362H
rings, with coordination via the N2 position of the 1,2,3-triazole group. While for pro-ligands 4a and
b, a six-membered chelate ring would be formed with coordination at the N3 position of the 1,2,3-
4
6
7
triazole group. Synthetic studies showed that Ir(III) complexes could only be prepared for pro-
ligands 4a and 4b (Scheme 3). It is likely that complexes could not be prepared for pro-ligands 3a
and 3b because of the larger chelate ring size and the known lower electron density at the N2 position
of the 1,2,3-triazole resulting in this position binding less strongly to the metal centre.68-70
In contrast to the 1,2,3-triazole containing ligands, the alkylated triazolium pro-ligands (5a, 5b, 6a,
and 6b) were efficiently metallated regardless of the chelate ring size (Scheme 3). This is consistent
with previously reported results, where 1,2,3-triazolylidenes have been shown to be generally more
7
1
efficient donors than imidazolidines. In the case of complex 5a, analysis of the crude reaction
1
mixture by H NMR showed evidence for the formation of the complex, however, despite several
attempts, the complex could not be satisfactorily purified. The structures of the successfully prepared
Ir(III) complexes are shown in Scheme 3.
R
N
R
N
N
N
N
N
Ir
N
Ir
N
Ir
N
N
N
N
N
N
I-
N
N
N
N N
X-
N
N
X-
(
(
7) R = C H (74%), X= PF -
(9) R = C H (64%), X= PF -
(11) (70%)
6
5
6
6
5
6
-
8) R = CH (75%), X= Cl-
(10) R = CH (45%), X= Cl
3
3
Scheme 3. Structures of Ir(III) complexes 7-11 synthesized in this work.
1
13
The expected number of signals were observed in the H and C NMR spectra for the Ir(III)
1
complexes 7-11 consistent with the low-symmetry structures. As expected, H NMR analysis
revealed the absence of the azolium pro-carbenic protons indicating deprotonation and coordination
of the NHC groups to the Ir(III) metal centres. All complexes prepared were mono-cationic and
analysis by high-resolution mass spectrometry showed a base peak in each case which corresponded
+
to the complex ion e.g m/z 830.2579 [C H IrN ] in the case for 7.
4
2
35
7

Page 7 of 26
Dalton Transactions
Structural Studies
View Article Online
DOI: 10.1039/C9DT01362H
The X-ray crystal structures of the pro-ligands 4a and 5b and the Ir(III) complex 11 are illustrated in
Figures 2 and 3 respectively and the crystallographic data for these compounds are tabulated in Table
S1 (Electronic Supplementary Information). Compound 4a displays a short hydrogen-bonding
interaction of 2.397(3) Å between the imidazolium proton (H1) and a fluorine atom of the
hexafluorophosphate counterion (F10). The structure of 5b confirms that this molecule is dicationic,
with the imidazolium unit being linked to the triazolium group via an ethyl group. Both cationic
azolium rings display hydrogen bonding interactions with the iodide counterions, with distances of
2
.8979(3) Å for H18 (imidazolium) - I1 and 2.7773(3) Å for H24 (triazolium) - I4. The molecular
structure of complex 11 shows a distorted octahedral coordination geometry about the Ir atom, with
the coordination sphere composed of two cyclometalated 2-phenylpyridine (ppy) ligands in
combination with the bidentate imidazolylidene / 1,2,3-triazolylidene ligand. In each case, the
pyridine groups of the cyclometalated ppy ligands are trans with respect to one another. The Ir-CNHC
bond distances for the imidazolylidene and 1,2,3-triazolylidene donors are similar with these being
2
.11555(5) Å (Ir1-C1) and 2.13457(4) Å (Ir1-C6) for these groups respectively. The ethyl linker
group of the bidentate NHC ligand adopts a staggered conformation and there is a short interaction
between one of the methylene hydrogen atoms (H4b) and the pyridine nitrogen atom (N7) of one of
the ppy ligands of 2.37300(7) Å.

Dalton Transactions
Page 8 of 26
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DOI: 10.1039/C9DT01362H
Figure 2. Representations of the cations found in the X-ray crystal structures of (a) 4a and (b) 5b.
The hydrogen atoms, anions and solvent of crystallization have been omitted for clarity. Thermal
ellipsoids are shown at 40% probability. Selected bond lengths for 4a: N3-C6 = 1.326(7) Å, N3-N4
=
1.338(6) Å, N4-N5 = 1.305(6) Å, N1-C1 = 1.320(6) Å, N2-C1 = 1.329(6) Å. Selected bond lengths
for 5b: N7-C17 = 1.323(3) Å, N6-C17 = 1.311(4) Å, N8-C24 = 1.354(3) Å, N8-N9 = 1.307(3) Å,
N9-N10 = 1.314(3) Å.

Page 9 of 26
Dalton Transactions
View Article Online
DOI: 10.1039/C9DT01362H
Figure 3. X-ray crystal structure of the Ir(III) complex 11. The hydrogen atoms the anion and solvent
of crystallization have been omitted for clarity. Thermal ellipsoids are shown at 40% probability.
Selected bond lengths: Ir1-C17 = 2.053(4)Å, Ir1-C1 2.116(5)Å, Ir1-C6 = 2.134(4) Å, Ir1-C28 =
2
.054(4) Å, Ir1-N6 = 2.041(4) Å, Ir1-N7 2.056(4) Å.
Photophysical and electrochemical studies
The electronic absorption and emissive properties of the Ir(III) complexes (7-11) were examined and
the results are summarised in Table 1. The five complexes 7-11 displayed similar absorption spectra
(Figure S1, Electronic Supplementary Information) with intense absorption bands below 300 nm
1
resulting from spin-allowed (π→π*) ligand-centred (LC) transitions originating on the NHC and
2
-phenylpyridine ligands. Lower-intensity bands were observed between 300 nm and 500 nm which
can be assigned to metal-to-ligand charge transfer (MLCT) transitions. As has been previously
reported, strong spin-orbit coupling from the Ir(III) centre promotes mixing of these charge-transfer
transitions with the higher energy spin-allowed LC transitions.54, 72

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Page 10 of 26
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DOI: 10.1039/C9DT01362H
1.0
0.8
0.6
0.4
0.2
0.0
450
500
550
600
650
700

 nm
-5
Figure 4. Normalised emission spectra for complexes 7-11 in (110 M in acetonitrile); 7 (green);
(pink); 9 (blue); 10 (orange) and 11 (red) ( = 385 nm for 7 and  = 380 nm for 8-11).
8
ex
ex
The emission spectra for complexes 7-11 are shown in Figure 4. Strong spin-orbit coupling from the
Ir metal centre facilitates intersystem crossing to triplet states with similar energy and enables the
7
3
formation of an emissive mixed triplet excited state. The spectra are similar for all complexes,
exhibiting structured emission bands centred at ~490 nm in acetonitrile at room temperature. It is
noteworthy that the nature of the substituent on either the triazole or imidazole rings had little effect
on the emission properties of the complexes, with the exception of complex 11 for which the emission
is bathochromically shifted by ~8 nm and shows a slight diminution of the higher order vibronic
bands. These observations tell us that the ancillary ligands play a minor role in the transitions leading
to the excited state, which are mainly associated to the phenylpyridine ligands
The photoluminescence quantum yields for the complexes were recorded from deoxygenated
acetonitrile solutions (Table 1) and compounds 9 and 10 (57.4% and 50.0% respectively) showed the
highest values. The brightness of complexes 9 and 10 compared to 7 and 8 can be credited to the
presence of a methyl group in the N3 position of the 1,2,3-triazoles, which influences their abilities
to destabilise thermally accessible metal centred non-emissive states. The lower quantum yield value
obtained for compound 11 (8.8%) can be attributed to the iodide counter ion, which is well known
7
4
for its propensity to efficiently quench luminescent emission. The excited state lifetimes (Table 1)
tend to support this trend showing a general enhancement when passing from aerated to deaerated

Page 11 of 26
Dalton Transactions
indicating an extreme sensitivity to the presence of oxygen, as has been observed previously for Ir(III)
View Article Online
7
5
DOI: 10.1039/C9DT01362H
complexes of this type. Upon degassing, compound 10 displays the longest lifetime of 1.43 s.
Table 1. Spectroscopic and electrochemical properties of Ir(III) complexes 7-11
-1
-1 b
λmax/nm (ε/M cm ) Photolum Quantum Lifetime
Lifetime
Eox
Ered
/ V
g
g
inescence yield
(aerated)
(deaerated) / V
c
d
e
f
λmax/nm
ϕp/%
τp/ ns
τp/ μs
7
8
9
1
1
258 (39,000), 310 475
5.9
34.66
31.80
46.81
43.12
32.44
0.37
0.88
0.69
1.43
0.85
0.78
0.76
(-2.48)
(13,
100),
380
(4,300)
255 (42,500), 310 485
14,600), 390 (4,400)
4.1
-2.55
(
260 (40,300), 310 475
15,400), 380 (5,100)
57.4
50.0
8.8
(0.77) -2.54
(
0h 258 (30,100), 310 475
11,800), 380 (4,600)
(
1
265 (43,700), 320 485
0.78
(-2.44)
(15,800), 390 (4.900)
a
-5
b
All complexes 10 M in acetonitrile. λ
is the position of the peak or shoulder in the absorbance
max
c
profile, and ε is the molar absorptivity. Emission corrected for variation in detector sensitivity with
d
e
f
wavelength. Absolute quantum yields in deaerated solution. lifetimes in aerated solution and in
g
deaerated solution. E and E refer to E values, peak potentials for irreversible processes are in
ox
red
1/2
h
parenthesis. The solubility of compound 10 in acetonitrile was insufficient to allow measurement of
the cyclic voltammogram for this compound.
The electrochemical properties of complexes 7-9 and 11 were studied using cyclic voltammetry in
2
+
degassed acetonitrile and the CVs for these complexes compared with that of [Ru(bpy) ] are shown
3
in Figure 5 and the results are summarized in Table 1. The complexes each displayed an irreversible
3
+
4+
oxidation process related to Ir /Ir , with the forward peaks being much greater in magnitude than
the reverse peaks at 0.1 V/s (i.e. ip,ox > ip,red). The oxidation processes (E ) all occurred at similar
ox
potentials within a short range (~40mV) suggesting that the HOMO for each complex is mainly

Dalton Transactions
Page 12 of 26
delocalized over the metal and the phenyl group (of the ppy ligands) in each case. In the cathodic
View Article Online
DOI: 10.1039/C9DT01362H
region each compound shows three one-electron ligand reductions at potentials more negative than
2
+
the bipyridine reductions of [Ru(bpy) ] . Only the second reduction (most likely associated with the
3
2
-phenylpyridine ligands), shows a degree of reversibility, in agreement with results previously
5
5
reported results for similar complexes. The electrochemiluminescence (ECL) properties of each
complex (7-9 and 11) were also tested by pulsing the applied potential between the oxidation and
reduction potentials of the complexes (annihilation ECL). In each case, an ECL emission profile
closely matching the photoluminescence spectrum obtained, however weak ECL was observed in
most cases. Interestingly, the strongest ECL emitter was complex 8, which gave an ECL efficiency
2
+
of 39% relative to [Ru(bpy) ] , despite having the lowest photoluminescence quantum yield. The co-
3
reactant ECL abilities of the complexes was also tested by scanning past the oxidation potential in
the presence of 10 mM tripropylamine (Figure S2, Electronic Supplementary Information). Similarly,
the co-reactant ECL efficiency of each complex was negligible with the exception of 8, for which the
efficiency was 84% relative to the ruthenium standard. These results highlight the fact that the
stability of the oxidised / reduced forms is often a more important factor than photophysical or
thermodynamic considerations, for ECL efficiency. This is manifested in the voltammetric responses
in Figure 5(a), where the oxidation process of 8 is significantly more chemically reversible compared
to the other complexes, (notwithstanding that the response is somewhat convoluted with an
irreversible peak for the oxidation of the chloride counterion).

Page 13 of 26
Dalton Transactions
View Article Online
DOI: 10.1039/C9DT01362H
50 A
A
-
3
-2
-1
Potential (V)
0
1
1
1
1
0
0
0
0
0
.4
.2
.0
.8
.6
.4
.2
.0
B
4
00
500
600

/ nm
Figure 5. (A) Cyclic voltammetric responses for complexes 7-9, 11 and [Ru(bpy) ]2+; 7 (green); 8
3
2
+
(
pink); 9 (blue); 11 (red) and [Ru(bpy) ] (black) using a glassy carbon working electrode at a scan
3
-1
rate of 0.1 V s . Complex concentrations were 1 mM in acetonitrile containing 0.1 M [Bu N][PF ]
4
6
as supporting electrolyte. (B) ECL spectra produced via annihilation between the oxidized and
-4
reduced forms of the complexes. All iridium complexes are 10 M solution in acetonitrile containing
2
+
0
.1 M [Bu N][PF ]. Intensities have been normalized to [Ru(bpy) ] to reflect ECL quantum
4 6 3
efficiencies; (green) 7; (pink) 8; (blue) 9; (red) 11.

Dalton Transactions
Page 14 of 26
Cell Imaging Studies
View Article Online
DOI: 10.1039/C9DT01362H
We are interested in the potential application of these Ir(III) complexes as luminescent probes for cell
imaging studies and complexes 8 and 11 were selected for these preliminary imaging studies due to
their good solubility in aqueous media. The uptake and distribution of these compounds were
evaluated in A549 human lung adenocarcinoma basal epithelial cells. The cells were treated with
either complexes 8 (100 M) or 11 (50 M) and the imaging experiments were begun immediately
after complex addition. To avoid prolonged exposure to the laser a new section of cells was imaged
at each time interval (5 min after complex addition and then at 15-minute intervals for 1 hour).
Differential image contrast (DIC) and luminescent images of the epithelial cells 15 minutes after
treatment are shown in Figure 6. The luminescence images show good uptake of the complexes into
the cells and intracellular distribution consistent with specific organellar staining. As these
compounds carry a cationic charge it was anticipated that they would display selective uptake into
mitochondria. To test this hypothesis, co-localisation studies were performed with the commercial
mitochondrial dye Mitotracker CMXRos. The merged images for the luminescence complex and
Mitotracker (Figure 6) are consistent with co-localisation, suggesting mitochondrial uptake for these
Ir(III) compounds.
Figure 6. Live cell microscopy images of A549 human lung adenocarcinoma basal epithelial cells
treated with complexes 8 (100 M) (upper panel) and 11 (50 M) (lower panel) and Mitotracker

Page 15 of 26
Dalton Transactions
CMXRos. From left to right: DIC, complex luminescence ( = 405 nm), Mitotracker CMXRos
ex
View Article Online
DOI: 10.1039/C9DT01362H
luminescence ( = 561 nm) and merged images.
ex
Although these complexes demonstrated high levels of cell permeability and mitochondrial
localization, they unfortunately also showed moderate cytotoxicity at the concentrations studied.
Complex 8 was evaluated at 100 μM with cell viability decreasing from 89% at 15 min to 0% by 75
min. Similarly, viability of cells treated with complex 11 at 50 μM decreased from 80% at 15 min to
0
% by 60 min. However, based on the results obtained in these studies, it is expected that lower
concentrations the Ir(III) complexes that do not compromise cell viability, will still offer suitable
luminescence intensity for cell imaging.
Conclusion
A series of bidentate imidazolium salt/1,2,3-triazole pro-ligands were prepared using the Cu(I)
catalyzed azide-alkyne cycloaddition or ‘click’ reaction. For safety reasons, the required azide
functionalized imidazolium salt precursors were formed in situ from the corresponding alkyl halides
and in the same reaction pot, the ‘click’ reaction was carried out to introduce the triazole unit. In the
case of the imidazolium salts functionalized with terminal alkyne groups, the cycloaddition reaction
was carried out using benzylazide to form the 1,2,3-triazole unit. The 1,2,3-triazole group of these
substituted imidazolium salts was then methylated using iodomethane to give a series of
imidazolium/1,2,3-triazolium pro-ligands. Both classes of pro-ligands were then used to prepare five
heteroleptic luminescent Ir(III) complexes. The photophysical properties of the complexes were
evaluated and the quantum yields ranged from 4.1% to 57.4%. Electrochemical investigations
revealed one formally Ir(III/IV) oxidation process and several ligand based reductions in each case.
Some of the complexes displayed moderate annihilation or co-reactant ECL, depending on the
reversibility of the electrochemical processes involved. Finally, due to the very well-known synthetic
versatility of the ‘click’ reaction for conjugation processes including the linkage of molecular probes
to biomolecules, it is our intention to utilize the ‘click reactions’ to prepare pro-ligands and to couple
these molecules to biologically active molecules thereby yielding targeted luminescent molecular
probes. With this in mind, a preliminary evaluation of two Ir(III) complexes as luminescent probes
for live cell imaging studies was undertaken. The complexes are cationic and showed high levels of
cell permeability in A549 human lung adenocarcinoma basal epithelial cells and co-localisation
studies using Mitotracker CMXRos showed probable mitochondrial localisation. These studies show
the significant potential for utilizing the click reaction for the synthesis of luminescent Ir(III)
complexes for bioanalytical applications.
Experimental section

Dalton Transactions
Page 16 of 26
General Procedures. All reagents were purchased from Sigma-Aldrich or Alfa Aesar and were of
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DOI: 10.1039/C9DT01362H
analytical grade or higher and were used without further purification unless otherwise stated. All
manipulations were performed under nitrogen unless otherwise stated. NMR spectra were recorded
1
13
on either a Bruker Avance ARX-300 (300.14 MHz for H, 75.48 MHz for C) or a Bruker Avance
1
13
ARX-400 (400.13 MHz for H, 100.61 MHz for C) or a Bruker Avance ARX-500 (500.13 MHz for
1
13
H, 125.77 MHz for C) spectrometer and were internally referenced to solvent resonances. Mass
spectra were obtained using a Bruker Esquire6000 mass spectrometer fitted with an Agilent
electrospray (ESI) ion source. UV-visible spectra were recorded using an Agilent Technologies Cary
3
00 UV-visible spectrophotometer using quartz cuvettes (1 cm). Fluorescence spectra were recorded
on a Varian Cary Eclipse spectrofluorimeter (5 nm band pass, 1 nm data interval, PMT voltage: 600
V) using quartz cuvettes (1 cm). All compounds were prepared in air unless otherwise specified.
X-ray Crystallography. Single crystals of the pro-ligands 4a and 5b and Ir(III) complex 11
suitable for X-ray diffraction studies were grown by slow diffusion of ether into DCM solutions (4a
and 11) and slow diffusion of ether into acetonitrile solution (5b). Crystallographic data for all
structures determined are given in Table S1. For all samples, crystals were removed from the
crystallization vial and immediately coated with paratone oil on a glass slide. A suitable crystal was
mounted in Paratone oil on a glass fiber and cooled rapidly to 173 K in a stream of cold N using an
2
Oxford low-temperature device. Diffraction data were measured using an Oxford Gemini
diffractometer mounted with Mo-Kα  = 0.71073 Å and Cu-Kα  = 1.54184 Å. Data were reduced
7
6
77
and corrected for absorption using the CrysAlis Pro program. The SHELXL2013-2 program was
used to solve the structures with Direct Methods, with refinement by the Full-Matrix Least-Squares
2
refinement techniques on F . The non-hydrogen atoms were refined anisotropically and hydrogen
atoms were placed geometrically and refined using the riding model. Coordinates and anisotropic
thermal parameters of all non-hydrogen atoms were refined. All calculations were carried out using
2
78
the program Olex . Further XRD details are provided in the Electronic Supplementary Information.
CCDC 1905286-1905288 contains the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallographic Data Centre via
https://www.ccdc.cam.ac.uk/structures/
Photophysical measurements. UV-visible spectra were collected using a Cary Series UV-visible
spectrophotometer (Agilent) with a 1 cm path length quartz cuvette, a spectral bandwidth of 1 nm,
signal averaging time of 0.1 sec, data interval of 0.25 nm, scan rate of 150 nm/min and baseline/zero
corrected. Steady-state emission spectra were collected on a Nanolog (HORIBA Jobin Yvon IBH)
spectrometer using a 1 cm quartz cuvette, a band pass of 2 nm, an increment of 1 nm and integration
time of 0.04 second. A 450 W Xenon-arc lamp was used to excite the complexes using a 1200
groves/mm grating blazed at 330 nm double excitation monochromator, a 1200 groves/mm grating

Page 17 of 26
Dalton Transactions
blazed at 500 nm emission monochromator and a thermoelectrically cooled TBX picosecond single-
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DOI: 10.1039/C9DT01362H
photon detector. A long pass filter KV399 was used on the emission side to block the excitation
scatter peaks and the spectra were corrected for source intensity, gratings, detector response and
sample optical density. 10 µM (Abs ~0.05 at 350 nm) solutions in an air-tight four-sided quartz
cuvette were prepared in an N glove box using acetonitrile free of any oxygen previously prepared
2
via the freeze-pump-thaw (three times) method. Lifetimes (10 µM solutions) were measured using
the time-correlated single photon counting (TCSPC) option on the spectrometer and correlated by a
time-to-amplitude converter (TAC) in forward TAC mode. Nanoled 340 (344 nm) and Nanoled 460
(451 nm) lasers were pulsed at 100 kHz repetition rate with the emission band width set to 5 nm.
Signals were collected using a FluoroHub counter and the data analyzed using DAS6 software
2
(
HORIBA Jobin Yvon IBH). Fitting of the curves was assessed by minimizing χ (0.95-1.2) and
visual inspection of the weighted residuals. For long lifetimes this involved fitting to the tail region
by omitting the delta prompt. Spectra for absolute quantum yields were measured at room temperature
(22 ± 2°C) with a Quanta-phi HORIBA Scientific 6 inch diameter integrating sphere connected to the
Nanolog via optical fibres. The complexes were excited using a 450 W Xenon lamp and detected with
a liquid nitrogen cooled Symphony II (model SII-1LS-256-06) CCD. Absolute quantum yields were
calculated by the 4-plot method using Fluorescence v3.5 software following the equation;
푃ℎ표푡표푛푠 푂푢푡
푃ℎ표푡표푛푠 퐼푛
(퐸푐 ― 퐸푎)/퐴
휙 =
푝
=
(1)
퐿푎 ― 퐿푐
where E is the integrated luminescence of the sample, E is the integrated luminescence of the blank,
c
a
A is the area balance factor due to CCD integration time, L is the integrated excitation from the blank
a
and L is the integrated excitation from the sample.
c
Electrochemistry. Electrochemical experiments were performed using a PGSTAT12 AUTOLAB
electrochemical potentiostat (MEP Instruments, North Ryde, NSW, Australia) with Nova 1.8
software. A conventional three-electrode cell configuration housed in an N atmosphere glovebox
2
was used, consisting of a silver wire quasi-reference electrode, a platinum wire auxiliary electrode
and a 3 mm diameter glassy carbon disc working electrode shrouded in Teflon (CH Instruments,
Austin, TX, USA). The working electrode was polished with 0.3 μm then 0.05 μm alumina slurry on
a felt pad, rinsed with Milli-Q water followed by acetone then sonicated in acetonitrile for 10 seconds
followed by a final rinse in acetonitrile and dried with a stream of N . Potentials were referenced to
2
the ferrocene/ferrocenium couple measured in situ in each case. Stock solutions of the complexes
were prepared at a concentration of 1.0 mM in freshly distilled oxygen-free acetonitrile and
[
Bu N][PF ] was added to give a concentration of 0.1 M of supporting electrolyte.
4 6
Electrochemiluminescence

Dalton Transactions
Page 18 of 26
Solutions were prepared with distilled acetonitrile, then deoxygenated by bubbling N for 10 mins
2
View Article Online
DOI: 10.1039/C9DT01362H
prior to and blanketed during measurements. Annihilation ECL was generated with a 3 mm diameter
glassy carbon electrode submerged at a constant height (2 mm from the cell bottom) in a 0.5 mM
solution of the complex containing 0.1 M [Bu N][PF ] as supporting electrolyte. ECL was generated
4
6
carrying out chronoamperometry experiments for 12 cycles with 0.25 s for each step potential at 0.1
V vs. the Ag wire past the oxidation peak potential and reduction potentials. An integration time of 6
s for the CCD detector was used for each ECL spectrum.
ECL signals were detected using the Nanolog CCD (detector used in spectroscopic measurements)
coupled via the FL-3000 Fibre-Optic Adapter and fibre optic bundle to the underside of a custom-
built light-tight Faraday cage. ECL efficiencies were evaluated by comparing the annihilation ECL
2
+
of each complex with that of 1 mM [Ru(bpy) ] (set at 100 and corrected for charge passed) at the
3
same concentration of supporting electrolyte and same pulsing.
Cell lines and Tissue Culture
A549 human lung adenocarcinoma basal epithelial cells were a kind gift from the Chen Laboratory,
LIMS, Department of Biochemistry and Genetics, La Trobe University. Cells were cultured in RPMI-
1
640 supplemented with 10% fetal bovine serum (FBS) containing penicillin (50 U/ml and
streptomycin (50 U/ml) (Life Technologies, Carlsbad, CA) and 0.2% (vol/vol) MycoZap (Lonza,
Basel, Switzerland). Microscopy experiments were performed in FBS-free RPMI-1640 supplemented
with 1% bovine serum albumin.
Confocal Laser Scanning Microscopy (CLSM)
On the day prior to imaging, A549 cells were seeded onto to 8-well live cell imaging Nunc™ Lab-
Tek™ II chamber slides (Nunc, Rochester, NY) and allowed to adhere overnight. Prior to imaging,
cells were stained with mitochondrial dye Mitotracker CMXRos (Invitrogen) as per the
manufacturer’s instructions. Cells were then imaged in the presence of complexes 8 (at 100 μM) and
1
1 (at 50 μM). Imaging took place at t = 0, 5 min and then at 15 min intervals for a total duration of
0 min for 8 and 75 min for 11. A new area of cells was imaged at each interval on a Zeiss LSM 780
6
confocal microscope (Zeiss, Oberkochen, Germany) using a 63x oil immersion objective and 405 nm
561 nm lasers. Microscope chamber was heated to 37°C with 5% CO . Images were then analyzed
/
2
using Zen software (Zeiss).
Synthesis
3
a A mixture of 1a (1.00 g, 2.89 mmol) and NaN (0.23 g, 13.47 mmol) were stirred in DMF/water
3
(
50 mL, 4:1 v/v) at 50 °C for 5 h under a N atmosphere. To the reaction mixture phenyl acelylene
2

Page 19 of 26
Dalton Transactions
(
0.26 mL, 2.41 mmol), CuI (0.11 g, 0.58 mmol) and anhydrous Na CO (0.78 g, 7.34 mmol) were
2 3
View Article Online
DOI: 10.1039/C9DT01362H
added and stirring was continued at RT overnight. The reaction mixture was filtered, and the solvent
removed in vacuo. Acetone was added to the residue and the resulting crude product was collected.
Recrystallization of the solid in acetonitrile gave the product as a pale yellow crystalline solid (0.60
1
g, 60%). H NMR (400 Hz, d - DMSO): δ 4.78 (dd, 2H, J= 4.12, 6.12 Hz, CH ), 4.95 (dd, 2H, J=
6
2
5
.04, 7.08 Hz, CH ), 5.39 (s, 2H, Bn-CH ), 7.22-7.37 (m, 6H, H ), 7.44-7.47 (m, 2H, H ), 7.77-7.79
2 2 Ar Ar
1
3
(
d, 2H, J= 1.65 Hz, H ), 7.8-7.81 (m, 2H, H ), 8.54 (s, 1H, H ), 9.16 (s, 1H, H ). C NMR (100
imi Ar az imi
Hz, d - DMSO): δ 49.20 (CH ), 49.52 (CH ), 52.34 (Bn-CH ), 122.25 (C ), 123.38 (C ), 123.53
6
2
2
2
az
imi
(
C ), 125.64 (C ), 128.37 (C ), 128.52 (C ), 129.07 (C ), 129.35 (C ), 129.40 (C ), 130.91 (C ),
imi Ar Ar Ar q Ar Ar Ar
+
+
1
3
35.07 (C ), 137.17 (C ), 146.99 (C ). HRESI-MS (CH OH): m/z 330.1713 [C H N ] calcd.
q imi q 3 20 20 5
30.1713.
3
b This compound was prepared using the same procedure as that described for 3a from 1b (1.12 g,
1
.72 mmol), NaN (0.385 g, 2.58 mmol), phenyl acelylene (0.35 mL, 1.38 mmol), CuI (0.15 g, 0.34
3
mmol) and anhydrous Na CO (1.25 g, 5.17 mmol). The crude product was recrystalised from a
2
3
mixture of acetonitrile and ether yielding the product as a pale yellow crystalline solid (0.58 g, 43%).
1
H NMR (400 Hz, d - DMSO): δ 1.33 (t, 3H, J= 8.0 Hz, CH ), 4.16 (q, 2H, J= 8.0, 12.0 Hz, CH ),
6
3
2
4
.75 (t, 2H, J= 4.0 Hz, CH ), 4.94 (t, 2H, J= 4.0 Hz, CH ), 7.34 (t, 1H, J= 8.0 Hz, H ), 7.45 (t, 2H,
2 2 Ar
J= 8.0 Hz, H ), 7.69 (s, 1H, H ), 7.78-7.79 (m, 2H, H ), 7.81 (s, 1H, H ), 8.54 (s, 1H, H ), 9.08
Ar
imi
Ar
imi
Az
1
3
(
(
(
s, 1H, H ). C NMR (100 Hz, d - DMSO): δ 15.1 (CH ), 44.3 (CH ), 48.6 (CH ), 49.1 (CH ), 121.8
imi 6 3 2 2 2
C ), 122.4 (C ), 122.6 (C ), 125. 1 (C ), 128.0 (C ), 128.9 (C ), 130.4 (C ), 136.2 (C ), 146.5
Az
imi
imi
Ar
Ar
Ar
q
imi
+
+
C ). HRESI-MS (CH OH): m/z 268.1554 [C H N ] calcd. 268.1557.
q
3
15 18
5
4
a A solution of benzyl chloride (0.22 mL, 1.82 mmol) and NaN (0.14 g, 2.18 mmol) in a mixture
3
of DMF/water (50 mL, 4:1 v/v) were stirred at 50 °C for 5 h under a N atmosphere. Compound 2a
2
(
0.47 g, 1.38 mmol), CuI (0.058 g, 0.30 mmol) and anhydrous Na CO (0.48 g, 4.54 mmol) were
2 3
added and the resulting mixture was stirred at RT overnight. The reaction mixture was filtered, and
the solvent removed in vacuo. Acetone was then added, and the solution was filtered, and the solvent
removed from the filtrate in vacuo. The crude product was triturated with ether to give the title
1
compound (0.48 g, 76%). H NMR (400 Hz, d - DMSO): δ 5.42 (s, 2H, CH ), 5.52 (s, 2H, CH ), 5.62
6
2
2
(
s, 2H, CH ), 7.31-7.42 (m, 10H, H ), 7.78 (dt, 2H, J= 1.88, 9.92 Hz, H ), 8.28 (s, 1H, H ), 9.35
2 Ar imi az
1
3
(
s, 1H, H ). C NMR (100 Hz, d - DMSO): δ 43.8 (CH ), 55.0 (CH ), 53.0 (CH ), 122.7 (C ),
imi 6 2 2 2 imi
1
1
3
23.0 (C ), 124.6 (C ), 128.0 (C ), 128.3 (C ), 128.3 (C ), 128.8 (C ), 129.0 (C ), 134.7 (C ),
imi az Ar Ar Ar Ar q q
+
+
35.7 (C ), 136.3(C ), 140.6 (C ). HRESI-MS (CH OH): m/z 330.1712 [C H N ] calcd.
q
imi
q
3
20 20
5
30.1713.

Dalton Transactions
Page 20 of 26
4
b To a solution of 2b (0.456 g, 2.67 mmol) in a mixture of DMF/water (20 mL, 4:1 v/v) was added
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DOI: 10.1039/C9DT01362H
benzyl azide (0.40 mL, 3.21 mmol), CuI (0.102 g, 0.53 mmol) and anhydrous Na CO (0.850 g, 8.02
2
3
mmol). This mixture was stirred at RT under an N atmosphere overnight. The reaction mixture was
2
filtered, and the solvent removed in vacuo. Acetone was then added to the residue and the solution
was filtered and the solvent removed from the filtrate in vacuo. The crude product was then dissolved
in CH Cl and this solution was extracted with water. The aqueous layers were collected and dried
2
2
and the residue was recrystallised from a mixture of isopropanol and ether followed by acetonitrile.
1
(
0.372 g, 46%). H NMR (500 Hz, d - DMSO): δ 0.67 (t, 3H, J= 7.22 Hz, CH ), 3.41 (q, 2H, J= 7.42,
6
3
1
5.21 Hz, CH ), 4.71 (s, 2H, Bn-CH ), 4.80 (s, 1H, CH ), 6.53-6.59 (m, 6H, H , H ), 6.69 (d, 1H,
2 2 2 Ar az
1
3
J= 1.94 Hz, H ), 6.74 (d, 1H, J= 1.94 Hz, H ), 7.42 (s, 1H, H ). C NMR (125 Hz, d - DMSO):
imi
imi
imi
6
δ 5.9 (CH ), 35.1 (CH ), 36.6 (CH ), 45.6 (CH ), 113.7 (C ), 114.0 (C ), 116.7 (C ), 119.5 (C ),
3
2
2
2
imi
imi
imi
Ar
+
1
19.7 (C ), 120.4 (C ), 120.5 (C ), 120.6 (C ), 126.1(C ). HRESI-MS (CH OH): m/z 268.1556
Ar Ar Az Ar q 3
+
[
C H N ] calcd. 268.1557.
15 18 5
5
a A mixture of 3a (0.19 g, 0.46 mmol) and iodomethane (3 mL, 47.8 mmol) were prepared in an
Ace pressure tube and the reaction was stirred at 80 °C for a week (after one day a dark red oil had
formed). The flask was cooled to RT and the remaining iodomethane was then removed in vacuo.
The residue was dissolved in a mixture of methanol and water (4.0 mL, 1:1 v/v) and a saturated
aqueous solution of KPF (~1 mL) was added to form a white solid. This solid was collected and
6
1
washed with water (0.26 g, 87%). H NMR (400 Hz, d - DMSO): δ 4.20 (s, 3H, CH ), 4.85 (t, 2H J=
6
3
5
7
.48 Hz, CH ), 5.19 (t, 2H, J= 5.14 Hz, CH ), 5,43 (s, 2H, Bn-CH ), 5.39-5.40 (m 5H, H ), 7.69-
2 2 2 Ar
.70 (m, 5H, H ), 7.82 (t, 1H, J= 1,71 Hz, H ), 7.87 (t, 1H, J= 1.71 Hz, H ), 9.08 (s, 1H, H ), 9.20
Ar
imi
imi
az
1
3
(
(
(
s, 1H, H ). C NMR (100 Hz, d - DMSO): δ 47.71 (CH ), 52.15 (Bn-CH ), 52.57 (CH ), 122.32
imi 6 2 2 2
C ), 123.07 (C ), 123.16 (C ), 128.23 (C ), 128.84 (C ), 129.03 (C ), 129.23 (C ), 129.52
q
imi
imi
Ar
Ar
Ar
Ar
+
C ), 129.57 (C ), 131.72 (C ), 134.56 (C ), 137.06 (C ), 142.49 (C ). HRESI-MS (CH OH):
Ar
imi
Ar
q
imi
q
3
+
m/z 490.1589 [C H N ]PF calcd. 490.1590.
2
1
23
5
6
5
b This compound was prepared using the same procedure as that described for 5a from 3b (0.15 g,
0
.43 mmol) dissolved in acetonitrile (2 mL) and iodomethane (3 mL, 47.7 mmol). The crude product
was recrystallized from a mixture of acetonitrile and ether to give the compound as a white crystalline
1
solid (0.17 g, 74%). H NMR (400 Hz, d - DMSO): δ 1.42 (t, 3H, J= 4.0 Hz, CH ), 4.22 (q, 2H, J=
6
3
4
.0, 12.0 Hz, CH ), 4.27 (s, 3H, CH ), 4.86 (t, 2H, J= 4.0 Hz, CH ), 5.21 (t, 2H, J= 4.0 Hz, CH ),
2 3 2 2
7
.68-7.80 (m, 5H, H ), 7.81 (d, 1H, J= 1.69 Hz, H ), 7.86 (t, 1H, J= 1.55 Hz, H ), 9.13 (s, 1H,
Ar
imi
imi
1
3
H ), 9.19 (s, 1H, H ). C NMR (100 Hz, d - DMSO): δ 15.0 (CH ), 44.4 (CH ), 47.5 (CH ), 52.6
Az
imi
6
3
2
2
(CH ), 122.4 (C ), 122.6 (C ), 122.7 (C ), 129.3 (C ), 129.4 (C ), 129.6 (C ), 131.6 (C ), 136.6
2 q imi imi Ar Ar Az Ar
+
+
(
C ), 142.4 (C ). HRESI-MS (CH OH): m/z 410.0837 [C H N ]I calcd. 410.0836.
imi
q
3
16 21
5

Page 21 of 26
Dalton Transactions
6
a This compound was prepared using the same procedure as that described for 5a from 4a (0.211 g,
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DOI: 10.1039/C9DT01362H
0
.46 mmol) and iodomethane (3 mL, 47.7 mmol). The resulting residue was re-dissolved in CH Cl
2 2
and water (4.0 mL, 1:1) and a saturated aqueous solution of KPF (~1 mL) was added. The organic
6
layer was collected and washed with water (3 x 15 mL), dried over MgSO and the solvent removed
4
in vacuo yielding a sticky red residue. The residue was triturated with ether to give the title compound
1
(
72 mg, 25%). H NMR (400 Hz, d - DMSO): δ 4.31 (s, 3H, CH ), 5.44 (s, 2H, CH ), 5.80 (s, 2H,
6
3
2
CH ), 5.91 (s, 2H, CH ), 7.41-7.46 (m, 10H, H ), 7.86 (d, 2H, J= 12.4 Hz, H ) , 9.03 (s, 1H, H ),
2
2
Ar
imi
Az
1
3
9
1
1
.37 (s, 1H, H ). C NMR (100 Hz, d - DMSO): δ 38.5 (CH ), 40.5 (CH ), 52.2 (CH ), 56.3 (CH ),
imi 6 3 2 2 2
23.0 (C ), 123.2 (C ), 128.4 (C ), 128.9 (C ), 129.0 (C ), 129.1 (C ), 129.4 (C ), 131.0 (C ),
imi
imi
Ar
Ar
Ar
Ar
Ar
Az
+
32.7 (C ), 134.4 (C ), 137.3 (C ), 137.6 (C ). HRESI-MS (CH OH): m/z 490.1585 [C H N ]PF
6
q
q
imi
q
3
21 23
5
+calcd. 490.1595.
6
b This compound was prepared using the same procedure as that described for 5a from 4b (0.202 g,
0
.66 mmol) dissolved in acetonitrile (2 mL) and iodomethane (3 mL, 47.7 mmol). Water was added
to the dark red residue and the resulting dark red precipitate was removed by filtration. The filtrate
1
was dried in vacuo and the residue was recrystalised from methanol (5 mL). (0.101g, 28%). H NMR
(
500 Hz, d - DMSO): δ 1.44 (t, 3H, J= 7.14 Hz, CH ), 4.22 (q, 2H, J= 7.42, 16.47 Hz, CH ), 4.32 (s,
6 3 2
3
1
H, CH ), 5.81 (s, 2H, CH ), 5.91 (s, 2H, CH ), 7.43-7.49 (m, 5H, H ), 7.84 (s, 1H, H ), 7.89 (s,
3 2 2 Ar imi
1
3
H, H ), 9.06 (s, 1H, H ), 9.30 (s, 1H, H ). C NMR (125 Hz, d - DMSO): δ 14.9 (CH ), 38.6
imi
Az
imi
6
3
(
(
[
CH ), 40.5 (CH ), 44.6 (CH ), 56.3 (CH ), 122.7 (C ), 122.8 (C ), 129.0 (C ), 129.2 (C ), 129.4
3 2 2 2 imi imi Ar Ar
+
C ), 131.0 (C ), 132.7 (C ), 136.9 (C ), 137.7 (C ). HRESI-MS (CH OH): m/z 410.0836
Ar
Az
q
q
imi
3
+
C H N ]I calcd. 410.0836.
1
6
21
5
7
A mixture of 4a (0.050 g, 0.11 mmol), Ag O (32 mg, 0.14 mmol) and [Ir(ppy) Cl] (59 mg, 0.06
2 2 2
mmol) in 1,2-dichloroethane (20 mL) was stirred at 80 °C in the dark overnight. The hot mixture was
filtered through a plug of Celite and the solvent removed from the filtrate in vacuo. The product was
purified by column chromatography (10% methanol/CH Cl ) on silica gel and the title compound
2
2
1
was obtained as a yellow crystalline solid (68 mg, 74%). H NMR (400 Hz, d - DMSO): δ 4.49 (q,
6
2
H, J= 15.88, 24.43 Hz), 5.22 (d, 1H, J= 16.25 Hz), 5.49 (q, 2H, J= 14.72, 18.50 Hz), 5.64 (d, 1H,
J= 16.55 Hz), 5.96 (d, 1H, J= 7.51 Hz), 6.19 (dd, 3H, J= 1.53, 7.08 Hz), 6.64 (t, 1H, 6.90 Hz), 6.74-
6
5
8
4
1
.78 (m, 2H), 6.86 (t, 1H, J= 7.45 Hz), 6.96-7.07 (m, 6H), 7.11 (d, 1H, J= 1.98 Hz), 7.23-7.32 (m,
H), 7.61-7.70 (m, 4H), 7.76 (d, 1H, J= 5.19 Hz), 7.84 (d, 1H, J= 8.31 Hz), 7.94 (t, 1H, J= 8.12 Hz),
1
3
.10 (d, 1H, J= 7.82 Hz), 8.42 (s, 1H), 8.47 (d, 1H, J= 4.95 Hz). C NMR (100 Hz, d - DMSO): δ
6
4.23, 50.80, 53.94, 199.56, 120.02, 120.53, 121.72, 123.86, 124.32, 124.73, 124.87, 125.13, 126.63,
27.84, 127.88, 128.35, 128.69, 129.01, 129.05, 130.26, 131.08, 134.70, 137.02, 138.27, 141.10,

Dalton Transactions
Page 22 of 26
+
1
43.40, 144.39m 149.33, 150.68, 153.08, 161.46, 166.56, 167.23, 169.14. HRESI-MS (CH OH):
3
View Article Online
+
DOI: 10.1039/C9DT01362H
m/z 830.2579 [C H IrN ] calcd. 830.2578.
4
2
35
7
8
This compound was prepared using the same procedure as that described for 7 from 4b (0.075 g,
0
.25 mmol), Ag O (0.068 g, 0.30 mmol) and [Ir(ppy) Cl] (0.106 g, 0.1 mmol). The crude product
2
2
2
1
was triturated several times with acetone and then dried in vacuo. (87 mg, 55%). H NMR (500 Hz,
d6- DMSO): δ 0.31 (t, 3H, J= 6.72 Hz), 3.45-3.49 (m, 1H), 5.27 (d, 1H, J= 16.42 Hz), 5.43-5.54 (m,
2
H), 6.01 (d, 1H, J= 7.95 Hz), 6.27 (d, 1H, J= 7.51 Hz), 6.73 (t, 1H, J= 7.51 Hz), 6.78 (t, 1H, J= 7.07
Hz), 6.84-6.92 (m, 4H), 7.15-7.21 (m, 2H), 7.24-7.30 (m, 3H), 7.32 (s, 1H), 7.57 (s, 1H), 7.73 (d, 1H
J= 7.51 Hz), 7.82 (d, 1H, J= 7.95 Hz), 7.96 (t, 2H, J= 7.95 Hz), 8.07 (d, 1H, J= 5.74 Hz), 8.15 (d,
1
3
1
H, J= 7.95 Hz), 8.21 (d, 1H, J= 5.74 Hz), 8.26 (d, 1H, J= 7.95 Hz), 8.45 (s, 1H). C NMR (125 Hz,
d6- DMSO): δ 15.6 43.5, 44.0, 53.8, 119.8, 120.0, 120.6, 121.5, 121.7, 122.7, 123.7, 123.8, 123.9,
1
1
7
24.5, 125.0, 127.6, 128.3, 128.7, 129.1, 130.9, 134.7, 137.5, 138.2, 141.0, 143.5, 144.6, 150.1, 151.1,
+
+
52.6, 161.7, 165.6, 167.1, 169.2. HRESI-MS (CH OH): m/z 768.2420 [C H IrN ] calcd.
3
37 33
7
68.2421.
9
This compound was prepared using the same procedure as that described for 7 from 6a (0.072 g,
0
.12 mmol), Ag O (0.068 g, 0.29 mmol), and [Ir(ppy) Cl] (0.062 g, 0.058 mmol) in a mixture of
2
2
2
CH Cl /methanol (20 mL, 1:1, v/v). The product was purified by column chromatography (CH Cl ,
2
2
2
2
then 1-5% methanol/ CH Cl ) on silica gel. The title compound was obtained as a yellow solid which
2
2
1
was then recrystallized in CH Cl (74 mg, 64%). H NMR (500 Hz, d - DMSO): δ 4.21 (s, 3H), 4.61
2
2
6
(
d, 1H, J= 15.42 Hz), 4.75 (d, 1H, J= 15.18 Hz), 4.85 (d, 1H, J= 15.42 Hz), 4.94 (d, 1H, J= 15.18
Hz), 5.57 (d, 1H, J= 16.89 Hz), 5.65 (d, 1H, J= 16.89 Hz), 6.09 (dd, 1H, J= 0.86, 7.59 Hz), 6.14 (dd,
H, J= 0.86, 7.53 Hz), 6.26 (d, 2H, J= 7.28 Hz), 6.31 (d, 2H, J= 7.16), 6.55 (td, 1H, J= 1.19, 7.53
Hz), 6.63- 6.65 (m, 2H), 6.74-6.76 (m, 1H), 6.00-7.12 (m, 9H), 7.61-7.63 (m, 2H), 7.63 (d, 1H, J=
1
1
3
8
.02 Hz), 7.93-7.96 (m, 2H), 8.26 (dd, 1H, J= 0.75, 5.78 Hz), 8.43 (dd, 1H, J= 0.80, 5.85 Hz). C
NMR (125 Hz, d - DMSO): δ 51.16, 54.03, 123.06, 123.19, 123. 79, 123.86, 124.19, 124.26, 125.02,
6
1
1
1
25.16, 126.16, 126.74, 126.83, 127.42, 127.67, 127.95, 128.34, 128.64, 134.52, 136.17, 136.88,
37.33, 137.40, 137.94, 142.12, 148.98, 150.27, 152.32, 154.40, 155.75, 156.60, 156.72, 157.61,
+
+
81.51. HRESI-MS (CH OH): m/z 844.2734 [C H IrN ] calcd. 844.2734.
3
43 37
7
1
0 This compound was prepared using the same procedure as that described for 7 from 6b (0.094 g,
0
.017 mmol), Ag O (0.049 g, 0.21 mmol) and Ir(ppy) Cl] (0.075 g, 0.07 mmol). The product was
2
2
2
1
collected by filtration and washed with acetone. (57 mg, 45%). H NMR (500 Hz, d - DMSO): δ 0.21
6
(t, 3H, J= 6.83 Hz), 3.47-3.51 (m, 1H), 3.83-3.87 (m, 1H), 4.22 (s, 3H), 4.49 (d, 1H, J= 15.74 Hz),
4
.85 (d, 1H, J= 15.12 Hz), 5.34 (d, 1H, J= 16.84 Hz), 5.68 (d, 1H, J= 16.84 Hz), 6.16 (q, 2H, J= 7.34,
4.25 Hz), 6.22 (d, 2H, J= 7.34 Hz), 6.66 (t, 1H, J= 7.34 Hz), 6.70 (t, 1H, J= 6.91 Hz), 6.77-6.83 (m,
1

Page 23 of 26
Dalton Transactions
2
7
1
H), 6.98-7.04 (m, 3H), 7.07 (t, 1H, J= 7.34 Hz), 7.13 (t, 1H, J= 7.34 Hz), 7.33 (d, 1H, J= 1.41 Hz),
View Article Online
DOI: 10.1039/C9DT01362H
.52 (d, 1H, J= 1.51 Hz), 7.64-7.70 (m, 2H), 7.73 (d, 1H, J= 7.63 Hz), 7.87-7.90 (m, 2H), 8.00 (d,
1
3
H, J, 5.62 Hz), 8.11 (d, 1H, J= 8.03 Hz), 8.57 (d, 1H, J= 5.62 Hz). C NMR (125 Hz, d - DMSO):
6
δ 15.1, 36.6, 44.0, 44.5, 53.7, 119.8, 119.9, 120.7, 120.9, 121.6, 122.7, 123.6, 123.8, 124.9, 125.7,
1
1
7
27.0, 127.9, 128.7, 129.0, 130.4, 131.4, 135.6, 136.7, 137.2, 140.7, 144.1, 144.2, 152.0, 152.3,
+
+
63.0, 163.2, 164.1, 168.0, 168.8. HRESI-MS (CH OH): m/z 782.2579 [C H IrN ] calcd.
3
38 35
7
82.2578.
1
1 This compound was prepared using the same procedure as that described for 7 from 5b (0.05 g,
0
.093 mmol), Ag O (0.027 g, 0.11 mmol) and Ir(ppy) Cl] (0.05 g, 0.05 mmol). The product was
2
2
2
1
recrystallized from acetone (59 mg, 70%). H NMR (500 Hz, d - DMSO): δ 0.31 (t, 3H, J=7.16 Hz),
6
3
.40 (s, 3H), 3.48-3.54 (m, 1H), 3.64-3.71 (m, 1H), 4.35 (dd, 1H, J= 6.05, 15.95 Hz), 4.65 (dd, 1H,
J= 11.55, 15.95 Hz), 4.75, (dd, 1H, J= 11.0, 14.85 Hz), 5.28 (dd, 1H, J= 5.5, 15.4 Hz), 5.69-5.74 (m,
2
6
H), 6.18 (d, 1H, J= 8.25 Hz), 6.31-6.40 (m, 3H), 6.58 (dd, 1H, J= 1.11, 8.10 Hz), 6.62-6.67 (m, 2H),
.77 (t, 1H, J= 7.39 Hz), 7.01-7.20 (m, 3H), 7.21 (d, 1H, J= 2.02 Hz), 7.27-7.30 (m, 1H), 7.34 (d, 1H,
J= 1.92 Hz), 7.49 (d, 1H, J= 7.49 Hz), 7.70 (d, 1H, J 8.30 Hz), 7.82-7.85 (m, 1H), 7.88-7.92 (m, 1H),
1
3
7
.97 (d, 1H, J= 8.30 Hz), 8.24 (d, 1H, J= 5.87 Hz), 9.02 (d, 1H, J= 5.77 Hz). C NMR (125 Hz, d -
6
DMSO): δ 15.66, 36.11, 44.54, 45.05, 55.72, 119.57, 119.69, 119.82, 120.23, 121.09, 121.33, 122.90,
1
1
23.27, 124.81, 127.23, 127.48, 127.70, 129.02, 131.91, 136.18, 136.99, 144.18, 145.42, 149.89,
+
54.45, 154.83, 160.68, 165.08, 165.49, 168.84, 168.91. HRESI-MS (CH OH): m/z 782.2579
3
+
[
C H IrN ] calcd. 782.2578.
3
8
35
7
Acknowledgments
The Australian Research Council is acknowledged for funding that supported part of this work
(DP150102741) and the La Trobe University Bioimaging Platform for allowing us to conduct cell
studies via Confocal Laser Scanning Microscopy (CLSM).
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Table of contents entry
Luminescent and electrochemiluminescent N-heterocyclic carbene-combined 1,2,3-triazole and
1
,2,3-triazolylidene Ir(III) complexes have been prepared and their potential as luminescent probes
in cell imaging has been evaluated.