Synthesis and Photophysical Properties of Triazolyl IrIIINucleosides

Article abstract of DOI:10.1002/ejic.201601227

DNA-based nanomaterials are the subject of numerous researches. A series of modified nucleobases were synthesized either to construct a double helix where the natural H-bonded bases are replaced by metal-coordinated liganosides or to introduce a punctual modification inside a natural DNA structure. Thanks to their photophysical and photochemical properties, iridium(III) complexes are of increasing interest in the development of sensors and photoreactants for biochemical applications. In this view, we previously demonstrated that some Ir^IIIcomplexes are able to photoreact with DNA through photoinduced electron transfer. In this study, we report the synthesis and characterization of nucleosides bearing iridium complexes with unaltered properties compared to their parent complexes.

Full text of DOI:10.1002/ejic.201601227

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Title: Synthesis and photophysical properties of triazolyl Ir(III)-nucleosides
´
Authors: Johan Passays; Christophe Rubay; Lionel Marcelis; Benjamin Elias
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European Journal of Inorganic Chemistry
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Synthesis and photophysical properties of triazolyl Ir(III)-
nucleosides
Johan Passays,[a]† Christophe Rubay,[a] Lionel Marcélis,[a] and Benjamin Elias*[a]
Abstract: DNA-based nanomaterials are the subject of numerous
researches. A series of modified nucleobases were synthesized,
either to construct a double-helix where natural H-bonded bases are
2,2’bipyridine is incorporated as ligandoside [14,15]. Artificial
helical-DNA structures were successfully obtained and
described, where hydrogen bonds between nucleobases are
replaced by coordinative bonds to metal ions [16]. The use of
bipyridine ligandoside in classic DNA helix placed in front of an
abasic site was also shown to stabilize the DNA-structure by
replaced by metal-coordinated liganosides, or to introduce
a
punctual modification inside a natural DNA structure. Thanks to their
photophysical and photochemical properties, Iridium(III) complexes
receive a growing interest for the development of sensors and
photoreactants for biochemical applications. In this view, we
previously demonstrated that some Ir(III) complexes are able to
photoreact with DNA via photo-induced electron transfer. In this
study, we report the synthesis and the characterization of
nucleosides bearing Iridium complexes with unaltered properties
compared to parent complexes.
favorable π-stacking interactions [17,18]
.
Many examples of β-nucleosides derivatives containing
a
triazole moiety at position 1’ were reported in literature
[19,20,21,22,23]. Some examples present biological activities as
antiviral HIV agents [24], for treating HCV infection (as Ribavirin
analogues) [25], for antiviral and antitumor potential activity (as
Eicar analogues), for anti-mycobacterial activity (as DPA
[26]
analogues)
, or for treatment of chronic myelogenous
leukemia (as Tiazofurin analogues) [27]
.
Introduction
Thanks to their photophysical and photochemical properties,
Iridium(III) complexes receive growing interest for the
and photoreactants towards DNA.
In this later case, we recently demonstrated that a Ir(III) terpy
(2,2′:6′,2″-terpyridine) derivative is able to photo-oxidize purine
bases of DNA [30]. Another cyclometalated Ir(III) complex was
shown to be able to photo-oxidize guanine and photo-reduce
cytosine [31]. Iridium(III) complexes are thus excellent candidates
to study charge transfer processes involving DNA and
polynucleotides.
The first example of a “click-reaction” dates back to the sixties
when Huisgen described the 1,3-dipolar cycloaddition between
alkynes and azide leading to 1,2,3-triazoles [1,2]. The concept of
“Click chemistry” itself has emerged thanks to its description by
Sharpless et al [3,4], but its use has been more and more
attractive since the development of the copper catalyzed version
of the Huisgen’s [3+2] azide-alkyne cycloaddition, namely the
CuAAC reaction [5]. This reaction presents many advantages,
mainly due to its mild conditions of use. “Click chemistry” is now
used in diverse fields of research such as bio-conjugation,
materials science or drug discovery [6]. Its popularity for these
applications is due to the large variety of “clickable” azides and
alkynes reagents available [7], and because it can proceed
readily in water, allowing the use of sensitive biomolecules like
a
[28,29]
development of sensors
DNA [8,9]
.
DNA-based nanomaterials are more and more developed; new
structures have emerged where the Watson-Crick base pairs
have been replaced by nucleoside analogues called
ligandosides, featuring metal-binding ligands in place of classical
nucleobases [10,11,12]. These ligand-like nucleobases can for
example be used to obtain DNA-like multichromophore systems
[13]
or to perform titration of metal ions in solutions when
[a]
J. Passays, C. Rubay, L. Marcélis, B. Elias
Institute of Condensed Matter and Nanosciences (IMCN), Université
catholique de Louvain (UCL)
Place Louis Pasteur 1/L4.01.02, 1348 Louvain-la-Neuve, Belgium
E-mail: Benjamin.Elias@uclouvain.be website:
https://www.uclouvain.be/en-237299.html
Figure 1. Synthetic scheme of the Ir(III) nucleosides (target molecules). Insert:
modified ethynyl ligands (a) 5-ethynyl-2,2’-bipyridine 9; (b) 5-ethynyl-1,10-
phenanthroline 12; (c) 11-ethynyldipyrido[3,2-a:2',3'-c]phenazine.
†present address: Oril Industrie, groupe Servier
Supporting information for this article is given via a link at the end of
the document.
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European Journal of Inorganic Chemistry
10.1002/ejic.201601227
FULL PAPER
In this context, we report the design, synthesis and
photophysical characterization of original iridium (III) complexes
with functionalized bpy (2,2’-bipyridyne), phen (1,10-
phenanthroline) and dppz (dipyrido[3,2-a;2’,3’-c]phenazine)
ligands at position 1’ to a 2’-deoxyribose structure via a triazolyl
linker formed by Huisgen click reaction (Figure 1). The goal of
this research is (i) to develop a facile synthesis of Ir-nucleoside
conjugates using mild conditions, and (b) to obtain such Ir-
nucleoside conjugate having unaltered photophysical and
photochemical properties compared to their parent complexes.
Results and Discussion
Scheme 2. Synthetic scheme for [Ir(ppy)2(Ethynyl-phen)]+ 2. Reagents and
conditions: (a) Ethynyl-SiMe3 (1.5 equiv.), [Pd(PPh3)2Cl2] (3mol%), CuI
(10mol%), THF, i-Pr2NH excess, rt, 24h, (85%); (b) [Ir(ppy)2Cl]2 (0.5 equiv.),
CH2Cl2/MeOH 1:1, 65°C, 16h, (85%), (c) K2CO3 (1.4 equiv.), MeOH, rt, 24h,
(72%).
Towards the synthesis of ethynyl-Ir(III) polypyridyl
complexes
Choi et al. recently report the synthesis of Iridium-nucleosides
[32]
derivatives
and studied them as potential anti-cancer agents.
Our Iridium nucleosides conjugates, presented in Figure 1,
differentiate by the mode of anchoring of the complex on the
sugar; in order to be able to vary more easily the nature of the
complex tethered, we did not use the triazole ring as chelating
moiety [32] in the Iridium complex but only as a linker. In this case,
the tethering of the complex onto the nucleoside thus not affect
the coordinating sphere around the Ir(III) and its photophysics
remains unaltered.
For the bpy and phen based conjugates, the ethynyl-modified
ligands are first synthesized and then chelated onto the Ir(III)
(Scheme 1 and 2). 5-bromo-2,2’-bipyridine 1a is obtained by a
two steps procedure with stannylation of 2-bromopyridine
followed by a [Pd(PPh3)4] catalyzed Stille coupling reaction with
[33]
2,5-dibromopyridine
.
Palladium catalyzed Sonogashira
reaction with (trimethylsilyl)acetylene allowed us to obtain the
[34,35]
protected ethynyl-bpy analogue 1b
.
5-bromo-1,10-
phenanthroline 2a was prepared from 1,10-phenanthroline by
The key precursors are designed to bear a single ethynyl
functional group on one of the ligand chelated onto the Iridium
center. We investigated three modified ligands based on bpy
(2,2’-bipyridine), phen (1,10-phenanthroline) and dppz
(dipyrido[3,2-a:2’,3’-c]phenazine) ligands (see insert Figure 1).
[36]
reaction
with
bromine
and
oleum
.
The
(trimethylsilyl)acetylene moiety was introduced via Sonogashira
reaction to obtain the intermediate 2b [34]. TMS-protected bpy
and phen ethynyl ligands were then individually reacted with
[Ir(ppy)2Cl]2 dimer. Obtained complexes were afterwards
deprotected under mild conditions upon treatment with K2CO3 in
methanol to give respectively the desired ethynyl complexes 1
and 2 [37]
.
Scheme 1. Synthetic scheme for [Ir(ppy)2(Ethynyl-bpy)]+ 1. Reagents and
conditions: (a) Ethynyl-SiMe3 (3.4 equiv.), [Pd(PPh3)2Cl2] (10mol%), CuI
(16mol%), THF, i-Pr2NH excess, rt, 48h, (79%); (b) [Ir(ppy)2Cl]2 (0.5 equiv.),
CH2Cl2/MeOH 1:1, 65°C, 16h, (94%), (c) K2CO3 (2.3 equiv.), MeOH, rt, 16h,
(71%).
Scheme 3. Synthetic scheme for [Ir(ppy)2(Ethynyl-dppz)]+ 3. Reagents and
conditions: (a) Ethynyl-SiMe3 (1.5 equiv.), [Pd(PPh3)4] (7mol%), CuI (14mol%),
THF, Et3N excess, rt, 18h, (82%); (b) TFA (50 equiv.), CH2Cl2, 2h, rt; (c)
[Ir(ppy)2(phendione)]+, CH2Cl2/MeOH 1:1, 65°C, 16h, (70%).
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European Journal of Inorganic Chemistry
10.1002/ejic.201601227
FULL PAPER
A different approach was considered for the synthesis of the
complex [Ir(ppy)2(Ethynyl-dppz)]+ 3 (Scheme 3). The synthesis
of the di-tert-butyl(4-iodo-1,2-phenylene)dicarbamate 3a was
performed from 5-iodo-2-nitroaniline by reduction of the nitro
nucleosides conjugates or the triazolyl Ir(III)-nonyl. In this case,
we faced solubility issues that should be responsible for the
inefficiency of the click reaction between the modified complex 3
and the azido substrates.
group and double protection of the diamine intermediate with
[31]
Boc protecting groups, as described in literature
. A
Sonogashira coupling reaction with (trimethylsilyl)acetylene was
then realized, followed by a one-step total deprotection to obtain
the 4-ethynylbenzene-1,2-diamine 3c. Condensation of this
diamine
intermediate
was
then
carried
out
with
[Ir(ppy)2(phendione)]+, previously prepared from an iridium
dichloro-bridged precursor and 1,10-phenanthroline-5,6-dione,
to obtain the desired [Ir(ppy)2(Ethynyl-dppz)]+ 3 complex.
Synthesis of triazolyl Ir(III)-nucleosides
Triazolyl Ir(III)-nucleosides synthesis was performed from the
Ethynyl-Iridium complexes and the 1’(α)-azido-(2’)-deoxyribose
(commercial) by classical click reaction (5 and 7, Scheme 4). In
order to investigate the photophysical influence of triazolyl
moiety in the Ir(III)-nucleosides, triazolyl Ir(III)-nonyl derivatives 4
and 6 were prepared as control analogs (Scheme 4). Briefly, 1-
azidononane (C9H19N3) was obtained quantitatively following a
straightforward procedure of nonyl-bromide and NaN3 in 10
minutes in DMF under microwave irradiation at 100°C [38]. Nonyl
conjugates were obtained by click reaction from their respective
Ethynyl-Iridium complexes.
Scheme 4. Structure of the triazolyl Ir(III) derivatives: (a) the nonyl-bpy
[Ir(ppy)2(nonyl-tl-bpy)]+
4
and the nucleoside conjugate [Ir(ppy)2((3',5'-
toluoyl,1'-tl-bpy)deoxynucleoside)]+
and (b) their phen counterparts
[Ir(ppy)2(nonyl-tl-phen)]+
and [Ir(ppy)2((3',5'-toluoyl,1'-tl-
5
6
phen)deoxynucleoside)]+ 7. General procedure for coupling reaction: azide
(1.5 equiv.), sodium ascorbate (1.0 equiv.), CuSO4 (1.0 equiv.), DMF/H2O 1:1,
argon, rt, overnight.
It should be noted that despite our synthetic efforts, the reaction
with [Ir(ppy)2(Ethynyl-dppz)]+ did not yield the desired Ir(III)-
Table 1. Photophysical and electrochemical properties of Iridium complexes and conjugates.
[c]
[d]
[e]
[e]
Complex
Absorption[a]
Emission[b]
0
ΦEm
Eox
Ered
[Ir(ppy)2(bpy)]+ [39]
265, 310 (3.6), 335 (1.6), 375, 410 (0.5),
455 (0.3), 465 (0.06)
606
337
0.093
1.32 [40]
-1.4 [40]
[Ir(ppy)2(Ethynyl-bpy)]+ 1
[Ir(ppy)2(nonyl-tl-bpy)]+ 4
265 (4.2), 310[f] (2.3), 383[f] (0.5)
250 (2.6), 263[f] (2.5), 287[f] (2.1), 317[f]
(1.7), 330 (1.6), 378[f] (0.4)
621
599
280
290
0.024
0.091
1.19
1.19
-1.06
-1.19
[Ir(ppy)2((2',5'-toluyl,1'-tl-
bpy)deoxynucleoside)]+ 5
[Ir(ppy)2(phen)]+
[Ir(ppy)2(Ethynyl-phen)]+ 2
[Ir(ppy)2(nonyl-tl-phen)]+ 6
243 (5.5), 264[f] (3.8), 288[f] (3.1), 316
(2.4), 330[f] (2.3), 380[f] (0.5)
266 (4.8), 376 (0.6) [41]
600
282
0.077
1.20
-1.16
590 [42]
596
360 [42] 0.27 [42]
1.22 [43]
1.18
-1.48 [43]
-1.11
242 (5.1), 265 (4.7), 367[f] (0.7)
249 (4.4), 264[f] (3.6), 278[f] (3.2), 328[f]
(1.2), 375[f] (0.6)
566
720
0.092
0.199
587
1.19
-1.16
[Ir(ppy)2((2',5'-toluyl,1'-tl-
phen)deoxynucleoside)]+ 7
[Ir(ppy)2(dppz)]+ [31,44]
241 (7.0), 264[f] (4.6), 279[f] (3.9), 332[f]
584
630
311
77
0.192
0.002
1.19
-1.15
(1.4), 376 (0.7)
270 (7.12), 360 (1.86), 382 (1.81)
278 (7.5), 366[f] (1.5), 387 (1.4)
1.25
1.18
-0.94
-0.68
[Ir(ppy)2(Ethynyl-dppz)]+ 3
-
-
-
[g]
[g]
[g]
[a] max in acetonitrile in nm (x10-4L.mol-1.cm-1). [b] max in acetonitrile in nm under argon at 298K; excitation wavelength = 375nm. [c] Luminescence lifetime in ns
in acetonitrile under argon. [d] Quantum yield of luminescence in acetonitrile under argon at 298K. Measure relative to [Ru(bpy)3]3+ in aerated aqueous solution
(Φref = 0.028). [e] Oxidation and first reduction potential measured in dry MeCN (oxidation) or dry DMF (reduction) with 0.1 M tetrabutylammonium perchlorate. All
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European Journal of Inorganic Chemistry
10.1002/ejic.201601227
FULL PAPER
potentials are reported in V/SCE. [f] shoulder. [g] not emissive upon excitation at 375 nm.
Spectroscopic and electrochemical investigation of triazolyl
Ir(III)-nucleosides conjugates
lifetime for complexes 2 and 6 is observed compared to
[Ir(ppy)2(phen)]+. These alteration of the luminescence lifetimes
cannot be correlated to a displacement of the emission, i.e. a
modification of the energy of the excited state, and could then be
related to modification of the non-radiative decay via the
dissipation of energy through the solvent; the different structures
could affect the solvation of the complex and thus the ability of
the solvent molecules to dissipate the energy.
Oxidation and reduction potentials of Ethynyl-Iridium complexes
and their conjugates were determined by cyclic voltammetry.
The potentials are gathered in Table 1 and compared with
reference complexes. By comparison with their parent
complexes, a small cathodic shift in the reduction potentials is
observed when ethynyl group (1-3) or triazole moieties (4-7) are
introduced on the bpy, phen or dppz ligand. This cathodic shift in
reduction can be rationalized by the extended delocalization
induced by the introduction of the alkyne or triazole moiety on
the modified ligand. Similarly, a small decrease of the oxidation
potential is also noticed. The absorption and emission spectra
of the two nucleoside conjugates are presented in Figure 2 and
Concerning the nucleoside conjugates
5
and 7, their
luminescence lifetime is similar to the one of the parent
complexes [Ir(ppy)2(bpy)]+ and [Ir(ppy)2(phen)]+ respectively.
This similarity demonstrates that no intramolecular quenching
processes are at stake in these conjugates. Indeed, if a
moderate shortening of the luminescence lifetime is noticed,
the spectroscopic data for all complexes are gathered in Table 1. consistent with the slight decrease of the quantum yield of
emission, this behavior is attributed to a more efficient non-
radiative decay via the dissipation of energy through the solvent;
we could expect that this non-radiative decay will also be
sensitive to the incorporation of the Ir(III)-nucleoside into a DNA
sequence. In conclusion, based on the steady-state and time-
resolved spectroscopic data, we can safely assert that the
photophysical characteristics of Ir(III)-nucleoside complexes are
similar to their parent complexes and that the photophysical
properties of the iridium complexes are thus conserved when
conjugated to a nucleoside moiety.
Conclusions
In this work, we reported the synthesis of Ir(III)-nucleosides
Figure 2 Absorption and normalized luminescence (excitation wavelength =
using click reaction. In contrast to previous studies, our synthetic
scheme allows the introduction of Iridium complexes that retain
their coordination core, and thus do not alter the photophysical
and photophysical properties. Despite our efforts, one of the
targeted conjugates could not be successfully obtained.
Nevertheless, the characterization of the phen- and bpy- Ir(III)
conjugates demonstrated that the anchoring of Ir(III) complexes
onto nucleosides via the triazoyl linker does not alter the
properties of these complexes. This tethering method paves the
way to the incorporation of photoreactive Ir(III) complexes in a
DNA structure, and a new way to study DNA charge transfer
process by using a photoreactive complex directly embeded
within the DNA base stack.
375nm) spectra of the nucleoside conjugates 5 (red line) and 7 (purple line) in
acetonitrile at room temperature under air.
In absorption, no clear-cut modification of the absorption spectra
can be noticed in the MLLCT (Metal-Ligand to Ligand Charge
Transfer) bands around 380 nm between parent complexes and
conjugates; shifts in the UV-region, corresponding to LC (Ligand
Centered) transitions, are related to the modification of the
structure of the ligand and the extended delocalization of the
ligand orbitals. In steady-state emission, the wavelength of the
luminescence maximum is shifted bathochromically upon
introduction of the alkyne function on bpy or phen for complexes
1 and 2 respectively, while the Ethynyl-dppz complex 3 appears
to be non-luminescent, although the parent complex
[Ir(ppy)2(dppz)]+ is emissive in acetonitrile, and slightly emissive
in water [31]. Interestingly, after the click reaction and formation of
the triazole moiety, the luminescence of complexes 4-7 is almost
unaffected in comparison with the parent complexes.
Experimental Section
Materials and Instrumentation
Hoffer’s chlorosugar was purchased from Carbosynth. 5-bromo-2,2’-
bipyridine (1a) [33], 5-bromo-1,10-phenanthroline (2a) [36], di-tert-butyl (4-
Luminescence lifetimes were measured for the bpy- and phen-
based complexes. Upon modification of bpy ligand with the
introduction of the ethynyl group (1) or the triazole moiety (4),
the luminescence lifetime of the resulting complexes is slightly
reduced. In contrast, a small enhancement of the luminescence
[45]
iodo-1,2-phenylene)dicarbamate (3a) [31], [Ir(ppy)2(phendione)]+.Cl-
[38]
and nonyl azide
were synthesized according to the literature methods.
The other chemicals were obtained from commercial sources and used
without further purification.
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European Journal of Inorganic Chemistry
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FULL PAPER
1H NMR experiments were performed on a Bruker AC-300 Avance II (300
MHz) or on a Bruker AM-500 (500 MHz). The chemical shifts (given in
ppm) were measured versus the residual peak of the solvent as the
internal standard. High-resolution mass spectrometry (HRMS) were
recorded on a Q-Extractive orbitrap from ThermoFisher. Samples were
ionized by electrospray ionization (ESI; capillary temperature = 250 °C,
vaporizer temperature = 250 °C, sheath gas flow rate = 20). UV–vis
absorption spectra were recorded on a Shimadzu UV-1700. Room
temperature fluorescence spectra were recorded on a Varian Cary
Eclipse instrument. Emission quantum yields were determined by
integrating the corrected emission spectra over the frequencies.
[Ru(bpy)3]2+ in water under air was chosen as the standard luminophore
gradient to 85:15) to give the iridium complex as a red solid in 94% yield
(242mg). TLC: Rf (dichloromethane/methanol, 90:10): 0.28. 1H NMR (500
MHz; CDCl3): δ = 9.58 (d, J = 8.6 Hz, 1H), 9.48 (d, J = 8.2 Hz, 1H), 8.28
(dd, J = 8.5, 1.8 Hz, 1H), 8.25 – 8.18 (m, 1H), 8.00 (d, J = 8.2 Hz, 2H),
7.92 (d, J = 1.8 Hz, 2H), 7.85 (t, J = 7.8 Hz, 2H), 7.72 (dd, J = 7.7, 2.3 Hz,
2H), 7.49 (d, J = 6.4 Hz, 1H), 7.47 – 7.40 (m, 2H), 7.06 (t, J = 6.4 Hz, 2H),
7.00 (q, J = 6.7 Hz, 2H), 6.96 – 6.85 (m, 2H), 6.33 (d, J = 7.4 Hz, 1H),
6.29 (d, J = 7.4 Hz, 1H), 5.30 (s, 1H), 0.24 (s, SiMe3, 9H). 13C NMR (126
MHz; CDCl3): δ = 167.36, 167.22, 154.87, 154.43, 151.86, 149.70,
149.38, 149.34, 147.87, 147.84, 143.09, 143.02, 142.26, 139.71, 138.12,
131.28, 131.12, 130.41, 127.89, 126.72, 125.95, 124.63, 124.55, 124.01,
123.02, 122.37, 122.32, 119.68, 119.59, 103.76, 98.70, 53.31, -0.83.
HRMS (ESI): calcd. for C37H32ClIrN4Si 753.20200 [M-Cl]; found
753.20130.
⁄
(ΦEm
=
0.028);
(
)( ⁄
)( ⁄
)
.
∫
∫
Luminescence lifetimes were measured with
a
modified Applied
Photophysics laser kinetic spectrometer by exciting the samples at 355
nm with a Nd:YAG pulsed laser (Continuum NY 61-10). Emitted light as a
function of time was detected with a R-928 Hamamatsu photomultiplier
tube whose output was applied to a digital oscilloscope (Hewlett-Packard
HP 54200A) interfaced with a Dell Dimension DE051 computer. Signals
were averaged over at least 16 shots and corrected for baseline. Igor 6.1
(Wavemetrics) software was used for decay analyses. Cyclic
voltammetry was carried out in a one-compartment cell, using a glassy
carbon disk working electrode (approximate area = 0.03 cm2), a platinum
wire counter electrode and an Ag/AgCl reference electrode. The potential
of the working electrode was controlled by an Autolab PGSTAT 100
potentiostat through a PC interface. For the sake of clarity, potentials are
converted to V vs SCE. The cyclic voltammograms were recorded with a
sweep rate of 100 mV s–1, either in dry acetonitrile (Acros, HPLC grade)
or in dry N,N-dimethylformamide (DMF; Sigma-Aldrich, HPLC grade) for
reduction. Tetrabutylammonium perchlorate (0.1 M) was used as the
supporting electrolyte and the samples were purged by argon before
each measurement.
[Ir(ppy)2(Ethynyl-bpy)]+.Cl- (1): [Ir(ppy)2(TMS-Ethynyl-bpy)]+.Cl- (1c)
(242 mg, 307 µmol) and potassium carbonate (97.6 mg, 706 µmol) were
placed in a 10mL flask and diluted with 5 mL anhydrous methanol. The
reaction was stirred during 20h at room temperature. The solvent was
then removed under vacuum. The crude product was purified by silica gel
flash column chromatography (dichloromethane/methanol 99:1) to give
the iridium complex as a red solid in 71% yield (155 mg). TLC: Rf
(dichloromethane/methanol, 90:10): 0.28. 1H NMR (500 MHz; CDCl3): δ =
9.47 (d, J = 8.3 Hz, 1H), 9.39 (d, J = 8.0 Hz, 1H), 8.10 (d, J = 8.7 Hz, 1H),
8.06 (d, J = 7.6 Hz, 1H), 7.82 (dd, J = 7.9, 3.6 Hz, 2H), 7.78 (d, J = 1.5
Hz, 1H), 7.76 (d, J = 4.9 Hz, 1H), 7.68 (t, J = 7.8 Hz, 2H), 7.55 (d, J = 7.8
Hz, 2H), 7.32-7.29 (m, 3H), 6.90 (t, J = 6.5 Hz, 2H), 6.83 (t, J = 7.4 Hz,
2H), 6.75-6.71 (m, 2H), 6.14 (d, J = 7.5 Hz, 1H), 6.12 (d, J = 7.5 Hz, 1H),
3.42 (s, 1H). 13C NMR (126 MHz; CDCl3): δ = 167.47, 167.35, 155.07,
154.93, 152.16, 149.85, 149.45, 149.40, 148.01, 143.14, 142.56, 139.90,
138.27, 131.37, 131.28, 130.64, 130.57, 128.12, 127.07, 126.22, 124.78,
124.69, 123.30, 123.18, 122.62, 122.53, 119.76, 119.71, 85.69, 77.85.
HRMS (ESI): calcd. for C34H24ClIrN4 681.16247 [M-Cl]; found 681.16195.
Syntheses
5-((trimethylsilyl)ethynyl)-1,10-phenanthroline (2b): Adapted from
literature [37,47]. 5-bromo-1,10-phenanthroline (2a) (324 mg, 1.24 mmol)
was placed in a 100mL flask and diluted with 38 mL of anhydrous THF.
Diisopropylamine (13 mL) was added and the solution was degassed by
freeze-thaw cycle and flushed with argon. [PdCl2(PPh3)2] (10mol%) and
copper iodide (11mol%) were then successively added and the resulting
mixture was degassed by bubbling with argon during 30 minutes.
Trimethylsilylacetylene (267 µL, 1.87 mmol) was then added and the
reaction was stirred at room temperature during 24h to obtain a
black/brown mixture. The solvent was removed under vacuum and the
crude product was dissolved in methanol (20mL). An aqueous solution
(15mL) of EDTA was added and the solution was stirred for 30 minutes
and extracted several times with dichloromethane. The organic phase
was subsequently dried with Na2SO4 and concentrated under vacuum.
The crude mixture was purified by silica gel flash column
chromatography (dichloromethane/methanol 99:1 with gradient until 97:3)
to obtain 293mg of the desired product as a white solid (85% yield). TLC:
5-((trimethylsilyl)ethynyl)-2,2’-bipyridine (1b): This product was
prepared according to procedures described in literature [34,35]. 5-bromo-
2,2’-bipyridine (1a) (300 mg, 1.28 mmol) was placed in a 50mL flask
under argon and diluted with 22 mL of degassed anhydrous THF.
Trimethylsilylacetylene (437 µL, 3.07 mmol), [PdCl2(PPh3)2] (10mol%)
and copper iodide (16mol%) were then successively added. The reaction
mixture was flushed with argon and diisopropylamine (4.5 mL) was
added dropwise with a syringe. The reaction was stirred at room
temperature during 48h. The solvent was removed under vacuum. The
crude product was purified by silica gel flash column chromatography
(hexane/AcOEt 95:5, gradient to pure AcOEt) to obtain 256 mg of the
desired product as a white solid (79% yield). TLC: Rf (hexane/AcOEt,
80:20): 0.50. 1H NMR (500 MHz; CDCl3): δ = 8.69 (dd, J = 2.1, 0.8 Hz,
1H, H6), 8.59 (ddd, J = 4.8, 1.7, 0.8 Hz, 1H, H6’), 8.35 – 8.27 (m, 2H, H3,
H3’), 7.80 (dd, J = 8.2, 2.1 Hz, 1H, H4), 7.71 (td, J = 7.8, 1.8 Hz, 1H, H4’),
7.20 (ddd, J = 7.5, 4.8, 1.1 Hz, 1H, H5’), 0.23 (s, 9H, SiMe3). 13C NMR
(126 MHz; CDCl3): δ = 155.32, 154.88, 151.97, 149.18, 139.71, 136.86,
123.87, 121.34, 120.13, 120.08, 101.90, 99.05, -0.12. MS (ESI): m/z =
253.34 [M+1].
1
Rf (dichloromethane/methanol, 99:1): 0.37. H NMR (300 MHz; CDCl3): δ
= 9.21 (dd, J = 4.3; 1.6 Hz, 1H, H2 or H9), 9.14 (dd, J = 4.3; 1.6 Hz, 1H,
H2 or H9), 8.72 (dd, J = 8.3; 1.7 Hz, 1H, H4 or H7), 8.13 (dd, J = 8.1, 1.7
Hz, 1H, H4 or H7), 7.98 (s, 1H, H6), 7.73 (dd, J = 8.2, 4.3 Hz, 1H, H3 or
H8), 7.58 (dd, J = 8.1, 4.4 Hz, 1H, H3 or H8), 0.41 (s, 9H, SiMe3). MS
(APCI): m/z = 277.33 [M+1], 278.31 [M+2].
[Ir(ppy)2(TMS-Ethynyl-bpy)]+.Cl- (1c): Adapted from procedure for the
preparation of the deprotected/PF6 analog [46]. 5-((trimethylsilyl)ethynyl)-
2,2’-bipyridine (1b) (82.4 mg, 326 µmol) and [Ir(ppy)2Cl]2 (175 mg, 163
µmol) were placed in a 10mL flask with a condenser and diluted with 2
mL of anhydrous dichloromethane and 2 mL of anhydrous methanol. The
reaction was stirred overnight at 65°C, during which time the color of the
solution changed from yellow-orange to red. The solvent was then
removed under vacuum. The crude product was purified by silica gel
flash column chromatography (dichloromethane/methanol 99:1 with
[Ir(ppy)2(TMS-Ethynyl-phen)]+.Cl- (2c): 5-((trimethylsilyl)ethynyl)-1,10-
phenanthroline (2b) (55.3 mg, 200 µmol) and [Ir(ppy)2Cl]2 (107 mg, 100
µmol) were placed in a 10mL flask with a condenser and diluted with 1
mL of anhydrous dichloromethane and 1 mL of anhydrous methanol. The
reaction was stirred overnight at 65°C, during which time the color of the
solution changed from yellow-orange to red. The solvent was then
This article is protected by copyright. All rights reserved

European Journal of Inorganic Chemistry
10.1002/ejic.201601227
FULL PAPER
removed under vacuum. The crude product was purified by silica gel
flash column chromatography (dichloromethane/methanol 99:1 with
gradient to 85:15) to give the iridium complex as a red solid in 85% yield
(139mg). TLC: Rf (dichloromethane/methanol, 95:5): 0.10. 1H NMR (500
MHz; CDCl3): δ = 8.89 – 8.81 (m, 2H), 8.38 (s, 1H), 8.23 (dd, J = 5.0, 1.2
Hz, 1H), 8.14 (dd, J = 5.0, 1.2 Hz, 1H), 7.96-7.92 (m, 2H,), 7.85 (d, J =
8.2 Hz, 2H), 7.71 – 7.67 (m, 2H), 7.62 (dd, J = 4.4, 3.3 Hz, 2H), 7.20 (t, J
= 5.3 Hz, 2H), 6.93 (t, J = 7.3 Hz, 2H), 6.89 – 6.79 (m, 4H), 6.28 (t, J =
6.2 Hz, 2H), 0.26 (s, 9H). 13C NMR (126 MHz; CDCl3): δ = 167.7, 167.7,
151.3, 151.3, 149.2, 149.0, 148.3, 148.2, 146.6, 146.1, 143.6, 143.5,
139.4, 138.5, 138.4, 137.3, 132.6, 131.8, 131.8, 131.1, 130.9, 130.8,
127.8, 127.2, 124.9, 124.9, 123.5, 123.4, 122.9, 122.1, 119.8, 119.8,
105.3, 98.7, -0.2. HRMS (ESI): calcd. for C39H32IrN4Si 777.20200 [M-Cl];
found 777.20161.
with absolute ethanol (2 mL) and methanol (1 mL). The reaction was
refluxed overnight and the solvent was afterwards removed under
vacuum. The crude product was purified by silica gel flash column
chromatography (dichloromethane/methanol 95:5 with gradient to 85:15)
to give the iridium complex as red solid in 70% yield over two steps
(130mg). TLC: Rf (dichloromethane/methanol, 90:10): 0.40. 1H NMR (500
MHz; CDCl3): δ = 9.76 (dd, J = 7.8, 1.1 Hz, 2H), 8.83 (d, J = 1.0 Hz, 1H),
8.38-8.25 (m, 4H), 8.10 (dd, J = 8.2, 5.2 Hz, 1H), 8.07 (dd, J = 8.2, 5.2
Hz, 1H), 7.89 (d, J = 8.1 Hz, 2H), 7.71 (t, J = 7.8 Hz, 2H), 7.66 (d, J = 7.8
Hz, 2H), 7.52 (t, J = 5.7 Hz, 2H), 7.01-6.94 (m, 4H), 6.89 (t, J = 7.4 Hz,
2H), 6.35 (d, J = 7.4 Hz, 2H). 13C NMR (126 MHz; CDCl3): δ = 196.99,
167.51, 152.70, 152.57, 149.48, 149.19, 148.87, 148.73, 144.42, 143.57,
142.33, 140.74, 140.26, 138.87, 138.58, 136.27, 136.12, 131.78, 131.44,
130.84, 130.75, 130.19, 129.68, 128.72, 128.57, 124.91, 123.74, 122.98,
119.86. HRMS (ESI): calcd. for C42H28O1IrN6 825.19484 [M-Cl+H2O];
found 825.19434.
[Ir(ppy)2(Ethynyl-phen)]+.Cl- (2): [Ir(ppy)2(TMS-Ethynyl-phen)]+.Cl- (2c)
(140 mg, 172 µmol) and potassium carbonate (33.5 mg, 241 µmol) were
placed in a 10mL flask and diluted with 5 mL anhydrous methanol. The
reaction was stirred during 20h at room temperature. The solvent was
then removed under vacuum. The crude product was purified by silica gel
flash column chromatography (dichloromethane/methanol 95:5 with a
gradient until 80:20) to give the iridium complex as a red solid in 72%
1-(β)-azido-3, 5-di-(O- p-toluoyl)-2-deoxy-D-ribose: A commercial 20%
aqueous solution of LiN3 (3 eq.) was added to 3 ml of DMF at 0°C.
Commercial Hoffer’s chlorosugar (300 mg, 772 µmol) was then added to
the suspension. The mixture was stirred 1h at 0°C, then 1h at room
temperature. It was diluted in Et2O and consequently washed with 10%
NaHCO3 and H2O. The organic layer was dried over Na2SO4 and the
solvents evaporated by rotavapor and vacuum pump. The obtained
mixture of isomers was then separated by silicagel column
chromatography (hexane/AcOEt = 95:5) to isolate each anomer with a
total yield of 70% (β 81 : 19 α) among which 226 mg of β-anomer.
Adapted from literature [19] [45-46]. TLC: Rf (hexane/AcOEt, 90:10): 0.30 for
β ; 0.20 for α. Analysis for β-anomer: 1H NMR (500 MHz; CDCl3): δ =
7.98 (d, J = 8.2 Hz, 2H, H2,6 p-Tol), 7.90 (d, J = 8.2 Hz, 2H, H2,6 p-Tol), 7.25-
7.23 (m, 4H, H3,5 p-Tol), 5.72 (t, J = 5.2 Hz, 1H, H1’), 5.57 (td, J = 5.4, 2.8
Hz, 1H, H3’), 4.60-4.52 (m, 3H, H4’, H5’), 2.42 (s, 3H, Me p-Tol), 2.41 (s, 3H,
Me p-Tol), 2.43-2.41 (m, 2H, H2’). MS (ESI): m/z = 418.22 [M+Na].
1
yield (92 mg). TLC: Rf (dichloromethane/methanol, 90:10): 0.30. H NMR
(500 MHz; CDCl3): δ = 9.01 (dd, J = 8.3, 1.2 Hz, 1H), 8.98 (dd, J = 8.4,
1.4 Hz, 1H), 8.57 (s, 1H), 8.30 (dd, J = 5.0, 1.4 Hz, 1H), 8.25 (dd, J = 5.0,
1.3 Hz, 1H), 8.03 (dd, J = 7.9, 4.7 Hz, 1H), 8.01 (dd, J = 7.9, 4.7 Hz, 1H),
7.92 (dd, J = 8.0, 4.6 Hz, 2H), 7.78 – 7.72 (m, 2H), 7.71 (d, J = 7.9 Hz,
2H), 7.33 (dd, J = 5.8, 0.8 Hz, 1H), 7.29 (dd, J = 5.9, 0.7 Hz, 1H), 7.09 –
7.01 (m, 2H), 6.98 – 6.88 (m, 4H), 6.36 (t, J = 8.0 Hz, 2H). 13C NMR (126
MHz; CDCl3): δ = 167.89, 167.82, 151.70, 151.44, 149.35, 149.09,
148.62, 148.41, 146.71, 146.44, 143.69, 143.61, 139.68, 138.52, 138.49,
137.35, 133.59, 131.94, 131.91, 131.34, 131.02, 130.99, 130.96, 127.93,
127.39, 125.02, 123.62, 123.52, 123.06, 123.06, 121.29, 119.95, 119.87,
86.93, 78.11. HRMS (ESI): calcd. for C36H24ClIrN4 705.16247 [M-Cl];
found 705.16224.
General
procedure
for
the
preparation
of
Iridium
complexe/triazolyl/nucleosides (5) and (7) via azide-alkyne
cycloaddition reaction: In a round-bottom flask fitted with a septum,
azide (1.0 equiv) and iridium-alkyne complex (1.0 equiv) were
dissolved in a solution THF:H2O and degassed for 10 min with argon.
After that, 20 mol% sodium ascorbate dissolved in a small quantity of
water was added, and the solution was degassed for another 5 min.
Then 10 mol% copper sulfate dissolved in a small quantity of water was
added followed by degassing 5 min. The final ratio of THF to H2O in the
reaction mixture was maintained as 3:1. Finally, diisopropylethylamine
(DIPEA) was added to the reaction mixture (1.5 equiv). The solution was
refluxed at 65°C overnight with stirring. The red solution become yellow
during the reaction. After full consumption of the starting azide, the
reaction mixture was evaporated and partitioned between water and
dichloromethane. The organic layer was then concentrated. The crude
product was then separated by silicagel column chromatography (DCM-
MeOH 95:5, gradient until 92:8) and characterized. Adapted from
Di-tert-butyl (4-((trimethylsilyl)ethynyl)-1,2-phenylene)dicarbamate
[31]
(3b):
Adapted
from
literature
.
di-tert-butyl(4-iodo-1,2-
phenylene)dicarbamate (3a) (200 mg, 460 µmol) was placed with
[Pd(PPh3)4] (7mol%) and copper iodide (14mol%) in a dried 25mL flask
under argon and diluted with 7 mL of degassed anhydrous THF.
Anhydrous triethylamine (0.5 mL) was then added, followed by a
dropwise addition of trimethylsilylacetylene (131 µL, 921 µmol). The
reaction mixture got dark and was stirred at room temperature during 18h
to obtain a black/brown mixture. The solvent was removed under vacuum
and the crude product was purified by silica gel flash column
chromatography (hexane/AcOEt 95:5) to obtain 153mg of the desired
product as a yellow solid (82% yield). TLC: Rf (hexane/AcOEt, 80:20):
0.62. 1H NMR (300 MHz; CDCl3): δ = 7.65-7.40 (m, 2H, 2xNH), 7.20 (dd,
J = 8.4; 1.7 Hz, 1H), 6.91 (br s, 1H), 6.75 (br s, 1H), 1.49 (s, 18H, 2xt-Bu),
0.22 (s, 9H, SiMe3).
literature [48]
.
[Ir(ppy)2(Ethynyl-dppz)]+.Cl- (3): Adapted from literature [31,45]. Di-tert-
butyl (4-((trimethylsilyl)ethynyl)-1,2-phenylene)dicarbamate (3b) (150 mg,
371 µmol) were placed in a 25mL flask under argon and dissolved with
anhydrous dichloromethane (3.3 mL). TFA was then added dropwise with
a syringe and the solution was stirred at room temperature during 2h.
The solvent was then removed under vacuum, an aqueous solution of
Na2CO3 was added, and the mixture was then extracted with AcOEt. The
solvent was then removed under vacuum to obtain the 4-
ethynylbenzene-1,2-diamine intermediate (3c). Thereafter, the latter
was engaged in excess (1.7 equiv.) for the subsequent condensation
reaction. This diamine and [Ir(ppy)2(phendione)]+.Cl- (166 mg, 222 µmol,
1.0 equiv.) were placed in a 25mL flask with a condenser and dissolved
[Ir(ppy)2((3',5'-toluoyl,1'-tl-bpy)deoxynucleoside)]+.Cl- (5): The above
procedure for azide-alkyne cycloaddition reaction was followed using 1-
(β)-azido-3, 5-di-(O- p-toluoyl)-2-deoxy-D-ribose (16.5 mg, 42 µmol) and
the complex [Ir(ppy)2(Ethynyl-bpy)]+.Cl- (1) to afford the desired product
as a yellow/orange solid (41 mg, 88%). 1H NMR (500 MHz; CDCl3): δ =
9.24 (t, J = 8.4 Hz, 1H), 9.16 (dd, J = 14.0, 8.1 Hz, 1H), 8.72 (t, J = 8.8
Hz, 1H), 8.63 (d, J = 38.7 Hz, 1H), 8.49 (d, J = 20.3 Hz, 1H), 8.20 (brs,
1H), 7.94 – 7.90 (m, 4H), 7.88 (dd, J = 13.4, 5.2 Hz, 2H), 7.80 (d, J = 8.2
Hz, 1H), 7.74 (dd, J = 17.2, 7.9 Hz, 2H), 7.71-7.65 (m, 2H), 7.56 (t, J =
6.6 Hz, 1H), 7.47 (d, J = 5.5 Hz, 1H), 7.43-7.36 (m, 1H), 7.24 (d, J = 8.1
Hz, 2H), 7.19 (d, J = 8.0 Hz, 1H), 7.14 (d, J = 8.0 Hz, 1H), 7.08-6.88 (m,
This article is protected by copyright. All rights reserved

European Journal of Inorganic Chemistry
10.1002/ejic.201601227
FULL PAPER
6H), 6.52 (dd, J = 13.3, 6.4 Hz, 1H, H1’), 6.31 (t, J = 6.5 Hz, 2H), 5.81-
5.75 (m, 1H, H3’), 4.66-4.59 (m, 1H, H4’), 4.59-4.46 (m, 2H, H5’), 3.33-
3.23 (m, 1H, H2’), 2.87-2.75 (m, 1H, H2’), 2.41 (s, 3H, Me p-Tol), 2.36 (d, J
= 5.8 Hz, 3H, Me p-Tol). 13C NMR (126 MHz; CDCl3): δ = 168.16, 167.89,
166.25, 165.92, 156.03, 154.51, 150.42, 150.12, 150.05, 148.77, 148.36,
146.97, 144.52, 144.13, 143.55, 143.35, 142.70, 140.06, 138.16, 136.92,
131.82, 131.38, 131.18, 130.90, 129.91, 129.86, 129.35, 129.31 , 127.82,
126.81, 126.54, 126.22, 125.16, 124.91, 123.42, 123.20, 122.72, 120.01,
119.72, 89.01 (C1’), 83.77 (C4’), 75.01 (C3’), 64.26 (C5’), 37.89 (C2’), 21.83
(2xMe p-Tol). HRMS (ESI): calcd. for C55H45IrN7O5 1076.31059 [M-Cl];
found 1076.30998
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[Ir(ppy)2((3',5'-toluoyl,1'-tl-phen)
deoxynucleoside)]+.Cl-
(7):The
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above procedure for azide-alkyne cycloaddition reaction was followed
using 1-(β)-azido-3, 5-di-(O- p-toluoyl)-2-deoxy-D-ribose (10.7 mg, 27
µmol) and the complex [Ir(ppy)2(Ethynyl-phen)]+.Cl- (2) to afford the
desired product as a yellow/orange solid (22 mg, 71%). 1H NMR (500
MHz; CDCl3): δ = 9.83 (br s, 1H), 9.79 (t, J = 8.7 Hz, 1H), 9.21 (br s, 1H),
9.05 (br s, 1H), 8.26 (d, J = 4.7 Hz, 1H), 8.21 (d, J = 4.8 Hz, 1H), 7.97-
7.92 (m, 6H), 7.85 – 7.80 (m, 1H), 7.80 – 7.76 (m, 1H), 7.75 – 7.70 (m,
4H), 7.34 (dd, J = 11.8, 5.7 Hz, 2H), 7.28 – 7.24 (m, 2H), 7.18 (d, J = 7.0
Hz, 2H), 7.08 (t, J = 7.5 Hz, 2H), 6.97 (t, J = 7.4 Hz, 2H), 6.92 – 6.75 (m,
3H), 6.41 (d, J = 7.4 Hz, 2H), 5.94 (brs, 1H, H3’), 4.74-4.60 (m, 3H, H4’,
H5’), 3.63-3.52 (m, 1H, H2’), 2.96-2.87 (m, 1H, H2’), 2.42 (s, 3H, Me p-Tol),
2.33 (s, 3H, Me p-Tol). 13C NMR (126 MHz; CDCl3): δ = 168.04, 166.38,
166.03, 150.53, 150.12, 149.70, 148.58, 147.19, 146.25, 144.56, 144.36,
143.74, 143.69, 140.04, 138.97, 138.25, 132.01, 131.60, 131.01, 130.25,
130.00, 129.34, 129.19, 127.21, 127.13, 126.79, 126.69, 126.63, 125.00,
123.37, 122.96, 119.80, 89.01 (C1’), 83.62 (C4’), 75.30 (C3’), 64.55 (C5’),
37.71 (C2’), 21.86 (Me p-Tol), 21.78 (Me p-Tol). HRMS (ESI): calcd. for
C57H45IrN7O5 1100,31059 [M-Cl]; found 1100.30995.
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Iridium complexes*
Johan Passays, Christophe Rubay,
Lionel Marcélis, Benjamin Elias*
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Synthesis and photophysical
properties of triazolyl Ir(III)-
nucleosides
*one or two words that highlight the emphasis of the paper or the field of the study
TOC abstract: Iridium(III) complexes receive a growing interest for the development of sensors and photoreactants for biochemical
applications. In our group, we previously demonstrated that some Ir(III) complexes are able to photoreact with DNA via photo-induced
electron transfer. In this article, we report the synthesis and the characterization of nucleosides Iridium conjugates.
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Title
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