Luminescent Iridium(III) Cyclometalated Complexes with 1,2,3-Triazole "Click" Ligands

Article abstract of DOI:10.1021/acs.inorgchem.5b02607

A series of cyclometalated iridium(III) complexes with either 4-(2-pyridyl)-1,2,3-triazole or 1-(2-picolyl)-1,2,3-triazole ancillary ligands to give complexes with either 5- or 6-membered chelate rings were synthesized and characterized by a combination of X-ray crystallography, electron spin ionization-high-resolution mass spectroscopy (ESI-HRMS), and nuclear magnetic resonance (NMR) spectroscopy. The electronic properties of the complexes were probed using absorption and emission spectroscopy, as well as cyclic voltammetry. The relative stability of the complexes formed from each ligand class was measured, and their excited-state properties were compared. The emissive properties are, with the exception of complexes that contain a nitroaromatic substituent, insensitive to functionalization of the ancillary pyridyl-1,2,3-triazole ligand but tuning of the emission maxima was possible by modification of the cyclometalating ligands. It is possible to prepare a wide range of optimally substituted pyridyl-1,2,3-triazoles using copper Cu(I)-catalyzed azide alkyne cycloaddition, which is a commonly used "click" reaction, and this family of ligands represent an useful alternative to bipyridine ligands for the preparation of luminescent iridium(III) complexes.

Full text of DOI:10.1021/acs.inorgchem.5b02607

Article
pubs.acs.org/IC
Luminescent Iridium(III) Cyclometalated Complexes with 1,2,3-
Triazole “Click” Ligands
Timothy U. Connell,†,‡ Jonathan M. White,†,‡ Trevor A. Smith,† and Paul S. Donnelly*,†,‡
†School of Chemistry and ‡Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, Victoria
3010, Australia
S
* Supporting Information
ABSTRACT: A series of cyclometalated iridium(III) complexes with
either 4-(2-pyridyl)-1,2,3-triazole or 1-(2-picolyl)-1,2,3-triazole ancillary
ligands to give complexes with either 5- or 6-membered chelate rings
were synthesized and characterized by a combination of X-ray
crystallography, electron spin ionization−high-resolution mass spectros-
copy (ESI-HRMS), and nuclear magnetic resonance (NMR) spectros-
copy. The electronic properties of the complexes were probed using
absorption and emission spectroscopy, as well as cyclic voltammetry. The
relative stability of the complexes formed from each ligand class was
measured, and their excited-state properties were compared. The emissive
properties are, with the exception of complexes that contain a
nitroaromatic substituent, insensitive to functionalization of the ancillary pyridyl-1,2,3-triazole ligand but tuning of the emission
maxima was possible by modification of the cyclometalating ligands. It is possible to prepare a wide range of optimally substituted
pyridyl-1,2,3-triazoles using copper Cu(I)-catalyzed azide alkyne cycloaddition, which is a commonly used “click” reaction, and
this family of ligands represent an useful alternative to bipyridine ligands for the preparation of luminescent iridium(III)
complexes.
via the reaction of 2-picolylazide with para-substituted benzyl
azides. These derivatives form 6-membered chelate rings,
following metal coordination.
INTRODUCTION
■
Octahedral organometallic iridium(III) complexes such as
[IrIII(ppy)3], where the cyclometalating ligand 2-phenylpyridine
(ppy) or its derivatives act as bidentate anionic ligands, exhibit
long-lived phosphorescence at room temperature.1−4 The strong
spin−orbit coupling induced by the heavy iridium(III) ion
promotes efficient intersystem crossing from the singlet state to
the triplet state. An attractive property of iridium(III)
luminescent complexes for application in emerging technologies
is the ability to tune the emissive properties across the visible
spectrum through control of the ligand architecture. Syntheti-
cally, this entails substitution of the cyclometalating ligands or
the replacement of one cyclometalating ligand with a different
(ancillary) ligand to form either neutral or positively charged
heteroleptic complexes.
Substituted 1,2,3-triazoles formed via the Cu(I)-catalyzed
azide−alkyne cycloaddition (CuAAC), which is a commonly
used “click” reaction, form metal complexes with a variety of
coordination modes.5,6 The reaction of 2-ethynylpyridine and an
organic azide yields 4-(2-pyridyl)-1,2,3-triazole and bidentate
“diimine-like” ligands capable of forming 5-membered chelate
rings that are the structural analogue of the classical 2,2′-
bipyridine. In comparison to the synthesis of singly function-
alized 2,2′-bipyridine ligands, the broad scope and functional
group tolerance of the CuAAC reaction allows for the easy
formation of bidentate unsymmetrical ligands in good yields and
in a single synthetic step. An alternative CuAAC approach is the
synthesis of 1-(2-picolyl)-1,2,3-triazole bidentate ligands, formed
Increased popularity in the CuAAC reaction to produce 1,2,3-
triazoles has led to several recent reports of iridium(III)
complexes with 1,2,3-triazoles introduced into either the
cyclometalating or ancillary ligands.7−20 Our interest in the
synthesis of this family of compounds was partially stimulated by
their considerable potential in electrochemiluminescence (ECL)
applications.17,20−24 It is of particular significance that 1,2,3-
trizole-containing ancillary ligands induce a large hypsochromic
shift in emission, compared to complexes prepared with 2,2′-
bipyridine, which enables multiple color detection when
combined with [Ru(bpy)3]2+, which is a commonly used ECL
emitter.25 The modular synthetic approach of “click”-derived
ligands, combined with the tunable emission and unique
photophysics of iridium(III) emitters, is also of interest for the
development of luminescent probes for imaging proteins in live
cells.26
In this manuscript, we present a systematic study of
luminescent cyclometalated iridium(III) complexes that contain
either 5- or 6-membered chelate rings with 4-(2-pyridyl)-1,2,3-
triazole or 1-(2-picolyl)-1,2,3-triazole based ligands, respectively.
To date, iridium(III) complexes with 1-(2-picolyl)-1,2,3-triazole
have not been reported and their properties are compared to the
Received: November 11, 2015
Published: March 3, 2016
© 2016 American Chemical Society
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Scheme 1. Synthesis of CuAAC-Derived Ancillary Ligands
complexes containing 4-(2-pyridyl)-1,2,3-triazole ligands.
Changes to the emission and electrochemical properties of the
iridium(III) complexes caused by altering the substituents on the
1,2,3-triazole ligands are presented.
Scheme 2. Synthesis of Cyclometalated Iridium(III)
Complexes with 1,2,3-Triazole-Containing Ancillary Ligands
SYNTHESIS
■
Triazole-containing ancillary ligands were synthesized using
modified CuAAC reaction conditions (see Scheme 1). The
organic azides benzyl azide and 2-picolylazide were isolated prior
to their use in CuAAC reactions, while the nitro- and methoxy-
substituted derivatives were prepared in situ and immediately
reacted with the corresponding alkyne.27 An organic solution of
each L1x ligand (where x = a−c) was washed with a basic aqueous
solution containing ethylenediamine tetraacetic acid
(H2Na2EDTA, pH 8) to remove the copper catalyst. The
products were purified by recrystallization and obtained in good
yield.
The iridium(III) complexes containing either L1x and L2x
ancillary ligands were synthesized by mixing the ancillary ligand
with the appropriate chlorido-bridged iridium(III) dimer,
[Ir(C^N)2(μ-Cl)]2 where C^N = ppy, 2-(2,4- difluorophenyl)-
pyridine (dfppy) or 1-phenylisoquinoline (piq), in a mixture of
dichloromethane and methanol at ambient temperature for 16 h,
during which the reactants fully dissolved (see Scheme 2). The
anions of the crude complexes were substituted via anion
methathesis with sodium tetrafluoroborate and the complexes
were isolated in good yields, following subsequent recrystalliza-
tion.
The metal complexes were analyzed by electrospray
ionization−high-resolution mass spectrometry (ESI-HRMS)
and spectra of the L1x complexes showed a single monocationic
species with the characteristic iridium isotopic pattern. In
contrast, the spectra of complexes with L2x ligands showed the
parent peak (for [Ir(ppy)2L2a]+ m/z 737.202), along with many
other species, including large amounts of the iridium(III)
cyclometalated core ([Ir(ppy)2]+ m/z 501.095), the protonated
ancillary ligand [L2a + H]+ (m/z 237.113), and even the solvated
complex [Ir(ppy)2(CH3CN)]+ (m/z 542.122). The relative
intensity of these peaks varied with the fragmentor voltage.
retained.1,28,29 The coordination of the L1x ligands to the
iridium(III) core formed a five-membered planar metallacycle
with a N3−Ir−N4 bite angle between 76.11(6)° and 76.8(2)°
(see Table 2), similar to other reported crystal structures of
iridium(III) complexes with 4-(2-pyridyl)-1,2,3-triazole ancillary
ligands.12,15,16,18
The L2x ancillary ligands formed six-membered chelate rings
when coordinated to the iridium(III) atom (Figure 2) and
exhibited larger bite angles compared to the complexes with 4-(2-
pyridyl)-1,2,3-triazole (L1x) ligands. For example, bite angles
were between 84.75(8) ° for [Ir(ppy)2L2c]BF4 and 86.1(4) ° for
[Ir(ppy)2L2a]BPh4. The L2x ancillary ligands coordinated in a
bent fashion, adopting a ‘boat-like’ conformation with fold angles
approximately 112.0(2) ° (C27−C28−N4 in [Ir(ppy)2L2c]BF4).
The Ir−Npyridyl bond length in the ancillary ligands is longer
than the Ir−Ntriazole bond. Bond lengths of Ir−N3 ranged from
2.162(2) Å in [Ir(dfppy)2L1a]BF4 to 2.206(2) Å in [Ir-
(ppy)2L2c]BF4 Previous reports suggest that the N5 atom
(according to atom labeling used in Figures 1 and 2) of the
X-RAY CRYSTALLOGRAPHY
■
Single crystals suitable for X-ray crystallography were obtained
for several of the complexes (see Table 1, Figure 1, and Figure 2),
as either the tetrafluoroborate, hexafluorophosphate, or
tetraphenylborate salt. We previously reported the single-crystal
X-ray structures of [Ir(ppy)2L1a]Cl and [Ir(dfppy)2L1a]BF4 as
part of earlier work describing their ECL properties and have
included their structures here for the benefit of this systematic
investigation.21 All complexes display a distorted octahedral
C2N4 geometry around the iridium(III) atom with the two
coordinated Npyridyl atoms trans to each other and the two
organometallic coordinated C atoms cis to each other, confirming
that the geometry of the iridium(III) precursor was
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a
Table 1. X-ray Crystallographic Data
[Ir(ppy)2L2a]BPh4·
[Ir(dfppy)2L2a]BF4·
[Ir(ppy)2L2c]BF4·
[Ir(piq)2L2a]PF6·
1.5CH2Cl2
[Ir(ppy)2L1b]PF6
[Ir(piq)2L1a]BF4
CH2Cl2
3CHCl3
CH2Cl2
formula
C36H27N7O2IrPF6
926.81
C44H32N6IrBF4
923.76
C61H50N6IrBCl2
1140.98
C39H27N6IrF8BCl9
1253.72
C38H32N6OIrBF4Cl2
938.60
C45.5H35N6IrPF6Cl3
molecular
weight, MW
color and habit yellow block
red slab
yellow needle
pale yellow prism
yellow block
orange-red needle
crystal size
0.44 mm × 0.39 mm 0.55 mm × 0.28 mm 0.47 mm × 0.04 mm 0.166 mm × 0.0754 mm 0.1845 mm × 0.1140
0.5115 mm × 0.0684
mm × 0.0351 mm
monoclinic
P21/c
× 0.18 mm
monoclinic
P21/c
× 0.08 mm
monoclinic
P21/n
× 0.02 mm
monoclinic
P21/c
× 0.0428 mm
triclinic
mm × 0.0584 mm
monoclinic
P21/c
system
space group
temp, T
P1
̅
130.0(1) K
130.0(1) K
130.0(1) K
130.0(1) K
130.0(1) K
130.0(1) K
unit-cell
parameters
a
b
12.7547(2) Å
19.0611(2) Å
14.2521(2) Å
90°
99.2370(10)°
90°
3420.02(8) Å3
4
9.62320(10) Å
17.0053(2) Å
22.3048(3) Å
90°
9.6124(6) Å
12.6634(13) Å
41.7159(3) Å
90°
93.(430)°
90°
5068.6(7) Å3
4
12.7660(6) Å
14.2197(9) Å
14.6535(8) Å
66.207(6)°
83.125(4)°
66.905(5)°
2236.5(2) Å3
2
13.70380(10) Å
15.24220(10) Å
17.1576(2) Å
90°
91.0140(1)°
90°
3583.25(5) Å3
4
14.3335(2) Å
14.05720(10) Å
21.5094(3) Å
90°
105.6790(10)°
90°
4172.64 Å3
4
c
α
β
90.591(1)°
90°
γ
U
Z
3649.88(8) Å3
4
calc density, D 1.800 g cm−3
1.681 g cm−3
1.495 g cm−3
1.5418 Å
6.430 mm−1
1.862 g cm−3
1.750 g cm−3
1.54184 Å
9.119 mm−1
1.766 g cm−3
1.54184 Å
8.929 mm−1
wavelength
0.7107 Å
4.029 mm−1
0.7107 Å
3.721 mm−1
1.5418 Å
11.370 mm−1
absorption
coefficient
F(000)
1816
1824
2296
1220
1848
2188
reflections
measured
55780
44482
24897
12559
26882
30894
independent
reflections
13647
16998
7515
7972
7489
8735
R [I > 2σ(I)]
0.0303
0.0654
0.0289
0.0623
0.0779
0.2035
0.0467
0.1094
0.0221
0.0586
0.0363
0.1028
wR(F2) (all
data)
a
Legend: ppy, 2-phenylpyridine; piq, 1-phenylisoquinoline; and dfppy, 2-(2,4-difluorophenyl)pyridine.
coordinated triazole heterocycle is a weaker sigma-donor than
the N4 atom and metal complexes that coordinate through the
N5 atom (e.g., L2x ancillary ligand) are less stable than complexes
featuring coordination through the N4 nitrogen (e.g., L1x
ligands).31−34 It was therefore surprising to find that Ir−Ntriazole
bond lengths found in the L2x series of complexes were not
significantly longer than the similar bond in the L1x series of
complexes (Table 2). Both the longest and the shortest Ir−
Ntriazole bond lengths were observed in complexes with L2x
ancillary ligands; Ir−N5 2.116(4) Å in [Ir(dfppy)2L2a]BF4 and
2.156(4) Å in [Ir(ppy)2L2c]BF4. The Ir−Ntriazole bond length in
the remaining L2x containing complexes and all the Ir−N4 bond
lengths in the L1x complexes were between these extremes.
Rhenium(I) tricarbonyl complexes with 4-(2-pyridyl)-1,2,3-
triazoles and 1-(2-picolyl)-1,2,3-triazoles as bidentate ligands
also showed no trend in the Re−Ntriazole bond length based on
chelation mode.31−34
Close contact interactions between the cation and anion were
observed in most solved structures and often occurred between
the anion and ancillary ligand, particularly the hydrogen atom of
the triazole heterocycle. This was most evident in [Ir(ppy)2L1b]-
PF6 with multiple close contacts between the ancillary ligand, L1b
and the hexafluorophosphate anion (Figure S1 in the Supporting
Information). The only compound with no close contact
interactions was [Ir(ppy)2L2c]BF4.
between the C30−C33 atoms of the ancillary L2c ligand (Figure
3). Similar π−π interactions between the C3−C6 atoms of the 2-
(2,4-difluorophenyl)-pyridinato cyclometalating ligands were
observed in the structure of [Ir(dfppy)2L2a]BF4 (see Figure 3).
CHARACTERIZATION BY NUCLEAR MAGNETIC
RESONANCE AND AN ASSESSMENT OF THE
RELATIVE STABILITY OF THE COMPLEXES
■
All complexes were characterized using a combination of one-
dimensional (1D) and two-dimensional (2D) NMR experi-
ments. Integration of all signals in each 1H NMR spectra and the
number of signals in each 13C NMR spectra matched the
respective number of H and C atoms in each metal complex.
Long-range C−F coupling was observed for many signals in the
two complexes with fluorine substituents: [Ir(dfppy)2L1a]BF4
and [Ir(dfppy)2L2a]BF4. Following coordination of the ancillary
ligand, most signals undergo a downfield shift; this shift was most
pronounced for the H atom of the triazole heterocycle (Figure
4). In the series of complexes with the L2x ligands, the methylene
carbon is part of the metallacycle formed, which prevents free
rotation of the C−C bonds and the now-diasterotopic hydrogen
atoms in [Ir(ppy)2L2a]BF4 are viewed as an AB doublet (2JH−H
=
15.9 Hz).
The 1H NMR spectra of cations [Ir(ppy)2L1x/2x]+ were anion-
dependent (particularly, the H atom of the triazole heterocycle).
The complex [Ir(piq)2L2a]BF4 showed limited solubility in
deuterated chloroform so spectra were also acquired in
Each complex crystallized as a racemic mixture of the Δ and Λ
isomers. The packing arrangement of the enantiomers in the
crystal lattice of [Ir(ppy)2L2c]BF4 exhibited π−π interactions
1
deuterated acetonitrile. Interestingly, the H NMR spectrum
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Figure 1. ORTEP30 representations (40% thermal ellipsoids) of (A) [Ir(ppy)2L1a]+, (B) [Ir(ppy)2L1b]+, (C) [Ir(dfppy)2L1a]+, and (D) [Ir(piq)2L1a]+.
Counter ions, hydrogen atoms, and solvent molecules were omitted for the sake of clarity. Structures shown in panels (A) and (C) have been reported
previously.21
changed over 12 hours as the complex partially dissociated (final
concentrations of 3:2 complex/dissociation products were
determined by integration of the methylene protons in the L2a
ligand) to the free ligand and what we suspected was the
acetonitrile solvated complex, [Ir(piq)2(CH3CN)2]BF4. Sub-
sequent study of the other L2a complexes showed similar levels of
dissociation while comparison of the 1H NMR spectra of
[Ir(ppy)2L2a]BF4 after 12 h and [Ir(ppy)2(CH3CN)2]BF4
confirmed the speculated dissociation product.
(1LC) in the UV region (λmax = 252 nm in [Ir(ppy)2L1a]BF4) and
weaker bands attributed to both spin-allowed and spin-forbidden
metal-to-ligand charge transfer transitions (1MLCT and
3MLCT) at wavelengths of λmax > 350 nm (Figure 6, Table 3).
The energy of the MLCT absorptions was affected by altering the
cyclometalating ligands; the absorption maxima of the 2-(2,4-
difluorophenyl)pyridinato-containing complexes exhibited a
hypsochromic shift (∼20 nm), relative to the 2-phenylpyridinato
derivatives, and the 1-phenylisoquinolinato ligands induced a
1
3
The complexes also showed similar relative stabilities when
analyzed by high-performance liquid chromatography (HPLC)
(see Figure 5), relative to chromatograms of the free ligands and
the iridium(III) precursor [Ir(ppy)2(μ-Cl)]2 (most likely, the
solvated complex [Ir(ppy)2(CH3CN)2]+ when dissolved in the
mobile phase). The complex [Ir(ppy)2L1a]BF4 eluted as a single
peak; the slight difference between the retention time of the
absorption and emission spectrum was due to the configuration
of the detectors. In contrast, analysis of [Ir(ppy)2L2a]BF4 under
the same conditions gave three peaks in the ultraviolet (UV)
chromatogram, the complex (Rt = 19.33 min) again dissociating
to give the ligand L2a (Rt = 10.12 min) and the cyclometalated
iridium(III) acetonitrile solvate complex (Rt =16.17 min). As
large bathochromic shift of both the MLCT and MLCT
absorption bands. Different substitution of the benzyl group in
the L1x ligands showed no significant change in the
corresponding absorption spectra. Absorption profiles of the
L2x containing complexes were also very similar with the
exception of [Ir(ppy)2L2b]BF4, which had a more prominent
shoulder at λmax = 300 nm (see Figure 7 and Table 4).
All of the complexes are luminescent at room temperature with
the exception of the nitroaromatic containing complexes
[Ir(ppy)2L1b]BF4 and [Ir(ppy)2L2b]BF4. The emission spectra
all show resolved vibronic structure, consistent with other
reported iridium(III) complexes of 1,2,3-triazole ligands, due to
mixing of the 3LC and 3MLCT excited states.12,13,15,35,36
Substitution of the 2-phenylpyridinato cyclometalating ligands
with 2-(2,4-difluorophenyl)pyridinato or 1-phenylisoquinolinato
resulted in a respective hypsochromic or bathochromic shift in
emission consistent with the relative position of the MLCT
expected, only the [Ir(ppy)2L2a]+ showed any emission at λem
=
480 nm.
Characterization by Electronic Spectroscopy. All the
complexes featured strong π−π* ligand centered transitions
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Figure 2. ORTEP30 representations (40% thermal ellipsoids) of (A) [Ir(ppy)2L2a]+, (B) [Ir(ppy)2L2c]+, (C) [Ir(dfppy)2L2a]+, and (D) [Ir(piq)2L2a]+.
Counter ions, hydrogen atoms, and solvent molecules were omitted for the sake of clarity.
quantum yield was reported to correlate with an increase in the
flexibility of 2-(2′-pyridyl)indole compounds.31,38,39 The com-
plex [Ir(piq)2L2a]BF4 was the exception to this trend; while the
relative quantum yield was approximately half that of [Ir-
(piq)2L1a]BF4, Φem = 0.09 compared with Φem = 0.22
respectively, the measured emission lifetimes were very similar,
τ = 3.6 μs compared with τ = 3.2 μs and there was no significant
increase in the calculated nonradiative rate constant (knr 2.2 and
2.8 × 105 s−1 respectively).
The two complexes with nitroaromatic-containing ancillary
ligands, [Ir(ppy)2L1b]BF4 and [Ir(ppy)2L2b]BF4, exhibit differ-
ent photophysical properties. The structure of the emission
spectra for [Ir(ppy)2L1b]BF4 was similar to the other L1x
complexes, although less-resolved. The relative quantum yield
and measured emission lifetime were several orders of magnitude
lower than the other L1x complexes. The complex [Ir(ppy)2L2b]-
BF4 was essentially nonemissive in solution at room temperature,
a weak featureless band was observed (λem = 513 nm) with a
quantum yield below Φem < 0.001. These differences are
consistent with electrochemical measurements (vide infra).
Table 2. Selected bond angles and distances
bite angle
(deg)
Ir−Npyridyl bond
Ir−Ntriazole bond
compound
length (Å)
length (Å)
a
[Ir(ppy)2L1a]Cl
76.8(2)
76.23(9)
76.34(9)
76.11(6)
86.1(4)
84.75(8)
86.0(2)
2.172(5)
2.174(3)
2.162(2)
2.169(2)
2.18(1)
2.142(5)
2.129(2)
2.137(2)
2.130(2)
2.12(1)
[Ir(ppy)2L1b]PF6
[Ir(dfppy)2L1a]BF4
[Ir(piq)2L1a]BF4
[Ir(ppy)2L2a]BPh4
[Ir(ppy)2L2c]BF4
[Ir(dfppy)2L2a]BF4
a
2.206(2)
2.193(7)
2.156(2)
2.116(4)
a
Structures were previously reported in ref 21.
absorption bands. Emission quantum yields and lifetimes were
measured in deoxygenated acetonitrile, quantum yields were
measured relative to known standards.37 The complexes with L1x
ancillary ligands had quantum yields between Φem = 0.2−0.3 and
emission lifetimes in the microsecond range. The quantum yields
and emission lifetimes of complexes containing L2x ancillary
ligands were lower by an order of magnitude. The calculated
radiative (Φem/τ) and nonradiative ((1-Φem)/τ) rate constants
show that the poorer photophysical properties of the L2x
containing complexes result from an increase in nonradiative
paths of decay (most likely promoted by the increased flexibility
of the L2x ligands relative to their L1x isomers); the knr values are
an order of magnitude greater than the L1x containing complexes,
despite having a similar range of kr values (Tables 3 and 4).
Rhenium(I) tricarbonyl complexes with L1x and L2x type ligands
show a similar trend in electronic spectra and a decrease in
ELECTROCHEMISTRY
■
The electrochemistry of the complexes was investigated by cyclic
voltammetry (see Table 5 and Figure 8). The complexes
exhibited two main features, formally assigned as either IrIV/IrIII
metal oxidation at positive potential or various ligand reductions
at negative potential. The metal oxidation process at positive
potentials was quasi-reversible, the cathodic current on the
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Figure 3. ORTEP30 representation of (A) π−π interactions between the C30−C33 atoms of the ancillary L2c ligand in [Ir(ppy)2L2c]BF4 and (B) π−π
interactions between the C3−C6 atoms of the 2-(2,4-difluorophenyl)-pyridinato cyclometalating ligands in [Ir(dfppy)2L2a]BF4.
Figure 4. Partial 1H NMR spectra (500 MHz, CDCl3) of the ligand L1a, [Ir(ppy)2L1a]BF4, L2a, and [Ir(ppy)2L2a]BF4. Residual solvent is marked with an
asterisk.
reverse sweep increased and peak separation (ΔEp) decreased
with an increase in the scan rate (Figure 9). The IrIV/IrIII process
in the [Ir(ppy)2L2x]BF4 series of complexes was slightly higher in
potential (E°′ > 0.04−0.07 V) than the [Ir(ppy)2L1x]BF4
derivatives; for example, for [Ir(ppy)2L2a]BF4, E°′ = 1.32 V,
compared to E°′ = 1.27 V for [Ir(ppy)2L1a]BF4 (Table 5). A
comparison between iridium(III) complexes with 4-(2-pyridyl)-
1,2,3-triazole ancillary ligands and previously reported 4-(2-
pyridyl)-1,2,4,-triazole ligands (where the ligand is deprotonated
and a better sigma donor) revealed a higher oxidation potential in
the positively charged complexes.40−42 The reduced sigma
donation makes the metal ion formally more positive, which
increases the difficulty of oxidation leading to a higher measured
potential.14,41 The N5 nitrogen of the coordinated triazole
heterocycle, as in the complex [Ir(ppy)2L2a]BF4, is thought to be
less electron-rich than the N4 position.31−34
Excluding the complexes with an aromatic nitro substituent,
the L1x series of complexes also showed quasi-reversible
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couple on the reverse sweep indicative of a chemical reaction,
following the irreversible cathodic processes.
Fluorination of the 2-phenylpyridinato ligands in [Ir-
(dfppy)2L1a]BF4 and [Ir(dfppy)2L2a]BF4 caused a small increase
in the reductive wave (+0.06 V, relative to the corresponding 2-
phenylpyridinato complexes) and a much larger increase of the
oxidative wave (+0.33 and 0.32 V, respectively) (see Figure 8).
The greater increase of the oxidation potential is thought to
occur because the cyclometalated phenyl rings (where the
fluorine substituents are located) provide a substantial
contribution to the metal-centered highest occupied molecular
orbital (HOMO). Fluorination of the cyclometalating ligands
causes a stabilization of the HOMO, which, in turn, increases the
oxidation potential. In contrast, the lowest unoccupied molecular
orbital (LUMO) is mainly centered on the pyridine rings of these
ligands and therefore the reductive processes are less affected by
fluorination.17 Extending the conjugation of the cyclometalating
ligands in [Ir(piq)2L1a]BF4 saw little change in the oxidation,
relative to [Ir(ppy)2L1a]BF4 (−0.02 V) and two reductive
couples (Figure 8A). These two waves at E°′ = −1.58 and −1.80
V were both reversible one-electron processes. The first
reductive wave in [Ir(piq)2L2a]BF4 was measured as E°′ =
−1.53 V and quasi-reversible (cathodic current on the reverse
sweep increased and peak separation decreased as the scan rate
was increased). The first reductive process in both 1-phenyl-
isoquinolinato complexes was formally assigned as the reduction
of a cyclometalating ligand.45,46 The ancillary ligand does not
contribute to the LUMO in either [Ir(piq)2L1a]BF4 or
[Ir(piq)2L2a]BF4 and may explain the improved emission
quantum yield and lifetime of [Ir(piq)2L2a]BF4, relative to the
other L2x-containing complexes.
Figure 5. RP-HPLC chromatograms detailing the stability of [Ir-
(ppy)2L1a]BF4 (left) and [Ir(ppy)2L2a]BF4 (right). Absorbance (λ = 254
nm), luminescence (λex = 337 nm, λem = 480 nm). Samples were loaded
onto a reverse-phase C18 column, 0−100% acetonitrile in water (0.1%
CF3CO2H) over 30 min.
The electrochemical data provides insight into the energies of
the frontier orbitals. The separation between the observed
oxidation and reduction potentials is related to the observed
optical transitions, and correlates especially well for MLCT
transitions in metal polypyridyl complexes.43,45,47,48 The HOMO
and LUMO energy for the iridium(III) complexes studied was
calculated (see Table 6) from the electrochemical data, according
to the equation
Figure 6. Absorbance (top) and normalized emission (bottom) spectra
of iridium(III) complexes containing L1x ancillary ligands in acetonitrile.
Absorbance was measured using 20 μM solutions; emission was
measured using 5 μM deoxygenated solutions irradiated at λex = 337 or
380 nm.
EHOMO(LUMO) = − Eonset − Eonset − 4.80 eV
(
)
Fc
where Eonset and E
are, respectively, the onset reduction
onset
Fc
potential of the sample and of ferrocene, while the value −4.80
eV is the HOMO energy level of ferrocene under vacuum.49,50
The complexes [Ir(ppy)2L1a]BF4, [Ir(ppy)2L2a]BF4, [Ir-
(ppy)2L1c]BF4, and [Ir(ppy)2L2c]BF4 all have calculated
ΔEHOMO−LUMO values between 3.04 eV and 3.13 eV,
corresponding to a transition energy at λcalc ≈ 400 nm. While
this is slightly lower in energy than the transition observed
experimentally (λmax = 379 nm), it remains consistent across
these complexes, which all share the same emission profile.
Correlation of the calculated transitions with measured 1MLCT
absorption bands showed similar trends for [Ir(dfppy)2L1a]BF4
(λcalc = 373 nm, λmax = 358 nm) and especially [Ir(piq)2L1a]BF4
(λcalc = 438 nm, λmax = 434 nm), as well as their L2a derivatives.
The calculated molecular orbital (MO) separation of the
complexes containing nitroaromatic functional groups, [Ir-
(ppy)2L1b]BF4 and [Ir(ppy)2L2b]BF4, did not correlate well
with the observed MLCT absorption bands but this is attributed
to the reduction of the nitro group that is not involved in the
optical transition. Similar results were observed in rhenium(I)
tricarbonyl complexes of 4-(2-pyridyl)-1,2,3-triazole ligands.38
processes at negative potentials attributed to ligand-based
processes. On the other hand, the L2x series of complexes
showed completely irreversible reductive waves (Figure 8). The
cathodic peak potential (Epc) of these complexes closely matched
those of the corresponding L1x analogue; for example, for
[Ir(ppy)2L1c]BF4 and [Ir(ppy)2L2c]BF4, the Epc was −1.81 and
−1.82 V, respectively. For the complexes containing 2-
phenylpyridinato cyclometalating ligands, the first reductive
wave was assigned to the pyridyl ring of the 4-(2-pyridyl)-1,2,3-
triazole ancillary ligand.13,17,43 The reduction of the cyclo-
metalating ligands was not observed in this solvent system. The
complexes featuring nitroaromatic functional groups, [Ir-
(ppy)2L1b]BF4 and [Ir(ppy)2L2b]BF4 show different electro-
chemical behavior. Both exhibit a reversible one-electron process
(ΔEp = 0.067 V, compared to ΔEp = 0.066 V for Fc+/Fc) at E°′ =
−1.03 and −1.02 V, respectively, assigned to the reduction of the
nitro group to a stable radical anion (see Figure S2 in the
Supporting Information).44 This was followed by a series of
irreversible processes that affected the reversibility of the first
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Table 3. Summary of Photophysical Data for 4-(2-pyridyl)-1,2,3-triazole Containing Iridium(III) Complexes
Absorbance
ε (M−1 cm−1
Emission
τ (μs)
λmax (nm)
)
λem (nm)
Φem
kr (× 105 s−1
)
knr (× 105 s−1
)
[Ir(ppy)2L1a]BF4
252
44400
4490
151
478
506
379
465
0.30
2.2
1.4
3.2
[Ir(ppy)2L1b]BF4
[Ir(ppy)2L1c]BF4
254
379
465
55100
4930
151
491
0.006
0.31
0.004
2.2
15
2500
252
379
465
51600
5030
200
478
506
1.4
3.1
3.7
[Ir(dfppy)2L1a]BF4
[Ir(piq)2L1a]BF4
245
358
445
51100
4960
159
453
481
0.19
0.22
2.2
3.6
0.86
290
43300
18300
17100
334(sh)
352(sh)
592
632
374(sh)
11100
0.6
2.2
434
520
540
6610
342
200
The iridium(III)−nitrogen bond lengths were similar when the
metal coordinated through either the N4 or N5 position of the
triazole heterocycle. The triazole complexes with 6-membered
chelate rings, formed by coordination of the L2x ligands, are less
stable than the L1x complexes. The [Ir(ppy)2L1x]BF4 complexes
showed better emission quantum yields and longer emission
lifetimes and were more stable to ligand substitution in solution.
Substitution of the triazole ligand did not affect the emission
maxima; however, both hypsochromic and bathochromic tuning
of emission was possible by modifying the cyclometalating
ligands. The presence of a nitroaromatic group lead to a marked
decrease in emission, and this was rationalized by changes to the
properties of the excited state, as measured by cyclic
voltammetry. The scope and versatility of the CuAAC reaction
means it is relatively straightforward to synthesize substituted
pyridine-1,2,3-triazole ligands for use as ancillary ligands in the
formation of cyclometalated organometallic iridium(III) com-
plexes. The resulting complexes have excellent emissive
properties that have potential application in electrochemilumi-
nescence, optical devices, photocatalysis, and cellular imaging.
Figure 7. Absorbance (top) and normalized emission (bottom) spectra
of iridium(III) complexes containing L2x ancillary ligands in acetonitrile.
Absorbance was measured using 20 μM solutions; emission was
measured using 5 μM deoxygenated solutions irradiated at λex = 337 or
EXPERIMENTAL SECTION
■
Reagents and solvents were purchased from various commercial sources
and used without further purification, unless otherwise stated. The
commercial iridium(III) precursor [Ir(dfppy)2(μ-Cl)]2 was provided by
colleagues from Deakin University (Waurn Ponds, Victoria, Australia).
Microanalyses for C, H, and N were carried out by the Campbell
Microanalytical Laboratory (Dunedin, New Zealand). NMR spectra
were acquired on a Model FT-NMR 500 spectrometer (Varian, Palo
Alto, CA, USA). 1H NMR spectra were acquired at 500 MHz, {1H}13C
NMR spectra were acquired at 125.7 MHz, and 19F NMR was acquired
at 470 MHz. All NMR spectra were recorded at 298 K. Chemical shifts
380 nm. The emission band of [Ir(ppy)2L2b]BF4 was very weak (Φem
<
0.001) and was therefore not included.
CONCLUSIONS
■
The synthesis and characterization of a series of iridium(III)
complexes with 1,2,3-triazole positional isomers that coordinate
to form either a 5- or 6-membered chelate ring are presented.
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Table 4. Summary of Photophysical Data for 1-(2-picolyl)-1,2,3-triazole Containing Iridium(III) Complexes
Absorbance
ε (M−1 cm−1
Emission
τ (μs)
λmax (nm)
)
λem (nm)
Φem
kr (× 105 s−1
)
knr (× 105 s−1
)
[Ir(ppy)2L2a]BF4
[Ir(ppy)2L2b]BF4
[Ir(ppy)2L2c]BF4
[Ir(dfppy)2L2a]BF4
[Ir(piq)2L2a]BF4
252
43800
4260
130
478
506
375
465
0.021
0.20
1.0
49
264
295
375
465
42600
30300
7150
260
513
<0.001
0.013
0.022
257
375
465
53400
4710
140
478
506
0.19
0.43
0.68
0.51
52
23
246
357
445
52200
5360
280
455
484
290
41100
18400
18300
340(sh)
352(sh)
600
635
375(sh)
10900
0.090
3.2
0.28
2.8
430
520
550
6990
240
100
a
Table 5. Summary of Electrochemical Data of Iridium(III) Complexes
Oxidation
Reduction
[Epc] (V)
E°′ (V)
[Epa] (V)
ΔEp (V)
E°′ (V)
ΔEp (V)
[Ir(ppy)2L1a]BF4
[Ir(ppy)2L1b]BF4
1.27
1.31
0.092
−1.74
−1.79
0.118
−1.64
−1.03
−1.70
−1.07
0.139
0.067
1.27
1.31
0.088
[Ir(ppy)2L1c]BF4
[Ir(dfppy)2L1a]BF4
[Ir(piq)2L1a]BF4
1.27
1.60
1.31
1.65
0.072
0.092
−1.75
−1.68
−1.81
−1.73
0.118
0.106
−1.80
−1.58
−1.83
−1.61
0.075
0.063
1.25
1.32
1.33
1.32
1.40
1.39
0.135
0.159
0.111
[Ir(ppy)2L2a]BF4
[Ir(ppy)2L2b]BF4
−1.81
−1.05
−1.85
−1.02
0.066
0.122
[Ir(ppy)2L2c]BF4
[Ir(dfppy)2L2a]BF4
[Ir(piq)2L2a]BF4
1.34
1.64
1.32
1.43
1.69
1.38
0.182
0.091
0.136
−1.82
−1.75
−1.60
−1.53
a
Experiments conducted at 100 mV s−1, 1 mM analyte in CH3CN, 0.1 M NBu4BF4 supporting electrolyte.
were referenced to residual solvent peaks and are quoted in terms of
parts per million (ppm), relative to tetramethylsilane (Si(CH3)4); 19F
NMR signals are quoted relative to an internal standard of
hexafluorobenzene. MS/HRMS spectra were recorded on a Model
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2-picolylazide were isolated in small quantities without using
halogenated solvents during “workup” procedures. The other azide
reagents used in this study were prepared in situ, according to previously
reported procedures.51
To a solution of the azide (1−1.1 equiv) in a 2:1 mixture of
dimethylformamide (DMF)/H2O was added the alkyne (1 equiv),
CuSO4·5H2O (1 mol %), and sodium ascorbate (10 mol %). The
solution was stirred at ambient temperature and the reaction quenched
with water (10−30 mL) when finished, as determined by thin layer
chromatography (TLC). The product was then isolated by filtration or
extraction with an organic solvent.
2-(1-(Benzyl)-1H-1,2,3-triazol-4-yl)pyridine (L1a). According to the
general procedure, a mixture of benzyl azide (0.35 g, 2.6 mmol), 2-
ethynylpyridine (0.25 mL, 2.47 mmol), sodium ascorbate (100 mg, 20
mol %), and CuSO4·5H2O (12 mg, 2 mol %) were stirred at ambient
temperature for 16 h and then quenched with water (100 mL). The
precipitate was collected by filtration then dissolved in ethyl acetate (100
mL) and washed with EDTA/NH4OH solution (1 M, 50 mL) and brine
(50 mL). The organic layer was separated and dried (MgSO4),
concentrated by evaporation under reduced pressure, then dried in
vacuo to yield a colorless powder (0.37 g, 62%). 1H NMR (500 MHz;
CDCl3): δ 5.58 (2H, s, triazole−CH2−phenyl), 7.20 (1H, dd, J = 6.9, 5.2
Hz, pyridyl-H), 7.40−7.32 (5H, m, phenyl-H), 7.76 (1H, td, J = 7.7, 1.7
Hz, pyridyl-H), 8.04 (1H, s, triazole-H), 8.17 (1H, d, J = 7.9 Hz, pyridyl-
H), 8.53 (1H, t, J = 1.4 Hz, pyridyl-H).
Figure 8. Cyclic voltammograms of iridium(III) complexes containing
(A) L1x ancillary ligands and (B) L2x ancillary ligands. Experiments
conducted at 100 mV s−1, 1 mM analyte in CH3CN, 0.1 M NBu4BF4
supporting electrolyte.
2-(1-(4-nitrobenzyl)-1H-1,2,3-triazol-4-yl)pyridine (L1b). This com-
pound was synthesized by modification of a previously reported
procedure.51 To a stirred solution of 2-ethynylpyridine (0.62 g, 6.0
mmol) in a 4:1 mixture of DMF/H2O (15 mL) was added NaN3 (0.43 g,
6.6 mmol), Na2CO3 (0.63 g, 5.9 mmol), CuSO4·5H2O (0.30 g, 1.2
mmol), and ascorbic acid (1.19 g, 6.0 mmol). To this was added 4-
nitrobenzyl bromide (1.08 g, 6.3 mmol) and the mixture was stirred at
ambient temperature for 16 h. This mixture was added to an aqueous
EDTA/NaOH solution (100 mL, 1 M) and extracted with ethyl acetate
(4 × 75 mL). The combined organic extracts were washed with brine
6510 electrospray ionization time-of-flight (ESI-TOF) mass spectrom-
eter (Agilent, Santa Clara, CA, USA). HPLC traces were acquired using
a 1200 Series HPLC system (Agilent, Santa Clara, CA, USA) with a
ProteCol C18 HPH125 120 Å column (4.6 × 150 mm, 5 μm) (SGE
Analytical Science, Ringwood, Victoria, Australia), with a gradient
elution of 0−100% acetonitrile in water (0.1% trifluoroacetic acid) at a
flow rate of 1 mL min−1 over 30 min, and were monitored at λ = 220,
254, 280, and 320 nm.
General Procedure for CuAAC “Click” Reactions. Caution: Low-
molecular-weight organic azides are potentially explosive. Benzyl azide and
Figure 9. Cyclic voltammograms of the reductive (left) and oxidative (right) processes of (A) [Ir(ppy)2L1a]BF4 and (B) [Ir(ppy)2L2a]BF4 at different
scan rates (50, 100, 200, 500 mV s−1). Experiments conducted at 1 mM analyte in acetonitrile, 0.1 M NBu4BF4 supporting electrolyte.
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Table 6. Calculated HOMO and LUMO Energies of Iridium(III) Cyclometalated Complexes
onset
ox
onset
E
(V)
EHOMO (eV)
E
(V)
red
ELUMO (eV)
ΔEHOMO−LUMO (eV)
[Ir(ppy)2L1a]BF4
[Ir(ppy)2L1b]BF4
[Ir(ppy)2L1c]BF4
[Ir(dfppy)2L1a]BF4
[Ir(piq)2L1a]BF4
[Ir(ppy)2L2a]BF4
[Ir(ppy)2L2b]BF4
[Ir(ppy)2L2c]BF4
[Ir(dfppy)2L2a]BF4
[Ir(piq)2L2a]BF4
1.20
−5.67
−5.67
−5.67
−6.00
−5.65
−5.73
−5.72
−5.72
−6.03
−5.70
−1.71
−0.99
−1.72
−1.65
−1.51
−1.72
−0.95
−1.74
−1.67
−1.51
−2.62
−3.34
−2.61
−2.68
−2.82
−2.61
−3.38
−2.59
−2.66
−2.82
3.05
2.33
3.04
3.32
2.83
3.12
2.34
3.13
3.37
2.88
1.20
1.20
1.53
1.18
1.26
1.25
1.25
1.56
1.23
(50 mL), dried (MgSO4) and concentrated by evaporation under
reduced pressure, then dried in vacuo to yield a brown solid. The crude
product was purified by silica gel chromatography, using ethyl acetate as
the eluent. The collated fractions were concentrated by evaporation
under reduced pressure and dried in vacuo to give the product as a
colorless powder (1.30 g, 77%). 1H NMR (500 MHz; CDCl3): δ 5.70
(2H, s, triazole−CH2−phenyl), 7.24 (1H, dd, J = 7.5, 4.9 Hz, pyridyl-H),
7.46 (2H, d, J = 8.8 Hz, phenyl-H), 7.79 (1H, td, J = 7.7, 1.6 Hz, pyridyl-
H), 8.13 (1H, s, triazole-H), 8.18 (1H, d, J = 7.9 Hz, pyridyl-H), 8.23
(2H, d, J = 8.7 Hz, phenyl-H), 8.55 (1H, d, J = 4.7 Hz, pyridyl-H).
{1H}13C NMR (125 MHz, CDCl3): δ 53.4, 120.4, 122.3, 123.3, 124.5,
128.9, 137.2, 141.6, 148.3, 149.4, 149.6, 145.0. MS m/z 282.09
([C14H11N5O2+H]+ requires 282.10).
was stirred for 16 h at ambient temperature. The solution was diluted
with water and stirred for 1 h, and the resulting precipitate was collected
via filtration. The crude solid was recrystallized from ethyl acetate/
diethyl ether to give the product as pale yellow crystals (587 mg, 55%).
1H NMR (500 MHz; CDCl3): δ 5.72 (2H, s, triazole−CH2−pyridyl),
7.31−7.28 (1H, m, pyridyl-H), 7.32 (1H, d, J = 7.8 Hz, pyridyl-H), 7.72
(1H, td, J = 7.7, 1.8 Hz, pyridyl-H), 8.01−7.98 (2H, m, phenyl-H), 8.13
(1H, s, triazole-H), 8.28−8.25 (2H, m, phenyl-H), 8.63−8.61 (1H, m,
pyridyl-H).
4-(1-(Picolyl)-1H-1,2,3-triazol-4-yl)anisole (L2c). According to the
general procedure, a solution of 4-ethynyl anisole (490 μL, 3.78 mmol)
and 2-picolylazide (507 mg, 3.78 mmol) sodium ascorbate (100 mg,
∼10 mol %) and CuSO4·5H2O (10 mg, 1 mol %) was stirred for 16 h at
ambient temperature. The solution was diluted with aqueous EDTA/
NaOH solution (1 M, pH 8, 100 mL) and extracted with ethyl acetate
(150 mL). The combined organic extracts were washed with EDTA/
NaOH (50 mL), water (50 mL), and brine (100 mL), then dried (using
Na2SO4) and evaporated to dryness. The crude solid was recrystallized
from ethyl acetate/diethyl ether to give a colorless solid (604 mg, 60%).
1H NMR (500 MHz; CDCl3): δ 3.83 (3H, s, −O−CH3), 5.68 (2H, s,
triazole−CH2−pyridyl), 6.96−6.93 (2H, m, phenyl-H), 7.23 (1H, d, J =
7.8 Hz, pyridyl-H), 7.28−7.25 (1H, m, pyridyl-H), 7.69 (1H, td, J = 7.7,
1.8 Hz, pyridyl-H), 7.76−7.73 (2H, m, phenyl-H), 7.84 (1H, s, triazole-
H), 8.61 (1H, ddd, J = 4.9, 1.7, 0.9 Hz, pyridyl-H).
General Procedure for Preparation of Iridium(III) Complex
Chloride Salts. The iridium(III) dimer precursors were synthesized
according to the published procedure.28 The appropriate iridium(III)
precursor and 1,2,3-triazole containing ligand were suspended in a 3:1
mixture of dichloromethane and methanol. Starting materials typically
solubilized within 1 h. Reactions were stirred in darkness under an inert
atmosphere for 16 h. The solvents were then removed and the residue
dissolved in acetonitrile and filtered through a filter aid (Celite). The
solvent was then removed by evaporation under reduced pressure and
the product was dried in vacuo.
General Procedure for Anion Metathesis of Iridium(III)
Complexes. Chloride exchange to an alternative anion occurred by
dissolution of the iridium complexes in ethanol, and the resulting
solutions were filtered through filter aid (Celite) to remove any
insoluble impurities. To this solution was added a large excess (at least
10 equiv) of either sodium tetrafluoroborate or ammonium
hexafluorophosphate and water until precipitation of a brightly colored
solid began to occur. The mixture was allowed to stir in darkness for 16
h, and the product was then collected by filtration and washed with
water, cold ethanol, ether, and lastly pentane, and then was dried in
vacuo.
2-(1-(4-Methoxybenzyl)-1H-1,2,3-triazol-4-yl)pyridine (L1c). This
compound was synthesized by modification of a previously reported
procedure.51 To a stirred solution of 2-ethynylpyridine (0.62 g, 6.0
mmol) in a 4:1 mixture of DMF/H2O (15 mL) was added NaN3 (0.43 g,
6.6 mmol), Na2CO3 (0.63 g, 5.9 mmol), CuSO4·5H2O (0.30 g, 1.2
mmol), and ascorbic acid (1.19 g, 6.0 mmol). To this was added 4-
methoxybenzyl chloride (0.99 g, 6.3 mmol) and the mixture was stirred
at ambient temperature for 16 h. An aqueous EDTA/NaOH solution
(100 mL, 0.5 M) was added and the solution stirred for 1 h. This
solution was extracted with ethyl acetate (3 × 100 mL) and the
combined organic extracts washed with aqueous EDTA/NaOH solution
(100 mL, 0.5 M), brine (100 mL), dried (MgSO4) and concentrated by
evaporation under reduced pressure then dried in vacuo to give a brown
solid. The crude product was purified by silica gel chromatography using
1:1 ethyl acetate/hexane as the eluent. The collated fractions were
concentrated by evaporation under reduced pressure (∼30 mL
remaining), and then hexane was added until turbidity just persisted.
The solution was cooled to 253 K for 24 h and the solid was collected by
filtration, washed with pentane, and dried to give the product as a
colorless crystalline solid (1.20 g, 75%). 1H NMR (500 MHz CDCl3): δ
3.79 (3H, s, O−CH3), 5.50 (2H, s, triazole−CH2−phenyl), 6.90−6.88
(2H, m, phenyl-H), 7.19 (1H, ddd, J = 7.5, 4.9, 1.2 Hz, pyridyl-H), 7.28−
7.26 (2H, m, phenyl-H), 7.75 (1H, td, J = 7.7, 1.8 Hz, pyridyl-H), 8.01
(1H, s, triazole-H), 8.16 (1H, dt, J = 8.0, 1.1 Hz, pyridyl-H), 8.52 (1H,
ddd, J = 4.9, 1.8, 0.9 Hz, pyridyl-H).
(1-(Picolyl)-1H-1,2,3-triazol-4-yl)benzene (L2a). According to the
general procedure, a solution of phenylacetylene (0.23 mL, 2.1 mmol)
and 2-picolylazide (257 mg, 1.9 mmol), sodium ascorbate (38 mg, 10
mol %) and CuSO4·5H2O (5 mg, 1 mol %) was stirred for 16 h at
ambient temperature. The solution was diluted with water (30 mL) and
cooled to 273 K for 1 h with stirring. The precipitate was collected by
filtration and dried in vacuo to yield the product as a light yellow powder
(392 mg, 87%). 1H NMR (500 MHz; CDCl3): δ 5.70 (2H, s, triazole−
CH2−pyridyl), 7.24 (1H, d, J = 7.8 Hz, pyridyl-H), 7.28 (1H, ddd, J =
7.6, 4.9, 1.1 Hz, pyridyl-H), 7.34−7.30 (1H, m, phenyl-H), 7.43−7.39
(2H, m, phenyl-H), 7.70 (1H, td, J = 7.7, 1.8 Hz, pyridyl-H), 7.84−7.82
(2H, m, phenyl-H), 7.93 (1H, s, triazole-H), 8.62 (1H, ddd, J = 4.9, 1.7,
0.9 Hz, pyridyl-H).
[Ir(ppy)2L1a]Cl. According to the general procedure, [Ir(ppy)2(μ-
Cl)]2 (50 mg, 47 μmol) and L1a (22 mg, 93 μmol) were combined. The
product was isolated as the chloride salt as a bright yellow powder (65
mg, 96%). 1H NMR (500 MHz; CDCl3): δ 5.71−5.65 (2H, m, triazole−
CH2−phenyl), 6.29 (1H, d, J = 7.6 Hz, phenyl-H), 6.31 (1H, d, J = 7.5
Hz, phenyl-H), 6.86 (1H, td, J = 6.6, 1.2 Hz, phenyl-H), 6.89 (1H, td, J =
6.6, 1.2 Hz, phenyl-H), 6.94−6.91 (1H, m, pyridyl-H), 6.96−6.93 (1H,
m, pyridyl-H), 6.99−6.96 (1H, m, phenyl-H), 7.01 (1H, td, J = 7.6, 0.8
Hz, phenyl-H), 7.18 (1H, t, J = 6.3 Hz, L1apyridyl-H), 7.30−7.28 (3H,
m, L1aphenyl-H), 7.43−7.39 (3H, m, L1aphenyl-H, pyridyl-H), 7.60
4-(1-(Picolyl)-1H-1,2,3-triazol-4-yl)nitrobenzene (L2b). According
to the general procedure, a solution of 4-ethynyl nitrobenzene (557
mg, 3.79 mmol) and 2-picolylazide (508 mg, 3.79 mmol) sodium
ascorbate (100 mg, ∼ 10 mol %) and CuSO4·5H2O (10 mg, 1 mol %)
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Inorganic Chemistry
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(1H, d, J = 5.7 Hz, pyridyl-H), 7.64 (2H, m, phenyl-H), 7.75−7.70 (3H,
m, pyridyl-H, L1apyridyl-H), 7.88 (2H, m, pyridyl-H), 7.96 (1H, td, J =
7.8, 1.2 Hz, L1apyridyl-H), 8.99 (1H, d, J = 7.9 Hz, L1apyridyl-H), 10.69
(1H, s, triazole-H). {1H}13C NMR (126 MHz; CDCl3): δ 55.6, 119.4,
119.5, 122.3, 122.7, 122.8, 123.3, 124.4, 124.8, 124.9, 126.0, 128.8, 128.9,
129.1, 129.3, 130.1, 130.8, 131.9, 132.0, 134.0, 137.9, 138.0, 139.8, 143.7,
143.8, 146.5, 148.4, 148.9, 149.4, 149.6, 150.1, 150.2, 167.7, 168.4.
HRMS m/z 737.199 ([C36H28N6Ir]+ requires 737.200). Elemental
analysis calculated for IrC36H28N6Cl·2H2O: C 53.49, H 3.99, N 10.40;
found: C 53.58, H 3.75, N 10.66. The complex was also isolated as the
L1cpyridyl-H), 7.36−7.34 (2H, m, L1cphenyl-H), 7.44 (1H, d, J = 5.8 Hz,
pyridyl-H), 7.62 (1H, d, J = 5.8 Hz, pyridyl-H), 7.67−7.65 (2H, m,
phenyl-H), 7.75−7.73 (3H, m, pyridyl-H, L1cpyridyl-H), 7.95−7.87
(3H, m, pyridyl-H, L1cpyridyl-H), 8.37 (1H, d, J = 8.0 Hz, L1cpyridyl-H),
9.16 (1H, s, triazole-H). {1H}13C NMR (126 MHz; CDCl3): δ 55.5
(2C), 114.6, 119.5 (2C), 122.4, 122.8, 122.9, 123.5, 123.8, 124.4, 124.8,
125.6, 126.2, 127.0, 130.2, 130.6, 130.8, 131.8, 132.0, 137.9, 138.1, 139.8,
143.7, 143.9, 146.4, 148.5, 148.8, 149.6, 149.8, 149.9, 150.0, 160.3, 167.6,
168.5. HRMS m/z 767.210 ([C37H30N6OIr]+ requires 767.211).
Elemental analysis calculated for IrC37H30N6OBF4·H2O: C 50.98, H
1
tetrafluoroborate salt for comparative purposes. H NMR (500 MHz;
3.70, N 9.64; found: C 51.26, H 3.50, N 9.74. UV-vis (CH3CN) λmax
252 nm (51 600 M−1 cm−1), 379 nm (5030 M−1 cm−1), 465 nm (200
−1 cm−1). Emission (5 μM, CH3CN, λex = 337 nm) λem: 478, 506 nm,
:
CDCl3): δ 5.62−5.56 (2H, m, triazole−CH2−phenyl), 6.33−6.30 (2H,
m, phenyl-H), 6.90 (2H, m, phenyl-H), 6.95 (1H, ddd, J = 7.4, 5.9, 1.5
Hz, pyridyl-H), 7.05−6.99 (3H, m, pyridyl-H, phenyl-H), 7.22 (1H,
ddd, J = 7.6, 5.5, 1.3 Hz, 1 L1apyridyl-H, 7.34−7.32 (3H, m, L1aphenyl-
H), 7.38−7.35 (2H, m, L1aphenyl-H), 7.45 (1H, ddd, J = 5.8, 1.5, 0.7 Hz,
pyridyl-H), 7.63 (1H, ddd, J = 5.8, 1.5, 0.7 Hz, pyridyl-H), 7.66 (2H, dt, J
= 7.9, 1.4 Hz, phenyl-H), 7.77−7.73 (3H, m, pyridyl-H, L1apyridyl-H),
7.93−7.88 (2H, m, pyridyl-H), 7.95 (1H, td, J = 7.9, 1.6 Hz, L1apyridyl-
H), 8.41 (1H, dt, J = 8.0, 1.0 Hz, L1apyridyl-H), 9.24 (1H, s, triazole-H).
Elemental analysis calculated for IrC36H28N6BF4·2H2O: C 50.30, H
M
Φ
em = 0.31, τ = 2.2 μs.
[Ir(dfppy)2L1a]BF4. According to the general procedure, [Ir-
(dfppy)2(μ-Cl)]2 (72 mg, 59 μmol) and L1a (28 mg, 118 μmol) were
combined. The crude reaction mixture was purified by silica gel
chromatography using a gradient of 0−10% methanol in dichloro-
methane as the eluent. The product was isolated as the tetrafluoroborate
1
salt as a pale yellow powder (74 mg, 70%). H NMR (500 MHz;
CDCl3): δ 5.61 (2H, d, J = 3.7 Hz, triazole−CH2−phenyl), 5.67 (1H, dd,
J = 8.5, 2.3 Hz, phenyl-H), 5.73 (1H, dd, J = 8.3, 2.3 Hz, phenyl-H), 6.55
(2H, m, phenyl-H), 7.00 (1H, ddd, J = 7.3, 6.0, 1.3 Hz, pyridyl-H), 7.09−
7.06 (1H, m, pyridyl-H), 7.33 (4H, m, L1aphenyl-H, L1apyridyl-H), 7.39
(2H, m, L1aphenyl-H), 7.43 (1H, dd, J = 5.7, 0.7 Hz, pyridyl-H), 7.58
(1H, d, J = 5.7 Hz, pyridyl-H), 7.82−7.77 (3H, m, pyridyl-H, L1apyridyl-
H), 8.02 (1H, td, J = 7.8, 1.3 Hz, L1apyridyl-H), 8.30 (2H, t, J = 9.8 Hz,
phenyl-H), 8.43 (1H, d, J = 8.0 Hz, L1apyridyl-H) 9.26 (1H, s, triazole-
H). {1H}13C NMR (126 MHz; CDCl3): δ 56.2, 99.07 (t, J = 26.8 Hz),
99.4 (t, J = 26.7 Hz), 114.2 (dd, J = 17.6, 2.6 Hz), 114.3 (dd, J = 18.0, 2.7
Hz, 123.3, 123.6 (d, J = 20.0 Hz), 123.7 (d, J = 19.8 Hz), 123.9, 124.3,
126.6, 127.7, 127.8, 129.0, 129.4, 133.2, 139.0, 139.2, 140.5, 148.5, 148.6,
149.6, 149.7 (2C), 161.2 (dd, J = 261.6, 12.6 Hz), 161.4 (dd, J = 261.1,
12.7 Hz), 163.3 (dd, J = 257.1, 12.4 Hz), 163.7 (dd, J = 258.0, 12.3 Hz),
164.1 (d, J = 7.0 Hz), 165.0 (d, J = 6.9 Hz). 19F NMR (471 MHz;
3.75, N 9.78; found: C 49.99, H 3.29, N 9.44. UV-vis (CH3CN) λmax
252 nm (44400 M−1 cm−1), 379 nm (4490 M−1 cm−1), 465 nm (151
−1 cm−1). Emission (5 μM, CH3CN, λex = 337 nm) λem: 478, 506 nm;
:
M
Φem = 0.30, τ = 2.2 μs.
[Ir(ppy)2L1b]PF6. According to the general procedure, [Ir(ppy)2(μ-
Cl)]2 (55 mg, 52 μmol) and L1b (29 mg, 104 μmol) were combined. The
product was isolated as the hexafluorophosphate salt as a bright yellow
powder (86 mg, 90%). H NMR (500 MHz; CDCl3): δ 5.67 (s, 2H,
1
triazole−CH2−phenyl), 6.30 (2H, m, phenyl-H), 6.85 (1H, td, J = 7.4,
1.3 Hz, phenyl-H), 6.90 (1H, td, J = 7.4, 1.3 Hz, phenyl-H), 6.98−6.95
(2H, m, pyridyl-H, phenyl-H), 7.02 (1H, td, J = 7.5, 1.2 Hz, phenyl-H),
7.07 (1H, ddd, J = 7.4, 5.9, 1.5 Hz, pyridyl-H), 7.24 (1H, ddd, J = 7.6, 5.5,
1.3 Hz, L1bpyridyl-H), 7.44−7.41 (2H, m, L1bphenyl-H), 7.47 (1H, ddd,
J = 5.8, 1.5, 0.7 Hz, pyridyl-H), 7.63 (1H, dd, J = 7.8, 1.1 Hz, phenyl-H),
7.66 (1H, dd, J = 7.8, 1.2 Hz, phenyl-H), 7.69 (1H, ddd, J = 5.8, 1.5, 0.7
Hz, pyridyl-H), 7.78−7.74 (3H, m, pyridyl-H, L1bpyridyl-H), 7.93−7.88
(3H, m, pyridyl-H, L1bpyridyl-H), 8.10−8.07 (2H, m, L1bphenyl-H),
8.16 (1H, dt, J = 7.9, 1.0 Hz, L1bpyridyl-H), 8.93 (1H, s, triazole-H).
{1H}13C NMR (126 MHz; CDCl3): δ 54.7, 119.5, 119.6, 122.5, 122.9,
123.0, 123.5, 123.7, 124.3, 124.4, 124.8, 126.5, 127.0, 129.8, 130.2, 130.8,
131.8, 132.1, 138.1, 138.2, 139.8, 140.1, 143.7, 143.9, 146.1, 148.3, 148.6,
149.0, 149.4, 149.6, 149.7, 150.1, 167.5, 168.4. HRMS m/z 782.184
([C36H27N7O2Ir]+ requires 782.186). Elemental analysis calculated for
IrC36H27N7O2PF6·2H2O: C 44.91, H 3.25, N 10.18; found: C 45.07, H
2.83, N 10.50. Complex was also isolated as the tetrafluoroborate salt for
comparative purposes. 1H NMR (500 MHz; CDCl3): δ 5.77 (1H, d, J =
14.5 Hz, triazole−CH-phenyl), 5.84 (1H, d, J = 14.6 Hz, triazole−CH-
phenyl), 6.29 (1H, dd, J = 7.7, 0.8 Hz, phenyl-H), 6.32 (1H, dd, J = 7.6,
0.8 Hz, phenyl-H), 6.88 (1H, td, J = 6.4, 1.3 Hz, phenyl-H), 6.90 (1H, td,
J = 6.3, 1.3 Hz, phenyl-H), 6.93 (1H, ddd, J = 7.3, 5.8, 1.4 Hz, pyridyl-H),
7.05−6.98 (3H, m, phenyl-H, pyridyl-H), 7.22 (1H, ddd, J = 7.6, 5.6, 1.1
Hz, L1bpyridyl-H), 7.43 (1H, d, J = 5.8 Hz, pyridyl-H), 7.60−7.57 (2H,
m, L1bphenyl-H), 7.68−7.63 (3H, m, phenyl-H, pyridyl-H), 7.78−7.72
(3H, m, pyridyl-H, L1bpyridyl-H), 7.90 (2H, d, J = 8.2 Hz, pyridyl-H),
7.94 (1H, td, J = 7.8, 1.5 Hz, L1bpyridyl-H), 8.09−8.07 (2H, m,
L1bphenyl-H), 8.53 (1H, d, J = 8.0 Hz, L1bpyridyl-H), 9.86 (1H, s,
triazole-H). Elemental analysis calculated for IrC36H27N7O2BF4·H2O: C
48.76, H 3.30, N 11.06; found: C 49.03, H 3.15, N 11.06. UV-vis
(CH3CN) λmax: 254 nm (55 100 M−1 cm−1), 379 nm (4930 M−1 cm−1),
−
CDCl3): δ −150.40 (4F, d, J = 24.6 Hz, BF4 ), −109.15 (1F, t, J = 11.2
Hz, phenyl-F), −108.16 (1F, t, J = 11.5 Hz, phenyl-F), −106.05 (1F, q, J
= 8.3 Hz, phenyl-F), −105.23 (1F, q, J = 9.0 Hz, phenyl-F). HRMS m/z
809.160 ([C36H24N6F4Ir]+ requires 809.163). Elemental analysis
calculated for IrC36H24N6F8B·H2O: C 47.33, H 2.87, N 9.20; found:
C 47.70, H 2.76, N 9.16. UV-vis (CH3CN) λmax: 245 nm (51 100 M−1
cm−1), 358 nm (4960 M−1 cm−1), 445 nm (159 M−1 cm−1). Emission (5
μM, CH3CN, λex = 337 nm) λem: 453, 481 nm; Φem = 0.19, τ = 2.2 μs.
[Ir(piq)2L1a]BF4. According to the general procedure, [Ir(ppy)2(μ-
Cl)]2 (81 mg, 63 μmol) and L1a (30 mg, 127 μmol) were combined. The
product was isolated as the tetrafluoroborate salt as a dark red powder
1
(100 mg, 85%). H NMR (500 MHz; CDCl3): δ 5.58−5.51 (2H, m,
triazole−CH2−phenyl), 6.30 (1H, dd, J = 7.7, 1.1 Hz, phenyl-H), 6.50
(1H, dd, J = 7.7, 1.1 Hz, phenyl-H), 6.84 (1H, td, J = 7.5, 1.1 Hz, phenyl-
H), 6.91 (1H, td, J = 7.4, 1.2 Hz, phenyl-H), 7.14−7.06 (4H, m, phenyl-
H, L1aphenyl-H), 7.22−7.16 (4H, m, L1aphenyl-H, L1apyridyl-H), 7.26
(1H, m, quinolyl-H), 7.34 (1H, d, J = 6.2 Hz, quinolyl-H), 7.35 (1H, d, J
= 6.4 Hz, quinolyl-H), 7.58−7.55 (2H, m, quinolyl-H, L1apyridyl-H),
7.80−7.77 (4H, m, quinolyl-H), 7.95−7.87 (3H, m, quinolyl-H,
L1apyridyl-H), 8.27 (2H, t, J = 8.6 Hz, phenyl-H), 8.42 (1H, d, J = 8.0
Hz, L1apyridyl-H), 9.01−8.94 (2H, m, quinolyl-H), 9.24 (1H, s, triazole-
H). {1H}13C NMR (126 MHz; CDCl3): δ 55.8, 121.5, 122.0, 122.1,
122.4, 123.9, 126.2, 126.4, 126.5, 126.9, 127.2, 127.3, 127.6, 127.8, 128.6
(2C), 128.8, 129.0, 129.1, 130.1, 130.4, 130.7, 130.8, 131.7, 131.8, 132.6,
132.7, 133.6, 137.0, 137.2, 139.7, 140.3, 141.4, 145.6, 145.8, 148.7, 149.5,
149.8, 149.9, 153.5, 168.8, 169.6. HRMS m/z 837.230 ([C44H32N6Ir]+
requires 837.232). Elemental analysis calculated for IrC44H32N6BF4·
3H2O: C 54.05, H 3.92, N 8.59; found: C 54.12, H 3.49, N 8.71. UV-vis
(CH3CN) λmax: 290 nm (43 300 M−1 cm−1), 334 nm (shoulder, 18 300
465 nm (151 M−1 cm−1). Emission (5 μM, CH3CN, λex = 337 nm) λem
491 nm, Φem = 0.006, τ = 0.004 μs.
:
[Ir(ppy)2L1c]BF4. According to the general procedure, [Ir(ppy)2(μ-
Cl)]2 (103 mg, 96 μmol) and L1c (52 mg, 193 μmol) were combined.
The product was isolated as the tetrafluoroborate salt as a bright yellow
powder (135 mg, 82%). 1H NMR (500 MHz; CDCl3): δ 3.78 (3H, s,
O−CH3), 5.54−5.47 (2H, m, triazole−CH2−phenyl), 6.31 (2H, d, J =
7.6 Hz, phenyl-H), 6.86−6.84 (2H, m, L1cphenyl-H), 6.89 (2H, m,
phenyl-H), 6.95 (1H, ddd, J = 7.4, 5.9, 1.4 Hz, pyridyl-H), 7.04−6.98
(3H, m, phenyl-H, pyridyl-H), 7.21 (1H, ddd, J = 7.6, 5.5, 1.3 Hz,
M
−1 cm−1), 352 nm (shoulder, 17 100 M−1 cm−1), 374 nm (shoulder,
11 100 M−1 cm−1), 434 nm (6610 M−1 cm−1), 520 nm (342 M−1 cm−1),
540 nm (200 M−1 cm−1). Emission (5 μM, CH3CN, λex = 380 nm) λem:
592, 632 nm; Φem = 0.22, τ = 3.6 μs.
[Ir(ppy)2L2a]BF4. According to the general procedure, [Ir(ppy)2(μ-
Cl)]2 (88 mg, 82 μmol) and L2a (39 mg, 165 μmol) were combined. The
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DOI: 10.1021/acs.inorgchem.5b02607
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product was isolated as the tetrafluoroborate salt as a bright yellow
powder (126 mg, 93%). 1H NMR (500 MHz; CDCl3): δ 5.91 (1H, d, J =
15.9 Hz, triazole−CH-pyridyl), 6.26 (1H, dd, J = 7.7, 0.8 Hz, phenyl-H),
6.32−6.28 (2H, m, triazole−CH-pyridyl, phenyl-H), 6.88 (2H, m,
phenyl-H), 6.96 (1H, td, J = 7.5, 1.2 Hz, phenyl-H), 7.02 (1H, td, J = 7.5,
1.1 Hz, phenyl-H), 7.04 (1H, ddd, J = 7.4, 5.9, 1.4 Hz, pyridyl-H), 7.13
(1H, ddd, J = 7.5, 5.8, 1.5 Hz, L2apyridyl-H), 7.16 (1H, ddd, J = 7.4, 5.9,
1.4 Hz, pyridyl-H), 7.32−7.25 (3H, m, L2aphenyl-H), 7.57 (1H, dd, J =
7.8, 1.2 Hz, phenyl-H), 7.61−7.59 (2H, m, L2aphenyl-H), 7.71 (1H, dd, J
= 7.9, 1.1 Hz, phenyl-H), 7.84−7.79 (2H, m, pyridyl-H), 7.92−7.87
(4H, m, L2apyridyl-H, pyridyl-H), 7.99 (1H, d, J = 7.9 Hz, pyridyl-H),
8.16 (1H, dd, J = 5.8, 0.7 Hz, pyridyl-H), 8.24 (1H, d, J = 7.6 Hz,
L2apyridyl-H), 8.92 (1H, s, triazole-H). {1H}13C NMR (126 MHz;
CDCl3): δ 53.9, 119.9, 120.0, 122.7, 123.1, 123.2, 123.3, 124.1, 125.0,
125.9, 126.6, 128.9, 129.0, 129.0, 129.3, 130.0, 130.7, 131.7, 132.7, 138.4,
138.6, 140.0, 143.7, 144.0, 144.8, 148.6, 149.5, 149.8, 150.1, 152.1, 152.6,
167.7, 169.4. HRMS m/z 737.202 ([C36H28N6Ir]+ requires 737.200),
m/z 501.095 ([C22H16N2Ir]+ requires 501.094), m/z 237.113
([C14H12N4+H]+ requires 237.114). Product recrystallized from
acetonitrile and diethyl ether and submitted for elemental analysis.
Elemental analysis calculated for IrC36H28N6BF4·2H2O: C 50.30, H
([C22H16N2Ir]+ requires 501.094), m/z 267.124 ([C15H14N4O+H]+
requires 267.125). Elemental analysis calculated for IrC37H30N6OBF4·
H2O: C 50.98, H 3.70, N 9.64; found: C 50.53, H 3.59, N 9.32. UV-vis
(CH3CN) λmax: 257 nm (53 400 M−1 cm−1), 375 nm (4710 M−1 cm−1),
465 nm (140 M−1 cm−1),. Emission (5 μM, CH3CN, λex = 337 nm) λem:
478, 506 nm; Φem = 0.013, τ = 0.19 μs. The complex was also isolated as
the hexafluorophosphate salt. Elemental analysis calculated for
IrC37H30N6OPF6·H2O: C 47.98, H 3.47, N 9.04; found: C 47.98, H
3.35, N 9.01.
[Ir(dfppy)2L2a]BF4. According to the general procedure, [Ir-
(dfppy)2(μ-Cl)]2 (85 mg, 70 μmol) and L2a (36 mg, 150 μmol) were
combined. The crude product was isolated as the tetrafluoroborate salt
and then recrystallized from dichloromethane and pentane to give a light
yellow powder (93 mg, 74%). 1H NMR (500 MHz; CDCl3): δ 5.69−
5.66 (2H, m, phenyl-H), 5.89 (1H, d, J = 16.2 Hz, triazole−CH-pyridyl),
6.32 (1H, d, J = 16.2 Hz, triazole−CH-pyridyl), 6.52 (1H, ddd, J = 12.4,
9.2, 2.4 Hz, phenyl-H), 6.58 (1H, ddd, J = 12.4, 8.9, 2.4 Hz, phenyl-H),
7.11 (1H, ddd, J = 7.4, 6.0, 1.4 Hz, pyridyl-H), 7.24 (2H, ddt, J = 7.5, 5.8,
1.7 Hz, pyridyl-H, L2apyridyl-H), 7.37−7.30 (3H, m, L2aphenyl-H),
7.63−7.61 (2H, m, L2aphenyl-H), 7.78 (1H, dt, J = 5.9, 0.8 Hz, pyridyl-
H), 7.91−7.85 (3H, m, pyridyl-H, L2apyridyl-H), 7.98 (1H, td, J = 7.7,
1.7 Hz, L2apyridyl-H), 8.16 (1H, dd, J = 5.9, 0.9 Hz, pyridyl-H), 8.29
(1H, dd, J = 7.7, 0.6 Hz, L2apyridyl-H), 8.34 (1H, d, J = 8.6 Hz, pyridyl-
H), 8.41 (1H, d, J = 8.5 Hz, pyridyl-H), 8.94 (1H, s, triazole-H). 13C
NMR (126 MHz; CDCl3): δ 53.9, 99.4 (t, J = 26.7 Hz), 99.7 (t, J = 26.7
Hz), 114.2 (dd, J = 18.1, 2.8 Hz), 115.0 (dd, J = 18.2, 2.8 Hz), 123.6,
123.7, 124.0 (d, J = 4.9 Hz), 124.1 (d, J = 4.2 Hz), 126.0, 126.3, 126.9,
128.0 (m, 2C), 128.6, 129.1, 129.4, 129.9, 139.5, 139.6, 140.6, 148.1 (d, J
= 7.4 Hz), 149.9, 150.0, 150.2, 152.0, 152.2 (d, J = 6.7 Hz), 152.5, 160.8
(dd, J = 260.0, 12.8 Hz), 161.6 (dd, J = 261.9, 12.1 Hz), 163.0 (dd, J =
256.6, 12.6 Hz), 163.5 (dd, J = 258.5, 12.3 Hz, 164.2 (d, J = 6.6 Hz),
165.9 (d, J = 6.6 Hz). 19F NMR (471 MHz; CDCl3 δ −150.40 (4F, d, J =
3.75, N 9.78; found: C 50.02, H 3.51, N 9.43. UV-vis (CH3CN) λmax
252 nm (43 800 M−1 cm−1), 376 nm (4260 M−1 cm−1), 465 nm (130
−1 cm−1). Emission (5 μM, CH3CN, λex = 337 nm) λem: 478, 506 nm;
:
M
Φem = 0.02, τ = 0.20 μs.
[Ir(ppy)2L2b]BF4. According to the general procedure, [Ir(ppy)2(μ-
Cl)]2 (58 mg, 54 μmol) and L2b (31 mg, 110 μmol) were combined. The
crude product was isolated as the tetrafluoroborate salt and then
recrystallized from chloroform and pentane to give a bright yellow
powder (66 mg, 70%). 1H NMR (500 MHz; CDCl3): δ 5.97 (1H, d, J =
15.9 Hz, triazole−CH-pyridyl), 6.31−6.25 (3H, m, triazole−CH-
pyridyl, phenyl-H), 6.90 (2H, m, phenyl-H), 6.99 (1H, td, J = 7.5, 1.1
Hz, phenyl-H), 7.04 (1H, td, J = 7.5, 1.1 Hz, phenyl-H), 7.09 (1H, ddd, J
= 7.4, 5.9, 1.4 Hz, pyridyl-H), 7.17 (2H, ddd, J = 7.4, 5.9, 1.4 Hz, pyridyl-
H, L2bpyridyl-H), 7.60 (1H, dd, J = 7.8, 1.1 Hz, phenyl-H), 7.71 (1H, dd,
J = 7.9, 1.1 Hz, phenyl-H), 7.78−7.75 (2H, m, L2bphenyl-H), 7.83 (1H,
td, J = 7.9, 1.2 Hz, pyridyl-H), 7.85 (1H, td, J = 7.7, 1.3 Hz, pyridyl-H),
7.96−7.91 (4H, m, pyridyl-H, L2bpyridyl-H), 8.00 (1H, d, J = 8.4 Hz,
pyridyl-H), 8.16−8.12 (3H, m, L2bpyridyl-H, L2bphenyl-H), 8.20 (1H,
dd, J = 8.3, 1.3 Hz, L2bpyridyl-H), 9.15 (1H, s, triazole-H). 13C NMR
(126 MHz; CDCl3): δ 54.2, 120.0, 120.1, 123.0, 123.2, 123.4, 124.2,
124.4, 125.1, 126.5, 126.7, 127.5, 129.3, 130.2, 130.8, 131.8, 132.6, 135.1,
138.5, 138.7, 140.0, 143.7, 143.9, 144.4, 147.4, 147.9, 148.1, 149.8, 150.1,
152.3 (2C), 167.7, 169.3. HRMS m/z 782.188 ([C36H27N7O2Ir]+
requires 782.186), m/z 501.095 ([C22H16N2Ir]+ requires 501.094),
m/z 282.010 ([C14H11N5O2+H]+ requires 282.099). Elemental analysis
calculated for IrC36H27N7O2BF4 C 49.78, H 3.13, N 11.29; found: C
49.29, H 3.20, N 11.03. UV-vis (CH3CN) λmax: 264 nm (42 600 M−1
cm−1), 295 nm (30 300 M−1 cm−1), 375 nm (7150 M−1 cm−1), 465 nm
(260 M−1 cm−1). Emission (5 μM, CH3CN, λex = 337 nm) λem: 513 nm,
−
25.2 Hz, BF4 ), −109.13 (1F, t, J = 11.5 Hz, phenyl-F), −107.28 (1F, t, J
= 11.7 Hz, phenyl-F), −106.00 (1F, q, J = 9.5 Hz, phenyl-F), −104.52
(1F, q, J = 10.0 Hz, phenyl-F). HRMS m/z 809.164 ([C36H24N6F4Ir]+
requires 809.163), m/z 573.056 ([C22H12N2F4Ir]+ requires 573.057),
m/z 237.111 ([C14H12N4+H]+ requires 237.114). Elemental analysis
calculated for IrC36H24N6BF8·H2O: C 47.33, H 2.87, N 9.20; found: C
47.51, H 2.69, N 9.05. UV-vis (CH3CN) λmax: 246 nm (52 200 M−1
cm−1), 357 nm (5360 M−1 cm−1), 445 nm (280 M−1 cm−1). Emission (5
μM, CH3CN, λex = 337 nm) λem: 455, 484 nm; Φem = 0.022, τ = 0.43 μs.
[Ir(piq)2L2a]BF4. According to the general procedure, [Ir(piq)2(μ-
Cl)]2 (103 mg, 81 μmol) and L2a (38 mg, 163 μmol) were combined.
The crude product was isolated as the tetrafluoroborate salt and then
recrystallized from ethanol to give bright orange crystals (85 mg,
56%).1H NMR (500 MHz; CDCl3): δ 5.94 (1H, d, J = 15.8 Hz, triazole−
CH-pyridyl), 6.27 (1H, d, J = 15.9 Hz, triazole−CH-pyridyl), 6.33 (1H.
dd, J = 7.8, 1.0 Hz, phenyl-H), 6.51 (1H, dd, J = 7.7, 1.0 Hz, phenyl-H),
6.90−6.84 (2H, m, phenyl-H), 7.05 (1H, ddd, J = 8.7, 6.6, 1.3 Hz,
phenyl-H), 7.13−7.09 (2H, m, phenyl-H, L2apyridyl-H), 7.28−7.27
(3H, m, L2aphenyl-H), 7.37 (1H, d, J = 6.2 Hz, quinolyl-H), 7.44 (1H, d,
J = 6.3 Hz, quinolyl-H), 7.53−7.51 (2H, m, L2aphenyl-H), 7.67 (1H, d, J
= 6.5 Hz, quinolyl-H), 7.84−7.76 (5H, m, quinolyl-H, L2apyridyl-H),
7.96−7.89 (4H, m, quinolyl-H, L2apyridyl-H), 8.18 (1H, dd, J = 8.0, 0.6
Hz, phenyl-H), 8.27 (1H, dd, J = 7.8, 0.7 Hz, L2apyridyl-H), 8.31 (1H, d,
J = 8.0 Hz, phenyl-H), 8.91 (1H, s, triazole-H), 8.98−8.96 (2H, m,
quinolyl-H). 13C NMR (126 MHz; CDCl3): δ 53.8, 121.5 (2C), 125.9
(2C), 126.6 (3C), 127.1, 127.6 (2C), 127.7, 128.8, 128.9 (2C), 129.0,
129.2, 130.0, 130.1, 130.6, 131.1, 132.0, 132.1, 132.5, 133.2, 137.2, 137.3,
139.9, 141.1, 141.8, 145.5, 145.9, 148.0, 149.7, 152.0, 152.7, 152.8, 169.2,
170.9 HRMS m/z 837.233 ([C44H32N6Ir]+ requires 837.232), m/z
601.125 ([C30H20N2Ir]+ requires 601.126), m/z 237.113
([C14H12N4+H]+ requires 237.114). Elemental analysis calculated for
IrC44H32N6BF4·H2O: C 56.11, H 3.64, N 8.92; found: C 56.12, H 3.50,
N 8.92. UV-vis (CH3CN) λmax: 290 nm (41 100 M−1 cm−1), 340 nm
(18 400 M−1 cm−1), 352 nm (18 300 M−1 cm−1), 375 nm (10 900 M−1
cm−1), 430 nm (6990 M−1 cm−1), 520 nm (240 M−1 cm−1), 550 nm
(100 M−1 cm−1). Emission (5 μM, CH3CN, λex = 380 nm) λem: 635 nm,
Φ
em < 0.001, τ not measured.
[Ir(ppy)2L2c]BF4. According to the general procedure, [Ir(ppy)2(μ-
Cl)]2 (63 mg, 59 μmol) and L2c (32 mg, 119 μmol) were combined. The
crude product was isolated as the tetrafluoroborate salt and then
recrystallized from dichloromethane and pentane to give a bright yellow
1
powder (75 mg, 74%). H NMR (500 MHz; CDCl3): δ 3.78 (3H, s,
−O−CH3), 5.87 (1H, d, J = 15.9 Hz, triazole−CH-pyridyl), 6.29−6.24
(3H, m, triazole−CH-pyridyl, phenyl-H), 6.87−6.83 (2H, m, L2cphenyl-
H), 6.90−6.87 (2H, m, phenyl-H), 6.97 (1H, td, J = 7.5, 1.2 Hz, phenyl-
H), 7.07−7.01 (2H, m, pyridyl-H, phenyl-H), 7.14 (2H, tdd, J = 7.5, 5.9,
1.5 Hz, pyridyl-H, L2cpyridyl-H), 7.54−7.52 (2H, m, L2cphenyl-H), 7.58
(1H, dd, J = 7.8, 1.2 Hz, phenyl-H), 7.71 (1H, dd, J = 7.9, 1.1 Hz, phenyl-
H), 7.84−7.80 (2H, m, pyridyl-H), 7.93−7.87 (4H, m, pyridyl-H,
L2cpyridyl-H), 7.99 (1H, d, J = 7.9 Hz, pyridyl-H), 8.15 (1H, dd, J = 5.8,
0.7 Hz, pyridyl-H), 8.24 (1H, d, J = 7.8 Hz, L2cpyridyl-H), 8.79 (1H, s,
triazole-H). 13C NMR (126 MHz; CDCl3): δ 53.8, 55.4, 114.4, 119.9,
120.0, 121.6, 122.8, 123.1 (2C), 123.3, 124.1, 125.0, 126.5, 127.3, 129.3,
130.1, 130.7, 131.8, 132.7, 138.4, 138.5, 139.9, 143.6, 144.0, 144.8, 148.7,
149.5, 149.8, 150.2, 152.1, 152.7, 160.3, 167.7, 169.5 HRMS m/z
767.212 ([C37H30N6OIr]+ requires 767.211), m/z 501.094
Φ
em = 0.090, τ = 3.2 μs.
2788
DOI: 10.1021/acs.inorgchem.5b02607
Inorg. Chem. 2016, 55, 2776−2790

Inorganic Chemistry
Article
X-ray Crystallography. Crystals were mounted in low-temperature
oil and then flash-cooled. Intensity data were collected at 130 K (unless
otherwise stated) on an X-ray diffractometer with a CCD detector using
Cu Kα (λ = 1.54184 Å) or Mo Kα (λ = 0.71073 Å) radiation. Data were
reduced and corrected for absorption.52 The structures were solved by
direct methods and difference Fourier synthesis using SHELX53 suite of
programs as implemented within the WINGX54 software. Thermal
ellipsoid plots were generated using the program ORTEP-3.30
Electronic Spectroscopy and Photophysical Measurements.
Absorbance spectra were obtained on a Model UV-1650 PC
spectrophotometer (Shimadzu, Kyoto, Japan). Samples were measured
at different concentrations (5−30 μM) in capped quartz cuvettes, and
extinction coefficients were calculated using the Beer−Lambert law.
Emission spectra were obtained using a CARY Eclipse fluorescence
spectrophotometer (Varian, Palo Alto, CA, USA) with the emission and
excitation spectral bandwidth set to 5 nm. Luminescence measurements
were performed in acetonitrile deoxygenated by three freeze-pump-thaw
cycles under an inert helium atmosphere in degassing cuvettes. Prepared
solutions had an absorbance of <0.1 at the appropriate excitation
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: pauld@unimelb.edu.au.
Author Contributions
The manuscript was written through contributions of all authors.
All authors have given approval to the final version of the
manuscript.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This research was partially funded by the Australian Research
Council. P.S.D. is an ARC Future Fellow.
REFERENCES
■
(1) Sprouse, S.; King, K. A.; Spellane, P. J.; Watts, R. J. J. Am. Chem. Soc.
1984, 106, 6647.
(2) Nazeeruddin, M. K.; Humphry-Baker, R.; Berner, D.; Rivier, S.;
Zuppiroli, L.; Graetzel, M. J. Am. Chem. Soc. 2003, 125, 8790.
(3) You, Y.; Park, S. Y. Dalton Trans. 2009, 1267.
wavelength, to minimize inner-filter effects, and were irradiated at λex
=
337 or 380 nm. Emission spectra were corrected for detection system
response. Luminescent quantum yields were reported relative to the
measured standards Norharmane (0.60 in 0.5 M H2SO4) or Rhodamine
6G (0.95 in ethanol).37 Time-resolved luminescence (lifetime)
measurements were carried out on dilute solutions using the
frequency-tripled output (355 nm) from a Q-switched Nd:YAG laser
(Quantel Ultra20 CFR (Les Ulis, France)), operating at 50 Hz, with a
photomultiplier (Hamamastu 1P28, wired to provide ∼15 ns response)
feed via a 50 Ω terminator to a digital storage oscilloscope (Tektronix
TDS 350) for detection. Emission was monitored at λ = 455, 480, or 590
nm as appropriate, using a variable bandpass filter.
Electrochemistry. Cyclic voltammetry was performed using a
Model PGSTAT100 electrochemical workstation (Metrohm Autolab,
Utrecht, The Netherlands) and GPES V4.9 software. Measurements
were conducted using a Pt working electrode, a platinum wire as the
counter electrode, and a Ag+/Ag reference electrode (silver wire in
acetonitrile (AgNO3, 0.01 mol L−1)). All measurements were carried out
in HPLC-grade acetonitrile that was dried over 3 Å sieves prior to use
with tetrabutylammonium tetrafluoroborate (NH4BF4) as the support-
ing electrolyte. The working electrode was polished using 0.3 mm
alumina with water on a felt pad, rinsed with acetonitrile and dried under
a stream of argon before each experiment. Measurements were
performed under an argon atmosphere and redox potentials were
reported relative to a Fc+/Fc internal standard (Eo1/′2 = 0.40 V vs SCE).55
(4) Barigelletti, F. Photochemistry 2010, 38, 234.
(5) Crowley, J. D.; McMorran, D. A. In Topics in Heterocyclic Chemistry,
̌
Vol. 28; Kosmrlj, J., Ed.; Springer: New York, 2012; p 31.
(6) Struthers, H.; Mindt, T. L.; Schibli, R. Dalton Trans. 2010, 39, 675.
(7) Beyer, B.; Ulbricht, C.; Escudero, D.; Friebe, C.; Winter, A.;
Gonzalez, L.; Schubert, U. S. Organometallics 2009, 28, 5478.
(8) Felici, M.; Contreras-Carballada, P.; Smits, J. M.; Nolte, R. J.;
Williams, R. M.; De Cola, L.; Feiters, M. C. Molecules 2010, 15, 2039.
(9) de Barros e Silva Botelho, M.; Fernandez-Hernandez, J. M.; de
́ ́
Queiroz, T. B.; Eckert, H.; De Cola, L.; de Camargo, A. S. S. J. Mater.
Chem. 2011, 21, 8829.
(10) Fernandez-Hernandez, J. M.; Yang, C. H.; Beltran, J. I.; Lemaur,
́ ́
V.; Polo, F.; Frohlich, R.; Cornil, J.; De Cola, L. J. Am. Chem. Soc. 2011,
133, 10543.
(11) Ladouceur, S.; Fortin, D.; Zysman-Colman, E. Inorg. Chem. 2011,
50, 11514.
(12) Felici, M.; Contreras-Carballada, P.; Vida, Y.; Smits, J. M.; Nolte,
R. J.; De Cola, L.; Williams, R. M.; Feiters, M. C. Chem.Eur. J. 2009,
15, 13124.
(13) Mydlak, M.; Bizzarri, C.; Hartmann, D.; Sarfert, W.; Schmid, G.;
De Cola, L. Adv. Funct. Mater. 2010, 20, 1812.
̌
(14) Jurícek, M.; Felici, M.; Contreras-Carballada, P.; Lauko, J.; Bou, S.
ASSOCIATED CONTENT
■
R.; Kouwer, P. H. J.; Brouwer, A. M.; Rowan, A. E. J. Mater. Chem. 2011,
21, 2104.
S
* Supporting Information
(15) Liu, S.; Muller, P.; Takase, M. K.; Swager, T. M. Inorg. Chem.
2011, 50, 7598.
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.5b02607.
(16) Sykes, D.; Ward, M. D. Chem. Commun. 2011, 47, 2279.
(17) Zanarini, S.; Felici, M.; Valenti, G.; Marcaccio, M.; Prodi, L.;
Bonacchi, S.; Contreras-Carballada, P.; Williams, R. M.; Feiters, M. C.;
Nolte, R. J.; De Cola, L.; Paolucci, F. Chem.Eur. J. 2011, 17, 4640.
(18) Maity, A.; Choi, J.-S.; Teets, T. S.; Deligonul, N.; Berdis, A. J.;
Gray, T. G. Chem.Eur. J. 2013, 19, 15924.
ORTEP representation of [Ir(ppy)2L1b]PF6 highlighting
close contacts interactions 1 (Figure S1). Cyclic
voltammograms of the ligand-based reductions in
complexes [Ir(ppy)2L1b]BF4 and [Ir(ppy)2L2b]BF4 (Fig-
ure S2) (PDF)
(19) Darmawan, N.; Yang, C.-H.; Mauro, M.; Frohlich, R.; De Cola, L.;
̈
Chang, C.-H.; Wu, Z.-J.; Tai, C.-W. J. Mater. Chem. C 2014, 2, 2569.
(20) Truong, J.; Spilstead, K. B.; Barbante, G. J.; Doeven, E. H.; Wilson,
D. J. D.; Barnett, N. W.; Henderson, L. C.; Altimari, J. M.; Hockey, S. C.;
Zhou, M.; Francis, P. S. Analyst 2014, 139, 6028.
Crystallographic data for [Ir(piq)2L2a]PF6·1.5CHCl2
(CIF)
Crystallographic data for [Ir(piq)2L1a]BF4 (CIF)
Crystallographic data for [Ir(ppy)2L2a]BPh4·CH2Cl2
(CIF)
(21) Barbante, G. J.; Doeven, E. H.; Kerr, E.; Connell, T. U.; Donnelly,
P. S.; White, J. M.; Lopes, T.; Laird, S.; Wilson, D. J. D.; Barnard, P. J.;
Hogan, C. F.; Francis, P. S. Chem.Eur. J. 2014, 20, 3322.
(22) Doeven, E. H.; Barbante, G. J.; Harsant, A. J.; Donnelly, P. S.;
Connell, T. U.; Hogan, C. F.; Francis, P. S. Sens. Actuators, B 2015, 216,
608.
(23) Kerr, E.; Doeven, E. H.; Barbante, G. J.; Connell, T. U.; Donnelly,
P. S.; Wilson, D. J. D.; Ashton, T. D.; Pfeffer, F. M.; Francis, P. S.
Chem.Eur. J. 2015, 21, 14987.
Crystallographic data for [Ir(ppy)2L1b]PF6 (CIF)
Crystallographic data for [Ir(ppy)2L2c]BF4·CH2Cl2 (CIF)
Crystallographic data for [Ir(dfppy)2L2a]BF4·3CHCl3
(CIF)
2789
DOI: 10.1021/acs.inorgchem.5b02607
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Inorganic Chemistry
Article
(24) Swanick, K. N.; Ladouceur, S.; Zysman-Colman, E.; Ding, Z.
Chem. Commun. 2012, 48, 3179.
(25) Kerr, E.; Doeven, E. H.; Barbante, G. J.; Hogan, C. F.; Bower, D. J.;
Donnelly, P. S.; Connell, T. U.; Francis, P. S. Chem. Sci. 2015, 6, 472.
(26) Connell, T. U.; James, J. L.; White, A. R.; Donnelly, P. S. Chem.
Eur. J. 2015, 21, 14146.
(27) Feldman, A. K.; Colasson, B.; Fokin, V. V. Org. Lett. 2004, 6, 3897.
(28) Garces, F. O.; King, K. A.; Watts, R. J. Inorg. Chem. 1988, 27, 3464.
(29) Maestri, M.; Balzani, V.; Deuschel-Cornioley, C.; Von Zelewsky,
A. In Advances in Photochemistry, Vol. 17; Volman, D. H., Hammond, G.
S., Neckers, D. C., Eds.; Wiley−Interscience: New York, 1992; p
110.1002/9780470133484.ch1.
(30) ORTEP-3, Version 2.02; Farrugia, L. J., Ed.; University of Glasgow:
Glasgow, U.K., 2008.
(31) Anderson, C. B.; Elliott, A. B. S.; McAdam, C. J.; Gordon, K. C.;
Crowley, J. D. Organometallics 2013, 32, 788.
(32) Kilpin, K. J.; Gavey, E. L.; McAdam, C. J.; Anderson, C. B.; Lind, S.
J.; Keep, C. C.; Gordon, K. C.; Crowley, J. D. Inorg. Chem. 2011, 50,
6334.
(33) Kilpin, K. J.; Crowley, J. D. Polyhedron 2010, 29, 3111.
(34) Guha, P. M.; Phan, H.; Kinyon, J. S.; Brotherton, W. S.; Sreenath,
K.; Simmons, J. T.; Wang, Z.; Clark, R. J.; Dalal, N. S.; Shatruk, M.; Zhu,
L. Inorg. Chem. 2012, 51, 3465.
(35) Sajoto, T.; Djurovich, P. I.; Tamayo, A.; Yousufuddin, M.; Bau, R.;
Thompson, M. E.; Holmes, R. J.; Forrest, S. R. Inorg. Chem. 2005, 44,
7992.
(36) Orselli, E.; Albuquerque, R. Q.; Fransen, P. M.; Frohlich, R.;
̈
Janssen, H. M.; De Cola, L. J. Mater. Chem. 2008, 18, 4579.
(37) Brouwer, A. M. Pure Appl. Chem. 2011, 83, 2213−2228.
(38) Kim, T. Y.; Elliott, A. B. S.; Shaffer, K. J.; John McAdam, C.;
Gordon, K. C.; Crowley, J. D. Polyhedron 2013, 52, 1391.
(39) Herbich, J.; Rettig, W.; Thummel, R. P.; Waluk, J. Chem. Phys. Lett.
1992, 195, 556.
(40) Coppo, P.; Plummer, E. A.; De Cola, L. Chem. Commun. 2004, 40,
1774.
(41) Orselli, E.; Kottas, G. S.; Konradsson, A. E.; Coppo, P.; Froehlich,
R.; De Cola, L.; van Dijken, A.; Buechel, M.; Boerner, H. Inorg. Chem.
2007, 46, 11082.
(42) Avilov, I.; Minoofar, P.; Cornil, J.; De Cola, L. J. Am. Chem. Soc.
2007, 129, 8247.
́ ́
(43) Fernandez-Hernandez, J. M.; Ladouceur, S.; Shen, Y.; Iordache,
A.; Wang, X.; Donato, L.; Gallagher-Duval, S.; de Anda Villa, M.; Slinker,
J. D.; De Cola, L.; Zysman-Colman, E. J. Mater. Chem. C 2013, 1, 7440.
(44) Smith, W. H.; Bard, A. J. J. Am. Chem. Soc. 1975, 97, 5203.
(45) Zhao, Q.; Liu, S.; Shi, M.; Wang, C.; Yu, M.; Li, L.; Li, F.; Yi, T.;
Huang, C. Inorg. Chem. 2006, 45, 6152.
(46) Okada, S.; Okinaka, K.; Iwawaki, H.; Furugori, M.; Hashimoto,
M.; Mukaide, T.; Kamatani, J.; Igawa, S.; Tsuboyama, A.; Takiguchi, T.;
Ueno, K. Dalton Trans. 2005, 1583.
(47) Juris, A.; Balzani, V.; Barigelletti, F.; Campagna, S.; Belser, P.; Von
Zelewsky, A. Coord. Chem. Rev. 1988, 84, 85.
̌ ́ ̌
(48) Vlcek, A.; Zalis, S. Coord. Chem. Rev. 2007, 251, 258.
(49) Pommerehne, J.; Vestweber, H.; Guss, W.; Mahrt, R. F.; Baessler,
H.; Porsch, M.; Daub, J. Adv. Mater. 1995, 7, 551.
(50) D’Andrade, B. W.; Datta, S.; Forrest, S. R.; Djurovich, P.;
Polikarpov, E.; Thompson, M. E. Org. Electron. 2005, 6, 11.
(51) Crowley, J. D.; Bandeen, P. H.; Hanton, L. R. Polyhedron 2010, 29,
70.
(52) CrysAlis CCD; Version 1.171.32.5; Oxford Diffraction, Ltd.:
Oxfordshire, U.K., 2007.
(53) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008,
64, 112.
(54) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
(55) Connelly, N. G.; Geiger, W. E. Chem. Rev. 1996, 96, 877.
2790
DOI: 10.1021/acs.inorgchem.5b02607
Inorg. Chem. 2016, 55, 2776−2790