Iridium complexes containing bis(imidazoline thione) and bis(imidazoline selone) ligands for visible-light-induced oxidative coupling of benzylamines to imines

Article abstract of DOI:10.1021/om4004412

Novel iridium(III) complexes containing bis(N-heterocyclic carbene), bis(imidazoline thione) L2, and bis(imidazoline selone) L3 were prepared. The iridium complexes bearing L2 and L3 showed the significant absorption of visible light with maximum intensit

Full text of DOI:10.1021/om4004412

Article
pubs.acs.org/Organometallics
Iridium Complexes Containing Bis(imidazoline thione) and
Bis(imidazoline selone) Ligands for Visible-Light-Induced Oxidative
Coupling of Benzylamines to Imines
†
‡
†
†
‡
,‡
Jaewon Jin, Hee-Won Shin, Joon Hyun Park, Ji Hoon Park, Eunchul Kim, Tae Kyu Ahn,*
,†
,†,‡
Do Hyun Ryu,* and Seung Uk Son*
†
‡
Department of Chemistry and Department of Energy Science, Sungkyunkwan University, Suwon 440-746, Korea
S Supporting Information
*
ABSTRACT: Novel iridium(III) complexes containing bis-
N-heterocyclic carbene), bis(imidazoline thione) L2, and
(
bis(imidazoline selone) L3 were prepared. The iridium
complexes bearing L2 and L3 showed the significant
absorption of visible light with maximum intensity at ∼460
nm. Bis(2-(2′-benzothienyl)pyridinato)iridium(III) complexes
(
Ir-6) with L3 showed excellent ability as a photosensitizer of
visible light. Under blue LED irradiation with maximum
emission at 460 nm, 0.25 mol % Ir-6 showed 94% conversion
of benzylamine for 5 h at room temperature. Through
mechanistic studies, it was suggested that the photoinduced
oxidative coupling of benzylamine by Ir-6 follows a singlet oxygen pathway. The excellent performance of Ir-6 originated from
the efficient visible light absorption at 460 nm and the enhanced triplet state due to the heavy-atom effect of L3. This work shows
that bis(imidazoline thione) and bis(imidazoline selone) can be efficient ligands for tuning the optical properties of iridium(III)
complexes.
INTRODUCTION
in photoinduced oxidative coupling of benzylamines to imines
in the presence of oxygen.
■
Recently, chemical reactions triggered by sustainable energy
sources such as solar energy and the relevant photoactive
systems have attracted the attention of scientists. Over the past
decade, iridium(III) complexes bearing the 2-phenylpyridinato
ppy) ligand have shown interesting optical properties.
1
RESULTS AND DISCUSSION
■
Scheme 1 shows the synthetic methods for new iridium
complexes. First, the bis(ppy)iridium chloride dimer (ppy = 2-
phenylpyridinato) was prepared using the method described in
2
(
Numerous iridium(III) complexes with various geometric and
electronic ligands have been prepared. In addition, two or
3
10
the literature. Bis(N-heterocyclic carbene)-2AgBr (L1-
more kinds of ligands have been introduced to iridium
2AgBr) was prepared by the reaction of the corresponding
4
11
complexes. The enhanced spin−orbit coupling due to the
imidazolium salt with silver oxide (Ag O). The reaction of
2
heavy-atom effect of iridium has been shown to result in the
efficient mixing of singlet and triplet states and to promote
[(ppy) IrCl] with L1-2AgBr in 2-ethoxyethanol resulted in the
2
2
+
11,12
formation of the complex [(ppy) L1Ir] (Ir-1).
Bis-
2
2
,3,5
intersystem crossing.
The major studies of these iridium
(imidazoline thione) L2 and bis(imidazoline selone) L3 were
complexes have focused on the phosphorescent properties for
organic light emitting diode (OLED) devices.
prepared by the reaction of the corresponding imidazolium salt
with elementary sulfur and selenium. Imidazoline thiones
6
13a
Due to their unique optical properties, iridium complexes
have recently been applied as photocatalysts and photo-
and selones have been used as versatile ligands toward various
1
2
transition metals. The reaction of [(ppy)
IrCl]
with L2 and
2
2
1
,7
+
L3Ir]+
initiators. For example, iridium complexes were applied as a
L3 resulted in the formation of [(ppy)
2
L2Ir] or [(ppy)
2
8
1
1
complexes (Ir-2, Ir-3). As observed in the literature, H NMR
peaks from protons in benzyl carbon and imidazoline rings of
L2 and L3 shifted (0.3−0.5 ppm) downfield through
photosensitizer to generate a singlet oxygen ( O ), which can
2
be used for various purposes, including photodynamic cancer
9
therapy (PDT). However, one of the drawbacks of iridium
13
coordination. Moreover, X-ray photoelectron spectroscopy
complexes is their low absorption of visible light. The shift of
absorption bands to a visible light range can be induced
through the screening of ligands.
(
XPS) revealed that the S 2p and Se 3d orbital peaks of L2 and
L3, respectively, shifted to higher energies by 1.6−2.0 eV in
In this work, we report the preparation of iridium complexes
containing bis(N-heterocyclic carbene), bis(imidazoline thi-
one), and bis(imidazoline selone) ligands and their properties
Received: May 18, 2013
Published: June 28, 2013
©
2013 American Chemical Society
3954
dx.doi.org/10.1021/om4004412 | Organometallics 2013, 32, 3954−3959

Organometallics
Article
Scheme 1. Synthesis of Iridium(III) Complexes Containing
Bis(N-heterocyclic carbene), Bis(imidazoline thione), and
Bis(imidazoline selone) Ligands
Figure 1. UV/vis absorption (solid line) and normalized emission
−5
(
dotted line) spectra of 1 × 10 M Ir-1−Ir-6 in CH Cl .
2
2
iridium complexes. (Figure S1, Supporting Information) Three
Table 1. Optical and Electrochemical Properties of
further iridium complexes (Ir-4−Ir-6) were prepared using the
Iridium(III) Complexes Ir-1−Ir-6 in CH Cl
1
4
2
2
2
-(2′-benzothienyl)pyridinato ligand (btpy) instead of ppy.
Chart 1 summarizes the iridium complexes prepared in this
work.
oxidn
potential
(V)
a
b
c
d
λabs, ε (nm,
λem
(nm)
ΔG°
HOMO
(eV)
Ees
es
(eV)
−1
−1
compd
M
cm
)
(eV)
a
Ir-1
Ir-2
Ir-3
Ir-4
Ir-5
Ir-6
380, 5900
431, 4600
428, 2600
419, 9000
464, 9900
461, 11000
473
486
499
577
604
603
2.68
2.60
2.54
2.17
2.09
2.09
1.16
1.05
1.01
1.02
0.96
0.91
−5.60
−5.49
−5.45
−5.46
−5.40
−5.35
−2.92
−2.89
−2.91
−3.29
−3.31
−3.26
Chart 1. Iridium(III) Complexes Used in This Study
a
ΔG° (the free energy of excited states above the ground states)
values were calculated by the method in ref 19. Potential (vs Ag/Ag )
of the first oxidative wave. HOMO energy calculated by the potential
of the oxidative wave. Excited state energy calculated by HOMO +
es
b
+
c
19 d
ΔG°es.
a
−
The counteranion, PF , is omitted.
6
The analogue of Ir-1 having fluorine groups in the ppy ligand
has been reported to show poor absorption in a range of visible
1
1
light. Similarly, Ir-1 has shown very poor absorption of visible
light (Figure 1 and Table 1) The introduction of L2 and L3,
instead of L1 resulted in a significant red shift of the absorption
band to ∼430 nm. However, the absorption intensity and shift
degree of Ir-2 and Ir-3 were not sufficient for the efficient
absorption of visible light. In comparison to Ir-1, Ir-4 showed a
red-shifted absorption at 419 nm. Moreover, Ir-5 and Ir-6
Figure 2. Cyclic voltammograms of Ir-1−Ir-6 in CH Cl .
2
2
1), while those of Ir-2 and Ir-3 shifted to lower values: +1.05
and +1.01 V, respectively. A similar trend was observed in the
series Ir-4−Ir-6. These observations imply that L3 and L2
provided a more electron rich effect, in comparison with L1.
Considering the significant absorption of visible light by Ir-
1−Ir-6, we investigated the photosensitizing performance of
iridium complexes under visible light irradiation. It has been
reported that the photoinduced oxidative coupling of benzyl-
−1
−1
showed significant absorption (ε = 9900−11000 M cm ) at
∼
460 nm and the a emission at ∼600 nm with a 140 nm Stokes
shift (Figure 1 and Table 1).
Figure 2 shows the electrochemical properties of Ir-1−Ir-6 in
methylene chloride. The reduction peaks were overlapped with
the reduction range of CH Cl , implying that the iridium
2
2
15
complexes are relatively electron rich systems. The oxidation
amines results in the formation of imines. Although a visible-
light-induced system has been reported, the reaction temper-
+
potential of Ir-1 was observed at +1.16 V (vs Ag/Ag ) (Table
3
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Organometallics
ature was relatively high, at ∼80 °C. The system working at
room temperature was relatively less explored. Table 2
summarizes the performance of Ir-1−Ir-6 in the visible-light-
induced oxidative coupling of benzylamine to imine.
Article
16
1
7
Table 2. Visible-Light-Induced Oxidative Coupling of
Amines in the Presence of Iridium Complexes Ir1−Ir-6
a
Figure 3. Two main mechanisms for the photoinduced oxidative
coupling of benzylamine to imine.
singlet oxygen, which induces the oxidative coupling of
benzylamine to imine. Both mechanisms work depending on
the optical and electrochemical properties of the photo-
sensitizers.
In the photoredox pathway, the energy levels of the reactants
and photosensitizer should match well. In this work, the excited
state energy level of the photosensitizer should be located at an
energy level higher than the LUMO of oxygen. The HOMO
energy level of benzylamine should be located at an energy level
higher than that of the photosensitizer or the oxidized
photosensitizer. On the basis of the oxidation potentials and
emission spectra of iridium complexes, their excited state
b
c
entry
cat./amt (mol %)
amine
benzylamine
yield (%)
1
2
3
4
5
6
7
8
Ir-1/0.1
Ir-2/0.1
Ir-3/0.1
Ir-4/0.1
Ir-5/0.1
Ir-6/0.1
Ir-6/0.25
no cat.
20
benzylamine
24
benzylamine
36
benzylamine
36
benzylamine
45
benzylamine
70
benzylamine
94 (90)
d
benzylamine
NR
e
9
Ir-6/0.25
Ir-6/0.25
Ir-6/0.25
Ir-6/0.25
Ir-6/0.25
Ir-6/0.25
Ir-6/0.25
benzylamine
NR
10
11
12
13
14
15
4-methoxybenzylamine
4-methylbenzylamine
4-chlorobenzylamine
4-fluorobenzylamine
1-phenylethylamine
(2-thienyl)methylamine
99 (92)
95 (92)
89 (83)
76 (71)
61 (58)
60 (56)
energy levels were calculated in the range of −2.9 to −3.3
19,20
eV,
which matches well with the LUMO level (∼−3.6 eV)
17,21
of oxygen.
In comparison, the HOMO energy values of
iridium complexes are higher than that (∼−6.5 eV) of
17,21
benzylamine.
Thus, it can be reasoned that the reduction
a
Reaction conditions: 1 mmol of amine, 1 atm of O , blue LED
of oxidized iridium complexes by benzylamine is not favorable.
2
b
irradiation, 3 mL of CH Cl , 5 h, room temperature. In mol % with
2
2
It is reported that the enhanced triplet states facilitate energy8
c
1
respect to amine. Conversion yield based on H NMR spectroscopy
isolated yield in parentheses). NR = no reaction. The glassware was
completely covered with Al foil.
transfer to triplet oxygen species, generating a singlet oxygen.
d
e
(
Considering the phosporescent emission properties of Ir-5 and
Ir-6, we conducted photophysical studies for the direct
detection of possible singlet oxygen under the laser irradiation
of 460 nm wavelength. As expected, typical emissions at 1270
nm from singlet oxygen generated by Ir-5 and Ir-6 were
observed in methylene chloride. Figure 4 shows the emission
decay curves of singlet oxygen generated by Ir-5 and Ir-6 with
the same concentration (1 × 10− M). The calculated lifetime
of singlet oxygen by Ir-5 and Ir-6 was 91 μs, which exactly
2
We used a conventional blue LED (0.9 mW/cm ) with a
maximum emission at 460 nm as a light source. As shown in
entries 1−6 in Table 2, 0.1 mol % of Ir-1−Ir-6 showed
relatively different activities as photosensitizers in the oxidative
coupling of benzylamine. First, Ir4−Ir-6 showed better
performances, in comparison with Ir1−Ir-3. Second, the
iridium complexes with L2 and L3 (Ir-2, Ir-3, Ir-5, Ir-6)
showed better activities, in comparison with Ir-1 and Ir-4.
These observations can be rationalized by the absorption
efficiencies of iridium complexes for visible light.
5
22
matches the value reported in methylene chloride. Interest-
ingly, the intensity of the generated singlet oxygen by Ir-6 was
2
.4 times higher than that by Ir-5. We believe that the superior
Interestingly, although Ir-5 and Ir-6 have similar optical and
electrochemical properties, they showed quite different
performances as photosensitizers in the oxidative coupling of
benzylamine in the presence of oxygen. (entries 5 and 6 in
Table 2). To understand this observation, we conducted
mechanistic studies on the photochemical process. Two main
1
b,15a,16
mechanisms, (1) a photoredox pathway
and (2) a
18
singlet oxygen pathway, have been reported for the photo-
oxidation of amine to imine in the presence of oxygen. As
shown in Figure 3, in the photoredox pathway (oxidative
quenching cycle), the excited iridium complex transfers an
electron to oxygen to form the reduced O2• . The oxidized
iridium complex obtains an electron via the oxidation of amine
−
•
+
to form a radical cation, RNH . Finally, the reaction of the
2
•
−
•+
reduced O2 and the oxidized RNH species results in the
2
16
formation of imine. In comparison, in the singlet oxygen
pathway, the excited iridium complex in the triplet state can
transfer energy to the triplet oxygen molecule to form active
Figure 4. Emission (1270 nm) decay curves of the singlet oxygen
generated by Ir-5 and Ir-6 in CH Cl under laser irradiation (460 nm
2
2
wavelength).
3
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Organometallics
Article
performance of Ir-6 over Ir-5 resulted from the additional
heavy-atom effect of selenium in L3, in comparison with sulfur
in L2. The dramatic heavy-atom effects of selenium have been
electrode. The counter electrode was a platinum wire. Ag/AgNO
3
+
(
Ag/Ag ) was used as the reference electrode. 0.1 M Bu NPF in
4
6
2
3
methylene chloride was used as the electrolyte.
In order to obtain the decay curve of singlet oxygen ( O )
1
2
reported in the optical properties of phosphorescent dyes, in
23
phosphorescence, an optical parametric oscillator (OPO) laser
comparison with the case for sulfur. This observation matches
well with the results in the photoinduced chemical conversions
by Ir-5 and Ir-6 (entries 5 and 6 in Table 2). The direct
observation of singlet oxygen species and the intensity trend
strongly support the assumption that the photoinduced
oxidative coupling of benzylamine in this work was conducted
through a singlet oxygen pathway. Moreover, the gradual
addition of benzylamine to the generated singlet oxygen species
(Spectra-Physics, basiScan) pumped by Nd:YAG (Spectra-Physics,
INDI-40-10) was utilized as an excitation source (λex 450−560 nm).
The time duration (fwhm) of the excitation pulse was 7 ns, and the
pulse energy was controlled by a neutral density filter set from 1.0 to
1
0
.1 mJ/pulse. The phosphorescence of O was investigated by the
2
characteristic peak at 1270 (1268) nm using a monochromator
(Princeton Instruments, SP2300) equipped with an NIR-PMT
(Hamamatsu, H10330-75). The output signal from an NIR-PMT
was recorded with a 500 MHz digital oscilloscope (Agilent, DSO-X
8
−1 −1
showed a decrease of life times with a 2.6 × 10 M
s
3
054A). A cutoff filter was used to remove scattered excitation light.
Synthetic Procedure for Ir-1 and Ir-4. [(ppy) IrCl] and
quenching rate at 298 K (Figure S2 in the Supporting
2
2
Information).
1
0,14
[
(btpy) IrCl] were prepared using the literature method.
1,1′-
2
2
A 0.25 mol % amount of Ir-6 showed 94% conversion of
benzylamine to the corresponding imine in 5 h at room
temperature under blue LED irradiation. It is noteworthy that
the 0.25 mol % phenothiazine-based organic dyes that have
been recently developed showed 83% conversion of benzyl-
Dimethyl-3,3′-methylenediimidazolium dibromide was prepared using
11
the literature method. 1,1′-Dimethyl-3,3′-methyleneimidazolium
dibromide (32 mg, 0.094 mmol) and Ag O (65 mg, 0.28 mmol)
2
were added to 2-ethoxyethanol (5 mL). [(ppy) IrCl] (50 mg, 0.047
2
2
mmol) was added. The reaction mixture was refluxed for 12 h in the
dark. After it was cooled to room temperature, the solution was filtered
through a glass filter. An excess of NH PF (0.10 g, 0.61 mmol in 20
17
amine in 12 h under the same conditions. In control
experiments, benzylamine showed no reaction in the absence of
Ir-6 under blue LED irradiation (entry 8 in Table 2).
Moreover, when the glassware was covered with aluminum
foil in the presence of Ir-6 under blue LED irradiation, no
conversion was observed (entry 9 in Table 2). These
observations demonstrate that the chemical conversion of
benzylamine in this work was triggered through the photo-
sensitizing of Ir-6. A 0.25 mol % amount of Ir-6 showed good
activity for various benzylamine derivatives and, interestingly,
showed higher conversion yields for more electron rich
benzylamines (entries 7 and 10−13 in Table 2). 1-Phenyl-
ethylamine with steric hindrance at the benzyl carbon site and
4
6
mL of water) was added to form yellow precipitates, which were
retrieved by filtration, washed with excess water, and then dried under
vacuum. The product (Ir-1) was purified by flash column
chromatography using a 9/1 mixture of CH Cl and CH CN as an
2
2
3
1
eluent. Isolated yield: 64%. H NMR (300 MHz, acetone-d ): δ 8.49
6
(d, J = 7.2 Hz, 2H), 8.20 (d, J = 7.8 Hz, 2H), 7.98 (t, J = 7.2 Hz, 2H),
7
2
.79 (d, J = 7.8 Hz, 2H), 7.52 (s, 2H), 7.21 (t, J = 7.5 Hz, 2H), 7.16 (s,
H), 6.87 (t, J = 7.2 Hz, 2H), 6.75 (t, J = 7.5 Hz, 2H), 6.42 (d, J = 7.5
13
Hz, 2H), 6.36 (s, 2H), 2.93 (s, 6H) ppm. C NMR (75 MHz,
acetone-d ): δ 169.7, 164.0, 162.7, 153.3, 144.7, 137.4, 131.7, 128.6,
6
124.4, 123.8, 123.0, 121.4, 121.3, 120.0, 62.6, 36.8 ppm. HRMS for
+
+
M , [C H N Ir] : calcd 677.2005, obsd 677.2007. Anal. Calcd for
31
28
6
(
6
1-thienyl)methylamine with a heteroatom showed 61% and
0% conversions, respectively.
C
31
H
28
N
6
IrPF : C, 45.31; H, 3.43; N, 10.23. Found: C, 45.40; H, 3.70;
6
N, 10.14. Mp: 328 °C dec.
For the synthesis of Ir-4, [(btpy) IrCl] was used instead of
2
2
1
[
(ppy) IrCl] . Isolated yield: 58%. H NMR (300 MHz, acetone-d ): δ
CONCLUSION
This work shows that bis(imidazoline thione) and bis-
imidazoline selone) can be used as ligands to tune the optical
2
2
6
■
(
8
2
7
.53 (d, J = 7.5 Hz, 2H), 8.05 (t, J = 7.5 Hz, 2H), 7.80 (d, J = 7.5 Hz,
H), 7.73 (d, J = 7.2 Hz, 2H), 7.60 (s, 2H), 7.24 (s, 2H), 7.13 (t, J =
.5 Hz, 2H), 7.11 (t, J = 7.2 Hz, 2H), 6.85 (t, J = 7.2 Hz, 2H), 6.57 (s,
13
properties of iridium(III) complexes. The introduction of
bis(imidazoline thione) and bis(imidazoline selone) to iridium
2H), 6.21 (d, J = 7.2 Hz, 2H), 2.99 (s, 6H) ppm. C NMR (75 MHz,
acetone-d ): δ 166.5, 160.9, 158.0, 154.2, 147.7, 142.6, 138.8, 136.9,
6
complexes resulted in significant absorption in the visible light
125.6, 125.1, 124.3, 123.7, 122.9, 121.8, 121.0, 119.6, 62.6, 37.0 ppm.
+
+
+
HRMS for M , [C H N S Ir] : calcd 789.1446, obsd 789.1444. Anal.
range. Especially, the complex [(btpy) L3Ir] (Ir-6) showed
35 28
6 2
2
Calcd for C H N S IrPF : C, 45.01; H, 3.02; N, 9.00. Found: C,
the highest performance as a photosensitizer in the visible-light-
induced oxidative coupling of benzylamine to imine. It was
speculated that the superior performance of Ir-6 resulted from
the additional heavy-atom effect of the L3 ligand. We believe
that further various iridium(III) complexes can be prepared by
designing new imidazoline thione and imidazoline selone
ligands.
35 28
6
2
6
4
4.86; H, 3.27; N, 8.73. Mp: 290 °C dec.
Synthetic Procedure for Ir-2, Ir-3, Ir-5, and Ir-6. L2 and L3
1
3
were prepared using the literature method. For the synthesis of Ir-2,
(ppy) IrCl] (50 mg, 0.047 mmol) and L2 (25 mg, 0.10 mmol) were
[
2
2
added to methylene chloride. The reaction mixture was refluxed for 12
h in the dark. The solvent was then removed by rotary evaporation.
The resultant solid was dissolved in methanol. An excess of NH PF
4
6
(
0.10 g, 0.61 mmol in 20 mL of water) was added to form yellow
EXPERIMENTAL SECTION
precipitates which were retrieved by filteration, washed with excess
water, and dried under vacuum. The product, Ir-2, was purified by
recrystallization in a mixture of methylene chloride and diethyl ether.
Isolated yield: 51%. H NMR (300 MHz, acetone-d ): δ 8.78 (d, J =
7
■
General Considerations. 1H and 13C NMR spectra for new
compounds were obtained using a Varian 300 MHz spectrometer.
Mass spectral data were obtained from the Korea Basic Science
Institute (Daegu) on a JEOL JMS 700 high-resolution mass
spectrometer. Elemental analysis was performed on a CE EA1110
instrument. The UV/vis absorption spectra were recorded using a
JASCO V-630 spectrophotometer. Emission spectra were recorded
using a JASCO FP-6200 spectrofluorometer.
1
6
.2 Hz, 2H), 8.17 (d, J = 8.4 Hz, 2H), 7.98 (t, J = 7.5 Hz, 2H), 7.73 (d,
J = 7.5 Hz, 2H), 7.70 (s, 2H), 7.33 (s, 2H), 7.28 (t, J = 7.2 Hz, 2H),
6.83 (t, J = 7.8 Hz, 2H), 6.73 (s, 2H), 6.71 (t, J = 7.2 Hz, 2H), 6.17 (d,
J = 7.8 Hz, 2H), 3.24 (s, 6H) ppm. 13C NMR (75 MHz, acetone-d
): δ
168.9, 157.6, 150.9, 144.0, 138.4, 131.0, 130.1, 124.8, 123.4, 122.3,
6
+
+
Cyclic voltammetry measurements were carried out using a CH
instruments Model CHI600 potentiostat and 5 mM Ir1−Ir6 in
CH Cl . A conventional three-electrode assembly was used to record
122.0, 120.0, 119.8, 59.7, 35.6 ppm. HRMS for M , [C31
calcd 741.1446, obsd 741.1448. Anal. Calcd for C31
42.03; H, 3.19; N, 9.49. Found: C, 42.23; H, 3.49; N, 9.34. Mp: 204
H
28
N
IrPF
6
S
2
Ir] :
: C,
H
N
S
28
6
2
6
2
2
cyclic voltammograms under argon. Carbon was used as the working
°C dec.
3
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Article
For the synthesis of Ir-3, L3 was used instead of L2. Isolated yield:
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1
■
7
8
1%. H NMR (300 MHz, acetone-d ): δ 9.24 (d, J = 7.2 Hz, 2H),
6
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(
4
Hz, 2H), 6.84 (s, 2H), 6.72 (t, J = 7.8 Hz, 2H), 6.13 (d, J = 7.5 Hz,
H), 3.41 (s, 6H) ppm. 1 C NMR (75 MHz, acetone-d ): δ 174.3,
3
2
1
1
8
6
(
51.9, 143.6, 137.6, 130.3, 129.6, 126.6, 124.3, 123.4, 123.0, 121.6,
+
+
20.9, 119.4, 68.9, 36.8 ppm. HRMS for M , [C H N Se Ir] : calcd:
31
28
6
2
37.0335, obsd 837.0335. Anal. Calcd for C H N Se IrPF : C, 38.01;
31
28
6
2
6
(
4
H, 2.88; N, 8.58. Found: C, 38.24; H, 3.20; N, 8.84. Mp: 217 °C dec.
For the synthesis of Ir-5, [(btpy) IrCl] was used instead of
2
2
1
[
(ppy) IrCl] . Isolated yield: 41%. H NMR (300 MHz, acetone-d ): δ
2
2
6
9
2
7
2
.05 (d, J = 7.5 Hz, 2H), 8.04 (t, J = 7.8 Hz, 2H), 7.82 (d, J = 7.5 Hz,
H), 7.75 (d, J = 7.8 Hz, 2H), 7.74 (s, 2H), 7.38 (s, 2H), 7.22 (t, J =
(
.5 Hz, 2H), 7.14 (t, J = 7.2 Hz, 2H), 6.83 (t, J = 7.2 Hz, 2H), 6.74 (s,
H), 6.09 (d, J = 7.5 Hz, 2H), 3.22 (s, 6H) ppm. 13C NMR (75 MHz,
(4) Selected examples: (a) Yang, C.-H.; Mauro, M.; Polo, F.;
Watanabe, S.; Muenster, I.; Fro
012, 24, 3684. (b) Baranoff, E.; Curchod, B. F. E.; Frey, J.; Scopelliti,
R.; Kessler, F.; Tavernelli, I.; Rothlisberger, U.; Gratzel, M.;
Nazeeruddin, M. K. Inorg. Chem. 2012, 51, 215. (c) Brulatti, P.;
Gildea, R. J.; Howard, J. A. K.; Fattori, V.; Cocchi, M.; Williams, J. A.
G. Inorg. Chem. 2012, 51, 3813.
5) Recent paper on spin−orbit coupling analysis of Ir(III)
complexes: Koseki, S.; Kamata, N.; Asada, T.; Yagi, S.; Nakazumi,
H.; Matsushita, T. J. Phys. Chem. C 2013, 117, 5314.
̈
hlich, R.; De Cola, L. Chem. Mater.
acetone-d ): δ 165.6, 161.6, 155.8, 151.3, 145.4, 142.4, 139.1, 135.0,
6
2
1
25.3, 124.9, 123.8, 123.0, 122.2, 120.5, 120.1, 119.0, 64.1, 35.1 ppm.
+
+
̈
HRMS for M , [C H N S Ir] : calcd 853.0888, obsd 853.0889. Anal.
35
28
6 4
Calcd for C H N S IrPF : C, 42.12; H, 2.83; N, 8.42. Found: C,
35
31
6
4
6
4
2.47; H, 2.95; N, 8.20. Mp: 205 °C dec.
For the synthesis of Ir-6, [(btpy) IrCl] and L3 were used instead
2
2
1
(
of [(ppy) IrCl] and L2. Isolated yield: 68%. H NMR (300 MHz,
2
2
acetone-d ): δ 9.38 (d, J = 7.5 Hz, 2H), 8.04 (t, J = 7.5 Hz, 2H), 7.85
6
(
s, 2H), 7.83 (d, J = 8.4 Hz, 2H), 7.75 (d, J = 8.1 Hz, 2H), 7.56 (s,
H), 7.21 (t, J = 7.2 Hz, 2H), 7.14 (t, J = 7.2 Hz, 2H), 6.89 (s, 2H),
.83 (t, J = 7.5 Hz, 2H), 6.09 (d, J = 8.1 Hz, 2H), 3.40 (s, 6H) ppm.
(
6) Reviews: (a) Costa, R. D.; Orti, E.; Bolink, H. J.; Monti, F.;
Accorsi, G.; Armaroli, N. Angew. Chem., Int. Ed. 2012, 51, 8178.
b) Holder, E.; Langeveld, B. M. W.; Schubert, U. S. Adv. Mater. 2005,
2
6
1
3
(
1
C NMR (75 MHz, acetone-d ): δ 165.5, 160.9, 159.3, 153.1, 147.7,
6
7, 1109.
1
1
9
45.4, 142.4, 138.9, 135.5, 125.4, 124.9, 123.9, 123.0, 121.7, 120.9,
+
+
(7) Selected examples: (a) Sato, S.; Morikawa, T.; Kajino, T.; Ishitani,
19.2, 62.1, 37.0 ppm. HRMS for M , [C H N S Se Ir] : calcd
35
28
6
2
2
O. Angew. Chem., Int. Ed. 2013, 52, 988. (b) Soman, S.; Bindra, G. S.;
Paul, A.; Groarke, R.; Manton, J. C.; Connaughton, F. M.; Schulz, M.;
Dini, D.; Long, C.; Pryce, M. T.; Vos, J. G. Dalton Trans. 2012, 41,
48.9777, obsd 948.9780. Anal. Calcd for C H N S IrPF : C, 38.50;
35
31
6
4
6
H, 2.58; N, 7.70. Found: C, 38.85; H, 2.91; N, 8.03. Mp: 232 °C dec.
Experimental Procedure for Photochemical Reactions. In a
0 mL vial, amine (1.0 mmol) and iridium complex were dissolved in
1
(
2678. (c) Lu, Z.; Yoon, T. Angew. Chem., Int. Ed. 2012, 51, 10329.
1
d) Lalevee, J.; Blanchard, N.; Tehfe, M.-A.; Peter, M.; Morlet-Savary,
́
CH Cl (3 mL). After a magnetic spin bar was added, the vial was
2
2
sealed using a rubber septum. The reaction mixture was stirred under
an O atmosphere (using an O balloon) with irradiation of a blue
F.; Fouassier, J. P. Macromol. Rapid Commun. 2011, 32, 917.
(e) Larraufie, M.-H.; Pellet, R.; Fensterbank, L.; Goddard, J.-P.;
Lacote, E.; Malacria, M.; Ollivier, C. Angew. Chem., Int. Ed. 2011, 50,
̂
2
2
2
LED (λmax 460 nm, 0.9 mW/cm ) strip at room temperature. The
reaction temperature was carefully maintained using a water bath. After
4463. (f) BiSalle, B. F.; Bernhard, S. J. Am. Chem. Soc. 2011, 133,
11819. (g) Jasimuddin, S.; Yamada, T.; Fukuju, K.; Otsuki, J.; Sakai, K.
Chem. Commun. 2010, 46, 8466. (h) Nagib, D. A.; Scott, M. E.;
MacMillan, D. W. C. J. Am. Chem. Soc. 2009, 131, 10875.
(8) (a) Sun, J.; Zhao, J.; Guo, H.; Wu, W. Chem. Commun. 2012, 48,
4169. (b) Takizawa, S.; Aboshi, R.; Murata, S. Photochem. Photobiol.
Sci. 2011, 10, 895. (c) Djurovich, P. I.; Murphy, D.; Thompson, M. E.;
Hernandez, B.; Gao, R.; Hunt, P. L.; Selke, M. Dalton Trans. 2007,
3763.
1
5
h, the reaction mixture was directly analyzed by H NMR
spectroscopy. The products were isolated by flash column
chromatography using neutral alumina. The NMR spectra of the
imine products in Table 2 exactly matched with those in our recent
17
paper.
ASSOCIATED CONTENT
Supporting Information
■
*
S
(9) DeRosa, M. C.; Crutchley, R. J. Coord. Chem. Rev. 2002, 233, 351.
(
10) (a) Nonoyama, M. Bull. Chem. Soc. Jpn. 1974, 47, 767.
b) Mauro, M.; Paoli, G. D.; Otter, M.; Donghi, D.; D’Alfonso, G.; De
Cola, L. Dalton Trans. 2011, 40, 12106.
11) Yang, C.-H.; Beltran, J.; Lemaur, V.; Cornil, J.; Hartmann, D.;
Sarfert, W.; Frohlich, R.; Bizzarri, C.; De Cola, L. Inorg. Chem. 2010,
9, 9891.
(12) Although the structural data were not converged due to the
Figures giving the XPS spectra of L2, L3, Ir-2, Ir-3, Ir-5, and Ir-
and the quenching curves of singlet oxygen species with
benzylamine. This material is available free of charge via the
Internet at http://pubs.acs.org.
(
6
(
̈
4
AUTHOR INFORMATION
■
disorder in the side benzene ring of the benzothiophene moiety, the
connectivity of the bis(NHC) ligand to Ir in Ir-4 was clearly confirmed
by single-crystal X-ray analysis.
(13) (a) Jia, W.-G.; Huang, Y.-B.; Lin, Y.-J.; Wang, G.-L.; Jin, G.-X.
Eur. J. Inorg. Chem. 2008, 4063. (b) Jia, W.-G.; Huang, Y.-B.; Lin, Y.-J.;
Jin, G.-X. Dalton Trans. 2008, 5612. (c) Crossley, I. R.; Hill, A. F.;
Humphrey, E. R.; Smith, M. K. Organometallics 2006, 25, 2242.
Corresponding Author
*
E-mail: sson@skku.edu (S.U.S.); taeahn@skku.edu (T.K.A.);
dhryu@skku.edu (D.H.R.).
Notes
The authors declare no competing financial interest.
(d) Kim, H. R.; Jung, I. G.; Yoo, K.; Jang, K.; Lee, E. S.; Yun, J.; Son, S.
U. Chem. Commun. 2010, 46, 758. (e) Choi, J.; Park, S. Y.; Yang, H. Y.;
Kim, H. J.; Ihm, K.; Nam, J. H.; Ahn, J. R.; Son, S. U. Polym. Chem.
ACKNOWLEDGMENTS
■
(
(
This work was supported by grants NRF-2011-0029186
Midcareer Researcher Program) and NRF-2012-1040282
Priority Research Centers Program). S.U.S. thanks the WCU
2
011, 2, 2512. (f) Choi, J.; Ko, J. H.; Jung, I. G.; Yang, H. Y.; Ko, K.
C.; Lee, J. Y.; Lee, S. M.; Kim, H. J.; Nam, J. H.; Ahn, J. R.; Son, S. U.
Chem. Mater. 2009, 21, 2571. (g) Choi, J.; Kang, N.; Yang, H. Y.; Kim,
H. J.; Son, S. U. Chem. Mater. 2010, 22, 3586.
program for the grant R31-2008-10029.
3
958
dx.doi.org/10.1021/om4004412 | Organometallics 2013, 32, 3954−3959

Organometallics
Article
(
́
14) Lalevee, J.; Dumur, F.; Mayer, C. R.; Gigmes, D.; Nasr, G.;
Tehfe, M.-A.; Telitel, S.; Morlet-Savary, F.; Graff, B.; Fouassier, J. P..
Macromolecules 2012, 45, 4134.
(
15) (a) Lang, X.; Ji, H.; Chen, C.; Ma, W.; Zhao, J. Angew. Chem.,
Int. Ed. 2011, 50, 3934. (b) Mitsumoto, Y.; Nitta, M. J. Org. Chem.
004, 69, 1256.
16) Su, F.; Mathew, S. C.; Mo
Blechert, S. Angew. Chem., Int. Ed. 2011, 50, 657.
17) Park, J. H.; Ko, K. C.; Kim, E.; Park, N.; Ko, J. H.; Ryu, D. H.;
Ahn, T. K.; Lee, J. Y.; Son, S. U. Org. Lett. 2012, 14, 5502.
18) Jiang, G.; Chen, J.; Huang, J.-S.; Che, C.-M. Org. Lett. 2009, 11,
568.
19) The free energy values of excited states (ΔG° ) above the
2
(
̈
hlmann, L.; Antonietti, M.; Wang, X.;
(
(
4
(
es
ground states of complexes were calculated using the following
2
−1
equations; ΔG° = E + χ′ and χ′ = (Δν ) (16k T ln 2) . For
es
0
1/2
B
definitions of terms, see more details in: (a) Opperman, K. A.;
Mecklenburg, S. L.; Meyer, T. J. Inorg. Chem. 1994, 33, 5295.
(
b) Kober, E. M.; Caspar, J. V.; Lumpkin, R. S.; Meyer, T. J. J. Phys.
Chem. 1985, 90, 3722.
20) HOMO energy values were calculated by the following
(
equation: HOMO (eV) = −4.8 − [E − E1/2(ferrocene)]. E1/2(Fc/
ox
+
Fc ) was observed at +0.36 V. Kim, J. H.; Park, J. H.; Lee, H. Chem.
Mater. 2003, 15, 3414.
(
21) The LUMO energy level of oxygen and HOMO energy level of
benzylamine were calculated by density functional theory (DFT)
calculations. Refer to the Supporting Information in ref 17.
(
(
22) Byteva, I. M. Zh. Prikl. Spektrosk. 1979, 31, 333.
23) Recent examples: (a) McCormick, T. M.; Calitree, B. D.;
Orchard, A.; Kraut, N. D.; Bright, F. V.; Detty, M. R.; Eisenberg, R. J.
Am. Chem. Soc. 2010, 132, 15480. (b) Ohulchanskyy, T. Y.; Donnelly,
D. J.; Detty, M. R.; Prasad, P. N. J. Phys. Chem. B 2004, 108, 8668.
3
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dx.doi.org/10.1021/om4004412 | Organometallics 2013, 32, 3954−3959