Design and synthesis of blue-emitting cyclometalated Iridium(III) complexes based on regioselective functionalization

Article abstract of DOI:10.1002/ejic.201100755

A series of tris-cyclometalated Ir^III complexes were prepared by regioselective substitution reactions (formylation, thiocyanation, and iodination) and subsequent conversions (cyanation, cross-coupling reaction, reduction, and oxidation) on a 2

Full text of DOI:10.1002/ejic.201100755

FULL PAPER
DOI: 10.1002/ejic.201100755
Design and Synthesis of Blue-Emitting Cyclometalated Iridium(III) Complexes
Based on Regioselective Functionalization
Yosuke Hisamatsu[a] and Shin Aoki*[a,b]
Keywords: Luminescence / Iridium / Synthesis design / Substituent effects
A series of tris-cyclometalated IrIII complexes were prepared
by regioselective substitution reactions (formylation, thio-
cyanation, and iodination) and subsequent conversions (cy-
anation, cross-coupling reaction, reduction, and oxidation)
on a 2-(4Ј-methoxyphenyl)pyridine (mppy) ligand of fac-
[Ir(mppy)3]. The introduction of electron-withdrawing groups
such as CHO, CN, and sulfonyl groups (SO2Me, SO2Ar) at
the 5Ј-position of the phenyl ring of the mppy portion induces
a considerable blueshift in luminescence emission (from
495 nm to approximately 465 nm) in degassed organic sol-
vents.
pyridine ring, it has been proposed that the introduction of
electron-withdrawing groups on the phenyl ring stabilizes
the HOMO energy level, thereby resulting in an increase in
the HOMO–LUMO energy gap.[1g] The modification of
IrIII complexes with electron-withdrawing groups such as
fluoro, trifluoromethyl,[8] cyano,[9] formyl,[10] or sulfonyl
groups[11] have been attempted to achieve this. Typically,
fluoro-substituted ligands are most widely used in represen-
tative blue-emitting IrIII complexes such as FIrpic,[2c,12g]
FIrtaz,[12g] and their analogues (Scheme 2).[12] Indeed, the
introduction of a fluorine atom is useful for the design and
synthesis of a blue-color IrIII complex. However, it is de-
scribed that OLED devices based on fluorine-substituted
IrIII complexes such as FIrpic tend to have short device op-
erational lifetimes, since IrIII compounds may undergo a
cleavage of the C–F bond on the ligand during device fabri-
Introduction
Cyclometalated iridium(III) complexes such as fac-
[Ir(ppy)3] (1; ppy = 2-phenylpyridine) and fac-[Ir(tpy)3] [2;
tpy = 2-(4Ј-tolylpyridine)] (Scheme 1) have received con-
siderable attention because of their unique photophysical
properties, which include high luminescent quantum yields
(e.g., Φ for 1 is 0.4), short phosphorescent lifetimes (τ in
about microsecond order), and emission-color tuning by
appropriate control of the ligand structure.[1] The strong
spin–orbital coupling of IrIII metal ion in the complexes
facilitates efficient intersystem crossing (ISC) from the sing-
let excited state to the triplet excited state, thereby resulting
in strong phosphorescence at room temperature. These at-
tractive photochemical properties make such IrIII com-
plexes important candidates for use as phosphorescent
emitters in organic light-emitting diodes (OLEDs),[1,2] oxy-
gen detection,[3] sensors for metal ions,[4] luminescent
probes for biological systems,[5] photoreductants,[6] and
photoredox catalysis.[7] The most extensively investigated
applications are phosphorescent emitters, which exhibit red,
green, and blue phosphorescence emission for highly ef-
ficient OLEDs.[1,2] To date, promising red-[2b,2d,2h] and
green-[2a,2i] emitting IrIII complexes for phosphorescent
OLEDs have been reported, and much research has been
focused on the design and synthesis of IrIII complexes that
emit a blue color. Since the highest occupied molecular or-
bital (HOMO) of IrIII–ppy-based complexes (such as 1) is
located on the phenyl π and Ir d orbitals, and the lowest
unoccupied molecular orbital (LUMO) is mainly on the
[a] Faculty of Pharmaceutical Sciences, Tokyo University of
Science,
2641 Yamazaki, Noda, Chiba 278-8510, Japan
E-mail: shinaoki@rs.noda.tus.ac.jp
[b] Center for Technologies against Cancer (CTC), Tokyo
University of Science,
2641 Yamazaki, Noda, Chiba 278-8510, Japan
Scheme 1.
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Blue-Emitting Cyclometalated Iridium(III) Complexes
cation and operation.[13] Therefore, the development of cy- emission wavelength (blue emission at 477 and 478 nm in
clometalated IrIII complexes with fewer or without the flu- CH2Cl2, respectively). These results suggest that modifica-
orine atoms on the ligand is important.[12s,12t] Examples of tions at the 5Ј-position of the tpy ligand of 2 can be effec-
blue-emitting tris-cyclometalated IrIII complexes[14] that ex- tive for the color-tuning of IrIII complexes.
hibit a somewhat higher thermal stability and luminescent
In this manuscript, we report on the synthesis of tris-
efficiency[2h,2i] are relatively limited {e.g., [Ir(dfpypy)3][14d] cyclometalated IrIII complexes 7–12 (Scheme 1) by regiose-
and [Ir(dfppy)3][2i,12q]}.
lective substitution reactions (formylation, thiocyanation,
iodination) and subsequent conversions (cyanation, cross-
coupling reaction, reduction, and oxidation) on a 2-(4Ј-
methoxyphenyl)pyridine (mppy) ligand of fac-[Ir(mppy)3]
(6) shown in Scheme 1 and their photochemical properties.
Results and Discussion
In this study, complex 6 was selected for use as a key
platform for new blue-emitting IrIII complexes, since its
emission wavelength is observed at 481 nm in EtOH/MeOH
glass at 77 K, which is 12 nm shorter than that of 2 under
the same conditions, as reported by Watts and co-
workers.[15] To direct the color of the emission of tris-cyclo-
metalated IrIII complexes to the blue region, a variety of
electron-withdrawing groups (CN, CHO, SCN, SO2Me, and
SO2Ar groups) were introduced at the 5Ј-position of 6. The
preparation 6 was carried out starting from 2-(4-meth-
oxyphenyl)pyridine 16 through a dichloro-bridged dimer,
[{(mppy)2IrCl}2] by using the synthetic procedure reported
by Thompson and co-workers.[2i] The formylation of 6 was
then carried out with DMF and POCl3 (Vilsmeier reaction)
to give the tris(formyl) derivative 7 in 75% yield (Scheme 3)
following a previously reported method.[17] At this point, 7
was converted into the tris(hydroxyimino) derivative 17 in
98% yield by treatment with NH2OH·HCl, followed by re-
action with Ac2O to afford the tris(cyano) derivative 8.[17,18]
Scheme 2.
Generally, fac-tris-cyclometalated IrIII complexes are pre-
pared by the reaction of IrCl3 or [Ir(acac)3] (acac = acetyl-
acetonate) with the corresponding ligands under high ther-
mal conditions (170–220 °C).[2h,2i,14,15] On the other hand,
regioselective substitution reactions after the preparation of
cyclometalated IrIII complexes would be an alternative
method to prepare functionalized IrIII complexes, which are
otherwise difficult to prepare. However, successful attempts
to functionalize ligands bound to the IrIII complexes are
few in number.[16]
We recently reported the regioselective halogenation, ni-
tration, and formylation of fac-[Ir(ppy)3] (1) and fac-
[Ir(tpy)3] (2) at the 5Ј-position (para to the C–Ir bond) of
the phenyl ring, and their subsequent conversions to amino,
formyl, and cyano groups (3, 4, and 5 in Scheme 1).[17] As
summarized in Scheme 1, fac-[Ir(atpy)3] (3), which contains
three amino groups at the 5Ј-position, exhibits a red lumi-
nescence emission in CH2Cl2 at 581 nm, which is a much
longer wavelength than that of 2 (green emission at
512 nm). In addition, the color of the emission of 3 in aque-
ous solutions is dependent on the pH of the aqueous solu-
tions. Namely, the red (around 600 nm) changes to green
(at around 530 nm) when the amino groups are protonated,
possibly because the electron-donating NH2 group is
Scheme 3.
The thiocyanation of 6 was performed using bromodi-
switched to an electron-withdrawing (NH3)+ group. On the methylsulfonium bromide (BDMS) and ammonium thiocy-
other hand, the introduction of electron-withdrawing anate [(NH4)SCN][19] to give 9 in 98% yield (Scheme 4).
groups such as CHO and CN groups at the same position The tris(thiocyano) derivative 9 was readily reduced to the
(4 and 5), induces an approximately 30 nm blueshift in the tris(thiol) derivative 13 with LiAlH4 at 0 °C, which was then
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Y. Hisamatsu, S. Aoki
FULL PAPER
methylated to give the tris(methylthio) derivative 14. The
desired tris(mesyl) derivative 10 was produced in 57% yield
by the oxidation of 14 with meta-chloroperbenzoic acid
(mCPBA).
Scheme 4.
To introduce sulfonyl groups, we iodinated 6 by reaction
with N-iodosuccinimide (NIS) to obtain 15 in 78% yield,[17]
and cross-coupling reactions of 15 with sodium p-toluene-
sulfinate or sodium 4-chlorophenylsulfinate in the presence
of CuI in DMF at 110 °C gave 11 and 12 (Scheme 5).[20]
The tris(mesyl) derivative 10 was also directly obtained
from 15 in 64% yield by treating it with sodium methane-
sulfinate.[21]
Scheme 5.
Figure 1. UV/Vis spectra of IrIII complexes in CH2Cl2 at 298 K. (a)
Compound 6 (bold curve), 7 (plain curve), and 8 (bold dashed
curve). (b) Compound 9 (bold dashed curve), 10 (bold curve), 13
(plain curve), and 14 (plain dashed curve). (c) Compound 11 (bold
curve), 12 (bold dashed curve), and 15 (plain curve); [Ir complex]
UV/Vis and Luminescence Spectra of Substituted
[Ir(mppy)3] Complexes
UV/Vis spectra of the Ir complexes 6–15 (10 μm) in
CH2Cl2 at 298 K are shown in Figure 1 and their photo- = 10 μm.
chemical and electrochemical data are summarized in
Table 1. The strong absorption bands in the ultraviolet re-
1
gion at 250–350 nm were assigned to the π–π* transition
Luminescence spectra of [Ir(mppy)3] derivatives 6–15
of the mppy ligands. The weak shoulder bands at 350– (10 μm) in degassed CH2Cl2 were measured at 298 K as
450 nm can be assigned spin-allowed singlet-to-singlet shown in Figure 2. All of the IrIII complexes were excited
metal-to-ligand charge transfer (1MLCT) transitions, spin- at 366 nm. The data for the emission wavelength and lumi-
3
3
forbidden singlet-to-triplet MLCT transitions, and π–π* nescent quantum yields (Φ) are summarized in Table 1. The
transitions.[2i,11a,14]
emission maxima of 6 (495 nm) is 17 nm shorter than that
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Blue-Emitting Cyclometalated Iridium(III) Complexes
Table 1. Photochemical and electrochemical properties of the sub-
stituted [Ir(mppy)3] at 298 K.
1/2
λmax [nm]
λmax [nm]
Φ
τ [μs][b]
E
[V][c]
ox
(absorption)[a]
(emission)[a]
6
7
8
9
289, 360
292, 356
285
495
0.65
0.52
0.60
0.29
0.39
0.56
0.68
0.21
0.31
1.8
2.7
2.6
1.1
2.6
0.30
0.66
0.73
0.61
0.69
463, 488
464, 492
486
465, 492
465, 492
463, 491
511
293, 352
10 283, 340
11 287
12 288
13 295, 373
14 297, 372
15 292, 364
2.2
0.70
2.4
0.75
n.d.[d]
3.0
n.d.[d]
n.d.[d]
0.43
520
491
0.002 Ͻ0.012[e]
[a] [Ir complex] = 10 μm in CH2Cl2. [b] Luminescence lifetime in
CH2Cl2. [c] DMF that contained 0.1 m nBu4NPF6 (V versus Fc+/
Fc). [d] Not determined. [e] Less than detection limit on our sys-
tem.
of 2 (λmax = 512 nm) in CH2Cl2, and the luminescent quan-
tum yield of 6 (Φ = 0.65) is higher than that of 2 (Φ =
0.50).[17] Unlike the absorption spectra, the emission spectra
are affected by the electron-withdrawing ability of the sub-
stituent groups. The emission maxima of 7 and 8, which
contain CHO and CN groups, have two emission maxima
at around 463 nm and around 490 m. Both complexes exhi-
bit a blue emission as shown in Figure 2 (a) and Figure 3,
and the luminescence quantum yields of 7 and 8 are com-
parable to that of 6. The introduction of a thiocyano group
induces only a 9 nm blueshift from 6, and the color of the
emission is green at 486 nm (Figure 2, b). The emission
maxima of tris(thiol) derivative 13 prepared by the re-
duction of 9, and the tris(methylthio) derivative 14 are 511
and 520 nm, respectively. These results indicate that thiol
and methylthio groups act as electron-donating groups to
induce a redshift in the emission.
The emission maxima of the tris(mesyl) derivative 10,
prepared by the oxidation of 14, appear at 465 and 492 nm.
The luminescence quantum yields of 9, 13, 14, and 10, pre-
pared by subsequent conversions (Scheme 4), are somewhat
lower than that of 6. The emission spectra of 11[22] and 12
are similar to that of 10 with luminescence quantum yields
(Φ) of 0.56 and 0.68, respectively (Figure 2, c). The slightly
shorter emission wavelength of 12 compared to that of 11
can be attributed to the electron-withdrawing effect of the
Cl substituent at the para position. The Φ value of the tris-
(iodo) derivative 15 is quite low (Φ = 0.002),[23] and the
emission maxima is observed at 491 nm. Pictures of the
emission color for IrIII complexes 6, 8, 11, and 12 are shown
in Figure 3. Luminescence lifetimes of these complexes (6–
12 and 14) measured in CH2Cl2 at 298 K are 1.1–3.0 μs,
as listed in Table 1 (see also Figure S3 in the Supporting
Information), thereby supporting their luminescence emis-
sion through excited triplet states.[1,24,25]
Figure 2. Emission spectra of IrIII complexes in degassed CH2Cl2
at 298 K (excitation at 366 nm). (a) Compound 2 (plain dashed
curve), 6 (plain curve), 7 (bold curve), and 8 (bold dashed curve).
(b) Compound 9 (bold dashed curve), 10 (bold curve), 13 (thin
curve), and 14 (plain dashed curve). (c) Compound 11 (bold curve),
12 (bold dashed curve), and 15 (thin curve). [Ir complex] = 10 μm.
Units a.u. are arbitrary units, and the emission intensity was nor-
malized with the absorbance of each compound at 366 nm, which
was used for the excitation of all of the Ir complexes.
Electrochemical Properties and Theoretical Calculations of
Ir Complexes
Cyclic voltammetry of complexes 6–12, and 15 were mea-
sured in anhydrous DMF that contained 0.1 m Bu4NPF6
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Y. Hisamatsu, S. Aoki
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LUMO energies were obtained by single-point calculation
of the optimized Ir complexes. The calculated HOMO–
LUMO shapes of the IrIII complexes are similar, as shown
in Figures S5–S10 in the Supporting Information. The
HOMO orbital consists of phenyl π and Ir d orbitals,
whereas the LUMO orbital is mainly localized on the pyr-
idine ring. The HOMO and LUMO energy levels by DFT
calculations (Table S3) indicate that the introduction of
electron-withdrawing groups such as formyl, cyano, and
sulfonyl groups stabilize the HOMO energy more than the
LUMO energy, thereby resulting in a spread of the
HOMO–LUMO energy gap (Eg = 3.79–3.90 eV) relative to
that of 6 (Eg = 3.66 eV).[30]
Figure 3. Photograph showing the color of the emission of IrIII
complex 6, 8, 11, and 12 in CH2Cl2 ([Ir complex] = 30 μm, exci-
tation at 365 nm).
of supporting electrolyte based on a ferrocenium/ferrocene
(Fc+/Fc) redox potential as an internal standard. The re-
sults are summarized in Table 1. These IrIII complexes show
quasireversible oxidation processes with a rate of 100 ms–1.
Conclusion
In this manuscript, we report on the synthesis of a series
Whereas the half-wave oxidation potential of 6 (R2 = H) is of tris-cyclometalated IrIII complex {fac-[Ir(mppy)3] (6)} by
0.30 V, those of 7 (R2 = CHO), 8 (R2 = CN), 9 (R2 = SCN), several regioselective substitution reactions, including for-
10 (R2 = SO2Me), 11 (R2 = SO2Tol), 12 (R2 = SO2PhCl), mylation, thiocyanation, and iodination of the ligand.
and 15 (R2 = I) are 0.66, 0.73, 0.61, 0.69, 0.70, 0.75, 0.43 V, Furthermore, the chemical conversions also led to the prep-
respectively, thereby implying that the introduction of elec- aration of compounds 8 and 10–14. To the best of our
tron-withdrawing groups causes positive shifts in the oxi- knowledge, carbon–heteroatom bond formation such as the
dation potentials (0.66–0.75 V versus Fc+/Fc) relative to C–SO2 bond by the cross-coupling reaction of the metal
that of 6, which suggests that these groups at the 5Ј-position complexes has been not reported.[31] The introduction of
effectively stabilize the HOMO energy levels of the electron-withdrawing groups such as CHO, CN, and sulf-
[Ir(mppy)3] complex.[26] Figure 4 shows the relationship be- onyl groups (SO2Me, SO2Ar) at the 5Ј-position of 6 induces
tween the wavelength of emission maxima and the oxi- an approximately 30 nm blueshift in the luminescence emis-
dation potentials of 6–12 and 15. Although sulfonyl and sion, thereby resulting in a blue emission (463 to 465 nm)
cyano groups are stronger electron-withdrawing groups in degassed organic solvents without the fluorine substitu-
than a formyl group,[27] further blueshifts of 8 and 10–12 ent on the ligands.[12s,13a] The findings reported herein pro-
are not observed in compared with 7, possibly because these vide important information for the design and synthesis of
groups also lower the LUMO energy level (Table S3 in the new blue-emitting phosphorescent compounds. Diverse di-
Supporting Information).
rect modifications after preparation of the parent metal
Density functional theory (DFT) calculations[28] of 6–15 complexes would provide useful methods for the molecular
were carried out using the Gaussian 03 program.[29] The design and synthesis that contribute to a wide range of ap-
B3LYP hybrid functional was used together with the plications in inorganic chemistry, materials chemistry, sup-
LanL2DZ basis set for Ir and I atoms and the 6-31G basis ramolecular chemistry, photochemistry, biological chemis-
set for H, C, N, O, S, and Cl atoms. The HOMO and try, and related fields.
Figure 4. Plot of wavelengths of emission maxima versus the oxidation potential of 6–12 and 15. For 7, 8, and 10–12, the wavelengths at
which highest emission is observed are plotted.
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Blue-Emitting Cyclometalated Iridium(III) Complexes
concentrated under reduced pressure. Water was added to the re-
sulting residue, and the pH of the solution was adjusted to pH 5–
6 by the addition of 1 m NaOH. The insoluble compounds were
then collected by filtration and washed with water to afford 17 as
a yellow-brown powder (116 mg, 98%); m.p. Ͼ 300 °C. IR (ATR):
Experimental Section
General Information: IrCl3·3H2O and Cu(NO3)2·3H2O were pur-
chased from KANTO CHEMICAL Co., Inc. Anhydrous CH2Cl2,
MeCN, and DMF were obtained by distillation from CaH2. All
aqueous solutions were prepared using deionized water. Bromodi-
methylsulfonium bromide (BDMS)[19] and 2-(4Ј-methoxyphenyl)-
pyridine[32] were prepared according to the reported literature pro-
cedure. Copper(I) iodide was purified according to the reported
literature procedure.[33] All synthetic procedures were carried out
under an atmosphere of argon. Melting points were measured with
a YANACO MP33 Micro Melting Point Apparatus and are uncor-
rected. IR spectra were recorded with a Perkin–Elmer FTIR Spec-
trum 100 (ATR). 1H NMR (300 MHz) and 13C NMR (75 MHz)
spectra were recorded with a JEOL Always 300 spectrometer. Ele-
mental analyses were performed with a Perkin–Elmer CHN 2400
analyzer. IrIII complexes for elemental analyses were recrystallized
from CHCl3/hexane. Electrospray ionization (ESI) mass spectra
were recorded with a Varian 910-MS instrument. Thin-layer (TLC)
and silica gel column chromatography was performed with a Merck
5554 (silica gel) TLC plate and Fuji Silysia Chemical FL-100D,
respectively.
ν = 3208, 3069, 2997, 2933, 2833, 1587, 1522, 1459, 1422, 1262,
˜
1247, 1228, 1151, 1020, 932, 780, 747, 589 cm–1. 1H NMR
(300 MHz, [D6]acetone/TMS): δ = 9.80 (s, 3 H), 8.30 (s, 3 H), 8.11
(s, 3 H), 8.01 (d, J = 8.4 Hz, 3 H), 7.79 (br. t, J = 7.2 Hz, 3 H),
7.62 (d, J = 5.6 Hz, 3 H), 7.07 (br. t, J = 7.2 Hz, 3 H), 6.60 (s, 3
H), 3.48 (s, 9 H) ppm. ESI-MS: m/z calcd. for C39H33IrN6O6
[M]+: 872.2062; found 872.2068.
Ac2O (1.5 mL) was added to 17 (13.0 mg, 14.9 μmol) and the reac-
tion mixture was stirred at 140 °C for 2 h. The reaction mixture
was concentrated under reduced pressure, and the resulting residue
was purified by silica gel column chromatography (CHCl3) to af-
ford 8 as a yellow powder (11.9 mg, 98% yield); m.p. Ͼ 300 °C
(recrystallized from CHCl /hexane). IR (ATR): ν = 3075, 3008,
˜
3
2933, 2831, 2213, 1584, 1523, 1464, 1423, 1281, 1251, 1231, 1148,
1
1020, 911, 780, 745, 629 cm–1. H NMR (300 MHz, CDCl3/TMS):
δ = 7.84 (d, J = 8.0 Hz, 3 H), 7.80 (s, 3 H), 7.74 (td, J = 8.0, 1.5 Hz,
3 H), 7.44 (d, J = 5.5 Hz, 3 H), 7.00 (ddd, J = 1.1, 5.5, 8.0 Hz, 3
H), 6.42 (s, 3 H), 3.54 (s, 9 H) ppm. 13C NMR: δ = = (75 MHz,
CDCl3/TMS): δ = 55.53, 93.77, 117.97, 118.38, 118.96, 122.50,
128.62, 137.46, 147.00, 161.25, 163.90, 171.76 ppm. ESI-MS: m/z
calcd. for C39H27IrN6O3 [M]+: 818.1745; found 818.1741.
C39H27IrN6O3·0.5CHCl3: calcd. C 53.94, H 3.15, N 9.55; found C
53.70, H 2.80, N 9.22.
Complex 6: A mixture of dichloro-bridged dimers, [{(mppy)2-
IrCl}2][34] (1.20 g, 1.01 mmol), 16 (0.561 g, 3.03 mmol), and K2CO3
(1.40 g, 10.1 mmol) in degassed glycerol (105 mL) was heated at
200 °C under an argon atmosphere for 24 h. After cooling the reac-
tion mixture to room temperature, H2O was added. The resulting
precipitate was filtered off, washed with H2O, and dried. The crude
residue was purified by silica gel column chromatography (CHCl3)
to afford 6 as a yellow powder (0.979 g, 65% yield); m.p. Ͼ 300 °C
Complex 9: Compound 6 (10.0 mg, 13.4 μmol) was added to a yel-
low suspension of bromodimethylsulfonium bromide (BDMS)[19]
(13.4 mg, 60.3 μmol) and ammonium thiocyanate (12.2 mg,
161 μmol) in MeCN (3 mL), and the reaction mixture was stirred
at room temp. for 1 h. The resulting reaction mixture was quenched
by sat. NaHCO3 (0.5 mL), and the solid residue was removed by
filtration. The residue was washed with CHCl3. The organic layer
was separated, washed with brine, dried with Na2SO4, and concen-
trated under reduced pressure. The resulting residue was purified
by silica gel column chromatography (CHCl3) to afford 9 as a yel-
low powder (14.3 mg, 98% yield); m.p. 298–300 °C (recrystallized
(recrystallized from CHCl /hexane). IR (ATR): ν = 3055, 2998,
˜
3
2961, 2934, 2831, 1578, 1544, 1456, 1422, 1272, 1209, 1040, 840,
766, 748, 584 cm–1. 1H NMR (300 MHz, CDCl3/TMS): δ = 7.74
(d, J = 8.4 Hz, 3 H), 7.57–7.45 (m, 9 H), 6.77 (ddd, J = 1.3, 5.6,
8.1 Hz, 3 H), 6.47–6.45 (m, 3 H), 6.44 (s, 3 H), 3.55 (s, 9 H) ppm.
13C NMR (75 MHz, CDCl3/TMS): δ = 54.63, 106.57, 118.03,
120.53, 120.62, 125.15, 135.70, 136.96, 146.92, 160.67, 163.90,
166.36 ppm. ESI-MS: m/z calcd. for C36H30IrN3O3 [M]+: 743.1888;
found 743.1892. C36H30IrN3O3·0.66CHCl3: calcd. C 53.42, H 3.75,
N 5.10; found C 53.58, H 3.88, N 4.99.
from CHCl /hexane). IR (ATR): ν = 3070, 3007, 2933, 2838, 2152,
˜
3
Complex 7: Phosphorous oxychloride (1.6 mL) was added dropwise
to dry DMF (4 mL), and the resulting mixture was stirred at room
temperature for 1 h, after which 6 (0.300 g, 0.403 mmol) was added
to obtain a yellow solution. After stirring at 80 °C for 18 h, the
deep-red reaction mixture was allowed to cool at 0 °C, and 1 m
NaOH (25 mL) was then added. After stirring at room temperature
for 2 h, the yellow solid was isolated by filtration and washed with
water to afford 7 as a yellow powder (0.250 g, 75% yield); m.p. Ͼ
1602, 1572, 1559, 1458, 1421, 1266, 1249, 1228, 1074, 1028, 881,
779, 744, 617 cm–1. 1H NMR (300 MHz, CDCl3/TMS): δ = 7.83
(d, J = 8.0 Hz, 3 H), 7.80 (s, 3 H), 7.68 (td, J = 1.5, 8.0 Hz, 3 H),
7.48 (d, J = 5.5 Hz, 3 H), 6.96 (ddd, J = 1.1, 5.5, 8.0 Hz, 3 H), 6.40
(s, 3 H), 3.55 (s, 9 H) ppm. 13C NMR (75 MHz, CDCl3/TMS): δ
= 55.74, 102.33, 111.61, 118.76, 122.12, 128.30, 137.02, 138.58,
147.07, 158.45, 164.37, 167.32 ppm. ESI-MS: m/z calcd. for
C39H27IrN6O3S3
[M]+:
914.0907;
found
914.0899.
300 °C (recrystallized from CHCl /hexane). IR (ATR): ν = 3070,
˜
C39H27IrN6O3S3·0.2CHCl3: calcd. C 50.09, H 2.92, N 8.94; found
3
3002, 2961, 2933, 2837, 1664, 1573, 1531, 1419, 1400, 1283, 1219,
1146, 1021, 929, 783, 745, 726, 529 cm–1. 1H NMR (300 MHz,
CDCl3/TMS): δ = 10.31 (s, 3 H), 8.16 (s, 3 H), 7.97 (d, J = 8.0 Hz,
3 H), 7.71 (td, J = 1.5, 8.0 Hz, 3 H), 7.47 (d, J = 5.5 Hz, 3 H), 6.96
(ddd, J = 1.1, 5.5, 8.0 Hz, 3 H), 6.52 (s, 3 H), 3.54 (s, 9 H) ppm.
13C NMR (75 MHz, CDCl3/TMS): δ = 55.19, 118.18, 119.03,
119.24, 122.20, 123.16, 137.19, 137.76, 146.85, 162.40, 164.70,
176.26, 189.62 ppm. ESI-MS: m/z calcd. for C39H31IrN3O3 [M +
H]+: 828.1813; found 828.1807. C39H30IrN3O6·0.66CHCl3: calcd. C
52.44, H 3.40, N 4.63; found C 52.84, H 3.53, N 4.64.
C 50.33, H 2.53, N 8.85.
Complex 13: LiAlH4 (41.3 mg, 1.09 mmol) was added to a solution
of 9 (80.0 mg, 0.087 mmol) in dry THF (15 mL) that had been
cooled to 0 °C, and the reaction mixture was stirred 30 min at 0 °C.
After unreacted LiAlH4 was destroyed by slowly adding of H2O
(20 mL) and 1 m HCl (20 mL) at 0 °C, the suspension was extracted
with CHCl3 (40 mL twice), dried with Na2SO4, and concentrated
under reduced pressure to afford 13 as a yellow powder (73.5 mg,
quant.); m.p. Ͼ 200 °C (dec.) (recrystallized from CHCl3/hexane).
IR (ATR): ν = 3061, 2995, 2931, 2832, 2559, 1599, 1569, 1557,
˜
Complex 8: Hydroxylamine monohydride (91.8 mg, 1.33 mmol) was
1520, 1455, 1420, 1262, 1245, 1217, 1155, 1029, 1014, 877, 853,
1
added to a solution of 7 (110 mg, 0.133 mmol) in MeOH (25 mL). 1029, 1014, 877, 777, 743, 617 cm–1. H NMR (CDCl3): δ = 7.72
The reaction mixture was stirred at room temperature for 11 h and
(d, J = 8.1 Hz, 3 H), 7.60–7.54 (m, 3 H), 7.58 (s, 3 H), 7.45 (d, J
Eur. J. Inorg. Chem. 2011, 5360–5369
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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5365

Y. Hisamatsu, S. Aoki
FULL PAPER
= 5.5 Hz, 3 H), 6.82 (br. t, J = 6.4 Hz, 3 H), 6.41 (s, 3 H), 3.52 (s,
ture, and sat. NaHCO3 (15 mL) was then added. The organic layer
was extracted with CHCl3 (15 mL twice), dried with Na2SO4, and
9 H) ppm. ESI-MS: m/z calcd for C36H30IrN3O3S3 [M]+: 839.1055;
found 839.1058. C36H30IrN3O3S3·0.33CHCl3: calcd. C 49.54, H concentrated under reduced pressure. The resulting residue was
3.47, N 4.77; found C 49.49, H 3.23, N 4.83.
purified by silica gel column chromatography (CHCl3/hexane =
2:1) to afford 11 as a yellow powder (35.1 mg, 65% yield); m.p. Ͼ
Complex 14: MeI (0.137 g, 0.964 mmol) and Cs2CO3 (0.186 g,
0.570 mmol) were added to a stirred solution of 13 (0.080 g,
0.095 mmol) in dry THF (15 mL). The reaction mixture was stirred
at room temperature for 17 h, after which H2O (40 mL) was added
and extracted with CHCl3 (40 mL twice). The organic layers were
combined, dried with Na2SO4, and concentrated under reduced
pressure. The resulting residue was purified by silica gel column
chromatography (CHCl3) to afford 14 as a yellow powder (0.068 g,
81%); m.p. 196–198 °C (recrystallized from CHCl3/hexane). IR
300 °C (recrystallized from CHCl /hexane). IR (ATR): ν = 3070,
˜
3
3007, 2933, 2838, 2152, 1602, 1572, 1559, 1458, 1421, 1266, 1 cm–1.
IR (ATR): ν = 3068, 2932, 2837, 1573, 1458, 1422, 1299, 1281,
˜
1228, 1145, 1097, 1069, 1016, 889, 711, 674, 567, 538 cm–1. 1H
NMR (300 MHz, CDCl3/TMS): δ = 8.31 (s, 3 H), 7.97 (d, J =
8.4 Hz, 3 H), 7.74 (d, J = 8.4 Hz, 6 H), 7.73–7.70 (m, 3 H), 7.49
(d, J = 5.5 Hz, 3 H), 7.18 (d, J = 8.1 Hz, 6 H), 6.99 (br. t, J =
6.0 Hz, 3 H), 6.10 (s, 3 H), 3.16 (s, 9 H), 2.37 (s, 9 H) ppm. 13C
NMR (75 MHz, CDCl3/TMS): δ = 21.53, 55.04, 118.90, 119.28,
121.38, 122.29, 124.77, 127.91, 128.85, 137.08, 137.29, 139.45,
143.04, 146.99, 157.25, 164.47, 172.96 ppm. ESI-MS: m/z calcd. for
(ATR): ν = 3066, 2915, 2833, 1599, 1570, 1558, 1516, 1455, 1421,
˜
1260, 1243, 1215, 1154, 1081, 1032, 1015, 884, 860, 778, 744, 617
1
cm–1. H NMR (CDCl3/TMS): δ = 7.76 (d, J = 8.4 Hz, 3 H), 7.61
C57H48IrN3O9S3
[M]+:
1205.2153;
found
1205.2148.
(s, 3 H), 7.57 (br. t, J = 7.3 Hz, 3 H), 7.49 (d, J = 5.5 Hz, 3 H),
6.83 (br. t, J = 5.9 Hz, 3 H), 6.40 (s, 3 H), 3.52 (s, 9 H), 2.40 (s, 9 H)
ppm. 13C NMR (75 MHz, CDCl3/TMS): δ = 17.11, 55.33, 115.78,
118.00, 118.21, 121.02, 126.83, 136.06, 137.43, 147.05, 159.12,
163.27, 165.66 ppm. ESI-MS: m/z calcd for C39H36IrN3O3S3
[M]+: 881.1519; found 881.1519. C39H36IrN3O3S3·0.5CHCl3: calcd.
C 50.32, H 3.90, N 4.46; found C 50.03, H 3.62, N 4.38.
C57H48IrN3O9S3 (1207.42): calcd. C 56.70, H 4.01, N 3.48; found
C 56.34, H 3.80, N 3.32.
Complex 12: CuI (127 mg, 668 μmol) was added to a solution of
15 (50.0 mg, 44.5 μmol) in dry DMF (3 mL) and stirred at room
temperature for 10 min. Sodium p-chlorobenzenesulfinate (159 mg,
801 μmol) was added, and the mixture was heated at 110 °C for
20 h. The reaction mixture was allowed to cool to room tempera-
ture, and sat. NaHCO3 (10 mL) was then added. The organic layer
was extracted with CHCl3 (30 mL four times), dried with Na2SO4,
and concentrated under reduced pressure. The resulting residue was
purified by silica gel column chromatography (CHCl3/hexane =
2:1) to afford 12 as a yellow powder (38.5 mg, 68% yield); m.p. Ͼ
Complex 10: mCPBA (40.0 mg, 232 μmol) was added to a solution
of 14 (31.4 mg, 35.6 μmol) in dry CH2Cl2 (6 mL) cooled to 0 °C,
and then stirred at 0 °C for 1 h. It was then warmed to room tem-
perature for 5 h. mCPBA (20.0 mg. 116 μmol) was added again,
and the mixture was stirred at room temperature for 22 h. After
the treating the mixture with 0.1 m NaOH (3 mL), the organic layer
was extracted with CHCl3 (10 mL twice), dried with Na2SO4, and
concentrated under reduced pressure. The resulting residue was
purified by silica gel column chromatography (CHCl3/MeOH =
300:1) to afford 10 as a yellow powder (20.0 mg, 57% yield); m.p.
300 °C (recrystallized from CHCl /hexane). IR (ATR): ν = 3073,
˜
3
3003, 2940, 2840, 1567, 1525, 1459 1421, 1305, 1278, 1260, 1227,
1148, 1097, 1069, 1014, 891, 744, 709, 631, 585, 563 cm–1. 1H NMR
(300 MHz, CDCl3/TMS): δ = 8.30 (s, 3 H), 7.98 (d, J = 8.0 Hz, 3
H), 7.81 (d, J = 8.4 Hz, 6 H), 7.76 (br. t, J = 8.0 Hz, 3 H), 7.48 (d,
J = 5.5 Hz, 3 H), 7.36 (d, J = 8.4 Hz, 6 H), 7.01 (ddd, J = 1.1, 5.5,
8.0 Hz, 3 H), 6.12 (s, 3 H), 3.19 (s, 9 H) ppm. 13C NMR (75 MHz,
CDCl3/TMS): δ = 55.04, 118.86, 119.35, 120.81, 122.47, 124.74,
128.53, 129.43, 137.28, 137.44, 138.89, 140.74, 146.99, 157.14,
164.24, 173.44 ppm. ESI-MS: m/z calcd. for C54H39IrN3O9S3Cl3
[M]+: 1265.0515; found 1265.0512. C54H39Cl3IrN3O9S3·0.33CHCl3:
calcd. C 49.87, H 3.03, N 3.21; found C 49.58, H 2.89, N 3.28.
Ͼ 300 °C (recrystallized from CHCl /hexane). IR (ATR): ν = 3070,
˜
3
3006, 2934, 2839, 1578, 1459, 1422, 1295, 1137, 955, 888, 772, 742,
534, 508 cm–1. 1H NMR (300 MHz, CDCl3/TMS): δ = 8.21 (s, 3
H), 7.96 (d, J = 8.1 Hz, 3 H), 7.73 (br. t, J = 7.9 Hz, 3 H), 7.47 (d,
J = 5.5 Hz, 3 H), 7.00 (br. t, J = 6.4 Hz, 3 H), 6.46 (s, 3 H), 3.58
(s, 9 H), 3.14 (s, 9 H) ppm. ESI-MS: m/z calcd. for C39H36IrN3O9S3
[M]+: 977.1214; found 977.1209. C39H36IrN3O9S3·0.25CHCl3:
calcd. C 46.72, H 3.62, N 4.16; found C 46.65, H 3.44, N 4.18.
Complex 10 was also obtained by a procedure analogous to that
used to prepare 11. A mixture of 15 (5.0 mg, 4.5 μmol), CuI (10 mg,
54 μmol), and sodium methanesulfinate (8.3 mg, 81 μmol) in dry
DMF (0.5 mL) was heated at 110 °C for 25 h. The resulting residue
was purified by silica gel column chromatography (CHCl3/MeOH
= 100:1) to afford 10 as a yellow powder (2.8 mg, 64% yield).
Complex 15: NIS (72.4 mg, 322 μmol) was added to a solution of
6 (60.0 mg, 80.6 μmol) in dry CH2Cl2 (15 mL) in the dark, and the
reaction mixture was stirred at room temperature for 8.5 h. The
reaction mixture was concentrated under reduced pressure, and the
resulting residue was purified by silica gel column chromatography
(CHCl3/hexane = 2:1 to CHCl3) to afford 15 as a yellow powder
(71.0 mg, 78% yield); m.p. 247–249 °C (recrystallized from CHCl3/
Measurements of UV/Vis Absorption and Luminescence Spectra:
UV/Vis spectra were recorded with a JASCO V-550 and V-630BIO
UV/Vis spectrophotometer, and emission spectra were recorded
with a JASCO FP-6200 spectrofluorometer at 298 K. Sample solu-
tions in quartz cuvettes equipped with Teflon septum screw caps
were bubbled with solvent saturated argon for 10 min before the
luminescence measurements. The quantum yields of luminescence
(Φ) were determined by comparison with the integrated corrected
emission spectrum of a quinine sulfate standard, the emission
quantum yield of which in 0.1 m H2SO4 was assumed to be 0.55[35]
(excitation at 366 nm). For the calculation of emission quantum
yields, Equation (1) was used, in which Φs and Φr denote the quan-
tum yields of the sample and reference compound, ηs and ηr are
the refractive indexes of the solvents used for the measurements of
the sample and reference, As and Ar are the absorbance of the sam-
hexane). IR (ATR): ν = 3063, 2995, 2951, 2930, 2831, 1599, 1555,
˜
1519, 1455 1418, 1262, 1245, 1225, 1154, 1064, 1026, 871, 849, 777,
1
738, 603 cm–1. H NMR (CDCl3/TMS): δ = 7.95 (s, 3 H), 7.74 (d,
J = 8.1 Hz, 3 H), 7.61 (dt, J = 8.1, 5.5 Hz, 3 H), 7.45 (d, J = 5.5 Hz,
3 H), 6.86 (br. t, J = 6.4 Hz, 3 H), 6.36 (s, 3 H), 3.49 (s, 9 H) ppm.
ESI-MS: m/z calcd. for C36H27IrN3O3I3 [M]+: 1120.8787; found
1120.8805. C36H27I3IrN3O3·1.2CHCl3: calcd. C 35.30, H 2.25, N
3.32; found C 35.15, H 1.97, N 3.26.
Complex 11: CuI (102 mg, 534 μmol) was added to a solution of
15 (50.0 mg, 44.5 μmol) in dry DMF (3 mL) and stirred at room
temperature for 10 min. Sodium p-toluenesulfinate (95.1 mg,
534 μmol) was added, and the mixture was heated at 110 °C for
44 h. The reaction mixture was allowed to cool to room tempera-
5366
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Eur. J. Inorg. Chem. 2011, 5360–5369

Blue-Emitting Cyclometalated Iridium(III) Complexes
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Acknowledgments
This work was supported by grants-in-aid from the Ministry of
Education, Culture, Sports, Science and Technology (MEXT) of
Japan (grant numbers 19659026, 22390005, and 22659055 – to
S. A. – and grant number 22890200, to Y. H.) and the “Academic
Frontier” project for private universities, a matching-fund subsidy
from MEXT, 2009-2013. Y. H. is thankful for a grant-in-aid for
Research Activity Start-up from MEXT. We thank Dr. Tatsuo
Nakagawa (Unisoku, Osaka, Japan) for the measurement of lumi-
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The emission spectrum of 11 in frozen CH2Cl2 at 77 K exhibits
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Information and ref.[11c]). The emission maxima of 11 appear
at 459 nm, and additional intense peaks appear 491 nm.
We assume the low emission quantum yield of tris(iodo) deriv-
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[23]
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The luminescence lifetime of 15 is Ͻ12 ns at 298 K. Some Ir
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peak) nm] (Figure S2), thereby suggesting its emission through
the triplet state.
5
–1
[25]
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Complexes 6–12 and 14 have similar radiative (kr ≈ 10 s ) and
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porting Information), which were calculated according to the
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manuscript are irreversible (Figure S4 in the Supporting Infor-
mation). Potential gaps (E1 [V] = E – Erped) between the first
ox
1/2
ox
oxidation (E ) and reduction (Erped) potential are 2.97 V for
1/2
6, 2.98 V for 15, 3.00 V for 9, and 3.1–3.3 V for 7, 8, and 10–
12 (Table S2). It is assumed that greater potential gaps of 7–12
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(4 nm), 9 (9 nm), and 7, 8, and 10–12 (approximately 30 nm).
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Published Online: October 25, 2011
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www.eurjic.org
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