Phosphorescent emitters from natural products: Cinchonine-derived iridium(III) complexes

Article abstract of DOI:10.1021/om100993u

The natural product cinchonine is readily converted into novel cyclometalating and coordinating ligands that can be used to prepare phosphorescent Ir(III) complexes. These phosphorescent emitters are very soluble in organic solvents and exhibit relatively

Full text of DOI:10.1021/om100993u

ARTICLE
pubs.acs.org/Organometallics
Phosphorescent Emitters from Natural Products: Cinchonine-Derived
Iridium(III) Complexes
Wenhua Zhang,† Jianjin Hu,† David J. Young,*,‡ and T. S. Andy Hor*,†,§
†Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543, Singapore
‡Faculty of Science, Universiti Brunei Darussalam, Jalan Tungku Link, Gadong BE 1410, Brunei Darussalam
§Institute of Materials Research and Engineering, Agency for Science, Technology and Research, 3 Research Link, S117602 Singapore
S Supporting Information
b
ABSTRACT: The natural product cinchonine is readily converted into
novel cyclometalating and coordinating ligands that can be used to
prepare phosphorescent Ir(III) complexes. These phosphorescent
emitters are very soluble in organic solvents and exhibit relatively high
quantum efficiencies.
’ INTRODUCTION
same way as the dendritic environments elegantly engineered by
Burn and co-workers.7
Cinchona alkaloids have a long therapeutic history and
are enjoying renewed interest as synthetic targets,1 efficient
organocatalysts,2 and chiral resolution reagents.3 Appropriately
placed donor atoms make them inexpensive chelating ligands
for chiral metal catalysts.4 We reasoned that, with relatively
straightforward synthetic modifications, Cinchona alkaloid deri-
vatives could also be a novel source of cyclometalating and
coordinating ligands for phosphorescent metal complexes with
potential applications as emitters in organic light-emitting diodes
(OLEDs) and light-emitting electrochemical cells (LECs).5 The
bulky 1-azabicyclo[2.2.2]octane moiety could impart improved
solubility in solvents or in a polymer host, reducing aggregation
and thereby reducing quenching of the luminescence through
tripletꢀtriplet annihilation.6 Herein, we report the synthesis and
photophysical properties of phosphorescent iridium complexes
of the three cinchonine-derived ligands L1ꢀL3 (Chart 1).
Neutral Ir(III) complexes were prepared from L1 or L2 as
cyclometalating ligands in combination with a variety of ancillary
ligands. The combination of L1 or L2 and coordinating ligand
L3 yields ionic Ir(III) complexes (Chart 2). The steric bulk of the
cinchonine-derived ligand protects the emissive core of the
complex and improves the solubility of the complex, in much the
’ RESULTS AND DISCUSSION
A five-step modification of inexpensive cinchonine provided
20-chloro-9-O-benzyl-10,11-dihydrocinchonine (28% overall
yield), from which ligands L1 and L2 were prepared by a
SuzukiꢀMiyaura coupling with the corresponding arylboronic
acid and L3 was prepared by SNAr displacement with hydrazine
followed by condensation with acetylacetone (Scheme 1). Alter-
natively, L1 could be directly synthesized from 9-O-benzyl-10,
11-dihydrocinchonine or 9-O-benzyl-10,11-dihydrocinchonine
N0-oxide as starting materials and phenyllithium or phenylmag-
nesium bromide. Reaction of IrCl3 xH2O with 3 equiv of L1 or
3
L2 by the well-established Nonoyama route8 provided the
dinuclear complexes [Ir(L1)2Cl]2 (1) and [Ir(L2)2Cl]2 (2) in
44% and 24% yields, respectively. Subsequent treatment of 1
with the ancillary ligands acetylacetone (acacH), dibenzoyl-
methane (dbm), 2-picolinic acid (pic), and isoquinoline-1-car-
boxylic acid (iq) in the presence of base yielded the four neutral
complexes Ir(L1)2(acac) (3), Ir(L1)2(dbm) (4), Ir(L1)2(pic)
Received: October 19, 2010
Published: March 31, 2011
r
2011 American Chemical Society
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(5), and Ir(L1)2(iq) (6) (Chart 2).9 Treatment of 1 with L3
followed by anion exchange with NH4PF6 gave rise to two
diastereomeric, ionic complexes [Ir(L1)2(L3)][PF6] (7a,b),
which were separated by chromatography on neutral alumina.
The analogous reaction of 2 with L3 provided the fluorine-
substituted [Ir(L2)2(L3)][PF6] (8) as a mixture of diastereo-
mers which were not separated. All of these complexes could be
prepared in moderate to high yield. Complexes 1ꢀ8 were highly
soluble in CH2Cl2, DMF, and DMSO and readily soluble in other
common solvents such as CHCl3, MeCN, and MeOH.
characterized by FT-IR spectra and their bulk purity confirmed
by elemental analyses. Unfortunately, single crystals suitable for
X-ray diffraction studies have so far proved elusive.
The UVꢀvis absorption and emission data for complexes
3ꢀ6, 7a, and 8 are recorded in Table 1 and Figures 1 and 2.
The diastereomeric complexes 7a,b exhibited identical UV/vis
absorption and emission profiles, quantum yields, and lifetimes.
The intense bands for all complexes in the high-energy portion of
the spectra between 230 and 350 nm can be assigned to the spin-
allowed 1(πꢀπ*) transitions of the ligands. The weaker and low-
energy bands at wavelengths longer than 440 nm suggests
Molecular ions [M þ H]þ (M = neutral complexes) or [M]þ
(M = charged complexes) were observed in the ESI mass spectra
at m/z 1214.6 (3), 1339.0 (4), 1238.3 (5), 1288.5 (6), 1595.7
(7a,b), and 1668.5 (8). The corresponding cationic fragments
[Ir(L1)2]þ and [Ir(L2)2]þ (3ꢀ8) and dicationic species [M þ
2H]2þ (3ꢀ6), [Ir(L1)2þH]2þ (7), and [Ir(L2)2þH]2þ (8)
were also diagnostic. 1H and 13C NMR spectra were complex, but
the protons ortho to the cyclometalated carbon appeared
characteristically at ca. 6.5 ppm.10 Complexes 3ꢀ8 were further
3
substantial mixing of spin-forbidden MLCT and higher lying
1MLCT transitions facilitated by the strong spinꢀorbit coupling
of the Ir(III) center.11 It should be noted that the spectra observed
for all these complexes are similar, suggesting that the dominant
absorptions are due to the “(L1)2Ir” or “(L2)2Ir” fragment.
Complexes 3ꢀ8 gave emissions in a broad color range from
green (547 nm, 8) to red (608 nm, 4) (Figure 3), with phospho-
rescence quantum yields between 0.05 and 0.51 and lifetimes in
the range of 4.2ꢀ11.5 μs for degassed CH2Cl2 solutions at room
temperature. By way of comparison, complex 3 has a UV/vis
absorption and emission profile almost identical with that reported
for the simple analogue Ir(QN)2(acac) (QN = 2-phenylquinolyl-N,
C) but exhibits a higher quantum efficiency (0.19 versus 0.1).12 The
triplet levels of the acac ligand of 3 lie above the energies of L1 and
MLCT excited states, and the luminescence is thus dominated by
the L1 and MLCT transitions. The longer emission wavelength and
relatively low quantum efficiency of 4 can be attributed to the lower
Chart 1
1
triplet-state energy of dbm relative to L1 or the MLCT in this
complex. The emission spectra of complexes 7a and 8 are blue-
shifted relative to 3ꢀ6, suggesting that for these cationic Ir(III)
complexes, the HOMO consists mainly of a mixture of Ir d and
phenyl π orbitals, while the LUMO has significant chelating ligand
character, as previously calculated for cationic complexes with a
bipyridyl auxiliary ligand.13,14 The emission of 8 is blue-shifted by
19 nm relative to 7a, because of the influence of the electron-
withdrawing fluorine atoms on the HOMO located predominantly
on the cyclometalating ligand.
Chart 2
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ARTICLE
Scheme 1. Synthetic Procedures for L1ꢀL3
Table 1. Photophysical Data of of 3ꢀ6, 7a, and 8 in Degassed
CH2Cl2 at Room Temperature
UVꢀvis (nm)
λmax (nm)
Φ a
τ (μs)
3
230, 272, 348, 431, 472
231, 271, 347, 429, 473
231, 274, 346, 408, 463
230, 279, 343, 413, 464
232, 276, 244, 444
597
608
580
592
566
547
0.19
0.05
0.20
0.51
0.06
0.29
4.2
4.3
4
5
4.6
6
4.6
7a
8
10.1
11.5
224, 260, 280, 336, 439
a With respect to Rhodamine 6G (Φ = 0.95 in ethanol).
Figure 2. Luminescence spectra of 3ꢀ6, 7a, and 8 recorded in degassed
CH2Cl2 solutions at room temperature.
focus on dispersion of these emitters on solid supports or in a
polymer host.
’ EXPERIMENTAL SECTION
General Considerations. All synthetic procedures involving
IrCl3 xH2O and other Ir(III) species were carried out in the dark and
3
under a N2 atmosphere using standard Schlenk techniques. Elemental
analyses were performed on a Perkin-Elmer PE 2400 CHNS elemental
analyzer. The 1H and 13C NMR spectra were recorded on a Bruker AMX
500 MHz spectrometer, and their chemical shifts were referenced to
Me4Si (TMS). The 19F NMR spectra were recorded on a Bruker ACF
300 spectrometer. IR spectra were recorded on a Bruker IFS 48 FTIR
spectrometer using KBr as pellets. UVꢀvis spectra were recorded on
a UVIKON spectrometer. Electrospray mass spectra were obtained in
positive-ion mode with a Finnigan/MAT LCQ mass spectrometer.
Peaks were assigned from the m/z values and the isotope distribution
patterns. Photoluminescence was measured using a Perkin-Elmer LS55
luminescence spectrometer, and the quantum yield was determined
using Rhodamine 6G (quantum yield 0.96 in ethanol) as reference at
room temperature using degassed CH2Cl2 or EtOH solvents.15 The
phosphorescence lifetime was measured using an Edinburgh FL920P
lifetime spectrometer.
Figure 1. UVꢀvis spectra of 3ꢀ6, 7a, and 8 recorded in degassed
CH2Cl2 solutions at room temperature.
In summary, we have demonstrated that the abundant natural
product cinchonine is readily converted to novel cyclometalating
and coordinating ligands that can be used to prepare phospho-
rescent Ir(III) complexes. These phosphorescent emitters are
very soluble in organic solvents and exhibit relatively high quantum
efficiencies. Some emission color tuning is possible by variation of
the auxiliary ligands. We propose that these changes in solubility
and photophysical properties relative to simple cyclometalated
Ir(III) complexes are the result of the extraneous bulk of the natural
product and benzyl protecting group, both of which increase solu-
bility and partially encapsulate the emitting core, reducing inter-
molecular quenching of the phosphorescence. Future work will
Synthesis of 20-Phenyl-9-O-benzyl-10,11-dihydrocincho-
nine (L1). Method A. Phenyllithium was prepared by adding bromo-
benzene (3.74 g, 24 mmol) in anhydrous Et2O (30 mL) to lithium metal
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2H), 8.01 (s, 1H), 7.73ꢀ7.76 (m, 1H), 7.57ꢀ7.60 (m, 1H), 7.34ꢀ7.38
(m, 4H), 7.28ꢀ7.32 (m, 1H), 7.03ꢀ7.07 (m, 1H), 6.94ꢀ6.98 (m, 1H),
5.38 (br, 1H), 4.41ꢀ4.56 (AB quartet, 2H), 3.12 (br, 1H), 3.03 (br, 1H),
2.80ꢀ2.91 (m, 2H), 2.69ꢀ2.75 (m, 1H), 2.07ꢀ2.09 (m, 1H), 1.31ꢀ1.51
(m, 7H), 0.85 (t, J = 7.0 Hz, 3H). 13C{1H} NMR (125 MHz, CDCl3): δ
171.6, 165.1 (d, JCꢀF = 12.0 Hz), 163.1 (d, JCꢀF = 12.0 Hz), 162.5 (d, JCꢀF
= 12.0 Hz), 160.5 (d, JCꢀF = 12.0 Hz), 153.3, 149.4, 147.4, 138.4,
133.2ꢀ133.4 (q), 131.2, 130.0, 128.9, 128.7, 128.3, 127.3, 126.2,
125.0ꢀ125.2 (dd, J = 3.7 Hz, 12.0 Hz), 123.8, 120.4, 112.5ꢀ112.7 (dd,
J = 3.5 Hz, 21.1 Hz), 104.8ꢀ105.2 (m), 81.7, 72.2, 61.2, 51.5, 50.8, 38.1,
28.0, 27.0, 25.9, 12.6. 19F{1H} NMR (282 MHz, CDCl3): δ ꢀ32.7 (d, J =
8.7 Hz, 1F), ꢀ36.5 (d, J = 8.7 Hz, 1F). MS (ESI): 499.2 [M þ H]þ. Anal.
Calcd for C32H32F2N2O: C, 77.08; H, 6.47; N, 5.62. Found: C, 74.85; H,
6.02; N, 5.22; corresponding to L2 þ 0.5EA.
Synthesis of 20-(3,5-Dimethylpyrazole)-9-O-benzyl-10,11-
dihydrocinchonine (L3). 9-O-Benzyl-20-chloro-10,11-dihydro-
cinchonine (0.84 g, 2 mmol) and NH2NH2 (4.27 g, 60% aqueous
solution, 40 equiv) were dissolved in EtOH (50 mL). After reflux under
N2 for 48 h, the mixture was cooled to room temperature and the solvent
removed under vacuum. Ethyl acetate (50 mL) was added, and the
organic phase was successively washed with water (3 ꢁ 50 mL) and
brine (50 mL). The organic phase was dried over anhydrous Na2SO4
and the solvent removed to give an orange, oily crude product (0.73 g),
which was dried under vacuum and used without further purification.
A mixture of crude 20-hydrazine-9-O-benzyl-10,11-dihydrocincho-
nine (0.73 g, 1.76 mmol) and acetylacetone (0.2 g, 2 mmol) was added
to EtOH (50 mL), and the mixture was refluxed under N2 for 48 h. The
solvent was removed to give an orange, oily product, which was dried
under vacuum. The product was purified by chromatography on silica
(EA/MeOH 20/1 (v/v)) to give a yellowish oil (0.50 g, 52% over two
steps). 1H NMR (500 MHz, CDCl3): δ 8.30 (s, 1H), 8.19 (br, 1H), 8.00
(d, J = 8.3 Hz, 1H), 7.60ꢀ7.63 (m, 1H), 7.45ꢀ7.48 (m, 1H), 7.36ꢀ7.38
(m, 2H), 7.29ꢀ7.32 (m, 2H), 7.23ꢀ7.25 (m, 1H), 5.99 (s, 1H), 5.35 (br,
1H), 4.37ꢀ4.53 (AB quartet, 2H), 3.18 (br, 1H), 2.99 (br, 1H),
2.85ꢀ2.89 (m, 1H), 2.80 (br, 4H), 2.64ꢀ2.70 (m, 1 H), 2.32 (s, 3H),
2.03ꢀ2.08 (m, 1H), 1.25ꢀ1.44 (m, 7H), 0.80 (t, J = 6.9 Hz, 3H).
13C{1H} NMR (125 MHz, CDCl3): δ 152.7, 150.2, 149.2, 147.5, 142.5,
138.2, 129.9, 129.8, 128.7, 128.1, 126.1, 125.1, 124.0, 113.4, 110.0, 81.4,
72.0, 60.9, 51.0, 50.3, 37.8, 27.6, 26.7, 25.6, 22.6, 15.6, 14.2, 12.3. MS
(ESI): 481.4 [M þ H]þ. Anal. Calcd for C31H36N4O: C, 77.47; H, 7.55;
N, 11.66. Found: C, 73.79; H, 6.00; N, 9.65; corresponding to L3 þ EA.
Figure 3. Emission photos of 3ꢀ6, 7a, and 8 recorded in degassed
CH2Cl2 solutions at room temperature.
(0.18 g, 26 mmol) in anhydrous Et2O under nitrogen. This was carried
out by adding a small aliquot of the bromobenzene solution (2 mL) with
heating to initiate the reaction. A white suspension indicated that
initiation had occurred, and then the remaining bromobenzene solution
was added dropwise and the reaction mixture stirred for 3 h. 9-O-Benzyl-
10,11-dihydrocinchonine (3.87 g, 10 mmol) was added to Et2O (40 mL)
and the solution vigorously stirred. The suspension was transferred to
the preformed lithium reagent and the reaction mixture stirred over-
night. The mixture was added to ice water, acidified with dilute HCl, and
extracted using CHCl3. The product was purified by chromatography on
silica (EA/MeOH 15/1 as eluent). Yield: 0.74 g (16%).
Method B. Phenylmagnesium bromide was prepared from bromo-
benzene (3.12 g, 20 mmol) and magnesium turnings (0.48 g, 20 mmol)
in freshly distilled THF (20 mL). 9-O-Benzyl-10,11-dihydrocinchonine
N0-oxide (4.03 g, 10 mmol) was dissolved in dry THF (40 mL) and
slowly added to the Grignard reagent. The resulting mixture was stirred
for 1 h, quenched with ice water, and acidified with HCl. CHCl3 (60 mL)
was added and stirred for 15 min. The organic layer was separated,
filtered, washed with water, concentrated, and purified by chromatog-
raphy on silica (EA/MeOH 15/1 as eluent). Yield: 2.77 g (60%).
Method C. 9-O-Benzyl-20-chloro-10,11-dihydrocinchonine (2.1 g, 5.0
mmol) and phenylboronic acid (0.58 g, 5.5 mmol) were dissolved in 1,
2-dimethoxyethane (50 mL), and the solution was degassed. PdCl2-
(dppf) (0.18 g, 0.025 mmol) was added and the mixture degassed again.
Finally, degassed aqueous Na2CO3 (5.3 g in 10 mL of water) was
injected via syringe and the solution refluxed for 5 h. After the mixture
was cooled to room temperature, the solvent was removed and CH2Cl2
(50 mL) added. The organic layer was washed with brine (3 ꢁ 50 mL)
and then dried over anhydrous Na2SO4. The solvent was removed, and
the crude product was purified by chromatography on silica using EA/
MeOH 15/1 as eluent to give a brown oil (1.90 g, 82%).
Synthesis of 1. IrCl3 xH2O (0.30 g, 1 mmol) and L1 (1.20 g, 2.6
3
mmol) were mixed in a double-necked flask, and the system was flushed
with N2 three times. A mixture of 2-ethoxyethanol and water (12 mL, 3/
1 v/v) was deoxygenated with a N2 stream for 3 min and injected into the
flask. The mixture was refluxed at 140 °C for 60 h in the dark. The
mixture was then cooled to room temperature, and CH2Cl2 (200 mL)
and brine (50 mL) were added. The CH2Cl2 phase was separated,
washed with brine (3 ꢁ 50 mL), and dried over anhydrous Na2SO4. The
solvent was removed and the crude product purified by chromatography
on neutral Al2O3 (ethyl acetate/methanol, 50/1 v/v) to give thr dark
red product 1 (0.51 g, 44% based on Ir). Mp: 142 °C. 1H NMR (500
MHz, CD2Cl2): δ 8.69ꢀ8.73 (m, 2H), 8.26ꢀ8.36 (m, 4H), 7.91ꢀ7.94
(m, 2H), 7.39ꢀ7.70 (m, 16H), 7.00ꢀ7.03 (m, 2H), 6.66ꢀ6.69 (m, 2H),
6.36ꢀ6.38 (m, 2H), 5.36ꢀ5.57 (m, 2H), 4.46ꢀ4.76 (m, 4H),
3.46ꢀ3.58 (m, 1H), 3.25ꢀ3.35 (m, 2H), 2.74ꢀ2.99 (m, 9H), 2.46
(br, 3H), 2.04ꢀ2.17 (m, 2H), 1.37ꢀ1.83 (m, 19H), 0.97ꢀ1.02 (m, 6H).
13C{1H} NMR (125 MHz, CD2Cl2): δ 186.2, 168.9, 150.8, 148.6, 148.3,
146.5, 146.5, 145.7, 138.3, 134.8, 130.7, 129.3, 128.7, 128.5, 128.1, 127.1,
126.7, 126.4, 123.9, 121.6, 120.9, 114.5, 80.0, 72.2, 62.0, 61.4, 51.3, 50.3,
50.2, 37.9, 27.7, 26.7, 25.8, 25.7, 24.8, 23.5, 12.1 ppm. MS (ESI,
CH2Cl2): m/z 558.7 [Ir(L1)2 þ H]2þ; 1115.8 [Ir(L1)2]þ. Anal. Calcd
for C128H132Cl2Ir2N8O4: C, 66.79; H, 5.78; N, 4.87. Found: C, 66.39; H,
5.73; N, 4.66.
1H NMR (500 MHz, CDCl3): δ 8.27 (d, J = 8.3 Hz, 1H), 8.15ꢀ8.20
(m, 3H), 8.04 (s, 1H), 7.74ꢀ7.76 (m, 1H), 7.53ꢀ7.59 (m, 3H),
7.46ꢀ7.49 (m, 1H), 7.36ꢀ7.38 (m, 4H), 7.32ꢀ7.34 (m, 1H), 5.43
(br, 1H), 4.47ꢀ4.55 (AB quartet, 2H), 3.09ꢀ3.12 (m, 2H), 2.90ꢀ2.95
(m, 1H), 2.83ꢀ2.88 (m, 1H), 2.71ꢀ2.77 (m, 1H), 2.10ꢀ2.14 (m, 1H),
1.41ꢀ1.54 (m, 6H), 1.26ꢀ1.30 (m, 1H), 0.90 (t, J = 7.0 Hz, 3H).
13C{1H} NMR (125 MHz, CDCl3): δ 157.6, 149.4, 147.8, 140.4, 138.6,
131.4, 130.0, 129.9, 129.4, 129.0, 128.6, 128.4, 128.2, 126.9, 126.2, 123.7,
117.0, 81.8, 72.2, 61.2, 51.6, 50.8, 38.2, 28.0, 27.1, 25.9, 22.4, 12.6. MS
(ESI): 463.3 [M þ H]þ. Anal. Calcd for C32H34N2O: C, 83.08; H, 7.41;
N, 6.06. Found: C, 74.38; H, 6.66; N, 4.64; corresponding to L1 þ 2EA.
Synthesis of 20-(2,4-Difluorophenyl)-9-O-benzyl-10,11-di-
hydrocinchonine (L2). Ligand L2 was prepared using the Suzuki
reaction described for L1. The crude product was purified by chroma-
tography on silica (EA/MeOH 20/1) to give a brown oil (2.0 g, 80%).
1H NMR (500 MHz, CDCl3): δ 8.23ꢀ8.24 (m, 1H), 8.13ꢀ8.20 (m,
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Synthesis of 2. Complex 2 was synthesized using the same
procedure described for 1. The crude product was purified by chroma-
tography on neutral Al2O3 (acetate/methanol, 100/1 v/v). Yield: 0.35 g
(24% based on Ir). Mp: 146 °C. 1H NMR (500 MHz, CD2Cl2): δ 8.75
(br, 1H), 8.67 (br, 1H), 8.53ꢀ8.56 (br, 3H), 8.38ꢀ8.39 (m, 1H), 7.69ꢀ7.72
(m, 4H), 7.37ꢀ7.51 (m, 12H), 6.55ꢀ6.59 (m, 2H), 5.85ꢀ5.90 (m, 2H),
5.70 (br, 1H), 5.53 (br, 1H), 4.61ꢀ4.74 (m, 4H), 3.48 (br, 1H), 3.34 (br,
2H), 2.79ꢀ3.02 (m, 10H), 2.15ꢀ2.16 (m, 2H), 1.83 (br, 2H), 1.35ꢀ1.66
(m, 21H), 0.93ꢀ0.96 (m, 9H). 13C{1H} NMR (125 MHz, CD2Cl2): δ
187.0, 168.9, 165.9, 165.8, 165.7, 165.6, 163.2, 163.1, 162.6, 162.5, 161.2, 161.1,
160.5, 160.4, 150.8, 150.4, 148.6, 148.5, 148.5, 148.4, 147.8, 147.6, 137.8, 130.8,
130.7, 130.6, 128.5, 128.4, 128.3, 128.3, 127.9, 127.8, 126.9, 126.8, 126.3, 126.0,
124.6, 123.9, 116.8, 116.7, 98.2, 98.0, 97.8, 72.1, 72.0, 61.4, 60.9, 50.9, 50.5, 49.9,
49.9, 37.4, 29.7, 27.0, 27.0, 26.4, 26.4, 25.4, 25.3, 24.4, 24.3, 22.7, 11.7 ppm.
19F{1H} NMR (282 MHz, CD2Cl2): δ ꢀ32.96 (ꢀ33.03) (m, 2F), ꢀ33.53
(ꢀ33.68) (m, 2F). MS (ESI, CH2Cl2): m/z 1187.5 [Ir(L2)2]þ. Anal. Calcd
for C128H124Cl2F8Ir2N8O4: C, 62.86; H, 5.11; N, 4.58. Found: C, 62.64; H,
5.44; N, 4.27.
Synthesis of 3. A mixture of 1 (0.23 g, 0.1 mmol), acetylacetone
(0.034 g, 0.34 mmol), and K2CO3 (0.14 g, 1.0 mmol) were dissolved in
1,2-dichloroethane (30 mL), and this mixture was then degassed, flushed
with N2 three times, and refluxed under N2 for 8 h. The mixture was then
cooled to room temperature, the solvent removed, and the resulting red
residue redissolved in CH2Cl2 (100 mL). The organic phase was washed
with brine (3 ꢁ 50 mL) and dried over anhydrous Na2SO4. The solvent
was removed, and the crude product was dried under vacuum and
purified by chromatography on neutral Al2O3 using ethyl acetate as
eluent to give a dark red solid (3). Yield: 0.19 g (78% based on Ir). Mp:
152 °C. 1H NMR (500 MHz, CD2Cl2): δ 8.36ꢀ8.40 (m, 2H),
8.01ꢀ8.14 (m, 3H), 7.73ꢀ7.79 (m, 2H), 7.20ꢀ7.41 (m, 12H),
6.84ꢀ6.87 (m, 2H), 6.45ꢀ6.56 (m, 3H), 5.35 (s, 1H), 4.64ꢀ4.64 (m,
1H), 4.43ꢀ4.56 (m, 3H), 3.06 (br, 1H), 2.75ꢀ2.89 (m, 4H), 2.53ꢀ2.69
(m, 4H), 2.27 (br, 1H), 1.88ꢀ2.00 (m, 2H), 1.60ꢀ1.63 (m, 2H),
1.22ꢀ1.45 (m, 18H), 0.78ꢀ0.82 (m, 6H). 13C {1H} NMR (125 MHz,
CDCl3): δ 186.2, 186.0, 169.6, 149.9, 149.8, 149.6, 149.3, 149.2, 147.7,
147.6, 138.1, 138.0, 136.1, 136.0, 130.2, 130.1, 128.8, 128.5, 128.4, 128.3,
128.2, 128.0, 127.9, 127.2, 127.1, 126.3, 126.2, 126.0, 125.9, 125.8, 123.7,
121.1, 100.3, 100.2, 71.9, 71.7, 61.4, 51.1, 51.0, 50.2, 50.1, 37.8, 37.7,
28.0, 27.9, 27.6, 27.5, 26.7, 26.6, 25.5, 25.4, 11.9. MS (ESI, CH2Cl2,
180 °C): m/z 558.6 [Ir(L1)2 þ H]2þ; 608.5 [3 þ 2H]2þ; 1115.6
[Ir(L1)2]þ; 1214.6 [3 þ H]þ. Anal. Calcd for C69H73IrN4O4: C, 68.23;
H, 6.06; N, 4.61. Found: C, 68.67; H, 6.21; N, 4.63.
8.82ꢀ8.84 (m, 1H), 8.35ꢀ8.37 (m, 2H), 7.97ꢀ8.20 (m, 6H),
7.81ꢀ7.83 (m, 1H), 7.68ꢀ7.72 (m, 1H), 7.41ꢀ7.61 (m, 14H),
7.29ꢀ7.34 (m, 1H), 7.09ꢀ7.19 (m, 2H), 6.93ꢀ7.00 (m, 2H),
6.77ꢀ6.87 (m, 2H), 6.44ꢀ6.47 (m, 1H), 5.36ꢀ5.49 (m, 2H),
4.43ꢀ4.78 (m, 4H), 3.25ꢀ3.31 (m, 1H), 2.67ꢀ3.06 (m, 8H), 2.48
(br, 2H), 2.15 (br, 2H), 1.81 (br, 2H), 1.52ꢀ1.65 (m, 13H), 0.96ꢀ1.00
(m, 6H). 13C{1H} NMR (125 MHz, CD2Cl2): δ 171.4, 170.0, 168.7,
152.8, 150.5, 150.4, 150.2, 148.3, 147.9, 147.4, 146.5, 145.9, 145.9, 138.1,
138.0, 137.7, 135.9, 134.8, 131.0, 129.8, 129.4, 129.3, 128.5, 128.4, 128.4,
128.3, 128.0, 128.0, 127.9, 127.9, 127.8, 127.8, 127.3, 127.0, 126.7, 126.5,
126.4, 126.4, 126.4, 126.2, 125.5, 124.7, 123.6, 122.0, 121.2, 72.0, 72.0,
71.8, 71.6, 61.6, 61.4, 61.2, 60.9, 60.3, 51.0, 51.0, 50.1, 50.1, 37.7, 27.6,
27.5, 26.6, 25.4, 25.4, 11.9. MS (ESI, CH2Cl2, 180 °C): m/z 557.6
[Ir(L1)2 þ H]2þ; 620.0 [5 þ 2H]2þ; 1115.6 [Ir(L1)2]þ; 1238.4 [5 þ
H]þ. Anal. Calcd for C70H70IrN5O4: C, 67.94; H, 5.70; N, 5.66. Found:
C, 62.77; H, 5.52; N, 5.28.
Synthesis of 6. Compound 6 was prepared in a fashion similar to
that for 3. The crude product was purified by chromatography on neutral
Al2O3 using ethyl acetate/methanol (50/1 v/v) as eluent. Yield: 0.21 g
1
(81% based on Ir). Mp: 200 °C. H NMR (500 MHz, CD2Cl2): δ
9.59ꢀ9.62 (m, 1H), 8.74ꢀ8.76 (m, 1H), 8.18ꢀ8.21 (m, 2H),
7.79ꢀ7.99 (m, 5H), 7.55ꢀ7.64 (m, 2H), 7.39ꢀ7.51 (m, 5H),
7.19ꢀ7.36 (m, 10H), 7.11ꢀ7.15 (m, 1H), 7.00ꢀ7.03 (m, 1H),
6.91ꢀ6.95 (m, 1H), 6.76ꢀ6.77 (m, 1H), 6.67ꢀ6.70 (m, 2H),
6.59ꢀ6.61 (m, 1H), 6.24ꢀ6.28 (m, 1H), 5.30ꢀ5.33 (m, 1H),
4.38ꢀ4.52 (m, 3H), 3.94 (s, 1H), 3.03ꢀ3.13 (m, 1H), 2.42ꢀ2.90 (m,
8H), 2.19 (br, 2H), 1.88ꢀ2.01 (m, 2H), 1.61ꢀ1.65 (br, 1H), 1.54 (br,
1H), 1.17ꢀ1.42 (m, 14H), 0.76ꢀ0.81 (m, 9H). 13C{1H} NMR (125 MHz,
CD2Cl2): δ 172.4, 170.2, 170.1, 169.3, 169.2, 152.1, 152.0, 151.3, 150.9,
150.8, 150.6, 150.1, 150.0, 150.0, 148.7, 148.6, 147.9, 147.9, 147.6, 147.5,
146.9, 141.9, 138.5, 138.3, 138.3, 138.3, 137.2, 136.9, 136.1, 135.0, 131.7,
131.7, 131.2, 131.2, 131.1, 130.8, 130.0, 129.7, 129.7, 129.5, 129.4, 129.3,
129.2, 129.2, 129.0, 128.9, 128.7, 128.7, 128.7, 128.6, 128.5, 128.4, 128.3,
128.3, 128.2, 128.1, 128.1, 128.0, 127.4, 127.1, 126.9, 126.7, 126.7, 126.6,
126.4, 126.4, 126.2, 126.0, 125.8, 124.2, 122.2, 121.4, 72.3, 72.2, 72.1, 71.8,
61.1, 53.0, 51.3, 50.4, 50.3, 50.3, 39.1, 38.0, 37.9, 30.7, 30.0, 29.3, 27.7, 27.6,
26.9, 26.9, 26.9, 25.7, 25.6, 24.1, 23.1, 14.1, 12.2, 12.1, 11.1. MS (ESI,
CH2Cl2, 180 °C): m/z 558.7 [Ir(L1)2 þ H]2þ; 645.2 [6 þ 2H]2þ; 1115.7
[Ir(L1)2]þ; 1288.4 [6 þ H]þ. Anal. Calcd for C74H72IrN5O4: C, 69.03; H,
5.64; N, 5.44. Found: C, 69.53; H, 6.10; N, 5.57.
Synthesis of 7a,b. Amixture of1(0.23 g, 0.1 mmol) andL3(0.096 g,
0.2 mmol) in a two-necked flask was flushed with N2 three times. A
CH2Cl2/MeOH mixture (20 mL/10 mL) was added under N2 and the
mixture refluxed for 12 h. The reaction mixture was cooled to room
temperature, and NH4PF6 (0.16 g, 1 mmol) in MeOH (5 mL) was added
under N2. The mixture was stirred for another 5 h and the solvent
evaporated. The resulting red residue was dried under vacuum, and
CH2Cl2 (5 mL) was added. NH4Cl was removed by filtration. The solvent
was evaporated and the product purified by chromatography on neutral
Al2O3 using ethyl acetate/hexane (4/1 v/v) and ethyl acetate/MeOH
(10/1 v/v) as eluents. Two red bands, 7a,b, were collected. Yield: 0.18 g
(51.7%) (7a) and 0.078 g (22.4%) (7b). Mp: 160 °C (7a), 165 °C (7b).
1H NMR (500 MHz, CD2Cl2) for 7a: δ 8.27ꢀ8.40 (m, 2H), 8.05ꢀ8.12
(m, 1H), 7.91ꢀ7.93 (m, 1H), 7.79ꢀ7.86 (m, 2H), 7.64ꢀ7.74 (m, 1H),
7.16ꢀ7.55 (m, 18H), 7.02ꢀ7.10 (m, 2H), 6.68ꢀ6.90 (m, 2H), 6.29ꢀ6.42
(m, 1H), 5.93ꢀ6.19 (m, 1H), 5.31ꢀ5.38 (m, 2H), 5.08ꢀ5.15 (m, 2H),
4.57ꢀ4.62 (m, 2H), 4.44ꢀ4.51 (m, 1H), 3.73ꢀ3.87 (m, 1H), 2.51ꢀ3.04
(m, 15H), 1.16ꢀ1.95 (m, 26H), 0.75ꢀ0.95 (m, 9H). 13C{1H} NMR(125
MHz, CD2Cl2) for 7a: δ 169.9, 169.7, 169.5, 169.2, 156.3, 155.8, 154.6,
152.6, 151.8, 151.2, 150.2, 149.8, 149.1, 148.9, 148.0, 147.3, 146.9, 146.7,
146.1, 146.0, 145.9, 144.9, 144.6, 144.0, 143.2, 137.7, 137.7, 137.6, 137.3,
137.2, 136.9, 133.4, 132.8, 132.3, 132.1, 131.8, 131.3, 131.1, 130.9, 130.9,
130.8, 130.7, 128.6, 128.6, 128.5, 128.5, 128.4, 128.4, 128.3, 128.2, 128.2,
128.1, 128.0, 128.0, 127.8, 127.7, 127.1, 126.9, 126.7, 126.7, 126.6, 126.5,
Synthesis of 4. Compound 4 was prepared using the method as
described for 3. The crude product was purified by chromatography on
neutral Al2O3 using ethyl acetate as eluent to give a dark red solid. Yield:
0.21 g (78% based on Ir). Mp: 178 °C. 1H NMR (500 MHz, CD2Cl2): δ
8.68ꢀ8.70 (m, 2H), 8.42ꢀ8.47 (m, 2H), 8.11ꢀ8.17 (m, 3H), 8.05ꢀ8.06
(m, 2H), 7.22ꢀ7.59 (m, 28H), 7.13ꢀ7.16 (m, 2H), 6.81ꢀ6.83 (m, 4H),
6.02ꢀ6.04 (m, 2H), 5.57 (br, 1H), 5.47 (br, 1H), 4.74ꢀ4.58 (m, 3H),
4.44ꢀ4.47 (m, 1H), 3.32ꢀ3.35 (m, 1H), 3.16 (br, 2H), 2.97ꢀ3.07 (m, 3H),
2.70ꢀ2.88 (m, 5H), 2.10ꢀ2.25 (m, 3H), 1.85 (br, 1H), 1.76 (br, 1H),
1.40ꢀ1.64 (m, 13H), 1.22ꢀ1.40 (m, 3H), 1.01ꢀ1.04 (m, 6H). 13C{1H}
NMR (125 MHz, CD2Cl2): δ 181.3, 181.1, 169.7, 169.5, 150.2, 150.1, 149.3,
149.2, 147.8, 147.7, 141.3, 141.2, 138.1, 138.0, 136.2, 130.3, 130.2, 130.0,
129.9, 128.8, 128.5, 128.4, 128.3, 128.1, 128.0, 127.9, 127.8, 127.2, 127.1,
126.4, 126.3, 126.3, 126.1, 125.9, 125.8, 125.6, 123.7, 121.2, 95.4, 95.3, 71.9,
71.6, 61.6, 60.8, 60.3, 51.1, 50.2, 50.1, 37.8, 37.7, 27.6, 27.4, 26.7, 26.6, 25.4,
11.9. MS (ESI, CH2Cl2, 180 °C): m/z 557.7: [Ir(L1)2 þ H]2þ; 670.5 [4 þ
2H]2þ; 1115.6 [Ir(L1)2]þ; 1339.0 [4 þ H]þ. Anal. Calcd for C79H77Ir-
N4O4: C, 70.88; H, 5.80; N, 4.19. Found: C, 70.53; H, 5.65; N, 4.04.
Synthesis of 5. Compound 5 was prepared in a fashion similar to
that for 3. The crude product was purified by chromatography on neutral
Al2O3 using ethyl acetate/methanol (75/1 v/v) as eluent. Yield: 0.12 g
1
(49% based on Ir). Mp: 227 °C. H NMR (500 MHz, CD2Cl2): δ
2141
dx.doi.org/10.1021/om100993u |Organometallics 2011, 30, 2137–2143

Organometallics
ARTICLE
126.3, 126.3, 126.2, 125.8, 125.5, 125.4, 125.3, 125.1, 125.0, 124.6, 124.4,
123.6, 123.2, 123.0, 122.9, 122.6, 114.2, 113.8, 108.7, 80.5, 80.0, 72.1, 72.1,
72.0, 71.9, 71.7, 61.9, 61.8, 61.6, 61.2, 51.0, 51.0, 50.9, 50.2, 50.1, 37.6, 37.5,
37.3, 27.5, 27.4, 27.4, 27.3, 27.3, 26.5, 26.5, 26.3, 26.2, 25.4, 25.3, 25.2, 25.2,
25.1, 22.0, 21.8, 14.8, 13.5, 12.3, 12.1, 11.8, 11.8, 11.7, 11.7, 11.6. 1H NMR
(500 MHz, CD2Cl2) for 7b: δ 8.28ꢀ8.40 (m, 2H), 8.05ꢀ8.13 (m, 1H),
7.80ꢀ7.93 (m, 3H), 7.54ꢀ7.74 (m, 1H), 7.18ꢀ7.51 (m, 14H), 7.04ꢀ7.10
(m, 2H), 6.68ꢀ6.90 (m, 2H), 5.93ꢀ6.42 (m, 2H), 5.10ꢀ5.41 (m, 2H),
4.44ꢀ4.62 (m, 2H), 3.73ꢀ4.29 (m, 2H), 2.52ꢀ3.28 (m, 12H), 1.18ꢀ2.05
(m, 24H), 0.76ꢀ0.93 (m, 7H). 13C{1H} NMR (125 MHz, CD2Cl2) for
7b: δ 169.7, 169.5, 156.3, 155.8, 150.2, 149.7, 148.0, 147.3, 146.7, 146.0,
144.9, 144.6, 144.0, 143.2, 137.7, 137.5, 137.3, 137.2, 136.9, 132.8, 132.2,
131.3, 131.1, 130.9, 130.7, 128.6, 128.6, 128.6, 128.6, 128.5, 128.5, 128.4,
128.3, 128.2, 128.2, 128.1, 128.1, 128.0, 127.8, 127.8, 127.6, 127.1, 126.9,
126.8, 126.7, 126.6, 126.5, 126.2, 125.5, 125.3, 125.1, 124.4, 123.6, 123.3,
123.0, 122.9, 122.6, 114.2, 108.7, 72.2, 72.1, 71.7, 61.8, 61.5, 50.1, 50.1,
37.6, 37.4, 37.3, 27.4, 27.2, 26.4, 26.4, 25.4, 25.1, 25.1, 14.8, 13.6, 12.3, 12.1,
11.8, 11.7, 11.6. MS (ESI, CH2Cl2) for 7a,b: m/z 799.1 [Ir(L1)2(L3) þ
H]2þ; 1115.8 [Ir(L1)2]þ; [Ir(L1)2(L3)]þ. Anal. Calcd for C95H102F6Ir-
N8O3P: C, 65.54; H, 5.91; N, 6.44. Found for 7a: C, 64.17; H, 5.12; N,
6.36. Found for 7b: C, 64.15; H, 5.05; N, 6.28.
Synthesis of 8. Complex 8 was synthesized from 2 (0.24 g, 0.1
mmol) and L3 (0.096 g, 0.2 mmol) using the same reaction conditions
described for the synthesis of 7. Purification by chromatography on a
neutral Al2O3 column using ethyl acetate/hexane (4/1 v/v) as eluent
provided 8 as a mixture of diastereomers which were not separated Yield:
0.12 g (33%). Mp: 190 °C. 1H NMR (500 MHz, CD2Cl2): δ
10.39ꢀ10.46 (m, 1H), 8.81ꢀ8.87 (m, 3H), 8.42ꢀ8.50 (m, 5H),
8.23ꢀ8.33 (m, 5H), 7.77ꢀ7.95 (m, 9H), 7.26ꢀ7.63 (m, 61H),
6.63ꢀ6.83 (m, 6H), 6.32ꢀ6.34 (m, 2H), 6.02ꢀ6.05 (m, 2H),
5.58ꢀ5.59 (m, 1H), 5.17ꢀ5.43 (m, 9H), 4.25ꢀ4.73 (m, 14H),
3.83ꢀ3.95 (m, 2H), 3.31ꢀ3.34 (m, 1H), 2.27ꢀ3.10 (m, 51H),
1.27ꢀ2.06 (m, 104 H), 0.83ꢀ0.99 (m, 40H). 13C{1H} NMR (125
MHz, CD2Cl2): δ 167.1, 167.0, 166.9, 166.8, 166.7, 166.6, 166.6, 164.2,
156.4, 156.2, 155.8, 155.2, 153.7, 153.5, 152.9, 152.9, 152.8, 152.2,
152.1, 152.0, 151.9, 150.2, 149.8, 148.9, 147.9, 147.0, 146.9, 146.8,
146.6, 146.6, 146.3, 145.3, 144.7, 144.6, 137.6, 137.6, 137.5, 137.2,
136.8, 132.3, 131.6, 131.4, 131.3, 131.1, 130.5, 130.4, 130.3, 130.2,
129.8, 128.7, 128.5, 128.5, 128.4, 128.4, 128.3, 128.2, 128.2, 128.1,
128.0, 128.0, 127.8, 127.7, 127.6, 127.3, 127.1, 127.1, 126.6, 126.4,
126.3, 126.1, 126.1, 125.9, 125.8, 125.5, 125.4, 125.3, 125.0, 124.7,
124.5, 124.0, 114.8, 114.1, 100.1, 100.0, 100.0, 99.8, 99.6, 99.5, 99.3,
99.3, 99.2, 99.0, 80.2, 72.2, 72.0, 71.9, 71.8, 71.7, 71.7, 69.3, 62.5, 61.7,
61.7, 61.4, 61.3, 51.0, 50.9, 50.7, 50.6, 50.2, 50.1, 50.0, 49.9, 49.9, 49.8,
37.6, 37.5, 37.4, 37.4, 37.3, 31.9, 31.6, 29.7, 29.4, 29.1, 29.0, 27.5, 27.4,
27.2, 26.5, 26.4, 26.3, 26.3, 26.2, 25.4, 25.3, 25.2, 25.1, 21.6, 21.4, 14.9,
13.9, 13.7, 13.5, 13.4, 12.7, 11.8, 11.7, 11.7, 11.6 ppm. 19F{1H} NMR
(282 MHz, CD2Cl2): δ 3.47, 0.95, ꢀ28.48 (d), ꢀ29.49 (d), ꢀ29.72
(d), ꢀ30.71 (d), ꢀ31.84 (d), ꢀ32.15 (d), ꢀ32.54 (d), ꢀ33.41, ꢀ33.75
ppm. MS (ESI, CH2Cl2): m/z 834.6 [Ir(L2)2(L3)þH]2þ; 1187.5
[Ir(L2)2]þ; 1668.5 [Ir(L2)2(L3)]þ. Anal. Calcd for C95H98F10IrN8O3P:
C, 62.93; H, 5.45; N, 6.18. Found: C, 62.06; H, 5.65; N, 5.86.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: andyhor@nus.edu.sg (T.S.A.H.); david.young@ubd.
edu.bn (D.J.Y.).
’ ACKNOWLEDGMENT
This work was supported by the Ministry of Education (R143-
000-323-112) and A*Star of Singapore. We thank Prof. Yun Chi
from National Tsing Hua University (Taiwan) for his help on the
phosphorescence lifetime measurements.
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’ ASSOCIATED CONTENT
S
Supporting Information.
Text giving the synthetic
b
procedure for 20-chloro-9-O-benzyl-10,11-dihydrocinchonine
and figures giving ESI, H NMR, 13C NMR spectra for all
1
complexes and decoupled 19F NMR spectra for L2, 2, and 8.
This material is available free of charge via the Internet at http://
pubs.acs.org.
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