Nucleophilic substitution of fluorine atoms in 2,6-difluoro-3-(pyridin-2- yl)benzonitrile leading to soluble blue-emitting cyclometalated Ir(III) complexes

Article abstract of DOI:10.1021/jo200357e

New functionalized phenylpyridine ligands and their derived heteroleptic cyclometalated Ir(III) complexes have been synthesized. The complexes possess a combination of important properties: (i) blue emission, (ii) good photoluminescence quantum yields, an

Full text of DOI:10.1021/jo200357e

NOTE
pubs.acs.org/joc
Nucleophilic Substitution of Fluorine Atoms in 2,
6-Difluoro-3-(pyridin-2-yl)benzonitrile Leading to
Soluble Blue-Emitting Cyclometalated Ir(III) Complexes
Valery N. Kozhevnikov,*,† Katja Dahms,‡ and Martin R. Bryce*,‡
†School of Life Sciences, Northumbria University, Northumberland Road, Newcastle upon Tyne NE1 8ST, U.K.
‡Department of Chemistry, Durham University, South Road, Durham DH1 3LE, U.K.
S Supporting Information
b
ABSTRACT: New functionalized phenylpyridine ligands and
their derived heteroleptic cyclometalated Ir(III) complexes have
been synthesized. The complexes possess a combination of
important properties: (i) blue emission, (ii) good photolumines-
cence quantum yields, and (iii) good solubility in organic
solvents, making them very attractive as phosphorescent dopant
emitters for solution-processable light-emitting devices.
Chart 1
he development of blue emitters which are required for
organic light-emitting diode (OLED) displays1ꢀ4 and light-
T
ing applications5,6 remains a significant challenge. Phospho-
rescent cyclometalated complexes provide improved electro-
luminescence efficiencies by utilizing both triplet and singlet
electroexcitation pathways.7,8 To date, at least two electron-
withdrawing substituents, usually fluorine atoms, have been
required on the phenyl ring of chelating phenylpyridine (ppy)
ligands to decrease the HOMO energy to the extent that
emission is shifted into the blue region.9ꢀ15 One of the most
widely studied complexes for blue emission is FIrpic 19ꢀ11
(Chart 1). Unfortunately, FIrpic suffers two major drawbacks:
(i) it has poor solubility in common organic solvents, which
means that OLED devices are usually fabricated by vacuum
thermal deposition, rather than by milder solution processing or
ink jet printing techniques. The latter methods are preferable for
low cost processing and large-area displays. (ii) Devices based on
FIrpic are not long-lived. One of the degradation mechanisms is
cleavage of a fluorine atom, which occurs during the harsh
vacuum deposition process and possibly also during device
operation.16,17 Therefore, there is a need for analogues with
(i) enhanced solubility in organic solvents to facilitate solution
processing in devices and (ii) fewer fluorine atoms in the ligands,
while retaining the blue emission.18 Solution processing has the
great advantage of being a room-temperature procedure for
assembly of thin films, so the molecules are not subjected to
the high temperatures of vacuum deposition procedures. We
now report an efficient way to achieve these aims by using the
new functionalized 2-phenylpyridine ligands 9a and 9b. The
ligands are synthesized using Suzuki cross-coupling reactions;
they are functionalized with long alkoxy chains to enhance
solubility and they retain only one fluorine atom.
It has recently been reported that 2,6-difluoro-3-(pyridin-2-
yl)benzonitrile 6 forms blue homoleptic phosphorescent Ir(III)
complexes,19,20 e.g. FCNIr 220 (Chart 1). The electron-with-
drawing cyano and fluoro substituents not only provide the large
HOMOꢀLUMO gap required for blue emission but also make 6
reactive toward nucleophilic substitution, enabling derivatization
with alkoxy chains to enhance solubility. Both of the fluorine
atoms of 6 are expected to have a very similar reactivity, so the
Received: February 17, 2011
Published: May 25, 2011
r
2011 American Chemical Society
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|

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Scheme 1
success of our strategy for further functionalization lies in the
ability to separate the product mixtures after replacement of a
fluorine atom by a nucleophile. With this in mind, we investigated
the reaction of 6 with hydroxide ions, since the resulting isomeric
phenols should have significantly different properties. This is
picolinic acid and potassium carbonate in 1,4-dioxane to afford
the desired complexes 11a and 11b.
To establish the versatility of the methodology, a pendant
carbazole unit was attached which should increase hole transport
ability26,27 and charge recombination28 at the emitting site. Com-
pound 7b was alkylated with 9-(4-bromobutyl)-9H-carbazole29
to give 12 and hence 13 (Scheme 3). Complexes 11a, 11b, and
13 are racemic; no attempts were made to separate their Δ and Λ
enantiomers.30
based on the possibility of intramolecular N OꢀH hydrogen
3 3 3
bonding in the phenol derivative 7a, which is not possible in 7b.
The synthesis and functionalization of 6 is shown in Scheme 1.
Compound 3 was converted to boronic acid derivative 4 using a
standard directed ortho metalation (DoM) reaction. Compound
4 was converted into the N-methyliminodiacetic acid (MIDA)
boronate21 derivative 5, which was cross-coupled with 2-bromo-
pyridine under palladium-catalyzed conditions optimized follow-
ing literature protocols21 to yield compound 6 (73% yield).22
(The comparable reaction of 4 and 2-bromopyridine gave 6 in
only 35% yield). The reaction of 6 with potassium hydroxide
gave the phenol derivatives 7a and 7b in isolated yields of 21%
and 41%, respectively. A range of conditions were explored with
the best yields achieved using aqueous KOH in refluxing 1,4-
dioxane, which gave synthetically viable quantities of 7a and 7b.23
2,6-Difluoro-3-(pyridin-2-yl)benzamide 8 was also isolated in
very low yield. The isomers 7a and 7b were readily separated due
to their drastically different solubility in dichloromethane; 7a is
readily soluble, whereas 7b is insoluble, presumably due to an
The solubilities of 11a, 11b, and 13 are considerably improved
compared to FIrpic. Thus, 25 mg of complexes 11a and 11b is
soluble in 1 mL of chlorobenzene, toluene, and 1,4-dioxane.
Complex 13 shows good solubility in chlorobenzene and
1,4-dioxane (g25 mg/mL) but is less soluble in toluene. The
solubility of FIrpic in these solvents is e5 mg/mL. Solutions of
11a, 11b, and 13 in 1,4-dioxane (25 mg/mL) are stable to storage
at 20 °C for at least 14 days: after this time, the complexes were
1
quantitatively recovered by evaporation and their H NMR
spectra and emission spectra were unchanged.
The complexes 11a, 11b, and 13 show strong absorption
bands in the 230ꢀ350 nm region which are assigned9 to ligand-
centered πꢀπ* transitions and closely resemble the absorption
spectra of the free ligands 9a, 9b, and 12 (see the Supporting
Information). The complexes also show absorption bands with
lower extinction in the range 350ꢀ400 nm, which are assigned to
singlet and triplet metal-to-ligand charge-transfer (1MCLT and
3MLCT) states, following literature precedents9 and the calcula-
tions of Hay.31 It is not possible to distinguish the singlet and
triplet absorptions, although the precedent is that the lower energy
bands are predominantly triplet in character. The luminescence
spectra of 11a, 11b, 13, and FIrpic 1 in dichloromethane solution
are shown in Figure 1, and the data are summarized in Table 1.
Efficient blue emission from iridium ppy complexes results
from large HOMOꢀLUMO gaps. One strategy to achieve this is
intramolecular N OꢀH bridge in 7a. Simple treatment of the
3 3 3
mixture of 7a and 7b with dichloromethane followed by filtration
allowed complete separation.
Phenol derivatives 7a and 7b were converted to the n-octyloxy
derivatives 9a and 9b, respectively, to improve the solubility of
the derived iridium complexes (Scheme 2). Subsequently, 9a and
9b were cyclometalated by reaction with iridium(III) chloride
trihydrate in a mixture of refluxing 2-ethoxyethanol and water24,25 to
yield the intermediate dichloro-bridged species 10a,b. These
species were used without further purification and refluxed with
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NOTE
Scheme 2
Scheme 3
Table 1. LuminescencePropertiesof11a, 11b, 13, and FIrpic 1
lifetime τd (μs)
b
c
compd
λPL (nm) CH2Cl2
ΦPL CH2Cl2
11a
465, 487
464, 486
460, 485
468, 489
0.30 ( 0.05
0.43 ( 0.05
0.44 ( 0.05
0.26 ( 0.05
1.6
1.6
1.8
1.9
11b
13
FIrpic 1a
a Data for FIrpic are consistent with those in ref 10. b Photoluminescence
quantum yield, determined using an integrating sphere. c λexc (nm) for
ΦPL 315 nm for 11a, 11b, and 13 and 325 nm for FIrpic. PLQY data
were obtained using an integrating sphere. d Measured in deaerated 1,
2-dichloroethane at 293 K.
Figure 1. Emission spectra of 1, 11a, 11b, and 13 in deaerated
dichloromethane at 293 K.
occurs at λmax values essentially the same as FIrpic 1 and is visible
as bright sky-blue emission. This is because of the balance of the
hypsochromic shift due to the cyano group and the bathochro-
mic shift due to the alkoxy group resulting in similar emission
wavelengths for 11a, 11b, 13, and FIrpic 1. A photograph of the
solutions of 11a and 11b in dichloromethane excited at 365 nm is
shown in the abstract. Quantum molecular calculations
to lower the HOMO energy by attachment of electron-with-
drawing groups to the phenyl ring of the ligands.10,11 It might be
expected that the electron donating alkoxy group in complexes
11a, 11b and 13 would cause a bathochromic shift of the
emission. However, the luminescence for 11a, 11b, and 13
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NOTE
performed in the gas phase (time-dependent density func-
tional theory: TDDFT using the B3LYP/6-31G* level) qua-
litatively support these observations. From these data, the
HOMOꢀLUMO gaps of complexes 11a (3.69 eV) and 11b
(3.72 eV) (with the structures simplified by replacing the octyl
chains with methyl groups to reduce the calculation time) are
located between FIrpic (3.62 eV) and the analogous complex of
ligand 6 (3.79 eV). The trend in the calculated HOMOꢀLUMO
data in line with the electron-withdrawing effect of the sub-
stituents is significant. (For further details, see the Supporting
Information.) Photoluminescence quantum yields of the new
complexes 11a, 11b, and 13 are similar to that of FIrpic 1,
measured under directly comparable conditions. Excited-state
lifetimes measured in deaerated 1,2-dichloroethane at 293 K
are in the microsecond regime (Table 1). Such long-lived
excited states clearly suggest that the emitting state has triplet
character.9,10
In summary, the phenylpyridine derivatives 9a, 9b, and 12
were synthesized and their derived heteroleptic Ir(C^N)2(pic)
complexes 11a, 11b, and 13 shown to be efficient blue emitters
(ΦPL 30 ꢀ 44%), whose λmax and PLQY and excited state
lifetime values compare favorably with FIrpic, which is the
standard blue phosphor for OLEDs. Importantly, these new
complexes possess significantly improved solubility in organic
solvents compared to FIrpic. The good solubility and stability of
the new complexes 11a, 11b, and 13 in solution means that their
thin films for device studies can be prepared by spin-coating at
room temperature in conditions which will not lead to any
decomposition of the complex. This contrasts with FIrpic for
which thin film formation requires vacuum deposition at high
temperatures, leading to partial degradation.16,17 Complexes 11a,
11b, and 13 are, therefore, very attractive as new phosphorescent
blue dopants in solution-processable LEDs. The synthetic meth-
odology should be versatile for the attachment of a range of
substituents to impart additional functionality.
and diethyl ether and dried in vacuum to give 5 as an off-white solid
(2.44 g, 89%): mp 295.5ꢀ296.6 °C dec; 1H NMR (400 MHz, DMSO-
d6) δ 7.85 (d, J = 8.6 Hz, 1H), 7.43 (t, J = 8.7 Hz, 1H), 4.44 (d, J =
17.4 Hz, 2H), 4.13 (d, J = 17.3 Hz, 2H), 2.65 (s, 3H); 13C NMR (101
MHz, DMSO-d6) δ 168.8, 141.8, 112.4, 112.3, 110.0, 62.4, 47.5; 19F
NMR (376 MHz, DMSO-d6) δ ꢀ97.70 (d, J = 7.3 Hz), ꢀ104.92 (s);
HRMS (ASAP) m/z calcd [C12H910BF2N2O4]þ 294.0738, found
294.0740.
2,6-Difluoro-3-(pyridin-2-yl)benzonitrile (6). A mixture of
2-bromopyridine (1.10 g, 6.96 mmol), 5 (2.50 g, 8.5 mmol), and 1,4-
dioxane (80 mL) was deoxygenated by bubbling argon for 10 min. Then
2-dicyclohexylphosphino-20,60-dimethoxybiphenyl (SPhos) (270 mg,
0.66 mmol), Pd(OAc)2 (73 mg, 0.33 mmol), and degassed aq K3PO4
(3.0 M, 17 mL) were added, and the mixture was degassed for an
additional 15 min. The reaction mixture was stirred under argon at 65 °C
for 20 h. Toluene (40 mL) was added, and the mixture was separated.
The organic layer was washed with water, dried over Na2SO4, and
evaporated to dryness. The product was purified by column chroma-
tography using silica gel and a mixture of petroleum ether/ethyl acetate
1:1 v/v as the eluent (Rf = 0.5) to give 6 as an off-white solid (1.10 g,
73%): mp 76ꢀ77 °C; 1H NMR (400 MHz, CDCl3) δ 8.73 (d, J = 4.8,
1H), 8.35 (td, J = 6.6, 8.8, 1H), 7.82ꢀ7.79 (m, 2H), 7.35ꢀ7.32 (m, 1H),
7.20ꢀ7.16 (m, 1H); 13C NMR (101 MHz, CDCl3) δ 164.5, 161.9,
161.9, 161.8, 159.3, 150.1, 136.9, 124.3, 124.2, 123.4, 112.7, 112.6, 112.5,
112.4, 109.2; 19F NMR (376 MHz, CDCl3) δ ꢀ103.06 (s), ꢀ107.25
(d, J = 8.2 Hz); HRMS (ES) m/z calcd [C12H6F2N2 þ H]þ 217.0577,
found 217.0576. Anal. Calcd for C12H6F2N2: C, 66.67; H, 2.80; N,
17.58. Found: C, 66.48; H, 2.60; N, 17.77.
6-Fluoro-2-hydroxy-3-(pyridin-2-yl)benzonitrile (7a),
2-Fluoro-6-hydroxy-3-(pyridin-2-yl)benzonitrile (7b), and 2,
6-Difluoro-3-(pyridin-2-yl)benzamide (8). An aqueous solution
of potassium hydroxide [prepared by dissolving KOH (450 mg, 8 mmol)
in water (5 mL)] was added to a solution of 6 (520 mg, 2.4 mmol) in 1,
4-dioxane (10 mL). The mixture was heated under reflux for 1 h and
then evaporated to a volume of ca. 1 mL. Water (20 mL) was added; the
mixture was gently heated with stirring to solubilize most of the residue
and filtered. The solid on the filter was washed with water to give 8. To
the filtrate was then rapidly added aqueous acetic acid (2 mL of concd
AcOH in 8 mL of H2O). The precipitate was collected, washed with
water, and dried under vacuum to give a mixture of 7a and 7b. The
mixture was then heated under reflux in DCM (30 mL) for 10 min,
allowed to cool to room temperature, and filtered; this operation was
repeated another two times. The combined filtrates were evaporated to
dryness. The residue was chromatographed on a silica gel column
(eluent DCM/ethyl acetate 10:1 v/v) to give pure 7a. The solid on
the filter was dried and recrystallized from methanol to give 7b. 7a (110
’ EXPERIMENTAL SECTION
2,4-Difluoro-3-cyanophenylboronic Acid (4). To a solution
of 3 (15.0 g, 108 mmol) in diethyl ether (300 mL) at ꢀ78 °C was added
a solution of lithium diisopropylamide (2 M in heptane/THF/ethyl-
benzene, 60 mL, 120 mmol) dropwise over a period of 40 min. The
mixture was stirred at ꢀ78 °C for 1 h. Triisopropyl borate (17.2 mL,
160 mmol) was slowly added, and the reaction mixture was stirred
at ꢀ78 °C for 1 h. The cooling bath was removed, and the reaction mixture
was stirred at room temperature for 1 h. Water (150 mL) was added; the
mixture was stirred for 15 min. The organic layer was separated and
washed with aqueous KOH (1 M, 150 mL). The aqueous solutions were
combined and acidified to pH 5 with concd HCl. The product was
extracted with ethyl acetate. The solvent was evaporated and the residue
was dried in vacuum to yield 4 as a yellow solid (16.0 g, 81%): mp
132.5ꢀ133.5 °C; 1H NMR (400 MHz, acetone-d6) δ 8.13 (q, J = 14.9 Hz,
7.1 Hz, 1H), 7.65 (br s, 2H), 7.31 (t, J = 8.6 Hz, 1H); 13C NMR
(101 MHz, acetone-d6) δ 169.1, 166.7, 164.1, 143.7, 143.6, 143.5, 113.0,
122.8, 110.3; 19F NMR (376 MHz, acetone-d6) δ ꢀ102.55, ꢀ109.54;
HRMS (ES) m/z calcd [C7H4BF2NO2 þ H]þ 184.0381, found
184.0380.
1
mg, 21%): yellow solid; mp 190.5ꢀ191.0 °C; H NMR (500 MHz,
CDCl3) δ 8.52 (m, 1H), 7.98 (dd, J = 9.0 Hz, J = 6.2 Hz, 1H), 7.96ꢀ7.91
(m, 1H), 7.87 (d, J = 8.4 Hz, 1H), 7.37 (ddd, J = 7.4 Hz, J = 5.1 Hz, J =
1.0 Hz, 1H), 6.72 (t, J = 8.9 Hz, 1H); 13C NMR (126 MHz, CDCl3) δ
164.7 (d, J = 5.2 Hz), 164.7 (d, J = 262.3 Hz), 155.5, 145.3, 138.7, 131.3
(d, J = 11.1 Hz), 122.6, 118.9, 115.4, 111.7, 105.7 (d, J = 19.9 Hz), 92.3
(d, J = 17.1 Hz); 19F NMR (470 MHz, CDCl3) δ ꢀ102.46 (dd, J =
8.2 Hz, J = 6.3 Hz); UV/vis (CH2Cl2) λmax (log ε) 232 nm (4.34), 288
(3.83), 328 (4.01); HRMS (ES) m/z calcd [C20H7FN2O þ H]þ
215.0621, found 215.0616. Anal. Calcd for C12H7FN2O: C, 67.29; H,
3.29; N, 13.08. Found: C, 67.40; H, 3.44; N, 13.47. 7b (210 mg, 41%):
colorless solid, mp 212.5ꢀ213.5 °C; 1H NMR (500 MHz, DMSO-d6) δ
12.04 (br s, 1H), 8.69 (ddd, J = 4.8 Hz, J = 1.8 Hz, J = 0.9 Hz, 1H), 8.10
(t, J = 9.2 Hz, 1H), 7.90 (td, J = 7.8 Hz, J = 1.8 Hz, 1H), 7.81ꢀ7.68 (m,
1H), 7.38 (ddd, J = 7.5 Hz, J = 4.8 Hz, J = 1.0 Hz, 1H), 6.99 (d, J = 8.9 Hz,
1H); 13C NMR (126 MHz, DMSO-d6) δ 162.3, 160.7 (d, J = 258.5 Hz),
151.0, 149.8, 137.1, 136.3 (d, J = 5.8 Hz), 123.6 (d, J = 9.1 Hz), 122.8,
117.7, 112.8, 112.3, 109.3, 89.4 (d, J = 18.6 Hz); 19F NMR (470 MHz,
2,6-Difluoro-3-(6-methyl-4,8-dioxo-1,3,6,2-dioxazaboro-
can-2-yl)benzonitrile (5). A mixture of 4 (1.71 g, 9.34 mmol),
methyliminodiacetic acid (MIDA) (1.51 g, 10.27 mmol), DMSO
(20 mL), and toluene (40 mL) was heated under reflux with a Deanꢀ
Stark trap for 4 h. The mixture was cooled to room temperature, and
water was added. The precipitate was filtered off, washed with toluene
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NOTE
DMSO-d6) δ ꢀ111.68 (dd, J = 9.5 Hz, J = 2.0 Hz); HRMS (ASAP) m/z
calcd [C20H7FN2O þ H]þ 215.0621, found 214.0616. Anal. Calcd for
C12H7FN2O: C, 67.29; H, 3.29; N, 13.08. Found: C, 67.63; H, 3.49; N,
13.37. 8 (13 mg, 2%): pale yellow solid; mp 189.5ꢀ190.5 °C; 1H NMR
(270 MHz, DMSO-d6) δ 8.72 (ddd, J = 4.8 Hz, J = 1.8 Hz, J = 0.9 Hz,
1H), 8.22 (br s, 1H), 7.89ꢀ8.03 (m, 3H), 7.76 (m, 1H), 7.43 (ddd, J =
7.5 Hz, J = 4.8 Hz, J = 0.9 Hz, 1H), 6.99 (td, J = 8.7 Hz, J = 1.0 Hz 1H);
13C NMR (68 MHz, DMSO-d6) δ 162.0, 159.2 (dd, J = 250.3 Hz, J =
8.3 Hz), 158.7 (dd, J = 252.6 Hz, J = 8.7 Hz), 152.0 (d, J = 2.7 Hz), 150.5,
137.7, 132.3 (dd, J = 9.8 Hz, J = 3.9 Hz), 124.6, 124.5, 124.4 (dd, J =
12.7 Hz, J = 3.9 Hz), 123.7, 116.9 (t, J = 24.0 Hz), 112.8 (dd, J = 21.8 Hz,
J = 3.6 Hz); HRMS (ES) m/z calcd [C12H8F2N2O þ H]þ 235.0683,
found 235.0672.
6-Fluoro-2-(octyloxy)-3-(pyridin-2-yl)benzonitrile (9a). A
mixture of 7a (320 mg, 1.5 mmol), 1-bromooctane (288 mg, 1.5 mmol),
K2CO3 (620 mg, 4.5 mmol), and acetonitrile (25 mL) was heated under
reflux for 16 h. The mixture was filtered, and the filtrate was evaporated
to dryness. The residue was purified by column chromatography on
silica gel with hexane/ethyl acetate (3:2, v/v) as eluent to give 9a as a
pale yellow oil (430 mg, 88%): 1H NMR (500 MHz, CDCl3) δ 8.70 (dd,
J = 4.8 Hz, J = 0.6 Hz, 1H), 7.99 (dd, J = 8.8 Hz, J = 6.7 Hz, 1H),
7.82ꢀ7.79 (m, 1H), 7.75 (td, J = 7.7 Hz, J = 1.8 Hz, 1H), 7.31ꢀ7.27 (m,
1H), 7.04 (dd, J = 8.7 Hz, J = 8.0 Hz, 1H), 3.89 (t, J = 6.5 Hz, 2H),
1.68ꢀ1.56 (m, 2H), 1.32ꢀ1.22 (m, 4H), 1.20 (s, 6H), 0.85 (t, J = 7.1 Hz,
3H); 13C NMR (126 MHz, CDCl3) δ 163.6 (d, J = 263.1 Hz), 160.3 (d,
J = 2.5 Hz), 153.4, 149.8, 137.0 (d, J = 11.03 Hz), 136.3, 130.5 (d, J = 4.2
Hz), 124.6, 122.7, 111.8, 111.4 (d, J=20.1 Hz), 97.2 (d, J = 15.3 Hz),
76.2, 31.7, 29.8, 29.1, 29.0, 25.6, 22.6, 14.0; 19F NMR (470 MHz,
CDCl3) δ ꢀ104.66 (t, J = 7.3 Hz); UV/vis (CH2Cl2) λmax (log ε):
230 nm (4.13), 274 (3.81); HRMS (ES) m/z calcd [C20H23FN2O þ
H]þ 327.1873, found 327.1879. Anal. Calcd for C20H23FN2O: C, 73.59;
H, 7.10; N, 8.58. Found: C, 73.28; H, 6.90; N, 8.77.
J = Hz, J = 5.8 Hz, J = 1.0 Hz, 1H), 7.29ꢀ7.23 (m, 2H), 7.06ꢀ7.04
(m, 1H), 5.83 (d, J = 8.6 Hz, 1H), 5.62 (d, J = 8.6 Hz, 1H), 4.46ꢀ4.25
(m, 4H), 1.98ꢀ1.93 (m, 4H), 1.55ꢀ1.50 (m, 4H), 1.41ꢀ1.37 (m, 4H),
1.35ꢀ1.25 (m, 12H), 0.90ꢀ0.87 (m, 6H); 13C NMR (126 MHz,
CDCl3) δ 172.3, 165.5, 164.5, 164.1, 162.3, 162.1, 162.0, 161.9, 161.6
(d, J = 8.5 Hz), 160.5 (d, J = 3.3 Hz), 160.4 (d, J = 3.3 Hz), 151.3, 148.5,
147.9, 138.9, 138.6 (d, J = 3.3 Hz), 133.5 (d, J = 3.3 Hz), 133.1 (d, J =
2.0 Hz), 128.7 (d, J = 19.2 Hz), 124.2, 123.7, 123.2 (d, J = 17.2 Hz),
114.4, 114.3, 114.3, 114.2, 113.4 (d, J = 3.1 Hz), 89.8 (d, J = 16.2 Hz),
88.7 (d, J = 17.2 Hz), 75.7 (d, J = 17.2 Hz), 31.7 (d, J = 4.1 Hz), 30.3,
30.2, 29.3 (d, J = 2.3 Hz), 29.2 (d, J = 2.9 Hz), 25.8 (d, J = 1.6 Hz), 22.6
(d, J = 2.6 Hz), 14.1 (d, J = 2.4 Hz); 19F NMR (658 MHz, CDCl3)
δ ꢀ103.67 (d, J = 8.6 Hz), ꢀ104.50 (d, J = 8.6 Hz); UV/vis (CH2Cl2)
λmax (log ε) 257 nm (4.69), 287 (4.61); HRMS (ES) m/z calcd
[C46H48F2191IrN5O4]þ 963.3280, found 963.3256. Anal. Calcd for
C46H48F2IrN5O4: C, 57.25; H, 5.01; N, 7.26. Found: C, 57.51; H,
4.69; N, 7.44.
Complex 11b. Compound 9b (335 mg, 1.03 mmol) was dissolved
in 2-ethoxyethanol (15 mL). Water (5 mL) and IrCl3 3H2O (186 mg,
3
0.53 mmol) were added, and the mixture was heated under reflux for 24
h. Water (5 mL) was added, and the mixture was allowed to cool to room
temperature. The yellow solid was filtered off, washed with methanol,
and dried (347 mg). The intermediate 10b was used in the next step
without further purification A mixture of 10b (92 mg, 0.05 mmol),
picolinic acid (104 mg, 0.85 mmol), and 1,4-dioxane (30 mL) was
heated under reflux for 60 h. The solvent was evaporated, and the
product was purified by column chromatography (silica gel, eluent
DCM/methanol, 10:1, v/v) to give 11b (24 mg, 25%): mp
119.0ꢀ120.0 °C; 1H NMR (500 MHz, CDCl3) δ 8.76 (d, J = 5.1 Hz,
1H), 8.36 (d, J = 7.7 Hz, 1H), 8.26 (d, J = 8.4 Hz, 1H), 8.20 (d, J = 8.4 Hz,
1H), 8.01 (td, J = 7.7 Hz, J = 1.4 Hz, 1H), 7.87ꢀ7.81 (m, 2H), 7.76 (d,
J = 4.9 Hz, 1H), 7.53ꢀ7.48 (m, 1H), 7.43 (d, J = 5.1 Hz, 1H), 7.25ꢀ7.20
(m, 1H), 7.05ꢀ6.99 (m, 1H), 5.68 (s, 1H), 5.44 (s, 1H), 3.68ꢀ3.53 (m,
4H), 1.70ꢀ1.46 (m, 7H), 1.37ꢀ1.17 (m, 17H), 1.03ꢀ0.73 (m, 6H);
13C NMR (126 MHz, CDCl3) δ 172.3, 165.0 (J = 6.5 Hz), 163.7 (J = 6.5
Hz), 162.5, 161.7, 161.3, 160.7, 160.4, 151.3, 148.7, 147.9 (J = 21.8 Hz),
138.9, 138.6 (J = 8.9 Hz), 128.8 (J = 7.7 Hz), 124.9, 124.8, 123.2, 123.0,
122.5, 122.3, 122.3, 112.7, 110.8, 86.0, 85.6, 69.0, 68.8, 31.7 (J = 4.9 Hz),
29.7, 29.2 (J = 4.0 Hz), 29.1 (J = 4.0 Hz), 28.5 (J = 8.9 Hz), 25.7 (J = 8.9
Hz), 22.6, 14.1; 19F NMR (470 MHz, CDCl3) δ ꢀ107.99 (s), ꢀ108.44
(s); UV/vis (CH2Cl2) λmax (log ε) 265 nm (4.79); HRMS (ES) m/z
calcd [C46H48F2191IrN5O4 þ H]þ 964.3359, found 964.3339. Anal.
Calcd for C46H48F2IrN5O4: C, 57.25; H, 5.01; N, 7.26. Found: C, 57.56;
H, 5.40; N, 6.87.
2-Fluoro-6-(octyloxy)-3-(pyridin-2-yl)benzonitrile (9b). A
mixture of 7b (421 mg, 1.97 mmol), 1-bromooctane (330 mg,
1.71 mmol), K2CO3 (667 mg, 4.83 mmol), and acetonitrile (25 mL)
was heated under reflux for 16 h. The mixture was filtered, and the
resulting solid was washed with acetone (3 mL). Water was added to the
filtrate, and the precipitate was filtered off and washed with water to give
1
9b as an off-white solid (377 mg, 68%): mp 68.0ꢀ68.5 °C; H NMR
(500 MHz, CDCl3) δ 8.70 (d, J = 4.7 Hz, 1H), 8.24 (t, J = 9.0 Hz, 1H),
7.76 (s, 2H), 6.88 (d, J = 8.9 Hz, 1H), 4.15 (t, J = 6.5 Hz, 2H), 1.95ꢀ1.81
(m, 2H), 1.53ꢀ1.45 (m, 2H), 1.42ꢀ1.24 (m, 9H), 0.89 (t, J = 6.9 Hz,
3H); 13C NMR (126 MHz, CDCl3) δ 149.8, 136.7, 136.3 (d, J = 5.7 Hz),
124.0 (d, J = 11.1 Hz), 122.6, 108.2 (d, J = 3.72 Hz), 69.9, 31.8, 29.2,
29.2, 28.8, 25.8, 22.6, 14.1; 19F NMR (470 MHz, CDCl3) δ ꢀ109.40 (d,
J = 8.9 Hz); UV/vis (CH2Cl2) λmax (log ε) 233 nm (4.45), 257 (4.22),
277 (4.21), 302 (3.87); HRMS (ES) m/z calcd [C20H23FN2O þ H]þ
327.1873, found 327.1868. Anal. Calcd for C20H23FN2O: C, 73.59; H,
7.10; N, 8.58. Found: C, 73.48; H, 6.86; N, 8.81.
6-[4-(9H-Carbazol-9-yl)butoxy]-2-fluoro-3-(pyridin-2-yl)-
benzonitrile (12). A mixture of 7b (420 mg, 1.96 mmol), 9-(4-
bromobutyl)-9H-carbazole (590 mg, 1.96 mmol) and K2CO3 (1.0 g,
7.25 mmol) in dry DMF (20 mL) was stirred at 105 °C for 17 h. Water
(20 mL) was added, and the precipitated solid was filtered off, washed
with methanol, and recrystallized from ethanol to give 12 (656 mg, 77%)
as an off-white solid: mp 115.0ꢀ116.0 °C; 1H NMR (500 MHz, CDCl3)
δ 8.69 (d, J = 4.6 Hz, 1H), 8.19 (t, J = 9.0 Hz, 1H), 8.10 (d, J = 7.8 Hz,
2H), 7.79ꢀ7.74 (m, 2H), 7.52ꢀ7.41 (m, 5H), 7.30ꢀ7.20 (m, 6H), 6.72
(d, J = 9.1 Hz, 1H), 4.46 (t, J = 6.8 Hz, 2H), 4.05 (t, J = 6.1 Hz, 2H),
2.25ꢀ2.12 (m, 2H), 2.07ꢀ1.75 (m, 2H); 13C NMR (126 MHz,
CDCl3) δ 161.7 (d, J = 4.23 Hz), 161.5 (d, J = 261.3 Hz), 151.1, 149.8,
140.3, 136.7, 136.3 (d, J = 5.8 Hz), 125.7, 124.0 (d, J = 9.8 Hz), 122.8,
122.7, 120.5 (d, J = 11.9 Hz), 120.4, 118.9, 111.5, 108.6, 108.1 (d, J =
3.5 Hz), 69.3, 42.6, 26.6, 25.5; 19F NMR (470 MHz, CDCl3)
δ ꢀ109.20 (d, J = 8.8 Hz); UV/vis (CH2Cl2) λmax (log ε) 237 nm
(4.78), 263 (4.55), 284 (4.32), 295 (4.34); HRMS (ES) m/z calcd
[C28H22FN3O þ H]þ 436.1825, found 436.1828. Anal. Calcd. for
C28H22FN3O: C, 77.22; H, 5.09; N, 9.65. Found: C, 76.88; H, 4.79;
N, 9.90.
Complex 11a. Compound 9a (430 mg, 1.32 mmol) was dissolved
in 2-ethoxyethanol (30 mL). IrCl3 3H2O (230 mg, 0.65 mmol) was
3
dissolved in boiling water (10 mL) and added to the above solution. The
mixture was heated under reflux for 24 h and then cooled to room
temperature, and the yellow solid was filtered off, washed with methanol,
and dried (285 mg). The intermediate 10a was used in the next step
without further purification. A mixture of 10a (285 mg, 0.16 mmol),
picolinic acid (215 mg, 1.75 mmol), and potassium carbonate (100 mg,
0.72 mmol) in 1,4-dioxane (40 mL) was heated under reflux for 24 h.
The solvent was evaporated, and the product was purified by column
chromatography (silica gel, eluent DCM/ethyl acetate, 1:2, v/v) to yield
11a (180 mg, 27%): mp 107.5ꢀ108.0 °C; 1H NMR (700 MHz, CDCl3)
δ 8.74ꢀ8.72 (m, 2H), 8.64 (d, J = 8.3 Hz, 1H), 8.35 (d, J = 7.7 Hz, 1H),
7.99 (td, J = 7.8 Hz, J = 1.5 Hz, 1H), 7.84 (ddd, J = 16.1 Hz, J = 7.6 Hz,
J = 1.6 Hz, 2H), 7.69 (d, J = 4.8 Hz, 1H), 7.47ꢀ7.45 (m, 1H), 7.41 (dd,
5147
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The Journal of Organic Chemistry
NOTE
Complex 13. A mixture of 12 (550 mg, 1.26 mmol), 2-ethoxyetha-
(10) Adachi, C.; Kwong, R. C.; Djurovich, P.; Adamovich, V.; Baldo,
M. A.; Thompson, M. E.; Forrest, S. R. Appl. Phys. Lett. 2001,
79, 2082–2084.
nol (40 mL), IrCl3 3H2O (200 mg, 0.57 mmol), and water (5 mL) was
3
heated under reflux for 36 h. The mixture was allowed to cool to room
temperature, water was added, and the solid was filtered and washed with
methanol to give a gray solid after drying (420 mg). This dichloro-
bridged complex was used in the next step without further purification. A
mixture of the complex (250 mg, 0.12 mmol), picolinic acid (85 mg,
0.69 mmol), potassium carbonate (48 mg, 0.35 mmol), and 1,4-dioxane
(15 mL) was heated under reflux for 4 h. The mixture was evaporated to
dryness, and the product was purified by column chromatography (silica
gel, eluent DCM/ethyl acetate, 1:1, v/v) to give 13 (25 mg, 18%): mp
188.0ꢀ189.0 °C; 1H NMR (500 MHz, CDCl3) δ 8.67ꢀ8.61 (m, 1H),
8.33 (d, J = 7.8 Hz, 1H), 8.17 (d, J = 8.6 Hz, 1H), 8.11 (t, J = 7.4 Hz, 4H),
8.07 (d, J = 8.6 Hz, 1H), 7.97 (td, J = 7.8 Hz, J = 1.5 Hz, 1H), 7.70 (t, J =
7.9 Hz, 1H), 7.67ꢀ7.60 (m, 2H), 7.51ꢀ7.42 (m, 5H), 7.38 (t, J = 8.6 Hz,
4H), 7.29 (d, J = 5.8 Hz, 1H), 7.25ꢀ7.20 (m, 3H), 7.07ꢀ7.00 (m, 1H),
6.87ꢀ6.80 (m, 1H), 5.54 (s, 1H), 5.31 (s, 1H), 4.38ꢀ4.34 (m, 4H),
3.54ꢀ3.41 (m, 2H), 2.03ꢀ1.97 (m, 2H); 13C NMR (126 MHz, CDCl3)
δ 172.2, 148.5, 147.9, 140.3 (d, J = 5.7 Hz), 138.7, 128.7, 125.7 (d, J =
3.5 Hz), 122.8 (d, J = 2.1 Hz), 122.4, 120.4 (d, J = 5.0 Hz), 118.9 (d, J =
8.7 Hz), 108.7 (d, J = 11.6 Hz), 68.5, 68.3, 42.5, 26.6 (d, J = 6.4 Hz), 25.8
(d, J = 4.3 Hz); 19F NMR (470 MHz, CDCl3) δ ꢀ107.74 (s), ꢀ108.22
(s); UV/vis (CH2Cl2) λmax (log ε) 238 nm (5.17), 263 (5.11), 295
(5.00); HRMS (ES) m/z calcd [C62H46F2191IrN7O4 þ H]þ 1182.3258,
found 1182.3259. Anal. Calcd for C62H46F2IrN7O4: C, 62.93; H, 3.92;
N, 8.29. Found: C, 63.35; H, 3.61; N, 8.54.
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’ ASSOCIATED CONTENT
Supporting Information. 1H, 13C, 19F NMR, mass spectra,
S
b
(22) Reference 19 reports the synthesis of compound 6 from 4 and
2-bromopyridine, but the yield is not stated and no characterization
data are given for 4 or 6. Reference 20 claims the synthesis of 6 in 88%
yield from reaction of 2,6-difluoro-3-(trimethylstannyl)benzonitrile and
2-bromopyridine. However, the only characterization data reported for 6
absorption spectra, and computational details. This material is
available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
1
is H NMR data, which do not agree with our NMR data reported
Corresponding Author
*E-mail: valery.kozhevnikov@northumbria.ac.uk; m.r.bryce@
durham.ac.uk.
herein. All our characterization data are consistent with structure 6.
(23) Alternative conditions and yields [KOH (4 M), 1,4-dioxane,
reflux 1 h, or K2CO3 (2 M), dioxane, reflux 17 h] gave 7a (15ꢀ18%), 7b
(15ꢀ19%), and 8 (ca. 1%). It is possible that the outcome of the reaction
could be rationalized in terms of the stability of the intermediate
Meisenheimer complexes (as suggested by a reviewer). However, this
would need more extensive optimization, and mechanistic studies than
have been performed.
’ ACKNOWLEDGMENT
We thank EPSRC for funding.
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Soc. 1984, 106, 6647–6653.
(26) Sun, Y.-H.; Zhu, H.-H.; Chen, Z.; Zhang, Y.; Cao, Y. J. Org.
Chem. 2006, 71, 6281–6284.
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