Syntheses, structures, and luminescence/electroluminescence of BPh2(mqp), Al(CH3)(mqp)2, and Al(mqp)3 (mqp = 2-(4′-Methylquinolinyl)-2-phenolato)

Article abstract of DOI:10.1021/om0006918

Three new complexes BPh₂(mqp) (1), Al(CH₃)(mqp)₂ (2), and Al(mqp)₃ (3) have been synthesized and characterized, where mqp = 2-(4′-methylquinolinyl)-2-phenolato. The mqp ligand in compounds 1 and 2 act as a chelate ligand, while in compound 3 it acts as both a chelate ligand and a terminal ligand. The boron center in 1 has tetrahedral geometry, while the aluminum ion in 2 and 3 has trigonal-bipyramidal geometry. In CH₂Cl₂ solution, these compounds emit a green, a green-blue, and a whitish blue color (λ = 514, 515, 497 nm), respectively, when irradiated by UV light. In the solid state, these three compounds emit a green, a blue, and a whitish blue color, respectively (λ = 520, 474, 500 nm). Electroluminescent devices using compound 3 as an emitter have been fabricated.

Full text of DOI:10.1021/om0006918

Organometallics 2000, 19, 5709-5714
5709
Syn th eses, Str u ctu r es, a n d Lu m in escen ce/
Electr olu m in escen ce of BP h 2(m qp ), Al(CH3)(m qp )2, a n d
Al(m qp )3 (m qp ) 2-(4′-Meth ylqu in olin yl)-2-p h en ola to)
Shi-Feng Liu,† Corey Seward,† Hany Aziz,‡ Nan-Xing Hu,‡ Zoran Popovic´,‡ and
Suning Wang*,†
Department of Chemistry, Queen’s University, Kingston, Ontario K7L 3N6, Canada, and
Xerox Research Center of Canada, 2660 Speakman Drive, Mississauga,
Ontario L5K 2L1, Canada
Received August 9, 2000
Three new complexes BPh2(mqp) (1), Al(CH3)(mqp)2 (2), and Al(mqp)3 (3) have been
synthesized and characterized, where mqp ) 2-(4′-methylquinolinyl)-2-phenolato. The mqp
ligand in compounds 1 and 2 act as a chelate ligand, while in compound 3 it acts as both a
chelate ligand and a terminal ligand. The boron center in 1 has tetrahedral geometry, while
the aluminum ion in 2 and 3 has trigonal-bipyramidal geometry. In CH2Cl2 solution, these
compounds emit a green, a green-blue, and a whitish blue color (λ ) 514, 515, 497 nm),
respectively, when irradiated by UV light. In the solid state, these three compounds emit a
green, a blue, and a whitish blue color, respectively (λ ) 520, 474, 500 nm). Electrolumi-
nescent devices using compound 3 as an emitter have been fabricated.
In tr od u ction
tions in electroluminescent devices, we investigated
aluminum and boron chelate compounds containing the
2-(4′-methylquinolinyl)-2-phenolato (mqp) ligand. The
quinolinyl portion of the mqp ligand is related to
8-hydroxyquinoline, thus ensuring the occurrence of
luminescence. The attachment of a phenol group at the
2-position would allow the ligand to form chelate
compounds with metal ions similarly to 8-hydroxy-
quinoline. Indeed, we have found that the mqp ligand
readily forms a variety of luminescent complexes with
aluminum(III) and boron(III) ions. The syntheses, struc-
tures, and luminescent and electroluminescent proper-
ties of three novel boron and aluminum complexes of
mqp are presented herein.
The best known electroluminescent (EL) metal che-
late compound is Al(q)3, where q is the 8-hydroxyquino-
linato ligand.1 Al(q)3 is not only a good green emitter
but also a highly efficient electron-transporting material
in EL devices.2,3 To improve the performance of Al(q)3,
various modifications of the 8-hydroxyquinoline ligand
have been investigated. It has been demonstrated that
one could shift the emission color of the complex by
modifying the 8-hydroxyquinoline ligand or the coordi-
nation environment around the aluminum ion in the
complex.4 In addition to the modification of the 8-hy-
droxyquinoline ligand, extensive research on the devel-
opment of new chelate compounds containing nitrogen
and oxygen donor atoms has also been carried out, the
most notable of which are chelate compounds based on
benzoxazole, oxadiazole, and their derivatives.5 In search
of new chelate compounds that have potential applica-
Exp er im en ta l Section
All starting materials were purchased from Aldrich Chemi-
cal Co. All syntheses were carried out under a nitrogen
atmosphere. Solvents were freshly distilled over appropriate
1
drying reagents prior to use. H NMR spectra were recorded
† Queen’s University.
on Bruker Avance 300 MHz spectrometers. Excitation and
emission spectra were recorded on a Photon Technologies
International QuantaMaster Model C-60 spectrometer. Ele-
mental analyses were performed by Canadian Microanalytical
Service Ltd., Delta, British Columbia, Canada. TLC was
carried out on SiO2 (silica gel F254, Whatman). Flash chro-
matography was carried out on silica (silica gel 60, 70-230
mesh). Melting points were determined on a Fisher-J ohns
melting point apparatus.
‡ Xerox Research Center of Canada.
(1) Schmidbaur, H.; Lettenbauer, J .; Wilkinson, D. L.; Mu¨ller, G.;
Kumberger, O. Z. Naturforsch. 1991, 46B, 901.
(2) (a) Tang, C. W.; VanSlyke, S. A. Appl. Phys. Lett. 1987, 51, 913.
(b) Tang, C. W.; VanSlyke, S. A.; Chen, C. H. J . Appl. Phys. 1989, 65,
3611. (c) Shirota, Y.; Kuwabara, Y.; Inada, H.; Wakimoto, T.; Nakada,
H.; Yonemoto, Y.; Kawami, S.; Imai, K. Appl. Phys. Lett. 1994, 65, 807.
(d) Hamada, Y.; Sano, T.; Fujita, M.; Fujii, T.; Nishio, Y.; Shibata, K.
J pn. J . Appl. Phys. 1993, 32, L514. (e) Bulovic, V.; Gu, G.; Burrows,
P. E.; Forrest, S. R. Nature 1996, 380, 29.
(3) (a) Adachi, C.; Tokito, S.; Tsutsui, T.; Saito, S. J pn. J . Appl. Phys.
1988, 27, L713. (b) Adachi, C.; Tsutsui, T.; Saito, S. Appl. Phys. Lett.
1990, 56, 799. (c) Hamada, Y.; Sano, T.; Fujita, M.; Fujii, T.; Nishio,
Y.; Shibata, K. Chem. Lett. 1993, 905. (d) Shen, Z.; Burrows, P. E.;
Bulovic, V.; Borrest, S. R.; Thompson, M. E. Science 1997, 276, 2009.
(e) Aziz, H.; Popovic, Z. D.; Hu, N.-X.; Hor, A.-M.; Xu, G. Science 1999,
283, 1900. (f) Wu, Q.; Esteghamatian, M.; Hu, N. H.; Popovic, Z.;
Enright, G.; Tao, Y.; D’Iorio, M.; Wang, S. Chem. Mater. 2000, 12, 79.
(4) Thompson, M. E.; Forrest, S. R.; Burrows, P. E.; You, Y. J .;
Shoustikov, A. U.S. Patent No. 5,861,219, 1999.
Syn th esis of 2-(4′-Meth ylqu in olin yl)-2-p h en ol (m qp H).
The synthesis of mqpH involves three steps as described below.
(5) (a) Chen, C. H.; Shi, J . Coor. Chem. Rev. 1998, 171, 161. (b) Hu,
N. X.; Esteghamatian, M.; Xie, S.; Popovic, Z.; Hor, A. M.; Ong, B.;
Wang, S. Adv. Mater. 1999, 11, 17. (c) Wang, J . F.; J abbour, G. E.;
Mash, E. A.; Anderson, J .; Zhang, Y.; Lee, P. A.; Armstrong, N. R.;
Peryhambarian, N.; Kippelen, B. Adv. Mater. 1999, 11, 1266.
10.1021/om0006918 CCC: $19.00 © 2000 American Chemical Society
Publication on Web 11/17/2000

5710 Organometallics, Vol. 19, No. 26, 2000
Liu et al.
(a ) (2-Meth oxyp h en yl)bor on ic Acid . n-Butyllithium (1.6
M in hexane, 25 mL, 40 mmol) was added to a solution of
2-bromoanisole (4.98 mL, 40 mmol) in 20 mL of THF at -78
°C under nitrogen. The mixture was stirred for 1 h and
transferred to a solution of B(OMe)3 (9.1 mL, 80 mmol) in 10
mL of THF at -78 °C under nitrogen, and this mixture was
warmed to room temperature. After the mixture had been
stirred overnight, HCl (10%, 20 mL) was added to it and
stirring was continued for 10 min. The organic phase was
separated, and the aqueous phase was extracted with diethyl
ether. The combined organic phases were washed with brine
twice and dried over anhydrous sodium sulfate. After removal
of solvents, the residue was added to NaOH (3.2 g, 80 mmol)
in 60 mL of ethanol and the mixture was stirred for 20 min at
room temperature. Water (50 mL) was added to the residue
after the solvent was evaporated. The aqueous phase was
extracted with diethyl ether. The combined organic phases
were washed with brine and dried over sodium sulfate. The
residue was recrystallized from diethyl ether/hexane to give
colorless crystals of (2-methoxyphenyl)boronic acid (3.7 g, yield
61%). Mp: 88-90 °C. 1H NMR (CDCl3, δ, ppm): 7.82 (1H, m),
7.42 (1H, m), 6.80-7.04 (2H, m), 5.87 (2H, s), 3.93 (3H, s).
(b) 2-(4′-Meth ylqu in olin yl)a n isole. A solution of 2-chlo-
rolepidine (1.78 g, 10 mmol) in 10 mL of anhydrous 1,2-
dimethoxyethane (DME) was added under nitrogen to a
solution containing a catalyst prepared by reaction of Pd-
(PPh3)2Cl2 (0.28 g, 0.40 mmol) in 5 mL of anhydrous DME with
diisobutylaluminum hydride (1.0 M in hexane, 0.8 mL, 0.80
mmol). After the mixture had been stirred at room tempera-
ture for 15 min, (2-methoxyphenyl)boronic acid (1.52 g, 10
mmol) and sodium ethoxide (2.0 M in ethanol, 10 mL, 20 mmol)
were added successively. The resulting mixture was heated
at reflux for 5 h under N2 and cooled to room temperature.
The suspension was filtered through Celite to give a clear
solution. The Celite was washed with CH2Cl2. The solution
was concentrated to give a brown residue, which was purified
by column chromatography using 4/1 hexane/ethyl acetate as
the eluent, yielding a white solid of 2-(4′-methylquinolinyl)-
anisole (2.12 g, 85%). Mp: 76-77 °C. 1H NMR (CDCl3, δ,
ppm): 8.20 (1H, d, J ) 8.4 Hz), 8.02 (1H, m), 7.82 (1H, dd, J
) 7.6 Hz, 1.8 Hz), 7.69-7.75 (2H, m), 7.54-7.60 (1H, m), 7.41-
7.47 (1H, m), 7.11-7.17 (1H, m), 7.05 (1H, d, J ) 8.2 Hz), 3.87
(3H, s), 2.75 (3H, s).
(c) 2-(4′-Meth ylqu in olin yl)-2-p h en ol (m qp H). A solution
of 2-(4′-methylquinolinyl)anisole (1.52 g, 6.1 mmol) in 25 mL
of dichloromethane was added to a solution of BBr3 (1.0 M in
hexane, 6.1 mL, 6.1 mmol) at -78 °C under nitrogen. The
reaction mixture was warmed to room temperature and stirred
overnight. H2O (40 mL) was then added, and the resulting
mixture was stirred for 20 min. The organic phase was
separated. The aqueous layer was neutralized with saturated
Na2CO3 to pH 6 and was extracted with CHCl3 (3 × 40 mL).
The combined organic phases were washed with brine and
dried over sodium sulfate. After the solvent was removed, the
residue was purified by column chromatography using 4/1
hexane/ethyl acetate as the eluent, yielding a yellow-orange
solid of 2-(4′-methylquinolinyl)phenol (0.89 g, yield 63%). Mp:
79-81 °C. 1H NMR (CDCl3, δ, ppm): 8.06 (1H, d, J ) 8.4 Hz),
8.02 (1H, d, J ) 8.5 Hz), 7.98 (1H, dd, J ) 8.1 Hz, 1.3 Hz),
7.91 (1H, s), 7.73-7.78 (1H, m), 7.57-7.62 (1H, m), 7.32-7.41
(1H, m), 7.11 (1H, d, J ) 8.2 Hz), 6.95-7.00 (1H, m), 2.83 (3H,
s). Anal. Calcd for C16H13NO: C, 81.68; H, 5.57; N, 5.95.
Found: C, 81.17; H, 5.52; N, 5.88.
(1H, d, J ) 9.0 Hz), 8.03 (1H, dd, J ) 8.2, 1.3 Hz), 7.97 (1H,
s), 7.70 (1H, dd, J ) 8.0, 1.2 Hz), 7.50 (1H, m), 7.25-7.40 (7H,
m), 7.12-7.24 (5H, m), 7.09 (1H, d, J ) 8.2 Hz), 6.87 (1H, m),
2.82 (3H, s). Anal. Calcd for C28H22NOB: C, 84.22; H, 5.55; N,
3.50. Found: C, 83.17; H, 5.87; N, 3.39. (This sample was
analyzed twice using crystals, but the carbon content is
consistently low.)
Syn th esis of Al(CH3)(m qp )2 (2). Trimethylaluminum (2.0
M in toluene, 0.10 mL, 0.20 mmol) was added slowly to 15
mL of a toluene solution containing mqpH (141 mg, 0.60 mmol)
at ambient temperature under N2. The mixture was stirred
for 3 h at ambient temperature, concentrated, and recrystal-
lized from CH2Cl2/toluene. Colorless crystals of 2 (74 mg, yield
73%) were obtained. Mp: 130 °C. 1H NMR (CDCl3, δ, ppm,
298 K): 8.55 (2H, m), 8.03 (2H, dd, J ) 8.1, 1.3 Hz), 7.86 (2H,
s), 7.81 (2H, d, J ) 7.5 Hz), 7.57-7.70 (4H, m), 7.18-7.36 (4H,
m), 6.96 (2H, m), 2.83 (6H, s), -0.34 (3H, s). Anal. Calcd for
C
33H27N2O2Al: C, 77.63; H, 5.33; N, 5.49. Found: C, 77.83; H,
5.47; N, 5.06.
Syn th esis of Al(m qp )3 (3). Trimethylaluminum (2.0 M in
toluene, 0.10 mL, 0.20 mmol) was added slowly to 15 mL of a
THF solution containing mqpH (164 mg, 0.70 mmol) at
ambient temperature under N2. The mixture was stirred for
3 h at ambient temperature, concentrated, and recrystallized
from CH2Cl2/hexane. Light yellow crystals of 3 (93 mg, yield
64%) were obtained. Mp: 213-215 °C. 1H NMR (CDCl3, δ,
ppm, 298 K): 8.33 (3H, d, J ) 8.4 Hz), 7.90 (3H, d, J ) 7.5
Hz), 7.75 (3H, s), 7.71 (3H, d, J ) 7.4 Hz), 7.48 (3H, m), 7.39
(3H, m), 7.05 (3H, m), 6.80 (3H, t, J ) 7.4 Hz), 6.31 (3H, d, J
) 8.2 Hz), 2.81 (3H s), 2.55 (6H, s). Anal. Calcd for C48H36N3O3-
Al‚0.5CH2Cl2: C, 75.43; H, 4.83; N, 5.44. Found: C, 75.30; H,
4.87; N, 5.42.
F a br ica tion of Electr olu m in escen t Devices. The EL
devices using 3 as the emitting layer were fabricated on an
indium-tin oxide (ITO) substrate. Organic layers and a metal
cathode composed of magnesium silver alloy (Mg0.9Ag0.1) were
deposited on the substrate by conventional vapor vacuum
deposition. Prior to the deposition, N,N′-di-1-naphthyl-N,N′-
diphenylbenzidine (NPB) and Al(q)3 were purified via a train
sublimation method.6 Train sublimation of 3 was unsuccessful.
Therefore, crystals of compound 3 obtained from repeated
recrystallization were used for film deposition. NPB was used
as the hole transport material in all devices, and Al(q)3 was
used as the electron transport material in one of the devices.
The device structures and the thickness of each layer are listed
in Table 3. To obtain the photoluminescence (PL) spectra, a
thin film (100 nm) deposited on a quartz substrate was
measured with a fluorescence spectrophotometer. The current/
voltage characteristics were measured using a Keithley 238
current/voltage unit. The light intensity of the EL device was
measured by a Minolta Chroma Meter, Model CS100. The EL
spectrum was obtained by an in-house setup made up of a
series of electronic components including a monochromator
(Instruments SA Inc.), a photomultiplier tube, and a photon
counter.
X-r a y Cr yst a llogr a p h y An a lysis. All crystals were
mounted on glass fibers. The data for mqpH, 1, and 2 were
collected on a Siemens single-crystal P4 X-ray diffractometer,
while the data for 3 were collected on a Bruker SMART CCD
1000 X-ray diffractometer with graphite-monochromated Mo
KR radiation operating at 50 kV and 35 mA at 23 °C. The data
collection ranges over the 2θ range are 2-45° for mqpH, 4.32-
47.4° for 1, 3.50-50.0° for 2, and 3.40-46.5° for 3. No
significant decay was observed during the data collection. Data
were processed on a Pentium PC using the Bruker AXS
Window NT SHELXTL software package (version 5.10).7
Syn th esis of BP h 2(m qp ) (1). Triphenylborane (242 mg,
1.00 mmol) was added to 20 mL of a THF solution containing
0.235 g (1 mmol) of mqpH under N2. The mixture was stirred
and heated at reflux for 4 h. After the mixture was cooled to
ambient temperature, it was concentrated under vacuum and
transferred to a drybox. The residue was recrystallized from
CH2Cl2/hexane to give a yellow crystalline product (296 mg,
yield 74%). Mp: 210 °C. 1H NMR (CDCl3, δ, ppm, 298 K): 8.20
(6) Wagner, H. J .; Loutfy, R. O.; Hsiao, C. K. J . Mater. Sci. 1982,
17, 2781.
(7) SHELXTL NT Crystal Structure Analysis Package, Version 5.10;
Bruker Axs, Analytical X-ray System, Madison, WI, 1999.

BPh2(mqp), Al(CH3)(mqp)2, and Al(mqp)3
Organometallics, Vol. 19, No. 26, 2000 5711
Ta ble 1. Cr ysta llogr a p h ic Da ta
mqpH
1
2
3
formula
fw
space group
a/Å
b/Å
c/Å
C
16H13NO
C28H22NOB
399.28
P21/c
12.3227(14)
9.684(4)
17.684(9)
90
95.503(14)
90
2100.6(13)
4
1.263
0.75
47
3265
3104 (0.0293)
280
C33H27N2O2Al‚0.5C7H8
556.62
P1h
C48H36N3O3Al‚0.5CH2Cl2
235.27
I2/a
22.686(7)
9.309(5)
23.114(5)
90
98.123(16)
90
4832(3)
16
1.294
0.81
45
3242
3145 (0.0539)
328
772.24
P21/n
10.786(5)
11.660(2)
11.977(2)
92.652(18)
104.04(2)
92.88(3)
1456.9(7)
2
1.269
1.06
50
5329
12.4161(6)
14.5747(7)
21.2238(9)
90
93.0580(10)
90
3835.2(3)
4
1.337
1.71
47
15 688
5508 (0.0175)
518
R/deg
â/deg
γ/deg
V/Å3
Z
Dc/g cm-3
µ/cm-1
2θmax/deg
no. of rflns measd
no. of rflns used (Rint
no. of variables
final R (I > 2σ(I))
R1a
)
5040 (0.0399)
375
0.0925
0.1550
0.0666
0.1332
0.0784
0.2088
0.0522
0.1562
wR2b
R (all data)
R1
0.3071
0.2296
0.986
0.1478
0.1672
1.029
0.1458
0.2749
1.051
0.0689
0.1650
1.053
wR2
goodness of fit on F2
R1 ) ∑|Fo| - |Fc|/∑|Fo|. wR2 ) [∑w[(Fo - Fc2)2]/∑[w(Fo
)
]]1/2; w ) 1/ [σ2(Fo2) + (0.075P)2], where P ) [Max (Fo2, 0) + 2Fc2]/3.
a
b
2
2 2
Ta ble 2. Bon d Len gth s (Å) a n d An gles (d eg) for
while the crystal of 2 belongs to the triclinic space group P1h.
All structures were solved by direct methods. A disordered
toluene solvent molecule was located in the lattice of 2 (0.5
toluene per molecule of 2), while a disordered CH2Cl2 solvent
molecule was found in the lattice of 3 (0.5 CH2Cl2 per molecule
of 3). There are two independent molecules in the asymmetric
unit of mqpH. All non-hydrogen atoms except the disordered
toluene molecule were refined anisotropically. The positions
of hydrogen atoms were either determined directly from the
difference Fourier maps or calculated, and their contributions
in structural factor calculations were included. The crystal
data are summarized in Table 1. Selected bond lengths and
angles for 1-3 are given in Table 2.
Com p ou n d s 1-3
Compound 1
O(1)-B(1)
N(1)-B(1)
1.337(5)
1.483(5)
C(1)-B(1)
B(1)-C(7)
1.352(5)
1.397(5)
O(1)-B(1)-C(1)
O(1)-B(1)-C(7)
C(1)-B(1)-C(7)
O(1)-B(1)-N(1)
C(1)-B(1)-N(1)
1.660(5)
1.609(6)
1.617(6)
109.8(3)
102.9(3)
C(7)-B(1)-N(1)
116.8(3)
105.9(3)
108.5(3)
112.3(3)
Compound 2
Al(1)-O(2)
Al(1)-O(1)
Al(1)-C(33)
1.748(4)
1.758(4)
1.964(6)
Al(1)-N(1)
Al(1)-N(2)
2.182(4)
2.197(4)
Resu lts a n d Discu ssion
O(2)-Al(1)-O(1)
106.93(19) C(33)-Al(1)-N(1)
93.1(2)
87.52(16)
88.50(16)
91.5(2)
O(2)-Al(1)-C(33) 124.7(2)
O(1)-Al(1)-C(33) 128.3(2)
O(2)-Al(1)-N(2)
O(1)-Al(1)-N(2)
Syn t h eses a n d St r u ct u r es. Th e m qp H Liga n d .
The synthesis of 2-(4′-methylquinolinyl)-2- phenol (mqpH)
is based on a modified procedure reported recently for
pyridylphenols,9 as shown in Scheme 1. The structure
of mqpH was confirmed by a single-crystal X-ray dif-
fraction analysis. As shown in Figure 1, the phenol
portion of the molecule is coplanar with the quinoline
portion. The hydroxy proton is shared between the
oxygen and nitrogen atom. There are no intermolecular
hydrogen bonds, but the unit cell packing diagram
shows that there is an extended intermolecular face-
to-face π-π stacking between molecules of mqpH in the
crystal lattice. The shortest intermolecular atomic
separation distance between the stacked molecules is
3.785 Å.
O(2)-Al(1)-N(1)
O(1)-Al(1)-N(1)
89.89(16) C(33)-Al(1)-N(2)
88.58(16) N(1)-Al(1)-N(2)
175.36(17)
Compound 3
Al(1)-O(3)
Al(1)-O(1)
Al(1)-O(2)
1.741(2)
1.742(2)
1.744(2)
Al(1)-N(1)
Al(1)-N(2)
2.120(2)
2.133(2)
O(3)-Al(1)-O(1) 125.66(10) O(2)-Al(1)-N(1)
O(3)-Al(1)-O(2) 121.02(10) O(3)-Al(1)-N(2)
O(1)-Al(1)-O(2) 113.26(11) O(1)-Al(1)-N(2)
O(3)-Al(1)-N(1)
O(1)-Al(1)-N(1)
89.30(10)
90.00(9)
87.61(9)
89.89(9)
93.22(9)
O(2)-Al(1)-N(2)
89.71(10) N(1)-Al(1)-N(2) 176.63(10)
Ta ble 3. EL Device Da ta
hole
emitting
layera
electron
eff,a
cd/A
device transporta
transporta
CIE (x, y)
Com p lexes of m qp . Three complexes containing the
mqp ligand have been synthesized and characterized
structurally. The first, BPh2(mqp) (1), was obtained by
the reaction of BPh3 with mqpH in a 1:1 ratio. The
second, Al(CH3)(mqp)2 (2), was prepared by the reaction
of Al(CH3)3 with mqpH in a 1:3 ratio in toluene (the
excess mqpH ligand is necessary to obtain 2 in good
yield). The synthesis of Al(mqp)3 (3) could not be
A
B
NPB (60)
NPB (60)
3 (80)
3 (20)
0.427, 0.475 0.21
Al(q)3 (60) 0.401, 0.479 0.29
a
b
The thickness (in nm) is given in parentheses. Efficiency at
25 mA/cm2.
Neutral atom scattering factors were taken from Cromer and
Waber.8 The crystals of mqpH, 1, and 3 belong to the
monoclinic space groups I2/a, P21/c, and P21/n, respectively,
(8) Cromer, D. T.; Waber, J . T. International Tables for X-ray
Crystallography; Kynoch Press: Birmingham, U.K., 1974; Vol. 4, Table
2.2A.
(9) Zhang, H.; Kwong, F. Y.; Tian, Y.; Chan, K. S. J . Org. Chem.
1998, 63, 6886-6890.

5712 Organometallics, Vol. 19, No. 26, 2000
Liu et al.
F igu r e 1. Diagram showing the molecular structure of
mqpH with 50% thermal ellipsoids and labeling schemes.
F igu r e 2. Diagram showing the molecular structure of 1
with 50% thermal ellipsoids and labeling schemes.
Sch em e 1
F igu r e 3. Diagram showing the molecular structure of 2
with 50% thermal ellipsoids and labeling schemes.
achieved in toluene even in the presence of excess
mqpH. However, compound 3 could be obtained readily
from the reaction of Al(CH3)3 with mqp in a 1:3.5 ratio
in THF. THF and a slight excess of mqpH are necessary
for isolating 3 and minimizing the formation of 2.
puckered six-membered chelate ring also was observed
in 2-pyridyl-2-phenolato complexes of Co(III) and Pd(II).12
The phenyl ring is no longer coplanar with the quinoline
portion but with a dihedral angle of 19.0°.
1
Compounds 1-3 have been fully characterized by H
The structure of 2 is shown in Figure 3. The two mqp
ligands in 2 are chelated to the Al(III) center in the same
manner as observed in 1. The Al(III) center has trigonal-
bipyramidal geometry with N(1) and N(2) atoms
occupying the axial positions (N(1)-Al(1)-N(2) )
175.36(17)°) and O(1), O(2), and C(33) atoms occupying
the basal plane (the sum of bond angles on the basal
plane is 359.9(1)°). A similar trigona-bipyramidal ge-
ometry has been observed previously in five-coordinate
Al(III) complexes.13,14 The Al-N and Al-O bond lengths
in 2 are similar to those observed in Al(q)3. The Al(1)-
C(33) bond length (1.964(6) Å) is similar to previously
reported values of five-coordinate alkylaluminum com-
NMR spectroscopy and elemental and single-crystal
X-ray diffraction analyses. Compounds 1 and 3 are air-
stable, while compound 2 decomposes slowly in the solid
state when exposed to air. The melting points of 1-3
are 210, 130, and 213 °C, respectively, significantly
higher than that of mqpH (80 °C). The high stability
and high melting points of 1 and 3 make them possible
candidates for electroluminescent applications.
The structure of 1 is shown in Figure 2. The boron
center has typical tetrahedral geometry with B-C,
B-N, and B-O bond lengths similar to those of BR2(q)
compounds.3f The mqp ligand chelates to the boron
center through the oxygen and nitrogen atoms. Unlike
the 8-hydroxyquinolinato ligand, which forms a planar,
five-membered ring with the central atom,1,11 the che-
late ring in 1 is six-membered and puckered. A similar
(12) Ganis, P.; Saporito, A.; Vitagliano, A. Inorg. Chim. Acta 1988,
142, 75.
(13) (a) Trepanier, S. J .; Wang, S. Organometallics. 1996, 15, 760.
(b) Trepanier, S. J .; Wang, S. Can. J . Chem. 1996, 74, 2032. (c)
Trepanier, S. J .; Wang, S. J . Chem. Soc., Dalton Trans. 1995, 2425.
(d) Trepanier, S. J .; Wang, S. Angew. Chem., Int. Ed. Engl. 1994, 33,
1265.
(10) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
(11) Kerr, M. C.; Preston, H. S.; Ammon, H. L.; Huheey, J . E.;
Steward, J . M. J . Coord. Chem. 1981, 11, 111.

BPh2(mqp), Al(CH3)(mqp)2, and Al(mqp)3
Organometallics, Vol. 19, No. 26, 2000 5713
F igu r e 5. PL of an amorphous film of 3 and EL of devices
A and B.
F igu r e 4. Diagram showing the molecular structure of 3
with 50% thermal ellipsoids and labeling schemes. For
clarity, hydrogen atoms are omitted.
interactions between mqp ligands, in comparison to the
Al(q)3 molecule. Compound 3 retains its five-coordinate
structure in solution, as indicated by the observation
of two distinct methyl resonances (due to the terminal
and chelating mqp ligands) in a 1:2 integrated ratio in
plexes.13,14 As observed in 1, the phenyl ring of the mqp
ligand is not coplanar with the quinoline portion. The
dihedral angles between the phenyl and the quinoline
ring are 17.7 and 24.5°, respectively, for the two mqp
ligands. The six-membered chelate rings are again
puckered.
1
the H NMR spectrum of 3 at ambient temperature.
The structures of 1-3 demonstrate that the mqp
ligand is capable of functioning as either a chelating
ligand or a terminal ligand.
The structure of 3 is shown in Figure 4. In composi-
tion, compound 3 appears to be an analogue of Al(q)3.
Therefore, initially we anticipated that compound 3
would have a structure similar to that of Al(q)3: i.e., a
six-coordinate octahedron.1 However, the crystal struc-
ture of 3 shows unequivocally that the Al(III) center in
3 is five-coordinate with a trigonal-bipyramidal geom-
etry similar to that of 2. The axial positions are occupied
by the N(1) and N(2) atoms (N(1)-Al(1)-N(2) )
176.63(10)°), while the basal positions are occupied by
the three oxygen atoms O(1), O(2), and O(3) (the sum
of bond angles on the basal plane is 359.9(1)°). Two of
the mqp ligands are chelated to the Al(III) center in the
same manner as observed in 2, while the third mqp
ligand coordinates to the Al(III) center as a monodentate
terminal ligand through the oxygen atom. The Al-N
bond lengths are somewhat shorter than those of 2, but
the Al-O bond lengths are essentially the same as those
of 2. Again, the six-membered chelate rings in 3 are
puckered. The dihedral angles between the phenyl ring
and the quinoline ring for the two chelating mqp ligands
are 27.7 and 29.7°, respectively. The increased nonpla-
narity of the chelating mqp ligands in 3, compared to
those in 2, is clearly caused by the presence of the bulky
terminal mqp ligand. The dihedral angle between the
phenyl ring and the quinoline ring of the terminal mqp
ligand is 42.4°, much larger than those of the chelating
mqp ligands, attributable to steric interactions. The
observed five-coordinate geometry (instead of six-
coordinate) in 3 is likely caused by the increased steric
Lu m in escen ce. In the solid state, mqpH has a weak
red-orange emission at λmax ) 579 nm. In solution
(CH3CN or CH2Cl2), the emission band of mqpH is
shifted to λmax ) 482 nm. The red shift of the emission
energy from solution to the solid state is mostly likely
caused by the π-π stacking of mqpH molecules in the
solid state, as shown by the crystal structure. The
emission maxima of compounds 1-3 in solution are at
497, 505, and 517 nm, respectively. The emission band
of 3 is very broad and covers the entire 400-650 nm
region. Consequently, the emission color of 3 in solution
is whitish blue. The emission maxima of compounds
1-3 in the solid state are at 520, 474, and 500 nm,
respectively, all blue-shifted in comparison to mqpH
itself. The dramatic difference in emission energy
displayed by mqpH and compounds 1-3 in the solid
state can be attributed to intermolecular interactions
in the solid state.
Electr olu m in escen ce. Compounds 1 and 3 are
suitable candidates as emitters for electroluminescent
devices because they are stable under air and have a
high thermal stability (high melting points). The lumi-
nescent properties of 1 are similar to those of BR2(q) (R
) ethyl, naphthyl, phenyl), investigated recently by our
group.3f The performance of BR2(q) compounds in EL
devices is not as good as that of Al(q)3. Therefore, we
did not conduct any investigation on the EL properties
of compound 1. Although the structure of 3 is not the
same as that of Al(q)3, it is a close analogue of Al(q)3.
Furthermore, in contrast to Al(q)3, which emits a green
color, compound 3 emits a whitish blue color in solution
and the solid state, making it an interesting candidate
for EL applications. Therefore, two EL devices using 3
as the emitter were fabricated. In both devices, NPB
(N,N′-di-1-naphthyl-N,N′-diphenylbenzidine) is used as
the hole transport layer. In device A no electron
(14) (a) Perego, G.; Dozzi, G. J . Organomet. Chem. 1996, 74, 2032.
(b) Trepanier, S. J .; Wang, S. Can. J . Chem. 1996, 74, 2032. (c) Mu¨ller,
G.; Kru¨ger, C. Acta Crystallogr. 1984, C40, 628. (d) Trepanier, S. J .;
Wang, S. Organometallics 1994, 13, 2213. (e) Liu, W.; Hassan, A.;
Wang, S.; Wu, Q. Organometallics 1997, 16, 4257. (f) Ashenhurst, J .;
Brancaleon, L.; Hassan, A.; Liu, W.; Schmider, H.; Wang, S.; Wu, Q.
G. Organometallics 1998, 17, 3186.

5714 Organometallics, Vol. 19, No. 26, 2000
Liu et al.
spectrum of an amorphous film of 3 obtained by vacuum
deposition (Figure 5), indicating that the observed EL
from A and B indeed originates from compound 3.
Although it is not uncommon for the PL spectrum of an
amorphous film to be different from that of solution or
the solid state, the difference between the PL spectra
of 3 in solution, the solid state, and the film form is
striking and is not understood yet. The fact that no
electron transport layer is used in device A indicates
that compound 3 can function not only as an emitter
but also as an electron transport material, as Al(q)3
does.
The J -V and L-J characteristics of the two devices
are shown in Figure 6. The turn-on voltage for device
A is ∼8 V, while the turn-on voltage for device B is much
higher, ∼11 V. The device B is, however, brighter than
A. The efficiency of device A is much less than that of
the EL device with NPB as the hole transport layer and
Al(q)3 as the emitter and electron transport layer.3f The
present experimental data indicate that compound 3 can
function as an emitter and an electron transport mate-
rial but its performance cannot compete with Al(q)3 in
EL devices. Device modification may improve the per-
formance of 3 in EL devices, which is being investigated
in our laboratory.
Ack n ow led gm en t. We thank the Natural Sciences
and Engineering Research Council of Canada and the
Xerox Research Foundation for financial support.
F igu r e 6. (top) J -V plots of devices A and B. (bottom)
L-J plots of devices A and B.
Su p p or tin g In for m a tion Ava ila ble: Tables giving crys-
tal data, atomic coordinates, all bond lengths and angles,
anisotropic thermal parameters, and hydrogen parameters for
mqpH and 1-3 and a unit cell packing diagram of mqpH. This
material is available free of charge via the Internet at
http://pubs.acs.org.
transport layer is used, while in device B Al(q)3 is used
as the electron transport layer. The details of device
structures and EL properties are given in Table 3.
Both devices A and B emit yellow light with an
emission maximum at 560 nm. The EL spectra from
devices A and B do not match the PL spectra of 3 either
in solution or the solid state, but they do match the PL
OM0006918