Synthesis and reactivity of A1(Et)q2′ (q′ = 2-methyl-8-quinolinolato) and crystal structures of [A1(Et)2q]2 and A1q′2q (q = 8-quinolinolato)

Article abstract of DOI:10.1016/S0022-328X(02)01405-5

A crystal structure of a dimeric aluminum complex ([Al(Et)₂(q)]₂, q = 8-quinolinolato) (1) obtained by reaction of A1Et₃ with 8-quinolinol has been determined by X-ray crystallography. Reaction of AlEt₃ with 2-methyl-8-quinolinol gave a new reactive complex (Al(Et)q′₂] (q′ = 2-methyl-8-qinolinolato) (2)) in good yield. Reaction of 2 with 8-quinolinol provided Alq′₂q (3) and the crystal structure of 3 was determined.

Full text of DOI:10.1016/S0022-328X(02)01405-5

Journal of Organometallic Chemistry 654 (2002) 229ꢂ232
/
www.elsevier.com/locate/jorganchem
Short Communication
Synthesis and reactivity of Al(Et)q? (q?ꢀ
/
2-methyl-8-quinolinolato)
2
and crystal structures of [Al(Et)2q]2 and Alq?q (qꢀ8-quinolinolato)
/
2
Isao Yamaguchi, Takayuki Iijima, Takakazu Yamamoto *
Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
Received 12 March 2002; accepted 15 March 2002
Abstract
A crystal structure of a dimeric aluminum complex ([Al(Et)2(q)]2, qꢀ
quinolinol has been determined by X-ray crystallography. Reaction of AlEt3 with 2-methyl-8-quinolinol gave a new reactive
complex ([Al(Et)q?2] (q?ꢀ2-methyl-8-qinolinolato) (2)) in good yield. Reaction of 2 with 8-quinolinol provided Alq?2q (3) and the
/8-quinolinolato) (1) obtained by reaction of AlEt3 with 8-
/
/
crystal structure of 3 was determined. # 2002 Elsevier Science B.V. All rights reserved.
Keywords: Aluminum; 8-Quinolinol; 2-Methyl-8-quinolinol; Crystal structures
1. Introduction
complex selectively, because a steric hindrance of the
methyl group will prevent formation of Alq?: In this
3
Tri(8-quinolinolato)aluminum (Alq3) is one of the
most widely used complexes for organic light emitting
devices (OLED), because Alq3 is not only a good green
emitter but also a highly efficient electron transporting
material [1,2]. Various modifications of 8-quinolinolato
ligand to improve the performance of Alq3 have been
carried out [3,4]. Recently, an aluminum complex having
a reactive OH group (Alq2(OH)) has also been reported
[5]. Such a reactive complex would be a good starting
material for high performance aluminum complexes in
OLED.
work, we report preparation of a new reactive aluminum
complex, Al(Et)q?2 and a crystal structure of the
[Al(R)2q]2-type dinuclear aluminum complex obtained
by reaction of AlEt3 with 8-quinolinol. Reaction of
Al(Et)q2? with 8-quinolinol and a crystal structure of the
reaction product (Alq?q) are also reported.
/
2
2. Results and discussion
Al(R)q2-type complex having a reactive MÃ
/
R (Rꢀ
/
We first followed the previously reported reaction
between AlEt3 and 8-quinolinol [6]. The reaction of
AlEt3 with 8-quinolinol in a 1:2 molar ratio gave a
mixture of Alq3 and [Al(Et)2q]2 (1) in 36 and 18% yields,
respectively Eq. (1). Complex 1 is sensitive to air and
changed slowly to Alq3 in solutions, which makes
isolation of 1 difficult. We now report isolation of 1
and characterization of 1.
alkyl group) bond is also expected as a promising
starting material for the high performance aluminum
complexes, if it can be isolated. Reaction of AlR3 with 8-
quinolinol has been reported [6]. However, the reaction
did not give the expected Al(R)q2-type complex but
afforded a mixture of an Alq3-type complex and a
dimeric aluminum complex ([Al(R)2q]2) [6]. The crystal
structure of the [Al(R)2q]2-type complex has not been
determined. We thought that 1:2 reaction of AlR3 with
2-methyl-8-quinolinol (q?H) would give an Al(R)q2?
* Corresponding author. Tel.:
9245276.
E-mail address: tyamamot@res.titech.ac.jp (T. Yamamoto).
ꢁ
/
81-45-9245220; fax:
ꢁ81-45-
/
ð1Þ
1H-NMR spectrum of 1 shows peaks in the range d
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 1 4 0 5 - 5

230
I. Yamaguchi et al. / Journal of Organometallic Chemistry 654 (2002) 229ꢂ232
/
7.39ꢂ8.73 and at 0.81 and 0.08 due to aromatic
/
hydrogens and Et groups, respectively.
The structure of 1 was confirmed by a single-crystal
X-ray crystallography, as shown in Fig. 1. Complex 1
has a dimeric structure with a lozenge plane occupying
Al(1), Al (2), O(1), and O(2) atoms. Each ethyl group
bonded to Al is on the opposite side from the lozenge
plane. The Al(1)Ã
essentially same to those of Al(2)Ã
respectively. The O(1)ÃAl(1)ÃO(2) and Al(1)Ã
Al(2) bond angles are 72.8 and 107.78, respectively.
N bond distances of 1 are comparable to those
/
O(1) and Al(2)Ã
/
O(1) bond lengths are
O(2) and Al(1)ÃO(2),
O(1)Ã
/
/
/
/
/
/
The AlÃ
/
of Alq3 [7].
Reaction of AlEt3 with 2-methyl-8-quinolinol (q?H) in
Fig. 2. 1H-NMR spectrum of 2 in CD2Cl2.
a 1:2 molar ratio selectively gave Al(Et)q? (2) in 97%
2
yield Eq. (2).
ratio of the 1H-NMR peaks and analytical data support
the structure of 2 (See Section 3).
In order to reveal chemical reactivity of 2, reaction of
2 with 8-quinolinol was carried out to obtain Alq?q (3)
in 27% isolation yield Eq. (3). Reaction of 2 with 2-
ð2Þ
2
methyl-8-quinolinol resulted in recovery of the starting
materials, suggesting that formation of Alq? was diffi-
cult due to steric reasons.
3
Fig. 2 depicts 1H-NMR spectrum of 2. The 1H-NMR
spectrum of 2 shows peaks due to aromatic hydrogens in
the range d 6.91ꢂ8.23 and assignment of the peaks is
/
shown in Fig. 2. The CH3 peak is observed at a lower
magnetic field (d 3.07) than that of 2-methyl-8-quino-
linol (d 2.70) presumably due to a magnetically aniso-
tropic effect in the aluminum complex. Methyl
hydrogens of the Et group give a triplet signal at d
0.59. The methylene hydrogens bonded to Al afford two
ð3Þ
Complex 3 is stable to air in solid state, while a THF
solution of 3 decomposed gradually under air.
multiplets centered at d ꢃ0.06 and 0.13, revealing that
/
the Al center has a chirality and the CH2 hydrogens
become diastereotropic due to the chirality. Integral
Fig. 1. Crystal structure of 1 (50% probability ellipsoids). Hydrogen
˚
atoms are omitted for clarity. Selected bond distances (A) and angles
(8): Al(1)Ã
Al(1)ÃC(19), 1.971(5); Al(1)Ã
Al(2)ÃN(2), 2.132(5); Al(2)ÃO(1), 2.003(4); Al(2)Ã
Al(2)ÃC(25), 1.982(5); O(1)ÃAl(1)ÃO(2), 72.8(1); O(1)Ã
72.7(2); O(1)ÃAl(1)ÃN(1), 79.3(2); O(2)ÃAl(2)ÃN(2), 78.9(2); Al(1)Ã
O(1)ÃAl(2), 107.7(2); Al(1)ÃO(2)ÃAl(2), 106.8(2).
/
O(1), 1.868(3); Al(1)Ã
C(21), 1.979(5); Al(2)Ã
C(23), 1.977(5);
Al(2)ÃO(2),
/
N(1), 2.132(5); Al(1)Ã
/
O(2), 2.009(4);
Fig. 3. Crystal structure of 3 (50% probability ellipsoids). Hydrogen
˚
atoms are omitted for clarity. Selected bond distances (A) and angles
/
/
/
O(2), 1.882(3);
/
/
/
(8): Al(1)Ã
Al(1)ÃN(1), 2.090(8); Al(1)Ã
O(1)ÃAl(1)ÃN(1), 83.1(3); O(2)Ã
N(3), 81.0(3).
/
O(1), 1.837(6); Al(1)Ã
N(2), 2.087(7); Al(1)Ã
Al(1)ÃN(2), 83.4(3); O(3)Ã
/
O(2), 1.830(6); Al(1)Ã
N(3), 2.101(8);
Al(1)Ã
/
O(3), 1.852(6);
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/

I. Yamaguchi et al. / Journal of Organometallic Chemistry 654 (2002) 229ꢂ
/
232
231
Fig. 3 shows an ORTEP diagram of 3 as determined by
X-ray crystallography. Complex 3 contains a solvated
CH2Cl2 molecule used as the recrystallization solvent
and has a six-coordinate octahedron structure similar to
3.3. Synthesis of 3
To a toluene solution (20 ml) of 2 (1.01 g, 2.71 mmol)
was added dropwise a toluene solution (10 ml) of 8-
quinolinol (0.42 g, 2.89 mmol) for 1 h. The reaction
mixture was stirred at r.t. for 6 h. The resulting
precipitate was washed with toluene, dried under
vacuum, and recrystallized from a CH2Cl2 solution at
r.t. to give 3 as yellow needles (0.36 g, 27%). Anal.
Found: C, 62.84; H, 4.14; N, 7.59; Cl, 12.14. Calc. for
Alq3. The AlÃ
/
N bond distances of 3 are similar to those
O bond lengths of 3 are
of Alq3, whereas the AlÃ
/
somewhat shorter than those of Alq3 [7]. As described
above, a new reactive complex of a type of Al(R)q2 has
been isolated, and this complex is expected to serve as a
starting material of aluminum complexes.
C29H22AlN3O3×
/
CH2Cl2: C, 62.95; H, 4.23; N, 7.34; Cl,
12.39%.
3.4. Crystal data for 1 and 3
3. Experimental
1: C26H32Al2N2O2, Mꢀ
/
458.51, monoclinic, space
All reactions and manipulations were carried out
under inert gas using standard Schlenk techniques. All
solvents were dried and distilled prior to use. IR and
NMR spectra were recorded on a JASCO-IR 810
spectrophotometer and JEOL EX-400 spectrometer,
respectively. Elemental analyses were carried out with
a Yanagimoto Type MT-2 CHN autocorder.
˚
˚
9.77(2) A,
group P21/a (No. 14), aꢀ
/
15.18(2) A, bꢀ
111.84(5)8, Vꢀ
Mgmꢃ3
F(000)ꢀ
CH2Cl2: Mꢀ
group P21/n (No. 14), aꢀ11.386(4) A, bꢀ
95.09(2)8, Vꢀ
1.448 Mgmꢃ3, F(000)ꢀ
/
3
˚
˚
cꢀ
4,
C28H22AlN3O3×
/
18.081(5) A, bꢀ
/
/
2487.8(5) A , Zꢀ
/
Dcꢀ1.224
/
,
/
976.00.
3:
/
/
572.43, monoclinic, space
˚
˚
/
/
13.571(2) A,
3
˚
˚
cꢀ
/
17.064(3) A, bꢀ
/
/
2026.4(1) A , Zꢀ
/4,
Dcꢀ
/
/1184.00. The diffraction
data were collected with a Rigaku AFC5R diffract-
ometer at ambient temperature (23 8C) using the v
3.1. Synthesis of 1
scan mode (2u 5558). Correction for Lorentz and
/
polarization effects and an empirical absorption correc-
tion (C scan) were applied. The structure was solved by
a common combination of direct methods (SAPI-91 and
SIR-92 for 2 and 3, respectively) and subsequent Fourier
techniques. The positional and thermal parameters of
non-hydrogen atoms were refined anisotropically, while
hydrogen atoms were located by assuming the ideal
geometry.
To a benzene solution (25 ml) of AlEt3 (1.52 ml, 10.0
mmol) was added dropwise a benzene solution (20 ml)
of 8-quinolinol (2.90 g, 20.0 mmol) for 1 h. The reaction
mixture was stirred at room temperature (r.t.) for 3 h.
The resulting yellow precipitate was washed with
benzene and dried in vacuo to give 1 as a yellow solid
(0.83 g, 18%). Evaporation of the benzene filtrate
afforded Alq3 (1.65 g, 36%). Crystals for microanalysis
and the X-ray crystallographic analysis were obtained
by recrystallization from a CHCl3 solution at r.t. Anal.
Found: C, 68.27; H, 7.23; N, 6.14. Calc. for
C26H32Al2N2O2: C, 68.11; H, 7.03; N, 6.11%. 1H-
NMR (400 MHz, CD2Cl2): d 8.73 (dd, 2H), 8.40 (dd,
2H), 7.64 (dd, 2H), 7.59 (t, 2H), 7.42 (dd, 2H), 7.39 (dd,
2H), 0.81 (t, 12H), 0.08 (m, 8H).
Acknowledgements
We gratefully acknowledge the help of Dr. Y.
Nishihara in our institute for the X-ray crystallographic
analysis of molecular structures of the complexes.
References
3.2. Synthesis of 2
[1] (a) C.W. Tang, S.A. VanSlyke, Appl. Phys. Lett. 51 (1987) 913;
(b) C.W. Tang, S.A. VanSlyke, C.H. Chen, J. Appl. Phys. 65 (1989)
3611;
To a toluene solution (50 ml) of AlEt3 (4.60 ml, 30.0
mmol) was added dropwise a toluene solution (80 ml) of
2-methyl-8-quinolinol (9.55 g, 60.0 mmol) for 1 h. After
stirring for 12 h, the resulting precipitate was washed
with toluene and dried under vacuum to give 2 as a
yellow solid (10.9 g, 97%). Anal. Found: C, 70.81; H,
5.39; N, 7.49. Calc. for C22H21AlN2O2: C, 70.76; H,
(c) Y. Hamada, T. Sano, M. Fujita, T. Fujii, Y. Nishio, K. Shibata,
Jpn. J. Appl. Phys. 32 (1993) L514;
(d) V. Bulovic, G. Gu, P.E. Burrows, S.R. Forrest, Nature 380
(1996) 29.
[2] (a) C. Adachi, S. Tokio, T. Tsutsui, S. Saito, Jpn. J. Appl. Phys. 27
(1988) L713;
(b) Z. Shen, P.E. Burrows, V. Bulovis, S.R. Borrest, M.E.
Thompson, Science 276 (1997) 2009;
1
5.68; N, 7.52%. H-NMR (400 MHz, CD2Cl2): d 8.23
(d, 2H), 7.45 (d, 2H), 7.13 (dd, 2H), 6.91 (dd, 2H), 3.07
(c) H. Aziz, Z.D. Popovic, N.-X. Hu, A.-M. Hor, S. Xu, Science
283 (1999) 1900;
(s, 12H), 0.70 (t, 3H), 0.13 (m, 1H), ꢃ0.06 (m, 1H).
/

232
I. Yamaguchi et al. / Journal of Organometallic Chemistry 654 (2002) 229ꢂ232
/
(d) Q. Wu, M. Esteghamatian, N.H. Hu, Z. Popovic, G. Enright,
Y. Tao, M. D’Iorio, S. Wang, Chem. Mater. 12 (2000) 79.
Organometallics 19 (2000) 5709;
(f) J. Ashenhurt, G. Wu, S. Wang, J. Am. Chem. Soc. 122 (2000)
2541.
[3] (a) W. Liu, A. Hassan, S. Wang, Organometallics 16 (1997) 4527;
(b) A. Hassan, S. Wang, J. Chem. Soc. Chem. Commun. (1998)
211;
[4] J. Yu, Z. Chen, S. Miyata, Synth. Methods 123 (2001) 239.
[5] L.M. Leung, W.Y. Lo, S.K. So, K.M. Lee, W.K. Choi, J. Am.
Chem. Soc. 122 (2000) 5640.
(c) J. Ashenhurst, L. Brancaleon, A. Hassan, W. Liu, H. Schmider,
S. Wang, Q. Wu, Organometallics 17 (1998) 3186;
[6] T.J. Hurley, M.A. Robinson, J.A. Scruggs, S.I. Troz, Inorg. Chem.
6 (1967) 1311.
(d) J. Ashenhurst, L. Brancaleon, S. Gao, W. Liu, H. Schmider, S.
Wang, G. Wu, Q.G. Wu, Organometallics 17 (1998) 5334;
(e) S.F. Liu, C. Seward, H. Aziz, N.-X. Hu, Z. Popovic, S. Wang,
[7] M. Brinkmann, G. Gadret, M. Muccint, C. Taliani, N. Masciocchi,
A. Sironi, J. Am. Chem. Soc. 122 (2000) 5147.