Novel Oxo-Bridged Blue Luminescent Organoaluminum Complexes: Al 4 (CH 3 ) 6 (μ 3 -O) 2 (dpa) 2 and Al 3 (7-azain) 4 (OCH(CF 3 ) 2 ) 2 (CH 3 )(μ 3 -O) (dpa ) Deprotonated Di-2-pyridylamine, 7-azain ) Deprotonated 7-Azaindole) Wang Liu, Abdi Hassan, and Suning Wang* Department of Chemistry, Queen’s University, Kingston, Ontario, K7L 3N6 Canada Received July 15, 1997 X Summary: Two novel blue luminescent organoaluminum complexes Al 4 (CH 3 ) 6 (μ 3 -O) 2 (dpa) 2 (1) and Al 3 (7-azain) 4 - (OCH(CF 3 ) 2 ) 2 (CH 3 )(μ 3 -O) (2) (dpa ) deprotonated di-2- pyridylamine, 7-azain ) deprotonated 7-azaindole) have been synthesized and characterized structurally. The unusual stability of these compounds is attributed to the presence of the triply-bridging oxo ligand. The chemistry of organoaluminum amido and imido compounds has attracted much attention due not only to their interesting structural and chemical properties but also to their applications in materials science. 1 We have been investigating the assembly of polynuclear organoaluminum complexes by using polydentate aro- matic amido or imido ligands. 2 During our investiga- tion, we have discovered that a variety of new orga- noaluminum compounds can be obtained by using either the di-2-pyridylamine or the 7-azaindole ligand. These new organoaluminum compounds display not only un- usual structural features and chemical reactivities, but, more importantly, they display a rare blue lumines- cence, which is much sought-after by scientists because of the potential applications in electroluminescent dis- plays. 3 Most of the previously reported blue lumines- cent compounds are organic oligomers or polymers. 3 Blue luminescent inorganic and organometallic com- plexes are rather rare and have been limited to 8-quino- line- or azomethine-based complexes where either alu- minum or zinc ions are involved. 4 The advantage of employing an aluminum ion in the complex is at least 2-fold. First, the Al(III) ion is colorless and contains no d electrons, thus not interfering with the blue luminescence. Second, the Al(III) ion has versatile coordination geometries, ranging from three-coordinate to six-coordinate, thus capable of accommodating vari- ous ligands. 1,2 Third, as a hard Lewis acid, the Al(III) ion binds well to hard donor atoms such as nitrogen and oxygen atoms, thus stabilizing the ligand. We report here the syntheses, structures, and luminescent proper- ties of two novel oxo-stabilized organoaluminum com- pounds, Al 4 (CH 3 ) 6 (dpa) 2 (μ 3 -O) 2 (1) and Al 3 (7-azain) 4 - (OCH(CF 3 ) 2 ) 2 (CH 3 )(μ 3 -O) (2), where dpa ) deprotonated di-2-pyridylamine and 7-azain ) deprotonated 7-azain- dole. Compound 1 was obtained in 50% yield by the reaction of dpaH with 2 equiv of Al(CH 3 ) 3 and 1 equiv of H 2 O in toluene at 23 °C. It was fully characterized by NMR spectroscopy, single-crystal X-ray diffraction, and elemental analyses. 5 Compound 1 contains four Al atoms and an inversion center of symmetry as shown in Figure 1. The dpa ligand binds to two aluminum centers through both pyridyl and amido sites. Two of the nitrogen atoms in the dpa ligand, the amido N(1) X Abstract published in Advance ACS Abstracts, September 15, 1997. (1) (a) Mole, T.; Jeffrey, E. A. Organoaluminum Compounds; Elsevier: New York, 1972. (b) Lappert, M. F.; Power, P.; Sanger, A. R.; Srivatava, R. C. Metal and Metalloid Amides; Ellis Horwood/ Wiley: New York, 1980. (c) Cesari, M.; Cucinella, S. Aluminum- Nitrogen Rings and Cages. In The Chemistry of Inorganic Homo and Heterocycles; Haiduc, I. Sowerby, B., Eds.; Academic Press: London, 1987. (d) Janik, J. F.; Duesler, E. N.; Paine, R. T. Inorg. Chem. 1988, 27, 4335. (e) Janik, J. F.; Duesler, E. N.; Paine, R. T. Inorg. Chem. 1987, 26, 4341. (2) (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. (3) (a) Rack, P. D.; Naman, A.; Holloway, P. H.; Sun, S.; Tuenge, R. T. Mater. Res. Bull. 1996, 21(3), 49. (b) Brouwer, H. J.; Krasnikov, V. V.; Hilberer, A.; Hadziioannou, G. Adv. Mater. 1996, 8, 935. (c) Edwards, A.; Blumstengel, S.; Sokolik, I.; Dorsinville, R.; Yun, H.; Kwei, K.; Okamoto, Y. Appl. Phys. Lett. 1997, 70, 298. (d) Ohmori, Y.; Uchida, M.; Muro, K.; Yoshino, K. Jpn. J. Appl. Phys. 1991, 30, L1941. (4) (a) Moore, C. P.; VanSlyke, S. A.; Gysling, H. J. U.S. Patent No. 5484922, 1996. (b) Sano, T.; Fujita, M.; Fujii, T.; Nishio, Y.; Hamada, Y.; Shibata, K.; Kuroki, K. U.S. Patent No. 5432014, 1995. (c) Hironaka, Y.; Nakamura, H.; Kusumoto, T. U.S. Patent No. 5466392, 1995. (d) VanSlyke, S. A.; Bryan, P. S.; Lovecchio, F. V. U.S. Patent No. 5150006, 1992. (e) Bryan, P. S.; Lovecchio, F. V.; VanSlyke, S. A. U.S. Patent No. 5141671, 1992. (5) Crystal data for 1, a ) 8.725(2) Å, b ) 14.158(3) Å, c ) 14.994- (3) Å, b ) 102.15(3)°, V ) 1810.7(6) Å 3 , monoclinic, P21/c. 2: a ) 8.429- (6) Å, b ) 20.464(8) Å, c ) 12.799(4) Å, b ) 91.22(4)°, V ) 2207(2) Å 3 , monoclinic, P21/m. Data were collected over the 2 θ 3-45° at 23 °C on a Siemens P4 diffractometer with Mo KR radiation, operated at 50 kV and 40 mA. Data were processed on a Pentium PC using Siemens SHELXTL software package. Convergence to the final R values of R1 ) 0.0525, wR2 ) 0.1325 for 1 and R1 ) 0.0918, wR2 ) 0.1946 for 2 were achieved by using 2343 reflections [I > 2σ(I)]and 199 parameters for 1 and 2899 reflections [I > 2σ(I)] and 312 parameters for 2. The details of the X-ray crystallographic analyses are given in the Sup- porting Information. Synthesis of compound 1: Al(CH3)3 (2.0 M, 1 mL, 0.002 mol) in toluene was added to di-2-pyridylamine (0.17 g, 0.001 mol) in 10 mL of toluene at 23 °C under nitrogen. After 30 min, 0.02 mL of H2O in 1 mL of toluene was added. The mixture was stirred for a few hours and filtered. Colorless crystals of 1 were obtained from the concentrated solution in >50% yield. Alternatively, compound 1 can be obtained in good yield by reacting Al(CH3)3 with di-2-pyridy- lamine in a 2:1 ratio using undistilled DMSO as the solvent. 1 H NMR for 1 (toluene-d8, 25 °C): δ -0.53 (s, 3H, CH3), -0.33 (s, 3H, CH3), -0.13 (s, 3H, CH3), 6.09 (t, 1H, Py), 6.22 (q, 1H, Py), 6.43 (d, 1H, Py), 6.74 (d, 1H, Py), 6.83 (m, 1H, Py), 6.90 (m, 1H, Py), 7.96 (d, 1H, Py), 8.26 (d, 1H, Py). Anal. Calcd for C26H34Al4N6O2‚C7H8: C, 59.82; H, 6.34; N, 12.69. Found: C, 60.21; H, 6.25; N, 13.29. Synthesis of compound 2: 0.200 g (1.7 mmol) of 7-azaindole in 7 mL of toluene was reacted with 0.423 mL (0.85 mmol) of Al(CH3)3 (2.0 M in toluene) at 23 °C under nitrogen for 3 h. A 142 g amount of hexafluoro-2-propanol (0.85 mmol) in 3 mL of toluene was added. The mixture was stirred for another 3 h and concentrated to about 2 mL by vacuum. A 2 mL amount of THF and 1 mL of hexane were added to the solution. After 2 days, colorless crystals of 2 were obtained in 62% yield. The reaction for compound 2, albeit nonstoichiometric, was found to be the best procedure for the synthesis of 2. A minor product from the same reaction was observed, but has not been fully characterized yet, which could account for the nonstoichiometry of the reaction. 1 H NMR for 2 (chloroform-d, 25 °C): δ -0.31 (s, 3H, CH3), 4.57 (m, 2H, CH), 6.30- 8.60 (m, 20H, 7-azain). Anal. Calcd for the vacuum dried THF-free sample of C35H25N8O3F12Al3: C, 45.91; H, 2.73; N, 12.24. Found: C, 46.28; H, 3.28; N, 11.51. 4257 Organometallics 1997, 16, 4257-4259 S0276-7333(97)00602-X CCC: $14.00 © 1997 American Chemical Society