Synthesis and characterization of aluminum complexes based on amino-benzotriazole phenoxide ligand: luminescent properties and catalysis for ring-opening polymerization

Aluminum complexes coordinated by a C1DEABTP ligand (C1DEABTP-H = 2-(2H-benzotriazol-2-yl)-6-((diethylamino)methyl)-4-methylphenol) were synthesized and structurally characterized. The formation of Al complexes is dependent on the stoichiometry of AlMe3 to C1DEABTP ligand ratio. The reaction of C1DEABTP-H with AlMe3 (1.0 molar equiv.) in hexane produced mono-adduct aluminum complex [(C1DEABTP)AlMe2] (1), but treatment of C1DEABTP-H with 2.0 molar equiv. of AlMe3 afforded mixtures of [(C1DEABTP)Al2Me5] (2) and [(C1DEABTP)Al3Me8] (3). The penta-coordinated bis-adduct aluminum complex [(C1DEABTP)2AlMe] (4) was synthesized through the reaction of AlMe3 with C1DEABTP-H (2.0 molar equiv.) in hexane. Tri-adduct Al complex [(C1DEABTP)3Al] (5) resulted from treatment of AlMe3 with C1DEABTP-H (3.0 equiv.); the Al center is hexa-coordinated with three N,O-bidentate C1DEABTP ligands. X-ray diffraction of single crystals indicates that the bonding modes of the C1DEABTP ligands in complexes 2–3 are greatly affected when excess AlMe3 is coordinated. The optical properties and catalysis for lactone polymerizations of C1DEABTP coordinated to Al complexes were tested. Tri-adduct Al complex 5 produced an intense green fluorescence in both solution and the solid state. Complex 4 is an active catalyst for the ring-opening polymerization of e-caprolactone (e-CL) and L-lactide (L-LA) in the presence of 9-anthracenemethanol (9-AnOH). In e-CL polymerization, Al complex 4 catalyzes efficiently in both a 'controlled' and 'immortal' manner, giving polymers with the expected molecular weights and narrow polydispersity indexes. Copyright © 2012 John Wiley & Sons, Ltd.