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 ε‐caprolactone (ε‐CL) and L‐lactide (L‐LA) in the presence of 9‐anthracenemethanol (9‐AnOH). In ε‐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.