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 C1DEA BTP ligand ( C1DEA BTP‐H = 2‐(2 H ‐benzotriazol‐2‐yl)‐6‐((diethylamino)methyl)‐4‐methylphenol) were synthesized and structurally characterized. The formation of Al complexes is dependent on the stoichiometry of AlMe 3 to C1DEA BTP ligand ratio. The reaction of C1DEA BTP‐H with AlMe 3 (1.0 molar equiv.) in hexane produced mono‐adduct aluminum complex [( C1DEA BTP)AlMe 2 ] (1), but treatment of C1DEA BTP‐H with 2.0 molar equiv. of AlMe 3 afforded mixtures of [( C1DEA BTP)Al 2 Me 5 ] (2) and [( C1DEA BTP)Al 3 Me 8 ] (3). The penta‐coordinated bis‐adduct aluminum complex [( C1DEA BTP) 2 AlMe] (4) was synthesized through the reaction of AlMe 3 with C1DEA BTP‐H (2.0 molar equiv.) in hexane. Tri‐adduct Al complex [( C1DEA BTP) 3 Al] (5) resulted from treatment of AlMe 3 with C1DEA BTP‐H (3.0 equiv.); the Al center is hexa‐coordinated with three N , O ‐bidentate C1DEA BTP ligands. X‐ray diffraction of single crystals indicates that the bonding modes of the C1DEA BTP ligands in complexes 2–3 are greatly affected when excess AlMe 3 is coordinated. The optical properties and catalysis for lactone polymerizations of C1DEA BTP 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.