Dialkylaluminium 2-imidazolylphenolates: Synthesis, characterization and ring-opening polymerization behavior towards lactides

Abstract The stoichiometric reaction of the 2-imidazolylphenols ( L1 – L9 ) with the trialkylaluminium reagents AlR 3 (R = Me, Et and i Bu), afforded the corresponding dialkylaluminium 2-imidazolylphenolate complexes [R 2 Al( L1 – L9 )] ( C1 – C11 ), which were characterized by 1 H/ 13 C NMR spectroscopy and by elemental analysis. The molecular structures of the representative complexes C1 , C2 , C4 , C6 and C11 were determined by single-crystal X-Ray diffraction, and revealed a distorted tetrahedral geometry at aluminum. These dialkylaluminium 2-imidazolylphenolates ( C1 – C11 ) could efficiently catalyze the ring-opening polymerization of lactides to afford high molecular weight polylactide, both in the presence and absence of BnOH, and as such represent rare examples of the use of bi-dentate ligation at aluminum in such lactide polymerization systems. On the basis of the polymerization results for l -lactide, d -lactide and rac -lactide, the nature of the ligands and the aluminum bound alkyls were found to significantly affect the catalytic activity as well as the properties of the resultant polylactides.