Bimetallic aluminum complexes supported by bis(salicylaldimine) ligand: Synthesis, characterization and ring-opening polymerization of lactide

Two types of bifunctional bis(salicylaldimine) ligands ( syn - L and anti - L ) were designed and synthesized to support bimetallic aluminum complexes. Owing to the rigid anthracene skeleton, syn - L and anti - L successfully locked two Al centers in close proximity ( syn - Al2 ) and far apart ( anti - Al2 ), respectively. The distance between two Al centers in syn - Al2 was defined by X-ray diffraction as 6.665 Å, which is far shorter than that in anti - Al2 . In the presence of stoichiometrical BnOH, syn - Al2 and anti - Al2 were both efficient for ring-opening polymerization (ROP) of rac -LA with the former being more active. In the presence of excess BnOH, syn - Al2 showed an efficient and immortal feature, consistent with high conversions, matched M n s, narrow molecular weight distributions and end group fidelity, while anti - Al2 had a much lower activity or even became entirely inactive due to rapid decomposition, indicated by in situ 1 H-NMR experiments of Al complexes with BnOH.