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 , 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 H-1-NMR experiments of Al complexes with BnOH.