Aluminum Complexes of Monopyrrolidine Ligands for the Controlled Ring-Opening Polymerization of Lactide

In this paper we report the full characterization (solution-state NMR spectroscopy and solid-state structures) of a series of Al­(III) half-salan complexes and their exploitation for the ring-opening polymerization of <i>rac</i>-lactide. Depending on the ligand employed and stoichiometry of the complexation, structures of the form Al­(<b>X</b>)₂Me or Al­(<b>X</b>)­Me₂ were isolated. Interestingly Al­(<b>2</b>)₂Me and Al­(<b>2</b>)­Me₂ produce PLA with a strong isotactic bias (<i>P</i>_m up to 0.80), whereas all other complexes produced atactic PLA. This is in contrast to recent studies on similar salan ligand systems. PLAs with predictable molecular weights and narrow distributions were achieved. The results are discussed in terms of steric and electronic properties of the ligands