Ring‐opening polymerization of rac‐lactide catalyzed by Al(III) and Zn(II) complexes incorporating Schiff base ligands derived from pyrrole‐2‐carboxaldehyde

A series of Al(III) chloride [LAl‐Cl]; Al(III) alkoxide [LAl‐OR] 2 ; and Zn(II) [LZn] 2 complexes with Schiff base ligands were obtained. 1 H NMR and X‐ray diffraction studies indicate that [LAl‐Cl] complexes have C s symmetry and the Al center is penta‐coordinated. The Al(III) alkoxide complex [L 5 Al‐O i Pr] 2 is a dimer bridged by O i Pr − with the Al center in a distorted octahedral environment. Zn complexes [LZn] 2 are double helix dimers with tetra‐coordinated Zn centers. The catalytic activity for the ring‐opening polymerization of rac ‐lactide was evaluated. The best activity in this series is shown by the aluminium chloride complex with a flexible three‐carbon bridge; more flexible four‐carbon bridges lower the activity.