Bimetallic salen aluminum complexes: cooperation between reactive centers in the ring-opening polymerization of lactides and epoxides.

Three dinuclear aluminum alkyl complexes of the general formula LAlMe, where L are salen ligands with an alkyl backbone of different lengths between the nitrogen atoms (1,3-propylene (1), 1,5-pentylene (2) and 1,12-dodecaylene (3)), have been prepared through alkane elimination reactions between each ligand and two equivalents of AlMe. The related hemi-salen aluminum complex 4 was prepared by an analogous reaction between a phenoxy-imine ligand and a single equivalent of AlMe. The activities of these aluminum complexes in the ring-opening polymerization (ROP) of rac-lactide and of several epoxides have been investigated and compared.