Aluminum Alkyl Complexes Bearing Salicylaldiminato Ligands: Versatile Initiators in the Ring-Opening Polymerization of Cyclic Esters

Linear aliphatic polyesters are degradable thermoplastic polymers, which can be obtainedby ring-opening polymerization (ROP) of cyclic esters through a coordination-insertion mechanism.Aluminum based organometallic complexes have a leading position as efficient catalysts for thispolymerization process. Aluminumalkyl complexes bearing salicylaldiminato ligands, althoughless explored, have been shown to be efficient and versatile catalysts for the ROP of various cyclicesters. These species have the potential to function as active catalysts in the ROP because of their lesscoordinatively saturated nature with respect to analogous SALEN-type complexes. They have beenused as efficient catalysts in the ROP of commercially available cyclic esters, such as "-caprolactone,L-lactide, rac-lactide, and glycolide. Moreover, they resulted in efficient catalysts for the ROP of cyclicesters with large ring-size and for the ROP of functionalized lactide. Furthermore, they have been usedin the co- and ter-polymerization of various cyclic esters affording well controlled polymerizationand a plethora of microstructural architectures, ranging from random to block to multiblock.