New catalysts for ring-opening polymerization of cyclic esters

Abstract

The Ring-Opening Polymerization of cyclic esters by metal complexes via coordination-insertion mechanism represents the most effective and versatile method for preparing aliphatic polyesters with a good control in terms of molecular weight, composition, microstructure and stereoselectivity. Among the large variety of species investigated, the heteroleptic metal complexes of type [LMX], in which L is an ancillary ligand and X a nucleophilic group, have been shown to be especially interesting for their high catalytic efficiency and good control. In the development of new and efficient catalytic systems a careful ligand design and an opportune choice of the metal are crucial features. Ideally, the presence of sterically demanding ancillary ligands could tune the electronic and steric properties of the metal center, modulate its Lewis acidity, minimize the aggregation processes and limit deleterious transesterification reactions to enhance the catalytic activity and the degree of control on polymerization process. Chelation, that is, the binding of a ligand to a metal through two or more bonds, is an efficient approach to realize this. As previously discussed, several classes of chelating ligands have been explored as ancillary ligands for stabilizing reactive metal centers of the catalytic active species... [edited by author]