Synthesis of Li(I), Zn(II) and Mg(II) complexes of amine bis(phenolates) and their exploitation for the ring opening polymerisation of rac-lactide

Abstract

In this paper a series of Mg(II), Li(I) and Zn(II) complexes based on two families of amine bis(phenolate)s have been prepared and structurally characterised. In the solid-state the Li(I) complexes form common Li4O4 cubes and there are subtle differences in coordination mode between the two salan ligands employed. We also have prepared a Li3Mg1O4 cube structure, by the reaction of 1 eq. of ligand 2H2, with 1 eq. of both nBuLi and MgnBu2. Upon addition of the ligands with Zn(II) either a trimetallic or tetrametallic structure was isolated. With 2H2 a complex with an –OMe was observed, this arises from the insertion of oxygen into the Zn-Me bond. Upon reaction with MgnBu2 dimeric complexes were isolated. All complexes were tested for the ROP of rac-lactide in solution. High molecular weight polylactide was isolated with narrow molecular weight distributions being observed. In most cases PLA with a very slight heterotactic bias was formed.