Synthesis and characterisation of unsymmetrical Zr(iv) amine tris(phenolate) complexes and their application in ROP of rac-LA

Abstract

Unsymmetrical amine tris(phenolate) ligands have been prepared and complexed to Zr(IV). In the solid-state dimeric species are observed, which persist in solution. The complexes show interesting coordination chemistry and the nature of which is discussed. These complexes are analogues of a highly stereoselective C₃-symmetric Zr(IV) amine tris(phenolate) alkoxide and have been prepared, characterised and trialled for the ring-opening of rac-lactide providing insight into the effect of symmetry and ligand steric bulk on selectivity. The polymerisations have been investigated in solution and under the industrially preferred melt conditions (130 °C). The rate law for the ROP has been determined – with Zr₂(1)₂(OⁱPr)₂, a pseudo first order dependency was seen, however for Zr₂(2)₂(OⁱPr)₂ this changed to a half order dependency in initiator.