Synthesis and characterisation of aluminium(iii) imine bis(phenolate) complexes with application for the polymerisation of rac-LA

Abstract

A series of tridentate imine bis(phenolate) ligands have been synthesised and complexed to aluminium. Solid-state analysis identified two structural motifs of an aluminium dimer [Al₂(Me)₂(X)₂]; one consisting of two five-coordinate aluminium centres and a second containing aluminium centres in both a six- and four-coordinate geometry. Pairing with solution-state NMR spectroscopic analysis suggested that the geometry isolated was influenced by the ligands’ steric bulk. Trialling of Al₂(Me)₂(1–5)₂ as initiators for the ring-opening polymerisation (ROP) of rac-lactide found them all to be active, producing atactic polymeric material. Al₂(Me)₂(1)₂ was found to have good molecular weight control and activity an order of magnitude higher than analogous aluminium dimers.