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

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 [Al 2 (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 Al 2 (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. Al 2 (Me) 2 ( 1 ) 2 was found to have good molecular weight control and activity an order of magnitude higher than analogous aluminium dimers.