Ligands and complexes based on piperidine and their exploitation of the ring opening polymerisation of rac-lactide

A range of ligands based upon 2-(aminomethyl)piperidine have been successfully complexed to Mg(II), Zn(II) and group IV metal centres. These complexes have been characterised both in solution and solid state with different coordination geometries realised dependant on the nature of the ligand. For the Mg(II) and Zn(II) complexes, M(1-2)₂, were isolated and analysed by DOSY NMR spectroscopy. These ligands also furnished diastereomeric group IV complexes, M(1-2)₂(OiPr)₂. Group IV salalen and salan complexes, M(4-5)(OR)₂ were also found to be diastereomeric in nature, with either β-cis or α-cis geometries respectively. The tridentate ligand, 6H₂, yielded five coordinate complexes with both Ti(IV) and Zr(IV). All complexes were screened for the ring opening polymerisation of rac-lactide under both solvent and melt conditions. For the Mg(II) and Zn(II) complexes, good activity was observed with Zn(1-2)₂ demonstrating immortal polymerisation characteristics.