Comparative study of the coordination chemistry and lactide polymerization of alkoxide and amide complexes of zinc and magnesium with a 6-diiminato ligand bearing ether substituents

A series of beta-diiminato complexes of the form (BDI-3)MX where (BDI-3) = [CH(CMeNC6H4-2-OMe)(2)]; M = Zn, Mg; X = (OPr)-Pr-i, (OBu)-Bu-t, or N(SiMe3)(2) has been synthesized. The (BDI-3) ligand is bidentate in (BDI-3)ZnN(SiMe3)(2) and tetradentate in (BDI-3)MgN(SiMe3)(2). The alkoxide complexes are shown to be active for lactide polymerization. Polymerization of rac-lactide with (BDI-3)(ZnOPr)-Pr-i gives a moderate preference for heterotactic PLA. Polymerization of rac-lactide with [(BDI-3)MgOtBu](2) shows a slight preference for heterotactic PLA in CH2Cl2 but is highly stereoselective in THF in the production of heterotactic PLA.