Homoleptic and heteroleptic ketodiiminate zinc complexes for the ROP of cyclic l-lactide

Abstract

Homo- and heteroleptic ketodiiminate zinc complexes L¹₂Zn₂ (1, L¹ = [Me₂NC₂H₄NC(Me)CH]₂CO), L²(ZnCp)₂ (2, L² = [Me₂NC₃H₆NC(Me)CH]₂CO, Cp = C₅H₅) and L²HZnCp* (3, Cp* = C₅Me₅) were synthesized and characterized by ¹H and ¹³C NMR and IR spectroscopy as well as by elemental analysis and single crystal X-ray diffraction (sc-XRD, 2, 3). The catalytical activity of heteroleptic complexes 2 and 3 were tested in the ring-opening polymerization (ROP) of L-lactide. Homobimetallic complex 2 showed the highest activity and selectivity for the synthesis of cyclic polylactide (cPLLA; TOF = 17 460 h⁻¹) at 100 °C in toluene solution, while linear polymers are formed with mononuclear complex 3.