Binuclear ketodiiminate magnesium complexes for the ROP of cyclic L-Lactide and ε-Caprolactone

In contrast to well-established linear and branched polyesters, which find widespread biomedical and materials applications, cyclic polyesters have been less explored. We report on ketodiiminate magnesium complexes (L2Mg3Cp+MgCp3-)-Mg-1 (1), L-1(MgCp*)(2) (2) and L-2(MgCp)(2) (3) (L-1 = (Me2NC2H4NC(Me)CH)(2)CO, L-2 = (Me2NC3H6NC(Me)CH)(2)CO), which were spectroscopically characterized (H-1, C-13 NMR, IR) as well as by elemental analysis and single crystal X-ray diffraction (sc-XRD). Complexes 1-3 were used in the ring-opening polymerization (ROP) of L-lactide (L-LA) and epsilon-caprolactone (epsilon-CL) under mild reaction conditions. Catalyst 2 showed excellent reactivity and selectivity for the synthesis of cyclic polylactide (cPLA; TOF = 17820 H-1) and cyclic polycaprolactone (cPCL; 712800 h(-1)).

Automated summary

Compared to linear and branched polyesters, the exploration of cyclic polyesters has been limited. In this study, ketodiiminate magnesium complexes were synthesized and used as catalysts for the synthesis of cyclic polylactide and cyclic polycaprolactone under mild reaction conditions. Catalyst 2 exhibited excellent reactivity and selectivity.