Synthesis, Characterization of Zinc Complexes with Neutral α-Diimine Ligands and Application in Ring-opening Polymerization of ε-Caprolactone.

A series of neutral α-diimine ligands with diacetyl and acenaphthenequinone skeletons were prepared by the reaction between diacetyl and the corresponding aromatic amine. These ligands reacted with ZnCl2 to generate symmetric α-diimine zinc complexes C1-C10. Experimental results indicated that the α-diimine zinc complexes with a diacetyl skeleton (C1-C4) were active in ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). The complexes with an acenaphthenequinone skeleton showed a small steric effect (C5, C8 and C9) but the complex substituted with an electron-withdrawing group (C10) showed high activity in the monomer conversion rate during ROP of ε-CL. The ROP catalysts of ε-CL demonstrated the mechanism of monomer activation in the presence of benzyl alcohol.