Tridentate anilido‐aldimine magnesium and zinc complexes as efficient catalysts for ring‐opening polymerization of ε‐caprolactone and L ‐lactide

A novel tridentate anilido‐aldimine ligand, [o‐C6H4(NHAr)HCNCH2CH2NMe2] (Ar = 2,6‐iPr2C6H3, L‐H, 1), has been prepared by the condensation of N, N‐dimethylethylenediamine with one molar equivalent of 2‐fluoro‐benzaldehyde in hexane, followed by the addition of the lithium salt of diisopropylaniline in THF. Magnesium (Mg) and zinc (Zn) complexes supported by the tridentate anilido‐aldimine ligand have been synthesized and structurally characterized. Reaction of L‐H (1) with an equivalent amount of MgnBu2 or ZnEt2 produces the monomeric complex [LMgnBu] (2) or [LZnEt] (3), respectively. Experimental results show that complexes 2 and 3 are efficient catalysts for ring‐opening polymerization of ε‐caprolactone (CL) and L‐lactide (LA) in the presence of benzyl alcohol and catalyze the polymerization of ε‐CL and L‐LA in a controlled fashion yielding polymers with a narrow polydispersity index. In both polymerizations, the activity of Mg complex 2 is higher than that of Zn complex 3, which is probably due to the higher Lewis acidity and better oxophilic nature of Mg2+ metal.