N-alkyl-β-ketoiminate zinc complexes: Synthesis, structure, and reactivity in ring-opening polymerization of lactide

A series of N-alkyl-beta-ketoiminate monozinc complexes [{tBuCN(R)CHC(O)CtBu}2Zn] (R = Me, 2a; Et, 2b; Pr, 2c; iPr, 2d; Cy, 2e) were synthesized from the reaction of diethyl zinc with the corresponding beta-ketimines. All these zinc complexes were characterized by NMR, elemental analysis and HRMS spectroscopy. The molecular struc-tures of complexes 2b-2e were further confirmed by single-crystal X-ray diffraction. The structures exhibit that each zinc center is four-coordinate, and surrounded by two bidentate beta-ketoiminate ligands, forming a distorted tetrahedral geometry. These homoleptic bis(beta-ketoiminate) zinc complexes are active towards the ring-opening polymerization of rac-lactide in the absence of alcohol, yielding over 90 % conversions within 1 h at 70 degrees C in toluene with the ratio of monomer to catalyst being 100.

Automated summary

A series of N-alkyl-beta-ketoiminate monozinc complexes were synthesized and characterized. The structures of these complexes were determined by single-crystal X-ray diffraction, revealing a distorted tetrahedral geometry around the zinc center. These bis(beta-ketoiminate) zinc complexes exhibited high activity towards the ring-opening polymerization of rac-lactide in the absence of alcohol.