Well-controlled ring-opening polymerization of cyclic esters initiated by dialkylaluminum β-diketiminates

A series of aluminum alkyl complexes nacnac(R)AlMe(2) (2a-2h) bearing aliphatic N-substituted beta-diketiminate ligands (nacnac(R)H = N,N'-dialkyl-2-amino-4-iminopent-2-enes), were prepared from the reaction of trialkyl aluminum and the corresponding beta-diketimines. All these aluminum complexes were characterized by NMR, elemental analysis and HRMS spectroscopy. The molecular structures of complexes 2a, 2c and 2h were confirmed by single-crystal X-ray diffraction. These aluminum alkyl complexes show notable activity towards the ring-opening polymerization of e-caprolactone in the absence and presence of alcohol, and the resulting polymers have narrow molecular weight distributions.