Synthesis and Characterization of Dialkylaluminum Amidates and Their Ring-Opening Polymerization of ε-Caprolactone

The stoichiometric reactions of N-(2-methylquinolin-8-yl) (R)amides (L1–L8; L1, R = Ph; L2, R = p-FPh; L3, R = p-ClPh; L4, R = p-(MeO)Ph; L5, R = o-MePh; L6, R = p-MePh; L7, R = Me; L8, R = CF3) with Me3Al afforded the corresponding dimethylaluminum amidate complexes [Me2AlL] (C1–C8). The treatment of N-(2-methylquinolin-8-yl)picolinamide (L9) with 1 or 2 equiv of Me3Al formed Me2AlL9 (C9) or Me2AlL9·Me3Al (C10), respectively; meanwhile, the stoichiometric reaction of L9 with iBu3Al gave iBu2AlL9 (C11). All organoaluminum amidate complexes were fully characterized by 1H/13C NMR spectroscopy and elemental analysis, and the unambiguous structures of complexes C2, C4, C9, and C11 were further determined by single-crystal X-ray diffraction. With the assistance of 1 equiv of BnOH, all dialkylaluminum amidate complexes showed appreciable activities toward the ring-opening polymerization of e-caprolactone and produced polycaprolactones with narrow polydispersity; the nature of the active species was also investigated