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

Abstract

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 = CF 3 ) with Me 3 Al afforded the corresponding dimethylaluminum amidate complexes [Me 2 Al L ] ( C1 – C8 ). The treatment of N -(2-methylquinolin-8-yl)picolinamide ( L9 ) with 1 or 2 equiv of Me 3 Al formed Me 2 Al L9 ( C9 ) or Me 2 Al L9 ·Me 3 Al ( C10 ), respectively; meanwhile, the stoichiometric reaction of L9 with i Bu 3 Al gave i Bu 2 Al L9 ( C11 ). All organoaluminum amidate complexes were fully characterized by 1 H/ 13 C 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 ε-caprolactone and produced polycaprolactones with narrow polydispersity; the nature of the active species was also investigated.