Synthesis and characterization of organoaluminum compounds containing quinolin-8-amine derivatives and their catalytic behaviour for ring-opening polymerization of ε-caprolactone

Abstract

Treatment of N-aryl-2-methylquinolin-8-amines (L1–L3) with one equivalent AlMe₃ or AlEt₃ afforded dialkyl aluminum compounds (C1–C5), whereas the stoichiometric reaction of 2-((2-(1H-benzo[d]imidazol-2-yl)quinolin-8-ylimino)methyl)phenols (L4–L6) with either AlMe₃ or AlEt₃ produced monoalkyl aluminum compounds (C6–C10). All the organoaluminum compounds were characterized by ¹H, ¹³C NMR and elemental analysis, and the molecular structures of representative compounds were confirmed by X-ray crystallography. With bidentate ligands, compounds C1 and C3 showed tetrahedron geometry around Al center, while compound C7 has a distorted square pyramidal geometry around Al center with the framework comprising the tetradentate ligand. The dialkyl aluminum compounds (C1–C5) performed high catalytic activities towards the ring opening polymerization (ROP) of ε-caprolactone (ε-CL), in parallel, the monoalkyl aluminum compounds (C6–C10) showed negative results for the polymerization of ε-CL. In the presence or absence of benzyl alcohol (BnOH), the four-coordination aluminum compounds (C1–C5) are both highly active towards the ring opening polymerization (ROP) of ε-caprolactone with resulting high conversation of ε-caprolactone and polymers with high molecular weight. In the presence of one equivalent of BnOH, polymerization of ε-caprolactone proceeded in a living manner and molecular weights of the obtained poly(ε-caprolactone)s could be precisely controlled by adapting the reaction conditions.