Methylaluminium 8-quinolinolates: synthesis, characterization and use in ring-opening polymerization (ROP) of ε-caprolactone

The stoichiometric reactions of 2-(2,6-R-phenylimino)quinolin-8-ol (L1–L5, L1: R = Me, L2: R = Et, L3: R = ⁱPr, L4: R = Cl, L5: R = F) with Me₃Al afforded the dimeric aluminium complexes [Me₂AlL]₂ (1–5) in good yields. By contrast, stoichiometric reactions of 2-(1-(2,6-R-phenylimino)propyl) quinolin-8-ol (L6–L10, L6: R = Me, L7: R = Et, L8: R = ⁱPr, L9: R = Cl, L10: R = F)) with Me₃Al gave the mononuclear aluminium complexes Me₂AlL (6–10) accompanied with by-products of the form Me₂AlL·Me₃Al (11–15). All methylaluminium complexes were characterized by NMR spectroscopy, elemental analysis, and the molecular structures of complexes 3, 6 and 8 were determined by single-crystal X-ray diffraction. Aluminium compounds 1–5 possessed negligible activity towards the ring-opening polymerization of e-caprolactone either in the presence or absence of BnOH. In contrast, in the presence of BnOH, the mononuclear aluminium compounds 6–10 could efficiently initiate the ring-opening polymerization of e-caprolactone; the polymerization proceeded in a living manner.