Synthesis, structural, and ε-caprolactone polymerization studies of heteroleptic derivatives of aluminum(III)

A series of metallo-organic complexes of Al(III), [(CH₃COCHCOCH₃)₂Al(OR)]₂ [where R = o-MeC₆H₄ (1), m-MeC₆H₄ (2), p-MeC₆H₄ (3), C₆H₅CH₂ (4), o-ClC₆H₄CH₂ (5), m-ClC₆H₄CH₂ (6), and p-ClC₆H₄CH₂ (7), were synthesized quantitatively by treating Al(OPrⁱ)₃ with CH₃COCH₂COCH₃ and the phenols (o-MeC₆H₄OH, m-MeC₆H₄OH, and p-MeC₆H₄OH) concerned as well as phenylmethanols (C₆H₅CH₂OH, o-ClC₆H₄CH₂OH, m-ClC₆H₄CH₂OH, and p-ClC₆H₄CH₂OH) in suitable stoichiometry using benzene as solvent. All these complexes were soluble in common organic solvents, having sharp melting points, and they were characterized by elemental analysis, IR, and NMR (¹H and ¹³C) spectral studies. Single-crystal XRD followed by ORTEP diagram of solvated complex (1a) revealed its dimeric nature and the existence of six-coordinate aluminum. The complexes were studied in ring-opening polymerization of ε-caprolactone. The molecular weight and polydispersity index values of polycaprolactone were obtained by gel permeation chromatography analysis.