Aluminium complexes containing pyrazolyl–phenolate ligands as catalysts for ring opening polymerization of ε-caprolactone

A series of pyrazolyl–phenolate ligand precursors has been described. Reactions of five pyrazolyl-phenolate ligand precursors, HOPhMePzMe, HOPhMePztBu, HOPhMePzPh, HOPhMePzF-Ph or HOPhHPztBu, with one molar equivalent of AlMe3 in THF gave the aluminium dimethyl complexes, Me2Al(OPhR1PzR2) [R1 = methyl, R2 = methyl, Me2Al(OPhMePzMe) (1); R1 = methyl, R2 = tert-butyl, Me2Al(OPhMePztBu) (2); R1 = methyl, R2 = phenyl, Me2Al(OPhMePzPh) (3); R1 = methyl, R2 = 4-fluorophenyl, Me2Al(OPhMePzF-Ph) (4); R1 = H, R2 = tert-butyl, Me2Al(OPhHPztBu) (5)], respectively. The molecular structures are reported for compounds 3 and 5. Their catalytic activities towards the ring opening polymerization reaction of ε-caprolactone in the presence of benzyl alcohol are also under investigation.