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.

Graphical abstractA series of pyrazolyl–phenolate ligand precursors has been described. Reactions of five ligand precursors with one molar equivalent of AlMe3 in THF gave the aluminium pyrazolyl–phenolate dimethyl complexes. Their catalytic activities towards the ring opening polymerization reaction of ε-caprolactone in the presence of benzyl alcohol are examined.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Aluminium dimethyl complexes bearing pyrazolyl–phenolate ligands have been prepared. ► All complexes are active catalysts for the ROP of ε-caprolactone in the presence of benzyl alcohol. ► Bulkier substituent on the nitrogen atom of pyrazolyl ring could enhance the catalytic activities.