Reactions of 4-methylidene-bis(1-phenyl-3-methylpyrazol-5-one) with trimethylaluminum: Synthesis, structure and catalysis for the ring-opening polymerization of ε-caprolactone

Aluminum complexes bearing ligand O,O-bidentate dipyrazolate are synthesized and structurally characterized. The reaction of 4-methylidene-bis(1-phenyl-3-methylpyrazol-5-one) (MBP-H) with AlMe3 (1.2 molar equiv) in toluene yields [(MBP)AlMe2] (1) as the four-coordinate monomeric aluminum complex. Tri-adduct complex [Al(MBP)3] (2) results from treatment of AlMe3 with MBP-H (3 molar equiv) in toluene in a high yield. In the presence of 9-anthracenemethanol, mono-adduct aluminum complex 1 catalyzes efficiently the ring-opening polymerization of ε-caprolactone (ε-CL) in a controlled manner, yielding PCLs with the expected molecular weights and narrow polydispersity indices (PDIs).

Graphical AbstractReactions of 4-methylidene-bis(1-phenyl-3-methylpyrazol-5-one) with trimethylaluminum: synthesis, structure and catalysis for the ring-opening polymerization of ε-caprolactone.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch Highlights► Aluminum complexes bearing the MBP ligand are synthesized and fully characterized. ► Complex 1 catalyzes the polymerization of ε-caprolactone in a “controlled” fashion. ► Al complex 1 catalyzes the polymerization of ε-caprolactone in an “immortal” manner.