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

Abstract

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 AlMe(3) (1.2 molar equiv) in toluene yields [(MBP)AlMe(2)] (1) as the four-coordinate monomeric aluminum complex. Tri-adduct complex [Al(MBP)(3)] (2) results from treatment of AlMe(3) 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 epsilon-caprolactone (epsilon-CL) in a controlled manner, yielding PCLs with the expected molecular weights and narrow polydispersity indices (PDIs). (C) 2010 Elsevier B.V. All rights reserved.